sealing elements - Eriks

sealingelementsPrecision O-ringTechnical ManualNUMBER OF THIS PUBLICATION:254106 (2002)

SEALING ELEMENTSTable of ContentsIntroduction 31. O-ring Standards 52. O-ring Sealing Principles 63. O-ring Applications 104. Basic Elastomers 125. Designing with Rubber 256. Compound Selection 36• Standard compounds 39• Vulc-O-Rings compounds 40• Specials 41• Viton ® compounds 44• Kalrez ® compounds 52• Encapsulated Teflex ® compounds 60• Data sheets 68• Water-Steam 69• Food - Pharma 70• Vacuum 75• Contact with plastics 76• High purity - FDA - USP 76• Permeability 77• Explosive decompression 78• Mineral oils 79• Fuels 81• Temperature 82• Abrasion 83• Ozone 84• Radiation 84• Shielding 84• Colours 85• Thermal expansion 867. Specifications 878. Qualifications 949. Test Procedures 9510. Control 9911. Storage 10012. O-ring Gland Design Information 10212.A Gland Design Static Axial 10812.B Gland Design Static Radial 11012.C Gland Design Dovetail Grooves 11212.D Gland Design Boss Seals 11412.E Gland Design Dynamic Hydraulic 11512.F Hydraulic Seals with Back-up Rings 117Standard Teflex ® O-ring Sizes12.G Gland Design for Encapsulated Teflex ® O-rings 12112.H Gland Design for PTFE O-rings 12412.I Grafics for O-ring deformations according todin 3771 Teil 5 12512.J Gland Design for Kalrez ® O-rings 12813. O-ring Assembling Conditions 13314. O-ring Size Chart 14014.A A.S.568A Standard O-ring Sizes 14114.B Metric Standard O-ring Sizes 15014.C JIS-Sizes 16915. Tolerances and Surface Imperfections 17416. Vulc-O-ring ® and O-ring Cord 18017. O-ring Accessories 18518. O-ring Kits 18619. Quad-rings 19119.A Gland Design for Quad-rings 19219.B Standard Quad-ring Sizes 19519.C For rotating Quad-ring applications 20320. Troubleshooting 20421. Glossary 20722. Conversion Tables 21623. Approvals and Acknowledgements 22024. ERIKS’ Global Network 2212

TECHNICAL DOCUMENTATION O-RINGSIntroductionERIKS started the distribution of O-Rings in 1952. From thisvery modest beginning in Alkmaar (the Netherlands), ERIKShas become a world leader in the production and distributionof O-Rings and elastomeric seals.ERIKS has 2000 collaborators in 50 locations worldwide. Weproduce and distribute seals, gaskets, rubberproducts, engineeringplastics, valves and hoses.Our focus on new markets and new applications has causedERIKS to expand in many O-Ring applications from standardindustrial to high tech semiconductor-applications.Our 25 year business relationship with DuPont DowElastomers on Viton ® and Kalrez ® seals, our 16.000 differentstock items worldwide, our one-day service production, ourhighly qualified engineering staff are only a few examples ofour goal: to be your partner for high performance sealsthroughout the world.ERIKS seals are manufactured in accordance with state ofthe art production and quality control procedures to satisfythe most demanding quality requirements of any industry.ERIKS inventory policies insure that a wide assortment ofseals and fluid sealing products are readily available.As your value-added partner, ERIKS offers the technicalexpertise to provide customized solutions to your sealrequirements. Because of our tremendous technical experience,special applications are no problem for ERIKS.Whether your requirement is for large quantities of durablemolded goods or small quantity engineered prototypes -ERIKS is your total seal source.ERIKS offers not only a broad range of products but a broadrange of services as well. When you need seal solutionsERIKS will be standing by to offer superior technical support,customer service, and inventories to satisfy your seal requirementsquickly and properly.The ERIKS organization is set up to allow direct contactbetween you and our seal specialists.Please call for additional information on these products orany other seal requirements you may have.ResponsibilityThe information in this catalog is based on years of accumulatedexperience in seal technology and is intended for the use of individualshaving technical expertise in the field of seal design. Glanddesigns are according the latest developments and can differ slightlyfrom previous issues. Due to the large variety of applications andoperating parameters, the user, through his own testing and analysis,is solely responsible for making the final selection of product andassuring that all performance and safety requirements are met.Please contact an ERIKS representative for assistance in making yourselection as required. The products, features, specifications, anddesign information in this catalog are subject to change by ERIKS atany time without notice.3

SEALING ELEMENTSIntroductionERIKS O-ring advantages:• Quality Plus: an integrated system of Quality Control• A world-wide network for standard compounds• A broad range of special compounds• Quick supply production• Viton ® and Kalrez ® license from DuPont-Dow-Elastomers• High purity compounds• Engineered solutions to problems• Logistics solutions• Controlled by independent labs4

TECHNICAL DOCUMENTATION O-RINGS1. O-ring StandardsThe O-ring has become the world’smost popular and versatile seal due toits simple shape, low space requirements,and its availability in a vastselection of sizes and compounds tomeet every industrial requirement.The ERIKS O-ring manual is intendedas a guide to assist in the selection ofthe best O-ring out of the correctrubber compound in the right applicationfor engineers, purchasers, andother users of O-rings. We hope thatyou find it both convenient and helpful.This book contains detailed informationconcerning elastomeric compounds,installation information, sizingtables, and groove dimensions.The dimension tables representstandards available from ERIKSinventories.These O-rings are manufactured inaccordance with a variety of standardsfor each country:There are also military material specificationsper a "MIL" designation andaerospace material specifications per a"AMS" designation.Our standard program covers 30.000sizes in a large variety of rubbercompounds for your specific purpose.Technical data and advice are availableat any time. Many non-standard sizesare available upon request.Please contact your ERIKS representative.Our qualified staff guarantees excellentservice. It’s our goal to be your partner.AS 568ABS 1806DIN 3771SMS 1586AFNOR 47501JIS B2401ISO 3601-1USAEnglandGermanySwedenFranceJapanInternational5

SEALING ELEMENTS2. O-ring Sealing PrinciplesO-rings are bi-directional seals, circularin shape and cross section.O-rings are generally made of an elastomericmaterial, but may be made ofother materials such as PTFE or metal.This handbook deals entirely withelastomeric O-rings and PTFE encapsulatedelastomeric O-rings.An O-ring seals through the deformationof the seal material by installationand media pressure to close off thegap between mating components.Higher system pressures can causedeformation through the gap, knownas extrusion, resulting in seal failure.Choosing a harder seal material orinstalling back-up rings to support theO-ring may alleviate this problem.ERIKS O-rings are precision sealcomponents made from a variety ofelastomeric compounds .When you specify an O-ring we needto know the inside diameter (I.D.), thecross section diameter (W), and thecompound (elastomer material) fromwhich the O-ring is to be made.All sealing applications fall into one oftwo categories - those in which theseal or sealed surface moves, andthose in which the seal is stationary.MediaIDMediawID= O-ring inside diameterw= O-ring cross section6

TECHNICAL DOCUMENTATION O-RINGS2. O-ring Sealing PrinciplesA seal that does not move, except forpulsation caused by cycle pressure, iscalled a static seal. Those seals that aresubjected to movement are dynamicseals. These are further defined as reciprocating(seals exposed to linearmotion) and rotary (stationary sealsexposed to a rotating shaft).O-rings can be successfully used instatic as well as dynamic applications.The rubber O-ring should be consideredas an incompressible, viscous fluidhaving a very high surface tension.Whether by mechanical pressure fromthe surrounding geometry or by pressuretransmitted through the hydraulicfluid or gas, this extremely viscous(elastomeric) fluid is forced to flow inthe gland to produce zero clearance ora positive block to the flow of the mediabeing sealed. The O-ring absorbs thestack-up of tolerances of the unit andits memory maintains a sealed condition.Proper seal design begins with thecareful consideration of the sealingapplication. Appropriate material hardness,for example, is determined by thefriction and pressure to which the sealwill be exposed, as well as the crosssectional dimensions of the seal. Otherkey factors include temperature range,adjacent surfaces, and media.Dynamic O-rings may fail by abrasionagainst the cylinder or piston walls.Therefore, the contacting surfacesshould be polished for long seal life.Moving O-rings that pass over ports orother surface irregularities while underpressure are quickly damaged.In designing an O-ring seal, there areusually several standard cross sectionalsizes available. Selecting the best crosssection depends on the application. Ina reciprocating application, the choiceis automatically narrowed because thedesign tables do not include all thestandard O-ring sizes. For any givenpiston or rod diameter, rings withsmaller cross sections tend to twist inthe groove while in motion. This leadsto leakage and failure. The smaller crosssections for each inside diameter aretherefore omitted in the reciprocatingdesign tables. For dynamic applications,the largest cross sectional sizesavailable should be used to increasestability.O-rings in reciprocating applicationsmust be radial compressed betweenthe bottom of the seal groove and thecylinder wall for proper sealing action.This compression or squeeze maycause the O-ring to roll slightly in itsgroove under certain conditions ofmotion, but the rolling action is notnecessary for normal operation of theseal.The shape of the groove is unimportantas long as it results in proper squeezeof the O-ring.Groove dimensions are shown in thetables beginning on page 105. Thegroove depth is measured includingthe gap.7

SEALING ELEMENTS2. O-ring Sealing PrinciplesThe tendency of an O-ring to return toits original shape when the cross sectionis deflected is the basic reasonwhy O-rings make excellent seals.The squeeze or rate of compression isa major consideration in O-ring sealdesign. Elastomers may take up thestack-up of tolerances of the unit andits memory maintains a sealed condition.O-rings with smaller cross sectionsare squeezed by a higher percentageto overcome the relativelyhigher groove dimension tolerances.In static applications the recommendedsqueeze is usually between 15-30%.In some cases the very small crosssections can even be squeezed up to30%.In vacuum applications the squeezecan even be higher. Squeezing morethan 30% induces additional stresswhich may contribute to early sealdeterioration.In dynamic applications therecommended squeeze is between8-16%; due to friction and wearconsiderations,smaller cross sections may besqueezed as much as 20%.O-ring deformationPression = 0 Pression = 8 Mpa0-Ring Sealing PrincipleLeakage(Leakage is possible due topermeability of rubber androughness of the surface)8

TECHNICAL DOCUMENTATION O-RINGS2. O-ring Sealing PrinciplesIdentifying a sealing application typeSealing Application TypesAlthough sealing applications can beclassified in many different ways.A common method for classifyingsealing applications is by the type ofmotion experienced by the application.The common application types aredepicted in the graphic on the right.Sealing tips• Provide detailed seal installation andassembly instructions, especially ifthe unit could be serviced by theend-user of the product. Whenappropriate or required, specify theuse of OEM sealing parts.• Within reason, the larger the crosssection,the more effective the seal.• Avoid sealing axially and radially atthe same time with the same O-ringor Quad ® -ring.• Don’t use a seal as a bearing tosupport a load or center a shaft.This will eventually cause seal failure.FaceAxialStaticDynamicSlow RotationSurface speed less than50 fpm (15 meters/min)OscillatingSlow rotation with areversal of directionReciprocatingLineair motion with areversal of directionRotaryhighSpeed RotationSurface speed greaterthan 50 fpm (15meters/min)Selecting the seal materialWhen selecting the seal material forthe application, carefully consider:• The primary fluids which the O-ringor Quad ® -ring will seal.• Other fluids to which the seal will beexposed, such as cleaning fluids orlubricants.• The suitability of the material for theapplication’s temperature extremes- hot and cold.• The presence of abrasive externalcontaminants.• Lubricating the seal and matingcomponents with an appropiratelubricant before assembling the unit.• Keeping the seal stationary in itsgroove - don’t let it spin with therotating member.• When using back-up rings,increasing the groove width by themaximum thickness of the backupring.• With a face seal, don’t try to sealaround a square corner. Cornersmust have a minimum radius of 4times the seal cross section.9

SEALING ELEMENTS3. O-ring ApplicationsThe O-ring is one of the most popular seal choices because:1.The O-ring is cost effective in purchase price and the cost to machine the sealgroove is relatively low.2.As a bi-directional squeeze seal, the O-ring can be used in an extremely widevariety of successful applications, both static and dynamic.3.The O-ring material allows for maximum stretch or compression and is thereforequite easy to install, generally requiring no special tools.Applications:Static:There are four varieties of staticapplications as noted below:1. AxialThe O-ring cross section is squeezedaxially in the groove similar to a flatgasket. See figure 1-10.Fig. 1-102. RadialThe O-ring cross section is squeezedradially in the groove between theinside (ID) and outside (OD). See figure1-11.Fig. 1-113. DovetailThe O-ring is also axially squeezed in adovetail groove. The groove designallows the O-ring to be retained in theface seal during assembly and maintenance.This is beneficial for specialapplications where the O-ring has tobe fixed by the groove e.g. a lid whichopens regularly. See figure 1-12.CHAMFER RELIEF TOFig. 1-12QFULL THREADSTO THIS POINT4. Boss SealsThe O-ring is used for sealing straightthread tube fittings in a boss. A boss isa cylindrical projection on a casting orforging. The end of that projection ismachined to provide a flat, smoothsurface for sealing. Straight threadsused with an O-ring provide a betterseal than tapered threads used alone.See figure 1-13.HEX FLATS SHOULDBE WITHIN THE 15°±5° ANGLE AND EDIA LIMITATIONSFSQUARENESS BETWEENTHREAD AND FACE OFHEX SHOULD NOTEXCEED H WHEN MEAS-URED AT DIAMETER E45° ±5°ETHREAD.015 RADFOR THREADRUNOUT.031.016RADOYDETAIL‘A’MIN.SPOT-FACEDIAMETERJ MIN. BOSSHEIGHTD DIA.KTHIS DIM. APPLIESTHD. ONLY WHEN TAPP DRILL CAN NOT PASSTHRU ENTIRE BOSSFig. 1-1310

TECHNICAL DOCUMENTATION O-RINGS3. O-ring ApplicationsDynamic Applications:There are three varieties of dynamicapplications as noted below:1. ReciprocatingReciprocating seals refer to seals usedin applications that slide back andforth. This motion introduces friction,which creates design considerationsdifferent from those of static seals.The O-ring may be housed in a groove(rod seal) in the cylinder wall insteadof a groove in the piston surface(piston seal) without any change indesign limitations or seal performance.See figure 1-14.Fig. 1-14Piston sealRod seal2. OscillatingOscillating applications are thoseseeing both rotary and reciprocatingmovement. A valve spindle is anexample of an oscillating application.See figure 1-15.3. RotaryRotary seals refer to seals used inapplications that rotate.See figure 1-16.Fig. 1-15Miscellaneous ApplicationsO-rings are used in a variety of applications.Wipers, buffers, and drivebelt applications are just some of theexamples. See figure 1-17.Fig. 1-16Fig. 1-17 aBeltFig. 1-17 bCrush seal application11

SEALING ELEMENTS4. Basic Elastomers4.1. Select the elastomerThough "elastomer" is synonymouswith "rubber", it is more formally apolymer that can be modified to astate exhibiting little plastic flow andquick or nearly complete recoveryfrom an extending force, and uponimmediate release of the stress, willreturn to approximately its own shape.According to the definition of theAmerican Society for Testing andMaterials (ASTM) for the term "elastomer"it is essential that:*An elastomer part must not breakwhen stretched approximately 100%.*After being stretched 100%, held for5 minutes and then released, it mustretract to within 10% of its originallength within 5 minutes after release.CompoundA compound is a mixture of base polymer(s)and other chemicals which forma finished rubber material. More precisely,the term ‘compound’ refers to aspecific blend of ingredients tailoredfor particular characteristics requiredto optimize performance in some specificservice.The basis of compound design isselection of the polymer type. To theelastomer, the compounder may addreinforcing agents, such as carbonblack, colored pigments, curing or vulcanizingagents, activators, plasticizers,accelerators, anti-oxidants or antiradiationaddiditives. There may behundreds of such combinations.The physics of RubberRubber is composed of long chains ofrandomly oriented molecules. Theselong chains are subject to entanglementand cross-linking. The entanglementhas a significant impact on theviscoelastic properties such as stressrelaxation. When a rubber is exposedto stress or strain energy, internalrearrangements such as rotation andextension of the polymer chains occur.These changes occur as a function ofthe energy applied, the duration andrate of application, as well as the temperatureat which the energy is applied.ISO 1629 identifies approximately 25elastomeric types. This chapter coversthe various material types used ino-ring manufacture.Resistance to the mediaAs used throughout this manual, theterm "media" denotes the substanceretained by the o-ring. It may be aliquid, a gas, or a mixture of both. Itcan even include powders or solids aswell. The chemical effect of the mediaon the O-ring is of prime importance. Itmust not alter the operational characteristicsor reduce the life expectancyof the o-ring. Excessive deteriorationof the O-ring must be avoided. It iseasy, however, to be misled on thispoint. A significant amount of volumeshrinkage usually results in prematureleakage of any O-ring seal, whetherstatic or dynamic. On the other hand,a compound that swells excessively,or develops a large increase ordecrease in hardness, tensile strength,or elongation, will often continue toserve well for a long time as a staticseal, in spite of undesirable test resultson elastomer compounds. The firststep in selecting the correct material isto select an elastomer that is compatiblewith the chemical environment.HighPhysical PropertyLowLowCross-link DensityRelationship of Cross-link Denisity and Physical PropertiesHigh12

TECHNICAL DOCUMENTATION O-RINGS4. Basic ElastomersAcrylonitrile butadiene, Nitrile or Buna N (NBR)Nitrile, chemically, is a copolymer of butadiene and acrylonitrile. Acrylonitrile contentvaries in commercial products from 18% to 50%. As the nitrile contentincreases, resistance to petroleum base oils and hydrocarbon fuels increases, butlow temperature flexibility decreases.Due to its excellent resistance to petroleum products, and its ability to be compoundedfor service over a temperature range of -30°F to +250°F (-35°C to+120°C), nitrile is the most widely used elastomer in the seal industry today. Alsomany military rubber specifications for fuel and oil resistant O-rings require nitrilebased compounds. It should be mentioned that to obtain good resistance to lowtemperature, it is often necessary to sacrifice some high temperature resistance.Nitrile compounds are superior to most elastomers with regard to compression set,tear, and abrasion resistance. Nitrile compounds do not possess good resistanceto ozone, sunlight, or weather. They should not be stored near electric motors orother ozone generating equipment. They should be kept from direct sunlight.However, this can be improved through compounding.NBR is the standard material for hydraulics and pneumatics. NBR resists oil-basedhydraulic fluids, fats, animal and vegetable oils, flame retardant liquids (HFA, HFB,HFC), grease, water, and air.Special low-temperature compounds are available for mineral oil-based fluids.By hydrogenation, carboxylic acid addition, or PVC blending, the nitrile polymercan meet a more specified range of physical or chemical requirements.The quality of Nitrile-compounds depends on the percentage of acrylonitrile in thebase polymer. The following table indicates the change of properties as a functionof acrylonitrile content.50% -15°CLowHigherLowAcrylonitrile %Flexibility at low temperatureVolume change in oilCompression setPermeability18% -55°CHighLowerHigh13

SEALING ELEMENTS4. Basic ElastomersHydrogenated nitrile, or highly saturated nitrile (HNBR)HNBR has recently been developed to meet higher temperatures than standardNBR while retaining resistance to petroleum based oils. Obtained by hydrogenatingthe nitrile copolymer, HNBR fills the gap left between NBR, EPDM and FKM elastomerswhere high temperature conditions require high tensile strength while maintainingexcellent resistance to motor oils, sour gas, amine/oil mixtures, oxidizedfuels, and lubricating oils.HNBR is resistant to mineral oil-based hydraulic fluids, animal and vegetable fats,diesel fuel, ozone, sour gas, dilute acids and bases. HNBR also resists new bio-oils(biological oils). HNBR is suitable for high dynamic loads and has a good abrasionresistance. HNBR is suitable for temperatures from -30°C to +150°C (-20°F to+302°F).Carboxylated nitrile (XNBR)The carboxyl group is added to significantly improve the abrasion resistance of NBRwhile retaining excellent oil and solvent resistance. XNBR compounds provide hightensile strength and good physical properties at high temperatures.XNBR is suitable for temperatures from -30°C to +150°C (-20°F to +302°F).Nitrile/PVC resin blends (NBR/PVC)PVC resins are blended with nitrile polymers to provide increased resistance toozone and abrasion. The PVC also provides a significant improvement in solventresistance, yet maintains similar chemical and physical properties, commonly notedamong nitrile elastomers. The addition of the PVC resins also provide a greaterpigment-carrying capacity which allow better retention of pastel and bright colors.Ethylene Propylene, and Ethylene Propylene Diene rubber (EPM, EPDM)Ethylene propylene rubber is an elastomer prepared from ethylene and propylenemonomers (ethylene propylene copolymer) and at times with an amount of a thirdmonomer (ethylene propylene terpolymers). Ethylene propylene rubber has atemperature range of -50°C to +120°/150°C (-60°F to +250°/300°F), depending onthe curing system.It has a great acceptance in the sealing world because of its excellent resistance toheat, water and steam, alkali, mild acidic and oxygenated solvents, ozone, and sunlight.These compounds also withstand the affect of brake fluids and Skydrol andother phosphate ester-based hydraulic fluids. EPDM compounds are not recommendedfor gasoline, petroleum oil and grease, and hydrocarbon environments.Special EPDM compounds have good resistance to steam.• EPDM Sulphur cured: inexpensive material for normal use, maximum temperatureof +120°C (+250°F).• EPDM Peroxide cured: for hot water, vapor, alcohols, ketones, engine coolants,organic and inorganic acids and bases. Not resistant to mineral oils. For maximumtemperatures of +150°C (+300°F).14

TECHNICAL DOCUMENTATION O-RINGS4. Basic ElastomersNeoprene rubber Polychloroprene (CR)Neoprene rubbers are homopolymers of chloroprene (chlorobutadiene) and wereamong the earliest synthetic rubbers used to produce seals. CR has good agingcharacteristics in ozone and weather environments, along with abrasion and flexcracking resistance. CR is not effective in aromatic and oxygenated solvent environments.Neoprene can be compounded for service temperatures of -40°C to + 110°C(-40°F to +230°F).Most elastomers are either resistant to deterioration from exposure to petroleumbased lubricants or oxygen. Neoprene is unusual in having limited resistance to both.This, combined with a broad temperature range and moderate cost, accounts for itsdesirability in many seal applications for refrigerants like Freon® and ammonia. CR isresistant to refrigerants, ammonia, Freon® ( R12, R13, R21, R22, R113, R114, R115,R134A), silicone oils, water, ozone, vegetable oils, alcohols, and low-pressure oxygen.CR has a very low resistance to mineral oils.Silicone rubber (VMQ).Silicones are a group of elastomeric materials made from silicone, oxygen, hydrogen,and carbon. Extreme temperature range and low temperature flexibility are characteristicsof silicone compounds. As a group, silicones have poor tensile strength, tearresistance, and abrasion resistance. Special compounds have been developed withexceptional heat and compression set resistance. High strength compounds havealso been made, but their strength does not compare to conventional rubber.Silicones possess excellent resistance to extreme temperatures -50°C to + 232°C(-58°F to +450°F). Some special compounds resist even higher temperatures.Retention of properties of silicone at high temperature is superior to most other elasticmaterials.Silicone compounds are very clean and are used in many food and medical applicationsbecause they do not impart odor or taste. Silicone compounds are not recommendedfor dynamic O-ring sealing applications due to relatively low tear strengthand high coefficient of friction.Silicone is resistant to hot air, ozone, UV radiation, engine and transmission oils, animaland vegetable fats and oils, and brake fluids. VMQ also has low resistance tomineral oils. Silicone can be compounded to be electrically resistant, conductive, orflame retardant.Many silicone compounds have a higher than normal mold shrinkage. Therefore productionmolds for silicone products are often different than molds for nitrile.15

SEALING ELEMENTS4. Basic ElastomersFluorosilicone (FVMQ)Fluorosilicone combines the good high- and low-temperature properties of siliconewith limited fuel and oil resistance. Fluorosilicones provide a much wider operationaltemperature range than Fluorocarbon rubbers. Primary uses of fluorosilicone O-ringsare in fuel systems at temperatures up to +177°C (+350°F) and in applications wherethe dry-heat resistance of silicone O-rings are required.Fluorosilicone O-rings may also be exposed to petroleum based oils and/or hydrocarbonfuels. In some fuels and oils; however, the high temperature limit in the fluidlist is more conservative because fluid temperatures approaching 200°C (390°F) maydegrade the fluid, producing acids which attack fluorosilicone O-rings. For lowtemperature applications, fluorosilicone O-rings seal at temperatures as low as -73°C(-100°F).Due to relatively low tear strength, high friction and limited abrasion resistance ofthese materials, they are generally recommended for static applications only.Fluorosilicones with high tear strength are also available. Some of these compoundsexhibit improved resistance to compression set. Many fluorosilicone compounds havea higher than normal shrinkage rate so production molds for fluorosilicone productsare often different from molds for nitrile.Polyurethane rubber (AU, EU)Polyurethanes (Polyester-urethane AU), (Polyether-urethane EU) exhibit outstandingmechanical and physical properties in comparison with other elastomers. Urethanesprovide outstanding resistance to abrasion and tear and have the highest availabletensile strength among all elastomers while providing good elongation characteristics.Ether based urethanes (EU) are directed toward low temperature flexibilityapplications. The ester based urethanes (AU) provide improved abrasion, heat, andoil swell resistance.Over a temperature range of -40°C to +82°C (-40°F to +180°F), resistance to petroleumbased oils, hydrocarbon fuels, oxygen, ozone and weathering is good.However, polyurethanes quickly deteriorate when exposed to acids, ketones andchlorinated hydrocarbons. Certain types of polyester-urethanes (AU) are also sensitiveto water and humidity. Polyether-urethanes (EU) offer better resistance to waterand humidity.The inherent toughness and abrasion resistance of polyurethane (EU) seals is particularlydesirable in hydraulic systems where high pressures, shock loads, widemetal tolerances, or abrasive contamination is anticipated.Fluorocarbon rubber (FKM)Fluorocarbon elastomers have grown to major importance in the seal industry. Dueto its wide range of chemical compatibility, temperature range, low compressionset, and excellent aging characteristics, fluorocarbon rubber is the most significantsingle elastomer developed in recent history.Fluorocarbon elastomers are highly fluorinated carbon-based polymers used inapplications to resist harsh chemical and ozone attack. The working temperaturerange is considered to be -26°C to +205°/230°C (-15°F to +400°/440°F). But forshort working periods it will take even higher temperatures.Special compounds having improved chemical resistance are also available withnew types always being developed. Generally speaking, with increasing fluorinecontent, resistance to chemical attack is improved while low temperature characteristicsare diminished. There are, however, specialty grade fluorocarbons that canprovide high fluorine content with low temperature properties.Ask for our original Viton®handbook on O-rings.16

TECHNICAL DOCUMENTATION O-RINGS4. Basic ElastomersFluorocarbon O-rings should be considered for use in aircraft, automobile and othermechanical devices requiring maximum resistance to elevated temperatures and tomany fluids. FKM (FPM, Viton®, Fluorel®) resist mineral oils and greases, aliphatic,aromatic and also special chlorinated hydrocarbons, petrol, diesel fuels, siliconeoils and greases. It is suitable for high vacuum applications.Many fluorocarbon compounds have a higher than normal mold shrinkage rate,molds for fluorocarbon products are often different from molds for Nitrile.Perfluorocarbons (FFKM)The relative inertness of fluorocarbon rubbers is provided by fluorine-carbon bondson the elastomer backbone. Generally speaking, with increasing fluorine content,resistance to chemical attack is improved. Where fluorocarbon rubbers have a fluorinecontent of 63 - 68 %, the perfluorocarbons have a fluorine content of 73%.Perfluorelastomers possess excellent resistance to extreme temperatures -26°C to+260°C (-15°F to +500°F). FFKM perfuoroelastomers: (Kalrez®) offers the bestchemical resistance of all elastomers.Some types are particularly suitable for hot water, steam and hot amines. Someresist temperatures up to +326°C (+620°F).Many perfluorocarbon compounds have unusual mold shrinkage, production moldsfor perfluorocarbon products are different from molds for nitrile.Teflon®-FEPFEP is a copolymer of tetrafluorethylene and hexafluorpropylene. FEP has a lowermelting point than PTFE making it suitable for injection moulding. FEP is used forencapsulation with TEFLEX ® O-rings. FEP has a wide spectrum of chemical compatibilityand temperature range and excellent aging characteristics. Maximum operatingtemperature for FEP is +205°C (+400°F). A Teflon PFA encapsulation is availablefor higher temperatures (260°C).TFE/P (Aflas®) (FEPM)TFE/P is a copolymer of tetrafluoroethylene and propylene with a fluorine content ofapp. 54%. This material is unique due to its resistance to petroleum products, steam,and phosphate-esters. In some respects it exhibits media compatibility propertiessimilar to ethylene propylene and fluorocarbon. The compression set resistance athigh temperatures is inferior to standard fluorocarbons. Service temperatures are-5°C (25°F) to +204°C (+400°F). TFE/P provides improved chemical resistance to awide spectrum of automotive fluids and additives. It is resistant to engine oils of alltypes, engine coolants with high level of rust inhibitors, extreme pressure (EP) gearlubricants, transmission and power steering fluids, and all types of brake fluidsincluding DOT 3, mineral oil, and silicone oil.TFE/P is ideal for heat transfer media, amines, acids and bases, as well as hot waterand steam up to +170°C (+340°F).17

SEALING ELEMENTS4. Basic ElastomersPolyacrylate rubber (ACM)Polyacrylate-Acrylic Acid Ester. These compounds are designed to withstand heatwhile retaining oil resistance. Specially designed for sulfur bearing oil applications ,ACMs are subjected to heat and bearing environments. They have good resistance todry heat, oxygen, sunlight, and ozone but their low temperature properties are relativelypoor and they have low swell in mineral oils. Service temperatures are -20°C(-5°F) to 150°C (300°F). ACM is mainly used for O-rings and shaft seals to seal heavyoils at high temperatures and in the automotive industry for transmission and powersteering applications.Epichlorohydrin (CO, ECO)Epichlorohydrin rubber compounds are noted for their superior gas impermeabilityand physical properties over a wide temperature range while maintaining excellentresistance to petroleum oils. It has a stable cycling capability from low to hightemperature. Resistance to ozone, oxidation, weathering, and sunlight are other typicalECO qualities. Service temperatures are -51°C to150°C (-60°F to +300°F).Compounds from this polymer can exhibit a corrosive nature and can be difficult toprocess in manufacturing.Vamac®Ethylene Acrylate. This material exhibits properties similar to polyacrylate but can beformulated to exhibit lower temperature capabilities. It has excellent resistance tooxidation, automatic transmission, and power steering fluids.The temperature service range is -40°C to +150°C (-40°F to +300°F).Styrene Butadiene (SBR, Buna S)This material is similar to natural rubber. O-ring usage has been on decline since theintroduction of ethylene propylene. SBR still finds service in brake fluid applications,although the high temperature range is inferior to that of ethylene propylenecompounds. Service range for this material is -50°C to +110°C (-65°F to +225°F).Butyl (IIR)Butyl has excellent resistance to phosphate ester fluids such as Skydrol, but has aninferior high temperature limit when compared to ethylene propylene. Butyl exhibitsthe best resistance to gas permeability and some rocket propellents. For O-ring applications,butyl has been all but replaced by ethylene propylene.The temperature service range for this material is -55°C to +105°C (-65°F to +225°F).Special materialsERIKS offers many possibilities in special O-rings compounds to improve certainproperties like: Silicone free and Labs free Coatings - Encapsulated FEP and PFA -PTFE O-rings - Internal Lubrication - High Purity - Micro O-rings - Vulc-O-rings.Ask for information in our‘High Purity Seals Handbook ’.www.eriks.comHomologationsERIKS offers many compounds with homologations, like: KTW – FDA – WRC –NSF – DVGW.KTWNSFWRC DVGW ACSKIWA18

TECHNICAL DOCUMENTATION O-RINGS4. Basic ElastomersTable 3A-1Elastomer NBR EPM CR VMQ FVMQ EU FKM FFKM PTFE-FEPASTM Nitrile EPR Neoprene Silicone Fluoro Urethane Fluoro Perfluoro encapsusiliconecarbon carbon latedGENERALHardness (Shore "A") 20/ 90 30/90 15/95 20/90 35/80 60/95 50/95 65/90 -Temp. range °F/°C max. 230/110 266/130 248/120 446/230 446/230 176/80 410/210 620/326 400/205Temp. range °F/°C min. -30/-35 -67/-55 -49/-45 -67/-55 -76/-60 -22/-30 5/-15 -58/504 -76/-605NOTE : The temperature range is strongly dependent by the specific compoundCompression Set B C C A B E C B EWear Resistance C C C E E A C C EGas Permeability C C C E E B C C ENOTE : The compression set value for Kalrez ® is relative to temperature. In low temperature applications this value is reasonable, in high temperaturesthis value is good to very good.Air E B C A B C B A +Alcohol B A B B B U E A +Aldehydes U B U C U U U Bfi +Aliphatic Hydrocarbons C U E E A C A A +Alkalis B A C B B B C A +Amines B1 B1 B1 E1 B1 U U Bfi +Animal Fats B U C C A C B A +Aromatic Hydrocarbons D U D U B D A A +Esters, Alkyl Phosphate U B U C U U U A +(Skydrol)Esters, Aryl Phosphate U A U C B U A A +Esters, Silicate C U E U B U A A +Ethers U E U U E E U A +Halogenated hydrocarbons U U U U B E A A +Inorganic Acids E C B B B U A A +Ketones U A A C A U U B +Mineral Oil, high analine fats B U C C B A A A +Mineral Oil, low analine fats B U U E B B A A +Organic Acids C C C B B U C A +Silicone Oils A A2 A E E A A A +Vegetable Oils A U C B B E A A +Water / Steam C A E E E U B⁄ C4 +A Good 1 See the list "compound selection for chemicals and fluids"B Satisfactory 2 EPDM/EPR may shrinkC Fair 3 Depending on FKM typeD Doubtful 4 Depending on compoundE Poor 5 Depending on elastomer coreU Unsatisfactory + in general "A" because the encapsulation is FEPThis information is intended only as a guideline. Chemical compatibility lists should be consulted. ERIKS will provide this on request.Whenever possible the fluid compatibility of the O-ring compound should be rated "A". For a static seal application a rating "B" is usually acceptable,but it should be tested.Where a "B" rated compound must be used, do not expect to re-use it after disassembly. It may have swollen enough that it cannot be reassembled.When a compound rated "C" is to be tried, be sure it is first tested under the full range of operating conditions.It is also particularly important to test seal compounds under service conditions when a strong acid is to be sealed at elevated temperaturesbecause the rate of degradation of rubber at elevated temperatures is many times greater than the rate of degradation at room temperature.19

SEALING ELEMENTS4. Basic ElastomersChemical and Physical TablesPolymerTensileStrength (MPa)Tensile Modulusat 100% (MPa)Hardness Durometer(Shore A)Enlongation (%)CompressionSet RatingLow TempRange °FLow TempRange °CHigh TempRange °FHigh TempRange °CHeat Aging at212°F (100°C)SteamResistanceFlameResistanceWeatherResistanceSunlightResistanceOzoneResistanceNBR 6.9- 2.0-15 20-100 100-650 Good -70 to 0 -57 to 210 to 99 to Good Fair- Poor Fair- Poor Fair-27.6 Exc. -18 250 121 Good Good Good GoodHNBR 31.0- 1.7- 30-95 90-450 Good- -50 to 0 -46 to 250 to 121 to Exc. Fair- Poor Good- Good- Good-10.0 20.7 Exc. -18 3000 149 Good Exc. Exc. Exc.FKM 3.4- 1.4- 50-95 100- Good- -50 to 0 -46 to 400 to 200 to Exc. Poor- Good- Exc. Good- Exc.20.7 13.8 500 Exc. -18 500 260 Good Exc. Exc.EP 2.1- 0.7- 30-90 100- Poor- -75 to -46 to 220 to 104 to Good- Exc. Poor Exc. Exc. Good-24.1 20.7 700 Exc. -40 -18 300 149 Exc. Exc.SBR 3.4- 2.1- 30-100 450- Good- -75 to -59 to 210 to 99 to Good Fair- Poor Fair- Poor Poor24.1 10.3 600 Exc. -55 -48 250 121 Good GoodCR 3.4- 0.7- 15-95 100- Poor- -70 to -57 to 200 to 93 to Good- Fair Good- Fair- Good- Good-27.6 20.7 800 Good -30 -34 250 121 Exc. Good Exc. Good Exc. Exc.IIR 13.8- 0.3- 30-80 300- Poor- -70 to -57 to 250 to 121 to Good- Good- Poor Exc. Exc. Exc.20.7 3.4 850 Good -400 -40 300 149 Exc. Exc.VMQ, Si, 1.4- 6.2 20-90 100- Good- -178 to -117 to 400 to 204 to Exc. Fair- Fair- Exc. Exc. Exc.PMQ, 10.3 900 Good -90 -68 500 260 Good Exc.PVMQFVMQ 3.4- 3.1- 35-80 100- Fair- -112 to -80 to 400 to 204 to Exc. Fair Exc. Exc. Exc. Exc.9.7 3.4 480 Good -90 -68 450 232ACM 8.6- 0.7- 40-90 100- Poor- -30 to 0 -34 to 250 to 121 to Exc. Poor Poor Exc. Good- Good-17.2 10.3 450 Good -18 350 177 Exc . Exc.EA 6.9- 0.7- 35-95 200- Poor- -35 to -48 to 250 to 121 to Exc. Poor- Poor Exc. Exc. Exc.20.7 10.3 650 Good -30 -34 350 177 FairCSM 3-15 0.2-10 40-100 100- Poor- -60 to -51 to 225 to 107 to Good- Poor- Good- Exc. Exc. Exc.700 Fair -40 -40 270 132 Exc. Good Exc.ECO 10-15 1-10 30-95 200- Good- -60 to -51 to 225 to 107 to Good- Fair- Poor- Good Good Good-800 Fair -15 -26 275 135 Exc. Good Good Exc.NR; IR 3.4- 0.5-0.8 20-10 300- Exc. -70 to -57 to 180 to 82 to Fair- Fair- Poor Poor- Poor Poor34.5 900 -40 -40 220 104 Good Good FairAU, EU 6.9- 0.2- 10-100 250- Poor- -65 to -54 to 180 to 82 to Fair- Poor Poor- Exc. Good- Exc.69.0 34.5 900 Good -40 -40 220 104 Good Good Exc.20

SEALING ELEMENTS4. Basic ElastomersChemical Terms, Abbreviations, and Trade NamesChemical Term ASTM Designated Polymer Trade NamesAbbreviationAcrylonitrile Butadiene NBR Chemigum ® , Nipol ® , Krynac ® , Paracril ® , Perbunan N ® , BunaN ®Highly Saturated Nitrile HNBR Therban ® , Zetpol ®Carboxylated Nitrile XNBR Nipol ® , Krynac ® , Chemigum ®Fluorocarbon FKM, FEPM Dyneon ® , Viton ® , Aflas ® , Fluorel ®Ethylene Propylene EP, EPDM, EPT, EPR Nordel ® , Royalene ® Vistalon ® , Buna EP ® , Keltan ®Styrene Butadiene SBR Ameripol Synpol ® , SBR ® , Plioflex ® , Stereon ®Polychloroprene CR Neoprene ® , Baypren ® , Butaclor ®Isobutylene Isoprene IIR Butyl ®Silicone VMQ, PMQ, PVMQ Silastic ® , SILPLUS ® , Elastosil, Wacker ®Fluorosilicone FVMQ FSE ® , Silastic ® , Sylon ®Polyacrylate ACM Cyanacryl ® , HyTemp ® , Thiacril ®Ethylene Acrylic AEM Vamac ®Chlorosulfonated Polyethylene CSM Hypalon ®Epichlorohydrin ECO/CO Gechron ® , Hydrin ®Polyisoprene• Natural NR SMR ® , Pale Crepe ® , Smoked Sheet ®• Synthetic IR Ameripol SN ® , Natsyn ®Polyurethane (Polyester or Polyether) AU or EU Adiprene ® , Millathane ® , Vibrathane ® , Vulkolan ® , PURPerfluoroelastomer FFPM Kalrez ® , Isolast ® , Chemraz ® , Simriz ® , Parofluor ®The following are registered trademarks of their respective companies:Cyancryl - American Cyanamid Co.; Ameripol CB, Ameripol SN, Ameripol Synpol - Ameripol Synpol Co.; Butaclor - distigil;Silastic - Dow Corning Corp.; Hypalon, Nordel, Vamac, Viton - Du Pont Dow Co.; Vistalon - Exxon Chemical Co.; Stereon -Firestone Tire & Rubber Co.; FSE, SILPLUS - General Electric Co.; Budene, Chemigum, Natsyn, Philoflex - Goodyear RubberProducts Corp.; Herclor - Hercules Inc.; Aflas, dyneon, sylon - Dyneon Co.; Hydrin, Hy Temp, Gechron, Nipol, Zetpol - ZeonChemicals Inc.; Krynac, Taktene, Tornac, Perbunan N, Buna EP, Baypren, Therban - Bayer Corp.; Millathane - TSE Industries,Inc.; Adiprene, Royalene, Paracril, Thiacril, Vibrathane; Uniroyal, Inc.24

TECHNICAL DOCUMENTATION O-RINGS5. Designing with RubberIn designing an O-ring seal, it is importantto determine the O-ring compoundearly, as the compound selected mayhave an influence on the gland design.The application determines the rubbercompound, the primary factor being thefluid to be sealed. But the elastomermust also resist extrusion whenexposed to the maximum anticipatedpressure and be capable of maintaininggood physical properties through the fulltemperature range expected.This chapter discusses the next criteriathat must be considered like compressionset, hardness, tensile strength,chemical compatibility, thermal effects,pressure, and extrusion. Data and proceduresenabling the designer to meetparticular requirements or obtain specificperformance from the seal will befound in this chapter.Compression Set and SqueezeCompression set is the percentage ofdeflection that the elastomer fails torecover after a fixed period of timeunder a specific squeeze and temperature.Compression set is a very importantsealing factor, because it is a measureof the expected loss of resiliencyor "memory" of a compound.Compression set is generally determinedin air and measured as a percentageof original deflection. Althoughit is desirable to have a low compressionset value, this is not so critical as itmight appear because of actual servicevariables. For instance, an O-ring maycontinue to seal after taking a 100%compression set, provided the temperatureand system pressure remainsteady and no motion or force causes abreak in the line of seal contact. Also,swelling caused by contact with theservice fluid, may compensate for compressionset. The condition most to befeared is the combination of high compressionset and shrinkage. This willlead to seal failure unless exceptionallyhigh squeeze is employed.Compression set is calculated asfollows:C =t 0 - t 1t 0 - t sx 100 %LoadSqueezecCompressionsett 0 t 1t sOriginalO-ring WUnderLoadAfter test and30 min. relaxationCompression set illustration25

SEALING ELEMENTS5. Designing with RubberLower compression set values indicateimproved remaining seal capacity.Compression set values generallyincrease with increased temperatureand time.For O-rings the minimum squeezeshould be about .007 inch. (0,175mm).The reason is that with a very lightsqueeze almost all elastomers quicklytake 100% compression set. A goodcompression set resistant compoundcan be distinguished from a poor oneonly when the squeeze is more than.005 inch. (0,127mm)Most O-ring seal applications cannottolerate the no squeeze condition, theexceptions are the floating ringdesigns in special pneumatic androtary applications.The most commonly used standardsfor the expression of compression setare ASTM D 395 and DIN 53517.Table 3A-1a gives compression setvalues for standard Eriks compounds,(Squeeze 25%).Table 3A-1aMaterial Hardness Compression set Temp. RangeIRHD ± 5 22h/100°C, 25%, °C °Fon O-ring 3.53 mm.NBR 36624 70 max. 20% -30+120 -22+248NBR 47702 90 max. 30% -30+120 -22+248EPDM 55914 70 max. 30% -50+120 -58+248EPDM 55914 PC 70 max. 25% (150 °C) -50+150 -58+302Silicone 71477 70 max. 40% (200 °C) -60+220 -76+428Neoprene 32906 70 max. 25% -35+110 -31+230Viton® black 51414 70 max. 18% (200 °C) -20+200 -4+392Viton® green 51414 70 max. 19% (200 °C) -20+200 -4+392Viton® black 514320 90 max. 18% (200 °C) -20+200 -4+392Viton® V black/brown 514075 75 max. 11% (200 °C) -20+200 -4+392Quad-rings in NBR/FPM/EPDM 70/90 - -30+120 22+248Note:It is important to notice that the compressionset changes with time anddepends on cross section diameter.This table shows these differentvalues, measured on the samecompound.NBR 36624 O-ringsCross section mm 1,78 3,53 6,99Compression set 22h/100°C (212°F) 14,8 12,8 9,2Compression set 70h/100°C (212°F) 23,9 22,7 16,826

TECHNICAL DOCUMENTATION O-RINGS5. Designing with RubberO-ring HardnessThe hardness of an O-ring is importantfor several reasons.The softer the elastomer, the better theseal material conforms to the surfacesto be sealed and lower pressure isrequired to create a seal. This is particularlyimportant in low pressure seals thatare not activated by fluid pressure.The softer the elastomer, the higher thecoefficient of friction. In dynamic applicationshowever, the actual running andbreakout friction values of a hardercompound with lower coefficients offriction are higher because the loadrequired to squeeze the harder materialinto the O-ring groove is much greater.The softer the elastomer the more riskthat at high operating pressure the elastomerof the O-ring will extrude into theclearance gap between the mating sealsurfaces.The harder materials offer greater resistanceto flow.With an increase in temperature, elastomersfirst become softer and theneventually harder as the rubber curingprocess continues with the applicationof heat.The hardness of most elastomers isindicated by a durometer rating on agauge manufactured by the ShoreInstrument Company or equivalent.Most elastomers are measured on theShore "A" scale. Shore A hardness of35° is soft; 90° is hard. Shore "D"gauges are recommended where theShore "A" rating is greater than 90°. Themost common standards for measuringhardness are ASTM D2240, DIN 53505,BS 2719, and ISO 7619. These standardsdefine a gauge reading on a standardsample with a thickness of 0,25 in.(6 mm.). Always use standard hardnessdiscs 1.28 in. diam. by 0,25 in. thick(ø32 x6 mm.), or 6 in.x 6 in.x 0.075 in.(150x150x2 mm.) sheets piled up to aminimum of 0,25 in. (6 mm.) to determinedurometer hardness.It has been almost impossible to obtainreliable and reproducible hardnessreadings on seals with curved surfacesand variable cross sections such as O-rings. This problem has plagued theindustry for years and is acknowledgedin some standard tests. Like ASTMMethod D 2240-00, paragraph 6.2.1states: "A suitable hardness determinationcannot be made on an uneven orrough point of contact with the indentor".Also MIL-P-5510B, paragraph4.4.2. states : "Test specimens for thepurpose of batch testing shall consistof one compression molded hardnessspecimen 0,25 in. thick and 1 in. diameterminimum ( 6 mm. thick and 25 mm.diameter)." The specification states in anote "Hardness shall not be determinedfrom actual packings."However, for specimens that are toothin or provide too small an area foraccurate Shore durometer readings,the Wallace Micro Hardness Tester isthe most recommended method.Measurements in Micro-IRHD are moreaccurate for O-rings. This method ofmeasurement is recorded in the standardsASTM D1415 and DIN 53519.Differences between IRHD and Shore"A" are negligible on the 6 mm thicksample.Normally, durometer hardness isreferred to in increments of five or ten,as in 60 durometer, 70 durometer, 75durometer, etc. Not as 62, 66, or 72durometer. This practice is based onthe fact that hardness is generallycalled out in specifications with a toleranceof ± 5 and also on the inherentvariance from batch to batch of a givenrubber compound due to slight differencesin raw materials and processingtechniques and the variability encounteredin reading durometers.27

SEALING ELEMENTS5. Designing with RubberIRHD and Shore ADurometer Ranges Rubber-Plastics150140PHENOLICSACRYLICS1,78130110120IHRD-MicroDIN 53 519 Teil 2Norm : 2 mm sheetTime : 30 sec.Shore A DIN 53 505Norm : 6 mm sheetTime : 3 sec.PLASTICSURETHANERUBBER110100908070605040100 110901008090707060505030402030ROCKWELL R20100DUROMETER DNYLONPOLYSTYRENEPOLYPROPYLENEFLUORCARBONSCAR TIRES3020RUBBER BANDS100DUROMETER AHardness versus TemperatureHardness (Shore A)Temperature °CTemperature °F28

TECHNICAL DOCUMENTATION O-RINGS5. Designing with RubberTensile Strength and ElongationModulusTensile strength is a measurement ofthe amount of force required to rupturean elastomeric specimen. Tensilestrength is a fair production controlmeasurement used to insure uniformityof the compound, and also useful asan indication of deterioration of thecompound after it has been in contactwith a fluid for long periods of time. If alarge reduction in the tensile strengthoccurs, the life of a seal may be relativelyshort. Exceptions to this rule dooccur.Elongation is an increase in lengthexpressed numerically as a percentageof initial length at the point of rupture.This property primarily determines thestretch which can be tolerated duringthe installation of a seal.An adverse change in the elongation ofa compound after exposure to a fluidis a definite sign of degradation of thematerial. Elongation, like tensilestrength, is used throughout the industryas a check on production batchesof compound.Tests are performed on dumb-bellshaped samples on a machine pullingthem apart axially at a constant speedof 500 mm per minute, during whichthe force and elongation of the sampleare recorded.Standards tests for Tensile strengthand Elongation are ASTM D412, DIN53505, and BS 903, Part A3.Modulus, as used by the rubber industry,refers to stress at a predeterminedelongation, usually 100%. It gives acomparison for good extrusion resistance.Modulus normally increaseswith increase in hardness and is probablythe best indicator of the strengthof a compound, all other factors beingequal.Stress (MPa)IRHD (degrees)Hardness (IRHD) versus Young’s Modulus (M)1= Speciality FKM2= Black FFKM3= Standard FKM4= White FKM5= Ethylene Propylene6= Nitrile7= Fluorsilicone8= SiliconeLog 10M (M in psi)213 47856Stress (PSI)Elongation (%)Stress versus Strain29

SEALING ELEMENTS5. Designing with RubberTensile Stress-StrainTensile strength is the maximum tensilestress reached in stretching a testpiece (either an O-ring or dumbbell).Elongation: the strain or ultimateelongtion is the amount of stretch atthe moment of break.Modulus: also called ‘Mod.100’; this isthe stress required to produce a givenelongation. In the case of Mod 100, themodulus would be the stress requiredto elongate the sample 100%.In elastomers, the stress is not linearwith strain. Therefore, the modulus isneither a ratio nor a constant slope -but rather denotes a specific point onthe stress-strain curve.Tensile tests are used for controllingproduct quality and for determining theeffect of chemical or thermal exposureon an elastomer. In the latter case, it isthe retention of these physical properties,rather than the absolute values ofthe tensile stress, elongation or modulus,that is often significant.Tear strengthThe tear strength or tear resistance isrelatively low for most compounds.This test measures the force to perpetuatea nick or cut. Seal compoundswith poor tear resistance will fail quicklyunder further flexing or stress, oncea crack is started. Low tear strength ofa compound is also indicative of poorabrasion resistance which may lead toearly failure of an O-ring used as adynamic seal.Volume changeVolume change is the increase ordecrease of the volume of an elastomerafter it has been in contact witha medium. It is measured as a percentage(%). Increase by swell or decreaseby shrinkage in volume is almostalways accompanied by a change inhardness.Volume swell is caused by absorptionof gaseous or liquid medium by the O-ring. In static applications, evenTensile Strength (MPa)extreme volume swell can sometimesbe tolerated. Actually an O-ring canswell only until 100% gland fill and furtherincrease of volume is not possible,regardless of how much volume swellis observed in a full immersion test. Ifthe free state swell exceeds 50 percent;however, a radially squeezeassembly may be almost impossible totake apart because of the friction generated.In dynamic applications, volume swellup to 15 or 20 percent is usuallyacceptable, but higher values are likelyto increase friction and reduce toughnessand abrasion resistance to thepoint that use of a particular compoundis no longer feasible.Volume shrinkage is often caused byfluids which extract the plasticizersfrom the compound. Decrease in volumeis usually accompanied by anincrease in hardness. Also, as swellcompensates for compression set,shrinkage will intensify the compressionset effect, causing the O-ring topull away from sealing surfaces -providing a leakage path. It is apparentthen, that shrinkage is far more criticalthan swell. More than 3 or 4%shrinkage can be a serious problemfor dynamic O-ring seals.Hardness (Shore A)30

TECHNICAL DOCUMENTATION O-RINGS5. Designing with RubberChemical CompatibilityThe chemical guide is intended toassist the user in determining the suitabilityof various elastomers in manydifferent chemical environments. Theratings are based on a combination ofpublished literature, laboratory tests,actual field experience, and informedjudgments. ERIKS uses the DuPont -Dow Elastomers guide.Note: Volume swell is only one indicatorof elastomer fluid compatibility andmay be based on the solubility parameteralone. Fluid attack on the backboneof the polymer may show up as achange in physical properties such astensile strength, elongation at break,and hardness.Elevated temperatures and extendedexposure times may create moreaggressive conditions.In some cases, specific elastomercompounds within a material family mayprovide improved compatibility. Pleasecontact the Application EngineeringDepartment for assistance or consultthe DuPont-Dow internet chemicalresistance guide - where you can findthe latest information.Elastomers can swell and/or degrade inchemical environments through reactionswith the polymer backbone andcross-link system, or by reactions withthe filler system. In the semiconductorindustry, this degradation can be seenin increased contamination and reducedseal life.www.dupont-dow.com/crgChemical Compatibility Guide Rating SystemRating Description Volume CommentsChangeA Little or no < 10% Elastomer may exhibit slight swelling and/or losseffectof physical properties under severe conditions.B Possible loss 10-20% Elastomer may exhibit swelling in addition to aof physicalchange in physical properties.propertiesMay be suitable for static applications.C Noticeable 20-40% Elastomer exhibits a noticeable change in swellingchangeand physical properties.Questionable performance in most applications.U Excessive change > 40% Elastomer not suitable for service.31

SEALING ELEMENTS5. Designing with RubberAttack mechanisms:Chemical Compatibility• The process of chemical degradationor chemical incompatibility is verycomplex. In general, degradation ofthe polymer backbone and cross-linkmay occur by means of:• nucleophilic attack - nucleophiles areions or molecules that candonate electrons. This is the maincross-linking mechanism. In certainchemical media, nucleophilic attackcan result in increased cross-linkingand embrittlement.• dehydrofluorination - in fluorocarbonelastomers the attack of aliphaticamines can result in the formation ofunsaturated bonds in the polymerbackbone.• polar attack - swelling caused byelectrostatic interactions betweenthe dipole and polymer chainIn many applications special considerationsshould be made for contaminationor vacuum performance.Contamination is critical in semiconductorfabrication and medical applications.This may take the form ofparticle generation, extractable ionsor other residual gas contamination.Test methods:ISO 1817 (Liquids)ASTM D471, D1460, D3137 (Liquids)Volume Swell:The most common measure of chemicalcompatibility is volume swell. Thefollowing formula is used in reportingvolume swell measurements.This takes into account dimensionalchanges in all three dimensions, andis more precise than specific dimensionalchange readings for mostsealingapplications.Nucleophilic Attack(Unsaturated)C = CPolar AttackH 2 OOxidationO -Chemical Attack MechanismsDegradation may also occur due tointeractions of the chemical environmentand elastomer filler systems.This type of degradation may be causedby oxidation of fillers, or by chemicalattack of certain fillers or processaids.Volume Swell:(Weight in Air-Wt. in Water) final - (Wt. in Air - Wt. in Water) initialVS (%) =(Weight in Air - Weight in Water) initialNote:The "Weight in Water" measurement isperformed by suspending a samplein a container of water and recordingit's weight. This takes into considerationthat the density of a solid is equalto it's weight in air divided by thedifference of it's weight in air and it'sweight in water.x10032

TECHNICAL DOCUMENTATION O-RINGS5. Designing with RubberThermal EffectsAll rubber is subjected to deteriorationat high temperature. Volume changeand compression set are both influencedby heat. Hardness is influencedin a complex way. The first effect ofhigh temperature is to soften the compound.This is a physical change, andwill reverse when the temperaturedrops. In high pressure applicationsthe O-ring may begin to flow throughthe clearance gap as the temperaturerises, due to this softening effect. Withincreasing time at high temperature,chemical changes occur. Thesegenerally cause an increase in hardness,along with volume and compressionset changes. Changes in tensilestrength and elongation are alsoinvolved. Being chemical in nature,these changes are not reversible.The changes induced by low temperatureare primarily physical andreversible. An elastomer will almostcompletely regain its original propertieswhen warmed.This can be a critical factor at hightemperature if the gland is nearly filledwith the O-ring or at low temperature ifthe squeeze is marginal. Leaking canbe the result of seal failure at low temperatureif the squeeze is small.There are certain reactions which insome circumstances cause an O-ringto exert relatively high forces againstthe sides of the groove. If the seal iscompletely confined and the gland is100% filled, the dominating force isthe force of thermal expansion of therubber. The groove must always besufficiently wide to allow for the maximumexpansion of the O-ring. Therehave been instances where a seal hasruptured a steel gland due to expansionwhen heated. Therefore it has tobe considered that in no case a glandfill in excess of 95% is allowed.This should be taken into considerationwhen designing O-ring grooves forapplications in excess of 300°F(150°C). Please contact your ERIKSrepresentative for assistance in groovedesign.Thermal ExpansionCoefficient of linear thermal expansionis the ratio of the change in length per°F or °C to the original length at 0°F or0°C. Coefficient of volumetric expansionfor solids is approximately 3 timesthe linear coefficient. As a roughapproximation, elastomers have acoefficient of thermal expansion 10-times that of steel. With Fluoroelastomersand Perfluoroelastomers the coefficientof thermal expansion is even greater.Thermal ExpansionMaterial Thermal Stability x10 -5 / °CFKM 200°C / 392°F 16NBR 120°C / 250°F 23VMQ 230°C / 450°F 59-79FFKM 300°C / 570°F 23EPDM 150°C / 300°F 16Stainless - 1.04Aluminium - 1.3TEFLON 230°C / 450°F 5-8KEL-F 280°C / 540°F 4-7Polyimide 275°C / 530°F 533

SEALING ELEMENTS5. Designing with rubberSelecting O-ring cross sectiondiameter (CSD)In general, when selecting O-rings,there are benefits to be gained fromhaving both smaller and larger CSD.Some of the benefits are given belowfor both cases.In static applications, where rapid highpressure cycling is not present, it isusually better to choose a larger CSDif possible. As noted above, largerCSD O-rings are less susceptible tothe problems of compression set,swell, and incidental surface damage.Also, larger CSD O-rings are morestable and tend not to rotate onassembly. However, if the seal will besubjected to rapid high pressurecycling then it is better to choose asmaller CSD if possible. The smallersection seals are less susceptible todecompression problems.Table 1 - Characteristics of CSD choiceLarger sectionSmaller sectionMore stableLess stableMore frictionLess frictionNeeds more spaceNeeds less spaceBetter compression setPoor compression setLess swell (%) Possibly more swell (%)Worse decompressionBetter decompressionLarger tolerancesCloser tolerancesLess sensitive to damageSensitive to damageTable 2 - CSD and surface contact speed (Dynamic seals)O-ring CSD (mm)Maximum surface contact speed (m/s)1,78 7,622,62 3,043,53 2,03In dynamic applications it may be betterto choose a smaller O-ring CSD toavoid friction problems. In dynamicapplications, the CSD is oftengoverned to a great extent by thesurface contact speed, as indicatedin Table 2.For dynamic applications with surfacecontact speeds less than 2,03 m/s theO-ring CSD is generally not critical.There are also some general rulesrelating O-ring CSD to O-ring ID asfollows:If : 0

TECHNICAL DOCUMENTATION O-RINGS5. Designing with rubberSelection of O-ring OD and IDWhen selecting an O-ring ID (or an O-ring OD), consider first the stretch thatwill be included on the O-ring on finalassembly. O-rings and grooves shouldbe dimensioned to give acceptablestrech both on assembly and on pressurization.Table 3 gives the O-ring/groove commondimensions for good sealingpractice for several groove types.Table 3 - O-ring/groove common dimensions for good seal fitSeal type Pressure Direction Common seal/groove dimensionsFlange Internal ODFlange External IDCrushIDTrapezoidal flange grooveCentroidPiston rod/housingIDFor flange-type grooves with internalpressure, design the system so thaton assembly, the O-ring OD seats ontothe OD of the groove. Make sure thatthe O-ring OD is not larger than thegroove OD to ensure a good seal. Thiswill ensure best possible seal fit, andminimize stretch on assembly.If the pressure direction is reversed,make sure that the O-ring ID seatsonto the ID of the groove. Effectively,this ensures that when the system ispressurized the O-ring does notstretch.In the case of a trapezoidal, or otherirregularly shaped groove, first look atthe pressure direction and then decideon how to minimize stretch. For thecase of a trapezoidal section grooveuse the groove centroid as a base fordetermining a suitable O-ring ID. Thisensures easy assembly and normallysmall stretch.In any case, initial stretch on assemblyshould not exceed 3%.35

SEALING ELEMENTS6. Compound SelectionOperating conditionsThe practical selection of a seal compounddepends on an adequate definitionof the operating conditions.In approximate order of applicationimportance/MediumThe first thing to be considered whenselecting a seal compound is its resistanceto the fluids with which it willcome in contact. This means all fluids,including the oil to be sealed, outsideair, lubricants, and cleaning agents.For example, in a crankcase, rawgasoline, diesel fuel, gaseous productsof combustion, acids formed in service,and water from condensation canbe expected to contaminate the engineoil. In this case, the seal compoundmust be resistant to all fluids includingthe lubricant to be used on the seal.Therefore, whenever possible, it is agood practice to use the fluid beingsealed as the lubricant, eliminating onevariable.Consideration must also be given tothe effect of the O-ring compound onsystem fluids. For example:• There are some ingredients used incompounds which cause chemicaldeterioration of Freon refrigerants.When choosing a compound for usewith Freon, it should not contain anyof the ingredients which cause thisbreakdown.• Compounds for food and breathingapplications should contain onlynon-toxic ingredients.• O-rings used in meters or otherdevices which must be read throughglass, a liquid, or plastic, must notdiscolor these materials and hinderclear vision.TemperatureTemperature ranges are often overspecified. Eriks has applied a realistictemperature range with a margin ofsafety when setting the general operatingtemperature range for seal compounds.The maximum temperaturerecommendation for a compound isbased on long term functional service.Since some fluids decompose at atemperature lower than the maximumtemperature limit of the elastomer, thetemperature limits of both the seal andthe fluid must be considered in determininglimits for a system.At low temperature applications a fewdegrees may sometimes be gained byincreasing the squeeze on the O-ringcross section. The low temperaturelimit on an O-ring seal may be compromisedif the O-ring is previouslyexposed to a fluid that causes theO-ring compound to shrink.Conversely, the limit may be loweredif the fluid causes the O-ring to swell.36

TECHNICAL DOCUMENTATION O-RINGS6. Compound SelectionLow TemperatureThe low temperature limit is generally 10°C below TR-10 for static seals.For dynamic seals the TR-10 is more relevant. The TR-10 is the temperature atwhich an elastomer is able to retract 10%.Low temperature performance is generally a reversible process.For design purposes compression is generally increased. The chemical media maycause swelling which may act as a plasticizer and lower the service temperature.(More information on TR-10 is on page 82).FluorsiliconeSilicone THTSiliconeNBR-Low TemperatureNBREPDMVITON®-GFLTFluoroelastomer-terpolymerFluoroelastomer-copolymerAFLASKalrez® 4079Teflex® SIL-80°C -60°C -40°C -20°C 0°CHigh TemperatureThe high-temperature limit is generally considered a 30-50% loss of physical propertiesand typically represents a maximum temperature for 1,000 hours continuousservice. It represents an irreversible change in the backbone or cross-link network.The effect of high temperature can be compounded by the interaction with thechemical media. Chemical reactions typically double with a 10°C increase intemperature.FluorsiliconeSilicone THTSiliconeNBR-High TemperatureNBREPDM PCVITON®Fluoroelastomer-terpolymer Viton® BFluoroelastomer-copolymer Viton AAFLASKalrez® 4079Kalrez® Spectrum 6375350°C 300°C 250°C 200°C 150°C 100°C 50°C 0°CSee °F/°C conversion table on page 216.37

SEALING ELEMENTS6. Compound SelectionPressurePressure has a bearing on seal designas it may affect the choice of compoundhardness. At very low pressuresproper sealing may be more easilyobtained with lower hardness. Withhigh pressures, the combination ofpressure and hardness control themaximum clearance that may safelybe tolerated. Cyclic fluctuation ofpressure can cause local extrusion ofthe seal, resulting in "nibbling",particularly if the peak pressures arehigh enough to cause expansion of thecylinder.TimeThe three obvious "dimensions" insealing are, fluid, temperature, andpressure. The fourth dimension, equallyimportant, but easily overlooked, istime. Temperature limits, both high andlow, have been published at conventionalshort term test temperatures.These have little bearing on actual longterm service of the seal in either staticor dynamic applications.For example, an industrial nitrile O-ringcompound can be recommended toonly 120°C (250°F), yet it is known toseal satisfactorily at 149°C (300°F) for3000 hours and for five minutes at538°C (1000°F).Therefore, when the applicationrequires a temperature higher than thatrecommended in the compound andfluid tables, check the temperaturecurve to determine if the total accumulatedtime at high temperature is withinthe maximum allowable limit.38

TECHNICAL DOCUMENTATION O-RINGS6. Compound Selection - GeneralTable 3A-2 STANDARD ERIKS CompoundsElastomer Compound Hardness Temperature ApplicationNumber °Shore A±5 °C / °FNitrile, NBR, Buna 36624 70 -35 to +110 °C Hydraulic Oils, Vegetable Oils, Animal Fats, Acetylene,-31 to +230 °F Alcohols, Water, Air, Fuels and many other products47702 90 -25 to +110 °C Chemical resistance of 36624 with higher-13 to +230 °F hardness for higher pressure applications.VariousERIKS is pleased to offer special compoundsfor special applications on request.Ethylene Propylene, 55914 70 -55 to +130°C Solvents, alcohols, ketones, esters, organic and inorganicEPDM, EPM -67 to +266 °F acids, hydraulic fluids. Highly age resistant.Not recommended for animal fats, vegetable or mineral oils.55914PC 70 -50 to +150 °C Chemical resistance of 55914 with improved temperature-58 to +302 °F range and compression set characteristics. Also for steamapplications.55918PC 80 -50 to +150 °C Chemical resistance of 55914 with higher hardness for-58 to +302 °F higher pressure applications.VariousERIKS is pleased to offer special compounds for specialapplications on request.Silicone, VMQ 714177 70 -55 to +230 °C For extremely high or low temperature range, air, oxygen,-67 to +446 °F dry heat, ozone, hot water to 302 °F (150 °C), and glycolbased brake fluids. Resistant to hydraulic fluids but is notresistant to many hydraulic fluid additives. Silicones andFluorosilicones are recommended only for static applications.Fluorosilicone, FVMQ F70 70 -60 to +200 °C Chemical resistance as noted above, with additional-76 to +392 °F resistance to fuels and parafin based lubricants.VariousERIKS is pleased to offer special compoundsfor special applications on request.Fluorocarbon, 51414 black 70 -15 to +210 °C Good chemical resistance to oils, fats, fuels. Has very lowFPM (Viton ®) and green +5 to +410 °F compression set characteristics at high temperatures.Suitable for vacuum applications.514320 black 90 -15 to +230 °C Chemical resistance of 51414 with higher hardnessand green + 5 to +446 °F for higher pressure applications.Various.ERIKS is pleased to offer a lot more standardcompounds for special applications on request.Perfluorocarbon, FFPM, 6375 75 -50 to +316 °C Broadest range of chemical and temperature resistanceKalrez ® Spectrum -58 to +600 °F for chemical processing industry. Recommended for acids,basics, amines, steam, ethylene oxide and many otheragressive chemicals.Kalrez ® 4079 75 -50 to +316°C Excellent chemical and temperature resistance.-58 to +600 °F Suitable for 95% of all perfluorinated applications.FFPM, Various ERIKS is pleased to offer special compounds for spe-Kalrez ®cial applications on request.Teflex® FEP FPM -15 to +205 °C High thermal and chemical resistance. Not recommendedPFA Core +5 to +400 °F for dynamic applications. Cannot be stretched in installation.VMQ -60 to +205 °C Chemical resistance of FPM with improved compression setCore -76 to +400 °F characteristics at low temperatures. Not recommended for+260°C (PFA) vacuum applications due to high gas permeability.Not for dynamic applications.Note:We have over 120 different compounds for specific applications. Ask for our datasheets.39

SEALING ELEMENTS6. Compound Selection- GeneralSTANDARD ERIKS Compounds (Vulc-O-rings)Elastomer Hardness Application°Shore A±5Genuine Viton® A 60° 60 Good chemical resistance to oils, fats, fuels.BrownHas very low compression set characteristics at high temperatures.BlackSuitable for vacuum applications.Genuine Viton® A 75° 75 Good chemical resistance to oils, fats, fuels.BlackHas very low compression set characteristics at high temperatures.BrownSuitable for vacuum applications.GreenGenuine Viton® A 90° 90 Good chemical resistance to oils, fats, fuels.GreenHas very low compression set characteristics at high temperatures.BlackSuitable for vacuum applications.Genuine Viton® A 75° 75 Good chemical resistance to oils, fats, fuels.FDA whiteHas very low compression set characteristics at high temperatures.Suitable for vacuum applications. Food Quality FDA.Genuine Viton® A 75° 75 Good chemical resistance to oils, fats, fuels.FDA blackHas very low compression set characteristics at high temperatures.Suitable for vacuum applications. Food Quality FDA.Silicone 75° 75 For extremely high or low temperature range, air, oxygen, dry heat,FDA redozone, hot water to 302 °F (150 °C), and glycol based brake fluids.Resistant to hydraulic fluids but is not resistant to many hydraulicfluid additives. Silicones and Fluorosilicones are recommended onlyfor static applications. Food Quality FDA.Fluorsilicone 75° 75 Solvents, alcohols, ketones, esters, organic and inorganic acids,Bluehydraulic fluids. Highly age resistant. Not recommended for animalfats, vegetable or mineral oils.EPDM 75° black 75 Solvents, alcohols, ketones, esters, organic and inorganic acids,hydraulic fluids. Highly age resistant. Not recommended for animalfats, vegetable or mineral oils.EPDM 60° black 60 Solvents, alcohols, ketones, esters, organic and inorganic acids,hydraulic fluids. Highly age resistant. Not recommended for animalfats, vegetable or mineral oils.EPDM 75° 75 Solvents, alcohols, ketones, esters, organic and inorganic acids,FDA blackhydraulic fluids. Highly age resistant. Not recommended for animalfats, vegetable or mineral oils. Food Quality FDA.NBR 60° black 60 Hydraulic Oils, Vegetable Oils, Animal Fats, Acetylene,Alcohols, Water, Air, Fuels and many other products.NBR 75° black 75 Hydraulic Oils, Vegetable Oils, Animal Fats, Acetylene,Alcohols, Water, Air, Fuels and many other products.NBR 90° black 90 Hydraulic Oils, Vegetable Oils, Animal Fats, Acetylene,Alcohols, Water, Air, Fuels and many other products.NBR 75° black FDA 75 Abrasion resistance.HNBR 75° black 75 Better oil and temperature resistance than NBR.HNBR 75° FDA black 75 Better oil and temperature resistance than NBR. Food Quality FDA.PUR 75° black 75 Abrasion resistance.AFLAS 75° black 75 Highly steam resistant up to 200°C / 392°FAFLAS 90° black 90 Highly steam resistant up to 200°C / 392°FChloroprene 60° black 60 High ozone resistance.Chloroprene 75° black 75 High ozone resistance.Chloroprene 75° FDA black 75 High ozone resistance. Food Quality FDA.Viton® GF 75° black 75 70% Fluor Viton® with highest chemical resistance.Viton® GLT 75° black 75 Low Temperature Viton® compoundViton® GFLT 75° black 75 Combination of GF and GLTViton® GFLT 75° Extreme 75 Highest resistance in paint industry.black40

TECHNICAL DOCUMENTATION O-RINGS6. Compound Selection- SpecialsFor extreme servicesEriks offers a number of compounds for “extreme” services in theirapplication field• Different NBR, EPDM-compounds for specific applications• Silicone THT for 280°C resistance• Fluorosilicone 61370 and 61380 - to MIL-R-25988B• Aflas ® for optimum resistance to steam and crude oils• HNBR for optimum hydraulic fluid resistance to 150°C - lowest compression set• And many more…• Over 120 data sheets are available upon request.O-rings with homologationsERIKS has developed a wide range ofcompounds for contact with food andpharma, drinking water, and gases.FDADVGWKTWWRCFDA• NBR 36690• NBR 70 WHITE 36615• MVQ Silicone 714991• Teflex-silicone FDA• Teflex VITON® FDA• Viton® 514641• Kalrez® 6230 and 6221• EPDM 55641• Vulc-O-rings in FDA compounds• and many more in hardnessesfrom 20 up to 90° shore.DVGW• NBR 36630 and NBR 36625• Silicone 714625• Viton® 514625 and 514630KTW• MVQ Silicone 714940• EPDM 55940WRC• EPDM 55950• Silicone 714950NSF• EPDM 55960Gastec• NBR 32770• NBR 32760ECE• NBR 32770ACS• EPDM 1520MILSPEC’s• ask for ourspecialbrochureACSKIWAKIWA• NBR 55111Ask our special edition on FDA and USP O-rings !41

SEALING ELEMENTS6. Compound Selection- SpecialsO-rings and special applications• X-rings• Quad-rings• Micro o-rings• Vulc-O-rings• Encapsulated o-rings• PTFE O-rings• PTFE back up rings• NBR 90 back up rings• Omniseals (with spring) PTFE• High-purity compounds• Silicone free• Labsfree• Plasma treated• Coatings with silicone, PTFE, graphite• With narrow tolerances• With surface-control• With homologations• Internal lubricants (PTFE, graphite, MOS2)• Eriflon PTFE hydraulic sealsERIKS O-rings aremade using the latesttechnology.42

TECHNICAL DOCUMENTATION O-RINGS6. Compound Selection- SpecialsTable 3A-2a Standard Special Kalrez® CompoundsKalrez® Hardness Mpa C:S Max. Temp. Colour and Segment ApplicationCompounds ° Shore A %* °C/°F FillerSpectrum 77 7.6 27 275 / 536 Black CPI/All Broadest Chem.6375 resistance4079 75 7.2 25 315 / 600 Black All General1050LF 82 12.4 35 280 / 536 Black All General, amines2035 85 8.6 25 210 / 410 Black All General, EO/PO, steam2037 79 6.2 27 220 / 430 White All Oxidizing environment3018 91 16.9 35 280 / 536 Black All Hot water/High pressure6221 71 7.0 27 250 / 480 White Pharma/Food FDA, replacing KLR 62206230 75 7.1 18 270 / 518 Black Pharma/Food FDA2085 92 15.2 35 210 / 410 Black Oil/all Explosive Decomp.3035 87 14.4 20 280 / 536 Black KVSP/CPI KVSP8101 65 2.5 18 300 / 570 Grey Semi Dry/Plasma8201 75 4.1 28 220 / 438 Brown, unfilled Semi Wet/Strip/Etch8375 76 5.1 20 300 / 570 White Semi Dry/Plasma (Sahara)8385 83 8.6 35 275 / 525 White Semi Dry/Plasma (Sahara)8475 72 2.2 23 300 / 570 White Semi Dry/High Temp (Sahara)In collaboration with DuPont Dow Elastomers ERIKS offers an FEA analysis of sealing applications to aid in the correct selection of Kalrez®O-ring compounds.www.dupont-dow.com/crg43

SEALING ELEMENTS6. Compound Selection - Viton®Genuine Viton®'Only the best is good enough for you'Today's industry sometimes operatesunder extreme conditions. Heat,aggressive media, corrosive gasses,and mechanical stress require theutmost performance from seals.Extreme requirements demand qualityassurance and the best materials. Inmany cases Genuine Viton®, thefluoroelastomer made by DuPont DowElastomers, is the solution. GenuineViton® is manufactured with 100%pure fluoroelastomers and is certifiedwith the Viton® certificate, which isgranted by DuPont Dow Elastomers.ERIKS is appointed a licensed distributorfor Genuine Viton® products.How do I make sure that I've gotGenuine Viton®?Only Genuine Viton® products carrythe specific, easy recognizableemblem on their package. All Viton®products are made according to thestrict guidelines of DuPont DowElastomers, the only manufacturer ofViton®.With Genuine Viton® parts one can beassured that the product has beenmanufactured and processed by bothDuPont Dow Elastomers and theirlicensed partners according to guidelinesspecified in the Materials IntegritySection of OSHA 1910.119 (ProcessSafety Management of HighlyHazardous Chemicals Preventivemaintenance).Please ask for a copy of ERIKS’Genuine Viton® brochure.The VITON® familiesViton® was introduced in 1958. Thereare now three major general usedfamilies of Viton® fluoroelastomer: A,B, and F. They differ primarily in theirresistance to fluids, and in particularaggressive lubricating oils and oxygenatedfuels, such as methanol andethanol automotive fuel blends. Thereis also a class of high performanceViton® grades: GB, GBL, GF, GLT,GFLT, Extreme, and Base resistant.Main Viton® FamiliesMain Viton® A B F GLT GFLT Extreme Base resistant% fluorine 66 68 70 64 66 56Extreme chemical resistance* ++ +++ ++++ + ++++ ++++ ++++High temperature resistance* +++ +++ +++ +++ +++ +++ +++Low temperature resistance* + 0 - ++++ ++ + +Compression-set* +++ ++ + + + + +*: the more + signs, the better the relative values are.Note: from these families, all possible Viton® products can be produced.44

TECHNICAL DOCUMENTATION O-RINGS6. Compound Selection - Viton®Viton® compounds are excellent forextreme chemical resistance. Sealsthat are exposed to extreme chemicals(amines, concentrated acids, superheatedsteam), require a compoundwith excellent chemical resistance.ERIKS offers the following solutions:Viton® BTerpolymer based on Viton® B withbetter chemical resistance than standardViton® A compound 51414,however, with a slightly higher compressionset.Viton® GFBased on Genuine Viton® GF. Thiscompound offers the best chemicalresistance of all standard Viton® families.Again, the compression set isslightly higher as compared to ERIKSstandard Viton® compound 51414Viton® Extreme provides the broadestchemical resistance of all Viton®families. Originally, it was designed byDuPont Dow Elastomers to be used inoil-field applications, or in contact withamines and sour oils. Because of itsexcellent properties, Viton® Extreme isnowadays also frequently used in theChemical Processing Industry (CPI),under the harshest conditions. Viton®Extreme can often solve problemsin cases where the high cost ofperfluoroelastomers such as Kalrez®is not acceptable. The following tableshows an overview of the chemicalresistance of Viton®A, Viton® GF,Aflas®, and Viton® Extreme.Volume Swell in Various FluidsViton® ExtremeViton® Extreme is the latest developmentin the Viton® family. It is a terpolymerof ethylene, tetrafluoroethylene,and perfluormethylvinylether.It bridges the gap between thefluoroelastomers (Viton®) andperfluoroelastomers (Kalrez®).It provides the best chemical resistanceof all fluoroelastomers and isavailable in a black and a white color.A chemical resistance list is availableon request.Viton® Extreme has proved its highestvalue in contact with fuels with additives,spray-coating processes, alcohols,and chemicals such as MTBEand ETBE. It is produced on demand.Percent Volume Swell250200150100500Gear LubeTolueneMTBEMEKKOHViton® A Viton® GF Aflas F Viton®Extreme45

SEALING ELEMENTS6. Compound Selection - Viton®Table 3A-2c Differences in Fluid ResistanceViton® Compound A B F Viton® GB, GF GLT GFLTExtreme GBLCHEMICAL ENVIRONMENTAutomotive and aviation fuels 1 1 1 1 1 1 1 1Automotive fuels oxygenated with MEOH, ETOH, MTBE, etc. NR 2 1 1 2 1 NR 1Engine lubricating oil, SE and SF 2 1 1 1 1 1 1 1Engine lubricating oil, SG and SH 3 2 1 1 1 1 2 1Aliphatic hydrocarbon process - fluids, chemicals 1 1 1 1 1 1 1 1Aromatic hydrocarbon process - fluids, chemicals 2 2 1 1 1 1 2 1Aqueous fluids, steam, mineral acids 3 2 2 1 1 1 1 1Strong base, high pH, caustic, aminesViton® for base resistance / Viton® ExtremeCOMPRESSION AND LOW-TEMPERATURE PERFORMANCEResistance to compression set 1 2 2 1 2 3 2 2Low-temperature sealing capability TR-10 test results °Celsius -17 -14 -7 -11 -15 -6 -30 -24" " " °Fahrenheit +1 +7 +19 +12 +5 +21 -22 -71 = Excellent, minimal volume swell / 2 = Very good, small volume swell / 3 = Good, moderate volume swellViton ® A-compounds for general useERIKS offers six standard O-ring compounds of which thousands of different sizesare available from stock. Please find the most important technical data for thesecompounds in Table 3A-2d.Table 3A-2d Standard Genuine Viton ® A compoundTechnical data 51414 51414 514320 514075 514090 51424 MC152black green black black Vulc-O-ringHardness IRHD ±5° DIN 53519 70 70 75 90 90 80 75Tensile strength Mpa.min. DIN 53504 13 12 14 14 18 11 10,7Elongation % DIN 53504 170 170 120 224 121 130 213Compression set % 24h/200°Con slab max. DIN 53517 12 14 14 10 117 15 4,6on OR 4.53 mm max. 18 19 18 11 20 7,5Heat aging 70h/200°CHardness ° DIN 53508 +4° +5° +5° +2° +4° +5° +3°Low temperature TR-10 / ASTM 1329 -16° -16° -16° -16° -16° -16° -16°Density ASTM 1817 1,85 2,07 1,87 1,90 1,92 1,87 2,32Max. temperature °C +200° +200° +200° +200° +200° +200° +200°Miscellaneous Information stock stock stock in MILSPEC's MILSPEC’s production 1 to 5 day-RAL 6011 black/green R-83248 C R-83248 C item productionon demand Type 1 cl 1 Type 1 cl 1 also in FDAstock46

TECHNICAL DOCUMENTATION O-RINGS6. Compound Selection - Viton®Petrochemical industryDue to the permeability of O-ring compounds,high pressure gas can enterinto the O-ring. There it builds microscopicbubbles between the molecularchains. Upon withdrawal of the pressure,the gas bubbles expand andcause cracks in the seal composition.ERIKS offers compound V-162 thatmeets the highest demands in theseapplications: high pressures, high temperatures,extrusion resistent, andexplosive decompression resistent, foruse in contact with natural gas, steam,and corrosion inhibitors, etc.Obviously, for less critical applicationsour standard Viton® compounds arealso perfectly suitable.Food industryERIKS offers a number of compoundswith approval for contact with foodstuffs.These compounds meet the demandsof the Code of Federal Regulations,title 21, Chapter 1, Subchapter B,Paragraph 177.2600 for use in contactwith unpacked food stuffs.For seals, two relevant FDA classesexist: Class 2 for contact with liquidsand drinks and Class 1 for contactwith milk, milk-derived products, andedible oils.ERIKS standard Viton® FDA O-ringsmeet Class 1 requirements. ERIKS canoffer the following approved O-ringsfor Class 1 compounds.• Viton® 514641;• Vulc-O-ring FDA-75 MC172 black,75 IRHD;• Vulc-O-ring 90 MC126 black 90IRHD.Low temperature applicationsFluoroelastomers do not really excelwith regard to low temperature resistance.Because of its molecular construction,Viton® becomes relativelyhard at temperatures lower than 10°F(-12°C). By means of a special molecularstructure and cross-linking technology,however, it is possible to create acompound which can be applied withtemperatures as low as -40°F (-40°C):514115 (based on Viton® GLT).Alternatively, Viton® GFLT has atemperature range as low as - 22°F(-30°C).The following table lists the test resultson the different Viton® families at lowtemperatures:Viton® Families at Low TemperaturesPolymer type Viton® A Viton® B Viton® Viton®51514 GLT GFLTCo- Ter- Tetra- Tetra-% Fluorine 66 66 65 67Compression Set 16 24 26 36TR 10, °C -17,2 -18,8 -31,1 -25,2Sealing Test Leakage at °C -32 -34 -45 -37Source: Low temperature Sealing Capabilities of Fluorelastomers, DuPontERIKS can also supply a number ofcompounds ranging from 60 to 95IHRD, that also meet Class 2 requirements.47

SEALING ELEMENTS6. Compound Selection - Viton®Special compoundsThe following compounds can beapplied under very specific circumstances.Only the main characteristicsare described. More specific details areavailable upon request.V-75 white and V-60 whiteBoth compounds have been designedin such a way that, despite the lack ofcarbon black, they possess optimalphysical properties. Chemical and temperatureresistance are identical to ourstandard Viton® compounds.514170This compound is of such a pure composition,that few if any additions areable to flow out under vacuum conditions.This causes the O-ring to optimallymaintain its sealing properties.514170 is based on Viton® A.Hardness is 80±5° IRHD.9021-95High modulus Viton® for optimalresistance against extrusion. Tensilestrength is 16.7 Mpa and the modulusat 100% elongation is 14 Mpa, ascompared to 6 Mpa for standardViton® compounds. Hardness 95°Shore A.High Purity CompoundThis compound offers a unique combinationof chemical resistance and verygood plasma resistance. Its contaminatingsubstance content is up to 600times lower than standard Viton®.It loses very little weight during plasmatreatment and contains only one tenthof the surface uncleannesses inreactive plasma. Therefore, a typicalcompound for the semicon industry.Note:For very specific requirements, ERIKScan develop special Viton® compoundsthat meet unique demands even betterthan these compounds describedhere. Presently ERIKS has about 65unique compounds that have alreadybeen applied successfully all over theworld. It goes without saying thatthese are custom-made items whichare usually not available from stock.Vulc-O-ring® MC 172Viton® Vulc-O-rings® are made out ofvery homogenous genuine Viton®O-ring cord with a hardness of 75° and90° Shore A. The O-rings are madeendless under a 45° biased angle, bymeans of a unique productionprocess. The joint undergoes a followuptreatment and is hardly visible.Every Vulc-O-ring® is made accordingto DIN 7715 E2. The O-ring cord hasan extremely low compression set,resulting in a lifetime for Vulc-O-rings®that exceeds the average for standardViton® A O-rings.Note:In the next chapter "Frequently askedquestions about Viton®" you will find acomparison table describing lifetimetest results. After 3.000 hours at 390°F(200°C), the joint in the Vulco-O-ring®showed the same elasticity value(compression set) as the original cord.This leads us to the conclusion thatVulc-O-rings® can be consideredequivalent to standard O-rings. A copyof the test report is available uponrequest.V-9062-95Anti extrusion-quality, resistant to acidsand steam. Hardness 95° Shore A.514158By the addition of PTFE particles, anoptimal friction coefficient is achieved,which gives this compound an excellentwear resistance. Therefore, anexcellent compound for dynamic seals!Ask for our special Viton® edition48

TECHNICAL DOCUMENTATION O-RINGS6. Compound Selection - Viton®Frequently asked questions about VITON®1. Does the compound colour affect the quality of the seal?Our experience is that chemical and temperature resistance do not change.Mechanical properties of black compounds, however, are often much better thanthose of coloured compounds.2. Does the type of carbon black affect the quality of a seal?Definitely! The standard MT990 carbon black filler offers very good results in allrespects. Specific carbon black, such as e.g. Austin Black, can strongly improve thesealing properties. Our compound 514075 brown is made with Austin Black andshows the lowest values in all compression set tests. Other carbon blacks offer theadvantage of higher tensile strength or wear resistance.3. How fast can you supply odd-size O-rings?Through our unique vulcanisation process, ERIKS can supply any Vulc-O-ring within48 hours, if required. Standard delivery time for odd-sizes is 1 to 2 weeks.4. What is post-curing?After moulding, Viton® parts have to be post-cured at 200°C / 392°F for 8 to 24hours, depending on the compound. Post-curing optimizes the vulcanisation,causing all links in the moleculear structure to develop. The method of post-curingcan strongly affect the final quality of the compound.5. Is there a difference in life among the various compounds?ERIKS has subjected some of our compounds to life tests.The compression set was measured in air at 200°C / 392°F for 1.000 hours.One may assume that an O-ring has lost its sealing properties after the compressionset has reached 100%. The following table gives an overview of four differentcompounds:• Viton® Lifetime Test100Compression set diam. 3.53 mm; in air 200°C / 392°F1908070601234Aflas MC 143 (80°)51414 (70°)Viton® MC 152 (75°)514075 (75°)234504030201001 h 24 h168 h 504 h 1008 h49

SEALING ELEMENTS6. Compound Selection - Viton®Frequently asked questions about VITON®6. What is the price difference among these various compounds?It is difficult to give an exact answer because prices highly depend on size andproduction quantities. As a guideline, one may use the following chart:CompoundPrice FactorViton® A - standard 1Viton® A - 514075 1,5Viton® B 5Viton® GF 10Viton® Extreme 507. How does media temperature affect the life of a Viton® seal?The life of a seal is strongly affected by media temperature. ERIKS has measuredthe time after which the elongation at break is reduced to 50%, at different mediatemperatures.Following are the results, these are only applicable to Genuine Viton® compounds.• Heat resistance (air)°C / °F3156002875502605002324462003921 10100 1000 10.000Time* (h) * time/temperature exposure to reduce elongation of Viton® to 100%experimentterminated8. How do I learn about the chemical resistance of a Viton® seal?ERIKS will gladly send out an updated chemical resistance list, upon request. A summarizedlist is included in this brochure. Since ERIKS is in close contact with DuPont DowElastomers’ laboratory in Geneva, Switzerland and Stow, OH, we are always assured ofpossessing the latest data. In our own test laboratory, we can also organise specific testswith our Viton® compounds in media provided by our customers. Visit the DuPont DowElastomers website for the latest details on chemical resistance. www.dupont-dow.com/crg50

TECHNICAL DOCUMENTATION O-RINGS6. Compound Selection - Viton®Frequently asked questions about VITON®9. When should I choose Kalrez®?Kalrez® is a perfluoroelastomer and, as such, offers chemical and temperatureresistance of a different grade, compared to Viton®. Please consult the local ERIKSoffice for more specific information about this “top of the list” problem solver.Following are the results of compression set tests with Viton® and Kalrez®.• Long-Term Compression Set in Air at 200°C (Comparison as a function of time)Compression set %100908070VITON® A 401 CCompetitive FFKMKalrez® 4079605040302010Standard Compression Set Test Duration 70 Hours00 25 75 175 340 500 750 1000Test Duration, HoursThis test prooves Kalrez ® has a much longer lifethan Viton ® O-rings at 200°C / 392°F.51

SEALING ELEMENTS6. Compound Selection - Viton® and Kalrez®ERIKS and DuPont Dow Elastomers25 years of partnership in Viton® and Kalrez®For 25 years Eriks and DuPont DowElastomers have been partners in theproduction and marketing of originalViton® and Kalrez® High-Tech rubbercompounds.Eriks produces genuine Viton® O-ringsand oil-seals. Eriks guarantees qualityfrom the raw material to the endproduct,for critical applications thatdemand the best seals.All information on Viton® and Kalrez®can be found in two different Erikspublications, summarizing the varioustypes, compounds, and applications.The many case studies described inthe publications, may offer suggestionsfor alternative uses for Viton®and Kalrez®.52

TECHNICAL DOCUMENTATION O-RINGS6. Compound Selection - Kalrez®Kalrez® for extreme serviceWhenever seals or rubber componentsare exposed to aggressive chemicals orhigh temperature, Kalrez® perfluoroelastomerparts outlast the alternatives.Only Kalrez® parts can match thevirtually universal chemical resistanceand high-temperature stability of PTFEwhile adding the resilient, no-creepproperties of a true rubber.For over 25 years, Kalrez® parts havedemonstrated their value in criticalapplications where other seals havefailed. They provide the most costeffectivesolution for high-performancesealing applications.Increased safetyWith Kalrez® parts you can rest easy.They last longer and perform betterthan other elastomeric materials inaggressive chemical environments.Kalrez® helps reduce the risk of sealfailure and chemical exposure.Reduce maintenance costsKalrez® parts help stretch your meantime between failure and lower yourmaintenance costs. Their durabilityminimizes unscheduled downtimewhile letting you extend timer betweenroutine inspections and replacementcycles for critical components.In difficult environments, there are noother elastomers that can equal theoverall performance of DuPont DowElastomers Kalrez® perfluoroelastomerparts. Kalrez® combines the resilienceand sealing force of a true elastomerwith chemical inertness andthermal stability similar to Teflon®fluorocarbon resin. That’s why Kalrez®parts can succesfully solve criticalsealing problems under conditions thatcause other rubbers to fail.Chemical resistanceKalrez® parts resist attack by nearly allchemical reagents, including ethers,solvents, ketones, esters, amines, oxidizers,fuels, acids, and alkalis. As aresult, they provide long-term servicein virtually all chemical and petrochemicalprocess streams, including manywhere corrosive additives or impuritiescan quickly destroy other elastomers.Thermal StabilityKalrez® parts retain their elastic propertiesin long-term service at temperaturesas high as 316°C / 600°F. That’sreliable performance at temperaturesup to 100°C higher than parts madefrom other commercial elastomers.Sealing PerformanceKalrez® parts outperform other elastomericsealing materials in difficult environments.Compared with other elastomers,including other perfluoroelastomers,Kalrez® parts are more resistant toswelling and embrittlement, and retaintheir elastomeric properties longer.Compared with metal seals, they areeasily installed and conform to thesealing surface despite irregularitesdue to assembly, wear, or surfacefinish.Compared with PTFE seals, they donot creep, flow, or cause shaft fretting.Actual service records prove thesuperior sealing performance ofKalrez® parts at high temperatures in awide variety of corrosive environments.• Over 3 years in Dowtherm* A at 246°C(475°F)• Over 24 months in sour gas (9% H 2 S15-19% CO 2 ) at 149°C (300°F)• Over 1 month in silicon water nitrideprocess with chlorine and ammoniagas at 218°C (425°F)• Over 1 year in O-nitrochlorobenzeneat 220°C (428°F)• Over 1 year in maleic anhydrideat 169°C (335°F)• Over 6 months in hot asphalt at 316°C(600°F)Field-provenSafest Sealing with Kalrez®:prevent leaks and eliminate unscheduledshutdowns.Over twenty years of experience in avariety of demanding application environmentshave proven the unrivalledresistance of Kalrez® perfluoroelastomerparts. Where aggressive chemicalmedia and/or elevated temperaturescan destroy lesser materials, Kalrez®parts keep right on working. By extendingthe life of seals, Kalrez® partshelp to eliminate leaks and reduce processstream losses. Maintenancecosts can be cut and downtime productionlosses minimized. Kalrez®parts often pay for themselves manytimes over, often in a very short periodof time.• Over 4 months in 70% acetic acid at220°C (428°F)• Over 1 year in dry steam at 250°C(482°F)• 3 months with lowest ppb ionicextractable levels in wet semiconductorprocess chemicals at 100°C (214°F)• Over 17 months in hydrocarbons at288°C (550°F)• Over 1 year in N-methyl-2-pyrrolidoneat 232°C (450°F)*Registered trademark of The DowChemical Company53

SEALING ELEMENTS6. Compound Selection - Kalrez®Kalrez®: Durable, safe seals in virtuallyany environmentBecause of the unique chemical structureof the material, Kalrez® parts canprovide the most durable seals at temperaturesup to 326°C/620°F in virtuallyany chemical media. No other seal,including other perfluoroelastomers,can perform for such extended periodsin such aggressive environments.Kalrez® parts provide an effective (andcost effective) solution in a variety ofindustries.1. In chemical processing and petroleumrefining, O-rings are used inmechanical seals, pump housings,reactors, mixers, compressor casings,valves, rotameters, and other equipment.Custom-designed parts are usedas valve seats, packings, diaphragms,gaskets, and U-cups. Kalrez® partscan be specified as standard seals formost mechanical seal types.2. In analytical and process instruments,septa, O-rings, diaphragms,valve seats, column fittings, ferrules,and gaskets, Kalrez® solves toughchemical sealing problems. They alsoprovide exceptional outgassing resistanceunder high vacuum at temperatures100°C / 232°F above the limits ofother elastomers.3. In chemical transportation, O-ringsand other seals are used in safety reliefand unloading valves to prevent leakagefrom tank trucks and trailers, rail cars,ships and barges carrying hazardousand corrosive chemicals. Compliancewith new government restrictions canbe easier with Kalrez® parts.4. In semiconductor manufacturingoperations, O-rings and other parts areutilized to seal aggressive chemicalreagents and specialty gases requiredfor processing silicon chips. Also, thecombination of thermal stability andlow outgassing characteristics aredesirable in furnaces for growing crystalsand in high vacuum applications.5. In energy production, V-ring packerseals, O-rings, T-seals, and customparts are used in sour gas and oil wellsat pressure differentials up to 138MPa(20.000 psi) and temperatures of232°C. Specialty electrical connectorboots are used in logging equipmentfor gas, oil, and geothermal steamwells at temperatures up to 307°C /575°F.6. In aircraft and aerospace industries,lip seals, diaphragms, O-rings, andcustom designed parts are used onaircraft engines and rocket propellantsystems. Because of their excellentthermal stability and resistance to aerolubricantsfuels, hydraulic media,hydrazine, oxidizers such as dinitrogentetroxide, and other aggressive fluids,Kalrez® parts are especially suited fora number of demanding applications.On the following pages, ERIKSpresents the next generation ofKalrez®-compounds.54

TECHNICAL DOCUMENTATION O-RINGS6. Compound Selection - Kalrez®Kalrez® Spectrum 6375This is the best combination of chemicaland temperature resistance in oneperfluoroelastomer seal.Kalrez® has proven itself in over 25years of cost effective perfluoroelastomersealing solutions in the mostdemanding chemical and temperatureenvironments.Spectrum is a new family of Kalrez®parts, designed to meet tougher CPIperformance and value needs in abroad range of applications.6375 is the first Kalrez® compoundbased on new polymer technologyfrom DuPont Dow combined with aninnovative, new patented crosslinkingsystem.What is Kalrez® Spectrum 6375?• Spectrum is a new family of Kalrez®parts, designed to meet tougher CPIperformance and value needs in abroad range of applications.• 6375 is the first Kalrez® compoundbased on new polymer technologyfrom DuPont Dow combined with aninnovative, new patented crosslinkingsystem.Physical propertiesThe physical properties of Kalrez®Spectrum 6375 allow it to be used ina variety of chemical processing applications.Extensive lab and field testinghas shown its outstanding performancecharacteristics. Kalrez® Spectrum6375 is expected to become thesealing standard in the demanding fieldof CPI.Table 1 - Typical physical properties (1)Hardness, Shore A 75100% Modulus (2) 7.2 MPa (1050 psi)Tensile at break15.1 MPA (2200 psi)Elongation at break 160%Compression set (3) , % 70 hrs at 204°C 30Maximum service temp.275°C (525°F)Lower service temp.-20°C (-4°F)(1)Not to be used for specifications(2)ASTM D412, 500 mm/min(3)ASTM D395 B, o-ringsTable 2 - Chemical resistanceCompound Kalrez® Kalrez® Kalrez® Kalrez®Resistance to: Spectrum 6375 4079 2035 1050LFAromatic/Aliphatic oils ++++ ++++ ++++ ++++Acids ++++ ++++ ++++ +++Bases ++++ +++ +++ ++++Alcohols ++++ ++++ ++++ ++++Aldehydes ++++ +++ ++++ ++++Amines +++ + ++ ++++Ethers ++++ ++++ ++++ ++++Esters ++++ ++++ ++++ ++++Ketones ++++ ++++ ++++ ++++Steam/Hot Water ++++ + +++ +++Oxidizers* ++ ++ ++ ++Ethylene Oxide ++++ x ++++ xHot air +++ ++++ ++ +++++++ = Excellent, +++ = Very good, ++ = Good, + = Fair, x = Not recommended.* In strong oxidizers a white compound like Kalrez® 2037 is recommended.Chemical ResistanceKalrez® Spectrum 6375 withstands aggressive chemicals (Table 2 and 3) includingacids, amines, bases, aldehydes, ethylene oxide, and hot water/steam. Such broadchemical resistance qualifies it for many CPI applications. Also, 6375 maintainssealing integrity in problematic mixed chemical streams to give an extra assuranceand broad applicability.Equipment clean out with solvents or steam is no problem for Kalrez® Spectrum6375. And if process upsets occur, broader chemical resistance and higher continuousoperating temperature deliver a lower risk of seal failure.When selecting sealing materials, Kalrez® spectrum 6375 is a replacement for mostperfluoroelastomer parts currently on the market. Its broad combination of chemicaland heat resistance means one can minimize the risk of misapplication in partreplacement with this ‘all in one’ seal. (Graph 1, 2, 3, 4).55

SEALING ELEMENTS6. Compound Selection - Kalrez®Table 3 - Resistance to volume swell (1)Chemical Temperature Kalrez® Nearest Competitive°C (°F) Spectrum 6375 FFKMWater 225 (437) A CGlacial acetic acid 100 (212) A ANitric acid (70%) 85 (185) B CSulfuric acid (98%) 150 (302) A CAmmonium hydroxide 100 (212) B BEthylene oxide 50 (122) A AEpichlorohydrin 100 (212) A AButyraldehyde 70 (158) A BToluene diisocyanate 100 (212) A BHCFC 134a 25 (77) A A(1) Exposure time = 672 hours.A = 1-10% volume swell, B = 10-20% volume swell, C= > 20% volume swell.Kalrez® Spectrum 6375 combines low volume swell with good physical propertiesretention.Low volume swell is critical to sealing performance in many applications. The resultof lab testing to determine volume swell of Kalrez® Spectrum 6375 whenexposed to some of the most aggressive fluids in the industry are shown here:Graph. 1 - Volume change in ethylene oxide at 50°C, size 214 O-rings, ASTM D471Volume change %1510Kalrez® 20355Competitive FFKMKalrez® Spectrum 63750100 200 300 400 500 600 700Exposure time, Hours56

TECHNICAL DOCUMENTATION O-RINGS6. Compound Selection - Kalrez®Graph. 2 - Volume change in 98% sulfuric acid at 150°C, size 214 O-rings, ASTM D471Volume change %35302520Competitive FFKM1510Kalrez® Spectrum 63755Kalrez® 40790100 200 300 400 500 600 700Exposure time, HoursGraph. 3 - Volume change in toluene diisocyanate at 100°C, size 214 O-rings, ASTM D471Volume change %353025Competitive FFKM2015105Kalrez® 4079Kalrez® Spectrum 63750Exposure time, Hours100 200 300 400 500 600 70057

SEALING ELEMENTS6. Compound Selection - Kalrez®Graph. 4 - Volume change in water at 225°C, size 214 O-rings, ASTM D471Volume change %604020Competitive FFKMKalrez® Spectrum 63750Kalrez® 2035100 200 300 400 500 600 700Exposure time, HoursThermal performanceKalrez® Spectrum 6375 combines the broadest chemical resistance of anyperfluoroelastomer with a continuous use service temperature range up to 275°C(525°F). This is approximately 55°C (100°F) higher than other products claiming broadchemical resistance. In demanding service conditions, Kalrez® spectrum 6375 hasdemonstrated very good compression set at elevated temperatures for extendedtime. (See Graph. 5)Graph. 5 - Compression set at 240°C, size 214 O-rings, ASTM D471Compression set %90807060Competitive FFKM5040Kalrez® Spectrum 63753020100 200 300 400 500 600 700Exposure time, Hours58

TECHNICAL DOCUMENTATION O-RINGS6. Compound Selection - Kalrez®Kalrez® in Semicon IndustryChemical resistance that is nearly universal,coupled with superior high temperatureproperties, enables Kalrez®parts to withstand virtually any processmedia - including plasma - attemperatures up to 316°C (600°F).By selecting the Kalrez® compoundthat is best suited to a specific application,processors can improve sealperformance in all wafer fabricatingoperations, including thermal, gas/vacuum,dry plasma, and wet chemicalsystems.Kalrez® gives long-term sealing performanceat high temperaturesKalrez® perfluoroelastomer partsretain elastic recovery properties andsealing force far better than other heatresistant elastomers - even after longterm exposure at temperatues as highas 316°C (600°F). This thermal relaxation/stressaging test is a direct indicationof long-term sealing effectivenessat elevated temperatures.Kalrez® Spectrum KLR7075 offersnew high temperature performancestandard for the CPI industryDuPont Dow has unveiled Kalrez®Spectrum KLR7075, the first Kalrez®Spectrum product line expansiondesigned specifically for high temperatureresistance in the chemical processingindustry.Customers have already reportedexceptional seal performance in preliminaryproduct testing, especially inmechanical seal applications.Kalrez® Spectrum KLR7075 buildson the exceptional performance ofKalrez® 4079. By choosing KLR7075,customers will benefit from evenlonger seal life and increased meantime between repairs as a result of:• Very low compression set at 204°Cfor 70 hours (15 %)• Enhanced sealing force retention.• Higher thermal resistance, up to326°C / 620°F.In addition KLR7075 offers broaderchemical resistance and better cooldown set recovery than Kalrez® 4079,and provides a smoother, glossier finishthan other Kalrez® products.Kalrez® Sahara 8575 for best performancein semicon plasma andgas processesKalrez® Sahara 8575 is enjoying avery successful introduction, particularlybecause of its reduced cost ofownership and improved seal lifetimebenefits.weight loss of Kalrez® Sahara 8575in such aggressive media. This benefitsfab lines in extended seal life andincreased equipment reliabilit andmean time between repair (MTBR).That means improved wafer yields andreduced costs.% Weight loss543210Kalrez® Sahara 8575Kalrez® Sahara 8375Kalrez® Sahara 8385Competitive FFKMNF 3 O 2 C 2 F 3 /O 2Process Gas(Fig. 1)CF 4Kalrez® Application GuideThe version 6.0 of the Kalrez®Application Guide is ready to be downloadedfrom the Internet.The easy guide to choosing the bestperfluoroelastomer seal for an applicationnow includes the latest chemicalprocessing and semi-conductor compoundsfrom Kalrez®. It helps incompound selection by rating theresistance of Kalrez® compounds tovirtually any combination of temperatureand chemical media, and it helpsyou in seal design.Semicon fabs are looking even moreclosely at seal costs while demandingexceptional performance in aggressivemedia. And this is where Kalrez®Sahara 8575 scores. It demonstratesexceptional resistance to plasma andgas deposition processes.New proprietary developments in thepolymer and crosslinking system haveresulted in reduced weight loss, particlegeneration and outgassing. Fig. 1clearly shows significantly reducedThe seal design selection will assist indesigning a groove for a specificO-ring, and calculate seal performanceparameters in various temperature andswell conditions at minimum and maximumO-ring groove tolerance.Download NOW at:www.dupont-dow.com/kag59

SEALING ELEMENTS6. Compound Selection - Encapsulated Teflex®Index1. Why are Teflex O-Rings needed?2. Introduction3. Material specifications4. Markets and applications5. Installation6. Availability7. Materials available8. Size range9. Chemical resistance10. Compressive load requirements11. Groove dimensions12. Approvals13. Quality control and inspection14. Design15. Answers to popular questions1. Why are Teflex O-Ringsneeded?PerfluoroelastomersThere are certain applications which prohibit the use of conventionalrubber O-Ring seals. The use of hostile chemicalsor extreme temperatures (both high and low) during variousprocesses can make effective sealing very difficult. Manyseal manufacturers have produced different "high performance"materials for these applications. ERIKS hascontributed to this area by introducing Teflex.The following is the summary of these "high performance"products compared with Teflex.Solid PTFESolid PTFE O-Rings enjoy true chemicalinertness. This is the only advantage overTeflex. PTFE suffers badly from cold flowand has little memory to return to its originalform.PTFE envelopedEnveloped O-Rings too enjoy true chemicalinertness and are low in cost to produce.The design of the PTFE envelopemay allow the chemical to reach andattack the core material resulting inpremature failure.PTFE coatedO-Rings coated with suspended PTFE dispersiongive some low friction propertiesbut the coating is easily removed. Thismethod of manufacture is low in cost butoffers practically no chemical protection.A Perfluoroelastomer is the most technicallyadvanced O-Ring material for corrosiveapplications. O-Rings made from Perfluorooffer very easy installation properties anddisplay conventional elastomer characteristics.They are however very expensive toproduce and do not offer any low friction advantages.Metallic (Tubular)Tubular metallic O-Rings offer very goodchemical resistance, high pressure ability,and flexible temperature ranges. They dohowever require very precise housing andsurface finish detail and again can bequite expensive to produce.There are certain applications for which we would not recommendthe use of Teflex.• Dynamic use where high speeds and poor surfacefinishes are encountered.• Where the housing design requires excessivestretch. Teflex is very difficult to stretch.• When the media in contact with the O-Ring has anabrasive nature, sand, slurry, etc..2. Introduction to TeflexA Teflex O-Ring comprises an elastomeric energising core,which has a seamless jacket made from a fluoropolymer.The elastomeric core may be Viton ® or Silicone. The jacket ismade from Teflon ® FEP or PFA.jacket10 years of experience with these O-Ringsindicate this product is a perfect sealingsolution for typical applications. ERIKS’worldwide experience with thousands ofcoreapplications ensures that Teflex is a quality product.60

TECHNICAL DOCUMENTATION O-RINGS3. Material specificationsFEP is a copolymer of hexafluoropropylene and TFE. PFA isalso a copolymer of TFE but with perfluorinated ether. ERIKSViton ® compound has been designed specifically to give optimuncompression set characteristics. This feature is paramountin the cores function of energising the Teflon jacketand aiding its recovery from compression.Mixers and vesselsFlangesERIKS Viton ® compound meets the following specifications:Hardness: ASTM D 2240 75° ±5° Shore ‘A’Tensile strenght: ASTM D 412 min. 10.7 MPaElongation: ASTM D 412 min. 213%Specific weight: ASTM D 1817 2.32 ± 0.04Compression set: ASTM D 395Bon slab4.6% (175°C)on O-Ring 5mm< 10% (200°C)Heat exchangersHeat ageing ASTM D 573Hardness +3°Tensile strenght +15%Elongation change -29%ERIKS silicone compound meets the following specification:Hardness: ASTM D 2240 min. 70 ± 5° Shore ‘A’Tensile strenght: ASTM D 412 min. 8.6 MPaElongation: ASTM D 412 min. 280%Specific weight: ASTM D 1817 1.26Compression set: ASTM D 395B22h/175° < 32%Silicone is FDA compliant.5. InstallationThe correct installation of Teflex O-Rings is essential for prolongedseal life. A very large percentage of seal problems arecaused by incorrect fitting procedures.4. Markets and applicationsThere is hardly a market in which Teflex O-Rings are notcurrently utilised and they are very well established in the followingindustries: chemical processing and production, oilextraction, petrochemical refining, pharmaceutical production,food and drink processing, paint and die manufacture,refrigeration engineering, cosmetics and perfumery, automotivecomponents, and aerospace engineering.Mechanical sealsFilter elementsValvesPumpsTo fit a Teflex O-Ring into an internal bore type housing theseal needs to be collapsed. This is best achieved by immersingthe seal in hot water (60°-80°C) prior to fitting which givesmuch greater flexibility to the jacket. Take the seals out of thewater one at a time and quickly slide the seal into the borepassing the leading edge over and past the groove. It isimportant that the groove is chamfered and free from burrs ordamage will be caused to the jacket. After the trailing edge ofthe seal is located into the groove, the leading edge has to bepulled backwards taking care to apply even pressure aroundthe circumference of the seal to avoid kinking of the jacket.Snap the O-Ring into the groove and smooth out evenly. It maybe wise to insert the shaft before the O-Ring cools down. It isimportant that the surface finish should not exeed 20 microinch.61

SEALING ELEMENTS6. AvailabilityThe following are examples of such formats but we wouldconsider any requests for special items not displayed here.CircularCircular shapes are by far the most common and account forover ninety percent of the current production. Available assmall as 5 mm inside diameter with no upper diameter limit.OvalOval shapes are used mainly in "inspection hatch" applicationson chemical vessels. ERIKS can produce most of thecommon hatch sizes as well as non standards.Semi circularSemi circular shapes are used for both inspection hatch andheat exchanger sealing. There are no standard sizes availablebut tooling costs are very low so most applications areworth serious consideration.Square and rectangularSquare and rectangular shapes are used in many applicationssuch as heat exchanger plate and pump housings. Allthe above shapes (excluding circular) have to be producedwith radiused corners and are priced on application.FEP Jacket on solid Viton ® coreThis the most popular combination and indeed the mosttechnically capable in providing a compression seal. TheViton ® core compound has been specifically formulated togive very low compression set results and this characteristicspeeds up the somewhat slow memory of the FEP jacket.The temperature range is -20°C to +204°C / -20°F to +392°F.FEP Jacket on solid Silicone corePFA Jacket on solid Silicone coreThis combination is preferred for higher temperature applications.The PFA jacket shares the same temperature servicelimits as the Silicone core.The temperature range is -60°C to +260°C / -76°F to +500°F.FEP Jacket on hollow Silicone coreUsed commonly where low seal loading is encountered. Forslow reciprocating or rotary movement, the hollow core doesnot offer as much of an energising load thus reducing jacketwear and premature failure.Temperature range is -60°C to +204°C / -76°F to +392°F.PFA Jacket on hollow Silicone coreUsed for the same applications as FEP on hollow Siliconecore but when additional abrasion resistance is necessary toprolong the seal life.Temperature range is -60°C to +260°C / -76°F to +500°F.FEP Jacket on Solid Viton ® or Silicone coreRectangular and square sections can be produced andERIKS has a standard range of gaskets in the price list sectionfor cam action type hose couplings. These provide a farsuperior alternative to envelope gaskets or solid PTFE joints.The temperature range is -20°C to +204°C / -4°F to +392°F.This combination again is very popular and this is due tolower cost against that of the Viton ® core. Technically it isinferior to Viton ® except when used for low temperature use.The temperature range is -60°C to +204°C / -76°F to +392°F.PFA Jacket on solid Viton ® corePFA offers higher abrasion resistance to that of FEP and thecost is approximately 50% higher.The temperature range is -20°C to +204°C / -4°F to +392°F.62

TECHNICAL DOCUMENTATION O-RINGS7. Size rangeTeflex O-Rings are manufactured both as standard sizes:• Metric• BS 1806• BS 4518• AS 568, AS 871• JIS B2401• and also as non-standards to customer requirement.Inside diameter tolerances are generally per DIN 3771, but thetolerance on cross section diameter varies slightly and they arelisted as follows:smallest inside dia possible (in mm)Ø Cord Tolerance Viton ® /Silicone Silicone(mm) +/- round cord hollow cord1,60 0,10 5,00 —1,78 0,10 5,28 8,02,00 0,10 6,80 10,002,50 0,12 7,40 12,002,62 0,12 7,60 16,003,00 0,15 12,00 20,003,53 0,15 13,00 24,004,00 0,25 14,00 28,004,50 0,25 15,00 35,005,00 0,25 20,00 42,005,34 0,25 23,00 50,005,50 0,25 23,00 55,005,70 0,25 23,05 60,006,00 0,30 27,00 75,006,35 0,30 40,00 90,006,99 0,30 50,00 100,008,00 0,40 75,00 150,008,40 0,40 80,00 160,009,00 0,40 100,00 175,0010,00 0,50 140,00 230,0011,10 0,50 150,00 250,0012,00 0,50 180,00 300,0012,70 0,50 200,00 350,0063

SEALING ELEMENTS8. Chemical resistanceThere is no upper limit to inside diameters. Please refer tothe design and installation section for housing details. It isnot recommend to stretch O-Rings smaller than 12 mminside diameter. This often results in breakage of the corewhich is not vulcanised on small sizes.Thickness of the FEP/PFA jacket:Following thickness are standard:Ø sectionfrom 1,78 mmfrom 2,62 mmfrom 3,53 mmfrom 5,34 mmfrom 6,99 mmThickness FEP/PFA0,25 mm0,25 mm0,25 mm0,40 mm0,50 mmFEP and PFA Teflex O-Rings don't absorbs most chemicaluntil the temperature reaches 200°C. In the next diagram arethe absorption figures at different temperatures:Chemical product Temp °C Time%AbsorptionAniline 185 168 h 0,3Benzaldehyde 200 168 h 0,7Tetrachloride 78 168 h 2,3Freon 113 47 168 h 1,23Nitrobenzene 210 168 h 0,8Toluene 110 168 h 0,8Sulfuric acid 50% 100 168 h 0,01Phosphoric acid 100 168 h 0,01Sulfuric acid 30% 70 1 year 0Chlorid acid 20% 70 1 year 0Aceton 70 168 h 0Benzene 78 168 h 0,5TEFLON ® FEPØ d2Ø d1Viton ®or SiliconeSolid coreSiliconehollowcoreEncapsulated O-ring dimensions comply with InternationalO-ring dimensional standards. The encapsulation does notincrease the cross section compared to a standard elastomerof the same size.64

TECHNICAL DOCUMENTATION O-RINGS9. Compressive load requirements11. Groove dimensionsDesigners may require information showing details of compressiveload required for Teflex O-Rings. In order to providethis information, ERIKS conducted tests on each of the commoncross sectional diameters within our range of products.Samples were taken from typical production batches andtested to 10,15, and 20% compression rates.It is possible, using the following table, to obtain the totalforce required to effect a desired compression of a TeflexO-Ring, thus allowing accurate selection of sufficientmechanical loading.Normal 10% 15% 20%VITON ® SILICONE SILICONEDIAM. SOLID CORE SOLID CORE HOLLOW COREmm Compression Compression Compression10% 15% 20% 10% 15% 20% 10% 15% 20%1,60 16 26 40 20 33 481,78 26 40 53 22 35 482,00 34 53 77 30 46 592,50 40 66 95 40 59 782,62 29 44 64 23 38 533,00 70 107 140 36 60 82 27 38 503,53 54 91 120 32 57 83 28 44 584,00 51 82 111 56 87 108 23 36 454,50 75 107 139 53 84 110 41 55 655,00 91 126 182 39 64 89 50 70 875,34 82 117 145 96 138 191 54 77 945,50 45 83 116 37 65 935,70 79 116 115 58 88 1126,00 86 126 169 53 86 113 46 72 916,99 95 135 201 101 135 201 46 63 808,00 101 147 213 82 122 163 66 96 1219,52 115 173 247 84 125 17510,00 122 192 281 117 174 24612,00 124 194 279 59 93 126Figures in N/25mm lengthTable 1 (page 66)Ø ‘t’ ‘b’1.60 1.20 1.901.78 1.30 2.302.00 1.50 2.602.50 1.90 3.202.62 2.00 3.403.00 2.30 3.903.53 2.75 4.504.00 3.15 5.204.50 3.60 5.805.00 4.00 6.505.34 4.30 6.905.50 4.50 7.105.70 4.65 7.406.00 4.95 7.806.35 5.25 8.206.99 5.85 9.108.00 6.75 10.408.40 7.20 10.509.00 7.70 11.709.52 8.20 12.3010.00 8.65 13.0011.10 9.65 14.3012.00 10.60 15.6012.70 11.45 16.80Table 2 (page 66)Ø ‘t’ ‘b’1.60 1.20 ± 0.05 2.101.78 1.30 ± 0.05 2.302.00 1.50 ± 0.05 2.602.50 1.90 ± 0.05 3.202.62 2.00 ± 0.05 3.403.00 2.30 ± 0.05 3.903.53 2.75 ± 0.05 4.504.00 3.15 ± 0.05 5.204.50 3.60 ± 0.05 5.805.00 4.00 ± 0.05 6.505.34 4.30 ± 0.05 6.905.50 4.50 ± 0.05 7.105.70 4.65 ± 0.05 7.406.00 4.95 ± 0.05 7.806.35 5.25 ± 0.05 8.206.99 5.85 ± 0.05 9.108.00 6.75 ± 0.10 10.408.40 7.15 ± 0.10 10.909.00 7.70 ± 0.10 11.709.52 8.20 ± 0.10 12.3010.00 8.65 ± 0.10 13.0011.10 9.70 ± 0.10 14.3012.00 10.60 ± 0.10 15.6012.70 11.40 ± 0.10 16.7065

SEALING ELEMENTSTable 1Table 111. ApprovalsFDA: Food and Drug AdministrationThis data pertains to the US Federal Food and DrugAdminihration regulations governing the use of fluoropolymersas articles or components intended for use in contactwith food.The Teflon FEP and PFA resins used to produce Teflex maybe used as articles or components to contact food incompliancewith FDA Regulation 21 CFR 177.1550.This specification includes acceptance by The United StatesDepartment of Agriculture for direct use in contact with meator poultry food products and Food Industries SupplyAssociation Inc for product contact surfaces for DairyEquipment.USP Class VI requirements are met by Teflon FEP and PFAfor use in Pharmaceutical Processing.Teflon FEP is approved for use with potable water under section5296 certificate no 930716.Teflon FEP - CONFORMITY21 CFR 177.1550 21 CFR 177.2600 21 CFR 175.10521 CFR 176.180 21 CFR 177.1520 21 CFR 175.30021 CFR 176.170Teflon PFA - CONFORMITY21 CFR 177.1550 21 CFR 175.105 21 CFR 176.18021 CFR 175.300 21 CFR 176.170Viton ® can be produced compliant to FDA.Table 212. Quality control and inspectionERIKS only uses the very best available materials andcomponents from manufacturers such as Dupont-Dow-Elastomers. The laser micrometer inspection equipment isstate of the art and every single Teflex O-Ring which leavesthe warehouse has been individually checked for visual andmechanical compliance. Dimensional inspection AQL is 10%unless otherwise agreed. ERIKS is able to offer 100% controlon dimensions.Prior to dispatch large Teflex O-Rings may be twined andcoiled to reduce shipping costs. It is advised to uncoil thering upon receipt. If this is not done, after some length oftime it may be necessary to place the seal in hot water or anoven (max 80°C) for 10-20 minutes to allow the seal to returnto shape.66

TECHNICAL DOCUMENTATION O-RINGS13. Design14. Answers to popular questionsThe following diagrams show the suggested adaptations ofBS, ISO, and DIN standard housing designs.The surface finish to all contact parts should be 20 microinchor better.The following diagram gives tolerances for axial face sealing:PressureSeal Surface Ra 0,4 – 0,8Rt 3- 6,3Surface Ra 1,6Rt 11- 16Is it possible to produce Teflex O-Rings with an EPDM orNBR core?It is possible with special EPDM (white). Due to the high temperaturesinvolved in the production process it is not possibleto produce Teflex O-Rings around normal elastomers.Is 48 hours emergency production possible?It is possible if we take down the set up of the actual production.So these O-Rings are more expensive.Why are small O-Rings relatively more expensive?Every O-Ring is made by hand. As one can imagine the verysmall items have to be manufactured, sized, and inspected inthe same way as larger O-Rings but the process is muchlonger.Are other cross sections possible than the standard ones?Due to a special process ERIKS produces special cross sectionsizes. Tooling costs are necessary.67

SEALING ELEMENTS6. Compound selection - DatasheetsAll ERIKS standard and some specialO-ring compounds have data sheetswith measured values of specific gravity,hardness, tensile strength, elongationat break, compression set, lowtemperature, and heat ageing indifferent test circumstances.Any specific data sheet can beobtained upon request.For several reasons data sheets cansometimes lead to considerable confusion.Manufacturers generally statevalues measured on test slabs or testbuttons. Though these test slabs aremade of the same rubber compoundas the O-ring, some factors however,are completely different: vulcanisationtime, vulcanisation temperature, postcuringtime, and size. The vulcanisationtime of such a slab can be 20 minutes,whereas the moulding/vulcanisationtime of an O-ring - for economicalreasons - can only be 2 minutes.Measuring results from a slab will givedifferent values than measuring on anO-ring.ERIKS has therefore decided thatwhenever possible most of their datasheets should show values based onmeasurements made on O-rings. Thisgives the customer a better picture ofthe properties to be expected from theO-ring. To put it in other words: thedata sheet with values measured onslabs demonstrates what propertiesthe O-ring could have, if producedunder the most ideal conditions.ERIKS, however, states the real sealingperformance of the O-rings.This can be illustrated as follows: inmost of the data sheets you will findthe compression set values measuredon slabs of .25 inch. (6 mm) thickness,e.g. 12%. If measured under the sameconditions, an O-ring of .139 inch(3.53 mm) will have a value of 19 to25%. For determining the service lifeERIKS has based their measurementson O-rings with a cross section of .139inch (3.53 mm).The other cross sections have beenextrapolated from these values.These differences also apply to theother values stated. It is therefore verydangerous to compare values of datasheets without knowing the exact testmethod.It is always better to carryout tests on the O-ring itself in theapplication rather than on a testspecimen.68

TECHNICAL DOCUMENTATION O-RINGS6. Compound SelectionO-ring compounds -Field of ApplicationMost of the preceding parts in thishandbook have dealt with selectingthe best rubber compound for a givenapplication. Here is information tounderstand the factors involved in theprocess and to provide some guidancein selecting the correct material. Onlybasic compounds are mentioned. A lotof special compounds are available,please ask the local ERIKS division forassistance.Water and Steam ApplicationMost elastomers can be used forwater applications up to 212°F(100°C). Water appears to be aninnocuous fluid, people are oftensurprised to learn that it can bringproblems if it is not sealed with theproper O-ring. The mere immersion inwater has an adverse effect on themechanical properties of rubber. Aftera long period of water immersion,many rubber compounds will swell. Ina static application, this may be quiteacceptable. Such a seal will not leak.And it can be replaced with a new oneafter disassembly. An advanced amountof swelling implies a larger volume andconsequently more friction. Used as along term dynamic seal, this gradualswelling of an O-ring in water cancause a slow but very annoyingincrease in friction. In tests, ethylenepropylene rubber has virtually no swell.This material is recommended forO-rings for sealing against water andsteam for temperatures up to 150°C(300°F).ERIKS has compounds in:EPDM PC 55914, HNBR, and AFLAS®.In FFKM a number of Perfluoroelastomercompounds are available which exhibitperfect sealing properties in steamsurroundings.Silicone (VMQ) can also be compoundedin such a way that it can be usedpressureless in a steam environmentup to 250°C (480°F).Note:When sealing steam or hot water withethylene propylene, it is important toremember that it will deteriorate whenexposed to petroleum lubricants.When lubrication is required, siliconeoil, glycerin, or ethylene glycol aresuggested.When water changes into steam, theO-ring must maintain an effective sealas the temperature increases. Thissometimes causes the rubber tobecome spongy as a consequence ofwhich all sealing properties are lost.Some compounds, however, aresteam resistant.Food ApplicationRubber in contact with foods mustmeet special requirements. There are anumber of institutions who regulate therules and tests. The main institutionsare: FDA and NSF in the USA; KTWand BGVV in Germany, WRC in the UK,and KIWA in the Netherlands.This book primarily discusses the FDAprogrambecause it is the mostdemanding requirement.69

SEALING ELEMENTS6. Compound Selection - FDAFDA CompliancyGeneral information about FDAFor many years ERIKS has had a leadingrole in the production and marketing ofhigh quality seals.ERIKS has also developed a vast rangeof elastomeric compounds that are formulatedto comply with the regulationsissued by the ‘United States Food andDrug Administration’ (FDA).These regulations are stipulated in Title21, Chapter 1, subchapter B, section177.2600 of the ‘Federal Food andCosmetic Act’.These regulations define which rubberpolymers and compounding ingredientscan be used in rubber articles, intendedfor repeated contact with food andpreventing the use of dangeroussubstances that might cause cancer.Types of FDA compliancyTwo important types (class 1 and class 2)of FDA compliance exist, depending onthe percentage of carbon black that isadded to the compound.Class 1 : for aqueous and greasy media;Class 2 : for aqueous media.USP class 6 was especially developedfor the pharmaceutical industry. ERIKSoffers 5 compounds of this type of USP,all meeting very strict requirements.CertificationERIKS guarantees ‘conformity’ by:• strict production methods,• an FDA sticker is put on thepackaging,• a certificate of conformity can beobtained with every delivery.In general ERIKS guarantees thatthe FDA materials are ‘FDA compliant’which means they are composedwith ingredients accordingthe FDA regulations.Migration testsSome compounds have been testedby independent laboratories. Rubberarticles intended for repeated use incontact with aqueous food shall meetthe following specifications: ‘The foodcontact surface of the rubber article inthe finished form in which it is to contactfood, when extracted with distilledwater at reflux 20 milligrams persquare inch during the first 7 hours ofextraction, not to exceed 1 milligramper square inch during the succeeding2 hours of extraction’.Rubber articles intended for repeateduse in contact with fatty foods shallmeet the following specifications: ‘Thefood-contact surface of the rubberarticle in the finished form in which itis to contact food, when extractedwith n-hexane at reflux temperature,shall yield total extractives not toexceed 175 milligrams per square inchduring the first 78 hours of extraction,nor to exceed 4 milligrams per squareinch during the succeeding 2 hours ofextraction’.70

TECHNICAL DOCUMENTATION O-RINGS6. Compound Selection - FDAVulc-O-rings FDA class 1Vulc-O-rings are produced in smallquantities.Inside diameter range from 30 mm upto 5.000 mm in the different cross sectiondiameters from 1,78 up to 25 mm.No chemical additive is added in thebonding of the core ends.Datasheets are available upon request.Vulc-O-rings, Class 1Standard Compounds Description Compliance Hardness°Shore ASilicone 60 FDA GP60 Vulc-O-ring - Silicone 60, transparent FDA, WRC 60Silicone 70 FDA GP70 Vulc-O-ring - Silicone 70, transparent FDA, WRC 70Silicone 75 714991 Vulc-O-ring - Silicone 75, red FDA 75Silicone 80 FDA GP80 Vulc-O-ring - Silicone 80, transparent FDA, WRC 80EPDM 75 FDA MC 187 Vulc-O-ring - EPDM 75, black FDA 75NBR 75 FDA MC 185 Vulc-O-ring - NBR 75, black FDA 75Viton® 75 FDA MC 172 Vulc-O-ring - Viton® 75, black FDA 75Neoprene® MC 186 Vulc-O-ring - Neoprene® 75, black FDA 75HNBR FDA Vulc-O-ring - HNBR 75, black FDA 75ERIKS has 25 FDA compliant compounds.Please contact the local ERIKS representative forinformation.For more information on Vulc-O-rings, pleaserefer to Chapter 16.Ask for an FDA brochure or visit the website:www.eriks.be (brochures)71

SEALING ELEMENTS7. 6. Compound Selection - FDAO-rings Kalrez® FDAKalrez® Perfluoroelastomer Partsfor Pharmaceutical and FoodHandling ApplicationsKalrez® parts made from compounds6221 and 6230 provide superior chemicalresistance and low contaminationfrom extractables in pharmaceuticaland food handling applications whereFDA compliance is required.Compounds 6221 and 6230 are especiallysuited for Water For Injection(WFI) systems, Steam In Place (SIP)cleaning, and other critical systems.Thermal StabilityUnlike other elastomeric seals madewith FDA compliant elastomers,Kalrez® perfluoroelastomer parts arethermally stable up to 260°C, permittinguse in applications such as Stage IISterilization processes, where otherelastomers lose their sealing capabilities.Aggressive Water ResistanceIn aggressive pharmaceutical andsemiconductor processing environments,seal failure from excessswelling, embrittlement, or decompositioncan cause unscheduled downtimeor product contamination. ElastomericTable 1- Elastomer Chemical Compatibility *Chemical Kalrez® EPDM VMQ FKMAcetic acid A A A BAcetone A A C UCitric acid A A AHydrogen peroxide A B B BIsopropyl alcohol A A AMetthyl ethyl ketone A A U UMineral oil A U B ANaOH A A B BNitric acid A B B ASodium Hypochlorite A B B ASoybean oil A C A ASteam (150°C) A C U UToluene A U U AXylene A U U AMaximum Service Temp. 260°C 135°C 200°C 200°Cmaterials that come in contact withhighly pure and aggressive water (e.g.WFI) must be chosen with care in orderto prolong seal life. The perfluoroelastomercompounds used in Kalrez®parts have been shown to haveextremely low to non-detectableextractable levels in aggressive watersystems. Because the perfluoroelastomerpolymer in Kalrez® parts is fullysaturated, it is also well suited forOzonated Deionized Water service.Kalrez® parts also exhibit very lowswell and loss of mechanical propertiesafter repeated steam cycling.General Chemical ResistanceThe overall chemical resistance ofEPDM’s, silicone elastomers, and fluoroelastomers(FKM) is limited by theirrespective polymer structures. Kalrez®parts, on the other hand, offer thesame universal chemical resistance asPTFE, but unlike PTFE, they have elastomericproperties, which help themmaintain their sealing capabilities.Table 1 lists the chemical compatibilityof Kalrez® perfluoroelastomer partsand other elastomers used as sealingmaterials in the pharmaceutical andfood handling industries.A = little or no effect ; B = slight swelling and/or loss of physical properties ; C = moderate tosevere swelling and/or loss of physical properties/limited functionality ; U = not suitable orrecommended.* Data has been drawn from DuPont Dow Elastomers tests and industry sources. Data is presented for useonly as a general guide and should not be the basis of design decisions. Contact DuPont Dow Elastomers orERIKS for further information.Table 2- Typical Physical Properties * *Compound Kalrez® 6221 Kalrez® 6230Colour White BlackDurometer hardness, Shore A, points±5 70 75100% Modulus, psi (MPa) 1,050 1,020Tensile strength at break (1) , psi (MPa) 2,200 2,400Elongation at break (1) , % 150 170Compression set (2) , 70h at 160°C 20 18(1) ASTM D412, (500 mm/min) ; (2) ASTM D395 B, Size 214 O-rings** Typical physical properties should not be the basis of design decisions. Contact DuPont Dow Elastomersfor further information.72

TECHNICAL DOCUMENTATION O-RINGS6. Compound Selection - FDA2.5. O-rings Kalrez® FDAKalrez® perfluoroelastomer parts arenot routinely tested using the USPtesting protocol. Cured samples madeonly from compounds 6221 and 6230have been tested in accordance withUSP protocols and meet the requirementsof a USP Class VI polymer. USPtesting was done to support use ofKalrez® parts in pharmaceutical processingand food processing applications.While USP Class VI compliantmaterials are not required for pharmaceuticaland food processing applications,many pharmaceutical and foodprocessing customers, including customersseeking ISO-9000 certification,have requested compliance. Testing ofany finished article that incorporatesKalrez® perfluoroelastomer parts isthe responsibility of the manufactureror seller of the finished article if certificationthat meets USP standards isrequired.Note:Please contact ERIKS engineers fordetermining the right Kalrez® O-ringfor an application.Medical useCaution: Do not use Kalrez® perfluoroelastomerparts in medical applicationsinvolving implantation in the humanbody. For other medical applications,see DuPont Dow Elastomers MedicalApplications Policy, H-69237. DuPontDow Elastomers will not sell or supportproducts for implantation in the humanbody. DuPont Dow Elastomers doesnot make surgical or medical grades ofKalrez® perfluoroelastomer parts anddoes not guarantee continuity ofprocess in our manufacturing operationsas changes may occur from timeto time.Kalrez® gains Food ContactSubstance NotificationWe are very pleased to announce thatthe United States Food and DrugAdministration (FDA) has reaffirmedthe compliance of Kalrez® 6221 and6230 perfluoroelastomer parts forrepeated use in contact with food.Food Contact Substance NotificationFCN000101 describing perfluorocarboncured elastomers Kalrez® 6221and 6230 became effective onDecember 19, 2000. Meeting this stringentrequirement in addition to existingcompliance with FDA 21 CFR 177.2600reinforces DuPont Dow’s determinationto exceed standards used by thepharmaceutical industry. The notificationprocess for food contact substances,described in section 409(h) ofthe Federal Food, Drug and CosmeticAct (FFDCA), emerged in 2000 as theprimary method by which the FDAauthorizes the use of food additivesthat are food contact substances. Anotification for a food contact substancecontains sufficient informationto demonstrate that the substance issafe for the intended use (that is thesubject of notification (21U.S.C.348(h)(1)).Proven suitability for food and pharmaprocessingDuPont Dow Elastomers welcomes thenew legislation as an opportunity toreaffirm the suitability of Kalrez® 6221and 6230 perfluoroelastomer parts forrepeat use food contact applications.The FCN requires Kalrez® 6221 and6230 to meet extractable levels not toexceed 0.2 milligrams per square inch.This provides further confirmation ofthe low risk of contamination fromKalrez® parts and the long term sealingsolution for challenging food andpharmaceutical applications.Statement of ComplianceKalrez® parts made from compounds6221 and 6230 meet the extractiverequirements of 21 CFR 177.2600(E)and may be used for repeated use incompliance with the Food, Drug andCosmetics Act and all applicable foodadditive regulations. Kalrez® partsmade from compounds 6221 and 6230have been tested in accordance withthe United States Pharmacopeia ClassVI (USP Class VI) testing protocol.Testing using the protocols citedabove was performed by an externaltesting facility in compliance with 21CFR, Part 58 Good LaboratoryPractice for Nonclinical LaboratoryStudies.6221 and 6230 offer excellent steamcycling resistance and reduceextractables from sealing materials totrace levels.Ask about the special ERIKSbrochure on High Purity Seals!73

SEALING ELEMENTS6. Compound Selection - CertificationKTW:KTW was adopted as a standard fordrinking water. KTW controls themigration of harmful substances. Anumber of these constituents are subjectedto limits. The O-rings are classifiedunder the scope D2.ERIKS has standard compoundswhich meet KTW in:• EPDM 70-compound 55940• Silicone 70-compound 714940WRC:WRC controls the harmful constituentsin rubber, like metal extraction andmicro organisms.ERIKS has compounds with WRCcompliance in EPDM 70 compound55950, Silicone 70 compound 714950,VMQ and NBR.DVGW certificatesERIKS has several compounds forapplications in the gas industry withDVGW-certificates.The following table lists a summary ofthe DVGW norms.Norm Application Temperatures (°C) Pressure (bar)minmaxDIN 35351 gas installation -20,-15 60,8 ≤ 5DIN EN 549EN 549 gas installation and -20 60,80,100 ≤ 5gas apparatus 125,150EN549 gas equipment -20 80 up to ≤ 5150DIN 3535-3 gas transport -5 50 ≤ 40EN 682 -5 50 ≤ 4NSF:NSF = National SanitationFoundation. This standard is mainlyapplied in the USA.ERIKS has a number of compoundswith NSF compliance.74

TECHNICAL DOCUMENTATION O-RINGS6. Compound SelectionVacuum ApplicationsThe rate of flow of gases from thepressure side to the vacuum side of anO-ring seal depends to a great extenton how the seal is designed. Increasedsqueeze by reducing the groovedimensions reduces the leak ratedramatically.Increased O-ring squeeze reducespermeability by increasing the lengthof the path the gas has to travel (widthof O-ring) and decreasing the areaavailable to the entry of the gas(groove depth). Increased squeeze canbe realized with smaller grooves.Increasing squeeze also tends to forcethe rubber into any small irregularitiesin the mating metal surface, and thusprevents leakage around the O-ring.Therefore, surfaces against which anO-ring in a vacuum application mustseal should have a surface roughnessvalue smoother than usual. Surfacefinishes of 16 RMS are quite common.Lubricating the O-ring with a high vacuumgrease also reduces the leakage.The vacuum grease aids the seal byfilling the microscopic pits andgrooves, thus reducing leakage aroundthe O-ring.Although a very high squeeze is necessaryto reduce leakage to anabsolute minimum in an O-ring seal,this kind of design may require heavyconstruction. When a shallow gland isdesirable, it must be wide enough toreceive the full O-ring volume, also athigher operating temperatures.The vacuum level denotes the degreeof vacuum evidenced by its pressurein torr (or mm. Hg).Rough vacuum 760 torr to 1 Torr,Medium vacuum 1 torr to 10 -3 Torr,High vacuum 10 -3 torr to 10 -6 Torr,Very high vacuum 10 -6 torr to 10 -9 Torr,Ultra high vacuum below 10 -9 Torr.For effective vacuum sealing the compoundmust possess certain properties:low compression set, low permeabilityto gas, and it should containfew softeners. The best choice isButyl, but this is very unusual asO-ring compound, followed by afluoroelastomer.Extracted plasticizers can leave a filmon the instruments. In static vacuumapplications it is recommended todesign for a squeeze of the O-ring ofat least 25-30% to absorb the irregularitiesof the metal surface.It is of great importance that a compoundis used with the lowest possiblecompression set, because temperaturefluctuations may impair thesealing properties even further.ERIKS has compounds that are wellsuited for vacuum applications:Viton® 51414 ( black in 70° IRHD)Viton® 514075 and 514090 (75° and90° IRHD respectively)Viton® 514170 is specifically designedfor vacuum applications.Vacuum ApplicationsPolymer type Loss of WeightButyl 0,18CR 0,13EPDM 0,76Fluorsilicone 0,28NBR 1,06Polyurethane 1,29Silicon 0,31FKM 0,07Loss of weight at 10 -6 Torr after 2 weeksat 23°C / 73°F.75

SEALING ELEMENTS6. Compound SelectionDegassingWhen using O-rings in high vacuum,permeability and degassing of O-ringsplay an important role and thereforethese aspects have to be taken intoaccount. The lower the permeability ofthe rubber, the easier it is to maintainthe vacuum.Some rubber compounds still containrelatively volatile substances after vulcanisation,which egress from thecompound in particular high vacuumapplications. Degassing is the loss ofvolatile elastomeric compounds invacuum application. This results insome volume loss of the seal materialwhich will lead to seal failure.The results are:Vacuum seals are improved by gradualchanges to system pressure, theinstallation of elastomers with greaterhardness and higher density, andlowering the system temperaturewhich will result in lower degassing.For this reason Fluoroelastomers andPerfluorinated elastomers are oftenused in vacuum applications.Vacuum applications in combinationwith service requirements such as hightemperature, radiation resistance, andexposure to combinations of fluidmedia will require careful analysis toselect the proper O-ring.Contact with plasticsO-rings are more and more being usedas a seal in contact with plastics. Theproblem being faced when the rubbercomes in contact with plastics, is themigration of softeners or other "processaids" from the rubber into theplastic. The offending ingredients areusually the ester plasticizers used insome rubber compounds. Additives inthe plastic can also migrate into theO-ring, causing substantial change ofproperties. After the migration of softenersinto the plastic, "surfacecracking" may arise, resulting in adeterioration of tensile strength. Not allplastics are susceptible to this phenomenonto the same extent. Plasticswhich are the most susceptible tothese softeners are: ABS, Noryl, andPolycarbonate.Tests have shown that EPDM peroxidecured, FKMs, neoprene, and some siliconesare the best choice.ERIKS also has an EPDM compound55914PC that will work well.High Purity CompoundsIn many modern industries high-purityO-rings are used more and more foran optimal progress of the productionprocess. Fluoroelastomer parts arewidely used in wet chemical and plasmaenvironments in the fabrication ofintegrated circuits.Traditional seals often contain carbonblack as a reinforcing filler. Manyspeciality fluoroelastomer compoundscontain inorganic or metallic fillers toachieve improved seal performance inaggressive environments. Use ofthese metal fillers, while beneficial toseal life, can increase particle generationand extractable contaminants.O-rings made with high purityfluoroelastomers and perfluoroelastomersare designed to meet thedemanding contamination needs ofthe semiconductor industry. Fromapplications in lithography to etchingand cleaning, O-rings manufacturedwith high purity fluoroelastomers offerunmatched extractable contaminationperformance versus traditionalfluoroelastomer O-rings.Thanks to specific production, compounding,inspection, and ambient factors,several levels of purity are available.ERIKS is able to provide several highpurity compounds in Viton® FKMU60W - U75W SCUBR 70 and 90 (upto 204°C, 400°F) and FFKM Kalrez®(up to 316°C, 600°F).Note:• Clean Room packaging on demand• ERIKS can deliver high-puritycompounds in silicone, Viton®, andKalrez® for the semicon industry.76

TECHNICAL DOCUMENTATION O-RINGS6. Compound SelectionPermeability / Contact with GasesAll rubber compounds are more or lesspermeable to gas. The rate ofpermeability to gas of the variouscompounds varies.Permeability is the tendency of a gasto pass or diffuse through the elastomer.This should not be confused withleakage, which is the tendency of amedium to go around the seal.All elastomers are permeable to someextent allowing air or other gasesunder pressure or volatile liquids, topenetrate into the seal material andgradually escape on the low pressureside. Permeability may be of primeimportance in vacuum service andsome pneumatic applications.Permeability is increased as temperaturesrise and is decreased by compressionof the sealing material. Thepermeability rate of various gasesthrough different rubber materialsvaries in an unpredictable way. Eventhe same basic compounds show largedifferences. Several gases give differentvalues for the same compound.Permeability is also affected by applicationparameters such as cross section,pressure, and temperature.It is typical that harder compounds,generally containing more carbonblack, exhibit better values. Whenusing NBR a higher ACN percentage ismore advantageous.The following list indicates othercompounds ranging from the lowestpermeability to the highest:• AU: Polyurethane• NBR: Nitrile• FKM: Fluorocarbons• FFKM: Perfluorinated Elastomers• EP/EPDM/EPR: Ethylene Propylene• SBR: Styrene/Butadiène• NR : Natural RubberSilicone and Fluorosilicones have evenhigher gas permeability. Ask for informationabout gas permeability rates ofother ERIKS compounds.Gas permeabilityThe following table gives the gas permeabilitycoefficient for different mediaand compounds.Gas permeabilityGas permeability IIR AU NBR NBR NBR CR NR VMQcoefficient (38% (33% (28%10 -17 m 2 / (s x Pa) ACN) ACN) ACN)Air 60°C / 140°F 2,0 2,5 2,5 3,5 7,5 6,0 25,0 330Air 80°C / 175°F 5,0 7,0 5,5 7,0 21,0 12,0 40,0 410Nitrogen 60°C / 140°F 1,5 2,5 1,0 2,0 4,0 4,5 18,0 280Nitrogen 80°C / 175°F 3,5 5,5 2,5 5,5 7,0 8,0 33,0 360CO2 60°C / 140°F 13 26 30 56 58 58 160 950CO2 80°C / 175°F 29 73 48 63 97 71 210 1500Laboratory tests have demonstratedthat permeability of lubricated O-ringsis lower than dry O-rings. These testalso show that more strongly squeezedO-rings show lower permeability.In fact, the permeability of a givenbase polymer will vary according tothe proportions of the copolymer.The best choices are Butyl,Fluoroelastomer (FKM 51414), andNitrile with a high percentage of ACN.Butyl is very unusual as an O-ringcompound.77

SEALING ELEMENTS6. Compound SelectionHigh Pressure Gases / ExplosiveDecompressionIn high pressure applications above1500 psi (100 bar), gases tend to fillthe microscopic small pores in the rubber.When using O-rings in high gas (orvolatile liquid) pressures or suddenpressure drops, the permeability ofelastomers has to be considered.If gas under high pressure has theopportunity to penetrate to a sufficientdegree into the elastomer, this penetratedgas (or volatile liquid) willexpand when a sudden pressure dropoccurs and will want to leave the elastomer.The greater the pressure, thelarger the amount of gas forced intothe rubber. When the pressure suddenlydrops, the gas expands in theO-ring and will find its way into theatmosphere. The gas may escapeharmlessly into the atmosphere, or itmay form blisters on the surface.Small cracks deep into the O-ring willconsequently develop. Some of thesemay rupture, leaving cracks or pits andwill damage the seal. This phenomenonis called Explosive Decompression.Generally it is assumed that this phenomenoncan occur in cases of pressuredrops greater than approx. 400psi ( ca. 30 bar or 3 Mpa.). Variablesto consider are the gas, pressure, temperature,and the rubber compound.Generally carbon dioxide (CO 2 ) causesmore problems than nitrogen does.Improvement can be realized ingradual reduction of the pressure anduse of rubber with a higher hardnessand a higher density. Resistance canbe improved by increasing hardnessup to 90-95° Shore A. Another methodis to decrease the cross section of theO-ring, though this method is notalways successful. Nitrile andFluoroelastomer are the best standardmaterials for this application.ERIKS has compounds in:Aflas® for applications with gas andsteam.FKM 514162 in 94° IRHD, special foroil and gas industry.Only by using highly selected rubbercompounds and by carefully mixing allingredients, an "explosive decompressionresistant" material can beachieved. Naturally all these compoundsare also extrusion resistant.Offshore ApplicationsIn offshore conditions O-rings areexposed to extreme pressures, temperatures,and aggressive media.The critical circumstances becomeeven greater by very aggressive oiladditives, varying temperatures, gapextrusion, and explosive decompression.Under such conditions only specialcompounds will be acceptable.ERIKS compounds:NBR-95, extremely extrusion resistant,tested by the American PetroleumInstitute.AFLAS-90, High molecular Aflas® withincreased extrusion resistance andvery good compression set. Ideallysuited for applications with amines andstrong lyes. Can be used up to 200°C(390°F).HNBR-XNBR 90, a blend of HNBR andXNBR 90° IRHD, ensuring an extremewear resistance combined with a veryhigh extrusion resistance. Can be usedto 150°C (300°F). Also available in 80°IRHD.Compatibility of elastomers withMineral Based OilsA well known rapid method for materialselection for O-ring applications inmineral oils is the selection based onthe aniline point of the oil. The ASTM D471 test reference oils cover a range ofaniline points found in lubricating oils.Test Oil ASTM No.1, has a high anilinepoint 124°C (225°F) and causes slightswelling;Test Oil IRM 902, has a medium anilinepoint 93°C (200°F) and causes intermediateswelling;Test Oil IRM 903, has a low anilinepoint 70°C (157°F) and causes high orextreme swelling of O-ring compounds.Note: The aniline point of a petroleumoil appears to characterize the swellingaction of that oil on rubber vulcanisates.In general, the lower the anilinepoint, the more severe the swellingaction caused by the oil. In staticO-ring applications, 20% volume swellmay be acceptable, in dynamic applicationsvolume swell may need to beless than 10%.Any other commercial oil with thesame or similar aniline point can beexpected to have a similar effect on aO-ring as the corresponding ASTMtest oil. However, it has been foundthat the aniline point method is notalways reliable. Some commercial oils,having the same aniline point, candiffer significantly because they containdifferent additives. It is recommendedto conduct compatibilitytests on materials in question in theoil that will be used in the application.B-test fluids make an extraction of thelow molecular softeners of the rubbercompound. The more softeners in acompound the more an O-ring hardensand shrinks in an application. Shrinkingin O-ring applications is not acceptable.Leakage can be the result.A popular B-test fluid is a mixture of42.25% toluene, 25.35% iso-octane,12.7% di-iso- butylene, 4.3% ethanol,15% methanol and 0.5% of water.78

TECHNICAL DOCUMENTATION O-RINGS6. Compound SelectionMineral Oils, Hydraulic FluidsThese oils are most frequently used inindustry. Their greatest disadvantageis their toxic character and incombustibility.These products are notexactly defined, but they are a mixtureof various hydrocarbons. The followingguidelines can be given for the severalkinds of rubber.General: Almost all hydraulic fluidscontain active additives which canattack the elastomers, certainly at hightemperatures.NBR is the workhorse of these fluids.The higher the ACN content in theNBR, the better the resistance.Standard NBR types tend to hardenfrom 110°C (230°F) and higher whenadditional cross linkage occurs.ERIKS compounds for hydraulic fluids• NBR: All types can be used. Pleaserequest a list of available types.• HNBR: Can be used up to 150°C(300°F), especially compounds whichare peroxide cured.• Neoprene®: Shows strong swelling inparaffin oils, as a result of which thereis hardly any demand for this rubber.• FKM: Can generally be used up to200°C (400°F). Resists many additives,with the exception of certainamines. These amines may cause therubber to harden quickly. That is whyperoxide cured FKM types (FKM GFtype) or FFKM are applied in thesecases. Also AFLAS® has excellentresistance at very high pressures.• Silicone: Silicone O-rings can beapplied in highly viscous oils only, butare very sensitive to active additives.• Fluorosilicone: very good up to 175°C(350°F), can also be used till -60°C(-76°F).• ACM: Generally good resistance tooils up to 150°C (300°F) .• ECO: Epichlorhydrin has good petroleumoil resistance and a wide temperaturerange -51°C (-60°F) to+150°C (+300°F).• Polyurethane: Very high resistance,though very sensitive to hydrolysis.Synthetic Oils, Hydraulic FluidsThese fluids have some advantagesover mineral oils.They exhibit better thermal stability, awider range of application temperature,and lower volatility. On the otherhand, prices are higher. A detailed listingof fluids would be too extensive.Following are a listing of general ruleson fluid resistance:The polar elastomers like NBR, FKM,ACM, HNBR, ECO, and AU have goodresistance.Resistance to hydraulic fluids cannotalways be predicted, because theadditives often play the major role inchemical attack. As in most casesthese additives are not always known,it is always recommend to perform atest to be certain.HFA and HFB FluidsThese fire resistant oils are moreaggressive. Specially formulatedNBRs should provide an acceptablelevel of swelling.ERIKS has several compounds in NBR.If a minimum amount of swelling isrequired, fluorocarbons such as FKM51414 should be used. The best possibleoption is the FKM 514075 compoundthanks to its minimal compressionset.Standard polyurethane is limited to50°C (122°F) due to its sensitivity tohydrolysis.Vegetable OilsThese are oils made from seeds, fruits,or plants, like olive oil, palm oil, andrape seed oil. They have the advantageof being biodegradable and nontoxic.Because recent advancementsin hydraulic fluids have made thembiodegradable, hydraulic fluids havebecome more and more popular.They have, however, a low temperatureresistance 80°C (176°F).Therefore, high temperature resistantelastomers are not necessary.In most cases NBR will perform well,though NBR compounds containing alot of plasticizers may sometimesbegin to swell. The use of polyurethaneis limited, though short-time use willonly show little swelling. Degradationwill mostly occur, certainly afterhydrolysis develops.EPDM and butyl exhibit good chemicalresistance, though swelling may occurup to 40%. They can therefore only beused in static applications.ERIKS has compounds in NBR 7036624 (70 IRHD); NBR 90 47702 (90IRHD); also special NBR compoundsfor FDA, WRC, and KTW applications.Note:This information on resistance is forreference only. The end-user isresponsable for ensuring compatibility.79

SEALING ELEMENTS6. Compound SelectionHydraulic and Transmission Oils andACN contentHigh ACN content with a low plasticizerlevel provides excellent resistance topetroleum oils. Low ACN content withhigh plasticizer level gives better flexibilityat lower temperatures. A peroxidecureprovides the best compressionset resistance at elevated temperatures.These properties are importantfor use in hydraulic applications.ERIKS has several NBR compoundswith high ACN content for the extremedemands of heavy equipment, forautomatic transmission fluid (ATF),crude oil, as well as NBR with lowACN content for flexibility at very lowtemperatures.Silicone FluidsSilicone fluids are chemically very stable.Referring to fluid compatibilitytables, all types of seal elastomers,except silicone rubber, may be usedfor silicone oils and greases. There aresome exceptions; however, siliconefluids have a tendency to remove plasticizersfrom elastomer compounds,causing them to shrink. The effect ismost severe with low viscosity fluidsand high temperature applications.Because of this, military nitrile compoundsand any other nitriles with alow temperature limit below -40°F(-40°C) should not be used to seal siliconefluids, because low temperaturenitriles must contain plasticizers. Othercompounds should be tested beforebeing used to be certain they will notshrink more than one or two percent.Silicone rubber has a poor chemicalcompatibility rating in contact with siliconefluids. This is because siliconerubber tends to absorb silicone fluids,resulting in swelling and softening ofthe O-ring. Occasionally, however, it isdesirable to seal a silicone fluid with asilicone rubber O-ring. This combinationis generally acceptable if the viscosityof the silicone fluid is 100,000centistokes or more, and if the maximumtemperature will not exceed150°C (300°F).Summary of the resistance for mineral and biological degradable oilsMineral oilsType:HH-LH-LPH-LPDH-VWaterbased oilsType:HFA (>80% water)HFB (40% water)HFC (35% water)HFD-RHFD-SElastomer to useNBR, FKM, HNBR, AUNBR, FKM, HNBR, AUNBR, FKM, HNBR, AUNBR, FKM, HNBR, AUNBR, FKM, HNBR, AUElastomer to use-5° +55°C - NBR, FKM, AU-5° +60°C - NBR, FKM, AU-20° + 60°C - NBR-20° + 150°C - EPDM (aeronotique)-20° + 150°C - FKMBiological oilsElastomer to useType:HETGfor agriculture up to 80°C: AU, NBR, HNBRHEPG for protected waterareas up to: 80°CAU, NBR, ANBR, FKM*+80°C: HNBR, FKM*(*only peroxide cured FKM’s)HEESup to 80°C: AU, NBR, HNBR, FKM+80°C: HNBR, FKM*(*only peroxide cured FKM’s)80

TECHNICAL DOCUMENTATION O-RINGS6. Compound SelectionContact with FuelsFuels are very complex fluids whenconsidering elastomers. Fuels are ablend of aromatic and aliphatic hydrocarbonswith the addition of alcohol. Itis always recommended to do tests,though Fluoroelastomer, Epichlorhydrin(ECO) and special NBR compounds aremost generally used.For a survey of the Fluoroelastomercompounds please refer to the generalFluoroelastomer brochure which will besent upon request.The UL (Underwriters Laboratories,Inc.) A Not For Profit Organization,sponsored by the American InsuranceAssociation, tests and lists many safeelectrical and fire protection devicesand equipment for use with hazardousliquids and chemicals. For many yearsthey have tested and reexamined elastomercompounds, as being suitablefor use with gasoline, naphta,kerosene, liquified petroleum gases,and fuel oils.UL listed O-ring compounds may beused with assurance for gasoline andLPG stations valves, pumps andmetering devices, LPG gas bottles,valves, and other types of equipmentrequiring reliable seals.Fuels for Automobile EnginesThere are several automotive fuels onthe market; leaded and unleadedgasoline with and without MTBE, eachtype of which can vary in compositionand gasohol content. Gasohol is amixture of gasoline with 10 to 20 percentalcohol. The alcohol may beeither ethyl (also called ethanol orgrain alcohol) or methyl (methanol orwood alcohol).The best rubber compound to usedepends not only on the fuel itself, butalso on the temperature range anticipatedand the type of usage, i.e.whether in a static or a dynamic application.In automotive fuel applications,extremely high temperatures are notanticipated, but in northern climates,temperatures as low as -40°C (-40°F)or even -55°C (-65°F) are sometimesencountered.Most of the compounds recommendedfor use in fuel have poor low temperaturecapability in air, but in a fluidthat swells them, low temperaturecapability improves.Fuels for Aviation SystemsAviation fuel systems are low temperatureapplications. NBR compoundsmust have good low temperature flexibility,generally low ACN, and higherplasticizer content. Fluorosilicone isalso used in aircraft fuel systems andis resistant down to -80°C (-112°F).Extreme TemperaturesWhen air or other gases must be containedat temperatures below -55°C(-65°F), the recommended low temperaturelimit for most silicone rubbers,special compounds must be used. Ifthe permeability rate of silicone rubbersis too high for the application,bear in mind that the rate decreases astemperature goes down, then an alternativecompound must be selected.For applications requiring moderatelyhigh temperatures as well as low, it isfeasible to use two O-rings, a siliconerubber O-ring to maintain the seal atlow temperature plus a fluorocarbon toreduce permeability when the seal iswarmer. If a low temperature O-ringmust have resistance to a fluid thatattacks silicone rubber, then an O-ringin fluorsilicone rubber is recommended.This material has excellent resistanceto a wide range of fluids, isusable up to 177°C (350°F) or higher inmany applications, and will often sealat temperatures as low as -73°C(-100°F).Other compounds will often seal attemperatures below their normal lowtemperature limit by increasing thesqueeze. This procedure, however, isgenerally limited to static face typedesigns. A heavy squeeze makes aradial seal difficult to assemble.81

SEALING ELEMENTS6. Compound SelectionExtremely High TemperaturesExtremely high temperatures causephysical and/or chemical attack whichmay lead to seal failure. Due to extremeheat energy the O-ring will start swellingin the groove, which increases frictionat dynamic applications. In many casesthe O-ring hardens considerably andthe compression set value is differentthan at lower temperatures. At hightemperatures thermoplastic materialsmay even start flowing so that leakageoccurs.Best choice: a series of special compoundshave been developed to provideoptimal sealing performance underthese conditions. These compoundsare: AFLAS ® , Fluoroelastomers,Perfluoroelastomers, Silicone, orFluorosilicone. PTFE, as a thermoplasticmaterial, can be the best choice ifelasticity is not required.Perfluoroelastomers can withstand continuoustemperatures of 326°C (620°F).Standard compounds NBR and EPDMcan be formulated such that a bettertemperature resistance is achieved. Forexample, the ERIKS EPDM PC 55914provides an exceptionally high temperatureresistance for EP-type elastomers.Certain fluoropolymers degrade above300°C and may release harmful gases ifthe temperature continues to rise.Please also note that high temperatureswill noticeably deteriorate many propertiesof the compound: permeability to gas,tensile strength, and compression set.ERIKS has compounds:• up to 200ºC (390ºF) all fluoropolymersFKM, Teflex®-FKM, Teflex®-Silicon;• up to 220ºC (430ºF) FFKM, Silicone714177, Fluorosilicones FS 60, FS 70,FS 75, FS 80;• up to 280ºC (540ºF) FFKM andspecial Silicone compounds;• up to 326ºC (620ºF) FFKM.Please be also aware that the temperatureresistance greatly depends on thesealing time and chemical environment.Consult ERIKS for assistance in selectingother compounds or consult thematerial data sheets.Extremely Low TemperaturesLow temperatures reduce molecularactivity causing elastomeric compoundsto appear harder. At extremelow temperatures elastomers achievea glass like state and become verybrittle, but may still seal and oftenresume their normal flexibility withoutharm when warmed. This condition isreversible as temperatures rise. Thetemperature at which this glass likestate occurs can be determined bytesting.The standards for this testing arerecorded in ISO 812, ASTM D2137, BS90 part 25, and ASTM D746.Extreme cold makes the O-ring shrinkin the groove which causes the seal tocontract which may cause the seal toleak. If the temperature falls even further,the O-ring will continue to shrinkand become brittle - it will be able tobe broken upon impact.The best choice may be Silicone whichremains flexible in temperatures downto -50°C (-58°F). Please note that siliconehas a very poor chemical resistanceand a high permeability to gas.Fluorosilicone is the solution whenfuels or oils are involved. It is generallyused in aircraft fuel systems and isresistant down to -80°C (-112°F).PTFE can be used to -170°C (-275°F)but does not have any elasticity properties.It will also start flowing underpressure very quickly (cold flow). PTFEwith fillers can reduce this problemnoticeably. The metal spring-loadedseal can be useful. Spring-loadedPTFE seals will provide good sealingperformance under these conditions.Please ask for the ERIKS technicalbrochures.Also TEFLEX®, FEP encapsulatedO-rings combine a low temperatureresistance (Silicone) with a very goodchemical resistance. The low temperatureresistance can also be increasedby applying more squeeze on theO-ring. This can of course only bedone when using static seals.ERIKS has compounds in:• FKM and NBR to -40ºC (-40ºF);• EPDM 55914 and EPDM 55914 PCto -50ºC (-56ºF);• Silicone 714177 till 60ºC (-76ºF);• Special Fluorosilicone for low temperaturesto -90ºC (-130ºF);• Metal spring activated FEP O-ring to-200ºC (-325ºF)The TR-10 value is a good indicator ofthe low temperature limit of a dynamicseal or a static seal exposed to pulsatingpressure. In a static steady pressureapplication, an O-ring will generallyfunction to a temperature approximately8°C or (15°F) lower than the TR-10 temperature. Please note that theTR-10 minimum temperatures as mentionedin the ERIKS data sheets aretest values only. Experience has taughtthat the service temperature is about10°C (18°F) lower than the TR-10 valuesindicated.Note:See also page 44 for Viton® information.82

TECHNICAL DOCUMENTATION O-RINGS6. Compound SelectionCoefficient of FrictionFriction causes wear, and seals do notform an exception to this rule. Thelevel of wear is determined by 4 factors:lubricating properties of themedium, surface roughness of themetal, pressure and temperature, andthe characteristics of the elastomer.Generally, breakout friction is manytimes greater than running friction, butthis varies with several factors,primarily the hardness of the O-ring.When only the hardness is changed,an increase will raise breakout frictionand a decrease will lower breakoutfriction.For special applications where externallubrication is impossible there areseveral compounds having selfcontainedlubricants.This internal lubrication is the incorporationof a friction reducing ingredientinto the rubber formula. Since thischanges the formula, internally lubricatedmaterials are assigned specialcompound numbers. Internal lubricantsmay be such materials asgraphite, molybdenum disulfide, powderedPTFE or, more commonly, anorganic lubricant. This lubricantmigrates through the O-ring and graduallycongregates on the surface.There also exist processes which canmodify the surface of an NBR O-ring.The coefficient of friction decreases byup to 50%. The surface is not faced toensure that all rubber properties arekept. This procedure is also very ecofriendlyand can also be applied fordrinking water applications.The so-called AF treatment for Viton®,EPDM, and silicone provides a surfaceoxidation which builds up an oily filmon the rubber. Here too, when therubber comes in contact with oil, thecoefficient of friction can be reducedup to 50%.Abrasion and Wear ResistanceAbrasion resistance is a general termwhich indicates the relative wear of acompound. It concerns scraping orrubbing of the O-ring surface and istherefore of importance for O-ringsused as dynamic seals. This is a verycomplex problem and cannot bedeeply discussed in this edition.Please consult the local ERIKS representative.The ideal contact surfaces should be 8to 16 RMS without longitudinal or circumferentialscratches. Best surfacesare honed, burnished, or hard chromeplated.Finishes of dynamic contactingsurfaces have a lot to do with the lifeof the O-ring seals. Appropriate surfacefinishes are important. Limits ofmaximum roughness for glands aregiven because rougher finishes willcause excessive wear. Finer finishesreduce lubrication to the O-ring andPUREu - Au)FKMCREPDMNBRAbrasion Resistancemay result in stick slipping and irregularwear. Surface roughness valuesless than 5 micro inches (0,15µmRa)are not recommended for dynamicO-ring seals. The surface must berough enough to hold small amountsof oil. Finishes below 5 RMS wipe tooclean for good moving seal life.Only some of the elastomers arerecommended for O-ring service wheremoving parts actually contact theO-ring. It is of interest that harder compounds,up to 85° IRHD, are normallymore resistant to abrasion than softercompounds. Of course, abrasion resistancemust be considered in the lightof other requirements such as surfacefinish and lubrication. The best wearresistance is offered by PUR(Polyurethane) and special XNBR compoundswhich have proved their valuein the offshore world.0 50 100 150 200 250Abrasion following DIN 53 516 in mm 383

SEALING ELEMENTS6. Compound SelectionContact with OzoneOzone is becoming an increasinglyinconvenient factor when using O-rings.The large concentrations which developin summer deteriorate certain elastomersvery quickly. Many elastomerslike Viton®, silicone, neoprene andEPDM are very suitable for high ozoneconcentrations. However NBR, theelastomer most commonly being used,is highly sensitive to ozone. At limitedconcentrations of 50 ppm, little cracks,perpendicular to the direction ofstretch, occur in NBR seals. There area number of possibilities to preventthis:- Use Viton® because of broad stockrange.- Use HNBR.- Use a compound such as NBR/PVC.The lower compression set ofNBR/PVC versus NBR should, however,be taken into account.- Use neoprene CR 32906.- Use different compounds, (mostly athigher prices e.g. FKM).- Use ozone resistant NBR.- Use white compounds for high ozone.RadiationOne of the most important propertiesof an elastomer, used as an O-ring, isits resistance to compression set. Withexposure to gamma radiation, thecompression set is most severely effected(of radiation types, gamma radiationhas the worst effect on elastomericmaterials). After experiencing 108 rads,all elastomers will take over 85% compressionset, enough loss of memorythat leakage can be expected. At 107rads, there are big differences betweencompounds, while at 106 rads, theeffects on all compounds are minor.Therefore in the range of 107 rads anO-ring compound must be selectedwith care, while at higher levels theyshould not be considered. At lowerlevels, factors other than radiation willbe more significant. It is thereforeimportant to test a seal in conditionssimilar to those it will encounter in service.Ask Eriks for data on radiationresistance of O-ring compounds.Electrical Conductivity / ShieldingElastomers can range from electricallyinsulating to conductive. This particularlydepends on the additives whichare added to the elastomers.Specifically:- insulating: more than 10 9 Ohmcm(almost all rubbers)- limited conductivity: 10 5 to 10 9Ohmcm (neoprene)- conductive: lower than 10 5 Ohmcm(special compounds)It is often essential to shield electronicdevices from electromagnetic interference(EMI) to prevent electromagneticenergy from escaping or to groundelectronic devices. Conductive elastomershave been developed to providehermetic sealing in combination withshielding and grounding. These materialscan be fabricated into O-rings,Quad-rings, molded shapes, sheetstock and die-cuts.Electrical PropertiesPolymer Specific Resistance (Ohm) Resistivityfrom up to from up toNBR 10 4 10 10 15 17FKM 10 10 10 14 20 35MVQ 10 15 10 16 20 40EPDM 10 6 10 16 10 25CR 10 2 10 13 5 15FFKM 10 17 5 x 10 17 16 18MVQ 0,002 5 - -MFQ 0,004 0,1 - -EPDM 0,006 10 - -FKM 0,006 0,006 - -84

TECHNICAL DOCUMENTATION O-RINGS6. Compound SelectionColored O-ringsColor compounds offer identificationfor positive assembly and traceabilityduring and after service. GenerallyO-rings are black (except silicone),because most of them are filled withcarbon black. Carbon black gives thebest mechanical sealing properties. Incertain cases, however, white additives,like titanium dioxide, can also beused. Green and brown are often usedfor Viton®, and for silicone red, ironoxide is generally known. In principleany color can be manufactured subjectto sufficient quantities ordered.Presently also fully transparent siliconeO-rings can be made.O-rings can also be identified byapplying a colored dot on the surfacewhich may ease in differentiating products.A colored dot can also be appliedduring the vulcanization process. Thisdot cannot be removed. The dot is ofthe same quality as the O-ring and nonegative reactions will occur.Another technique to recognize therubber material is used by certain FKMViton® O-rings. By adding a specialsubstance, a tracer, the O-ring will befluorescent under UV-light whichmakes identification of the O-ringeasier.O-rings in drive belt applicationsO-rings are frequently used for drivebelts in relatively low power applicationson audio visual equipment.O-rings are designed to maintain aseal while being compressed, whereasa drive belt must maintain its shapeand dimensions against a constantstretching load. Therefore, the materialof the O-ring used for a drive belt mustprovide resistance in a number ofareas;• Resistance to creep, the tendency ofrubber to slowly stretch or relax.• Resistance to severe flex, commonat high rotational speed.• Resistance to the abrasion thatoccurs as the belt travels over thepulleys and sprockets at high speed.Critical environmental factors mayinclude the presence of ozone, extremeoperating temperatures, and otherfactors.For optimum results the following arerecommended:• Limit the O-ring stretch to 10-15%of the outside diameter.• Semi-circular grooves should be halfrounded and have a radius equal tothe O-ring cross section.• The diameter of the sheave shouldbe larger than 4 times the O-ringcross section.• Abrasion resistance is important.Most O-rings used in drive belt applicationsare made from EthylenePropylene or Polyurethane.Polyurethane can exhibit good servicelife when stretched 20-25%.Depending on the application variouselastomeric compounds may also beused effectively. Please contact anERIKS representative for additionalinformation.85

SEALING ELEMENTS6. Compound SelectionLinear ExpansionsElastomers have different expansionrates than platics or steel. So thedesign of the grooves have to beadapted to that.Coefficient of Thermal ExpansionEPDM FKM NBR VMQ CR FFKM Steel Al.Linear expansion 160 ca 200 150 200 185 231 ca 10 ca 20coëfficient 10 -6 x 1/°CLow Temperature °C -45 -30 -40 -50 -40 -15 - -Max. Temperature °C 200 250 135 250 135 316 - -Linear expansion at 3,2 5,0 2,0 5,0 2,5 7,3 - -high temp.limit in %Volume expansion 9,6 15,0 6,0 15,0 7,5 21,9 - -at high temp. limit in %Gas PermeabilityThe following table gives the gas permeabilitycoefficient for different mediaand compounds.Gas permeabilityGas permeability IIR AU NBR NBR NBR CR NR VMQcoefficient (38% (33% (28%10 -17 m 2 / (s x Pa) ACN) ACN) ACN)Air 60°C / 14°F 2,0 2,5 2,5 3,5 7,5 6,0 25,0 330Air 80°C / 175°F 5,0 7,0 5,5 7,0 21,0 12,0 40,0 410Nitrogen 60°C / 140°F 1,5 2,5 1,0 2,0 4,0 4,5 18,0 280Nitrogen 80°C / 175°F 3,5 5,5 2,5 5,5 7,0 8,0 33,0 360CO2 60°C / 140°F 13 26 30 56 58 58 160 950CO2 80°C / 175°F 29 73 48 63 97 71 210 150086

TECHNICAL DOCUMENTATION O-RINGS7. Specifications - MILSPEC’ sSpecifications are important. Thereforeeven though it may be difficult to prepare,a performance specification isrecommended. Avoid specifying howto compound materials or how toprocess compounds. A well qualifiedsupplier knows the materials andprocesses to produce the best compoundfor an application. However itshould be understood that if onephysical property of a compound ischanged or adjusted by compounding,all of its other properties may beaffected and it will no longer be thesame compound. This is important forO-rings meeting Military Specifications.Once the specification is designated,all its requirements must be met. Evenif a new compound will meet all thephysical and chemical requirements ofa given Military Specification, it is stillimpossible to certify that it meets thatMILSPEC because the MILSPEC iscovered by a Qualified Products List(QPL) which means all test resultsmust be verified and approved by theU.S. Government. They will not allow avariation to a Military Specification andit will be necessary to run a completeevaluation of the new compound to allthe requirements.ERIKS offers compounds approved tonearly every industry wide specificationfor elastomeric seals. Those specificationsinclude military, aerospace,ASTM, SAE, automotive, petroleumindustry, and commercial.The most widely used specificationsare the AN, M, MS, and NAS.This reference table is arranged bydrawing number.Currently many MILSPEC’s are beingconverted to non-military AMS spec’s.Popular military/aerospace specificationsDrawing Specification Fluid Recommended Elastomer Commentsnumber Temp. range °FAs 3569 AMS 7270 Aircraft fuels -67 +302 Nitrile Formerly AN 123951 - AN 123040AS 3570 AMS 7274 Petroleum basedaircraft lubricating oil -67 +302 Nitrile Formerly AN 123851 - AN 123950AS 3578 AMS 7271 Aircraft fuels -58 +257 Nitrile Formerly MS 9020 and MS 9021AS 3582 AMS 3304 Dry heat and Not recommended for high pressurepetroleum based lube oils -85 +400 Silicone dynamic applicationsM 25988/1 MIL-R-25988 Aircraft fuels and -70 +392 Fluorosilicone Blue color as required by MILSPEC.Class 1, lubricants Not recommended for high pressureGrade 70 Idynamic applications.M 25988/2 MIL-R-25988 Aircraft fuels and -70 +437 Fluorosilicone Blue color as required by MILSPEC.Class 3, lubricants Higher modulus and temperatureGrade 75 IresistanceM 25988/3 MIL-R-25988 Aircraft fuels and -70 +392 Fluorosilicone Blue color as required by MILSPEC.Class 1, lubricants Lower hardness.Grade 60 IFor low pressure applicationsM 25988/4 MIL-R-25988 Aircraft fuels and -70 +392 Fluorosilicone Blue color as required by MILSPEC.Class 1, lubricants Higher hardness.Grade 80 IM 83248/1 MIL-R-83248 Aircraft fuels and -20 +400 Fluorosilicone Excellent resistance toClass 1 I lubricants compression set.M 83248/2 MIL-R-83248 Aircraft fuels and -20 +400 Fluorosilicone Higher hardness.Class 2 IlubricantsM 83461/1A MIL-P-83461 I MIL-H-5606 -65 +275 Nitrile Better dynamic performance andlonger service life at 257 °F.MS 28775 MIL-P-25732 I MIL-H-5606 -65 +275 Nitrile MIL-H-5606 is a petroleum-based hydraulicfluid used in military aircraft. Inactive for newdesigns. See M 83461/1A.MS 28900 AMS 3209 Ozone -40 +212 Neoprene For weather resistant seals.(Nonstandard sizes).MS 29512 MIL-P-5315 I Aircraft fuels -65 +158 Nitrile This drawing covers tube fitting sizes only.MS 29513This drawing covers all sizes except thetube fitting sizes.MS 29561 MIL-R-7362, Synthetic diester jet -65 +257 Nitrile This drawing covers all sizes except the .Type I engine lubricants tube fitting sizes(MIL-L-7808)MS 9385 AMS 7267 Dry heat and petroleum- -85 +500 Silicone This drawing covers tube fitting sizes only.MS 9386 based lube oils This drawing covers all sizes except thetube fitting sizes.NAS 617 MIL-R-7362, Synthetic diester jet engine -65 +257 Nitrile This drawing covers all sizes except theType I lubricants (MIL-L-7808) tube fitting sizes .87

SEALING ELEMENTS7. SpecificationsThere are some major points whichmust always be considered when preparingany specification. Different sizeparts give different results and all partswith varying cross section or shape willnot meet specific properties set up onanother particular part or on test specimenscut from a standard test sheet.Therefore always use standard testspecimen or the same cross section ofthe O-ring. It is also recommendedthat standard test methods be usedwhenever possible.ERIKS data are specified accordingISO, ASTM, and DIN Test standards.KTWNSFWRC DVGW ACSKIWA88

TECHNICAL DOCUMENTATION O-RINGS7. Specifications - ASTM D2000ASTM D2000 Specification.One of the most versatile specificationsin the Rubber Industry is ASTM D2000.In this specification the various classes,grades, and suffixes are used to definespecific properties of elastomers.ASTM D2000 protocol.Because there are at least as manyelastomer compound choices as thereare metallic products, how can onemake an informed elastomer sealselection?The relative performance capabilities ofelastomers can be generally defined bya test protocol identified as AmericanSociety for Testing and Materials(ASTM) D-2000. This protocol positionsan elastomer as a function of itsthermal stability and oil resistance,both measured under well-defined testconditions.Significant differences exist in the performancecapabilities of the differentelastomers. Those with more limitedperformance are recognized as midperformanceelastomers, includingbutyl rubber, chloroprene rubber (CR),ethylene propylene rubber (EDPM), andacrylonitrile-butadiene rubber (NBR).Those with the broadest capabilitiesare high-performance elastomers.They include fluoroelastomers andperfluoroelastomers.Yet, ASTM D2000 does not addressresistance to harsh media and aggressiveenvironments encountered in thechemical industry. These include acids,bases, solvents, heat-transfer fluids,oxidizers, water, steam, etc. UnlikeASTM #3 oil used in the ASTM D2000protocol, chemical plant media mayattack the elastomer's back-bone,crosslinks, and/or fillers leading to lossof resiliency (memory) and seal failure.Although ASTM D2000 is a good predictivestarting point, one must accuratelyidentify the media to correctlyselect an elastomer for many applications.The following example shows a typicalASTM D2000 callout. Below is a breakdownexplaining what the differentpositions mean.ASTM D2000-90 M 2 HK 7 14 A1-10, B38, C12, EF31, EO88, F15, Z1Additional requirement suffixesDeviations from standardtest proceduresTensile Strength (MPa if M is present; psi if not)Hardness (Durometer)Type and ClassGrade NumberIf present, use Metric UnitsYear of Standard revision89

SEALING ELEMENTS7. Specifications - ASTM D2000Confusion often seems to start at thenumber 90. This just defines the revisionyear of ASTM D2000 to which theparticular line callout makes reference.The appearance of an ‘m’ (or lack of)determines the units to be used forproperties such as tensile strength,temperature or tear strength. If an Mbegins the line callout, Sl units (metric)will be used - MPa (tensile), °C, kN/m(tear). If it is not there, English units areemployed so that tensile will be in psi,temperatures in °F, and tear strengthin psi.After the M, a Grade Number is selectedthat defines the test requirements towhich a material of a given Type andClass can be tested. A grade of 1 indicatesonly basic properties arerequired while numbers 2-9 imply additionaltesting requirements such as lowtemperature brittleness or special heataging tests. (Note: not all grade numbersare applicable to all material typesand classes).The various material Types and Classes available are best summarized inthe following table:Material Designation(type and class)AAAKBABCBEBFBGCACECHDADFDHFCFEFKGEHKType of Polymer Most Often UsedNatural, Reclaim, SBR, Butyl, EPDM, PolyisoprenePolysulfidesEPDM, High Temp SBR and Butyl CompoundsChloropreneChloropreneNBRNBR, UrethanesEPDMChlorosulfonated Polyethylene (Hypalon®)NBR, EpichlorohydrinEPDMPolyacrylic (Butyl acrylate type)PolyacrylicSilicones (High Temp)SiliconesFluorosiliconesSiliconesFluorocarbonsASTM D2000-90 M 2 HK 7 14 A1-10, B38, C12, EF31, EO88, F15, Z1Additional requirement suffixesDeviations from standardtest proceduresTensile Strength (MPa if M is present; psi if not)Hardness (Durometer)Type and ClassGrade NumberIf present, use Metric UnitsYear of Standard revision90

TECHNICAL DOCUMENTATION O-RINGS7. Specifications - ASTM D2000Next in line are three numbers used tostate hardness range and minimumtensile strength requirements. The firstnumber 7 indicates the nominal hardness70 (in Shore A units) of thedescribed material plus or minus 5points. In this case the materialrequired would be 70°±5° Shore Ahardness. Similarly, if a 6 was used,the material specified would be 60°±5°Shore A hardness. The next two digitsare used to define the minimum tensilestrength to be possessed by the material.Since the callout is metric, the 14requires that the material suppliedhave a minimum tensile strength of 14MPa. If the M was not present, theunits would be in psi so the 14 wouldbe replaced by 20 (14 MPa =2031psi;use the first two digits of the tensilestrength in psi).In most applications, however, basicproperties are not enough to ensure anacceptable material.Specialized testing is often requiredand this is where suffixes come intouse. Suffixes are letter-number combinationsthat, together with a gradenumber, describe specific tests andperformance criteria which an elastomermust pass. Below is a listing ofthe relationship between suffix lettersand the type of test each calls out:ABCDEAEFEOFGHJKMNPRZHeat ResistanceCompression SetOzone or Weather ResistanceCompression-DeflectionResistanceFluid Resistance (Aqueous)Fluid Resistance (Fuels)Fluid Resistance(Oils and Lubricants)Low Temperature ResistanceTear ResistanceFlex ResistanceAbrasion ResistanceAdhesionFlammability ResistanceImpact ResistanceStaining ResistanceResilienceAny Special Requirement(Specified in Detail)91

SEALING ELEMENTS7. Specifications - ASTM D2000The numbers connected with eachsuffix letter describe the test methodto be used (including time) and thetest temperature.Due to space limitations we will not gointo these subtitles. Z-requirementsare typically used to skew hardnessrange (eg; 75 ±5), tighten limits on agiven test, specify color (default isblack), or add additional testsdesigned by another party.Looking back at the original example forthis particular application the callout is:A 70°+5° hardness, black fluorocarbonwith a minimum tensile strength of14MPa. The material will also have topass the limits outlined in the grade 2column (of the 1990 revision of D2000)for Heat Resistance, Compression Set,Ozone Resistance, Fuel Immersion,Lubricating Oil Immersion, LowTemperature Resistance, and a specifiedZ-requirement.Example:2 BG 720 B14 EO14 EO34 EF11 EF21 F17 EA14 , NBR shore A 70 ± 52 Quality numberB Type (based on heat resistance)G Class (based on swell resistance in test oil IRM 903)7 Hardness shore A 70 ± 520 Tensile strength 2000 psi (13,8 Mpa)B Compression set (Test ASTM D395)1 Testing time: 22 hours4 Testing temperature: 212 F° (100°C)EO Swelling in test oil ASTM No1 (ASTM D471)1 Testing time: 70 hours4 Testing temperature: 212°F (100°C)EO Swelling in test oil IRM 903 (test ASTM D471)3 Testing time: 70 hours4 Testing time: 212°F (100°C)EF Swelling in test fuel No.1 (Reference Fuel A) Isookan. (test ASTM D471)1 Testing time: 1 hour1 Testing temperature: 70°F (21°C)EF Swelling in test fuel Nr. 2 (Refer. Fuel B) Isookan/Toluol 70:30 (test ASTM D471)2 Testing time: 70 hours1 Testing temperature: 70°F (21°C)F Low temperature testing (test ASTM D746), Method B1 Testing time: 3 minutes7 Tesing temperature: -40°F (-40°C)EA Swelling in water, (test ASTM D471)1 Testing time: 70 hours4 Testing temperature: 212°F (100°C)(For reference test results ASTM Rubber Handbook Section 9 Volume 09.01)92

TECHNICAL DOCUMENTATION O-RINGS7. Specifications - ASTM D2000Different international norms for elastomersexist. In the following table is acomparison of the DIN, ISO, and ASTMnorms. These norms are comparative,but can be slightly different.International norms for ElastomersDIN-norm ISO-norm Comments ASTM-normDIN 53 519/T2 ISO 48 Method M IRHD hardness ASTM D 1415DIN 53 479 ISO 2781 Specific weight ASTM D 1817DIN 53 505 ISO 868 Shore A hardness ASTM D 2240DIN 53 517 ISO 815 Compression set ASTM D 395DIN 53 504 ISO 37 Tensile strength ASTM D 412DIN 53 518 ISO 2285 Tensile setDIN 53 521 ISO 1817 Volume change ASTM D 471DIN 53 508 ISO 188 AgingISO 2921 TR 10 ASTM D 1329DIN 53 509 ISO 1431 Ozone resistanceDIN 53 515 ISO 34 Tear strength93

SEALING ELEMENTS8. QualificationsFunctional requirements should always be given first. A functional test is worth morethan a physical and chemical property test. Thus the first step is to set the originalphysical property limits which will assure that the mechanical properties desired inthe O-ring are present. Be aware of the fact that there is a difference between theoriginal physical properties and the aged physical properties.Original Physical PropertiesHardnessDetermine the IRHD hardness best suitedfor the application and round off to40°, 50°, 60°, 70°, 80°, 90° or 95°-shoreA or IHRD. A ±5 point tolerance isestablished to allow the manufacturer arealistic working range and permit normalvariations experienced in measuringhardness.Tensile StrengthDetermine the minimum tensile strengthnecessary for the application. Alwaystake into consideration the inherentstrength of the elastomers most likely tobe used to meet the specification. Mostsilicones have a much lower tensilestrength than other elastomers. Oncethe minimum tensile strength has beenset, multiply it by 1.20. This is the limitset for tensile strength variation of±15% experienced between productionbatches of a compound.ElongationInvestigate and determine the maximumamount of stretch a seal mustundergo for assembly in the application.Multiply this figure by 1.25 to allowa safety factor and to provide for normalproduction variation of ±20%.ModulusChoose a minimum modulus which willassure a good state of cure, good extrusionresistance, and a good recoveryfrom peak loads. Modulus is directlyand related to tensile and elongation,and refers to the stress at a predeterminedelongation, usually 100%.Specific GravityA value for specific gravity should notbe set in the qualification section of thespecification but the value must bereported "as determined". The realisticfigure will then be used in the controlsection.94Age Physical PropertiesDetermine the resistance of the O-ringto the anticipated service environment.This is done by measuring the changein volume and physical properties oftest samples after exposure to variousconditions for a specified time at aspecified temperature. Recommendedtimes, temperatures, and test fluids foraccelerated tests can be found inASTM D471. It is usually desirable touse the actual service fluid. Becausethese fluids are not as controlled astest fluids, there can be some variations.This fluid variation accounts fordifferences in test results.Hardness ChangeHardness Change is usually controlledto avoid excessive softening (causingextrusion from pressure) or hardening(causing cracking).Tensile Strength ChangeA reasonable tolerance limit is usuallyset as insurance against excessivedeterioration and early seal failure.Each individual fluid dictates its ownspecific limits. Experience will probablydictate these limits. However, 10%tolerance is not realistic since muchwider variance in tensile strength canbe experienced on two test specimenscut from the same sample.Elongation ChangeExperience will dictate this limit asnoted under tensile change.Volume ChangeDetermine the maximum amount ofswell which can be tolerated in the O-ring application (usually 15% to 20%for dynamic and 50% for static applications).Determine the maximumamount of shrinkage which can betolerated in the O-ring application (usually3 % for both dynamic and static).Include a dry-out test after the immersiontest to provide a control for dryoutshrinkage. Shrinkage of O-ringscan be a cause of failure. It is necessaryto stress the difference betweentest results on different size seals. AnO-ring with a thinner cross section willnot have the same volume swell as anO-ring with a thicker cross sectionwhen tested under the same conditions.This difference is at its peakduring the first 70 hours of testing(most accelerated testing is specifiedwithin this period). Only after four tosix weeks the volume swell of differentcross section rings approaches anequilibrium value.Compression Set.A realistic value for compression set isoften all that is necessary to assure agood state of cure and resilience of acompound.Low Temperature ResistanceDetermine the lowest temperature atwhich the O-ring is expected to function.Most low temperature tests aredesigned to indicate the brittle point ofa material which only tells at whattemperature the compound is mostlikely to be completely useless as aseal in a standard O-ring design, butvery little about the temperature atwhich it is useful. Only the TR-10 testgives information about the lowesttemperature at which the compoundexhibits rubber-like properties andtherefore relates to low temperaturesealing capabilities. O-rings in dynamicapplications will seal at the TR-10value. O-rings in static applications willfunction satisfactorily to about 10°C(ca. 15°F) below this value.

TECHNICAL DOCUMENTATION O-RINGS9. Test ProceduresThere are standard ASTM, ISO, andDIN procedures for conducting most ofthe tests on rubber materials. It isimportant to follow these procedurescarefully in conducting tests if uniformresults are to be obtained. For instance,in pulling specimens to find tensilestrength, elongation and modulus values,ASTM method D412 requires a uniformrate of pull of 20 inches (500 mm) perminute. In a test, tensile strength canbe found to decrease 5% when thepulling speed is reduced to 2 inchesper minute, and a decrease of 30%when the speed is reduced to 0.2inches per minute.Test SpecimensASTM test methods include descriptionof standard specimens for eachtest. Often two or more specimens arepermitted, but results from the differentspecimens will seldom agree. The waythat properties vary with the size of thespecimen is not consistent. For instance,as the cross section increases,nitrile O-rings produce lower values oftensile strength, elongation, and compressionset. Likewise, ethylene propyleneO-rings produce a similar patternfor tensile and elongation values butnot for compression set.In Fluorocarbon compounds, only theelongation changes.In fluid immersion tests, O-rings with asmaller cross section can be found toswell more than larger O-rings, while inexplosive decompression tests thesmaller cross sections will have betterresistance to high pressure gas.95

SEALING ELEMENTS9. Test ProceduresHow to properly deal with Hardnessand Compression SetHardness Testing is the easiest testto carry out on O-rings, but a properinterpretation of the hardness may bedifficult. The hardness commonly mentionedin the various data sheets refersto the standard measuring method byDIN or ASTM. This means that the testhas been carried out on a standardslab of .08 inch (2 mm) or a button of.5 inch (12 mm) thickness. O-ring hardnessmeasurements differ from measurementson slabs. In addition, thevalue per each individual O-ring crosssection will vary as well: a small crosssection of e.g. .08 inch (2 mm) will givehigher values than a crosssection of.275 inch (7 mm) for the samecompound.To make it even more complex, a distinctionmust be made between thetwo measuring standards: Shore A andIRHD. IRHD is more and more beingused for O-rings. Measuring results ofboth methods may differ. It is peculiarthat the difference depends on thekind of rubber. HNBR will show moredeviations than FKM.What conclusion should consequentlybe made? With a view to the application,hardness is a parameter of relativelyminor importance. The service lifeof an O-ring will not drastically bechanged by a small difference in hardness.Please also note that data sheetsalways state ±5 points on IRHD orShore A values.It is recommended that when testinghardness, testing methods shouldalways be the same (same equipment,same specimen). In these circumstancesa comparison is useful.Hardness Shore A readings taken onactual O-rings are notoriously variablebecause O-rings do not have flat surfaceand operators will vary in theaccuracy with which they apply theindenter to the crown of the O-ring,the point that gives the best reliablereading. Therefore it is better to ordercompression set buttons from thesame batch as the O-ring for the hardnesstest.As to compression set it should beobserved that one should carefullywatch the information in the datasheet. In most cases the compressionset stated has been measured on aslab or a button. This gives totally differentvalues than measurements onactual O-rings. O-rings will show differentvalues depending on the thicknessof the sample. Small crosssections willgive a higher value than large crosssections.The NBR and EPDM compressionset values are commonly statedat 100°C (212°F ); for EPDM PC at150°C (300°F) and for VMQ and FKMat 200°C (390°F).The lower the values, generally thebetter the sealing performance. Seealso the calculations of service life inwhich this subject is discussed extensively.Compression set of the standardERIKS O-rings is measured on anO-ring with a crosssection of .139 inch(3.53 mm). Consequently all qualitiescan be compared.Changes in EnvironmentChanges in a fluid medium can occurdue to the effect of heat and contaminantsduring service so that a rubberthat is virtually unaffected by new fluidmay deteriorate in the same fluid afterit has been used for a certain time. Forthis reason it is sometimes better torun tests in used fluids.AgingDeterioration with time or aging relatesto the nature of the bonds in the rubbermolecules. Three principle typesof chemical reactions are associatedwith aging.• Cracking. The molecular bonds arecut, dividing the molecular chain intosmaller segments. Ozone, ultravioletlight, and radiation cause degradationof this type.• Cross linking. An oxidation processwhereby additional intermolecularbonds are formed. This process maybe a regenerative one. Heat and oxigenare principle causes of this typeof attack.• Modification of side groups.A change in the molecular complexdue to chemical reaction. Moisture,for example, could promote this activity.All mechanisms by which rubber deteriorateswith time are attributable toenvironmental conditions. Selectionand application of O-rings to provideacceptable service life is the mainsubject of this handbook.96

TECHNICAL DOCUMENTATION O-RINGS9. Test ProceduresService life of an O-ringCalculations of Service LifeFor calculating the service life ofO-rings ERIKS makes the assumptionthat the sealing life of an O-ring is zero,once the compression set has reached100%. This indicates that the rubberhas practically no elasticity and thatthe sealing force has become minimalso that leakage can easily develop.The best method to determine thesevalues is to carry out "long-term" testsat a certain temperature under a certainpressure in a certain media. This isgenerally done in air, being the mostreceptive to aging. Field tests haveshown that within the same polymernameservice life can vary widely e.g.1000 to 6000 hours. Several compoundshave been field tested by ERIKS forthousands of hours to determine thetime at which the leakage occursunder specified conditions.As mentioned before, the service life ofO-rings depend on both the formulationquality and the product quality.The formulation quality indicates themaximum properties of the compound.This quality is generally tested on eachbatch. The product quality stronglydepends on the production processcontrol.Life TestsThe extensive tests which precededthe determination of the O-ring servicelife have enabled ERIKS to give anindication of service life by means ofshort term tests i.e. life time tests.A service life test is a laboratory procedureused to determine the amountand duration of the resistance of anarticle to a specific set of destructiveforces or conditions. Today, it is possibleto perform these tests under thesame conditions as those prevailing inmany actual situations. In this way apicture of the service life of the sealcan be achieved.Hours70.00060.00050.00040.00030.00020.00010.0000Please observe that service life variesdepending on the cross section andthe temperature. The latest, moststate-of-the-art computer programscan now predict these service lifegraphs by each individual cross section.This chapter gives an example of theresults of life time tests according ISO815 for different NBR compounds: A,B, and C, 70° shore O-rings with crosssection .139 inch (3,53mm). This showsthat different NBR-70 compounds givedifferent life times.Life tests for O-rings NBR 70° shore.139 inch (3,53 mm) / acc. ISO 815 / compression set 100% / hot airHours65.000Compound5.0004.500Compound4.000A48.000A3.500BB3.00040.0003.000CC2.5001.9002.0001.80017.0001.50010.0001.000740 5009.500 500450140°F(60°C)175°F(80°C)0212°F(100°C)257°F(125°C)NBR compound Compound A Compound B Compound CAt 140°F (60°C) 65.000 hr (6.5 yr.) 48.000 hr (4.8 yr.) 40.000 hr (4 yr.)At 175°F (80°C) 17.000 hr (1.7 yr.) 10.000 hr (1 yr.) 9.500 hr (11 m.)At 212°F (100°C) 3.000 hr (4 m.) 1.900 hr (2.3 m.) 1.800 hr (9 wk)At 257°F (125°C) 740 hr (4 wk.) 500 hr (18 d.) 450 hr (16 d.)* Consult ERIKS for other lifetime tests.97

SEALING ELEMENTS9. Test ProceduresLife tests on 70° shore O-rings with a cross section of .139 inch (3,53 mm) in a sulphurcured EPDM and a peroxide cured EPDM give the following values. These valuesshow the large difference in results between the two curing systems.EPDM compound Sulphur cured Peroxide curedAt 140°F (60°C) 100.000 hr (10 yr.) 1000.000 hr (100 yr.)At 175°F (80°C) 52.000 hr (5.2 yr.) 250.000 hr ( 25 yr.)At 212°F (100°C) 8.500 hr (10 m.) 34.000 hr ( 3.4 yr.)Factors for small c.s. .070 inch (1,78 mm)For large c.s. .275 inch (6,99 mm)At 175°F (80°C) : x 0.75 : x 1.80At 212°F (100°C) : x 0.65 : x 1.60At 257°F (125°C) : x 0.65 : x 1.50Generally, in air, the service life for NBR 70° O-rings at 100°C (212°F) in the variouscompounds range from 2000 to 3000 hours. EPDM O-rings at 100°C (212°F) sulphurcured or peroxide cured range from 8.500 to 34.000 hours, depending on the compound.Other Eriks O-ring compound life test results are available. Please contact anERIKS representative for more information.These test results give the number of expected hours, during which the compressionset reaches (100%) when tested in air. When testing in oils, the service life is considerablyhigher (not for EPDM).Warm air can be a very aggressive environment for rubber.Since the interpretation of this data requires some explanation, please contact anERIKS representative for more information.Extra service for O-ringsIn addition to test procedures specified by ERIKS, there are also differentpossibilities for specific quality assurance systems:• compression set testing• hardness control following Shore A or IRHD• surface control to Sortenmerkmal S (surface defect control)• specific measurement to special tolerances• special surface control• tear strength test• tensile strength test• ozone testing• lifetime testing• chemical resistance tests• infrared spectroscopy• TGA-analysis• FDA migration test• TOC analysis• FEA calculations98

TECHNICAL DOCUMENTATION O-RINGS10. ControlThe purpose of control is to insure uniformityof purchased parts from lot tolot. Control may be based on therequirements of the qualification sectionor actual qualification test results.One should be careful not to betrapped by writing a specificationbased on test reports having only asingle set of values. Any single set oftests made on a particular batch isvery unlikely to reflect mean valuesthat can be duplicated in everydayproduction. Control tests should belimited to only those properties reallypertinent to the control section of thespecifications.Dimensions and surface quality arechecked according AS 568A and AS871 A , MIL-STD-413C, and DIN 3771Part 1 and Part 4.Hardness is often specified as a controland is frequently problematicbecause of inherent difficulties in measuringhardness with O-ring specimensrather than standard hardnessdiscs. A tolerance of ± 5 points is thestandard allowance for experimentalerror caused by reading and productionvariance in batches of the samecompound. Hardness also has apotential for discrepancies betweendurometer gauges, most manufactureshave a ± 3 hardness pointstolerance range. Hardness is a parameterof relatively minor importance,the service life of an O-ring will not besignificantly changed by a smalldifference in hardness.Elongation, a tolerance of ±20% isgenerally acceptable.Modulus, a tolerance of ±25% is standard.This is a more sensitive indicatorof the condition of the compound thantensile strength and elongation. Thismeans that it varies more from batchto batch, requiring a wider tolerancerange.Specific GravityA tolerance of ± 0.02 may be applied.(±0.03 for silicone)Volume Change, a plus or minustolerance on this property is frequentlyunrealistic because for expedience,the most critical time is usually specifiedfor the test. This, combined withvariance in commercial fluids andsample size, gives such an accumulationof negative factors, that it is notalways feasible to use volume swell asa control.TGATo determine the composition of arubber compound, thermogravometricanalysis (TGA) is a relative inexpensivemethod. ERIKS uses this TGA-analysisto control compounds by essentiallyfingerprinting the customer compound.In cooperation with thecustomers’ quality-control department,specific TGA standards can be developed.The table below illustrates anexample of TGA.% WeightFrom: 52.38To: 51.33% change: 3.63From: 451.33To: 848.88% change: 47.04From: 848.88To: 947.22% change: 41.38Temperature (C)96.38%WT: 9.3815 mg - Rate: 40.00 dsg/min49.31%7.93%99

SEALING ELEMENTS11. Storage and Age Control of ElastomersStorage LifeAccording SAE-ARP5316 issue 1998-11, storage life is the maximum periodof time, starting from the time of manufacture,that an elastomeric sealelement, appropriately packaged, maybe stored under specific conditions,after which time it is regarded asunserviceable for the purpose forwhich it was originally manufactured.The time of manufacture is the curedate for thermoset elastomers or thetime of conversion into a finishedproduct for the thermoplastic elastomers.Shelf life of elastomers when storedproperly is especially determined bythe specific compound.Table 3A-3 is taken from MIL-HDBK-695C and distinguishes 3 basic groupsof elastomers.The values in this chart are minimalvalues. In practice, longer storageperiods may be used especially when10 or 20 year categories are involvedprovided the parts are properly storedand periodic checks are performed.Generally, polyethylene bags stored incardboard containers or polyethylenelined craft paper bags insure optimalstorage life.Due to major improvements in compoundingtechnique, storage life ofrelatively age-sensitive elastomers innormal warehousing conditions is considerable.MIL-HDBK-695C providesguidelines for recommended shelf lifefor different O-ring compounds.Table 3A-3 MIL-HDBK-695CCommon or ASTM D1418 ASTM D2000 MIL-STD-417Type of rubber Trade Name Abbreviation Abbreviation Designation20 YEARS OR HIGHER:Silicone Silicone Q FE TAFluorosilicone Silastic LS FVMQ FK TAPolysulfide Thiokol T BK SAFluorocarbons Fluorel, Viton® FKM HK -Polyacrylate Acrylic ACM, ANM DF, DH TBUP TO10 YEARS:Chlorosulfonated Polyethylene Hypalon CSM CE -Isobutylene/Isoprene Butyl IIR AA, BA RSPolychloroprene Neoprene CR BC, BE SCPolyether Urethane Urethane EU BG -Polypropylene oxide Propylene oxide GPO - -Ethylene/propylene Ethylene propylene EPDM BA, CA -Ethylene/propylenediene Ethylene propyleneterpolymercopolymer EPM BA, CA -Epichlorohydrin Hydrin 100 CO - -UP TO5 YEARS:Butadiene/acrylonitrile Nitrile, NBR NBR BF, BG, BK, CH SBButadiene/styrene SBR SBR AA, BA RSCis-polybutadiene Butadiene BR AA RNCis 1, 4, polyisoprene Natural, pale crepe NR AA RNCis 1, 4, polyisoprene Synthetic natural IR AA RNPolyester Urethane Urethane AU - -100

TECHNICAL DOCUMENTATION O-RINGS11. Storage and Age Control of ElastomersExperience has demonstrated thatstorage conditions are much moreimportant in determining the useful lifeof O-rings than is time.SAE-ARP5316 addresses the generalrequirements for data recording procedures,packaging, and storing of aerospaceelastomeric seals:1. TemperatureThe storage temperature shall bebelow 100°F (38°C), except when highertemperatures are caused by temporaryclimate changes, and articles shallbe stored away from direct sources ofheat such as boilers, radiators, anddirect sunlight.2. HumidityThe relative humidity shall be such thatgiven the variations of temperature instorage, condensation does not occur.If the elastomers are not stored insealed moisture proof bags, the relativehumidity of the atmosphere instorage shall be less than 75% relativehumidity, or if polyurethanes are beingstored, shall be less than 65% relativehumidity.3. LightElastomeric seals shall be protectedfrom light sources, in particular directsunlight or intense artificial light havingan ultraviolet content. The individualstorage bags offer the best protectionas long as they are UV resistant.Note: It is advisable that windows ofstorage rooms where elastomers arestored in bulk be covered with a red ororange coating.4. RadiationPrecautions shall be taken to protectstored articles from all sources ofionizing radiation likely to causedamage to stored articles.5. OzoneAs ozone is particularly damaging tosome elastomeric seals, storagerooms shall not contain any equipmentthat is capable of generating ozonesuch as mercury vapor lamps, highvoltage electrical equipment giving riseto electrical sparks or silent electricaldischarges. Combustion gases andorganic vapor shall be excluded fromstorage rooms as they may give rise toozone via photochemical processes.6. DeformationElastomeric seals shall be stored freefrom superimposed tensile and compressivestresses or other causes ofdeformation. Where articles are packagedin a strain-free condition, theyshall be stored in their original packaging.O-rings of large inside diametershall be formed into at least threesuperimposed loops so as to avoidcreasing or twisting.Note: It is not possible to achieve thiscondition by forming just two loops,three are required.7. Contact with Liquid and Semi-Solid MaterialsElastomeric seals shall not be allowedto come in contact with liquid or semisolidmaterials (for example, gasoline,greases, acids, disinfectants, andcleaning fluids) or their vapors at anytime during storage unless thesematerials are by design an integral partof the component or the manufacturer'spackaging. When elastomericseals are received coated with theiroperational media, they shall be storedin this condition.8. Contact with MetalsCertain metals and their alloys (in particular,copper, manganese, and iron)are known to have deleterious effectson elastomers. Elastomeric seals shallnot be stored in contact with suchmetals (except when bonded to them)but shall be protected by individualpackaging.9. Contact with Dusting PowderDusting powders shall only be used forthe packaging of elastomeric items inorder to prevent blocking or sticking. Insuch instances, the minimum quantityof powder to prevent adhesion shall beused.10. Contact between DifferentElastomersContact between different elastomersand elastomers of different seals shallbe avoided.11. Elastomeric Seals bonded toMetal PartsThe metal part of bonded elastomericseals shall not come in contact with theelastomeric element of another seal.The bonded seal shall be individuallypackaged. Any preservative used onthe metal shall be such that it will notaffect the elastomeric element or thebond to such an extent that the sealwill not comply with the product specification.12. Stock RotationElastomeric seal stock should berotated on the FIFO (First In, First Out)principle.In general Eriks recommends thefollowing storage parameters:- Ambient temperature (preferably nothigher than 50°C (120°F).- Dry environment and exclusion ofcontamination.- Protect against direct sunlight.- Protect against radiation.- Protect against artificial light containingUV-radiation.- Protect from ozone generating electricaldevices.- Store parts without tension(never hang O-rings).101

SEALING ELEMENTS12. O-ring Gland DesignThe following pages contain basicO-ring gland design information.Please contact the local ERIKS representativeif an application does notclearly fall into these design parameters.PressureoutsidePressureinsideStatic ApplicationsThere are five types of static O-ringapplications:• Flange seal• Radial seal• Dovetail seal• Boss seal• Crush sealFig. 1-26 Fig. 1-27Flange Seal (Axial Seal)In flange seal glands, the two flangesare assembled with metal to metalcontact. So in fact there is noremarkable gap and no risk forextrusion of the O-ring as long as theconstruction does not deform undersystem pressure.(fig. 1-26).When system pressure is from the outside,the groove inside diameter is ofprimary importance and the groovewidth then determines the outsidediameter. When system pressure isfrom the inside the reverse is true.Radial SealBecause the metal parts are pressedor screwed together there is always aclearance gap with risk for extrusion.(fig. 1-27).Dovetail sealAlso here there is a metal to metal contactas long as the construction will notdeform under system pressure.(fig. 1-30).Boss sealThe groove dimensions are incorporatedin the standard dimensions.x = surface finish in µ R aFig. 1-30Surface Finish Static GroovesStraight-sided grooves are best to preventextrusion or nibbling. Five degreesloping sides are easier to machineand are suitable for lower pressures.Surface finishes up to 64 to 125 RMSwith no burrs, nicks, or scratches arerecommended.The method used to produce the finishis important. If the finish is producedby machining the part on a lathe, or bysome other method that producesscratches and ridges that follow thedirection of the machinehead, a veryrough surface will still seal effectively.Other methods, however, such as endmilling, will produce scratches that cutacross the O-ring. Even these mayhave a rather high roughness value ifthe profile across them shows roundedscratches that the rubber can readilyflow into.102

TECHNICAL DOCUMENTATION O-RINGS12. O-ring Gland DesignDynamic ApplicationsThere are three types of dynamic applications:• Reciprocating Seal• Oscillating Seal• Rotating SealApplication in reciprocating andoscillating motionsGroove dimensions for reciprocatingand oscillating applications are thesame.Dynamic applications, due to themotion against the O-ring, are morecomplicated than static applications.Fluid compatibility must be more carefullyscrutinized because a volumeswell of more than 20% may lead todifficulties with high friction problemsand only a minimum of shrinkage, atmost 4%, can be tolerated to avoidleakage problems.Because of the movement between thegland parts there always is a clearancegap with a potential risk for extrusion ofthe O-ring.O-ring seals are best in dynamic applicationswhen used on short stroke,relatively small diameter applications.Long stroke, large diameter seals aremore susceptible to spiral failure.Application of O-rings in rotarymotionsIn a rotating application a shaft continuouslyrotates in the inside diameter ofthe O-ring, causing friction and heat.Because rubber is a poor conductor ofheat, the O-ring can loose its properties.To minimize or reduce wear, thefollowing could be done; howeverconsult the local ERIKS representative:• confirm amount of squeeze.• use the smallest possible crosssection.• select an O-ring with internal lubricationor use low friction minerals.• do not exceed a temperature of212°F (100°C).• do not use a shaft which is largerthan the inside diameter of the O-ring.• provide lubrication.• do not let the O-ring rotate in thegroove, only relative to the shaft.• rough sealing surfaces of the groovewill prevent rotation.• check surface finish(may be too rough)Installing the O-ringMating metal surfaces are generally ofdifferent metals, with one metal beingsofter than the other. The O-ringgroove should be put in the softer ofthe metals. In the event that the metalswear on each other the harder metalwill be less damaged, thus insuring agood sealing surface.Fig. 1-33Surface Finish for Dynamic GroovesStraight-sided grooves are best to preventextrusion or nibbling. Five degreesloping sides are easier to machineand are suitable for pressures up to1500 psi. (100 bar). The rubbing surfacesshould be 8 to 16 RMS withoutlongitudinal or circumferential scratches.Best surfaces are honed, burnished, orhard chrome plated. Finishes ofdynamic contacting surfaces have a lotto do with the life of the O-ring seals.Appropriate surface finishes are important.Limits of maximum roughness forglands are given. Rougher finishes willcause excessive wear. Finer finishesreduce lubrication to the O-ring andmay result in stick slipping and irregularwear. Surface roughness valuesless than 5 micro inches (0,15µmRa)are not recommended for dynamic O-ring seals. The surface must be roughenough to hold small amounts of oil.Finishes below 5 RMS wipe too cleanfor good moving seal life.Steel or cast iron cylinder bores arepreferred. They should be thickenough not to expand or breathe withpressure, otherwise the radial clearancegap may expand and contractwith pressure fluctuations-causingnibbling of the O-ring.103

SEALING ELEMENTS12. O-ring Gland DesignFrictionIn normal applications harder materialsprovide less friction than softer materials.However, the higher the hardnessof the O-ring, above 70° Shore A, thegreater the friction. This is because thecompressive force at the samesqueeze, is greater than with softermaterials.Compound swell decreases the hardnessand may increase friction. Thelower the operating temperature theharder the seal becomes which canalso increase friction. However, thermalcontraction of the seal materialwhich reduces effective squeeze mayoffset any increased friction caused byan increase of hardness.Breakout friction is the force necessaryto start relative motion. This is dependentupon the length of the timebetween cycles. It also depends on thesurface finish of the metal, the rubberhardness, squeeze, and other frictionaffectingfactors. After standing 10days, the breakout friction will be 2 to5 times the friction of a seal under lightload. Breakout friction can be reducedby utlizing softer O-ring or speciallymodified compounds.Soft metals like aluminum, brass,bronze, monel, and some stainlesssteels should be avoided.Metallic moving surfaces sealed by anO-ring preferably should never touch,but if they must, then the one containingthe O-ring groove should be a softbearing material.If excessive clearance is created,extrusion will result. If adequatesqueeze has not been applied, leakagewill result.If friction is excessive a variety ofpossible solutions exist:• Select a different O-ring hardness.• Select a different O-ring material withimproved coefficient of friction.• Increase the groove depth.• Consider the use of an alternatedesign of seal.• Viton® has much lower friction thanNBR or EPDM or Silicone.• Check to ensure squeeze is withinthe recommended range.• Do not reduce the squeeze belowrecommended levels in an attempt toreduce friction. The reduction insqueeze will cause the application toleak.Seal extrusionIf the radial clearance gap betweenthe sealing surface and the groovecorners (clearance gap) is too largeand the pressure exceeds the deformationlimit of the O-ring, extrusion ofthe O-ring material will occur.When this happens, the extrudedmaterial wears or frays with cyclingand the seal starts to leak.For extrusion and direction of pressureinformation for static seals seefig. 1-26. In a reciprocating applicationthe tendency for extrusion willincrease if friction and system pressureact on the O-ring in the samedirection. Groove design can reducethe tendency for extrusion.See figures 1-32 a & b.If the friction of the moving metal surfaceacross the O-ring is in the samedirection as the direction of the pressure,the O-ring will be dragged intothe clearance gap more readily andthus extrude at about 35% of thepressure normally necessary to causeextrusion. By placing the groove in theopposite metal part, the friction willwork against pressure.Running friction depends on two factors:the force exerted on the ring'srubbing surface by the compressionforce of the squeeze and the force ofthe system's pressure against andtending to distort the O-ring into a "D"shape. The former depends on thehardness of the O-ring, its percentagesqueezeand the length of the rubbingsurface.P MediaOne of the best ways to reduce extrusionis to use the back-up ring (seepage 117).The surface over which the O-ring willslide also becomes very important. Itmust be hard and wear resistant, itmust be sufficiently smooth that it willnot abrade the rubber, and yet theremust be minute pockets to hold lubricant.FrictionMovementFig. 1-32 aClearancegapP MediaFrictionMovementFig. 1-32 bClearancegap104

TECHNICAL DOCUMENTATION O-RINGS12. O-ring Gland DesignGroove depth and clearance gapThe right groove depth in O-ring applicationsis very important because itstrongly influences the squeeze of theO-ring cross section. In the tables thegroove depth always includes themachined groove depth and theclearance gap. The clearance gapinfluences the rate of extrusion.Because it is very difficult to measurethe groove depth it is better to makethe calculation with the bore, plug andgroove diameter as stated below.clearance gapFig. 1-19pressureSeal DesignSeals are divided into three primarycategories: Static Face or Flange,Static Radial type, and Dynamic Radialtype.Face or Flange type seals have noclearance gap, but consist of a groovecut into one flange with a flat matingflange bolted together to give a surfaceto surface contact.Static Radial Seals and Dynamic RadialSeals require the presence of a diametricalclearance gap for installation.There are two types of radial designs:1. Male or Plug - the O-ring groove islocated on a plug which is inserted intothe housing or cylinder (fig. 1-23)2. Female or Tube - the O-ring grooveis located in the housing or cylinderand a tube is installed through theO-ring l.D. (fig. 1-24).Male or Plug Seal design is based onthe following factors (refer to fig. 1-23).Bore Diameter (A)Plug Diameter (H)Groove Diameter (B)Groove Width (F) as shown in thedimension tables.Gland Depth (E) as shown in thedimension tables.Mechanical Squeeze for the gland isdetermined by the bore diameter andthe groove diameter in a plug or maletype seal (fig. 23). The formula fordetermining the groove diameter(B)when the bore diameter(A) and glanddepth(E) are known is:B min. = A min. minus 2 x E max.B max. = A max. minus 2 x E min.Squeeze is measured from the bottomof the groove to the mating surfaceand includes the clearance gap. Thefollowing formula is used to determinethe actual gland depth with tolerances:Max. Gland Depth = max. bore minusmin. groove diameter, divided by 2.Min. Gland Depth = min. bore minusmax. groove diameter, divided by 2.Break corners app. R = .005 (0,15)AHBFig. 1-23Ex = surface finish µ R agroove depth is incl. gapADHFig. 1-24F105

SEALING ELEMENTS12. O-ring Gland DesignTotal Diametrical Clearance is the differencebetween the bore diameter (A)and the plug diameter (H) dimensions.Tolerances of the bore and plugdiameters determine the maximum andminimum diametrical clearance gap.These values divided by two will givethe radial maximum and minimumclearance gaps.Female or Tube seals (fig 24) arebased upon the following:Bore Diameter (A)Plug Diameter (H)Groove Diameter (D)Groove Width (F) as shown in thedimension tables.Gland Depth (E) as shown in thedimension tables.Mechanical Squeeze for this type ofseal is determined by the groovediameter (D) and the plug diameter (H).The formula for determining the groovediameter (D) when the plug diameter(H) and the groove depth (E) areknown is:D max. =H max. Plus 2 E max.D min. = H min. plus 2 E min.Squeeze is measured from the bottomof the groove to the mating surfaceand includes the clearance gap. Usethe following formula for determiningthe actual gland depth with tolerance:Max. Gland Depth =Max. groove diameter minus min. plugdiameter, divided by 2.Min. Gland Depth =Min. groove diameter minus max. plugdiameter, divided by 2.Total Diametrical Clearance is the differencebetween the bore diameter (A)and the plug diameter (H). Tolerancesof the bore diameter and the plugdiameter determine the maximum andminimum total diametrical clearancegap. The size of the clearance gap isalso influenced by the degree of"breathing" of the metal parts. Whenusing the values from the tables,include in the diametrical clearanceany breathing or expansion of themating metal parts that may beanticipated due to pressure.In some constructions the clearancegap is equal on the whole circumferenceof the O-ring. This is total clearancewith maximum concentricity. Ifconcentricity between piston andcylinder is rigidly maintained, radialclearance is diametrical clearance.In practice in most constructions, dueto side loading and misalignment, onone spot of the O-ring circumferencethe clearance gap is minimum or evenzero and on the opposite spot it will bemaximum. This is total clearance withmaximum eccentricity. (fig.20)• Please contact the local ERIKSrepresentative for additional informationon wear bands and bearing forimproving concentricity.SborerodStotal clearancewith max. eccentricitytotal clearancewith max. concentricityFig. 1-20106

TECHNICAL DOCUMENTATION O-RINGS12. O-ring Gland DesignThe most effective and reliable sealingis generally provided with the diametricalclearance as shown in Table 3.B-1a. The maximum allowable gaps areindicated for 70° hardness O-ringswith different cross sections withoutback-ups for reciprocating and staticseals. These values correspond to apressure of ca. 1200 PSI (80 bar)(8 Mpa) at 70°F (21°C). When greaterclearances occur, fig. 1-21 indicatesconditions where O-ring seals may beused - depending on the fluid pressureand O-ring hardness.[See Table 3.B-1a]Note: for silicone and fluorosiliconeO-rings reduce all the clearancesshown by 50%.The diagram (fig. 1-21) gives a guideto the relation between hardness,pressure, clearance, and extrusion.This figure is based on NBR O-ringswith a cross section of .139 inch (3,53mm) without back up rings. Whenthere is risk for extrusion use contouredhard rubber or plastic back-uprings. The results are based on tests attemperatures up to 70°C.Table 3.B-1a Gland clearance in relation to hardness and O-ring cross sectionPressure psi (bar)Cross sectionMax. clearance 70 ° Shore Ainch mm inch mm.070 1,0-2,0 .002 - .004 0,05 - 0,1.103 2,0-3,0 .002 - .005 0,05 - 0,13.139 3,0-4,0 .002 - .006 0,05 - 0,15.210 4,0-6,0 .003 - .007 0,07 - 0,18>.275 >6,0 .004 - .010 0,1 - 0,2510.500 (700)9.000 (600)4.500 (300)3.000 (200)2.000 (140)1.500 (100)1.000 (70)825 (55)600 (40)450 (30)300 (20)225 (15)150 (10)inchmmnoextrusion.0100,2570°Sh.A.0200,5extrusion90°Sh.ATotal Diametral Clearance Gap.0300,7.0401,0Fig. 1-21107

SEALING ELEMENTS12. O-ring Gland Design12 A. Gland Design Static AxialApplicationGland Design for Static Application forO-rings with Axial SqueezePressureoutsidePressureinsideFig. 1-26Surface Finish Xgroove top and bottom :for liquidsX = 32 micro inches (0.8 µm Ra)Break corners app. R = .005 (0,15)for vacuum and gasesX = 16 micro inches (0.4 µm Ra)groove sides:X = 63 micro inches (1.6 µm Ra)x = surface finish µ R agroove depth is incl. gapFig. 1-27 aTable AS C1 - Gland Dimensions (inches) Industrial Face or Flange TypeO-ring Gland Depth Static Squeeze Groove Width Groove RadiusCross section Axial Static In. for Face Seals W RWENominal Actual Actual In % Liquids Vacuum & Gases1/16 .070 .050/.054 .013/.023 27 .101/.107 .084/.089 .005/.0153/32 .103 .074/.080 .020/.032 21 .136/.142 .120/.125 .005/.0151/8 .139 .101/.107 .028/.042 20 .177/.187 .158/.164 .010/.0253/16 .210 .152/.162 .043/.063 18 .270/.290 .239/.244 .020/.0351/4 .275 .201/.211 .058/.080 16 .342/.362 .309/.314 .020/.035These dimensions are intended primarily for face type seals and normal temperature applications.108

TECHNICAL DOCUMENTATION O-RINGS12. O-ring Gland DesignGland Design for Static Applicationfor O-rings with Axial SqueezeFace Seal Glands (METRIC)O-rings which are compressed axiallyin a static application are also calledflange seals. (see fig. 26 and 27).Surface Finish Xgroove top and bottom :for liquidsX = 32 micro inches (0.8 µm Ra)for vacuum and gasesX = 16 micro inches (0.4 µm Ra)groove sides:X = 63 micro inches (1.6 µm Ra)* = dimensions in mm *US/BS standardAS.568ATable 3.C-1 Gland Dimensions Static Application-Face Seal Glands-MetricW E F RO-ring cross section Gland Depth Groove Width Groove RadiusDiam. Tol. +/- Liquids Vacuum/mm DIN.3771 Tol. -0/+ Tol. -0/+0,13 gases0,90 0,08 0,68 0,02 1,30 1,10 0,21,0 - 1,02 0,08 0,75 0,02 1,45 1,20 0,21,20 0,08 0,90 0,02 1,75 1,45 0,21,25 - 1,27 0,08 0,94 0,02 1,80 1,50 0,21,42 0,08 1,07 0,02 2,05 1,70 0,21,50 0,08 1,13 0,02 2,20 1,80 0,21,60 - 1,63 0,08 1,20 0,03 2,35 1,90 0,21,78* - 1,80 0,08 1,34 0,03 2,60 2,15 0,21,90 0,08 1,43 0,03 2,75 2,30 0,22,0 0,08 1,51 0,04 2,90 2,40 0,22,20 - 2,21 0,08 1,67 0,04 2,90 2,55 0,22,40 0,08 1,82 0,04 3,20 2,80 0,22,46 0,08 1,87 0,04 3,25 2,85 0,22,50 0,08 1,90 0,04 3,30 2,90 0,22,62* 0,08 1,99 0,04 3,50 3,05 0,22,70 0,09 2,05 0,04 3,60 3,15 0,22,95 0,09 2,24 0,04 3,90 3,40 0,53,0 0,09 2,27 0,04 3,90 3,45 0,53,15 0,09 2,38 0,05 4,15 3,60 0,53,50 - 3,53* 0,09 2,67 0,05 4,60 4,05 0,53,60 0,1 2,72 0,05 4,70 4,10 0,54,0 0,1 3,03 0,06 5,25 4,60 0,5PressureoutsidePressureinsideFig. 1-26Break corners app. R = .005 (0,15)4,50 0,1 3,60 0,06 6,10 5,10 0,54,70 0,1 3,76 0,06 6,40 5,35 0,54,80 0,1 3,84 0,06 6,50 5,45 0,55,0 0,10 4,00 0,06 6,80 5,70 0,75,33* - 5,34 0,13 4,26 0,08 7,25 6,05 0,75,50 0,13 4,40 0,08 7,45 6,25 0,75,70 0,13 4,56 0,08 7,75 6,50 0,75,80 0,13 4,64 0,08 7,90 6,60 0,76,0 0,13 4,98 0,08 7,80 7,75 0,76,40 0,13 5,31 0,1 8,30 7,20 0,76,50 0,13 5,40 0,1 8,40 7,30 0,76,90 0,13 5,73 0,1 8,95 7,75 0,76,99* 0,15 5,80 0,1 9,05 8,85 0,77,0 0,15 5,81 0,1 9,05 7,90 0,77,50 0,15 6,23 0,1 9,70 8,40 1,08,0 0,18 6,64 0,1 10,35 9,00 1,08,40 0,18 6,97 0,15 10,90 9,45 1,0x = surface finish µ R agroove depth is incl. gapFig. 1-27 a9,0 0,2 7,65 0,15 11,10 10,40 1,010,0 0,2 8,50 0,15 12,30 11,55 1,011,0 0,2 9,35 0,15 13,55 12,70 1,012,0 0,2 10,20 0,15 14,80 13,85 1,513,0 0,2 11,05 0,15 16,00 15,00 1,514,0 0,2 11,90 0,3 17,25 16,15 1,516,0 0,2 13,60 0,3 19,70 18,45 1,518,0 0,2 15,30 0,3 22,15 20,80 1,520,0 0,2 17,00 0,3 24,65 23,10 1,5109

SEALING ELEMENTS12. O-ring Gland Design12 B. Gland Design Static RadialApplicationGland Design for Static Applicationfor O-rings with Radial SqueezeIndustrial Radial Glands INCHESSurface Finish Xgroove top and bottom :for liquidsX = 32 micro inches (0.8 µm Ra)Fig. 1-28Break corners app. R = .005 (0,15)for vacuum and gasesX = 16 micro inches (0.4 µm Ra)groove sides:X = 63 micro inches (1.6 µm Ra)x = surface finish µ R agroove depth is incl. gapFig. 1-27 aTable AS.C2 Gland Dimensions Static Seals - Industrial Radial Applications (Inches)O-ring Gland Depth. Static Clearance Groove Groove Max.Cross section Radial Static Squeeze for Diametral Width Radius AllowableW E Radial Seals F R Eccentricity 1Nominal Actual Actual % Standard One TwoBackup BackupWasher 2 Washers 21/16 .070 .050/.052 .015/.023 22/32 *.002 min. .093/.098 .138/.143 .205/.210 .005/.015 .005/.0153/32 .103 .081/.083 .017/.025 17/24 *.002 min. .140/.145 .171/.176 .238/.243 .005/.015 .005/.0151/8 .139 .111/.113 .022/.032 16/23 *.003 min. .187/.192 .208/.213 .275/.280 .010/.025 .010/.0253/16 .210 .170/.173 .032/.045 15/21 *.003 min. .281/.286 .311/.316 .410/.415 .020/.035 .020/.0351/4 .275 .226/.229 .040/.055 15/20 *.004 min. .375/.380 .408/.413 .538/.543 .020/.035 .020/.0351. Total Indicator Reading between groove and adjacent bearing surface.2. These groove dimensions are for compounds that free swell less than 15%. Suitable allowances should be made for higher swell compounds.* For max. allowable cleareance, refer to fig. 22 to determine value based upon pressure requirement and compound hardness.* Maximum clearance should be reduced by 1/2 for compounds exhibiting poor strength such as silicone and fluorosilicone.Male plug dimensions and female throat (bore) dimensions must be calculated based upon maximum and minimum clearance gaps.110

TECHNICAL DOCUMENTATION O-RINGS12. O-ring Gland Design12 B. Gland Design Static RadialApplicationGland Design for Static Applicationfor O-rings with Radial SqueezeIndustrial Radial Glands INCHESSurface Finish Xgroove top and bottom :for liquidsX = 32 micro inches (0.8 µm Ra)for vacuum and gasesX = 16 micro inches (0.4 µm Ra)groove sides:X = 63 micro inches (1.6 µm Ra)Fig. 1-28Break corners app. R = .005 (0,15)x = surface finish µ R agroove depth is incl. gapFig. 1-27 aTable 3.C-2 Gland dimensions Static Application-Industrial Radial Seals, METRICW E S Diametr. F Groove R Groove Max.O-ring cross section Gland Depth Clearance Width Radius EccentricityDiam. Tol. +/- Tol.mm DIN.3771 Tol. -0/+ Tol. -0/+0,130,90 0,08 0,65 0,02 0,1 1,20 0,2 0,051,0 - 1,02 0,08 0,72 0,02 0,1 1,35 0,2 0,051,20 0,08 0,87 0,02 0,1 1,60 0,2 0,051,25 - 1,27 0,08 0,91 0,02 0,1 1,65 0,2 0,051,42 0,08 1,03 0,02 0,1 1,90 0,2 0,051,50 0,08 1,09 0,02 0,1 2,00 0,2 0,051,60 - 1,63 0,08 1,16 0,03 0,1 2,10 0,2 0,051,78* - 1,80 0,08 1,29 0,03 0,1 2,35 0,2 0,051,90 0,08 1,38 0,03 0,1 2,50 0,2 0,052,0 0,08 1,45 0,04 0,1 2,65 0,2 0,052,20 - 2,21 0,08 1,74 0,04 0,1 3,00 0,2 0,052,40 0,08 1,90 0,04 0,1 3,25 0,2 0,052,46 0,08 1,94 0,04 0,1 3,35 0,2 0,052,50 0,08 1,98 0,04 0,1 3,40 0,2 0,052,62* 0,08 2,07 0,04 0,1 3,55 0,2 0,052,70 0,09 2,13 0,04 0,1 3,65 0,2 0,052,95 0,09 2,33 0,04 0,1 4,00 0,5 0,053,0 0,09 2,40 0,04 0,15 4,05 0,5 0,073,15 0,09 2,52 0,05 0,15 4,25 0,5 0,073,50 - 3,53* 0,09 2,82 0,05 0,15 4,75 0,5 0,073,60 0,1 2,88 0,05 0,15 4,85 0,5 0,074,0 0,1 3,20 0,06 0,15 5,40 0,5 0,074,50 0,1 3,64 0,06 0,15 6,00 0,5 0,074,70 0,1 3,80 0,06 0,15 6,30 0,5 0,074,80 0,1 3,88 0,06 0,15 6,40 0,5 0,075,0 0,1 4,04 0,06 0,15 6,70 0,7 0,105,33* - 5,34 0,13 4,31 0,08 0,15 7,15 0,7 0,105,50 0,13 4,45 0,08 0,15 7,35 0,7 0,105,70 0,13 4,61 0,08 0,15 7,65 0,7 0,105,80 0,13 4,69 0,08 0,15 7,75 0,7 0,106,0 0,13 4,91 0,08 0,18 8,15 0,7 0,136,40 0,13 5,24 0,1 0,18 8,70 0,7 0,136,50 0,13 5,32 0,1 0,18 8,85 0,7 0,136,90 0,13 5,65 0,1 0,18 9,40 0,7 0,136,99* 0,15 5,72 0,1 0,18 9,50 0,7 0,137,0 0,15 5,73 0,1 0,18 9,55 0,7 0,137,50 0,15 6,14 0,1 0,18 10,20 1,0 0,138,0 0,18 6,55 0,1 0,18 10,90 1,0 0,138,40 0,18 6,87 0,15 0,18 11,45 1,0 0,139,0 0,2 7,65 0,15 0,18 11,85 1,0 0,1310,0 0,2 8,50 0,15 0,18 13,20 1,0 0,1311,0 0,2 9,35 0,15 0,18 14,50 1,0 0,1312,0 0,2 10,20 0,15 0,18 15,85 1,0 0,1313,0 0,2 11,05 0,15 0,18 17,15 1,5 0,1314,0 0,2 11,90 0,3 0,18 18,45 1,5 0,1316,0 0,2 13,60 0,3 0,18 21,10 1,5 0,1318,0 0,2 15,30 0,3 0,18 23,75 1,5 0,1320,0 0,2 17,00 0,3 0,18 26,40 1,5 0,13111

SEALING ELEMENTS12. O-ring Gland Design12 C. Gland Design Dovetail GroovesGland Design for a StaticApplication; for O-rings in DovetailGrooves, INCHESDovetail grooves are used to hold theO-ring in place during installation ormaintenance. This groove design isrelatively uncommon as it is expensiveto machine and should not be usedunless absolutely required.The dovetail groove construction isonly recommended for O-rings withcross sections of .139 inch(3,53 mm) and larger.Surface Finish Xgroove top and bottom :for liquidsX = 32 micro inches (0.8 µm Ra)for vacuum and gasesX = 16 micro inches (0.4 µm Ra)groove sides:X = 63 micro inches (1.6 µm Ra)x = surface finish in µ R aFig. 1-30Table AS.C3 Gland Dimensions Dovetail Grooves, INCHESO-ring Gland Depth. Squeeze Groove Width Groove RadiusCross section % to Sharp CornerW E F 21/16 .070 .050/.052 27 .055/.059 .005 .0153/32 .103 .081/.083 21 .083/.087 .010 .0151/8 .139 .111/.113 20 .113/.117 .010 .0303/16 .210 .171/.173 18 .171/.175 .015 .0301/4 .275 .231/.234 16 .231/.235 .015 .0603/8 .375 .315/.319 16 .315/.319 .020 .090Radius "R2" is critical. Insufficient radius will cause damage to the seal during installation,while excessive radius may contribute to extrusion. R2 is size radius, R1 is machining radius.112

TECHNICAL DOCUMENTATION O-RINGS12. O-ring Gland Design12 C. Gland Design Dovetail GroovesGland Design for a StaticApplication for O-rings in DovetailGrooves, METRICDovetail grooves are used to hold theO-ring in place during installation ormaintenance. This groove design isrelatively uncommon as it is expensiveto machine and should not be usedunless absolutely required.The dovetail groove construction isonly recommended for O-rings withbigger cross sections, .139 inch(3,53 mm) and bigger.Surface Finish Xgroove top and bottom :for liquidsX = 32 micro inches (0.8 µm Ra)for vacuum and gasesX = 16 micro inches (0.4 µm Ra)groove sides:X = 63 micro inches (1.6 µm Ra)Table 3.C-3 Gland Dimensions Dovetail Grooves, METRICW E F RCross section Groove Depth Groove Width Radiusmm E+0/-0,05 F 2 +/-0,05 F 1 +/-0,05 R 1 R 23,0 2,40 2,45 2,60 0,4 0,253,5 - 3,53* 2,80 2,80 3,05 0,8 0,254,0 3,20 3,10 3,40 0,8 0,254,5 3,65 3,50 3,75 0,8 0,255,0 4,15 3,85 4,10 0,8 0,255,33* 4,40 4,10 4,35 0,8 0,255,5 4,6 4,20 4,60 0,8 0,45,7 4,8 4,35 4,75 0,8 0,46,0 5,05 4,55 4,95 0,8 0,46,5 5,50 4,90 5,30 0,8 0,46,99* - 7,0 5,95 5,25 5,65 1,5 0,47,5 6,40 5,60 6,00 1,5 0,48,0 6,85 6,00 6,50 1,5 0,58,4 7,25 6,25 6,80 1,5 0,58,5 7,35 6,35 6,90 1,5 0,59,0 7,80 6,70 7,25 1,5 0,59,5 8,20 7,05 7,60 1,5 0,510,0 8,70 7,40 7,95 1,5 0,5Dimensions in mm *US/BS standard AS 568ARadius "R 2 " is critical. Insufficient radius will cause damage to the seal during installation,while excessive radius may contribute to extrusion.R 2 is size radius. R 1 is machining radius.F 1 is groove width to sharp corner. F 2 is groove width to round cornerx = surface finish in µ R aFig. 1-30113

SEALING ELEMENTS12. O-ring Gland Design12 D. Gland Design for Static Boss SealsO-ring boss Gaskets for StraightThread Tube FittingsThe 900-series of dash numbers identifythe size of boss seals. The digitsafter the 9 identify the nominal tubesize in 16ths of an inch. The tube sizeis the outside diameter (OD). For example,size 903 is intended for use with3/16-inch OD tube.CHAMFER RELIEF TOHEX FLATS SHOULDBE WITHIN THE 15°±5° ANGLE AND EDIA LIMITATIONSFSQUARENESS BETWEENTHREAD AND FACE OF HEXSHOULD NOT EXCEED HWHEN MEASURED AT DIA-METER EQFULL THREADSTO THIS POINT45° ±5°THREADE.015 RAD FORTHREAD RUNOUT.031.016RADO YDETAIL‘A’MIN.SPOT-FACEDIAMETERJKTHD.PMIN. BOSSHEIGHTDIAMETER D SHOULD BE CON-CENTRIC WITH THREAD P.D.WITHIN .005 F.I.R.ZD DIA.THIS DIM. APPLIESONLY WHEN TAPDRILL CAN NOT PASSTHRU ENTIRE BOSS.010.005RADU DIA.10045° ±5°DETAIL‘A’Boss DimensionsAS 568 Cross- I.D. Tube Thread J D U K Y P Z 0O-ring section Outside min. min. +.005 +.015 min. min. ±1° min.Size Nr. Ø THD -.000 -.000Depth-902 .064 ± .003 .239 ± .005 1/8 5/16-24 UNF-2B .390 .062 .358 .074 .672 .468 12° .438-903 .064 ± .003 .301 ± .005 3/16 3/8-24 UNF-2B .390 .125 .421 .074 .750 .468 12° .500-904 .072 ± .003 .351 ± .005 1/4 7/16-20 UNF-2B .454 .172 .487 .093 .828 .547 12° .563-905 .072 ± .003 .414 ± .005 5/16 1/2-20 UNF-2B .454 .234 .550 .093 .906 .547 12° .625-906 .078 ± .003 .468 ± .005 3/8 9/16-20 UNF-2B .500 .297 .616 .097 .909 .609 12° .688-908 .087 ± .003 .644 ± .009 1/2 3/4-16 UNF-2B .562 .391 .811 .100 1.188 .688 15° .875-910 .097 ± .003 .755 ± .009 5/8 7/8-14 UNF-2B .656 .484 .942 .100 1.344 .781 15° 1.000-912 .116 ± .004 .924 ± .009 3/4 1 1/16 -12 UN-2B .750 .609 1.148 .130 1.625 .906 15° 1.250-913 .116 ± .004 .986 ± .010 13/16-914 .116 ± .004 1.047 ± .010 7/8 1 3/16 -12 UN-2B .750 .719 1.273 .130 1.765 .906 15° 1.375-916 .116 ± .004 1.171 ± .010 1 1 5/16 -12 UN-2B .750 .844 1.398 .130 1.910 .906 15° 1.500-920 .118 ± .004 1.475 ± .014 1 1/4 1 5/8 -12 UN-2B .750 1.078 1.713 .132 2.270 .906 15° 1.875-924 .118 ± .004 1.720 ± .014 1 1/2 1 7/8 -12 UN-2B .750 1.312 1.962 .132 2.560 .906 15° 2.125-932 .118 ± .004 2.337 ± .018 2 2 1/2 -12 UN-2B .750 1.781 2.587 .132 3.480 .906 15° 2.750Fitting End Dimensions (MS33656)O-ring Cross- I.D. Tube Thread F D U KSize Nr. section Outside + .002 max. ± .010 + .015Ø - .003 - .000AS-902 .064 ± .003 .239 ± .005 1/8 5/16-24 UNF-2B .250 .005 .549 .063AS-903 .064 ± .003 .301 ± .005 3/16 3/8-24 UNF-2B .312 .005 .611 .063AS-904 .072 ± .003 .351 ± .005 1/4 7/16-20 UNF-2B .364 .005 .674 .075AS-905 .072 ± .003 .414 ± .005 5/16 1/2-20 UNF-2B .426 .005 .736 .075AS-906 .078 ± .003 .468 ± .005 3/8 9/16-18 UNF-2B .481 .005 .799 .083AS-908 .087 ± .003 .644 ± .009 1/2 3/4-16 UNF-2B .660 .005 .986 .094AS-910 .097 ± .003 .755 ± .009 5/8 7/8-14 UNF-2B .773 .005 1.111 .107AS-912 .116 ± .004 .924 ± .009 3/4 1 1/16 -12 UN-2B .945 .008 1.361 .125AS-914 .116 ± .004 1.047 ± .010 7/8 1 3/16 -12 UN-2B 1.070 .008 1.475 .125AS-916 .116 ± .004 1.171 ± .010 1 1 5/16 -12 UN-2B 1.195 .008 1.599 .125AS-920 .118 ± .004 1.475 ± .014 1 1/4 1 5/8 -12 UN-2B 1.507 .008 1.849 .125AS-924 .118 ± .004 1.720 ± .014 1 1/2 1 7/8 -12 UN-2B 1.756 .008 2.095 .125AS-932 .118 ± .004 2.337 ± .018 2 2 1/2 -12 UN-2B 2.381 .008 2.718 .125114

TECHNICAL DOCUMENTATION O-RINGS12. O-ring Gland Design12 E. Gland Design Dynamic HydraulicBreak corners app. R = .005 (0,15)Gland Design for DynamicApplication HydraulicINCHESThe following table indicates groovedimensions for reciprocating and oscillatingapplications when sealinghydraulic fluids and other viscousliquids.Surface Finish Xgroove top and bottom :X = 16 micro inches (0.4 µm Ra)x = surface finish µ R agroove depth is incl. gapFig. 1-33/34 Fig. 1-27groove sides:X = 32 micro inches (0.8 µm Ra)Table AS.D1 Gland Dimensions Dynamic Seals - Industrial Reciprocating Applications, InchesO-ring Gland Depth. Dynamic Clearance Groove Groove Max.Cross section Radial Dynamic Squeeze for Diametral Width ** Radius AllowableW E Radial Seals F R Eccentricity 1Nominal Actual Actual % Standard One TwoBackup BackupRing 2 Rings 21/16 .070 .055/.057 .010/.018 15/25 *.002 min. .093/.098 .138/.143 .205/.210 .005/.015 .0023/32 .103 .088/.090 .010/.018 10/17 *.002 min. .140/.145 .171/.176 .238/.243 .005/.015 .0021/8 .139 .121/.123 .012/.022 9/16 *.003 min. .187/.192 .208/.213 .275/.280 .010/.025 .0033/16 .210 .185/.188 .017/.030 8/14 *.003 min. .281/.286 .311/.316 .410/.415 .020/.035 .0041/4 .275 .237/.240 .029/.044 11/16 *.004 min. .375/.380 .408/.413 .538/.543 .020/.035 .0051. Total Indicator Reading between groove and adjacent bearing surface.2. These groove widths are for compounds that free swell less than 15%. Suitable allowances should be made for higher swell compounds.** Groove width is based on rubber backups. For groove width with pdfe spiral wound backups see table 3.D-2.* For max. allowable cleareance, refer to table 13.A to determine value based upon pressure requirement and compound durometer.* The piston dimension for male glands must be calculated by using the max. gap derived from the extrusion table 13.A and the min. gap listed above.* The bore diameter for female glands must be calculated by using the max. gap derived from the extrusion table 13.A and the min. gap listed above.115

SEALING ELEMENTS12. O-ring Gland Design12 E. Gland Design Dynamic HydraulicGland Design for DynamicApplication HydraulicMETRICThe following table indicates groovedimensions for reciprocating and oscillatingapplications when sealinghydraulic fluids and other viscousliquids.Surface Finish Xgroove top and bottom :X = 16 micro inches (0.4 µm Ra)groove sides:X = 32 micro inches (0.8 µm Ra)Table 3.D-1 Gland Dimensions Dynamic Application-Industrial Reciprocating Seals, METRICW E S Diametr. F Groove R Groove Max.O-ring cross section Gland Depth Clearance Width ** Radius EccentricityDiam. Tol. +/- Tol.DIN.3771 in mm Tol. -0/+ -0/+130,90 0,08 0,72 0,02 0,1 1,20 0,2 0,051,0 - 1,02 0,08 0,80 0,02 0,1 1,35 0,2 0,051,20 0,08 0,96 0,02 0,1 1,60 0,2 0,051,25 - 1,27 0,08 1,00 0,02 0,1 1,70 0,2 0,051,42 0,08 1,13 0,02 0,1 1,90 0,2 0,051,50 0,08 1,20 0,02 0,1 2,00 0,2 0,051,60 - 1,63 0,08 1,28 0,03 0,1 2,10 0,2 0,051,78* - 1,80 0,08 1,42 0,03 0,1 2,40 0,2 0,051,90 0,08 1,52 0,03 0,1 2,50 0,2 0,052,0 0,08 1,60 0,04 0,1 2,65 0,2 0,052,20 - 2,21 0,08 1,89 0,04 0,1 3,00 0,2 0,052,40 0,08 2,06 0,04 0,1 3,25 0,2 0,052,46 0,08 2,11 0,04 0,1 3,35 0,2 0,052,50 0,08 2,15 0,04 0,1 3,40 0,2 0,052,62* 0,08 2,25 0,04 0,1 3,55 0,2 0,052,70 0,09 2,32 0,04 0,1 3,70 0,2 0,052,95 0,09 2,53 0,04 0,1 4,00 0,5 0,053,0 0,09 2,61 0,04 0,15 4,05 0,5 0,073,15 0,09 2,74 0,05 0,15 4,25 0,5 0,073,50 - 3,53* 0,09 3,07 0,05 0,15 4,75 0,5 0,073,60 0,1 3,13 0,05 0,15 4,85 0,5 0,074,0 0,1 3,48 0,05 0,15 5,40 0,5 0,07Fig. 1-33/34Break corners app. R = .005 (0,15)x = surface finish µ R agroove depth is incl. gapFig. 1-274,50 0,1 3,99 0,05 0,15 6,00 0,5 0,074,70 0,1 4,17 0,05 0,15 6,30 0,5 0,074,80 0,1 4,26 0,05 0,15 6,40 0,5 0,075,0 0,1 4,44 0,05 0,15 6,70 0,7 0,105,33* - 5,34 0,13 4,73 0,05 0,15 7,15 0,7 0,105,50 0,13 4,88 0,05 0,15 7,40 0,7 0,105,70 0,13 5,06 0,05 0,15 7,60 0,7 0,105,80 0,13 5,15 0,05 0,15 7,75 0,7 0,106,0 0,13 5,19 0,05 0,18 8,15 0,7 0,136,40 0,13 5,54 0,05 0,18 8,70 0,7 0,136,50 0,13 5,63 0,05 0,18 8,85 0,7 0,136,90 0,13 5,97 0,05 0,18 9,40 0,7 0,136,99* 0,15 6,05 0,05 0,18 9,50 0,7 0,137,0 0,15 6,06 0,05 0,18 9,55 0,7 0,137,50 0,15 6,49 0,05 0,18 10,20 1,0 0,138,0 0,18 6,92 0,05 0,18 10,90 1,0 0,138,40 0,18 7,27 0,05 0,18 11,45 1,0 0,139,0 0,2 7,92 0,05 0,18 12,10 1,0 0,1310,0 0,2 8,80 0,05 0,18 13,40 1,0 0,13* US/BS Standard AS 568A** For groove width with back-up rings for O-rings AS 568A, see table 3.D-2. For groove widthwith back-up rings for metric O-rings, ask for more information.116

TECHNICAL DOCUMENTATION O-RINGS12. O-ring Gland Design12 F. Groove Design for Static andDynamic Applications when usingBack-up RingsExtrusionBackup ringPressureThe use of Back-up ringsExtrusion occurs when part of theO-ring material is forced through thegap between mating metal partsbecause of system pressure.Fig. 1-38Extrusion can be prevented inseveral ways:- Reducing the gap will help preventextrusion.- A harder O-ring material i.e. NBR 90°shore, FKM 90 or 95° Shore A, AU,EU, PUR (Polyurethane) can be usedto prevent extrusion. (FKM 95° shoreis also excellent for explosivedecompression applications, seepage 10).- An O-ring can be installed with aback-up ring of a harder material toclose the gap and support the O-ring.SpiralDifferent shapes of Back-up rings:Split (skarf-cut)SolidThe use of back-up rings is related toO-ring hardness, media pressure, andwhether it is a static or dynamic application.In general the guidelines are:Pressure static application:up to 1000 psi (70 bar, 7 MPa) withoutback-up ring, up to 6000 psi (400 bar,40 MPa) with back-up ring, up to 30000psi (2000 bar, 200 MPa) with specialconstruction.Pressureb 2Pressureb 3PressureDynamic application:reciprocating up to 750 psi (50 bar,5MPa) without back-up ring, higherpressures with back-up ring.Speedreciprocating up to 0.5 m/sec.117

SEALING ELEMENTS12. O-ring Gland DesignSolution with Back-up RingsIn practice extrusion of a 70° Shore AO-ring at 20°C (70°F) with correctgland clearance, does not occur atpressures under 1200 psi (80 bar, 8MPa) in static applications.back-up ringpressureback-up ringTo avoid risks of extrusion, it is recommendedto use 90°Shore A O-rings atpressures higher than 750 psi (50 bar,5MPa) if the dimension of the groove istoo small for back-up rings or if thegroove cannot be machined to allowfor back-up rings. In general it isrecommended in dynamic applicationsto use back-up rings at pressures over750 psi (50 bar, 5 MPa).Back-up rings are generally made of amaterial that is harder than the O-ringmaterial. Back-up rings can be madefrom PTFE and PTFE blends, 90°-95°hardness elastomers, and some plasticssuch as polyamides or PEEK forhigh temperature applications.Back-up rings are installed downstream from the system pressure in theO-ring gland. See figure 22.back-up ringsTpressureFig. 1-22O-Ringback-up ringsPressurepressureIn double acting applications twoback-up rings are installed, one oneach side of the O-ring. When backuprings are used the groove dimensionsmust be adapted to accommodatethe back-up rings. Groove widthsas indicated on the table should beincreased by the thickness of theback-up ring or rings.MBack-up ringFFig. 1-35Back-up ring118

TECHNICAL DOCUMENTATION O-RINGS12. O-ring Gland DesignBack-up Ring StylesSpiral and split (or skarf-cut) PTFEback-up rings are a common choicedue to the ease of installation of thesedesigns. Note that the width of theback-up ring is equal to the groovedepth plus the clearance gap. Seefigure 1-23.The solid PTFE back-up ring is recommendedfor applications with highersystem pressures; however, thisdesign can only be installed in twopiece applications.Contoured nitrile back-up rings arerecommended at higher system pressureswhere the ability to stretch theback-up in installation is required.See figure 1-24.Standard dimensions for US StandardAS568 O-rings with back-ups are listedin table 3.D.-2.PTFE back-up rings are available incustom dimensions. Please contact anERIKS representative for assistance ingroove design.SpiralTSplit(skarf-cut)45°O-Ring0,5 RSolidPressureFig. 1-23Fig. 1-24For US standard O-rings in accordancewith AS568, standard spiral PTFEback-ups are available. See table 3.D-2 for groove dimensions for O-ringswith standard back-ups. See figure 1-35.MBack-up ringFBack-up ringFig. 1-35Table 3.D-2 Groove Dimensions for O-rings with Standard Spiral Wound Back-up rings.O-ring Back-up ring Groove Depth GrooveCross section Thickness (incl. clearance) WidthW T M Fmm inch inch mm inch mm inch mm inch mm+0 / -.001 +0 / -0,25 +0 / -.002 +0 / -0,25 +.004/-0 +0,10 / -0 +.004/-0 +0,10 / -01,78 .070 1,5 .057 1,45 .150 3,80 .209 5,302,62 .103 1,5 .090 2,25 .197 5,00 .256 6,503,53 .139 1,5 .123 3,10 .244 6,20 .303 7,705,33 .210 1,8 .188 4,70 .350 8,90 .421 10,707,0 .275 2,6 .238 6,05 .476 12,10 .579 14,70Note:We also stock the Parbak® back-uprings in different compounds of 90°Shore A, mainly in AS-dimensions.119

SEALING ELEMENTS12. O-ring Gland DesignPTFE BACK-UP RINGS StandardSizes for O-rings according AS 568The dimension ‘E’ of the back-up ringis dependent upon the depth of thegroove for dynamic O-ring applications.The standard groove widthneeds to be increased with one or twotimes the width of the back-up ringdepending if one or two back-up ringsneed to be installed.(See fig 1-39,1-40)Fig. 1-39It is only needed to install a back-upring at the side where the extrusion ofthe O-ring or Quad-ring exists.Only in the case of changing pressuredirections are back-up rings neededon both sides of the seal.Standard back-up rings are availablefor O-rings according the table 3.D-2APlease ask an ERIKS back-up ringspecialist for special sizes.Fig. 1-40120

TECHNICAL DOCUMENTATION O-RINGS12. O-ring Gland Design12 G. Gland design For Teflon®Encapsulated O-rings, Teflex® O-ringsThe Teflex® O-ring consists of asolid or hollow elastomeric core encapsulatedin a Teflon® FEP or PFAsheath. The elastomeric core may befluorocarbon or silicon rubber.Solid core Teflex® O-rings are generallyused in static applications. HollowSilicone core Teflex® O-rings are commonlyused in applications where lowersealing force is required as in semidynamicapplications.The Teflex® O-ring offers an effectivesolution for many difficult applications.The Teflon® FEP or PFA encapsulationactually effects the seal. The elastomericcore insures consistent compression onthe seal. The result is an overall sealingcompression, increasing with mediumpressure. The encapsulated O-ringbehaves like a highly viscous fluid, anypressure exerted on the seal is transmittedundiminished in all directionsFEP and PFA are suitable for injectionmolding. Maximum operating temperaturefor FEP is 205°C (400°F) and forPFA 260°C (500°F). Chemical and electricalproperties are similar to PTFE.PFA offers additional abrasion resistance.(See fig.43).Why are TEFLEX® O-rings needed?There are certain applications whichprohibit the use of conventional rubberO-ring seals. The use of hostile chemicalsor extreme temperatures (bothhigh and low) during various processescan make effective sealing very difficult.Many seal manufacturers haveproduced different "high performance"materials for these applications. ERIKScontributed to this area by introducingTEFLEX®.The Teflex® O-ring is available inseveral standard size ranges:• AS 568, BS 1806• JIS B2401• Swedish Standard.• Metric Dimensions.Teflex® O-rings are available in otherdimensions and alternative cross sections,oval, square, rectangular.Contact an ERIKS representative foradditional information. For full information:ask for the special brochure onTEFLEX® O-rings.Teflex® O-rings offer:- Excellent chemical resistance due tothe FEP/PFA encapsulation.- Temperature range from -60°C to205°C (-75°F to 400°F) with siliconecore and -15°C to 205°C(5°F to 440°F) with fluorocarboncore. Special applications arepossible up to 260°C (500°F).- Overall hardness 85° Shore A ±5durometer.- Sterilizable.- Pressures from vacuum to 10000 psi(700 bar, 70 MPa).- Low compression set characteristics.- Anti-adhesive properties, non sticksurface, low coefficient of friction.- FDA compliant- Quick supply- No restriction on inside diameter®Fig. 1-43121

SEALING ELEMENTS12. O-ring Gland Design12 G. Gland design For Teflon®Encapsulated O-rings, Teflex® O-ringsTEFLEX® O-rings are available in thefollowing dimensions.Upon request TEFLEX® O-rings canalso be supplied in a special design ordimensions.Table 3E-1 Teflex® O-ring standard dimensionsCross section WSmallest I.D.With silicone coreWith Viton® coreInch mm inch mm inch mm.059 - .079 1,5 - 2 .301 7,65 .487 12,37.094 - .103 2,4 - 2,62 .361 9,19 .487 12,37.130 - .139 3,31 - 3,53 .482 12,25 .813 20,64.150 - .157 3,80 - 4,0 .734 18,64 .859 21,82.169 - .177 4,3 - 4,5 .787 20,00 .866 22,00.197 5,0 .826 21,00 .912 23,16.210 5,33 .850 21,59 .945 24,00.217 - .236 5,5 - 6,0 1.102 28,00 1.299 33,00.248 - .276 6,3 - 7,0 1.417 36,00 2.00 50,80.295 - .315 7,5 - 8,0 2.00 50,80 3.00 76,20.354 - .374 9,0 - 9,5 3.50 88,90 3.50 88,90.394 10,0 4.00 101,60 4.00 101,60.433 - .492 11,0 - 12,5 4.75 120,65 4.75 120,65.551 14,0 6.00 152,40 6.00 152,40.591 - .709 15,0 - 18,0 7.00 177,80 7.00 177,80.748 - .787 19,0 - 20,0 8.00 203,20 8.00 203,201.0 25,4 9.00 228,60 9.00 228,601.25 31,75 10.00 250,00 10.00 250,00®Fig. 1-43122

TECHNICAL DOCUMENTATION O-RINGS12. O-ring Gland Design12 G. Gland design For Teflon®Encapsulated O-rings, Teflex® O-ringsInstallation of Teflex® O-ringsIt is critical that the Teflex® O-ring isnot damaged during installation. It isnot recommended to stretch Teflex®O-rings. Break all sharp corners andlubricate the groove before installation.Take care not to bend the O-ring toosharply as buckling of the PTFE/FEPcovering may result. The Teflex®O-ring may be heated to make it slightlymore flexible to facilitate installation.Teflex® O-rings are subject to compressionset. Smaller diameter crosssection O-rings will demonstrate highercompression set than larger diametercross sections. For this reason the useof the biggest possible cross section isrecommended. ERIKS recommendsthe use of Teflex® O-rings in staticapplications. For use in dynamic applicationstests should be conducted forsuitability. (See fig. 44).Surface Finish Xgroove top and bottom :for liquidsX= 32 RMS micro inches (0.8 µm Ra)for vacuum and gasesX= 16 RMS micro inches (0.4 µm Ra)groove sidesX= 63 RMS micro inches (1.6 µm Ra)Fig. 1-44Table 3E-1N Standard dimensions Teflex® O-ringsCross section WSmallest I.D.With Viton® Core With Silicone Core With HollowSilicone Coremm inch mm inch mm inch mm inch1,60 10,00 5,00 --1,78 .070 10,00 .40 5,28 .20 8,00 .302,00 10,00 6,80 10,002,50 12,00 7,40 12,002,62 .103 12,00 .50 7,60 .30 16,00 .603,00 15,00 12,00 20,003,40 15,00 2,50 23,003,53 .139 15,00 .60 13,00 .50 24,00 14,00 16,00 14,00 28,004,25 17,00 14,50 32,004,50 18,00 15,00 35,005,00 22,00 20,00 42,005,33 .210 24,00 1.00 22,00 .90 48,00 25,50 27,00 23,00 50,005,70 27,00 24,00 60,006,00 30.00 27,00 75,006,35 40,00 40,00 90,006,99 .275 50,00 2.00 50,00 2 100,00 48,00 75,00 75,00 150,008,40 80,00 80,00 160,009,00 100,00 100,00 175,009,52 .375 120,00 5.00 105,00 4 200,00 810,00 140,00 110,00 230,0011,10 150,00 115,00 250,0012,00 180,00 120,00 300,0012,70 .500 190,00 7.50 130,00 5 350,00 1414,30 230,00 180,00 390,0015,00 350,00 250,00 400,0015,90 .625 400,00 16 280,00 11 450,00 1819,05 .750 500,00 20 350,00 14 500,00 2020,63 .812 550,00 22 400,00 16 550,00 2225,40 1 600,00 24 425,00 17 600,00 24123

SEALING ELEMENTS12. O-ring Gland Design12 H. Gland Design for solid PTFEO-ringsPTFE has very poor elasticity. For thisreason it is recommended that PTFEO-rings are only used in static applicationswith an axial load.PTFE O-rings require much highercompression than elastomers to causea seal. Rigidity of the material makesPTFE O-rings relatively difficult toinstall. Heating them to approximately100°C (215°F) will make them slightlymore flexible and facilitate easierinstallation.Perfluorinated elastomers have similarchemical resistance and thermal propertieswhile offering the advantages of anelastomeric seal. In extreme or criticalapplications consideration of the useof a perfluorinated elastomer isrecommended.(See fig. 1-45, 1-46, 1-47).E= 10% to 20% of cross section (.070to .210 inch) (1,78 o 5,33 mm).Fig. 1-45 Fig. 1-46Fig. 1-47E= 10% to 15% of cross section (.210to .275 inch) (5,33 to 7 mm)Surface Finishgroove top and bottom :for liquidsX = 32 micro inches (0,8 µm Ra).for vacuum and gasesX = 16 micro inches (0,4 µm Ra).124

TECHNICAL DOCUMENTATION O-RINGS12. O-ring Gland Design12 I. O-ring Compression in Different Applications1. Pneumatic Outside Sealing (Piston Seals)3025,5Compression in%2520151059,58,5226,520175,515,5 Max.compression5Min.compression01,8 2,65 3,55 5,3 7.070 .103 .139 .210 .275cross section in mm / inches2. Pneumatic Inside Sealing (Rod Seals)201819,5161614,514Compression in%121086425413,5133 3 3Max.compressionMin.compression01,8 2,65 3,55 5,3 7.070 .103 .139 .210 .275cross section in mm / inches125

SEALING ELEMENTS12. O-ring Gland Design12 I. O-ring Compression in Different Applications3. Hydraulic Inside Sealing (Rod Seals)25202521Compression in%1510510,59819 17 16,577Max.compressionMin.compression01,8 2,65 3,55 5,3 7.070 .103 .139 .210 .275cross section in mm / inches4. Hydraulic Outside Sealing (Piston Seals)3028,525Compression in%20151051311,52423 20,519,59,5 9 9Max.compressionMin.compression01,8 2,65 3,55 5,3 7.070 .103 .139 .210 .275cross section in mm / inches126

TECHNICAL DOCUMENTATION O-RINGS12. O-ring Gland Design12 I. O-ring Compression in Different Applications5. Static Outside Sealing (Piston Seals)353030,5Compression in%2520151013,5132827,511,5262411 10,5Max.compressionMin.compression501,8 2,65 3,55 5,3 7.070 .103 .139 .210 .275cross section in mm / inches6. Static Inside Sealing (Rod Seals)3027Compression in%252015101125,510,524,510239,5 920,5 Max.compressionMin.compression501,8 2,65 3,55 5,3 7.070 .103 .139 .210 .275cross section in mm / inches127

SEALING ELEMENTS12. O-ring Gland Design12 J. Gland design for Kalrez® O-ringsKalrez® parts are manufactured fromexceptionally stable materials whichare serviceable in most chemicalenvironments up to 316°C (400°F)(depending on the specific compound).The purpose of this design guide is toprovide engineers with guidance in theselection of O-rings and the design ofgrooves for specific applications. Innon-aggressive media, at modestpressures and temperatures, there isusually little problem in developing agroove design or selecting an O-ring.In the case where the operating environmentis more aggressive and theapplication is more specialized designproblems may occur. The informationprovided is intended to facilitate thegroove/seal design process, especiallywith Kalrez® perfluoroelastomer parts.General considerations in sealselection or groove designFrom a knowledge of the temperatureand chemical media, a suitable sealingcompound can be selected. To designa groove, or select the best O-ring sizefor a given groove, however, theapplication environment must beconsidered in more detail.• What is the application temperaturerange?• Is the temperature cyclic?• What is the pressure differential anddirection?• If it is a vacuum application, where isthe vacuum applied?• Is the pressure or vacuum cyclic?• What is the compression/decompressionrate if the presssure is high(In excess of 80 bar)?• Is it a radial seal (piston rod/housingtype)?• Is it a face seal (flange type)?• Is it a standard groove section or is itnon-standard: crush-type, dovetailsection?• Is it a gasket application?• What is the chemical media to besealed?• If it is a replacement for a failure,what was the old seal?• What is the consequence of failure?• Is the application static or dynamic?• If it is dynamic, define the motion.• What are the groove dimensions andtolerances if it is in existence?128

TECHNICAL DOCUMENTATION O-RINGS12. O-ring Gland Design12 J. Gland design for Kalrez® O-ringsThe ratio of the O-ring CSD to thegroove depth will dictate the initialcompression. There are some generalrules for initial compression whenusing Kalrez® O-rings as given inthese tables.The condition in Table 1 represents the‘Normal Case’ where the operatingtemperatures are not particularlyaggressive and therefore the thermalexpansion will not be excessive.The scenario in Table 2 is the ‘HighTemperature’ region. The application isnow at a temperature in excess of thatat which thermal expansion becomessignificant. The volumetric thermalexpansion for Kalrez® is 0% at 21°Cand up to 20.42% at 316°C.Note that the effective squeeze willincrease at high temperature as aresult of this expansion.In the scenario in Table 3 the O-ringdimensions actually reduce as thesurrounding environment is changedfrom the assembly conditions to theoperating conditions.The reduction inO-ring size is a result of low temperatureshrinkage (may be regarded as areversal of expansion), or the directeffect of vacuum. In either ease, theinitial squeeze may decrease significantlyand it is necessary to compensatefor this in the design stage.Table 1 Initial Squeeze for Applications Running at 25° to 200°CCross section Initial Squeeze at 20°C (%)in mm Static Dynamic1,78 18 122,62 17,5 11,53,53 17 115,33 16,5 10,56,99 16 10Table 2 Initial Squeeze for Applications Running at > 200°CCross section Initial Squeeze at 20°C (%)in mm Static Dynamic1,78 16 122,62 15,5 11,53,53 15 115,33 14,5 10,56,99 14 10Table 3 Initial Squeeze for Applications Running at Low Temperature & VacuumCross section Initial Squeeze at 20°C (%)in mm Static Dynamic1,78 27 202,62 25 183,53 23 165,33 21 146,99 19 12In general, initial compression inexcess of 25% is undesirable since itwill cause over-compression at highertemperatures. In dynamic applications,high initial compression may causeproblems associated with excessivefriction.Temperature cycling applications mayrequire different squeezes.129

SEALING ELEMENTS12. O-ring Gland Design12 J. Gland design for Kalrez® O-ringsCompensating for thermal expansioneffectsAs stated before, one effect of thermalexpansion is to cause the initialsqueeze to increase. Another problemwhich may occur is over-filling of theO-ring groove as a result of the changein volume of the seal. In general, thegroove should be designed accordingto the following expression:Table 4 Linear & Volumetric Expansion of Kalrez ®Temperature Expansion (%)in °C Linear Volumetric21 0 038 0,41 1,2493 1,68 5,04149 2,96 8,90204 4,23 12,79260 5,50 16,56316 6,81 20,42Volume GROOVE = volume O-RING * (1 + C EXP + T EXP )* 1,2where:C EXP is the volumetric expansion due to chemical swell,T EXP is the volumetric thermal expansion.• Please contact the local ERIKS representative for additional informationAs a margin of safety, the grooveshould have a volume which is at least20% larger than the fully expandedO-ring. The thermal expansion data forKalrez® is given in Table 4.If the effects of thermal expansion arenot adequately considered, the O-ringwill fill the groove and attempt to burstout of it, resulting in extrusion andcatastrophic mechanical failure.Additional swell may occur due toexposure to chemical media. Chemicalswell data for Kalrez ® is given inAppendix 1 of this document for manygeneric chemical classes. For data onspecific chemicals and chemicalmixtures it is usually necessary toperform swell tests. Much of this datafrom DuPont Dow Elastomers isavailable from an ERIKS representative.Tolerance effects on groove designUsually, when designing grooves, astandard (BS or AS) O-ring groove willbe sufficient. However, in cases whereswell and expansion are likely to be highit is often necessary to design a specialgroove. O-rings of small ID and relativelylarge CSD often cause problems. In thesecases, the area bounded by the O-ringID is small and it does not take muchexpansion to cause stretch and grooveoverfill problems. It is necessary totake great care when designing andtolerancing grooves for these classesof O-ring. It is possible to check for thissort of problem at the groove designstage, by comparing the extra O-ringvolume due to swell with that availablefor swell, ensuring that the extremes ofgroove and seal tolerance are includedin the calculation.130

TECHNICAL DOCUMENTATION O-RINGS12. O-ring Gland Design12 J. Gland design for Kalrez® O-ringsExtrusion of O-rings in serviceExtrusion is a common mode of failureand is often the result of inadequateconsideration of expansion and swell.These problems are considered in theprevious section “Compensating forthermal expansion effects”. It may be,however, that the maximum clearancegap (as defined by tolerances onjoining surfaces) in the seal systemhas not been defined correctly.The required maximum clearance gapin a seal is a function of the compoundhardness and the pressure beingsealed. Table 5 gives the requiredmaximum clearance as a function ofpressure and hardness if back-up ringsare not used.As illustrated by this data, the softercompounds require closer tolerancesthan the harder compounds. It must beremembered that this data refers torelatively low temperature applications,up to 100°C. For high temperatureapplications it is necessary to considerthe effect of temperature on the compoundhardness. One rule of thumb isto assume a drop of hardness of about10° (Shore A) for every 100°C temperaturerise. Remember also that thisclearance data is based on totaldiametral clearance.It may not be feasible to machine tosuch close tolerances as required insome cases. Elastomers behaveessentially as highly viscous incompressiblefluids and tend to flow underthe application of pressure and temperature.Table 5 Maximum Clearance Gap vs Pressure/Hardness (mm)Maximum PressureHardness Shore Ain bar 60 70 80 907 0,7 0,79 0,84 0,8615 0,56 0,66 0,73 0,7920 0,43 0,56 0,66 0,7330 0,36 0,48 0,58 0,6835 0,28 0,40 0,51 0,6440 0,20 0,36 0,48 0,6150 0,15 0,31 0,43 0,5655 0,13 0,25 0,38 0,5360 0,10 0,23 0,36 0,5170 0,08 0,20 0,33 0,48140 0,05 0,15 0,28200 0,08 0,15275 0,02 0,10345 0,01 0,05410 0,04480 0,025550 0,02620 0,01700 0,00The use of back-up rings is recommendedif the pressure/temperature ofthe operating environment may causethe seal to flow. If, at a particular pressure,the maximum clearance gap isgreater than the value specified inTable 5, a back-up ring should beused.Back-up rings can be made fromTeflon® fluoropolymer resin fileld with25% glass, or another material that isresistant to the enviroment beingsealed. If a back-up ring is used, thegroove should be modified to provideincreased volume to avoid over fillingat high temperatures.131

SEALING ELEMENTS12. O-ring Gland Design12 J. Gland design for Kalrez® O-ringsCompression setCompression set is essentially a measureof a seal’s ability to retain sealingforce and, therefore, the capability tofunction. The degree of compressionset will depend on the operating environmentand, importantly, the durationof exposure. (It is typical in materialdatasheets to quote this property after70 hrs exposure, which is hardly representativeof long term performance. Infact, after an initial increase in compressionset, Kalrez® tends to retainits elastomer propezrties much longerthan conventional elastomers.Compression set causes most problemsin applications where thermal cycling isextreme. When continually exposed tovery high temperatures, even Kalrez®will take on a cross sectional formwhich is no longer circular; This maynot effect the seal integrity provided itis considered at the initial designstage. Kalrez® has a relatively slowelastic recovery rate. During thermalcycling, while the seal volume reducesdue to temperature drop in the coolingphase, the form of the seal, takenduring the high temperature phase,may be retained. At this time, thepotential loss of sealing force will be atits greatest and the system may beprone to leakage. Such set is usuallynot permanent. The elastic recoveryrate of Kalrez® increases rapidly withincreasing temperature and if the sealtemperature is raised, the normalcircular cross section will return - alongwith the sealing properties.It is evident, then, that the sequenceof loading of a system can greatlyinfluence the integrity of the seal.This is indicated by the followingexample loading sequence and theconsequences on seal integrity:Start▼Increase PressureRaise TemperatureStatic conditions (minutes)▼Reduce PressureLower TemperatureStatic conditions (minutes)▼INCREASE PRESSURE(POSSIBLE LEAKAGE)Raise TemperatureStatic conditions (minutes)... etc.Start▼Raise TemperatureIncrease PressureStatic conditions (minutes)▼Reduce PressureLower TemperatureStatic conditions (minutes)▼Raise TemperatureIncrease Pressure(integrity retained)Static conditions (minutes)... etc.Simply by reversing the loadingsequence seal leakage can be avoided.Compression set is often acceleratedby chemical attack - the total environmentmust be considered. Since thechemicals and chemical mixtures usedin industry are so numerous, it is notfeasible to either perform all testcombinations or to present here allavailable data.Installation of O-ringsA very important aspect of sealing isthe installation of the seal. There aremany ways to avoid damage to sealsurfaces during assembly. The use oflubricants can minimize surface damageand, by reducing the coefficient offriction between seal and gland, alloweasier sliding into position.Since Kalrez® is resistant to almost allchemical media, almost any lubricantmay be used. In fact, it is often easierto lubricate the seal with the chemicalit is going to be sealing. Fluorinatedoils such as Krytox® or powderedgraphite can also be used to aidassembly. It is normal to design sealingsystems such that the seal will nothave to encounter any sharp edgesduring assembly. However, if this is notpractical, it is simple to fabricate anassembly tool, often in the form of acone, to help get the seal over manysharp edges.The elongation at break for Kalrez®ranges from 120% to 170% dependingon the compound being used.Remember when assembling that it ispossible to break an O-ring by overstretchingit. Since part of the molecularstructure of Kalrez® is a materialhaving plastic properties, it is alsopossible to cause plastic deformationdue to overstressing. If you stretchKalrez® too much, particularly when itis cold, it will first flow as a plastic andthen fracture. For small CSD O-rings itis recommended that the stretch onassembly not exceed 20% to avoidthese problems.Remember that O-rings can be softenedby immersion in hot water prior toassembly.Take note: if the O-ring is rolled intoposition be sure to not leave a permanenttwist on the part. This may resultin overstressing and mechanical failureat high temperature.132