SOUND ENGINEERING FROM - Loctite.ph

More documents

Recommendations

Info

Assembling Speakers with Loctite ® AdhesivesPole Piece to Magnet to Top PlateThe three essential components bonded in the magnetassembly are the magnet itself (most commonlyceramic ferrite rings) and either a T-yoke, whichincludes a pole piece, or a plate and pole combination,and a top plate, or washer, made of steel. The T-yoke(referred to as the back plate, end plate or pole andplate) is bonded onto one face of the magnet, and thetop plate (referred to as the washer or front plate) isbonded to the other face.To achieve consistent bonding performance, matingsurfaces must be clean. Steel parts may be contaminatedwith plating residues, or lubricants, and the natureof the problem varies with the production process. Aby-product of the Blanchard grinding process thatmakes magnet faces smooth and parallel, is a coating offine dust which should be cleaned from the matingsurface before bonding, using a damp cloth. If any otherresidues are suspected, the mating surfaces of the partsshould be cleaned with isopropyl alcohol or acetone.Bonding the magnet assembly together is oftenaccomplished with two-part epoxy adhesives, especiallyin Asia, where the adhesive is widely known as"A/B glue". When mixed properly at a 1:1 ratio, the resultingadhesive is typically gray. A combination of poor orabsent mixing technique (running two beads over eachother), and assembly line workers failing to rotate theparts while pressing them together, is a recipe for disaster.This approach requires that the operator dispensethe correct ratio by eye, which may be difficult withcomponents of differing viscosities. An emerging trend isthe use of static mix nozzles or equipment to obtaina more consistent, reliable method.Cyanoacrylates have been used for magnet and steelassembly in small and specialized drivers, and althoughthey can be very fast, their long term bond strengthto ceramic materials remains questionable. The successof the method suggests that in low stress applications,a rubber toughened cyanoacrylate may provide thedesired performance. Occasionally, cyanoacrylatesare used to tack parts together quickly, in combinationwith structural acrylics to insure the needed long termdurability.Current thinking on magnet to steel bonding runsin favor of structural acrylic adhesives, with severalvariations formulated for different surfaces, gap fillcapability and fixture times. These structural adhesivesare economical, fast, strong, easily dispensed, and createthin bondlines to minimize magnetic energy losses.Loctite ® structural acrylics develop good handlingstrength in 30 to 90 seconds, which allows the magnetassembly to be magnetized within 5 minutes of assembly.This speed of fixture also allows the magnetassembly to be placed briefly into a clamp, where it canbe pressed to create a very thin and uniform bondline.This extra step can be beneficial in high performancedrivers and compression drivers, where tolerances mustbe very tight. Structural acrylics are used with primers,and the latest solventless primers for dichromatedsurfaces can bond to steel that has been dichromated,or plated with clear, black or yellow zinc.8
Ideally, the adhesive should not be applied over apainted surface, as the bond between the paint and thesubstrate can limit overall bond strength. Activators foracrylics or any other adhesives, should be applied onlyonto the steel parts (at room temperature), so that thecarrier solvents in the activator can evaporate entirelybefore assembly. Since ceramic magnets are quiteporous, the activator applied to them can wick deepbelow the surface. So while appearing to be dry on thesurface and ready for bonding, the magnet may stillbe loaded with solvents. Trapped solvents maysignificantly slow the cure, and can weaken the ultimatebond strength.A note about the use of Ferrofluids. Ferrofluids arecoloidal suspensions of magnetic particles in an oil-likecarrier liquid, and provide improved thermal transmissionfrom the voice coil to the surrounding steel parts.Since the fluid is magnetic, it remains in the gap, completelyenveloping the voice coil, and any fluid migration(by wicking or splashing) onto nearby bondlines mustbe avoided. Ferrofluidics Corporation (603-883-9800) hasevaluated loudspeaker assembly adhesives for compatibilitywith their fluids, and has approved many Loctite ®adhesives as fully compatible.The Loctite adhesives typically used in speakerassembly do not effect, nor are effected by, incidentalcontact with Ferrofluids, once fully cured. However,uncured acrylic adhesives are known to have catastrophiceffects upon Ferrofluids if they come into contact,causing the magnetic fluid viscosity to rise dramatically.Since Loctite ® structural acrylics are anaerobic(curing in the absence of oxygen), any excess adhesiveoutside the bondline will not cure, and will remain hazardousto Ferrofluid.Other Types of MagnetsAlong with tremendous magnetic density, Neodymium-iron-boron(NdFeB) magnets have introducedanother unwelcome feature, rapid corrosion. The qualityof the protective coatings can be a significant problemwith these magnets, depending on their source.Neodymium magnets are currently available witha variety of surface treatments such as: 1) vapordeposited aluminum, 2) electro-plated nickel, 3) electrodepositedepoxy paint, and 4) plasma depositedtitanium-nitride. Each of these coatings requires specialconsideration. Neodymium magnets should be inspectedclosely before assembly operations begin, and thosethat show oxidation should be discarded. Bonding toalready oxidized surfaces will neither create a strongbond, nor inhibit further corrosion.Neodymium, samarium-cobalt and alnico magnetsgenerally use a "pot and pole-tip" topology, rather thantop plate and pole plate. The steel parts involve thesame finishes and the adhesive recommendations arethe same as for ceramics.Assembling Speakers with Loctite ® AdhesivesRecommended products for the Pole Piece to Magnet to Top Plate Assembly:Loctite ® SpeedBonder Adhesives 324, 326 or Loctite ® Structural Adhesives 332, 392 or 3270.See detailed Product Information on SpeedBonder and Structural Adhesives on pages 18 and 19.9
Page 1 and 2: S O U N D E N G I N E E R I N G F R
Page 3: • Loctite Speaker Applications .
Page 6 and 7: Speaker Applications Recommended Pr
Page 10 and 11: Assembling Speakers with Loctite ®
Page 18 and 19: SPEEDBONDER and Structural Adhesive
Page 20 and 21: Activators for SPEEDBONDER and Stru
Page 22 and 23: Loctite ® Product, Ordering and Te
Page 24 and 25: Accelerators and Primers for Cyanoa
Page 27 and 28: TECHNICAL PRODUCT INFORMATIONProduc
Page 29 and 30: TECHNICAL PRODUCT INFORMATIONProduc
Page 31 and 32: Loctite offers a complete line of d
Page 33 and 34: Light Cure SystemsMedium Intensity
Page 35 and 36: SurroundDust CapGasketConeSpiderLea

SOUND ENGINEERING FROM - Loctite.ph

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?