vdoc
Share Embed Flag
Download ePaper

vdoc

huu.bui
03.05.2023 Views

Chapter 11: E. Specialized Inspection Equipment 95• Analytical balances• Precision balances• Industrial scales• Bench scales• Counting scales• Mechanical balances• Spring scales• Jewelry scalesThere are several national and international organizations that establish standardsfor weights and measures such as:• National Institute for Standards and Technology (NIST) is the U.S.standards-defining authority. NIST Handbook 44 (Specifications,Tolerances, and Other Technical Requirements for Weighing and MeasuringDevices) sets forth the minimum requirements for standards usedprimarily to test commercial or legal-for-trade weighing devices forcompliance. NIST’s Special Publication 881, Guide for the Use of theInternational System of Units (SI), is also a good source.• The American Society for Testing and Materials (ASTM) is anorganization that establishes test standards for materials, products,systems, and services for a wide range of industries. ASTM developedthe E617-97 Standard (Specification for Laboratory Weights and PrecisionMass Standards) to cover various classes of weights and mass standardsused in laboratories.• The International Organization of Legal Metrology (OIML) is anintergovernmental treaty organization. OIML has two grades ofmembership: member states—these are countries who activelyparticipate in technical activities—and corresponding members—these are countries who join the OIML as observers. OIML wasestablished in 1955 in order to promote the global harmonizationof legal metrology procedures. It has since developed a worldwidetechnical structure, providing metrological guidelines for theelaboration of national and regional requirements concerningthe manufacture and use of measuring instruments for legalmetrology applications.• ISO (International Organization for Standardization) is the world’slargest developer and publisher of international standards. ISO isa network of the national standards institutes of 157 countries, onemember per country, with a central secretariat in Geneva, Switzerland,that coordinates the system.Part II.E.1

96 Part II: MetrologySurface MetrologyPart II.E.1The measurement of the difference between what a surface actually is and whatit is intended to be defines surface metrology. Surface measurement, however, isinvolved with the relationship of a surface on the workpiece to a reference thatis not actually on the workpiece. The most common aspect of surface metrology isthe measurement of surface roughness as an average deviation from a mean centerline (Bosch 1984).The quality of a surface finish is commonly specified along with linear andgeometric dimensions. This is becoming more common as product demandsincrease, because surface quality often determines how well a part performs.Heat-exchanger tubes transfer heat better when their surfaces are slightly roughrather than highly polished. Brake drums and clutch plates work best with somedegree of surface roughness. On the other hand, bearing surfaces for high-speedengines wear-in excessively and fail sooner if not highly polished, but still needcertain surface textures to hold lubricants. Thus there is a need to control all surfacefeatures, not just roughness alone.Surface Characteristics. The American National Standards Institute (ANSI) hasprovided a set of standard terms and symbols to define such basic surface characteristicsas profile, roughness, waviness, flaws, and lay. A profile is defined asthe contour of any section through a surface. Roughness refers to relatively finelyspaced surface irregularities such as might be produced by the action of a cuttingtool or grinding wheel during a machining operation. Waviness consists of thosesurface irregularities that are of greater spacing than roughness. Waviness may becaused by vibrations, machine or work deflections, warping, and so on. Flaws aresurface irregularities or imperfections that occur at infrequent intervals and at randomlocations. Such imperfections as scratches, ridges, holes, cracks, pits, checks,and so on, are included in this category. Lay is defined as the direction of the predominantsurface pattern. These characteristics are illustrated in Figure 11.1.Surface Quality Specifications. Standard symbols to specify surface quality areincluded in Figure 11.1c. Roughness is most commonly specified and is expressedin units of micrometers (mm), nanometers (nm), or microinches (min.). Accordingto ANSI/ASME B46.1-1985, the standard measure of surface roughness adopted bythe United States and approximately 25 countries around the world is the arithmeticaverage roughness, R a (formerly AA or CLA). R a represents the arithmeticaverage deviation of the ordinates of profile height increments of the surface fromthe centerline of that surface. An approximation of the average roughness may beobtained by:y y y yR = + + + ... +a+ na b c nwhereR a+ = approximation of the average roughnessy a . . . y n = absolute values of the surface profile coordinatesn = number of sample measurements

Chapter 11: E. Specialized Inspection Equipment 95

• Analytical balances

• Precision balances

• Industrial scales

• Bench scales

• Counting scales

• Mechanical balances

• Spring scales

• Jewelry scales

There are several national and international organizations that establish standards

for weights and measures such as:

• National Institute for Standards and Technology (NIST) is the U.S.

standards-defining authority. NIST Handbook 44 (Specifications,

Tolerances, and Other Technical Requirements for Weighing and Measuring

Devices) sets forth the minimum requirements for standards used

primarily to test commercial or legal-for-trade weighing devices for

compliance. NIST’s Special Publication 881, Guide for the Use of the

International System of Units (SI), is also a good source.

• The American Society for Testing and Materials (ASTM) is an

organization that establishes test standards for materials, products,

systems, and services for a wide range of industries. ASTM developed

the E617-97 Standard (Specification for Laboratory Weights and Precision

Mass Standards) to cover various classes of weights and mass standards

used in laboratories.

• The International Organization of Legal Metrology (OIML) is an

intergovernmental treaty organization. OIML has two grades of

membership: member states—these are countries who actively

participate in technical activities—and corresponding members—

these are countries who join the OIML as observers. OIML was

established in 1955 in order to promote the global harmonization

of legal metrology procedures. It has since developed a worldwide

technical structure, providing metrological guidelines for the

elaboration of national and regional requirements concerning

the manufacture and use of measuring instruments for legal

metrology applications.

• ISO (International Organization for Standardization) is the world’s

largest developer and publisher of international standards. ISO is

a network of the national standards institutes of 157 countries, one

member per country, with a central secretariat in Geneva, Switzerland,

that coordinates the system.

Part II.E.1

logo

products

Resources

Company

Terms of service
Privacy policy
Cookie policy
Cookie settings
Imprint
Change language
Made with love in Switzerland
© 2024 Yumpu.com all rights reserved

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!