ASTM_B_772_-_97_2012.pdf

Designation:B77297(Reapproved 2012)Standard Guide forSpecifying the Chemical Compositions for ElectricalContact Materials(Arcing and Nonarcing)1This standard is issued under the fixed designation B772;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This guide provides suggested methods for users andproducers of electrical contact materials to specify the chemi-cal compositions of these materials.1.2 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to become familiarwith all hazards including those identified in the appropriateMaterial Safety Data Sheet(MSDS)for this product/materialas provided by the manufacturer,to establish appropriatesafety and health practices,and determine the applicability ofregulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2E1282 Guide for Specifying the Chemical Compositions andSelecting Sampling Practices and Quantitative AnalysisMethods for Metals,Ores,and Related Materials3.Significance and Use3.1 This guide should be used by committees or individualsin specifying the chemical composition of electrical contactmaterials.4.Procedure4.1 For Basic Alloy Element(s)and Component(s):4.1.1 Specify the numerical limits of the elements as fol-lows:4.1.1.1 Major fractions of the alloy,4.1.1.2 Tighter tolerances,or4.1.1.3 Higher unit cost(s)or combination thereof.4.1.2 One of these elements may be chosen to be specifiedby“report by difference.”List the minimum value of thiselement in a pair of parentheses before the clause“report bydifference.”Select this element or component according to oneor more of the following considerations:4.1.2.1 Least precious,4.1.2.2 Widest tolerance,and4.1.2.3 Requiring the least precise or most costly method toanalyze.4.2 For Impurities:4.2.1 Specify only the tolerance limits of the elementscommonly occurring with the major elements(for example,copper in silver);and the tolerance limits of the detrimentalelements(as recognized by the industry)which may be aresidue after fabrication(for example,sodium in Ag-CdOmaterial by the coprecipitation method).4.2.2 Specify the tolerance limits for total impurities of allthe impurity elements.4.3 Place the following note under the Table of ChemicalCompositions(see Table 1 for example)in the text of eachspecification:NOTE1Analysis is regularly made for the elements for which specificlimits are listed.If,however,the presence of“other”elements is suspectedor indicated in the course of routine analysis,further analysis shall bemade to determine that the total of these“other”elements and the listedimpurities is not in excess of the total impurities limit.4.4 State under the section of Chemical Composition in thetext of each specification a clause as follows:4.4.1 These specification limits do not preclude the possiblepresence of other unnamed elements,impurities,or additives.Analysis shall be regularly made only for the minor elementslisted in the table.However if a user knows of elements thatmight be detrimental to their application or has other reasonsfor requiring analysis for specific elements,then agreementbetween manufacturer and purchaser for both limits andmethods of analysis should be required for elements notspecified.4.5 Additional guidelines for specifying the chemical com-positions and selecting sampling practices are covered in GuideE1282.1This guide is under the jurisdiction of ASTM Committee B02 on NonferrousMetals and Alloys and is the direct responsibility of Subcommittee B02.05 onPrecious Metals and Electrical Contact Materials.Current edition approved Nov.1,2012.Published November 2012.Originallyapproved in 1987.Last previous edition approved in 2008 as B772 97(2008).DOI:10.1520/B0772-97R12.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 4.6 Example(For a hypothetical alloy):75A-24.5B-0.5Cwhere:A=precious metal,B=base metal,C=base metal,andd,e,f,g=typical or detrimental impurities.5.Keywords5.1 analysis;chemical composition;contacts;electrical con-tact materials;impurities;tolerance limitsASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard.Users of this standard are expressly advised that determination of the validity of any such patent rights,and the riskof infringement of such rights,are entirely their own responsibility.This standard is subject t