ASTM_B_576_-_94_2016.pdf

Designation:B57694(Reapproved 2016)Standard Guide forArc Erosion Testing of Electrical Contact Materials1This standard is issued under the fixed designation B576;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 covers the major variables which affect therate of arc erosion of electrical contact materials and serves asa guide in developing more detailed specifications for arc-erosion tests.1.2 Arc erosion testing involves some vaporization of ma-terial.It is the responsibility of the user to become familiarwith all hazards including those identified in the appropriateMaterial Safety Data Sheet for the material being tested.1.3 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 appropriateSafety Data Sheet(SDS)for this product/material as providedby the manufacturer,to establish appropriate safety and healthpractices,and determine the applicability of regulatory limi-tations prior to use.2.Significance and Use2.1 The significance of the variables set forth in this guidewas proved by various laboratories using several test systemsat test currents ranging from 100 to 35 000 A.These variableswill be significant for any case where voltage and current aresufficient to produce arcing.3.Major Variables3.1 Shape,Area,and Thickness:3.1.1 The area,shape,and thickness of the contact affect theerosion rates.As an example of shape effects,the radius of thespherical crown affects the erosion in at least two ways:(1)itchanges the effective diameter of the contact and,(2)it affectsthe manner in which the arc moves about on the surface of thecontact.A contact with a hemispherical crown presents nosharp edges that would result in different amounts of erosionproducts for a given amount of arcing and aids in the control ofthe arc when operating in air and other gases.3.1.2 The contacts may be given a type of normal shape andsurface roughness by a number of arcing operations prior torecording the contact loss.There may be a difference in theeffect of shape and diameter for different environments.3.1.3 Contact mounting,attachment,and bond integrity canaffect the arc erosion of materials and should be specified.3.2 Contact Velocity and Maximum Arc LengthThe veloc-ity of separation and the maximum arc length affect the erosionrate and,therefore,should be specified in formulating a test.3.3 Contact Orientation:3.3.1 The orientation of the contacts with respect to theearths gravitational field may affect the erosion rate and,therefore,should be specified.For example,the mating planesof the contacts might be vertical or horizontal.3.3.2 If the contacts mating planes are horizontal and adirect test current is used,the specifications should statewhether the anode or cathode is in the upper position.3.4 Environment:3.4.1 The type,pressure,temperature,and humidity of thegas atmosphere or the type,pressure,and temperature of thesurrounding oil,affect the erosion rate and should be specified.3.4.2 The erosion rate in air may be quite different than thatunder oil.3.5 Arcing Current:3.5.1 An increase in arc current will cause an increase in thearc-erosion rate per coulomb of arcing,and thus it must bespecified.3.5.2 It follows then that the wave form of the arc current isimportant and source voltage and load current should bespecified.3.6 Arcing TimeThe time duration of individual arcs on anelectrical contact affects the erosion rate and thus it should bespecified.3.7 Closing Force,Speed,and BounceThe severity of thedamage caused by the closing arcs depends on the closingspeed,closing force,and the number of bounces.All thesethree can be measured.The arc erosion that occurs because ofclosing arcs caused by contact bounce can be duplicated byproperly specifying other items in this list with particularemphasis on contact velocity and maximum arc length.Un-wanted closing arcs can be effectively eliminated from a1This 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 May 1,2016.Published May 2016.Originallyapproved in 1973.Last previous edition approved in 2010 as B576 94(2010).DOI:10.1520/B0576-94R16.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 contact test device,for example,by causing the test current toflow through the contacts after the contacts have been closed.3.8 Contact Body TemperatureThe mating contacts of acontact pair might have different temperatures and both shouldbe measured o