ASTM_B_277_-_95_2012.pdf

Designation:B27795(Reapproved 2012)Standard Test Method forHardness of Electrical Contact Materials1This standard is issued under the fixed designation B277;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 test method covers the determination of the hard-ness of metallic materials used for electrical contacts.Rockwell,Rockwell superficial,Brinell,and microhardnesstests are included,along with information on the limitationsand use of these tests.1.2 The values stated in inch-pound units are to be regardedas standard.The values given in parentheses are mathematicalconversions to SI units that are provided for information onlyand are not considered standard.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 familiarwill 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:2E10 Test Method for Brinell Hardness of Metallic MaterialsE18 Test Methods for Rockwell Hardness of Metallic Ma-terialsE384 Test Method for Knoop and Vickers Hardness ofMaterials3.Significance and Use3.1 The Rockwell hardness and Rockwell superficial testsare useful when the test specimens are sufficiently thick(inrelation to the indentor load)to ensure that the results are notaffected by the flow of metal on the surface of the anvil.On asolid piece the flow of metal on the under surface may bedetected by a bulge or marking.On composite pieces where thecontact materials are attached to backings of a differentmaterial,the thickness limitations imposed for a solid pieceshall apply to the contact material portion of such compositepieces.NOTE1As a matter of information,it may be stated that tests on finesilver showed that on annealed samples having a Rockwell 15T hardnessof 27,the readings were not affected on thicknesses116in.(1.6 mm)orover.On thicknesses of132in.(0.8 mm)Rockwell 15T scale readings of72 and higher were not affected.3.2 The microhardness test is of questionable significancewhen the metallic phases in a material are so large that theindentation does not represent an accurate average hardness.Sintered contact materials usually contain segregates differinggreatly in hardness from the matrix hardness and may destroythe validity of microhardness readings.3.3 Other aspects of significance and use shall be asdescribed in the particular ASTM test method used,as listed inSection 2.4.Sampling4.1 Prepare test samples in accordance with the methodselected from those listed in Section 2 and,where applicable,supplemented with the requirements in 5.3.5.Procedure5.1 Determine the hardness in accordance with one of thefollowing:5.1.1 Test Methods E18 subject to the additional require-ments and precautions in 3.1,5.2,and 5.3.5.1.2 Test Method E384 subject to the additional require-ments and precautions in 3.2 and 5.4.5.1.3 Test Method E10.5.2 When employing the Rockwell superficial hardness test(Test Methods E18)the specimen hardness shall be within therange of the selected scale,as shown in Table 1.5.3 When using the Rockwell or Rockwell superficial hard-ness tests on contacts which are in rivet form,the shanks ofsuch rivets may have insufficient cross-sectional area to sup-port the test pressure.In such cases the shank shall be removedto form a flat surface for placement against the anvil.Thewelding projection on contacts designed for assembly byprojection welding shall also be removed.Some rivet contacts1This test method is under the jurisdiction of ASTM Committee B02 onNonferrous Metals and Alloys and is the direct responsibility of SubcommitteeB02.11 on Electrical Contact Test Methods.Current edition approved May 1,2012.Published May 2012.Originallyapproved in 1952.Last previous edition approved in 2006 as B277 95(2006).DOI:10.1520/B0277-95R12.2For 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 are too small for the use of Rockwell superficial hardnesstesting,in which case the microhardness tests may be used.5.4 When employing the microhardness test(Test MethodE384)the minimum indentor load shall be 100 gf,except forspecimens that have a thickness or diameter less than 0.005 in.(0.13 mm)in which case a 25 or 50 gf load shall be used.5.4