ASTM_G_98_-_02_2009.pdf

Designation:G9802(Reapproved 2009)Standard Test Method forGalling Resistance of Materials1This standard is issued under the fixed designation G98;the number immediately following the designation indicates the year of originaladoption or,in the case of revision,the year of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscriptepsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method covers a laboratory test which ranksthe galling resistance of material couples.Most galling studieshave been conducted on bare metals and alloys;however,non-metallics,coatings,and surface modified alloys may alsobe evaluated by this test method.1.2 This test method is not designed for evaluating thegalling resistance of material couples sliding under lubricatedconditions because galling usually will not occur under lubri-cated sliding conditions using this test method.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 establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2G40 Terminology Relating to Wear and ErosionG83 Test Method for Wear Testing with a Crossed-CylinderApparatus(Withdrawn 2005)33.Terminology3.1 Definitions:3.1.1 gallinga form of surface damage arising betweensliding solids,distinguished by macroscopic,usually localized,roughening and creation of protrusions above the originalsurface;it often includes plastic flow or material transfer,orboth.3.1.1.1 DiscussionThe onset of galling usually requiresthat the contact pressure exceeds some threshold value.Gallingcan be a precursor to seizing or loss of function.The identifi-cation of galling is somewhat subjective,and complete agree-ment does not exist,even among experts.G403.2 Definitions of Terms Specific to This Standard:3.2.1 threshold galling stressthe stress midway betweenthe highest non-galled stress and the lowest galled stress asdetermined by this test method.4.Summary of Test Method4.1 This test method uses available laboratory equipmentcapable of maintaining a constant,compressive load betweentwo flat specimens,such as hydraulic or screw feed compres-sion testing machines.One specimen is slowly rotated onerevolution 360 relative to the other specimen.The surfaces areexamined for galling after sliding.The criterion for whethergalling occurs is the appearance of the specimens based onunassisted visual examination.If the specimens have notgalled,a new set of specimens is tested at increased load.Thisprocess is continued until galling occurs.4.2 Appropriate load intervals are chosen to determine thethreshold galling stress within an acceptable range.4.3 The higher the threshold galling stressing,the moregalling resistant is the test couple.5.Significance and Use5.1 This test method is designed to rank material couples intheir resistance to the failure mode caused by galling and notmerely to classify the surface appearance of sliding surfaces.5.2 This test method should be considered when damaged(galled)surfaces render components non-serviceable.Experi-ence has shown that galling is most prevalent in slidingsystems that are slow moving and operate intermittently.Thegalling and seizure of threaded components is a classicexample which this test method most closely simulates.5.3 Other galling-prone examples include:sealing surfacesof value trim which may leak excessively due to galling;andpump wear rings that may function ineffectively due to galling.5.4 If the equipment continues to operate satisfactorily andloses dimension gradually,then mechanical wear should beevaluated by a different test such as the crossed cylinder TestMethod(see Test Method G83).Chain belt pins and bushingsare examples of this type of problem.1This test method is under the jurisdiction of ASTM Committee G02 on Wearand Erosion and is the direct responsibility of Subcommittee G02.40 on Non-Abrasive Wear.Current edition approved Oct.1,2009.Published February 2010.Originallyapproved in 1989.Last previous edition approved in 2002 as G9802.DOI:10.1520/G0098-02R09.2For 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.3The last approved version of this historical standard is referenced onwww.astm.org.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 5.5 This test method should not be used for quantitative orfinal design purposes since many environmental factors influ-ence the galling performance of materials in service.Lubrica-tion,alignment,stiffness and geometry are only some of thefactors that can affect how materials perform.This test methodhas proven valuable in scre