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1-4BearingSelection(3)MaterialsTheinnerring,outerring,andballmaterialsareimportantelementsofthebearing,andtheirselectionsignificantlyaffectsbearingperformance.Ultra-highpressureofroughly1,000MPaormoreisrepeatedlyappliedtothebearinginnerring/outerringandballcontactparts.Becauselonglifeisrequiredevenunderthisrepeatedstress,thematerialtype,cleanness,hardness,andsoonareextremelyimportantelements.MinebeaMitsumimainlyuseshigh-carbonchromiumbearingsteelandhighlycorrosion-resistantmartensiticstainlesssteelasracewayringandballmaterials.Forhigh-carbonchromiumbearingsteel,high-qualityvacuumdegassedhigh-carbonchromiumbearingsteel(JISG4805SUJ2,SUJ2MD,AISI/SAE52100)anditsequivalentsareused;quenchinghardnessenablesexcellentloadresistance,life,andnoiseproperties.Forstainlesssteel,MinebeaMitsumi'soriginalDD400isused.DD400hashigherquenchinghardnessthanSUS440C,withexcellentnoisepropertiesandloadresistance;withregardtocorrosionresistance,testsbasedonASTM-A380haveshownresultsequivalenttothoseofSUS440C.Aswell,wehavedevelopedtheGigaProtection®Seriesforapplicationsrequiringextremecorrosionresistance,suchasexposuretoseawaterorchemicalliquids;comparedtoDD400,extremelyhighcorrosionresistanceisavailable.ConsultMinebeaMitsumiwithquestionsabouttheGigaProtection®Series.Inordertorespondtodemandsofrecentyearsforlonglifeandlownoise,MinebeaMitsumiprovidesbearingsusingceramic(siliconnitride).Whileusingtheconventionalhigh-carbonchromiumbearingsteelorstainlesssteelfortheracewayring,theuseofceramicfortheballenablesabalanceofgoodnoiseperformanceandlonglife.Aswell,thealmosttotalnon-conductivitypeculiartosiliconnitrideisalsoeffectiveasameasureagainstelectriccorrosiongeneratedbyconductionwithinthebearing.30
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