>> P.61
SuitablepreloadamountforafocusonnoiseperformanceMinebeaMitsumirecommendsthatwhentheloadonthebearingsispredominantlypreload,thesuitablepreloadsettingforlifeemphasizingnoiseperformanceshouldbecalculatedthroughaveragesurfacepressure.Whenpreload(Fa)isappliedtothebearing,theballandracewaygroovecontactpartsundergoelasticdeformation,creatinganellipticalcontactsurface.Thevalueperballoftheverticalcomponentofforcegeneratedatthecontactpartsoftheballandracewaygroove(rollingelementload:Q)dividedbythecontactellipsesurfacearea(S)iscalledaveragesurfacepressure.Fig.12-1showsthatwhentheratioofthecircumferenceisπ,themajoraxisradiusisa,andtheminoraxisradiusisb,thecontactellipse(S)generatedinthecontactpartsoftheballandracewaygrooveisS=πab(mm2).Aswell,whentheaveragesurfacepressureisP,P=Q/S(MPa).Thepreloadamountwhenfocusingonnoiselifemustbeminimized;thecalculationmethodandsampleapplicationsusingsimplecalculationfromthedynamicratingloadCrasaguidelineareshownbelow.Noiselifeguideline10,000hoursup5000~10,000hoursSimplecalculationmethodbasedondynamicratingloadCrSampleapplications0.005Cr~0.010Cr0.010Cr~0.015CrFanmotors,airconditioners,ventilationfans,etc.ConceptofloadSettingforpreloadandloadatorbelowaveragesurfacepressure1000MPa(maximumsurfacepressure1500MPa)adoptstheregioninwhichfatiguewillnotbegeneratedinthebearingmaterialregulatedbythefatiguelimitloadCuusedinthemodifiedratinglifeLnmregulatedbyISO281:2007andJISB1518:2013.Aswell,forhigh-carbonchromiumbearingsteel,averagesurfacepressureexceeding2700MPawillentertheplasticdeformationarea.However,thebearinglifeismoresignificantlyaffectedbyelementssuchasrotationspeed,operatingenvironment,lubricantstatusandsoonincomparisontoloadconditions;therefore,consultMinebeaMitsumifordetailsonthesuitablepreloadamountandloadinconsiderationoftheseconditions.61
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