>> P.56
runningforlongperiodsoftime,itstemperaturerises.Thisresultsinoxidationofthelubricantandformationofoxides,whichleadtocorrosionofthebearing.Thus,whenabearingistobeoperatedforlongperi-odsoftimewithoutregreasing,antioxidantsareadded.Inaddition,greasecontainingextremepres-sureadditivesissuitableforuseinplacesthataresubjectedtoheavyloads.5MiscibilityofdifferentgreasesInprinciple,itisdesirabletousegreaseofthesamebrand.However,whenthemixingofdifferentgreasesisunavoidable,greaseswiththesametypeofthick-enerandwithasimilartypeofbaseoilshouldbeused.Itshouldbenotedthatifdifferenttypesofgreasearemixed,theymayinteractwitheachotherandthecon-sistencywillbecomesofterthanthatfortheindividualgreases.LubricatingoilForrollingbearings,refinedmineraloilorsyntheticoilisused.Toimproveitsproperties,antioxidantaddi-tives,extremepressureadditivesanddetergentaddi-tivesareaddedasrequired.Whenselectinglubricatingoil,itisimportanttoselectoilwhichhasadequateviscosityunderoperatingtem-peratures.Iftheviscosityistoolow,theformationoftheoilfilmwillbeinsufficient,causingabnormalwearandseizure.Ontheotherhand,iftheviscosityistoohigh,itwillgenerateexcessiveheatorincreasepowerlossduetoviscousresistance.Asageneralstandard,oilhavinghigherviscosityshouldbeusedforheavierloadsandoilhavinglowerviscosityshouldbeusedforhigherrotationalspeeds.Underconditionsofnormaluseforvariousbearings,thevaluesofviscosityshowninTable37willbeaguideline.TherelationshipbetweenviscosityandtemperaturecanbeobtainedfromFig.25.Also,Table38showsexamplesofselectinglubricatingoilaccordingtotheconditionsofbearinguse.Table37BearingseriesandrequiredviscosityoflubricatingoilBearingseriesNeedlerollerbearingsRollerbearingsKinematicviscosityatoperatingtemperatures13mm2/sormoreCrossedrollerbearings20mm2/sormoreThrustneedlerollerbearingsThrustrollerbearings32mm2/sormorethethebaselubricatingoilisusuallyusedas1BaseoilPetroleumoil.Aslubricatingperformanceofgreasedependsmainlyonthatofbaseoil,theviscosityofthebaseoilisanimportantproperty.Ingeneral,lowviscosityissuitablelight-loadandhigh-speedrotations,andhighviscosityforheavy-loadandlow-speedrotations.Syntheticlubricantsofthediesterorsiliconseriesareusedthepetroleumseriesinconsiderationofthepourpointandhightemperaturestability.lubricantsofinsteadofforthickeners.Inparticular,Na-soap2ThickenerAsshowninTable35,metalsoapbasesaremostlyusedasiswater-solubleandemulsifieseasily,anditcannotbeusedinthickenerandthedamporwetareas.pourpointofgreasehaveacloserelationship.Ingeneral,thehigherthepourpoint,thehigherthemax-imumusabletemperatureofgrease.However,evenwhenthegreaseusesathickenerhavingahighpourpoint,itsupperoperatingtemperaturelimitislowifitsbaseoilhaslowheatresistance.typeofTheisformedrepresentsthehardnessgradeofgrease.inproportiontotheamount3ConsistencyThisGreasebecomesharderofthickenerifthesamethickenerisused.Immediatelyaftergreasehasbeenstirred(usually60times),adepressioninaspecifiedtimeusingaspecifiedcone.Theconsisten-cy(combinedconsistency)isexpressedbythevalueofdepthofdepression(mm)multipliedby10.Thisvaluegivesanestimateofthefluidityduringoperationwithagreatervalueforsoftergrease.Table36showstheconsistencynumberofgreaseandtheconsistencyandoperatingconditions.therelationshipbetweenthegreasein385〜355340〜310295〜265250〜220205〜175Forcentralizedlubrication,ForoscillatingmotionForgeneraluseForgeneraluse,ForhightemperatureForsealingwithgrease01234Table36ConsistencyandoperatingconditionsofgreaseNLGIconsistencynumberCombinedconsistencyApplication4AdditivesAdditivesincludevarioustypesofsubstances,whichareaddedtogreaseinsmallquantitiestoimproveitscharacteristics.Forexample,whenabearingiskeptA53
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