>> P.56
A53Table36ConsistencyandoperatingconditionsofgreaseNLGIconsistencynumberCombinedconsistencyApplication01234385〜355340〜310295〜265250〜220205〜175Forcentralizedlubrication,ForoscillatingmotionForgeneraluseForgeneraluse,ForhightemperatureForsealingwithgreaseTable37BearingseriesandrequiredviscosityoflubricatingoilBearingseriesNeedlerollerbearingsRollerbearingsCrossedrollerbearingsThrustneedlerollerbearingsThrustrollerbearingsKinematicviscosityatoperatingtemperatures13mm2/sormore20mm2/sormore32mm2/sormore1BaseoilPetroleumlubricatingoilisusuallyusedasthebaseoil.Asthelubricatingperformanceofgreasedependsmainlyonthatofbaseoil,theviscosityofthebaseoilisanimportantproperty.Ingeneral,lowviscosityissuitableforlight-loadandhigh-speedrotations,andhighviscosityforheavy-loadandlow-speedrotations.Syntheticlubricantsofthediesterorsiliconseriesareusedinsteadoflubricantsofthepetroleumseriesinconsiderationofthepourpointandhightemperaturestability.2ThickenerAsshowninTable35,metalsoapbasesaremostlyusedasthickeners.Inparticular,Na-soapiswater-solubleandemulsifieseasily,anditcannotbeusedindamporwetareas.Thetypeofthickenerandthepourpointofgreasehaveacloserelationship.Ingeneral,thehigherthepourpoint,thehigherthemax-imumusabletemperatureofgrease.However,evenwhenthegreaseusesathickenerhavingahighpourpoint,itsupperoperatingtemperaturelimitislowifitsbaseoilhaslowheatresistance.3ConsistencyThisrepresentsthehardnessgradeofgrease.Greasebecomesharderinproportiontotheamountofthickenerifthesamethickenerisused.Immediatelyaftergreasehasbeenstirred(usually60times),adepressionisformedinthegreaseinaspecifiedtimeusingaspecifiedcone.Theconsisten-cy(combinedconsistency)isexpressedbythevalueofdepthofdepression(mm)multipliedby10.Thisvaluegivesanestimateofthefluidityduringoperationwithagreatervalueforsoftergrease.Table36showstheconsistencynumberofgreaseandtherelationshipbetweentheconsistencyandoperatingconditions.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.4AdditivesAdditivesincludevarioustypesofsubstances,whichareaddedtogreaseinsmallquantitiestoimproveitscharacteristics.Forexample,whenabearingiskept
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