>> P.49
A46ABCDEFGHIJKLMentryofharmfulforeignsubstances,suchasdirt,dustandwater.Forthisreason,sealingdevicesmustalwaysworkeffectivelytosealandpreventagainstdustpenetrationunderalloperatingconditions.Also,whenselectingasuitablesealingmethod,itisneces-sarytoconsidersuchfactorsasthetypeoflubricant,peripheralspeedoftheseal,operatingtemperature,shafteccentricity,sealfriction,etc.aswellaseaseofassemblyanddisassembly.Sealingmethodsareofthenon-contactandcontacttypes,anditisnecessarytoselecttheappropriatetypedependingontheapplication.Non-contacttypesealingmethodTherearemanymethodsofnon-contacttypesealing,includingtheuseofoilgrooves,flingersandlabyrinths,whichutilizethecentrifugalforceandnar-rowgaps.Sincetheydonotmakedirectcontactwiththeshaftorhousing,itisunnecessarytoconsiderfrictionandwear,andthenon-contactsealingmethodissuitableforhighspeedrotationandhighoperatingtempera-tures.However,becauseofgaps,thismethodisnotalwayssufficientinpreventingoilleakageanddustentrywhenthemachineisnotinoperation.1OilgrooveOilgroovesareprovidedoneithertheshaftorhousingbore,oronbothformoreeffectivesealing(SeeFig.14.).Theclearancebetweentheshaftandthehous-ingboreshouldbeassmallaspossible,andtheval-uesshowninTable30aregenerallyused,takingintoconsiderationerrorsinmachiningandassembly,shaftdeformation,etc.Threeormoregroovesaremadewithawidthof3〜5mmandadepthof4〜5mm.Ifthegroovesarefilledwithgrease,itwillbemoreeffec-tivefordustprevention.AsshowninFig.15,helicalgroovesaresuitableforhorizontalshaftswhichhaveafixeddirectionofrota-tion.Rightorlefthandedgroovesareusedaccordingtothedirectionofrotation,andtheyareusedforoillubricationnormallyinconjunctionwithasuitableanti-dustdevice.SealingToobtainthebestperformanceofrollingbearings,itisnecessarytopreventleakageoflubricantandtheFig.14(1)(2)(3)Table29Filletreliefdimensionsforgroundshaftsandhousings unit:mm rsminSmallestpermissiblesinglechamferdimensionFilletreliefdimensionstrgsb11.11.522.134567.50.20.30.40.50.50.50.50.60.60.61.31.522.52.53456722.43.2444.75.97.48.610hrsminbtrgsTable28Largestpermissiblesinglecornerradiusofshaftsandhousings rasmaxrsminSmallestpermissiblesinglechamferdimension0.10.150.20.30.40.611.11.522.12.53450.10.150.20.30.40.6111.52222.534rasmaxLargestpermissiblesinglecornerradiusofshaftsandhousingsunit:mm HousingShaftrsminrsminrasmaxrasmaxrsminrsmin1N=0.102kgf=0.2248lbs.1mm=0.03937inch
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