王宝帅机械类外文文献翻译毕业设计.docx

王宝帅机械类外文文献翻译毕业设计.docx

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王宝帅机械类外文文献翻译毕业设计

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沈阳工业大学工程学院

毕业设计（论文）外文翻译

毕业设计（论文）题目：

工具盒盖注塑模具设计

外文题目：

Friction,LubricationofBearing

译文题目：

轴承的摩擦与润滑

系（部）：

机械系

专业班级：

机械设计制造及其自动化0801

学生姓名：

王宝帅

指导教师：

魏晓波

2010年10月15日

外文文献原文：

Friction,LubricationofBearing

Inmanyoftheproblemthusfar,thestudentaskedtodisregardorneglectfriction.Actually,frictionispresenttosomedegreewhenevertwopartsareincontactandmoveoneachother.Thetermfrictionreferstotheresistanceoftwoormorepartstomovement.

Frictioniswhereitoccurs.frictionisnecessaryforfasteningdevicessuchasscrewsandrivetswhichdependuponfrictiontoisnecessary.

Thefrictionofmovingpartsinamachineisislostenergybecausenoworktakesplace.Also,greaterpowerisrequiredtoovercometheincreasedfriction.Heatisdestructiveinthatitcausesexpansion.Expansionmaycauseabearingorslidingsurfacetofittighter.Ifagreatenoughpressurebuildsupbecausemadefromlowtemperaturematerialsmaymelt.

Therearethreetypesoffrictionwhichmustbeovercomeinmovingparts:

（1）starting,

（2）sliding,and（3）rolling.Startingfrictionisthefrictionbetweentwosolidsthattendtoresistmovement.Whentwopartsareatastateofrest,thesurfaceirregularitiesofbothpartstendtointerlockandformawedgingaction.Toproducemotionintheseparts,thewedge-shapedpeaksandvalleysofthestationarysurfacesmustbemadetoslideoutandovereachother.Therougherthetwosurfaces,thegreaterisstartingfrictionresultingfromtheirmovement.

Sincethereisusuallynofixedpatternbetweenthepeaksandvalleysoftwomatingparts,theirregularitiesdonotinterlockoncethepartsareinmotionbutslideovereachother.Thefrictionofthetwosurfacesisknownasslidingfriction.Asshowninfigure,startingfrictionisalwaysgreaterthanslidingfriction.

Rollingfrictionoccurswhenrollerdevcesaresubjectedtotremendousstresswhichcausethepartstochangeshapeordeform.Undertheseconditions,thematerialinfrontofarollertendstopileupandforcestheobjecttorollslightlyuphill.Thischangingofshape,knownasdeformation,causesamovementofmolecules.Asaresult,.

Thefrictioncausedbythewedgingactionofsurfaceirregularitiescanbeovercomepartlybytheprecisionmachiningofthesurfaces.However,eventhesesmoothsurfacesmayrequiretheuseofasubstancebetweenthemtoreducethefrictionstillmore.Thissubstanceisusuallyalubricantwhichprovidesafine,thinoilfilm.Thefilmkeepsthesurfacesapartandpreventsthecohesiveforcesofthesurfacesfromcominginclosecontactandproducingistousedifferentmaterialsforthebearingsurfacesandrotatingparts.Thisexplainswhybronzebearings,softalloys,andcopperandtiniolitebearingsareusedwithbothsoftandthebearingisdippedinoil,capillaryactioncarriestheoilthroughthespacesofthebearing.Thistypeofbearingcarriesitsownlubricanttothepointswherethepressuresarethegreatest.

Movingpartsarelubricatedtoreducefriction,wear,andslowmovingpartswithaminimumofpressure,anoilgrooveisusuallysufficienttodistributetherequiredquantityoflubricanttothesurfacesmovingoneachother.

Asecondcommonmethodoflubricationisthesplashsysteminwhichpartsmovinginareservoiroflubricantpickupsufficientoilwhichisthendistributedtoallmovingpartsduringeachcycle.Thissystemisusedinthecrankcaseoflawn-mowerenginestolubricatethecrankshaft,connectingrod,andpartsofthepiston.

Alubricationsystemcommonlyusedinindustrialplantsisthepressuresystem.Inthissystem,apumponamachinecarriesthelubricanttoallofthebearingsurfacesataconstantrateandquantity.

Therearenumerousothersystemsoflubricationandaconsiderablenumberoflubricantsavailableforanygivensetofoperatingconditions.Modernindustrypaysgreaterattentiontotheuseoftheproperlubricantsthanatprevioustimebecauseoftheincreasedspeeds,pressures,andoperatingdemandsplacedonequipmentanddevices.

Althoughoneofthemainpurposesoflubricationisreducefriction,anysubstance-liquid,solid,orgaseous-capableofcontrollingfrictionandwearbetweenslidingsurfacescanbeclassedasalubricant.

Varietiesoflubrication

Unlubricatedsliding.Metalsthatcarefullytreatedtoremoveallforeignmaterialsseizeandweldtooneanotherwhenslidtogether.Intheabsenceofsuchaandthetendencytoseizebutusuallyresultinseverewear;thisiscalled“unlubricated”ordrysliding.

Fluid-filmlubrication.Interposingafluidfilmthatcompletelyseparatestheslidingsurfacesresultsinfluid-filmlubrication.Thefluidmaybeintroducedintentionallyastheoilinthemainbearingofanautomobile,orunintentionally,asinthecaseofwaterbetweenasmoothtubertireandawetpavement.Althoughthefluidisusuallyaliquidsuchasoil,water,andawiderangeofothermaterials,itmayalsobeagas.Thegasmostcommonlyemployedisair.

Boundarylubrication.Aconditionthatliesbetweenunlubricatedslidingandfluid-filmlubricationisreferredtoasboundarylubrication,alsodefinedasthatconditionoflubricationinwhichthefrictionbetweensurfacesisdeterminedbythepropertiesofthesurfacesandpropertiesofthelubricantotherthanviscosity.Boundarylubricationencompassesasignificantportionoflubricationphenomenaandcommonlyoccursduringthestartingandstoppingoffmachines.

Solidlubrication.Solidsuchasgraphiteandmolybdenumdisulfidearewidelyusedwhennormallubricantsdonotpossesssufficientresistancetoloadortemperatureextremes.Butlubricantsneednottakeonlysuchfamiliarformsasfats,powders,andgases;evensomemetalscommonlyserveasslidingsurfacesinsomesophisticatedmachines.

Functionoflubricants

Althoughalubricantprimarilycontrolsfrictionandordinarilydoesperformnumerousotherfunctions,whichvarywiththeapplicationandusuallyareinterrelated.

Frictioncontrol.Theamountandcharacterofthelubricantmadeavailabletoslidingsurfacesthefrictionthatisencountered.Forexample,disregardingsuchrelatedfactorsasalonebetweenthesamesurfaceswithonlubricant.Underfluid-filmconditions,frictionisencountered.Inagreatrangeofviscositiesandthuscansatisfyabroadspectrumoffunctionalrequirements.Underboundarylubricationconditions,theeffectofviscosityonfrictionbecomeslesssignificantthanthechemicalnatureofthelubricant.

Wearcontrol.wearoccursonlubricatedsurfacesbyabrasion,corrosion,andsolid-to-solidcontactwearbyprovidingafilmthatincreasesthedistancebetweentheslidingsurfaces,therebylesseningthedamagebyabrasivecontaminantsandsurfaceasperities.

Temperaturecontrol.Lubricantsassistincontrollingcorrosionofthesurfacesthemselvesistwofold.Whenmachineryisidle,thelubricantactsasapreservative.Whenmachineryisinuse,thelubricantcontrolscorrosionbycoatinglubricatedpartswithaprotectivefilmthatmaycontainadditivestoneutralizecorrosivematerials.Theabilityofalubricanttocontrolcorrosionisdirectlyrelatlytothethicknessofthelubricantfilmremainingonthemetalsurfacesandthechermicalcompositionofthelubricant.

Otherfunctions

Lubricationarefrequentlyusedforpurposesotherthanthereductionoffriction.Someoftheseapplicationsaredescribedbelow.

Powertransmission.Lubricantsarewidelyemployedasfluidtransmissiondevices.

Insulation.Inspecializedapplicationssuchastransformersandswitchgear,lubricantswithenergytransferringdevicessuchasshockabsorbersandaroundmachinepartssuchasgearsthataresubjectedtoofformingasealtoretainlubricantsortoexcludecontaminants.

Theobjectoflubricationistoreducefriction,wear,andinsertedbetweenthemovingsurfaces,accomplishesthesepurposes.Mostlubricantsareliquids（suchasmineraloil,siliconefluids,andwater）,buttheymaybesolidforuseindrybearings,greasesforuseinrollingelementbearing,orgases（suchasair）foruseingasbearings.Thephysicalandchemicalinteractionbetweenthelubricantandlubricatingsurfacesmustbeunderstoodinordertoprovidethemachineelementswithsatisfactorylife.

Theunderstandingofboundarylubricationisnormallyattributedtofilmsadheringtosurfaceswereoftensufficienttoassistrelativesliding.Theyconcludedthatundersuchcircumstancesthechemicalcompositionoffluidisimportant,andtheyintroducedtheterm“boundarylubrication”.Boundarylubricationisattheoppositeendofthespectrumfrom.

Fivedistinctofformsoflubricationthatmaybedefined:

（a）meansthattheload-carryingsurfacesofthebearingareseparatedbyarelativelythickfilmoflubricant,soastopreventmetalcontact,andthatthestabilitythusobtainedcanbeexplainedbythelawsofthelubricantunderpressure,thoughitmaybe;butitdoesrequiretheexistenceofanadequatesupplyatalltimes.Thefilmpressureiscreatedbythemovingsurfacesitselfpullingthelubricantunderpressure,thoughitmaybe.Thefilmpressureiscreatedbythemovingsurfacetocreatthepressurenecessarytoseparatethesurfacesagainsttheloadonthebearing.isalsocalledfullfilm,orfluidlubrication.

Hydrostaticlubricationisobtainedbyintroducingthelubricant,whichissometimeairorwater,intotheload-bearingareaatapressure,motionofonesurfacerelativetoanotherisnotrequired.

Elasohydrodynamiclubricationisthephenomenonthatoccurswhenalubricantisintroducedbetweensurfaceswhichareinrollingcontact,suchasmatinggearsorrollingbearin