1、毕 业 设 计（论 文）外 文 参 考 资 料 及 译 文译文题目： Friction And Lubrication 摩擦与润滑 学生姓名： 学 号： 专 业： 所在学院： 指导教师： 职 称： 20xx年 2月 27日Friction And LubricationInmanyoftheproblemthusfar,thestudenthasbeenaskedtodisregardorneglectfriction.Actually,frictionispresenttosomedegreewhenevertwopartsareincontactandmoveoneachother.The
2、termfrictionreferstotheresistanceoftwoormorepartstomovement. Frictionisharmfulorvaluabledependinguponwhereitoccurs.frictionisnecessaryforfasteningdevicessuchasscrewsandrivetswhichdependuponfrictiontoholdthefastenerandthepartstogether. Thefrictionofmovingpartsinamachineisharmfulbecauseitreducesthemec
3、hanicaladvantageofthedevice.Theheatproducedbyfrictionislostenergybecausenoworktakesplace.Also,greaterpowerisrequiredtoovercometheincreasedfriction.Heatisdestructiveinthatitcausesexpansion.Expansionmaycauseabearingorslidingsurfacetofittighter.Therearethreetypesoffrictionwhichmustbeovercomeinmovingpar
4、ts:(1)starting,(2)sliding,and(3)rolling.Startingfrictionisthefrictionbetweentwosolidsthattendtoresistmovement.Whentwopartsareatastateofrest,thesurfaceirregularitiesofbothpartstendtointerlockandformawedgingaction.Toproducemotionintheseparts,thewedgeshapedpeaksandvalleysofthestationarysurfacesmustbema
5、detoslideoutandovereachother.Therougherthetwosurfaces,thegreaterisstartingfrictionresultingfromtheirmovement.Sincethereisusuallynofixedpatternbetweenthepeaksandvalleysoftwomatingparts,theirregularitiesdonotinterlockoncethepartsareinmotion.Thefrictionofthetwosurfacesisknownasslidingfriction.Asshownin
6、figure,startingfrictionisalwaysgreaterthanslidingfriction.Rollingfrictionoccurswhenrollerdevcesaresubjectedtotremendousstresswhichcausethepartstochangeshapeordeform.Undertheseconditions,thematerialinfrontofarollertendstopileupandforcestheobjecttorollslightlyuphill.Thischangingofshape,knownasdeformat
7、ion,causesamovementofmolecules.Asaresult,heatisproducedfromtheaddedenergyrequiredtokeepthepartsturningandovercomefriction. Thefrictioncausedbythewedgingactionofsurfaceirregularitiescanbeovercomepartlybytheprecisionmachiningofthesurfaces.However,eventhesesmoothsurfacesmayrequiretheuseofasubstancebetw
8、eenthemtoreducethefrictionstillmore.Thissubstanceisusuallyalubricantwhichprovidesafine,thinoilfilm.Thefilmkeepsthesurfacesapartandpreventsthecohesiveforcesofthesurfacesfromcominginclosecontactandproducingheat.Anotherwaytoreducefrictionistousedifferentmaterialsforthebearingsurfacesandrotatingparts.Th
9、isexplainswhybronzebearings,softalloys,andcopperandtiniolitebearingsareusedwithbothsoftandhardenedsteelshaft.Theiolitebearingisporous.Thus,whenthebearingisdippedinoil,capillaryactioncarriestheoilthroughthespacesofthebearing.Thistypeofbearingcarriesitsownlubricanttothepointswherethepressuresarethegre
10、atest.Movingpartsarelubricatedtoreducefriction,wear,andheat.Themostcommonlyusedlubricantsareoils,greases,andgraphitecompounds.Eachlubricantservesadifferentpurpose.Theconditionsunderwhichtwomovingsurfacesaretoworkdeterminethetypeoflubricanttobeusedandthesystemselectedfordistributingthelubricant. Onsl
11、owmovingpartswithaminimumofpressure,anoilgrooveisusuallysufficienttodistributetherequiredquantityoflubricanttothesurfacesmovingoneachother. Asecondcommonmethodoflubricationisthesplashsysteminwhichpartsmovinginareservoiroflubricantpickupsufficientoilwhichisthendistributedtoallmovingpartsduringeachcyc
12、le.Thissystemisusedinthecrankcaseoflawn-mowerenginestolubricatethecrankshaft,connectingrod,andpartsofthepiston. Alubricationsystemcommonlyusedinindustrialplantsisthepressuresystem.Inthissystem,apumponamachinecarriesthelubricanttoallofthebearingsurfacesataconstantrateandquantity. Therearenumerousothe
13、rsystemsoflubricationandaconsiderablenumberoflubricantsavailableforanygivensetofoperatingconditions.Modernindustrypaysgreaterattentiontotheuseoftheproperlubricantsthanatprevioustimebecauseoftheincreasedspeeds,pressures,andoperatingdemandsplacedonequipmentanddevices. Althoughoneofthemainpurposesoflubricationisreducefriction,anysubstance-liquid,solid
