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外文翻译--砂型铸造.doc

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外文翻译--砂型铸造.doc

附录附录1SandCastingThefirststageintheproductionofsandcastingsmustbethedesignandmanufactureofasuitablepattern.Castingpatternsaregenerallymadefromhardwordandthepatternhastobemadelargerthanthefinishedcastingsizetoallowfortheshrinkagethattakesplaceduringsolidificationandcooling.Theextentofthisshrinkagevarieswiththetypeofmetaloralloytobecast.Forallbutthesimplestshapesthepatternwillbemadeintwoormorepiecestofacilitatemoulding.Ifahollowcastingistobemadethepatterndesignwillincludeextensionpiecessothatspacestoacceptthesandcorearemouldedintosand.Theseadditionalspacesinthemouldaretermedcoreprints.Sandmouldsfortheproductionofsmallandmediumsizedcastingsaremadeinamouldingbox.Themouldismadeintwoormorepartsinorderthatthepatternmayberemoved.Thedraghalfofthemouldboxisplacedonaflatfirmboardandthedraghalfofthepatternplacedinposition.Facingsandissprinkledoverthepatternandthenthemouldboxisfilledwithmouldingsand.Thesandisrammedfirmlyaroundthepattern.Thisprocessoffillingandrammingmaybedonebyhandbutmouldproductionisautomatedinalargefoundrywiththemouldboxesmovingalongaconveyor,firstlytobefilledwithsandfromhoppersandthentopassundermechanicalhammersforramming.Whenrammingofthesandiscomplete,excesssandisremovedtoleaveasmoothsurfaceflushwiththeedgesofthemouldingbox.Thecompleteddragisnowturnedoverandtheupper,orcope,portionofthemouldingboxpositionedoverit.Thecopehalfofthepatternisplacedinposition,correctalignmentbeingensuredbymeansofsmalldowelpins.Patternsforthenecessaryfeeder,runnerandrisersarealsoplacedsoastogiveanevendistributionofmetalintothemouldcavity.Therisersshouldcoincidewiththehighestreadilyescapefromthemould.Thesizesofrisersshouldbesuchthatthemetalinthemdoesnotfreezetoorapidly.Animportantfunctionofariseristoactasreservoirofliquidmetaltofeedsolidificationwithinthemould.Athincoatingofdrypartingsandissprinkledintomouldatthisstage.Thisistopreventthecopeanddragstickingtogetherwhenthecopehalfismoulded.Thecopeisnowfilledwithmouldingsandandthisisrammedfirmlyintoshapeinthesamemannerasinthemakingofthedrag.Aftertherammingofsandinthecopeiscompletedthetwohalvesofthemouldingboxarecarefullyseparated.Atthisstageventingofthemouldingboxarecarefullyseparated.Atthisstageventingofthemouldcanbedone,ifnecessary,toincreasethepermeabilityofthemould.Afterventingthepatternsarecarefullyremovedfrombothcopeanddrag,andagateorgatesarecarefullycuttoconnecttherunnerchannelwiththemaincavity.Gatesshouldbesitedtoallowforentryintomouldwithaminimumofturbulence.Anyloosesandisgentlyblownawayandifacoreistobeuseditthecopeuponthedraganditisthenreadyforuse.Liquidmetalispouredsmoothlyintothemouldviathefeeder.Pouringceaseswhenliquidmetalappearsatthetopoftherisersandthefeederchannelisalsofull.Whenthemetalthathasbeenpouredintoasandmouldhasfullysolidifiedthemouldisbrokenandcastingisremoved.Thecastingstillhastherunnerandrisersattachedtoitandtherewillbesandadheringtoportionsofthesurface.Runnersandrisersarecutoffandreturnedtothemeltingfurnace.Sandcoresarebrokenandadherentsandiscleanedfromthesurfacebyvibrationorbysandblastingwithdrysand.Anyfinsormetalflashformedatmouldpartinglinesareremovedbygrindingandthecastingsarethenreadyforinspection.EngineAnengineisadevicethatusestheenergyinafueltodowork.Theenergyinthechemicalsofthefuelisturnedintoheatenergy.Theheatisthenusedtomovethemetalpartsofamachine.Therearemanykindsoffuel.Mostenginesusegasoline,oil,kerosene,coal,orcoke.Theheatthatcomesfromburningthefuelmakesagasexpand.Thisexpandgasdrivespistonsorturbineblades.Thepistonsorturbinesturnshafts.Theturningshaftsmovegearsandotherwheels.Weusetheserotatingwheelsandshaftstomoveautomobiles,airplanes,andothertransport.Wecanalsousethemforpumping,drilling,digging,andothersuchactivities.Earlyenginesburnedcoalorwoodtoheatwater.Thesteamwasusedtodrivesteamengine.Untilthemiddleofthiscentury,mostlocomotiveswerepoweredbysteam.Atthebeginningofthecentury,evensomeautomobileswererunonsteam.Westillusesteamengines,butmostofthemarebeingreplacedbymoreefficientengines.Todaywehavepowerfulgasolineanddieselenginestoworkforus.Thesteamengineisanexternalcombustionengine.Thismeansthatfueliscombustion,orburned,outsidethecylinderthatproducespower.SincetheinventionofthesteamenginebyJamesWattin1769s,steamengineshadagreateffectontheindustrialrevolutionintheeighteenthcentury.Untilthemiddleofthetwentiethcentury,mostlocomotiveswerepoweredbysteam.Attheendofthecentury,evensomeautomobileswererunonsteam.Todaymostofthefunctionsofsteamenginehavebeentakenoverbyinternalcombustionenginesfueledbygasolineanddieseloil.However,therearemanysteamenginesinuseatsea.Steamisalsousedtogenerateelectricity.Thekindofsteamenginethatisusedtodaydoesnothavecylinders.Itisgenerallyasteamturbine.ThesteamturbinewasinventedbySirCharlesParsons.Steamturbinescanhandlesteamathigherpressuresthanpistonenginescan,andtheyaremorecompactthanpistonenginesofsimilarpower.ThegasolineengineTheengineofmostautomobilesandsmallvehicleusegasolineasfuel.Thegasolineengineisacombustionengine.Thefuelisburnedincombustionburningchambersinsidetheengine.Thecombustionchambersareplacedatoneendofthecylinders.Pistonsmoveupanddowninthecylinders.Theyarepushedbythehotgasesfromtheburningfuel.Whenthefuelismixedwithairitburnssoquicklythatitexplodes.Thecombustionchambersandcylinderapartlikeabomb,theexplosionsimplykickshandagainsttheheadofthepiston.Itpushesitasfarasitcan.Eachmovementofapistonupordowninitscylinderiscalledastroke.Mostgasolineenginesworkonafourstrokecycle.Thismeansthateachpistongoesupanddowntwiceforeachexplosion.Thatmakesfourmovementorstrokes.Thiscycleofeventsisrepeatedoverandoveragain.Onthefirstdownstroke,thepistonmovestothelowestpartofthecylinder.Amixtureofgasolinedropletsandairisdrawnintothecylinderaboveit.Nowthepistonmovesupagain.Thisisitssecondstroke.Itsqueezesthemixtureintoasmallspace.Anelectriclightsthemixture,anditexplodes.Thepistonisforcedownagainforitsthirdstroke.Thisiscalledthepowerstroke.Forthefourthstroke,thepistonmovestothetopagain.Thistimeitpushestheburntgasesoutofthecylinder.Thegasesleavetheengineasexhaustfumes.Thefirstenginethatusedthefourstrokecyclewasmadeinabout1876.ItwasdesignedbyaGermanengineer,AugustOtto.Heusedcoalgas,notgasoline.ThefirstenginestoburngasolineweredevelopedbyKarlBenzandGottlieb.Thesetwomenwerefamousasautomobilepioneers.Apistonsimplygoingupanddowncannotpushanautomobilealong.Itsmovementmustbechangedtoaturningmovement.Todothis,acrankshaftisused.Eachpistonoftheengineislinkedtopartofthecrankshaft.Eachpushitgivesmakestheshaftturn.Thespinningshaftpassesthepowerontotheautomobilestransmissionsystem.Itusuallydoesthisthroughaheavyflywheel.Thetransmissionsystemtransmitspowertotheclutchandtothepropellershaft,throughagearbox.Thepropellershaftdrivestheroadwheelsbymeansofaxles.Tokeepanautomobileenginegoing,thereneedtobeseveralsystems.Theremustbeafuelsystem.Thishastosupplygasolinetotheenginecylindersintherightamounts.Ithasalsotomixitwiththerightamountofair,sothatitwillexplodeproperly.Theremustbeanignitionsystem.Thishastoprovidesparkstoignitetheexplosivemixturefatexactlytherighttime.Therehastobeacoolingsystem,otherwisetheenginewouldoverheat.Thelubricationsystemmustkeepallthemovingpartsoiledandmovingfreely.Toomuchfrictioncauseswearofthemetalandmakestheengineoverheat.TheengineunitGasolineenginehastwobasicparts.Theyarecalledthecylinderheadandthecylinderblock.Thecylinderblockismachinedfromsolidmetal.Themetalsusuallycastsidethecylinderblocksarethecylinders.Thewallsofthecylindershavetobeveryaccuratelymade,andarehighlypolished.Thepistonsthatmoveupanddowninthecylindersmustbeaccuratelymade,too.Theyhavespringybandsofmetalaroundthemtopresstightagainstthecylinderwallsandstopgasesleaking.Thebandsarecalledpistonrings.Theyareoftenmadeofaluminumalloyforstrengthandlightness.Anenginemayhaveanynumberofcylinders.Theymaybearrangedinaline,orinoppositepairs.TheyareoftenarrangedinaVshape.Inmanyairplaneswithpitonengines,thecylindersarearrangedinaringaroundthecrankshaft.Thelowerpartofthecylinderblockiscalledthecrankcase.Thisiswherethecrankshaftlies.Thecrankshaftislinkedtoeachpitonbyaconnectingrod.Thecrankshaftismadeinasinglepiece.Itmustbetoughandaccuratelymachined.Itmayspinasmanyas6000timesaminute.Itchangesupanddownmotion.Itdoesthisbymeansofcranks,oneforeachpiston.Thecranksaresetatdifferentanglesroundtheshaft.Eachpistongivesapushtoitscrankduringitspowerstroke.Duringtheotherthreestrokes,thecrankpushesthepistonup,downandupagain.Theheavyflywheelisboltedtooneendofthecrankshaft.Itkeepstheshaftturningsmoothlybetweenthepowerstrokes.Strongmainbearingssupportthecrankshaftinitscase.Thecylinderheadisboltedtothecylinderblock.Insideitarethecombustionchambers.Eachcombustionchamberisaspaceaboveapistoninsideacylinder.Thisiswheretheexplosionofthemixtureoffuelandairtakesplace.Asparkplugissetintothetopofthechamber.Eachchamberhasapairofvalves.Thereisaninletvalvetoallowthefuelandairmixtureintothechamber.Theothervalveisanoutletorexhaustvalve.Throughthispasstheburntgasesaftertheexplosion.Thevalvesareopenedandclosedbypushrodsandsprings.Thepushrodsaremovedupanddownbylinkswiththecrankshaft.Thelinkageisthroughaturningshaftcalledthecamshaft.Tocarrywatertocooltheengine,therearepassagesinthemetalofthecylinderheadandcylinderblock.Oilpassesthroughotherpassages.Betweenthecylinderheadandblockisagasket.Thisisathinplateofmetalthatactsasaseal.Itisputinwhenthepartsoftheengineareboltedtogether.Itisoftenmadeofcopper.ThefuelsystemFuelsystemoftheenginesuppliesthegasolinetobeburnt.Thegasolineisstoredinalargetank.Inapowerfulcar,thetankholdsmanygallonsoffuel.Thetankisplacedwellawayfromtheengine,toreducetheriskoffire.Thegasolineispumpedthroughafuelline.Thepumpmaybedrivenbylinkswiththeenginecamshaft.Sometimesithasitsownelectricmotor.Beforethegasolinereachesthecylinders,itmustbemixedwithair.Thefuelline

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