建筑.docx
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建筑.docx
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建筑
附:
英语材料翻译
Material1
MachineElements
Howeversimple,anymachineisacombinationofindividualcomponentsgenerallyreferredtoasmachineelementsorparts.Thus,ifamachineiscompletelydismantled,acollectionofsimplepartsremainssuchasnuts,bolts,springsgears,camsandshaftsthebuildingblockofallmachinery.Amachineelementis,therefore,asingleunitdesignedtoperformaspecificfunctionandcapableofcombiningwithotherelements.Sometimescertainelementsareassociatedinpairs,suchasnutsandboltsorkeysandshafts.Inoterinstances,agroupofelementsiscombinedtoformasubassembly,suchasbearings,couplings,andclutches.
Themostcommonexampleofamachineelementisagear,which,fundamentally,isacombinationofwheelandthelevertoformatoothedwheel.Therotationofthisgearonahuborshaftdrivesothergearsthatmayrotatefasterorslower,dependinguponthenumberofteethonthebasicwheels.
Otherfundamentalmachineelementshaveevolvedfromwheelandlever.Awheelmusthaveashaftonwhichitmayrotate.Thewheelisfastenedtotheshaftswithcouplings.Theshaftmustrestinbearings,maybeturnedbyapulleywithabeltorachainconnectingittoapulleyonasecondshaft.Thesupportingstructuremaybeassembledwithboltsorrivetsorbywelding.Properapplicationofthesemachineelementsdependsuponknowledgeoftheforceonthestructureandthestrengthofthematerialsemployed.
Theindivedaulreliabilityofmachineelementsbecomesthebasisforestimatingtheoveralllifeexpectancyofacompletemachine.
Manymachineelementarethoroughlystandardized.Testingandpracticalexperiencehaveestablishedthemostsuitabledimensionsforcommonstructuaralandmechanicalparts.Throughstandardization,uniformityofpracticeandresultingeconomicsareobtained.Notallmachinepartsinusearestandardized,however.Intheautomotiveindustryonlyfasteners,bearings,bushings,chains,andbeltsarestandardized.Crankshaftsandconnectingrodsarenotstandardized.
Gears
Gearsarevitalfactorsinmachinery:
Oneorthefirstmechanisminventedusinggearswastheclock.Infact,aclockislittlemorethanatrainofgears.Considerablestudyandresearchhavebeenmadeongearsnrecentyearsbecauseoftheirwideuseunderexactingconditions.Theyhavetotransmitheavierloadsandrunathigherspeedsthaneverbefore.Theengineersandthemachinistsallconsidergearingtheprimeelementinnearlyallclassesofmachinery.
SpurGears
Spurgearsareusedtotransmitpowerandrotarymotionbetweenparallelshafts.AscanbeseeninFig.Theteethaercutparalleltotheaxisoftheshaftonwhichthegearsaremouted.Thesmalleroftwogearsinmeshiscalledthepinion.andthelargeriscustomarilydesignatedasthegear.Inmostapplicationsthepinionisthedrivingelementwhereasthedrivenelement.
HelicalGears
Figshowshelicalgearsinmesh.Thepairshownismountedonparallel,themostcommonsituationforwhichhelicalgearsareused.However,helicalgearsaresometimesusedfornon-parallel,non-intersectingshaftapplications.Whenusedinthismanner,theyareknownascrossedhelicalgears.Figillustratesapairofcrossedhelicalgearsinmesh.Spurgearsareusedforlowspeedapplicationandthosesituationswherenoisecontrolisnotaproblem.Useofhelicalgearsisindicatedwhenapplicationinvolveshighspeeds,largepowertransmission,orwherenoiseabatementisimportant.Whereasspurgearshavetheirteethcutparalleltothegearaxis,helicalgearteetharecutintheformofhelicesmakingaconstantanglewithrespecttothegearaxis.
WormGears
Althoughcrossedhelicalgearscanbeusedforapplicationsinvolvingnon-parallel,non-intersectingshafts,theyareratherlimitedintheirloadtransmissioncapacith.Inaddition,largespeedratios,ontheordrofsay200to1couldnotbereasonablyachievedinonereductionbecauseofthesizeofgearrequired.Forexample,ifthesmallergearhad20teeth,thelargerwouldhavetohave4000teeth.Amuchmorefeasiblesolutiontotheproblemwouldbetheuseofawormgearset.
AwormgearsetsuchasshowninFigconsistsoftheworm,whichisverysimilartoascrew,andthewormwheel,whichisahelicalgear.Theshaftsuponwhichthewormandthegeararemountedareusually90degreesapart.Oneoftheadvantagesassociatedwiththeuseofwormgearsisthatthetoothengagementoccurswithouttheshockprevalentinothergeartypes.Infactthemeshingoftwoteethoccurswithaslindingactionwhich,whileresultinginveryquietoperation,mayproduceoverheating.
BevelGear
Themostimportanttypeofgearusedtotransmitpowerbetweennon-parallelorintersectingshaftsisthebevelgear.Bevelgearscanperhapsbebestdescribedasbeingconicalgears,becausetheyarecutonconicalblanks.Therearethreeprimarytypesofbevelgears:
straightbevelgears,spiralbevelgearsandHypoidbevelgears.
Material2
Technologiesofmetal-cutting
1.DrillingandBoring
Drilling,abasicmachineshoptechniqueconsistsofcuttingaroundholebymeansofarotatingdrill.boring,ontheotherhand,involvesthefinishingofaholealreadydrilledorcoredbymeansofarotating,offsetandsingle-pointtool.Fig.8-1showsthedrillingmachine.
2.milling
Millingmeansmachiningapieceofmetalbybringitintocontactwitharotatingcuttingtoolwhichhasmultiplecuttingedges.Therearemanytypesofmillingmachinesdesignedforvariouskindsofwork.forexample,verticalmillingmachineandhorizontalmillingmachineandNCmillingmachine,Fig.8-2showshorizontalmillingmachine.
3.Grinding
Grindingconsistsofshapingapieceofworkbybringingitintocontactwitharotatingbrasivewheel.Grindingcanbeperformedonflat,cylindricaloreveninternalsurfacesbyemployingspecializedmachinetools,whicharerefettedtoasgrindingmachines.Theprocessisoftenusedforthefinalfinishingtoclosedimensionsofapartthat;hasbeenheat-treatedtomakeitveryhard.Fig.8-3showsthegrindingmachine.
4.turning
Thelather,astheturningmachineiscommonlycalled,isthefatherofallmachinetolls.Thepieceofmetaltobemachineisrotatedandthecuttingtoolisadvancedagainstit.Theprocessofturningareoftencompletedbymeansofaturretandanenginelathe.
5.Planingandshaping
Planingmetalwithamachinetoolisaprocesssomewhatsimilartoplanningwoodwithacarpenter’shandplane,Theessentialdifferentliesinthefactthatmachinetoolisgreatinsize,thatitisnotportable,andthatthecuttingtoolremainsinaffixedpositionwhiletheworkismovedbackandforthbeneathit.
Plannersareusuallylargepieceofequipment;Ashaperdifferformaplanner.Inshaping,theworkpieceisheldstationaryandthecuttingtravelsbackandforth.Fig.8-4showstheplanningmachine
Material3
KindsofSteel
Therearetwogeneralkindsofsteel:
carbonsteelandalloysteel.Carbonsteelcontainsonlyironandcarbon,whileallousteelcontainssomeother“alloyingelements”suchasnickel,chromium,manganese,molybdenum,tungsten,vanadium,etc.
Carbonsteels
Lowcarbonsteelcontainingfrom0.05to0.15percentcarbon,thissteelisalsoknownasmachinesteel.
Mediumcarbonsteelcontainingfrom0.15to0.60percentcarbon.
Highcarbonsteelcontaingingfrom0.6to1.50percentcarbon,thissteelissometimescalled“toolsteel”.
Alloysteels
Specialalloysteel,suchasnickel,chromiumsteel.
High-speedsteelalsoknownasself-hardeningsteel.
Thepropertiesofcarbonsteelsdependonlyonthepercentageofcarbontheycontain.Lowcarbonsteelsareverysoftandcanbeusedforboltsandformachinepartsthatdonotneedstrength.
Mediumcarbonsteelisabettergradeandstrongerthanlowcarbonsteel.Itisalsomoredifficulttocutthanlowcarbonsteel.
Highcarbonsteelmaybehardenedbyheatingittoacertaintemperatureandthenquicklycoolinginwater.Themorecarbonthesteelcontainsandthequickerthecoolingis,theharderitbecomes.Becauseofitshighstrengthandhardnessthisgradeofsteelmaybeusedfortoolsandworkingpartsofmachines.Butforsomespecialuses,forexample,forgears,bearings,springs,shaftsandwire,carbonsteelscannotbealwaysusedbecausetheyhavenopropertiesneededfortheseparts.
Somespecialalloysteelshouldbeusedforsuchpartsbecausethealloyingelementsmakethemtougher,stronger,orharderthancarbonsteels.Somealloyingelementscausesteeltoresistcorrosion,andsuchsteelsarecalledstainlesssteels.
Heat-specialismadebyaddingsometungstenandmolybdenuim,whilemanganeseincreasesthewearresistanceofsteel.Vanadiumsteelresistcorrosionandcanstandshocksandvibration.
Toolsmadeofhigh-speedsteelcontainingtungsten,chromium,vanadium,andcarbon,maydotheworkatmuchhigherspeedsthancarbontoolsteels.
CastIron
Whitecastironisthehardesttypeofcastiron.Itisunweldable.
Thecommonesttypeofcastironisgraycastiron,analloyofironandcarboncontainingabout3%to3.5%carbon.andmorethan1!
Silicon.Thesearelargeamountsofcarbonandsilicon,andintheseproportions,allthecarbonisnottakenupbytheironorironcarbide.Apartofthiscarbonseparatesoutasgraphiteflakesdistributedthroughoutthecastiron.Thesegraphiteflakesgiveacharacteristicallydarkappearancetoafreshlybrokensurfaceofgraycastiron.
Graycastcastironhaslittleductility,andcansustainhighcompressiveloads.
Nodularironisavariationofgraycastiron,andhasamicroscopicstructurethatovercomesmostofthelimitationsofgraycastiron.Nodularironlikewisecontainsgraphite,buttheironisinoculatedwithasmallamountofmagnesiumwhilebeingpouredintotheladle.Asaresult,thegraphite
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