《机械专业英语》课件第7章

Unit7TEXT

LEARNTOSPEAKNEWWORDSANDEXPRESSIONSNOTES

EXERCISESREADINGMATERIALPROFESSIONALWORDSANDPHRASES

MachineElements

Howeversimple,anymachineisacombinationofindividualcomponentsgenerallyreferredtoasmachineelementsorparts.Thus,ifamachineiscompletelydismantled,acollectionofsimplepartsremainssuchasnuts,bolts,springs,gears,camsandshafts—thebuildingblocksofallmachinery.Amachineelementis,therefore,asingleunitdesignedtoperformaspecificfunctionandcapableofcombiningwithotherelements.Sometimescertainelementsareassociatedinpairs,suchasnutsandboltsorkeysandshafts.Inotherinstances,agroupofelementsiscombinedtoformasubassembly,suchasbearings,couplings,andclutches.

Themostcommonexampleofamachineelementisagear,which,fundamentally,isacombinationofthewheelandthelevertoformatoothedwheel.Therotationofthisgearonahuborshaftdrivesothergearsthatmayrotatefasterorslower,dependinguponthenumberofteethonthebasicwheels.Fig.7-1NutandboltFig.7-2SpringFig.7-3ShaftandbearingFig.7-4Clutch

Otherfundamentalmachineelementshaveevolvedfromwheelandlever.Awheelmusthaveashaftonwhichitmayrotate.Thewheelisfastenedtotheshaftswithcouplings.Theshaftmustrestinbearings,maybeturnedbyapulleywithabeltorachainconnectingittoapulleyonasecondshaft.Thesupportingstructuremaybeassembledwithboltsorrivetsorbywelding.Properapplicationofthesemachineelementsdependsuponknowledgeoftheforceonthestructureandthestrengthofthematerialsemployed.

Manymachineelementsarethoroughlystandardized.Testingandpracticalexperiencehaveestablishedthemostsuitabledimensionsforcommonstructuralandmechanicalparts.Throughstandardization,uniformityofpracticeandresultingeconomicsareobtained.Notallmachinepartsinusearestandardized,however.Intheautomotiveindustryonlyfasteners,bearings,bushings,chains,andbeltsarestandardized.Crankshaftsandconnectingrodsarenotstandardized.LEARNTOSPEAKMr.Liu: Goodafternoon,Mr.Xie.Mr.Xie: Goodafternoon,Mr.Liu.Mr.Liu: MayIaskyouafewquestions?Mr.Xie: Yes,ofcourse.Whataretheproblems?Mr.Liu: Howmanykindsofgearsarethereincommonuse?Mr.Xie: Therearefourkindsofgears.Mr.Liu: Whatarethey? Mr.Xie: Theyarespurgears,helicalgears,wormgears,andbevelgears.Mr.Liu: Aregearsimportantinnearlyallofmachinery?Mr.Xie: Yes,theyare.Mr.Liu: Whatcanthespurgearsbeusedfor?Mr.Xie: Spurgearsareusedtotransmitpowerandrotarymotionbetweenparallelshafts.Mr.Liu: Howdoyoudistinguishthedrivingelement,andthedrivenelement?Mr.Xie: Thesmalleroftwogearsinmeshiscalleddrivingelement,andtheotheriscalleddrivenelement.Mr.Liu: Wherearethespurgearsusedfor?Mr.Xie: Theyareusedforlowspeedapplicationsandthosesituationswherenoisecontrolisnotaproblem.Mr.Liu: Andwherearethehelicalgearsusedfor?Mr.Xie: Theyareusedforhighspeed,largepowertransmission,orwherenoiseabatementisimportant.Mr.Liu: Thankyoufortellingmeaboutthese.Mr.Xie: Notatall.

NEWWORDSANDEXPRESSIONScombination [kBmbI5neIF(E)n] n.组合，组合物component [kEm5pEJnEnt] n.元件，组件dismantle [dIs5mAnt(E)l] vt.分解(机器)，拆开nut [nQt] n.螺母，螺帽

v.上(拧，装)螺母spring [sprIN] n.弹簧

v.弹回cam [kAm] n.凸轮，偏心轮machinery [mE5Fi:nErI] n.机器，机械perform [pE5fC:m] v.执行，完成associate [E5sEJFIEt] v.联合，结合key [ki:] n.键subassembly [

sQbE5semblI] n.组合件，部件coupling [5kQplIN] n.联轴节，联轴器clutch [klQtF] n.离合器fundamentally[fQndE5mentElI] adv.(从)根本上hub [hQb] n.轮毂evolve [I5vRlv] v.进化，演变assemble [E5semb(E)l] v.安装，装配

n.组件rivet [5rIvIt] n.铆钉 v.铆接，铆weld [weld] v.&n.焊接，熔焊

adj.焊接的thoroughly [5WQrElI] adv.完全地，彻底地standardize [5stAndEdaIz] vt.标准化establish [I5stAblIF] vt.确定，建立dimension [dI5menF(E)n] n.尺寸

v.标尺寸uniformity [

jU:nI5fR:mEtI] n.均匀性，一致性obtain [Eb5teIn] v.获得automotive [C:tE5mEJtIv] adj.自动的，汽车的distinguish [dIs5tIN^wIF] v.区别abatement [E5beItmEnt] n.消除referto 指的是，称为combinewith 与……相结合inotherinstances 在其它情况下spurgear 直齿轮drivingelement 主动元件drivenelement 被动元件

NOTES

1．Thus,ifamachineiscompletelydismantled,acollectionofsimplepartsremainssuchasnuts,bolts,springs,gears,camsandshafts—thebuildingblocksofallmachinery.

因此，如果把机床完全拆开，就可以得到像螺母、螺栓、弹簧、齿轮、凸轮及轴等简单零件——这是所有机器的标准元件。

if引导条件状语从句，表示“如果……”。

2．Themostcommonexampleofamachineelementisagear,which,fundamentally,isacombinationofthewheelandthelevertoformatoothedwheel.Therotationofthisgearonahuborshaftdrivesothergearsthatmayrotatefasterorslower,dependinguponthenumberofteethonthebasicwheels.机械零件中最常见的是齿轮，它实际上是由轮子和杆组成的带有齿的轮子。装在轴套轮毂或轴上的旋转齿轮驱动其它齿轮做加速或减速转动，这取决于基准齿轮的齿数。“which”引导非限制性定语从句，修饰“gear”；不定式“toformatoothedwheel”作状语，表示结果；分词“dependingupon”作状语。

3．Notallmachinepartsinusearestandardized,however.然而，并不是所有已经使用的零件都是标准的。

“Notall”是不完全否定，其含义是“并非所有”。句中“however”的位置比较灵活，可以放在句首，也可以放在句子中间，还可以放在句子后面。

EXERCISES1．DiscussthefollowingquestionsinEnglish:(1) Whatismachineelement?(2) Whatdotheboltsdo?(3) Wherearethespringsused?(4) Whichelementsareassociatedinpairs?

2．UseEnglishforreplacingChineseoruseChineseforreplacingEnglish.

(1)机器零件

(2)单个元件

(3)特定功能

(4) Thespeedofrotatingofashaft

(5) Thesizeofakey

(6) Apairofmeshinggears

3．Placea“T”aftersentencesthataretrueandan“F”afterthosethatarefalse.

(1) Gearsareusedasbuildingblocksfortheconstructionofmostdevices,apparatus,andmachinery.()

(2) Apairofgearswithdifferentnumbersofteethwillrotateatdifferentspeeds.()

(3) Themostcommonmachineelementisthegearfromwhichotherfundamentalmachineelementshavedeveloped.()

(4) Acouplingisamachineelementwhichjoinstwoshafts.()

(5) Allmachinepartshavebeendevelopedintostandardizeddesigns.()

4．Contextualreference.

(1) Insentencetwo,“thebuildingblocks”refersto().

(a) machineelements.

(b) devices,apparatusandmachinery.

(2) Insentence9,the“it”refersto().

(a) thebrake.

(b) theshaft.

(c) theclutch.

(3) Insentence11,the“it”refersto().(a) thepulley.(b) theshaft.(c) thebelt.(4) Insentence13,“thesemachineelements”refersto().(a) boltsandrivets.(b) wheels,shafts,bearings,clutches,couplings,etc.5．Rephrasing.

(1) Themostcommonmachineelementisthegear,whichcombinesfeaturesofthewheelandthelever.

(2) Thehardnessofageardeterminesitsabilitytoresistwear.

(3) Inthedesign,calculationsmustmaketheforcesfitthematerialsinthesimplestconstruction.

(4) Manufacturingengineershavecenteredtheireffortsonthedevelopmentofstandardizedelements.

(5) Thesepartsareproducedinlargequantitieswithahighdegreeofperfectionatreducedcost. READINGMATERIAL

Gears

Thetransmissionofrotarymotionfromoneshafttoanotheroccursinnearlyeverymachineonecanimagine.Gearsconstituteoneofthebestofthevariousmeansavailablefortransmittingthismotion.

Agearisvirtualawheelwithveryaccuratelyshapedteeth.Theseteethmeshwiththeteethofanothergear,thusprovidingapositive-motiondrive.Thespeedratiobetweentheshaftscarryingapairofgearsdependsuponthenumberofteethinthegears.Forexample,ifa20-toothgeardrivesagearof50teeth,thesmallergearwillhavetoturn21/2timestocausethelargeronetomake1turn.

Varioustypesofgearinghavebeendevelopedfordifferentpurposes.Iftheshaftsareparallel,anyofthreetypesmaybeused:spur,helical,orherringbone.Spurgearsarethesimplestandleastexpensivetype.Theyaregenerallyusedondrivesrequiringmoderatespeeds.Bevelgearsservetotransmitpowerbetweentwointersectingshafts.Withaworm-geardrive,itispossibletoobtainlargespeedreductionataright-angledrive.Rack-and-piniondrivesareusedwhereitisdesirabletotransformtherotarymotionofonepartintolinearmotionfortheotherpart,orviceversa(asshowninFig.7-8).Fig.7-5SpurgearandpinionFig.7-6BevelgearsFig.7-7WormgearandwormFig.7-8PinionandrackPROFESSIONALWORDSANDPHRASESmesh [meF]n.&v.啮合，配合positive [5pBzItIv]adj.正的，肯定的，阳性的positively adv.确定，确实地，正ratio [5reIFIEJ]n.比，比率gearing [5^IErIN]