《機(jī)械專業(yè)英語》課件第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.組合，組合物component [kEm5pEJnEnt] n.元件，組件dismantle [dIs5mAnt(E)l] vt.分解(機(jī)器)，拆開nut [nQt] n.螺母，螺帽

v.上(擰，裝)螺母spring [sprIN] n.彈簧

v.彈回cam [kAm] n.凸輪，偏心輪machinery [mE5Fi:nErI] n.機(jī)器，機(jī)械perform [pE5fC:m] v.執(zhí)行，完成associate [E5sEJFIEt] v.聯(lián)合，結(jié)合key [ki:] n.鍵subassembly [

sQbE5semblI] n.組合件，部件coupling [5kQplIN] n.聯(lián)軸節(jié)，聯(lián)軸器clutch [klQtF] n.離合器fundamentally[fQndE5mentElI] adv.(從)根本上hub [hQb] n.輪轂evolve [I5vRlv] v.進(jìn)化，演變assemble [E5semb(E)l] v.安裝，裝配

n.組件rivet [5rIvIt] n.鉚釘 v.鉚接，鉚weld [weld] v.&n.焊接，熔焊

adj.焊接的thoroughly [5WQrElI] adv.完全地，徹底地standardize [5stAndEdaIz] vt.標(biāo)準(zhǔn)化establish [I5stAblIF] vt.確定，建立dimension [dI5menF(E)n] n.尺寸

v.標(biāo)尺寸uniformity [

jU:nI5fR:mEtI] n.均勻性，一致性obtain [Eb5teIn] v.獲得automotive [C:tE5mEJtIv] adj.自動(dòng)的，汽車的distinguish [dIs5tIN^wIF] v.區(qū)別abatement [E5beItmEnt] n.消除referto 指的是，稱為combinewith 與……相結(jié)合inotherinstances 在其它情況下spurgear 直齒輪drivingelement 主動(dòng)元件drivenelement 被動(dòng)元件

NOTES

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

因此，如果把機(jī)床完全拆開，就可以得到像螺母、螺栓、彈簧、齒輪、凸輪及軸等簡單零件——這是所有機(jī)器的標(biāo)準(zhǔn)元件。

if引導(dǎo)條件狀語從句，表示“如果……”。

2．Themostcommonexampleofamachineelementisagear,which,fundamentally,isacombinationofthewheelandthelevertoformatoothedwheel.Therotationofthisgearonahuborshaftdrivesothergearsthatmayrotatefasterorslower,dependinguponthenumberofteethonthebasicwheels.機(jī)械零件中最常見的是齒輪，它實(shí)際上是由輪子和桿組成的帶有齒的輪子。裝在軸套輪轂或軸上的旋轉(zhuǎn)齒輪驅(qū)動(dòng)其它齒輪做加速或減速轉(zhuǎn)動(dòng)，這取決于基準(zhǔn)齒輪的齒數(shù)。“which”引導(dǎo)非限制性定語從句，修飾“gear”；不定式“toformatoothedwheel”作狀語，表示結(jié)果；分詞“dependingupon”作狀語。

3．Notallmachinepartsinusearestandardized,however.然而，并不是所有已經(jīng)使用的零件都是標(biāo)準(zhǔn)的。

“Notall”是不完全否定，其含義是“并非所有”。句中“however”的位置比較靈活，可以放在句首，也可以放在句子中間，還可以放在句子后面。

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

2．UseEnglishforreplacingChineseoruseChineseforreplacingEnglish.

(1)機(jī)器零件

(2)單個(gè)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.嚙合，配合positive [5pBzItIv]adj.正的，肯定的，陽性的positively adv.確定，確實(shí)地，正ratio [5reIFIEJ]n.比，比率gearing [5^IErIN]