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1、机械制造专业英语4B原文及翻译（章跃主编）CHAINDRIVESChaindrivesoccupyauniquepositioninthemechanicalfield・Inasense,theyaresimilartobeltdrives;achainconnectssprocketsonthedrivinganddrivenshafts.Thevelocityratiotransmittedfromoneshafttotheotherdependsonthesizeofthetwosprockets(atthepitchlinc);unlikothatfoundwith
2、belts,theratioispositive・Inbeltdrive,creepandslipplayimportantrolesandmustbeconsidered;inachaindrive,whichismadeupofnumerouslinks,thereisasmallamountofplayinthetotallengthofthechain.Thismaybedesirableincaseofsmal1overloads.Achaindriveissimilartotheopen-belttypeofdirveinthatthedrivinganddri
3、venshaftsrotateinthesamedirection.Therearealsosimilaritiesbetweenchaindrivesandgeardrives.Bothtypestransmitapositivevelocityrertio.Inaregularspur-geardrive,thedrivinganddrivenshaftsturninoppositedirectionsunlessanidlerisemployed.Ingeardrivesernployinganannulatorringgear,however,theinputand
4、outputshaftsrotateinthesamedirection.Inaspur-geardrivethereisverylittiecontactbetweenmeshinggears;therefore,toothloadsareexcessive.Sincetheconnectionbetweenachainanditssprocketextendsoverseveralteeth,noonetoothissubjectedtoheavyloads.Chaindrivesareoftennoisy.Thesilentchaintypeofdrivewasdev
5、elopedtocounteractthisundesirablecharacteristic.Belt,chain,andgeardrivesarealldangerous.Beltandchainspeedsarehigh,asisthepitch-linevelocityofmostgeardrives.Allshouldbeadequatelycoveredbysuitableguards(orcompletelyenclosed)sothatnobobyorclothingpartscanpossiblybecaughtinthemovingcomponents.
6、Othercomparisonscanbemadeamongchain,belt,andgeardrives.Geardrivescanoperateathigherspeedsthantheothers,andareusuallymorecompact.However,chaindrivesdonotrequirethemountingprecisionthatissoessentialforgearing.Anadvantdgeofchaindrivesincomparisontobeltdrivesisthattheformerdonotrequiretensiono
7、ntheslackside;thisleadstobetterbearinglife・Ingeneral,chaindrivesaremorecompactthanthebelttype;foragivenratio,thesprocketscanbesmallerthanbeltpulleys.Foragivenload,chainwidthsarenarrowerthancomparableflatbelts.Theconnectinglinkonchaindrivesmakesthemeasytoinstal
