机械专业英语翻译

1.MetalsandTheirUseItisknownthatmetalsareveryimportantinourlife.Metalshavethegreatestimportanceforindustry.Allmachinesandotherengineering[]constructionshavemetal[]parts;someofthemconsistonlyofmetalparts.Therearetwolargegroupsofmetals:1)Simplemetal-moreorlesspurechemicalelements[]2)Alloys[]-materialsconsistingofasimplemetalcombinedwithsomeotherelements.Abouttwothirdsofallelementsfoundintheeartharemetals,butnotallmetalsmaybeusedinindustry.Thosemetalswhichareusedinindustryarecalledengineeringmetals.Themostimportantengineeringmetalisiron[],whichintheformofalloyswithcarbon[]andotherelements,findsgreaterusethananyothermetal.Metalsconsistingofironcombinedwithsomeotherelementsareknownasferrous[]metals;alltheothermetalsarecallednonferrous[]metals.Themostimportantnonferrousmetalarecopper[],aluminum[],lead[],zinc[],tin[],butallthesemetalsareusedmuchlessthanferrousmetals,becausetheferrousmetalsaremuchcheaper.Engineeringmetalsareusedinindustryintheformofalloysbecausetheproperties[]ofalloysaremuchbetterthanthepropertiesofpure[]metals.Onlyaluminummaybelargelyusedintheformofsimplemetal.Metalshavesuchagreatimportancebecauseoftheirusefulpropertiesortheirstrength,hardness,andtheirplasticity[].Differentmetalsareproducedindifferentways,butalmostallthemetalarefoundintheformsofmetalore[](ironore,copperore,etc[etcetra].)Theoreisamineral[]consistenceofametalcombinedwithsomeimpurities[].Inordertoproduceametalfromsomemetalore,wemustseparatetheseimpuritiesfromthemetalthatisdonebymetallurgy[].2.PlasticsandOtherMaterialsPlastics[]havespecificpropertieswhichmaymakethempreferable[]totraditionalmaterials[]forcertainuses.Incomparison[]withmetals,forexample,plasticshavebothadvantagesanddisadvantages.Metalstendtobecorroded[]byinorganic[]acids[],suchassulphuric[]acidandhydrochloric[]acid.Plasticstendtoberesistanttotheseacids,butcanhavedissolvedordeformedbysolvent[],suchascarbontetrachloride[],whichhavethesamecarbonbaseastheplastics.Colormustbeappliedtothesurfaceofmetals,whereasitcanbemixedinwithplastics.Metalsaremorerigid[]thanmostplasticswhileplasticsareverylight,withaspecific[]gravitynormallybetween0.9and1.8.Mostplasticsdonotreadily[]conduct[]heatorelectricity[].Plasticssoftenslowlyandcaneasilybeshaped[]whentheyaresoft.塑料具有特殊的性能。对于某种用途而言，这些性能使得塑料比传统材料更为可取。例如，跟金属相比较，塑料既有优点也有缺点。金属易受到无机酸的腐蚀，如硫酸和盐酸，塑料能抵抗这些酸的腐蚀，但可被溶剂所洛解或引起变形，例如溶剂四氯化碳与塑料具有同样的碳基。颜色必定只能涂到金属的表面。而它可以跟塑料混合为一体。金属比大多数塑料刚性要好，而塑料则非常之轻，通常塑料密度在0.9-1.8之间。大多数塑料不易传热导电。塑料能缓慢软化，而当其还是在软的状态时，能容易成形。Itistheirplasticity[]atcertaintemperatures[]whichgivesplasticstheirmainadvantagesovermanyothermaterials.Itpermitsthelarge-scaleproductionofmolded[]articles,suchascontainers,ataneconomicunitcost,whereothermaterialsrequirelaborious[]andoftencostlyprocessesinvolvingcutting,shaping,machining,assembly[]anddecoration.在某一温度下塑料是处于塑性状态的，这就使塑料具备超过许多其他材料的主要优点。它容许大量生产单位成本低廉的模制式器件，例如，各种容器。于此，若用其他材料则需要大量劳力和往往需要很费钱的加工工艺，比如，切割、成形、加工、装配和装饰。Plasticsnotonlyreplaceothermaterials.Theirpropertiescanbeexploited[]forentirely[]newapplications.Forexample,plasticsheartvalves[]andotherhuman'spareparts'havemakepossiblemanyrecentdevelopmentsinsurgery[].Thereisnosingleplasticsmaterialwhichissuitableforallapplications.Itisimportantthatthemostsuitableplasticsshouldbechosen,andifnecessaryadapted[],foreachparticularrequirement.Itisalsoimportantthatthepropertiesoftheplasticschosenshouldbeexploitedtothebestadvantage.Aplasticsarticlemayneedtodifferindesignandappearancefromasimilararticlemadefromanothermaterialsuchasmetalorwood.Thisisduenotonlytothepropertiesofplasticsbutalsotothetechniques[]employedinfabricating[]plastics.Thesetechniquesincludeinjection[]molding[],blowmolding,compressionmolding,extrusion[]andvacuum[]forming.3.CastingandDie-CastingAlloysCasting[]isoneoftheoldestmetalworkingtechniquesknowntoman.Ourcountrymademetalcastingsasearlyas2000B.C.,andtheprocessusedthenisnotmuchdifferentinprinciple[]fromtheoneusedtoday.铸造是入类所掌握的最古老的金属加工技术之一。我国早在公元前2000年就已把金属制成铸件，而所使用的工艺从原理上和今天的工艺没有多大的区别。Foundry[]processesconsistofmakingmolds,preparingandmelting[]themetal,pouring[]themetalintothemolds,andcleaningthecastings.Theproductofthefoundryisacasting,whichmayvaryfromafraction[]ofakilogramtoseveralhundredtons.Itmayalsovaryincomposition[]aspracticallyallmetalsandalloyscanbecast.铸造工艺由制模、备料和金属熔炼，金属液浇注入模和铸件清砂等。铸造的产品是铸件，铸件可能从零点几公斤到几百吨范围变化。实际上所有金属在成分上也是变化的，而合金也可以铸造。Themetalsmostfrequentlycastareiron,steel,aluminumandsoon.Ofthese,iron,becauseofitslowmeltingpoint,lowpriceandeaseofcontrol,isoutstandingforitssuitability[]forcastingandisusedfarmoretha