机械工程专业英语.ppt

Tolerance:thedifferencebetweenthemaximumlimitofsizeandtheminimumlimitofsize.Shaft:thetermusedbyconventiontodesignateallexternalfeaturesofapart.byconvention:按照惯例Hole:thetermusedbyconventiontodesignateallinternalfeaturesofapart.第133页,共161页，星期六，2024年，5月2.FitFitsareconcernedwiththerelationshipbetweentwoparts.Considerashaftandholecombination:iftheshaftislargerthanthehole,theconditionissaidtobeofinterference;andifsmallerthanthehole,theconditionissaidtobeofclearance.Inorderthatthepreciseconditionisensured,thelimitsofsizeofboththeshaftandtheholemustbestipulated.Fitscanbeclassifiedasfollows:clearancefit,interferencefit,andtransitionalfit.第134页,共161页，星期六，2024年，5月Hole-basedsystemandshaft-basedsystemInordertoobtainarangeofdegreesofclearance,andthedegreesofinterference,itisnecessarytouseawidevariationofholesizesandshaftsizes.Forexample,amanufacturingcompanycouldbemakinganumberofparts,allofanominal25mmdiameter,butwhichallslightlydifferentinactuallimitsofsize,tosuittheactualfitrequiredofeachpairofparts.Thissituationcouldmeanthatalargenumberofdrills,reamers,gauges,etc.wererequired第135页,共161页，星期六，2024年，5月Itislogicalthat,toreducethisnumber,astandardholecouldbeusedforeachnominalsize,andvariationoffitbeobtainedbymakingthematingshaftsmallerorlargerthanthehole.Thisisknownasahole-basedsystem.第136页,共161页，星期六，2024年，5月Exercise6TranslatethefollowingsentencesintoChinese:(1)Sinceitisimpossibletomachineaparttoanexactsize,adesignermustspecifyanacceptablerangeofsizethatwillpermittheparttofitandfunctionasintended.2）Themaximumandminimumsizesinpartdimensionsthatareacceptablearelimitsbetweenwhichtheactualpartdimensionmustfall.3）Toleranceondr