英文原文ScrewMachineDesignHolmes,1999reportedthatevenhigheraccuracywasachievedonthenewHolroydvitrifyingthread-grindingmachine,thuskeepingthemanufacturingtoleranceswithin3meveninlargebatchproduction.Thismeansthat,asfarasrotorproductionaloneisconcerned,clearancesbetweentherotorscanbeassmallas12m.Screwmachinesareusedtodayfordifferentapplicationsbothascompressorsandexpanders.Fig.1.4.ScrewcompressormechanicalpartsFig.1.5.CrosssectionofascrewcompressorwithgearboxForoptimumperformancefromthemaspecificdesignandoperatingmodeisneededforeachapplication.Hence,itisnotpossibletoproduceefficientmachinesbythespecificationofauniversalrotorconfigurationorsetofworkingparameters,evenforarestrictedclassofmachines.Industrialcompressorsarerequiredtocompressair,refrigerantsandprocessgases.Foreachapplicationtheirdesignmustdiffertoobtainthemostdesirableresult.Typically,refrigerationandprocessgascompressors,whichoperateforlongperiods,musthaveahighefficiency.Inthecaseofaircompressors,especiallyformobileapplications,efficiencymaybelessimportantthansizeandcost.Oilfreecompressedairisdeliveredalmostexclusivelybyscrewcompressors.Thesituationisbecomingsimilarforthecaseofprocessgascompression.Inthefieldofrefrigeration,reciprocatingandvanecompressorsarecontinuouslybeingreplacedbyscrewandadramaticincreaseintheneedsforrefrigerationcompressorsisexpectedinthenextfewyears.Therangeofscrewcompressorssizescurrentlymanufacturediscoveredbymalerotordiametersof75to620mmandthispermitsthedeliveryofcompressedgasflowratesof0.6m3/minto600m3/min.Apressureratioof3.5isattainableinthemfromasinglestagefordrycompressorsandupto15foroilfloodedones.Normalpressuredifferencesareupto15bars,butmaximumpressuredifferencessometimesexceed40bars.Typically,foroilfloodedaircompressionapplications,thevolumetricefficiencyofthesemachinesnowexceeds90%andthespecificpowerinputhasbeenreducedtovalueswhichwereregardedasunattainableonlyafewyearsago.1.1ScrewCompressorPracticeTheSwedishcompanySRMwasapioneerandtheyarestillleadersinthefieldofscrewcompressorpractice.Othercompanies,likeCompairU.K.,Atlas-CopcoinBelgium,Ingersol-RandandGardnerDenverintheUSAandGHHinGermanyfollowthemclosely.York,TraneandCarrierleadinscrewcompressorapplicationsforrefrigerationandairconditioning.Japanesescrewcompressormanufacturers,likeHitachi,MycomandKobe-Steelarealsowellknown.ManyrelativelynewscrewcompressorcompanieshavebeenfoundedintheMiddleandFarEast.NewmarketsinChinaandIndiaandinotherdevelopingcountriesopennewscrewcompressorfactories.AlthoughnotdirectlyinvolvedincompressorproductiontheBritishcompany,Holroyd,arethelargestscrewrotormanufacturer,theyareworldleadersintooldesignandtoolmachineproductionforscrewcompressorrotors.Despitetheincreasingpopularityofscrewcompressors,publicknowledgeandunderstandingofthemisstilllimited.ThreescrewcompressortextbookswerepublishedinRussianintheearlynineteensixties.Sakun,1960givesafulldescriptionofcircular,ellipticandcycloidalprofilegenerationandareproduciblepresentationofaRussianasymmetricprofilenamedSKBK.Theprofilegenerationinhisbookwasbasedonanenvelopeapproach.Andreev,1961repeatsthetheoryofscrewprofilesandmakesacontributiontorotortoolprofilegenerationtheory.Golovintsovstextbook,1964,ismoregeneralbutitssectiononscrewcompressorsisbothinterestingandinformative.Asomov,1977,alsoinRussian,gaveareproduciblepresentationoftheSRMasymmetricprofile,fiveyearsafteritwaspatented,togetherwiththeclassicLysholmProfile.TwotextbookshavebeenpublishedinGerman.Rinder,1979,presentedaprofilegenerationmethodbasedongeartheorytoreconstructtheSRMasymmetricprofile,sevenyearsafteritwaspatented.Konka,1988,publishedsomeengineeringaspectsofscrewcompressors.OnlyrecentlyanumberoftextbookshavebeenpublishedinEnglish,whichdealwithscrewcompressors.ONeill,1993,onindustrialcompressorsandArbon,1994,onrotarytwinshaftcompressors.Thereareafewcompressormanufacturershandbooksonscrewcompressorsandanumberofbrochuresgivingusefulinformationonthem,buttheseareeitherclassifiedornotinthepublicdomain.Someofthem,liketheSRMDataBook,althoughavailableonlytoSRMlicensees,arecitedinliteratureonscrewcompressors.Thereisanextraordinarilylargenumberofpatentsonscrewcompressors.Literallythousandshaveappearedinthepastthirtyyears,ofwhichSRM,alone,holds750.Thepatentsdealwithvariousaspectsofthesemachines,butespeciallywiththeirrotorprofiles.TheSRMpatentsofNilson,1952,forthesymmetricprofile,Shibbie,1979,fortheasymmetricprofileandAstberg1982,forthe“D”profilearethemostwidelyquotedinreferenceliteratureonthistopic.Ohman,1999,introducedthe“G”profileforSRM.Otherexamplesofsuccessfulprofilingpatentsmayalsobementioned,namely:Atlas-Copco,CompairwithHough,1984,GardnerDenverwithEdstroem,1974,HitachiwithKasuya,1983,andIngersoll-RandwithBowman,1983.Morerecently,severalhighlysuccessfulpatentsweregrantedtorelativelysmallcompaniessuchasFuSheng,Lee,1988,andHanbel,Chia-Hsing,1995.Anewapproachtoprofilegeneration,usingarackasthebasisfortheprimarycurves,wasproposedbyRinder,1987,andStosic,1996.Allpatentedprofilesweregeneratedbyaprocedurebutinformationonthemethodsusedishardlydisclosedeitherinthepatentsorinaccompanyingpublications.Thusittookmanyyearsbeforetheseproceduresbecameknown.Examplesofthisare:Margolis,whopublishedhisderivationofthesymmetriccircularprofilein1977,32yearsafterithadbeenpatentedandRinder,whousedgearmeshingcriteriatoreproducetheSRMasymmetricprofilein1979,9yearsafterpatentpublication.ItmayalsobementionedthatTang,1995,derivedtheSRM“D”profileanalyticallyaspartofaPhDthesis13yearsafterthepatentpublication.Manyotheraspectsofscrewcompressorswerealsopatented.Theseincludenearlyalltheirmostwellknowncharacteristics,suchas,oilflooding,thesuctionanddischargeportsfollowingtherotortiphelices,axialforcecompensation,unloading,theslidevalveandtheeconomiserport,mostofwhichwerefiledbySRM.However,othercompanieswerealsokeentofilepatents.ThegeneralimpressiongainedisthatpatentexpertsareasimportantforscrewcompressordevelopmentasengineersThereisasurprisinglackofscrewcompressorpublicationsinthetechnicalliterature.Lysholmspapersin1942and1966wereamidtwentiethcenturyexception,buthedidnotincludeanydetailsoftheprofilingdetailswhichheintroducedtoreducetheblow-holearea.Thus,journalpaperslikethoseofStosicetal.,1997,1998,mayberegardedasanexception.Inrecentyears,publicationofscrewcompressormaterialsinjournalshasbecomemorecommonthroughtheInternationalInstitutionofRefrigerationStosic,1992andFujiwara,1995,theIMechE,withpapersbySmith,1996,Fleming,1994,1998andStosic1998,andtheASME,byHanjalic,1997.Togetherthesemademoreinformationavailablethanthetotalpublishedinallpreviousyears.Stosics,1998paperisatypicalexampleofthemodernpracticeoftimelypublishing.Therearethreecompressorconferenceswhichdealexclusivelyorpartlywithscrewcompressors.Thesearethebiennialcompressortechnologyconference,heldatPurdueUniversityintheUSA,theIMechEinternationalconferenceoncompressorsandtheirsystems,inEnglandandthe“VDISchraubenkompressorenTagung”inDortmund,Germany.Despitethenumberofpapersonscrewcompressorspublishedattheseevents,onlyafewofthemcontainusefulinformationonrotorprofilingandcompressordesign.TypicalPurduepaperscitedaspublicationsfromwhichareadercangaininformationonthisare:Edstroem,1992,Stosic,1994andSingh,1984,1990.Zhang,1992,indicatesthattheyusedenvelopetheorytocalculatesomegeometricfeaturesoftheirrotors.TheDortmundproceedingsgivesomeinterestingpaperssuchasthatbyRinder,1984,whopresentedtherackgenerationofascrewrotorprofile,includingafullyreproduciblepatternbasedongeartheory.Hanjalic,1994andHolmes,1994,givemoredetailsonprofiling,manufacturingandcontrol.Kauder,1994,1998andStosic,1998aretypicalexamplesofsuccessfuluniversityreseachappliedtorealengineering.Sauls,1994,1998,mayberegardedasanexampleoffineengineeringwork.TheLondoncompressorconferenceincludedsomeinterestingpaperslikethoseofEdstroem,1989andStosicetal.,1999.Manyreferencetextbooksongearsgiveusefulbackgroundforscrewrotorprofiling.Howeverallofthemarelimitedtotheclassicalgearconjugateactioncondition.Litvin,1968and19561994mayberegardedasanexceptiontothispractice,ingiv