中英文文献翻译螺杆式压缩机Word文档格式.docx
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Thedirectionnormaltothehelicoids,canbeusedtocalculatethecoordinatesoftherotorhelicoidsandfromxandytowhichtheclearanceisaddedas:
,,(2.19)
wherethedenominatorDisgivenas:
(2.20)
andservetocalculatenewrotorendplanecoordinates,x0nandy0n,withtheclearancesobtainedforanglesθ=/pandτrespectively.Theseandnowservetocalculatethetransverseclearanceδ0asthedifferencebetweenthem,aswellastheoriginalrotorcoordinatesand.
Ifbyanymeans,therotorschangetheirrelativeposition,theclearancedistributionatoneendoftherotorsmaybereducedtozeroontheflatsideoftherotorlobes.Insuchacase,rotorcontactwillbeprohibitivelylongontheflatsideoftheprofile,wherethedominantrelativerotormotionissliding,asshowninFig.2.29.Thisindicatesthatrotorseizurewillalmostcertainlyoccurinthatregioniftherotorscomeintocontactwitheachother.
Fig.2.29.Clearancedistributionbetweentherotors:
atsuction,midrotors,anddischargewithpossiblerotorcontactatthedischarge
Fig.2.30.Variableclearancedistributionappliedtotherotors
Itfollowsthattheclearancedistributionshouldbenon-uniformtoavoidhardrotorcontactinrotorareaswhereslidingmotionbetweentherotorsisdominant.
InFig.2.30,areducedclearanceof65μmispresented,whichisnowappliedinrotorregionsclosetotherotorpitchcircles,whileinotherregionsitiskeptat85μm,aswasdonebyEdstroem,1992.AscanbeseeninFig.2.31,thesituationregardingrotorcontactisnowquitedifferent.Thisismaintainedalongtherotorcontactbeltclosetotherotorpitchcirclesandfullyavoidedatotherlocations.Itfollowsthatifcontactoccurred,itwouldbeofarollingcharacterratherthanacombinationofrollingandslidingorevenpuresliding.Suchcontactwillnotgenerateexcessiveheatandcouldthereforebemaintainedforalongerperiodwithoutdamagingtherotorsuntilcontactceasesorthecompressorisstopped.
2.6ToolsforRotorManufacture
Thissectiondescribesthegenerationofformedtoolsforscrewcompressorhobbing,millingandgrindingbasedontheenvelopegearingprocedure.
2.6.1HobbingTools
Ascrewcompressorrotoranditsformedhobbingtoolareequivalenttoapairofmeshingcrossedhelicalgearswithnonparallelandnonintersectingaxes.TheirgeneralmeshingconditionisgiveninAppendixA.Apartfromthegashesformingthecutterfaces,thehobissimplyahelicalgearinwhich.
Fig.2.31.Clearancedistributionbetweentherotors:
atsuction,midofrotoranddischargewithapossiblerotorcontactatthedischarge
Eachreferredtoasathread,Colburne,1987.Owingtotheiraxesnotbeingparallel,thereisonlypointcontactbetweenthemwhereasthereislinecontactbetweenthescrewmachinerotors.TheneedtosatisfythemeshingequationgiveninAppendixA,leadstotherotor–hobmeshingrequirementforthegivenrotortransversecoordinatepointsandandtheirfirstderivative.Thehobtransversecoordinatepointsandcanthenbecalculated.ThesearesufficienttoobtainthecoordinateTheaxialcoordinate,calculateddirectly,andarehobaxialplanecoordinateswhichdefinethehobgeometry.
Thetransversecoordinatesofthescrewmachinerotors,describedintheprevioussection,areusedasanexampleheretoproducehobcoordinates.herotorunitleadsare48.754mmforthemainand−58.504mmfortheaterotor.Singlelobehobsaregeneratedforunitleads:
6.291mmforthemainrotorand−6.291mmforthegaterotor.Thecorrespondinghobhelixanglesψare85◦and95◦.Thesamerotor-to-hobcentredistanceC=110mmandtheshaftangleΣ=50◦aregivenforbothrotors.Figure2.32containsaviewtothehob.
Reversecalculationofthehob–screwrotortransformation,alsogiveninAppendixApermitsthedeterminationofthetransverserotorprofilecoordinateswhichwillbeobtainedasaresultofthemanufacturingprocess.Theseaybecomparedwiththoseoriginallyspecifiedtodeterminetheeffectof
Fig.2.32.Rotormanufacturing:
hobbingtoolleft,rightmillingtool
manufacturingerrorssuchasimperfecttoolsettingortoolandrotordeformationuponthefinalrotorprofile.
Forthepurposeofreversetransformation,thehoblongitudinalplanecoordinatesandandshouldbegiven.Theaxialcoordinateisusedtocalculate,whichisthenusedtocalculatethehobtransversecoordinates:
,(2.21)
Thesearethenusedasthegivencoordinatestoproduceameshingcriterionandthetransverseplanecoordinatesofthe“manufactured”rotors.
AcomparisonbetweentheoriginalrotorsandthemanufacturedrotorsisgiveninFig.2.33withthedifferencebetweenthemscaled100times.Twotypesoferrorareconsidered.Theleftgaterotor,isproducedwith30umoffsetinthecentredistancebe