外文翻译--简单的双螺杆挤压设备的设计制造和测试.doc

ASIMPLIFIEDTWINSCREWCOROTATINGFOODEXTRUDERDESIGN,FABRICATIONANDTESTINGABSTRACTASIMPLIFIEDCOROTATINGTWINSCREWFOODEXTRUDERWASDESIGNED,FABRICATEDANDTESTEDINENGLAND,FOLLOWEDBYEXTENSIVETESTINGINSRILANKAITWASBUILTASAMODELTOMEETTHESPECICPRODUCTANDNANCIALCONSTRAINTSOFLESSDEVELOPEDCOUNTRIESANDWASEXPECTEDTOBEUSEDINTHOSECOUNTRIESTOWIDENTHEPRODUCTIONCAPABILITIESOFEXTRUDEDFOODSTHEMACHINEHADANESTIMATEDDELIVERYOF10KG/HANDWASMADEMAINLYWITHMILDSTEELTWOTYPESOFSCREWWEREMADE,ONEWITHACONSTANTPITCHOF14MMANDTHEOTHERWITHVARYINGPITCHINSEGMENTSOF14,12AND10MMTHEMACHINEWASPOWEREDBYA22KWELECTRICMOTORWITHELECTRONICSPEEDCONTROLSTHEMACHINEALSOHADELECTRICALHEATINGWITHATEMPERATURECONTROLLERANDAPRESSURESENSINGDEVICETHECOSTOFFABRICATIONOFTHEMACHINEWASESTIMATEDAT2000WITHMOSTOFTHEPARTSBUILTINAFAIRLYSIMPLEWORKSHOPAMIXTUREOFRICEANDDRIEDBANANAWASSUCCESSFULLYEXTRUDEDASAPOTENTIALSNACKFOODANDONTHEBASISOFMAXIMUMEXPANSIONTHEBESTRESULTSWASOBTAINEDFROMABARRELTEMPERATUREOF120C,SCREWSPEED125RPM,FEEDMOISTURE15ANDWITHADIEORICESIZEOF3MMWHENTHEALTERNATIVECOMPRESSIONSCREWWASTESTEDVERYSIMILARRESULTSWEREACHIEVEDWITHNOSIGNICANTIMPROVEMENTINPRODUCTEXPANSION1999ELSEVIERSCIENCELTDALLRIGHTSRESERVEDKEYWORDSTWINSCREWEXTRUDER；DESIGN；LOWCOST；SNACKFOOD；CONTINUOUSCOOKER；LOCALCONSTRUCTION；CEREALMIXTURESNOMENCLATUREADIEDIAMETERMMBCHANNELWIDTHMMCSCREWCIRCUMFERENCEMMDSCREWCOREDIAMETERDOUTERDIAMETEROFSCREWSMMHFLIGHTDEPTHMMMMOISTURECONTENTWETBASISNNUMBEROFFIGHTTURNSNSPEEDANGULARREV/MINPPITCHMMQDELIVERYRATEMM3/MINSTOTALHELICALLENGTHOFSCREWSMMTTEMPERATURECTRESIDENCETIMEMINOVERLAPANGLEOFSCREWFIGHTSDEGREESCALENDERGAPMMSIDECLEARANCEMMPRODUCTDENSITYG/MM3HELIXANGLEDEGREES1INTRODUCTIONEXTRUSIONCOOKINGISFINDINGEVERINCREASINGAPPLICATIONSINTHEFOODPROCESSINDUSTRYAPARTFROMPROVIDINGAMEANSOFMANUFACTURINGNEWPRODUCTS,ITHASSUCCESSFULLYREVOLUTIONISEDMANYCONVENTIONALMANUFACTURINGPROCESSESHARLOW,1985,FRAME,1994TODAY,EXTRUDERSCOMEINAWIDEVARIETYOFSIZES,SHAPESANDMETHODOFOPERATIONTHEREARETHREETYPESOFFOODEXTRUDERFOUNDININDUSTRYHYDRAULICRAM,ROLLERANDSCREWTYPEEXTRUDERSFRAME,1994THESCREWEXTRUDERSAREVERYDIFFERENTTOTHEOTHERTWOHAVINGSPECIALFEATURESSUCHASCONTINUOUSPROCESSINGANDMIXINGABILITYSINGLEANDTWINSCREWTYPESAREBOTHWIDELYUSEDINTHEFOODPROCESSINDUSTRYUNFORTUNATELY,MOSTOFTHEFOODEXTRUDERSAVAILABLEINTHEMARKETAREEITHERSOCOSTLYTHATLESSDEVELOPEDCOUNTRIESCANNOTAORDTOBUYTHEMEXCEPTBYSOMEFORMOFASSISTANCEOROUTSIDEINVESTMENTORELSEARENOTAPPROPRIATEFORTHEWIDEVARIETYOFMATERIALSTHATNEEDTOBEPROCESSEDASARESULTTHEGROWTHOFEXTRUSIONTECHNOLOGYOFFOODINTOTHESECOUNTRIESHASBEENHINDEREDDESPITEITSMANYADVANTAGESINPARTICULARTHEREAPPEARSNOTTOBEASUITABLETWINSCREWEXTRUDERAVAILABLEATSUFFCIENTLYLOWCOSTFORUSEINDEVELOPINGCOUNTRIESTHEHIGHCOSTOFTHESEMACHINESISLARGELYDUETOTHESOPHISTICATEDCONSTRUCTIONALFEATURESWITHMANYCONTROLSTHATARENOTESSENTIALFORMANYAPPLICATIONSTHEINITIALPURCHASECOSTISTHEREFOREAMAJORBARRIERTOTHEWIDERINTRODUCTIONOFEXTRUSIONTODEVELOPINGCOUNTRIESWHEREMANYRAWMATERIALSAREAVAILABLETOBEPROCESSEDINTONUTRITIOUSANDPALATABLEFOODITEMSATTEMPTSHAVEBEENMADETOUTILISELOWPRESSUREANDSIMPLEEXTRUDERSFORBABYWEANINGFOODSSOMEOFWHICHHAVEBEENVERYSUCCESSFULWITHPROGRAMSTHROUGHORGANIZATIONSSUCHASFEEDTHEMILLIONSSANTAMONICA,CALIFORNIA,90406,USAANDTHRIPOSHAUSDA/USAIDTHENEEDHASLONGBEENRECOGNISEDFORSIMPLE,YETVERSATILEMACHINESATAFFORDABLEPRICESWHICHARECAPABLEOFEXPLOITINGTHENATURALFOODRESOURCESSAHAGUN,1977,JANSENANDHARPER1980,HARPERANDJANSEN1985THESECOULDINCORPORATEALLTHEUSUALCEREALSSUCHASRICE,MILLET,MAIZEANDSORGHUMWITHARICHVARIETYOFNUTRITIONALANDTASTYADDITIVESSUCHASFRUITS,VEGETABLESANDSPICESTHEOBJECTIVEOFTHISSTUDYTHEREFOREWASTOELIMINATEORSIMPLIFYMANYOFTHEUNNECESSARYFEATURESOFTHECURRENTLYAVAILABLEMACHINESSOTHATFABRICATIONCOULDBEDONEINANUNSOPHISTICATEDWORKSHOP,WHILEENSURINGTHEVERSATILITYTOPERMITTHEPRODUCTIONOFACCEPTABLEEXTRUDEDFOODSESPECIALLYUSINGBLENDSOFFRUITSANDCEREALSTHISLATTERTECHNIQUEWASDEVELOPEDBYGAMLATH1995USINGASINGLESCREWEXTRUDERTOPRODUCEARANGEOFEXTRUDATESTHATSHEADJUDGEDTOSHOWGREATPROMISEASASNACKFOODORBREAKFASTCEREALINSRILANKAINPARTICULARBUTALSOINMANYDEVELOPINGCOUNTRIESANDALSOASAHIGHVALUEEXPORTTHESEPRODUCTSWERELARGELYBASEDONMIXTURESOFFRUITANDCEREALSSUCHASMANGO,BANANAANDTOMATOWITHMAIZE,RICEANDWHEATATTRACTIVELYTEXTUREDANDFLAVOUREDITEMSWEREPRODUCEDWHICHCOULDEASILYBEFURTHERFLAVOUREDWITHSPICES,SUGARANDSALTMANYDEVELOPINGCOUNTRIESUSEHOMEBASEDBUSINESSESTOPRODUCESNACKSANDREADYTOEATMEALSANDTHESEPRODUCTWELLINTOTHISWELLESTABLISHEDCULTUREMACHINESMADEINTHEDEVELOPINGCOUNTRY,HOWEVER,NEEDTOBELOWCOSTANDRELATIVELYSIMPLE,EASYTOMAINTAINANDOPERATEINTHISSTUDYTHEPARTICULARFEATURESREQUIREDWEREGOODTRANSPORTCHARACTERISTICSFORSTICKYMATERIALSANDGOODMIXINGABILITYWHICHARENEEDEDFORTHEBLENDEDCROPSSELECTEDSHORTRESIDENCETIMESANDLOWTOMEDIUMPRESSURESWEREACCEPTABLE2DESIGNAPPROACHTHEDESIGNOFTHEEXTRUDERINTHISSTUDYWASMOSTLYBASEDONTHERESULTSOFEXTRUSIONSTUDIESDONEUSINGASINGLESCREWLABORATORYSCALEEXTRUDERSBRABENDER,WARRINGTON,CHESHIRE,UKASPARTOFTHESAMEPROGRAMME,ANDSUPPORTEDBYENGINEERINGPRINCIPLESANDCONSTRAINTSAPPLICABLETOADEVELOPINGCOUNTRYINTHEDESIGNPROCESS,THELEVELOFPRESSURELIKELYTOBEDEVELOPEDWITHINTHEEXTRUDERBARRELBECOMESTHEMOSTIMPORTANTFACTORASITDETERMINESTHESIZESOFALLTHEIMPORTANTCOMPONENTSOFTHEEXTRUDERSUCHASBEARINGS,SHAFTDIAMETERSANDBARRELDIMENSIONSASTHESEMACHINESOFTENOPERATEUNDERELEVATEDTEMPERATURES,PRESSURETENDSTOVARYUNPREDICTABLYBECAUSEOFCOMPLEXRHEOLOGICALPROPERTIESOFFOODDOUGHASRELATEDTOVARYINGTEMPERATUREALONGTHEBARRELTHEREFORE,ACTUALMEASUREMENTSOFEXTRUDERPROCESSVARIABLES,WEREMADEONTHECHOSENRANGEOFFOODMATERIALSONTHELABORATORYSINGLESCREWEXTRUDERTHISAPPROACHWASRECKONEDTOBEMOREAPPROPRIATERATHERTHANATHEORETICALONE,THATCANNOTBEGENERALISEDESPECIALLYFORMATERIALSOFUNKNOWNRHEOLOGYHENCE,APPROXIMATEVALUESFORSOMEOFTHEMOSTIMPORTANTPARAMETERSSUCHASDIESIZES,PRESSURES,TEMPERATURESETCWEREQUANTIFIEDTHESEVALUESWERETHENTESTEDAGAININTHEEXPERIMENTSDESCRIBEDLATERFORTHETWINSCREWSYSTEM21SINGLEVSTWINSCREWSMANYCOMPARISONSBETWEENTWINANDSINGLESCREWEXTRUDERSHAVEBEENMADEHARPER,1992HAUCK,1985HAUCKBENGERA,1987VANZUILICHEM,STOLPJANSSEN,1984ANDMANYOFTHEFEATURESDISCUSSEDARERELEVANTTOTHECURRENTAPPLICATIONSINGLESCREWMACHINESMEETMOSTOFTHECRITERIAFORDEVELOPINGCOUNTRIESBUTUNFORTUNATELYCERTAINOFTHETECHNICALREQUIREMENTSCANONLYBEMETBYTWINSCREWSSUCHASVERSATILITY,ADEQUATEOWOFFEEDINTOTHESCREWSAND,PARTICULARLYINTHISCASE,OWOFTHEMATERIALDOWNTHEBARRELWITHOUTSPINNINGWITHINITTHISISACOMMONPROBLEMWITHTHERATHERSTICKYORHIGHMOISTUREMATERIALSTHATWEREENVISAGEDWITHTHEINCORPORATIONOFFRUITSANDVEGETABLESANDOTHERTROPICALCROPSANDFLAVOURSANDEXPERIENCEDBYGAMLATH1995THEFORWARDMOTIONOFTHEFOODDOUGHRELIESENTIRELYONTHEFRICTIONBETWEENTHEMATERIALANDTHEINTERIORSURFACESOFBOTHSCREWANDBARRELTHISISPARTICULARLYSOINASINGLESCREWBUTLESSSOINATWINSCREWSINGLESCREWEXTRUDERSAREGENERALLYCHEAPERTHANTHETWINSCREWTYPEOWINGTOTHEIRSIMPLERCONSTRUCTION,BUTTHEYAREMORELIKELYTOBLOCKTHANTWINSCREWEXTRUDERSTHEDILEMMAFACINGTHEDESIGNER,THEREFORE,ISTHATALTHOUGHTHEOPERATIONALPROBLEMSCANBEAVOIDEDBYUSINGTWINSCREWSTHEIRSOPHISTICATEDCONSTRUCTIONALFEATURESWOULDHAVETOBESIMPLIFIEDSIGNIFICANTLYTOACHIEVETHELOWCOSTOBJECTIVEINTWINSCREWEXTRUDERSTHESCREWSCANBEMADEASEITHERCOROTATINGORCOUNTERROTATING,WITHDIFFERINGAMOUNTSOFINTERMESH,PITCHANDCLEARANCES,ALLOFWHICHAFFECTTHEPROCESSINGCHARACTERISTICSOFTHEMACHINEMARTELLI,1983SINCETHEFLIGHTOFONESCREWENGAGESTHECHANNELOFTHEOTHERTHETWINSCREWSPREVENTMATERIALFROMSTICKINGTOTHESCREWSANDROTATINGWITHTHESCREW,HENCEENCOURAGINGFORWARDMOTIONOFDOUGHWITHREDUCEDSLIPJANSEN,1978THISALSOENHANCESTHEMIXINGOFMATERIALSINTHECHANNELSOFTHESCREWSTHECOUNTERROTATINGTYPEOFTWINSCREWEXTRUDERCANGIVEBETTERMATERIALOWCHARACTERISTICSPUSHINGTHEMATERIALPOSITIVELYFORWARDTOWARDSTHEDIEBUTREDUCINGTHEDEGREEOFMIXINGOFMATERIALSWITHINTHEEXTRUDERANOTHERUNFORTUNATEFEATUREISTHATSEPARATINGFORCESBETWEENTHESCREWSCANCAUSESEVEREWEAROFTHESIDEWALLSONTHEOTHERHAND,COROTATING,TWINSCREWEXTRUDERSGIVEADDITIONALADVANTAGESSUCHASPRESSUREBALANCEINTRANSVERSEPLANESOFTHESCREWSANDAWIPINGACTIONOFTHEFIGHTSDUETOTHEOPPOSINGLINEARVELOCITIESATTHEFIGHTSOFINTERMESHINGREGIONTHEREFORE,ITWASDECIDEDTHATATWINSCREWCOROTATINGEXTRUDERWOULDPROVIDEALLTHEVERSATILITYANDCHARACTERISTICSREQUIREDFORPROCESSINGTHEFOODMATERIALSENVISAGEDINADEVELOPINGCOUNTRYTHEONLYPROBLEMTHENWASTODESIGNASATISFACTORYMACHINETHATWOULDALSOMEETTHECOSTCRITERIA22SCREWSTHECENTRALPARTOFANEXTRUDERISTHESCREWTHESCREWSROTATEINATIGHTLYFITTINGBARRELANDCONVEYTHEMATERIALFROMFEEDENDTODIEEND,MIXINGANDCOMPRESSINGTHEINGREDIENTSTHECAPACITYOFTHEEXTRUDERISMAINLYDETERMINEDBYTHESCREWOUTERANDROOTDIAMETERS,PITCHANDFIGHTWIDTHFIG1THEREFORE,THESCREWOVERALLDIMENSIONSHAVETOBEFIRSTDETERMINEDACCORDINGTOTHEDESIREDOUTPUTTOINITIATETHEDESIGNPROCESSONEOTHERIMPORTANTFACTORISTHERESIDENCETIME,ASITDETERMINESTHEDEGREEOFCOOKINGTAKINGPLACEINTHEEXTRUDEREXPLORATORYTRIALSANDTHEWORKOFGAMLATH1995INDICATEDTHATARESIDENCETIMEOFABOUT16SWOULDBEADEQUATEATTHEMEANSPEEDITIS,HOWEVER,INFLUENCEDBYMANYOFTHEDESIGNPARAMETERSINCLUDINGTHELENGTH,DIAMETERANDPITCHOFTHESCREWSALTHOUGHITCANBECONTROLLEDLARGELYBYTHEOPERATIONALSCREWSPEEDOFTHEEXTRUDERANDTHESELECTEDDIESIZETHERHEOLOGYOFTHEMATERIALALSOHASAMAJORINFLUENCEONTHETHROUGHPUTSORESIDENCETIMECANNOTBEACCURATELYPREDICTEDINTHISSTUDYSEVERALDIMENSIONSOFTHESCREWSWEREDETERMINEDINORDERTOSUITTHEEXPECTEDOUTPUTANDRESIDENCETIMETHEGEOMETRYANDEQUATIONSRELATINGMANYOFTHESEFACTORSAREGIVENINFIG1ANDEQS13BELOWTHEMAXIMUMOUTPUTWASNOTTHERSTPRIORITYBUTSIMILARSIZEDEXTRUDERSANDSINGLESCREWTRIALSINDICATEDATYPICALDELIVERYRATEOFUPTO10KG/HTHERESIDENCETIMEWASDESIGNEDTOBESHORTASTHENOVELPRODUCTSPLANNEDWERENOTEXPECTEDTORELYONLONGPROCESSINGTIMESTHESHORTRESIDENCETIMEWASPARTICULARLYSOUGHTINORDERTOMAINTAINTHEVITAMINCCONTENTOFPERISHABLEPRODUCTSWHICHCOULDBEEASILYDESTROYEDIFCOOKEDTOOLONGSEILER,1984THEINFLUENCEOFSCREWPITCHISSUCHTHATLOWVALUESWITHSMALLHELIXANGLESLEADTOLONGERRESIDENCETIMESBECAUSEOFTHEINCREASEDNUMBEROFCYCLESTHATTHEMATERIALHASTOGOTHROUGHONTHEOTHERHAND,LARGEPITCHESWOULDREDUCETHEDEGREEOFMIXINGANDUNIFORMITYOFHEATDISTRIBUTIONDUETOTHEINCREASEINVOLUMEOFMATERIALCONTAINEDINTHESCREWCHANNELS