HANDBOOKOFCANESUGARENGINEERINGSUGARSERIESVol. StandardFabrication Practices for Cane Sugar Mills (Delden)Vol.2.Manufacture and Refining of RawCane SugarVol.3.By-Products of the Cane Sugar IndustryVol.4.UnitOperations in Cane Sugar Production (Payne)Vol.5. Noel Deerr:Classic Papers of a Sugar Cane Technologist (Payne, Compiler)Vol.6. The Energy Cane Alternative (Alexander)Vol.7.Handbook of Cane Sugar Engineering (Hugot,3rd edition)HANDBOOKOFCANESUGARENGINEERINGE.HUGOTet Manufactures, des Sucreries de Bourbon,Saint-Denis(Reunion)Revisedbytheauthor,with thecollaborationof thetranslator,andtranslatedbyG.H.M.Sc.App.UniversityofQueensland(retired),St.Lucia,Brisbane (Australia)THIRD,COMPLETELYREVISED,EDITIONAMSTERDAM-OXFORD-NEWYORK-TOKYO1986ELSEVIERSCIENCEPUBLISHERSSara 25P.O. BoxAEThe NetherlandsDistributors fortheUnitedStates andCanada:ELSEVIERSCIENCEPUBLISHINGCOMPANYINC.52,VanderbiltAvenueNew York,Firstedition1960Second impressionSecond, completely revised, edition1972Second impression1979Third,completely revised,edition1986ISBN (Vol.7)ISBN(Series) SciencePublishersB.V.,1986All rights reserved. No part of this publication may be reproduced,in a retrieval system, ortransmitted in anyformor by anymeans,mechanical, photocopying, recording, orwithout the prior writtenpermissionof thepublisher,Elsevier Science Publishers B.V./Science & TechnologyDivision,P.O. BoxAH Amsterdam, The NetherlandsSpecial regulationsforreaders intheUSA-Thispublicationhas been registeredwiththe CopyrightClearance CenterInc.(CCC),Salem,Massachusetts.InformationcanbeobtainedfromtheCCC aboutconditionsunderwhichphotocopies of parts of this publication may be made in theUSA.othercopyrightquestions, includingphotocopyingoutside of theshouldbereferredtothepublisher.PrintedinTheNetherlandsPrefacetothethirdeditionThetechnologyofsugarmanufacturehasevolvedsomuchinthecourseofthelasttwelveyearsthatthepreparationof athirdeditionhasnecessitatednotonlytherevisionof thema-jor portion of the text but also the addition of numerous,entirely new sections.As importantrevisions and new sections,there will be found in particular in this new edition,the following:PowerfulmodernshreddersPressurefeederstomills,AustraliantypeNewformulaeformaximalspeedofmillsAnewformulaformillcapacityAmorecompletetableforcalculationofpowerrequirementsinmillingNewsystemsof driveformillsMillrollersTheLotusrollerCalculationofweightofbagasseandweightofjuicesinthemillingtandemCalculationofmaterialbalanceinthetandemAnewformulaforreducedextractionAnewtypeofdiffuserlimingofjuiceRapidclarifiersModificationofexistingclarifiersforrapidDorrclonesNewformulaeforheat-transfercoefficientinheatersEvaporatorvesselswithlateralorannulardowntakeHeatbalanceforthefactoryFalling-filmevaporatorsFormulaeforestimatingcoefficientkforflowinvesselandpancalandriaFormulaeforsteamconsumptionofpansThemethodof calculatingthematerialbalancefortheboilinghouseContinuousvacuumpans,includingLangreneyVertical-crystalliser coolersContinuouscentrifugalsSugardryersStandardfactorycontrolLiquid-annulusairpumpsWaterrequirementsofthefactoryForced-draughtcoolingtowersRain-typecondensersandcondenserheatersDryingofbagasseSteambalanceofthefactoryformaximumeconomyPelletisationofbagasse.Ontheotherhand,sectionsdiscussingequipmentorprocesseswhichareoutdatedorob-soletehavebeendeleted.Readerswhoarestillusingsuchequipmentormethodswillfindthemdescribedinthesecondedition.Theseinclude:CrushersReciprocatingsteamenginesCompoundclarificationCirculatorsinevaporatorsairpumps.For basic measures and quantities,wehave adoptedthe metricsystem,whichisbecomingmore andmore general.Among countrieswhichhave adoptedit recently,somehave chosenthe International System Accordingly,the table of equivalent units has been completedbyaddingthesebut,onaccountofthepracticefollowedverygenerallyandwhichretainsthetraditionalunits,suchaskilogramforce, thesehavebeenutilisedforpreference.Conversionwithinthemetricsystem,moreover,isverysimpleandimmediate.To avoidany difficultyfor those engineersin English-speaking countries whofind themselvesmoreateasewiththeirBritishunits,andtoavoidinvolvingourfriendsoftheAmericanhemisphere inconversionswhichare sometimes awkward,we have giveninthe greatmajori-tyofcases,informulaeandcalculations,valuesinBritishunitsalongsidethoseinmetricunits.Wheregiven,tonsandgallonsinallcasesarelongtons(2,240 or1,016.047kg)andImperialgallons (4.5461),respectively.Tablesoffigureshaveinmostcasesbeengiveninbothsystemsofunits.Wehopewehavethusgivensugartechnologistsausefulworkofreference,particularlyusefulforcalculationsanddesignprojects.Theintroductionofsubjectsofpresent-dayin-terest,such as continuous pans and centrifugals,or steam economy tofacilitate sale of powertooutsideauthorities,shouldassistthosesugarproducersexposedtoeconomicorfinancialdifficulties.Weshallbehappyifthesugarworldisabletobenefitbyit.Thechapteroninformationandautomationinthesugarfactoryhasbeenwrittenentirelyby George Windalof SNFS,Directorof the andhiscolleagueJ.C.Giorgi,bothworldauthoritiesinthatfield.Thischapterenhancesthevalueandtheinterestofthebook,andweexpressourdeepgratitudetothem.We thankourfriendsof SASTA,QSSCTand as wellas thedirectorsof engineer-ingfirms(FCB,BMA,deSmetandmanyothers),whohaverepliedinclearandfriendlyfashiontoourrequestsforinformation;andweexpressourdeepgratitudetoourfriendGeorgeJenkinswho,inhisusualfriendlyandcooperativeway,hasinterruptedawell-deserved retirement to take on the heavy taskof translation.To ithe has brought all his com-petenceandknowledgeandhisclearandpleasantstyle.E.forewordOnce again it has been a pleasanttask to cooperate withmy friendHugotin translationof arevisionoftheHandbook.Theextentof revisionhasbeenrather greaterthanexpected,butthisisnotsurprisinginviewofMr.Hugot'sthoroughnessintreatmentandrevisionofhiswork.Inadditiontokeepingupwiththeliteraturevery hehasvisitedprac-ticallyalltheleadingsugarindustriesof the worldinrecentyears.Ihave indeedfoundthattherevisionincludesmuchmaterialnewtome,coveringnewdevelopmentsintheindustrysinceIwaslastincontactwithsugartechnologysometwelveorfourteenyearsago.Thanks again to Mrs.JoanHodgson,whodid the typing for the first edition and has againdoneanexcellentjobwiththepresentrevision.G.H.Thisthirdeditionof theHandbookofCaneSugarTechnologyisdedicated tothe memoryof George Jenkins,avery good friend andavalued colleague,whodied suddenlywhile thevolumewas inthefinal stagesof production.Hewasthetranslator forallthreeedi-tionsof the Handbook,anditis fittingthatthis editionshould bededicatedtohiminacknowledgementofhisimportantcontribu-tiontothework.E.HUGOTListof chapterheadingsDelivery,unloadingandhandlingofcane.2.Thecanecarrier.3.Caneknives.4.Tramp-ironseparators.28.5.Crushers.6.Shredders.JO.7.Combinationsofcanepreparators.8.Feedingofmillsandconveyingof52.bagasse.53.9.Rollergrooving.54.10.Pressuresinmilling.55.Millspeeds.56.Millcapacity.37.13.Millsettings.38.14.Powerrequirementsofmills.39.15.Electricdriveofmills.40.16.Milldrivebysteamturbine.41.17.Millgearing.42.18.Constructionofmills.43.19.Imbibition.44.20.Extraction.45.Millingcontrol.46.22.Fine-bagasseseparators.23.Diffusion.Defecation.Sulphitation.Clarificationwithphosphoricacid.Carbonatation.Useofmagnesiainclarification.Subsidation.Juiceheating.Filtration.Evaporation.Sugarboiling.Crystallisation.Centrifugalseparation.Storageanddryingofsugar.Sugar.Molasses.Boiling-housecontrol.Vacuumequipment.Steamproductionandusage.Steamturbines.Electricity.Pumps.Pipingandfluidflow.Automationanddataprocessing(byG.WindalandJ.C.Giorgi).ReferencesReferencesarelistedattheendofeachchapter,followingtheusualmethodinEnglish-language publications.The abbreviations used are generally self-evident,with the possible ex-ceptionofthefollowing:-InternationalSocietyofSugarCaneTechnologistsQSSCT-QueenslandSocietyofSugarCaneTechnologistsSASFPI-SouthAfricanSugarFactoryPlantInstallationsSASTA-SouthAfricanSugarTechnologists'Association-SugarMillingResearchInstituteTSJ-TheSugarJournal.ContentsPrefacetothethirdedition,vTranslator'sforeword,viiListofchapterheadings,ixReferences,xChapter1.Delivery,unloadingandhandlingofcane,1Organisationofcanesupplythroughouttheday,1Unloadingofcane,3Cane-handlingequipment,6Lateralfeedingtablesandcarriers,16References,20Chapter2.Thecanecarrier,21Chapter3.Caneknives,32References,48Chapter4.Tramp-ironseparators,49Chapter5.Crushers,51Object,crushers,51Valueof2-rollercrusher,56crusher,56Extractionofacrusher,59Large3-rollercrusher,59References,59Chapter6.Shredders,60Object,60Location,60Functionoftheshredder,60Searby-typepulveriser,63Bulkdensityofcanepreparedbyshredder,70Totalpowerforcanepreparation,70References,72Chapter7.Combinationsofcanepreparators,73Chapter8.Feedingofmillsandconveyingofbagasse,74Feedplateto 74Feedhopperbetweencrusherandfirstmill,75Intermediatecarriers,76Deliveryplateatlastmill,85Feedingarrangements,85Bagasseconveyors,98Coefficientoffrictionforcaneandbagasse,99References,100Chapter9.Rollergrooving,101Object,101Circumferentialgrooves,101Messchaertgrooves,107Chevrons,111Kaygrooving,Wearofrollers,References,Chapter10.Pressuresinmilling,117Hydraulicpressure,Pressureconsideredfromtheoperatingviewpoint,125Pressuresinmills,130Nomenclature,175Reference,176Chapter Millspeeds,178Linearspeedandspeedofrotation,178Maximalspeedsemployed,Speedsingeneralpractice,181References,185Chapter12.Millcapacity,186Definition,186Factorsinfluencingcapacity,186Capacityformulaeproposed,188Capacityformulae,188Relationofcapacityoffibreloading,195Tonnagerecords,197References,197Chapter13.Millsettings,199Object,199A.Feedanddeliveryopenings,200Measureoftheopenings,200Javamethod,201Methodofcalculatingoperatingopenings,206Deliveryopeningsandfibreloading,212Effectof housings,214Settingsemptyandopeningsinoperation,216B.Trashplate,217References,226Chapter14.Powerrequirementsofmills,227Factorsinfluencingpowerrequirements,227Generalformulaforpowerconsumptionofmills,229Generalrelationships,235References,239Chapter15.Electricdriveofmills,241Systemsofelectricdriveformills,244References,248Chapter16.Milldrivebysteamturbine,249Turbinesformilldrive,250Chapter17.Millgearing,253Speedreduction,253Drivetotherollers,256References,258Chapter18.Constructionof 259Housings,259Rollers,266References,279Chapter19.Imbibition,280Object,280Differentsystemsofimbibition,280Mathematicalstudyofimbibition,281Relativeweightsofbagasseandjuice,297Materialbalanceofthetandem,299Generalconsiderations,304Methodsofapplicationofimbibition,References,214Chapter20. 315Measureofefficiencyofmillingwork,315Factorsinefficiencyofmills,321Sanitationatthemills,326References,327Chapter21.Millingcontrol,328Extractionbydrycrushing,328Brixgraphs,331Basicequationformillcontrol,333Brixofabsolute 335Fibre,336Variousrelationshipsinmilling,337Sucroseextracted%cane,341Determinationofthevalueofthecoefficientk,347Normalvaluesofefficiencycoefficientk,348Useofthecoefficient,348Specialuseforfactorycontrol,348References,350Chapter22.Fine-bagasseseparators,352References,358Chapter23.Diffusion,359Briefhistoricalnote,359Limitationsofmills,359Diffusion,360Diffusionandlixiviation,365Batchdiffusionandcontinuousdiffusion,366Canediffusionandbagassediffusion,367Typesofdiffusion,369Generalconsiderationsondiffusion,396Choiceofmillsordiffusion,398References,398Chapter24.Defecation,399Clarificationofjuices,399Actionoflimeonthejuice,399XVDefecationprocedures,401Reactionofdefecatedjuice,404pHcontrol,404Eliminationofstarch,404Otherreagentsused,405References,406Chapter25.Sulphitation,407References,414Chapter26.Clarificationwithphosphoricacid,415References,416Chapter27.Carbonatation,417References,427Chapter28.Useofmagnesiainclarification,429References,430Chapter29.Subsidation,431orsubsiders,432References,447Chapter30.Juiceheating,448Calculationsforheaters,449Designofabatteryofheaters,457Constructionofheaters,462References,468Chapter Filtration,469Conditionsforgoodfiltration,469Typesoffilter,469Filterpresses,469Continuousrotaryvacuumfilters,476Accessoriesforcontinuousrotaryfilters,487Filtrationofsyrups,492References,492Chapter32.Evaporation,494General,494Multiple-effectevaporation,504Principleofmultipleeffects,504Constructionofmultipleeffects,506Circulationofsteamandvapour,514Condensates,516Incondensable gases,525Juicecirculation,529Entrainment,538Inversionlosses,541Heatlosses,543Incrustations,545Operationinparallel,553Vapourbleeding,554Vapourrecompression,555Operationofmultipleeffects,561Heatingsurface,570Calculationsanddesignofamultipleeffect,579Multiple-effectcalculations,588Evaporatoroperation,608Specialmultipleeffects,612Evaporationunderpressure,615Falling-filmevaporators,617References,624Chapter33.Sugarboiling,627Vacuumpans,635Effectsofhydrostaticpressure,647Massecuitecirculationinvacuumpans,649Evaporationcoefficient,662Heatingsteam,663Steamconsumptionatthepanstage,664Heatingsurfaceandratioofheatingsurfacetovolume,667Heightofmassecuite,circulation,heatingsurfaceandgrainingvolume,668Capacityofpans,669Sugar-boilingprocedures,670Molasses,677Conductofthesugarboiling,681Centralandindividualvacuum,685Instrumentsforpancontrol(G.H.J.),686Otherfactors,691Panswithmechanicalcirculation,707Continuousvacuumpans,712References,721Chapter34.Crystallisation,724Typesofcrystalliser,734References,756Chapter35.Centrifugalseparation,757Batchcentrifugals,757Electricdrive,779Operationofcentrifugals,790Continuouscentrifugals,794Accessoryprocessesandequipment,807References,816Chapter36.Storageanddryingofsugar,Sugarstores,818References,830Chapter37. 832References,835Chapter38.Molasses,836References,837Chapter39.Boiling-housecontrol,838References,851Chapter40.Vacuumequipment,852Vacuumsystems,853Thecondenser,855Weightofvapourtobecondensed,861Weightofcoolingwater,864Airpumps,868Rotaryliquid-annulusairpumps,870Thebarometriccolumn,880Waterpumps,883Sprayponds,885Raintypecondensers,894894Jetcondensers,897XV111Steam-jetejectorcondensers,901References,905Chapter41.Steamproductionandusage,906Steam,906BagasseCombustionofbagasse,924Fuelsotherthanbagasse,940Furnaces,942Thegrate,952Performanceofdifferentfurnaces,956Heatingsurface,958Superheatandsuperheaters,960Economisers,965Air-heaters,972Choicebetweeneconomiserandair-heater,980Dryingofbagasse,984Boilersettings,988Draught,989Fans,993Boilerfeedwater,995Steamaccumulators,1000Steam-reducingvalves,De-superheating,1004Typesofboiler,1006Constructionofboilers,1009Maintenanceofboilers,1012Steambalance,1012Maximumeconomy-powerforexternaluses,1016Saleofpowerbythesugarfactory,1023Generalarrangementofthesteamcycle,1029References,Steamtables,1035Chapter42.Steamturbines,1047Concisetheoryofthesteamturbine,1047Impulseturbinesandreactionturbines,1050Specificationsforaturbine,1065References,1071Chapter43.Electricity,1072Directcurrentandalternatingcurrent,1072Three-phasealternatingcurrent,1072Generationofelectricity,1075Alternators,1079Electricmotors,1082Conductors, 1097Powerhouse,References,110144.Centrifugalpumps,Rotarypumps,1108Screwpumps,References,Chapter45.Pipingandfluidflow,GeneralFlowofsteamandgases,1123References,Chapter46.Automationanddataprocessing(byG.WindalandJ.C.Giorgi),1126Ahistoricalexample:operationofsugarboiling,Modernconceptsofautomation,Astructureofautomation,Anexampleoftechnicalmanagement,Managementandcontrolofproductionprocesses,Conversiontables - metrictoBritishunits,Conversiontables - Britishtometricunits,Equivalentsofforeign,Britishandmetricunits,Subjectindex,1.Delivery,UnloadingandHandlingofCaneThefactorytakesdeliveryof thecane,eitherdirectlyatthefactoryweighbridge,orataux-iliary weighbridges serving certain important or remote points in the area from which the milldrawsitssupplies.Transportisarrangedbythefactory,eitherbyrailway,ormoreoftenbylorries,orbytractorsandtrailers.Thebulkdensity,orweightperunitvolume,of caneinthetruckdependsonthemannerinwhichitisloaded.InHawaii,forinstance,itmaybepickedupinbulkinthefieldbyamobilecranemountedoncaterpillartracksandfittedwithagrab.Thissimplydropsthecaneinatangledmassintothetrailer;inthiscasethebulkdensitymaybetakenasabout200 kg/m3 (12 If the loading is done rather more carefully:300 (18In afigure of 225 - 256 (14-16Ib./cu.ft.)isused.If the caneisloadedbyhand,thestalksbeingplacedparalleltoeachotherinbundlesorpackages,asisoftendone withsmallsuppliers,the densitymay betakenasabout350 (22Ib./cu.ft.)andmayreach400 (26Ib./cu. Ifthecaneiscutbyachopperharvesterandloadedinbulk,thedensityisapproximately300-380 (18-24Ib./cu. averaging340forpieces28cm in.)inlength.InHawaii,figuresofIb./cu.ft. )aregiven;in 300-330 (19-21Ib./cu.Thisbulkdensitydependsonthestandofthecane.Straightanderectstalkswillgiveamorecompactloadingthancurvedorlodgedcanes.ORGANISATIONOFCANESUPPLYTHROUGHOUTTHEDAYAcanesugarfactorygenerallyoperatescontinuouslyfromMondaymorningtillSaturdayevening.Itshutsdownforabout36hours,includingSunday,forcleaningthemultipleef-fectsandforminorrepairs.Itoperatesthenforabout132hoursperweek.Duringtheday,canetransportisgenerallycarriedonforonly12hours,from6a.m.to6 p.m.So that the mill willnotrun outof cane,itisnecessary thatthefactoryshouldreceivein12hours,duringtheday,thetonnagewhichitcrushesin24hours.Towards6p.m.thentherewillhaveaccumulatedastockatleastequaltohalfthedailytonnage:Overnightprovision=12A+aA=quantityofcanecrushedbythefactoryperhoura=marginofsafety,whichshouldalwaysbemaintainedtoavoidbeingobligedtostopthemillforlackofcane.UNLOADINGANDHANDLINGOFCANE Ch.IThismarginaisnecessarytomakeprovisionforaccidentalfluctuationsin rainretardingthecuttingandrestrictingtransport,irregularitiesinsupplybythefarmers,etc.Itshouldnotbetoosmall,nortoolarge. thelattercase,thecaneyardwillbeuselesslyen-cumbered,andthedelayoccurringbetweenthecuttingof thecaneanditspassagethroughthe beunnecessarilyincreased.Asuitablequant i t yisthatcorrespondingtothreehours'crushing:a=3A (1. 2)tf thisvaluebeadopted,theyardshouldbeabletoaccommodateanovernightstockof:P= + = (1.3)Fig.1. 1.Slingwi t hautomatichook.Fig.1.2.Li f t i ngabundleUNLOADINGOFCANE3OFCANEAsdrayshavepracticallydisappearedfromthescene,wediscussonlycanetransportedbymechanicalmeans:trailers,lorriesandrailwaywagons.Lorriesandothervehiclesareeitherunloadedontoapilebymeansof acraneorareself-discharging.A.Unloading bycrane.Thiscaneisoftenloadedin"packets"orbundles,boundbythreechainsor"slings"(Fig. Atone endtheseslingsslideinaspecialhookfittedwi t hapawl,whilearingisattachedtotheotherend.Theunloadingdeviceatthefactory,generallyacrane,liftsthebundleofcanewiththeaidofa"swingle-bar"orsteelbarfittedwi t hthreehooks.Thecraneliftsthebundleanddepositsitontheheapof cane whichiscalleda The catchesof the sling-hooksarethenreleased,andthecraneliftstheswingle-barwiththeslingshanging(Fig.1.2).Releaseofthecatchmaybecontrolledelectrically.For a 3-tonne crane,eachbundleisof the order of kg ofcane,generallyabout2.500kg(5,000 A4-or5-tonnet ruckcarriestwosuchbundles.Whentheswinglebarisreplacedbyagrab(Fig.1.7),t ruckscarryingcaneinbul kmayalsobeunloaded.Thegraboperatesmainlyatnighttotransfertothelateraltablesthecanestackedduringtheday.1.3.Unl oadi ngbytippingt r uck.DELI VERY,UNLOADINGANDHANDLI NGOFCANE Ch.1B.Self-dischargingvehicles.Severaltypesoftheseareinuse,t hemai nonesbeing:(a)Tippingtrucks.Thesearet r ucksf i t t edwi t habodywhi chisarrangedtopivotaboutitslowerrearedge,andact uat edbyahydraul i cdevicewhicht i l t sthet ruckbodytowardsthebackt i l litsloadofcaneslidesintotheconveyorarrangedtoreceiveit(Fig.1.3).Thisconveyorisgeneral l yani ncl i nedl at eraltable,ri si ngt owardst hefrontsot hatitdischargest hecanei nt othecarrierfromaheightofabout1.5 (5f t . )abovei t ;itsrearendislocatedinapi tofapproxi mat el y2m(6f t . )indept h.Thecanefallsi nt ot hi spi t ,whi chisdefinedatt hebackbyaplateri si ngabout0.6m(2f t . )abovegroundlevel,lowenoughnottoin-terferewi t hthet i ppi ngoft het r uc k.Theslopeoft hi slateralt abl eisapproxi mat el y15fort heslatconveyortype,and8forthetypewi t hfixedplatesandmovingbrackets. lengthaccordinglydependsontheleveloft hecarrierrel at i vetotheground,andisgenerallyoftheorder m(20 30 Thecaneslidesfromthet r uckbodywhenitreachesani ncl i nat i onofabout40-45.(b)Truckswithdetachablebodies.Thisisasi mi l arsystem,exceptt hatthet r uckbody,calleda"bin"or"basket",isseparatefromthechassisonwhichitrests,andmaybeplacedonthegroundorl i ft edontothechassisbymeansofeithermobilecranej i bscarriedonthechassisor a winchplacedbehindt he cabin.Int heformer case,itcanbe tippedi nt ot he carrierint hesamewayasat i ppi ngt r uck.I fseveralbinsaresuppliedforeacht ruck,thesecanbefi l l edint hefieldwhi l et het r uckisr et ur ni ngwi t hanempt ybi n;assoonastheempt ybinisunloadedataconveni entpoi ntfort hecanecut t ers,af ul lbincanbeloadedont het ruckimmediatelywi t houtlossoft i me.Asimilardeliveryandpick-upcanbeeffectedatt hefac-Fig.1.4.Canet r anspor tbydet achabl econt ai ner(l oadi nginUNLOADINGOFCANEFig.1.5.Unl oadi ngtory;thusarapidturnaroundof thet ruckisachieved,andagoodcapacityintonnesof canetransportedperday(Fig.1.4).Numerousmodificationsofthissystemareinuse.(c)Tractorsand withnets.Semi-trailersgenerallyoflargetonnage(25 - 40tonnes)arefittedwithabodyofsteelmesh(Fig.1.5).Ononeofthesidesofthebodyisfixedasteelnetwhichdropsdownthatside,passesacrossthebottom,risesontheoppositeside,towhichtheendofthenetisattached.Inthefieldoratthecaneloadingstation,thecaneisloadedinapileonthisnet.Onarrivalatthefactory,thetractorstopsalongsideadeep,large-capacityauxiliarycarrier,thesideofthetrailerbodycarryingt hefixedendofthenetbeinglinedupalongsidethecarrieranddirectlyabovethesideofit.AcranethenDELIVERY, ANDHANDLINGOFCANE Ch.hooks onto the opposite endof thenetand it;the contentsarethustippedintotheaux-iliarycarrier(Fig.(d)Flat-toppedbulktrailers.Smalltrailersthatcanbeattachedbehindlightfieldtractorsareoftenused,especiallyinSouthAfrica.Thecaneisplacedin onthegroundwithstalksasfaraspossiblelyingparalleltoeachother.Acableisplacedunderthepile,andbroughtbackaboveit;awinchplacedonthetractorthenhaulsinthecable,thushaulingthe pile of cane up on to the trailer.Many versionsthis device are withrear or lateralloading.Suchdevicesarcinexpensivebut,thecanesbeinglooselypacked,thewidthof theloadmay themaximumpermittedonthe andtheiruseshouldbelimitedtofieldsdirectlyconnectedtothefactorybyprivateroads(Fig.1.6).CANE-HANDLINGTheprincipaltypesofequipmentusedatt hefactorycaneyardare:The crane,or"derrick"(2)Thetravellingcrane(3) tippingplatformortrucktip(4)Thecanerake.1.6.LoadingCANE-HANDLING1.CanecraneThisisbyfarthemost-used I(isoftencalledbyits name: Itconsists(Fig.1.8)ofamastoffabricatedsteel,mountedonapivot,so itcanrotatethroughafullcircle.Ata height!hisverticalmastcarriesahorizontalarmforminga trackon which a trolley,carrying two pulleys,canrunto andfro.A cable passes over thesepulleysandhangs t husformingaloopwhichcarriesa block,onwhichmaybehung the orthegrab.worksinacabin,whichis atthe ofthemastorbelowthearmandhouses forthevariousmovements:rotation,traversing,raisingorloweringof hook.Italso houses windingdrums.These aredrivengenerallybyelectricmotor.Theyareclassifiedaccordingtotheirmodeofsupport,into:(a)Guyedcranes(Fig.1.8),nowusedlessandless(b)Self-supportingcranes 1.9).(a)Guyedcranes.Thisisthelighterform,thestabilityof cranebeingensuredbyre-tainingcablesorguyropes toaringatthetopofthemast(Fig.1.8).Theseguysmustpermitofrotationof horizontalarm,andsomust fixedingroundataconsiderable fromtheaxisofthecrane. of guys. Strictly speaking, 3 guy ropes, arranged at an angle of 120 to each other,besufficient.However,thenumberofguysisgenerallychosensothatbreakageofDELIVERY,UNLOADINGANDHANDLINGOFCANECh.1Fig.1.8.Canederrick guys.Fig.1.9.Ten-tonneself-supportingderrick.CANE-HANDLINGEQUIPMENT9oneofthemdoesnotcausethederricktofall.Thisconditionrequiresaminimumof 5,at72.Forpreference6or8shouldbeused,ifpossible.Itwouldbenecessarythentofix5,6,7,or8anchorblocks,placedsymmetricallyonacircleof55-75 (180-240ft.)radiuswiththeaxisofthecraneascentre,towhichtheguysareattached.Thepresenceoffactoryandofficebuildingsmakesthesolutionofthisproblemverydifficult.If itisnecessarytomodifythespacingoftwocablestoavoidinpar-ticularthefactorybuildings,itisnecessarytoensurethatabreakageof oneof thesewidelyspacedcableswillnotleaveasectorofmorethan whichisthelimitpermissibleforstabilityoftwoadjacentcables.Obviously,in case of breakage,itwillbe necessary to stop the crane immediately untilthedamagedcableisreplaced,sincetheremainingguyswouldnotbeabletoensurestabilityunderthedynamicloadingofthecraneinoperation.Tensionof thecables.Toobtainmaximumrigidity,thecablesmustbetightenedsothatthemastdescribesonlyaverysmallconeasthederrickisrotated,butwithoutincreasingundulythetensionof thecablesthemselves.Thistensionshouldbecheckedfrequently.Thecablesshouldbepaintedortarredeverytwoorthreeyears(topreventcorrosion).Thicknessof the cables.Foracraneof3tonnescapacity, cablesof 25mm(1in.)diameterareprovided.(b)Self-supportingcranes.Theseareobviouslyheavierandmoremassive(Figs. and1.9),butavoidthenuisanceanddangerof guys,whichrestrictmovementatthecaneyardandwhicharesometimesverydifficulttolocateconveniently.Incountriessubjecttocyclones,thesecranesshouldbedesignedforawindpressureofatleast350orpreferably400 (80 (liveload).Capacityofcranes.Theimportantcharacteristicsofanunloadingcraneare:(1)Theliftingforce(2)Theradiusofoperation(3)Themaximumheightofliftofthegrab.(1)Lifting force.Thisisthemaximumweightwhichthecranecanlift,attheendofthearm.Itisthemostimportantfactor,whichservestospecifyitscapacity.Forinstance,onespeaksofa3-tonneor5-tonnecrane.Theusualvaluesare3,5and10tonnes.(2)Radius of operation.This is the horizontal distance between the pivotof the crane anda vertical line through the pulley of the snatch block(corresponding to the centre of the grab)whenthetrolleyisatitsextremepositionattheendofthecranearm.Typicalvaluesare:18,25and30m (60, 100(3) Maximumheight of lift.Thisistheheightfromtheendof thetinesof the grababovetheplatformlevel,whenthegrabisraisedtoitsmaximumheight.To increase this height,and atthe same timeto enable the driver to oversee the operations10DELIVERY,UNLOADINGANDHANDLINGOFCANECh.1andtrafficoftheplatform,thebaseofasmall(3t.)derrickisgenerallyraisedbyplacingitonatruncatedconeofmasonryabout2 (6ft.)inheight.Theheightofliftisgenerallyoftheorderof m(20-25Asageneralrule,forafactoryhavingonlyonederrickatitsunloadingstation,thecharacteristicsadoptedareapproximatelyasfollows:(1)Liftingforce:F=0.1A(1.4)F=liftingforce,intonnesA=crushingrateofthefactory,int.c.h.(2)Radiusofoperation:R=3 (R= (1.5)R=radiusofoperation,inm(3)Maximumheightoflift:H=8m(25ft.)(1.6)Whentwoderricks (or two unloading devices) are available,the total tonnage Ais dividedbetweenthembyallottingthetonnages and respectively,suchthat+ =ASpeedsandpowerrequirements.Thespeedsadoptedforthevariousmovementsofthecrane,andthepowerrequiredforthecorrespondingmotors,aregenerallyofthefollowingorder:(1)Lifting:LiftingspeedPowerrequired7.5kW(10 pertonnenominalcapacity(2) Rotation:Rotational speed 1.5 2.5Powerrequired1.0kW(1.5h.p.)pertonnenominalcapacity(3)Traversing:Speed of the trolleym/minft./min)Powerrequired0,75kW(1h.p.) tonnenominalcapacityWhenthecraneisdrivenbycompressedair,thesinglemotorrequiresapproximately7.5kW(10h.p.)pertonnenominalcapacity.CANE-HANDLINGEQUIPMENT 11Lateral tables.I nlargeormedi umfactories,i tisnecessarytoprovideoneormorel at eraltables,onwhicht he crane or cranesdepositcane.Int hi scase,t hecarrier doesnotreceivethecanedirectly,butisfedbytheselateraltables,controlledbyanoperatorwhoregulatestheirspeedasrequired.Thefeedingofacarriersuppliedint hi swayismuchmoreregularthanint hecaseofdirectfeed.Bulkdensityof caneinthepile.Thisdensi t yissi mi l artot hatof caneloadedmechanically,orabout200 ( 12 if i treferstocanedumpedatrandom.Itincreasesto300(18I b. / cu. f t . )ifthepileismadeupofbundlesofparallelst al ks,depositedbyt heswingle-bar. estimates400 (25Forcanecutinsmallpieces0.3-0.6 f t . )inl engt h,asproducedbycert ai nmechanicalharvesters,afi gureof350 (22I b. / cu. f t . )maybe2.TransportercraneFactorieshandl i ngmoret han150or200 mayfi ndt hederri ckbarelyadequateforstorageandhandlingof the cane.Theythenresorttouseofthetransportercrane,whichhasgreatercapacityandismoreeasilyaccommodated.Thesystemiscloselyanalogoustot hatofthederrick.Insteadofacircle,itservesarec-tangle,thelengthandbreadthofwhichmaybefixedatwi l l .Fort hi sreason,itwillbein-dicatedforcertainlongandnarrowcaneyardswhi chhavenotsuf f i ci entspaceforacranetoswing.Thet ransport ercranemustobviouslyspanthecanecarri erwhi chitserves(Fig.1.10).Fig. Tr avel l i ngcrane(Fi ves -12 DELIVERY,UNLOADINGANDHANDLINGOFCANE Ch.1Normalspeedsareapproximately:RaisingthehookorgrabLongitudinalmovementofthecraneTraversingmovementofthetrolley15-30 m/minft./min)30-60m/min(100-200ft./min)In addition,two minutesmust be allowedfor each movementfor detaching the chains andreturningforthenextThecorrespondingpowerrequirementsofthemotorsareapproximately:Lifting:4.5kW(6 pertonnenominalcapacityLongitudinalmovement:1.0kW(1.5h.p.)pertonnenominalcapacityTraversingmovement:0.25kW(0.3h.p.)pertonnenominalcapacityOftenboththederrickandtransportercraneareused,andthiscombinationisreadilyadaptabletoalltypesof unloadingarea.Oneadvantageof thetransporter craneisthatthestorage capacity canbe readily increased,by increasing itslengthof travel.When it becomesverylong,itmaybeof advantage toprovide thelengthof trackbymeansof twotransportercranes,whichcanthenworksimultaneously,eachoneservingoneendofthecarrier.Theworkisfurtherfacilitatedifeachoneisprovidedwithitsownlateraltable.Thewidthof transportercranesisof theorderof100 Theircostin-creases muchmore rapidly withincreasing width thanwithincreasing length.The lengthmayhavealmostanyvalueupto100m(300ft.)foradoubletransportercrane.Theheightofliftis8- 13m ft.)andthecapacitygenerally tonnes.3.TipfortrucksortrailersWhen the cane arrives by railway trucks,itis more practical to empty the truck inone action,Fig. Lateraltipfortrucks. Fig.1.12.Smalltruckforend-tipping.CANE-HANDLINGEQUIPMENT 13Fig.1.13."Wicks"rakeratherthantoliftseparately,withthecrane,thebundlesofcanepiledinthetruck.Thispresentsseveraladvantages:(1)Savingintime(2)Savinginslings(thisisbynomeansnegligible)(3)Lesshandling,becausethecaneisemptieddirectlyintothecarrier,aswithdrays(4)Thankstotheabsenceofslings,theriskofpassingpiecesofchainorratchethooks14DELIVERY,UNLOADINGANDHANDLINGOFCANECh.1throughthe isavoided.Withacraneandslings,itisveryrarelyt hataseasoniscom-pleted,int heabsenceofamagneticseparator,wi t houtremovingtwoort hreesuchpiecesfromthemills;therollergroovingsuffersseverelyasaresult.Therearetwotypesoftip:(1)Thelateraltip,forlargewaggons(Fig.(2)Theendwiset i p,forsmallt r ucks.Thet rucks(Fig. areprovidedwithaU-shapedironframeformingacradle,inwhicht hecaneisplacedlengthwiseparalleltothetrack.Theendsarefree,andthecane,wellcom-pactedduri ngthej ourneyfromthefieldstot hefactory,fallsoutwhenthet i preachesthedesiredi ncl i nat i on(40-45).Tipsaresometimesi nst al l edforlorriesalso.Thelorryisgenerallytippedendwise,t owardtherear.Theangleofdischarge,forwholeorchoppedcaneloadedinbul k,isapproxi mat el yTipsaredesignedforamaximuminclinationofapproximately48.4.RakesTheseformanauxi l i aryunloadingdevice,whichisusedmostlyinJavaandinsomeBri t i shcountries.Figure givesaviewwhi chwillmakedescriptionsuperfluous.Itwillbenotedt hattherakehasnotonlya"picking"movementanda move-mentinameanplane,butt hati tcanalsomaket hesamemovementinagreatnumberofplanes,formingadihedralangleof some3040toonesideort heotherof t hi smeanplane.Fig.1. 14.Loading inbi l l et sLcgrasCANE-HANDLINGEQUIPMENT 15Chopper-harvestedcaneMechanicalharvestingof caneisgenerallycarriedoutbychopperharvesterssuchastheMas-sey-Ferguson, Toft, Cameco,Thomson,J.& L.(Fig. These are machines whichcutthe cane,chopping iti nt o pieces 25 - 30 cmin.)inlength,and discharging iti nt oat ruckort rai l ermovingalongsidet heharvester.Whent hevehicleisfilleditisremovedandreplacedbyanother.Theset rucksortrailerscirculateint hefield,holding tonnesofcane,andthentransfertheirloadtoaroad(orrail)vehiclewhichrunst helengthofthefield,holding25- 30tonnesofcaneandtransportingitsloadtothefactory(Fig. OnesuchFig. Trailerwi t hmovi ngboltom(Legras).Fig.1.16.Transferri ngcanei n (Legras).16DELIVERY,UNLOADINGANDHANDLINGOFCANECh.1transportwidelyusedinFrenchcountries,andelsewhere,istheLegrastrailerwithconveyorbottom.Thistrailerhasaslatconveyorwhichformsthefloor,andadoorattheback.Onarrival at the factory, it stops above a pit,the door is opened and the conveyor set in motion;thechoppedcanefallsontoatableatthebottomofthepit(Fig.1.16).StorageincontainersAmong newly established sugar enterprises,some produce themselvesthe greater part of thecanewhichtheycrush.Thesehaveadoptedthefollowingsystem:thecutcaneisstackedincontainers of large volume,for example,12 m(40ft.)inlength,2.50 (8ft.)inwidth,2.50 (8ft.) in height and of 75(255in volume,holding abouttonnes of cane.Thesecontainersaretransportedfromthefieldtothefactoryonflat-toptrucksanddepositedinrowsontheunloadingareaatthefactory.Theyareunloadedintheorderinwhichtheyarrive,ontothelateraltables,eitherbytipsorbydischargingnets.Pusher - stackertransferOtherestablishments,equallynew,arecontentwithdischargingthecaneonareservedsec-tionofthecaneyardwhichisconcretedandonwhichoneortwospecialisedmachines,equippedwithapusherbladeorlargescoop,pushthecaneintoaregularheap2or3m(6or9ft.)inheight.Thesesamemachineslaterbringthecanebacktofeedthecanecarriertables.Generally,therearetwosuchmachines,onereceivingthecaneandstackingit,theotherbringingitbackandfeeding the conveyor.Thisarrangementpermitstheformationoftwostacks,onoppositesidesof theyard;thusitispossibletofinishonestackbeforecom-mencing onthe other and so to avoidleaving one portion of the caneslonger in the yard thanthe other.Delivery of the cane may be carriedout around the clockor over12 hours per day.In the latter case,the area of the unloading yardshould consequently be calculated as afunc-tion of the height of the stack,arranging the space necessary for manoeuvring the two mobilemachines.These are generally provided withfour-wheelsteering,to give a very small turningcircle.LATERALFEEDINGTABLESANDCARRIERSWhenthenumberoftrucksisinsufficient(whichmayoccuratcertainfixedtimesofday,oraccidentallyatanymoment),thecranemakesupthecanesupplytothecarrierwiththeaidofthegrab.However,variationsoccurinthequantityof canesodepositedperunitlengthof thecar-rier;thereare gaps which cannot be filledintime.On the otherhand,a bundleof canefromalorry,depositedalmostintactonthecarrier,cancauseanoverloadattheknives,inthecaseofelectricdrive,openingthecircuitbreaker.Whensuchdensebundlesof parallelcanesoccur,itisnecessarytoslowdownthecarrierand practically stop it,otherwise there is a riskof chokingtheknives.Even withclose atten-tion,theattemptisnotalwayssuccessful.These difficulties,due tothe directfeedingof the carrier,haveledtothe adoptionof aux-iliarycarriers.ManyofthesedisadvantagesareindeedovercomebyprovidingasecondorLATERALFEEDINGTABLESANDCARRIERS 17auxiliarycarrieratri ghtanglestot hemaincarrier.Suchacarriermaytaketheformof:(1)Awideandrelativelyshortplatformor"lateraltable"(2)Acarrieridenticalwi t ht hemaincarrier,butatright-anglestoi t .Thisisoftencalledan"auxiliarycarrier".1.LateraltableThisisineffectaverywideandshortcarrier,drivenbyanindependentmotor.Inplanitisrectangularorapproximatelysquareinshape.Theupperrunofthelateraltableshouldendatapproximately2 (6ft . )abovethatofthemaincarrieranditsdischargeendalmostverticallyabovethesideplateoft hecarrier.Thecranedepositsthecaneonthistable,andkeepsupt hesupplytoitasitdischarges.Anattendant,convenientlylocatedtowatchthewholeofthecaneyard,andhandytothespeedcontrolofthemotorwhichdrivesthelateraltable,st art situpwheneverheseesthatthemaincarrierwouldotherwisebei nsuffi ci ent l yloaded.Thecanefallsfromthelateraltablei nt o carrier,andoneadvantageofthissystemisthatthecanefallsinamoreorlesstangledcondition,greatlyfacilitatingtheworkof thecaneknives.Assoonasthedesiredquant i t yof canehasfallenontothecarrier,thelateraltableissloweddownorstopped.Themovementofthelatteristhusveryirregular,interruptedandjerky,anditisadvantageoustodriveitbymeansof averyflexiblevariable-speeddevice,suchastheFrenchor the Englishand drive.These provide a drive withoutsolidcontact:asteelflywheelcoupledtothemotortransmitsthedrive,byinducedFoucaultcurrents,toasleevesurroundingitandconnectedtothedrivenshaft.The lateraltableispart i cul arl yusefulincountrieswherepaymentforcaneismadeaccor-dingtosugarcontentorrecoverablesugar.Thecanetobetestedfromaparticularsuppliermaythenbeaccumulatedonaspeciallateraltable,wi t houti nt er f er i ngwi t hthefeedingofthemills.Whenthetableisfilled,itsloadofcaneisfedtothemillswithoutinterruptingFig. Canet umbl er(Fives18DELIVERY,UNLOADINGANDHANDLINGOFCANECh.1themovementofthemaincarrier;thebeginningandendofthebatchtobeanalysedaresimplymarkedwithlime,insuchaway thatthe juicesampleboycanseeclearlythebeginn-ing andendof the batch.Tumbler.Thelateraltableismuchmoreeffectiveiffittedwitha"tumbler".Thisisahorizontalshaft(Fig.1.17),placedabovetheaxisof thefrontdrumof thetable,andwhichrotatesslowlyinthereversedirection.Itisprovidedwitharmsarrangedinahelixalongitslength,whichensurethatthecanefallsintothecarrierinsmalllots,avoidingaheavyfalloflargemasseswhichwouldbeliabletoprovokechokesattheknives.High-speed tumblers may also be used,running at100 and furnished with smallknives atthe endof the arms;these give a more regularfeed andcut someof the cane stalks,thusassistingtheworkoftheknives.Areaofthelateraltable.Thedimensionsofthetablevaryconsiderablyaccordingtoin-dividualcases.Agooddimension,designingforamplecapacity,is:= (S=6 A)(1.7)S=areaofthelateraltable,in (sq.ft.)A crushingrateofthefactory,int.c.h.Forexample,atableof5x7m(16x20ft.)for50t.c.h.Forcrushingratesgreaterthan70 itisof advantagetoprovidetwolateraltablesratherthanonelargeone.Thedimensionsof thesewillbearrangedtofollowthesamerule:+ = A/3(S,+ =6A)(1.8)Threeorfourtablesmaybeusedforonecanecarrier.Speed of the table.By reason of its width,the speed of the lateral table is made much lowerthan that of the main carrier. A value of 3 6(10 20may be adopted. Withahigherspeed,thereisariskthattoomuchcanewillbedroppedonthecarrieratatime.Powerrequiredforthemotor.AmotorshouldbeprovidedofpowerroughlyequaltoT=0.25S(T=0.023S)(1.9)T=powerofthedrivingmotor,inh.p.S=areaofthetable,in (sq.ft.).Thisvalueisobviouslyappreciablygreaterthanthemeanpowerabsorbedbythemotorinoperation.Slope.Lateraltablesmaybehorizontal,ormayhaveaslightforwardslopeofabout5,oraslopeof15towardstherear.Thislastarrangementallowsthelengthtobeextendedtothepointwheretippingtruckscandelivertheirloaddirectlyontothetable,thusavoidingextrahandlingandlossoftime.LATERALFEEDINGTABLESANDCARRIERS 19Fig.1. 18. cane- craneandl at eral t abl es2.Auxiliarycarrier(crosscarrier)Thisisacarrieroft hesamedimensionsast hemaincarrier,butwi t hitsaxisatright-anglestot hatoft helatter,anddi schargi ngtoi t .I tsuppliest hemai ncarrierinthemannerofaregulatingt r i but ar ywhi chfeedsandevensoutt hemainstream.Speed.Itwi l lbedrivenataspeedabouthal ft hatofthemaincarrier.Power.Sinceitissubjecttosomewhatmoref r i ct i on,wemayprovide,iftheconveyorishori zont al :T = 0.34 5 (T=0.05T=powerabsorbedbyt he carri er,inS arealoadedwi t hcaneont heauxi l i ar ycarri er,in ( sq. f t . ) .ConstructionofcrossconveyorsThesetablesorcarriersshouldmovebetweentwol at eral plates,designedtoguidet hecaneandpreventitfromfal l i ngbesidet hecarri er.Thesesideplatescanconveni ent l ybe givena10bat t er .20DELIVERY,UNLOADINGANDHANDLINGOFCANECh.1REFERENCES1L.FOLEY,Sugar Azucar,1(1977)46.2U.A.PERALTA, ABDUKADIKOV,M.FONSECAANDM.DOMINGUEZ,Int.Sugar 83(1981)210.3L.A.TROMP,Int.Sugar 60(1958)40.4Sugar Azucar,56 (1961)28.5L.A.TROMP,Int.Sugar 62(1960)67.6 (116)(1978)114.2.TheCaneCarrierThecanecarrieristhemovingapronwhichconveysthecaneintothefactoryandwhichassuresthefeedtothemillsbytransportingthecanefromtheyardtothecrusher.Sinceeffectivefeedingofthecrusherrequiresanelevatedhopper,andthecanemustberaisedtothishighlevelfromthelevelof theyard,wherethecarrierisgenerallyinapit,thecarrieralwaysincludesaslopingportion(Fig.2.1).Wehave:(a)The horizontalportion(b)Theinclinedportion(c)Theheadwherethecanearrivesabovethecrusher.Fig. Canecarrier(Fives- Babcock).SlopeTheslopeoftheinclinedportionvariesfrom27%(15)toamaximumof40%(22).Generally,avaluebelow27%isnotused.If too aslopeisadopted,thecostof thein-stallationandthespaceoccupiedareincreased.Avalueof 40%isnotexceeded,otherwisethe cane would beliable toslipand the conveyorwould moveforward withoutpicking itup.Thebestandcommonestvaluesare30%(17)to38%(21).Whennoknivesareinstalled,orwhentheknifesetisatthetopofthecarrier(whichamounts to the same thing),it isadvisable to keepthe slope at33or Whenone or twosetsofknivesprecedetheinclinedportion,orarelocatedatthebeginningofthelatter,aslopeof38%(21)maysafelybeadopted,andmayevenattain40%(22)ifnecessary.LengthofinclinedportionThislengthwillbethatnecessarytoattain,withtheinclinationadopted,thedesiredlevelabove the crusher.Generally,the height from the ground level at the mills to the highest pointofthecarrierwillbeabout:22THECANECARRIERCh.26-7m ft.)inthecaseof anordinary crusher,locatedabovethefirstmillm ft.)inthecaseof a mill-crusher(3rollers).Assumingthefloor-levelofthehorizontalportionofthecarrier,intheyard,tobe1m(3ft.)belowthegroundlevelatthemills,andbasingourfiguresonaslopeof36%,thein-clinedportionofthecarrierwillhavealengthof:(a)Withanordinarycrusher:=m (64-72ft.)(2.1)0.36(b)Witha crusher:= = m ft.)(2.2)0.36LengthofhorizontalportionThe lengthof thehorizontalportionisdeterminedbythewidthof lateraltablesorthespacerequiredforotherunloadingdevices.WidthThe widthof thecarrierisalwaysmade equaltothelengthof themillrollers.Awider carrierwouldnotfeedthecrusheruniformlyoveritswidth,sinceitwouldnecessitateafeedhopperin theform of a portionof apyramid,convergingtowards the crusher;the endsof the rollerswillthusreceiveaheavierfeedthanthecentre.Anarrowercarrierwouldhavetheoppositedisadvantage,which,however,wouldbelessmarkedonaccountof thespreadingof thecutcanesinthechute.SpeedThespeedofthecarrierisnotfixedinanyabsolutefashion.However,itisadvisablethatitberelatedtotheperipheralspeedofthemills,forexample,halfofthelatter: ==meanspeedofthecarrierv=meanperipheralspeedofthemills,inthesameunit.Weshallconsider howthe thicknessof caneonthecarrierwillvary,underthiscondition.Thecapacityofthecarrierhasthevalue:1,000A=60 (2,240A=60 (2.4)A=crushing rate,in t.c.h.M=speedofthecarrier,inL=widthofthecarrier,inm(ft.)SPEED23h=meandepthofthelayerofcaneonthecarrier,inm(ft.)d=bulkdensityofthecaneonthecarrier:d=150 (9Ib./cu.ft.)(tangledcanes)d=175 (11Ib./cu.ft.)(parallelcanes)d=300 (18Ib./cu.ft.)(caneafterknifepreparation).Weshallassumethecaseoftwosetsofknivesandashredder,thekniveslocatedbeforetheslopingportion.Wehavethen:A=18Luh(A=0.536Luh)(2.5)Weshallseelater(eqn. thatthenormalcapacityofthemills,A,hasavalue:0.9 (1-0.06 nD) _ (1-0.018nD)A (A=o./ /A=capacityofmillswithknifepreparation,int.c.h.=speedofrotationofthemills,inL=lengthofrollers,inm(ft.)D=diameterof inm(ft.)N=numberofrollersinthetandem/=fibreperunitweightofcane.But:v= or: =-(2.6)v=peripheralspeedofthemillrollers,inWhence:0.285cLvD (1-0.02v) 0.008cLvD(1-0.06v) 0.=Substitutingthisvalueineqn.(2.5)andtakingu=v/2,wehave:0.032 -0.02v)_0.03 cD(1 -0.06 v)-_0.03 cD(1-0.06- (2.7)h=beinginm(ft.)c=coefficentforpreparatoryplant.If we neglect the correctionterm(1-0.06v),whichvariesonly slightly withvandcausesaslightdecreaseinthecanelayerwithincreasingmillspeeds,weseethatthethicknessofcane,fornormaloperationofthemills,willvary:24THECANECARRIERCh.2InverselyasfibreincaneDirectlyproportionaltorollerdiameterProportionaltothesquarerootofthenumberofrollers.If,insteadof acarrierspeedproportionaltothatof themills,wehadadoptedaconstantspeed,independentof thatof themills,forexample,5 (15 wewouldhavefoundthathwouldvaryas:thatis,thethicknessofthecanelayerwouldbeproportionaltothesquareoftherollerdiameter,andwewouldarriveatexcessivethicknessesinthecaseoflargemillsandlongtandems,workingathighspeeds.For this reason it is preferable to relate the speed of the cane carrier to the mean peripheralspeedvof themillrollers.Thethicknessof thecanelayeristhenproportionaltoD,whichislogicalsinceitvariesproportionallytoalineardimensionofthemill.In general,we adopt:=v(2.8)CarrierslatsCanecarrierslatswerepreviouslymadeofwood.Thismaterialisnolongerfoundexceptincertainlateraltables;itisunsuitableforuse withknives,onaccountof the stressesimpos-ed onthe carrier apron in its passage below the knives,and especially because piecesof canewouldfallthroughthespacesbetweentheboards.Fig.2.2.Steelcarrierslats(Fives- Babcock).Carrieraprons(Fig.2.2)aremadeupofsteelslatswhichoverlapbyaroundededgeintheformof acylinderconcentricwiththerollerswhichcarrythechainandthepinswhichjoinsuccessivelinksof thechaintogether.Thisroundededgepermitsapassageof theslatsoverthesprocketsattheheadandfootofthecarrier,whilemaintainingtheoverlap,andgivestheapronthenecessaryflexibility.Theapronisgenerallysupportedbytwochains,sometimesthreeinverywidemills.PowerThemeanpowerabsorbedbythecanecarrierconsistsoftwoterms:(a)Thepowernecessarytoovercomefriction.Ithasthevalue:60x7560x550POWER25=powernecessarytoovercomefriction,inQ=weightofcaneonthecarrier,inkg=weightoftheupperrunoftheconveyor,inkg=weightofthelowerrun=halfthetotalweightofthemovingpartofthecarrier/=coefficientoffrictionoftheupperrun,oftheorderof0.30/=coefficientofrollingfrictionofthelowerrun,oftheorderof=speedoftheconveyor,inX=coefficientof theorderof- allowingforthe efficiency of the gearingtransmit-tingthedrive.The valuesgiven takeintoaccountallsourcesof friction,aswellasallowingforacertainproportionofrollerswhichdonotrotate,ordonotrotatefreely.Theyalsoallowforthedifferencebetweentherollingfrictionoftheupperrun,onalltherollers,andthe lower run, on loose pulleys of large diameter.If the upper run slides,instead of workingon rollers,itwouldbe necessary to =0.60.The theoreticalcoefficientforrollingfric-tionisThecoefficients0.30and0.15takeintoaccounttheinclinedportionof thecarrier,whichtheoreticallyshouldbecalculatedseparately,takingintoaccountthecosineandsineoftheangleofinclination.However,themarginoferrorinthecoefficientsoffrictionmakesitsuperfluoustointroducethisrefinement.Theterm:(6 +60X75 60x550representsthefrictionoftheupperrununderload.Theterm:60x75 x550thatofthelowerrun,empty.Also,wehave:Q= (2.10)=loadedlengthofthecarrier,inm(ft.)(forsafetywetakethefulllengthoftheapron)L=widthofthecarrier,inm(ft.)h=thicknessofthecanelayeronthecarrier,inm(ft.)d=bulkdensityofthecaneonthecarrier(cf.eqn.(2.4)h=isgivenbyeqn.(2.5).Wehavealsomoresimply:26THECANECARRIER 22,240Ontheotherhand:(2.12)Z,=totallengthofthecarrierapron,inm(ft.)p=weightperunitlengthoftheactualchain,inkg/m (weassumetheslatsarecarriedby2chains)-weightoftheapron(orslats)perunitlengthofthecarrier,inkg/m(Ib./ft.)Weshalltake:p kg/m(12-20Ib./ft.)accordingtothetypeof chainp '=kg/m per m of width (i.e.(8 - 10for steel slats. Hence,Ib./ft.length)fora 2m(6ft.)carrier.(b)Thepower necessarytoelevatethecane:3,600x75 3,600x550=powernecessarytoelevatethecane,inh.p.A-crushingrateofthemills,int.c.h.H=differenceinheightbetweenthehighestpartof thecarrier,abovethecrusher,andthehorizontalpartof thecarrierintheyard,inm(ft.)X=coefficientdependingontheefficiencyofthegearing,varyingfrom1.4to1.5.Finally:P=meantotalpowerabsorbedbythecarrier,inh.p.Roughly,wemayreckon,asafirstapproximation,3Z.+A' '(2.14)+Ah.p.(P ==totallengthofthecarrier,inm(ft.)A=crushingrateofthemills,int.c.h.Theinstalledpowershouldbeappreciablyhigher,say:3 +A Z.+A\(2.15)' V'10/CARRIERDRIVE27CarrierdriveThecanecarrierisalwaysdrivenindependently,byelectricmotor.Asthisisessentiallyaconstant-speed machine,and the carrier speedmustbefrequently varied,the drive is effectedthroughavariable-speedcoupler.Variable-speedcoupling using Foucault current.Some organisations,particularlythefirmof and inEngland,supplycouplingswhichmaybeinterposedbetweenthe motorand thedrivengears,permittingaveryprogressiveandflexiblespeedvariationofthedrivenshaftfrom0to Thisdrivehasalreadybeenmentionedinconnectionwiththedriveforlateraltables(p.17).Aflywheel,drivenbytheelectricmotor,turnsfreelyin-side a sleeve.Thelatter,bymeansof gearsorbelts,drivesthe shaftatthe headof the carrier.Bymeansof asuitablecontrol,actuatedbyaknurledknoborahandwheel,Foucaultcur-rentscanbeinducedintheflywheel,andtheirintensityvariedatwill.Asthesecurrentsareincreased,the drive betweenflywheel andsleeve becomes more and more positive.Thus anydesireddegreeofslipcanbeobtainedbetweenthesetwoelements,andconsequentlyanydesiredspeedofthedrivenshaft.Thismethodisneatandflexible;itscostisnotexcessive.Itmaybeemployed,notonlyfordrivingthecanecarrier,butalsoforlateraltablesandauxiliarycarriers.Inadditiontohandcontrol,thecouplingmaybecontrolledbyanelectricmotor,e.g.,byonephaseof theknifemotor.Inthisway,thespeedofthecarrierisautomaticallyreducedwhentheknivesareloaded,andincreasedintheoppositecase;thisservestoavoidchokesattheknivesandtoassurearegularfeedtothemills.Inplaceof electricalcontrol,speedvariationmaybeeffectedbyhydraulicmotor(seep.37).TensionThefreeendof thecarrierisfittedwithanadjustmentpermittingthetensionof theconveyorto beadjusted.Sincethedriveislocatedattheheadof thecarrier,andtheresistancetothemovementisproducedbytheloadedupperrunof thecarrier,itisthelowerrunwhichwillbeslack.Careisnecessarytoensurethatthisslackisneithertoomuch,nortoolittle.TheFig.2.3.Effectofshapeofcarrierhead.Straighthead.Fig.2.4.Effectofshapeofcarrierhead.Curvedhead.28THECANECARRIERCh.2tensionmoreoverneednotbegreat;thelowerrunisallowedtoform pronouncedcurvesbetweentheidlerpulleys.FormofheadofthecarrierTheknivessometimesleaveacertainproportionofuncutsticksatthebottomofthecanelayer.These sticksform a kindof grating at the bottom of the layer,which supports the chipsandpiecesofcutcaneandpreventsthemfromfallingcontinuouslyfromthetopofthecar-rier.Ifthecarrierweretoterminateabruptly,theinclinedportionfinishingrightatthetopsprockets,thecanereachingtheupperendofthecarrierinthiswaywouldfirstjutoutbeyondthecarrierandthenfallinbatchesintothefeedhopperofthecrusher(Fig.2.3)ormill.Thefeedofthecrusherwouldbeirregular,jerkyanddefective.Toavoidthisdisadvantage,theheadofthecarrierisdesignedwithagradualcurve,tangentialtotheslopingportion,sothatthesurfaceofthecarrierbecomesfirsthorizontal,thenslopesdownwardsuntilitalmostreachestheangleofreposeofcane(orcutpiecesofcane).Thecanewillcontinuetofallinbatches,butthesebatchesaresmallerandmorenumerous,andtheintervalsbetweenthemmoreuniform.Thecanemayevenformacon-tinuousblanketfromthecarriertothecrusher(Fig.2.4)orthemill.Itisnecessarythereforetogivecarefulattentiontotheformoftheheadofthecarrier.CaneelevatorsWhenspaceisrestricted,theinclinedportionof thecanecarriermaybereplacedbyacaneelevator.Thisisasimilarpieceof equipment,butdesignedtoliftthecaneatamuchsteeperangle(Fig.2.5).Itoperatesoncutcanes,sincetheelevatorisalwayslocatedafteratleastthefirstsetofknives,andgenerallyafterbothsetsofknives.The slope may thus be increased up to In general it is maintained between 35andHowever,above the conveyor is no longer an ordinary carrier and it is desirable to makeprovisionforpreventingslipofthepiecesofcane:angleirons,spikes,orhooksplacedontheslatstogiveapositivegriponthecane.Such elevators have,almost inevitably,the disadvantage described above; they end abrupt-ly,anditwouldbedifficulttogivethemasuitablecurvedformatthetop.Speed.Theelevatorsaregenerallygivenaspeedof6- 10 Forpreference,avaluewillbechosen:u=0.3-0.5v(2.16)Fig.2.5.Caneelevator.EQUALISERS 29=speedoftheelevatorv=meanperipheralspeedofthemills.Power.The power required is calculatedfor elevatorsasfor carriers.Since the inclinationis no longer negligible,the term eqn.(2.9)should,however,be multipliedby the cosineoftheangleofelevationandwillconsequentlybereducedproportionately.EqualisersTheterm"equaliser"isusedtodescribeanapparatusdesignedtoevenoutthedistributionof cane on the carrier,and to level the layer of cane to a certain extent(Fig.2.6).Thismustnotbeconfusedwiththe"leveller",whichisasetofknives,andwhichevensoutthelayerofcanewhilecuttingFig.2.6.Equaliser.Description.Anequaliserconsistsofashaftplacedacrossthecarrier,carryingcurvedarms,and rotating in sucha direction that thearmspassing nearest thecarrierboards movein the opposite direction tothelatter.Thus the direction of rotation of the equaliseris suchastothrowthecanebackwards(Fig.2.6),whereasthecaneknivesgenerallyrotateinsuchadirectionastothrowthepiecesofcaneforward(Fig.Use.Anequaliserisinstalledwhenthecaneisverytangledonthecarrierandwhenthelevellingknives,setfairlylow,wouldthemselvesbeunabletolevelthecaneadequately.Theequaliser isthus a secondary andinexpensive piece of equipment,placedafter theknives,anddesignedtolightentheirduty.Itisnotoftenfoundsincetheuseofasecondsetofkniveshas become general.Speed.Anequalisershouldrotateatabout40-50Clearance.Theshaftwillbesetatsuchaheightthatthedistancebetweentheendsofthearms and the carrierslats is slightly lessthanthe height given byeqn.(2.5),inwhichmaybetakenas130 (830THECANECARRIER Ch.2,Fig.2.7."Auto-cane".Feeler(EdwardsEng.Corp.).Fig.2.8. Drive assembly,wi t hmotors,f i l t er ,hydr aul i ctransmission,speedcontrolandoilreservoir(EdwardsEng.Corp.).Power.AmotorofpowerP = 0.15 A(P=0.2A)(2.17)p=power thedrivingmotor,inA=crushingrate,inAUTOMATICCONTROLOFSPEEDwillgenerallysufficetocopewiththefrequentoverloadscausedbythepassageofcompactbundlesofcanedepositedonthecarrierbythecrane.AutomaticcontrolofspeedMostfactoriesinrecentyearshaveinstalledtheirownsystemforensuringtheregularfeedofcaneintothemillingplant,orhaveadoptedasystemofferedwiththesameobjectbyamachinerymanufacturer.Thebestknownsystemforsuchregularisationofcanefeedisthe madebythe EdwardsEngineeringCorporation.Itcomprisesadetector,ahydraulicmotor,andcontrolequipment.Thedetector(Fig.2.7)consistsofanumberofbars,oneendofwhichrestsonthelayerof cutcaneaftertheknives,whiletheotherendispivotedonashaftandactuatesasleevemountedconcentricallyonthatshaft.Variationsintheheightofthecanelayerarethusregisteredinandtotalised,andfurnishasignalwhichistransmittedtoamotor.Thelatterdrives an oil pump the output of whichdrives a hydraulic motor which inturndrivesthe shaftattheheadofthecarrier.Thespeedofthelatteristhusmaintainedinverselyproportionalto the thicknessof thelayerof cutcane,insucha way thatthe volumedeliveredbythe carrierremainsconstant.Thecontrolequipmentallowsof adjustmentofspeedtosuitthedesiredtonnage.Thiscanberegulatedfrom25to100%ofitsmaximumcapacity.Thedetectorcanbeusedonlyonthecutcaneafterpassingthroughtheknives;ifashred-derisinuse,theresultcanindeedbebetter.Thepoweroftheelectricmotoris8-16kWdependingonthecapacityof thetandem.The"Autocane"andsimilardevicesassureaveryuniformfeed,eliminatingthenecessityforanoperatorplacedatthecarrier,andleadingtoagainincrushingrate,thankstotheregularityoffeedandtheeliminationofchokes.CaneKnivesObjectandusesKnivesarenotanindispensableitemofequipmentinthesugarfactory,inthesensethatitwouldbepossibletooperatewithoutthem.Before1920,manyfactoriesdidnotpossessknives.However,thisequipmentgivessuchanimprovementinfeedingthattodayitisnolongeraquestionofdoingwithoutthem.Aknifeset,forafactorywhichdoesnotpossessone,wouldverysoonpayforitself.With whole cane,the attempt atobtaining a completely evenfeed to the mill isnever reallysuccessful.Byplacingan"equaliser"(seep.29)overthecarrier,acanelayerofnearlyuniform thicknessmaybe obtained.However,thislayerwillreachthe millonly insuccessivelumps,andits smallbulkdensitywillrenderdifficult the workof the crusher,which consists,inshort,of"swallowing"asmuchcaneaspossibleinagiventime.Furthermore,themetalofthemillrollersoftenslipsonthesmooth,waxyandpolishedrindofthecane;hencechokesoccur,withshortorlonginterruptionstothefeedoradecreaseincrushingrate.The ontheotherhand,supplythecaneinveryshortandsmall pieces.Whereas whole canes lean one against the other,arching over and leaving voidsbetween them,these small pieces settle together into a compact mass,which drops easily intothefeedhopper,andwhichthecrusherwillgripwithouttroubleandwillabsorbinacon-tinuousmanner.Betweenwholecanesandcaneswhichhavepassedthroughtheknives,thereisthesamedifferenceasbetweenahandfulof matchesandahandfulof sawdust.Thedifferenceexistingbetweenthesetwostatesof thesamematerialcanbereadilyrealised.Itisshownintheirrespectivebulkdensities:Wholecanesmoreorlesstangled:Canespassedthroughknives: Ib./cu.ft.)Thecaneknivesthenperformtwofunctionsandhavetwoadvantages:(a)Theyfavourthecapacityofthemills(b)Theyassisttheextractionofthemillsbybreakingtherindofthecaneandsofacilitatingitsdisintegrationandtheextractionofitsjuice.Fromthepointofviewofitsresistancetopressure,canecaninfactbecomparedwitha longcylinder reinforcedwithtransverse dividingwalls(the nodes).Accordingly,it presentstothe aresistancesimilartothatofastickofbamboo,theinternodesofwhichhavebeenfilledwithasugar-bearingpulp(caneismoreoververycloselyrelatedtobambooandsuccessfulattemptshavebeenmadetocrossthesetwoplantsandsoobtainhybrids).Thepulpintheinteriorof thesecylinders,whichlieendtoend,willbemorerapidlyrecoveredasthecylindersareopenedandthedividingwallsbroken.DESCRIPTION 33However,thevalueofknivesforthetwofunctionsdescribedaboveisveryunequal:(a)Fromthepointofviewof capacity,nothingcanreplacethem.Iftherearenoknivesthecrushercanonlytakewhatitsucceedsingrippingoutofthelightandbulkymassofwholecanes.(b)Fromthepointofviewof extraction,onthecontrary,thecrusherandthemillshaveprecisely theobjectof breaking upthe cane,andcrushingthecasingof itsrindandthehardstructure of its nodes.It is possible then to carry out thisfunction of the knivesby good workat crusher andmills.Inparticular,the gainobtainedfromaknife installationfromthispointof view is appreciably inferior to the gainwhichone wouldobtainby the additionof afurthermill.Itisthenpredominantlytoimprovethecapacityof themills,thatknivesaregenerallyin-stalled.Chopped cane. The preceding remarks apply to the general case of cane delivered as wholestalks.Ifthefactoryreceivesallornearlyallofitscaneascutpiecesfromchopper-thecaseisverydifferentandthemainreasonforusingknivesdisappears.InAustralia,for example,the cane supply is100%chopper-harvested;the pieces moreover areclean-cut,straightandfreeofraggedends.Australianfactoriestakeadvantageofthisandhave completelyabandonedknives.Thecarrierthusdeliversthe canedirecttotheshredder,whichbecomestheonlypreparationdevice.Itisahigh-power,heavy-dutymachine,sincethechoppedcaneoffersmoreresistancethannormalknife-preparedcane.Fig.3.1.Caneknives.DescriptionStandardtype.Weshow(Fig.3.1)astandardtypeofknifeinstallation.Itconsistsofaheavyshaftof hexagonaloroctagonalsectionmountedonrollerbearings,andonwhicharethreadedorfixedarmseachcarryingtwobladessymmetricallyplacedwithrelationtotheshaft.Thesecondarmisoffset60relativetothefirst,iftheshaftishexagonal;thefollowingone is offset a further 60and so on.In this way,if thereare 36 arms,for example,the knifeinstallationwillconsistof 72bladesdistributedinrowsof12in6differentaxialhalf-planes(or 3 planes).In order to reduce the pitch and increase the number of cutting planes,the arms34 CANEKNIVES Ch.3carryingthekni vesaresofabricatedthatthetwobladesoneacharmrotateintwodifferentplanesseparatedbyhalfapitch.Thisdoublesthenumberofcuttingplanes.Viewedfromthefront,the72bladesthenrotatein72planesperpendiculartotheaxis,orso-called"cuttingplanes",consistingofsomanycirclesofrotation.The term"pitch"of knivesisthemeandistance,measured paralleltotheaxis,separatingtwosuccessivecirclesofrotation.Thekni febladesareremovable,sot hattheycanbeeasilytakenoffforresharpeningorforreplacementbyanothersetofblades.Itispreferabletofixakni fetothearminsuchawaythattheedgeaffectedbyshocksissupportedbyaflangeorawidestirrupratherthanfixingitsothatshocksareabsorbedbytheboltsorpinssecuringtheknife.Inthelattercase,theboltholebecomesovalisedandsomeplaydevelops,accentuatingtheeffectofshocks;theholet husformsasectionofweaknessinthekni fe,leadingtobreakage.Otherdesigns.Apartfromthisstandardtype,certainmanufacturershaveintroducedvariousmodificationsofdetail,theprincipalonesofwhichhavetheobjectsof:(1)Prolongingtheworkinglifeofthebladesbydiminishingwearofthecuttingedge.(2)Producingaself-sharpeningeffectoftheknivesonthetrailingedge,andsorenderingthemreversible(Figs.3.2and3.3).(3)Avoidingreductionofthelengthofthebladeswi t hwear.WiththeMirrlees bentorhoeknife,notonlydoestheradiusofactionremainconstantwi t hwear,butonealsoobtainstheeffectofatransversecutduetothebentendofthekni fe(Fig.3.4);andthistransversecutissuperimposedonthelongitudinalcutmadebytheradialpartoftheknife.(4)Diminishingorreducingtheconsequencesofshocks,bymount i ngtheknivessoastoswingonapin,obtainingatthesametimeaslightdisplacementofthecut t i ngpoints(Fig.3.5).Fig.3.2.Knifesetwith reversibleblades(Fives Fig.3.3.Reversibleblade.EFFECTONCANECARRIER 35Fig.3.4. "Hoe"knife.Fig.3.5.Swingingknives.Fig.3.6.Kni fedrivebyelectricmotor(Fives- Babcock).EffectoncanecarrierCane carriers were previouslyfurnishedwithwoodenslats.Itis the adoptionof kniveswhichhasnecessitatedtheprovisionofsteelslats,sincethewoodenboardswouldbedamagedundertheknives,andchipsofcanewouldpassthroughthespacesbetweenthecarrierboards.Even with steel slats,it is necessary to reinforce the carrier where it passes under the knives;a reinforcingbeamisplacedundereachrailsupportingthecarrierchains,andanangleironsupportundertheendsofthecarrierslats.MethodsofdriveKnivesmaybedrivenbytwodifferentsourcesofpower:(1)Electric motor(2)Steamturbine.36CANEKNIVES Ch.3,II:!I!I IIn iFig.3.7.Knifedrivebysteamturbine.(1)Electricdriveiseffectedbyawoundrotorinductionmotorwithslip-ringsandwithorwithoutprovisionforliftingthebrushes(Fig.3.6).(2)Drive by steam turbine is the most attractive (Fig.3.7).It permits some degree of speedvariation,but is expensive,as the cost of the turbine sometimes exceeds twice that of the elec-tric motor.Moreover,itnecessitates either a special attendant or at least partialsupervision,anditdoesnotwarrantconsiderationexceptforlargetandemsabove150t.c.h.Asregardstransmissionofthedrive,wemaydistinguish:(a)beltdrive,(b)directdrivethroughaflexiblecoupling.NUMBEROFBLADES37(a)Beltdriveoriginallyhadtheprimeobjectof avoidingtoodrasticshocksontheknives;incaseofanoverload,thebeltwouldcomeoff.Actuallythisadvantageisveryslightanditissometimesjustasmuchtroubletohavetoreplacethebeltwhichhascomeoff,astoreplaceabrokenknifeblade.Inanycase,ifitisamatterofapieceoftrampironpassingthroughwiththecanethebeltcomesoffbut,generally,theknifeisbrokenjustthesame.Theonlyadvantageisthat,havingstoppedthemill,theknifeandthepieceofironcanbemoreeasilyrecovered;orindeedthedriverofthecrusherisalertedandismorelikelytoseethemdropintothefeedhopper.Fig.3.8.Flexiblecoupling.(b)In modernpractice the preference is generallyfordirectdrive throughaflexible coupl-ing (Fig.3.8).Theknife assemblyisconnecteddirectlytothe motorshaftbythesimpleinter-positionof a device whichisrelativelyflexibleandconsistsof acordorropelacedalternatelybetweenpinsorstudsfixedintwodiscs,thedrivingdiscbeingattachedtothemotor,thedrivendisctotheshaftassemblyof theknives.Thisarrangementismuchsimplerandmoreeconomical,andgiveseverysatisfaction,providedthatthemotorissuffcientlypowerful.Beltdriveisnowretainedonlyforconnectingtwoadjacentsetsofknives.PitchofknivesWe have already seenthatthe pitchof theknivesistheintervalseparating the circlesof rota-tionorthecuttingplanesoftwoadjacentblades.Generally,2or3setsofknivesareinstalled,thefirstof50mm(2in.)pitch,thesecond(andthird)of20 22mm(justbelow1NumberofbladesThepitchfixesthenumberofblades.Inthecasewhereeachknifeturnsinadifferentplanewe have:N - (3.1)PN=numberofknivesL=widthofcarrier,incm(in.)p=pitchofknives,incm38 CANEKNIVESCh.3Fig.3.9.Clearanceofknives.Wheneqn.givesanoddnumberfor the evennumberimmediatelylowerisalwaysadopted;theintervalbetweentheextremebladesandthesidesofthecarrierwillthenbegreaterthanthepitch.ClearanceTheclearanceofaknifesetisthedistancerbetweenthecircledescribedbytheextremityoftheknivesandtheplanepassingthroughthehighestportionsofthecarrierapron(Fig.3.9).The clearance isanimportantfactor intheoperation of aknife set.On it depends thepro-portionofcanecutandconsequently,tosomeextent,theefficiencyoftheknives.Theclearancemaybeadjustedbyraising orlowering bodilythesteelframesupportingthecarrierbelow the knives.However,it is preferable to adjust it by moving the knivesandtheirdrivingmotoronhorizontalslides.Sincetheknivesareplaced(preciselywiththisobject)ontheinclinedportionofthecarrier,theclearancecanthusbesetatwilltothedesiredvalue.Clearancemayalsobeadjustedbyplacingpackingpiecesundertheknivesandmotor.ProportionofcanenotcutThisisimmediatelyobtained:=-x100h(3.2)=weightofuncutcane,%ofweighttreatedr=clearanceofknives,inmm(in.)h=heightofcanelayer,inmmRememberthathisgiveninm(ft.)byeqn.(2.4):PROPORTIONOFCANENOTCUT3960 60A=crushingrateofmills,int.c.h.=speedofcarrier,inL=widthofcarrier,in (ft.)=bulkdensityofcanefedtotheknives,ind=150 (9Ib./cu.ft.)(tangledcane)d=175 (11Ib./cu.ft.) (parallelcane)d=300 (18Ib./cu.ft.)(cutcane,inthecaseof2ndknifeset).Thesevaluesofdshouldbesomewhathigherthanthoseindicatedbyeqn.(2.4)sinceitisactuallyaquestionofthedensityofcaneasitpassesthroughtheknives,andsincetheknives,astheystrikethecane,packthecanetosomeextentontheapronofthecarrier.Theproportionofcanecutisobviously:It isnoteasytodetermine accuratelythemeanspeeduforthe cane carrier.Thebestwayistomeasurethetotallengthofthecarrierapron,tomarkwithpaintonelinkoroneslat,andtodeterminethetimeforthislinktoreturntoagivenpoint,forexampletheheadofthecarrier,oppositeamarkmadeforthispurpose.Ifthetotallengthoftheapronisandifthemarkedslattakes minutestocompleteitscourse,theaveragespeedwillbe:u=m/min(ft./min)(3.5)Itwillbeadvisabletotakethemeanof3,5or10completecyclesofthecarrier.DirectionofrotationThealmostuniversalpracticeistoarrangetheknivestorotateinsuchamannerthattheknivesatthelowestpartoftheirrotationwillmoveinthedirectioncorrespondingtothemovementofthecarrier(Figs.3.1and3.9).However,somefactoriesarrangeforoneorsometimes both sets of knives to rotate in the inverse direction. This is not always easily done;itaugmentsthecuttingeffectonthecanebutatthesametimeincreasesthepowerre-quirements.Theknivesshouldalwaysbe installedeitheratahighclearanceorinsuchawayastothrowthepiecesofcutcaneupwards.KnifeKnifebladesshouldbeinspecialsteel.FCBsuppliestheminsteeloftype55 8withheated,temperedandhardened,withBrinellhardnessof360/40040 CANEKNIVES Ch.3HB.Whentheknivesaresubjecttowearduetosandandstone,carbonsteelXC32maybeused;thiscanberesurfacedinplacebyapplicationoftungstenorstellite.Balancing.Asetofknivesmustbewellbalanced.Inordertoavoidlackofbalancewhenthe knivesarereassembled,at the beginning of aseasonorafter re-sharpening,it isnecessarytoweighthebladesandreplacetheminpairssuchthatoneacharmcarryingtwoopposedblades,theweightof thesebladesispracticallyequal.Inthesameway,whenaknifehastobe replaced,two opposite blades should be removed,and replaced by two new or used blades,ofequalweight.Maintenance.Amechanicshouldbedetailedandchargedwiththejobofinspectingtheknifeseteveryweekatthetimeoftheweeklyshut-down,inordertocheckwhetherthereareanyloosebolts,orloose,ovalisedorcrackedkniveswhichshouldbechanged.ofutilisingknivesdistinguishes two types of knives,according to the role which is demanded of them:(a)Thelevellerkniveswhicharerequiredmainlytoevenoutthelayerofcane.Theyarearrangedtoworkwithahighclearanceandinconsequenceleavealargeproportionof uncutcane.(b)Thecuttingknives.Thissecondeffectissoughtonlywhentwosetsofknivesarein-stalled:thefirst,atthebottomof theslopingportionofthecarrier,wouldplaytheroleoflevellers,the second,immediately after thefirstor attheheadof the carrier,wouldthen havethefunctionof finishingthe complete disintegrationof the cane,andwouldbeusedataverysmallclearance(Fig.3.10).This distinction,we fear,is somewhat artificial.A single set of knives performs a task con-siderablymoreimportantthansimplelevellingof thecanelayer.It"minces"thecaneintosmallpieceswhichcoverupandfillinthegapsinthefeedandsoimprovethefeedingofthecrusher.Manysinglesetsofknivesareemployed,withsuchaclearancethattheyareinrealitycuttingknives.However,thegeneralpracticeistoinstallatleasttwosetsofknives.Finally,we consider that the above distinction hasnosignificance exceptwhenit is a mat-terof describingtheeffectiverolesoftwosetsof caneknivesworkingonthesamecarrier.Itisthenratherappropriate.2ndKnifeset1 stKni fesetFig.3.10.Installationoftwosetsofknives.KNIFEBLADES41Thesecondknifeset.Wehaveseenthegreatvalueofasetofknives,onaccountofitsfavourableinfluenceonthefeedingandthecapacityofthemills.Toobtainthefulleffectdesired,it is necessary tohave two setsof knivesatleast.One setcannotreduce the thicknessof the cane layer sufficiently nor canit cut the cane sufficiently fine.This actionis achievedbythesecondsetofknives,whichcutsthelowerlayerwhichthefirstsethasnottouched,anddeliversthecutcaneinsmallerandthinnerpieces.Thesecondsetthusfacilitatingthefeedingofthemills:(7)Fromthepointof viewof extraction,accordingtoseveraltests,thegainobtainedbyasecondsetisfoundtobesmallanddifficulttodetect.(2)From the pointof viewof capacity,itseffect ismuchmore definite,althoughobvious-lyappreciablylessthanthatofthefirstset.Wecanreckonapproximately:knivesWith1setWith2 setsRelative capacities1 1.20Inotherwords,thefirstsetof knivesgivesagainof approximately thesecondaddsanother 4 or 5%.Thisisindeedmuchlessbut,taking intoaccountthe costsof purchaseandupkeepofaknifeset,itisstillveryprofitable.Thesecondsetisparticularlyusefulwithashort tandem,since itisthendesirable topresenttothemillspiecesof caneasfinely dividedaspossible,insuchawayastoenabletheearliermillstoobtainthemaximumextraction.It is with tandems of 5mills(say rollers)or morethat advised againsta secondset;he consideredonthecontrarythatwith4mills(12rollers) less,thesecondsetcouldbe useful.We thinkthatif hiscomments,datingfrom1932,hadbeenwritten30yearslater,hisconclusionwouldhavebeendifferentandtwosetsofkniveswouldhavebeenrecom-mendedinallcases.Thethirdknifeset.Itisdifficulttoassessthegainincapacityachievedbyathirdsetofknives.Itcouldperhapsbeexpressedby insertingacoefficientof intheaboveformulaforcapacity.Itiscertainlyasmallgainonly,butathirdknifesetisfairlywidelyused.Itcompletestheworkofpreparationandpermitsattainingabetterindexofpreparation(cf.p.61).Canepreparationtodayisconsideredsoimportantthattheinstallationofathirdset of knives does not completelyoutthe additionof a shredder asthefourthpreparatorydevice.Theshredder,however,hasoneadvantageoverknives.Incountrieswherenumerousstonesoccurinfieldsandmechanicalloadingallowsthemtoarriveatthemill,theycausemuch lessdamagetothe shredderthantotheknives.However,theknivesareunfortunatelythefirstinline,andreceiveallthestoneswhichhaveescapedthemeansofdetectionandsosufferconsiderably.Thefirstknivesthusdetectthestone,thecarrierisstopped,thefollowing knives and shredder are protected,but several blades have beendamaged andaccidentsareveryexpensive,owingtothestoppage,thelossoftimeandthelossofknifeblades.Itisthusveryimportanttotakeallpossiblemeasurestodetectstonesbeforethefirstsetof knives.Thefactoryof Bois-Rouge,inReunion,whichcrushesat100t.c.h.,has3setsofknives,arrangedanddrivenasfollows:42CANEKNIVESCh.3Knives1st2nd3rdNumberofblades323280Pitch(mm)505022(in.)2278Speed(r.p.m.)480480640Clearance(mm)305106.5(in.)12314Nominal power(kW)130130255175175340Mean power absorbed(kW)557590(h.p.)75100120Thevalueofthethirdsetisdebatable:itdoesnotgiveanappreciablegainincapacity,butitssupportersassertthatitassuresthatahighextractioncanberegularlymaintained.Itseffectisoftencomparedwiththatof ashredder.Itwouldbeparticularlyindicatedinthecaseofextractionbydiffusion,asthemassofchipsfurnishedby3setsofknivespermitsof abetter circulation of liquidthanthe mattressfurnishedby 2sets of knives anda shredder.SpeedofrotationThespeedof rotationof aknifesetvariesfrom400to720r.p.m.Thespeedmostfrequentlyusedis500r.p.m.InSouth itvariesfrom500to700,withanaverage of 600r.p.m.ThefirmofFletcherconsidersthattheoptimumspeedliesbetween500and600andthathigherspeedsgivescarcelyanybetterresultswhile,ontheotherhand,oneortwobrokenbladescanputthesetbadlyoutofbalanceandcausemoreseriousdamagewithhigherspeeds.Incertaincountriesthespeedhasbeenpushedupasfaras1200r.p.m.Itmaybecon-sidered thatthis wouldgive veryfine preparation,butat suchspeedswearonthebladesmustbeveryrapid,powerconsumedmustbeconsiderableandaccidentswouldbemoreserious.Werecommend500r.p.m.forthefirstsetand600r.p.m.forthesecond,whileagreeingthatif,forthesakeof uniformity,itispreferredtoadoptthesamespeedforboth,therewouldbelittledisadvantageindoingso.PowerGeneralconsiderations.Theaveragepowerabsorbedbyasetofknivesdependson:(1)Thetonnageofcane(2)Thefibreinthecane(3)Thenatureofthefibre,whethermoreorlessresistant(4)Theproportionofcaneactuallycut - thatis,ontheclearance(5)Thenumberof(6)Thespeedofrotation(7)Theradiusofthecuttingcircle(8)Diversevariablefactors:friction,lubrication,knivesmoreorlessworn.Theselatterfactorscannotbe measuredaccuratelyanditisscarcelyeasiertotakeintoac-countthefirstthreefactors,althoughtheyaremeasurable,sincetheirinfluenceisvariableandproblematical.Thenumberof bladesinparticularseemsparadoxicallytohavelittlein-fluence.Nicklin4in Australia cites a set of 70 blades which,in analogous conditions,consum-edlesspowerpertonneofcanethananothersetwith36blades.ConsequentlyweshallbePOWER 43contentwithrelatingthepowertothetonnage,whichremainsthemostimportantfactor.While sometimes expressedintermsof it isonly thefibre rate thatisrelevant.Morerecently,Australian havefoundaverymarkeddifferencebetweenthepowernecessarywhenthecanesaredeliveredinpiecesfurnishedbyachopper-harvester,relativetothepowernormallyrequiredforwholecanes.Thisdifferenceisobviouslymoremarkedforthefirstsetofknivesthanforthesecond.TheygivethefiguresshowninTable3.1.TABLEPOWERCONSUMPTIONOFKNIVES(QUEENSLAND)set2ndset0.75(1)WholecanePM3.2(4.2)3.3(4.4)Choppedcane1.8(2.4) 0.33(0.4)0.45(0.6)PM0.75(1)1.2 (1.6)Pi0.45(0.6)0.60(0.9)=meanpowerabsorbed,inkW/t.c.h.(inbrackets,in=maximumpeakpower,inkW/ t . c. h.p.=powertobeinstalled,inkW/t.c.h.Thistableisbasedontheprinciplethatanelectricmotorcanfurnishfor15secondsapowerequalto timesitsnominalpower.Farrell,in gavefiguresfor powerasshowninFig. forelectricmotorstobe100200300400500t.c.h.Fig.3.11.Knifeabsorbedpower44CANEKNIVESCh.3stalledfordrivingknivesat600 Theupperlineinthegraphisapplicableforknivesof mm in.)pitchatasettingof25mm(1 thelowerlineforknivesof38-50 mmin.)pitch,setat150-200mm (6-8 If theknifesetisdrivenbyasteamturbine,Farrelladvisesprovidingaturbineofnominalpower33%higherthanthatindicatedfortheelectricmotor.Herecommendsarotationalspeedof3,600 with6 reductiongearandpower50%abovetheindicatedpowerrequirements.FarrelPslowercurve(forlevellerknives)stillremainsappropriateforthepresentday;itallowsformotorsasgenerallyprovided.However, hasdevelopedsince1971and,forshreddingknives,hasledtomuchhigherpowerrequirements.AgoodexampleisgivenbySouthAfricanpractice.Table3.2givesthepowerinstalledforknivesinthatcountry.ThefiguresareinkW/t.f.h.andarederivedfromthemeanof22 tandems;extreme values are indicated in brackets.Power consumed is of the order of 60%ofthemeanpowerinstalled.TABLE3.2POWER FORCANE-KNIVES,INkW/t.f.h.MethodofoperationOperatingaslevellersLevellersinWorkingasShredderinreverserotationshredderreverserotation1st knives7102024(3(7(14(20-15)-30)-30)2nd knives2040(10(30 -70)3rd knives1216(9-(14-18)19)Influenceof clearance.Wehavesometimesfoundthatfactoryemployeeshavetheimpres-sionthatbydiminishingtheclearancebyhalf,passingforexamplefrom10 cmto5cm,onewould double the necessary power.But,as we have just seen,the clearance is concerned onlyasitaffectsthedepthbywhichtheknivesplungeintothelayerof cane.If thisdepthis0.65m(2 aclearanceof (6in.) -r=0.5 willrequireapoweronly50%greaterthanaclearanceof0.30m(12in.)(h-r=0.35m).Effectofwear.Inproportionasthebladesbecomeworn,thepowerconsumptionin-creases.Ithasbeenfoundin forkniveswhichhadbeensharpenedonSunday,anincreaseof11-17%inpowerconsumptionbetweenMondayandFriday.Variationsinpower.Itisnecessarymerelytostandalongsideanelectricallydrivenknifesetfurnishedwithanammeter inordertoseethe continualandfierce variationsinthe powerconsumptionofsuchaset.Themean valuewhichwehave givencorrespondstothe sumof instantaneousvaluesrang-ingfromalittlemorethanhalf tomorethandouble,accordingtothedensityof loadingoftheportionof thecarrierarrivingattheknives.Abundleof parallelcaneswouldcausethecircuit breaker tofunctionif the crane were to depositsucha bundle directly into the carrier.Automaticregulationofcarrierspeed.Inordertoavoid:(a)ThedisadvantagesofanexcessivevariationinrateofcanearrivingattheknivesCLEARANCESFORTWOKNIFESETS45(b)Irregularityinfeedingofthemills(c)ChokesattheknivesandstoppagesinvolvedforclearingtheseMost factories interpose a coupler of theandtype between the carrier andits driving motor p.27)and actuate the coupler bymeans of onephase of the motor driv-ing thefirst setof knives,forexample.Withthis thecarrierslowsdownwhenthe knives are overloaded,andthis allowsmore timeto treat theheavily loaded pile of cane,and evensout the distributionof the cut cane on the carrier.Theoverloadonthe secondsetofknivesismuchlowerandthisinturnisevenedout.Whentwosetsofknivesare itwillbesatisfactorytoprovideforeachoftheseaninstalledpowerequaltoapproximately oftheprecedingvalues.manyfactoriestendtoinstallasecondsetofknivesmuchmorepowerfulthanthefirst,thepowerofthemotorsbeingforexampleintheproportionof2to3.Thetotalpowerinsuchcasesisnotalwaysdesignedtobedifferentfromtheforegoing,andismain-tained equal to double the value givenabove.Everything depends on theduty demandedofeachofthesetwosets;averypowerfulsecondsetcanwellrecoverorcompensatefortheinadequateworkof afirstsetwhichisold,sloworhasonlyasmallnumberofblades.Theopposite is sometimes seen,the majorpartof the worksoughtbeing obtainedby thefirst set.Drive to adjacent knife sets.Thetwosetsof knivesmaybeconnectedby abelt,providedof coursethatthepulleysizescorrespondtotherespectivespeedsofthetwomotors.Thisarrangement,whichislogical,allowsthetwomotorstoassisteachotherwhenoneortheotherisoverloaded;atthesametimeitallowsthetotalpowerprovidedforthe twomotorstobereducedbyperhaps Itmaybeemployedwhereverthedistancebetweenthetwosetsof knivespermits.Bothsetsof knivesinfactmaybedrivenfromasinglemotordirectlycoupledtooneset.Suchaninstallationthusprovidesgreatflexibility.Thenominalpowerof thetwomotorsmaywellbereducedto7.5and12kW/t.f.h.(10and15 respectively,withlittleadverse affect ontheresultssought.Tobe able todrivetheknivesinthisway,itisadvisablethat,evenwith drives,thedistancebetweentheshaftsofthetwosetsshouldnotbemore than4.25 (14ft.)orpreferably3.6 (12 Itisalsorecommendedthatthetwomotorsbeofthesametypeandnaturallyofthesamespeed,otherwisetheamountofslipwouldbedifferent.Itisalsorecommendedin thattheratioofthepowerofthefirstmotortothatofthesecondshouldbebetween0.8and1.0iftheloadonthebeltistobeaslowaspossible.ClearancesfortwoknifesetsThecaseoftwosetsofknivesisbyfarthecommonest.Thefirstsetisthengivenahighclearanceand,forthisroleofleveller,knivesoffairlyhighpitchareprovided:generally50mm(2 withasmallnumberofblades;itisdrivenat500 sometimes600.The second set on the otherhand is very close to the carrier,for example,witha clearanceof 50 mm(2 moreoften25mm(1in.)oreven aslowas10mm Itmaybedrivenat 500 more oftenat 600,sometimes at750 r.p.m.It has a greater number of blades,thepitchbeingaslowas25mm(1in.)andeven22mmTheclearanceadoptedforthefirstsetshouldbeapproximatelyone-quarteroftheheightofthelayerofcane.46CANEKNIVES 3BulkdensityofcanepreparedbyknivesThebulkdensityofcaneafterpassingthroughtwosetsofknivesisgivenbyKerr8asbeingoftheorderof480 (30 thisvaluecorrespondstoanexcellentdegreeofpreparation.InReunion,itisonlyoftheorderof320 (20DucasseknivesAmongtheinterestingdevicesforcanepreparation,Ducasseknivesareworthyof mention(Fig. Thisequipmentconsistsof ashaftcarryingdiscsorbossestowhichknife bladesarefixed,eachbythreebolts;thisshaftisenclosedinacasing rotatesat 1000Theknifesetislocatedatthetopofthecanecarrierandarrangedsothattheplaneof theconveyorbringingthecane(orchipsof canecutbya precedingleveller)istangentialtothecircleofcutof theblades.Thedirectionofrotationoftheassemblyissuchthatthebladespassupwardsthroughthebedofcaneonthecarrier;theythusthrowthecutpiecestowardtheroof of thecasing.Theystrikeaninclinedplatewhichisprolongedtoatoothedanvilsetveryclosetothecircleofcut,35mm in.)atentry,10mm in.)atdelivery.Theknivesforcethepiecesthroughthisnarrowpassageandarefurnishedwithplateswhichactashammersandsoaddashreddingactiontotheircuttingaction.Theinventorofthisequipment has called it a Power installed is approximately 9 (12h.p./t.f.h.).Ducassehasalsodevelopedaknifesetinwhichtheknivesaremountedonstoutpins,onwhichtheycanoscillatefreelyaboutaverticalplane;thustheysuffermuchlessdamageduetostonesorotherforeignbodies.Thistypeofknifepresentstwoadvantages:Fig.3.12.Ducasseknives-operatingprinciple.MECHANICALLOADINGANDSTONES47(a)Thefreeoscillationpermittedforthebladesformsavaluableprotectionagainsttheeffectsofdamageduetostones(b)The size of the pins assures a long life and muchlesswear thaninthe standardmodels.MechanicalloadingandstonesWiththemechanisationofcanegrowing,thetraditionalhandcuttingofcanehasbeenreplacedinmanycountriesbymechanicalharvesting,andisprogressivelybeingreplacedinother countries.This development has led to the use of chopper-harvesters which cut the caneinto short sections whicharetransportedtothefactorybytipping trucksor truckswithothertypes of mechanical unloading.Thismethodof harvesting presents greatriskof deteriorationof the chopped cane:the cane should go tothe mills as rapidly aspossible,preferably in 2 - 6hoursaftercutting,otherwisethere beconsiderablelossesofsugar.Thechoppedcanemay contain topsandleavesbutthesedonotinclude anyhardmaterial.Unfortunately,onaccountofthecostsofchopper-harvesters,introductionofmechanisationgenerallyprises an intermediate phase betweenmanual and chopper-harvesting,which consists of plac-ingthecanesinpilesonthegroundandpickingthemupbyconveyor-elevatorsorothermachines suchasrakesor grabs.Thismethodof harvesting presentsthe gravedisadvantageof sending to the factory,among such bundles of cane picked up,stones and sometimes rocksof some 30-40 kgin weight(onefactory inHawaiihaseven thus pickedup apig,somewhatmutilated,whichwasdetectedandtakenoutonlysecondsbeforethefirstsetof knives).Theserocks,if notdetectedbeforepassingtotheknives,haveadisastrouseffectonthelatter:knivesaredamagedorbroken,sometimesknifeholderssimilarly,knifeshaftsare bent,andthepiecesof knivesnotremovedonreachingthemillsmaydamagethe groov-ingoftherollers.It is therefore desirable,if possible,to avoid picking upstones with the cane,and the onlysure method of doingthisisthe carefulandcompleteremovalof stonesinthefield;andthenthose whichpersistintothefactorymustbedetectedintime.Onesuchmethodistotipthecane intoa pitfromwhichitisremovedby anelevator,setatasteepslope,whichfeedsthecarrier.The Cameco organisation has adopted 28.5;others use 35,andourrecommenda-tion is30.Conveyorchainswithhooksattachedandspacedatabout60cm(2ft.)pickupthe canefromthepit,takeituptheslope,anddeliveritintothecarrier.Thestones,beingheavier,remainatthebottom,orrollorslidedowntheslope.Theaccumulatedstonesareremovedfromthepitonceortwiceadayaccordingtothequantity.Itissometimesconsideredsufficienttouseanordinarylateralconveyorwhichdropsthecaneontoasteelplateinclinedat40or fromwhichthecanefallsontothecarrier.Astonefallingfromtheheightofsome2 (6ft.)ontothisplateproducesacharacteristicbang:the conveyor andthe carrier are thenstoppedandthenthestone removed.For amorepositivearrangement,amicrophonemaybeplacedbelowtheplateandconnectedtoanamplifier,sothataboveacertainsoundintensity,analarmissetoff.Withoutsuchprecautions,factoriesworkingatthestageofpusher-loadingofcanecansufferaveryunfortunateseason;wemayquoteonecaseof 45hours'stoppageduetothiscauseonlyinthecourseofoneseason,withmorethan200bladesbrokenandalmost100bent.48CANEKNIVESCh.3REFERENCES1F.MAXWELL,ModernMillingof SugarCane,NormanRodger,London,1932,p.60.2F.MAXWELL,op.cit.,p.127.3J.H.G.ROYSTON,Int.SugarJ.,50(1948)14.4J.H.NICKLIN, 34thConf.QSSCT,1967,p.174.5J.H.NICKLIN,Proc.34thConf.QSSCT,1967,p.180.6Mackay ofMillingEngineers,Proc.31stConf.QSSCT,1964,p.78.7MackayInst.ofMillingEngineers,Proc.31stConf.QSSCT,1964,p.79.8H.W. ConferenceinMauritius,September1957.4.Tramp-IronSeparatorsGenerally,nostrictaccountiskeptof thenumberorweightofpiecesof steelandcastironwhichpassthroughamillinthecourseofaseason.Thecommonestobjectsare:piecesofknife-blades,sling-hooks,brokenpiecesofslings,monkeywrenches,horse-shoes,boltsandnuts.Piecesofcastironorspecialsteelarethemost dangerous.Sometimes,the engine-driver atthe millshearsthe noise made bythe pieceof ironfallingintothefeedhopper,ortheabnormalnoiseofthecrusherorfirstmill.Themillisthenstopped,theforeignbodyfoundandremoved.Whetheritisdetectedintimeornot,butespeciallyinthelattercase,suchincidentsareexpensive.Inparticular,whencontemplatingthedestructionofacertainlengthofrollergrooving,onemayestimatethelosssufferedbycalculatingthevalueof1.5mm in.)ofthicknessorof acubiccentimetreof rollermetal.Therollersareoftenturneddownduringthe slack season to restore their grooving,and in this operation several sixteenths in diameterarelost-thislossbeingaddedtothatduetonormalwear.Itisnecessarytotakedeepercutswhentherollersurfacehasbeenmoreseverelydamaged.Toavoidsuchdamageandlosses,effortsaremadetoeliminatethepiecesof"trampiron".The amountof trampironmaybereducedbytakingprecautionsintheloadingandunloading of the cane,by insistingonstrict tidinessatthe cane platform,andbysupervisingFig.4.1.Suspendedmagneticseparator.50TRAMP-IRON 4the tightening of boltsatthe carrier andtheknives.Butthe best guaranteeliesinthe installa-tionofamagneticseparator,generallyknownasa"tramp-ironseparator".DescriptionOriginally,magneticseparatorstooktheformof electromagnetsfixedonthebottomof thefeedchutetothefirstmill,orconstructedintheformofarotatingcylinderprojectingintothatchute.Thesedeviceshadsomedisadvantagesandwerenoteffective.Thedevicenowrecommendedconsistsof anelectromagnetcontainedinsidearectangularboxsuspendedabovethelastcaneconveyorbeforetheentrytothefirstmill,andcoveringthefullwidthof theconveyor(Fig. Thisisgenerallyarubberbandconveyorandshouldrunataminimumspeedof1.20 (4 preferably2 (6 thusthepiecesofcanewillformathinlayerlessthan140mm in.)inthickness,preferably 100mm(2-4 Itisadvisabletoarrangefortheconveyortopasscloselyoverasupportingflatplate,toavoidsaggingoftheconveyor.Theboxholdingthemagnetshouldbeatmost400mm(16in.)abovethesurfaceoftheconveyor,preferably250 300mm(10 12This device consumes about 7kW (9andhasanefficiency of nearly100%asfaraslargepiecesofironareconcerned.Wehaveknownthistypeofseparatortopickupfromthecanecarrieraknifeholderwithitstwoblades,weighing70kg(155 Itmaybereckonedthatthemagneticseparatoravoidsabout90%of thedamagethatwouldother-wisebesufferedbytherollersurfaces.FinancialaspectThe magnetic separator is expensive,but consumeslittle power and gives efficient protectiontotherollers.Itthereforepaysforitselfrapidly;itisaprofitableandusefulpieceof equip-ment.It becomes all the more necessary:(a) with a long train of mills;(b) when a higher hydraulicpressureisemployed.Actually,muchtrampironpassesundetectedthroughthewholetandemandsodamagesalltherollers.Further,thedamagesufferedbytherollersrapidlybecomesmoreseriouswithincreasingpressure.5.CrushersOBJECTThecrusheristhefirstmachineapplyingpressurewhichthecaneencountersonarrivingatthemillingplant.Itconsistsofamill,generallyoftworollers,whichperformstwomainfunctions:Itassuresthefeedingofthewholetandem(b)It prepares the cane in such a way astofacilitate the grip of the rollers and the extrac-tionofjuicebythemills.Thecharacteristicsofacrusherthereforearethefollowing:(1)Itpossessesasurfaceespeciallyconstructedtopermitittogripthecaneorpiecesofcanewhicharefedtoit,inthebestconditionspossible.(2)This surface must atthe same time be designed in such a way as to break,tear up,andcrushthecane,inordertopermitthemillstogettoworkimmediatelyandeffectivelyonthebroken-upmaterial,whichisalreadyofthenatureofbagasseratherthancane.(3)It should have a peripheral speed superior to thatof the mills which it has to feed,sincethematerialwhichisfedtoithasnotyetassumedtheformofbagasse,andisstilldifficultto grip.If it had the same speed as the mills,it would be handicapped in its attempt to supplythequantityofmaterialwhichtheyarecapableoftreating.CRUSHERSTypesManytypesofcrushershavebeendesignedandtried,butonlytwohaveachievedgeneralimportance.Thesewere:(a)TheKrajewski(nowof historicalinterestonly;seefirstedition,pp.(b)The Fulton.The Fultontypeisnamedafterthefirmwhichhaspredominantlycontributedtoitsdesignandwideuse.Itistheonlytypeusedatthepresentday.TheFultonrollerisreallyamillrollertreatedsoastoserveinacrusher.Itisasurfaceof revolution,obtainedbytakingaserratedline,enclosedbetweentwolinesparalleltotheaxis,and rotating thisaroundthe axisof the roller.Thusthereis obtained circular groovingof Vform,separatedbyridgesorteethofinvertedVshape(Fig.5.1).Sinceasurfaceof revolution,evenwithgrooving,isscarcelysuitableforassuringagriponthecane,groovesarecutlongitudinallyintheformofchevronswhichformanumberof notchesineachtoothoftheroller.Theprofileoftheseteethissochosenastofavourthegriponthecane(Fig.5.2).52 CRUSHERS Ch.5Fig.5.1.Fultoncrusherrollers(Fives -Babcock).60Fig.5.2.NotchesofFultonroller. Fig.5.3.Fultongrooves.SincetheFultongroovestendtobecomeblockedwithbagasse,itisgeneralpracticetofitscraperstothetworollersofthiscrusher.GroovingTheangleof thegroovesisabout35- 55(Fig.5.3),often45wi t hFrenchfirms.Thepitch,whichheremeansthedistancefromonetoothtothenext,variesfrom38to100mm to4 Themostfrequentvaluesare50-75mm(2-3Whentheangleis50,thedepthisslightlygreaterthanthepitch.Inpractice,however,themanufacturerdoesnotfinishthetoothprofileatapoint;itwouldbetoofragile.Hefinishesitwithasmallflatsurfaceaa(Fig.5.3)thewidthofwhichisapproximatelyone-tenthoftheheightofthetooth,withoutgoinglowerthan1.5mmWhatpitchshouldbe chosen?