Qingdao Zhaoxing Extruder Machinery Co, Ltd
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Qingdao Zhaoxing Extruder Machinery Co, Ltd

Lägg till: Nr. 1188, West Lanzhou Road, Jiaozhou City, Qingdao, Kina


Tel: + 86 532 82222628

Mobil: + 86 13583211497
Skype: suen.jackie
E-post: tony@plastic-extrusion.cn

Hur man kan förbättra Feeder prestanda

Hur man kan förbättra Feeder prestanda


Det iscrucialtounderstandthedifferenttypesandtheadvantages/disadvantagesofscrewtrough,

omrörare, andthescrewitself. Manyloss-i-weightfeedersincorporateascrewasthefeeddevice
duetoitswidefeed-rangecapability.
Eachselectedfeeddevicehasarangeofavailablescrewswithdifferentdiametersandpitches.
Eachfeedersupplierprovidesarangeofmodelscapableofprovidingfeedratesoverthespectrum
ofnormalapplications. Thefeeddeviceiscomprisedofseveralcomponents.
Thescrewtroughisacriticalcomponentofascrewfeeder.Itconvergesdimensionallyfromtheinlet,
attachedtotheextensionhopper, andintothescrew. Ittransitionsthemassofdryingredient
containedinthefeederfromthelarger-dimensionextensionhopperintothesmaller-dimensionscrew.
Mostdryingredients (pulver, granulat, pellets, fibrer, andflakes) donotflowreliablythrough
convergingtransitions. Thereisfrictionbetweentheparticlesandaninterlockingtendencythat
restrictsorstopstheflow. Whentheflowstopsitiscalleda "brygga".
Alldryingredientshaveaminimumbridgingdimension.Flowstopsandabridgeformsatthis
Cross-sectiondimension. Thereducingcross-sectiondimensionsinthescrewtrougheventually
reachthebridgingdimension. Anagitationdeviceisincorporatedinthescrewtroughinorderto
preventthebridgefromforming.
Flexiblewalled/externalpaddleandinternalstirringaretwocommontypesofagitationdevices.
Thescrewtroughisconstructedofaflexiblematerial, normallypolyurethane, inawedgeshapeon
twosidesandnearverticalontheothertwosides. Movablemetalpaddlescontactthetwo
inkilad-shapedsidesand massage"" dem, pushingthesidesinandoutcontinuously.
Thismovementcausesanunstablesupportforthedryingredientparticles.Arestrictionmovement
followedbyavoidmovementcausesanybridgesthatarestartingtoformtocollapse. Gravityacts
ontheparticlestomovethemdownandeventuallyintothescrew.
Comparisonoffeedercomponentsforexternalpaddleagitationandinternalstirringagitation
Thescrewtroughisconstructedofmetal, normallystainlesssteel, andiscurvedinaconstant
radiustoaccommodatetheclosemovementofrotating, agitatingblades. Theagitatorblades
movethroughthedryparticlesoneachsideofthescrew, whichispositioneddirectlybelowthe
agitatorblades. Movementisdownintothescrewononesideofthescrewtroughanduponthe
Otherside. Thisblademovementpreventsbridginginthescrewtrough.
Theshapeofthescrewtroughiscritical.Aloss-i-weightfeeder'smainpurposeistofeedthe
ingredientaccuratelyatthedesiredsetpoint. Theweight-feedbackcontrolrequiresthateachscrew
flightbefilledwiththesameweightofingredient. Repeterbara-weightfillingofeachscrewflightis
achievedbyaproperlydesignedagitationdevice (flexibel-walledwithexternal-paddlemassage
orwithinternalstirring).
Också, theremustbesufficientscrewflightsexposedopenlyinthebottomofthescrewtrough
sothatcompleteandrepeatablefillingoccursbeforetheingredientisenclosedinthescrewtube.
Thebestscrew-troughshapeisawedge, ratherthanasphericalorconicalshapeatthebottom
ofthescrewtrough, inordertoexposetherequiredlengthofscrewtofillproperly.
Theflexible-walled/externa-paddel-massagedscrewtrough, availablefromseveralsuppliers,
hasdrawnmoreinterest. Oneimportantreasonforthisisthatthemovementoftheflexing
screwtroughdirectlycontactsandmassagestheingredientinthescrewtroughonboth
sidesofthewedgesurfaces, fromthetopinlettothetopofthescrew.
Sincethestirringagitatorhasacircularmotion, therearetwodeadzones (noagitation) på
thetopofthescrewtrough. Thescrewtroughissizedtoreducethevolumeofthedeadzone.
Asaresult, theflexible-walled/externa-paddel-massagedscrewtroughtypicallyhasalarger
volumeandinletdimensionthantheinternal-stirringscrewtrough. Sincetheextension
hopperismounteddirectlyabovethescrewtrough, thebottomdimensionoftheextension
hopperistypicallythesameastheinlettothescrewtrough.
Förlust-i-weightfeederextensionhoppersarecommonlysized (ruleofthumb) för att
contain4minutesofstorageatthemaximumfeedrate/minimumbulkdensityoftheingredient.
Theextensionhopperoftencanbesuppliedwithverticalsides, whichprovidesfloorspace
advantagesoverconicalextensionhoppers. Också, thereisnorequirementforadditional
stirringagitationintheextensionhopper,sincethesidesarevertical(noconverging).
I allmänhet ascrewfeeddevicewithflexible-walled/externa-paddel-massagedscrewtrough
isafirstchoiceforloss-i-weightfeeders. Therearesituationswherethestirringagitator är dock
krävs: cohesiveingredientsandingredienttemperature. Cohesiveingredientsformasolid
masswhenexposedtocompression. Somearesosensitivethattheforceofgravityactingontheir
ownheadmasscancausethemtosolidify. Theseingredientsaredifficult, sometimesimpossible, till
feedreliablywithoutexcessivemaintenance. Testingishighlyrecommendedatfeedermanufacturers,
whoofferseveraltypesoffeeddevices. Stirringagitatorsmayhavethebestchanceofsuccessinsuch
fall. Polyurethanebecomestoosoftatingredienttemperaturesabove50C (122F), som kräver
ametalscrewtrough.
Thescrewisthecomponentofthefeederthatprovidesthefeeding.Theagitationonlyensuresthat
thescrewflightsfilluniformly. Screwsareselectedtoachievemaximumandminimumfeedrates.
Thescrewdiameterandpitcharesizedtoachievethefeedrateatanoptimalscrewrotationalspeed.
Attoolowascrewspeedthe "pulsingflow" maycauseanundesiredvariationinthefinalproduct.
Toohighascrewspeedmaycauseincompletefillingofthescrew.
Therearethreecommonscrewtypes:spiralscrew, bladescrewandtwinconcavescrew.
Thesingle-spiralscrewisthemostcommonselection.Itis "öppna" fortheingredienttoflow
freelyintotheflightsofthescrew. Ithasasmallersurfaceareathathelpsreduceadhesionof
theingredient, whichchangesthescrewvolumetricgeometry. Ingredientsaretransferredwith
lowshear. Onthenegativeside, aeratedingredientscaneasilyfloodpastthescrewflights.
Thesingle-bladescrewoffersmoreresistancetoaeratedingredients, butbecause
thereismoresurfacearea, stickyingredientscanadhere, reducingthevolumetricgeometry.
Bladescrewsareoftenpreferredforheavypowderswithbulkdensitiesofmorethan80lb/ft3.
Twinconcavescrewscanprovidesuperiorperformanceforpoorlyflowingpowders.Twinconcave
screwsareco-roterande, intermeshing, andself-torka. Thepowderflowsaroundtheflightsof
bothscrews. Thenegativeeffectsofsomeadhesivepowdersarereducedbytheself-torka
ofthetwoscrews. Twinconcavescrewsaresolidandthescrewflightshavealowvolumecompared
withspiralandbladescrews. Theshearonthepowderishigh, particularlyinthescrewtube.
Thescrewtubeistypicallyshorttoreducenegativeeffectsofhighshear.
Twinconcavescrewsareideallysuitedtopowderswithfeedratesbelow5ft³/hr. Thecross-avsnitt
ofthetwoscrewsiswiderthananequivalentsinglescrew, reducingthetendencytobridgeinthe
transitionfromthescrewtroughintothescrew. Också, screwspeedsfortwinconcavescrewscanbe
higherthansinglescrewsforthesamefeedratebecauseofthelargerinletandlowvolumeofthe
screwflight. Higherscrewspeedsreducethenegativeeffectsofpulsation.