Hacim Kalibi Tasarim Unsurlari 11 06

8/3/2019 Hacim Kalibi Tasarim Unsurlari 11 06

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TECHNICAL INFORMATION

DuPontDelrin acetal resinMolding Guide

Kalipteknolojisi.com


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Table o Contents

Pages

General Inormation 1

Description 1

Compositions 1

SaetyPrecautionstoObserve

WhenMoldingDelrinAcetalResins 2

Packaging 3

Polymer Structure and Processing Behavior 4

GlassTransitionandMelting 4

PVTDiagrams 4

Heating-CoolingBehavior 6

ViscosityandRheologicalBehavior 6

Injection Molding Unit 8

ScrewDesign 9

ELCeeScreworOptimumProductivity 10

CylinderTemperatureControl 10

CylinderAdaptor 10

Non-ReturnValve(BackFlowValveBFV) 10

Nozzle 11

EvaluationoMeltQuality 11

Molds 13

AbilitytoFill 13

Gates 14

RunnerSystem 16

NozzleandSprue 17

HotRunnerMoldorCrystallinePolymers 18

Vents 19

Undercuts 20

SharpCorners 21RibsDesign 21

WeldLines 21

MoldMaintenance 22

MoldCleaning 22

(continued)



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Table o Contents (continued)

Pages

Molding Process 23

Start-upandShutdownProcedures 23

OperatingConditionsorDelrin

TemperatureSettings 24

OperatingConditionsorDelrin

MoldingCycle 26

OptimumProductivityMolding 29

StandardMoldingConditions

orISOTensileBars 30

HoldPressureTime

viaIn-cavityPressureMeasurement 30Dimensional Considerations 31

FundamentalsoDimensional

Control 31

MoldShrinkage 31

FactorsAectingMoldShrinkage 31

MoldShrinkageoFilledResins 31

EectoPigments 33

Post-MoldingShrinkage 34

InsertMolding 35Annealing 35

EnvironmentalChanges 35

DimensionalTolerances 36

Auxiliary Operations 37

MaterialHandling 37

RegroundResin 37

Drying 37

Coloring 38

Disposal 38

Troubleshooting Guide 39

Index 42



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1

General Inormation

Description

Delrinacetalresinsaresemi-crystalline,thermoplasticpolymers

madebythepolymerizationoormaldehyde,andarealso

commonlyreerredtoaspolyoxymethylene(POM)Theyhave

gainedwidespreadrecognitionorreliabilityinmanythousands

oengineeringcomponentsallovertheworldSincecommercial

introductionin1960,Delrinhasbeenusedintheautomotive,

appliance,construction,hardware,electronics,andconsumer

goodsindustries,amongothers

Delrinisnotedor:

Highmechanicalstrengthandrigidity

Excellentdimensionalstability

Naturallubricity

Fatigueendurance

Highresistancetorepeatedimpacts

Excellentresistancetomoisture,gasolines,solventsand

manyotherneutralchemicals

Toughnessatlowtemperature(downto50C[58F])

Wideuseultemperaturerange(inair:50to90C

[58to194F],withintermittentuseupto120C[248F])

Goodelectricalinsulatingcharacteristics

Easeoabrication

Delrinacetalresinsareavailableinavarietyocompositionsto

meetdierentend-useandprocessingrequirements

CompositionsThemainavailableDelrincompositionscanbe

classiedasollows:

a Standard

b Toughened

c Lowwear/Lowriction

d Glasslled/Reinorced

e UV-stabilized

Thestandardcompositionscoverabroadrangeomelt

viscositiesThehighestviscositycomposition,solike

Delrin

100P,areotenmoldedwhenmaximumtoughnesspropertiesareneededTheintermediatemeltviscosityDelrin

500Pisusedorgeneral-purposeinjectionapplicationsThe

resinshavinglowermeltviscosity,Delrin900Pisusuallychosen

orinjectionmoldingapplicationswithhard-to-llmolds

AsummaryothemaincompositionsisshowninTable 1

Safety Precautions to ObserveWhen Molding Delrin Acetal Resins

Delrinaswellasmanyotherthermoplasticpolymers

decomposestogaseousproductswhenheatedoraprolonged

timeThesegasescangeneratehighpressuresiconnedI

materialisnotreetoexitromaninjectioncylinderthroughthe

nozzle,itmayblowbackthroughthehopper

InthecaseoDelrinacetalresin,decompositionisalmost

entirelytogaseousproducts,sopressurebuild-upcanberapid

Theproductodecompositionisormaldehyde

Aswithanyacetalpolymer,Delrin,whenoverheated,can

discolorandormgaseousdecompositionproducts,whichare

largelyormaldehydeLowlevelsoormaldehydeemissions

canalsooccurattypicalprocessingtemperaturesRepeated

exposuretoormaldehydemayresultinrespiratoryandskin

sensitizationinsomeindividualsFormaldehydeisapotential

cancerhazard

ProcessingtoughenedgradesoDelrin

canreleaselowlevelsoisocyanatesRepeatedexposuretoisocyanatesmayresultin

respiratoryandskinsensitizationinsomeindividuals

Lowlevelsoormaldehydemayoccurintheheadspaceo

bagsasreceivedorincontainersoormedpartsater

processingBagsoresinorormedpartsshouldbeopenedin

wellventilatedareas

Useadequatelocalexhaustventilationinprocessareasto

maintainexposuresbelowrecommendedcontrollimitsDropair

shotsintowatertoreduceemissions

WhenmoldingDelrin,itisimportantthattheoperatorbe

amiliarwiththeactorsthatcancausedecomposition,withthe

dangersignalsthatwarnothisproblem,andwiththeactionthat

shouldbetakenThisinormationissummarizedonacardor

displayatthemoldingmachine

Theinormationgivenhereisbasedonourexperiencetodate

Itmaynotcoverallpossiblesituationsanditisnotintendedasa

substituteorskillandalertnessotheoperator

Follow correct start-up, operating and shut-down procedures

as described later in this guide.

Be aware o troublemakerscauses o decomposition:

Hightemperaturestickingtemperaturecontroller,aultythermocoupleconnections,incorrectreading,burned-out

heaterorheaterwithahotspot,heatsurgesonstart-up

DonotoverheatMaintainpolymermelttemperaturebelow

230C(446F)

CycledelayAvoidprolongedexposureatorabovethe

recommendedprocessingtemperatureRecommendedmelt

temperaturesaregiveninTable 5



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High Viscosity Grades

Delrin100/II100

POMhomopolymerHighviscositymoldingmaterialExcellent

tensilestrengthandresistancetocreepoverawidetemperature

range,evenunderhumidambientconditionsHighatigue

enduranceandimpactresistanceApplications:moldedparts

suchashighlyloadedgears,plainbearingsandsnap-ts

Delrin100P

SamecharacteristicsandapplicationsasDelrin100,plus

improvedthermalstabilityorlowdepositmoldingindemanding

processingconditions,eg,hotrunnertools

Delrin111P

Characteristics:Delrin100Pwithenhancedcrystallinity

Resistancetocreepandatigueenduranceimprovedover

Delrin100PTypicalapplications:Highlyloadedgears,

bearings,snap-ts

Medium-High Viscosity Grades

Delrin311DP

POMhomopolymerOptimizedstabilizerormulationwithenhancedcrystallinity;excellentdimensionalstability

Excellentresistancetouels,lubricants,solventsandmost

neutralchemicals

Medium Viscosity Grades

Delrin500P

POMhomopolymerGeneralpurposemoldingresinwith

improvedprocessingstabilityorlowdepositmoldingin

demandingprocessingconditions,eg,hotrunnertools

Delrin511P

Characteristics:Delrin500Pwithenhancedcrystallinity,

goodresistancetocreepandatigue

Applications:uelsystemcomponents,gears,astenersLow Viscosity Grades

Delrin900P

Characteristics:Lowviscosity,astmoldingresinplusimproved

processingstabilityorlowdepositmoldingindemanding

processingconditions,eg,hotrunnertoolsApplications:

Multicavitymoldsandpartswiththinsections,eg,consumer

electronicsparts,zippers

Toughened Grades

Delrin100ST

POMhomopolymer,SuperToughHighviscosity,super

toughmaterialorinjectionmoldingandextrusionExcellent

combinationosuper-toughness,impactatigueresistance,

solventandstresscrackresistance,aswellashightensile

elongationatlowtemperatureApplications:Mainlyusedor

partsrequiringresistancetorepeatedimpactsandloads,

suchasautomotiveasteners,helmets,hosesandtubing

Delrin100T

POMhomopolymer,ToughenedHighimpactresistance

Delrin500T

Mediumviscosity,toughenedresinorinjectionmoldingand

extrusionExcellentnotchedIzodandtensileimpactstrength

Applications:Mainlyusedorpartssubjectedtorepeated

impactsandalternatingloads,suchasautomotiveasteners,

helmets,hosesandtubing

Low-Wear/Low-Friction Grades

Delrin100AL

Highviscositylubricatedgradewithpackageoadvanced

lubricants

Delrin100KM

Delrin100PmodiedwithKevlararamidresinorabrasivewearreductionApplications:Specialtyrictionandwear

Delrin500AF

Mediumviscositygradewith20%TefonPTFEbers,

outstandingrictionandwearpropertiesApplications:Specialty

rictionandwear,conveyorsystems

Delrin520MP

Delrin500Pwith20%TefonPTFEmicropowder,with

low-wearandlow-rictionpropertiesApplications:Specialty

rictionandwear

Delrin500TL

Delrin500with15%Tefonpowder,withlow-wearandlow-

rictionpropertiesApplications:Specialtyrictionandwear,

conveyorsystems

Delrin500AL

Mediumviscosityresinwithadvancedlubricantsystem,very

goodlow-rictionandlow-wearpropertiesApplications:Gears,

drivetrains,slidingdevices

Delrin500CL

ChemicallylubricatedDelrin500,verygoodlow-rictionandlow

wearpropertiesApplications:Gears,drivetrains,slidingdevices

Delrin500MP

MediumviscositygradewithTefonPTPEmicropowder

Delrin911AL

Lowviscsoitygradewithadvancedlubricants;excellent

dimensionalstability

Glass-Filled/Glass-Reinorced Grades

Delrin570

Mediumviscosityresin,with20%glassberllerApplications:

Wherehighstinessandcreepresistancearerequired

Delrin510GR

10%glass-reinorcedresinApplications:Partsrequiringhigh

stinessandstrength,andcreepresistance

Delrin525GR

25%glass-reinorcedresinApplications:Partsrequiringvery

highstinessandstrength,andcreepresistance

UV-Stabilized GradesDelrin127UV

Delrin100PwithUVstabilizerApplications:Automotiveinterior

partswithmaximumUVperormancerequirements,skibindings

seatbeltrestraintparts

Delrin327UV

Medium-highviscositygradewithUVstabilizerandenhanced

crystallinity

Delrin527UV

Delrin500PwithUVstabilizerApplications:Automotiveinterior

partswithmaximumUVperormancerequirements,interiortrim

seatbeltrestraintparts

Table 1

Main Compositions o Delrin Acetal Resins



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Hold-upareasincylinder,adapter,nozzle,screwtip,hot

runnerandcheckvalveassembly

Pluggednozzleromscrapmetalorhighermeltingpoint

resin,orromclosednozzlevalve

Foreignmaterials

Additives,llersorcolorantsotherthanthosespecically

recommendedoruseinDelrin

Contaminants(especiallythosecontainingchlorineorgeneratingacidmaterials)suchaspolyvinylchlorideresin

orfameretardants

Copper,brass,bronzeorothercopperalloysincontactwith

moltenDelrin(notinmoldswheretheresinsolidiesater

eachcycle)

Copper-basedlubricantsorgreaseorthreads

Contaminatedreworkespeciallyreworkorreprocessed

resinromoutsideorunknownsources

DonotmixDelringradeswithotherDelringrades,nor

withanyotherresins,withoutrstconsultingDuPont

AvoidprocessingDelrinonequipmentthatisalsoused

orincompatibleresins,particularlyhalogenatedpolymers,suchasPVCorhalogenatedthermoplasticelastomers,or

UVstabilizedorfameretardantmaterials

Watch or Danger Signals

Frothynozzledrool

Spittingnozzle

Pronouncedodor

Discoloredresinbrownorblackstreaking

Badlysplayedpartswhitishdepositonmoldingormold

Screwpushbackromgaspressure

Action Required When Any o the Danger Signals Occur AVOIDPERSONALEXPOSUREWhenDANGERSIGNALS

arepresent,DONOTlookintohopperorworkaroundnozzle

asviolentejectionomeltispossible

MINIMIZEPERSONALEXPOSURETODECOMPOSITION

GASESbyusinggeneralandlocalventilationInecessary,

leaveareaomachineuntilventilationhasreduced

concentrationoormaldehydetoacceptablelevelsPersons

sensitizedtoormaldehydeorhavingexistingpulmonary

disabilitiesshouldnotbeinvolvedinprocessingDelrin

FREENOZZLEPLUGbyheatingwithtorchIthisails,cool

downcylinder,makesurePRESSUREISRELIEVED,and

CAREFULLYREMOVENOZZLEandclean TAKEAIRSHOTStocooltheresinPURGEWITHCRYSTAL

POLYSTYRENEDROPALLMOLTENDelrinINTOWATERto

reduceodorlevel

Turnocylinderheaters

Checktemperaturecontrolinstruments

Discontinueautomaticmoldingandrunmanuallyuntiljobis

runningsmoothly

Provideadequatemeansoventingeedmechanismincase

oblowback

Useexhaustventilationtoreduceormaldehydeodor

Idecompositionoccurs:

1 Shutoandpurgemachine

2 Minimizepersonalexposuretodecompositiongases

byusinglocalandgeneralventilation

3 Inecessary,leaveareaomachineuntilventilationhas

reducedconcentrationoormaldehydetoacceptablelevels

Packaging

Delrinacetalresinissuppliedassphericalorcylindricalpellets

approximately3mm(012in)indimensionsTheyarepackaged

in1,000kg(2,200lb)netweightbulkcorrugatedboxes,

500kg(1,100lb)netweightfexiblecontainer,or25kg(5516lb)

moistureprotected,tearresistantpolyethylenebagsThebulkdensityotheunlledresingranulesisabout08g/cm3



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Polymer Structure andProcessing Behavior

Thebehavioroapolymerduringthemoldingprocessandthe

behavioroamoldedpartduringitswholeend-useliearehighly

dependentonthetypeostructurethatthepolymertendstoormduringsolidication

Somepolymersexhibitinthesolidstateroughlythesame

moleculararrangementasinthemelt,ie,arandommass

oentangledmoleculeswithnoorderThisclassisnamed

amorphouspolymersandincludesorexampleABS,

polycarbonateandpolystyrene

Otherpolymerstendtosolidiyinanorderedmanner:the

moleculesarrangingintocrystallineorms(lamellae,spherulites)

Becauseothelengthothemacromolecules,partsothem

cannotbelongtocrystals(duetolackospaceandmobility)and

createanamorphousinter-crystallinezoneThesepolymersarethereorepartiallycrystallineorsemi-crystalline;orsimplicity,in

thistextwewillreertothemascrystalline(asopposed

toamorphous)

TypicalcrystallinematerialsareDelrin(acetalresins),Zytel(polyamideresins),RynitePETandCrastinPBT(thermoplasticpolyesterresins),polyethyleneandpolypropylene

Table 2summarizessomeundamentaldierencesbetween

amorphousandcrystallinepolymersThesepointsare

describedinmoredetailintheollowingparagraphsThis

inormationisessentialtounderstandwhytheoptimization

othemoldingprocessissubstantiallydierentorthetwocategoriesopolymers

Table 2Comparison of Amorphous and Crystalline Polymers

Resin type Amorphous Crystalline

PropertiesThermal parameters T

gT

g, T

m

Maximum T in use* Below Tg

Below Tm

Specifc volume vs. T Continuous Discontinuity at Tm

Melt viscosity vs. T High dependence Low dependence

ProcessingSolidication Cooling below T

gCrystallization below T

m

Hold pressure Decreased during cooling Constant during

crystallization

Flow through gate Stops ater dynamic lling Continues until end o

crystallization

Deects i bad process Over-packing, stress-cracking, Voids, deormations,

sink marks sink marks

* For typical engineering applications

Glass Transition and MeltingAmorphous Polymers

Theoverallbehavioroamorphouspolymersislargely

determinedinrelationtotheirglasstransitiontemperatureTg

Belowthistemperature,themoleculesareessentiallyblocked

inthesolidphaseThematerialisrigidandhasahighcreep

resistance,butitalsotendstobebrittleandsensitivetoatigue

Whenthetemperatureisincreasedabovetheglasstransition

temperatureTg,themoleculeshavesomereedomtomove

byrotationaroundchemicalbondsTherigiditydecreases

graduallyandthematerialshowselastomericproperties,lending

itseltoprocesseslikethermoorming,blowmoldingand(at

temperatures120150C[248302F]aboveTg)injectionmolding

AmorphouspolymersusedinengineeringapplicationshaveTg

abovetheambienttemperature,andthemaximumtemperature

orend-useshouldbebelowTg;orexamplepolystyrenehasT

g=

90100C(194212F),andisinjectionmoldedbetween210and

250C(410and482F)

Crystalline Polymers

Incrystallinepolymers,theonsetomolecularmovementinthe

materialalsodenestheglasstransitiontemperatureTg

WhenthetemperatureisincreasedaboveTg,thecrystalline

polymersmaintainrigidityappropriateorengineering

applications(orexamplewithDelrinapartcaneasilywithstand

temperatureswellabovetheTg)

Uponurtherheatingthematerialreachesitsmelting

temperatureTm,wherethecohesionothecrystallinedomains

isdestroyedWithinaewdegrees,thereisaconsiderablechangeomechanicalpropertiesromsolidtoliquidbehavior

AboveTm,thecrystallinepolymersbehaveashighviscosity

liquids,andcangenerallybeprocessedbyinjectionmolding,

typicallyattemperatures3060C(86140F)abovetheirmelting

temperatureAsaconsequence,thetemperaturedomainorthe

useocrystallinepolymersisnotlimitedbytheglasstransition

temperatureTg,butbythemeltingtemperatureT

mForDelrin,

theeectotheTgisnegligibleandverydiculttomeasure,due

toitsverylowamorphouscontentTherearetwotransitionsor

Delrin,aweakonearound015C(3259F)andastrongerone

at80C(112F)Thetransitionjustbelowroomtemperatureis

soweakthereisminimaleectonpropertiesForDelrinacetalhomopolymrs,T

m=178C(352F)andthetypicalprocessing

rangeis210220C(410446F)

PVT Diagrams

ThePVTdiagramisacondensedpresentationothe

interrelationsothreevariablesthataecttheprocessingoa

polymer:Pressure,VolumeandTemperature

Theeectothetemperature(T)orvolume(V)isillustratedin

Figure 1oranamorphousandacrystallinepolymerWhenthe



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temperatureothematerialisincreased,itsspecicvolume

(theinverseodensity)alsoincreasesduetothermalexpansion

Therateoincreasebecomeshigherattheglasstransition

temperature,becausethemoleculeshavemorereedomto

moveandtheyoccupymorespaceThischangeoslopeis

observedwithbothamorphousandcrystallinepolymersAt

highertemperature,themeltingocrystallinepolymersis

markedbyasuddenincreaseothespecicvolume,whenthewell-orderedandrigidcrystallinedomainsbecomerandomly

orientedandreetomoveThespecicvolumeisthereore

asignatureothechangesostructureothepolymerasa

unctionotemperature

APVTdiagramissimplythepresentationotheseriesocurves

obtainedwhenthemeasurementospecicvolumeversus

temperatureisrepeatedatdierentpressuresThePVTdiagram

oatypicalamorphouspolymer(polystyrene)isshownin

Figure 2,andthePVTdiagramoDelrinisshowninFigure 3

Themoldingprocesscanbeillustratedbyacycleotransitions

onthePVTdiagramForsimplication,itwillbeassumedintheollowingdescriptionthatheatingtakesplaceatconstant

pressure(alongisobarlines)andthatapplicationopressureis

isothermal(verticallines)

Foranamorphousmaterialthemoldingcycleisas

ollows(seeFigure 2):

Startingromroomtemperatureand1MPapressure(point

A)thematerialisheatedinthebarrelThespecicvolume

increasesaccordingtotheisobarat1MPatoreachthe

moldingtemperature(pointB)

Thematerialisinjectedintothecavityandthepressureis

appliedThisprocessisroughlyisothermal(topointC),and

thespecicvolumeisdecreasedtoavalueclosetothatat

1MPaandTg

Theresiniscooledinthemold,andatthesametimethe

holdpressureisdecreased,toollowahorizontallineinthe

PVTdiagramandreachpointDwherethepartcanbeejected

whenitisat1MPapressureandatemperaturebelowTg

Ideally,thereshouldbenofowomaterialthroughthegate

duringthiscoolingphasetoproduceastress-reepart

Foracrystallinematerial,thepictureisdierent(seeFigure 3):

thematerialisheatedat1MPapressureromroom

temperature(pointA)uptotheprocessingtemperature

(pointB)Thisresultsinalargechangeovolume(almost25%orDelrin);

theresinisinjectedandcompressedinthecavityThespecic

volumeisdecreasedtopointC,whereitsvalueisstillmuch

higherthanat1MPa/23C(73F);

crystallizationtakesplaceinthemoldunderconstant

holdpressureWhenthecrystalsbuildupromtheliquid

phase,alargedierenceovolumeoccurs,whichmustbe

compensatedbyinjectionoadditionalliquidresinthroughthe

gate(otherwisevoidsarecreatedwithinthepart);

Temperature, C

Specificvolum

e,

cm3/g

Tg

Temperature, C

Specificvolume,

cm3/g

Tm

"Liquid" phase

"Solid" phase

Tg

AMORPHOUS

CRYSTALLINE

Figure 1. Specic Volume as Function o Temperature orAmorphous And Crystalline Polymers

Figure 2. Pressure-Volume-Temperature (PVT) Diagram orPolystyrene. Points A, B, C, and D Reer to DierentSteps o the Molding Process (see text).

Temperature, C

Spe

cificvolume,

cm3/g

30050

AD

B 1

4060

160

100C

100 150 200 2500

0.95

1.00

1.05

1.10

0.90

20

Polystyrene

P (MPa)



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attheendocrystallization(pointD),thepartissolidandit

canbeejectedimmediately;themoldingshrinkageisthe

dierencebetweenthespecicvolumesatthecrystallization

temperature(pointD)andatroomtemperature(pointA)

Thisdierenceinbehaviorhasimportantimplicationsor

injectionmoldingDuringthesolidicationprocess(ater

dynamiclling):

theholdpressureisdecreasedwithtimeoramorphous

polymers,whereasitismaintainedconstantorcrystalline

polymers;

thefowthroughthegateisstoppedoramorphouspolymers,

whileitcontinuesuntiltheendothecrystallizationor

crystallinepolymersThisimpliesthatorcrystallinematerials

thedesignoparts,gates,runnersandsprueshouldollow

specialrulesthatwillbedescribedintheMoldssection

Heating-Cooling Behavior

Foranysubstance,theenergyneededtoincreasethe

temperatureo1gmaterialby1C(18F)isdenedasits

specicheatThisquantityisgenerallydeterminedbyDierential

ScanningCalorimetry,andtheresultsorDelrin,polyamide

6-6andpolystyreneareshowninFigure 4Thetwocrystalline

polymers,Delrinandpolyamide6-6,showalargepeakthatis

duetotheadditionalheatrequiredtomeltthecrystallinephase

(latentheatousion)Theamorphouspolymerdoesnotshow

suchapeak,butexhibitsachangeoslopeatTg

Thetotalenergytobringeachmaterialuptoitsmolding

temperatureisgivenbytheareaunderthecurveFrom

Figure 4itisclearthatthecrystallinepolymersneedmore

energythantheamorphousonesThisexplainswhythe

designoascreworacrystallinepolymerlikeDelrin

shouldbedierent(andusuallymorecritical)thanoran

amorphouspolymer

Temperature, C

Specificvolume,

cm3/g

25050

A

C

D

B

100 150 2000

0.70

0.75

0.80

0.85

0.90

0.65

Delrin 500 1

40

80

120140

180

P (MPa)

Figure 3. Pressure-Volume-Temperature (PVT) Diagram ForDelrin 500. Points A, B, C, and D Reer to DierentSteps o the Molding Process (see text).

Figure 4. Specic Heat versus Temperature or Delrin 500,PA66 and Polystyrene

Specific

heat,

kJ

kg

1K

1

400300

PS

PA66

2001000

0.4

0.8

1.2

1.6

2.0

2.4

2.8

0

Temperature, C

Delrin 500

Viscosity and Rheological Behavior

Meltviscositydeterminestoalargeextenttheabilitytollthe

moldcavityHighviscositymeansdicultfowthroughthin

sectionsandhigherinjectionllpressure

Temperatureandshearratearecrucialparameterswhen

consideringtheviscosityomoltenpolymers,andtheyshould

alwaysbespeciedtogetherwithavalueormeltviscosity

ForpolymersconsistingolinearmoleculeslikeDelrin,

theviscosityisalsoindirectrelationtotheaverage

molecularweight

Inuence o Temperature

Thegeneralrulethatliquidsbecomelessviscouswhen

increasingtemperatureisalsotrueormoltenthermoplastics

Howevercrystallineandamorphouspolymersbehavedierently

asshowninFigure 5ThecurvesorDelrinandpolystyrene

werebothobtainedbyreducinggraduallythetemperatureothe

materialsrom230to100C(446to212F)Twodierencesare

worthmentioningFirst,attemperaturesabove180C(356F),

thedependenceoviscosityontemperatureismorepronounced

ortheamorphouspolystyrenethanorDelrin;thereore,

increasingthemelttemperatureoDelrindoesnotgreatly

improveitsabilitytofowthroughathinsectionSecond,below

170C(338F)theviscosityoDelrinrisessharplybecausethe

materialcrystallizeswithinaewdegreesothattemperature



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Figure 5. Viscosity/Temperature Curves for Delrin 500Pand or Polystyrene at a Constant Shear Rate o1000 s1 (Temperature Reduced rom 230 to 100C[446 to 212F])

Temperature, C

Apparentvisco

sity,

Pa.s

180 220 240200120 140 160100

600

400

200

0

Delrin 500

Polystyrene

Thermoforming

Extrusion

Injection molding

Y

V (Y)

Figure 6. Approximate Shape o the Velocity DistributionBetween Two Parallel Plates. The Shear Rate is theDerivative dv(y)/dy.

Figure 7. Viscosity versus Shear Rate o Delrin 500P atThree Temperatures

Figure 8. Viscosity versus Shear Rate or Various Grades oDelrin at a Constant Temperature o 215C (419F)

Inuence o Shear Rate

Theshearratecharacterizestherateodeormationothe

materialandisdenedasthederivativeothevelocityoverthe

directionperpendiculartofow(seeFigure 6);inotherwords,the

shearrateisproportionaltothevariationospeedwithinthepart

thicknessSoitdependsonthevelocityothefowandonthe

geometryothefowchannels

Shear rate, s-1

Viscosity,

Pas-1

200C

215C

230C

102 103 104

100

1000

10

Table 3Viscosity, Flow and Molecular Weight (Mw)

o the Delrin Grades

Spiral fow lengthMFR MFR (215C/100 MPa/2 mm

(190C/ (190C/ Ease Mw, 90C moldGrade 1.06 kg) 2.16 kg) o fow toughness temperature

100 1 2.3 lowest highest 170 mm

300 3.5 7

500 7 14 295 mm

900 11 24 350 mm

ForDelrin,themeltviscositydecreasesconsiderablywhenthe

shearrateincreases,asshowninFigure 7Thiseectismore

importantthanthedierencesresultingromvariationsothe

melttemperaturewithintheprocessingwindoworinjection

molding

Inuence o Molecular Weight

DelrinisavailableinourgradesomolecularweightTheyare

codedaccordingtotheirabilitytofow,asmeasuredbyMFRor

meltfowrate(seeTable 3)Highvaluesmeaneasyfowand

abilitytollthinparts,whereaslowvaluesmeanhighviscosity,

highmolecularweightandhightoughness(impactresistance,

elongationatbreak)

Shear rate, s-1

Viscosity

,Pas-1

100 1,000 100,000

100

1,000

10

900500

100

MFRisameasurementperormedatlowshearrate,butthe

relativedierencesbetweenthegradesaremaintainedathigh

shearrates,asshowninFigure 8

Amoredirectcomparisonotheabilitytollcanbeobtained

usinganopen-endedsnake-fowmoldResultsorthedierent

gradesoDelrinarepresentedintheMoldssection



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Hold-up time, min

Meltte

mperature,

C

60 80 10040200

200210

220

230

240

250

190

Minimum recommended

melt temperature

Recommended operatingzone

Figure 9. Eect o Temperature on Hold-up Timeo Delrin 500

Withascrewstrokeo1diameter(asmallshot)andacycletime

o1min(averylongone),theaverageHUTisequalto8min

AccordingtothedegradationcurveshowninFigure 9,Delrin

shouldbestableenoughorinjection-moldingwiththisHUTat

amelttemperatureo240C(464F)Somecustomershave

experiencedmoldingDelrinsuccessullyatthattemperature

Attherecommendedmelttemperatureo215C(419F),the

maximumHUTisover30minandDelrin(standardgrades)is

thermallystableevenundertheseextremeconditions

Thereare3mainpotentialcausesodegradation:

Material trapped in Hold-up spotsIntheinjectionunit,

trappedmoltenmaterialwillstayorverylongtimesinany

deadspotsandwillstarttodegradeSoalltheinjectionunit

(screw,backfowvalve,adaptor,nozzleandhotrunners)

shouldbedesignedtoavoidHold-upspots(seeollowing

recommendeddesign)

Material sticking to hot steelDuetothehighviscosityo

polymers,thespeednexttothesteelotheinjectionunit

(screw,backfowvalve,adaptor,nozzleandhotrunner)isalmostzeroandtheresidencetimeisalmostinnite(as

evidencedbyhowlongittakestochangecolorsinaninjection

unit)Whereasinsidethebarrelthemoltenpolymeriscleaned

bythescrewandthevalve,insideallotherareasthematerial

willsticktothewallsTowithstandaverylongresidencetime

thesteelincontactshouldbecontrolledatatemperature

lowerthan190C(374F)(seeFigure 9)

Chemical degradationContamination(eg,PVC,fame

retardantresins,acidgeneratingresins),incompatible

coloringsystems(acidorbasicpigments),contactwith

copper(pure,alloys,grease)willacceleratethethermal

degradationomoltenDelrinintheinjectionunitNotethat

moldcomponentsincopperorcopperalloys(suchascopper-

beryllium)donotcauseanydegradationandhavebeenused

oryearswithoutproblems

Injection Molding Unit

Delrinacetalresinsaremoldedthroughouttheworldina

widevarietyotypesanddesignsoinjectionandextrusion

equipment

Therstpurposeotheinjectionunitormoldingacrystalline

materialistodelivertothemoldthenecessaryamountoa

homogeneousmelt(withnounmeltandnodegradedmaterial)

Therulesoconstructionotheinjectionunitarethendependent

onthemoldingmaterialrequirementsintermothermal

behaviorandheatneededTherstpointtotakeintoaccountor

acrystallinematerialisthethermalstabilityatmelttemperature,

toavoiddegradationThen,screw,nozzle,backfowvalve,

adaptor,shouldbedesignedtoprovideecientmeltingo

crystallinematerialanddeliveryomoltenpolymertothemold

Tworoughmethodstoevaluatethepresenceounmeltand

odegradedmaterialwillbepresentedinEvaluationoMelt

Quality(seepage11)

Thermal Stability During Processing

Aspresentedinthepreviouschapter,onedierencebetween

amorphousandcrystallinematerialisthemeltingbehavior

TheamorphouspolymerstartssoteningjustaterTgand

presentsacontinuouschangeinviscosityThisgivesavery

largetemperaturerangetooperate(butalargevariationo

viscositywithtemperature)Incontrast,thecrystallinepolymer

stayssoliduptothemeltingpointandsuddenlymeltstothe

liquidphaseathightemperatureThislimitstheprocessing

rangeotemperaturebetweenunmeltandthermaldegradation

(specicallyorDelrin

190250C[374482F])

Thesecondactoristhetimethematerialstaysatthat

temperatureForallpolymers,themoleculescanwithstanda

certaintimeatacertaintemperaturebeoredegradationcan

startObviouslythisacceptabletimelimitbecomesshorter

whenthetemperatureishigherThetypicalbehavioroDelrin

ispresentedinFigure 9DegradationoDelrinwillresultin

generationogaseswhichcausebubblesinthemelt,splayson

parts,molddeposit,yellowandbrownmarksontheparts

Theaverageresidencetime(orHold-UpTime,HUT)intheinjection

unitislinkedtotheamountopolymerinthecylinder,theshot

weightandthecycletimeandcanbecalculatedwiththeollowingequation:

AverageHUT= weightoresinincylindercycletime

shotweight

Aquickapproximationcanbedoneby:

AverageHUT=maximumscrewstroke2cycletime

currentscrewstroke*

*Eectivescrewstroke=distancethescrewtravelsduringrotationonly



13/48

9

Screw Design

Screwdesignisakeyparameterorproductivity,becauseor

crystallinematerialsthescrewrotationtimeisaninherentparto

thecycletime

Asmentionedabove,itshouldtakeinconsiderationthespecic

meltingbehaviorothecrystallinematerial,ie,soliduptothe

meltingpoint,highdemandoheatduringmeltingandlow

viscosityothemoltenmaterial

Althoughgeneral-purposescrewsarewidelyusedormolding

Delrin,optimumproductivitywillrequireaspecicdesign

Exceedingtheoutputcapabilityoaninadequatelydesigned

screwwillcausewidetemperaturevariationsandunmelted

particles(sometimesunmeltanddegradedmaterialhavebeen

observedatthesametime)Theresultislossotoughness,

variabilityinshrinkageanddimensions,warping,surace

deects,pluggedgates(leadingtoshortshots)orothermolding

problems

Duetothespecicsothemeltingprocessoacrystalline

polymer,ascrewdesignedorDelrinwillhaveshallowfight

depthsinthemeteringsectionandaslightlyhighercompression

thanageneral-purposescrewSpecicsuggestionsaregivenor

variousscrewdiametersandcompositionoDelrinacetalresin

inTable 4Compressionratioistheratioovolumeooneturn

intheeedsectiontothatinthemeteringsection(canbeap-

proximatedtotheratioothedepthothetwozones)

Thelengthothescrewwillalsoaectthemeltquality(an

insulatingmaterialneedssometimetogetthethermalenergy

transerredevenitheshearcontributestotheheatingprocess)

Thepreerredlengthisabout20timesthescrewdiameteror

20turnswhenthepitchanddiameterareequalThescrew

shouldbedividedasollows:3040%(68turns)eedsection,

3545%(79turns)transitionand25%(5turns)metering

Table 4Screw Design or Delrin Acetal Resins

Medium and Low Viscosity Grades: Delrin

500P, 900P, 500T High Viscosity Grades of Delrin

: Delrin

100P, 100STNominal diameter (D) Depth o eed section (h

1) Depth o metering section (h

2) Depth o eed section (h

1) Depth o metering section (h

2)

mm mm mm mm mm

30 5.4 2.0 5.2 2.645 6.8 2.4 6.5 2.860 8.1 2.8 7.5 3.090 10.8 3.5 8.7 3.6

120 13.5 4.2

(in) (in) (in) (in) (in)

(1-12) (0.240) (0.087) (0.230) (0.105)(2) (0.290) (0.100) (0.270) (0.115)

(2-12) (0.330) (0.110) (0.300) (0.120)(3-12) (0.420) (0.140) (0.340) (0.140)(4-12) (0.510) (0.160)

Dh1

FEED SECTION

Pitch h2

METERINGSECTION

TRANSITION

(20/1 Length/Diameter Ratio)

sectionScrewswith20turnsarecommonlydividedinto7turns

eed,8turnstransitionand5turnsmeteringInscrewslessthan

16diameterslong,itmaybenecessarytoreducethepitchtoget

upto20turnsDenitively,theeedsectionshouldneverbeless

than6turns

TherelativelyhighcompressionratioscrewssuggestedorDelrin

aredesignedtoincreasetheheatinputbymechanicalworking

otheresinBecausetheenergyorthisincreasecomesrom

thescrewmotor,additionalhorsepowermustbeavailableian

increaseinmeltingcapabilityistoberealized

Screw Size

Theidealscrewsizeisdeterminedbythevolumeothecurrent

shotOptimumproductivitywillbeachievedwhentheshotsize

requiresascrewtravelduringplasticizationequaltoorlower

than50%othecapacityotheinjectionunitOtherwise,screw

rotationspeedwillhavetobedecreasedattheendothe

traveltoguaranteeanhomogeneousmelt,leadingtoalossin

productivityPractically,optimumproductivityisachievedwitha

screwtravelobetween1and2diametersothescrew

Thermalsettingsotheinjectionunitwillbedependentonthe

residencetime(HUT)andhencedependentonthecycletime

RuleswillbepresentedunderMoldingProcess

Screw Design or the Use o Color Concentrate

Afowanalysisshowsthatthemajorpartothefowinthe

screwislaminar,thendividedinthebackfowvalve(duetothe

changesinfowdirection),andstilllaminarintheadaptor,nozzle,

sprue,etcTogetoptimummeltquality,todispersepigments

andcolorconcentrates,itisstronglyrecommendedtoadda

mixingheadThepurposeoaproperlydesignedmixingheadis

nottomixmaterialbyturbulence(turbulentfowisimpossible

withhighlyviscousmoltenpolymer),butbyorcedchangesin

fowdirection



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10

ELCee Screw for Optimum Productivity

Anothersolutiontoachieveoptimumproductivitywhenmolding

highlycrystallineresinssuchasDelrin,istouseaspecial

screwdesignedbyDuPontcalledtheELCeescrew(patent

appliedor)TheELCeescrewisdesignedtocapitalizeonthe

rheologicalcharacteristicsoresinswithbettercontroloshear

onthemelt,makingthescrewmoreecientThisallowsthe

moldertorunthemoldingmachinesatastercyclesandproduce

partsohigherquality(ConsultyourlocalDuPontrepresentative

ormoreinormation)

Cylinder Temperature Control

Thisisdeterminedbythemachinemanuacturer,buttwo

commentsshouldbemade

Thetemperaturecontrolshouldprovideatleastthree

independentzones,withthermocouplesplacednear

thecenteroeachzoneBurn-outooneormoreheater

bandswithinazonemaynotbereadilyapparentrom

thetemperaturecontrollers,sosomemoldershaveused

ammetersineachzonetodetectheaterbandmalunctions

UsuallyorDelrinthereisnoneedtocooltheeedthroat,

butincasesuchaneedexists,thewaterfowshouldbekept

toaminimumOvercoolingtheeedthroathasbeenobserved

asamajorreasonorcontaminationbyblackspecksThese

aregeneratedinthebarrel,between therstandsecond

heatingzones,withtheollowingmechanism(seeFigure 10)

ThethermocoupleTC1isinfuencedbythelowtemperature

duetoexcessivecooling,andthesystemwillrespondby

switchingONtheheatingbandsHB1andHB2Thiscausesno

problemwithHB1,butresultsinoverheatinganddegradation

intheareaunderHB2Toreducetheriskoormationoblack

specks,theollowingrecommendationsshouldbeobserved:

a) theeedthroatcoolingshouldbelimitedtoaminimum

temperatureo8090C(176194F);

b) theheaterbandHB2shouldbecontrolledbyTC2,orTC1

shouldbeplacedinthemiddleoHB2,orHB2shouldhave

halthepowerdensityoHB1

HB1 HB2

TC1

Cooling channels Contamination

source

TC2 TC3 TC4

HB3 HB4 HB5 HB6 HB7

HB8

Figure 10. The Risk o Black Specks ContaminationThat Could Arise From the Presence o a CoolingSystem o the Feed Throat

Figure 11. Design o Adaptor and Non-Return Valve

Cylinder Adaptor

TheadaptorshowninFigure 11isdesignedtoavoidholdup

areasandfowrestrictions,thetwomaincausesodegradation

andproblemslinkedtothisareaNotethattheconceptisthe

sameorscrewedadaptorsasrepresentedinFigure 11(used

orsmallscrews40mm)andorboltedadaptors(usedor

largerscrews)Theadaptorshasshortcylindricalsections(Aand

B)whereitjoinsboththenozzleandthecylindertomaintain

accuratematchingothesediameters,eveniitbecomes

necessarytoreacethematingsuracesThematingsuraces(C)

shouldbenarrowenoughtodevelopagoodsealwhenthenozzle

oradaptoristightenedandyetwideenoughtoavoiddeormation

Inadditiontoitsmechanicalunctionoreducingthediameter,

theadaptoractstoisolatethenozzlethermallyromtheronto

thecylinderorbettercontrolonozzletemperatureAseparate

adaptor,madeosotersteelthantheoneusedorthecylinder,

iseasierandlessexpensivetorepairandchangethanacylinder

Italsoprotectsthecylinderromdamageduetorequent

changingothenozzleWiththeboltedadaptor,specialcare

shouldbetakenduringassemblytoensureparallelism(dont

overtightenscrewsromonesideonly)

Nozzle

Adaptor

A

D H

E

B

G FC

Non-Return Valve (Back Flow ValveBFV)

Thenon-returnvalveorcheckringshowninFigure 11prevents

meltromfowingbackwardduringinjectionThisunitis

requentlynotproperlydesignedtoeliminateholduporesin

andfowrestrictionsMalunctioningthatallowsresinbackfowisalsoacommonexperienceandiscausedbypoordesign

ormaintenanceAleakingnon-returnvalvewilladdtoscrew

retractiontime,whichcanincreasecycle,anditwillalsocause

poorcontrolopackinganddimensionaltolerances

Thenon-returnvalvemustmeettheollowingrequirements:

Noholdupspots

Nofowrestrictions

Goodseal

Controlowear



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11

Figure 12. Reverse Taper Nozzle

Heater Band

Thermocouple well

A

B

Thermocouple wellHeater BandA B

Figure 13. Straight Bore Nozzle, Only or Machines WithoutScrew Decompression

Theserequirementsareprovidedorinthenon-returnvalve

showninFigure 11

Theslotsorfutes(D)inthescrewtiparegenerously

proportioned,andthespace(E)betweenthecheckringandtip

issucientorresinfow

Theseatingothexedringiscylindricalwhereitjoinsboththe

endothescrew(F)andthescrewtip(G)topermitaccurate

matchingothesediametersandavoidholdup

Thescrewtipthreadhasacylindricalsection(H)aheadothe

threadsthattscloselyinamatchingcounterboreorsupport

andalignmentothescrewtipandseatring

Thescrewtipandcheckringseatshouldbeharder(about

Rc52)thanthefoatingring(Rc44),becauseitislessexpensive

toreplacethefoatingringwhenwearoccurs

CorrosionresistantsteelissuggestedorthetipGoodmatching

ocylindricaldiametersisessentialtoavoidholdupspots

NozzleAswithothersemi-crystallinepolymers,Delrinmaydroolrom

thenozzlebetweenshotsithenozzleistoohot,oritmayreeze

itoomuchheatislosttothespruebushing

ThenozzledesignshowninFigure 12cansolvetheseproblems

Theollowingshouldbeconsidered:

1 Theheaterband(A)shouldextendasclosetothenozzletip

aspossibleandcoverasmuchotheexposedsuraceas

practicalThiscounteractsanyheatloss,especiallyheatloss

tothespruebushing

2 ThethermocouplelocationisimportantAnappropriate

location(B)isshowninthesamepicture

3 Adequatetemperatureuniormityisrequiredsothatlocal

overheatingorprematurereezingisavoided

4 Topreventpolymerdegradationthesteeltemperatureshould

notexceed190C(374F)

5 Thenozzleheatershouldhaveitsownindependent

temperaturecontroller

Screwdecompressionorsuckbackisrequentlyusedtomake

controlodrooleasierwiththeseopennozzlesThiseatureis

availableinmostmachines

Whennotavailable,adesignsuchastheoneillustratedin

Figure 13shouldbeused

Althoughshutonozzleshaveoccasionallybeenused

successullywithDelrin,theytendtocauseholduporesinthat

resultsinbrownstreaksorgassing,especiallyatersomewear

hasoccurredinthemovingpartsothenozzleThesenozzlesare

notgenerallyrecommendedorDelrinonsaetygroundsalone

Note:Withalongnozzle,thethermocouplewellBshouldbe

positionedinthemiddleothenozzleandnotatthebackothe

nozzle

Evaluation of Melt Quality

Belowarepresentedtwoquickandeasyteststoevaluatethe

meltqualitydeliveredbytheinjectionunitAlthoughtheresultis

linkedwiththetemperaturesettingotheinjectionunit,itisalso

highlydependentonthedesignotheinjectionunit

Foaming Test

Theoamingtestisrecommendedtodeterminethequalityo

theresinatermeltingintheinjectionunit,ie,thequalityothe

resinANDthequalityotheinjectionunit

Procedure:

1 Whenthemachineisrunningincycle,stop

themachineaterscrewretractionor3minorpigmentedDelrin(10minornaturalmaterial)

2 Purgeatlowspeed(toavoidhotsplashes)intoacupand

observethemoltenmaterialor1or2minThenputthe

moltenmaterialinabucketowater

3 Thenrechargethescrewandwait2moreminutes

(10moreminutesornaturalmaterial)

4 Repeatoperation2



16/48

12

Anunstablemeltwillgrow(oam)duringtheobservationand

foatinthebucketAstablemeltwillstayshinywithatendency

toshrinkduringtheobservation,andwillsinkinthebucket

Foamingresinwillquicklycausemolddepositandwillaccelerate

screwdeposit,whichmayleadtoblackspeckcontamination

Thistechniqueisuseultoevaluatenon-DuPontcolorsystems

(colormasterbatches,liquidcoloring)

Theoamingtestcanalsobeusedtodetectinadequatequality

otheinjectionunit(eg,problemsothroatcoolingand

consequentoverheating,excessivenozzletemperature,hold-up

spots,etc)

Unmelt Test

Theunmelttestisrecommendedtoevaluatemelthomogeneity:

Whenthepressisrunningoncycle,stopattheendoacycle

andpurgeoneshot;

chargethescrewimmediatelywiththeshotvolumeusedand

purgeagain;

repeattheoperationuntildetectionolumps/irregularitiesin

thepurgecomingoutothenozzle

Isuchlumps/irregularitiesappearaterlessthan3purges,the

riskounmeltisveryhighandshouldbedealtwithbyincreasing

cylindertemperature,byloweringscrewRPMandbyincreasing

backpressureIsuchchangeslengthenthecycletimetoo

much,amoreappropriatescrewdesignshouldbeused(see

Table 4)Ilumps/irregularitiesappearater3purgesbutbeore

6,thesituationisacceptable,butthereisnotmuchsaety

marginItheyappearater6purges,thereisaverylowriskounmelt



17/48

13

Figure 14. Exploded View o Mold

LocatingRing

SprueBushing

FrontClampingPlate

FrontCavityPlate(APlate)

LeaderPins

LeaderPinBushings

RearCavityPlate(BPlate)

SupportPlate

Cavity

SpacerBlock

EjectorRetainerPlate

ReturnPin

EjectorPlate

KnockOutPins

RearClampingPlate

SpruePuller

SupportingPuller

StopPin

Ability to Fill

Meltviscositylargelygovernstheabilityoaresintollamold

DelrinacetalresinsrangeinmeltviscosityromDelrin900P,

thelowestinviscosityormostfuid,toDelrin100P,thehighest

TheviscosityoDelrindoesnotdecreaserapidlyasmelt

temperatureincreases,incontrasttoamorphousthermoplastic

resinsIncreasingmelttemperaturewillnotgreatlyimprovethe

abilityoDelrintollathinsection

Inadditiontothepropertiesotheresin,themoldingconditions

andcavitythicknessdeterminethedistanceofowFigure 15

showsthemaximumfowdistancesthatcanbeexpectedat

twocavitythicknessesorDelrinacetalresinsasaunctiono

injectionllpressureThesecomparisonsweremadeinanopen-

endedsnakefowmoldwithnogaterestrictionObstructionsin

thefowpath,suchassuddenchangesinfowdirectionorcore

pins,cansignicantlyreducethefowdistance

Molds

Delrinacetalresinshavebeenusedinmanytypes

omolds,andmoldershaveawealthoknowledgeconcerning

molddesignorDelrinMoldsorDelrinarebasicallythesame

asmoldsorotherthermoplasticsThepartsoatypicalmoldare

identiedinFigure 14

Thissectionwillocusontheelementsomolddesignthat

deservespecialconsiderationorprocessingDelrinandcanlead

tohigherproductivityandlowercostorthemolderThesetopics

are:

Abilitytoll Undercuts

Gates Runnerlessmolds

Runners Moldmaintenance

Vents

Moldshrinkageandotheraspectsomoldsizingarediscussedin

DimensionalConsiderations(seepage29)



18/48

14

Gates

Thegatesoamoldplayamajorroleinthesuccessorailure

oamoldingjobThelocation,design,andsizeoagatearekey

actorstoallowoptimumpackingObviously,thedesignwillbe

dierentthantheoneusedormoldingamorphousmaterialIn

thatcasethefowshouldstopassoonaspossibleaterllingthe

cavitytoavoidoverpacking(fowin)andsinkmarksatgate(fow

back)Withcrystallinematerial,thelocation,designandsizeo

thegateshouldbesuchthatitwillallowacontinuousfowduring

ALLthepackingphase(Holdpressuretimeseepage27)

Gate Location

Asakeyrule,whenapartisnotuniorminwallthickness,the

gatemustbelocatedinthethickestsectionTherespecto

thisbasicprincipleplaysanessentialroleinobtainingoptimum

packingandconsequentlythebestmechanicalproperties,dimensionalstabilityandsuraceaspectOcourseevery

bottleneck(reducedsectionalongthefowothemelt)shouldbe

avoidedbetweenthegateandallareasothepart

Anareawhereimpactorbendingwilloccurshouldnotbe

chosenasthegatelocation,becausethegateareamayhave

residualstressandbeweakenedsinceitworksasanotch

Similarly,thegateshouldnotcauseaweldlinetooccurina

criticalarea

Thegateshouldbepositionedsothattheairwillbeswept

towardapartinglineorejectorpinwhereconventionalvents

canbelocatedForexample,aclosed-endtubesuchasapen

capshouldbegatedatthecenterotheclosedend,soairwill

beventedatthepartinglineAnedgegatewillcauseairtrapping

attheoppositesideneartheclosedendWhenweldlinesareun

avoidable,orexamplearoundcores,anescapeorgasesmust

beprovidedtoavoidseriousweaknessandvisualfawsSpecicrecommendationsorventingaregivenlaterinthissection

AnotherconsiderationinchoosingagatelocationorDelrin

issuraceappearanceGatesmearorblush,aswellasjetting,

areminimizedbylocatingthegatesothatthemeltenteringthe

cavityimpingesagainstawallorcorepin

Acentralgatelocationisotennecessarytocontrolroundnesso

gearsandothercriticalcircularpartsMultiplegates,usuallytwo

toour,arecommonlyusedwhenthereisacentralholetoavoid

adicult-to-removediaphragmgate

Gate Design

Asmentionedabove,orcrystallinematerialslikeDelrinthe

thicknessothegateoritsdiameter(orapin-pointgateor

tunnelgate)determinesthereeze-otime,andthereore

alsodetermineswhetheritispossibletopackthepart(to

compensatethevolumereductionduetocrystallization)and

maintainthepressureduringsolidicationThegateshould

remainopenuntilthepartdensityismaximumoraspecic

materialThethickness(ordiameter)othegateshouldamount

to5060%othewallthicknessatthegateThewidthothe

gateshouldalwaysbeequalorgreaterthanthegatethickness

Thelengthothegateshouldbeasshortaspossibleandnever

exceed08mm(003in)ThegateareaothepartshouldnotbesubjectedtobendingstressesduringactualserviceImpact

stressesareparticularlyliabletocauseailureinthegatearea

ThemostcommontypesogatesaresummarizedinFigure 16

DIAPHRAGMGATE:Circulargateusedtollasingle

symmetricalcavityTheadvantagesareareductionoweld

lineormationandimprovementollingratesHoweverthe

parthastobemachinedtoremovethegate

DIRECTGATE:Thesprueeedsdirectlyintothemold

cavitywithoutrunnersThisdesignmayotenleadtosurace

deectscomingromthenozzle(eg,coldslug,coldskin,

entrappedair)

EDGEGATE:UsualtypeogatewithtwoplatemoldsItisno

seldegating

FANGATE:ThisgateisusedtoenlargethefowrontUsually

itleadstoareductionostressconcentrationsinthegate

areaLesswarpageopartscanusuallybeexpectedbythe

useothisgatetype

PINPOINTGATE:Thisgateisusedwiththreeplatemolds

Itisseldegating

Injection pressure, MPa

Flowd

istance,mm

Flowd

istance,

in

12080 100

Injection pressure, psi

17.40011.600 15.000

500 20

15

10

5

600

400

300

200

100

0

100

100ST

100

500100ST

900

500

900

2.5 mm (0.100 in)

1 mm (0.04 in)

Figure 15. Maximum Flow Distance o Delrin Acetal Resins



19/48

15

Diaphragm gate

Submarine gate(bucket type)

Direct gate

Edge gate

Fan gate

Fan gate

Pin point gate

Ring gate

Figure 16. Schematic View o the Most CommonTypes o Gates

Figure 17. Details o a Typical Edge Gate Suitable or Delrin

Runner

Side View

z = Max. 0.8 mm

T = Part ThicknessT

x = 0.5T

T+1.0

D1

30

D

D1

d

T

Figure 18. Details o a Submarine Gate (Tunnel Gate)Adequate or Delrin (let side). The One on theRight is Not Adequate or Crystalline Polymersand Would Give Problems with Delrin.

RINGGATE:SeeDIAPHRAGMGATE

SPRUEGATE:SeeDIRECTGATE

SUBMARINEGATE:Atypeoedgegatewheretheopening

romtherunnerintothemoldisnotlocatedonthemold

partinglineItisusedtoseparatethegateromthepartwith

atwoplatemold(sel-degating)

TUNNELGATE:SeeSUBMARINEGATE

DetailsoatypicaledgegatesuitableorDelrinareshownin

Figure 17

Figure 18showsdetailsoasubmarinegateadequate

orDelrin(let),comparedtoasimilartypeogatenot

recommendedorcrystallinematerials(right)

Design criteria:

alwaysgateinthickestareaothepart;

diameterothegatedmustbeatleasthalthepart

thicknessThelengthmustbeshorterthan08mm(003in)

topreventprematuregatereezingduringpacking;

theinscribeddiameterDothetunnelnexttothegatemustbeatleast12thepartthicknessT

ThegateshownontherightsideoFigure 18isnot

recommendedorcrystallinematerialslikeDelrin,because

suchconicalgatesectionscrystallizebeoretheendocomplete

partpackoutThisresultsinlowmechanicalperormanceand

uncontrolledshrinkage

Figure 19showsdetailsoathreeplategatedesignadequate

orDelrin(let),comparedtoasimilartypeogatenot

recommendedorcrystallinematerialsThedesigncriteria

illustratedabovearealsoapplicabletothiskindogate

Note:Restrictionsaroundthespruepullerwillleadtoincomplete

partpackoutSo,thediameterD1 inFigure 19shouldbeatleast

equaltodiameterD



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16

Runner SystemGuidelines

Keyguidelinestoollowwhendesigningarunner

systeminclude:

a runnersshouldstayopenuntilallcavitiesareproperlylled

andpacked;

b runnersshouldbelargeenoughoradequatefow,minimum

pressurelossandnooverheating;

c runnersizeandlengthshouldbekepttotheminimum

consistentwithpreviousguidelines

Eachotheseactorscanaectqualityandcostomolded

partsFactor(a)shouldberegardedasthemostcritical

Thecrosssectionotherunnersismostotentrapezoidal,which

representsanoptimumpracticalcompromisewithrespectto

theullroundsectionTheeectivecrosssectionotherunner

isinthiscasethediameterotheullcirclethatcanbeinscribed

init

ForpartsoDelrintohavethebestphysicalproperties,

therunnersnexttothegatemusthaveatleastaninscribed

diameterthepartthicknessT+1mm

Whenthemoldingsareverythin,however,thisrunnercannotbelessthanabout15mm(006in)inthicknessTherunner

thicknessisusuallyincreasedateachotherstoneortwo

turnsromthecavity,asshownintheexampleoFigure 20

Figure 21. Direct Gating (Let) and Indirect Gating to Breakthe Flow (Right), in a One-Cavity Mold

Figure 22. Balanced (Let) and Unbalanced (Right) RunnerSystems in a 16-Cavity Mold

Single Cavity Mold

Thesimplestrunnercongurationorasinglecavitymoldcould

bedirectgating(seeFigure 21)Inthiscase,however,itwould

benecessarytohaveacoldslugcatcherdirectlyonthe

part,withassociatedsuraceproblemsandlowermechanical

propertiesinthatareaThepreerredsolutionisthentobreak

thefowasindicatedinFigure 21

Runner Layout

Aperectlybalancedlayout(withequalfowdistanceromthe

spruetoeachcavity)isbestachievedithenumberocavities

isequaltoapowero2(2,4,8,16,32,64,128,etc)Seean

exampleoa16-cavitymoldinFigure 22withbalanced(let)and

unbalancedrunnersystemsAperectlybalancedlayoutmaybe

impracticalandexpensive

D

d

2

D1

T*

Figure 19. Details o a Three Plate Gate Design Adequate orDelrin (Let Side). The One on the Right is NotAdequate or Crystalline Polymers and WouldGive Problems with Delrin. *Gate Length Shouldbe


21/48

17

Figure 23. Examples o Unbalanced 16-Cavity Mold. TheSolution on the Right is Provided with OverfowWells to Trap Cold Slugs.

Figure 24. Example o Spiral Eect in a 32-Cavity Mold.Cavities 11, 14, 19, 22 Will Be Filled First and MayShow Splays and Mold Deposits.

1

16 14

1917

32

24

9

22

11

25

8

Figure 25. Sprue and Nozzle Design Oten Used withDelrin. The Dimensions are Linked with theDimensions o the Part and o the Runners.

Figure 26. Example o a Design o a Nozzle Without SprueUsed with 2 Plate Molds. Remember that orDelrin the Nozzle Temperature Should NotExceed 190C (374F).

D N1

D N2

1

D N1

D N2

5 mm

Whenanunbalancedrunnersystemisselected,thelayout

showninFigure 23(let)couldpresentmorerisksoquality

problemsThefowtendstostopateachotheearlygates

duetotherestrictionandthematerialstartstocrystallize

Then,astherunnercontinuestobelled,thepressurerises

andthethecoldslugswhichstartedtobebuiltup,arepushed

intothecavity

Toreducesuchrisk,thesolutionshowninFigure 23(right)isrecommendedInsuchconguration,thecoldslugstendtobe

trappedintoeachoverfowwell

Incaseomulti-cavitymolds(16cavities),theso-calledspiral

eectcouldtakeplaceintheinternalcavitiesothelayout

(seeorinstanceFigure 24),duetoover-heatingothemeltin

runners,causedbylocalizedshearTominimizenegativeeect

likesplaysormolddeposit,shearshouldbereducedbyusing

appropriaterunnerdimensions

Formulti-cavitymoldsorsmallthicknessparts(1mm[004in]),

thedesignorunnersshouldbecheckedbyrunningadetailed

fowanalysisstudy

Nozzle and Sprue

Nozzleandspruediametersaredirectlylinkedwiththe

dimensionsothepartandotherunnersThedesignershould

rstdecideithesprueisneededornotIyes,adesignlike

theoneshowninFigure 25couldbeselected,onethatin

manycaseshasprovedtobethemosteectivewithcrystalline

materialslikeDelrinDuetoitsparallelcylindricalshapeitis

easytomachineandpolish,allowslargenozzlediameters,

anditiseasytoejectduetohighshrinkageGuidelinesorthe

dimensionare:

aspruediameter1atleastequaltotheinscribeddiameter

othemainrunner;

anozzlediameterDN1equalto1minus1mm

Incasethedesignerselectsadesignwithoutasprue,along

nozzlemayberequiredasshowninFigure 26ora2platetool,

andinFigure 27ora3platetoolAgain,thedimensionsare

linkedtothedimensionsothepartandotherunners(guideline

nozzlediameterDN1equalstothemainrunnerinscribed

diameterminus1mm)



22/48

18

AreviewothekeyrecommendationsrelatedtothesprueandrunnersystemollowsItcanbeusedasaquickreerencelistto

checktheirdesign

1 Cylindricalparallelspruepreerred:seeFigure 25and

Figure 28-1

2 Spruepulleror2platemold:seeFigure 28-2.

3 Coldslugwellor3platemold:seeFigure 28-3.

4 Perpendicularfowsplitswithcoldslugwellsateachsplit,see

Figure 28-4

Temperature

Modulus

C

A T

BM

IM

Tg

Tm

Figure 29. Sotening/Melting Behaviour o Amorphous andCrystalline Polymers

5 Nofowrestrictioncausedbyspruepullerin3platemold,see

Figure 28-5

6 Runnerdimensions:

orpartshavingthickness>15mm(006in),ollowgenera

rulesorcrystallinepolymers(Figure 20);

orthinnerpartsandmulti-cavitymolds,afowanalysis

mayberequiredtoselectdimensionsthatwillavoid

over-shearing7 Runnersshouldbeproperlyvented,seeFigures 28,

29and30

8 Balancedrunnersrecommended(seeFigure 24)

9 Forthinpartsandlargenumberocavities,unbalanced

runnersmaybeacceptableHowever,partsshouldneverbe

gateddirectlyontothemainrunner(seeFigure 23)

Hot Runner Mold for Crystalline PolymersPreliminary Comments

Thissectionincludesallhotrunner,hotspruebush,and

runnerlessmoldsTheollowingisnotintendedtorecommend

anytrademarkorsystembuttopresentthebehaviorandthe

needsocrystallinepolymersinsuchtools

Thequestionthatrequentlyarisesiswhentousehotrunner

moldswithcrystallinepolymerslikeDelrinThechoicedepends

onmanyactors,andparticularlyonthequalityneeded,ie,

mechanicalperormance,suraceaspect,percentageorejects

Status

Allsuchmoldsgivetheobviousadvantagesolessmaterial

toplastiy,no(orminimum)regrindandshortercyclesOnthe

otherhand,hotrunnermoldsaremoreexpensiveandheavier;

theyneedmoremaintenanceandbetter-trainedoperators

thanconventionalmoldsInaddition,itheyarenotproperly

designed,theheatneededtorunthemcouldspreadtoallparts

othemoldandcaninactcausethecycletimetoincrease

Figure 27. Example o a Design o a Nozzle without SprueUsed with 3 Plate Molds. Remember that orDelrin the Nozzle Temperature Should NotExceed 190C (374F).

Figure 28. Key Rules or the Design o the Sprue and

Runners o a 2 Plate Mold (Top) and o a3 Plate Mold (Bottom).

D N1

D N2

DSP 1

2

5 mm

1

4

6

Vent

channel

2

3

5 6



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19

Oneapproachistoevaluatetheexpectedincreaseotheoretical

productivityversusconventionalmoldsIsuchanincreaseis

lowerthan25%,itwouldbewisetostaywitha3platemoldthat

willbecheapertobuild,startandrun

Thebreak-evenoabout25%appliestoullhot-runnersystems;

orothermolds(withhotspruebushes,coldsub-runners)the

break-evenpointismuchlower

Direct Gating Versus Cold Sub-Runners or CrystallinePolymers

Whendesigningahotrunnermoldorcrystallinepolymers,it

shouldbekeptinmindthatdirectgatingviahotrunnerismore

dicultwithcrystallinepolymersthanwithamorphousonesThedierencecomesromthesoteningormeltingbehaviorothese

twotypesopolymers

Anamorphousmaterialexhibitsagradualsoteningbehavior

aboveTgromthesolidstatetotheliquidstate,allowingawide

processingwindowintermsotemperatureandviscosityIn

act,asitstemperatureincreasesaboveTg(seeFigure 29)an

amorphouspolymer(curveA)lendsitselrsttothermoorming

(T),thentoblowmolding(BM)andnallytoinjection

molding(IM)

Vent LandEnd of flow

Vent channels

L 0.8 mm

W > 2 mm

D < 0.03 mm

* 0.3 mm

Figure 30. Recommended Venting o a Part and oits Runner System

Onthecontrary,theTghasusuallyalimitedornegligibleeect

onthestructureocrystallinepolymers,whicharesolidabove

TgAtthetemperatureT

m,crystallinepolymersmeltsharplyand

becomeliquid(curveC)

Suchbehavioroacrystallinematerialmayinvolvetherisko:

Droolingaroundthegatewithconsequentproblemsobad

suraceaspectanddeormation

Pluggingothegatesbysolidiedmaterial,plugswhich

willbepushedintothecavities,withconsequentproblems

osuracedeectsandlowermechanicalperormances

ThebestwaytopreventsuchproblemsistouseCOLD

SUB-RUNNERS

Thermal Control o Hot Runner Molds

Thermalmanagementandstreamliningothefowarevery

importantorhotrunnertoolsItshouldbecheckedthata

relativelylowtemperaturesetting(190C[374F])givesan

easyfowothematerialwithnohold-upspots

Thereasonisthat,duetotheviscosityothepolymer,itsfowis

alwayslaminarThismeansthatthematerialwillremainagainst

thesteelwallothehotrunner,andresidencetimewillbevery

longForDelrin,toavoidthermaldegradationwithprolonged

times,thesteeltemperatureshouldneverexceed190C(374F)

Ithehotrunnersystemsolidiesatthattemperature,then

itmustbemodiedtoimprovethermalinsulationandheat

distributiontoremovecoldspotsDegradationcanresultin

splays,odor,blackspecksandmolddeposit

Conclusions

WithcrystallinepolymerssuchasDelrin,werecommend

theollowing:

Aminimumo25%theoreticalcostdecreaseshouldbe

expectedbeoreahotrunnerisconsidered

Highlytrainedmachineoperatorsandmoldmaintenance

toolmakersshouldbeavailable

Useocoldsub-runners,neverdirectgatingstraight

ontothepart

UseoDelrinPgrades

Alltemperaturesinthehotrunnersystemmustnotexceed

190C(374F)

Avoidtheuseohotrunnermoldsisuracedeectsarenot

acceptableandhighpartmechanicalperormanceisrequired

Avoidtheuseohotrunnersortoughenedgrades

Vents

VentingamoldorDelrinisparticularlyimportant,andspecial

attentionshouldbegiventothisactorduringboththedesign

othemoldanditsinitialtrialThisattentionisrequiredbecause

burningopartscausedbyinadequateventingisnoteasily

observedwithDelrinWithotherresins,poorventingresultsin

ablackenedandburnedspotonthepartWithDelrin,however,

theremaybeeithernovisiblefaworaninconspicuouswhitish

markonthemolding



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20

VentingproblemswithDelrinacetalresinsmaybemade

moreobviousbysprayingthemoldwithahydrocarbonor

kerosene-basedsprayjustbeoreinjectionIventingispoor,the

hydrocarbonwillcauseablackspotwheretheairistrappedThis

techniqueisparticularlyuseulordetectingpoorventsinmulti-

cavitymoldsAconvenientsourceohydrocarbonspray

isarustpreventativespray

Ventsshouldbelocatedat:

1 theendoanyrunner;

2 anyfowjunctionwhereairisentrappedandaweldline

resultsThepositionoweldlinescanbedenedby

shortshots

OnlyNOventingtogetherwithexcessiveastinjectionspeedwill

causecorrosionothetoolattheweldlineswithDelrin(diesel

eect)InadequateventingomoldsorDelrinmaycausea

gradualbuildupomolddepositwhereventsshouldbelocated

andinmoldcrevicesthroughwhichlimitedventinghastaken

placeThesedepositsconsistoawhitesolidmaterialormed

romthetracesogasevolvedduringnormalmoldingGoodventsallowthisgastoescapewiththeairromthecavities

Poorventingmayalsoreducephysicalpropertiesatweldlines

Ventingproblemsmaybeaggravatedbyhighmelttemperature,

longholduptime,orholdupareasintheinjectioncylinder,which

willgeneratemorethannormalamountsogasFastinjection

llspeedwillalsoaggravatetheseproblemsRemediesormold

depositproblemsarelistedintheTroubleshootingGuide(see

page39)

Ventingusuallyoccursthroughthepartinglineoamoldandis

providedbymachiningchannelsinthecavityplateandinserts

Insomecases,ventingmaybeaccomplishedaroundanejector

pinThisventwillalsobeimprovedbygrindingfatsonthepin

andrelievingtheventaterashortlandPinsthatdonotmove

withtheejectionsystemtendtoclogandnolongerprovide

ventingaterashorttime

Ventingtherunnersystemishelpulinreducingtheamounto

airthatmustbeventedthroughthecavitiesBecausefashis

unimportantontherunner,theseventscanbeslightlydeeper

thancavityvents,orexample,006mm(00024in)

ThedrawingsinFigure 30showtherecommendeddimensions

orventsincavitiesorDelrin

Note:Duringmoldmaintenance,ventdepthand/orhobbing

shouldbecareullycheckedVentsshouldbemodiedithevent

depthislessthan0010015mm(0000400006in)

Undercuts

GeneralsuggestionsorstrippingundercutswithDelrinacetal

resinsare:

Theundercutpartmustbereetostretchorcompress,that

is,thewallothepartoppositetheundercutmustclearthe

moldorcorebeoreejectionisattempted

Theundercutshouldberoundedandwell-lletedtopermit

easyslippageotheplasticpartoverthemetalandto

minimizestressconcentrationduringthestrippingaction

Adequatecontactareashouldbeprovidedbetweenthe

knockoutandplasticparttopreventpenetrationothemolded

partorcollapseothinwallsectionsduringthestripping

action

ThelengthothemoldingcycleandspecicallytheHold

(Pressure)Time(HPT)shouldbeoptimumtoavoidexcessive

shrinkagewithinsideundercutsSucientpartrigiditymust

bedevelopedwithoutcausingbindingduetoexcessive

shrinkagearoundpinsorminganinternalundercutEjection

opartswithundercutsontheoutsidediameterwillbeaided

bymoldshrinkage

Highermoldtemperature,whichkeepstheparthotterand

morefexiblewhenthemoldopens,mayaidejectionrom

anundercut

Generally,partsoDelrinacetalcanbemoldedwitha

maximum5%undercutCalculationoallowableundercut

isillustratedinFigure 31Theallowableundercutvaries

somewhatwithbothwallthicknessanddiameter

A

R

BInside undercuts

Outside undercuts

A

B

R

A

B

30

A

B

R

R

Figure 31. Calculations or % Undercut (BA)/B 5%



25/48

21

Notch radius, mm

Impactstrength,

kJ/m2

0,50,1 0,2 0,3 0,40

20

40

60

80

0

Delrin 100P NC10

Delrin 500P NC10

Figure 32. Impact Strength as a Function o MoldedNotch Radius

Figure 33. Suggested Rib Dimensions Versus Wall Thickness

0.5-0.7T

R = 0.2-0.3T

T

Filling time, s

Tensilestrengthatyield,

MPa

Izodunnotched,

J/m

5 10 15 200

50

60

70

1,000

800

600

400

200

0

80

40

Tensile strength at yield, MPa

Izod unnotched

Figure 34. Tensile Strength (Let Scale) and Unnotched IzodImpact (Right Scale) o a Delrin 100P Test Bar,4 mm thick, Molded at Both Ends with DierentFilling Times.

Sharp Corners

Oneomajorcausesoailureoplasticpartsareinternalsharp

cornersAsharpcornerinapartactsasanotchandinitiates

breakataverylowenergyThediagraminFigure 32showsthe

eectonotchradiusonimpactresistanceotestbarsmolded in

twogradesoDelrinNotethatthenotcheshavebeenmolded

(simulationoreallieandnotmachinedasrequiredbythe

standardIzodtest)

Fromthisdiagramitcanbeseenthatanincreaseo aninternal

radiusocurvaturerom001(almostasharpcorner)to02mm

doublestheimpactresistance

Notealsothatsharpcornersarenotdesirableinplasticparts

becausetheyareanimportantcontributingactortowarpage

Ribs Design

Veryoten,ribbedpartswillperormmuchbetterintermo

cycletime,mechanicalperormancesandwarpagethanvery

thickunproperlypackedpartsItiseconomicallyimpossibleto

packsectionsabove68mm(024032in)thicknessduring

allthecrystallizationtime(solidication:seeFigure 30or

Hold[pressure]Timevspartthickness)Howeveranimproper

ribdesigncouldalsocausedeectssuchassinkmarks

RecommendedribdimensionsareshowninFigure 33Note

thattheradiusatthebaseotheribshouldnotbetoosmallto

preserveparttoughness(seeFigure 32)

Weld Lines

WeldlinesoccurwheretwomeltfowsjointogetherWeldline

positioncanbedenedbyshortshots,orbyfowsimulations(i

themolddoesnotexistyet)Ithemoldisprovidedwithproper

venting(seepage18),theweldlinestrengthshouldbeatleast

8090%othenominalstrengthvalueotheresin

Tooptimizeweld-linestrength,twoparametersareimportant:

1 optimumHold(Pressure)Time,toensuretheweldingothe

fowrontsunderpressure(orthecorrectHPTseepage26);

2 optimumllingrate,whichwilldependonpartthickness

(approximately1secondpermm(004in)opartthickness)

Figure 34showstheweldlinestrengthoa4mm(016in)

thicktestbarinDelrin100PgatedatbothendsBothtensile

strengthandtoughnessareseriouslyaectedillingtimeisnot

optimized



26/48

22

Mold Maintenance

Asageneralrule,moldsorprocessingDelrinrequirethe

samecareasthoseorprocessingotherthermoplastic

materialsWipingthemoldandapplyingarust-preventing

solutionisusuallyadequateateraproductionrun

Vent Maintenance

Duetothecriticalnatureothevents,theventdimensionsshouldbecheckedduringroutinemaintenanceVentdepth

and/orhobbing(deormationothepartinglineoppositethe

vent)shouldbecareullycheckedVentsshouldbemodiedi

theventdepthislessthan001mmto0015mmAnyhobbing

thatblockstheventsshouldbegroundo

Mold Cleaning

Dependingonthetypeodepositthecleaningprocedureisas

ollows:

White deposit

Whitedepositisduetotheaccumulationo

paraormaldehydeThisdepositcanberemovedwithbenzyl

alcoholorisopropanolFrequentcleaningothetoolwith

thesesolventsduringmoldingwillpreventtheaccumulationothisdeposit

Translucent or colored deposit

Thisdepositisnormallyobservednearthegate(incaseo

overshearothematerial),onpinsornearhotspotsTheuse

oalessshearinggate(seegatedesignrecommendations)

oramoreevenmoldtemperaturewillstoportremendously

decreasethebuildupothisdepositItcanberemoved

withcommercialalkalinechemicalcleanersEciencyothe

cleaningagentcanbeimprovedwithanultrasonicbath



27/48

23

Molding Process

InjectionmoldingoDelrinacetalresinissimilartothatoother

thermoplasticresinsTheengineeringapplicationsorwhich

Delrinisused,however,requentlyrequiretightspecications

onstrength,dimensionsandsuracecondition,sothatcontrolo

themoldingoperationbecomesmorecritical

Theinormationdiscussedinthissectionincludes

suggestionsor:

Start-upandshutdownprocedures,handlingprecautions

OperatingconditionsorDelrin

Techniquesoroptimumproductivitymolding

Start-up and Shutdown ProceduresStart-up with Resin Change

Thesuggestedstart-upprocedurewithDelrinisdesigned

topreventoverheatingotheresinandcontaminationintheinjectionunitwithmaterialrompreviousruns

Tostartupamachinewhichcontainsanotherresin,theinjection

unitmustbepurgedwithcrystalpolystyreneuntilthecylinder

andotherhightemperaturezoneshavebeenclearedThiscan

normallybedonewithcylindertemperaturesintherange

210250C(410482F),iappropriateorthepreviousmaterial

Thenozzleisquitediculttocleanbypurging,becausethe

laminarfowinthisarealeadstoalayeropolymersticking

tothemetal(thisisalsotrueorhotrunners)Itisthereore

recommendedtoswitchothenozzleheater,removethe

nozzle,cleanittogetridalltracesopreviouspolymer,and

reassembleitThecylindertemperaturesshouldthenbe

adjustedtoabout215C(419F),andthenozzletemperatureto

190C(374F)Whenbothcylinderandnozzlehavereachedthe

expectedtemperatures,Delrincanbeaddedtothehopper

Inunusualcircumstances,anintermediatepurgewithaharsher

compoundmayberequiredtoremoveadherentdepositsrom

thescrewandcylinderSpecialpurgecompoundsareusedor

thispurpose

Thesepurgecompoundsmustalsoberemovedromthecylinder

bypurgingwithpolyethyleneorpolystyrenebeoreDelrin is

introducedIntheworstcases,eg,ateruseoglass-reinorced

resinsorseveredegradationopreviousmaterial,itmaybe

necessarytopullthescrewandcleantheequipmentmanuallyto

preventcontaminationomoldings

Saety point:Polystyreneischemicallycompatiblewith

Delrin,whereasevenatraceopolyvinylchloride(PVC)is

notContaminationoDelrinwithsuchmaterialcancause

objectionableodororevenaviolentblowback

Start-Up From a Cylinder Containing Delrin

Aterasaeshut-downprocedure,thescrewandthecylinder

shouldbeessentiallyemptyTorestart,thenozzleandcylinder

temperaturesshouldbesetat190C(374F)topreheatthe

cylinderandtheresinitcontainsWhenthecylinderhasreached

thesettemperature,ensurethatthenozzleisopenandincrease

thecylindersettingstonormaloperatingtemperaturesWhenall

temperaturesareintheoperatingrange,thehoppercanbelledandmoldingcanbeginaterabriepurgewithDelrin

Shutdown When a Restart with Delrin is Planned

Shutothehoppereedandcontinuemoldinguntilthecylinder

isemptyForlargemachines(withascrewdiameterabove

40mm[157in])itisrecommendedtopurgethecylinderwith

crystalpolystyrene,movethescrewullyorward,thenswitch

otheheaterbandsForsmallmachinesmovethescrewully

orwardandswitchotheheaterbands

Shutdown When a Restart with Another Resin is Planned

Shutothehoppereedandcontinuemoldinguntilthecylinder

isemptyPurgewithcrystalpolystyrene,leavethescrewully

orward,thenswitchotheheaterbands

Temporary Interruption

AmoldingmachinewithDelrininthecylinderatmolding

temperaturesshouldnotbeallowedtostayidleThemaximum

recommendedcylinderresidencetime,undernormalmolding

conditions,is10minorpigmentedmaterialand20minor

naturalstandardmaterialInexcessothesetimes,resin

decompositionmayoccur

I,duringthetemporaryinterruption,thecylinderresidence

timereachestheabovelimits,closethehoppereed,emptythecylinderandleavethescreworwardThecylindertemperatures

shouldbereducedtoabout150C(302F)(atthesetemperatures

Delrinwillbestableevenoraweekendshutdown)

Action to Follow When the Nozzle Heater Band Breaks Down

Retracttheinjectionunit,closethehopperandslideitouto

thewayIthenozzleisstillopen,ollowthenormalshutdown

proceduresIthenozzleisrozen,heatthenozzlewithagas

torchtomelttherozenmaterialinsidethenozzleandthen

purge

Start-up ater Emergency Shutdown

Adierentprocedureshouldbeusedateranemergency

shutdownduetolossopowerorothercausesInthiscase,the

screwmaybeulloDelrinthatcooledslowlyandwasexposed

tomelttemperaturesoraprolongedperiodThescrewmay

evenbeintheretractedpositionwithalargequantityoDelrin

inrontothescrewInordertoventgasesromresinthatmay

bedegraded,itisessentialthatthenozzlebeopenandheated

tooperatingtemperatureandDelrininthisareabecompletely

meltedbeorethecylinderreachesmelttemperatureThe

cylinderzonesshouldbeheatedtoanintermediatetemperature



28/48

24

belowthemeltingpointoDelrinandthemachineallowed

toequilibrateatthattemperatureCylindertemperatureso

150175C(300350F)aresuggestedAterallzoneshavebeen

atthistemperatureor30min,cylindertemperaturesshouldbe

raisedto195C(380F)AssoonastheDelrinhasmelted,it

shouldbepurgedromthecylinderwithreshDelrinThepartly

degraded,hotpurgeresinshouldbeplacedinapailowateri

itemitsanodorWhentheoldresinispurgedromthecylinder,thecylindertemperaturesmayberaisedtonormalproduction

settings

Operating Conditions for Delrin Temperature SettingsIntroduction

Thebasicpurposeotheinjectionunitistodelivertothemold

thenecessaryamountoahomogeneousmelt(nounmeltand

nodegradedmaterial)Therulesoconstructionotheinjection

unitormoldingacrystallinematerialhavebeenpresentedin

InjectionMoldingUnit,(seepage7);therulesorthesettings

arepresentedbelow

Note:Tworoughbutpracticalmethodstoevaluatethepresence

ounmeltandodegradedmaterialweredescribedonpage11

andcanbeusedhereaswell

Delrinacetalresinisacrystallinepolymerwithameltingpoint

o178C(352F)FormostgradesoDelrinhomopolymerthe

preerredmelttemperaturerangeis215C(419F)5C*,as

measuredwithaneedlepyrometerinthemeltThecalories

neededtoheatandmeltDelrinwillbeprovidedbyshear(rom

scewrotation)andthebalancebyconductionintheheated

cylinder(slowheattranserduetotheinsulatingcharactero

polymers)

Cylinder temperature

Themainparameterinfuencingthetemperatureproleothe

cylinderistheresidencetime(orHold-UpTimeHUT)othe

polymerintheplasticationunit(seepage8tocalculateHUT)

WithashortHUT(5minutes,longcycletime,lowmeltoutput),

lowersettings,especiallyintherearzone,maybeusedSince

generalizationocylindertemperaturesettingsisdicult,itis

otenwisetobeginwithalevelproleandadjustasneededThediagramshowninFigure 35canbeusedasaguidelineorinitial

temperaturesettings

Notes:

1 AsthepreerredmelttemperatureorDelrin100STand

Delrin500Tisabout10C(18F)lower,thezonesettings

shouldbe10C(18F)lowerthanshowninFigure 35

2 Hoppercoolingisnotneededandshouldnotbeusedor

DelrinAsdescribedinChapter3,excessivehoppercooling

maycreateproblemsoscrewdepositandblackspecks

3 Withverysmallinjectionunitsand/orshortresidencetime

(HUT),pre-heatingthegranules(eg,withaheatedhopper)

mayhelptoachieveanhomogeneousmelt

Nozzle Temperature

Thenozzletemperatureisadjustedtocontroldroolandreezing

(seeNozzlepage11),butitshouldneverbesetabove190C

(374F)inordertopreventpolymerdegradation(thelaminar

fowandhighviscosityothemoltenpolymerresultinverylong

contacttimewiththemetalwall)Ithenozzlereezeswitha

settingo190C(374F),itsinsulationromthespruebushing

shouldbeimproved,oritsinsidediametershouldbeincreased

ieasible

Notes:

1 Practically,itisalwayseasiertosetthenozzletemperature

correctlybyusingspruebreakTheinjectionunitispulledbac

aterscrewrotationandthenthenozzleisinsulatedrom

thecoldmoldThisallowsthecaloriestofowtothetipo

thenozzlewithouthavingtosettoohighatemperature,and

reducestheriskostringingromthenozzle

2 HotrunnerByanalogy,ahotrunnersystemisanozzle

transerringthemoltenresinromtheinjectionunittothe

partHencetheprinciplesandrecommendationsornozzles

*ThepreerrredmelttemperatureorDelrin100STandDelrin 500Tisabout205C(401F)

Figure 35. Cylinder Temperatures Prole VersusResidence Time or a Given Recommended MeltTemperature. Recommended Nozzle Temperatureis 190C (374F) or All Delrin Grades.

Residence time

215

220

225

195

180

FRONT ZONE CENTER ZONE REAR ZONE

< 3 min

> 5 min

Hopper

no cooling or 8090C (176194F) min

3 5 minRecommendedmelt

temperature,C



29/48

25

arealsovalidorhotrunnersInparticular,thelaminarfow

andhighviscosityothemoltenpolymeragainresultinvery

longcontacttimeswiththemetalwall;sothetemperature

othemetalinthehotrunnershouldneverexceed190C

(374F),inordertopreventdegradationothepolymer

Screw Rotation Speed

Screwrotationspeedbehavesasathermalsetting,because

therotationothescrewwillshearthematerialandsupplyaroundhalothecaloriesneededtomeltandheatDelrinto

therecommendedmelttemperaturerangeo215C(419F)

5C(205C[401F]5CorDelrinTandST)Aswithall

polymers,Delrinissensitivetoshearandamaximumo

02to03m/soscrewperipheralspeedisrecommended

Figure 36showstheoptimumscrewrotationspeedorhigh

viscosityDelrin(type100)andlowviscosityDelrin(types

500to900)asaunctionoscrewdiameter

Back Pressure

BackpressurealsobehaveslikeathermalsettingIncreasing

backpressureincreasestheworkdonebythescrewon

themelt

Theuseotheoptimumscrewdesignorcrystallinematerials,

suchasDelrin,shouldprovidethenecessaryworktomeltand

bringDelrintotherecommendedmelttemperaturewiththe

minimumbackpressureOnlymeltingohighlyviscous

DelrinsuchasDelrin100Pmayrequiresomebackpressure

toavoidthescrewwormingback(leadingtoinconsistentshot

volumeandpad)

Figure 36. Maximum Screw Rotation Speed as Function

o Screw Diameter. The Curve or Delrin

500Pis Also Valid or the Low Viscosity GradesDelrin 900.

Screw diameter, mm

Max.s

crewr

otationspeed,rpm

80 1006040200

50

100

150

200

250

300

0

Delrin 500P

Delrin 100P

Theuseoaninappropriatescrewmayrequiresomeback

pressuretoincreasetheworkdonebythescrewonthemelt,

toincreasethemelttemperatureanditsuniormityHigher

backpressuremaybeusedtoeliminateunmeltedparticles

andtoimprovecolormixingwhencolorconcentratesareused

Increasingbackpressure,however,tendstoreduceglassbre

lengthandchangepropertiesolledresinssuchasDelrin570

Moreimportantly,increasingbackpressurealwaysdecreasestheoutputothescrew,leadingtolongercycletimesandlower

productivityThisincreasesthebuilduposcrewdepositleading

tocontaminationandlowpartperormance

Thereore,backpressureshouldbeusedonlywhenincreasing

cylindertemperatureorotherchangesarenoteectiveor

possible

Forallmaterials,thebackpressureused(specicorinherentto

theinjectionunit)willcreatesomepressureonthemeltinronto

thescrewTocontroldroolattheendothescrewrotation,some

suckbackisrequiredThisshouldbekepttoaminimum

Mold Temperature

Thebestmoldtemperatureorlongtermpartperormance

wouldbejustbelowthecrystallizationtemperatureoDelrin,

eg,155C(311F)Thistemperaturewouldallowthepolymer

tocrystallizeinanoptimumstateandeliminateanyrisko

re-crystallization(postmoldingshrinkage)Obviouslyitis

economicallyimpossibletosetthemoldatthattemperatureas

thecrystallizationtimebecomesalmostinnitealongwiththe

cycletime

Practically,alowermoldtemperatureisused,leadingtoshorter

crystallizationtime(HPT),henceshortercycletime,lowermold

shrinkagebuthigherpostmoldshrinkage(especiallyipartsare

thenexposedtoelevatedtemperatures)Acompromiseshould

beounddependingonthetemperatureinuseandtherequired

dimensionalprecisionothemoldedpartshortandlongterm

ForstandardDelrin,amoldtemperatureo80100C

(176212F)isagoodcompromiseornormaluse,giving

relativelyshortcrystallizationtime,highshrinkagebutlowpost

moldshrinkage(seeDimensionalConsiderations,page31)

Ahighermoldtemperaturewillleadtohighermoldshrinkage,

longercycletimebutlowerpostmoldshrinkageItisspecially

recommendedorhighprecisionpartsusedathightemperature

Alowermoldtemperatureleadstoshortercycletime,lowermoldshrinkagebutmuchhigherpostmoldshrinkageleadingto

stressesanddistortion

FortoughenedresinssuchasDelrin100STand500T,theuse

oalowermoldtemperature(50C[122F]10C[50F])is

acceptablewithoutendangeringlongtermpartperormances



30/48

26

Note 1:Moldtemperatureisalwaysthetermusedbutthe

importantparameteristhesuracecavitytemperatureWith

astcyclingoperations,itmaybenecessarytousealowermold

coolanttemperaturetomaintainthemolds

Hacim Kalibi Tasarim Unsurlari 11 06

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