delrin(r) molding guide - lawrence berkeley national...
TRANSCRIPT
Molding Guide
acetal resinDelrin®
e
DEL
RIN
®
StartwithDuPont
Table of Contents
PagesGeneral Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Compositions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Safety Precautions to Observe
When Molding Delrin® Acetal Resins . . . . . . . . . . . . . . . . . . . . . . . 2Packaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Polymer Structure and Processing Behavior . . . . . . . . . . . . . . . 3Glass Transition and Melting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4PVT Diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Heating-Cooling Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6Viscosity and Rheological Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Injection Molding Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Screw Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Cylinder Temperature Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Cylinder Adaptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Non-Return Valve (Back Flow Valve—BFV) . . . . . . . . . . . . . . . . . . . . 10Nozzle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Evaluation of Melt Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Molds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Ability to Fill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Gates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Runner System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Nozzle and Sprue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16Hot Runner Mold for Crystalline Polymers . . . . . . . . . . . . . . . . . . . . . . 18Vents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19Undercuts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20Sharp Corners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20Ribs Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20Weld Lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20Mold Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21Mold Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
continued next page
Table of Contents (continued)
PagesMolding Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21Start-up and Shutdown Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22Operating Conditions for Delrin®
—Temperature Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Operating Conditions for Delrin®
—Molding Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25Optimum Productivity Molding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28Standard Molding Conditions
for ISO Tensile Bars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29Hold Pressure Time
via In-cavity Pressure Measurement . . . . . . . . . . . . . . . . . . . . . . . . 30
Dimensional Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30Fundamentals of Dimensional
Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30Mold Shrinkage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31Factors Affecting Mold Shrinkage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31Mold Shrinkage of Filled Resins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33Effect of Pigments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33Post-Molding Shrinkage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33Insert Molding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34Annealing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34Environmental Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35Dimensional Tolerances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Auxiliary Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36Material Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36Reground Resin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36Drying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36Coloring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37Disposal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Troubleshooting Guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
General InformationDescriptionDelrin® acetal resins are semi-crystalline, thermo-plastic polymers made by the polymerization offormaldehyde, and are also commonly referred toas polyoxymethylene (POM). They have gainedwidespread recognition for reliability in manythousands of engineering components all over theworld. Since commercial introduction in 1960,Delrin® has been used in the automotive, appliance,construction, hardware, electronics, and consumergoods industries, among others.
Delrin® is noted for:
• High mechanical strength and rigidity• Excellent dimensional stability• Natural lubricity• Fatigue endurance• High resistance to repeated impacts• Excellent resistance to moisture, gasolines,
solvents and many other neutral chemicals• Toughness at low temperature (down to –50°C
[–58°F])• Wide useful temperature range (in air: –50 to
90°C [–58 to 194°F], with intermittent use up to120°C [248°F]).
• Good electrical insulating characteristics• Ease of fabrication
Delrin® acetal resins are available in a variety ofcompositions to meet different end-use and pro-cessing requirements.
CompositionsThe main available Delrin® compositions can beclassified as follows:a.Standardb.Toughenedc.Low wear/Low frictiond.Glass fillede.UV-stabilized
The standard compositions cover a broad range ofmelt viscosities. The highest viscosity composition,Delrin® 100, is often molded when maximumtoughness properties are needed. The intermediatemelt viscosity Delrin® 500 is used for general-purpose injection applications. The resins havinglower melt viscosity, Delrin® 900 and 1700, areusually chosen for injection molding applicationswith hard-to-fill molds.
A summary of the main compositions is shown inTable 1.
1
Table 1Main Compositions of Delrin® Acetal Resins
High viscosity grades
Delrin® 100POM homopolymer. High viscosity molding material.Excellent tensile strength and resistance to creep over awide temperature range, even under humid ambientconditions. High fatigue endurance and impact resistance.Applications: molded parts such as highly loaded gears,plain bearings and snap-fits.
Delrin® 100 PSame characteristics and applications as Delrin® 100, plusbest molding stability for deposit free molding in demandingprocessing conditions, e.g., hot runner tools.
Delrin® 111 PCharacteristics: Delrin® 100 P with enhanced crystallinity.Resistance to creep and fatigue endurance improved overDelrin® 100 P. Typical applications: Highly loaded gears,bearings, snap-fits.
Medium viscosity grades
Delrin® 500POM homopolymer. General-purpose molding resin withmedium viscosity. Applications: general mechanical parts.
Delrin® 500 PSame characteristics and applications as Delrin® 500, plusbest processing stability for deposit-free molding indemanding processing conditions, e.g., hot runner tools.
Delrin® 511 PCharacteristics: Delrin® 500 P with enhanced crystallinity.Applications: fuel system components, gears, fasteners.
Low viscosity grades
Delrin® 900POM homopolymer. General purpose molding resin with lowviscosity. Applications: Multicavity molds and parts with thinsections, e.g., consumer electronics parts, zippers.
Delrin® 900 PCharacteristics: Low viscosity, fast molding resin plus bestprocessing stability for deposit-free molding in demandingprocessing conditions, e.g., hot runner tools. Applications:Multicavity molds and parts with thin sections, e.g.,consumer electronics parts, zippers.
Delrin® 911 PCharacteristics: Delrin® 900 P with enhancedcrystallinity. Resistance to creep and fatigue enduranceimproved over Delrin® 900 P. Excellent resistance togasoline, lubricants, solvents and many neutral chemicals.Applications: Multicavity molds and parts with thin sections,e.g., consumer electronic parts, zippers.
Delrin® 1700 PPOM homopolymer. Characteristics: Very low viscosity, bestflow, easy mold ejection. Applications: Multicavity moldsand parts with thin sections which require best flowproperties.
(continued on page 2)
Table 1Main Compositions of Delrin® Acetal Resins
Toughened grades
Delrin® 100 STPOM homopolymer, Super Tough. High viscosity, supertough material for injection molding and extrusion. Excellentcombination of super-toughness, impact fatigue resistance,solvent and stress crack resistance, as well as high tensileelongation at low temperature. Applications: Mainly used forparts requiring resistance to repeated impacts and loads,such as automotive fasteners, helmets, hoses and tubing.
Delrin® 500 MTCharacteristics: Medium toughness, medium viscosity resin.Applications: Fasteners, seats belt restraint systems, gears.
Delrin® 500 TMedium viscosity, toughened resin for injection molding andextrusion. Excellent notched Izod and tensile impactstrength. Applications: Mainly used for parts subjected torepeated impacts and alternating loads, such as automotivefasteners, helmets, hoses and tubing.
Low-wear/low-friction grades
Delrin® 100 AFHigh viscosity grade with 20% Teflon® PTFE fibers, outstand-ing friction and wear properties.
Delrin® 100 KMDelrin® 100 P modified with Kevlar® aramid resin forabrasive wear reduction. Applications: Specialty friction andwear.
Delrin® 500 AFMedium viscosity grade with 20% Teflon® PTFE fibers,outstanding friction and wear properties. Applications:Specialty friction and wear, conveyor systems.
Delrin® 520 MPDelrin® 500 P with 20% Teflon® PTFE micropowder, with low-wear and low-friction properties. Applications: Specialtyfriction and wear.
Delrin® 510 MPDelrin® 500 P with 10% Teflon® PTFE micropowder, with low-wear and low-friction properties. Applications: Specialtyfriction and wear.
Delrin® 500 TLDelrin® 500 with 1.5% Teflon® powder, with low-wear andlow-friction properties. Applications: Specialty friction andwear, conveyor systems.
Delrin® 500 ALMedium viscosity resin with advanced lubricant system,very good low-friction and low-wear properties. Applica-tions: Gears, drive trains, sliding devices.
Delrin® 900 SPDelrin® 900 P with special polymer additive for low-wear/low-friction against itself and other plastics. Applications:Gears, drive trains, sliding devices.
Delrin® 500 CLChemically lubricated Delrin® 500, very good low-frictionand low-wear properties. Applications: Gears, drive trains,sliding devices.
(continued)
2
Glass-filled/glass-reinforced grades
Delrin® 570Medium viscosity resin, with 20% glass filler. Applications:Where high stiffness and creep resistance are required.
Delrin® 577 BKDelrin® 570 with carbon black for improved weathering.Applications: General engineering parts for high stiffnessand strength.
Delrin® 510 GR10% glass-reinforced resin. Applications: Parts requiringhigh stiffness and strength, and creep resistance.
Delrin® 525 GR25% glass-reinforced resin. Applications: Parts requiringvery high stiffness and strength, and creep resistance.
UV-stabilized grades
Delrin® 127 UVDelrin® 100 P with UV stabilizer. Applications: Automotiveinterior parts with maximum UV performance requirements,ski bindings, seatbelt restraint parts.
Delrin® 527 UVDelrin® 500 P with UV stabilizer. Applications: Automotiveinterior parts with maximum UV performance requirements,interior trim, seatbelt restraint parts.
Delrin® 927 UVDelrin® 900 P with UV stabilizer. Applications: Automotiveinterior parts, loudspeaker grills.
Delrin® 1727 UVDelrin® 1700 P with UV stabilizer. Applications: Automotiveinterior parts, loudspeaker grills.
Safety Precautions to ObserveWhen Molding Delrin® Acetal ResinsDelrin® as well as many other thermoplasticpolymers decomposes to gaseous products whenheated for a prolonged time. These gases cangenerate high pressures if confined. If material isnot free to exit from an injection cylinder throughthe nozzle, it may blow back through the hopper.
In the case of Delrin® acetal resin, decomposition isalmost entirely to gaseous products, so pressurebuild-up can be rapid. The product of decomposi-tion is formaldehyde.
When molding Delrin®, it is important that theoperator be familiar with the factors that can causedecomposition, with the danger signals that warn ofthis problem, and with the action that should betaken. This information is summarized on a card fordisplay at the molding machine.
The information given here is based on our experi-ence to date. It may not cover all possible situationsand it is not intended as a substitute for skill andalertness of the operator.
Follow correct start-up, operating and shut-down procedures as described later in this guide.
Be aware of troublemakers—causes ofdecomposition:• High temperature—sticking temperature control-
ler, faulty thermocouple connections, incorrectreading, burned-out heater or heater with a hotspot, heat surges on start-up
• Cycle delay• Hold-up areas—in cylinder, adapter, nozzle,
screw tip, hot runner and check valve assembly• Plugged nozzle—from scrap metal or higher
melting point resin, or from closed nozzle valve• Foreign materials
– Additives, fillers or colorants other than thosespecifically recommended for use in Delrin®
– Contaminants (especially those containingchlorine or generating acid materials) such aspolyvinylchloride resin or flame retardants
– Copper, brass, bronze or other copper alloys incontact with molten Delrin® (not in moldswhere the resin solidifies after each cycle)
– Copper-based lubricants or grease for threads– Contaminated rework—especially rework or
reprocessed resin from outside or unknownsources
Watch for Danger Signals
• Frothy nozzle drool• Spitting nozzle• Pronounced odor• Discolored resin—brown or black streaking• Badly splayed parts—whitish deposit on molding
or mold• Screw push back from gas pressure
Action Required When Any of the DangerSignals Occur
• AVOID PERSONAL EXPOSURE—WhenDANGER SIGNALS are present, DO NOT lookinto hopper or work around nozzle as violentejection of melt is possible.
• MINIMIZE PERSONAL EXPOSURE TODECOMPOSITION GASES by using generaland local ventilation. If necessary, leave area ofmachine until ventilation has reduced concentra-tion of formaldehyde to acceptable levels. Per-sons sensitized to formaldehyde or havingexisting pulmonary disabilities should not beinvolved in processing Delrin®.
• FREE NOZZLE PLUG by heating with torch. Ifthis fails, cool down cylinder, make sure PRES-SURE IS RELIEVED, and CAREFULLYREMOVE NOZZLE and clean.
• TAKE AIR SHOTS to cool the resin—PURGEWITH CRYSTAL POLYSTYRENE. DROP
3
ALL MOLTEN Delrin® INTO WATER to reduceodor level.
• Turn off cylinder heaters.• Check temperature control instruments.• Discontinue automatic molding and run manually
until job is running smoothly.• Provide adequate means of venting feed mecha-
nism in case of blowback.• Use exhaust ventilation to reduce formaldehyde
odor.
PackagingDelrin® acetal resin is supplied as spherical orcylindrical pellets approximately 3 mm (0.12 in)in dimensions. They are packaged in 1,000 kg(2,200 lb) net weight bulk corrugated boxes or25 kg (55.16 lb) moisture protected, tear resistantpolyethylene bags. The bulk density of the unfilledresin granules is about 0.8 g/cm3.
Polymer Structure andProcessing BehaviorThe behavior of a polymer during the moldingprocess and the behavior of a molded part during itswhole end-use life are highly dependent on the typeof structure that the polymer tends to form duringsolidification.
Some polymers exhibit in the solid state roughlythe same molecular arrangement as in the melt, i.e.,a random mass of entangled molecules with noorder. This class is named “amorphous polymers”and includes for example ABS, polycarbonate andpolystyrene.
Other polymers tend to solidify in an orderedmanner: the molecules arranging into crystallineforms (lamellae, spherulites). Because of the lengthof the macromolecules, parts of them cannot belongto crystals (due to lack of space and mobility) andcreate an amorphous inter-crystalline zone. Thesepolymers are therefore partially crystalline or semi-crystalline; for simplicity, in this text we will referto them as “crystalline” (opposed to “amorphous”).
Typical crystalline materials are Delrin® (acetalresins), Zytel® (polyamide resins), Rynite® PETand Crastin® PBT (thermoplastic polyester resins),polyethylene and polypropylene.
Table 2 summarizes some fundamental differencesbetween amorphous and crystalline polymers.These points are described in more detail in thefollowing paragraphs. This information is essentialto understand why the optimization of the moldingprocess is substantially different for the two catego-ries of polymers.
Table 2Comparison of Amorphous and Crystalline Polymers
Resin type Amorphous Crystalline
PropertiesThermal parameters Tg Tg, TmMaximum T in use* Below Tg Below TmSpecific volume vs. T Continuous Discontinuity at TmMelt viscosity vs. T High dependence Low dependence
ProcessingSolidification Cooling below Tg Crystallization
below Tm
Hold pressure Decreased during Constant duringcooling crystallization
Flow through gate Stops after Continuesdynamic filling until end of
crystallizationDefects if bad Over-packing, Voids, deforma-process stress-cracking, tions, sink marks
sink marks
* For typical engineering applications
Glass Transition and MeltingAmorphous Polymers
The overall behavior of amorphous polymersis largely determined in relation to their glasstransition temperature Tg.
Below this temperature, the molecules are essen-tially blocked in the solid phase. The material isrigid and has a high creep resistance, but it alsotends to be brittle and sensitive to fatigue.
When the temperature is increased above the glasstransition temperature Tg, the molecules have somefreedom to move by rotation around chemicalbonds. The rigidity decreases gradually and thematerial shows elastomeric properties, lendingitself to processes like thermoforming, blowmolding and (at temperatures 120–150°C[248–302°F] above Tg) injection molding.
Amorphous polymers used in engineering applica-tions have Tg above the ambient temperature, andthe maximum temperature for end-use should bebelow Tg; for example polystyrene has Tg = 90–100°C(194–212°F), and is injection molded between 210and 250°C (410 and 482°F).
Crystalline Polymers
In crystalline polymers, the onset of molecularmovement in the material also defines the glasstransition temperature Tg.
When the temperature is increased above Tg, thecrystalline polymers maintain rigidity appropriatefor engineering applications (for example withDelrin® a part can easily withstand temperatureswell above the Tg).
Upon further heating the material reaches itsmelting temperature Tm, where the cohesion of the
4
crystalline domains is destroyed. Within a fewdegrees, there is a considerable change of mechani-cal properties from solid to liquid behavior. AboveTm, the crystalline polymers behave as highviscosity liquids, and can generally be processedby injection molding, typically at temperatures30–60°C (86–140°F) above their melting tempera-ture. As a consequence, the temperature domain forthe use of crystalline polymers is not limited by theglass transition temperature Tg, but by the meltingtemperature Tm. For Delrin®, the effect of the Tg
is negligible and very difficult to measure, due toits very low amorphous content. There are twotransitions for Delrin®, a weak one around 0–15°C(32–59°F) and a stronger one at –80°C (–112°F).The transition just below room temperature is soweak there is minimal effect on properties. ForDelrin® acetal homopolymer, Tm = 178°C (352°F)and the typical processing range is 210–230°C(410–446°F).
PVT DiagramsThe PVT diagram is a condensed presentation ofthe interrelations of three variables that affect theprocessing of a polymer: Pressure, Volume andTemperature.
The effect of the temperature (T) or volume (V) isillustrated in Figure 1 for an amorphous and acrystalline polymer. When the temperature of thematerial is increased, its specific volume (theinverse of density) also increases due to thermalexpansion. The rate of increase becomes higher atthe glass transition temperature, because themolecules have more freedom to move and theyoccupy more space. This change of slope is ob-served with both amorphous and crystalline poly-mers. At higher temperature, the melting of crystal-line polymers is marked by a sudden increase of thespecific volume, when the well-ordered and rigidcrystalline domains become randomly oriented andfree to move. The specific volume is therefore asignature of the changes of structure of the polymeras a function of temperature.
A PVT diagram is simply the presentation of theseries of curves obtained when the measurement ofspecific volume versus temperature is repeated atdifferent pressures. The PVT diagram of a typicalamorphous polymer (polystyrene) is shown inFigure 2, and the PVT diagram of Delrin® is shownin Figure 3.
The molding process can be illustrated by a cycle oftransitions on the PVT diagram. For simplification,it will be assumed in the following description thatheating takes place at constant pressure (“alongisobar lines”) and that application of pressure isisothermal (vertical lines).
Figure 1. Specific Volume as Function of Tempera-ture for Amorphous And CrystallinePolymers
Temperature, °C
Spec
ific
volu
me,
cm
3 /g
Tg
Temperature, °C
Spec
ific
volu
me,
cm
3 /g
Tm
"Liquid" phase
"Solid" phase
Tg
AMORPHOUS
CRYSTALLINE
Figure 2. Pressure-Volume-Temperature (PVT)Diagram For Polystyrene. Points A, B, C,and D Refer to Different Steps of theMolding Process (See Text).
Temperature, °C
Spec
ific
volu
me,
cm
3 /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)
For an amorphous material the molding cycle is asfollows (see Figure 2):• Starting from room temperature and 1 MPa
pressure (point A) the material is heated in thebarrel. The specific volume increases accordingto the isobar at 1 MPa to reach the moldingtemperature (point B).
• The material is injected into the cavity and thepressure is applied. This process is roughlyisothermal (to point C), and the specific volumeis decreased to a value close to that at 1 MPaand Tg.
• The resin is cooled in the mold, and at the sametime the hold pressure is decreased, to follow ahorizontal line in the PVT diagram and reachpoint D where the part can be ejected when it isat 1 MPa pressure and a temperature below Tg.Ideally, there should be no flow of materialthrough the gate during this cooling phase toproduce a stress-free part.
For a crystalline material, the picture is different(see Figure 3):• the material is heated at 1 MPa pressure from
room temperature (point A) up to the processingtemperature (point B). This results in a largechange of volume (almost 25% for Delrin®);
• the resin is injected and compressed in the cavity.The specific volume is decreased to point C,where its value is still much higher than at1 MPa/23°C (73°F);
• crystallization takes place in the mold underconstant hold pressure. When the crystals buildup from the liquid phase, a large difference ofvolume occurs, which must be compensated byinjection of additional liquid resin through thegate (otherwise voids are created within the part);
• at the end of crystallization (point D), the partis solid and it can be ejected immediately; themolding shrinkage is the difference between thespecific volumes at the crystallization tempera-ture (point D) and at room temperature (point A).
This difference in behavior has important implica-tions for injection molding. During the solidifica-tion process (after dynamic filling):• the hold pressure is decreased with time for
amorphous polymers, whereas it is maintainedconstant for crystalline polymers;
• the flow through the gate is stopped for amor-phous polymers, while it continues until the endof the crystallization for crystalline polymers.This implies that for crystalline materials thedesign of parts, gates, runners and sprue shouldfollow special rules that will be described in theMolds section.
5
Figure 3. Pressure-Volume-Temperature (PVT)Diagram For Delrin® 500. Points A, B, C, andD Refer to Different Steps of the MoldingProcess (see text).
Temperature, °C
Spec
ific
volu
me,
cm
3 /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
80120140180
P (MPa)
Figure 4. Specific Heat versus Temperature forDelrin® 500, PA66 and Polystyrene
Spec
ific
heat
, kJ
kg–1
K–1
400300
PS
PA66
2001000
0.4
0.8
1.2
1.6
2.0
2.4
2.8
0
Temperature, °C
Delrin® 500
Heating-Cooling BehaviorFor any substance, the energy needed to increasethe temperature of 1 g material by 1°C (1.8°F) isdefined as its specific heat. This quantity is gener-ally determined by Differential Scanning Calorim-etry, and the results for Delrin®, polyamide 6-6 andpolystyrene are shown in Figure 4. The twocrystalline polymers, Delrin® and polyamide 6-6,show a large peak that is due to the additional heatrequired to melt the crystalline phase (latent heat offusion). The amorphous polymer does not showsuch a peak, but exhibits a change of slope at Tg.
The total energy to bring each material up to itsmolding temperature is given by the area under thecurve. From Figure 4 it is clear that the crystallinepolymers need more energy than the amorphousones. This explains why the design of a screw for acrystalline polymer like Delrin® should be different(and usually more critical) than for an amorphouspolymer.
Viscosity and Rheological BehaviorMelt viscosity determines to a large extent theability to fill the mold cavity. High viscosity meansdifficult flow through thin sections and higherinjection fill pressure.
Temperature and shear rate are crucial parameterswhen considering the viscosity of molten polymers,and they should always be specified together with avalue for melt viscosity.
For polymers consisting of linear molecules likeDelrin®, the viscosity is also in direct relation to theaverage molecular weight.
6
Influence of Temperature
The general rule that liquids become less viscouswhen increasing temperature is also true for moltenthermoplastics. However crystalline and amorphouspolymers behave differently, as shown in Figure 5.The curves for Delrin® and polystyrene were bothobtained by reducing gradually the temperature ofthe materials from 230 to 100°C (446 to 212°F).Two differences are worth mentioning. First, attemperatures above 180°C (356°F), the depen-dence of viscosity on temperature is more pro-nounced for the amorphous polystyrene than forDelrin®; therefore, increasing the melt temperatureof Delrin® does not greatly improve its ability toflow through a thin section. Second, below 170°C(338°F) the viscosity of Delrin® rises sharplybecause the material crystallizes within a fewdegrees of that temperature.
Figure 5. Viscosity/Temperature Curves for Delrin®
500 and for Polystyrene at a ConstantShear Rate of 1000 s–1 (TemperatureReduced from 230 to 100°C [446 to 212°F])
Temperature, °C
App
aren
t vis
cosi
ty, P
a.s
180 220 240200120 140 160100
600
400
200
0
Delrin® 500
Polystyrene
Thermoforming
Extrusion
Injection molding
Influence of Shear Rate
The shear rate characterizes the rate of deformationof the material and is defined as the derivative ofthe velocity over the direction perpendicular to flow(see Figure 6); in other words, the shear rate isproportional to the variation of speed within thepart thickness. So it depends on the velocity of theflow and on the geometry of the flow channels.
For Delrin®, the melt viscosity decreases consider-ably when the shear rate increases, as shown inFigure 7. This effect is more important than thedifferences resulting from variations of the melttemperature within the processing window forinjection molding.
Influence of Molecular Weight
Delrin® is available in four grades of molecularweight. They are coded according to their ability toflow, as measured by MFR or melt flow rate (seeTable 3). High values mean easy flow and abilityto fill thin parts, whereas low values mean highviscosity, high molecular weight and high tough-ness (impact resistance, elongation at break).
MFR is a measurement performed at low shear rate,but the relative differences between the grades aremaintained at high shear rates, as shown in Figure 8.
Figure 6. Approximate Shape of the Velocity Distri-bution Between Two Parallel Plates. TheShear Rate is the Derivative dv(y)/dy.
Y
V (Y)
Figure 7. Viscosity versus Shear Rate of Delrin® 500at Three Temperatures
Shear rate, s-1
Visc
osity
, Pa·
s-1 200°C
215°C230°C
102 103 104
100
1000
10
7
A more direct comparison of the ability to fill canbe obtained using an open-ended snake-flow mold.Results for the different grades of Delrin® arepresented in the Molds section.
Table 3Viscosity, Flow and Molecular Weight (Mw)
of the Delrin® Grades
Spiral flow lengthMFR MFR (215°C/100 MPa/2 mm)
(190°C/ (190°C/ Ease Mw, 90°C moldGrade 1.06 kg) 2.16 kg) of flow toughness temperature
100 1 2.3 lowest highest 170 mm
500 7 14 295 mm
900 11 24 350 mm1700 17 37 highest lowest 400 mm
Figure 8. Viscosity versus Shear Rate for VariousGrades of Delrin® at a Constant Tempera-ture of 215°C (419°F) (source: Campus)
Shear rate, s-1
Visc
osity
, Pa·
s-1
1700
100 1,000 100,000
100
1,000
10
900500
100
Injection Molding UnitDelrin® acetal resins are molded throughout theworld in a wide variety of types and designs ofinjection and extrusion equipment.
The first purpose of the injection unit for moldinga crystalline material is to deliver to the mold thenecessary amount of a homogeneous melt (with nounmelt and no degraded material). The rules ofconstruction of the injection unit are then dependenton the molding material requirements in term ofthermal behavior and heat needed. The first point totake into account for a crystalline material is thethermal stability at melt temperature, to avoiddegradation. Then, screw, nozzle, back flow valve,adaptor, should be designed to provide efficientmelting of crystalline material and deliveryof molten polymer to the mold.
Two rough methods to evaluate the presence ofunmelt and of degraded material will be presentedin “Evaluation of Melt Quality” (see page 12).
Thermal Stability During Processing
As presented in the previous chapter, one differencebetween amorphous and crystalline material is the“melting” behavior. The amorphous polymer startssoftening just after Tg and presents a continuouschange in viscosity. This gives a very large tem-perature range to operate (but a large variation ofviscosity with temperature). In contrast, the crystal-line polymer stays solid up to the melting point andsuddenly melts to the liquid phase at high tempera-ture. This limits the processing range of tempera-ture between unmelt and thermal degradation(specifically for Delrin® 190–250°C [374–482°F]).
The second factor is the time the material stays atthat temperature. For all polymers, the moleculescan withstand a certain time at a certain tempera-ture before degradation can start. Obviously thisacceptable time limit becomes shorter when thetemperature is higher. The typical behavior ofDelrin® is presented in Figure 9. Degradation ofDelrin® will result in generation of gases whichcause bubbles in the melt, splays on parts, molddeposit, yellow and brown marks on the parts.
The average residence time (or Hold-Up Time, HUT)in the injection unit is linked to the amount of polymerin the cylinder, the shot weight and the cycle timeand can be calculated with the following equation:
Average HUT = weight of resin in cylinder × cycle timeshot weight
A quick approximation can be done by :
Average HUT = maximum screw stroke × 2 × cycle timecurrent screw stroke*
* Effective screw stroke = distance the screw travels during rotation only
With a screw stroke of 1 diameter (a small shot)and a cycle time of 1 min (a very long one), theaverage HUT is equal to 8 min. According to thedegradation curve shown in Figure 9, Delrin®
should be stable enough for injection-molding withthis HUT at a melt temperature of 240°C (464°F).Some customers have experienced molding Delrin®
successfully at that temperature.
At the recommended melt temperature of 215°C(419°F), the maximum HUT is over 30 min andDelrin® (standard grades) is thermally stable evenunder these extreme conditions.
There are 3 main potential causes of degradation:• Material trapped in Hold-up spots. In the injec-
tion unit, trapped molten material will stay forvery long times in any dead spots and will start todegrade. So all the injection unit (screw, backflow valve, adaptor, nozzle and hot runners)should be designed to avoid Hold-up spots (seefollowing recommended design).
8
• Material sticking to “hot” steel. Due to the highviscosity of polymers, the speed next to the steelof the injection unit (screw, back flow valve,adaptor, nozzle and hot runner) is almost zero andthe residence time is almost infinite (as evidencedby how long it takes to change colors in aninjection unit). Whereas inside the barrel themolten polymer is cleaned by the screw and thevalve, inside all other areas the material will stickto the walls. To withstand a very long residencetime, the steel in contact should be controlled ata temperature lower than 190°C (374°F) (seeFigure 9).
• Chemical degradation. Contamination (e.g., PVC,flame retardant resins, acid generating resins),incompatible coloring systems (acid or basicpigments), contact with copper (pure, alloys,grease) will accelerate the thermal degradation ofmolten Delrin® in the injection unit. Note thatmold components in copper or copper alloys(such as copper-beryllium) do not cause anydegradation and have been used for years withoutproblems.
Figure 9. Effect of Temperature on Hold-up Time ofDelrin® 500
Hold-up time, min
Mel
t tem
pera
ture
, °C
60 80 10040200
200210220230240250
190
Minimum recommendedmelt temperature
Recommended operatingzone
Screw DesignScrew design is a key parameter for productivity,because for crystalline materials the screw rotationtime is an inherent part of the cycle time.
As mentioned above, it should take in considerationthe specific melting behavior of the crystallinematerial, i.e., solid up to the melting point, highdemand of heat during melting and low viscosityof the molten material.
Although general-purpose screws are widely usedfor molding Delrin®, optimum productivity willrequire a specific design. Exceeding the outputcapability of an inadequately designed screw willcause wide temperature variations and unmeltedparticles (sometimes unmelt and degraded materialhave been observed at the same time). The result isloss of toughness, variability in shrinkage anddimensions, warping, surface defects, plugged gates(leading to short shots) or other molding problems.
Due to the specifics of the melting process of acrystalline polymer, a screw designed for Delrin®
will have shallow flight depths in the meteringsection and a slightly higher compression than ageneral-purpose screw. Specific suggestions aregiven for various screw diameters and compositionof Delrin® acetal resin in Table 4. Compressionratio is the ratio of volume of one turn in the feedsection to that in the metering section (can be ap-proximated to the ratio of the depth of the two zones).
The length of the screw will also affect the meltquality (an insulating material needs some time toget the thermal energy transferred even if the shearcontributes to the heating process). The preferredlength is about 20 times the screw diameter or20 turns when the pitch and diameter are equal. Thescrew should be divided as follows: 30–40% (6–8turns) feed section, 35–45% (7–9 turns) transitionand 25% (5 turns) metering section. Screws with20 turns are commonly divided into 7 turns feed,8 turns transition and 5 turns metering. In screwsless than 16 diameters long, it may be necessary toreduce the pitch to get up to 20 turns. Definitively,the feed section should never be less than 6 turns.
The relatively high compression ratio screws sug-gested for Delrin® are designed to increase the heatinput by mechanical working of the resin. Becausethe energy for this increase comes from the screwmotor, additional horsepower must be available if anincrease in melting capability is to be realized.
Screw Size
The ideal screw size is determined by the volumeof the current shot. Optimum productivity will beachieved when the shot size requires a screw travel
9
TabScrew Design for D
Delrin® 500, 900, 500 T, 1700
Nominal diameter (D) Depth of feed section (h1) Depth of metering
mm mm mm30 5.4 2.045 6.8 2.460 8.1 2.890 10.8 3.5
120 13.5 4.2
(in) (in) (in)(11⁄2) (0.240) (0.087(2) (0.290) (0.100
(21⁄2) (0.330) (0.110(31⁄2) (0.420) (0.140(41⁄2) (0.510) (0.160
D h1
FEED SECTION
(20/1 Length
during plasticization equal to or lower than 50% ofthe capacity of the injection unit. Otherwise, screwrotation speed will have to be decreased at the endof the travel to guarantee an homogeneous melt,leading to a loss in productivity. Practically,optimum productivity is achieved with a screwtravel of between 1 and 2 diameters of the screw.
Thermal settings of the injection unit will bedependent on the residence time (HUT) and hencedependent on the cycle time. Rules will be pre-sented under “Molding Process.”
Screw Design for the Use of ColorConcentrate
A flow analysis shows that the major part of theflow in the screw is laminar, then divided in theback flow valve (due to the changes in flow direc-tion), and still laminar in the adaptor, nozzle, sprue,etc. To get optimum melt quality, to dispersepigments and color concentrates, it is stronglyrecommended to add a mixing head. The purpose ofa properly designed mixing head is not to mixmaterial by turbulence (turbulent flow is impossiblewith highly viscous molten polymer), but by forcedchanges in flow direction.
Cylinder Temperature ControlThis is determined by the machine manufacturer,but two comments should be made.• The temperature control should provide at least
three independent zones, with thermocouplesplaced near the center of each zone. Burn-out ofone or more heater bands within a zone may notbe readily apparent from the temperature control-lers, so some molders have used ammeters ineach zone to detect heater band malfunctions.
le 4elrin® Acetal Resins
Delrin® 100, 100ST
section (h2) Depth of feed section (h1) Depth of metering section (h2)
mm mm5.2 2.66.5 2.87.5 3.08.7 3.6
(in) (in)) (0.230) (0.105)) (0.270) (0.115)) (0.300) (0.120)) (0.340) (0.140))
Pitch h2
METERINGSECTION
TRANSITION
/Diameter Ratio)
• Usually for Delrin® there is no need to cool thefeed throat, but in case such a need exists, thewater flow should be kept to a minimum.Overcooling the feed throat has been observed asa major reason for contamination by black specks.These are generated in the barrel, between thefirst and second heating zones, with the followingmechanism (see Figure 10). The thermocoupleTC1 is influenced by the low temperature due toexcessive cooling, and the system will respond byswitching ON the heating bands HB1 and HB2.This causes no problem with HB1, but results inoverheating and degradation in the area underHB2. To reduce the risk of formation of blackspecks, the following recommendations should beobserved:a) the feed throat cooling should be limited to
a minimum temperature of 80–90°C(176–194°F);
b) the heater band HB2 should be controlled byTC2, or TC1 should be placed in the middle ofHB2, or HB2 should have half the powerdensity of HB1.
Figure 10. The Risk of Black Specks ContaminationThat Could Arise From the Presence of aCooling System of the Feed Throat
HB1 HB2
TC1
Cooling channels Contaminationsource
TC2 TC3 TC4
HB3 HB4 HB5 HB6 HB7
HB8
Cylinder AdaptorThe adaptor shown in Figure 11 is designed toavoid holdup areas and flow restrictions, the twomain causes of degradation and problems linked tothis area. Note that the concept is the same forscrewed adaptors as represented in Figure 11 (usedfor small screws ≤ ∅ 40 mm) and for bolted adap-tors (used for larger screws). The adaptors has shortcylindrical sections (A and B) where it joins boththe nozzle and the cylinder to maintain accuratematching of these diameters, even if it becomesnecessary to reface the mating surfaces. The matingsurfaces (C) should be narrow enough to develop agood seal when the nozzle or adaptor is tightenedand yet wide enough to avoid deformation. Inaddition to its mechanical function of reducing thediameter, the adaptor acts to isolate the nozzle
10
thermally from the front of the cylinder for bettercontrol of nozzle temperature. A separate adaptor,made of softer steel than the one used for thecylinder, is easier and less expensive to repair andchange than a cylinder. It also protects the cylinderfrom damage due to frequent changing of thenozzle. With the bolted adaptor, special care shouldbe taken during assembly to ensure parallelism(don’t overtighten screws from one side only).
Non-Return Valve (Back FlowValve—BFV)The non-return valve or check ring shown inFigure 11 prevents melt from flowing backwardduring injection. This unit is frequently not prop-erly designed to eliminate holdup of resin and flowrestrictions. Malfunctioning that allows resinbackflow is also a common experience andis caused by poor design or maintenance. A leakingnon-return valve will add to screw retraction time,which can increase cycle, and it will also causepoor control of packing and dimensional tolerances.
The non-return valve must meet the followingrequirements:• No holdup spots• No flow restrictions• Good seal• Control of wear
These requirements are provided for in the non-return valve shown in Figure 11.
Figure 11. Design of Adaptor and Non-Return Valve
Nozzle
Adaptor
A
D HE
B
G FC
The slots or flutes (D) in the screw tip are gener-ously proportioned, and the space (E) between thecheck ring and tip is sufficient for resin flow.
The seating of the fixed ring is cylindrical whereit joins both the end of the screw (F) and the screwtip (G) to permit accurate matching of these dia-meters and avoid holdup.
The screw tip thread has a cylindrical section (H)ahead of the threads that fits closely in a matchingcounterbore for support and alignment of the screwtip and seat ring.
The screw tip and check ring seat should be harder(about Rc 52) than the floating ring (Rc 44),because it is less expensive to replace the floatingring when wear occurs.
Corrosion resistant steel is suggested for the tip.Good matching of cylindrical diameters is essentialto avoid holdup spots.
NozzleAs with other semi-crystalline polymers, Delrin®
may drool from the nozzle between shots if thenozzle is too hot, or it may freeze if too much heatis lost to the sprue bushing.
The nozzle design shown in Figure 12 cansolve these problems. The following should beconsidered:
1. The heater band (A) should extend as close tothe nozzle tip as possible and cover as much ofthe exposed surface as practical. This counter-acts any heat loss, especially heat loss to thesprue bushing.
2. The thermocouple location is important. Anappropriate location (B) is shown in the samepicture.
3. Adequate temperature uniformity is required sothat local overheating or premature freezing isavoided.
4. To prevent polymer degradation the steeltemperature should not exceed 190°C (374°F).
5. The nozzle heater should have its own indepen-dent temperature controller.
Screw decompression or “suck back” is frequentlyused to make control of drool easier with theseopen nozzles. This feature is available in mostmachines.
Figure 12. Reverse Taper Nozzle
Heater Band
Thermocouple well
A
B
11
When not available, a design such as the oneillustrated in Figure 13 should be used.
Although shutoff nozzles have occasionally beenused successfully with Delrin®, they tend to causeholdup of resin that results in brown streaks orgassing, especially after some wear has occurred inthe moving parts of the nozzle. These nozzles arenot generally recommended for Delrin® on safetygrounds alone.
Note: With a long nozzle, the thermocouple well Bshould be positioned in the middle of the nozzleand not at the back of the nozzle.
Evaluation of Melt QualityBelow are presented two quick and easy tests toevaluate the melt quality delivered by the injectionunit. Although the result is linked with the tempera-ture setting of the injection unit, it is also highlydependent on the design of the injection unit.
Foaming Test
The foaming test is recommended to determine thequality of the resin after melting in the injectionunit, i.e., the quality of the resin AND the qualityof the injection unit.
Procedure:
1. When the machine is running in cycle, stopthe machine after screw retraction for 3 minfor pigmented Delrin® (10 min for naturalmaterial).
2. Purge at low speed (to avoid hot splashes) intoa cup and observe the molten material for 1 or2 min. Then put the molten material in a bucketof water.
3. Then recharge the screw and wait 2 moreminutes (10 more minutes for natural material).
4. Repeat operation 2.
An unstable melt will grow (foam) during theobservation and float in the bucket. A stable melt
Figure 13. Straight Bore Nozzle, Only for MachinesWithout Screw Decompression
Thermocouple wellHeater BandA B
will stay shiny with a tendency to shrink during theobservation, and will sink in the bucket.
Foaming resin will quickly cause mold deposit andwill accelerate screw deposit, which may lead toblack speck contamination.
This technique is useful to evaluate non-DuPontcolor systems (color masterbatches, liquid coloring).
The foaming test can also be used to detect inad-equate quality of the injection unit (e.g., problemsof throat cooling and consequent overheating,excessive nozzle temperature, hold-up spots, etc).
Unmelt Test
The unmelt test is recommended to evaluate melthomogeneity:• When the press is running on cycle, stop at the
end of a cycle and purge one shot;• charge the screw immediately with the shot
volume used and purge again;
Figure 14. Exploded View of Mold
1
• repeat the operation until detection of lumps/irregularities in the purge coming out of thenozzle.
If such lumps/irregularities appear after less than3 purges, the risk of unmelt is very high and shouldbe dealt with by increasing cylinder temperature,by lowering screw RPM and by increasing backpressure. If such changes lengthen the cycle timetoo much, a more appropriate screw design shouldbe used (see Table 4). If lumps/irregularities appearafter 3 purges but before 6, the situation is accept-able, but there is not much safety margin. If theyappear after 6 purges, there is a very low risk ofunmelt.
MoldsDelrin® acetal resins have been used in many typesof molds, and molders have a wealth of knowledgeconcerning mold design for Delrin®. Molds forDelrin® are basically the same as molds for otherthermoplastics. The parts of a typical mold areidentified in Figure 14.
Locating Ring
Sprue Bushing
Front Clamping Plate
Front Cavity Plate (“A” Plate)
Leader Pins
Leader Pin BushingsRear Cavity Plate (“B” Plate)
Support Plate
Cavity
Spacer Block
Ejector Retainer Plate
Return PinEjector PlateKnock Out Pins
Rear Clamping PlateSprue PullerSupporting PullerStop Pin
2
This section will focus on the elements of molddesign that deserve special consideration for pro-cessing Delrin® and can lead to higher productivityand lower cost for the molder. These topics are:• Ability to fill • Undercuts• Gates • Runnerless molds• Runners • Mold maintenance• Vents
Mold shrinkage and other aspects of moldsizing are discussed in “Dimensional Consider-ations” (see page 30).
Ability to FillMelt viscosity largely governs the ability of a resinto fill a mold. Delrin® acetal resins range in meltviscosity from Delrin® 1700, the lowest in viscosityor most fluid, to Delrin® 100, the highest. Theviscosity of Delrin® does not decrease rapidly asmelt temperature increases, in contrast to amor-phous thermoplastic resins. Increasing melt tem-perature will not greatly improve the ability ofDelrin® to fill a thin section.
In addition to the properties of the resin, the mold-ing conditions and cavity thickness determine thedistance of flow. Figure 15 shows the maximumflow distances that can be expected at two cavity
Figure 15. Maximum Flow Distance of Delrin® AcetalResins
Injection pressure, MPa
Flow
dis
tanc
e, m
m
Flow
dis
tanc
e, in
12080 100
Injection pressure, psi17.40011.600 15.000
500 –20
–15
–10
–5
600
400
300
200
100
0
100
100ST
100
500100ST
900
1700 P
1700 P
500
900
2.5 mm (0.100 in)1 mm (0.04 in)
thicknesses for Delrin® acetal resins as a functionof injection fill pressure. These comparisons weremade in an open-ended snake flow mold with nogate restriction. Obstructions in the flow path, suchas sudden changes in flow direction or core pins,can significantly reduce the flow distance.
GatesThe gates of a mold play a major role in the successor failure of a molding job. The location, design,and size of a gate are key factors to allow optimumpacking. Obviously, the design will be differentthan the one used for molding amorphous material.In that case the flow should stop as soon as possibleafter filling the cavity to avoid overpacking (flowin) and sink marks at gate (flow back). Withcrystalline material, the location, design and size ofthe gate should be such that it will allow a continu-ous flow during ALL the packing phase (Holdpressure time—see page 26).
Gate Location
As a key rule, when a part is not uniform in wallthickness, the gate must be located in the thickestsection. The respect of this basic principle plays anessential role in obtaining optimum packing andconsequently the best mechanical properties,dimensional stability and surface aspect. Of courseevery bottleneck (reduced section along the flow ofthe melt) should be avoided between the gate andall areas of the part.
An area where impact or bending will occur shouldnot be chosen as the gate location, because the gatearea may have residual stress and be weakenedsince it works as a notch. Similarly, the gate shouldnot cause a weld line to occur in a critical area.
The gate should be positioned so that the air will beswept toward a parting line or ejector pin—whereconventional vents can be located. For example, aclosed-end tube such as a pen cap should be gatedat the center of the closed end, so air will be ventedat the parting line. An edge gate will cause airtrapping at the opposite side near the closed end.When weld lines are unavoidable, for examplearound cores, an escape for gases must be providedto avoid serious weakness and visual flaws. Spe-cific recommendations for venting are given later inthis section.
Another consideration in choosing a gate locationfor Delrin® is surface appearance. Gate smear orblush, as well as jetting, are minimized by locatingthe gate so that the melt entering the cavity im-pinges against a wall or core pin.
A central gate location is often necessary to controlroundness of gears and other critical circular parts.
13
Diaphragm gate
Submarine gate(bucket type)
Direct gate
Edge gate
Fan gate
Fan gate
Pin point gate
Ring gate
Figure 16. Schematic View of the Most CommonTypes of Gates
Figure 17. Details of a Typical Edge Gate Suitable forDelrin®
Runner
Side View
z = Max. 0.8 mm
T = Part ThicknessT
x = 0.5T
1,2 T
Multiple gates, usually two to four, are commonlyused when there is a central hole to avoid a diffi-cult-to-remove diaphragm gate.
Gate Design
As mentioned above, for crystalline materials likeDelrin® the thickness of the gate or its diameter (fora pin-point gate or tunnel gate) determines thefreeze-off time, and therefore also determineswhether it is possible to pack the part (to compen-sate the volume reduction due to crystallization)and maintain the pressure during solidification. Thegate should remain open until the part density ismaximum for a specific material. The thickness (ordiameter) of the gate should amount to 50–60% ofthe wall thickness at the gate. The width of the gateshould always be equal or greater than the gatethickness. The length of the gate should be as shortas possible and never exceed 0.8 mm (0.03 in). Thegate area of the part should not be subjected tobending stresses during actual service. Impactstresses are particularly liable to cause failure in thegate area.
The most common types of gates are summarizedin Figure 16.
• DIAPHRAGM GATE: Circular gate used to filla single symmetrical cavity. The advantages area reduction of weld line formation and improve-ment of filling rates. However the part has to bemachined to remove the gate.
• DIRECT GATE: The sprue feeds directly into themold cavity without runners. This design mayoften lead to surface defects coming from thenozzle (e.g., cold slug, cold skin, entrapped air.)
• EDGE GATE: Usual type of gate with two platemolds. It is not self degating.
• FAN GATE: This gate is used to enlarge the flowfront. Usually it leads to a reduction of stressconcentrations in the gate area. Less warpage ofparts can usually be expected by the use of thisgate type.
• PIN POINT GATE: This gate is used with threeplate molds. It is self degating.
• RING GATE: See DIAPHRAGM GATE.• SPRUE GATE: See DIRECT GATE.• SUBMARINE GATE: A type of edge gate where
the opening from the runner into the mold is notlocated on the mold parting line. It is used toseparate the gate from the part with a two platemold (self-degating).
• TUNNEL GATE: See SUBMARINE GATE.
Details of a typical edge gate suitable for Delrin®
are shown in Figure 17.
14
D1
30°
D
D1
d
T
When the moldings are very thin, however, thisrunner cannot be less than about 1.5 mm (0.06 in) inthickness. The runner thickness is usually increasedat each of the first one or two turns from the cavity,as shown in the example of Figure 20.
Figure 18. Details of a Submarine Gate (Tunnel Gate)Adequate for Delrin® (left side). The Oneon the Right is Not Adequate for Crystal-line Polymers and Would Give Problemswith Delrin®.
Figure 19. Details of a Three Plate Gate DesignAdequate for Delrin® (Left Side). The Oneon the Right is Not Adequate for Crystal-line Polymers and Would Give Problemswith Delrin®. *Gate Length Should be<0.8 mm (0.03 in).
D
d
2°
D1
T*
Figure 20. Correct Runner Thickness for an EightCavity Mold
Ø1 = D1 + 1 mm
Ø3 = D1
Ø2 = D1 + 0.5 mm
Figure 18 shows details of a submarine gateadequate for Delrin® (left), compared to a similartype of gate not recommended for crystallinematerials (right).
Design criteria:• always gate in thickest area of the part;• diameter of the gate “d” must be at least half the
part thickness. The length must be shorter than0.8 mm (0.03 in) to prevent premature gatefreezing during packing;
• the inscribed diameter “D” of the tunnel next to thegate must be at least 1.2 × the part thickness “T.”
The gate shown on the right side of Figure 18 isnot recommended for crystalline materials likeDelrin®, because such conical gate sections crystal-lize before the end of complete part pack out. Thisresults in low mechanical performance and uncon-trolled shrinkage.
Figure 19 shows details of a three plate gate designadequate for Delrin® (left), compared to a similartype of gate not recommended for crystallinematerials. The design criteria illustrated above arealso applicable to this kind of gate.
Note: Restrictions around the sprue puller will leadto incomplete part pack out. So, the diameter D1in Figure 19 should be at least equal to diameter D.
Runner SystemGuidelines
Key guidelines to follow when designing a runnersystem include:
a. runners should stay open until all cavities areproperly filled and packed;
b. runners should be large enough for adequateflow, minimum pressure loss and no overheating;
c. runner size and length should be kept to theminimum consistent with previous guidelines.
Each of these factors can affect quality and cost ofmolded parts. Factor (a) should be regarded as themost critical.
The cross section of the runners is most oftentrapezoidal, which represents an optimum practicalcompromise with respect to the full round section.The effective cross section of the runner is in thiscase the diameter of the full circle that can beinscribed in it.
For parts of Delrin® to have the best physicalproperties, the runners next to the gate must have atleast an inscribed diameter of 1.2 times the partthickness “T.”
15
Figure 23. Examples of Unbalanced 16-Cavity Mold.The Solution on the Right is Provided withOverflow Wells to Trap Cold Slugs.
Single Cavity Mold
The simplest runner configuration for a singlecavity mold could be direct gating (see Figure 21).In this case, however, it would be necessary to havea “cold slug catcher” directly on the part, withassociated surface problems and lower mechanicalproperties in that area. The preferred solution isthen to “break the flow” as indicated in Figure 21.
Runner Layout
A perfectly balanced layout (with equal flowdistance from the sprue to each cavity) is bestachieved if the number of cavities is equal to apower of 2 (2, 4, 8, 16, 32, 64, 128, etc.). See anexample of a 16-cavity mold in Figure 22 withbalanced (left) and unbalanced runner systems. Aperfectly balanced layout may be impractical andexpensive.
When an unbalanced runner system is selected, thelayout shown in Figure 23 (left) could presentmore risks of quality problems. The flow tends tostop at each of the early gates due to the restrictionand the material starts to crystallize. Then, as therunner continues to be filled, the pressure rises andthe the cold slugs which started to be built up, arepushed into the cavity.
To reduce such risk, the solution shown in Figure23 (right) is recommended. In such configuration,the cold slugs tend to be trapped into each overflowwell.
In case of multi-cavity molds (≥16 cavities), theso-called “spiral effect” could take place in the
Figure 21. Direct Gating (Left) and Indirect Gating toBreak the Flow (Right), in a One-CavityMold
Figure 22. Balanced (Left) and Unbalanced (Right)Runner Systems in a 16-Cavity Mold
1
“internal” cavities of the layout (see for instanceFigure 24), due to over-heating of the melt inrunners, caused by localized shear. To minimizenegative effect like splays or mold deposit, shearshould be reduced by using appropriate runnerdimensions.
For multi-cavity molds for small thickness parts(≤1 mm [0.04 in]), the design of runners should bechecked by running a detailed flow analysis study.
Nozzle and SprueNozzle and sprue diameters are directly linked withthe dimensions of the part and of the runners. Thedesigner should first decide if the sprue is needed ornot. If yes, a design like the one shown in Figure25 could be selected, one that in many cases hasproved to be the most effective with crystallinematerials like Delrin®. Due to its parallel cylindri-cal shape it is easy to machine and polish, allowslarge nozz1e diameters, and it is easy to eject due tohigh shrinkage. Guidelines for the dimension are:• a sprue diameter ∅
1 at least equal to the inscribed
diameter of the main runner;• a nozzle diameter “DN1” equal to ∅
1 minus 1 mm.
Figure 24. Example of “Spiral Effect” in a 32-CavityMold. Cavities 11, 14, 19, 22 Will Be FilledFirst and May Show Splays and MoldDeposits.
1
16 14
1917
32
24
9
22
11
25
8
6
In case the designer selects a design without asprue, a long nozzle may be required as shown inFigure 26 for a 2 plate tool, and in Figure 27 for a3 plate tool. Again, the dimensions are linked to thedimensions of the part and of the runners (guide-line: nozzle diameter “DN1” equals to the mainrunner inscribed diameter minus 1 mm).
Figure 25. Sprue and Nozzle Design Often Used withDelrin®. The Dimensions are Linked withthe Dimensions of the Part and of theRunners.
D N1D N2
Ø1
Figure 26. Example of a Design of a Nozzle WithoutSprue Used with 2 Plate Molds. Remem-ber that for Delrin® the Nozzle Tempera-ture Should Not Exceed 190°C (374°F).
D N1
D N2
5 mm
Figure 27. Example of a Design of a Nozzle withoutSprue Used with 3 Plate Molds. Remem-ber that for Delrin® the Nozzle Tempera-ture Should Not Exceed 190°C (374°F).
D N1
D N2
DSP 1
2°
5 mm
1
A review of the key recommendations related to thesprue and runner system follows. It can be used asa quick reference list to check their design.
1. Cylindrical parallel sprue preferred: seeFigure 25 and Figure 28-1.
2. Sprue puller for 2 plate mold: see Figure 28-2.
3. Cold slug well for 3 plate mold: see Figure 28-3.
4. Perpendicular flow splits with cold slug wellsat each split, see Figure 28-4.
5. No flow restriction caused by sprue puller in3 plate mold, see Figure 28-5.
6. Runner dimensions:– for parts having thickness >1.5 mm (0.06 in),
follow general rules for crystalline polymers(Figure 20);
– for thinner parts and multi-cavity molds, aflow analysis may be required to selectdimensions that will avoid over-shearing.
7. Runners should be properly vented, seeFigures 28, 29 and 30.
8. Balanced runners recommended (seeFigure 24).
9. For thin parts and large number of cavities,unbalanced runners may be acceptable. How-ever, parts should never be gated directly ontothe main runner (see Figure 23).
Figure 28. Key Rules for the Design of the Sprue andRunners of a 2 Plate Mold (Top) and of a3 Plate Mold (Bottom)
1
4
6
Ventchannel
2
35 6
7
8
Hot Runner Mold for CrystallinePolymersPreliminary Comments
This section includes all hot runner, hot sprue bush,and runnerless molds. The following is not intendedto recommend any trademark or system but topresent the behavior and the needs of crystallinepolymers in such tools.
The question that frequently arises is when to usehot runner molds with crystalline polymers likeDelrin®. This is a highly controversial subject. Thechoice depends on many factors, and particularlyon the quality needed, i.e., mechanical perfor-mance, surface aspect, percentage of rejects.
Status
All such molds give the obvious advantages of lessmaterial to plastify, no (or minimum) regrind andshorter cycles. On the other hand, hot runner moldsare more expensive and heavier; they need moremaintenance and better-trained operators thanconventional molds. In addition, if they are notproperly designed, the heat needed to run themcould spread to all parts of the mold and can in factcause the cycle time to increase.
One approach is to evaluate the expected increaseof theoretical productivity versus conventionalmolds. If such an increase is lower than 25%, itwould be wise to stay with a 3 plate mold that willbe cheaper to build, start and run.
The break-even of about 25% applies to full hot-runner systems; for other molds (with hot spruebushes, cold sub-runners) the break-even point ismuch lower.
Direct Gating Versus Cold Sub-Runnersfor Crystalline Polymers
When designing a hot runner mold for crystallinepolymers, it should be kept in mind that directgating via hot runner is more difficult with crystal-line polymers than with amorphous ones. Thedifference comes from the softening or meltingbehavior of these two types of polymers.
An amorphous material exhibits a gradual softeningbehavior above Tg from the solid state to the liquidstate, allowing a wide processing window in termsof temperature and viscosity. In fact, as its tempera-ture increases above Tg (see Figure 29) an amor-phous polymer (curve “A”) lends itself first tothermoforming (“T”), then to blow molding(“BM”) and finally to injection molding (“IM”).
On the contrary, the Tg has usually a limited ornegligible effect on the structure of crystallinepolymers, which are solid above Tg. At the tem-perature Tm, crystalline polymers melt sharply andbecome liquid (curve “C”).
1
Such behavior of a crystalline material may involvethe risk of:• Drooling around the gate with consequent
problems of bad surface aspect and deformation.• Plugging of the gates by solidified material, plugs
which will be pushed into the cavities, withconsequent problems of surface defects andlower mechanical performances. The best wayto prevent such problems is to use COLDSUB-RUNNERS.
Figure 29. Softening/Melting Behavior of Amor-phous and Crystalline Polymers
Temperature
Mod
ulus
C
A T
BM
IM
Tg Tm
Thermal Control of Hot Runner Molds
Thermal management and streamlining of the floware very important for hot runner tools. It should bechecked that a relatively low temperature setting(≤190°C [≤374°F]) gives an easy flow of thematerial with no hold-up spots.
The reason is that, due to the viscosity of thepolymer, its flow is always laminar. This meansthat the material will remain against the steel wallof the hot runner, and residence time will be verylong. For Delrin®, to avoid thermal degradationwith prolonged times, the steel temperature shouldnever exceed 190°C (374°F). If the hot runnersystem solidifies at that temperature, then it must bemodified to improve thermal insulation and heatdistribution to remove cold spots. Degradation canresult in splays, odor, black specks and molddeposit.
Conclusions
With crystalline polymers such as Delrin®, werecommend the following:• A minimum of 25% theoretical cost decrease
should be expected before a hot runner isconsidered.
• Highly trained machine operators and moldmaintenance toolmakers should be available.
Figure 30. Recommended Venting of a Part and of itsRunner System
Vent LandEnd of flow
Vent channels
L ≤ 0.8 mm
W > 2 mm
D < 0.03 mm
* ≈ 0.3 mm
• Use of cold sub-runners, never direct gatingstraight onto the part.
• Use of Delrin® P grades.• All temperatures in the hot runner system must
not exceed 190°C (374°F).• Avoid the use of hot runner molds if surface
defects are not acceptable and high part mechani-cal performance is required.
• Avoid the use of hot runners for toughenedgrades.
VentsVenting a mold for Delrin® is particularly impor-tant, and special attention should be given to thisfactor during both the design of the mold and itsinitial trial. This attention is required becauseburning of parts caused by inadequate venting isnot easily observed with Delrin®. With other resins,poor venting results in a blackened and burned spoton the part. With Delrin®, however, there may beeither no visible flaw or an inconspicuous whitishmark on the molding.
Venting problems with Delrin® acetal resins maybe made more obvious by spraying the mold witha hydrocarbon or kerosene-based spray just beforeinjection. If venting is poor, the hydrocarbon willcause a black spot where the air is trapped. Thistechnique is particularly useful for detecting poorvents in multi-cavity molds. A convenient source ofhydrocarbon spray is a rust preventative spray.
Vents should be located at:
1. the end of any runner;
2. any flow junction where air is entrapped and aweld line results. The position of weld lines canbe defined by short shots.
Only NO venting together with excessive fastinjection speed will cause corrosion of the tool atthe weld lines with Delrin® (diesel effect). Inad-equate venting of molds for Delrin® may cause agradual buildup of mold deposit where vents shouldbe located and in mold crevices through whichlimited venting has taken place. These depositsconsist of a white solid material formed from thetraces of gas evolved during normal molding. Goodvents allow this gas to escape with the air from thecavities.
Poor venting may also reduce physical propertiesat weld lines.
Venting problems may be aggravated by high melttemperature, long holdup time, or holdup areas inthe injection cylinder, which will generate morethan normal amounts of gas. Fast injection fill
19
speed will also aggravate these problems. Remediesfor mold deposit problems are listed in the Trouble-shooting Guide (see page 38).
Venting usually occurs through the parting line of amold and is provided by machining channels in thecavity plate and inserts.
In some cases, venting may be accomplishedaround an ejector pin. This vent will also be im-proved by grinding flats on the pin and relieving thevent after a short land. Pins that do not move withthe ejection system tend to clog and no longerprovide venting after a short time.
Venting the runner system is helpful in reducing theamount of air that must be vented through thecavities. Because flash is unimportant on therunner, these vents can be slightly deeper thancavity vents, for example, 0.06 mm (0.0024 in).
The drawings in Figure 30 show the recommendeddimensions for vents in cavities for Delrin®.
Note: During mold maintenance, vent depthand/or hobbing should be carefully checked. Ventsshould be modified if the vent depth is less than0.01–0.015 mm (0.0004–0.0006 in).
UndercutsGeneral suggestions for stripping undercuts withDelrin® acetal resins are:• The undercut part must be free to stretch or
compress, that is, the wall of the part opposite theundercut must clear the mold or core beforeejection is attempted.
• The undercut should be rounded and well-filletedto permit easy slippage of the plastic part over themetal and to minimize stress concentration duringthe stripping action.
• Adequate contact area should be providedbetween the knockout and plastic part to preventpenetration of the molded part or collapse of thinwall sections during the stripping action.
• The length of the molding cycle and specificallythe Hold (Pressure) Time (HPT) should beoptimum to avoid excessive shrinkage with insideundercuts. Sufficient part rigidity must be devel-oped without causing binding due to excessiveshrinkage around pins forming an internalundercut. Ejection of parts with undercuts on theoutside diameter will be aided by mold shrinkage.
• Higher mold temperature, which keeps the parthotter and more flexible when the mold opens,may aid ejection from an undercut.
• Generally, parts of Delrin® acetal can be moldedwith a maximum 5% undercut. Calculation ofallowable undercut is illustrated in Figure 31.The allowable undercut varies somewhat withboth wall thickness and diameter.
Figure 31. Calculations for % Undercut (B–A)/B ≤ 5%
A
R
B Inside undercuts
Outside undercuts
A
B
R
A
B
≥30°
A
B
R
R
2
Sharp CornersOne of major causes of failure of plastic parts areinternal sharp corners. A sharp corner in a part actsas a notch and initiates break at a very low energy.The diagram in Figure 32 shows the effect of notchradius on impact resistance of test bars molded intwo grades of Delrin®. Note that the notches havebeen molded (simulation of real life and not ma-chined as required by the standard Izod test).
From this diagram it can be seen that an increase ofan internal radius of curvature from 0.01 (almost asharp corner) to 0.2 mm doubles the impact resistance.
Note also that sharp corners are not desirable inplastic parts because they are an important contrib-uting factor to warpage.
Ribs DesignVery often, ribbed parts will perform much betterin term of cycle time, mechanical performances andwarpage than very thick unproperly packed parts.It is economically impossible to pack sectionsabove 6–8 mm (0.24–0.32 in) thickness during allthe crystallization time (solidification: see Figure30 for Hold [pressure] Time vs part thickness).However an improper rib design could also causedefects such as sink marks. Recommended ribdimensions are shown in Figure 33. Note that theradius at the base of the rib should not be too smallto preserve part toughness (see Figure 32).
Weld LinesWeld lines occur where two melt flows join to-gether. Weld line position can be defined by shortshots, or by flow simulations (if the mold does notexist yet). If the mold is provided with properventing (see page 19), the weld line strength shouldbe at least 80–90% of the nominal strength value ofthe resin.
To optimize weld-line strength, two parameters areimportant:
1. optimum Hold (Pressure) Time, to ensure thewelding of the flow fronts under pressure (forthe correct HPT see page 26);
2. optimum filling rate, which will depend on partthickness (approximately 1 second per mm(0.04 in) of part thickness).
Figure 34 shows the weld line strength of a 4 mm(0.16 in) thick test bar in Delrin® 100 gated at bothends. Both tensile strength and toughness areseriously affected if filling time is not optimized.
0
Figure 32. Impact Strength as a Function of MoldedNotch Radius
Notch radius, mm
Impa
ct s
tren
gth,
kJ/
m2
0,50,1 0,2 0,3 0,40
20
40
60
80
0
Delrin® 100P NC10
Delrin® 500P NC10
Figure 33. Suggested Rib Dimensions Versus WallThickness
0.5-0.7T
R = 0.2-0.3T
T
Figure 34. Tensile Strength (Left Scale) andUnnotched Izod Impact (Right Scale) of aDelrin® 100 Test Bar, 4 mm thick, Moldedat Both Ends with Different Filling Times
Filling time, s
Tens
ile s
treng
th a
t yie
ld, M
Pa
Izod
unn
otch
ed, 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
Mold MaintenanceAs a general rule, molds for processing Delrin®
require the same care as those for processing otherthermoplastic materials. Wiping the mold andapplying a rust-preventing solution is usuallyadequate after a production run.
Vent Maintenance
Due to the critical nature of the vents, the ventdimensions should be checked during routinemaintenance. Vent depth and /or hobbing (deforma-tion of the parting line opposite the vent) should becarefully checked. Vents should be modified if thevent depth is less than 0.01 mm to 0.015 mm. Anyhobbing that blocks the vents should be ground off.
Mold CleaningDepending on the type of deposit the cleaningprocedure is as follows:• White deposit
White deposit is due to the accumulation ofparaformaldehyde. This deposit can be removedwith benzyl alcohol or isopropanol. Frequentcleaning of the tool with these solvents duringmolding will prevent the accumulation of thisdeposit.
• Translucent or colored depositThis deposit is normally observed near the gate(in case of overshear of the material), on pins ornear hot spots. The use of a less shearing gate(see gate design recommendations) or a moreeven mold temperature will stop or tremendouslydecrease the build up of this deposit. It can beremoved with commercial alkaline chemicalcleaners. Efficiency of the cleaning agent can beimproved with an ultrasonic bath.
Molding ProcessInjection molding of Delrin® acetal resin is similarto that of other thermoplastic resins. The engineer-ing applications for which Delrin® is used, how-ever, frequently require tight specifications onstrength, dimensions and surface condition, so thatcontrol of the molding operation becomes morecritical.
The information discussed in this section includessuggestions for:• Start-up and shutdown procedures, handling
precautions• Operating conditions for Delrin®
• Techniques for optimum productivity molding
21
Start-up and Shutdown ProceduresStart-up with Resin Change
The suggested start-up procedure with Delrin® isdesigned to prevent overheating of the resin andcontamination in the injection unit with materialfrom previous runs.
To start up a machine which contains another resin,the injection unit must be purged with crystalpolystyrene until the cylinder and other hightemperature zones have been cleared. This cannormally be done with cylinder temperatures in therange 210–250°C (410–482°F), if appropriate forthe previous material. The nozzle is quite difficultto clean by purging, because the laminar flow inthis area leads to a layer of polymer sticking to themetal (this is also true for hot runners). It is there-fore recommended to switch off the nozzle heater,remove the nozzle, clean it to get rid all traces ofprevious polymer, and reassemble it. The cylindertemperatures should then be adjusted to about215°C (419°F), and the nozzle temperature to190°C (374°F). When both cylinder and nozzlehave reached the expected temperatures, Delrin®
can be added to the hopper.
In unusual circumstances, an intermediate purgewith a harsher compound may be required toremove adherent deposits from the screw andcylinder. Special purge compounds are used for thispurpose.
These purge compounds must also be removed fromthe cylinder by purging with polyethylene or poly-styrene before Delrin® is introduced. In the worstcases, e.g., after use of glass-reinforced resins orsevere degradation of previous material, it may benecessary to pull the screw and clean the equipmentmanually to prevent contamination of moldings.
Safety point: Polystyrene is chemically compatiblewith Delrin®, whereas even a trace of polyvinylchloride (PVC) is not. Contamination of Delrin®
with such material can cause objectionable odor oreven a violent blowback.
Start-Up From a Cylinder Containing Delrin®
After a safe shut-down procedure, the screw and thecylinder should be essentially empty. To restart, thenozzle and cylinder temperatures should be set at190°C (374°F) to preheat the cylinder and the resinit contains. When the cylinder has reached the settemperature, ensure that the nozzle is open andincrease the cylinder settings to normal operatingtemperatures. When all temperatures are in theoperating range, the hopper can be filled andmolding can begin after a brief purge with Delrin®.
22
Shutdown When a Restart with Delrin® isPlanned
Shut off the hopper feed and continue molding untilthe cylinder is empty. For large machines (with ascrew diameter above 40 mm [1.57 in]) it is recom-mended to purge the cylinder with crystal polysty-rene, move the screw fully forward, then switch offthe heater bands. For small machines move thescrew fully forward and switch off the heater bands.
Shutdown When a Restart with AnotherResin is Planned
Shut off the hopper feed and continue moldinguntil the cylinder is empty. Purge with crystalpolystyrene, leave the screw fully forward, thenswitch off the heater bands.
Temporary Interruption
A molding machine with Delrin® in the cylinderat molding temperatures should not be allowedto stay idle. The maximum recommended cylinderresidence time, under normal molding conditions,is 10 min for pigmented material and 20 min fornatural standard material. In excess of these times,resin decomposition may occur.
If, during the temporary interruption, the cylinderresidence time reaches the above limits, close thehopper feed, empty the cylinder and leave the screwforward. The cylinder temperatures should bereduced to about 150°C (302°F) (at these tempera-tures Delrin® will be stable even for a weekendshutdown).
Action to Follow When the Nozzle HeaterBand Breaks Down
Retract the injection unit, close the hopper and slideit out of the way. If the nozzle is still open, followthe normal shutdown procedures. If the nozzle isfrozen, heat the nozzle with a gas torch to melt thefrozen material inside the nozzle and then purge.
Start-up after Emergency Shutdown
A different procedure should be used after anemergency shutdown due to loss of power or othercauses. In this case, the screw may be full ofDelrin® that cooled slowly and was exposed to melttemperatures for a prolonged period. The screwmay even be in the retracted position with a largequantity of Delrin® in front of the screw. In order tovent gases from resin that may be degraded, it isessential that the nozzle be open and heated tooperating temperature and Delrin® in this area becompletely melted before the cylinder reaches melttemperature. The cylinder zones should be heatedto an intermediate temperature below the meltingpoint of Delrin® and the machine allowed to equili-brate at that temperature. Cylinder temperatures of
150–175°C (300–350°F) are suggested. After allzones have been at this temperature for 30 min,cylinder temperatures should be raised to 195°C(380°F). As soon as the Delrin® has melted, itshould be purged from the cylinder with freshDelrin®. The partly degraded, hot purge resinshould be placed in a pail of water if it emits anodor. When the old resin is purged from the cylin-der, the cylinder temperatures may be raised tonormal production settings.
Operating Conditions for Delrin®
—Temperature SettingsIntroduction
The basic purpose of the injection unit is to deliverto the mold the necessary amount of a homoge-neous melt (no unmelt and no degraded material).The rules of construction of the injection unit formolding a crystalline material have been presentedin “Injection Molding Unit,” (see page 8); the rulesfor the settings are presented below.
Note: Two rough but practical methods to evaluatethe presence of unmelt and of degraded material weredescribed on page 12 and can be used here as well.
Delrin® acetal resin is a crystalline polymer with amelting point of 178°C (352°F). For most grades ofDelrin® the preferred melt temperature range is215°C (419°F) ± 5°C*, as measured with a needlepyrometer in the melt. The calories needed to heatand melt Delrin® will be provided by shear (fromscew rotation) and the balance by conduction in theheated cylinder (slow heat transfer due to theinsulating character of polymers).
Cylinder temperature
The main parameter influencing the temperatureprofile of the cylinder is the residence time (orHold-Up Time—HUT) of the polymer in theplastification unit (see page 8 to calculate HUT).
With a short HUT (<3 minutes, short cycle time,high melt output), higher than normal cylindersettings may be required. With a long HUT (>5minutes, long cycle time, low melt output), lowersettings, especially in the rear zone, may be used.Since generalization of cylinder temperaturesettings is difficult, it is often wise to begin with alevel profile and adjust as needed. The diagramshown in Figure 35 can be used as a guideline forinitial temperature settings.
* The preferred melt temperature for Delrin® 100ST and Delrin® 500T is about205°C (401°F).
2
Residence time
215
220
225
195
180
FRONT ZONE CENTER ZONE REAR ZONE
< 3 min
> 5 min
Hopper
no cooling or 80–90°C (176–194°F) min
3 ÷ 5 minRecommendedmelttemperature,°C
Notes:
1. As the preferred melt temperature for Delrin®
100 ST and Delrin® 500 T is about 10°C (18°F)lower, the zone settings should be 10°C (18°F)lower than shown in Figure 35.
2. Hopper cooling is not needed and should not beused for Delrin®. As described in Chapter 3,excessive hopper cooling may create problemsof screw deposit and black specks.
3. With very small injection units and/or shortresidence time (HUT), pre-heating the granules(e.g., with a heated hopper) may help toachieve an homogeneous melt.
Nozzle Temperature
The nozzle temperature is adjusted to control drooland freezing (see “Nozzle” page 11), but it shouldnever be set above 190°C (374°F) in order toprevent polymer degradation (the laminar flow andhigh viscosity of the molten polymer result in verylong contact time with the metal wall). If the nozzlefreezes with a setting of 190°C (374°F), its insula-tion from the sprue bushing should be improved, orits inside diameter should be increased if feasible.
Notes:
1. Practically, it is always easier to set the nozzletemperature correctly by using sprue break. Theinjection unit is pulled back after screw rotationand then the nozzle is insulated from the coldmold. This allows the calories to flow to the tipof the nozzle without having to set too high atemperature, and reduces the risk of stringingfrom the nozzle.
Figure 35. Cylinder Temperatures Profile VersusResidence Time for a Given Recom-mended Melt Temperature. Recom-mended Nozzle Temperature is 190°C(374°F) for All Delrin® Grades.
3
2. Hot runner. By analogy, a hot runner system isa nozzle transferring the molten resin from theinjection unit to the part. Hence the principlesand recommendations for nozzles are also validfor hot runners. In particular, the laminar flowand high viscosity of the molten polymer againresult in very long contact times with the metalwall; so the temperature of the metal in the hotrunner should never exceed 190°C (374°F), inorder to prevent degradation of the polymer.
Screw Rotation Speed
Screw rotation speed behaves as a “thermal set-ting,” because the rotation of the screw will “shear”the material and supply around half of the caloriesneeded to melt and heat Delrin® to the recom-mended melt temperature range of 215°C (419°F)± 5°C (205°C [401°F] ± 5°C for Delrin® T and ST).As with all polymers, Delrin® is sensitive to shearand a maximum of 0.2 to 0.3 m/s of screw periph-eral speed is recommended. Figure 36 shows theoptimum screw rotation speed for high viscosityDelrin® (type 100) and low viscosity Delrin® (types500 to 1700) as a function of screw diameter.
Back Pressure
Back pressure also behaves like a thermal setting.Increasing back pressure increases the work doneby the screw on the melt.
The use of the optimum screw design for crystallinematerials, such as Delrin®, should provide thenecessary work to melt and bring Delrin® to therecommended melt temperature with the minimumback pressure. Only melting of highly viscousDelrin® such as Delrin® 100 may require some back
Figure 36. Maximum Screw Rotation Speed asFunction of Screw Diameter. The Curvefor Delrin® 500 is Also Valid for the LowViscosity Grades Delrin® 900 and 1700.
Screw diameter, mm
Max
. scr
ew ro
tatio
n sp
eed,
rpm
80 1006040200
50
100
150
200
250
300
0
Delrin® 500Delrin® 100
24
pressure to avoid the screw worming back (leadingto inconsistent shot volume and pad).
The use of an inappropriate screw may requiresome back pressure to increase the work done bythe screw on the melt, to increase the melt tempera-ture and its uniformity. Higher back pressure maybe used to eliminate unmelted particles and toimprove color mixing when color concentrates areused. Increasing back pressure, however, tends toreduce glass fibre length and change properties offilled resins such as Delrin® 570. More importantly,increasing back pressure always decreases theoutput of the screw, leading to longer cycle timesand lower productivity. This increases the buildupof screw deposit leading to contamination and lowpart performance.
Therefore, back pressure should be used only whenincreasing cylinder temperature or other changesare not effective or possible.
For all materials, the back pressure used (specificor inherent to the injection unit) will create somepressure on the melt in front of the screw. To controldrool at the end of the screw rotation, some suckback is required. This should be kept to a minimum.
Mold Temperature
The best mold temperature for long term partperformance would be just below the crystallizationtemperature of Delrin®, e.g., 155°C (311°F). Thistemperature would allow the polymer to crystallizein an optimum state and eliminate any risk of re-crystallization (post molding shrinkage). Obviouslyit is economically impossible to set the mold at thattemperature as the crystallization time becomesalmost infinite along with the cycle time.
Practically, a lower mold temperature is used,leading to shorter crystallization time (HPT), henceshorter cycle time, lower mold shrinkage but higherpost mold shrinkage (especially if parts are thenexposed to elevated temperatures). A compromiseshould be found depending on the temperature inuse and the required dimensional precision of themolded part short and long term.
For standard Delrin®, a mold temperature of80–100°C (176–212°F) is a good compromise fornormal use, giving relatively short crystallizationtime, high shrinkage but low post mold shrinkage(see “Dimensional Considerations,” page 30). Ahigher mold temperature will lead to higher moldshrinkage, longer cycle time but lower post moldshrinkage. It is specially recommended for highprecision parts used at high temperature. A lowermold temperature leads to shorter cycle time, lowermold shrinkage but much higher post mold shrink-age leading to stresses and distortion.
For toughened resins such as Delrin® 100 STand 500 T, the use of a lower mold temperature(50°C [122°F] ± 10°C [50°F]) is acceptable withoutendangering long term part performances.
Note 1: “Mold temperature” is always the termused but the important parameter is the surfacecavity temperature. With fast cycling operations, itmay be necessary to use a lower mold coolanttemperature to maintain the mold surface tempera-ture in the recommended range. Chilled water isoften used for very short cycles or to cool core pinsand other mold sections that tend to run very hot.
Note 2: Coolant: Closed cooling circuits are themost common types used today. Coolants forclosed circuits need to resist heat, freezing, pressureand vacuum. They should neither leave deposits inthe circuit, nor corrode the cooling channels andtubes (tubes can be in steel, copper, plastic, rubberetc.). By analogy, the situation is similar to automo-tive engine cooling systems, and hence it is recom-mended to use the same fluid (anti-freeze + corro-sion inhibitor) but in lower concentration. Initiallythe thermal exchange is less efficient than withwater, as the fluid is more viscous due to the glycol(more power is needed for turbulent flow). How-ever, for long term use, a coolant (such as thoseused in cars) is the most effective solution (nocorrosion or deposit, low erosion from cavitation).
In the case of coolants for open tower circuits, thereis a need for chemical treatment to prevent build-upof micro-biological organisms that could causedisease and respiratory problems.
Operating Conditions for Delrin®
—Molding CycleIntroduction
As previously mentioned, the fact that Delrin® isa crystalline material leads to a molding cycledifferent from that of amorphous polymers. ForDelrin®, a molding cycle generally consists of thefollowing phases (see Figure 37):
A = Mold Open Time. This includes the OpeningTime, the Ejection Time and the Closing Time.
B = Filling Time or Injection Time. Molten resin isintroduced into the mold in a “dynamic fillingphase.”
C = Hold (Pressure) Time. During this “packingphase,” the resin is solidified under pressure,while additional resin is introduced into themold to compensate for volume shrinkageoccurring within the mold.
D = Screw Retraction Time. The screw rotates andprepares new molten material for the next shot.
2
E = Cooling Time. Since the part is crystallized(solid) and ready to be ejected at the end of theHPT, there is no need for a cooling time; hencethe cooling time is only the Screw RetractionTime plus a short safety time.
The Overall Cycle Time (OAC) for Delrin® is theaddition of the various times set for each of themolding operations.
Figure 37. The Molding Cycle for Delrin®
B. Filling time
E.Cooling time
C. Hold (pressure)time
A. Mold opened
D. Screw retraction time
Note: Frequently the sum of the Filling (Injection)Time and the Hold (Pressure) Time is defined asScrew Forward Time (SFT), as often stated inprevious Delrin® literature.
The cycle estimation graph in Figure 38 shows arange of total cycle times that have been used forgood quality molding of Delrin® in parts of variousthickness. The actual cycle will be close to thelower limit when a high productivity resin such asDelrin® 1700 P is used and when end-use require-ments are less stringent.
Figure 38. Estimation of Overall Molding Cycle Timesfor High Quality Molding of Delrin® Parts
Wall thickness of the part, mm
Tota
l cyc
le ti
me
OA
C, s
3 4 5 61 20
30
50
70
90
110
10
In this arearisk of porosity,voids, warpage
5
Filling Phase
Injection Time
The optimum fill rate for a mold depends on thepart geometry and thickness, the runner size, thesize and location of the gate.
As rule of thumb, a filling time of 1 sec per mm(0.04 in) of part thickness is a good starting pointfor fill speed setting. The surface aspect will governthis adjustment. Higher and more uniform surfacegloss can be obtained if the injection rate is fastenough to allow the cavity to be filled before theresin begins to solidify, although localized surfaceflaws, such as jetting and gate smear, are oftenreduced by decreasing the initial injection rate.
If maximum part toughness is required for theapplication, the shear applied to the material in therunner(s) and part should be checked to ensureoptimum molding performance and part properties.Figure 39 shows the impact performance of a2 mm (0.08 in) part versus the shear during filling.If needed, please contact your DuPont representa-tive to analyze your specific case.
Note: Minimizing the shear in the gate can alsobe an important factor towards optimum partperformance.
Figure 39. Shear Strain Rate at the Wall (s–1) andImpact Resistance (J/m2) as Function ofthe Filling Time. This Data was Obtainedwith the Sample Shown (180 by 27 mmwith 2 mm thickness). For Impact Resis-tance, the Part is Clamped Under the Riband Hit by a Pendulum.
Filling time, s3 4 5210
0
Impact resistance, J/m-2
Shear rate at wall, s-1
Impact
Delrin® 500
With non-optimum gate designs (conical, excessivegate length), shear in the gate may become animportant limiting factor for part toughness.
With the optimum gate design presented in themold design section (dimensions that allow opti-mum packing during crystallization, gate length<0.8 mm), in most cases the shear at the gate has no
2
effect on part performance. Flow analysis should beperformed to check the shear at the gate for mold-ing very large parts only.
Injection Pressure
This terminology often leads to misunderstanding.
The so-called “injection pressure” serves to movethe screw and push the material in the mold. Duringthis dynamic filling phase, the pressure built up infront of the screw is only equal to the pressure dropin the mold, from the nozzle to the position of theflow front. There is no pressure at the flow frontitself during this dynamic filling phase.
Before the front of the flow reaches the end of themold (when around 95% of the part volume is full),the machine should switch from dynamic filling(under velocity control) to quasi-static feeding(controlled by the HOLD pressure). This is the V-Pswitching point. The hold pressure will then beapplied everywhere in the mold during the wholepacking phase. For a crystalline material, morematerial (≈14% for Delrin®) should be added tothe part to compensate the crystallization, leadingto a slow screw forward movement during Hold(Pressure) Time.
With that definition, the injection fill pressure canbe set to whatever value needed by the geometry ofmold (including runners), as long as the filling rateis adequate for the part performance.
In case the V-P switch is incorrectly set (no switchor too late of a switch), the inertia of the system willcreate a pressure peak at the end of filling, leadingto molded-in stresses and flash. For that reason, inmost practical cases it is safer to set the V-P switchpoint with distance rather than with pressure (aswould typically be done for an amorphous material).
Packing Phase
Hold (Pressure) Time (HPT)
The recommended Hold (Pressure) Time (HPT) forDelrin® is the time for the molten polymer to fullycrystallize in the mold cavity.
As the crystallization (solidification) leads to alarge volume drop (≈14%, see page 4), more meltedmaterial has to be pushed into the cavity during allthe HPT. This leads to special design rules for thegate and runners, as discussed in the Molds section,so that the gate will not freeze before the cavity isproperly packed.
The HPT is obviously a function of the part thick-ness. Figure 40 shows the optimum HPT forDelrin® 500 as a function of the part thickness (withthe recommended HPT of 85 MPa (12.3 kpsi or12,300 psi) and the recommended mold tempera-ture of 90°C [194°F]).
6
Note: For the Delrin® Eleven Series resins, theenhanced crystallization leads to a shorter HPT ofup 10%.
To check the efficiency of the HPT for a given partgeometry, the traditional method is to plot the partweight as a function of the HPT. The maximumpart weight should correspond to the optimum HPTthat can be read in Figure 40 for the part thicknessat the gate. At this time, the part is solidified andno more material can be added to the part. As anexample, Figure 41 shows the effect of HPT onpart weight for a 4 mm thick ISO test bar. Figure41 also shows the evolution of part shrinkage withthe HPT, which will be discussed in more detail in“Dimensional Considerations” (see page 30).
Figure 40. Hold (Pressure) Time Versus Part Thick-ness of Delrin® 500
Figure 41. Hold (Pressure) Time Versus Part Weightand Mold Shrinkage of Delrin® 500
Hold (pressure) time, s
Part
wei
ght,
g
Mol
d sh
rinka
ge, %
40 50 6020 30100
17.2
17.4
17.0
16.8
16.6
Test bar thickness, 4 mm
16.4
16.2
16.0
3.2
3.0
2.8
2.6
2.4
2.2
2.0
15.8
Hold (pressure) time for part crystallization, s
Part
thic
knes
s, m
m
Part
thic
knes
s, in
10060 8040200
Mold temperature, 90°C (194°F)
1
2
3
4
5
6
7
0
0.280
0.200
0.100
0.040
2
Another technique to define optimum HPT, usinginstrumented molds, has been developed and ispresented as an appendix later in this guide.
All the above considerations on HPT and its effectsassume that the non return valve functions properlyand maintains a cushion of melt in front of thescrew as discussed earlier in the “Injection MoldingUnit” section.
Too short or inefficient HPT leads to higher thannormal and uncontrolled shrinkage. Additionalside-effects such as voids, porosity, warpage, sinkmarks should be expected (see “DimensionalConsiderations”).
Hold Pressure
Optimum hold pressures for Delrin® acetal resinslie in a range of 60–110 MPa (8.7–16 kpsi) toachieve an homogeneous crystallization. If higheror lower pressures are used in special conditions,they tend to lead to lower part performance. Thefollowing table shows the hold pressure rangerecommended for the various Delrin® types.
Hold pressure,Resin type Grades of Delrin® MPa (kpsi)
High viscosity 100, 100 P, 111 P 90–110 (13–16)
Medium- and 500, 500 P, 511 P,low-viscosity 900 P, 911 P, 1700 P 75–100 (11–14.5)
Toughened 100 ST, 500 MT, 500 T 60–80 (8.7–11.6)
To obtain a homogeneous crystallization, the holdpressure should remain constant until the part isfully packed (solidified).
Clamping Force
This does not really belong to the description of themolding cycle, but it is directly correlated to thehold pressure and for that reason it is discussedhere.
The clamping force is the force required to keep themold closed during filling and hold (pressure) time.This force is calculated by multiplying the pro-jected area of the cavity (cavities), including runnersystem, by the maximum internal pressure (the holdpressure).
Commonly, molds are set using the maximumclamping force of the molding machine. Howeverin many cases, the machine used has a much higherclamping force than actually needed. In theseconditions, it is recommended to lower the clamp-ing to the force actually needed by the mold (seecalculation following). This will prevent excessivepressure at the parting line (compression of the
7
vents, hobbing of the parting line, deformation ofthe mold components), leading to longer lifetime ofthe mold and less costly mold maintenance.
Estimating the maximum internal pressure can bedone by carrying out a flow analysis. However, forparts with a flow length to thickness ratio less than100 to 1, normally the internal pressure is equal tothe hold pressure. The following guidelines can beused:
1. For parts needing optimum mechanical proper-ties, the specific clamping pressure must be1 ton/cm2 for Delrin® 100, and 0.85 ton/cm2 forother Delrin® grades.
Example calculation:• projected area of part (or parts), including
runner system = 115 cm2
• material = Delrin® 500• machine clamping force required =
115 × 0.85 = 98 tons
2. For parts not requiring optimum mechanicalproperties, it may be possible to mold accept-able parts with lower specific hold pressures(and lower clamping forces).
Plastification Phase
Screw Retraction Time
Given a fixed amount of resin to plasticize for thenext shot, the screw retraction time is directlydependent on the screw rotation speed.
It is crucial to check that the applied screw rotationspeed is low enough to avoid over-shearing theresin in the barrel (which may lead to degradation),but high enough to provide a homogeneous melt(with no unmelted particles). This can be done withthe two practical tests for the presence of unmeltand degraded material, as described on page 12.
Note: since Delrin® is a highly crystalline polymer,its thermal requirements are different from those ofamorphous materials. Screws specifically designedfor Delrin® and an appropriate ratio of shot weightto machine capacity provide an efficient plastifi-cation. For more details about screw dimensions,see pages 9–10.
Cooling Time
The cooling time is an important parameter for theinjection molding of amorphous polymers. Thesituation is completely different with Delrin® (seealso pages 6–7). At the end of a correctly set andefficient hold pressure time (HPT), the Delrin® partis crystallized and solid. There is no need forfurther cooling time, and the part could in principlebe ejected immediately from the mold. This can bedemonstrated by stopping the cycle at the end of theHPT and ejecting the part immediately.
28
In most practical cases the part is ejected after thescrew retraction time, so the cooling time (asdefined in Figure 37) is simply the screw retractiontime plus a small safety margin. An exception is thecase of machines with shut-off nozzles, where partejection can take place during the screw rotation.This theoretically gives shorter cycles, althoughpractical problems may arise and limit productivity(see page 11 for more details on shut-off nozzles).
Optimum Productivity MoldingEconomic constraints are pushing for lower partcost, which can be reached by increasing the yieldof quality parts and/or shortening the Over AllCycle time. This guide recommends the parametersto achieve optimum part properties in the short andin the long term, leading to an optimum Over AllCycle time (OAC).
Any modification to the cycle should be done onlyafter realistic evaluation of part performance shortand long term. Decreasing the cycle too much maylead to a) lower part properties and other qualityproblems (especially shrinkage, warpage and postshrinkage), and b) process not running in a robustarea, which could lead to lower yield of qualityparts and higher part cost.
Before trying to shorten the current OAC, thefollowing items should be considered:• The design of the part may not be optimum, i.e.,
the part may be too thick. Changes to the design(adding ribs, use of pins) are costly but mayallow significant reduction of the cycle time.
• The design of injection unit may not be optimum.With Delrin® the cooling time can be minimizedto the time required for proper screw retraction.Optimum screw size and design will facilitate this.
• The sorting of parts from runners may not beoptimized.
Having decided to decrease the OAC, the followingactions may be carried out (in order of increasingrisk):• Investigate obvious bottlenecks in the cycle.• Minimize the Mold Open stroke.• Minimize the Mold Open time by increasing the
opening/closing speeds. Rubber bumpers orsprings can be used to prevent banging of thefloating plate in 3 plate molds, giving no effecton part quality.
• Minimize time between the screw stopping andthe mold opening. No effect on part quality.
• Minimize Filling Time (faster injection fill). Itmay result in overshearing and decreased weldline strength. Larger nozzle and runners, as wellas improved venting may be required.
• Decrease Screw Retraction Time:1. Use a larger screw and limit the stroke to
between 1 and 2 screw diameters, no effect onpart quality.
2. Use an optimized screw design for Delrin®
(screw for crystalline polymers with correctdepth of metering zone, mixing head). Thisensures a homogeneous melt even at highscrew rotation speeds, hence there are noeffects on part quality. Using higher screwrotation speeds with a general purpose screwwould reduce SRT, but with the risk of poormelt quality and part failure.
Note: as there is no need for cooling time,shutoff nozzles (where the screw can berotated during mold opening) have been tried.Unfortunately, problems such as wear, con-tamination, hold up spots etc. have beenobserved, and no long-term satisfactorysolution was found.
TabProcessing conditions for
Delrin® 100, DelResin grade 100 P, 111 P 511
MedHigh viscosity lowpolyacetal poly
Characteristics homopolymer hom
PretreatmentMoisture level for processing <0.2% <0.2Drying temperature, °C (°F) 80 (176) 80 (Drying time, hr 2 hr 2 hr
General parameterType of screw HC screw HC Max. screw tangential speed, m/s 0.2 0.3Melt temperature, °C (°F) 215 (419) ± 5 215 Mold temperature, °C (°F) 90 (194) ± 10 90 (Hold pressure, MPa 90–110 75–Back pressure, MPa <1.0 <0.2
Specific parameters, insert AInjection fill time, s 1–5 0.5–Flow front velocity, mm/s 40–200 100–Hold (Pressure) Time, s 35–45 35–Cycle time, s 40–60 40–
2
• Decrease Hold (Pressure) Time. With a lowerthan optimum HPT, higher mold shrinkage anddeformation leading to warpage will be seen.Voids will also be formed in the center of thepart, leading to lower mechanical properties(lower elongation at break), and quality controlshould be carried out on larger lots of moldedparts. If the mold temperature is decreased as anattempt to compensate for the shorter HPT, thisaction will lead to a lower mold shrinkage butwill result in very high post molding shrinkage,deformation and warpage.
Standard Molding Conditionsfor ISO Tensile BarsStandard processing parameters to injection moldDelrin® into tensile bars ISO 294-1 are shown inTable 5. They can help molders in establishingmolding parameters when processing Delrin® acetalresins. However, it must be emphasized that forparts of different shapes and dimensions suchparameters should be modified using the informa-tion presented on pages 30–35.
le 5ISO 294 tool (insert type A)
rin® 500, 500 P,P, 900, 900 P, 911 P Delrin® 100 ST Delrin® 500 T
ium and Super tough Toughened viscosity high viscosity medium viscosityacetal polyacetal polyacetalopolymer homopolymer homopolymer
% <0.05% <0.05%176) 80 (176) 80 (176)
4 hr 4 hr
screw HC screw HC screw0.15 0.3
(419) ± 5 205 (401) ± 5 205 (401) ± 5194) ± 10 50 (122) ± 10 50 (122) ± 10100 60–80 60–805 <1.0 <0.25
2 0–5 0.5–2400 40–200 100–400
45 25–35 25–3560 35–50 35–50
9
Hold Pressure Time via In-cavityPressure MeasurementThis technique has been developed during recentyears, particularly for amorphous resins. The mainobjective was to optimize and control the holdpressure profile in order to reduce internal stresses,which have been a frequent cause of failure ofmolded articles in amorphous polymers.
Even if such problems of internal stresses do notapply to a crystalline polymer like Delrin®, thistechnique is proving to be an effective method todetermine the crystallization time (HPT) of a partmolded with a specific polymer grade at givenprocessing parameters.
A flexible data acquisition system has been set upby DuPont. It consists of a computer with a dataacquisition card and proprietary software CAVAN(CAVity ANalysis), and allows all available analogsignals (e.g., injection fill speed, hydraulic pressure,etc.) to be acquired, displayed and analyzed. Thesystem measures the crystallization time of eachcycle with a precision, depending on the sensorlocation, down to 0.1 sec.
A single pressure sensor close to the gate is usuallysufficient to determine the crystallization time of aDelrin® part. This is done within a single moldingcycle, by analysing the pressure changes during thepacking phase. Figure 42 shows a typical CAVANcurve from which the Hold (Pressure) Time of a2 mm (0.08 in) thick Delrin® part can be determined.
Figure 42. Cavity Pressure Measured During theFilling and Packing (1 sensor)
Time, s
00
In-c
avity
pre
ssur
e in
MPa
20
40
2 4 16 1812 148 106
20
80
60
Hold (Pressure) Time
Dynamicfillingtime
Single pressure transducer Delrin® 500 wall thickness: 2 mm
3
Dimensional ConsiderationsDelrin® acetal resins have good dimensionalstability, compared to other polymers, over a widerange of temperatures and in the presence ofmoisture, lubricants or solvents. They find exten-sive use in industry for the fabrication of precisiongears, bearings, housings and similar devices,because of their unique combination of dimensionalstability with other properties, such as fatigueresistance and tensile strength. However, as with allmaterials of construction, there are factors affectingthe dimensional stability of Delrin® which must beconsidered when close tolerances are essential.
Fundamentals of DimensionalControlThe dimensions of a molded part are determinedprimarily by the dimensions of the cavity, andsecondly by all those variables that affect resinpacking and crystallinity (for example hold pres-sure, HPT, mold temperature). It may seem obviousto mention cavity dimensions as the main factor forpart dimensions; however experience has demon-strated that dimensional problems are often ad-dressed by changes in molding conditions, generallywith a limited success. Isotropic dimensionalproblems can in principle be corrected by changesto hold pressure. In the more frequent cases where afew dimensions are out of specification, attempts tocorrect with the molding parameters generallygreatly reduce the acceptable processing window,leading to a higher risk of rejects.
Mold shrinkage and post-mold shrinkage occuras natural consequences of the molding process.They influence the tolerances that can be obtainedfor molded parts. Data on these effects are pre-sented in this section.
Further dimensional variations in molded parts ofDelrin® can arise from changes in the temperatureor nature of the surroundings. Reversible changesresult from thermal expansion or contraction andfrom absorption of water or other solvents. Theseare discussed later in this section, under “Environ-mental Changes.”
Irreversible changes in dimension occur whenpolymer chains frozen in an unstable conditionmove towards a more stable state. An example iswhen parts molded in a tool at low mold tempera-ture are exposed to elevated temperatures. Thesechanges are discussed under “Post-Mold Shrink-age” and “Annealing.”
0
Mold ShrinkageMold shrinkage is the shrinkage that occurs within24 hr of molding. It is defined as the differencebetween cavity and actual part dimension, bothmeasured at room temperature. It is due to thedifference in specific volume of Delrin® at thecrystallization temperature and its specific volumeat room temperature (see “PVT Diagrams,” page 4).
The typical mold shrinkage of Delrin® resins isbetween 1.8 and 2.2%, except for the supertoughand fiber-containing grades (Delrin® 100 ST,500 AF, 570 and 577) which have a lower shrink-age. Table 6 summarizes the average mold shrink-age of a 4 mm (0.16 in) thick part molded in thespecific recommended conditions. These valuesshould be considered as an approximate guide only,because the shrinkage for an actual part depends onits design and on the molding conditions, as de-scribed in more detail below.
Table 6Average Mold Shrinkage for Various
Grades of Delrin®
Average mold shrinkage
Delrin® grade in flow (% ± 0.2%) transverse (% ± 0.2%)
100, 100 P, 127 UV 2.1 1.9500, 500 P, 527 UV 2.1 2.0511 P, 911 P 1.9 1.8900, 900 P, 927 UV 2.1 2.01700 P 1.9 1.81727 UV 1.7 1.7colors* 1.8–2.1 1.7–2.0500 T 1.8 1.7500 MT 1.4 1.5100 ST 1.3 1.4500 TL 1.9 1.9500 AF 2.1 1.5500 CL, 500 AL 1.9 1.9570, 577 1.2 2.1510 GR 1.0 1.4525 GR 0.5 1.2
* depends on the pigments
Tab
Parameter Effect on Shrinkage
Hold (Pressure) Time (HPT) ➘
Hold Pressure ➘
Mold Temperature (cavity) ➚
Part Thickness ➙ or ➘Gate Thickness ➘
Melt Temperature ➙
Key parameters affecting mold shrinkage: Symbol ➚ means that the shrinkage increaSymbol ➙ means that there is no effect on shrinkage provided that the conditions list
3
Factors Affecting Mold ShrinkageMold shrinkage is dependent on the factors thataffect the crystallinity of Delrin®. These include:• hold pressure• hold (pressure) time• mold temperature• part thickness• gate dimensions
Table 7 summarizes the effect of these parameterson mold shrinkage. They are discussed in moredetail below.
Furthermore, mold shrinkage is also highly depen-dent on the geometry of the part and on the flowpattern of the resin. Experiments have been done inour laboratory with 180 × 27 mm plaques withthicknesses from 1.5 to 6 mm. Four values ofshrinkage were measured, close to and far from thegate, parallel and perpendicular to the flow. Formost Delrin® grades it is observed that the shrink-age is higher far from the gate than close to the gate(typically by 0.1 to 0.3%), and that the shrinkage inthe flow direction is about 0.1% higher thantransverse to the flow.
Hold Pressure
Injection pressure has two functions in the moldingprocess:
1. Transfer the molten polymer from the injectionunit into the mold. This “injection fill pressure”is needed only to overcome the resistance toflow of the polymer from the injection unit tothe cavity. Usually this is a high speed process(dynamic phase of the screw).
2. Control the packing and crystallization process.The hold pressure pushes more material intothe cavity to compensate for the volumereduction that occurs in the polymer duringcrystallization. This is a low speed process(slow motion of the screw). This phase is moreimportant for the dimensional stability since it
le 7
Remarks
up to optimum HPT, then no effect
but post-mold shrinkage ➘
if all settings optimizedup to optimum thickness, then no effect
if mold temperature is kept constant and HPT is optimized
ses when the value of the parameter increases, and the opposite for the symbol ➘ .ed under “Remarks” are met.
1
Figure 44. Effect of Hold (Pressure) Time on MoldShrinkage of Delrin® 500 P
Hold (Pressure) Time HPT, s
Mol
d sh
rink
age,
%
10 20 30 40 50 60 70 80 900
2
2.2
2.4
2.6
2.8
3
3.2
3.4
1.8
6 mm
4 mm
1.5 mm
Optimum HPT1.5 mm 10 seconds 4 mm 40 seconds 6 mm 80 seconds
Molding conditions:Hold pressure 90 MPa (13 kpsi)Mold temperature 90°C (194°F)Melt temperature 215°C (419°F)
helps maintain a uniform and gradual crystalli-zation. When a lower hold pressure is used, itwill pack less material into the cavity and theshrinkage will be higher. This is shown inFigure 43 for three mold temperatures.
Small changes of hold pressure may be used to helpfine tune the dimensions of a part, because thisparameter is essentially independent and hasrelatively small adverse effects.
Note that hold pressure should be constant duringthe whole packing time.
Hold (Pressure) Time (HPT)
Hold (Pressure) Time is the time during which thehold pressure is applied. The HPT is important forthe value of shrinkage and its uniformity over thepart.
Figure 44 shows the effect of HPT on moldshrinkage for Delrin®.
When the HPT is below the optimum value re-quired for the specific part (see pages 26–27), thepacking process is interrupted before completionand mold shrinkage is higher than its optimumvalue. Additional side-effects of a short HPT areporosity, voids, warpage, sink marks, lower me-chanical properties.
On the contrary, any increase of HPT above itsoptimum value would have no effect on moldshrinkage, because the part (and the gate) arealready solidified.
Figure 43. Effect of Hold Pressure on Mold Shrinkageat Three Mold Temperatures, for Delrin®
500. Hold Pressure Can be Used for SmallAdjustments of Part Dimensions, as ithas Negligible Effect on Post-MoldingShrinkage.
Hold pressure, MPa
Mol
d sh
rink
age,
%
140100 12080
1.6
1.7
1.8
1.9
2
2.1
2.2
2.3
1.5
Part thickness 4 mm (0.16 in)Melt temperature 215°C (419°F)
HPT optimized for thickness and mold temperature
Mold temp. = 100°C (212°F)HPT = 43 s
Mold temp. = 90°C (194°F)HPT = 39 s
Mold temp. = 80°C (176°F)HPT = 36 s
32
Mold Temperature
Mold temperature influences mold shrinkagethrough its effect on cooling rate and crystallizationtemperature of the molten polymer. The effect ofmold temperature on shrinkage is also shown inFigure 43.
At high mold temperatures, the polymer crystallizesslowly. In such conditions the mold shrinkage is high,but since the crystallization is more complete, a betterlong-term dimensional stability is to be expected forthe molded parts (less post-mold shrinkage).
Low mold temperatures, on the other hand, tend tocool the polymer at a very high rate. This results ina lower mold shrinkage and better toughness.However, in the long term, higher dimensionalvariations leading to build up of internal stresseswill occur, particularly if the part is exposed duringits end-use life to temperatures exceeding the moldtemperature at which the part was molded.
Part Thickness
As shown in Figure 44 for Delrin® 500, the thick-ness has a minor influence on mold shrinkage,provided that the gate dimensions and the Hold(Pressure) Time are correct for each thickness.Figure 45 shows the shrinkage of various Delrin®
compositions vs. part thickness, as measured withcorrect HPT. Note that, to optimize toughness, themold temperature is reduced from 90°C (194°F) forthe standard grades to 50°C (122°F) for the tough-ened grades (without leading to a high post-mold-ing shrinkage).
For parts of uniform wall thickness, the moldshrinkage tends to be uniform. In the case ofvariable thickness, shrinkage will tend to be nearly
uniform if the part is gated into the thickest section,if the gate is properly sized and if the Hold (Pres-sure) Time equals or exceeds the gate freeze time.When these criteria are not met, the mold shrinkagetends to be greater for larger sections, with possibleproblems of voids, warpage, sink marks and lowermechanical properties.
Gate Dimensions
Adequate gate dimensions are required to ensureproper packing of the part (see “Gates,” pages 13–15).
When the thickness of the gate is smaller than itsoptimum value, mold shrinkage will increase due tothe premature solidification of the resin at the gate.This situation is then equivalent to a shorter Hold(Pressure) Time, and the approximate effect onshrinkage can be observed in Figure 44. In thisrange the mold shrinkage is not stable, and it is verydifficult to control. The resulting warpage couldeven make difficult the measurement of certaindimensions of the part.
Melt Temperature
Melt temperature has an effect on mold shrinkage.It is however limited by the narrow range of melttemperatures needed to maintain a consistentquality of the molded part. Consequently, the melttemperature should not be considered as a variableto adjust mold shrinkage.
Mold Shrinkage of Filled ResinsThe mold shrinkage of compositions containingfibrous fillers, such as Delrin® 570 (glass) andDelrin® 500 AF (Teflon®), is less predictable,because of the fiber orientation effects. The shrink-age in the direction of flow tends to be significantly
Figure 45. Average Mold Shrinkage Versus Thick-ness, for Various Delrin® Compositions
1.6
Mol
d sr
hink
age,
%
Thickness, mm0
1.2
1
2.2
2
82 4
100 P, 500 P
500 T
100 ST
6
1.4
1.8
33
different from that in the transverse direction (seeFigure 45).
In general, the mold shrinkage of Delrin® 500 AFin the flow direction is similar to that of Delrin®
500. The mold shrinkage in the transverse direction,however, ranges up to 50% of the shrinkage ofDelrin® 500.
In contrast, the mold shrinkage of Delrin® 570 inthe flow direction is about half of that for Delrin®
500. In the transverse direction, the mold shrinkageof Delrin® 570 approaches that of Delrin® 500.
Effect of PigmentsThe presence in the melt of crystallization nucleisuch as pigments and regrind can have an influenceon crystallization and consequently on moldshrinkage.
An accurate study has been carried out to evaluatethe effect of various types of pigments on the moldshrinkage of Delrin®. It appears, as depicted inFigure 46, that pigment systems giving the sameresin color may have a different effect on moldshrinkage and part dimensions.
Note: This study has been carried out on standardbars and in typical molding conditions. The shrink-age values shown here should not be consideredvalid for all parts of different geometry and/ormolded in different molding conditions.
Figure 46. Effect of Selected Pigments on MoldShrinkage of Delrin® 500. Part Thickness2 mm
Color
Shri
nkag
e, %
NC-
10
Yello
w
Beig
e
Mau
ve
Whi
te
Red
(1)
Blue
(1)
Blue
(2)
Blac
k
Purp
le
Gree
n (1
)
Gree
n (2
)
Pink
Brow
n
Red
(2)
1.80
1.90
2.00
2.10
2.20
1.70
Post-Molding ShrinkagePost-molding shrinkage is defined as the shrinkagewhich takes place more than 24 hr after molding. Itis a consequence of continued crystallization andrelaxation of molded-in stresses, where the resinmoves towards a more stable state.
The post-mold shrinkage of parts molded in Delrin®
can be estimated from Figure 47.
Figure 47. Post-Molding Shrinkage of Delrin® AcetalResins
1.0
Post
-mol
ding
shr
inka
ge, %
Exposure temperature, °C (°F)
50 80 11020
0.2
0
1.2
1.4
1009040 706030
0.4
0.6
0.8
40°C mold
65°C mold
95°C mold
120°C mold
AnnealedAll mold temperatures
0.6
Post
-mol
ding
shr
inka
ge, %
Exposure temperature, °C (°F)
50 80 10020
0.2
0
1.0
11060 70 9030 40
0.4
0.8 40°C
mold
65°C
mold
95°C m
old
120°C mold
AnnealedAll mold temperatures
Thickness – 0.8 mm (0.03 in)
Thickness – 1.6 mm (0.06 in)
0.7
50 80 11020
0.4
01007060 9030 40
0.5
0.6
0.3
0.1
0.2
Thickness – 3.2 mm (0.125 in)
Exposure temperature, °C (°F)Exposure time = 1,000 hr
Post
-mol
ding
shr
inka
ge, %
40°C mold
65°C mold
95°C mold
120°C mold
AnnealedAll mold temperatures
(104) (176)(68) (212)(140)(122) (194)(86) (230)(158)
(104) (176)(68) (212)(140)(122) (194)(86) (230)(158)
(104) (176)(68) (212)(140)(122) (194)(86) (230)(158)
Parts molded with the recommended mold tempera-ture (90°C [194°F]) or higher will have a low post-mold shrinkage, which ensures good dimensionalstability over the lifetime of the part.
However, parts molded with a cold mold (<80°C[<176°F]) will have a higher post-mold shrinkage,because fast cooling leaves the Delrin® in anunstable crystalline state and results in more signifi-cant recrystallization. If such Delrin® parts are thenexposed to high temperatures, the recrystallizationcauses a high and rapid post-mold shrinkage.
Remarks:
1. For parts requiring tight tolerances and expo-sure to elevated temperatures for prolongedperiods of time, it is strongly recommended touse high mold temperatures (up to 120°C[248°C]). This provides a more effectivesolution than annealing a part molded at lowmold temperature.
2. For exposure at moderate temperatures, gooddimensional stability and part performancecan be achieved using a 90°C (194°C) moldtemperature.
Insert MoldingAlmost all the problems of insert molding arelinked with shrinkage around the insert, moldshrinkage and post-molding shrinkage. To mini-mize total shrinkage, the following should be takeninto consideration:• High mold temperatures should be used (90°C
[194°F] or above) in order to minimize the totalshrinkage (sum of mold shrinkage and post-moldshrinkage). At lower temperatures the moldshrinkage is indeed smaller, but the post-moldshrinkage is much higher.
• Optimum Hold (Pressure) Time for the partthickness, to minimize part shrinkage. Theshrinkage increases dramatically with shorterHPT (see Figure 44).
• Inserts should be preheated to the same tempera-ture as the mold. This is very important for largeinserts.
• Inserts should be free of sharp corners andcontamination.
• To minimize cracking, high-viscosity Delrin® isrecommended due to its higher elongation.
Note: If a cracking problem cannot be overcomeby using the above measures, other insertingtechniques should be evaluated, such as insertionafter molding by press-fitting, insertion by sonicenergy, or a self-tapping insert.
34
AnnealingAnnealing is occasionally used to accelerate stressrelaxation and dimensional stabilization of parts.It is a complex process and should only be usedwhen molded parts require very tight tolerances andexposure to high temperatures for prolonged periods.
Figure 48. Environmental Dimensional Change ofDelrin® 100 and 500
Chan
ge in
leng
th, %
12040 8020 100600(248)(104) (176)(68) (212)(140)(32)
0.2
0.4
0.6
0.8
1.0
1.2
1.4
0
Immersion
100% RH
80% RH
50% RH
0% RH
Temperature, °C (°F)
Annealing is also suggested as a test procedure insetting up molding conditions on a new mold, toevaluate post-molding shrinkage and molded-instresses. The changes in dimensions during anneal-ing will closely represent the ultimate change inpart size in use.
When dimensional precision is a prime requirement,the use of a high mold temperature (90–120°C[194–248°F]) is strongly recommended. Attemptsto reach good dimensional stability by annealingparts molded in a cold mold (<80°C [<176°F]) willlead to high post-molding shrinkage and mayintroduce stresses during the re-crystallizationprocess, resulting in uncontrolled deformation.
Annealing Procedure
Annealing should be performed in air or in inertmineral oils at 160 ± 3°C (320°F), for 30 minutes+ 5 minutes per mm of wall thickness. Overheatingand hot spots should be avoided, and parts shouldneither contact each other nor the walls of the oven/bath. Parts should be left in the oven to cool slowlyuntil 80°C (176°F) is reached. Stacking or piling,which may deform the parts while they are hot,should be delayed until the parts are cool to thetouch. This procedure was used to obtain the resultsshown in Figure 47, and permits evaluation of theultimate dimensional changes that a part is likely toexperience in normal use.
To simply stabilize parts for continuous hightemperature use (<90°C [<194°F]), parts may beheated to 90°C (194°F) for up to 24 hr. Post-molding shrinkage of around 0.1 to 0.2% will thenbe seen if the parts were molded in a mold at90°C (194°F) ± 10°C.
Environmental ChangesPart dimensions of Delrin® acetal resin change withthe environmental temperature and with the absorp-tion of small amounts of water. Data concerningdimensions for various Delrin® acetal resins areplotted in Figure 48, which combines the effects ofmoisture content and temperature. The graph showsseveral lines representing different exposureconditions with respect to moisture (50% RH,80% RH, 100% RH, and immersion).
Dimensional TolerancesGeneral
Taking into account mold dimensions and process-ing variability, experience suggests that the follow-ing dimensional tolerances are achievable withgood molding practice:
3
• dimensions up to 150 mm (5.9 in):±0.15% for precision molding±0.3% for technical molding
• dimensions above 150 mm (5.9 in):±0.25% for precision molding±0.4% for technical molding
Molds
For multi-cavity molds, the tool making tolerancesare important. They have a direct effect on thedimensional tolerance of the part. As an example,for a mold dimension of 30 mm (1.2 in) manufac-tured to within ± 0.01 mm, experience has shownthat dimensional consistency better than ± 0.03–0.04mm cannot be expected for parts from differentcavities in a single shot.
Molding Conditions
Parts molded under recommended conditions (gate,runner, nozzle, screw, machine parameters) asdefined in the molding guide are subject to smallshot-to-shot variations in dimensions. Any changein machine parameters or conditions will effectdimensional tolerance. For example, a colder moldleads to higher post-molding shrinkage, too shortHold (Pressure) Time leads to inconsistent shrink-age, deformation and larger variability in partdimensions.
5
Auxiliary OperationsSeveral auxiliary operations associated with themolding of Delrin® acetal resins are discussed inthis section. They include the following subjects:• Material handling• Drying• Reground resin• Coloring• Disposal
Material HandlingDelrin® acetal resin is shipped dry and need not bedried before molding. Resin that has been stored ina cold warehouse area should be brought to roomtemperature prior to molding. This will preventmoisture condensation and variations in heatrequired to melt and thus in melt temperature.
Particular care is required for the toughenedcompositions of Delrin®. Bags of Delrin® 500 T,500 MT and 100 ST should not be opened untilthey are ready to be used. If a bag is opened for anysignificant period of time and the resin has pickedup moisture, the material should be dried before itis molded.
Pellets of Delrin® are surface lubricated withethylene di-stearamide. Further lubrication of thesecompositions is not necessary.
Reground ResinRecommendations to Regrind Delrin®
The use of contamination free and uniformlyreground Delrin® has minimal influence onmechanical properties and molding performanceof standard grades (see details below). To regrindthe material properly, the following should beconsidered:• Do not regrind molded parts, sprues or runners
that are discolored or splayed—these conditionsmay indicate that the resin was degraded duringprocessing.
• Avoid accumulation of reground resin wheneverpossible by continuous reuse of sprues andrunners. Ideally regrind at the molding machineand feed back immediately using a close loopsystem to avoid any contamination. If grinding isdone in a batch process away from the moldingmachine, care should be taken to avoid contami-nation of sprues and runners. Protect regroundresin from contamination and dirt by storing inclean, dry, clearly labelled, covered containers.
• Maintain a constant ratio of virgin to regroundresin, and mix adequately prior to molding. Asuitable ratio depends upon the quality of the
3
reground resin and the requirements of the part. A3 to 1 ratio of virgin to reground resin is common,although larger quantities of reground resin canbe used successfully.
• Ideally use a low speed grinder, but higher speedgrinders are acceptable if knives are well sharp-ened and if holes in the screen are large enough(4 mm) to avoid fines. The grinder should bethoroughly cleaned before grinding a differentmaterial.
• Excessive fines should be removed.• Avoid reprocessed resin from outside sources.• For optimum properties of toughened grades,
sprues and runners should be reground and usedas soon as possible, as moisture pick-up is fast forthese resins (see previous paragraph). Thefraction of regrind for these compositions shouldnot exceed 25% in the feed, and it should be fedimmediately back into the hopper.
Effect on Mechanical Properties
Figure 49 shows the results of a 10 pass regrindstudy which has been run using either 100% or 50%regrind with Delrin® 500. A 10 pass 50% additionregrind study is equivalent to a molder continuouslyregrinding 50% of the shot weight. Excellentretention of mechanical properties is observed inthese conditions.
DryingAs a general rule, Delrin® does not require drying.However drying is recommended in some cases.
Standard Grades
• When a resin container stays open for a signifi-cant time, drying at 80°C (176°F) for two hoursmay improve the melt quality. The water absorp-tion rate of Delrin® acetal resins at varioushumidity levels is shown in Figure 49.
• When using more than 50% of the capacity of themachine, preheating the resin at 80°C (176°F) fortwo hours may improve the homogeneity of themelt and decrease the torque on the screw.
• When thermal stability is a concern (e.g., withsome difficult colors), blowing air at 80°C(176°F) through Delrin® may help. This willresult in less mold deposit and better surfacefinish.
Toughened Grades
Molding of toughened Delrin® compositions withexcessive moisture (>0.05%) has a negative effecton toughness. Therefore, it is recommended that theresin is dried for 4 hr at 80°C (176°F) in a dehu-midified dryer (see the drying behavior of Delrin®
100 ST in Figure 50).
6
Figure 49. Rate of Water Absorption at VariousConditions
Figure 50. Drying Behavior of Delrin® 100 ST
Time, hr
Moi
stur
e, %
53 41 20
0.1
0.2
0.3
0.4
0.5
0.6
0
Hopper dryertemperature : 80°C (176°F)
Dew point : –23°C (–9°F)
Measurements were made on a shallowlayer of Delrin® molding powder.
Note:
Time, days
Wat
er b
y w
eigh
t, %
10 20 30 40 50 600
0.2
0.4
0.6
0.8
0
100% RH, 25°C (77°F)
83% RH, 25°C (77°F)
50% RH, 25°C (77°F)
12% RH, 25°C (77°F)
Delrin® 100, 500, and 900
3
At 23°C (73°F) and 50% RH, Delrin® 100 ST picksup 0.1% moisture in 4 hr; at 30°C (86°F) and 85%RH it will pick up 0.3% moisture in 2 hr. For thisreason runners and sprues should be reground andreused as soon as possible.
ColoringDelrin® is available in a range of standard andcustom colors.
When molding natural Delrin® with a coloringsystem from a manufacturer other than DuPont, thefollowing should be noted:• The pigment or masterbatch manufacturer’s safe
handling procedures must be applied.• Small scale tests should be run initially to check
melt stability (see page 12, foaming test), as someacidic, basic or metallic pigments will decomposeDelrin®.
• Different coloring systems (even those giving thesame color) could cause different shrinkages,as can be seen from Figure 46. Part dimensionsshould be checked in the small scale tests.
• Flow along injection unit screws is laminar andcolor dispersion could be unsatisfactory. A propermixing head should be used (see page 10).
• Total pigment loading should be as low aspossible to maintain resin properties.
DisposalWaste disposal must be in accordance with allapplicable regulations. Preferred options fordisposal are:
1. recycling,
2. incineration with energy recovery, and
3. landfill.
Recycling of sprue and runners is best done directlyat the molding machine (see Reground Resin, page36). Mechanical recycling of post-consumer parts israrely attractive. Since resin stability and mechani-cal properties can be severely affected by contami-nation, the separation and cleaning logistics becomecomplicated and expensive. Chemical recycling istechnically possible, but again it is presently limitedby waste collection and separation.The high fuel value of acetal resins makes option(2) very desirable for material that cannot berecycled. However, parts or regrind of resinscontaining Teflon® (such as Delrin® 500 AF and520 MP) should not be incinerated.
7
Troubleshooting Guide
Problem Suggested remedies (listed in order of convenience)
Melt quality problemsMold deposit • Decrease injection fill rate
• Decrease melt temperature• Avoid resin contamination• Correct hold-up spots in cylinder, screw, nozzle assembly• Increase gate size, flare gate• Enlarge vents• Change vent location• Use hopper drier to improve the resin’s thermal stability in extreme cases
Odor • Observe melt appearance (gassing) and measure melt temperature• Reduce cylinder temperatures if melt temperature is high• Avoid resin contamination• Reduce overall cyle to decrease holdup time• Correct holdup spots in cylinder, adaptor, nozzle, screw tip, and check valve assembly• Use smaller injection unit
Unmelted particles • Increase cylinder temperatures• Increase back pressure• Reduce screw rpm• Use hopper drier to preheat resin• Increase overall cycle• Use screw designed for Delrin®
• Use larger machine or injection unit
Screw deposit • Lessen severity of screw (esp. for Delrin® 100 flow grades)—within recommendations• Avoid overcooling the feed throat• Check % of feed/transition/metering—within recommendations
Black spots or brown streaks • Decrease residence time in injection unit (smaller screw)• Avoid resin contamination• Correct holdup spots in cylinder, screw, nozzle assembly• Check hopper cooling (80–90°C [176–194°F])
Pigment streaks • Increase back pressure to improve dispersion• Use a mixing head screw• Evaluate other coloring systems• Evaluate fully precompounded color
Filling problemsShort shots • Maintain uniform pad
• Repair leaking back flow valve if pad cannot be maintained• Increase injection fill pressure• Increase injection fill rate• Increase melt temperature• Increase mold temperature• Enlarge vents• Change vent location• Increase overall cycle• Use screw designed for Delrin®
• Use larger machine or injection unitNote: Minimize nozzle length when molding at or near limit of injection pressure capacity of molding equipment. This will be particularly true for Delrin®100 type resins having high melt viscosity.
Voids in parts • Increase hold pressure• Increase hold (pressure) time• Locate gate in thickest area• Decrease injection fill rate• Decrease melt temperature; improve melt uniformity• Repair leaking back flow valve if pad cannot be maintained• Enlarge vents• Improve gate thickness or location• Eliminate any restrictions in runner or nozzle
Weak weld lines • Increase hold pressure• Adjust injection fill rate (around 1 s per mm of part thickness)• Increase melt temperature, but avoid excessive temperature• Enlarge vents• Increase mold temperature• Avoid mold release spray• Change vent or gate location• Use larger machine or injection unit
38
Problem Suggested remedies (listed in order of convenience)
Ejection problemsParts sticking in mold • Increase hold (pressure) time
• Correct mold defects (undercuts)• Change or add ejector pin locations• Decrease hold pressure• Decrease injection fill rate• Increase cycle (possibly only temporarily)• Use mold release temporarily
Sprue sticking • Remove burrs on sprue• Correct alignment between sprue and nozzle• Radius sharp corners where the sprue meets the runner (or the part)• Increase hold (pressure) time• Increase nozzle temperature• Increase mold cooling time• Use nozzle orifice smaller than sprue bushing• Improve sprue puller• Increase taper of sprue• Use mold release temporarily
Dimensional problemsShot-to-shot dimensional variations • Increase injection hold pressure
• Maintain uniform pad (cushion)• Repair leaking back flow valve if pad cannot be maintained• Increase hold (pressure) time• Increase gate thickness and/or location• Maintain uniform cycle• Eliminate unmelted particles (see below)• Use larger machine or screw designed for Delrin®
Warpage • Balance mold temperature• Locate gate in thickest area• Increase hold (pressure) time• Increase gate thickness and/or location• Round sharp corner• Clean water channels in mold; improve mold cooling system• Improve part design (e.g., avoid bottlenecks in melt flow)• Change or add ejector pin locations
Surface problemsBlush, frost, and folds • Decrease injection fill rate
• Increase mold temperature• Change gate location
Gate smear • Decrease injection fill rate• Flare gate• Increase gate size• Change gate location
Jetting • Increase or decrease injection fill rate• Increase gate size, flare gate• Increase mold temperature• Change gate location
Pits, orange peel, wrinkles • Increase hold pressure• Increase injection fill rate• Increase hold (pressure) time• Increase mold temperature• Increase melt temperature• Enlarge vents• Increase gate size
Sink marks • Repair leaking back flow valve if pad cannot be maintained• Increase hold pressure• Increase hold (pressure) time• Increase gate size• Change gate location• Decrease melt temperature if it is too high
Splay • Decrease melt temperature if it is too high• Avoid resin contamination• Decrease injection fill rate• Correct holdup spots in cylinder screw, nozzle assembly• Increase size of small gate
39
40
Du
Po
nt
En
gin
eeri
ng
Po
lym
ers
Mo
ldin
g D
ata
Reco
rd
JOB
MOL
D DE
SCRI
PTIO
NM
ACHI
NE
SETU
P IN
STRU
CTIO
NS
SPEC
IAL
INST
RUCT
ION
S
OPER
ATOR
SSC
REW
USE
DSA
FETY
CHE
CK
ENGI
NEE
RSPR
ESS
NO.
NOZ
ZLE
#
COM
MEN
TS O
N M
OLDI
NG
OPER
ATIO
N, S
TART
-UP,
ETC
.
PAGE
NO.
DATE
TIM
E
Run Number
Resin
Lot Number
Rear
Center
Front
Nozzle
Fixed
Movable
Melt
Clamp (Tons)
Back
Injection
Hold
Open
Overall
Booster
Ram in Motion
Screw Retraction
Pad (Inches)
RPM
Full Shot
Part Only
Injection1st Stage
Injection2nd Stage
TEM
PERA
TURE
S, °C
(°F)
PRES
SURE
S, M
Pa (P
SI)
CYCL
E TI
MES
, sec
WEI
GHTS
, gRE
MAR
KS
Index
A
Adaptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Air Shots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Air Trapping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Annealing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30, 34, 35
B
Back Flow Valve . . . . . . . . . . . . . . . . . . . . . 7, 8, 9, 10, 38, 39
Back Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . 12, 24, 29, 38
Blowback . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3, 22
Brown Streaks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11, 38
Burning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
C
CAVAN Cavity Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Cavity Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Check Ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10, 11
Clamping Force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27, 28
Coloring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8, 12, 36, 37
Compositions . . . . . . . . . . . . . . . . . . . . . . . . . . 1, 2, 32, 33, 36
Compression Ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Contamination . . . . . . . . . 8, 10, 12, 22, 24, 29, 34, 36, 37, 39
Corrosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11, 19, 25
Crystallinity . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1, 3–6, 30, 31
Cushion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27, 39
Cycle . . . . . . . . . . . . . 3–5, 8–12, 18, 20, 23–25, 27, 28, 38, 39
Cycle Estimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Cylinder Temperature Control . . . . . . . . . . . . . . . . . . . . . . . . 9
D
Decomposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2, 3, 22
Degradation . . . . . . . . . . . . . . . 7, 8, 10, 11, 18, 22, 23, 24, 28
Delrin® 100 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Delrin® 100 ST . . . . . . . . . . . . . . . . . . . . . 2, 23, 25, 29, 36, 37
Delrin® 111 P . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Delrin® 1700 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13, 25
Delrin® 1700 P . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Delrin® 500 . . . . . . . . . . . . 1, 6, 7, 9, 24, 26, 27–29, 32, 33, 36
Delrin® 500 AF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2, 33, 37
Delrin® 500 CL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Delrin® 500 MT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Delrin® 500 P . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1, 32
Delrin® 500 T . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2, 23, 29, 36
Delrin® 511 P . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Delrin® 570 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2, 24, 33
Delrin® 900 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1, 24
Delrin® 900 P . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Delrin® 911 P . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Delrin® P . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Dimensional Stability . . . . . . . . . . . . . 1, 13, 30–32, 34, 35, 39
Disposal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Drool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3, 11, 23, 24
Drying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29, 36, 37
E
Ejection . . . . . . . . . . . . . . . . . . . . . . . . . 1, 3, 19, 20, 25, 28, 39
Elongation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2, 7, 29, 34
Emergency Shutdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3, 22
Environmental Dimensional Change . . . . . . . . . . . . . . . . . . 35
F
Fill Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26, 38, 39
Flash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19, 26
Flow . . . . . . . . . 1, 4–10, 13, 15–20, 22–26, 28, 29, 31, 37, 39
Foaming Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11, 12
Formaldehyde . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1–3
G
Gassing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11, 38
Gate Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14, 15, 21, 26
Gate Freeze Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Gate Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13, 38, 39
Gate Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38, 39
Gate Smear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13, 26, 39
Gates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5, 8, 13, 14, 16, 18
Glass Transition Temperature . . . . . . . . . . . . . . . . . . . . . . . . 4
Gloss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
H
Handling Precautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Heat of Fusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Hold Pressure . . . . . . . . . . . . . . . . . . . . . . 4, 25–27, 29, 30, 31
Hold Pressure Time . . . . . . . . . . . . . . . . . . . 25–27, 29, 30, 31
Hot Runner Molding . . . . . . . . . . . . . . . . . . . . . . . . . . . 18–19
Hold-Up Areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Hold-Up Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8, 23
41
I
Injection Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . 26, 31, 38
Injection Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Injection Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Insert Molding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
ISO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27, 29
J
Jetting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13, 26, 39
L
Lubricants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1, 3, 30
M
Material Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Melt Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Melt Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11, 38
Melt Temperature . . . . . . . . 6–8, 13, 22–24, 31, 33, 36, 38, 39
Melt Viscosity . . . . . . . . . . . . . . . . . . . . . . . . . . 1, 4, 6, 13, 38
Mold Deposit . . . . . . . . . . . . . . . . . . . 8, 12, 16, 18, 19, 36, 38
Mold Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12, 13, 26
Mold Maintenance . . . . . . . . . . . . . . . . . . . . 13, 18, 19, 21, 28
Mold Open Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25, 28
Mold Shrinkage . . . . . . . . . . . . . . . . . . . . . . 13, 20, 24, 29–34
Mold Temperature . . . . . . . . 20, 21, 24–26, 29–32, 34, 38, 39
Molded-In Stresses . . . . . . . . . . . . . . . . . . . . . . . . . . 26, 33, 35
N
Non-Return Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Nozzle . . . . . . . . . . . . . . . . . . 2, 3, 7–12, 16, 17, 22, 23, 38, 39
O
Odor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3, 18, 22, 38
Open Nozzle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Optimum Productivity . . . . . . . . . . . . . . . . . . . . . . 8, 9, 21, 28
P
Packaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3, 43
Part Weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Pigments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8, 9, 31, 33, 37
Post-Molding Shrinkage . . . . . . . . . . . . . . . . . . . . . . 32, 33, 35
Projected Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27, 28
Purging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22, 23
PVT Diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4–6
R
Recycling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Reground Resin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36, 37
Runnerless Molds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13, 18
Runners . . . . . . . . . . . . . . . . 5, 8, 13, 15–19, 22, 26, 28, 36, 37
Runners, Balanced . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
S
Safety Precautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2–3
Screw Deposit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Screw Design . . . . . . . . . . . . . . . . . . . . . . . . . . 8, 9, 12, 24, 29
Screw Forward Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Screw Retraction Time . . . . . . . . . . . . . . . . . . . . 10, 25, 28, 29
Screw Rotation . . . . . . . . . . . . . . . . . . . . . . 8, 9, 23, 24, 28, 29
Screw Rotation Speed . . . . . . . . . . . . . . . . . . . . . . . . . . . 9, 24
Shutdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3, 22
Sink Marks . . . . . . . . . . . . . . . . . . . . . 4, 13, 20, 27, 32, 33, 39
Snake Flow Mold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Spiral Flow Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Splay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8, 16, 18, 36, 39
Sprue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16–17, 39
Start-Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2, 3, 21, 22
T
Thermal Stability . . . . . . . . . . . . . . . . . . . . . . . . . . 7, 8, 36, 38
Tolerances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10, 30, 34, 35
Toughness . . . . . . . . . . . . . . . . . . . . . . . . . 1, 2, 7, 8, 20, 26, 32
Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38, 39
U
Undercuts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13, 20, 39
Unmelted Particles . . . . . . . . . . . . . . . . . . . . . 8, 24, 28, 38, 39
V
V-P Switch Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Venting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3, 13, 19, 20, 28
Viscosity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6, 7
Voids . . . . . . . . . . . . . . . . . . . . . . . . . . 4, 5, 27, 29, 32, 33, 38
W
Warping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9, 39
Water Absorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36, 37
Weld Line . . . . . . . . . . . . . . . . . . . . . . . . 13, 14, 19, 20, 28, 38
42
Identity and Trademark Standards
Guidelines for Customer Use—Joint ventures and authorizedresellersOnly joint ventures and resellers who have signed special agreements with DuPont to resell DuPontproducts in their original form and/or packaging are authorized to use the Oval trademark, subject to theapproval of an External Affairs representative.
Guidelines for Customer Use—All other customersAll other customer usage is limited to a product signature arrangement, using Times Roman typography,that allows mention of DuPont products that serve as ingredients in the customer’s products. In this signa-ture, the phrase, “Only by DuPont” follows the product name.
Delrin®
Only by DuPont
A registration notice ® or an asterisk referencing the registration is required. In text, “Only by DuPont” mayfollow the product name on the same line, separated by two letter-spaces (see above example). When aDuPont product name is used in text, a ® or a reference by use of an asterisk must follow the product name.For example, “This device is made of quality DuPont Delrin® acetal resin for high strength and rigidity.”
*Delrin® is a DuPont registered trademark.
Delrin® Only by DuPont or
acetal resinDelrin®
e
Printed in U.S.A.[Replaces H-64530]Reorder No.: H-78783 (00.8) DuPont Engineering Polymers
e
For more information onEngineering Polymers:
For Automotive Inquiries: (800) 533-1313
(800) 441-0575
StartwithDuPont
U.S.A.EastDuPont Engineering PolymersChestnut Run Plaza 713P.O. Box 80713Wilmington, DE 19880-0713(302) 999-4592
AutomotiveDuPont Engineering PolymersAutomotive Products950 Stephenson HighwayTroy, MI 48007-7013(248) 583-8000
Asia PacificDuPont Asia Pacific Ltd.P.O. Box TST 98851Tsim Sha TsuiKowloon, Hong Kong852-3-734-5345
CanadaDuPont Canada, Inc.DuPont Engineering PolymersP.O. Box 2200Streetsville, MississaugaOntario, Canada L5M 2H3(905) 821-5953
EuropeDuPont de Nemours Int’l S.A.2, chemin du PavillonP.O. Box 50CH-1218 Le Grand-SaconnexGeneva, SwitzerlandTel.: ##41 22 7175111Telefax: ##41 22 7175200
JapanDuPont Kabushiki KaishaArco Tower8-1, Shimomeguro 1-chomeMeguro-ku, Tokyo 153Japan(011) 81-3-5434-6100
MexicoDuPont S.A. de C.V.Homero 206Col. Chapultepec Morales11570 Mexico D.F.(011 525) 722-1456
South AmericaDuPont America do SulAl. Itapecuru, 506Alphaville—CEP: 06454-080Barueri—São Paulo, BrasilTel.: (055-11) 7226-8182Fax: (055-11) 7226-8513Telex: (055-11) 71414 PONT BR
DuPont Argentina S.A.Avda.Mitre y Calle 5(1884) Berazategui-Bs.As.Tel.: (541) 319-4484/85/86Fax: (541) 319-4417
The data listed here fall within the normal range of properties, but they should not be used to establish specification limits nor used alone as the basis ofdesign. The DuPont Company assumes no obligations or liability for any advice furnished or for any results obtained with respect to this information.All such advice is given and accepted at the buyer’s risk. The disclosure of information herein is not a license to operate under, or a recommendation toinfringe, any patent of DuPont or others. DuPont warrants that the use or sale of any material that is described herein and is offered for sale by DuPontdoes not infringe any patent covering the material itself, but does not warrant against infringement by reason of the use thereof in combination with othermaterials or in the operation of any process.
CAUTION: Do not use in medical applications involving permanent implantation in the human body. For other medical applications, see “DuPontMedical Caution Statement,” H-50102.
http://www.dupont.com/enggpolymers