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Zytel®
Molding Guide
nylon resin
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Table of Contents
Chapter 1 PageGeneral Information␣ ........................................... 2Composition and Properties............................... 2Physical Form ...................................................... 2Containers ............................................................ 2
Chapter 2The Injection Molding Process␣ .......................... 4Processing Characteristics .................................. 4Melting or Softening Temperature .................... 4Energy Requirements ......................................... 4Melt Viscosity ...................................................... 4Stability and Behavior at
Melt Temperature ............................................ 5Cycle Time ........................................................... 5Shrinkage ............................................................. 5
Chapter 3The Injection Molding Machine␣ ........................ 6Machine Melt Capacity ....................................... 6Screw Design ....................................................... 6Nonreturn Valve .................................................. 6Nozzle ................................................................... 6Nozzle Shutoff Valve ........................................... 6Hydraulic System ................................................ 7Injection Pressure ................................................ 7Clamping Capacity .............................................. 8Temperature Control ........................................... 8
Chapter 4Machine Operating Conditions␣ ......................... 9Cylinder Temperature Profile ............................. 9Melt Temperature................................................ 9Nozzle Temperature ............................................ 9Injection Pressure .............................................. 10Injection Rate ..................................................... 11Screw Forward Time ......................................... 11Overall Cycle ...................................................... 11Screw Speed ...................................................... 11Back Pressure .................................................... 13Mold Temperature ............................................ 13Start-Up .............................................................. 13Shutdown........................................................... 14Purging ............................................................... 14
Chapter 5Handling of Molding Resin␣ .............................. 15Effects of Moisture and Contamination
on Molding Resin........................................... 15Handling Regrind .............................................. 16Drying ................................................................. 17
Chapter 6 PageHow To Obtain Optimum Toughness ␣ ............ 19Selection of Zytel®␣ ............................................ 19Molding Zytel® 3189, 408L and ST801
for Toughness ................................................ 19Part Design......................................................... 19
Chapter 7Interrelationship of Part Design,
Molding Conditions, Resin Selection
and Mold Design ␣ .............................................. 20Thickness of Section ......................................... 20Ribs and Strengthening Members ................... 21Bosses ................................................................ 21Fillets and Radii ................................................. 21Undercuts ........................................................... 22
Chapter 8Mold Design␣ ...................................................... 23Sprue Bushing␣ .................................................. 23Runner Design ................................................... 23Gate Design ....................................................... 23Mold Cooling ..................................................... 25Venting ............................................................... 25Undercuts ........................................................... 25Runnerless Molds—Types and Terms............. 26
Chapter 9Dimensions ␣ ....................................................... 28Mold Shrinkage␣ ................................................ 28Post-Mold Shrinkage......................................... 29Effects of Moisture and Temperature
on Dimensions ............................................... 29Dimensional Tolerances ................................... 30
Chapter 10Quality Control␣ ................................................. 34Resin Specifications .......................................... 34Specifications on Molded Parts ....................... 34
Chapter 11Troubleshooting Guide for
Zytel® Nylon Resins␣ ......................................... 36
Chapter 12Operating Precautions␣ ..................................... 38Handling of Zytel® Nylon Resins␣ ..................... 39Slipping Hazards ............................................... 39Spontaneous Ignition........................................ 39
Chapter 1
Zytel® Nylon Resins for Injection Molding
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Composition and PropertiesZytel® nylon resins are thermoplastic polyamideshaving properties that place them high on the list engineering plastics. Zytel® nylon resins are toughand withstand repeated impact. They are highlyresistant to abrasion and to most chemicals. Moldarticles retain their shape at elevated temperatureare strong in thin sections and have low coefficienof friction. Many of the compositions, includingZytel® 101L, are classified by Underwriters’Laboratories. Also, flame retardant nylons qualifying for the UL94 V-1 and 94 V-0 are under con-tinuing development.
The principal Zytel® nylon resins may be dividedby chemical composition into four basic groups—66 nylon, 612 nylon, 6 nylon and copolymers—alof which may be modified to give special proper-ties. Resins in any of these groups may also bemade with different molecular weights. Propertiessuch as melting point, water absorption and modulus of elasticity are determined primarily by thetype of nylon. Impact resistance is determined bythe type of modifier used (if any) and molecularweight of the nylon. Melt viscosity is determinedmainly by molecular weight. Additives of variouskinds may be used to enhance properties (e.g., mrelease, screw retraction).
Zytel® nylon resins may be reinforced with glassfibers to increase their tensile strength, stiffness,and dimensional stability, but this Molding Guideis limited to a discussion on unreinforced nylons.For information on glass-reinforced Zytel® resinsand Minlon® mineral reinforced resin, contact yourDuPont representative. The commercially codedZytel® nylon resins are listed and described inFigure 1. In addition, there are some experimentaresins, coded “FE,” designed to have specificattributes. These resins are on commercial trial aif found suitable, will be given full commercialdesignation. Information concerning current Zytel®
nylon “FE” resins can be obtained from yourDuPont representative.
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Physical FormMost Zytel® nylon resins are supplied as rightcylinder pellets of approximately 2.3 × 2.6 mm(0.090 × 0.100 in). A few are supplied in a rectan-gular cut, approximately 3.2 × 3.2 × 3.2 mm(0.125 × 0.125 × 0.125 in).
ContainersMost Zytel® nylon resins are packaged in 25-kg(55.1-lb) net weight pinch-pack bags, foil coatedwith the innerply laminated with polyethyleneresin.
Certain nylon resins are available in otherpackages:• Corrugated boxes with polyolefin liner, 750 kg
(1,653 lb) net weight or more.• Disposable four-way entry pallets used for 40-ba
units and on bulk corrugated boxes.
Overall dimensions on palletized loads:Bags: 109 × 127 × 137 cm high
(43 × 50 × 54 in high)
Boxes: 107 × 122 × 109 cm high(42 × 48 × 43 in high)
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Figure 1. Zytel® Nylon Molding Resins
Designation Description Characteristics and Major Uses
66 Nylons—Melt at 262°C (504°F)—Stiff and strong over a wide range of temperature. Excellent toughness and chemical resistance.
Zytel® 101 General Purpose— Basic 66 nylon. Unmodified 66 nylon of medium viscosity.Unlubricated The industry standard.
Zytel® 101L General Purpose— A 66 nylon lubricated for improved machine feed and mold releaseLubricated characteristics. Widely used in injection molding for mechanical parts,
consumer products, etc.
Zytel® 101F General Purpose— A non-nucleated 66 nylon for optimum molding performance.Fast Cycle
Zytel® 132F General Purpose— 66 nylons nucleated for fast molding cycles. Stiffer andNucleated, Fast Cycle stronger than unmodified nylons at some sacrifice in toughness.
Zytel® 103HSL, 103FHS Heat Stabilized— New, improved heat-stabilized 66 nylons designed to retardLubricated embrittlement at high service temperatures. Have 130°C UL ratings for
electrical use. Lubricated for improved machine feed and mold release.Zytel® 103FHS is fast cycling version.
Zytel® 105 BK010A Weather Resistant Contains well-dispersed carbon black for outstanding resistance toweathering.
Zytel® 122L Hydrolysis Resistant Stabilized to resist hydrolysis and oxidation in long-term exposure tohot water. Lubricated for improved machine feed and mold release.
Zytel® 42A High Viscosity For extrusion into rod, tubing and complex shapes. Can be molded intofor Extrusion parts requiring high impact resistance.
Toughened 66 Nylons—Melt at 262°C (504°F). Added toughness and flexibility.
Zytel® 408L, 408HS General Purpose—Heat Superior toughness and moldability at some sacrifice in strength and408 BK010 Stabilized, Weather Resistant stiffness.
Zytel® 450HSL, BK152 Heat Stabilized Economy grade. Similar to Zytel® 408L.
Zytel® 3189, 3189HSL General Purpose Superior toughness/stiffness, balance, outstanding flow andprocessibility.
Super Tough Nylons. Highest impact strength of any engineering thermoplastic.
Zytel® ST801, ST801HS, General Purpose—Heat Outstanding toughness. Good moldability. Some sacrifice in strengthST801 BK010 Stabilized, Weather Resistant and stiffness.
Zytel® ST800L, ST8000HSL, General Purpose—Heat Similar to Zytel® ST801. Economy grades.ST800HSL BK010 Stabilized, Weather Resistant
Zytel® ST811HS General Purpose Super tough nylon 6. Highest toughness even at low temperatures.
Zytel® ST901L General Purpose—Amorphous Low shrinkage and warpage. Properties relatively unaffected byCharacteristics moisture. Excellent combination of stiffness and toughness.
612 Nylons—Melt at 218°C (424°F)—Low moisture absorption and excellent dimensional stability.
Zytel® 151L General Purpose—Lubricated A 612 nylon lubricated for improved machine feed and mold release.
Zytel® 158L General Purpose—Lubricated Higher melt viscosity and greater toughness than Zytel® 151L.Lubricated for improved machine feed and mold release.
Zytel® 153HSL Heat Stabilized—Lubricated Heat-stabilized Zytel® 158L to retard embrittlement at high servicetemperatures. Primarily for wire jacketing.
Zytel® 157HSL BK010 Weather and Heat Resistant— Contains well-dispersed carbon black for outstanding resistance toLubricated weathering. Heat stabilized. Lubricated for improved machine feed and
mold release.
Flame Retardant Nylon—UL 94 V-O Rating
Zytel® FR10 General Purpose UL 94 V-0 down to 0.71 mm (0.028 in) in natural and black color.
Miscellaneous Products—Copolymers, Blends, Plasticized Resins, Unextracted Nylon 6
Zytel® 91AHS Plasticized Nylon Copolymer High flexibility and toughness. Primarily for extrusion but may bemolded into hammer heads, etc.
Zytel® 109L General Purpose—Color Easy processing at the expense of stiffness and high temperatureStabilized, Nucleated, properties. Excellent for heavy section moldings.Lubricated
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Chapter 2
The Injection Molding Process
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The injection molding of thermoplastic resins isa well-known and widely practiced science. Itconstitutes a major processing technique forconverting nylon into a variety of end-use productIn basic terms, the process involves heating thesolid molding powder to melt it, then transferring ito a mold and holding it under pressure until itfreezes, or solidifies.
Plastic molding compounds represent a range ofchemical types. Each type has its own specificprocessing characteristics which must be consid-ered and understood before it can be successfullymolded. The information in this book is intendedto provide guidance in the injection molding ofunreinforced Zytel® nylon resins, which are chemi-cally classified as polyamides.
Processing CharacteristicsThe physical and chemical properties of a plasticdictate the way in which it must be molded. Amonthese are:• Melting or softening temperature• Energy content (specific heat and latent heat)• Melt viscosity• Stability and behavior at melt temperatures• Freezing rate, crystallization rate, and cycle tim• Shrinkage
Melting or SofteningTemperatureMost Zytel® nylon resins are crystalline materialswith melting points higher than those of many oththermoplastic materials. However, some arenoncrystalline and have softening temperatures, ntrue melting points. Melting points of Zytel® nylonresins are compared with those of other plasticmaterials in Figure 2.
Energy RequirementsZytel® nylon resins must be heated to their procesing temperatures before they can be molded (seeFigure 3). Crystalline materials such as Zytel®
101L and acetal resins can require greater energyinput than amorphous or noncrystalline resinsbecause considerable energy is needed just tocoalesce the ordered structure. The heat energyrequired for doing this is known as heat of fusion
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and is a significant part of the heat energy requiredto bring crystalline plastic resins to their properprocessing temperature. On the other hand, polystyrene is an amorphous material and consequently hano heat of fusion. Even though it can be run at thesame processing temperature as nylon, the totalheat energy to bring polystyrene to the processingtemperature is about one-half the energy requiredfor a 66 nylon. The heat energy required to bringZytel® and several other plastic materials to theproper processing temperature is listed in Figure 3.
Melt ViscosityMelt viscosity is the property which, in largemeasure, governs the characteristic of filling amold. The melt viscosity of thermoplastic resinsis temperature dependent, as shown in Figure 4.Melt viscosity is primarily a function of molecularweight. For example, Zytel® 42A has a highermolecular weight and, therefore, a higher meltviscosity than Zytel® 101L.
Melting or Softening TemperatureType °C °F
Polyethylene (low density) 105 221Polystyrene 168 334Acetal (homopolymer) 175 347Zytel® 151L (612 nylon) 218 424Polycarbonate 221 430Zytel® 101L (66 nylon) 262 504Zytel® 408L, 3189
(modified 66 nylons) 262 504Zytel® ST801 262 504
Figure 2. Melting Points of Plastic Materials
Processing Heat of Total HeatTemperature Fusion Required
Resin °C (°F) kj/kg (BTU/lb) kj/kg (BTU/lb)
Polystyrene 260 (500) 0 (0) 372 (160)Acetal Resin 205 (400) 163 (70) 419 (180)Polyethylene 225 (440) 130 (56) 637 (274)
(low density)Polyethylene 225 (440) 242 (104) 310 (721)
(high density)Zytel® 101L 275 (530) 130 (56) 791 (340)
(66 nylon)
Figure 3. Heat Energy Required for Processing
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Stability and Behavior at MeltTemperatureZytel® nylon resins can be molded easily andwithout problems when processed at the recom-mended temperatures and when kept dry. They apackaged at low moisture content suitable formolding. When exposed to the atmosphere for aperiod of time, nylon absorbs moisture and must bdried before it can be molded. This importantaspect of resin handling is discussed in detail inChapter 5.
500 550 600450400350
Temperature, °F
1,000
10,000
100,000
Temperature, °C250 275 300225200175
Vis
cosi
ty*,
Po
ise
*Shear Rate 100 sec
Polyethylene
Delrin® 500
Zytel® 42A
Zytel ® ST801Zytel ® 408LZytel® 101L
Figure 4. Melt Viscosity of Thermoplastics
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Cycle TimeThe minimum cycle time possible with a thermo-plastic resin is an important economic consideratioand is directly proportional to part wall thickness.Because Zytel® nylon resins are strong and stiffengineering materials, part walls can frequently bedesigned for minimum possible thickness, resultinin fast injection molding cycles.
Special fast cycle compositions such as Zytel® 132Fand ST801 have been developed.
ShrinkageFor typical mold shrinkage values, refer toFigure 37.
Chapter 3
The Injection Molding Machine
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Zytel® nylon resins have been successfully moldein many types of molding machines. Since mostnylon is molded on screw machines, this section devoted only to that type.
Machine Melt CapacityThe plastifying capacity (ideal) of any screwinjection molding machine primarily depends onthe screw diameter and screw design.
Shot WeightShot size is equal to the volume (weight) of molteresin injected by the screw during the cycle. Themelt densities of Zytel® nylons are approximatelyequal to the melt density of polystyrene (thestandard used for specifying molding machines) anormal processing temperatures and pressures.Therefore, the maximum shot weight for Zytel®
nylons will be approximately equal to the name-plate or specified polystyrene shot weight.
For best molding (reasonable residence time), theactual shot size should be between 10% and 70%the machine rated capacity. Although it is possiblto mold parts outside of the specified range, molding outside those extremes should be done cau-tiously because of the possibility of too long of ahold-up time or inadequate melt capacity.
Recovery Rate (Plastifying Rate)This is the instantaneous rate in pounds per hour(kg per hour) at which molten polymer can beproduced. The recovery rate is affected by thescrew speed, screw design, back pressure, cylindtemperature profile, shot size, resin characteristicand the desired melt quality.
Screw DesignThe general-purpose screws that are supplied wimost injection molding machines are usuallysuitable for molding Zytel® nylon resins at low(recovery) output rates. At high output rates,however, a screw specifically designed for moldinZytel® nylons will provide greater uniformity ofmelt temperature and freedom from unmeltedparticles. The recommended screw design for higoutput rates is given in Figure 5. For uniform melttemperature control, length/diameter ratios of 16/to 20/1 and compression ratios between 3/1 and
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are recommended. Screw design is very importantfor Zytel® nylon resins because most of them havehigh energy requirements and low viscosities. Thisusually means that a shallow metering screw with ahigh L/D is recommended. Zytel® resins have beenrun on general purpose screws, higher compression(shallow metering) screws, double wave screws,two-stage vented barrel screws, and barrier screws
Nonreturn ValveNonreturn valves ensure consistency of shot weighand cavity pressure from shot to shot. Either themore common ring check type or a ball check valvemay be used with the low melt viscosity Zytel®
nylons. In either case, the flow passages must bestreamlined and nonrestricted to prevent problemsassociated with hold-up spots. See Figure 6 for agood generalized design of a nonreturn valve.
NozzleFigure 7 shows the type of nozzles recommendedfor use in molding Zytel® nylon resins. The mainfeature is a reverse taper bore which, in effect,extends the sprue into the heated nozzle.
This design permits operation of the nozzle at alower overall temperature, eliminates the likelihoodof a hot spot at the rear of the nozzle, and mini-mizes drooling. Any material that solidifies in thereverse taper bore during the molding cycle will beattached to the sprue and withdrawn with the shot.The 0.25 mm (0.01 in) radius at the front boredecreases the possibility of peening in the edges atthis point. Such a peened undercut would preventremoval of the chilled material from the nozzle tip,causing the sprue to stick. Both the heater band anthermocouple should be placed as far front aspractical for good temperature control.
For small diameter sprues the nozzles shown inFigure 8 are acceptable alternatives.
Nozzle Shutoff ValveZytel® nylon resins are satisfactorily run onmachines that do not have nozzle shutoff valves.However, the use of a nozzle shutoff valve willincrease the time available for screw retraction andreduce drooling and stringing sometimes associatewith conventional nozzles. Again, streamlining is
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Figure 5. Suggested General-Purpose Screw Design for Zytel® Nylon Resins
Low Viscosity Resins1 High Viscosity Resins2
Screw Diameter (DS) Feed Depth Metering Depth Feed Depth Metering Depthmm (in) mm hF (in) mm hM (in) mm hF (in) mm hF (in)
20 L/D 38.1 (1.5) 7.62 .300 1.52 .060 7.62 .300 2.03 .080square pitch 50.8 (2.0) 7.87 .310 1.65 .065 8.13 .320 2.29 .090
screws 63.5 (2.5) 8.13 .320 1.90 .075 9.65 .380 2.54 .100nF = 10nT = 5 (4)*nM = 5(6)*
16 L/D 38.1 (1.5) 7.62 .300 1.40 .055 7.62 .300 1.90 .075square pitch 50.8 (2.0) 7.87 .310 1.52 .060 8.13 .320 2.16 .085 screws 63.5 (2.5) 8.13 .320 1.78 .070 9.65 .380 2.41 .095nF = 7.5nT = 3.5nM = 5.0
General practice in the industry is to have the land width (e) = 1/10 the distance between the flights (t), and the radial clearance (δ) = 1/1000 of thediameter of the screw (Ds).*Alternate design for higher output rates1 Zytel® 101L, 408L, 3189, etc.2 Zytel® ST901L, etc.
Length
Feed Section
DS hF hMe LandWidth
TransitionSection
MeteringSection
10δ
5 5
Figure 6. Nonreturn Valve
Ring
Ring seat Flow
very important. Both hydraulic rotary plug andspring melt pressure valves have been used.Frequent check of the nozzle should be made toverify that it has not worn excessively.
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Hydraulic SystemWhen molding Zytel®, it is often important to beable to inject the resin into the mold at a rapid andcontrolled rate. Machines with shot capacities of20 oz (570 g) or less should have hydraulic pumping capacities that allow the rated shot capacity tobe injected into the mold in two seconds or less.The ability to control the rate of injection is justas important as the ability to fill rapidly. For thisreason, it is desirable to have pressure- andtemperature-compensated flow control valvesinstalled in the hydraulic system.
Injection PressureThe injection system should be capable of injectinthe nylon at melt pressures up to 20,000 psi(140 MPa). Accurate and reproducible control ofthe injection pressure is essential to maintainingtolerance of molded dimensions and other qualitycharacteristics.
Figure 8. Nozzle
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Figure 7. Nozzle (with Reverse Taper) Recommended for Molding Zytel® Nylon Resins
������������������������
10D
Diameterto Suit
Taper to Suit
3D
D Minimum = 0.32 cm (1/8"), D Typical = 0.48 cm (3/16") – 0.64 cm (1/4") Not To Scale
D4°
0.25 mm (0.10")Radius
ThermocoupleWell
0.32 cm (1/8")
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Clamping CapacityMolds should be designed and machines selectethat the clamping force is 3-5 tons/in2 (45–80 MPa)of projected shot area. The higher value is necessary for hard-to-fill parts or more precise toleranccontrol.
Temperature ControlIn screw machines, the melt temperature is determined by cylinder temperatures, back pressure,cycle time, screw speed, and screw design. Thesvariables should be adjusted to produce:
• A melt at the correct temperature for injection• A uniform temperature throughout the shot• Shot-to-shot uniformity of melt temperature
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The temperature of each cylinder zone should beindependently controlled. In all cases, the tempeture of the nozzle should be independently andprecisely controlled. Nozzle heater bands shouldbe of sufficient wattage to maintain a temperaturof at least 330°C (625°F). A means of controllingthe temperature at the feed throat of the barrel malso be incorporated.
Cooling water to the feed throat should be con-trolled by a needle valve. A dial thermometer canbe used to measure the temperature of the throa
The influence of back pressure, cycle time, screwspeed and screw design on melt temperature arediscussed in other sections of this manual.
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Chapter 4
Machine Operating Conditions
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Cylinder Temperature ProfileFor optimum molding performance, it is importanto match the cylinder temperature profile to thespecific material, machine, and shot being molde(see Figure 10). The rear zone temperature isparticularly critical. Rear zone temperatures that too low will not allow sufficient heat to be trans-ferred to the polymer by conduction and willimpose high torque loads on the screw drivesystem. This could result in erratic screw retracti(feed). High torque loads may even stall the scremotor. If this happens, rear zone temperaturesshould be gradually raised until the screw is ableto rotate freely. Rear zone temperatures that arehigh may cause premature melting of the polymediscoloration and bridging. (A bridge is theagglomeration of partially melted particles thatadhere to the feed section of the screw or clog thfeed throat.)
The rear zone temperature should be adjusted athe lowest possible value to achieve consistentfeeding, optimum screw retraction time and reasable torque values. Since heat transfer charactertics of screw machine cylinders can vary frommachine to machine, it is not possible to specify temperature profile that will be applicable to allscrew machines. Typical screw machine temperature profiles are shown in Figure 9. In some cases,temperature profiles that vary widely from thesetypical values may be necessary.
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Typical Cylinder Tem
RearResin °C °F
66 nylons:Zytel® 101, 101L, 103HSL,105 BK010A, 122L, 132F 280 540 2
Zytel® 42A 290 550 2
Modified 66 nylons: 295 560 2Zytel® 408L, 408HS,ST801, 3189
612 nylons: 240 460 2Zytel® 151L, 158L, 153HSL,157HSL, BK010A
Amorphous Nylons:Zytel® ST901L 300 570 2
Figure 9. Typical Processing Conditions for Molding Zy
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Figure 10 illustrates how cycle and shot sizeinfluence the temperature profile.
Melt TemperatureIn establishing the proper operating characteristicsfor an injection molding machine, one of the mostimportant is the actual temperature of the moltenplastic at the time it is injected into the mold cavity.This is called the melt temperature. While Figure 9shows typical cylinder pyrometer settings, thosevalues are just a starting point for arriving at theproper melt temperature.
The actual melt temperature is determined by theinteraction of screw design, screw retraction time,back pressure, overall cycle and the pyrometersettings. Since it is not possible to predetermine theeffect of each variable, the actual melt temperatureshould be measured after the machine operation hcome to equilibrium. Figure 10 shows how some ofthe variables are related.
Nozzle TemperatureThe nozzle should act merely as a melt conveyingpipe and must not affect the temperature of themelt. Ideally, the temperature of the plastic enteringand leaving the nozzle should be the same. Thenozzle temperature setting will depend largely onthe design of the nozzle, the heater band placemen
peratures for Screw Machines
Center Front°C °F °C °F °C °F
75 525 270 520 280–305 535–580
75 530 270 520 280–310 540–590
80 535 275 525 290–295 550–560
30 445 225 440 230–290 450–550
85 545 280 535 255–295 490–560
PreferredMelt Temperature
tel® Nylon Resins
3 Min Hold-Up Time (HUT)
7 Min HUT
11 Min HUT
Front Zone Center Zone Rear Zone
80% Stroke*(Decreasing Profile)
50% Stroke*(Flat Profile)
20% Stroke*(Increasing Profile)
ControllerSet Point Difference
From SpecifiedMelt Temperature, °C
20
15
10
5
0
–5
–10
–15
–20
Nozzle Hopper
*The percent stroke refers to the portion of the actual machine shot capacity.
Figure 10. Cylinder Settings for a Specified Melt Temperature—Recommended Controller Set Points fromTarget Value
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the temperature of the mold in contact with thenozzle, the overall cycle and the type of nylonbeing processed. Improperly located heater bandcould cause freezing or drooling. The nozzletemperature should generally be 270–300°C(520–570°F) when molding 66 nylons.
Injection PressureNormal injection pressures for Zytel® nylons are5,000–20,000 psi (35–140 MPa). Parts should bemolded at the highest practical injection pressureconsistent with the desired cavity pressure. How-ever, the product of the injection pressure and theprojected area of the mold cavity and runner systemust not exceed the clamping force of the machinIf this happens, the mold will be forced open andthe part and/or runner will flash.
Injection pressure may also be limited by moldconstruction. If the mold does not have sufficientsupport, high pressures will distort the mold and
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allow flashing. Inadequate pressure will result inparts that are not sufficiently packed. Excessivepressure just before the part is full can result in ahighly stressed area near the gate and lead toreduced performance of the part in use.
It is sometimes desirable to use a two-stage pres-sure cycle:
1. Initially injecting at high speed to fill the part atthe desired rate, and then
2. Holding under a reduced pressure to allow thegate to freeze and to prevent overstressing.
Injection pressure and injection rate, althoughindependently controlled, are interrelated. Themaximum injection pressure is controlled by arelief valve that limits the maximum oil pressure onthe injection piston. The injection rate is controlledby a flow control valve that regulates the rate offlow of oil to the injection hydraulic cylinder and isinfluenced by the melt viscosity of the resin. As the
screw or ram moves forward, the injection pressurincreases to overcome the resistance of the melt tflow in the sprue, runners, and cavity.
In Figure 11, typical snake flow data, which aresomewhat indicative of melt viscosity, are shownfor a number of Zytel® nylon resins.
Injection RateThe optimum fill rate for a part depends on thegeometry of the part, the size of the gate and themelt temperature. When molding thin section partshigh injection rates are usually required to fill thepart before the resin freezes. When molding thinsection parts or parts with relatively small gates, itis sometimes desirable to use a slow injection rateto delay freezing of the gate and thereby allowpacking of the part for the longest possible time.
40
36
32
28
24
20
16
12
8
4
35 69 104 138
102
91
81
71
61
51
41
31
20
5,000 10,000 15,000 20,000
Injection Pressure, psi
Flo
w, i
n Flo
w, cm
Injection Pressure, kg/cm2
Part Thickness= 0.100 in (2.54 mm)
Part Thickness= 0.040 in (1.0 mm)
Mold Temperature = 65°C (150°F)
Melt Temperature = 290°C (555°F)
Figure 11. Flow vs. Pressure for Zytel® 101L
Relative Flow of Other Zytel® Nylon Resins
Melt Flow Relative toTemperature Zytel® 101 at
Resin °C (°F) 290°C (555°F)
Zytel® 103HSL, 122L 290 (555) 1.00Zytel® 408L 290 (555) 0.90Zytel® 105 BK010A 290 (555) 0.75Zytel® 42A 290 (555) 0.40Zytel® 151 260 (500) 0.90Zytel® 158 260 (500) 0.55Zytel® ST801 290 (555) 0.55Zytel® ST901 290 (555) 0.30Zytel® 3189 290 (555) 0.80
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Surface gloss will be more uniform if the injectionrate is fast enough to allow the cavity to be filledbefore the nylon begins to solidify.
The maximum cavity fill rate for Zytel® nylonresins can be determined from Figure 12, whichgives the rate as a function of gate dimensions. Todetermine the maximum fill rate for the entire shot,multiply the maximum cavity fill rate by the ratioof shot weight/weight of all the parts.
Screw Forward TimeScrew forward time is the time interval between thestart of the forward motion of the screw (injection)and the start of screw retraction. If this time intervalis long enough, the molten polymer is held underpressure until the gate freezes. If the gate is notcompletely frozen before the injection hold pres-sure is removed, increased shrinkage, voids andsink marks could be present. The optimum screwforward time can be determined by molding andweighing a series of parts at different screw for-ward times (holding the overall cycle constant)until the part reaches maximum weight, as illus-trated in Figure 13.
The minimum screw forward time for 66 nylonscan be estimated from Figure 14, which givesthe time to freeze various thicknesses of Zytel® 66nylons. The minimum screw forward time willbe approximately equal to the sum of the time tofreeze the gate and the time to fill the mold(ram-in-motion time).
Overall CycleA rough guide to estimate total cycle time forZytel® 101L is 30 sec per 3.2 mm (0.125 in)thickness. Nucleated resins, like Zytel® 132F, canoften be molded on much shorter overall cyclesthan Zytel® 101L. Toughened crystalline resins likeZytel® 3189, 408L and ST801 also can be moldedon much shorter cycle times.
Screw SpeedFor a given injection unit, molten polymer through-put is controlled primarily by the speed (RPM) ofthe screw. The effects of screw speed on melttemperature depend strongly on screw design. For ascrew of optimum design running at optimumoutput, slight changes in screw speed should havealmost no effect on the melt temperature. Increas-ing the screw speed when using a low compressiongeneral-purpose screw often results in a decrease inmelt temperature. Screws with deep and shortmetering sections may pump unmelted particles athigh screw speeds.
12
Max
imu
m C
avit
y F
ill R
ate,
oz/
sec
10
765432
1.0
0.70.60.50.40.30.2
0.02 (0.5) 0.04 (1.0) 0.06 (1.5) 0.08 (2.0) 0.10 (2.5)0.1
0Gate Thickness (Rectangular Gates) or Gate Diameter (Round Gates), in (mm)
Rectangular Gates Round Gates280
Maxim
um
Cavity F
ill Rate, g
/sec
11284
56
28
14
5.6
Melt Temperature = 280°C (540°F)
Gat
e W
idth
= 1
0x G
ate
Thic
knes
s
Gat
e W
idth
= 5
x G
ate
Thick
ness
Gate W
idth =
2x G
ate Thic
knes
s
Figure 12. Maximum Fill Rate for Zytel® 101L vs. Gate Thickness or Diameter
100
80
60
40
20
T1 T2
P1
P2
Injection Forward Time
% o
f M
axim
um
Par
t Wei
gh
t
Note: P1 > P2 (Injection Pressures) T1 < T2
T1 = Minimum Screw Forward Time
Figure 13. Effect of Screw Forward Time on PartWeight
Figure 14. Influence of Gate Dimsensions on GateSeal Time for Zytel® 66 Nylon Resins
Tim
e to
Fre
eze
the
Gat
e, s
ec
102
0.01 (0.2)
Inches (mm)Gate Thickness for Rectangular Gates
or Gate Diameter for Round Gates
7654
3
2
7654
3
2
10
1.00.02 (0.5)
0.05 (1.2)
0.1 (2.5)
0.2 (5.1)
0.5 (12.7)
1.0 (25.4)
Round Gates
Rectangular Gates
Melt Temperature 282°C (540°F)Mold Temperature 66°C (150°F)
e
d
Screw speed should be selected so that screwretraction time is appoximately 90% of the timeavailable for recharging the melt.
Energy input from the screw should constituteabout 80% of the energy to raise the temperaturea uniform value (heater bands contribute a minoramount). Therefore the design and operationalcharacteristics of the screw should be considered
Back PressureIncreasing back pressure increases the work donby the screw on the molten polymer. This couldincrementally increase melt temperature anduniformity. Where melt quality is marginal, higherback pressure may reduce unmelted particles, buwill not substantially increase melt quality.
Increasing back pressure also increases recoverytime. The lowest possible back pressure consistewith good melt quality is recommended during themolding of Zytel® nylons.
Mold TemperatureMold surface temperatures of 0–95°C (30–200°F)are used but 70°C (160°F) is recommended. Themold surface temperature is not a directly con-trolled variable as such, but is a complex functionof cycle time, melt temperature, cooling channeldesign and cooling fluid flow rate and temperatureand mold heat exchange rate. Any change in onemore of these parameters can change the moldsurface temperature.
Since the mold surface temperature (not the coolifluid temperature) determines part quality aspectssuch as shrinkage, surface appearance and post-molding shrinkage, proper care must be given to control. The surface temperature should be mea-sured at several locations in the cavity and the vamust be held constant from run to run. Remembeit may take several hours for the surface temperature to reach thermal equilibrium.
1
to
.
e
t it
nt
or
ng
its
luer,-
Start-UpThe cylinder and screw can be cleaned prior tostart-up by using the method described underPurging (Chapter 4). If thermally-sensitive resins(e.g., acetals or PVC) are present in the barrel,lower temperatures are recommended until themachine is purged. The recommended startupprocedure is:
1. Set the cylinder temperature 30°C (50°F) belowthe minimum processing temperature, and thenozzle 10°C (20°F) above the minimumprocessing temperature. Allow the heat to“soak in” for at least 20 min. Raise the cylindertemperatures to the desired operating tempera-tures. (Use Figure 9 as a guide.)
2. Check and make sure that the nozzle is at settemperature and that it is open and contains nofrozen material.
3. Jog the screw. If the screw will not rotate,allow a longer heat “soak in” time.
4. When the screw begins to rotate, open thehopper feed slot briefly and then close. As thematerial is being pumped forward by the screw,check the load on the screw motor. If it isexcessive, increase cylinder temperatures.
5. Open the feed slide, and increase back pressurto hold the screw in the forward position.Extrude melt and adjust operating conditionsuntil visual observation of the melt shows noindication of unmelted particles or froth.Release the back pressure.
6. Take several air shots with the stroke size andcycle anticipated for the molding operation.Now check melt temperature with a hand-heldpyrometer. Make any adjustments in the barreltemperatures necessary to get the recommendemelt temperature.
7. Bring the injection cylinder forward. Startmolding on cycle at low injection pressure(except where short shots will interfere withpart ejection), and then adjust operating condi-tions to produce quality parts.
3
p
ShutdownThe following shutdown procedure isrecommended:
1. While molding on cycle, shut the hopper feedslide, empty the hopper, add a quantity ofpolyethylene and extrude until the screw pumitself dry. This procedure will reduce contami-nation and the time required for subsequentstart-ups.
2. Leave the screw in the forward position.
3. Turn off barrel heaters leaving the nozzle andadaptor heaters on until barrel temperaturesare cool.
1
s
PurgingHigh-density polyethylene, glass-reinforced poly-ethylene, polystyrene, and cast acrylic are materialsthat effectively purge Zytel® nylon resins. If castacrylic is used, the nozzle must be removed duringpurging. The following purging procedure isrecommended:
1. Retract the injection unit from the platen andincrease the back pressure so that the screw isheld in the forward position.
2. Run the screw at high RPM and pump out asmuch of the resin as possible. Feed purgingmaterial until the extrudate comes out clean.Cylinder temperatures may have to be adjusted,depending on purge material. Prior to switchingto another resin, release back pressure and takeseveral air shots using long strokes and fastinjection rates. (Refer to Chapter 12 for adescription of the proper safety considerations.)
4
Chapter 5
Handling of Molding Resin
n
n
le
Effects of Moisture andContamination on Molding ResinMoistureZytel® nylon resins are supplied dry (less than0.25% moisture by weight) and are ready to molddirectly from the shipping containers. However,nylon can either absorb water from or lose water the surrounding atmosphere, depending on thewater content of the nylon and the temperature arelative humidity of the atmosphere. Figures 15and 16 show the rate at which 66 nylon will absorbwater from humid air.If the nylon molding resin is allowed to absorbexcessive amounts of water prior to molding,mechanical properties, the viscosity of the melt a
Figure 15. Moisture Absorption of Virgin Zytel® 66Nylon Resins
1
1.2
1.0
0.8
0.6
0.4
0.20 2 4 6 8 10 12
Exposure Time, hr to Humid Air at 23°C (73°F)
Wei
gh
t P
erce
nt
Mo
istu
reA
bso
rbed
by
Vir
gin
Zyt
el® 6
6 N
ylo
ns
100%
RH
75% RH
50% RH
2 4 6 8 10
9
8
7
6
5
4
3
2
1
Exposure Time, hr to Hum
Wei
ght P
erce
nt M
oist
ure
Abs
orbe
d by
Zy
tel®
66
Nyl
on R
egri
nd
Figure 16. Moisture Absorption of Reground Zytel® 66
el
to
d
d
the appearance of molded parts are affected. Nozzdrool and frothy melts are also noticeable. Attemperatures above the melting point, water reactsrapidly with nylon. This reaction (hydrolysis)results in a decrease in molecular weight (meltviscosity) and toughness of the resin. At the sametime, absorbed water can form steam that results insplay marks and internal bubbles in the moldedpart. The reaction between water and molten nylonis accelerated by prolonged exposure to tempera-tures above the melting point. If melt temperaturesexceed 315°C (600°F) and/or long cycles areemployed, a very low (0.1%) molding powdermoisture content may be needed.
Molding difficulties due to moisture can be avoidedif the following handling procedures are observed:
• See that the molding resin container and itscontents are at or above the temperature of theoperating area before the container is opened.This procedure prevents condensation of moisturon the resin (cold material also requires additionaheat/time for melting).
• Use a hopper dryer. For all Zytel® nylonsthe recommended drying temperature is80°C (175°F).
• Do not expose unused molding resin to theatmosphere.
• Zytel® is commonly supplied both in bagsand boxes. The bag is a heat-sealed, four-plycontainer (Figure 17) designed for extra strength,minimum storage space, easy opening and
5
20 40 60 80100 1 2 3 4 5
id Air at 23°C (73°F) Weeks
75% Relative Humidity
50% Relative Humidity
100% Relative Humidity
Nylon Resins (Regrind Screens—6 mm [1/4″])
-
Figure 17. Bag Construction
aZytel®nylon resin
disposal, and excellent resistance to moisture.Opened bags should be rolled down and used soon as possible to minimize moisture pickup.Bags can be heat-sealed with an ordinary heatsealing iron or closed tightly with a slit piece ofpolyethylene pipe.
• Zytel® is also available in boxes constructed of single ply of tough heavy duty polyolefin linerprotected by a double ply of corrugated board.Box liners should fit snugly around the pneumaconveying tube and should be twisted and closwhen not being used,
ContaminationLike moisture, contamination can affect both theappearance and toughness of molded parts. Goohousekeeping is necessary to limit the exposure the resin to sources of contamination.
Some suggestions for avoiding contaminationare to:• Maintain a “clean” shop.• Make sure reground material is free of
contamination.• Minimize the handling of sprues and runners.
Use lint-free gloves.• Clean scrap grinders and regrind containers
frequently.• Store reground material in covered containers.
AU containers and machine hoppers should hatight-fitting lids. Whenever possible, eliminateintermediate storage of the regrind.
1
as
a
ticed
dof
ve
• Handle and store reground material only inmoisture-proof containers. Cardboard containersare not recommended, since lint and paper fibersare a source of moisture and contamination.Remove and discard all fines adhering to themachine and containers, preferably by vacuumcleaning. Do not paint the inside of hoppers,hopper lids, and storage containers; paint mayflake off.
• Discard all runners and sprues that arecontaminated.
• Clean the hopper and the machine when changingmaterials. Discard the purge.
• Avoid placing nylon in an oven with othermaterials. The materials can be cross-contaminated. Clean the oven trays andthe oven frequently.
Successful use has been made of automated sys-tems to handle reground material. In these systems,sprues and runners drop from the mold onto aconveyor belt that carries them to the grinder. Thereground material is then moved to the hopper ofthe machine by a pneumatic or vacuum conveyorthat also feeds virgin nylon in the correct ratio.These systems work best in conjunction with ahopper dryer.
Handling RegrindIt is possible to grind up and reuse previouslymolded virgin Zytel® nylon resins without a signifi-cant sacrifice in physical properties. However,proper precautions must be taken in the initial andsubsequent molding and in handling the material.To use reground material successfully, the follow-ing principles should be followed:
• Do not use molded parts and runners that arediscolored or splayed. These may be indicationsthat the resin has been degraded.
• Protect the reground material from moisture.Keep in sealed moisture proof containers.
• Keep scrap grinders close to the moldingmachine. Sprues, runners and trimmings shouldbe reground as soon as they are removed from themachine.
• Maintain a constant proportion of virgin resin toreground material in the feed. Virgin resin andreground material should be mixed prior tomolding. The ratio depends on the quality of thereground material and part specifications. Toavoid accumulation of rework, use it as it isgenerated.
6
• Keep the particle size of the reground materialuniform. Fine particles rapidly absorb moisture(because of the large surface-to-volume ratio)and stick to the cylinder walls. Fine particlesalso develop an electrostatic charge that attractcontamination that can plug the filters on vacuuloaders. Keep grinder blades sharpened andproperly set to minimize fines. Fines can beseparated from the reground material byvibrating screening units equipped with 12 or 16mesh screens.
DryingThe rate at which nylon can be dried depends on:
• The relative humidity of the drying atmosphere.Drying time decreases as the water content of tdrying air decreases. A dew point of –18°C (0°F)or less is recommended.
• The drying temperature. Increasing the dryingtemperature reduces the drying time. But airtemperatures in excess of 95°C (200°F) for longerthan 3 hr will discolor nylon. Compromises arerequired between drying time and temperature.The recommended temperature for drying Zytel®
nylons is 80°C (175°F). See Table 1.• The surface-to-volume ratio of the nylon. Particl
size is preset by manufacturing specifications aby regrinder screen size.
• Initial and final water content. The initial watercontent of the nylon can be estimated fromFigures 15 and 16, which show the moisturecontent of 66 type Zytel® nylon resins at variousrelative humidities as a function of exposuretime. When in doubt, quantitative analysis formoisture is a more accurate measure and willestablish the exact drying schedule. The requirefinal water content is determined by moldingrequirements and is usually less than 0.25%.
An efficient drying system circulates the moistureladen air through a dehumidifier where the wateris removed. The dried hot air is then passed overthe nylon.
In order for any dehumidification system to beeffective, the oven and air ducts must be airtight.The system should be periodically checked forleaks to be sure the equipment will permit efficiendrying. The drying air should have a dew point ofless than –18°C (0°F). The time to dry as a functionof resin moisture content is shown in Figure 18.
Hopper DryersA typical dehumidified hopper dryer systemconsists of a filter, blower, dehumidifier, heater ana hopper. Air is recirculated by the blower through
1
sm
he
end
d
-
t
d
Table 1Approximate Drying Times for 66 Nylon
Condition Approximate Drying Time, hr
–18°C (0°F) Dew Point Air,80°C (175°F) Temp.
Freshly-Opened Bag 3
Bag Opened for Several Days 20
Reground Material Stored inNon-Moisture Proof Containers 60
the dehumidifier. The dehumidified air is thenheated and passed through the resin bed in thehopper and back to the dehumidifier after passingthrough a filter. Pneumatic conveyors are used tofeed resin into the hopper.
The rate of drying in a hopper dryer will beessentially the same as that in a tray oven for thesame drying temperature and inlet air humidity.Necessary drying times can be estimated by usingFigure 18. Air temperature should be 80°C (175°F)and the operating dew point should be less than 0°F(–18°C). One advantage of the hopper dryer systemis the counter-current flow of polymer to air. Theair introduced at the bottom of the bed is the driestair and contacts the driest polymer since the poly-mer exits at the bottom of the hopper.
A number of suggestions that may prevent prob-lems with hopper dryers includes:• Selecting a reasonable drying schedule (see
Table 1). Do not overdry—it will discolor thenylon. Severe discoloration can indicate a lossof mechanical properties.
• Making sure that resin flows evenly through thehopper.
• Selecting proper hopper size for the anticipatedproduction rate.
• Making sure there are no leaks in the system.• Maintaining a constant drying temperature.
Vacuum DryingZytel® nylon resins can be dried in vacuum ovensor in rotary vacuum tumbler dryers. Figure 19shows the absolute pressure in inches of mercury(mm of mercury or kPa) required to achieve agiven equilibrium moisture content for a 66 typeZytel® nylon (e.g., Zytel® 101L) at various dryingtemperatures.
The preferred way to operate a vacuum drying ovenis as follows:1. Charge the oven or drying vessel with the nylon
resin to be dried.
7
Figure 18. Drying Data for Virgin Zytel® 66 Nylon Resin in a Dehumified Oven at 80°C (175°F)
.9
Dew Point–19°C (–2°F)
200 10 30 40 50 60Time, hr
109876
5
4
3
2
1.0.9.8.7.6
.5
.4
.3
.2
.1
Mo
istu
re, %
Figure 19. Vacuum Required to Dry Zytel® 66 NylonResins
0.3
0.2
0.1
00.5 1.0 1.5 2.0 2.5
12.7 25.4 38.1 50.8 63.5
kPa 1.7 3.4 5.1 6.8 8.5(mm of Mercury)
Absolute Pressure (in of Mercury)
30 29 28 (in of Vacuum)
Wat
er in
66
Nyl
on (a
t Equ
ilibr
ium
), w
t%
79°C(175°F)
91°C(195°F)
110°C(230°F)
2. Apply vacuum to the drying vessel. To mini-mize discoloration, it is desirable to evacuatethe vessel before heating the polymer.
3. Heat the vessel to the selected dryingtemperature.
4. The drying process is complete when the ovenpressure reading corresponds to the pressurerequired at the desired moisture level, as givenin Figure 19. Vacuum should be measured inthe drying vessel itself, not at the vacuumsource.
Any leakage of room air into the oven or dryingvessel will make the above described dryingtechnique invalid. This does not mean that nyloncannot be dried in a vacuum vessel that has someleaks. In such cases, estimation of the final mois-ture content of the nylon is not possible unless theamount of leakage and the relative humidity of theair leaking into the oven is known.
18
s
is
cn
Chapter 6
How To Obtain Optimum Toughness
When the end-use toughness requirements areunusually severe, normal considerations andhandling may be inadequate. If this appears to bethe case:• Select the best (toughest) Zytel® nylon resin forthe application.• Use molding conditions that provide the highest
toughness.• Reevaluate part design.
Selection of Zytel®Zytel® 101L is a general purpose type 66 nylonwith good toughness and is frequently a first choicfor a variety of uses. However, greater toughnesscan sometimes be obtained with other Zytel® nylonresins.
Zytel® 3189 and 408L, modified 66 nylon resins,have outstanding toughness and are superior toZytel® 101L in many uses. Their notch sensitivity iconsiderably better than that of Zytel® 101L.Consequently, Zytel® 3189 and 408L have per-formed well in many applications where thisattribute is important. Zytel® 3189 and 408L areeasy to mold, and, although their melt viscositiesare slightly higher than Zytel® 101L, they will fillthe mold cavity with little difficulty.
Zytel® ST801 is a modified 66 nylon able towithstand extremely high and repeated impacts.It has maximum toughness and will outperformalmost all engineering plastics in Izod impactstrength. The melt viscosity of Zytel® ST801 isslightly higher than that of Zytel® 3189 and 408L.
Molding Zytel® 3189, 408L andST801 for ToughnessAlthough the basic processing conditions thatprovide tough moldings from Zytel® 101L can beused in molding Zytel® ST801, 3189 and 408L,some additional considerations are necessary foroptimum toughness. These are:.• Minimize exposure of the molding powder to the
atmosphere in order to limit moisture absorption(see Chapter 5). The resin loses toughness if it molded with a higher moisture content.
19
e
• Take extra care to minimize overall thermalexposure due to holdup time and temperature.
• Use a melt temperature of 286–295°C(550–560°F) to obtain maximum toughness.Temperatures above 295°C (560°F) can reducethe toughness.
• Design parts so that weld lines will not appear inan area subject to impact. Weld lines can consti-tute a source of weakness. If the weld line islocated in a high impact area, molding Zytel®
408L with a higher melt temperature—303–315°C (575–595°F) can improve weld linestrength, although at some sacrifice in overalltoughness. Higher melt temperatures are notgenerally recommended for molding Zytel®
ST801.• Pack out parts of Zytel® 3189, 408L and ST801
to maximum part weight.• Use a screw retraction time equal to 90% of the
hold cycle in order to obtain a high uniformity oftoughness.
• Verify that the melt quality is acceptable.
Part DesignThe importance of avoiding sharp corners in plastiparts is discussed in Chapter 7. A careful evaluatioof part design will sometimes indicate areas inwhich corners may be given more generous radiiwhich will improve in overall toughness. Theoptimum corner radii is a function of the wallthickness (see Figure 26).
All parts should have generous radii. However,Zytel® ST801 shows less notch sensitivity andcan tolerate a smaller radius without significanttoughness loss.
Chapter 7
Interrelationship of Part Design, MoldingConditions, Resin Selection and Mold Design
d;p-
.
t
ion
Not this Not this
This This
Not thisNot this
ThisThis
This
Figure 21. Uniform Wall Thickness in Part Design
The performance of molded parts in end-useapplications is influenced by:• Part design• Molding conditions• Resin type• Mold designFactors in each of these four areas are interrelatefor an application to be successful, the relationshibetween them must be understood and accommodated. See Figure 20 for a listing of some of thesefactors. The following examples partially illustratethe importance of considering these relationships
Thickness of SectionSince the primary determinant of cycle time is parwall thickness, plastic parts should be designedwith the minimum wall thickness that will satisfythe specified structural requirements. Minimumthickness saves material and allows high productrates.
Wall thickness should be made as uniformly aspossible throughout the part to minimize partdistortion, internal stresses and cracking. Figure 21illustrates the incorporation of uniform sectionthickness in part design. If nonuniform wall
20
Figure 20. Interrelationship of Part Design, Molding Conditions, Resin Selection and Mold Design
Part Design Molding Conditions Resin Selection Mold Design
Properties Process Control Properties Gate Size, Location, TypeMechanical Melt/Mold Temperature Mechanical Runner/Cavity Layout
(Toughness, etc.) Cycle (Toughness, etc.) Draft AnglesThermal Pressure Thermal UndercutsChemical Ram Speed Chemical TolerancesElectrical Materials Handling Electrical Mold ShrinkageDimensional Stability Use of Regrind Dimensional Stability Location of Parting LineSunlight Temperature Profile Processing: Vent Size and Location
Bearing Areas Effects of Molding Flow Side ActionsRibs Toughness Mold Shrinkage Surface FinishBosses Mold Shrinkage Ejectability Coring for Water CoolingSharp Corners & Radii Weld Lines Cycle Runnerless MoldsUndercuts Post-Mold ShrinkageSection Thickness Part SurfaceSurface Finish Post-Molding Operations:Tolerances Quality ControlGate Size/Location Moisture Conditioning
AnnealingFinishingAssembly
e
f
-
s
thicknesses must be used in a part, blend wallintersections gradually, as shown in Figure 22.Also, under such circumstances, considerationshould be given to the appropriate technique forassembling two or more molded components.
Figure 22. Blend of Different Wall Thicknesses inPart Design
Ribs and StrengtheningMembersFlanges, beads or ribs can be used to increase pastrength without thickening the walls. Theseelements not only provide strength, but improvematerial flow and help prevent distortion duringcooling. In general, the base of a rib should be lesthan the thickness of the wall to which it is joinedand should be tapered in cross section for easyejection from the mold. Unsupported ribs and beashould be no higher than three times their wallthickness. Ribs and beads on side walls must beperpendicular to the parting line to insure ejectionfrom the mold. Careful placement of ribs and beadis important since they can lead to sink marks andsurface discontinuities. Properly handled in designribs can be decorative and functional.
Figure 23 illustrates the effect of heavy beads onpart surface and shows one solution to the probleof surface imperfections.
Figure 23. Effect of Beads on Part Surfaces
Where wall thicknesses are increased to provideadded strength, such as bosses surrounding holewhere machining is to be done, varying thicknessshould be blended gradually into each other asshown in Figure 24.
2
rt
s
ds
s
,
m
s ores
Figure 24. Blend of Varying Wall Thicknesses
BossesBosses are protruding pads that reinforce holes orincrease strength for assembly or mounting. Theseprotrusions are easily molded into the part. How-ever, it is essential that rounded corners and ad-equate fillet radii be incorporated in the design.
It is considered good design practice to limit theheight of the boss to twice its diameter to obtain threquired structural strength. Higher bosses can beprovided easily in a molded part at the discretion othe designer.
Fillets and RadiiSharp corners in plastic parts can contribute significantly to part failure. Eliminating them reducesstress concentration and produces a molding withgreater structural strength.
Fillets streamline the flow path for the moltenpolymer within the mold and permit easier ejectionof the part. Both inside and outside corners shouldhave radii as large as possible to reduce stressconcentrations. The recommended minimum radiuof 0.5 mm (0.020 in) is usually permissible evenwhere a sharp edge is required. The radius alsoextends mold life. A larger radius should be speci-fied wherever possible.
Figure 25 illustrates the effect of a fillet radius onstress concentration. Assume a force “P” is exertedon the cantilever section shown. As the radius “R”is increased, with all other dimensions remainingconstant, R/T increases proportionally, and thestress-concentration factor decreases as shown bythe curve.
The figure illustrates how readily the stress-concentration factor can be lowered by using alarger fillet radius. For example, the stress-concentration factor is reduced 50% (from 3.0 to1.5) by increasing the ratio of fillet radius tothickness sixfold (from 0.1 to 0.6). A fillet ofoptimum design is obtained with an R/T of 0.6, anda further increase in radius reduces the stress-concentration only a marginal amount. This is truein general for most shapes; however, other ratiosmay have to be used on specific parts because ofother functional needs.
1
Figure 25. Effect of Fillet Radius on Stress-Concentration Factor
3.0
2.5
2.0
1.5
1.0.0 .2 .4 .6 .8 1.0 1.2 1.4
R/T
Str
ess-
Co
nce
ntr
atio
n F
acto
r
P = Applied LoadR = Fillet RadiusT = Thickness
PR
T
22
UndercutsGenerally parts of Zytel® nylon can be molded witha 5% undercut, although in a few cases undercutsup to 10% have been successfully elected. Calcula-tion of the allowable undercut is illustrated inFigure 31. The wall thickness, diameter, length ofthe bending section and mold temperature arefactors which determine if the undercut isstrippable. Once the part with the undercut ismolded, it should be checked for excessive defor-mation or stress.
Chapter 8
Mold Design
itat
s
-
The design of molds for Zytel® nylon resins isgenerally similar to the design of molds for othersemicrystalline resins. However, a number ofspecific points should be considered.
Sprue BushingTo facilitate the removal of the sprue from themold, the internal bore of the sprue bushing istapered. Two standard tapers (0.5 and 1.5″) areavailable from various suppliers. The bore shouldbe well polished and free of machine marks.
Runner DesignRunner system design involves a compromisebetween several factors:• To minimize the amount of rework, the runner
system should be as compact as possible.• To provide adequate cavity pressure, a flow pat
that minimizes losses in pressure and heattransfer is desired. Proper packing of the cavityproduces parts with good physical properties anuniform dimensions.
• To provide cavity-to-cavity uniformity, therunner system should allow all cavities to fill atthe same rate and at the same time. In unbal-anced, or family molds, the runner system mayneed to be designed to provide a nearly constanfill rate.
Balanced vs. UnbalancedRunner SystemsIn balanced runner systems, flow distances from tsprue to the various cavities are equal. Balancedrunner systems give the greatest uniformity of flowfrom the sprue to each cavity, which promotes tigdimensional control in multicavity molds. Unbal-anced runner systems can cause mold fillingproblems and poor control of tolerances. Figure 26shows the difference between a balanced andunbalanced (lateral) runner system for an eight-cavity mold.
Occasionally, balancing the runner system conflicwith the design philosophy of minimum runnervolume (lateral layout). In some cases, it may bebetter to accept the additional amount of rework(greater runner volume) that results from thebalanced runner system. The runner system shoube designed for proper molding, part quality, and
2
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d
t
he
ht
ts
ld
minimum regrind. Careful design, engineering andattention to the demands of part quality shoulddictate whether the runner is to be a balanced orlateral one.
Runner ShapeWhen possible, round runners are preferred. Around runner has the minimum surface area per unvolume, thereby giving the lowest pressure and helosses. The minimum diameter of a round runner isusually about 3 mm (0.125 in) although thickerones should be used for thick parts and thinner onemight be used for thin parts. The most accurateway to determine runner size is to calculate theanticipated pressure drop and size the runneraccordingly.*
Trapezoidal runners might be preferred overrectangular runners because of greater ease ofejection and machining. The slope of the sidesshould be 5° per side, while the depth should bedetermined by the diameter of an inscribed circle.
Gate DesignThe gate connects the runner and the cavity. It isdesigned to act as throttling and shut off valve forthe cavity. It regulates the flow to the cavity and itshould freeze quickly when flow ceases.
Selecting the Type of GateGates are usually round or rectangular. A rectangular gate is preferred since it can independentlycontrol the flow rate through the gate and the gatefreeze time. The thickness (or diameter) of a gatedetermines the time for the gate to freeze, while thegate width (or diameter) determines the volumetricflow rate through the gate. With a round gate, a
Figure 26. Cavity Layout
Balanced(Preferred)
Unbalanced(Lateral)
*For information on sizing runners, see: PLAST. TECH, April 1980.
3
f
e
h
e
change in radius changes both the gate freeze timand the flow rate.
Round gates are preferred for automatic three-plaand tunnel-gated molds because of ease of gateseparation and part ejection.
In addition to round and rectangular gates, there amany other types of gates. Several are describedTable 2.
Table 2Table of Gates
Gate Type Application
Rectangular Conventional
Fan (see Figure 27) Uniform filling large thin parts
Slit (Flash) Rapid fill and freeze time for thin to wide(see Figure 28) parts and to avoid certain weld lines
Diaphragm Eliminate weld lines and improve(see Figure 29) circularity for cylindrical parts
Sprue Single cavity molds or thick parts
Pinpoint Simple and clear degating(size 0.25 to 1.5 mm [0.010 to 0.060 in])
Tunnel Gates Automatic degating. Design is critical(see Figure 30)
Cavity Fan gate
Section A-A
Runner
Partingline
A
Runner
Cavity
A
Fan gate
Figure 27. Fan Gate
Figure 28. Flash Gate
Runner
GateLarge
thin section part
2
e
te
re in
When there are large differences in the thickness othe part, it is best to gate into the thicker section tosimplify filling and to minimize sinks and voids.
To minimize surface defects and jetting, the flowfrom the gate should impinge against the wall of thcavity or a core pin. However, gates should not bepositioned so that the incoming melt stream isdirected against a core that is not registered in botmold halves.
Location of the gate will determine the position ofthe vents. Consequently, it is desirable to positionthe gate so that venting is simple an adequate. (seChapter 8, Venting.)
Circular parts should be centergated if closetolerances or roundness are required. However,with parts of small diameter, it is often possibleto gate at the edge and still maintain adequateroundness and flatness.
Figure 29. Diaphragm Gate
Part
Gate
Figure 30. Tunnel Gates
Short tunnel gate
Long tunnel gate
Ejector pin
Angle not critical
30˚ max.
4
f
t
Estimating Gate DimensionsFor rectangular gates, the gate thickness should 65% of the part thickness, the gate width should one to two times the gate thickness, and the gateland should be no more than 1 mm (0.040 in).
For round gates, the gate diameter should be 55%of the part thickness.
The gate sizes recommended are conservative awill permit adequate filling of average cavities.
Mold CoolingMolds operated without any cooling ultimatelyreach an equilibrium temperature, as the heat adto the mold by the molten polymer equals the healost by conduction and convection. The moldtemperature at the optimum molding cycle will becompromise between a hot mold for ease of fillinand surface quality and a cold mold for rapidsolidification and ejection of the part. Therefore,facilities for heating or cooling the mold must beprovided. Ideally, the mold-cooling channels shoube located in those areas that require the most htransfer. These channels should not be closer to cavity wall than one channel diameter.
For uniform mold temperature, the temperaturedifference between the entering and exiting coola(water, oil, etc.) should be as small as possible(5°C [10°F] maximum). The flow rate of coolantthrough the channels should be high enough thatsmall fluctuations in flow rate will not alter themold temperature. For high tolerance molding, thcavities should be cooled in a parallel arrangemewhich makes each cavity temperature more unifothan a series configuration.
VentingInadequate mold venting can cause the followingproblems:• Discoloration (burning) of the nylon• Erosion or corrosion of the mold
2
% Undercut(A–B) • 100
B
= Insideof
moldedpart
B
A
B
A
Figure 31. How to Calculate Undercuts for Molding Zy
bebe
nd
dedt
ag
ldeatthe
nt
entrm
• Poor weld line strength• Large dimensional variation on the molded part• Short shots• Surface blemishes on the molded part
The location of the vents will be determined bycavity design, mold design, and molding condi-tions, but it is not always possible to determine theoptimum vent location prior to molding. Usuallyvents are required at weld lines and at the bottom oblind cavities.
Runners should be vented at the sprue puller and athe parting line. Cavities should be vented at theparting line, at ejector or fixed pins, or by insertinga dummy pin into the cavity at the point where airis trapped.
The vents for cavities and runners at the parting lineare usually grooves 3.2–6.4 mm (0.125–0.25 in)wide and 0.013–0.019 mm (0.0005–0.00075 in)deep, extending from the cavity wall out to about1.6 mm (0.0625 in) from the cavity. Beyond thispoint, the grooves are relieved to 0.13–0.25 mm(0.005–0.010 in) deep, out to the exterior ofthe mold.
UndercutsThe following are general suggestions for ejectingundercuts with Zytel® nylon resins:• The undercut should be rounded and well fitted to
permit easy slippage of the plastic part over themetal.
• If deformation of the undercut is evident, themolding parameters should be adjusted to mini-mize the effect. Frequently, higher mold tempera-tures or shorter cycles can be useful in strippinginternal undercuts while longer cycles and highershrinkage could aid the stripping of externalundercuts.
5
% Undercut(A–B) • 100
C
=Outside
of molded
part
C
AB
C
AB
tel® Nylon Resins—Calculations for % Undercut
Runnerless Molds—Typesand TermsThe term runnerless includes all types of moldsfrom which no frozen runner is ejected as the mocycles. The simplest runnerless mold is a singlecavity mold with a hot sprue bushing (Figure 32).Like the hot sprue bushing, a hot manifold or hotrunner (Figure 33) maintains all of the moltenplastic in the melt distribution system to the partgate at a temperature above its melting point.
Heaterto here
Gate Reverse taper
Meltflowpath
Coilheater
Figure 32. Hot Sprue Bushing
Heatedprobe
Hotrunner
Drop
Gate Hot manifold Gate
Figure 33. Hot Manifold Runnerless Mold
An insulated runner (Figure 34) usually has a largediameter that permits the melt to flow through thecenter of a frozen insulating skin of plastic. Insu-lated runners depend on frequent replacement ofhot molten plastic in the center during uninterruptcycling of the mold. Because a cycle interruptioncan freeze the inner molten core, it may be necessary to open the mold at a secondary parting lineand to discard the insulated runner before startinagain.
A hot and insulated runner hybrid that could becalled an internally heated, insulated runner systeis shown in Figure 35. The large insulated runnerhas a frozen skin, but the melt flows around aheated tube in the center of the insulated runner.Internally heated insulated runner molds willtolerate cycle interruptions and can be restartedwithout discarding the insulated runner by heatinthe internal tubes.
2
ld
theed
-
g
m
g
Figure 34. Insulated Runnerless Mold
Heatedprobe
InsulatedRunner
Runnerextractingbushing
Gate Drop
Movable torpedo(valve gate)
Fixed torpedo(open gate)
Heatedtube
Gate DropMeltpath
Cartridgeheater
Figure 35. Hybrid Hot Manifold—InsulatedRunnerless Mold
Some molds may be semi-runnerless; that is,several small frozen runners may be molded off abasic runnerless system. This is often done tocluster a number of very small parts around eachrunnerless gate. It is also a useful means for intro-ducing the multiple gates through a central core tocontrol roundness.
Gate ApproachesIn any runnerless system, heat must be supplied tothe drops with heater bands, coil heaters, or otherexternal sources; or with an internally heated probeor torpedo. Sometimes the probe reciprocates,doubling as a valve pin. In externally-heated dropsa simple valve pin may be used. In either case, thevalve may be operated by hydraulic or air cylinders,or by a combination of injection pressure andspring action. Another variation is to allow thesmall amount of plastic at the gate to freeze duringevery cycle and then remelt it by means of aseparate small heater element in the tip of theprobe. A valve gate helps to control drool, string-ing, gate vestige or stub, and gate freeze-off thatmight occur with Zytel® nylons.
6
m,
-s
t
Insulated RunnerThe choice between insulated and hot runner typhinges on some important characteristics associawith these systems. The insulated runner producestreamlined melt flow path, since all resin that donot flow will freeze and become a permanent parof the insulating layer. This streamlined systemdecreases the possibility of overheating and degring the plastic melt in the runner, although not inthe drops where the heat is added.
Insulated runners require a certain minimumamount of resin per minute moving through eachbranch to maintain thermal equilibrium and toprevent runner freeze-off. The amount varies withthe resin, design features, and molding conditionsbut the minimum is generally in the range of0.18–0.35 oz/min (5–10 g/min) at each gate.
Insulated runners also require adequate machineclamping force to keep the runner parting lineclosed during start-up. This is important only whethe runner projected area is outside the perimetethe cavities.
Hot RunnerIn true hot runner molds, the melt flow path shoulbe streamlined to avoid holdup spots. Trapped regradually degrades and bleeds into the melt streaoccasionally discoloring it and causing blackspecks. The difficulty in developing a good streamlined flow path increases as the number of cavitieincreases.
2
esteds a
est
ad-
,
nr of
dsin
A fairly uniform melt temperature must be main-tained to avoid overheating and to avoid variationsin melt flow and resin quality delivered to differentdrops. Good temperature control for Zytel® can be adifficult task. A differential of 220°C (400°F) ormore between the runner and cavity plates iscommon. Reduction of metal-to-metal contactbetween the manifold and the rest of the mold, pluscareful cavity cooling, can help maintain thisdifferential.
DropsTemperature control and streamlining are majorareas for consideration in the drops and the cornersleading to the drops. Since heat losses are greatesnear the gate, this area sets the minimum tempera-ture needed to maintain flow. Unless provisions aremade to distribute the heat, maintaining minimumtemperature near the gate could cause overheatingin other areas. When internally heated probes areused, the plastic on the outside surface of the dropsfreezes and insulates the runner. If the internalheater extends too high, stagnant areas where theprobe enters the runner may be heated to melttemperature, constituting a holdup spot where resincould degrade.
7
Chapter 9
Dimensions
The difference between mold cavity dimensionsand end-use dimensions of parts molded fromZytel® nylon resins depends on a number of factorThese include:• mold shrinkage (as measured on the dry-as-molded part at 23°C (73°F) within 24 hr aftermolding)
• post-mold shrinkage due to annealing• end-use temperature and humidity
Mold ShrinkageMold shrinkage depends on the type of nylon beinprocessed, molding conditions, and mold design.Mold shrinkage for:• Zytel® 101L NC101,• Zytel® 103HSL NC010,• Zytel® 105 BKO10A, and• Zytel® 408L NC010
can be approximated by the use of Figure 36,which is a nomograph that has been divided intotwo sections. Section A depends on mold designand Section B depends on molding conditions and
28
Gate Widthinch mm
b1.0
.8
.6
.4
.3
.2.15
.1.08.06
.04
.03
.02
.01
25
15
108
543
2
1
.5
GateThickness
inch mmh
.01
.02
.03
.04
.05
.06
.08
.10
.15
.20
.30
.40
.50
.60
.801.0
.5
.75
1
1.5
2
3
4
6
8
10
15
2025
R
PartThickness
inch mm
AValue
mil/inch
.5
.75
1
1.5
2
3
4
6
8
10
15
2025
.25
3
6
9
12
15
18
21
24
27
30
33
Mold Shrinkage = A + B
.01
.02
.03
.04
.05
.06
.08
.10
.15
.20
.30
.40
.50
.60
.80
1.0
Section A: Mold Variables
Figure 36. Mold Shrinkage Nomograph for Zytel® Nylon
s.
g
type of nylon. The use of Figure 36 is illustrated inthe following example.
ExampleEstimate the mold shrinkage of Zytel® 101L NC010in a 76 × 152 × 3.2 mm (3 × 6 × 0.125 in) plaquemold with a rectangular gate 2.3 mm (0.09 in) thickand 3.2 mm (0.125 in) wide.
Inserting the mold dimensions into the moldvariables section of Figure 36 gives a value ofA = 20.5 mil/in (2.05%).
Molding experience indicates that the followingassumed molding conditions are reasonable: 288°C(550°F) melt temperature, 65°C (150°F) moldtemperature, and 15,000 psi (103 MPa) injectionpressure. These data are now inserted into theprocessing variables side of Figure 36 until lineB1 is reached. A value of –6 is obtained. The moldshrinkage of Zytel® 101L NC010 is now deter-mined by adding the value A obtained from moldvariables and the value B obtained from processingvariables. A mold shrinkage of 14.5 mil/in (1.45%)is obtained for Zytel® 101L NC010.
Melt Temperature°C°F
MeltPressure
Valuemil/inch
KeyB1 = Zytel® 101 NC010, 101L NC010, 103 HSL, NC010, 122LB2 = Zytel® 105 BK010AB3 = Zytel® 408L NC010
Section B: Process Variables
590
580
570
560
550
540
530
520
510
500
490
260
270
280
290
300
310 °C°F200
Mold Temperature
1000PSI MPa
20
10
40
30
60
50
80
70
90
180
160
140
120
100
80
60
400
B1 B2 B3
25
20
15
10
5
0
40
20
80
60
120
100
160
140
–14
–12
–10
–8
–6
–4
–2
0
+2
+4+2
0
–2
–4
–6
–8
–12
–10
–14
–2
+2
+4
+6
0
–4
–6
–8
–10
–12
–14
Resins
e
a
e
lff
s
-
Mold Shrinkage, mil/inResin 1/16″″″″″ thick 1/8″″″″″ thick
Zytel® ST801, ST800L, 3189 11–18 15–20
Zytel® ST811HS 5–11 8–14
Zytel® ST901L 3–5 4–6
Zytel® 151L, 153HSL,Zytel® 158L, 157HSL BK010 8–14 10–16
Zytel® 132°F 2–9 4–12
Zytel® FR10 8–12 8–14
Data based on 3 × 5 in plaques.
Figure 37. Mold Shrinkage of Zytel® Nylon ResinsNot Covered in Figure 36.
The mold shrinkage of the other resins may beestimated in a similar way by using the correct Bfactor.
For half-round gates, the effective gate thickness80% of the radius and the effective gate width istwice the radius. For round gates, the effective gathickness is 80% of the diameter and the effectivgate width is equivalent to the diameter.
Mold shrinkage values of other Zytel® nylon resinsnot shown in Figure 36 are given in Figure 37.
Post-Mold ShrinkageThe as-molded crystallinity of parts molded inZytel® depends on mold temperature, part thickneand the type of nylon being processed. The crystlinity of thick section parts remains fairly constantand independent of mold temperature. However,thin sections molded in cold molds undergo apprciable post-molding crystallization that results inadditional part shrinkage.
Post-mold shrinkage can be accelerated by anneing. The annealing process should be carried outthe absence of air at a temperature of 28°C (50°F)above the end-use temperature—temperatures o150–177°C (300–350°F) are often used for generaannealing. The annealing time should be 15 min each 3.2 mm (1/8 in) of cross section. Heat transfluids that are currently used include high boilinginert mineral oils, such as Dow Corning 500 silicooil. The annealing shrinkage of plaques of Zytel®
101L nylon (51 × 51 mm [2 × 2 in]) × variousthicknesses versus mold temperature is given inFigure 38. These data show that:• For any part thickness, annealing shrinkage
decreases with increasing mold temperature.• Annealing shrinkage is more significant for part
with thin walls.
2
is
te
ssl-
-
al-in
f
orer
n
Figure 39 shows the combined mold shrinkage andannealing shrinkage as a function of mold temperature for the same plaque of Zytel® 101L. Totalshrinkage (mold and annealing shrinkage) is onlyslightly affected by mold temperature.
149(300)
177(350)
121(250)
93(200)
66(150)
38(100)
.001.002.003.004.005.006.007.008.009.010.011.012
Mold Temperature °C (°F)
Ann
ealin
g S
hrin
kag
e,m
m/m
m (i
n/in
)
0.8 mm thick(1/32 in)
1.6 mm (1/16 in)
3.2 mm (1/8 in)
6.4 mm (1/4 in)
51 mm x 51 mm (2 in x 2 in)Plaques, Gate Thickness = 1/2 Part Thickness Gate Width = Part ThicknessAnnealed at 163°C (325°F) for 1 hr
Figure 38. Shrinkage During Annealing vs. MoldTemperature for Zytel® 101L NC010
121(250)
149(300)
93(200)
66(150)
38(100)
Tota
l Shr
inka
ge,
mm
/mm
(in/
in)
6.4 mm (1/4 in)
51 mm x 51 mm (2 in x 2 in)Plaques, Gate Thickness = 1/2 Part Thickness Gate Width = Part ThicknessAnnealed at 163°C (325°F) for 1 hr
Mold Temperature, °C (°F)
.010
.015
.020
.025
1.6 mm (1/16 in)
0.8 mm (1/32 in)
Total Shrinkage = Mold Shrinkage + Annealing Shrinkage
Figure 39. Total Shrinkage after Annealing vs. MoldTemperature for Zytel® 101L NC010
Effects of Moisture andTemperature on DimensionsWhen parts molded of Zytel® nylon are ejectedfrom the mold, they have a relatively low watercontent. These dry-as-molded parts will slowlyabsorb moisture from the atmosphere until anequilibrium with the moisture in the air is reached.Absorption of water by the nylon results in anincrease in part dimensions.
Dimensional changes due to water absorption canbe accelerated by conditioning the parts in boilingwater. Moisture-conditioning procedures arediscussed in detail in the “Design Handbook forZytel® Nylon Resins,” bulletin H-58636. The timerequired to condition Zytel® 101L nylon to 50%
9
relative humidity and 100% relative humidity(saturation) is given in Figure 40. When theexposure time is relatively short and the moistureabsorption is not at equilibrium, the water isconcentrated preferentially near the surface.
It redistributes itself after an extended time.
Thickness, mm0 2.5 5.1 7.6 10.2 12.7 15.2
Thickness, in0 0.1 0.2 0.3 0.4 0.5 0.6
Tim
e, h
r
1,000
100
10
1
0.1
To 100% RH
To 50% RH
Figure 40. Time to Condition Zytel® 66 Nylon Resinsin Boiling Water
The combined dimensional changes due to moistabsorption and temperature for annealed partsmolded in Zytel® 101L and 151L are given inFigures 41 and 42. In these figures, the coefficientof thermal expansion has been assumed to be0.00009 mm/mm/°C (0.00005 in/in/°F) for bothresins over the temperature range listed.
Dimensional TolerancesThe allowable variations in the dimensions of aninjection molded part are called the tolerances ofthe part. The tolerances set on any fabricated artirepresent a compromise between the functioning the part and the cost of manufacturing.
SPI Standards for tolerances on articles moldedfrom nylon resins (including Zytel® nylons) areshown in Figure 43. The information given in thisfigure is based upon industry experience. Thisinformation does not represent hard and fast rulesapplicable to all conditions, but rather the consensus of molders as to what may be achieved undeaverage conditions. Experience has shown that, i
3
ure
cleof
-rn
100% Relative Humidity (RH)
90% RH
70% RH
50% RH
30% RH
10% RH
Annealed Dry
30
25
20
15
10
5
0
–5
Temperature
°C –20 0 20 40 60 80°F –4 32 68 104 140 176
Dim
ensi
onal
Cha
nge
Leng
th (m
il/in
or µ
m/m
)
Figure 41. Dimensional Changes of Zytel® 101L vs.Temperature at Various Humidities(Annealed Samples)
Figure 42. Dimensional Changes of Zytel® 151L vs.Temperature at Various Humidities(Annealed Samples)
15
10
5
0
–5
Temperature
°C –20 0 20 40 60 80°F –4 32 68 104 140 176
Dim
ensi
onal
Cha
nge
Leng
th (m
il/in
or µ
m/m
)
100%
Relative
Humidit
y
50% Rela
tive Hum
idity
Annea
led-Dry
0
e
many cases, the fine tolerance band can be reducby at least 50%. The table indicates what may bereasonably achieved in normal operation.
The ability to maintain minimum tolerances isdependent on part design, the number of cavities,mold design, the injection molding system used,molding conditions, and the ability of the molder.Only by optimizing all of these variables can thetightest of tolerances be maintained.
Effect of Part DesignA part with several critical dimensions will natu-rally be more difficult to mold than a part with fewcritical dimensions. Wherever possible, the numbeof critical dimensions per part should be reason-able. Tight tolerances should not be put on dimen-sions across a parting line or on sections formed bmovable cores or sliding cams.
Effect of Mold DesignTo improve the control over tolerances inmulticavity molds, the differences in size betweenthe various inserts must be negligible. Also, thesize of the runners and gates must be identical.Otherwise, the rate of fill and cavity pressures willvary, resulting in poor control over tolerances.Whenever possible, balanced runner systemsshould be used for molding close tolerance parts.Minimum tolerances are more difficult to achievein family molds.
31
ed
r
y
Effect of Molding ConditionsIf fine tolerances are to be maintained, moldingvariables must be closely controlled becausevariations in molding conditions affect both partweight and shrinkage. Variations in melt tempera-ture affect gate freeze-off time, rate of fill, cavitypressure, and therefore the part dimensions. Mod-ern instruments can control temperatures to ±1°C(± 2°F). To maintain close control over tolerances,the overall molding cycle time must be constant;otherwise, melt temperature fluctuations willreduce tolerance control.
Changes in mold temperature occur over a longerperiod of time, and would more likely be seen as along term drift in part dimensions rather than as ashot-to-shot variation. However, temperaturedistributions across the face of the mold can resultin differences in part size on a part-to-part basis.
Fluctuations in cavity pressure affect packing of thpart, and hence its final dimensions. Moderninjection molding machines with good hydraulicsystems in good repair can maintain the constantinjection rates and pressures required for moldingwithin fine tolerances.
32
Figure 43. Standards and Practices of Plastics Custom Molders (inches)Engineering and Technical Standards—Zytel® Nylon Resins
Note: The Commercial values shown below represent common production tolerances at the most economical level.The Fine values represent closer tolerances that can be held but at a greater cost.
A
F
F
B
PL
J
E
GD
C
DrawingCode
Dimensions(Inches) 1
0.000A = Diameter(see Note #1)
B = Depth(see Note #3)
C = Height(see Note #3)
D = Bottom Wall(see Note #3)
E = Side Wall(see Note #4)
F = Hole SizeDiameter
(see Note #1)
G = Hole SizeDepth
(See Note #5)
Draft Allowanceper side
(see Note #5)
Flatness(see Note #4)
Thread Size(class)
Concentricity(see Note #4)
J = Fillets, Ribs,Corners
(see Note #6)
Surface Finish(see Note #7)
Color Stability(see Note #7)
2.000
3.000
4.000
5.000
6.000
0.003
0.004
0.005
6.000 to 12.000for each additional
inch, add:
0.000 to 0.125
0.125 to 0.250
0.250 to 0.500
0.250 to 0.500
0.500 and Over
0.500 to 1.000
0.000 to 3.000
3.000 to 6.000
Internal
External
(T.I.R.)(in/in diameter)
.010
.015
1
1
.010
0.000 and 0.250
0.002
0.003
0.003
0.004
0.005
0.005
1 1/2°
0.004
1.000
2 3 4 5 6 7 8 9 10 11 12 13 14Plus or Minus in Thousands of an Inch
15 16 17 18 19 20 21 22 23 24 25 26 27 28
Reference Notes
1. These tolerances do not include allowance for aging characteristics of material.
2. Tolerances based on 1/8" wall section.
3. Parting line must be taken into consideration.
4. Part design should maintain a wall thickness as nearly constant as possible. Complete uniformity in this dimension is impossible to achieve.
5. Care must be taken that the ratio of the depth of a cored hole to its diameter does not reach a point that will result in excessive pin damage.
6. These values should be increased whenever compatible with desired design and good molding technique.
7. Customer-Molder understanding necessary prior to tooling.
—
—
—
020
—
—
0.002
0.003
0.003
0.001
0.002
0.002
0.003
0.003
0.004
0.002
Comm. ± Fine ±
Commercial
Fine
1/2°
.004
.007
2
2
.006
.012
33
Figure 43. Standards and Practices of Plastics Custom Molders (millimeters)Engineering and Technical Standards—Zytel® Nylon Resins
Note: The Commercial values shown below represent common production tolerances at the most economical level.The Fine values represent closer tolerances that can be held but at a greater cost.
A
F
F
B
PL
J
E
GD
C
DrawingCode
Dimensions(mm) 0.1
0A = Diameter(see Note #1)
B = Depth(see Note #3)
C = Height(see Note #3)
D = Bottom Wall(see Note #3)
E = Side Wall(see Note #4)
F = Hole SizeDiameter
(see Note #1)
G = Hole SizeDepth
(see Note #5)
Draft Allowanceper side
(see Note #5)
Flatness(see Note #4)
Thread Size(class)
Concentricity(see Note #4)
J = Fillets, Ribs,Corners
(see Note #6)
Surface Finish(see Note #7)
Color Stability(see Note #7)
50
75
100
125
150
0.08
0.10
0.13
150 to 300for each additional
mm, add (mm):
0 to 3
3 to 6
6 to 13
6 to 13
13 and Over
13 to 25
0 to 75
75 to 150
Internal
External
(T.I.R.)mm/mm diameter
0.25
0.38
1
1
0.25
0 and 6
0.05
0.08
0.08
0.10
0.13
0.13
1 1/2°
0.10
25
Plus or Minus in Millimeters
—
—
—
0.50
—
—
0.05
0.08
0.08
0.03
0.05
0.05
0.08
0.08
0.10
1/2°
0.05
Comm. ± Fine ±
Commercial
Fine
0.10
0.18
2
2
0.15
0.30
0.2 0.3 0.4 0.5 0.6 0.7
Reference Notes
1. These tolerances do not include allowance for aging characteristics of material.
2. Tolerances based on 1/8" wall section.
3. Parting line must be taken into consideration.
4. Part design should maintain a wall thickness as nearly constant as possible. Complete uniformity in this dimension is impossible to achieve.
5. Care must be taken that the ratio of the depth of a cored hole to its diameter does not reach a point that will result in excessive pin damage.
6. These values should be increased whenever compatible with desired design and good molding technique.
7. Customer-Molder understanding necessary prior to tooling.
Chapter 10
Quality Control
The quality of a molded part of nylon is a reflectioof the quality of the resin used and the moldingprocedures employed. If acceptable moldingconditions, mold design, and quality resin are usepart quality will be satisfactory. If either resin ormolding procedures are deficient, part quality coube unacceptable. Usually, part quality problems cbe classified into three general areas: toughness,appearance, and dimensions. See the previouschapter for a discussion of dimensions.Resin SpecificationsAll Zytel® resins are monitored and carefullycontrolled for uniform quality. This quality will bepreserved if the shipping containers remain intactduring transit or storage. If the container or seal isbroken, the resin will absorb moisture which willaffect its quality.
All additives such as color stabilizers and UVstabilizers, lubricants, and colorants are controlledto give consistency of performance both in moldinand in end use.
The tests run on Zytel® to assure that every lot hasthe consistent quality that has been the tradition fZytel® resins include:• Moisture content• Solution or melt viscosity• Toughness-lzod impact strength• Tensile strength and elongation• Additive concentration
Moisture ContentMoisture content of Zytel® resins as shipped iscontrolled to a level where only routine dryingshould be required prior to molding. Since dryingschedules vary from resin to resin, consult indi-vidual product sheets for a typical set-up. If resin iallowed to stand exposed to the atmosphere in opcontainers for long times, the drying scheduleshould be modified accordingly. If a precise dryingschedule is needed, a moisture determination on resin will permit setting an appropriate schedule.The “as shipped” moisture specification varies froone resin type to another.
Excessive moisture not only affects the flow of theresin but also reduces toughness as well as produing other common flaws. (See Chapter 5.)
3
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ldan
g
or
sen
the
m
c-
Solution ViscosityThe solution viscosity (relative viscosity [RV]) or(inherent viscosity [IV]) of a resin is a measure ofthe molecular weight, which in turn controlstoughness and moldability. Zytel® nylons aremanufactured with a good molecular weightbalance between flow in the machine and parttoughness. Since excessive moisture and heat cancause a loss of molecular weight and hence a lossof toughness, care must be exercised to protect thisproperty. For resins that are soluble in commonnylon solvents, the RV can be measured. For resinsthat have been modified with insoluble additives(glass, minerals, tougheners, etc.) other means suchas melt viscosity must be employed to evaluatemolecular weight.
ToughnessSince Zytel® nylons are often specified because oftheir toughness, Izod impact strength is closelycontrolled on the “as shipped” resin. Excessivemoisture during molding degrades the molecularweight and reduces toughness. (See Chapter 6.)
Specifications on Molded PartsIn injection molding certain visual observations andlaboratory results can be used to determine thequality of a part. These are discussed below.
AppearanceThe molding operator can detect flash, burn marks,etc., by visually inspecting the molded parts.Usually these problems can be corrected by chang-ing molding conditions or revising the mold.
For many resins, contamination, voids, and sinkscan best be detected by illumination from a stan-dard lamp such as “Illuminant” C or by transmittedlight. In some cases, microscopic examination(10 to 100× magnification) can be used to inspectsmall but important details of the molding (voids,crystallinity and contamination). Some of the morecommon problems that affect the appearance andtoughness of molded nylon parts are:• Color—Rating may be done with respect to both
the actual shade and the uniformity of colorthroughout the part. Discolored parts should bediscarded and not reground.
4
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• Splay—Although major amounts of splay areusually observed at the machine, small amounmay go undetected until subjected to closer visexamination. The observation of small amountsof splay may also give clues to molding machintrends that will lead to large amounts of splay.Usually splay is caused by excessive moistureor heat.
• Flash—Visual examination is the simplest way check for flash.
• Burn Marks—These marks may be detected atthe machine. They could be indicative of too faa fill speed or poor venting.
• Short Shots—Gross short shots are easily de-tected at the machine. However, small depres-sions can be caused by incomplete fill.
• Weld Lines—The presence of visual weld linesconstitutes a cosmetic defect and may also resin reduced part strength.
• Contamination—Surface contamination can oftebe detected at the machine. Internal contamination within thin section parts can often be foundby viewing with a strong light. For small amounof contamination, microscopic examination canbe used.
• Finish—The accuracy of reproduction of themold surface as well as the existence of unwanscratches can be detected by visual examinatio
• Unmelted Particles—These can often be seen bcareful visual inspection of the part. They appeas discrete particles of different shade.
• Voids—In thin sections, voids can be detected bviewing the molded part through a powerful lighbeam. Microscopic examination of sliced sectioof the parts also can be used to detect small vo
ToughnessThe toughness of parts molded in Zytel® nylon canbe estimated by relative viscosity, pass-or-fail tesdestructive testing techniques and end-use testsany of these tests, water content must be specifiesince the toughness of molded nylon parts isinfluenced by moisture.
Relative Viscosity (RV)The potential level of toughness of nylon is roughproportional to its molecular weight. The relativeviscosity, which is a measure of the molecular
3
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ult
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tedn.
yar
ytnsids.
ts,. Ind
ly
weight, can be determined as described in ASTMProcedure D789. Since this test depends upon thesample dissolving in formic acid, its usefulness islimited to unmodified nylons such as Zytel® 101Land 103HSL. An acceptable RV is necessary butnot sufficient to ensure toughness of a given part.Uneven molecular degradation throughout the partcontamination, and stress risers reduce toughnessbut will not necessarily be detected by measure-ment of relative viscosity.
Pass-or-Fail Impact TestsThe results from these tests are difficult to quantifyIn most cases, a large number of individual testsmust be conducted before a trend can be discerneFrequently a criterion is chosen where 50% of allsamples pass a given height (or weight) and theother 50% fail. The corresponding height or weightis a measure of the toughness.
Gardner impact, dart impact or instrumented impactests all fall into this category. In some cases theactual test parameters are specified (see ASTMD3029 for Gardner impact and ASTM D256 forIzod) and in others the conditions are chosenarbitrarily. In establishing a test program, severalfactors must be specified and controlled.
• Sample Orientation and Geometry—The impactdart must apply the same load to the samelocation every time.
• Sample Temperature—Must be constant andcontrolled. This is particularly important at testtemperatures other than room temperature. Anyunusual temperature variation will influence theresult. Cold temperature impact tests are espe-cially difficult to control.
• Sample Moisture Content—The moisture contentin each part influences its behavior in an impacttest. Moisture content must be kept constant foreach sample and preferably should be measured
End-Use TestsThese tests should be representative of the end-usapplication of the part. Care must be taken to makesure that meaningful conditions are employed.These conditions should simulate and not exceedthe design stress level; otherwise, good parts maybe rejected.
5
36
Chapter 11
Troubleshooting Guide
Problem Areas
Drooling 2 1
Splay 2 3 4 1 6 5
Short Shots 2 3 4 5
Sinks 2 4 3 6 7 5
Voids in Part 2 4 3 5 6
Flash 2 3 4
Burn Spots on Part 1 2
Poor Weld Lines 1 2 3 4
Parts Stick in Mold 2 3 4
Shot to Shot Variation inPart Size 2
Warpage 4 5 6 2 3 7
Screw Does Not Retract orRetracts Erratically 1 2
Unmelted Particles 2 1
Sprue Sticking 1
Incr
ease
Inje
ctio
n P
ress
ure
Suggested Remedies
(Try in order recommended)
Dec
reas
e In
ject
ion
Pre
ssu
re
Incr
ease
Inje
ctio
n R
ate
Dec
reas
e In
ject
ion
Rat
e
Incr
ease
Scr
ew F
orw
ard
Tim
e
Dec
reas
e S
crew
Fo
rwar
d T
ime
Incr
ease
Mel
t T
emp
erat
ure
Dec
reas
e M
elt
Tem
per
atu
re
Incr
ease
Mo
ld T
emp
erat
ure
Dec
reas
e M
old
Tem
per
atu
re
Dec
reas
e N
ozz
le T
emp
erat
ure
Incr
ease
Cyl
ind
er T
emp
erat
ure
Incr
ease
Bac
k P
ress
ure
37
Use
Mel
t D
eco
mp
ress
ion
(su
ck b
ack)
4 7 6 3 5
7 9 8
7 6 1
8 1
7 8 1
1 5
4 3 5 6
5 6
5 1
1 3
1 8
3 3
3
2 3 4 5 6 7
Incr
ease
Cyc
le T
ime
Ch
eck
Pad
Siz
e (C
ush
ion
)
En
larg
e N
ozz
le O
rifi
ce
Incr
ease
Cla
mp
Pre
ssu
re
Rep
air
Mo
ld
Use
Mo
ld R
elea
se
Ch
eck
Scr
ew R
etra
ctio
n
Incr
ease
Tap
er
Ch
eck
for
Bu
rns/
Rad
ius
of
No
zzle
Incr
ease
No
zzle
Tem
per
atu
re
En
sure
Res
in is
Dry
Ch
ang
e G
ate
Loca
tio
n
Use
Su
rfac
e Lu
bri
can
t
Incr
ease
Siz
e o
f G
ate
En
larg
e V
ents
Use
Sh
ut
Off
Val
ve (
Scr
ew M
ach
.)
Use
Rev
erse
Tap
er N
ozz
le
Dec
reas
e C
ycle
Tim
e
Chapter 12
Operating Precautions
s
While the molding of Zytel® is ordinarily a safeoperation, consideration should be given to thefollowing potential hazards(1):• Thermal effects• Off-gases and particulate• Slipping hazards• Spontaneous ignition
Thermal EffectsSkin contact with molten Zytel® nylon resins caninflict severe burns. This could happen whenmoisture and other gases that generate pressurethe machine cylinder can violently eject moltenpolymer through the nozzle or hopper.
To minimize the chance of an accident, the instrutions given in this manual should be followedcarefully. Potential hazards must be anticipated aeither eliminated or guarded against by followingestablished procedures including the use of propeprotective equipment and clothing.
Be particularly alert during purging and wheneverthe resin is held in the machine at higher than usutemperatures or for longer than usual periods oftime, as in a cycle interruption. Pay particularattention to Chapter 4 on Machine OperatingConditions.
When purging, be sure that the high volume(booster) pump is off and that a purge shield is inplace. Reduce the injection pressure and “jog” theinjection forward button a few times to minimizethe possibility that trapped gas in the cylinder willcause “splattering” of the resin.
If polymer decomposition(2) is suspected at anytime, a purge shield should be positioned, thecarriage (nozzle) retracted from the mold and thescrew rotated to empty the barrel. After the screwstarts to rotate, the feed throat should be closed athen a suitable purge compound introduced. Thetemperature can then be gradually lowered and thmachine shut down. If jogging the injection or
1 Refer also to “Operator Safety Tips,” a leaflet published by theSociety of Plastics Engineers, Inc., Greenwich, CT 06830.
2 Excessive gas from nozzle, severely discolored molten polymer,screw backing up beyond the rear limit switch, etc.
3 29CFR1910.1000
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al
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e
screw rotation buttons does not produce melt flow,the nozzle may be plugged. In that case, shut offcylinder heats and follow your established safepractices.
Always assume that gas at high pressure could betrapped behind the nozzle and that it could bereleased unexpectedly. A face shield and protectivelong sleeve gloves should be worn at such times
Before restarting, both the machine and materialshould be evaluated to determine the cause of thedecomposition.
In the event that molten polymer does contact theskin, cool the affected area immediately with coldwater or an ice pack and get medical attention forthermal burn. Do not attempt to peel the polymerfrom the skin. Questions on this and other medicalmatters may be referred to 800-441-3637.
Off-Gases and ParticulatesSmall amounts of gases and particulate matter(i.e., oligomers) are released during the molding orextrusion of Zytel®. As a general principle, localexhaust ventilation is recommended during theprocessing of all plastic resins. However, gaseousproducts are produced in much smaller quantitiesthan is particulate matter and, as long as the latter ikept below the OSHA limit(3) of 15 mg/m3 fornuisance dusts, gases should be well below toxiclevels.
Figure 44 shows, for selected resins, the ventilationrequired to maintain concentration of particulates(and other volatiles) below the OSHA limit fornuisance dust during extrusion at the maximumrecommended temperatures.
Injection molding normally releases substantiallyless volatile material and, therefore, requires lessventilation. However, during purging, volatilerelease is similar to that in extrusion. Because ofthe possibility that organic halides can be volatil-ized from Zytel® FR10, extra care in avoiding theinhalation of fumes from the resin is recommended.Local exhaust ventilation should be used to conveysuch fumes outside the workplace (see DuPontpublication “Proper Use of Local Exhaust Ventila-tion During Processing of Plastics”).
8
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Handling of Zytel® Nylon ResinsMaterial Safety Data Sheets (MSDS) are requiredby OSHA to be provided by the material manufacturers to their customers. MSDS include suchinformation as hazardous components, healthhazards, emergency and first aid procedures,disposal procedures and storage information.DuPont supplies MSDS information to its custom-ers with the initial order of a Zytel® nylon resin andon the next order after an MSDS is revised. DuPoZytel® nylon resin MSDS will be furnished uponrequest from your DuPont representative.
Refer to the DuPont Safety Bulletin (A-95219) onsafe handling practices. This should be posted onnear all operating equipment.
3
Figure 44. Recommended Ventilation for Molding and
Recommended Ventilation Per Po
Type of Resin ft3 air/min (m3 air/m
Zytel® 101L, 103HSL, 151L 2 (0.06)
Zytel® 408L, ST801, 132F, 3189 4 (0.12)
Zytel® FR10 25 (0.70)
-
nt
Slipping HazardsGranules of Zytel® are a slipping hazard if spilledon the floor. They a cylindrical in shape and have alow coefficient of friction. Any spills should beswept up immediately.
Spontaneous IgnitionLarge masses of nylon at or near the melting pointand in the presence of air may ignite spontaneouslWater quenching of such masses is recommended
9
Extrusion of Selected Zytel® Nylon Resins
und of Resin Processed Per Hour
Minimum Ventilation Required byin) Industrial Building Codes
Usually adequate
Usually adequate
May be adequate, depending onprocessing rate.
If not, use added ventilation orlocal exhaust hood at die.
Mo
ldin
g D
ata
Re
co
rd
Temperatures, °F
Pressures, psi
Cycle T
imes, sec
Weights, g
Job
Operators
Engineers
Mold D
escription
Screw
Used
Press N
o.
Machine S
etup Instructions
Nozzle #
Special Instrum
entation
Safety C
heck
Date
Tim
e
Run Number
Resin
Lot Number
Rear
Center
Front
Nozzle
Fixed
Movable
Melt
Injection1st StageInjection2nd StageClamp,Tons
Back
Injection
Hold
Open
Overall
Booster
Pad, in
RPM
Full Shot
Part Only
Rem
arks
Ram inMotionScrewRetraction
Mold
Com
ments on M
olding Operation, S
tartup, etc.
Page N
o.
40
Identity and Trademark Standards
Guidelines for Customer Use—Joint ventures and authorized resellersOnly 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 tothe approval 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 typog-raphy, that allows mention of DuPont products that serve as ingredients in the customer’s products.In this signature, the phrase, “Only by DuPont” follows the product name.
Zytel® only by DuPont or Zytel®
Only by DuPont
A registration notice ® or an asterisk referencing the registration is required. In text, “Only byDuPont” may follow the product name on the same line, separated by two letter-spaces (see aboveexample). When a DuPont product name is used in text, a ® or a reference by use of an asterisk mustfollow the product name. For example, “This device is made of quality DuPont Zytel® nylon resin fordurability and corrosion resistance.”
Zytel® is a DuPont registered trademark.
Rev. August 1995
dZytel®
nylon resin
198118E Printed in U.S.A.[Replaces: H-57475 R1]Reorder No.: H-57475 (R
2 98.10) DuPont Engineering Polymers
For more information onEngineering Polymers:
For Automotive Inquiries: (800) 533-1313
(302) 999-4592
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—Sao Paulo, BrasilTel.: (055-11) 7266-8531/8647Fax: (055-11) 7266-8513Telex: (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.
d
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