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Rynite PET®
Molding Guide
thermoplastic polyester resin
d
StartwithDuPont
Table of Contents
Chapter 1 PageGeneral Information␣ ........................................... 2Compositions....................................................... 2Melt Properties of Rynite® PET ........................... 4Heat Requirements for Processing .................... 4
Chapter 2Molding Equipment␣ ........................................... 5Barrel .................................................................... 5Vented Barrel ....................................................... 5Screw.................................................................... 5Screw Check Ring Assembly .............................. 6
Screw Tip.......................................................... 6Check Valves .................................................... 6
Nozzle ................................................................... 6Machine Controls ................................................ 6
Chapter 3Drying Guidelines␣ ............................................... 7Effects of Moisture .............................................. 7Dehumidified Hopper Dryer Conditions ............ 8Dehumidified Hopper Dryer Equipment............ 8
New Systems ................................................... 8Retrofit of Existing Systems ......................... 10
Dryer Maintenance ............................................ 10Filters .............................................................. 10Desiccant Beds ............................................... 10Desiccant Bed Transfer System
and Air Circuits ........................................... 11Blowers, Heaters, Thermocouples,
Amperage ................................................... 11After-cooler and Volatiles Trap..................... 11Dew Point Temperature
and Air Flow Monitors ............................... 11Partial List of Dew Point
Meter Suppliers .......................................... 11Desiccant Suppliers ....................................... 11
Drying System Troubleshooting Guide........... 12
Chapter 4 PageMolding Conditions␣ ......................................... 13Cylinder and Melt Temperatures ..................... 13Nozzle Temperature .......................................... 13Mold Temperature ............................................ 13Injection Pressure/Flow..................................... 14Fill Rate ............................................................... 14Screw Speed/Back Pressure ............................. 14Purging ............................................................... 14Start-up .............................................................. 15Shutdown........................................................... 15
Chapter 5Mold Design␣ ...................................................... 17Sprues and Runners .......................................... 17Gates .................................................................. 17Vents ................................................................... 17Undercuts and Taper ........................................ 17Wear ................................................................... 17Tolerances.......................................................... 18
Chapter 6Other Considerations␣ ....................................... 19Rework ............................................................... 19Lubricants .......................................................... 19Warpage ............................................................. 19Mold Shrinkage ................................................. 20Summary of Variables
Affecting Toughness and Strength........... 21Safety Precautions ............................................ 21
Chapter 7Troubleshooting Guide␣ .................................... 23Model of Molding Data Record Sheet ............. 24
Chapter 1General Information
e
eosts
CompositionsRynite® PET glass-reinforced thermoplastic polyter resins contain uniformly dispersed glass orglass/mineral fibers in polyethylene terephthalat(PET), specially formulated for rapid crystallizatiduring the injection molding process. This makepossible the production of high performance parby conventional injection molding techniques.
General Purpose Grades
StandardCompositions
Rynite® PET 520
Rynite® PET 530
Rynite® PET 545
Rynite® PET 555
General-Purpose Grades
TabComp
Rynite® PET 935
Rynite® PET 940
35% mica/glass-reinforced modified pterephthalate—exceptionally low walent electrical properties, high stiffneheat resistance.
40% mica/glass-reinforced modified pterephthalate—greater strength, stiffwarpage.
Characteristics
20% glass-reinforced modified polyetterephthalate—good balance of strenspecific gravity, and toughness with gappearance.
30% glass-reinforced modified polyetthalate—outstanding balance of streand toughness, excellent electrical psurface appearance, and chemical re
45% glass-reinforced modified polyetthalate—greater strength and stiffnedimensional stability, and creep resis
55% glass-reinforced modified polyetthalate—superior stiffness, dimensioheat resistance, and outstanding resicreep.
Low Warp Grades
s-
n
Rynite® PET resins are available in a variety ofcompositions. A description of these compositionsfollows. Recommended molding conditions arecovered in Chapter 4.
Candidate Uses
Housings, electrical components, covers,frames, bobbins.
Electrical/electronic parts such as ignitioncomponents, relay bases, lamp sockets,bobbins; housings and other parts for pumps;mechanical components including gears,sprockets, vacuum cleaner parts, motor endbells; chair arms, casters, and other furnitureparts.
Lamp housings, compressor housings, fuel,air, and␣ temperature sensor housings, sunroofframes, spools, bobbins, transmission compo-nents, medical␣ devices.
Structural support brackets, housings andcovers, auto parts, bicycle components,propellors.
le 1ositions
olyethylenerpage, excel-ss, and high
olyethyleneness, and low
Exterior body parts, structural housings andframes, irrigation components, electricalcomponents including transformer andignition coil housings.
Frames, exterior body parts; structuralsupports.
hylenegth, stiffness,ood surface
hylene tereph-ngth, stiffness,roperties,sistance.
hylene tereph-ss, excellenttance.
hylene tereph-nal stability,stance to
(continued)
2
Rynite® PET FR330
Rynite® PET FR515
Rynite® PET FR530
Rynite® PET FR543
Rynite® PET FR943
Rynite® PET FR945
Rynite® PET FR946
Flame-Retardant Grades*
Table 1Compositions
StandardCompositions Candidate UsesCharacteristics
Electrical and electronic connectors andcomponents such as relays, switches, lampsockets, and fans. Used in structural compo-nents such as office equipment, fans, fanhousings, and oven handles.
Electrical and electronic connectors andcomponents such as relays, switches, lampsockets, and fans.
Electrical and electronic connectors andother components requiring flame-retardantcharacteristics. Used in applications employ-ing vapor phase and wave solderingtechniques.
Electrical/electronic applications such asrelays, switches, lighting ballasts, andterminal blocks.
Electrical and electronic connectors andother components requiring low warp charac-teristics. Used in electronic applications suchas connector bodies and terminal blocks.
Electrical and electronic components.Economical for large parts requiring flame-retardant characteristics, such as motorhousings, bobbins, terminal blocks, and fans.
Electrical and electronic components.Economical for large parts requiring flame-retardant characteristics, such as connectorbodies, bobbins, and terminal blocks.
Flame-retardant, 30% glass-reinforced modifiedpolyethylene terephthalate. Recognized by UL as 94V-0 at 0.032″. Has a 140°C (284°F) temperature index.Excellent balance of electrical and mechanicalproperties. High temperature resistance and flow.
Flame-retardant, 15% glass-reinforced modifiedpolyethylene terephthalate. Recognized by UL as 94V-0 at 0.034″. Has a 140°C (284°F) temperature index.Excellent balance of electrical and mechanicalproperties. High temperature resistance and flow.
Flame-retardant, 30% glass-reinforced modifiedpolyethylene terephthalate. Recognized by UL as 94V-0 at 0.014″. Has a 150°C (302°F) temperature index.Outstanding balance of properties and excellentflow characteristics.
Flame-retardant, 43% glass-reinforced polyethyleneterephthalate. Has a 155°C (311°F) temperatureindex—equivalent to many thermosets. Recognizedby UL as 94 V-0 at 0.032″.
Flame-retardant, 43% glass-reinforced modifiedpolyethylene terephthalate. Recognized by UL as 94V-0 at 0.014″. Has a 155°C (311°F) temperature index.Excellent balance of electrical and mechanicalproperties. Low warp characteristics.
Flame-retardant, 45% mineral/glass-reinforcedmodified polyethylene terephthalate. Recognized byUL as 94 V-0 at 0.032″. Has a 150°C (302°F) tempera-ture index. Low warpage, high stiffness, and eco-nomical price.
Flame-retardant, 46% glass-reinforced modifiedpolyethylene terephthalate. Recognized by UL as94 V-0 at 0.032″. Has a 150°C (302°F) temperatureindex. Excellent balance of stiffness, strength,toughness, good surface appearance, and electricalproperties.
*This numerical flame spread rating is not intended to reflect hazards presented by this or any other material under actual fire conditions.
(continued)
30% glass-reinforced modified polyethylene tereph-thalate with improved impact resistance. Excellentbalance of strength, stiffness, toughness, andtemperature resistance.
15% glass-reinforced modified polyethylene tereph-thalate—improved for easy, fast processing over abroad molding range—excellent balance ofstrength, stiffness, and temperature resistance.
35% stiffened, super-tough, glass-reinforcedmodified polyethylene terephthalate—superiorcombination of toughness and stiffness. Excellentsurface appearance, moldability, and temperatureresistance.
Water pump housings, structural housingsand brackets, electrical and electronichousings, luggage rack components.
Snap fit applications, encapsulation ofsensors, coils, etc.
Automotive parts, wheels, yard and shoptools, sporting goods, luggage components,appliance housings, structural furniturecomponents.
Toughened Grades
Rynite® PET 408
Rynite® PET 415HP
Rynite® PET SST 35
3
us
Figure 1. Melt Viscosities of Rynite® PET
1,000987654
3
2
100987654
3
2
Mel
t Vis
cosi
ty, p
asca
l sec
on
ds
At a Shear Rate of 1,000 sec–1
Delrin® 100
Zytel® 42
Delrin® 500
Alathon® 7240
Rynite® PET FR 530
Zytel® 101 Zytel® 70G33
Rynite® PET 935
Rynite® PET
545/530
Hytrel® 5556
Melt Properties of Rynite® PETRynite® PET thermoplastic polyester resins haveexcellent melt flow characteristics. The meltviscosity and, hence, melt flow, varies dependingon the type and level of reinforcement and othercomposition factors. The melt viscosities of variocompositions of Rynite® PET versus temperatureand comparisons to several other thermoplasticresins are shown in Figure 1.
Heat Requirements forProcessingThe polyester base resin for Rynite® PET is acrystalline polymer which requires a greater heatinput for melting than amorphous polymers do.This additional heat is required to break up theordered crystalline structure of the solid polymer,and it is called the heat of fusion. The total heatrequired for processing Rynite® PET is similar tothat of glass-reinforced PBT polyester and glass-reinforced nylon resins.
4
10178
(350)204
(400)232
(450)260
(500)288
(550)316
(600)
Melt Temperature, °C (°F)
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lt
Rynite® PET glass-reinforced polyester resins canbe molded in all standard screw injection moldingmachines. General-purpose screws should be usto reduce fiber breakage. Rynite® PET resins, likeother glass-reinforced resins, often cause wearin certain areas of the barrel, screw and mold.Equipment and materials of construction arerecommended below.
BarrelGeneralThree-zone heating control of the barrel (corre-sponding to the screw’s three functional zones)should be provided for close temperature controland high output rates. In all cases, the temperatuof the nozzle should be independently and preciscontrolled.
WearBimetallic liners, e.g., “Xaloy” 800 or equivalenthave shown outstanding resistance to wear.
Chapter 2Molding Equipment
5
Figure 2. Suggested General-Purpose Screw* Design R
Screw Diameter (DS) mm (in) Feed Depth (
38.1 (1.5) 7.6250.8 (2.0) 8.1363.5 (2.5) 9.6588.9 (3.5) 11.18
114.3 (4.5) 12.7
General practice in the industry is to have the land width e = 11/1000 the diameter of the screw.*20L/D; square pitch; 10/5/5 turns for feed, transition, and mete
Feed Section
DS hF e LandWidth
10δ
d
ely
Vented BarrelThe use of vented barrels is not recommended foprocessing Rynite® PET. Dehumidified hopperdryers should be used to remove moisture toachieve desired processing and propertycharacteristics.
ScrewGeneralThe general-purpose gradual compression screwsthat are installed (OEM) in molding machines areusually suitable for molding glass-reinforcedpolyester resins. At high output rates, specificscrew designs will provide better uniformity of metemperature and freedom from unmelt. Screwlength should be at least an 18 to 1 (length todiameter) ratio for uniform melt temperatures athigh outputs. (see Figure 2.)
ynite® PET Glass-Reinforced Polyester Resins
hF) mm (in) Metering Depth (hM) mm (in)
(0.300) 2.17 (0.085)(0.320) 2.67 (0.105)(0.380) 3.05 (0.120)(0.440) 3.56 (0.140)(0.500) 3.81 (0.150)
/10 the distance between the flight, and the radial clearance =
ring zones, respectively.
Length
hM
TransitionSection
MeteringSection
5 5
g
i
ee
it
tt
n
WearAbrasive wear of injection screws occurs primarion the lands and edges of the screw flights. In timthe root will wear in the transition and meteringzones.
Use heat treated and stress relieved alloy steel wa hard surface. An abrasion resistant coating, e.“Colmonoy” 56, e.g., UCAR WT-1, is necessary.Nitriding is not recommended. Coating solely thetips of the flights will not be adequate.
Screw Check Ring AssemblyScrew TipWearThe recommended material of construction is astress relieved AISI 4140 steel, hardened to Rc5with an abrasion resistant surface coat, e.g.,“Borafuse.” This treatment will lead to an apprecbly harder surface than that of the check ring.
Check ValvesGeneralHardened check (nonreturn) valves should be usfor processing Rynite® PET resins. Either ringcheck or ball check valves may be used. With thlatter, flow passages must be carefully streamlinto prevent holdup. Check valves are necessaryduring injection to ensure constant cavity pressuand part weight uniformity from shot to shot.
WearSliding type ring check valves (nonreturn valves)especially when not hardened, undergo rapid an
Figure 3. Nozzle (with reverse taper) Recommended fo
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10D
3D
D Minimum = 0.32 cm (1/8"), D Typical = 0.48 cm (3/
D4°
0.25 cm (0.10")Radius
ThermocouplWell
1/8" (0.32 cm)
lye,
ith.,
2
a-
ed
d
re
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appreciable wear when used with glass-reinforcedresins. Even when properly hard surfaced, thesevalves should be considered expendable after3 to 4 months of use. Prior to that, worn seats andring sleeves should be reground or replaced sinceis important to maintain a pad (cushion) duringinjection of melt. Nitriding has been found usefulfor extending the life of check rings. A typicalmaterial of construction is Nitralloy 135M. The seais usually hardened more than the sleeve; e.g., seaRc55; sleeve Rc45 are typical. Experience hasshown that when the nonreturn valve fails tofunction correctly, additional screw wear occurs,and as the performance (wear) of the check valvedeteriorates, so does the condition of the screw.
NozzleHeated, reverse tapered nozzles (Figure 3) arerecommended for use in molding Rynite® PETresins. Straight-through nozzles have been usedsuccessfully as Rynite® PET resins have lesstendency to drool than do glass-reinforced nylons.Positive shut-off nozzles can only be used whenproper temperature control is provided, but shouldnot be used for flame retardant grades.
Machine ControlsNo special equipment features are required toprocess Rynite® PET resins. Using either electricalor hydraulic screw drive, these materials can be ruin both toggle and hydraulic clamp machines.Clamp pressure of 3–5 tons/in2 (40–70 MPa) ofprojected shot area is desirable when moldingRynite® PET.
6
r Molding
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Diameterto Suit
Taper to Suit
16") – 0.64 cm (1/4") Not To Scale
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illis
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Molded parts of Rynite® PET provide an outstand-ing combination of high flexural modulus, strengtand toughness, dimensional stability and goodsurface appearance. However, these properties wnot be achieved in finished molded parts unless tmaterial has been properly processed with particlar attention given to thorough drying of the resinWhile the required drying can be accomplished insome conventional drying equipment, the continuous manufacture of high quality production parts assured when careful attention is given to equip-ment selection, dryer operating conditions andmaintenance procedures.
Effects of MoistureLike many other engineering thermoplastics suchnylons, polycarbonates, polysulfones and otherpolyesters, Rynite® PET is hygroscopic (absorbsmoisture from the atmosphere). When excessmoisture is present in the polymer melt in aninjection molding machine, a hydrolysis reactionoccurs. This reaction degrades the material causlower part toughness and strength and increasedmelt flow. Figure 4 illustrates the significant lossof physical properties of Rynite® PET at moisturelevels above 0.02% moisture. In addition, the meflow increases rapidly as resin picks up moisture
Chapter 3Drying Guidelines
7
Figure 4. Effects of Feed Moisture on Properties ofRynite® PET 530
% Moisture.01 .02 .03 .04 .05
100
90
80
70
60
50
% o
f U
ltim
ate
TensileStrength
Elongation
UnnotchedIzodImpact
ille-
-s
as
ng
t
This can result in overpacking, parts and runnersticking, and flash. Parts molded from wet resin dnot exhibit surface defects such as splay seen winylon resins. Therefore, parts could be molded wexcellent surface appearance and yet have poorend-use performance. As with any degraded resithe lower properties cannot be restored by furtheprocessing. Such regrind should be discarded.
Virgin resin is shipped in special moisture-proofbags or boxes at a moisture level up to 0.04%.Therefore, both virgin and regrind resins must bedried to and maintained at less than 0.02% moistduring molding. Figure 5 depicts the moisturepick-up rate of Rynite® PET which is typical ofpolyester resins. At exposure levels of 50% R.H.or more, resin dried as low as 0.01 % moisture wlikely exceed the 0.02% level after 15 min. For threason, the use of remote tray oven dryers withmanual transfer to the hopper is not recommende
Since the reaction of moisture with Rynite® PETmelt is quite rapid, the use of vented barrels inplace of dryers is also not recommended. Therefodehumidified hopper dryer systems are necessarfor successful drying of Rynite® PET below 0.02%moisture content and maintaining the resin belowthis moisture level.
Figure 5. Moisture Pick-up of Rynite® PET 530
% M
ois
ture
0.1100% RH
0.08
.06
.04
.03
.02
.01
15 min 1hr 1day 1week
50% RH
15% RH
ad
d
i
Dehumidified HopperDryer ConditionsProperly operating dehumidified hopper dryers cdry Rynite® PET resin adequately in a short perioof time. The air flow rate is very important. Foreach pound per hour of resin processed, 0.8–1.0cubic foot per min (CFM) of air is required. Forexample, if 60 lb/hr (27 kg/hr) of Rynite® PETare to be molded, dry air capacity of 48–60 CFM(82–102 m3/hr) will be needed. Depending upondryer design, lower rates will significantly reducethe resin temperature in the hopper.
The air temperature is equally important. lt shoulbe measured at the point of entry to the hopper(not at the dryer). Figure 6 illustrates the requireddrying times for virgin resin and wet resin.Normally, a 121°C (250°F) to 135°C (275°F)temperature is recommended with drying timesranging from 2–3 hr (for virgin resin from sealedpackages) to 4–6 hr (for exposed wet resin). Ifthe Rynite® PET resins are dried overnight(e.g., 8–16 hr), the drying temperature should bereduced to 107°C (225°F). Similarly if productionrates result in the hopper residence time exceed8 hr, the temperature should be reduced to 107°C(225°F). Over-weekend drying may be accom-plished at 93°C (200°F). Prolonged drying at 121°C(250°F) (or higher temperatures) is not recom-mended and may result in volatizing a smallamount of additives from the Rynite® PET resin.
16
Res
iden
ce t
ime,
hr
Maximum
14
12
10
8
6
4
2
104(220)
110(230)
116(240)
121(250)
127(260)
132(270)
138(280)
°C(°F)
Hopper Inlet Temperatureat –18°C (0°F) Dew Point
Wet Resin
Resin As Received
Figure 6. Residence Time vs. Air Temperature at–18°C (0°F) Dew Point to Obtain 0.02%Moisture
n
ng
The third important variable is the dew point* ofthe air entering the hopper This must be –18°C(0°F) or lower throughout the drying cycle in orderto adequately dry Rynite® PET resins.
All three of these key variables—air flow, airtemperature, and air dew point—should be moni-tored. Table 1 summarizes the required conditionsfor drying Rynite® PET resins. More specific datacan be obtained from your DuPont Representative.If these conditions are not being maintained by thedryer, consult the Troubleshooting Guide at the endof this chapter.
*Dew Point is the temperature to which the air must be cooled beforethe water vapor will condense. The more moisture there is in the air,the higher the dew point. This value can be obtained by measuringdry and wet bulb temperatures and using a psychometric chart.Hygrometer instruments giving a direct reading are more commonlyused.
Table 1Drying Conditions for Rynite® PET
Inlet HopperAir Temperature 121°C (250°F) to 135°C (275°F)Dew Point of Air –18°C (0°F) or lowerAirflow Rate 0.8–1.0 CFM per lb/hr resin
processed(3.0–3.7m3 per kg/hr resinprocessed)
Inlet Desiccant BedAir Temperature 66°C (150°F) or lower
Drying Time at: 107°C 121°C 135°C(225°F) (250°F) (275°F)
Virgin Resin 8 3 2Recycled Regrind 8 4 3Wet Resin 8 6 4Maximum 16 9 6
Dehumidified HopperDryer EquipmentThe key elements to successful drying of Rynite®
PET and all hygroscopic materials are the properselection of drying equipment and proper mainte-nance of the system (discussed later). A properdrying system is depicted in Figure 6. The numbersin parentheses below refer to the same numbereditems in Figure 7.
New SystemsSince Rynite® PET resins absorb moisture quickly,automatic hopper loaders (1) are strongly recom-mended. If regrind is to be used, a proportionatingfeeder should be used. For optimum drying effi-ciency, the hopper dryer must be kept full. Lowlevels will result in decreased residence time, andsome resin may not be dried adequately.
8
Figure 7. Recommended Dehumidified Hopper Dryer System
.
fit,
to-
d.
f
g
Figure 8. Maximum Desiccant Bed MoisutreLoading
21
Res
iden
ce ti
me,
hr
–18°C (0°F)Inlet Air Dew Point
38(100)
20
18
16
14
12
10
8
6
4
2
093
(200)149
(300)204
(400)°C(°F)
Temperature
e
Air FlowMeter
Dew PointMeterand Alarm
9
B
ProcessHeater
88 DesiccantBeds
7
FilterBlower
To Atmosphere
From AtmosphereBlower
Filter
2
RegenerationHeater
6Filter
After-cooler
4
5
VolatilesTrap
A
Hopper InletTemperatureMonitor
Insulation
C
Hopper
1
Automatic Feeder
3
Since an air temperature of at least 121°C (250°F)at the hopper inlet is normally required, a hightemperature dryer is recommended. The dryershould be located as close as possible to the ma-chine hopper and the air transfer line (2) to thehopper should be insulated. As much as 6°C (10°F)can be lost per foot to an uninsulated transfer lineMost dryer manufacturers provide these insulatedfeatures with high temperature dryers. For a retrothe equivalent of 25–38 mm (1–11⁄2") glass fiberinsulation should be adequate. The temperature athe hopper inlet (A) should be measured by thermcouple or thermometer. In addition, the hopperitself (3) should be insulated. If the system is notinsulated, the time required to dry will be increase
Once the air leaves the hopper, it requires coolingbefore entering the desiccant beds. Figure 8 showsthat molecular sieve desiccant beds are capable oremoving twice the amount of moisture at 54°C(130°F) versus 93°C (200°F) return air temperature.Since inlet air drying temperatures up to 121°C(250°F) are recommended, the use of an after-cooler (4) on the return air line is required. Anafter-cooler is simply a small heat exchanger usinwater cooling coils or jackets to lower the airtemperature. This can be purchased with a trap (5
9
)
at the bottom to collect any volatiles which maycondense. Another benefit is after-coolers can bequipped with a filter (6) that gives further safe-guard in removal of entrained resin “fines” beforereaching the desiccant beds.
The cooled return air passes through a filter (7)which must be made of adequate size to removefines or any contaminant that could poison thedesiccant beds (8). Filters must be checked andcleaned regularly. See Dryer Maintenance Section
Exiting the desiccant beds, the dew point (B) of thdried air should be measured continuously. Mostdryer manufacturers offer dew point warningsystems which indicate by a green light when thedew point is below a set point and by a red lightwhen the set point is exceeded. This could also beconverted to actuate an audible alarm. Othersystems giving a continuous readout of actual dewpoint are also available. These are more expensivbut more useful in process control and trouble-shooting. It is also recommended that an air flowmeter (C) be installed at this point. This can indi-cate when process air filter plugging is occurringand is a good supplement to the dew point alarmand hopper inlet temperature control. A filteralarm system that alerts to plugged filters is alsoavailable.
Retrofit of Existing SystemsTo convert existing hopper dryer systems toachieve proper drying, the following is required:automatic resin feeder, insulation (e.g., glass fiberwrap) of hopper and its inlet air line, after-coolerwith filter and volatiles trap, adequate area filter ondryer, continuous dew point, temperature and airflow measurement. Table 2 is a checklist fornecessary drying equipment.
All but one of these items are readily available forretrofit of existing dryer installations. The excep-tion is if a high temperature dryer is required. Theheater element and power system would need to brebuilt.
Table 2Dryer Equipment Checklist
Automatic Hopper LoaderHigh Temperature DryerInsulation of Inlet Air LIneInsulation of HopperAfter-cooler/Volatiles TrapTemperature Monitor at Hopper InletContinuous Dew Point AnalyzerAirflow Meter
10
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Dryer MaintenanceEqually important to successful drying of Rynite®
PET is a simple but good preventive maintenanceprogram. The key dryer elements (particularly thefilters) should be checked frequently. Dew point,hopper inlet temperature and airflow should becontinuously monitored. Whenever these are not atdesired levels, other elements require investigationover and beyond routine maintenance. They includeprocess and regeneration heating elements, desic-cant beds and bed transfer system, O-rings, gasketsand hoses, blowers, thermocouples, voltages andthe meters themselves.
FiltersThe primary cause of dryer failure is contaminationof desiccant beds with fines, dirt, or dust due topoor filter maintenance. Even when filters areoperating properly, they, in turn, will plug up andreduce airflow to unacceptable levels. Filters mustbe kept clean and undamaged. For sock type filters,a good practice is to replace with a spare and cleanthe filter at leisure. All three filters (before after-cooler, desiccant bed, and regeneration heater)should be checked once a shift to determine neces-sary cleaning/replacement frequency. This typicallyranges from twice a week to once every two weeks.Most dryers should be turned off before inspectingthe filters.
Desiccant BedsFigure 9 illustrates that most of the water isabsorbed in the initial contact with the desiccantand very little toward the end (Curve A). As themolecular sieve repeatedly goes through thesaturation/regeneration cycle, it loses some of itscapacity to absorb water (Curve B). This is due, inpart, to a slight loss of crystallinity which some-what reduces efficiency. But, to a much largerdegree, this can come about by “coking,” which is acontinuous buildup of residue resulting fromdegrading of any foreign materials in the bedduring the regeneration cycle.
As a result, the desiccant has less initial capacityand requires a longer length of bed to achieve thedesired dew point of existing air. Eventually thedesiccant bed life is exhausted and it must bechanged—usually within two years (Curve C). Ifcontamination by plastic fines occurs, regenerationtemperatures will melt them and form a seal in andaround the pores of the molecular sieve. The resultcan be an early loss of bed life.
Figure 9. Service Life of Molecular Sieve
Note: The values for % moisture absorbed and dew pointare arbitrary but typical. Actual values would depend ondesign of the dryer and other operating conditions.Source: Union Carbide Corporation, Linde Division
e
20
15
10
5
0
New DessiccantA
B
C
Aged Desiccant
Thickness of Desiccant Bed
% M
oist
ure
Abs
orbe
d in
Des
icca
nt B
ed
Dew
Poi
nt o
f A
ir to
Hop
per
164
–7–18–29–40
(60)(40)(20)(0)(–20)(–40)
°C (°F)
Thickness of Desiccant Bed
AirFromHopper
AirToHopper
Replacement of desiccant in cartridges is relativeeasy for new dryers but older models may requireskilled maintenance man. With any dryer, refer tothe manufacturer’s owners manual for the properprocedures. All safety precautions called for by thmanufacturer should be followed. When replacingdesiccant, the cartridge must be packed tightly byvibrating the cartridge as it is filled. Any void areawould allow the wet air to bypass the desiccant,since they are the paths of least resistance.
Desiccant Bed Transfer System andAir CircuitsWhether the transfer mechanism is by valves or ban indexing system, these require checking forimproper alignment. All seals must be in place anin good condition (particularly after cartridgereplacement). O-rings, gaskets, hoses and allmechanical fittings should be checked for leaks.
Blowers, Heaters, Thermocouples,AmperageBlower rotation should be checked after mainte-nance is performed. Process and regenerationheaters should be checked along with the conditiof the thermocouple at the hopper inlet. It is a goidea to have permanently mounted ammeters oneach heater element. Amperage should be periodcally checked since amperage drops can result insignificant loss of heating power.
1
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onod
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After-cooler and Volatiles TrapThe cooling in the chambers will necessarily trapadditives and lubricants which will collect at thebottom. They should be checked periodically andany residue removed.
Dew Point Temperature and Air-flow MonitorsThe dew point meters should be checked andcalibrated. Meters for continuous use and portableones for calibration are available from dryermanufacturers and from suppliers listed below.Temperature monitors are easily calibrated andshould be. Airflow meters should also be main-tained in good working order. False low pressurereadings are usually the result of pitot tubesplugged with contamination. Airflow meters canalso be purchased from dryer manufacturers.
Unless specified differently above, all maintenancitems should be checked at least once every twomonths.
Partial List of Dew Point MeterSuppliersPanametrics221 Crescent StreetWaltham, MA 02154(617) 899-2719
Alnor Instrument Company7301 N. Caldwell AvenueNiles, IL 60648(312) 647-7866
Union Carbide CorporationMolecular Science DepartmentMoorestown, NJ 08057(609) 778-6283
Newport Scientific, Inc.8246-E Sandy CourtJessup, MD 20794-0189(301) 498-6700
Desiccant SuppliersUnion Carbide CorporationMolecular Science DepartmentMoorestown, NJ 08057(609) 778-6283
Newport Scientific, Inc.8246-E Sandy CourtJessup, MD 20794-0189(301) 498-6700
1
12
Drying System Troubleshooting Guide
Problem Probable Cause Corrective Action
Low airflow 1. Plugged filters Inspect/clean2. Damaged airflow meter Check/repair3. Incorrect blower rotation Check/correct4. Desiccant assembly not transferring Check/repair5. Collapsed air hose Check/replace6. Plugged desiccant beds Inspect/replace
High dew point 1. Low airflow See above2. Regeneration heaters not working Check/replace3. Temperature entering desiccant bed too high Check aftercooler4. Moist air leaking into system Check hoses, etc.5. Dew point meter incorrect Calibrate6. Contaminated desiccant bed Inspect/replace
Dew point 1. Electrical malfunction Check systemcycling high 2. One or more contaminated desiccant beds Inspect/replaceto low 3. Equipment too small Use larger unit
Process air 1. Incorrect setting Checktemperature 2. Low airflow See airflowtoo low 3. Hose hook up incorrect Check
4. No insulation Insulate5. Heating elements burnt out Check6. Equipment too small Use larger unit
erze,s
l.
time
e
in
Figure 10. Processing Range: Modified PET MeltTemperature vs. Residence Time
600
580
560
540
520
500
2 4 6 8 10 12 14 16Residence Time, Min
Mel
t Tem
per
atu
re, °
F
FR.Toughened
Resin
260
270
280
290
300
310
Mel
t Tem
per
atu
re, °
C
The melt temperature processing window depends upon theresin grade, as well as the barrel residence time.
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Chapter 4Molding Conditions
Machine Set-upCylinder and Melt TemperaturesCylinder temperature settings depend on a numbof factors; e.g., size and type of machine, shot sicycle, etc. Typical cylinder and melt temperaturefor Rynite® PET resins are shown in Table 3. Thenozzle and melt temperatures are the most criticaMelt temperature for optimum properties varieswith hold-up time. As a guide in selection of melttemperature, a temperature vs. barrel residence grid is presented in Figure 10. The melt tempera-ture should be checked periodically with a needlepyrometer during a molding run to be sure that thtemperature does not exceed the recommendedlimits.
Nozzle TemperatureThe nozzle temperature should be adjusted toprevent nozzle freeze-off or drool. Temperaturesthe range of 270–300°C (520–570°F) should beused.
Mold TemperatureMold surface temperature between 90 and 120°C(190 and 250°C) is suggested for optimum dimen-sional stability, surface appearance, and cycle, wthe preferred range being 100–120°C (210–250°F).Table 3A shows how the preferred minimumtemperature varies with thickness. High moldtemperatures yield a better surface with highergloss. High-temperature rated water hoses or oilheaters are recommended to obtain the desired
1
TabTypical Cylinder and
ResinSeries Rear Center
500, 900 °C 260–290 260–295°F 500–550 500–560
400, Flame °C 260–275 260–280retardant °F 500–530 500–540
*Melt temperature must not exceed 330°C (625°F).
Cylin
ith
mold surface temperatures. When mold temperatures below 90°C (190°F) are used, the initialwarpage and shrinkage will be lower, but thesurface appearance will be poorer and the part’sdimensional change will be greater when heatedabove 90°C (190°F). If minimum out-of-the-moldwarpage is the only requirement, Rynite® PETresins may be molded with surface temperaturesless than 65°C (150°F).
3
le 3Melt Temperatures*
PreferredFront Nozzle Melt Temp.
265–295 275–300 280–300510–560 530–570 540–570
266–280 260–290 270–290500–540 500–560 520–550
der Settings
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Injection Pressure/FlowRynite® PET resins have higher flow than glass-reinforced 6/6 nylon and glass-reinforcedpolybutylene terephthalate under normal operatinconditions. Injection pressures should be set lowethan comparable settings for the above mentionematerials.
The effect of injection pressure on the flow ofglass-reinforced Rynite® PET resins in the 0.040and 0.100 in. (1.02 and 2.54 mm) snake flowconfigurations are shown in Figure 11.
Figure 11. Snake Flow—Rynite® PET 530Melt Temperature = 290°C (555°F)Mold Temperature = 93°C (200°F)
Flo
w, m
m (
in)
711 (28)660 (26)610 (24)559 (22)508 (20)457 (18)406 (16)356 (14)305 (12)254 (10)203 (8)152 (6)102 (4)51 (2)
8(56.2)
10(69)
12(76.8)
14(98.6)
16(110.4)
18(124.2)
Injection Pressure, psi x 103 (MPa)
2.54 mm (0.100 in) thickness
1.02 mm (0.040 in) thickness
Fill RateRynite® PET resins exhibit fast “set-up” in themold. To prevent premature surface freezing(which results in poor surfaces and weak weldstrengths), moderate to fast fill rates (1-4 sec)should be used. Adequate mold venting must beprovided to prevent part burning associated withthese fill rates (see Mold Venting, page 17).
Table 3AMold Temperatures
Part Preferred MinimumThickness Mold Temperarure*mm (in) °C (°F)
0.75 (0.030) 110 (230)1.5 (0.060) 105 (220)3.1 (0.125) 100 (210)6.3 (0.250) 90 (190)
*Subtract 25°F for HP and SST grades.
14
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Screw Speed/Back PressureThe screw RPM (speed) should be adjusted so thatthe screw retraction time is about 75% of theavailable mold closed time. The screw RPM shouldbe slow (with little or no back pressure) in order tominimize glass fiber breakage.
PurgingPurging is essential before and after moldingRynite® PET resins because many other plasticsdegrade at the Rynite® PET melt processing tem-perature. Contamination of Rynite® PET withother resins such as nylon, polycarbonate, acetal,polybutylene terephthalate (PBT), or polyarylatemay cause molding difficulty and/or resindecomposition.
The best purging materials are polystyrene, castacrylic (the nozzle must be removed during purg-ing) and high density polyethylene (or glass-reinforced polyethylene, followed by high densitypolyethylene). The following purge procedure isrecommended for standard injection moldingequipment:
A. Retract screw injection unit from sprue bush-ing,and keep the screw in the forward position.
B. Run the screw at high RPM and pump out asmuch of the material as possible. Add andextrude purge compound until it comes outclean. Cylinder temperatures may have to beadjusted, depending on purge material used.
C. lt is good practice to “shoot” several air shots ata fast injection rate to scrub walls of cylinderbefore switching to another resin. Care shouldbe employed to avoid possible splatter ofmolten resin when this is done.
The following purge procedure is recommended forhot runner systems:
A. Shield personnel from mold.
B. Raise manifold temperatures 528°C (50°F)above first resin’s melt temperature or 11°C(20°F) above desired Rynite® PET melt tem-perature (but less than 310°C [590°F] actual),whichever is lower.
C. Extrude dried Rynite® PET through open moldusing machine back pressure, until purge is“clear.”
D. Drop manifold temperature to operatingconditions. Purge out “hot” Rynite® PET(1–2 min maximum).
E. Drop pressures to usual lower Rynite® PETlevels.
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Start-upA. Start with a clean machine.
B. Set the cylinder temperature to 28°C (50°F)below the minimum molding temperature andthe nozzle at operating temperatures. Allowheat to soak in for at least 20 min. Raisecylinder temperature to the operating temperature (use Table 2 as a guide).
C. Check to see if nozzle is at temperature.
D. Jog screw. If screw will not rotate, allow longesoak time for cylinder temperatures.
E. When the screw begins to rotate, open feed sbriefly and then close. Check the load on thescrew drive. If it is excessive, increase rearzone temperature. The nozzle must be “openat this time.
F. Open feed slide, keep screw in forward posi-tion. Extrude melt and increase the front zonetemperature if unmelted particles are seen.
G. Adjusting stroke to approximate shot weight,take several air shots at the approximate ovecycle. The melt temperature should now bechecked with a needle probe pyrometer. Makany adjustments in the cylinder temperatures
1
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r
lot
all
necessary to get the recommended melt tem-perature. (This procedure should be repeatedwhen a significant cycle change occurs.)
H. Bring injection cylinder forward. Start at a lowinjection pressure (except where short shotswill interfere with part ejection) and adjustmolding variables for best part appearance anmaximum part weight.
ShutdownThe machine should be purged thoroughly withpolystyrene or polyethylene, which cuts the timerequired for subsequent start-up and reducesproblems of contamination. The following shut-down procedure is suggested:
A. Shut hopper feed slide, while continuing tomold on cycle.
B. Empty hopper, add a quantity of polystyrene opolyethylene; extrude until the screw pumpsitself dry
C. Leave screw in forward position.
D. Shut down power supply.
5
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Rynite® PET glass-reinforced polyester resins havbeen molded in a variety of molds. Insulated andhot runner molds are well suited to these materiaOwing to the low shrinkage and high flow ofRynite® PET resins, prototype tools which wereoriginally designed for higher shrinkage materialsmay not eject automatically.
Polished cavities and well designed hot watercoring produce a high gloss surface on Rynite® PETmolded parts. To facilitate high injection rates, alsnecessary for good part surface, melt flow shouldnot be restricted.
In a properly designed mold, employing standardRynite® PET operating procedures, weld strengthof these resins pose no particular problem.
Sprues and RunnersThe entrance diameter of the sprue should be inthe range of 3.81–711 mm (0.15–0.28 in). Thesmallest-diameter sprue should be used wherepossible. Hot sprue bushings have been usedsuccessfully with Rynite® PET resins and should beconsidered.
Full round or trapezoidal runners are recommendRunner diameters in the range of 3.2–6.4 mm(0.125–0.250 in) have been successfully used wiRynite® PET resins. In certain molds, runners oflarger diameter may be necessary. However, duethe excellent flow characteristics of Rynite® PETresins, the smallest diameters for runners shouldconsidered first. Length should be as short aspossible to minimize rework. Layout of runnersshould be balanced and generously radiused forsmooth and uniform melt flow.
GatesThe number and location of the gates have asignificant effect on the orientation of the glassfibers and therefore on the warpage of the part.Careful consideration should be given to these twvariables. Suggested gate dimensions are:
Round Gates. Tunnel gates can be used providedthe gate diameter is greater than 0.508 mm(0.020 in); 0.020 in is a minimum and can only beused with short land length. In three-plate molds,the gate diameter should be less than 2.29 mm(0.090 in) to ensure automatic degating. For roun
Chapter 5Mold Design
17
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d.
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e
gates, the gate diameter should be about 45–55%,of part thickness.
Rectangular Gates. The gate thickness should begreater than 50% of the part thickness and the gatewidth should be 1.5 to 2 times the gate thickness.
For both round and rectangular gates, the gate landshould be short; between 0.76 and 1.52 mm (0.030and 0.060 in).
VentsMolds must be adequately vented in order toprevent localized burning of the parts, damage tothe mold, poor weld line strength and to alloweasier filling of the cavity. The vents should be lessthan 0.025 mm (0.001 in) deep and as wide aspractical. About .76 mm (0.030 in) from the cavitythe vents should be deepened to about 3.2 mm(0.125 in) and extended to the edge of the mold.
Undercuts and TaperBecause of the low elongation of glass-reinforcedpolyester, undercuts should be avoided. A taper(draft) of 1⁄2 to 1° on ribs, bosses, sides and spruesshould be satisfactory.
Runnerless MoldsProperly designed modified insulated runnerlessand hot runner molds are well suited for Rynite®
PET resins. Numerous Rynite® PET parts, diversein size, complexity and end use, are being massproduced from runnerless systems. All Rynite® PETresins are runnerless candidates. Melt temperature,hold-up time (including runnerless manifoldresidence time) and streamlined melt flow path arecritical factors. Melt temperature and hold-up timeguides for specific resins are discussed in the firstsection of Chapter 4 (“Molding Conditions, Cylin-der and Melt Temperatures”).
WearExperience to date indicates wear can be minimizedby properly hardened tool-steel cavities, cores,runner systems and sprue bushings. Cavities mustbe vented at welds to minimize pitting from hightemperature gas entrapment. Also, gates (blocks)are subject to considerable heat buildup and loss ofhardness as a result of the fast injection rates usedin processing glass-reinforced polyesters.
sf
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Specific recommendations on materials of constrution can be found in the Molding EquipmentSection.
TolerancesTolerances for parts molded of Rynite® PET resinsvary according to the complexity and wall thickneof the design. Predicting dimensional uniformity o
Drawing Code
A = Diameter(see Notes #1 & #2)
B = Depth(see Note #3)
C = Height(see Note #3)
D = Bottom Wall(see Note #3)
E = Side Wall(see Note #4)
F = Hole Size Diameter
(see Note #1)
G = Hole SizeDepth
(see Note #5)
Draft Allowanceper side
(se Note #6)
0.000 to 0.125
0.125 to 0.250
0.250 to 0.500
0.500 & Over
0.000 to 0.250
0.250 to 0.500
0.500 to 1.000
6.000 to 12.000for each additional
inch add (in.)
0.0000.5001.0002.0003.0004.0005.0006.000
Dimensions, Inches
Plus or Minusin Thousandths of
1 2 3 4 5 6 7
comme
fine
18
TabA Guide to Tolerances of Rynite® PE
Note: The commercial values shown below represent colevel. The fine values represent closer tolerances th
c-
s
glass-reinforced resins can be difficult as it willdepend to a large degree on glass fiber orientatioin the part. The tolerances in Table 4 (based on theSPI format) do not represent hard and fast rulesapplicable to all conditions, but rather the consensus of molders for what may be achieved undernormal conditions.
0.002
0.003
0.003
0.004
0.003
0.004
0.005
1/2–1°
± Typical,inches0.002
0.004
0.004
an Inch
8 9 10 11 12
rcial
A
F
F
B J
E
GD
CP
L
le 4T Glas-Reinforced Polyester Resins
mmon production tolerances at the most economicalat can be held but at a greater cost.
Reference Notes
1. These tolerances assume a moldtemperature ≥93°C (200°F). Annealingat 150°C (300°F) will cause ≤0.1% overalldimensional change.
2. Tolerances based on 3.2 mm (1/8")wall section.
3. Parting line must be taken intoconsideration.
4. Part design should maintain a wallthickness as nearly constant as pos-sible. Complete uniformity in thisdimension is impossible to achieve.
5. Care must be taken that the ratio of thedepth of a cored hole to its diameterdoes not reach a point that will result inexcessive pin damage.
6. These values should be increassedwhenever compatible with desireddesign and good molding techinique.
SI conversion
Inches x 25.4000 = millimeters
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Chapter 6Other Considerations
ReworkFigure 12 shows how several levels of reworkaffect the tensile strength properties of Rynite® PET530 and 545, as related to the number of passesthrough an injection molding machine. Althoughthe drop in tensile strength is minimal at both 25%and 50% regrind levels, higher rework loadings(particularly 100%,) will reduce the glass fiberlength in the molding, leading to a significant lossof tensile strength. Thus, to prevent fiber damageand to retain maximum physical properties, theaddition of rework should be kept as low as pos-sible, preferably less than 25%. Rework shouldalways be ground hot to minimize glass fiberbreakage. In addition, grinder screens should havhole size of 5/16" or greater and the cutting bladeshould be kept sharp to reduce fines. Limitedexperience has shown that carbide-tipped bladesexhibit good performance and durability.
19
Figure 12. Regrind vs. Tensile Strength
1Number of Passes
Rynite® PET 530
2 3 4 5
90
80
100
% In
itia
l Ten
sile
Str
eng
th
•• • • •
25% Regrind/75% Virgin
50% Regrind/50% Virgin
a
LubricantsThe addition of surface lubricants to Rynite® PETresins is generally not recommended, because themay cause a reduction in the physical properties othe molded part.
WarpageWarpage is caused by non-uniform shrinkage of thresin. The non-uniform shrinkage may be due to:
Non-Uniform Wall Thickness of the Part.Whenever possible, parts should be designed withuniform wall thickness; thick parts should alwaysbe cored in order to minimize higher shrinkage.
Mold Design. Typically round parts should becenter-gated and long flow parts should beend-gated.
1Number of Passes
Rynite® PET 545
2 3 4 5
90
80
100
% In
itia
l Ten
sile
Str
eng
th
• • •25% Regrind/75% Virgin
50% Regrind/50% Virgin
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Processing Conditions. The mold and cavitytemperatures must be carefully controlled toprevent uneven cooling of any part prior to ejec-tion. Usually a cold mold will temporarily reducewarpage but may reduce surface gloss. SeeTroubleshooting Guide for a complete list ofprocessing variables affecting warpage.
Anisotropic Shrinkage. Anisotropic shrinkage(difference in shrinkage in the flow and transversdirections, see Tables 5 and 6) probably contrib-utes more to warpage problems in glass-reinforceresins than any other factor. Anisotropic shrinkagmost often arises because of orientation of the glfibers in the direction of flow which, in turn,restricts normal resin shrinkage. Therefore, anycondition that can create a random distribution ofthe glass fibers will reduce the warpage, i.e., abruchange in flow direction, multiple gating, differentgate location, etc.
Mold ShrinkageThe mold shrinkage of Rynite® PET, glass-reinforced resins depends on the orientation of th
20
TablEffect of Part Thickness on
Plaque: End-gated 101.6 x 254 m
Mold Rynite® PET 530 Rynite® PET RyThickness Temp. Rynite® PET 430 545
Trans- Trans-Flow verse Flow verse Flo
mm (in) °C °F Length Width Length Width Len
3.2 (1/8) 93 (200) 0.2 0.9 0.2 0.8 06.4 (1/4) 104 (220) 0.3 1.0 0.2 0.9 —
TablEffect of Mold Surface Temperatu
Plaque: End-gated 1.58 x 76.
Mold Rynite® PET 530 Rynite® PET Rynite® PET Rynite® Temp. Rynite® PET 430 545 555 935
Trans- Trans- Trans- TrFlow verse Flow verse Flow verse Flow ve
°F °C Length Width Length Width Length Width Length W
48 (100) 0.09 0.35 0.07 0.29 0.10 0.29 0.1691 (195) — — — — — — —93 (200) 0.15 0.75 0.13 0.75 0.12 0.6 0.24
104 (220) 0.16 0.88 0.14 0.77 — — —
d
ss
pt
glass fibers, part thickness and processing condi-tions. Rynite® PET glass-reinforced resins shrinkless in the flow direction than in the transversedirection. Shrinkages listed in Table 5 are intendedas a guide for estimating out-of-mold dimensions asa function of part thickness from a hot (104°C,220°F) mold. The effect of mold temperature onshrinkage is demonstrated in Table 6 for a 1.58 ×76.2 × 127 mm (1/16 × 3 × 5 in) plaque. As withmany other semi-crystalline plastics, the fastcooling of a part in a low-temperature mold doesnot permit development of full crystallinity Thisleads not only to less shrinkage, but a less dimen-sionally stable part. Upon annealing, the cold-molded part will shrink perceptibly whereas aRynite® PET part molded at 104°C (220°F) willchange less than 0.1%.
For complicated precision parts, prototype molds(cavities) should be utilized to obtain more accuratedimensional data.
e 5Mold Shrinkage (% units)m (4 x 10 in) for 6.4 mm (1/4 in)
nite® PET Rynite® PET Rynite® PET Rynite® PET555 935 940 FR-530
Trans- Trans- Trans- Trans-w verse Flow verse Flow verse Flow versegth Width Length Width Length Width Length Width
.2 0.7 0.4 0.8 0.2 0.7 0.2 0.9— — — — — — —
e 6re on Mold Shrinkage (% units)*2 x 127 mm (1/6 x 3 x 5 in)
PET Rynite® PET Rynite® PET Rynite® PET Rynite® PETFR-530 SST 35 415 HP 430 HP
ans- Trans- Trans- Trans- Trans-rse Flow verse Flow verse Flow verse Flow verseidth Length Width Length Width Length Width Length Width
0.3 0.09 0.35 — — — — — —— — — — — — — 0.18 0.980.6 0.15 0.75 — — — — — —— — — — — — — — —
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Summary of VariablesAffecting Toughness andStrengthThe variables that may cause a reduction in thetoughness and strength of Rynite® PET glass-reinforced polyester resins include:
1 . Moisture in the virgin or rework resin. Foroptimum properties, Rynite® PET resins,virgin and rework, must be dried and main-tained at moisture levels less than 0.02% durinprocessing.
2. Long melt residence times (>10 min).
3. Too high or too low melt temperature(see Figure 10).
4. Combination of all three above. The toughnesof Rynite® PET glass-reinforced resins dependupon moisture, hold-up time and melttemperature.
5. Improper mold venting.
6. Glass fiber length. In order to minimize glassfiber breakage:• Use minimum allowable screw speed.• Use little or no back pressure.• Keep the rework low (25% or less).• Use proper rear zone temperature.
7. Contaminated rework or molding equipment.
8. The use of additives, e.g., certain types of molrelease lubricants, pigments, etc.
9. Part design—sharp corners, non-uniform wallthickness.
Safety PrecautionsWhile processing Rynite® PET resins is ordinarily asafe operation, consideration should be given to thfollowing:
A. Since Rynite® PET resins are molded at hightemperatures, the molten resin can inflict severeburns. Furthermore, above the melting point,moisture and other gases may generate pressure the cylinder which, if suddenly released, can causthe molten polymer to be violently ejected throughthe nozzle.
To minimize the chance of an accident, the instructions given in this manual should be followedcarefully. Potential hazards must be anticipated aneither eliminated or guarded against by followingestablished procedures—including the use of propprotective equipment and clothing.
21
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er
Be particularly alert during purging and wheneverthe resin is held in the machine at higher than usuatemperatures or for longer than usual periods oftime—as in a cycle interruption. Pay particularattention to the section on Molding Conditionsbeginning on page 13.
In purging, be sure that the high volume (booster)pump is off and that a purge shield is in place.Reduce the injection pressure and “jog” the injec-tion forward button a few times to minimize thepossibility that trapped gas in the cylinder willcause “splattering” of the resin.
If polymer decomposition is suspected at any time,a purge shield should be positioned, the carriage(nozzle) retracted from the mold and the screwrotated to empty the barrel. After the screw starts torotate, the feed throat should be closed and then asuitable purge compound introduced. The tempera-ture can then be gradually lowered and the machinshut down. If jogging the injection or screw rotationbuttons does not produce melt flow, the nozzle maybe plugged. In that case, shut off cylinder heats andfollow your established safe practices.
Always assume that gas at high pressure could betrapped behind the nozzle and that it could bereleased unexpectedly. A face shield and protectivelong-sleeved gloves should be worn at such times.
In the event molten polymer does contact the skin,cool the affected area immediately with cold wateror an ice pack and get medical attention for thermaburn. Do not attempt to peel the polymer from theskin.
B. Since Rynite® PET resins are dried at hightemperature, contact with hot hoppers, ovens or airhose lines could result in severe burns. Insulation othese components will reduce this possibility.
C. Small amounts of gases and particulate matter(i.e., low molecular weight modifiers) may bereleased during the molding, purging or drying ofRynite® PET. We recommend adequate localexhaust ventilation be provided during the process-ing of Rynite® PET. We have calculated that aventilation rate of 75 cubic feet of air per minuteper pound of resin processed per hour will keep theconcentration of particulates well below the OSHA(15 mg/m3) and TLV (10 mg/m3) exposure limitsfor nuisance dust while being processed at themaximum recommended times and temperatures(molding, purging, and drying).
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D. Rynite® PET resins, like all thermoplasticpolymers, can form gaseous decomposition proucts with long hold-up times at the maximumrecommended melt temperatures. This is acceleated above 330°C (625°F).
E. Adequate local exhaust ventilation should alsbe provided during the regrind operation.
F. Prior to cleaning of any barrel that containsRynite® PET resins, the machine should be thor-oughly purged with polyethylene or polystyrene.
G. If Rynite® PET resin is accidently purged ovethe heater bands, it should be removed and notallowed to degrade.
2
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H. Adequate local exhaust ventilation must beprovided during the burnout of any equipment thatcontains Rynite® PET resin; e.g., nozzles, etc.
I. Granules of Rynite® PET present a slippinghazard if spilled on the floor. They are cube shapedand have a low coefficient of friction. They shouldbe swept up immediately.
For more detailed information on safety, see theRynite® PET Safety Precautions During Moldingflyer (E-75332 7/87).
2
23
Chapter 7Troubleshooting Guide
Problems
Suggested Voids Poor PartRemedies Brittle Short in Weld Sprue Part Surface(Try in order listed) Parts Shots Parts Burning Warpage Strength Sticking Sinks Sticking Appearance
Ensure resin is dry 1 1
Change injection pressure 2 2 2 3 2 2 2 2
Increase injection speed 3 4 2 5
Decrease injection speed 3 3 4 4
Increase screw forward time 3 3
Decrease screw forward time 3
Check melt temperature 2 4 5 1 6 6 5 3(a)
Increase mold temperature 5 5 3 1 1
Increase nozzle temperature 1
Increase gate size 7 6 5 6 8
Increase vent size 6 7 2 4 7
Use reverse taper nozzle 4
Decrease hold-up time 3
Change cycle 4 4 4 6
Check pad size (cushion) 1 1 1
Repair mold 5 5
Increase taper 6 6
Change gate location 6 5 7 9
Reduce rework level 4
Balance mold temperature 1
Check puller design 7
Check for contamination 5
Check for voids 6
Decrease mold temperarture 7
Mo
ldin
g D
ata
Re
co
rd
Temperatures, °F
(°C)
Pressures, psi (kp/cm
2)C
ycle Tim
es, secW
eights, 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
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Identity and Trademark StandardsGuidelines 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.
Rynite® PET only by DuPont or Rynite® PET 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 Rynite® PET polyesterelastomer for durability and corrosion resistance.”
Rynite® PET is a DuPont registered trademark.
Rev. August 1995
dRynite® PETthermoplastic polyester resin
228760D Printed in U.S.A.[Replaces: H-57470]Reorder No.: H-57470 (R1 98.8) 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(313) 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.
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http://www.dupont.com/enggpolymers/americas
