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KOPA®-PA66 resin is kept at max. 0.2% moisture content in packages. However, it is apt to absorb moisture during processing work. Therefore, processing should be completed in less than two hours after the package is opened. Once moisture is absorbed, the resin must be dried by means of a hot-air dryer or dehumidifying dryer. Normally, the latter is better. Drying normally requires 5 hours at 70~80℃ .
Selection of Injection Molding Machine
In is preferable to adopt in-line screw and screw-plunger type, as these are advantageous for melting power, temperature adjustment,
prevention of material loss, and speedy internal pressure formation.
Pressure
If injection pressure is too low, part structure will be defective, and if too high, the resin layer floats during cooling, or causes deviation
in structure or density, and/or easy breakage or damage from stress.
Temperature of Cylinder
Temperature is adjusted in accordance with the structure of parts and specification of injection molding machines. The resin melts at 255℃,
and standard grade is maintained at 265~280℃, whereas a 10~20℃ increase in temperature is applied for glass fiber reinforced grade.
Resin properties may be degraded if the temperature is too high and/or injection time is too long.
Temperature of Mold
Mold temperature is adjusted between 40℃ and 80℃ depending on the required property of molded parts.
Cosmetic and mechanical properties of parts can be improved by increasing mold temperature.
Item | Unit | KN311 KN333H R |
KN333 HI |
KN3322 VO |
KN333 G30 |
KN3321 G15V0 |
KN333 MS |
|
---|---|---|---|---|---|---|---|---|
Cylinder | Rear | ℃ | 260 | 260 | 260 | 265 | 260 | 255 |
Temp | Middle Front Nozzle |
270 | 270 | 270 | 285 | 280 | 270 | |
280 | 275 | 275 | 290 | 290 | 280 | |||
270 | 265 | 270 | 280 | 280 | 270 | |||
Mould Temperature | ℃ | 80 | 70 | 80 | 80 | 80 | 80 | |
Injection Pressure |
1st 2nd |
㎏/㎠ | 900 | 1000 | 950 | 1100 | 1200 | 850 |
㎏/㎠ | 450 | 520 | 450 | 420 | 600 | 500 | ||
Back Pressure | Sec | 10 | 10 | 10 | 15 | 15 | 10 | |
Injection Time | Sec | 5 | 5 | 5 | 4 | 4 | 4 | |
Cooling Time | Sec | 10 | 20 | 14 | 10 | 10 | 8 | |
Delay Time | Sec | 2 | 3 | 2 | 2 | 2 | 3 | |
Screw RPM | Sec | 100 | 100 | 100 | 110 | 110 | 100 | |
Injection Speed | 1st step | Low | Low | Low | Middle | Middle | Middle | |
2nd step | Middle | Middle | Middle | high | high | Middle | ||
3rd step | Low | Low | Middle | Middle | Middle | Low |
To achieve optimum part quality and minimum cycle time, the molder must know how to overcome molding problems.
The follow figure is a guide for troubleshooting and offers solutions for most problems encountered with KOPA®-PA66 resin.
Item | Britt leness |
Short Shot |
Poor Surface |
Stain | Flash | Void | Flow Mark |
Poor Mold Release |
Warpage | Burning |
---|---|---|---|---|---|---|---|---|---|---|
Cylinder Temp |
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Mold Temp |
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Nozzle Temp |
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Injection Speed |
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Injection Pressure |
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Holding Pressure |
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Back Pressure |
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Cooling Time |
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Screw rpm |
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Nozzle Diameter |
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Gas Vent |
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Gate Size |
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Gate Position |
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Drying | ![]() |
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Note. : Need to Increase
: Need to Decrese
: Study for Effecting Factors
Parts Design
In designing an injection molded part using KOPA®-PA66, thicknesses of 0.75~3mm for glass fiber reinforced grade and 0.5~5mm for non-reinforced
grade are standard. If they are too thick, distortion or shrinkage is likely to occur. Therefore, changes should be done on a gradual basis.
A rib 0.5 or 0.6 times thicker can prevent shrinkage, though for painting work, a thickness of 0.3 times is advised.
The tolerance of injection molding under normal conditions is + 2%, though this figure can be adjusted down to + 0.5~0.1% when mold
temperature is well controlled, processing cycles are normal, and no undue impact occurs to the injection molding machine.
Mold Design
Steel is the ideal material for making molds, as KOPA®-PA66 does not corrode metal.
But for the flameproof grade, it is desirable to use a base metal with higher chrome content, as the grade can corrode metal.
A 0.5~1% of taper is good. For the shrinkage factor, parallel to flow direction, 2.5~3% is the standard for the general grade, 0.5~1%
for the glass fiber reinforced grade. The shrinkage factor of molds for any resin vary in accordance with the additive used, process condition,
thickness and shape of the part, the position of mold gate, cooling circuit, etc., making it very hard to determine. When processed parts
are loosening from stress and finally stabilized, an additional 15~30% shrinkage occurs.