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Gloss level of glass filled nylon

The gloss level of glass filled nylon is mostly controlled by the injection mold heat. Because the resin shears away from the fiberglass with the fountain flow effect you get a resin rich surface. Higher mold heats allow the resin to mirror the tool surface best.

Surface interruptions that disrupt the fountain flow will create dull spots. If you shoot past a pin, as the plastic moves past the pin, you will see a duller surface on the opposite side. You can reduce the effect of pins that do not go through the entire wall by generous radii. The same holds true with ribs.

Lastly, as you increase the injection mold temperature, you will also increase the crystallinity of the plastic part. This will change the plastic properties, most notably, the shrink rate. Your plastic part will get smaller.

Injection mold temperature is for sure the biggest factor in achieving high gloss with glass-reinforced polymers. Depending on your application, you may or may not want to explore the various mold temperature control systems mentioned by others above. There are other alternatives and some are less costly to implement - induction or radiant heating equipment on robot tooling, for instance.

I have found with nylon of 30% glass filled that a surface temperature of 235F (113C) gives best finish. Further dependent on wall thickness, it than depends on which nylon used, since a type 6 has a wider processing window it can be packed out a bit better. Measure your part temperature on ejection to maintain cycle time, and have a reference point.

I have experienced problems in the past after injection molds were nitrided. We completed development and approval of parts, nice and glossy, then sent the injection mold out for nitriding before releasing to production. The plastic parts looked terrible after they came back, and it was clear the surface had become matte after close inspection with an eye lens.
Another reason for poor gloss on glass filled nylon is inadequate venting. Depending on the sprue/runner situation, the more vents on the tooling, including pins, will help immensely. The faster you can inject the material into the mould, will prevent the glass fibres coming to the surface of the part. Sufficient venting will allow you to achieve this.
- - - -> by: Delnorth

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