Defect: Blistering, heavy section
- lncrease cure.
- Close mold slowly on low pressure, then apply high pressure to purge gas.
- Vent mold.
- Preheat to eliminate moisture. lncrease preform temperature.
- Breathe mold as soon as possible.
- Increase pressure.
- Use stiffer material.
- Lower mold temperature.
- Check mold temperature for uniformity.
- Vent mold at dead ends with vent pins.
Defect: Porosity (not filled out in every section)
- Try a range of plasticities for best grade.
- lncrease pressure.
- Lower temperature.
- Close mold faster if external porosity, apply high pressure sooner; close mold slower if internal porosity, apply low pressure longer
- Preheat material.
- Adjust charge weight.
- Try a higher density material to obtain greater "hack pressure" in the mold.
- Breathe mold earlier.
- Use semi-positive molds to minimize porosity.
Defect: Mold sticking
- Raise mold temperature.
- Preheat to eliminate moisture.
- Clean mold.
- Use stiffer material.
- Remove dents and undercuts in mold cavity and force.
- Polish mold.
- lncrease cure.
- Lower pressure, softer material if plunger molding. Electron Bean Welding
- Check knockout pin adjustment.
- Be sure cavities have sufficient drait.
Defect: Dull surface
- Adjust mold temperature - usually reduce temperature for better appearance.
- Polish mold.
- Chrome plate.
- Close mold more slowly.
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Defect: Orange peel (rough, pimply surface)
- Close slowly on low pressure. Delay 2 sec. before applying high pressure.
- Preheat (radio frequency).
- Use stiffer material.
- Use finer ground material.
- Use large preforms and as few as ~ossible.
- use lower mold temperature.
Defect: Pitted surface
- Use stiffer material.
- Preheat.
Defect: Clouded or segregated surface.
- Reduce molding temperature (for colors, 300 to 310°F)
- Preheat preforms.
- Adjust plasticity.
- Adjust pressure and closing speed
Defect: Dimpled surface
- Close slowly, longer on low pressure, no breathe, then high pressure.
- Use stiffer material.
- Lower mold temperature.
- lncrease charge weight.
- Shape preforms more closely to piece.
- lncrease pressure.
Defect: Warped piece
- Heat mold more uniformly.
- Use stiffer material.
- Preheat if soft plasticity.
- lncrease cure. Cantilever racks
- Use lower shrinkage material. and/or material more rigid at discharge.
- Redesign mold; use wider knockout pins.
- Adjust temperature of force arid cavity - lower temperature may reduce warpage.
- Preheat for irregular shaped pieces.
- Cool uniformly and use shrink fixtures.
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Defect: Cracking after molding
- lncrease wall thickness around inserts.
- Check knockout pins.
- Correct size of shrink fixture.
- Use more flexible material.
- lncrease radii and ribs.
- Oven anneal 2 hr. at 200°F.
Defect: Poor electrical properties
- Close slowly.
- Preheat 112 hr. at 185°F.
- Increase cure.
- Reduce temperature.
- Use stiffer grade.
Defect: Weak mechanically
- Increase temperature.
- Increase cure.
- Increase pressure.
- High frequency preheat.
- Increase charge.
- Afterbake to increase strength, if economical. Try 2 hr. at 250°F
Defect: Pimpling
- Breathe mold.
- Use higher fines material.
- Use softer material.
- R.F. preheat.
- Lower mold temperature,
Defect:Burned marks
- Reduce preheat temperature.
- Reduce mold temperature.
- Open gates; be sure vents are * clear; check plunger travel time to see if it is between 5 and 12 sec. (faster close will entrap gas; slower close causes burn marks).
- void or minimize breathing.
Defect: Thick flash
- Reduce mold charge.
- Reduce mold temperature.
- lncrease high pressure.
- Close on low, apply high pressure sooner.
- Eliminate breathing, follow (4).
- Use softer grade material for more pressure.
- Be sure of 0.002-in. between force and cavity.
- Be sure overfiow grooves are clean.
- Reduce transfer pressure andlor increase clamping pressure.
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