Trouble Shooter - Defects - Formulation Problems :: M.J. Gordon Company -- The Aerosol Mold Release Specialists

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Trouble Shooter

Defect: Blistering, heavy section

  1. lncrease cure.
  2. Close mold slowly on low pressure, then apply high pressure to purge gas.
  3. Vent mold.
  4. Preheat to eliminate moisture. lncrease preform temperature.
  5. Breathe mold as soon as possible.
  6. Increase pressure.
  7. Use stiffer material.
  8. Lower mold temperature.
  9. Check mold temperature for uniformity.
  10. Vent mold at dead ends with vent pins.

Defect: Porosity (not filled out in every section)

  1. Try a range of plasticities for best grade.
  2. lncrease pressure.
  3. Lower temperature.
  4. Close mold faster if external porosity, apply high pressure sooner; close mold slower if internal porosity, apply low pressure longer
  5. Preheat material.
  6. Adjust charge weight.
  7. Try a higher density material to obtain greater "hack pressure" in the mold.
  8. Breathe mold earlier.
  9. Use semi-positive molds to minimize porosity.

Defect: Mold sticking

  1. Raise mold temperature.
  2. Preheat to eliminate moisture.
  3. Clean mold.
  4. Use stiffer material.
  5. Remove dents and undercuts in mold cavity and force.
  6. Polish mold.
  7. lncrease cure.
  8. Lower pressure, softer material if plunger molding. Electron Bean Welding
  9. Check knockout pin adjustment.
  10. Be sure cavities have sufficient drait.

Defect: Dull surface

  1. Adjust mold temperature - usually reduce temperature for better appearance.
  2. Polish mold.
  3. Chrome plate.
  4. Close mold more slowly.

Defect: Orange peel (rough, pimply surface)

  1. Close slowly on low pressure. Delay 2 sec. before applying high pressure.
  2. Preheat (radio frequency).
  3. Use stiffer material.
  4. Use finer ground material.
  5. Use large preforms and as few as ~ossible.
  6. use lower mold temperature.

Defect: Pitted surface

  1. Use stiffer material.
  2. Preheat.

Defect: Clouded or segregated surface.

  1. Reduce molding temperature (for colors, 300 to 310°F)
  2. Preheat preforms.
  3. Adjust plasticity.
  4. Adjust pressure and closing speed

Defect: Dimpled surface

  1. Close slowly, longer on low pressure, no breathe, then high pressure.
  2. Use stiffer material.
  3. Lower mold temperature.
  4. lncrease charge weight.
  5. Shape preforms more closely to piece.
  6. lncrease pressure.

Defect: Warped piece

  1. Heat mold more uniformly.
  2. Use stiffer material.
  3. Preheat if soft plasticity.
  4. lncrease cure. Cantilever racks
  5. Use lower shrinkage material. and/or material more rigid at discharge.
  6. Redesign mold; use wider knockout pins.
  7. Adjust temperature of force arid cavity - lower temperature may reduce warpage.
  8. Preheat for irregular shaped pieces.
  9. Cool uniformly and use shrink fixtures.

Defect: Cracking after molding

  1. lncrease wall thickness around inserts.
  2. Check knockout pins.
  3. Correct size of shrink fixture.
  4. Use more flexible material.
  5. lncrease radii and ribs.
  6. Oven anneal 2 hr. at 200°F.

Defect: Poor electrical properties

  1. Close slowly.
  2. Preheat 112 hr. at 185°F.
  3. Increase cure.
  4. Reduce temperature.
  5. Use stiffer grade.

Defect: Weak mechanically

  1. Increase temperature.
  2. Increase cure.
  3. Increase pressure.
  4. High frequency preheat.
  5. Increase charge.
  6. Afterbake to increase strength, if economical. Try 2 hr. at 250°F

Defect: Pimpling

  1. Breathe mold.
  2. Use higher fines material.
  3. Use softer material.
  4. R.F. preheat.
  5. Lower mold temperature,

Defect:Burned marks

  1. Reduce preheat temperature.
  2. Reduce mold temperature.
  3. 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).
  4. void or minimize breathing.

Defect: Thick flash

  1. Reduce mold charge.
  2. Reduce mold temperature.
  3. lncrease high pressure.
  4. Close on low, apply high pressure sooner.
  5. Eliminate breathing, follow (4).
  6. Use softer grade material for more pressure.
  7. Be sure of 0.002-in. between force and cavity.
  8. Be sure overfiow grooves are clean.
  9. Reduce transfer pressure andlor increase clamping pressure.