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How to Set Up or Optimize An Existing Injection Molding Process for TPE

Part Filling:

  1. Set pack and hold timers to zero.
  2. Set pack and hold pressures to zero.
  3. Set shot size and injection high pressure to ensure a short shot.
  4. Set mold temperatures to a nominal value.
  5. Set injection rate to the desired value.
  6. Start a single cycle.
  7. Increase shot size to barely fill the part.
  8. Set cushion to approximately 0.25 inches. Add same to shot size. Set cutoff point to just before cushion. Note injection fill time.
  9. Increase injection pressure in 250 psi increments. Note where fill time starts to plateau. You have to have an injection maximum 200-300 psi over the minimum fill pressure or the injection velocity will not be met. I.E. the fill pressure is a process limit. As the controller reads pressures approaching the pressure limit it will begin to slow the ram forward speed to ensure the pressure is not exceeded.
  10. Adjust cut off point to achieve 95% fill. Note the injection pressure needed.
  11. Perform injection time optimization if required.

Part Pack Out and Gate Freeze Off:

  1. Set packing pressure to 1/2 to 2/3 of injection pressure.
  2. Set packing time to time required to pack out the part.
  3. Set hold time long enough to freeze gates.

Cooling:

  1. Cooling time has to be long enough to allow screw recovery.
  2. Check ejected parts by hand. If cold, cooling can be reduced. If very hot or parts are deforming to tearing in the mold, increase the cool time.

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