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Last Updated on Friday, 04 May 2012 10:40
Written by Technical Team
Internal Gas - CGI's PEP - PLASTIC EXPULSION PROCESS

CGI's PEP is based on first filling the mould cavity with plastic, temporarily holding back pack pressure exerted by the moulding machine, commencing gas injection to apply further packing pressure, and then sequencing the opening of one or more shut-off valves to enable the expulsion of molten plastic to one or more secondary cavities.

The amount of plastic expelled is not variable by timing of the gas injection. In the PEP processes the amount of plastic expelled is controlled by the fixed volume of the secondary cavity or cavities.

Advantages of PEP 1*
  1. Injection of an unpressurised accurate shot weight or fill volume (as in the 'Short Shot' process) is not necessary. Timing of the gas injection is not critical.
  2. Pack pressure from the machine and/or the gas ensures a good reproduction of the mould cavity surface on the plastic.
  3. No possibility of 'hesitation' marks as in the 'Short Shot' method.
  4. Improved gas core out with reduced weight and moulding time cycles.
  5. Suitable for most thermoplastics, including glass-filled nylon.
  6. Suitable for multi-cavity moulds.
  7. Location of plastic feed gates is not critical.

 

Plastic is expelled back into the moulding machine cylinder by the injection of gas forcing back the injection screw or piston against a controlled back pressure. The nozzle valve is used instead of the PEP outflow valves.

Advantages of PEP 2 include:

  1. Expelled plastic will be remoulded in succeeding shots and no regrinding or recovery of the expelled material is necessary.
  2. No trimming of the moulding is necessary.
  3. No in-mould shut-off valves.

* Subject to US, PCT and UK patent applications.
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