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Improved pressure-holding chamber type injection molding process and apparatus for injection molding of products

  • US 5,219,512 A
  • Filed: 07/30/1990
  • Issued: 06/15/1993
  • Est. Priority Date: 10/13/1988
  • Status: Expired due to Fees
First Claim
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1. A process for injection molding an article comprising the steps of:

  • heating, plasticizing and metering a plastic material within a body of an injection machine, the injection machine having an injection plunger in communication via a nozzle passage with a mold arrangement, the mold arrangement having a mold cavity that includes a gate for communication between the mold cavity and the nozzle passage;

    injecting the metered material using the injection plunger through the nozzle passage toward the mold cavity;

    exerting an external holding pressure using the injection plunger on the injected material so as to compact the injected material within the nozzle passage and the mold cavity;

    interrupting the nozzle passage at a location in the nozzle passage spaced from the gate of the mold cavity to define a closed space comprising the mold cavity and a preselected portion of the nozzle passage between the gate and the location of the interruption, the closed space being fixed in volume by the interruption to cause an internal holding pressure by the compacted material within the fixed space of the mold cavity and the preselected portion of the nozzle passage;

    the step of interrupting the nozzle passage being carried out by using a non-pressurizing valve to interrupt communication between the body and the mold cavity without applying pressure to the compacted material within the closed space;

    heating, plasticizing and metering further material in the body of the injection machine for a subsequent article while the nozzle passage is interrupted;

    and, during said nozzle passage interruption, cooling the mold arrangement to thereby automatically and continuously decrease said internal holding pressure due to self-contraction of the compacted material, and during said pressure decrease, freezing or solidifying a portion of the compacted material received in the mold cavity to provide the first mentioned article.

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