Extrusion of plastics
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United States of America Patent
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Jan 21, 1992
Grant Date -
N/A
app pub date -
Nov 19, 1990
filing date -
Nov 19, 1990
priority date (Note) -
Expired
status (Latency Note)
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Abstract
A method and apparatus for the molding of a thermoplastic with a large cross-section is provided. The plastic is extruded into a closed mold where sufficient pressure is maintained on the plastic to offset the shrinkage to the extrudate during cooling. In particular, the mold cavity is capable of changing its volume as molten plastic is forced into it while also changing the pressure within it against which the plastic is being extruded. This is achieved by positioning a movable piston as one end of the mold, and applying pressure to the piston so that a predetermined pressure within the mold is maintained. Once the desired amount of plastic is within the cavity, pressure is maintained while it solidifies, following which the finished product is ejected.
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