Method of reverse degassing an extrusion melt and an extrusion d

Details Method of reverse degassing an extrusion melt and an extrusion d Method of reverse degassing an extrusion melt and an extrusion d

1991-05-31

1992-07-14

Thurlow, Jeffrey

Plastic and nonmetallic article shaping or treating: processes

Vacuum treatment of work

To degas or prevent gas entrapment

159 22, 366 75, 366 88, 366 76, 425203, B29C 4776

Patent

active

051300702

ABSTRACT:
A method for reverse degassing a melt of thermoplastic plastics material and an extrusion device therefor. Thermoplastic plastics materials are fed into the extrusion device either in the form a melt or as a granulated, which latter is fused to form a melt. A portion of the melt is separated from the main melt stream. The extrusion device includes, in a downstream direction, a return-blocking zone, a degassing zone, a feed zone and a conveying zone. The separated portion is removed from the feed zone, the conveying zone or even a feed conduit leading into the feed zone if the material is already molten. The extrusion device also includes screw means rotating in a barrel. The screw has at least two different flight portions, one in the returning-blocking zone and the other in at least the degassing zone. The separated melt portion is fed, through a by-pass conduit, into the return-blocking zone in an amount sufficient to fill the screw flight in this zone but which only partially fills the screw flight in the degassing zone when it is transferred thereunto, by the screw means, from the return-blocking zone. The partially-filling of the flight in the degassing zone must, however, be sufficient to ensure continued conveyance of the melt into the downstream feed and conveying zones.

REFERENCES:
patent: 3376603 (1968-04-01), Colombo
patent: 3416189 (1968-12-01), Welt
patent: 3712594 (1973-01-01), Schippers et al.
patent: 4197268 (1980-04-01), Anders
patent: 4265547 (1981-05-01), Martin
patent: 4900494 (1990-02-01), Wobbe
patent: 4902455 (1990-02-01), Wobbe

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