Hermann Berstorff Maschinenbau Gmbh

Gerhard Martin

Joachim Meyke

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.

Method of reverse degassing an extrusion melt and an extrusion device

A method of extruding a foamed thermoplastic plastics material wherein the thermoplastic plastics material, together with a pore regulating agent, is introduced into an extruder and is fused. Gaseous nitrogen, in an amount of 0.2% to 0.5% by weight, and an incompletely halo-substituted hydrocarbon, in an amount of from 0.5% to 2% by weight, are sequentially injected into the fused mixture. The injected material then enters an extrusion head in which the mixture is maintained at a pressure in excess of 55 bar and the temperature thereof is maintained above a temperature pre-determined in dependence upon the nature of the plastics material. The material foams as it leaves the extrusion head.

Method for extruding a thermoplastic plastics material foam

A screw extruder for processing thermoplastic materials wherein a vacuum is applied to the feed opening for the material and/or to a filling section of the cylinder for the purpose of reverse degasification, said extruder having a simultaneously rotating pressure piece between a screw and a back pressure bearing and having a stationary end piece disposed on the screw side in front of the rotating pressure piece and sealing means comprising at least two axially spaced radial sealing rings and a vacuum source to apply vacuum to an annular interspace formed between the sealing rings.

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Hanover, Germany

Gerhard Martin