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United States Patent 6062718
Douris , ê et al.

hermoplastic foam extrusion assembly with an extrusion screw including a circulation channel defined therein

Fogarty May 16, 2000

Abstract

A thermoplastic extrusion assembly having a melt region wherein a plurality of material pellets are melted and mixed by a mixing assembly with a foaming agent, in the case of a thermoplastic foam extrusion assembly, introduced via an agent addition assembly. The thermoplastic extrusion assembly further includes a heat extraction region structured to extract excess heat from the mixture of melted material pellets such that the mixture achieves an extrudable temperature. The heat extraction region includes an elongate barrel having at least one inlet and at least one outlet, the inlet being structured to receive the extrusion mixture therethrough for passage into the barrel wherein a heat extraction structure cooperatively disposed with the barrel draws heat therefrom. An extrusion screw is disposed in the barrel and includes at least one screw flight structured to rotate within the barrel and urge the extrusion mixture towards the outlet of the barrel where a die is disposed in order to form the finished product. Moreover, the screw flight includes at least one circulation channel having an asymmetrical, at least partially inwardly tapered inlet area defined therein and structured to receive quantities of the extrusion mixture therethrough upon rotation of the extrusion screw, thereby circulating the extrusion mixture towards the barrel for more effective and uniform cooling of the extrusion mixture prior to passage through the die.