Apparatus for extruding a thermoplastic material

Claim 1

IN AN APPARATUS FOR EXTRUDING A THERMOPLASTIC MATERIAL, A BARREL HAVING AN INLET AND A DISCHARGE WITH A CHAMBER THEREBETWEEN, A POWER DRIVEN SCREW ROTATABLE WITHIN THE BARREL CHAMBER, SAID CHAMBER AND SAID SCREW HAVING FACING SURFACES OF REVOLUTION DEFINING AN ANNULAR PASSAGE EXTENDING FROM SAID INLET TO SAID DISCHARGE IN WHICH THE MATERIAL IS ADVANCED AND PLASTICATED, SAID PASAGE HAVING A PLASTIC WORKING PORTION AND A PLASTIC MELTING PORTION IN COMMUNICATION WITH SAID WORKING PORTION, SCREW THREADS ON AT LEAST ONE OF THE SURFACES FOR THE FULL LENGTH OF THE WORKING PORTION OF THE PASSAGE FOR ADVANCING AND PLASTICATING THE MATERIAL, SAID SURFACES OF THE WORKING PORTION OF THE PASSAGE SHAPING SO THAT THE PASSAGE EXTENDS TO A FIRST AXIAL DIRECTION, AXIALLY DOUBLES BACK ON ITSELF TO EXTEND IN THE OPOSITE DIRECTION, AND THEN AGAIN DOUBLES BACK ON ITSELF TO EXTEND IN SAID FIRST AXIAL DIRECTION WITH THE PASSAGE CONTINUALLY INCREASING IN DIAMETER TO INCREASE THE RELATIVE CIRCUMFERENTIAL ROTATIONAL SPEED OF THE SURFACES.