Screw extruder for the treatment of pulverized material

Claim 1

A single screw extruder for processing melts of synthetic plastic material and synthetic plastic materials in powder or granulated form, said screw extruder comprising in combination: an elongate casing having at one end a feed zone including a feed port and at the other end a discharge port; a long main conveyor screw rotatably mounted in said casing and extending through substantially the length thereof, said screw and casing defining adjacent to the feed port a feed-in zone, the remaining lengths of the casing and the screw constituting a treatment zone; a short auxiliary screw rotatably mounted in said casing and terminating at the end of the feed-in zone as defined by the screw and the casing, said screws being disposed in axially parallel but non-meshing relationship with each other; a first drive means coupled with the main screw for rotating the same; a second drive means coupled with the auxiliary screw for rotating the same; and transmission means interposed between the second drive means and the auxiliary screw, the transmission ratio of said transmission means being variable for varying the rotational speed of the auxiliary screw independently of the rotational speed of the main screw.