Two-stage single screw extrusion apparatus

Claim 1

An extrusion apparatus for extruding plastic resinous material comprising: a. a tubular barrel member having a feed port near one end and a discharge port at the opposite end, said barrel member having an interior surface extending substantially throughout the length of the barrel between the feed port and the discharge port to define a substantially constant diameter bore therebetween, said bore being comprised of a first entrance high viscosity zone and a second lower viscosity mixing discharge zone, said first zone having longitudinal grooves along the interior surface; b. a two-zoned screw member rotatably mounted within the bore of said barrel, said screw member having an effective length substantially equal to that of the bore of the barrel member and having a predetermined thread, hand, land, pitch, and diameter for each of said first entrance zone of the bore and the second discharge zone of the bore; the first zone of the screw has a close fit with the interior surface of the bore of the barrel member, the pitch of the thread is substantially constant and is less than the diameter of the screw and the thread of the screw has a depth that decreases along the length of the screw to provide a compression ratio within the range of about 2 to 3.5 and; the second zone of the screw has a shaft and thread diameter that is substantially less than the diameter of the bore of the barrel, the screw in said second zone has a multiple lead thread with a pitch at least two times the diameter of the bore to provide substantial blowback for mixing and discharge of resinous material; c. rotating means operatively associated with the screw member for rotating the screw member; d. heating means operatively associated with the barrel member to maintain temperature of the resinous material within the bore at predetermined temperatures; and e. an extrusion die operatively associated with the discharge port of the tubular barrel member.