Degassing extruder

Claim 1

An extruder for degassing viscous thermoplastic plastics materials in the form of a melt comprising a barrel; at least one screw mounted for rotation with said barrel, shaft means mounting said at least one screw, said screw comprising core means mounted on said shaft and flight means helically disposed about the periphery of said core means, said barrel having a wall surface, said wall surface defining a first throughbore for the introduction of said plastics material into said barrel and a second throughbore downstream of said first throughbore for degassing said plastics material within said barrel, an intake and metering zone defined within said barrel between said first and said second throughbores and means for degassing said thermoplastic material communicating with the interior of said barrel through said second throughbore wherein said flight of each said screw is discontinuous in the region of said second throughbore; a plurality of disc members and spacer discs are alternately mounted on each said screw shaft in said region of said second throughbore, each said disc member and spacer disc having first and second opposed major surfaces, said first major surface being downstream of said second major surface, said first major surface of each said disc member defining profile means enhancing conveyance of said material in said downstream direction, each said disc member having a major dimension substantially equal to the overall diameter of said screw in said flighted region and each said spacer member having a major dimension substantially equal to the diameter of said screw core and wherein the thickness of each said disc member and spacer disc measured from said first major surface to said second major surface lies in the range of from 0.1 to 0.5 times said screw diameter.