Reverse degasification screw extruder with vacuum seal

Claim 1

A screw extruder for processing thermoplastic materials fed thereto, comprising a cylinder; a screw mounted in the cylinder; first vacuum means for applying a vacuum to the cylinder in the region where material is fed to the extruder for the purpose of reverse degasification of the material to be processed in the extruder; back pressure bearing means; a pressure member rotatable with the screw and located between said screw and said back pressure bearing means; an annular non-rotatable end member disposed in front of said rotatable pressure member relativey adjacent said screw, sealing means comprising at least two radial sealing rings surrounding the rotatable pressure member and mounted within said end member, said sealing rings being spaced axially from each other to form an annular interspace therebetween, and second vacuum means for applying a vacuum to said annular interspace, the vacuum applied to said annular interspace being higher than the vacuum applied to the cylinder for the purpose of reverse degasification.