Patent ID: 6305922
Filing Date: 2001-10-23
Classification: B29C

Abstract:
An extrusion die apparatus for extruding a multiple layer tubular product comprising, in combination: an elongated cylindrical mandrel having a forward and a rearward end; a plurality of annular die elements mounted co-axially one behind the other on said mandrel and forming contiguous annular thickness control passages between said die elements and said mandrel, said die elements including inner and outer conical surfaces inclined rearwardly along the longitudinal axis of said mandrel and forming acute angles therewith, said die elements being nested together with said outer conical surfaces facing said inner conical surfaces and forming conical passages therebetween communicating with said annular thickness control passages, said inner conical surface of each of said die elements being inclined at substantially the same acute angle with respect to said longitudinal axis of said mandrel and said outer conical surface of each of said die elements being inclined at an acute angle with respect to said longitudinal axis which is less than that of said inner conical surface of an adjacent die element, said outer conical surface of said die elements having a helical groove therein, the depth of said helical groove decreasing as said groove approaches said annular thickness control passages, and means for delivering a molten thermoplastic material to said conical passages, wherein said material is substantially uniformly distributed over said conical surfaces, entering said annular thickness control passages to form overlapping tubular layers, said overlapping tubular layers being extruded from the in the form of a multiple layer tube.