SPIRAL FED MULTI-LAYER TUBULAR DIE

摘要

An extrusion die apparatus for extruding a multiple layer tubular product comprising an elongated cylindrical mandrel and a plurality of annular die elements mounted co-axially one behind the other on the mandrel forming contiguous annular thickness control passages between the die elements and the mandrel. The die elements have inner and outer conical surfaces inclined rearwardly at a predetermined angle with respect to he longitudinal axis of the mandrel. The die elements are nested together with the outer conical surfaces of one die element facing the inner conical surfaces of an adjacent die element. The inner and outer conical surfaces form conical passages therebetween which communicate with the annular thickness control passages and a helical groove is provided on the outer conical surface of each die element. Means are provided for delivering a molten thermoplastic material to the conical passages wherein the material is substantially uniformly distributed over the outer conical surface containing the helical groove. The molten thermoplastic material is preferably delivered from an inlet to a plurality of outlets on each die element by a binary divider system including a plurality of channels each communicating with a pair of channels dividing the flow of molten material into separate paths which eventually lead to the plurality of outlets. The material forms overlapping tubular layers in the thickness control passages which are then extruded from the die as a multiple layer tube.