Abstract: 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 the 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.

Abstract: An extrusion die apparatus for extruding a multiple layer tubular product including a plurality of annular die elements mounted co-axially one behind the other on a mandrel forming annular thickness control passages between the die elements and the mandrel. The die elements have inner and outer conical surfaces inclined rearwardly with respect to the 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 which communicate with the annular thickness control passages and a plurality of helical grooves are provided on the outer conical surface of each die element. A binary divider system is provided for distributing a molten thermoplastic material from an inlet to a plurality of outlets communicating with said grooves on each die element.

Abstract: The invention relates to the kind of die which has many helical grooves (40) spiralling around a mandrel, and to a new way of feeding the liquid resin from the main supply duct (48) to the grooves. Instead of the usual one groove to one conduit relationship, in the invention the channels (41) to the grooves are intercalated with the conduits (47). Each groove is fed via feed-channels (45,46) from two of the conduits, and each conduit feeds two of the grooves. The result is that the cooler liquid resin from the walls of the main duct is constrained to move to the centre of the stream in the groove. The arrangement leads to an improvement In the homogeneity of the resulting film.