Composite die assembly for use in the production of thermoplastic tubing

A die assembly for use in the production of thermoplastic tubing, comprising:

• an elongate nozzle member adapted for attachment to an extrusion head, the nozzle member providing a longitudinally extending supply passage for the delivery of thermoplastic material to the delivery end thereof,
• the nozzle member including a longitudinally extending cylindrical stem terminating in a sleeve portion at said delivery end,
• the sleeve portion providing a peripheral lip and defining an internal recess of circular cross section extending axially therefrom,
• axially extending coupling means on said stem defining within said recess a first coupling member,
• a mandrel located coaxially within said recess, the mandrel defining with said peripheral lip an annular die orifice,
• the mandrel having an external surface spaced from said sleeve portion and defining therewith an annular chamber communicating with said die orifice,
• axially extending coupling means on said mandrel defining a second coupling member engageable with said first coupling member for locating the mandrel operatively within said recess,
• means defining within the mandrel a flow passage having an inlet positioned to communicate with said supply passage for receiving thermoplastic material therefrom, and an outlet positioned to communicate with said annular chamber,
• said annular chamber defining an uninterrupted annular flow passage extending from said outlet to said orifice.