Abstract: The twin-nozzle extrusion head in accordance with the invention includes basically three axially spaced but radially overlapping annular housing members, together establishing two nozzle gaps and a first and a middle one of the two members are provided with annular feeder ducts for these nozzles. Each of these ducts has on its exit side a baffle ring wherein one baffle ring is effective on its radially inner surface while the second baffle ring is effective on a radially outer surface of larger diameter. These surfaces are nonround in a particular determined manner to establish nonuniform gap width related directly to the location of feed ducts for the annular channels, generally, the gaps are wider in locations away from a proximity of such feed ducts. The nozzle gaps are both frustoconical of different steepness and terminate in a common plane. The nozzles are particularly provided for disposing an adhesive on top of a steel pipe and a polyethylene coating and envelope on top of the adhesive.

Abstract: A steel pipe is jacketed by concurrent extrusion of an ethylene hose concentric with a copolymer hose serving as an adhesive, the pipe passing through the extruder heat at an approximately 10% higher speed. The copolymer is predried, and the pipe is preferably precoated with heat-curable phenol or epoxy.