Melt extrusion of multi-wall plastic tubing

Claim 1

METHOD OF PRODUCING MULTI-WALL THERMOPLASTIC TUBING BY MELT-EXTRUSION WHICH COMPRISES, FORMING A CYLINDRICAL SOLID STREAM OF DIFFERENT MELTED THERMOPLASTIC MATERIALS IN WHICH THE THERMOPLASTIC MATERIAL TO FORM THE INNERMOST WALL OF SAID TUBING CONSTITUTES THE CORE OF SAID STREAM, AND AT LEAST ONE THERMOPLASTIC MATERIAL DIFFERENT FROM THE THERMOPLASTIC MATERIAL IN SAID CORE IS COAXIALLY DISTRIBUTED AS AN ANNULUS ENVELOPING AND CONTRACTING SAID CORE, MOVING SAID SOLID STREAM THROUGH A SYLINDERICAL PASSAGE AT A VELOCITY BELOW THE THRESHOLD OF TURBULENCE TO THEREBY MAINTAIN THE COAXIAL DISTRIBUTION OF THE MELTED THERMOPLASTIC MATERIALS, CONVERTING SAID SOLID STREAM AT THE TERMINUS OF SAID CYLINDERICAL PASSAGE INTO A TUBULAR STREAM BY AXIALLY PIERCING AND RADIALLY DISTRIBUTING THE SOLID STREAM, EXTRUDING THE TUBULAR STREAM THROUGH AN ANNULAR DIE ORFICE TO FORM TUBING AN COOLING THE TUBING TO A SET CONDITION.