Process for producing corrugated multi-layer tubing having layers of differing plastic characteristics

A method for producing fuel and vapor tubing having at least one region defined by at least one corrugated region, the method comprising the steps of:

• extruding tubular polymeric material from one extrusion head, said tubular polymeric material having at least three concentric layers of thermoplastic material in overlying bonded relationship to one another, wherein at least two concentric layers are composed of thermoplastic materials having different chemical compositions, said extruded multi-layer tubular polymeric material having a first outer diameter, an inner surface, and an opposed exterior surface;
• introducing said extruded multi-layer tubular thermoplastic material into a mold device while still in a molten state upon exit of said tubular thermoplastic material from said extrusion head, said mold device comprising:
• a) a plurality of segmented die sets, each die set having a first end, a second end, and an essentially cylindrical shaft extending from said first end to said second end of said die set, said cylindrical shaft defining an inner surface having a first inner diameter greater than said first outer diameter of said introduced multi-layer tubular thermo-plastic material wherein at least one of said die sets has at least one annular depression having a second inner diameter greater than said first inner diameter;
• b) means for sequentially positioning said die sets in an end-to-end fashion such that said first end of an initial die set engages said second end of a subsequent die set at said point said molten tubular material is introduced into said mold device;
• c) means for moving said die sets laterally away from said extrusion head at a uniform rate of travel;
• and
• d) means for permitting removal of said tubular material from said die sets at a point distal from said extrusion head;
• drawing said tubular material away from said extrusion head at a rate essentially equal to movement of said die sets, said drawing step sufficient to effect elongation of said tubular material by an amount between about 10% and about 20% greater elongation of said tubular material as initially extruded;
• expanding said tubular material from said first outer diameter to a second outer tubular diameter sufficient to permit deformable contact between said exterior surface of said tubular material and said inner surface of said essentially cylindrical shaft of said segmented dies, wherein said second outer diameter is between about 40% and about 60% greater than said first outer diameter and said inner surface of said tubular material is deformed to correspond to said annular depression positioned in said die set;
• and
• sequentially opening said segmented dies to permit said tubular material to exit therefrom, said tubular material having said second tubular outer diameter and convolutions essentially equivalent to said annular depression located in at least one die set, wherein said multi-layer tubing material comprises an exterior layer composed of an extrudable melt processible thermoplastic and at least one inner layer is a fluoroplastic material selected from the group consisting of polyvinylidine fluoride, polyvinyl fluoride, ethylene tetrafluoroethylene and mixtures thereof.