Extrusion of sheath onto elongated support using decompression zones

Claim 1

An extrusion head for coating a support with a plastic material comprising a substantially cylindrical elongated body having at one end a first opening for the introduction of said plastic material under pressure in a generally radial direction and a second opening for the axial introduction of a solid or hollow elongated support, and, at the other end, a third opening for the axial exit of the coated support; said body containing, in succession in the axial direction: a. a first decompression chamber, b. a homogenizing and flow-equilibrating distributor means, c. a second decompression chamber, d. an expansion chamber, and e. a die means; the first decompression chamber being an annular chamber defined in part by the walls of said body encircling said support and being in communication with said first opening; the second decompression chamber being an annular chamber encircling said support and separated from the first chamber by said homogenizing and flow-equilibrating distributor means; said latter means comprising an annular diaphragm having a constricting passageway therethrough for homogenizing and evenly distributing said plastic material around the second decompression chamber; said second chamber communicating with the expansion chamber through an annular orifice, said expansion chamber being defined by a divergent outflow cone forming said material into an unconstricted sheath, and said die means being associated with said exit and having an inwardly convergent wall for forming and constricting a compacted coating of desired thickness onto said support.