| 摘要 |
A melt extrusion process and apparatus for producing a multiple-layered pipe (preferably of two or more thermoplastic resins) are disclosed. The process comprises extruding a cylindrical stream of thermoplastic material, converting the cylindrical stream to an annular stream, applying at least one inner annular layer of thermoplastic to the inner surface of the annular stream, applying at least one outer annular layer of thermoplastic material to the annular stream, and extruding the resultant multiple-layered annular stream. Apparatus for producing this pipe includes a modular pipe die having inside and outside laydown means, flow equalizing means within each of the inner and outer laydown means to obviate layer imperfections, and adjustable means to control the concentricity of the outer layers. The invention finds particular application in the production of a thermoplastic pipe having an intermediate expanded core.
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