Coextrusion apparatus for producing multiple layered thermoplastic pipe

摘要

An apparatus for the formation of a multiple layered pipe comprising a die housing having a bore therethrough with a mandrel longitudinally supported within the bore by a spider to provide an annular extrusion passageway defined by the inside surface of the housing and the outer surface of the mandrel. The mandrel comprises a series of sequentially positioned annular feed rings for the laydown of thermoplastic material on the inner surface of the main thermoplastic material flowing thereover through the extrusion passageway. The extrusion passageway is constricted downstream of the spider but prior to the annular sequentially positioned feed rings to reunite the thermoplastic material after the flow disruption created by the spider. Also included in the mandrel is a longitudinal passageway in communication with the inlet section of the bore for the transportation of thermoplastic material therethrough to one or more of the annular feed rings. The mouth of the mandrel bore includes a restrictor orifice therein to balance the pressure differential created therein by the constriction in the extrusion passageway.