Coextrusion method and apparatus

摘要

The present invention is an improved method and apparatus for the coextrusion of layered wall conduit wherein a flow of a first resin is advanced along a longitudinal axis and two flows of a second resin is advanced along paths that straddle the flow of first resin. The advancing flows of second resin are progressively spread into arcuate fanned shapes that extend about the flow of first resin until the edges of the fanned flows meet to form a first axially extending annular flow surrounding the flow of first resin. The flow of first resin is then shaped into a second axially extending annular flow that is inwardly concentric relative to the first annular flow and the first and second annular flows are moved into confluence to form a layered flow that is shaped in a sizing due into layered wall conduit. In one embodiment, a third outwardly concentric annular flow is moved into confluence with the layered flow forming a three-layer flow for shaping into conduit.