| 摘要 |
<p>A die assembly for the extrusion of thermoplastic pipe from a plastic exhibiting an appreciable amount of memory and thus having an elongated heated portion defined by an elongated outer bushing ring with an inside diameter substantially equal to the nominal outside diameter of the pipe to be produced and an inner mandrel ring having an outside diameter smaller than the inside diameter of the bushing ring and disposed within the bushing ring to form an annular extrusion channel, the essentially straight portion of the extrusion channel defining the land length of the die and the width of the extrusion channel defining the die opening of the die, the improvement comprising a mandrel formed in two sections, including a longer upstream section, fixedly mounted in the die and having a fixed mandrel outside diameter and a downstream mandrel section removably mounted in the die as an extension of the upstream section and replaceable by downstream mandrel sections of equal length but different mandrel outside diameters. The improved die assembly is capable of producing a given diameter pipe having a plurality of different SDR Ratings which closely approximates a predetermined land length to die opening ratio for each of the different SDR ratings, thereby eliminating the necessity of providing a complete new die assembly for each different SDR rating desired.</p> |
