| 摘要 |
A hybrid extruder provides plastic insulation which is as uniformly and tightly disposed about a substrate as that produced in a conventional pressure extruder and accommodates irregular substrates. The hybrid extruder includes a core tube which is positioned in a die cavity to form a flow passage which includes a restriction to the flow at the end of the core tube to maximize the pressure in the plastic material. The leading end of the core tube is spaced a distance from the land of a die which is substantially less than in conventional pressure extruders to form another portion of the flow passage having a predetermined configuration. After flowing through the restriction, the plastic material expands. This avoids any backflow of the plastic material into the core tube in the event the core tube is to allow the passage of oversized spliced portions of the substrate. Advantageously, this arrangement also prevents the occurrence of melt fracture when extruding relatively high molecular weight plastic materials which because of excellent mechanical and dielectric properties are desired for insulating particular substates.
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