| 摘要 |
The tubing comprises a core of expanded material between inner and outer walls of dense material, which is co-extruded through a distribution head then through a conventional tube die (1) comprising a divergent-convergent portion (2, 3) and a straight portion (6) for shaping the tube, having a narrowed flowpath zone (7) in order to bring about an increase in pressure from 2 x 10<6> to 15 x 10<6> Pascals in the thermoplastic materials flowing into the convergent portion of the die. The pressure increase removes lines of weakness, which would otherwise be caused by the flow of the materials around supporting fins (4) for the core (5) of the die (1). <IMAGE> |
