| 摘要 |
880,391. Making tubular thermoplastic articles. SHAW, H. June 10, 1960 [June 10, 1959], No. 19856/59. Class 87(2). An extruded tubular thermoplastic article, immediately on leaving the extrusion die 1, passes in contact with the surface 14 of a cooling member 3, which cools its surface to below the softening temperature of the thermoplastic, and then passes over the surface 15 of a sizing member 4 against which it is sucked by the application of a vacuum, the surface 15 being maintained at a temperature which will not substantially cool the extrusion further. Further cooling and sizing members, e..g cooling members 5, 6 and sizing member 7, may follow. The extrusion is finally cooled to, or near to, ambient temperature by means of a water bath (not shown) or by means of jets 24 of air or water. The surfaces 14, 15, 18, 21 are preferably coated with, or made from, a material having a low coefficient of friction such as polytetrafluoroethylene. The method is particularly applicable to polyethylene piping which is subject to internal stresses that reduce its bursting strength when cooled and stretched simultaneously. The invention is not limited to the extrusion of piping, however, and may be applied to other extrusions, such as channels and troughs. Specification 780,900 is referred to. |
