| 摘要 |
<p>1537573 Plastics pipes WAVIN BV 9 Jan 1976 [13 Jan 1975] 00822/76 Heading F2P [Also in Division B5] An extruded polyvinyl chloride material pipe, Fig. 4, comprises a wall defined between inner and outer concentric surfaces of substantially circular cross-section, and a plurality of circumferentially circular cross-section, and a plurality of circumferentially spaced cylindrical bores 12 extending longitudinally of the pipe within the wall, and an undulatory configuration of the inner and outer surfaces of the pipe around its circumference, Fig. 3, is prevented by extruding the pipe from a tubular passage (Divisions B4-B5) whose outer and/or inner wall is undulatory circumferentially of the passage, so that flow of the material is restricted between mandrels which are located within the passage to define the bores.</p> |
