15-06-1980 дата публикации
Номер: SU741790A4
1439294 Moulding double walled pipes W HEGLER 10 July 1974 [22 March 1974] 30611/74 Heading B5A [Also in Division F2] A plastics tube comprising an outer annularly or helically corrugated wall, and a cylindrical inner wall, e.g. of 0À05 mm. thickness, fused thereto, is continuously made by extruding concentric tubes from extrusion die passages 1,4, into a continuous corrugating mould cavity defined by the co-operation of a pair of endless moving chains of mould halves. The tubes are urged outwardly in the cavity, respectively to define the outer and inner walls and, to prevent undulations being formed during cooling of the inner wall at its locations intermediate its fusion to the outer wall, air is admitted to between the extruding tubes at controlled pressure and temperature, which are respectively above atmospheric and at, or above, that of the softening point of the plastics. In the embodiment, the moulds are externally cooled, and the outer tube is urged against the corrugating cavity by vacuum admitted through mould passages 20, 21, and the innter tube is urged outwardly against the outer corrugated tube by air admitted at a raised temperature and a pressure, e.g. 15 to 30% above atmospheric, which is higher than that, e.g. 10 to 20% above atmospheric, of the air admitted between the exterior and interior tubes. The inner wall is pressed against the outer wall in passage over an extension 9, of the mandrel 6 of the die from which the inner tube is extruded. The air at pressures above atmospheric is heated by means (not shown), and admitted to within the tubes, via separate die inlets 12, 16, and passages 10, 7, the temperature and pressure of each air supply being measured by instruments 14, 13, and 18, 17, the temperatures being measured at the location of the instruments, but the presssures being measured at locations 15, 19, in the die, beyond which the pressure drop is insignificant.
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