| 摘要 |
599465 A plastic (PVC) pipe extrusion line for producing bi-axially oriented tube or pipe is provided with improvements, a first of which is to provide a sealing member at the head of the run on part 201 within the lumen of the tube 10 in preform condition before expansion. The sealing member forms a seal with the moving internal surface of the preform 10 so that pressurized gas introduced into the space 210 between the internal surface of the preform and the downstream run on part 201 and the expansion part 200a, 200b does not leak into the lumen of the preform upstream of the seal. One or more gas discharge ducts 250 are formed in the expansion device, said one or more gas discharge ducts having one or more inlet ports 250a in the exterior surface of the expansion part of the expansion device, an inlet port being open or closed dependent on whether or not the inlet port is covered and closed by the tube 10, the gas discharge duct allowing – in use of the installation - for the relief of gas pressure from the fluid volume 210 when the one or more corresponding inlet ports are open thereby reducing the expansion of the tube caused by internal gas pressure, the relief of gas pressure continuing until the one or more corresponding inlet ports are covered and closed again by the tube. |
