A method for producing biaxially oriented pipes from thermoplastic materials, wherein preformed pipes are extruded from thermoplastic materials and subjected to temperature conditioning. An expansion device and a stretching unit arranged downstream of the expansion device are adopted. The expansion device includes a non-deformable expansion section and a continuous section located upstream with upstream sealing members. The expansion device is provided with a first gas discharge pipeline having one or more first inlets on its outer surface, which open, close or partially close depending on whether they are covered or blocked by the pipe. A first gas volume is formed between the expansion device and the pipe, confined at its upstream end by sealed contact between the preformed pipe and the upstream sealing members of the outlet section, and confined at its downstream end by sealed engagement between the pipe and at least the downstream part of the expansion section near the transition to the outlet section. A first gas flow is delivered from a first gas source through a first gas supply pipeline and outlets into the first gas volume, and the gas pressure inside gradually expands the pipe before it contacts the expansion section. The first gas flow is maintained at a constant flow rate independent of gas pressure.
Area Code: NL
Application Number: CN201980092209.6
