| 摘要 |
PURPOSE: A method is provided which a plastic of tube blank is not abruptly solified even though a cold fluid is circulated inside the plastic tube and improves a productivity properly. CONSTITUTION: A tube blank (Te) is brought to a temperature close to molecular orientation temperature is subjected to a bi-axial drawing, by radial expansion of the tube blank inside a forming shaft (2), with formation of a contraction cavity at one end of the tube, by controlled displacement of this contraction cavity to the other end of the tube, and by longitudinal drawing. The radial expansion is carried out in at least two phases, viz. a first phase during which the tube blank (Te) is inflated to an intermediate diameter (Di) determined by a double-walled envelope (21), introduced into the forming shaft (2), with circulation of a hot fluid between the two walls of the envelope (21), and then the envelope is gradually removed from the forming shaft(2) to enable, during a second phase, the radial expansion of the plastic tube up to an internal diameter of the forming shaft (2), and its longitudinal drawing.
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