| 摘要 |
A seamless parison extruded from an extruder via an annular die, passes through a calibrator and coaxially surrounds a probe pipe, which is made to extend through the annular die beyond the calibrator. On the probe pipe there is mounted a sealing element. Ahead of the sealing element, a pressure equal to atmospheric pressure prevails inside the tube and, after the sealing element, a higher pressure than atmospheric pressure prevails. The pressurization is achieved in that a second belt take-off folds together the tube, so that the compressed air fed in through the probe pipe causes a higher tube internal pressure, since the sealing element bears in a sealing manner against the inside of the tube. As a result, a substantial pressure separation is effected at the point of the sealing element. In a first heating chamber, the tube is heated to the stretching temperature and is transported by a second belt take-off at a stretching speed, increased relative to the take-off speed of the first belt take-off, to a second heating chamber, in which a heat setting of the tube takes place. From the heating chamber, the tube is transported onward at the same, greater or lower speed than the stretching speed by a third belt take-off and wound up by a deflection roller onto a wind-up roller. |
