| 摘要 |
The heating unit comprises a descending series of contact heating rings (3a-d). These rest against the outer surface of the sheet (1) and commence just below the first pinch roller pair (2). They are preferably individually-adjustable. Preferred Features: The inner surface of the contact heating ring is cylindrical and/or conical. Internal diameter of successive heating rings increases by 1.2-2.0. They number 2-10 in total, depending on the required degree of stretching. The rings are optimized for the individual sheet material, in terms of induction angle, outlet radius and -angle. They are made of high thermal conductivity material, e.g. copper or aluminum. Their contact surfaces have special, anti-adhesion coatings of e.g. plastic, ceramic or metal. Grooves, bores and/or pores are included for vacuum connection. The contact cooler or tempering ring (4), employs e.g. air or water, and is located closely below the last heating ring. It is height-adjustable. Its characteristics resemble those of the heaters. The second pinch roller pair (6) is height-adjustable, to closely below the cooling ring. Its diameter exceeds the maximum sheet diameter following stretching. If necessary, it has automatic diameter control.
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