Process for continuous production of biaxial drawing plastic tubing and production line for this process

摘要

Method for continuous production of tubes of plastic material by biaxial drawing. Method for continuous production of tubes of plastic material by biaxial drawing comprises: (1) forming a rough shape (E) by extrusion; (2) adjusting (E) to the temperature of molecular orientation; (3) subjecting it to radial expansion by applying an internal fluid pressure (P), through two axially spaced shutters; and (4) ensuring calibration and cooling, while exerting an axial traction on the tube. The new feature is that a pressure (P1), opposing (P), is applied externally against the wall of (E) in at least one zone that is subjected to radial expansion. P1 is smaller than P, so does not prevent expansion, but is sufficient to ensure a controlled expansion so that material thickness is constant over a given circumference. An independent claim is also included for a production line for performing the new method.