METHOD AND APPARATUS FOR PRODUCING BIAXIALLY STRETCHED THERMOPLASTIC TUBING

摘要

A method of producing biaxially stretched thermoplastic tubes, using an installation comprising a plastics extruder, the output of which is controllable on an open circuit or closed circuit basis and which has a head for the extrusion of highly viscous tubing, a stretching mandrel and a speed-controllable puller and draw-off device. In the region of the follower section of the mandrel adjacent the extrusion head is a surrounding bath for controlling the temperature of the tube at the stretching temperature. A cooling bath is placed in the region of the take up section of the mandrel. A Raman spectrometer operating with laser light is placed in the zone following the cooling bath. The frequency of the laser light is adapted to the plastics used and the energy of the laser is adapted to the wall thickness of the tube in the zone. In addition to the incident light scattered or reflected by the plastics, at least one Raman spectral line is developed in the tube. The extent of axial orientation of the plastics molecules is thus determined from properties of the light scattered, and reflected from the tube. The extrusion rate, the pulling and take up speed, and the bath and mandrel temperatures can be modified accordingly. PAT 16422-1