Process and device for maintaining a constant wall thickness in the extrusion of blown films, pipes or tubular profiles made of plastic

摘要

In the simultaneous extrusion of a plurality of blown films, pipes or tubular profiles made of plastic, the maintenance of constant wall thicknesses of all plastic profiles is effected. In this process, plastic material is fed in an adequate amount to the feed of the extruder, whilst the finished plastic profiles are constantly taken off at the discharge of the extruder. It is essential in this that on the one hand the amount of the plastic material taken from the extruder per unit time is determined exclusively by weighing and on the other hand the length of each individual plastic profile forced out by the extruder is measured, that a reference parameter is formed in each case from the weighing of the length measurements and, by means of this reference parameter, a control of the weight per metre for the associated plastic profile is brought about via the screw speed and/or the take-off rate, that the wall thickness of each plastic profile is also recorded and, by means of this, the relative profile weight is determined from the specific weight of the plastic material, that, via these values, the individual wall-thickness recordings are calibrated and then the absolute profile weights are determined and that, finally, the centring and/or weight distribution at the discharge of each extruder head or extruder die is controlled via the reference parameters analogous to the individual weight determinations.