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

摘要

During the simultaneous extrusion of a plurality of blown films, pipes or tubular profiles of plastic, the maintenance of constant wall thicknesses of all plastic profiles is influenced. In this process, plastic is fed at an adequate rate constantly, for example in portions or continuously, to the extruder feed, whereas at the outlet from the extruder, the final plastic profiles are taken off continuously. It is essential in this that on the one hand a wall thickness measurement is carried out on each extruded plastic profile downstream of the extruder and on the other hand a predetermined unit length of each extruded plastic profile is cut off and weighed. The wall thickness measurement is in this case carried out with a movement component running transversely to the take-off direction and the measured values taken along the complete distance traversed by the movement are integrated to form mean values. Then these mean values are compared with the weighings and adjusted to the latter before direct wall thickness measurements on the plastic profile are then carried out continuously using the calibrated or corrected mean values, and the actual values resulting from this are constantly fed to the extruder and/or to the profile take-off as a control feedforward.