Controlling dimensions and quality of plastic extrudates - by controlling withdrawal velocity in accordance with pressure on molten extrudable mass

Semi-finished plastic prod. e.g. a tube, produced by extruding a molten plastic material from an extruder towards a calibration device connected to an electrically driven, withdrawing device. The extrudate is transported between the extruder and the calibration device without use of an intermediate volume-compensating vessel, and the withdrawal velocity is controlled by using the pressure on the molten mass in the extruder as control parameter. System accurately controls the extrusion, transportation, calibration and withdrawal of the extrudate. Damage to the extrudate is avoided. The extrudate has a smooth uniform surface without marks or grooves, and a uniform size over its entire length.