Control unit for wall thickness

摘要

A control unit for pipe wall thickness for use in an extruder for the extrusion of a rigid plastics pipe. A pipe made from thermoplastic polymer, for example polyvinyl chloride, is extruded with an extruder comprising an extrusion die 2 having a shaping end piece and heating elements 11 surrounding the latter. The wall thickness of the pipe is checked in order to obtain a pipe of substantially even wall thickness. For this check, the wall thickness of the extruded pipe is measured at 360 points evenly distributed around the circumference and, in addition, the mean is determined in eight measurement sectors, each comprising 45 measuring points per sector. The mean of the measured values in one measurement sector is compared with the circumferential mean of the 360 points, the deviation from the desired wall thickness in the said one sector being offset by the effect of the heating elements. In a preferred embodiment, a polyvinyl chloride pipe produced with a double-screw extruder has an even wall thickness over the whole of its circumference.