in the production of profiles from rubber and / or plastic mixtures , the throughput of the extruder should be kept constant . to this end , an identification of the mixture of material to be processed is fed in the form of a code to a computer system in which the characteristic mixture properties and the set - point operating values for a given profile to be made by the extruder are stored in memory . during the extrusion process , at least one operating variable , preferably the pressure occurring in the mixture of material being processed , is measured continuously , the difference between a measured value at a given time and the corresponding set - point value of the operating variable stored in memory is formed , and this difference is used as a control variable for a governing system for the speed or rpm of the extruder which is operated by the computer system .