The invention relates to a process and an apparatus for optimal operation of an extruder for the processing and production of rubber and thermoplastic materials.  The invention constitutes an improvement over the extruder disclosed in Ser.  No.  07/693,225, now U.S. Pat.  No.  5,127,741, granted Jul. 7 1992 which is incorported herein by reference. 
In the field of extruder technology, it has long been known to design an extruder in such a way that, in mixing sections, metal pins protrude through its barrel into the processing space for the extrudate.  In such pin-lined barrel extruders, the flights of the extruder screw are interrupted at the points at which the pins protrude into the extruder barrel.  Such extruders are known, for example, from German Offenlegungsschrift 2,235,784 or German Offenlegungsschrift 3,003,615. 
These extruders are distinguished by a very good mixing and homogenizing effect on the material to be processed and, in addition, permit an increased material throughput per unit time through the extruder at the same screw speed.  These advantages, and constant improvements, have resulted in pin-lined barrel extruders becoming the most frequently used mixing and homogenizing extruders in the last 15 years. 
Independently of this, a mixing section for an extruder which has become known as the Transfermix mixing section has been developed and is disclosed in DE-A 1,142,839.  This mixing section essentially comprises the feature that both the extruder screw and the inner wall of the extruder barrel are provided with grooves and flights over a certain length, the channel depth of the extruder screw decreasing to zero and subsequently increasing again in the longitudinal direction of the extruder barrel to the same degree as the channel depth of the barrel grooves respectively increases and decreases.  Due to this design of extruder screw and barrel, when the mixing screw is rotating, extrudate is completely exchanged between the screw grooves and the barrel grooves, providing a good mixing effect on the extrudate. 
The Transfermix extruder was able to claim a certain share of the market over the pin-lined barrel extruder, in particular whenever the overall length of the extruder was to be kept small.  However, what is disadvantageous about this mixing section design is the comparatively high manufacturing outlay.