Operating mode

As the screws of a counter-rotating extruder rotate in opposite directions, they cause a calendering effect in the interpenetration zone, which creates pressure that is all the greater as the screws are interpenetrated. This pressure will tend to push the screw shafts apart, which could be detrimental in terms of friction on the sleeve and resulting wear. To avoid this effect, rotation speeds are limited, generally to a few dozen revolutions per minute. This is of course less important for non-interpenetrating screws, for which speeds can be higher.