screw, thereby closing the way around the screws. The material
therefore must stop its revolving motion, and as the screws keep rotating, it slides within the channels, assuming an almost linear motion
toward the end of the barrel. This is positive pumping.
When the screws rotate in opposite directions, as we have seen,the
material is more or less sealed into chambers formed by the intermeshing conjugated threads. The material must remain in these
separate chambers and, as the screws rotate, must advance forward.
The maximum possible output of these types of extrudcrs wouU
be, therefore, per each screw equal tothe volume of one of these
chambers, already calculated before, by the rpm of the screws. For
two screws, we can write