The parallel twin-screw barrel has two identical screws that mesh with each other. They are installed in a matching barrel. The screw and barrel can be parallel or conical. If the threads intersect in such a way that the thread tip of one screw almost touches the bottom or root of the channel of the other screw, it is called a fully engaged screw.
The parallel screws are too close to provide enough thrust bearing is a problem. Obviously, one screw shaft must extend beyond the other screw shaft to accommodate a suitable thrust bearing. In the case of conical screws, this problem is solved due to the larger diameter of the feed end, which provides a wider spacing between the screws.
The conical extruder was pioneered by Cincinnati, and many manufacturers such as Battenfeld introduced parallel screw extruders. In a conical extruder, the extruder is specified by the screw diameter at the end of the metering section. At the same time, the size of the parallel extruder is the diameter of the thread.