What is the effect of the diameter and pitch of the conical screw barrel on the extrusion pressure?

In the field of plastic extrusion processing, the diameter and pitch of the conical screw barrel are two extremely critical parameters, which have a profound impact on the extrusion pressure.
First of all, the size of the screw diameter directly determines the volume space of the material in the screw channel. The larger the diameter of the screw, the more material can be accommodated inside it. At the same screw speed, the larger diameter screw can push more material forward, thereby exerting greater shear and extrusion forces on the material. For example, in the extrusion production of large plastic products, such as the manufacture of plastic pipes or sheets, a larger diameter conical screw barrel is usually used to meet the needs of high output and high extrusion pressure. On the contrary, a smaller diameter screw is suitable for some small plastic products or production processes with lower extrusion pressure requirements, because its material handling volume is relatively small and the extrusion pressure generated is relatively small.
The role of pitch should not be underestimated either. The pitch affects the advancement speed and filling degree of the material on the screw. A smaller pitch means that the material moves forward a shorter distance when the screw rotates one circle, and the material stays in the screw channel for a relatively longer time, and is more fully sheared and squeezed, which will lead to an increase in extrusion pressure. A larger pitch speeds up the material advancement speed, shortens the residence time in the screw channel, and the material filling degree may be relatively low, and the extrusion pressure will be reduced accordingly. For example, in some plastic modification processes that require high mixing effect and high extrusion pressure, a screw design with a smaller pitch is often used to ensure that the material is fully plasticized and mixed evenly, while obtaining a higher extrusion pressure to meet the molding requirements; and for some simple plastic granule extrusion granulation processes, a screw with a larger pitch may be selected to improve production efficiency and reduce energy consumption. At this time, the requirements for extrusion pressure are relatively less stringent.