The movement of materials in the extruder screw is divided into three sections for research, so the design of the screw is often carried out in sections. Since each section is a continuous channel, in actual production, as long as it can meet the requirements, it is not necessary to divide the screw into three sections. In fact, some screws have only two sections, and some are not segmented. For example, when extruding nylon, a material with good crystallinity, there are only feeding sections and homogenization sections. The general screw extrusion soft polyvinyl chloride plastic screw can use all compression sections without dividing into feeding sections and homogenization sections. The segmentation of the screw is obtained from experience and is mainly determined by the properties of the material. The length of the feeding section can be from 0 to 75% of the total length of the screw. Generally speaking, it is the longest when extruding crystalline polymers, followed by hard amorphous polymers, and the shortest for soft amorphous polymers. The length of the compression section usually accounts for 50% of the total length of the screw, of course, the above-mentioned nylon and soft polyvinyl chloride plastics are exceptions. When extruding polyethylene, the length of the homogenization section can be 20-25% of the total length. However, for some heat-sensitive materials (such as polyvinyl chloride), the material should not stay too long in this section, and the homogenization section can be omitted. The length of the homogenization section of some high-speed extruders is as long as 50%.
