The movement of materials in the extruder screw is divided into three segments, so the design of the screw is often segmented. Because each segment is a continuous channel, so in the actual production, as long as the requirements can meet, not the screw is not divided into three segments, in fact, some screw only two paragraphs, some are not segmented. For example, extrusion nylon this kind of crystallization good material, only the feeding section and the Homogenization section, the general screw extrusion soft PVC plastic screw, can use all compressed segments, without dividing the feeding section and the homogenization segment.
The segmental type of screw is derived from experience, and is mainly determined by the nature of the material. The length of the feeding section can be from 0 to 75% of the screw rod length, generally speaking out of the crystallization polymer is the longest, rigid non-stereotyped polymer second, soft-stereotyped polymer shortest. The length of the compressed segment usually occupies 50% of the length of the screw, of course, like the above nylon and soft PVC exceptions. The average length of extrusion polyethylene is 20,125%. However, some thermal sensitive materials (such as polyvinyl chloride), materials in this paragraph should not stay too long, can not be the homogenization of segments. Some high speed extruder the length of the segment took 50%.