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What are the sections of the screw extruder? What is the principle of segmentation?

by:TENGDA     2023-06-29
When the material moves forward along the screw, it will experience changes in different factors such as temperature, pressure, viscosity, etc., and the changes are different in the process of dispute, so the screw can be segmented according to the change characteristics of the material. The single screw is generally divided into three sections in terms of effective length, and the effective length of the three sections is determined according to the diameter of the screw, the pitch and the depth of the screw, and is generally divided according to each accounting for one-third. So what is the specific shape of each section of the screw? And what principle is used to segment the screw design? TENGDA Plastic Extruder Machine Manufacturers has sorted out the following information, let’s have a look together.

1. What are the three sections of the screw?

1. The last thread of the feed port is called the conveying section: the material here is not required to be plasticized, but it must be preheated and squeezed. In the past, the old extrusion theory believed that the material here is a loose body. Later, it was proved that the material here In fact, it is a solid plug, that is to say, the material here is a solid like a plug after being squeezed, so as long as it completes the conveying task, it is its function.

2. The second section is called the compression section. At this time, the volume of the screw groove gradually decreases from large to small, and the temperature reaches the degree of plasticization of the material. The compression here is generated by the conveying section 3, and it is compressed to 1 here. This is called the compression ratio of the screw. 3:1, some machines also have changes, and the plasticized materials enter the third stage.

3. The third section is the metering section, where the material maintains the plasticizing temperature, just like the metering pump, accurately and quantitatively conveys the melt material to supply the machine head. At this time, the temperature cannot be lower than the plasticizing temperature, generally slightly higher.

2. What is the basic principle of screw segmentation

1. The segmentation of the screw is obtained from experience and mainly depends on the nature of the material. The length of the feeding section can range 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.

2. The length of the compression section usually accounts for 50% of the total length of the screw, except for the nylon and soft PVC plastics mentioned above. When extruding polyethylene, the length of the homogenization section can be 20-25% of the total length.

3. But for some heat-sensitive materials (such as polyvinyl chloride), the material should not stay in this section for too long, and the homogenization section is not necessary. Some high-speed extruders take 50% of the length of the homogenization section.

This is the so-called three-segment screw. Different segments correspond to different situations, which is very beneficial to production. I hope the above content can be helpful to you.
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