A single screw is generally divided into three effective lengths, determined by the diameter, pitch, and depth of the screw, with each segment accounting for one-third of the total effective length. The last thread of the material mouth is called the conveying section: the material here is required not to be plasticized, but to be preheated and compressed. In the past, the old extrusion theory believed that the material here was loose, but later it was proven that the material here is actually a solid plug, which means that the material here is a solid plug after being compressed. Therefore, as long as the conveying task is completed, it is its function. The second stage is called the compression stage, where the volume of the screw groove gradually decreases and the temperature reaches the degree of material plasticization. Compression occurs in this stage through the conveying stage three, where it is compressed to one, which is called the compression ratio of the screw -3:1. Some machines also have changes, and the material that has completed plasticization enters the third stage. The third paragraph is the metering section, where the material is maintained at the plasticizing temperature, just like a metering pump that accurately and quantitatively delivers molten material to the machine head. At this time, the temperature cannot be lower than the plasticizing temperature, usually slightly higher.