In view of the problems existing in conventional screws, the extrusion process was deeply studied, and various new types of screws were developed on the basis of a large number of experiments and production practices. Compared with conventional screws, the advantages are as follows:
Increased the amount of extrusion,
Improve the quality of plasticization,
Reduced production fluctuations, pressure fluctuations, temperature fluctuations in the MD direction, and temperature differences in the TD direction improve the uniformity of mixing and the dispersion of the filler.
New types of screws are becoming more and more widely used. There are many new types of screws, but there is no comprehensive scientific screw classification. The following are just a few of the more popular classification methods.
4.2.1 Separate screw (main and auxiliary threaded screw)
Design idea: the solid solution phase separates as soon as possible, the solid melts as soon as possible, the liquid phase is extruded at low temperature, the quality is guaranteed, and the yield is increased. For the conventional full-thread three-stage screw, the solid-liquid phase coexists in the same groove, and measures are taken. The molten material and the unmelted material are separated as soon as possible, thereby promoting the faster melting of the unmelted material, so that the molten material is no longer subjected to shearing which causes overheating, and low temperature extrusion is obtained, and the plasticizing quality is improved. The amount of extrusion.
A typical representative is a BM screw. Also called the main and secondary threaded screws.
1, the principle of BM screw
1) Structural principle
According to the melting law of the material in the screw groove revealed by the melting theory, a thread is added to the melting section of the screw. The two threads divide the screw groove formed by the original thread into two screw grooves, one screw groove and the feeding section. The slots are connected, and the other slot is in communication with the homogenization section. The former is used to hold the solid phase and the latter is used to hold the liquid phase. The gap δ between the additional thread and the wall of the barrel is greater than the gap δ between the original thread (main thread) and the wall of the barrel.
