The injection screw is operated for a long time under h […]
The injection screw is operated for a long time under high temperature, high pressure, high mechanical torque and high friction environment. The first few factors are required for the process conditions, while the losses due to friction are inevitable. Generally, the screw has been subjected to surface nitriding treatment to increase the surface hardness, that is, to improve the wear resistance. However, if the cause of wear is neglected, and the failure to try to reduce the wear as much as possible will inevitably greatly reduce the working life of the screw.
The following explains the causes of screw wear and the method of reducing wear.
1. Each plastic has an ideal plasticizing processing temperature range, and the barrel processing temperature should be controlled to bring it close to this temperature range. When the granular plastic enters the barrel from the hopper, it will first reach the feeding section. Dry friction will inevitably appear in the feeding section. When these plastics are insufficiently heated and melted unevenly, it is easy to cause the inner wall of the cylinder and the surface of the screw to wear more. Similarly, in the compression section and the homogenization section, if the molten state of the plastic is disordered, the wear is increased.
2, the speed should be adjusted properly. Some plastics are supplemented with reinforcing agents such as fiberglass, minerals or other fillers. These materials tend to have a much greater frictional force on metallic materials than molten plastics. When injecting these plastics, if they are made at a high rotational speed, the shearing force on the plastic is increased, and the reinforcement is correspondingly produced to produce more shredded fibers. The shredded fibers contain sharp ends and wear. The power is increasing. When the inorganic minerals slide at high speed on the metal surface, the scraping effect is not small. Therefore, the speed should not be adjusted too high. Screw barrel
3. Remove debris from plastics. In general, the original purchased fresh plastic does not have any sundries, but after transportation, weighing, drying, color mixing, especially adding recycled materials, it is possible to mix debris. Small as metal scraps, as big as heating ring nut paper clips, even a string of warehouse keys, mixed into the barrel has occurred, the damage to the screw is self-evident (the barrel will of course be damaged at the same time ), therefore, magnet holders must be installed to strictly manage and monitor the materials.
4. The moisture contained in the plastic has a certain influence on the wear of the screw surface. If the plastic does not completely remove the moisture before the injection, the residual moisture enters the compression section of the screw, and the high-pressure "steam particles" melted in the molten plastic are formed before the injection, and the screw advances with the injection process. From the section to the head of the screw, these "steam particles" are relieved and expanded during the course of the shot, like a fine impurity of hard particles, which causes friction damage to the wall surface. In addition, for certain types of plastics, at high temperatures and pressures, moisture may become a catalyst for cracking the plastic, producing harmful impurities that can attack the metal surface. Therefore, the drying work before plastic injection molding is not only directly related to the quality of the workpiece, but also affects the working life of the screw.