Understanding how high-speed screw barrels
reduce wear is really important!
The high-speed screw barrel works under high temperature, high pressure, high mechanical torque and high friction environment for a long time. The first few factors are required by the process conditions, and the wear caused by friction is unavoidable. Generally, the screw has been subjected to a surface nitriding treatment to improve the surface hardness, that is, to improve the wear resistance. However, if the cause of the wear is ignored, if we do not try to reduce the wear as much as possible, the working life of the screw will be greatly reduced.
Therefore, how to reduce the wear of high-speed screw barrels is very important:
1. Each plastic has an ideal plasticizing processing temperature range, and the barrel processing temperature should be controlled to bring it closer to this temperature range. When granular plastic enters the barrel from the hopper, it will first reach the feeding section. Dry friction will inevitably occur in the feeding section. When these plastics are insufficiently heated and unevenly melted, it is easy to cause increased wear on the inner wall of the barrel and the screw surface. Similarly, in the compression section and the homogenization section, if the molten state of the plastic is disordered and uneven, the wear will also increase.
2. The speed should be properly adjusted. Because some plastics are added with reinforcing agents, such as fiberglass, minerals or other fillers. The friction of these materials on metallic materials is often much greater than that of molten plastic. In the injection molding of these plastics, if it is made with a high speed, it will not only increase the shear force on the plastic, but also cause the reinforcement to generate more shredded fibers. The shredded fibers contain sharp ends, which will cause abrasion. The force is greatly increased. When inorganic minerals glide on the metal surface at high speed, its scraping effect is not small. Therefore, the speed should not be adjusted too high.
3. Detect debris in plastic. Generally speaking, fresh plastic purchased in the original has no debris, but after transportation, weighing, drying, color mixing, especially adding recycled materials, it may be mixed with debris. It is as small as metal shavings, as large as a heating coil nut paper clip, and even a string of warehouse keys. It has been mixed into the barrel. It is self-evident that the screw is damaged. Therefore, it is necessary to install a magnet frame and strictly charge the material Management and monitoring.
4. The water content in the plastic has a certain effect on the wear of the screw surface. If the plastic has not completely eliminated the moisture before injection, and the remaining moisture enters the screw compression section, it will form steam particles with high temperature pressure that were previously melted and mixed in the molten plastic. With the advancement of the screw during the injection process, from the homogenization section Up to the head of the screw, these steam particles expand and decompress during the injection process, like hard particles of fine impurities, which cause friction and damage to the wall surface. In addition, for certain types of plastics, under high temperature and pressure, moisture may become a catalyst that promotes the cracking of plastics, generating harmful impurities that can erode the metal surface. Therefore, the drying work before plastic injection is not only directly related to the quality of the part, but also affects the working life of the screw.