Reduce the wear out of the screw of injection molding machine

Reduce the wear out of the screw of injection molding machine

The screw of injection molding machine works under the environment of high temperature, high pressure, high mechanical torque and high friction for a long time. The first few factors are required by the process conditions, and the loss caused by friction is inevitable.

Generally, the screw has been subject to surface nitriding treatment to improve the surface hardness, that is, to improve the wear resistance. However, if the causes of wear are ignored and the wear is not reduced as much as possible, the working life of the screw will be greatly reduced.
The following will focus on the causes of screw wear and the methods to reduce wear:
Each plastic has an ideal plasticizing processing temperature range. The processing temperature of the barrel should be controlled to make it close to this temperature range. When granular plastics enter the barrel from the hopper, they will first reach the feeding section. Dry friction will inevitably occur in the feeding section. When these plastics are not heated enough and melt unevenly, it is easy to increase the wear of the inner wall of the barrel and the surface of the screw.
Similarly, in the compression section and homogenization section, if the melting state of the plastic is disordered and uneven, it will also increase the wear.
The speed should be adjusted properly. Some plastics are fortified, such as glass fiber, minerals or other fillers. The friction force of these substances on metal materials is often much greater than that of molten plastics. When these plastics are injected, if they are made at a high speed, while increasing the shear force on the plastics, the reinforcement will correspondingly produce more torn fibers. The torn fibers contain sharp ends, which greatly increases the wear force.
When inorganic minerals slide at high speed on the metal surface, their scraping effect is not small. Therefore, the speed should not be adjusted too high.
Check and remove the sundries in the plastic. Generally speaking, the original purchased fresh plastic has no sundries, but it may be mixed with sundries after transportation, weighing, drying, color mixing, especially adding recycled recycled materials.
Small as metal chips, large as heating rings, nuts, paper clips, and even a series of warehouse keys have been mixed into the barrel. The damage to the screw is self-evident (of course, the barrel will also be damaged at the same time). Therefore, a magnet frame must be installed to strictly manage and monitor the feeding.
The moisture contained in the plastic has a certain impact on the wear of the screw surface. If the plastic does not completely remove the water before injection molding, when the residual water enters the screw compression section, it will form "steam particles" with high temperature pressure that are melted and mixed in the molten plastic before injection. With the advancement of the screw in the injection process, from the homogenization section to the screw head, these "steam particles" will be relieved and expanded in the injection process, like fine impurity hard particles, Friction and damage to the wall.
In addition, for some kinds of plastics, under high temperature and high pressure, water may become a catalyst for plastic cracking, producing harmful impurities that can erode the metal surface. Therefore, the drying work before plastic injection molding is not only directly related to the product quality, but also affects the working life of the screw.