How to improve the wear resistance of extruder screw barrel?

How to improve the wear resistance of extruder screw barrel?

The extruder screw barrel of injection molding machine runs under high temperature, high pressure, high mechanical torque and high friction for a long time. The first few factors are process conditions, friction caused by wear is inevitable. General screw through surface nitriding treatment, in order to improve the surface hardness, that is, improve wear resistance. However, if the cause of wear is ignored and wear is not minimized, the working life of the lead screw will be greatly reduced.

The following will focus on the reasons for screw wear and reduce wear methods:
Each plastic has an ideal plasticizing temperature range, and the barrel processing temperature should be controlled to be close to this temperature range. When the granular plastic enters the bucket from the hopper, it first reaches the feeding section. Dry friction will inevitably occur in the feed section. When these plastics are not heated enough and melting is not uniform, it is easy to cause increased wear on the inner wall of the barrel and the surface of the good extruder screw barrel. Similarly, in the compression and homogenization sections, if the melting state of the plastic is disorderly and uneven, the wear will also increase.
The speed should be adjusted appropriately. Because some plastics have reinforcers added, such as fiberglass, minerals, or other fillers. These materials tend to exert much more friction on metal than molten plastic. In the injection molding of these plastics, if manufactured at high speed, it will not only increase the shear force on the plastic, but also enhance the production of more shredded fibers. Chopped fibers contain sharp ends, which can cause fraying. The power is greatly increased. When 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.
Detect debris in plastic. Generally speaking, the fresh plastic purchased by the original factory is free of debris, but after transportation, weighing, drying, color mixing, especially after adding recycled materials, it may be mixed with debris. It can range from metal shavings to heating ring nut paper clips and even a set of warehouse keys. It has been mixed into the bucket. Extruder screw barrel damage is self-evident. , need to install magnet rack, strict management and monitoring of the feed.
The water content in plastic has a certain effect on the wear of screw surface. If the plastic has not been completely drained of water before injection, the residual water enters the compression section of the screw and forms "vapor particles" with high temperature pressure that melt and mix in the molten plastic before injection. As the new extruder screw barrel advances during the injection, these "vapor particles" expand into the screw head during the pressure release, expanding during the injection. They act like tiny particles of hard particles that cause friction and damage to walls.
In addition, for some types of plastics, at high temperatures and pressures, moisture may act as a catalyst to promote plastic cracking, producing harmful impurities and corroding metal surfaces. Therefore, the drying work before injection molding is not only directly related to the output, but also affects the working life of the screw.