The extruder screw runs for a long time in high temperature, high pressure, high mechanical torque and high friction environment. The process conditions of the screw barrel of the extruder require the first few factors, and the loss caused by friction is inevitable.
Usually, the screw has been surface nitriding to increase surface hardness, that is, to improve wear resistance. However, if the cause of wear is ignored and the wear is not reduced, the service life of the screw will inevitably be greatly reduced.
The following explains the reasons for the wear of the extruder screw barrel and the methods to reduce wear.
(1) Each plastic screw barrel has an ideal plastic treatment temperature range, and the treatment 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 occur in the feeding part. When these plastics are not heated enough and melted unevenly, it is easy to wear more on the inner wall of the cylinder and the surface of the extruder screw. Similarly, in the compressed part and homogenized part, if the melting state of the plastic is disorderly, the wear increases.
(2) The speed should be adjusted correctly. Some plastic supplements have enhancers, such as fiberglass minerals or other fillers. Compared with molten plastics, these materials tend to have greater friction on metal materials. When injecting these plastics, if they are made at a high rotational speed, the shear force on the plastics increases and correspondingly produces reinforcements to produce more fiber fragments. Shredded fibers contain sharp ends and wear, and the strength is increasing. When inorganic minerals slide at high speed on metal surfaces, the scratching effect is not small. Therefore, the speed should not be adjusted too high.
During the extrusion production process, the extruder screw barrel may suddenly get stuck. At this time, if the extruder protection device does not work, the operator should immediately stop the machine. More often, screws can still rotate, but the speed slows down and makes a harsh metal scratching sound. The current rises sharply, and the operator should stop immediately. The reasons are:
(1) Foreign matter enters the barrel and blocks the screws. If it is a ferrous metal foreign body, it will cause great damage to the extruder screw barrel.
(2) Deformation of extruder screw or barrel.
(3) The temperature of the extruder barrel is too low, or the filter plate is blocked, resulting in a sharp increase in the barrel pressure and the screw deformation.
(4) The design of the extruder screw barrel is unreasonable, and the compression ratio of the screw design is too large, which is easy to deform the screw during use.
(5) The thermal expansion coefficient of the material used for the extruder screw barrel is too large. When the barrel is heated and the barrel is cooled, if the screw is not cooled, it may be locked.
