Each plastic has an ideal plasticizing temperature rang […]
Each plastic has an ideal plasticizing temperature range, and the extruder screw barrel processing temperature should be controlled to make it close to this temperature range. Granular plastic enters the barrel from the hopper and first reaches the feeding section. Dry friction will inevitably occur in the feeding section. When these plastics are not heated enough and melted unevenly, it is easy to increase the abrasion of the inner wall of the barrel and the surface of the screw. Similarly, in the compression section and homogenization section, if the molten state of the plastic is disordered and uneven, it will also cause faster wear.The screw rotates in the barrel, and the friction between the material and the two causes the working surface of the screw and the barrel to gradually wear: the diameter of the screw gradually decreases, and the diameter of the inner hole of the barrel gradually increases. In this way, the matching diameter gap between the screw and the barrel increases a little as the two gradually wear. However, since the resistance of the head and the manifold in front of the barrel has not changed, this increases the leakage flow when the extruded material advances, that is, the amount of material flowing from the diameter gap to the feeding direction increases. As a result, the output of plastic machinery decreased. This phenomenon increases the residence time of the material in the barrel and causes the material to decompose. In the case of polyethylene, the hydrogen chloride gas produced by decomposition enhances the corrosion of the screw and barrel.
The speed should be adjusted properly. Because some plastics are added with strengthening agents, such as glass fibers, minerals or other fillers. The friction of these substances on metal materials is often much greater than that of molten plastics. When injection molding these plastics, if they are made with a high rotation speed, it will increase the shearing force to the plastic, and at the same time, the reinforcement will produce more shredded fibers. The shredded fibers contain sharp ends, causing wear Power is greatly increased. 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.
If there are fillers such as calcium carbonate and glass fiber in the material, it can accelerate the wear of the screw and barrel.
Because the material is not plasticized uniformly or metal foreign matter is mixed into the material, the torque of the screw is suddenly increased. This torque exceeds the strength limit of the screw and the screw is twisted. This is an unconventional accident damage.