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Screw wear causes

Apr 10, 2018

  1. Each type of plastic has an ideal plasticizing processing temperature range. It is necessary to control the processing temperature of the cylinder to make it close to this temperature range. When the granular plastic enters the cylinder from the hopper, it will reach the feeding section first, and dry friction will occur in the feeding section. When these plastics are heated insufficiently and unevenly molten, it is easy to cause the wear of the inner wall of the cylinder and the surface of the screw to increase. In the same way, in the compression section and the homogenization section, if the plastic's molten state is unbalanced, wear will increase. 

2, the speed should be adjusted properly. Due to the addition of reinforcing agents to some plastics, such as glass fibers, minerals or other fillers. The friction of these materials on metal materials is often much greater than that of molten plastics. In the injection molding of these plastics, if the high rotational speed is used, the shearing force of the plastic will be increased, and the reinforcing fibers will be correspondingly produced with more shredded fibers. The shredded fibers have sharp ends and wear. The force is greatly increased. When inorganic minerals slide at high speed on the metal surface, their scraping effect is not small. So the speed should not be adjusted too high. 

3, the screw in the barrel rotation, friction between the material and the two, so that the working surface of the screw and the barrel gradually wear: the diameter of the screw gradually reduced, the barrel diameter gradually increased. In this way, the clearance between the screw and the barrel is slightly increased with the gradual wear of the two. However, since the resistance of the nose and the manifold in front of the barrel is not changed, this increases the leakage flow when the extruded material advances, that is, the flow of material from the diameter gap to the feed direction increases. As a result, the production of plastic machinery declined. This phenomenon in turn increases the residence time of the material in the barrel, causing the material to decompose. In the case of polyvinyl chloride, hydrogen chloride gas generated by the decomposition enhances the corrosion of the screw and the barrel. 

4. Materials such as calcium carbonate and glass fiber fillers can accelerate the wear of the screw and barrel. 5. As the material is not plasticized evenly, or there is metal foreign matter mixed into the material, the screw torque force suddenly increases, this torque exceeds the screw strength limit, so that the screw is broken. This is an unusual accident damage. 

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