The screw rotates in the barrel and friction between the material and the two causes the working surface of the screw and the barrel to gradually wear out: the diameter of the screw will be reduced and the diameter of the bore of the barrel will increase due to friction. As a result, the clearance between the screw and the barrel becomes larger and larger (the surface of the screw has been nitrided during operation to increase the surface hardness). Since the resistance of the nose and the manifold in front of the barrel has not changed, this increases the Leakage flow when the extruded material advances, ie, the flow of material from the diameter gap to the feed direction increases. As a result, the throughput of the extruder is reduced. This leads to an increase in the residence time of the material in the barrel, resulting in material decomposition. If the material is polyethylene, the hydrogen chloride gas generated by the decomposition strengthens the corrosion of the screw and the barrel, creating a vicious circle.
Physical properties of the material: If calcium carbonate and glass fiber fillers are present in the material produced by the crusher, the friction of these materials on metal materials tends to be much greater than that of molten plastics. In the injection molding of these plastics, if the high rotational speed increases the shearing force on the plastic, correspondingly, more shredded fibers are also produced. The shredded fibers have sharp ends and the abrasion force is greatly increased. So the extruder studio speed should not be adjusted too high.
The material is not plasticized uniformly or metal foreign materials are mixed into the material: This situation causes the sudden increase of the screw torque, which exceeds the screw extruder screw's strength limit, and causes the screw to exercise, which is unconventional damage.
The range of plasticization of various plastics is different: Each plastic has an ideal plasticizing processing temperature range. When granular plastic enters the cylinder from the hopper, it will reach the feeding section first. In the feeding section, dry friction will inevitably appear when these plastics are used. When the heat is insufficient and the melting is uneven, it is easy to cause the wear of the barrel inner wall and the screw surface to increase. In the same way, in the compression section and the homogenization section, if the molten state of the plastic is uneven, the wear increases.