What are the reasons why the screw and barrel are easily damaged?

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 will be reduced by friction, and the diameter of the inner hole of the barrel will increase due to friction. Therefore, the matching diameter gap between the screw and the barrel will become larger and larger (the screws have been subjected to surface nitriding treatment during work to improve the surface hardness). Since the resistance of the head and the manifold in front of the barrel has not changed, this increases The leakage flow rate of the extruded material when it advances, that is, the increase in the amount of material flowing from the diameter gap to the feeding direction. As a result, the output of the extruder decreased. This leads to an increase in the residence time of the material in the barrel and causes the material to decompose. If the material is polyethylene, the hydrogen chloride gas produced by decomposition strengthens the corrosion of the screw and barrel, forming a vicious circle.

The physical properties of the material: If the material produced by the crusher contains fillers such as calcium carbonate and glass fiber, the friction of these materials on metal materials is often much greater than that of molten plastics. When injecting these plastics, if the high rotation speed increases the shearing force to the plastic, it also produces more shredded fibers. The shredded fibers contain sharp ends, which greatly increase the abrasion force. Therefore, the rotation speed of the extruder working room should not be adjusted too high.

The material is not plasticized uniformly or metal foreign matter is mixed into the material: This situation causes the screw rotation torque to increase suddenly, this torque exceeds the strength limit of the screw extruder screw, resulting in the screw exercise. This situation is unconventional damage.

The plasticization range of various plastics is different: each plastic has an ideal plasticization processing temperature range. The 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 Insufficient heating and uneven melting can easily cause increased wear on the inner wall of the barrel and the surface of the screw. Similarly, in the compression section and the homogenization section, if the molten state of the plastic is not uniform, it will also cause increased wear.