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Causes of damage to the screw and barrel

Update:28 Jun 2019

1. The screw rotates in the barrel, and the friction be […]

1. 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 wear gradually: the diameter of the screw is gradually reduced, and the diameter of the inner hole of the barrel is gradually increased. Thus, the matching diameter gap between the screw and the barrel increases little with the gradual wear of the two. However, since the resistance of the front head and the splitter plate of the barrel is 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 feed direction increases. As a result, the extruder production is reduced. This phenomenon causes the residence time of the material in the barrel to increase, causing the material to decompose. In the case of polyethylene, the hydrogen chloride gas produced by the decomposition enhances the corrosion of the screw and the barrel.

2. If there are fillers such as calcium carbonate and glass fiber in the material, it can accelerate the wear of the screw and the barrel.

3. Since the material is not plasticized evenly, 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 broken. This is an unconventional accident damage.

4. The horizontal, straightness and clearance of the screw and barrel are not adjusted in place, and the fastening screws are not reinforced. At the time of starting, the screw barrel has friction, which accelerates the damage of the screw barrel.

5. The preheating time before starting is insufficient. The raw materials accumulated in the screw barrel are not fully softened, the starting torque is too large, or there is a large piece of unsoftened material, causing the screw barrel to sprain or break. Damage to the gearbox.

Domestic high-quality extruders generally add overload protection to the main motor of the extruder, which can protect the screw barrel to a certain extent, greatly reducing the occurrence of screw sprains and twisting. However, if the screw structure at the point of force is weak or the time is abrupt, the damage of the screw may still occur.