Screws and barrels are like screws and nuts

Update:15 May 2020

Screws and barrels are like screws and nuts and are a combination of parts that are inseparable. The perfect meshing and just the right gap between them makes the material plasticization, product quality and production efficiency significantly improved. However, the sharp knife can't stand the polishing of time. When the two parts wear each other seriously, it will seriously affect the output of the extruder. Then it is especially important to rebuild this pair of CPs!

Causes of damage to the screw and barrel

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.

Repair of the barrel

The inner surface of the barrel is harder than the screw, and its damage is later than the screw. The scrapping of the barrel is such that the diameter of the inner diameter increases due to time wear. Its repair method is as follows:

 If the diameter of the barrel is increased due to wear, if there is a certain layer of nitrided, the inner hole of the barrel can be directly bored, ground to a new diameter, and then the new screw can be prepared according to the diameter.

The inner diameter of the barrel is machined and trimmed to recast the alloy, the thickness is between 1 and 2 mm, and then finished to size.

Under normal circumstances, the homogenization section of the barrel wears faster. This section (take 5~7D long) can be trimmed through the borehole, and then a nitriding alloy steel bushing is used. The diameter of the inner hole is referenced to the screw diameter, and the normal fit is left. Clearance, processing and preparation.

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