How to Repair Plastic Extruder Screws and Barrels


As everyone knows, the screw and barrel are two important components of a plastic extruder. If they are damaged, they will affect the operation of the machine. So what should we pay attention to when repairing them?


Screw Repair

Twisted screws should be considered according to the actual inner diameter of the barrel. The new screw’s outer diameter deviation should be given according to the normal clearance with the barrel.


The threaded surface of the worn screw with a reduced diameter is processed and then hot sprayed with a wear-resistant alloy. Then, it is machined to size by grinding. This method is generally processed and repaired by professional spray coating factories, and the cost is relatively low.


The wear-resistant alloy is welded on the threaded part of the worn screw. The thickness of the weld is 1-2 mm according to the degree of wear of the screw. Then, the screw is machined to size by grinding. This wear-resistant alloy is composed of materials such as C, Cr, V, Co, W, and B, which increases the screw’s wear resistance and corrosion resistance. The cost of this processing is very high in professional welding factories, so it is generally not used except for screws with special requirements.


Screws can also be repaired by surface hard chrome plating. Chromium is also a wear-resistant and corrosion-resistant metal, but the hard chrome layer is easy to fall off.

How to Repair Plastic Extruder Screws and Barrels


Barrel Repair

The hardness of the inner surface of the barrel is higher than that of the screw, and its damage is later than that of the screw. The scrap of the barrel is that the inner diameter diameter increases due to wear over time. Its repair methods are as follows:


If the diameter of the barrel increases due to wear, and there is still a certain nitriding layer, the inner hole of the barrel can be directly bored and ground to a new diameter size, and then a new screw can be matched to this diameter.


The inner diameter of the barrel is machined and repaired by recasting alloy with a thickness of 1-2 mm, and then it is machined to size.


In general, the homogenization section of the barrel wears faster. This section (takes 5-7D length) can be bored and repaired, and then a nitrided alloy steel sleeve with an inner diameter referring to the screw diameter can be used. The inner diameter is left in the normal clearance for processing and matching.

It is important to emphasize that the screw and barrel are two important components, one is a thin-walled threaded rod, and the other is a small-diameter and long hole. Their mechanical processing and heat treatment processes are relatively complex, and the guarantee of accuracy will be more difficult. Therefore, it is necessary to comprehensively analyze from the economic point of view whether to repair or replace the new parts after the wear of these two parts. If the repair cost is lower than the cost of replacing the new screw, it is decided to repair. This is not necessarily the right choice, because the comparison of repair cost and update cost is only one aspect. In addition, it is also necessary to see the ratio of repair cost to the use time of the repaired screw after repair and the ratio of update cost and update screw use time. The scheme with the lower cost ratio is the most economical and correct choice.


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