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The two important parts of the screw and the barrel, one is a slender threaded rod, the other is a small and long hole, their machining and heat treatment processes are more complicated, and it is difficult to ensure accuracy. After the wear of these two parts, whether to repair or replace with new parts must be fully analyzed from an economic point of view. If the repair cost is lower than the cost of replacing a new screw, it is decided to repair it. This is not necessarily the right choice. The comparison between the repair cost and the replacement cost is only one aspect.

In addition, it also depends on the ratio of the repair cost and the time of using the screw after the repair to the replacement cost and the use time of the updated screw. It is economical to adopt a scheme with a small ratio, which is the correct choice.

Repair of the screw:
1. The twisted screw should be considered according to the actual inner diameter of the barrel, and the outer diameter deviation of the new screw should be given according to the normal clearance with the barrel.
2. After the thread surface with the reduced diameter of the worn screw is treated, the wear-resistant alloy is thermally sprayed, and then ground to size. This method is generally processed and repaired by a professional spraying factory, and the cost is relatively low.
3. Overlay welding wear-resistant alloy on the thread part of the worn screw. According to the degree of screw wear, surfacing welding is 1~2mm thick, and then the screw is ground and processed to size. This wear-resistant alloy is composed of materials such as C, Cr, Vi, Co, W and B, which increases the wear resistance and corrosion resistance of the screw. Professional surfacing plants have high costs for this kind of processing, and are generally rarely used except for special requirements for screws.
4. The surface of the repair screw can also be plated with hard chrome. Chromium is also a wear-resistant and corrosion-resistant metal, but the hard chrome layer is easier to fall off.

Repair of the barrel:
The inner surface hardness of the barrel is higher than that of the screw, and its damage is later than that of the screw. The scrapping of the barrel is the increase in the inner diameter due to wear and tear over time.
Here's how to fix it:
1. If the diameter of the barrel increases due to wear, if there is still a certain nitriding layer, the inner hole of the barrel can be directly bored, ground to a new diameter, and then a new screw is prepared according to this diameter.
2. The inner diameter of the barrel is machined and trimmed to re-cast the alloy, the thickness is between 1~2mm, and then finish to size.
3. Under normal circumstances, the homogenization section of the barrel wears quickly. This section (5~7D length) can be trimmed by boring, and then equipped with a nitrided alloy steel bushing. The diameter of the inner hole refers to the diameter of the screw. The normal fit clearance is processed and prepared.
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