Screw and barrel are two important parts. One is a slender threaded rod, and the other is a small and long hole. Their machining and heat treatment processes are complex, and it is difficult to ensure the accuracy. Whether to repair or replace these two parts after wear must be comprehensively analyzed from an economic point of view. If the repair cost is lower than the cost of replacing the new screw, it is decided to repair. This is not necessarily the correct choice. The comparison between the repair cost and the renewal cost is only one aspect.

In addition, it also depends on the ratio of the repair cost and the time of using the extruder screw after repair to the renewal cost and the time of using the renewal screw. The scheme with small ratio is economical and the right choice.

Ⅰ. Repair of extruder screw

1. The twisted extruder screw shall be considered according to the actual inner diameter of the barrel, and the outer diameter deviation of the new screw shall be given according to the normal clearance with the barrel.

2. The thread surface with reduced diameter of the worn screw is treated, thermally sprayed with wear-resistant alloy, and then ground to size. This method is generally processed and repaired by professional spraying plants, and the cost is relatively low.

3. Wear resistant alloy is overlaid on the thread part of the extruder screw. According to the wear degree of extruder screw, build-up welding 1 ~ 2mm thick, and then grind the screw to size. This wear-resistant alloy is composed of C, Cr, VI, Co, W and B, which increases the wear and corrosion resistance of the screw. The cost of this kind of processing is very high in professional surfacing plants. Except for the screw with special requirements, it is rarely used.

4. The repair screw can also be plated with hard chromium on the surface. Chromium is also a wear-resistant and corrosion-resistant metal, but the hard chromium layer is easy to fall off.

Ⅱ. Repair of extruder barrel

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

1. For the barrel with increased diameter due to wear, if there is still a certain nitriding layer, bore the inner hole of the extruder barrel directly, grind it to a new diameter, and then prepare a new screw according to this diameter.

2. The inner diameter of the barrel is machined, trimmed and recast with alloy with the thickness between 1 ~ 2mm. Then finish to the required size.

3. Generally, the homogenizing section of the barrel wears quickly. This section (5 ~ 7D long) can be bored and trimmed, and then equipped with a nitrided alloy steel bushing. The inner hole diameter refers to the diameter of the extruder screw, which is left in the normal matching gap for processing and preparation.

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