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Method for repairing extruder screw and barrel

Update:29 Nov 2019

Screw and barrel are two important parts of a plastic m […]

Screw and barrel are two important parts of a plastic mechanical extruder. If the screw and barrel of a plastic mechanical extruder are damaged, it will affect the operation of the machine. So what should we pay attention to during maintenance? ?

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 manufactured according to the normal clearance with the barrel.

2. After the thread surface of the reduced screw diameter 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. The wear-resistant alloy is surfacing welded on the screw part of the worn screw. According to the degree of screw wear, overlay welding is 1 ~ 2mm thick, and then the screw is ground to size. This wear-resistant alloy is composed of C, Cr, Vi, Co, W, and B materials, which increases the ability of the screw to resist wear and corrosion. Professional surfacing plants have a high cost for this kind of processing, except for special requirements of screws, they are rarely used.

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

The hardness of the inner surface of the barrel is higher than that of the screw, and its damage occurs later than the screw. Scrap of the barrel is that the inner diameter increases with time. Its repair method is as follows:

1. The barrel with increased diameter due to wear. If there is still a certain nitriding layer, the bore in 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 recast the alloy, with a thickness of 1 ~ 2mm, and then finished to size.

3. In general, the homogenization section of the barrel wears quickly. This section (5 ~ 7D long) can be trimmed by boring, and then equipped with a nitrided alloy steel bushing. The inner hole diameter refers to the screw diameter. Normally fit the gap for processing and preparation.

It is emphasized here that the two important parts of the screw and barrel, one is an elongated threaded rod, and the other is a relatively small and long hole. Their machining and heat treatment processes are relatively complicated, and the guarantee of accuracy will be relatively difficult. Therefore, it is necessary to comprehensively analyze whether the two parts are worn or repaired after the wear and tear. If the cost of repair is lower than the cost of replacing a new screw, it is decided to repair. This is not necessarily the right choice. The comparison between repair cost and renewal cost is only one aspect. It also depends on the ratio of the repair cost to the screw time after the repair and the renewal cost and the renewed screw time.