Maintenance and Repair of Extruder Screws and Barrels

Screw and barrel are two important parts of plastic mechanical extruder. If the screw and barrel of the plastic machinery extruder are damaged, it will affect the operation of the machine.


1. What should we pay attention to during the maintenance of the extruder screws and barrels?


(1) Whether to use twisted-pair screws should be considered according to the actual inner diameter of the barrel, and the outer diameter tolerance of the new screw should be made according to the normal gap with the barrel.

(2) After processing the thread surface of the screw and barrel screw whose diameters have been reduced, thermal spray the wear-resistant alloy, and then grind it to a certain size. This method means generally the process and repair are conducted by a professional spraying factory, and the cost is relatively low.

(3) The surface of the wear-resistant alloy is welded on the worn screw part by the means of surfacing. According to the degree of wear of the screw and barrel screw, the surfacing thickness is 1 to 2mm, and then the screw is ground to a certain size. This wear-resistant alloy is composed of C, Cr, Vi, Co, W and B materials, which increases the screw's ability to resist wear and corrosion. It is expensive for professional surface treatment factories to conduct this kind of treatment, so we rarely find them except for special requirements for screws.

(4) Hard chrome can also be plated to repair the surface of the screw components. Chromium is also a wear-resistant and corrosion-resistant metal, but the hard chromium layer is more likely to fall off.


2. Repair method of the extruder screws and barrels


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 means that its inner diameter increases with time. The repair method is as follows:

(1) The diameter of screw and barrel increases due to wear. If there is still a certain nitriding layer, you can directly drill a hole in the barrel, grind to a new diameter, and then prepare a new screw according to this diameter.

(2) The inner diameter of the screw and barrel are machined and trimmed to cast an alloy with a thickness of 1 to 2mm, and then finished to a certain size.

(3) Generally, the homogeneous part of the barrel wears quickly. This part (the length is 5 to 7D) can be trimmed by boring a hole, and then equipped with the nitrided alloy steel bushing. The inner hole diameter refers to the screw diameter. Usually it is suitable for the machining and preparation of gap.


It should be emphasized here that there are two important parts of the screw and barrel: one is a slender screw, and the other is a relatively small and long hole.


The processing and heat treatment technology of the screw and barrel are relatively complicated, and it will be relatively difficult to guarantee the accuracy. Therefore, it is necessary to comprehensively analyze whether the two parts are worn or require repair after wear.


If the repair cost is lower than the cost of replacing the new screw components, the repair is decided. This is not necessarily the right choice. The comparison between maintenance cost and replacement cost is only one aspect. It also depends on the ratio of repair cost to tightening time, update cost and re-tightening time after repair.

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