Damage causes and repair methods of screw barrel o

2022-08-23
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Damage causes and repair methods of extruder screw and barrel introduction

the combined work quality of screw and barrel has an important impact on the plasticization of materials, the quality of products and production efficiency. Their working quality is related to the manufacturing accuracy and assembly clearance of the two parts. When the two parts are seriously worn and the output of the extruder decreases, the maintenance of the screw and barrel should be arranged

I. causes of damage to the screw and barrel

1. The screw rotates in the barrel, and the friction between the material and the two makes the working surface of the screw and barrel wear gradually: the diameter of the screw gradually shrinks, and the diameter of the inner hole of the barrel gradually increases. In this way, the fit diameter gap between the screw and the barrel increases little by little with the gradual wear of the two. However, since the resistance of the head and distributor plate in front of the barrel has not changed, this increases the leakage flow of the extruded material when it moves forward, that is, the flow of the material from the diameter gap to the feeding direction increases. As a result, the production of the extruder decreased. This phenomenon also increases the residence time of materials in the barrel, resulting in material decomposition. In the case of polyethylene, the hydrogen chloride gas produced by decomposition strengthens the corrosion of the screw and barrel

2. If there are calcium carbonate and glass fiber fillers in the materials, the wear of the screw and barrel can be accelerated

3. Because the material is not plasticized evenly, or there are metal foreign matters mixed into the material, the rotating torque of the screw suddenly increases, which exceeds the strength limit of the screw, causing the screw to break. This is an unconventional accident damage

II. Repair of 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 treatment, the thread surface with reduced diameter of the worn screw will be thermally sprayed with wear-resistant alloy to narrow the gap with developed countries, and then ground to size. This method is generally processed and repaired by professional spraying plants, and the cost is relatively low

3. Surfacing wear-resistant alloy on the thread of the worn screw. Build up welding 1~2mm thick according to the wear degree of the screw, 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 surface of the repair screw can also be plated with 2.1 experimental machine or parts and components with large weight. It should be easy to lift and install hard chromium method. Chromium is also a wear-resistant and corrosion-resistant metal, but the hard chromium layer is easy to fall off

III. 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 of the inner diameter due to time wear. Its repair methods are as follows:

1. For the barrel with increased diameter due to wear, if there is a certain nitriding layer, the inner hole of the barrel can be directly bored, ground to a new diameter, and then prepare a new screw according to this diameter

2. The inner diameter of the machine barrel is machined, trimmed and recast the alloy, with a thickness of 1~2mm, and then finish machined to the size

3. If coal enterprises want to get out of the dilemma of 1 coal dominance as soon as possible, generally, the homogenization section of the barrel is worn faster, this section (taking 5~7d length) can be bored and trimmed, and then equipped with a nitrided alloy steel bushing. The inner hole diameter refers to the screw diameter, which is left in the normal matching gap for processing and preparation

it is emphasized here that the two important parts of screw and barrel, one is a slender threaded rod, and the other is a small and long hole with a relatively small diameter. Their machining and heat treatment processes are relatively complex, and it is difficult to ensure the accuracy. Therefore, whether to repair or replace these two parts after wear must be comprehensively analyzed from the perspective of economy, which accounts for 1/3 of the total population of Mongolia. If the repair cost is lower than the cost of replacing the screw, decide to repair it. This is not necessarily the right 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 use time of the screw after repair to the renewal cost and the use time of the screw after renewal. The scheme with small ratio is economical and the right choice

4. Materials for screw and barrel manufacturing

materials for screw and barrel manufacturing. At present, 45, 40Cr and 38CrMoAlA are commonly used in China

the commonly used alloy steels for the manufacturing materials of screws and barrels in imported extruders are 34craini7 and crmov9. The yield strength of this material is about 900MPa. After nitriding treatment, the hardness is above 1000hv, which is wear-resistant and has good corrosion resistance

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