Why Are the Screw and Barrel Destroyed?

The combined working quality of the screw and barrel has an important impact on the plasticization of materials, product quality and production efficiency. Their work quality is related to the manufacturing precision and assembly gap of the two parts. When the two parts are severely worn or the output of the extruder decreases, the extruder screw and barrel should be repaired or replaced.


Ⅰ. Causes of damage to the screw and barrel


1. The extruder screw rolls in the barrel, and the conflict between the materials and the two causes the working appearance of the screw and the barrel to gradually wear out. Specifically, the diameter of the screw is gradually reduced, and the diameter of the inner hole of the barrel is gradually increased. In this way, the matching diameter gap between the screw and the barrel increases little by little with the gradual wear of the two.


However, because the resistance of the head and the splitter plate in front of the extruder barrel has not been changed, this increases the leakage flow when the extruded material travels. That is, the amount of material flowing from the diameter gap to the feeding direction increases, resulting in a decrease in the output of the extruder.


This phenomenon increases the residence time of materials in the barrel and causes material differentiation. If it is polyethylene, the hydrogen chloride gas generated by the differentiation strengthens the corrosion of the screw and barrel.


2. If there are fillers such as calcium carbonate and glass fiber in the material, it can accelerate the wear of the screw and barrel.


3. Because the material is not plasticized uniformly, or metal foreign matter is mixed into the material, the screw rolling torque is suddenly increased. This torque exceeds the strength limit of the extruder screw, causing the screw to twist off. This is an unconventional accident damage.


4. When the screw and barrel are installed, the level, straightness, and clearance are not adjusted in place, and the fastening screws are not reinforced. There is a conflict between the screw and barrel when starting up, which speeds up the damage of the screw and barrel.


5. The material accumulated in the screw barrel has not been sufficiently softened due to the lack of warm-up time before starting up. The starting torque is too large, or there is a large piece of unsoftened material. These cause the screw and barrel to be sprained or broken, and cause damage to the reduction gearbox.


High-quality extruders generally install overload maintenance on the main motor of the extruder, which can protect the screw and barrel to a certain extent, and greatly reduce the occurrence of screw sprain and twisting. However, if the screw structure at the stress point is weak or the time is sudden, damage to the screw may still occur.


Ⅱ. Repair of the extruder screw


1. If the screw is twisted off, carefully check whether the barrel is severely damaged. If the barrel can be used continuously, it should be considered according to the actual inner diameter of the barrel. According to the normal gap between the screw and the barrel, the outer diameter error of the new screw is given for manufacturing.


2. After the surface of the thread with the reduced diameter of the worn screw is treated, it is thermally sprayed with a wear-resistant alloy. The thickness is generally increased to 2-3mm, and then processed to size by grinding. This method is generally sprayed and processed by a professional extruder screw manufacturer.


3. Overlay welding of wear-resistant alloy is on the threaded part of the worn screw. According to the degree of screw wear, surfacing welding is 1-2mm thick, and then grinding the screw to size. This wear-resistant alloy is composed of materials such as C, Cr, Vi, Co, W, and B, adding the wear resistance and corrosion resistance of the screw. The professional surfacing factory has a high cost for this kind of processing. Except for the special requirements of the screw, it is generally rarely used.


4. Hard chromium plating can also be used to trim the extruder screw. Chromium is also a wear-resistant and corrosion-resistant metal, but the hard chromium layer is easier to fall off.

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