The screw and barrel together play an important role in the plasticization of the material, quality, and production. The quality is related to manufacturing precision and assembly clearance of two parts. When the wear of two parts is severe and the output of the extruder is reduced, maintenance of the screw and barrel should arrange.
How the screw and barrel is damaged?
In the screw barrel, the screw rotates in the barrel. And the friction between the materials causes the working surface of the screw and barrel wear. The diameter of the screw is reduced and the diameter of the inner hole of the barrel is increased gradually. The diameter gap between screw and barrel increases with the gradual wear of two. As the resistance of the front head and splitter plate, the barrel is not changed and this increases the leakage flow for extruded material advances. the quantity of the material flowing from the diameter gap to feed the direction increases. And this causes the reduction of extruder production. This causes the residence tome of material in the barrel to increase and it causes the material to decompose. The hydrogen chloride gas is produced if the polyethylene is decomposed and this causes the corrosion of screw and barrel.
If the fillers like calcium carbonate and glass fiber are the material, this increases the speed of wear of screw and barrel.
As the material is not plasticized or metal foreign matter is mixed with the material the torque of screw is increased suddenly. This took the screw to the maximum strength limit and it results in the broken off the screw and it is unconventional damage.
How to repair the screw?
The broken screw should be considered as an actual inner diameter of the barrel and the outer diameter deviation of the new screw is given according to normal gap of the barrel.
After the surface of the thread with a reduced diameter of the wear. The screw is treated the wear-resistant alloy is thermally sprayed and ground to size. This restoration process is done in a spray factory and the cost is very low.
This surfaces the wear-resistant alloy on the threaded portion of wear the screw. Now build the 1 to 2 mm thick according to a degree of the screw wear and grind the screw to size. The wear-resistant alloy consists of materials like C, Cr, Vi, Co, W, and B. This increases the anti-wear and corrosion resistance of the screw. This process cost more so it is done only on special requirements.
The screw is repaired with the hard chrome plating method. As the chromium is wear-resistant and corrosion-resistant metal. The hard chrome layer is easy to fall off.
