1. Twisted damage and repair:
The screw barrel
is twisted and broken, generally because of improper operation, failure of the equipment safety control system, or the mixing of metal foreign matter in the machine with the feed material, the low temperature of the extrusion material, etc., the torque of the screw suddenly increases, resulting in deformation of the screw or twisted.Single screw barrel of recycling granulation machine
Ratio of length to diameter:L/D=20-50
Ratio of length to diameter:L/D=8-20
Because the depth h1 of the screw feeding section is greater than other sections, the torsional strength in the feeding section L1 is the lowest, and the torsional breaking generally occurs in the feeding section. The broken screw should be corrected or updated according to the actual situation. Because the screw is a slender threaded rod, its machining and heat treatment processes are more complicated, and it is difficult to ensure the accuracy. Therefore, whether to correct or refurbish the original after the screw is broken must be comprehensively analyzed from an economic point of view.
The correction process generally adopts the welding process, and its basic process is:
(1) Establish a positioning hole for the two end faces of the screw crack;
(2) Installation. When installing, pay attention to the continuity of the thread groove at the fracture, and measure the pitch at the weld;
(3) Welding. When welding, it should be ensured that the weld metal has certain mechanical properties, and no hardening structures, cold cracks and crystallization cracks occur, and that the mechanical properties of the weld and the base metal of the screw are approximately the same;
(4) Proofreading. If the new screw is replaced, it should be considered according to the actual inner diameter of the machine, and the outer diameter error of the new screw should be given according to the normal clearance with the barrel.
2. Wear damage and repair:
Generally, the pressure of L3 in the homogenization section is the highest and the wear is the most severe. There are many reasons for the formation of screw wear, mainly including:
(1) The surface friction of the material, screw and barrel makes the outer diameter of the screw smaller, and the installation gap between the screw and the barrel becomes larger;
(2) The process temperature control is unstable, and the raw materials decompose a lot of gas, causing the surface of the screw to corrode;
(3) The production and installation do not meet the requirements of the working conditions, so that the screw is deformed or worn prematurely.
The fixes are:
(1) The surface of the thread with reduced diameter of the worn screw is treated, thermally sprayed with wear-resistant alloy, and then ground to size. This method is generally processed and corrected by a professional spraying factory, and the cost is relatively low.
(2) Because the repairing screw is relatively simpler than the barrel, the hardness of the screw should be lower than that of the barrel during heat treatment and nitriding, and fillers can be welded on the surface of the worn thread groove. When surfacing, the wear-resistant and relatively soft hardness should be selected. In this way, only the screw can be repaired and the barrel can be simply honed when reworked. Generally, surfacing is 1-2mm thick according to the degree of wear, and then the screw is ground to the size.
(3) The correction screw can also be plated with hard chrome on the surface, but the hard chrome layer is relatively easy to fall off.