Repairing Shearer Motor Rotor Shaft by Oxygen-Acetylene Flame Powder Spraying

       The rotor shaft of the motor is a hollow water-cooled type, and the failure mode is mainly wear. When it fails, the inner ring of the bearing has been engaged with the journal, and it is forcibly cut off by electric welding during disassembly, and the damage area at the journal is more than 800mm2. There are hard spots and pits in many places, and there are several strains up to 0.7mm deep. This piece is characterized by thin-walled and hollow, and the concentricity of the bearing parts at both ends is very high.



      It is repaired by oxygen-acetylene flame powder spraying. The main process is as follows:

     (1) Thoroughly clean the spraying parts of the parts and their vicinity with metal cleaning agent, and then use a low-magnification magnifying glass and a magnetic flaw detector to check for surface damage and cracks.

     (2) Preheat the parts with an electric furnace or flame, and the preheating temperature is 120 ℃. In order to ensure the bonding strength, the parts should be heated evenly inside and outside.

     (3) Install the shaft on the lathe and align it, and cut off the surface fatigue layer. If the local damage is deep, use a small grinding wheel to grind until the base material is exposed, and then cut the thread to roughen the surface, the depth of cut is 0.2mm, and the pitch is 0.4mm~0.6mm. The temperature of the parts is kept above 80 ℃, which can meet the spraying requirements. If the parts are small, you can also install the card to align and then preheat with flame. In order to reduce the pollution and oxidation of the surface, it is advisable to preheat first and then cut the thread. The tools used should be cleaned with acetone to avoid contamination of the workpiece.

     (4) QSH-4 type or SPH-E type spray gun can be used for spraying. The oxygen pressure is 0.5MPa~0.7MPa, the acetylene pressure is 0.05MPa~0.1MPa, and the gun distance is 180mm~220mm. First spray a layer of Ni/AI (F501, F502) or AI/Ni (F505) primer with a thickness of about 0.1mm~0.15mm; then spray Ni222 (or powder 112, powder 313) to a certain thickness. The flame should be neutral flame, the temperature of the workpiece should be kept less than 250 ℃, and the rotation speed of the workpiece should be about υ=20m/min. During the spraying process, it is necessary to slightly loosen the rear top of the lathe at any time, so as to prevent the workpiece from being deformed due to the obstruction of expansion after the workpiece is heated.

     (5) Cooling and spray layer processing. After spraying, the parts continue to be stuck on the lathe for rotation and air-cooled to room temperature. When cooling, be careful not to allow the air flow to blow directly on the spray surface, and the tip can be slightly tightened as the temperature drops.

     (6) YA6 or YW type inserts can be used for turning. Cutting speed 30m/min~50m/min. When semi-finishing, the cutting depth is 0.1mm~0.2mm; when finishing, select 0.065mm~0.1mm. Green silicon carbide grinding wheel is used for grinding, and the longitudinal feed is 0.01mm~0.05mm reciprocating.

    There are many similar parts in mining machinery, such as various motor shafts, gear shafts, drum spindles, and even the sky wheel shaft of the hoisting winch, which can be repaired by this process with good results.