Before screw spray welding, the remaining plastic attachments on the surface of the extruder screw should be removed. The method of removal is to rotate the screw of the extruder on the spraying machine, baking with a neutral flame of the spray welding gun, and shoveling it with a shovel knife after plasticization. Then use a sandblasting gun to repair the exterior to further remove the oxide layer.
When preheating, use the spraying machine tool or vibration surfacing machine tool to clamp the head (transmission part) of the extruder screw. The speed of the machine tool is adjusted to a minimum speed of 15r/nin. Use a neutral flame, the muzzle to the screw is about 100mm, and the screw of the extruder is preheated to about 270°C to reduce the thermal stress of the shaft and ensure the quality of the spray welding layer.
The one-step spray welding process is adopted. Select SPH-1/h spray gun and No. 2 nozzle. The oxygen pressure is 0.25MPa and the acetylene pressure is 0.06MPa.
Spray welding repair on the wear part of the extruder screw during rotation, and the maximum wear of the screw is about 2-3mm. The operation spray should be standardized enough at one time, and the processing allowance should be considered. If the one injection is not enough, special attention should be paid to the preheating temperature and preheating uniformity during the next replenishment to prevent cracks in the welding layer.
Self-melting alloy spray welding has good external quality. Due to the technical requirements of the extruder screw, that is, the straightness, the appearance of the thread and the beating of the axis of the extruder screw on the working side of the extruder, the screw of the extruder should be trimmed after welding.
The trimming method is to process the core shaft of a central hole and press it into the bearing hole of the screw head of the extruder. One end of three claws is tightened, and the other end is fixed. It can be used by turning or grinding to eliminate screw bending formed in spray welding. YMO53 is used for cutting tools. The hardness of the screw welding layer of the extruder repaired by self-melting alloy powder spray welding can reach HRC60, and the thickness of the welding layer is 2-3mm. It not only repairs the screw of the extruder that fails to wear, but also strengthens the screw and prolongs the service life of the extruder screw.
It is possible to produce a small looseness between the coating and the roller neck to enhance the bonding strength between the coating and the roller neck. The combination between spray particles is mainly mechanical bonding, supplemented by loose bonding, metallurgical bonding, crystal epitaxy and physical bonding between coatings.
The preheating of the workpiece before spraying has great practical significance, which can remove the moisture from the surface and reduce the stress accumulation of the coating. Especially for standard shaft parts, the preheating temperature is about 100 °C.
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