Surface cleaning
Before the screw spray welding, the plastic attachments on the surface of the screw need to be cleaned. The cleaning method is to install the screw on a spraying machine to rotate, use a neutral flame torch to spray, and remove it with a spatula after plasticizing. Then use a sandblasting gun to further remove the oxide layer on the repaired surface.
2. Warm up
Hold the screw head (drive part) with a spraying machine or a vibration surfacing machine during preheating. The machine speed is adjusted to a minimum speed of 15r / nin, and the entire screw is preheated to about 270 ° C with a neutral flame, about 100mm from the muzzle to the screw, to reduce the thermal stress of the shaft and ensure the quality of the spray coating.
Spray welding
A one-step spray welding process was adopted, using SPH-1 / h spray gun, No. 2 nozzle, oxygen pressure of 0.25 MPa, and acetylene pressure of 0.06 MPa.
During the rotation, the worn parts of the screw are spray-welded and repaired. The maximum wear of the screw is about 2-3mm. To spray enough size in one operation, and consider the machining allowance. If one spray is not enough, you should pay attention to the preheating temperature and preheating uniformity to prevent welding layer cracks.
4. Trimming and Straightening
Ni60 self-fluxing alloy has better surface quality. Due to the technical requirements of the screw, that is, the straightness, the runout of the screw surface and the working side of the screw to the screw axis, etc., the screw must be trimmed after welding. The trimming method is to process a mandrel with a central hole and press it into the bearing hole of the screw head. One head and three claws are tightened, and the other center is centered, and processed by turning or grinding. At the same time, the screw bending caused by spray welding can be eliminated. The cutting tool is YMO53. After welding with Ni60 self-fluxing alloy powder, the hardness of the screw welding layer can reach HRC60, and the thickness of the welding layer is 2-3mm. Not only the worn-out screw can be repaired, but also the screw can be strengthened and the service life of the screw can be extended. There may be a slight diffusion between the coating and the roll neck, which enhances the bonding strength between the coating and the roll neck. The bonding between sprayed particles is mainly mechanical, and the diffusion bonding, metallurgical bonding, crystal epitaxy, and physical bonding between coatings are supplemented.