Detailed introduction
31
2018
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07
How to repair and strengthen the screw
How to repair and strengthen
The repair and strengthening of the screw is as follows:
1. Surface cleaningScrew
Before the screw spray welding, it is necessary to clean up the plastic attachments remaining on the screw surface. The cleaning method is to install the screw on the spraying machine to rotate, bake with the neutral flame of the spray gun, and remove it with a shovel knife after plasticizing. Then use a sandblasting gun to weld the surface to further remove the oxide layer.
2. Preheating
During preheating, use spraying machine tool or vibration surfacing machine tool to clamp the screw head (transmission part). The rotation speed of the machine tool is adjusted to the minimum rotation speed below 15r/nin, and the whole screw is preheated to about 270 ℃ with a neutral flame from the muzzle to about 100mm of the screw, so as to reduce the thermal stress of the shaft and ensure the quality of the spray welding layer.
3. Spray welding
With one-step spray welding process, SPH-1/h type spray gun, nozzle 2, oxygen pressure 0.25MPa, acetylene pressure 0.06MPa.
Spray welding and repair the worn parts of the screw during rotation, with the maximum wear of the screw being about 2-3mm. To spray enough size in one operation, and to consider the machining allowance. If one spray is not enough, pay attention to the preheating temperature and preheating uniformity during the next repair welding to prevent cracks in the welding layer.
4. Finishing and straightening
Ni60 self-fluxing alloy spray welding has better surface quality. Due to the technical requirements of the screw, that is, the straightness, the thread surface and the runout of the thread working side to the screw axis, etc., the screw should be trimmed after welding. The dressing method is to process a mandrel with a center hole and press it into the bearing hole of the screw head. A three-claw tightening, a center centering, with turning or grinding processing, while eliminating the welding caused by the screw bending. Cutting tool selection YMO53. The hardness of the screw welding layer repaired by Ni60 self-fluxing alloy powder spray welding can reach HRC60, and the thickness of the welding layer is 2-3mm. Not only the wear failure of the screw can be repaired, but also the screw can be strengthened, and extend the service life of the screw. It is possible to generate a slight diffusion between the coating and the roll neck to enhance the bonding strength between the coating and the roll neck. The bonding between spray particles is mainly mechanical bonding, and the diffusion bonding, metallurgical bonding, crystal epitaxy and physical bonding between coatings are supplemented.
5. Preheating of the workpiece before spraying
Preheating of the workpiece before spraying has great practical significance, which can remove the moisture on the surface and reduce the stress accumulation of the coating. Especially for shaft parts of this size, the preheating temperature is about 100°C. Aluminum-nickel composite powder F505 is sprayed on the surface of the treated journal as a bonding layer. The thickness of the combined layer is 0.10-0.15mm, and the layer is only used for combination, so it is not necessary to spray too thick. After spraying the bonding layer, spray the G101 powder working layer. G101 powder must be preheated and baked at a temperature of 105-250 ℃ before use to ensure the fluidity of the powder spray and avoid clogging the spray channel. During the spraying process, the gas pressure, flame temperature, spraying distance, spraying angle and moving speed are strictly controlled to make the coating uniform and smooth and firmly bonded. The specific control parameters are as follows: the coating position is the outer circular arc surface; The preheating temperature is 100-200 ℃. The spray distance is 180-200mm; The spray angle is 90 degrees; The moving speed of the spray gun is 6-12 mm/min; The linear speed of the roll is 8-12 m/min.
When spraying the working layer, neutral flame is used. Powder can be observed from the flame. The powder is white and bright at the end of the flame, which indicates that the temperature is high. If it is dark red or red, the temperature is not enough. At this time, it is necessary to adjust the size of the powder feeding air flow and the flame energy rate to heat the powder to white and bright. At this time, the powder temperature is higher, the speed is faster, and the deposition effect is good.
6. Metal processing after spraying
After spraying, asbestos shall be used to wrap the spraying part with multiple layers to make it cool slowly to avoid cracks. When cooling to room temperature, roughing can be carried out, leaving a grinding allowance (about 0.3-0.5mm) before grinding. Grinding shall be in accordance with the dimensions and specified roughness required by the drawings. At this point, the repair of the roll is completed. The repair cost of the roll is about 10,000 yuan, which can save the factory more than 100,000 yuan (30000 yuan per ton of finished roll products and 3 tons of weight per roll).
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