If the engine crankshaft is seriously worn and the grinding method cannot be repaired or the effect is poor, the plasma spraying method can be used to repair it.
(1) Spray the surface treatment of the front journal
① According to the wear of the journal, it is rounded in the crankshaft grinder, and the diameter is generally reduced by 0.50-1.00mm.
② Shield and protect the adjacent journal to be sprayed with copper.
③ The coating surface is treated with a hair drawing machine. Using nickel strip as electrode, nickel is melted on the journal surface under 6~9V, 200~300A AC.
(2) Spraying
Clamp the crankshaft on the rotating workbench and adjust the distance between the spray gun and the workpiece (about 100mm). Nickel-clad aluminum (Ni/AL) was selected as the base material, and the mixture of wear-resistant alloy cast iron (NT) and nickel-clad aluminum was selected as the working layer material. The bottom thickness is generally about 0.20mm, and the thickness of the working layer is determined according to needs.
During the spraying process, the temperature of the sprayed journal is generally controlled at 150~170 ° C. The sprayed crankshaft is kept warm for 2h in an oven at 150-180℃, and cooled with the oven to reduce the stress between the sprayed layer and the shaft neck.
(3) Treatment after spraying
After spraying, check whether the spraying layer is closely combined with the journal matrix. If it is not tight enough, remove the heavy spraying. If the inspection is qualified, the crankshaft can be ground. Due to the high hardness of the plasma spraying layer, a softer tin carbide grinding wheel is generally used for grinding, and the feed rate is smaller (0.05-0.10mm) during grinding, so as not to crack the coating. In addition, it is necessary to grind the oil passage hole with sand bar after grinding, so as not to scratch the tile with burrs. After cleaning, the crankshaft is immersed in 80-100℃ lubricating oil for 8~10h, and the lubricating oil can be fully penetrated into the coating before loading.