Repair after severe wear of the crankshaft

If the crankshaft machining of the engine is severely worn, the grinding method cannot be repaired or the effect is poor, and it can be repaired by plasma spraying.

(1) Surface treatment of the journal before spraying

1 According to the wear condition of the journal, it is rounded on the crankshaft grinding machine, and the diameter is generally reduced by 0.50-1.00mm.
2 Use copper to shield the adjacent journals of the journal to be sprayed.
3 Use a plucking machine to apply the brushed surface. Using a nickel strip as an electrode, nickel is melted on the surface of the journal at 6 to 9 V, 200 to 300 A alternating current.

(2) spraying

Clamp the crankshaft on a rotatable table and adjust the distance between the gun and the workpiece (about 100mm). Nickel-clad aluminum (Ni/AL) is selected as the primer material, and the mixture of wear-resistant alloy cast iron (NT) and nickel-clad aluminum is the working layer material; the thickness of the bottom layer is generally about 0.20 mm, and the thickness of the working layer is determined according to needs. The spray specifications are shown in Table 1.

During the spraying process, the temperature of the spray journal is generally controlled at 150 to 170 °C. The sprayed crankshaft is placed in an oven at 150-180 ° C for 2 h and cooled with the tank to reduce the stress between the spray coating and the journal.

(3) Treatment after spraying

After spraying, check whether the sprayed layer and the journal base are tightly combined. If it is not tight enough, remove the heavy spray. If the inspection is qualified, the crankshaft can be ground. Due to the high hardness of the plasma sprayed layer, a softer tin carbide grinding wheel is generally used for grinding, and the feed amount during grinding is smaller (0.05-0.10 mm) to avoid squeezing the coating. In addition, the grinding hole must be ground with sand bars after grinding to prevent the burrs from scratching the tiles. After cleaning, the crankshaft is immersed in the lubricating oil of 80-100 ° C for 8 to 10 hours. After the lubricating oil is fully infiltrated into the coating, it can be used for loading.

During the overhaul of the engine, the crankshaft must be inspected to determine the wear and correct repairs to ensure the required fatigue strength and wear resistance of the crankshaft.