Reasons for black spots on the surface of bolts

2023-05-08 14:54:15

Deteriorated cleaning fluid has a reduced cleaning ability, and the surface of bolts is not thoroughly cleaned with quenching oil, resulting in excessive oil smoke in the tempering furnace and posing a threat to human health. Deteriorated cleaning solution has strong corrosiveness, and the residual cleaning solution on the bolt surface causes black spots on the bolt. Sometimes, sandblasting or shot peening is still difficult to remove, which affects the appearance quality and surface treatment.

After quenching, thoroughly replace the water in the cleaning tank and clean it without black spots. A month later, black spots reappeared. After thoroughly cleaning the tank, replace the water configuration cleaning solution, and the resulting black spots on the bolts disappear again. In short, black spots on the surface of bolts are surface quality defects caused by the corrosion of the deteriorated cleaning solution after quenching. 

This local defect affects the appearance quality and service life of the product, and is an important factor leading to some bolt pitting corrosion.