Appearance Requirements for Blackening of High Strength Bolts

Appearance requirements for blackening of high strength bolts:
1. The appearance of blackening treatment is blue black or dark black.
2. The film crystallizes compactly and evenly, and the product has no bottom exposure, obvious color difference, whitening and other abnormal phenomena.

If the blackening treatment of high strength blackened bolt is abnormal, the following conditions will occur:
1) White spot, hair flower
This phenomenon is mainly manifested as the oxide film of different colors, white spots, flowers.
2) The color is not right
The product turns blue or red after blackening.
3) The oxide film is not firm.
Due to incomplete degreasing and cleaning of the product before blackening, too long blackening treatment time, too thick blackening layer, forming a blackening floating layer and poor adhesion, the clean water after pickling of the product is not clean, and the residual acid is brought into the blackening liquid, resulting in local excessive reaction and floating rust on the surface of the workpiece.
4) Rust spot
The reason for changing the color of the product is oxidation reaction, so the blackened product needs to be dehydrated and sealed in time. If the blackened product is not immersed in oil and sealed in time, the activated elements will continue to react with air, and sometimes discoloration will occur.

Blackening of High Strength Bolts