Appearance requirements for blackening of high-strength bolts
1. The appearance of blackening is blue-black or dark black.
2, the film layer is dense and uniform, the product has no exposed bottom, no obvious color difference, no abnormal phenomenon such as whitish.
If the blackout is not working properly, the following will happen:
1) White spot, hair flower
This phenomenon is mainly manifested in the fact that the color of the oxide film is different, white spots appear and hair is formed.
2) Color is not correct
The product appears bluish or red when it turns black.
3) The oxide film is not strong.
Because the oil removal before the blackening is not thorough, the blackening treatment time is too long, the black layer is too thick, and the black floating layer is formed. The adhesion is poor. The water rinse after the product pickling is not clean, and the residual acid is brought to the In the blackening liquid, the local reaction is excessive and the surface of the workpiece is rusted.
4) rust spots
The reason for changing the color of the product is the oxidation reaction, so the product after blackening needs to be dehydrated and sealed in time. If the product after blackening is not properly immersed in oil, the activated elements and air continue to react, and sometimes discoloration occurs.