The blackening treatment of high strength bolts mainly requires the appearance, including the following points:
1. The appearance of blackening treatment is blue black or dark black.
2. The crystal of the film is compact and uniform, and the product has no exposed bottom, no obvious color difference, no whitening and other abnormal phenomena. If the blackening process is not normal, the following will occur.
3. White spots, patterns. This phenomenon is mainly manifested in the color of the oxide film, white spots, patterns.
4. The color is not correct. The product appears blue or red after blackening.
5. The oxide film is not firm. Due to the incomplete degreasing and cleaning of the product before blackening, too long blackening treatment time, and too thick blackening layer, a blackening floating layer is formed, with poor adhesion, and the product is not washed clean with clean water after pickling. The residual acid is brought into the blackening liquid, resulting in local excessive reaction and floating rust on the surface of the workpiece.
6. Rust spots. The reason for changing the color of the product is oxidation reaction, so the blackened product should be dehydrated and sealed in time. If the blackened product is not immersed in oil and sealed in time, oxidation reaction will occur.

High Strength A490 Bolts

High Strength A490 Bolts High Strength Bolt grade 8.8 10.9 DIN931 DIN933 A325 A490 Material: Carbon Steel, Stainless steel, Alloy Steel etc Size: M4-M100 1/4″-4″ Length: 6mm to 100mm Thread: UNC, UNF are available Surface Treatment: Black oxide, zinc plate, copper plating, Dacromet, Teflon, phosphating Certificate: ISO9001:2008, ROHS, SGS, CE Standard: DIN, ISO, ANSI, ASTM, […]