The blackening treatment of the elastic pin coupling is to create a layer of oxide film on the metal surface to isolate air and achieve the purpose of rust prevention. Blackening is a common method of chemical surface treatment, which involves producing an oxide film on the metal surface to isolate air and achieve rust prevention. When the appearance requirements are not high, blackening treatment can be used, and the surface of steel parts is blackened, also known as bluing. Purpose of blackening treatment: to prevent rust on the surface of fasteners; Increase the gloss effect on the surface of fasteners to enhance their aesthetics; Reduce the stress effect during the quenching process.
Treatment principle: When the elastic pin coupling is immersed in the black liquid, the corrosion of the acid, metal dissolution, and metal iron are oxidized into divalent Fe2+; Copper and iron undergo Single displacement reaction, and Cu2+is reduced to metal copper and deposited on the metal surface; The addition of oxidation promoter in the solution accelerated the reduction of tetravalent selenium in nitrite to Se2-, and promoted the oxidation and reduction of metal on the surface of workpiece. Due to the oxidizing nature of nitrite_ Strong, he can quickly oxidize Cu deposited on the metal surface into Cu2+and react with divalent selenium to generate copper selenide. But its precautions are to control the blackening speed of the tank liquid. The blackening speed of the tank solution has a significant impact on the quality of the film layer. The higher the blackening speed, the more loose the adhesion and corrosion resistance of the film layer. The lower the blackening speed, the worse the blackness of the film layer. However, the finer the crystallization, the better the corrosion resistance. Usually, the speed should be controlled within 3-8 minutes to reach a uniform depth; The pH value of the tank solution should be controlled between 1-3. Practice has shown that the lower the pH value, the faster the blackening speed, and the blacker the film layer. However, the tissue balance is loose, and vice versa; Coating treatment. The passivation treatment process should be cleaned thoroughly. If burrs appear, a brush can be used without affecting the quality of the film layer. Place the parts immersed in dehydrated rust resistant oil for 10 hours before using them for performance.