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Principle and purpose of coupling blackening treatment

Principle and purpose of coupling blackening treatment

Blackening treatment purposes :(1) the fastener surface rust; (2) Increase the gloss effect of fastener surface to improve the aesthetic degree; (3) Reduce the stress in the quenching process.

Treatment principle: when the coupling is immersed in blackening liquor, the first acid corrosion, metal dissolution, metal iron is oxidized into bivalent Fe2+; The substitution reaction of copper and iron occurs, and Cu2+ is reduced to copper and deposited on the metal surface. Due to the addition of oxidation catalyst in the solution, the reduction of selenium tevalent in nitrite to Se2- is accelerated, and the oxidation and reduction reaction of metal on the workpiece surface is catalyzed. Due to the strong oxidability of nitrite, it can quickly oxidize Cu deposited on the metal surface to Cu2+, and react with selenium divalent to form copper selenide. However, it is important to control the blackening speed of tank liquid. The blackening speed of tank liquid has an important influence on the quality of the film layer. The higher the blackening speed, the darker the film layer, the worse the loose adhesion and corrosion resistance. The lower the blackening speed, the worse the film layer blackness, but the crystallization is meticulous, the corrosion resistance is not improved, usually the speed control within 3-8min to achieve uniform depth is appropriate; It is better to control the PH value between 1 and 3. Practice has proved that the lower the PH value, the faster the blackening speed, the darker the film layer, but the tissue balance is loose, otherwise it is the opposite. Membrane treatment. Passivation process, must be cleaned, such as burr available brush does not affect the quality of the film layer. For immersed in dehydrated anti-rust oil parts placed for 10h, later use performance can be good.

Coupling products include diaphragm coupling, drum gear coupling, quincunx coupling and so on. Some Tianshuo coupling products choose black process, can meet the appearance of the coupling, rust prevention requirements, and low cost, high production efficiency; The blackening process can reduce the quenching stress and make the coupling have good mechanical properties under stress condition.