Spring blackening process

Alkaline chemical oxidation treatment black, is to finish the processing of qualified spring into the solution containing strong alkali heat treatment, so that the surface of the spring to obtain a thin layer of dense oxide film, this oxide film has corrosion resistance.

Spring in the heated solution, due to alkali corrosion on the surface of the spring, iron ions (ferrous compounds) in the alkali adding oxidant - sodium nitrite can change the oxidation process and generate a dense oxide film on the surface of the spring (ferric oxide). The oxide film is mainly composed of magnetic iron oxide, and the formation time of the oxide film is 30 ~ 60 minutes. The thickness of oxide film cannot be increased if the time is prolonged.