Spring blackening process
Blackening by alkaline chemical oxidation treatment is to heat the qualified springs processed in concentrated alkali solution, so that a thin dense oxide film can be obtained on the surface of the springs, which has anti-corrosion effect.
In the heated solution of spring, due to the corrosion of the spring surface by alkali, iron ions (ferrous compounds) are produced. The oxidation process can be changed by adding oxidant - sodium nitrite in alkali, and a dense oxide film (ferric oxide) is formed on the spring surface. The oxide film is mainly composed of magnetic iron oxide. The formation time of the oxide film is 30~60 minutes. If the time is prolonged, the thickness of the oxide film can not be increased.