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Thread cutting tapping screws oxidation is steel immersed in alkaline solution containing antioxidant, such as sodium hydroxide Nathaniel solution of potassium nitrate and nitric acid, and maintain the boiling point of 140 degrees Celsius, or partial melting salt soak steel in sodium nitrate and potassium nitrate, removal of the water quenched, a layer of black oxide, iron oxide surface the film, a mixture of iron oxide and iron oxide composition, is to improve the corrosion resistance of a simple and economical method of black metal. Chemical oxidation of steel thin film thickness, usually 0.5 ~ 1.6 m, the corrosion resistance is limited, in the 2 M film thickness, the appearance is black, black or dark grey. The film has good adsorption, such as antirust oil or paint, salt fog corrosion resistance can be increased several times or more times.

Tapping screws, iron and steel parts of the oxidation treatment, degreasing, pickling, surface oil less, non corrosive parts of the product, can be directly in the chemical oxidation of alkaline solution. An oxidation treatment is carried out in a slot, two oxidation treatments are different, two baths complete solution composition, and oxidation treatment is used to produce thin film layer and poor corrosion resistance. The thickness of the film layer produced by the two oxidation treatments has better corrosion resistance. The oxidized treated parts must be thoroughly washed and then boiled in soapy water, in dry oil.