Anti corrosion treatment of tensile spring

What should be paid attention to in the anti-corrosion treatment of tensile spring:
1. Oxidation treatment of steel is also called bluing, blackening and boiling. After oxidation treatment, protective magnetic iron oxide is formed on the surface of tension spring. The oxide film is generally blue or black, sometimes black brown. Its color depends on the surface state of spring, chemical composition of spring material and oxidation treatment process.
The oxidation treatment methods include: alkaline oxidation, alkali free oxidation and electrolytic oxidation. Most of them are alkaline oxidation.

The basic oxidation method is to put the spring into the sodium hydroxide solution containing oxidant at about 140 ℃ for a certain time. The oxidant and sodium hydroxide interact with iron to form sodium ferrite and sodium ferrite, and then react with each other to form magnetic iron oxide.
The thickness of the oxide film is about 0.6 ~ 2 / μ M. Although the oxide film can improve the corrosion resistance of spring, its protection ability is poor because of its thin film and pores, so it can only be used in the spring working in the corrosive medium. The anti-corrosion performance depends on the density and thickness of the oxide film, so it depends on the concentration of sodium hydroxide, oxidant and solution temperature.

In order to improve the corrosion resistance and lubricity of oxide film, the treatment before and after oxidation treatment should be strengthened. Before oxidation treatment, the rust, oxide skin, oil stain, salt residue of heat treatment and copper layer on the surface of spring must be thoroughly removed. After oxidation treatment, the spring is usually filled in soap solution or dichromate solution, then washed, dried or dried with flowing warm water, and finally replaced with antirust oil by water film or soaked with machine oil at a certain temperature.

The surface grain boundaries of some hot-rolled spring materials are corroded by oxidation treatment, which will reduce the fatigue strength to a certain extent. Therefore, it is necessary to be careful when using oxidation treatment.
The traditional oxidation treatment needs heating. In recent years, some domestic manufacturers use room temperature blackening agent, which overcomes the defects of traditional blackening process and saves a lot of energy.