A dense protective film is created on the surface of the spring by means of a chemical reaction to prevent spring corrosion. Oxidation and phosphating are usually used.
Oxidation treatment and phosphating treatment, low cost, high production efficiency, general spring manufacturing plants are using oxidation treatment, as anti-corrosive treatment.
(1) Oxidation treatment steel oxidation treatment is also known as blue, black, boiled black. After oxidation treatment, the spring surface produces a protective magnetic iron oxide, this oxide film is generally blue or black, and sometimes black-brown. Its color is determined by the surface state of the spring, the chemical composition of the spring material, and the oxidation process.
The methods of oxidation treatment are: salty oxidation method, alkali-free oxidation method and electrolytic oxidation method. To use alkaline oxidation method as many.
Alkaline oxidation is the spring is put into the temperature of about 140 degrees C, containing oxidant sodium hydroxide solution soaked for a certain time, oxidant and sodium hydroxide and iron action, the generation of sodium iron atwhichmate acid and sodium ferrite, and then react to each other, the formation of magnetic iron oxide.
The thickness of the oxide film layer is about 0.6 to 2 m. Although the oxide film can improve the corrosion resistance of the spring, but because of the thin film, and also have pores, so its protection is poor, can only be used in the corrosive medium to work in the spring. The antiseptic properties depend on the degree of density of the oxide film and its thickness, so it is determined by the concentration of sodium hydroxide, oxidant concentration, the temperature of the solution and other factors.
In order to improve the corrosion resistance and lubrication capacity of the oxide film, the treatment before and after oxidation treatment should be strengthened. The rust, oxide skin, oil, heat-treated salt residue, surface contact layer, etc. of the spring surface shall be thoroughly removed before oxidation treatment. After oxidation treatment, usually the spring in soap solution or heavy chromite filled treatment, and then washed, blow-dry or dry with flowing warm water, and finally on the water film to replace rust-proof oil or a certain temperature of mechanical oil for oil immersion treatment.
The oxidation treatment is subject to erosion of the surface crystal boundary of some hot-rolled spring materials, which will reduce fatigue strength to a certain extent, so it should be treated with caution when picking oxidation treatment.
Traditional oxidation treatments need to be warmed. In recent years, some domestic manufacturing units also use room temperature blackening agent, it overcomes the shortcomings of the traditional blacking process, saving a lot of energy.
Blackened agent for blue-green concentrate liquefaction, no impurities, no odor, non-combustion, non-explosion, non-corrosive, transport safety.
The dilution ratio commonly used when the spring is blacked out is about 1.5.
The operation process of the black agent is relatively simple, its route is: de-oiling, rinsing, acid line, rinsing, blacking (at room temperature 2 to 5min) rinsing, water film replacement rust-proof oil. Note: be sure to put the spring workpiece on the oil to go, clean, in order to put in the room temperature agent for oxidation treatment.
The oxidation treatment is low cost, the process formula is simple, the production efficiency is high, the oxidizing film has a certain elasticity, basically does not affect the characteristic curve of the spring, so the oxidation treatment is more widely used as the form of the coil spring, spring washer and chip spring, such as anti-corrosion and decoration measures.
The quality inspection of the spring after oxidation includes appearance inspection and corrosion resistance inspection.