A compact protective film is formed on the surface of the spring by chemical reaction to prevent the corrosion of the spring.Generally, oxidation treatment and phosphating treatment are used.
Oxidation treatment and phosphating treatment have low cost and high production efficiency. Generally, spring manufacturers adopt oxidation treatment as corrosion prevention treatment.
1.Oxidation treatment of steel is also known as bluing, blackening and boiling black.After oxidation treatment, the surface of the spring produces protective magnetic iron oxide, which is generally blue or black or sometimes dark brown.The color depends on the surface state of the spring, the chemical composition of the spring material and the oxidation process.![The chemical protective layer of the spring]( "The chemical protective layer of the spring")
The methods of oxidation treatment include alkaline oxidation, alkali free oxidation and electrolytic oxidation.Use alkaline oxidation method is much.
Alkaline oxidation will spring into the temperature about 140 ℃, the sodium hydroxide solution of oxidant soaking in a certain time, oxidant and sodium hydroxide with iron, ferrous generate acid sodium and sodium, iron reacts to each other, to generate the magnetic iron oxide.
The thickness of the oxide film is about 0.6 ~ 2 / negative m.Although the oxide film can improve the corrosion resistance of the spring, it has poor protective ability due to its thin film and air hole, so it can only be used for the spring in the medium with weak corrosion.The anti-corrosion property depends on the density and thickness of the oxide film, which is determined by the concentration of sodium hydroxide, the concentration of oxidant and the temperature of the solution.
In order to improve the corrosion resistance and lubrication ability of the oxide film, the treatment before and after oxidation treatment should be strengthened.Prior to the oxidation treatment, the spring surface rust, oxide skin, oil pollution, heat treatment of salt slag, surface contact copper layer and so on to be thoroughly cleared.After oxidation treatment, the spring is usually filled in soap solution or bichromate solution, and then washed, blown dry or dried with flowing warm water. Finally, the rust prevention oil or mechanical oil at a certain temperature is replaced by the water film for immersion treatment.
The surface grain boundary of some hot-rolled spring materials has been eroded by oxidation treatment, which can reduce fatigue strength to a certain extent. Therefore, care should be taken when using oxidation treatment.
Conventional oxidation treatments require heating.In recent years, some domestic manufacturers also use room temperature blackening agent, which overcomes the defect of traditional blackening process and saves a lot of energy.
Blackening agent is blue and green concentrated liquid, no impurity, no odor, no fire, no explosion, no corrosion, transport safety.
The dilution of the blackening agent with water is about 1:5.
The operation process of blackening agent is relatively simple, and its process route is as follows: degreasing, rinsing, pickling, rinsing, blackening (2-5min at room temperature), rinsing, water film replacement anti-rust oil.It should be noted that the spring workpiece must be thoroughly cleaned of the oil, and then put into room temperature blackening agent for oxidation treatment.
Oxidation treatment has low cost, simple process formulation, high production efficiency, and a certain elasticity of the oxide film, which basically does not affect the spring characteristic curve. Therefore, oxidation treatment is widely used as the anti-corrosion and decoration measures of cold-formed spiral spring, spring washer and sheet spring.
The quality inspection of the spring after oxidation treatment includes appearance inspection and corrosion resistance inspection.
2.The process of phosphating a spring into a phosphate solution containing manganese, iron, and zinc to form a layer of water-insoluble phosphate film on the metal surface is called phosphating.The appearance of phosphating film is dark gray, gray or black gray, not shiny.The thickness of the phosphating film is usually 5-20 / pressure m.Phosphating film is stable under general atmospheric conditions, and its corrosion resistance is 2 ~ 10 times of that of bluing film.Phosphating film has micropore structure and good adsorption capacity for paint and oil.After phosphating, dichromate filling, oil soaking or painting can further improve its corrosion resistance.Phosphating film is stable in animal oil, vegetable oil and mineral oil, and also stable in some organic solutions (such as benzene and toluene).
Phosphating film can withstand temperatures up to 400 ~ 500 ℃, as a result, some of the work under the high temperature of the spring, such as shell part of spring that common phosphating treatment.
The spring had better be sandblasted before phosphating.After sandblasting, the tongue should not be left for too long and should be phosphated immediately.If there is no sandblasting equipment, chemical oil removal and pickling can also be used to remove oil.The phosphating spring produces a lot of hydrogen in the process of phosphating, so the phosphating spring has hydrogen embrittlement.For the key part of the spring, after phosphating treatment should be dehydrogenated.