Why is manganese phosphating solution also called black phosphating solution?

Manganese phosphating and rust proof phosphating solution process is to produce a dense and wear-resistant black phosphating liquid color coating on the surface of steel, so it is also called black phosphating solution. Manganese phosphating liquid film is composed of a series of different sizes of crystals, which forms a small crack porous structure at the junction of the crystal. The porous crystal structure can significantly improve the corrosion resistance, adsorption and wear resistance of steel surface in the environment of lubricating oil or rust proof oil.

It is suitable for the anti abrasion and self lubrication film treatment of high speed running parts such as automobile, motorcycle and ship, as well as wear-resistant and corrosion resistant coating treatment of tools, tools and standard parts with high requirements.

Process flow: degreasing → water washing → rust removal → water washing → neutralization → table adjustment → phosphating → water washing → anti rust oil

Manganese phosphating solution parameters: dilution ratio: 1:10

Operating temperature: 95-98 ℃

Time of use: 10-20 minutes


1. every morning, salvage sediment and turn the tank once in 10 days.

2. total acidity 60-80 and free acid 6-9. The acid ratio is 6-9.

3. the total acidity is not enough, phosphating solution is added, and neutralizer is added when free acid is too high.

Manganese phosphating film has a large hardness, bearing capacity and thermal stability. Therefore, the coating is especially suitable for handling sliding friction parts (such as gear, shaft sleeve, cylinder sleeve, piston ring, camshaft, valve tappet, weapon parts, etc.), so as to improve the wear resistance and the running in performance of friction pair. When lubrication is interrupted suddenly, the coating is used to improve the wear resistance and the running in performance of friction pair, Phosphating film can absorb certain mechanical stress and prevent the surface damage of parts. It can be seen from the film forming reaction of phosphating film that when the steel surface contacts phosphating solution, the iron dissolution will be produced in the micro positive region on the steel surface, and the phosphating film will also be formed. The surface of steel under phosphating coating is also etched to form compact and deep pits. During the running in process, a large amount of phosphate is squeezed into the pit. On the one hand, the phosphate squeezed in the pit can improve the roughness of friction surface, on the other hand, the phosphate in the pit can absorb lubricant and keep it free from loss. When entering the friction zone from non friction area, the positive pressure on the friction surface increases gradually, and the hydraulic pressure in the pit increases accordingly. The lubricant is extruded from the pit, which makes the friction surface form a coherent lubricating oil film, which can obviously improve the wear resistance of the friction pair. It can be concluded that only when the steel surface is etched can a compact pit be formed, and the pit can be filled with enough phosphate to reduce friction.

The choice of coating weight and thicker phosphating film are used for friction pair, which is conducive to improving the wear resistance and service life of parts. However, not any friction pair can adopt thick film. It must be determined according to the product design requirements, tolerance matching of friction pairs and actual service conditions. In gb/t11376 1997 phosphate conversion film of metals, the selection of coating weight data and surface adjustment processing suitable for different friction reduction requirements is recommended. The friction reduction properties of zinc phosphate film are not as good as that of manganese phosphate film. Zinc or manganese phosphating film can be used for parts with low friction reduction requirements. In order to meet the requirements of tolerance matching, the surface adjustment treatment can be used before phosphorus generation, and the fine grain and film weight can be added to the phosphating solution. The surface modifier used before the phosphorus generation of manganese is different from that of zinc phosphating, and its main component is manganese monohydrogen phosphate colloid. The concentration of the surface adjustment in the surface adjustment solution is usually 2-4G / L, the working temperature is 40-50 ℃, and the time is 1-3min. The solution is stirred with compressed air and the solution is replaced regularly.

The control of ferrous ion shows that manganese, phosphate and nitrate are mainly contained in the phosphating solution. The content of ferrous ion in the solution should be controlled below 2G / L. if it is more than 4G / L, oxidant must be added. For example, hydrogen peroxide is used to oxidize the excess iron divalent to trivalent iron and precipitate. The total acidity of the solution is about 40-60, and the free acidity is about 2-4.5. The working temperature of the solution should be controlled at 92-98 ℃. The crystalline structure of phosphating film shall be prism, and no branching or flake crystallization is allowed.

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