Phosphating is a method of producing a stable insoluble phosphate film on the surface of a metal workpiece through an acid solution containing dihydrogen phosphate, which is called a phosphating film. The main purpose of phosphating film is to increase coating adhesion and improve corrosion resistance of coatings. There are many kinds of phosphating methods. According to the temperature of phosphating, they can be divided into high temperature phosphating (90-98 C), medium temperature phosphating (60-75 C), low temperature phosphating (35-55 C) and normal temperature phosphating.
In order to provide a good coating substrate, the phosphating film thickness is suitable and the crystallization is compact and fine.
Although the medium and high temperature phosphating process is fast, the phosphating film has a good corrosion resistance, the phosphating film has large crystallization, heavy ash hanging, the liquid surface volatilization is fast, the bath liquid is unstable, and the sediment is many. The phosphating film formed by the low temperature phosphating process is meticulous, the thickness is suitable, the film is very few clutter, the amount of lacquer is less and the coating lustre is less. It can greatly improve the adhesion, flexibility and impact resistance of the coating, which can better meet the requirements of phosphating film on the coating. It is worth noting that the phosphating film has been considered thick, and the coating has high corrosion resistance. The phosphating film itself does not bear much corrosion resistance in the whole coating system. It mainly makes the film with strong adhesion, and the corrosion resistance of the whole coating system depends mainly on the corrosion resistance of the film and the film and the film. The strong adhesion force formed by the excellent coordination of phosphating film.
Phosphating solution is generally composed of main salts, accelerators and neutralizer. Most of the phosphating liquid used in the past used sodium nitrite (NaNO2) as a promoter is very obvious, but it has great harm in the phosphating liquid of NaNO2: first, it affects the stability of the phosphating solution, NaNO2 is extremely unstable under the acid condition and is decomposed in a very short time. Therefore, it has to be added frequently. The characteristics of NaNO2 often cause the instability of the main salt of phosphating liquid, more precipitation of phosphating liquid, serious dust in phosphating film, difficult to control slots and the instability of phosphating quality; two, NaNO2 is recognized as a carcinogenic substance in the world, and the long-term contact endangering human health and serious environmental pollution. Solutions: first, reduce the amount of NaNO2; two, look for alternatives.
Formula: XH-1B 4%+H2O