Function and classification of phosphating

1、 The function of phosphating is to produce a layer of non-metallic, non-conductive and porous phosphate film on the metal surface (mainly steel) by chemical reaction Phosphating process is widely used in industry, such as metal forming, lubrication, antirust, coating and so on The phosphating film has porosity, and the coating can penetrate into these pores, so the adhesion of the film can be significantly improved In addition, the phosphating film can make the metal surface change from good conductor to bad conductor, thus inhibiting the formation of the metal surface micro battery, effectively hindering the corrosion of the film, and can multiply the corrosion resistance and water resistance of the coating, so the phosphating film has been recognized as the best substrate of the coating Therefore, phosphating treatment has become an indispensable link in the coating surface treatment process 2、 The classification of phosphating there are several different methods of phosphating treatment According to the composition of phosphating film, it can be divided into three categories: iron series, zinc series and manganese series According to the thickness of the film, it can be divided into thin film type and thick film type According to the treatment temperature, it can be divided into high temperature phosphating, medium temperature phosphating and low temperature phosphating This section discusses the analysis based on the composition of the phosphating film （1） Iron phosphating iron phosphating is mainly used for coating The iron phosphating film is very thin, most of the films are in the range of 0.3-0.5g/m2, rarely up to 1g / m2 The iron phosphating film is composed of ferric phosphate and ferric oxide, and the color ranges from blue to brown The main components of the iron phosphating solution are acid alkaline phosphates (such as sodium dihydrogen phosphate, ammonium dihydrogen phosphate), polyphosphate containing alkali metals (such as sodium tripolyphosphate) and a small amount of catalyst promoters and additives In the phosphating process, the iron phosphating has the advantages of fast reaction speed, short processing time, low processing temperature, large process range, low acidity of the bath solution and less phosphating sludge Therefore, the equipment requirements are not high, the drug consumption is low and the cost is low If a suitable surfactant is selected, a "two in one" degreasing and phosphating process can be formed, which can simplify the phosphating process However, due to the thin iron phosphating film, its corrosion resistance is not as good as that of zinc phosphating film, so it is mainly used in workpieces with low requirements for corrosion resistance （2） Zinc phosphide zinc phosphide is used in lubrication, antirust, coating and so on The weight of zinc phosphating film is 1-6g / m2 The weight of phosphating film for coating is 1-3 g / m2, which is film type The composition of the membrane is mainly composed of phosphate of zinc and iron, and the color ranges from gray to grayish brown The main components of zinc phosphating solution are zinc dihydrogen phosphate, sodium tripolyphosphate, catalyst, promoter, slag reducer and other additives Due to the different formulations, the process parameters of zinc phosphating vary greatly In terms of coating, at present, the medium temperature phosphating and film type are used, so the reaction speed is fast, the time is short, the temperature is low, and the sludge is less, but the zinc phosphating can not form the "two in one" oil removal phosphating, so the process is more The quality of zinc phosphating film is better than that of iron film, so zinc phosphating is used in automobile coating and home appliance coating （3） Manganese phosphating manganese phosphating is loose due to long treatment time, high temperature, high concentration and thick film Now it is not used in coating industry, and it is mostly used in lubrication, corrosion prevention and other aspects 3、 Requirements for phosphating film for coating: the weight of the film is generally 1-5g / m2, which is equivalent to 0.6-3.5 μ m of the film thickness At the same time, the crystal of the phosphating film is fine, uniform, continuous, dense, with good adhesion, high hardness and low porosity.