The chemical solution can eliminate the uneven surface state of the steel substrate caused by the oil removal by alkaline solution or the rust removal by pickling
It can form a large number of very fine product centers on the surface, thus speeding up the phosphating reaction and facilitating the formation of the chemical film
Cheng. However, there are several factors that affect the quality of the chemical
membrane in the chemical treatment
(1) Impact of water quality. If the water quality used in the tank solution is seriously rusted and the content of calcium and magnesium ions is large, the chemistry will be affected
For the stability of
the solution, the softener can be added at the top to eliminate the influence of water quality on the chemical solution.
(2) Usage time. Generally, colloidal titanium salt is used as surface conditioner, which has colloidal activity. When it is
used for a long time orWhen there are many impurity ions, the colloid activity will be lost. At this time, the stable state of the colloid will be destroyed, and the bath solution will be precipitated and stratified, which is flocculent
the tank fluid must be replaced.
(3) Acid ratio of phosphating solution. The ratio of total acidity to free acidity can accelerate the phosphating reaction and make the phosphating
The film is thin and fine, but too high acid ratio will make
the film too thin and easy to cause ash hanging; too low acid ratio, slow terminal reaction speed, phosphorus
The surface of the substrate is prone to yellow rust. Generally speaking, the transients system or formula is different from their acids
The requirement of specific size is also different.
(4) temperature. If the temperature of bath liquid is increased properly, the film forming speed will be accelerated, but if the temperature is too high, the change of acid ratio will be affected
However, the stability of the bath solution is affected. At the same time, the crystal nucleus of the film is thick, and the amount of slag from the bath solution is increased.
(5) Sediment volume. With the continuous phosphating reaction, the
amount of sediment in the bath solution will gradually increase, and excessive sediment will
The interface reaction on the surface of the workpiece is affected, which leads to the blooming and ash hanging of the phosphating film, or even no film
formation. Therefore, the bath solution must be based on the
The amount of workpieces to be processed and the use time shall be timely inverted for slag cleaning and desilting.
(6) Nitrite. Nitrite can accelerate the phosphating reaction speed
and improve the compactness and corrosion resistance of phosphating film
When the amount is too high, the film is easy to appear white spots or color phenomenon; when the amount is too low, the film forming speed is slow, and the phosphating film
is easy to produce yellow rust.
(7) Sulfate. If the concentration of pickling solution is too high or the water washing control is not good, the sulfate ion in the phosphating bath solution will increase,
Too high sulfate ion will slow down
the phosphating reaction speed, make the phosphating film grain coarse and porous, hang ash seriously, and change the base resistance of the film
(8) Ferrous ion. If the content of ferrous ion in phosphating solution
is too high, the anticorrosion ability of phosphating film at room temperature will be reduced
The results show that the grain size of the medium temperature phosphating film is coarse, the surface is floating with white ash, and the anti-corrosion
ability is decreased
It becomes turbid and free acidity increases.
(9) passivation. The purpose of sealing passivation is to seal the pores of phosphating film, improve the corrosion resistance of phosphating film, especially to improve the
overall adhesion and corrosion resistance of paint.