Introduction to antirust and phosphating process

Phosphating for protection belongs to thick film phosphating, with a film thickness of more than 20um, and the film weight is generally 10 ~ 30g / m2, or even heavier. In order to obtain good protective performance, the parts should be soaked with oil, grease or wax after phosphating treatment, so as to further improve the anti-corrosion performance. It is often used in fasteners, springs, etc.

In principle, this kind of film cannot be used for the bottom layer of organic film. It is very sensitive to mechanical deformation. When it is deformed, the film will crack and loosen, resulting in the separation of parts and paint film. In addition, the coating consumes a lot, and the gloss and finish are poor.

(1) Slow phosphating

The tank liquid is composed of one or two of zinc dihydrogen phosphate, dihydrogen phosphate, iron dihydrogen phosphate and free phosphoric acid. Because there is no oxidant, the concentration of Fe2 + ions increases and the sediment increases with the increase of treatment area. The processing time takes 40 ~ 60 minutes.

(2) Accelerated high temperature phosphating

Adding N03 -, ci03 -, etc. to the above phosphating solution can greatly shorten the phosphating time. Their role is to maintain the content of Fe2 + in the solution at the same level by the hydrogen ion generated by the reaction of oxidized steel and acid and the ferrous ion generated by the dissolution of iron.

In the phosphating solution containing accelerator, although the zinc content initially decreases, under a certain acid ratio, the whole process of using the bath solution can be maintained at a constant level, and the composition of the phosphating film will not change significantly due to the treatment area. In addition, the sediment in the phosphating tank with accelerator is significantly less than that without accelerator. The corrosion resistance of phosphating film remains unchanged and the service life of bath solution is obviously prolonged.

During the production process, the solution shall be tested and supplemented regularly to maintain the formation of uniform film. There are many ways to put parts into the groove, such as special spreader or net basket for large work; For large quantities of small parts, rollers can be used.

For the purpose of energy saving, the decrease of phosphating temperature does not affect the formation of sufficiently thick film, which is undoubtedly the direction of people's pursuit. The latest research results show that the original temperature can be reduced from 92 ~ 98 ℃ to 65 ~ 85 ℃ by adjusting the components, and the phosphating film can be applied with standard copper sulfate solution for 20 ~ 30 minutes without corrosion.

High carbon steel and high carbon low alloy can form black or dark gray black film, while medium and low carbon steel can only form silver gray to gray film. If black phosphating film is required, three methods can be used: first, dyeing before phosphating, second, black phosphating (adding black dye to phosphating solution), and third, dyeing black after phosphating.