Workpiece surface phosphating and adjusting the function of the process and control points

1, after degreasing phosphating before the surface adjustment

Is an important process for the formation of phosphate film crystals. It can change the microscopic state of the metal surface to promote the formation of fine, uniform, dense phosphate film in the phosphating process. In particular, the metal surface cleaned by acid or high-temperature strong alkali and immersion low-temperature phosphating of low zinc film, especially the need for surface adjustment.

The main components of the surface adjustment solution are titanium salts (titanium colloids) and sodium phosphate, a slightly alkaline colloidal solution. Due to the high surface energy of colloidal particles, they have a strong adsorption effect on the metal surface. When a large number of nuclei are formed on the treated surface, uniform phosphate crystals form rapidly around the nuclei in the early stages of phosphatization. This limits the growth of large crystals and promotes the refinement and denseness of the phosphate film, which improves the film formation rate, shortens the phosphating time, reduces the film thickness, and also eliminates the differences in the state of the metal surface on the quality of phosphating.

2, there are a variety of methods of surface adjustment

Such as soaking, spraying, coating, etc., the specific choice of method depends on the nature of the material, the scale of production and requirements and other factors. Surface adjustment time is generally 10-30 minutes, the concentration of the adjustment solution also has certain requirements, too high or too low concentration will affect the phosphating effect. In the process of surface adjustment, attention needs to be paid to control the temperature of the adjustment solution, pH and other parameters to ensure the adjustment effect.

Surface adjustment also has a great impact on the performance of the phosphate film. Surface adjustment can improve the corrosion resistance, hardness and adhesion of the phosphate film, which in turn improves the service life of the phosphate film. Therefore, the surface adjustment is a necessary step in the manufacture of high-quality phosphate film.

3, the surface adjustment process control and management points are as follows.

(1) effective titanium concentration:

10ppm or more (i.e. 1kg of aqueous solution of 1mg of titanium for 1ppm), pH 8.5 to 9.5. When the Ti (titanium) concentration is lower than 10ppm, the phosphate film will become thicker; pH decreases, the surface adjustment is reduced, the formation of iron phosphate film (blue), corrosion resistance decreases.

(2) In order to prevent sudden agglomeration

Of the main component titanium colloid in the treatment solution, the crystallization of the phosphate film becomes larger and the film thickens after attaching to the steel plate for phosphating treatment. Preparation of surface conditioning treatment solution water should be pure water, its conductivity should be less than 200MS/cm. When the water quality of tap water is not good (containing chlorine is not suitable), it is best to use deionized water.

(3) At room temperature,

The maximum temperature should not exceed 35℃ and the treatment time should be 30~60s.

(4) To ensure the stability of the treatment solution,

Fresh water must be supplied frequently and surface conditioner must be added. The amount of surface conditioner used on the production line is not proportional to the number of processed pieces. In general, it should be added regularly and the treatment solution should be completely renewed once a week (management should follow the material supplier’s instructions). The treatment solution should be kept well agitated to avoid precipitation.

The focus of the surface adjustment process management is that the temperature of the workpiece should be as low as possible and that strict pH management is carried out.

Conclusion

In short, surface adjustment is an indispensable step in the phosphating process and has an important impact on ensuring the quality of the phosphate film. Companies in the production process should pay attention to surface adjustment and strengthen its control to ensure the production of high-quality phosphate film.

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