What kind of pretreatment should be done before painting hardware, and what treatment should be used?

High-quality phosphating film is only formed on the surface of the workpiece, and impurities such as oil stain, rust and scale on the surface of the workpiece have been completely removed. Because the residual oil, rust and scale on the surface of the workpiece will seriously hinder the growth of phosphating film. In addition, it will also affect the adhesion, drying performance, decorative performance and corrosion resistance of the coating, and thorough removal of these foreign bodies is a necessary condition for phosphating.

Step 2: Wash

Although washing after degreasing and rust removal is an auxiliary process before painting, it also needs to be paid enough attention. After degreasing and rust removal, some nonionic surfactants and CL- are easy to attach to the surface of the workpiece.

If these residues are not thoroughly cleaned, the phosphating film may become thinner, resulting in linear defects, or even unable to phosphatize. Therefore, in order to improve the washing quality after degreasing and derusting, it is necessary to rinse for several times, twice for 1-2min, and change clean water frequently to ensure that the PH value of clean water is between 5 and 7.

3. Phosphate antirust treatment on metal surface

The so-called phosphating refers to the method of treating metal workpiece with acidic solution containing dihydrogen phosphate and forming a stable insoluble phosphating film on its surface through chemical reaction. The obtained film is called phosphating film. The main purpose of phosphating film is to increase the adhesion and corrosion resistance of the coating.

There are many phosphating methods, which can be divided into high-temperature phosphating (90-98℃), medium-temperature phosphating (60-75℃), low-temperature phosphating (35-55℃) and normal-temperature phosphating according to phosphating temperature.

4. Passivation

Passivation technology of phosphating film is widely used in North America and European countries. Passivation technology is based on the characteristics of phosphating film. The phosphating film is thin, generally at 1-4g/m2, and the maximum is not more than 10g/m2. Its free pore area is large and the corrosion resistance of the film itself is limited.

Some even develop yellow rust rapidly in the drying process. After phosphating, the exposed metal in the pores of phosphating film can be further oxidized or form a passivation layer, which can be filled with oxidized phosphating film to make the phosphating film stable in the atmosphere.

5. Drying of phosphating film

Drying phosphating film can play two roles. On the one hand, it prepares for the next working procedure, removes the moisture on the surface of phosphating film, on the other hand, it further improves the corrosion resistance of coating film.

In order to establish a pretreatment production line for painting, the process design must be completed before the design, manufacture and installation of non-standard equipment can be carried out. Therefore, process design is the basis of establishing production line, and the correct and reasonable route will have a good impact on production operation and product quality.

Extended data

The storage period of metals after different treatments is as follows:

1, aluminum alloy wet sandblasting for 72h；;

2. Chromic acid-sulfuric acid treatment of aluminum alloy for 6h;

3. Anodizing aluminum alloy for 30 days;

4. The stainless steel is treated with sulfuric acid for 20 days;

5, sandblasting steel, 4h;

6. Brass is wet sandblasted for 8 hours.

Baidu Encyclopedia-Metal Surface Pretreatment

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