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Development history and new technology prospects of industrial aluminum surface treatment technology
- 2019-10-28-

In order to meet the needs of users, industrial aluminum profiles for construction are generally surface treated to be placed on the market. There are three types of surface protection methods for building aluminum:

( 1) Anodizing, Shanghai aluminum profiles have been introduced into aluminum alloy doors and windows in the 1950s, and are still the commonly used surface treatment measures for aluminum doors and windows;

(2) Electrophoretic acrylic resin after anodization, which was commercialized in Japan in the 1960s, and used in Europe in the 1970s, and is currently mainly used in Asia. The technology has been developed from transparent bright film to matt transparent film and color film, the variety is more diversified, industrial control and product quality are relatively stable;

(3) Electrostatic spraying after chemical conversion treatment includes electrostatic powder spraying and electrostatic liquid phase spraying, and electrostatic liquid phase spraying of fluorocarbon resin has been commercialized in the United States in the 1960s. The electrostatic powder coating of thermosetting polyester coatings has been commercialized in Europe in the late 1960s and is still the dominant surface treatment in Europe. Today, single anodized aluminum doors and windows are significantly reduced in Japan and abroad, and Japan prefers electrophoretic coatings. White electrophoretic coatings have developed rapidly and are used in Europe. Electrostatic powder coating has become the preferred surface treatment method in Europe and America for its various colors, convenient control, environmental protection and excellent performance. In recent years, the electrostatic powder coating market is also rapidly expanding in China.

The temperature of the anodizing solution has an important influence on the uniformity of the film thickness. The high temperature causes the dissolution rate of the anodized film to be accelerated, and the oxide film is thin, and conversely, the oxide film is thick. The anodizing reaction is carried out at a lower temperature. The production is carried out by heat exchange with cold water and the bath. The bath at the upper end of the oxidation tank is passed through the heat exchanger and then pumped back to the oxidation tank to withdraw the bath and the original tank. There is a temperature difference in the liquid. Because the volume of the oxidation tank is relatively large, the circulation of the bath liquid is insufficient, and the distribution of the pump back to the bath is not uniform, which causes a temperature difference in the oxidation bath. Taking the horizontal production line as an example, the film thickness at both ends of the same profile may be different because there is a temperature difference between the two ends of the bath, which may be different from the upper and lower film thickness of the hanging material, which may be due to the temperature difference between the upper and lower sides of the bath.

On several sides of the same aluminum profile, even in the groove, the film is uniform and has a large relationship with the corresponding cathode area. The cathode area is large, so that the current density distributed in each part of the aluminum profile is uniform, and the film thickness is also uniform. In the horizontal line production, the film thickness of the same part of each profile of the hanging material sometimes appears to be low, which is probably because the cathode plate corresponding to the part appears loose or even falls off, which reduces the cathode area. , resulting in a low film thickness.

In the actual production process, there are other reasons that may cause uneven film thickness of the oxide film, such as poor contact between the clamp and the profile, and the contact area is too small, which may make the oxide film incomplete or oxide-free. In addition, the wide range of sulfuric acid concentration will make the oxide film thickness of different tank materials different.   A large range of changes in sulfuric acid concentration makes the k in the empirical formula ( δ = kIt) for calculating the thickness of the oxide film inaccurate, and thus the film thickness of the obtained oxide film is inconsistent. In the production, as long as the above problems are solved one by one, the film thickness of the oxide film can be ensured to be uniform.