1. The pretreatment of workpiece and alkali washing are not thorough enough.

2. The temperature of dyeing melt is too low.

3. There is oil stain on the surface of dyeing solution.

4. Reworked products with unreturned film.

5. The oxide film is polluted.

6. The water washing after oxidation is not thorough enough and is not cleaned thoroughly.

7. When anodizing aluminum profile, the current density is too high.

8. The temperature of anodizing solution is too low and the current density is too low.

9. The anodizing solution temperature of aluminum profile is too high.

There are two main methods for oxidation treatment of aluminum and aluminum alloys:

① In chemical oxidation, the oxide film is thin, about 0.5 ~ 4 microns thick, porous, soft and has good adsorption. It can be used as the bottom layer of organic coating, but its wear resistance and corrosion resistance are not as good as anodic oxide film; ② For electrochemical oxidation, the thickness of the oxide film is about 5 ~ 20 microns (the thickness of the hard anodic oxide film can reach 60 ~ 200 microns), with high hardness, good heat resistance and insulation, higher corrosion resistance than the chemical oxide film, porous and good adsorption capacity. Choose the oxidation method suitable for the requirements of customers to improve the quality of finished products.

As we all know, the anodic oxide film is composed of a large number of hexagonal cells perpendicular to the metal surface. There is a membrane hole in the center of each cell and has strong adsorption force. When the oxidized aluminum products are immersed in the dye solution, the dye molecules enter the membrane hole of the oxide film through diffusion, and form covalent bonds and ionic bonds with the oxide film that are difficult to separate. This bond is reversible and desorption will occur under certain conditions. Therefore, after dyeing, the hole must be sealed, and the dye must be fixed in the film hole to increase the corrosion resistance and wear resistance of the oxide film. 2 Influence of anodic oxidation process on dyeing in the whole process of oxidative dyeing, poor dyeing caused by oxidation process is more common. The uniform thickness and pores of the oxide film are the premise and basis for obtaining uniform color during dyeing. In order to obtain a uniform oxide film, it is important to ensure sufficient circulation, cooling and good conductivity. In addition, it is the stability of the oxidation process. The concentration of sulfuric acid shall be controlled at 180-200g / L. Slightly higher sulfuric acid concentration can accelerate the dissolution reaction of oxide film, which is conducive to the expansion of pores and easier to dye; Aluminum ion concentration shall be controlled at 5-15 g / L. When the aluminum ion is less than 5g / L, the adsorption capacity of the generated oxide film decreases and affects the coloring speed. When the aluminum ion is greater than 15g / L, the uniformity of the oxide film is affected and it is easy to appear irregular film. When the oxidation temperature is controlled at about 20 ℃, the temperature of the oxidation tank solution has a significant impact on the dyeing. Too low temperature makes the pores of the oxide film dense and the dyeing speed slow down significantly; The temperature difference should be within 2 ℃, which is not conducive to loose film dyeing, and the temperature difference should be controlled within 2 ℃. The current density is controlled at 120-180a / m2. If the current density is too high, when the film thickness is certain, the electrolysis time of aluminum products in the tank should be shortened accordingly. In this way, the dissolution of oxide film in the solution is reduced, the film pores are dense, and the dyeing time is prolonged. At the same time, the film is easy to pulverize. Film thickness: the thickness of oxide film required for dyeing is generally 10? Wash the solution above M.

If the film thickness is too low, the dyeing is prone to uneven phenomenon. At the same time, when it is required to dye dark colors (such as black), the deposition amount of dyes is limited due to insufficient film thickness, which can not reach the required color depth. In a word, anodizing, as the pre process of dyeing, is the basis of dyeing. The problem of anodizing is difficult or impossible to see before dyeing. Once dyed, we will clearly see the phenomenon of uneven color. At this time, production workers often attribute the cause of the problem to the abnormal dyeing, and ignore looking for the cause in the oxidation process. I often make these mistakes when I first come into contact with oxidative dyeing.