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Aluminum profile oxidation coloring is not uniform, many people do not know the real reason

Posted time:2021-05-26 Page View:1891

Principle of oxidation dyeing of aluminum profiles


Aluminum or aluminum anodic oxide film is made of a large number of hexagonal crystal cell is perpendicular to the metal surface, each cell center there is a film hole, and with a strong adsorption capacity, when the oxidation of aluminum in the dye solution, dye molecules by diffusion into the film hole of oxide film, at the same time and the oxide film is hard to the covalent and ionic bonds of separation. This bond binding is reversible and desorption will occur under certain conditions. Therefore, after dyeing, it must be sealed, the dye is fixed in the film hole, with the addition of oxidation film corrosion resistance, wear resistance and other functions.

Influence of anodic oxidation process on dyeing

In the whole process of oxidation dyeing, poor dyeing due to oxidation process is common. The film thickness and pore uniformity of the oxide film are the conditions and foundation for obtaining uniform common color when dyeing. In order to obtain uniform common oxide film, it is very important to ensure sufficient circulation, cooling, and excellent conductivity. In addition, the stability of the oxidation process is also very important.

Sulfuric acid concentration, control in 180-200g/L. A slightly higher sulfuric acid concentration can accelerate the dissolution reaction of the oxide film, which is conducive to the expansion of pores and is easier to dye.

The concentration of aluminum ions should be controlled at 5-15 g/L. When the aluminum ion is less than 5g/L, the adsorption capacity of the oxide film generated by the aluminum profile is reduced, which affects the color speed. When the aluminum ion is greater than 15g/L, the uniformity of the oxide film is affected, and irregular film is prone to appear.

The oxidation temperature is controlled at about 20℃. The temperature of the oxidation bath has a great influence on the dyeing. The low temperature of the aluminum profile causes the film hole of the oxide film to be fine, and the dyeing speed is obviously slowed down. If the temperature is too high, the oxide film is loose and easy to be pulverized, which is not conducive to the control of dyeing. The temperature difference of the oxidation tank should be changed within 2℃.

The current density is controlled within 120-180A/m2. The current density is too large, in the case of a certain thickness of the film, it is necessary to shorten the electrolytic time of aluminum products in the tank, so that the dissolution of the oxide film in solution is reduced, the film hole is fine, and the dyeing time is lengthened. At the same time, the film is easy to powder.

Film thickness, dyeing requirements of the oxide film thickness is generally more than 10 m in the solution of aluminum profile. Film thickness is too low, dyeing is prone to uneven phenomenon, at the same time in the requirements of dark color (such as black), due to the film thickness is not good, resulting in a limited amount of dye accumulation, can not meet the required color depth (not black).

In a word, anodic oxidation, as a pre-dyeing process, is the basis of dyeing. The problem of anodizing is difficult to see or impossible to see before dyeing. Once the color is dyed, we can clearly see the phenomenon such as uneven color. At this time, the production workers will often attribute the problem to the abnormal dyeing, and neglect to find the reason in the oxidation process.