Three reasons for the color difference of aluminum profile
1、 Causes of anodizing
1. Principle of oxidation dyeing
As we all know, the anodic oxide film is composed of a large number of hexagonal cells perpendicular to the metal surface, each cell center has a membrane hole, and has a 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 a covalent bond and an ion bond which are difficult to separate with the oxide film at the same time. The bond binding is reversible, and under certain conditions, desorption will take place. Therefore, after dyeing, the dye must be sealed and fixed in the film hole to increase the corrosion resistance and wear resistance of the oxide film.
2. Effect of anodizing process on dyeing
In the whole process of oxidation dyeing, it is common to cause poor dyeing due to oxidation process. The uniform thickness of oxide film and pore is the premise and basis of uniform color in dyeing. In order to obtain uniform oxide film, ensure enough circulation, cooling capacity, and ensure uniform color
Good conductivity is very important, in addition to the stability of the oxidation process.
The concentration of sulfuric acid is controlled at 180-200g / L. Slightly higher sulfuric acid concentration can accelerate the dissolution reaction of oxide film, facilitate the expansion of pores, and make it easier to dye;
The concentration of aluminum ion is controlled at 5-15 g / L. When the aluminum ion is less than 5g / L, the adsorption capacity of the oxide film is reduced, which affects the coloring speed. When the aluminum ion is more than 15g / L, the uniformity of the oxide film is affected, and irregular film is easy to appear.
The oxidation temperature is controlled at about 20 ℃. The temperature of the oxidation bath has a significant effect on the dyeing. Too low temperature causes the film pores of the oxide film to be dense and the dyeing speed to be slowed down significantly. Too high temperature makes the oxide film loose and easy to be powdered, which is not conducive to the control of dyeing. The temperature difference of the oxidation bath should be within 2 ℃.
The current density is controlled at 120-180a / m2. If the current density is too large, the electrolytic time of aluminum products in the cell should be shortened correspondingly when the film thickness is fixed. In this way, the dissolution of oxide film in the solution is reduced, the membrane pores are dense, and the dyeing time is longer. At the same time, the film is easy to be powdered.
The thickness of the oxide film is required to be more than 10? M for dyeing. When the film thickness is too low, the dyeing is prone to uneven phenomenon. At the same time, when it is required to dye dark color (such as black), because the film thickness is not enough, the deposition amount of dye is limited, and the required color depth cannot be achieved.
2、 Reasons for staining
1. Washing before dyeing
After anodizing, sulfuric acid remains in the pores of the oxide film, so the aluminum products must be thoroughly cleaned before dyeing. It is necessary to set up pure water for cleaning before the dyeing tank and monitor the water quality.
2. Preparation of dyeing tank
Most of the dyes used in dyeing are organic dyes, which are prone to mildew. In order to effectively prevent the tank liquor from mildew, bleaching powder and phenol can be used to disinfect the tank body before preparing the tank liquor. When preparing the bath solution, adding mildew inhibitor can effectively prolong the use time of the dyeing solution. After the tank solution is prepared, it needs to be stored for several hours before it can be put into use. To ensure the pH value is stable, acetic acid sodium acetate can be added to slow down
3. Dyeing process control
In the process of dyeing, the dyeing rate increases with the increase of temperature, so the time needed to dye a certain depth of color decreases with the increase of temperature. At the same time, when the bath temperature rises, the synchronous sealing will also speed up. If the temperature is too high and the synchronous sealing is too fast, before the dye molecules have enough adsorbed in the membrane pores, the accumulation of dye will stop because the membrane pores of the oxide film are closed, unable to reach the required depth. When dyeing at a relatively low temperature, it can dye a deeper color, but the corresponding time is longer. Therefore, the needle For different color requirements, the dyeing temperature can be properly adjusted to avoid too long or too short dyeing time.
(2) Dye concentration
According to the adsorption law, under certain working conditions, the adsorption capacity of dye on the anodized film increases with the increase of dye concentration. However, this law is only applicable when the oxide film itself has adsorption capacity. For colors of different depths, the dye concentration should also be adjusted accordingly. In the initial preparation of tank solution, the solution of lower concentration should be prepared as much as possible. As the production goes on, the dye is constantly consumed, and the consumed part should be continuously supplemented, which should be a few times. If the concentration of dye is measured, the influence of impurity ions should be considered. The actual effective concentration may be different from the detection. Therefore, the actual dyeing power of the dyeing tank should be tested regularly.
In order to ensure a stable dyeing power, after a period of production, part of the bath solution can be changed.
As with electrolytic coloring, when other conditions remain unchanged, the color gradually deepens with the extension of time. In general, when the oxidation conditions are determined, the dye concentration and temperature are determined. We can only get the color depth required by customers by adjusting the dyeing time. If the dyeing time is too short, the required color will be obtained. There are two disadvantages: one is that the color is too fast, it is not easy to get uniform color; the other is that the color is too fast, and the color weather resistance obtained is not enough. If the dyeing time is too long, or the required color depth cannot be obtained no matter how long the dyeing time is, we need to consider whether the oxide film is too thin or the dye concentration is too low.
(4) PH value
Generally, the pH value is 5-6, stable
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