[China Aluminum Network] 1.1 Dye Selection
A wide variety of dyes are used in the dyeing of aluminum products, and suitable dyes are selected according to different uses and product requirements. For example, dyes include acid dyes, acid complex dyes, acid mordants, direct dyes, disperse dyes, soluble vat dyes, reactive dyes, basic dyes, alcohol-soluble dyes, oil-soluble dyes, and the like. According to their composition, solubility, color fastness, dye uptake, consumption rate, PH value and other properties to select similar dyes, and combined with brown requirements, later choose 600 gray dyes and 900 yellow dyes mixed in a certain proportion , With the tank concentration: 4.8g/L. Prior to mixing, the same concentration of 600 gray dye had a pH of 7.3, while the 900 yellow dye had a pH of 5.4 and the mixed dye had a pH of 6.2. With this dye ratio, the anodized aluminum film can be dyed brown with a reddish yellow background.
1.2 Test Materials and Processes
The test material is 6063 aluminum alloy, according to sample preparation → degreasing → two-stage cleaning → alkali etching → two-stage cleaning → light-emitting → two-stage cleaning → anodizing → two-stage cleaning → mixed-staining → two-stage cleaning → closed → two-stage cleaning → The appearance and sealing quality inspection process is tested.
1.3 Degreasing Process and Precautions
Selection of immersion degreasing, chemical degreasing specification: sulfuric acid concentration 100 ~ 150g / L; AC degreaser concentration 30 ~ 60g / L;
Temperature: 20 ~ 30 °C, processing time: 4 ~ 6 minutes. Degreasing can remove the oil on the aluminum surface and elute the natural oxide film. If the degreasing treatment is not good, it will easily lead to the occurrence of oil stains and corrosion points on the surface of the aluminum material, which will lead to scrapping of the material.
1.4 Alkaline Erosion Process and Precautions
Alkaline erosion specification: sodium hydroxide concentration 50 ~ 80g/L; ADD additive concentration 10 ~ 30g/L; temperature: 50 ~ 70 °C, processing time: 7 ~ 13 minutes. Alkali etching time control has a great influence on the vividness of color after dyeing. When the alkali etching time is too short, the surface of the sand surface is small and the gloss is high. After dyeing, the color is too bright to achieve the effect of soft gloss; Alkaline erosion time is too long, the surface of the sand surface is too large, it will lead to the surface color dark and dumb. Therefore, in batch production, each day needs to select a specific alkali etching time according to the alkali corrosion rate of the alkali tank in the day and the sand surface of the standard swatch to achieve a better surface effect.
1.5 Anodizing Process
1.5.1 Current Density
The current density directly affects the pore size of the oxide film and the number of oxide film pores. When the current density is higher, the pore size is larger, and the number of oxide film pores is smaller. On the contrary, when the current density is lower, the pore size is smaller. The smaller, the more the number of oxide film holes. The greater the number of oxide film holes, the faster the dyeing speed. In other words, the current density directly affects the dyeing speed. We confirmed in production practice that when the current density increases from 0.8A/dm2 to 1.6A/dm2, the dyeing speed slows down as the current density increases. According to the color requirements and considering the production efficiency, the corresponding coloring speed is selected, and the current density is determined to be 1.2 A/dm2 to be produced later. The color effect of the dyeing is more beautiful.
1.5.2 Oxidation bath temperature
In the experiment, the effect of oxidation bath temperature on the dyeing is very obvious. When the temperature is below 18°C, the coloring time is very long, and even the standard color background or color depth requirements cannot be met; when the temperature is 21°C Above, its coloring speed is very fast, and its color appears red and black background color within 2 minutes, causing color difference and requiring rework. When the temperature is oxidized at 18 to 21°C, the dyeing time is 8 to 12 minutes, and a stable brown color can be obtained. The reason is that the increase in oxidation temperature will enlarge the pore size of the oxide film and improve its adsorption ability to the dye. Therefore, after choosing the right current density, it means that the number of holes in the oxide film is also needed. Determine the appropriate oxidation temperature. Through several comparison tests, the temperature was set at 18-21 °C later for oxidation.
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