The electrolytic coloring of aluminum profiles has good decorative properties, and therefore it is widely used both domestically and internationally, especially in the surface treatment production of architectural aluminum profiles. Currently, the main process uses a tin-nickel mixed salt electrolytic coloring method, with the products primarily exhibiting a champagne color. Compared to single nickel salt coloring, products produced with tin-nickel mixed salt electrolytic coloring have bright colors and full tones. The main issue is that the products may have color differences, which can result from unreasonable extrusion processes and anodizing coloring processes during aluminum profile production.
The influence of the extrusion process on anodizing coloring mainly involves how mold design, extrusion temperature, extrusion speed, and cooling methods affect the surface condition and uniformity of the extruded profiles. The mold design should allow the material to blend sufficiently; otherwise, defects such as bright (or dark) bands may appear, and color differences may occur on the same profile. Additionally, the mold condition and extrusion marks on the profile's surface also affect anodizing coloring. Differences in extrusion temperature, speed, cooling method, and cooling time can result in uneven profile structures.
1. It can also cause color variation.
Anodizing has a significant impact on the color variation in electrolytic coloring, especially in the production process of vertical anodizing lines, where color differences at both ends are prone to occur. Vertical anodizing tanks are 7.5 meters deep, and temperature differences easily develop between the top and bottom of the tanks. Temperature has an important effect on anodizing; higher temperatures accelerate the dissolution of the oxide film in the anodizing solution, increasing the pore size on the surface of porous anodic oxide films, whereas lower temperatures result in smaller surface pores. Additionally, higher temperatures lead to higher porosity of the anodic oxide film, and lower temperatures result in lower porosity.
Electrolytic coloring primarily works by causing metal ions in the coloring solution to undergo an electrochemical reduction reaction on the surface of the barrier layer within the micropores of the oxide film. This leads to the deposition of metal ions at the bottom of the pores in the anodic oxide film, scattering incident light and producing different colors. The more material deposited in the micropores, the deeper the color. Under the condition of the same applied current, the same amount of metal or metal compounds will deposit in areas of high and low temperature, but in areas with high porosity and larger surface pores, each pore will receive less deposit, resulting in a lighter color, while the color will be darker in areas with low porosity and smaller pores. This causes color variation at both ends of the material. During anodizing, conductivity also affects the oxide film and can result in color differences. This issue is more common in horizontal production lines, mainly because during the pre-anodizing setup, if the clamps are not tight, some materials conduct poorly, leading to differences in the anodic film. After coloring, this results in color variation.
The electrolytic coloring process can directly reveal color variation issues. The ability of the coloring solution to distribute current plays a decisive role in achieving uniform coloring. Uneven current distribution leads to noticeable color differences. The solution's current distribution capability is mainly related to the conductivity and polarization of the solution. The coloring solution contains certain conductive salts to enhance conductivity. If such salts are not replenished in time, conductivity decreases, reducing current distribution ability and causing color variation. Additionally, additives in the coloring solution can have specific adsorption properties, increasing polarization. Excessive consumption of these substances reduces the polarization of the electrolyte, decreases current distribution capability, and causes color variation. In actual production, it is necessary not only to improve the conductivity of the solution but also to ensure that the conductive rods and copper supports have good conductivity. Poor conduction causes uneven power line distribution, leading to color differences.
The main focus is on several factors that cause color differences in the same batch of material. Variations in the process parameters of anodizing and electrolytic coloring can lead to color differences between different batches. Therefore, in production, it is necessary to control the stability of the oxidation and coloring processes and ensure consistency in all parameters, thereby reducing the occurrence of color differences in oxidized and colored materials.
