Anodic oxidation treatment plays a vital role in the surface treatment of energy-saving industrial fan blades. On one hand, fan blades made of pure aluminum or aluminum sheets have a relatively single color and may lose their luster over time due to oxidation with oxygen. On the other hand, anodic oxidation films can be dyed in various bright colors, making the surface of the blades more attractive, and customized colors can be tailored to meet different customer needs.
Although anodic oxidation treatment can solve the problem of surface color for fan blades, the dyed oxide film has a high porosity and adsorption capacity, which makes it easy to be contaminated. Especially when industrial fans are used in corrosive environments, the corrosive medium may enter the pores and cause corrosion. Furthermore, the color fastness and sun resistance of the colored film after dyeing is poor without special treatment. Therefore, appropriate sealing technology is needed to close the micro-pores of the oxide film on the fan blades to reduce their adhesion and improve their corrosion resistance, while maintaining the beautiful color.
There are various methods for sealing the aluminum oxide film on fan blades. These methods include boil sealing and steam sealing based on hydration reactions, physical sealing based on surface coating, and sealing filled pores through hydrolysis reactions. The latter provides chromium salt sealing, chromate sealing, nickel acetate sealing, and nickel-fluoride sealing systems at room temperature.
Currently, the use of sealing agents abroad mainly involves the use of nickel salt sealing agents, with high-temperature nickel acetate sealing agents in Japan and room-temperature nickel acetate sealing agents in Europe and America being the main types. The sealing quality of high-temperature nickel acetate sealing agents is better than that of room-temperature nickel acetate sealing agents, making them more widely used. The principle behind it is that nickel ions, under certain pH conditions, act together with water and surfactants to cause hydrolysis, and the hydrolysis products appropriately aggregate into the pores of the aluminum surface oxide film to achieve sealing. The pH buffer plays a role in stabilizing the solution pH value and controlling the degree of nickel ion hydrolysis, while surfactants coordinate with counterions to form complexes, controlling the concentration and hydrolysis of simple nickel ions. At the same time, appropriate dispersion and wetting effects are produced in the sealing liquid. This keeps the hydrolysis products of nickel ions properly aggregated, ensuring that no powdery frost appears and minimizing the impact on dye dispersion while achieving a relatively fast sealing rate.
For domestic energy-saving industrial fan manufacturers, most of the sealing agents for the anodic oxidation of fan blades are currently imported from abroad. Although the cost is high, the production step of sealing cannot be omitted to ensure the color and long-term effect of the fan blades.