Clear anodizing is an anodizing process that produces a uniform clear film on the surface of various metals, typically aluminum, which provides the metal with increased corrosion and wear resistance. Utilizing the process of electrolytic passivation, this film is an oxide coating, meaning a hard non-reactive surface, which typically has a thickness of less than .0010”.
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Application of Clear Anodizing
Clear anodizing is typically a sulfuric acid anodizing process, and as a result, offers better wear resistance than chromic acid anodizing and comparable corrosion resistance. Used in a variety of applications, clear anodizing benefits diverse industries including: architecture, for use in window and door frames, railings and siding; automotive, for use in trim and housings for various exposed parts; printing, for use as commercial photolithography plates; and industrial manufacturing, for sheet metal and various extrusions such as profiles and cases for additional surface protection.
Additionally, clear anodizing can be colored by means such as organic dyes and metallic salts to create colors such as red, yellow, blue and green for decorative applications such as jewelry or artwork. Some further benefits of clear anodizing include decreased part maintenance, reduced metal weight, being environmentally-friendly and increased production efficiency.
Process of Clear Anodizing
The clear anodizing process is basically identical to the Type II sulfuric acid anodizing process. A commonly used anodizing process, Type II sulfuric acid requires the metal to be fully immersed into sulfuric acid, a highly corrosive and oil-like acid that is formed from sulfur dioxide. When the metal is immersed in the acid an electric current, generally direct current, is sent through the sulfuric acid and reacts with anodes on the surface of the material. The reaction of the current and the anodes creates the hard outer film of oxidation. After the material is removed from the sulfuric acid bath, it is then sealed through the use of hot water in order to enhance the corrosion-resistant properties of the film.
If a color is going to be added, then the dye or salt must be introduced after immersion in the sulfuric acid bath but before sealing, so that when sealed, the color will become locked in. While the addition of color can be eye-catching, clear anodizing allows the natural luster of the metal to shine through. Although aluminum is the most common material used in clear anodizing, other metals may be anodized as well including: titanium, magnesium, zinc, niobium and tantalum.