Anodized finishes are chemically applied to metal surfaces to add protection and strength. Colors can be created by exposure time or dyes, and softer metals like aluminum benefit from the protective properties. Machined holes should be slightly oversized, and sealing may be required. Anodizing involves placing aluminum in a chemical bath with an electric current to create a rust-like material that increases surface strength.
An anodized finish is a clear or colored finish that is chemically applied to the surface of many metals. Used for a variety of purposes, from reducing thread seizure on some fasteners to preventing corrosion on others, an anodized finish not only adds protection to the metal surface, it also adds strength. The color of the anodized finish is not always created by colors or dyes, rather the colors are often directly related to the amount of time the piece has been exposed to the anodizing chemicals. There are, however, a large number of dyes that allow you to create almost any color on an anodized product.
Softer metals, such as aluminum, can often benefit from the protective properties of an anodized finish. On surfaces that will be stripped and excess replaced, the anodized finish allows lubricants to be infused into the surface of the threads, increasing ease of installation. A small amount of dye can be put into the chemicals to give the look of something special to an anodized part, and most anodized parts can be anodized to any color desired. The anodizing film is thick enough that it requires opening a screw hole before attempting to drive the screw into the hole.
Any holes that can be machined into the component to be anodized should be reamed or machined slightly oversized to take into account the anodized finish by adding slightly to the inside dimensions of the hole. If not, a hole that is too narrow for the pin or component to fit into the hole once the piece is assembled. For anodized surfaces that are not critical to lubricating properties, sealing of the surface is often required once the anodization is complete. Immersion in very hot water is usually all that is needed to close the small holes left in the surface of the anodized metal.
By placing aluminum in a bath of liquid chemicals that are often nothing more than acetone and applying an electric current through the aluminum component, a chemical reaction similar to a type of rust forms on aluminum. This rust-like material is the anodized finish and actually works to increase the surface strength of the aluminum. Similar to gold or silver plating, the color of the anodized finish depends on the types of metal sheets dipped in liquid chemicals.
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