Anodizing at Anodex Finishing Inc

Anodizing Technical Information

  • Certified MIL-A-8625E Type-2 Class-1 and Type-2 Class-2 anodizing.
  • Chromate conversion - clear & gold
  • Passivation

Blue Anodization

Tank Size: 6-ft x 2-ft x 3-ft

Red Anodization

Tank Size: 2-ft x 2-ft x 3-ft

Gold Anodization

Tank Size: 11-ft x 5-ft x 4-ft


Black Anodization

Tank Size: 11-ft x 5-ft x 4-ft

Clear Anodization

Tank Size: 11-ft x 5-ft x 4-ft

Anodizing is the formation of a layer of oxide on the surface of an aluminum piece, using a bath of dilute sulfuric acid as an electrolyte, and charging the piece electrically. This is where the name comes from; the piece being anodized is the anode, or positively-charged pole of an electrical circuit. In the anodizing bath, usually a large lead plate is also immersed in the electrolyte, which becomes the negative ground pole, or cathode. While magnesium, titanium and even copper can be plated similarly to aluminum, the process is rarely used for those metals, and does not provide as wide a range of colors. Steel, iron, stainless steel, brass and other metals cannot be anodized. In fact, if a steel or iron part is left on the piece to be anodized, such as a setscrew or plug, it will react violently with the charged electrolyte bath, usually burning itself away, as well as heavily eroding the aluminum piece.

The electrical charge and mild acid oxidize the surface of the aluminum, forming microscopic crystals of aluminum oxide. This oxide surface is very hard, much harder than the base material, but very thin, often only a thousandth of an inch. While most aluminums average about 35 to 40 on the Rockwell C scale, the oxide layer is closer to 52 to 55. A file, usually very hard steel, is often 55 to 58 Rockwell C. Most automotive-grade ("wet & dry") sandpapers use aluminum oxide grains as the abrasive. The anodizing prevents further oxidation, so the piece wont rust or corrode any further, and also makes the surface much more wear and scratch resistant.

The anodic layer is also very porous as it comes out of the bath. Because of this porosity, it will absorb and hold dyes and colors well. The piece is usually colored simply by dipping it in a vat of concentrated dye for several minutes. Once the piece has been dyed, it is sealed, simply by immersing it in clean, boiling water for several more minutes. This process, because of the porosity of the oxide, hydrates the crystalline layer, which swells the oxide, closing the pores, sealing the dye within. Because the layer is so thin, the dye must be heavily concentrated, and even then, the color will be somewhat translucent. This is what gives the color anodizing its characteristic metallic sheen; the shiny base aluminum shows through the color. Because of this semi-transparency, the piece cannot be anodized white; the aluminum would show through, giving a light grey color.


Anodex Finishing

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