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Anodizing Improves the Performance of Your Parts

Aluminum Anodizing

Anodizing (conventional Type II sulfuric anodizing) improves the performance of your parts for:

During sulfuric anodizing, no metallics are involved other than aluminum. Unlike electro-deposited metallic plating, where plating builds up by depositing on a base metal, an anodic coating penetrates and grows on the base metal by converting aluminum to aluminum oxide. The ratio of growth/penetration for anodic coatings is typically 50/50.

Proper formation of aluminum oxide coatings provides aluminum with a natural decorative appearance and increased resistance to corrosion and abrasion. Normally between .0001" to .001" thick, sulfuric anodizing lends itself readily to clear and color work, as the coating is more transparent than other types of anodizing. In addition, it serves as a base for color absorption to create decorative finishes. Dyes can be deposited into the pores of the anodized layer and then sealed. The result is a highly desirable, rich, intense, permanent color finish.

Dye Anodizing

Proper formation of aluminum oxide coatings provides aluminum with a natural decorative appearance and increased resistance to corrosion and abrasion. Normally between .0001" to .001" thick, sulfuric anodizing lends itself readily to clear and color work, as the coating is more transparent than other types of anodizing. In addition, it serves as a base for color absorption to create decorative finishes. Dyes can be deposited into the pores of the anodized layer and then sealed. The result is a highly desirable, rich, intense, permanent color finish.

Aluminum can be anodized and dyed to match a given decor or to assimilate a particular metal.

The Anodizing Process

Anodizing entails the immersion of an aluminum part in an electrolyte where an electric current is passed through the part. The surface is converted to aluminum oxide - one of the hardest substances known.

Proper formation of aluminum oxide coatings provides aluminum with a natural decorative appearance and increased resistance to corrosion and abrasion. In addition, it serves as a base for color absorption to create decorative finishes.

Sealing
The final treatment of clear or dyed anodized aluminum is sealing to close the pores of the aluminum oxide and render the coating non-absorptive. Sealing is accomplished by immersion in deionized water containing either nickel acetate, nickel fluoride, sodium dichromate or near boiling ionized water (water chemically distilled to a high degree of purity).

Sealing hard coat yields:

Alloys And Castings:
The Effects On Anodizing Processes

Each alloy anodizes differently because alloy metals change the conductivity of the part and cause it to form aluminum oxide, either faster or slower. All aluminum can be anodized, but some alloys work better than others. Castings tend to give the anodizer the most problems because of the porosity in the castings and alloying materials used.

Properties

Sulfuric anodizing has superb dielectric strength, good abrasion resistance, and excellent corrosion resistance. Type II anodizing is mostly used for decorative anodizing as it lends itself to the dying of light and dark colors, depending on the coating thickness. Where a colorless film is important, as for ornamental purposes or reflectors, Type II anodizing is used. There are some disadvantages to consider when contemplating the sulfuric acid process. The following types of parts should be avoided due to the corrosion nature of sulfuric acid: assembled parts, parts containing welds, joints, and recesses in which the anodizing solution may be retained.

Compatibility

Anodized aluminum is very compatible with other metals due to its dielectric qualities. Aluminum oxide minimizes galvanic corrosion where aluminum touches other metals.

Bright Dip Anodizing

Bright Dip anodizing enhances the glossy appearance of aluminum for cosmetic applications. Common products acquiring this bright dipped anodized surface include decorative trims, light frames, shower doors, carpet molding, and reflectors.

Bright Dip anodizing achieves a highly electro polish finish similar to the quality of plating. In contrast to plating, Bright Dip is a chemical process that brightens aluminum and does not leave deposits on the surface of the part. The degree of brightness is dependent on the type of alloy as well as the surface finish of the part. With some alloys making it more possible than others to get a reflective, mirror type of finish.

After aluminum is Bright Dipped, it can be anodized clear or dyed to a variety of colors. At this point, the anodized aluminum is not only bright, but also protected from corrosion, scratching, and fading by the anodizing process.

This technical information has been contributed by
Alexandria Metal Finishers

Click on Company Name for a Detailed Profile

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