January 21, 2008

Aluminum Anodizing

aluminum anodized product
anodized aluminum product
Article Contents:
Aluminum Anodizing Practice
Aluminum Anodizing Steps
Alkaline Solution Treatment
Racking and Rinsing
Sealing and Coloring
Polishing after Anodized
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Aluminum Anodizing Practice

Aluminum anodizing is a process to cover aluminum surface with substance below the oxidized aluminum layer on the surface. This layer is very thin and transparent so the substance below this surface can be seen and can be coloring etc. To make aluminum surface have good color usually use textile coloring agent.

The electro deposition of anodized aluminum has been investigated for use in coating steel strip, in electrorefening and in the cladding of uranium. Upto 76-cm diameter parabolic mirrors have been electroformed in 750-liter solutions. Limited commercial applications of aluminum plating have been reported.

Aluminum, because it is much more chemically active than hydrogen, probably cannot be electrodeposited from solution that contain water or any other compound with an acidic hydrogen, for example, acids, alcohols, esters, ammonia, and primary and secondary amines. It can be electrodeposited from inorganic and organic fused salt mixtures and from solutions of aluminum compounds in certain organic solvents, only the National Bureau of Standards hydride process has achieved a modest degree of use and is considered in this chapter.

Aluminum Anodizing Steps:

The step to anodized aluminum should be as follows:

1. Electropolishing of Aluminum

Before the aluminum being proceed by anodizing, the material must treat use electropolishing first, this process will open the surface film above the aluminum surface, because in the store or travel after the aluminum be produced will react with free air build an aluminum oxide that cover the surface of aluminum. On this process aluminum oxide film like being peeled up. To open the surface pore can't use just dipped in water but must use electric current. Even if dipped in hot water the pores still closed. To open before aluminum anodized should proceed in electric current on the acid solution.

2. Alkaline Solution Treatment

The next step of aluminum anodizing is treated in alkali solution. The concentration of free alkali in the solution is one of the major factors which determines the program of the polishing process when treating aluminum in an alkaline solution. Although alkali is not one of the constituents used in making up the solution. It is formed in the bath as a result of hydrolysis. As the solution is used, the concentration of free alkali rises as a result of reaction of aluminum with sodium hydrogen phosphate. The optimum of alkali in the solution is 15 – 18 gram per liter.

3. Rinsing

Rinsing is a process that does in between of aluminum anodizing process step, rinsing also do in preparation for plating. The result quality will depend on the rinsing process, if many chemicals or organic substance left on the metal surface will result a bad electroplated or anodized product.

4. Jigging

Jigging is a process to parts which have been polished with polishing pastes are degreased using organic solvent, such as benzine or dichloromethane, and are dried in air until the traces of the solvent is disappeared. They are then mounted on anodizing jigs made of aluminum or clad alloy. The design of the jig requires special considerations. It should ensure a firm contact with both the work and the anode bar and at the same time the area of contact should be as small as possible because this area will remain not anodized. It should be just sufficient to avoid local heating of the metal, which is usually the cause of an attack on the surface of the work during the anodizing process.

5. Aluminum Anodizing

Aluminum anodizing takes into account the composition of the solution, the alloy and the service requirement. To maintain the required temperature cooling arrangements in the case of sulfuric acid anodizing and heating solution is agitated by means of compressed air which is introduced trough a perforated coiled pipe arranged along the bottom of the vat. The cathodes used in anodizing baths, especially those of sulfuric acid, is very great. It is therefore almost unnecessary to use auxiliary cathodes when anodizing of the interior of pipes. If the length of the pipe exceed ten time the diameter, an internal cathode must be used.

6.Racking and Rinsing

Aluminum racks are preferred for plating aluminum alloys. It is recommended that 1100 alloy be used for the spines and 2024 alloys for the contacts. By increasing the cross sectional area of the spines by about 40%, a conductance equal of that of a copper rack is obtained. Where contact marks are not important, regular phosphor-bronze contact may be used. When phosphor-bronze contacts are used, however, the area adjacent to the contact may develop a small blister as a result of galvanic action in the zinc immersion bath. When nitric-hydrofluoric acids etch is used for conditioning, aluminum contacts should be used. Racking and rinsing several time to make sure that the part really clean.

7. Sealing and Coloring

The oxide films obtained after aluminum is anodized have considerable porosity and high adsorption capacity. Sealing of the film increases their resistances to corrosion and improves their electrical insulating properties. Sealing is essential for films that have been produced by anodizing in sulfuric acid, because only after sealing do the film acquire a sufficiently high resistance to corrosion, because surface of aluminum is anodized. The following methods can be used for sealing anodic oxide films:

8. Polishing after Anodized

One of the major applications of anodized aluminum involves the production of finishes resembling bronze, brass, gold, silver and their alloys. In such cases apart from the choice of suitable coloring materials, an important part is played by the conditioning and preparation of the surface of the metal prior to anodizing. A mechanically polished surface become dull after the first four minutes of anodizing in sulfuric acid. The absence of a metallic luster effects the appearance, the dyed film giving the appearance of a plastic surface. To retain the metallic lustrous, it is necessary to produce a passive film capable of withstanding the action of sulfuric acid. This can be achieved by electro polishing. After electro polishing, the surface of the metal retains its luster even after one hour's anodizing. A pretreatment of this nature also helps the production of more intense color.

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Example of Anodizing Products:
Black Anodized Aluminum Bar

Black anodized aluminum bar

Black Anodized Aluminum Sheet:
Black anodized aluminum sheet

Black Anodized Aluminum Part:

Black anodized aluminum part

Black Anodized Aluminum for Electronic Casing:

Black anodized aluminum electronic casing

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