Mass production of aluminum structures and parts is associated with the unique properties of this material. It has a minimum specific gravity, is resistant to many aggressive environments and is easy to process. But for long-term operation of products, it is necessary to anodize aluminum.
Why is it necessary
During the interaction of any metal with oxygen contained in the atmosphere, the surface layer is oxidized. This is called the formation of an oxide film, which prevents the spread of rust into the metal.
Depending on the type of material, the process of surface oxidation takes place in different ways. Iron and steel practically do not form an oxide film, but precious metals (gold, silver, platinum) are protected from corrosion. Aluminum occupies a middle position, therefore, it requires the artificial creation of a film. This is especially important if a similar profile is used in the manufacture of windows. Anodized aluminum is resistant to the effects of external weather factors, which can lead to corrosion and a quick loss of the structural performance.
Technology
In order for an effective protective film to form on the surface of the profile , anodizing of aluminum is required. The essence of the process is the transfer of molecules of another material, which is more resistant to oxygen, in the structure of the product. In addition, it is possible to artificially increase the oxide layer without the addition of other metals.
Regardless of the selected method, it is necessary to fulfill the conditions of the process. It consists of the following steps:
- Preparatory.
- Anodizing process.
- Securing the layer.
For each of them, the appropriate equipment and supplies are selected. The result should be high-quality anodized aluminum. This will make it possible to use the profile for the manufacture of facade and window structures.
Preparatory stage
The surface of the product is thoroughly cleaned of dust, dirt and debris. If there are irregularities or mechanical damage, then they are eliminated even before anodizing. Next, remove the old oxide layer, otherwise it will prevent the uniform formation of a protective film.
After mechanical processing (grinding and degreasing), the profile must be placed in an alkaline solution. To properly anodize aluminum, you must first “etch” its surface. The formation of microcavities and irregularities increases the total area of the protective layer. Next, in an acid solution, the product is clarified. Upon completion of all steps, the aluminum must be thoroughly rinsed.
Anodizing
After passing through the preparatory phase, you can begin the process of anodizing. For this, an aluminum product is immersed in a special bath. The procedure is performed using crane equipment (for large structures) or manually using ropes.
It is necessary to say separately about the design of the bath. It represents a large capacity of thick-walled stainless steel, in which 2 cathodes are placed. The technology of immersion of the profile should be such that the electrolyte in the bath contacts the entire area of the product. Sulfuric acid is used as such a liquid, which places special demands on the safety of production. If the product has a complex configuration, it is better to use oxalic acid.
After immersion of the profile by electrolysis, a protective layer begins to form. Its thickness directly depends on the composition of the electrolyte, temperature and current density. The higher the latter, the more oxide film will form on the surface. After completion of the procedure, the layer thickness can vary from 2 to 7 microns, depending on the technological parameters of the process.
Fastening
However, it is too early to stop anodizing aluminum at this point - it is necessary to fix the formed surface layer. It will adhere to a porous structure that will quickly peel off without treatment. In addition, it does not have the required hardness characteristics.
Fixing can be done by placing the product in fresh water, brought to a boiling state. According to another technology, the surface is treated with hot steam. In any case, the oxide film is rejected and its molecular compound with the aluminum surface.
If in the future the profile is painted, then the fastening can be omitted. Subject to the powder coating technology, the film will be protected by heat treatment.
We found out what anodized aluminum is. Such metal processing is a guarantee against the appearance of rust on the surface of the product. Anodizing technology is constantly being improved, and today it is possible to paint aluminum products using the cathodic reaction.