In the anodic oxidation of aluminum, unlike in conventional varnishing, no further layer of other material is created on the surface, but the surface of the aluminum material changes to alumina. This layer prevents further corrosion of the material and is much more resistant to abrasion and scratching than the original material. The layer has a microporous structure that can be filled with color and subsequently sealed, so that the surfaces coloured this way are compact and non-peelable.

Anodizing process:

The components are fastened to a hinge and pass through the individual tubs of pretreatment baths, such as degreasing, pickling, and brightening, to anodizing bath, where the hinge is subjected to electrolytic process in a sulfuric acid solution where oxygen is formed on the surface of the components and oxidizes basic Al material to alumina. In natural anodizing, a layer of 10 to 20 µm is formed and is used for decorative anodizing, in hard anodizing a layer is formed in thicknesses of 10 - 80 µm. Subsequently, electrolytic or organic coloring processes and various sealing types are optional.

During sealing the porous structure of the oxide closes, obtaining high corrosion resistance. The resulting anodized material becomes smooth, hard and more chemically, corrosion- and wear-resistant than the metal itself.

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Layer growth

The oxide layer in the anodic oxidatiaon process grows both inwards and outwards from the original surface, while the nominal outward growth, i.e. increment is about 50% of the layer thickness. This means that with a layer thickness of 30 µm, the oxidation layer will cause a reduction of the hole 2x15µm = 30µm.