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Colour with the power of anodisation

Colour with the power of anodisation

Anodisation of aluminium profiles is done for several reasons: for extra corrosion protection, to repel dirt, to ensure a better glue seal or coating adhesion or just because it looks more attractive.

The anodisation process consists of a number of phases: pre-treatment, anodisation, colouring (possibly) and sealing. The anodised layer - coloured or uncoloured - is transparent.

In pre-treatment, the staining, a certain quantity of aluminium on the surface of the profile is dissolved. This produces a completely smooth, matte surface. Tint and dullness will depend on the alloy that is used. The aluminium that is dissolved at this stage is collected as aluminium hydroxide sediment. After separation, the sediment can be reused as a component or discarded.

In the anodisation bath, a profile is connected to a source of direct current at the anode (hence the name), while the cathodes are found on the side of the bath. The bath usually consists of diluted sulphuric acid at room temperature. With this electrolysis process, the metal surface is converted into metal oxide. The process is completed when the required layer of thickness is attained.

The layer of oxidation that is formed, generally between 5 and 25 µm in thickness, is porous. In order to achieve a perfect seal, the pores must be sealed off. This is done in a water bath, with sealing occurring at boiling point. The final result is an extremely hard, sealed layer that protects the aluminium. Colour and layer thickness are variable and depend on specifications. Sapa Profiles Nederland anodises both horizontally and vertically up to a maximum of 7,800 mm.

Updated: 2012-07-19