Finishes For Aluminium Anodising

The process of anodising thickens the natural aluminium oxide film to typically 10-25 micron. The component is immersed in sulfuric acid and elec-trolytically made anodic, which converts the surface metal into a porous aluminium oxide film, which is then sealed by boiling in water. The anodising process increases durability and can be used for trapping dyes within the surface to produce a wide range of coloured products. Some dyes fade with exposure to sunlight, the most durable colours being gold, blue, red and black. Exact colour matching for replacement or extensions to existing buildings may be difficult, and manufacturers will normally produce components within an agreed band of colour variation. If inorganic salts of tin are incorporated into the surface during the anodising process then colour-fast bronzes are produced. Depending upon the period of exposure to the electrolytic anodisation process, a range of colours from pale bronze to black may be produced. Different aluminium alloys respond differently to the anodising treatment. Pure aluminium produces a silver mirror finish, whereas the aluminium-silicon alloys (e.g. alloy EN AW-6063) produce a grey finish.

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