Anodising Glossary
Anodising is extensively used for the production of protective and decorative films on aluminium. The most widely used processes for preventing oxidation of aluminium are based on sulphuric acid and chromic acid.
Hard Anodising
Hard anodising is mainly applied to components for the production of hard wear-resistant surfaces on aluminium for the aerospace industry and general engineering uses.
The coating has exceptional wear resistance and excellent mechanical strength. Hard anodising provides very good corrosion resistance and can withstand short exposures at temperatures up to 2000°C.
A dark grey deposit is applied to components which has been hard anodised. However the smoothness can be dependent upon the thickness deposited, and can be reduced if the base metal has been previously polished.
The usual thickness of Hard anodising applied on a commercial basis is 25 microns (0.001”) or to the relevant BS or Aerospace spec.
Chromic acid process
The chromic acid process is ideal when high resistance to corrosion is required, and where non-destructive testing is a subsidiary requirement.
The chromic film is an excellent undercoat for paints and lacquers. The coating is also suitable for parts which are in contact, or near contact with explosives. The chromic acid film is relatively thin and produces an opaque grey / black decorative finish.
Sulphuric acid process
The sulphuric acid process allows for a wide range of film thicknesses and gives excellent corrosion resistance which can also be enhanced by sealing in a chromate solution. The film can provide a range of surface textures with many different finishes. Matt, satin or a polished finish may be produced with this type of process.
After sulphuric anodising EIC Finishing Services can offer a wide range of dyes to give a very attractive finish:
- Black
- Blue
- Red
- Gold
- Green
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