The anodising process applies to the metal surface a coating of aluminium oxide. The nature of the process is such that adhesion of the oxide to the substrate can be taken for granted, unlike ceramic and other coatings which are dependant upon cleanliness and other factors. The melting point of aluminium oxide is over 2000C, which is far above that of the metal itself, and it is largely unaffected by temperatures within the useful range of the metal.
Sealing, dyeing and Ano-lube treatments do not share the properties of the oxide itself and trials should be carried out to establish their suitability at elevated temperature.
Coatings are unaffected by sub-zero temperatures except insofar as differential contraction between oxide and metal may give rise to a greater tendency to crazing; this effect is dependant upon alloy, process conditions and the physical shape of the workpiece, so trials should be carried out to determine suitability.
APPLICATIONS INCLUDE:
Protecting turbo diesel engines piston crowns...
The ever higher ratings demanded by users necessitate higher charge pressures which entail higher temperatures and mechanical stresses at the piston crown, beside thermal cycling over a wider range. Conventional aluminium pistons begin to suffer failure, and the methods of protection tried anodising has the advantages of cheapness, insignificant weight increase and reliability. Thousands of pistons are anodised each week, many of them demanding quite complicated masking to ensure that only the required areas are anodised. Coatings of up to 120 microns have been produced on pistons made from LM13 alloy.
Parts for cryogenics equipment...
In which the insensitivity of the oxide to temperature change, coupled with chemical inertness and general cleanliness gives an attractive combination of properties.
Electrical coilwinding materials...
Where the extreme thinness of the coating compared with organic insulants gives excellent space factor and heat dissipation coupled with extreme resistance to 'hotspots' to provide good reliability at an affordable price.
