Architectural anodizing is anodizing to produce an architectural finish to be used in permanent, exterior situations where both appearance and long life are important. Such applications include window frames and facade coverings.
The specifications for architectural anodizing can also be applied to anodizing and products that are used in other outdoor applications where both appearance and long life are important. Such applications can include automotive ones.
Anodized aluminium has been used in external architectural applications since the 1930s. Some surviving buildings are now about 80 years old and the anodized aluminium is still in good condition. Well-known examples are the Montecatini building in Milan and the New Bodleian (Weston) Library in Oxford, which were both completed in the late 1930s. Such examples demonstrate that anodized aluminium can have excellent weathering resistance.
Customers and users of anodized aluminium for architectural applications are interested that the initial appearance of the anodized aluminium is retained to a great extent, with maintenance as necessary, over the design lifetime of the component. A long service life can be expected from good quality anodized aluminium. Scientific investigations have been undertaken where samples of anodized aluminium were tested at outdoor exposure sites for periods up to 20 years. A thickness loss of 0.2 to 0.4 µm per year for coatings initially 10 to 25 µm thick was typical for urban areas. The thickness loss was similar or slightly less for marine areas and negligible for rural environments. The highest rate of thickness loss was 1.2 µm per year for a heavily polluted site in the middle of a steel-making area.
The important product quality criteria are:
- visible defects, surface texture and, if appropriate, colour
- coating thickness
- coating quality
- sealilng quality
- light fastness
The inspection of QUALANOD-licensed anodizing plants includes the testing of samples of anodized products to verify that the correct quality is being achieved.