Aluminium Anodic Oxidation is the second type of aluminium surface treatment after aluminium powder coating treatment that we dealt in detail in our previous blogpost.
The anodic oxidation – also called anodising – is an electrolytic process by which an oxide layer is created on an aluminium surface.
Why prefer Anodic Oxidation?
This oxide layer is more than hundred times thicker than the naturally formed layer. This way weather resistance and also resistance against chemical pollution is ensured. Additionally, the metallic character of profiles is being conserved over a long period.
Due to practical experiences as well as through weather experiments such as outdoor exposure in countryside, town, industrial and maritime climates, it was found that certain layer thicknesses are required to achieve a certain protective effect. In the building industry, protective layers of 20 μm are usual for outside applications (up to 30 μm for industrial atmosphere).
Next to thickness, proper compression is crucial for good protective effect of the oxide layer. Proper regular cleaning is required to retain the protective effect and keep it looking good.
Anodising is carried out according to quality control of EURAS/EWAA guidelines (Called QUALANOD now). QUALANOD is a quality label organisation founded in 1974. It is a standard set by several national associations encompassing architectural anodizers in the European Anodizers Association (EURAS) and in conjunction with the European Wrought Aluminium Association (EWAA). This organisation is committed to maintaining and promoting the quality of anodised aluminium and its alloys.
Evaluation of decorative looks of colour and structure is done without any aids, for outside viewing from a distance of 5 m, for inside viewing from a distance of 3 m.
Pre-treatment of anodised aluminium parts through transparent oxide layer is crucial for optical effect. Chemical pre-treatment through pickling (results in matt surface) or mechanical pre-treatment through brushing, sanding or polishing.
Types of anodized surfaces
As a consequence to the above varying types of pre-treatment, various types of surfaces-dull, even-looking surface, gloss-surface, even light surface, smooth glossy surface or matte rough surface can be made. Two versions which imitate a metal surface look like stainless steel. As the surface treatment is based on anodising, the application is only available for aluminium elements in anodised quality.
Limitations of anodized aluminium surface treatment:
Although, this treatment has a lot of pros, there are reasons that weigh it down as listed below:
- With the anodised version, big colour differences can occur between aluminium profiles and aluminium sheets. Special sheet quality (Alcan red dot) is required to achieve a good match between profile material and aluminium sheet. Sheets with the conventional anodised quality are not sufficient.
- Quite a few of the parts of the doors and windows are not available anodized. Eg: Two-coloured portal profiles,Designer panels,glass covers (e.g. aluminium entrance door model ET-F); Ray connection (no anodised quality),
- With wielded (heat-treated) aluminium elements, structure difference can become a source of possible marks through heat treatment of semi-finished products. Please note this is specifically with weld connections (threaded bolt).
- Untreated semi-finished aluminium elements need to be stored in dry ventilated rooms as otherwise there is danger of pre-corrosion. Furthermore, always wear clean gloves during processing to prevent formation of corrosion (sweat from hands).
- One of the biggest disadvantages of anaodized surface treatment is that once scratched, it cannot be fixed or re-done.
But this is where Internorm’s aluminium anodized coated products have a higher edge over the other products as they are available in durax al colours. The option of having the durax al colours is advantageous in terms of getting them re-touched and re-done when scratched. So, it is highly recommended that one goes for durax al colours if you are choosing aluminium anodized oxidized surface treatment for your Internorm windows or doors. Below is a list of DuRAxal colour options that is available for Internorm products.
With the brief explaination on the topic above, one needs to weigh the pros and cons of using anodic oxidation versus other forms of aluminium surface coating.
Internorm uses both powder coating as well as anodic oxidation as methods of surface treatment on aluminium products.