Anodising for preserving aluminium
Anodising is a synthetically accelerated electrochemical oxidising process strengthening the natural oxide skin of aluminium. As a result, the transparent oxide layer becomes considerably thicker than the natural oxide film. This way, the aluminium is given a strong corrosion resistance and long-term protection. Thanks to the transparent layer the metal character is maintained.
Special features of anodising
The various anodising processes, such as anodising, hard anodising, Nituff®, CompCote® or colour anodising, result in anodised layers with different features. For instance a specific layer thickness, a certain colour or hardness, high resistance to wear, strong anti-corrosion or sliding features.
How does anodising work?
In a bath with diluted sulphuric acid the aluminium parts are connected to the positive pole – or anode – of a rectifier. The electrochemical process creates oxygen (O2), which binds directly with the aluminium to form aluminium oxide (Al2O3). After the anodising all sulphuric acid rests are carefully rinsed out from the pores of the anodised layer. The newly formed aluminium oxide can still absorb pigments or other substances immediately after the anodising process. Through sealing, during which the pores in the layer are condensed, the surface converts in a sealed layer, creating a corrosion-resistant layer that stays clean and preserves its colour. Anodised aluminium is easy to recycle because the aluminium is protected by a metallic coating.
The result of the anodising process depends on:
- the aluminium alloy
- the anodising system
- the anodising procedure
- the required or desired pre- and after-treatment.
Technical features of anodising
Depending on the applied process and the alloy used anodised layers have the following features:
- layer thickness up to 100 micron (μm)
- hardness up to 600 micro Vickers
- resistance to wear is higher than that of hardened steel
- break-down voltage ca. 40 Volt/μm
- the aluminium no longer gives off black smears
- resistant to most chemicals and solvents
- the layers can be applied locally with a very high accuracy
Maximum dimensions for anodising
Length: up to 7.30 metres
Width: up to 0.6 metres
Depth: up to 1.10 metres
Deviating sizes may be possible on request.
Hard anodising
In hard anodising the aluminium is given a very thick, hard layer, but in spite of the layer thickness the aluminium still maintains an accuracy margin of ca. five micron. Hard anodising is resistant to extreme high loads and offers a higher resistance to wear than hardened steel or hard-chromium plating. It offers a very high scratch-resistance and a high electric insulation. Hard anodised aluminium is suited for pistons, cylinders, gear wheels, shock absorbers, pulleys and the ironwork of vessels.
Nituff®
Nituff® is a hard anodised layer impregnated with polytetrafluorethylene (PTFE or Teflon®), making it superior to normal hard anodised layers with an improved resistance to wear, high corrosion-resistance and excellent non-stick features. It also creates a self-lubricating, sliding anodised layer with low frictional resistance. These impregnated anodised layers are particularly suited for textile factory machines and are frequently used in the food industry (approved of by the FDA) and in moulds for the plastics industry. Nituff® must be cleaned less frequently and requires only little maintenance.
Both Nituff® and hard anodising can only be applied on aluminium alloys. Most alloys can be treated, but those with a low copper and silicon content give the best results. On Aluselect you’ll find a comprehensive (English) database of the most commonly applied aluminium alloys.
CompCote®
CompCote® is an oxide polymer composite coating for aluminium and aluminium alloys. Thanks to its dense structure, the composite layer offers significant improvements compared to conventional (hard) anodised sulphuric acid layers, resulting in:
- improved corrosion resistance
- higher resistance to wear
- improved colourfastness under UV-light
- smoother surface
- higher tenacity, breaking strength and fatigue strength
- excellent adhesive features
- anodised layers on heavily alloyed aluminium alloys
Colour anodising
The silver-white anodised aluminium is timeless and that is no luxury considering the product’s sustainability. However, anodising can also be combined with a considerable number of colours. You can check the colour chart of Anox. The special metallic character of the aluminium is preserved when anodising in colour.
Anografic®
Anografic® is a sustainable, digital printing technique enabling wear-resistant printing on anodised aluminium. Text or image, such as logos, photographs and trademarks, are printed pinpoint-sharp in the hard, wear-resistant anodised layer. Anografic® is highly wear-resistant, resistant to scratches, solvents and chemicals and offers an excellent image quality and colourfastness. The technique can be applied on cylinder shapes and surfaces of 1 by 1.5 metres.
