What is anodising?
Anodising, is a form of coating aluminium. It is the successful development and control of a natural oxidation process of aluminium. In fact anodising is a form of corrosion on aluminium which occurs when the metal reacts with the environment. Producing a hard, transparent surface that is integral with base aluminium, is possible through jointly using electricity and chemicals; electrolytic passivation.
Benefits of aluminium coating?
Anodising as aluminium coating brings along many benefits; not only does it give matt finish but also other advantages. Abrasion and corrosion resistance as well as insulation from electricity. Anodising is also suitable for pre-treating aluminium due to the fact that the anodised surface is somewhat rough and thus guarantees better adhesion. Anodised aluminium has also further benefits including:
- A hard saffire-like surface
- A transparent look comparable to matt glass
- The surface becomes insulating and also statically resistant
- It is possible to make the surface appear in a wide range of colours
- The coating is integral with aluminium surfaces and it is non-flaking
The anodising process
Batch (or piece), sheet, and coil anodising all consist of three processing stages:
The aluminium surface is first cleaned and then chemically treated (etching). Etching results in a satin matte appearance and it can appear in various degrees (i.e. light, medium, heavy).
After preparing the surface,it is time to build the anodic film; electrical current is passed through an electrolyte bath in which the aluminium has been immersed. The anodise film consists of the aluminium itself. It is thus not another substance but the original aluminium surface changes its appearance on the surface. It becomes hard and porous. Strictly controlling the coating thickness maybe necessary depending on the end use of the product.
- Post treatment
In this stage the anodic film can get a colour. Organic dyes are suitable for filling pores with colour. It is also possible to electrothermically deposit metal salts at the base of the pores to create a broader spectrum of colours. Many of the colours are fade-resistant. Finally, sealing the anodic film takes place. This normally consists of a hot water bath that basically swells the pores shuts them.
Advantages of anodising
The anodising treatment makes aluminium surfaces easy to maintain; it is possible to periodically clean them with water and a mild detergent which restores its original lustre. Being part of the metal, the anodic coating will not peel or flake and also imparts a translucent metallic appearance. Sunlight does not affect anodic surfaces; the colours are immune to fading. Furthermore, they do not emit VOCs; they are thus more environmentally friendly than many other coatings. Additionally, there is no use of heavy metals in the process.
Disadvantages of anodic coating
Anodised coatings may become vulnerable to acidic pollutants in urban areas. The translucence of the coating may lead to colour variation issues between batches, although this lack of uniformity has not been such an issue in recent times. Furthermore, anodised finishes have a limited range of options and are normally only available in a matt and polished finish. Since anodised finishes can only be applied to aluminium, other building elements in a similar colour may look conspicuously different.
Even before surface treatment, the appearance and surface quality of extruded aluminium profiles is perfectly satisfactory for many applications. Thanks to good corrosion resistance, surface treatment is rarely necessary for only providing corrosion protection. However, there are many other reasons for treating the surfaces of profiles. Surface treatment changes many attributes such as:
- Surface structure
- Corrosion resistance
- Wear resistance
- Electrical insulation
Nonetheless, surfaces do not always need treatment after extrusion. For example load bearing structures and machine parts are products where the surface quality is satisfactory without any treatment.
Anodising aluminium and anodised coatings in Australia
In Australia anodising services are available in all major cities. For example the following providers in Perth and Melbourne.
a division of George Lovitt (Manufacturing) Pty Ltd
202 Holt Parade
Thomastown VIC 3074, MelbourneTelephone +61 3 9464 0922
Fax +61 3 9464 0548
Aluminium anodising Perth
AAEP PTY LTD
Unit: 2 & 3
Address: 29 Gillam Drive KELMSCOTT Western Australia 6111, Perth
Phone: +618 9495 4995 or +61 8 0473 447 323
3 Ladner street
O’connor wa 6163, Perth
(08) 9337 7644
(08) 9337 7234