Acorn Surface Technology

On exposure to air, Aluminium will immediately form a stable oxide layer. This natural oxide film is, however, very thin, approximately 1/100th of a micron, is easily damaged and provides little corrosion resistance under normal atmospheric conditions. 

Anodising is the controlled formation of an oxide coating on the surface of components made, primarily, from Aluminium and its alloys. The anodic coating is produced by passing an electric current through a dilute Sulphuric acid solution, Hydrogen is released at the cathode (the negative side of the cell) and Oxygen is formed at the anode (i.e. the work piece) forming Aluminium oxide. The thickness, density, hardness and colour of the coating can be varied depending on the solution and the processing conditions. 

By modifying the processing conditions and electrolytes, a wide range of properties and coatings can be achieved, making anodising an ideal surface engineering technique for a wide range of applications.

The Main Anodising Processes 

Sulphuric Anodising 

Sulphuric anodising or 'normal' anodising is used extensively for general protective and decorative applications. It produces a clear film which can be left natural or dyed to produce a range of colours, depending on the base material used. 

The nature of sulphuric films enables them to be used with a range of pre-treatments to produce a variety of attractive visual finishes. 

Chromic Anodising

Chromic anodising is normally used for the corrosion protection of critical engineering components that require only a thin film, with minimum dimensional effect, or to ensure maximum fatigue integrity. 

It is also used for crack detection and is an ideal pre-treatment for paint. 

Chromic anodising is the preferred treatment for components containing deep crevices, since any residual electrolyte is non-corrosive to Aluminium. 

Hard Anodising 

Hard anodising uses formulated acid solutions normally operated at low temperatures, under high current density and voltage conditions. This produces an exceptionally hard coating with excellent wear, abrasion and corrosion resistance, and high electrical resistivity. "Hardas", "Hardex" and "Dioxal" are variations of the hard anodising process all in use at Acorn Surface Technology, selected for use depending on the design requirements of the application. The colour of the anodic film will depend on the alloy type used as well as the process. 

Hard anodised films are usually supplied unsealed for maximum abrasion resistance, but can be further treated with dyes, solid phase lubricants or chemically sealed for high levels of corrosion protection. 

By careful selection of the correct processing conditions, anodising can offer the complete answer to many Aluminium protection problems.


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(previously Acorn Surface Technology Ltd)

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