Southampton Model Aeroplane Club

Established 1932

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Home workshop anodising

By Nathan Attridge

Anodising is a protective and decorative surface treatment used to enhance the working qualities and visual appeal of items made from a range of metals including aluminium alloys, zinc and titanium. The treatment involves manipulation of the natural oxide layers on the metals to produce thicker and more durable films. These enhanced oxide layers lend the items increased resistance to wear and corrosion and provide surfaces which are more receptive to paints, dyes, and adhesives.

The anodising process involves passing an electric current through an electrolyte solution between a positively charged anode, in this case the anodised item, and a negatively charged cathode. This resultant reaction changes the crystal structure of the anode surface and causes a layer of oxide to be deposited on it in what is known as an electrolytic passivation process. The characteristics of this oxide film can be manipulated during this process, thereby allowing for a high degree of control over the end result. Generally the synthesized layers are more robust than those occurring naturally. As a matter of interest, the anode role played by the product is the source of the anodising name.

Anodised oxide layers are porous and require the application of sealant to ensure maximum corrosion and wear resistance. The film's adhesion to the metal is far stronger than conventional plating or painting films though, thus making anodised finishes particularly durable. This durability offers an excellent base for the post-treatment application of paints and dyes, with coloured anodised finishes exhibiting outstanding longevity even with continuous use. Anodising also helps prevent galling, or adhesive wear, of threaded or sliding parts at their points of friction. For this reason myself and Barrie have anodised some moving parts for a disk valve induction system on an MB40 pylon racing engine.

Anodising at home can be a very easy process if you buy an anodising kit from a specialist website or from eBay for a cost of around £00.

Step by Step DIY anodising of aluminium

Air retract unit by Nathan Attridge

Pneumatic retract unit for F3D pylon  racing model Rear induction backplate for  MB40 racing engine