Anodising is a chemical process that leads to a rise in the oxide layer thickness on the surface of aluminium. In its natural state, the layer is highly thin. Since the layer is attached to a soft metal, it is susceptible to damage. The thicker layer protects the integrity of the aluminum underneath it.
The coating produced by anodising the metal is more proof against laceration and corrosion. In some cases, the oxide layer is permeable allowing the method to add color. This gives the aluminium a protecting finish that's also decorative.
Makers of appliances, automobile parts and marine clobber use this process. Architectural pieces including doors and windows are commonly anodised. The process assists in producing lighting equipment, furniture and certain sporting products.
Correct coating of a part needs preparation. A feeble alkali solution washes away any oil or grease sticking the surface. Etching of the surface removes any heavy oxides that can interfere with the coating. The method of etching leaves insoluble material on the surface and requires submersion in a desmut solution to get rid of it. Water rinses the part and completes the preparation process.
The step after that is to submerge the part in an acid and water mix. The acid used relies upon the desired coating. Organic acids work best for hard coatings while sulphuric acid is utilized for soft coatings that accept dye easily.
With the appliance of direct current, the water breaks down and oxygen deposits form on the aluminum part. This forms the oxide film. When the anodic film is the desired thickness, the processor takes away the part and washes away the acids.
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3 different systems of coloring are employed in this process. Full immersion in an inorganic pigment or organic dye will allow the film pores to take in the colour. UV radiation has no effect on some inorganic pigments but nearly all organic dyes will change color with prolonged exposure to UV rays.
Integral color involves processing the part and manipulating assorted parameters. The electrolyte composition, current density and temperature react with the metal’s alloying elements to provide varied colours. The intermetallic particles are coloured and spread thru the film.
Electrolytic deposition is the 3rd way to add colour. This is a method where the anodic film base accepts deposits of oxide particles and stable metals. After sealing, the clear film locks in the required colour.
Clear or coloured films are equally effective in defending the metal surface. When utilised for exterior architectural or structural applications the coating thickness goes from 20 to 25 microns. This is also a suitable range for marine applications. The film thickness may be as little as 10 nanometers for some environments.
Anodizing is a useful way to strengthen the structural integrity. It also defends the part from abrasions, corrosion and exposure to the elements. It is widely used in the sea industry because it gives great protection against the tough climate, which can cause damage to metal. The process is not used in places where parts bend because the film can crack.
Badger Anodising (Birmingham) Limited are a UK based anodising, metal finishing and metal polishing company. Alumimium extrusion gets passed to the company and they can then work their wizardry.