Sulphuric acid anodising is a controlled electrochemical process that thickens aluminium’s natural oxide. The resulting layer is hard, adherent and porous enough to accept dye before sealing. Because growth occurs partly into the metal and partly on top, dimensions change only modestly when the process is planned correctly.
What the Process Does
In an acid bath, the aluminium workpiece becomes the anode while current passes through the electrolyte. Oxygen forms at the surface and builds a uniform oxide with fine pores. By adjusting temperature, acid strength and current density, technicians balance hardness against speed and porosity against dye take-up. The appeal is practical: improved wear resistance, better paint adhesion and reliable corrosion protection after sealing.
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Steps in a Typical Setup
Preparation matters most. Parts are degreased, lightly etched and rinsed, then racked for good electrical contact. They enter a chilled sulphuric electrolyte where current is applied for a set time to reach the target oxide thickness. Rinsing follows, then optional colouring. Finally, sealing in hot water or nickel acetate closes the pores and locks in the finish.
Applications, Finishes and Care
Everyday uses include camera and optical components, fixtures, valves and aerospace hardware. Clear, black and bright colours are common, while matte or satin textures depend on the pre-treatment.
Maintenance is simple. Wash with mild detergent, avoid abrasive cleaners, and re-seal only if a harsh environment demands it. With the right preparation, sulphuric acid anodising delivers durable, attractive surfaces for many sectors.