Galvanizing is a method of protecting a steel surface from corrosion by providing a surface coating of Zinc. Galvanised coatings corrode preferentially to steel, providing sacrificial or cathodic protection to small areas of steel exposed through damage to the coating. Unlike organic coatings no touch up is needed.
The galvanising process involves the following stages:
- Any surface oil or grease is removed by suitable degreasing agents.
- The steel is then usually cleaned of all rust and scale by acid pickling. This may be preceded by blast cleaning to remove scale and roughen the surface but such surfaces are always subsequently pickled in inhibited hydrochloric acid.
- The cleaned steel is then immersed in a fluxing agent to ensure good contact between the steel and zinc during the galvanising process.
- The cleaned and fluxed steel is dipped into a bath of molten zinc at a temperature of about 450oC. At this temperature, the steel reacts with the molten zinc to form a series of zinc/iron alloys integral with the steel surface.
- As the steel workpiece is removed from the bath, a layer of relatively pure zinc is deposited on top of the alloy layers.
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