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The Hot Dip Galvanising Process


The hot dip galvanising process starts by suspending steel articles and dipping them into a series of cleaning baths. Once cleaned, the steel is lowered at an angle into a bath of molten zinc.

Immersing the steel on an angle allows air to escape from vented tubular shapes or pockets that may be within the design and permits the molten zinc to displace the air.

The steel reacts with the molten zinc to form the galvanised coating. After being withdrawn from the zinc, the final step in most hot dip galvanising processes is a quench to promote passivation of the zinc surface.


Structure of Coating

The formation of the galvanised coating on the steel surface is a metallurgical reaction, where the zinc and steel combine to form a series of hard intermetallic layers. The outer layer is, typically, 100% zinc which covers the surface after withdrawal from the molten zinc bath.

The gamma, delta and zeta alloy layers are all harder than the base steel they are metallurgically bonded to, which gives hot dip galvanising its great abrasion resistance.

The galvanising process naturally produces coatings on the corners and edges which are at least as thick as the coating on the rest of the article. As the reaction between iron and zinc is a diffusion reaction, the crystalline structure of the coating forms perpendicular to the steel surface.


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