The Process

The Problem

Steel generally corrodes between 0.05mm and 0.125mm per year when freely exposed to air. However, in heavily polluted regions this rate can increase considerably. In many situations the natural corrosion rate would be acceptable purely from a safety point of view, but the appearance of flaky rust on steel is generally unacceptable. The protection therefore is more often than not to preserve the general appearance rather than the structural strength of the material.

At the normal Galvanizing temperatures of 445-465 deg centigrade, the rate of reaction is very rapid at first, with a 'boiling off' action. The main thickness of coating forms during this initial period and it is therefore impractical for the galvaniser to form a very thin coating. The normal period of immersion is a minute or two but longer for work that requires draining from internal spaces or is particularly heavy.

 

The Solution

When immersed in the galvanizing bath, iron or steel are immediately wetted by the zinc and react to form zinc-iron layers. As the work is removed from the bath, some molten zinc is taken out on top of the alloy layers, the whole coating being metallurgically bonded to the basis metal.