The application at industrial scale of hot dip galvanizing is now 200 years old. Yet it remains a very effective way to protect steel from rust. The process consists of immersing the steel in a 450 °C.
In order to remove greases and oils from the steel, it is first immersed in a degreasing bath. After a rinse, all surface oxides, such as rust and calamine are removed in a pickling bath consisting of diluted hydrochloric acid. Rinsed once again and the perfectly cleaned steel is ready to be “fluxed”. The flux bath consists of ammonia zinc chloride, a small layer of which protects the steel surface against oxidation while waiting for it to come into contact with the hot zinc. A small flux layer is melted into this, which gives excellent metallic contact and assures a good irrigation of the steel through the zinc. With the immersion into the zinc dip, the steel gradually takes on the temperature of the zinc. Diffusion occurs that gives rise to the forming of zinc-iron alloys. During this process, a layer of pure zinc is deposited on top of the alloy layers. Not all gates and fencing are treatable by hot dip galvanising. The processing of perforated or full steel plates entails that if they are hot dip galvanised, on the one hand, the perforations would be full of zinc and on the other hand (in the case of larger surface areas) the plates would be warped by the high temperature. These types of gate and fencing have to be metallized.