Hot dip galvanising process is the immersion of iron or steel articles in molten zinc to apply a protective coating. All material processed is in accordance with EN ISO 1461: 2009
The galvanising reaction will only occur on a chemically clean surface. Like most coating processes the secret to achieving a good quality coating lies in the preparation of the surface. It is essential that this is free of grease, dirt and scale before galvanising.
Contamination is removed by a series of processes. Firstly, we degrease using a caustic solution into which the component is dipped. The article is then rinsed and then dipped in hydrochloric acid at ambient temperature to remove rust and mill scale.
Welding slag, paint and heavy grease will not be removed by these cleaning steps and should be removed before the work is sent to the galvaniser. After further rinsing, the components are then dipped in a flux solution – usually about 30% zinc ammonium chloride at around 65-80°C.
When the clean iron or steel component is dipped into the molten zinc (at 450°C) a series of zinc-iron alloy layers are formed by a metallurgical reaction between the iron and zinc. Upon withdrawal from the galvanising bath a layer of molten zinc will be taken out on top of the alloy layer. This cools to exhibit the bright shiny appearance associated with galvanised products.
When the reaction between iron and zinc has ceased and the article is taken out of the galvanising bath complete with its outer coating of zinc, the process is complete. In reality, there is no demarcation between steel and zinc but a gradual transition through the series of alloy layers which provide the metallurgical bond.
Toughness – the coating bonds metallurgically with the steel giving a much greater resistance to damage than other coatings.
Complete coverage – because it is dipped in molten zinc, all parts of the surfaces are coated – inside and out – including awkward corners and narrow gaps.
Three Way Protection – Hot Dip Galvanising protects in three ways.
- It weathers at a slow rate giving a long and predictable life.
- The coating sacrifices itself to any small areas exposed through drilling, cutting or accidental damage.
- If large areas get damaged it prevents the sideways creep of rust.