Galvanisation is the process where a zinc coating is applied to steel or iron, in order to give it a protective layer, resistant to corrosion. The most common method of galvanisation is dipping the steel or iron into a pool of molten zinc. This method is called ‘hot-dip galvanisation’.
How Does Galvanisation Protect Metal?
The zinc coating prevents corrosive substances from reaching the metal underneath because the zinc acts as a barrier. However, this also means that the zinc corrodes first in a sacrificial manner to prevent the steel from corroding
Step 1: Before any molten zinc can be added to the metal, the steel must first be cleaned. The steel is immersed in a hot, caustic solution to remove impurities before being rinsed off and sent in for an ‘acid pickling’ treatment. This acid pickling treatment removes oxides from the surface of the metal. The final step of the preparation stage is to put the metal through a hot flux treatment which prepares the steel fabrication by depositing a zinc ammonium chloride onto the clean surface.
Step 2: this is where the main event happens. Molten zinc is heated to 450ºC and the metal is submerged and covered in the solution. The time spent in the molten zinc depends on the size and thickness of the metal.
Step 3: The metal is taken out of the molten zinc and put into a cooling solution where it is given a chemical treatment to prevent white rust occurring on the surface. The metal then goes through a fettling where uneven surfaces are smoothed to a quality finish.
Although galvanising creates a resistant layer to corrosion, it does not prevent the inevitable rusting that will occur after decades of exposure to the elements. Galvanising does significantly slow the process however, and will allow your homes and cars to last longer than they would without protection.