The two most popular forms of galvanizing are hot-dip galvanizing and electro-galvanizing. These two methods, and others, are discussed below. Knowing which type of galvanizing to choose may require the help of an expert.
1) Hot-dip galvanizing
During hot-dip galvanizing, the metal is immersed in a hot zinc bath at around 450 °C. When it is removed, the coated surface reacts with oxygen to form zinc oxide, which then reacts with carbon dioxide to form zinc carbonate. Before galvanizing, the metal must be cleaned with a caustic solution and then pickled in an acidic solution; ammonium zinc chloride is also used to prevent premature oxidation of the metal before galvanizing.
2) Electro-galvanized
Electrogalvanizing combines galvanizing with electroplating: an electric current is passed through a zinc bath with a zinc anode and a steel conductor. The process produces a thinner coating than hot-dip galvanizing and also produces a brighter surface finish suitable for cosmetic applications.
3) Zinc sherardizing
This form of galvanizing goes by several names: thermal diffusion galvanizing, vapor galvanizing, and dry galvanizing. It involves heating steel components to 500°C in an enclosed rotating drum containing zinc dust. The evaporated zinc diffuses to the steel surface to form a firmly bonded coating. It is ideal for small parts and parts that need to be coated on the inside.
4) Galvanized
Galvanizing is a combination of hot drop galvanizing and annealing. The hot-dip galvanizing process proceeds as normal, before the coated metal is passed through an air knife to remove any excess zinc. The metal is then briefly heated in an annealing furnace at 500–565 °C to interdiffuse the iron and zinc layers and form a zinc-iron alloy layer.