The chemical composition of the steel
The surface condition of the steel In general, rough steel surfaces will cause the galvanizing reaction to produce thicker coatings due to the increased surface area. These thicker coatings, however, will be rough and have a generally poor appearance.
Bath immersion time Galvanizing is a diffusion process. As with all diffusion processes, the reaction between the molten zinc and the steel or iron will proceed quickly at first but will slow down as the alloy layers grow and become thicker. Thus, continued immersion or dipping material more than once will not produce a significantly thicker coating except in the case of reactive steels.
Bath withdrawal rate The withdrawal rate of material from the galvanizing bath has the greatest effect on the outermost layer of pure zinc. A rapid withdrawal will produce the thickest coating because the largest amount of zinc will be carried out on the material and will subsequently solidify and become the pure zinc layer. Slower withdrawal allows the zinc to effectively drain back into the kettle producing smoother, thinner, and more uniform coatings.
Steel cooling rate Slower cooling rates, such as those experienced with air cooling or even with thicker sections that have been water quenched, allow the zinc/iron alloying reaction to continue. The inner alloy layers will use the outer Eta layer for their supply of zinc causing the coating to become dull, matte gray. Quickly reducing the temperature to less than 300 degrees Fahrenheit will halt the galvanizing reaction and minimize the formation of dull or matte surfaces.