¿What is it?
Galvanizing or galvanization is a very common process in the metallurgical industry to protect steel from oxidation and corrosion. Although it is very confused with zinc, they are not the same. Here I explain their differences. Let’s now see its characteristics.
Types of galvanization
2 types of galvanizing can be differentiated in the industry
Cold galvanizing is an electrolytic process, also called electrodeposition, by which carbon steel is coated with a protective film about 80 microns thick. It is achieved by immersing the piece in a solution of specific metal salts for this process, together with a zinc anode, in a bath with DC.
Hot-dip galvanizing has a different process from cold galvanizing. Here the piece is immersed in a molten zinc bath at a temperature of 450 ºC. It is the most recommended system for steel that will be in areas with very abrasive contamination or very close to the sea.
It is a very affordable process if we compare it with other materials such as stainless steel that can also be used in the same conditions. With the advantage that the manufacturing process prior to galvanizing, it is much cheaper since it is a much more malleable metal.
Features of hot dip galvanizing
Once we submerge the carbon steel in the zinc crucible at 450 ºC, a reaction takes place whereby the zinc adheres to the surface, creating several layers, each one harder the closer we are to the steel. This process is regulated by the ISO 1461 standard. You can find more information in this PDF from APTA (Association for the Technical Promotion of Steel).
Obviously, the production processes for hot or cold galvanizing are different.
Hot dip galvanizing
As you can see in the image, which can be found in the APTA PDF, the hot dip galvanizing process has several steps, of which, none can be avoided, all are necessary.
- Degreasing and washing: First process by which we superficially clean any oil or grease that the steel has with a specific alkaline product. Then we go through water to wash it.
- Pickling and washing: As we already explained in this other publication, pickling with hydrochloric acid removes impurities and scale that it may have on steel on its surface so that zinc adheres correctly. Then it is washed for the next step.
- Salt bath, drying and zinc bath: The protective layer is applied here by immersing the steel in the zinc crucible at 450 ºC. It is subsequently cooled in a water bath.
The cold galvanizing process is quite similar as it also requires the degreasing and pickling process. Subsequently it is immersed in a zinc electrolytic bath and is subsequently washed.
Galvanized service life
Hot dip galvanizing
Galvanizing has a very long life until it begins to rust. We can speak of up to 100 years in an environment without contamination and without any maintenance treatment, such as in rural areas, but far from farms as this environment is very corrosive.
In environments such as the city where pollution can be medium level, we speak of a duration of between 40 and 80 years.
For maritime environments, the duration is reduced to about 20 or 40 years, depending on whether you only suffer from sea humidity, or if you also suffer splashes or are submerged in sea water.
The years of life of cold galvanizing are reduced by the type of surface treatment it is. We can estimate that its useful life is approximately 25% shorter when compared to hot-dip galvanizing. It can be perfectly useful depending on the protection we need.
So far the lesson on galvanizing. I hope I have solved your doubts about the process and what is the difference between the different processes.