Any metallic structure has to be durable and maintain this property for as long as possible. Without a doubt, steel has a lot of strength but there are many alloys of it that are vulnerable to certain environmental conditions. When it comes to protecting the metal from corrosion, galvanizing appears to be the best option in this regard. Before coming to the main context, let’s have a look at some advantages of galvanizing and why it is performed.
- 1 What is Galvanized Steel
- 2 Why this process is performed
- 3 Applications of Galvanized Steel
- 4 Methods to Galvanize Steel
What is Galvanized Steel
The process of galvanizing includes placing a thin coating of another metal on top of the existing one. In most cases, zinc is used as a coating material in metal structures. This protective layer of zinc protects the metal against the surrounding environment. This ability of galvanized steel to withstand harsh environmental circumstances makes it durable and perfect for open-air use.
Why this process is performed
The primary purpose of galvanization is to prevent rusting; that’s why galvanized steel is covered with zinc oxide. The idea behind galvanization is that the layer of zinc has to be corroded first so the steel remains safe for a far longer period. If there is no zinc coating on the metal, the chances of metal corrosion will become more significant and the metal gets corroded much quicker, as the metal is exposed to the elements.
This one is an outcome of the protective properties of the coating. Research reveals that a galvanized piece of industrial steel may serve up to 50 years in normal conditions. The same metal piece would serve up to 20 years if it is located in a highly corrosive environment where there is a lot of contact with water.
This advantage is kind of subjective but most would agree that galvanized steel looks better in comparison with most steel alloys. Usually, it’s brighter and it is way shinier with certain types of coatings.
Applications of Galvanized Steel
The use of galvanized steel is not limited. In fact, it is used in many industries like construction, energy plants, agriculture, and the sports sector. Galvanizing steel also plays a pivotal role when it comes to the construction of roads, buildings, bridges, railway tracks, gates, signal gantries, storage containers, and sculptures. So, whenever corrosion is to be avoided, galvanizing must be done to secure the metal.
Methods to Galvanize Steel
Different processes can be carried out to perform galvanizing:
- Hot-Dip Galvanizing
- Metallic Spraying
1. Hot-Dip Galvanizing
In this process of galvanization of steel, steel is immersed in the tub of molten zinc. Hot-dip galvanizing (HDG) has three basic steps; surface groundwork, galvanizing, and inspection.
In Surface groundwork, fabricated steel is brought for galvanizing, and the steel is passed through three cleaning stages; degreasing, pickling and fluxing. Without this cleaning process, galvanizing could not be performed as zinc does not react with impure steel.
After surface groundwork, steel is immersed in 98% molten zinc having a temperature of 830F. The immersion of steel in the kettle is done at such an angle, which may allow air to outflow from tubular shapes or other pockets. It also allows the zinc to flow over and into the whole steel body. In this way, zinc comes in contact with whole steel. The iron inside steel starts reacting with zinc and forms inter-metallic coatings of zinc-iron. While on the outer side, there deposits pure zinc coating.
The last step is performed for the checkup of this coating. Visual inspection is performed to see if there is any uncoated place on the steel body, as a coating does not stay on uncleaned steel. A magnetic-thickness gauge may also be utilized to ascertain the thickness of the coating.
The electrochemical process is carried out to make Electro-Galvanized Steel. In this process, steel is submerged in a zinc bath, and then an electric current is allowed to flow from it. This process is also referred to as electroplating.
Before the electro-galvanizing process is carried out, steel must be cleaned. Here, zinc performs the duty of anode to shield the steel. For the purpose of electrolysis, zinc-sulfate or zinc-cyanide is used as the electrolyte, while cathodes protect steel from corrosion. This electrolytic solution will allow the zinc to stay on the surface of steel as a coating. The coating layer will be as thicker as greater will be the time of immersion in the zinc bath.
To increase the resistance against corrosion, some conversion coatings are then useful. This process creates another layer of zinc and chromium hydroxides, and the metal will show a blue-tinted surface.
Sherardizing refers to form an identical zinc coating on the surface of the iron or steel to secure the metal from corrosion.
In this process, the steel is put in a container with divided zinc, and the container is sealed and heated to the temperature below the melting point of zinc. The result of this reaction, two metals form zinc and iron alloys with a strong external coating of pure zinc that sticks on the surface of steel and presents considerable resistance against corrosion. This coating also facilitates better paint on the surface.
Sherardizing is the best method in the case of small metallic objects. This process is exceptionally suitable for shaped steel metal pieces, as the external layer can easily follow the patterns of the base steel.
4. Metal Spraying
In metal spray galvanizing, charged or atomized particles of molten zinc are sprayed onto the surface of the steel. The process is carried out through a handgun applicator or an exceptional flame.
Before applying zinc coating through a spray, all contaminates like unwanted surface coatings, oil and rust must be removed. Having done with the cleaning procedure, atomized particles of molten zinc are sprayed onto the coarsened surface, and these particles get solidified on the surface.
If flaking and peeling are to be avoided, this metal spraying method of coating is the best to apply, but it is less suitable to provide considerable resistance against corrosion.