What Is Galvanized Steel?
Galvanization is the process of application of zinc as a coating onto the surface of steel metal. Therefore, Galvanized steel is steel that has been treated with a coating of zinc on all its surfaces. Normally, the coating is done on the steel metal to enhance its properties on resistance to corrosion and rusting.
Besides, the coating happens as a result of dipping the steel metal into molten zinc and a reaction takes place. This reaction creates the bond between zinc and steel creating the required coating.
What Does Galvanized Steel Imply?
To galvanize is to create a coating of zinc on the surface of a metal. The coating can take place through hot dipping the metal into molten zinc or through electro galvanizing.
Steel when dipped into molten zinc or when electro galvanized, acquires a thin coating of zinc. When steel undergoes this kind of secondary treatment, it is then called galvanized steel.
The galvanized steel, therefore, becomes more durable and highly resistant to corrosion and rust and can be used for various applications. Combining the strength, the steel has to offer and the rust and corrosion resistance properties of zinc create a quality metal.
Where Did The Word “Galvanize” Come From
The word galvanizes could also mean stimulating someone into action.
It was initially used as the word to honor Luigi Galvani for discovering that a spark could make the legs of a frog move. However, this scientist had no steel or iron coating ideas in mind, his main intention was to explain the animal electricity.
Additionally, the word galvanization has been used in the modern world to refer to coating other metals using zinc as the coat. This process was innovated by Sorel Stanislas and he referred to it as galvanizing associating it with the action of zinc against rust.
How does Galvanization Work?
Galvanization acts as a protection for metals in various ways. One, it can create a coating that will protect the metal underneath from the environment. This is due to the fact that zinc can stand moisture and water and other environmental elements. In case of a deep scratch on the zinc coating that exposes the steel to the environment, the steel will rust.
Another way that galvanizing works is by offering galvanic corrosion which happens when two metals come into contact. In this case, the zinc coating acts as the anode which slows down the corrosion of the steel metal underneath.
Process Of Galvanizing Steel
Step 1: Surface Preparation
Zinc cannot get to react with a steel metal surface that is full of dirt and other contaminants. It is therefore important to clean it through the following steps.
Degreasing the metal – this can be done by dipping the metal into a hot alkali solution or any acidic baths. This will get rid of all the dirt, grease, and any other contaminants on the surface of the metal.
Pickling – Pickling is done to remove mill scales or rust on the surface of the steel metal. It is achieved by the use of a diluted acidic solution accompanied by or can be replaced with air blasting.
Fluxing – fluxing is meant to eliminate the presence of any oxides on the surface of the steel. It is also meant to prevent the formation of other oxides that may form after cleaning.
Step 2: Galvanizing Steel
Once the steel metal has been prepared and cleaned, it is dipped into a 98% pure zinc. The zinc must be in its molten state at a temperature of approximately 830° F.
A chemical reaction takes place between the two metals that forms the protective layer of zinc on the surface of steel. The steel metal has to be submerged into the molten zinc until it reaches the same temperature with it.
Subsequently, it is then removed, drained and the cooling process takes place through quenching of metal. The steel galvanizing process can go for 10 or less minutes and this will depend on the size of steel.
Step 3: Post Treatment Of Galvanized Steel
The process of post-treating the galvanized steel could be referred to as quenching. It can be done by dipping the galvanized steel into water with maybe other chemicals that will form a protective layer. Another finish that can be done on galvanized zinc is to grind off the zinc drips to come up with a finish that is smooth.
Step 4: Inspection Of The Galvanized Steel
At this stage, the manufacturer must now ensure that coating adheres to the ASTM Standards by carrying out various inspections. This is in terms of thickness, appearance and weight of the coating that has been created.
Level of thickness – this can be determined through optical microcopy or magnetic gauges. Magnetic gauges method is always preferred because it is non-destructive and very simple.
Coating weight – This to be able to tell the volume of zinc coating that took place on the surface of steel. There are two methods that can be used to determine the amount of zinc coating; weigh-strip-weigh or weigh-galvanize-weigh.
Appearance and coating finish – this inspection step will check all the sections of the metal surface for any kind of errors.
The appearance of the galvanized steel will tell if the steel metal had any contaminants before being galvanized. It is easy to tell because there is a standard appearance and finish that zinc coated should conform to. After the inspection process, the galvanized steel is ready for the various applications in different industries.
Galvanized Steel Vs Regular Steel
Galvanized steel is any steel that has been treated with zinc to create a protective coating on its surface.
Additonally, zinc coating on the steel surface is bonded to it metallurgically giving it superior resistance to any kind of damage. The coating also enhances the abrasion and corrosion resistance properties of the galvanized steel.
The forming process of galvanized steel is divided into three stages, cleaning, galvanizing and inspection. Galvanized steel has its applications in various industries such as the construction, wind and solar, automotive, agriculture and many more. Some benefits include self-healing, durability, metal protection and low initial cost.
Regular steel is a low carbon steel with a small percentage of carbon in its chemical content. The carbon content is meant to improve the pure iron properties.
Regular steel is formed through three stages; primary steel making, secondary steel making, casting and forming. It is very popular and very cost effective compared to other steels like galvanized steel.
Regular steel has the following physical properties; high tensile strength, good ductility, high impact strength and can be treated through cold-forming.
Also, the metal is used for various applications in different industries such as construction, machinery, pipelines, cutlery, fencing and many more.
Benefits Of Galvanized Steel
Comparing galvanized steel with other treated types of steel, it does not need further finishing processes, since it is ready to use.
In average environment, a galvanized steel can last for over 50 years.
Over 20 years in severe corrosive environments with no maintenance required.
Damaged steel can steel remain protected by the zinc coating.
The steel metal cannot corrode until the zinc coating has corroded.
Iron in steel is very prone to rusting, the zinc coating prevents water and oxygen from reaching the surface of the steel metal.
Galvanized steel is sustainable due the fact that it does not require much maintenance and this cuts on the frequent expenses incurred by companies.
The galvanizing process is closely controlled, straight forward and the zinc coating is very consistent and predictable.
Remember, the metal conforms to the ASTN Standards.
Once the coating has been done and inspected, from day one, the metal is ready to protect against corrosion and rust.
It can be trusted.
The lifespan of a galvanized steel can be predicted considering the application environment since it weathers in a linear style depending on coating thickness.
The zinc coating ensures a complete coverage of the steel metal including the corners unlike other methods that do not cover them.
The abrasion resistance offered by the zinc coating is ten times better than what the ordinary paints can offer making the metal tougher.
Disadvantages Of Galvanized Steel
When the galvanized steel is exposed to a magnet, the coating is removed exposing the metal to water and oxygen.
The galvanized surface is very hard and cannot be used with applications that need flexibility in metals like welding or other forming processes.
Galvanizing can only be done with a few selected steel grades and this limits its application in industries.
Cooling time of zinc is a bit long and requires a lot of patience, because if rushed, the coating will be poorly done.
There are steel metal pieces that are too large or too small and may not be practical to be dipped into molten zinc.
Galvanized Steel Product Options
It is used for making solar panel frames, windmill components,s and the moving parts of the system.
Galvanized steel is also used to make almost 80% of the body in white of a car for strength and corrosion resistance.
Other parts include bumber reinforcements, door beams, chassis frame, etc.
For the strength, aesthetic appearance and corrosion resistance, galvanized steel in used for making rails, tubing, gutters and other structural pieces.
Telecommunication equipment, wires, communication boxes, etc.
Framing equipment, irrigation systems, chemical spraying equipment, etc.
Tanks, piping systems, flanges, and fitting are made from galvanized steel.
Spangle In Galvanized Steel
This is a visible aesthetic feature containing crystallites present on the galvanized steel metal. It can be seen as a snowflake or six-pointed star on the surface of the galvanized steel. Again, this happens as a result of contaminants or alloying elements on the zinc coating. This can lower the corrosion resistance properties of the galvanized steel.
Spangle can be altered through alloying the zinc with other elements such as lead, aluminum, tin and many others. The spangle in the zinc coating does not alloy for other finishes like painting on the metal surface. It also reduces the mechanical properties of the galvanized steel.
Does Galvanized Steel Rust.
Yes and no.
Galvanized steel takes a very long time to rust because the zinc coating prevents water and oxygen from reaching the surface of the metal. Rusting may take place after a very long time, maybe after 20 years of rust-free service.
This is because rusting can only take place after the zinc coating has worn out and the metal has been exposed to the environment. Rusting in a galvanized steel is a slow process that can take up to 50 years in average environments and 20 years in severe environments.
However, this depends on the method of coating used and the thickness of the coating on the steel metal surface. In cases where the coating was not done properly due to a fast cooling process or poor cleaning. Then the coating may pill off after a short period of time. This will lead to rust in the metal after a short period of time.
Methods Of Galvanizing Steel Metal
Here iron is dipped into a molten zinc at the temperature of about 830° F for approximately 10 or less minutes. Then, steel metal is left in the molten zinc until it reaches the same level of temperature of the zinc.
It is then removed and drained then taking through the quenching process using water mixed with other chemicals for a protective coating. Additionally, galvanized steel is then taken through the inspection process.
This is to ensure that the thickness, weight and appearance of the galvanized steel conform to the ASTN Standards.
In this process, once the steel has been cleaned and prepared for galvanization, it is treated with an electrically charged electrolyte solution. The process can be carried out during the first stage of production.
The steel sheet is rolled through a solution that cleans it and then it is passed into a pool of the zinc in its molten state. After the coating, it is immediately recoiled. This method is suitable for galvanizing steel in large scale for big companies.
This method combines the hot-dip process and the annealing process to produce a matte surface for the galvanized steel.