How Is Galvanised Steel Made?

What Is Galvanised Steel?

Galvanisation is the process of applying a zinc coating to steel or iron which acts as a barrier to protect it from particle corrosion, rust, general surface scratches and abrasions. Galvanised steel is used in a range of residential and commercial applications and industries including Structural Steel, Balustrading, household decorations and garbage cans. 

Galvanised Steel Advantages

The durable abrasion-resistant zinc coating gives the steel a set of unique properties and benefits, which is summarised below:

1. Cost-Effective

Galvanising is more affordable than most types of protective coating application techniques. As galvanising relies more on automated factory operations, where the full protective coating can be applied within minutes, unlike other protective coating techniques that require manual labour. Once galvanisation has been completed, it can be used immediately with no additional surface preparation, painting or inspection required.

2. Low Maintenance

Galvanised steel has a much lower long-term cost than other forms of coating. Its minimal recoating requirements and abrasion resistance mean that it is less likely to need maintenance. This makes it suitable to use in remote and regional areas of Australia due to the low ongoing maintenance required. 

3. Durability

Galvanised steel has a long life expectancy and exceeds non-galvanised steel by 25 years if used in urban and coastal areas or even over 50 years in rural environments. When steel is galvanised, the whole structure is protected including the edges meaning that it is durable all around.

4. Mechanical Resistance

The unique metallurgical structure achieved by the galvanisation process provides a greater resistance to mechanical damage, which makes it a suitable coating for steel that is used for transport and building erection purposes.

Galvanising Process

The most common galvanising process is hot-dip galvanisation. Hot-dip galvanisation is where iron is immersed in a bath of molten zinc to produce a protective coating. We have summarised the galvanising process below:

1. Degreasing

This step is to remove all organic surface contaminants off the steel using a surface treatment. A caustic solution is commonly used to remove all containments.

2. Pickling

When all the oils and other containments are cleared, pickling is undertaken to remove all rust and scale. It is usually performed using hydrochloric or sulphuric acid and done to remove all surface impurities.

3. Fluxing

The steel is then immersed in the flux solution, which contains zinc ammonium chloride. The operation is usually performed at 50°C to 70°C and removes any oxide film that has formed on the steel surface. This is performed to activate the surface and prevent further oxidisation before the galvanisation process. 

4. Galvanising

The steel is immersed in molten zinc, which reacts and forms alloy layers. The thickness of the alloy layers will depend on the mass of the steel that is being galvanised. The temperature of the molten zinc must be between 445°C to 465°C to allow the formation of the coating. The steel is gradually withdrawn and the outer layer of the molten zinc then solidifies to form a protective zinc coating. The time required for galvanising can take between a few minutes to multiple cycles depending on the mass of the steel that is being galvanised.

5. Cooling

A quench solution is applied to the steel to cool it down. This solution usually contains an inhibitor to avoid premature oxidation if the steel is passivated.

Galvanised steel has been proven to be an extremely reliable material suitable for various applications, thanks to its abrasion and corrosion resistance. If you are interested in sourcing or more information about galvanised steel, contact the team at Ogis Engineering today.