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How does hot-dip galvanisation work?

Jul 1, 2018, 17:46 PM by User Not Found

Whether you're looking at using metal as a material for outdoor walkways, architectural facades, or anything in between, you will likely have come across the term "hot-dip galvanisation". The term refers to the process of zinc coating your materials for a host of benefits. Let's take a more in-depth look at hot-dip galvanisation, why it's so important, and how the process works.

What is hot-dip galvanisation?

If steel isn't adequately protected, it will rust and corrode over time. Hot-dip galvanisation is a method of applying a protective zinc coating to prevent this from happening. The process allows the surface of your materials to be covered completely in the protective coating, and ensures a far longer life once the metal has been installed in its proper application.

You may be wondering, why zinc? There are two key reasons. The first is that zinc bonds with the iron present in all steel, forging a layer that is tightly bonded and difficult to remove. Secondly, zinc itself is corrosion resistant, self-healing, and sustainable. Zinc was first used in construction circa 79AD, though increasingly formal galvanising processes have have been used since around 1837.

What is hot-dip galvanisation?Any metal used in outdoor, water or chemical treatment will be galvanised.

How is hot-dip galvanising done?

The process of hot-dip galvanising steel works like this (for the sake of the example, we are hot-dip galvanising a sheet of metal).

  1. Cleaning: The first step involves removing the surface contaminants from the sheet. These might be dirt, grease, oil or paint, and are generally removed with a mild acid. This step is extremely important to the strength of the bond between the zinc and sheet metal.
  2. Pickling: Nowhere near as delicious as it sounds, and generally required to remove rust from older sheets, the pickling process involves applying a solution that strips any buildup of rust, stains or other inorganic contaminants. Cleaning steps may need to be repeated for sheets in rough condition.
  3. Hot-dip: Once sufficiently cleaned, the sheet is dipped into a bath of molten zinc. The zinc will generally be heated to around 450 degrees celsius. When fully immersed, a metallurgic reaction takes place between the molten zinc and the iron in your sheet metal. This is where the coating forms, and this part of the process takes only a few minutes, depending on the desired coating thickness.
  4. Remove from bath: The sheet is then slowly removed from the zinc bath, allowing excess zinc to drain off.
  5. Cooling off: The sheet is now ready to be cooled. Cooling can be done in a few ways. It can be left in the open air, which takes a little bit longer, or it can be dipped in another bath of either water or a passivation solution such as potassium hydroxide.
  6. Inspect: Once the steel is cooled it can be inspected for quality. There are numerous methods in which an inspection can be carried out, all of which are governed by compliance codes in the country of manufacture.

Why does steel need to be hot-dip galvanised?

Approximately 30 per cent of zinc used today is recycled.

The benefits to hot-dip galvanisation are huge. We've established that it provides a coating that is very tough, strongly bound, and covers the entirety of the sheet without leaving anything exposed. The hot-dip method of galvanising steel is also extremely long lasting. In many cases, steel that is galvanised today will not show rust in our lifetimes.

Hot-dip galvanising is also sustainable. Zinc is recyclable, and approximately 30 per cent of zinc used today is recycled. Steel with zinc coating does not restrict the recyclability of either, and as such, puts far less strain on the environment. It also significantly reduces the amount of time and money required to maintain hot-dipped materials.

Finally, hot-dip galvanising is a relatively fast way of weather proofing your materials. The preparation (cleaning, as noted above) is generally considered the most time-consuming part of the process, as the hot dipping element only takes a few minutes. Generally speaking, turnaround time can be within a few days, though that obviously depends on the volume of materials you need to galvanise.

Why galvanise metal?Hot-dip galvanisation protects the metal long term, letting you avoid eyesores like this.

How does hot-dip galvanisation compare to other galvanising methods?

There are a few other methods for galvanising:

  • Electrogalvanising (or electroplating): A solution containing zinc ions are applied to a surface and then an electric current ensures uniform cover.
  • Metallic spraying: Zinc powder is sprayed onto a surface and heated.
  • Sherardising: Surround the metal with zinc powder and heat in an airless enclosure.

It should be noted that all of these methods result in a similar level of protective cover, but the hot-dip method is the fastest, easiest, and reduces the potential for error considerably. That, and it's also time-tested.

At Webforge, our products are hot-dip galvanised to ensure they hold up against anything the climate can throw at them. To find out more about how our solutions can meet your needs, get in contact with the team now.

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