Galvanising steel is a chemical process which is used to create a protective coating in order to prevent corrosion of steel through atmospheric exposure. So called “hot dipped” galvanising involves a process where the steel is literally dipped into a bath of molten zinc to create the protective layer.
The hot-dipped galvanising process
Step 1: Cleaning the steel
Firstly the steel is thoroughly cleaned by immersing is in a highly caustic solution in order to remove any surface impurities like oil, dirt, or paint which could disrupt the galvanising process later on.
Step 2: Pickling the steel
Next the steel is “pickled” in an acidic solution to remove mill scale to ensure that the steel surface is completely clean and free from debris.
Step 3: Hot dipped galvanising
Now that the steel surface is fully prepared is it dipped into the bath of molten sinc.
The steel will remain in the bath until it reaches the same temperature as the zinc bath itself (around 449 degrees celsuis) to ensure that the chemical reaction is thoroughly complete.
Step 4: Cooling
The final step is to cool the steel in a “quench tank” rather than simply let it air cool.
This is done to ensure that the atmoshpere doesn’t prematurely begin to interact with the galvanised surface before it has properly cooled.
Hot dipped galvanising is considered a superior method compared to cold galvanising (sometimes called cold plating) because it ensures that the steel is thoroughly coated and the galvanising layer is extremely durable.
Since galvanised steel is typically used in outdoor applications where the prevention of corrosion can be assured, hot dipped galvanised steel is the usual choice.