First Facts: What is Hot Dip Galvanising?
At a glance
Prevents corrosion- A method to prevent steel from corroding by dipping it into a bath of molten zinc heated to 450°C, creating a metallurgical bond with the steel.
Process- The process (at a glance) includes steps, consisting of cleaning, fluxing, galvanising and post treatment (if required).
ISO 1461:2022- The British Standard that specified the properties and test methods for hot-dip galvanised coatings on iron and steel.
Thickness- Steel articles will receive a uniform coating, with thickness determined by the Steel Surface Area per Tonne (m²/t). Fencing posts and pales, typically under 6mm, should have a coating of 85μm.
Our Top Tips:
For maximum corrosion resistance, ensure your galvanised metals come from a ISO 1461 source.
For any damage to galvanised steel fencing components, thoroughly wire brush the area and apply enough zinc-rich paint (spray or brush) to achieve the thickness specified by ISO 1461.
Process of Hot Dip Galvanising
1. The steel undergoes pickling or acid cleaning to eliminate rust and mill scale. Hydrochloric acid is the most commonly used, though sulfuric acid is also utilised.
2. Steel is then rinsed using plenty of fresh water.
3. The acid-cleaned steel is immersed in a zinc ammonium chloride flux at 50-70°C, which removes oxide film, preventing oxidation and activating the surface before galvanising.
4. The steel is then left to dry.
5. The clean steel is immersed in a 450°C bath of molten zinc. While submerged, the steel alloys with the zinc, forming zinc/iron alloy layers. As the steel is withdrawn, a coating of free zinc forms over these layers.
6. In this final step, quenching is the process of ensuring freshly galvanised steel is dipped into an anti-white rust chemical mixed with water. This bath quickly cools the steel to halt the reaction between the iron and zinc.
Commonly Asked Questions about Hot Dip Galvanising
What is a vent hole?
For safety reasons, all sealed hollow sections must be vented. This allows air to escape and zinc to enter and drain during the dipping process. A vent hole is required at each sealed end, either in the end plate or the section itself
Can the coat of galv be thicker?
To attain a thicker zinc coating, steel typically necessitates blasting to SA2.5 with G24 chilled iron grit. For standard or high-volume orders, consider specifying controlled silicon steels, which enhance reactivity and coating thickness.
Do galvanised products rust?
Galvanised steel is highly resistant to rust but isn't entirely immune. The zinc coating provides excellent protection, but if damaged, the underlying steel can corrode. Factors influencing rust susceptibility include the zinc coating's thickness, environmental conditions (humidity, salt exposure), temperature, and proximity to water.
How long does galvanised coating last?
Given typical corrosion rates of 1-2 microns per year, galvanized coatings can often exceed a 30-year lifespan. However, actual performance is influenced by environmental factors.
Why does galvanised steel often have different shades of colour?
Steel type affects zinc coating. More reactive steels create a duller finish due to post-dip alloying.
How thick will the galvanised coating be?
Typical thicknesses: Steel ≥ 6mm: 85µm Steel ≥ 3mm to < 6mm: 70µm Steel ≥ 1.5mm to < 3mm: 55µm
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