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Galvanised Wrought Iron

What Is Galvanised Wrought Iron? Methods, Examples & Images

Galvanised wrought iron is iron with a protective layer of zinc added to it during the production process, to prevent rusting. Galvanisation is necessary for outdoor wrought iron products like gates and fences because they’re exposed to plenty of rain and sun, which causes them to rust. By adding a layer of zinc to the iron’s surface, including any hard-to-reach joints, the iron is fully protected against the corrosive effects of water, oxygen, and heat that speeds up the process. Galvanisation can even protect wrought iron and steel products from salt-heavy environments like the seaside, but it doesn’t completely protect them. If the product is exposed to elements like acid rain, tannic acids from trees, and excessive moisture, it might eventually rust (although not for a long time).

Without galvanisation, wrought iron will start rusting within days of being left outside. After months and years, the excessive rust will start to eat holes in the metal, damaging its integrity and eventually leading to collapse. Galvanised wrought iron also requires a lot less maintenance, with the product only needing to be cleaned with soap and water a couple of times a year, and primed if necessary.

A fence that hasn’t been galvanised (or re-galvanised), causing severe rust

There’s a variety of ways to galvanise wrought iron and steel, but the most common is hot dipping. This technique works by dipping the iron in a bath of molten zinc, which is at a temperature of around 450°C. When this happens, the zinc forms an alloy with the iron, and then forms zinc carbonate when lifted back into the air—an incredibly strong material that provides the protective layer. There’s also preparation for the dipping process, including cleaning the iron with a caustic solution, pickling it with an acidic solution, and adding flux in the form of zinc ammonium chloride or another substance. After the iron has been dipped, it’s cooled in a quench rank to lower its temperature and prevent other chemical reactions that might sabotage the integrity of the protective layer.

Other galvanising methods include:

  • Thermal spraying—a coating process where zinc is sprayed onto the iron or steel.
  • Electroplating (also known as Electrogalvanization)—a process that uses electrodeposition to coat the product.
  • Sherardizing—a process that uses zinc vapor to form zinc alloys, which is then coating onto the iron.
  • Mechanical plating—a cold-welding process that coats the product in fine zinc particles.
  • Painting with zinc-rich paints—painting the product with a zinc-rich paint, which can contain up to 95% zinc.

This image from the Galvanizers Association in the UK gives an idea of how thick the zinc layer is for some of these methods. The thicker the layer, the better the protection for the iron or steel underneath, which is one of the reasons that hot dipping is so common—it provides excellent protection.

Image from the Galvanizers Association

If a piece of iron or steel has been galvanised and then welded to another piece, the welded area must be thoroughly cleaned and then galvanised itself, otherwise, it will be a highly vulnerable area for rust.

When the wrought iron product has been fully galvanised, further rust protection can be added through a process called electroplating. Powder coating also helps to prevent rust on the iron’s surface, as does e-coating. If necessary, iron can be re-galvanised after a period of time, using any of the methods described above.

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