What is the difference between Zinc and Galvanized?
What Does Galvanised Mean?
Galvanisation is when a protective zinc coating is applied to steel or iron, to prevent rusting. A zinc coating can be used on anything from small nuts and bolts to large beams for buildings. Optimally, the steel is put in a big bath, where the coating is applied – including paint.
What are the available Galvanising processes?
- Hot Dip: characteristically – dull grey and a little rough.
- Electroplating: characteristically – shiny and smooth, and
- Cold Spray: characteristically – you can probably scrape it off
As not all processes are equal, you are advised to be careful when choosing your product! The fact that it says ‘galvanised’ that doesn’t tell you how the zinc coating was applied. So, when you see ‘galvanised’ make sure the product is exactly what you want.
What is the preparation for the Different Galvanisation Processes?
Whether the steel is to be hot dip galvanised or zinc plated or painted, it is prepared in a similar way. The steel is cleaned to remove all oils, paint, grease, mill scale (small flakes of metal) and rust in a bath of acid.
Process Details
Hot Dip is the most effective method for rust prevention is when metal parts are fully submerged in a bath of molten zinc. This is hot-dip galvanising. Steel, when being hot dip galvanised is dipped into a 450°C bath of molten liquid zinc. The steel and the liquid zinc bond together because of the high temperature. The steel and the zinc become one. Hot dip galvanising requires a minimum thickness of 45μm (.045mm) and goes beyond 100μm (.1mm)
Electroplating is a process where zinc is applied by using a current of electricity. This zinc plating is also known as electro-galvanising. While is does provide some rust protection, its thinner coating is not as rust resistant as hot dip galvanising. Its main advantage is it is cheaper and easier to weld. Zinc plating is achieved when the steel is immersed in a cold chemical solution of zinc and an electrical current applies a layer of zinc. The thickness of the coating is measured in microns or micrometer’s (μm). Zinc plating requires a minimum thickness of 5μm (.005mm) and a maximum of 25μm (.025mm). It would become too technical and expensive to coat the steel any thicker than this.
Cold Spray galvanising is basically applying zinc-based paint. This is the cheapest, quickest, and least protective method of applying a zinc coating.