Galvanising refers to a process that protects iron and steel by applying a special zinc coating to these metals.
Why use galvanising? The chief reason is to prevent corrosion. The zinc coating shields the iron or steel part, product or surface from the environment that surrounds it.
This makes galvanisation a cost-effective alternative to using corrosion-resistant materials such as austenitic steel alloy or aluminium.
Galvanising is a form of protection for metal. It forms a protective seal against moisture, water and airborne elements.
The process protects metals from galvanic corrosion.
Galvanic corrosion is an electrochemical process and it occurs when prolonged contact with one metal causes another metal to corrode. For this to happen, one metal is the anode and the other the cathode. The cathode metal corrodes.
Because zinc is an anode metal, using it as a coating in galvanisation prevents the metal underneath from corroding.
There are three main galvanising processes:
In hot dip galvanising, you dip the base metal into a bath of molten zinc, which covers the entire object. This process forms a metallurgical bond and produces an outer layer of pure zinc.
To prepare for this galvanisation method, you must degrease the metal surface and clean it chemically, remove any remaining oxide, and coat it to prevent further oxidation build-up.
Then you submerge the object in the molten zinc bath.
This is a similar process to hot dip galvanising, but it normally takes place in steel mills, on steel products such as sheets.
You first clean the sheet then pass it through a bath of hot, liquid zinc.
Electro-galvanising, or electroplating, is a very different process from the other two. It uses an electric current to transfer zinc ions onto the base metal in an electrolyte solution.
This causes the zinc metal to dissolve and migrate onto the negatively-charged base metal object. To get a thicker zinc deposit, you leave the object for longer in the electrolyte solution.
The advantage of this method is that it provides a uniform coating and you can define thicknesses precisely. You can also control the process using grain refiners to create smoother coatings.
The process best suited to you will depend largely on the end function of the object or surface you wish to coat.
Hot-dip and electro-galvanisation each have their pros and cons (see below).
For example, using the hot-dip method, you can have much thicker zinc coatings. This is important for structural steel that is constantly exposed to outdoor elements.
Where you have much smaller iron or steel components, which do not need life-long protection from corrosion and outdoor elements, then electro-galvanising may be a more appropriate, and cost-effective, option. It also produces a shiny, attractive finish.
But all galvanising processes can generally prove cost-effective when treating metal to make it more durable. These processes enable fast turnarounds too.
Ultimately, both hot-dip galvanisation and electroplating, or electro-galvanising, will result in coating a surface with a protective zinc layer.
But the processes are different, and resulting finishes are different too. Both processes have their pros and cons, depending on how and where you choose to apply them.
Hot-dip galvanisation requires a rigorous and rigid cleaning process before the coating can take place. It requires multiple baths, including an alkaline solution, pickling, water rinsing, and fluxing.
This method will produce a tough zinc alloy with a long life. Hot-dip galvanising zinc coats are of a thickness between 80 and 100 µm (micrometres).
Electro-galvanisation (electroplating will produce a thinner zinc coat with a much shorter life. Electro-galvanised zinc coats are between 10 and 12 µm.
The electroplating finish is uniform and attractive
Hot-dip galvanisation produces a duller finish and a non-uniform coating.
Hot-dip galvanisation is generally the more costly process, but if you require a thicker coating using electro-galvanisation then this can increase its costs.
Electro-galvanisation is suitable for smaller parts and components, whereas hot-dip galvanisation will work for objects of all sizes.
Galvanising protects metals from corrosion.
Metal corrodes when it deteriorates in reaction to its environment. Corrosion is a chemical reaction, and anything that stimulates this reaction can cause it to occur in metal.
Corrosion is a natural process, arising from chemical and atmospheric conditions, and it’s always damaging. In the form of rust, it reduces the thickness of iron and steel, causing these metals to lose their mechanical strength, increasing the potential for structural breakdown.
Rust weakens the bonds in structural steel when it gets exposed to oxidising agents. It can damage machinery and equipment such as valves and pumps and reduce electrical conductivity and the surface reflectivity of metal.
Along with the protection from corrosion that galvanising provides, it also has these advantages:
It’s more cost-effective than using stainless steel.
It’s easy to maintain.
Galvanised surfaces have a long life expectancy.
Galvanisation provides resistance to mechanical damage.
Galvanising offers full protection to objects and surfaces, covering all cracks, corners and uneven surfaces.
Here are some examples of industries that use galvanising:
Automotive – electroplated zinc-coated bodies combine attractive finishes with corrosion resistance
Wind and solar – galvanised steel extends the lifespan of outdoor equipment, ensuring decades of maintenance-free use
Agriculture and farming – galvanised metal performs well in environmentally harsh conditions, where there is plenty of wet and windy weather
Construction – galvanised steel structures are resistant to corrosion, and this finish can also improve their overall appearance
Electrical – electro-galvanised components include high voltage National Grid components, and low voltage parts for IT and other applications.
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