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What’s Pre-Galvanised Steel?

Published by Lucy Thurston on

When it comes to making galvanised steel sheet metal, pre-galvanising is one of the two most popular methods. Despite this, there’s an ongoing misconception that any zinc coating can be defined as hot-dipped galvanisation, when this simply isn’t the case. Although pre-galvanising is very similar to hot-dipped galvanisation, there are some clear differences. For instance, pre-galvanising is performed at the steel mill on materials that already have a specific shape; however, this doesn’t apply to hot-dipped steel. With this being said, what is pre-galvanised steel, and what sets it apart from other forms of galvanised steel?

What is Pre-Galvanising?

First thing’s first, it needs to be established what pre-galvanising is. As previously mentioned, pre-galvanising, otherwise known as mill galvanising, takes place at the steel mill. The process involves the surface being cleaned before the metal is dipped into a hot zinc liquid bath and the recoiling process takes place. Following this, you’ll be left with a multitude of galvanised steel sheet sizes, depending on the galvanised steel sheet thickness that you began the process with.

Advantages and Disadvantages of Pre-Galvanising

Perhaps the greatest advantage to pre-galvanising is that any galvanised sheet cut to size can be promptly and evenly coated. Despite this, upon the fabrication process taking place, any uncoated and exposed areas will be made apparent. For instance, when it comes to cutting a galvanised steel sheet, the edges will be left exposed. It’s for this reason that pre-galvanising is typically applied to a material that already has a specific shape. 

Application of Pre-Galvanising

As the name suggests, pre-galvanising takes place in the initial production stages. This is why it usually occurs at the mills, as the galvanised product will usually be fashioned at a later date. 

Coating of Pre-Galvanised Steel

In terms of thickness, pre-galvanising allows for uniform thickness, which is typically around 20-30 μm when it comes to pre-galvanising. 

As earlier touched on, pre-galvanising is one of the initial stages, meaning that edges often don’t get coated at this time should they be cut later on in the process. 

Similarly, the cleaning of the steel allows for a strong and metallurgical bond between the zinc coating and the base metal. This cleaning is either executed via chemical or mechanical means and, in some instances, both methods are applied. 

Since pre-galvanising takes place at the mills, the coating is typically applied with zero damage to the layer, whilst producing a uniform and bright finish. 

Abrasion Resistance

As opposed to other galvanisation forms, pre-galvanised steel can often be prone to rusting. This is because the pre-galvanising process results in a thinner coating, which can often lead to corrosion.

Despite this, there are measures that can be taken to prevent galvanised steel from rusting. For instance, you may be able to develop a thin barrier film of insoluble zinc corrosion products. This includes patina, which can be applied to the steel’s outer surface to prevent too much exposure to the atmosphere.

Sacrificial Protection

Since galvanised steel is formed by coating steel in zinc, this results in a protective layer. Consequently, the zinc acts as a protective anode, which becomes an integral feature of the steel. 

The Lifespan of Galvanised Steel

Galvanised steel is incredibly durable, meaning that it can last anywhere between 34 and 170 years. This is why galvanised steel is ideal for the construction industry, as it can be relied on for a number of years, providing strength and durability.

Galvanised Steel Sheet Cost

In spite of its various benefits, galvanised steel is typically the same price as untreated structural steel. This is a much more affordable option when compared with stainless steel, which can cost between four and five times as much as galvanised steel. 

Painting Pre-Galvanised Steel

When it comes to using pre-galvanised steel, you may be wondering whether it can be painted to enhance its appearance. Unfortunately, paint won’t adhere to pre-galvanised steel. This is due to the zinc layer that actively rejects paint, resulting in shedding or peeling. 

Cleaning Pre-Galvanised Steel

If you were looking to spruce up your pre-galvanised steel, only to find that paint won’t take to it, a simple clean may be all you need. All you need to do is make a solution of washing up liquid and hot (but not boiling) water. Following this, you cab firmly scrub the metal in circular strokes using a soft-bristled brush. Finally, you can rinse the product and wipe it dry. 

Buy Galvanised Steel Sheets from Rapid Metals

Here at Rapid Metals, we’re one of the leading galvanised sheet suppliers in the UK. As a result, we’re here to help you with any of your metal needs. Whether you’re looking for a certain product or have any specific questions, don’t hesitate to get in touch with our expert team today. 

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