By | April 17, 2016

Many people would be confused with the term color coating of steel. Now, what is a colour coating of steel? Colour coating is a basic term that is used to describe the application of a protective coating to steel substrate that is abounding in the nature of a coil. Colour coated steel is known as pre-painted steel as well.

What is known by colour coatings?

Colour coatings are the paint coatings and are special products that are generally used to give steel a long term protection and durability so that they can be protected from rust and corrugation, moist and humid weather conditions, and from extreme atmospheric  exposure as well as from corrosive solutions and chemicals. Though a colour coating offers little strength to the steel, it also helps in protecting the steel so that the power and veracity of the steel can be upheld properly. Now, what is the process of colour coating of steel? The colour coating of steel is known to be an intrinsic process as well as a much automated industrial process that helps in coating the coils of steel in a smooth manner. The substrate steel is offered a protective coating with the application of colour. This process of steel coating is also known as the duplex coating.


                   Fig 1. Colour Coated Material

The process of colour coating of steel

The colour coating of steel is a process where some organic material is applied on a rolled metal strip. This is a recurring process that incorporates cleaning as well as chemical pretreatment of the metal surface as well. One side or two sides of the metal are coloured with liquid paints or with the help of coating powders which are cured or laminated with the help of plastic films. The process of colour coating is very famous and popular as well and it is very prevalent in various industries due to a variety of advantages.

What are the advantages of the colour coating of steel?

Colour coating of steel has higher productivity and it is a very sophisticated as well as computerized as well as controlled application. It has an assortment of environmental benefits and is energy saving as well. Colour coated steel sheets are always known to be more consistent when used for any kind of work and the best thing about color coating steel is that they are wasted lesser than bare steel.

Colour coating is usually the application of liquid colour on steel in a recurring and automatic process after the pre-treatment of the steel. Pre-painted colour coated steel is a value added product that has some of the best properties of a substrate as well as organic coating. They are easy to install, recyclable and environment-friendly, and light as well.


Why do people prefer colour coated steel?

People are usually known to prefer colour coated steel because they are much durable and long lasting than the ordinary steel. At the same time, it has an aesthetic finish with high corrosion resistance. The thickness of a colour coating steel is usually in the 15 microns to 40-micron range and they are smooth and good to look at. The thickness of substrate steel is 0.2 mm to 1.6 mm and the width varies from 600 mm to 1600 mm


                   Fig 2. Layers of Coating

Which steels are ideally ideal for colour coating?

Colour coating is done, especially on various substrates of steel to produce the best kind of steel products which are suited for the environment. The different substrate steels that are covered with colour coating are steels like

Cold rolled steel

Electro galvanized steel

Hot dipped galvanized steel



Colour coating process

The colour coating process involves cold rolled as well as metal-coated steel coils. The coil is uncoiled in order to be coated and the head is mechanically joined to the end of the tail strip of the previous coil. Due to the recurring procedure, the line of colouring involves two strip accumulators that feed the strip to the coating process during the changes in the coil. At the initial phase, pre-treatment is carried out so that the surface is clean and smooth. It is a very important procedure that is required for better bond formability of colour coated steel sheets. The surface is also activated by a chromate-free conversion so that it is protected from corrosion and is adhesive as well. The coating is applied on the top as well as the bottom. The strip must also be dried well before the next step. The colour coating line has two coatings where the first one is applied on both sides of the strip and the second is applied to the top coat as well as the backing coat. They are then dried up by hot air.


                                 Fig 3. Line Process

No rinse technology

Many industries take the help of the no rinse technology in place phosphate coating over the substrate steel strip as it has the better bath maintenance as well as uniform crystal structure of coating so that it can meet the requirements of the customers. The no-rinse treatment is a thin layer of chemical treatment that helps the bond the coating to the steel surface to the organic coating materials. The strip surface is washed and a layer is incorporated in four phases. After pretreatment, the primer of the uniform layer is applied on the pre-treated surface. The primer technology provides suppleness to the colour coating system and resistance as well. As it contains decomposition inhibitors

Colour coating steels are used in construction markets as well as roofing industries which are usually based on polyester, fluorocarbon, and silicone modified polyester and plastisols

In order to test the quality of colour coating steel, some tests are conducted that comprise of impact tests, bending adhesion test, flexibility tests, hardness test, chemical resistance tests, salt spray test, heat resistance test, methyl ethyl ketone test and much more. They are usually used in cold storages as well as warehouses, false ceilings as well as Venetian blinds, fence, and walls.

These are the things that you need to know about the colour coating of steel and its various advantages and techniques as well.

colour chart

                               Fig 4. Colour Chart

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