Coil coating – the efficient method of coating metal sheet before fabrication
Coil coating is an immensely efficient method of coating metal. It is a continuous and highly automated process which takes a coil of metal through every step of finishing, from cleaning to curing, before being packaged for shipment. The metal arrives entirely finished and ready to be used – the slogan of the industry is “Finish first, fabricate later!”. By opting for coil coating you are choosing a product of consistently high quality that is durable, corrosion resistant, cost-effective, recyclable, and greener than other alternatives. It is also available in a range of coating chemistries and the resulting painted metal sheet can be formed without loss of performance.
In this article we will look at the coil coating process, the different coating technologies used for coil coating, how coil coating benefits fabricators, and coil coaters operating in Sinagpore.
The coil coating process and automated coil coating lines
The continuous process of coil coating starts with an untreated coil of metal sheet which is unwound, treated, coated, cured, rewound, and packaged for shipment at a rate of 100-200 metres per minute. This process can be for one or both sides of the metal sheet, and can apply and cure up to three layers of paint. The metal sheet is most commonly aluminium, steel or galvanised steel, and coil dimensions vary – for steel the average coil is 1.6m wide and 0.5mm thick, where aluminium lines are typically larger at 2m wide. The typical line will include decoilers, entry accumulators, brushers, coaters, treatment and quenching tanks, curing ovens, and finally recoilers. The coil coating process looks like this:
- Stitching the strip to the previous coil
- Cleaning the strip
- Power brushing
- Pre-treating with chemicals
- Drying the strip
- Application of primer on one or both sides
- First curing oven (15-60 seconds)
- Cooling the strip
- Top coating on one or both sides
- Second curing oven (15-60 seconds)
- Cooling to room temperature
- Rewinding of the coated coil
As you can see, the process is intensive and thorough. This production line allows for a consistent, accurate, and high performance coating application.
The reasons why industry is turning to coil coating
Businesses in the building and construction, HVAC, appliance, automotive, transportation, and furniture industries are increasingly using pre-painted or coil coated materials in their manufacturing and building. The reasons for this are manifold:
- Cost efficiency – Coil coating significantly reduces or eliminates paint wastage, material handling costs, energy consumption, hazardous waste disposal, insurance premiums, capacity restraints, and the cost of compliance.
- Eco-friendly – The closed loop of the coil coating system eradicates an enormous percentage of waste associated with the paint process. The coating application efficiency is over 90%, excess metals are recyclable, emissions and disposal are low and well-controlled.
- Customisation – Coil coated metals allow for a wide range of colours, thickness, performance characteristics, and even aesthetics, including printing, stripes, embossing and more.
- High quality finish – Coating a smooth flat sheet of metal allows the finish to be smooth and consistent while removing the risk of nooks and crannies causing adhesion problems and hiding imperfections. The uniform layer of coating also allows strict maintenance of colour consistency.
- Corrosion resistance – Studies have shown that coil coated metal consistently offers better corrosion resistance than post-painted surfaces. The consistency and accuracy of the painting process also ensures the best possible protection and finish.
Choose the type of coil coating based on the end use of the metal sheet
For a process so finely tuned, there is a remarkable degree of flexibility with regards to coating technologies. The metal sheet can be coated with your specific end use in mind. Available coatings include polyesters, polyurethanes, epoxies, fluoropolymers, and more. These can also be applied with different finishes, from matte to high gloss, and textures like wrinkle.
Suitable for: Heating, ventilation, and air conditioning (HVAC) equipment, garage doors, warehouses, appliances such as refrigerators, freezers, water heaters, washers, and dryers.
Polyester is available in a range of formulations which means there is diversity in its properties. This is usually indicated by cost – the lower the cost, the less durable the coating. Polyester is an extremely hard and tough coating, used across a wide range of heavy-duty surfaces. When you combine this with the lower cost, it is clear why polyester is a common choice for warehouses and industrial or storage buildings. Polyester is also used for appliances due to its superior scratch resistance, great flexibility and formability, and stain and dirt resistance.
Silicone modified polyester (SMP)
Suitable for: Commercial and residential metal roofing, agricultural and industrial building components, siding, gutters, and downspouts.
Silicone modified polyester is created by adding silicone resin to a polyester resin coating. The resulting coating is somewhere between polyester and PVDF, with the hardness of polyester and a fade and chalk resistance more comparable with that of PVDF. SMPs are more scratch and abrasion resistant that PVDF, meaning they are able to withstand rougher handling conditions. They can be modified to have an expected lifespan of up to 20 years. SMPs are durable, and have good weatherability, colour consistency, colour and gloss retention, and resistance to chalking, fading, and scratching.
Polyvinylidene fluoride (PVDF)
Suitable for: Architectural and residential metal roofing systems, composite and insulated metal wall panel systems, curtain walls, siding, canopies.
Also called 70% PVDF (from the percentage of resin), polyvinylidene fluoride is a high performance fluoropolymer coating which is particularly used for architectural applications. Though known for their non-stick properties, fluoropolymer coatings bring a host of other benefits due to their stable and strong chemical structure. They are chemical resistant, corrosion resistant, and temperature resistant as well as having superior colour and gloss retention due to its UV stability. In short, they provide excellent protection against weathering, sun exposure, chemicals, heat, and other harsh outdoor elements.
The growing coil coating industry in Singapore
The biggest user of coil coated metal is the building and construction industry, accounting for 75% of the global market in 2017. South East Asia including Singapore is the fastest growing region in terms of coil coating and the need for pre-coated metal sheet due to the construction of high-rise buildings and industrial facilities.
The world’s leading coil coatings producers are AkzoNobel, Axalta, Beckers, Valspar, and PPG Industries. AkzoNobel bought the Industrial Coatings business of BASF in 2016 and became the biggest manufacturer of coil coatings.
If you are interested in what coil coating can do for your project, our experts are here to help. Get in touch through the button below or through our contact form and let us know about your coating needs. Then we collaborate with our coating partners to determine the best coating solution for your project.