FOCUS ON COIL PROCESSING
Image: @ Nucor.
“ For customers preparing for CBAM( the EU’ s Carbon Border Adjustment Mechanism), verifiable emission reductions in the coating process are becoming increasingly relevant to their competitive position. The value of carbon abatement in cold rolled steel is currently around 90 euros per ton CO2e in the EU market, and coating-level decarbonisation initiatives need to operate within this pricing environment,” explained coil-coating specialist, Beckers.
Coil-coating process.
The coil-coating process, which is used to produce prepainted metal, is continuously evolving to produce better products of higher quality, faster and with lower environmental impact. Coil coating is a reel-fed continuous process for painting metal which is then used to make a finished part. In one continuous reel-to-reel process, a metal coil of material is unwound, cleaned, primed and then coated with up to two layers of paint on each side, before being thermally cured and then rewound.
“ The process allows for different colours and patterns to be applied to each side of the sheet. In addition, a strippable plastic film layer can be added for extra surface protection. Once coated, the coil is then further processed to give users the material in the dimensions and formats that they require,” outlined coilcoating specialist, Cooper Coated Coil.
“ The consistency and accuracy of the coilcoating process generates excellent corrosionresistance properties compared to other painting methods. This is due to the highly controlled cleaning, pre-treatment, coating application and curing stages within the process. These controls are virtually impossible
Image: Cooper Coated Coils. to attain with other painting processes. Dealing with a‘ flat sheet’ allows the material to be thoroughly cleaned prior to the paint being applied. Coating in this way provides excellent control of paint film weights, which can be measured in microns,” it added.
The coil-coating process
“ Using pre-painted metals enables businesses to focus on their core competencies and operate with greater flexibility and efficiency, compared to postpaint processes. Companies can anticipate future cost savings on both metal and coating expenses. Additionally, capital costs can be avoided by reducing the square footage dedicated to post-paint operations. Optimised inventory management and better supply-chain utilisation further enhance cost efficiency,” commented coil coating supplier, AZZ.
Coated coil can be slit for narrow widths, cut to required lengths, bent, profiled or deepdrawn without damaging the organic coating. It can be processed into any number of shapes, depending upon the end use. The coil-coating process itself offers a range of economic and environmental benefits. It is a closed loop process, so the release of harmful elements is eradicated. All solvents / organic compounds are captured and treated before emission.
The process provides coating application efficiency of reportedly over 90 %. Pre-painted metals can also be fully recycled, providing further environmental advantages.
The method includes cleaning and chemically pre-treating the metal surface.
Prepainted aluminium coil.
Pre-painted, slit steel coil.
Image: Haomei Aluminum.
Steps on a modern coating line
■ Mechanical stitching of the strip to its predecessor.
■ Cleaning the strip.
■ Power brushing.
■ Surface treatment by chemical conversion.
■ Drying the strip.
■ Application of primer on one or both sides.
■ Passage through the first curing oven( between 15 to 60 seconds).
■ Cooling down the strip.
■ Coating the finish on one or both sides.
■ Passage through the second curing oven( between 15 to 60 seconds).
■ Cooling down to room temperature.
■ Rewinding of the coated coil.
Before the final product is created, one or both sides of the metal are painted or coated with powders or liquids, which are then dried or bonded with plastic films. Coil coating employs processes such as cleaning; pre-treating; pre-priming’ pre-painting and coating flat metal coils of steel or aluminium. The coated metal coil is subsequently supplied to equipment manufacturers to be formed into a range of ready-painted parts.
Pretreatments are often used to help provide improved corrosion resistance of the substrate, often by passivating or converting the metal surface, typically via phosphate or chromate chemistries. The type of chemical treatment varies with the type of metal being used. Additionally, pretreatment can enhance performance of the fully coated product by adding topography to the metallic surface to help facilitate the bonding between the metal and the coating.
Image: @ Alliance Steel.
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