Coil coating is one of the most advanced, efficient and environmentally friendly means of coating metal. Using prepainted metal can provide manufacturers with a streamlined manufacturing process, cost savings and a more environmentally friendly plant.
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In the old days of traditional manufacturing, steel and other metals arrived at factories in a raw, untreated, unpainted state. Companies would fabricate and paint or treat the metal components of their product at the plant. This was a costly, time-consuming and environmentally harmful practice. The coil coating process was pioneered in the s for painting, coating and pretreating large coils of metals before they ever arrived at a manufacturing facility. The Venetian blind industry was the first to discover the benefits of prepainted metal.
Today, more than 800 million tons of coil coated steel and aluminum are produced and shipped in North America alone each year. Industry leaders using coil coated metal include GE, Whirlpool, Trane, Mercedes Benz, Nordyne and Steelcase, to name just a few. Thousands of products in dozens of different industries are made more efficiently with prepainted metal.
Major industries include building products such as metal roofs, wall panels and garage doors; office furniture (desks, cubical divider panels, file cabinets and modular cabinets); home appliances (refrigerators, dishwashers, freezers, range hoods and microwave ovens); heating and air-conditioning outer panels and ductwork; commercial appliances; vending machines; foodservice equipment and cooking tins; beverage cans; automotive panels and parts (fuel tanks, body panels and bumpers); and other components. New applications make the switch every year.
Coil coating is one of the most advanced, efficient and environmentally friendly means of coating metal. Large coils of metal (including cold-rolled steel, hot dip galvanized, electro galvanized, zinc-steel, aluminum, stainless steel, copper and brass) can be coated in a continuous, highly automated process prior to fabrication. During this continuous process, the metal is unwound and then cleaned and chemically treated. Depending on the product specifications, one or both sides may then be primed and/or topcoated, oven cured, and rewound for shipment.
The variety of coatings available is almost unlimited and includes polyesters, polyurethanes, epoxies, vinyls, plastisols, acrylics, waterborne emulsions, zinc-rich coatings, fluorocarbons, dry lubricants, and treatment and primer combinations. Moreover, product quality is continually improving as a result of new industry-specific coatings that are regularly coming to market and advanced testing performed throughout the coil coating process.
The prepainting process is designed to produce highly uniform, impeccable-quality coatings. The coatings are precisely applied with special equipment that provides a high-quality finish. The coatings can be on both sides of the metal and meet the finished product specifications. Manufacturers using prefinished metals will find consistent color, texture, thickness and performance in their finished products.
To ensure the best possible results, numerous quality control tests are performed during the coil coating process. For example, before coating, the metal substrate and the viscosity, color, gloss and physical performance of the paints are tested. As the uncoiled metal is coated, the surface treatment process is tested and adjusted continuously to ensure a high-quality finish. In addition, the paint thickness, curing temperature and production line speed are controlled and measured. Coating performance, including features like gloss, color, hardness, adhesion, and resistance to cracking and marring, are inspected as the coated parts leave the production line. After production, parts are tested for corrosion resistance with salt, chemical sprays and/or water immersion. Additionally, they&#;re examined for heat resistance, accelerated ultraviolet and environmental exposure. Other tests conducted on coil coated parts include stain-resistance, welding capability, and resistance to abrasion.
Prepainted parts can outperform post-painted applications because prepainted metal coils are uniformly cleaned, pretreated and painted as a flat surface. The primer coat also prevents the undercutting of paint and enhances corrosion resistance, the durability of the product and overall quality. Furthermore, the coatings are tightly bonded to the metal and often are applied to both sides of the metal.
Moreover, there is almost an unlimited selection of available prepaint coatings. These coatings are available in various degrees of gloss, color, textures, lubricity, flexibility and combinations thereof. Various primers can be selected to help create an industry-specific coating system that maximizes the performance of the product for special end-use applications.
For a manufacturer using painted steel, aluminum or other metals in the manufacturing process, the process of coil coating can dramatically improve productivity, reduce processing costs, improve quality, and reduce inventory and environmental/emission concerns, all at the same time. Just ask Trane, Inc., a manufacturer of commercial air handlers. Quality has always been a top priority for the company, and this led to the switch from post-painted metal to coil coating technology.
Several products at the Trane facility in Cullen, LA, are currently being produced using a new prepainted FAS-NER from AKH Inc., with prepainted metal. The fastener system is a simple punch and die operation, which automatically feeds, punches, inserts and locks a self-piercing fastener to produce a solid joint in one high-cycle operation. The fastener is inserted directly into prepainted metal without the need for pre-punched holes. This feature saves time and labor costs associated with tooling maintenance.
In the past, the Trane air handlers were spot-welded and then post-painted. Now, the products are completely assembled with prepainted metal. Since converting, Trane has seen an increase in productivity and profitability. Trane reports they have also experienced more consistency in the strength of the joint, as well as a better product appearance.
Several major appliance manufacturers also have experienced the benefits of using the combination of the AKH FAS-NER and prepainted metal. The fastener color is matched to the color of the finished product, allowing for the elimination of post-paint operations.
The benefits of prepainted metal are many. It can be used for most product applications and will provide manufacturers with a streamlined manufacturing process, cost savings and a more environmentally friendly plant.
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Although the prepainted metal process has been around for years, a few misconceptions about the process still exist.
Like most manufacturers, companies are often burdened with adapting their paint shop to changing environmental standards, strict health regulations and increasing overhead. Businesses are trying to lower costs and remain competitive. Outsourcing the metal treatment and coating operations can alleviate or even eliminate these costs.
One recommendation is to establish a prepaint conversion team, consisting of internal and external managers and suppliers, to analyze the products and process to determine if prepaint conversion is practical. This team can also act as a steering committee once implementation begins.
After the initial analysis determines that the use of prepaint is practical, a cost justification study should be conducted to determine the full economic impact of the proposed conversion. This analysis should answer three major questions:
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Once the conversion process is complete, the plant will run more efficiently, more effectively and more economically. Switching to prepainted metal can improve your product and your bottom line.
Coil coated metal can be formed without any loss in surface quality or appearance. In fact, the paint system can be designed to have greater flexibility than the metal and can be shaped with a finish that is actually superior to post-paint. This is because post-painted surfaces often suffer from dirt and oil residue, uneven application, and other imperfections. After the metal has been precleaned, preprimed, pretreated and prepainted, it can be formed. The paint layer is often more flexible than the underlying metal substrate.
Some manufacturers are concerned with exposed cut-edge on prepainted metal, but research has shown that prepainted cut-edge actually holds up better over time than post-painted surfaces. The National Coil Coating Association (NCCA), with the help of PPG Industries, Inc. and the North American Zinc-Aluminum Coaters Association (NamZAC), compared the corrosion resistance of prepainted cut-edge with three types of post-paint.
Prepainted metal louvers with exposed cut edges were tested in the field alongside three sets of metal louvers, one with a post-painted electrocoat, a second with a powder finish and a third with a spray finish. The parts were made of hot dipped galvanized steel, and the louvers were exposed to the same environment over time in Daytona Beach, FL. After 16 months, 44 months and 68 months of exposure to the elements, comparisons showed that the corrosion resistance of the prepainted parts was repeatedly and significantly better than the post-painted parts.
The reason the prepainted parts outperformed post-painted ones is that prepainted metal sheet is uniformly cleaned, pretreated and painted as a flat surface, so the edge-to-edge and side-to-side variability is virtually eliminated. In addition, the prepainted part has two coats (primer and topcoat), and each is tightly bonded to the metal as compared to a post-painted part, which generally has only one coat of paint. In most cases, the prepainted part has paint (one or two coats) on the backside; in comparison, post-painted parts at best have a minimal amount of overspray. Uniform pretreatment and paint on the backside of a part increases the corrosion resistance of the part, enhancing long-term durability.
More and more manufacturers are realizing that precoated metal can be joined easily - using adhesives, a variety of mechanical assemblies with or without fasteners, or even welding - and still retain a more beautiful and flawless surface than post-painted metal.
Using adhesives as a joining method offers a variety of benefits such as smooth surfaces, clean contours and uniform stress distribution. Adhesives also seal joints away from the elements. Mechanical assembly works well with prepainted metals, both with and without fasteners. Nuts, bolts and screws are cost-effective fasteners that offer design flexibility and allow for parts to be disassembled. Using rivets offers excellent shear and tensile strength as a fastener. Prepainted metals can also be assembled without fasteners by using a variety of methods, including lock and seam, pierce and tab, or stake and clinching methods. Welding is also an option for joining prepainted metals. Working closely with a coil coater can make welding an attractive joining option.
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5. Myth: You can&#;t handle coil-coated metal without marring the surface.
Fact: Precoated metal can be shipped on flatbed trucks, moved using forklifts, stored as coils for long periods - and still retain a more beautiful and flawless surface than post-painted metal. Prepainted metal can be handled successfully without harming the surface.
Source: NCCA
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Converting from in-house post-painted metal to outsourced prepainted metal can save manufacturers money and time, and can ensure that products are the highest possible quality. The most important issues to consider when converting to a prepaint operation are timing, capital outlay, manufacturing costs and environmental compliance. Following are 10 indicators that a manufacturer should consider using prepainted steel or aluminum:
1. In-house paint shop expenses are on the rise. When maintenance budgets are growing and capital investments are required to comply with strict EPA regulations, prepainted metal and aluminum is often a cost-effective alternative to in-house paint lines. Many hidden costs are associated with in-house spray or powder operations. Staffing with trained personnel, equipment, supplies and even environmental compliance all contribute to the expenses of owning an in-house paint shop.
2. Internal operating costs need to be lower. Many manufacturers are searching for ways to lower operating costs in order to remain competitive. Through outsourcing prepainted metals, factories can eliminate costly in-house paint operations and the associated expenses of manning the production line. Some of the major cost savings of prepaint conversion include inventory, environment, insurance, cleaning and waste removal, purchasing raw materials, and operating costs.
3. Plant capacity must be increased. By purchasing prepainted metal, plants are actually outsourcing the painting process and can eliminate or greatly reduce the size of in-house paint shops, generating more floor space for other uses.
4. Coating quality needs improvement. Coil coated metals are uniformly cleaned, pretreated, painted and cured as a flat surface, so that the edge-to-edge and side-to-side variability is virtually eliminated. The prepainted part has two coats of paint (unlike powder coating, which has only one) that are bonded tightly to the metal.
5. Downsizing and/or combining plants is taking place. A good time to consider using coil coated metals is when other major manufacturing changes are taking place. Manufacturers can reduce expenses significantly and increase paint quality greatly by outsourcing the painting process. Coil coated metals can be effectively handled, cut with superior corrosion resistance, joined with welding and adhesives, and formed for many uses&#;all with a beautiful finish.
6. New product models are being considered. Many times when design changes are being made, a prepainted metal can be specified and the new design can be more cost-effective to produce.
7. Manufacturing bottlenecks are reducing productivity. Many delays in a plant are caused by paint issues such as stoppage while parts are painted, dried and cured before moving to the next phase of assembly. These bottlenecks can be eliminated with prepainted metal. Prepainted steel and aluminum are uncoiled, cleaned, primed and painted to a manufacturer&#;s specifications and re-coiled prior to shipping to the factory.
8. It&#;s time to update or replace the paint line. Capital expenditures can be avoided and long-term cost savings achieved by choosing prepainted steel and aluminum, rather than refurbishing or replacing a paint line.
9. A strategy of outsourcing is being implemented. Purchasing prepainted metals is a cost-effective outsourcing option that actually improves the durability of the coating.
10. New fabricating or material handling equipment is being evaluated. When significant changes are made at the plant, it creates an opportunity to improve many aspects of the manufacturing process, including the use of prepainted metal.
Source: NCCA
How does the coil coating process work?
Coil coating is a continuous and highly automated process for coating metal before fabrication. In one continuous process, a coil of metal, up to 72 inches wide moving up to 700 feet per minute, is unwound and both the top and bottom sides are cleaned, chemically treated, primed, oven cured, top coated, oven cured again, rewound and packaged for shipment.
More specifically, bare coils of metal are placed on an unwinder or decoiler where the metal is observed for defects. The metal is then cleaned and chemically treated in preparation for painting. Brushes can be used to physically remove contaminants from the sheet, or the metal may be abraded by flap sanders to further enhance the surface. Pretreatments may be used to provide the bond between the metal and the coating, in addition to making the product corrosion resistant. The type of chemical treatment varies with the type of metal being used.
After drying, the strip enters a coating room for a coat of primer usually on both sides of the sheet. The pickup roll transfers the coating liquid from the pan to the applicator roll. The liquid is then pumped into the pan, and then overflows back to the supply reservoir, where it is remixed and filtered.
The direction of the rotation of the applicator roll plays a part in determining the type of coating. Reverse roller coating, when the applicator roll turns in the opposite direction of the strip, is used to apply thick coatings. Direct roller coating, turning in the same direction as the strip, is used for thinner coatings, 0.5 mils or less.
The paint sheet then enters an oven in which the coating is cured at high temperatures for 15 to 30 seconds. The strip exits the oven and is cooled with air and water. A majority of specifications call for two coats (primer and top coat) on each side of the sheet, requiring a pass through a second coater room and oven. The fully painted sheet then exits the second oven and is cooled before inspection and rewind.
Since the process allows metals to be finished in one continuous pass, there is flexibility in how the metal is coated and the types of coatings. Organics and inorganics, such as polyesters, epoxies, vinyls, plastisols, acrylics, water-born emulsions, fluorocarbons, dry lubricants, treatment and primer combinations, can be applied. Prepainted coils can also be printed, striped and embossed to create special visual effects.
Coil coating provides for controls that are virtually impossible to attain with most other painting processes. Dealing with a flat sheet allows for mechanical cleaning in addition to the spray cleaning. The flat sheet also enables excellent control of coating weights of both the pretreatment and the paint to within a tenth of a mil or less, depending upon the equipment and the paint system being applied. Such advantages, along with the economic and environmental benefits, make coil coating the right choice for many manufacturers.
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