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Art and science meet in anodized aluminum coil

Above: Coil anodizing is one of the most efficient and reliable metal preparation methods that exists within the fabrication industry.

Art and science meet in anodized aluminum coil

July 2022- There is an art and a science to modern metal processing and fabrication. Industry leaders are tapping into their historic metal fabrication expertise and weaving in the latest available processing methods to help meet customer demand.

One of the most popular methods is coil processing, which delivers benefits to fabricators and their customers alike. First-time users might ask how it works, why it’s important to manufacturers and how it stacks up against other forms of metal processing in terms of consistency, aesthetics and performance.


With aluminum, coil processing refers to series of steps to prepare the material, including anodizing, cutting to length (CTL), cutting to width (slitting), surface embossing and more.

Coil anodizing is one of the most efficient and reliable metal preparation methods that exists within the fabrication industry for a variety of reasons. First, it’s cost-efficient, because not nearly as much labor is involved compared to batch anodizing.


      Aluminum’s oxide layer does not rust, erode or deteriorate the substrate.

The anodizing process is highly reliable in terms of aesthetic finish because the entire length of an aluminum coil spends the same amount of time submerged in an anodizing bath. Therefore, color consistency of the final product is much more certain and predictable compared to batch anodizing individual components.

Other basic coil processing methods include cut-to-length, which encompasses unrolling portions of coil and cutting it to precise lengths as dictated by the customer. Slitting is a process that uses sharp rotary blades to cut through sheet in coil at specific widths. The aluminum is then fed through a guide and rewound into a narrower coil that can be shipped directly to customers in the precise size they ordered.

By adopting coil processing, fabricators and their manufacturing customers can obtain aluminum (raw or anodized) in bulk quantities. 


     Automation and continuity throughout the coil coating process minimizes the risk of color variation.


There are instances where batch anodizing is necessary, such as for anodizing individual components, extrusions, or unique or very large shapes that cannot be made with sheets of anodized coil. However, if coil or the many products that can be made from coil fit the need, choosing anodized aluminum can pay dividends.


Batch anodizing requires racking the aluminum component so that it can be dipped into an anodizing bath. There will be a rack mark wherever the racking mechanism is screwed or clamped onto the material. In addition, batch anodizing requires added labor just to rack the material in the first place, then operation of a crane to lift the metal into at least six and up to 12 tanks, unracking it, and all of the labor and supervision that process requires. These added steps are not required for coil anodizing.

“With coil anodizing, we can operate with three individuals in the entire facility,” explains John McClatchey, vice president of sales and marketing at SAF, a metal fabricator, distributor and finisher headquartered in Atlanta. “Coil anodizing is much less of a labor-intensive process compared to batch anodizing. Once you set up the coil and get the line running, the anodizing line does all of the work. You just need someone to monitor for quality and defects.”

The coil anodizing line can be set up to run for hours but the labor involved is not nearly as significant as batch anodizing, freeing up employees to tend to other tasks throughout the plant. At SAF, this reduced labor requirement can be passed on to the customer through appreciable cost savings.


“Coil anodizing is automated and continuous, which greatly reduces the risk of color variation,” McClatchey says. “Because the coil serpentines through anodizing baths, there are no rack marks, and the final product possesses a uniform coating with regard to both thickness and color.”

Standard anodized finishes typically include matte, satin and natural clear in a variety of tones (light to dark) based on the customer’s request. Color dye coil anodizing is also an option when specific colors are needed to complete a project. For example, if an architect specifies royal blue building facade panels to match an organization’s brand colors, special dyes can be added to the anodizing bath to achieve that custom color on an as-requested basis. McClatchey likens the processes to staining wood: The longer you leave it on, the darker the stain gets. In theory, anodizing is a very similar process. The more time aluminum coil spends in an anodizing bath, the darker the color becomes and the thicker the anodized layer gets.


The anodizing process yields a highly durable anodic coating on the surface of the aluminum sheet. It oxidizes the aluminum, but unlike what happens to other metals such as iron or steel, aluminum’s oxide layer does not rust, erode or deteriorate the substrate. In fact, the anodized layer protects the metal from corrosion and makes it a supremely durable metal finish. The aluminum oxide layer that is produced from anodizing is chemically bonded at the molecular level. Therefore, it will not chip or flake even after years of exposure to long-term and extreme weather conditions or other conditions. This is another reason why anodized aluminum is used in high-traffic areas on buildings, such as around walkways or entrances. Customers who choose coil processing can purchase thousands of pounds of this highly durable aluminum already anodized and ready for fabrication. It can come in a variety of gauges (up to 0.063 inch thick), lengths and widths to match customer specifications. Once aluminum is anodized, it’s ready for all other processes that customers need, such as cutting and stamping.


Metal fabricators are pressured to continuously identify ways to keep shelves stocked and manufacturing customers happy by supplying quality materials. For those on the hunt for high-performance, cost-effective metal, opting for coil over individual metal sheet panels is a logical choice. This is especially true for organizations that are consistently ordering aluminum because coil is sold in bulk by nature. “Coil processing and anodizing is the most budget-friendly solution for any kind of cladding or sheet metal project, and it provides superior durability and performance,” McClatchey says. MM



SAF, Atlanta, 800/241-7429, SAF.com/coil

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