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4/1/1996 | 6 MINUTE READ

Modernizing an Obsolete Coil Anodizing Line

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Able to meet any challenge, modernizing an old coil line was a formidable task...


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Give Southern Aluminum Finishing (SAF) a design challenge and its aluminum fabrication and applications experts will provide a solution. Headquartered in Atlanta, Georgia, the company was founded in 1946. Within a few years it expanded into metals distribution. By 1962, plant capacity had grown and Alcoa's Duranodic process was incorporated. A decade later a second anodizing plant came on line in Charlotte, North Carolina. In 1977 the Atlanta paint line opened, followed by state-of-the-art two-step anodizing. The 1980s brought about the expansion of SAF's custom aluminum fabrication business, and in 1989 powder coating came on line.

Purchasing an old coil line. In August, 1993 the coil anodizing division faced a challenge when it purchased an old coil line from a recently closed coil anodizing facility. Much of the badly neglected equipment needed repair, reconditioning or replacement. Problems that prevented the line from operating were addressed first.

Reconditioning the line. Reconditioning began with repairing leaks in processing tanks that had developed after years of galvanic corrosion. Both the pre-seal and hot-seal tanks required complete relining with fabricated stainless sheet.

Problems with the boiler and related systems were tackled next. The boiler was in miserable shape and the second pass tubes required replacing. Massive scale deposits had accumulated during years of operation without chemical treatments. Workers removed the scale and set up a chemical treatment system.

A state-of-the-art Honeywell controller replaced the obsolete vacuum tube boiler controls. Many steam coils were also replaced, and steam traps and vacuum breakers added.

The design of the steam ventilation system was inadequate for solution heating. It was modified in order to reach the temperatures necessary to achieve seals needed to pass the Acid Dissolution Test (ADT). There were no temperature control systems on any of the individual process tanks; consequently, controllers were added to each tank.

Two of 28 anodizing power-supply modules were completely missing. Faulty transformers plagued three of the remaining 26 units. The result was a reduction in the original design capacity of 17.8 pct. All five modules were replaced. In addition, all the remaining 23 modules were completely reconditioned. The power-supply control package required factory repair. All bussing connections were remade and new cable connections installed. Even the cathodes required repositioning for even distribution of the anodic coating over both sides of the sheet.

The refrigeration system also required attention. Workers replaced two of four system compressors immediately. The condenser operated temporarily until its replacement arrived. Refrigeration controls were also replaced.

Violations by the previous owner had forced the local regulatory agency to plug the discharge line in the wastewater system. SAF designed and installed a PLC-controlled wastewater treatment system before the first test coil was pulled through the line to ensure compliance with all federal, state and local environmental regulations.

In early 1994, many engineering projects were scheduled around production. Some of the more prominent projects included roller leveling and alignment, frictionless anodizing roller rotation, improved color uniformity and water conservation.

SAF personnel quickly learned the importance of precision balancing, leveling and roller alignment. During the first alignment project, entire tanks were moved as much as three inches. One end of a set of pinch rollers was raised more than two inches. Machinists performed the roller balancing. SAF personnel, however, performed all leveling and alignment activities. Leveling equipment progressed from a carpenter's level to precision machinist level, while alignment techniques progressed from using strings to lasers. Through SAF-developed techniques, the entire line can be aligned and leveled to plus or minus 0.001 inch within one eight-hr shift.

One particularly difficult roller problem involved the Teflon bushings used as anodizing roller bearings. Not only did they require frequent replacement, resulting in downtime, but even new bushings were not sufficiently friction free to allow foil range gages to turn the rollers. Complete redesign was required.

Adding dyeing. When SAF entered the dye market, new problems arose. Coating uniformity on both the sheet's top and bottom became critical. In addition, uniform dye distribution was necessary. SAF engineered the necessary modifications and began producing consistent color both across and on both sides of the sheet. Using a HunterLab spectrocolorimeter allows SAF to maintain color throughout production runs with variation that is undetectable by the human eye.

Water conservation is also a priority. With the addition of numerous recycling streams, water use dropped 83 pct for some materials processed. As SAF's success with water conservation increased, concentrations of metals in the wastewater also increased. To ensure compliance, separate batch systems for separation and removal of nickel and copper were installed.

During the first year of operation, the company did not aggressively seek sales. This allowed time for SAF to complete major engineering projects. As projects concluded, sales activity increased. During the second year increasing the capabilities of the line was a priority. If the line was to produce a high-performance, highly aesthetic, quality product, much work was still required. Although SAF employed four degreed engineers and two degreed chemists with anodizing experience, many obstacles they confronted were unknowns due to the differences in batch and coil anodizing. Troubleshooting was often difficult. With these obstacles removed, SAF's capabilities increased and quality coil anodizing projects were sought aggressively, including large and small jobs.


One-side or two-side option. Immediately upon entering the coil anodizing market, SAF discovered the necessity of offering customers the option of having either one or both sides of the coil anodized. Although many customers require anodizing on both sides, it is not necessary in many applications.

Tight color tolerances maintained. SAF uses a spectrocolorimeter to ensure each customer's color specifications match consistently. In the past, anodizing relied on operator subjectivity using high- and low-range samples. Sometimes light booths were added to help. Color matching was more of an art than a science. The spectrocolorimeter makes color matching a science.

Eight stock colors. SAF stores eight stock colors on site, including red, yellow, teal, green, brown, black, purple and lavender.

On-site color matching. For customers requesting a custom color, SAF has a dye lab on site. The customer supplies a sample and tells the chemist the application. A match is recommended using an appropriate dye. Light-fast dyes are recommended if the product will be used outdoors.

Seal to specification. Many customers require a seal that passes the ADT seal quality test (ASTM B680-80), including many automotive and architectural applications. The line produces coating thicknesses ranging up to 0.425 mil for both clear and dyed coatings. For coating thicknesses greater than 0.425 mil, the dye tank provides additional seal time but eliminates the dye step, limiting the product to clear coatings.

Many interior applications do not require a passing ADT. In this case, SAF offers a seal that simply passes a dye stain test (ASTM B136-69), and is less expensive.

PVC application. To protect the anodized finish during handling, PVC application is available as the anodized coil is recoiled.

Slitting. On-site slitting is available to tolerances of plus or minus 0.005 inch. With the addition of an edge guide, the company now offers "zero edge trim" slitting capability.

Someone once said, "Be thankful for problems. If they were less difficult, someone with less ability might have your job." Loosely translated, if it was easy, everyone would be doing it. These were some of the difficulties SAF faced during its renovation of an old coil anodizing line. The result is a one-stop shopping.

When combining all the coil anodizing and slitting capabilities in Nashville, with the cut-to-length, fabricating, painting and batch anodizing capabilities of the Atlanta and Charlotte facilities, SAF offers one-stop shopping for aluminum coil processing.

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