The first extraction and commercial applications of aluminum happened in the early 1800s, but by the end of the 19th century, aluminum was being produced in small, industrial-viable, amounts. By the early 1900s, aluminum production accelerated and rapidly became one of the most important materials in modern architecture with applications in both exterior construction and interior finish work. Aluminum is lightweight, resists corrosion, and has excellent finishing characteristics. Thanks to these qualities, the production of aluminum is second only to steel production worldwide.

As Advanced Finishing has become more involved in architectural aluminum coating services we have seen a significant increase in the amount of aluminum extrusion we finish. Most of this material is mill finish and in stock lengths anywhere from 10 to 24 feet. We pretreat and powder coat it per the customer’s specifications, usually before any fabrication or cutting operations. Thanks to the nature of the product and its high visibility, a high-quality finish product is expected, and defects due to dirt or contamination are not acceptable.

Architectural aluminum is frequently used for doors, windows, trim, handrails, and both indoor and outdoor applications. To further protect and prolong the product lifespan, there are four primary finishing methods offered by Advanced Finishing for architectural aluminum:

• Paint
• Powder-Coating
• Anodizing
• Dye-Sublimation

In this article, we will delve into the benefits of each as well as the so-called “pursuit of perfection” in architectural aluminum coating services and some of the complications that can arise during the process.

Finishing Architectural Aluminum – Stone Age to the Green Age

Aluminum is strong, lightweight, and easy to produce. It can be cast, extruded, welded, or otherwise fabricated into practically any shape or product. For many years, the dominant architectural aluminum coatings were solvent-based wet paint and anodizing. Millions of linear feet of curtain wall, window, and doorframe products are finished with these processes every year. Most likely, if you are an architect you have used products finished with these methods in some of your projects. As technology progressed, so too did the procedures for coating architectural aluminum. Advanced Finishing specializes in offering four coating methods:

Painting Architectural Aluminum

When early humans first started to scratch on the walls of their caves with burned sticks and crushed berries, they set the foundation of an industry that has continued and evolved for thousands of years. From cave painting to the painting of skyscrapers, the basic science of painting has remained virtually unchanged. The colored pigment suspended in a smelly liquid once spread over the surface of cave walls is still the most common type of finish used in modern architecture. Only today’s paints are not simple crushed flowers and berries.

Paints utilize many different elements and minerals for color and volatile organic compounds (VOCs) as solvents to help give them the performance characteristics that are required to maintain their color, gloss, and adhesion for many years.

Powder Coating

Fortunately, modern finishers have progressed out of the Stone Age and have entered “The Green Age”. Although architectural aluminum finishes such as solvent-based wet paint and anodizing will never disappear entirely, there are competitive finishes that the conscientious objectors of global warming and negative environmental impact can choose from. Some of these finishes are truly revolutionary. Powder coating has been a growing force in architectural aluminum for many years. With the growing importance of concepts like LEEDS and Cradle to Cradle (C2C), powder coating for architectural aluminum is likely to blossom to a full bloom over the next several years.

Powder coating is an organic, thermoset, dry film finish. It uses no solvents, contains no VOCs, and is non-hazardous, non-flammable, and non-toxic. Though it does take significant energy to produce, apply, and remove, powder coatings are extremely tough and durable. Additionally, the final colors and textures of powder coating are endless with more being developed each year. Powder coatings are already used on many C2C Silver and Gold certified products. A handful of companies, including Advanced Finishing, are certified to apply AAMA-2605 finishes to architectural aluminum, and the number is growing.

Anodizing

One unfortunate characteristic of aluminum is that it oxidizes very quickly and as a result, the exposed surface must be thoroughly protected. The surface of mill-finished aluminum already has a thin film of oxide on its surface. If the oxide is not treated, or passivated, any supplemental coating applied to it will eventually lose adhesion and fail. The process of treating the surface of aluminum with chrome has been widely accepted for many years. This procedure involves the use of strong acids and toxic heavy metals to build up a stable layer of aluminum oxide called an anodic film. The resulting film is porous and can be sealed with either a clear or colored material. This final finishing process is called anodizing. Anodized aluminum is by far the most common material for storefronts and the popular curtain walls used in modern architecture.

Dye-Sublimation

Currently, the newest technology in “green” or more eco-friendly architectural aluminum coating services is called dye-sublimation. This process must begin with a cleaned, pretreated, and AAMA-2604 powder-coated product. High-resolution computer-generated images, most commonly wood grain or replicated stone patterns, are then permanently tattooed into the powder coating. The result is a piece of architectural aluminum that is virtually impossible to distinguish from real wood or stone with all the physical advantages of tough and durable powder coating. Many abstract images or patterns are available through dye-sublimation, such as denim, tiger stripes, and camouflage, as well as custom images to suit several unique applications. Dye-sublimation can create an entire office wall system in incredibly realistic teak or mahogany without so much as cutting off a limb of real wood. It can also provide a large, durable winding stair rail resembling marble that would be impossible to manufacture out of real stone. This process has been in use in Europe and Asia for almost 20 years and is just now being offered here in the US.

Pursuit of Perfection – Troubleshooting Architectural Aluminum

At Advanced Finishing, we have had very good success to date, with a few exceptions. We recently ran a large fencing job with several thousand pickets. Near the end of the run, we started to find an increasing number of contamination particles under the powder coating. These particles ranged in size from as small as a spec of dust to as large as a flake of freshly ground pepper. By the end of the run, most of the parts were scrap and we had to strip and re-coat them. The customer was pressing us to ship, so at the time, we were unable to complete an exhaustive investigation.

After the parts shipped on time, we checked our wash line for concentration, temperature, and possible contamination, and found everything to be in order. The wash line is the first line of defense in physically and chemically removing any oils, soils, or contaminants that could be detrimental to the final finish. Next, we checked the dry oven to see if maybe there was dirt blowing around and sticking to the parts. A quick walk-through proved that the oven was clean. Then, it was on to the spray booth and the powder. Seeing as the problem gradually increased through the length of the product run, a member of the team suggested that there may have been some contamination in the box of powder, and as the box became empty, the concentration of contaminants increased as well. A quick check with the sprayer eliminated that possibility, as he had opened a new box near the end of the run. Besides, we ran some posts behind the pickets with the same powder and they all looked fine.

There was still something getting under my skin. Since the contamination was underneath the layer of powder coating, it had to be there before the parts were coated. Furthermore, with the contamination being limited to the pickets, and not affecting the other products, the problem had to be originating somewhere else. Despite this rigid detective work, the mystery persisted.

That is, until we were running an architectural job for a different customer, and guess what happened? We started seeing the same type of sub-finish layer contamination. The parts had been cleaned and coated and were being taken down when we noticed the contamination under the coating, only this time we had caught the culprit red-handed. We took an individual part displaying a few nice-sized pieces of contamination and hit it with a stripper. The stripper removed the powder coating but left the contamination on the part. It was a piece of aluminum chip pressed into the part! A little more investigation revealed the whole story.

First, the type of product was not mill-finished full lengths of the profile, they were cut to size and had machined areas. Just like the fence pickets, the parts were covered with aluminum chips from the cutting operation. But we have run parts with chips before and our wash line removes any chips. We have not seen this problem in the past, so why now?

This answer can be found in the old saying, “The road to success is filled with many potholes”. We have become more successful in the architectural aluminum market, and a significant portion of that aluminum is a work in process, so the presence of chips is unavoidable. With higher volumes of aluminum and bigger jobs moving through our facility, the cut product is shipped to us in larger bundles, and larger bundles have…more weight. The increased product weight is causing the chips to be further pressed and embedded into the aluminum itself. This is why the problem became worse as we moved further down the bundle of parts, with the worst parts at the bottom of the pile.

So what have we learned? Well first of all, when we run a job consisting of cut aluminum parts, we examine the parts for pressed chips, especially if the job is of a significant volume. Second, we recommend that our customers do not try to stack all of the parts on one skid. If possible they should break up the load into smaller stacks of product, or try to wipe off the parts before they pack them. Finally, when we see the potential for this problem, we notify the customer that we may have to charge extra for wiping each part to be sure there are no embedded chips. And the moral to this story is…”Don’t gamble on quality. Cash in your chips before you run the job!”

Unlimited Possibilities of Architectural Aluminum Coating Services

By specifying environmentally responsible finishes such as powder coating in place of wet painted or anodized finishes, architects can be sure that their projects are not just meeting GBA standards, but are leaving no trail of VOCs, heavy metals, or toxic waste in their wake. By using dye-sublimated finishes in place of natural hardwoods and quarried stone, architects can create their designs with a wider range of finishes that are practically unlimited in possibilities. Powder coating and dye sublimation are just as practical and effective on steel and other metals as well. Certainly, we have come a long way from the days of cave painting. We have truly gone from the Stone Age to the Green Age!

Editor’s note:

For more information, see Powder Coating magazine’s Web site at www.pcoating.com. Click on Article Index, Subjects, where you’ll find numerous case histories and technical articles on the topics covered in this article. If you would like to submit a question, click on Problem-solving. Select the column that fits your question, fill out the form, and send it to us.

Greg Yahn is president of Advanced Finishing USA, 7401 Klier Drive, Fairview, PA 16415, and Archi-Texture Finishing, LLC (A-Tex), 7401 Klier Drive, Fairview, PA 16415. He can be contacted at 814/474-5200, ext. 101; e-mail [greg@afusa.net]. He holds a degree in industrial engineering with a foundry emphasis from Pennsylvania State University, and an MBA from Penn State Erie, the Behrend College. He serves on the Penn State Cast Metals Advisory Board in State College, Pa.