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Advanced finishes: Environmental benefits of extruded aluminum

New painting and coating processes for extruded aluminum products offer unmatched environmental advantages for the green building and construction industry. Versatile,strong and long-lasting, extruded aluminum is the material of choice for architects and contractors.In addition to its flat-rolled form, which is easily fabricated, aluminum can be extruded into virtually any constant cross-sectional shape in continuous lengths. Applications range from building and column coverings to windows and doors to railing systems, divider panels, decorative trim, fencing and more.

Aluminum's attractive and corrosion-resistant natural finish never needs painting and is virtually maintenance free. Now, new technologies for powder coating and anodizing are expanding the design possibilities and aesthetic benefits of architectural aluminum products.

Powder Coating
Environmentally Friendly and Durable with Wide Color Choices
Compared to liquid painting, powder coating is a solvent-free process that uses no volatile organic compounds that are detrimental to the environment. It is available in a wide selection of colors and gloss values, all offering superior corrosion and weather resistance, as well as durability. Starting with a clean metal surface,products are pretreated with a five-stage phosphate process. Next, resins (binding agents that form the surface) are applied in combination with pigments for color and strong coverage,fillers for specific properties, and hardeners to increase the surface strength. Painted parts are oven cured at 375 F (190 C) for at least 20 minutes. The newest powder coating materials can be finished under lower temperatures, reducing energy consumption.

Sapa Extrusions operates advanced powder coating facilities at many of its 16North American plants. At Gainesville, Ga., the company's Eco-Powder Coating system uses dual powder coating booths, each with 32 oscillating guns and an operating system that quickly adapts to a variety of customer shapes and specifications. The line can paint 25- foot- (8-m-) long extrusions at speeds up t25 feet per minute. The process utilizes over 97 percent of the coating material by reclaiming overspray to minimize material waste and reduce environmental impact.

Powder coating is unique for painted extrusions that meet or exceed AAMA 2603, -04 or-05 standards and is also RoHS compliant. The coatings can uphold specified color and gloss during 1,500 to 4,000 hours of accelerated salt spray corrosion tests. These coatings can also be tailored to meet solar reflectance requirements and reduce heat island effects in more developed spaces. Overall, powder coating provides environmentally conscious industrial finishes, creating sustainable products that are visually pleasing and corrosion resistant.

 

Anodic Coatings
Superior Finish Without Hazardous By-products
Anodizing is one of the most environmentally friendly metal finishing processes. As the green finish for aluminum, anodizing is the controlled electrochemical process that converts the barrier layer of aluminum into aluminum oxide.

Aluminum parts are immersed in a sulfuric acid electrolyte and electrical current is passed through the solution to produce aluminum oxideon the parts. The resulting aluminum oxide film is similar in hardness to a ruby or sapphire.The anodic coating is formed from the barrier layer of the substrate aluminum (the coating is actually part of the metal), not an externally applied substance such as paint. The porosity of the aluminum oxide allows for subsequent finishing with electrolytically deposited color or any number of dyed finishes.

The process produces no hazardous byproducts- many of the process baths (which are filtered by a dedicated process) are reused or recycled. The recycled acid etch by-product has several industrial applications.

Sapa plants in Portland, Ore., and Delhi, La., use Sapa Select advanced acid etch processes installed in 2009. An improved process over traditional caustic soda etch, Sapa Select hides metal imperfections (streaks, die lines, etc.) and provides a superior uniform matte finish. The surface has gloss readings from 4.0 to 6.0, compared to caustic etch readings typically from 9.0 to 18.0. In addition, Sapa Select removes 90 percent less aluminum during processing, advantageous when tight tolerances are required, and leads to an 85 percent reduction in the amount of landfill waste sludge.

Using traditional sulfuric/dye equipment,anodizing is available in Clear, Gold and Black, and Brite Dip (chemical polish) finishes in lengths to 18 feet (5 m). Fine, medium and coarse matte etched finishes are offered in clear, as well as the full range of architectural bronze colors (Champagne to Black) are available up to 30 feet (9 m) in length. For applications requiring extreme abrasion resistance, hardcoat anodizing is available. All anodized finishes provided by Sapa Extrusions meet or exceed the requirements AAMA 611-98 and/ or military specification MIL-A-8625F.

 

Green Aluminum
Recycled and Recyclable
Many Sapa facilities now offer Sapa Green billet on request with external/internal recycled content that exceeds the U.S. Green Building Council's LEED Standards. Remarkably, 75 percent of all aluminum produced since 1888 is still in use.

With its recyclability, ease of fabrication, environmentally friendly coatings and finishes,aluminum extrusions are the natural choice for versatility, economy and beauty in a wide range of architectural and building applications.

Wendell Nash is the paint manager at Sapa Extrusions in Gainesville, Ga., and Bill Bishop is the anodizing manager at Sapa Extrusions in Portland, Ore. For more information, go to www.sapagroup.com.