POWDER COATING 101
An Important Part of Lighting Design

Improve Fixture Durability: Conversion Coating + Powder Coat
The durability and longevity of exterior lighting products are important aspects of their sustainability. If the products have a short lifespan, they will create more trash year after year than will a product that stands the test of time. If the product still works, but is an eyesore, it is not considered functional by sustainable standards either.

Metal is an excellent material to use for exterior lighting, because of its ability to absorb heat and be recycled. However, many metals, including aluminum, naturally corrode when they are exposed to water and oxygen.

Corrosion weakens the metal, first forming a pit or crack in the surface, which then spreads, causing deterioration and the eventual failure of the product. In order for metal lighting fixtures to provide reliable performance in the wind, snow, rain, heat, humidity and salt spray, the aluminum must be protected against the elements.

It should be noted that when aluminum is exposed to moisture or air, it naturally forms an aluminum oxide layer on the surface of the metal.

Unfortunately, this oxidized layer is non-uniform, provides poor corrosion protection, and creates a surface on the fixture that is difficult to paint.

Luckily, aluminum products and components can be protected against corrosion by being sealed inside and out with a pretreatment process called conversion coating and then finished with a dry coat of paint called a powder coat.

The conversion coating changes the surface of the metal to be more corrosion-resistant and to better grip the protective powder coating that will be applied to the metal after the conversion treatment has been completed.

The key to longevity for outdoor fixtures is to begin with a quality metal, such as copper-free aluminum. Then pre-treat the metal with a conversion coating to create a clean and corrosion-resistant surface and apply a tough powder coating that will protect the fixture from chipping, fading, cracking, or becoming otherwise defective. This combination treatment of conversion coating and powder coating significantly improves the durability and lifespan of the exterior lighting fixture in even the harshest atmospheric conditions.

Aluminum components can undergo a conversion coating by either being dipped into a solution or sprayed. When dipped, the conversion coating not only bonds to the metal surface, but wraps around the entire product creating an extra protective layer. With a dipped conversion coating, even if the surface paint is compromised, the aluminum will not deteriorate.

A conversion coating that is sprayed onto the surface of the aluminum creates a protective coat that is thinner and more easily penetrated. The spraying process also has a greater potential for creating a less uniform coating, which, subsequently, impacts its effectiveness in the field.

The Differences in Conversion Coating
Today, the two most popular corrosion pretreatments applied to exterior lighting fixtures are non-chromate conversion and chromate conversion coatings. The environmental impact of these two processes is staunchly different. One process employs a toxic chemical that pollutes the environment, is dangerous to handle, and hazardous to dispose. The other pretreatment process exists in a closed loop water system where all of the water is treated on-site and then reused. The differences between the non-chromate conversion process and the chromate conversion process significantly impact the environment, and the durability and the sustainability of the product.

Chromate-based Corrosion Treatment
The chromate-based pretreatment is the most typical conversion coat used in lighting. The Environmental Protection Agency (EPA) now strictly monitors this process and most manufacturers pre-treat their aluminum components offshore to minimize costs and regulatory oversight. These systems employ toxic chromium compounds that pollute the environment and present grave problems with handling and hazardous waste disposal. Workers must be instructed in safe handling procedures, because chromates are acidic and will attack living tissue.

Special disposal requirements are in place to regulate the discarding of materials that include chromate compounds. One reason for the extra care is that chromates may cause spontaneous combustion if concentrated products are mixed with other substances, especially paper, rags, wood or flammable solvents. The Environmental Protection Agency (EPA) has classified chromium as a hazardous waste and requires that special measures be taken to remove the toxic material before the product is dropped into special, pre-determined landfills in the United States.

Another reason for the cautious disposal of chromate-treated materials is that the materials could contain hexavalent chromium. Hexavalent chromium (the dangerous toxin exposed in the film,Erin Brockovich) is highly toxic, a carcinogen and can have disastrous effects on the surrounding population if it seeps from a landfill into the soil or water.

Exterior lighting fixtures that undergo the chromate conversion treatment are exposed to and contain hexavalent chromium. Because of the presence of hexavalent chromium in the metal, exterior lighting fixtures that have been pretreated with a chromate conversion process are not allowed to be sold in the European Union (EU). The directive, entitled the Restriction of Hazardous Substances (RoHS), bans selling electrical or electronic equipment that contains hexavalent chromium in that EU in the hopes of preventing chrome from leaking into the soil.

Non-chromate Conversion Treatment
Over the past few years, a new, non-toxic, non-chromate conversion process has been developed. This non-chromate conversion coat process is completely safe, non-hazardous and environmentally responsible. It cleans and conditions the substrate of the alloy through a non-toxic method to provide the long-term resistance to corrosion and tenacious adhesion to the protective powder coat required in a conversion treatment.

The active ingredient is de-ionized water-- water that has been electrically charged. This natural resource is a powerful metal cleaner. It reacts with the aluminum, penetrating the pores of the metal and removing dirt and impurities. In fact, de-ionized water is so successful at penetrating the surface of the metal that if left in the cleanser too long, the solution will start to etch the surface of the aluminum.

There are many steps in both the chromate and non-chromate conversion process. In the non-chromate process the best results are achieved if de-ionized water is used in each step. The use of water throughout the treating process does not create a lot of water waste. The non-chromate process exists in a closed loop water system that filters the water after each treatment and then reuses it, eliminating emissions and water waste.

The material filtered out of the metal is simply dried and disposed of in the regular trash.

The non-chromate process creates corrosion-resistant products that are chromium free. These chromium free fixtures meet RoHS compliance and are welcome on the EU market and in the EU landfills.

Aluminum treated in the two different processes also performs differently.
Chromate treatments dry and crack at temperatures above 150 °F. Non-chromate conversion coatings stay hydrated in temperatures up to 600 °F. The non-chromate method also provides a visual indication of the successful coating of the product and identifies those areas that may require additional attention.

A Closer Look at the Powder Coat
Powder coating is the fastest-growing finishing technique in North America and for good reason. Powder coating applies decorative and protective powder coat finishes to a wide range of metal parts. The powder used in this process is a mixture of finely ground particles of pigment and resin, which is sprayed with a special spray gun that electro-statically charges the powder. The charged powder adheres to the electrically grounded parts. Then the powder is heated and fused into a smooth coating in a curing oven. The result is a uniform, high-quality and attractive finish that is highly durable, as well as scratch- and chip-resistant. Powder coating can be done in a variety of colors, a wide range of glosses, diverse textures and different base resins to create a broad selection of coating properties.

Powder Coat Warranty
While the powder coating process may be described similarly from manufacturer to manufacturer, the durability of each powder coat can be significantly different. Warranties on conversion-coated powder coat outdoor luminaires are 5 years and more often than not these fixtures will retain their original finish. By contract other inferior powder coating processes will need to be replaced up to eight times to match the lifetime of a more durable product.

The American Architectural Manufacturers Association
AAMA
is the group within the aluminum products industry responsible for certifying that a powder coat warranty is accurate.

The warranty guarantees that the finish on the exterior aluminum fixture will withstand the elements for that specified period of time. In order to verify these claims, the certification process places materials under a variety of stresses designed to simulate an extreme outdoor experience including intense heat, salt spray, boiling water and abrasion tests.

 

 
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