Corrosion Resistant Powder Coatings

Question:

Some of the outdoor equipment (switchgear, transformers, etc.) we make is mounted in extremely corrosive atmospheres in Korea. It often corrodes within a year of installation. These products are liquid coated using air-dry enamel after being sandblasted and coated with an iron phosphate pretreatment. Will we obtain better results if we switch to powder coatings? If so, what coating is preferred? M.K.

Answer:

Products similar to yours have successfully been powder coated for over 30 years. In fact, some of the first powder coating systems ever installed were designed to coat transformer and switchgear products. However, successful programs take advantage of more than just powder coating technologies. For instance, you must first design a product that allows for moisture and corrosive chemicals to freely shed from the product's surface. Allowing these corrosion-producing agents to pool on the product's surface will shorten the product's life in the field.

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Next, select a corrosion resistant substrate to build your product. Galvannealed steel has proven to be a good choice for this application. Then select a good powder coating formula to achieve your desired results. Epoxy is the best powder coating for corrosion resistance and is normally used on transformer products. Yeah, I know that epoxies will chalk and fade in outdoor environments. However, most all transformer manufacturers don't particularly care if this happens since these transformers are pole-mounted.

Finally, you must install and operate a process that is capable of producing a corrosion resistant coating. This means using zinc phosphate and a good sealer over the galvannealed steel, along with DI water final rinses. If these chemistries are not properly controlled and the equipment properly maintained, your customer will still be disappointed. Don't forget about fully curing the powder coating, since corrosion properties are developed late in the cure cycle of powder coatings.