Using zinc-based coatings to protect galvanized steel from corrosion has been standard practice in the steel industry for decades, but these processes have several key disadvantages. First, achieving longer corrosion performance requires thicker layers of zinc, which raises costs and also limits the ability to shape and bend the steel subsequently. Also, the coating processes often involve compounds containing hexavalent chromium, which presents serious health and environmental risks.
A series of coating formulations, known collectively as Intercoat ChemGuard, developed by Chemcoaters Inc. (Gary, Ind.; www.chemcoaters.com), overcomes these limitations. Using a reverse roll-coating process, the anti-corrosion coatings are applied over a steel substrate that has been coated with low levels of zinc. The coatings generate covalent bonds with the zinc on the steel surface, forming a layer of reacted material. Meanwhile, the outermost layer of the coatings remains unreacted, allowing the coating to have self-healing properties, which allows the corrosion protection to persist after the steel is cut or punctured.
“When Intercoat ChemGuard is applied over the lightest possible coating of zinc that is commercially available in flat-rolled hot-dip-galvanized (G30) steel, the anti-corrosion performance exceeds that of steel with the heaviest possible coating of zinc that is available in flat-rolled hot-dip-galvanized (G235),” explains Mike Tieri, vice president of sales and marketing with Chemcoaters (see photo). “And the coating process is based on trivalent chromium chemistry, which means it is compliant with the RoHS (restriction of hazardous materials) directive for hexavalent chromium,” he adds.
The proprietary coatings, containing both inorganic and organic components, can be adjusted depending on the requirements of an application. The coatings form surface crosslinks that allow the steel coated with Intercoat ChemGuard to be bent, flexed or welded. Other formulations maximize adhesion of paints and other subsequent coatings on the steel.
Intercoat ChemGuard products are available commercially now, and have been used to treat steel for the transportation industry and elsewhere. Chemcoaters is looking for partners to develop new applications for the technology.