San Joaquin Helicopters is an FAA-certified repair station in Delano, Calif. that offers services for contracted helicopter maintenance. In 2005, Steve Randalls, director of maintenance and Larry Bynum, component overhaul shop manager for the company, were trying to improve the process for stripping and cleaning aircraft components and parts. The challenge was to remove a polyurethane paint from a magnesium part without removing the chromate conversion coating.

The process being used at the time was ineffective and time consuming. It consisted of putting parts in a Panther 140 Paint Stripper for 16-18 hours followed by a pressure washer rinse to remove the paint which took another 15 minutes. Unfortunately the stripper also removed the magnesium film treatment which then required a new conversion coating to be applied.

This chemical removal process also required that the solid wastes be pumped to a holding vessel to remove the sludge and then the hazardous sludge had to be manifested and hauled away several times a week. Randalls was investigating options on the Internet when he came across www.armex.com, a Web site explaining the benefits of using a baking soda-based abrasive for cleaning and depainting. Soon Randalls was in touch with a local California distributor representative, Bob Strohmeier of International Surface Preparation, who would demonstrate the process for him.

Initial tests showed that ARMEX Blast Media was effective in removing the paint and leaving the chromate conversion coating intact. But, there was more work to be done. The team moved on to specify the necessary equipment and utilities to run the system. Strohmeier recommended a BioBlast DBS 4848. This is a fully contained glove box blast unit specifically designed to handle baking soda. There are a number of differences between stripping with a baking soda-based abrasive and a more conventional harder grit like plastic or glass beads. First, the baking soda particle is very soft, having a Mohs hardness of only 2.5. It is also extremely friable so that upon impact the particle shatters completely releasing all its energy onto the surface. As it breaks apart these smaller particles work to shear off the coating. The benefit inherent in this is that it has a minimal impact on the surface material and in this case the chromate coating. ARMEX can be used to strip in layers and will not pit or peen a surface nor will it cause crack closure.

"As for the time savings, we’ve cut the cleaning time in half for most jobs and by 10-15 percent more on others," said Randalls. ARMEX, www.armex.com, 800-332-5424.