News

Chromate extraction makes paint process safer, easier

  • Published
  • By Wayne Crenshaw
  • 78 ABW/PA
ROBINS AIR FORCE BASE, Ga. --  Preventing corrosion on aircraft is a top priority of the Air Force, and for many years hexavalant chromium has helped the service win that battle.

The substance is used in the conversion coat, which is applied before the primer to help the primer and paint stick to the aircraft. It's also used in the primer to aid in corrosion control.

The trouble is, it is hazardous, and requires painters to use air-supplied protective equipment. However, after years of persistence, the F-15 division at Robins became the first here to use a non-chromated exterior coat painting system.

At one point it seemed as if eliminating hex chromate might not even be possible, said John Stephens of the Aerospace Sustainment Directorate's F-15 Engineering section.

Numerous non-chromate primers were tested but none was found to be sufficiently effective. Stephens and other aerospace engineers feared the best they might ever do is a 50/50 mix of chromate and non-chromate primer.

But, in 2005, in conjunction with Deft Inc., an F-15 was painted with a 100-percent non-chromate primer which proved to be fully effective. The primer has been used on F-15s ever since, said Robert Harris, deputy chief of the paint flight.

"It's easy to apply too," Harris said. "It doesn't go on with a lot of the same issues."

Then, at Stephens' urging, Deft developed a product to eliminate hex chromate from the conversion coat. The product was shown to be effective in tests and, in November, it was used for the first time on a production F-15 here.

Since that time, the exterior surfaces of all F-15s painted at Robins have been chromate free. It is a dream-come-true for the 73-year-old Stephens.

"I'm elated about it because I've been working toward it for many years," Stephens said. "I postponed retirement because of it."

Painters still have to use a considerable amount of protective gear, including full suits and filtered masks, but they do not have to use air-supplied hoods.

More important, their exposure to hex chromate when painting exterior surfaces is 100-percent eliminated. It also means workers will eventually not be ex-posed to hex chromate during the stripping process, when the aircraft comes in for programmed depot maintenance.