June 24, 2006 (by Bill Orndorff) - To remove sealant from the wings of F-16 Fighting Falcons, Airmen at Hill AFB are replacing elbow grease and plastic scrapers with dry ice.
The new process, which uses a machine to blast material with dry ice pellets, saves time, money and manpower, and is easy to clean up, said officials from the 574th Aircraft Maintenance Squadron, adding the machine has already paid for itself.
"This is so much easier," said Dennis Hathaway, F-16 wing shop supervisor. "I used to crawl into a hole and scrape these wings upside down when I could have just stood and blasted it. Scraping sealant by hand is one of the worst jobs for a sheet metal mechanic. It uses too much manpower and can cause carpal tunnel syndrome."
At a cost of $27,000, the machine uses ice pellets in 600-pound containers purchased from a Salt Lake City ice company at 40 cents a pound.
Sealant is removed from F-16 wings before they are repainted with fuel-resistant paint. Mr. Hathaway estimates that an entire F-16 wing could be blasted in four shifts by one person. He said the process of scraping the wings took four shifts and three to four people per shift.
"In man-hours, the machine was almost paid for after the first use," Mr. Hathaway said. "The shop does six or seven wing skins per year; now all will be done by blast instead of scraping."
To remove the sealer, pellets are driven at 3.5 pounds per minute. The machine, which is not much bigger than a mid-sized barbecue grill, is capable of operating at one-half pound per minute up to seven pounds per minute. The ice is blasted through a blast swath nozzle using building-supplied air pressure at 80 pounds per square inch.
"The sealer is in a dry state, so once it's removed, it can be swept up and placed in the trash," said Marion Long, 574th AMXS structures section chief. "There's no biohazard or bead media to contain, and it's safe to use on aluminum as thin as thirty one-hundredths of an inch."
Workers do not need to wear a hazardous material suit to operate the blaster. The only extra equipment needed is a face shield to protect against sealant residue particles, thick gloves for handling the dry ice, and hearing protection.
With the blast pressure adjusted to 3.5 pounds per minute, dry ice pellets remove only the sealant and not the paint, Mr. Long said.
Dry ice blast machines often are used in the southern United States to remove mold spores from walls or other objects without damaging the surface. Indeed, one Salt Lake City business has used dry ice pellets for a gentler job -- removing soot from book covers.