Throw away little things and save big bucks? It hardly seems likely, but that's just what the U.S. Air Force is doing. At Randolph AFB, TX, they are putting usedand hazardous-air filters into a state-of-the-art industrial compaction machine and saving thousands of dollars in hazardous waste disposal.
The air filters contain aircraft paint removed by plastic media blasting (PMB). Small plastic pellets 'sand blast' off old paint to provide a fresh surface for repainting. Plastic pellets do not abrade the aircraft skin as a harder blasting medium can, thereby prolonging the life of the aircraft. The pellets are 'captured' by a filtering system and recycled. When the filters become clogged with paint residue, they are disposed of by a compaction machine built by Compacting Technologies International (CTI), Portland, OR.
The paint removal operation is conducted in a negative-pressure stripping booth where technicians in protective clothing operate the four high-pressure nozzles which direct the plastic pellets onto the aircraft skin. The stripping booth air is drawn through the filtering system to control emissions from the process and to collect the pellets for reuse.
About 134 T-37 and T-38 jet trainers of the Air Training Command are stripped each year at Randolph AFB. Approximately SO aircraft can be stripped before the 74 filters, each measuring 18 by 36 inches, in the PMB system must be changed. The CTI machine compacts several used filters at once in a SS-gallon drum for appropriate disposal. Air Force officials indicate that hazardous waste compaction and PMB are big improvements over the formerly used stripping system. Prior to adopting PMB, chemical stripping agents were used; this method generated 4,000 pounds of waste byproduct per aircraft. The use of PMB reduces the per-aircraft waste stream to just under 400 pounds.
According to CTI officials, high compaction ratios are possible because their machine offers advanced technology and design. The SS-gallon steel drums fit snugly into the machine's steel containment chamber and rest on a steel anvil which conforms to the underside of the barrel. The containment chamber's tight fit and the design of the anvil prevent the drums from distorting or splitting. Further, a hydraulically driven compression plate, or platen, conforms closely to the interior diameter of the barrels. It provides efficient compaction and prevents the escape of any waste material.