| Maskant Material Substitution in the Aerospace Industry | United States | 1990 | Full scale |
MANUFACTURE OF OTHER TRANSPORT EQUIPMENT # 8
Background
Chemical milling is a weight reduction process utilized on aerospace and missile component parts without affecting their structural integrity. In the chemical milling process; most aircraft component parts are covered with a coating called maskant. The coated parts are scribed resulting in the removal of the maskant in certain selected areas as specified by the customer. The areas where the coating/ maskant has been removed are etched in the appropriate solutions, resulting in the removal of excess weight.
The maskant utilized in the operation had an adverse affect on the environment and workers. The formulation contained as much as eighty percent perchloroethylene and only about twenty per cent solids. Caspian in conjunction with Malek developed a high solids low volatile organic compound (VOC) maskant that replaces the solvent base formulation.
Cleaner Production Principle
Material substitution
Cleaner Production Application
This new technology not only reduces fugitive emissions from spraying and dipping applications it also eliminates any emissions from clean-up operations. The equipment instead of being cleaned with solvents is now cleaned with water. The water from the clean-up operation is flocculated and processed though a filter press and a standard activated charcoal cartridge. The remaining water is then recycled back to the clean-up operation and the dry solid is placed into a regular landfill.
Some companies have chosen to install expensive add on equipment; i.e., solvent recovery units to their operations instead of switching to less polluting waterborne products. Solvent recovery units are energy intensive thereby transferring the pollution source to the energy source. Also the carbon bed in the unit must eventually be disposed of at a hazardous waste landfill.
Caspian utilized approximately 23,000 gallons of the CAX waterborne maskant every year. Utilization of CAX waterborne maskant is proven technology. This material has been successfully applied at Caspian for over three years. It is also listed on the Boeing Process Specification BAC 5772.
The CAX waterborne maskant is readily available. Most of the equipment that is used for applying solvent base maskant can be easily adapted for waterborne maskant usage. There are several different formulations which can be modified depending upon the needs. The major equipment change would be the dip tank for which a design is readily available.
Environmental and Economic Benefits
This process reduces VOC emissions by as much as 95%. Therefore the workers are not being exposed to the carcinogen perchloroethylene. The cleaner production measures received positive support from the news media and regulatory agencies due to the drastic emission reductions at the facility. Table below provides the details.
| Waste Generation | Quantity Before (1987) | Quantity After (1990) |
| VOC emissions (tons) | 450 | < 8 |
| VOC emissions (g/l) | 1200 | 70 |
This is further illustrated by the fact that the San Diego Air Pollution Control District awarded Caspian l06.9 tons per year of Class "A" Pollutant Emission Reduction Credits. These credits are in the bank and can be used later for offsets at our facility or can even be sold to other industries that may want to expand.
The capitol investment to switch over to CAX waterborne maskants is the cost of a new dip tank and possibly an oven if one is not already available. Many facilities already have ovens, which are often already in use for solvent-based maskants. The cost of the oven and redesign of the dip tank are totally dependent upon the size of the unit.
Payback is instantaneous, due to more stringent environmental regulations. It is inevitable that industry will soon be required to: (a) switch over to waterborne technologies or (b) invest in expensive add-on control equipment. When all of the costs of these two compliance options are systematically compared, the CAX product requires one-tenth of the capital and only 80% of the operating costs verses solvent recovery.
Constraints
The major obstacle for switching to waterborne CAX is the method in which it is applied. Since water takes longer to dry and does not flash off like solvents the worker must be trained in the proper application. Even though the same equipment is used the method of application is different. Another obstacle is drying time in the oven. Since water is vehicle that carries the material to the part, it has a slightly longer drying cycle. VOC emissions are reduced but not eliminated by the technology.
Contacts
Citation: "Test Methods to Evaluate Waterborne Chemical Mill Maskant by Tom Foulds, Boeing Commercial Airplane Company", in 1st International (SAMPE) Environmental Conference, May 21-25, 1991, p. 104.
Level of Detail of the Source Material: additional information is available for all phases of this study by contacting the industry/ program contacts listed below.
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Review Status
This case study was abstracted from the document abstracted above for the US EPA's Pollution Prevention Information Clearinghouse. In 1994 it underwent a UNEP IE funded review for quality and completeness. It was edited for the ICPIC diskette in August 1995.
Subsequently the case study has undergone another technical review by Dr Prasad Modak at Environmental Management Centre, Mumbai, India, in September 1998.