Cleaning technologies often depend on the dilution of contamination with an organic solvent, aqueous solvent, or blast cleaning media. Cleaning by one of these techniques results in large quantities of contaminated cleaning media which then must be disposed of or treated. Environmental regulations concerning these large volumes of waste make treatment and disposal options increasingly costly. However, several cleaning technologies circumvent this pollution problem by not generating any contaminated cleaning media. Unfortunately, none of the techniques alone will meet the cleaning needs required for aerospace detailed-part cleaning.
There are two technical objectives to be achieved by this project: (1) to develop and transition to a using customer a cleaning process for large (and small) aircraft components that does not require the use of water or volatile organic compounds and (2) to develop a process that will allow components to proceed directly to the next step in the process of surface cleaning without the need for subsequent treatments involving water or organic solvents.
Under this task, McDonnell-Douglas Aerospace-East (now Boeing Corporation) analyzed carbon dioxide (CO2 pellet blasting coupled with ultraviolet (UV) light and an activated oxygen technique to clean aluminum alloy. The CO2/UV light-activated oxygen cleaning technology is applicable to small- and medium-sized components which require a surface cleanliness suitable for bonding and produces no collectible by-products other than the soil being removed. This cleaning approach combines two established cleaning methods into a single system, namely CO2 pellet cleaning and UV light cleaning. CO2 pellet cleaning is an established technology which currently is being used at a number of Department of Defense depots. This cleaning method is used to remove carbon and other soils from airframe and engine components prior to inspection and repair. However, the cleanliness level achieved is not sufficient for bonding operations. UV light cleaning of organic contamination has been used primarily in the electronics industry for precision cleaning. However, UV light is only effective for cleaning thin film contamination. Laboratory testing (i.e., wet tape adhesion and salt spray) was performed to define and measure surface cleanliness levels needed for various subsequent processing steps to maintain and improve the performance of subsequent operations.
The dry ice pellet/UV ozone combination previously has been shown to be effective for cleaning metal surfaces. In the present effort, the utility of these techniques was extended to include the cleaning of complex parts, the cleaning of non-metallic parts, and the cleaning of objects prior to the application of optical and thermal protective coatings. In addition, an engineering model was developed that can be employed to design new UV/ozone systems and was utilized in a follow-on effort, sponsored by the Navy, that employed these techniques to coat thermally-protective coatings. These coatings were applied on shields used by Navy firefighters. At the conclusion of this effort, the CO2 UV/ozone technique was awarded the prestigious Clean Air Technology Award by the Union Electric Company of St. Louis, MO, for the utilization of a new technology that will reduce air pollution significantly. This project was completed in FY 1997.
The project benefits include improved worker safety; reduced environmental liability; uninterrupted production and repair of metal aircraft components; and reduced cost of storage, tracking, handling, and disposal of hazardous waste. The Army has estimated that seven times the purchase cost of a hazardous material is applied to managing the material. Assuming $.50/lb as an average, the cost would be $512,463/year. This results in a total savings of $603,474/year. Waste mitigation eliminates more than 340,000 pounds of waste annually. Qualitative benefits such as improved mission readiness, improved worker safety and health, and reduced liability must also be taken into consideration.