7bis paper examines the use of selected solvents in degreasing, cold
PRIMARY AEROSPACE APPLICATIONSPrior to 1995, the most commonly used solvents in industry were chlorinated: 1,1,2-trichloro-1,2,2-trifluoroethane (CFC-113); 1,1,1 -trichloroethane (TCA, also called methyl chloroform); trichloroethylene (TCE); tetrachloroethylene (also called perchloroethylene, or PERC); and dichloromethane (or METH for methylene chloride) 111.In our experience with aerospace operations, the WREAFS program has also found significant use of methyl ethyl ketone (MEK) and xylene, which are EPA 17 chemicals. Major uses of these chemicals are in vapor degreasing, cold cleaning, spot cleaning and adhesives, including adhesive removal.Traditionally, chlorinated hydrocarbon solvents have been used to remove oils, fats, waxes and other organics from surfaces. Their popularity was due both to their effectiveness as cleaners and the safety benefit from being nonflammable. A member of the ketone family, MEK was used heavily in cold cleaning, coatings and adhesives applications, while xylene, an aromatic hydrocarbon, is used in coatings and adhesives. For the purposes of this paper, we will discuss vapor degreasing, cold cleaning and spot cleaning.In the aerospace industry, the traditional solvent of choice in vapor degreasing has been TCA. The solvent is heated to its boiling point, producing vapor that contacts the part to be cleaned, which is suspended over the solvent. The vapor condenses on the cooler areas of the part, dissolving contaminants-and flushing them back into the hot liquid below. When the temperature of the part warms to equal the solvent vapor temperature, the vapor will no longer condense upon the part and the cleaning process is completed. The parts are removed and quickly dry in the air due to the latent heat content of the part and high vapor pressure of the solvents.Cold cleaning and spot cleaning are very simple. The part to be cleaned is immersed in a tank of solvent and typically agitated mechanically or ultrasonically. In this instance, the cleaning performance degrades with use because the solvent bath becomes loaded with contaminants -a distinct disadvantage as compared to vapor degreasing, because solvent vapors remain relatively pure. The typical method of spot cleaning is to use a lint-free cloth saturated in solvent to clean a specific area of a part or work piece, often as a part of a repair operation.
REDUCTION STRATEGIESThere are a variety of techniques being implemented by industry participants to reduce their reliance on these chemicals. The first is to improve operating practices by controlling purchases and tracing inventory to prevent over
