Published: 01 January 1962
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The required characteristics for solvents to be used in the vapor degreasing process are: 1. High solvency for the removal of oils, greases, and other contaminants commonly encountered. The contaminants must dissolve rapidly and completely in the solvent at or near its boiling point. 2. Nonflammable and nonexplosive under normal operating conditions. Because the process is run at the boiling temperature of the solvent, it must have no flash point or explosive mixture with air at that temperature. 3. A low latent heat of vaporization and a low specific heat so that the maximum amount of solvent will condense on a given weight of metal and to keep the heat requirements to a minimum. In addition to heating the work load up to the temperature of the vapor, a large part of the heat is used to distill the solvent continuously to provide clean solvent for spraying or rinsing. 4. A high vapor density by comparison with air and a low rate of diffusion into the air so that losses of solvent to the atmosphere from the vapor-air interface during normal operations are kept to a minimum. 5. Chemical stability under conditions of use. The degreasing solvent must be able to withstand all of the stress conditions encountered in vapor degreasing. This includes exposure to heat, air (oxygen), active metal chips and fines, acidic salts, alkaline and acidic metal working lubricants, and moisture that may be brought in with the work or from atmospheric condensation. Resistance to these stresses can either be part of the inherent properties of a solvent or be accomplished through the addition of suitable stabilizers. Solvents that hydrolyze readily are not broadly suitable. 6. Noncorrosive to common metals used in construction. The solvent should retain this characteristic after continuous use and redistillation. 7. A boiling point low enough to permit the solvent to be easily separated from oil, grease, or other contaminants by simple distillation. A low boiling point also serves to keep the temperature of the degreased work at a reasonable level for subsequent handling. 8. A boiling point high enough so that sufficient solvent vapors will be condensed on the work load in heating it up to the vapor temperature to ensure adequate final rinsing in the clean vapor. The boiling point should also be high enough so that the vapors will readily be condensed and the vapor level controlled with simple water cooling and without the need for auxiliary refrigeration. 9. Readily available at a reasonable cost. 10. Relatively safe under the operating conditions of the vapor degreasing process. With proper operation and properly designed equipment, concentrations in the working atmosphere at the vapor degreaser should be maintainable at well below the established limits without the use of auxiliary exhaust equipment. The solvent should retain its original composition during use and not decompose to give toxic by-products under the conditions of the process.