Metal Finishing Guide Book


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Table I: Physical Properties of Chlorinated Solventsa Properties Chemical formula Molecular weight Boiling point Freezing point Specific gravity Density (lb/gal) Density (kg/L) Vapor density Viscosity Flash point Flammable limits (volume of solvent in air) Kauri butanol value Solubility (g/100g) Water in solvent Solvent in water Trichloriethylene Perchloroethylene Methylene Chloride C2HCI3 131.4 189��F 87��C ���124��F ���86.7��C C2Cl3 165.8 250��F 121.1��C ���9��F ���22.8��C CH2CI2 84.9 103.5��F 39.7��C ���139��F ���95��C 1.456 12.11 1.456 4.53 0.54 None 8-9.2% (saturation) 129 1.619 13.47 1.619 5.76 0.84 None None 1.32 10.98 1.32 2.93 0.41 None 14-22% 90 136 0.04 0.10 0.0105 0.015 0.17 1.70 pleting potential (ODP). In fact these three solvents have been approved under the U.S. Environmental Protection Agency's Significant New Alternatives Policy (SNAP) as replacements for 1,1,1-trichloroethane. When the EPA published its SNAP ruling for ozone depleting substances on March 18, 1994 (see Federal Register 59 FR 13044-13161), it gave industry the official go-ahead to consider the three chlorinated solvents as acceptable alternatives to 1,1,1-trichloroethane in surface cleaning as well as other applications. This policy also pointed out that worker exposure and environmental emissions of these solvents should be controlled properly and in accordance with other workplace, environmental, and consumer regulations established by the EPA and other agencies. The policy is particularly applicable, however, in cases where nonflammability is a critical prerequisite for safety and where effects on personal health and the environment are reduced to a minimum by engineering and operating design. Each of the three chlorinated solvents has its own advantages for specific applications, based on its physical profile (see Table I for physical properties). Trichloroethylene (TCE) is a clear, heavy liquid (12.11 lb/gal) with excellent solvency. Long recognized for its cleaning power, TCE boils at 189��F (87��C) and freezes at -124��F (-86.7��C). The high density of TCEs vapor (4.53 times that of air) assures low vapor loss and easy recovery from vapor degreasing systems. TCEs aggressive solvent action works well on the oils, greases, waxes, tars, lubricants, and coolants generally found in the metal processing industries. It is especially effective in removing difficult soils such as semicured varnish or paint films, heavy rosins, and buffing compounds. Perchloroethylene (PCE or perc, also called tetrachloroethylene) is a clear, colorless liquid with a distinctive, somewhat ether-like odor. It has the highest boiling point (250��F, 121.1��C) and freezing point (-9��F, -22.8��C), weight (13.47 lb/gal), and vapor density (5.76 times that of air) of the chlorinated solvents. The high boiling point of PCE makes it especially effective in removing high-melting pitches and waxes and for cleaning grossly contaminated parts. 105

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