Metal Finishing Guide Book

2012 Organic Finishing Guidebook Issue

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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 Solubility (g/100g) Water in solvent Solvent in water Trichloriethylene C2 HCI3 131.4 189°F 87°C –124°F –86.7°C 1.456 12.11 1.456 4.53 0.54 None (volume of solvent in air) (saturation) Kauri butanol value 8-9.2% 129 0.04 0.10 Perchloroethylene C2 Cl3 165.8 250°F 121.1°C –9°F –22.8°C 1.619 13.47 1.619 5.76 0.84 None None 90 0.0105 0.015 Methylene Chloride CH2 CI2 84.9 103.5°F 39.7°C –139°F –95°C 1.32 10.98 1.32 2.93 0.41 None 14-22% 136 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 Poli- cy (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 Reg- ister 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 emis- sions 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 per- sonal 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 ap- plications, based on its physical profile (see Table I for physical properties). Trichloroethylene (TCE) is a clear, heavy liquid (12.11 lb/gal) with excellent sol- vency. 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, lu- bricants, and coolants generally found in the metal processing industries. It is es- pecially 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. 17

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