Degreasing, vapour

The Occupational Exposure Standards imposed for trichloroethylene are Maximum Exposure Limits of 100 ppm (8 hr TWA) and 150 ppm (15 minute reference period). A skin notation Sk is applicable because of the potential for skin absorption. Because of its volatility, trichloroethylene is not recommended for cold cleaning it is normally used in partially enclosed vapour degreasing equipment provided with local exhaust ventilation. 

Selden A, Hultberg B, Ulander A, et al. 1993. Trichloroethylene exposure in vapour degreasing and the urinary excretion of N-acetyl-beta-D-glucosaminidase. Arch Toxicol 67 224-226. 

One of the most important direct uses for nitromethane is in the stabilization of halo-genated hydrocarbons. For example, small amounts of nitromethane are widely used in industry to form stable non-corrosive mixtures with 1,1,1-trichloroethane for vapour degreasing, dry cleaning and for cleaning semiconductors and lenses. It is also used to stabilize the halogenated propellants for aerosols and to inhibit corrosion on the interiors of tin-plated steel cans containing water-based aerosol formulations (Markofsky, 1991 Angus Chemical Co., 1998). 

Fig. 109. Rocket chamber being lowered into a vapour degreasing pit to remove all traces of grease and oil (according to Dykstra [11]).

Dichloromethane is available in several grades based on its intended end use technical aerosol vapour degreasing special urethane and decaffeination or Food Chemicals Codex/National Formula (food and pharmaceutical applications). Purity, when reported, ranges from 99 to 99.99%. Acidity (as hydrochloric acid) may be up to 5 mg/kg. The maximum concentration of water in these grades of dichloromethane is 100 mg/kg (Rossberg et al., 1986 Holbrook, 1993 Dow Chemical Co., 1995 Vulcan Chemicals, 1995, 1996a,b,c,d). 

Trichloroethane is likely to enter the environment from air emissions or in wastewater from its production and use in vapour degreasing, metal cleaning and other applications. It can also enter the environment in leachates and volatile emissions from landfills. It has been detected at low levels in wastewater, groundwater, drinking-water, ambient water, ambient air, and urban air samples (United States National Library of Medicine, 1997). 

Of even more practical importance in determining the behaviour of systems is the tendency of many component materials, and some brazes, to form chemically stable and physically tenacious oxide films when their surfaces are exposed to even mildly oxidising environments. (Note that these oxides are in turn covered by absorbed layers of organic contaminants, but these can be removed relatively easily by washing in solvents, vapour degreasing or baking in a vacuum). Oxide films can... 

CHCl-CClj ("Tri") vapour degreaser Excessive heating of solvent 1 1932... 

Vapour degreasing is an excellent way to obtain highly clean surfaces. The efficiency of cleaning can be checked by determining the coefficient of friction, in addition to dark-field-inspection, contact-angle and thin-film-adhesion measurements methods. High values are typical for clean surfaces [7]. 

Trichloroethylene (widely used as a vapour degreasing solvent in the metal-working industries) may be produced from tetrachloroethane by cracking, using milk of lime (33.27). 

In the U.S.A., environmental pressures are causing a continuing fall in demand for the two major products, perchloroethylene (120 kt per annum), used for dry cleaning and chlorofluorocarbon manufacture, and 1,1,1-trichloroethane (200 kt per annum), for cold cleaning and vapour degreasing of metals. European production of 1,1,1-trichloroethane is believed to be on a similar scale. 

B) Vapour blast with garnet grit (200 grade and 400 grade) protect with oil, vapour degrease with trichloroethylene. 42.6 34.2 33.2... 

Chromic acid anodise O Chromic-sulphuric acid etch A Sulphuric acid anodise A Vapour degrease... 

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