This invention relates to vapor/immersion cleaning apparatus of the degreaser type for removing soils such as greases, waxes or the like from metal and other parts which is programmably controlled and a microprocessor controlled method for eliminating undesirable vaporization of expensive and/or toxic solvents from the open topped plural-tank cleaning apparatus during periods of shut down, start up, and normal cleaning operation.
Dry cleaning machines and metal degreasing apparatus having an open top and one or more solvent tanks using a single vaporizable solvent such as trichloroethylene or perchloroethylene had been used in the United States commercially by as early as the mid 1950's. Such apparatus and processes for cleaning metal by vapor phase cleaning, or combinations of vapor phase with immersion cleaning in an agitated solvent, or by agitating the parts while immersed in such solvent, are disclosed in expired U.S. Pat. Nos. 3,216,431 and 3,593,727. By the mid 1960's apparatus having water cooled conduits located peripherally on the walls of open top metal cleaning apparatus for creating a vapor zone above the cleaning liquids and methods for cleaning and for condensing solvent vapors and reusing the condensed solvent were being used commercially. Such apparatus and methods are disclosed in U.S. Pat. Nos. 3,227,629, 3,610,260 and 3,676,307.
The continuing problem of escape of some quantity of solvent vapors from such apparatus continued into the late 1960's and led to improvement in recovery processes by distillation such as is disclosed in U.S. Pat. No. 3,483,092. By the late 1970's low boiling fluorocarbon solvents, or azeotropes thereof with methylene chloride that boiled below 100.degree. F., had been developed along with ultrasonic transducers. Commercial use of the combination of such solvents with the sonic transducers led to the invention of a compression-expansion type refrigeration system and apparatus that improved control of solvent vapor zones and decreased solvent losses. That apparatus and process is disclosed in U.S. Pat. No. 4,055,196, issued Oct. 25, 1977, to Thomas J. Kearney and entitled Immersion Type Metal Degreaser With Compression-Expansion System for Heating and Cooling of Liquid Solvent and Solvent Vapors.
Technical information extant by the mid 1980's that ozone depletion in the atmosphere is partially attributable to the presence of chlorine made metal cleaning with chloro-fluoro hydrocarbons less desirable and has sparked renewed research efforts for identifying and developing substitute solvents for cleaning soil from parts. An effective, no-fail system for eliminating solvent vapor losses in open topped metal cleaning apparatus during shut down times had not been found prior to the present invention.