Metal Finishing Guide Book


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Fig. 2. Totally enclosed vapor degreaser can meet stringent environmental regulations. complete cleaning cycle. Each of these procedures used alone will reduce solvent loss by a respectable amount while combining two or three procedures reduces loss even further. For example creating a freeboard ratio of 1.0 in an open-top degreaser will reduce loss by 30 to 40% over the traditional process. Combining an increased freeboard ratio with superheated vapor or reduced room draft increases the control level to 60%. And in most cases, if a user combines three of the procedures, this will bring the control up to 70%. Table III illustrates how these incremental improvements can be brought about. Many companies have found it cost effective to adopt one of the new degreasers, which have no air/vapor interface. These sealed and virtually emissionless units were first introduced in Europe to meet the stringent environmental regulations of some countries (see Fig. 2). Typically these degreasers perform the cleaning operation in a sealed chamber into which solvent is introduced after the chamber in closed. Solvent vapor is introduced as the final rinse and all vapors are exhausted after each cycle and passed into a solvent recovery system. With the sealed chamber control of solvent loss exceeds 90%; in other words virtually no solvent escapes. Programmed automated operation permits a variety of cleaning programs including cold or warm solvent dipping, as well as vapor degreasing. Solvent recovery cycles make use of advanced methods of carbon adsorption and hot air desorption. The manufacturer of one such unit, a "closed open-top degreaser" with a large cleaning chamber, claims that solvent emission losses average less 114

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