Metal Finishing Guide Book

2012 Organic Finishing Guidebook Issue

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Page 16 of 331

PRINCIPLES OF VAPOR DEGREASING The traditional vapor degreasing process is carried out in either a batch or an in- line degreaser. The standard batch degreaser is an open-top tank into which the dirty parts (the "work") are lowered (see Fig. 1). Solvent in the bottom of the tank is heated to produce vapor, and since the vapor is heavier than air it re- mains in the tank. Cooling coils below the lip of the tank create a cool zone, which forms the upper boundary of the vapor zone. On contact with the cooler work the vapor condenses into pure liquid solvent, which dissolves the grease and carries off the soil as it drains from the parts into the reservoir of solvent below. The cleaning process continues until the work reaches the temperature of the vapor, at which point condensation ceases and the work is lifted out of the vapor, clean and dry. The degreasing process may be supplemented by adding a spray lance to the open-top degreaser so that hard-to-remove soils can be flushed off by the oper- ator. In addition many degreasers also contain one or several immersion tanks below the vapor zone so that parts can be lowered into liquid solvent — often in a tumbling basket — before being raised into the vapor for final rinsing. If scrubbing is required to remove heavy oil deposits and solid soils, ultra- sonic cleaning can be added by installing transducers in the degreaser. When ultrasonic energy is transmitted to a solution, it produces cavitation — the rapid buildup and collapse of thousands of tiny bubbles, which impart a scrubbing ac- Fig. 1. Typical batch open-top vapor degreaser. 15

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