Metal Finishing Guide Book

2013

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Power Density, watts/gal 200 180 160 140 120 100 80 60 40 A A AA A A B A C BDD D C A D D D A A BC C DC A 20 0 0 20 40 C B C C 60 C 80 100 Tank Volume, gal Figure 5. Power density provided in "standard" ultrasonic cleaning systems. EFFECT OF TANK SIZE Size (fluid volume) of the tank in which the cleaning work is being done matters — substantially. Less power is used in tanks with smaller volumes — substantially. Ultrasonic power level is normally specified as a density — power per volume. Specifications for standard tank systems produced by four major U.S. suppliers have been collected. The suppliers are identified only as "A," "B," "C," and "D." The power density provided in standard systems is graphed in Figure 5. Recall that supplier "A" is not necessarily providing superior cleaning systems because their systems have a higher power density, nor is supplier "C" supplying inferior systems. EFFECT OF PART SIZE Ultimately, all mechanical energy added to a cleaning or rinsing tank by ultrasonic transducers is converted to heat. ¥ The mechanical energy is consumed in doing frictional work Ñ either against the mass load of parts, against the walls of the tank, within the water, or as heat and additional frictional forces produced by the collapse of cavitation bubbles. Consequently, if the parts are a large dense mass of metal (castings, forgings, etc.), more ultrasonic power will be required to compensate for that absorbed by the metal. If parts are left too long within an ultrasonic-powered cleaning tank, they — along with the fluid within the tank and the tank walls — will become warm. Further, if the parts occupy a large amount of the volume within a tank, it is likely that internal surfaces may not be effectively cleaned. Some suppliers recommend that the weight of parts in a ultrasonic cleaning tank be no more than about one-third to one-half of the weight of water in the tank. (This author's experience favors the lower value.) Such a recommendation doesn't mean that more large systems be purchased; it may only mean that multiple loads be processed in a smaller and less expensive machine. TEST, TEST, TEST! A manager's objective, in every demonstration with a supplier's ultrasonic (or megasonic) facilities, should be to identify the power level and the cycle time that should be used to design a commercial system. 75

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