ULTRASONIC PICKLING OF STEEL STRIP

An investigation into the use of power ultrasound to enhance strip ste el pickling performance has been carried out. This has involved pickli ng coupons of low carbon steel at various temperatures with and withou t the use of ultrasound (20 kHz). It was found that ultrasound produce d a significant enhancement to the pickling process by reducing pickli ng times and allowing a reduction in acid temperature. Tests were also conducted using single and multiple sound pulses at various stages of the pickling cycle. The influence of ultrasound was most effective to wards the end of the pickling cycle suggesting that loosening and deta ching of undercut oxide is a significant part of the mechanism of ultr asonic pickling in which the applied ultrasound provides a strong mech anical effect (by cavitation) for physically removing the oxide. To pr ovide further evidence that a strong mechanical effect was present, fu rther tests were conducted using larger coupons that had undergone a s mall degree of pickling without the use of ultrasound. These were then ultrasonically agitated in water. The tests showed that ultrasound ha d a strong oxide removing effect in the absence of an acid solution. T ests were also carried out in water using resistance thermometer and l ead weight loss measurements to determine the cavitation activity of v arious types of transducer. The lead weight loss tests proved a very e asy and effective method of measuring the cavitation activity directly . The information from these tests can be used to assist the design of commercial strip pickling operations. (C) 1998 Elsevier Science B.V.