Ultrasonic pickling of steel strip

An investigation into the use of power ultrasound to enhance strip steel pickling performance has been carried out. This has involved pickling coupons of low carbon steel at various temperatures with and without the use of ultrasound (20 kHz). It was found that ultrasound produced a significant enhancement to the pickling process by reducing pickling 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 towards the end of the pickling cycle suggesting that loosening and detaching of undercut oxide is a significant part of the mechanism of ultrasonic pickling in which the applied ultrasound provides a strong mechanical effect (by cavitation) for physically removing the oxide. To provide further evidence that a strong mechanical effect was present, further tests were conducted using larger coupons that had undergone a small degree of pickling without the use of ultrasound. These were then ultrasonically agitated in water. The tests showed that ultrasound had a strong oxide removing effect in the absence of an acid solution. Tests were also carried out in water using resistance thermometer and lead weight loss measurements to determine the cavitation activity of various types of transducer. The lead weight loss tests proved a very easy 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.