Intensive ultrasonic cleaning of surfaces by means of lead-free ultrasonic transducer with focussing sonotrode

Intensive ultrasonic cleaning of surfaces by means of a lead-free ultrasonic transducer with focusing sonotrode Ultrasonic cleaning baths are probably a coincidental development: After underwater sonars had already been successfully used to detect submarines before 1920, it was probably observed in this environment that the ultrasonic oscillators not only showed a self-cleaning effect but also cavitation damage. At the beginning of the 1950s, the first ultrasonic cleaning devices finally came onto the market. Today, the range of applications ranges from household appliances for jewellery and eyewear cleaning to classic cleaning baths for metal parts and systems for cleaning highly sensitive electronic components. There is a certain gap in handheld, mobile cleaning equipment. Although devices for spot cleaning of textiles are known, the cleaning effect is usually low. Due to the directive 2011/65/EU on the restriction of the use of hazardous substances in electrical and electronic equipment (RoHS) [1] lead should no longer be used in technical devices. As today’s standard ceramics for medium and high-power ultrasonic transducers typically contain lead, there is a need to explore the use of lead-free ceramics in this field. Honda [2] already offers a cleaning transducer based on lead-free piezoelectric ceramics, but it is designed to be used in cleaning baths. This article presents the model-based development of a highly innovative ultrasonic cleaner. On the one hand, lead-free piezoelectric ceramics are used, and on the other hand, a special sonotrode has been developed that concentrates the sound in such a way that a strong cavitation and thus cleaning effect is achieved with comparatively low power in a short time. Coupled field finite element method was used to find an appropriate geometry for the focussing sonotrode. The comparison of simulation and measurement results shows that the lead-free piezoceramics used do their job well and can keep up with standard ceramics, but more ceramic volume is needed to achieve same power. An advanced control concept was elaborated to ensure continuous hard cavitation at varying distances between the sonotrode and the part to be cleaned. Cleaning results for different surfaces and contaminations are presented. The concept of the focusing sonotrode shows that a convincing cleaning result can be achieved even with low power and in short time, provided that the oscillation system and control electronics are suitably coordinated. References [1] http://data.europa.eu/eli/dir/2011/65/2024-08-01 [2] https://en.honda-el.co.jp/product/ceramics/lineup/lead_off/lead-off