Ultrasonic cleaning baths are found in nearly all commercial and industrial sectors since they can be used for various purposes. They clean things that are as different as engine parts, microchips, optical glasses or surgical equipment, but can also be used for the pre-treatment of sewage sludge or as reaction accelerators, for example, in the production of biodiesel. Even workpieces having a complex shape are thoroughly cleaned without brushes. The efficiency of the cleaning is based on cavitation, the short-term generation of the smallest oscillating gas bubbles which can locally create very high pressures and temperatures when collapsing. The forces and micro currents generated hereby cause dirt particles to come off, enabling an intensive and yet gentle cleaning.
Cavitation processes are, however, complex and difficult to predict. At PTB, uniform and objective measurement procedures have now been determined that are suited to characterise ultrasonic baths. The investigations took place within the scope of a project carried out by the AiF Research Association DECHEMA Gesellschaft für Chemische Technik und Biotechnologie e. V. (Society for Chemical Engineering and Biotechnology) and were funded via the AiF within the scope of the “Programme for the promotion of industrial joint research and development (IGF)” of the Federal Ministry of Economics and Technology.
The new measuring arrangement offers the possibility of controlling all essential ambient parameters such as, e.g., the water temperature and the gas content. By means of suitable indicators, manufacturers and users can determine the properties of an ultrasonic bath objectively. Among these cavitation indicators are: the chemical effect, the erosion of aluminium foil, and sonoluminescence, i.e., the occurrence of ultrashort light flashes in the imploding bubbles. For each indicator, there is a corresponding measurement procedure that has been developed by PTB. A self-developed computation method searches for correlations in the measurement results by means of statistical methods and identifies the measurands which can be used as an “adjusting screw” in order to optimise an ultrasonic bath for a specific use.
These procedures for the characterisation of ultrasonic cleaning baths are available to industry.
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