Application of the ultrasound Doppler velocimetry in model experiments for casting and solidification

The optimisation of methods and facilities for material processing technologies such as melting, refining or casting of metals or alloys has to be considered as an enduring challenge. Key issues are an improvement of the final product quality, an enhancement of the process efficiency and an economical consumption of resources and energy. Further advancement often requires a better knowledge with respect to the details of the flow structure, the heat and mass transfer properties of the flow especially during phase transitions like melting or solidification. Experimental studies on industrial scale with hot metallic melts (T > 600°C) may require formidable effort and expense. Cost-saving model experiments using low melting point metallic melts permit detailed investigations of the flow structure and related problems with a high grade of flexibility. Experiments at room temperature are possible using the ternary alloy GaInSn. The ultrasound Doppler velocimetry (UDV) became an accepted method for flow investigations in various liquid metals. In this presentation various applications of UDV in liquid metal flows will be shown to demonstrate the capabilities and current restrictions of this technique. For instance, we consider single- and multi-transducer arrangements for flow mapping or present velocity measurements obtained during the solidification of a metallic melt. Besides the determination of velocity profiles in the liquid phase the UDV data allow for an assessment of the current position of the solidification front, too. Specific problems arising in the context of UDV measurements in liquid metal experiments will be discussed. The following examples have been selected to demonstrate the benefit of using UDV for flow measurements in cold model experiments, namely the electromagnetic stirring of a metallic melt in a pool, the directional solidification of Pb-Sn alloys under the influence of an electromagnetically driven flow and the
behaviour of the mould flow in continuous casting under the effect of a DC magnetic field.