Development of High Temperature Ultrasonic Sensors for Molten Metals Monitoring

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High temperature ultrasonic sensors with acoustic wave-guides and their applications to molten metals monitoring have been studied. The main results obtained are the following:(1) A focused ultrasonic sensor with a tapered clad buffer rod is designed and its focusing ability for particles detection in molten metals such as aluminum and magnesium have evaluated by a numerical simulation method. It is found that the focused ultrasonic wave could be useful to detect a small particle with a diameter almost equal to one wavelength. The amplitude of the scattered wave from the particle strongly depends on the clustering condition of the several particles.(2) Laboratory validation of the use of focused ultrasonic sensors for alumina particles detection in molten aluminum at 800℃ has been demonstrated. Back-scattered signals from the particles of 160 μm in average diameter are clearly observed in the focal region of the acoustic lens at 10 MHz.(3) A new high temperature ultrasonic sensor with a titanium buffer rod has been applied to the in situ monitoring of the solid-liquid interface of an aluminum alloy (Al-12.6%Si) during unidirectional solidification at 700℃. A clear reflected echo from a stable solid-liquid interface of the aluminum alloy has been successfully monitored. In addition, the reflected echo from the growing interface during unidirectional solidification has also been monitored. The growth rate of the interface was determined to be 0.12 mm/s from the monitored echo.It is therefore considered that the developed ultrasonic technique is a promising candidate for on-line monitoring during molten metal processing.