Oscillation Characteristics of Molten Metal Free Surface Under Compound Magnetic Field

The free surface waves of a molten low-melting point Sn-32% Pb-52% Bi alloy under the imposition of an AC and a static magnetic field were visualized and recorded by use of a laser displacement sensor and a high speed video camera. The Fourier analysis method was used to analyze the oscillation characteristics. The results show that at the center of the free surface, the azimuthal and radial oscillation mode can be found simultaneously owing to AC magnetic field. With increasing coil current intensity, the amplitude and the main frequencies of the oscillations increase, and the azimuthal fluctuation at the center of the free surface is also enhanced. The fluctuation characteristics are closely related to the turbulent flow induced by the alternating electromagnetic force. A series of regular traveling waves can be observed on free surface, and the main frequencies of oscillations at three-phase points decrease owing to superposing AC and static magnetic field. The static magnetic field can remarkably control the unstable swinging behavior of free surface. With increasing static magnetic flux density, the amplitude of oscillations at the center of free surface decreases firstly, and then increases, but the fluctuation amplitude at the triple-phase point always reduces and keeps within 1 mm, and the azimuthal waves at the center of free surface are weakened. Especially at 1.44 T, the radial waves are dominant. The static magnetic flux density should be controlled in an appropriate range to obtain more stable free surface. With compound magnetic field, even if the static magnetic flux density is above 1.0 T, the free surface still vibrates with lower amplitude and dominant frequency.