The frequency effect on electromagnetic confinement and shaping of liquid metal

Electromagnetic confinement and shaping is a kind of newly developing solidification technology. With the electromagnetic field imposed, the metal is melted to some superheating degree by Joule heating and is confined and shaped to the desired form by the electromagnetic force at the same time. The frequency effect of the electromagnetic field on the electromagnetic confinement and shaping is investigated. The relationship between the Joule heat, the electromagnetic force and the frequency is revealed from the viewpoint of the magnetohydrodynamics theory. The results show that, given the condition of the same magnetic field strength, the time-averaged volume electromagnetic force at the melt surface is approximately proportional to the field frequency, whilst at the same time the volume Joule heating rate is approximately proportional to the square of the field frequency. However, as the frequency increases, the shaping stability and the surface quality decrease due to the violent surface electromagnetic stir. The frequency effect is also correlative to the sample's size and electric conductivity. The bigger is the sample, the lower ought to be the frequency and vice versa. The bigger is the electric conductivity, the lower can be the frequency and vice versa. Thus there is an optimum frequency range for each different sample, which is tens to hundreds of kilohertz for the small-size or medium-size steel sample. The experimental research is carried out with aluminium, copper and stainless steel samples, and the results show good agreement with the theoretical predictions. (C) 2001 Elsevier Science Ltd. All rights reserved.