Metalloid Particles' Migration In Molten Metals In An Electromagnetic Force Field And It's Application

In recent years, metallurgists have paid close attention to the application of the electromagnetic field in metallurgy. Taking advantage of the force and the heat generated by electromagnetic field, one can heat or stir or transmit the molten metals or even control the shape of the molten metal in casting without contacting it, which cannot be easily done by other ways. So, the join of the electromagnetic field with metallurgical process always leads to the birth of a new technology. For example, electromagnetic stirring and electromagnetic casting was widely used in industry. Now, another potential one in metallurgical process, which was called particles electromagnetic separation from molten metals, absorbed much interest from the metallurgists in Japan, France and America.On the basis of brief review of the history and the evaluation of previous research works, the behavior of the particles in liquid metals under alternate and unalterable electromagnetic force field was investigated experimentally and theoretically. Using three kind of conductive liquid-particle systems, three key topics, namely, particles' electromagnetic migration in liquid metal, purifying molten metal by electromagnetic field, as well as the particles' behavior in front of the solid/liquid (S/L) interface in the electromagnetic field was stressed in this paper.In the first part, the principle of the particles' migration in molten metals in electromagnetic field is focused. Contrapose that the relation between the rate of hard particle and the electromagnetic force (EMF) was not so far studied, we carried out further research by using electrolyte and travelling magnetic field (TMF). It is found that, if the Reynolds numberlarger than 5.8 and the Hartman number close or larger than one, with increasing the diameter of the particles, the rate of which will be progressively lower than the theoretical one, and the ratio between them trend to be closed to 0.5. However, if the diameter is less than I millimeter, the ratio goes up to one due to the decrease of the Reynolds and Harman number.In the experiments using hypereutectic aluminum-silicon alloys, it was found that the shape and size of the pipe would take important effects on the behavior of the particles. Abnormal phenomenon was observed with circular pipe. Better results were obtained with rectangular pipe or triangle pipe. Further experiments revealed that the inner surface of the circular pipe couldn't restrain the metal turbulent flow efficiently, which will disturb the migrating behavior of the particles. The flat surface of the rectangular pipe or triangle pipe will change the direction of the metal flow by the angle larger than 90 degree, and their inner surface area were larger than that of the circular pipe, both of which will result in restraining the turbulent more efficiently.The turbulent in liquid metals was resulted mainly from the inhomogeneous electromagnetic force, however, for a long time, no appropriate way was put forth to evaluate the turbulence and the homogeneity of the EMF, which hindered the application of the technology. By investigating the factors affected the inhomogeneity of the EMF, it is revealed that when the cross section size of pipe is lower than the skin depth, the homogeneity of the EMF depends mainly on that of the MFD in TMF. To evaluate its effect, the parameter named inhomogeneity degree (IHGD) of the MFD was used. The experiments using liquid metal showed that, if the IHGD of the MFD is lower than 5%, even if the cross section area was increased apparently, the metal turbulent flow was weak or nearlydisappeared in a rectangular or triangle pipe, then the particle can move steadily in the metal. If the IHGD of the MFD is larger than 9%, vigorous turbulent appeared in the molten metal, which will disturb the particle's migration badly. In travelling magnetic field, the space over the core or the central area over the slot have small IHGD, so it is suitable to be used for particles' electromagnetic migration.The migrating rate of the...