SOLIDIFICATION CONTROL MAKING USE OF HIGH-FREQUENCY ELECTROMAGNETIC-FIELD IN A MOLD CONNECTED WITH TUNDISH

In an attempt to overcome the surface defect originated from the intersection of melt, refractory and mould in a tundish and mould connected type caster, a billet was continuously cast under applying the electromagnetic field. To intensify the magnetic flux density at the intersection, specially designed mould and coil, distance between which becomes small with getting close to the billet surface, were adopted. For the better understanding about the initial solidification, a numerical model of fluid flow coupled with heat transfer under electromagnetic field was developed, taking account of the free shape of the melt formed by the electromagnetic pressure. Validity of the model was confirmed through the fundamental measurement. Depth of the wrinkles, which were the disconnected surface shell defect formed during continuous withdrawal, was reduced and the pitch of them became narrow by the application of the electromagnetic field. Cooling rate of the shell was decreased and the same result was obtained through the numerical model. Even in the presence of electromagnetic field, it was not expected from the model that a vacancy was formed at the intersection by the removal of a liquid metal. Improvement of surface quality is considered to be responsible for the decrease in the initial shell thickness by the induction heating.