Flow transitions in vacuum arc remelting

The metallurgical structure of an ingot produced by vacuum are remelting (V AR) depends critically on the temperature distribution within the liquid po rtion of the partially solidified ingot. This, in turn, depends on the flui d motion in the pool, since the dominant mechanism for transporting heat is convection. There are three primary sources of motion: buoyancy; Lorentz f orces arising from the passage of current through the pool; and Lorentz for ces arising from the presence of external inductors, These forces are const antly in competition with each other, and each tends to induce a quite diff erent distribution of velocity and temperature. We examine the transition b etween these different flow regimes and derive dimensionless criteria which determine which regime is dominant. We show that the structure of an ingot produced by VAR depends critically on the temperature distribution within the liquid portion of the partially solidified ingot. This, in turn, depend s on the fluid motion in the pool, since the dominant mechanism for transpo rting heat is convection. There are three primary sources of motion: buoyan cy; Lorentz forces arising from the passage of current through the pool; an d Lorentz forces arising from the presence of external inductors, These for ces are constantly in competition with each other, and each tends to induce a quite different distribution of velocity and temperature. We examine the transition between these different flow regimes and derive dimensionless c riteria which determine which regime is dominant. We show that modest chang es in ingot current can produce radical changes in temperature distribution , and that weak, steady magnetic fields, of only similar to 1 Gs, can induc e a powerful swirling motion which suppresses the normal flow. MST/4376.