Continuous casting of metal using electromagnetic stirring

In the continuous casting of metal wherein the liquid metal is poured through a submerged shroud into a cooled mold through which the metal moves in one direction with an outer solidifying shell defining a solid-liquid interface within the mold and which is lined with electrically conductive material, said shroud having a closed bottom and delivering metal to exit outwardly into a region located in an upper portion of the mold, the procedure comprising:

• (a) pouring the metal through a slag layer in contact with the metal substantially upstream of said region;
• and
• (b) electromagnetically circulating the metal in the mold by producing an alternating current field adjacent to the mold between approximately the slag-metal interface and a locality situated downstream of said outward exit, said alternating current being supplied to have at least two successively different phases in longitudinally successive regions to thereby provide circulation of the liquid metal in a direction generally opposite to said one direction along said solid-liquid interface from said locality to the slag layer and generally in said one direction along the outer surface of the shroud, said current being supplied at a frequency sufficiently high to move the metal in the described circulation and sufficiently low that effective metal-moving power is transmitted despite attenuation by said conductive lining such that the electromagnetically induced metal flow acts to positively sweep nonmetallic inclusions intrained in the outflow from the shroud along said solid-liquid interface in spaced relation thereto along the slag layer whereby removal of inclusions into the slag is promoted;
• wherein the improvement comprises
• (c) the pouring step comprising pouring the liquid metal through a shroud having a central bore tapering continuously throughout the entire length of the shroud in a downstream direction to constitute a nozzle, and into a well defined by the closed bottom of the shroud downstream of and opening toward the nozzle, for outward exit of metal to the mold through ports opening laterally through the shroud between the well and the nozzle and oriented at an obtuse angle to said one direction, while maintaining a metal level in the mold at least several inches above said ports;
• and
• (d) injecting an inert gas into the liquid metal being poured through the shroud, at a locality upstream of said region, for dispersing the gas through the liquid metal in the form of fine bubbles prior to exit of the metal into the mold.