This invention relates to an improved process and apparatus for control of corner shape in continuous or semi-continuous electromagnetic casting of desired shapes, such as for example, sheet or rectangular ingots of metal and alloys. The basic electromagnetic casting process had been known and used for many years for continuously or semi-continuously casting metals and alloys.
One of the problems which has been presented by electromagnetic casting of sheet ingots has been the existence of large radius of curvature corners thereon. Rounding off of corners in electromagnetic cast sheet ingots is a result of higher electromagnetic pressure at a given distance from the inductor near the ingot corners, where two proximate faces of the inductor generate a larger field. This is in contrast to lower electromagnetic pressure at the same distance from the inductor on the broad face of the ingot remote from the corner, where only one inductor face acts.
There is a need to form small radius of curvature corners on sheet ingots so that during rolling cross-sectional changes at the edges of the ingot are minimized. Larger radius of curvature corners accentuate tensile stress at the ingot edges during rolling which causes edge cracking and loss of material. Thus, by reducing the radius of curvature of the ingot at the corners there is a maximizing in the production of useful material.
It has been found in accordance with the present invention that rounding off of corners in electromagnetically cast ingots can be made less severe or of smaller radius by bringing about a net downward displacement of the screening current at the corners of a shield placed at the molten metal or alloy input end of the casting zone and/or by contouring the field producing inductor so as to enlarge the air gap between the inductor and the ingot at areas between the inductor and the ingot corners. Thus, since undesirable rounding off of the corners results from the action of excess electromagnetic force at the ingot corners, the desired modification of the field shape can be obtained by increased local screening of the field and/or by contouring the inductor at the corners.
Various embodiments of the present invention increase local screening of the electromagnetic field by locally increasing shield depth, by locally providing deeper displacement of the shield, or by certain local changes in shield section or orientation.