Strip casting apparatus with electromagnetic confining dam

A strip casting apparatus comprising:

• a pair of horizontally disposed, counter-rotating rolls having a vertically extending gap therebetween for containing a pool of molten metal, said gap having an open end;
• said rolls having facing surfaces converging downwardly toward a nip between said rolls;
• said rolls comprising means for accommodating a molten metal pool having a predetermined maximum height and a top part;
• an electromagnetic dam comprising means for preventing the escape of molten metal through the open end of said gap;
• said dam comprising a vertically disposed confining coil having a front surface facing said open end of the gap, adjacent thereto;
• said front surface having a relatively wide upper part, for positioning opposite the top part of said molten metal pool when said pool is at said predetermined maximum height;
• said front surface tapering in width from said upper part to a relatively narrow lowermost part, for positioning opposite the nip between said rolls;
• means for flowing, through said upper part of the coil's front surface, a time-varying electric current having a pre-selected amperage for electromagnetically containing the top part of the pool when the pool is at said predetermined maximum height;
• and means for flowing, through said lowermost part of the coil's front surface, another time-varying electric current, separate and distinct from said first-recited time-varying current, and having a pre-selected amperage substantially less than said first-recited pre-selected amperage, for electromagnetically containing the pool at said nip when the pool is at said predetermined maximum height.

A strip casting process comprising the steps of:

• providing a pair of horizontally disposed, counter-rotating casting rolls (a) having a gap therebetween with an open end and (b) having facing casting surfaces converging downwardly toward a nip between the rolls;
• containing a pool of molten metal in said gap, said pool having a predetermined maximum height, a relatively wide top part and a relatively narrow lowermost part at said nip;
• casting said molten metal into a strip as the metal in said pool descends toward said nip;
• providing an electromagnetic dam comprising a vertically disposed confining coil having a front surface with upper and lower parts;
• positioning said front surface of the confining coil adjacent said open end of the gap (i) with said upper part of the front surface located opposite said wide top part of the molten metal pool, when the pool is at its predetermined maximum height, and (ii) with said lower part to the front surface located opposite said narrow, lowermost part of the pool;
• flowing a current, having a first pre-selected amperage, through that part of the front surface of the confining coil opposite the wide top part of the molten metal pool, to confine that part of the pool;
• and flowing a current having a second pre-selected amperage, substantially less than said first pre-selected amperage, through that part of the front surface of the confining coil opposite the narrow lowermost part of the molten metal pool, to confine that part of the pool.