Patent ID: 8418893

Claim:
An immersion nozzle comprising: a tubular-shaped straight nozzle body formed to extend in a vertical longitudinal direction and adapted to allow molten steel from a molten-steel inlet provided at an upper end thereof to pass downwardly therethrough; and a pair of discharge ports provided in a lower portion of the straight nozzle body in bilaterally symmetrical relation and adapted to discharge the molten steel from a lateral surface of the straight nozzle body in a lateral direction, wherein an inner surface of each of the discharge ports has, at least in part or in its entirety, a shape defined by a curved line along which an inner bore of the discharge port in a longitudinal cross-section of the immersion nozzle passing through respective centers of the immersion nozzle and the discharge port is gradually reduced in diameter in a direction from a start position to an end of the discharge port, and wherein the curved line is represented by a diameter Dz in the longitudinal cross-section of the immersion nozzle in the following formula 1: Dz = ( H + L H + Z ) 1 n × Do ( 1 ) where: L is a wall thickness of the immersion nozzle; Di is a diameter of the discharge port at the start position of the discharge port (a boundary position between the discharge port and an inner bore wall of the immersion nozzle; the same applies to the following formula 2); Do is a diameter of the discharge port at the end of the discharge port (a boundary position between the discharge port and an outer peripheral wall of the immersion nozzle; the same applies to the following formula 2); Z is a distance between the start position of the discharge port, and an arbitrary position apart from the start position toward the end of the discharge port; Dz is a diameter of the discharge port at the position Z in the longitudinal cross-section of the immersion nozzle; and H is represented by the following formula 2, H = L { ( Di Do ) n - 1 } , ⁢ where ⁢ ⁢ Di Do ≥ 1.6 , and ⁢ ⁢ n ≥ 1.5 . ( 2 )