Immersion nozzle

Abstract

It is intended to provide a flat immersion nozzle capable of stabilizing a molten steel discharge flow to stabilize an in-mold bath surface, i.e., reduce the fluctuation of the in-mold bath surface. Provided is an immersion nozzle having a flat portion whose inner bore has a thickness and a width greater than the thickness, wherein two lateral protrusions each protruding in a thickness direction are provided on each of opposed walls of the flat portion extending in a width direction. The lateral protrusions are arranged at axial symmetrical positions with respect to a longitudinal central axis of the width-directionally extending walls, in pairs, such that each of them extends obliquely downwardly in the width direction, wherein two pairs of the lateral protrusions are arranged, respectively, on the opposed width-directionally extending walls, in opposed relation.

1 . An immersion nozzle having a flat portion whose inner bore has a thickness Tn and a width Wn greater than the thickness Tn, and which comprises opposed short-side lateral walls and opposed long-side walls extending in a width direction of the flat portion, wherein a pair of discharge ports are provided, respectively, in lower parts of the short-side lateral walls, the immersion nozzle comprising
 two portions provided on each of the width-directionally extending walls, and arranged at axial symmetrical positions with respect to a longitudinal central axis of the width-directionally extending walls, in pairs, each of the portions extending obliquely downwardly in the width direction and protruding in a thickness direction of the flat portion (the portion will hereinafter be referred to as “lateral protrusion”),   wherein two pairs of the lateral protrusions are arranged, respectively, on the width-directionally extending walls, in opposed relation, and   wherein two sets of opposed lateral protrusions in the two pairs of lateral protrusions have a same value falling within a range of 0.18 to 0.90 in terms of a total protruding length Ts in the thickness direction, expressed as an index on the basis of 1 indicative of a thickness of the inner bore at a position where the opposed lateral protrusions are provided.   
     
     
         2 . The immersion nozzle as claimed in  claim 1 , which further comprises a protrusion provided on each of the width-directionally extending walls at a position between two lateral protrusions in each of the two pairs of lateral protrusions (this protrusion will hereinafter be referred to as “central protrusion”),
 wherein the central protrusion has a thickness-directional protruding length less than that of the lateral protrusion, and 
 wherein two central protrusions in the two pairs of lateral protrusions have a value of 0.40 or less (not including zero) in terms of a total protruding length Tp in the thickness-direction, expressed as an index on the basis of 1 indicative of the thickness of the inner bore at the position where the opposed lateral protrusions are provided. 
 
     
     
         3 . The immersion nozzle as claimed in  claim 2 , wherein an upper end surface of the central protrusion has one selected from the group consisting of a shape extending horizontally in the width direction, a curved shape having a top at a midpoint thereof, and an upwardly protruding shape including a bending point. 
     
     
         4 . The immersion nozzle as claimed in  claim 1 , wherein an upper end surface of the lateral protrusion or the central protrusion has a shape extending horizontally in a direction toward a center of the inner bore, or a planar or curved shape extending obliquely downwardly in the direction toward the center of the inner bore. 
     
     
         5 . The immersion nozzle as claimed in  claim 1 , wherein one or each of the lateral protrusion and the central protrusion has a shape in which the thickness-directional protruding length thereof is constant, or becomes shorter linearly, curvilinearly or stepwisely in a direction toward a center of the width-directionally extending wall. 
     
     
         6 . The immersion nozzle as claimed in  claim 1 , wherein one or each of the lateral protrusion, and the lateral protrusion combined with the central protrusion is provided plurally in an up-down direction. 
     
     
         7 . The immersion nozzle as claimed in  claim 1 , which comprises a protrusion provided around a center of a bottom of the inner bore to protrude upwardly. 
     
     
         8 . The immersion nozzle as claimed in  claim 1 , which is used for continuous casting carried out under conditions including a molten steel flow rate of 0.04 (t/(min·cm 2 )) or more, as measured with reference to a position of minimum cross-sectional area in a region around an upper end of the immersion nozzle where a transverse cross-section of the inner bore has a circular shape.