Bottom-pouring-type ladle, and melt-pouring method using it

1. A bottom-pouring ladle comprising a melt-pouring nozzle, a vertically movable stopper rod for opening and closing an upper opening of said nozzle, and an arm supporting the stopper rod;

the upper opening of said nozzle having a reverse-conically tapered surface or a spherically tapered surface providing an inward projecting fan-shaped cross section;

a lower end portion of said stopper rod having a reverse-conically tapered surface or a spherical surface, provided that it has a spherical surface when the upper opening of said nozzle has a reverse-conically tapered surface and it has either a spherical surface or a reverse-conically tapered surface when the upper opening of said nozzle has a spherically tapered surface;

the arm comprising a vertical arm portion and a horizontal arm portion;

the horizontal arm portion having an elongated hole in which a male screw portion of a core shaft of the stopper rod penetrates;

the male screw portion having an outer diameter substantially equal to a width of the elongated hole, so that the core shaft of the stopper rod can be set at an arbitrary horizontal position;

a center axis of said stopper rod always being horizontally separate from a center axis of said nozzle in a state where said stopper rod is upward separate from said nozzle;

when the lower end portion of said stopper rod moving downward comes into contact with the tapered surface of said nozzle, the horizontal distance between the center axis of said stopper rod and the center axis of said nozzle being 2-23 mm, and an angle between a normal line of the tapered surface of said nozzle or the lower end portion of said stopper rod and the center axis of said nozzle is 25° or more, at their contact point;

when said stopper rod further moves downward, the lower end portion of said stopper rod sliding downward along the tapered surface of said nozzle, thereby closing the upper opening of said nozzle; and

said stopper rod moving upward along the tapered surface of said nozzle from a position where the upper opening of said nozzle is closed, such that the center axis of said stopper rod is horizontally separated from the center axis of said nozzle.

2. The bottom-pouring ladle according to claim 1 , wherein said stopper rod is supported by an arm vertically movable such that its center axis is horizontally separated from the center axis of said nozzle.

3. The bottom-pouring ladle according to claim 1 , wherein

when said stopper rod is lifted from a state where said nozzle is closed, said stopper rod moves upward along the tapered surface of said nozzle, until the horizontal distance between the center axis of said stopper rod and the center axis of said nozzle becomes 2-23 mm; and

when said stopper rod is further lifted, said stopper rod is separated from the tapered surface of said nozzle to open the upper opening of said nozzle.

4. The bottom-pouring ladle according to claim 1 , wherein when said nozzle is closed by said stopper rod, an angle between a normal line of the spherically tapered surface of said nozzle or the spherical lower end portion of said stopper rod and the center axis of said nozzle is 60° or less, at their contact point.

5. A method for pouring a melt using a bottom-pouring ladle comprising a melt-pouring nozzle, and a vertically movable stopper rod for opening and closing an upper opening of said nozzle;

the upper opening of said nozzle having a reverse-conically tapered surface or a spherically tapered surface providing an inward projecting fan-shaped cross section; and

the lower end portion of said stopper rod having a reverse-conically tapered surface or a spherical surface, provided that it has a spherical surface when the upper opening of said nozzle has a reverse-conically tapered surface and it has either a spherical surface or a reverse-conically tapered surface when the upper opening of said nozzle has a spherically tapered surface;

said method comprising

a first opening step, in which said stopper rod is upward separate from said nozzle, with a center axis of said stopper rod always horizontally separate from a center axis of said nozzle;

a first closing step, in which said stopper rod moves downward, such that the lower end portion of said stopper rod comes into contact with the tapered surface of said nozzle, at a position where the horizontal distance between the center axis of said stopper rod and the center axis of said nozzle is 2-23 mm, and an angle between a normal line of the tapered surface of said nozzle or the lower end portion of said stopper rod and the center axis of said nozzle is 25° or more, at their contact point;

a second closing step, in which said stopper rod further moves downward to slide the lower end portion of said stopper rod downward along the tapered surface of said nozzle, thereby closing the upper opening of said nozzle; and

a second opening step, in which said stopper rod moves upward along the tapered surface of said nozzle, such that the upper opening of said nozzle is opened, and that the center axis of said stopper rod is horizontally separated from the center axis of said nozzle.

6. The method for pouring a melt according to claim 5 , wherein said stopper rod is supported by an arm vertically movable such that its center axis is horizontally separated from the center axis of said nozzle.

7. The method for pouring a melt according to claim 5 , wherein said second closing step is conducted, until the horizontal distance between the center axis of said stopper rod and the center axis of said nozzle becomes 2-23 mm.

8. The method for pouring a melt according to claim 5 , wherein when said nozzle is closed by said stopper rod, an angle between a normal line of the spherically tapered surface of said nozzle or the spherical lower end portion of said stopper rod and the center axis of said nozzle is 60° or less, at their contact point.