Stopper for continuous casting and continuous casting method
The precision of grasping or controlling backpressure around a gas discharge portion in a stopper for continuous casting can be improved with a stopper for continuous casting which includes a cavity for conveying gas in a vertical direction center of the stopper, one or a plurality of gas discharge holes passing through from the cavity to the outside in a distal center or a side surface of a reduced-diameter region including a fitted portion to a lower nozzle, and a pressure control component in a part of an area above the gas discharge hole within the cavity.
1. A stopper for continuous casting comprising:
a cavity for conveying gas in a vertical direction center of the stopper;
one or a plurality of gas discharge holes passing through from the cavity to the outside in a distal center or a side surface of a reduced-diameter region including a fitted portion to a lower nozzle; and
a pressure control component in a part of the reduced-diameter region, the part being above the gas discharge hole within the cavity,
wherein the pressure control component is made of a dense refractory having no gas permeability under a condition of pressurizing a sample of the refractory having a length of 20 mm at 8×10 −2 MPa,
wherein the pressure control component includes one or a plurality of through holes disposed within the pressure control component or between an outer periphery of the pressure control component and a body of the stopper so as to pass through from an upper end to a lower end between the pressure control component or the outer periphery of the pressure control component and the body of the stopper,
wherein the through hole has a diameter having a size between φ0.2 mm and φ2 mm both inclusive, the size being obtained by assuming a cross section of the hole as a circular shape and converting the cross section into a circle, and
wherein the number of through holes satisfies Equations 1 and 2:
(−0.44× Hd 2 +1.88 Hd− 0.08)≤ Ha≤{ 1.67×ln( Hd )+3.66} Equation 1
Hn=Ha ÷( Hd 2 ×π÷4) Equation 2, where
Ha is a numerical value of a total cross-sectional area of the through hole(s),
Hn is the number of through holes,
Hd is a numerical value of a diameter of the through hole, and
π is a circular constant,
with the total cross-sectional area measured in mm 2 and the diameter of the through hole measured in mm.
2. The stopper for continuous casting as claimed in claim 1 , wherein
the pressure control component is placed in an area below a diameter reduction starting position of a stopper distal end.
3. The stopper for continuous casting as claimed in claim 1 , wherein
the through hole has a slit shape (hereinafter referred to as “slit”), where a total cross-sectional area of the slit(s) is regarded as said Ha (mm 2 ) and a thickness of the slit is regarded as said Hd (mm), a value obtained by dividing the total cross-sectional area of the slit(s) by the thickness of the slit is a total length of the slit(s).
4. A continuous casting method using the stopper for continuous casting as claimed in claim 1 , the method comprising
A discharging gas into molten steel from the gas discharge hole of the stopper of claim 1 by setting gas pressure in the cavity on an upstream side of the pressure control component to a value between 2×10 −2 (MPa) and 8×10 −2 (MPa) both inclusive.