Title of the invention: Stopper for continuous casting and continuous casting method
Technical field
[0001]
　According to the present invention, in continuous casting of molten steel, when the molten steel is discharged from the tundish into a mold, the flow rate of the molten steel is controlled by fitting the molten steel into a nozzle installed at the bottom of the tundish from above. The present invention relates to a stopper for continuous casting having a function, and a continuous casting method using this stopper.
Background technology
[0002]
　In the continuous casting of molten steel, the stopper that controls the flow rate of the molten steel when discharging the molten steel from the tundish to the mold is used for the purpose of floating inclusions in the molten steel or preventing inclusions from adhering to the inner wall of the nozzle. ， Some have a gas blowing function.
[0003]
　For example, Patent Document 1 provides a gas discharge port (gas outlet) that discharges (spouts) the gas guided through the stopper and penetrates from the inlet of the nozzle hole at the bottom of the pouring container to the lower outlet. It is configured so that the molten metal remaining in the nozzle hole is discharged downward from the nozzle hole, and in order to prevent the molten metal from flowing into the gas discharge port, gas pressure is applied to the gas discharge port even during pouring. A pouring device to be added is disclosed.
Prior art literature
Patent documents
[0004]
Patent Document 1: Japanese Patent Application Laid-Open No. 2013-043199
Outline of the invention
Problems to be solved by the invention
[0005]
　In general, the amount of gas discharged from the stopper (hereinafter, simply referred to as "gas discharge amount") needs to be changed according to the casting speed, that is, the molten steel discharge rate, the steel type, and other individual operating conditions. Therefore, it is necessary to design the size and quantity of through holes for gas discharge so that the required gas discharge amount can be obtained in the maximum case of fluctuating operating conditions.
　On the other hand, the gas discharge rate has a large effect on the quality of steel, so it is necessary to manage the discharge rate (flow rate) appropriately in response to changes in conditions during casting.
　Therefore, when the gas discharge amount is controlled to a certain level or less, especially when the gas discharge amount is small, even if the gas pressure (back pressure) is applied to the gas discharge port as shown in Patent Document 1, the gas pressure (back pressure) is maintained. Generally, since the gas pressure is controlled only by the device of the gas supply source farther from the gas discharge port of the stopper which is the gas discharge part, the gas pressure, that is, the back pressure in the vicinity of the gas discharge part becomes low. Therefore, it is often difficult to grasp or manage the back pressure near the gas discharge part.
[0006]
　An object to be solved by the present invention is to improve the accuracy of grasping or managing the back pressure in the vicinity of the gas discharge portion in the stopper for continuous casting.
Means to solve problems
[0007]
　The present invention is the stopper for continuous casting according to the following 1 to 4 and the continuous casting method according to 5.
1. 1.
　A stopper for continuous casting having a cavity for gas flow in the center in the vertical direction,
　and penetrates from the cavity to the outside through the center or side surface of the tip of the reduced diameter region including the fitting part with the lower nozzle. A
　stopper for continuous casting, which is provided with one or more gas discharge holes, and is further provided with a pressure control component at a position above the gas discharge holes in the cavity and in a part of the diameter reduction region.
2. 2.
　The stopper for continuous casting according to claim 1, wherein the pressure control component is installed in the vicinity immediately above the gas discharge hole.
3. 3.
　The pressure control component is made of a dense fireproof material having no gas permeability under the condition of pressurizing a sample having a length of 20 mm at 8 × 10 −2 MPa, and is
　inside the pressure control component or the pressure. It is provided between the outer circumference of the control component and the stopper body, and is provided with one or more through holes penetrating from the upper end to the lower end between the outer circumference of the pressure control component or the pressure control component and the stopper body. ,
　the diameter of the through hole is a cross-section of the holes is φ0.2mm more φ2mm less a size obtained by converting the section thereof to the circle is regarded as circular,
　the number of the through-hole of the formula 1 below, the formula 2
The stopper for continuous casting according to claim 1 or 2, which meets the requirements .
　(−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
　Here,
　　Ha: Total cross-sectional area of ​​the through hole (mm 2 )
　　Hn: Number of through holes (pieces)
　　Hd: Diameter of the through hole (mm)
　　π: Pi
4.
　The through hole has a slit shape (hereinafter referred to as “slit”), the total cross-sectional area of ​​the slit is regarded as the Ha (mm 2 ), and the thickness of the slit is regarded as the Hd (mm). The stopper for continuous casting according to 3 above, wherein the total length of the slit is a value obtained by dividing the total cross-sectional area of ​​the slit by the thickness of the slit.
5.
　Using the stopper for continuous casting according to any one of 1 to 4 above, the pressure of the gas in the cavity on the upstream side of the pressure control component is 2 × 10-2 (MPa) or more and 8 × 10 −. A continuous casting method in which gas is discharged into molten steel from the gas discharge hole of the stopper as 2 (MPa) or less.
[0008]
　It will be described in detail below.
　In an operation in which gas is discharged from the vicinity of the tip of the stopper, a structure in which a gas discharge hole is provided at the end of a cavity inside the stopper, which is a gas distribution path, tends to cause large fluctuations in gas back pressure and tends to be unstable. .. The stopper is immersed in the molten steel, and the vicinity of the tip thereof is close to the nozzle hole for discharging the molten steel, and also plays a role in controlling the flow rate of the molten steel, so that the flow velocity of the molten steel fluctuates greatly. Therefore, fluctuations in the flow rate and pressure of the gas discharged from the vicinity of the tip of the stopper also become large, and it becomes difficult to control the gas accurately and with high accuracy.
[0009]
　In the present invention, a component (pressure) that controls the pressure by interrupting the continuity of the cavity in the vicinity of the stopper end of the cavity inside the stopper and dividing the cavity into two spaces, an upstream side and a downstream side. Control parts ") are installed.
　With this pressure control component, the pressure fluctuation of the gas from the tip of the stopper is not directly transmitted to the upstream side, but the pressure of the gas is controlled in the space (cavity) on the upstream side.
　This pressure control component is installed at a position above the gas discharge hole of the cavity and in a part of the reduced diameter region near the tip of the stopper.
[0010]
　When this pressure control component is composed of a porous refractory that has gas permeability almost entirely, the gas permeability in this porous refractory gradually decreases with the passage of casting time, and gas passes or is discharged. The present inventors have found that the gas often stops.
　This is not due to a single cause, and the mechanism is not always clear, but the pressure control component is composed of a dense refractory material, and the pressure control component or the outer circumference of the pressure control component and the stopper body The present inventors have found that the phenomenon of stopping the passage or discharge of gas in a porous refractory can be eliminated by providing a through hole through which gas can pass.
[0011]
　By the way, in order to control the gas pressure or flow rate accurately and with high accuracy, it is preferable that the gas pressure in the zone for adjusting the gas pressure is high.
　On the other hand, as the stopper body, a so-called monoblock stopper (hereinafter referred to as "MBS") in which a refractory material such as an alumina-based inorganic material-graphite is integrally molded is generally used. In such an MBS, the present inventors have found that when the gas pressure in the cavity is increased to approximately 1 × 10 -1 (MPa) or more, the gas permeates or dissipates in the side wall portion of the MBS main body.
　Further, in consideration of the case where such MBS is used, the present inventors further set the pressure of the gas in the cavity upstream of the pressure control component to 2 × 10 -2 (MPa) or more and 8 × 10 -2 (MPa). ) It was found that it is preferable to discharge the gas into the molten steel from the gas discharge hole of the stopper as follows.
　8 × 10-2 (MPa) as the upper limit of the preferable range is a pressure of generally less than 1 × 10 -1 (MPa) for preventing gas permeation or dissipation from the side wall portion of the MBS main body. In addition, it is a value that takes into account the so-called safety factor, such as variations in the individual shapes and materials of MBS.
　If the pressure of the gas is less than 2 × 10-2 (MPa), the accuracy and accuracy of pressure control may decrease.
[0012]
　The dense refractory in the present invention is a method for measuring a refractory sample in a laboratory, when a sample having a length of 20 mm (regardless of width or area) is pressurized by 8 × 10-2 MPa. In addition, it refers to refractories that have the property of not allowing gas to permeate.
　For the pressurization of 8 × 10 -2 MPa in this test, the upper limit of the gas pressure during operation in MBS is 8 × 10 -2 MPa, so the same pressing force as this upper limit is selected and the length is long. In other words, it is the practical axial length of the pressure control component, and is the length selected as the shortest (thinnest) length in consideration of its strength and installation stability. If the length is longer than 20 mm, the gas permeation becomes smaller. Therefore, if there is no gas permeation under these conditions, there should be no gas permeation in MBS operation even if pressure control parts longer than this are used. become.
[0013]
　The present inventors have found that it is preferable to specify the diameter and number of through holes related to the pressure control component required for such pressure control by performing a simulation as shown in 3 above. This simulation was performed using general fluid analysis software.
　To summarize this, every arbitrary-specific through-hole in the range of φ2.0mm than 0.2 mm in diameter, 8 × the pressure of the gas in the cavity on the upstream side of the pressure control part 10 -2 (MPa) or less 2 × 10 - It is a specific condition for determining the number of through holes required to be within the range of 2 (MPa) or more, and the required number of through holes is the total cross-sectional area of ​​the through holes calculated by Equation 1. Is divided by the cross-sectional area of ​​the through hole.
[0014]
　The through hole is preferably circular, but is not necessarily limited to a circular shape, and has a length that is relatively close in all diameter directions, such as an ellipse or other curved surface (non-perfect circle), or a polygon. It may be a so-called single hole shape or a slit shape (slit).
　In applying the present invention, in the case of a single hole shape other than a circle, the size (diameter) may be determined by converting the cross-sectional area of ​​the hole into a circle.
　In the case of a slit, its thickness and length may be determined by the conversion method shown in 4 above.
Effect of the invention
[0015]
　The conventional technology without pressure control parts has the following problems.
(A) Since the back pressure during casting is low and the tendency is similar to the situation where gas leaks, it is difficult to judge whether the gas is stably discharged into the molten steel (inside the nozzle).
(B) Since the absolute value of the back pressure of gas is also low, it is extremely difficult to control the back pressure of gas.
(C) Back pressure fluctuations and flow rate fluctuations are likely to occur during gas discharge, making stable gas discharge difficult.
(D) Since stable gas discharge is not possible, nozzle clogging, deterioration of flow in the mold, deterioration of inclusions in the mold, etc. are likely to occur, and these eventually deteriorate the quality of steel due to inclusions. Will be invited.
[0016]
　By providing the stopper of the present invention with a pressure control component, these problems can be solved.
　That is, according to the present invention, it is possible to grasp the back pressure of the gas near the gas discharge hole near the tip of the stopper, and to grasp, manage / control the state of the gas discharged into the molten steel with higher accuracy. Will be possible. As a result, the distribution of gas in the molten steel can be controlled with higher accuracy, and the quality of the steel can be stabilized or improved.
[0017]
　When the pressure control component is installed in an upper area other than the diameter reduction area, molten steel invades into the gas discharge hole and is concerned, especially when the amount of gas discharged from the gas discharge hole installed near the tip of the stopper is small. The gas discharge hole may be blocked.
　On the other hand, in the present invention, the temperature of the pressure control component itself can be increased by providing the pressure control component at a part of the position of the reduced diameter region where the thickness of the refractory is small from the outer circumference of the stopper to the inner cavity. At the same time, the temperature of the gas that has passed through the pressure control component can be increased quickly, and the pressure of the gas near the gas discharge hole can be increased. As a result, even if molten steel invades the gas discharge hole, it is possible to prevent the invaded molten steel from easily solidifying, and it is possible to reduce the possibility of blocking the gas discharge hole.
[0018]
　Furthermore, in response to the above-mentioned phenomenon of stopping gas passage or discharge due to a decrease in gas permeability in the porous refractory when the pressure control component is composed of a porous refractory having gas permeability almost entirely. However, it is possible to prevent the amount of gas passing through the pressure control component and the amount of gas discharged from the tip of the stopper from decreasing or stopping.
A brief description of the drawing
[0019]
[Fig. 1] An example of a stopper provided with a pressure control component and a gas discharge hole of the present invention, in which the gas discharge hole exists in the center of the tip of a reduced diameter region.
[Fig. 2] An example of a stopper provided with a pressure control component and a gas discharge hole of the present invention, in which the gas discharge hole exists on a side surface of a reduced diameter region.
FIG. 3 is an image view of the upper end surface of the pressure control component of the present invention as viewed from above.
FIG. 4 is a graph obtained by simulation of the relationship between the diameter of a through hole and the total cross-sectional area at pressures of 2 × 10 -2 (MPa) and 8 × 10 -2 (MPa).
[Fig. 5] An example in which the difference in gas pressure (adjusted by the number of through holes) when the total area of ​​through holes is the same when the through holes are of two types, circular and oval, is obtained by simulation. Graph to show.
FIG. 6 is a graph showing an example of gas back pressure during casting between the case where the pressure control component of the present invention is provided and the case where the conventional technique does not include the pressure control component.
FIG. 7 is a graph showing an example of fluctuations in gas back pressure and flow rate during casting between the case where the pressure control component of the present invention is provided and the case where the conventional technique does not include the pressure control component.
[Fig. 8] Thickness of deposits of alumina-based inclusions on the inner wall of the nozzle in the case where the pressure control component of the present invention is provided and in the case of the conventional technique which does not include the pressure control component (index with which 1 is set in the case of the prior art). ) Example.
FIG. 9 shows the average number of occurrences (times / ch) of sudden fluctuations in the molten metal level of 10 mm or more in the mold when the pressure control component of the present invention is provided and when the conventional technique does not include the pressure control component. A graph showing an example.
[Fig. 10] An experimental example of a water model showing gas flow rate / back pressure characteristics at different gas discharge hole morphologies and diameters.
[Fig. 11] An experimental example in a water model showing the bubble diameter and abundance ratio assuming the inside of a mold with different gas discharge hole morphologies and diameters.
Mode for carrying out the invention
[0020]
　A mode for carrying out the present invention will be described together with an example (water model experimental example).
[0021]
　FIG. 1 shows a main part of a stopper, which is an example of the present invention, in a vertical cross section together with a lower nozzle. The stopper 10 shown in the figure is provided with a cavity 2 for gas flow at the center thereof in the vertical direction. That is, the cavity 2 is provided at the center of the stopper body 1 so as to extend in the vertical direction, and a gas supply source (not shown) is connected to the upper end of the cavity 2. The stopper 10 is typically arranged in the tundish, and controls the flow rate of the molten steel by fitting the stopper 10 into the nozzle (lower nozzle) 20 installed at the bottom of the tundish from above.
　The stopper 10 is provided with one gas discharge hole 4 penetrating from the cavity 2 to the outside at the center of the tip of the reduced diameter region including the fitting portion 3 with the lower nozzle 20, and further, the cavity 2 is provided. A pressure control component 5 is provided above the gas discharge hole 4 of the above and at a part of the position of the reduced diameter region.
　As shown in FIG. 2, the gas discharge holes 4 may be provided on the side surface of the reduced diameter region, and the number of the gas discharge holes 4 may be plural. Further, the gas discharge hole 4 may be formed in a slit shape.
[0022]
　As described above, the stopper of the present invention includes a pressure control component at a part above the gas discharge hole, preferably in the vicinity immediately above the gas discharge hole. The reason is that in order to grasp and control the state of the gas discharged from the vicinity of the tip of the stopper more accurately and with high accuracy, it is preferable to grasp and control the pressure at a portion as close as possible to the discharge hole. The part as close as possible to this discharge hole is the area below the diameter reduction start position of the tip of the stopper. Specifically, it is within about 150 mm from the tip of the stopper body.
[0023]
　In the stopper of the present invention, the gas discharge hole is the tip opening of the cavity for gas flow, and the discharge hole may be arranged at one place in the center of the tip of the reduced diameter region, near the fitting portion (side surface portion). It may be in multiple places. However, the total opening area of ​​the gas discharge holes is preferably about 3.1 mm 2 (corresponding to the opening area of ​​2 mm diameter) or less.
[0024]
　The pressure control component may be in the form of a porous body (porous refractory) or a through hole, but it is preferable to control the gas flow rate under a higher pressure. The gas ventilation characteristics of the pressure control component specified in the above formula 1 and the gas ventilation characteristics of the gas discharge hole are measured independently in the laboratory.
[0025]
　Further, when the pressure control component is a porous body (porous refractory) and the amount of gas decreases, blockage, etc. occurs, the pressure control component is used so as to meet the conditions of the formula and the like described in 4 above. It is preferable to have a structure in which a through hole is provided in the pressure control component or between the outer periphery of the pressure control component and the stopper main body as the dense refractory.　
[0026]
　An example of installation and a shape of the through hole are shown in FIGS. 3 (A) to 3 (J).
　FIG. 3A is an example in which the pressure control component 5 having one through hole 6 is installed in the stopper main body 1 via the joint material 7.
　FIG. 3B is an example in which the pressure control component 5 having a plurality of through holes 6 is installed in the stopper main body 1 via the joint material 7.
　FIG. 3C shows an example in which a plurality of through holes 6 are formed as grooves on the outer peripheral edge of the pressure control component 5, and the pressure control component 5 is installed on the stopper body 1 without using a joint material. Is.
　FIG. 3D shows an example in which a plurality of through holes 6 are installed in the joint material 7 between the outer circumference of the pressure control component 5 and the stopper main body 1.
　In FIG. 3 (E), a plurality of through holes 6 are installed in a groove shape between the outer circumference of the pressure control component 5 and the stopper body 1 and on the cavity 2 side of the stopper body 1 without using a joint material. This is an example in which the pressure control component 5 is installed in.
　FIG. 3F is an example in which a pressure control component 5 having a plurality of slit-shaped through holes 6 (slits) is installed in the stopper main body 1 via a joint material 7.
　FIG. 3 (G) shows an example in which a plurality of slit-shaped through holes 6 (slits) are installed between the outer circumference of the pressure control component 5 and the stopper main body 1.
　FIG. 3H is an example in which the pressure control component 5 made of a porous refractory is installed in the stopper main body 1. Although FIG. 3 (H) shows the case where there is no joint material, there may be a case where there is a joint material.
　FIG. 3 (I) is a diagram showing a thickness t and a length L of an example in which the through hole 6 has a slit shape.
　FIG. 3J is a diagram showing the thickness t and the length L of another example in which the through hole 6 has a slit shape.
[0027]
　In the present invention, the through hole can have various shapes as in the examples of the through hole shown in FIGS. 3 (A) to (G), (I), (J), and FIG. Note that FIG. 3 (H) shows an example in which the pressure control component 5 is a porous body (porous refractory). It can be in various forms such as.
[0028]
　As shown in FIG. 4, the through holes are the diameter and total of the circular through holes at pressures of 2 × 10 -2 (MPa) and 8 × 10 -2 (MPa) (pressure of the cavity on the upstream side of the pressure control component). It may be arranged so as to be within the range of the approximate curve showing the relationship of the cross-sectional areas. In other words, the cross-sectional area (Hd 2 × π ) of the through hole having the value (Ha) of the total cross-sectional area of ​​the through hole shown on the vertical axis of the graph of FIG. 4 and the value (Hd) of the diameter of the through hole on the same horizontal axis. The value divided by ÷ 4) may be used as the number of through holes and placed in the pressure control component.
[0029]
　As described above, the shape of the through hole may be a circular shape, an ellipse or other curved surface shape (non-perfect circle), a single hole shape such as a polygonal shape, or a slit shape.
　FIG. 5 shows an example in which the shapes of the through holes are compared between a circular shape and a slit shape. The shape of the slit in this example is a slit shape in which both ends are part of a circle and the circles at both ends are extended outward. In this example, the pressure value (pressure value of the cavity on the upstream side of the pressure control component) was observed when the total cross-sectional area was the same. Here, the total cross-sectional area is changed so that the total cross-sectional area is the same by changing the number of each of these through holes.
　As a result, it can be seen that there is almost no difference in pressure between the circular shape and the slit shape. That is, in the case of a slit-shaped through hole, it can be seen that the shape and number of the through holes may be determined by the conversion method shown in 5 above.
[0030]
　Back pressure of gas (Ar) during casting when the pressure control component of the present invention is provided (the same applies hereinafter in the case of FIGS. 1 and 3 (A)) and when the conventional technique does not include the pressure control component. An example of is shown in FIG. It can be seen that the back pressure can be increased and managed when the pressure control component of the present invention is provided, whereas the back pressure is extremely low in the conventional technique without the pressure control component.
[0031]
　FIG. 7 shows an example of fluctuations in the back pressure and flow rate of the gas (Ar) during casting between the case where the pressure control component of the present invention is provided and the case where the conventional technique does not include the pressure control component. It can be seen that when the pressure control component of the present invention is provided, not only the back pressure but also the gas flow rate (discharge amount) is more stable than in the case of the conventional technique which does not include the pressure control component.
[0032]
　An example of the thickness of the alumina-based inclusions on the inner wall of the nozzle (index of 1 in the case of the prior art) in the case of the case where the pressure control component of the present invention is provided and the case of the conventional technique which does not include the pressure control component. It is shown in FIG. It can be seen that when the pressure control component of the present invention is provided, the thickness of the deposits of the alumina-based inclusions on the inner wall of the nozzle is smaller than that of the prior art without the pressure control component.
[0033]
　FIG. 9 shows an example of the average number of occurrences (times / ch) of sudden fluctuations in the molten metal level of 10 mm or more in the mold when the pressure control component of the present invention is provided and when the conventional technique does not include the pressure control component. Shown in. It can be seen that when the pressure control component of the present invention is provided, the average number of occurrences of sudden fluctuations in the molten metal level of 10 mm or more in the mold is also smaller than that in the case of the prior art without the pressure control component.
[0034]
　Here, when the gas discharge hole is arranged at one place in the center of the tip of the reduced diameter region of the stopper, it may be provided at a position within ± 10 mm in the radial direction of the stopper with reference to the vertical central axis of the stopper. preferable. The reason is that if the gas flow is placed at the above position, the discharged gas flow is less likely to be affected by the molten steel flow flowing along the outer circumference of the stopper tip (so-called head portion), the bubbles are less likely to coalesce, and coarse bubbles are generated. This is because it can be prevented, and as a result, it is possible to effectively suppress nozzle clogging and promote the floating of intervening portions in the mold.
[0035]
　Here, when the gas discharge holes are arranged at a plurality of locations near the tip of the reduced diameter region of the stopper, the fitting portion (with the lower nozzle) is 10 mm or more in the radial direction of the stopper with reference to the vertical central axis of the stopper. It is preferable to provide it at a position within the contact point). The reason for this is that if it is placed at the above position, the discharged gas flow is dispersed and it is difficult for bubbles to coalesce, and it is possible to prevent the formation of coarse bubbles. As a result, nozzle clogging can be suppressed and the inside of the mold can be prevented. This is because the inclusions can be effectively promoted, and by discharging the gas below the fitting portion (contact point with the lower nozzle), the gas can be reliably blown into the lower nozzle inner hole. Is.
[0036]
　When the gas discharge hole is arranged at one place in the center of the tip of the diameter reduction region of the stopper or at a plurality of places on the side surface, the diameter of the tip opening (discharge port) of the gas discharge hole is 2 mm or less as a result of the experiment. Is preferable. The reason for this is that the flow rate can be controlled with higher accuracy, and that the proportion of small-diameter bubbles (generally less than 3 mm) that easily float inclusions in the molten steel and are less likely to cause steel defects is large. The results of these water model experiments are shown in FIGS. 10 and 11.
Code description
[0037]
　10 Stopper
　1 Stopper body
　2 Cavity
　3 Fitting part
　4 Gas discharge hole
　5 Pressure control component
　6 Through hole
　7 Joint material
　20 Lower nozzle
The scope of the claims
[Claim 1]
　A stopper for continuous casting having a cavity for gas flow in the center in the vertical direction,
　and penetrates from the cavity to the outside through the center or side surface of the tip of the reduced diameter region including the fitting part with the lower nozzle. A
　stopper for continuous casting, which is provided with one or more gas discharge holes, and is further provided with a pressure control component at a position above the gas discharge holes in the cavity and in a part of the diameter reduction region.
[Claim 2]
　The stopper for continuous casting according to claim 1, wherein the pressure control component is installed in the vicinity immediately above the gas discharge hole.
[Claim 3]
　The pressure control component is made of a dense fireproof material having no gas permeability under the condition of pressurizing a sample having a length of 20 mm at 8 × 10 −2 MPa, and is
　inside the pressure control component or the pressure. It is provided between the outer circumference of the control component and the stopper body, and is provided with one or more through holes penetrating from the upper end to the lower end between the outer circumference of the pressure control component or the pressure control component and the stopper body. ,
　the diameter of the through hole is a cross-section of the holes is φ0.2mm more φ2mm less a size obtained by converting the section thereof to the circle is regarded as circular,
　the number of the through-hole of the formula 1 below, the formula 2
The stopper for continuous casting according to claim 1 or 2, which meets the requirements .
　(−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
　Here,
　　Ha: Total cross-sectional area of ​​the through hole (mm 2 )
　　Hn: Number of through holes (pieces)
　　Hd: Diameter of the through hole (mm)
　　π: Pi
[Claim 4]
　The through hole has a slit shape (hereinafter referred to as “slit”), the total cross-sectional area of ​​the slit is regarded as the Ha (mm 2 ), and the thickness of the slit is regarded as the Hd (mm). The stopper for continuous casting according to claim 3, wherein the total length of the slit is a value obtained by dividing the total cross-sectional area of ​​the slit by the thickness of the slit.
[Claim 5]
　Using the stopper for continuous casting according to any one of claims 1 to 4, the pressure of the gas in the cavity on the upstream side of the pressure control component is 2 × 10-2 (MPa) or more and 8 ×. A continuous casting method in which gas is discharged into molten steel from the gas discharge hole of the stopper as 10-2 (MPa) or less.