JPWO2011055484A1 - Method for continuous casting of molten metal - Google Patents

Abstract

A hollow cylindrical, conical or frustoconical refractory structure with one or more side holes in the side wall above the immersion nozzle in the tundish with the axis of the refractory structure vertical A molten metal continuous casting method for supplying molten metal from the tundish into an immersion nozzle, the imaginary line extending radially from the center of the horizontal circular cross section of the refractory structure and the An angle formed by the central axis of the side hole is an angle θ1, and a swirling flow of the molten metal supplied into the immersion nozzle is formed by passing the molten metal in the tundish through the side hole, and the molten metal Flow rate Q, the total opening area S of the side holes, the average inner radius R of the horizontal circular section in the portion where the side holes are open, and the angle θ1 is 0.015 m 2 / s ≦ Continuous molten metal satisfying R × Q / S × Sinθ1 ≦ 0.100m2 / s Casting method. By providing a swirl flow imparting mechanism in the tundish, the flow of the molten metal in the mold can be stabilized.

Description

  The present invention relates to a technique for imparting a swirl flow to a molten metal passing through an immersion nozzle in continuous casting of a molten metal such as molten steel. Giving a swirl flow to the molten metal passing through the immersion nozzle is effective for stabilizing the flow of the molten metal in the immersion nozzle and the mold.

  In continuous casting using a wide mold such as continuous casting of slabs, molten metal is usually supplied through a single immersion nozzle having opposed discharge holes. In this case, self-excited vibration occurs in the flow in the mold, causing fluctuations in the flow velocity and undulation of the molten metal surface. As a result, a reduction in casting speed is required to prevent quality defects in the slab surface layer.

  2. Description of the Related Art Conventionally, for the purpose of controlling the flow in a mold, an immersion nozzle that imparts an electromagnetic brake or electromagnetic stirring using electromagnetic force or a swirling flow as disclosed in Patent Document 1 or Patent Document 2 is known. Patent Document 1 describes an immersion nozzle including a twisted plate-like component for imparting swirl to a molten steel flow. Patent Document 2 discloses an immersion nozzle having a torsion plate-type swirl blade installed therein, and the swirl blade twist pitch, swirl blade twist angle, swirl blade outer diameter, and swirl blade thickness are within a predetermined range. A continuous casting immersion nozzle that squeezes the inner diameter between the lower end of the swirling blade and the discharge hole, defines the cross-sectional area after squeezing, and keeps the required head predicted value between the tundish and the mold within the appropriate range. Have been described.

  Furthermore, an immersion nozzle in which the depth of the waterfall-shaped dent at the bottom of the nozzle is increased as disclosed in Patent Document 3, or an immersion nozzle having a step on the nozzle inner diameter as disclosed in Patent Document 4 is known. . In the above-mentioned Patent Document 3, a nozzle main body positioned inside the slab short side wall, a discharge hole formed in the side wall of the nozzle main body and opened downward toward the slab short side wall, and a bottom concave shape of the nozzle main body are formed. In a continuous casting nozzle having a box, a continuous casting immersion nozzle is disclosed in which the ratio between the depth and inner diameter of the box and the discharge angle of the discharge holes are defined. And in patent document 4, the refractory material which comprises the part which contact | connects molten steel contains graphite, In the nozzle for continuous casting which has a plurality of level | step difference structures in which the level | step difference structure site | part has length in a nozzle inner hole part An immersion nozzle is disclosed in which the minimum inner diameter, the minimum cross-sectional area, and the cross-sectional area of the discharge hole are defined with respect to the passing amount of molten steel.

  However, the method using the electromagnetic force has a high equipment cost and it is difficult to obtain a merit commensurate with the investment. Since it is difficult to measure a molten metal flow that is a control target, it is required to perform control without grasping the state of the control target. Therefore, it is technically difficult to exert a sufficient effect.

  On the other hand, the technique relating to the immersion nozzle for imparting the swirl flow disclosed in Patent Document 1 or 2 (hereinafter also referred to as “swirl flow imparting immersion nozzle”) is a practical measure that can stabilize the flow in the mold. Its effectiveness has been confirmed. However, when casting molten metal containing a large amount of non-metallic inclusions, it is difficult to continuously cast a large amount of molten metal because non-metallic inclusions are likely to adhere to the swirl vanes provided in the nozzle. There is.

  If the immersion nozzle disclosed in Patent Document 3 is used, the surface flow velocity in the mold does not increase even if the casting speed is increased, and it is said that the entrainment of mold powder can be effectively prevented. In actual operation, it is difficult to obtain a stable entrainment preventing effect. The immersion nozzle disclosed in Patent Document 4 prevents clogging of the immersion nozzle due to alumina adhesion, and suppresses the drift of molten steel in the immersion nozzle, thereby making the flow in the mold uniform, improving slab quality, and breaking It aims to prevent out. However, even if such a nozzle is used, nozzle clogging is likely to occur in an actual casting operation, and it is difficult to obtain a stable drift suppression effect.

  As a method for solving the above problems, the present inventor has made the inventions shown in Patent Document 5 and Patent Document 6. These inventions provide a simple and effective swirl flow imparting mechanism for forming a swirl flow of molten metal in the tundish, which is a disadvantage of the swirl flow imparting immersion nozzle having the swirl vanes described above. It eliminates clogging. As a result, the flow of the molten metal in the mold is stabilized, and stable casting operation and improvement in the quality of the slab can be expected.

WO99 / 15291 JP 2002-239690 A Japanese Patent No. 3027645 Japanese Patent No. 3207793 JP 2007-69236 A JP 2008-300069 A

  However, as a result of further research and development, the present inventor has found that the technical elements described in Patent Document 5 and Patent Document 6 do not necessarily have an effect of stabilizing the flow of molten metal in the mold. .

  The present invention has been made in view of this problem, and the subject thereof is a continuous casting method in which the effect of stabilizing the flow of molten metal in a mold is improved as compared with the inventions described in Patent Document 5 and Patent Document 6. Is to provide.

  In order to solve the above-mentioned problems, the present inventor imparts a swirl flow to the molten metal flow passing through the immersion nozzle without causing nozzle clogging in the immersion nozzle, and stabilizes the flow of the molten metal in the mold. As a result of repeated examination and consideration of the casting method that can be performed, the following knowledge (a) to (g) was obtained and the present invention was completed.

(A) A method of forming a swirl flow by installing a twisted plate-like swirl vane in an immersion nozzle produces a stagnation or vortex of the flow when the molten metal descending flow in the immersion nozzle hits the swirl vane, and Al ₂ O Non-metallic inclusions such as ₃ are attached. In addition, when a swirl flow imparting mechanism such as a twisted plate swirl blade is installed in a submerged nozzle having a high flow rate, there is a problem that the flow resistance of the molten metal is large and the energy efficiency of swirl imparting is low. Therefore, when the required throughput is large, the turning strength that can be formed is limited.

(B) The tundish above the immersion nozzle has a hollow cylindrical, conical or frustoconical side with a relatively large diameter, and a circumferential velocity component is imparted to the flowing molten metal on the side. Devised a swirl flow imparting mechanism with side holes. Since this swirl flow imparting mechanism has a large cross-sectional area of the side hole, which is a molten metal flow path, the flow rate of the molten metal passing through the swirl flow imparting mechanism can be reduced.

(C) By adopting the configuration of (b) above, the flow path shape is less likely to cause stagnation and vortices, so that non-metallic inclusions such as Al ₂ O ₃ are less likely to adhere to the inner wall of the molten metal flow path. Become. Even if it adheres, the channel cross-sectional area is large, so that it is difficult to block the channel. Furthermore, since the low flow velocity and the difficulty of generating flow vortices realize the flow resistance of a small molten metal, the potential energy can be used effectively and a strong swirling flow can be obtained.

(D) In order to obtain a swirl with an appropriate strength that has a positive effect on the flow of the molten metal in the mold, the molten metal formed in the swirl flow imparting mechanism of (b) above when passing through the side hole. It is necessary to optimize the angular momentum of the swirling flow.

(E) As an index of the angular momentum of the swirl flow of the molten metal formed in the immersion nozzle, an index P represented by the following formula (1) using the flow rate of the molten metal and the shape of the swirl flow imparting mechanism was devised. . By designing the swirl flow imparting mechanism into a proper shape so that the value of the index P falls within a predetermined proper range, a swirl flow having a proper strength can be obtained.
P = R × Q / S × Sin θ1 (1)
Here, each symbol in the above formula (1) means the following quantities. R: Average inner radius of horizontal circular cross section of swirl flow imparting mechanism at side hole opening portion, Q: Flow rate of molten metal, S: Total opening area of side hole, θ1: Outlet opening portion The angle formed by the center axis of the side hole with respect to the imaginary line. The total opening area S of the side holes means the sum of the cross-sectional areas of all the side holes, and Q / S in the above equation (1) means the average velocity of the molten metal passing through the side holes.

(F) The minimum required index T (T = side hole) according to the average flow velocity Q / S in the side hole in order for the side hole of the swirl flow applying mechanism (b) to give the circumferential flow velocity to the molten metal There is a value of partial sidewall thickness / side hole width). That is, T is 1.0 or more when Q / S is less than 0.05 m / s, 0.8 or more when Q / S is 0.05 m / s or more and less than 0.1 m / s, and Q / S is 0. 0.6 or more when 1 m / s or more and less than 0.4 m / s, 0.5 or more when Q / S is 0.4 or more and less than 1.2 m / s, Q / S is 1.2 m / s In these cases, a value of 0.4 or more is required.

(G) When the swirl flow imparting mechanism (b) is immersed in the molten metal in the tundish, if there is an opening at the upper end of the swirl flow imparting mechanism, the swirl flow from the hot water surface in the tundish A vortex leading into the application mechanism is induced. This vortex is not preferable because slag and non-metallic inclusions on the tundish hot water surface are involved. In order to prevent this vortex, it is required not to provide an opening at the upper end of the swirl flow imparting mechanism, or to insert a stopper rod extending from the upper part of the tundish into the opening at the upper end of the swirl flow imparting mechanism.

  This invention is completed based on said knowledge, The summary exists in the continuous casting method of the molten metal shown to following (1)-(4).

(1) A hollow cylindrical, conical or frustoconical refractory structure with one or more side holes provided in the side wall is placed in the tundish with the axis of the refractory structure vertical. A molten metal continuous casting method that is disposed above an immersion nozzle and supplies molten metal from the tundish into the immersion nozzle, and is a virtual extension extending radially from the center of a horizontal circular section of the refractory structure. The central axis of the side hole intersects at the intersection of the line and the inner surface of the refractory structure, and the angle formed by the central axis of the side hole inclined with respect to the virtual line is the angle θ1 The molten metal in the tundish is passed from the entrance opening of the side hole opened in the outer surface of the refractory structure to the exit opening opened in the inner surface of the refractory structure. From the tundish A circumferential flow velocity is imparted to the molten metal supplied into the immersion nozzle to form a swirling flow, and the average inner diameter 2R of the horizontal circular cross section in the portion where the side holes are open is 250 mm to 1200 mm, The height of the side hole is 30 mm to 500 mm, the angle θ1 is 15 ° to 80 °, the flow rate Q of the molten metal, the total opening area S of the side hole, and the side hole is open. An index P consisting of an average inner radius R of the horizontal circular cross section in the portion and the angle θ1 and expressed by the following formula (1) is 0.015 m ² /s≦P≦0.100 m ² / s. The molten metal continuous casting method (hereinafter, also referred to as “first invention”).

(2) The relationship between the index T expressed by the thickness of the side hole portion side wall / the width of the side hole, the flow rate Q of the molten metal, and the total opening area S of the side hole satisfies the following conditions: The molten metal continuous casting method described in (1) above (hereinafter, also referred to as “second invention”).
When Q / S is less than 0.05 m / s: T is 1.0 or more,
When Q / S is 0.05 m / s or more and less than 0.1 m / s: T is 0.8 or more,
When Q / S is 0.1 m / s or more and less than 0.4 m / s: T is 0.6 or more,
When Q / S is 0.4 m / s or more and less than 1.2 m / s: T is 0.5 or more, and when Q / S is 1.2 m / s or more: T is 0.4 or more.

(3) The entire refractory structure is immersed in the molten metal in the tundish, and an opening is provided at the upper end of the refractory structure, and the tundish is formed through the opening. A molten metal continuous casting method according to (1) or (2) above (hereinafter also referred to as “third invention”), wherein a refractory stopper rod is inserted from above.

(4) The whole of the refractory structure is immersed in the molten metal in the tundish, and no opening is provided at the upper end of the refractory structure. The molten metal continuous casting method according to the above (1) or (2) (hereinafter also referred to as “fourth invention”).

  In the present invention, “the angle θ1 formed by the central axis of the side hole with respect to the imaginary line in the outlet opening” is also referred to as “the inclination angle (θ1) of the side hole” in the following description.

  The “inner radius of the horizontal circular cross section” means the intersection of the imaginary line and the central axis of the side hole (intersection forming the angle θ1) in the outlet opening of the side hole and the horizontal direction of the refractory structure. It is the distance from the center of the circular cross section, and R is defined as the average value of the inner radii in the portion where the side holes are open.

  The method of the present invention can solve the nozzle clogging problem, which is a drawback of swirl flow imparting immersion nozzles having swirl vanes, and forms a swirl flow having an appropriate strength on the molten metal in the immersion nozzle, thereby imparting swirl flow. It realizes the flow stability of the molten metal in the mold and the removal of non-metallic inclusions, which are excellent effects of the immersion nozzle, and enables stable continuous casting operation and improved quality of the slab.

FIG. 1 is a view schematically showing a continuous casting apparatus for carrying out the method of the present invention. FIG. 1 (a) is a cross-sectional view taken along line AA in FIG. 1 (b), and FIG. ) Represents a longitudinal sectional view of the continuous casting apparatus. FIG. 2 is a view schematically showing another continuous casting apparatus for carrying out the method of the present invention. FIG. 2 (a) is a cross-sectional view taken along line AA in FIG. (B) represents the longitudinal cross-sectional view of a continuous casting apparatus. FIG. 3 is a view schematically showing another continuous casting apparatus for carrying out the method of the present invention. FIG. 3 (a) is a cross-sectional view taken along line AA in FIG. (B) represents the longitudinal cross-sectional view of a continuous casting apparatus. FIG. 4 is a diagram schematically showing a continuous casting apparatus as a comparative example of the present invention, in which FIG. 4 (a) represents a cross-sectional view taken along line AA in FIG. 4 (b), and FIG. The longitudinal cross-sectional view of a continuous casting apparatus is represented. FIG. 5 is a view schematically showing another continuous casting apparatus as a comparative example of the present invention. FIG. 5 (a) is a cross-sectional view taken along line AA in FIG. 5 (b), and FIG. ) Represents a longitudinal sectional view of the continuous casting apparatus.

As described above, the present invention is directed to “a hollow cylindrical, conical or truncated cone-shaped refractory structure having one or more side holes provided on the side wall, and the axis of the refractory structure structure being vertical. In the continuous casting method of molten metal, which is disposed above the immersion nozzle in the tundish and supplies the molten metal from the tundish into the immersion nozzle, the horizontal cross section of the refractory structure The central axis of the side hole intersects at the intersection of a virtual line extending radially from the center and the inner surface of the refractory structure, and the central axis of the side hole inclined with respect to the virtual line forms at the intersection. An exit side opening having an angle θ1 and opening the molten metal in the tundish to the inner surface of the refractory structure from the entrance side opening of the side hole opened to the outer surface of the refractory structure By passing towards the front A circumferential flow velocity is imparted to the molten metal supplied from the tundish into the immersion nozzle to form a swirling flow, and an average inner diameter 2R of the horizontal circular cross section in a portion where the side holes are open is 250 mm to 1200 mm, the height of the side hole is 30 mm to 500 mm, and the angle θ1 is 15 ° to 80 °, the flow rate Q of the molten metal, the total opening area S of the side hole, and the side hole is open The index P which consists of the average inner radius R of the circular section in the horizontal direction and the angle θ1 and is expressed by the following formula (1) is 0.015 m ² /s≦P≦0.100 m. ² / s is satisfied, The molten metal continuous casting method characterized by the above-mentioned.
P = R × Q / S × Sin θ1 (1)
Is. The contents of the present invention will be described in more detail below.

  FIG. 1 is a diagram schematically showing a continuous casting apparatus for carrying out the method of the present invention. FIG. 1 (a) is a cross-sectional view taken along line AA in FIG. 1 (b), and FIG. ) Represents a longitudinal sectional view of the continuous casting apparatus.

  As shown in the figure, in the tundish 5 above the submerged nozzle 4, the center of the hole outlet is located on virtual lines X1 to X5 extending radially from the center O of the horizontal circular section, and the virtual lines X1 to X5 A hollow cylindrical refractory structure 1 in which one or more side holes 2 that are opened by inclining the directions of the central axes Y1 to Y5 of the holes are provided on the side wall is disposed. The axis 3 of the refractory structure is vertical. When the molten metal 6 in the tundish 5 passes through the side holes 2 and flows into the refractory structure 1, the molten metal 6 is given a circumferential velocity component to form a swirling flow and is immersed from the tundish 5. It is supplied to the mold 11 through the nozzle 4.

(1) 1st invention As above-mentioned, 1st invention is a refractory structure 1 made from a hollow cylindrical, cone shape, or truncated cone shape refractory body in which one or more side holes 2 are provided in the side wall. It is a continuous casting method of molten metal that is arranged above the immersion nozzle 4 in the tundish 5 with the axis of the manufacturing structure 1 being vertical, and supplying the molten metal 6 from the tundish 5 into the immersion nozzle 4. An imaginary line X1 to XN (where N represents the number of imaginary lines) radially extending from the center O of the horizontal circular section of the refractory structure 1 has a center on the exit side of the hole, The side hole 2 is formed by inclining the direction of the central axis of the hole with respect to the lines X1 to XN by the angle θ1, and the molten metal 6 in the tundish 5 is opened to the outer surface of the refractory structure 1 Passes from the entrance side opening of the hole 2 toward the exit side opening that opens to the inner surface of the refractory structure 1 By applying a circumferential flow velocity to the molten metal supplied from the tundish 5 into the immersion nozzle 4 to form a swirling flow, and the average of the horizontal circular cross section in the portion where the side hole 2 is open The inner diameter 2R is 250 mm to 1200 mm, the side hole height is 30 mm to 500 mm, the angle θ1 is 15 ° to 80 °, the molten metal flow rate Q, the total opening area S of the side holes, and the side holes are open. The index P which consists of the average inner radius R of the circular cross section in the horizontal direction and the angle θ1 in the portion that is represented by the above equation (1) is 0.015 m ² /s≦P≦0.100 m ^{This is} a molten metal continuous casting method that satisfies ² / s.

  Since the refractory structure 1 includes the side holes 2 having the inclination angle θ1, a circumferential flow velocity component can be imparted to the molten metal 6 to form a swirling flow. The number of the side holes 2 having the inclination angle θ1 may be one, but from the viewpoint of dispersing the risk of clogging by non-metallic inclusions contained in the molten metal 6, the entire side of the refractory structure 1 is distributed. It is preferable that there are a plurality. A plurality of side holes 2 may be provided on the entire circumference of the refractory structure 1 and in a plurality of stages in the height direction of the refractory structure 1 (axis 3 direction). However, when a plurality of side holes 2 are provided, it is preferable to provide the side holes 2 at the same height from the viewpoint of not unnecessarily increasing the height of the refractory structure 1.

  The inclination angle θ1 of the plurality of side holes 2 provided may be the same or may vary within a certain range. However, it is preferable that the rotational direction of the swirl flow applied to the molten metal 6 is the same. Further, the partition wall of the side hole 2 may be a thin fin shape and may have a shape having a large number of side holes in the circumferential direction of the refractory structure 1.

  It is preferable that the side hole 2 has a size that allows foreign matter having a maximum particle size in the molten metal of about 30 mm to pass through. The upper and lower inner wall surfaces of the side hole 2 may be horizontal or inclined. However, the height of the lower end of the side hole 2 should be low enough to prevent the molten metal 6 from remaining in the tundish 5 at the end of casting and causing a decrease in yield, that is, a height within 200 mm from the bottom of the tundish. Is preferred.

  The upper end of the refractory structure 1 may or may not be provided with an upper lid. When an upper cover is provided on the upper end 7 of the refractory structure 1, limiting the internal height of the refractory structure 1 to 150 mm or less from the upper end of the side hole 2 attenuates the swirling flow formed. It is preferable from the viewpoint of not making it happen.

  Further, when the upper end of the refractory structure 1 is open, the molten metal 6 in the tundish 5 (the upper outside of the refractory structure 1) is placed inside the refractory structure 1. It is driven and rotated by the swirling flow of the formed molten metal 6. In this case, since the angular kinetic energy of the swirling flow is consumed for this driving, the swirling flow of the molten metal 6 inside the refractory structure 1 is weakened. This energy consumption increases as the opening area at the upper end of the refractory structure 1 increases. Therefore, when the upper cover 7 is not provided on the upper end portion 7 of the refractory structure 1, the side hole 2 is provided on the inner diameter above the height at which the side hole 2 is provided from the viewpoint of not attenuating the swirling flow. It is preferable to reduce the inner diameter of the portion below the height being 50 mm to 200 mm. Furthermore, when the upper lid is not provided, it is preferable from the viewpoint of preventing the tundish slag from being mixed into the refractory structure 1 to make the height of the upper end 7 higher than the height of the hot water surface in the tundish 5. .

  In the present invention, the average inner diameter 2R of the horizontal circular section in the portion where the side hole 2 of the refractory structure 1 is opened is in the range of 250 mm to 1200 mm. The reason is that if the average inner diameter 2R is less than 250 mm, it is too small as a swirling flow imparting mechanism, so that it is difficult to obtain a sufficient angular momentum. Problems such as clogging of the molten metal and increase in frictional resistance of the molten metal 6 occur. In addition, if the average inner diameter 2R exceeds 1200 mm, the swirl flow imparting mechanism becomes excessive, so that not only the cost of the refractory structure 1 is increased, but a dedicated tundish is required, which increases the cost of casting equipment. Because it invites.

  The horizontal cross-sectional shape of the refractory structure 1 is preferably a perfect circle, but the same effect can be obtained even if it is a polygon or an ellipse. In that case, the average value of the distance from the center is regarded as the average inner diameter 2R. However, when the cross-sectional shape is not a perfect circle, the energy efficiency of the swirl flow formation is reduced as compared with a perfect circle.

  The height of the side hole 2 of the refractory structure 1 is in the range of 30 mm to 500 mm. This is because if the height of the side hole 2 provided in the refractory structure 1 is less than 30 mm, the flow path of the molten metal is too small and clogging is likely to occur. Further, if the height of the side hole 2 exceeds 500 mm, the flow area of the molten metal (cross-sectional area of the side hole 2) becomes excessive, and the flow rate of the molten metal passing through the side hole 2 is ensured and a sufficient angle is obtained. This is because it becomes difficult to obtain momentum. In addition, if the height of the side hole 2 exceeds 500 mm, the height of the refractory structure 1 is undesirably increased. A more preferable range of the height of the side hole 2 is 50 to 250 mm.

  Here, the height of the side hole 2 refers to the height of the side hole 2 itself when the side hole 2 is provided in only one step in the vertical direction, and the side hole 2 is provided in a plurality of steps side by side in the vertical direction. In this case, it indicates the total height of the side holes 2 in a plurality of stages (for example, when two stages of the side holes 2 having a height of 200 mm are provided, the height is 400 mm from 200 [mm] × 2. And). Further, when the cross-sectional shape of the side hole 2 is not rectangular, the maximum height is determined as the height of the side hole 2. Furthermore, when the heights of the plurality of side holes 2 provided in the circumferential direction are different, the average value of the heights of the side holes 2 is determined as the height of the side holes 2.

  The width of the side hole 2 is preferably in the range of 30 mm to 200 mm. When the width of the side hole 2 is less than 30 mm, blockage is likely to occur, and when it exceeds 200 mm, the strength of the structure 1 decreases. Furthermore, if the width of the side hole 2 exceeds 200 mm, the cross-sectional area of the side hole 2 becomes excessive, and it becomes difficult for the value of the expression (1) to satisfy the specified range. When the cross-sectional shape of the side hole 2 is not rectangular, the maximum width is regarded as the width of the side hole 2.

  The inclination angle θ1 of the side hole 2 is in the range of 15 ° to 80 °. The reason is that if the inclination angle θ1 of the side hole 2 provided in the refractory structure 1 is smaller than 15 °, the strength of the swirling flow applied is insufficient. In addition, if the inclination angle θ1 exceeds 80 °, the thickness of the side wall of the refractory structure 1 is reduced, which causes a problem in strength.

In the method of the present invention, the side hole passage average flow velocity Q / S determined from the flow rate Q of the molten metal and the total opening area S of the side holes, and the average of the horizontal circular cross section in the portion where the side holes are open and the inner radius R, the range of the index consisting angle θ1 P (P = R × Q / S × Sinθ1), to define a 0.015m ² /s~0.100m 2 / s for the following reason.

  The inventor forms a product P of the average inner radius R and the tangential direction (direction perpendicular to the radius) component of the average flow velocity Q / S of the molten metal passing through the side hole 2 inside the refractory structure 1. It was found that a swirl flow having an appropriate strength can be formed in the submerged nozzle by using the index P as an index of the angular momentum of the swirling flow of the molten metal and keeping the index P in an appropriate range.

  The swirl flow formed in the refractory structure 1 is subjected to a restriction by a flow rate adjusting mechanism such as a stopper or a sliding gate before flowing into the immersion nozzle. The swirling flow damping behavior due to this restriction is complicated, and the stronger the swirling flow formed in the structure 1 (the larger the angular momentum), the more the phenomenon of receiving a significant damping occurs. That is, when the swirl flow formed in the structure 1 is too strong, the swirl flow is attenuated by the flow rate adjusting mechanism, and the energy efficiency of swirl flow formation is reduced.

The inventor investigated the damping behavior of the swirling flow by the flow rate adjusting mechanism through repeated experiments and studies. As a result, as long as it is within the range value of the index P is 0.015m ² /s~0.100m ² / s, the attenuation of the swirling flow by squeezing the flow rate adjusting mechanism (energy loss) is not significant, and, dipping The present invention has been completed by finding that the swirling flow generated in the nozzle has sufficient strength from the viewpoint of stably controlling the flow in the mold.

When the value of the index P exceeds the upper limit value of 0.100 m ² / s, significant swirling flow attenuation occurs due to the restriction of the flow rate adjusting mechanism, and the energy efficiency of swirling flow application decreases due to the pressure loss. Furthermore, excessive circumferential flow velocity causes vibration of the immersion nozzle. On the other hand, when the value of the index P is less than the lower limit value 0.015 m ² / s, the swirl flow formed in the immersion nozzle is weak and a sufficient flow stabilization effect in the mold cannot be exhibited. Index P, more preferred range ^is 0.020m ² /s~0.085m 2 / s.

  Here, the definitions of the cross-sectional area S and the angle θ1 of the side hole 2 when the two side walls of the side hole 2 are not parallel are described below. When the side wall of the side hole 2 is parallel, since the central axis of the side hole 2 and the side wall are parallel, the angle θ1 is the imaginary line at the outlet opening of the central axis of the side hole 2. It can be uniquely determined as an angle. Similarly, the width of the side hole 2 can be uniquely determined as the distance between the side walls. On the other hand, when the side walls of the side holes 2 are not parallel, the angle θ1 varies depending on how the central axis of the side holes 2 is determined, and the width of the side holes 2 varies depending on the angle θ1. In such a case, the angle θ1 and the width of the side hole 2 are determined as follows. Two parallel and straight lines in the side hole 2 that are sufficiently longer in the direction of the flow of the molten metal 6 than the side wall (longer than the entire length of the side hole 2) are in contact with the two side walls, respectively. Deploy. When the distance between the parallel lines is the widest, the line running through the center of the parallel lines is defined as the central axis of the side hole 2. And the angle which the center axis | shaft of a side hole makes with a virtual line in the exit side opening part of the side hole 2 is defined as angle (theta) 1. The interval between the parallel lines is the width of the side hole. The opening area of each side hole 2 is the area at the place where the cross section of the side hole 2 perpendicular to the central axis is the smallest.

(2) Second Invention A second invention of the present invention will be described with reference to FIG. 1 as in the first invention.

In the second invention, the relationship between the average flow velocity Q / S in the side hole 2 of the refractory structure 1 and the index T (T = side hole side wall thickness / side hole 2 width) satisfies the following condition. The molten metal continuous casting method according to the first aspect of the present invention.
That is, when Q / S is less than 0.05 m / s: T is 1.0 or more,
When Q / S is 0.05 m / s or more and less than 0.1 m / s: T is 0.8 or more,
When Q / S is 0.1 m / s or more and less than 0.4 m / s: T is 0.6 or more,
When Q / S is 0.4 m / s or more and less than 1.2 m / s: T is 0.5 or more, and when Q / S is 1.2 m / s or more: T is 0.4 or more.

  When the average flow velocity Q / S in the side hole 2 is small, the function of imparting the circumferential flow velocity to the molten metal is deteriorated unless the side wall length is increased with respect to the width of the side hole. The minimum value of the index T (T = side hole side wall thickness / side hole 2 width), which is the ratio of the side wall length to the side hole width, is the above value. The upper limit of the index T is not particularly defined, but an excessive T causes the side wall thickness to be increased unnecessarily, leading to an increase in the size of the refractory structure 1. Therefore, the substantial upper limit of T is 2.0. Here, the thickness of the side hole portion side wall is a value obtained by dividing the difference between the outer diameter and the inner diameter of the refractory structure 1 in the portion where the side hole is formed by two.

(3) Third Invention FIG. 2 is a diagram schematically showing another continuous casting apparatus for carrying out the method of the present invention. The figure (a) represents the AA sectional view in the figure (b), and the figure (b) represents the longitudinal section of a continuous casting device. In the continuous casting apparatus shown in FIG. 2, substantially the same parts as those in the continuous casting apparatus shown in FIG.

  In the third invention, as shown in FIG. 2, an opening is provided at the upper end of the refractory structure 1 entirely immersed in the molten metal, and the refractory stopper rod 14 is formed from the upper part of the tundish through the opening. Is a molten metal continuous casting method according to the first or second invention.

  When the entire refractory structure 1 is immersed in the molten metal, a swirling flow of the molten metal is generated inside the refractory structure 1, so that an opening is formed at the upper end of the refractory structure 1. If the slag is provided, a vortex extending from the molten metal surface to the immersion nozzle 4 is generated, and the slag on the molten metal surface in the tundish 5 is sucked and mixed into the mold 11. In order to avoid this phenomenon, it is effective to insert the stopper rod 14 made of refractory from the upper part of the tundish into the center of the circular cross section of the structure 1 made of refractory.

  In this case, the shape of the refractory structure 1 having an opening at the upper end may be any of a cylindrical shape, a conical shape, or a truncated cone shape. Further, from the viewpoint of making the refractory structure 1 compact, the inner surface height of the refractory structure 1 is the same as the upper end height of the side hole 2 or at most 150 mm above the upper end height of the side hole 2. It is preferable. The diameter of the opening provided in the upper lid of the refractory structure 1 is preferably 1 to 20 mm larger than the diameter of the stopper rod 14.

  Since the stopper rod 14 normally opens and closes the molten metal passage from the tundish 5 to the immersion nozzle 4, the stopper rod 14 is located several mm to several tens of mm above the bottom of the tundish 5 during casting. There is a lower end of the rod 14, and the upper end is connected to an elevating mechanism installed at the upper part of the tundish 5.

  In the present invention, the stopper rod 14 is used for the purpose of preventing the generation of vortices caused by the formation of the swirling flow. However, when the stopper rod 14 has a lifting / lowering function, it may be used for the hot water level control in the mold 11. Alternatively, it may be used only for opening and closing the molten metal passage at the start and end of casting. When the stopper rod 14 is used only for opening and closing the molten metal passage at the start and end of casting, it is provided between the immersion nozzle 4 and the upper nozzle 8 for controlling the level of the molten metal in the mold 11 during casting. It is preferable to use a sliding gate 9.

(4) Fourth Invention FIG. 3 is a diagram schematically showing another continuous casting apparatus for carrying out the method of the present invention. The figure (a) represents the AA sectional view in the figure (b), and the figure (b) represents the longitudinal section of a continuous casting device. In the continuous casting apparatus shown in FIG. 3, substantially the same parts as those in the continuous casting apparatus shown in FIG.

  As shown in FIG. 3, the fourth invention is characterized in that no opening is provided at the upper end of the refractory structure 1 entirely immersed in the molten metal. This is a continuous casting method for molten metal.

  When the entire refractory structure 1 is immersed in the molten metal, a swirling flow of the molten metal is generated inside the refractory structure 1, so that an opening is formed at the upper end of the refractory structure 1. If the slag is provided, a vortex extending from the molten metal surface to the immersion nozzle 4 is generated, and the slag on the molten metal surface in the tundish 5 may be sucked and mixed into the mold 11 in some cases. In order to avoid this phenomenon, it is effective not to provide an opening at the upper end of the refractory structure 1.

  The effect of the molten metal continuous casting method of the present invention will be described in detail based on examples. In addition, the following description is an example for molten steel as a molten metal.

(Invention Example 1)
FIG. 1 is a diagram schematically showing a continuous casting apparatus for carrying out the method of the present invention as described above, and FIG. 1 (a) shows a cross-sectional view taken along line AA in FIG. The figure (b) represents the longitudinal cross-sectional view of a continuous casting apparatus. The embodiment shown in the figure is an embodiment that satisfies the conditions specified in the first and second inventions.

  As shown in the figure, the hollow cylindrical refractory structure 1 has an inner diameter of 400 mm, an outer diameter of 550 mm, and a total height of 1200 mm, including the portion where the side holes are open. -Consists of silica-based refractories. That is, the average inner radius R at the portion where the side hole 2 is open is 200 mm. The height of the molten metal surface in the tundish 5 during the continuous operation of continuous casting is 200 mm lower than the upper end 7 of the refractory structure 1.

On the side wall of the refractory structure 1, the central axes Y1 to Y5 are inclined at an angle θ1 = 40 ° with respect to the virtual lines X1 to X5 on the inner surface of the refractory structure as shown in FIG. 5 side holes 2 having a height of 180 mm and a width of 80 mm are provided in the circumferential direction. That is, the total opening area S of the side holes 2 is 72000 mm ² from S = 180 [mm] × 80 [mm] × 5 [pieces]. The molten steel flow rate Q during steady casting is 60 m ³ / hr. Therefore, the value of the index P represented by the formula (1) is P = R × Q / S × Sin θ1 = 200 [mm] × 60 [m ³ / hr] / 72000 [mm ² ] × 0.643 0.030 m ² / s.

  Further, the value of the index T (T = side hole side wall thickness / side hole width) is 75 [mm] / 80 [mm] = 0.938, and the side hole passage average flow velocity Q / S of the molten steel. = Appropriate value for 0.231 m / s (T: 0.6 or more).

  In the present invention example 1 shown in FIG. 1, the molten steel 6 is given a circumferential flow velocity by passing through the side hole 2, and when passing through the upper nozzle 8 and the sliding gate 9 with a narrowed inner diameter, the angular momentum is obtained. The circumferential flow velocity is increased according to the law of conservation, and a strong swirling flow is formed in the immersion nozzle 4. The swirl flow formed in the immersion nozzle 4 is uniformly and evenly discharged from the two discharge holes near the lower end of the immersion nozzle 4 by the action of centrifugal force, and forms a stable flow in the mold 11.

  Furthermore, when Ar gas is blown from the inner periphery of the fixed plate above the two-layer sliding gate 9, the Ar gas forms an inverted conical bubble film by the centrifugal force acting on the molten steel 6. In that case, the non-metallic inclusions in the molten steel 6 flowing down across the bubble film are effectively trapped in the bubbles, and also have the effect of floating and removing in the mold 11 together with the bubbles. The same effect can be obtained even if Ar gas is blown from the upper nozzle 8. Regardless of the blowing location, the effect can be enhanced by blowing from the entire circumference instead of a part of the inner circumference.

  The effect of stabilizing the flow in the mold described above makes it easy to control the molten steel flow rate in the mold within an appropriate range, and is therefore suitable for obtaining clean steel. In addition, the inclusion trapping and levitation effect due to the bubbles described above also promotes steel cleaning. Further, when the swirl flow is formed, the flow in the vicinity of the inner wall of the submerged nozzle 4 is stabilized, so that the submerged nozzle is less likely to be blocked by adhesion of non-metallic inclusions.

  The refractory structure 1 shown in FIG. 1 has an upper end 7 higher than the hot water surface in the tundish 5 to prevent the slag in the tundish 5 from entering the inside. Therefore, even if a vortex is generated in the refractory structure 1, the slag in the tundish 5 is not caught in the mold 11.

(Invention Example 2)
FIG. 2 is a diagram schematically showing another continuous casting apparatus for carrying out the method of the present invention, as described above, and FIG. 2 (a) is a cross-sectional view taken along line AA in FIG. 2 (b). FIG. 2B shows a longitudinal sectional view of the continuous casting apparatus. The embodiment shown in the figure is an embodiment that satisfies any of the conditions defined in the first to third inventions.

  As shown in the figure, the hollow frustum-shaped refractory structure 1 has an inner diameter of 550 mm at the lower end portion of the side hole 2 and 400 mm at the upper end portion of the side hole 2 in the portion where the side hole 2 is open. is there. In the portion where the side hole 2 is opened, the outer diameter is 700 mm at the lower end of the side hole 2 and 550 mm at the upper end of the side hole 2. Further, the inner surface height is 140 mm, and the total height is 180 mm. The material of the refractory structure 1 is an alumina-magnesia refractory. The average inner diameter 2R at the portion where the side hole 2 is open is 475 mm from (550 [mm] +400 [mm]) / 2, and the average inner radius R is 237.5 mm.

On the side wall of the refractory structure 1, the central axes Y1 to Y4 are inclined at an angle θ1 = 55 ° with respect to the virtual lines X1 to X4 on the inner surface of the refractory structure as shown in FIG. 4 side holes 2 having a height of 100 mm and a width of 100 mm are provided in the circumferential direction. That is, the total opening area S of the side holes 2 is 40000 mm ² from S = 100 [mm] × 100 [mm] × 4 [pieces]. The molten steel flow rate Q during steady casting is 50 m ³ / hr. Therefore, the value of the index P expressed by the equation (1) is P = R × Q / S × Sin θ1 = 237.5 [mm] × 50 [m ³ / hr] / 40000 [mm ² ] × 0. 819 to 0.068 m ² / s.

  The value of the index T (T = side hole side wall thickness / side hole width) is 75 [mm] / 100 [mm] = 0.75, and the side hole passage average flow velocity Q / S = 0 of the molten steel. It is an appropriate value (T: 0.6 or more) for 347 m / s.

  The upper end portion 7 of the hollow truncated cone has an opening portion having a diameter of 110 mm, and a stopper rod 14 having a diameter of 100 mm is inserted from above the tundish 5 to the vicinity of the upper nozzle 8 through the opening portion. The height of the hot water surface in the tundish 5 during steady operation is a height at which the refractory structure 1 is completely immersed.

  Also in the present invention example 2 shown in FIG. 2, the molten steel 6 passing through the side hole 2 is given a circumferential flow velocity, and the upper nozzle 8 and the sliding gate with a narrowed inner diameter are provided, as in the case of the present invention example 1. When passing 9, the circumferential flow velocity is increased according to the law of conservation of angular momentum, and a strong swirling flow is formed in the immersion nozzle 4. The swirl flow formed in the immersion nozzle 4 is uniformly and evenly discharged from the two discharge holes near the lower end of the immersion nozzle 4 by the action of centrifugal force, thereby forming a stable flow in the mold.

  In addition, when Ar gas is blown from the inner peripheral portion of the upper nozzle 8, the Ar gas forms an inverted conical bubble film by the centrifugal force acting on the molten steel 6, so that the molten steel flows down across the bubble film. The non-metallic inclusions in 6 are effectively trapped in the bubbles, and have the effect of floating and removing in the mold 11 together with the bubbles. The same effect can be obtained even when Ar gas is blown from the sliding gate 9. Regardless of the blowing location, this effect can be enhanced by blowing from the entire circumference instead of a part of the inner circumference.

  The effect of stabilizing the flow in the mold described above makes it easy to control the molten steel flow rate in the mold within an appropriate range, and is therefore suitable for obtaining clean steel. In addition, the inclusion trapping and levitation effect due to the bubbles described above also promotes steel cleaning. Further, when the swirl flow is formed, the flow in the vicinity of the inner wall of the immersion nozzle 4 is stabilized, so that the immersion nozzle is less likely to be blocked due to adhesion of non-metallic inclusions.

  In Example 2 of the present invention, since the stopper rod 14 is present, the generation of vortex due to the swirling flow is prevented, and the possibility that the slag in the tundish 5 is brought into the mold 11 is very low. Further, during steady casting, the flow rate of the molten steel flowing out into the mold can be controlled by the height of the stopper rod 14 by making the opening of the sliding gate 9 fully open and the cross section of the flow path into a perfect circle. In that case, it is possible to form a swirl flow that is uniform in the circumferential direction in the immersion nozzle 4. Such a circumferentially uniform swirl flow provides a more uniform and stable molten steel flow in the mold as compared with the first example of the present invention.

(Invention Example 3)
FIG. 3 is a diagram schematically showing another continuous casting apparatus for carrying out the method of the present invention as described above, and FIG. 3 (a) is a cross-sectional view taken along the line AA in FIG. 3 (b). FIG. 2B shows a longitudinal sectional view of the continuous casting apparatus. The embodiment shown in the figure is an embodiment that satisfies any of the conditions defined in the first invention, the second invention, and the fourth invention.

  As shown in the figure, the hollow frustum-shaped refractory structure 1 has an inner diameter of 550 mm at the lower end portion of the side hole 2 and 400 mm at the upper end portion of the side hole 2 in the portion where the side hole 2 is open. is there. In the portion where the side hole 2 is opened, the outer diameter is 700 mm at the lower end of the side hole 2 and 550 mm at the upper end of the side hole 2. Further, the inner surface height is 140 mm, and the total height is 180 mm. The material of the refractory structure 1 is an alumina-magnesia refractory. The average inner diameter 2R at the portion where the side hole 2 is open is 475 mm from (550 [mm] +400 [mm]) / 2, and the average inner radius R is 237.5 mm.

On the side wall of the refractory structure 1, the central axes Y1 to Y4 are inclined at an angle θ1 = 55 ° with respect to the virtual lines X1 to X4 on the inner surface of the refractory structure as shown in FIG. 4 side holes 2 having a height of 100 mm and a width of 100 mm are provided in the circumferential direction. That is, the total opening area S of the side holes 2 is 40000 mm ² from S = 100 [mm] × 100 [mm] × 4 [pieces]. The molten steel flow rate Q during steady casting is 60 m ³ / hr. Therefore, the value of the index P represented by the formula (1) is P = R × Q / S × Sin θ1 = 237.5 [mm] × 60 [m ³ / hr] / 40000 [mm ² ] × 0. 819 to 0.081 m ² / s.

  The value of the index T (T = side hole side wall thickness / side hole width) is 75 [mm] / 100 [mm] = 0.75, and the side hole passage average flow velocity Q / S = 0 of the molten steel. It is an appropriate value (T: 0.5 or more) for 417 m / s.

  Further, the upper end portion 7 of the hollow truncated cone has no opening. The height of the hot water surface in the tundish 5 during steady operation is a height at which the refractory structure 1 is completely immersed.

  Also in the present invention example 3 shown in FIG. 3, as in the case of the above-described invention example 1, the molten steel 6 passing through the side hole 2 is given a circumferential flow velocity, and the upper nozzle 8 and the sliding gate with a narrowed inner diameter are provided. When passing 9, the circumferential flow velocity is increased according to the law of conservation of angular momentum, and a strong swirling flow is formed in the immersion nozzle 4. The swirl flow formed in the immersion nozzle 4 is uniformly and evenly discharged from the two discharge holes near the lower end of the immersion nozzle 4 by the action of centrifugal force, thereby forming a stable flow in the mold.

  In addition, when Ar gas is blown from the inner peripheral portion of the upper nozzle 8, the Ar gas forms an inverted conical bubble film by the centrifugal force acting on the molten steel 6, so that the molten steel flows down across the bubble film. The non-metallic inclusions in 6 are effectively trapped in the bubbles, and have the effect of floating and removing in the mold 11 together with the bubbles. The same effect can be obtained even when Ar gas is blown from the sliding gate 9. Regardless of the blowing location, this effect can be enhanced by blowing from the entire circumference instead of a part of the inner circumference.

  The effect of stabilizing the flow in the mold described above makes it easy to control the molten steel flow rate in the mold within an appropriate range, and is therefore suitable for obtaining clean steel. In addition, the inclusion trapping and levitation effect due to the bubbles described above also promotes steel cleaning. Further, when the swirl flow is formed, the flow in the vicinity of the inner wall of the immersion nozzle 4 is stabilized, so that the immersion nozzle is less likely to be blocked due to adhesion of non-metallic inclusions.

  In Example 3 of the present invention, since there is no opening at the upper end 7 of the hollow truncated cone, the generation of vortices due to the swirling flow is prevented, and the possibility that the slag in the tundish 5 is brought into the mold 11 is very high. Very low. Inventive Example 3 is low in cost because the refractory structure 1 is smaller than Inventive Example 1. Compared to Example 2 of the present invention, the stopper rod 14 is not used, which is advantageous in terms of low cost.

  The molten metal continuous casting method of the present invention shown in the above Invention Examples 1 to 3 is swirled in the immersion nozzle 4 as compared with a normal continuous casting method in which the refractory structure 1 is not installed. Since a flow can be formed, the flow in the vicinity of the inner wall of the immersion nozzle 4 is stabilized, and adhesion of nonmetallic inclusions to the inner wall can be suppressed. Therefore, the method of the present invention exerts a great effect on improving the quality of slab and improving the productivity of continuous casting through stabilizing the flow in the mold.

(Comparative Example 1)
FIG. 4 is a diagram schematically showing a continuous casting apparatus as a comparative example of the present invention. FIG. 4 (a) shows a cross-sectional view taken along the line AA in FIG. 4 (b), and FIG. The longitudinal cross-sectional view of a continuous casting apparatus is represented. In the continuous casting apparatus shown in the figure, the same reference numerals are given to the substantially same parts as those in the continuous casting apparatus shown in FIG. The embodiment shown in the figure is an embodiment that does not satisfy the conditions defined in the first invention.

  As shown in the figure, the hollow frustum refractory structure 1 has an inner diameter of 600 mm at the lower end portion of the side hole 2 and 400 mm at the upper end portion of the side hole 2 in the portion where the side hole 2 is open. is there. Further, in the portion where the side hole 2 is opened, the outer diameter is 700 mm at the lower end portion of the side hole 2 and 500 mm at the upper end portion of the side hole 2. Furthermore, the inner surface height is 350 mm, the total height is 400 mm, and it is made of an alumina-magnesia refractory. The average inner diameter 2R at the portion where the side hole 2 is opened is 500 mm from (600 [mm] +400 [mm]) / 2, and the average inner radius R is 250 mm.

On the side wall of the refractory structure 1, the central axes Y1 to Y8 are inclined at an inclination angle θ1 = 55 ° with respect to the virtual lines X1 to X8 on the inner surface of the refractory structure as shown in FIG. 8 side holes 2 having a height of 250 mm and a width of 100 mm are provided in the circumferential direction. That is, the total opening area S of the side holes 2 is 200000 mm ² from S = 250 [mm] × 100 [mm] × 8 [pieces]. The molten steel flow rate Q during steady casting is 32 m ³ / hr. Therefore, the value of the index P represented by the formula (1) is P = R × Q / S × Sin θ1 = 250 [mm] × 32 [m ³ / hr] / 200000 [mm ² ] × 0.819 It is 0.009 m ² / s, which is a value smaller than the range defined in the present invention.

  The value of the index T (T = side hole portion side wall thickness / side hole width) is 50 [mm] / 100 [mm] = 0.5, and the side hole passage average flow velocity Q / S = 0 of the molten steel. 0.04 m / s is a value that is too small as compared with an appropriate value (T: 1.0 or more).

  The upper end portion 7 of the hollow truncated cone has an opening portion having a diameter of 110 mm, and a stopper rod 14 having a diameter of 100 mm is inserted from above the tundish 5 to the vicinity of the upper nozzle 8 through the opening portion. The height of the hot water surface in the tundish 5 during steady operation is a height at which the refractory structure 1 is completely immersed.

  In Comparative Example 1 shown in FIG. 4, the molten steel 6 that has passed through the side holes 2 is given a circumferential flow velocity, and when passing through the upper nozzle 8 and the sliding gate 9 with a narrowed inner diameter, the law of conservation of angular momentum. Accordingly, the circumferential flow velocity is increased to form a swirling flow in the immersion nozzle 4. However, as described above, since the value of the index P and the value of the index T are small outside the specified range of the present invention, a sufficiently strong swirl flow cannot be formed.

(Comparative Example 2)
FIG. 5 is a view schematically showing another continuous casting apparatus as a comparative example of the present invention. FIG. 5 (a) is a cross-sectional view taken along line AA in FIG. 5 (b), and FIG. ) Represents a longitudinal sectional view of the continuous casting apparatus. In the continuous casting apparatus shown in the figure, the same reference numerals are given to substantially the same parts as those in the continuous casting apparatus shown in FIG. The embodiment shown in the figure is an embodiment that does not satisfy the conditions defined in the first to third inventions.

  The hollow cylindrical refractory structure 1 has an inner diameter of 400 mm, an outer diameter of 550 mm, and an overall height of 1250 mm, including the portion where the side holes are open, and is an alumina-silica refractory. It is configured. That is, the average inner radius R at the portion where the side hole 2 is open is 200 mm. The height of the molten metal surface in the tundish 5 during the continuous operation of continuous casting is 100 mm lower than the upper end 7 of the refractory structure 1.

On the side wall of the refractory structure 1, the central axes Y1 to Y3 are inclined at an angle θ1 = 40 ° with respect to the virtual lines X1 to X3 on the inner surface of the refractory structure as shown in FIG. 3 side holes 2 having a height of 80 mm and a width of 80 mm are provided in the circumferential direction. That is, the total opening area S of the side holes 2 is 19200 mm ² from S = 80 [mm] × 80 [mm] × 3 [pieces]. The molten steel flow rate Q during steady casting is 65 m ³ / hr. Therefore, the value of the index P represented by the formula (1) is P = R × Q / S × Sin θ1 = 200 [mm] × 65 [m ³ / hr] / 19200 [mm ² ] × 0.643 It is 0.121 m ² / s, which is a value larger than the range defined in the present invention.

  The value of the index T (T = side hole side wall thickness / side hole width) is 75 [mm] / 80 [mm] = 0.938, and the side hole passage average flow velocity Q / S = 0 of the molten steel It is a sufficiently large value with respect to an appropriate value (T: 0.5 or more) for 940 m / s.

  In the comparative example 2 shown in FIG. 5, the molten steel 6 that has passed through the side hole 2 is given a circumferential flow velocity, and when passing through the upper nozzle 8 and the sliding gate 9 with a narrowed inner diameter, the law of conservation of angular momentum. Accordingly, the circumferential flow velocity is increased and a swirling flow is formed in the immersion nozzle 4. However, since the value of the index P is excessive as described above, excessively strong swirling flow causes a decrease in energy efficiency. Furthermore, the problem that the immersion nozzle 4 vibrates arises.

  The method of the present invention forms a swirl flow in the molten metal in the immersion nozzle without causing nozzle clogging, which is a defect of the swirl flow swirl nozzle having a twisted plate-shaped swirl blade inside. By exhibiting the excellent flow stability of the molten metal in the mold and the removal of non-metallic inclusions, it is possible to achieve stable continuous casting operation and improved quality of the slab. Therefore, the molten metal continuous casting method of the present invention is a technique that can be widely applied in the casting field aiming at stabilization of continuous casting and high cleanliness of metal cast pieces by inexpensive equipment and a simple method.

1: refractory structure, 2: side hole, 3: refractory structure shaft,
4: Immersion nozzle,
5: Tundish, 51: Tundish refractory,
52: Tundish iron skin,
6: Molten metal (molten steel), 7: Upper end of refractory structure, 8: Upper nozzle,
9: sliding gate, 10: inert gas, 11: mold,
12: solidified shell,
13: Mold powder, 14: Stopper rod,
O: center of a circular section in the horizontal direction, X1 to X8: imaginary lines extending radially,
Y1 to Y8: central axis of side hole, θ1: angle of inclination of side hole

Claims (4)

A hollow cylindrical, conical or frustoconical refractory structure with one or more side holes in the side wall above the immersion nozzle in the tundish with the axis of the refractory structure vertical A molten metal continuous casting method for supplying molten metal from the tundish into an immersion nozzle,
The imaginary line extending radially from the center of the horizontal cross section of the refractory structure and the inner axis of the refractory structure intersects the central axis of the side hole, and at the intersection, the phantom line The angle formed by the central axis of the side hole inclined with respect to the angle is the angle θ1;
The molten metal in the tundish is allowed to pass from the entrance side opening of the side hole opened on the outer surface of the refractory structure to the exit side opening opened on the inner surface of the refractory structure. By providing a circumferential flow velocity to the molten metal supplied from the tundish into the immersion nozzle to form a swirling flow,
The average inner diameter 2R of the horizontal circular cross section in the portion where the side hole is open is 250 mm to 1200 mm, the height of the side hole is 30 mm to 500 mm, and the angle θ1 is 15 ° to 80 °,
The molten metal flow rate Q, the total opening area S of the side holes, the average inner radius R of the horizontal circular cross section in the portion where the side holes are open, and the angle θ1, The index P represented by the formula (1) satisfies 0.015 m ² /s≦P≦0.100 m ² / s, and is a molten metal continuous casting method.
P = R × Q / S × Sin θ1 (1) The relationship between the index T expressed by the thickness of the side hole portion side wall / the width of the side hole, the flow rate Q of the molten metal, and the total opening area S of the side hole satisfies the following condition. The method for continuous casting of molten metal according to claim 1, characterized in that it is characterized in that
When Q / S is less than 0.05 m / s: T is 1.0 or more,
When Q / S is 0.05 m / s or more and less than 0.1 m / s: T is 0.8 or more,
When Q / S is 0.1 m / s or more and less than 0.4 m / s: T is 0.6 or more,
When Q / S is 0.4 m / s or more and less than 1.2 m / s: T is 0.5 or more, and when Q / S is 1.2 m / s or more: T is 0.4 or more. The entire refractory structure is immersed in the molten metal in the tundish,
3. The refractory structure according to claim 1, wherein an opening is provided at an upper end portion of the refractory structure, and a refractory stopper rod is inserted from above the tundish through the opening. A method for continuous casting of molten metal. The entire refractory structure is immersed in the molten metal in the tundish,
3. The molten metal continuous casting method according to claim 1, wherein an opening is not provided at an upper end portion of the refractory structure.

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