JP4670762B2 - Method for continuous casting of molten metal - Google Patents

Description

  In the present invention, in continuous casting of molten metal such as molten steel, swirling flow is generated in the molten metal supplied from the tundish into the immersion nozzle to prevent nozzle clogging and stabilize the flow of molten metal in the mold. The present invention relates to a continuous casting method.

  In continuous casting where a molten metal is supplied by immersing a single immersion nozzle having opposing discharge holes in a wide mold like a continuous casting of a slab, the flow in the mold causes self-excited vibration, Fluctuations in flow velocity and ripples on the surface of the water are likely to occur. As a result, abnormalities occur in the quality of the slab surface layer, and the casting speed may be reduced.

  Conventionally, for the purpose of controlling the flow in the mold, an electromagnetic brake or electromagnetic stirring using electromagnetic force, or an immersion nozzle that imparts a swirling flow as disclosed in Patent Document 1 or Patent Document 2 is known. is there. That is, Patent Document 1 describes an immersion nozzle including a twisted tape-like member for imparting swirl to a molten steel flow in the immersion nozzle. 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 values within a predetermined range. A continuous casting submerged nozzle that squeezes the inner diameter between the lower end of the swirl vane and the discharge hole, defines the cross section after squeezing, and keeps the predicted value of the required head between the tundish and the mold within the appropriate range. Are listed.

  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 in many cases, a merit corresponding to the equipment investment cannot be obtained. In addition, since it is difficult to measure the flow of the molten metal that is a control target, control is often performed while the state of the control target is unclear, and it is difficult to achieve a sufficient technical effect.

  On the other hand, the technique relating to the immersion nozzle for imparting the swirl flow disclosed in Patent Document 1 or Patent Document 2 (hereinafter, also referred to as “swirl flow imparting immersion nozzle”) is realistic that can stabilize the flow in the mold. Although its effectiveness has been confirmed as a means, when casting a molten metal with a lot of non-metallic inclusions and low cleanliness, non-metallic inclusions are likely to adhere to the swirl blades provided in the nozzle, and a large amount of melting There is a problem that it is difficult to continuously cast metal.

  Further, 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. However, it is difficult to obtain a stable entrainment preventing effect in actual operation. Furthermore, the immersion nozzle disclosed in Patent Document 4 prevents clogging of the immersion nozzle due to the adhesion of alumina, and suppresses the drift of the molten steel in the immersion nozzle, thereby uniformizing the flow in the mold and improving the quality of the slab. It aims to improve and prevent breakout. However, even if such a nozzle is used, nozzle clogging is likely to occur in an actual continuous casting operation, and it is difficult to obtain a stable drift suppression effect.

WO99 / 15291 (Claims and 5 pages 10 lines to 6 pages 8 lines) JP 2002-239690 A (Claims and paragraphs [0010] to [0013]) Japanese Patent No. 3027645 (Claims and paragraph [0005]) Japanese Patent No. 3207793 (Claims and paragraphs [0015] and [0016]) Japanese Patent Application No. 2005-258647 (Claims and paragraphs [0015] to [0018])

  The present invention has been made in view of the above problems, and the problem is that a swirl flow imparting immersion nozzle having swirl vanes is provided by providing a simple swirl flow imparting mechanism in the tundish above the immersion nozzle. It is an object of the present invention to provide a continuous casting method that can eliminate nozzle clogging, which is a drawback, and stabilize the flow of molten metal in a mold to achieve improved quality of a slab. Specifically, the present invention is a continuous molten metal casting method previously proposed by the present inventor in Patent Document 5, in which the swirling flow generated inside the refractory structure is immersed from the tundish hot water surface. There is a problem that a vortex that reaches the inside of the nozzle is generated, and the slag existing on the surface of the tundish hot water may be sucked and mixed into the mold. The problem is solved by arranging the structure.

  In order to solve the above-mentioned problems, the present inventor gives a swirl flow to the molten metal flow passing through the immersion nozzle without causing nozzle clogging in the immersion nozzle based on the conventional problems, As a result of repeated investigations on a casting method capable of stabilizing the flow of the molten metal, the following findings (a) to (d) were obtained and the present invention was completed.

(A) A method of forming a swirl flow by installing a twisted plate-shaped swirl vane in the submerged nozzle produces a stagnation or vortex of the flow when the molten metal descending flow in the submerged nozzle hits the swirl vane, and Al ₂ O Non-metallic inclusions such as ₃ are attached. In addition, if a swirl flow imparting mechanism such as a twisted plate swirl blade is installed in a submerged nozzle having a high flow rate, the frictional resistance of the molten metal is increased, which is preferable in terms of effective use of molten metal drop, that is, position energy. Absent.

  (B) In the tundish above the immersion nozzle, there is a hollow cylindrical, conical or frustoconical side surface having a relatively large diameter, and the molten metal that flows through the side surface and flows into the inside is provided on the side surface. By installing a swirl flow imparting mechanism with a side hole that imparts a velocity component in the circumferential direction, the cross-sectional area of the molten metal passage in the swirl flow imparting mechanism can be increased, and the molten metal flow rate is low. A swirling flow can be applied.

(C) With the configuration of (b) above, non-metallic inclusions such as Al ₂ O ₃ are less likely to adhere to the swirl flow imparting mechanism, and even if they adhere, the swirl flow imparting mechanism is blocked. Is difficult to reach. Furthermore, since the frictional resistance of the molten metal can be reduced, the tundish head can be used effectively and a strong swirling flow can be obtained.

  (D) In the method of (b), the swirl flow imparting mechanism has a double structure of the outer cylinder and the inner cylinder, and the length of the inner cylinder is arranged so that the lower end of the outer cylinder is in contact with the bottom surface of the tundish The side hole provided in such a manner that a gap through which the molten metal can pass can be secured between the lower end of the inner cylinder and the bottom surface of the tundish or the upper surface of the upper nozzle, and is inclined in the circumferential direction on the side wall of the outer cylinder. It is effective to have a structure with This swirl flow imparting mechanism is placed in the tundish above the immersion nozzle with the axis of the refractory structure vertical, and the molten metal in the tundish is inserted into a side hole opened on the outer surface of the outer cylinder. By passing from the side opening toward the exit opening that opens to the inner surface of the outer cylinder, a swirling flow is imparted to the molten metal, and harmful vortices that reach the immersion nozzle from the inner surface of the tundish are generated. The problem of mixing of slag into the mold due to suction of slag existing on the surface of the tundish is suppressed.

  The present invention has been completed based on the above findings, and the gist thereof lies in the molten metal continuous casting method shown in the following (1) to (3).

  (1) Having a double structure of an outer cylinder and an inner cylinder, the outer cylinder is a cylindrical, conical or truncated cone-shaped refractory structure, and the axis of the refractory structure is vertical, A continuous casting method in which a molten metal is cast in a tundish disposed above an immersion nozzle, wherein the inner cylinder has a lower end of the inner cylinder when the lower end of the outer cylinder is disposed in contact with the bottom surface of the tundish. And a bottom surface of the tundish or a top surface of the upper nozzle, and a length of 10 to 300 mm, and one or more side holes are provided on the side wall of the outer cylinder, The outlet side opening has the center of the outlet opening of the side hole of the outer cylinder at the intersection of the virtual line extending radially from the center of the horizontal circular cross section of the refractory structure and the inner surface of the outer cylinder. In which the central axis of the side hole of the outer cylinder is inclined with respect to the virtual line by an angle θ1 in a horizontal plane The structure body is placed in the tundish above the immersion nozzle with the axis of the refractory structure body vertical, and the molten metal in the tundish is opened on the entrance side of the side hole opened on the outer surface of the outer cylinder. The molten metal is cast by applying a swirling flow to the molten metal supplied from the tundish into the submerged nozzle by passing it from the portion toward the outlet opening that is opened on the inner surface of the outer cylinder. Continuous casting method (hereinafter also referred to as “first invention”).

(2) The maximum inner diameter in the horizontal circular section of the outer cylinder of the refractory structure is 150 mm to 3000 mm, the maximum inner diameter in the horizontal circular section of the inner cylinder is 50 mm to 1000 mm, and the outer cylinder is horizontal. The maximum inner diameter in the circular cross section in the direction is 1.5 times or more than the maximum inner diameter in the horizontal cross section of the inner cylinder, the inner surface height of the outer cylinder is 50 mm to 2000 mm, and the angle θ1 is 15 ° to 80 °. The molten metal continuous casting method according to (1) above (hereinafter also referred to as “second invention”).
(3) The at least one of an upper nozzle, a sliding gate, and an immersion nozzle disposed in the lower part of the tundish, wherein an inert gas is blown into the molten metal from one or more positions on the inner surface (1) ) Or a continuous casting method of molten metal as described in (2) (hereinafter also referred to as “third invention”).

  In the present invention, the “maximum inner diameter in a circular cross section” means the maximum value of the inner diameter of the horizontal section of the refractory structure, and when the inner diameter changes in the axial direction of the structure, the maximum value is means.

  Further, “angle θ1” is also referred to as “side hole inclination angle θ1” in the following description.

  According to the method of the present invention, the swirl flow is formed in the molten metal in the submerged nozzle without adverse effects such as clogging of the submerged nozzle, and the swirl flow imparting submerged nozzle has excellent flow stability of the molten metal in the mold. And effects such as removal of non-metallic inclusions can be obtained, and stable continuous casting operation and slab quality improvement can be achieved. In particular, even in the case of a continuous casting machine that does not have a stopper rod, the formation of harmful vortices that reach the immersion nozzle from the inner surface of the tundish that tends to occur with the swirling flow is suppressed, and slag is mixed into the mold. Can be prevented.

  As described above, the present invention has a double structure of an outer cylinder and an inner cylinder, and the outer cylinder is arranged in a tundish above the immersion nozzle in a cylindrical, conical or frustoconical refractory structure. And a continuous casting method for casting molten metal. Here, when the inner cylinder is arranged so that the lower end of the outer cylinder is in contact with the bottom surface of the tundish, the inner cylinder has a length having a gap of 10 to 300 mm between the lower end of the inner cylinder and the bottom surface of the tundish or the upper surface of the upper nozzle. There is a side hole in the side wall of the outer cylinder, and the side hole of the outer cylinder is located at the intersection of the imaginary line extending radially from the center of the horizontal section of the refractory structure and the inner surface of the outer cylinder. The center of the outlet side opening of the hole is provided, and the center axis of the side hole of the outer cylinder is inclined at an angle θ1 in the horizontal plane with respect to the virtual line in the outlet side opening. This refractory structure is placed in the tundish above the immersion nozzle with its axis vertical, and the molten metal in the tundish is removed from the entrance opening of the side hole opened in the outer surface of the outer cylinder. By making it pass toward the exit side opening part opened to the inner surface of a pipe | tube, a swirling flow is provided to the molten metal supplied in a submerged nozzle from a tundish, and it casts. 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 (c), and FIG. Represents a plan view of FIG. 2C, and FIG. 2C represents a longitudinal sectional view of the continuous casting apparatus.

  As shown in the figure, virtual lines X1 to X5 having a double structure of an outer cylinder 101 and an inner cylinder 102 in the tundish 5 above the immersion nozzle 4 and extending radially from the center O of the horizontal circular cross section. There is one side hole 2 on the side wall of the outer cylinder 101 that has the center of the hole outlet and is opened by inclining the direction Y1 to Y5 of the center axis of the hole by an angle θ1 with respect to the virtual lines X1 to X5. The hollow cylindrical refractory structure 1 provided as described above is arranged with the axis 3 of the refractory structure 1 vertical. When the molten metal 6 in the tundish 5 passes through the side holes 2 and flows into the refractory structure 1, a circumferential velocity component is applied to form a swirling flow. It is supplied to the mold 11 via the immersion nozzle 4.

(1) 1st invention As mentioned above, the 1st invention has the double structure of the outer cylinder 101 and the inner cylinder 102, and the outer cylinder 101 is cylindrical, a cone shape, or a truncated cone-shaped refractory structure 1 Is placed in the tundish 5 above the immersion nozzle 4 and the molten metal 6 is cast. Here, when the inner cylinder 102 is arranged so that the lower end of the outer cylinder 101 is in contact with the bottom surface of the tundish 5, the inner cylinder 102 is placed between the lower end of the inner cylinder 102 and the bottom surface of the tundish 5 or the upper surface of the upper nozzle 8. It is a length having a gap of ˜300 mm, and one or more side holes 2 are provided on the side wall of the outer cylinder 101, and the side holes 2 of the outer cylinder 101 have a circular cross section in the horizontal direction of the refractory structure 1. It has the center of the outlet opening of the side hole 2 of the outer cylinder 101 at the intersection of the virtual lines X1 to XN (where N is the number of virtual lines) radially extending from the center and the inner surface of the outer cylinder 101, In the opening, the central axis of the side hole 2 of the outer cylinder 101 is inclined with respect to the virtual lines X1 to XN by an angle θ1 in the horizontal plane.

  The refractory structure 1 is placed in the tundish 5 above the immersion nozzle 4 with the axis 3 of the refractory structure 1 vertical, and the molten metal 6 in the tundish 5 is placed in the outer cylinder 101. The molten metal supplied from the tundish 5 into the immersion nozzle 4 is swung from the entrance side opening of the side hole 2 opened to the outer surface of the outer tube 101 toward the exit side opening opened to the inner surface of the outer cylinder 101. Cast with flow.

  The present inventor previously described in Patent Document 5 as the third invention, in order to prevent the vortex from the hot water surface in the tundish to the immersion nozzle, in the center of the refractory structure. A casting method to install a refractory stopper rod was proposed. The main object of the present invention is to provide a continuous casting method capable of preventing the generation of the harmful vortex generated with the generation of the swirling flow even when the stopper rod as described above is not used.

  As the swirl flows, the vortex that penetrates the center of the refractory structure 1 and reaches the immersion nozzle 4 from the molten metal surface sucks the slag on the molten metal surface in the tundish 5 and mixes it in the mold 11. , Reduce the slab quality. In the present invention, the refractory structure 1 has a double structure of an outer cylinder 101 and an inner cylinder 102, the outer cylinder 101 plays a role of imparting a swirling flow into the immersion nozzle 4, and the inner cylinder 102 generates swirling flow. It plays a role in preventing the formation of harmful vortices associated with. The swirling flow generated by passing through the side hole 2 on the outer cylinder side wall flows down into the immersion nozzle 4 through the gap between the lower end of the inner cylinder 102 and the bottom surface of the tundish 5 or the upper surface of the upper nozzle 8. At this time, when the inner cylinder 102 is present, a damping effect on the swirling flow is exhibited, and the swirling flow is prevented from reaching the inner hot water surface of the tundish 5 so that generation of harmful vortices can be suppressed. .

  Here, the reason why the distance from the bottom surface of the tundish 5 or the upper surface of the upper nozzle 8 to the lower end of the inner cylinder 102 is in the range of 10 to 300 mm is as follows. That is, if this distance is less than 10 mm, the molten metal passage when the swirling flow of the molten metal 6 flows into the immersion nozzle 4 becomes too narrow, and the possibility that the passage is blocked increases. Further, when the hot water surface height in the tundish 5 becomes lower than the lower end of the inner cylinder, the vortex suppressing action of the inner cylinder 102 is lost, so the distance from the bottom surface of the tundish 5 or the upper surface of the upper nozzle 8 to the lower end of the inner cylinder. When the thickness exceeds 300 mm, it becomes impossible to suppress the formation of harmful vortices caused by the swirling flow under the condition that the molten metal surface height in the tundish 5 is reduced as at the start of casting or immediately before the end of casting. Because.

  The number of the side holes 2 having the inclination angle θ1 provided in the outer cylinder 101 of the refractory structure 1 may be one, but a plurality of side holes 2 may be provided over the entire circumference of the outer cylinder 101 from the viewpoint of preventing occlusion. preferable. Further, a plurality of side holes 2 may be provided on the entire circumference of the outer cylinder 101 and in a plurality of stages in the height direction. The inclination angle θ1 of the plurality of side holes provided may be the same or may be varied within a certain range, but is the inclination angle θ1 that makes the rotation direction of the swirl flow applied to the molten metal the same direction. It is preferable.

(2) 2nd invention 2nd invention is 1st invention. WHEREIN: The largest internal diameter in the horizontal circular cross section of the outer cylinder 101 of the structure 1 made from a refractory 1 is 150 mm-3000 mm, in the horizontal circular cross section of the inner cylinder 102 The maximum inner diameter is 50 mm to 1000 mm, and the maximum inner diameter of the outer cylinder 101 in the horizontal circular section is 1.5 times or more the maximum inner diameter of the inner cylinder 102 in the horizontal circular section. This is a continuous casting method of molten metal having a height of 50 mm to 2000 mm and an inclination angle θ1 of the side hole of 15 ° to 80 °.

  If the maximum inner diameter of the horizontal circular cross section of the outer cylinder 101 of the refractory structure 1 is less than 150 mm, the swirl flow imparting mechanism is too small, so that the cross-sectional area of the molten metal passage is reduced and the side holes 2 are blocked. Problems such as an increase in frictional resistance of the molten metal 6 are likely to occur. Further, if the maximum inner diameter of the circular cross section of the outer cylinder 101 of the refractory structure 1 is larger than 3000 mm, the refractory structure becomes too large, so that the cost of the refractory structure increases. In addition, a dedicated tundish is required, which increases the cost of casting equipment. Therefore, it is preferable that the maximum inner diameter of the horizontal circular cross section of the outer cylinder 101 of the refractory structure 1 is 150 mm to 3000 mm. In addition, the more preferable range of the maximum internal diameter of the horizontal circular cross section of the outer cylinder 101 of the refractory structure 1 is 300 mm to 800 mm.

  When the maximum inner diameter of the horizontal circular cross section of the inner cylinder 102 of the refractory structure 1 is less than 50 mm, oxygen passes through the inner cylinder 102 from the upper part of the tundish 5 and passes through the upper nozzle 8, the sliding gate 9, and the immersion nozzle 4. When there is a problem that the molten metal 6 is solidified from the upper nozzle 8 to the immersion nozzle 4 at the start of casting or when the casting is started, the solidified metal is dissolved from the upper portion of the tundish 5 through the inner cylinder 102 by the oxygen lance. Work becomes difficult. Further, if the maximum inner diameter of the horizontal circular cross section of the inner cylinder 102 of the refractory structure 1 is larger than 1000 mm, the refractory structure becomes too large, and a dedicated tundish is required. Increases equipment costs. Therefore, it is preferable that the maximum inner diameter of the horizontal circular cross section of the inner cylinder 102 of the refractory structure 1 is 50 mm to 1000 mm. A more preferable range of the maximum inner diameter of the circular cross section in the horizontal direction of the inner cylinder 102 of the refractory structure 1 is 100 mm to 300 mm.

  The reason why the maximum inner diameter of the circular cross section of the outer cylinder 101 in the horizontal direction is 1.5 times or more than the maximum inner diameter of the circular section of the inner cylinder 102 is that the maximum inner diameter of the outer cylinder 101 is less than 1.5 times. This is because the dampening effect of the swirling flow by the inner cylinder 102 becomes relatively strong, and it becomes difficult to generate a strong swirling flow in the immersion nozzle 4, which is not preferable.

  If the height of the inner surface of the outer cylinder 101 of the refractory structure 1 is less than 50 mm, the side hole 2 is likely to be blocked because the side hole 2 cannot be sufficiently high. Further, when the upper end portion of the refractory structure 1 has a lid, the passage of the molten metal 6 becomes too narrow, and blockage inside the refractory structure 1 is likely to occur. Since the height of the outer cylinder 101 of the refractory structure 1 is restricted by the depth inside the tundish 5, the height of the inner surface of the refractory structure 1 is usually within 2000 mm. Therefore, the inner surface height of the outer cylinder 101 of the refractory structure 1 is preferably 50 mm to 2000 mm. The upper end portion 7 of the outer cylinder 101 of the refractory structure 1 may be higher or lower than the hot water surface in the tundish 5.

  In the second invention, the length of the inner cylinder 102 is not particularly defined, but if the length of the inner cylinder 102 is too short, the action of suppressing the generation of harmful vortices is insufficient, so that the length is at least 200 mm or more. It is preferable to have. Since the maximum value of the length of the inner cylinder 102 is limited by the depth inside the tundish, the length is preferably about 2000 mm or less. The upper end of the inner cylinder 102 may be higher or lower than the hot water surface in the tundish 5, but the case where the upper end portion is higher than the hot water surface in the tundish 5 is located inside the inner cylinder 102. It is preferable because tundish slag is difficult to enter.

  When the inclination angle θ1 of the side hole 2 provided in the outer cylinder 101 of the refractory structure 1 is less than 15 °, the strength of the swirling flow applied is insufficient. On the other hand, when the inclination angle is larger than 80 °, the thickness of the side wall of the outer cylinder 101 of the refractory structure 1 is reduced, so that the strength as the structure may be reduced. For the above reason, the inclination angle θ1 of the side hole 2 is preferably in the range of 15 ° to 80 °.

(3) Third invention In the first invention or the second invention, the third invention is the first invention or the second invention, wherein at least one of the upper nozzle, the sliding gate and the immersion nozzle disposed in the tundish 5 is formed from one or more locations on the inner surface. This is a continuous casting method of molten metal in which an inert gas is blown into the molten metal.

  The swirling flow of the molten metal 6 formed by passing through the side hole 2 provided in the outer cylinder 101 of the refractory structure 1 follows the law of conservation of angular momentum as the inner diameter of the upper nozzle 8 decreases. Therefore, a larger swirl flow rate is obtained. Here, a large turning flow velocity means, for example, a peripheral speed of 1 m / s or more.

When an inert gas such as Ar gas is blown from the periphery of the swirling flow, that is, from the inner wall surface of the upper nozzle 8, the sliding gate 9 or the immersion nozzle 4 in a state where such a strong swirling flow is generated, the blown inert gas is blown. Is sucked out toward the center by centrifugal force acting on the molten metal 6 to form a bubble film from the periphery to the center to efficiently remove non-metallic inclusions such as Al ₂ O ₃ in the molten steel. Since it captures, the adhesion amount of the nonmetallic inclusion in the immersion nozzle 4 decreases. Nonmetallic inclusions trapped in the bubble film float with the bubbles in the mold and are removed. From the viewpoint of forming the bubble film as described above, the inert gas 10 is preferably blown evenly from the entire circumference of the inner wall surface of the upper nozzle 8, the sliding gate 9 or the immersion nozzle 4.

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

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 the line AA in FIG. Fig. (B) shows a plan view of Fig. (C), and Fig. (C) shows a longitudinal sectional view of the continuous casting apparatus. The embodiment shown in the figure is an embodiment that satisfies the conditions defined in any of the first invention, the second invention, and the third invention.

  The refractory structure 1 includes an outer cylinder 101 and an inner cylinder 102. The outer cylinder 101 has an inner diameter of 400 mm, an outer diameter of 550 mm, and a height of 1200 mm. The inner cylinder 102 has an inner diameter of 90 mm, an outer diameter of 140 mm, and a height of 1200 mm. The lower end of the outer cylinder 101 is in contact with the bottom surface of the tundish, and the gap between the lower end of the inner cylinder 102 and the bottom surface of the tundish or the upper surface of the upper nozzle 8 is 200 mm. The outer cylinder 101 and the inner cylinder 102 are connected at four locations in the circumferential direction at the upper end of the outer cylinder 101, and both the outer cylinder 101 and the inner cylinder 102 are made of an alumina / silica refractory, Side holes 2 having an inclination angle θ1 of 40 °, a height of 200 mm and a width of 110 mm are provided in the outer cylinder side wall at five locations in the circumferential direction and in two steps in the height direction. Side holes are not provided in the inner cylinder side wall.

  Here, as shown in the plan view of FIG. 1A, the inclination angle θ1 in the present invention is the center axis Y1, Y2, Y3 of the side hole 2 on the inner surface of the outer cylinder 101 of the refractory structure 1. It is defined as the angle at which Y4 and Y5 intersect with the virtual lines X1, X2, X3, X4 and X5 extending radially from the center of the refractory structure 1 respectively. In addition, the hot water level in the tundish 5 during steady operation is located 200 mm below the upper end 7 of the outer cylinder 101.

  In FIG. 1, the molten steel 6 that has passed through the side hole 2 is given a turning peripheral speed and turns according to the law of conservation of angular momentum when passing through the upper nozzle 8 and the sliding gate 9 whose inner diameter is reduced as it advances downward. The peripheral speed is increased, and a strong swirling flow is formed in the immersion nozzle 4. The swirling 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 molten steel flow in the mold 11.

  Further, as shown in the figure, Ar gas 10 is blown from the inner peripheral part of the fixed plate on the upper side of the two-layer sliding gate 9, and Ar gas forms an inverted conical bubble film by centrifugal force acting on the molten steel 6. Thus, the non-metallic inclusions in the molten steel 6 flowing down across the bubble film are effectively trapped in the bubbles, and floated together with the bubbles in the mold 11 and removed.

  Clean steel can be obtained by the effect of stabilizing the flow in the mold 11 and the effect of capturing and floating the inclusions. At the same time, when a swirling flow is generated, a stagnation region of the flow is less likely to occur in the vicinity of the inner wall of the immersion nozzle 4, so that a merit that the immersion nozzle 4 is not easily blocked due to adhesion of nonmetallic inclusions is also found.

  In the refractory structure 1 shown in FIG. 1, the upper end 7 of the outer cylinder 101 is made higher than the hot water surface in the tundish 5 to prevent the tundish slag from entering the refractory structure 1. Therefore, even if a vortex is generated inside the refractory structure 1, there is little risk of the slag in the tundish 5 being caught in the mold 11. Moreover, since the refractory structure 1 has the inner cylinder 102, even if the tundish slug enters the outer cylinder 101 or the inner cylinder 102 when the tundish 5 is reused, the inner cylinder 102 is used. Can suppress the generation of harmful vortices and prevent the tundish slag from being brought into the mold 11.

(Example 2)
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 the line AA in FIG. b) represents a longitudinal sectional view of the continuous casting apparatus. The embodiment shown in the figure is also an embodiment that satisfies the conditions defined in any of the first to third inventions.

  The refractory structure 1 includes a hollow frustoconical outer cylinder 101 and an inner cylinder 102. The outer cylinder 101 has an inner diameter of 700 mm at the lower end and 400 mm at the upper end, an outer diameter of 860 mm at the lower end and 560 mm at the upper end 7, an inner surface height of 400 mm and an outer surface height of 480 mm. And made of alumina / magnesia refractories. On the inner wall of the outer cylinder 101, as shown in FIG. 5A, the central axes Y1 to Y8 of the side holes 2 make an inclination angle (θ1) of 60 ° with respect to the imaginary lines X1 to X8, respectively, Side holes 2 having a height of 300 mm and a width of 100 mm are provided at eight locations in the circumferential direction. The lower end of the outer cylinder 101 is in contact with the tundish bottom surface.

  Further, as shown in FIG. 4B, the inner cylinder 102 has an inner cylinder body portion 112 having an inner diameter of 120 mm, an outer diameter of 180 mm, and a height of 400 mm, and gradually expands to 200 mm as the inner diameter goes upward. In the same manner, the outer diameter gradually increases to 260 mm and consists of an inner cylinder upper part 122 having a height of 400 mm. The lower end of the inner cylinder 102 is positioned 80 mm above the tundish bottom surface or the upper surface of the upper nozzle 8, and the upper end portion of the inner cylinder main body portion 112 and the lower end portion of the inner cylinder upper portion 122 are both of the outer cylinder 101. Combined with the top. Moreover, the hot water surface height in the tundish 5 at the time of steady operation exceeds the upper end part of the inner cylinder 102, and becomes a height at which the refractory structure 1 is completely immersed in the molten steel 6.

  As described above, the inner cylinder upper portion 122 has an inner diameter and an outer diameter that are enlarged toward the top. This is because the inclusion removal rod is inserted from above the tundish 5 during the casting operation in which the molten steel 6 is filled in the tundish 5, and the immersion nozzle 4 is inserted into the upper nozzle 8 or the sliding gate 9. In order to remove the inclusions adhering to the surface or to insert the oxygen lance to remove the adhering inclusions or solidified metal, it is necessary to insert the above removal rod or oxygen lance. This is because it has a guiding role.

  Even when the refractory structure 1 shown in FIG. 2 is used, the molten steel 6 that has passed through the side holes 2 has a swirling peripheral speed as in the case where the refractory structure 1 shown in FIG. 1 is used. When passing through the upper nozzle 8 and the sliding gate 9 whose inner diameter is reduced as it goes downward, the swirling peripheral speed is increased according to the law of conservation of angular momentum, and a strong swirling flow is formed in the submerged nozzle 4. The swirl flow formed in the immersion nozzle 4 is uniformly and evenly discharged from the two discharge holes provided in the vicinity of the lower end of the immersion nozzle 4 by the action of centrifugal force, and a stable molten steel flow is generated in the mold 11. Form.

  Further, in the method shown in FIG. 2, Ar gas 10 is blown from the inner peripheral portion of the upper nozzle 8, and Ar gas forms an inverted conical bubble film by centrifugal force acting on the molten steel 6. The non-metallic inclusions in the molten steel 6 flowing down across the bubble film are effectively trapped in the bubbles, and float in the mold 11 together with the bubbles and are removed.

  Clean steel can be obtained by the effect of stabilizing the flow in the mold 11 and the effect of capturing and floating the inclusions. At the same time, when the swirling flow is generated, a stagnation region of the flow is hardly generated in the vicinity of the inner wall of the immersion nozzle 4, so that there is an advantage that the immersion nozzle 4 is not easily blocked due to adhesion of nonmetallic inclusions.

  Also in the method shown in FIG. 2, the presence of the inner cylinder 102 prevents the formation of harmful vortices that are likely to occur due to the swirling flow, so the tundish slag may be brought into the mold 11. Can be reduced.

  According to the method of the present invention, the swirl flow is formed in the molten metal in the submerged nozzle without adverse effects such as clogging of the submerged nozzle, and the swirl flow imparting submerged nozzle has excellent flow stability of the molten metal in the mold. And effects such as removal of non-metallic inclusions can be obtained, and stable continuous casting operation and slab quality improvement can be achieved. In particular, even in the case of a continuous casting machine that does not have a stopper rod, the formation of harmful vortices that reach the immersion nozzle from the inner surface of the tundish that tends to occur with the swirling flow is suppressed, and slag is mixed into the mold. Can be prevented.

  Therefore, the molten metal continuous casting method of the present invention is a technique that can be widely applied in the metal refining and casting fields that require stable operation and high slab cleanliness with high economic efficiency. .

It is a figure which shows typically the continuous casting apparatus for enforcing the method of this invention, The figure (a) represents AA sectional drawing in the figure (c), The figure (b) is the figure ( The top view of c) is represented, The same figure (c) represents the longitudinal cross-sectional view of a continuous casting apparatus. It is a figure which shows typically another continuous casting apparatus for enforcing the method of this invention, the same figure (a) represents the AA sectional drawing in the same figure (b), and the same figure (b) is continuous. The longitudinal cross-sectional view of a casting apparatus is represented.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1: Refractory structure 101: Outer cylinder of refractory structure 102: Inner cylinder of refractory structure 112: Inner cylinder main body 122: Inner cylinder upper part 2: Side hole 3: Shaft of refractory structure, 4: immersion nozzle, 5: tundish, 51: tundish refractory, 52: tundish iron skin, 6: molten metal (molten steel), 7: outer cylinder of refractory structure Upper end, 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 the side hole, θ1: inclination angle of the side hole,

Claims (3)

It has a double structure of outer cylinder and inner cylinder, and the outer cylinder is cylindrical, conical or frustoconical refractory structure, the axis of the refractory structure is vertical, above the immersion nozzle A continuous casting method for casting molten metal, which is placed in a tundish,
The inner cylinder has a length having a gap of 10 to 300 mm between the lower end of the inner cylinder and the bottom surface of the tundish or the upper surface of the upper nozzle when the lower end of the outer cylinder is disposed in contact with the bottom surface of the tundish. Yes,
The side wall of the outer cylinder is provided with one or more side holes, and the side holes of the outer cylinder are imaginary lines extending radially from the center of the horizontal circular section of the refractory structure, and the inner surface of the outer cylinder. The center of the outlet opening of the side hole of the outer cylinder at the intersection of
A refractory structure body provided by inclining the central axis of the side hole of the outer cylinder with respect to the imaginary line by an angle θ1 in the horizontal plane at the exit side opening, and the axis of the refractory structure body being vertical And placed in the tundish above the immersion nozzle,
The molten metal in the tundish is supplied from the tundish into the immersion nozzle by passing it from the entrance opening of the side hole opened on the outer surface of the outer cylinder toward the outlet opening opened on the inner surface of the outer cylinder. A method for continuously casting a molten metal, characterized in that the molten metal is cast by applying a swirling flow.   The maximum inner diameter in the horizontal circular cross section of the outer cylinder of the refractory structure is 150 mm to 3000 mm, the maximum inner diameter in the horizontal circular cross section of the inner cylinder is 50 mm to 1000 mm, and the horizontal circular shape of the outer cylinder. The maximum inner diameter in the cross section is at least 1.5 times the maximum inner diameter in the horizontal circular section of the inner cylinder, the inner surface height of the outer cylinder is 50 mm to 2000 mm, and the angle θ1 is 15 ° to 80 °. The continuous casting method for molten metal according to claim 1. The inert gas is blown into the molten metal from at least one of the inner surfaces in at least one of the upper nozzle, the sliding gate, and the immersion nozzle disposed in the lower portion of the tundish. The molten metal continuous casting method described.

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