TWI770616B - Nozzle structure on liquid steel distributor and continuous casting method - Google Patents

Abstract

The present invention provides a nozzle structure on a molten steel distributor capable of floating inclusions in the molten steel distributor, and a continuous casting method. In the present invention, a part or the whole circumference of the upper end of the upper nozzle (11) of the molten steel distributor is provided with a convex collar (12) larger than the outer shape of the upper end of the upper nozzle of the molten steel distributor; And any one or a plurality of surfaces below the convex collar (12), the outer peripheral surface, the upper surface, and the outer peripheral surface of the upper nozzle (11) of the molten steel distributor that is lower than the convex collar (12). , with one or a plurality of gas discharge holes (13a). By adjusting the length (L) of the upper nozzle structure of the molten steel distributor, substantially all the gas is floated, or the flow rate of the gas to the lower side of the inner hole and the amount of the float are adjusted.

Description

Nozzle structure on molten steel distributor and continuous casting method

The present invention relates to a tundish upper nozzle structure with gas blowing function and a continuous casting method.

In the continuous casting of steel, the operation of blowing gas from a nozzle on a molten steel distributor is mostly performed. The blowing of this gas is mainly aimed at the following. (1) Air bubbles flow downward from the inner hole of the upper nozzle of the molten steel distributor, thereby suppressing the adhesion of inclusions toward the inner hole surface of the upper nozzle of the molten steel distributor or the inner hole surface of the nozzle below it, or by the inclusion of inclusions. Inner pore occlusion due to attachment. (2) The flow pattern of molten steel in the mold is suppressed from below the nozzle on the molten steel distributor. (3) The inclusions are floated under the nozzle of the molten steel distributor or in the mold. (4) The inclusions are floated in the molten steel distributor. These influence the stability and productivity of casting operations, and the quality of casting slabs.

Regarding the above (1) to (4), the gas discharge from the nozzle on the molten steel distributor is performed in various conventional forms. Mainly regarding the above (1) to (3), for example, in Patent Document 1, there is proposed a structure in which a porous part for gas discharge is provided in the inner hole of the nozzle of the molten steel distributor, and a porous part is provided in the inner hole of the nozzle of the molten steel distributor. The annular collar portion of the annular refractory on the outer periphery of the upper end of the upper nozzle of the liquid distributor is to cover the upper part of the upper nozzle of the molten steel distributor. Thereby, the gas supply to the inner hole of the upper nozzle of the molten steel distributor can be set reliably.

Also in Patent Document 2, the purpose is to prevent inclusions or parent metal from adhering to the vicinity of the contact portion between the stopper and the upper nozzle, and to perform stable flow control to obtain a good cast slab. , and proposes a nozzle for receiving the stopper rod at the bottom of the molten steel distributor, which is characterized in that: with the contact portion with the stopper rod as the boundary, porous refractories are arranged on the respective upper and lower molten steel contact surfaces thereof, and can be removed from the respective The porous refractory is independently blown with argon gas.

Furthermore, focusing on the above-mentioned (4), Patent Document 3 proposes a continuous casting method in which a non-porous refractory is injected from an annular upper porous refractory provided on the upper part of a nozzle provided at the bottom of a molten steel distributor. Active gas, and inert gas is blown from the annular lower porous refractory provided in the lower part of the nozzle. Thereby, the upper porous refractory can be configured to blow inert gas toward the molten steel of the molten steel distributor, and the lower porous refractory can blow inert gas toward the opening of the nozzle. [Prior Art Literature] [Patent Literature]

Patent Document 1: Japanese Patent Laid-Open No. 2003-220450 Patent Document 2: Japanese Patent Application Laid-Open No. 6-297118 Patent Document 3: Japanese Patent Laid-Open No. 2016-182612

[The problem to be solved by the invention]

In order to improve the quality of the cast slab, it is also important to float the inclusions in the molten steel distributor of (4). The balance (balance) of (1) to (3) and (4) above is a property appropriately determined by individual operating conditions (including know-how), steel type, and target quality. However, in the blowing methods and the like by the prior art such as the aforementioned patent documents, it has been found that most of the gas blown flows to the inner hole side of the upper nozzle of the molten steel distributor, and it is impossible to make the gas above , that is, floating in the molten steel in the molten steel distributor.

Furthermore, in the above-mentioned (4), that is, in order to float the inclusions in the molten steel distributor, there is also the following method: in any position of the bottom of the molten steel distributor other than the nozzle on the molten steel distributor, the gas is Blow into the molten steel distributor. However, in order to blow gas into the molten steel distributor at any position on the bottom of the molten steel distributor other than the nozzle on the molten steel distributor, special equipment for its use, initial cost and operation are required. The cost (running cost) will increase, and the risk of breakout during operation will also increase. From such a viewpoint, in order to remove the inclusions by the gas in the molten steel distributor, it is preferable to use the upper nozzle of the molten steel distributor to form a floating flow of the molten steel gas into the molten steel distributor, and to adjust the Proportion.

The problem to be solved by the present invention is to provide a molten steel distributor upper nozzle structure and a continuous casting method in which gas is blown from the molten steel distributor upper nozzle, and the nozzle can be blown from a specific location of the nozzle. All the blown gas floats in the molten steel distributor (from the top of the nozzle on the molten steel distributor), or the flow rate of the gas toward the inner hole side or the bottom of the nozzle on the molten steel distributor, and the direction can be adjusted arbitrarily. The balance of the floating gas flow in the molten steel distributor (from the top of the nozzle on the molten steel distributor). Furthermore, the discharge position of the nozzle on a molten steel distributor, the shape of the discharge holes such as the porous body or the through hole, the number of discharge holes, etc., are various; The whole of the gas blown into the place” means one gas outflow part, in other words, it means “the whole of the gas expelled from one through-hole, or if it is considered that even a plurality of spit holes including a porous body, etc., remain the same. A plurality of bubbles immediately after being spit out are combined into one bubble, for example, each of the collection parts of the extremely small discharge holes that form one bubble, and all the gas that is expelled from there”, not from a molten steel distributor. All the gas ejected from the nozzle is targeted. [Means of Solving Problems]

The inventors of the present invention have obtained the following knowledge and insight: as in the aforementioned patent documents, most of the gas blown from the vicinity of the upper end of the upper nozzle of the molten steel distributor flows to the inner hole side of the upper nozzle of the molten steel distributor, and it is impossible to make the gas The reason why the molten steel floats above, that is, the molten steel in the molten steel distributor, is because the molten steel flow to the inner hole of the nozzle near the gas discharge hole near the upper end of the upper nozzle of the molten steel distributor will become the main body, and the molten steel flow is stronger than the floating flow of bubbles.

That is, the gist of the present invention is to provide a flow velocity of molten steel in which the gas is discharged to the inner hole of the nozzle to be higher than the flow velocity of the floating bubbles in order to make the floating flow of the bubbles stronger than the flow of molten steel to the inner hole of the nozzle. A nozzle structure on a molten steel distributor capable of adjusting the balance between the flow rate of gas to the inner hole of the nozzle and the flow rate of floating gas, and a continuous casting method using the nozzle structure on the molten steel distributor.

其中，M：鑄造速度(t／min)。 6. 如前述1至4中任一項所述之鋼液分配器上噴嘴結構體，其中，該鋼液分配器上噴嘴結構體，是藉由止塞桿進行熔融鋼之流量控制以供鋼的連續鑄造用； 從前述鋼液分配器上噴嘴的下端之內孔面的鉛直位置直至前述凸鍔狀物的上面之氣體吐出孔或外周面為止的長度L(mm)，是滿足下述之數式2：

其中，M：鑄造速度(t／min)。 7. 如前述1至5中任一項所述之鋼液分配器上噴嘴結構體，其中，從前述鋼液分配器上噴嘴的下端之內孔面的鉛直位置直至前述凸鍔狀物的上面之氣體吐出孔或外周面為止的長度L(mm)，為60mm以上。 8. 如前述1至7中任一項所述之鋼液分配器上噴嘴結構體，其中，前述凸鍔狀物，係接合於前述鋼液分配器上噴嘴。 9. 如前述8所述之鋼液分配器上噴嘴結構體，其中，前述凸鍔狀物與前述鋼液分配器上噴嘴，是藉由螺絲或是卡口結構(bayonet structure)、或接著材料所接合。 10. 如前述1至7中任一項所述之鋼液分配器上噴嘴結構體，其中，前述凸鍔狀物，係嵌合於前述鋼液分配器上噴嘴的外周，且接合於與該鋼液分配器上噴嘴鄰接的風口或鋼液分配器底部耐火物層。 11. 如前述10所述之鋼液分配器上噴嘴結構體，其中，前述凸鍔狀物與前述風口或前述鋼液分配器底部耐火物層，是藉由螺絲或是卡口結構、或接著材料所接合。 12. 一種連續鑄造方法，係使用前述1至4中任一項所述之鋼液分配器上噴嘴結構體的連續鑄造方法，其特徵在於： 前述鋼液分配器上噴嘴結構體，是藉由止塞桿進行熔融鋼之流量控制以供鋼的連續鑄造用； 將從前述鋼液分配器上噴嘴的下端之內孔面的鉛直位置直至前述凸鍔狀物的上面之氣體吐出孔或外周面為止的長度L(mm)，設成滿足下述之數式3的邊界長度LB(mm)以上來使氣體大致全部浮起、或設成未滿前述邊界長度LB(mm)來調整氣體往內孔側下方的流量與浮起的量；

其中，M：鑄造速度(t／min)。 [發明效果]Specifically, the present invention relates to a continuous casting method for the nozzle structure and 12 of the molten steel distributor of the following 1 to 11. 1. A nozzle structure on a liquid steel distributor, characterized in that: a part or the whole circumference of the outer periphery of the upper end of the nozzle on the liquid steel distributor has a larger convex shape than the shape of the upper end of the nozzle on the liquid steel distributor. A collar; any one or a plurality of surfaces below the convex collar, the outer peripheral surface, the upper surface, and the outer peripheral surface of the nozzle of the molten steel distributor below the convex collar, with a Or a plurality of gas discharge holes. 2. The upper nozzle structure of the molten steel distributor as described in the above 1, wherein the gas discharge hole of the convex collar is the end of the gas flow path of the space in the convex collar or from the convex collar. The bottom of the collar penetrates the hole above. 3. The upper nozzle structure of the molten steel distributor according to the above 1 or 2, wherein one or a plurality of grooves through which the gas can pass are provided under the convex collar. 4. The upper nozzle structure of the molten steel distributor according to the above 1 or 2, wherein in the state that the upper nozzle structure of the molten steel distributor has been mounted on the molten steel distributor, in the above-mentioned convex flange. Part or all of the lower part has a space through which gas can pass. 5. The upper nozzle structure of the molten steel distributor according to any one of the aforementioned 1 to 4, wherein the upper nozzle structure of the molten steel distributor is to control the flow of molten steel by means of a stopper rod to supply steel. For continuous casting; the length L (mm) from the vertical position of the inner hole surface of the lower end of the nozzle of the molten steel distributor to the gas discharge hole or the outer peripheral surface of the upper surface of the convex collar is the following: Formula 1:

Among them, M: casting speed (t/min). 6. The upper nozzle structure of the molten steel distributor according to any one of the aforementioned 1 to 4, wherein the upper nozzle structure of the molten steel distributor is to control the flow rate of molten steel by means of a stopper rod to supply steel. For continuous casting; the length L (mm) from the vertical position of the inner hole surface of the lower end of the nozzle of the molten steel distributor to the gas discharge hole or the outer peripheral surface of the upper surface of the convex collar is the following: Formula 2:

Among them, M: casting speed (t/min). 7. The upper nozzle structure of the molten steel distributor according to any one of the above 1 to 5, wherein from the vertical position of the inner hole surface of the lower end of the upper nozzle of the molten steel distributor to the upper surface of the above-mentioned convex collar The length L (mm) to the gas discharge hole or the outer peripheral surface is 60 mm or more. 8. The upper nozzle structure of the molten steel distributor according to any one of 1 to 7 above, wherein the protruding collar is connected to the upper nozzle of the molten steel distributor. 9. The upper nozzle structure of the molten steel distributor according to the above 8, wherein, the protruding collar and the upper nozzle of the molten steel distributor are made of screws, bayonet structures, or adhesive materials. joined. 10. The upper nozzle structure of the molten steel distributor according to any one of the above 1 to 7, wherein the convex flange is fitted to the outer circumference of the upper nozzle of the molten steel distributor, and is joined to the upper nozzle of the molten steel distributor. The tuyere adjacent to the nozzle on the molten steel distributor or the refractory layer at the bottom of the molten steel distributor. 11. The upper nozzle structure of the molten steel distributor according to the aforementioned 10, wherein, the protruding flange and the tuyere or the refractory layer at the bottom of the molten steel distributor are made of screws or a bayonet structure, or a material joined. 12. A continuous casting method using the continuous casting method of the nozzle structure on the molten steel distributor described in any one of the aforementioned 1 to 4, characterized in that: the nozzle structure on the aforementioned molten steel distributor is made by The stopper rod is used to control the flow of molten steel for continuous casting of steel; from the vertical position of the inner hole surface of the lower end of the nozzle of the molten steel distributor to the gas discharge hole or the outer peripheral surface of the upper surface of the convex collar The length L (mm) up to this point is set to be equal to or greater than the boundary length LB (mm) satisfying the following equation 3 to float almost all the gas, or set to less than the above-mentioned boundary length LB (mm) to adjust the gas inward The flow below the hole side and the amount of float;

Among them, M: casting speed (t/min). [Inventive effect]

According to the present invention, the gas can be guided to the molten steel by arranging a portion or the entire circumference of the upper end portion of the nozzle on the molten steel distributor with a protrusion larger than the outer shape of the nozzle on the molten steel distributor. The outer peripheral side of the nozzle on the distributor, that is, the area where the flow rate of molten steel to the inner hole is small, and from its vicinity, the gas is diverted upward. Thereby, the gas can be floated in the molten steel distributor, and the effect of floating inclusions in the molten steel distributor can be obtained. Even casting slab quality can be improved. In addition, by arbitrarily adjusting the vertical position of the convex collar larger than the outer shape of the nozzle on the molten steel distributor from the lower end of the inner hole until the gas discharge hole or after flowing along the convex collar, it can reach the upward release. The length of the part to the gas discharge part (the above-mentioned L) can arbitrarily adjust the flow rate of the gas to the lower side of the nozzle inner hole and the floating flow rate to the molten steel distributor according to individual operations.

Fig. 1 shows a main part of a nozzle structure on a molten steel distributor according to an embodiment of the present invention. The upper nozzle structure 10 of the molten steel distributor of the present embodiment is used for continuous casting of steel by controlling the flow rate of molten steel by means of the stopper rod 20; , which is provided with a convex collar 12 larger than the outer shape (outer diameter) of the nozzle 11 on the molten steel distributor. Further, the upper nozzle structure 10 of the molten steel distributor of the present embodiment is attached to the outer peripheral surface of the upper nozzle 11 of the molten steel distributor below the convex collar 12, and includes a plurality of (arranged at equal intervals in the circumferential direction) Six) gas discharge holes 13a. Furthermore, the molten steel distributor upper nozzle structure 10 of the present embodiment is attached to the upper end surface of the molten steel distributor upper nozzle 11, and also includes a plurality of (24 in the circumferential direction arranged at equal intervals) gas discharge holes 13b. . Furthermore, as shown in FIG. 1 , in the molten steel distributor upper nozzle structure 10, in the state where it has been installed in the molten steel distributor 30, a part or all of the lower surface of the convex collar 12 is provided with gas. The space S that can pass through (during casting, since the molten steel distributor is filled with molten steel, molten steel exists in this space).

As described above, by providing the convex flange 12 in the molten steel distributor upper nozzle structure 10 of the present embodiment, the gas can be guided to the outer peripheral side of the molten steel distributor upper nozzle 11, that is, to the inner hole The area of 11a where the flow rate of molten steel (direction of arrow A) is small (direction of arrow B), and the gas is diverted upward from its vicinity. Thereby, the gas can be floated in the molten steel distributor 30, and the effect of floating inclusions in the molten steel distributor 30 can be obtained. Even casting slab quality can be improved.

Furthermore, the inventors of the present invention have obtained the following knowledge in the upper nozzle structure 10 of the molten steel distributor as described above: The ratio largely depends on the length L (mm) and the casting speed M (t/min) shown in FIG. 1 . Here, the so-called length L shown in FIG. 1 refers to the length from the vertical position of the inner hole surface 11b of the lower end of the nozzle 11 of the molten steel distributor to the gas discharge hole or the outer peripheral surface of the upper surface of the convex collar 12; The casting speed M (t/min) is synonymous with the throughput of molten steel.

In addition, the length L is calculated from the vertical position of the inner hole surface 11b of the lower end of the upper nozzle 11 of the molten steel distributor, because although the outer periphery or the vicinity of the upper end of the upper nozzle of the molten steel distributor can be set to each There are various shapes, but the position of the inner hole surface at the lower end (approximately the same as the inner hole diameter) is mostly unchanged as long as the casting speed is the same, that is, there is no difference in the speed of the molten steel flowing into the inner hole. It is caused by a large difference; moreover, even in the case of the stopper rod control, the position of the fitting portion is still the same radial position according to the diameter of the inner hole.

That is, the inventors of the present invention have found the following knowledge: when the length L (mm) satisfies the following equation 1, almost all of the gas can be floated in the molten steel distributor ; In the case of satisfying the following equation 2, the flow rate of the gas to the lower side of the inner hole and the amount of floating can be adjusted.

As described above, in the present invention, the control of the inner hole side or the floating ratio of the gas is performed according to the gas discharged from the respective discharge holes each time. Therefore, in the case where there are gas discharge holes on the upper surface of the convex collar that serves as a reference for determining the length L (mm), whether there are one or a plurality of gas discharge holes means the above-mentioned gas discharge holes related to each of the discharge holes. length; or, in the case of flowing gas from any one of the underside of the aforesaid protruding flanges or from the outer peripheral surface and releasing the gas upwards on the outer peripheral surface of the protruding flanges, it means up to the protruding flanges. The length of a thing up to its outer circumference. Even if these coexist, the ratio of inner hole side/floating obtained by the above-mentioned formula can be determined by the length L (mm) of each discharge gas. Whether to coexist or how to determine the number is related to the control of the gas discharge amount and form as the entire nozzle on the molten steel distributor, and this point can be set according to individual operating conditions (optional).

Furthermore, when the right sides of the equations 1 and 2 are graphed as shown in Fig. 2, when the length L is located in the region above the approximate line, almost all of the gas can be contained in the molten steel distributor. Floating: When it is located in the area less than the approximate line, the flow rate of the gas to the lower side of the inner hole and the amount of floating can be adjusted.

Next, the technical basis (derivation basis) and the like of the aforementioned Expressions 1 and 2 will be described.

First, a flow analysis software (FLUENT (computational fluid dynamics software)) was used, and a simulation was performed under the following conditions. • Set the inner diameter of the nozzle on the molten steel distributor to 80mmφ; • As the stopper rod control, the space is set to about 12mm relative to the diameter of the fitting part when it is fully closed: 100mmφ; • The gas discharge hole is a 0.3mmφ through hole, → 13b (24 holes), 13a (6 holes); •Set the bubble diameter to 3.5mmφ; • The casting speed is set from 0t/min to 5t/min. Furthermore, a water model experiment was performed under the following conditions. • Set the inner diameter of the nozzle on the molten steel distributor to 80mmφ; • As the stopper rod control, the space is set to about 15mm relative to the diameter of the fitting part when fully closed, 100mmφ; • The gas discharge hole is a through hole with a diameter of 0.3mmφ (the diameter of the bubble is about 1.5mmφ to 3.5mmφ); • The casting speed is set to 3t/min.

Furthermore, the inventors of the present invention have found the following knowledge based on the results of previous experiments and actual work. In the water model, when the diameter of the gas discharge hole is 0.3 mmφ, the bubble diameter is about 1.5 mm. mmφ to 3.5 mmφ, and 2 to 3 times larger in molten steel; and through holes of 0.3 mmφ of the gas discharge holes and alumina-graphite porous bodies (so-called porous refractories, average pores The diameter of the bubbles with a diameter of ≒ 100 μm to 120 μm) is mostly the same size.

The above-mentioned length L (mm) as a boundary value at which almost all of the (13a) gas blown in from the outer periphery can be floated is obtained by changing the casting speed by simulation (each locus diagram in Fig. 2 ( plot)), and the result is represented by an approximate line and an approximate expression obtained by regression analysis, and the following Equation 3 is obtained.

In the comparison between these simulations and water model experiments, the aforementioned length L (mm) is approximately the same.

In other words, the above-mentioned length L (mm) may be set to be equal to or larger than the boundary length LB (mm) satisfying the above-mentioned Equation 3, so that almost all of the gas can be floated, or less than The boundary length LB (mm) is used to adjust the flow rate of the gas to the lower side of the inner hole and the amount of floating.

In addition, in this FIG. 2, the vertical axis L (mm) is the length from the vertical position of the lower end of the nozzle inner hole of the molten steel distributor, so it is the convex flange including the nozzle structure of the molten steel distributor. The length including the wall thickness where the object is placed. Therefore, the case where the above-mentioned wall thickness (mm)<LB (mm) of the convex collar falls within the scope of the present invention. In addition, in general (most of) casting, when the casting speed per nozzle of the molten steel distributor is about 3 (t/min) or more, the amount of gas floating is often reduced. , when considering such an actual situation, as long as the length L (mm) is approximately 60 mm or more, approximately all the gas will float upward. That is, in general (mostly) casting, in order to float all the gas (13a) blown from the outer periphery upward, L≧60mm is required, and when L<60mm, L becomes smaller. , the flow rate of the gas to the lower side of the inner hole becomes larger (refer to FIG. 3 ).

Hereinafter, a modification of the present embodiment ( FIG. 1 ) will be illustrated. (A) In the present embodiment, although the convex collar 12 is provided on the entire circumference of the upper end portion of the upper nozzle 11 of the molten steel distributor, it may be provided on the outer circumference of the upper end portion of the upper nozzle 11 of the molten steel distributor. one part. Even if the position of the protruding collar 12 is assumed to be a part of the outer circumference of the upper end of the upper nozzle 11 of the molten steel distributor, a lot of effects of making the gas float in the molten steel distributor (in the molten steel distributor) can still be obtained. The effect of floating inclusions). In addition, the shape of the convex collar 12 in plan view is not limited to a circle, and may be, for example, an ellipse or a polygon.

(B) In the present embodiment, although the gas discharge holes 13a are provided on the outer peripheral surface of the upper nozzle 11 of the molten steel distributor which is located below the convex flange 12 (six holes are provided at equal intervals in the circumferential direction) However, one or more of the gas discharge holes 13a may be provided on any one of the lower surface, the outer peripheral surface, and the upper surface of the convex collar 12, or on a plurality of surfaces. When the gas discharge hole 13a is provided in the flange 12 in this way, the gas discharge hole 13a of the flange 12 can be provided as the end of the gas flow path of the space in the flange 12. It is a hole penetrating from the lower surface of the convex collar 12 to the upper surface.

(C) In this embodiment, although the space S through which the gas can pass is provided on the lower surface of the convex collar 12 , one or a plurality of grooves through which the gas can pass may be provided on the lower surface of the convex collar 12 . In addition, the groove includes a form in which the lower surface of the convex collar 12 is curved in the circumferential direction, a part of the circumferential direction is formed into a concave shape, and the concave portion is extended in the radial direction. That is, the above-mentioned grooves only need to have a structure as a gas flow path in which the gas can concentrate and move toward the outer peripheral side. Furthermore, the position of the space S may be replaced with a space, and a porous refractory with high gas permeability may be installed.

(D) In this embodiment, although the protruding collar 12 is connected to the upper nozzle 11 of the molten steel distributor by an adhesive material, it can also be connected to the upper nozzle of the molten steel distributor by a screw or a bayonet structure 11 Engage. In addition, the protruding collar 12 may be fitted on the outer periphery of the upper nozzle 11 of the molten steel distributor, and may be joined to the tuyere 31 adjacent to the upper nozzle 11 of the molten steel distributor or the refractory layer 32 at the bottom of the molten steel distributor. The joining can be performed by means of screws or bayonet structures, or adhesive materials.

(E) Although the upper nozzle structure 10 of the molten steel distributor of the present embodiment is used to control the flow rate of molten steel by the stopper rod 20 for continuous casting of steel, it can also be used as a sliding nozzle device (sliding Nozzle device) for flow control of molten steel for continuous casting of steel. That is, it can also be applied to a structure in which there is no so-called obstacle above the nozzle of the molten steel distributor that changes the flow of molten steel. [Example]

Under the following casting conditions and the conditions of the nozzle on the molten steel distributor, a conventional product (comparative example) without the convex collar 12 was used, and the convex collar 12 was provided so that the aforementioned length L (mm) was between 30 mm and 30 mm. The product of the present invention (Example) varied within a range of 60 mm, to carry out a continuous casting test of steel in which the flow rate of molten steel is controlled by a stopper rod, and to evaluate the thickness of alumina adhesion in the nozzle of the molten steel distributor, The number of occurrences of surface defects related to the coil as a product. Specifically, the thickness of the alumina adhesion in the nozzle of the molten steel distributor in the conventional product was set to 1.0, and the thickness of the aluminum oxide adhesion in the nozzle of the molten steel distributor in the product of the present invention was indexed. The smaller the aluminum oxide adhesion thickness index in the nozzle, the smaller the aluminum oxide adhesion thickness in the nozzle on the molten steel distributor. In addition, the number of occurrences of surface flaws in the coil in the conventional product was set to 1.0, and the number of occurrences of surface flaws in the coil in the product of the present invention was indexed. The smaller the coil surface defect occurrence index, the smaller the number of coil surface defects, that is, the better the quality of the cast slab.

<Casting conditions> • Steel grade: general aluminum deoxidized steel (aluminium killed steel) •Casting size: 250mm(thickness)×1250mm(width) • Casting speed (production capacity of molten steel): about 3 (t/min) <Conditions for nozzles on the molten steel distributor> • Bore diameter: 80mm • Diameter x number of gas discharge holes: 0.3 (mm) x 13b (24 holes), 13a (6 holes) Gas (argon) discharge volume: 10 (L/min) Gas (argon) discharge flow rate: 1.56 (m/min)

Table 1 shows the results of the continuous casting test. In addition, in this continuous casting test, since the casting speed (production capacity of molten steel) was about 3 (t/min), the boundary length LB in the above-mentioned formula 3 was about 60 mm.

The floating amount (ratio) of air bubbles is an index with the total amount set to 100, and is obtained from the estimated value (example) from visual observation and water model experiments, etc., 100 means almost all floating, 0 It means that all flows into the inner hole side.

As shown in Table 1, the product of the present invention (Example 3) whose L (mm) is the boundary length LB (about 60 mm) or more is higher than the conventional product (Comparative Example 1), and the alumina in the nozzle of the molten steel distributor The adhesion thickness is reduced, and the number of occurrences of surface flaws on the coil is also reduced. In addition, regarding the product of the present invention (Examples 1 and 2) whose L (mm) is less than the boundary length LB (about 60 mm), it is shown that the amount of bubble floating/inner hole side can be adjusted by adjusting L (mm). and it can also adjust the quality of the cast slab.

10: Nozzle structure on the molten steel distributor 11: Nozzle on the molten steel distributor 11a: Inner hole 11b: Bore surface 12: Convex collar 13a, 13b: Gas discharge holes 20: stop rod 30: Liquid steel distributor 31: Air outlet 32: Refractory layer at the bottom of the molten steel distributor L: length S: space

1 is a schematic cross-sectional view showing a main part of a nozzle structure on a molten steel distributor according to an embodiment of the present invention. [ Fig. 2 ] It is a graph in which the right-hand sides of the above-mentioned Expressions 1 and 2 are plotted. [ Fig. 3] Fig. 3 is a diagram showing the results of analysis of gas behavior in the nozzle structure of the molten steel distributor of Fig. 1 .

10: Nozzle structure on the molten steel distributor

11: Nozzle on the molten steel distributor

11a: Inner hole

11b: Bore surface

12: Convex collar

13a, 13b: Gas discharge holes

20: stop rod

30: Liquid steel distributor

31: Air outlet

32: Refractory layer at the bottom of the molten steel distributor

L: length

S: space

Claims (12)

An upper nozzle structure of a molten steel distributor is characterized in that: a part or the whole circumference of the upper end of the upper nozzle of the molten steel distributor has a convex flange shape larger than that of the upper end of the upper nozzle of the molten steel distributor. Object; any one or a plurality of surfaces on the lower surface, the outer peripheral surface, the upper surface, and the outer peripheral surface of the upper nozzle of the molten steel distributor that is lower than the aforementioned convex collar-shaped object, with one or more When there are one or more gas discharge holes on the upper surface of the convex collar, from the vertical position of the inner hole surface of the lower end of the upper nozzle of the molten steel distributor to the upper surface of the convex collar The length L (mm) to the gas discharge hole is 60 mm or more. The upper nozzle structure of the molten steel distributor according to claim 1, wherein the gas discharge hole of the protruding flange is an end portion of the gas flow path of the space in the protruding flange or the gas discharge hole from the protruding flange The bottom of the shape penetrates the hole above. The upper nozzle structure of the molten steel distributor according to claim 1 or 2, wherein one or a plurality of grooves through which gas can pass are provided under the protruding collar. The upper nozzle structure of the molten steel distributor according to claim 1 or 2, wherein in a state where the upper nozzle structure of the molten steel distributor is attached to the molten steel distributor, the lower surface of the above-mentioned convex collar is Part or all of them have spaces through which gas can pass. The upper nozzle structure of the molten steel distributor according to claim 1 or 2, wherein the upper nozzle structure of the molten steel distributor is used for continuous casting of steel by controlling the flow of molten steel by means of a stopper rod; The length L (mm) from the vertical position of the inner hole surface of the lower end of the upper nozzle of the molten steel distributor to the outer peripheral surface of the convex collar satisfies the following equation 1: L≧-1.875M ² + 26.332M-0.3929‧‧‧Formula 1 , where M: casting speed (t/min). The upper nozzle structure of the molten steel distributor according to claim 1 or 2, wherein the upper nozzle structure of the molten steel distributor is used for continuous casting of steel by controlling the flow of molten steel by means of a stopper rod; The length L (mm) from the vertical position of the inner hole surface of the lower end of the upper nozzle of the molten steel distributor to the outer peripheral surface of the convex collar satisfies the following equation 2: L<-1.875M ² + 26.332M-0.3929‧‧‧Formula 2 , where M: casting speed (t/min). The molten steel distributor upper nozzle structure according to claim 1 or 2, wherein the length L from the vertical position of the inner hole surface of the lower end of the molten steel distributor upper nozzle to the outer peripheral surface of the convex collar (mm), is 60mm or more. The upper nozzle structure of the molten steel distributor according to claim 1 or 2, wherein the protruding collar is connected to the upper nozzle of the molten steel distributor. The upper nozzle structure of the molten steel distributor according to claim 8, wherein the protruding collar and the upper nozzle of the molten steel distributor are joined by screws, bayonet structures, or adhesive materials. The molten steel distributor upper nozzle structure according to claim 1 or 2, wherein the protruding collar is fitted to the outer periphery of the molten steel distributor upper nozzle, and is joined to the molten steel distributor. The tuyere adjacent to the nozzle or the refractory layer at the bottom of the molten steel distributor. The upper nozzle structure of the molten steel distributor according to claim 10, wherein the protruding collar and the tuyere or the refractory layer at the bottom of the molten steel distributor are made of screws, bayonet structures, or adhesive materials. to join. A continuous casting method, which is a continuous casting method using the nozzle structure on a molten steel distributor according to any one of claims 1 to 4, wherein the nozzle structure on the molten steel distributor is made of a stopper rod. Control the flow of molten steel for continuous casting of steel; set the length L (mm) from the vertical position of the inner hole surface of the lower end of the upper nozzle of the molten steel distributor to the outer peripheral surface of the convex collar. The gas is almost completely floated so as to satisfy the boundary length LB (mm) or more of the following equation 3, or the flow rate of the gas to the lower side of the inner hole and the floating volume are adjusted to be less than the boundary length LB (mm). amount; LB=-1.875M ² +26.332M-0.3929‧‧‧Formula 3 , where M: casting speed (t/min).

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