JP5076693B2 - Continuous casting tundish and steel continuous casting method - Google Patents

Description

  The present invention relates to a tundish for continuous casting and a continuous casting method of steel using the tundish.

  In continuous casting of steel, the molten steel in the ladle is once poured into the tundish, and with a predetermined amount of molten steel staying in the tundish, the molten steel in the tundish is placed on the bottom of the tundish, such as an immersion nozzle. Each mold is injected through a tundish nozzle. At that time, a solidified shell with a predetermined thickness is obtained by ensuring the cooling time in the mold, and the molten steel surface position in the mold is cast at a substantially constant position on the upper part of the mold in order to improve the slab surface properties. ing.

  Here, as a method of controlling the molten steel surface position in the mold, the following two methods are performed. One method is a method in which the drawing speed of the slab is set to a constant value, and the amount of molten steel injected from the tundish into the mold is controlled to a flow rate that matches the drawing speed of the slab, and the other method is a method in the tundish. Is injected into the mold at an injection amount determined by the molten steel depth and the size of the tundish nozzle, and the slab drawing speed is adjusted according to the molten steel injection amount from the tundish to the mold. When the slab cross-sectional area of a slab continuous casting machine or the like is large and the amount of molten steel injected from the tundish into the mold is large, the former method is generally performed.

  Various methods such as a method using electromagnetic force have been proposed as a method for controlling the amount of molten steel injected from the tundish into the mold. Generally, any one of the following three methods has been proposed. Has been done.

The first method is to control the amount of molten steel injected by moving the stopper that opens and closes the outlet of the tundish nozzle up and down and adjusting the area of the gap between the tundish nozzle and the tip of the stopper (“stopper method” (Refer to Patent Document 1, for example). The second method is formed by combining two or three refractory plates having nozzle holes for passing molten steel, and sliding the refractory plates to overlap the nozzle holes of the respective refractory plates. This is a method of controlling the amount of molten steel injected by adjusting the area of the opening (referred to as “sliding nozzle method”) (for example, see Patent Document 2). The third method is a combination of a stopper method and a sliding nozzle method. For example, when the amount of molten steel injected from the tundish into the mold is low, the stopper method is used, and when the flow rate is high, the sliding nozzle method is used. It is a method of controlling properly according to casting conditions, such as controlling (see, for example, Patent Document 3). This is to prevent the nozzle hole from being clogged by solid metal solidification in the sliding nozzle method when the molten steel injection amount from the tundish to the mold is low as at the start of casting.
JP 2004-249338 A Japanese Patent Laid-Open No. 10-328801 Japanese Patent Laid-Open No. 7-88607

  However, in controlling the amount of molten steel injected from the tundish into the mold, the above prior art has the following problems.

  In the stopper method, the amount of flow fluctuation is basically large with respect to the stopper opening. For example, even if the stopper opening is slightly changed, the change in the molten steel injection amount is large. Since the area of the gap between the dish nozzle and the stopper tip fluctuates, the control accuracy of the molten steel surface position in the mold is not good. Also, the alumina in the molten steel adheres to the tip of the stopper and the flow control becomes unstable, or the adhered alumina peels off and is captured by the slab, resulting in inclusion defects in the steel product. Also occurs.

  In contrast, in the sliding nozzle method, the area of the opening formed by overlapping the nozzle holes of the respective refractory plates can be adjusted with high accuracy, so the flow rate controllability is superior to the stopper method. The sliding nozzle method is adopted in many continuous casting machines. However, when there is less molten steel in the tundish at the end of casting, a vortex is generated in the molten steel in the tundish just above the sliding nozzle, and the slag existing on the molten steel is caught in the vortex. There is a problem that the quality of the slab is deteriorated by flowing out into the slab and trapping the soot in the slab. When the amount of residual molten steel in the tundish is increased in order to avoid the generation of vortices, another problem that the slab yield is reduced occurs.

  The stopper method and sliding nozzle method are used together, and the casting method is controlled by the stopper method when the flow rate is low at the start and end of casting, and by the sliding nozzle method when the flow rate is high during steady casting. By using properly, it is excellent in flow rate controllability in all flow ranges, can prevent nozzle clogging with bare metal, and also prevents vortex generation of molten steel immediately above the sliding nozzle because the stopper becomes an obstacle. Can do. However, since the stopper method and the sliding nozzle method are used in combination, two series of hot water level control devices are required in parallel, and there is a problem that the equipment cost increases. Moreover, since the stopper and the sliding nozzle are both important flow rate control devices, those that have melted and changed their shape cannot be reused and must be replaced each time, resulting in an increase in refractory costs. There's a problem. In addition, during the casting, when changing the molten metal level control method, such as shifting from the molten metal level level control of the stopper method to the molten metal level control of the sliding nozzle method, if both of them cannot be delivered smoothly, There is also a risk that the inner molten steel surface fluctuates temporarily and the slab quality is deteriorated.

  The present invention has been made in view of the above circumstances, and its object is to provide a stopper and a sliding nozzle, but the equipment cost and refractory cost are low, and the molten steel in the tundish at the end of casting is low. The present invention is to provide a continuous casting tundish capable of preventing the generation of a vortex directly above a sliding nozzle at that time, and to provide a continuous casting method of steel using this tundish.

  A continuous casting tundish according to a first aspect of the present invention for solving the above-mentioned problem is a continuous casting tundish provided with a stopper and a sliding nozzle, wherein the stopper is directly above the sliding nozzle and the sliding nozzle. Is capable of turning to a separate retreat position and capable of moving up and down just above the sliding nozzle and at the retreat position.

  The tundish for continuous casting according to the second invention is the tundish for continuous casting according to the first invention, wherein the stopper automatically controls the amount of molten steel injected into the mold via the sliding nozzle in accordance with the position of the molten steel surface in the mold. It is characterized by not being connected to an automatic flow control device for controlling automatically.

  Further, a continuous casting method for steel according to a third invention uses the tundish for continuous casting according to the first or second invention, and the sliding is performed while the stopper is disposed at a retracted position during steady casting. The amount of molten steel injected from the tundish into the mold is controlled using a nozzle, and at the end of casting, the stopper is swung directly above the sliding nozzle to inject the molten steel in the tundish into the mold. Is.

  According to the present invention, the stopper can be swung to a position immediately above the sliding nozzle and a retreat position away from the sliding nozzle, so that the stopper can be disposed immediately above the sliding nozzle at the end of casting, Even if the molten steel in the tundish decreases, the stopper becomes an obstacle, preventing the vortex formation of the molten steel directly above the sliding nozzle, and preventing the deterioration of the quality of the slab due to the defects present on the molten steel in the tundish it can. Since this stopper does not require the function of automatically controlling the molten steel injection amount from the tundish to the mold, the stopper does not require the hot water level control device required for automatic injection amount control. Can be an obstacle to vortex formation and can be reused even if it is somewhat melted. Therefore, although it has a stopper and a sliding nozzle, the equipment cost and the refractory cost can be reduced.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic sectional view of a tundish for continuous casting according to the present invention. FIG. 2 is a schematic sectional view showing a sliding nozzle portion of the tundish shown in FIG.

  As shown in FIGS. 1 and 2, the continuous casting tundish 1 according to the present invention has an outer shell covered with an iron skin 20, and an inner portion is enforced with a refractory 21. The upper nozzle 3 that fits the refractory 21 is installed. The upper nozzle 3 has a hole therein, and forms a part of the molten steel outflow hole 16 from the tundish 1 to the mold 6.

  A base 7 is installed on the side wall of the tundish 1, and an elevating device 8 is installed on the base 7. The elevating device 8 incorporates a spindle 9 oriented in the vertical direction. A rack (not shown) for raising and lowering is cut into the spindle 9, and this rack is fitted with a pinion gear (not shown) provided in the raising and lowering device 8, and the pinion gear of the raising and lowering device 8 is fitted. The spindle 9 is configured to move up and down by rotating. The pinion gear is rotated manually or by a manually operated electric motor. In addition, the spindle 9 is configured to be able to turn with respect to the lifting device 8 with the axial center direction of the spindle 9 as an axis while being fitted to the lifting device 8.

  A stopper arm 10 facing the horizontal direction is attached to the upper end of the spindle 9, and the other end of the stopper arm 10 is inserted into the tundish 1 through the opening 19 a of the upper lid 19. A stopper 2 that is oriented vertically downward is attached. The upper lid 19 covers the upper opening of the tundish 1 and carries out heat retention of the molten steel 24 in the tundish, replacement of inert gas in the tundish, and the like.

  The stopper 2 can be swung to an upper position of the upper nozzle 3 and a retracted position off the upper position of the upper nozzle 3 by the spindle 9 pivoting in the axial direction with respect to the lifting device 8. The spindle 9 is moved up and down by the lifting device 8 so that it can be lifted and lowered at both the upper position and the retreat position of the upper nozzle 3. Of course, the outflow of the molten steel 24 from the tundish 1 to the mold 6 can be stopped by fitting the tip of the stopper 2 to the upper nozzle 3. The opening 19a of the upper lid 19 serves as a burner flame inlet when the tundish 1 is heated by a burner (not shown) before casting. By turning the stopper 2 to the retracted position, the stopper 2 is configured not to obstruct burner heating. In FIG. 1, a stopper 2 indicated by a broken line indicates a stopper that has been turned to the retracted position.

  On the other hand, a sliding nozzle 4 comprising an upper fixing plate 11, a sliding plate 12, a lower fixing plate 13 and a rectifying nozzle 14 is disposed below the upper nozzle 3 in contact with the lower surface of the upper nozzle 3, and further the sliding nozzle. An immersion nozzle 5 is disposed in contact with the lower surface of 4, and a molten steel outflow hole 16 for flowing the molten steel 24 from the tundish 1 to the mold 6 is formed. The sliding plate 12 is connected to a reciprocating actuator 17, and the sliding plate 12 remains in contact with these fixing plates between the upper fixing plate 11 and the lower fixing plate 13 by the operation of the reciprocating actuator 17. The amount of molten steel passing through the molten steel outflow hole 16 is controlled by moving and adjusting the opening area formed by the sliding plate 12, the upper fixing plate 11 and the lower fixing plate 13. A pair of discharge holes 15 are installed in the lower part of the immersion nozzle 5. The sliding nozzle 4 has an outer shell covered with a steel case, but this case is omitted in FIG.

  A part of the upper nozzle 3 is formed of an alumina porous brick (not shown), and an inert gas supplied from an inert gas supply pipe 18 in order to prevent alumina from adhering to the inner wall surface of the immersion nozzle 5. The gas is blown into the molten steel outflow hole 16 through the porous brick portion of the upper nozzle 3. Ar gas or nitrogen gas can be used as the inert gas.

  The mold 6 is provided with an opposing mold long side 22 and an opposing mold short side 23 provided inside the mold long side 22 to form a rectangular mold internal space. A plurality of pairs of slab support rolls (not shown) such as guide rolls and pinch rolls are disposed below the mold 6 and a secondary cooling zone in which a spray nozzle is disposed between adjacent slab support rolls. (Not shown) is configured.

  An eddy current distance meter 29 for measuring the position of the molten steel surface 26 is installed above the molten steel surface 26 in the mold, and the measured value by the eddy current distance meter 29 keeps the position of the molten steel surface 26 constant. It is input to the hot water level control device 30 for maintaining the position. The signal of the molten metal level control device 30 is input to the actuator control device 31, and the actuator control device 31 determines that the position of the molten steel molten metal surface 26 in the mold is approximately based on the signal input from the molten metal level control device 30. The reciprocating actuator 17 is operated so as to be constant, and the molten steel injection amount flowing down the molten steel outflow hole 16 is controlled. That is, the sliding nozzle 4 is automatically controlled by an automatic flow control device including the eddy current distance meter 29, the molten metal level control device 30, and the actuator control device 31 so that the position of the molten steel molten metal surface 26 is constant. . As a matter of course, the sliding nozzle 4 can be manually operated by directly inputting it to the actuator control device 31. The stopper 2 is not connected to the molten metal level control device 30, that is, not connected to the automatic flow rate control device, and when the position of the molten steel molten metal surface 26 in the mold is controlled by the stopper 2. It is configured to be performed manually.

  Using the tundish 1 for continuous casting having such a configuration, the continuous casting operation of the molten steel 24 is performed as follows.

  Before casting, the tundish 1 is heated with the stopper 2 placed at the retracted position, and the tundish 1 heated for a predetermined time is placed at a predetermined position above the mold 6. A ladle (not shown) that accommodates molten steel 24 melted in a primary refining furnace such as a converter or electric furnace or a secondary refining furnace such as an RH vacuum degassing apparatus is placed at a predetermined position above the tundish 1. Arrange and pour molten steel 24 from the pan into the tundish 1. In this case, a sump pipe (not shown) is arranged around the upper nozzle 3 at the bottom of the tundish 1, the sliding nozzle 4 is closed, or the upper nozzle 3 is closed with the stopper 2. Then, a predetermined amount of molten steel 24 is allowed to stay in the tundish 1. When closing the upper nozzle 3 with the stopper 2, the stopper 2 is swung from the retracted position to above the upper nozzle 3.

  When the amount of molten steel in the tundish reaches a predetermined amount, the molten steel 24 is poured into the mold 6 through the molten steel outflow hole 16 by tilting the sump pipe, opening the sliding nozzle 4 or raising the stopper 2. To do. The molten steel 24 is cast into the mold 6 regardless of whether a hot water pipe is disposed when the predetermined amount of molten steel 24 is stored in the tundish 1, whether the sliding nozzle 4 is closed, or the upper nozzle 3 is closed with the stopper 2. After the injection into the molten steel, the amount of molten steel injected from the tundish 1 to the mold 6 is controlled by automatic control or manual control by the sliding nozzle 4. When the upper nozzle 3 is closed with the stopper 2 when the predetermined amount of molten steel 24 is stored, the stopper 2 is placed at the retracted position after the molten steel 24 is injected into the mold 6.

  The molten steel 24 becomes a discharge flow 25 from the discharge hole 15 toward the mold short side 23 and is injected into the mold. The molten steel 24 injected into the mold is cooled by the mold 6 to form a solidified shell 28. When a predetermined amount of molten steel 24 is injected into the mold, the pinch roll installed below the mold 6 is driven in a state where the discharge hole 15 is immersed in the molten steel 24 in the mold, and the outer shell is turned into a solidified shell. 28, and the drawing of the slab having the unsolidified molten steel 24 inside is started. After the start of drawing, the slab drawing speed is increased while maintaining the speed while automatically controlling the position of the molten steel surface 26 to a substantially constant position in the mold by the molten metal level control device 30 and the actuator control device 31. Continue casting. Mold powder 27 is added onto the molten steel surface 26 in the mold, and a predetermined amount of inert gas is blown into the molten steel outflow hole 16 from the inert gas supply pipe 18. The mold powder 27 melts and exhibits the function of preventing the molten steel 24 from being oxidized and serving as a lubricant between the solidified shell 28 and the mold 6.

  The slab drawn from the mold 6 is cooled by cooling water sprayed from a spray nozzle disposed in the secondary cooling zone, solidifies to the center, and is solidified to the center and then cut to a predetermined length. The

  In this way, when the continuous casting operation is continued and the molten steel 24 in the ladle is lost and the ladle is replaced with another ladle containing another molten steel, or when the continuous casting operation is terminated, from the ladle When the injection of the molten steel 24 into the tundish 1 is completed, or immediately before or after the completion of the injection, the stopper 2 is pivoted and disposed immediately above the upper nozzle 3 from the retracted position.

  By disposing the stopper 2 directly above the upper nozzle 3, the vortex of the molten steel 24 above the upper nozzle 3 can be prevented even when the stopper 2 becomes an obstacle and the amount of molten steel in the tundish decreases. Can do. On the molten steel in the tundish, there is a soot composed of a heat insulating agent, inclusion absorption flux, slag that has flowed out of the ladle, etc., but since the vortex does not occur in the molten steel 24, it exists on the molten steel in the tundish The spear does not flow out into the mold 6 and a clean slab can be manufactured.

  In this case, when the amount of molten steel in the tundish decreases, the amount of molten steel flowing down the molten steel outflow hole 16 may be controlled by the stopper 2 or may be controlled by the sliding nozzle 4. However, it is desirable that the stopper 2 be reused. If the upper nozzle 3 is closed with the stopper 2, the residual molten steel in the tundish and the stopper 2 are solidified and cannot be reused. It is preferable to control with the nozzle 4, and even when controlled with the stopper 2, the sliding nozzle 4 is finally closed and the stopper 2 is preferably raised to a position higher than the remaining molten steel 24.

  Since the stopper 2 is used only at the end of casting, it is possible to prevent alumina from adhering to the tip of the stopper 2. Even if alumina adheres, the adhered alumina can be dropped by raising and lowering the stopper 2 at the retracted position. Accordingly, inclusion defects due to alumina adhering to the stopper 2 can be prevented.

  As described above, according to the tundish 1 for continuous casting according to the present invention, the stopper 2 can be swung to the retreat position that is just above the sliding nozzle 4 and away from the sliding nozzle 4. The stopper 2 can be placed directly above the sliding nozzle 4, so that even if the molten steel in the tundish is reduced, the stopper 2 becomes an obstacle and the vortex formation of the molten steel directly above the sliding nozzle is prevented. It is possible to prevent deterioration of the quality of the slab due to the flaws existing on the inner molten steel. With respect to the stopper 2, the molten metal level control device 30 necessary for the automatic control of the molten steel injection amount is unnecessary, and the stopper 2 can be reused. Therefore, the equipment cost and the refractory cost can be reduced.

It is a schematic sectional drawing of the tundish for continuous casting which concerns on this invention. It is a schematic sectional drawing which shows the part of the sliding nozzle of the tundish shown in FIG. 1, and the part of the casting_mold | template under it.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tundish 2 Stopper 3 Upper nozzle 4 Sliding nozzle 5 Immersion nozzle 6 Mold 7 Base 8 Lifting device 9 Spindle 10 Stopper arm 11 Upper fixed plate 12 Sliding plate 13 Lower fixed plate 14 Rectification nozzle 15 Discharge hole 16 Molten steel outflow hole 17 Reciprocating Type Actuator 18 Inert Gas Supply Pipe 19 Upper Lid 20 Iron Skin 21 Refractory 22 Mold Long Side 23 Mold Short Side 24 Molten Steel 25 Discharge Flow 26 Molten Steel Surface 27 Mold Powder 28 Solidified Shell 29 Eddy Current Meter 30 Molten Surface Level Control Device 31 Actuator control device

Claims (1)

A tundish liftable and pivotable stopper supported on the installed lifting device on the side wall portion of a tundish for continuous casting, comprising: a sliding nozzle installed in the tundish bottom, and the stopper The sliding nozzle can be swung to a retreat position in a tundish that is separated from the sliding nozzle, and can be moved up and down at the retreat position immediately above and in the sliding nozzle. Using a tundish for continuous casting that is not connected to an automatic flow control device that automatically controls the injection amount of molten steel flowing down to the mold through the sliding nozzle according to the position of the molten steel surface in the mold,
When casting the molten steel stored in the tundish into the mold at the start of casting, the amount of molten steel injected from the tundish to the mold is controlled using the sliding nozzle,
During steady casting, the amount of molten steel injected from the tundish to the mold is controlled using the sliding nozzle with the stopper placed in the retracted position,
At the end of casting, with the stopper pivoted directly above the sliding nozzle, the molten steel in the tundish is injected into the mold while controlling the amount of molten steel injected from the tundish to the mold with the sliding nozzle ,
When the casting is finished, the sliding nozzle is closed, and the stopper is raised to a position higher than the molten steel remaining in the tundish .

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