JP2006231398A - Continuous casting method for steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve a high natural opening ratio of a nozzle even if a long nozzle attached in connection with a flow rate control mechanism on a ladle is opened with its tip immersed in molten steel in a tundish, while pouring the molten steel of the next heat into the tundish during the ladle change for sequential continuous casting. <P>SOLUTION: A molten steel holding vessel to be used is equipped with the molten steel flow rate control mechanism having an atmospheric pressure communication means 16 to communicate air between the inside of long nozzle and the outside atmosphere when the long nozzle 5 connected to the lower side of the molten steel flow rate control mechanism is immersed into the molten steel 8 in the tundish, while the molten steel flow rate control mechanism 4 is in the closed state and a molten steel discharging hole in the upper side is in the plugged state with a plugging material 19. When starting to pour the molten steel into the tundish from the molten steel holding vessel, the tip of the long nozzle is immersed into the molten steel in the tundish. Then, after the pressure inside the long nozzle comes to be equivalent to the atmospheric pressure, the molten steel flow rate control mechanism is activated to start pouring of the molten steel from the molten steel holding vessel. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a continuous casting method of steel, and more particularly to a continuous casting method of steel in which molten steel injected from a ladle into a tundish is injected while being cut off from air using a long nozzle.

  In continuous casting of steel, a method is widely used in which molten steel contained in a ladle is once poured into a tundish, and then the molten steel poured into the tundish is cast into a mold from a nozzle installed at the bottom of the tundish. It has been. Tundish distributes and supplies molten steel to multiple molds, floats and separates non-metallic inclusions in molten steel, and supplies molten steel during continuous continuous casting of multiple heats (hereinafter referred to as “continuous casting”) The purpose is to continue. At that time, in order to prevent oxidation of the molten steel injected from the ladle into the tundish by the air, a long nozzle made of refractory is connected to the molten steel outflow hole at the bottom of the ladle, and the lower end of the long nozzle is A method of preventing oxidation of molten steel by air by immersing the molten steel in the dish and shutting off the molten steel injected from the ladle into the tundish and air is widely performed.

  In order to control the amount of molten steel injected from the ladle into the tundish, the molten steel outflow hole at the bottom of the ladle is called a sliding refractory plate (hereinafter referred to as a sliding nozzle or rotary nozzle). A molten steel flow control device provided with a “sliding plate” is installed. In this molten steel flow control device, the opening of the sliding plate is aligned with the opening of a fixed refractory plate (hereinafter referred to as “fixed plate”), and the molten steel flows out. Yes. Moreover, the outflow amount of molten steel can be adjusted now by adjusting both opening area.

  In this molten steel flow control device, for the initial opening, the molten steel outflow hole in the upper part of the fixed plate is filled with a filler mainly composed of silica sand, and when the openings of the fixed plate and the sliding plate are combined. Furthermore, the filler is pulled out by its own weight and the gravity due to the molten steel in the ladle so that it opens naturally. The ratio in the case of natural opening is referred to as “natural aperture ratio”. If it does not open naturally, it is necessary to force it to flow out by blowing oxygen gas into the filler, etc. In that case, the slab of this part is oxidized by air or blown oxygen gas, so the quality deteriorates For this reason, operational changes such as strengthening the slab surface care method and strict product inspection are unavoidable.

  However, a high natural opening rate can be obtained under normal use conditions, but a long nozzle is connected to the molten steel outflow hole of the molten steel flow control device in order to shut off the air, and the tip of this long nozzle is placed in the tundish. When immersed in molten steel, the air trapped inside the long nozzle flows into the long nozzle and is compressed by the molten steel. At the same time, it is heated and expanded by the molten steel and the preheated long nozzle. The pressure inside the nozzle rises. For this reason, when opening in this state, there is a problem that the filler does not flow smoothly due to the pressure increase inside the long nozzle, resulting in poor opening.

In order to solve this problem, the present inventors previously proposed Patent Document 1. In this closed steel flow control device in a closed state, a groove for communicating the inside of the long nozzle and the outside air is provided in the fixed plate or the sliding plate, and the inside of the long nozzle when the tip of the long nozzle is immersed is provided. It is a technology that makes the pressure equal to atmospheric pressure.
JP 2003-145255 A

  By the technique proposed in Patent Document 1, the natural aperture ratio when the tip of the long nozzle is opened while being immersed in the molten steel in the tundish is greatly improved. However, compared with the case where the tip of the long nozzle is not immersed in the molten steel in the tundish, the natural aperture ratio still remains low.

  The present invention has been made in view of the above circumstances, and the object of the present invention is to use the ladle equipped with the molten steel flow rate control device proposed in Patent Document 1 to replace the molten steel of the next heat during continuous ladle replacement. When injecting into the tundish, the tip of the long nozzle connected to the ladle flow control device of the ladle can be opened with a high natural opening ratio even if it is immersed in the molten steel in the tundish and opened. It is possible to provide a continuous casting method of steel.

  The present inventors have investigated and studied to solve the above problems. As a result, even if a groove for communicating the inside of the long nozzle and the outside air is installed, the air inside the long nozzle is immediately discharged if the tip of the long nozzle is immersed in the molten steel in the tundish. However, it has been found that the interior of the long nozzle does not equal atmospheric pressure unless a time of about 10 seconds elapses after the tip of the long nozzle is immersed in the molten steel in the tundish. That is, after the tip of the long nozzle is immersed in the molten steel in the tundish, the inside of the long nozzle must be kept in communication with the outside air until the inside of the long nozzle becomes equal to the atmospheric pressure. And gained knowledge.

  The present invention has been made on the basis of the above knowledge. In the continuous casting method of steel according to the first invention, the molten steel flow rate control device is closed and the molten steel outflow hole on the upper side is filled with a filler. When the long nozzle connected to the lower part of the molten steel flow control device is immersed in the molten steel in the tundish, the molten steel flow control is provided with an atmospheric pressure communication means for communicating the inside of the long nozzle with the outside air. When starting the injection of molten steel from the molten steel holding container to the tundish using the molten steel holding container installed at the bottom of the apparatus, the long nozzle is immersed in the molten steel in the tundish. After the internal pressure of the steel becomes equal to the atmospheric pressure, the molten steel flow rate control device is operated to start injecting the molten steel from the molten steel holding container into the tundish.

  In the continuous casting method of steel according to the second invention, in the first invention, the molten steel flow rate control device is operated after 10 seconds or more have passed since the tip of the long nozzle is immersed in the molten steel in the tundish. It is a feature.

  According to the present invention, the molten steel flow control device is operated after the internal pressure of the long nozzle becomes equal to the atmospheric pressure. Therefore, when the molten steel flow control device is operated, the internal pressure of the long nozzle is the tip of the long nozzle. Thus, the pressure is the same as when not dipping the molten steel in the molten steel, and therefore, the tip of the long nozzle can be opened with a high natural aperture ratio equivalent to that when not dipping in the molten steel. As a result, industrially beneficial effects such as improvement of the quality of the slab and avoiding a change in the operation of the slab are brought about.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic view of a continuous casting facility embodying the present invention, and FIG. 2 is a detailed view of a long nozzle mounting structure in FIG.

  1 and 2, a tundish 1 having an inner surface made of a refractory is mounted on a tundish car (not shown) and disposed at a predetermined position above the mold 3. The ladle 2 which accommodated the molten steel 8 is arrange | positioned in the position as a molten steel holding | maintenance container. At the bottom of the ladle 2, an upper nozzle 7 that penetrates the iron skin 14 and fits with the ladle refractory 15 is installed, in contact with the lower surface of the upper nozzle 7, the fixed plate 10, the sliding plate 11 and A sliding nozzle 4 comprising a rectifying nozzle 12 is installed as a molten steel flow rate control device, and further, a long nozzle 5 is connected to the lower surface of the sliding nozzle 4 to shut off the atmosphere, and from the ladle 2 to the tundish 1 A molten steel outflow hole 13 is formed. The sliding plate 11 is connected to a reciprocating actuator (not shown), and is moved in close contact with the fixed plate 10 by the operation of the reciprocating actuator, and the opening of the fixed plate 10 and the sliding plate 11 are moved. The amount of molten steel passing through the molten steel outflow hole 13 is controlled by adjusting the opening area with the opening.

  That is, the molten steel 8 accommodated in the ladle 2 has a long nozzle 5 whose tip is immersed in the molten steel 8 staying in the tundish 1 while the flow rate is adjusted by the sliding nozzle 4 installed as a molten steel flow rate control device. The molten steel 8 injected into the tundish 1 is cast into the mold 3 via the immersion nozzle 6 installed at the bottom of the tundish 1. The molten steel 8 cast in the mold 3 is cooled in contact with the mold 3 to form a solidified shell (not shown), and the slab 9 having an outer shell as a solidified shell and an inside of the unsolidified molten steel 8 is a mold. 3 is continuously drawn down to 3 and finally completely solidified to the center to produce a slab 9. During drawing of the slab 9, the molten steel surface position in the mold is controlled to a substantially constant position. An injection flow of the molten steel 8 from the ladle 2 to the tundish 1 is blocked from the atmosphere by the long nozzle 5, and an injection amount of the molten steel 8 from the tundish 1 to the mold 3 is blocked from the atmosphere by the immersion nozzle 6.

  By casting in this way, the molten steel 8 accommodated in the ladle 2 will eventually disappear. Furthermore, when continuous casting is continued, the ladle 2 that has been emptied is removed, and another ladle 2 containing molten steel 8 is placed at a predetermined position above the tundish 1 and connected to the lower portion of the sliding nozzle 4. The tip of the nozzle 5 is immersed in the molten steel 8 staying in the tundish 1. In this case, the sliding nozzle 4 of the ladle 2 newly disposed is in a closed state. FIG. 3 shows a state in which the sliding nozzle 4 is closed and the tip of the long nozzle 5 is immersed in the molten steel 8 staying on the tundish 1. As shown in FIG. 3, the molten steel outflow hole 13 at the site of the upper nozzle 7 is filled with a filler 19 mainly composed of silica sand for the initial opening.

  The stationary plate 10 of the sliding nozzle 4 used in the present invention is provided with an atmospheric pressure communicating means for communicating the inside of the long nozzle 5 and the outside air when the sliding nozzle 4 is closed. Specifically, an atmospheric communication groove 16 and an atmospheric communication groove 17 are provided for communicating the inside of the long nozzle with the outside air. FIG. 4 shows a view of the fixed plate 10 viewed from the sliding surface side with the sliding plate 11. In FIG. 4, reference numeral 18 denotes an opening, and S denotes a portion where the opening of the sliding plate 11 is positioned when the sliding nozzle 4 is closed.

  As shown in FIG. 4, on the sliding surface of the fixed plate 10, one atmospheric communication groove 16 and two atmospheric communication grooves 17 extending from the region S to the side surface of the fixed plate 10 are installed. As shown in FIG. 3, when the sliding nozzle 4 is closed, the inside of the long nozzle 5 is configured to communicate with the outside air through the atmosphere communication groove 16 and the atmosphere communication groove 17. As shown in FIG. 2 and the like, when the opening of the sliding plate 11 overlaps the opening 18 of the fixed plate 10, the atmospheric communication groove 16 and the atmospheric communication groove 17 do not communicate with the opening of the sliding plate 11. In this way, the positions of the atmospheric communication groove 16 and the atmospheric communication groove 17 are set.

  When another ladle 2 containing the molten steel 8 is arranged at a predetermined position above the tundish 1 and the tip of the long nozzle 5 connected to the lower part of the sliding nozzle 4 is immersed in the molten steel 8 staying in the tundish 1, The molten steel 8 flows into the immersion part of the long nozzle 5. When the atmosphere communication groove 16 and the atmosphere communication groove 17 are not installed, the air inside the long nozzle 5 is heated by the molten steel 8 and the long nozzle 5 and at the same time the pressure is caused by the molten steel 8 flowing in from the lower part. Although the air communication groove 16 and the air communication groove 17 are installed in the fixing plate 10 used in the present invention, the air inside the long nozzle 5 passes through the air communication groove 16 and the air communication groove 17. It flows out to the open air.

  However, the air inside the long nozzle 5 whose pressure has increased flows out through the atmosphere communication groove 16 and the atmosphere communication groove 17, and it takes a certain amount of time for the inside of the long nozzle 5 to be equal to the atmospheric pressure. Therefore, the sliding nozzle 4 is not operated until this time elapses, and the state shown in FIG. 3, that is, the closed state is maintained. Although it is sufficient for this time to be about 10 seconds, the internal pressure of the long nozzle 5 is measured in advance using a pressure gauge or the like because it varies depending on the number of installed atmospheric communication grooves 16 and the atmospheric communication grooves 17 and their cross-sectional areas. It is preferable to do. Once measured, it is not necessary to measure the pressure each time and can be dealt with by the elapsed time.

  When the inside of the long nozzle 5 becomes almost equal to the atmospheric pressure, the sliding nozzle 4 is actuated to align the opening of the sliding plate 11 with the opening of the fixed plate 10. Since the internal pressure of the long nozzle 5 is almost equal to the atmospheric pressure, the filler 19 smoothly flows down from the upper nozzle 7 and the sliding nozzle 4 opens naturally. After opening, the injection of molten steel 8 is continued while adjusting the opening of the sliding nozzle 4 so that the amount of molten steel staying in the tundish 1 becomes substantially constant.

  In the present invention, since the pouring of the molten steel 8 from the ladle 2 to the tundish 1 is started in this way, when the sliding nozzle 4 is operated, the pressure inside the long nozzle 5 causes the tip of the long nozzle 5 to move toward the molten steel 8. Therefore, the tip of the long nozzle 5 can be opened with a high natural aperture ratio equivalent to that when the tip of the long nozzle 5 is not immersed in the molten steel 8.

  In the above description, the example of the sliding nozzle 4 including one fixed plate and one sliding plate has been described as the molten steel flow rate control device. However, the sliding in which one sliding plate slides between the two fixed plates. Even if it is a nozzle, this invention can be applied according to the above by installing an air | atmosphere communication groove | channel in a sliding plate. The sliding nozzle is a type in which the sliding plate reciprocates on a straight line, but the present invention is applied to the molten steel flow control device of the type in which the sliding plate rotates with respect to the fixed plate. can do. In short, what is the model of the molten steel flow control device as long as the molten steel flow control device having an air communication groove that communicates the inside of the long nozzle with the outside air when the molten steel flow control device is closed is used? It does not matter. Furthermore, a total of three atmospheric communication grooves 16 and atmospheric communication grooves 17 are installed as the atmospheric pressure communication means for communicating the inside of the long nozzle 5 with the outside air. Can be any number.

  The present invention was carried out using the continuous casting equipment shown in FIGS. The cross-sectional shape of the air communication groove installed on the fixed plate was a rectangle having a width of 10 mm and a depth of 5 mm. And when the long nozzle was immersed and 10 seconds passed, the sliding nozzle was actuated and injection from the ladle into the tundish was started. In addition, for comparison, when a fixed plate without an air communication groove is used (conventional example) and immediately after a long nozzle tip is immersed, although an air communication groove is installed in the fixed plate The case where the sliding nozzle was operated (comparative example) was also carried out. And the immersion opening operation | work of 100 charges or more was implemented, respectively, and the ratio (natural opening failure rate) which did not open naturally was investigated and compared. FIG. 5 shows the survey results.

  As shown in FIG. 5, the natural aperture failure rate was reduced to 0.4% by applying the present invention. This value was equivalent to the case where the long nozzle was opened without being immersed. On the other hand, the natural opening failure rate of the conventional example was 11.6%, and the natural opening failure rate of the comparative example was 3.4%.

It is the schematic of the continuous casting installation which implemented this invention. FIG. 2 is a detailed view of a long nozzle mounting structure in FIG. 1. It is a figure which shows embodiment of this invention, Comprising: It is a figure which shows the state which made the sliding nozzle the closed state and immersed the front-end | tip of the long nozzle in the molten steel in a tundish. It is the schematic of the fixing plate used by this invention. It is a figure which shows the result of having investigated the natural opening failure rate in Example 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tundish 2 Ladle 3 Mold 4 Sliding nozzle 5 Long nozzle 6 Immersion nozzle 7 Upper nozzle 8 Molten steel 9 Cast slab 10 Fixed plate 11 Sliding plate 12 Rectification nozzle 13 Molten steel outflow hole 14 Iron skin 15 Ladle refractory 16 Atmospheric communication Groove 17 Atmospheric communication groove 18 Opening 19 Filler

Claims (2)

  When the long nozzle connected to the lower part of the molten steel flow control device is immersed in the molten steel in the tundish with the molten steel flow control device closed and the molten steel outlet hole filled with filler. A molten steel flow control device equipped with an atmospheric pressure communication means for communicating the inside of the long nozzle with the outside air uses a molten steel holding vessel installed at the bottom, and starts injecting molten steel from the molten steel holding vessel to the tundish In so doing, after the tip of the long nozzle is immersed in the molten steel in the tundish, the molten steel flow control device is operated after the pressure inside the long nozzle becomes equal to the atmospheric pressure, and the molten steel holding container is moved to the tundish. A method for continuously casting steel, characterized by starting injection of molten steel.   2. The continuous casting method of steel according to claim 1, wherein the molten steel flow rate control device is operated after 10 seconds or more have passed since the tip of the long nozzle is immersed in the molten steel in the tundish.

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