JP2008173672A - Method for detecting slag outflow in continuous casting - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for detecting slag outflow in continuous casting capable of rapidly and reliably detecting the slag outflow at the terminating state of filling even when performing the continuous casting of high-grade steel using a seal tube. <P>SOLUTION: A hole 10 for measurement is formed in the upper side wall of the seal tube 6 installed between a ladle 2 and a tundish 1, and the radiation energy of a filling flow 7 is measured via the hole 10 for measurement by a radiation energy measuring instrument 11 installed at a remote position. When the slag starts to flow out, a radiation energy level is raised, and the slag outflow is detected on the basis of the change of the level. Inert gas is blown into the seal tube 6 to prevent any contact of air with a molten metal. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a slag outflow detection method in continuous casting that can quickly and accurately detect that slag has started to flow out of a pan at the end of pouring of molten steel from the pan into a tundish.

  Continuous casting of molten steel is performed while pouring molten steel from the pan into the tundish, but at the end of the pouring, the slag floating on the molten steel surface in the pan flows out toward the tundish, reducing the quality of the slab. Let For this reason, it is necessary to quickly detect that the slag has started to flow out of the pan at the end of the pouring, and stop pouring the molten steel from the pan into the tundish.

  Moreover, when air is entrained in the molten steel injected from the pan, the amount of oxygen and nitrogen in the air rises (pickup) and the quality of the slab is lowered. For this reason, when manufacturing high-grade steel that dislikes picking up oxygen and nitrogen, a molten pipe is injected by installing a seal pipe between the pan and the tundish. In this case, the seal tube becomes an obstacle and the injection flow cannot be observed from the outside, and the slag outflow cannot be detected.

  For this reason, in order to detect slag outflow in continuous casting using a seal pipe, a method has been adopted in which the pan is slightly raised from the upper end of the seal pipe at the end of injection and the injection flow is visually observed from the gap. However, in visual observation, the discovery of slag outflow was delayed, and there was a problem that a large amount of slag, which is a contamination source of molten steel, flowed out and product quality was easily deteriorated. In addition, the variability by the observing operator is large, and in the case of detection delay, the quality of the slab is lowered, and conversely, in the case of early false detection, the molten steel yield is deteriorated. Furthermore, since air entrained in the molten steel flow from the gap between the seal tubes also becomes a source of molten steel contamination, it has been impossible to avoid a reduction in slab quality.

  Therefore, as disclosed in Patent Document 1, a method has been developed in which a measuring device is attached to the side wall of a seal tube and slag outflow is detected from the magnitude and distribution of the radiant energy of the injected flow. According to this method, it is possible to eliminate the detection delay of the slag outflow and the variation in detection by the operator. However, this method places a heat load on the measuring device, and the measuring device must be reattached each time the seal tube is replaced. Since the seal tube is frequently exchanged, it is impractical to reattach the measuring device each time. Furthermore, the molten steel adheres to the inner surface of the seal tube and solidifies, which may prevent the field of view of the measuring device, resulting in a lack of reliability.

Further, Patent Document 2 discloses a method for detecting a slag by photographing an molten steel flow discharged from a converter to a pan with an imaging device installed at a distant position, but does not use a seal pipe. There was a problem of air entrainment and it was not a method applicable to the production of high-grade steel.
JP-A-2-251362 JP 2003-183720 A

  The present invention solves the above-described conventional problems, and slag in continuous casting that can detect slag outflow at the end of pouring quickly and reliably even when high-grade steel is continuously cast using a seal pipe. It aims at providing the outflow detection method.

  In order to solve the above problems, the present invention provides a measurement hole in a side wall of a seal tube installed between a pan and a tundish, and a radiant energy measurement device installed at a remote position through the measurement hole. Then, the radiant energy of the injected flow is measured, and the slag outflow is detected based on the change.

  It is preferable to measure the radiant energy of the injection flow while blowing an inert gas into the seal tube to prevent the intrusion of air that causes molten metal contamination into the seal tube. Preferably, the average radiant energy or the maximum radiant energy is measured, and it is determined that the slag is discharged when the threshold value is exceeded. The measurement hole is preferably provided in the upper side wall of the seal tube.

  According to the first aspect of the present invention, since the radiant energy of the injected flow is directly measured by the radiant energy measuring device installed at a remote position through the measurement hole provided in the side wall of the seal tube, the measuring device reduces the heat load. In addition, since only the seal tube can be replaced, there is no increase in the burden on the operator. Further, by appropriately setting the size of the measurement hole, it is possible to secure the field of view of the measurement device, so that slag outflow can be detected quickly and reliably based on the change in radiant energy. In addition, it is not preferable that the seal tube is made of glass because there is a risk of fogging due to the injection flow and there is a problem of heat load.

  According to the second aspect of the present invention, an inert gas is blown into the seal tube to prevent the entry of air that causes contamination of the molten metal into the seal tube. There is no decline in quality.

  According to the invention of claim 3, since the average radiant energy or the maximum radiant energy within a specific range of the injection flow is measured and it is determined that the slag flows out when the threshold value is exceeded, an automatic determination is possible, and the operator Can be reduced.

  According to the fourth aspect of the invention, since the measurement hole is provided in the upper side wall of the seal tube, it is difficult to be affected by the adhesion of the molten metal to the inner surface of the seal tube, and the field of view of the measuring device can be secured.

Preferred embodiments of the present invention are shown below.
In FIG. 1, 1 is a tundish for continuous casting, 2 is a pan for transporting the molten steel 3 to the tundish 1, and a slag 4 floats on the upper surface of the molten steel. A sliding nozzle 5 is provided at the bottom of the pan 2, and molten steel is injected into the tundish 1 while the flow rate is controlled by the sliding nozzle 5.

  In the case of high-grade steel that does not like oxygen or nitrogen pick-up, a seal tube 6 is installed between the pan 2 and the tundish 1 to prevent air entrainment in the injection flow 7. The seal tube 6 is held by placing a protrusion 8 provided on the outer periphery on the lid 9 of the tundish 1. An inert gas is blown into the inside of the seal pipe 6, and the internal air is purged to prevent contact between the injection flow 7 and the air.

  As shown in FIG. 2, a measurement hole 10 is formed by cutting out the upper side wall of the seal tube 6. The position for forming the measurement hole 10 may be anywhere as long as it is above the lid 9 of the tundish 1. However, as shown in FIG. 1, the molten steel scatters and adheres to the lower inner surface of the seal tube 6, so that the position is as high as possible. In this embodiment, the measurement hole 10 is formed by cutting out a part of the seal tube 6 from the upper end surface. The size is set to a size sufficient to observe the injection flow 7 from the outside, and is preferably a size capable of preventing air mixing, for example, a width of about 70 to 150 mm and a height of about 50 to 75 mm.

  As shown in FIG. 1, a radiant energy measuring device 11 is installed at a position sufficiently away from the seal tube 6, the injection flow 7 is observed through the measurement hole 10, and the radiant energy from the surface is measured. When the commercially available radiant energy measuring device 11 is used, it can be observed from a remote position of about 10 meters, and the radiant energy measuring device 11 can be prevented from receiving a heat load.

  As shown in FIG. 3, the radiant energy from the slag is larger than the radiant energy from the surface of the molten steel, and the radiant energy level rapidly rises when slag is mixed in the injection flow 7. For this reason, by measuring the average radiant energy or the maximum radiant energy within a specific range of the injection flow 7 that can be seen from the measurement hole 10, and automatically determining the slag outflow when the threshold is exceeded, the slag outflow can be detected quickly and accurately. It is possible to detect.

  The detection result can be transmitted to the worker by an alarm or the like. Further, the sliding nozzle 5 can be closed simultaneously with the detection of the slag outflow, and the slag inflow into the tundish 1 can be automatically stopped.

In order to confirm the effect of the present invention, (1) a method in which the pan described as the conventional method is lifted from the upper end surface of the seal tube 6 and the slag outflow is visually observed from the gap, and the operation of the sliding nozzle 5 is also performed manually. (2) The seal tube 6 in which the measurement hole 10 is formed is used. The observation is performed by visual observation and the sliding nozzle 5 is manually operated. (3) The seal tube 6 in which the measurement hole 10 is formed is observed. Is performed by the radiant energy measuring device 11 but the sliding nozzle 5 is operated manually. (4) The sealing tube 6 having the measurement hole 10 is used to perform the observation by the radiant energy measuring device 11 and the sliding nozzle 5 is operated. In four cases of the automatic method, the slag thickness in the tundish and the oxygen concentration in the molten steel in the tundish were measured.
The results are shown in Table 1.

  As shown in the data of Table 1, according to the methods of the present invention of (3) and (4), the slag thickness in the tundish can be halved compared to the conventional method. Moreover, since the entrainment of air can be prevented, the oxygen concentration in the molten steel can be reduced to 1/3 to 1/2 of the conventional one. The most favorable result can be obtained particularly in the case of (4) in which the operation of the sliding nozzle is also automated.

It is sectional drawing which shows embodiment of this invention. It is a perspective view of the upper half part of a seal pipe. It is a graph which shows the change of radiant energy.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tundish 2 Pan 3 Molten steel 4 Slag 5 Sliding nozzle 6 Seal pipe 7 Injection flow 8 Protrusion 9 Lid 10 Measurement hole 11 Radiation energy measuring device

Claims (4)

  A measurement hole is provided in the side wall of the seal pipe installed between the pan and the tundish, and the radiant energy of the injected flow is measured through the measurement hole by a radiant energy measuring device installed at a remote location, and based on the change. A method for detecting slag outflow in continuous casting, wherein slag outflow is detected.   2. In continuous casting according to claim 1, wherein the radiant energy of the injected flow is measured while injecting an inert gas into the inside of the seal tube to prevent intrusion of air that causes molten metal contamination into the seal tube. Slag outflow detection method.   2. The slag outflow detection method in continuous casting according to claim 1, wherein an average radiant energy or a maximum radiant energy within a specific range of the injected flow is measured, and a slag outflow is determined when a threshold value is exceeded.   2. The slag outflow detection method in continuous casting according to claim 1, wherein a measurement hole is provided in an upper side wall of the seal pipe.

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