JP2010253504A - Method for detecting cast slab joint part in continuous casting - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately detect a step-shaped joint part formed when withdrawal of a cast slab is once stopped at the half way of continuous casting due to exchange of a tundish, successive casting of different steel kinds or the like in continuous casting of steel. <P>SOLUTION: A method for detecting a cast slab joint part in continuous casting is directed for detecting the step-shaped joint part formed when injection of molten steel 11 into a mold 5 and the withdrawal of the cast slab 12 are once stopped at the half way of the continuous casting in carrying out the continuous casting of the steel and thereafter the injection of the molten steel into the mold and the withdrawal of the cast slab are restarted. The thermal image of the surface of the cast slab during the continuous casting is photographed by a thermal image photographing device 17 and the joint part is detected based on a surface temperature profile in the thermal image. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  In the present invention, when continuously casting steel, for the purpose of tundish exchange or continuous casting of different steel types, the injection of molten steel into the mold is temporarily stopped and the slab extraction is temporarily stopped. The present invention relates to a method for detecting a step-like joint formed when resuming pouring of molten steel into a mold and resuming drawing of a slab.

  In continuous casting of steel, in order to improve productivity, molten steel with many charges is continuously cast. Continuous casting of a large number of charges is called continuous continuous casting (also called “continuous casting”). However, there is a limit to the usable time of the tundish to be used (mainly the time limit for using the immersion nozzle installed at the bottom of the tundish). Therefore, continuous casting is performed while replacing the tundish or immersion nozzle. ing. In this case, at the time of tundish replacement or immersion nozzle replacement, once the molten steel injection into the mold is stopped and the slab extraction is stopped, and after the new tundish or new immersion nozzle is installed, the tundish is replaced with the mold. Is resumed, and slab extraction is resumed.

  In addition, in recent small-lot, multi-product steel product configurations, continuous casting of the same steel type alone does not improve the productivity of continuous casting machines. Therefore, continuous casting (“different” Steel type continuous casting ”). In the case of continuous casting of different steel types, in order to prevent the molten steel of the preceding charge and the molten steel of the subsequent charge from mixing in the mold, the drawing of the slab is temporarily stopped at the end of casting of the preceding charge, and at the same time, A so-called “partition metal” is immersed in the molten steel, and then a subsequent charge is injected into the mold and drawing of the slab is resumed.

  Since the tundish exchange part of the same steel type and the joint part of continuous casting of different steel types once stop the injection of molten steel into the mold and the drawing of the slab, a step-pour-like seam part is formed. . The seam portion has a double skin shape in which the surfaces of the slabs overlap each other, is not clean with a lot of inclusions, and may contain a partition metal, cannot be used as a product, and is cut and removed after casting.

  The method of tracking (tracking) this seam is performed by a length measuring device (major roll) installed in the continuous casting machine, and the principle is that the signal (number of revolutions) of the pulse generator installed on the axis of the major roll ) And the diameter (or circumferential length) of the major roll set in advance in the calculation device, the casting length is calculated, and the seam position is tracked based on this casting length. In this case, the length from the major roll when the casting is stopped to the position of the joint is uniquely calculated from the equipment specifications of the continuous casting machine.

  However, this method has a problem in that the calculation accuracy is not so high for the following reasons, and when the seam portion is cut, it must be cut longer than necessary, resulting in a large yield loss. The reason why the accuracy is not high is that the influence of the thermal expansion of the slab is reflected in the calculation of the casting length in consideration of the slab temperature due to the secondary cooling, but this is inaccurate, the wear of the major roll and the major This is because the measurement of the major roll fluctuates because the diameter of the major roll changes due to foreign matter adhering to the roll, or the major roll itself slips.

  Thus, many means for accurately specifying the seam portion have been proposed. For example, in Patent Document 1, a thermometer for measuring the surface temperature of the slab is installed on the exit side of the continuous casting machine, the surface temperature of the slab is measured by the thermometer, and the surface temperature of the joint portion is low. Thus, a method for detecting a joint portion from a decrease in temperature measurement value has been proposed. Patent Document 2 proposes a method of measuring a load torque of a slab drive roll (pinch roll) installed in a continuous casting machine and detecting a joint portion from a change in the load torque. Furthermore, Patent Document 3 proposes a method of installing a laser distance meter for measuring the surface shape of a slab and detecting a seam portion based on the slab appearance shape measured by the laser distance meter. Yes.

Japanese Patent Laid-Open No. 62-162410 Japanese Patent Laid-Open No. 8-215813 JP-A-8-94309

  However, the above prior art has the following problems.

  That is, in Patent Document 1, the range in which the slab surface temperature is measured is narrow, that is, only a part of the slab width direction can be measured, and it is easily affected by the influence of water vapor and temperature variations around the measured part. There is a limit to accurately identifying the seam portion.

  In Patent Document 2, in order to increase the accuracy of identifying the joint portion, it is necessary to provide a large number of determination values depending on the steel component conditions of the slab, the casting width, the slab temperature, etc., which is complicated and difficult to determine. There is a concern about erroneous detection due to changes in casting conditions, such as changes in the slab drawing speed.

  In Patent Document 3, in order to ensure the accuracy of the laser distance meter, it is necessary to bring the laser distance meter close to the slab to some extent. It is possible to detect only when the value changes significantly, that is, it can be applied only when the above-mentioned “partition hardware” has a unique shape, and it is highly possible that a normal seam portion cannot be detected.

  The present invention has been made in view of the above circumstances, and its object is to provide molten steel to a mold in the middle of continuous casting in order to perform tundish replacement or continuous casting of different steel types when continuously casting steel. A method to accurately and reliably detect the stepped pour-shaped seam formed when injection of molten steel and slab drawing are temporarily stopped and then molten steel is poured into the mold and slab extraction is resumed. It is to be.

  The method for detecting a slab joint in continuous casting according to the first aspect of the invention for solving the above-described problem is that when continuous casting of steel, injection of molten steel into the mold and drawing of the slab are performed during continuous casting. A method for detecting a slab joint for detecting a stepped joint formed when the molten steel is once poured into the mold and the casting is resumed. A thermal image of the surface of the slab is taken, and the joint portion is detected based on a surface temperature profile in the thermal image.

  According to a second aspect of the present invention, there is provided a method for detecting a slab joint portion in the continuous casting according to the first aspect, wherein in the thermal image, the surface temperature is lower by 25% or more than the normal casting region and the full width in the slab width direction. When the belt-like zone is detected, the belt-like zone is detected as the seam portion.

  The seam portion of the slab during continuous casting is basically lower in surface temperature than the normal casting area. According to the present invention, a thermal image of the surface of the slab during continuous casting is taken, and this thermal image Since the seam portion is detected based on the surface temperature profile, that is, the seam portion is detected based on the surface temperature distribution in the slab width direction, the surface temperature measurement range is expanded in the slab width direction, and as a result, The seam portion can be detected accurately and reliably, and industrially beneficial effects such as improvement in slab yield are brought about.

1 is a schematic side view of a vertical bending slab continuous casting machine to which the present invention is applied. It is a figure which shows the example which converted and displayed the thermal image of the image | photographed slab surface as a temperature profile of a slab. It is a figure which shows the example which converted and displayed the thermal image of the image | photographed slab surface as a temperature profile of a slab.

  Hereinafter, the present invention will be described in detail.

  The present invention temporarily stops the injection of molten steel into the mold and the drawing of the slab for several seconds during the continuous casting for the purpose of replacing the tundish, continuously casting different steel types, or replacing the immersion nozzle. Or, after stopping for several minutes, when the molten steel is poured into the mold and the slab extraction is resumed, the step-like joint formed on the slab has a lower temperature than the normal casting zone, In addition, focusing on the fact that this low temperature region extends in the slab width direction, this seam can be easily detected by taking a thermal image of the slab surface and monitoring the slab surface temperature profile. It was made based on the knowledge that it is. That is, the present invention is characterized in that a thermal image of the surface of a slab during continuous casting is taken and the joint portion is detected based on a surface temperature profile in the thermal image.

  As a criterion for determining whether or not it is a seam portion, “the slab surface temperature in the thermal image is lower by 25% or more than the normal casting region, and this low temperature region is formed in a strip shape over the entire width of the slab width. It is possible to detect with 100% establishment without overlooking the seam portion. When a thermal image of the entire width of the slab cannot be captured due to some influence, a portion where a low temperature region over the entire width of the slab reflected in the image is detected may be determined as the joint portion. The “normal casting zone” in the present invention means “a slab excluding the range of the seam part”, but the surface temperature of the slab part staying in the mold also becomes low when the slab is stopped. Therefore, since the temperature difference from the seam portion is small and there is a risk of misdetection, the “slab site 1 m or more, preferably 2 m or more away from the seam portion” is defined as “normal casting zone”.

  Since the joint portion is scrapped, the slab during continuous casting is usually cut at a position spaced a predetermined distance upstream from the joint portion. In both cases of continuous casting of the same steel type and continuous casting of different steel types, the slab including the seam portion is the preceding charge, and the slab upstream of the seam portion is the subsequent charge. The slab including the seam portion is further cut off-line at a predetermined position downstream of the seam portion, the slab including the seam portion is scrapped, and the other slab cut is according to the length of the slab, It becomes a product or is scrapped. As a matter of course, there is no problem in applying the present invention even if the slab is cut at a position spaced a predetermined distance downstream from the joint, but the charge classification in the slab is not limited. Since it is clear and the subsequent operation of the slab is smooth, it is preferable to cut on the upstream side of the joint portion.

  Hereinafter, the present invention will be specifically described with reference to the drawings. FIG. 1 is a schematic side view of a vertical bending slab continuous casting machine to which the present invention is applied.

  As shown in FIG. 1, a slab continuous casting machine 1 is provided with a mold 5 for cooling molten steel 11, and a molten steel supplied from a ladle (not shown) at a predetermined position above the mold 5. A tundish 2 for relaying 11 to the mold 5 is installed. A sliding nozzle 3 for adjusting the flow rate is disposed at the bottom of the tundish 2, and an immersion nozzle 4 is disposed on the lower surface side of the sliding nozzle 3, and is accommodated in the tundish 2 via the sliding nozzle 3 and the immersion nozzle 4. The molten steel 11 is injected into the mold 5.

  On the other hand, below the mold 5, a plurality of pairs of slab support rolls including a support roll 6, a guide roll 7 and a pinch roll 8 are arranged. Among these, the pinch roll 8 is a drive roll for pulling out the slab 12 at the same time as supporting the slab 12. A secondary cooling zone in which a spray nozzle (not shown) such as a water spray nozzle or an air mist spray nozzle is arranged in the gap between the slab support rolls adjacent in the casting direction is configured. The slab 12 is cooled while being drawn out by cooling water sprayed from (also referred to as “secondary cooling water”). On the downstream side of the slab support roll, a plurality of transport rolls 9 for transporting the cast slab 12 are installed. Above the transport roll 9, a predetermined slab 12 is cast from the slab 12 to be cast. A gas cutting machine 10 for cutting the length slab 12a is arranged. The gas cutting machine 10 is connected to a cutting control device 22 and performs a cutting operation of the slab 12 based on a signal input from the cutting control device 22.

  Further, a measure roll 15 that rotates in contact with the lower surface of the slab 12 to be pulled out is installed between the slab support roll on the most downstream side in the drawing direction and the gas cutter 10. A pulse generator (not shown) is attached to the shaft of the major roll 15, and a signal from the pulse generator is input to the tracking device 16. The tracking device 16 is input in advance with a signal from the pulse generator. The cast length of the cast slab 12 is measured from the diameter or circumferential length of the major roll 15 to track each position of the slab 12. The tracking device 16 transmits the measured casting length and tracking information of each position of the slab to the cutting control device 22, and the cutting control device 22 is based on the information input from the tracking device 16 and has a predetermined length. The cutting position is set to obtain 12a, and the set signal is transmitted to the gas cutting machine 10.

  Furthermore, between the slab support roll on the most downstream side in the drawing direction and the major roll 15, the gas injection nozzle 19 and the thermal image capturing device 17 have the gas injection nozzle 19 as the upstream side in the casting direction and the slab 12. It is installed facing the top of the.

  The gas injection nozzle 19 is connected to the blower 20 so that the air supplied from the blower 20 is injected to the entire width of the slab 12 through the gas injection nozzle 19. The gas injection nozzle 19 is a device for blowing off steam that hinders photographing when the thermal image photographing device 17 takes a thermal image of the slab surface.

  The thermal image capturing device 17 can capture a thermal image of the entire width of the slab 12, and the thermal image capturing device 17 is connected to the image processing device 18, and is continuously cast imaged by the thermal image capturing device 17. The thermal image of the surface of the slab inside is input to the image processing device 18, and the input thermal image is converted into digital data by the image processing device 18 so that it can be grasped as a temperature profile of the slab 12. The image processing device 18 also has a function of detecting a joint portion of the slab 12 based on the temperature profile of the slab 12. The method for determining the joint portion of the slab 12 is performed by the method described above.

  When the seam portion of the slab 12 is detected in the image processing device 18, the detection data of the seam portion of the slab 12 by the image processing device 18 is transmitted to the tracking device 16, and this seam detection data is input. The tracking device 16 corrects the casting length obtained from the signal from the major roll 15 and the information on the slab tracking based on the information on the input seam position, and each position of the slab based on the corrected content. Continue tracking for.

  In this case, the thermal image capturing device 17 and the blower 20 may be continuously operated during continuous casting, but since the device detects only the joint portion of the slab, from the viewpoint of energy saving, the joint portion is It is preferable to operate several minutes before entering the shooting range and stop after the seam passes the shooting range. For this purpose, the thermal image capturing device 17 and the blower 20 are connected to the process computer 21 and are configured to be activated and stopped by signals from the process computer 21. The process computer 21 is connected to the tracking device 16 and transmits start and stop signals to the thermal image capturing device 17 and the blower 20 based on the tracking information of the slab input from the tracking device 16.

  In this embodiment, a thermal image of the upper surface of the slab 12 is taken. However, the lower surface of the slab 12 may be taken, or both the upper and lower surfaces may be taken. Although a commercially available thermography apparatus can be sufficiently applied as the thermal image capturing apparatus 17, the surface of the slab 12 in a red hot state is imaged so that the thermographic apparatus is not damaged by the radiant heat of the slab 12. Therefore, it is preferable to take measures against radiant heat such as providing a heat shield or installing in a cooling box.

  In the slab continuous casting machine 1 having this configuration, molten steel 11 is poured into a tundish 2 from a ladle (not shown), and a predetermined amount of molten steel 11 is retained in the tundish 2, and then the molten steel retained in the tundish 2. 11 is injected into the mold 5 through the immersion nozzle 4. The molten steel 11 injected into the mold 5 is cooled by the mold 5 to form a solidified shell 13 and is supported by a slab support roll provided below the mold 5 as a slab 12 having an unsolidified phase 14 therein. However, it is continuously pulled out below the mold 5 by the driving force of the pinch roll 8. While the slab 12 passes through the slab support roll, it is cooled with the secondary cooling water in the secondary cooling zone to increase the thickness of the solidified shell 13 and complete the solidification to the inside. Then, the casting length of the slab 12 is measured by the measure roll 15 and the tracking device 16, and the cutting control device 22 receiving the signal from the tracking device 16 sets a cutting position to obtain a slab 12a having a predetermined length. , Output the set signal to gas cutting. Thus, the solidified slab 12 is cut by the gas cutter 10 to become a slab 12a.

  During this casting, the tundish exchange in the continuous casting of the same steel type, the tundish exchange in the continuous casting of different steel types, or the continuous casting of the different steel types with the stop of drawing of the slab 12 without the tundish replacement, Furthermore, the injection of the molten steel 11 into the mold 5 is interrupted by replacing the immersion nozzle 4 during casting, and at the same time, the drawing of the slab 12 during casting is temporarily stopped, and after a few seconds to several minutes, a new tank is When the dish 2 is installed and the molten steel 11 is poured into the mold 5 and the slab 12 is withdrawn again, a step is formed in the slab portion corresponding to the position of the molten metal surface in the mold when the slab 12 is stopped. A pour-like seam (not shown) is formed. The seam moves to the downstream side in the casting direction as the slab 12 is pulled out.

  When the seam portion is formed on the slab 12, the tracking device 16 grasps the position of the seam portion based on a signal from the process computer 21 that detects the stoppage of the pinch roll 8 or a signal manually input by an operator. . Specifically, the slab length from the tracking device 16 to the joint portion is grasped based on the equipment specifications of the slab continuous casting machine 1. The tracking device 16 then slabs on the basis of the slab length measured by the measure roll 15 until the seam portion exits the range where the slab support roll is installed and is pulled out to the installation position of the thermal imaging device 17. 12 tracking is performed, and the information is transmitted to the cutting control device 22. The distance from the tracking device 16 to the seam portion at a certain time is subtracted from the distance to the seam portion determined based on the equipment specifications of the slab continuous casting machine 1 by subtracting the casting length from the resumption of drawing to the time point. Can be sought.

  When the seam portion reaches the photographing range of the thermal image capturing device 17, the seam portion is detected by the image processing device 18 from the thermal image captured by the thermal image capturing device 17. When the joint portion reaches a position directly below the thermal image capturing device 17, the image processing device 18 transmits to the tracking device 16 that the position of the joint portion is a position directly below the thermal image capturing device 17. The tracking device 16 to which this signal is input is compared with the position of the seam portion based on the slab length measured by the measure roll 15, and if there is a difference between the two, the tracking device 16 of the seam portion input from the image processing device 18 is detected. The tracking information stored in the tracking device 16 is corrected by setting the position to “positive”. Then, the corrected tracking information is transmitted to the cutting control device 22. The cutting control device 22 transmits a cutting command to the gas cutting machine 10 based on the corrected tracking information. Thereby, the slab 12 is cut | disconnected in the position away from the joint part by the predetermined position in the casting direction.

  At that time, several minutes before the joint portion of the slab 12 reaches the thermal image capturing device 17, specifically, when the joint portion passes near the final slab support roll, image processing is performed from the process computer 21. An “activation” signal is transmitted to the device 18 and the blower 20, and based on this signal, the thermal image photographing device 17 starts photographing, and the blower 20 is activated. If the position of the seam portion is corrected in the tracking information of the slab, the process computer 21 that receives the signal from the tracking device 16 transmits a signal for stopping the shooting and stopping the operation to the image processing device 18 and the blower 20. . With this signal, the thermal image capturing device 17 finishes capturing, and the blower 20 stops operation.

  Thus, according to the present invention, a thermal image of the surface of the slab during continuous casting is taken, and the seam portion of the slab 12 is detected based on the surface temperature profile in this thermal image. Therefore, the seam portion can be detected and the slab yield can be improved. In Patent Document 1, the slab surface temperature is measured by “point”, and misdetection of the seam portion occurs. However, in the present invention, the slab surface temperature is measured by “line” or “surface”. The seam portion can be detected. In addition, the normal step-poured seam portion may be difficult to detect visually, and in Patent Document 3, the seam portion is detected from the outer shape of the slab 12, and there is a high risk of misidentification of the seam portion. In this invention, since it determines from the difference in the surface temperature of a slab, a seam part can be detected correctly and reliably.

  When continuously casting extremely low carbon steel, low carbon steel and medium carbon steel while performing tundish replacement using the slab continuous casting machine shown in FIG. The slab during continuous casting was cut based on the information (Example of the present invention). The target cutting position is a position 300 mm away from the seam portion upstream in the casting direction.

  2 and 3 show examples in which a thermal image of the slab surface photographed by the thermal image photographing device is converted into digital data by the image processing device and displayed as a temperature profile of the slab. FIG. 2 is an example of a slab width direction temperature distribution in a normal casting region 2 m away from the seam portion downstream in the casting direction, and FIG. 3 is an example of a slab width direction temperature distribution of the seam portion. As shown in FIG. 3, the slab surface temperature of the seam is at most about 510 ° C., while the surface temperature of the normal casting region is 700 to 730 ° C. as shown in FIG. The difference was 190 to 220 ° C., and the seam portion was usually at a low temperature of 26% or more with respect to the casting zone, and the seam portion could be easily detected. 2 and 3 are examples of a slab slab having a slab width of 1350 mm.

  For comparison, a slab tracking was performed based only on the slab length measured by the measure roll, and a test was performed to cut the seam portion based on the tracking (comparative example). The target cutting position is the same as that of the present invention example, and is a position 300 mm away from the joint portion upstream in the casting direction.

  Then, after cutting, the slab including the seam is cooled to room temperature, the position of the seam is confirmed, a cutting setting position determined by the seam (position 300 mm away from the seam upstream in the casting direction) and the actual cutting position. And compared. When the tracking of the slab is accurate, the difference between the cutting setting position and the actual cutting position is small, and this difference becomes larger as the tracking of the slab becomes inaccurate. Table 1 shows a comparison of the results of the inventive examples and the comparative examples.

  As is clear from Table 1, in the example of the present invention, cutting was performed in the vicinity of the cutting setting position, and the difference between the cutting setting position and the actual cutting position was 20 mm at the maximum. Moreover, when the average value of 20 times of the absolute value of this difference was calculated | required, it was 10.5 mm. On the other hand, in the comparative example, a maximum difference of 94 mm was generated, and the average value of 20 times of the absolute value of this difference was 53.1 mm. Thus, it has been confirmed that by applying the present invention, the cutting accuracy of the seam portion is greatly improved.

DESCRIPTION OF SYMBOLS 1 Slab continuous casting machine 2 Tundish 3 Sliding nozzle 4 Immersion nozzle 5 Mold 6 Support roll 7 Guide roll 8 Pinch roll 9 Conveyance roll 10 Gas cutting machine 11 Molten steel 12 Cast slab 12a Slab 13 Solidified shell 14 Unsolidified phase 15 Major roll Reference Signs List 16 Tracking device 17 Thermal imaging device 18 Image processing device 19 Gas injection nozzle 20 Blower 21 Process computer 22 Cutting control device

Claims (2)

  When steel is continuously cast, it is formed when the injection of molten steel into the mold and the drawing of the slab are temporarily stopped during the continuous casting, and then the injection of molten steel into the mold and the drawing of the slab are resumed. A method for detecting a slab seam part for detecting a step-poured seam part, wherein a thermal image of a slab surface during continuous casting is taken, and the seam part is defined based on a surface temperature profile in the thermal image. A method for detecting a slab seam portion in continuous casting, wherein the detection is performed.   In the thermal image, when a band-like region is detected that has a surface temperature lower by 25% or more than the normal casting region and covers the entire width in the slab width direction, the belt-like region is detected as the seam portion. The detection method of the slab joint part in the continuous casting of Claim 1.

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