JP5915374B2 - Method for measuring surface temperature of continuous cast slab and continuous casting method using this method - Google Patents

Description

  The present invention relates to a method for measuring the temperature of a continuously cast slab and a continuous casting method using this method, and in particular, suppresses the influence of cooling water in a secondary cooling zone of a continuous casting machine, and increases the surface temperature of the slab for a long period of time. The present invention relates to a method that can be measured stably and with high accuracy.

  Continuous casting of steel is performed using a continuous casting machine. That is, the molten steel is cooled in the mold to form a solidified shell, the solidified shell is pulled out from the mold, cooled in the secondary cooling zone immediately below the mold by spraying cooling water, and finally solidified to the center.

  At that time, when bending stress is applied to the slab in the continuous casting machine, if the surface temperature of the slab is in the embrittlement temperature zone of steel, surface defects may occur in the slab. The section where bending stress is applied to the slab is included in the secondary cooling zone. For this reason, in order to prevent the occurrence of surface defects on the slab during continuous casting, the temperature of the slab is grasped in the secondary cooling zone, and the amount of cooling water is set so that the temperature of the slab becomes a temperature at which no surface defects occur. It is important to make adjustments accurately.

  The surface temperature of the slab varies depending on the composition and temperature of the molten steel during continuous casting, the casting speed, and the temperature, amount and distribution of the cooling water. Therefore, conventionally, the surface temperature of a slab has been measured using a non-contact type thermometer such as a radiation thermometer in a secondary cooling zone in a continuous casting machine (for example, Patent Document 1).

  However, when measuring the surface temperature of the slab continuously using a non-contact type thermometer in the secondary cooling zone, a large amount of spray cooling water or a gap between the roll and the slab is contained in the atmosphere. Disturbances such as drooping water that travels through the steam and steam generated when the cooling water hits the high-temperature slab are generated. Due to this disturbance, heat radiation from the surface of the slab is scattered, so that sufficient temperature measurement accuracy cannot be obtained.

  Scattering of thermal radiation occurs when an interface between moisture such as water droplets or steam and air exists in the optical path of thermal radiation to be detected by a thermometer. If the light path changes due to this scattering, the area and position of the surface area of the slab that is to be measured with a thermometer will change, or heat radiation from areas other than the measurement area will be detected, resulting in measurement errors. .

  As a method for avoiding such disturbance, in Patent Document 2, in a hot rolling process in which a large amount of cooling water is used, a purge water is sprayed from a nozzle toward the lower surface of the steel plate, and a radiation thermometer, a slab surface, A method of measuring the surface temperature of the slab by forming a water column in the vertical direction and detecting thermal radiation emitted from the surface of the slab through the water column has been proposed.

  However, unlike the hot rolling process, in the continuous casting machine that performs the continuous casting process, there is a portion in which the slab is perpendicular to the casting direction. Therefore, when applying the method described in Patent Document 2, Must be level. However, the water column cannot be made completely horizontal due to the influence of gravity. Also, by increasing the amount of water to be injected and the injection pressure, it is possible to secure the optical path of the heat radiation light by making the water column almost horizontal, but in this case the slab is excessively cooled by the water column. Since the temperature of the measurement site is lowered, the reliability and accuracy of the measured temperature are not sufficient.

  As a method not using a water column, in Patent Document 3, a purge air is injected from a nozzle toward the surface of a water-cooled steel material having a surface temperature of 180 ° C. to 350 ° C. A method has been proposed in which an air column is formed between the two and the thermal radiation emitted from the slab through the air column is detected.

  However, as will be described later, the present inventors have examined that, in the method described in Patent Document 3, the stability of temperature measurement and the slab are determined depending on the size of the portion of the surface of the slab surface that is in contact with the air column during water cooling. It has been found that the cooling stability of the water changes greatly. This is because the stability of the temperature measurement is greatly affected by the above disturbance, and the cooling of the slab is hindered if the portion of the surface of the slab surface that is in water cooling contact with the air column is too large.

JP 2009-50913 A Japanese Patent No. 4151022 JP 2011-53047 A

  The present invention has been made in view of the above problems, and the surface temperature of a slab that is being cooled in a secondary cooling zone in a continuous casting machine using a radiation thermometer capable of forming an air column for a long period of time. It is an object of the present invention to provide a method capable of measuring stably over a long period of time and a continuous casting method using this temperature measuring method. The following two problems must be solved.

First problem: Measurement temperature error due to scattering of thermal radiation due to disturbances such as spray cooling water, dripping water, and steam, which exist between the surface of the slab to be measured and the radiation thermometer To suppress the occurrence of.
Second problem: To measure the surface temperature of the slab without inhibiting the cooling of the slab in the continuous casting machine. That is, it is possible to measure the surface temperature of the slab without reducing or stopping the amount of spray cooling water and without modifying the cooling device.

  As a result of conducting a preliminary test using an apparatus simulating the inside of an actual continuous casting machine, the inventors have determined that the size of the air column formed by the purge air at a portion in contact with the slab surface is a predetermined size. Then, it has been found that a method for measuring the surface temperature of a slab that solves the above two problems can be realized. The preliminary test will be described later.

  The present invention has been made on the basis of this finding, and the gist thereof is in the method for measuring the surface temperature of the slab shown in the following (1) and (2) and the continuous casting method shown in (3).

(1) A method of measuring a surface temperature with a surface temperature measuring device in a secondary cooling zone in which the slab is cooled with cooling water during continuous casting of the slab, wherein the surface temperature measuring device includes a radiation thermometer and And a nozzle for injecting purge air, and by injecting purge air from the nozzle of the surface temperature measuring device toward the surface of the slab, the radiation thermometer and the surface of the slab An air column is formed therebetween, and when the radiation thermometer detects thermal radiation from the surface of the slab through the air column and measures the surface temperature of the slab, the light receiving axis of the radiation thermometer is: The radiation thermometer is disposed so as to pass through the air column formed by the purge air injected from the nozzle from the radiation thermometer to the surface of the slab, and the surface temperature measuring device Nozzle diameter 10-18m And then, the measurement method of the surface temperature of the slab, characterized in that the 30~40mm the diameter at a portion in contact with the slab surface of the air column.

(2) The surface temperature of the slab according to (1), wherein the flow rate of the purge air is determined according to a distance between the radiation thermometer and a portion at which the temperature of the slab is measured. Measuring method.

(3) Continuous slabs using a continuous casting machine having a mold, a bending part for bending a slab cast in the vertical direction, and a horizontal part for correcting the curved slab into a flat plate and transporting it horizontally. A casting method, wherein the surface temperature of the slab is measured by the method for measuring the surface temperature of a slab according to (1) or (2) at least at one point in a secondary cooling zone from the mold to the horizontal part. A continuous casting method of a slab characterized by measuring

  According to the method for measuring the surface temperature of the slab of the present invention, the surface temperature of the slab being cooled in the secondary cooling zone in the continuous casting machine can be stably measured with high accuracy over a long period of time. In addition, according to the continuous casting method of the present invention, the casting conditions can be controlled based on the surface temperature of the slab measured stably and with high accuracy, so that a slab excellent in quality can be continuously cast.

It is the schematic of the apparatus used for the preliminary test of examination of the injection conditions of purge air. It is a figure which shows the relationship between the aperture diameter of the nozzle which injects air, and the average flow velocity of the air injected from a nozzle for every flow volume of air. It is a figure which shows the relationship between the flow volume of purge air, and the injection diameter of an air column, The figure (a) is the case where the aperture of the nozzle which injects purge air is 10 mm, The figure (b) is 18 mm FIG. It is an enlarged view of the part by which the surface temperature measuring apparatus in a continuous casting machine is arrange | positioned. It is a figure which shows the relationship between the casting time of the example of this invention, and the measured surface temperature. It is a figure which shows the relationship between the casting time of a comparative example, and the measured surface temperature.

  The contents of preliminary tests for completing the present invention and the modes for carrying out the present invention will be described below.

1. Preliminary test 1-1. Apparatus Used for Preliminary Test FIG. 1 is a schematic view of an apparatus used for a preliminary test for examining the purge air injection conditions. This apparatus simulates a secondary cooling zone in a continuous casting machine, and includes a transparent acrylic plate 11 that assumes a slab, and two spray nozzles 12 that spray spray water 13 toward the acrylic plate 11. And a surface temperature measuring device 14 disposed between the spray nozzles 12. The surface temperature measuring device 14 includes a radiation thermometer having a light receiving portion at the tip, and forms an air column between the surface temperature measuring device 14 and the surface of the acrylic plate 11 by jetting air 15 from the tip. it can. The distance D1 between the two spray nozzles 12 was 457 mm, and the distance D2 from the spray nozzle 12 to the acrylic plate 11 was 160 mm. The surface temperature measuring device 14 can move in the direction of arrow A perpendicular to the acrylic plate 11, and the distance L between the tip of the nozzle of the surface temperature measuring device 14 and the acrylic plate 11 can be adjusted.

  In addition, a video camera 16 is disposed on the opposite side of the surface of the acrylic plate 11 from which the spray water 13 and air 15 are jetted so as to face the acrylic plate 11, and the spray water 13 for the acrylic plate 11 that looks like a slab. And the injection situation of air 15 can be checked.

1-2. FIG. 2 is a diagram showing the relationship between the diameter of the nozzle for injecting air and the average flow velocity of the air injected from the nozzle for each flow rate of air. As can be seen from the figure, the larger the air flow rate and the smaller the nozzle diameter, the greater the average flow velocity of the injected air.

  Further, the size of the air column formed by the purge air at the portion in contact with the slab surface (hereinafter, the diameter of the air column at the portion where the air column contacts the object is also referred to as “injection diameter”) is the radiation temperature. When the temperature is smaller than the visual field in which the temperature measurement is performed (hereinafter also referred to as “measurement visual field”), the measured temperature is affected by the temperature of the tip of the nozzle that injects air. Therefore, the diameter of the nozzle for injecting the purge air needs to be larger than the measurement field of view of the radiation thermometer.

  Considering the above, in the preliminary test, the diameters of the nozzles for injecting the air at the tip of the surface temperature measuring device were 10 mm and 18 mm.

1-3. First preliminary test 1-3-1. Test conditions Using the apparatus shown in FIG. 1, light that is regarded as thermal radiation is emitted from a light source (not shown) through the acrylic plate 11 toward the surface temperature measuring device 14, and air is ejected by the surface temperature measuring device 14. While detecting this light. The test was conducted in the case where there was spray water 13, dripping water, and steam applied to the acrylic plate 11 as a disturbance, and the relationship between the air injection conditions and the light detection status was investigated. The spray water 13 and the dripping water were discharged to the acrylic plate 11 using the spray nozzle 12 used in the actual machine of the continuous casting machine, and the steam was discharged from below the surface temperature measuring device 14.

Diameter of the nozzle for injecting purge air is 10mm and 18 mm, the air flow rate was set to ^{12Nm 3 / h, 18Nm 3 /} h, 24Nm 3 / h and 30 Nm ³ / h, from the tip of the surface temperature measuring device 14 to the acrylic plate 11 The distance was set to 60 mm, 80 mm, 100 mm, and 160 mm. Furthermore, the distance from the front-end | tip of the surface temperature measuring apparatus 14 to the acrylic board 11 was 200 mm about the case where the aperture of a nozzle is 18 mm.

1-3-2. Test results FIG. 3 is a diagram showing the relationship between the flow rate of purge air and the injection diameter. FIG. 3A shows the case where the nozzle diameter for injecting purge air is 10 mm, FIG. It is a figure in the case of 18 mm. As a result of the preliminary test, when the nozzle diameter for injecting the purge air is 10 mm and 18 mm, as shown in the figure, the larger the air flow rate, the more the tip of the surface temperature measuring device 14. It was found that the smaller the distance from to the acrylic plate 11, the larger the spray diameter.

  Further, as a result of evaluating the stability of detection of light from the light source by the surface temperature measuring device 14, if the injection diameter is 30 mm or more, light scattering by the water film on the acrylic plate 11 is suppressed, and light is stably emitted. It was found that can be detected. When the spray diameter is less than 30 mm, a water film may be generated between the light source and the surface temperature measuring device 14, and light could not be detected stably. Further, it was found that in the range of the air flow rate applied in this test, the measurement visual field of the radiation thermometer can be secured if the distance from the tip of the surface temperature measuring device 14 to the acrylic plate 11 is 160 mm or less. The injection diameter was also investigated in detail in the second preliminary test described later.

  Furthermore, it was found that by optimizing the distance from the tip of the surface temperature measuring device 14 to the acrylic plate 11, light larger than the measurement visual field of the radiation thermometer can be detected, and light can be detected stably.

  Further, by adjusting the flow rate of the air 15 and the distance from the tip of the surface temperature measuring device 14 to the acrylic plate 11, the optical path can be secured without blocking the spray water 13 even if the surface temperature measuring device 14 is installed. I found it possible.

  In the apparatus shown in FIG. 1, the flow rate of the air 15 is optimized even when the spray water 13 is stopped and the spray water 13 does not affect the temperature measurement between the surface temperature measuring device 14 and the acrylic plate 11. By reducing the distance from the tip of the surface temperature measuring device 14 to the acrylic plate 11 to a predetermined value, disturbance due to dripping water or steam traveling on the surface of the acrylic plate 11 is reduced, and light from the light source is stably detected. I knew it was possible.

  Furthermore, in order to stably detect light from the light source, it is ideal that the angle formed by the light receiving axis of the surface temperature measuring device 14 and the surface of the acrylic plate 11 is 90 °, and the inclination from 90 °. It was found that the light from the light source can be detected stably if is within 15 °.

1-4. Second preliminary test 1-4-1. Test conditions Using the apparatus shown in FIG. 1, the relationship between the jetting diameter of purge air and the stability of detection of light from the light source was investigated. The diameter of the nozzle for injecting the purge air of the surface temperature measuring device, the distance between the acrylic plate and the nozzle tip, the flow rate of the purge air, and the injection diameter at the portion of the purge air in contact with the acrylic plate surface are described later. (See Table 1 below). No. 1-6, the nozzle diameter is 10 mm, In 7-12, it was 18 mm, and by changing the distance between the acrylic plate and the tip of the nozzle, and the air flow rate, the jet diameter of the portion of the purge air in contact with the acrylic plate surface was changed.

1-4-2. Test results Table 1 also shows the results of investigations on whether or not stable detection of light from a light source is possible, along with test conditions. As can be seen from the table, stable detection of light from the light source is possible only when the jet diameter is 30 to 40 mm, and impossible when the jet diameter is 25 mm or less. Although not shown in the table, when the spray diameter is larger than 40 mm, the light from the light source can be detected stably, but the area of the portion where the spray water hits is a slab. It was narrowed to such an extent as to inhibit the cooling of the.

2. FIG. 4 is an enlarged view of a portion where a surface temperature measuring device is arranged in a continuous casting machine. The surface temperature measuring device 30 includes a radiation thermometer 31 that faces the slab 21, and a nozzle 32 that injects purge air toward the surface of the slab 21.

  The radiation thermometer 31 can detect the thermal radiation emitted from the surface of the slab 21 and measure the surface temperature of the slab 21. The radiation thermometer 31 is disposed so that the light receiving shaft 31 c passes through an air column formed by purge air ejected from the nozzle 32.

  The radiation thermometer 31 is housed in the temperature measuring head 31a, a light receiving portion that is received in the temperature measuring head 31a, receives heat radiation light from the slab 21, and transmits the received heat radiation light to a control panel (not shown). An optical fiber 31b is provided. The control panel can photoelectrically convert the heat radiation light transmitted by the optical fiber 31b and output a current corresponding to the light amount. The current output from the control panel is subjected to current-voltage conversion and AD conversion, and an operation for conversion into temperature is performed. Through the above process, the surface temperature of the slab 21 can be measured by receiving the heat radiation light with the radiation thermometer 31.

  The nozzle 32 of the surface temperature measuring device 30 is connected to the tip of the temperature measuring head 31a, and can introduce the purge air toward the surface of the slab 21 by introducing air from the outside.

  The surface temperature measuring device 30 is disposed between the adjacent slab support rolls 22 so as to be able to detect the heat radiation emitted from the surface of the slab 31. The arrangement of the surface temperature measuring device 30 is preferably as the angle formed between the light receiving shaft 31c of the radiation thermometer 31 and the temperature measured portion of the slab 21 is closer to 90 °. However, as a result of the preliminary test described above, it has been found that the temperature can be measured with sufficient stability if the angle from 90 ° is within 15 °. FIG. 4 shows a case where the inclination from 90 ° between the light receiving shaft 31c of the radiation thermometer 31 and the temperature-measured portion of the slab 21 is 15 °.

  Further, in order to suppress the inhibition of cooling of the slab 21 due to the injection of purge air onto the slab 21, it is preferable that the purge air injection diameter is small. The flow rate of purge air is set according to the layout of the slab support roll 22 in the continuous casting machine and the distance L between the slab 21 and the surface temperature measuring device 30, and the jet diameter of the purge air is set to 30 to 40 mm. To do. The distance L is the shortest distance between the tip of the nozzle 31 and the cast piece 21.

  The surface temperature measuring device 30 adjusts the angle so that (1) spray water does not exist between the surface temperature measuring device and the slab, and (2) is sprayed from the tip of the surface temperature measuring device. It is possible to prevent the spray air and spray water injection ranges from being the same, and (3) the state of contact with the slab of spray water does not change due to the installation of the surface temperature measuring device. Therefore, it is possible to measure the surface temperature of the slab without hindering the cooling of the slab, that is, without reducing or stopping the amount of spray cooling water and without modifying the secondary cooling device. The distance L between the slab 21 and the surface temperature measuring device 30 is preferably as short as possible so long as the purge air does not affect the spray water.

  The method for measuring the surface temperature of a slab according to the present invention is applicable to a vertical bending type continuous casting machine. The vertical bending type continuous casting machine includes a casting mold, a top zone immediately below the casting mold, a bending part, and a horizontal part from the casting mold toward the downstream side in the casting direction. The bending portion is composed of a bending unit and a plurality of guide roll segments. A secondary cooling zone is provided in a section from immediately below the mold to the final guide roll segment. In the bending portion, the slab cast in the vertical direction by the mold is curved, and in the horizontal portion, the curved slab is corrected into a flat plate and conveyed horizontally.

  By applying the method for measuring the surface temperature of the slab of the present invention in any part of the secondary cooling zone of the vertical bending type continuous casting machine, the surface between the surface of the slab and the surface temperature measuring device is applied. The surface temperature of the slab can be stably measured with high accuracy over a long period of time while suppressing the influence of scattering due to moisture in the optical path of the heat radiation light. By adjusting the amount of cooling water in the secondary cooling zone and other casting conditions based on the measured temperature, the occurrence of surface defects on the slab can be suppressed, and a slab excellent in quality can be continuously cast. .

The flow rate of the purge air when measuring the surface temperature of the slab is preferably 30 Nm ³ / h or less because an excessive flow has a great influence on spray water spraying and may hinder cooling of the slab. .

  In order to confirm the effect of the method of measuring the surface temperature of the slab of the present invention and the continuous casting method of the slab of the present invention to which the method is applied, the following actual machine test was performed.

1. Test conditions The above-described vertical bending type continuous casting machine was used as the continuous casting equipment, and the surface temperature measuring apparatus shown in FIG. 4 was used. The measurement position of the surface temperature of the slab by the surface temperature measuring device was between the bending unit on the lower surface side of the slab and the guide roll segment adjacent thereto. The measurement objects were three places in the width direction of the slab (center of the slab width direction, and positions 20 mm and 40 mm from the end).

  This measurement position has the largest amount of spray water from the spray and the amount of dripping water in the secondary cooling zone, and the amount of steam generated due to the high surface temperature of the slab. This is a part where the measurement condition of the surface temperature of the slab is severe due to the influence of the slab, and is also a part where the cooling strength of the slab is high.

  Table 1 shows the diameter of the nozzle for injecting the purge air of the surface temperature measuring device, the distance between the slab and the nozzle tip, the flow rate of the purge air, and the jet diameter at the portion of the purge air in contact with the slab surface. It was street.

  No. 3-5, 7-10, and 12 are examples of the present invention that satisfy the provisions of the present invention. No. 1, 2, 6, and 11 are comparative examples in which the jetting diameter of the purge air did not satisfy the regulations of the present invention.

2. Test results Table 1 also shows the results of investigating the stability of temperature measurement along with the test conditions. As can be seen from the table, the surface temperature of the slab can be measured stably only when the injection diameter is 30 to 40 mm, and the surface temperature of the slab cannot be measured stably when the injection diameter is 25 mm or less. It was.

  5 is a diagram showing the relationship between the casting time and the measured surface temperature of the inventive example (No. 10). The casting time means the elapsed time from the case where continuous casting is started. From the figure, it can be seen that according to the method for measuring the surface temperature of the slab of the present invention, the surface temperature of the slab could be measured stably.

  6 is a graph showing the relationship between the casting time of the comparative example (No. 11) and the measured surface temperature. From this figure, it can be seen that in this case, since the spray diameter was as small as 20 mm, the surface temperature of the slab was greatly affected by the influence of cooling water, and the surface temperature of the slab could not be measured accurately and stably. .

  According to the method for measuring the surface temperature of the slab of the present invention, the surface temperature of the slab being cooled in the secondary cooling zone in the continuous casting machine can be stably measured with high accuracy over a long period of time. In addition, according to the continuous casting method of the present invention, the casting conditions can be controlled based on the surface temperature of the slab measured stably and with high accuracy, so that a slab excellent in quality can be continuously cast.

11: Acrylic plate, 12: Spray nozzle, 13: Spray water,
14: Surface temperature measuring device, 15: Air, 16: Camera, 21: Slab,
22: slab support roll, 30: surface temperature measuring device, 31: radiation thermometer,
31a: Temperature measuring head, 31b: Optical fiber, 31c: Light receiving axis, 32: Nozzle

Claims (3)

In the secondary cooling zone in which the slab is cooled with cooling water during continuous casting of the slab, the surface temperature is measured by a surface temperature measuring device,
The surface temperature measuring device includes a radiation thermometer and a nozzle for injecting purge air,
Purge air is jetted from the nozzle of the surface temperature measuring device toward the surface of the slab to form an air column between the radiation thermometer and the surface of the slab, and the casting is passed through the air column. When the thermal radiation light from the surface of the piece is detected by the radiation thermometer and the surface temperature of the slab is measured,
The radiation thermometer is arranged so that the light receiving axis of the radiation thermometer passes through the air column formed by the purge air injected from the nozzle from the radiation thermometer to the surface of the slab. And
A method for measuring the surface temperature of a slab, wherein the nozzle of the surface temperature measuring device has a diameter of 10 to 18 mm and a diameter of a portion of the air column in contact with the slab surface of 30 to 40 mm.   The method for measuring the surface temperature of a slab according to claim 1, wherein the flow rate of the purge air is determined in accordance with a distance between the radiation thermometer and a portion at which the temperature of the slab is measured. In a continuous casting method of a slab using a continuous casting machine having a mold, a bending part for bending the slab cast in the vertical direction, and a horizontal part for correcting the curved slab into a flat plate and transporting it horizontally. There,
The surface temperature of the slab is measured by the method for measuring the surface temperature of the slab according to claim 1 or 2, in at least one place of a secondary cooling zone from the mold to the horizontal portion,
A method for continuously casting a slab comprising adjusting the amount of cooling water in the secondary cooling zone based on the measured temperature.

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