JP4842195B2 - Slab surface temperature measuring device and slab surface temperature measuring method - Google Patents

Description

  The present invention relates to a slab surface temperature measuring apparatus and a slab surface temperature measuring method capable of stably measuring a slab surface temperature for a long time even under a severe atmosphere.

  In continuous casting of slabs, in order to cast high quality slabs with good surface and internal quality with high productivity, it is necessary to prevent the occurrence of operational troubles such as breakout. There are the following methods for preventing breakout. When the solidified shell is completely restrained on the surface of the copper plate in the mold, the temperature of the solidified shell is lowered to the Curie point. Thus, by detecting that the temperature of the solidified shell has dropped to the Curie point, the solidified shell is restrained and the drawing of the slab is temporarily stopped. Specifically, it is possible to detect whether or not the solidified shell has lowered to the Curie point by applying a DC magnetic field from the outside to the slab in the mold to magnetize the solidified shell and detecting changes in the magnetic field lines. (See, for example, Patent Document 1)

Japanese Patent Publication No. 56-7456 (Claims)

  By the way, when the molten steel flow injected into the mold is biased and the remelting of the solidified shell becomes significant when the molten steel collides with the solidified shell, the local solidified shell thickness becomes insufficient, resulting in perforation. It may cause operational troubles called sex breakout. Such operational troubles cannot be sufficiently prevented by the method for detecting that the solidified shell has been lowered to the Curie point as described above. That is, the perforated breakout can be avoided if the temperature of the slab surface can be accurately measured to control the slab surface to an appropriate temperature. Therefore, a method for measuring the temperature of the slab surface will be described next.

  First, there is a method of measuring the temperature of the slab surface with a radiation thermometer. However, when measuring with a radiation thermometer, there are restrictions depending on the measurement site. Specifically, there is no water vapor or water in the atmosphere between the measurement site and the radiation thermometer, and if there is water vapor or water, the water vapor or water on the front of the radiation thermometer should be It is necessary to measure while blowing away with high-pressure air.

  When the above-described radiation thermometer is used to prevent perforated breakout, it is necessary to control the surface temperature of the slab immediately below the mold. In other words, by placing a radiation thermometer directly under the mold and measuring the slab surface temperature directly under the mold, it is possible to detect that the slab surface temperature rises to the extent that a perforated breakout occurs. As a result, it is possible to prevent the occurrence of perforated breakout. However, since the slab is cooled with a large amount of water immediately below the mold, a harsh atmosphere in which a large amount of water, water vapor, powder, scale, etc. scatters between the radiation thermometer and the surface of the slab. For this reason, even if high-pressure air is used, it is extremely difficult to accurately measure the slab surface temperature with a radiation thermometer.

  Further, a radiation thermometer using a short wavelength region having a wavelength of 1 μm or less, which is considered to be relatively strong in the severe atmosphere as described above, has been devised. However, even if this radiation thermometer is used, measurement data vary greatly and it is difficult to perform stable measurement.

  Another method for measuring the slab surface temperature is to embed a large number of thermocouples in the mold copper plate and monitor the temperature change of the slab surface with the thermocouples, thereby making a perforated breakout. It is conceivable to prevent this in advance. However, with this method, the change in the slab surface temperature can be measured with high sensitivity if it is close to the level of the molten metal surface in the mold, but an air gap is formed between the slab surface and the copper plate in the mold below the mold. It is difficult to accurately measure the slab surface temperature.

  The present invention has been made in consideration of the above-described circumstances, and the purpose thereof is to stably measure the slab surface temperature for a long time even in a harsh atmosphere where a large amount of water, water vapor or the like is present. An object of the present invention is to provide a slab surface temperature measuring device and a slab surface temperature measuring method.

In order to solve the above problems, a slab surface temperature measuring device according to the present invention includes a magnetic field excitation means for applying an alternating magnetic field substantially perpendicular to the surface of a slab,
Magnetic field detection means for detecting an alternating magnetic field to detect lines of magnetic force changed by the surface temperature of the slab,
Surface temperature deriving means for deriving the surface temperature of the slab from the induced electromotive force obtained by detecting an alternating magnetic field by the magnetic field detecting means and predetermined correspondence data;
Comprising
Said correspondence data is Ri Ah with data representing the correspondence between the predetermined Curie point below the slab surface temperature and the induced electromotive force,
The slab is a slab obtained by continuous casting drawn from below the mold using a mold,
The magnetic field excitation means and the magnetic field detection means are disposed on the slab short side below the cooling zone for cooling the slab short side directly under the mold,
The slab surface temperature below the predetermined Curie point is a temperature range from the Curie point to the Curie point minus 100 ° C.
The lower limit of the slab surface temperature in the correspondence data is preferably about the Curie point minus 100 ° C. The reason is that the relative permeability of steel changes abruptly from about 1 to about 200 at the Curie point.

  Further, in the slab surface temperature measuring apparatus according to the present invention, the correspondence relationship data may be a calibration formula that expresses the correspondence relationship between the slab surface temperature and the induced electromotive force by a mathematical expression.

  In the slab surface temperature measuring device according to the present invention, the magnetic field excitation means has a solenoid-like excitation coil, and the magnetic field detection means has a solenoid-like detection coil, and the detection coil Is preferably arranged away from the exciting coil with respect to the surface of the slab. Thereby, even when the slab moves in the applied magnetic field, the influence of the induced magnetic field due to the movement of the slab can be reduced, and the slab surface temperature can be measured more accurately.

  Further, in the slab surface temperature measuring apparatus according to the present invention, the slab is a slab obtained by continuous casting using a mold and drawn from below the mold, and the magnetic field excitation means and the magnetic field detection means are directly under the mold. It is also possible to arrange on the short side of the slab below the cooling zone for cooling the short side of the slab. This allows the slab surface temperature to be temporarily cooled below the Curie point in the cooling zone that cools the slab short side, and immediately after that, the surface temperature of the part where the slab surface temperature rises due to recuperation can be measured. it can.

  Moreover, in the slab surface temperature measuring device according to the present invention, it is preferable that the applied frequency of the magnetic field excited by the magnetic field excitation means is 0.5 Hz or more and 20 Hz or less.

The method for measuring the slab surface temperature according to the present invention applies an alternating magnetic field substantially perpendicularly to the surface of the slab by a magnetic field excitation means, and detects a magnetic field line that changes due to the surface temperature of the slab. An AC magnetic field is detected by the detection means,
Deriving the surface temperature of the slab from induced electromotive force obtained by detecting an alternating magnetic field with the magnetic field detection means and predetermined correspondence data;
Said correspondence data is Ri Ah with data representing the correspondence between the predetermined Curie point below the slab surface temperature and the induced electromotive force,
The slab is a slab obtained by continuous casting drawn from below the mold using a mold,
The magnetic field excitation means and the magnetic field detection means are disposed on the slab short side below the cooling zone for cooling the slab short side directly under the mold,
The slab surface temperature below the predetermined Curie point is a temperature range from the Curie point to the Curie point minus 100 ° C.

  As described above, according to the present invention, a slab surface temperature measuring device and a slab surface capable of stably measuring a slab surface temperature for a long time even in a harsh atmosphere where a large amount of water, water vapor, or the like exists. A method for measuring temperature can be provided.

Embodiments of the present invention will be described below with reference to the drawings.
In the present embodiment, an apparatus and a method for measuring the surface temperature of a slab immediately below a mold when a slab is drawn from below using a mold having a rectangular parallelepiped shape and continuously cast will be described.

  Below the long side of the mold, the slab is supported by a large number of rolls up to the position where the slab drawn from directly below the mold is finally solidified. The slab is only supported by several rolls provided. Therefore, the long side of the slab can be cooled by placing a cooling nozzle tip between the rolls to the solidification completion position, but on the short side, the surface temperature is lowered within the range of the roll directly under the mold. It is necessary to secure a solidified shell thickness that can withstand the molten steel head. Therefore, the short side of the slab immediately below the mold is strongly cooled with water or the like, whereby the slab surface has a temperature pattern as schematically shown in FIG. What should be noted in FIG. 1 is that the slab surface temperature once decreases to the Curie point Tc or less by strong cooling from the short side of the slab, and then rises by recuperation. The Curie point is a magnetic transformation point, and steel has the property that the relative permeability rapidly changes from about 1 to about 200 at the Curie point. In the present embodiment, the slab surface temperature is measured using a temperature sensor utilizing this property.

  FIG. 2 (A) is a schematic diagram for explaining the basic principle of measuring the slab surface temperature, and FIG. 2 (B) shows in detail a slab surface temperature measuring device according to the embodiment of the present invention. FIG.

  As shown in FIG. 2 (A), the basic principle of measuring the slab surface temperature is that when a vertical magnetic field is applied to the surface of the slab 1 by the exciting coil 2, the line of magnetic force changes depending on the surface temperature of the slab 1, and Is detected by the detection coil 3, and the surface temperature of the slab 1 is measured by using a calibration formula of the induced electromotive force obtained by this detection, the predetermined slab surface temperature and the induced electromotive force. is there.

  More specifically, as shown in FIG. 2A, the main configuration of the slab surface temperature measuring device according to the present embodiment is a solenoid for applying an alternating magnetic field to the surface of the slab 1. The slab surface temperature is calculated using a magnetic excitation coil 2, a solenoid-like detection coil 3 for detecting a change in magnetic field lines, and a calibration equation indicating a relationship between a predetermined slab surface temperature and an induced electromotive force. And calculating means (not shown). The detection coil 3 is arranged behind the excitation coil 2, that is, away from the excitation coil 2 with respect to the surface of the slab 1. The reason is that if the detection coil is arranged close to the slab 1, the change of the magnetic field lines cannot be detected accurately due to the influence of the induction magnetic field caused by the slab 1 moving in the applied magnetic field at the casting speed. .

  As shown in FIG. 2 (B), the exciting coil 2 is obtained by winding a polyester-coated copper wire 5 having an outer diameter of 1 mm around a glass epoxy pipe 4 having an outer diameter of 30 mm 500 times. The detection coil 3 is obtained by winding a polyester-coated copper wire 6 having an outer diameter of 0.3 mm around the glass epoxy pipe 4 40 times. The coil set of the excitation coil 2 and the detection coil 3 is housed in a stainless steel cylindrical case (not shown) as a sensor, and the inside of the cylindrical case is forcibly cooled with dry air.

  A constant current amplifier 7 is connected to the exciting coil 2 by wiring, and an oscillator 8 is connected to the constant current amplifier 7. A signal processor 9 is connected to the detection coil 3 by wiring. The signal processor 9 is composed of an operational amplifier, a resistor, a capacitor, and the like, and has a voltage amplification and filter processing function such as a low-pass filter and a band-pass filter. A lock-in amplifier 10 is connected to the signal processor 9. The lock-in amplifier 10 is an analog device that takes a 1.5 Hz signal from the constant current amplifier 7 as a reference signal and outputs a voltage having the same frequency, and can detect a phase difference from the reference signal.

  The signal processor 9 and the lock-in amplifier 10 can be replaced with a personal computer. In that case, the signal detected by the detection coil 3 may be taken into a personal computer through an AD converter, and the functions of the signal processor 9 and the lock-in amplifier 10 may be realized by a software program.

  The measuring device is fixed to the short side of the slab below the cooling zone that strongly cools the short side of the slab 1 immediately below the mold. The reason why the slab 1 is fixed below the cooling zone is that the slab 1 is once cooled to a temperature below the Curie point in the cooling zone immediately below the mold, and immediately after that, the slab surface temperature rises due to reheating. It is for measuring the surface temperature of this.

  In this measuring apparatus, the excitation coil 2 is alternated by generating an AC signal of 1.5 Hz by the oscillator 8, amplifying the signal to an AC current having a constant magnitude by the constant current amplifier 7 and energizing the excitation coil 2. Magnetic flux φ is excited on the slab 1. That is, an alternating magnetic field is applied substantially perpendicularly to the surface on the short side of the slab 1 by the exciting coil 2. When the surface temperature of the slab 1 is equal to or higher than the Curie point, as shown by the broken line in FIG. When the surface of the slab 1 is magnetized, the magnetic field lines change significantly due to the concentration of the magnetic field at the site as shown by the solid line. This change in magnetic field lines is determined by the surface temperature of the slab 1, that is, the magnetic permeability of the surface of the slab 1. Therefore, the change in the magnetic field lines is detected by the detection coil 3.

  The detection of the change in the lines of magnetic force by the detection coil 3 will be described in detail. An AC voltage of N × dφc / dt (N: the number of turns of the detection coil, φc: the number of flux linkages of the detection coil, t: time) is induced in the detection coil 3. The AC voltage is subjected to noise removal through a 5 Hz low-pass filter by the signal processor 9 and processed by the lock-in amplifier 10 to detect a voltage value of a frequency component of 1.5 Hz. That is, when the distribution of the alternating magnetic flux φ changes depending on the surface temperature of the slab 1, the interlinkage magnetic flux number φc of the detection coil 3 changes, so that the alternating voltage induced in the detection coil 3 changes. To detect. Thus, the surface temperature of the slab 1 is calculated by the calculation means from the induced electromotive force obtained by detecting the change of the magnetic field lines by the detection coil 3 and the calibration equation. In this way, the surface temperature of the slab 1 can be measured.

  As described in the basic principle, in order to measure the slab surface temperature with the measuring device, a calibration formula showing the relationship between the slab surface temperature and the induced electromotive force (that is, the voltage detected by the detection coil 3). Must be determined in advance. Therefore, an experiment for deriving an example of the calibration equation was performed, and the experiment and results will be described below.

FIG. 3 is a diagram showing the relationship between the slab temperature (slab surface temperature) and the voltage (voltage detected by the detection coil 3). FIG. 4 is a diagram showing the relationship between the voltage and the slab surface temperature in the temperature region from 700 ° C. to the Curie point Tc shown in FIG. This relational expression, that is, the calibration expression indicating the relation between the voltage and the slab surface temperature is as shown in the following expression (1).
Note that x is a value obtained by subtracting 6.25 V from the voltage Z1 detected by the detection coil 3, y is a slab surface temperature (° C.), and R is a correlation coefficient.

y = -20665x ³ + 8752.8x ² -1390.8x + 785.83 (1)
R ² = 0.9967

  In the experiment, the slab sample was heated to about 1200 ° C. in a heating furnace, and the measuring device shown in FIG. 2B was arranged so as to apply a vertical magnetic field to the surface of the heated slab sample. The glass epoxy pipe 4 and the slab sample surface were fixed at a position where the distance was 30 mm. In addition, a thermocouple was set 3 mm from the slab sample surface, and the temperature of the slab sample was measured. The result is shown in FIG.

  As shown in FIG. 3, the voltage detected by the detection coil 3 is substantially constant on the high temperature side, but it has been confirmed that the voltage changes suddenly at the Curie point Tc. Further, for the temperature region in which the voltage changes rapidly, the relationship between temperature and voltage can be obtained, for example, by performing polynomial approximation as shown in FIG. 4 to obtain a relational expression (calibration expression) like the above expression (1). . This indicates that the measuring apparatus according to the present embodiment can detect a change in magnetic characteristics due to a change in permeability in the vicinity of the Curie point with high sensitivity. For example, in the temperature range from the Curie point to the Curie point minus 100 ° C. It means that it can be used as a thermometer on one surface.

  In addition, the frequency applied from the oscillator 8 and applied to the exciting coil 2 is preferably 0.5 Hz or more and 20 Hz or less. This is because if the frequency is lower than 0.5 Hz, a time constant for phase detection of a signal detected from the detection coil 3 is required for one minute or more, and the response speed of the measuring apparatus becomes slow. On the other hand, if the frequency is higher than 20 Hz, the skin depth, which is the depth at which the magnetic field penetrates, becomes thinner, and the magnetic field is more concentrated on the surface of the slab. As shown in FIG. 5, even if the relative permeability is about 200 up to 20 Hz, the skin depth can be secured about 10 mm (about 0.01 m). This means that the slab surface has irregularities such as oscillation marks, and in addition, the distance between the slab surface and the measuring device varies slightly due to bulging, etc. Since it becomes easy to receive, it is preferable that the skin depth can be secured about 10 mm. Therefore, the upper limit of the frequency is preferably 20 Hz.

  Experiments were conducted to confirm the effectiveness of the slab surface temperature measuring device of the present invention. The experimental conditions are as shown below.

(Experimental conditions)
Cast slab width: 1000-1800mm
Casting speed: 0.75 to 1.2 m / min Steel type: Medium carbon Al-killed steel Sensor installation position (measurement device installation position): 1 m below the mold surface level in the mold and directly under the mold short side cooling zone Sensor ( Distance between measuring device) and slab surface: 30mm
Frequency of alternating current applied to exciting coil: 1.5Hz

  In the present embodiment, the measuring apparatus is installed directly below the mold short side by fixing the measuring apparatus to the mold. For this reason, even if the mold is adjusted to change the width of the slab in various ways, the distance between the measuring device and the surface of the slab is made substantially constant, that is, the surface of the short side of the slab is almost constant by the exciting coil. The alternating magnetic field applied vertically can be made substantially constant.

  FIG. 6 (a) is a measurement result of a comparative experiment in which the measurement device under the above experimental conditions is replaced with a conventional radiation thermometer, and is a diagram showing the relationship between the measured time and the slab surface temperature. . FIG. 6B is a measurement result under the above experimental conditions, and is a diagram showing a relationship between the measured time and the slab surface temperature.

  As shown in FIG. 6 (a), in the comparative experiment, the measurement value greatly varies because of the influence of a water film and water vapor existing between the radiation thermometer and the slab surface. It was not possible to measure accurately. On the other hand, as shown in FIG. 6B, the experimental results according to the present example confirmed that the slab surface temperature can be stably measured by using the measuring apparatus of the present invention.

  According to the above-described embodiments and examples, by using the above-described measurement apparatus, a slab can be obtained even under a severe atmosphere immediately below a mold for continuous casting of steel and containing a large amount of water, water vapor, and the like. The surface temperature can be measured directly and stably for a long time. In other words, the slab surface temperature is once cooled to the Curie point or less in the cooling zone immediately below the mold, and immediately after that, the surface temperature of the part where the slab surface temperature rises due to recuperation is directly and stable for a long time. Can be measured automatically. Further, the slab surface temperature can be measured without depending on the slab size. Therefore, by using the measuring apparatus and the measuring method of the present invention, it is possible to detect a breakout that is an operation abnormality and a drift that causes a deviation in the molten steel flow.

  The present invention is not limited to the above-described embodiment and examples, and various modifications can be made without departing from the spirit of the present invention. For example, when measuring the slab surface temperature, the above-described measuring devices are arranged on both short sides of the slab directly under the mold, and the slab surface temperature measured by one measuring device exceeds the Curie point. It is also possible to adopt a method of recognizing that there is a risk of occurrence of a perforated breakout and detecting the occurrence of breakout by temporarily stopping continuous casting.

  Further, in the above embodiment, the surface temperature of the slab 1 is derived by using a calibration formula between a predetermined slab surface temperature and an induced electromotive force, but the predetermined slab surface temperature and the induced electromotive force are derived. It is also possible to derive the surface temperature of the slab 1 by using correspondence data representing the correspondence with electric power (for example, data representing the correspondence shown in FIG. 4).

It is a figure which shows the relationship between the distance from the hot_water | molten_metal surface and slab surface temperature in the process of drawing out a slab from the downward direction and carrying out continuous casting, strongly cooling the slab short side below a casting_mold | template. (A) is a schematic diagram for demonstrating the basic principle which measures a slab surface temperature, (B) is a block diagram which shows in detail the measuring apparatus of the slab surface temperature by embodiment of this invention. It is a figure which shows the relationship between slab temperature and a voltage. It is a figure which shows the relationship between the voltage and slab surface temperature in the temperature range from 700 degreeC shown in FIG. 3 to the Curie point Tc. It is a figure which shows the relationship between the frequency applied to an exciting coil, and skin depth. (A) is a measurement result of a comparative experiment, and is a diagram showing the relationship between the measured time and the slab surface temperature, (b) is a measurement result according to the example, the measured time and the slab surface temperature, It is a figure which shows the relationship.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cast piece 2 Excitation coil 3 Detection coil 4 Glass epoxy pipe 5 Polyester coated copper wire with outer diameter of 1 mm 6 Polyester coated copper wire with outer diameter of 0.3 mm 7 Constant current amplifier 8 Oscillator 9 Signal processor 10 Lock-in amplifier

Claims (5)

Magnetic field excitation means for applying an alternating magnetic field substantially perpendicular to the surface of the slab,
Magnetic field detection means for detecting an alternating magnetic field to detect lines of magnetic force changed by the surface temperature of the slab,
Surface temperature deriving means for deriving the surface temperature of the slab from the induced electromotive force obtained by detecting an alternating magnetic field by the magnetic field detecting means and predetermined correspondence data;
Comprising
Said correspondence data is Ri Ah with data representing the correspondence between the predetermined Curie point below the slab surface temperature and the induced electromotive force,
The slab is a slab obtained by continuous casting drawn from below the mold using a mold,
The magnetic field excitation means and the magnetic field detection means are disposed on the slab short side below the cooling zone for cooling the slab short side directly under the mold,
The slab surface temperature measuring apparatus is characterized in that the slab surface temperature below the predetermined Curie point is in a temperature range from the Curie point to the Curie point minus 100 ° C.   2. The apparatus for measuring a slab surface temperature according to claim 1, wherein the correspondence data is a calibration formula that expresses the correspondence between the slab surface temperature and the induced electromotive force by a mathematical expression.   3. The magnetic field excitation means according to claim 1 or 2, wherein the magnetic field excitation means has a solenoid-like excitation coil, the magnetic field detection means has a solenoid-like detection coil, and the detection coil is against the surface of the slab. An apparatus for measuring the slab surface temperature, which is arranged apart from the exciting coil. In any one of claims 1 to 3, the measuring device of the slab surface temperature, wherein the magnetic field applied frequency of the magnetic field excited by the excitation means is 20Hz or less than 0.5 Hz. An alternating magnetic field is applied by the magnetic field excitation means substantially perpendicularly to the surface of the slab, and the alternating magnetic field is detected by the magnetic field detection means for detecting lines of magnetic force changed by the surface temperature of the slab,
Deriving the surface temperature of the slab from induced electromotive force obtained by detecting an alternating magnetic field with the magnetic field detection means and predetermined correspondence data;
Said correspondence data is Ri Ah with data representing the correspondence between the predetermined Curie point below the slab surface temperature and the induced electromotive force,
The slab is a slab obtained by continuous casting drawn from below the mold using a mold,
The magnetic field excitation means and the magnetic field detection means are disposed on the slab short side below the cooling zone for cooling the slab short side directly under the mold,
The method for measuring the slab surface temperature, wherein the slab surface temperature below the predetermined Curie point is in a temperature range from the Curie point to the Curie point minus 100 ° C.

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