JPS61147126A - Measuring method of temperature of steel material by electromagnetic induction - Google Patents

Abstract

PURPOSE:To measure temperature speedily without any restriction of plate thickness even if a lift-off is large by using an exciting coil and two induction coils, setting an excitation frequency above a value determined by a specific expression according to the plate thickness of a steel material to be measured, and detecting the quantity of variation in each induced voltage and calculating a parameter from a specific expression. CONSTITUTION:The exciting coil 60 which is arranged at either side of the steel material 16 to be measured and the induction coils 62 and 64 which are arranged at said side at different distances from the coil 60 are used to set the excitation frequency of the coil 60 above the value fc determined of a rela tion of fc=12.5/t<2> according to the plate thickness (t) of the steel material. Then, the coil 60 is excited to detect the quantities DELTAE1 and DELTAE2 of variation from the reference states of induced voltages of the coils 62 and 64, and the parameter M is calculated from M=DELTAE1.K<alpha>,(alpha=-DELTAE2/DELTAE1), so that the temperature of the steel material is calculated from the value.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a method for measuring temperature of steel materials by electromagnetic induction,
In particular, the present invention relates to a method of measuring the temperature of steel using a magnetic induction detection coil, which is suitable for controlling the material quality of steel produced in a hot rolling line or a heat treatment line such as continuous annealing.

[Conventional technology]

For example, in hot rolling lines such as hot strip mills or plate mills, a method is adopted in which the steel material after hot rolling is cooled by 111m to strengthen the mechanical strength of the steel, and in heat treatment lines, The mechanical properties of steel are adjusted by subjecting it to various thermal treatments such as quenching, tempering, and annealing. In the above-mentioned treatment, the most important thing in adjusting the mechanical properties of the final steel to the desired range is to control the thermal history of the steel to be treated, and its III m 18
Accurately detecting the temperature of the steel during the treatment process is a fundamental requirement for improving the temperature. Conventionally, radiation thermometers have been commonly used in the above-mentioned production lines on a T-intensive scale, but as is well known, radiation thermometers can directly measure fluctuations in the emissivity of the object to be measured. This may affect the accuracy, and it is virtually impossible to measure in a measurement environment where the steel material is water-cooled, is covered with a water belly caused by cooling water, or is filled with water vapor, etc. This was impossible, and it was extremely insufficient for use at a temperature of 11J III. Temperature measurement methods using eddy current thermometers are also known, but most of them have a temperature measurement range of about 200 mm due to measurement accuracy.
Since it is limited to a low temperature range below .degree. C., it cannot be applied to the above manufacturing line. In order to improve such an eddy current thermometer so that it can be used for temperature measurement in a high temperature range, Japanese Patent Application Laid-Open No. 59-87
330 has been proposed. In the temperature measurement method according to this proposal, as shown in FIG.
and a secondary coil 14.
0 is used. When a high-frequency current is passed through the primary coil 12 of the detection coil 10, the secondary coil 14 has the magnetic permeability μ, the electrical conductivity σ, and the distance between the detection coil 10 and the measurement object 16 ( (hereinafter referred to as lift-off)h,
A constant induced voltage v2 determined by the excitation 81 (current) frequency of the primary coil 12 is induced.
is sufficiently large relative to the diameter of the detection coil 10;
Under conditions that are considered to be practically infinite, and by specifying the range of magnetic permeability μ and excitation frequency f, the above induced voltage (2) on the complex voltage plane due to magnetic permeability μ, conductivity σ, and excitation frequency [ If the lift-off h is considered as a fixed condition, the change will move on the flRII CM shown in FIG. 7 in response to the parameters K(-μ, ·σ · [). Under such a specified range of measurement conditions, point X' is set, and the reference excitation frequency [1111 temperature is performed at 0, 11
When the induced voltage V2 deviates from the reference point due to a change in the magnetic permeability μ or conductivity σ due to a temperature change in the measured object 16 during cooling, the excitation frequency r is varied so as to restore this deviation. ill Ill. At this time, the reference excitation frequency “
Deviation Δr between excitation frequency 0 and corrected excitation frequency 1 <-rr
, > is the amount of change Δ(
Since the relationship is directly proportional to μ7・'ρ), a relationship curve between Δ(μ,・'σ) of the measured object 16 and the amount of temperature change is determined in advance, and the change I(μ/σ) is determined from the frequency deviation Δ1. ), and then the temperature is detected from Δ(μ, ./σ). These measurements are performed using, for example, a circuit configuration as shown in Fig. 8, but under measurement conditions where the lift-off h fluctuates, measurement accuracy will deteriorate significantly if this fluctuation correction is not performed accurately. Therefore, a phase shifter 20, a synchronous detector 22, an integrator 24, a lift-off fluctuation correction calculator 2
It is necessary to use 6th grade. In FIG. 8, 28 is a high frequency oscillator, 30 is an amplifier, 31 is a reference phase difference calculator, 3
2.34 is a phase shifter, 36.38 is a synchronous detector, 40.4
2 is an integrator, 44 is a phase difference calculator, 46 is a frequency converter, 48 is a frequency-to-temperature conversion calculator, and 50 is an oscillation frequency control circuit.

[Problems to be solved by the invention]

However, the temperature measurement method proposed in JP-A-59-87330 can only be applied to the case of measuring 1 degree of the object to be measured 16 whose thickness is considered to be infinite compared to the diameter of the detection coil 10. It's a method. Therefore, the plate thickness is 0
．． Cold-rolled steel strips heat-treated in a continuous annealing furnace with a thickness of 2 to 2n, hot-rolled steel strips manufactured in a hot strip mill with a thickness of 1 to 20m, or hot-rolled steel strips with a thickness of 1
When measuring the temperature of a hot-rolled III plate manufactured by a plate mill in the range of 0 to 70 zm, the diameter of the detection coil 10 must be significantly reduced, resulting in deterioration of measurement accuracy and detection Due to the decrease in critical lift-off, etc., it could not be used for practical measurements. In addition, in order to detect the necessary frequency deviation Δr in the case of Takido Karitake, the excitation frequency must be variably controlled, and under conditions where the lift-off h fluctuates,
Due to the necessity of performing this fluctuation correction, a complicated mechanism is required in terms of both hardware and software, which not only makes ii[ expensive but also takes time. Therefore, it is not possible to detect a continuous cooling curve for measurements that cause rapid temperature changes, such as for example during hardening of steel. Also, on the runout table of a hot strip mill? 1! When the object to be measured is moving at high speed, such as when measuring temperature, the measurement position changes while calculating the frequency deviation Δf, so it is difficult to obtain the accurate temperature corresponding to each measurement position. This has caused problems such as the inability to detect it.

[Purpose of the invention] The present invention has been made to solve the above-mentioned conventional problems, and allows measurements to be made extremely quickly with a relatively simple device configuration, even under conditions of large lift-off, without being limited by the thickness of the steel material to be measured. The purpose of the present invention is to provide a method for measuring the temperature of steel materials. [Means to solve the problem]

The present invention provides the following advantages when measuring the temperature of steel materials by electric induction and induction.
an excitation coil that generates an alternating magnetic flux through alternating current excitation, which is placed on either side of the steel material to be measured; Using 211 independent induction coils that are mutually induced by the excitation coil, the excitation frequency of the excitation coil is determined according to the plate thickness t by the following formula %
The excitation coil is excited by setting iiiI fc determined by the relationship of formula % (1) or more, and the changes ΔE1 and ΔE2 from the reference state of the induced voltage of each induction coil at that time are detected, and from this, the following formula % The above object is achieved by determining the parameter M shown in formula % (2) and determining the temperature of the steel material from the value of the parameter M. Further, in an embodiment of the present invention, the two induction coils are arranged at positions whose distances from the excitation coil differ from each other by 20 m or more, so that they are particularly less susceptible to lift-off fluctuations. .

[Effect]

In the present invention, as shown in FIG. 1, an excitation coil 60 and first and second induction coils 62 and 64 are provided on one side (lower side in the figure) of the object to be measured 16, and the excitation coil The distance between 60 and the first induction coil 62 is 11J! 1 and
The detection coils 58 are arranged such that the distance 12 between the excitation coil 60 and the second induction coil 64 is different. In such a configuration of the detection coil 58, when an alternating current of a predetermined frequency is passed through the excitation coil 60 by the AC excitation faW device 66, the alternating magnetic fluxes Φ1 and Φ2 cause the first induction coil 62 and the second Vg conducting coil 64 to flow. An induced voltage is generated.Here, the object to be measured 16 is placed on the detection coil 58.
The eleventh! If the amount of change in the induced voltage of the induction coil 62 is ΔE+, and the amount of change in the induced voltage of the second induction coil 64 is ΔE2, then the shape and arrangement of the detection coil 58,
When the number of turns per cross-sectional area, the excitation frequency 1t1, and the excitation frequency are constant, the amounts of change ΔE1 and ΔE2 vary depending on the magnetic permeability μ and conductivity σ of the object to be measured 16, the lift-off h, and the plate thickness of the object to be measured 16. Among the above factors, the measured object 1
The magnetic permeability μ and conductivity σ of No. 6 are factors that depend on temperature, and the temperature can be detected from the amount of change caused by these factors. On the other hand, the lift-off h and the plate thickness t are disturbance factors in detecting the temperature. Here, the relationship between the changes in the amounts of change ΔE1 and ΔE2 due to each of the factors is shown in FIG. 2. In addition,
Point 0 in FIG. 2 is the position in the reference state. First, when the lift-off 11 changes, for example, the second
When the measurement condition is the condition of point a in the figure, the magnetic permeability μ
and lift-off when the conductivity σ is constant (i.e. the temperature is constant)
When only 1 becomes smaller, point a moves away from point 0 on curve X, and when lift-off h becomes infinite, point a moves away from point 0.
converges to. The amount of change ΔE1 and ΔE2 is the lift-off h
It is large in a small region of , and becomes smaller as it approaches point 0. On the other hand, when the temperature of the measured object 16 changes, for example, if the lift-off h and plate thickness t are constant and only the temperature decreases from the conditions of point a, point a will move along the line shown by the broken line a - *
Move in the direction b-*c. Also, when the plate thickness changes, the behavior is qualitatively similar to that when the temperature changes, but the details of this behavior have a clear correspondence with the plate thickness t, as will be explained later. , plate thickness (
In the region where t is small, the amount of change due to the difference in plate thickness t is large, and as the plate thickness t increases, the amount of change tends to be saturated. As the excitation frequency r increases, the plate thickness at which the change is saturated becomes smaller. Based on the above knowledge, the inventors determined that the amount of change ΔE1 and Δ
The way E2 changes on Figure 2 is lift-off b
, humidity, and plate thickness, each exhibiting its own unique behavior.
Even under conditions where temperature, lift-off h, and plate thickness t change simultaneously, if the change due to lift-off h and plate thickness t, which are disturbance factors, can be separated, it is possible to independently grasp the temperature, which is a factor to be measured. Based on this idea and as a result of repeated studies, we have discovered the following and devised the present invention. That is, as a result of the studies conducted by the present inventors, the following was found. (1) When the plate thickness and temperature are constant, the parameter M shown in equation (2) above takes a constant value regardless of fluctuations in lift-off h. In FIG. 3, a hot rolled steel plate (C-0, 15%, ~1n-0
．． 60%, 5i-0.15%) was used as the measured object 16, and the lift-off 11 was varied in the range of 20 to 130 degrees under the condition that the temperature was maintained at a predetermined temperature (500°C, 600°C, 700°C). The relationship between the parameter M determined by the above-mentioned equation (2) and the lift-off 11 when measured is shown. As is clear from FIG. 3, the parameter M has a constant value depending on the temperature, regardless of the lift-off h. Therefore, by using the parameter M, it is possible to remove disturbances due to variations in liftoff h. The constants used in equation (2) above include the shape, arrangement, cross-sectional area, number of turns, and excitation l! of the detection coil 58. It is a constant determined by the current and excitation frequency. (2) By setting the excitation frequency f to be equal to or higher than il fc shown in equation (1) above, the change due to the plate thickness of the object to be measured 16 on the parameter M is saturated. FIG. 4 shows a case where steel plates with different thicknesses t are measured at a predetermined temperature (700° C.) under the condition of excitation frequency f-50)fz using the detection coil 58 having the configuration shown in FIG. 1. The relationship between the parameter M and the plate thickness t of the object to be measured 16 is shown. As is clear from FIG. 4, as the plate thickness t increases, the parameter M shows a saturation f1Ms depending on the temperature. III (c is the excitation coil 60
It depends on the excitation frequency f, and the higher the excitation frequency Wlf, the smaller [C] becomes. Therefore, the excitation frequency "
By selecting , the parameter M becomes independent of the plate thickness and indicates a value corresponding to humidity. Regarding this, the inventors believe that the temperature of the object to be measured 16 is between room temperature and 720°C.
As a result of examining the excitation frequency "C" to satisfy the above conditions in the range of Figure 5 shows the board thickness [is 3.0cm, 5.On,
10. C) Attach a thermocouple to the depth of 1/4 of the thickness of three types of steel plates different from +m, and after heating to 750℃,
The method of the present invention (excitation frequency r = 50 H
The relationship between the parameter M and the thermocouple temperature measured by y, ) is shown. As is clear from Figure 5, it is clear that there is a clear correspondence between the two for any steel plate, and by determining such a relationship in advance, the temperature of the material to be measured can be determined. I can do it. Example 1 An example of a temperature measuring device to which the present invention is applied will be described in detail below with reference to the drawings. This embodiment, as shown in FIG. an excitation device 66 and the induction coil 62
．． Amplifier 6 for amplifying the induced voltage induced in 64
8.70, a detector 72.74 for converting an AC signal corresponding to the induced voltage amplified by the amplifier 68.70 into a DC signal, and each induction input via the detector 72.74. The parameter M is calculated from the induced voltage signal of the coils 62 and 64 and the plate thickness signal of the measured object 16 transmitted from a separately provided plate thickness measuring device (or inputted in advance), and then the humidity is calculated from the parameter M. At the same time, calculate the value "C" specified by the above formula (1) from the plate thickness signal, select the optimum excitation frequency f according to the plate thickness of the object to be measured 16, and perform the AC excitation. It is composed of an arithmetic control lv & position 76 that is input to the device 66. The distance 12 between the excitation coil 60 and the second induction coil 64, and the distance 1 between the excitation filter 60 and the first induction coil 62.
It is desirable that the difference (i+ -122) of 1 is at least 2011 or more. It is the difference (A t −122>
If is less than 20n, the changes in the amounts Δε1 and ΔE2 due to variations in lift-off h will be similar, and the parameter M will change due to variations in lift-off h, so sufficient temperature measurement accuracy may not be obtained. This is because there is. By using such a device, the amount of change ΔE? By calculating the parameter M from . In order to confirm the usefulness of applying the method of the present invention, the present inventors investigated the Il temperature of a steel plate during cooling in an accelerated cooling device immediately after a plate rolling mill, and the cooling temperature on a runout table of a hot strip mill. When the method of the present invention was used to measure the temperature of the steel plate in the equipment and the temperature of the steel plate in the cooling zone of the continuous annealing line,
In either case, there is a difference between the temperature fat layer of the steel plate measured by the method of the present invention and the mechanical resistance, which was separately conducted in a laboratory. ! There was a good correspondence with the results of the II history simulation experiment, and it was confirmed that the temperature measurement was performed with sufficient accuracy. [Effects of the Invention] As explained above, according to the present invention, the thickness of the object to be measured can be reduced to 1/4a! becomes possible. Further, even in a state where the lift-off is large, a temperature of 11 degrees is possible, and from the viewpoint of the transportability of the object to be measured and the durability of the sensor, it is possible to set the lift-off large so as not to cause any problems. Furthermore, the measuring mechanism and device configuration are simple and inexpensive, and measurements can be performed extremely quickly. Therefore, the temperature of the steel plate in the cooling equipment in various hot rolling processes such as hot strip mill lines and plate mill lines, or the temperature of the steel plate in the furnace in heat treatment processes such as continuous annealing, quenching, and tempering lines, etc. Continuous temperature measurement becomes possible in temperature ranges and measurement environments where accurate measurement was difficult. Therefore, from these temperature data, the heat aWi of the steel material can be determined by
This makes it possible to control the material quality of steel materials during manufacturing and predict material quality after manufacturing with high precision. Therefore, it has excellent effects such as being extremely useful collectively.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view, including a partial block diagram, showing the configuration of an embodiment of a temperature measuring device in which the method for measuring temperature of steel materials by electrical conduction according to the present invention is adopted; FIG. 2 is a cross-sectional view including a partial block diagram; FIG. 3 is a diagram showing an example of the relationship between the value of the parameter M and lift-off, and FIG. 4 is a diagram showing the relationship between the value of the parameter M and the lift-off. Figure 5 is a diagram showing an example of changes in the value of due to plate thickness.
Similarly, a diagram showing an example of the relationship between the value of the parameter M and the temperature of the object to be measured, and FIG. 6 is a cross-sectional view showing the configuration of an eddy current detection coil used in an example of a conventional temperature measurement method. ,
FIG. 7 shows two diagrams for explaining the measurement principle of the conventional example.
FIG. 8, which is a diagram showing the behavior of the reference point on the complex voltage plane of the next coil induced voltage, is a block diagram showing an example of the circuit configuration of the device for implementing the conventional example. 16... Object to be measured, 11... Lift-off, f... Excitation frequency, 58... Detection coil, 60... Excitation coil, 62.64... Induction coil, 11, λ2... Distance, 66... AC excitation device, Φ1, Φ2... Alternating magnetic flux. ΔE + , ΔE2...Amount of change in induced voltage, (...
Plate thickness.

Claims (2)

[Claims] (1) An excitation coil that generates an alternating magnetic flux by AC excitation, which is placed on either side of the steel material to be measured;
Excitation of the excitation coil using two independent induction coils that are mutually induced by the excitation coil and are placed on the same side as the excitation coil and at different distances from the excitation coil. The frequency is determined according to the steel plate thickness t,
The excitation coil is excited by setting it to a value fc or more determined by the relationship of the following formula fc = 12.5/t^2, and the changes ΔE_1 and ΔE_2 from the reference state of the induced voltage of each induction coil at that time are detected. From this, the following formula M = ΔE_1・K^-^Δ^(E_2)^/^Δ^(E
_1) A method for measuring the temperature of a steel material by electromagnetic induction, characterized in that the parameter M shown in (K is a constant) is determined, and the temperature of the steel material is determined from the value of the parameter M. (2) The method for measuring temperature of steel material by electromagnetic induction according to claim 1, wherein the two induction coils are arranged at positions different from each other by 20 mm or more in distance from the excitation coil.