JPH049450B2 - - Google Patents

Description

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

The present invention relates to a method for measuring the temperature of steel materials using electromagnetic induction, and in particular, a magnetic induction method suitable for use in controlling the material quality of steel materials manufactured in hot rolling lines or heat treatment lines such as continuous annealing. This invention relates to a method for measuring the temperature of steel using a detection coil.

[Conventional technology]

For example, in hot rolling lines such as hot strip mills or plate mills, controlled cooling is applied to the steel material after hot rolling to strengthen the mechanical properties of the steel. In this method, various heat treatments such as quenching, tempering, and annealing are applied to adjust the mechanical properties of steel. In the above-mentioned treatments, 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.
As a basic requirement for improving the control accuracy, it is important to accurately detect the temperature of the steel during the treatment process. Traditionally, radiation thermometers have been commonly used in industrial-scale manufacturing lines such as those mentioned above, but as is well known, radiation thermometers are sensitive to fluctuations in the emissivity of the object being measured, which directly affects measurement accuracy. to influence,
In addition, it is virtually impossible to measure in a measurement environment that is covered with a film of cooling water, such as when steel is being water-cooled, or is filled with water vapor, etc., and temperature control is difficult. It was extremely inadequate for use. Temperature measurement methods using eddy current thermometers are also known, but most of them are limited to low temperature ranges below about 200℃ due to measurement accuracy.
It is impossible to apply it to the production line. Japanese Patent Application Laid-Open No. 87330/1983 has proposed an improvement to such an eddy current thermometer so that it can be used for temperature measurement in a high temperature range. In the temperature measurement method proposed by this proposal, as shown in FIG. 6, a probe-type detection coil 10 consisting of a primary coil 12 and a secondary coil 14 arranged coaxially 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), and a constant induced voltage V ₂ determined by the excitation (current) frequency f of the primary coil 12 is induced. Under the condition that the thickness of the object to be measured 16 is sufficiently larger than the diameter of the detection coil 10 and is considered to be substantially infinite, and the magnetic permeability μ and the excitation frequency f
If we specify the range of , the variation of the induced voltage V ₂ on the complex voltage plane due to the magnetic permeability μ, the conductivity σ, and the excitation frequency f becomes the curve C shown in FIG. 7, assuming that the lift-off h is fixed. It begins to move on _M in accordance with the parameter K (=μ/σ·f). Under such a specified measurement condition range, as a specific point on the curve C _M in FIG. 7,
Point X is set for temperature measurement in a high temperature range, and point X' is set for temperature measurement in a low temperature range, and the reference excitation frequency f is set such that an induced voltage V ₂ corresponding to these reference points X and X' is generated. ₀ , and if the induced voltage V ₂ deviates from the reference point due to a change in magnetic permeability μ or conductivity σ due to a temperature change in the measured object 16 during temperature measurement, this deviation can be corrected. The excitation frequency f is variably controlled so as to return to the original state. At this time, the deviation Δf (= f - f ₀ ) between the reference excitation frequency f ₀ and the corrected excitation frequency f is directly proportional to the amount of change Δ (μ / ρ) in μ / ρ of the measured object 16 due to temperature. Since there is a relationship, Δ of the object to be measured 16 is
Find the relationship curve between (μ/σ) and the amount of temperature change, find the amount of change (μ/σ) from the frequency deviation Δf,
Next, 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, the measurement accuracy will deteriorate significantly unless this fluctuation correction is performed accurately. For correction, it is necessary to use a phase shifter 20, a synchronous detector 22, an integrator 24, a lift-off fluctuation correction calculator 26, etc. In FIG. 8, 28 is a high frequency oscillator, 30 is an amplifier, 31 is a reference phase difference calculator, 3
2 and 34 are phase shifters, 36 and 38 are synchronous detectors, 4
0 and 42 are integrators, 44 is a phase difference calculator, 46 is a frequency converter, 48 is a frequency-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 is a method that can only be applied to the case of measuring the temperature of the object to be measured 16 whose thickness is considered to be infinite compared to the diameter of the detection coil 10. It is. Therefore, cold-rolled steel strips with a thickness in the range of 0.2 to 2 mm that are heat-treated in a continuous annealing furnace, and hot-rolled steel strips that are produced in a hot strip mill with a thickness in the range of 1 to 20 mm. When measuring the temperature of a steel strip or a hot-rolled steel plate manufactured by a plate mill with a thickness of 10 to 70 mm, the diameter of the detection coil 10 must be made extremely small, making it difficult to measure. Due to the deterioration of accuracy and the decrease in the detection limit lift-off, it was virtually impossible to use it for measurements. In addition, when calculating the temperature, it is necessary to variably control the excitation frequency f in order to detect the necessary frequency deviation Δf, and under conditions where the lift-off h fluctuates, this fluctuation correction must be performed. As a result, the device requires a complex mechanism in terms of both hardware and software, which not only makes the device expensive but also takes time to measure the temperature. 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. In addition, when the object to be measured is moving at high speed, such as when measuring temperature on the runout table of a hot strip mill, the measurement position may change while calculating the frequency deviation Δf. Since the temperature changes, it has been difficult to detect an accurate temperature corresponding to each measurement position.

[Purpose of the invention]

The present invention has been made to solve the above-mentioned conventional problems, and even in a state of large lift-off without being constrained by the thickness of the steel material to be measured.
It is an object of the present invention to provide a method for measuring the temperature of steel material, which can perform measurements extremely quickly with a relatively simple device configuration.

[Means to solve the problem]

When measuring the temperature of a steel material by electromagnetic induction, the present invention provides an excitation coil that generates an alternating magnetic flux by alternating current excitation, which is placed on either side of the steel material to be measured, and on the same side as the excitation coil. Further, by using two independent induction coils disposed at different distances from the excitation coil and mutually induced by the excitation coil, the excitation frequency of the excitation coil is adjusted to the steel sheet thickness t. Accordingly, the excitation coil is excited by setting f _c to a value determined by the following formula f _c = 12.5/t ² ... (1) or more, and the induced voltage of each induction coil at that time is changed from the reference state. Detect the amount of change ΔE ₁ and ΔE ₂ ,
From this, find the parameter M shown in the following formula M = ΔE ₁・K ^- 〓 ^E2/ 〓 ^E1 ...(2) (K is a constant), and calculate the parameter M
The above objective is achieved by determining the temperature of the steel material from the value of . 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 mm or more, so that they are particularly difficult to be affected by lift-off fluctuations.

[Effect]

According to the present invention, as shown in FIG.
The detection coils 58 are arranged such that the distance l ₁ between the excitation coil 60 and the first induction coil 62 is different from the distance l ₂ between the excitation coil 60 and the second induction coil 64. In such a configuration of the detection coil 58, when an alternating current of a predetermined frequency f is caused to flow through the excitation coil 60 by the alternating current excitation device 66, the alternating magnetic fluxes Φ ₁ and Φ ₂ cause the first
An induced voltage is generated in the induction coil 62 and the second induction coil 64. Here, a state in which the object to be measured 16 is not on the detection coil 58 (hereinafter referred to as a reference state)
The amount of change in the induced voltage of the first induction coil 62 in the state where the object to be measured 16 is on the detection coil 58 (hereinafter referred to as the measurement state) is ΔE _{1, and the amount of change in the induced voltage of the first induction coil 62 is ΔE 1} ,
If the amount of change in the induced voltage of the induction coil 64 is ΔE ₂ , the shape, arrangement, cross-sectional area, number of turns of the detection coil 58,
When the excitation current and excitation frequency are constant, the above-mentioned changes ΔE ₁ and ΔE ₂ change depending on the magnetic permeability μ and conductivity σ of the object to be measured 16, the lift-off h, and the plate thickness t of the object to be measured 16. . Among the above-mentioned factors, the magnetic permeability μ and the electrical conductivity σ of the object to be measured 16 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 ΔE ₁ and ΔE ₂ due to each of the factors is shown in FIG. 2. Note that point O in FIG. 2 is the position in the reference state. First, when the lift-off h changes, for example, when the measurement condition is the condition of point a in Fig. 2, the magnetic permeability μ and the conductivity σ are constant (that is, the temperature is constant), and only the lift-off h is small. Then, point a
moves away from point O on curve X and converges to point O when liftoff h becomes infinite. The amounts of change ΔE ₁ and ΔE ₂ are large in a region where lift-off h is small, and become smaller as they approach point O. On the other hand, if the temperature of the object to be measured 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 from a→b→ Move in direction c. Also, when the plate thickness t changes, the behavior is qualitatively similar to that when the temperature changes, but
The details of this method have a clear correspondence with the plate thickness t as described later, and in the area where the plate thickness t is small, the plate thickness t
The amount of change due to the difference in is large, and as the plate thickness t increases, the amount of change tends to be saturated. and,
As the excitation frequency f increases, the plate thickness t at which the change is saturated becomes smaller. Based on the above knowledge, the present inventors have determined that the manner in which the amounts of change ΔE ₁ and ΔE ₂ change in FIG. Even under conditions where temperature, lift-off h, and plate thickness t change simultaneously, if it is possible to separate the changes due to lift-off h and plate thickness t, which are disturbance factors, it is possible to independently grasp the temperature, which is a factor to be measured. Based on this idea, as a result of repeated studies, we 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 t and temperature are constant, the parameter M shown in equation (2) above takes a constant value regardless of fluctuations in lift-off h. FIG. 3 shows a detection coil 5 having the configuration shown in FIG.
8, a hot rolled steel plate with a thickness of 5 mm (C = 0.15
%, Mn=0.60%, Si=0.15%) for measured object 1
6 and the specified temperature (500℃, 600℃, 700℃)
Lift-off h is maintained at 20 to 130
(2) above when measured with fluctuations in the range of mm.
The relationship between the parameter M defined by the formula and the lift-off h 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. Note that the constant K used in equation (2) above is a constant determined by the shape, arrangement, cross-sectional area, number of turns, excitation current, and excitation frequency of the detection coil 58. (2) By setting the excitation frequency f to be equal to or higher than the value f _c shown in equation (1) above, the change in the parameter M due to the plate thickness t of the object to be measured 16 is saturated. FIG. 4 shows a detection coil 5 having the configuration shown in FIG.
8, under the condition of excitation frequency f = 50Hz,
The relationship between the parameter M and the plate thickness t of the object to be measured 16 is shown when measuring steel plates with different plate thicknesses t at a predetermined temperature (700° C.). As is clear from FIG. 4, as the plate thickness t increases, the parameter M shows a saturation value Ms depending on the temperature. The plate thickness value t _c indicating this saturation value Ms varies depending on the excitation frequency f of the excitation coil 60, and the higher the excitation frequency f becomes, the smaller t _c becomes. Therefore, by selecting the excitation frequency f so that the value of _tc is smaller than the plate thickness t of the object to be measured 16, the parameter M becomes independent of the plate thickness and shows a value corresponding to the temperature. Become something. Regarding this, the inventor investigated the excitation frequency f _c to satisfy the above condition when the temperature of the object to be measured 16 is in the range of room temperature to 720° C., and as a result, found the relationship expressed by the above-mentioned equation (1). . Next, the relationship between the parameter M and the temperature of the object to be measured 16 will be considered. Figure 5 shows that the plate thickness t is
A thermocouple was installed at a depth of 1/4 of the thickness of three different types of steel plates: 3.0mm, 5.0mm, and 10.0mm, and the temperature was 750℃.
The relationship between the parameter M and the thermocouple temperature measured by the method of the present invention (excitation frequency f = 50 Hz) is shown when the sample was heated to 100° C. and then cooled at a cooling rate of 10 to 50° C./sec. 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】

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of a temperature measuring device to which the present invention is applied will be described in detail below with reference to the drawings. As shown in FIG. 1, the present embodiment includes a detection coil 58 consisting of the excitation coil 60 and induction coils 62 and 64 described above, and an AC excitation device 66 that supplies alternating current at an excitation frequency f to the excitation coil 60.
and amplifiers 68 and 70 for amplifying the induced voltage induced in the induction coils 62 and 64, and for converting an alternating current signal corresponding to the induced voltage amplified by the amplifiers 68 and 70 into a direct current signal. The induced voltage signals of the induction coils 62 and 64 are input via the detectors 72 and 74, and the induced voltage signals are transmitted from a separately provided plate thickness measuring device (or input in advance). ) Calculate the parameter M from the plate thickness signal of the object to be measured 16, then calculate the temperature from the parameter M, and calculate the value f _c defined by the above equation (1) from the plate thickness signal, body 16
and an arithmetic and control device 76 that selects the optimum excitation frequency f according to the plate thickness t and inputs it to the AC excitation device 66. It is desirable that the difference (l 1 − l ₂ ) between the distance l ₂ between the excitation coil 60 and the second induction coil 64 and the distance l ₁ between the excitation coil 60 and the first induction coil 62 (l ₁ −l 2 ) be at least 20 mm. . It is the difference (l ₁ − l ₂ )
If is less than 20 mm, the amount of change ΔE ₁ and ΔE ₂ due to variations in lift-off h will change in a similar manner, and the parameter M will change depending on variations in lift-off h, so sufficient temperature measurement accuracy cannot be achieved. This is because there are cases where it cannot be obtained. By using such a device, the parameter M can be calculated from the measured changes ΔE ₁ and ΔE ₂ , and by using the relationship between the parameter M and temperature determined in advance, it is possible to calculate the parameter M from the measured changes ΔE 1 and ΔE 2. Temperature measurement of steel plates becomes possible even under conditions where lift-off constantly fluctuates. In order to confirm the usefulness of applying the method of the present invention, the present inventors measured the temperature of a steel plate during cooling in an accelerated cooling device immediately after a plate rolling mill, and measured the temperature of a steel plate on a runout table of a hot strip mill. When the method of the present invention was used to measure the temperature of a steel plate in a cooling device and the temperature of a steel plate in a cooling zone of a continuous annealing line, in both cases, the temperature history of the steel plate measured by the method of the present invention was There was a good correspondence between the temperature and the mechanical properties, as was the case with the results of a separate laboratory thermal history simulation experiment, and it was confirmed that the temperature measurements were carried out with sufficient accuracy.

【Effect of the invention】

As explained above, according to the present invention, temperature measurement is possible without being restricted by the thickness of the object to be measured. Furthermore, temperature measurement is possible even in a state where the lift-off is large, and it is possible to set the lift-off large so as not to cause problems in terms of the transportability of the object to be measured and the durability of the sensor. 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 is now possible in temperature ranges and measurement environments where accurate measurement has been difficult. Therefore, it becomes possible to control the thermal history of the steel material from these temperature measurement data, and it becomes possible to control the material quality of the steel material during manufacturing and predict the material quality after manufacturing with high accuracy. Therefore, it has excellent effects such as being extremely useful industrially.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view, partially including a block diagram, showing the configuration of an embodiment of a temperature measuring device in which the method for measuring temperature of steel materials by electromagnetic induction according to the present invention is adopted;
Fig. 2 is a diagram showing the behavior of the induced voltage of the induction coil to explain the principle of the present invention, and Fig. 3 is a diagram showing the behavior of the induced voltage of the induction coil.
Similarly, FIG. 4 is a diagram showing an example of the relationship between the value of the parameter M and lift-off.
FIG. 5 is a diagram showing an example of the relationship between the value of parameter M and the temperature of the object to be measured. FIG. 6 is a diagram showing an example of the relationship between the value of parameter M and the temperature of the object to be measured. FIG. 7 is a cross-sectional view showing the configuration of the eddy current detection coil used in one example, which shows the reference point on the complex voltage plane of the secondary coil induced voltage, for explaining the measurement principle of the conventional example. FIG. 8 is a block diagram showing an example of the circuit configuration of an apparatus for implementing the conventional example. 16...Object to be measured, h...Lift-off, f...
Excitation frequency, 58...detection coil, 60...excitation coil, 62, 64...induction coil, _l1 , _l2 ...
Distance, 66...AC excitation device, _Φ1 , _Φ2 ...alternate magnetic flux, _ΔE1 , _ΔE2 ...change in induced voltage, t...plate thickness.

Claims (1)

[Scope of Claims] 1. An excitation coil that generates an alternating magnetic flux through alternating current excitation, which is placed on either side of a steel material to be measured, and an excitation coil that is on the same side as the excitation coil and that generates an alternating magnetic flux from the excitation coil. Two independent coils placed at different distances and mutually induced by the excitation coil
The excitation frequency of the excitation coil is set to a value f _c or more determined by the following equation f _c = 12.5/t ² according to the steel plate thickness t, and the excitation coil is is excited, and the changes ΔE ₁ and ΔE ₂ from the reference state in the induced voltage of each induction coil at that time are detected, and from this, the following formula M = ΔE ₁・K ^- 〓 ^E2/ 〓 ^E1 (K is a constant) 1. A method for measuring the temperature of a steel material by electromagnetic induction, characterized in that: a parameter M is determined, and the temperature of the steel material is determined from the value of the parameter M. 2. The method for measuring the temperature of a 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.