JP2663767B2 - Transformation rate measuring method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transformation rate measuring method and a transformation rate measuring apparatus for measuring a transformation rate in a metal plate such as a steel plate using a mutual induction method.

[0002]

2. Description of the Related Art It is very important to maintain a high quality of a steel sheet manufactured in a steel mill. It is important to maintain a final structure which has a great influence on various mechanical and physical properties. It is.

For example, among magnetic properties, magnetic permeability has a high correlation with mechanical properties such as hardness and grain size. For this reason, if the correlation between the magnetic permeability and the mechanical properties is measured in advance, the mechanical properties of the steel sheet can be estimated to some extent by measuring the magnetic permeability.

In the production process control, the austenite phase is transformed into the ferrite phase during the heat treatment of the hot steel. However, the transformation time and the transformation rate cannot be accurately monitored.
An extremely large effect on production quality can be expected in the field of manufacturing various steel products using a hot rolling line and a heat treatment line. Further, in order to measure the magnetic properties of a steel sheet that is actually continuously flowing in a manufacturing process, it is necessary to perform these measurements in a non-contact and online state.

[0005] In the measurement of the phase transformation, since the magnetic properties naturally change, it is sufficient to detect this magnetic change. Conventionally, when measuring the magnetic properties of such a steel sheet in a non-contact and on-line state, utilizing the property that the attenuation rate of the magnetic flux passing through the steel sheet to be inspected changes according to the magnetic properties of the steel sheet, FIG. A transformation rate measuring device shown in the following is proposed (JP-A-56-82443).

That is, a magnetized iron core 2 and an exciting coil 3 are spaced apart from each other by a predetermined distance d ₁ on one side of a steel plate 1 to be inspected.
Is disposed such that the pair of magnetic poles 4 a and 4 b face the steel plate 1. An exciting current is applied to the exciting coil 3 of the magnetizer 4 from the magnetizing power supply 5. And
Magnetic detecting element 6 is disposed at a distance from each other in the other side of the steel sheet 1 by a distance d _2. The surface temperature of the steel sheet 1 is measured by a thermometer 7. The magnetic flux detected by the magnetic detection element 6 is transmitted to the arithmetic unit 8.

According to the transformation rate measuring device having such a configuration, most of the magnetic flux output from one magnetic pole 4a of the magnetizer 4 passes through the inside of the steel plate 1 and is input to the other magnetic pole 4b. When the magnetic field generated by the magnetizer 4 is large, a part of the magnetic flux 9 output from one magnetic pole 4a of the magnetizer 4
Through the space on the opposite side, and again through the steel plate 1 in the reverse direction to be input to the other magnetic pole 4b.

When the transformation rate of the steel sheet 1 changes, magnetic properties such as the magnetic permeability of the steel sheet 1 change, and the strength Φ of the magnetic flux 9 penetrating the steel sheet 1 changes. Therefore, the reference magnetic flux intensity in the test steel sheet having a known transformation rate is determined in advance, and the measured magnetic flux strength Φ is compared with the reference magnetic flux strength to determine the transformation rate. Further, while moving the steel sheet 1 in a certain direction, the magnetic detection element 6 continuously measures the strength Φ of the magnetic flux 9 leaking to the opposite side of the steel sheet 1, and a point at which the magnetic flux strength Φ greatly changes is transformed on the steel sheet. It can be considered as a rate change point.

[0009]

However, the conventional transformation rate measuring apparatus shown in FIG. 6 still has the following problems.

That is, the magnetic detecting element 6 detects the floating magnetic flux output from the peripheral device in addition to the magnetic flux 9 output from the magnetic poles 4a and 4b of the magnetizer 4 and penetrating the steel plate 1. In particular, when this transformation rate measuring device is installed on the production line in the above-described steel mill, since a large number of motors and various electric devices are arranged around the device,
The magnetic flux leaking from these devices to the surroundings is large. When these magnetic fluxes intersect with the magnetic detection element 6, the signal derived from the stray magnetic flux is superimposed as a noise component on the signal component derived from the regular magnetic flux 9 detected from the magnetic detection element 6.

Accordingly, the signal component ratio of the normal magnetic flux 9 occupied in the output signal of the magnetic detecting element 6 is reduced, and the S / N of the entire output signal is reduced. Cannot be detected accurately. Therefore, the measurement accuracy of the transformation rate of the steel sheet 1 decreases.

In order to eliminate such inconvenience, the distance d ₂ between the magnetic sensing element 6 and the steel plate 1 may be set short to increase the number of magnetic fluxes 9 crossing the magnetic sensing element 6. However, since the steel plate 1 is moving at a considerable speed while vibrating, there is a concern that a contact accident or the like may occur if the magnetic detection element 6 is excessively approached. In addition, when the temperature of the steel sheet 1 is high, if the temperature is excessively approached, there is a concern that the magnetic detection characteristics of the magnetic detection element 6 change or the signal level of the detection signal fluctuates.

The present invention has been made in view of such circumstances, and has a structure in which a pair of magnetic poles and a pair of magnetic sensors of a magnetizer are arranged so as to face each other with a metal plate to be inspected interposed therebetween, so that an external device is provided. It is an object of the present invention to provide a transformation rate measurement method and apparatus capable of canceling a noise component caused by a stray magnetic flux, accurately detecting the intensity of a magnetic flux penetrating a metal plate, and greatly improving the transformation rate measurement accuracy. I do.

[0014]

According to the transformation rate measuring method of the present invention, in order to solve the above-mentioned problem, a magnetizing method for generating a magnetic flux for magnetizing a metal plate to be inspected close to one surface of the metal plate to be inspected. A pair of magnetic sensors are disposed so that a pair of magnetic poles face the metal plate, and a pair of magnetic sensors are disposed at respective opposing positions of the magnetic poles with the metal plate interposed therebetween and in a direction in which each magnetic sensitive direction is orthogonal to the metal plate. Then, a subtraction magnetic flux between the respective magnetic fluxes penetrating the metal plate detected by the pair of magnetic sensors is obtained, and the transformation rate of the metal plate is measured based on the subtraction magnetic flux value.

A transformation rate measuring apparatus according to the present invention further comprises a magnetizer for disposing a pair of magnetic poles on one surface of a metal plate to be inspected so as to face the metal plate and generating a magnetic flux for magnetizing the metal plate; A pair of magnetic sensors are disposed at respective opposing positions of the magnetic poles with the respective magnetic sensitive directions orthogonal to the metal plate, and detect a magnetic flux penetrating the metal plate, and each detection of the pair of magnetic sensors It comprises a subtraction circuit for subtracting a signal, and a signal processing unit for calculating a transformation rate of the metal plate based on the subtraction magnetic flux value obtained by the subtraction circuit.

[0016]

The principle of operation of the transformation rate measuring method and the apparatus constructed as described above will be described with reference to FIG.

In FIG. 2, each magnetic pole 10 of the magnetizer 10
Reference numerals a and 10b face one surface of the metal plate 12 to be inspected. The magnetic poles 10a, 10a sandwiching the metal plate 11
A pair of magnetic sensors 13a and 13b are provided at positions opposing to each other. The magnetic responsive direction of each of the magnetic sensors 13a and 13b is set in a direction orthogonal to the metal plate 11 indicated by the Y direction in the figure. For example, most of the magnetic flux output from one magnetic pole 10 a of the magnetizer 10 is input to the other magnetic pole 10 b via the inside of the metal plate 11. However, part of the magnetic flux output from the magnetic pole 10a of the magnetizer 10 is
1 through. The magnetic flux 14 that has penetrated the metal plate 11 passes through the space on the opposite side of the metal plate 11, penetrates the metal plate 11 in the opposite direction again, and is input to the other magnetic pole 10 b.

Each of the magnetic sensors 13a and 13b is a metal plate 11
Φa, Φb of the Y-direction component of the magnetic flux 14 penetrating through
Is detected. If there is a stray magnetic flux output from a device around the transformation rate measuring device, the magnetic flux intensity Φn of the stray magnetic flux in the Y direction is detected by each of the magnetic sensors 13a and 13b. Therefore, the magnetic flux intensities Φ _A and Φ _B in the respective Y directions detected by the respective magnetic sensors 13a and 13b are as follows. Φ _A = Φa + Φn Φ _B = Φb + Φn Therefore, when the magnetic flux strength difference ΔΦ between the magnetic flux strengths Φ _A and Φ _B detected by the magnetic sensors 13a and 13b is calculated, the floating magnetic flux strength Φ n is canceled. ΔΦ = Φa−Φb

Each of the magnetic sensors 13a and 13b is
Are arranged at positions facing the magnetic poles 10a and 10b, the magnetic flux intensities Φa and Φb of the magnetic flux 14 have the same value and opposite polarities (Φb = −Φa). Therefore, by calculating the magnetic flux intensity difference ΔΦ between the magnetic flux intensities Φ _A and Φ _B detected by the magnetic sensors 13a and 13b, it is possible to measure the correct magnetic flux intensity without the stray magnetic flux. ΔΦ = Φa−Φb = Φa − (− Φa) = 2Φa As described above, since the stray magnetic flux detected by each magnetic sensor can be canceled, the transformation ratio of the metal plate can be measured with a high S / N.

[0020]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing a schematic configuration of a transformation rate measuring apparatus to which the transformation rate measuring method of the embodiment is applied. The transformation rate measuring apparatus of this embodiment is incorporated in a heat treatment line in an iron mill, and is used to measure the transformation rate of a steel sheet continuously moved at a high speed.

The magnetizing power supply 21 outputs an AC exciting current I having a constant frequency f ₁ . The exciting current I output from the magnetizing power supply 21 is applied to an exciting coil 24 wound around a magnetized iron core 23 of a magnetizer 22. The magnetizer 22 is provided with magnetic poles 23a and 23b of a magnetized iron core 23 having a substantially U-shape.
Is the distance La on the lower surface of the steel plate 25 as the metal plate to be inspected.
(Lift-off) so as to face each other. The steel plate 25 is transported in a direction perpendicular to the plane of the drawing.

A pair of magnetic sensors 26a, 26b having the same configuration are disposed at a position separated by a distance Lb on the upper surface of the steel plate 25 and at positions opposed to the magnetic poles 23a, 23b of the magnetizer 22. The output signals a ₁ and a ₂ of the magnetic sensors 26a and 26b are input to the magnetic detection circuits 27a and 27b, respectively. The output signals a ₁ and a ₂ of the respective magnetic sensors 26a and 26b are converted by the magnetic detection circuits 27a and 27b into the intensities Φ _A and Φ _{B of} the respective magnetic fluxes crossing the respective magnetic sensors 26a and 26b.
Are converted into the detection signals b ₁ and b ₂ corresponding to. Each detection signal b ₁ , output from each magnetic detection circuit 27a, 27b,
b ₂ is input to the next differential amplifier 28. This differential amplifier 28 detects a difference signal c between the detection signals b ₁ and b ₂ and sends it to the next signal processing unit 29.

The signal processing unit 29 is composed of, for example, an amplifier and a recorder, and uses a calibration curve previously experimentally determined from the magnetic flux intensity ΔΦ included in the input difference signal c to obtain a transformation rate A. And outputs it to the recorder. The recorder records the change over time of the transformation rate A.

As the magnetic sensors 26a and 26b, supersaturated magnetic sensors described in JP-A-1-308982 are employed. That is, the magnetic sensor 26
In a and 26b, detection coils 31a and 31b are wound around rod-shaped cores 30a and 30b formed of a ferromagnetic material. Further, high-frequency excitation currents are continuously supplied to the detection coils 26a and 26b from the high-frequency power supplies 32a and 32b having the same configuration via the resistors 33a and 33b. Each rod-shaped core 30a, 30b is in a state of being excited to a supersaturated region. Therefore, each detection coil 31
The amplitude value of the output voltage waveform at both ends of a and 31b is constant.

The bar core 3 excited to such supersaturation
When the external magnetic flux approaches 0a and 30b, the amplitude value of the voltage waveform at both ends does not change, but the positive and negative peak values Va and -V
b changes. Therefore, the magnetic detection circuits 27a, 27
In b, the peak values Va and -Vb are detected by a detector, converted into direct current, and added by an adder to obtain a difference voltage (Va-Vb). That is, the difference voltage (Va-Vb) corresponds to the external magnetic flux applied to the magnetic sensors 26a and 26b. Therefore, the respective magnetic sensors 26a, 2b are output from the respective magnetic detection circuits 27a, 27b.
Detection signals b ₁ and b ₂ corresponding to the magnetic flux intensities Φ _A and Φ _B of the respective magnetic fluxes applied to 6b are output. In addition, each magnetic detection circuit 27a, 2 in these magnetic sensors 26a, 26b
The frequency response performance of each of the detection signals b ₁ and b ₂ output from 7b is sufficiently higher than the frequency f _{1 of the} exciting current I. Therefore, the difference signal c output from the differential amplifier 28 indicates the magnetic flux intensity ΔΦ of the difference between the magnetic flux intensities Φ _A and Φ _B. ΔΦ = Φ _A −Φ _B

In the transformation rate measuring apparatus thus configured, when the magnetization power supply 21 is activated, the steel plate 25 is magnetized by the magnetizer 22. Then, for example, one magnetic pole 23
a, most of the magnetic flux output from the first magnetic pole 23b passes through the inside of the steel plate 25.
5 through the space of the steel plate 25 on the side of the magnetic sensors 26a and 26b, and again through the steel plate 25 in the reverse direction and is input to the other magnetic pole 23b.

Since the magnetic sensing direction of each of the magnetic sensors 26a and 26b is orthogonal to the steel plate 25, each of the magnetic sensors 26a and 26b has a magnetic flux passing through the steel plate 25.
The magnetic flux intensity Φn in the direction orthogonal to the steel plate 25 out of the magnetic fluxes Φa and Φb in the direction orthogonal to 5 and the stray magnetic flux output from the surrounding electric devices is detected. Therefore, as described above, the magnetic flux intensities Φ _A and Φ _B detected by the magnetic sensors 26a and 26b are as follows. Φ _A = Φa + Φn Φ _B = Φb + Φn

Therefore, the component of the floating magnetic flux intensity Φn can be removed from the magnetic flux intensity difference (subtracted magnetic flux) ΔΦ (= Φa−Φb) obtained by the differential amplifier 28. In addition, each magnetic sensor 26
Since a and 26b are disposed at positions facing the magnetic poles 23a and 23b of the magnetizer 22, the magnetic flux intensities Φa and Φb have the same value and opposite polarities (Φb = −Φa). Therefore, by calculating the magnetic flux intensity difference ΔΦ between the magnetic fluxes Φ _A and Φ _B detected by the magnetic sensors 26a and 26b,
The correct magnetic flux intensity without the stray magnetic flux can be measured. ΔΦ = Φa−Φb = 2Φa

Therefore, this magnetic flux intensity difference ΔΦ is
The value corresponds to the transformation rate A of 5. The signal processing unit 29 records the time conversion of the transformation rate A converted from the magnetic flux intensity difference ΔΦ using the calibration curve.

FIG. 3 shows the difference corresponding to the magnetic flux intensity difference ΔΦ of the differential amplifier 27 when the transformation rate is measured by the embodiment apparatus for a large number of test steel sheets having a known transformation rate A of 0 to 100%. FIG. 9 is a characteristic diagram illustrating a relationship between an output level (mV) of a signal c and the transformation A. However, the thickness T of the test steel sheet is 5.6 mm, the distance B of the magnetic poles 23a, from 23b to the magnetic sensors 26a, 26b is 500 mm, the magnetization frequency f ₁ of the magnetizer 22 is set to 10Hz ing. The average voltage e _m of the high-frequency signal outputted high-frequency power source 32a, from 32b is 3 mV. The characteristic shown by a solid line in the figure is a characteristic under the condition that the lift-off La is 100 mm, and the characteristic shown by a broken line is a characteristic under the condition that the lift-off La is 100 mm. Therefore, the characteristics shown in FIG. 3 are calibration characteristics.

As shown in the characteristics of FIG.
Output voltage is 83 to 240 mV for a change range of 00%
And a very wide measurement range was obtained. Therefore, the distance Lb between the magnetic sensors 26a, 26b and the steel plate 25 is
Even if it is set large, a sufficiently high detection level can be secured. The lift-off La is 100 to 125 mm (25
%), The output signal level was less than 5% in terms of the transformation rate A, and a very good value was obtained.
Although not shown in the graph of FIG. 3, since the component of the stray magnetic flux is removed as described above, high repeat measurement accuracy can be secured.

In FIG. 4, the exciting coil 2 of the magnetizer 22
4 when the exciting frequency f1 of the exciting current I applied to the sample _No. 4 is changed from 0 Hz (DC) to 240 Hz, and the supersaturated magnetic sensors 26a and 26b of the embodiment. 7 shows a comparison with a change in output level when a conventional ordinary search coil type magnetic sensor is used instead of the supersaturation type magnetic sensor. In addition,
2. Description of the Related Art A conventional search coil type magnetic sensor is a magnetic sensor in which a coil is wound around a ferrite core and an induced voltage generated in the search coil by an external magnetic field is detected. As shown in FIG. 4, in the search coil type magnetic sensor, the detection sensitivity greatly depends on the frequency of the measurement magnetic flux, and at a frequency of about 220 Hz or less, the detection sensitivity is much lower than that of the saturable type magnetic sensor. In addition,
The number of coil turns in this search coil type magnetic sensor is 15
00 times.

On the other hand, the detection sensitivity of the oversaturated magnetic sensor of the present embodiment does not depend on the number of turns, but is much smaller than the conventional search coil type magnetic sensor (200 times in this embodiment). I'm done.

In general, the excitation frequency f ₁ depends on the purpose of inspection and the steel plate 2.
The optimum frequency is set according to the thickness T of No. 5. And
The purpose of the inspection is to measure the transformation rate, and the thickness T of the steel sheet 25 is 1 to
In the range of 10 mm, the exciting frequency f ₁ is often set in a range of several Hz ~ several tens Hz. Therefore, as shown in the frequency characteristic diagram of FIG. 4, the magnetic sensors 26a and 26b
By using a supersaturated magnetic sensor, a constant output signal level can be obtained in a wide frequency range. FIG. 5 is a schematic configuration diagram of a transformation rate measuring apparatus according to another embodiment of the present invention. The same parts as those in the embodiment of FIG. 1 are denoted by the same reference numerals.

In this embodiment, the detection coils 36a and 36b are wound around the respective rod-shaped cores 35a and 35b of the magnetic sensors 34a and 34b disposed opposite to the magnetic poles 23a and 23b of the magnetizer 22, respectively. Have been. The winding directions of the detection coils 36a and 36b are the same. Then, a high-frequency signal output from the high-frequency power supply 32 is applied to the winding start terminal St of the detection coil 36a of one magnetic sensor 34a via the resistor 33. The winding terminator En of the detection coil 36a is connected to the winding terminator En of the detection coil 36b of the detection coil 34b of the other magnetic sensor 36b. The winding start terminal S of the detection coil 36b
t is grounded.

An output signal a taken from the winding start terminal St of the magnetic sensor 34a is input to the magnetic detection circuit 27. The magnetic detection circuit 27 detects the magnetic flux intensity from the output signal a and sends it to the next signal processing unit 29.

In the transformation rate measuring apparatus having such a configuration, each of the magnetic sensors 34a and 34b acts so that the signal level shifts in the opposite direction to the external magnetic field.
Therefore, the stray magnetic flux intensities Φn detected by the magnetic sensors 34a and 34b have opposite polarities. Therefore, in the output signal a of the magnetic sensors 34a and 34b connected in series, the stray magnetic flux intensities Φn cancel each other. Also,
Since the magnetic flux penetrating the steel plate 25 from the magnetizer 22 acts on the magnetic sensors 36a and 36b in opposite directions, the output signal a includes information on the added strength 2Φa of each magnetic flux.

Therefore, in this embodiment, each detection coil 36a, 36b of each magnetic sensor 34a, 34b
The wiring between these constitutes a subtraction circuit. Therefore, it is possible to remove the differential amplifier 28 in FIG. 1 and directly apply the output signal g of the magnetic detection circuit 27 to the signal processing unit 29.

Therefore, substantially the same effects as in the embodiment of FIG. 1 can be obtained. Further, in this embodiment, as compared with the embodiment shown in FIG. 1, only one high-frequency power supply 32 can be implemented and the differential amplifier 28 can be eliminated, so that the entire apparatus can be reduced in size and weight and at low manufacturing cost. Can be manufactured.

The present invention is not limited to the embodiment described above. In the embodiment device, the magnetic sensor 2
Although a supersaturated magnetic sensor having excellent temperature characteristics and detection sensitivity characteristics is used as 6, for example, a semiconductor magnetic sensor using a Hall element provided with a temperature assurance circuit may be used. Further, the effect of the present invention can be sufficiently achieved even if the detection sensitivity is low or a normal search coil type magnetic sensor is used.

[0041]

As described above, according to the transformation rate measuring method and the transformation rate measuring apparatus of the present invention, the pair of magnetic poles of the magnetizer and the pair of magnetic sensors are opposed to each other with the metal plate to be inspected interposed therebetween. Are arranged. Therefore, by taking the difference between the outputs of the respective magnetic sensors, it is possible to cancel the noise component caused by the external stray magnetic flux. Also, since the magnetic flux penetrating the metal plate acts on each magnetic sensor in the opposite direction,
By taking the difference, the magnetic flux penetrating the metal plate can be detected with twice the sensitivity. Therefore, the intensity of the magnetic flux penetrating the metal plate can be accurately detected with a high S / N, and as a result, the transformation rate of the metal plate can be measured more accurately.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a schematic configuration of a transformation rate measuring apparatus to which a transformation rate measuring method according to one embodiment of the present invention is applied;

FIG. 2 is a diagram showing the operation principle of the present invention;

FIG. 3 is a diagram showing a relationship between a transformation rate of a sample steel sheet and an output voltage level measured by the apparatus according to the embodiment;

FIG. 4 is a diagram showing frequency characteristics of different types of magnetic sensors employed in the apparatus of the embodiment;

FIG. 5 is a schematic diagram showing a schematic configuration of a transformation rate measuring apparatus according to another embodiment of the present invention;

FIG. 6 is a schematic diagram showing a schematic configuration of a conventional transformation rate measuring device.

[Explanation of symbols]

21 ... magnetization power supply, 22 ... magnetizer, 23 ... magnetization core, 23
a, 23b: magnetic pole, 24: exciting coil, 25: steel plate, 2
6a, 26b, 34a, 34b ... magnetic sensor, 27, 2
7a, 27b: magnetic detection circuit, 28: differential amplifier, 29
... Signal processing unit, 32, 32a, 32b ... High frequency power supply.

Claims (2)

(57) [Claims] 1. A magnetizer for generating a magnetic flux for magnetizing a metal plate in close proximity to one surface of a metal plate to be inspected is disposed such that a pair of magnetic poles is opposed to the metal plate. A pair of magnetic sensors are disposed at respective opposing positions of the magnetic poles and in a direction in which each magnetically sensitive direction is orthogonal to the metal plate,
A transformation rate measuring method for determining a subtraction magnetic flux between respective magnetic fluxes penetrating the metal plate detected by the pair of magnetic sensors, and measuring a transformation rate of the metal plate with the subtraction magnetic flux value. 2. A magnetizer for disposing a pair of magnetic poles on one surface of a metal plate to be inspected to generate magnetic flux for magnetizing the metal plate, and a magnetizer for generating magnetic flux for magnetizing the metal plate. At each opposing position, each magnetic sensitive direction is arranged in a direction orthogonal to the metal plate, and a pair of magnetic sensors for detecting magnetic flux penetrating the metal plate, and subtracting respective detection signals of the pair of magnetic sensors. A transformation rate measuring device comprising: a subtraction circuit; and a signal processing unit for calculating a transformation rate of the metal plate based on a subtraction magnetic flux value obtained by the subtraction circuit.