JP3050042B2 - Transformation rate measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for online measuring the transformation ratio of a steel sheet after hot rolling by electromagnetic means.

[0002]

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

For example, magnetic permeability among magnetic properties 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 steel is transformed from an austenite (γ) phase in a high-temperature state to a ferrite (α) phase in a low-temperature state during the heat treatment of the hot steel. Monitoring is extremely important in managing the material of the steel sheet, and development of a sensor that measures the transformation rate online is desired.

In the measurement of this phase transformation, a magnetic detector is used by utilizing the fact that the γ → α transformation of steel involves a physical phenomenon of changing from non-magnetic (γ phase) to ferromagnetic (α phase). There is a method to detect the transformation behavior. In this method, the magnetic properties of the steel greatly change around the Curie point, and the Curie point of most commercial steels is as high as 750 ° C. or higher, while the γ-α transformation of the steel in the cooling process is performed at a lower temperature. Since the magnetic field advances in the region, it is only necessary to detect a change in the magnetic characteristic accompanying the progress.

In order to measure the magnetic properties of a steel sheet that is actually continuously flowing during the manufacturing process, it is necessary to perform these measurements in a non-contact and online state. Conventionally, when measuring the magnetic properties of such a steel sheet in a non-contact and online state, a transformation rate measurement device that uses the property that the attenuation rate of the magnetic flux passing through the steel sheet changes according to the magnetic properties of the steel sheet has been proposed. Has been
For example, there is one disclosed in JP-A-56-82443.

FIG. 4 is a block diagram showing the configuration of a conventional transformation rate measuring device disclosed in the above-mentioned document. In FIG. 4, a magnetizer 24 composed of a magnetized iron core 22 and an exciting coil 23 is provided on one side (a lower side in the figure) of a steel plate 21 to be inspected at a predetermined distance d ₁ from a pair of magnetic poles 24 a. , 24b is steel plate 2
1. And magnetizer 24
An exciting current is supplied from a magnetizing power supply 25 to the exciting coil 23, and a magnetic flux is generated between the magnetic poles 24a and 24b. This magnetic flux includes a magnetic flux 29 leaking to the outside in addition to a magnetic flux passing through the inside of the steel plate 21, and the magnetic flux 29 leaking to the outside.
Is detected by a magnetic detection element 26 arranged on the other side (upper side in the figure) of the steel plate 21 at a distance d ₂ . The leakage magnetic flux detection signal detected by the magnetic detection element 26 is transmitted to the arithmetic unit 28. Further, the surface temperature of the steel plate 21 is measured by a thermometer 27, and this temperature measurement signal is also transmitted to the arithmetic unit 28.

According to the transformation rate measuring device having such a configuration, if the steel plate 21 as a ferromagnetic material exists between the magnetizer 24 and the magnetic detection element 26, the output from one magnetic pole 24a of the magnetizer 24 is output. Most of the applied magnetic flux passes through the inside of the steel plate 21 and is input to the other electrode 24b, but a part of the magnetic flux passes through the steel plate 21 and is detected by the magnetic detection element 26.

When the transformation rate of the steel plate 21 changes,
The magnetic properties such as the magnetic permeability of the steel plate 21 change. Then
Since the amount of magnetic flux passing through the inside of the steel plate 21 changes, the magnetic flux density detected by the magnetic detection element 26 also changes accordingly. Therefore, the reference magnetic flux density in the test steel sheet having a known transformation rate is determined in advance, and the measured magnetic flux density is compared with the reference magnetic flux density to quantitatively determine the transformation rate. In addition, while moving the steel plate 21 in a certain direction, the density of the magnetic flux 29 leaking to the opposite side of the steel plate 21 is continuously measured by the magnetic detection element 26, and a point where the magnetic flux density greatly changes is a change in the transformation rate of the steel plate. It can be considered as a point.

[0010]

However, the conventional transformation rate measuring apparatus as described above still has the following problems. That is, the conventional transformation rate measuring device is configured to detect the transformation rate of the steel sheet by measuring the amount of transmission of the magnetic flux emitted from the excitation coil through the steel sheet with a magnetic flux detector in principle. If a disturbing magnetic field other than the magnetic field exists, the disturbing magnetic field is mixed as noise with respect to the detection signal and causes a deterioration in S / N. One of the disturbance magnetic fields is terrestrial magnetism and residual magnetism of the steel plate itself to be inspected. Since these magnetic fields are DC magnetic fields,
To eliminate that effect, the magnetic field emanating from the magnetizer must be an alternating magnetic field. In the water-cooling process after hot rolling, a table roll for guiding the steel sheet is arranged, and as a disturbance magnetic field separately from the above-mentioned disturbance DC magnetic field, the roll below the steel sheet has residual magnetism. There is rotational noise.

[0011] As a countermeasure, it is extremely difficult to replace the roll with a non-magnetic material such as SUS in consideration of seizure of the steel sheet and abrasion resistance. The present invention has been made in order to solve such a problem, and an object of the present invention is to obtain a high-precision steel sheet transformation rate measuring apparatus in which S / N is improved by removing noise due to roll rotation during the conveyance of the steel sheet. .

[0012]

According to the present invention, there is provided a transformation rate measuring device which sandwiches a steel sheet running by rotation of a roll,
On one side thereof, an AC magnetic flux generating means for generating an AC magnetic flux is provided, and on the other side, a magnetic flux detecting means for detecting an AC magnetic flux generated by the AC magnetic flux generating means and leaking through the steel plate is provided. In a transformation rate measuring device that measures the transformation rate of the steel sheet from the magnetic flux density detected by the means, in order to avoid the influence of a disturbance magnetic field generated by a frequency corresponding to the roll rotation speed based on the residual magnetism of the roll, When the rotation speed of the roll is changed, an AC magnetic flux generating unit that changes an excitation frequency according to the roll rotation speed and generates an AC magnetic flux having a frequency different from a frequency of a disturbance magnetic field according to the roll rotation speed is provided. Things.

[0013]

According to the present invention, an AC magnetic flux generating means for generating an AC magnetic flux is provided on one side of a steel sheet running by rotation of a roll, and the AC magnetic flux generating means is provided on the other side. In a transformation rate measuring device for providing a magnetic flux detecting means for detecting an AC magnetic flux leaking through the steel sheet, and measuring a transformation rate of the steel sheet from a magnetic flux density detected by the magnetic flux detecting means, the AC magnetic flux generating means includes: In order to avoid the influence of the disturbance magnetic field generated by the frequency corresponding to the roll rotation speed based on the residual magnetism, the excitation frequency is changed according to the roll rotation speed when the roll rotation speed is changed, and An AC magnetic flux having a frequency different from the frequency of the disturbance magnetic field according to the roll rotation speed is generated.

[0014]

FIG. 2 is a diagram for explaining the operation principle of the transformation rate measuring apparatus according to the present invention. In FIG. 2, reference numeral 10 denotes a magnetizer, which includes a magnetized iron core 10a and an exciting coil 10b, is installed between the lower table rolls 17 and 18 of the steel plate 12, and is connected to a magnetizing power supply 13. Reference numeral 15 denotes a magnetic flux detection element, which is connected to the magnetic detection circuit 16 and is installed above the steel plate 12. The output signal of the magnetic detection circuit 16 is supplied to an arithmetic circuit 19 for calculating a transformation rate. The magnetic flux detector 15 detects the magnetic flux transmitted through the steel plate among the magnetic fluxes emitted from the magnetizer, and the amount of transmission depends on the transformation rate of the steel sheet. Is required.

The magnetizing power supply 13 has a built-in oscillator 14 which oscillates at a frequency f, and excites the exciting coil 10b with an alternating current at the frequency f. Here, the magnetizing power supply 13 excites the exciting coil 10b with the alternating current of the frequency f based on the output of the oscillator 14 because the magnetic field generated by the magnetizer 10 has an error due to the influence of the terrestrial magnetism when the applied magnetic field is direct current. Since an error is detected, an excitation method using an AC magnetic field is employed to remove this error.

In the hot rolling line, Cr-based rolls are used for the lower rolls 17 and 18, and since they have residual magnetism, when the rolls 17 and 18 rotate, a disturbance having a frequency corresponding to the number of rotations occurs. A magnetic field is generated. Accordingly, when the speed at which the steel sheet is conveyed is accelerated from a low speed to a maximum speed, the rotation speeds of the lower rolls 17 and 18 change accordingly. At this time, the output signal of the magnetic detection circuit 16 includes the roll rotation speed. Noise having a corresponding frequency is mixed in, and causes S / N deterioration.

For this reason, the oscillator 1 for driving the magnetizer 10
As the frequency f of 4, a frequency corresponding to the above-described roll rotation speed or a frequency excluding the vicinity of this frequency is selected.
The frequency corresponding to the number of rotations of the roll is such that the roll diameter is d.
(Unit is m) and the traveling speed of the steel sheet is v (unit is m / s), which is represented by v / (πd) (Hz). Therefore, either a frequency higher or lower than the frequency f of the oscillator 14, which is the excitation frequency, and v / (πd) (Hz), which is a frequency corresponding to the rotation speed of the roll, is selected.

As a first method of selecting the excitation frequency f,
When selecting a frequency higher than the frequency corresponding to the number of rotations of the roll, if the excitation frequency f is gradually increased,
It is necessary to consider the upper limit that the magnetic flux concentrates on the plate surface and hardly penetrates inside. Therefore, the upper limit of the excitation frequency f is limited depending on how far the penetration depth of the magnetic flux into the steel sheet is maintained.

Therefore, in the first selection method, the excitation frequency f for generating an AC magnetic field is set to a lower limit value for avoiding mixing of the roll residual magnetic noise, a generally known excitation frequency and Selection is made so as to satisfy the following expression (1) between upper limit values determined from the relational expression of the penetration depth. v / (πd) <f <1 / (πμσt ² ) (1) where v is the traveling speed of the steel sheet (unit is m / s), d is the roll diameter (unit is m), and t is the thickness of the steel sheet. (Unit is m), μ is the magnetic permeability of the steel sheet (unit is H / m), and σ is the electric conductivity of the steel sheet (unit is 1 / Ωm).

As a second method of selecting the excitation frequency f, when selecting a frequency lower than the frequency corresponding to the number of rotations of the roll, the excitation frequency f is selected so as to satisfy the following equation (2). v / (πd)> f (2)

In order to satisfy the expressions (1) and (2), it is necessary to provide a margin between the excitation frequency f and the upper and lower limits thereof in order to cover uneven rotation of the roll. Needless to say, it is preferable to provide a manual adjusting means capable of variably adjusting the excitation frequency f when the rotation number of the roll is controlled and changed, or an automatic adjustment means interlocked with the rotation number of the roll.

FIG. 1 is a block diagram showing one embodiment of a transformation rate measuring apparatus according to the present invention. In FIG. 1, reference numeral 10 denotes a magnetizer, which includes a magnetized iron core 10a and an exciting coil 10b, and is connected to a magnetizing power supply 13. In this example,
The magnetizer 10 is installed at a predetermined distance d1 below the steel plate 12 traveling online. The magnetizing power supply 13
A low-frequency oscillator 14 oscillating at a frequency f is built in,
The excitation coil 10b is driven by the AC power source having the low frequency f.
Is excited. In this example, the frequency f of the low-frequency oscillator 14 is selected so as to satisfy the above equation (1), that is, v / (πd) which is a frequency corresponding to the roll rotation speed or a value higher than a frequency in the vicinity thereof. Is done.

In FIG. 1, 1 is a high-frequency power supply, 2 is a resistor, 3 is a magnetic sensor, which is constituted by a sensor core 3a and a detection coil 3b.
Is supplied to the magnetic detection circuit 4. The magnetic detection circuit 4 outputs a voltage signal V2 proportional to the detected magnetic flux density based on the input signal V1 from the magnetic sensor 3. This voltage signal V2 is
After passing through a low-pass filter 5 (hereinafter referred to as LPF) and a high-pass filter 6 (hereinafter referred to as HPF), it is supplied to a lock-in amplifier 7. The lock-in amplifier 7 has
In order to synchronously detect the output signal of the HPF 6, the output signal of the low-frequency oscillator 14 is also supplied. The output signal V4 of the lock-in amplifier 7 is output as a signal V7 indicating a transformation rate after passing through a signal processing circuit composed of a zero adjustment circuit 8, an inverter 9 and a linearizer 11.

Here, a magnetic measuring device comprising the high-frequency power supply 1, the resistor 2, the magnetic sensor 3 and the magnetic detecting circuit 4 shown in FIG.
The same apparatus as that described in "Magnetic Measurement Method and Magnetic Measuring Apparatus" of JP-A No. 2 is used. That is, the magnetic sensor 3 is configured by winding a detection coil 3b around a sensor core 3a formed of a ferromagnetic material, and a high-frequency constant voltage signal output from the high-frequency power supply 1 is applied to the detection coil 3b via the resistor 2. , The exciting current always flows. Then, the sensor core 3a is in a state of being excited up to the supersaturation region. The magnetic detection circuit 4 includes, at both ends of the detection coil 3b, a positive voltage detector and a negative voltage detector that individually detect a positive voltage and a negative voltage that are alternately generated based on the high-frequency excitation current, respectively. And an adder for adding the output voltage of the detector to obtain a difference voltage.

In the state where no magnetic flux exists in the installation region of the magnetic sensor 3 excited to the supersaturation region in this manner, the peak values V _p of the positive voltage and the negative voltage alternately generated at both ends of the detection coil 3b and − equal to the V _n. Therefore, the output obtained by adding the positive and negative DC voltages obtained by detecting these two peak values by the adder becomes zero. However, the external magnetic flux is applied to the magnetic sensor 3, but the sum of the peak value of the positive voltage and a negative voltage generated across the detection coil 3b does not change, a difference in values of the peak value V _p and -V _n positive and negative Occurs. Thus by adding a DC voltage of positive and negative which detects the two peak value in the adder, the difference voltage (V _p -V _n) is obtained. The difference voltage (V _p -V _n) becomes a value corresponding to the external magnetic flux density given to the magnetic sensor 3. The detection signal V ₂ corresponding to the magnetic flux density leaked from the running steel plate 12 and applied to the magnetic sensor 3 is sequentially output from the magnetic detection circuit 4.

The response frequency of the detection signal V ₂ output from the magnetic detection circuit 4 based on the detection signal of the magnetic sensor 3 is sufficiently higher than the frequency f of the low frequency oscillator 14. By using the supersaturated magnetic sensor 3 as a magnetic flux detector, a high-sensitivity magnetic sensor is realized, and the distance d ₂ between the steel plate 12 and the magnetic sensor 3 can be measured at a distance of 1 m or more. Separating by more than 1
2 eliminates the influence of the pass line fluctuation, and enables measurement of the transformation ratio of the steel sheet at a high S / N.

The output signal of the magnetic detection circuit 4 is input to a lock-in amplifier 7 after passing through LPFs 5 and HPFs 6 in order to remove high-frequency noise components and roll rotation noise caused by low-frequency roll residual magnetism. Is done. The output signal of the oscillator 14 is also used as a synchronization signal for the lock-in amplifier 7.
Is input to The lock-in amplifier 7 incorporates a synchronous detector and an amplifier, synchronously detects an input signal from the magnetic detection circuit 4 by an output signal of the low-frequency oscillator 14, and outputs an electric signal obtained by amplifying the detected signal. . Then, the voltage value of this output signal becomes a measurement signal corresponding to the transformation rate.

FIG. 3 is a waveform diagram for explaining the operation of the signal processing circuit of FIG. 1. The signal processing of FIG. 1 will be described with reference to FIG. The vertical axis of the waveform diagram of FIG. 3 is voltage, and the horizontal axis is cooling time. The high temperature side where the cooling time is short is the γ phase,
The long-time low-temperature side is the α phase. The output voltage V ₄ of the lock-in amplifier 7 is supplied to the zero adjustment circuit 8. The zero-tone circuit 8 shifts the level of the input signal, and supplies an output signal (see FIG. 3B) to the inverter 9 such that the signal level in the γ phase becomes zero. The inverter 9 inverts the polarity of the input signal, outputs the negative voltage V ₅ as the positive voltage V ₆ (see FIG. 3C), and supplies the same to the linearizer 11.

Since the linearizer 11 has a non-linear gradient of the γ-α transformation of the input signal, the voltage signal V ₇ (see FIG. 3 (d)) obtained by converting this into a linear signal is used as a measurement signal corresponding to the transformation rate. Output. For example, when the output signal V ₇ linearizer 11 varies between 0~10V is, V ₇
The voltage values of 0V, 1V, 2V, 3V,... 10V are 0%, 10%, 20%, 30%,.
Adjust to correspond to%. Thus, a measurement signal V7 corresponding to the transformation rate is obtained on the output side of the linearizer 11.

[0030]

As described above, according to the present invention, an AC magnetic flux generating means for generating an AC magnetic flux is provided on one side of a steel sheet running by rotation of a roll, and the other side is provided with the AC magnetic flux generating means. Provided is a magnetic flux detecting means for detecting an AC magnetic flux generated by the AC magnetic flux generating means and leaking through the steel sheet,
In the transformation rate measuring device for measuring the transformation rate of the steel sheet from the magnetic flux density detected by the magnetic flux detection means, the AC magnetic flux generation means, by a frequency according to the number of rotations of the roll based on the residual magnetism of the roll. In order to avoid the influence of the generated disturbance magnetic field, when the rotation speed of the roll is changed, the excitation frequency is changed according to the roll rotation speed, and the AC magnetic flux having a frequency different from the frequency of the disturbance magnetic field according to the roll rotation speed is changed. , It is possible to avoid the influence of the disturbance magnetic field generated by the frequency corresponding to the roll rotation speed, and to remove the influence of the DC disturbance magnetic field due to the geomagnetism and the residual magnetism of the steel sheet to improve the transformation rate with high accuracy. Can be measured.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of a transformation rate measuring device according to the present invention.

FIG. 2 is a diagram for explaining the operation principle of the transformation rate measuring device according to the present invention.

FIG. 3 is a waveform chart for explaining an operation of the signal processing circuit of FIG. 1;

FIG. 4 is a configuration block diagram of a conventional transformation rate measuring device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 High frequency power supply 2 Resistance 3 Magnetic sensor 3a Sensor core 3b Detection coil 4 Magnetic detection circuit 5 Low pass filter 6 High pass filter 7 Lock-in amplifier 8 Zero adjustment circuit 9 Inverter 10 Magnetizer 10a Magnetized iron core 10b Magnetized coil 11 Linearizer 12 Steel plate 13 Magnetized Power supply 14 Oscillator 15 Magnetic detection element 16 Magnetic detection circuit 17, 18 Lower table roll 19 Operation circuit

Claims (1)

(57) [Claims] An AC magnetic flux generating means for generating an AC magnetic flux is provided on one side of a steel sheet running by the rotation of a roll, and the steel sheet generated by the AC magnetic flux generating means is provided on the other side. In a transformation rate measuring device provided with a magnetic flux detecting means for detecting an alternating magnetic flux that leaks through, and measuring a transformation rate of the steel sheet from a magnetic flux density detected by the magnetic flux detecting means, a roll based on residual magnetism carried by the roll In order to avoid the influence of the disturbance magnetic field generated by the frequency corresponding to the rotation speed, when the rotation speed of the roll is changed,
A transformation rate measuring device comprising: AC magnetic flux generating means for generating an AC magnetic flux having a frequency different from a frequency of a disturbance magnetic field according to the roll rotation speed by changing an excitation frequency in accordance with the magnetic field.