JPH05232087A - Magnetic damage detecting device - Google Patents

Abstract

PURPOSE:To realize the maintenance of uniform detection sensitivity over the whole width of a metal band by conducting the series connection of plural magnetic sensors provided in the width direction of the metal band, obtaining a wide series addition signal at each step of a detection sensitivity distribution characteristic. CONSTITUTION:A fixation shaft 2 is provided at the center of a non-magnetic hollow roll 1, and one end is fixed. A magnetizer 4 and a magnetic sensor group 7 whose plural magnetic sensors 7a are arranged axially between magnetic poles 4a, 4b, are fixed at the fixation shaft 2. Adjoining two sensors 7a1, 7a2 are connected mutually in series, and one end is connected to a pulse voltage generator 15 and a defect detecting circuit 16 through a resistance 14. Hereupon, a metal band 10 is made to travel in an arrow (a) direction, and a magnetizing electric current is supplied to a magnetizing coil 6, and then, a magnetic passage closed by means of the magnetizer 4 and the metal band 10 is formed. If there is a defect on the inside or the surface of the metal band 10, the magnetic passage in the metal band 10 falls into disorder, and leak magnetic flux is generated. This leak magnetic flux is detected by means of the sensors 7a1, a2 of the sensor group 7 that are opposite to the position of the defect, and a series addition signal al to cope with the defect is outputted to the circuit 16.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnet arranged in the width direction of a metal strip by generating a magnetic field in the metal strip by a magnetizer housed in a hollow roll rotating in contact with the running metal strip. The present invention relates to a magnetic flaw detector that detects a defect in a metal band with a sensor.

[0002]

2. Description of the Related Art In an inspection line in a steel factory, it is particularly important to detect defects existing on the surface or inside of a thin steel strip that flows continuously in the inspection line among many quality inspection items. .. For example, thin steel strips used as materials for beverage cans and food cans are subject to processing under harsh conditions, so if minute flaws or non-metallic inclusions are present inside or on the surface, cracks will occur during processing and As a cause of a fatal leak. In order to prevent this processing leakage, it is necessary to detect defects due to minute non-metallic inclusions over the entire width and the entire length of the thin steel strip.

In order to detect such a defect in the thin steel strip, a leakage magnetic flux flaw detection method has been conventionally put into practical use. In this leakage magnetic flux flaw detection method, if there is a defect inside the thin steel strip magnetized by direct current, a leakage magnetic flux corresponding to the size of the defect is generated on the surface of the thin steel strip at that portion, The leakage magnetic flux is detected by a magnetic sensor to detect the size of the defect and the defect occurrence position.

A magnetic flaw detector for arranging a plurality of magnetic sensors in the width direction of a thin steel strip to detect defects in the thin steel strip in an online state has been proposed (JP-A-56-61645, JP-A-56-16645). 63-107849).

Usually, the detection sensitivity of the magnetic sensor has a maximum distribution at the center position of the magnetic sensor, and has a normal distribution characteristic type distribution that gradually decreases as the distance from the center position increases.
Therefore, in the magnetic flaw detector disclosed in Japanese Patent Laid-Open No. 56-61645, a plurality of magnetic sensors are arranged in a zigzag pattern between the magnetic poles of the magnetizer that magnetizes the thin steel strip and arranged in the width direction. In addition, the total sensitivity of all magnetic sensors can be maintained at a constant level, and the detection failure of defects in the width direction of the thin steel strip is prevented.

Further, in the magnetic flaw detector disclosed in Japanese Patent Laid-Open No. 63-107849, a magnetizer for magnetizing a thin steel strip is provided in a hollow roll provided so as to come into contact with the thin steel strip. ing. And 1/3 between the magnetic poles of the magnetizer
Alternatively, the detection sensitivity is increased by arranging a plurality of magnetic sensors at the position of 2/3.

[0007]

However, in a general metal plate, when a magnetic field is generated in the metal plate, if a defect exists, a leakage magnetic flux is generated corresponding to the size of the defect, and even if there is a defect at all. Even in the non-healthy part, some leakage magnetic flux is generated. This is generally called stray magnetic flux.

In the magnetic flaw detector, since the magnetic sensor is arranged at a position displaced from the central position between the magnetic poles in order to increase the detection sensitivity as described above, the stray magnetic flux in the normal portion of the thin steel strip is provided. The vertical component to the thin steel strip of is not zero. Therefore, S of the output signal of the magnetic sensor
There is a problem that / N is lowered and is greatly affected by noise, and minute defects cannot be accurately detected.

Further, in the magnetic flaw detector disclosed in Japanese Patent Laid-Open No. 56-61645, since the magnetic sensors are arranged in two rows in the width direction of the thin steel strip, the longitudinal direction of the thin steel strip. There is also a problem in that the defect position detection accuracy of 1 is deteriorated.

Further, each magnetic sensor requires an amplifier circuit, a signal processing circuit, and a filter circuit for removing noise, and the number of constituent circuits for obtaining the total sensitivity of all the magnetic sensors arranged in the width direction is large. This increases the complexity of the entire defect detection circuit and increases the manufacturing cost.

The present invention has been made in view of such circumstances, and by improving the connection method of each magnetic sensor, an addition signal of two or more magnetic sensors adjacent in the width direction can be obtained, A uniform detection sensitivity can be maintained over the entire width of the band, and the number of constituent circuits of the defect detection circuit can be reduced,
It is an object of the present invention to provide a magnetic flaw detector which can reduce the manufacturing cost of the entire apparatus.

Further, By using a magnetic sensor in which a detection coil is wound over a plurality of cores arranged in the width direction of the metal strip, the width of the sensitivity region of one magnetic sensor can be widened. It is an object of the present invention to provide a magnetic flaw detector capable of maintaining uniform detection sensitivity over the entire width of, and reducing the number of constituent circuits of the defect detection circuit.

[0013]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a hollow roll that rotates by contact with the surface of a running metal strip, and a hollow roll disposed in the hollow roll. A magnetizer that generates a magnetic field, a plurality of magnetic sensors that are arranged in the vicinity of the metal band and in the width direction of the metal band, and that detect a magnetic flux leakage caused by a defect inside or on the surface of the metal band, In a magnetic flaw detector equipped with a defect detection circuit for synthesizing output signals of respective magnetic sensors to obtain a defect signal in the entire width of a metal strip, two or more magnetic sensors adjacent in the width direction of the metal strip are connected in series. A serial addition signal obtained by serially adding the output signals of the magnetic sensors is sent to the defect detection circuit.

Further, in another invention, the two or more magnetic sensors are connected in parallel and the output signals of the magnetic sensors are added in parallel, and a parallel addition signal is sent to the defect detection circuit.

In still another aspect of the invention, each magnetic sensor is provided with a plurality of cores arranged at predetermined intervals in the width direction of the metal strip, and detections wound around the outer periphery of the plurality of cores. It is composed of a coil.

[0016]

With the magnetic flaw detector constructed as described above,
Leakage magnetic flux from a metal band magnetized by a magnetizer arranged in the hollow roll is detected by a plurality of magnetic sensors arranged in a row in the width direction of the metal band. Then, the output signals from the magnetic sensors are combined in the defect detection circuit to obtain the defect signal in the entire width of the metal strip.

In the present invention, two or more magnetic sensors adjacent to each other in the width direction of the metal strip are connected in series or in parallel. Then, the serial addition signal or the parallel addition signal is sent to the defect detection circuit.

When the output signals of a plurality of magnetic sensors adjacent to each other in the width direction of the metal strip are added in series or in parallel in this manner, the detection sensitivity distribution characteristic in the width direction of the series addition signal or the parallel addition signal is one. Compared with the detection sensitivity distribution characteristic in the width direction of the output signal of the magnetic sensor, the peak value in the detection sensitivity characteristic distribution is low, but the distribution characteristic is wide in the width direction.

The detection sensitivity distribution characteristic of each magnetic sensor is
Since each has a steep sensitivity distribution characteristic, when viewed as the entire metal band, the sensitivity distribution characteristic synthesized in the width direction of the metal band becomes a sensitivity distribution characteristic with a large unevenness. On the other hand, in the present invention, the detection sensitivity distribution characteristics for each magnetic sensor are compared with the overall detection sensitivity distribution characteristics,
Although the detection sensitivity is slightly lowered, the sensitivity distribution characteristics combined in the width direction of the metal band become uniform in the width direction. Also,
Since the number of signals input to the defect detection circuit is reduced, the number of constituent circuits in the defect detection circuit can be reduced.

Further, in another invention, a magnetic sensor is used in which a plurality of cores arranged at predetermined intervals in the width direction of the metal strip are wound with a detection coil. Therefore,
This magnetic sensor has a wider detection sensitivity distribution characteristic in the width direction than the conventional magnetic sensor. As a result, uniform sensitivity characteristics can be realized in the width direction of the metal strip. Further, if the width of the metal strip as the measurement target is constant, the number of magnetic sensors arranged in the width direction is reduced, so that the structure of the defect detection circuit can be simplified.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a schematic sectional view of the magnetic flaw detector of the embodiment, taken along a plane parallel to the running direction of the metal strip.
FIG. 3 is a schematic cross-sectional view of the same device taken along a plane orthogonal to the traveling direction of the metal strip.

One end of the fixed shaft 2 penetrates the center of the hollow roll 1 made of a non-magnetic material. The other end of the fixed shaft 2 is supported by a frame of a building (not shown). The fixed shaft 2 is supported on the inner peripheral surfaces of both ends of the hollow roll 1 by a pair of rolling bearings 3a and 3b so as to be located at the center of the hollow roll 1. Therefore, the hollow roll 1 freely rotates about the fixed shaft 2 as the rotation center axis.

A magnetized iron core 4c having a substantially U-shaped cross section is provided in the hollow roll 1 with the magnetic poles 4a and 4b thereof being close to the inner peripheral surface of the hollow roll 1, and the fixed shaft is interposed via the support member 5. It is fixed at 2. A magnetizing coil 6 is wound around the magnetized iron core 4c. Therefore, the magnetized core 4c and the magnetized coil 6 constitute the magnetizer 4. Magnetized iron core 4
A magnetic sensor group 7 in which a plurality of magnetic sensors 7a are linearly arranged at intervals of, for example, 10 mm in the axial direction between the magnetic poles 4a and 4b of c is also fixed to the fixed shaft 2.

Each magnetic sensor 7a, as shown in FIG.
The core 11 is made of a ferromagnetic material such as permalloy and fixed by an insulator 12, and a detection coil 13 is wound around the core 11 together with the insulator 12.

Then, as shown in FIG. 1, two adjacent magnetic sensors 7a (7a ₁ ) and 7a (7a ₂ ) are connected in series. That is, one magnetic sensor 7a
The winding end of the detection coil 13 of ₁ is the other magnetic sensor 7a ₂
Is connected to the winding start end of the detection coil 13, and the winding end of the detection coil 13 of the other magnetic sensor 7a ₂ is grounded.
The winding start end of the detection coil 13 of _one magnetic sensor 7a ₁ is connected to a pulse voltage generator 15 via a resistor 14. Further, the series addition signal a ₁ is sent to the defect detection circuit 16 from the winding start end of the detection coil 13 of the magnetic sensor 7a ₁ .

The magnetic sensor 7a ₁ thus constructed,
At 7a ₂ , the pulse voltage generator 15 outputs positive and negative pulse voltages at a constant cycle. The output pulse voltage is applied to each detection coil 13 of each magnetic sensor 7a ₁ and 7a ₂ via the resistor 14. As a result, each core 11 made of a ferromagnetic material is magnetized to the saturation region. The serial addition signal a ₁ output from the magnetic sensors 7a ₁ and 7a ₂ connected in series is input to the defect detection circuit 16. Therefore,
The serial addition signal a ₁ becomes a pulse waveform signal having a constant amplitude centered on the ground level (0V).

When an external magnetic field crosses the magnetic sensors 7a ₁ and 7a ₂ in this state, the amplitude of the series addition signal a ₁ does not change but only the signal level changes. Therefore, the strength of the external magnetic field is detected from the amount of change in the signal level of the series addition signal a ₁ . Such magnetic sensors 7a ₁ , 7
a ₂ is said to be a saturable magnetic sensor.

Further, in order to take out each series addition signal a ₁ output from each magnetic sensor 7a ₁ and 7a ₂ connected in series of the power cable 8 for supplying an exciting current to the magnetizing coil 6 and the magnetic sensor group 7. The signal cable 9 is routed through the fixed shaft 2 to the outside. Therefore, the positions of the magnetizer 4 and the magnetic sensor group 7 are fixed, and the hollow roll 1 rotates around the outer circumference of the magnetizer 4 and the magnetic sensor group 7 with a minute gap.

The metal strip 1 running on the outer peripheral surface of the hollow roll 1 of the magnetic flaw detector having the above-described structure, for example, in the direction of arrow a.
0 against one side with a predetermined pressure, the fixed shaft 2
Is fixed to the frame, the hollow roll 1 rotates in the direction of arrow b.

In such a magnetic flaw detector, when an exciting current is supplied to the magnetizing coil 6, a closed magnetic path is formed by the magnetic poles 4a and 4b of the magnetized iron core 4c and the running metal strip 10. If there is a defect inside or on the surface of the metal strip 10, the magnetic path in the metal strip 10 is disturbed, and a leakage magnetic flux is generated. This leakage flux is detected by the magnetic sensor 7a _1, 7a ₂ facing the corresponding defect position constituting the magnetic sensors 7, serial sum signal a ₁ corresponding to the relevant defect from the magnetic sensor 7a _1, 7a ₂ is output It

Further, such magnetic sensors 7a (7a
₁ , 7a ₂ ) The output level of a single unit is the magnetic sensor 7
It greatly changes depending on a distance d called lift-off from a to the surface of the metal band 10 to be flaw-detected. FIG. 4 is an output voltage characteristic diagram when the lift-off d is changed by intentionally forming an artificial defect of a certain scale on the metal strip 10. As shown in the figure, when the lift-off d increases, the voltage value indicating the leakage magnetic flux due to the defect sharply decreases.

Next, as shown in FIG. 1, the signal level of the series addition signal a ₁ output from the _two magnetic sensors 7a ₁ and 7a ₂ , that is, the detection sensitivity will be verified in more detail using the formula. In FIG. 1, for example, the output voltage of the pulse voltage generator 15 is e, the resistance value of the resistor 14 is R, and the cross-sectional area of each detection coil 13 of each magnetic sensor 7a ₁ and 7a ₂ is S.
₁ and S ₂ , the impedance of each detection coil 13 is Z
_1, when Z _2, voltage e ₁ of the serial sum signal a ₁ is (1)
It becomes an expression. e ₁ = e (Z ₁ + Z ₂ ) / (Z ₁ + Z ₂ + R) (1)

The impedances Z ₁ and Z ₂ are the number of turns N of each detection coil 13, the winding width L of the detection coil 13, the magnetic permeability μ of the core 11, and the oscillation frequency ω of the pulse voltage oscillator 15.
It can be expressed as in Eq. Z ₁ , Z ₂ = N ² μω / L (2)

Now, it is assumed that stray magnetic flux which is not caused by defects exists in the sound portion of the metal strip 10. The pair of magnetic sensors 7a ₁ and 7a ₂ connected in series is a pulse voltage generator 15
It is magnetized to the saturation region by the exciting current from. Then, in the saturated region, the magnetic permeability μ of each core 11 extremely decreases. Therefore, the magnetic sensors 7a ₁ and 7a connected in series are
The positive and negative amplitude values of the voltage of the serial addition signal a ₁ of ₂ are equal.

Under this condition, for example, one magnetic sensor 7
If there is a defect on the lower side of a ₁ , the operating point of the detection coil 13 of the _one magnetic sensor 7a ₁ changes due to the leakage magnetic flux generated by this defect. Therefore, equation (1) can be approximated as equation (3). Since the leakage magnetic flux due to the defect is small, it is assumed that it is not detected by the adjacent magnetic sensor 7a ₂ . e ₁ = e [(Z ₁ ± ΔZ ₁ ) + Z ₂ ] / [(Z ₁ ± ΔZ ₁ ) + Z ₂ + R] (3) Therefore, the amplitude of the positive polarity side and the negative polarity side of the series addition signal a ₁ A difference occurs with the amplitude. This difference voltage is detected by the defect detection circuit 16.

For the voltage e ₁ of the series addition signal a ₁ when the pair of magnetic sensors 7a ₁ and 7a ₂ are connected in series, for example, the voltage of the output signal a output from only _one magnetic sensor 7a ₁ e _O is represented by the equation (4). e _O = e (Z ₁ ± ΔZ ₁ ) / [(Z ₁ ± ΔZ ₁ ) + R] (4) As can be seen by comparing equations (3) and (4), it is clear that the amount of change in the voltage e _1, e _O is the greater of the voltage e _O when the magnetic sensor is one. Then, a defect is present on the lower side of the other magnetic sensor 7a _2, the voltage e ₁ of the serial sum signal a ₁ with a similar procedure is (5). e ₁ = e [Z ₁ + (Z ₂ ± ΔZ ₂ )] / [Z ₁ + (Z ₂ ± ΔZ ₂ ) + R] (5) Magnetic sensor 7 a ₁ . If the characteristics of 7a ₂ are equal, (3) (5)
The expressions are equal. On the other hand, if there is a defect at the same position,
In the case of _one magnetic sensor 7a ₁ , the output voltage e
_As shown in Eq. (6), ₁ does not show the effect of defects. e _O = eZ ₁ / [Z ₁ + R] (6)

This means that the two magnetic sensors 7a ₁ and 7a ₁
The detection sensitivity to the defect of the series addition signal a ₁ when a ₂ is connected in series is lower than that when only _one rage sensor 7a ₁ is used, but has a wide detection sensitivity distribution characteristic in the width direction of the metal strip 10. Means that.

The inventors have found that the diameters are 0.2 mm, 0.3 mm and 0.6 mm.
Using the metal strip 10 having standard defects of mm, these defects are arranged at the center position in the width direction of the conventional one-sensor type magnetic flaw detector using only one magnetic sensor 7a. The detection sensitivity distribution characteristics in the width direction of one magnetic sensor 7a and _two magnetic sensors 7a ₁ and 7a ₂ arranged in the width direction shown in FIG.
The detection sensitivity distribution characteristic in the width direction of the _two magnetic sensors 7a ₁ and 7a ₂ arranged at the center position in the width direction of the sensor type magnetic flaw detector was determined. The experimental results are shown in FIG. In an actual experiment, the metal band 10 in which the standard defect is formed at the center position in the width direction is moved by 1 mm in the width direction, and each deviation amount (mm) from the center position and each signal a,
The detection level of a ₁ was measured. However, the detection signal level for the standard defect having a diameter of 0.6 mm was extremely large, and the correct value could not be obtained at the position where the amount of deviation was small due to the saturation of the amplifier of the measuring device.

As can be understood from the experimental results shown in FIG.
In detecting defects of each size of 2 mm and 0.3 mm, the one-sensor method can obtain higher detection sensitivity, but the two-sensor method can obtain wider detection sensitivity distribution characteristics.

It should be noted that the noise level contained in the two-sensor type serial addition signal a ₁ is 1
That is, the noise level is higher than the noise level included in the output signal a of the sensor system.

The inventors of the present invention conducted the same test using a three-sensor type magnetic flaw detector in which three magnetic sensors are connected in series in addition to the one-sensor type and the two-sensor type described above. The relationship between each method and the measured defective signal level of the output signal is shown in the upper part of FIG. At the same time, the relationship between each system and the S / N of each output signal is shown in the lower part of FIG. As shown in the figure, as the number of constituent magnetic sensors increases, the detection sensitivity and S / N decrease.

On the other hand, when the number of magnetic sensor components is increased,
The detection sensitivity distribution characteristic in the width direction of the metal band 10 tends to be wide and uniform. Therefore, it is desirable to increase the number of magnetic sensor components while maintaining the detection sensitivity and the S / N within the allowable range. For example, in FIG. 7, if the minimum allowable limit of S / N is 3, the magnetic sensor 7a has 2 components. In this way, the number of constituents of the magnetic sensor 7a for obtaining one series addition signal a ₁ is almost uniquely determined by the required detection sensitivity and S / N.

FIG. 5 is a block diagram showing a schematic structure of the defect detection circuit 16. A pair of magnetic sensors 7 connected in series
Each serial addition signal a ₁ output from a ₁ and 7a ₂ is amplified by the amplifier 17 and input to each subsequent signal processing unit 18. The signal processing unit 18 detects the (+) peak level and the (-) peak level of the input pulse-shaped serial addition signal a ₁ and changes the signal level of the input serial addition signal a ₁ from the difference between them. The amount is obtained and each detection signal b proportional to the leakage magnetic flux is output. Each detection signal b output from each signal processing circuit 18 is input to the next noise automatic removal unit 19. Each automatic noise removing unit 19 removes a noise component less than the reference signal output from the reference signal generating unit 20 and sends the noise component to the adding and combining unit 21.

The summing / combining unit 21 is provided for each automatic noise removing unit 1
After the noise removal, the detection signals b having the detection sensitivity distribution characteristic A of the two-sensor type of FIG. 8 after the noise removal are added and integrated to obtain a uniform width direction of the metal strip 10 as shown in FIG. A defect signal c having a sensitivity distribution B is obtained. That is, since the sensitivity distribution of a simple substance of each of the magnetic sensors 7a _1, 7a ₂ has a trapezoidal shape, a detection signal b of the magnetic sensor 7a _1, 7a ₂ when taken out as it is, in the width direction of the metal plate 10 A valley has a discontinuous sensitivity distribution at regular intervals, and the defect detection rate in the middle of each magnetic sensor 7a ₁ and 7a ₂ decreases. Therefore, the adding and combining unit 21 adds and integrates the detection signals b of the magnetic sensors 7a ₁ and 7a ₂ adjacent to each other to the detection signals b to obtain the sensitivity distribution B shown in FIG. The defect signal c output from the addition combining unit 21 is input to the discrimination level automatic setting unit 22 and the defect discrimination unit 23.

The discrimination level automatic setting unit 22 determines the metal plate 10 from the signal level of the normal portion in the input defect signal c.
A reference signal level is set according to the material and the degree of processing, and the reference signal level is sent to the defect discrimination section 23.

The defect discriminator 23 compares the defect signal c input from the addition and integration unit 21 with the reference signal level input from the discrimination level automatic setting unit 22, and finally determines the signal exceeding the reference signal level. Record display unit 24 as defect signal d
Send to. The defect discriminator 23 receives position information from a distance counter 26 and a speed counter 27 that count the number of pulses output from the pulse generator 25 and calculate the moving position and speed of the metal strip 10. Therefore, the defect signal d is displayed on the record display unit 24 together with the defect occurrence position information. Further, the defect occurrence position and the defect scale are recorded.

FIG. 9 shows the lift-off d between the magnetic sensors 7a ₁ and 7a ₂ and the metal plate 10 in consideration of the strength of the hollow roll 1 and the processing accuracy of the hollow roll 1, for example, d = 3.5.
mm, known defect scale (volume = 5.0 × 10 ^-4 mm ³ ) Defect signal c when flaw detection is performed on the metal band 10 having an artificial defect
It is a waveform. Thus, even if the volume is 5.0 × 10 ^-4 mm
³ Even small defects can be reliably detected. Further, as a result of measuring the response times of the magnetic sensors 7a ₁ and 7a ₂ , the moving speed of the metal strip 10 can be reliably followed up to 1200 m / mim.

In the magnetic flaw detector having such a structure, a pair of magnetic sensors 7a ₁ and 7a ₂ connected in series are provided.
The magnetic detection sensitivity characteristic in the width direction in FIG. 8 has a trapezoidal shape as shown in FIG. Therefore, the detection sensitivity in the width direction can be made more uniform as compared with the conventional magnetic sensor using one core and the magnetic sensor using a normal semiconductor Hall element or the like. Further, by using the addition coupling section 21, finally, the defect signal c having the uniform sensitivity characteristic B over the entire width direction of the metal strip 10 shown in FIG. 8 can be obtained.

The number of output signals input from the magnetic sensor 7a provided in the hollow roll 1 to the defect detection circuit 16 is about half that of the conventional device. Therefore, the number of each of the amplifier 17, the signal processor 18, and the automatic noise eliminator 19 included in the defect detection circuit 16 is reduced to about half. Therefore, since the defect detection circuit 16 can be simplified, the manufacturing cost of the entire device can be reduced. FIG. 10 is a diagram showing a connection state of each magnetic sensor 7a in a magnetic flaw detector according to another embodiment of the present invention.

In this embodiment, two magnetic sensors 7a ₁ and 7a ₂ adjacent to each other in the width direction of the metal strip 10 are connected in parallel. Then, the magnetic sensors 7a ₁ and 7
The winding ends of the detection coils 13 of a ₁ are commonly grounded. The winding start ends of the respective detection coils 13 are connected to each other and are connected to the pulse voltage generator 15 via the resistor 14.
In addition, the parallel addition signal a ₂ from the connection point is detected by the defect detection circuit 16
sent to a.

In this way, the pair of magnetic sensors 7a ₁ , 7a
When the voltage e ₂ of the parallel addition signal a ₂ in the case of connecting a ₂ in parallel is obtained by the same procedure as in the case of connecting in series, the equation (7) is obtained. e ₂ = eR (Z ₁ ± ΔZ ₁ · Z ₂ ) / (Z ₁ ± ΔZ ₁ + Z ₂ ) ... (7)

Therefore, as can be understood from the equation (7), the parallel addition signal a ₂ has a distribution characteristic similar to the detection sensitivity distribution characteristic in the width direction in the above-mentioned embodiment.
Therefore, it is possible to obtain almost the same effect as the magnetic sensor of the two-sensor type connected in series in the previous embodiment.

FIG. 11 is a block diagram showing a schematic configuration of the defect detection circuit 16a. Defect detection circuit 1 shown in FIG.
6 has almost the same configuration and performs the same operation. Therefore, it is possible to obtain substantially the same effect as the circuit of the embodiment shown in FIG. 5. FIG. 12 is a diagram showing a schematic configuration of a magnetic sensor incorporated in a magnetic flaw detector according to another embodiment of the present invention. is there.

As shown in the figure, each magnetic sensor 7a ₃ of this embodiment is made of an insulator 12a, for example, 10 mm to 1000 mm.
A plurality of cores 11a. 11
b and the insulator 1 on the outside of the pair of cores 11a and 11b.
It is composed of a detection coil 13a wound around every 2a. One end of the detection coil 13a is grounded, and the other end is connected to the pulse voltage generation circuit 15 via the resistor 14. The detection signal a ₃ from the other end is the defect detection circuit 1
Input to 6b. Magnetic sensor 7 configured in this way
impedance Z across the sense coil 13a at a ₃ is represented by the equation (8). Z = ωSN ² (Μ ₁ + μ ₂ ) / L (8) where μ ₁ and μ ₂ are the magnetic permeability of the cores 11 a and 11 b. S
Is the cross-sectional area of the detection coil 13a, and L is the winding width of the detection coil 13a.

Therefore, this two-core type magnetic sensor 7a
One of the core 11a voltage e ₃ of the output signal a ₃ in the case where a defect is present directly below the the ₃ permeability of the core 11a mu
_{If 1} changes by Δμ, then equation (9) is obtained. e ₃ = e [ωSN ² (Μ ₁ + Δμ + μ ₂ ) / L] (9) Then, for example, when the same defect is located directly below the other core 11b, the formula (10) is obtained. e ₃ = e [ωSN ² (Μ ₁ + μ ₂ + Δμ) / L] (10)

That is, if the magnetic characteristics of the cores 11a and 11b are equal, the equations (9) and (10) are equal. Therefore, 1
Compared with the detection sensitivity distribution characteristic in the width direction in the 1-core type magnetic sensor 7a formed by only one core 11, the detection sensitivity distribution characteristic in the 2-core type magnetic sensor 7a ₃ shown in FIG. This results in uniform characteristics.

FIG. 15 shows a conventional 1-sensor 1-core system,
Each measured value of each detection sensitivity distribution characteristic of the 1-sensor 2-core system of the embodiment is shown. However, the output value on the vertical axis is a relative value when the peak value of each characteristic is 1. As shown in the actual measurement values of FIG. 15, the magnetic sensor 7a ₃ of the embodiment can obtain a much wider and uniform detection sensitivity distribution characteristic than the conventional one-sensor / one-core type magnetic sensor. Further, the degree of spread of the detection sensitivity distribution characteristic can be controlled by changing the distance between the cores 11a and 11b.

When the number of cores included in one magnetic sensor is increased, the detection oversensitivity itself is lower than that in the conventional one-sensor / one-core system, so two cores 11 are used.
It is optimal to form one magnetic sensor 7a ₃ with a and 11b.

Further, when one magnetic sensor 7a ₃ is formed by a plurality of cores in this way, the number of magnetic sensors arranged in the width direction of the metal strip 10 decreases, so the defect detection circuit 16
The number of constituent circuit components of b is reduced. Therefore, as shown in FIG. 11
It is possible to obtain substantially the same effect as the defect detection circuits 16 and 16a. FIG. 13 is a diagram showing a schematic configuration of a magnetic sensor incorporated in a magnetic flaw detector according to still another embodiment of the present invention.

In this embodiment, two magnetic sensors 7a having the structure shown in FIG.
₄ , 7a ₅ are connected in series. Thus, by connecting the one-sensor / two-core type magnetic sensors in series, a wider and more uniform detection sensitivity distribution characteristic can be obtained. Therefore, it is possible to obtain substantially the same effects as those of the above-described embodiments. However, each magnetic sensor 7a ₄ , 7
Since two a ₅ are connected in parallel as shown in the figure, the parallel addition signal a ₄ input to the defect detection circuit 16c is input.
The number is about half as compared to the series sum signal a number ₁ in Figure 1. Therefore, the number of constituent circuits of the defect detection circuit 16c can be further reduced. FIG. 14 is a diagram showing a schematic configuration of a magnetic sensor incorporated in a magnetic flaw detector according to still another embodiment of the present invention.

In this embodiment, two magnetic sensors 7a having the structure shown in FIG.
₄ , 7a ₅ are connected in parallel. The parallel addition signal a ₅ is sent to the defect detection circuit 16d. In this way, by connecting the 1-sensor 2-core type magnetic sensors 7a ₄ and 7a ₅ in parallel, a wider and more uniform detection sensitivity distribution characteristic can be obtained. Therefore, it is possible to obtain substantially the same effect as that of the embodiment shown in FIG.

The present invention is not limited to the above embodiments. In each example, the hollow roll 1
Each magnetic sensor 7a within, has been disposed 7a ₁ ~7a _5,
It may be arranged outside the hollow roll 1 and at a position opposite to the magnetizer 4 provided inside the hollow roll 1 with the metal strip 10 interposed therebetween.

Although the S / N is lowered, in the case where the welded connection portion of the metal strip 10 is exclusively detected, three or more magnetic sensors 7a can be connected in parallel or in series to operate the device. Can be simplified.

[0065]

As described above, according to the magnetic flaw detector of the present invention, a plurality of magnetic sensors arranged in the width direction of the metal strip are connected in series or in parallel to generate a series addition signal or a parallel addition signal. It has gained. The detection sensitivity distribution characteristics of the serial addition signal and the parallel addition signal in the width direction of the metal band are much wider than the characteristics of the output signal of only one magnetic sensor. Therefore, uniform detection sensitivity can be maintained over the entire width of the metal band, the number of constituent circuits of the defect detection circuit can be reduced, and the manufacturing cost of the entire device can be reduced.

A magnetic sensor in which a detection coil is wound around a plurality of cores adjacent in the width direction of the metal strip is used. Therefore, the sensitivity region in the width direction of one magnetic sensor can be widened, and each effect described above can be obtained with a small number of magnetic sensors.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a magnetic sensor of a magnetic flaw detector according to an embodiment of the present invention,

FIG. 2 is a cross-sectional view showing the configuration of the entire apparatus of the embodiment,

FIG. 3 is a sectional view showing the configuration of the entire apparatus of the embodiment,

FIG. 4 is a diagram showing a relationship between lift-off and an output voltage of a magnetic sensor,

FIG. 5 is a diagram showing a defect detection circuit of the embodiment apparatus;

FIG. 6 is a detection sensitivity characteristic diagram in the width direction of the metal strip in the magnetic sensor of the embodiment,

FIG. 7: Detection sensitivity and S in the magnetic sensor of Example
Showing the relationship between / N and the number of magnetic sensors,

FIG. 8 is a detection sensitivity distribution characteristic diagram in the width direction of the metal strip as a whole of the embodiment apparatus,

FIG. 9 is a defect signal waveform diagram in the metal band of the embodiment apparatus,

FIG. 10 is a diagram showing a connection relationship of magnetic sensors of a magnetic flaw detector according to still another embodiment of the present invention;

FIG. 11 is a view showing a defect detection circuit of the apparatus of the embodiment,

FIG. 12 is a diagram showing a connection relationship of magnetic sensors of a magnetic flaw detector according to still another embodiment of the present invention;

FIG. 13 is a view showing a connection relationship of magnetic sensors of a magnetic flaw detector according to still another embodiment of the present invention.

FIG. 14 is a diagram showing a connection relationship of magnetic sensors of a magnetic flaw detector according to still another embodiment of the present invention;

FIG. 15 is a diagram showing a detection sensitivity distribution characteristic of each configuration method of the magnetic sensor in the embodiment apparatus.

[Explanation of symbols]

1 ... hollow roll, 4 ... magnetizer, 7a, 7a ₁ ~7a ₅ ...
Magnetic sensor, 10 ... Metal band, 11, 11a, 11b ... Core, 12, 12a ... Insulator, 13, 13a ... Detection coil, 15 ... Pulse voltage generator, 16, 16a, 16b,
16c ... Defect detection circuit, 18 ... Signal processing section, 21 ... Addition integration section, 23 ... Defect discrimination section, 24 ... Record display section.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Maki 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Inventor Shigo Go Ando 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Pipe Co., Ltd. (72) Inventor Taidai Matsufuji 1-2-2 Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Pipe Co., Ltd.

Claims (5)

[Claims] 1. A hollow roll that rotates by coming into contact with the surface of a running metal strip, a magnetizer disposed in the hollow roll to generate a magnetic field in the metal strip, and a proximity position of the metal strip. And a plurality of magnetic sensors that are arranged in the width direction of the metal strip and detect leakage magnetic flux generated due to defects inside or on the surface of the metal strip, and the output signals of the magnetic sensors are combined to synthesize the metal strip. In a magnetic flaw detector equipped with a defect detection circuit for obtaining a defect signal in the entire width of a strip, two or more magnetic sensors adjacent in the width direction of the metal strip are connected in series, and output signals of the respective magnetic sensors are added in series. The magnetic flaw detector, wherein the serial added signal is sent to the defect detection circuit. 2. A hollow roll that rotates by coming into contact with a surface of a running metal band, a magnetizer that is disposed in the hollow roll and generates a magnetic field in the metal band, and a proximity position of the metal band. And a plurality of magnetic sensors that are arranged in the width direction of the metal strip and detect leakage magnetic flux generated due to defects inside or on the surface of the metal strip, and the output signals of the magnetic sensors are combined to synthesize the metal strip. In a magnetic flaw detector equipped with a defect detection circuit for obtaining a defect signal in the entire width of a strip, two or more magnetic sensors adjacent in the width direction of the metal strip are connected in parallel, and the output signals of the respective magnetic sensors are added in parallel. The magnetic flaw detection device, wherein the parallel added signal is sent to the defect detection circuit. 3. A hollow roll that rotates by coming into contact with the surface of a running metal band, a magnetizer that is disposed in the hollow roll and generates a magnetic field in the metal band, and a proximity position of the metal band. And a plurality of magnetic sensors that are arranged in the width direction of the metal strip and detect leakage magnetic flux generated due to defects inside or on the surface of the metal strip, and the output signals of the magnetic sensors are combined to synthesize the metal strip. In a magnetic flaw detector having a defect detection circuit for obtaining a defect signal in the entire width of the strip, each magnetic sensor, in the width direction of the metal strip, a plurality of cores arranged at a predetermined interval between each other, A magnetic flaw detector comprising a plurality of detection coils wound around the outer periphery of the core. 4. The two or more magnetic sensors adjacent to each other in the width direction of the metal strip are connected in parallel and a parallel addition signal obtained by adding output signals of the respective magnetic sensors in parallel is sent to the defect detection circuit. The magnetic flaw detector described. 5. The two or more magnetic sensors adjacent in the width direction of the metal strip are connected in series, and a series addition signal obtained by adding the output signals of the respective magnetic sensors in series is sent to the defect detection circuit. The magnetic flaw detector described.