JPH11108900A - Method and apparatus for calibration of sensitivity of magnetic flaw-detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an apparatus in which the sensitivity of a magnetic flaw- detecting device can be calibrated simply without newly adding a coil for calibration, a hollow roll or the like by a method wherein an AC current is superposed on a DC current, for magnetic-field generation, which is made to flow to a magnetizer and the sensitivity of a group of magnetism sensing elements is calibrated by a pseudo magnetic flux leakage. SOLUTION: A magnetic flaw-detecting device 100 is provided with a magnetizer 102 which is composed of a magnetizing yoke 104 and of a magnetizing coil 106, with a flaw detecting head 110 and with a power supply 112, and it is faced with a thin steel strip 10 at the outside of a nonmagnetic roll 80. In the flaw-detecting head 110, 1000 pieces of magnetism sensing elements 111 are arranged linearly in the width direction of the thin steel strip 10. The power supply 112 is provided with a power supply for excitation, with an AC power supply for pseudo-magnetic-flux-leakage generation and with a circuit which superposes both power supplies. In a flaw detecting operation, the DC power supply is supplied to the magnetizing coil 106. In a calibrating operation, the output of the superposing circuit is supplied. In a simple calibrating operation, the the magnetic flaw-detecting device 100 in an on-line position is raised by about 200 mm by using a raising and lowering device 150, an alternating current is applied to the magnetizing coil 106 from the power supply 112, and the output of all the magnetism sensing elements as a group is verified so as to judge whether it is proper or not.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for calibrating the sensitivity of a magnetic flaw detector, and more particularly to an inspection object suitable for simple calibration of a magnetic flaw detector which flaws a traveling thin steel strip online. A magnetic field is generated in the running direction of the strip by a magnetizer disposed near the strip,
The present invention relates to a method and an apparatus for calibrating the sensitivity of a magnetic flaw detector which detects a leakage magnetic flux generated by an internal or surface defect by a group of magnetic sensitive elements arranged in parallel in the width direction of the strip and generates a defect signal.

[0002]

2. Description of the Related Art As a method for detecting non-metallic inclusions in a thin steel strip by using magnetism, a steel plate of about 1.0 m square (thickness of about 1.0 m) is used.
15-0.35mm) on a stationary table,
A direct magnetic field is applied to this to perform magnetic particle flaw detection, but this is applied for quality control including shipping inspection, and is a sampling inspection and cannot be applied to all steel strips.

On the other hand, in recent years, a flaw detection head having a group of magnetically sensitive elements for detecting magnetic flux arranged in a straight line is provided, and a defect existing in the entire width of a thin steel strip running at a constant speed is continuously detected online. A magnetic flaw detector has been proposed (Japanese Utility Model Application Laid-open 63)
-107849).

[0004] In such a magnetic flaw detector, FIG.
As shown in FIG. 2, an exciting current is supplied to a magnetized coil 28 disposed near the thin steel strip 10 to be inspected, and a closed magnetic path is formed between the magnetized iron core 26 and the running thin steel strip 10. . If a defect exists inside or on the surface of the thin steel strip 10, the magnetic path in the thin steel strip is disturbed, and a leakage magnetic flux is generated. This leakage magnetic flux is detected by a magnetic sensitive element group constituting the flaw detection head 22. , As a defect signal corresponding to the corresponding result.

Since the signal level of the detected defect signal corresponds to the size (magnitude) of the defect inside or on the surface of the thin steel strip, by detecting the defect signal, the presence or absence of the defect signal on the inside or surface of the thin steel strip The position and size of the defect occurring in the width direction can be grasped.

In the drawing, reference numeral 30 denotes a hollow roll which rotates in synchronization with the running of the thin steel strip 10;
0, a fixed axis penetrating through the inside of the magnetized iron core 26
A support member for fixing the magnetizer 24 and the flaw detection head 22 constituted by the magnetizing coil 28 to the fixed shaft 32; 36, a power cable for supplying an exciting current to the magnetizing coil 28; A signal cable 40 for extracting a detection signal output from the magnetic sensitive element group in the flaw detection head 22 is a rolling bearing that rotatably supports the hollow roll 30.

[0007] In such a magnetic flaw detector 20,
The magnitude of the defect existing inside or on the surface of the thin steel strip 10 is determined based on the intensity of the leakage magnetic flux detected by each of the magnetic sensitive elements constituting the flaw detection head 22. Therefore, it is necessary to make adjustments so that the sensitivity of each magnetic element is uniform. It is also necessary to match the sensitivity of the entire flaw detection head with other magnetic flaw detectors. Further, it is necessary to periodically adjust for a change in sensitivity over time. It is also necessary to grasp the correspondence between the detected amount and the absolute value of the defect scale.

[0008] For this reason, conventionally, Japanese Patent Application Laid-Open No. 63-27747
As shown in FIG. 1, a plate-shaped standard defect sample having an artificial defect serving as a standard is prepared, and the standard defect sample is
Was placed on each of the magnetic sensitive elements, and the sensitivity was calibrated one by one. Specifically, before starting calibration, first inspect the thin steel sheet with a magnetic particle flaw detector to obtain the part where inclusions are present, and identify the size of the inclusions using magnetic particle flaw detection, X-ray photography, a microscope, etc. I do. Next, the output of the inclusion is verified by a magnetic flaw detector. At this time, the spatial distance (lift-off) between the thin steel plate and the magnetic sensitive element is about 0.5 mm, and the magnetic excitation current is 1.0
Understand the measurement conditions such as A. Next, an artificial linear flaw having an output related to the identified inclusion is created from the sound portion of the thin steel sheet, and the output is verified by a magnetic flaw detector in which measurement conditions are grasped. At this time, the output of the inclusion and the artificial linear wound are compared to confirm the relevance. The output of the artificial linear wound requires that the length of the same portion of the output is about 50 mm or more.

In addition, for the other magnetic sensitive element groups, the artificial linear flaw is measured while being moved in the width direction, and adjusted so as to have the same output by the gain of the amplifier.

As described above, the output of the magnetic sensitive element group becomes constant due to the artificial linear flaw related to the output of the inclusion requiring detection, and the calibration is completed.

The above-mentioned full-scale calibration is performed when the apparatus is installed, but is not frequently performed because it requires time and labor.

On the other hand, Japanese Patent Application Laid-Open No. 3-134 discloses a method for eliminating the inconvenience of using such a standard defect sample.
No. 555 proposes to eliminate the use of a standard defect sample by applying a uniform magnetic field, which becomes a pseudo leakage magnetic flux, from the outside to the entire flaw detection head.

That is, in the calibration device proposed in Japanese Patent Application Laid-Open No. 3-134555, as shown in FIG. 3, an elongated magnetizer 50 for generating a uniform magnetic field serving as a pseudo leakage magnetic flux in a region wider than the magnetic detection region of the flaw detection head. A fixing jig 56 for fixing the relative position between the flaw detection head and the magnetizer 50 so that the uniform magnetic flux is uniformly detected by the flaw detection head; and a leakage magnetic flux intensity whose uniform magnetic field strength is caused by a defect of a known scale. And a power supply device 70 for variably controlling the exciting current of the magnetizer 50 so as to have an intensity corresponding to.

In this calibration apparatus, the fixed shaft 32 of the magnetic flaw detector 20 is mounted on the fixing members 58A and 58B of the mounting jig 56, and the flaw detection head 22 in the hollow roll 30 constitutes the magnetizer 50. Elongate yoke 52
Is installed so as to face the upper surface 52A of the.

Then, the power supply 70 is activated to supply an exciting current to the elongated exciting coil 54 of the magnetizing device 50 for calibration, thereby generating a magnetic field around the yoke 52.
The same magnetic field is applied to each of the magnetic sensitive elements constituting the flaw detection head 22 in the magnetic flaw detection apparatus 20 facing the upper surface 52A of the magnetic head, and the defect size detected by the defect signal detected from the output of the magnetic sensitive element at this time is The sensitivity of each magnetic sensitive element is adjusted to match the known defect size.

Further, in Japanese Patent Laid-Open No. Hei 5-10926 which is an improvement of the Japanese Patent Laid-Open No. Hei 3-134555, an exciting coil 5 for calibration is used.
4 is wound around the flaw detection head 22 and the magnetized iron core 26, is disposed in the magnetized iron core 26, and is not a thin steel strip 1 instead of a separate calibration device as disclosed in JP-A-3-134555.
It has been proposed to dispose it together with a second hollow roll at a position opposite to zero.

[0017]

However, according to the method described in Japanese Patent Application Laid-Open No. HEI 5-10926, a new calibration coil is wound around the entire magnet-sensitive element group or magnetized core in a complicated and narrow space, or a hollow roll is used. However, there is a problem that a great deal of labor, cost and equipment cost are required.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and it is an object of the present invention to easily perform calibration without newly adding a calibration coil, a hollow roll, and the like.

[0019]

According to the present invention, a magnetic field is generated in the running direction of the strip by a magnetizer disposed near the strip to be inspected, and a leakage magnetic flux generated by an internal or surface defect is reduced. In the method of calibrating the sensitivity of a magnetic flaw detector, which is detected by a group of magnetic sensing elements arranged side by side in the width direction and is used as a defect signal, a pseudo-leakage corresponding to a pseudo defect is added to a direct current for generating a magnetic field flowing through the magnetizer This problem is solved by superimposing an alternating current for generating a magnetic flux and calibrating the sensitivity of the magnetic sensitive element group by the pseudo leakage magnetic flux.

Further, in the same sensitivity calibration apparatus, means for generating an AC current for generating a pseudo leakage magnetic flux corresponding to a pseudo defect, and superimposing the AC current on a DC current for generating a magnetic field flowing through the magnetizer. Means for correcting the sensitivity of the magnetic-sensitive element group using the pseudo leakage magnetic flux.

A thin steel sheet used as a material for a food can or the like is subjected to high strength processing when a two-piece can (DI can) is manufactured, and nonmetallic inclusions (hereinafter simply referred to as “intervening”) existing inside the steel sheet. Etc.) also cause processing cracks.
The size of the inclusion required to be detected is 1.0 × 0.1 × 0.01 mm (0.5 × 10 ^{−3 by} elliptical calculation).
mm ³ ), and the number of magnetically sensitive elements installed in the width direction of the thin steel sheet is required to be about 1,000.

It is not easy to make the characteristics of the 1,000 magnetic sensitive elements uniform even if they are installed in the sensor holder. This is because the magnetic sensitive element group is manually assembled in the width direction of the plate, so that the spatial distance (lift-off) between each magnetic sensitive element and the steel sheet varies, and the deviation of the angular deviation from the magnetic field direction for detecting the leakage magnetic flux. This is because a difference in sensitivity to the magnetic field of the magnetic sensitive element itself occurs.

In particular, lift-off is a problem. The published inclusion detector lift-off is 0.5 mm, ± 0.5 mm.
Although this is about 0.1 mm, this difference greatly affects the detection sensitivity of inclusions. FIG. 4 shows an example of the relationship between the lift-off and the output of the magneto-sensitive element. About ± 20% in change from 0.4mm to 0.6mm with respect to 0.5mm lift-off on the horizontal axis
2 shows the output change.

The displacement angle with respect to the horizontal magnetic field direction is also ± 2.
A difference of about 0 ° may occur. FIG. 5 shows the inclination of the magnetic sensitive element in the horizontal magnetic field direction and the output reduction rate. Horizontal axis is 0
When it changes from ° to 20 °, the maximum reduction is 6.0%.

In addition to the above error, a difference in sensitivity of the magnetic sensitive element itself to the magnetic field is added.

As shown in FIG. 6, for example, the circuit of the magnetic flaw detector to be calibrated according to the present invention passes a capacitor 162, an amplifier 164, and an output of the amplifier 164 provided for each magnetic element 111. Band pass filter 166
A dual-wave rectifier 168 that rectifies the output of the band-pass filter 166; a buffer 170 that passes the output of the dual-wave rectifier 168; and an integrated circuit that combines the outputs of many magnetically sensitive elements 111 via the buffer 170 172 and a comparator 174 for comparing the output of the aggregation circuit 172 with a set value.

Therefore, the error appears as a gain of the amplifier 164, and an output difference occurs. This output is recorded for all of the first to n-th magnetically sensitive elements, and is compared with the output at the time of the next simple calibration to determine whether full-scale calibration by artificial linear flaws is necessary. According to the present invention, this simple calibration can be easily performed simply by separating the magnetic flaw detector from the strip and passing an alternating current to the magnetizer.

FIG. 7 shows the exciting current of the magnetizer and the strength of the magnetic field between the poles. Up to 1.5A, there is a linear relationship with 1.5 kilogauss.

FIG. 8 shows the excitation current of the magnetizer and the output relative value due to inclusions. The sensitivity is low in the early stage, high in the middle stage, and decreases in the late stage. Therefore, it is desirable to use the magnetizer at a current of about 0.81 A.

FIG. 9 shows the excitation current of the magnetizer and the output due to inclusions. Generally, the sensitivity of a magnetic element to a magnetic field is
As shown in FIG. 9, the sensitivity is initially low (0.25).
A), high in the middle phase (0.81A) and low in the late phase (1.50A). FIG. 8 is a differential value of FIG.
The magneto-sensitive element operates with the characteristics shown in FIG.
Since the DC voltage passes through the capacitor 162 at step 4, the DC voltage is cut off, and only the change due to the inclusion can pass.

[0031]

Embodiments of the present invention will be described below in detail with reference to the drawings.

As shown in FIGS. 10 and 11, the magnetic flaw detector 100 to be calibrated according to the present embodiment includes a magnetizer 102 including a magnetized yoke 104 and a magnetized coil 106;
A flaw detection head 110 including, for example, 1000 magnetically sensitive elements 111 linearly arranged in the width direction of the thin steel strip 10 to be inspected, and a DC current for excitation and a pseudo leakage magnetic flux for the magnetized coil 106. Power supply 1 for supplying AC current
12 is provided at a position facing the thin steel strip 10 outside the non-magnetic roll 80 that transports the thin steel strip 10 in the direction of arrow A.

As shown in detail in FIG. 12, the power supply 112 includes a DC power supply 114 for excitation, an AC power supply 116 for generating a pseudo leakage magnetic flux, and the output of the AC power supply 116 superimposed on the output of the DC power supply 114. A superimposing circuit 118 for performing
During normal flaw detection, a direct current is supplied to the magnetizing coil 106, and during simple calibration according to the present invention, a switching circuit 120 is provided which supplies the output of the superimposing circuit 118.

In FIG. 10, reference numeral 150 denotes an elevating device for raising the magnetic flaw detector 100 in the direction of arrow B to separate it from the non-magnetic roll 80 at the time of simple calibration, etc., and 152 denotes an offline device at the time of full calibration or the like. This is a moving device that moves the magnetic flaw detector 100 in the direction of arrow C in order to perform calibration using a calibration roll or the like.

The operation of the embodiment will be described below.

First, in a normal online state, the magnetic flaw detector 100 is at a position shown by a solid line in FIG. 10, and the thin steel strip 10 is wound around the non-magnetic roll 80 by, for example, 180 °, and runs in the direction of arrow A. At a position 0.5 mm below the thin steel strip 10 below the magnetic flaw detector 100, the thin steel strip 1
A magnetized yoke 104 for introducing a magnetic flux into the magnetic head 110 is disposed between the magnetized yoke 104 and the flaw detection head 11 including the magnetically sensitive element 111.
0 is also arranged. At the time of flaw detection, a power supply 112 is provided to the magnetized coil 106 provided above the magnetized yoke 104.
The thin steel strip 10 is magnetized in the traveling direction to about 1 kilogauss by the excitation of the direct current from the magnet. The magnetizing current at this time is
For example, it is 0.81A (600 ampere turn). The running speed of the thin steel strip 10 is, for example, 1200 mpm at the maximum. The number of the magnetic sensitive elements 111 is about 1,000.

On the other hand, at the time of simple calibration or when it is not necessary to detect the inclusion, the magnetic flaw detector 100 can be retracted upward, for example, by about 200 mm as shown by the arrow B by the elevating device 150.

Defects that can be detected are 0.5 × 10
These defects, which are about ⁻³ mm ³ or more and are close to internal defects called gouges, cannot be detected by the optical surface defect detection device.

At the time of simple calibration, the magnetic flaw detector 100 located at the online position is raised upward by, for example, about 200 mm as shown by the arrow B by the lifting device 150. Next, the power supply 112 causes the magnetization coil 106 to:
For example, by applying an alternating current of 1000 Hz and 0.01 A, the outputs of all the magnetic sensitive element groups are tested. At this time, a comparison with a simple calibration value performed immediately after the gain adjustment of the amplifier 164 due to the above-mentioned artificial linear flaw is performed to judge the suitability. The collation is
The pattern up to the n-th magnetic sensitive element, the overall average, the maximum value, and the minimum value are calculated by a computer. FIG. 13 shows an example of a comparison table in which the simple calibration values have different dates and times.

In the electric circuit of the magnetic flaw detector shown in FIG. 6, inclusions and surface flaws detected by the magnetic sensitive element 111 are:
As shown in FIG. 14, a flaw signal is superimposed on the strength (DC current) of the magnetic field generated in the magnetic sensitive element. For example, when a DC voltage of 4.5 V is applied to the magnetic sensitive element 111, a 1.0 kilogauss magnetic field is applied by the magnetizer 102, and
The DC voltage becomes 5V. At this time, when an inclusion that needs to be detected passes, an output component due to the inclusion is added, and an AC component (about 5 mV) is generated. FIG. 15 shows a waveform at the time of simple calibration.

The output of the magnetic sensitive element 111 is
After passing through 62, the direct current component is cut off and becomes only the alternating current component, resulting in a flaw signal and magnetic noise as shown in FIG.

The output of the capacitor 162 is
, The signal is amplified about 1000 times, but the waveform is the same as that in FIG. The output of the amplifier 164 passes through the band-pass filter 166, and unnecessary waveforms in high and low frequencies are cut and shaped, thereby improving SN. The band pass moves according to the running speed of the thin steel strip 10, and moves to a higher frequency side when the speed increases, and moves to a lower frequency side when the speed decreases.

The output of the band-pass filter 166 has a waveform from zero to plus only by the dual-wave rectifier 168, and becomes a flaw signal and noise generated from the thin steel plate as shown in FIG. Here, the dual-wave rectification is performed in order to unify and detect a waveform larger than 0. The waveform obtained by the simple calibration corresponding to FIG. 17 is 1000 HZ as shown in FIG.
And 10 mA is added. 17 and 18 show final waveforms of the output of the magnetic sensitive element alone.

FIG. 19 is a waveform in which the outputs of the respective magnetic sensitive elements are aggregated. The magnitude of the detected flaw signal is compared with the set value of the comparator 174, and is discriminated as large, medium or small.

In this embodiment, since the AC current for generating the pseudo leakage magnetic flux is a sine wave, the adjustment is easy. Note that the waveform of the alternating current is not limited to a sine wave, but may be a triangular wave or a pulse wave. In the above embodiment, the frequency and amplitude of the alternating current are set to 1000 HZ and 10 mA, but these values can be changed according to the speed of the traveling thin steel strip.

In the above embodiment, the present invention is applied to the sensitivity calibration of a magnetic flaw detector for a thin steel strip provided opposite to a non-magnetic roll, but the present invention is not limited to this. Instead, the present invention can be applied to a magnetic flaw detector provided in a hollow roll as shown in FIGS. 1 and 2 and a sensitivity calibration of a general magnetic flaw detector.

[0047]

According to the present invention, simple calibration can be performed only by adding an AC current to a DC current flowing through the magnetizer and superimposing the DC current to produce a pseudo leakage magnetic flux. Therefore, it is not necessary to frequently perform full-scale calibration using an artificial linear wound that requires labor and time,
Also, it is not necessary to newly wind a coil for calibration. Therefore, since the simple calibration can be easily performed, the performance of the flaw detector can be compensated.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of a configuration of a conventional sensitivity calibration device described in Japanese Patent Application Laid-Open No. 3-134555.

FIG. 2 is also a longitudinal sectional view

FIG. 3 is a perspective view showing the configuration of another example of a conventional sensitivity calibration device described in Japanese Patent Application Laid-Open No. 3-134555.

FIG. 4 is a diagram illustrating an example of the relationship between lift-off due to inclusions and the output of a magneto-sensitive element for explaining a conventional problem.

FIG. 5 is a diagram showing an example of the relationship between the inclination of the magnetically sensitive element in the horizontal magnetic field direction and the output reduction rate.

FIG. 6 is a block diagram showing a circuit configuration example of a magnetic flaw detector to be calibrated according to the present invention.

FIG. 7 is a diagram showing an example of a relationship between an exciting current of a magnetizer and a magnetic field strength between poles for explaining the principle of the present invention.

FIG. 8 is a diagram showing an example of a relationship between an exciting current of a magnetizer and an output relative value due to inclusions.

FIG. 9 is a diagram showing an example of a relationship between an exciting current of a magnetizer and an output by an inclusion.

FIG. 10 is a side view showing the online position of the embodiment of the present invention.

FIG. 11 is also a front view

FIG. 12 is a block diagram showing a configuration example of a power supply used in the embodiment.

FIG. 13 is a chart showing a comparative example obtained by the above-described embodiment, in which the simple calibration values have different dates and times.

FIG. 14 is a diagram showing an example of an output waveform of a magnetic sensitive element during normal flaw detection in the circuit of the magnetic flaw detection apparatus.

FIG. 15 is a diagram showing an example of an output waveform of a magneto-sensitive element during simple calibration.

FIG. 16 is a diagram showing an example of a capacitor output waveform during normal flaw detection.

FIG. 17 is a diagram showing an example of a double-wave rectifier output waveform during normal flaw detection.

FIG. 18 is a diagram showing an example of an output waveform of a double-wave rectifier during simple calibration.

FIG. 19 is a diagram showing an example of an output waveform of a collective circuit during normal flaw detection.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Thin steel strip 80 ... Non-magnetic roll 100 ... Magnetic flaw detector 102 ... Magnetizer 104 ... Magnetization yoke 106 ... Magnetization coil 110 ... Flaw detection head 111 ... Magnetic sensitive element 112 ... Power supply 114 ... DC power supply 116 ... AC power supply 118 ... Superposition Circuit 120 Switching circuit 162 Capacitor 164 Amplifier 166 Bandpass filter 168 Dual-wave rectifier 170 Buffer 172 Collective circuit 174 Comparator

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Yoshihide Yamamoto 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Prefecture Inside the Chiba Works of Kawasaki Steel Corp. In company system high tech

Claims (2)

[Claims] 1. A magnetic field is generated in the running direction of the strip by a magnetizer disposed near the strip to be inspected, and a large number of leakage magnetic fluxes generated due to internal or surface defects are arranged in the width direction of the strip. In the method of calibrating the sensitivity of a magnetic flaw detector, which is detected by a group of magnetically sensitive elements and serves as a defect signal, an alternating current for generating a pseudo leakage magnetic flux corresponding to a pseudo defect is superimposed on a direct current for generating a magnetic field flowing through the magnetizer. A method of calibrating the sensitivity of the magnetic flaw detection device, wherein the pseudo leakage magnetic flux is used to calibrate the sensitivity of the magnetic sensitive element group. 2. A magnetic field is generated in the running direction of the strip by a magnetizer disposed near the strip to be inspected, and a large number of leakage magnetic fluxes generated by internal or surface defects are arranged in parallel in the width direction of the strip. In a sensitivity calibration device of a magnetic flaw detector which detects a defect signal and detects a defect signal, a means for generating an alternating current for generating a pseudo leakage magnetic flux corresponding to a pseudo defect, and supplying the alternating current to the magnetizer Means for superimposing on a direct current for generating a flowing magnetic field, wherein the sensitivity of the magnetic sensitive element group is calibrated by the pseudo leakage magnetic flux.