JPH10293122A - Equipment and method for detecting flaw of metallic body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable detection of a minute defect such as an inclusion existing inside a metallic body or in the surface thereof and to make sensitivity and resolution excellent. SOLUTION: An E type core 5 and a U type core 12 are disposed on one side and a DC magnetizer 2 on the other so that they hold a steel sheet 1 between. The part to be inspected of the steel sheet 1 is magnetized to a saturation level by the DC magnetizer 2. A coil (a) wound on the central pole of the E type core 5 is used as a magnetic detector. The U type core 12 is so disposed outside the E type core 5 as to cover this core. A high-frequency excitation signal for eddy current flaw detection sent from an exciting current generator 4 is supplied to coils (d) and (e) provided at the two poles of the U type core 12, not to the poles in the opposite ends of the E type core 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flaw detection apparatus and a flaw detection method for detecting minute defects such as inclusions inside and on a metal body, particularly a magnetic metal body, and more particularly to a leakage magnetic flux flaw detection method and eddy current. The present invention relates to a flaw detection apparatus and a flaw detection method for a magnetic metal body using a flaw detection method.

[0002]

2. Description of the Related Art In the case of a metal material or the like, if there is a defect in the inside or on the surface, a problem such as strength may occur. Therefore, in terms of quality control or quality assurance, an X-ray transmission method, an ultrasonic Various non-destructive inspections such as flaw detection are being performed. On the other hand, regarding the detection of a defect near the surface and the detection of the surface and the inner surface of a thin band-shaped material, an electromagnetic method, that is, a leakage magnetic flux method or an eddy current flaw detection method is often used particularly online.

[0003] In ultra-thin steel sheets for can-making materials, if there are defects such as inclusions, problems such as generation of flange cracks during can-making may occur. As a method of detecting such a defect, an on-line high-speed defect detector using a leakage magnetic flux method or the like has been developed.

For example, Japanese Patent Application Laid-Open No. 3-175352 discloses a magnetizer 22 for magnetizing a steel plate on one side with a steel plate 21 interposed between the steel plate 21 and a defect on the other side, as shown in FIG. Magnetic sensor array 2 for detecting generated leakage magnetic flux
3 are arranged in the width direction, and the non-magnetic rolls 24 and 25 are respectively provided.
There has been proposed a method of detecting flaws by putting them in a space.

According to this method, the distance between the sensor 23 and the steel plate 21 to be inspected can be kept small and stable.
A minute defect in the steel plate 21 can be detected at high speed with high sensitivity.

Japanese Patent Application Laid-Open No. 5-164745 proposes a method for detecting pits and the like existing on the surface of a steel plate or the like by an eddy current flaw detection method using a differential probe. This uses an E-shaped core as shown in FIG. 3, using a coil 32e wound around a middle magnetic pole 32b for excitation, and coils 32d and 32f wound around magnetic poles 32a and 32c at both ends for detection. A defect is detected by processing a difference signal between the outputs of the coils 32d and 32f. By processing the difference signal, a minute change in the eddy current signal due to the defect can be detected with high sensitivity. Therefore, even when the defect is small or the plate is thick, the defect can be accurately detected.

[0007]

However, the technique described in Japanese Patent Application Laid-Open No. 3-175352 has a problem that although crack-like defects can be detected with high accuracy, the detection accuracy of pit-like defects is poor. Conversely, Japanese Patent Application Laid-Open
In the technique described in Japanese Patent Application Laid-Open No. 164745/1994, although pit-like defects can be detected with high accuracy, there is a problem that the detection accuracy of crack-like defects is poor.

In order to solve these problems, the inventors have previously proposed a new technique in Japanese Patent Application No. 8-83506. This combines the advantages of magnetic flux leakage and eddy current testing. The outline is shown in FIG.

In FIG. 4, reference numeral 1 denotes a steel plate to be inspected;
2 is a DC magnetizer, 3 is a non-magnetic roll, 4 is an exciting current generator, 5 is an E-shaped core, a is a coil wound around the center pole of the E-shaped core, and b and c are E-shaped cores. Coils wound on the poles at the ends, 6, 7, and 9 are band-pass filters, 8 is a phase detector, 10 is a multiplier as an arithmetic unit, and 11 is a decision unit.

An E-shaped core 5 is provided on one side of the steel plate 1.
And the DC magnetizer 2 is arranged on the other side. The DC magnetizer 2 magnetizes the portion to be inspected of the steel plate 1 to the saturation region. The steel plate 1 moves between the E-shaped core 5 and the DC magnetizer 2, and three poles of the E-shaped core 5 are arranged along the moving direction. Of the three coils, the coil a wound around the center pole of the E-shaped core is used as a magnetic detector, and the time differential value of the magnetic flux linked to the coil is measured, so that the leakage is detected. A magnetic flux signal and an eddy current signal are detected.

Due to the structural feature that the core 5 is E-shaped, the magnetic flux linked to the coil is divided into a magnetic flux passing through a magnetic loop including a pole at one end and a pole at the center, and the other magnetic flux. It is the difference between the magnetic flux passing through the magnetic loop including the end pole and the center pole. Therefore, a noise component common to both loops is canceled, and a defective signal component not common to both loops is selectively detected.

On the other hand, coils b and c wound on the poles at both ends
Are excited by the exciting current generator 4 and used for eddy current excitation. Various excitation phase differences can be selected. Here, a phase difference (a phase difference of 180 degrees) is used in which a magnetic flux from one pole returns to the other pole. The eddy currents generated by the magnetic fluxes from the poles b and c are strengthened just below the middle detection coil a.

After passing the output of the coil a through the band-pass filter 6, phase detection is performed by the phase detector 8 to extract only the defective signal component, and the defective signal is obtained by passing the output again through the band-pass filter 9.

Further, by passing the output of the coil a through an appropriate band-pass filter 7, a leakage magnetic flux detection signal (differential value) can be obtained. Outputs of the band-pass filters 7 and 9 are calculated by a multiplier 10 which is a calculator. The determination circuit 11 determines the presence and degree of a defect according to the magnitude of the output of the multiplier 10.

The defect detection apparatus according to this method has the advantage that it has both the advantages of magnetic flux leakage inspection and eddy current inspection.
However, since the coils are wound around the three magnetic poles of the E-shaped core, the interval between the magnetic poles must be increased. Therefore, there is a problem that the resolution and the detection sensitivity are reduced. In addition, when the width of the magnetic pole is reduced and a coil is wound around the magnetic pole, there is a problem that the E-type core is magnetically saturated and the sensitivity as a sensor is reduced. Due to these problems, there is a problem that both the leakage magnetic flux inspection method and the eddy current inspection method cannot obtain a sufficient S / N ratio, and the detection results obtained by calculating their signals are not sufficient.

The present invention has been made to solve these problems, and is disclosed in Japanese Patent Application No. 8-83506 filed earlier.
It is an object of the present invention to improve the invention according to the above item and to provide a more accurate metal body flaw detection apparatus and method.

[0017]

The gist of the present invention is that the E-shaped core is not used as the exciting coil, but is used only as the detecting coil, and the U-shaped coil provided outside the E-shaped core is used as the exciting coil. To use.

That is, the above-mentioned problems are caused by a magnetizer for magnetizing a portion to be inspected of a magnetic metal body, and a coil wound around a center pole of an E-shaped core for detecting a leakage magnetic flux generated from a defective portion of the magnetic metal body. A first defect signal processing unit for processing a signal from the coil to detect a defect; an exciting coil for generating an eddy current in a portion to be inspected of the magnetic metal body; A coil for detecting a disturbance of the current, and a second signal processing unit for processing a signal of the disturbance of the eddy current detected by the coil to detect a defect; Are wound around the center pole of the E-shaped core, and the exciting coils are not wound around the poles at both ends of the E-shaped core. The exciting coil to be used is a U-shape provided outside the E-shaped core. It is solved by the flaw detector of a magnetic metal material, wherein (claim 1) which are wound on both poles of the core.

A portion to be inspected is magnetized by a magnetizer, and a leakage magnetic flux generated from a defective portion of the magnetic metal body is detected by a coil wound around a central pole of the E-shaped core, and processed by a first signal processing unit. Then, the defect is detected by the leakage magnetic flux method. on the other hand,
A high-frequency current is applied to the exciting coil wound around both poles of the U-shaped core provided outside the E-shaped core to generate an eddy current in the portion to be inspected. Detection is performed by a coil wound around the center pole of the core, processing is performed by the second signal processing unit, and a defect is detected by an eddy current method.

At this time, since the portion to be inspected is magnetized to almost the saturation region by the DC magnetizer, noise due to magnetic unevenness of the material of the magnetic metal body is eliminated, and the S / N ratio is reduced.
An eddy current detection signal having a good ratio can be obtained.

In the present invention, since no exciting coil is wound around the E-shaped core, the distance between the poles can be reduced, and the resolution and the detection sensitivity can be improved. Further, since the core is not saturated by the exciting magnetic flux, detection with high sensitivity can be performed.

In the first aspect of the present invention, a means for judging the presence or absence of a defect by combining a signal of the first defect signal processing section and a signal of the second defect signal processing section is provided (claim 2). And accurate defect detection.

As a method of combining the signals of the first defect signal processing section and the signals of the second defect signal processing section, by multiplying both signals, it is possible to detect defects with high accuracy.

Also, a first defect signal (leakage magnetic flux detection)
Is directed to a change in the DC component, and the second defect signal (eddy current flaw detection) is directed to a change in the AC component. Therefore, there is a time difference between the detection timings of the two. As a countermeasure against this, if at least one signal is delayed and the timings of the two signals are matched and then a combination of signals such as multiplication is performed (claim 4), an accurate defect can be detected.

Further, the combination of the E-shaped core and the U-shaped core according to the present invention is not effective only for the combination of the leakage magnetic flux inspection method and the eddy current inspection method as described in the above claims. The same effect is produced by the eddy current flaw detection method alone (claim 5). In this case, since the magnetic flux leakage detection is not used, the inspection object may be a non-magnetic metal body.

The portion to be inspected of the magnetic metal body is magnetized, the leakage magnetic flux generated from the defective portion of the magnetic metal body is detected, signal processing is performed to detect the defect, and an eddy current is generated in the inspected portion of the magnetic metal body. The method for detecting and processing a signal of turbulence of eddy current caused by a defective portion of a magnetic metal body by a coil, and detecting a defect of the magnetic metal body by detecting a defect, wherein the coil for detecting the turbulence of the eddy current, Wrap around the center pole of the E-shaped core,
The exciting coil that does not wind the exciting coil around the poles at both ends of the E-shaped core and generates an eddy current in the portion to be inspected of the magnetic metal body includes both the U-shaped core provided outside the E-shaped core. The same operation as in the first aspect of the invention can be obtained by the flaw detection method for magnetic metal bodies characterized by being wound around the above-mentioned pole.

In addition to the above, a method of flaw detection of a magnetic metal body for judging the presence or absence of a defect by combining a signal obtained by processing a signal of a leakage magnetic flux and a signal obtained by processing a signal caused by disturbance of an eddy current is claimed. The same function as the invention of item 2 is obtained.

Further, if the signal processed by the signal processing of the leakage magnetic flux is multiplied by the signal processed by the signal processed by the turbulence of the eddy current, the presence or absence of a defect is determined based on the magnitude of the signal (claim 8). The same action as described above is obtained.

In addition, at least one of the signals is delayed in order to obtain a temporal coincidence between the signal processed by the signal processing of the leakage magnetic flux and the signal processed by the signal due to the disturbance of the eddy current. The same operation as that of the fourth aspect is obtained.

The present invention also provides a flaw detection method for a metal body, wherein an eddy current is generated in a metal body, a signal of turbulence of the eddy current generated by a defect in the metal body is detected and processed by a coil, and the defect is detected. A coil for detecting turbulence of the eddy current is wound around the center pole of the E-shaped core. Excitation coils are not wound around the poles at both ends of the E-shaped core, and an eddy current is generated in the portion to be inspected of the metal body. The invention according to claim 5, wherein the exciting coil to be wound is wound around both poles of a U-shaped core provided outside the E-shaped core by a flaw detection method for a metal body (Claim 10). The same effect is obtained.

[0031]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an example of an embodiment of the present invention. In FIG. 1, 1 is a steel plate to be inspected, 2 is a DC magnetizer, 3 is a non-magnetic roll, 4 is an exciting current generator, 5 is an E-shaped core, and a is wound around the center pole of the E-shaped core. Coils 6, 7, 9 are band-pass filters,
8 is a phase detector, 10 is a multiplier as an arithmetic unit, 11 is a decision unit, 12 is a U-shaped core, d and e are cores wound around poles of a U-shaped core, and 13 and 14 are It is a time adjuster.

In the embodiment of the present invention, the coil for detecting the leakage magnetic flux and the coil for detecting the turbulence of the eddy current are the same coil a, but separate coils may be used.

[0033] The first signal processing unit described in the claims includes:
This corresponds to the band pass filter 7. The second signal processing unit described in the claims corresponds to the band pass filter 6, the phase detector 8, and the band pass filter 9.
That is, in this embodiment, a signal exceeding the threshold value of each of the band-pass filters 7 and 9 is determined as a defective signal.

The means for judging the presence or absence of a defect by combining the signal of the first defect signal processing section and the signal of the second defect signal processing section according to the present invention is characterized in that in this embodiment, Device 10 and a judgment device 11.

The delay circuit described in the claims corresponds to the time adjusters 13 and 14 in this embodiment.

The embodiment of the present invention shown in FIG. 1 is different from the conventional example shown in FIG. 4 in that a U-shaped core 12 is disposed outside the E-shaped core 5 so as to cover the E-shaped core 5. And
The high frequency excitation signal for eddy current flaw detection of about 64 KHz from the excitation current generator 4 is supplied not to the poles at both ends of the E-shaped core but to the coils d and e provided on the two poles of the U-shaped core. That is.

As a result, it is not necessary to wind the exciting coil around the E-shaped core, and it is possible to increase the resolution and the detection sensitivity by reducing the distance between the poles by downsizing. Further, since the E-type core is not saturated by the exciting magnetic flux, the detection sensitivity by the coil a does not decrease.

With the steel plate 1 interposed therebetween, the E-shaped core 5 and the U-shaped core 12 are arranged on one side, and the DC magnetizer 2 is arranged on the other side. The DC magnetizer 2 magnetizes the portion to be inspected of the steel plate 1 to the saturation region. The steel sheet 1 moves between the E-shaped core 5 and the U-shaped core 12 and the DC magnetizer 2, and three poles of the E-shaped core are arranged along the moving direction. Part 3
Among the books, the coil a wound around the center pole of the E-shaped core is used as a magnetic detector, and a voltage generated by a temporal change of a magnetic flux linked to the coil is measured, and the leakage is measured. A magnetic flux signal and an eddy current signal are detected.

Due to the structural feature that the core 5 is E-shaped, the magnetic flux interlinking the coil a wound around the center pole is a magnetic flux including the pole at one end and the center pole. The difference is the difference between the magnetic flux passing through the loop and the magnetic flux passing through the magnetic loop including the pole at the other end and the center pole. Therefore, a noise component common to both loops is canceled, and a defective signal component not common to both loops is selectively detected.

The output of the coil a is passed through a band-pass filter 6 having an excitation frequency as a center frequency, and then phase-detected by a phase detector 8 with reference to a signal obtained by shifting the eddy current excitation signal to a defect signal. An eddy current defect signal can be obtained by extracting only the component and passing the component again through the band-pass filter 9 (1 KHz to 5 KHz).

In the eddy current detection signal, the phase of the defect signal and the noise phase have different phase differences from the phase of the excitation signal. Therefore, by extracting the signal of the phase having the defect by the phase detection, the S / N ratio can be improved.

Further, by passing the output of the coil a through an appropriate band pass filter 7 (1 KHz to 5 KHz), a leakage magnetic flux detection signal (differential value) can be obtained. Outputs of the band-pass filters 7 and 9 are calculated by a multiplier which is a calculator 10. The determination circuit 11 determines the presence and degree of a defect according to the magnitude of the output of the multiplier 10.

The leakage magnetic flux signal is obtained by processing a low frequency signal, and the eddy current flaw detection signal is obtained by processing a high frequency signal. Further, in the processing of the eddy current detection signal, the signal output timing is shifted because phase detection is performed. Therefore, the timings of the defect signals output from the two band-pass filters 7 and 9 may be shifted. In such a case, by installing at least one of the time adjusters 13 and 14 and adjusting the timing of both signals, and then inputting them to the multiplier 10, accurate defect determination can be performed. .

[0044]

As described above, in the present invention, the E-shaped core is not used as the exciting coil, but is used only as the detection coil, and the U-shaped coil provided outside the E-shaped core is used as the exciting coil. , The size of the E-shaped core can be reduced. Therefore, resolution and detection sensitivity can be improved. In addition, since the E-type core does not become magnetically saturated, accurate detection becomes possible.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of an embodiment of the present invention.

FIG. 2 is a diagram showing an example of an embodiment of the invention according to the prior application of the invention.

FIG. 3 is a diagram showing an example of the related art.

FIG. 4 is a diagram showing another example of the prior art.

[Explanation of symbols] [Explanation of symbols]

 Steel plate 1 Steel plate 2 DC magnetizer 3 Non-magnetic roll 4 Excitation current generator 5 E-type core 6 Band-pass filter 7 Band-pass filter 8 Phase detector 9 Band-pass filter 10 Multiplier 11 Judge 12 U-shaped core 13 hours Adjuster 14 Time adjuster

Continuation of the front page (72) Inventor Kozo Maeda 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Inventor Akira Nagato 1-1-2, Marunouchi, Chiyoda-ku, Tokyo Japan Inside Steel Pipe Co., Ltd. (72) Inventor Mika Murakami ▲ Hiro ▼ 2447-2 Niiso, Toda City, Saitama Prefecture

Claims (10)

[Claims] 1. A magnetizer for magnetizing a portion to be inspected of a magnetic metal body, a coil wound around a center pole of an E-shaped core for detecting a leakage magnetic flux generated from a defective portion of the magnetic metal body, and the coil A first defect signal processing unit that detects a defect by processing a signal from a magnetic metal body, an exciting coil that generates an eddy current in a portion to be inspected of a magnetic metal body, and a turbulence of an eddy current generated by the defect part of the magnetic metal body. A coil to be detected, and a second process for processing a signal of turbulence of the eddy current detected by the coil to detect a defect.
And a coil for detecting the turbulence of the eddy current is wound around a center pole of the E-shaped core, and coils are wound around the poles at both ends of the E-shaped core. The exciting coil that is not turned and generates an eddy current in the portion to be inspected of the magnetic metal body is wound around both poles of a U-shaped core provided outside the E-shaped core. A flaw detector for a magnetic metal body, characterized in that: 2. The magnetic metal body according to claim 1, further comprising means for judging the presence or absence of a defect by combining a signal of the first defect signal processing unit and a signal of the second defect signal processing unit. Flaw detection equipment. 3. The apparatus according to claim 2, further comprising means for multiplying the signal of the first defect signal processing unit by the signal of the second defect signal processing unit and determining the presence or absence of a defect based on the magnitude of the multiplication.
2. A flaw detector for a magnetic metal body according to claim 1. 4. The magnetic metal according to claim 2, further comprising a delay circuit for delaying at least one of the first defect signal processing unit signal and the second defect signal processing unit signal. Body flaw detector. 5. An excitation coil for generating an eddy current in a portion to be inspected of a metal body, a coil for detecting a turbulence of the eddy current generated by a defective portion of the metal body, and a signal of the eddy current turbulence detected by the coil And a signal processing unit for detecting a defect by processing the eddy current. The coil for detecting the turbulence of the eddy current is wound around a center pole of the E-shaped core. No coil is wound around the pole, and an exciting coil for generating an eddy current in the portion to be inspected of the metal body is wound around both poles of a U-shaped core provided outside the E-shaped core. A metal object flaw detection device characterized by being turned. 6. A portion to be inspected of a magnetic metal body is magnetized, a leakage magnetic flux generated from a defect portion of the magnetic metal body is detected, and signal processing is performed to detect a defect. A method for detecting a defect of the eddy current caused by a defective portion of the magnetic metal body by detecting and processing the signal with a coil, and detecting a defect of the magnetic metal body, wherein the coil detects the disturbance of the eddy current. Around the center pole of the E-shaped core,
An exciting coil that does not wind a coil around the poles at both ends of the E-shaped core and generates an eddy current in the portion to be inspected of the magnetic metal body has both U-shaped cores provided outside the E-shaped core. A flaw detection method for a magnetic metal body, which is wound around a pole. 7. The flaw detection method for a magnetic metal body according to claim 6, wherein the presence or absence of a defect is determined by combining a signal obtained by processing a signal of a leakage magnetic flux and a signal obtained by processing a signal resulting from turbulence of an eddy current. . 8. The method according to claim 6, wherein a signal obtained by processing the signal of the leakage magnetic flux and a signal obtained by processing the signal obtained by the disturbance of the eddy current are used to determine the presence or absence of a defect based on the magnitude of the signal.
The flaw detection method for a magnetic metal body according to the above. 9. The signal processing device according to claim 7, wherein at least one of the signals is delayed in order to obtain a temporal coincidence between the signal processed by the signal processing of the leakage magnetic flux and the signal processed by the signal due to the disturbance of the eddy current. The flaw detection method for a magnetic metal body according to the above. 10. A flaw detection method for a metal body, wherein an eddy current is generated in a metal body, a signal of turbulence of the eddy current generated by a defect in the metal body is detected and processed by a coil, and the defect is detected. A coil for detecting turbulence of the eddy current is wound around the center pole of the E-shaped core. Excitation coils are not wound around the poles at both ends of the E-shaped core, and an eddy current is generated in the portion to be inspected of the metal body. An exciting coil to be wound is wound around both poles of a U-shaped core provided outside the E-shaped core.