JPH0772122A - Leak flux flaw detection method and apparatus for internal defect of magnetic material - Google Patents

Abstract

PURPOSE:To achieve accurate detection of a plurality of adjacent internal defects without being affected by magnetic leakage and poor contact by a method wherein an output signal of a magnetic field detector is compensated by a signal of a magnetizing force detector and one of outputs is subjected to a differentiation processing while the other thereof to an integration processing to evaluate a defect from a wave form of a combined output thereof. CONSTITUTION:Both ends of a magnetic path of a magnetizer 9 is brought into contact with a magnetic material 3 and a constant current and a constant voltage are applied to a coil 2 to generate a magnetic field so that the material 3 is magnetized. A leak magnetic flux 4 is generated from a internal defect 7 on the surface of the material 3 to detect it with a magnetic field detector 6 and a signal corresponding to the size of the defect 7 is sent to a signal compensator 15. A signal corresponding to the intensity of a surface magnetic field of the material 3 is sent to the device 15 with a magnetizing force detector 8 to compensate the state of contact between the magnetizer 1 and the material 3. The leak magnetic flux 5 from the magnetizer 1 is shielded with a magnetic field shielding device 10. The output of the device 15 is branched and one thereof is subjected to a differentiation processing while the other thereof to an integration processing and then, the two signals are combined to judge the adjacent internal defect 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a leakage magnetic flux flaw detection method for an internal defect of a magnetic material and an apparatus therefor.

[0002]

2. Description of the Related Art Conventionally, various nondestructive inspection methods have been put into practical use as flaw detection methods for defects in magnetic materials, and appropriate flaw detection methods are adopted according to the types of defects expected to exist. For example, if ultrasonic flaw detection is used to detect planar defects such as cracks, the defect position can be easily detected, and if a radiation transmission method is applied to detect defects with a depth on the subject surface, the defect shape can be easily detected. I can detect. However, the former ultrasonic flaw detection method is difficult to quantitatively evaluate the defect shape, and the latter radiation transmission method is also difficult to grasp the defect position. Also, although the magnetic flux leakage flaw detection method has excellent detectability for surface or subcutaneous defects of magnetic materials,
It has the drawback of being inferior in detectability to internal defects. By the way, the leakage magnetic flux damage method of the internal defect of the magnetic material and the apparatus therefor will be taken up, and the prior art thereof will be described as follows.

In the prior art, as shown in FIG. 8, a constant voltage and a constant current are applied to a coil 2 of a magnetizer 1 forming a magnetic path to generate a constant magnetic field, and both ends of the magnetic path of the magnetizer 1 are generated. The abutting magnetic material 3 is magnetized. The internal defect leakage magnetic flux 4 appearing on the surface due to the internal defect of the magnetic material 1 and the magnetizer leakage magnetic flux 5 leaking from the magnetizer 1 are transferred to the magnetic material 3
The electric signal detected and output by the magnetic field detector 6 arranged on the surface of is amplified by the amplifying device 11, and the noise component is removed by the filter 12, and then the electric signal is output to the display device 13 and the recording device 14. Then, the internal defect 7 is evaluated by this.

[0004]

The evaluation of the internal defect 7 of the magnetic material 3 according to the above-mentioned conventional technique is performed by the magnetic field detector 6 which is output in proportion to the density of the internal defect leakage magnetic flux 4 and the magnetizer leakage magnetic flux 5. It is based on the electric signal level of. However, since the density of the internal defect leakage magnetic flux 4 is very small compared to the magnetic flux density leaked from the surface defect or the subcutaneous defect, even if the amplification process is performed, it is greatly affected by the change in the magnetizing force of the magnetic material 3. The magnetizing force received by the magnetic material 3 changes depending on the contact state between the magnetizer 1 and the magnetic material 3, even if the magnetizer 1 that has generated a constant magnetic field magnetizes the magnetizing force. For this reason, the electric signal level output from the magnetic field detector 6 is greatly affected by the contact state between the magnetizer 1 and the magnetic material 3, and the internal defect with high accuracy cannot be evaluated.

Further, the magnetic field detector 6 also detects the magnetizer leakage magnetic flux 5, and since this component is almost the same as the component of the internal defect leakage magnetic flux 4, it is difficult to remove it by the filter, and as a noise signal, the display device 13 and recording are performed. Since it is output to the device 14, it has been an obstacle to the evaluation of internal defects.

Next, a case of inspecting a magnetic material having a plurality of adjacent internal defects by the above-mentioned leakage magnetic flux flaw detection method will be described with reference to FIGS. The magnetic flux 4 leaking from the internal defect 7 to the surface of the magnetic material 3 is distributed considerably wider than the defect width even in the case of a single defect as shown in FIG.
The signal output to the display device and the recording device has a wide waveform indicating a situation where the output is slowly changing as shown in FIG. Then, as shown in FIG. 11, in a plurality of adjacent internal defects, the magnetic fluxes leaking from the respective defects interfere with each other and are distributed over a wider range. Therefore, the signals output to the display device and the recording device are as shown in FIG. In addition, a separated waveform corresponding to each internal defect was not obtained, and it was difficult to accurately evaluate each defect.

Therefore, there is a demand for the development of a new magnetic flux flaw detection method for magnetic defects inside the magnetic material and a device therefor.

The present invention has been made in view of the above circumstances, and is capable of accurately evaluating a plurality of adjacent internal defects without being affected by the contact state between the magnetizer and the subject and the magnetic flux leaking from the magnetizer. (EN) It is an object to provide a magnetic flux leakage flaw detection method for a magnetic material and an apparatus therefor that can be well performed.

[0009]

In order to achieve the above-mentioned object, the magnetic flux internal flaw leakage magnetic flux flaw detection method of the present invention magnetizes an object made of a magnetic material, and the surface of the object is removed from the internal defect. The magnetic flux that leaks into the magnetic field is detected by a magnetic field detector, and its output signal is compensated by the magnetizing force received by the subject, then the compensated signal is branched, one of them is differentiated, and the other is integrated. The differential processed signal and the integrated processed signal are combined, and the flaw detection is evaluated from the waveform of the combined output.

Further, the magnetic flux internal flaw detection apparatus for magnetic defects according to the present invention includes a magnetizing device which has a magnetizer for magnetizing the subject and has means for shielding the magnetic flux leaking from the magnetizer, and the magnetizing device. A magnetic field detector that detects the magnetic flux leaking from the internal defect to the surface, a magnetizing force detector that detects the magnetizing force received by the subject, and a signal compensator that compensates the signal of the magnetic field detector with the signal of the magnetizing force detector. And the signal from this signal compensator is amplified, and the amplified signal is branched,
A signal processing device that performs differential processing on one side and integrates the other side, and then combines and outputs the differentiated signal and the integrated signal, and a display unit that displays the output from the signal processing device as a flaw detection result. , Are provided.

[0011]

In the leakage magnetic flux flaw detection method of the present invention, since the signal of the magnetic field detector is compensated by the signal of the magnetizing force detector,
The signal of the magnetic field detector, which is the basis of the defect evaluation, is not affected by the magnetizing force applied to the magnetic material, which changes depending on the contact state between the magnetic material and the magnetizer, and the signal processed by the signal compensator. Is differentiated to form a steep output waveform, and integrated to remove low-frequency (drift) components, so that even if a widely distributed magnetic flux leaking from a plurality of adjacent internal defects is detected, each defect is detected. Since the signals can be separated correspondingly, the defects can be easily evaluated from the waveforms displayed on the display means.

In the leakage magnetic flux flaw detector of the present invention, since the magnetic flux leaking from the magnetizer is shielded by the magnetic field shield included in the magnetizing device, the magnetic field detector detects only the internal defect leakage magnetic flux. The signal is processed by the signal compensator that compensates with the signal of the magnetizing force detector, and the signal processor further amplifies the output signal of the signal compensator, and then branches and one branch signal is differentiated and steepened. Since the output signal of the other branch is shaped, the other branch signal is integrated to remove low-frequency components, the differential processing is performed, the waveform is integrated and the waveform is synthesized and output, so that noise is generated in the signal output to the display means. Therefore, even if adjacent internal defects are close to each other, the waveform displayed on the display unit is separated correspondingly, and the internal defects can be easily evaluated.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a control circuit that embodies the magnetic flux leakage flaw detection method for defects inside a magnetic material according to the present invention. This control circuit includes a magnetic field detector 6 for detecting a magnetic flux leaking from the internal defect portion of the subject to the surface by magnetizing the subject made of a magnetic material, and a magnetizing force detection for detecting a magnetizing force received by the subject. Device 8, a signal compensator 15 for compensating the signal of the magnetic field detector 6 with the signal of the magnetizing force detector 8, and an amplifier 1 for amplifying an output signal from the signal compensator 15.
7. Differentiator 18 for differential processing and integrator 1 for integral processing
And a signal processing device 16 including the signal processing device 16.
The display device 13 and the recording device 14 function as a display unit for displaying the output of (1) as the flaw detection result.

Next, the control circuit configured as described above is
Further, a detailed description will be given with reference to the signal processing circuit diagram shown in FIG. The magnetic field detector 6 whose internal resistance value R ₁ changes in proportion to the internal defect leakage magnetic flux density and the magnetic force detector 8 whose internal resistance value R ₂ changes in proportion to the magnetizing force received by the subject are differentially detected. The magnetic field detection signal is differentially compensated by the magnetizing force detector signal by the configured signal compensator 15 and output to the signal processor 16. The signal input to the signal processing device 16 is arbitrarily amplified by changing the variable resistor R ₃ by the amplifier 17, and the amplified signal is branched and one is fed to the differentiator 18 and the other is fed to the integrator 19. Is output. In the differentiator 18, even with a slow input signal waveform as shown in FIG. 3, a steep output waveform as shown in FIG. 4 can be obtained by reducing the time constant (τ = R ₄ C ₁ value) of the differentiating circuit.
Further, even with input signals of a plurality of adjacent internal defects as shown in FIG. 5, output waveforms are separated for each defect as shown in FIG. Note that the differentiator 18 can remove a frequency component (noise) higher than the defect signal by inserting the resistor R ₅ and the capacitor C ₂ in parallel with the capacitor C ₁ and the resistor R _4, respectively. Further, the integrator 19 is connected in parallel to the differentiator 18, removes high frequency components, gives a gain equal to that of the differentiating circuit, and cancels low frequency (drift) components.

The signals thus processed by the differentiator 18 and the integrator 19 are combined, and the combined signal is output to the display unit 13 as a flaw detection result and recorded by the recording unit 14, and the flaw detection result is obtained. Due to this, highly accurate defect evaluation is performed.

FIG. 7 is an overall configuration diagram showing an embodiment of a magnetic flux leakage flaw detection apparatus for defects in magnetic materials according to the present invention, showing a situation in which internal defects in magnetic materials are inspected. Reference numeral 9 in the drawing is a magnetizing device including a magnetizer 1 having a magnetic path for magnetizing the magnetic material 3 and a magnetic field shield 10 for shielding the leakage magnetic flux 5 from the magnetizer 1. The magnetic field detector 6 is adapted to scan the surface of the magnetic material 3 in the vertical and horizontal directions by moving means (not shown). Detect magnetic field. Further, the signal compensator 15 is adapted to compensate the magnetic field detection signal with the magnetizing force detection signal. The signal subjected to the compensation processing is amplified by the signal processing device 16, and the amplified signal is branched so that one of the signals is branched. The differential processing is performed, the other is integrated, and then the two are combined and output to the display device 13 that displays the flaw detection result and the recording device 14 that records the flaw detection result.

Next, the case of inspecting the internal defects 7 of the magnetic material 3 using the present apparatus having the above-described structure will be described. First, both ends of the magnetic path of the magnetizing device 9 are applied to the magnetic material 3, a constant current and a constant voltage are applied to the coil 2, a constant magnetic field is generated in the magnetizer 1, and the magnetic material 3 is magnetized.

When the magnetic material 3 is magnetized, a leakage magnetic flux 4 is generated from the internal defect portion on the surface of the magnetic material 3. The magnetic flux 4 is detected by a magnetic field detector 6 which scans the surface of the magnetic material 3 vertically and horizontally. It Here, the internal defect leakage magnetic flux 4
Is distributed in proportion to the size of the defect, the output signal of the magnetic field detector 6 also outputs a signal corresponding to the size of the defect and sends it to the signal compensator 15. In addition, magnetic material 3
The magnetizing force detector 8 arranged on the surface of detects the surface magnetic field of the magnetic material 3, outputs a signal corresponding to the surface magnetic field strength, and sends it to the signal compensator 15. Here, since the magnetizer leakage magnetic flux 5 leaking from the magnetizer 1 is shielded by the magnetic field shield 10, it is not detected by the magnetic field detector 6 and the magnetizing force detector 8.

The signal compensator 15 compensates the magnetic field detection signal with the magnetizing force detector signal, sends this signal to the signal processor 16 for amplification processing, differentiation processing and integration processing, and displays the flaw detection result on the display device 13. The record is output together with the recording device 14.

In the above-mentioned embodiment, the case where the shield plate of the magnetic field shield 10 for shielding the magnetizer leakage magnetic flux 5 is a single shield plate has been described, but this may be doubled or tripled, or made of copper and steel. It can also have a double structure.

In the embodiments shown in FIGS. 1 to 7 described above, the case where the magnetic flux internal flaw detection of the magnetic material is inspected has been described. However, in the present invention, if the magnetic material is a magnetic material, flaw detection generated on the surface and the inner surface of the magnetic material is performed. It goes without saying that it can be applied to. Further, as the magnetic field detector signal compensating means of the present invention,
Although the case where the magnetizing force received by the magnetic material is used as the compensation value has been described, the contact state between the magnetizer and the magnetic material is related to the magnetic flux density leaking from the magnetizer. There is no problem as a compensation value.

[0022]

According to the method of the present invention, since the signal of the magnetic field detector for detecting the leakage magnetic flux due to the internal defect of the magnetic material is compensated by the magnetizing force received by the magnetic material, the contact between the magnetizer and the magnetic material. The signal that is not affected by the state and that has been compensated is branched after amplification processing, one signal is differentiated to form a steep waveform, and the other signal is integrated to remove low frequency components. Then, since both signals are combined and output, a signal waveform that allows easy identification of a plurality of adjacent internal defects can be obtained, and highly accurate internal defect evaluation becomes possible.

According to the apparatus of the present invention, since the apparatus for carrying out the above method is provided and the means for shielding the leakage magnetic flux from the magnetizer is provided, the magnetic flux detected by the magnetic field detector is caused by internal defects. Only the leakage magnetic flux can be used, and the generation of noise can be prevented.

[Brief description of drawings]

FIG. 1 is a block diagram of a control device that embodies a magnetic flux leakage flaw detection method of the present invention.

FIG. 2 is a diagram illustrating a signal processing circuit that processes a detection signal of a leakage magnetic flux.

FIG. 3 is a diagram showing an example of a signal waveform before signal processing corresponding to a single internal defect.

FIG. 4 is a diagram showing an example of a signal waveform before signal processing corresponding to a plurality of adjacent internal defects.

FIG. 5 is a diagram showing an example of a flaw detection output signal waveform subjected to signal processing corresponding to a single internal defect.

FIG. 6 is a diagram showing an example of a flaw detection output signal waveform obtained by signal processing corresponding to a plurality of adjacent internal defects.

FIG. 7 is a configuration diagram of a leakage magnetic flux flaw detector according to an embodiment of the present invention.

FIG. 8 is an explanatory diagram showing a conventional flaw detection method and flaw detection apparatus.

FIG. 9 is an explanatory diagram showing the appearance of leakage magnetic flux in a single internal defect.

FIG. 10 is an explanatory diagram showing the appearance of leakage magnetic flux in a plurality of adjacent internal defects.

FIG. 11 is a flaw detection signal waveform diagram corresponding to a single internal defect in the related art.

FIG. 12 is a flaw detection signal waveform diagram corresponding to a plurality of adjacent internal defects in the related art.

[Explanation of symbols]

 1 Magnetizer 2 Coil 3 Magnetic Material 4 Internal Defect Leakage Flux 5 Magnetizer Leakage Flux 6 Magnetic Field Detector 7 Internal Defect 8 Magnetizing Force Detector 9 Magnetizing Device 10 Magnetic Field Shielder 11 Amplifying Device 12 Filter 13 Display Device 14 Recording Device 15 Signal compensator 16 Signal processor 17 Amplifier 18 Differentiator 19 Integrator

Claims (2)

[Claims] 1. A magnetic field detector magnetizes a subject made of a magnetic material, detects a magnetic flux leaking from an internal defect portion of the subject to the surface, and the subject receives an output signal of the magnetic field detector. After branching after compensating with the magnetizing force, one is differentiated, the other is integrated, and then the differentiated signal and the integrated signal are combined, and the flaw detection is evaluated from the waveform of the combined signal. A leak magnetic flux flaw detection method for defects inside a magnetic material, comprising: 2. A magnetizing device having a built-in magnetizer for magnetizing a subject made of a magnetic material and having means for shielding a magnetic flux leaking from the magnetizer, and a magnetic flux leaking from an internal defect portion of the subject to a surface. A magnetic field detector for detecting a magnetic field, a magnetic force detector for detecting a magnetic force received by the subject, a signal compensator for compensating an output signal of the magnetic field detector with an output signal of the magnetic force detector, and the signal. A signal processing device for amplifying a signal from a compensating device, branching the signal, differentiating one of the signals, integrating the other, and synthesizing and outputting the differentiated signal and the integrated signal, and the signal processing A leakage magnetic flux flaw detector for magnetic material internal defects, comprising: a display unit that displays the waveform of the output signal of the apparatus as the flaw detection result.