JPH08248002A - Magnetizer for flaw detection of steel member - Google Patents

Abstract

PURPOSE: To detect a pinhole highly accurately by forming a stabilized remanence on a steel plate by means of an AC exciter. CONSTITUTION: AC power being fed to a magnetizing means is generated from a waveform control means 30 based on an AC signal produced from an AC signal output means 20. AC sine wave power having stabilized amplitude and frequency is fed to an exciting coil 11 and a hysteresis loop in a steel plate is stabilized, power supply to the exciting coil 11 is interrupted abruptly by a switching means in the vicinity of a peak in the AC waveform. A timing control means 40 controls the interval for supplying power to the exciting means and sustains power supply to the exciting means at least over several cycles of the AC signal. Since eddy current is not generated under remanent state, even a pinhole can be detected with high accuracy when the inspection is carried out under remanent state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetizing device for inspecting a steel material for defects, and can be used, for example, when magnetically detecting a thick plate.

[0002]

2. Description of the Related Art When inspecting for flaws on the surface or surface layer of a steel plate such as a thick plate, a magnetic inspection device is generally used. In this type of inspection apparatus, the presence or absence of a flaw is detected by monitoring the leakage magnetic flux emitted from the surface of the steel sheet while the steel sheet is magnetized. That is, in a steel sheet with no flaws, since the magnetic flux passes inside the steel sheet with a relatively high magnetic permeability, almost no magnetic flux leaks to the outside of the steel sheet, but in the case of a steel sheet with flaws, the path of the magnetic flux is The magnetic flux leaks to the outside of the steel sheet because it changes so as to avoid flaws. Therefore, the presence or absence of a flaw can be identified by disposing a detector such as a hall element at a position close to the surface of the steel sheet and detecting the magnetic flux leaking from the surface layer of the steel sheet.

In order to identify the presence or absence of a flaw on the steel sheet by detecting the leakage magnetic flux as described above, generally an inspection is carried out while an alternating current is passed through the exciting coil to excite the steel sheet with the alternating current. Moreover, as the excitation frequency, 1 KHz or more is used. The reason is to downsize the magnetizer and to perform a quick inspection. In particular, when a thick steel material is to be inspected, if a direct current is applied to the magnetizer to magnetize it,
The magnetized state required for inspection cannot be obtained unless a large and powerful magnetizer is used. On the other hand, if an AC current of about 1 KHz is applied to the magnetizer to magnetize it, even a relatively small magnetizer can be used for inspection. The magnetization state can be obtained.

It is considered that this is because the penetration depth of the exciting magnetic field into the steel sheet changes according to the exciting frequency. The leakage magnetic flux detected by the inspection device is generated by the magnetic flux in the vicinity of the surface layer of the steel sheet and is hardly affected by the magnetic flux passing through the deep layer of the steel sheet. On the other hand, the penetration depth of the excitation magnetic field tends to become shallower as the frequency increases, so when excited with a high frequency current, the effect of applied energy should be concentrated only near the surface of the steel sheet necessary for inspection. And the efficiency is improved.

Further, in this type of inspecting device, every time the inspection object position on the steel plate is changed, it is necessary to move the magnetizer to that position. Therefore, the size of the moving device for realizing this is also the size of the magnetizer. It is decided according to the size. Therefore, miniaturization of the magnetizer is a very important issue.

[0006]

However, in an apparatus for inspecting while exciting a steel sheet with an alternating current, a flaw such as a crack can be detected, but a flaw such as a pinhole can be extremely detected. There is a problem that it is difficult.

There are two possible causes for the difficulty in detecting flaws such as pinholes. One is that the magnetic flux wraps around the pinhole flaws and the leakage flux is less likely to occur, and the other is that the vertical component of the leakage flux from the defect is suppressed by the eddy current generated by the wraparound of the magnetic flux. Is Rukoto.

Although direct current magnetization can eliminate the effect of eddy currents, it is impractical because the direct current magnetizing device must be large as described above.

Therefore, it is an object of the present invention to enhance the ability to detect pinhole flaws and to enable inspection of thick steel plates with a relatively small magnetizer.

[0010]

In order to solve the above-mentioned problems, the magnetizing device for inspecting a steel material of the present invention has a magnetizing means (10) for generating a magnetic flux according to the electric power supplied thereto; AC signal output means (20) for outputting a constant AC signal; switching means for interrupting power supply to the magnetizing means in the vicinity of the peak of the AC signal waveform output by the AC signal output means, A waveform control means (30) for generating AC power to be supplied to the magnetizing means based on a signal; and a period for supplying power to the magnetizing means, and at least during a plurality of cycles of the AC signal waveform. Timing control means (40) for maintaining power supply to the means.

According to a second aspect of the present invention, the AC signal output means includes an oscillator for generating an AC signal having a stable frequency and amplitude, and the waveform control means is the AC signal or the AC signal controlled by the switching means. Power amplification means (50) for amplifying the power of

In the third aspect, a sine wave is used as the waveform of the AC signal output by the AC signal output means.

The symbols shown in parentheses are the reference numerals of corresponding elements in the embodiments described later, but each constituent element of the present invention is a concrete element in the embodiments. It is not limited to only.

[0014]

In the present invention, the AC power supplied to the magnetizing means (10) is generated by the waveform control means (30) based on the AC signal output by the AC signal output means (20). And, the switching means of the waveform control means,
The power supply to the magnetizing means is shut off near the peak of the AC signal waveform. In addition, timing control means (4
0) controls the period for supplying power to the magnetizing means, and maintains the power supply to the magnetizing means for at least a plurality of cycles of the AC signal waveform.

Therefore, when energization to the magnetizing means is started in a state where the magnetizing means (10) is brought close to the steel material to be inspected, the steel material to be inspected is brought into an alternating current magnetized state due to the magnetic flux generated from the magnetizing means by the alternating current power, and thereafter. Excitation is cut off near the peak of the AC signal waveform.

The relationship between the magnetic field H and the magnetic flux density B of the steel material is non-linear, and in the AC magnetized state, the change is repeated according to a curve called a hysteresis curve as shown in FIG. 6, for example. That is, even if the magnetic field H applied to the steel material is set to zero, the magnetic flux density B does not become zero, and the residual magnetization state is obtained. Therefore, when AC power is supplied to the magnetizing means to bring the steel material into an AC magnetized state and then the power supply is stopped, generally, residual magnetism remains in the steel material. By using this residual magnetism, it is possible to inspect whether or not there is a flaw in the surface layer portion of the steel material, that is, whether or not there is a leakage magnetic flux from the steel material.

However, when the voltage or the current is gradually attenuated when the power supply is stopped, the demagnetization effect works, and the residual magnetism becomes very small. Moreover, since the voltage and current of the AC power constantly change, the magnitude of the residual magnetism changes significantly depending on the difference in the timing of cutting off the power supply. Further, in a ferromagnetic material such as steel, at least about 10 times of magnetization reversal is required until the hysteresis loop becomes stable, and the magnitude of the residual magnetism is not stable in DC excitation. Further, as described above, in the case of direct current excitation, it is inevitable that the size of the exciter becomes large.

In the present invention, since the switching means of the waveform control means shuts off the power supply to the magnetizing means in the vicinity of the peak position of the AC waveform having a stable amplitude, the power supply to the magnetizing means is shut off. At that time, the voltage and current are constant, and if the type of steel material is the same, the magnitude of residual magnetism is also constant. Further, since the power supply to the magnetizing means is maintained for a plurality of cycles of the AC signal waveform by the function of the timing control means, the power supply to the magnetizing means is not performed after the hysteresis loop of the steel material is stabilized. As a result, the residual magnetism of the steel material becomes more stable. Moreover,
Since the alternating current excitation device is used to excite the steel material, a sufficiently large magnetization state can be obtained even when a small excitation device is used. In the remanent magnetization state, eddy current does not occur in the steel material. Therefore, if inspection is performed in that state, high detection capability can be obtained even for pinhole flaws.

Further, a more stable AC excitation is provided by providing an oscillator for generating an AC signal having a stable frequency and amplitude, amplifying the power of the signal output by the oscillator, and generating the power applied to the exciting means. A state can be obtained and the level of remanent magnetization can be stabilized. Furthermore, by using a sine wave as the waveform of the AC signal, the hysteresis loop can be stabilized and the level of residual magnetization can be stabilized.

[0020]

FIG. 1 shows the configuration of an electric circuit of a magnetizing device according to the embodiment, and FIG. 2 shows a usage pattern of the magnetizing device. As shown in FIG. 2, the magnetizing device includes a magnetizer 10 including a core 12 and an electric coil 11 wound around the core 12, and an exciting power supply device 100 that supplies electric power to the magnetizer 10. When actually inspecting for flaws on the surface layer of the steel sheet, first, referring to FIG.
As shown in FIG.
It is mounted on the magnet and the alternating current power is supplied from the excitation power supply device 100 to the magnetizer 10 to magnetize the inspection region 1a. The power supply from the excitation power supply device 100 to the magnetizer 10 is temporary, and in this example, the power is supplied for about 0.2 seconds. In this embodiment, magnetic flaw detection is performed on the steel sheet 1 in the remanent magnetization state. Therefore, after the power supply to the magnetizer 10 is stopped, the magnetizer 10 is manually or by a predetermined transfer device the inspection target area 1a. To another location. Then, a detector (not shown) (for example, a hall element, a magnetoresistive element, etc.) is brought close to the inspection target region 1a, and the presence or absence of leakage magnetic flux (magnetic flux in the direction perpendicular to the surface of the steel sheet) from the surface layer of the steel sheet is inspected. It In the case of a steel sheet having no flaw, the leakage magnetic flux is hardly detected, but since the leakage magnetic flux is detected in the vicinity of the portion where the flaw exists, the presence or absence of the flaw can be identified. Further, in the case of inspecting a very small flaw such as a pinhole flaw, a signal obtained by magnetizing and inspecting a reference steel plate having no flaw and a signal obtained by magnetizing and inspecting the inspection target region 1a By comparing with, it is possible to detect the presence or absence of a defect with high sensitivity.

With reference to FIG. 1, an electric circuit of the magnetizing device, that is, an exciting power supply device 100 will be described. This electric circuit includes a sine wave oscillator 20, a waveform control circuit 30, a timing control circuit 40, and a power amplifier 50. The sine wave oscillator 20 outputs a sine wave signal SG1 (see FIG. 3) having a constant frequency (50 Hz in this example) and a constant amplitude. The sine wave signal SG1 is applied to the power amplifier 50 via the analog switch 31. The power amplifier 50 is
The power of the sine wave signal SG1 is amplified and AC power is supplied to the electric coil 11.

The electric coil 11 is controlled by controlling the signal SG7 applied to the control terminal of the analog switch 31.
It is possible to turn on / off the AC power supplied to the. That is, when the signal SG7 is at the high level H, the analog switch 31 is turned on and the sine wave signal SG1 is input to the power amplifier 50, but when the signal SG7 is at the low level L, the analog switch 32 is turned on. The input of the power amplifier 50 is grounded.

The signal SG7 for controlling the analog switches 31 and 32 is generated by the flip-flop 44. The output signals of the inverter 42 and the AND gate 43 are applied to the set terminal S and the reset terminal R of the flip-flop 44, respectively. The output signal of the inverter 42, the output signal of the monostable multivibrator 41, and the output signal of the analog comparator 35 are applied to the three inputs of the AND gate 43, respectively. The signal SG3 from the switch SW is applied to the inputs of the inverter 42 and the monostable multivibrator 41.

When performing the exciting operation, the operator switches the switch SW from open to closed. When the switch SW is closed, the signal SG3 becomes low level L, and the inverter
Output of the flip-flop 4 becomes high level H.
4 is set and the signal SG7 becomes high level H, so that the supply of AC power to the electric coil 11 is started.
The output signal SG4 of the monostable multivibrator 41 is a predetermined time T10 after the input signal SG3 becomes low level L.
(0.2 seconds in this example: 10 cycles of AC waveform)
It goes to the low level L only until the time elapses. Signal SG4
Is low, the flip-flop 44 is not reset.

A predetermined time T has passed since the switch SW was closed.
When the signal SG2 becomes high level H after 10 has passed, the signal SG6 becomes high level H, the flip-flop 44 is reset, and the signal SG7 becomes low level L, so that the AC power to the electric coil 11 is changed. The supply is cut off.

The analog comparator 35 is a sine wave oscillator 20.
Outputs the result of comparing the level of the signal SG1 output from the reference level Vr with the level of the signal SG2. The reference level Vr is generated by dividing the voltage Vp output by the peak detector 34 by a voltage dividing circuit including resistors R1 and R2. The peak detector 34 has a sine wave AC signal SG1.
The peak value Vp of the voltage is held and output. Resistor R1,
The voltage dividing circuit formed by R2 outputs a voltage slightly lower than the peak value voltage output by the peak detector 34 as the reference level Vr. Therefore, in the signal SG2 output from the analog comparator 35, a pulse signal which becomes the high level H appears only in the vicinity of the peak of the waveform of the sine wave AC signal SG1.

Therefore, the AC power is supplied to the electric coil 11 for a predetermined time T after the switch SW is closed.
This is until the sine wave AC signal SG1 further approaches the peak of the waveform after 10 has passed.

In this embodiment, the sinusoidal AC signal S is always
Since the AC power supply to the electric coil 11 is cut off near the peak of the G1 waveform, the magnitude of the electric power applied to the electric coil 11 is almost constant immediately before the power supply is cut off. And it's big enough. When the power supplied to the electric coil 11 is suddenly cut off, a relatively large residual magnetization is generated in the steel sheet 1 that is AC-magnetized by the magnetizer 10. Since the magnitude of the electric power before shutting off the electric power supplied to the electric coil 11 is constant, the magnitude of the residual magnetization is also constant if the type of the steel sheet 1 is the same. In particular, switch S
Since electric power is reliably supplied to the electric coil 11 from the time when W is closed until the predetermined time T10 elapses, the hysteresis loop (see FIG. 6) of the magnetization target region stabilizes and remains during that time. The magnitude of magnetization is also more stable.

Since the magnitude of remanent magnetization is always constant,
By comparing two steel plates, it is possible to determine the presence or absence of a flaw. That is, a reference steel plate (of the same type as the steel plate to be inspected) that is confirmed to have no flaws in advance is prepared, the reference steel plate is magnetized, and a signal of the leakage magnetic flux detected in the vicinity of the surface, By magnetizing the steel sheet to be inspected and comparing it with the signal of the leakage magnetic flux detected in the vicinity of the surface, even a slight difference in the leakage magnetic flux can be identified as the presence or absence of a flaw.

The signal waveforms of the respective parts of the electric circuit shown in FIG. 1 are shown in FIGS. 3, 4 and 5, which should be referred to.
The signal S45 in FIG. 4 indicates the logical product of the signal S4 and the signal S5.

FIG. 7 shows the electric circuit configuration of the magnetizing device of the modified embodiment, and FIG. 8 shows the signal waveform of each part in FIG. In FIG. 7, the same components as those in FIG. 1 are designated by the same reference numerals. Referring to FIG. 7, in this embodiment, the zero cross detector 36 and the delay circuit 37 are used to generate the signal SG2B applied to the AND gate 43. Signal SG2A output by the zero-cross detector 36
Is a pulse signal that becomes a high level H only near the zero cross point of the waveform of the sine wave signal SG1, and the signal SG2B output by the delay circuit 37 is the signal SG2A output by the zero cross detector 36 and the sine wave signal SG1. Is a signal delayed by a time Td corresponding to 90 degrees of the phase (see FIG. 8).
Therefore, the signal SG2B becomes the high level H only in the vicinity of the peak point of the waveform of the sine wave signal SG1, like the signal SG2 in FIG.

In the electric circuit of FIG. 7, the counter 45 is used to generate the signal SG4B similar to the signal SG4 of FIG. The counter 45 counts the number of pulses of the signal SG2A output by the zero-cross detector 36, and when the counted number of pulses reaches a predetermined value (20 in this example), the signal SG4B becomes high level H. Also, the counter 45
When the signal SG3 is at the high level H (when SW is open), it is reset, and when the signal SG4B becomes the high level H, the counting is stopped.

Therefore, in the electric circuit of FIG. 7 as well, after the switch SW is closed, a predetermined time (equivalent to 10 cycles of the AC waveform) elapses until the peak of the AC waveform is reached. Power is supplied to 11.

According to the embodiment described above, when the energizing of the magnetizing means is started in the state where the magnetizing means (10) is brought close to the steel material to be inspected, the steel material to be inspected is AC by the magnetic flux generated from the magnetizing means by the AC power. The magnetized state is reached, and thereafter, the excitation is cut off near the peak of the AC signal waveform.

The relationship between the magnetic field H and the magnetic flux density B of the steel material is non-linear, and in the AC magnetization state, the change is repeated according to a curve called a hysteresis curve as shown in FIG. 6, for example. That is, even if the magnetic field H applied to the steel material is set to zero, the magnetic flux density B does not become zero, and the residual magnetization state is obtained. Therefore, when AC power is supplied to the magnetizing means to bring the steel material into an AC magnetized state and then the power supply is stopped, generally, residual magnetism remains in the steel material. By using this residual magnetism, it is possible to inspect whether or not there is a flaw in the surface layer portion of the steel material, that is, whether or not there is a leakage magnetic flux from the steel material.

However, when the voltage or current is gently attenuated when the power supply is stopped, the demagnetizing effect is exerted, and the residual magnetism becomes extremely small. Moreover, since the voltage and current of the AC power constantly change, the magnitude of the residual magnetism changes significantly depending on the difference in the timing of cutting off the power supply. Further, in a ferromagnetic material such as steel, at least about 10 times of magnetization reversal is required until the hysteresis loop becomes stable, and the magnitude of the residual magnetism is not stable in DC excitation. Further, in the case of DC excitation, it is inevitable that the exciter becomes large.

In the above embodiment, the switching means (31, 32) of the waveform control means shuts off the power supply to the magnetizing means in the vicinity of the peak position of the AC waveform having a stable amplitude. The voltage and current at the time of cutting off the power supply become constant, and the magnitude of the residual magnetism becomes constant if the type of steel material is the same. Further, since the power supply to the magnetizing means is maintained for a plurality of cycles of the AC signal waveform by the function of the timing control means, the power supply to the magnetizing means is not performed after the hysteresis loop of the steel material is stabilized. As a result, the residual magnetism of the steel material becomes more stable. Moreover, since the steel material is excited using the AC exciter, a sufficiently large magnetization state can be obtained even when a small exciter is used. In the remanent magnetization state, eddy current does not occur in the steel material, so if you inspect in that state,
High detection capability can be obtained even for pinhole flaws.

Since an oscillator for generating an AC signal having a stable frequency and amplitude is provided and the power of the signal output by the oscillator is amplified to generate the power to be applied to the exciting means,
A more stable AC excitation state can be obtained, and the level of residual magnetization is stabilized. Further, since the sine wave is used as the waveform of the AC signal, the hysteresis loop is stabilized and the level of residual magnetization is stabilized.

[Brief description of drawings]

FIG. 1 is a block diagram showing an electric circuit configuration of a magnetizing device according to an embodiment.

FIG. 2 is a vertical cross-sectional view showing a magnetizing device in use.

3 is a time chart showing a signal waveform of each part of the circuit of FIG.

4 is a time chart showing a signal waveform of each part of the circuit of FIG.

5 is a time chart showing a signal waveform of each part of the circuit of FIG.

FIG. 6 is a graph showing BH characteristics of a steel sheet to be inspected.

FIG. 7 is a block diagram showing a configuration of an electric circuit of a modified example.

8 is a time chart showing a signal waveform of each part of the circuit of FIG.

[Explanation of symbols]

1: Steel plate 1a: Area to be inspected 10: Magnetizer 11: Electric coil 12: Core 20: Sine wave oscillator 30: Waveform control circuit 31, 32: Analog switch 33, 42: Inverter 34: Peak detector 35 : Analog comparator 36: Zero cross detector 37: Delay circuit 40: Timing control circuit 41: Monostable multivibrator 43: And gate 44: Flip-flop 45: Counter 50: Power amplifier 100: Excitation power supply device SW: Switch

Claims (3)

[Claims] 1. A magnetizing means for generating a magnetic flux according to electric power supplied thereto; an alternating current signal output means for outputting an alternating current signal having a substantially constant frequency and amplitude; a peak of an alternating current signal waveform output by the alternating current signal output means. -Including switching means for shutting off power supply to the magnetizing means in the vicinity of
Waveform control means for generating AC power to be supplied to the magnetizing means based on the AC signal; and a period for supplying power to the magnetizing means, and magnetizing means for at least a plurality of cycles of the AC signal waveform. A magnetizing device for inspecting a steel material for defects, comprising a timing control means for maintaining power supply to the steel. 2. The AC signal output means includes an oscillator that generates an AC signal having a stable frequency and amplitude, and the waveform control means amplifies the power of the AC signal or the AC signal controlled by the switching means. The magnetizing device for inspecting a steel material according to claim 1, further comprising a power amplifying means for controlling the magnetism. 3. The magnetizing device for steel material flaw inspection according to claim 1, wherein the AC signal output by the AC signal output means is a sine wave.