JPH0353155A - Detector for internal defect or damage for steel material - Google Patents

Abstract

PURPOSE:To detect an internal defect or the like with a high sensitivity without destruction by constituting the electro-magnet where AC currents having the same phase are supplied to exciting coils wound around both side exciting cores of a yoke core to generate magnetic fields having opposite polarities and moving front ends of these cores while closely bringing them into contact with the surface of a steel plate or keeping them a certain minute gap apart from this surface. CONSTITUTION:AC currents having the same phase are supplied to exciting coils 9 and 10 of a sensor part 1 to generate magnetic fields having opposite polarities and the same magnetic flux density, and in this state, lower ends of exciting cores 5 and 6 of the sensor part 1 are moved while being brought into contact with or being kept the certain minute gap apart from the surface of a body 14 to be examined which is made of a ferromagnetic body. Then, magnetic flux density distributions of magnetic fields which are generated by coils 9 and 10 and penetrate the body 14 are changed if an internal defect due to porosity or the like in the casting stage of a steel material as the body 14 or a thin part (a) or the like due to corrosion on the front or rear face of a steel plate or a steel pipe exists between either of cores 5 and 6 and a detecting core 7. Consequently, a difference in magnetic resistance is generated and outputted to a detecting coil 11 as the change of the induced voltage ampli tude.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention is directed to the prevention of internal defects caused by cavities during the casting process of steel materials such as machine parts, and corrosion holes or thinning areas caused by corrosion on the front or back side of steel plates or steel pipes. This invention relates to an internal defect or damage detection device for steel materials that non-destructively detects defects or damages in steel materials.

[Conventional technology]

Conventionally, various devices have been provided for nondestructively detecting minute cracks and defects occurring in conductive objects to be inspected, but most of them utilize eddy currents induced in the objects to be inspected. For example, as disclosed in Japanese Unexamined Patent Publication No. 60-66156, a coil wound in a torus shape around an annular core is inserted with its center line parallel to the axial direction of the tube, and the coil generates energy. A device that uses a detection coil to detect a signal due to a lagoon current induced in the circumferential direction of a tube by an axial magnetic field, or a device that uses a ferrite core with an excitation coil as disclosed in Japanese Utility Model Application Publication No. 108148/1983. A device is provided in which a detection coil is wound, the ferrite core is moved approximately perpendicularly to or in contact with an object to be inspected, and the detection coil detects a signal due to i-current induced in the object to be inspected by an excitation coil. However, although the accuracy is relatively high,
1kHz to increase the detection signal level due to eddy current.
It is necessary to supply the excitation coil with an alternating current with a frequency higher than that or a rectangular wave current with steep rises and falls, and as a result, the magnetic field from the excitation coil does not penetrate sufficiently into the object to be inspected, especially for ferromagnetic materials. Furthermore, since the penetration depth becomes shallower, it is theoretically possible to inspect only defects in the area or shallow part of the surface layer of the object to be inspected, in other words, only to inspect objects with a thickness of several n or less. Ta.

[Problem to be solved by the invention]

In view of the above-mentioned situation, the present invention aims to solve internal defects caused by cavities during the casting process that exist deep inside steel materials made of ferromagnetic material up to a thickness of about 10 m, and the surface or surface of steel plates or steel pipes. It is an object of the present invention to provide an internal defect or damage detection device for a steel material that can non-destructively and sensitively detect pits or internal loss due to corrosion on the back side.

Means for Solving Problem C] In order to solve the above-mentioned problem, the present invention provides a method in which an excitation coil is arranged in both excitation cores of a yoke-shaped core consisting of excitation cores on both sides and a detection core in the middle. In addition, a detection coil is wound around the detection core, and alternating current of the same phase is supplied to both excitation coils so that they have opposite polarities, and one end of both excitation cores is made of a ferromagnetic material. The detection coil moves the steel material closely or at a constant minute interval, and the detection coil detects changes in magnetic resistance due to defects, pits, and internal reduction in the steel material as induced voltage amplitude changes, and detects the voltage amplitude signal. In the signal processing circuit, when a defect etc. is located between the detection core and one excitation core and between the other excitation core, a different signal is generated, and the processed signal is output to the display to display the steel material. An internal defect or damage detection device was constructed.

Then, the characteristics of the excitation core on both sides and the excitation coil are made to match, and magnetic fields with opposite polarities and equal magnetic flux densities are generated by alternating currents of the same phase supplied to the excitation coils on both sides, or The supplied alternating currents of the same phase and different magnitudes generate magnetic fields of opposite polarity and different magnetic flux densities.

Furthermore, the frequency of the alternating current supplied to the excitation coil is
The frequency is set to a low frequency of several tens of Hz or less so that the magnetic field penetrates deep into the steel material.

Furthermore, as the yoke-type core, a yoke-type core is used in which a core for excitation on both sides and a core for detection are arranged in parallel, and their lower ends are set to be on the same plane, or a core for excitation on both sides is excited. We used a yoke-type core whose height can be adjusted vertically relative to the core.

[Effect]

The steel internal defect detection device of the present invention having the above-mentioned contents supplies an alternating current of the same phase to the excitation coils wound around the excitation cores on both sides of the yoke type core, and the excitation coils have opposite polarity. Be wary of electromagnets that generate magnetic fields,
When the tip of the excitation core is moved closely to the surface of the steel plate or at a certain minute distance, if there are defects inside the steel material, pits, or thinner parts on the front or back side, the excitation coil Is it generated inside the steel material? A change in the magnetic flux density of the magnetic field, that is, a change in magnetic resistance occurs, and this change is detected as a change in induced voltage amplitude by a detection coil wound around the detection core to confirm the existence of defects, etc. A signal processing circuit converts the output signal of the detection coil into a different signal depending on whether a defect is located between the detection core and one excitation core or between the other excitation core, and displays the processed signal on the display. The output is used to detect which side of the excitation core the defect, etc. is located between the detection core and the excitation core. In addition, if the excitation cores and excitation coils on both sides generate magnetic fields with equal magnetic flux densities and opposite polarities and are balanced at the midpoint, there will be no output to the detection coil in the middle if there is no defect. If this is not possible and there is a defect between both excitation cores, the magnetic resistance between the excitation core and detection core will change, causing the balance at the midpoint to collapse and some of the lines of magnetic force to be distorted. Since it passes through the detection coil, an induced voltage is generated in the detection coil, but it is not possible to determine on which side of the detection core the defect is located based only on the induced voltage of the detection coil, so the signal In order to distinguish between defects, the signal processing circuit performs phase detection, and when a defect is located on a different side via the detection core, it is converted to a signal voltage with a different sign and output to the display. be.

On the other hand, if the excitation cores and excitation coils on both sides generate magnetic fields with opposite polarities and different magnetic flux densities, the detection coil will always output a constant reference voltage amplitude even if there is no defect, etc. If a defect, etc. exists, an output voltage larger or smaller than the reference voltage amplitude can be obtained depending on which side the defect, etc. is located via the detection core, so the signal is sent to the signal processing circuit. The signal is then amplified, rectified, and output to the display.

Also, the frequency of the alternating current supplied to the excitation coil is set to several + t.
The magnetic field is set to a low frequency of 10 oz or less, so that the magnetic field penetrates deep into the steel material made of ferromagnetic material.
It is possible to detect internal defects of steel materials, corrosion holes on the front or back side, and thinned parts of the steel material.

Further, the height of the detection core can be adjusted relative to both excitation cores, so that the detection core can be adjusted along the surface of the steel material, which has a flat or curved surface.

[Example] Next, the present invention will be further explained in detail based on the example shown in the accompanying drawings.

1 to 3 show typical embodiments of the present invention, in which 1
2 indicates a sensor section, 2 an AC power supply, 3 a signal processing circuit, and 4 a display device.

As shown in FIG. 1, the sensor section 1 is a yoke-type core in which excitation cores 5 and 6 are arranged in parallel on both sides, and a detection core 7 is arranged in parallel in the middle, and the upper part of each core is integrally extended. 8, excitation coils 9 and 10 are wound in opposite directions around both excitation cores 5 and 6, and a detection coil 11 is wound around the detection core 7. here,
The characteristics of the electromagnets constituted by the excitation core 5 and the excitation coil 9 and the excitation core 6 and the excitation coil 10 are matched, and magnetic fields of opposite polarity are generated by alternating current supplied to each. In addition, both excitation coils 9.10
A fixed resistor R is provided in one excitation coil 9 so that the current value of the alternating current supplied to the coil can be adjusted. A variable resistor VR is connected in series to each of the excitation coils 10.

In addition, when both excitation coils 9 and 10 are both wound in the same direction, they may be connected so that the directions of current flow are opposite to each other.

Further, the yoke type core 8 is formed by laminating thin iron plates or formed by ferrite, and its shape is detected as the dual excitation core 5.6 as shown in Fig. 1. The upper parts of the excitation cores 7 are integrally connected, and the lower ends of the excitation cores 5 and 6 and the lower end of the detection core 7 are in contact with the surface of a flat object to be inspected, or as shown in FIG. Only both excitation cores 5.6 are integrally connected, and the detection core 7 is provided separately, so that the height of the detection core 7 can be adjusted up and down with respect to both excitation cores 5.6, and the curved surface A device in which the detection core 7 is arranged along the surface of an object to be inspected is also used.

The AC power supply 2 includes an oscillator l2 that generates a low frequency sine wave, and a current amplifier l3 that amplifies the output of the oscillator 12 to a desired current value, and branches the output of the AC power supply 2, one of which is connected to a fixed resistor. It is supplied to the excitation coil 9 via R0, and the other is supplied to the excitation coil 10 via the variable resistor VR.
are supplied to generate magnetic fields with the same phase and opposite polarity.

The frequency of the sine wave generated by the oscillator 12 is
For example, it is set to 10 to 30 Hz.

Then, alternating currents of the same phase are supplied to the excitation coils 9 and 10 of the sensor section 1 to generate magnetic fields with opposite polarities and the same magnetic flux density! Q (hereinafter referred to as an equilibrium state), the lower ends of the excitation cores 5 and 6 of the sensor section 1 are moved in contact with the surface of the object to be inspected 14 made of ferromagnetic material or at a constant minute interval. At this time, both excitation cores 5,
6 and the detection core 7, there are internal defects such as cavities during the casting process of the steel material to be inspected 14, and corrosion holes or thinned areas a (hereinafter referred to as , defect, etc. a) exists, the magnetic flux density distribution of the magnetic field generated in both excitation coils 9 and 10 and penetrating into the inspected object 14 changes, resulting in a difference in magnetic resistance. , is outputted to the detection coil 11 as an induced voltage amplitude change.

Here, the width l between the excitation cores 5 and 6 of the yoke-shaped core 8 is appropriately set within the range of 20 to 500 mm, but if the width is too narrow, the generated magnetic field will be inside the object to be inspected 14. If it does not penetrate deeply and if the width is too wide, the spatial resolution for detecting defects etc. a will be poor, so it is necessary to set the optimum width in consideration of the thickness of the object 14 to be inspected. Normally, when the thickness d of the inspected object 14 is about 3fi, the width l is about 30mm.
A setting of ˜40n gives good results.

Figure 2 shows the state of equilibrium when the sensor unit 1 is moved at a constant speed U in the direction in which the excitation core 5.6 and the detection core 7 are lined up (hereinafter referred to as the X direction). An amplitude voltage V generated in the detection coil 11. is shown as a function of the positions iA, B of both excitation cores 5.6 and the relative position of the defect a.

In this way, when the equilibrium state is set, when the defect etc. a is located between the detection core 7 and the excitation core 5, and between the detection core 7 and the excitation core 6, approximately the same Although it is possible to detect the presence of a defect or the like, it is difficult to specify its position, so the following signal processing circuit 3 converts each into a signal voltage of a different sign.

As shown in FIG. 4, an alternating current (2) is generated by the oscillator l2 of the alternating current power supply 2. A detection voltage V, is outputted from the detection coil l1 in accordance with the period of , and the envelope of the detection voltage V, coincides with the amplitude voltage V0, but with the position of the detection core 7 as the boundary. The phase is reversed between left and right.

The signal processing circuit @3 amplifies the detected voltage V to a predetermined voltage using an AC amplifier 15, and outputs the output from the photocoupler 16.
The alternating current I from the oscillator 12 is input to the field effect phototransistor of the oscillator 12. The field-effect phototransistor becomes conductive only while the light-emitting diode connected to the transistor l7, which is switched on by As shown in FIG. 4, a phase detection voltage v2 is generated across the capacitor C, and the phase detection voltage v2 is generated by the oscillator 12 using an integrating circuit consisting of a resistor R2 and a capacitor C2. is smoothed to generate a signal voltage v3, and the signal voltage v
3 is amplified to a desired voltage by a DC amplifier 18.
Here, the light emitting diode of the photocoupler 16 is forward-energized with a positive voltage and connected to the collector of the transistor 17 whose emitter is grounded, and the base is connected to the oscillator 12 by a resistor R. It is set so that when a positive predetermined current value is input to the base, enough current flows between the collector and the main body to immediately saturate it, as shown in Figure 4. The alternating current of the oscillator 12 is as shown in FIG.

The approximately rectangular wave pulse current I1 flows only when is a positive value. Therefore, in FIG. 4, the detection voltage V.
The positive voltage is on the left side of the photocoupler l, and the negative voltage is on the right side of the photocoupler l.
Note that the time constant RIC+ of the charging/discharging circuit is equal to the alternating current I of the oscillator 12. The time constant R2C2 of the integrating circuit is set to be sufficiently larger than the time constant RICl.

Then, the output obtained by phase detection and processing by the signal processing circuit 3 is input to a recorder 19, an analog meter 20, and a display 4 such as an oscilloscope for display.

Furthermore, when the sensor unit 1 is moved in a direction perpendicular to the X direction, a defect, etc. a passes between the central detection core 7 and the excitation cores 5.6 on both sides. However, in that case, only the positive part or the negative part of the signal voltage v3 is output, and it is possible to determine the position of the defect etc. a. 9. The alternating current I supplied to 10. By setting the frequency to a low frequency of several tens of Hz or less, if the abrasion d of the object to be inspected 14 is within about 10 m, the magnetic field can sufficiently penetrate to the back side and eliminate defects that occur on the back side. Therefore, it becomes possible to detect even a.

Also, by adjusting the variable resistor VR, both excitation coils 9.
When alternating currents of the same phase and different magnitudes are supplied to the terminals 10 (hereinafter referred to as unbalanced state).

), even if there is no defect a, a constant level amplitude voltage is generated as shown in FIG. 5, and the sensor section 1 is
When the waveform is moved in the direction and passes through the defect etc. a, the amplitude voltage V has a waveform having the same maximum and minimum as the waveform of the signal voltage v3. is born. The signal processing circuit 3 in this case has a simpler configuration, namely, an AC amplifier 15 for amplifying the detection voltage V of the detection coil l1, a rectifier circuit composed of a diode 21 and a capacitor c3, and an integrating circuit similar to the above. and a DC amplifier l8. The DC amplifier 18 has a positive terminal of the operational amplifier 22 inputted with a voltage generated in a resistor R3 connected in parallel to the capacitor C2 of the integrating circuit, and a negative terminal supplied with a variable resistor VR, which is energized to a positive voltage. A predetermined voltage is applied through a resistor R4 connected to the slider, and the amplification factor determined by the bottle width resistor R5, the resistor Ra, and the variable resistor V R + is made variable. Here, the voltage waveform at each representative part in FIG.
As shown in the figure.

Said amplitude voltage V that occurs in the case of an unbalanced state. The voltage value becomes maximum and minimum between the detection core 7 and one of the excitation cores 5 and 6, so there is no need to perform phase detection as described above, and the maximum and minimum determines whether the defect, etc. You can determine whether it has passed. Furthermore, even when moving in a direction perpendicular to the X direction, the output voltage of only one of the maximum and minimum portions can be obtained as described above.

Further, in another embodiment of the sensor unit 1 shown in FIG. 8, the detection core 7 is movable up and down relative to the excitation cores 5 and 6 as described above, and the It can be adjusted so that the excitation cores 5 and 6 come into contact with the steel material that is the body 14 at the same time.

Further, another embodiment of the sensor unit 1 shown in FIGS. 9 and 10 uses an elongated yoke-type core 8 having excitation cores 5 and 6 on both sides and a U-shaped cross section. Core 5.
A plurality of detection cores 7, . In this embodiment, six pairs of detection cores 7 and detection coils 11 are provided.

In this case, by setting the movement direction of the seven-sensor section 1 in the X direction as shown in the figure, it becomes possible to simultaneously detect defects, etc. a over a wide width, and the inspection time can be significantly shortened. For example, the same signal processing circuit 3 as described above is connected to each detection coil 11, and the detection coil 1
After processing the detected voltages V, occurring in the channels 1 and 1 independently, they are displayed on the display 4 or on the multi-channel display 4.
It is also possible to display both at the same time. Also,
After each detection voltage v1 of the detection coil II is processed by the signal processing circuit 3, it is binarized by a comparator, and each is input to an OR circuit, and when an output is obtained from which detection coil 11, a sound or It is also practical to emit light and compare the outputs of the detection coils 11 to display the position of the detection coil 11 with the largest output.

〔Effect of the invention〕

The steel internal defect detection apparatus of the present invention as described above has the following effects.

According to claim 1), j? is wound around the excitation core on both sides of the yoke type core. An alternating current of the same phase is supplied to the I-magnetic coils, each excitation coil generates a magnetic field of opposite polarity, and the tip of the excitation core is brought into contact with the surface of the object to be inspected or is spaced at a certain minute distance. By moving the test piece in this condition, if there are internal defects such as cavities during the casting process of the steel material to be inspected, or corrosion holes or internal loss due to corrosion on the surface or back side of the steel plate or steel pipe, it can be detected between both excitation cores. , a change in the magnetic flux density of the magnetic field generated by the excitation coil and penetrating inside the object to be inspected occurs, that is, a change in magnetic resistance, and the change is detected as a change in induced voltage amplitude by a detection coil wound around the detection core. The presence of defects, etc. can be confirmed by using the output fB of the detection coil, and the defect, etc. can be detected between the detection core and one excitation core and between the other excitation core using the signal processing circuit. Since the signal voltage is converted to a signal voltage having a different sign or maximum and minimum when the defect is located in between, and the processed signal is output to the display, it is possible to determine which side the defect is detected via the detection core. It is possible to detect whether it is located between the core and the core, and it is also possible to detect the position of defects, etc.

According to claim 2), the excitation cores and excitation coils on both sides generate magnetic fields with equal magnetic flux densities and opposite polarities and are balanced at the midpoint, so that the excitation cores and excitation coils on both sides generate magnetic fields of opposite polarity and are balanced at the midpoint. By minimizing the output of the intermediate detection coil in the set state, 0 point adjustment can be easily performed, and only the output voltage due to defects etc. can be amplified, increasing detection sensitivity. can be easily done. According to claim 3, when the excitation cores and excitation coils on both sides generate magnetic fields of opposite polarity and different magnetic flux densities, if a defect or the like exists between both excitation cores, the detection Depending on which side of the core the defect, etc. is located on, an output larger or smaller than the reference voltage amplitude when there is no defect, etc. can be obtained, so subsequent signal processing can be easily performed with a simple circuit. It is possible.

According to claim 4), by setting the frequency of the alternating current supplied to the excitation coil to a low frequency of several + Ilz or less, the magnetic field can penetrate deep inside the object to be inspected made of ferromagnetic material, It is possible to detect internal defects such as cavities during the casting process of a steel material to be inspected having a thickness of about 1 On, and corrosion holes or thinned parts due to corrosion on the front or back side of a steel plate or steel pipe.

According to claim 5), by using a yoke-type core in which both-side excitation cores and detection cores are arranged in parallel and their lower ends are set to be on the same plane,
The detection core can be stably moved along the surface of the planar object to be inspected.

According to claim 6), by using a yoke-type core in which the excitation core on both sides and the detection core are arranged in parallel, and the height of the detection core is adjustable in the vertical direction with respect to the excitation core on both sides. Even when the object to be inspected has a flat or curved surface, it is possible to adjust the height of the detection core and move it along the surface of the object to be inspected.

[Brief explanation of drawings]

Figure 1 is a simplified explanatory diagram of the sensor section and the steel plate showing the principle of detecting defects in steel plates according to the present invention, and Figure 2 shows the voltage amplitude change that occurs in the detection coil when alternating current is supplied to the excitation coil in a balanced state. 3 is a simplified circuit diagram of the entire device including the signal processing circuit in an equilibrium state, and FIG. 4 is a graph showing the function of position. Fig. 5 is a time chart showing the signal waveforms of each part shown in Fig. Figure 6 is a simplified circuit diagram showing the signal processing circuit in the same non-equilibrium state, Figure 7 is a time chart diagram showing signal waveforms of each part shown in Figure 6, and Figure 8 is another example of the sensor section. FIG. 9 is an overall perspective view showing still another embodiment of the sensor section, and FIG. 10 is a bottom view. a: Defects, etc., 1: Sensor section, 2: AC power supply, 3: Signal processing circuit, 4: Display unit, 5: Excitation core, 6: Excitation core, 7: Detection core, 8: Yoke type core, 9: Excitation coil, lO: Excitation coil, l: Detection coil, 12: Oscillator, 13: Current amplifier, 14: Test object, l5: AC amplifier, l6: Photocoupler, l7: Transistor, 18:
DC amplifier, 19: recorder, 20: analog meter,
21: Diode, 22: Operational amplifier.

Claims (1)

[Scope of Claims] 1) An excitation coil is wound around both excitation cores of a yoke-type core consisting of excitation cores on both sides and a detection core in the middle, and a detection coil is wound around the detection core. Then, an alternating current of the same phase is supplied to both excitation coils so that the polarities are opposite to each other, and one end of both excitation cores is placed close to the surface of the steel material made of ferromagnetic material or at a certain minute distance. to remove defects or pits in the steel material,
The change in magnetic resistance due to the thinned portion is detected as a change in induced voltage amplitude by the detection coil, and the voltage amplitude signal is sent to a signal processing circuit to detect defects, etc. between the detection core and one excitation core, and between the other excitation core. A device for detecting internal defects or damage in a steel material, characterized in that a signal is generated differently when the core is located between cores, and the processed signal is output to a display. 2) The properties of the excitation core on both sides and the excitation coil are matched, and magnetic fields of opposite polarity and equal magnetic flux density are generated by alternating currents of the same phase supplied to the excitation coils on both sides. The device for detecting internal defects or damage in steel according to item 1. 3) The characteristics of the excitation core on both sides and the excitation coil are matched, and magnetic fields of opposite polarity and different magnetic flux densities are generated by alternating currents of the same phase and different magnitudes supplied to the excitation coils on both sides. An apparatus for detecting internal defects or damage in steel materials according to claim 1. 4) Detection of internal defects or damage in steel materials according to claim 1, 2, or 3, in which the frequency of the alternating current supplied to the excitation coil is set to a low frequency of several tens of Hz or less. Device. 5) As the yoke-type core, a yoke-type core is used in which a core for excitation on both sides and a core for detection are arranged in parallel, and their lower ends are set to be on the same plane. The internal defect or damage detection device for steel materials according to item 1, item 2, or item 3. 6) As the yoke-type core, a yoke-type core is used in which both-side excitation cores and detection cores are arranged in parallel, and the detection core is vertically adjustable with respect to the both-side excitation cores. An apparatus for detecting internal defects or damage in steel materials according to claim 1, 2, or 3.