JPH0113533B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electromagnetic ultrasonic receiving transducer useful for flaw detection of hot materials in, for example, continuous casting processes.

As an electromagnetic ultrasonic transducer that can excite and detect ultrasonic waves in a material to be inspected in a non-contact manner, there are, for example, those having the following configuration. That is, as shown in FIG. 1, a plurality of permanent magnet plates 11, _{11 1} , 11 ₂ , 11 ₃ . . . are magnetized in the thickness direction.
..., high magnetic permeability magnetic materials 12, _{12 1} , 12 ₂ , 1
It has a magnetic field generation mechanism which is arranged in the thickness direction so that the polarity is alternately reversed between 2 ₃ ......, and the permanent magnet plate 11 is arranged near the end of this magnetic field generation mechanism.
There is a transducer for electromagnetic ultrasonic flaw detection that has a periodic magnet structure and is constructed by arranging wave-shaped coils 13 that meander along an array.

In such a transducer, now,
When a current is passed through the wave-shaped coil 13, the inspected material 14
Eddy currents I with the polarities shown are generated in various parts directly below the permanent magnet plate 11 on the surface. This eddy current I and the permanent magnet plate 1
Due to the interaction with the horizontal magnetic field H directly below 1,
A Lorentz force F of the illustrated polarity acts on the surface of the material 14 to be inspected. Therefore, by passing an alternating current through the wave-shaped coil 13, longitudinal ultrasonic waves whose vibration direction and propagation direction are both perpendicular to each other are excited in the inspected material 14.

In this way, ultrasonic waves are excited in the inspected material 14, and the reflected waves of the ultrasonic waves from the defective parts are detected by, for example, the corrugated coil 13 by following the conversion process reverse to the above-mentioned ultrasonic excitation. This is how flaw detection is performed. According to such a transducer, a strong magnetic field can be obtained due to the configuration of its magnetic field generation mechanism, and the interaction between this field and the eddy current induced by the corrugated coil allows for a uniform and wide flaw detection surface. can be obtained.

By the way, when performing flaw detection on a hot material in a continuous casting process or the like using such an electromagnetic ultrasonic transducer, several considerations are required, unlike when testing in a cold process. It is especially important to make the gap distance between the transducer and the material under test sufficiently large.
For example, it must be about 5 mm. The reason for this is that in the case of hot materials, the temperature of the material is extremely high, the surface is extremely uneven, and the transducer is used as a cooling structure so that a cooling medium is used in the gap between the end face of the transducer and the material to be inspected. It is necessary to flush the water, etc.

Therefore, from this perspective, compared to other transducers, the electromagnetic ultrasonic flaw detection transducer using the above-mentioned periodic structure magnet has a shorter air gap distance with the inspected material. Although this method has the advantage of making it possible to perform flaw detection with a relatively large value, it is still not sufficient.

Therefore, conventionally, a transducer has been developed that ultrasonically excites a material to be inspected while maintaining a sufficient gap distance between the transducer and the material to be inspected. As shown in FIG. 2, this transducer has an insulating layer 22 on the outside of a high-frequency magnetic core 21 formed in a U-shape, and a shield plate made of a copper plate to reduce leakage of magnetic flux in the middle of the high-frequency magnetic core 21. 23 and an insulating layer 24 in this order, and a transmitting coil 25 is further wound around the outermost insulating layer 24.

This transducer sends a high-frequency current through the transmitting coil 25 wound around the U-shaped high-frequency magnetic core 21, thereby inducing high-frequency magnetic flux and high-frequency eddy current on the surface of the material to be inspected, and the interaction between these two. This method excites ultrasonic waves to the material to be inspected. At this time, the excited ultrasonic waves travel within the material to be inspected, and if there is a defect, it is reflected there and returns. The returned ultrasonic waves are detected by a completely separate detection coil to detect flaws in the inspected material. Therefore, by using the high-frequency magnetic core 21, the transducer described above can guide high-frequency magnetic flux with a large magnetic flux density to the surface of the material to be inspected even if it is installed at a position sufficiently far from the surface of the material to be inspected. Since a large high-frequency current can be passed directly through the coil 25, ultrasonic waves can be excited in the inspected material without bias without requiring a static magnetic field for bias.

However, the above-mentioned non-bias transducer has the disadvantage that it cannot receive ultrasonic waves because it does not have a bias static magnetic field.

The present invention has been made in view of the above circumstances, and it is possible to receive ultrasonic waves by increasing the air gap distance with the material to be inspected, similar to a non-bias transducer. The purpose of the present invention is to provide a transducer for receiving electromagnetic ultrasonic waves that is effective for use in non-destructive testing of materials.

Embodiments of the present invention will be described below with reference to FIGS. 3 and 4.
This will be explained with reference to the figures.

FIG. 3 shows a first embodiment of the present invention, in which the entire magnetic core is covered with an insulating layer 33 except for the end faces 32 of both legs of a high-frequency magnetic core 31 formed in a U-shape, that is, the part facing the material to be inspected. The entire outside is covered with a first shield plate 35 made of, for example, a 0.2 mm thick copper plate. Further, an insulating layer 38 is applied again to the outside of the first shield plate 35 only near the ends of both legs, and a second shield plate 34 made of a copper plate having a thickness of 0.5 mm, for example, is attached to the outside of the insulating layer 38. Furthermore, these shield plates 35 and 34 are partially cut and insulated so as not to form a short circuit surrounding the high frequency magnetic core 31. (This point also applies to the shield plates in the following embodiments.) Then, on the first shield plate 35 of both legs of the magnetic core,
Bias excitation coils 36a, 36b are wound around, and receiving coils 37a, 37b are also wound around the second shield plate 34 of each leg.

The excitation coils 36a, 36b create a bias static magnetic field, and both coils 36a, 3
The connection 6b is such that the magnetic flux generated by the coil current is U
It is connected so as to circulate the character-shaped high-frequency magnetic core 31 . The number of turns of each of the excitation coils 36a and 36b is such that the excitation current flowing therein can magnetize the magnetic core 31 until it is almost saturated, for example, 50 turns each, and if necessary, winding may be done with two or more layers. It is something to do.

Similarly to the excitation coils, the receiving coils 37a and 37b are also connected so that the magnetic flux generated by the coil current circulates within the magnetic core. In this case, the receiving coils 37a and 37b each have, for example, 23 turns, and are wound in a single layer.

The shield plates 35 and 34 efficiently transmit the high frequency magnetic flux generated by the incoming ultrasonic waves to the receiving coil 36.
a, 36b.

The second shield plate 34 is also provided between both magnetic poles of the magnetic core 31, but the shape of the second shield plate 34 is simply that it is wound around both legs of the high frequency magnetic core 31 so as not to form a short circuit loop. Furthermore, even if the shield plate, especially the second shield plate 34, is omitted, the operating principle of the transducer remains the same and does not go beyond the scope of the present invention.

Next, FIG. 4 shows a second embodiment of the present invention. For example, this applies to the entire outside of the insulating layer 33.
A shield plate 35 made of a copper plate with a thickness of 0.2 mm is provided to prevent short-circuit loops from being created. Bias excitation coils 36a and 36b are wound on the outside of the shield plate 35 near the lower end of the magnetic core legs, while a receiving coil 37 is wound on the body side of the high-frequency magnetic core 31. In this reception transducer, the shield plate 35 allows the high frequency waves generated by the ultrasonic waves arriving at the material to be inspected to be efficiently circulated into the high frequency magnetic core 31.

Next, an experimental block diagram for obtaining the characteristics of the receiving transducer as described above will be explained with reference to FIG. In this case, the material to be inspected 61 is an aluminum block, the transmitting transducer 62 is a non-biased one as shown in FIG. 2, and the receiving transducer 63 is as shown in FIGS. 3 and 4. The high-frequency magnetic cores of these transducers 62 and 63 were wound with 50 μm thick silicon steel plates. In the figure, 64 is a trigger pulse generator;
Reference numeral 5 denotes a DC power supply, and reference numeral 66 denotes an instantaneous large current generation circuit for bias having the configuration shown in FIG. By turning on the SCR with a trigger pulse, a resonance discharge is caused through the chiyoke coil L, and a large current is supplied to the excitation coil 36. In the chiyoke coil L shown in FIG. 6, the excitation coil is short-circuited,
This is to prevent the voltage of the receiving coil from dropping. The transmission transducer 62 is driven by delaying the trigger pulse in a delay circuit 67 so as to generate an ultrasonic wave when the discharge current to the excitation coil 36 reaches almost the maximum, and then driving the transmission impulse large current generation circuit 68. In addition to 69 is a high voltage DC power supply. On the other hand, the received output of the receiving coils 37a and 37b by the receiving transducer 63 is transmitted to the oscilloscope 7 via a high-pass filter 70, a preamplifier 71, a low-pass filter 72, and an amplifier 73.
Observed at 4. Note that the high-pass filter 70 uses a CR filter with a cutoff of 120 KHz, for example, and the preamplifier 71 uses the low-pass filter 7 at the rear stage.
The voltage gain is 1, the input impedance is about 10KΩ, and the output impedance is 50Ω. The low-pass filter 72 uses, for example, an image parameter filter with a cutoff of 706 kHz. The amplifier 73 used has, for example, a gain of 32 dB, a gain of 80 times when the output is open, and an input impedance of 50 Ω.

Characteristic diagrams obtained based on the experimental block diagrams as described above are shown in FIGS. 7 and 8.
First, FIG. 7 is a characteristic diagram showing the relationship between exciting current and received voltage. However, in this experimental example, the air gap distance for both transmitting and receiving transducers 62 and 63 is set to almost zero, and the voltage of the high voltage DC power supply for transmitting is set to zero.
It was set to 16KVdc. Also, the chiyoke coil L in Fig. 6
An inductor with an inductance of 81.4 μH was used, and a high-pass filter 70 with a cutoff frequency of 120 to 170 kHz was used. Examining this characteristic diagram, it can be seen that the structure shown in FIG. 4 has a higher received voltage than the structure shown in FIG. 3 even if the excitation current is smaller. This means that because the position of the excitation coil was lowered to the end of the magnetic core, a large bias magnetic field was applied to the material to be inspected.

Next, FIG. 8 is a characteristic diagram showing the relationship between wave reception sensitivity and gap distance for the structure of FIG. 4. However, in this experimental example, the air gap distance of the transmitting transducer 62 is 50 μm, and the voltage of the high voltage DC power supply for transmitting is
The voltage was 16KVdc, the excitation current was 200A, and the amplifier 73 had a gain of 40dB. For comparison,
Similar experiments were conducted on the transducer using the periodic structure magnet shown in Fig.
Also shown in the figure.

Examining this characteristic diagram, it can be seen that the receiving electromagnetic ultrasonic transducer of the present invention has a smaller rate of decrease in sensitivity even with a large gap distance than that using a conventional periodic structure magnet. It is possible to arrange it with a sufficient gap distance from the test material.

As described in detail above, according to the present invention, a high-frequency magnetic core of the same type as that of a non-bias transducer is used, and the same high-frequency magnetic core is equipped with an excitation coil and a receiving coil, so that it can be used as a receiving transducer. As with the transmitting transducer, it can be placed at a sufficient gap distance from the material to be inspected. In addition, by applying a shield plate coating, the bias magnetic field generated by the excitation coil current increases, increasing reception efficiency, and it is also possible to wind the receiving coil at a position sufficiently far from the surface of the object to be examined. It is possible to provide an electromagnetic ultrasonic receiving transducer that is very advantageous for non-destructive testing.

[Brief explanation of drawings]

Fig. 1 is a side view showing an example of a transducer using a conventional periodic structure magnet, Fig. 2 is a front sectional view of a non-bias transmitting transducer using a conventional high frequency magnetic core, and Figs. FIG. 4 is a front sectional view showing the first and second embodiments of the electromagnetic ultrasonic receiving transducer according to the present invention, FIG. 5 is an experimental block diaphragm diagram of the same embodiment, and FIG. The configuration diagram of the instantaneous large current generating circuit for bias shown in FIG. 5, and FIGS. 7 and 8 are characteristic diagrams obtained as a result of experiments, respectively. 31... High frequency magnetic core, 33, 38... Insulating layer,
34, 35... Shield plate, 36a, 36b...
Excitation coil, 37, 37a, 37b... receiving coil.

Claims (1)

[Claims] 1 In a device that detects defects or abnormalities in a test object by receiving ultrasonic waves propagating through the test object by ultrasonic excitation, a high-frequency magnetic core formed in a U-shape and both legs of this high-frequency magnetic core are used. A shield plate is attached to the entire part except for the end face, a bias magnetic field excitation coil is wound on the upper side of the shield plate, and a bias magnetic field excitation coil is wound on the upper side of the shield plate and the magnetic field is propagated through the object to be inspected. 1. A transducer for electromagnetic ultrasonic reception, comprising: a receiving coil for receiving ultrasonic waves.