JPS623900B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a transducer for electromagnetic ultrasonic flaw detection that is useful for flaw detection of steel materials, particularly hot materials in continuous casting processes.

Conventionally, as a transducer for electromagnetic ultrasonic flaw detection, a yoke-shaped electromagnet or a permanent magnet is used to narrow the magnetic flux, and a coil is placed at the tip of the magnet to generate eddy currents on the surface of the material to be inspected. A method is known in which ultrasonic energy is input into the material to be inspected using the Lorentz force caused by the interaction between the two. The basic configuration is shown in Figure 1. As shown in the figure, when a current in a certain direction is passed through the coil 2, an eddy current I is generated on the surface of the inspected material 3, and due to the interaction between this and the magnetic field H generated by the magnet 1, the inspected material Lorentz force F acts on the surface of . Therefore, by passing an alternating current through the coil 2, in the case of FIG. 1, longitudinal ultrasonic waves whose vibration direction and propagation direction coincide are applied to the inspected material 3.

The ultrasonic waves applied to the material to be inspected 3
If there is a defect inside, it will be reflected back.
Flaw detection is performed by detecting the returning ultrasonic waves with a detection coil through a conversion process that is the reverse of the input process. In this case, as the detection coil, the excitation coil 2 shown in FIG. 1 can be used as is, or it can be prepared separately.

In order to increase the input energy by an electromagnetic ultrasound transducer, it is necessary to make the generated magnetic field stronger. However, in order to do so, the first
In the configuration shown in the figure, the yoke is extremely large,
From a practical standpoint, it has no choice but to be limited to a certain scale. Therefore, input energy is also limited, making it difficult to obtain high sensitivity.

To solve these problems, we have developed a new electromagnetic superstructure that allows a small magnet to generate a large bias magnetic field by localizing the magnetic field near the surface of the material under test and reducing the overall magnetostatic energy. Sonic transducers have recently been proposed. The basic structure consists of a magnetic field generation mechanism in which multiple permanent magnet plates magnetized in the thickness direction are sandwiched between high permeability magnetic materials and arranged in the thickness direction so that the polarity is alternately reversed, and and a wave-shaped coil arranged in a meandering manner along the arrangement of the permanent magnet plates.

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 reasons for this are that hot materials have severe surface irregularities, and that the transducer has a cooling structure in which a cooling medium must flow into the gap between the end face of the transducer and the material to be inspected.
While maintaining such a gap distance, it is required to input a large amount of ultrasonic energy to detect defects of approximately 15 mm x 15 mm or larger, which are a problem in hot materials, with high sensitivity.

This invention was made in view of the above points,
By using a combination of a magnetic field generation mechanism that can form a uniform and strong magnetic field over a wide area of the surface of the material to be inspected, and a corrugated coil, it is possible to effectively detect defects, especially in hot materials. The present invention provides an electromagnetic ultrasonic transducer.

The electromagnetic ultrasonic flaw detection transducer according to the present invention includes a plurality of permanent magnet plates magnetized in the thickness direction, sandwiched between high permeability magnetic materials and arranged in the thickness direction so that the polarities are alternately reversed. The magnetic field generating mechanism has a magnetic field generating mechanism configured by arranging a wave-shaped coil that meanders along the arrangement of the permanent magnet plates near the end of the magnetic field generating mechanism, and the effective area of the magnetic field generating mechanism is 2.5 to 2.5 mm. It is characterized by being set at 3.5 inches square. In this case, as detailed below, by selecting the arrangement relationship between the corrugated coil and the permanent magnet plate, it is possible to select whether the ultrasonic waves excited in the material to be inspected are longitudinal waves, transverse waves, or surface waves. You can choose between waves.

A longitudinal wave and surface wave transducer according to an embodiment of the present invention will be described with reference to FIGS. 2 to 4. As is clear from these figures, a plurality of permanent magnet plates 11 (11 ₁ , 11
₂ , 11 ₃ ……………), high permeability magnetic material 12
(12 ₁ , 12 ₂ , 12 _{3 .} . . ) are arranged in the thickness direction so that the polarity is alternately reversed to form a magnetic field generation mechanism. In this example, the wave-shaped coil 13 that generates an eddy current is arranged in a meandering manner so as to creep only directly under the end face of the permanent magnet plate 11, as shown in FIG. 14 is a material to be inspected. The effective area of the magnetic field generation mechanism shall be 2.5 to 3.5 inches square.

FIG. 4 is a schematic vertical cross-sectional view, and to explain how ultrasonic energy is applied to the inspected material 14 using this, the wave-shaped coil 13 is now directed in the direction indicated by the arrow in FIG. 3. When a current of 1 is applied to the inspected material 1
Eddy currents I having the polarities shown are generated in each part directly under the permanent magnet plate 11 on the fourth surface. Due to the interaction between this eddy current I and the horizontal magnetic field H directly below the permanent magnet plate 11, a Lorentz force F of the illustrated polarity acts on the surface of the inspected material 14. 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 the inspected material 14 are transmitted.
It will be excited by

In this case, the main ultrasonic waves are longitudinal waves, but since there is some interaction between the vertical component of the magnetic field generated on the surface of the material to be inspected and the eddy current, surface waves are also excited at the same time.

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. Of course, a detection coil paired with the wave-shaped coil 13 may be provided separately from the wave-shaped coil 13.

According to this embodiment, due to the configuration of the magnetic field generation mechanism, a uniform and strong magnetic field can be obtained, and the interaction between this and the eddy current induced by the corrugated coil allows a uniform and wide flaw detection surface to be obtained. Obtainable.
Furthermore, as the effective area of the transducer increases, the distance between the transducer and the material to be inspected can be made sufficiently larger than in the past, and defects can be detected with high sensitivity.

Experiments have shown that the effective area of the transducer is
The relationship between the air gap distance and the output voltage when designed to be 1.0 inches square is as shown in Figure 5, and according to the following experiment, when the effective area is designed to be 2.5 inches square to 3.5 inches square, the transducer and A defect with a size of 15 mm x 15 mm was able to be detected with sufficiently high sensitivity when the gap distance between the test material and the material to be inspected was 5 mm. If the effective area is set too large, small defects cannot be detected, and if the effective area is set too small, the gap distance between the transducer and the material to be inspected cannot be set large, making it difficult to detect the transducer. As a cooling structure, it is not possible to effectively detect defects in hot materials. The above relationship is illustrated in FIG. 6, and it can be seen that it is preferable for the effective area to be 2.5 to 3.5 inches square for flaw detection of hot materials.

FIGS. 7 to 9 show the main structure of still another embodiment of the present invention. In these embodiments, wave-shaped coils 13, 13' are arranged on both sides of the magnetic field generating mechanism to constitute a double-sided transducer. That is, the embodiment shown in FIG. 7 is a double-sided transducer in which the lower surface is used for longitudinal waves and the upper surface is used for transverse waves.
The embodiment of FIG. 8 is the permanent magnet plate 11 in FIG.
Experiments have shown that by doubling the thickness of the material, longitudinal waves are approximately doubled. On the other hand, the ninth
On the contrary, the figure shows a case in which the thickness of the high permeability magnetic plate 12 in FIG. 7 is doubled, and it has been found that transverse waves are strengthened approximately twice as much.

As described above with reference to the embodiments, the transducer for electromagnetic ultrasonic flaw detection according to the present invention has a magnetic field generation mechanism that applies a uniform and strong magnetic field to the inspected material, and a corrugated coil. By setting the effective area to 2.5 to 3.5 inches square by the combination of Defects can be detected with sufficiently high sensitivity even in hot materials.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a typical example of a conventional electromagnetic ultrasonic transducer, and FIG. 2 is a perspective view showing an electromagnetic ultrasonic transducer according to an embodiment of the present invention.
FIG. 3 is a diagram showing the arrangement pattern of the wave-shaped coil, FIG. 4 is a schematic longitudinal cross-sectional view for explaining the operation, FIG. FIG. 6 is a diagram similarly showing the relationship between the effective area and the detection capability, and FIGS. 7 to 9 are diagrams showing the main part configuration of an embodiment of the transducer for both sides. 11 (11 ₁ , 11 ₂ , 11 ₃ ……………)…
...Permanent magnet plate, 12 (12 ₁ , 12 ₂ , 12 ₃ ...
………)……High permeability magnetic material, 13,13′…
... Wave-shaped coil, 14 ... Material to be inspected.

Claims (1)

[Claims] 1. A plurality of permanent magnet plates magnetized in the thickness direction,
A magnetic field generating mechanism arranged in the thickness direction so that the polarity is alternately reversed while being sandwiched between high permeability magnetic materials, and a magnetic field generating mechanism arranged near the end of the magnetic field generating mechanism and meandering along the arrangement of the permanent magnet plates. A transducer for electromagnetic ultrasonic flaw detection, characterized in that the effective area of the magnetic field generation mechanism is set to 2.5 to 3.5 inches square. 2 Set the thickness of the permanent magnet plate to the thickness of the high permeability magnetic material.
The transducer for electromagnetic ultrasonic flaw detection according to claim 1, wherein the transducer is 1.5 to 2.5 times larger. 3 The thickness of the high permeability magnetic material is the thickness of the permanent magnet plate.
The transducer for electromagnetic ultrasonic flaw detection according to claim 1, wherein the transducer is 1.5 to 2.5 times larger.