JPS6217704B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electromagnetic ultrasonic flaw detector, and more particularly to an electromagnetic ultrasonic flaw detector suitable for detecting vertical crack defects.

Hereinafter, the present invention will be explained based on the drawings. FIG. 1 shows the configuration of a conventional electromagnetic ultrasonic flaw detection device. In the figure, reference numeral 1 denotes an E-shaped core whose end is placed facing the subject 2. An excitation coil 3 is wound around the core 1, and the end of the excitation coil 3 is connected to a DC power source. 4 to form an electromagnet 10. Furthermore, a subject 2 is placed in the center of the E-shaped core 1.
(for example, a steel plate) to generate ultrasonic waves and
A transmitter/receiver coil 5 is provided for detecting reflected waves from defects present in the transmitter/receiver coil 5, and an end of the transmitter/receiver coil 5 is connected to an output end of a pulse generator 6 that generates a pulse voltage.

On the other hand, the output end of the pulse generator 6 is connected to the input end of an amplifier 7 for amplifying the signal detected from the transmitting/receiving coil 5, and the output end of the amplifier 7 has a display means 8 for displaying the detected signal, such as a cyclotron. Scope is connected.

The operation of the conventional electromagnetic ultrasonic flaw detection apparatus having the above configuration will be explained with reference to FIGS. 2 and 3.

Now, when the excitation coil 3 is supplied with power by the DC power supply 4, a DC magnetic field is generated in the subject 2.

On the other hand, an eddy current is generated in the subject 2 by the transmitting/receiving coil 5 receiving the pulse signal from the pulse generator 6. Due to the interaction between this eddy current and the DC magnetic field, a force based on Fleming's law acts on the subject 2, and an ultrasonic wave 41 is generated. This ultrasound 4
1 propagates from the surface of the object almost perpendicularly toward the back surface, is reflected by the defect 31, the back surface, etc., and returns to the front surface.
Here, the ultrasonic waves that are reflected from the defect and return to the front surface are called defect waves 21, and the ultrasonic waves that are reflected from the back surface and return to the front surface are called back waves 22. The defective wave 21 and the backside wave 22 undergo inverse transformation according to Fleming's law by interaction with the DC magnetic field, and appear as an electromotive force in the transmitting/receiving coil 5.

The defective wave 21 and the backside wave 22 are amplified by the amplifier 6, and displayed by the display means 8 as shown in FIG.
Displayed together with transmit pulse 19. In this case, the transmission pulse 19 with a high signal level is also input to the amplifier 6 in FIG. During the duration of the transmit pulse 19, the amplifier 6 saturates and then the amplifier 6
Since it takes time for the amplification degree to recover, the output signal of the amplifier 6 becomes the saturated pulse signal 20 in FIG.
appears, and during that time, a minute defective wave 21 with a signal level as low as 100 dB relative to the transmitted pulse appears.
is buried in the saturated pulse signal and cannot be detected.

That is, with the conventional device, it is possible to detect defects that are located deeper than the surface of the object 2 to be inspected, but it is not possible to detect defects that are located at shallower positions or vertical crack-like defects (hereinafter referred to as cracks). be.

The purpose of the present invention is to eliminate the drawbacks of the above-mentioned conventional devices,
An object of the present invention is to provide an electromagnetic ultrasonic flaw detection device capable of detecting cracks existing inside an object.

A feature of the present invention is that leakage magnetic flux attributable to cracks existing inside the test object in the DC magnetic field applied to the test object by an electromagnet constituting an electromagnetic ultrasonic flaw detection device is eliminated by a pair of magnetic fluxes provided in the E-shaped core of the electromagnet. The present invention is configured to detect the presence of the crack by detecting the difference signal obtained from the magnetic detection element.

Embodiments of the present invention will be described below with reference to FIGS. 4 to 6.

FIG. 4 is a block diagram showing the configuration of an embodiment of the present invention. This embodiment differs from the conventional example shown in FIG.
A pair of magnetic detection elements 9A, 9B is provided at a position where the magnetic flux density in the direction perpendicular to the surface of the object 2 is minimum, and a difference signal is further amplified between the detection signals obtained from the pair of detection elements 9A, 9B. A dynamic amplifier 10 is provided, and a switch means 11 is provided in front of the display means 8 for switching between the output signal of the differential amplifier 10 and the output signal of the amplifier 7 for amplifying the detection signal of the transmitting/receiving coil.

Here, an important point in the present invention is the mounting position of the magnetic detection elements 9A and 9B, and the distribution of magnetic flux density of the E-shaped core 1 as shown in FIG. If the Y-axis is taken perpendicular to the surface of the object 2, as shown in FIG. It has been experimentally confirmed that the value is minimum (zero) at the center of the shape.

Therefore, in order to use the magnetic detecting elements 9A, 9B with good detection sensitivity, it is necessary to provide the detecting elements 9A, 9B in the U-shaped center of the E-shaped core 1.

In the above structure, when a defect located deep from the surface of the object 2 is to be investigated, the contact C of the switch means 11 is switched to the A side, and in this case, the structure is exactly the same as that of the conventional example shown in FIG.

Next, when a crack existing in the subject 2 is to be investigated, the contact point C is switched to the B side. In this case the fifth
As shown in the figure, the magnetic detection element 9A in the subject 2
If the crack 12 exists directly below the magnetic detection element 9B, and no crack exists directly below the magnetic detection element 9B, leakage magnetic flux is detected by the detection element 9A, and no leakage magnetic flux is detected by the detection element 9B.
The outputs of the pair of magnetic detection elements 9A and 9B are input to the differential amplifier 10, and the difference signal provides a signal indicating the presence of a crack.

Furthermore, if a similar crack exists directly below the magnetic detection elements 9A and 9B, the signal obtained from the differential amplifier 10 may not be able to be distinguished from the noise level; This can be avoided by changing the scanning direction, for example, in the vertical direction and in the horizontal direction, when scanning relatively.

Here, the magnetic detection elements 9A and 9B are, for example, Hall elements, magnet diodes, or the like.

As described above, according to the present invention, it is possible to detect cracks present in a subject that were undetectable with conventional devices.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the configuration of a conventional magnetic ultrasonic flaw detection device, Figs. 2 and 3 are explanatory diagrams for explaining the operation of the conventional example shown in Fig. 1, and Fig. 4 is an example of the present invention. 5 is a block diagram showing the configuration of the embodiment, FIG. 5 is a block diagram for explaining the operation of FIG. 4, and FIG. 6 is the magnetic flux density distribution of the E-shaped core and the magnetic detection element in the embodiment shown in FIG. 4. It is an explanatory view showing a positional relationship with. 1...E-type core, 2...subject, 3...excitation coil,
4... DC power supply, 5... Transmitting/receiving coil, 6... Pulse generator, 7, 10... Amplifier, 8... Display means, 9A,
9B...Magnetic detection element, 11...Switch means.

Claims (1)

[Claims] 1. An excitation coil wound around an E-type core, an electromagnet excited by a DC power source, a transmitting/receiving coil provided at one end of the E-type core, and an amplifier for amplifying a detection signal output from the transmitting/receiving coil. The electromagnet comprises a pulse generator that supplies a pulse voltage to the transmitter/receiver coil and the amplifier, and a display means that displays the output signal of the amplifier, and is configured such that the end of the E-shaped core of the electromagnet faces the subject. An ultrasonic flaw detection device includes: a pair of magnetic detection elements provided in an E-type core at a position where the magnetic flux density in a direction perpendicular to the surface of a test object is minimized; and a differential amplifier that amplifies a difference signal between the pair of detection elements. , a switch means provided in front of the display means for switching between the output of the differential amplifier and the output of the amplifier.