JPS58223751A - Electromagnetic ultrasonic probe - Google Patents

Abstract

PURPOSE:To improve detection performance greatly by flattening the surface of the center leg of an electromagnet iron core facing oppositely to a transmitting and receiving coil. CONSTITUTION:A step for improving magnetic flux density at the tip of the center leg 9 of the iron core is eliminated to constitute draw the surface to retain neither ruggedness nor steps extending from the root 11 of the center leg 9 of the iron core to the tip part 10. Consequently, surface area is drawn from the root 11 of the iron core center leg 9 to the tip part 10 to eliminate ruggedness and step so necessary magnetic flux density is obtained by the same magnetomotive force as before; and an ultrasonic wave generated at the iron core center leg 9 itself is only an ultrasonic wave 24 returning after being reflected by the top surface of the iron core and no ultrasonic wave returns from the tip part 10. Consequently, the detection performance is improved greatly.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a center leg structure of an electromagnetic ultrasound probe suitable for removing noise that may be misjudged as a defect.

An electromagnetic ultrasonic flaw detection apparatus that detects flaws by electromagnetically generating ultrasonic waves in a test object using a magnetic field and an eddy current is generally shown in FIG. In the figure, l is an electromagnetic core, and an excitation coil 2 and a transmitting/receiving coil 3 are provided inside the core. Further, the excitation coil 2 is connected to an excitation power source 4, and the transmitting/receiving coil 3 is connected to a pulse generator 5. 6 is an amplifier whose input goes to the detection coil and pulse generator, and its output goes to the waveform observer 7
(For example, it is connected to a synchronoscope).

By exciting the coil 2, a magnetic field is applied to the specimen 8. Due to this magnetic field and the eddy current generated in the test material by exciting the transmitter/receiver coil 3 with a pulse current,
A force based on Fleming's left hand rule acts on the material under test,
Ultrasonic waves 41 are generated. This ultrasonic wave 41 propagates from the surface of the material to be inspected perpendicularly to 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. Defect wave 21 and backside wave 2
2 undergoes inverse transformation according to Fleming's law due to the interaction with the DC magnetic field, and appears as an energizing force in the transmitter/receiver coil 3.

The defective wave 21 and the backside wave 22 are amplified by the amplifier 6 and displayed together with the transmitted pulse 20 by the waveform observer 7 as shown in FIG.

Similarly, the reason why the tip of the central leg 9 of the iron core is narrowed is to obtain a DC magnetic field as high as possible.

Conventional devices such as those described above have drawbacks as explained below. That is, when the transmitter/receiver coil 3 is pulse-excited as shown in FIGS. 1 and 2, the electromagnet core center leg 9 is made of a conductive material such as iron, so eddy currents also occur in the core center leg 9. is generated, and a rainbow electromagnetic force moves due to the interaction with the magnetic field. Therefore, ultrasonic waves are also generated in the iron core itself. By the way, it is called the near-field sound field limit distance (referred to as "xo"), and is the distance X from the vibration plane (in electromagnetic ultrasonic flaw detection equipment, the surface of the material to be inspected) expressed by the following formula. exists, and the directivity a (characteristic that f is strongly radiated in a certain direction) is bad.

x, 2a2/λ Here, Xo = Near field limit distance a = Transducer radius λ = Wavelength Therefore, in conventional probes, the tip 10 of the central leg 9 of the core is narrowed to improve magnetic flux density. So, iron lL? Self ()
Ultrasonic waves 23 generated in the body are reflected and returned. Further, the ultrasonic wave 24 is also reflected from the upper surface of the iron core and returns.

In addition, in order to prevent an increase in leakage magnetic flux, the tip of the central leg of the core
The length t of 0 is shorter than the maximum thickness t3 of the test material. On the other hand, the height of iron I is 1. can be set freely, so for example, if the maximum thickness of the material 8 to be inspected is t9 and the height of the iron core l is determined so that lv>ts, the output waveform of the waveform observation device 7 at that time will be as shown in Figure 2. become that way.

The ultrasonic wave 24 is displayed at a position where it is not mistakenly determined to be a defect 31 during flaw detection. However, the ultrasound 23
It was displayed at the position t, where there is a possibility that it could be mistakenly determined as defect 31, resulting in noise, which was a major problem in terms of performance.

In FIG. 2, the defective wave is displayed at the position t, and the bottom wave is displayed at the position t.

An object of the present invention is to provide an electromagnetic ultrasonic probe that greatly improves detection performance.

We cannot avoid this when using an iron core of conductive material. If the ultrasonic waves generated and reflected from the core itself are detected outside the time required for flaw detection, they will not be mistakenly judged as defective waves reflected by defects, and will not have any effect on flaw detection. We focused on

The key point of the present invention is to eliminate surface irregularities and internal through-holes in the core center leg, and to create a core center leg structure that allows ultrasonic waves generated and reflected from the core to be detected outside of the time required for flaw detection. It is in.

Hereinafter, the present invention will be explained in detail using FIG. 3.

What is different from the prior art in FIG. 3 is that the step for improving the magnetic flux density at the tip of the core central leg 9 is eliminated, and as shown in FIG.
The point is that it has a narrow structure with no unevenness or steps on the surface. The operation of the device having such a configuration will be explained. The generation and detection of ultrasound waves are exactly the same as in the prior art. However, in the case of the present invention, since the iron core central leg 9 is narrowed from the root 11 to the tip 10 without surface irregularities or steps, the required magnetic flux density can be obtained with the same magnetomotive force as the conventional probe. Moreover, the ultrasonic waves generated in the core central leg 9 itself are only the ultrasonic waves 24 that are reflected from the upper surface of the core and return, and no ultrasonic waves return from the p1 core central leg tip 10. Therefore, the height t of the iron core 1 is adjusted so that the height of the iron core 1, s t, and the maximum thickness 1s of the test material 8 satisfy t t > t n ! If this is determined, the output waveform of the waveform observation device 7 at that time will be as shown in FIG. 4, and the ultrasonic wave 24 reflected from the top surface of the iron core and returned will not be mistakenly judged as a defect 31 during flaw detection.

, and nothing other than the signal from the defect wave 21 from the defect 31 is displayed between 0 and t3 on the time axis necessary for flaw detection.

The present invention solves the problem of reflected echoes from the vicinity of the tip 10 of the central leg of the core, and greatly improves the detection ability.

[Brief explanation of the drawing]

Figures 1 and 2 are configuration diagrams and explanatory diagrams of the prior art;
FIG. 4 is a configuration diagram and an explanatory diagram of the present invention.

Claims (1)

[Claims] 1. An electromagnetic ultrasonic probe for flaw detection by electromagnetically generating ultrasonic waves using an ffl field and an eddy current, characterized in that the surface of the central leg of the electromagnetic core facing the transmitting/receiving coil is flat.