JPS5831872B2 - Non-contact ultrasonic flaw detection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic flaw detection method that allows inspection of materials at high temperatures without contacting them.

Conventionally, ultrasonic flaw detection uses a piezoelectric element vibrator for both transmitting and receiving probes, which requires acoustic coupling between the material and the probe, and a medium such as water or oil is used as a couplant. was used as.

Therefore, non-destructive testing of high-temperature materials during hot processing of steel products is limited by temperature, and effective flaw detection has not been possible.

However, in order to improve product yield, it is desirable to perform non-destructive testing as early as possible during the process to prevent defective materials from being passed on to subsequent processes.

In order to satisfy this demand, the present invention proposes an ultrasonic flaw detection method that does not require contact with the material for transmitting and receiving ultrasonic waves.

That is, the present invention focuses a pulsed laser having a wavelength in the infrared region using a lens or the like, makes it perpendicularly or obliquely incident on the material, and propagates the ultrasonic waves generated by the thermal shock during the incident into the material. This is a non-contact ultrasonic flaw detection method in which flaws are detected by receiving ultrasonic waves using an electromagnetic ultrasonic probe consisting of an electromagnet or permanent magnet and a flat detection coil placed on the same or opposite surface of the incident surface.

Next, embodiments of the invention will be described based on the drawings.

As shown in FIG. 1, a laser head 1 is placed at a distance of 10 to 20 m from a conveyance line for a material 4 in a high temperature state, for example, a steel material being hot rolled at 800 to 1200'C.
The laser is guided by a waveguide, and a lens 3 for narrowing down the pulsed laser is installed between them.

Then, an electromagnetic ultrasonic probe 5 consisting of a permanent magnet or electromagnet that applies a static magnetic field to the material surface and a flat detection coil that detects eddy currents generated by the displacement caused by the ultrasound and the static magnetic field is placed on the laser incidence surface. 1 to 15 mm from the material surface on the opposite side
Place them apart and opposite each other.

An example of this electromagnetic ultrasonic probe 5 is shown in FIG.

In the figure, 11 is a permanent magnet, 12 is a flat detection coil, 13.
14 is a magnetic pole, 15 is a slot, 16 is a flat detection coil 12
This is a cable that connects between the connector 17 and the connector 17.

This electromagnetic ultrasonic probe 5 is provided with a cooling shield plate to avoid thermal effects.

Further, a laser power source 2 and an ultrasonic flaw detector 7 are provided between the laser head 1 and the electromagnetic ultrasonic probe 5, and are electromagnetically coupled.

This ultrasonic flaw detector 7 is composed of, for example, a tuning amplifier 3, a detector 9, and a CRTlo shown in FIG. are connected to the laser power supply 2.

According to the above device, the laser head 1 oscillates a pulsed laser in the infrared region using the laser power source 2.

This laser is guided to the surface of the material 4 through the waveguide, during which time it is focused by the lens 3, and the laser absorption energy density on the material surface reaches a level necessary for generating ultrasonic waves, and is incident on the material surface.

The ultrasonic waves generated by the thermal shock caused by the laser on the material surface are propagated into the material.

At this time, if a defect 6 exists on the way, the ultrasonic waves will be attenuated.

By detecting the degree of attenuation, the degree of the defect can be known.

The ultrasonic flaw detector 7 performs amplified detection of the received signal and displays it on a display device such as a cathode ray tube.

The markings are synchronized with the oscillation of the pulsed laser.

Figure 4 shows an example of the marking.

The figure a shows the case of the material 4 without defects, and the height of the received echo 18 is determined by the attenuation of the material itself.

In the figure, the zero point on the time axis indicates the oscillation point of the pulsed laser, and 20 indicates the laser beam.

Figure b shows the case of a material 4' in which a defect 6 exists, and the height of the received echo 18' becomes smaller depending on the degree of the defect.

Note that T in Figure 3 corresponds to the time it takes the ultrasonic wave to propagate through the material, and if the speed of sound is known for the material, the thickness of the material can be immediately determined.

This is because the speed of light is significantly higher than the speed of sound, so it can be considered that the laser oscillation and the ultrasonic wave are generated at the same time, and the reception is also simultaneous with the arrival of the ultrasonic wave on the surface because the eddy current on the surface due to the ultrasonic wave is detected. This is because it can be considered.

The above is a transmission method flaw detection in which the transmitting side and the receiving side are on opposite surfaces of the material, but as shown in FIG. 5, an electromagnetic ultrasonic probe 5 is installed near the point of incidence of the pulsed laser beam 20 , flaw detection can also be performed using a pulse reflection method in which ultrasonic waves reflected from the defect 6 are received.

In this case, the pulsed laser beam 20 is applied from diagonal directions at various angles, and the reflection from the defect 6 can be efficiently received by using a transverse wave probe or a longitudinal wave probe as the electromagnetic ultrasonic probe 5.

FIG. 6 shows an example of marking when an electromagnetic ultrasonic probe for transverse wave detection is used in the apparatus shown in FIG. 5.

Figure a shows the case without a defect, and figure B shows the case with a defect. In the figure, the zero point on the time axis is relative to the laser oscillation point, and 22 is the time when the longitudinal wave generated by laser incidence is reflected at the bottom of the material. , 23 shows a transverse wave that is mode-converted into a transverse wave and received by the electromagnetic ultrasonic probe, and 23 indicates a transverse wave generated by laser incidence that is reflected on the bottom surface of the material and received on the surface.

Also, received echoes 24°25.26 are those that propagate and are received at the surface as shown in Figure C when there is a defect approximately in the center of the material.

In Figure C, solid lines indicate vertical waves and dotted lines indicate transverse waves.

In this way, the markings are clearly different between a sound material and a defective material, and defects can be detected.

Further, ultrasonic waves can be received by detecting displacement of the material surface by utilizing the laser interference phenomenon, and the principle thereof is shown in FIG.

In the figure, 1 is a laser head, 4 is a material, 27 is a total reflection mirror, 28 is a photomultiplier, and 29 is a half mirror.A solid line with an arrow indicates a path of a signal laser, and a broken line with an arrow indicates a path of a reference laser.

Now, if the surface of material 4 is vibrating due to ultrasonic waves, the path length of the signal laser will change, so the interference phenomenon that occurs between it and the reference laser whose path length is constant will be due to the ultrasonic vibrations on the receiving surface of the photomultiplier. produces a corresponding change in intensity.

By receiving this with the photomultiplier 28, it is possible to receive ultrasonic vibrations.

For example, the laser source is a He-Ne laser (wavelength 0.6
3 μm), and if the material surface is in a stationary state and the optical path difference between the reference beam and the signal beam is O, then if the material surface is displaced by λ/4, or approximately 0.15 μm, the difference between the reference beam and the signal beam will be There is a difference of λ/2 in optical path length between them, and they cancel each other out.

That is, the intensity of the received light becomes zero when the material displacement is 0.15 μm.

That is, a surface vibrating with a displacement of ±0.15 μm vibrates with O=Peak as the receiving intensity.

On the other hand, when there is no surface vibration, it is always Peak.

In this way, by measuring the amplitude of the intensity change of the received light, it is possible to detect the displacement of the optical surface due to the ultrasonic waves.

Note that since the material surface is usually rough, it is necessary to focus the laser beam with a lens and position the material surface at the focal point so that the laser beam is incident on approximately one point.

Further, the above displacement amount of ±0.15 μm is smaller than the amplitude of the minute ultrasonic waves used for hollow flaw detection, and according to this principle, the ultrasonic waves can be received as a change in the intensity of the received light.

The interferometer shown in FIG. 8 is known as a Michelson interferometer, and a paternal interferometer can also be used.

FIG. 8 shows a flaw detection method when a longitudinal wave electromagnetic ultrasonic probe 30 is used for ultrasonic transmission and a laser interferometer 31 is used for ultrasonic reception.

The ultrasonic waves transmitted by the electromagnetic ultrasonic probe propagate through the material, and the displacement of the opposite surface is received by a laser interferometer as the width of the intensity change of the received light.

Figure 9 shows an example of the size of a defect in a material with a thickness of 20 mm in the arrangement shown in Figure 8 and the width of the intensity change of the received light.As the defect gets larger, the intensity width becomes smaller. I know that there is.

Using this reception principle and the transmission of the electromagnetic ultrasound, the first
Flaws can be detected using a method similar to the one shown in the figure.

However, in this case, since displacement in the vertical direction of the surface is detected, flaw detection is limited to using longitudinal waves.

FIG. 10 shows the results of testing the relationship between the beam and the intensity of the ultrasonic longitudinal wave component when the Nd:YAG laser was made into a sharp pulsed laser using a Q switch.

This figure shows that the intensity of the longitudinal wave component depends on the surface energy density of the laser, and that in order to increase the intensity of ultrasonic wave generation, it is necessary to increase the surface energy density of the laser.

Furthermore, FIG. 11 shows an outline of the waveform of the Nd:YAG pulse laser, and it can be seen that a sharp rise is important for generating ultrasonic waves.

The frequency of the ultrasonic waves generated by such a pulsed laser is distributed from several 100 Kl (z to several 10 MHz), and by providing an appropriate bandpass frequency filter on the receiving side, the characteristics of the material (thickness, Flaw detection can be performed at an optimal frequency that takes into consideration the ultrasonic attenuation characteristics of the material and the size of the defect to be detected.

Furthermore, when we investigated the relationship between the incident angle of the laser on the material and the intensity of the generated ultrasonic waves, we found that the ultrasonic intensity has almost no relationship to the laser incident angle, as shown in FIG.

This means that the laser incident point can be freely changed using a mirror or the like, and the material surface can be scanned over a wide range.

As mentioned above, this invention focuses a laser beam and makes it incident on the material surface, and detects flaws using ultrasonic waves that remove insects. Therefore, it is possible to eliminate the thermal influence from high-temperature materials, so it can be used for slabs, billets, etc. It can be applied to hot flaw detection of high-temperature steel slabs or continuously cast slabs during casting, and is extremely useful industrially.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of an apparatus according to an embodiment of the present invention, Fig. 2 is a longitudinal sectional front view and bottom view showing an example of an electromagnetic ultrasonic probe, and Fig. 3 is a detailed example of an ultrasonic flaw detector. Explanatory diagram, 4th
The figure shows the received echo displayed on the display device, a
The figure shows the case of a material with no defects, the figure b shows the case of a material with defects, the figure 5 is an explanatory diagram of the case where the electromagnetic ultrasonic probe is installed on the laser incidence side of the material, and the figure 6 shows the case of a material with defects. Figure 5 shows received echoes when flaws are detected using the equipment shown in Figure 5. Figure A shows the case where there is no defect, Figure B shows the case where there is a defect, and Figure C shows the state of incidence and reflection of echoes generated by the defect. Figure 7 is an explanatory diagram showing the principle of receiving ultrasonic waves by detecting the displacement of the material surface using the interference phenomenon of lasers. An explanatory diagram showing the principle of the flaw detection method when an ultrasonic probe is used with a laser interferometer to receive ultrasonic waves. Figure 9 shows the defect size of the material and the intensity change of the received light using the flaw detection method shown in Figure 8. A chart showing the relationship between the widths; FIG. 10 is a chart showing the relationship between the laser beam diameter and ultrasonic longitudinal wave intensity; FIG. 11 is a chart showing the relationship between the frequency of ultrasonic waves generated by a pulsed laser and the laser output; FIG. 12 is a chart showing the relationship between laser incident angle and ultrasonic intensity. In the figure, 1... Laser head, 2... Power supply, 3... Lens, 4... Material, 5...
... Electromagnetic ultrasound probe, 6 ... Defect, 7.
... Ultrasonic flaw detector, 8 ... Tuning amplifier,
9...Detector, 10...CRT, 11
...Permanent magnet, 12...Flat detection coil, 13.14...Magnetic pole, 15...
Slot hole, 16... Cable, 17... Connector, 27... Total reflection mirror 28...
...Photomaru, 29...Half Mirror-130
・・・・・・Electromagnetic ultrasonic probe for longitudinal waves, 31・・・・・・
・Interferometer.

Claims (1)

[Claims] 1 A pulsed laser with a wavelength in the infrared region is focused with a lens, etc., and is incident perpendicularly or obliquely on the surface of the material to be tested, and the ultrasonic waves generated by the thermal shock at the time of incidence are propagated into the material to be tested. A non-contact ultrasonic flaw detection method characterized by receiving ultrasonic waves using an electromagnetic ultrasonic probe consisting of an electromagnet or permanent magnet and a flat detection coil placed on the same or opposite surface of the incident surface.