JPS6036020B2 - Non-contact ultrasonic flaw detection method and equipment used for its implementation - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a non-contact ultrasonic flaw detection method for detecting flaws in thick steel plates, etc. (hereinafter referred to as strips) at high temperatures (60,000 to 120,000 ℃) during hot rolling in the manufacturing process of thick steel plates, etc., and its implementation. This relates to equipment used for.

- For example, when testing a wide strip as an object to be tested, conventionally, as shown in Fig. 5, the strip probe A is placed facing the surface of the strip M that is being transported in the longitudinal direction indicated by the white arrow. A method of reciprocating in the width direction of M at an appropriate speed over almost the entire width, and scanning continuously in a zigzag pattern as shown by the solid line G to create deep scratches, or a method of making deep scratches as shown in FIG. facing the surface of the strip M being transported in the direction of the arrow,
A large number of probes B, B...Bn are arranged in the width direction of the strip M.
are installed, each of these probes is electrically scanned, and the G
, , G2...Gn, methods of detecting flaws in a dotted manner are being explored.

However, probes A, B, and B used for such deep wounds
2...Bn uses a vibrator such as a piezoelectric element on both the transmitting and receiving sides, so probes A, B1, horse...Bn
It is necessary to couple acoustically between the probes A, B, B2...Bn and the strip M, which is the object to be tested. Between contact soot such as water and oil between W. , W2 must intervene. Therefore, if the object to be tested is at a very high temperature, such as a hot-rolled strip, suitable contact soot quality cannot be obtained, and acoustic coupling cannot be obtained between the probe and the object to be tested. Therefore, it has been virtually impossible to perform flaw detection on high-temperature objects. Furthermore, for wide materials to be inspected, there is a demand for changing the flaw detection pitch or the number of points depending on the position in the width direction, but conventional devices have not been able to meet such demands.

In addition, a method using a so-called electromagnetic ultrasonic probe is known as a method for detecting flaws in hot-rolled materials at high temperatures without contact. It has the disadvantage of being easy to accept.

The present invention has been made in view of the above circumstances, and its purpose is to use a laser beam to transmit shock waves (ultrasonic waves) generated by the impact when the laser beam enters the object to be detected. Enables non-contact flaw detection by propagating into the object, eliminating the need for contact soot.

Therefore, flaws can be detected accurately and at high speed regardless of the temperature of deeply flawed objects, and for wide materials to be inspected, the flaw detection pitch can be varied depending on the position in the width direction.Furthermore, it is non-contact with less influence of lift-off fluctuations. An object of the present invention is to provide an ultrasonic deep injury method and a device used for its implementation. In the non-contact ultrasonic deep wound method according to the present invention, a pulsed laser beam is made incident on a plurality of half mirrors arranged in its path, and a part of the incident light is reflected from each half mirror, and the transmitted laser beam is sequentially The laser beam reflected from each half mirror is made incident on each rotating mirror whose reflection surface angle with respect to the object to be inspected changes over time, and the laser beam reflected from each rotating mirror is Projection scans different areas on the surface of the object to be tested, and the shock waves (ultrasonic waves) generated by the impact during projection are propagated into the object to be tested.
It is characterized by receiving propagating waves with an electromagnetic ultrasonic probe.

EMBODIMENT OF THE INVENTION Hereinafter, the method of this invention and the apparatus used for carrying out the same will be concretely demonstrated based on the drawing which shows an Example. FIG. 1 is a plan view showing an example of the method of the present invention and a coating used in its implementation, FIG. 2 is a side view thereof, and FIG. 3 is a
- It is a partial front view seen in the m line direction, and M in the figure is a high-temperature strip during hot rolling, and it is conveyed at a substantially constant speed in the direction of the blank square, and this strip M is the object to be tested.
A high-output laser generating device L is disposed on the upper surface side of the conveying area when facing from the side, with its head facing the strip M side and perpendicular to the conveying direction.

The laser generator L uses a very short-duration pulsed laser beam (for example, 1
00Hz), and the laser beam emitted from this laser beam has a plurality of laser beams (in the example, 2 )'s half day,. The light is incident on a group of mirrors consisting of a mirror 2 and one total reflection mirror K. Half mirror day,, day 2 and total reflection mirror K located behind this half mirror day 2 are placed on the center of each area M, , M2, M8 divided into three equal parts in the width direction perpendicular to the conveying direction of the strip M, respectively. It is arranged. The transmittance of each half-mira day, day 2 is the half-mira day. will be on 2/3, and half mira day 2
is set to 1/2, therefore, 1/3 of the total light intensity of the beam emitted from the laser generator L is reflected by the half-mirror beam, and 2/3 is transmitted, resulting in the half-mirror beam.
At this point, 1/2 of the amount of light incident on Half Mira Day 2, that is, 1/3 of the total amount of light, is reflected, and the other 1/2 amount of light,
In other words, 1/3 of the total light is transmitted and reaches the total reflection mirror K, where it is totally reflected and as a whole each half mirror day, day 2
, the amount of light reflected from the total reflection mirror K is 1/3 of the amount of light emitted from the laser generator L, and the rotating mirrors R, in which laser beams with exactly the same amount of light are respectively arranged, correspond to each other.
, R2, and R3 in parallel. In the example, the case where the reflecting mirror group is composed of two half mirrors and one total reflection mirror is shown, but this reflecting mirror group is composed of n-1 half mirrors and one total reflection mirror. When configured with n reflecting mirrors K, the transmittance of each half mirror is sequentially n-1/n, n in the traveling direction of the laser beam.
If the beam is set to -2/n-1...1/2, the light intensity of the beam is divided into n equal parts, and each beam is incident on corresponding rotating mirrors R,, R2...Rn' with equal light intensity. That will happen. The rotating mirrors R, , R2, and R3 are respectively located on the areas M, , M2, and M3 of the strip M, and are at equal distances from the half mirrors, , 2, and the total reflection mirror K, respectively, in the conveying direction of the strip M. The rotating mirrors R, , R2, and R3 are driven by a drive source E via a transmission system T such as a timing belt, so that they are rotated in the same direction at the same speed. There is. Also, each rotating mirror R,,
Both R2 and R3 are formed in the shape of a hexagonal prism, and have reflective surfaces R, ′, R2′, and R3′ on the six outer surfaces, and each fin It is arranged parallel to the direction. Each half-mira day mentioned above,,
2. The laser beam reflected from the total reflection mirror K is located on the lower side of the rotating mirrors R, , R2, and R3, respectively, and on the straight strip M.
A reflective surface R,′, rotated to the side opposite to the surface.
The light enters R2' and R3', is reflected from there, and enters regions M, , M2, and M3 of the strip M, respectively.
While each rotating mirror R,, R2, R3 rotates by 60 degrees around the axis
, R3', the laser beam reflected from each reflecting surface R,', R2', R3' moves from the front end R^ in the rotational direction of the rotating mirror to the rear end RB in the rotational direction. In the width direction of each region M, M2, M3 of the strip M, for example, region M, the projection point sequentially moves within an angle of 1200 from one end 0 to the other end 02, as shown in FIG. Now, the pulsed laser beam with a firing period of 100 days2 is 1/6 Hz (1 rotation every 6 seconds).
If the laser beam is incident on the rotating mirrors R, , R2, R3 which are rotating at
From R^ to RB for each reflective surface R,', R2', R3'
Since each area of the strip M is incident 100 times and reflected toward the surface of the strip M, each area M,, M2,
The laser beam is projected at 100 locations in one scan for each M3, and approximately 30 locations can be detected over the entire width. If rotating mirrors R, , R2, and R3 are rotated, 1/3 Hz (
1 rotation per 3 seconds), each reflective surface R. ', R2'
, R3', the laser beam will be incident 50 times, and each area M, , M3 of the strip M will be searched for 5 lids in one scan, and the rotation speed of the rotating mirror must be adjusted. The number of flaw detection points can be adjusted by Therefore, it is possible to lower the rotational speed of the rotating mirrors R, . In addition, in the example, the rotating mirror R
, , R2, and R3 are shown as having a regular hexagonal prism shape, but they are not limited to this in any way, and may be appropriately selected from, for example, a regular octagonal prism shape or a regular la prism shape. In general, when using a regular m-prismatic rotating mirror, the reflection direction of the laser beam changes by 720o/m, and the smaller m is, the wider the projection area of the laser beam onto the strip M, or in other words, the wider the flaw detection area. As the flaw detection area becomes larger, the flaw detection area becomes narrower, so by changing this m, the flaw detection area can be arbitrarily adjusted.

Needless to say, the depth of the damage can be adjusted by changing the installation height of the rotary mirror from the surface of the strip M.

When a laser beam is projected onto the surface of the strip M, ultrasonic waves are generated at each projection point due to the impact during the projection, and are propagated within the strip M.

If there are no kinks in the strip M, the ultrasonic waves will reach the bottom surface of the strip M with normal attenuation depending on the thickness of the strip M. If there are kinks, the ultrasonic waves will be reflected here, and depending on the size of the eaves. It will be attenuated depending on the value and reach the lower surface of the strip M, or it will not reach the lower surface of the strip M at all. As is clear from FIG. 3, the incident angle of the laser beam reflected from each rotating mirror R, etc. and projected onto the surface of the strip M changes in the width direction of the strip M. It has been confirmed through experiments that the change in angle has almost no effect on the ultrasonic generation level.

Figure 4 shows a graph of the actual measured values in this experiment, with the incident angle (degrees) on the horizontal axis and the ultrasonic generation level (dB) on the vertical axis. ,
Although there is a slight tendency for the ultrasonic generation level to decrease as the incident angle increases, it can be seen that the decrease is very small and has almost no effect on flaw detection accuracy.
Although not shown, a static magnetic field is applied to the strip M by a permanent magnet or an electromagnet, and this strip M
When ultrasonic distortion is applied to the projection of a laser beam, eddy currents are generated.

The probe P is equipped with a flat coil that detects this eddy current, detects eddy current according to changes in the ultrasonic level, and outputs it to the ultrasonic flaw detector S (see Figure 2). do. The probe P is not in contact with the strip M, and although not shown in the drawings, it is equipped with a forced cooling mechanism to prevent overheating, and is not affected by the temperature of the strip M in any way. The ultrasonic wound instrument S is designed to amplify and detect the received signal and display it on a display device such as a cathode ray tube.

Since the number of projection points of the laser beam on the strip surface is 100 under the above-mentioned conditions, probes P may be arranged on the lower surface side of the strip M so as to correspond to each of these projection points. , an appropriate number of scanning probes P may be provided by using several Z projection points. These probes are then scanned electrically or mechanically. In the above-described embodiment, the total reflection mirror K was used to make the laser beam incident on the rotary mirror JR3, but instead of this, a half mirror may be used and all the reflecting mirror groups may be constituted by half mirrors.

In this case, the transmittance of each half mirror is different from that described above, but it goes without saying that the half mirror on the side of the laser generator L is made large so that the amount of light reflected to each rotating mirror is uniform. In this way, if everything is done using a half mirror, some laser beam will pass through and leak from the half mirror that replaces the total reflection mirror K, but this leaked beam is caused by the rotation of the rotating mirror and the probe P. It can be used as a synchronization signal with scanning operations. Furthermore, in the embodiment shown in the drawings, the probe P is disposed on the opposite side of the strip M to the rotating mirrors R, , R2, R3, and a transmission method is used in which the ultrasonic waves transmitted through the strip M are received. As shown, the flaw detector P is connected to the strip M using a rotating mirror R.
, , R2, R3 may be disposed on the same side as the strip M to receive the ultrasonic waves appearing in the laser beam projection direction. In addition, there are no particular limitations on the ultrasonic reception method, such as a method that uses the interference phenomenon of laser beams to detect the displacement of the surface of the strip, which is the object to be inspected, and receives distortion caused by ultrasonic waves. What is known can be selected as appropriate. As mentioned above, in the present invention,
Ultrasonic waves are generated on the surface of the object to be tested by projection of a laser beam and propagated within the object, so it is possible to perform flaw detection without contacting the object.
Not only can flaws be detected regardless of the temperature of the object to be inspected, but the number of detection points can be freely adjusted by adjusting the rotation speed of the rotating mirror, and the object to be detected can be divided into multiple areas for flaw detection, allowing for a wide range of flaws. It is possible to perform high-density flaw detection even on objects to be detected, improving the depth accuracy, and by changing the flaw detection pitch or number of points depending on the position in the width direction, flaw detection can be performed according to the needs of each layer. be able to.

Furthermore, the deep flaw area can be easily adjusted depending on the object to be inspected by adjusting the height of the rotating mirror relative to the object to be inspected or by adjusting the shape of the rotating mirror. Since the present invention uses a laser beam for ultrasonic oscillation and an electromagnetic ultrasonic probe for reception, lift-off is lower than in the conventional method that uses an electromagnetic ultrasonic probe for emission and reception. It has the advantage of being less affected by fluctuations.

In other words, according to the conventional method in which the oscillating electromagnetic ultrasonic probe and the receiving electromagnetic ultrasonic probe face both sides of the inspected material, the lift-off fluctuation for both probes of the inspected material is smaller than that of the one side. As a result, the effect is doubled because it acts as an increase on the probe and a decrease on the other side, but in the present invention, since the ultrasonic probe is used only on the receiving side, the effect of lift-off fluctuation is becomes less. As described above, the present invention has excellent effects.

[Brief explanation of drawings]

FIG. 1 is a plan view showing an embodiment of the method of the present invention and the apparatus used for carrying out the method, FIG. 2 is a side view of the same, and FIG. 3 is a partial front view of FIG. Figure 4 is a graph showing the relationship between the incident angle of the laser beam on the surface of the object to be tested and the ultrasonic generation level, Figure 5 is a perspective view showing the state of implementation of the conventional method, and Figure 6 is the implementation of another conventional method. It is a perspective view showing a state. E... Drive source, day,, day 2... half mirror, K...
- Total reflection mirror, M...Strip, R,, R2, R3...Rotating mirror, R,', R2', R3'...Reflecting surface. Figure 1 Figure 2 Figure 4 Figure 3 Figure 5 Figure 6

Claims (1)

[Scope of Claims] 1. A pulsed laser beam is made incident on a plurality of half mirrors disposed in its path, and a portion of the incident light is reflected at each, and the transmitted laser beams are sequentially made incident on a rear half mirror. , the laser beam reflected from each half mirror is incident on each rotating mirror whose reflection surface angle with respect to the object to be tested changes over time, and the laser beam reflected from each rotating mirror is directed to different areas on the surface of the object to be tested. Non-contact ultrasonic flaw detection characterized by projecting and scanning the object, propagating shock waves (ultrasonic waves) generated by the impact during projection into the object to be tested, and receiving the propagated waves with an electromagnetic ultrasonic probe. Method. 2. A pulsed laser generator, and a plurality of half mirrors disposed substantially parallel to each other so as to intersect the laser beam at substantially equal angles in the path of the laser beam generated by the laser generator. , a non-contact superstructure characterized by comprising a plurality of mirrors disposed in the respective paths of the laser beams reflected from each half mirror so as to change the angle of the reflecting surface with respect to the object to be inspected over time. Sonic flaw detection equipment. 3. The non-contact ultrasonic flaw detection device according to claim 2, wherein the transmittance of the half mirror increases as it approaches the laser generator.