JP3446288B2 - Ultrasonic method for detecting defects inside metal sheets - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting internal defects in a thin metal plate by ultrasonic waves.

[0002]

2. Description of the Related Art Generally, the ultrasonic flaw detection method is most suitable for detecting defects such as flaws inside a thin metal plate. In this method, ultrasonic waves are propagated inside the material and disturbances in ultrasonic wave propagation due to flaws are detected. For example, FIG.
As shown in, the ultrasonic transmitter 11 and the ultrasonic receiver 12 are arranged so as to face each other with the metal thin plate 1 interposed therebetween, and the ultrasonic wave 51 is vertically transmitted from the transmitter 11 to the receiver 12, and the ultrasonic wave 51 is transmitted. This is a method of detecting weakening of transmitted ultrasonic waves 52 that is caused by reflection and scattering due to defects inside the thin metal plate 1 (hereinafter referred to as a transmission type ultrasonic flaw detection method). Water 2 is interposed between the transmitter 11 and the metal thin plate 1 and between the metal thin plate 1 and the receiver 12.

As another method, as shown in FIG. 7, an ultrasonic wave 51 is transmitted from a transmitter / receiver 13 which also serves to transmit and receive ultrasonic waves.
Is transmitted vertically to the metal thin plate 1, the bottom surface reflected ultrasonic wave 53 reflected by the bottom surface of the metal thin plate 1 is received, and weakness due to a defect of the bottom surface reflected ultrasonic wave 53 is detected to detect a flaw. (Hereinafter referred to as bottom surface echo loss type ultrasonic flaw detection method)
(For example, Irie et al. “Basic Experiment for Continuous Inspection of Fine Inclusions by Ultrasonic Focusing Probe Method (CAMP-ISIJ Vol.2, (1
989) -1452) ").

Further, as an application example of this reflection type ultrasonic method, as shown in FIG. 8, a transmitter 11 and a receiver 12 are arranged on the same surface side with respect to the thin metal plate 1, and the transmitter 11 is predetermined. The ultrasonic wave 51 transmitted at the inclination angle θ of is reflected by the bottom surface of the metal thin plate 1, and the bottom surface reflected ultrasonic wave 53 is received by the receiver 12, and the bottom surface is generated by being reflected and scattered by the defect inside the metal thin plate 1. There is a method of detecting weakening of the reflected ultrasonic wave 53 (hereinafter referred to as a V transmission type ultrasonic flaw detection method).

[0005]

However, in any of the above-mentioned conventional ultrasonic flaw detection methods, the detectability is determined by the size of the ultrasonic beam diameter, so that the defect size is smaller than the ultrasonic beam diameter. When it becomes smaller, there is a drawback that the detectability is extremely lowered. That is, now the sender
11, frequency 25MHz, transducer diameter 6mm, underwater focal length
If a 24 mm ultrasonic probe is used, if the thin metal plate 1 is a steel plate, the ultrasonic beam diameter in the steel plate is about 1 mm, and sufficient detectability is obtained for defects larger than this. However, for example, in the case of a defect with a diameter of 0.5 mm, even if it is assumed that this defect does not transmit ultrasonic waves at all, the drop in the amplitude of transmitted ultrasonic waves due to this defect will be as small as about 2.5 dB.

The present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is to provide a method for detecting defects inside a metal thin plate by ultrasonic waves, which enhances the detectability of small defects.

[0007]

The present invention is a method for detecting an internal defect in a thin metal plate using ultrasonic waves, in which ultrasonic waves are transmitted to and received from the thin metal plate, and the received ultrasonic waves are transmitted at a predetermined time from the time of ultrasonic wave transmission. Extraction is performed by the first gate means that opens for a predetermined time t _M1 after the time t _D1 , and it is determined that there is a defect when the amplitude of the extracted ultrasonic wave is below a predetermined level L ₁ , and the first gate is used. When it is determined that the amplitude of the ultrasonic wave extracted by the means exceeds a predetermined level L ₁ , 1
A second gate signal is generated by the second gate means for generating the next determination signal, and opening the predetermined time t _M2 after the predetermined time t _D2 has elapsed from the generation of the primary determination signal .
A method of detecting defects inside a metal thin plate by ultrasonic waves, characterized in that it is judged that there is a defect when the amplitude of the extracted signal is below a predetermined level L ₂ .

[0008]

[Operation] The inventors of the present invention have conducted the following experiments and researches to solve the above-mentioned problems, and have obtained the following findings, and have completed the present invention based on the findings. That is, FIG. 9 shows signals of transmitted ultrasonic waves or bottom surface reflected ultrasonic waves when a thin metal plate is flaw-detected by the above-mentioned transmission type ultrasonic flaw detection method, bottom echo loss type ultrasonic flaw detection method or V transmission type ultrasonic flaw detection method. The waveform is shown in (a)
Shows the waveform of the defect-free portion, and (b) shows the waveform of the defective portion smaller than the ultrasonic beam diameter.

As a result of comparing and observing the two, when the area (S) of the defect is smaller than the ultrasonic beam diameter (d), the waveform of the transmitted ultrasonic wave or the bottom surface reflected ultrasonic wave starts from its rising time t. Until the passage of ₁ , its amplitude is S
/ D, that is, by A%. However, it was found that the width B% of the decrease in amplitude becomes larger than A% after the lapse of time t ₁ , and reaches about 3 times the size of A in some cases.

This is because the transmitted ultrasonic wave or bottom surface reflected ultrasonic wave which is not blocked by the defect is overlapped with the transmitted ultrasonic wave or the bottom surface reflected ultrasonic wave which wraps around the edge of the defect, and the phases of the two are different, so that the amplitude is canceled. It is considered that this is due to the occurrence of a match. Therefore, by detecting the amplitude of the transmitted ultrasonic wave or the bottom surface reflected ultrasonic wave only after the lapse of time t ₁ and comparing the amplitude with the amplitude of the defect-free ultrasonic wave, when the level is low, “defect” is detected. Since it can be determined that there is a defect, the detectability of a defect smaller than the ultrasonic beam diameter can be enhanced.

[0011]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing an embodiment in which the method of the present invention is applied to a transmission ultrasonic flaw detector.
In the figure, the same elements as those of the conventional example are designated by the same reference numerals and the description thereof will be omitted.

As shown in the figure, the transmitter 11 and the receiver 12 are arranged so as to face each other with the metal thin plate 1 interposed therebetween. An electric pulse is applied by an electric pulse transmitter 14 to an ultrasonic transducer (not shown) of the transmitter 11, and an ultrasonic wave 51 is transmitted. On the other hand, the transmitted ultrasonic wave 52 received by the receiver 12 is received by the receiving amplifier 15.
Is amplified by and output to the defect determination device 20. Reference numeral 16 is a synchronization signal generator that generates a synchronization pulse 60 for periodically transmitting and receiving the ultrasonic waves 51, and outputs the synchronization pulse 60 to the electric pulse transmitter 14 and the defect determination device 20.

Here, the structure of the defect determining device 20 will be described in detail with reference to FIG. As shown in the figure, the defect determining device 20 includes a first gate circuit 21 that passes only the primary signal 61 of the transmitted ultrasonic wave 52 output from the reception amplifier 15, and the transmission extracted by the first gate circuit 21. Ultrasonic 52 of 1
The first level discriminator 22 for judging by comparing the amplitude of the next signal 61 with a predetermined level L ₁ and 1 from the first level discriminator 22
A secondary signal 63 which is a part of the primary signal 61 of the transmitted ultrasonic wave 52 extracted by the first gate circuit 21 in response to the next determination signal 62.
Second gate circuit 23 for passing through the second gate circuit 23
A second level determiner 24 that compares the amplitude of the secondary signal 63 of the transmitted ultrasonic wave 52 from a predetermined level L ₂ to make a determination;
A first AND circuit 25 that produces an AND signal 65 of the outputs of the first level determiner 22 and the second level determiner 24, and a delay pulse generation circuit 26 that produces a delay signal 66 from the output pulses of the first AND circuit 25. An inverter 27 that inverts the output of the delay pulse generation circuit 26, and a second AND circuit 28 that produces a defect detection signal 68 formed by ANDing the inversion signal 67 output from the inverter 27 and the synchronization signal 60.

The operation of the transmission ultrasonic flaw detector of the present invention will be described below with reference to the time charts of FIGS. 3 and 4 and 5. Note that FIG. 3 shows the case of FIG.
If there is a defect smaller than the diameter of the ultrasonic beam,
Shows the case where there is a defect larger than the diameter of the ultrasonic beam. In any case, it is assumed that there was no defect in the immediately preceding ultrasonic wave transmission / reception. (1) The electric pulse transmitter 14 receives the periodic synchronizing pulse 60 from the synchronizing signal generator 16 and outputs a pulsed high voltage electric signal to the transmitter 11. (2) When a high-voltage electric signal is applied to the built-in ultrasonic transducer, the transmitter 11 transmits an ultrasonic wave 51 to the thin metal plate 1 which is the material to be inspected. (3) The transmitted ultrasonic wave 52 transmitted through the thin metal plate 1 is received by the receiver 12, appropriately amplified by the receiving amplifier 15, and output to the first gate circuit 21. (4) The first gate circuit 21, whose operation timing is controlled, transmits the transmitted ultrasonic wave 52 output from the reception amplifier 15,
After receiving the synchronization pulse 60 from the synchronization signal generator 16, allow a predetermined time t _M1 after a predetermined time t _D1 has passed,
Only the primary signal 61 of the transmitted ultrasonic wave 52 is extracted. (5) The first level determiner 22 receives the transmitted transmitted ultrasonic wave 52.
Of the primary signal 61 of the predetermined level L ₁
When it is determined that the value exceeds, the primary determination signal 62 is output.
This determination signal 62 partially becomes high level HL when there is no defect (FIG. 3) and when it is smaller than the ultrasonic beam diameter (FIG. 4), and when there is a defect larger than the ultrasonic beam diameter (FIG. 5). Remains at the low level LL. (6) Transmitted ultrasonic wave 52 extracted by the first gate circuit 21
The primary signal 61 of is also introduced to the second gate circuit 23,
After receiving the primary determination signal 62, the gate circuit 23 of FIG. 1 passes the primary signal 61 of the transmitted ultrasonic wave 52 extracted by the first gate circuit 21 for a predetermined time t _M2 after the predetermined time t _D2. Of the primary signal 61 of the transmitted ultrasonic wave 52, only the secondary signal 63 of a portion having a large amplitude change due to a small defect is extracted. (7) The second level determiner 24 outputs the secondary determination signal 64 when determining that the amplitude of the extracted secondary signal 63 exceeds the predetermined level L ₂ . The secondary determination signal 64 is a signal that partially becomes high level HL when there is no defect,
In other cases, that is, when there is a defect, low level L
It is in the L state. (8) The primary judgment signal 62 and the secondary judgment signal 64 are the first AN
It is input to the D circuit 25 and an AND signal 65 of both signals is produced. The AND signal 65 is a pulse signal which becomes the high level HL only when there is no defect. (9) The AND signal 65 is guided to the delay pulse generation circuit 26, and the delay signal 66 is created using a monostable multivibrator or the like. The delay signal 66 actually becomes a pulse signal only when there is no defect, and when there is a defect, it is in the low level LL state. (10) The delayed signal 66 is further inverted by the inverter 27,
This inversion signal 67 is ANDed with the synchronization pulse 60 from the synchronization signal generator 16 in the next second AND circuit 28. Only when there is a defect, the inversion signal 67 is output as the defect detection signal 68 which becomes the high level HL at the same timing as the synchronizing pulse 60.

Using a transmission ultrasonic flaw detector of the present invention, flaw detection of a thin metal plate having a thickness of 0.8 mm was performed.
It becomes possible to detect defects of ^-2 mm ² , and the detectability is improved compared to the detection limit of the defect area of 5 × 10 ^-1 mm ^{2 in} the conventional transmission ultrasonic flaw detector. found. In addition, in the above-described embodiment, the case where the invention is applied to the transmission type ultrasonic flaw detection method has been described, but the present invention is not limited to this, and is applicable to the bottom surface echo loss type ultrasonic flaw detection method and the V transmission type ultrasonic flaw detection method. It goes without saying that it can be applied.

[0016]

As described above, according to the present invention,
Since the internal defect of the thin metal plate can be detected with high detectability, it can be effectively used for quality control and its guarantee in the production of the thin metal plate, and its industrial value is enormous.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment in which the method of the present invention is applied to a transmission ultrasonic flaw detector.

FIG. 2 is a block diagram showing a configuration of a defect determination device used in the present invention.

FIG. 3 is a characteristic diagram showing each signal level when there is no defect.

FIG. 4 is a characteristic diagram showing each signal level when the size of a defect is smaller than the diameter of an ultrasonic beam.

FIG. 5 is a characteristic diagram showing each signal level when the size of the defect is larger than the diameter of the ultrasonic beam.

FIG. 6 is an explanatory diagram of a transmission type ultrasonic flaw detection method.

FIG. 7 is an explanatory diagram of a bottom surface echo loss type ultrasonic flaw detection method.

FIG. 8 is an explanatory diagram of a V transmission type ultrasonic flaw detection method.

9A is a waveform of a transmitted ultrasonic wave or a bottom surface reflected ultrasonic wave in a defect-free portion, and FIG. 9B is a waveform of a transmitted ultrasonic wave or a bottom surface reflected ultrasonic wave in a defective portion smaller than an ultrasonic beam diameter. It is a characteristic view which shows a waveform.

[Explanation of symbols]

1 thin metal plate 2 water 11 sender 12 receiver 13 transceiver 14 Electric pulse transmitter 15 Receiver amplifier 16 Sync signal generator 20 Defect determination device 21 First gate circuit 22 First level judge 23 Second gate circuit 24 Second level determiner 25 First AND circuit 26 Delay pulse generator 27 Inverter 28 Second AND circuit 51 ultrasound 52 transmitted ultrasound 53 Bottom reflected ultrasound 60 sync pulses 61 Primary signal 62 Primary judgment signal 63 Secondary signal 64 Secondary judgment signal 65 AND signal 66 delayed signal 67 Inverted signal 68 Defect detection signal

─────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-61-97565 (JP, A) JP-A-60-249052 (JP, A) JP-A-52-17879 (JP, A) JP-A-3- 125961 (JP, A) Actual development Sho 59-23661 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01N 29/00-29/28

Claims (3)

(57) [Claims] 1. A method of detecting an internal defect of a metal thin plate using ultrasonic waves, wherein ultrasonic waves are transmitted / received to / from the metal thin plate, and a predetermined time t _D1 has elapsed from a time point at which the received ultrasonic waves are transmitted, extracted by the first gate means for opening time t _M1, extracted amplitude of the ultrasonic are determined to be defective when below a predetermined level L _1, ultrasound extraction by the first gate means ultra predetermined level L ₁ amplitude
When it is determined that the signal has been obtained, the primary determination signal is generated.
Then, after a lapse of a predetermined time t _D2 from the generation of the primary determination signal, a part of the ultrasonic signal is extracted by the second gate means which opens for a predetermined time t _M2 , and the amplitude of the extracted signal is predetermined. The method for detecting an internal defect of a metal thin plate by ultrasonic waves is characterized in that it is determined that there is a defect when the level is lower than the level L ₂ . 2. The method according to claim 1, wherein the ultrasonic waves used for the reception are transmitted ultrasonic waves transmitted through the metal thin plate. 3. The method according to claim 1, wherein the ultrasonic wave used for the reception is a reflected ultrasonic wave reflected from a thin metal plate.