JP3653785B2 - C-scan ultrasonic flaw detection method and apparatus - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a C-scan ultrasonic flaw detection method and apparatus, and more particularly to a C-scan ultrasonic flaw detection method and apparatus suitable for use in detecting an internal defect of about 10 to 100 μm in a cut sample of a rolled metal sheet. It is.
[0002]
[Prior art]
In recent years, thin steel sheets used as materials for automobiles, cans, etc. have been made thinner in order to reduce weight and reduce material costs, and to reduce production costs by reducing the number of parts and materials used in processing such as pressing and drawing. Strong processing with significant deformation of the material is applied. When performing strong processing on the steel sheet, cracks occur if there are internal defects consisting of non-metallic inclusions, etc., in the part where the deformation is significant, but the occurrence of cracks due to internal defects becomes more pronounced as the thickness of the steel sheet is thin, and The size of internal defects that cause cracking is also reduced. There is also a relationship between the form of defects and the occurrence of cracks. Defect forms include spherical single bodies, single bodies that extend in one direction, and aggregates of microspherical defects. Is seen. In addition, products with severe usage conditions such as thick steel plates used in sour gas line pipes are increasing, and even small inclusions with a size of about 10 μm are considered to be harmful and cause hydrogen-induced cracking. Ease of occurrence is different. For this reason, it is required that the above-described steel sheet has as few internal defects as possible, and that the defect form is less likely to be cracked. It is necessary to do.
[0003]
As a means for detecting the internal defect of such a steel sheet and evaluating its form, a part of the product is cut out as a sample, and the internal defect in this sample is detected using a device called a C-scan ultrasonic flaw detector. Has been widely used. FIG. 9 shows a flaw detection method using a conventional C-scan ultrasonic flaw detector.
That is, the point-focusing type ultrasonic transceiver 102 above the inspection plate 101 immersed in the solvent liquid is scanned by the scanning device 104 that is moved by the signal of the controller 114 and is spaced from the electric pulse generator 116 at a constant time interval. The electrical pulse transmitted in step 1 is converted into an ultrasonic wave, and the ultrasonic beam 103 is transmitted substantially vertically toward the inspected plate 101, and the internal defect of the inspected plate 101 and the reflected wave from the surface are received. Convert to signal. The received signal is amplified by the receiving amplifier 111, and the reflected wave from the defect is extracted by the gate circuit 112. The extracted signal is sent to the peak value detection circuit 113, where the amplitude of the defect reflected wave is detected and transmitted to the controller 114. The controller 114 outputs the amplitude of the defect reflected wave and the position signal of the scanning device 104 to the display 115, and the display 115 displays a two-dimensional distribution map of the internal defects, thus detecting the internal defects. .
[0004]
In such a method in which ultrasonic waves are transmitted substantially perpendicularly to the inspected plate 101 by one point-focusing type ultrasonic transmitter / receiver 102 and a reflected wave from the inspected plate 101 is received to detect a defect, an ultrasonic beam is used. When a surface is incident on the surface, a surface echo having a large amplitude and reverberation is generated for a while, so that a defect reflected wave in the vicinity of the surface overlaps the surface echo or the reverberation, and the presence cannot be identified. There was a problem that it was not possible to detect defects.
[0005]
Further, as conventional techniques relating to a C-scan ultrasonic flaw detection method or apparatus, there are JP-A-59-17153 and JP-A-5-333000 which use high-frequency ultrasonic waves. The former is 30 to 100 MHz, and the latter is 15 to 50 MHz, both using high frequency ultrasonic waves and reducing the beam diameter, thereby improving resolution and improving internal defect detection ability. The latter also optimizes the ultrasonic frequency, focal length, and the relationship between the inspected plate and the focal position, thereby ensuring the detection of minute defects existing near the surface and enabling quantitative evaluation of flaw detection results. It is a thing.
[0006]
[Problems to be solved by the invention]
However, as described in JP-A-59-17153 and JP-A-5-333000, it is generally known that when the focal beam diameter is reduced using high-frequency ultrasonic waves, the depth of focus decreases. (See, for example, R. Saglio et al "THE USE OF FOCUSED PROBES FOR DETECTION, IMAGING, AND SIZING OF FLAWS", in Proc. First Intrenational Symposium on Ultrasonic Materials Characterization-Gaithersburg Md. (1978)).
[0007]
The depth of focus is, for example, the length of the range in which the sound pressure on the central axis of the ultrasonic beam to be transmitted and received is within −6 dB compared to the sound pressure at the focus position, and the greater the depth of focus, the greater the depth of focus. It is possible to detect internal defects over a wide range in the direction of the plate thickness of the plate to be inspected. According to the above document, when the frequency of ultrasonic waves is f, the velocity is C, the diameter of the transducer built in the ultrasonic transceiver is D, and the focal length is F, the ultrasonic beam diameter d at the focal position is as follows. And the focal depth L are expressed by the equations (1) and (2), respectively.
[0008]
d = (C / f) × (F / D) (1)
L = (C / f) × (F / D)²                  ………………… (2)
From the equation (1), it can be seen that when the frequency f is increased in order to reduce the ultrasonic beam diameter d at the focal position, the focal depth L is reduced from the equation (2). For this reason, in flaw detection using high-frequency ultrasonic waves, it is difficult to detect the entire cross section in the plate thickness direction of the inspected plate with uniform sensitivity, and the ability to detect defects existing at depths other than the focal position is greatly reduced. There is a drawback in that detection omissions occur frequently. For this reason, in order to detect a defect without omission in the thickness direction, it is necessary to change the focal position and perform the flaw detection as many times as necessary.
[0009]
In the above-mentioned Japanese Patent Application Laid-Open No. 5-333000, although the dead zone directly under the surface is reduced, it cannot be said that there is none, and the fine defect still exists in the vicinity of the surface in the C-scan ultrasonic flaw detection by the vertical flaw detection method. The problem remains that cannot be detected.
By the way, in order to solve the above-mentioned problems, the present inventors have already faced the line focus type ultrasonic transmission sensor and the one-dimensional array type ultrasonic sensor with Japanese Patent Application No. 6-7176 across the board to be inspected. And transmitting a band-like ultrasonic beam from the transmitting sensor toward the inspection plate substantially perpendicularly, and reflecting a reflected wave from an internal defect caused by the ultrasonic wave incident on the inspection plate to the one-dimensional array type ultrasonic wave. Proposing an ultrasonic flaw detection method and apparatus characterized by detecting the presence or absence of a reflected wave that has reached a predetermined amplitude after amplifying the received ultrasonic wave received by a receiving sensor and extracting only the reflected wave, As a result, it became possible to detect a linear region having a constant width all over the thickness without a dead zone immediately below the surface.
[0010]
However, with this method, the presence or absence of a minute defect can be clearly seen, but since the ultrasonic waves to be transmitted and received are not two-dimensionally focused, the resolution in the width direction is low, and there is a problem that the form of the defect cannot be identified. It was.
The present invention has been made to solve the problems of the prior art, and in C-scan ultrasonic flaw detection, there is no dead band near the surface of the plate to be inspected, and flaw detection in the entire cross section in the plate thickness direction in one scan. It is an object of the present invention to provide a C-scan ultrasonic flaw detection method and apparatus capable of detecting even fine internal defect forms.
[0011]
[Means for Solving the Problems]
  The present invention scans a point-focusing type ultrasonic transmitter and a point-focusing type ultrasonic wave receiver facing each other with a test plate immersed in a liquid interposed between the ultrasonic transmitter and the ultrasonic transmitter. Point-focused ultrasonic waves are incident almost perpendicularly into the inspected plate, and the ultrasonic waves are reflected on the upper side of the internal defect and directed to the surface of the inspected plate, reflected on the surface, and propagated from the back surface into the liquid. The reflected wave to be received and the reflected wave that is first reflected on the back surface of the inspection plate, directed to the internal defect, reflected on the lower side of the internal defect, and then propagated into the liquid from the back surface and received.BothFrom the internal defect from the amplified signal.BothA C-scan ultrasonic flaw detection method characterized in that a reflected wave signal is extracted and an internal defect of a plate to be inspected is detected based on the extracted signal.
[0012]
  The signal of the reflected wave from the internal defect is expressed as τ when the transmitted wave of the ultrasonic wave reaches the ultrasonic receiver.₀age,The time from the arrival of the directly transmitted wave to the end of the reverberation of the transmitted wave is expressed as τ _D age,The time required for the ultrasonic wave to propagate in the thickness direction of the plate to be inspected is τ₁WhendidWhenTimes of Day(Τ₀+τ _D ) And after (τ₀+ 2 × τ₁) It is better to extract from the previous received signal.
[0013]
Further, the focal lengths of the ultrasonic transmitter and the ultrasonic receiver are compared. If the focal lengths are different, the larger focal length is set to F._LOr if the focal lengths are equal, the focal length is F_LAnd the distance L between the ultrasonic transmitter and the ultrasonic receiver, where t is the thickness of the plate to be inspected_SAre preferably arranged so that the following equation is satisfied.
[0014]
    L_S≦ F_L-{(C_M/ C_L) -1} × t + F_L× 5/38
  However, C_M; Ultrasonic wave propagation speed in the material to be inspected, C_LThe propagation speed of ultrasonic waves in the liquid.
  The present invention also provides a point-focusing ultrasonic transmitter that transmits ultrasonic waves substantially vertically to the surface of the board to be inspected, and a position facing the point-focusing ultrasonic transmitter across the board to be inspected. Then, the ultrasonic wave is reflected on the upper side of the internal defect and directed to the surface of the inspected plate, reflected on the surface, propagated from the back surface into the liquid and received, and the ultrasonic wave is first inspected. Reflected wave that reflects on the back side of the plate, faces the internal defect, reflects on the lower side of the internal defect, then propagates into the liquid from the back side and is receivedBothA point-focusing type ultrasonic receiver, a support arm that supports the ultrasonic transmitter and the ultrasonic receiver with an inspection plate interposed therebetween, a scanning device that scans the support arm, and the ultrasonic An electric pulse generator for generating an electric pulse to be transmitted to a piezoelectric vibrator incorporated in the acoustic wave transmitter, an amplifying device for amplifying a received signal, and an amplified signal from an internal defectBothReflected waveSignalAnd a C-scan ultrasonic flaw detector characterized by comprising:
  The gate means uses the reflected wave signal from the internal defect as a time τ when the transmitted ultrasonic wave reaches the ultrasonic receiver.₀age,The time from the arrival of the directly transmitted wave to the end of the reverberation of the transmitted wave is expressed as τ _D age,The time required for the ultrasonic wave to propagate in the thickness direction of the plate to be inspected is τ₁WhendidWhenTimes of Day(Τ₀+τ _D ) And after (τ₀+ 2 × τ₁) A distance L between the ultrasonic transmitter and the ultrasonic receiver that is set to extract from the previous received signal._SCompares the focal lengths of the ultrasonic transmitter and the ultrasonic receiver, and if the focal lengths are different, the larger focal length is F_LOr if the focal lengths are equal, the focal length is F_LAnd the thickness of the board to be inspected is t, and both should be arranged so as to satisfy the following formula.
    L_S≦ F_L-{(C_M/ C_L) -1} × t + F_L× 5/38
  However, C_M; Ultrasonic wave propagation speed in the material to be inspected, C_LThe propagation speed of ultrasonic waves in the liquid.
[0015]
[Action]
According to the present invention, a point-focusing type ultrasonic transmitter and a point-focusing type ultrasonic receiver are arranged to face each other with a test plate immersed in a liquid interposed therebetween, and the ultrasonic transmission is performed. Ultrasound that has been point-focused from the child is incident substantially perpendicularly into the inspected plate, and the ultrasonic wave transmitted by the ultrasonic wave and the reflected wave from the internal defect generated by the ultrasonic wave are received by the ultrasonic wave receiver. Since the signal of the reflected wave from the internal defect is extracted from the amplified signal, and the internal defect of the inspection board is detected based on the extracted signal, the vicinity of the front and back surfaces of the inspection board It is possible to detect even an internal defect with a uniform sensitivity over the entire cross section without a dead zone.
[0016]
【Example】
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram including a partial perspective view showing the configuration of an embodiment of the present invention.
In FIG. 1, 11 is a point-focusing ultrasonic transmitter (hereinafter simply referred to as an ultrasonic transmitter), 12 is a point-focusing ultrasonic receiver (hereinafter simply referred to as an ultrasonic receiver), Oppositely arranged with a sandwich. Reference numeral 14 denotes a U-shaped support arm that supports the ultrasonic transmitter 11 and the ultrasonic receiver 12. Note that water that is suitably used as an ultrasonic propagation medium is interposed between the ultrasonic transmitter 11 and the ultrasonic receiver 12 and the board 13 to be inspected. A scanning device 15 scans the support arm 14.
[0017]
Reference numeral 16 denotes an electric pulse generator that transmits electric pulses from a built-in clock circuit (not shown) to a piezoelectric vibrator (not shown) built in the ultrasonic transmitter 11 at regular time intervals. Reference numeral 17 denotes a receiving amplifier that receives a signal from the ultrasonic receiver 12, 18 denotes a gate circuit, 19 denotes a peak value detection circuit, 20 denotes a controller, and 21 denotes a display.
The ultrasonic transmitter 11 converts the electric pulse transmitted from the electric pulse generator 16 at a predetermined time interval into an ultrasonic wave, and transmits the ultrasonic transmission beam 11A substantially perpendicularly to the inspected plate 13 through water. . The ultrasonic receiver 12 receives an ultrasonic reception beam 12A including a reflected wave from an internal defect caused by the ultrasonic wave incident on the inspection plate 13 through water. Then, the support arm 14 is scanned by the scanning device 15 driven by a signal from the controller 20, and the ultrasonic transmitter 11 and the ultrasonic receiver 12 which are arranged to face each other are squarely scanned on the surface of the inspected plate 13. Investigate its internal defects.
[0018]
The received signal amplified by the receiving amplifier 17 is extracted by the gate circuit 18 from the received signal. The extracted signal is transmitted to the peak value detection circuit 19, and the peak value detection circuit 19 detects the amplitude of the reflected wave and outputs it to the controller 20 as an analog amount or a digital amount. The controller 20 outputs the amplitude of the reflected wave and the position signal of the scanning device 15 to the display 21 to create a two-dimensional distribution map of internal defects.
[0019]
Here, the function of the gate circuit 18 will be described in detail with reference to FIG.
First, when the thickness of the inspected plate 13 is t and the internal defect 22 is near the surface 13a of the inspected plate 13, that is, the distance d from the surface 13a is equal to or less than t / 2, ultrasonic transmission is taken as an example. When the ultrasonic transmission beam 11A transmitted from the child 11 propagates in the liquid and reaches the surface 13a of the inspected plate 13, it enters the inspected plate 13 and propagates therein.
[0020]
At this time, a part of the ultrasonic wave propagated inside the board to be inspected 13 travels straight and is received by the ultrasonic receiver 12 as a direct transmitted wave 30. Further, when the internal defect 22 exists in the ultrasonic wave propagation path, first, it is reflected once on the upper side of the internal defect 22, directed to the surface 13 a, reflected by the surface 13 a, and within the thickness t of the inspected plate 13. 0.5 reciprocally propagates, and the reflected wave 31 propagates from the back surface 13b into the liquid and is received, and first propagates 0.5 reciprocally within the thickness t of the plate to be inspected and is reflected by the back surface 13b toward the internal defect 22, After being reflected once under the defect 22, a reflected wave 32 is generated which propagates from the back surface 13 b into the liquid and is received.
[0021]
The reflected waves 31 and 32 are further reflected once or more on the back surface 13b, and the reflected wave received by the ultrasonic receiver 12 is generated one or more times within the thickness t of the board 13 to be inspected. However, illustration is omitted here. As described above, the present invention extracts the reflected wave signal from the internal defect from the received and amplified signal, and detects the internal defect based on the extracted signal. When the internal defect 22 has a distance d from the surface 13a of the inspection plate 13 of t / 2 or less, the reflected wave 32 reaches the ultrasonic receiver 12 later than the reflected wave 31.
[0022]
Further, the temporal transition of the signal received by the ultrasonic receiver 12 will be described with reference to FIG. In this figure, τ₀Is the time when the directly transmitted wave 30 that has propagated 0.5 reciprocating times within the thickness t of the inspected plate 13 reaches the ultrasonic receiver 12, τ₁Is the time required for the ultrasonic wave to propagate 0.5 reciprocating times within the thickness t of the plate 13 to be inspected. Reference numeral 33 denotes a transmitted wave signal that travels 0.5 reciprocatingly within the thickness t of the inspected plate 13 and then reciprocates once through the inspected plate 13.
[0023]
Thus, since the propagation distance of the reflected wave 32 is larger than the propagation distance of the reflected wave 31, the reflected wave 32 is received later than the reflected wave 31. From this figure, the reflected wave 32 due to the internal defect 22 is the time τ when the directly transmitted wave 30 that has propagated 0.5 reciprocatingly within the thickness t of the inspected plate 13 reaches the ultrasonic receiver 12.₀From the time τ required for the ultrasonic wave to propagate 0.5 times in the thickness t of the plate to be inspected τ₁After a lapse of time and appearing outside the dead zone region due to the direct transmitted wave 30, and at time τ₀To (2 × τ₁) Appears before the passage and earlier than the transmitted wave 33. Further, the closer the position of the internal defect 22 is to the surface 13a, the τ₂(Τ₂Is smaller than the distance d required to propagate the distance d to the internal defect 22 in the inspected plate 13 (that is, the time required for propagation by the distance 2d), but appears earlier than the transmitted wave 33. Therefore, even if the internal defect 22 exists directly under the surface 13a, the reflected wave 32 caused by the internal defect 22 can be clearly identified and extracted. Therefore, it is preferable to extract this and detect the internal defect 22.
[0024]
The time τ when the reflected wave 32 appears due to the internal defect 22 is expressed by the following formula (3).
(Τ₀+ Τ₁) ≦ τ ≦ (τ₀+ 2 × τ₁) ……………… (3)
The time from the arrival of the direct transmitted wave 30 to the end of the reverberation of the transmitted wave is expressed as τ_D(See FIG. 3), the time (τ₀+ Τ_D) And after (τ₀+ 2 × τ₁) If the previously received signal is extracted, it is possible to detect both the reflected waves 31 and 32.
[0025]
The above description is about the case where the internal defect exists near the front surface. Next, the case where the distance d from the front surface 13a is located near the rear surface 13b, that is, at a position where the distance d is t / 2 or more will be described. In this case, unlike FIG. 2, the propagation distance of the reflected wave 31 due to the internal defect 22 is longer than the propagation distance of the reflected wave 32, so that the reflected wave 31 is received with a delay. As described above, the reflected wave 31 appears outside the dead zone region due to the direct transmitted wave 30 and appears earlier than the transmitted wave 33. Therefore, even if the internal defect 22 exists directly under the back surface 13b, the reflected wave 31 due to the internal defect 22 can be clearly identified and extracted, so that the internal defect 22 can be detected and is preferable.
[0026]
As explained so far, the direct propagation wave 30 that has propagated 0.5 reciprocatingly through the plate 13 to be inspected and the transmitted wave 33 that has propagated 1 reciprocating propagation through the substrate 13 to be inspected from the internal defect with the longer propagation distance. It is more preferable to extract the reflected wave because the noise component that makes noise is small. However, the ultrasonic wave propagates 0.5 times reciprocatingly through the board 13 to be inspected, and further propagates through the board 13 to be reciprocated an integer number of times. A reflected wave from an internal defect having a longer propagation distance appearing between the wave and the transmitted wave that has propagated one reciprocating propagation through the inspection target plate 13 may be extracted.
[0027]
In the present invention, a two-dimensionally focused point-focusing ultrasonic transmitter and a point-focusing ultrasonic receiver are used, and the ultrasonic transmitter and the ultrasonic receiver are scanned relative to the inspected plate. Therefore, the resolution in the width direction is high, and the form of internal defects can be detected.
Further, in the present invention, as shown in FIG. 4, the ultrasonic transmission beam 11A from the ultrasonic transmitter 11 is focused on the surface of the ultrasonic receiver 12, and the ultrasonic wave of the ultrasonic receiver 12 is set. The focal point G of the reception beam 12A may be the surface of the ultrasonic transmitter 11. In this way, the intensity of the ultrasonic transmission beam 11A transmitted from the ultrasonic transmitter 11 becomes lower as it approaches the surface of the inspected plate 13, so the intensity of the reflected wave from the internal defect existing there is small. On the other hand, since the reception efficiency of the ultrasonic receiver 12 is larger near the focal point F, it becomes larger as it is closer to the surface of the inspected plate 13. Therefore, the intensity of the reflected wave from the internal defect received by the ultrasonic receiver 12 can be made almost constant even if the position where the internal defect exists is changed by canceling the effect of both, and the thickness direction This is because the sensitivity can be uniform over the entire area.
[0028]
FIG. 5 shows the result of detecting an artificial defect by the method of the present invention and the conventional method. That is, the method of the present invention was measured using an ultrasonic transmitter 11 and an ultrasonic receiver 12 having a frequency of 25 MHz and an underwater focal length of 38 mm arranged so that the focal points F and G are connected as shown in FIG. In the conventional method, as shown in FIG. 9, the measurement is performed by transmitting and receiving ultrasonic waves from one direction to one point focusing type with a frequency of 25 MHz and an underwater focal length of 38 mm. It is what. The artificial defect was manufactured by changing the distance from the surface of the inspected plate 13 having a thickness of 5.5 mm and making a 0.2 mmφ horizontal drill hole perpendicular to the thickness direction.
[0029]
From this figure, compared with the conventional method, the method of the present invention has a constant amplitude of the reflected wave regardless of the distance from the surface of the defect, has a remarkably excellent focal depth, and is uniform over the thickness direction. It can be seen that it can be detected with sensitivity.
Next, the positional relationship among the point-focusing type ultrasonic transmitter 11, the point-focusing type ultrasonic receiver 12, and the inspected plate 13 will be described in detail based on experimental data. That is, in FIG. 6, the ultrasonic transmitter 11 and the ultrasonic receiver 12 are arranged so that the focal points F and G are connected as shown in FIG. 4, and the ultrasonic transmitter 11 and the ultrasonic receiver at that time are arranged. The distance between the children 12 is L_SAnd a distance L between the ultrasonic receiver 12 and the inspection plate 13 by moving the inspection plate 13 having a thickness t of 4.5 mm between the ultrasonic transmitter 11 and the ultrasonic receiver 12.₂The amplitude and S / N of the reflected wave from the internal defect of the inspected plate 13 are measured. The used ultrasonic transmitter 11 and ultrasonic receiver 12 have a frequency of 25 MHz and an underwater focal length of 38 mm. As a result, the amplitude and S / N of the reflected wave due to the internal defect hardly change at any position between the ultrasonic transmitter 11 and the ultrasonic receiver 12 in the inspection target plate 13. That is, it can be seen that the inspected plate 13 may be at any position between the ultrasonic transmitter 11 and the ultrasonic receiver 12.
[0030]
Now, when the focal lengths of the ultrasonic transmitter 11 and the ultrasonic receiver 12 are equal, that is, as shown in FIG. 4, the focal point F of the ultrasonic transmission beam 11 </ b> A is on the surface of the ultrasonic receiver 12. When the ultrasonic transmitter 11 and the ultrasonic receiver 12 are arranged so that the focal point G of the ultrasonic reception beam 12A coincides with the surface of the ultrasonic transmitter 11, the ultrasonic transmitter 11 and the ultrasonic receiver 12 are arranged. The distance between and_S0Then, this distance L_S0Is expressed by the following equation (4).
[0031]
L_S0= F_L-{(C_M/ C_L) -1} × t (4)
However, F_LThe focal length of the point-focusing type ultrasonic transmitter 11 or the focal length of the point-focusing type ultrasonic receiver 12, t; the thickness of the plate to be inspected, C_M; Ultrasonic wave propagation speed in the material to be inspected, C_LThe propagation speed of ultrasonic waves in the liquid.
FIG. 7 shows the distance L when the ultrasonic transmitter 11 and the ultrasonic receiver 12 have the same focal length._S0Is the reference distance, the distance between the ultrasonic transmitter 11 and the ultrasonic receiver 12 is changed in water, and the amplitude of the reflected wave from the internal defect of the inspection board is measured. The ultrasonic transmitter 11 and the ultrasonic receiver 12 used had a frequency of 25 MHz, an underwater focal length of 38 mm, and a thin steel plate having a thickness t of 4.5 mm was used as the inspected plate. Distance L_SIs the reference distance L_S0Is smaller than the amplitude of the reflected wave, the distance L_SIs the reference distance L_S0It can be seen that the amplitude of the reflected wave suddenly decreases as the value becomes larger. The amplitude of the reflected wave is the reference distance L_S0Since a reduction of 3 dB or more than in the case of (3) leads to a decrease in S / N in defect detection, which is not preferable, the distance L between the ultrasonic transmitter 11 and the ultrasonic receiver 12 is not preferable._S(mm) must satisfy the following formula (5).
[0032]
L_S≦ L_S0+ F_L× 5/38 ……………… (5)
That is,
L_S≦ F_L-{(C_M/ C_L) -1} × t + F_L× 5/38 ………… (6)
Represented as:
Note that F in equation (6)_LThe coefficient 5/38 is generalized in consideration of the case where the focal lengths of the ultrasonic transmitter 11 and the ultrasonic receiver 12 are other than 38 mm.
[0033]
Next, even when the focal length of the ultrasonic transmitter 11 and the focal length of the ultrasonic receiver 12 are not equal, the same arrangement as shown in FIGS. An effect can be obtained. For example, when the focal length of the ultrasonic transmitter 11 is larger than the focal length of the ultrasonic receiver 12, the ultrasonic transmitter 11 so that the focal point F of the ultrasonic transmission beam 11 A coincides with the surface of the ultrasonic receiver 12. And an ultrasonic receiver 12 are arranged. At this time, if the inspected plate 13 is positioned closer to the ultrasonic receiver 12 than the focal point G of the ultrasonic reception beam 12A, the same thing as that described with reference to FIG. Further, when the focal length of the ultrasonic receiver 12 is larger than the focal length of the ultrasonic transmitter 11, the ultrasonic transmitter 11 so that the focal point G of the ultrasonic reception beam 12A coincides with the surface of the ultrasonic transmitter 11. And an ultrasonic receiver 12 are arranged. At this time, if the inspected plate 13 is positioned closer to the ultrasonic transmitter 11 than the focal point F of the ultrasonic transmission beam 11A, the same thing as that described with reference to FIG.
[0034]
The distance L between the focal length of the ultrasonic transmitter 11 and the focal length of the ultrasonic receiver 12 is not equal._SWill be described in detail based on experimental data. Now, a case where the focal length of the ultrasonic transmitter 11 is larger than the focal length of the ultrasonic receiver 12 will be described as an example. At this time, the larger focal length is set to F_LAnd
Therefore, when the ultrasonic transmitter 11 and the ultrasonic receiver 12 are arranged so that the focal point F of the ultrasonic transmission beam 11A coincides with the surface of the ultrasonic receiver 12, the ultrasonic transmitter 11 and the ultrasonic receiver The distance between 12 and L_S0Then, this distance L_S0Is expressed by the following equation (7).
[0035]
L_S0= F_L-{(C_M/ C_L) -1} × t (7)
FIG. 8 shows this distance L_S0Is the reference distance, the distance between the ultrasonic transmitter 11 and the ultrasonic receiver 12 is changed in water, and the amplitude of the reflected wave from the internal defect of the inspection board is measured. The ultrasonic transmitter 11 used has a frequency of 25 MHz and an underwater focal length of 38 mm, and the ultrasonic receiver 12 has a frequency of 25 MHz and an underwater focal length of 25 mm. A thin steel plate having a thickness t of 4.5 mm was used as the inspected plate.
[0036]
Similar to FIG. 7, the distance L_SIs the reference distance L_S0Is smaller than the amplitude of the reflected wave, the distance L_SIs the reference distance L_S0It can be seen that the amplitude of the reflected wave suddenly decreases as the value becomes larger. The amplitude of the reflected wave is the reference distance L_S0Since a decrease of 3 dB or more than in the case of the above leads to a decrease in S / N in defect detection and is judged to be undesirable, the distance L between the ultrasonic transmitter 11 and the ultrasonic receiver 12_S(mm) must satisfy the following formula (8).
[0037]
L_S≦ L_S0+ F_L× 5/38 ……………… (8)
That is,
L_S≦ F_L-{(C_M/ C_L) -1} × t + F_L× 5/38 ………… (9)
Represented as:
Note that F in equation (9)_LThe coefficient 5/38 is generalized in consideration of the case where the focal lengths of the ultrasonic transmitter 11 and the ultrasonic receiver 12 are other than 38 mm.
[0038]
Next, when the focal length of the ultrasonic receiver 12 is large, the ultrasonic transmitter 11 has a large focal length; the ultrasonic transmitter 11 has a frequency of 25 MHz, an underwater focal length of 25 mm, and the ultrasonic receiver 12 has a frequency. An experiment was carried out using 25 MHz and an underwater focal length of 38 mm, and although the illustration was omitted, a result almost equivalent to FIG. 8 could be obtained. Therefore, when the focal length of the ultrasonic transmitter 11 and the focal length of the ultrasonic receiver 12 are not equal, the larger one is F._LAnd the distance L between the ultrasonic transmitter 11 and the ultrasonic receiver 12_STherefore, the ultrasonic transmitter 11 and the ultrasonic receiver 12 may be arranged so that the above equation (9) is satisfied.
[0039]
The present invention method was applied when defect inspection was performed on a thin steel plate having a thickness of 1.2 to 5.5 mm as the inspected plate 13. As the ultrasonic transmitter 11 used at this time, an ultrasonic wave having a frequency of 25 MHz and an underwater focal length of 38 mm was used to transmit an ultrasonic wave having a frequency of 25 MHz, and as the ultrasonic receiver 12, a frequency of 25 MHz and an underwater focal length of 38 mm was used. We used a thing to detect flaws. As a result, it was possible to detect an ultra-fine defect of 10 μm φ regardless of the position in the thickness direction of the defect.
[0040]
Note that, in the above-described embodiment, the ultrasonic transmitter 11 and the ultrasonic receiver 12 that are disposed to face the board to be inspected by holding the ultrasonic transmitter 11 and the ultrasonic receiver 12 with the support arm 14. Although the child is scanned, the present invention is not limited to this, and it goes without saying that it may be configured to scan the inspected plate side.
[0041]
【The invention's effect】
According to the present invention, internal defects such as fine inclusions such as rolled metal sheets can be detected with uniform sensitivity over the entire cross section, eliminating the dead zone on the surface. It is possible to contribute to improvement.
[Brief description of the drawings]
FIG. 1 is a block diagram including a partial perspective view showing a configuration of an embodiment of the present invention.
FIG. 2 is an explanatory diagram showing a propagation path and a positional relationship of a reflected wave from a defect.
FIG. 3 is an explanatory diagram showing a relationship between a received ultrasonic signal and time.
FIG. 4 is an explanatory diagram showing focal points of ultrasonic beams of a transmitter and a receiver.
FIG. 5 is a characteristic diagram showing the relationship between the distance from the surface of the defect and the amplitude of the reflected wave.
FIG. 6 is a characteristic diagram showing amplitude and S / N of a reflected wave from an internal defect.
FIG. 7 is a characteristic diagram showing the amplitude of a reflected wave from an internal defect.
FIG. 8 is a characteristic diagram showing the amplitude of a reflected wave from an internal defect.
FIG. 9 is a block diagram including a partial perspective view showing a configuration of a conventional example.
[Explanation of symbols]
11 Ultrasonic Transmitter (Point Focusing Ultrasonic Transmitter)
11A Ultrasonic transmission beam
12 Ultrasonic receiver (Point-focusing type ultrasonic receiver)
12A Ultrasonic receiving beam
13 Board to be inspected
  13a surface
  13b reverse side
  14 Support arm
  15 Scanning device
16 Electric pulse generator
  17 Receiver amplifier
  18 Gate circuit
  19 Peak value detection circuit
  20 Controller
  21 Display
22 Internal defects
  30 Direct transmitted wave
31, 32 Reflected wave
33 Transmitted wave

Claims (5)

While interposing the inspection plate immersed in the liquid, scanning with the point-focusing type ultrasonic transmitter and the point-focusing type ultrasonic wave receiver facing each other,
Ultrasound that is point-focused from the ultrasonic transmitter is incident on the inspected plate substantially perpendicularly,
The ultrasonic wave is reflected on the upper side of the internal defect and is directed to the surface of the inspected plate, reflected by the surface, propagated from the back surface into the liquid and received, and the ultrasonic wave is first reflected on the inspected plate. Reflected on the back surface, directed to the internal defect, reflected on the lower side of the internal defect, and then received by the ultrasonic receiver both reflected waves propagated and received from the back surface into the liquid,
Extracting both reflected wave signals from the internal defect from the amplified signal
A C-scan ultrasonic flaw detection method comprising detecting an internal defect of a plate to be inspected based on the extracted signal. The signal of the reflected wave from the internal defect is defined as τ ₀ when the transmitted ultrasonic wave reaches the ultrasonic receiver, and τ is the time from the arrival of the transmitted wave to the end of the reverberation of the transmitted wave. is _D, when the ultrasonic is the tau ₁ the time required to propagate in the thickness direction of the test plate, the time in (τ ₀ + τ _D) after, and _{(τ 0 + 2 × τ 1} ) previous 2. The C-scan ultrasonic flaw detection method according to claim 1, wherein the method is extracted from a received signal. Wherein comparing the focal length of the ultrasonic receiver and ultrasonic transmitter element, the focal length of the person when the distance focal point is different from large as F _L, or if the focal length is equal to the focal length F _L The both are arranged so that a distance L _S between the ultrasonic transmitter and the ultrasonic receiver satisfies the following expression, where t is the thickness of the plate to be inspected. 3. The C-scan ultrasonic flaw detection method according to 1 or 2.
L _S ≦ F _L − {(C _M / C _L ) −1} × t + F _L × 5/38
Where C _M is the ultrasonic wave propagation speed in the material to be inspected, and C _L is the ultrasonic wave propagation speed in the liquid. A point-focusing type ultrasonic transmitter that transmits ultrasonic waves substantially vertically to the surface of the inspection plate;
Arranged at a position facing the point-focusing ultrasonic transmitter across the board to be inspected, the ultrasonic wave is reflected on the upper side of the internal defect and directed to the surface of the board to be inspected, reflected on the surface, and from the back surface The reflected wave that is propagated and received in the liquid and the ultrasonic wave are first reflected on the back surface of the board to be inspected, directed to the internal defect, reflected on the lower side of the internal defect, and then propagated into the liquid from the back surface and received. A point-focusing ultrasonic receiver that receives both reflected waves , and
A support arm that supports the ultrasonic transmitter and the ultrasonic receiver with an inspection plate interposed therebetween;
A scanning device for scanning the support arm;
An electric pulse generator for generating an electric pulse to be transmitted to a piezoelectric vibrator incorporated in the ultrasonic transmitter;
An amplifying device for amplifying the received signal;
Gate means for extracting signals of both reflected waves from internal defects from the amplified signal ;
A C-scan ultrasonic flaw detector characterized by comprising: The gate means sets the reflected wave signal from the internal defect to τ ₀ when the ultrasonic transmitted wave reaches the ultrasonic receiver, and the reverberation of the transmitted wave ends from the arrival of the direct transmitted wave. and the time until the tau _D, when the time for ultrasound takes to propagate in the thickness direction of the test plate was tau _1, at time (τ ₀ + τ _D) after, and (τ ₀ + 2 × τ ₁ ) set to extract from previous received signal,
The distance L _S between the ultrasonic transmitter and the ultrasonic receiver is compared with the focal length of the ultrasonic transmitter and the ultrasonic receiver. distance and F _L, or if the focal length is equal to the focal length F _L, claims, characterized in that to place the plate thickness of the test plate as t, the two so as to satisfy the following formula 4. The C-scan ultrasonic flaw detector according to 4.
L _S ≦ F _L − {(C _M / C _L ) −1} × t + F _L × 5/38
Where C _M is the ultrasonic wave propagation speed in the material to be inspected, and C _L is the ultrasonic wave propagation speed in the liquid.

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