JP4143527B2 - Thin plate ultrasonic flaw detector - Google Patents

Description

  The present invention generates a plate wave in a thin plate by making an ultrasonic wave incident on the thin plate at an incident angle corresponding to the plate thickness, receives a reflected wave generated by a discontinuous portion of acoustic impedance in the thin plate, and receives the reflected wave in the thin plate. The present invention relates to a thin plate flaw detection apparatus that detects flaws.

  An example of a plate wave probe for on-line nondestructive inspection of defects on the surface or inside of a relatively thin plate-like metal material (thin plate) such as a hot-rolled steel plate, cold-rolled steel plate, lead frame, etc. The plate-type ultrasonic flaw detection is performed to detect the presence or absence of a defect by propagating a plate-wave ultrasonic wave to a material to be inspected using a tire-type probe.

  In other words, as a plate wave ultrasonic flaw detection method, a plate wave is generated in a thin plate by making an ultrasonic wave incident on the thin plate at an incident angle according to the plate thickness, and a reflected wave generated by a discontinuous portion of acoustic impedance in the thin plate. A thin plate flaw detection method for detecting flaws in a thin plate by receiving the above has been used for a long time. However, with the diversification of the composition of target specimens in recent years, there is a case where the ultrasonic attenuation in the specimen is large at the center frequency of the ultrasonic wave used conventionally and a reflected signal from a flaw cannot be obtained sufficiently. On the other hand, it is known that by reducing the center frequency of the ultrasonic wave, the attenuation of the ultrasonic wave is reduced and the reflected signal from the flaw is increased, but on the other hand, the attenuation of the ultrasonic wave is small, The end surface multiple echo that reciprocates between both end surfaces of the thin plate may not be sufficiently attenuated until the next transmission repetition, and may be erroneously determined as a defect signal. In order to avoid this, it is necessary to wait for a time during which the end-face multiple echoes are sufficiently attenuated before the next transmission is performed, resulting in a decrease in the flaw detection speed.

  FIG. 3 shows an example of a conventional thin plate ultrasonic flaw detector, in which 2 is a synchronization signal generator, 3 is a transmitter, 4 is a plate wave probe, 5 is a reception amplifier, 6 is a gate signal generator, 7 is a peak detector, 8 is a determination unit, 9 is a thin plate, 10a and 10b are end faces of the thin plate, 11 is a vibrator, and 12 is a contact medium.

  FIG. 4 shows an example of a synchronization signal, an echo signal, and a time gate signal generated by a conventional thin-film ultrasonic flaw detector, 16 is a synchronization signal, 17 is an echo signal, 18 is a time gate signal, 13 is a transmission signal, and 14a. Is an end face echo signal for the first time, 14b to 14d are end face multiple echo signals generated by a plate wave ultrasonic wave reciprocating a plurality of times between the end faces 10a and 10b of the thin plate, and 15 is a flaw echo signal.

  Next, the operation will be described. The transmitter 3 supplies an electric pulse signal to the vibrator 11 by the synchronization signal 16 output from the synchronization signal generator 2 at a constant repetition period. The vibrator 11 converts the electric pulse signal output from the transmitter 3 into an ultrasonic signal and emits it into the contact medium 12 as a longitudinal wave. The emitted longitudinal wave ultrasonic signal propagates through the contact medium 12 and then enters the thin plate 9 to be converted into a plate wave ultrasonic signal, and propagates through the thin plate in the direction of one end face 10a of the thin plate. Then, it is reflected by one end face 10a of the thin plate, propagates again in the thin plate in the direction of the plate wave probe 4, and a part of the plate wave ultrasonic wave becomes a longitudinal wave ultrasonic wave at the interface between the thin plate 9 and the contact medium 12. After being converted and propagated through the contact medium 12, it returns to the vibrator 11 and is received. The received longitudinal wave ultrasonic signal is again converted into an electric signal by the vibrator 11 and amplified by the receiving amplifier 5, and then an end face echo signal 14 a is obtained. Further, a part of the plate wave ultrasonic wave reflected by one end face 10a of the thin plate and again propagating in the thin plate toward the plate wave probe 4 is not converted into a longitudinal wave at the interface between the thin plate 9 and the contact medium 12. Then, it propagates as it is to the other end surface 10b of the thin plate, is reflected by the end surface 10b, and propagates toward the one end surface 10a of the thin plate. Then, it is reflected again at one end face 10a of the thin plate and propagates in the direction of the plate wave probe 4, and a part of the plate wave ultrasonic wave is converted into a longitudinal wave ultrasonic wave at the interface between the thin plate 9 and the contact medium 12, After propagating through the contact medium 12, it returns to the transducer 11 and is received and superimposed on the echo signal to obtain an end face multiple echo signal 14b. Further, when the plate wave ultrasonic waves reciprocate between the both end faces 10a and 10b of the thin plate and return to the vibrator, the end face multiple echo signals 14c and 14d are obtained by being superimposed on the echo signal. The end face multiple echo is an interval of the reciprocating propagation time of the plate wave ultrasonic wave between the both end faces 10a and 10b of the thin plate, the attenuation of the plate wave ultrasonic wave in the thin plate, the reflection efficiency at the both end faces 10a and 10b of the thin plate, Each time the multiple reflection is repeated, the amplitude is reduced and is repeatedly generated.

  Here, if there is a flaw on the propagation path of the plate wave ultrasonic wave in the thin plate 9, the plate wave ultrasonic signal is reflected even by the flaw, and is superimposed on the plate wave ultrasonic signal reflected by one end face 10a of the thin plate, And it returns to the vibrator | oscillator 11 and is received by the propagation time shorter than the plate wave ultrasonic signal reflected by the one end surface 10a of the thin plate, and the echo signal 15 is obtained without being superimposed on the echo signal. On the other hand, the gate signal generator 6 starts at a certain time before the time at which an echo signal is generated at one end face 10a of the thin plate, starting from the time delayed by a certain time from the time when the ultrasonic wave enters the thin plate. The time gate signal 18 whose end point is the time is generated, and the peak detector 7 detects the peak voltage of the echo signal in the time gate signal. Then, the determiner 8 determines whether or not the peak voltage is equal to or higher than a specified level, and determines that there is no flaw when the peak voltage is equal to or higher than the specified level.

For a tire-type probe as an example of a plate-wave probe, the mounting angle of the ultrasonic transducer attached to this type of tire probe can be changed, and the ultrasonic wave on the material to be inspected (thin plate) can be changed. Prior arts for changing the incident angle are described (for example, see Utility Model Document 1 and Utility Model Document 2).
Japanese Utility Model Publication No. 45-10471 No. 2-13973

  Since the conventional thin-plate ultrasonic flaw detector is configured as described above, as shown in FIG. 4, a time gate signal generated with the ultrasonic attenuation amount of the end face multiple echo 14d being large and the next synchronization signal as a starting point. In the section, there is no problem if the flaw echo signal is sufficiently small with respect to the flaw echo signal. However, as shown in FIG. 5, the attenuation of the plate wave ultrasonic wave is small, and the end face multiple echo 14d is generated from the next synchronization signal as a starting point. There is a problem that the determination unit 8 erroneously determines that there is a flaw when it occurs at a voltage equal to or larger than the flaw echo within the time gate signal interval. In order to avoid end face multiple echo, it is necessary to increase the period T of the synchronization signal so that the next ultrasonic transmission / reception is performed after the end face multiple echo is sufficiently attenuated. When the thin plate travels vertically and the entire surface of the thin plate is inspected, if the distance of the thin plate traveling in the period of the synchronization signal is equal to or greater than the beam width of the plate wave ultrasonic wave, the plate wave ultrasonic wave There is a problem in that a portion where no propagation occurs occurs on the thin plate and an event that a flaw is overlooked occurs, so that the traveling speed of the thin plate needs to be lowered and the inspection speed is lowered.

  An object of the present invention is to provide a thin plate ultrasonic flaw detector capable of flaw detection at high speed without increasing the transmission repetition period T even when the ultrasonic frequency is lowered.

A thin plate ultrasonic flaw detector according to the present invention is a thin plate flaw detector that uses a plate wave probe having a transducer for transmitting and receiving ultrasonic waves to detect defects in a thin plate having an end face.
A synchronization signal generator that generates a plurality of synchronization signals at a predetermined repetition period;
A plurality of transmission pulse signals are generated based on the plurality of synchronization signals generated by the synchronization signal generator, and each transmission pulse signal of the generated plurality of transmission pulse signals is associated with each synchronization signal of the plurality of synchronization signals. A transmitter that transmits the ultrasonic wave from the transducer by transmitting to the plate wave probe in synchronization with,
Starting from the time until the ultrasonic wave transmitted by the transducer is delayed for a predetermined period from the time when the ultrasonic wave is incident on the thin plate, the reflected ultrasonic signal reflected by the end face of the thin plate reaches the transducer A gate signal generator for generating a time gate signal whose end point is a time before a predetermined period;
An electric signal based on a reflected ultrasonic signal reflected by the thin plate through the plate wave probe is input, and a peak located in a section of a time gate signal generated by the gate signal generator in the input electric signal. A determiner that determines a defect when the voltage is equal to or higher than a predetermined determination level; and
The peak voltage of the electrical signal based on the reflected ultrasonic signal previously reflected by the end face of the thin plate is transmitted from the next ultrasonic wave transmitted by the transducer until it enters the thin plate. And a synchronization signal period calculator for calculating the predetermined repetition period so as to be located in the period of (2).

  As described above, according to the present invention, by determining the synchronization signal period according to the following equation (1), the end face multiple echo is first reflected by the reflection on the end face of the thin plate from the time when the plate wave ultrasonic wave is incident on the thin plate. Therefore, the end-face echo signal first reflected from the end face is the time that is delayed for a certain time from the time when the ultrasonic wave is incident on the thin plate. It can be configured such that no end face multiple echo signal is generated even in a time gate signal section whose end point is a time before a certain time.

  Therefore, even when the ultrasonic attenuation in the thin plate is small, the thin plate ultrasonic flaw detector capable of performing the inspection at the same inspection speed as that in the case where the ultrasonic attenuation in the thin plate is large without reducing the synchronization signal period can be obtained. There is.

Embodiment 1 FIG.
The thin-plate ultrasonic flaw detector according to the first embodiment can detect defects generated on the surface or inside of a relatively thin plate-shaped metal material (thin plate) such as a hot-rolled steel plate, a cold-rolled steel plate, and a lead frame. In order to perform non-destructive inspection, a tire-type probe as an example of a plate wave probe is used to propagate plate wave ultrasonic waves to the material to be inspected, and the reflected waves are received to detect the presence or absence of defects. Perform plate wave ultrasonic testing.

  An embodiment of the present invention shown in FIG. 1 will be described below.

  In FIG. 1, reference numeral 1 denotes a synchronization signal period calculator. 2 to 12 are the same as those in FIG. The thin-plate ultrasonic flaw detector includes a synchronization signal period calculator 1, a synchronization signal generator 2, a transmitter 3, a receiving amplifier 5, a gate signal generator 6, a peak detector 7, and a determiner 8. The thin plate ultrasonic flaw detector is connected to the plate wave probe 4.

  2 is an example of a synchronization signal, an echo signal, and a time gate signal obtained by the embodiment of FIG. 1, and 13 to 18 are the same as FIG.

Next, the operation will be described. First, the distance between both end faces 10a and 10b of the thin plate 9 is W, the group velocity of the plate wave in the thin plate 9 is C, and the distance from one end surface 10b of the thin plate 9 to the ultrasonic wave incident point of the plate wave probe 4 is the distance. Wc, the round-trip propagation time in the contact medium 12 is Tr, an arbitrary integer n, and an arbitrary time t ₀ less than or equal to the round-trip propagation time in the contact medium 12, and the synchronization signal period calculator 1

Determined by The transmitter 3 supplies the electric pulse signal to the vibrator 11 by the synchronization signal 16 generated by the synchronization signal generator 2 in the synchronization signal period determined by the synchronization signal period calculator 1. The vibrator 11 converts the electric pulse signal output from the transmitter 3 into an ultrasonic signal and emits it into the contact medium 12 as a longitudinal wave. The emitted longitudinal wave ultrasonic signal propagates through the contact medium 12 and then enters the thin plate 9 to be converted into a plate wave ultrasonic signal, and propagates through the thin plate in the direction of one end face 10a of the thin plate. The plate wave ultrasonic signal is reflected by one end face 10a of the thin plate and propagates again in the direction of the plate wave probe 4 through the thin plate. Then, a part of the plate wave ultrasonic waves is converted into longitudinal wave ultrasonic waves at the interface between the thin plate 9 and the contact medium 12, propagates through the contact medium 12, returns to the transducer 11, and is received. The received longitudinal wave ultrasonic signal is again converted into an electric signal by the vibrator 11 and amplified by the receiving amplifier 5, and then an end face echo signal 14 a is obtained. Further, a part of the plate wave ultrasonic wave reflected by one end face 10a of the thin plate and again propagating in the thin plate toward the plate wave probe 4 is not converted into a longitudinal wave at the interface between the thin plate 9 and the contact medium 12. Then, it propagates as it is to the other end face 10b of the thin plate. Then, it is reflected by the end face 10 b and propagates in the direction of one end face 10 a of the thin plate, is reflected again by the one end face 10 a of the thin plate and propagates in the direction of the plate wave probe 4, and the interface between the thin plate 9 and the contact medium 12. Thus, a part of the plate wave ultrasonic wave is converted into a longitudinal wave ultrasonic wave, propagates through the contact medium 12, returns to the transducer 11, is received, and is superimposed on the echo signal to obtain the end face multiple echo signal 14 b. Further, when the plate wave ultrasonic waves reciprocate between the both end faces 10a and 10b of the thin plate and return to the vibrator, the end face multiple echo signals 14c and 14d are obtained by being superimposed on the echo signal. The end face multiple echo is an interval of the reciprocating propagation time of the plate wave ultrasonic wave between the both end faces 10a and 10b of the thin plate, the attenuation of the plate wave ultrasonic wave in the thin plate, the reflection efficiency at the both end faces 10a and 10b of the thin plate, Each time the multiple reflection is repeated, the amplitude is reduced and repeatedly generated. However, since the synchronization signal period T is determined by the equation (1), for example, in FIG. 2, the end face multiple echo signal 14c is the next synchronization signal period. Is generated within the reciprocating propagation time in the contact medium 12 at the time, i.e., before the ultrasonic wave is incident on the thin plate, and the end face multiple echo signal 14d is the time at which the echo signal of one end face 10a of the thin plate is generated in the next synchronization signal period. It occurs afterwards.

  In other words, in the period until the ultrasonic wave transmitted from the transducer 11 enters the thin plate 9, the echo that has been previously incident on the thin plate 9 as an ultrasonic wave and is reflected by the end face 10a or the end face 10b and remains without being attenuated. If the period T is set so that the signal is positioned, an echo signal that has not been reflected and attenuated before in a period corresponding to the position from which the ultrasonic wave enters the thin plate 9 to be measured to one end surface 10a of the thin plate. No longer appears. Therefore, it is possible to prevent erroneous determination by using an echo signal that has not been attenuated as a flaw (as a flaw position).

  Here, if there is a flaw on the propagation path of the plate wave ultrasonic wave in the thin plate 9, the plate wave ultrasonic signal is reflected even by the flaw, and is superimposed on the plate wave ultrasonic signal reflected by one end face 10a of the thin plate, And it returns to the vibrator | oscillator 11 and is received by the propagation time shorter than the plate wave ultrasonic signal reflected by the one end surface 10a of the thin plate, and the echo signal 15 is obtained without being superimposed on the echo signal. On the other hand, the gate signal generator 6 starts at a time delayed by a certain time from the time when the ultrasonic wave enters the thin plate, starting from the synchronization signal, and is a certain time before the time when the echo signal is generated at one end face 10a of the thin plate. The time gate signal 18 whose end point is the time is generated, and the peak detector 7 detects the peak voltage of the echo signal in the time gate signal. Then, the determiner 8 determines whether or not the peak voltage is equal to or higher than a specified level, and determines that there is no flaw when the peak voltage is equal to or higher than the specified level.

  As described above, the thin plate ultrasonic flaw detector according to the present embodiment includes a synchronization signal generator that outputs a synchronization signal at a constant repetition period, a transmitter that generates a transmission pulse signal based on the synchronization signal, and a transmission pulse. Converts the signal into an ultrasonic signal, makes the plate wave ultrasonic wave almost perpendicular to one side of the parallel end face of the thin plate with two parallel end faces, and receives the reflected ultrasonic signal from the flaw in the thin plate or the end face of the thin plate The plate wave probe for converting into an electric signal, the receiving amplifier for amplifying the electric signal received by the plate wave probe, and the synchronization signal as a starting point are delayed for a certain time from the time when the ultrasonic wave enters the thin plate. A gate signal generator that generates a time gate signal whose end point is a certain time before the echo at the first end surface reaches the plate wave probe, starting from the time, and a received signal output from the receiving amplifier Time In a thin-plate ultrasonic flaw detector comprising a peak detector that detects a peak voltage in a signal section and a determination device that determines that the peak voltage is equal to or higher than a determination level, After entering the plate wave ultrasonic wave, it is reflected at the end face and propagates through the thin plate, then the ultrasonic wave reaches the other end face, and the plate wave ultrasonic wave reflected at the end face propagates through the thin plate. Are repeatedly reflected at the end face in the direction of incidence of the plate wave ultrasonic wave and received by the plate wave probe. The distance between the parallel end faces of the two thin plates, the group velocity of the plate wave ultrasonic waves, and the plate wave search so that the next transmission trigger signal is generated a certain time before the time at which one of the end face multiple echoes occurs. Synchronized according to the distance from the toucher to the plate edge A thin ultrasonic flaw detection apparatus characterized by comprising a synchronizing signal period calculator for calculating a period of No..

  In other words, the thin plate ultrasonic flaw detector according to the present embodiment is configured so that the end surface multiple echoes are ultrasonic waves in the contact medium from the time when the transmission signal generated by the next synchronization signal is generated to the incident point of the thin plate. The period T of the synchronization signal is determined so as to overlap within the round-trip propagation time.

  Then, the end face multiple echo in the thin plate ultrasonic flaw detector is superposed within the round-trip propagation time of the ultrasonic wave in the contact medium from the time when the transmission signal generated by the next synchronization signal is generated to the incident point of the thin plate. By determining the period T of the synchronization signal at the same time, it is possible to prevent the end face multiple echo from being erroneously determined without significantly increasing the period of the synchronization signal and to provide a highly reliable flaw detection result. it can.

It is a figure which shows the block diagram which shows the thin-plate ultrasonic flaw detector by the Example of this invention. It is a figure which shows an example of the synchronizing signal, echo signal, and time gate signal which are obtained by the Example of this invention. It is a block diagram which shows the conventional thin plate ultrasonic flaw detector. It is a figure which shows an example of the synchronizing signal, echo signal, and time gate signal which are obtained by the conventional thin plate ultrasonic flaw detector. It is a figure which shows an example of the synchronizing signal, echo signal, and time gate signal which are obtained by the conventional thin plate ultrasonic flaw detector.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Synchronous signal period calculator, 2 Synchronous signal generator, 3 Transmitter, 4 Plate wave probe, 5 Receiving amplifier, 6 Gate signal generator, 7 Peak detector, 8 Determinator, 9 Thin plate, 10a, 10b End face , 11 vibrator, 12 contact medium, 16 synchronization signal, 17 echo signal, 18 time gate signal, 13 transmission signal, 14a end face echo signal, 14b, 14c, 14d end face multiple echo signal, 15 flaw echo signal.

Claims (1)

In a thin plate ultrasonic flaw detector for detecting defects in a thin plate having an end surface using a plate wave probe having a transducer for transmitting and receiving ultrasonic waves,
A synchronization signal generator that generates a plurality of synchronization signals at a predetermined repetition period;
A plurality of transmission pulse signals are generated based on the plurality of synchronization signals generated by the synchronization signal generator, and each transmission pulse signal of the generated plurality of transmission pulse signals is associated with each synchronization signal of the plurality of synchronization signals. A transmitter that transmits the ultrasonic wave from the transducer by transmitting to the plate wave probe in synchronization with,
Starting from the time until the ultrasonic wave transmitted by the transducer is delayed for a predetermined period from the time when the ultrasonic wave is incident on the thin plate, the reflected ultrasonic signal reflected by the end face of the thin plate reaches the transducer A gate signal generator for generating a time gate signal whose end point is a time before a predetermined period;
An electric signal based on a reflected ultrasonic signal reflected by the thin plate through the plate wave probe is input, and a peak located in a section of a time gate signal generated by the gate signal generator in the input electric signal. A determiner that determines a defect when the voltage is equal to or higher than a predetermined determination level; and
The peak voltage of the electrical signal based on the reflected ultrasonic signal previously reflected by the end face of the thin plate is transmitted from the next ultrasonic wave transmitted by the transducer until it enters the thin plate. A thin-film ultrasonic flaw detector comprising: a synchronization signal period calculator for calculating the predetermined repetition period so as to be located in the period.

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