RU2560753C1 - Mirror-shadow method for ultrasonic inspection with differential compensation for interfering factors - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: method includes forming a first and a second measurement channel, comprising generator-receiver pairs of electroacoustic converters and displaced in space on the axis of movement, wherein the centres of the acoustic axes of all converters lie on the same line in a row such that the displacement between the centres of receivers is equal to the displacement between the centres of generators; receiving a differential signal from the outputs of said channels and comparing the strength of said signal with a rejected level, and determining the presence of a defect from the decrease in the strength of the differential signal.

EFFECT: high reliability of ultrasonic inspection.

13 cl, 22 dwg

Description

Mirror-shadow method of ultrasonic testing with differential compensation of interfering factors.

The invention relates to measuring equipment, and in particular to means for ultrasonic (ultrasound) high-speed operational control of a rail track. Also, the invention can be used for ultrasonic testing of products of sheet, long and shaped steel.

From the copyright certificate SU 1497561 A1 (07/30/1989) there is a known method of mirror-shadow ultrasonic testing of products of equal cross section, including railway rails, and a flaw detector for its implementation. The known method of ultrasonic testing includes the formation of a single measuring channel through a pair of generator-receiver of the flaw detector, intended for radiation and reception of ultrasound according to the mirror-shadow control scheme. The system of flaw detector converters is set in motion and the object of ultrasonic beam monitoring is heard. In this case, signal processing is performed from the output of the measuring channel. The presence of a defect is determined by the value of the measured slope of the change in the amplitude envelope of the received oscillations, which allows to increase the reliability and accuracy of control at significant scanning speeds due to the fact that in case of disturbance of the acoustic contact due to bouncing of the transducers on irregularities of the path, the specified slope of the change is less than the same value when the defect occurs.

The mirror-shadow method of ultrasonic testing remains relevant at the present time. However, the practical implementation of the mirror-shadow method, based on recording a decrease in the amplitude of the transmitted ultrasonic wave under the influence of a defect, is difficult due to possible false responses caused by a drop in the level of the useful signal for reasons other than those specified in SU 1497561 A1, which makes a well-known technical solution not effective enough. An increase in the gap between the rail surface and the transducer when bouncing on irregularities of the path causes a weakening of the measurement signal, and since the shape of the working face in the rail section differs from the nominal one due to wear, the measurement signal from the electro-acoustic transducer is weakened due to the scattering of part of the energy of ultrasonic waves in different directions or due to changes in the path of propagation of elastic vibrations relative to the receivers. The presence of corrosion on the reflecting surface of the rail head also causes partial scattering of ultrasonic waves and, as a result, attenuation of the recorded signal. Pollution on the reflecting surface of the rail head leads to the absorption of ultrasonic waves and the weakening of the useful signal. In addition, the attenuation of ultrasonic waves differs in rails of different manufacturers, which means that the amplitudes of the received signals differ from the same defects if such rails are laid in the same way.

In each of these cases, at some point in time, the level of the useful signal in the receiver will drop so much that it will become lower than the rejection level and the flaw detector will be triggered spontaneously, caused not by the presence of a defect, but by too much scattering or absorption of the ultrasonic beam. For this reason, the mirror-shadow method of ultrasonic testing has so far found insufficient distribution in high-speed flaw detection of such an important object as a rail track.

The closest analogues of the present invention in terms of the device and method are, respectively, an ultrasonic flaw detector according to the copyright certificate SU 564592 A1 (04/04/1975) and the mirror-shadow method of ultrasonic testing that it implements with differential compensation of interfering factors.

Ultrasonic flaw detector according to SU 564592 A1 contains two pairs of generator-receiver from electromagnetic-acoustic transducers (EMAP) for radiation and reception of ultrasonic ultrasound according to the mirror-shadow control scheme, two detectors, a comparison unit and an indicator. During the operation of the flaw detector, the first and second measuring channels are formed, containing pairs of generator-receiver electroacoustic transducers and displaced in space along the axis of movement. Measuring signals are detected and compared. The resulting signal is characterized by a higher noise amplitude than the attenuated signal during processing of the useful signal. However, the interference signals have a shorter duration, which allows you to filter them.

The known technical solution allows to increase the reliability of ultrasonic monitoring due to an increase in the signal-to-noise ratio, but it is of little use for operational ultrasonic monitoring of a rail track, in which in real conditions access to the rail head is limited due to the design features of the rail track and is practically only provided along the entire length of the track from the side of the working side face of the rail head, which requires slow manual control of individual sections (arrows, crossings, etc.). In addition, when scanning a rail track at high speeds, it is preferable to use solutions with simpler processing of the measurement signals.

The objective is to increase the effectiveness of prospective ultrasonic testing with differential compensation of interfering factors necessary for operational ultrasonic monitoring of a rail track.

Provided by the present invention, the first technical result is to increase the effectiveness and reliability of control when scanning a rail track at high speeds, and the second technical result consists in simplifying the method of ultrasonic testing with differential compensation of interfering factors and a device for its implementation.

These technical results are achieved due to the fact that in the mirror-shadow method of ultrasonic testing, including the formation of the first and second measuring channels containing pairs of generator-receiver electroacoustic transducers and offset in space along the axis of movement, the centers of the acoustic axes of all transducers are placed on one line in a row so that the offset between the centers of the receivers is equal to the offset between the centers of the generators. And in the process of scanning, a difference signal is obtained from the outputs of these channels and the level of this signal is compared with the rejection level. Moreover, the presence of a defect is judged by a drop in the difference signal level.

In the particular case, the offset between the measuring channels is selected in the range from 3 to 900 mm.

In another particular case, the number of measuring channels is selected from the condition N> 2, where N is the number of channels that is even. In this case, the channels are shifted evenly, and the measurement information signal is obtained as the average difference between the signals from the channels with even and odd numbers, or the channels are shifted unevenly, and weight coefficients are given to the difference signals and averaged.

Technical results are also achieved due to the fact that in an ultrasonic flaw detector containing pairs of generator-receiver for emitting and receiving ultrasound according to a mirror-shadow control scheme, as well as a data processing device connected to its inputs with outputs of ultrasonic receivers, the generators and receivers of ultrasound are located at one line in a row, and the offset between the receivers is equal to the offset between the generators, and the data processing device is configured to receive a differential signal from the outputs of the measuring channels and compare the level d signal with rejection level.

In a particular case, the flaw detector contains pairs of the generator-receiver with the same characteristics of the electro-acoustic path.

In another particular case, the flaw detector contains a pair of generator-receiver located with mutual overlap.

In another particular case, the displacement between the generators is from 3 to 900 mm.

Also in the particular case, all the generators and receivers are assembled into groups of homogeneous elements.

In another particular case, N> 2, where N is the number of generator-receiver pairs, which is even, and the data processing device is configured to receive differential signals from the outputs of alternating measuring channels.

In a particular case, the flaw detector contains a pair of generator-receiver, offset uniformly. In this case, the data processing device is configured to averag the measurement result.

In another particular case, the flaw detector contains pairs of generator-receiver, shifted unevenly, and the data processing device is configured to give the difference signals weighting coefficients during averaging.

The invention is illustrated by the following illustrations.

FIG. 1-2: mirror-shadow scheme of ultrasonic inspection of a railway rail in the absence of defects, top view, and waveform at the output of the measuring channel.

FIG. 3-4: mirror-shadow rail monitoring scheme when a defect appears near the working edge of the rail head and the shape of the corresponding output signal.

FIG. 5-6: mirror-shadow scheme of rail monitoring in the presence of a defect in the central part of the head and the signal shape at the output.

FIG. 7-8: mirror-shadow diagram of the control rail with a defect near the outer part of the head and the shape of the measuring signal.

FIG. 9-10: shows the increase in the width of the dip of the measuring signal when a longer defect is detected.

FIG. 11: Ultrasound control circuit of rails with two pairs of converters, top view.

FIG. 12: monoblock arrangement of ultrasonic converters on the rail head with an internal defect, view from the end of the rail.

FIG. 13: arrangement of a two-channel monoblock of ultrasonic converters on the rail head, side view.

FIG. 14: simplified circuit diagram of an ultrasonic flaw detector with differential compensation of interfering factors.

FIG. 15-16: waveform at the output of the first measuring channel for a short-term separation of the monoblock from the rail head and in the absence of separation, respectively.

FIG. 17-18: waveform at the output of the second measuring channel for a short-term separation of the monoblock from the rail head and in the absence of separation.

FIG. 19-20: the form of the difference signal when the monoblock is torn off the rail surface and in the absence of separation.

FIG. 21: four-channel monoblock with uniform channel offset.

FIG. 22: four-channel monoblock with uneven channel offset.

The implementation of the present invention is shown on the example of the design of ultrasonic flaw detector, preferred for high-speed operational control of the rail track.

Using a mirror-shadow scheme of ultrasonic testing, the flaw detector contains a pair of acoustically-connected electro-acoustic transducers 1 and 2 (Fig. 1). Converter 1 performs the function of a generator of ultrasonic vibrations, and converter 2 serves as a receiver of reflected ultrasonic waves and generates a measuring electric signal at its output (Fig. 2). Both transducers are placed on the side of the working side surface of the rail 3. The mirror-shadow circuit of the ultrasonic inspection of the rail allows us to determine the depth of the internal defect 4 and its size from the waveform (Fig. 3-10).

EMAC 1, 2, 5 and 6 were used as electroacoustic transducers. EMAP 1 and 2 form the first pair of acoustically coupled transducers. The second pair is formed by EMAT 5 and 6. EMAT 1 and 5 serve as generators of ultrasonic vibrations, and EMAT 2 and 6 serve as receivers of ultrasonic waves reflected from the opposite face of the rail head 3. At the same time, the centers of the acoustic axes of all EMATs are located in one row and are on the same line 1-1 (Fig. 11-13), constructively forming a linear monoblock of 7 transducers on a common carrier platform. The working surfaces of EMAT 1, 2, 5 and 6 lie in the same plane and face the object of control. EMAP pairs are located with mutual overlap, because elements of the first pair of converters alternate with elements of the second pair. Due to the alternation of the elements of the pairs, the generators 1, 5 form in their arrangement the first homogeneous group, and the receivers 2, 6 form the second homogeneous group, distant from the first group.

The first pair of EMAT is part of the first measuring channel, and the second pair of EMAT is part of the second measuring channel. Both channels are located in the same sounding plane and are characterized by acoustic coupling, respectively, of generator 1 with receiver 2 and generator 5 with receiver 6 according to a mirror-shadow control scheme, for which generators 1, 5 provide an inclined input of the ultrasound beam into the object of control, and receivers 2 , 6 are shifted from them by a distance corresponding to the thickness of the rail head 3 and the angle of entry of the ultrasound beam. The offset d between the centers of the receivers is equal to the offset between the centers of the generators (Fig. 13) and is 100 mm for this example. Since EMAT 1, 2, 5, and 6 are of the same type, and the regularity of their location is the same, the characteristics of the electron acoustic paths are completely identical.

EMAP 1, 2, 5 and 6 are electrically connected by their inputs / outputs to a control device and a data processing device, structurally made as a single digital computing device 8 with an interface part and analog functional units. The difference amplifier (subtractor) 9 of the measuring signals is one of the indicated analog functional units (Fig. 14) or is implemented by computer means in the form of a digital functional unit.

The ultrasonic flaw detector is mounted on a railway carriage and the monoblock 7 is brought to the working side surface of the rail 3. The device is put into operation and they begin to move along the rail by scanning the head 3 of the ultrasonic rail with the beam in search of internal defects such as transverse cracks 4. In the figures, the direction of movement is arbitrary shown by arrow V, however, due to the uniformity of EMAT 1, 2, 5 and 6 and the symmetry of the sounding scheme, the device is also able to work when moving in the opposite direction.

The control device supplies electric pulses to the generators 1, 5 for the emission of ultrasonic vibrations at the same angle to the rail surface. In the absence of defect 4, receivers 2 and 6 constantly receive an acoustic through signal reflected from the opposite wall of the rail head 3. The appearance of defect 4 leads to a drop in the level of the useful signal. During scanning, two identical measuring channels are formed with as close as possible characteristics, the second channel being offset in space by a distance d relative to the first channel along the axis of movement coinciding with the longitudinal axis of the rail (Fig. 11).

The electrical signals from the outputs of the receivers 2 and 6 have the form shown in FIG. 15-18, where: A is a small defect; B is a medium-sized defect, accompanied by a separation of the monoblock of 7 converters from the surface of the rail head 3; C - rail joint; D is a significant defect. If necessary, the measuring signals first undergo auxiliary pre-processing, in particular, filtering or preamplification, and then are fed to the input of the differential amplifier 9. The received differential signal (Fig. 19 or 20) from the output of the amplifier 9 is transmitted to the input of a computing device 8 comparing the level of the received difference signal in its original form, or subjected to additional post-processing, with a set rejection level and implementing other algorithms for processing results Measurements. If the drop in the difference signal level exceeds a predetermined rejection level, then the ultrasonic flaw detector informs the operator about the presence of defect 4 in the rail head 3.

Since the generators and receivers are located on the same line in a row, and the offset between the receivers is equal to the offset between the generators, the second measuring channel is displaced in space relative to the first channel along the axis of motion in the implementation shown in FIG. 11 schemes. In this case, defect 4 first crosses the first ultrasound beam, and after a while the second beam. The delay between the drops of the signals from the outputs of the receivers 2 and 6 will be δt = d / υ, where: δt is the time delay between the signals; d is the offset between the channels; υ is the speed of the transducers relative to the control object. The delay between the measuring signals leads to almost doubling the total amplitude of the signal from defect 4 on the difference signal. However, any interfering factor that reduces the level of the received signal (bouncing, scattering, corrosion, changing the shape of the profile, the difference between the properties of the real rail from the tuning rail, etc.) acts on the measuring channels simultaneously and equally. Accordingly, changes in the measuring signals caused by the interfering factor do not have a time delay, and therefore their difference will be close to zero, which allows you to filter out this interference signal in this way, rather than fighting the interfering factor by increasing the flaw detector gain, which can lead to the omission of a small or even medium defect. As can be seen from FIG. 15 and 16, the signal at the output of the first measuring channel with a short-term separation of the monoblock 7 from the rail head 3 differs significantly from the signal in the absence of separation. A similar picture is observed for the second channel (Fig. 17, 18). However, the curve of the difference signal at separation (Fig. 19) is almost identical to the curve of the difference signal in the absence of separation (Fig. 20). Thus, the separation of the monoblock 7 from the rail head 3 did not affect the resulting signal difference, although for each channel individually this was significant.

To conclude that there is a defect in the control object, it is enough to compare with the rejection level the drop in the level of the difference signal received from the outputs of the measurement channels constructed in the mirror-shadow scheme from the outputs of the displaced in space along the axis of movement identical (offset between the centers of the receivers equal to the offset between the centers of the generators). The absence of the need for any other signal processing, including the detection required in the previously known method, makes the method and device of the present invention as simple, efficient and reliable as possible, which is especially important when scanning a rail track at high speeds, up to 200 km / hours Due to the location of the centers of the acoustic axes of all ultrasonic transducers in one line in a row with a mirror-shadow scheme, the ultrasound control is possible on one side of the control object - from the side of the working side of the rail head, which eliminates manual operations, and therefore makes monitoring easier, increases it efficiency and reliability when scanning rail tracks at high speeds.

During the scanning process, the selectivity of the ultrasonic flaw detector to the controlled defects of the test object will be the higher, the closer to each other the characteristics of the electron-acoustic path of the measuring channels, which is determined to a large extent by the accuracy of setting the equality of the offset between the receivers to the offset between the generators. The distance d is chosen empirically depending on the requirements, in particular, on the speed of control and the size of the detected defects. In practice, increasing the effectiveness and reliability of control when scanning a rail track at high speeds is achieved if the value of d is in the range of 3 ÷ 900 mm.

The arrangement of generator-receiver pairs with mutual overlap, when all the generators and receivers are assembled in groups of homogeneous elements, is necessary if the value of d should not exceed the base distance between the converters in the pair.

In addition, it is possible to increase the effectiveness and reliability of ultrasonic testing when scanning a rail track at high speeds when receiving measurement information from a larger number of channels. The number of generator-receiver pairs for this is chosen from the condition N> 2, where N is the number of channels, which is even. In this case, two options for the location of the pairs of the generator-receiver are possible: uniform and uneven. With a uniform mutual offset of the pairs of converters (Fig. 21), the measurement information signal is obtained as the average difference between the signals from the channels with even and odd numbers, which allows you to get rid of random noise. If the channels are shifted unevenly (Fig. 22, where S is a constant), then the difference signals are first weighted, thereby adjusting the result for more accurate selectivity, and then averaged.

Possible implementation of the present invention is not limited to the presented example. The technical solution is also suitable for monitoring the track from the rolling surface to sound the entire rail and even from the side of the rail neck. It is also possible to improve the selectivity of ultrasonic flaw detectors operating, for example, on the basis of the shadow method or the multiple shadow method.

Claims (13)

1. Mirror-shadow method of ultrasonic testing, including the formation of the first and second measuring channels containing pairs of generator-receiver electro-acoustic transducers and offset in space along the axis of movement, characterized in that the centers of the acoustic axes of all the transducers are placed on one line in a row so that the offset between the centers of the receivers is equal to the offset between the centers of the generators, receive a differential signal from the outputs of these channels and compare the level of this signal with the rejection level And the presence of a defect is judged by the residual signal level drop. 2. The control method according to claim 1, characterized in that the offset between the measuring channels is selected in the range from 3 to 900 mm. 3. The control method according to claim 1, characterized in that the number of measuring channels is selected from the condition N> 2, where N is the number of channels, which is even. 4. The control method according to claim 3, characterized in that the channels are shifted uniformly, and the measurement information signal is obtained as the average difference between the signals from the channels with even and odd numbers. 5. The control method according to claim 3, characterized in that the channels are shifted unevenly, and weight coefficients are added to the difference signals and averaged. 6. An ultrasonic flaw detector containing pairs of generator-receiver for emitting and receiving ultrasound according to a mirror-shadow control scheme, as well as a data processing device connected by its inputs to the outputs of ultrasound receivers, characterized in that the generators and receivers of ultrasound are located on one line in a row, and the offset between the receivers is equal to the offset between the generators, and the data processing device is configured to receive a differential signal from the outputs of the measuring channels and compare the level this signal with a rejection level. 7. The flaw detector according to claim 6, containing pairs of the generator-receiver with the same characteristics of the electronic acoustic path. 8. The flaw detector according to claim 6, containing pairs of the generator-receiver located with mutual overlap. 9. The flaw detector according to claim 6, characterized in that the displacement between the generators is from 3 to 900 mm. 10. A flaw detector according to claim 6, characterized in that all the generators and receivers are assembled into groups of homogeneous elements. 11. The flaw detector according to claim 6, characterized in that N> 2, where N is the number of generator-receiver pairs, which is even, and the data processing device is configured to receive differential signals from the outputs of alternating measuring channels. 12. The flaw detector according to claim 11, containing the generator-receiver pairs displaced uniformly, while the data processing device is configured to average the measurement result. 13. The flaw detector according to claim 11, containing the generator-receiver pairs displaced unevenly, and the data processing device is configured to impart weighting coefficients to the difference signals during averaging.

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