RU2308027C1 - Method of ultrasonic test of rail head - Google Patents

Abstract

FIELD: testing engineering.

SUBSTANCE: method comprises setting two identical pairs of electroacoustic converters on the surface of the rail. The electroacoustic converters are arranged and directed so that the signal emitted by the first converter being reflected from the rail boundary enters the second converter.

EFFECT: reduced sizes.

3 dwg

Description

The invention relates to non-destructive testing of materials and can be used for ultrasonic (US) defectoscopy of railway rails, in particular rail heads.

Known methods for ultrasonic monitoring of the rail head, patents [1], [2], which consist in the fact that a pair of electro-acoustic transducers (EAP) are installed on the rail surface, directed to opposite radial transitions of the side and lower faces of the rail head, combined into a measuring unit, emit sounding and receive the reflected ultrasonic signals by electro-acoustic transducers, move the measuring unit along the longitudinal axis of the rail, the presence of a defect is judged by a joint analysis of the signal s taken electroacoustic transducers.

The disadvantages of these methods are limited capabilities and low reliability of measurements. Limited capabilities are associated with the sound of only one side of the rail head. Low reliability is associated with the lack of control of the acoustic contact of the EAA with the rail surface, as a result of which the absence of a signal between the EAA can indicate not only the absence of a defect, but also their poor contact with the rail surface.

With ultrasonic testing of products, it is necessary to provide an acoustic EAP of contact with the surface. To solve this problem, clamping devices of various designs and special contact liquids are used. However, for various reasons, this contact may be violated, which leads to errors in the operation of ultrasonic inspection systems - to false alarms or omissions of defects. Various methods are used to control the acoustic contact of an EAP:

1. Measurement of the amplitude of bottom reflection of a longitudinal wave emitted by an additional piezoelectric plate into the prism of an inclined transducer and introduced into the metal at the same place where the main transverse wave is introduced [3], [4]

2. Evaluation of the quality of the acoustic contact by the intensity of the continuous low-frequency reference signal (white noise) supplied to the working EAP, specially created by a separately spaced source of white noise [5].

3. The creation of an auxiliary beam of surface waves to control the quality of the acoustic contact [6].

4. Assessment of acoustic contact by the duration of the probe pulse [7] allows only approximately to judge the degree of contact and cannot be used with mechanized and automated control due to the low reliability of the control.

5. Isolation of structural reverberation noise against the background of received echo signals from possible defects and, based on its level, the assessment of the presence of acoustic contact [8].

All these methods involve the use of additional devices and circuits that complicate and cost the flaw detector.

For ultrasonic flaw detection of rails, due to the complexity of the shape of the object, as a rule, multichannel sounding schemes are used [9]. In this case, several EAFs are combined into a block, which for continuous control is moved along the rail. An important role for ensuring the reliability of control is played by the correct position of the EAA block relative to the rail. In particular, usually an ultrasonic rail flaw detector contains several EAPs in which the sensing circuits are directed along the neck of the rail. At the same time, even with a small (± 3 mm) lateral displacement of the measuring unit, such EAPs cease to work. To ensure the alignment of the EAP block, various devices are used, for example [10], [11]. Despite the measures taken, when moving the EAF unit for various reasons, for example, due to wear of the side surface of the rail head, undesirable displacements of the measuring unit can occur and an unreliable measurement result is obtained. To identify such a situation, it is necessary to control the position of the EAA block during measurements.

Closest to the claimed is a method of ultrasonic monitoring of the rail head, patent [12], which consists in the fact that two identical pairs of EAA are installed on the rolling surface of the rail, directed to opposite radial transitions of the side and lower faces of the rail head, united in a measuring unit and located mirror relative to the longitudinal axis of symmetry of the rail, probing radiate and receive reflected ultrasonic signals by all EAP, move the measuring unit along the longitudinal axis of the rail, about the presence defect judged by a joint analysis of the signals received by the EA.

The disadvantage of this method is the limited capabilities and low reliability of the measurements. Limited opportunities are associated with the fact that when using four EAPs, more information can be obtained and the quality and reliability of measurements can be increased. Low reliability is associated with the lack of control of the acoustic contact of the EA with the rail surface, as a result of which the absence of a signal between them can indicate not only the absence of a defect, but also poor contact with the rail surface.

The problem to be solved in the present method is to increase the reliability of ultrasonic monitoring of the rail head due to the continuous monitoring of the contact of the EAP with the rail surface, as well as the position of the EAP block on the rail by cheap means.

To solve this problem, in the method of ultrasonic monitoring of the rail head, which consists in the fact that two identical pairs of electroacoustic transducers are installed on the rolling surface of the rail, directed to opposite radial transitions of the side and lower faces of the rail head, combined into a measuring unit and located specularly relative to the longitudinal axis of symmetry rail, emit sounding and receive reflected ultrasonic signals by all electro-acoustic transducers, move the meter The unit along the longitudinal axis of the rail, the presence of a defect is judged by a joint analysis of the signals received by the electro-acoustic transducers, the location and direction of the electro-acoustic transducers in each pair is chosen so that the ultrasonic signal emitted by one of them, reflected from the rail boundary, is received second and vice versa , when receiving this ultrasonic signal, evaluate it and use it to control the contact of electro-acoustic transducers with the rail surface, evaluate the difference in distribution times elimination of these ultrasonic signals in the first and second pair of electro-acoustic transducers, which assess the symmetry of the position of the measuring unit relative to the longitudinal axis of symmetry of the rail.

Significant differences of the proposed method in comparison with analogues known to the authors are: the location and direction of the EAP in each pair is chosen so that the ultrasonic signal emitted by one of them, reflected from the radius transition of the side and lower faces of the rail head of the rail border, is adopted second and vice versa. This allows you to receive a signal reflected from the defect emitting EAP, and in the absence of defects to receive a signal reflected from the rail border by the second EAP in each pair. The latter circumstance allows you to continuously monitor the presence of the acoustic contact of the EAP with the rail.

In the prototype, the acoustic contact is not controlled. As a result, the absence of an ultrasound response from a defect can indicate both the absence of a defect and the contact of the EAP with the rail, which can lead to the omission of the defect.

Evaluation of the difference in the propagation times of the ultrasonic signals in the first and second pairs of EAP makes it possible to assess the symmetry of the position of the measuring unit relative to the longitudinal axis of symmetry of the rail, and thereby increase the reliability of the inspection. In particular, if there are EAPs directed along the neck of the rail, to detect measurement errors caused by the incorrect position of the measuring unit, and repeat the measurements if necessary.

In the prototype, the control of the position of the measuring unit is impossible.

These significant differences can improve the quality and reliability of ultrasonic monitoring of the rail head by changing the sounding scheme and processing algorithms of the measurement results, i.e. cheap means.

The inventive method is illustrated by the following graphic materials:

Figure 1 is a diagram of the sounding of the rail head.

Figure 2 - sounding scheme with lateral displacements of the measuring unit.

Figure 3 - device that implements the inventive method.

Consider the possibility of implementing the proposed method.

On the rolling surface of the rail of Fig. 1, two identical pairs of EAA 1 and 2, 3 and 4 are installed, directed to opposite radial transitions of the side and lower faces of the rail head, the location and direction of the electro-acoustic transducers in each pair is chosen so that the ultrasonic signal emitted by the EAA 1 (3), reflected from the rail border, EAP 2 (4) was adopted and vice versa. EAP pairs 1-2 and 3-4 are located mirror-image relative to the longitudinal axis of symmetry of rail Y and are combined into a measuring unit 5, and each EAP has its own system of clamping to the rail surface. The measuring unit 5 ensures the preservation of the relative distance between the EA. The distance between EAP 1 and 2 (3 and 4) is selected based on the tasks to be solved. If they are close, then the angle between the Y axis and the direction of input of the ultrasonic signals approaches 90 °. At the same time, the conditions for the detection of longitudinal cracks in the rail head and the accuracy of measuring the symmetry of the position of the EAF relative to the Y axis are improved. When the EAA is removed from 2 and 3 from 4, the conditions for the detection of transverse rail defects are improved, but the accuracy of measuring the symmetry of the position of the EAA relative to the Y axis is reduced.

The sounding ultrasonic signals are emitted according to the described EAP schemes 1 and 3, and due to their different directions, the radiation can be produced simultaneously. Reception of the reflected signals is carried out by EAP 2 and 4, respectively, as well as EAP 1 and 3, switched to the reception mode. Then, in the same way, sounding is carried out during the reverse stroke of ultrasonic signals, i.e. emit ultrasonic signals EAP 2 and 4, and take 1, 2, 3 and 4 EAP.

The sounding results are evaluated by a joint analysis of the signals received by all EAPs. The following options are possible:

1. The absence of reflected signals in each pair of EAPs indicates a poor acoustic contact between the EAP and the rail surface.

2. The arrival of the reflected signal in the emitted EAP indicates the presence of a transverse defect in the rail head.

3. The signal reflected from the rail boundary and received in the second EAA indicates the absence of a defect and the presence of acoustic contact of the EAA with the rail surface.

The measuring unit 5 is moved along the longitudinal axis of the rail, repeating the measurements described above. In this case, it becomes possible to sound the entire volume of the rail head. For example, defect 6, perpendicular to the Y axis, will be detected when sounding from the EAP 1 and EAP 2 sides, but due to the lateral part of the radiation pattern. Defect 7 is collinear to the sound line of EAP 1 and cannot be detected by it, however, at a certain position of the measuring unit 5, EAP 2 can successfully detect this defect. Similarly, defect 8 is invisible to EAP 2, but EAP 1 is easily detected.

Estimate the difference in the propagation times of ultrasound signals between the EAP 1-3 and 2-4. If EAP 1-2 and 3-4 (measuring unit 5) are located symmetrically with respect to the Y axis, Fig. 2, then the propagation times of ultrasonic signals from the EAP 1 to the border of the rail 9 to the EAP 2 and from the EAP 3 to the border of the rail 9 to the EAP 4 are the same and the indicated difference is zero. If the measuring unit 5 is displaced, then the rail borders occupy the position 10 or 11. At the same time, the propagation times of ultrasonic signals between pairs of EAP 1-2 and 3-4 become different, and the signals themselves are smaller in amplitude, since the EAP take the side of the radiation pattern.

The structural diagram of a device that implements the inventive method is presented in figure 3, where:

1-4 - EAP.

12 is the first switch.

13 - the second switch.

14 - generator of ultrasonic sounding signals.

15 - receiver of the reflected signal.

16 - analog-to-digital Converter.

17 is a computer.

18 is a monitor.

EAP 1-4 are designed for radiation and reception of ultrasonic signals and can be implemented on the basis of piezoelectric transducers. Each of them has its own radiation - reception angle, based on the chosen method and sounding scheme.

The first switch 12 is designed for the sequential supply of sounding signals to the EAA 1 and 2 or 3 and 4. It can be implemented on the basis of electronic keys with a common input, control inputs and outputs connected to the corresponding EAA.

The second switch 13 is designed to supply reflected from the defect signals received by the EAE 1-4, to the inputs of the processing device.

The generator of ultrasonic sounding signals 14 is designed to generate a pulsed sounding signal and can be implemented on the basis of any of the traditional schemes.

The receivers of the reflected signal 15 are designed to receive, amplify and generate signals received by the EA. They can be implemented on the basis of amplifier-forming devices.

Analog-to-digital converters (ADCs) 16 are designed to input signals received by the EAP 1-4 into a digital processing device. Signal conversion is carried out according to clock signals, which are not shown in the diagram for the purpose of simplification.

Computer 17 is designed to process measurement results. The processing algorithms are obvious and include the following program blocks:

- management of the first 12 and second 13 switches;

- start generator ultrasonic probe signal 14;

- reception of digitized signals;

- comparison of amplitudes of received signals with detection thresholds;

- calculation of signal propagation times between EAP;

- display of all measurement results (defect location) on the monitor screen 18.

Monitor 18 is designed to display measurement results.

The operation of this device is as follows.

Before starting the measurement, the measuring unit 5 with EAP 1-4 is installed on the rolling surface of the rail with the possibility of movement along the rail.

According to the control code from the computer 17 to the first switch 12 EAP 1 and 2 are connected to the output of the probe signal generator 14. According to the signal from the computer 17 of the ultrasonic probe, the probe signal from the generator 14 is fed to the rail head. The second switch 13 according to the control code from the computer 17 connects all the EAFs to the receivers 15. The receivers 15 receive the reflected signals and feed them to the ADC 16, which, with a high frequency specified by the clock, form the digitized values of the reflected signals received by the computer 17. The latter compares the received responses with detection thresholds and calculates the propagation times of signals in the rail. The results obtained according to the above rules are used to assess the presence or absence of defects in the rail, to assess the quality of the acoustic contact of the EA with the rail, as well as to monitor the position of the measuring unit 5 on the rail. The processing results are displayed on the monitor 18. According to this image, the operator decides on the state of the measuring system and the quality of the rail head. Repeat measurements with the opposite direction of sounding. Moving the measuring unit 5, measure the rails along the entire length.

Thus, the claimed method is technically feasible and provides improved quality and reliability of ultrasonic monitoring of the rail head.

Literature

1. Patent RU No. 2060493.

2. Patent RU No. 2184960.

3. US patent No. 2667780.

4. Autosvid. USSR No. 1534388, 603896.

5. Autosvid. USSR N 574668.

6. Autosvid. USSR No. 1405494.

7. Autosvid. USSR No. 1597719.

8. Autosvid. USSR N 1753405.

9. Patent RU No. 2227911.

10. Patent RU No. 2184372.

11. Patent FR No. 1214058.

12. Patent RU No. 2184374.

Claims (1)

The method of ultrasonic monitoring of the rail head, namely, that two identical pairs of electroacoustic transducers are installed on the rail surface, directed to opposite radial transitions of the side and lower faces of the rail head, combined into a measuring unit and located specularly relative to the longitudinal axis of symmetry of the rail, emit probing and receive reflected ultrasonic signals by all electro-acoustic transducers, move the measuring unit along the longitudinal the axis of the rail, the presence of a defect is judged by a joint analysis of the signals received by the electro-acoustic transducers, characterized in that the location and direction of the electro-acoustic transducers in each pair is chosen so that the ultrasonic signal emitted by one of them, reflected from the rail boundary, is received second and vice versa when receiving this ultrasonic signal, evaluate it and use it to control the contact of electro-acoustic transducers with the rail surface, estimate the difference in the propagation times neniya these ultrasonic signals in the first and second pair of electroacoustic transducers, which is evaluated by measuring the symmetry of the block position relative to the longitudinal axis of symmetry of the rail.

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