RU2793171C1 - Method for assessment of expansion gaps for rails of a railway track - Google Patents

Abstract

FIELD: railways.

SUBSTANCE: invention relates to methods for non-destructive testing of a railway track, in particular, to methods for estimating gaps in bolted rail joints. During the movement of the mobile flaw detection tool, a magnetic field in the rails is generated , the scattered magnetic field is recorded with magnetically sensitive sensors, wherein the rail is magnetized with a magnetization system to a level close to magnetic saturation, which ensures a stable magnetic flux in the rail, the bolted joint area is determined, parameters of the signal caused by the scattering of the magnetic field in the zone of the gap are measured, and the measured parameters are used estimate the value of the expansion gap. The measured parameters are the distance between the extrema and the amplitude of the signal from the expansion gap.

EFFECT: increased veracity and reliability during estimation of the expansion gap values, resulting in higher safety of rail track operation.

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Description

The invention relates to methods for non-destructive testing of materials by studying magnetic stray fields and can be used in the current maintenance and maintenance of railway (railway) tracks, in particular, by assessing the gaps in the bolted joints of the rails.

The safety of train traffic both on the link and on the "jointless" track largely depends on the state of the bolted joints. A jointless track usually consists of welded rail lashes 800 m or more in length, which are separated by leveling spans (two, three or four pairs of bit rails 12.5 m long on both lines of the track, fastened with bolted joints), zones of turnouts and station tracks [1 , 2]. The ends of jointless rail lashes become "breathable", i.e. can change their original length with changes in ambient temperature. In addition, there may be places of temporary restoration on jointless tracks (if a defect is detected, a section of a rail lash 8-11 m long is cut out and a temporary rail is installed, connected to the lash rails using bolted joints).

Despite the trend towards a seamless track (more than 75% of the main tracks on the Russian Railways road network by 2022), on the rail tracks of the railway. the network contains more than 9.5 million bolted joints.

It is known that in the cold season the rails are shortened, and in the hot season they are lengthened. Gaps are left in the bolted joints of the rails during their laying so that when the temperature changes, the rails can change their length in order to avoid the occurrence of significant thermal stresses (compression in summer, tension in winter).

At low temperatures, to prevent bending or shearing of butt bolts, the gaps in the joints should not exceed 22 mm (when using rails 25 m long with hole diameters of 36 mm) [1, 2].

At elevated temperatures (in summer), for lateral stability of the link track, it is not allowed to have more than two zero gaps in a row for rails 25 m long and more than four - for rails 12.5 m long. Uncontrolled thermal expansion of the rail string (in summer) can lead to: called "ejection" of the track and to the derailment of the rolling stock. According to current standards [1, 2], a change in gaps by more than 52 mm with three leveling rails requires the replacement of one of them [3].

Periodic assessment of the butt gaps makes it possible to predict the reliability of the rail track and prevent undesirable consequences when extreme and close to them temperatures occur [2, 4]. Thus, depending on the time of year, there are two fundamentally different approaches to monitoring the state of butt gaps: at low temperatures, it is impossible to allow an increase in butt gaps above the permissible value, and at high positive temperatures, a decrease in butt gaps to zero. This means that the approaches to estimating the desired value can also be different.

Known acoustic method for detecting faults in the track [5], where the parameters of the acoustic pulses resulting from the mechanical impact of the wheel of the movable unit on the edge of the bolted joint of the rail track, estimate the value of the butt gap. The known method is difficult to implement and provides low accuracy and reliability of the assessment.

Known methods and devices for video recording of a rail track using equipment installed on diagnostic cars for track measurement [6] and flaw detection [7], with the help of which, of course, it is possible to estimate the magnitude of butt gaps. There is also a method for detecting stresses in rails [8], where one of the main operations is to determine the butt gap using a video recording system for bolted joints. However, the dependence of the obtained results on climatic conditions (snow, rain, shadows on the rails from infrastructure facilities), gross errors due to the influx (visors) of metal at the ends of the rails, as well as the complexity of video signal processing, cause low reliability and reliability of known technical solutions.

Known devices [9, 10 and 11] and methods for assessing butt gaps using eddy current transducers [12]. The known method and devices require the creation of special equipment, significantly depend on the position of the sensors relative to the rail tread surface and have low reliability and reliability.

Known methods for detecting a break in the rails of the railway. tracks (for example, [13]), implemented using electric or fiber optic cables laid along the rails to detect a break in the railway. way. However, these methods require a significant initial investment and do not provide the ability to determine gap values with the required accuracy.

There is a known method for detecting defects in rails by the magnetodynamic method of non-destructive testing [14, 15] (the term “MFL method” is used in foreign literature - the method of displacement of the magnetic flux), which consists in excitation by appropriate means of a constant magnetic flux in the rail and fixing the magnetic field using anomaly sensors (induction coils or Hall sensors) installed on a rail section with a constant magnetic flux. With the joint movement of the specified excitation means and sensors, it becomes possible to detect magnetic field anomalies in the rail head, in particular, caused by defects in the rail head and gaps (bolted joints) of the railway. way.

A known method for detecting a break in rails railway. path [16], in which a magnetic field is generated in the rails, the scattered magnetic field is recorded by two sensors shifted relative to each other along the rails by a certain distance, and the differential signal from these sensors is calculated. The disadvantage of the known method, taken as a prototype, is the limited scope, which consists in the inability to determine and evaluate the values of the butt gaps equalization links of the rail track with the required reliability.

The task solved by the proposed method is to increase the reliability and reliability of the assessment of the values of the joint gaps of the railway. paths in a wide temperature range in automatic mode.

The problem is solved by generating a magnetic field in the rails in the method for assessing the butt gaps, detecting the scattered magnetic field with magnetically sensitive sensors, and the rail is magnetized to a level close to magnetic saturation using a magnetization system that provides a stable magnetic flux in the rail, and the bolted joint area is determined , measure the parameters of the signal caused by the scattering of the magnetic field in the zone of the gap and the measured parameters estimate the value of the butt gap. In a particular case, at negative ambient temperatures, the time interval between signal extrema from the butt gap is mainly used as a signal parameter. In another particular case, at positive ambient temperatures, the amplitude of the signal from the joint gap is mainly used as the signal parameter.

Distinctive features of the proposed method in comparison with the prototype and the prior art are:

1. The rail is magnetized to a level close to magnetic saturation using a special magnetization system that provides a stable magnetic flux in the rail, for example, known from patents [14, 15] with the placement of electromagnets on the axles of the wheel pairs of a two-axle bogie and the use of wheels as magnet poles . Unlike the prototype, this reduces false readings in the analysis of anomalous sections with an influx of rail metal with the formation of "visors" in the area of the butt gap. In the prototype, an overlaid magnet with a certain technological gap of the pole relative to the tread surface does not allow magnetization of the investigated rail head to a sufficient depth, which reduces the reliability of determining signals from butt gaps (railway breaks).

2. The use of a magnetization system that provides a stable magnetic flux in the controlled rails increases the reliability and reliability of estimating the values of the butt gaps. The prototype uses an overhead magnet, the pole of which is at a certain distance (40 mm in [16]) from the rail rolling surface. During the movement of the system, due to dynamic influences, the value of this technological gap will fluctuate, which leads to a distortion of the magnetic field excited in the surface layer of the rail head, and to a decrease in the reliability and accuracy of determining the desired value. In addition, the operation of the system, where a massive object (in the prototype, a permanent magnet) hangs at a small distance from the rail running surface, is unsafe and can lead to damage and complete inoperability of the method on operated railways. ways.

3. Preliminary detection of the bolt joint zone allows more accurate determination of the butt gap, increases the reliability of determining the values of the butt gaps and reduces the load on the processing unit, while increasing the productivity of the method, because on jointless tracks, butt gaps are relatively rare (mainly in the area of equalizing spans). In the prototype, the procedure for determining the bolted joint is not provided, which leads to the need for powerful and continuous processing of the entire flow of signals arriving at the magnetically sensitive sensors. At the same time, both re-rejection and skipping of signals from bolted joints are possible.

4. The parameters of the signal caused by the scattering of the magnetic field are measured and the size of the butt gap is estimated from the measured parameters. In the general case, to implement the method, it is sufficient to use one sensor for each rail, or one line of Hall sensors installed across the rail head, which simplifies the design of the device that implements the proposed method and improves the accuracy of the estimate. In the prototype, to obtain a differential signal, the use of two magnetically sensitive sensors is required. This complicates the implementation of the known method and reduces the measurement accuracy, since the sensors are spaced apart along the length of the rail and can react differently to dynamic effects on them in the rail break zone.

5. As a measured parameter, the distance between the signal extrema from the butt gap is used, which gives reliable data when assessing significant (up to 50 mm) gaps, which is typical for negative air temperatures (and rails), and can lead to shearing of butt bolts and to violation track integrity. In the prototype, the issues of evaluating the gaps of bolted joints at low temperatures are not considered.

6. For small values of butt gaps (from 0 to ≈7 mm), the signal amplitude from the butt gap, which is sensitive for small values, is used as a measured parameter. This parameter is relevant in summer conditions, when a decrease in the joint gap to zero limits the thermal expansion of the rails and can lead to a violation of the geometry (to a blowout) of the track. In the prototype, the issues of estimating the values of butt gaps near zero are not considered.

Thus, the set of distinguishing features of the proposed method allows to obtain the desired technical result: increasing the reliability and reliability of assessing the values of butt gaps and, as a result, improving the safety of rail track operation.

The implementation of the method is demonstrated by the following illustrative materials:

Fig. 1. The nature of the change in the magnetic field (Fig. 1b) and the shape of the signal of the induction sensor (Fig. 1c), when the magnetizing system with the sensor passes over the area of the bolted joint (Fig. 1a), where:

1 - controlled railway rail;

2 - bolted joint area with pads 3 and butt gap 4;

5 - signal from the butt gap 4 and reactions 6 and 7 from the beginning and from the end of the butt plates 3 when they are fixed by the Hall sensors (Fig. 1b) and the induction sensor (Fig. 1c)

Fig. 2. View of the signal from the butt gap 4, where:

a - amplitude (range) of the signal;

w is the width of the positive ejection;

d is the distance between signal extrema.

Fig. Fig. 3. Simulation results and experimental dependences of the signal parameters on the size of the butt gap 4 over the entire measurement range: Fig. 3a - simulation results; fig. 3b - experimental dependences.

Fig. Fig. 4. Simulation results and experimental dependences of the signal parameters on the size of the butt gap 4 at small values: Fig. 4a - simulation results; fig. 4b - experimental dependences.

The method is implemented as follows. The mobile flaw detection tool moves along the rail track at a given speed. Electromagnetic coils (solenoids) mounted on the axles of the wheelsets of a two-axle bogie (not shown in Fig.) in a known manner [14, 15] excite a constant magnetic flux on the sections of the rails located between the poles of the electromagnet (the contact patches of the wheelsets with the rails). Magnetically sensitive sensors (not shown in Fig.) installed on the tread surface in the interpolar space perceive magnetic field anomalies: defects and structural elements of the rail track (turnouts, bolted joints and gaps between the connected rails, welds, etc.). As a rule, the amplitudes of signals from butt gaps are large compared to signals from welded joints and potential rail defects. Based on this feature and with the use of technical solutions according to patents [14, 17, 18], it is possible to recognize signals from butt gaps against the background of other signals with high reliability.

Induction coils can be used as magnetically sensitive sensors when implementing the method; Hall sensors (single, in the form of rulers or a matrix); thin film magnetoresistive sensors [19]. Induction sensors, as the most reliable for operation in a wide temperature range and easy to operate, are preferable for implementing the method. When using Hall sensors, the incoming signals must first be subjected to a differentiation operation.

In traditional mobile flaw detection tools that implement the MFL method [20], the sensors are mounted on a wear-resistant non-magnetic protector (composite materials or stainless steel) that slides along the rolling surface of the monitored rails. This provides a constant gap (in practice 2-4 mm) between the measuring sensors and the rail surface, which further increases the stability of the measured parameters and does not require special technical solutions known from the prior art to monitor the gap between the sensor and the rail surface. Since the degree of pressing the sensors to the rail is low, the operational properties of the protectors provide control of 1000 km of the rail track and more without replacing them.

In the process of scanning rails in the general flow of signals sequentially arriving at magnetically sensitive sensors, signals from bolted joints can be distinguished by their characteristic features: the presence of signals (responses 6 and 7 in Figs. 1b and 1c) from the ends of butt plates 3 and signal 5 of a significant amplitudes of a certain shape (Fig. 1 and 2) from the butt gap 4 in the middle between the ends of the overlays [20 and 21]. The reliability of recognition of signals from bolted joints can be further increased using special processing [22].

The dependence of the individual parameters of the signal 5 on the size of the butt gap was preliminarily estimated by mathematical modeling (Fig. 3a). An almost linear dependence of the distances d between the maxima (extrema) of the bipolar pulse 5 on the size of the butt gap 4 (Figs. 1 and 2) is observed in the gap range from ≈7 to 30 mm. The simulation results are also confirmed by experimental studies. An analysis of the values of more than 180 butt gaps (on the high-speed section of the railway track Moscow - St. Petersburg) and their comparison with the values of d on the defectograms of the magnetic channel of the flaw detector car periodically plying along this section convincingly shows the fundamental possibility of estimating the desired parameter by the value d (Fig. 3b). The flaw detector car is equipped with a magnetization system, where the electromagnets are placed on the axles of the wheel pairs, and the wheels of the two-axle bogie of the car (Fig. 3a [14, 15, 21]. In the general case, the magnetization system, which creates a stable magnetic flux in the rail during movement, may also have a different design (for example, similar to [23]).

On the dependences (Fig. 3) in the region of small (from 0 to ≈7 mm) gaps, an area of uncertainty is observed. From the value of d (in Fig. 3a, in the zone where d ≈10 mm), we can only conclude that the butt gap is in the region of small (≈ up to 7 mm) values. Under conditions of elevated positive temperatures, this knowledge for the effective maintenance of the rail track according to the requirements of regulatory documents [1, 2] may be insufficient.

The search for additional methods for estimating small values of butt gaps from magnetic control signals shows that in this case, the magnitude of the range (a - amplitude) of the signal from the gap (Fig. 2) is more informative. Both the results of mathematical modeling (Fig. 4a) and practical data (Fig. 4b) obtained under the above conditions confirm this conclusion. By measuring the amplitude of the signal from the joint gap, it is possible to estimate the size of the gap in the range from 0 to 7 mm with sufficient accuracy for practice.

The issues of determining the amplitudes a of signals from the butt gap and the distance d between the extrema (at a known speed of the diagnostic tool) are not difficult and are performed by known radio engineering methods.

Thus, during the movement of a mobile diagnostic tool equipped with a magnetization system and magnetically sensitive sensors, signals from the zones of bolted joints are extracted from the stream of recorded signals, the parameters of the signals from the butt gaps (the distance between the extrema and the signal amplitude) are determined, and the values of the butt gaps are estimated from the measured parameters. railroad bolted connections. Under conditions of significant negative temperatures (below minus 20°C), the stage of measuring signal amplitudes can be excluded from the analysis procedure, further simplifying the implementation of the method.

The high reliability and reliability of the assessment of butt gaps by the claimed method is ensured by the use of magnetic (MFL) control, based on the generation of a stable magnetic flux in the controlled rail and the fixation of magnetic flux scattering using magnetically sensitive sensors with a constant technological gap between the sensor and the scanning surface [14, 20-22 ].

The information obtained about the size of the butt gaps, with further digital processing, makes it possible to carry out in an automated form:

- determination of the presence of two or more joints with zero gaps;

- an assessment of the increase in clearances by more than 52 mm with three-section leveling spans;

- to monitor the state of butt gaps and the rail track in the process of high-speed scanning.

Currently, all these operations required in the regulatory and technical documentation for the current maintenance of the rail track are mainly performed manually.

It is important to note that the proposed method is implemented without interrupting the main function of the high-speed flaw detection tool: the detection of surface and internal defects in the rail head by the magnetic flux displacement (MFL) method. The approaches proposed in the application are implemented by introducing additional processing of the current control signals received during the working passage of a mobile vehicle along the rail tracks. In addition to detecting defects, the implementation of the method makes it possible to estimate, with sufficient accuracy for practice, the size of the gaps in the bolted joints of railway rails. way.

Sources

1. Instructions for the current maintenance of the railway track. Order of Russian Railways No. 2288/r dated November 14, 2016.

2. Instructions for laying, maintaining and repairing a seamless track. Order of Russian Railways No. 2544/r dated December 14, 2016 (as amended on September 9, 2022).

3. Stoyankovich G.M., Pupatenko V.V. Temperature deformations in the zone of leveling spans of a jointless track // Way and track facilities. 2019, No. 6, p. 34-37.

4. Melikhov S.N., Bondarenko A.A., Matvetsov V.I. Picket control of butt gaps and temperature reliability of a link track // Way and track facilities. 2022, no. 8, p. 29-32.

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Claims (3)

1. A method for assessing the butt gaps of the rails of a railway track, which consists in the fact that during the movement a magnetic field is generated in the rails, the scattered magnetic field is fixed with magnetically sensitive sensors, characterized in that the rail is magnetized to a level close to magnetic saturation using a magnetization system that provides stable magnetic flux in the rail, determine the area of the bolted joint, measure the parameters of the signal caused by the scattering of the magnetic field in the area of the gap, and the measured parameters estimate the magnitude of the butt gap. 2. The method for assessing the butt gaps of rails of a railway track according to claim 1, characterized in that the distance between the signal extrema from the joint gap is used as a measured parameter. 3. The method for assessing the butt gaps of rails of a railway track according to claim 1, characterized in that the amplitude of the signal from the butt gap is used as a measured parameter.

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