JP2000081418A - Stress sensor plate for electric railroad rail - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive stress sensor plate for an electric railroad rail, capable of obtaining a sufficient accuracy for measuring rail axial stresses even if the motor current of an electric car flows in the rail. SOLUTION: This stress sensor plate is used by bonding to the web of a rail with an adhesive, and is in the form of a rectangle for measuring rail axial stresses from generated Barkhausen noises. If an index N equals b/(a×c)1/2 where (a) and (b) are respectively the long and short sides of the rectangle and (c) is the thickness of the plate, then the index N is 5.00 or less and the plate thickness (c) is from 0.6 to 1.2 mm inclusive. The stress sensor plate is placed with its long sides parallel to the direction of the axis of the rail. Desirably, the length (a) of the long side of the stress sensor plate is 100 mm or less and the length (b) of the short side is from 15 to 30 mm inclusive.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stress sensor plate attached to an electric railway rail in order to non-destructively measure an axial stress generated in the rail.

[0002]

2. Description of the Related Art Normally, railroad rails are restrained on a track bed through sleepers and fastening jigs, so that they cannot be freely expanded and contracted due to a rise or fall in temperature. Stores axial stress. In particular, when the axial stress of the compression exceeds a certain critical value, the rail may buckle or the like, so that diagnosing these axial stresses is important in maintaining the track.

As a method for non-destructively diagnosing the axial stress of a rail, a stress sensor plate is attached to the rail, and Barkhausen noise generated from the stress sensor plate is detected by a magnetic head, and the magnitude of the Barkhausen noise is detected. A method of obtaining a rail axial stress from the above is disclosed in Japanese Patent Application Laid-Open No. 7-280669. The stress sensor plate is a carbon steel having a structure in which cementite is precipitated, and a stress sensor plate having excellent temperature characteristics by optimizing the particle size and particle size distribution of spheroidized cementite is disclosed in JP-A-7-324.
No. 996.

In the above-mentioned stress sensor plate, the magnitude of the Barkhausen noise changes when a motor current for running the vehicle flows on the rail, so that the measurement accuracy of the rail shaft stress is increased in the electrified section where the motor current flows. There was a problem of lowering. The path of the motor current travels from the trolley wire to the train via the pantograph, rotates the traveling motor, flows from the wheels to the rails, and then returns from the rails to the substation through electric wires. When a motor current flows through the rail, a magnetic field is generated on the rail surface, and this magnetic field may affect Barkhausen noise generated from the stress sensor plate attached to the rail surface.

Since the surface magnetic field generated by the motor current decreases as the distance from the rail increases, the motor current is reduced in a stress sensor plate in which a magnetic gap is provided between a ferromagnetic material that generates Barkhausen noise and an object to be measured. Influence can be reduced. Japanese Patent Application Laid-Open No. Hei 8-145815 discloses a stress sensor plate in which a nonmagnetic material is attached to a ferromagnetic material that generates Barkhausen noise. However,
In order to manufacture a stress sensor plate in which a non-magnetic material is attached to a ferromagnetic material, there is a problem that a complicated process is required and the manufacturing cost increases. Therefore, a stress sensor plate whose measurement accuracy is not affected by the motor current cannot be provided at low cost.

[0006]

As described above, in the prior art in which a stress sensor plate is attached to a rail and the axial stress of the rail is measured from the magnitude of Barkhausen noise generated therefrom, there is a conventional technique. The measurement accuracy is not affected by the normal magnitude of motor current flowing through the wire rail, and an inexpensive stress sensor plate cannot be provided.

An object of the present invention is to obtain sufficient rail axial stress measurement accuracy even when a train motor current flows through a rail.
Another object is to provide an inexpensive stress sensor plate for an electric railway rail.

[0008]

A stress sensor plate for an electric railway rail according to the present invention is used by attaching it to a rail web with an adhesive and measuring a rail axial stress by a generated Barkhausen noise. If the length of the long side of the rectangle is a, the length of the short side is b, the plate thickness is c, and the index N = b / (a × c) ^1/2 , the index N Is 5.00 or less, and the plate thickness c is 0.6 mm or more.
2 mm or less, and the long side is arranged parallel to the rail axis direction.

In this case, the length a of the long side of the stress sensor plate is 100 mm or less, and the length b of the short side is 15 mm or more and 30 mm or less.
mm or less.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to what kind of stress sensor plate can accurately measure the axial stress of a rail without being affected by a train current and can reduce manufacturing cost. Is a technique achieved as a result of various studies. Hereinafter, specific embodiments of the present invention will be described.

When a motor current flows in the axial direction of the rail, a magnetic field is generated in the vertical direction connecting the head and the leg of the rail near the rail web surface according to Ampere's law. The stress sensor plate in which the long side of the rectangle is attached to the rail web in parallel with the rail axis direction is magnetized in the direction of the short side by the magnetic field generated by the motor current. The magnitude of the Barkhausen noise is affected by the magnetization of the stress sensor plate in this manner.

The stress sensor plate disclosed in Japanese Patent Application Laid-Open No. 8-145815 aims to reduce the influence of a surface magnetic field by separating a ferromagnetic material that generates Barkhausen noise from an object to be measured. On the other hand, the stress sensor plate of the present embodiment has the effect of reducing the influence of the surface magnetic field, and furthermore, is hardly magnetized in the direction of the short side of the stress sensor plate even when an external magnetic field is applied in the direction of the short side. Stipulates the dimensions of the stress sensor plate. Further, since the structure of the stress sensor plate is integrated, the manufacturing cost can be remarkably lower than that of the conventional multilayer structure.
Therefore, according to the present embodiment, it is possible to provide an inexpensive stress sensor plate that is not affected by the surface magnetic field generated by the motor current.

The stress sensor plate of the present embodiment focuses on the fact that the easiness of magnetization of the ferromagnetic material changes depending on its size.
The dimensions are specified for the purpose of measuring rail axis stress. When a magnetic field is applied from the outside, the ferromagnetic material is magnetized in the direction of the magnetic field. At this time, magnetic poles are generated on both end surfaces in the magnetization direction of the ferromagnetic material. Inside the ferromagnetic material, a magnetic field (referred to as demagnetizing field) is formed by the magnetic poles in a direction opposite to the magnetic field applied from the outside. The resulting magnetic field is subtracted. The demagnetizing field increases as the distance between the magnetic poles on both end faces decreases and as the area of both ends where the magnetic poles generate increases, and in such a case, the effective magnetic field acting on the ferromagnetic material decreases. The rectangular shape stress sensor plate of the present embodiment is magnetized in its short side direction by the surface magnetic field caused by the motor current.

Therefore, the length of the long side of the stress sensor plate is a,
Assuming that the length of the short side is b and the plate thickness is c, the shorter the length b of the short side of the stress sensor plate is, the larger the product (a × c) of the length a of the long side and the plate thickness c is. As the effective magnetic field becomes smaller, the stress sensor plate becomes harder to be magnetized. Here, as an index representing this effect, the exponent N (dimensionless number) = b / (a × c ) 1/2
Is defined. As b becomes shorter and (a × c) becomes larger, the index N becomes smaller, the effective magnetic field becomes smaller, and the influence of the motor current becomes smaller. In addition to the above-described effects, when the plate thickness c increases, the same effect as in the related art can be obtained in which the distance between the measurement surface of the stress sensor plate and the rail surface increases and the surface magnetic field decreases.

The method for attaching a stress sensor plate according to the present embodiment is a method of attaching a stress sensor plate to a rail web with an adhesive such that the direction of the long side of the stress sensor plate is parallel to the axial direction of the rail. is there. If the length b of the short side is attached in parallel to the rail axis direction, the demagnetizing field becomes small, and it is easily affected by the motor current flowing through the rail. Therefore, the long side is attached with an adhesive so as to be parallel to the rail axis direction.

The present inventors have prepared stress sensor plates of various dimensions and determined in detail the influence of Barkhausen noise on the surface magnetic field due to the motor current to determine the optimal dimensions of the stress sensor plate. Here, as a criterion for determining the optimum dimensions, for example, when the current density of the motor current flowing through the rail is 5 A / cm ² , the change in the effective value voltage of Barkhausen noise is set to 2% or less. . This means that the maximum value of the motor current flowing through the rails of an electric railway is 15 A /
cm ^2, but at most 5A / cm ²
If the change in the effective value voltage of Barkhausen noise is 2% or less, the measurement accuracy of the axial stress is 5 or less.
This is because it is ± 3 tons or less in terms of 0 KgN rail, and sufficient measurement accuracy is obtained for practical use.

Experiments were conducted using stress sensor plates of various dimensions having different indices N. As a result, when the range of the indices N was 5.00 or less, the Barkhausen noise was reduced when the motor current density was 5 A / cm ² . It has been found that the change in the effective value voltage is 2% or less. If the index N exceeds 5.00, the stress sensor plate is likely to be magnetized by the motor current, and the change in the effective value voltage of Barkhausen noise becomes larger than 2%, which lowers the measurement accuracy of the rail axial stress. Therefore, the index N must be less than 5.00.

The thickness c of the stress sensor plate is limited to 0.6 mm or more and 1.2 mm or less. Since the Barkhausen noise is measured on the surface opposite to the surface of the stress sensor plate attached to the rail web portion, as the thickness c of the stress sensor plate increases, the surface of the stress sensor plate where the Barkhausen noise is measured and the rail are measured. The interval increases. The effect of the magnetic field generated by the motor current decreases as the interval increases. When the plate thickness c is less than 0.6 mm, the distance between the rail surface and the stress sensor plate surface is not sufficient, and the magnetic field is not attenuated due to the motor current. Therefore, even when the index N is small, the measurement accuracy of the axial stress is small. Will decrease. Therefore,
The thickness c was limited to 0.6 mm or more. On the other hand, when the thickness c of the stress sensor plate exceeds 1.2 mm, the distortion of the rail is not accurately transmitted to the stress sensor plate, so that the measurement accuracy of the rail axial stress is reduced. Therefore, the thickness c was limited to 1.2 mm or less.

The length a of the long side of the stress sensor plate is 100 mm
The following is desirable. If a exceeds 100 mm, the fatigue strength of the bonded portion fixed with an adhesive at the end in the direction of the long side of the stress sensor plate decreases. The range of the length b of the short side is 15 mm
It is desirable to limit it to 30 mm or less. b is 15
If it is less than mm, the demagnetizing field in the direction of the short side becomes large and the influence of the motor current becomes strong, but the stress sensitivity of Barkhausen noise decreases. Further, even if b exceeds 30 mm, no improvement in the stress sensitivity of Barkhausen noise is observed, and it becomes difficult to attach the rail to the rail web. Therefore, b is set to 15 mm or more and 30 mm or less.

The material of the stress sensor plate of the present invention is disclosed in
No. 324996, and α-Fe
Cementite was precipitated in the inside. The stress sensor plate of the present invention controls the thickness c when processing carbon steel into a thin plate by rolling, and adjusts the structure to an optimal structure by heat treatment. Thereafter, it can be manufactured by cutting the long side a and the short side b with a shear or the like so as to fall within the scope of the present invention.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail according to several embodiments.

(Embodiment 1) Barkhausen noise and rail generated from each stress sensor plate when a stress sensor plate of various dimensions is attached to a model rail and a direct current is passed in the axial direction of the rail under no stress. The relationship between the current densities was examined. Here, the current density of the direct current is 0 to 30 A / cm.
Changed to ² .

The material of the stress sensor plate is carbon steel (0.8%
C) is subjected to quenching and tempering to precipitate particulate cementite in the ferrite. From the carbon steel, three types of stress sensor plates shown in Table 1 were cut out.

[0024]

[Table 1]

A 50 kg rail having a length of 1 m was prepared, and these stress sensor plates were attached to a rail web near the center with an adhesive. At this time, the direction of the long side of the stress sensor plate was parallel to the axial direction of the rail. After the adhesive was cured, an experiment was performed to detect a Barkhausen noise by installing a magnetic head on a stress sensor plate while applying a direct current in the axial direction of the rail. Here, the conditions for detecting Barkhausen noise are as follows. Exciting magnetic field is 100Hz
The magnetic field application direction is the direction of the long side of the stress sensor plate. The detection of Barkhausen noise was performed by amplifying the voltage induced in the detection head of the magnetic head with an amplifier and then passing through a band-pass filter of 10 kHz to 100 kHz. The effective value voltage was calculated from the obtained Barkhausen noise voltage signal using a microcomputer.

FIG. 1 shows the relationship between the current density of the DC current flowing through the rail and the effective voltage of Barkhausen noise.
The rate of change of Barkhausen noise is determined based on the effective voltage when the current density is 0.

As a result, it was found that the effective voltage of the Barkhausen noise detected from the stress sensor plate of Comparative Example 1 was significantly reduced as the DC current flowing through the rail was increased. In the stress sensor plates of Invention Examples 1 and 2, when the current density was 5 A / cm ² , the change in the effective value voltage was 2% or less, and the change in Barkhausen noise with the increase in the current density was smaller than that in the comparative example. Less.

As is apparent from the above results, the stress sensor plate of the present invention is hardly affected by the direct current flowing through the rail, and the decrease in Barkhausen noise when the current density increases is small.

Example 2 A stress sensor plate having a different long side length a shown in Table 2 below was attached to a model rail having a length of 1 m with an adhesive, and ± 10 kg / m in the axial direction of the rail.
Experiments were carried out to apply the repeated stress of m ^2. The material of the stress sensor plate is the same as that of the first embodiment. Before the experiment of applying the stress repeatedly, a direct current having a current density of 5 A / cm ² was applied to the rail to examine the rate of change of Barkhausen noise.
The rate of change was 2% or less for any of the stress sensor plates.

[0030]

[Table 2]

As a result of the repeated stress test, in the stress sensor plate of Inventive Example 3 in which the length a of the long side exceeded 100 mm, when the stress was applied several hundred thousand times, the bonded portion at the end in the long side direction was broken.
In the stress sensor plate of Invention Example 4, no abnormality was observed in the bonded portion even after hundreds of thousands of repeated stresses were applied. As can be seen from this example, the length a of the long side of the stress sensor plate is desirably 100 mm or less from the viewpoint that more excellent fatigue strength of the bonded portion can be obtained.

As described above, it is understood that the Barkhausen noise is not affected by the rail current and also has excellent durability.

(Example 3) The stress sensor plates of Comparative Examples 2, 3 and Inventive Example 5 having different short side lengths b shown in Table 3 below were adhered to a model rail having a length of 1 m with an adhesive. The material of the stress sensor plate is the same as that of the first embodiment. When attaching the stress sensor plate of Comparative Example 3 in which the length b of the short side exceeded 30 mm, it was found that the attaching operation was difficult and was not practical.

After the adhesive was cured, a load was applied in the axial direction of the rail, and the stress sensitivity of each stress sensor plate to Barkhausen noise was examined.

[0035]

[Table 3]

The stress sensitivity of the stress sensor plate of Comparative Example 3 in which the short side length b was less than 15 mm was low, and it was found that the stress sensor plate was not at a practical level. The stress sensitivity of the stress sensor plate of Invention Example 5 was sufficiently high for practical use.

As described above, it was found that the stress sensor plate of the present invention can be easily attached to the rail, and that there is no practical problem with the sensitivity to Barkhausen noise.

Example 4 A stress sensor plate having a different thickness c shown in Table 4 below was attached to a 1 m model rail with an adhesive. The material of the stress sensor plate is the same as that of the first embodiment.

[0039]

[Table 4]

After the adhesive was cured, a direct current having a current density of 5 A / cm ² was passed in the axial direction of the model rail, and Barkhausen noise was measured under the same conditions as in Example 1. As a result, the Barkhausen noise measured by the stress sensor plate of Comparative Example 4 in which the plate thickness c was less than 0.6 mm changed significantly when a direct current flowed, and the effective voltage changed 5.1%. This large change is due to the fact that the index N of Comparative Example 4 is less than 5.00, and the demagnetizing effect works sufficiently. However, since the distance between the rail surface and the stress sensor plate surface is small, the effect of the magnetic field generated by the rail current is small. Due to the large Barkhausen noise measured by the stress sensor plates of Comparative Example 5 and Inventive Example 6 showed a small change due to DC current, and the respective change rates were 1.1% and 1.7%.

Next, the strain of the rail base material and the strain of the surface of the stress sensor plate when a load was applied in the axial direction of the model rail were measured using a strain gauge. As a result, in the stress sensor plate of Comparative Example 5 in which the plate thickness c exceeded 1.2 mm, the distortion of the surface of the stress sensor plate was smaller than that of the rail, and the distortion of the base material rail was not transmitted accurately. Do you get it. There was no problem in the transmission of the strain of the stress sensor plate of Inventive Example 6, and it was found that the measurement accuracy of the axial stress used for practical use was obtained.

As is clear from the above results, it is understood that the stress sensor plate of the present invention is not only susceptible to the current flowing through the rail, but also has excellent strain transmission.

[0043]

By using the stress sensor plate for an electric railway according to the present invention for measuring the rail axial stress, the accuracy of measuring the axial stress is not affected by the motor current of the train flowing on the rail. For this reason, the axial stress of the rail can be measured with high accuracy even when the motor current is flowing, and the track maintenance can be performed with high accuracy.

[Brief description of the drawings]

FIG. 1 shows the relationship between the current density of a DC current flowing through a rail and the rate of change of the effective value voltage of Barkhausen noise in Comparative Example 1.
FIG. 4 is a characteristic diagram shown for Invention Examples 1 and 2.

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroaki Sakamoto 3-35-1, Ida, Nakahara-ku, Kawasaki-shi N-Technology Development Division F-term (reference) 2G053 AA19 AB20 BA13 BC02 CA04 CA18 DB01 DB14

Claims (2)

[Claims] 1. A stress sensor plate for an electric railway rail having a rectangular shape, which is used by attaching to a rail web with an adhesive and measuring rail axial stress by generated Barkhausen noise. If the length of the long side is a, the length of the short side is b, and the plate thickness is c, and the index N = b / (a × c) ^1/2 , the index N is 5.00 or less, and the plate thickness is c is 0.6 mm or more and 1.2 m
m or less, and the long side is arranged in parallel with the rail axis direction. 2. The length a of the long side is 100 mm or less,
The stress sensor plate for an electric railway rail according to claim 1, wherein the length b of the short side is 15 mm or more and 30 mm or less.