JPH0238043B2 - RONGUREERUKYOKUBUHEKOMINOTATEKYOSHOBO - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention relates to a method for vertically correcting local dents in long rails, which flattens the top surface of a long rail by removing the local dents that have occurred on the top surface of the long rail while it is being laid. .

[Conventional technology]

For high-speed railway rails, welded long rails are made by welding standard length rails of 25 m in length to increase the length from 1.0 to 1.5 km in order to improve train running stability, reduce joint noise, and reduce track maintenance costs. is used.

For rail welding, we use flash welding, gas pressure welding,
Enclosed arc welding or thermite welding is used, but in either method, due to the heating during rail welding, the area around the rail weld has a different property from the rail base material, which has uniform properties as manufactured at the factory. It is given the ivy property.

Figure 11 shows the top of the rail near the weld when the rail is welded by flash welding, with the horizontal axis representing the distance from the center of the weld (mm) and the length of the top surface (HB) representing the vertical axis. An example of surface hardness distribution is shown. As is clear from the figure, the base metal portion, which is not affected by heat during welding, exhibits a constant hardness, but the portions that are affected by heat during welding have areas where the hardness is significantly reduced.

As the wheels roll over the top surface of the rail, the portions of the top surface that come into contact with the wheels wear out. Figure 12 shows the distance (mm) from the weld center on the horizontal axis.
The wear amount (mm) of the top surface of the rail is taken as the vertical axis, and the wear condition of the top surface of the rail with the hardness distribution shown in FIG. 11 at a tonnage of 2.2 billion tons is shown. The wear state of the top surface of the rail is almost flat in the base metal parts other than the welded parts, but near the welded parts it wears into a shape that corresponds to the change in hardness.

For this reason, when a high-speed train is running, significant impact noise is generated depending on the condition of the tread of the rail weld, so in order to maintain or increase the train speed,
It is necessary to remove minute irregularities on the tread surface. These minute irregularities can be flattened only by grinding, but if the irregularities exceed a certain limit, the amount of grinding becomes large, which is inefficient and uneconomical.

Conventionally, the vertical rail straightening method for removing minute irregularities on the top surface of the rail is mainly based on external force, which applies a bending load exceeding the elastic limit to the rail at ambient temperature to cause it to plastically deform. A local heat treatment straightening method in which the head or bottom of the rail is locally heated and cooled using a hand-held burner to thermoplastically deform the rail, while the restraining force is limited to the level of binding, and the entire cross section of the rail is fixed using an appropriate device such as a gas burner. A There is a total heating straightening method that involves heating to a temperature above the ₃ transformation point and then applying an external force using a hydraulic device.

[Problems to be solved by the invention] The correction method that mainly uses external force uses a hydraulic device,
This method performs static bending at around room temperature, and because the amount of bending deformation can be easily adjusted, the finishing accuracy after straightening is good.

However, since the bending device is required to have the rigidity to withstand the large load corresponding to the rail, the bending device is large in size and is usually used for factory or base work. Even if this is made portable and workability is improved, the following problems may occur when straightening long rails that have been installed for many years. In other words, surface defects such as creaks and cracks often exist on the top surface of aged rails, and when large bending stress is applied to correct such areas, the defects may expand due to stress concentration, or if the defects are severe. There is even a risk of brittle fracture.

The local heat treatment straightening method is simple and does not require any special equipment, but the reproducibility of the straightening amount is poor, and if the heating temperature is low, it cannot be straightened, whereas if the heating temperature is high, quench cracking will occur, so temperature control is required. difficult,
There was a problem in that a high degree of skill was required to improve the correction accuracy.

In the whole heating straightening method, the entire cross section of the rail is kept at a high temperature using a ring burner or the like, so the external force required for straightening may be small. However, this method of straightening long rails has the following problems.

Figure 13 shows the results of the tensile test of the rail, with the horizontal axis representing the tensile test temperature (°C) and the vertical axis representing the tensile strength TS and yield strength YS (Kg/mm ² ). If the entire cross section of the rail is heated above 750°C, which is the _A3 transformation point, the rail strength will decrease and it can be easily straightened. However, if the rail temperature during straightening is below the set temperature, a tensile axial force acts on the rail, and there is a significant temperature difference, for example, the rail temperature when straightening is 40°C lower than the temperature when it was laid. The tensile force (pulling axial force/rail cross-sectional area) is approximately 10Kg/ ^mm2 . On the other hand, when the entire cross section of the rail is heated, the yield strength YS is 7Kg/mm ² as shown in Figure 13.
The tensile strength will be less than 9Kg/ ^mm2 , and the heating range will no longer be able to withstand the tensile force, causing a depression in the heating range.
In other words, the phenomenon of weight loss also occurs. For this reason, correction work in winter is severely restricted.

In addition, if cooling is slowed down after heating the entire rail cross section, a softened area will appear in the heating range of the top surface of the installed rail, which has hardened under rolling load, and this area will wear more selectively than other areas. As a result, the corrected area will have a short lifespan.

The present invention has been made to solve these problems, and an object of the present invention is to provide a method for vertically straightening long rails that can perform vertically straightening with high accuracy without closing the track.

[Means for solving problems]

The vertical correction method for localized dents in long rails according to the present invention involves applying an external force from the bottom of the rail around the location of the local dents on the top surface of the long rail so that the head is on the tension side.
A pre-strain of 2.5 mm is applied, and the length direction of the bottom of the rail, which is under compressive stress in this state, is heated to 750°C to 880°C over a range of 100 to 220 mm.
This method corrects local dents in long rails by heating and cooling the rails to a temperature of 300°C or less, and then maintaining the rail head below 300°C during heating and cooling of the rails.

[Effect]

In this invention, after pre-straining the rail within its elastic limit, the bottom of the rail is heated above the _A3 transformation point to cause thermoplastic deformation, and the head of the rail is
By maintaining the temperature below 300°C, softening of the top of the rail due to heating, that is, a decrease in wear resistance, is prevented.

〔Example〕

Hereinafter, as shown in FIG. 1, a method for correcting a rail 1 having a minute dent 3 formed in one place or two consecutive places on the top surface 2 will be explained in detail. In FIG. 1, 4 is the head of the rail 1, 5 is the abdomen, and 6 is the bottom.

First, as shown in FIG. 2a, the rail fastening device 7 is released by 5 to 6 sleepers 8, centering on the recess 3 of the laid rail 1, and the pressurizing table 9 is moved around the recess 3 on both sides of the recess 3. Attach it in the position. In addition, holders 10 are attached to the sleepers 8 on both sides of the pressurizing platform 9 to prevent the rail 1 from moving due to lateral pressure and causing gauge expansion even if the train runs during work.

Next, as shown in FIG. 2b, a hydraulic ram 11 is installed under the pressurizing table 9, and pressurized using a hydraulic pump 13 connected by a hose 12 to lift the rail 1.

The amount x by which the rail 1 is lifted at approximately 2 m in length is the sum of the recess depth d shown in FIG. 3 and the lifting amount u shown in FIG. 4. The recess depth d is usually
It is about 0.5 to 2.0 mm, and the overhang amount u is the result of the experiment.
Approximately 0.5mm is appropriate. Therefore, the range of the amount x by which the rail 1 is lifted is 1.0 to 2.5 mm per 2 m of rail length. When a 60Kg/m rail is lifted by 2.5mm with a 2m string, the tensile stress applied to the rail head 4 is approximately 8Kg/ ^mm2 , which is the same as that applied to the rail head in the case of the conventional correction method that plastically deforms only by external force. This is significantly smaller than the tensile stress of approximately 50Kg/mm ² or more.

Therefore, even if some defects such as creaks and cracks are present on the top surface 2 of the rail 1, there is no risk of the defects expanding or brittle fracture.

With the rail 1 lifted as described above, a small furnace 14 for bottom heating is attached to the rail bottom 6 directly below the recess 3 as shown in Fig. 2c, and the gas burner 15 is used to heat it to a predetermined temperature. Cooling.

As mentioned above, when the rail bottom 6 is heated with the rail 1 prestrained, the rail 1 deforms downward into a concave shape because the bottom 6 has a large thermal expansion. Thermoplastic deformation occurs in this area, stress relaxation also occurs, and after cooling, a slight convex amount r remains as shown in FIG. 5, and the rail 1 is corrected. After correction, if necessary, finish by grinding as shown in Figure 6. The height difference h during grinding is +0.3 to -0.1 mm/m.

As a result of experiments, the appropriate range of the bottom of the rail to be heated in the small furnace 14 is about 100 to 200 mm for a 50N rail, and 120 to 220 mm for a 60 kg/m rail, that is, about ±50 mm of the rail height. If the range of the bottom of the rail to be heated is narrow, correction will not be performed sufficiently, and conversely, if this range is too wide, buckling will occur.

Further, the maximum heating temperature in the cross section of the rail is 750 to 880°C at the bottom 6 and 300°C or less at the head 4.

Heating the bottom part 6 above 750°C is because rail steel (C; 0.6 to 0.75%) has an extremely small yield point above 750°C, which is the _A3 transformation point, and easily loses its deformation resistance. This is because thermoplastic deformation occurs. On the other hand, if the temperature is below 750°C, the deformation resistance is large and it is difficult to perform sufficient correction.

The reason why we set the upper limit of the heating temperature of the bottom part 6 to 880℃ is because
If rail steel is heated to a maximum temperature of 880°C or higher, the crystals will become coarser and the material will deteriorate, becoming brittle. At the same time, if the bottom part 6 is heated to a high temperature of 880°C or higher, the rail head 4 will be maintained at 300°C or lower. This is because it becomes difficult.

The reason why the rail head 4 is heated to 300°C or lower is because the tensile strength TS is lower than 300°C as shown in Figure 13.
This is because the yield strength YS does not decrease, no softening portion occurs on the rail top surface 2 hardened by rolling load, and wear resistance is not impaired.

FIG. 7 shows an example of a heating/cooling curve of each part of the rail when the rail 1 is heated/cooled, with the horizontal axis representing the time (min) from the start of heating and the vertical axis representing the temperature (° C.). The heating/cooling curve shown in the figure is for a rail temperature of 6 to 12℃, where a is the top surface and b
is the heating/cooling curve at the center of the abdomen, and c is the heating/cooling curve at the center of the bottom.

This heating/cooling curve first heats the rail bottom 6 in a small furnace 14, and when the rail bottom 6 reaches a predetermined temperature, for example, 750°C, the gas burner 15 is extinguished.
After that, the rail bottom 6 is gradually cooled by furnace cooling and air cooling.
When the temperature reaches around 300℃, cool it with water. During this heating and cooling, the maximum heating temperature of the rail abdomen 5 is 500.
℃ or less, and the maximum heating temperature of the parietal surface 2 is 300℃ or less.

As mentioned above, the temperature of the rail bottom 6 is 750℃, the temperature of the abdomen 5 is 500℃ or less, and the temperature of the top surface 2 is 300℃
In the following cases, the yield strength of rail 1 is approximately 25Kg/mm ² and the tensile strength is approximately 45Kg/mm ² , which is minus the set temperature.
Even in winter at 40°C, the rail strength far exceeds the tensile force (axial tensile force/rail cross-sectional area) of approximately 10 kg/ ^mm2 , making it safe.

Next, the results of specifically correcting the rail 1 according to the above embodiment will be shown.

Corrected the dent in the top surface 2 of the 60kg/m long rail that had been installed and used for many years on high-speed railways in the stationary section. In this straightening, the number of tightening devices for the sleepers is 6, the rail temperature is approximately 6 to 12 degrees Celsius, and the heating and cooling of the rail is approximately within the heating range of the rail bottom 6.
200 mm, and the heating and cooling curve shown in Figure 7 was applied.

When vertically straightening this rail, lift amount x (mm/2
FIG. 9 shows the relationship between the correction amount y (mm/2m) and the correction amount y (mm/2m). The linear tendency between the lifting amount x and the correction amount y is expressed by the regression equation y = 1.095x - 0.537, and the correlation coefficient r is 0.908, indicating an almost perfect correlation between the lifting amount x and the correction amount y. The correction accuracy is extremely high.

Further, FIG. 10 shows the hardness of each part of the parietal surface 2 before and after correction, with the horizontal axis representing the distance (mm) from the center of the weld and the vertical axis representing the hardness (Hs). As shown in FIG. 10, the hardness of the parietal surface 2 does not change due to heating, and the hardness before correction can be maintained even after correction.

〔Effect of the invention〕

As explained above, in this invention, after pre-straining the rail within its elastic limit, the bottom of the rail is heated to above the _A3 transformation point to thermoplastically deform it, and the top of the rail is held at below 300°C. Since vertical straightening is performed, the rail has sufficient tensile strength during straightening.
It has a high strength and can perform vertical straightening with high accuracy without reducing the cross-sectional area of the rail, which often occurs with conventional straightening methods, and without closing the track.

Furthermore, since the hardness of the top surface of the rail does not change even after correction, the wear resistance of the top surface of the rail can be maintained.

Furthermore, since no large tensile stress is applied to the rail head, it is possible to prevent the expansion of minute flaws existing on the top surface of the rail.

[Brief explanation of drawings]

Figure 1 is a perspective view of the rail, Figure 2 a, b, c,
d is an explanatory diagram of an embodiment of the present invention, and FIG.
is a plan view, FIG. 2b is a sectional view taken along line A-A in FIG. 2a,
FIG. 2c is a sectional view taken along line BB in FIG. 2a, FIG. 2d is a sectional view taken along line C-C in FIG. The figure is a distribution diagram of heating/cooling curves, Figure 8 is an explanatory diagram of lifting amount x and correction amount y, Figure 9 is a characteristic diagram of lifting amount x and correction amount y, and Figure 10 is a distribution diagram of parietal surface hardness. , Figure 11 is a hardness distribution diagram of the rail top surface during long rail welding,
FIG. 12 is a wear amount distribution diagram of the welded part, and FIG. 13 is a diagram of the temperature-tensile strength and yield strength characteristics of the rail. 1: Rail, 2: Parietal surface, 3: Recess, 4: Head, 6: Bottom.

Claims (1)

[Claims] 1. Apply an external force from the bottom of the rail around the local concave position on the top surface of the long rail so that the head is on the tension side, and apply an external force of 1.0 to 2.5 per 2 m of rail length.
A pre-strain of mm is applied, and in this state, a heating furnace is used to cover a range of 100 to 220 mm in the length direction of the bottom of the rail, which is under compressive stress.
After heating to 750℃ to 880℃, the rail head is heated to 300℃.
Vertical correction method for long rail local dents held below.