JP2007175707A - Method of improving fatigue strength in rail weld zone - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an easily operable method of improving the fatigue strength in a rail weld zone, for the purpose of obtaining a rail weld zone having high fatigue strength, which does not give trouble to a rail welding process. <P>SOLUTION: When rails 1 are welded in such a manner that an excess metal 2 is formed by thermite welding and a long rail is manufactured, at the time when the surface temperature of each rail within each 100 mm from the excess metal edge in the thermite weld zone to the longitudinal direction of each rail is reduced to ≤300°C, the surface in the range is recessed by a mechanical means and is subjected to plastic working (formation of each recessed part 3), so as to apply compressive stress thereto, thus the fatigue strength in the rail weld zone is improved. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for improving the fatigue strength of a rail welded part when a long rail is produced by thermite welding of rails.

  For railroad tracks, the short rails are integrated into a long rail by welding the used rails with thermite welding method for the purpose of improving the ride comfort and speeding up and improving the efficiency of track maintenance. To be done.

The rail thermite welding method performed on the railway track is performed by the following procedure.
First, as shown in FIG. 9, the end surfaces of the rails are brought into contact with each other with a certain gap, and then the periphery of the gap is covered with a refractory material made of silica sand. In this refractory material, a convex weld surplus part having a height of 2 to 10 mm and a width of 40 to 100 mm is formed in order to reliably melt the end surface of the rail 1 and the periphery of the end surface.
Next, after the inside of the gap 100 is heated to about 1000 ° C. with an oxygen / propane burner, a thermite reaction crucible 102 is disposed on the gap 100 and blended so as to have the same chemical composition as the rail 1 in the crucible 102. The thermite agent 102 is added to cause the thermite reaction.

Then, the molten metal having a high temperature of 2200 ° C. or higher generated by the thermite reaction in the gap 100 is poured from the automatic hot water tap 104 and the gaps 100 are filled with the molten metal, thereby welding the rails 1 to each other.
After that, only the weld surplus on the top surface and both sides of the head of the rail 1 that the train wheel contacts is removed with a dedicated hot shear when the weld is hot, and only the surface irregularities are polished by grinder polishing. After that, the weld is allowed to cool to a temperature of 100 ° C. or lower.

When the temperature of the welded portion becomes 100 ° C. or lower, the top surface of the rail 1 and both side surfaces of the head are finished and polished so that the train can pass without any trouble and finished in the same shape as the rail head.
Finally, the weld is inspected for scratches to finish the work, and a weld rail as shown in FIG. 10 is obtained. In the welding rail, the abdomen and the bottom of the welded part 105 after welding are used with the convex weld surplus part 2 attached.

  Since the weld rail obtained by the above-described thermite welding method has a convex weld surplus 2 around the rail other than the rail top surface and both sides of the head portion of the weld portion 105, the weld portion 105 remains. When a load at the time of passing through the train was applied to this, stress concentration occurred at the end of the weld surplus 2 and fatigue failure sometimes occurred.

The site where fatigue failure occurs varies depending on the situation. For example, when the row wheel weight is large or the train speed is high, there is a tendency for fatigue failure to occur at the welded edge of the rail foot surface.
Further, in the case of having a welded portion where a new rail and a worn rail are joined in a normal train passing situation, fatigue failure may occur at the weld surging edge of the rail foot surface portion on the new rail side.
Also, when laying with the rail tilted in a sharply curved section of R300m or less, fatigue failure will occur at the weld overfill end of the lower part of the rail jaw, and in the overfilled end of the abdomen in sections where the train wheel weight is very large, such as 200KN or more. was there.
For this reason, the thermite welding method which raises the fatigue strength of the welding surplus edge in the welding part of the welding rail has been desired.

  The present invention has been made in view of the above circumstances, and in order to obtain a rail welded portion having high fatigue strength, there is provided a method for improving the fatigue strength of a rail welded portion that is simple in operation and does not interfere with the rail welding process. The purpose is to provide.

In order to achieve the above object, the fatigue strength improving method in the rail welded portion of the first aspect of the present invention is the following procedure when producing a long rail by welding the rails by forming a surplus by thermite welding. It is characterized by including.
At the time when the rail surface temperature within 100 mm each in the longitudinal direction of the rail from the surging edge of the thermite welded portion has dropped to 300 ° C. or less, the surface of the range is dented by mechanical means to form plastic working (forming the dented portion 3) And compressive stress is applied.

  According to a second aspect of the present invention, there is provided a method for improving a fatigue strength in a rail welded portion.

  According to a third aspect of the present invention, there is provided a method for improving fatigue strength in a rail welded portion, wherein the range to be dented and plastically processed is a rail surface with respect to a position corresponding to a part or all of the surplus.

According to the above-described method for improving the fatigue strength in the rail welded portion, the rail surface within 100 mm from the weld surplus edge is recessed and plastically deformed, so that compressive residual stress can be applied to the surface. Even if tensile stress acts sometimes, the tensile stress value can be reduced by this compressive residual stress.
Thereby, even if a higher tensile stress is applied, the occurrence of fatigue cracks from the weld surging edge is prevented.

  In addition, the dent processing is performed at a time when the portion becomes 300 ° C. or less. This is because the recrystallization temperature of the rail steel is 300 to 400 ° C, and even if a residual stress is applied at a temperature higher than the recrystallization temperature, the value changes when the recrystallization temperature is reached. has no effect. On the other hand, the residual stress applied by the dent processing when the temperature is lower than the recrystallization temperature hardly changes even at room temperature.

That is, according to the method of the present invention, when the thermite welding of the rail is finished and the rail surface temperature near the welded portion is cooled to 300 ° C. or lower, the rail surface near the surging edge of the thermite welded portion is recessed by a mechanical method. By applying compressive stress, the tensile residual stress is reduced in the place where the tensile residual stress is as it is in welding, and the compressive residual stress is increased in the place where it is the compressive residual stress as it is in welding. .
Thus, the fatigue strength of a thermite weld can be improved by improving the residual stress on the rail surface around the weld.

A method for improving the fatigue strength of a thermite weld of a rail as an example of an embodiment of the present invention will be described with reference to FIGS.
The method for improving the fatigue strength in the rail welded portion according to the present invention is to perform a dent treatment on the welded portion between the rails 1. This dent treatment is performed after the rough finish polishing is completed in the thermite welding process and the temperature of the portion of the rail surface within 100 mm in the rail longitudinal direction from the surging edge of the thermite weld is lowered to 300 ° C. or lower. This is because the dent processing is performed at a temperature lower than the recrystallization temperature so that the residual stress applied by the dent processing hardly changes even when the room temperature becomes normal temperature.

As shown in FIG. 1, the position where the dent processing is performed is the head top portion 1 a and the head at a portion within 100 mm from the both ends of the thermite weld surplus 2 to the outside in the longitudinal direction of the rail in the welded portion 105 of the welded rail 1. This is performed on the dent processing portion 3 around the rail such as the jaw and the abdomen excluding the side surfaces 1b.
As a method of denting the surface of the rail 1, a peening machine 4 as shown in FIG. 2 is used to hit the surface of the rail 1 or it is attached to the tip of the hydraulic cylinder 5 as shown in FIG. 3. This is done by pressing the indenter 6 against the surface of the rail 1.

In the case of hitting the surface of the rail 1 by the peening machine 4, the depth of the recess processing in the recess processing unit 3 can be controlled by the hitting time. Further, in the case of pressing with the indenter 6 of the hydraulic cylinder 5, it can be adjusted by controlling the hydraulic pressure to be used.
In addition, the main place which presses the indenter 6 with the hydraulic cylinder 5 is the bottom face side of the rail 1 which is hard to hit with the peening machine 4. The other recesses 3 of the rail 1 are processed by a peening machine 4.

  In addition, since a dent process is performed at the time of 300 degrees C or less which is within the cooling time of a welding part, it does not give trouble to welding work. Moreover, since a dent processing tool uses a commercially available peening machine or a hydraulic cylinder, it can be easily performed without preparing a special apparatus.

Further, in the dent processing, the hardness of the rail 1, the striking force of the peening machine 4 and the tip shape of the hitting tool, the oil pressure of the hydraulic cylinder 5 and the tip shape of the indenter 6 are also taken into consideration.
When the dent depth and the processing width are changed to 5, 25, 100 mm when the dent processing is performed on the rail (carbon content 0.7%) whose residual stress value is known (the processing width is 5 mm when using a hydraulic cylinder) Table 1 shows the relationship with the residual stress value in the rail longitudinal direction of (fixed).

From Table 1, it can be seen that the tensile residual stress (original residual stress) is improved to the compressive residual stress (residual stress after processing) in the dent processing with any processing width.
Further, the relationship between the residual stress on the rail surface in the vicinity of the thermite welded portion and the fatigue strength of the thermite welded portion is as shown in FIG. Accordingly, when a dent processing with a depth of 0.1 mm is performed by hitting the peening machine shown in Table 1, a tensile residual force of 200.9 MPa becomes a compressive residual stress of 186.2 MPa, which is shown in FIG. 4 to 84.3 MPa. This corresponds to an improvement in fatigue strength.

Based on the results shown in Table 1, the actual fatigue test of the thermite welded part in which the recessing depth of 0.1 mm and the width of 5 mm was applied to the entire circumference of the weld surfacing end as shown in FIG. Each test condition (4 each) was carried out under each fatigue condition as shown in Table 2 (3 points bending, tensile fatigue at the bottom of the welded portion, 3 points bending, tensile fatigue under the chin of the welded portion). However, under the test conditions that conventionally caused fatigue failure (when stress of 254.8 MPa or 205,8 MPa was applied), no fatigue failure occurred in any of the test pieces.
Thus, if the dent processing was performed under the condition that the dent depth was 0.1 mm and the width was 5 mm, the fatigue strength could be greatly improved. Further, as apparent from Table 1, if the depth and width of the dent are increased, the fatigue strength can be further improved.

In Table 1, when dent processing is performed by hitting with the peening machine 4 and pressing the indenter 6 with the hydraulic cylinder 5 to make the dent depth 1 mm or more, the rail 1 may be damaged such as cracks. Because it is not suitable.
In addition, when the indenter 6 is pressed by the hydraulic cylinder 5, if a recess having a width of 10 mm or more is applied, the rail 1 may be similarly cracked or the like, which is not suitable. This is because the rail steel constituting the rail 1 is high carbon steel, so the deformation capacity of the material is low.

  The dent processing position performed by the method for improving the fatigue strength of the rail welded portion of the present invention varies depending on the situation where the rail welded portion is actually laid (the range of plastic working corresponds to a part or all of the surplus Rail surface for the position to do.) For example, under conditions where there is concern about the occurrence of fatigue damage at the bottom of the welded part, that is, when the train's own weight is large, when the number of passing vehicles is large, when the train speed is high, etc., as shown in FIG. A dent process (formation of the dent process part 3) is performed only on the bottom part.

Further, the dent processing depth and width are selected according to the strength of the welded rail. That is, when a rail having a large cross-sectional dimension is laid in the laying section, the rigidity of the rail is increased, so that the stress acting on the welded portion is reduced. At this time, a small dent processing depth and width are processed in the dent processing portion 3 of the rail 1.
On the other hand, when a rail having a small cross-sectional dimension is laid, the stress acting on the welded portion increases due to the low rigidity of the rail. At this time, a relatively large recess depth and width are processed in the recess processing portion 3 of the rail 1.

Also, when welding the worn rail 1 and the new rail 10 in a condition where there is a risk of fatigue damage on the upper surface of the welded portion, that is, in a normal train passage section, welding is performed with the top surface passing through the train horizontal. Since this is done (see FIG. 6), a difference in level occurs at the bottom of the rail by the difference in rail height. In such a welded portion, a large stress concentration is generated at the surging edge on the upper surface of the rail bottom on the new rail 10 side when the train passes.
In this case, as shown in FIG. 6, dent processing (formation of the dent processing portion 3) is performed only on the extra-end of the upper surface of the rail bottom portion on the new rail 10 side. The dent processing depth and width are selected according to the strength of the welded rail as described above.

Also, under conditions where there is a risk of fatigue damage at the extra-end of the lower part of the rail jaw, that is, when laying the welded part in a sharply curved section of R300 or less, the extra-end of the weld jaw on the side where the train wheel flange does not hit Large stress concentration occurs.
In this case, as shown in FIG. 7, the dent processing (formation of the dent processing portion 3) is performed only on the extra-end of the rail 1 below the jaw. The dent processing depth and width are selected according to the strength of the welded rail as described above.

  Further, in a condition where fatigue damage is likely to occur in the welded abdomen, that is, in a section where the train's own weight is very large and a large stress concentration occurs at the abdomen extra-end of the welded part, as shown in FIG. The dent processing (formation of the dent processing part 3) is performed only on the extra-strip end. The dent processing depth and width are selected according to the strength of the welded rail as described above.

  According to the fatigue strength improving method of the rail welded portion described above, the recess processing of the rail surface near the welded portion can be easily performed without hindering the rail welding step in the same welding construction process as before. And the residual stress of a welding part can be improved significantly. As a result, the fatigue strength of the welded portion was greatly improved, and fatigue damage of the welded portion that had occurred conventionally could be prevented.

It is an isometric view explanatory drawing of the rail welding part which gave the dent processing by the fatigue strength improvement method in the rail welding part of this invention. It is a schematic explanatory drawing of the rail welding part in the case of performing a dent processing using a peening machine in the fatigue strength improvement method in the rail welding part of this invention. It is a schematic explanatory drawing of the rail welding part in the case of performing a dent processing using the indenter of a hydraulic cylinder in the fatigue strength improvement method in the rail welding part of this invention. It is a graph which shows the relationship between the residual stress of the rail surface of the thermite weld part surplus edge vicinity, and the thermite weld part fatigue strength. It is rail cross-section explanatory drawing which shows the example of the processing position of a dent process in case a fatigue damage is concerned about the bottom part of a rail welding part. It is rail cross-section explanatory drawing which shows the example of the process position of a dent process in case fatigue damage is worried about a rail weld bottom part upper surface. It is rail cross-section explanatory drawing which shows the example of the processing position of a dent process in case fatigue damage is worried about the extra-banking end of a rail jaw lower part. It is rail cross-section explanatory drawing which shows the example of the process position of a dent process in case fatigue damage is worried about a rail welding abdomen. It is front explanatory drawing of the rail welding part for demonstrating the outline of thermite welding. It is an isometric view explanatory drawing which shows the state of the rail welding part after thermite welding.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Rail 2 Welding surplus 3 Recess processing part 4 Peening machine 5 Hydraulic cylinder 6 Indenter 7 Support | pillar 100 Gap 101 Mold 102 Crucible 103 Thermite solvent 104 Automatic tap 105 Welded part

Claims (3)

When making a long rail by forming a surplus by welding the rails together with thermite welding,
At the time when the rail surface temperature within 100 mm in each rail longitudinal direction from the surging edge of the thermite welded portion has dropped to 300 ° C or less, the surface of the range is dented by mechanical means and subjected to plastic processing to give compressive stress A feature of improving fatigue strength in a rail welded portion. The method for improving fatigue strength in a rail weld according to claim 1, wherein the amount of recess on the rail surface is 1 mm or less within a range where the recess is plastically processed. The method for improving fatigue strength in rail welds according to claim 1, wherein the range where the recess is subjected to plastic working is a rail surface with respect to a position corresponding to a part or all of the surplus.

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