JP2007289970A - Flash butt welding method of rail - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress softening of an HAZ of a rail weld zone and to reduce uneven wear of a rail. <P>SOLUTION: A backing metal 4 is used whose contact range with the rail includes at least the top face of the rail in the cross section of the rail, whose length of the contact range in the top face in the axial direction of the rail is ≥15 mm, and whose thickness of the part in contact with the top face is ≥10 mm. The backing metal 4 is attached in the manner that the tip end of the backing metal 4 on the rail end face side is situated within 20-50 mm from the end face of the rail before welding. The rail is then welded in this state by flash butt welding, so that the top 1 of the rail is cooled by the backing metal 4 during the welding. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a rail flash butt welding method that can suppress HAZ softening of a rail welded portion and reduce uneven wear of the rail.

  Flash butt welding is widely used as a welding method for steel materials. Its features include that it can be automated, has high quality stability, and has a short welding time.

  The principle of the flash butt welding method will be described with reference to FIGS. First, as shown in FIG. 5 (a), a voltage is applied to the materials to be welded arranged opposite to each other via electrodes, an arc is generated between the end surfaces of the materials to be welded, and the end surfaces of the materials to be welded are melted. . At this time, as shown in FIG. 5 (b), an arc is generated on the end face of the material to be welded and discharged as a flash outside the system, and the material gradually melts. When an arc is generated between the end faces, the arc generating portion is locally melted to generate a dent called a crater. Further, since welding is performed in an air atmosphere, a large amount of metal oxide is generated in the molten metal portion. The weld end face is finally in a molten state. In addition, the material in the vicinity of the weld is softened by the temperature rise.

  Next, as shown in FIG. 5C, axial upset pressurization is performed. By this upset pressurization, the materials to be welded are joined to each other at the end faces. At this time, the unevenness by the crater formed on the end face is crushed and deformed, and the molten metal is discharged out of the system. Further, the softened material in the vicinity of the weld surface is increased in cross section due to plastic deformation during upset, and a bead is formed. This bead is removed by hot shearing or the like in a later step.

  Such a flash butt welding method is automated, has a short welding time of 2 to 4 minutes, and has a high welding efficiency. Therefore, the flash butt welding method is often used as a factory welding method in the rail field. In addition, the equipment has been made compact and used as field welding on tracks.

As a conventional rail flash butt welding technique, in Patent Document 1, a control device and each unit half are provided with two unit halves including a pair of fastening clamping portions that are movable in the directions of each other by a pivoting motion. A welding unit having is disclosed. Patent Document 2 discloses a welder structure having a casing and a carriage that can move linearly therethrough. These are inventions related to the structure of the welder body.
JP 2003-260567 A Japanese Patent Laid-Open No. 06-226454

  As described above, flash butt welding is a technique in which the material end surfaces are melted by heating and then the molten surfaces are pressed and adhered to each other to join the materials. Since the steel material undergoes a temperature rising process from the room temperature to the melting point and a subsequent cooling process, the metal structure changes. The structure of the material to be welded during welding and the altered region of hardness are called heat affected zone, HAZ.

Rail steel contains a large amount of carbon (C) and has a pearlite structure. The pearlite structure has a layered structure in which pure iron phase called ferrite containing almost no carbon and iron carbide (Fe ₃ C) layers called cementite are alternately and densely stacked. In the process of generating pearlite, transformation energy is converted into interfacial energy between ferrite and cementite, and thus such a layered structure is formed.

  The changing process of pearlite due to the temperature rise is as follows. 1. The pearlite structure does not change from room temperature to 500 ° C. 2. When the temperature exceeds 550 ° C., the structure changes in a direction to reduce the interfacial energy of the layered structure, that is, the cementite is divided and spheroidized. As the temperature increases, the cementite spheroidizes. 3. In the case of rail steel, the ferrite structure begins to transform into an austenite structure from around 720 ° C. As a result, there exists a temperature range in which three phases of ferrite, spheroidized cementite, and austenite coexist in the metal. 4). When the temperature further increases, either the ferrite or cementite phase disappears, and a two-phase structure of austenite and spheroidized cementite or austenite and ferrite is obtained. 5. When the temperature is further increased, a single phase structure of austenite is obtained. 6). When the temperature further rises and exceeds the melting point (solidus temperature), a molten phase is generated in the austenite structure. 7). When the temperature rises further, it melts completely.

  In welding, the maximum temperature reached varies depending on the distance from the weld end. That is, it reaches the melting point or more at the weld end face, but remains at room temperature sufficiently far away. The material undergoes any of the structural changes 1 to 7 according to the maximum temperature reached. Specifically, as the distance from the weld end to the weld end increases, Perlite area (no change) → 2. Spheroidized cementite region → 3. 3. Three-phase region where austenite, ferrite and spheroidized cementite coexist. 2. Two-phase region of austenite and ferrite or austenite and spheroidized cementite → 5. Austenite single phase region → 6. 6. Austenite zone where melt zone exists → 7. Complete melting zone.

  When the heating process of welding is completed in these structures, cooling causes a structure change corresponding to the temperature decrease from each structure. Further, a hardness distribution is generated according to the change in the structure. Although the hardness distribution varies depending on the structure and components, here, an example of a high-strength rail with a base material hardness of Hv390 level for heavy-duty railways is taken as an example.

1. The pearlite region (the part that does not undergo structural changes during the heating process) does not change from the original structure after cooling.
2. In the spheroidized cementite region, the spheroidized cementite is cooled as it is and exhibits a spheroidized structure even at room temperature. The hardness of the spheroidized cementite structure is low, about Hv300. As the maximum temperature rises, spheroidization progresses, so the closer to the welding point, the softer.
3. In the three-phase region where austenite, ferrite, and spheroidized cementite coexist, the austenite transforms into pearlite as the temperature decreases, but the spheroidized cementite is cooled as it is to room temperature. As the maximum temperature rises, the austenite phase ratio increases and the fraction that becomes pearlite after cooling increases, so the hardness recovers the closer to the welding point. The hardness of the spheroidized cementite structure is low, about Hv300.
4). In the two-phase region of ferrite and austenite, or austenite and cementite, austenite transforms into a pearlite structure during cooling. As the maximum temperature rises, the austenite fraction increases and the fraction that becomes pearlite after cooling increases, so the hardness recovers the closer to the welding point.
5). In the austenite single phase region, austenite is transformed into a pearlite structure. Hardness is almost constant.
6). In the austenite region where the melt phase exists, the liquid phase first solidifies to become austenite, so that it becomes an austenite single phase and then transforms into a pearlite structure. Hardness is almost constant.
7). The molten region first solidifies to an austenite single phase and then transforms to a pearlite structure. Hardness is almost constant.

  Even in a portion cooled from any temperature range, a structure of ferrite and cementite is finally obtained. The layered structure of ferrite and cementite is the same pearlite as the base material. Since the above-mentioned regions 2 to 3 contain a spheroidized cementite structure, the hardness changes according to the fraction. FIG. 6 schematically shows the temperature in the vicinity of the weld, the structure at high temperature, and the structure after cooling. As a quantitative definition method of HAZ softening, there are cases where, as an evaluation index, the softening width softening more than a certain value and the minimum hardness are compared with the base material hardness. Hereinafter, the width in which the Vickers hardness is reduced by Hv50 or more from the base material hardness is referred to as a softening width.

As described above, in the rail welded portion, the HAZ has a portion with reduced hardness (HAZ softened region). If the hardness is significantly reduced in the HAZ softened region, uneven wear in the HAZ softened region may progress due to the passage of the wheel at the head of the rail, which may cause noise vibration. Further, when the uneven wear increases, the impact on the rail is large when passing through the wheel, and this may cause fatigue failure of the rail.
An object of the present invention is to provide a rail flash butt welding method capable of suppressing the HAZ softening of a rail welded portion and reducing the uneven wear of the rail.

As a countermeasure against the above-mentioned problems, the present invention reduces the HAZ width at the rail head, reduces the softened region, and suppresses uneven wear of the rail. The specific method is as follows.
(1) The contact surface with the rail includes at least the top surface of the rail, the length of the contact range on the top surface in the rail axial direction is 15 mm or more, and the thickness of the portion in contact with the top surface is During welding, the rails are flash-butt welded with a 10 mm or more metal fitting attached so that the tip on the rail end surface side of the gold is located within 20 mm to 50 mm from the rail end surface before welding. A method of flash butt welding a rail, wherein the head of the rail is cooled by the pad.

  (2) The range of contact with the rail includes at least the top surface of the rail in the cross section of the rail, the length of the contact range on the top surface in the rail axial direction is 15 mm or more, and the top surface In the state where the thickness of the part in contact with the rail head is 20% or more relative to the thickness of the rail head, and the tip of the corresponding gold is mounted so that it is located within 20 mm to 50 mm from the rail end surface before welding, A flash butt welding method for rails, wherein the rail head is cooled by the metal pad during welding by flash butt welding the rails.

  (3) The flash butt welding method for rails according to (1) or (2) above, wherein a water-cooled pipe is provided on the metal pad.

  (4) The contact range with the rail includes at least the top surface of the rail in the cross section of the rail, the length of the contact range on the top surface in the rail axial direction is 15 mm or more, and the water-cooled piping is When welding, the rail is flash-butt welded with the corresponding metal fitting mounted so that the tip of the gold rail end surface side is located within 20 mm to 50 mm from the rail end surface before welding. A method of flash butt welding a rail, wherein the head of the rail is cooled by the pad.

  By performing the rail welding with the pad attached, the rail head is cooled during welding, so the width of the HAZ is reduced and the decrease in hardness is reduced. As a result, uneven wear due to contact with the wheel at the head is reduced, and noise and vibration of the train can be reduced and the life of the rail can be extended.

  The rail flash butt welding according to the embodiment of the present invention will be described in detail. In this flash butt welding, a stopper for cooling the rail head is attached in the vicinity of the end face of each rail arranged in opposition. Next, a voltage is applied to the rail through an electrode, and an arc is generated between the end surfaces of the rail to melt the end surface of the material to be welded. Next, axial upset pressurization is performed to join the rails to each other at the end faces. During welding, the region near the end surface of the rail top is cooled by a metal pad. For this reason, the width of the HAZ of the rail head is narrowed compared to the conventional case, and the decrease in hardness is reduced.

In railroad rails, it is said that uneven wear is unlikely to occur if the softening width is smaller than the contact area between the wheels and the rails. Since the contact area between the wheel and the rail is considered to be about 15 mm, it is desirable that the softened width, which is reduced by Hv50 or more from the base material hardness, is 15 mm or less. According to the present embodiment, the softening width reduced by Hv50 or more from the base material hardness can be made 15 mm or less.
Hereinafter, the structure of the backing metal and the mounting position thereof will be described in detail.

  FIG. 1 is a cross-sectional view of a rail. In this figure, 1 is a rail head, 2 is a rail pillar part, and 3 is a rail foot part. In the present embodiment, the rail head 1 and the rail foot 3 are defined as follows. First, in the rail cross section of FIG. 4, a point that intersects each other when the lower surface 1d of the head 1 is extended is defined as an intersection A, and a horizontal line A1-A2 that passes through the intersection A (that is, a line parallel to the bottom surface of the foot 3). A portion located at the upper part is referred to as a head 1. Further, a point that intersects with each other when the upper surface 3a of the foot 3 is extended is defined as an intersection B, and a portion that is located below a horizontal line B1-B2 (that is, a line parallel to the bottom surface of the foot 3) passing through the intersection B is defined. The foot 3 is assumed. The column part 2 is defined as a part other than the head part 1 and the foot part 3.

  In this embodiment, the radius of curvature including the central axis C1-C2 of the rail is as large as 50 mmR to 600 mmR, and the substantially horizontal portion 1a is referred to as the top surface (300 mmR or more near the center). The straight portion 1b is called a head side surface. Further, a portion 1c having a small radius of curvature of 7 mmR to 13 mmR between the top surface and the head side surface is called a gauge corner.

  FIG. 2 is a bird's-eye view with the head cooling paddle of the present invention. FIG. 3 is a cross-sectional view at the position where the backing metal is mounted, and FIG. 4 is a side view of the state where the backing metal is mounted. The head cooling pad 4 is a substantially “U” shape that covers the rail head 1 from above, and is placed on the rail by its own weight. The material of the contact metal 4 is metal, but copper, copper alloy, aluminum, and aluminum alloy having high thermal conductivity are desirable. The pad 4 needs to be attached to both the rails to be welded. In the embodiment shown in the figure, the contact metal 4 is mounted independently from the welder body, but the welder body may automatically mount the contact metal 4 on the rail.

  If the distance L2 (see FIG. 4) between the tip position of the stopper 4 and the rail end surface before welding exceeds 50 mm, the effect of cooling the head is weakened. On the other hand, if the distance is less than 20 mm, the rail material may be deformed during upset during welding, which is not preferable. For this reason, the distance L2 is preferably 20 mm to 50 mm.

  Also, if the length L1 of the stopper 4 in the rail axial direction is within 15 mm, the effect of cooling the rail is weak and the contact with the rail tends to be incomplete, which is not preferable. Although there is no upper limit on the length L1, if it is 200 mm or more, the mounting effort increases, so it is desirable to implement the mounting mechanism as an apparatus.

  In addition, when the thickness T1 (see FIG. 3: the thinnest part of the head in the example of FIG. 3) and the thickness T2 (see FIG. 3) of the head side of the pad 4 are thin, the cooling capacity is weak. Therefore, it becomes difficult to achieve the object of the present invention. Since it is an object of the present invention to suppress a decrease in hardness at the rail head portion and the gauge corner portion where the contact with the wheel is the harshest, cooling from the rail head surface is particularly important. For this reason, the thickness T1 of the portion where the contact metal 4 is in contact with the rail head top surface is important, and T1 is at least 10 mm or more or 20% or more of the rail head thickness, preferably 25 mm or more, or 50 of the rail head thickness. % Or more is desirable. The main purpose of the portion of the pad 4 in contact with the head side is to obtain stability when the pad is mounted on the rail, and the thickness T2 is less important. Note that the thickness of the rail head is, for example, the distance between the point A and the top surface shown in FIG.

  In order to cool the rail head, it is desirable that the cover cover covers the head widely. It is desirable that the metal pad is in contact with the top of the head where contact with the wheel occurs. Further, it is desirable to attach the backing metal at least during the welding flushing step.

  A water-cooled pipe may be attached to the pad 4. In this case, the cooling effect of the rail head by the pad 4 is increased. For this reason, the thickness T1 of the top of the pad 4 may be thinner than the above value.

Next, examples of the present invention will be described.
Welding was performed by changing the shape, material, and mounting position of the backing metal to various conditions shown in Table 1, and the effect of the backing metal was confirmed. Table 2 shows specific combinations of the respective factors and welding results. In addition, the rail used for welding used the rail size 136Lbs of the US AREMA standard, and the high-strength heat-treated rail (heat-treated part hardness Hv410). The rail cross section has a rail height of 185.7 mm, a foot width of 152.4 mm, a column thickness of 17.5 mm, and a head width of 74.6. In all the weldings with the metal pads attached, the metal pads 4 are attached to the rail top part 1a, the gauge corner part 1c, and the head side part 1b, but there are various regions where the rails and the metal pads are in contact.

  The welding conditions were a welding flushing time of about 3 minutes, a rail melt amount of about 10 mm, and an upset load of 55 tf. The amount of shrinkage between the rails due to upset pressurization was about 16 mm.

Evaluation of the effect of the metal pad was performed by measuring the surface hardness of the rail weld. The hardness measurement position was set to 100 mm on both sides at a pitch of 5 mm from the welding center. The evaluation index was the hardness in the longitudinal direction where the hardness was lower by Hv50 or more than the base material hardness in the softened region of HAZ and the minimum hardness. The narrower the width in the longitudinal direction, which is lower by Hv50 or more than the base material hardness, is preferable. Generally, it is said that uneven wear is unlikely to occur if the softening width is less than or equal to the contact area between the wheel and the rail. Since the contact area between the wheel and the rail is considered to be about 15 mm, the goal was to reduce the hardness of the base metal by Hv50 or more, that is, the softening width of Hv340 or less was 15 mm or less. In addition, the minimum hardness was set so as not to decrease by Hv100 or more from the base material hardness, that is, not lower than Hv290.
In addition, in order to confirm the cooling effect by the metal plating, a temperature is measured by attaching a thermocouple in the vicinity of the weld, that is, at the center of the top surface of the head 20 mm from the rail end surface before welding, and the maximum temperature reached immediately before the upset I investigated.

  Welding No. 1 is a comparative example, and a copper metal 4 having a thickness of 5 mm and a length of 50 mm was set at a position where a distance L2 from the end surface of the metal and the rail end before welding was 30 mm. The pad is in contact with the top surface, the gauge corner, and the head side surface in the mounting cross section. The pad was attached symmetrically to the two welded rails. As a result of the hardness measurement, the range of hardness Hv340 or less was 23 mm, and the minimum hardness was 262. The top surface temperature near the weld was 1002 ° C. Although the rail head was cooled with a metal pad, the thickness of the metal pad was thin, resulting in poor cooling efficiency and a significant decrease in hardness due to a rise in head temperature.

  Welding number 2 is a comparative example, and a copper metal pad 4 having a thickness of 30 mm and a length of 10 mm was set at a position where a distance L2 from the end surface of the metal pad and the rail end before welding was 30 mm. The pad is in contact with the top surface, the gauge corner, and the head side surface in the mounting cross section. The pad was attached symmetrically to the two welded rails. As a result of the hardness measurement, the range of hardness Hv350 or less was 20 mm, and the minimum hardness was 261. The top surface temperature near the weld was 950 ° C. Although the rail head was cooled with a metal pad, the length of the metal pad was short, resulting in poor cooling efficiency and a significant decrease in hardness due to a rise in head temperature.

  Welding number 3 is an example of the present invention, and a copper metal 4 having a thickness of 30 mm and a length of 50 mm was set at a position where the distance L2 from the end surface of the metal and the rail end before welding was 30 mm. The pad is in contact with the top surface, the gauge corner, and the head side surface in the mounting cross section. The pad was attached symmetrically to the two welded rails. As a result of the hardness measurement, the range of hardness Hv350 or less was 7 mm, and the minimum hardness was 305. The top surface temperature near the weld was 710 ° C. It was shown that the temperature rise of the head was suppressed and the decrease in hardness was suppressed small because the head was cooled at an appropriate position with an appropriately shaped paddle.

  Welding number 4 is an example of the present invention, and a copper metal plate 4 having a thickness of 30 mm and a length of 180 mm was set at a position where the distance L2 from the end surface of the metal plate 4 and the rail end before welding was 30 mm. The pad 4 is in contact with the top surface, the gauge corner, and the head side surface in the mounting cross section. The pad 4 was attached symmetrically to the two welded rails. As a result of the hardness measurement, the range of hardness Hv350 or less was 12 mm, and the minimum hardness was 312. The top surface temperature near the weld was 705 ° C. It was shown that the temperature rise of the head was suppressed and the decrease in hardness was suppressed small because the head was cooled at an appropriate position with an appropriately shaped paddle.

  Weld No. 5 is a comparative example in which welding was performed without using the metal 4. As a result of the hardness measurement, the range of hardness Hv350 or less was 26 mm, and the minimum hardness was 264. In the vicinity of welding, the top surface temperature rose to 1010 ° C., indicating a significant decrease in hardness.

  Welding number 6 is a comparative example, and a copper metal plate 4 having a thickness of 30 mm and a length of 50 mm was set at a position where the distance L2 from the end surface of the metal plate 4 and the rail end before welding was 15 mm. The pad is in contact with the top surface, the gauge corner, and the head side surface in the mounting cross section. The pad 4 was attached symmetrically to the two welded rails. As a result of the hardness measurement, the range of hardness Hv350 or less was 11 mm, and the minimum hardness was 318. The top surface temperature in the vicinity of the weld is 620 ° C., and the head is cooled at a position very close to the welded portion with an appropriately shaped pad, so that the temperature rise of the head can be sufficiently suppressed and the hardness is reduced. Was shown to be kept small. However, since the cooling position is too close to the welding position than the position within the proper range of the present invention, the set metal plate is detached from the rail and dropped due to the rail deformation at the time of upsetting.

  Welding number 7 is an example of the present invention, and a copper metal 4 having a thickness of 30 mm and a length of 50 mm was set at a position where the distance L2 from the end surface of the metal 4 and the rail end before welding was 45 mm. The pad 4 is in contact with the top surface, the gauge corner, and the head side surface in the mounting cross section. The pad 4 was attached symmetrically to the two welded rails. As a result of the hardness measurement, the range of hardness Hv 350 or less was 13 mm, and the minimum hardness was 299. The top surface temperature near the weld was 740 ° C. It was shown that the temperature rise of the head was suppressed and the decrease in hardness was suppressed small because the head was cooled at the proper position by the metal pad 4 having an appropriate shape.

  Welding number 8 is a comparative example, and a copper metal pad 4 having a thickness of 30 mm and a length of 50 mm was set at a position where the distance L2 from the end surface of the metal pad 4 and the rail end before welding was 60 mm. The pad 4 is in contact with the top surface, the gauge corner, and the head side surface in the mounting cross section. The pad was attached symmetrically to the two welded rails. As a result of the hardness measurement, the range of hardness Hv350 or less was 19 mm, and the minimum hardness was 286. The top surface temperature near the weld was 960 ° C. Although the head is cooled with a metal pad, the mounting position of the metal pad 4 is far from the range that is appropriate for the present invention, so that the cooling efficiency is poor, and the decrease in hardness is remarkable due to the temperature rise of the head. Indicated.

  Welding number 9 is an embodiment of the present invention, and an aluminum-made 30 mm thick and 50 mm long metal pad 4 was set at a position where the distance L2 from the end surface of the metal pad and the rail end before welding was 45 mm. . The pad is in contact with the top surface, the gauge corner, and the head side surface in the mounting cross section. The pad was attached symmetrically to the two welded rails. As a result of the hardness measurement, the range of hardness Hv 350 or less was 10 mm, and the minimum hardness was 302. The top surface temperature near the weld was 750 ° C. It was shown that the temperature rise of the head was suppressed and the decrease in hardness was suppressed small because the head was cooled at an appropriate position with an appropriately shaped paddle.

  Welding number 10 is an embodiment of the present invention. A stainless steel (SUS-304) thickness of 30 mm and a length of 50 mm is used as the distance L2 between the end surface of the plating and the rail end before welding is 30 mm. Set to the position. The pad 4 is in contact with the top surface, the gauge corner, and the head side surface in the mounting cross section. The pad was attached symmetrically to the two welded rails. As a result of the hardness measurement, the range of hardness Hv 350 or less was 14 mm, and the minimum hardness was 320. The top surface temperature in the vicinity of the welding was 830 ° C. It was shown that the temperature rise of the head was suppressed and the decrease in hardness was suppressed small because the head was cooled at an appropriate position with an appropriately shaped paddle.

  Welding number 11 is an example of the present invention, and a cooling water capacity was further improved by attaching a copper water-cooled pipe by brazing to a copper metal 4 mm having a thickness of 30 mm and a length of 50 mm. The mounting position on the rail was set such that the distance L2 from the end face of the metal pad and the rail end before welding was 30 mm. The pad is in contact with the top surface, the gauge corner, and the head side surface in the mounting cross section. The pad was attached symmetrically to the two welded rails. As a result of the hardness measurement, the range of hardness Hv350 or less was 6 mm, and the minimum hardness was 334. The top surface temperature near the weld was 560 ° C. It was shown that the temperature of the head was further suppressed and the decrease in hardness was suppressed to a small level because the head was cooled at the appropriate position with a paddle with water cooling in an appropriate shape.

  Welding number 12 is an example of the present invention, and a cooling water capacity was further improved by attaching a copper water-cooled tube to brazing metal 4 made of mild steel (SS400) 30 mm thick and 50 mm long by brazing. The pad is in contact with the top surface, the gauge corner, and the head side surface in the mounting cross section. The mounting position on the rail was set such that the distance L2 from the end face of the metal pad and the rail end before welding was 30 mm. The pad was attached symmetrically to the two welded rails. As a result of the hardness measurement, the range of hardness Hv350 or less was 7 mm, and the minimum hardness was 328. The top surface temperature near the weld was 680 ° C. It is shown that the temperature of the head is suppressed and the decrease in hardness is suppressed to a small level because the temperature of the head is suppressed by the appropriate shape and the water cooled cooling of the appropriate position. It was.

  Welding number 13 is an example of the present invention, and a copper metal plate 4 having a thickness of 30 mm and a length of 50 mm was set at a position where the distance L2 from the end surface of the metal plate and the rail end before welding was 30 mm. The pad is in contact with the top surface and the gauge corner. The pad was attached symmetrically to the two welded rails. As a result of the hardness measurement, the range of hardness Hv350 or less was 13 mm, and the minimum hardness was 310. The top surface temperature near the weld was 825 ° C. It was shown that the temperature rise of the head was suppressed and the decrease in hardness was suppressed small because the head was cooled at an appropriate position with an appropriately shaped paddle.

  Welding No. 14 is a comparative example, and a copper metal 4 having a thickness of 30 mm and a length of 50 mm was set at a position where the distance L2 from the end surface of the metal and the rail end before welding was 30 mm. The pad is in contact with only half of the top. The pad was attached symmetrically to the two welded rails. As a result of the hardness measurement, the range of hardness Hv350 or less was 17 mm, and the minimum hardness was 275. The top surface temperature near the weld was 950 ° C. Although the head is cooled with a metal pad, the cover coverage by the metal pad is narrower than that which is appropriate for the present invention, so the cooling efficiency is weak, the head temperature rises greatly, and the hardness drop is significant. It was done.

  As described above, it has been shown that, when the rail is flash-butt welded, the temperature rise of the head can be suppressed and the decrease in hardness can be suppressed small by cooling the appropriate position using a metal pad having an appropriate shape.

Rail cross section showing rail parts Bird's eye view showing implementation Sectional view showing the mode of implementation Side view showing implementation Diagram showing the principle of flash butt welding Schematic diagram showing the structure and hardness change of the weld

Explanation of symbols

1 Rail head
1a Rail head
1b Rail head side
1c Rail gauge corner
2 Rail column 3 Rail foot 4 Latch 5 Upper electrode 6 Lower electrode

Claims (4)

  The contact surface with the rail includes at least the top surface of the rail, the length of the contact range on the top surface in the rail axial direction is 15 mm or more, and the thickness of the portion in contact with the top surface is 10 mm or more. The rail is flush-butt welded in a state in which the rail is mounted so that the tip on the rail end surface side of the gold is located within 20 mm or more and 50 mm or less from the rail end surface before welding. A method for flash butt welding a rail, wherein the head of the rail is cooled by the metal pad.   The contact range with the rail includes at least the top surface of the rail in the cross section of the rail, the length of the contact range on the top surface in the rail axial direction is 15 mm or more, and is in contact with the top surface. In the state that the thickness of the portion is 20% or more with respect to the thickness of the rail head, and the rail is mounted so that the tip of the gold is located within 20 mm to 50 mm from the rail end surface before welding. A flash butt welding method for rails, wherein the head of the rail is cooled by the metal pad during welding by flash butt welding.   The method of flash butt welding of rails according to claim 1 or 2, wherein water cooling pipes are provided on the metal pads. The contact range with the rail includes at least the top surface of the rail in the cross section of the rail, the length of the contact range on the top surface in the rail axial direction is 15 mm or more, and a water-cooled pipe is provided. The rail is flush-butt welded in a state in which the rail is mounted so that the tip on the rail end surface side of the gold is located within 20 mm or more and 50 mm or less from the rail end surface before welding. A method for flash butt welding a rail, wherein the head of the rail is cooled by the metal pad.

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