METHOD, APPARATUS AND VEHICLE FOR WELDING RAILS

Abstract

Railway rails are welded in situ by induction welding with an insert (3) between the ends of the rails (1) being welded. The insert (3) compensates, at least in part, for the loss of rail length that occurs in the welding process. Preferably the ends of the rails are pushed apart (e.g. by the length of rail consumed in the welding process) before the insert (3) is placed in position, thereby allowing a longer insert to be used. Induction heating may be performed with a split head (5) that can be opened so as to be placed around a rail in situ and then closed to carry out induction heating.

Claims

1. A method of welding railway rails comprising: placing a metal insert between the ends of first and second rails; heating the ends of the first and second rails by electromagnetic induction, to reach a welding temperature; forcing the ends of the first and second rails towards each other with a forging pressure, while the insert is between the ends of the first and second rails, and thereby welding each of the first and second rails either to the insert or to the other of the first and second rails.

2. A method according to claim 1 in which the step of forcing the ends of the first and second rails towards each other with a forging pressure comprises moving the rails towards each other to create a forge welded joint.

3. A method according to claim 1 in which the ends of the first and second rails are pressed together with a force of 250 to 350 kN during the said step of forcing the ends of the first and second rails towards each other with a forging pressure.

4. A method according to claim 1 in which the ends of the first and second rails are pressed together with a force of 280 to 300 kN during the said step of forcing the ends of the first and second rails towards each other with a forging pressure.

5. A method according to claim 1 in which the insert is at least 6 mm long.

6. A method according to claim 1 in which the ends of the first and second rails are moved away from each other before the insert is placed between them.

7. A method according to claim 6 in which the ends of the first and second rails are moved away from each other by at least 4 mm in total before the insert is placed between them.

8. A method according to claim 7 in which the insert is at least 10 mm long.

9. A method according to claim 6 in which the ends of the first and second rails are moved away from each other by at least 10 mm in total before the insert is placed between them.

10. A method according to claim 9 in which the insert is at least 16 mm long.

11. A method according to claim 1 in which the temperature, to which the ends of the rails are heated, is below the liquidus temperature of the insert.

12. A method according to claim 1 in which the temperature, to which the ends of the rails are heated, is above the solidus temperature of the insert.

13. A method according to claim 1 in which a piece is cut from the end of each of the first and second rails before the insert is placed between them.

14. A method according to claim 1 that is carried out in air without the provision of an inert gas atmosphere.

15. A method according to claim 1 which is carried out while the rails are attached to members that are in turn attached to other rails.

16. A method according to claim 1 in which the first and second rails are part of a pre-formed portion of railway track that includes at least one switch and at least one crossing.

17. Apparatus for welding railway rails, comprising: first clamping means for gripping a first rail; second clamping means for gripping a second rail; means for applying force to move the first and second clamping means towards each other and for applying force to move the first and second clamping means away from each other; and induction heating means, including at least one induction heating coil, placeable around rails gripped by the first and second clamping means at a position between the first and second clamping means.

18. Apparatus according to claim 17 in which the induction heating means is movable between a closed state in which it can heat a rail by electromagnetic induction, and an open state in which it can be withdrawn from a rail by movement transversely of the rail.

19. Apparatus according to claim 17 in which the induction heating means comprises first and second induction heating coils, which are movable relative to each other in a direction parallel to the direction of the said movement of the first and second clamping means towards and away from each other.

20. Apparatus according to claim 17 in which the means for applying force is arranged to apply force to move the first and second clamping means towards each other with a force of 250 to 350 kN.

21. Apparatus according to claim 17 in which the means for applying force is arranged to apply force to move the first and second clamping means towards each other with a force of 280 to 300 kN.

22. Apparatus according to claim 17 21, further comprising a power supply and control means.

23. Apparatus according to claim 22 in which the power supply comprises means to generate electricity.

24. A vehicle comprising apparatus according to claim 17.

Description

[0041] Embodiments of the present invention, given by way of non-limiting example, will now be described with reference to the accompanying drawings.

[0042] FIG. 1 shows the track layout for a crossover between two parallel tracks, manufactured in eight parts.

[0043] FIGS. 2(a) to 2(e) show schematic side views of steps in a rail welding process in an embodiment of the present invention.

[0044] FIGS. 3(a) to 3(e) show schematic side views of steps in an alternative rail welding process in an embodiment of the present invention.

[0045] FIGS. 4(a) and 4(b) show an end view (a) in a closed position and (b) in an open position of an induction coil unit used in an embodiment of the present invention.

[0046] FIG. 5 is a side view of the induction coil unit.

[0047] FIG. 6 is a side view of a pair of induction coil units.

[0048] FIG. 7 shows the main components of a welding head for use in an embodiment of the present invention.

[0049] FIG. 8 shows the main components of a welding apparatus in an embodiment of the present invention.

[0050] FIG. 9 show a vehicle carrying the welding apparatus of FIG. 8.

[0051] FIG. 10 shows a container carrying the welding apparatus of FIG. 8.

[0052] FIG. 2 shows schematically the main steps in a method of welding railway rails 1 together in situ, according to one embodiment of the present invention. FIGS. 2(a) to 2(e) show the end portions of the rails 1 in side view, and for ease of understanding FIG. 2(a) also shows a rail in end view.

[0053] Although it may not always be necessary, it is usually preferable to clean the ends of the rails 1 before welding. One way to do this is to cut a short distance off the end of each rail 1. This is shown in FIG. 2(a), where the broken lines indicate where the new end face of each rail 1 will be after cutting. The positions of the rails 1 after cutting is shown in FIG. 2(b).

[0054] In the present embodiment, it is intended that, following the welding operation, the rails 1 should neither have moved nor be placed under tensile stress. It is anticipated that the induction welding operation will consume about 10 mm to 12 mm length of rail. Therefore, each rail 1 is pushed back by 5.5 mm in order to increase the gap between them by 11 mm, corresponding to the length of rail that will be consumed in the welding process, and an insert 3, which will partially be sacrificed during the welding operation, is inserted into the gap, as shown in FIG. 2(c). The insert 3 will normally have the same cross-section as the rails 1, and may be made of the same or a different material, depending on the requirements for obtaining a strong welded joint. In order to move the ends of the rails 1 apart, as shown in FIG. 2(c), each rail 1 is gripped near its end by rail grippers or clamps (not shown), which are then forced apart (typically using a hydraulic cylinder) to separate the rails. Hydraulically driven rail clamps are well-known in the art. It may be necessary to unclip the rails from their supports (bearers or sleepers) along part of their length before pushing them apart. The unclipped length of rail can bow out from its correct position to accommodate the movement of the end of the rail.

[0055] In FIG. 2(b) there might be a gap of, for example, 8 mm between the ends of the rails 1 after they have each been cut in order to obtain a clean end. This is a reasonably practical gap to create between the ends of the rails by cutting the ends with a rail saw. Consequently, in FIG. 2(c) the rails 1 are 19 mm apart (11 mm+8 mm=19 mm). The insert 3 is 19 mm long and fills the gap.

[0056] Once the insert 3 has been inserted, the rails 1 are in the state shown in FIG. 2(d), and are ready for welding. Preferably, the force used to separate the rails 1 is relaxed at least partially in this state, so that the rails 1 grip the insert 3 firmly and hold it in place. If necessary, preheating can be carried out at this stage, for example using a gas flame or an induction coil. For the welding process, an induction welding head is fitted round the position of the insert 3 and the ends of the rails 1. The induction welding head may have a single induction coil which will heat the ends of both rails 1, and possibly the full length of the insert 3 as well, or alternatively a separate induction coil may be provided for the end of each rail 1. The choice will depend in part on the size of the insert 3 used and the extent to which it is desired to heat the full length of the insert 3.

[0057] During the welding operation, heat is induced in the end regions of the rails 1 by electric current flowing in the coil or coils of the induction head. Once the welding temperature is reached, the welding operation moves from its heating stage to its upset stage and the ends of the rails 1 are forced together with a forging force (which can be provided if necessary by driving the clamps near the ends of each rail towards each other), in order to create a forge welded joint between the ends of the rails 1. The welded joint normally comprises the insert 3 and a weld at each end of the insert 3, welding the insert 3 to the corresponding rail 1. Each weld normally has a grain boundary and a heat-affected zone on each side of the grain boundary. Depending on the pattern of heating and the length of the insert 3, the heat affected-zone within the insert 3 arising from the weld at one end of the insert may be separate from the heat-affected zone arising from the weld at the other end of the insert, or the heat-affected zones may merge.

[0058] The movement of the ends of the rails 1 towards each other to create the forge welded joint during the upset phase of the welding operation inevitably results in some material being displaced sideways from the welding zone. The displaced material can be removed, at least from the top and sides of the head of the rail, while the weld zone is still hot and the material is soft. This material may originate partially from the insert 3 and partially from the rails 1. However, because the upset length (the distance by which the rails 1 are moved towards each other to create the forge welded joint) is equal to the amount by which the rail ends were pulled apart from each other when moving from FIG. 2(b) to FIG. 2(c), the rails at the end of the welding operation as shown in FIG. 2(e) are in the same position as they were in FIG. 2(b), before they were pushed back, and are not under tensile stress. The length of the insert 3 has provided material both to bridge the gap between the ends of the rails 1 in FIG. 2(b) and to compensate for the material lost in the forging process. Accordingly, this welding method can be used to form at least some of the welded joints required in the crossover shown in FIG. 1 without distorting the track geometry in the crossover.

[0059] As discussed above, the ends of the two rails 1 are pushed together in the upsetting phase of the welding process, to form a forge welded joint, and it is estimated that around 10 to 12 mm of rail is consumed in the welding process. Accordingly, in the method of FIG. 2, after the ends of the rails 1 have been cleaned, they are pulled back by a total of 10 to 12 mm, so that the loss of rail length in the welding process merely returns the rails to their original positions and the entirety of the rail length lost in the welding process is made up by the excess in the length of the insert 3 over the distance between the ends of the rails 1 before they are pushed back.

[0060] However, in practice it may not always be advisable, or even possible, to push the ends of the rails 1 apart by this much. The crossover of FIG. 1 is built in a workshop, with highly accurate track geometry. In order to ensure and maintain the track geometry, the crossover is made as eight track panels a to h, and in each track panel the respective lengths of rail are clipped to bearers fixed accurately in the correct positions. In order to reduce the amount of work involved, and to avoid disturbing the track geometry, it is desirable not to unclip the rails from the bearers in the welding process. However, it is difficult to push the end of a rail 1 back by as much as 5 to 6 mm while the rail is clipped to the bearers, and any attempt to do so might cause the entire track panel concerned to move, which would itself upset the overall track geometry of the crossover. In these circumstances, it might be more realistic to push each rail end back by about 2 mm. This results in a slightly modified welding process, as illustrated in FIG. 3.

[0061] FIGS. 3(a) to 3(e) correspond to FIGS. 2(a) to 2(e). FIGS. 3(a) and 3(b) are identical to FIGS. 2(a) and 2(b), and the steps of cleaning/cutting the ends of the rails 1 are the same as in the method of FIG. 2. Accordingly, in FIG. 3(b) the ends of the rails 1 are about 8 mm apart, as in FIG. 2(b). However, when moving from the state shown in FIG. 3(b) to the state shown in FIG. 3(c), the end of each rail 1 is moved away from the other rail 1 by only 2 mm, so that the gap between the ends of the rails 1 increases by a total of 4 mm to make a gap in FIG. 3(c) of 12 mm (as compared with 19 mm in FIG. 2(c)). Accordingly, the insert 3 used in the process of FIG. 3 is only 12 mm long.

[0062] After the insert 3 is placed in position, the induction welding process is carried out in the same way as in the method of FIG. 2. In order to form a good welded joint, the upset length (i.e. the distance by which the end portions of the rails 1 are forced towards each other to create a forge welded joint) is the same in FIG. 3 as in FIG. 2. Because the rails 1 were not pulled apart from each other as much as in the process of FIG. 2, the rails 1 in FIG. 3 do not merely return to their original positions but have to be pulled towards each other by the rail clamps, placing the rails 1 under tension. In FIG. 3, the insert 3 was 12 mm long, thereby providing sufficient rail length to fill the 8 mm gap between the ends of the rails 1 in FIG. 3(b) and additionally contributing 4 mm towards the length of rail that is consumed in the welding process. Assuming that 11 mm of rail is consumed, this means that the rails 1 must contribute 7 mm (or 3.5 mm each) to the length of rail that is consumed in the welding process, and therefore the rails 1 will end up by being stretched by this much once the welded joint is formed, as shown in FIG. 3(e).

[0063] The stressing of the rails 1 at the end of the welding process of FIG. 3 is not necessarily problematic, even when it occurs in the welding of a region of track with complex precise geometry such as the crossover of FIG. 1. The total loss of rail length in the welding process of FIG. 3 is about 7 mm, which is much less than the 30 mm that is typically lost in a flash butt welding process. It is often the case that track work is carried out when the rails are at a temperature that is considerably less than the required stress free temperature of the rail (the stress free temperature is normally set to be towards the upper end of the temperature conditions that can be expected in normal weather conditions, and for example is 27° C. in the United Kingdom). Consequently, at the end of the track welding process it will normally be necessary to tension the track to restore it to the correct stress free temperature, and the stress created in the track by the relatively short length of rail loss in the process of FIG. 3 can often be absorbed in the stress restoration process.

[0064] As discussed above, the insert 3 is preferably at least 10 mm long. This enables it to provide enough material to fill the gap left by cutting the ends off the rails 1 in order to provide clean ends for the welding operation, since it will normally be possible to leave a gap of less than 10 mm between the ends of the rails after cutting. The additional length of the insert, beyond the length of the gap between the two rails, will depend on how far the rails will be pushed back. In some circumstances, it may only be possible to push each rail back by 2 to 3 mm, in which case an insert length of 12 to 16 mm will usually be appropriate. However, if the rails can be pushed back further, and it is not desired to introduce any tension into the rail after welding, an insert length in the range of 18 to 22 mm is likely to be appropriate. In general, the length of an insert is likely to fall within the range of 10 to 25 mm. Even longer inserts can be used, for example because the separation between the rails after cleaning is greater than usual or because the rail temperature while the work is being carried out is above the desired stress free temperature and so it is useful, from the point of view of stress restoration, to leave the rails in compression after welding. However, it becomes difficult to carry out the welding operation satisfactorily if the insert is too long, and it is anticipated that in practice the inserts are unlikely to exceed 40 mm.

[0065] FIG. 4 shows an end view of an induction coil unit that may be used in the induction welding processes described with reference to FIGS. 2 and 3. It might typically take about 50 to 60 kW of power, at a frequency of about 10 kHz.

[0066] The welding operation may be carried out in situ on a railway track, or in other situations where the rails are attached to further components such as sleepers. Therefore it is usually not possible to position the induction coil unit 5 around the rail 1, and remove the induction coil unit 5 from the rail 1 after welding, by passing the end of the rail 1 through the induction coil unit 5. Consequently, the induction coil unit 5 has a split coil construction and is formed of two parts 5a, 5b joined at a hinge 7. In FIG. 4(a) the induction coil unit 5 is shown in its closed position, extending fully around the rail 1 and ready for induction heating of the rail 1. In FIG. 4(b) the induction coil unit 5 is shown having been partially opened by rotation around the hinge 7, enabling it to be placed over and removed from the rail 1. The use of split coils is known in the art of induction welding, and does not need to be described further.

[0067] The induction coil unit 5 does not have a circular shape, as would conventionally be used for induction welding of pipes, but is formed to take account of the non-circular cross-sectional shape of the rail 1. The precise shape of the induction coil unit 5 will normally be chosen depending on the cross-sectional shape of the rails that it is intended to be used with. It should be noted that the shape of the induction coil unit 5 does not necessarily follow the cross-sectional shape of the rail 1 precisely. In order to obtain substantially uniform heating of the rail 1, and taking into account the different thicknesses of the different parts of the rail 1, the induction coil unit 5 may be shaped so as to come closer to some parts of the rail cross-section than to others. Additionally, different frequencies of the AC current supplied to the induction coil may be appropriate for heating different parts of the rail 1 and the insert 3, according to the different thicknesses of the different parts. Consequently, the current frequency may be varied over time to provide the desired heating effect, and/or two or more current frequencies may be applied to the induction coil simultaneously for at least a part of the induction heating period.

[0068] The induction coil unit 5 is shown in side view in FIG. 5. As can be seen in FIG. 5, the induction coil unit 5 is long enough so that it overlaps and heats the ends of both rails 1. Accordingly, it also encloses the insert 3. In order to avoid heating the insert 3 excessively, as compared with the rails 1, the coil in the coil unit 5 may be wound more densely where it encloses the ends of the rails 1, in order to heat these regions preferentially.

[0069] FIG. 6 shows an alternative arrangement, in which two shorter induction coil units 5 are used, one placed around the end of each rail 1. Optionally, the induction welding apparatus may include means to move the two induction coil units of FIG. 6 towards and away from each other, as indicated by the double arrow in FIG. 6. This enables the induction welding apparatus to be used with a variety of lengths of insert 3.

[0070] FIG. 7 shows schematically the main components for an induction welding head for welding railway rails in situ, according to one embodiment of the present invention.

[0071] First and second clamping means 9 are provided to grip the end portions of the first and second rails 1 respectively. A high power double action hydraulic cylinder 11 and piston 13 connect the two clamping means 9 and can apply strong and controlled forces to push the clamping means (and therefore the clamped end portions of the rails 1) apart or pull them together. In this way, the hydraulic cylinder 11 and piston 13 act as drive means for applying force to move the first and second clamping means towards each other and for applying force to move the first and second clamping means away from each other. In the present embodiment, the cylinder 11 and piston 13 are positioned so that they are alongside the rails 1 in use, in order to keep them out of the way of the induction coil units 5. Preferably, a second high power hydraulic cylinder 11 and piston 13 are provided on the other side of the rails 1, to ensure that pushing and pulling forces are applied symmetrically to the clamping means 9, and to avoid any tendency to twist the rails 1 by asymmetric application of force. The hydraulic cylinder 11 and piston 13 are connected to the clamping means 9 in a manner that ensures that they are spaced sideways from the rails 1 sufficiently to enable the induction coil units 5 to be inserted downwardly, and removed upwardly, from around the rail with the coil units 5 in their open position.

[0072] The arrangement of FIG. 7 uses two separate induction coil units 5, as shown in FIG. 6. They are supported by a small low power hydraulic cylinder 15 and piston 17 which can move the induction coil units 5 towards and away from each other, depending on the length of the insert 3 used on any particular occasion. It is not necessary to use a hydraulic cylinder and piston to drive the induction coil units, and any other convenient arrangement can be used, such as a worm screw drive. Electric cables 19 supply electric power to the induction coil units 5.

[0073] The hydraulic cylinders 11, 15 may be fitted with pumping handles for manual operation, or may have connections to receive pressured hydraulic fluid from a reservoir or pump.

[0074] The induction coil unit or units 5 and the hydraulic cylinder 15 and piston 17 (or other apparatus for moving the induction coil units 5) will normally be enclosed in a casing for protection, and a casing may also be provided around the high power hydraulic cylinder 11 and piston 13. A cooling system is normally provided to prevent the induction coil or coils from overheating.

[0075] FIG. 8 shows schematically a welding apparatus using the welding head components shown in FIG. 7. The components shown in FIG. 7 are contained in a welding head 21. This is connected to a power supply 23 for providing electric power to the induction coil unit or units 5, and also to other components requiring electric power. A hydraulic reservoir and pump unit 25 maintains a supply of pressurised hydraulic fluid and supplies it to the welding head 21 to drive the hydraulic cylinder 11, and also the hydraulic cylinder 15 if present. A cooling system 27 is connected to the welding head 21 to cool the induction heating coils. A control unit 29 is connected to the other components to control the operation of the welding apparatus, and includes input and output devices for an operator.

[0076] It is anticipated that the power supply 23 will normally need to deliver approximately 60 kW of electric power in order to drive the induction coil unit or units 5. By contrast, a flash butt welding apparatus may consume about 500 kW. Consequently, the power supply unit 23 can be substantially smaller and lighter than the power supply required in a flash butt welding apparatus. This in turn can make a welding apparatus according to the present embodiment substantially smaller, lighter and easier to manoeuvre than a flash butt welding apparatus. The power supply unit 23 may contain an electric generator, in order to make the welding apparatus self-contained. However, the relatively low power consumption of the induction coil unit or units 5 means that it may be possible in some circumstances to use an external source of electricity. For example, a metropolitan underground railway system may have three-phase electricity outlets in its tunnels. For a system that uses 230 V single phase, 400 V three phase, a three phase connection might need to supply about 175 A to power the apparatus as a whole, and this magnitude of current may be within the capacity of the electrical system powering the outlets. Consequently, the apparatus of FIG. 8 may omit the electric generator from the power supply 23 in some cases. This further reduces the cost, size and weight of the apparatus.

[0077] The apparatus of FIG. 8 may be provided as a free-standing unit, possibly without the hydraulic reservoir and pump unit 25 in order to save space if manual operation of the hydraulic cylinders is acceptable. However, the welding apparatus will more normally be provided on a vehicle.

[0078] FIG. 9 shows a vehicle 31 comprising the welding apparatus of FIG. 8. The vehicle 31 has an arrangement of wheels 33 which enable it to be driven on the ground and also to drive on a railway, as is known in the railway maintenance art. An arm 35, extending from the vehicle 31, carries a rail-engaging unit 37. The arm 35 can be raised and lowered, so as to allow the rail-engaging unit 37 to be placed over a rail join where a welded joint is to be formed.

[0079] The rail-engaging unit 37 includes the welding head 21 of FIG. 8, and preferably also includes at least part of the control unit 29 together with some controls for moving the arm 35, in order to enable the welding apparatus to be controlled by an operator standing beside the track. However, the power supply 23 will normally be located in the main part of the vehicle 31 in view of its weight and bulk, and the hydraulic reservoir and pump unit 25 may be provided in the main part of the vehicle 31 also. The vehicle 31 of FIG. 9 is a fully independent unit. It can be self-propelled and may include an electricity generator so that it can work substantially anywhere on a railway network.

[0080] Alternatively, the apparatus may be mounted on a frame or in a container 39, as shown in FIG. 10. The apparatus of FIG. 10 includes the arm 35 and the rail-engaging unit 37, and all the other parts of the welding apparatus of FIG. 9. It may omit the electricity generator. The apparatus of FIG. 10 may be mobile, and may be mounted on a road or rail vehicle for transport to a site where welding is required. It may be moved from vehicle to vehicle if this is desired.

[0081] The embodiments described above are provided by way of example, and are not intended to limit the scope of the invention. Various alternatives and modifications will be apparent to a reader skilled in the art.