The invention relates to the joining of railway (railroad) rails, for the installation and replacement of railway infrastructure.

Various specialised machines have been developed over many years to assist in the installation of railways. Some of these machines are vehicles designed to run alternatively on road and rail, having alternate wheels for each mode. Other machines, including very large and heavy machines, run on rail only. Lifting machines are also known which can span a whole rail track, running on "caterpillar" type tracks on the ballast either side of the railway. In the course of installing or renewing a railway, there may be a need to manoeuvre lengths of steel rail from tens of metres to hundreds of metres in length. The rail lengths need to be delivered to the installation site, and also they need to be 'transposed' so that they lie along a desired line on the bearers (sleepers),

In WO 2005/095716 Al, the present applicant disclosed a compact, low-cost machine for performing transposition of a very long length of continuous welded rail from a track-side to its location on the bearers (sleepers). The 'track rail transposed or TRT machine is compact yet powerful, by virtue of the fact that the load-bearing parts are located within the footprint of its ground-engaging wheels or tracks, i.e. within the vertical projection on the ground of the area bounded by its ground-engaging wheels. In WO 2009/050439 Al the applicant disclosed further methods and accessories allowing the machine to carry long rails, as well as transposing them, once on site. In these methods, a gang of two or more machines are used to carry the rail, supporting and guiding it at points along its length. The machine can operate in locations and in windows of opportunity unavailable to conventional techniques. Prior to the arrival of rails, the sleepers need to be installed and in WO 2010/097628 Al the applicant disclosed novel machinery for installation of sleepers in batches, including the fine positioning of the sleepers by a template. A task that remains after the operations mentioned above is to weld lengths of rail end-to end. Electric resistance welding, including so-called 'flash butt welding', is a process currently favoured for this, but other types of welding are available. Flash butt welding systems for mobile use on railways are known, and are generally mounted on vehicles that run on road and/or rail. The large vehicles are required to support the welding head, which includes a clamping arrangement for pushing the ends of the rails together in a forceful yet controlled manner while applying a strong electric current across the joint. Power units are required for mechanical force and the electric current, which means that even the smallest known welding systems require substantial vehicles, cranes etc. to deploy them. These vehicles generally cannot operate without a good deal of space around and above the work site. Some vehicles require good road access, and/or require to run on an adjacent rail track. So-called 'all-terrain' mobile welding systems are also available, based on a large, tracked vehicle, similar to a large digger. Well-known suppliers of mobile welding systems for rail including flash butt welding are Holland (see wvvvv.honandco.com/rail-vvelding-services), and Baltresurs (see http://www.baltresurs.com and Russian patent RU2366550C1). Normally in the preferred manner of use existing flash butt welding vehicles are positioned on the track adjacent to that on which rails are being welded. This requires at least two railway tracks to be constructed for the works, and reduces the operational capacity of the railway.

Summary

The invention in a first aspect provides apparatus for joining railway rail, the apparatus comprising a self-propelled vehicle having ground-engaging rolling means spaced either side of a working space, whereby said working space can be brought to a location where two rail ends are to be joined, said vehicle further comprising a rail welding head supported within said working space, said welding head being adapted to hold together the two rail ends and, by application of electric current,weld them together to form a welded joint; and wherein a connection is provided for receiving the electric current from a power source located off the vehicle.

The vehicle may further comprise an elevated chassis joining the ground-engaging rolling means above said working space, the welding head being suspended from said elevated chassis.

The rail welding head may comprise a flash butt welding head, comprising in particular a pair of clamp assemblies each for clamping one of the rails near its end, a mechanism for aligning the clamp assemblies to hold the rail ends abutting one another and to force them together so as to expel molten material during a welding operation, and electrodes for contacting each rail to provide for electric current to be driven through the abutting rails so as to cause heating sufficient to melt the abutting ends of the rails.

The rail welding head may be connected to a source of mechanical, for example hydraulic, power located on the vehicle, for operating said clamp assemblies and forcing the rail ends together. Alternatively, the rail welding head may have a connector for receiving mechanical (for example hydraulic) power from a source located off the vehicle.

In a preferred embodiment, the centre of gravity of the rail welding head is supported above a point within the footprint of the ground-engaging rolling means, i.e. within the vertical projection on the ground of the area bounded by the ground- engaging rolling means; or in other words above a point within the wheelbase of the vehicle.

The ground-engaging rolling means may comprise continuous tread tracks running substantially the length of the vehicle at each side. The ground-engaging rolling means may alternatively comprise wheels, but rubber tracks are more effective for traversing rough ground and railway lines. The vehicle may optionally be provided with rail wheels deployable to support the vehicle and load in a journey along a rail track.

The vehicle including the welding head is preferably less than 2.5m, more preferably less than 2 metres, in one or more of height, width and length. The vehicle including the welding head is preferably less than 2 metres in each dimension. However, a greater size may be permitted, if the welding head size or other functions assigned to the vehicle require it. The width between the ground-engaging rolling means may be such that the vehicle can straddle one rail but not both rails of a Standard Gauge railway. The width between the ground-engaging rolling means may be approximately the same as the Standard Gauge rail spacing (1435 mm inside spacing). The apparatus may further comprise a second self-propelled vehicle carrying electricity generating plant, and a flexible interconnection for supplying electric current from said generating plant to the welding head on the first-mentioned vehicle. The second vehicle may have ground-engaging rolling means of a similar form to the first vehicle.

The second vehicle may further comprise a chassis joining the ground-engaging rolling means at a clearance height above the ground, the electricity generating plant being supported on top of said chassis.

The second vehicle also may be less than 2.5m or less than 2m in some or all dimensions, as discussed already for the first vehicle. The clearance height may be more than 30cm, for example 35cm or more.

In a modified embodiment, the apparatus comprises a ground-engagable mechanical jack spaced either side of the working space. The mechanical jack may be telescopically extendable from within the vehicle chassis so as to be engageable with the ground either side of the ground-engaging rolling means. The mechanical jack may comprise arms which are extendable horizontally over the ground-engaging rolling means; and legs depending substantially perpendicularly from each arm and extendable towards the ground.

The invention in a second aspect provides a method of joining the ends of two railway rails, the method comprising:

providing apparatus for joining railway rail, the apparatus comprising a self- propelled vehicle having ground-engaging rolling means spaced either side of a working space and further comprising a rail welding head supported within said working space;

manoeuvring the vehicle so as to bring said working space, to a location where two rail ends are to be joined;

- connecting said welding head to receive electric current from a power source located off the vehicle; and

operating said welding head so as to hold together the two rail ends and by application of electric current from said power source to weld them together to form a welded joint.

The power source may comprise an electricity generating plant supported on a second vehicle.

The method may be performed using an apparatus according to the first aspect of the invention, set forth above. Optional features of the first aspect set forth above may be applied.

The method may include driving the vehicle over a rail track from a track-side location, to an on-track location.

The method may be performed using an apparatus according to the modified embodiment of the invention, set forth above wherein the step of manoeuvring the vehicle involves deploying the mechanical jack such that it engages the ground and lifts the vehicle off the ground. The step of deploying the mechanical jack may involve extending the arm(s) on one side of the working space further than the arm(s) on the other side of the working space and subsequently retracting the former once the vehicle is off the ground so as to laterally displace the vehicle relative to the ground.

Brief Description of the Drawings

Embodiments of the invention will now be described, by way of example only, by reference to the accompanying drawings, in which:

Figure 1 shows a known track rail transposer machine handling a length of rail on a conventional railway in (a) side view and (b) longitudinal view; Figure 2 is a plan view of a rail transposing operation performed using the machine of Figure 1;

Figure 3 is a plan view of a rail welding operation performed using a known apparatus;

Figure 4 is a schematic diagram of a welding head adaptable for use in embodiments of the present invention;

Figure 5 is a plan view illustrating novel welding apparatus according to an embodiment of the present invention, approaching a welding site;

Figure 6 is a plan view of the novel welding apparatus in use at the weld site;

Figure 7 is a side view of a welding head vehicle forming part of the welding apparatus of Figures 5 and 6;

Figure 8 is a rear view of the welding head vehicle of Figure 7; Figure 9 is a schematic side view of a power plant vehicle forming another part of the apparatus of Figures 5 and 6; Figure 10 is a side view of a modified welding head vehicle, adaptable for on-rail use;

Figure 11 is a rear view of a modified version of the of the welding head vehicle of Figure 8 which facilitates its lateral movement relative a rail; and

Figures 12a-e are plan views illustrating a possible sequence of movements of the welding head vehicle of Figure 11.

Detailed Description of the Embodiments

The apparatuses and methods to be described herein are generally used in the installation, maintenance and repair of railway (railroad) infrastructure. Referring to Figure 1 of the drawings, typical railway comprises two or more lengths of steel rail 10 mounted on bearers (sleepers) 12, laid along a prepared bed of ballast 14 or concrete ground. The rail 10 historically would be formed of short sections carried to the site and lifted into place by machines and/or men, and joined by fishplates and so forth. In more modern times, particularly for high speed rail traffic, continuous welded rail (CWR) is used, which can be delivered to the work site from the steel works in lengths of over 200 metres. The rails 10 are fixed to the sleepers in chairs 16. The skilled person will understand that many different forms of bearer, supporting ground, rail and chair or other fixing are available and suitable for use in different applications. The illustration or mention of any particular form of rail, bearer, chair etc. in the present description is merely to serve as an example, without any limitation as to the field of application of the apparatus and processes described herein. WO 05/095716 Al of the present applicant describes the "track rail transposer" (TRT) machine which can be seen in Figure 1 (a) side and (b) longitudinal views. The machine is a self-propelling vehicle, running on motorised tracks 102, 104. The width between the track centres is in this example roughly the same as the space between the rails of the railway (the gauge), for example 1.4 metres. The overall footprint of the machine is roughly square, with dimension 1.7 metres long by 1.7 metres to the extremity of the tracks. The machine chassis 106 is supported just over a metre above the ground on four legs 108 to 114 (Leg 114 is not visible in these views). On top of the chassis are mounted a power source such as a diesel motor, and associated fuel tank, hydraulic pumps and control systems. Housings for these works are indicated generally at 116.

As seen in Figure 1(b), the TRT machine is of a scale similar to a human operator, being less than 2 metres, certainly less than 2.5 metres high in total. Load bearing components are carried beneath chassis 106 in the working space, roughly a 1 metre cube, between the legs 108 to 114. As the machine moves in the course of its operations, this working space may be above ground beside the track on the track- side ballast, or directly above the bearers. The small dimensions of the machine do not permit it to straddle the entire Standard Gauge rail pair, but rather to straddle one rail or rail bed at a time. As explained in the prior patent applications, the fact that loads are supported always within the footprint of the tracks 102, 104, that is to say within the vertical projection on the ground of the area bounded by the tracks 102, 104 (i.e. within the wheelbase of the vehicle), it can be of compact size and light weight, in particular because there is no need for counterweights to balance an off- set load. By its small size, many advantages are gained, while the machine is capable of several different operations to be described further below, which traditionally would be undertaken by very large numbers of men (in developing countries) or by very large and very expensive machinery in more developed countries. The small size of the machine allows operations to be performed with minimal disruption to the regular running of the rail network, either in terms of isolation of overhead supplies or of blocking the traffic on neighbouring tracks. The small size of the machine also allows it to be transported to relatively inaccessible locations, for example, in the back of a small truck or van. Access through roads and tracks allows the machine to operate on single track railways, as it does not require an adjacent track to gain access to its working location. The type of operation specifically described in WO 2005/095716 Al is that of transposing a length of continuous welded rail from a location at the side of a track onto its operating location, and the reverse operation of removing an existing rail for replacement. WO 2009/050439 Al describes further applications, including carrying rails. For these purposes, the known TRT machine 100 is provided with two primary accessories, both supported from the chassis. Firstly, a transposing arm 118 is extendable and pivotally mounted beneath the centre of the chassis, and carries a transposing head 120. The pivot mounting at the top of the arm 118 is optionally motorised to drive it from side to side within the chassis. The other accessory hanging from the chassis is a hoist with a rail gripper depending from a variable length of chain 124. This too can either be passively or actively driven along transverse tracks 125, and is powered by a motorised or manually operated winch in housing 126.

Using the accessories described above, a number of TRT machines can be used to manipulate a single piece of rail 10. In the case of a short piece of rail, for example 20 metres in length, it is a simple matter for two TRT machines to pick it up, one at either end, and carry it along a track, onto a track and so forth, to and from a storage location. In the case of a very long length of continuous welded rail 400, for example over 200 metres in length, it may be carried by a gang of TRT machines. Each machine is provided with its own controls and human operator (not shown) who both drives and steers it by operation of hydraulic motors driving the tracks 102, 104.

In addition to single lengths of rail, bulkier items such as components of switch points and other types of track junctions and ancillary equipment also need to be manoeuvred on and off the railway. WO 2009/050439 Al, mentioned above, describes a turntable accessory for use in such applications. Figure 2 illustrates the transposing process by which a length of continuous welded rail 10 is eased from a location where it has been deposited beside the track by a special freight train, to a location on the bearers, where it can be fixed in shoes and the railway very quickly returned to operation. This operation simply involves the TRT machine 100 with a length of rail being transposed being loaded into the transposing head 120, motoring along the track and moving its transposing head along the length of the rail, while being steered to apply a transverse force to progressively bend the rail and deposit it along the desired line. The process can be reversed to remove an existing rail. Experience has shown that the TRT machine is able to remove and replace rail extremely quickly and efficiently, minimising disruption to the rail service and with minimal capital expenditure. In addition to steering the machine itself, the transverse force can be applied and varied by driving the mounting of the transposing arm, if motorised.

Figure 3 illustrates an operation to weld the ends of two pieces of rail 10a and 10b that have been laid on the bearers 12 using the TRT machine 100. Even where long lengths of continuous welded rail are laid, at some position 300, a joint has to be made. A welded joint has many advantages, and flash butt welding is particularly suitable. In order to form the welded joint, a vehicle 302 that carries a welding head 304 on an extending arm 306 is brought to the work site. Such vehicles and welding systems are available in North America and Europe from suppliers including Holland (see www.hollandco.com/rail-welding-services] and Baltresurs (see www.baltresurs.com]. A welding head marketed by from Blatresurs is described in Russian patent RU2366550C1.

Figure 4 illustrates schematically the main components and principles of operation of a flash butt welding apparatus 400, including the welding head. The welding head comprises various components mounted on a rigid body 402 or frame. In particular, clamping jaws 404 and 406 are provided for securely gripping the ends of the rails 10a and 10b. At least one of the jaws 404, 406 is mounted to be slideable on the body 402, and a hydraulic actuator 408 is operable to provide a very forceful closing movement 410. Hydraulic power for the ram 408 is provided from a source 412, shown only schematically in this diagram. In addition to mechanically clamping the rail ends, the jaws 404 and 408 include electrodes for connecting each rail end to one side of an electrical power source 414. Transformers for adapting the current & voltage characteristics of the electric power may also be included. In operation, as is well known, the jaws 404 and 406 force the rail ends together, while a high welding current is driven through the abutting ends of the rails. This causes melting and fusion of the rail metal, and movement of the rails together causes substantial expulsion of flash material. By suitable control of the closing force 410 and electrical current, a high-quality weld can be formed. Finishing steps to remove the upset material (flash) can be performed, by means well known to those skilled in the art.

While the welding head itself is not a great size, it is a heavy unit. One commercially available mobile welding head weighs over 2.5 tonnes (2500 kg). Referring again to the vehicle 302 seen in Figure 3, as well as the boom 306 and lifting gear for the welding head 304, are various items of power & cooling plant 308. These are provided to generate both hydraulic power for the operation of the welding head and boom 308, and electrical power for the butt welding operation itself. The need for the hydraulic and particularly the electric power sources 412, 414 means that the total weight and size of the equipment is substantially greater than that of the welding head alone (in the mentioned example, nearly 4 tonnes).

Compared with the TRT apparatus used in the previous operations, even the most compact and mobile welding plant available today is much larger. In most cases the operation of welding will require the closure of adjacent tracks and the isolation of overhead power lines. The capital cost of the welding equipment is also very great, of which a large component is the cost of the vehicle, and not the cost of the welding head and power plant. Therefore resistance welding is not so economic for smaller projects, leading to use of less satisfactory types of joint. Figure 5 illustrates in a schematic plan view novel welding apparatus approaching the location 300 of a joint, where rails 10a and 10b are to be joined by welding. Rather than the single large vehicle carrying both the welding head and the power plant, the novel apparatus 500 comprises separately manoeuvrable welding head vehicle 502 and power plant vehicle 504. Each of these vehicles has a basic form similar to the TRT vehicle 100 shown in Figures 1 and 2, although its size and form may be adapted to suit its different purpose applied in the present invention.

Figure 6 shows the novel welding apparatus 500 deployed at the joint location 300. Welding head vehicle 502 is straddling the joint location, while power plant vehicle 504 sits nearby. Once on location, the vehicles are coupled by a power cable 506, which conveys electrical and/or hydraulic power.

Figures 7 and 8 are a schematic side view and a rear view respectively of welding head vehicle 502. Vehicle 502 is a self-propelling vehicle, running on motorised tracks 702, 704. The width between the track centres is in this example roughly the same as the space between the rails of the railway (the gauge) for example 1.4 metres. A chassis 706 is supported above the ground on four legs 708 to 714. (Leg 714 is not visible in these views.) On top of the chassis are mounted a motive power source such as a diesel motor, and associated fuel tank, hydraulic pumps and control systems. Housings for these works are indicated generally at 716. By hydraulic motors mounted within the tracks 702 and 704, this power source allows the vehicle to be driven forwards and backwards, and steered in a manner well known. Beneath the chassis 706 and between the legs 708 to 714 is a working space. In this space, there is suspended a welding head 731, of the same general form as that shown in Figure 4. As seen in the rear view of Figure 8, the body of welding head 731 is suspended by a mounting 732 that permits it to be adjusted relative to chassis 706 in transverse and vertical directions, and also to swing about a pivot axis, so as to remain vertical even when the ground, and consequently the chassis 706, is not level. Because the weight of the welding head is suspended within the footprint (or wheelbase) of the vehicle, i.e. within the vertical projection on the ground of the area bounded by the tracks 702 and 704, there is no need to provide counterweights or bracing legs to prevent the vehicle tipping over. This, together with the fact that ancillary plant for electric power generation, cooling etc. are located off the welding head vehicle, allows the entire apparatus to be much smaller and lighter than the vehicle 302 conventionally required.

Probably slightly larger in scale than the TRT machine 100, welding head vehicle 502 is preferably less than 3.3 or 3.1 metres in height, to stay below the safe working height under UK standard overhead line equipment (OLE). For compactness, it is preferred that the vehicle is less than 2.5 metres high in total, for example approximately 1.8 to 2.2m. The vehicle in overall width (transverse to the driving direction) may be between 2m and 4m. The dimensions of the working space 730, and consequently of the vehicle as a whole, will depend on the selected design of welding head 731. The working space may be roughly cubic, and perhaps 1 to 1.5 metres each horizontal dimension. In reality the working space may be more completely filled by the welding head which is not shown to scale in Figure 8. The space should be sufficient for the welding head to be raised to a clearance height above the ground, for transit to and from the work site. Clearance may be over 30cm, for example 35cm or more.

The chassis may be partly open to allow part of the welding head or its support to project above the level shown in the diagram. The chassis and/or legs may be made expandable in a manner described in WO 2010/097628 Al, mentioned above. The height of the chassis and the width between the ground-engaging rolling means (tracks) can be made adjustable in this way. In that case, ranges of dimension given in the introduction and claims should be interpreted as referring to the most compact configuration, unless otherwise stated.

Figure 9 is a schematic side view of the power plant vehicle 504. This vehicle is also based on a pair of tracks 902, 904, supporting a chassis 906. Chassis 906 provides a platform that may be lower in height than chassis 706 of the welding head vehicle 502. This provides a clearance 910 above the ground that may be on the order of 0.35 metres, or 0.5 metres. No working space is provided in this embodiment. The height is sufficient for the vehicle to straddle rails, allowing it to move over the work site and railway tracks in the same manner as the TRT machine is accustomed to do. Chassis 906 provides a platform for motive power plant such as a diesel motor, with associated fuel tank, hydraulic pumps and control systems. A housing for these works is indicated generally at 916. By hydraulic motors mounted within the tracks 902 and 904, this power source allows the vehicle to be driven forwards and backwards, and steered in a manner well known. Also carried on platform 906 is an electric generator 930 which may have a diesel motor separate from that of the motive power plant in housing 916, and may be identical to the generating plant included in the known flash butt welding system. Referring again to Figures 7 and 8, as well as Figure 9, it will be seen that each vehicle 502 and 504 is provided with a pluggable electrical connector 740, 940 respectively. When the vehicles are in use for welding rails together, cable 760 is deployed between these connectors, to carry the welding current from generator 930 to welding head 930. In this way, the bulky conventional welding apparatus is sub divided and mounted on small self-propelled vehicles that can access more locations on a railway, and can operate with less disruption to surrounding tracks and overhead lines. While the electrical connector 740 is shown mounted on chassis 706 on the welding head vehicle 502, the electrical connector may be mounted directly on the welding head body 730 if desired. The length of cable 760 may be for example between 2 and 5 metres, or even 10 metres. In a case where hydraulic power is also passed between the vehicles 502, 504, electrical cable 760 and hydraulic hoses can be combined in an umbilical connection.

Cooling plant, not separately illustrated here, may be another requirement of the welding apparatus. The same considerations of locating the plant off the welding head vehicle and on a second (third, etc) vehicle can be applied, as in relation to the electrical and hydraulic power plant mentioned above. Numerous variations are possible without departing from the principle of the novel apparatus described above. In the example illustrated here, hydraulic power for the mechanical clamping and forcing actions of the welding head 731 is provided by a pump 762 on the welding head vehicle 502. This pump can share the same power source as the motive power for the vehicle itself, or there may be a separate power source. In an alternative embodiment, hydraulic power may also be delivered from the power plant vehicle 504, through a suitable hose, parallel to the cable 760. In principle, of course, if the situation demanded it, a third vehicle could be provided for hydraulic power, though this is not expected to be necessary.

Similarly, different options are available on the power plant vehicle. A diesel power unit could be shared between the electric generator 930 and the motive power plant that drives the vehicle tracks 902, 904. The power plant vehicle does not need to be as manoeuvrable as the welding head vehicle. Although less versatile, a trolley-like power plant vehicle, that requires the already-laid track on which to run, could be adequate for some situations. In the embodiment illustrated, however, it is expected that the power plant vehicle will be able to attend any site that the welding head vehicle can reach, maximising the potential of the novel welding head vehicle. In addition to the welding head, the welding head vehicle 502 may be provided with a hoist (not shown) similar to hoist 124 on the TRT vehicle. This may be provided to add versatility to the functions of the vehicle, and/or for the particular purpose of raising rail into the jaws of the welding head 731. Vehicle 502 may be an adapted TRT vehicle, in which the welding head 731 is carried by all or part of the same coupling that at other times carries the transpose arm 118 and transpose head 120 in the TRT machine 100. Given the size of current welding heads, however, it may need to be a larger vehicle than current TRT vehicles. A larger vehicle of similar general form is proposed for use in sleeper laying in the applicant's prior application WO 2010/097628 Al. The welding head vehicle 502 and/or power plant vehicle 504 could be based on such a vehicle. Again, the same vehicle could be made adaptable to carry a sleeper spacing accessory at one time, and a welding head or power plant at another. The vehicle can be made extendible in width and/or height, as described in the prior application. Figure 10 shows a modified welding head vehicle 502', in which the same components are recognisable as in the machine 502 of Figures 7 and 8, but there are additionally provided pairs of rail wheels 1002, 1004. The rail wheels can be deployed or retracted, so that the machine has the option, like a road/rail vehicle, to ride on the ground or along the railway in the manner of a train. Linkages 1006 and 1008 are driven by manual or hydraulic jacks 1010, 1012, so that the wheels 1002, 1004 can be moved from their stowed position, shown in solid lines in Figure 10, to their operational position, shown in dotted lines. In their operational position, the bearing surfaces of the rail wheels are at a level 1014 just below the lower portion of the ground-engaging tracks 702, 704. The wheels 1002, 1004 in their deployed position allow the apparatus 502', and any load which it is carrying to run along an existing railway. The rail wheels 1002, 1004 may be powered by hydraulic motors, or may be passive, so that the machine is simply pushed or pulled by another vehicle or human operator. The power plant vehicle 504 can be provided with rail wheels in a similar fashion, if desired. Both vehicles can be small and light enough, however, that they can be transported also on the back of a modest-sized pickup truck, unlike the conventional mobile welding system. Figure 11 shows a modified welding head vehicle 502" in which many of the same components are recognisable from the machine 502 of Figures 7 and 8. However, the vehicle 502" is additionally provided with arms 780" which are telescopically extendable from within its chassis 706". The arms 780" may be extended and retracted in a horizontal direction with respect to the chassis 706" at opposite sides of the chassis 706" over the underlying tracks 702", 704" (i.e. transverse to the driving direction). A leg 782" depends perpendicularly from each arm 780" near its end. At least part 784" of each leg 782" is telescopically extendable in a vertical direction towards the ground. Each leg 784" is provided with a pivotable foot 786" which may be in the form of a ball joint. It is anticipated that each welding head vehicle 502" would be provided with two spaced apart pairs of telescopic arms and legs 780", 784" as shown in Figures 12a-e so as to improve stability during operation. It will be appreciated that the arms and legs (780", 784") may be extended and retracted using any suitable jacking means, for example, a hydraulic, pneumatic or screw jack.

The modified apparatus of Figure 11 allows the welding head vehicle 502" to be relocated from a first position - e.g. where it straddles one rail - to a second position located laterally with respect to the first position. Importantly, the welding head vehicle 502" can be quickly relocated without the need to drive its tracks 702", 704" over any newly laid rails which may not yet be fastened to the bearers (sleepers). In order to do so, the arms and legs 780", 784" may be deployed from a stowed position (not shown) where they are each fully retracted at a location above the tracks 702", 704".

The arms 780" are firstly extended outwardly so that each leg 782", 784" depending from their ends moves clear of the outside of the respective tracks 702", 704". The arms 780" on the side of the vehicle 502" corresponding to the desired direction of lateral movement are each extended further than the arms 780" on the opposite side of the vehicle 502", the difference being commensurate with the desired lateral displacement. Once the arms 780" are correctly positioned, each leg 784" is extended towards the ground. The foot 786" of each leg 478" engages the ground and pivots to conform to the underlying ground profile. Further extension of the each leg 478" overcomes the weight of the vehicle 502" and lifts it off the ground, via the arms 780" and vehicle chassis 706". Once sufficient vertical clearance is achieved, the arms 780" on the side of the vehicle 502" corresponding to the desired direction of lateral movement are retracted within the chassis 706" whilst those on the opposite side of the vehicle 502" are simultaneously extended at the same rate. In doing so, the vehicle 502" is displaced laterally and may then be lowered to the ground by retracting all legs 478". Figure 12a-e show a welding head vehicle 502" which has been brought to a track- side location and its subsequent two-step lateral movement to an over-track location (e.g. at a track welding site) and then an on-track location (where rail wheels 790" may be deployed for a journey along a rail track). The welding head vehicle 502" may be self-powered, or passively towed by a towing vehicle as indicated in dashed lines in Figure 12e.

It will be appreciated that the maximum lateral displacement of the welding head vehicle 502" is dictated by the total telescopic reach of each arm 780" but incremental lateral movement may be desirable in certain circumstances, particularly when negotiating inclined ballast etc. The hydraulic control of the arms and legs 780", 784" may be controlled manually or automatically under software control. At least a degree of automation would be preferable to ensure that the pairs of arms 780" on each side of the vehicle 502" extend or retract to the same extent, and to ensure that the simultaneous extension and retraction of the arms 780" occurs at the same rate to ensure a stable displacement of the vehicle 502".

More complex arrangements are possible whereby the vertical movement of the legs 784" occurs simultaneously with the horizontal movement of the arms 780" so as to cause simultaneous lifting and lateral displacement of the vehicle 502".

Sensors may be employed to minimise the degree of vertical lifting required dependent on changes in ground incline or other obstacles. A degree of pivotable movement may be permitted between the arms 780" and legs 782" so as to accommodate lateral displacement over steeper ground inclines.

The above and other modifications of the apparatus and methods can be made within the spirit and scope of the invention.