Embedded rail

Abstract

 A rail track assembly comprises a concrete bed or beam 10 in which is embedded a rail 1 which is clad in an elastomer sheath 2, and coated within the sheath with a coating layer 3 of an electrically insulating and corrosion resistant material such as an epoxide or polyurethane resin. The running surfaces 16 are left exposed. A fabrication method comprises first abrading the surface of the rail, applying the coating 3, inserting the rail into the sheath 2 and casting the concrete bed about the sheathed rail.

Description

[0001] This invention relates to improvements in embedded rail constructions for use in the construction of railway and tram tracks.

[0002] Embedded rail systems generally comprise cast support slabs having pairs of parallel troughs formed therein, in which the rails are seated in a manner which leaves the running surface of the rail exposed but which allows the rails to be assembled by location in the troughs without need for adjustment of alignment or the use of separate clips to retain the rails on supports such as sleepers. Such embedded rail systems are particularly suitable for use in street installations of tramlines, and level crossings in other railways, as the rail can be completely recessed to leave only the running surfaces exposed.

[0003] To combat noise and vibration and provide for some resilience of support to the rail, there have been many proposals to partially or completely sheath the rails with resilient material. For example, US 5,464,152 discloses a precast grade crossing where the rails are embedded in a concrete raft and encased in a rubber boot or sheath which conforms to the cross-section of the rail and encases the base, central web, the underside of the head of the rail, and the outer side face of the head of the rail, leaving only the top running surface and the inner side face of the rail exposed, for contact with the tyres and flanges of the wheels of rail vehicles respectively. The boot or sheath is of elastomeric material, and is fitted about the rail. The boot provides vibration and noise damping, and electrical insulation of rails which serve as a return electric conductor for power systems, or as part of track signalling circuits.

[0004] Alternatively, a shell may be cast into a continuous reinforced concrete slab to allow an elastomeric layer of controlled dimensions to be placed between the rail and the shell to provide resilient support to a rail, for example from WO 03/018912 (Hyperlast Limited), and also from WO 99/63160 (Penny) which is also disclosed in connection with standard rail sections.

[0005] The rail is capable of being removed for replacement for example in the event of cracking of the rail or excessive wear.

[0006] The factory pre-coated embedded rail system described above has the disadvantage that to ensure the integrity of the coating, the rails must be coated under factory conditions away from the track construction site using bespoke moulds with which it is difficult to ensure close tolerances in the thickness of the coating material.

[0007] An object of the invention is to provide a method and construction of sheathing for embedded rail which will enable a resilient sheath to be affixed to the rail at or near the track location so that the rail can be assembled with the minimum handling during preparation and installation.

[0008] According to the invention a method of preparing a rail for assembly as an embedded rail comprises the step of coating at least part of the metal surface of the rail with a layer of an electrically insulating and corrosion resistant material.

[0009] The rail is advantageously prepared before coating by abrading the surface of the rail to ensure evenness and remove any rust which may have begun to form, and primed if necessary.

[0010] The coating layer may be allowed to cure over a suitable period, and after sufficient cure time has been allowed, a factory moulded elastomer pad, sheath or boot can be fitted around the rail and fixed in place with a low-tack adhesive or other material with similar effect.

[0011] The invention also provides a rail construction for use in an embedded rail assembly comprising a metal rail body, at least one outer surface area of which has been coated with a layer of an electrically insulating and corrosion resistant material. The rail body is further preferably covered on at least said coated surface area with an elastomer pad which may be fixed in place with a low-tack adhesive or other material with a similar effect.

[0012] The electrically insulating and corrosion resistant material may comprise a polyurethane or epoxide film which is brush coated or spray coated onto the abraded surfaces of the rail. The elastomer pad may comprise a body of a suitable elastomeric material which may be expanded or unexpanded, and may comprise a suitable polyurethane material.

[0013] All surfaces of the rail except the running surfaces (the upper side and the upper part of one side face of the rail) are preferably coated with the electrically insulating and corrosion resistant material and covered by the elastomer pad, which may be provided in the form of a sheath or boot which can be put onto the rail due to its elasticity and flexibility.

[0014] The method may be applied to all rail sections, including flat bottomed main line and tram rails, double-headed reversible rails, older style "bull-headed" rails and more recently developed generally rectangular cross-sectional rails.

[0015] Embodiments of rail systems according to the invention will now be described by way of example with reference to the accompanying drawings, wherein:-

Fig. 1 is a cross-sectional view of an embedded rail system of the invention as applied to a flat bottomed tram line or street rail system;

Fig. 2 is a similar view of an embedded rail system of the invention as applied to a flat-bottomed main line rail;

Fig. 3 is a similar view of an embedded rail system of the invention as applied to a first form of generally rectangular rail; and

Fig. 4 is a similar view of an embedded rail system of the invention as applied to a second form of generally rectangular rail.

[0016] Fig. 1 shows in cross-section a part of an embedded rail system which includes a concrete base slab, or beam 10 having a channel 11 therein to receive a rail. If the concrete base is a slab, a second channel 11 is provided parallel to that shown at a spacing equal to the gauge of the tramway.

[0017] The channel 11 contains a steel tram rail 1 having a flat bottomed base 12, a shank 13, and a head 14 divided by a groove 15 into a running surface 16 and a guard lip 17. The rail 1 is set in the concrete base in such a way that only the running surface 16, groove 15 and lip 17 are exposed. The remaining parts of the rail are embedded within the concrete base and are covered firstly with a coating 3 of a layer of electrically insulating and corrosion resistant material. This is achieved by abrading the surfaces of the rail to remove any rust or other corrosion which may have begun to affect the surface, and then applying a coating to form a film which is sufficiently thick to be continuous and coherent, without pores or pinholes which could allow the formation of corrosion to begin, but still relatively thin, preferably less than 1 mm. Application may be by brush or spray gun, or less preferably by dip-coating. The coating material preferably is an epoxy or polyurethane resin but other materials with the required properties may be used.

[0018] The coating step may be carried out at a factory or depot before transporting to the site of use, or may be carried out at or close to the site of use.

[0019] After coating, the rail is, at or close to the site of use, inserted into a sheath or boot 2 of elastomeric material such as a polyurethane material, with the flexibility of the elastomer sheath enabling the awkwardly sectioned rail to be inserted. After insertion into the sheath, the sheathed rail is located in channel 11, and concrete poured about the sheathed rail to embed the rail 1 in the concrete slab or beam.

[0020] Figure 2 shows a variation where a main line rail 1 is used in place of a tram line or street rail. In this case the running surface and one side face of the head of the rail is left exposed by the sheath 2, and is not contained within the concrete slab or beam 10. the rail 1 is coated and sheathed in the same way as the tram rail of Fig. 1 however.

[0021] Figs. 3 and 4 differ by showing two versions of a rectangular sectional rail 4, seated in a concrete base or beam 20. Each rail is coated as before with a polyurethane or epoxy resin or other suitable material layer coating 6 applied to all but the exposed head of the rail 4, and the coated rail 4 is received in an e.g. polyurethane sheath or boot 5 which is contoured with ribs 7 to key with the concrete to resist dislodgement. The rail 4 of Fig. 3 differs from that of Fig. 4 in that a recess 8 is provided towards the bottom on each side of the rail, whilst in Fig. 4 this recess 9 extends over all of the flanks of the rail except for the head and foot regions, giving the rail a very shallowly "waisted" configuration.

[0022] As with Figs. 1 and 2 the rails are coated with a coating 6 before employment, and are inserted into the sheaths 5 at or near the site of use, then cast in situ into the concrete base or beam 20.

[0023] The initial polyurethane or epoxy or other suitable film coating provides reliable corrosion protection and electrical insulation to the rail. Thin coatings can provide good protection to steel so long as their integrity as a barrier is maintained. Where coatings are subject to local damage the use of such coatings can lead to accelerated degradation particularly where there are impressed electrical currents flowing through the steel as is often the case with rail tracks.

[0024] The outer elastomer pad or sheath mitigates this effect once assembled and provides protection for the inner coating during handling and installation of the rail, as well as serving as a resilient foundation for the rail.

[0025] In the case of Fig. 1 and 2 rails, the rail 1 cannot be removed from the sheath 2, but the rails shown in Figs. 3 and 4 can be removed if required. The sheath 5 here needs to be held sufficiently firmly to the rail during handling and installation to avoid damage, and an adhesive may be used for this purpose.

Claims

1. A method of preparing a rail for assembly in an embedded rail system comprises the step of coating at least part of the metal surface of the rail with a coating layer of an electrically insulating and corrosion resistant material.

2. A method according to claim 1, wherein the said at last part of the metal surface is first prepared by abrading the surface of the rail.

3. A method according to claim 1, wherein at least the coated surface part of the rail is covered with a pad, sheath or boot of elastomer material.

4. A method according to claim 3, wherein the pad, sheath or boot is fixed in place with a low-tack adhesive.

5. A rail assembly prepared by a method according to any one of claims 1 to 4.

6. A rail assembly comprising one or more rails said rail being coated on at least part of the metal surface thereof with a coating layer of an electrically insulating and corrosion resistant material.

7. A rail assembly according to claim 6, wherein at least the coated surface part of the rail is covered with a pad, sheath or boot of elastomer material.

8. A rail assembly according to claim 7, wherein the or each of the rails is embedded in a concrete base or beam, cast about the rail and pad combination.

9. A rail assembly according to claim 6, wherein the coating layer comprises a polyurethane or epoxide material.

10. A rail assembly according to claim 7, wherein the elastomer material is a polyurethane.

11. A rail assembly according to claim 8, wherein the running surfaces of the or each rail are left exposed by the coating layer, the pad, sheath or boot and the concrete bed or beam.

Drawing