GB2500660A

GB2500660A - Rail pad

Info

Publication number: GB2500660A
Application number: GB1205510.9A
Authority: GB
Inventors: Hugh Rogers
Original assignee: TIFLEX Ltd
Current assignee: TIFLEX Ltd
Priority date: 2012-03-28
Filing date: 2012-03-28
Publication date: 2013-10-02
Also published as: GB201205510D0

Abstract

Rail pad for absorbing vibration comprises a resilient material with a static stiffness of at least 20kN per millimetre and a dynamic stiffness of less than 180kN per millimetre. A first major surface 10 comprises a sealing surface between the rail and the pad to inhibit water ingress. The sealing surface occupies at least the outer 30 millimetres of the first major surface. A second major surface 12 has a plurality of surface features 14 having gaps or recesses in between. The surface features have at least one of a shape and a spatial distribution that modulates at least one of the dynamic and static stiffness of the pad. Gaps remain between the surface features when they are compressed by a vehicle. Also claimed: A method of securing a rail to a sleeper comprising arranging a composite pad between the base of the rail and the sleeper, the surface of the pad adjacent the rail forms a seal between the pad and the rail; a rail pad having first and second surfaces, at least one feature to modulate the stiffness of the pad and a portion to provide a seal; a kit of parts for carrying out the claimed method.

Description

Rail Pad The present invention relates to rail pads and the installation of rails on sleepers. Rail pads are typically iiistalled beneath rails for impact attenuation and typically but not exclusively are installed between sleeper and rail, pads according to the invention may also be used for impact attenuation between base plates and chairs and/or rails.

The passage of trains over rail tracks applies compressive stresses to the sleepers beneath the rails and to the ballast beneath the sleepers. Typically sleepers need to be relatively rigid and as such provide very little shock attenuation. The repeated passage of trains can cause damage to the sleeper or cause loss of or damage to the underlying ballast. It has been proposed to provide vibration damping pads between railway sleepers and the metal rails which lie over them. In some cases a sofi foam pad can be interposed between the sleeper and the rail.

1 5 Typically rails are held in place on sleepers by robust metal clips, these clips place significant compressive stress on any pad p'aced between rail and sleeper. Tn addition trains passing along the rails also exert considerable compressive forces. As a result it has been found that soft foam pads suffer from "creep". Gradually the foam material breaks down and is forced out from between rail and sleeper. To counter this problem it is possible to use composite pads that are sufficiently rigid Qmve a sufficiently high e'astic moduhis) to resist creep. It then becomes necessary to modu'ate the stiffness of the pads using surface grooves and ridges in order to absorb vibration caused by passing trains. Otherwise the pads are too rigid. The grooves or ridges are arranged on both faces. To provide shear flexibility in addition to vertica' compressibility the grooves/ridges are often arranged in an offset pattern so that a groove on one face coincides with a ridge on the opposite face to provide the necessary reduction in rigidi'.

Such pads have been used for many years without any problems having been recognised. However, the inventors in the present case have now appreciated that the surface features (grooves or ridges) on the upper surface of such rail pads allow water to seep in and become trapped between the pad and the rail in a manner which causes corrosion of the rails. The inventors have fouid that the pattern of this corrosion follows the pattern of the pads, so for example where apad carries grooves on the surface which abuts the pad corrosion of the rail will occur preferentially along these ooves. Eventually this pattern of corrosion can cause the rail to crack. Although this problem has not previously been understood the inventors have found that it is a siñficant cause of the failure and breakage of rails.

Aspects and examples of the invention are set out in the claims and aim to address at least a part of the above described technical problem. In one aspect there is provided a rail pad adapted to sit beneath a rail for absorbing vibration caused by the passage of vehicles along the rail, the rail pad comprising: a resilient material arranged so that the pad has a static stiffness of at least 2OkN per millimetre and a dynamic stiffness of less than 1 SOkN per millimetre; a first major surface which at least partially comprises a sealing surface configured to provide a seal between the rail and the pad 1 0 to that extends around the periphery of the pad to inhibit the ingress of water between the rail and the pad; a second major surface having a plurality of surface features having gaps or recesses disposed therebetween and wherein the surface features have a shape and/or spatial distribution selected to modulate the dynamic stififiess and/or the static stiffness of the pad, wherein the surface features are arranged on the second major surface so that, in use, gaps remain between the surface features when they are compressed by the passage of a vehicle along the rails. This and other examples of the invention have the advantage of providing reliable vibration damping but without enabling water to seep between the pad and the rail.

Preferably the sealing surface occupies at least the outer 30 millimetres of the first major surface of the pad. The inventors have found that a sealing border of at least this idth is effective at keeping out water and protecting the rail. Tn some cases the sealing surface may extend across thc entire surface of the pad. Tn these cases, the sealing surface may comprises a flat, smooth surface and in which the material of the pad is sufficiently pliant that when the pad is disposed beneath a rail the sealing surface conforms to the rail to inhibit the ingress of water therebetween. This and other examples of the invention have the advantage of providing a reliable seal between rail and pad and providing a pad which is simple to manufacture. Typically the gaps or recesses between the surface features are at least 50% as wide as the adjacent surface features. The inventors have found that, in this configuration when the pad is placed under a compressive load such as that associated with a passing train, compression of the surface features (and so the stiffness modulation provided by the features) is not compromised by the features buffing up against one another.

In an aspect there is provided a method of securing a rail to a sleeper comprising arranging a composite pad between the base of the rail and the sleeper such that the surface of the pad adjacent the rail forms a seal between the pad and the rail so as to inhibit the ingress of water between the rail and the pad. In another aspect there is provided a rail pad having a first major surface and a second major surface, wherein the first major surface comprises a plurality of surface modulations which modulate the thickness of the pad and the second major surface comprises a border portion adapted to lie flush against the rail and provide a sealing surface between the rail and the pad.

In some possibilities the border portion extends across the entire surface of the pad, so that the surface of the pad which lies against the foot of the rail is completely flat. This and other examples allow a pad designer to alter the stiffness of the pad using surface features on the pad but also 1 0 provide a flat surface against the rail foot to prevent the ingress of water and eliminate rail corrosion thus providing vibration damping whilst also protecting the rail from corrosion at the interface between the pad and the rail. In some possibilities the pad carries equally spaced grooves and ridges (up stands) but by adjusting the groove width and the rubber compound stiffness it is possible to tune the pads to meet the working stiffness ranges required for mainline and underground trains, 1 5 preferably the pad has a static stiffness of at least 3OkN per millimetre, preferably this is at least 4OkN per millimetre, preferably the static stiffness is less than I SOkN per millimetre in some cases it may be less than I 2OkN per millimetre. Tn some possibilities the pad has a dynamic stiffness ofat least SOkN per millimetre to I SOkN per millimetre. Typically the width, height and spacing of the features which modulate the stiffness of the pad are selected so that, in use under a working load, the features can deform and the spacing between them is such that the deformed features do not abut one another so that the static and/or dynamic stiffness of the pad is maintained in operation.

The width and/or spacing between the ridges is typically selected so that under a working load of at least 2 MPa, the features can deform and the spacing between them is such that the deformed features do not abut one another so that the static and/or dynamic stiffliess of the pad is substantially maintained in operation. Preferably the ridges are selected for a working load of at least 3 Mpa, in some cases between 4 MPa and S MPa. Whilst the features may be provided by ridges and/or grooves this is not essential, other patterns or dimples will also serve to modify the surface area of the pad thereby to tune the stiffness of the pad.

Typically the pad comprises a natural and/or synthetic polymer, or a composite material. Examples of material used include polyurethane, rubber, natural rubber, and elastomer/polymer composites.

Other materials and combinations of materials may also be used. However, in preferred examples of the invention the material of the pad has a hardness of between 40 and 90 as measured on the international Rubber Hardness Degrees (IRHD) scale. Preferably the material has an IRHD hardness of at least 60. Preferably the IRHD hardness is less than 80, still more preferably, less than 70.

As will be appreciated, the IHRD measure of hardness is based on the depth of indentation made in a test specimen by an indenter of a standard size and shape. The method employs a preliminary test load that is applied to the specimen to be tested via the indcnter. The resulting indentation position provides a "zero" setting then the total test force is applied. The displacement in response to the test forcc is measured and converted to an IRHD hardness value. The displacement/IRI-ID dcgrees conversion table is published in ISO 48:1994 (as reviscd by ISO 48:20 10).

Preferably the surface features are arranged on the second major surface of the pad to provide an impact attenuation of at least 15% and preferably at least 30 %. Impact attenuation is defined in BSEN-13146-3. Methods of testing impact attenuation are known to those of skill in the art and 1 5 include, inter a/ia impact hammer modal testing and shaker modal testing.

Tn the method aspects of the invention the pad may be sealed to the rail using a sealant compound or adhesive however this is labour intensive and impractically costly, particularly where many hundreds or thousands of pads need to be laid. Thus, typically the pad i&lf comprises a border portion at least surrounding the periphery of the pad on one major surface so that, when the pad lies against a rail, the sealing surface abuts the rail to inhibit the ingress of water between the rail and the pad. This and other examples of the invention have the advantage of being quick and simple to use in practice whilst providing effective protection against corrosion. One or both major surfaces of the pad may comprise a plurality of surface features such as protrusions or recesses. The protrusions or recesses may include grooves, ridges, dimples, lugs, bumps or any other modulations of the pad thickness. The grooves and/or ridges may be arranged in a waffle pattern.

in one possibility a first major surface of the composite pad comprises the surface features and the second major surface of the pad comprises the border portion. Preferably the border portion extends substantially around the periphery of the first major surface. In one possibility the border portion comprises at least 2% of the surface area of the second major surface, in one possibility the border portion comprises at least 10% of the area of the at least one major surface. in one possibility the border portion comprises less than 90%, in some possibilities less than 70%, of the surface area of the second major surface. These and other examples of the invention have the advantage that, at the interface between the pad and the rail, the periphery of the pad is well sealed against the rail to inhibit water from getting trapped between the pad and the rail and causing conosion.

In one possibility the composite pad comprises a substantially flat pad of a first composite material having a plurality of surface features on at least one major surface of the pad and a second material of lower elastic modulus than the pad arranged between the surface features on one side of the pad so that, when the pad lies against a rail, the first composite material and/or the second material provide a sealing surface that lies flat against thc rail around the periphery of a major surface of the 1 0 pad to inhibit ingress of water between the rail and the pad. The second material is optional and need not be present, for example, hi one possibility a first major surface of the pad carries surface features such as recesses or protrusions (e.g. grooves, ridges, or dimples) and the second major surface of the pad is substantially plane surfaced and carries no surface features, thus the second major surface of the pad is adapted so that, in use it lies flush against the rail and this inhibits 1 5 ingress of water between the rail and the pad.

The pads may comprise a variety of both natural and synthetic materials and examples of suitable materials comprise rubber (microcellular, ridged or rubber bonded cork composite), composites, Ethylene Vinyl Acetate (EVA), polyurethane and other resilient compounds.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure I shows a rail, on a rail pad and affixed to a sleeper; Figure 2 shows two rail pads for use in Figure I, the first pad in Figure 2A is a "Type-A" pad, whilst the second pad in Figure 2B is a "Type-B" pad.

In Figure 1, Figure 1A shows a top view of rails 1, affixed to sleepers 3. Figure lB shows the section B-B of Figure 1A. The rail 1 is fixed to the sleeper 3 by a clip 5 and a resilient pad 7 is interposed between the sleeper 3 and the rail ito provide vibration attenuation.

Figure 2A shows a "type-A" pad 20 having a first major surface 10 and a second major surface 12.

The first major surface 10 carries a plurality of ridges 24 whilst the second major surface 12 is fiat to provide a seal against the base of a rail 1. The first and second major surfaces of the pad 20 are substantially rectangular but with two rcctangular cut out sections 1 on two opposite edges of the rectangle. Thc other two edges of the rectangle are straight. The cffect of the cut outs 1 is that, between thc cut outs 18 and the straight edges are two shoulders, so that thc overall shape of the pad is roughly H-shaped. The corners of the pad are bevelled.

Each straight edge is 185mm long. Each cut out 18 is 78mm in length and positioned 17.5mm from each straight edge so that it sits in the centre of an edge 176mm in length.

The pad of Figure 2A is 5mm thick, to within a tolerance of +O.5nim. The first and second major 1 0 surfaces of the pad 20 are substantially rectangular but with two rectangular cut out sections 18 on two opposite edges of the rectangle. The other two edges of the rectangle are straight. The effect of the cut outs 18 is that, between the cut outs 18 and the straight edge is a shoulder 19, so that the overall shape of the pad is roughly H-shaped, with one shoulder 19 at each corner of the pad 20.

The ridges 24 extend parallel to the two cut out edges to within a few millimetres of the two straight edges and are bevelled or rounded at their ends. The ridges 24 are carried on the mid section 22 of the pad 20. The shoulders 19 are 5mm thick, the mid section 22, between the four shoulders 19, is approximately 3mm thick. The mid section 22 extends along the pad between the two cut outs I 8 and extends all the way across the pad between the two straight edges. The ridges 24 are 6mm wide and extend 2mm out from the first major surface I 0 of the mid section 22 of the pad 20. The thickness of the pad, the material from which it is made and the depth/width of the surface features on type A pad provide an impact attenuation of at east 30%.

Specific widths and thicknesses have been quoted here but other configurations are possible.

Preferably the width and thickness of the surface features is selected so that, when the pad is under a working load of at least 3MPa the surface features (e.g. ridges) still have room to be further compressed. If the ridges are too closcly spaced, then undcr heavy loads adjacent ridges may but up against cach othcr and prevent the surface fcatures from providing thc required impact attenuation.

In Figure 2B a type B pad is shown which has substantially similar features to the type A pad shown in Figure 2A but is of slightly different proportions. The thiclrncss of thc pad and the depth of the groovcs is the same as for the type A pad and in Figure 2B likc reference numerals are used to indicate like elcments. The straight cdges of the type B pad arc 170mm long. The cut out edges are 166mm long and the cut outs 1 are 104mm in length so that the shoulders 19 are each 31mm long.

The cut outs 1 and the shoulders 19 are 16.5mm wide. Typically the type B pad is selected to provide an impact attenuation of at least 15%.

The dimensions and relative sizes described above are merely examples and other sized pads may be used having components of differing sizes. Typically the major surfaces of the pads arc at least 100mm square and may be up to 250mm square. The ridges or other surface features may be relatively deeper/thicker than the rest of the pad. Instead of ridges other protruding surface features may be used. In some cases the ridges may be arranged in a waffle pattern or grid. In some cases the surface features may be recesses such as dimples or grooves. In these examples the mid section need not be thinner than the shoulders. The pads of Figure 2A and Figure 2B are both 5mm thick, to within a tolerance of +0.5mm but other thicknesses and tolerances may be appropriate depending on circumstances, preferable thickness ranges are at least 4mm thick and less than 15mm thick, preferably at east 5mm thick and less then 12mm thick. The ridges 12 are shown as parallel to the 1 5 two cut out edges but they may be at an angle to these edges or they may be perpendicular to them, e.g. parallel with the straight edges of the pad. Any shape or configuration of surface features may be used. Tt is a'so possible to provide hollow regions in the pad or to use regions filled with a different material in order to modulate the stiffness. The ridges are shown as being bevelled or rounded at their ends but in some examples they have square or tapered ends. Afthough the surface I 0 is shown as being flat it may aho carry some surface features provided that a border portion of the surface which substantially surrounds all of the surface 10 is smooth and arranged to he flush against a rail when in use to provide a seaL Preferably this border portion is at east 20mm wide, in some cases at east 30mm wide.

Tn use a rail I is assembled to a steeper 3 and a rail pad, 7, 20 is interposed between the two. The pad 7, 20 is arranged with its sealing surface 10 lies against the base of the rail to prevent water seeping in and becoming trapped between the rail 1 and the pad 7, 20. The rail is then secured to the sleeper using a clip 5. Clips, rails and multiple pads may be provided together in kits to enable the fifting/ installation of rails. The kits may also include sleepers.

Claims

Claims: 1. A rail pad adapted to sit beneath a rail for absorbing vibration caused by the passage of vehicles along the rail, the rail pad comprising: a resilient material arranged so that the pad has a static stiffness of at least 2OkN per millimetre and a dynamic stiffness of less than l8OkN per millimetre; a first major surface which at least partially comprises a sealing surface configured to provide a seal between the rail and the pad to that extends around the periphery of the pad to inhibit the ingress of water between the rail and the pad wherein the scaling surface occupies at least the outer 30 millimetres of the first major surface of the pad; a second major surface having a plurality of surface features having gaps or recesses disposed therebetween and wherein the surface features havo a shape and/or spatial distribution selected to modulate the dynamic stififiess and/or the static stiffness of the pad, wherein the surface features are arranged on the second major surface so that, in use, gaps remain between the surface features when they are compressed by the passage of a vehicle along the rails.

2. The nfl pad of claim I in hich, the sealing surface comprises a flat, smooth surface and in which the material of the pad is sufficienfly pliant that when the pad is disposed beneath a rai' the sealing surface conforms to the rail to inhibit the ingress of water therebetween.

3. The rai' pad of daim I or 2 in which the sealing surface extends across substantially the entire contact surface.

4. The rai' pad of any preceding daim in which the gaps or recesses between the surface features are at least 50% as wide as the adjacent surface features.

5. A method of securing a rail to a sleeper comprising arranging a composite pad between the base of the rail and the sleeper such that the surface of the pad adjacent the rail forms a seal between the pad and the rail to inhibit the ingress of water between the rail and the pad.

6. The method of claim 1 in which the pad comprises a features which modulate the stiffness of the pad and a second major surface which is adapted to form the seal.

7. The method of claim 5 or 6 comprising securing the rail to the sleeper with the pad trapped between the sleeper and the rail and a flat surface of the pad abutting the base of the rail to exclude water from the surface of the rail adjacent the pad.

8. The method of claim 7 comprising, prior to securing the rail to the sleeper, adjusting the height of the rail by positioning one or more shim elements beneath the pad so that the shims are not intcrposed betwecn the flat surface of the pad and the base of the rail.

9. The method of any of claims 5 to 8 in which the pad comprises a pad according to any of claims ito 5.

10. A rail pad having a first major surface and a second major surface and at least one feature selected to modulate the stiffness of the pad, wherein the second major surface comprises a border portion adapted to lie flush against the rail and provide a seal between the rail and the pad.

I. The rail pad of claim I 0 in which the features which modulate stiffness comprise surface features such as recesses such as grooves or dimples or protrusions such as ridges, bumps or lugs.

I 2. The rail pad of claim I I in which the features which modulate stiffness comprise hollow regions inside the pad.

13. The rail pad of claim 12 in which the hollow regions contain a material of a different elastic modulus than the material of the bulk of the pad.

14. The rail pad of claim 12 in which the surface features comprise a plurality of gaps between adjacent features are arranged so that when, in use, the pad is compressed by a load applied to a rail, gaps remain between adjacent surface features.

15. A rail pad according to any of claims 10 to 14 in which the border portion extends across the entire surface of the pad, so that the surface of the pad which lies against the foot of the rail is substantially fiat.

16. A kit of parts for carrying out the method of any of claims S to 9 to fix a sleeper to a rail. -10-

17. The kit of parts of claim 16 further comprising one of the sleeper and the rail iS. A rail pad substantially as described herein with reference to the accompanying drawings.