GB2582778A

GB2582778A - Railway sleeper

Info

Publication number: GB2582778A
Application number: GB1904605.1A
Authority: GB
Inventors: James Whiteley Christopher
Original assignee: Oxford Plastic Systems Ltd
Current assignee: Oxford Plastic Systems Ltd
Priority date: 2019-04-02
Filing date: 2019-04-02
Publication date: 2020-10-07
Also published as: GB201904605D0

Abstract

A composite railway sleeper 10 comprising a body 11 and a base layer 12 to be placed on ground 14 underneath, wherein the body 11 which has an elongate extension from a first end to a second end and is made from a composite material comprising reinforcing fibres oriented along the elongate extension, wherein the base layer 12 is provided on a side of the body 11, and wherein at least a portion of the base layer 12 comprises a surface configuration (32, figure 5b) providing better ground-engaging grip than the composite material. The specification also comprises a method of manufacturing a railway sleeper and comprises the steps of forming from a composite material a sleeper 10 body 11 having reinforcing fibres orientated along an elongate extension of the body, providing a base layer 12 to be bonded to the sleeper body, allowing the base layer to bond, and provide the base layer with a surface configuration (32, figure 5b) that may provide better ground engaging grip than that of the body.

Description

Railway sleeper

Field of the Invention

This invention relates to a railway sleeper. More particularly, the invention relates to railway sleepers comprising a body from a material other than wood, in particular fibre-reinforced plastics material.

Background

Referring to Figure 1, a series of railway sleepers 1 is provided in a spaced-apart relationship and each sleeper 1 extends transversely underneath a pair of rails 2, which are attached to the sleeper by appropriate rail baseplates, clips and screws. The sleeper rests on a bed of track ballast 3. Traditionally, railway sleepers have been made of timber or concrete. There are endeavours to provide sleepers from other materials such as steel and plastic materials. United States Patent 6604689 discloses a steel sleeper. GB2473729 discloses a railway sleeper in the form of an elongate member of plastics material. GB2495763 discloses a railway sleeper of a composite plastics material, which may be formed from recycled materials. GB2554718 discloses a plastic railway sleeper comprising an inner support structure.

Although materials other than wood have the potential to offer several advantages over sleepers made from wood, their different material properties mean that it is not normally possible to replace a single sleeper or a short run of sleepers where this would lead to different sleepers being used, as the different material properties would unfavourably affect the stability of the track. As such, if wooden sleepers are replaced with non-wooden sleepers, such an undertaking tends to require the replacement of substantial lengths of track.

An object of the present invention is to provide a railway sleeper of improved construction.

Summary of the Invention

According to a first aspect, the present invention provides a railway sleeper as defined in claim 1, comprising a body and a base layer. The base layer is to be placed on ground underneath the railway sleeper. The body has an elongate extension from a first end to a second end and is made from a composite material comprising reinforcing fibres oriented along the elongate extension. The base layer is provided on a side of the body. At least a portion of the base layer comprises a surface configuration providing a better ground-engaging grip than the composite material.

The composite material of the body may be a polymer, such as a plastics material, combined with reinforcement such as glass fibre reinforcement and formed by any suitable technique, such as moulding, extrusion or pultrusion. In some embodiments, the body comprises a matrix provided by a resin, such as vinyl ester, polyester, epoxy or polyurethane. Embedded within composite material (e.g. the matrix) are reinforcing fibres. The fibres may be embedded, for instance, during the moulding of the body, for instance by placing fibre or fibre mats in appropriate locations. The fibres may be embedded by coextruding fibres with the body. The fibres are of generally elongate structure to impart strength and stiffness to the body, whereby it is believed that the strength and stiffness of the body increases generally with the length and volume fraction of the fibres.

The elongate extension from the first end to the second end of the railway sleeper is understood to be the longest dimension of the sleeper, usually positioned perpendicular to the railway tracks underneath which it is installed. Preferably the fibres extend from one end of the body to another end, although it will be understood that fibres due to their nature and manufacturing method may be shorter and not perfectly aligned with the elongate extension. Likewise, as fibres are embedded or co-extruded, there may be occasional misaligned or bending of fibres, or the fibres may be intentionally meandering to a certain degree. However, it will be understood that the fibres oriented along the elongate extension are purposefully placed such that a large proportion of the fibres, e.g. more than a quarter, or more than half, is generally aligned with the elongate extension. As a simplified illustration, the fibres can be understood as generally unidirectionally aligned with the elongate extension (which may be a pultrusion axis) to provide strength to the body, such that the majority of the fibres are oriented in the elongate extension of the railway sleeper.

The volume fraction of elongate fibres in the matrix may be higher than 35, 40, 45, 50, 55 or 60 volume percent. The structural stability of the sleeper increases the higher the volume fraction is.

The volume fraction of elongate fibres in the matrix may be no more than 80, 75, 70, 65 or 60 volume percent. The remainder of the volume may be predominantly matrix resin. This improves the ability to form the sleeper body.

One of the body surfaces, which is understood to constitute a down-facing surface of the sleeper body, is provided with a base layer that comprises a surface configuration providing better ground-engaging grip than the composite material.

The applicant has appreciated that railway sleepers, particularly non-wooden sleepers such as those manufactured from plastics material, benefit from a surface texture to provide sufficient grip. In practice, applying a texture to a sleeper body involves some effort, given their size, weight, and complex requirements so as to be suitable as a railway sleeper. By providing an additional base layer that is configured with grip properties in mind, the manufacture of the grip element can be effectively de-coupled from the manufacture of the sleeper body. This provides much more freedom during the design stage of a sleeper body, as this can be optimised for weight distribution and/or material composition, e.g., to provide a more durable product, without also having to consider ground-engaging grip properties of the sleeper body. In particular, adding a surface configuration directly to a fibre-reinforced body carries a risk of damaging, and thereby shortening, the reinforcing fibres, which risks affecting the strength of the body. The risk can be reduced by providing, separately, a base layer.

The base layer may be provided by depositing resin into a mould to form a base layer and depositing on top of the base layer resin further resin material as matrix for elongate fibres. The process may be quasi-continuous such that the same matrix material is used, with different a different or no fibre in the base than in the body.

In some embodiments, the base layer is attached to a side of the body.

The base layer may be provided by attaching a base layer to at least one body surface of the sleeper body. Both the sleeper body and the base layer may be pre-fabricated and attached to each other. One of the sleeper body or the base layer may be pre-fabricated and the other component may be attached, by moulding one onto the other.

As such, the attachment may be achieved by moulding one component onto the other.

Underlying aspects of the invention is the appreciation that it is a requirement of many rail governing bodies that a sleeper interacts with the crushed stones in the track ballast on which it rests in order to prevent lateral movement of the sleeper as a train travels over it. The applicant appreciated that different sections of ballast (stones) and different geographical markets may require different grip properties, such as a different texture pattern and sizes of stones, and so the provision of a separate grip component, in the form of a base layer, facilitates the tailoring of the texture pattern without having to alter the manufacture of the sleeper body for different sites.

In some embodiments, the surface configuration of the base layer comprises texture features providing a varying profile along the elongate extension.

It will be understood that "the elongate extension" refers to longest extension of the railway sleeper. As set out above, this would be expected to correspond to the general orientation of the elongate reinforcing fibres. For instance, the elongate extension may correspond to an extrusion axis of the sleeper body. It can be imagined that the base layer is provided on a side of the sleeper body extending along the elongate extension, and that the base layer can be arranged in a manner such that surface texture features of the base layer extend perpendicular to the elongate extension of the sleeper body. In that manner, the surface texture features provide a varying profile along the elongate extension. This helps to provide better grip with the track ballast.

A separately provided base layer is particularly suitable when used in combination with extruded or pultruded sleeper bodies, because this allows a texture to be easily provided that varies along the extrusion axis. Likewise, for moulded sleeper bodies with embedded reinforcing fibres, the applicant has appreciated that the reinforcing fibres tend to be oriented in the direction of the elongate extension, as this allows a longer uninterrupted length of fibre to be provided.

In some embodiments, the at least one body surface and the base layer are formed from different materials. For example, the base layer may be formed from a softer material than the at least one body surface.

The base layer may be made from different material than the body and may or may not be reinforced with fibres. For instance, the base layer may comprise the same matrix material as the body, reinforced with fibres that are shorter than the elongate fibres of the body, such that the shorter fibres are more prone to arrange anisotropically, or randomly, and thereby are better suited for being moulded with a particular surface configuration, or for adding a surface configuration. The material of the body and the base layer may therefore be distinguished by the length of the reinforcing fibres. In other words, the volume fraction of elongate fibres in the base layer is smaller (or none) compared to the body. As such, the railway sleeper may comprise a first and a second material. The first material, of the body, comprises longer fibres alignable with the elongate extension of the railway sleeper and providing strength. The second material, of the base layer, comprises shorter fibres tending not to align and being better suited for adding a surface configuration providing better ground-engaging grip. The railway sleeper may be manufactured by depositing matrix material into a mould to form the base layer, and continuing to deposit matrix material, together with elongate fibres, to transition from the base layer to the body structure.

Softer material and/or a texture may be provided to improve the grip properties of the base layer relative to the sleeper body.

In some embodiments, the base layer is made from a composite material comprising reinforcing fibres that are oriented randomly in relation to the elongate extension.

The reinforcing fibres of the base layer may be shorter than the fibres of the body, and thereby show a tendency to arrange in a more anisotropic manner. However, it is not necessarily a requirement for the base layer to be fibre reinforced. As such, in embodiments, the base layer comprises no reinforcing fibres or only a negligible amount thereof.

In some embodiments, a body-facing side of the base layer and/or at least one body surface is provided with interface features facilitating attaching the base layer to the body.

The base layer can be understood as a structure with an, when installed, upper (sleeper-body-facing) side and a lower (ground-facing) side. For example, at least one body surface and the body-facing side may comprise complementary interface features and/or flat surface portions.

In some embodiments, the interface features are provided by a roughened surface, resulting in a stronger bond between the body and the base layer.

In some embodiments, the at least one body surface has been cleaned before the base layer is attached to the body.

By "interface feature", a feature is meant which is formed on a surface during manufacture such as surface roughening, surface smoothing and/or surface flattening. For example, complementary interface features may include a plurality of protrusions such as ridges formed on a first surface configured to fit into a plurality of complementary recesses such as grooves formed on a second surface.

In some embodiments, the railway sleeper comprises a plurality of base layer components each provided on a different portion of one body surface.

The base layer may be provided in the form of base layer components, akin to tiles arranged side-by-side, to cover a portion, or substantially all, of the ground-engaging body surface. The components may abut each other or be provided in a spaced-apart relationship. The base layer components may be practically the same, e.g. made from the same mould. This typically reduces manufacturing costs in line with the size of the mould required. The base layer components may differ, e.g. they may comprise different texture and/or different material.

The body and/or the base layer may be formed from a polymer such as a plastics material. For example, the base layer may be formed from a recycled plastics material and/or a virgin plastics material.

The at least one body surface may be formed from a polymer. For example, the at least one body and/or the base layer may comprise glass fibre. This is suitable for pultrusion and other manufacturing processes.

In some embodiments, the base layer is prefabricated prior to attachment to the body.

In some embodiments, the base layer is bonded and/or overmoulded to the at least one body surface.

In some embodiments, the surface configuration is provided during fabrication of the base layer.

In some embodiments, the surface configuration is added after the fabrication of the base layer.

In some embodiments, the base layer is moulded onto the at least one body surface via a moulding process.

In some embodiments, the surface configuration is provided during the moulding process.

In some embodiments, the surface configuration is provided after the moulding process.

In some embodiments, the surface configuration comprises a plurality of grip-improving features such as indentations or protrusions. The grip-improving features may comprise dome-shaped, cone-shaped, pyramid-shaped or blade-shaped protrusions and/or indentations, or a combination of two or more thereof.

In some embodiments, the base layer is shaped such that it covers substantially all of the at least one body surface.

This facilitates alignment of the base layer with the body surface and thereby facilitates manufacture.

In accordance with a second aspect, there is provided a method of manufacturing a railway sleeper in accordance with the first aspect, as defined in claim 20.

The method comprises the steps of forming from a composite material a sleeper body comprising reinforcing fibres oriented along an elongate extension between a first end and a second end of the sleeper body, providing a base layer to be bonded to the sleeper body, allowing the base layer to bond to the body; and providing the base layer with a surface configuration providing better ground-engaging grip than the body.

In some embodiments, the step of providing the base layer with a surface configuration is carried out after providing the step of bonding the base layer to the body.

However, the step of providing the base layer with a surface configuration may be carried out during or after manufacture of the base layer, before it is bonded to the body.

In some embodiments, the step of providing a base layer comprises placing the sleeper body into a mould containing a liquid such that the liquid covers at least one side of the sleeper, and allowing the liquid to solidify to a solid base layer while bonding to the body.

In some embodiments, the step of providing the base layer with a surface configuration comprises providing the mould with mould shapes complementary to the surface configuration prior to placing the sleeper body into the mould.

In some embodiments, the method comprises roughening and/or cleaning at least one body surface of the sleeper body prior to bonding the base layer to the body surface.

In some embodiments, the method comprises trimming the base layer after bonding such that it corresponds in size and shape to a side of the body.

It will be understood that features described in relation to the first aspect may be present and/or manufactured in embodiments of the second aspect.

Description of the Figures

Embodiments of the invention will now be described by way of example and with reference to the accompanying Figures, in which: Figure 1 is a perspective view of a prior art arrangement comprising multiple (here: four) railway sleepers.

Figure 2 is a perspective view of an arrangement of multiple (here: four) sleepers in accordance with the invention in an intended environment.

Figure 3 is a longitudinal cross-section of one of the sleepers of Figure 2; Figure 4 is a lateral cross-section of one of the sleepers of Figure 2; Figure 5a is a perspective underside view of a sleeper in accordance with the invention; Figure 5b is an enlarged view of a portion of Figure 5a; and Figure 6 is a lateral cross-section of a sleeper in accordance with another embodiment of the invention in an environment.

Description

Referring to Figures 2 to 4, Figure 2 shows a perspective view of an arrangement including a plurality of railway sleepers 10 supporting a pair of railway tracks 13. Figure 3 depicts a single railway sleeper 10 of Figure 2 in a longitudinal side elevation, i.e. viewed in the extension of the tracks 13. Figure 4 depicts a single railway sleeper 10 of Figure 2 in a lateral side elevation such that only one railway track 13 is visible, with the sleeper 10 beneath the depicted track 13. The same reference numerals are used in Figures 2 to 4 for corresponding elements without repeating the description thereof.

The railway sleeper 10 comprises an elongate body 11 indicated in Figures 2 to 4 as a generally cuboidal body although it will be understood that the profile could be more complex, e.g. a box profile. The body 11 is formed from a pultruded fibreglass reinforced polymer (see also Figure 6 and description below). As a consequence of the pultrusion manufacturing process, the body 11 has a constant cross-section along a pultrusion axis 15 extending longitudinally across the length of the body 11, as illustrated in Figures 3 and 5a. The pultrusion axis 15 constitutes an elongate extension of the railway sleeper 10. It will be appreciated by those skilled in the art that the body 11 could alternatively be manufactured via an extrusion process. References to a pultrusion axis and to an extrusion axis are in this respect equivalent. Likewise, the body could be manufactured by a moulding process. Reinforcing fibres can in that case be embedded during a moulding step, for instance in the form of a fibre mat. It would be understood that the fibres would be aligned in the elongate extension because this allows a longer continuous fibre to be embedded in a straight manner than would otherwise be the case in any other extension of the railway sleeper 10.

To provide an illustration of the typical size of a railway sleeper, the body 11 may have a length of 2.7 metres, a width of 0.3 metres and a depth of 0.1 metres. The 2.7 m extension exceeds the other dimensions and corresponds to the elongate extension. These dimensions are provided as an example and the invention is not intended to be limited to a body with these specific dimensions. For the purposes of the description in Figures 2 to 4, the body 11 has six outer surfaces: a lower surface constituting a ground-facing surface, an upper surface substantially parallel to the ground-facing surface that constitutes a rail-facing surface 16, two end surfaces 17 extending between the upper and lower surface at opposite ends of and perpendicular to the pultrusion axis 15, and two side surfaces 18 extending along the pultrusion axis 15 between the end surfaces and between the upper and lower surface.

The railway sleeper 10 shown in Figures 2 to 4 rests on a ground 14. Typically, a railway sleeper 10 lies on an area of ground 14 which consists of track ballast, i.e. crushed stone or gravel. The track ballast usually surrounds or partially surrounds the sleeper to restrict lateral and longitudinal movement (i.e. sliding movement) of the sleeper relative to the ground 14 when a train travels over it.

It is a requirement of many railway governing bodies that a sleeper interacts with the crushed stones in the track ballast on which it rests in order to prevent sliding movement of the sleeper as a train travels over it. For wooden sleepers, stones are able to dig into the surface of the sleeper due to the relative softness of the material and this provides sufficient friction to prevent the sleepers from moving. However, this imposes a restriction on the type of wood that can be used and, more generally, on the type of materials suitable as sleeper. For fibre-reinforced sleepers such as pultruded sleepers in particular, due to the pultrusion manufacturing process, the body 11 may have a relatively hard and smooth outer surface compared to a sleeper formed from timber. The applicant appreciated that if a fibre-reinforced sleeper body were to be placed directly onto track ballast, it would be relatively difficult to provide a surface configuration directly onto an outer body surface, particularly without damaging the fibres, and track ballast would be less able to dig into the outer surfaces of the body 11 to restrict sliding of the sleeper 10.

In order to provide the railway sleeper 10 with better ground-engaging grip than would otherwise be provided by the outer surfaces of body 11 alone, the railway sleeper 10 is provided with a base layer 12, which comprises a surface configuration 32 (shown in Figures 5a and 5b) providing better ground-engaging grip than the outer surface of body 11. The base layer 12 has been attached to the ground-facing surface of body 11. By "attached", it is meant that the base layer is connected to the ground-facing surface of body 11 either directly, indirectly, or a combination of indirect and direct means, for instance using a structured interface in which only some portions touch the body directly. For example, if an intermediate layer is provided between a portion of the ground-facing surface of body 11 and base layer 12, the base layer 12 will be attached indirectly to the ground-facing surface of body 11 within said portion. The invention provides for sleeper bodies that are made from pultruded material and onto which the base layer is attached directly. However, in some embodiments the base layer may be formed by depositing base layer material and body material in sequence to form a relatively continuous resin matrix. In that case, the portion of the matrix forming the body may be provided with elongate reinforcing fibres to provide stability whereas the portion of the matrix forming the base layer is provided with shorter, or no, reinforcing fibres. The Figures show a separation line between the body 11 and the base layer 12 although in practice no line may be visible depending on how the base layer 12 formed on the body 11.

In the particular embodiment shown in Figures 5a and 5b, the base layer 12 and the surface configuration 32 are prefabricated. The prefabricated base layer 12 is manufactured from a polymer such as a virgin plastics material and is bonded to the ground-facing surface of body 11, for instance using an adhesive. However, it will be appreciated by those skilled in the art that a prefabricated base layer 12 may be attached to any outer surface of body 11 by any suitable attachment means (e.g. overmoulding, riveting, bolting, heat-shrinking etc.), and that the base layer 12 may be manufactured from any suitable material (e.g. rubber, etc.). Polymer materials have been found by the applicant to be particularly suitable for adhesion onto the outer surface of the body 11 when this is also manufactured with a polymer matrix such as the type used, e.g., in a glass fibre-reinforced polymer pultrusions or moulded structures. The base layer 12 may be formed from a reinforced plastic such as, for example, polyurethane reinforced with glass fibre. The same reference numerals are used in Figures 2 to 5b for corresponding elements without repeating the description thereof.

In some embodiments, the base layer 12 and surface configuration 32 are prefabricated in order to simplify manufacture of the railway sleeper 10. By "prefabricated", it is meant that the base layer 12 and surface configuration 32 are manufactured before the base layer 12 is attached to the body 11. This allows for the base layer 12 to be formed separately, without having to handle the relatively larger and bulkier body 11 at the same time as a texture is formed in the base layer, because the grip-providing feature, (here: texture) is prefabricated on the base layer. However, it will be understood by the skilled person that the surface configuration 32 could be formed on the base layer 12 separately to the fabrication of the base layer 12 and either before, during, or after the base layer 12 is formed on, or attached to, the body 11.

In some embodiments, the base layer 12 is formed directly onto the ground-facing surface of body 11, for example via a moulding process. For example, to form the base layer 12 directly onto the ground-facing surface of body 11, the body 11 may be placed into a horizontal mould containing a liquid polymer. The body 11 may be lowered into the horizontal mould such that the liquid polymer covers the ground-facing surface of the body 11. In that case, contact of the liquid polymer with any of the remaining surfaces of the body 11 may be negligible. The liquid polymer may then be allowed to solidify, or cured, to produce a solid base layer 12 attached to the ground-facing surface of the body 11. If the footprint of the horizontal mould is larger than the ground-facing surface of the body 11, then the base layer 12 may be trimmed to ensure that the footprint of the base layer 12 corresponds to the footprint (area size and shape) of a side of the body that is to constitute the ground-facing surface of the body 11. The base layer 12 may not need to be trimmed if the footprint of the horizontal mould corresponds to the size and shape of the ground-facing surface of the body 11. The liquid polymer may be liquid polyurethane, and may include glass fibres in order to reinforce the base layer 12 once the liquid polymer has cured. The surface configuration 32 may be formed on the base layer 12 during the moulding process. For example, one or more surfaces of the mould may be shaped to correspond to the negative mould of the desired surface configuration 32, such that the base layer 12 is provided with the desired surface configuration 32 once the liquid polymer has cured. Alternatively, or additionally, the surface configuration 32 may be formed on the base layer 12 after the base layer 12 has been moulded to the body 11. For example, the surface configuration 32 may be formed onto the base layer 12 after it solidified, via milling, 3D printing or laser cutting the base layer 12, or by affixing additional components to the base layer 12. Although the aforementioned example moulding process describes a mould containing a liquid polymer, it will be appreciated by those skilled in the art that the mould could contain any liquid which is configured to solidify under predefined conditions. For example, the mould could contain molten metal which when cooled, produces a solid base layer 12 attached to the ground-facing surface of the body 11.

The material used for the base layer may be able to cure by cooling, such that the base layer is solid at ambient temperature. This allows the sleeper body to be placed into the mould at a higher temperature, e.g. 60 to 90 degrees Celsius, to then allow it to cool to solidify. However, the material used for the base layer may solidify with the help of other means, such as radiation.

The base layer 12 has two major opposite surfaces: a ground-engaging surface 31 (shown in Figures 5a and 5b) and a body-facing surface (indicated in Figures 5a and 5b as the interface between the base layer 12 and the body 11). The body-facing surface of the base layer 12 contacts the ground-facing surface of body 11 when the base layer 12 is attached to the body 11. The body-facing surface of the base layer 12 and/or the ground-facing surface of the body 11 may be provided with interface features which facilitate attaching the base layer 12 to the ground-facing surface of body 11. The interface features may consist of a roughened surface finish which has the effect of increasing the surface area of the body-facing surface of the base layer 12 and the ground-facing surface of the body 11 which is in contact with the ground-facing surface of the body 11/body-facing surface of the base layer 12. Without wishing to be bound by theory, it is believed that roughening a surface exposes micro-scale sized cracks and crevices which were previously under the surface. Therefore, a roughened surface finish may also have the effect of allowing, for example, adhesive or liquid polymer to perfuse into exposed micro-sized cracks and crevices in the body-facing surface of the base layer 12 and/or the ground-facing surface of the body 11. This provides a much stronger structural adhesion than if both the body-facing surface of the base layer 12 and the ground-facing surface of the body 11 were smooth (i.e. not roughened).

The surface roughening affects only a few micrometres and after application of a base layer it may not be easily possible, after application of a base layer, to visually distinguish between a finished sleeper product that underwent a roughening process and another product that did not. However, it is believed that destructive testing would show the improved bonding of a roughened surface. If both surfaces were smooth prior to the attachment of the base layer 12 to the body 11 via any of the means previously described, prising the base layer 12 off the body 11 would likely result in a relatively clean separation, leaving little to no base layer material on the body 11 and body 11 material left on the base layer 12. Whereas, if either or both the attachment surfaces of the body 11 and base layer 12 were roughened prior to the attachment of the base layer 12 to the body 11 via any of the means previously described, prising the base layer 12 off the body 11 would likely result in an amount of base layer 12 material left on the body 11 and/or body 11 material left on the base layer 12, in other words there is a more intimate fusion of material that is believed to result in the two layers no being as easily separable. A roughened surface finish may be realised by, for example, sanding or sandblasting a surface. Therefore, a roughened surface finish allows for a stronger connection, especially when the base layer 12 is moulded or bonded to the body 11. Alternatively or additionally, the interface features may consist of a smooth and/or flattened surface finish.

In one aspect, both the body-facing side of the base layer 12 and the ground-facing surface of body 11 are provided with complementary interface features, or complementary flat surface portions, or the combination of complementary interface features and flat surface portions. For example, the body-facing side of the base layer 12 may be provided with a plurality of protrusions such as ridges configured to fit into a plurality of complementary recesses such as grooves that can be manufactured by either pultrusion or extrusion in the ground-facing surface of body 11.

In the embodiment shown in Figure 5a, the body 11 is formed from a pultruded fibreglass reinforced polymer. Typically, when manufacturing a pultruded fibre-reinforced polymer body, the resulting product can be imagined as a polymer matrix comprising a distribution of fibres within the matrix. The extrusion process can be controlled to some extend such that fibres tend to accumulate towards the centre of the matrix and are not present in the same density nearer the surface of the body, such that the polymer-reinforced portions can be imagined as being covered by a portion of matrix polymer that does not contain fibres. The reinforcing characteristics of the fibres are associated with the fibre length. As such, it is believed that damaging such a body's reinforcing fibres may reduce the reinforcing characteristic of the body. Therefore, when providing the ground-facing surface of a pultruded fibreglass reinforced polymer body 11 with a roughened surface finish, it is beneficial to ensure that the depth of the abrasions is less than the thin layer of polymer covering the reinforcing fibres. The applicant has appreciated that it is relatively safe to remove a thin layer of a fibre-reinforced extruded body when the outer surface consists primarily of matrix material without fibres.

The presence of surface contaminants on the outer surfaces of body 11 may weaken the overall strength of the attachment of the base layer 12 to the body 11. Surface contaminants such as, for example, dust produced from a surface roughening process, or grease, may inhibit the efficacy of any of the means previously described for attaching the base layer 12 to the body 11. Therefore, in some embodiments, the ground-facing surface of the body 11 is cleaned prior to the base layer 12 being attached. For example, the ground facing surface of the body 11 may be cleaned via a solvent wiping and/or degreasing process.

When installed, a railway sleeper may experience substantial lateral forces when a train travels over it. For the sleeper of the present invention, these substantial lateral forces may induce substantial shear stresses between the base layer 12 and the body 11 due to the resulting ground friction experienced by the base layer 12. Those skilled in the art may not consider the aforementioned means for attaching a base layer 12 to a body 11 as being strong enough to prevent the base layer 12 from detaching from the body 11 under high shear stress conditions. Hence, those skilled in the art may consider using additional or alternative means for attaching the base layer 12 to the body 11, such as bolts, rivets, brackets, spikes and similar structures. However, the present applicant has appreciated that the surface area of the ground-facing surface of a sleeper body, which is typically in the region of 2.5-3 metres long, is large enough to provide a suitably strong surface-to-surface bond with a base layer, without requiring additional attachment means. This is of use particularly when the sleeper is manufacturing with a pre-fabricated base layer component or a pre-fabricated body.

Manufacturing a single base layer 12 to cover the entire ground-facing surface of body 11 and attaching the single base layer 12 to body 11 are potentially relatively complex procedures because they require the handling and aligning of parts of significant size, of about 3 metres length. In one embodiment, multiple smaller base layer elements, for example two base layer elements of identical materials, sizes, shapes and surface configurations are attached, one each to one half of the ground-facing surface of base 11. Being half the size of the single base layer 12 shown in Figure 5a, the two half-sized base layer elements are potentially easier to manufacture, align and attach to the body 11. It will be appreciated by those skilled in the art that any number of base layer elements may be attached to different portions of the outer surfaces of the body 11. At least one base layer element may be of a different material, size, surface configuration and/or shape to the remaining base layer elements. For example, three base layer elements formed from different materials, comprising different surface configurations, different sizes, and/or different shapes may be attached to different portions of the outer surfaces of the body 11, in particular to the ground-facing side of the body 11.

In the embodiment shown in Figure 5b, the surface configuration 32 provided on the ground-engaging surface 31 of base layer 12 comprises a plurality of grip-improving features in the form of dome-shaped protrusions 33. The dome-shaped protrusions 33 enhance the gripping characteristics of the base layer 12 by, for example, engaging stones in the underlying track ballast 14. The base layer 12 is then restricted from sliding over the track ballast 14 since the stones engage and interlock with the dome-shaped protrusions inducing a sliding resistance between the underlying stones and the dome-shaped protrusions 33. In particular, the dome-shaped protrusions 33 are provided as a pattern, in two dimensions (here: extending hexagonally as a repeat pattern) thereby to provide a varying surface configuration along the elongate extension (e.g. the pultrusion axis 15) of the body 11. As shown in Figure 5b, the surface configuration 32 comprises a pattern which alternates between dome-shaped protrusions 33 and substantially flat interstitial regions 34 along any axis which is parallel to the pultrusion axis 15. It will be appreciated that such a texture would not be obtainable integrally with the body 11 via a pultrusion process, because a pultrusion process will only allow elongate texture profiles such as ridges or grooves in the extension of the pultrusion axis. The pattern on the base layer 12 allows a varying profile to be provided in two dimensions, and therefore varying also along the pultrusion axis, which provides improved resistance against slipping along the elongate dimension of the sleeper 10.

In some embodiments, the surface configuration 32 comprises other grip-improving features such as a plurality of protrusions of a different shape, or a plurality of indentations, or a combination of shaped protrusions and indentations, which may provide a varying profile along the pultrusion/extrusion axis 15. Shaped indentations enhance the grip of the base layer by, for example, trapping stones in the underlying track ballast. Further, both shaped protrusions and indentations increase the surface area of the surface configuration 32, thereby increasing the contact surface area with the underlying ground and increasing sliding friction. This allows the surface configuration of a base layer to be tailored for a particular type of ground without requiring a re-design of the sleeper body. In some embodiments, the grip-improving protrusions/indentations comprise dome shapes, cone shapes, pyramid shapes, blade shapes, and/or combinations of any two or more of these shapes.

In some embodiments, the surface configuration 32 comprises texture features providing a roughened surface finish. A roughened surface finish has the effect of increasing the surface area of the ground-engaging surface 31 and thereby increasing sliding friction.

In some embodiments, the base layer 12 is manufactured from a softer material than the body 11. A softer material is less resistant to localised plastic deformation by mechanical indentation than a harder material. Therefore, forming the base layer 12 from a softer material than body 11 increases the likelihood that crushed stones in track ballast 14 are able to penetrate the ground-engaging surface 31 of the base layer 12 deeper than they would be able to penetrate the ground-facing surface of body 11. Deeper penetration by surrounding crushed stones in the track ballast 14 ensures that the ground-engaging surface 31 of base layer 12 provides better ground-engaging grip than the ground-facing surface of body 11. Alternatively, the base layer 12 and/or the body 11 could be manufactured as composites of two or more different materials, and at least the ground-engaging surface 31 of the base layer 12 is made from a softer material than at least the ground-facing surface of body 11. However, the base layer 12 need not necessary be softer. By manufacturing the base layer 12 from a resin without elongate fibres as the body 11, it is more suited to moulding or otherwise providing grip-improving features even if the base layer is practically as hard as the body 12.

Figure 6 illustrates another feature that may be used in embodiments of the invention.

The railway sleeper 40 comprises an elongate body 41 with a box-profile cross-section supporting two steel railway tracks 13 and resting on ground 14. The body 41 is formed from a pultruded fibreglass reinforced polymer and has been pultruded along a pultrusion axis similar to the axis 15 (not shown in Figure 6; shown in Figures 3, 5a and 5b). A base layer 42 of the same general construction as the base layer 12 of the first embodiment is attached to the ground-facing surface of body 41. The body 41 comprises a central cavity 47. The central cavity may be hollow or may be at least partially filled with a material which differs to the material from which the body 41 is formed. The box profile cross-section forms two channels 48 along the longitudinal sides of the body 41. The channels 48 are covered by removable cover plates 46 which are of substantially the same longitudinal length as the body 41. Although, the cover plates 46 are illustrated schematically in Figure 6 as having rectangular cross-sections, the cover plates 46 may be of any cross-sectional shape which allows them to be removably attached to the longitudinal sides of the body 41 in order to cover the channels 48.

Likewise, the end surfaces 17 may be provided with caps to close off the sleeper body.

As illustrated in Figure 6, the constant cross-section of body 41 comprises two upper flanges 44a and 44b adjacent railway tracks 13, and two lower flanges 45a and 45b adjacent to base layer 42. Although not shown in Figure 6, base layer 42 may be moulded, overmoulded or bonded to lower flanges 45a and 45b as well as the ground-facing surface of the body 41, and as such the lower flanges 45a and 45b can be considered to constitute part of the ground-engaging surface to which the base layer is attached.

Claims

CLAIMS: 1. A railway sleeper comprising a body and a base layer to be placed on ground underneath, wherein the body which has an elongate extension from a first end to a second end and is made from a composite material comprising reinforcing fibres oriented along the elongate extension, wherein the base layer is provided on a side of the body, and wherein at least a portion of the base layer comprises a surface configuration providing better ground-engaging grip than the composite material.
2. The railway sleeper according to claim 1, wherein the base layer is attached to a side of the body.
3. The railway sleeper according to claim 1 or 2, wherein the surface configuration of the base layer comprises texture features providing a varying profile along the elongate extension.
4. The railway sleeper according to claim 1, 2 or 3, wherein the body and the base layer are formed from different materials, wherein, optionally, the base layer is formed from a softer material than the body.
5. The railway sleeper according to any one of the preceding claims, wherein the base layer is made from a composite material comprising reinforcing fibres that are oriented randomly in relation to the elongate extension.
6. The railway sleeper according to any one of the preceding claims, wherein a body-facing side of the base layer and/or at least one body surface is provided with interface features facilitating attaching the base layer to the body.
7. The railway sleeper according to claim 6, wherein the interface features are provided by a roughened surface, resulting in a stronger bond between the body and the base layer.
8. The railway sleeper according to any one of the preceding claims, wherein the at least one body surface has been cleaned before the base layer is attached to the body.
9. The railway sleeper according to any one of the preceding claims, comprising a plurality of base layer components each provided on a different portion of one body surface.
10. The railway sleeper according to any preceding claim, wherein the body and/or the base layer is formed from a polymer, wherein optionally the polymer comprises virgin plastics material or recycled plastics material.
11. The railway sleeper according to any one of the preceding claims, wherein the base layer is prefabricated prior to attachment to the body.
12. The railway sleeper according to claim 11, wherein the base layer is bonded to the at least one body surface.
13. The railway sleeper according to claim 11 or 12, wherein the surface configuration is provided during fabrication of the base layer.
14. The railway sleeper according to any one of claims 11 to 13, wherein the surface configuration is added after the fabrication of the base layer.
15. The railway sleeper according to any one of claims 1 to 10, wherein the base layer is moulded onto the at least one body surface via a moulding process.
16. The railway sleeper according to claim 15, wherein the surface configuration is provided during the moulding process.
17. The railway sleeper according to claim 15, wherein the surface configuration is provided after the moulding process.
18. The railway sleeper according to any preceding claim, wherein the surface configuration comprises a plurality of grip-improving features such as indentations and/or protrusions.
19. The railway sleeper according to any preceding claim, wherein the base layer is shaped such that it covers substantially all of the at least one body surface.
20. A method of manufacturing a railway sleeper according to any one of the preceding claims, the method comprising the steps of: forming from a composite material a sleeper body comprising reinforcing fibres oriented along an elongate extension between a first end and a second end of the sleeper body; providing a base layer to be bonded to the sleeper body; allowing the base layer to bond to the body; and providing the base layer with a surface configuration providing better ground-engaging grip than the body.
21. The method according to claim 20, wherein the step of providing the base layer with a surface configuration is carried out after providing the step of bonding the base layer to the body.
22. The method according to claim 20 or 21, wherein the step of providing a base layer comprises placing the sleeper body into a mould containing a liquid such that the liquid covers at least one side of the sleeper, and allowing the liquid to solidify to a solid base layer while bonding to the body.
23. The method according to any one of claims 20 to 22, wherein the step of providing the base layer with a surface configuration comprises providing the mould with mould shapes complementary to the surface configuration prior to placing the sleeper body into the mould.
24. The method according to any one of claims 20 to 23, comprising roughening and/or cleaning at least one body surface of the sleeper body prior to bonding the base layer to the body surface.
25. The method according to any one of claims 20 to 24, comprising trimming the base layer after bonding such that it corresponds in size and shape to a side of the body.