WO2004097115A1

WO2004097115A1 - A damper for a rail

Info

Publication number: WO2004097115A1
Application number: PCT/GB2004/001608
Authority: WO
Inventors: David Farrington
Original assignee: Corus UK Ltd
Current assignee: Corus UK Ltd
Priority date: 2003-04-30
Filing date: 2004-04-15
Publication date: 2004-11-11
Anticipated expiration: 2005-10-30
Also published as: GB2401139A; GB2401139B; GB0309795D0; EP1620606A1

Abstract

A damper (10) for a rail comprises a section of deformable material (11) defining a face attachable to a surface of the rail and a plurality of elongate resonant members (12, 14) positioned within the deformable material and separate from the attachment face. One or more permanent magnets (15) is positioned at or close to the damper surface for attaching the damper to a steel rail. The resonant members are of a stiff material as compared to the deformable material and are sized to exhibit at least two resonant frequencies in the range of vibration frequencies of the rail.

Description

A DAMPER FOR A RAIL

The present invention relates to rail dampers. More especially, the invention is concerned with rail dampers that exhibit advantageous noise characteristics.

The noise emitted by moving rail vehicles is a major limitation on their use. The noise emitted limits the ability of operators to install new lines in populated areas, and also limits speeds and traffic volumes on existing lines. The noise tends to be dominated by rolling noise from the interface between the steel rails and rail vehicle wheels. This is caused partly by vibration of the wheels and partly by vibration of the track.

As mentioned in our earlier European Patent Application 1015698A, it is not possible to select alternative materials for steel rails because they are subject to high transient loads during use and must be sufficiently robust to withstand these. Materials which would be able to absorb vibration and hence reduce noise would be unable to survive in use for any appreciable time. Resilient rail fastenings have been employed to reduce track forces and thereby reduce component damage and structure- borne noise. However, they have an adverse effect on track noise as they tend to reduce the attenuation of rail vibration.

Our earlier European Application is directed to reducing the track noise emitted by a rail system through use of a rail damper which comprises at least one deformable material attachable to a surface of the rail and a plurality of elongate resonant members. The resonant members are of a stiff material as compared to the deformable material and are sized to form a resonant system with at least two resonances in the frequency range where rail vibration is to be reduced.

An embodiment of a rail damper disclosed in our earlier European Application is illustrated in Figure 1.

This Figure shows a vertical section through a rail 1 having a head 2 which carries the traffic and a narrower web 3 extending downwardly from the head 2 to a foot 4 on which the rail section rests. The foot generally wider than both the head 2 and web 3.

The junction between the web 3 and the foot 4 is smoothed inter alia for fatigue reasons, but is essentially a transition from a substantially vertical face to a gently downwardly sloping top surface of the foot 4. Typically, the angle is in the region of 120°.

In this junction, a damper 5 is provided on each side of the rail. Each damper comprises a block of rubber 6 in which is embedded a first resonant member 7 and a second resonant member 8. The first resonant member is an elongate angled member, the angle corresponding to the junction between the head and foot. The second resonant member is an elongate solid section, positioned in the angle of the first and with two faces at a corresponding angle. The mass per unit length of the first member is greater than that of the second member.

Although not visible in Figure 1, the resonant members are discontinuous to allow the damper section to be cut. This eases application of dampers to a rail. A suitable maximum length for the sections is 1 metre for application to existing rail.

The damper illustrated in Figure 1 is typically preformed and glued to the rail. The use of adhesive can be disadvantageous on occasions, particularly when there is a requirement to move the position or replace a damper.

The present invention sets out to provide an improved rail damper which can readily be repositioned along the length of a rail (or removed) and is an improvement to that disclosed in our earlier European Application.

In one aspect, the invention provides a damper for a rail, the damper comprising a section of deformable material defining a face attachable to a surface of the rail, a plurality of elongate resonant members positioned within the deformable material and separate from the attachment face, and one or more permanent magnets positioned at or close to the damper surface for attaching the damper to a steel rail, the resonant members being of a stiff material as compared to the deformable material and being sized to exhibit at least two resonant frequencies in the range of vibration frequencies of the rail.

The magnets may be surface mounted or may be set into recesses formed in the damper surface. Alternatively, the magnets may be wholly or partially embedded within the deformable material of the damper.

The resonant members are suitably embedded in the deformable material to ensure adequate vibrational transfer from the rail to the resonant members and also provides environmental protection. They are ideally more dense than the resilient material. They are suitably of steel.

The deformable member is preferably visco-elastic, for example rubber or a rubber-like material.

Preferably, dampers are attached by magnets to the rail to cover the junction between the web and the foot of the rail. This has been found to be exceptionally advantageous in terms of the amount of damping needed to achieve adequate noise reduction. At these positions, a damper with at least two resonant frequencies according to the invention reduce significantly the noise level of the rail. One resonant member can be a elongate angled section, the angle preferably matching the angle between external surfaces of the head and foot. Another resonant member can be a solid elongate block, the external faces adjacent the web and foot being angled to match. Further resonant members can be employed as necessary.

The damper will be easier to manufacture and easier to apply to existing rail if the resonant members are discontinuous within the deformable material. Ideally, the discontinuities in the plurality of resonant members will coincide. It is also possible to apply the damper in discrete sections, leaving gaps (for example) for rail fasteners. However, a continuous length of damper is preferred.

It is preferable for there to be a pair of such dampers, one either side of the rail.

The invention will now be described by way of example only with reference to the accompany diagrammatic drawings, in which:-

Figure 2 is a vertical section through a rail incorporating dampers in accordance with the invention.

In Figure 2, the same reference numerals have been used to denote the same or similar features to those illustrated in Figure 1.

Figure 2 shows a vertical section through a rail fitted with a damper according to the present invention. As for Figure 1, a damper 10 is positioned at the junctions between the web and foot on each side of the rail. As illustrated, the dampers are identical, which is preferred. As discussed above, each damper comprises a block of rubber 11 in which is embedded a first resonant member 12 and a second resonant member 14. The first resonant member is an elongate angled member. This angle corresponds to the junction between the head and foot. The second resonant member is an elongate solid section, positioned in the angle of the first and with two faces at a corresponding angle. The mass per unit length of the first member is greater than the others, significantly so.

Although not visible in Figure 2, the resonant members are discontinuous to allow the damper section to be cut. This eases application of the damper to rail. A suitable maximum length for the sections is one metre for application to existing rail.

The top surface of the damper 10 can be profiled to prevent water from building up and seeping into the system.

The dampers 10 are attached to the rail by surface mounted permanent magnets 15 set in suitably shaped channels formed in the surfaces of the dampers which contact the web and/or foot of the rail. The magnetic attachment enables the dampers to be re-sited or removed at will.

In an alternative embodiment, the magnets 15 are embedded within the block of rubber.

This arrangement of dampers provides a particularly compact arrangement which is nevertheless able to absorb a wide band of frequencies efficiently from the rail. This frequency band, which may be different for vertical and lateral vibration of the rail, is determined by the resonances of the damper. These resonances are controlled by the choice of mass per unit length of the resonant members and by the surrounding geometry and the physical properties (principally the stiffness) of the material between the resonant members. The width of the frequency band is also determined by the damping properties of the visco-elastic material in the inter-layers. The visco-elastic provides a support medium for the resonant members and by its damping properties dissipates vibrational energy. It may be preferable to use different materials for the different inter-layers instead of or as well as different thicknesses to obtain the required stiffness and thereby affect the resonance frequencies. Positioning the damper at the junction between the web and foot is particularly efficient for absorption, and also avoids interference with passing wheels, track maintenance operations and rail clips. It is also easily accessible for fitting dampers to existing lengths of rail. The compactness of the damper is significant in minimising the noise radiation from the damper itself.

The dampers of the present invention could be applied in conjunction with known resilient rail fasteners. This would enable the other advantages of resilient fasteners to be achieved without an unacceptable increase in noise.

Other variations could be made to the embodiments without departing from the scope of the present invention. For example, the resonant members could be arrange end-to-end instead of adjacent as illustrated. They would then be in the same mass of deformable material or in adjacent masses.

Claims

1. A damper (10) for a rail, the damper comprising a section of deformable material (11) defining a face attachable to a surface of the rail, a plurality of elongate resonant members (12, 14) positioned within the deformable material and separate from the attachment face, the resonant members being of a stiff material as compared to the deformable material and being sized to exhibit at least two resonant frequencies in the range of vibration frequencies of the rail, the damper being characterised in that one or more permanent magnets (15) are positioned at or close to the damper surface for attaching the damper to a steel rail.

2. A damper as claimed in claim 1 wherein the magnets are surface mounted.

3. A damper as claimed in claim 1 wherein the magnets are set into recesses formed in the damper surface.

4. A damper as claimed in claim 1 wherein the magnets are wholly or partially embedded within the deformable material of the damper.

5. A damper as claimed in any one of the preceding claims wherein the resonant members are embedded in the deformable material.

6. A damper as claimed in claim 5 wherein the resonant members are more dense than the resilient material.

7. A damper as claimed in claim 6 wherein the resonant members are produced from steel.

8. A damper as claimed in any one of the preceding claims wherein the deformable member is visco-elastic.

9. A damper as claimed in claim 8 wherein the deformable member is produced from rubber or a rubber-like material.

10. A damper as claimed in any one of claims 1 to 9 which is attached by the magnets to the rail at or alongside the junction between the web and the foot of the rail.

11. A damper as claimed in any one of the preceding claims wherein at least one resonant member is an elongate angled section, the angle matching the angle between external surfaces of the head and foot of the rail.

12. A damper as claimed in claim 11 wherein another resonant member comprises a solid elongate block.

13. A damper for a rail substantially as herein described with reference to Figure 2 of the accompany drawings.