IMPROVEMENTS IN RAILWAYS

Abstract: A rail which has secured to it a composite body for absorbing vibrational energy whereby to reduce noise generated by vehicular traffic on the rail. The composite body comprises a visco-elastic damping medium 5 bonded to, and sandwiched between, both the rail and a constraining member, eg a steel strip 6, substantially stiffer in tension than the damping medium.

Description: This invention relates to railways, and more particularly relates to reducing wheel/rail noise arising in same. As environmental consideration increase, and the speed of railways increases, the noise generated by railways especially in urban areas is particularly important. For this reason methods of reducing the noise generated by railways are of increasing interest. It is now appreciated that the rails and wheels of the railways act as radiators of sound, and various methods have been proposed for reducing the energy radiated from wheels and rails. A particular application to rails is disclosed in the French specification FR-A-2012921 (corresponding to the first part of claim 1). This document discloses the method of applying a medium to the outside of the rail which will absorb energy. However, as is explained later in this specification the reduction in the radiating length of the rail is also beneficial in reducing the energy omitted from it, and therefore it is suggested that the physical characteristics of the damping medium can be exploited to change the vibrating characteristics of the rail itself by damping the vibrations of the rail and absorbing energy directly therefrom rather than by absorbing the sound that has already been omitted from the rail in an absorbing layer. It is therefore an object of the present invention to increase the effectiveness of damping layers in reducing the energy transmitted into the environment by a rail. The present invention comprises a steel rail having secured to it a composite body comprising a damping medium bonded to and sandwiched between both the rail and a constraining member substantially stiffer in tension than the damping medium for absorbing vibrational energy generated by vehicular traffic on said rail by damping vibrations of said rail in which the damping medium is a visco-elastic material. The visco-elastic material may be bonded to the underside of the foot and or the upper sides of the foot and/or one or both sides of the web and/or the bulk of the non-wheel contacting parts of the head. The constraining member strip steel and the visco-elastic medium may be bonded to the underside of the foot and the strip bent upwardly around the side of the foot and crimped over the top of said foot. The visco-elastic medium and the constraining member may be continuous along the length of the rail and the visco-elastic medium may be bonded to the underside of the foot of the rail and the constraining member may be constituted by the track support which may be a paved concrete foundation. The visco-elastic medium may be bonded by an adhesive. The rail itself may be of standard cross-section but reduced in height compared with common permanent way railway track and the thickness at the foot of the rail may be increased compared with the relative thickness of the rail foot in common permanent way railway track. The rail may be used in conjunction with vehicular traffic having wheels which are being treated to reduce their own resonant response. It is recognised that train noise arises about equally from the wheels of same and the rails on which they run, and this invention is dedicated to reducing the rail contribution to the total. Noise radiation from the rails normally extends over a frequency range from a little below 250Hz to, at most, 5kHz. In tackling a reduction in rail noise it is desirable to reduce the effective radiating length of the rail, that is, to increase the vibration decay rate, with distance, along the rail of wave motions propagating along the rail from the wheel/rail contact position. For this purpose the application of the constrained layer damping material in the manner specified above has a most beneficial effect above a frequency of about 2kHz where it damps this motion, particularly in the embodiment where the foot motion is damped, which is increasingly the more dominant radiating component. Considering now frequencies below this level, the noise radiation efficiency of a vibrating beam (rail) depends on its projected width/depth compared with the wavelength of sound, in air, at the frequency concerned. Efficient radiation only occurs when the 'effective diameter' of the rail is greater than the wavelength - when the projected width/depth is significantly less than the wavelength the radiation efficiency falls drastically. The boundary between these two regimes is the critical frequency, and the adoption of the reduced height rail is beneficial up to about 1kHz based on an increase in the critical frequency and, thereby, a reduction in radiating efficiency. An additional benefit arising from the use of this rail section is that it reduces the radiating surface area. In order that the invention may be fully understood, four embodiments thereof will now be described with reference to the accompanying drawings each of which schematically illustrates a rail according to this invention Referring now to Figure 1, the 'dumpy' steel rail section 1 has a head 2 a reduced vertical web 3 and a foot 4. The rail height is of the order of 110 mm and the width of the foot is of the order of 140 mm; its weight, per metre length, is of the order of 50 kg. Bonded, e.g. by an adhesive, to the foot is a visco-elastic (that is, not simply elastic) layer 5 of, for example, the proprietary material T.MAT PD4 and likewise this is bonded on its other side to a metallic, eg steel, constraining layer 6. The layer 5 may have pre-treated adherent surfaces for this purpose. Visco-elasticity is a property of materials where on deformation under stress there is implied complete recovery after removal of the stress although part of deformation is viscous. See, for example, "An Encyclopaedia of Metallurgy and Materials" by C R Tottle (The Metals Society/MacDonald & Evans 1984) P351-2. The layer 5 may additionally be sufficiently resilient to perform the function of a rail seating pad. Figure 2 shows a better proportioned rail whereby the height of the foot has been increased by 5 mm. This effectively alters the neutral axis to better balance the stress distribution and facilitate easier rolling, in particular a straighter rail is achieved on the cooling beds. The extra weight in this rail furthermore facilitates 'matching' dimensional changes between rail of this section and standard sections to which it must join, eg in switches and crossings. Additionally, as shown in Figure 2, the steel layer 6 which may be a "soft" steel, eg. 110 Brinel, may optionally be bent upwardly around the sides and crimped over the top of the foot, as shown - the visco-elastic layer 5 may also be wrapped round in this fashion, cf, Figure 4. The layers 5, 6 are continuous along the length of the rail in both embodiments and the rail is periodically supported along its length by sleepers (not shown). Alternatively, the rail may in some circumstances be supported continuously along its length on e.g. a concrete bed, and in this instance the separate contraining layer 6 may be omitted, the layer 5 being bonded to this bed as shown in Figure 3. Alternatively, or additionally, to siting the composite body, 5,6 on the underside of the foot this body may be sited elsewhere on the rail, eg. on one or both sides of the web and/or around the bulk of the non-wheel contacting parts of the head and/or, most notably, the upper sides of the foot. Figure 4 shows one such example of the latter where the visco-elastic layer 5 is bonded on one side to the upper sides of the foot and on its other side to a steel strip 7 which is otherwise freely exposed. As before the vibrational energy travelling within the rail is absorbed by the visco-elastic layer, being manifested as heat within the composite body. As foreshadowed above, this composite body may be extended over the web and the underside of the head, as shown be the dotted outline in this Figure, and indeed it may embrace the sides of the head as well. Although the invention has been described with reference to the particular embodiments illustrated it is to be understood that various changes may readily be made without departing from this invention. For example the dimensional relationships of the composite layers shown, in relation to one another and to the rail, may readily be changed as indeed may the shape of the rail itself consistent with the object of this invention, indeed the rail might in fact have no web. Further, it is desirable but not essential for the composite layer to be continuous, the same object would be achieved by discrete bonded layers between each sleeper and/or rail fastening and the rail itself but this would be less effective at lower frequencies. Moreover, although the layers 5, 6/7 are shown as being pre-formed one or both may alternatively be sprayed or trowelled on, and the layers 6/7 may be any material stiffer in tension than layer 5 eg. a plastics material could be used. Clearly, the greatest benefit in noise reduction will be achieved when the wheels of the vehicles traversing these rails have themselves been treated to reduce their own resonant response; thus the invention is particularly beneficial when rails as described herein are used in conjunction with damped wheels eg wheels the web and/or rim of which have a composite body affixed thereto in the fashion described.

Claims: A steel rail having secured to it a composite body comprising a damping medium (5) bonded to and sandwiched between both the rail and a constraining member (6) substantially stiffer in tension than the damping medium for absorbing vibrational energy generated by vehicular traffic on said rail by damping vibrations of said rail, characterised in that the damping medium is a visco-elastic material (5). A rail according to Claim 1 characterised in that the visco-elastic material (5) is bonded to the underside of the foot (4) and/or the upper sides of the foot and/or one or both sides of the web (3) and/or the bulk of the non-wheel contacting parts of the head (2). A rail according to any preceding Claim characterised in that the constraining member is strip steel. A rail according to Claim 3 characterised in that the visco-elastic medium is bonded to the underside of the foot and the strip is bent upwardly around the side of the foot and crimped over the top of said foot. A rail according to Claim 4 wherein the visco-elastic medium is also bent around the sides and over the top of said foot. A rail according to any preceding claim characterised in that the visco-elastic medium and the constraining member are continuous along the length of the rail. A rail according to Claim 1 characterised in that the visco-elastic medium is bonded to the underside of the foot of the rail and the constraining member is constituted by the track support. A rail according to Claim 7 characterised in that the visco-elastic medium is continuous along the length of the rail and the track support is a paved concrete foundation. A rail according to any one of Claims 1 to 8 characterised in that the visco-elastic medium is bonded by an adhesive. A rail according to any one of Claims 1 to 9 characterised in that the rail itself is of standard cross-section but is reduced in height compared with common permanent way railway track. A rail according to Claim 10 characterised in that the thickness at the foot of the rail is increased compared with the relative thickness of the rail foot in common permanent way railway track. A rail according to any one of Claims 1 to 11 characterised in that it is used in conjunction with vehicular traffic having wheels which are being treated to reduce their own resonant response.

Inventors: HODGSON, WILLIAM HENRY, STANWORTH, COLIN GRAHAM, THOMPSON, DAVID JOHN
Applicants: BRITISH RAILWAYS BOARD, BRITISH STEEL PLC
Application year: 1989
Main classification: E01B5
IPC codes: E01B5, E01B19, E01B9