EP1897993A1

EP1897993A1 - Heat shield for rails

Info

Publication number: EP1897993A1
Application number: EP07116103A
Authority: EP
Inventors: Darryl Mark Stephenson
Original assignee: Unitchain Ltd
Current assignee: Unitchain Ltd
Priority date: 2006-09-11
Filing date: 2007-09-11
Publication date: 2008-03-12

Abstract

A heat shield 2 for a rail 1 comprises engagement means 4 for engaging with the rail and a reflective surface 11 for reflecting heat energy away from the rail 1.

Description

This invention relates to a heat shield for a rail, more specifically for a rail of a railway track.
Railway tracks typically comprise two parallel steel rails, each rail being formed of a series of individual rail sections placed end to end. It is clear that excessive heating of the rails, most particularly by incident solar heating, could expand the rail sections and in the extreme case cause buckling of the rails.
It is important therefore to take steps to minimise the effect of heating. Currently, rail sections are laid in a pre-tensioned state, such that heat applied to the rail initially causes the tension to decrease, and the rail does not expand significantly. However, there is a limit to the amount of pre-tensioning that can be applied to a rail. There is also the problem that when rails are replaced, which may for example be in urgent situations where the rail needs to be repaired as quickly as possible, it may be impossible to adequately pre-tension the rails.
In circumstances of high rail temperatures, it is common to impose speed restrictions for vehicles on the rail track, to minimise damage to the rails. The speed restrictions are determined according to the arrangement of the rail (for example the level of ballasting provided, whether the rail is on a shoulder of a bend etc) and to the measured rail temperature. To take one example, for a mechanised stoneblown track in the UK, there may be no speed restrictions imposed until the rail temperature reaches about 43C, a speed restriction of 60 mph may be imposed at rail temperatures between about 43C and about 46C, and a speed restriction of 20 mph for rail temperatures over about 46C. These temperatures are not uncommon.
In order to reduce the heating of rails as far as possible, it has been known to paint the side of the rail which catches most of the incident sunlight throughout the day with white paint, to increase reflection of the sunlight. While this measure has some effect, there are drawbacks. For example, the painting is usually carried out in a somewhat haphazard manner, and the effectiveness cannot be accurately predicted. The paint may also require regular maintenance, for example reapplication or cleaning. Painting of the rails does not protect the rails from heat transferred by conduction or re-radiation from the surrounding ballast material. Furthermore, as the paint contacts the surface of the rail, there is no possibility for direct ventilation of the rail.
It is an aim of the present invention to provide heat shield for a rail that overcomes or mitigates the above problems.
According to the present invention there is provided a heat shield as set out in the accompanying claims.
The invention will now be described, by way of example, with reference to the accompanying drawings, in which:-

Fig. 1 shows a sectional view of a rail with a heat shield according to an embodiment of the present invention; and
Fig. 2 shows part of the heat shield viewed along the line A-A of Fig. 1.

Fig. 1 shows a sectional view of a rail 1, with part of a heat shield 2 according to an embodiment of the present invention attached thereto. The heat shield is shown from the side in Fig. 2. The rail 1 is of standard design, and includes a base 3, which is typically surrounded by ballast material (not shown). The heat shield 2 includes an engagement means 4 for engaging the rail 1. In the embodiment shown, the engagement means 4 comprises a resiliently deformable clip which may be easily attached to the base 3 and held there by friction. The clip supports a bracket 5 which extends upwardly therefrom. The bracket 5 includes a frame 6 which includes first and second guide channels 7 and 8 at its ends. The frame 6 is curved away from the rail, and extends past the base of the rail in a horizontal so that it lies above a portion of the ballast material if present. The bracket 5 is shaped so as to maintain an air gap 9 between itself and the rail 1.
An elongate sheet 10 is retained by the guide channels 7 and 8, so that it extends along the length of the rail 1. The outer surface 11 of the sheet 10 is reflective, and is glossy and coloured white to maximise reflection. The sheet 10 comprises a plastics material with a closed-cell structure for rigidity. The sheet is bent into an arcuate shape by the frame 6 when retained by the guide channels 7, 8, with the reflective surface 11 facing away from the rail 1. The length of the sheet is predetermined according to any curvature of the rail 1. For example, on a relatively tight bend of the railway track, a relatively short length of sheet may be used in comparison to a relatively straight track section. Although not shown in Figs. 1 or 2, additional engagement means, brackets and frames may be used to support the sheet at various points along its length if necessary.
In use, the heat shield is attached to that side of the rail which receives the most incident sunlight during the day. This side of the rail may also be painted with white paint, as is known in the art, on areas of the rail which are not protected by the heat shield. The other side of the rail may be coated with heat-dissipating paint. The reflective surface 11 of the sheet 10 acts to reflect incident solar radiation away from the rail. Because the sheet lies over the portion of the ballast material around the base of the rail, this ballast material is also shielded, which prevents it transmitting heat to the rail 1 by conduction or re-radiation. The provision of air gap 9 provides ventilation for the rail 1 to improve cooling. Furthermore, the shaping of the heat shield produces a venturi effect which acts to draw air through the gap, further improving cooling of the rail 1. Because the reflective surface is smooth and glossy, it is easier to keep clean than a painted surface, and rainfall alone may be sufficient for this purpose.
The above-described apparatus is exemplary only, and various alternatives will be possible within the scope of the invention. For example, various types of sheet may be used, even those using a cardboard-type material have been shown to be beneficial. There are various methods for retaining the sheet on the bracket, for example using adhesive, screws etc. Furthermore, it is even possible to use an integrally-formed heat shield, wherein the reflective surface, bracket and engagement means are all formed from the same piece of plastics material.

Claims

A heat shield for a rail, comprising engagement means for engaging with the rail and a reflective surface for reflecting heat energy away from the rail.
A heat shield according to Claim 1, wherein the engagement means comprises a clip for engaging a base of the rail.
A heat shield according to either of Claims 1 and 2, wherein in use, the reflective surface is arranged so as to form an air gap between the rail and the reflective surface.
A heat shield according to Claim 3, wherein the heat shield is shaped so as to draw air through the air gap using a venturi effect.
A heat shield according to any preceding claim, wherein in use the reflective surface is curved in an arcuate manner such that its internal circumference faces away from the rail.
A heat shield according to any preceding claim, wherein the reflective surface is dimensioned so as to extend beyond the rail in use to additionally shield rail ballast material.
A heat shield according to any preceding claim, comprising a support bracket connected to the engagement means for supporting the reflective surface.
A heat shield according to Claim 7, comprising at least one additional respective engagement means and support bracket.
A heat shield according to any of Claims 1 to 6, wherein the heat shield is integrally formed.
A heat shield according to any preceding claim, wherein the reflective surface comprises a substantially white material.
A heat shield according to any preceding claim, wherein the reflective surface is glossy.
A heat shield according to any preceding claim, wherein the reflective surface comprises a plastics material.
A heat shield according to any preceding claim, wherein the reflective surface comprises a closed-cell material.
A heat shield according to any preceding claim, wherein the reflective surface is elongate to reflect heat energy away from a substantially corresponding length of rail.
A heat shield according to Claim 14, wherein the length of the reflective surface is predetermined in dependence of a radius of curvature of the rail.