GB2366315A

GB2366315A - Rail heater cover

Info

Publication number: GB2366315A
Application number: GB0120397A
Authority: GB
Inventors: Mark Hockney
Original assignee: Darchem Engineering Ltd
Current assignee: Darchem Engineering Ltd
Priority date: 2000-08-22
Filing date: 2001-08-22
Publication date: 2002-03-06
Anticipated expiration: 2021-08-22
Also published as: GB2366315B; GB0120397D0

Abstract

The cover (22, 26) is shaped to fit over a rail heater element (14, 16) and allow the rail heater to be held between a railway line and the cover comprising an casing made of a substantially rigid material and a thermally insulating material fully enclosed within the casing. The casing may be dimpled and fabricated from a single sheet, sealed around the insulating material by crimping portions together. The insulating material may be ceramic fibre and have a thermal conductivity of less than 0.06 W/m {C.

Description

<Desc/Clms Page number 1> Rail Heater Shield This invention relates to apparatus for providing protection and thermal insulation to heating elements used to prevent rail track equipment freezing during cold weather. Railway systems have certain components, notably points/switches that are prone to freeze during cold weather conditions and thereby lead to failure or interruption of rail services. It is essential during such adverse conditions to keep such components operational. Electrically heating elements are commonly attached to appropriate parts of the components in order to prevent freezing. Such heaters are commonly protected from harsh environmental conditions by channel-shaped covers/shields made from metal or fibreglass.

Rail heaters, commonly provided in strips, are relatively costly to operate owing to their energy supply being electrical and an appreciable proportion of the heater output not reaching the rails bur rather being dissipated elsewhere in the form of heat losses. Typically such losses account for 25% or more of the power input to the heaters. While conventional covers generally provide effective protection against environmental forces they have only a minimal effect on heat losses.

There are presently a wide variety of rail point/switch heaters in use with ineffective thermal insulation. Many such heaters are attached to rails using specifically designed brackets or clips. Fitting covers to track heaters normally requires that these covers are secured by additional suitably dimensioned brackets.

An object of this invention is to provide an improved rail heater cover. Another object is to provide a one piece insulated rail heater cover and to provide such a cover that can be readily fitted over existing rail heaters using existing securing clips or brackets.

According to one aspect the invention comprises a rail heater cover shaped to fit over a rail heater element and allow the rail heater to be held between a railway line and the cover comprising an outer casing made of a substantially rigid material and a thermally insulating material enclosed within the casing Preferably, the outer casing is dimpled and preferably the outer casing is fabricated from a single sheet of material. The rail heater cover may be sealed around the insulating material by crimping foiled portions of the cover together Preferably, the rail heater cover is made of stainless steel, more preferably austenitic stainless steel, most preferably type 304. Preferably, the wall thickness of the casing is 0.05-0.2 mm thickness.

The insulating material preferably may have a thermal conductivity of less than 0.06 W/m.'C, and preferably be less than 0.035 W/m.'C, and most preferably approximately 0. 0 15 W/m.'C. The insulating material may be ceramic fibre and may be in the form of a sheet of thickness in the range I to 10 mm, preferably within the range 2-4mm.

In another aspect the invention comprises a rail heating system with a rail heater and a cover for the heater made of insulating material having a thermal conductivity of less than 0.06 W/m.'C, and preferably be less than 0.035 W/m.'C, and most preferably approximately 0.015 W/m.'C.

The invention will now be described, by way of example only, with reference to the following schematic figures, in which:

Figure 1 relates to a first embodiment of the invention and shows a cross section through part of a rail point comprising a stock rail and a switch rail, showing rail heater elements, heater covers and brackets for securing these items, Figure 2 is an enlarged cross section of the rail heater cover for a stock rail heater shown in Figure 1, Figure 3 is an enlarged cross section of the rail heater cover for a switch rail heater, shown in Figure 1, Figure 4 is an enlarged cross section of a dimpled face, Figure 5 relates to a second embodiment of the invention and shows an enlarged cross section of a rail heater cover for use with either a stock rail heater or a switch rail heater, and Figure 6 is a section through Figure 5 along lines A to A.

Referring to Figure I a cross section through part of a rail point comprising a stock rail 10 and a switch rail 12 are shown with two rail heaters 14,16 a first heater 14 mounted under the head 18 of the stock rail 10 and a second heater 16 mounted above the base flange 20 of the switch rail 12. In this example both heaters comprise copper elements in strip form. However, the invention is not limited to use with any particular type or shape of heater element.

In a first embodiment of the invention, the first heater 14 has a generally S-shaped or Z-shaped rail heater cover 22 configured to fit over the heating element 14 and interface closely with the underside profile of the head 18 of stock rail 10. The rail cover of the invention is particularly suitable for retrofitting. Thus conventional bracket 24 originally provided for holding the first heater 14 in place under head 18 may also be used to hold the first rail heater 14 and rail heater cover 22 in place. This function is assisted by the shape and structure of the rail heater covers, as discussed below.

The second rail heater 16 has a cover 26 comprising a central U-Shaped portion (see Figure 3) 42 again shaped to fit over the heating element 16. Flanges 43 extend outwardly from each side of central portion 42 and in use interface closely with the upper base flange 20 of switch rail 12. Conventional bracket 28 (see Figure 1), originally provided for holding the second heater 16 in place against base flange 20, may also be used to hold the second rail heater 16 and rail heater cover 26 in place. This function is assisted by the shape and structure of the rail heater covers, as discussed below.

The invention is not limited to covering rail heaters located solely in the positions shown in Figure 1. In principle a cover with an appropriately shaped profile may be used in combination with various shaped heaters located at any practical position on the stock rail and switch rail, including the web portion 30. Thus, the rail heater cover of the invention may be shaped to both snugly cover the heater and also to interface closely with various rail profiles.

Figures 2 and 3 show cross section of the two rail heater covers 22 and 26 illustrated in Figure 1, at an enlarged scale. Each cover 22 and 26 comprises an outer casing or shell 40 that fully encloses insulating material 42 contained therewithin. The shell is made from a rigid material, preferably a single sheet of thin metal, typically stainless steel of 0.05 to 0.2 mm thickness. It has been found that austenitic stainless steels, especially type 304 have excellent corrosion resistance properties ideal for the trackside environment having possible contaminants such as oil, grease, brake dust, weed killer and general debris.

The layer of insulation sealed within the shell is typically 2 to 4 mm thickness. Thus, the rail cover typically has an overall thickness of 3 mm. The shell may be sealed by providing overlapping foil portions 44a and 44b and crimping them together. The

rail heater covers of the invention are typically manufactured in I m lengths sealed at each end by overlapping and crimping foil portions.

In a second embodiment of the invention (see Figures 4 and 5), the first heater 14 and the second heater 16 may both have the same or similar U-shaped rail heater covers 50. Cover 50 comprises an outer casing or shell 52 that fully encloses an insulating material 54 contained therewithin. The shell or skin is made from a rigid material, preferably a single sheet of thin metal, typically stainless steel. It has been found that austenitic stainless steels, especially type 304 have excellent corrosion resistance properties ideal for the trackside environment having possible contaminants such as oil, grease, brake dust, weed killer and general debris. The inner skin 56 is typically 0.05 to 0.20 mm thick, preferably about 0. 1 mm thick and the outer skin 58 is typically 0.2 to 0.8 mm thick, preferably about 0.4 mm thick. The layer of insulation may have a generally U-shaped cross section 54 sealed within the shell. The shell may be in the form of a sheet of thickness in the range I to 10 mm and is typically 2 to 4 mm thickness. The shell may be sealed by overlapping portions, for example by overlapping inner skin portions 56a and 56b. The rail heater covers 50 are typically manufactured in Im lengths sealed at each end by spot welding (see Figure 5) or other means such as overlapping and crimping foil portions Preferably, the inner skin 56 of the shell is thinner than the outer skin 58 of the shell. The thin inner shell protects the layer of insulation 54 from mechanical damage during fitting and removal of the cover from around a heater; while the thicker outer skin 58 helps provide the necessary rigidity. The thinner inner skin 56 also results in reduced heat loss from the inside to the outside of the shell by then-nal conduction.

It has been found that it is preferable to use dimpled sheet material. These dimples may take a variety of forms, generally known to the person skilled in the art, for

example, they may be generally sineusoidal in cross section (see Figure 4) typically being 1.1 to 1.5 mm in amplitude (peak to peak) when using sheet material of 0.1 mm thickness. It has been found that dimpled steel (foil) enables the cover to be flexible enough to deal with thermal expansion resulting from location adjacent the heater, Further the dimples provide a shell that has some resilience when held by force against the rail using a securing bracket. This feature combined with the small thickness of the cover generally allows the cover to be fitted to an existing uncovered rail heater using the brackets/clips as originally provided before retrofitting (see Figure 1).

The insulating material is preferably ceramic fibre either in blanket or paper form. However, alternative insulating materials such as rockwool and glass-fibre may be used.

It has been found that the close fitting nature of the cover over a heater element 16 concentrates the heat being dissipated by the heater to the rails and thereby reduces heat loss to the surroundings.

Claims

Claims 1. A rail heater cover shaped to fit over a rail heater element and allow the rail heater to be held between a railway line and the cover comprising an casing made of a substantially rigid material and a thermally insulating material fully enclosed within the casing.
2. A rail heater cover according to Claim I wherein the outer casing is dimpled.
3. A rail heater cover according to Claim I or 2 wherein the outer casing is fabricated from a single sheet of material.
4. A rail heater cover according to any preceding claim wherein the outer casing is sealed around the insulating material by crimping foiled portions of the cover together.
5. A rail heater cover according to any preceding claim wherein the casing is metallic, preferably stainless steel, and more preferably austenitic stainless steel.
6. A rail heater cover according to any preceding claim wherein the wall thickness of the casing is 0.05 to 0.2 mm thickness.
7. A rail heater cover according to any preceding claim wherein the insulating material has a thermal conductivity of less than 0.06 W/m.'C, preferably less than 0.035 W/m.'C, and most preferably approximately 0.015 W/m.*C.
8. A rail heater cover according to any preceding claim wherein the insulating material is ceramic fibre

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9. A rail heater cover according to any preceding claim wherein the insulating material is in sheet form having a thickness in the range I to 10 mm, preferably within the range 2 to 4 mm, and most preferably approximately 3 mm.
10. A rail heating system comprising a rail heater and a cover for the heater made of insulating material having a thermal conductivity of less than 0.06 W/m.'C, preferably less than 0.035 W/m.'C, and most preferably approximately 0.015 W/M.'C.
11. A rail heater cover according to any of Claims I to 5 and 7 to 10 wherein the inner wall thickness of the casing is less than the outer wall thickness of the casing.
12.A rail heater cover according to any of Claims 11 wherein the inner wall thickness of the casing is 0.05 to 0.2 mm thickness.
13. A rail heater cover according to any of Claims I I or 12 wherein the outer wall thickness of the casing is 0.2 to 0.8 mm thickness.
14. A rail heater cover according to any preceding claim wherein the outer casing is sealed around the insulating material by welding.
15. A rail heating system substantially as described herinbefore with reference to Figures I to 5.