Railway tracks which carry wheeled vehicles are made up of rails that are laid end-to-end. Rails that form part of a track that is straight or slightly curved can have an extremely long service life typically of the order of fifty years subject to traffic loadings. However rails which form part of a sharply curved section of track have a significantly shorter life due to lateral wear caused by the action of the flange on the wheel of the vehicle coming into contact with the gauge face of the rail. This contact occurs principally on sharply curved sections of rail and is avoided on straight or slightly curved sections by the inward inclination of the rails and a taper or coning profile which is machined onto the tread of the wheel in such a way as to generate a self-steering effect to guide the train along the track and avoid such contact.

The lateral wear of the rails which is known as side cut can result in the need to replace the rails after periods of as little as a few months. Another problem with sharply curved rails is that of noise since the contact between the wheel and the face of the rail results in significant vibration and consequent noise.

Traditional techniques for dealing with these problems have involved providing some form of lubrication between the wheel and the rail. A number of methods have been developed with varying degrees of success. All known methods require replenishment of the lubricant and careful control of its application in order to avoid either an excess or an insufficient supply.

Furthermore, these techniques require deployment of labour which in the case of track mounted lubricators is a time consuming and inefficient process.

The present invention is concerned with a technique for coating rails which attempts to deal with these problems.

According to the present invention there is provided a method of coating rails comprising heating the rail in the region to be coated to a preselected temperature, spraying onto the heated surface a powder, the temperature of the rail being such that the powder particles become sufficiently softened that they adhere to the rail, and fusing the powder so that it forms a mechanical bond with the rail and thereby creates a protective coating on the rail.

The method may include, prior to the heating step, the step of subjecting the rail to a pre-treatment in which the rail is cleaned and its surface roughened. The pre-treatment step may comprise shot blasting the surface of the rail.

The heating step may include locating heaters at spaced positions along

the length of the rail. The heaters may be ceramic heaters. The rail may be laid on its side to effect said heating. One or more thermocouples may be arranged along the length of the rail in order to sense the temperature of the rail.

The powder may be sprayed onto the rail by means of a nozzle carried on a gantry which is movable longitudinally relative to the rail. The gantry may be movable along guide tracks located on either side of the rail.

The rail may be coated to a thickness of approximately 0.5 mm. The powder may comprise a nickel based powder such as Eutalloy SF 15285.

The fusing step may be carried out using a nozzle which produces a flame which can be directed onto the powder. The nozzle may be carried by the gantry.

The final step in the process may comprise cooling the treated rail to ambient temperature.

The invention will be described now by way of example only, with particular reference to the accompanying drawings. In the drawings: Figure 1 is a cross-section through a typical rail which forms part of a railway track; Figure 2 is a schematic view illustrating an arrangement for coating rail, and Figure 3 is a cross-sectional view of a rail illustrating a step in the

coating process.

Referring to Figure 1 there is shown a transverse section through a typical rail used to form part of a railway track. This comprises a foot portion shown at (10), a web (11) and a head portion (12) which in use is engaged by the wheel of a railway vehicle. The part of the rail shown at region (14) is that which particularly in the case of a curved rail is subject to wear due to contact between the rail surface and the flange on the wheel of the vehicle.

The following is a description of an embodiment of a method for coating this region of the rail in order to make it resistant to such wear.

Figure 2 is a schematic view of an apparatus which can be used to carry out the method which will be described below.

This apparatus includes a gantry shown generally as (20), this gantry including a horizontal cross beam (21) which is mounted on spaced side frames (22,23), the side frames are carried upon guide rails (24,25) in such a way that the gantry can be moved longitudinally along the length of the guide rails in either direction.

The gantry supports equipment shown generally at (30) for supplying powder to a rail to be coated and also for treating that powder. This equipment includes a source of powder which is to be used to coat a rail. The powder can be fed to a nozzle (31) of an SF Lance which can also receive a mixture of oxygen and acetylene gases. The SF Lance is an oxyacetylene Lance which is

coupled to the source of oxygen and acetylene so that it can produce a flame at the nozzle (31). The nozzle of a CastoFuse torch (33) is located alongside the SF Lance.

In order to coat a rail the following procedure is carried out. Initially a straight length of rail is cut to an appropriate length. The rail is then subjected to an initial treatment which serves to clean and roughen the surface of the rail.

This is a shot blasting process in which the area of the rail to be coated is grit blasted with, for example, G24 grit. This process removes any oxidisation which has formed on the surface of the rail and also roughens the surface of the rail.

The rail (35) is then laid on its side and located over a number of ceramic heating elements (36) which are spaced longitudinally along the length of the rail so that they locate against the web of the rail (35) between its head and its foot, as shown in Figure 3. A series of spaced thermocouples may also be located along the web of the rail in order to act as temperature sensors. The ceramic heating elements are energised and the rail is heated to a temperature of around 120°C as sensed by the temperature sensors. A baffle (38) can be located over the rail to speed up the heating process.

The next step in the process is to coat the area (14) of the rail shown in Figure 1 with powder. In order to carry this step the gantry (20) is located initially at one end of the rail (35) and the nozzle (31) is positioned at an

appropriate position relative to the surface of the rail to be coated. The powder is fed to the nozzle (31) and that nozzle creates a spray of powder which is directed to the surface of the rail and the heat in the rail is such as to sufficiently soften the powder to cause it to adhere to the surface of the rail.

During this process the gantry is being moved along the length of the rail at a speed which typically is in the region of 168 cm per minute. Also at the same time the SF Lance is provided with a supply of oxygen and acetylene which is ignited and the flame adjusted to a neutral setting. The powder is sprayed onto the surface of the rail so as to create a thickness which is in the region of 0.5 mm with a margin of error of-0.1 mm to +0.5 mm. The powder used may be that known as Eutalloy SF 15285 which is a commercially available, nickel based, powder.

The powder is applied in two passes the first with the gantry moving in one direction along the length of the rail and the second with the gantry moving in the opposite direction so that at the end of the spraying process the gantry has returned to its original position. It has been found that it is better to apply the powder in two passes in this way in order to ensure full coverage of the required area along the entire length of the rail.

Once the powder has been coated onto the rail, it is subjected to a fusing step. In the fusing step the CastoFuse torch (32) carried by the gantry is supplied with a mixture of oxygen and acetylene which is then ignited in order

to form a flame. The gantry is moved along the length of the rail and at the same time the flame from the CastoFuse torch is directed onto the coating.

The action of the flame is to melt the powder in order to fuse it and form a mechanical bond with the rail. During this stage of the process the gantry is moved at a rate of approximately 10 cm per minute.

After the powder has been fused so that it adheres to the surface of the rail in order to form a protective coating the rail and the powder is allowed to cool to ambient temperature. The rail is then subjected to a curving treatment if it is required to form a curved portion of a track.

The powder which is used is selected in order to provide certain characteristics. It should have a coefficient of friction which reduces relative to that which conventionally exists the friction between the rail and the wheel.

The material also needs to be sufficiently hard to resist where when railway vehicle wheels run over the material. Typically a coefficient of friction of. 1 to . 2 is the preferred value and the hardness of the material will typically be in the range 380 to 400 V.