Addressing Seasonal Low-Adhesion Issues (continued)
Special-purpose two-car trains (see Figure 4) are designed to spray a 15,000-psi water jet directly onto the railhead to clean the rail of debris. This system is effective at speeds up to 40 mph. Many service trains are modified to apply Sandite, a water-based paste with particles of sand embedded in it, to break down the leaf-film and re-establish adhesion. Some Sandite mixtures contain metal particles in order to aid the operation of track circuits.
The AWG, working with RSSB, the standard-setting body in the UK, has worked with a manufacturer to develop a laser-cleaning system that promises to do the job of the water-jetting machines more efficiently. Five years ago, this system operated at 5 mph and weighed 7 tons. Today it operates at 40 mph and weighs only 1 ton. The goal is to get the system down to a size and weight that would allow it to be installed on passenger trains. Ideally, the system would be placed on a small percentage of the fleet to continuously clean the rail as the trains circulate throughout the day.
While they differ in approach, all of these techniques have the same goal in mind: to allow the finely-tuned WSP systems, which detect wheel slippage when braking is initiated, to effectively modulate train braking and deceleration. The system is designed to control brake cylinder pressure to allow about a 5% wheel slip. This reduces stopping distances and controls wheel wear.
The WSPer test and simulation system (WSP evaluation rig) can also accurately predict when the wheel tread surface on individual wheelsets will be damaged during braking using a particular vehicle type and WSP combination. Virtually all commuter and longer-distance express passenger trains in the UK are now equipped with optimized WSP systems.
These efforts have enabled the railways in the UK to improve safety, reduce damage to wheelsets and run more frequent trains. These improvements have led to a 40% increase in ridership since privatization of the former British Rail network. This could not have been done without finding ways to deal with seasonal adhesion issues that impact operations on the railway network.
This article is based on "Addressing Seasonal Low-Adhesion Issues," a presentation by Adrian Shooter, Chairman, Chiltern Railways, and Graham Curtis of AEA Technology, at Interface Journal and Advanced Rail Management's Wheel/Rail Interaction '05 Seminar.
