Signalling block occupancy is triggered by the wheelset of a rail vehicle "shunting" the track circuit. Rail head contamination remains the main cause of loss of shunting. There are many materials that could be present on the rail head. These include iron oxides, leaves, dust from ballast, oil, wear particles, as well as products deliberately applied to the rail/wheel by the network operator such as grease, friction modifiers, lubricants and sand. The presence of rail head contaminants may lead to false signalling indicating that a signal block is unoccupied when in fact a vehicle is present within its limits. Friction modifiers are being increasingly used on rail networks for the mitigation of curve squeal, increased fuel economy, reduction of lateral forces, reductions in wear, RCF and corrugations. The Kelsan HPF solid stick friction modifier is applied directly to the wheel tread creating a thin film at the wheel/rail interface. Although no significant effects have been observed during field operation over a range of railways and systems, the intention in this work was to build on previous studies and evaluate conductance across a wider range of contact conditions as studies have shown that loss of shunt is more common with light axle loads where films could have a greater effect. This testing was performed at a contact pressure of 470MPa which correlates to an axle load of approximately 4.9 tonnes. An HPF stick was spring loaded under constant force against the rotating wheel disc to generate a friction modifier film at the contact. Tests were run to measure the impedance across the discs using a modified TI21 track circuit. Static testing was also performed using discs with a pre-generated HPF film. Analysis of the results showed than the application of HPF friction modifier had no significant effect on the measured level of impedance. In cases where the application increased impedance, the measured values were lower than the highest values measured in the absence of friction modifier.
The Effect of Friction Modifiers on Wheel/Rail Isolation at Low Axle Loads
2012
11 Seiten, 28 Bilder, 3 Tabellen, 15 Quellen
Conference paper
English
The effect of friction modifiers on wheel/rail isolation at low axle loads
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