Wheel/Rail Contact Tribology: Characterising Low Adhesion Mechanisms and Friction Management Products

Friction management and control of adhesion at the wheel/rail interface is vital for an efficient and cost effective railway network. The understanding of how the friction management products (grease and friction modifiers) work and effectively test these products is necessary to improve the performance of a railway network.
The papers presented concern the effective benchmarking of wayside curve lubricants (grease) in a twin disc test rig. They compare the effectiveness of several greases in respect to adhesion, wear protection and retentivity (number of cycles of adequate lubrication). A new method for assessment of grease carry down has been trialled in the field. The modified pendulum was able to detect the difference between a dry and lubricated rail gauge face.
Top of rail friction modifiers (TOR-FMs) have been tested at two different laboratory test scales. The results showed the difference in operational behaviour of the chosen TOR-FM when used in a laboratory versus the field.
The ‘wet-rail’ phenomena, where low adhesion as a result of water on the rail head, has been investigated at two scales of laboratory test and results have been used to generate a model to predict adhesion coefficients for a range of water and iron oxide mixtures. The results presented show how the addition of small amounts of water to a wheel/rail contact can cause reduced adhesion to ‘low/ultra-low’ levels when combined with third body materials (iron oxides, wear debris etc.).
A novel treatment method to protect the rail head using hydrophobic solutions was investigated using twin disc and pendulum testing. Tests showed that these products, when sufficiently diluted, do not reduce friction to dangerous levels or isolate the vehicle from the track circuit. However, the benefits of use in the field are questioned.