Effect of the presence of moisture at the wheel–rail interface during dew and damp conditions

Abstract

Incidents involving low levels of adhesion between the wheel and rail are a recurrent issue in the rail industry. The problem has been mitigated using friction modifiers and traction enhancers, but a significant number of incidents still occur throughout the year. This study looks at the environmental conditions that surround periods of low adhesion in order to provide an insight into why low adhesion events occur. Network Rail Autumn data, which provided details on the time and location of low adhesion incidents, were compared against weather data on a national and then local scale. Low adhesion incidents have often been attributed to contamination on the rails, such as organic leaf matter, but these incidents also occur when no contamination is visible. The time, date and location of incidents were linked to local weather data to establish any specific weather conditions that could lead to these events. The effects of precipitation, temperature and humidity on rails were analysed in order to further the understanding of low adhesion in the wheel–rail contact, which will lead to adopting better methods of mitigating this problem.

Simulation and understanding the wet-rail phenomenon using twin disc testing

“…This shows that iron oxides could play a role in low adhesion due to leaf layers, as well as throughout the year due to the wet-rail phenomenon. Previous analysis of Network Rail station overruns showed that during the autumn season, no railhead leaf contamination was seen for approximately 50 % of incidents as seen in Table 1 [7]. Table 1.…”

“…Table 1. Incidents where contamination has been reported after an incident [7] Outside the autumn season, or in situations such as tunnels [8], low adhesion still occurs due to the wet-rail phenomenon so although organic contamination certainly results in low adhesion, there are many more incidents where organic contamination is unlikely to be present.…”

The low adhesion problem due to leaf contamination in the wheel/rail contact: Bonding and low adhesion mechanisms

“…The high probabilities between 05:00 -10:00 and 20:00 -24:00 in Figure 3 and Figure 4 could be attributed to the dew on the track [28]. Generally, mixtures of leaves and a small amount of water decrease the friction coefficient dramatically [7].…”

Full-scale testing of low adhesion effects with small amounts of water in the wheel/rail interface

“…Work carried out to analyse the frequency of the braking related incidents during the autumn period has shown that the cause is split 50:50 between leaves and 'wet-rail' syndrome [1]. Wet-rail syndrome relates to low adhesion caused by the presence of small amounts of water along with some solid material, such as oxides generated naturally in the wheel/rail interface.…”