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FEATURE
Adhesion Research Seminar 2025
PHOTO: WILL SKIPPER
MALCOLM DOBELL
(Above) Test rig for demonstrating effect of adhesion enhancing products on insulated blockjoints
T
he collision between two trains at Talerddig, Powys, Wales on 21 October 2024 once again highlighted the issue of poor wheel rail adhesion, particularly in the autumn with ‘leaves on the line’. This continues to be a risk that can be realised despite the industry spending significant sums on mitigation and management. Rail Engineer has frequently reported on the work carried out by the Adhesion Research Group. This year’s seminar included four topics including original research, experience with variable rate sanders, and kicking off studies into techniques for improving adhesion for freight trains.
Conductive sand
IMAGE: WILL SKIPPER
During the 2024 Seminar, Dr Will Skipper from the University of Sheffield reported on the residual risk that applying sand to improve adhesion could cause trains not to be detected by track circuits (Issue 207, May/
Sand application rates for dry rail track circuit tests on the GCR
Rail Engineer | Issue 213 | Mar-Apr 2025
June 2024). Summarising, approximately 5% of wrong side track circuit failures (WSTCF) have been attributed to sand or sandite. This led to the notion of ‘conductive sand’ and previous laboratory work had identified two promising materials. Further track trials led to just one remining: Product D, produced by LB Foster. Will described work to demonstrate that the conductive material improved track circuit detection compared to sand (known as braking sand or 10/18 sand), that it did not cause insulated block joints to become conductive, and that it was an effective adhesion enhancer. Laboratory tests were carried out with a 10mm end post set up between two pieces of rail in full-scale rig. The objective was to demonstrate that the resistance between the two rails remained above the required 0.5 MΩ when the adhesion enhancers were applied. Measurements were taken when material was applied and after each subsequent wheel pass – three passes for each test. Some interesting results were obtained. Neither GB ‘standard’ sand nor Product D created issues with end post insulation in dry conditions with material deposition rates up to 15g/m. Product D created issues when applied at 30g/m and above, far in excess of the application rate permitted. In wet conditions, Product D did not cause end post failure at 7.5g/m, but, curiously, GB sand did. Will suggested that this is because GB sand is less dense, has more particles, and displaced more water. Finally, the end post was lowered to simulate wear and no change in results were observed. Track tests were carried out on the Great Central Railway on a low voltage DC track circuit using a Class 20 locomotive on sand laid at various application rates.