A new understanding of leaf-induced low adhesion to reduce delays
Controlling adhesion is an important part of managing the railway. The ability of a train to accelerate and brake is dependent on the adhesion available in the contact between the wheel and rail. Improving our understanding of adhesion will help improve management of the railway.
The contact patch between the wheel and rail is an open system that can be exposed to several contaminants lowering adhesion levels. These include crushed leaves, general moisture, sands, oils, iron oxides, and excess lubricant from defective flange lubricators.
To cause prolonged low adhesion, these contaminants need to form a highly adherent coating. There has been difficulty in the past with reproducing these conditions in a laboratory. This project carried out new research to help improve our understanding of low adhesion.
Through the Strategic Partnership with the University of Huddersfield, testing was carried out using the full-Scale Bogie Rolling Contact, Adhesion and Braking Rig (HAROLD).
HAROLD is capable of emulating conditions found in the network, under controlled conditions. A systematic approach to testing was taken which included a range of parameters. Observations were taken on the highly adherent coatings and the low adhesion levels reached as a result.
This research has developed a structured method for the development of consistently highly adherent leaf layers in laboratory settings. They reproduce the exceptionally low adhesion characteristics found on the network.
In addition, observations around the formation of highly adherent leaf layers were made in relation to the conditions tested. These conditions were water quantity, wheel load, presence of iron oxides, and leaf type.
This work can be used to drive a better understanding of low adhesion conditions at the wheel-rail interface in future.