Wheel-rail wear and surface damage caused by adhesion sanding

Sanding is used in train operation to improve adhesion at the wheel/rail interface in both braking and traction. An experimental study has been carried out to determine the effect of sanding on the wear of wheel and rail materials. Static tests were performed using actual wheel and rail sections, and dynamic tests were carried out on a twin disc machine, where wheel and rail steel discs are loaded together and driven under controlled conditions of rolling and sliding. Sand was fed into the disc contact through a standard compressed air sanding valve. After static crushing of sand both wheel and rail surfaces showed evidence of severe damage and indentations up to 100 mu m deep had been formed. It was found during the dynamic tests that on the application of sand, wear rates of wheel and rail discs were increased by factors of between 2 and 10. The wheel steel wear rates showed the largest increases. Wear in wet conditions was higher than dry because the wet discs entrained a larger amount of sand through the contact that otherwise bounced off when the discs were run dry. For tests run with sand, severe plastic flow resulted as well as high material loss and some surface corrugation. Rail discs exhibited abrasive score marks. This was because the softer wheel material was trapping most of the sand particles that then abraded the rail material. The wheel disc showed evidence of surface cracking and material spallation caused by a fracture process. With no sand in the contact, plastic deformation again occurred as well as surface corrugation on the rail disc. No abrasive wear marks could be seen on the rail disc surface, but small pits usually associated with ratchetting wear were evident. The wheel disc exhibited evidence of delamination wear. The outer layer of material was seen to be "peeling" away from the surface of the disc. There was no indication of the low cycle fatigue process observed when passing sand through the disc contact.