Improving rail grinding surface integrity across grades through stone topography assessment

Rail grinding is a critical maintenance practice for managing surface defects, restoring rail profiles and ensuring reliable wheel–rail contact. Rotating cup stones operate dry at high speed, with self-sharpening governing stone topography, producing high surface roughness (Ra >10 µm) and intense frictional heating at the abrasive–rail interface. Rapid cooling drives white etching layer formation (WEL), a hard and brittle microstructural transformation that, combined with elevated roughness, may promote crack initiation in harder grades. Although well recognised, understanding of how stone wear, metallurgy and grinding parameters interact to shape surface integrity remains limited.

This thesis commissions a laboratory grinding test rig with a reduced-scale stone (150 mm diameter) mounted on a vertical CNC milling machine and a methodology reproducing field-equivalent surface integrity. Post-grinding field measurements on a metro railway characterised surface integrity across three rail grades (R260, R350HT and R400HT), revealing differences in roughness and WEL characteristics with rail grade and facet location. New and field-used stones showed distinct topographical differences; used stones exhibited reduced peak volume (Vmp) and greater wear flat coverage across all life stages, indicating most grinding occurs in this worn state.

Building on these field references, controlled laboratory tests revealed field stone wear resistance exceeded the operational window, preventing natural wear replication. A dressing methodology conditioned stones to sharp, worn and dull topographies replicating field conditions. Tests across these three topographies, three rail grades (R260, R350HT and HP335) and two depths of cut (100 and 180 µm) identified stone topography as the dominant driver of surface roughness and WEL morphology, with rail grade effects significant only under dull conditions. The methodology successfully reproduced field-equivalent surface integrity, providing a validated platform for studying grinding mechanics and specifying stone composition to balance productivity and surface integrity.