A study on iron oxides and surface roughness in dry and wet wheel−rail contacts

Abstract

In addition to contaminants such as dirt, precipitation and leaves, iron oxides are constantly present on railway wheel and rail surfaces. Iron oxides potentially influences adhesion and wear between wheels and rails, which in turn affect railway operation, safety and maintenance. Surface roughness also has a large impact on wheel−rail adhesion and wear. Rolling−sliding tests were conducted on a typical rail and wheel steel combination using a disk-on-disk machine to study the influence of iron oxides and surface roughness on the wheel−rail adhesion and wear. The iron oxides were created in a climate-controlled chamber, and two levels of roughness were investigated under both dry and wet conditions. Worn surfaces were examined using scanning electron microscopy, energy dispersive spectrometry and X-ray diffractometer. An extra set of tests was also performed to study the influence of surface roughness on the removal of the oxide layers and to investigate its role in recovering adhesion.Results indicate that the surface roughness after testing tends towards a saturation level in dry contacts under the given contact condition. The low adhesion problem is unlikely to occur under dry conditions, while thick oxides on rough surfaces result in extremely high adhesion and wear. Under wet conditions, thin oxides help to protect contacting surfaces, producing negligible wear and a smooth surface. Either increasing surface roughness or having thick oxides increases wear. A rough surface is efficient in removing the thin oxide layer in order to recover adhesion under the wet conditions.