Effects of oxide and water on friction of rail steel – new test method and friction mapping

Abstract

A novel tribo-testing method using a pin-on-plate tribometer was developed to test and visualize the coefficient of friction over surfaces with oxides present to examine low adhesion issues. Tribo-test data was recorded each pass over test surfaces showing how friction changes with mechanical action. Trackside environmental monitoring and railhead swabbing was performed to investigate the physical and chemical environment of the railhead. Iron oxides were both synthesized on and deposited on rail steel substrates to simulate ‘wet-rail’ conditions. Powdered oxide layers of magnetite, haematite, goethite and lepidocrocite were deposited on rail steel substrates to investigate individual oxides. Composition was analysed using X-ray diffraction and scanning electron microscopy before testing. Magnetite, Haematite and Lepidocrocite were formed when water alone was applied to the surfaces. Low friction was observed on oxidized sample surfaces only outside high roughness, oxide pitted, areas, but these conditions were shown to be difficult to achieve and transient.