Railway Open System Tribology

Sammanfattning: Tribology in the railway system is of increasing interest in the new railway era due to the demand for higher speed and load capacity. Since railway vehicles operate in an open environment, their performance depends greatly on temperature, humidity and natural and artificial contaminants. Meanwhile, the “feedback” of railway vehicles to the surroundings, such as noise and airborne particles, is of great importance to the human health and the environment. Therefore, this thesis aims to investigate the strong interaction between railway tribology and the open environment. The effects of temperatures from -35 °C to 20 °C, relative humidity from 40% to 85%, natural contaminants such as ice particles on friction, wear, noise and airborne particle emissions at the wheel–rail and wheel–block brake contacts have been investigated in both lab- and full-scale contexts.Papers A and B investigated the effect of temperature, humidity and ice particles on the friction and wear at unoxidized and oxidized wheel–rail contacts. The results indicate that increasing humidity reduces the wear at unoxidized contacts. A decrease in temperature tends to intensify the wear until an ice layer has condensed on the wheel and rail surfaces at -25 °C. Ice particles encourage the generation of oxide flakes at the contacting path, largely inhibiting the wear process.Paper C, which was a lab-scale test, studied the friction, wear and noise generation from pre-oxidized wheel–rail contact with varied surface features. Major results include that the wear regime transition from mild wear to severe wear is always accompanied by an increase in noise level of 10 dB and a broader bandwidth of noise.Paper D was a validation of the major findings of paper C in a full-scale test, which also saw an increase in noise level as well as a broader bandwidth when the wheel–rail contact transformed from mild to severe wear.Paper E studied the effect of humidity on the friction, wear and airborne particle emissions of three railway brake-block materials. The results show that cast iron generated the highest friction coefficient, wear and particle emission, and organic composite the lowest levels.Paper F conducted a thorough literature review on the open system tribology at the wheel–rail contact. Commonly seen parameters such as temperature, humidity and natural and artificial contaminants on friction, wear, noise and particle emissions were investigated.