Effect of humidity, temperature and railhead contamination on the performance of friction modifiers: Pin-on-disk study

Abstract

Commercially available friction modifiers are used in many different countries that have widely different atmospheric conditions. These variations in atmospheric conditions lead to varying levels of railhead oxidation and debris build-up. Friction modifiers can be applied to the rail without any prior cleaning of the rail and this can lead to varying friction modifier/iron oxide ratios potentially affecting the performance of the friction modifier. This paper reports the results of an investigation that was performed to determine the effects of varying atmospheric and oxide conditions on the performance of friction modifiers. A pin-on-disk test rig with an attached environmental chamber was used for the study. Results show that relative humidity has a pronounced effect on the way in which the friction modifier affects friction levels, and also the amount of time it remains on the disk. This also depends on the concentration of oxide in the friction modifier. Glow discharge optical emission spectroscopy analysis was also carried out to assess the effect of the friction modifier and atmospheric conditions on the chemical composition of the surface of the disk. Results show that the depth of surface modification is vastly different depending on the conditions and level of railhead debris.

A Review on Wear Between Railway Wheels and Rails Under Environmental Conditions

“…A number of test approaches exist for assessing wheel and rail material performance as shown in Table 1 and Figure 7. The most commonly used approaches are small-scale pin-on-disc tribometers [34][35][36][37] and twin-disc machines [12,[38][39][40][41], largely due to their availability and because tests are relatively quick and cheap to carry out. Scaled test-rigs exist [42] and full-scale experiments are possible [25,[43][44][45][46].…”

“…Using small-scale and full-scale allows, for example, parameterisation of a model to be carried out using small-scale data and then predictions for full-scale used as validation. Pin-on-Disc [37]. The vast majority of wear tests are carried out using small-scale approaches, such as pin-on-disc and twin-disc.…”

“…Types of iron oxides detected on the tracks[64] (summarized from[63])Beagley pioneered the laboratory tests that study the influence of iron oxides in the 1970s by mixing Fe2O3 with fluids[65,66]. Other researchers followed a similar procedure to study the influence of iron oxides on friction and wear[37,67,68]. However, iron oxides created by manual mixing are still unlike what is found in the field.…”

Influence of environmental conditions and oxidation on the coefficient of friction using microalloyed rail steels

“…Some authors have investigated the influence of environmental conditions (temperature and humidity) and iron oxides on the COF of the wheel-rail contact. Lewis et al [6] analysed the effects of atmospheric variations and oxide conditions on the performance of friction modifiers.…”

Tribology of the wheel–rail contact – aspects of wear, particle emission and adhesion

“…Thus it is important to take weather conditions which affect oxidation, such as temperature and humidity [58,59], into consideration. Lewis et.al [60] used at pin-on-disc rig to investigate the effect of humidity and temperature on a sliding contact with iron oxides and friction modifier mixtures. This study pointed out that when Magnetite (black oxide) is mixed with friction modifier the friction rises at a greater rate than when Haematite (red oxide) is present in the friction modifier.…”