Experimental study of train sanding

Abstract

Train sanders are ubiquitous in remediating low wheel–rail adhesion. Sanders operate by taking sand stored in a hopper, pneumatically conveying it through a nozzle, then spraying it into the wheel–rail interface. In this research, the wheel–rail–sander system was simulated experimentally in a laboratory. The system was optically accessible, and Particle Tracking Velocimetry was used to observe the trajectory of sand particles approaching the nip. The percentage of sand conveyed through the nozzle that makes it to the wheel–rail nip – the deposition efficiency – was measured gravimetrically. The maximum efficiency was found to be 91% for 1.15 mm mean diameter silica sand with a proprietary coating, and the minimum efficiency was 59% for uncoated aluminum oxide with a 0.91 mm mean diameter, both at a simulated train speed of 18 km/h. Irregular particles were found to be less efficient when compared to spherical particles with a similar size and composition. Increasing the size of silica sand from 0.18 mm to 1.05 mm in diameter slightly decreased the sanding efficiency from 67% to 60%. There was no statistically significant dependence of the efficiency on the particle coefficient of restitution. The single parameter most closely correlated with the deposition efficiency is the expansion of the particle-laden jet downstream of the nozzle. Larger, round particles typically had the smallest jet expansion and the highest efficiency, whereas rough particles with large diameters were found to have a large jet expansion and lowest efficiency. Finally, the effect of train speed on deposition efficiency was studied. The deposition efficiency was found to be very low at low train speeds and asymptotically approaches a fixed value at higher speeds. A simple physical model is proposed that explains the low efficiency at low speeds.