Electrostatic spray deposition efficiency optimization

Top of rail friction modifiers (TOR-FM) are commonly used on railway tracks to reduce the friction between the wheel and the rail. TOR-FM may provide a decrease in maintenance costs and noise, while providing an increase in fuel efficiency. Current methods of applying TOR-FM to tracks involve suspending the FM in a liquid, and either spraying the liquid onto the tracks from a moving train, or oozing it onto the track from a trackside location. An alternative application method is proposed, involving depositing the TOR-FM directly, using electrostatic spray-coating. Previous studies of electrostatic spray coating of TOR-FM have demonstrated deposition efficiencies below 15%, which are far too low to be economically viable. This work improves upon the techniques used to estimate the mass deposition efficiency of spraying powder onto a moving belt developed in previous work. The improved measurement techniques were then validated gravimetrically for a variety of experimental parameters, thus demonstrating their robustness and accuracy. This experimental method was then utilized to optimize the first pass deposition efficiency on a moving track. Parameters studied include the effects of increasing corona-voltage applied at the nozzle exit, mass loading ratio of particles, and nozzle geometry. Increasing the corona-voltage results in a large increase in deposition efficiency, while mass loading ratio had little effect on deposition efficiency. It is shown that a relatively minor change in nozzle geometry will result in a large change in deposition pattern upon the surface to which the particles are applied. Finally, the experiments show that the corona-electrode must be external to the nozzle to produce good deposition. If the correct operating parameters are use, deposition efficiencies in excess of 60% can be achieved.