Environmentally friendly
The laser glazing technique produces a solid-state lubricant that, besides being better than others at ameliorating cracking along the corners, stays where it is applied, can be applied to rails in service and is environmentally benign.
Laser glazing involves a rapid solidification of a thin melt layer produced on the rail by a moving laser beam. The result is a more than 50 percent higher yield strength than the substrate material -- in this case, steel. Laser-treated railroad tracks are also 30 percent more elastically compliant.
The researchers used a pulsed 1.6-kW Nd:YAG laser from Electrox to lubricate a 6-ft length of rail. The 1.06-µm wavelength allows glazing without the need for application of an absorptive coating. About 1 kW was delivered to the sample.
At its test facilities in Pueblo, Colo., the Association of American Railroads conducted friction tests on the laser-glazed sample. After more than 30,000 back-and-forth cycles at typical loads, the treated rails showed reduced friction by as much as 40 percent, which can reduce rail cracking by up to 75 percent.
Another advantage is the portability of the system: The beam can be delivered through flexible fiber optic cable, which is useful for remote applications.
"In addition to rail and wheels, the process can be applied to many steel surfaces, such as bearings and gears," DiMelfi said.