Interface - The Journal of Wheel/Rail Interaction

RAIL GRINDING & RE-PROFILING

Wheel Re-Profiling and Rail Grinding Strategies on Wiener Linien (Part 2 of 2)
By Edgar Fischmeister, Markus Ossberger, Roman Pongracz and Paul Mittermayr • January, 2008

Part 1 of this article examined wheel re-profiling strategies as part of Wiener Linien's profile optimization strategy.
Part 2 focuses on the rail profile and grinding strategies.

Rail Grinding

Traditionally, the rail head at Wiener Linien was ground as a five-sided polygon (see Figure 1). This approach has some negative impact on wheel wear, especially in the area of the flange root (see the red-ringed area in Figure 2.) While it is not possible to machine rail heads true to their profile, with genuine head radii — the current grinding machines leave a sharp-edged polygon on the rail head, in most cases — a condition-based grinding program can reduce the number of edges generated in grinding. Wiener Linien found that it can produce higher-precision polygons (with a greater number of edges) by means of more frequent grinding operations with a lower rate of cut. Wiener Linien also has learned to avoid any "bluing" or "heat tints" (unintentional hardening of rail steel caused by excessive heat generated by too intensive grinding operations), which can have a negative impact on the wheel profiles.

The "track dynamics" portion of the "profile optimization" program, along with the accompanying long-term studies of rail and wheel profile wear patterns, helped to identify target profiles (based on an adaptation of the Vignole rail profile) and possible changes to grooved rail profiles (see Figure 3).

Track components, such as crossing frogs, can be damaged by the "false flanges" of worn tires (see the red-ringed zones in Figure 4). The photograph on the left in Figure 4 shows one wheel from an Ultra Low Floor (ULF) tramway car with less than 20,000 km and less than six months of service on Wiener Linien. (The right side of the figure shows several wheel profiles in different colors plotted on top of one another.)

Wiener Linien has also begun challenging some of the assumptions that govern track design. Should, for example, the running edge radii of grooved rails be enlarged? The current radii ratio of 10 mm in the tire groove versus roughly 9 mm at the running edge of the grooved rail is very unfavorable. In mathematical terms, this results in an almost infinite equivalent conicity and, thus, unstable running behavior. Visual inspection and wear data obtained through periodic profile measurement have shown that wear in the tire groove and rail head radius tends to create a sharp edge on both components, i.e. the radius of the flange groove and of the rail head become successively smaller. This would not deserve much attention, were it not for wheel re-profiling and its requirements.

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