Interface - The Journal of Wheel/Rail Interaction

RAIL PROFILE OPTIMIZATION

Profile Optimization in the Urban Rail Context
By Edgar Fischmeister, Markus Ossberger, Roman Pongracz
and Paul Mittermayr • April, 2007

Measurement is an essential aspect of optimizing wheel/rail interaction on urban transit systems. After extensive research and development work, Wiener Linien, the Vienna (Austria) Urban Transit System, implemented an integrated wheel/rail measurement system that enabled the railway to closely monitor wheel/rail contact and optimize wheel/rail profiles on the system.

Wiener Linien is the first urban transit provider to utilize two measurement cars for regular rail measurement runs across its entire network. One measurement vehicle is suited for metro track testing; the other is designed for measuring grooved, or girder, rail for embedded streetcar track testing (see Figure 1). High-precision laser measurements are taken every 0.5 meters to capture the shape of rail head from the outer to the inner edge, and to calculate head wear. The measured part of the rail web and the upper part of the base are used to identify the rail type. (The underside of the rail head typically cannot be “seen” by the laser beams.) In the case of grooved rail, only the head surface, the groove and the guide flange can be measured. In addition to these measurements, a circle is approximated at the inner flange of the rail head. This diameter is used to estimate wheel wear and to calculate the contact geometry, as well.

Evaluating the Data
Following measurement of the Wiener Linien system, data was processed (with checking and two-dimensional smoothing) and used to analyze wheel/rail interaction. First, the theoretical profiles were examined to highlight the contact geometry potential. For this purpose the wheel profiles were laterally offset from their center position, while the wheel/rail contact was calculated iteratively. This enabled the railway to determine the regularity of contacts on both the rail and wheel — an important aspect of wheel/rail interaction on the system since spot contact on one of the profiles leads to concentrated wear and a rapidly changing in-service profile in the same spot. Computation also showed rolling radius difference as a function of lateral displacement (see Figure 2), where shifts in contact points and striking of the flange against the rail head can be seen. The equivalent conicity for certain amplitudes resulting from the rolling radius difference was also calculated. A standard requiring that conicity does not exceed 0.5 was established. Conicity that is too low is also unfavorable, as it provides an insufficient turning angle for proper sinusoidal motion.

The location and distribution of contact points under (cyclical) lateral subsidence helps identify the wear tendencies of interacting (wheel/rail) components. The contact patch locations are used to compute equivalent conicity, which helps characterize stability on tangent track, whereas rolling radius difference affects performance on curves.

While optical rail measurement has been performed for years on standard open-track railways, Wiener Linien’s streetcar measurement car is the first to monitor the profile quality of grooved rails. However, owing to the fact that grooved rails are built into the street, only part of the rail head (running surface, groove and check) can be measured. Nevertheless these profile data provide important parameters such as wear surface, depth and width of groove, and the radius of the running edge. With this information, rail profile conditions can be monitored and maintenance planned throughout the network.

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