Interface - The Journal of Wheel/Rail Interaction

RAIL GRINDING & RE-PROFILING

Wheel Re-Profiling and Rail Grinding Strategies on Wiener Linien
(continued)

Corrective measures require re-profiling of the wheels. Preventative measures include ensuring that the tire material has sufficient strength and/or hardness without having too great of an abrasive effect on the rails. A more proactive measure is to spread wheel-on-rail contact across the entire tire tread. This is only possible when there is a balanced mix of tangent and curved line sections within a rail network.

If wheel hollowing cannot be avoided, transit systems should aim to have as few outliers as possible within the wear profiles of a single vehicle. Wiener Linien has specified as part of its delivery requirements that same-type tires be measured and sorted by Brinell hardness (BHN) so that the maximum difference within one pallet is no more than 10 BHN.

Wheel hollowing of greater depth generates a "false flange." The causes of this condition are basically the same as those that cause hollow-worn treads, with a few notable exceptions. The false flange shown on the left in Figure 2 is from a wheel on a ULF tramway car with less than 20,000 km and less than six months of service on Wiener Linien. Why would this condition occur after such a short period of time?

ULF tramway cars are equipped with very small wheels, which generate higher surface pressure at the wheel/rail contact patch. ULF vehicles also have fewer wheels per “vehicle running meter” (as compared to predecessor models), resulting in much higher — almost twice as high — wheel loads. In addition to the higher wheel loadings, the last pair of wheels of a ULF car is steered too precisely by its suspension system. This pair of wheels cannot follow a sinusoidal movement. Because of their very low flange steering forces, this pair of wheels virtually always runs along the same path and infrequently contacts the rail at the outside of the wheel tread.

With the small wheels and high wheel loads on the ULF vehicles, Wiener Linien elected to widen the tires on one of the prototype vehicles to ensure sufficient fatigue strength for the rubber-cushioned wheels. While this may reduce the incidence of false flange activity, the wider tire will not allow the wheel / rail contact to be spread evenly across the wheel / rail running surface.

Wiener Linien has begun to chamfer the outer zone of the wheel tread — a preventative measure that can extend the period until displaced material collects on the outer tread portion of the wheel tread and builds a false flange. Another measure that can control the incidence of false flange is the use of UIC-coded "B6" maximum-strength tires, along with re-profiling as early as six months after their introduction. (An under-floor lathe is virtually indispensable for carrying out this type and frequency of re-profiling jobs.)

These issues underscore the importance of direct communication between the vehicle and track maintenance managers, the vehicle manufacturer and the maker of the running gear / wheels. The last one in the vehicle development chain very often is the wheel designer. Frequently he is expected to design running gear and wheels in compliance with applicable standards and service life requirements without being told how heavy the finished vehicle will be. This approach serves none, in that even the best wheel / rail profile pairing can be reduced to absurdity by overly wide tires. To combat this trend, tender documents for new tires used on Wiener Linien now include an optimized wheel profile.

Edgar Fischmeister, Dipl.-Ing, is Head of the Track Maintenance and Construction Department, Wiener Linien; Markus Ossberger, Dipl.-Ing. Dr., is former Maintenance Process Manager for Light Rail Systems, now Department of Construction and Subway-Planning, Wiener Linien; Paul Mittermayr, Dipl.-Ing. Dr., is Director of BAMM, research consultant to Wiener Linien and the Austrian Federal Railways (ÖBB); Roman Pongracz, Dipl.-Ing, is a former Manager of Wiener Linien, and Vehicle Consultant.

References
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Ossberger, M., Mittermayr, P., "Messstrategien für den Oberbau im urbanen Bereich." EI – Der Eisenbahningenieur, 56(9), 12–16, 2005. (Measuring strategies for the track system in the urban area.)

Pongracz, R., "Radverschleißaspekte im Schienennahverkehr." Special ETR Austria, 2, 729–737, 2005. (Aspects of wheel wear in the urban traffic.)

Schoech, W., "The European Approach to Quality Control in Rail Grinding," Interface – The Journal of Wheel/Rail Interaction, August 2004.

TCRP Transit Cooperative Research Program, Report 57: Track Design Handbook for Light Rail Transit. Transportation Research Board, National Research Coun–cil. Washington, D.C., National Academy Press 2000.

Tuzik, B., "Specialized Rail Profile Grinding on MBTA," Interface – The Journal of Wheel/Rail Interaction, April 2005.

Zarembski, A., The Art and Science of Rail Grinding. Omaha, NE, Simmons-Boardman Books, Inc., 2005.

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