Interface - The Journal of Wheel/Rail Interaction

RAIL GRINDING & RE-PROFILING

Wheel Re-Profiling and Rail Grinding Strategies on Wiener Linien
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As Figure 5 indicates, the worn inside face of the flange exhibits not only a small groove radius but also a steep course. If a transit system now wants to machine a new wheel profile with the original flange width, it has to cut deeper into the residual cross section of the tire than it would have to on a worn flange with larger residual width. The transit system could adopt a less material-consuming approach to grinding wheel diameter (see the right chart, Figure 5) if the rail head with its running edge and 9 mm radius did not dig itself so deeply into the wheel profile due to two-point contact conditions.

Experience has shown that the minimal gauge clearance in both tramway and metro operations is unfavorable in terms of wear behavior and riding stability. A small gauge clearance in new rolling stock on new track will result in high initial wear, especially at the flange faces. This is why considerations have been made to match the geometry of wheelset and track.

The Longitudinal Profile
Regular inspection of wheels ensures that the tires can be re-profiled as needed in order to control wheel tread hollowing and false flange contact. On the rail side, the next step toward a proper grinding strategy is to have a precise knowledge of the longitudinal profile of the rail. (The transverse profile is not very indicative of ride stability and wear behavior.) Surface irregularities (short, medium and long wavelength corrugations, surface defects and material flaws such as head checks, squats, cracks or crushed areas) impact rail (and wheel) wear and vehicle / track performance. Surface irregularities also generate high dynamic loads, which are noticeable in the form of structure- and air-borne noise, and reduced passenger comfort.

Wiener Linien began to perform a manual survey of the rail surface using an electronic measurement system called the "1 m straight edge." It found, however, that the data was not reproducible, as the system could not accurately identify the precise locations at which pre- and post-grind measurements were obtained. Manual gauges were augmented by visual inspection of the rails, especially the grooved rails, in order to better assess rail conditions. While the ability of inspectors to judge rail conditions improved, their assessments were difficult to incorporate into a systematic database.

This led Wiener Linien in 2007 to begin measuring the entire metro network and parts of the tramway network with measurement cars. Through the use of this equipment, Wiener Linien identified that short-pitch corrugations posed minor problems for metro and tramway service, whereas medium-wavelength corrugations had a much greater effect on dynamic loads and deviations from the design track position. It also identified the need to focus its maintenance activities on rail joints and crossing frogs.

Based on these measurements, rail hardness measurements and preliminary information from an alternative eddy current-based measurement system, Wiener Linien, in association with Dr. Stuart Grassie of RailMeasurement Ltd., prepared a tender document for the implementation and review of rail grinding programs.

From Strategy to Implementation
Wiener Linien has catalogued the rail, wheel and vehicle / track interaction-related problems it identified to develop a "surface and transverse profile strategy." The key aspect of the strategy is that there is no universal solution or universally applicable method of rail grinding. Each segment of the system must be looked at independently.

The U3 metro line, for example, has geometry defects that stem from the original design. There are long sections with tight gauge along the line. While the head-hardened (HSH) rail used in curves of up to 1,500 m on the line has favorable wear properties, the rail must be ground regularly to prevent brittle cracks and other surface anomalies.

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