RTR 4/2010 18 Hard rails in tight curves For the sake of completeness, it ought to be mentioned that the inner rail was ground for the first time on 31 November 2007 for the purpose of reducing noise, although there was not yet any compelling reason to do so from the permanent-way engineering point of view. That alone, however, means a lengthening of the grinding cycle of at least 1–2 years compared with the previous situation with less wear-resistant rails. The length of the corrugations showed very marked scatter between measurements. There is, however, a detectable tendency for corrugations to form with wave lengths of around 0.18–0.25 m. The corrugation intensity in the experimental curve that is the subject of this report was scattered between some 30% at the beginning of the curve and approximately 60% at the end of it. The mean number of corrugations per running metre in the zones around the measuring points is also very unevenly scattered, ranging from 1 to 5. 3.2 Wear parameters The lateral wear on the outer rail of the curve displays a very considerable increase from the beginning of the curve to its end. This is a common occurrence on track curves over which trains run predominantly in one direction. Figure 3 shows this development over the whole length of the experimental curve. This phenomenon was also taken into consideration in deciding on the sequence in which to install the various grades of steel. The chosen trend line was a second-order polynominal. According to the final measurement made on 6 May 2008 (grey line), the lateral wear values on the outer rail range from less than 2 mm to 3.9 mm at the end of the curve. No lateral wear occurs on the rail on the inside of the curve, but instead of that there are rolling laps over the whole curve, scattered with an order of magnitude of 0.1–0.7 mm. The vertical wear on the outer rail (Fig. 4) is in the approximate range of 0.7 to 1.5 mm. The vertical wear on the inner rail, on the other hand, is within the range of 2.9 to 3.9 mm (Fig. 5). One conclusion that is applicable equally to both rail suppliers (Corus and Voestalpine) is that both the vertical and lateral wear is clearly dependent on the grade of steel: the harder the rail material, the less the wear. (Editor’s remark: It is the 400 UHC grade, which was laid in the measurement crosssections 5, 8 and 11, that displays the lowest amount of wear). 3.3 Development of the rail surface In the course of the five-year observation period, the following changes were ascertained in the surface of the rails: Several wheel-slip marks. These were caused by fully-laden freight trains that became “stuck” on the upgrade, Minor head checks on the running edge of the outer rail over the whole length of the experimental track, and Slight depressions in a few of the welded joints. These show up the urgent need for the development of suitable weld portions for welding hard rails to one another. 4 Concluding remarks The Austrian Federal Railways have now completed a five-year test of rails from Corus and Voestalpine with different degrees of hardness, laid in a tight curve on a heavily trafficked railway line. The evaluation of the measurements performed by the University of Innsbruck showed clearly the advantages of rails with strong mechanical properties, including a Brinell hardness of greater than 350 HB – namely a slowing down in the formation of corrugations caused by wheel skid on the inner rail at the same time as much reduced vertical and lateral wear on both the inner and outer rail. The use of harder rails made it possible to extend the tamping and grinding intervals and also the service life of rails in the track by a very considerable margin (likely to be a factor of 2-3). It would, however, be wrong to ignore the fact that harder rails might also cause undesired side effects, which have not been adequately analysed to date. These might include, inter alia, developments affecting the surface of rails (such as head checks and spalling), impacts on the wearing properties of wheels and stresses acting on other components of the permanent way, especially the rail fastenings, the fatigue strength of the rail and the propensity for factures to occur in rails and/or welds. Given the positive experience with the experimental section, hard rails (> 350 HB) are now being laid in greater numbers in tight curves on heavily trafficked lines within the ÖBB network, and developments are continuing to be observed. Fig. 4: Ver tical wear on the rail on the outside of the curve [mm] at the measurement crosssections along the length of the curve Fig. 5: Ver tical wear on the rail on the inside of the curve [mm] at the measurement crosssections along the length of the curve
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