Interface - The Journal of Wheel/Rail Interaction

RAIL GRINDING

Target Profiles for Rail Grinding: A Never Ending Story
(continued)

Other railways have investigated the use of special profiles and have come up with similar solutions. The infrastructure company of Dutch Railways (ProRail) has developed a particular Anti-Headcheck-Profile with 1-mm gauge-corner relief, compared to the standard UIC 54 profile (see Figure 2 right).

French Railways (SNCF) have defined two new particular target profiles. An anti-headcheck “preventive” profile with limited gauge corner relief is applied where headchecks are not yet visible. A “corrective” profile with considerable gauge corner relief is ground where headchecks are clearly visible. Headchecks often cannot be completely removed, as the cracks are deeper than the prescribed metal to be removed (see Figure 2 left).

After an extensive test program, the German Railways incorporated a standard target profile, which permits only negative production tolerances (that are equal to moderate gauge-corner undercutting), into its grinding specifications.

Specific target profiles ensure that the equivalent conicity is kept within low limits in order to maintain vehicle stability at higher speeds. The German Railways introduced special gauge-widening profiles. The Austrian railways (ÖBB) developed a so-called “convex” rail head profile with a 22-mm gauge corner radius in order to combine the effects of low conicity and reduced surface fatigue development.

Wheel/rail interaction specialists can define ideal target profiles for grinding, knowing the feasibility of producing them within tight tolerances at low extra costs. The current focus is on the development of optimized target profiles for:

• Specific wheels (wear-adapted profiles).

• Fatigue reduction (anti-headcheck profiles).

• Running behavior (gauge-widening, equivalent-conicity profiles).

• Wear reduction (asymmetric profiles).

Profiles for Heavy Haul

Sweden’s 473-km “Malmbanan” heavy-haul line, which connects the city of Luleå on the Baltic Sea and the Norwegian city of Narvik, located on the Atlantic coast (see Figure 3), is characterized by small radius curves and steep gradients. The electrified line handles 30 million gross tonnes per year of mixed passenger and freight traffic, predominantly 30-tonne axle load iron ore cars. Temperatures on the line range from -40 ºC to +25 ºC. The resulting stresses in the rails vary from high tensile stresses during winter, increasing the risk of crack propagation and rail breakage, to compressive stresses in the summer.

Head checking, spalling and shelling defects were quite common in the 1990s. Earlier these phenomena were considered “unavoidable,” and rails were frequently changed. Today, Banverket’s maintenance strategy on Malmbanan includes yearly maintenance grinding (including rail head re-profiling) and extensive rail lubrication in curves of less than 600 meter in radii.

When rail profiling was introduced (using a planing machine) in 1987, asymmetric profiles were applied over distances of 200 meters in order to check their effect with regard to wear reduction. At about the same time, spalling and shelling started to appear on the gauge corner of the high rails. With that, the focus of rail profiling changed toward surface fatigue, and so-called “wear-adapted” profiles emerged. Tests continued using a grinding train, and “gauge-corner relief” became a leading principle in the continued development of grinding profiles.

These experiences led to the development of a profile that was more specifically adapted to the fairly hollow-worn wheels of the ore trains. In 1994, a new (MB1) profile was developed. At first, this new profile was only ground in selected curves at the high rails, while the low rails and tangents still were ground to the standard BV50 profile (see Figure 4, left). In this profile design, the gauge corner area is much lower in order to accommodate the hollow worn wheels. The field corner side remains unchanged. The initial results showed reduced wear and delayed appearance of RCF defects.

A five-year grinding project was initiated on Malmbanan in 1997. Test curves were ground once a year; profiles at 60 locations were selected for evaluation of the transverse profile. As the contact path of the MB1 profile is better adapted to the hollow-worn wheels, the amount of RCF defects, such as head-checking, spalling and shelling, decreased. But the old RCF defects could not be removed entirely by grinding. However, with the use of the MB1 profile, an unloading of the gauge corner was achieved, resulting in a decreased growth rate of existing RCF defects. In 2000, the MB1 profile was introduced as the standard profile on all high rails, and the BV50 profile was restricted to the low rails and tangents.

Damage to a series of older rails made it necessary to develop a profile that could prevent emergency rail renewal. It was also determined that the MB1 profile was not the optimal profile in some curves, and the head-checks became too large before the following grinding program took place. Experience on other railways indicated that more pronounced gauge-corner grinding could reduce further wheel contact at the damaged contact zone on the rail.

Another profile (MB3) (see Figure 4, right) was developed to shift the contact band farther to the field side and thereby optimize gauge corner relief. The application of this profile had the desired effect and the rails could be kept longer in track. The MB1 profile is now standard on all rails (tangents, low and high rails in curves), except for specific, “problematic” high rails to which the MB3 profile is applied.

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