Interface - The Journal of Wheel/Rail Interaction

RAIL GRINDING

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

An economic evaluation of the heavy haul grinding program between 1990 and 2005 (shown in Figure 5) indicates that rail maintenance costs were significantly reduced after the introduction of the rail grinding program. The grinding program soon provided a “pay-back” in the reduced need for rail renewal.

Turnout Grinding
Rails in turnouts are ground for the same reasons as rails in open track. Switches at Malmbanan were first ground in 1994. The results were encouraging, but it took some time to establish a strategic rail grinding policy for turnouts. Today, almost every switch on Malmbanan is ground every year (30 MGT). Initially, the target profile was the “standard” BV50 profile with an inclination of 1:30, instead of the installed vertical profile. However, as in open track, this standard profile resulted in unacceptable wear and the rapid occurrence of RCF defects. Consequently, another profile (MB 4) (see Figure 4, left, on prior page) was developed. This profile has a reduced gauge corner relief compared to the MB1 profile.

The reason for not grinding directly to MB1 profile was due to the reduced production capacity of the switch grinder in service at that time. To grind the MB1 profile from a deformed profile would have been very time consuming. Grinding in steps was the answer to the problem. In 2007, some switches were ground to the target MB1profile for test purposes. These switches are monitored closely, and the MB1 profile is expected to become the standard for turnouts.

On Malmbanan, the upper part of the switch blade point is in many cases exposed to cracking due to a local overload when the wheels are moving from the stock rail to the switch blade. Due to wear, both natural and artificial by repeated grinding, the stock rail is lowered over time with respect to the tip of the switch blade. To minimize the risk of cracking of the critical upper part, the switch blade is lifted 6 mm before grinding (see Figure 6). Because of the metal removal by grinding from the top portion of the switch blade, the transition point from the blade to stock rail is moved toward the frog.

In Sweden, the annual grinding budget was earlier decided by each region or local hub. In many cases, the grinding budget was reduced due to economic measures or postponed until the following year. In 2001, a central funding source was established, with each region reporting its grinding needs to the head office in order to “jointly” determine maintenance priorities. Rail grinding has since become a higher priority maintenance procedure on Malmbanan and other lines at Banverket.

Today, planning of the grinding operation is managed in a “turnkey” fashion. Spark Trade AB, a Swedish company, is subcontracted by the grinding company to plan, execute and ensure quality control of the daily work, including the organization of pilots, road guards and responsibility for all necessary service arrangements.

At present, grinding on the Malmbanan ore line is performed once a year. All curves are ground and switches are ground each year at 30-MGT intervals. Tangent track is ground every third year, at 90-MGT intervals. The development of grinding profiles on Malmbanan has been performed in close cooperation between Banverket, the transportation company MTAB (responsible for the vehicles) and the grinding contractor. This cooperation has been characterized by open discussion between the three parties, aimed at improving the contact between wheel and rail.

Future Work
Future grinding work of the ore line will focus on increasing the 30-tonne axle loads and 30-MGT annual tonnage. The MB1 and MB3 profiles will be used on open track and the MB1 and MB4 profiles will be used in turnouts. A new research project will be launched on Malmbanan this year to identify the presence and number of RCF defects through the use of manually operated Eddy-Current equipment. Depending on the results, the grinding strategy — grinding cycles, metal-removal rates, optimized profile designs — may be modified. A complete track renewal between Kiruna and the Norwegian border will be completed by 2009. All of the existing 50E3 rail will be replaced by 60E1 rail. The new rail will be immediately profiled to the appropriate profiles MB1 or MB3 profiles.

Banverket also continues to investigate lubrication techniques and the development of improved grades of rail steels, such as bainitic steels and steel grades with higher carbon content, which should provide improved fatigue properties and wear resistance. These and ongoing improvements to rail grinding practices continue to contribute to improving overall life cycle costs on the Malmbanan and other railway lines.

Anders Frick is Senior Metallurgist, Banverket, Swedish Rail Administration, Track Engineering. Dr. Wolfgang Schoech is Manager of External Affairs, Speno International SA

References
(1) Nilsson P., Wheel/Rail Interaction – From theory to practice, 6th International Conference on contact Mechanics and Wear or Rail/Wheel Systems – CM2003, Gothenburg

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