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Milling technology for efficient rail treatment

An efficient, safe, and environmentally friendly railway system is crucial to meeting future requirements for mobility and freight transport. The wheel-rail contact point plays a key role, as both system partners "meet" in this point. Despite the use of state-of-the-art wheel and rail materials, damage in the form of plastic material deformation, profile wear, and cracks (rolling contact fatigue) will invariably develop. Rails must be maintained regularly to still achieve the maximum service life of the rail as a crucial track component.

Dipl.-Ing. Dr. Richard Stock
Global Head of Rail Solutions, Plasser & Theurer

Maintenance strategies

Infrastructure operators can implement various measures for advanced rail maintenance. Ideally, a preventive maintenance strategy is used. This is the optimum solution in terms of costs and the service life of rails. This method keeps rails in virtually perfect condition. With regular maintenance interventions, small amounts of material are removed to keep surface defects and profile deviations in a manageable condition.

With a corrective maintenance strategy, defects can reach a medium/greater depth. Using this strategy, intervention intervals can be extended accordingly, but much more rail material has to be removed per intervention. Overall, the rail service life achieved with this strategy is shorter compared to that of a preventive strategy, and life cycle costs are correspondingly higher.

Regenerative maintenance represents a special scenario. Almost independently of its initial state, the rail is put into a "new condition": it is regenerated. This strategy is mainly characterised by the complete removal of all surface defects and the full restoration of the target profile. It is mainly used when other methods are no longer applicable

due to the characteristics of the defects, but the rail still has sufficient wear reserves. After successful regeneration, a preventive strategy can be (re)adopted to maximise the remaining service life of the rail. With the application of this strategy, premature rail replacement can be successfully prevented.

For all the maintenance strategies mentioned above, it is absolutely necessary to determine the condition of the rail using appropriate measurement technology. The appropriate strategy combined with the correct amount of metal removal is only possible if the damage condition of the rails (transversal profile, longitudinal profile, crack depth) is known. Measurement technology is then also used to document the rail condition after the successful application of rail maintenance (quality control).

Milling technology for rail treatment

Apart from classic rail grinding (abrasive process), rail milling has become a key technology worldwide over the last 25 years. This maintenance technology cuts material out of the rail surface (dry process). The resulting chips are collected by a highly efficient suction system and are temporarily stored in a chip bunker on the milling machine. Compared to rail grinding, where grinding dust is distributed evenly in the vicinity of the track, milling transforms a "waste product" into a valuable, recyclable raw material. In addition, rail milling is a completely spark-free process. As a result, it can also be used in areas with a high risk of fire. Since the method is dust- and spark-free, rail milling can also be used in tunnels and similar environments. The variable material removal of 0.1 to a few mm per pass (depending on the machine size) enables the complete removal of deep surface defects as well as the full restoration of the rail target profile. The cutterhead (rotating cutting tool) defines the resulting profile. Therefore, required user interaction is minimal. Rail milling produces a precise transverse and longitudinal profile. Using an integrated polishing process, it also creates a rail surface that complies with the most stringent standards regarding surface roughness and permissible noise emissions. Rail milling is a gentle treatment process that avoids unwanted heat input into the rail surface.

Due to the characteristics listed above, rail milling is primarily a complementary technology to classic rail grinding, although there are certain overlapping areas where milling technology can replace or has already replaced rail grinding.

Innovative milling technology for North America

Plasser American will put the world’s first Romill Urban 3 E³ rail milling machine into operation in North America. This rail milling machine has been built by Robel and Schweerbau International. It was designed specifically for use in urban areas. Thanks to its compact design, it fits into the tightest tunnel clearances. In addition to numerous innovations concerning the milling technology itself, this machine integrates a hybrid drive concept on a rail milling machine for the first time. Thanks to the installed battery technology, it can work up to three hours without any emissions (no dust, sparks, or exhaust). The integrated diesel engine serves as a range extender and fast-charge station when in operation for longer. Of course, the batteries can also be charged externally.

With the Romill Urban 3 E³, Plasser American will primarily serve customers in urban areas (metros, light rails, trams), but it also has application scenarios for heavy haul conditions readily available. During the second half of 2022, the Romill Urban 3 E³ will begin operation in North America, using its state-of-the-art maintenance technology to sustainably maximise the service life of rails.

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