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Quiet rails thanks to ATMO ​

​Rail grinding helps prevent unwanted noise, vibrations, and consequential damages. Plasser & Theurer’s newly developed rail grinder for operations in tramway and urban railway networks combines two work processes. ​

Rail surfaces need to be regularly inspected and maintained, just like track and substructure. Waves, corrugations, and other defects on the surface of the rails occur over time and cause structure-borne noise and airborne noise emissions. This is particularly unpleasant in urban areas. The acoustic emissions that inevitably result from rail head and running edge damage affect people’s health. According to the World Health Organization (WHO), noise pollution is one of the greatest environmental hazards. It negatively affects people’s physical and mental health. Preventive rail surface maintenance is essential for reducing traffic noise; it is caused, in part, by rail traffic. This maintenance method prevents loss of comfort for passengers as well as consequential damages for lineside residents, infrastructure, and vehicles. The grinding stones of special rail grinding vehicles have proven to be effective for preventive maintenance and acoustic rail grinding in urban areas. Plasser & Theurer recently developed the ATMO rail grinding trailer (Automatic Track Machine Oscillator) for urban tramway networks. It combines the sliding grinding method and the oscillating grinding method.

Acoustic grinding and preventive rail grinding

The noise emitted by rail vehicles at lower and medium speeds depends strongly on the condition of the contact surface between wheel and rail. The rolling of the wheel is the main cause of this noise. Acoustic grinding can help reduce noise. The ATMO rail grinding trailer grinds the rail head. The result are smooth grooved and Vignole rails. The reduced dynamic excitation of the wheel significantly reduces rail wear and noise emissions.

Regular preventive maintenance in the form of preventive rail grinding reduces emissions and lowers costs in the long term: prevent rail head defects early on, use rails longer. Eliminate consequential damage to infrastructure and costly repairs. Extend intervals between maintenance operations.

By the way, cleaning tramway rails of leaf litter and the oily film it produces also benefits safety as it reduces braking distance. Shorter braking distances are a different kind of preventive measure. Another positive effect of using the machine is that it grinds new rail sections by removing rolling skin on the rail head.

Rail grinding trailer for tram networks

The new rail grinding trailer designed for tram networks grinds plain track and turnouts. A power wagon or road-rail vehicle tows it to the worksite. No staff is required on the flat rail grinding trailer. The ATMO grinds at travelling speeds of up to 30 km/h and can be used in normal tram traffic. Grinding is equally possible in both directions of travel. In view of rising passenger numbers, public transport providers increasingly operate 24 hours a day. This leaves hardly any time for scheduled track possessions or routine maintenance. Nevertheless, preventive rail grinding is essential, especially with increasing traffic volumes. That is why the ATMO power wagon duo will blend seamlessly into normal traffic without interrupting vehicles en route. While developing the rail grinding trailer, a challenge was how to work in track curves. Compared to heavy rail, urban rail networks often have relatively tight radii. The new rail grinding trailer can travel along radii as small as 16.25 m and can grind radii down to 17.25 m. When travelling along curves, the grinding stones are aligned in relation to the radius so that they are always positioned above the rail head. This allows them to work freely through possible raised pavements in sections with grooved rails, also in tight radii. In the past, this presented an issue for some rail grinding machines. Unlike with conventional grinding vehicles, there is no need to lift the grinding stones when passing over turnouts and crossings. The machine is equipped with a 2,800 L water tank for wet grinding. A thin water film supports the rail grinding process and improves results. It also prevents flying sparks that pose a fire hazard in dry surroundings and tunnels.

Oscillating and sliding grinding

This machine, the first of its kind, combines the oscillating grinding with the classic sliding grinding method. Sliding grinding is also possible at high travelling speeds. However, the oscillating method increases rail grinding by at least 8 km/h. Increases in oscillating grinding speed are being tested. During oscillating rail grinding, a hydraulic mechanism moves the grinding saddles horizontally, in the longitudinal direction of the rails, back and forth with variable frequency. Each saddle features two grinding stones per side, making grinding of the rail head more precise. Additionally, they remove more material in a single pass as compared to the sliding grinding method. Oscillating grinding is recommended especially for areas prone to developing rail defects. Examples include stations or stops where waves form or other "hotspots" where corrugations occur. The ATMO employs a water-cooled, sound-insulated 100 kW Deutz diesel engine with exhaust after-treatment that meets the Euro 5 emission standard.

The research project and practical tests

The ATMO rail grinding trailer is the result of a unique collaboration between industry partners, university experts, and infrastructure operators. This project started in 2016 as part of the EU-wide Shift2Rail research initiative. It is oriented towards tram and light rail operation. A needs assessment conducted by the Vienna University of Technology forms the project's scientific basis. This assessment addresses the growing challenges of maintaining rails in urban areas. Plasser & Theurer, the industry partner, provided the know-how that shaped the ATMO's design and manufacture. In short, university experts do the research, Plasser & Theurer develops the prototype, urban transport companies use it, and residents enjoy the peace and quiet.

In May 2020, Plasser & Theurer began to tweak its prototype at the factory in Linz. This was followed by practical tests simulating various conditions on tramway tracks. We expect the following findings from the various test series and practical operations (starting with standard gauge): ideal frequency and amplitude for oscillating operation, best working speed, vertical load and selection of grinding stones that are equally well suited for both grinding methods. Of course we also perform sound measurements as well as comparative tests on the track prior to and after rail grinding.

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