Rail replacement and track maintenance on the Shinkansen network
Track possessions on Japanese high-speed lines are short – rails and sleepers must be exchanged within a few hours. There are no line closures for maintenance work. This is why staff, machines, and design engineers must meet particularly high requirements.
Speed and perfection according to schedule
Japan is a prime example for speed and precision in rail traffic. There is nowhere else in the world where trains run at such high speeds and where they are on time with such a high level of consistency. On average, 270,000 passengers are transported on the Tōhoku Shinkansen every day between 6:00 AM and midnight. Maintenance work on the infrastructure is expected to be performed with the same level of punctuality. A time window from midnight to 5 AM is scheduled for track maintenance. Due to the maintenance vehicles’ long travelling times to the worksite, the time window effectively available for maintenance work is 150 minutes.
Before the track is reopened for the first high-speed train, the entire line is scanned by inspection vehicles, which search for tools or other objects that were left in the track but do not belong there. On the Shinkansen, temporary or long-time speed restrictions are not an option, It is perfection according to plan – even when maintaining the track or exchanging rails or sleepers.
REX-S Rail Exchange System
Optimal planning and excellent technological support are in demand. Together with the partner companies Nippon Plasser and ROBEL Bahnbaumaschinen GmbH (Freilassing, Germany), Plasser & Theurer supplied the REX-S 1200 rail exchange system in late 2016, after two years of development and construction. It uniquely combines transporting, depositing, and welding rails. Due to the short time windows, a complete exchange of the rails is not possible. Therefore, 150 m long rail sections are pre-deposited and the APT 1500 RA mobile flash-butt welding machine welds them on a section of up to twice 1200 m. In addition, the rails are ground and fixed. During a second night-time track possession, the old material is exchanged with new material within 30 minutes using two REX-S special vehicles, and the rail ends are joined with pre-tension – also using the APT 1500 RA welding robot.
Strict requirements for machines
For the first time since the Tōhoku Shinkansen of East Japan Railway Corporation (JR East) was put into operation in June 1982, the rails are being exchanged. The works started in February 2017. They are scheduled to be completed by 2026. Using the REX-S, the length of the rails to be installed was increased fourfold. At the same time, the welding time per joint was reduced from 40 to about 6 minutes.
The specially designed REX-S machine formation for 1,435 mm standard gauge consists of a traction vehicle – a modified SILAD loading and unloading train for twenty rails up to 150 m in length by ROBEL – two rail unloading and positioning wagons, and an APT 1500 RA welding machine in lightweight design. All machines reach the worksite at the same time. The machine had to be designed according to certain specifications: To fit in the parking space at the Japanese depots, the REX-S must not exceed a total length of 230 m. The distance between the bogie pivots must not exceed 14.4 m. Their maximum axle loads are limited to 15 t.
Welding on narrow-gauge tracks
In 2015, Plasser & Theurer supplied an APT 1500 RA for the operation on 1,067 mm narrow gauge tracks to JR Kyushu. The maintenance windows are not as short as on JR East’s Shinkansen tracks; the technological requirements, however, are similar. Before we were able to launch the innovative electric flash-butt welding process on the market – a type of method new in Japan – we had to provide extensive quality certificates. The welding method traditionally used in Japan is similar to the flash-butt welding process, but uses a gas burner. This is why the critical welding heat-affected zone in the rails is unequally larger. To verify the consistently high welding quality during flash-butt welding, the welding machine was tested using rails from Japan, which were specifically delivered to Austria for testing. The Japanese Railway Technical Research Institute (RTRI) checked the results. A second verification concerned tension welding, which is required when replacing rails. A test rig was set up in our factory specifically for this purpose.
Exchange of sleepers without exchange of rails
JR East had to exchange rails, JR West had to exchange sleepers. For these works, Plasser & Theurer supplied a special unit to Japan in 2015: The SES 170 continuous action sleeper exchange system. It exchanges old sleepers with new sleepers within intervals of 20 seconds, without spreading or cutting the rails. Following preparatory work such as loosening rail fastenings, and vacuum excavating the ballast, the old sleepers are turned underneath the rails and removed. Prior to installation of the new sleepers, the ballast formation is levelled. The new sleepers are significantly larger and heavier than standard European sleepers and are placed at less of a distance. Moreover, there are two types of sleepers – with and without cable bushing. A gantry crane on the SES 170 brings new material in and removes old sleepers. Close to the place of installation, the machine has three sleeper tables. The SES places the ballast previously removed by the vacuum excavator into the track wherever required. Following behind, a tamping machine and a ballast profiling machine finish the track.
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