PROMISES of improved lifecycle and reduced capital costs, as well as reductions in the time that a specific track section is out of service, is convincing infrastructure managers to increasingly adopt preventative rail maintenance techniques.

For example, results from various projects show that corrugation, slip waves and rolling contact fatigue can be sustainably kept in check by regular treatment with Vossloh’s High Speed Grinding (HSG) technology.

The process removes defects at an early stage, preventing their development into something serious. In the long-term, preventive grinding also results in significantly lower “artificial wear” compared with the substantial material removal associated with the conventional grinding process which is carried out less frequently.

DB Networks has used HSG on high-speed and some mixed traffic lines since 2007. The machine operates at 80km/h, preventing the need for track possessions within the regular timetable.

However, HSG has previously been limited to grinding only conventional rails including level crossings, with grinding units retracted from the rail around 50m either side of the turnout to avoid potential damage to the grinding wheels in the frog gap. This left an untreated section of at least 180m (depending on the size of the turnout), the grinding of which had to be planned and coordinated separately.

In early 2013, DB Networks approached Vossloh with a view to developing the HSG system to include turnout grinding within the regular timetable. The infrastructure manager had the following three objectives in mind:

  • achieve a sustainable reduction in maintenance costs
  • reduce planning and time spent on operating and assembly instructions, and
  • exploit the benefits of HSG technology.

In order to benefit from these advantages in the medium term, a series of tests were carried out on various DB Networks’ lines between 2013 and 2015. The first turnout grinding tests were performed at Allersberg station on the Nuremberg - Ingolstadt line from July to December 2013. Tests were performed at various speeds, and the fundamental criteria for HSG deployment on turnouts was defined.

For the tests, only turnouts with a moveable-point frog were selected since these have neither guard rails nor a frog gap. Turnouts were passed both in trailing-point movement and in facing-point movement with identical material removal. The tests showed that there was no need to change the conventional HSG grinding process apart from raising the dust extraction system slightly above the top of rail in the same manner as at level crossings. Indeed, the straight track section of the turnout is fully machined by the lowered grinding wheels without any reduction in speed and this results in a continuous transverse profile.

The tests carried out early in 2015 were designed to examine grinding pattern, transverse profile, and potential contamination with grinding residue following the elevation of the dust extraction system along with possible cleaning options. For these tests, DB Network made two turnouts available: turnout 903 on the Bremen - Hamburg line at Oberneuland station, which was ground on February 2 2015; and turnout 6761 on the Halle - Lutherstadt Wittenberg line at Bitterfeld station on March 31 2015. The transverse profiles of both turnouts were in good condition.

HSG grinding patternIn each case, three passes were made during regular traffic and in dry conditions. Two of the passes were made with coarse grinding wheels and one was made with fine grinding wheels to arrive at a surface finish proven to prevent rolling contact fatigue. On both turnouts, it was possible to completely grind the straight track section including its connections with the frog and switch blade. Approximately 0.1mm of material was removed after three passes and the transverse profile was retained or even improved (Figure 1.)

The tests also showed that the air draft from regular trains passing over the turnout in either direction between the grinding passes has a substantial cleaning effect to the extent that hardly any grinding dust was found in the turnout. After completion of all work, a functional test was performed in agreement with the traffic controller which did not indicate any functional trouble.

To rule out the possibility of traffic interruptions occurring if no cleaning work is performed after turnout grinding, a long-term test in Goddelau is underway. Since October 2013, the accumulation of dirt has been observed both over several grinding cycles and during changing weather conditions with no interruptions in switch operation or train services reported thus far.

Following these positive results, since early 2016 Vossloh has been grinding both normal track and a total of 28 turnouts in several sections on both tracks on the Kassel - Fulda line. Approximately 300km will be ground three times each year.

However, successfully grinding the diverging track requires additional measures not available in the conventional HSG. As a result, Vossloh developed the Flexis system which meets the special requirements of any turnout while not imposing limits on the availability of the rail network.

Each of the system’s devices are hand-guided and can be removed and re-railed by two operators within the specified clearing time. Moreover, no switching and signalling equipment needs be removed during maintenance, and in contrast to the deployment of large machinery, Flexis can be used during track possessions lasting 10 minutes.


Flexis is designed to accommodate the peculiarities of any turnout when performing maintenance. For example, it can treat components that are out of reach of larger machines, such as the stock rail in case of an open point or the frog with lowered point and super-elevated wing rails.

Similarly, the maintenance team is able to examine each part of the turnout enabling them to treat individual components in line with specific requirements. Even in case of the more sensitive turnout components, the amount of material removed is adaptable to specific needs. For instance, Flexis allows full reprofiling of the frog, and, where required, specially-trained superstructure welders join the team to take care of any welding rework required.

HSGgraphBoth the number of machines and the number of operators are adaptable to the desired scope of work, and the deployment can be planned ahead. Depending on the assigned manpower, the time needed to grind a turnout can be reduced by as much as 40%.

Forward-planning is achieved through Flexis’ digital transverse profile gauge for the exact identification and recording of the transverse profile of the rail and a corrugation system for the precise measurement of the longitudinal profile. A rail height system developed by Vossloh measures the loss in the rail height, while the depth and distribution of cracks are identified with an eddy current tester. Turnout-specific templates and gauges are used.

Based on the recorded data, engineers calculate the required and economically expedient material removal. The rail grinding trolleys have a movable wheel base, so each device is adjustable to the existing track gauge. This ensures a uniform machining of the longitudinal and transverse profiles over the entire turnout.

The Flexis system has been deployed in several European countries for more than three years and has been approved by DB Networks for all lines and speeds. And in light of the results of the tests in Germany, Vossloh expects to obtain an unlimited user clearance for its HSG train according to DB Network’s operating regulations by the middle of next year. This update will mean that the HSG train can be commissioned without any special permits for the preventive grinding of turnouts with spring moveable frogs.

In 2017, the HSG train will also perform preventive grinding on turnouts on the Cologne Rhine - Frankurt high-speed line in the Cologne area. On this line, the rails of the tracks in both directions were replaced in 2015. Included in the plans for 2017 are the turnouts on the Erfurt - Leipzig/ Halle high-speed line.