Solutions

High Speed Grinding technology

Rail fault prevention during scheduled service

The contact forces from the rolling wheel cause a thin martensitic layer to form on the running surface. This layer, hardened by cold deformation, is approx. 0,1 mm thick and provides fertile ground for rolling contact fatigue damage. Due to high speeds and heavy axle loads, the initially micro-fine surface cracks grow exponentially into head checks and squats, especially on high-speed tracks. The now severe rail defects are spreading into the intact base material and can only be removed through substantial material removal, such as milling. 

Vossloh has completely reimagined mobile rail grinding for preventive maintenance that begins at the early stages of defect development. High Speed Grinding (HSG) is the first process worldwide that, thanks to its high working speed of up to 80 km/h, is excellently suited for: 

 

 

  • Increasing network capacity: For the first time, the speed of freight trains makes it possible to carry out preventive rail maintenance during scheduled service, completely eliminating the need for track closures. 

  • Maximizing rail service life: In a well-calibrated preventive cycle, HSG consistently removes only the metallurgically altered surface layer; the “healthy” substrate beneath remains untouched and free from thermal damage. 

  • Keeping noise levels low: The facet-free grinding pattern achieves an acoustically low rail roughness (Ra) of less than 10 μm, which also ensures a comfortable ride. 

 

 

This logistical advantage also translates into greater operational safety and network availability, while aligning with sustainably low and predictable maintenance costs. 

Noticeable acoustic impact

Two further features of HSG technology are particularly beneficial in local transportation: the combination of a rigid grinding beam and passive circumferential grinding stones positioned at an angle to the direction of travel ensures continuous improvement in longitudinal corrugation and thus counteracts the problem of noise-producing corrugation. Unlike conventional methods, the grinding stones in HSG are not driven by their own motors. On the contrary, the peripheral grinding wheels begin to rotate independently (passively driven) due to the inclined position of the grinding wheel axis relative to the longitudinal axis of the rail. With continuous, uniform, and controlled material removal of 0,1 mm in multiple passes, the abrasives remove more than just the brittle surface. The elongated contact line smooths out the beginnings of corrugations and slip waves. More frequent but minimal artificial wear preserves the wear reserve and enables a longer rail service life. In the long term, this leads to lower life cycle costs. 

Other areas of application

 

Initial grinding of new installations: A mill scale and initial-layer grind eliminates installation-related rail defects and provides the ideal starting point for preventive maintenance. In the long term, this results in enormous time and cost savings. 

  • Material removal of 0.2 mm in coarse grinding 
  • Low roughness (Ra <6–10 µm) for serial squat prevention using fine grinding stones 

 

Grinding intensity and performance are determined by the grinding vehicle’s speed and grinding pressure; removal rates can be easily scaled by increasing traction power or the number of grinding stones. During the grinding process, the circumferential surface of the cylindrical grinding stones becomes concave, enabling them to machine the crowned (convex) curved rail head. The areas in which material is to be removed are determined by adjusting the track setting of the grinding beam. 

Acoustic Grinding

The facet-free grinding pattern results in both noise reduction and improved ride comfort for passengers following rail treatment.

Since 2011, the HSG grinding train has been approved for BüG maintenance ("specially monitored track") and is therefore an economical alternative to acoustic rail grinding with sliding stones. Compliance with the requirements of EN ISO 3095 has been verified. 

Lubricant film removal

Especially due to leaf debris and airborne contaminants—or following extended dry periods – rainfall can lead to the formation of lubricant films on the rail surface. Lubricant film grinding improves the friction between the wheel and the rail and increases electrical conductivity. 

  • improved switch control 
  • lower noise emissions 
  • improved traction

 

Tunnel grinding

During operations in the Gotthard Base Tunnel in October 2016, six grinding runs were carried out, each covering a distance of 61 km (366 km in total). At the customer's request, three shifts with a total of twelve grinding runs (approx. 240 km grinding distance per shift) were planned and implemented during the second deployment in May 2017.

 

Challenges: 

  • Temperatures of up to 37°C and a maximum gradient of 7‰ (despite flat track construction) 

  • While thermal track maintenance machines may have to leave the tunnel to cool down or reduce their output after a certain period of operation, the HSG was able to work non-stop on the tunnel section of approx. 57 km plus 4 km on the open new line in each direction. 

  • A mineral-reinforced composite material is used for dust collection in HSG machines. The patented material meets all requirements for temperature resistance, wear resistance, damage tolerance, etc., necessary for safe railway operation. Since it is non-metallic, the dust collector does not interfere with any of the switching devices attached to the rail or in the center of the track. Unlike conventional grinding methods, HSG leaves the structure gauge of the tracks completely intact. Planning is further simplified without the need for time-consuming dismantling and reassembly of the switching equipment, and operational disruptions due to delays, which cannot be ruled out during track installation work, are avoided. 

Possible carrying of water tanks if operators are concerned about flying sparks grinding in dry conditions: thanks to the irrigation concept, the HSG-2 can also grind at fire protection level 4. Flexibly connected as needed, embankments are watered on both sides in an area of up to 4 m during grinding.

 

 

Turnout grinding

 

  • Turnouts with movable frogs without wheel guides have been ground through in Germany since 2017. 

  • Depending on requirements, the diverging track, the switch blade, and the frog are reworked with Flexis. 

  • To safely pass over track installations, the dust extraction system is slightly raised during grinding of turnouts and level crossings. 

 

Zero-emission grinding in Shenzhen

By connecting to an electric traction unit, three compact hybrid grinding machines are are performing emission-free grinding for the Shenzhen Metro for the first time. Another advantage is that they can be controlled by just one operator. This enables: 

 

  • greater range, 

  • threefold material removal, or 

  • a combination of coarse and fine grinding stones to achieve both removal and fine grinding in a single pass. 

 

Functionality & Performance

With three passes, shift outputs of up to 100 km are achievable without disrupting regular rail operations. This is because the metal volume removed using the HSG process is 260 g per second and rail. That is up to four times more than with conventional methods. 

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