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Tamping technology: Key parameters under control

What matters when it comes to track tamping? What are the advantages of the renowned quality of Plasser & Theurer tamping machines? It is worth taking a closer look at the technology that ensures the lasting consolidation of the track bed.

The higher the level of quality and, particularly, sustainability of maintenance actions, the longer the intervals between maintenance operations. This seems to be a simple formula. Nonetheless, there are challenges track experts face in day-to-day track maintenance. The offer of machines and technologies has been constantly expanded, mostly triggered by economic aspects. But what matters when it comes to track tamping?

The track geometry is affected by many factors. In this article, we place a particular focus on levelling, lifting, lining and tamping sleepers. 

Measuring during tamping. The safe tamping process starts with reliable measuring equipment on the machine. In recent decades, numerous procedures have been tested. The results have confirmed our decision: The best system is simple and robust. It must produce precise data under all conditions: rain, snow, vegetation or dust. This is why we use large measuring wheels, closed pendula housings and steel chords. Pendula determine the crossfall of the track, while steel chords determine the reference base for the longitudinal level and alignment of the track.

The 3-point method is used to measure the track geometry at three points on the machine before, during and after tamping. Our machines can work according to the precision method or the compensation method. The precision method uses correction values calculated in advance, while the compensation method uses only the machine’s chord length as reference base.

The ALC automatic guiding computer provides the machine with the information required for track geometry correction.

Positioned precisely. The lifting and lining unit places the track grid in the desired position. For this purpose, the bending line of the rails and the uniform distribution of forces is important. The distribution of the lifting forces is particularly vital in heavy concrete sleepers and turnout designs. Even in obstacles, we lift and line the rails with utmost precision. For this purpose, we offer a vast range of lifting and lining units for tracks and turnouts.

Why does the track need to be tamped?

Consisting of rails, sleepers and ballast, tracks form an elastic system. Traffic loads subject this system to enormous dynamic forces causing the entire track to deflect and return to its original position. In the long run, these high stresses lead to deviations from the ideal track position. 

If the track quality falls below a certain level, the track must be maintained. To restore the ideal track position, a tamping machine is used to level, lift, line and tamp the track. This measure aims at ensuring safe operation and, thus, the customers’ satisfaction. Delays in maintenance lead to speed restrictions hindering rail traffic.

Lasting consolidation. We tamp the track to fix the corrections in the track geometry. To ensure this, no parameter is left to chance. Every Plasser & Theurer tamping unit is the result of more than six decades of experience and countless development studies. A decisive step in this development was non-synchronous uniform-pressure tamping. This principle enables all tines to work with the same pressure within the hydraulic system.

Safe tamping process. Plasser & Theurer tamping technology ensures the durable consolidation of the sleeper bed. High-quality mechanical components combined with high-precision hydraulics ensure the consistent quality of the work performed. Brought to perfection in further development, this principle has proven its efficiency under varied ballast conditions and in different track structures around the world.

Key parameters for a stable sleeper bed

  • Squeeze frequency of 35 Hz at the tamping tines
  • Tamping force (static) 10 to 12 kN
  • Squeeze time 0.8 to 1.2 sec.
  • Amplitude of 4 to 5 mm

Are you interested in more detailed information on tamping technology?

Order the technology brochure “The safe tamping process” from our series “Technology -> Our knowledge for your benefit”.