Ballast cleaning machines

Regular ballast cleaning of tracks and turnouts can be a prerequisite for the economic operation of railway permanent way.
A clean, elastic and homogeneous ballast bed is an absolute essential for problem-free functioning of the wheel on rail system. This is gaining importance, particularly on high speed lines and other highly loaded sections of track.  

The most important functions of the ballast bed

Characteristic wear pattern by ballast break-up
Characteristic wear pattern by ballast break-up
© Fabian Hansmann
  • Uniform distribution of the wheel loads on the subgrade.
  • Ensure the track elasticity to reduce the dynamic forces and provide a solid and immovable position of the sleepers.
  • Easy restoration and conservation of the track geometry obtained during track maintenance.
  • Good permeability and ventilation to ensure a long service life of the sleepers and avoidance of frost heaves.

Neglected ballast cleaning can lead to extremely high maintenance costs, speed restrictions and a lower service life of the permanent way. The follow-up costs can then be far higher than the costs of a timely ballast cleaning.

Contaminated track = no water drainage = reduced durability of the track bed  

Various causes of fouling:

Increase of the percentage of fine-grained material caused by chipping, aggregate displacement and friction caused by the normal operating load bringing up material from the subgrade, transport and environmental influences.

As a result, the friction between the ballast stones falls, the pressure distribution angle is reduced and the pressure on the subgrade rises. Fouling reduces the elasticity of the track and consequently the durability of the track geometry. The decreased ability to drain off water also has a negative influence on the state of the track geometry, wooden sleepers and the ballast material.

Ballast cleaning today:

Further development has produced the current generation of ballast cleaning machines from Plasser & Theurer, RM 76 UHR as well as RM 80 U for tracks and turnouts. A further step led to the development of even more powerful cleaning machines for tracks, which meet today's highest requirements, the series RM 800/RM 900.  

Ballast cleaning in turnouts with RM 80 U, ballast cleaning with supply of new ballast:

Due to the high proportion of spoil discarded after using the ballast cleaning machine, it is often necessary to place additional ballast in the track. Therefore, Plasser & Theurer has designed and built the latest generation of ballast cleaning machines, the RM 802, RM 900 and RM 95. These machines are capable of adding new ballast from the MFS type material conveyor and hopper units, together with cleaned ballast in the course of ballast cleaning. The proportion of new ballast can be metered accurately appropriate to the specific situation.  

Bild von Fa. Plasser&Theurer
RM 802
© Plasser&Theurer

The equipment

The excavating unit:

Digging chain with five scraper fingers
Digging chain with five scraper fingers
© Plasser & Theurer

The excavating unit is designed so that the entire subgrade is completed in one operation. Excavating widths up to 8 m are possible, depending on the design. The chains consist basically of scraper plates with 2 to 5 fingers, connecting links and bolts. The fingers loosen the encrusted material, the scraper plates lift and convey the material into the chain guides directly up to the screening unit. This process already loosens the spoil from the ballast.  

Schematic representation of the excavation chain
Schematic representation of the excavation chain
© Plasser & Theurer

The chain is guided underneath the track in a cutter bar. This enables an exact, straight cut over the entire excavating width in one operation. In this way the necessary cross-fall of the subgrade can be produced accurately. For an even faster preparation, the excavating units of some machines can be fitted with hydraulic quick release fastenings.  

The screening unit:

Triple deck vibration screening unit with three screening levels:

  • 1st level: separation of over-sized stones.
  • 2nd level: recovery of medium-sized stones.
  • 3nd level: recovery of small stones, separation of fine particles.

The results of the screening using ballast cleaning machines made by Plasser & Theurer are excellent as the fine grain proportion is often lower than in new ballast. When working on superelevation in track curves, the screening unit can always be held horizontally with the help of hydraulic cylinders.

The placement of ballast

The cleaned ballast coming from the screening unit can be transported via hydraulically adjustable baffles and slewing distributor conveyor belts or unloaded directly into the track. This technology of ballast placement allows the height of the track to be regulated exactly.  

 

Bild von Fa. Plasser&Theurer
Placement of ballast
© Plasser&Theurer

Sleeper end consolidation:

After the track has been filled with cleaned ballast, the ballast is compacted around the sleeper ends. This achieves an immediate fixation of the skeleton track in the cleaned ballast bed.

Bild von Fa. Plasser&Theurer
Sleeper end consolidation
© Plasser&Theurer

Completely hydraulically powered high-capacity ballast cleaning machine for tracks with supply of new ballast.  

Drive and screening car:

  • Cabin with driver's control desk.
  • Engine and hydraulic system.
  • Spoil conveyor belt, transfer conveyor belt can be swivelled out and retracted in for transfer travel.
  • Two eccentric oscillating screens.
  • Conveyor belts for excavated material and cleaned Ballast.

Excavating car:

  • High-performance excavating chain.
  • Crane for assembling chain cutter bar.
  • Track lifting and slewing devices.
  • Conveyor belts for the transport of excavated material to the screening cars.
  • Return transport of the cleaned ballast and transport of new ballast.
  • Ballast hopper for cleaned ballast.
  • Slewing distribution conveyor belt for the placement of ballast.
  • Ballast placement shaft for the introduction of new ballast.
  • Ballast distributing and regulating plough.
  • Device for compacting the ballast that has been brought.
  • Cab in front of the excavating chain and for the introduction of new ballast.

Trailer:

Trailer with new ballast supply
Trailer with new ballast supply
© Plasser & Theurer
  • Sweeper brush with transverse conveyor belt.
  • Conveyor belts for the transport of the new ballast from the MFS units to lift cars.
  • Track geometry measuring system.
  • Drive engine and hydraulic system.
  • Cabin with driver's control desk.
  • Measuring, control and recording units for excavation depth, formation crossfall, track settlement as well as cross level, twisting and versine.

You can find suitable specialist literature to the topic here:

The Basic Principles of Mechanised Track Maintenance

The Basic Principles of Mechanised Track Maintenance

This book is dedicated to the many people involved in the day to day planning and performance of track maintenance activities. Providing a practical approach to everyday challenges in mechanised track maintenance, it is not just intended as a theoretical approach to the track system. 
Railways aim at transporting people and freight safely, rapidly, regularly, comfortably and on time from one place to another. This book is directed to track infrastructure departments contributing to the above objective by ensuring the track infrastructure’s reliability, availability, maintainability and safety – denoted by the acronym RAMS. Regular, effective and affordable track maintenance enable RAMS to be achieved.