Figure 1: Coach 1 Floor Plan
Investigation Into The Removal Of Leaf Contamination Using A Train Mounted Laser.
A very successful trial which clearly demonstrated the potential for the use of lasers to remove leaf, oil, grease, ice, and rust contamination from the rail head to restore electrical contact and substantially improve adhesion.
This will now lead to the development of a train mounted unit and a vehicle mounted unit.
Introduction
Main Objectives Of The Trial
The Trial
The Laser System
Railhead Delivery
Leaf Contamination
Laser And Rail Safety
ResultsSafety
Removal Of Leaf Contamination
Removal Of Other Contamination
Conductivity And Interaction With Signals Infrastructure
The Effect Of Laser Radiation On The Track Surface
‘Leaves on the line’ is a term that attracts ridicule yet the problem is real and can be serious. Autumn leaves get caught under train wheels and compressed onto the track, resulting in a black coating of the running surface of the rail. This black ‘teflon-type’ coating causes two problems; a lack of adhesion which causes trains to pass signals set at danger (SPADS) and over-run stations; and, a loss of electrical contact within the signalling system causing the train to be ‘lost.’
The first idea of using lasers to solve this problem was conceived in 1998. Initial laboratory experiments were commissioned which showed lasers could be used for this purpose but also raised questions of practicality. A track side demonstration of the idea to Railtrack senior managers in November 1999 convinced everyone of the merits of running a full scale trial in the autumn of 2000.
The original concept was for lasers to be mounted on commercial rail transport to keep the ‘Leaf problem’ under control. The trial carried out during the autumn of 2000 was specifically designed to test that premise.
Whilst much has been written about leaves on the line it was apparent from our background reading and enquiries that there were gaps in the knowledge base. Those gaps were particularly in the areas of what were the optimum conditions for the formation of the problem and why the problem recurs so quickly. It was therefore necessary to combine some investigation of these issues into the trial.
Readers should note this report is a summary in lay terms of the conduct and findings of the trial. A full technical report has been compiled but will only have a limited distribution due to the commercially confidential nature of the contents.
The main objectives for the trial were to:
Initially the trial was planned for twelve consecutive Sundays from mid October to be carried out on a section of main line between Effingham Junction and Leatherhead (Bookham). The first trial day was carried out on the Bookham section with Railtrack signalling and engineering managers in attendance. However, the sad events of the Hatfield train crash and the consequent disruption to all rail services resulted in a major review of the trial, as the allocated section of line was needed for diverted traffic.
The Mid Hants Railway, a private line of about 11 miles mainly used for steam trains, were able to make a four mile section of their line available for the trial to continue. As their track was not electrified they also provided a diesel locomotive to move the two-car EPB unit provided by Railtrack. The Mid Hants Railway line was used for a concentrated two week period.
A final trial day was carried out on the main line at Bookham in mid December. This was a welcome and important final opportunity to demonstrate the laser in use on Railtrack main line.
It was expected that a variety of weather situations would occur during the trial days but that was not the case. The autumn of 2000 proved to be a very wet period and the predominant weather throughout the trial was either rain, often heavy, or damp and wet conditions. In either case the leaves by the side of the track were heavy with moisture. Dry conditions with dry or only moist leaves were only rarely seen.
Part of the trial plan was to experiment with ‘Spotting’ the track. This entailed delivering a 2cm diameter circular beam on to the track at a pre-determined rate but not to achieve a continuously clean strip of track. The theory to be tested was that the natural action of the friction of the wheel on the track between the ‘Spots’ might cause the contamination to be displaced, thus joining the ‘Spots’ up. In addition, we wished to see if the ‘Spots’ would provide sufficient electrical contact to restore signalling circuitry. In the event the weather conditions prevented any meaningful testing of these hypotheses.
Close communication was maintained with the signalman throughout the main line trials. At no time were any problems or unusual occurrences reported. Attached as Appendix III is a report on the absence of any adverse effect on the signalling system when the laser was operating.
Tests to measure electrical conductivity and the restoration of trackside signalling after the laser had been used to remove contamination were carried out on the Mid Hants line.
In addition to the principle reason for the trial, removal of leaf contamination, it was decided to consider the potential of the laser removing other track contaminants such as oil, grease, water, ice, and rust.
The set-up for the trial consisted of a two car electric train unit being converted to a class IV laser laboratory, including a generator and chiller unit. Figures 1 and 2 show the set-up of the unit. The laser beam was directed into a six mirror adjustable arm down a tube through the floor of the carriage to the track. A shielding device was placed at the end of the tube where the laser beam met the railhead to screen the process and contain the laser beam. The laser selected for the trial allowed for a range of set-ups thus providing maximum flexibility in experimenting with the configuration of the system.
Figure 1: Coach 1 Floor Plan
Figure2: Coach 2 Floor Plan
The laser beam was directed down a tube to the railhead via a number of mirrors. At the railhead the beam was aligned onto the pinch point (section of rail that the wheel of the train actually comes into contact with). A screening device was positioned to prevent the beam reflecting off the line and into the surrounding area. The screening device was satisfactory but it was recognised before the start of the trial that a more robust and comprehensive device would need to be developed for the final product.
Careful inspection of the main line at the start of each trial day did reveal some leaf contamination but it was patchy and insufficient for trial purposes. The lack of contamination was put down to the unduly wet conditions. The Mid Hants line again had some contamination but not enough for trial purposes.
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In view of the lack of contamination it was necessary to cause contamination by running the train up and down the line. Careful note was taken of the conditions, the number of passes and the results. Video camera footage of the production of leaf contamination was taken.
It was noted that it only took four or five passes of the train travelling at around 40 mph to create heavy contamination. Indeed we were so effective at being able to re-create the problem that on one occasion the train was unable to stop for approximately 500metres due to lack of adhesion.
Careful study of the passing train from the trackside also established that the vortex created by the moving train ‘sucked’ the leaves onto the track and under the wheels of the train. Figure 3 clearly shows this effect.
The experiments to re-create the leaf problem led to five categories of contamination being identified. These are described as follows:
Type 0Figure 4 Covers all lightly spotted and transparent contamination on the pinch point. Such as water, light rust, thin leaf contamination, oil, etc. |
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Type IFigure 5. A single leaf pinned down to the rail by the action of only one or two of the rear wheels of a slow or fast moving train. The picture shows a leaf run over by one wheel at about 2 mph. The leaf retains its colour but is only weakly adhered to the pinch point and the debris is easy to remove with light rubbing or wetting. Type I is the first step in the generation of track contamination since, unless washed off, it will remain for a following train to compress it to form type II leaf contamination. |
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Type IIFigure 6. Single leaf run over more than once at high speed (ca 40-50 mph) by many wheels on a single pass of the train or by further compression of type I contamination by following trains. In this case there is a spread of blackened debris along the pinch point and compression of the bulk of the leaf out of the pinch point. |
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Type IIIHeavy leaf contamination built up after several high speed passes caused by an accumulation of type I & II contamination. In the example shown in Figure 7. The contamination was freshly made and shows skid marks as the train lost traction during breaking. This contamination was almost completely removed by heavy overnight rain, by rubbing with a damp cloth or by scraping with a sharp implement. |
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Type IVFigure 8 is a more persistent thick Type II debris from individual leaves left after a single night of heavy rain. This debris is strongly adhered to the track. The appearance of standing droplets of water only on the leaf debris indicated a reduction of water reaching the rail. This would be consistent with a component of the debris that is not miscible with water; for example plant oils. |
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Railtrack Acceptance Services and Railtrack Southern Zone issued Certificates of Authority for Product Trial in October 2000. The Certificates are reproduced as Appendices I and II.
All aspects of laser safety were controlled by an appointed Laser Responsible Officer from the Central Laser Facility (CLF). The laser laboratory was a class IV facility with failsafe switches at all points of entry and at critical points of the laser operation. In addition to the screening device above the track all personnel working trackside while the laser was operating also wore safety goggles. Trials were mainly carried out in remote ‘enclosed’ locations.
Prior to the start of the trial the CLF performed laboratory experiments to determine the effect of the laser beam on the surface of the rail. The conclusion was that it would take approximately 800 years of continuous operation of the laser beam on the same track before any damage to the rail would occur.
During the first day’s trial a Railtrack Senior Track Engineer carefully inspected the track and could discern no damage or change in the track at all. No damage to the track occurred during any of the experiments.
The trials were completed safely and without incident or accident.
The trials clearly demonstrated that lasers can be used to remove leaf contamination from the railhead. As might be expected, there was a clear relationship between the grade of contamination and the effectiveness of the laser. It was also clear that the desired speed of the train significantly influenced the effectiveness of the laser cleaning process. There is a clear trade off between the power, set-up, and beam size of the laser against the desired speed of the train. The relationship of these factors was identified and a table produced to show the laser set-up requirements against desired speed. Results included:
Experiments clearly demonstrated the potential for using lasers to remove oil, grease, ice, water and rust from the track surface. It must be stressed that the thickness and degree of translucence of the contaminant will influence the effectiveness of the ablation process. It is therefore more likely to be effective using a portable unit to solve a ‘local’ problem.
Trials on the Mid Hants line clearly demonstrated the ease with which the laser restored signal circuitry, even when the track had only been ‘Spotted.’ Railtrack signalling staff could find no disruption of any kind to their systems when the laser was being operated. Specifically, it was reported that:
A senior Railtrack engineer carefully inspected the track surface and could find no damage to any part of the track.
We wish to thank the staff of Railtrack Headquarters and Railtrack Southern Zone for their unstinting support and co-operation during a period of immense difficulty for the rail industry.
We wish to thank the staff of South West Trains who operated the ECB unit and assisted in many ways when the unit was being fitted out at Wimbledon.
We are most grateful to the staff of the Mid Hants Railway who responded so quickly and helpfully in providing an alternative site for trials.
The trials and the technical report could not have been achieved without the very able and willing work of the staff from the Central Laser Facility of the CLRC Rutherford Appleton Laboratory at Chilton and we are most grateful to them for their efforts.
We are most grateful to Spectron Laser Systems Limited who provided the laser for the trial on a free loan basis, and who also provided other assistance prior to the commencement of the trial.
We wish to thank and to fully acknowledge the considerable contribution to the planning, pre trial preparation, running of the trial, and post trial evaluation provided by PMC Consultants Ltd
