Figure 1
A Report On The Research Carried Out In 2001 Into The Removal Of Railhead Contamination Using A Train Mounted Laser
A productive year in which many safety issues were addressed and resolved, and a new laser was tested.
Introduction
Choice Of Laser
Railhead Delivery System
Pre Trial Work
Autumn Trials
Other Project Work
Conclusions
Recommendations
Acknowledgements
References
Annex A - Objectives For Autumn 2001 Trial
Overall objectives:
Technical Objectives:
Business Objectives
Marketing
The idea to use a laser to remove leaf contamination from the railhead was first conceived in 1998. After some elementary laboratory experiments a demonstration of the potential use of lasers was provided to senior Railtrack managers in November 1999. This lead to Railtrack providing an EPB unit and access to main line track for train-based trials to be carried out in the autumn of 2000.
The autumn trials were successful in demonstrating the ability of a laser system mounted on a train being used to remove leaf contamination and provide a clean dry track, thus solving the adhesion problem and restoring track circuits. The trials also showed the laser system could remove other forms of railhead contamination such as oil, grease, ice, and water, leaving a clean dry surface.
Despite the success of the trials it was apparent that a different laser would be needed for the final product. The laser used for the trials was essentially a laboratory tool and not suited to meeting the harsh requirements of a railway environment. The choice of laser is discussed in detail below.
With Railtrack support trials and final testing were planned for autumn 2001. Matters were progressing well until the unexpected and untimely death of our Technical Director in the early summer. The sad loss of an extremely able person occupying a key position severely disrupted preparations for the forthcoming trials. As a consequence orders for key components were placed late which inevitably impacted on the start and subsequent conduct of the trials.
Nevertheless, substantial work was achieved and many issues, particularly safety related, were investigated and resolved.
Readers should note this report is a summary in lay terms of the conduct and findings of the trial. Two detailed technical reports have been compiled but will only have limited distribution due to the commercially confidential nature of the contents.
The basic specification of the laser was determined in the original laboratory work carried out in 1999. The medium used to generate laser light, the wavelength of the light, and the requirement for a pulsed beam were all established. Issues that remained elusive were the length of the pulse, the peak power requirement, delivering the beam to the railhead, and ensuring the whole system could be operated safely in a railway environment.
The autumn 2000 trials demonstrated very effectively that a short-pulsed system was efficient at removing leaf contamination. However, it also identified limitations and difficulties, in particular: the laser was unlikely to be suitable for the railway environment, delivery of the beam safely to the railhead would be challenging, and it was unlikely that cleaning rates of more than 2 or 3 mph could be achieved.
Investigations into alternative solutions led to some experiments in a private laboratory using a laser with a longer pulse but much faster repetition rate. The results showed promise and the decision was taken to find a suitable laser for testing in autumn 2001.
A laser development laboratory was found that was capable of building a laser to meet our requirements. At that time no such laser, combining such high power output with pulsed beams delivered down fibre optics, had been built. The potential advantages of this emerging technology were:
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However, there were also some potential disadvantages that had to be considered:
Nevertheless, it was felt there was sufficient potential in the new technology to proceed with the trials and a new laser, Figure 1, was purchased.
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The set up for the optics, which were used to shape and focus the beam, also required a new design. The combination of the significant concentrations of power in each pulse together with the high pulse repetition rate meant that conventional devices could not be used as a practical application in this case. In any case conventional devices were designed for laboratory use and would not survive the railway environment, especially as they would have to be fitted close to the railhead. To overcome these issues a fixed lens arrangement was used incorporating a state of the art ‘micro step’ mirror; collectively known as the optics box.
The fibre optic connected to the optics box via the black cylindrical tube shown in the Figure 2. The laser beam was then directed through the box, exiting via a protective glass shield onto the track. The red line shown in the photograph illustrates the direction and width of the beam. The handles were removed for ease of fitment.
Experience gained from the Autumn 2000 trials meant it was a relatively straightforward matter to design effective safety procedures for the safe operation of the new laser. The requirement was to design a railhead delivery system (RHDS) that would meet the requirements of Class I laser legislation1.
W S Atkins (Rail) Ltd (WSA) were contracted to design and build a suitable RHDS. The RHDS had to meet the Class I laser requirement, be suitable and accepted for use in the railway environment by Railtrack, and be fitted with a variety of monitoring sensors. The monitoring sensors were to be linked to the laser as safety cut-outs in the event of all or part of the RHDS becoming detached from the bogie, or moving beyond pre-determined tolerances out of alignment, and for detecting gaps in the rail such as points or joints.
The RHDS was mounted at one end of the bogie set and attached to the bogie via a welded base plate and bolts. The arrangement proved robust and withstood the railway environment. However, there was significant movement laterally and vertically of the unit which made it difficult to maintain alignment and accurate focussing of the laser beam. It was recognised that positioning between the wheel sets of the bogie should be explored in the future as it may reduce the adverse motions.
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As part of our general progress towards producing a product WSA were appointed to carry out a Hazard Analysis and Operability Study (HAZOP). The HAZOP study identified a number of issues that required investigation. These issues were divided into those that had to be included within the autumn trial, and those that could be looked into before the start of the trial.
CCLRC Rutherford Appleton Laboratory, Lasers for Science Facility (RAL) were appointed to determine what effect, if any, there was on block joints when exposed to the laser beam. Their report [2] concluded that whilst there was some blackening of the surface of the block joint it was only superficial, and that there was no conductivity across the ablated section, although under extreme conditions there may be the possibility to induce damage the level of operation has been specified to prevent this.
RAL were also appointed to carry out a series of experiments to determine if any damage occurred to the clean railhead when repeatedly exposed to the laser beam. Samples of rail were obtained, uniquely marked, and exposed to the laser beam at varying intensities and for varying lengths of time. The laser beam exposure varied from a single spot through to leaving the laser firing on the same spot continuously for one hour. The samples were then passed to Scientifics Ltd for expert metallurgical examination. Scientifics examined the laser-exposed samples under a microscope and compared them against control samples. The Scientifics report [3] found there was a range of observation from no apparent damage through to definite damage that was not conducive to the railway environment. However, it is clear from their findings that the threshold beyond which damage occurs is significantly higher than any process either envisaged or likely to arise with the chosen laser.
Another issue addressed before the autumn trial was an investigation into the potentially harmful effects to humans of fumes ablated from the railhead. RAL and Scientifics were appointed to obtain and analyse contaminants produced by ablation of diesel fuel oil, grease, 3rd rail anti-icing agent, and Sandite. Specifically, samples were analysed for: particulates, metals, volatile organic compounds, aldehydes and ketones, ozone, oxides of nitrogen, and oxides of carbon. The report [4] concluded, “Diesel exhaust fumes from the vehicle on which the laser is mounted are thought to be much more significant than any minor fumes caused by the action of the laser on rail head contamination.”
WSA developed a prototype RHDS, shown at Figure 3, which RAL then tested for light emission. This led to modification by adding an extra layer of bristles and inserting rubber sheeting between the layers of bristles.
Objectives for the trial are reproduced at Annex A. WSA were appointed to project manage the trial, with RAL appointed to provide all aspects of laser safety and laser operations.
Railtrack’s Infrastructure Safety Review Panel and Railtrack Southern Zone had given conditional approval for testing the laser system on main line track on five Sundays in the autumn period using the same EPB two car unit that had been used for the autumn 2000 trials. The conditional approval was that the system had to be proven to be laser safe to Class I before final approval would be granted and permission given to operate on main line. The work to test and prove Class I was carried out on the private Mid Hants Watercress Line in Hampshire.
One carriage of the EPB two car unit was used to house the laser and a generator to provide self-contained power. The laser half of the carriage was partitioned and equipped for use a Class IV laser laboratory in case the need arose. In the event the Class IV facility was not used. The laser beam was transferred to the railhead through an armoured fibre optic cable which connected to the optics box, which in turn was connected to the RHDS.
Late delivery of the laser, and even later delivery of the optics box delayed the start of the testing period. The delays also limited the time available in the laboratory to carry out pre trial testing and checking. A number of teething problems arose with the laser and the optics box was found to be incorrectly aligned, necessitating a return to the manufacturer for adjustment, causing further delay.
To prove the laser adhered to Class I specifications level it had to be shown that all safety interlocks were working and that there were no emissions from any part of the system, especially the RHDS. Laser safety throughout the system down to the RHDS was quickly established. However, the teething troubles with the laser and optics box slowed the process of determining the integrity of the RHDS and the operability of the sensors.
With the laser and optics box fully operational it was then possible to test the remaining elements of the system. Those tests showed that we had achieved the fitting of a laser system on to a train and operating the laser system at 5 mph in a safe manner that conformed to the laser emission regulations1 for a Class I laser. It is believed that this has not been achieved by anyone else before.
The testing and proving phase of the trial had taken much longer than anticipated. It was not possible to move to the main line as the main autumn leaf fall period had passed. Thus, further ablation work could not be carried out and a comparison of the laser used in autumn 2000 against the new laser could not be made. Nevertheless, important progress was made on many fronts that will contribute to the development of the final product.
Detailed technical reports were produced by RAL [5] and WSA [6] and are held under separate cover as their contents are commercially confidential.
A separate objective of the trial was to look into the wheel/rail aerodynamics. This work was carried out by the Wolfson Unit, Southampton University. Wolfson Unit produced a report [7] that indicated potential for developing another product, the nature of which is commercially confidential and so is not discussed any further in this report.
We wish to thank Railtrack Headquarters staff and Southern Zone staff for their considerable patience and support throughout this trial period.
Railway Safety provided some funding towards the cost of the initial HAZOP study and have continued to maintain an interest in the development of the system.
We are grateful to the staff of South West Trains for their assistance in moving the EPB unit and for the support from the Depot staff.
The staff of Mid Hants Railway are thanked for the provision of line and traction unit facilities, and for their co-operation and support.
Rutherford Appleton Laboratory staff continue to provide significant expertise and assistance to the project and they are particularly thanked for their contribution to the work carried out in 2001.
W S Atkins (Rail) Ltd staff made a significant contribution to the progress achieved last year, including the development of the RHDS, and are thanked for their assistance.
Fraunhofer Institut für Lasertechnik built the laser and developed and built the optics box used in the trials.
Scientifics Ltd carried two separate sets of analysis in a co-operative and professional manner.
Wolfson Unit, Southampton University carried out the aerodynamic trials that proved to be most successful.
Mickleover Engineering Ltd provided the Board of LaserThor with independent railway engineering advice and their contribution was greatly appreciated.
We also wish to thank the Dti for approving our Exceptional SMART Award application.
[1] BS EN 60825-1 1994 “Safety of Laser Products:
Part 1. Equipment Classification requirements and user guide.”
[2] RAL, Railhead Block-Joint Damage Tests, June 2001.
[3] Scientifics, Metallurgical Analysis of Laser Ablated
Railheads, 1 August 2001.
[4] Scientifics, Rail Laser System: Emissions
Monitoring, 30 November 2001.
[5] RAL, LaserThor Autumn Trials 2001, January 2002.
[6] WSA, V-MARC System 2001 Product Development Report,
14 January 2002.
[7] Wolfson Unit, Design and Trial of a Rail Wheel
Fairing to Deflect Leaves from the Rail, Report No. 1623, January 2002.
The autumn trial includes: all experiments carried out on the train and trackside, together with experiments carried out at RAL and other contracted scientific laboratories between the period 1 October and 31 December 2001.
