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Do lasers have the answer to railhead contamination? Tests look promising
When it comes to whizzo equipment that will solve the railway industry's most intractable problems this column's default setting is Didimus-mode. So when I was invited to Bicester in September by a one-man start-up firm called Laserthor to see a laser-based railhead conditioning system, the most I expected was a jolly day out observing Mr Shooter's railway at work.
Equally, as with Diaghelev, you always hope to be amazed and after a presentation by Laserthor, plus a practical demonstration on a test rig, I left with a conditional version of Lincoln Steffens' reaction to Soviet Russia. I have seen what may well be the future and I think it will probably work.
What do I know about rail head contamination and its removal? Well back in the bad old days I researched, wrote and edited British Rail's first Leaf Fall manual.
As part of that work we compiled a long list of measures that had been tried and failed. One contender we didn't mention was the British Rail Research plasma torch.
This was a classic over-hyped product of Research's early Ivory Tower days. The concept was simple: you blasted a jet of high temperature gas plasma onto the rail. The only problem was that it needed a small power station to drive it.
Plasma torch was, of course, not far from my mind as Malcolm Higgins explained the background to Laserthor. It began in September 1999 when he was driving down the M3 and heard a radio item about ‘leaves on the line' and how ridiculous it was that leaves could stop trains running.
Malcolm knew that high power lasers could be used to remove surface contamination and wondered whether they could be applied to the rail head. His first step was to commission a feasibility study, which came up with three conclusions.
A laser could indeed remove leaf contamination from the railhead. The best equipment for the job would be a Neodinium Ytrium Aluminium Garnet laser (henceforth Nd:YAG) with an ideal pulse length of 10nano seconds (nano = one billionth) and operating in the infrared (IR) part of the spectrum. Unfortunately, while technically feasible, the concept would never be commercially viable because it would need a laser the size of a railway carriage and a power supply big enough to light up Welwyn Garden City.
‘Two out of three was good enough for me' says Malcolm Higgins. He next asked Rutherford Appleton Laboratory to review the consultants' study. They agreed with the first two conclusions but were able to point Mr Higggins towards an Nd:YAG laser that had commercial potential.
Preliminary tests using a borrowed laser showed that a laser working in the infra red end of the spectrum did indeed clear leaf deposits and other contamination. The next stage was to see whether it would work on the rails with real leaves.
One of the problems with ‘leaves on the line' is that the lay person cannot comprehend how leaf mould can affect trains. The answer is that we are not talking about the rotting leaves that make your path slippery in autumn.
When a leaf is caught in the nip between wheel and rail it is subjected to a force of five tonnes or more applied to an area the size of a five pence piece. This compresses the organic matter into a hard coating which has a low coefficient of friction when wet and insulates the wheel from the rail when dry, thus preventing track circuits working. So think Teflon coated cookware rather than squidgy leaf mould.
Creating this coating in the laboratory is difficult and time consuming, making real life trials essential. So in 2000, Laserthor persuaded Railtrack to carry out a trial on the main line using a Sandite EPB as the test vehicle.
Now, lasers are potentially harmful. Before I entered the test rig at Bicester I was given a comprehensive safety briefing. The point was made that with an IR laser you won't see the beam. And if you look at it without the special goggles, you may not see anything else afterwards.
So the EPB had to be converted into what is known as a class 4 laser laboratory on wheels. This included interlocking the doors with the laser power supply.
To protect the borrowed laser from vibration and shock its optics bed, the clever but delicate bit, was mounted on a bed of rubber tyres. Mirrors turned the horizontal beam through 90 degrees into a vertical pipe through a hole in the floor and at the bottom of the pipe was a simple rubber skirt to shield the laser beam.
Power was provided by a 64kW diesel generator in another coach.
This was very much a bread-board installation. As Malcolm Higgins explained ‘there were no speed issues with this first trial, we just wanted to see if it could clean real contamination'. And clean it did. At a running speed of 1 mile/h ‘big fat spots of ablated material' were coming off the rail head.
And not just leaf detritus. The laser also removed grease, water and ice – in big sheets.
After the laser had passed there was no damage to the steel. Nor did it interfere with signalling. Subsequent laboratory tests showed that it had no adverse effect on rail with rolling contact fatigue.
But while Laserthor had learnt that the concept worked and could be operated safely, Malcolm Higgins ‘didn't get excited'. The equipment was slow, it needed Class 4 laboratory conditions and the spectrum was not ideal.
But now that Mr Higgins knew what was wanted it was time to look at the technology again. He had a demanding application.
Lasers are generally designed to sit in warm buildings on solid foundations. They also come in all shapes and sizes for different applications – ‘from bicycles to lorries' as Malcolm Higgins puts it.
Extending this analogy, an industrial Nd:YAG is a lorry. But Laserthor's application needed ‘a racing car that could carry forty tonnes and drive cross country'. ‘We didn't realise what we were asking for', adds Mr Higgins.
For a start, Railtrack needed a minimum operating speed of 40mile/h. The faster the train runs, the faster the laser has to pulse to ensure that the cleaned areas over lap. The bread board trial had a maximum pulse speed of 50 times a second (50Hz).
Then there was the matter of getting the laser beam to the rail head. For a practical application the ‘pipe and mirrors' had to be replaced with a fibre optic cable. That sounds simple, but at the high energies and pulse rates of an Nd;YAG you are getting near the limits of the nuclear bonds in the glass.
Not surprisingly, no such laser existed. But Laserthor found someone who could build one. The Fraunhofer Institut for Laser Technology (ILT) in Aachen specialises in Nd:YAG lasers for industrial applications and during 2001 they built what Malcolm Higgins calls it ‘the mother of all Nd:YAGs'.
At 1kW output it is the most powerful of its kind in the world and rugged enough for railway applications. Initially rated for a 120ns pulse it now gives an 80ns pulse at a pulse rate of 25kHz and can deliver these pulses to the railhead through optical fibre. Each pulse is equivalent to around 5MW – the power of a Channel Tunnel shuttle loco – and generates a temperature of 5000 degrees C.
This kit is housed in a self contained cubicle 1.5metres high by 1.2metres square which allows industrial Class 1 rather than Class 4 lab protection so that the unit can be mounted on a Multi Purpose Vehicle. There is plenty of room in this housing for uprating and for the Autumn 2002 trials, of which more later, a 3kW output could be available.
But back in Autumn 2001, the new laser was fork-lifted into the EPB. ILT had also designed an ‘optical delivery box' to get the laser beam to the rail head without any moving parts.
In the box the horizontal beam hits what is called a micro-step mirror which rotates it through 90 degrees and turns it into a line of light across the rail head. Not only that, the beam width and shape are adjustable
These trials were more realistic and thus threw up several problems.
One was the new design of cleaning head. This is, about the size of a brick and sits just above the rail head. The laser beam enters through a hole in the top and a screen of metal bristles around the sides of the head surrounded the rail to prevent reflected radiation escaping.
As the laser hits contamination it generates a lot of dust and debris which explodes outward. This gradually blocked the hole in the top of the head.
During the trials the laser was still giving a 120ns pulse which mean that the energy input to the contamination was less concentrated. This was exacerbated by the fact that the beam could not be focused sufficiently to cover the rail.
Finally, Laserthor discovered the age old truth, that equipment mounted on axles boxes gets shock loadings of 50g or more.
While development had so far fitted into the railways' annual leaf fall cycle, the lessons learned from the autumn 2001 trials had to be implemented and solutions evaluated for production standard equipment to be trialled in Autumn 2002 . And the potential market was looking better than expected
In November 2001 Malcolm Higgins had taken poster space at the World Railway Research Congress in Cologne . As he was putting up his poster a queue started to form, and there were people waiting to discuss problems for all three days of the event.
This revealed a universal concern with adhesion and detection problems caused by railhead contamination in many forms. Tyre rubber at level crossings, contamination from non metallic brake pads, even fuel dumped from airliners over Arizona
Clearly Laserthor needed to look at removing a wide range of contaminants. So the test rig I saw at Bicester was commissioned.
This is made up from 17 sections of curved rail which form a circle around 3metres diameter which can be rotated by an electric motor in either direction at speeds of up to 50mile/h in 1mile/h increments. The optical delivery box is mounted over the railhead on a stand.
A tribometer on another stand measures the railhead adhesion. It was calibrated by coating a rail with ptfe which has a known and consistent coefficient for friction.
Laserthor has used this rig to evaluate the laser on different types of contamination, including their own baked-on leaf fall substitute.
With the Mk 1 optical delivery box there is a line of laser light across the rail head, 40mm wide by 70microns (1 micron = one millionth of a metre) deep. Pulsing at 25kHz this means you will get continuous ablation of the railhead at 4mile/h.
In theory, if you run faster, you should get 70micron deep stripes across the track, but tests at 8mile/h showed the railhead to be clean and dry. Clearly the concentrated power of the line of laser light means that the effect extends beyond the area directly affected.
An improved Mk2 box was built which looked promising, so a Mk 3 optical delivery box was commissioned. This can produce a combination of beams.
Initially the idea was to have two beams across the track in parallel – effectively doubling the coverage and thus the speed. But now Laserthor is looking at a Mk 3 box able to generate a two by three matrix of individual beams, each 15mm wide by 70 microns deep.
In other words, instead of a 40mm continuous line across the railhead, there are three pairs of 15mm lines. This means that one pulse effectively provides a depth of 3 x 70 microns. Together with the overlap effect, Laserthor reckon the ‘six block', in conjunction with a scaled-up laser, should allow operating speeds of 30-40mile/h
This Autumn's trials, with the laser mounted on an MPV, will start with two parallel 40mm wide beams, but, with the Mk 3 optics box Laserthor is hoping to have the ‘six block' operational before the end of the leaf fall season.
A point to note here is that laser technology is akin to microprocessors where the computing power has been roughly doubling every 18months, With me at Bicester was a manufacturer of high power lasers and they were very optimistic that their latest units could pack in more power with shorter pulses and greater efficiency.
This allow Laserthor to be fitted under a train or locomotive. Malcolm Higgins acknowledges the potential but has his feet firmly on the ground. For the moment the company is focused on the MPV mounted module. ‘It's a maintenance tool first, because that's where the market is' Malcolm Higgins emphasises.
Even so, advancing technology could see the laser scaled up to 8kW. Similarly, the six block could become a four by two or even eight by two matrix, which would further increase the operating speed.
For my test run the optics box was providing a single 70microm beam across the railhead. The sections of railhead had been contaminated with either rust, which can reduce adhesion when wet, or a sticky axle grease.
With the test rig running at 4mile/h the laser was switched on. Viewed close up you could see the high energy in the pulsed beam exploding off detritus.
After one revolution the laser was switched off. Inspecting two test sections I had nominated showed the railhead to be clean and dry. Rust had been removed, except in the odd pitted area. The test rig includes an insulated block joint and that showed no sign of damage after many passes.
This year's trials see the laser operating as production equipment. Other than a large stop button, the safety functions are integral in the form of interlocks on the cubicle doors.
Last year the equipment was operated by laser technicians. This year Laserthor-trained AMEC or Serco operators will be in charge.
And there are other detailed improvements. The fibre optic down to the track runs in an armoured cable and a compressed air feed will blow the detritus away. The optical delivery box no longer needs cooling. And the 34kW will be provided by the MPV's auxiliary supply.
So there we are. I came away convinced that LaserThor has a working technology. My old chum Adrian Shooter, who commissioned me to write that first Leaf Fall manual and is now Chairman of the industry's Adhesion Working Group (AWG) is also impressed to the extend that the Group is funding a monitoring programme for the 2002 trials between Guildford and Reigate.
Commercially, LaserThor is hoping that Railtrack will buy two of the current modules for maintenance work and on-going development. These would be custom built and cost a nominal £500,000 each.
In writing this I am very conscious of past innovations that have flattered to deceive. But Laserthor has come so far so fast that I am confident enough to give laser railhead conditioning this much space.
Thus far the work has been funded by a combination of venture capital, a private investor and government innovation grants. If this year's trials go well – and the way the leaves are still clinging on the trees augurs well for LaserThor and ill for commuters – a submission will be made to the SRA for research money to look at on train installations.
And whatever happens, you know I will; report back