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Trains May Soon Come Equipped With Debris-Zapping Lasers
Molly McHugh writes: Holland's chief transportation service is testing a unique new way to clear the rails of fallen leaves and other small debris: by mounting lasers on the fronts of locomotives. The lasers will cause the leaves, which produce a condition commonly referred to as "slippery rail" in the fall and winter months, to vanish in a puff of smoke.
Leaves burn well below the annealing temperature of most steels.
My point not shot down at all, shoes are replaced every 50,000km in the cars in my city. Brush of proper material could have huge life, wear not a barrier to use. In fact, they do put in "scrapers" next to the pickup shoes in the winter months for ice and snow. Is any of this getting through to you? can you connect the dots?
Sorry to reply to myself but since Wikipedia doesn't actually bother to talk about mechanisms, I will. You can remove a surface with a laser through heating, which applies enough photons to the surface atoms that they vibrate loose, which is a slow process that transmits piles of heat downwards. Or you can use a laser whose wavelength is shorter than the strength of the sigma electron bonds in the material, in which case the electrons absorb the photons, get popped into a higher orbital, and the bond that held the two atoms together simply isn't there anymore and the now free atoms can just drift away. There is in theory no heat generated at all. In practice there are so many photons coming in all at once that there's a metric buttload of photons being absorbed by everything, so what actually happens is the wavefront hits and turns the first couple of atomic layers into a plasma, that erupts away from the surface and leaves the underlying surface close to untouched. So that's the mechanistic difference between burning and ablation: photon flux and wavelength.
Nostalgia's not what it used to be.
About a decade ago the Brits had a slew of leaves-on-the tracks failure-to-brake accidents. Why now? everyone thought. In a bunch of places the embankments had been designed for coal-burning trains, which spit sparks, so the embankments were gravelled or very sparsely grassed. What trees the fires didn't suppress were cut down as seedlings every few years.
Time passes, the engines change fuel, someone notices they're spending money on maintaining the gravel and stops.
*Decades* pass and there are beautiful trees on the embankments tall enough to shed onto the tracks -- *that's* when the accidents start.
They're not "just leaves".
I thought this looked familiar, and sure enough, google turned up this article from 2007 about the system and the guy who spent eight years and 5 million GBP to try to solve it.
"Every time a train runs over a pile of leaves, they are squashed into a hard, black, shiny, Teflon-like substance that makes it more difficult for trains to slow down and stop."
"Rofin-Sinar created a monster. The final version of the laser railhead cleaner contains two lasers capable of producing 2kW each. The pulsed energy is channelled via a fibre optic, which delivers a round beam in a straight line across the rail.
The pulsed beam hits the rail 25,000 times per second. The leafy mulch absorbs each 5,000C pulse of light, causing it to heat rapidly, expand and lift off the rails. Tests have found that the laser cleaner also works on oil, grease, ice and other problematic substances."
"Total destruction the only solution" - Bob Marley