With the recent heat spell hitting the Midwest, I would like to know how do the rails handle (disipitate) the heat. It seems to me, that the solid rails would eventually buckle somewhere. I know that extreme cold can cause rail to break, but what’s the effect of the heat?
Sun kinks, they do happen. That’s why most railroads have speed restrictions in extream heat conditions.
A fair hefty well consolodated ballast shoulder with a big do not disturb sign on it to try and hold the track in place and a stress free temperature that to some seems excessive (round our gaf, 27 degrees C) to reduce the longitudinal stresses that cause buckling is really all you can do apart from installing slab track…
it’s over 100 today and so far i have not yet noticed any melting on the rails. though some of the track in altoona is kinda “mushrooming” down the edges likely from heavy use (4 wayfreights and a local every day is considerable. i think… )
Basically, heat causes rail to expand. A well-maintained roadbed will limit the expansion to the width and height of the rails, holding the rail firmly in place along its length. Less well-maintained track will suffer from lengthening rails, and a sun-kink may develop, either on its own or as the result of a train disturbing the roadbed. All railroads slow down to some degree during times of extreme heat (as the do in extreme cold); those with more to worry about slow down more (and still make the news more often).
Hmmmm…this sounds like the same theory in physics that says if you heat an iron plate which has a hole in it, the hole will get smaller because the iron expands. They fianally convenced me that EVERY thing expanded equally, along all dimensions, and therefore the hole will expand by the same proportion as the steel plate.
How does ballesting and maintenance allow expansion in two dimensions (width, height) and keep it from affecting the third (Length)?[?]
SOunds like magic to me…I had always thought there must be some sort of expansion joint, similar to the points of a turnout, which would allow one rail to grow a bit in the length direction…
If you’ve ever wondered why even well-groomed CWR has joints in it every so often, this is why.
Welded rail in combination with the extremes of weather are a technology that the railroads have yet to MASTER.
In the Summer ‘Sun Kinks’ are a relatively frequent occurence as the heat expansion of the rails will eventually find the weakest location in the roadbed and change the alignment of the tracks.
In the Winter (mostly that first night of extreme temperature change from a 60/70 F daytime temperature to a 10/20 F nighttime temperature) will apply the shrinking stress to the rail and find the weakest rail joint or rail weld, thus having a broken rail.
Both conditions are dangerous as either occurence can cause catastrophic derailments.
Welded Rail is not a technology that the railroads have MASTERED.
Lots of rail anchors, properly applied…plus lots of watchfull roadmasters, motor track inspectors and foremen who have been careful to balance rail stresses all year long.
I know in Tx.both UP and BNSF just about shut down in the heat of the day,then run like **** all night and into early am to make up for it…I was in Wichita Falls ,Tx.this w/end the temp was 103-5 during the day and no trains ran after about 9am til almost dark every day…I did see 1 stack train about 11oclockish…Not a good w/end for rail fanning Anywhere in Tx…Danny
Here in Milwaukee the CP has started running the fast stuff later at night, and not as much during the day. But, Amtrak still races the Empire Builder out of town every afternoon in peak temperatures like its running for its life. Cheers! ~METRO
Jointed track has expansion gaps at each joint (which have enlarged bolt holes to allow limited movement).
Continous welded rail (ribbon rail) is tensioned along it’s length when it’s laid, so that as it heats up and expands the internal tension reduces until at the ‘stress free temperature’ (chosen to be around 27C in the UK according to Hugh Jampton) there is neither longitudinal tension or compression. Above this temperature the rail is in longitudinal compression and relies on the ties, ballast and rail anchors to keep it in place without buckling.
As others have mentioned, the downside of pre-tensioning it is that it increases the stress in cold conditions, making it more likely that welds etc will pull apart, so choosing the right ‘stress free temperature’ is a balancing act for any given location.
Tony
5 trains in 24 hours is nothing, not sure what your talking about there. I havent noticed too much of the “rolling” of the rails yet, but then again I havent looked very closely. Alec
In partial reply – and keeping in mind MC’s remarks about very very careful maintenance and inspection! – what is supposed to happen is that the rail tries to expand (or, in cold weather, contract) as the temperature changes. If the rail cannot expand – that is, the roadbed and track structure are properly designed and built and maintained – the expansion is resisted by a compression force (tension in cold weather) which keeps it the same length. Hard to believe, but steel is elastic – just like a rubber band (well… takes more force to change the length, but the principle applies). These forces can be very large indeed.
Sun kinks, a cheery phenomenon referred to here, happen when the resisting forces which the track structure can provide are overwhelmed. They don’t happen slowly – they happen, like any structural failure, very rapidly. A track which is perfectly straight one minute can, in less than a few seconds, develop an 18" or more sun kink. Boing. This can ruin your whole day if it happens right in front of or under your train – which it usually does, because of the little extra stress from the train.
This historic replica portions of the Golden Spike Historical Site, where I volunteeer, have stub switches. In hot weather, rail expansion will sometime close the gap between the rail ends and make the switch impossible to throw. When that happens, we use a hose from the tender to cool the rails with water until the switch can be thrown. One day, it took two of us, pushing on the harp stand, to get the sticking switch to throw.
dd