Hot rail tracks

I took my daughter to the railway station tonight - she was worried because we were a bit behind time. It'll be OK I said, it's an unusually hot day, something's bound to go wrong and the trains will be late. The rails will be too hot or something. I thought I was joking. She texted me later - trains delayed due to 'the high temperature of track'. Apparently they had to slow down. I  can only think it must be something to do with expansion links, but I'm sure there will someone here who can explain properly!

Rob

Edited By Robin Graham on 25/06/2018 23:31:25

Expansion gaps etc can only cope with so much expansion. In parts of Australia they are painting track rails with a white insulating paint. Drops the rail temp by 16 degrees C and reduces expansion accordingly.

Here's why:

https://www.youtube.com/watch?v=_LoXgN1QWZM

Skip to 00:45 if you get bored. Sorry I can't post as a hyperlink.

John.

Tracks are not like they used to be. In the days of ‘clickety-click’ rail lines (in the steam days) where each short rail section was butt jointed to the next, but with enough gap to allow for expansion, things have changed to longer welded sections with joints ‘scarfed’ so they are much, much less noisy and more wear resistant. But there are limits as to how much expansion can be accommodated in any joint, so there is a trade-off between lengths of track (with reduced number of joints) and allowable temperature limits.

Look at the modern joints on road bridges (perhaps safer than checking out rail tracks) - they have ‘finger jointed’ expansion allowance - as opposed to a plain gap of long ago, thus allowing fewer expansion joints or longer bridges along with a quieter, and less bumpy ride, for motorists.

In Australia it is a never ending process for the rail maintenance crews. In the summer hot months they shorten some of the rail sections because they have expanded and when they cool in the winter months, they extend the rails.

The 1,420km long rails from Alice Springs to Darwin in the middle of Australia, expand 16.3 metres for every degree of temperature change. The rail temperature can get down to -10°C in winter and up to +65°C in summer, a difference of 75 degrees. This would mean that the rails would expand and contract up to 1.2 km between the coldest night and hottest day during the year.

Paul

It's not uncommon to see white rails in the U.K., but usually just around the pointwork. I always assumed this was just to make cracks in the rails more obvious, but I wonder if that is secondary the insulating benefits. Points can be easily affected by the heat due to the tolerances involved (certain designs are more susceptible than others). Certainly the casings of the point machines have been painted white to reflect the heat.

I remember at some point in the 70/80s experiments were done using ‘Invar’ rails which had a much lower coefficient of linear expansion than ‘ordinary’ steel rails. I’m pretty sure Invar went into general use but don’t know how extensive it’s use became. I’m sure somebody who knows will be along shortly..... unless of course delayed by the heat 😊

There was a photo of some buckled track near Glasgow in various papers...

Now if they let the trees grow up and shade the track...

But they sold the trackside land.

Heavy rain, gales, landslips,trees on line,leaves on line, snow now too hot, looks like they have all the bases covered

Mick

Why does hot track not slow or delay the bullet trains in Japan? They have a very similar maritime climate.

Is it just because Network Rail is incompetent?

Regards

Richard.

Yes, that's what prompted my jest (as I thought) to my daughter - the old moan about how seasonal variations which would be thought small in some climates seem to make UK infrastructure grind to a halt. So presumably the trains have to slow down so the driver can spot buckled rails in time, or at least avoid capsizing if they hit a warped section?

Invar would be an ideal solution no doubt, but it would be quite expensive - 36% nickel at 15,000 US$ a ton against 500 - 1000 for steel. But I have no idea what proportion of the cost of constructing a railway goes on the rails - maybe it's negligible compared to the overall cost. And how hot do the rails actually get in direct sunlight? I'm guessing maybe 50C? I feel a Googlefest coming on!

Thanks for replies, Robin.

Edited By Robin Graham on 26/06/2018 23:54:48

Edited By Robin Graham on 27/06/2018 00:05:31

Temperature is also a problem for the phone and cable TV boxes along your street, often painted a nice dark green. The equipment inside can cope to some extent but eventually it just falls over big time. It would help to paint them white but the local authorities won't allow it.

With the state of our railways today it could only be the sun that makes our rails hot nothing moves fast enough to generate heat.

I can get from Lichfield to London in 1 hour and 43 minutes. Apparently we need to spend several billion to knock fifteen minutes off that and there won't be a sop at Lichfield...

Continuously welded tracks are pretensioned before being welded to give neutral rail forces at some temperature, I think it might be 20 degC or maybe 25 degC. When the temperature exceeds the neutral temperature the rails are in compression and looking to buckle like the picture above. To counter this the ballast (loose stones holding the sleepers or ties in place) is extended a minimum distance either side of the sleepers (one foot springs to mind) to constrain movement. At the limit, all is well until a train comes along and gives everything a good rattling. At higher speeds the rattling is worse and the track is more likely to spring out of line. Hence the speed restrictions on very hot days.

I think that's because nobody wants to go to Lichfield.

.

au contraire, Clive

It's probably that 'they' don't want people from Lichfield travelling to London.

MichaelG.

And don't forget the high tides for us in South Devon

Lionel