Continuous Welded Rail

DimTim · 12 Jul 2019

Simple question
We've all probably seen lengths of cwr laid between tracks for subsequent renewal. I understand it is transported on the special wagons from viewing You Tube. But how does it get round curves / junctions etc. on its journey?
My understanding of steel is it doesn't bend and some lengths I've noticed appear very long!

RailUK Forums

class 9 · 12 Jul 2019

Of course it bends

class 9 · 12 Jul 2019

800002 · 12 Jul 2019

I think that is called 'flexing' to be honest.

Most excellent choice of picture, I must say.

jopsuk · 12 Jul 2019

fundamentally, it never has to bend through a significantly smaller radius in transport compared to when it is installed. Solidly built wagons take care of the rest.

a_c_skinner · 12 Jul 2019

Ha! Never thought of that.

800002 · 12 Jul 2019

It certainly gets interesting though when a partial derailment happens in transit, where some rail carrying bogies come off the road.
Thinking back to the Hoo Jn derailment (as the loco entered the yard it came off the road) the rails in transit had to be cut in order for the bulk of the train to be pulled clear before they could even think about re-railing anything.

hexagon789 · 12 Jul 2019

jopsuk said:
fundamentally, it never has to bend through a significantly smaller radius in transport compared to when it is installed. Solidly built wagons take care of the rest.

Aren't they also held in place in such a way that they can flex as well?

edwin_m · 12 Jul 2019

They must also move longitudinally a bit during transit, as when the train is on a curve the distance from one end to the other will be less when measured on the inside of the curve than on the outside. I guess they are on some kind of roller to allow them to be fed out, but I hope someone remembers to fix them securely at (only) one end!

furnessvale · 12 Jul 2019

edwin_m said:
They must also move longitudinally a bit during transit, as when the train is on a curve the distance from one end to the other will be less when measured on the inside of the curve than on the outside. I guess they are on some kind of roller to allow them to be fed out, but I hope someone remembers to fix them securely at (only) one end!

IIRC fixed at the centre.

big all · 12 Jul 2019

from memory [over 25 years ago]
rail trains at redhill where some thing like 5mph over p and c[points and crossings ]and 25mph plain track later increased to something like 15 and 45mph
the wagons where marlins and mantas recycled from 4cor/nelsons underframes
yes the rails would flex quite a bit but not dangerously
off loading them was quite a skill as you needed enough power to break the friction then reduce enough to to stop it galloping away at around to say 3-5mph but without coming back to a stand
although slimline cromptons had slow speed it was useless for this task as it was far too crude to give a controlled smooth drop

3973EXL · 13 Jul 2019

LWRT (long welded rail) & RDT (rail delivery) trains use roller banks and a clamp wagon, central on LWRT, towards one end on RDT.
Long rails can also be moved loaded over multiple wagons on support frames or bolstered wagons. Depending on the type of frame, there maybe a clamping frame.

DimTim · 14 Jul 2019

Thanks for responses
Never thought rail would 'bend' as much although laying round curves would require bending on site.

Ploughman · 14 Jul 2019

DimTim said:
Thanks for responses
Never thought rail would 'bend' as much although laying round curves would require bending on site.

You only need precurved rail on very tight curves and those locations would not be CWR anyway.
This is one way of threading the rail on site. About 1.45 on the attached Network Rail time lapse sequence from Market Harborough.

An other method is to use a Road Railer but similar principle.

Highlandspring · 15 Jul 2019

380101 · 19 Jul 2019

Ploughman said:
You only need precurved rail on very tight curves and those locations would not be CWR anyway.
This is one way of threading the rail on site. About 1.45 on the attached Network Rail time lapse sequence from Market Harborough.

An other method is to use a Road Railer but similar principle.

Good Scottish rail engineering company there, McCulloch Rail that design, build and own those Tracked Rail Transposer (TRT) machines. They're a fairly local company to me and I've visited their head office and workshop a few times. They now have their machines working on the New York subway, various US mainlines and also out in Australia. They've done not bad for 2 boys off a farm!

Ploughman · 26 Jul 2019

Over the last couple of years has the CWR SFT of 27 C changed at all?

There was talk before I retired from Relaying of the temperature limit being revised upwards.
Is there a publically accessible version of NR/SP/TPK/0011?

superkev · 26 Jul 2019

Ploughman said:
Over the last couple of years has the CWR SFT of 27 C changed at all?

There was talk before I retired from Relaying of the temperature limit being revised upwards.
Is there a publically accessible version of NR/SP/TPK/0011?

27deg seems very low.
K

civ-eng-jim · 26 Jul 2019

superkev said:
27deg seems very low.

If 38 degrees becomes the norm, then yes, 27 may be determined to be a little low.

But even 30 degrees is even pretty warm for the UK and -5 is pretty normal for winter. (The minimum/maximum averages range from 0 - 22C which surprised me) This gives a rail temperature range of -5 to 50 degrees (Rail temp can be 20 degrees hotter than air temp) which gives an average of just 22 - 23 degrees. Stress Free Temperature can allowably range from 21 to 27 so a target SFT of 27 appears sound.

The primary consideration of SFT is to prevent buckling which presumably indicates that track has a better resilience to failing in extreme cold compared to extreme heat. IE, can rail temperature drop to, say, 40 degrees below stress-free temperature before cracking vs 40 degrees above SFT where it may likely have already buckled?

Bald Rick · 26 Jul 2019

It’s still 27 AIUI.

I wouldn’t be surprised if there was some discussion about lifting it a degree. I’d expect SNCF to be having similar discussions too (they use 28C for the SFT IIRC)

edwin_m · 26 Jul 2019

The SFT is, as the name suggests, the temperature at which the rails are stress free. As temperatures increase the weight of the ballast and sleepers prevents them moving so they have an increasing amount of compressive stress until eventually it gets too much, the rail buckles and the sleepers move sideways. Even allowing for the fact that the rail can get a lot hotter than the air, the track can cope with a temperature well above the SFT. But the temperature yesterday was such that a significant amount of track was at risk of buckling particularly under the forces of a passing train, so speed limits were imposed to reduce those forces.

AM9 · 26 Jul 2019

civ-eng-jim said:
If 38 degrees becomes the norm, then yes, 27 may be determined to be a little low.

But even 30 degrees is even pretty warm for the UK and -5 is pretty normal for winter. (The minimum/maximum averages range from 0 - 22C which surprised me) This gives a rail temperature range of -5 to 50 degrees (Rail temp can be 20 degrees hotter than air temp) which gives an average of just 22 - 23 degrees. Stress Free Temperature can allowably range from 21 to 27 so a target SFT of 27 appears sound.

I understand the up to 20K rise of rail temp above air temp, but would the rail temp track air temp more closely at -20 as there's not usually any solar radiation at night or much at all, early in the morning?

Bald Rick · 26 Jul 2019

AM9 said:
I understand the up to 20K rise of rail temp above air temp, but would the rail temp track air temp more closely at -20 as there's not usually any solar radiation at night or much at all, early in the morning?

Pretty close to air temp; it can get a little colder - presumably in the same way you can get a ground frost before an air frost.

AM9 · 26 Jul 2019

Bald Rick said:
Pretty close to air temp; it can get a little colder - presumably in the same way you can get a ground frost before an air frost.

So if the default SFT is raised in the near future, will this slightly increase the risk of failures at the low temperature end of the range?

Bald Rick · 26 Jul 2019

AM9 said:
So if the default SRT is raised in the near future, will this slightly increase the risk of failures at the low temperature end of the range?

Yes it would.

mcmad · 26 Jul 2019

There would probably also now be a case for (slightly) different SFT's across the country with Scotland and the North of England probably sticking with the current but the South raising the SFT a degree or two to reflect the changing temperature range.

Bald Rick · 26 Jul 2019

mcmad said:
There would probably also now be a case for (slightly) different SFT's across the country with Scotland and the North of England probably sticking with the current but the South raising the SFT a degree or two to reflect the changing temperature range.

There may well be.

The issue when changing the SFT is the length of time it will take to get it all done. After final stressing on initial installation, rail rarely needs restressing again until it is replaced. It could take 30 years+ to get it all done through the renewals programme; obviously it could be done more quickly wit a campaign renewal, but that would then cost extra money.

BarryD · 26 Jul 2019

Surely there are many other places around the world that experience a much larger temperature range than we do: the American Mid-West, for example, has much colder winters and much hotter summers. How do their rails cope with this?

Bald Rick · 26 Jul 2019

BarryD said:
Surely there are many other places around the world that experience a much larger temperature range than we do: the American Mid-West, for example, has much colder winters and much hotter summers. How do their rails cope with this?

Possibly for the umpteenth time (across 2 or 3 threads)

They are content with a higher incidence of broken rails in winter, and a higher rate of track buckles in summer. And content with the consequences, which is a rather higher rate of derailments than we in the U.K. experience. Being largely a low speed, freight only operation, it doesn’t matter so much, of course.

As also mentioned elsewhere, AIUI on the trans Siberian railway the Russians restress the rails every spring and autumn. Not practical on the U.K. network with our level of traffic.

Deepgreen · 26 Jul 2019

AM9 said:
So if the default SFT is raised in the near future, will this slightly increase the risk of failures at the low temperature end of the range?

Yes - something has to give - we can either have fewer stress issues in summer or winter. I would favour summer, as being stuck on a train owing to a broken rail in winter rarely leads to heat stroke! Of course, more expansion joints might provide relief if the SFT remains 27C.
A flippancy occurs to me; how much longer do CWR trains get in hot weather?!

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