4 ms·

I don't see how this really explains anything. I have never understood how continuously-welded rails work compared with the old-style track using short rails a

I don't see how this really explains anything. I have never understood how continuously-welded rails work compared with the old-style track using short rails and fishplates joining them, and this link doesnt help (for me at least).

dazc 4y ago
Considering this is Network Rail, I agree, the opportunity to answer a lot of obvious questions has been seriously overlooked.
scrlk 4y ago
I found this article and associated video, along with the Wikipedia article to be useful for filling in the gaps from the article: https://broadwayextensionblog.blogspot.com/2017/03/stressing-at-laverton.html https://broadwayextensionblog.blogspot.com/2017/03/stressing... https://www.youtube.com/watch?v=I8EZ6pEAyLc https://www.youtube.com/watch?v=I8EZ6pEAyLc https://en.wikipedia.org/wiki/Rail_stressing https://en.wikipedia.org/wiki/Rail_stressing
bombcar 4y ago
http://vinchad.blogspot.com/2014/06/ever-wondered-why-continuously-welded.html http://vinchad.blogspot.com/2014/06/ever-wondered-why-contin... > Its laid it's in tension by hydraulically stretching it before cutting to length and welding to the previous length. Sufficient tension is applied to achieve a 'Stress Free Temperature' (SFT) of 27 degrees C (i.e to relieve the tension by expansion the rail would need to be heated by the sun to 27C, whereupon it would neither be in tension or compression). Apparently they lay it "hot" and so normally when it is cooler than that it is actually "pulling" on itself trying to shrink, and when it gets hotter than that it begins to compress. If it can't compress it buckles, if it can't shrink then the tension grows, but steel has incredible tensile strength.
- ssl232 4y ago
  I wonder if you can combine rail sections with different zero-stress temperatures to cancel out across a wider range?
  - Gare 4y ago
    The tension is between each pair of sleepers (60 cm distance), how would that work?
    - ssl232 4y ago
      Aha, I thought it was over longer segments of track.
- robocat 4y ago
  Here’s a link showing the tensioning process using a petrol powered hydraulic cylinder: https://broadwayextensionblog.blogspot.com/2017/03/stressing-at-laverton.html https://broadwayextensionblog.blogspot.com/2017/03/stressing...
gattilorenz 4y ago
It mentions the pre-stressing, but a better explanation is at https://worldwiderails.com/how-do-railroads-deal-with-thermal-expansion/ https://worldwiderails.com/how-do-railroads-deal-with-therma... It also explains some of the maintenance procedures.
- robocat 4y ago
  This article shows mechanical tensioning using a hydraulic cylinder: https://broadwayextensionblog.blogspot.com/2017/03/stressing-at-laverton.html https://broadwayextensionblog.blogspot.com/2017/03/stressing... although it is clearly a straight section. Do curved sections of rail just expand and contract? The parent link says “Railroads deal with thermal expansion by heating the rail prior to installation”. reddit/etmidust wrote “I was a manager of track maintenance for a US railroad for a while. When they lay new rail, part of the process is a ‘heater car’[1]. This machine rides the rail and is basically a multi headed blow torch to heat the new rail to the ‘rail neutral temperature’(SFT). At this point the rail is not yet spiked down to the ties so that it has a chance to grow and expand. After the heater car some other rail cars called spikers follow to spike the new rail down. That is how they ‘pre-stress’ the rail. I am skipping some steps, but that is the gist of it.” [1] https://imgur.io/tvCy9C2 https://imgur.io/tvCy9C2
aaaaaaaaaaab 4y ago
https://en.m.wikipedia.org/wiki/Rail_stressing https://en.m.wikipedia.org/wiki/Rail_stressing
smcl 4y ago
Pasting a couple of @GarethDennis tweets which answer this: It is worth pointing out that jointed rather than welded track WILL NOT solve the buckling problem. In fact, jointed track is at a MUCH HIGHER risk of buckling in heat than welded rails as gaps close and there are 160+ joints PER MILE to maintain... ...plus jointed track is generally lighter, weaker and thus at higher risk of buckling (most GB buckles are in jointed, not welded track). Bolted joints also have a nasty habit of disintegrating under traffic and derailing trains (hence use of welded track to start with)
- adrian_b 4y ago
  Your arguments make sense, so it appears that continuously-welded rails should be better than the traditional jointed rails. Nevertheless, when I was young I traveled frequently by train. During some decades, I have never seen problems caused to the train traffic by too high temperatures, on traditional jointed rails. On the other hand, in the last few years, whenever I happened to travel by train through Germany on continuously-welded rails and the weather was hot, there were train delays due to the rails. So it seems that there is some disconnection between theory and practice. Maybe the new continuously-welded rails have been designed based on ancient recorded temperature ranges that are no longer valid due to climate changes, as already suggested in the parent article, but in any case something is wrong with the design of modern rails. In the parent article it is mentioned that changing the stress-free temperature to a higher value is not good enough, because the strength of the rails could be exceeded during cold winters. So it is likely that the rails would have to also be thicker, increasing their cost.
  - mook 4y ago
    I don't know anything about German weather, but according to a random article on Wikipedia: https://en.m.wikipedia.org/wiki/List_of_extreme_temperatures_in_Germany https://en.m.wikipedia.org/wiki/List_of_extreme_temperatures... says 9 of 16 extreme maximums are within the last year (with one about a month over).
- vladvasiliu 4y ago
  > In fact, jointed track is at a MUCH HIGHER risk of buckling in heat than welded rails as gaps close and there are 160+ joints PER MILE to maintain... Why? Don't the gaps give the track some amount of play which would lower the pressure and therefore the risk of buckling?
webmobdev 4y ago
How do engineers plan for thermal expansion when laying traintracks in deserts where the daytime and nighttime temperatures are vastly different? - https://old.reddit.com/r/askscience/comments/8yxd21/how_do_engineers_plan_for_thermal_expansion_when/ https://old.reddit.com/r/askscience/comments/8yxd21/how_do_e...
konschubert 4y ago
Steel is a bit like rubber if your holding it with enough force…
adrian_b 4y ago
It seems that the answer to your question is that the continuously-welded rails work only within a relatively narrow temperature range. As mentioned at this link, the continuously-welded rails are made to be stress free at a specified temperature, for example 27 degrees Celsius in UK. At lower temperatures the rails contract, which does not have bad consequences unless the temperature becomes so low that the rails will crack, because their strength has been exceeded by the contraction stress. At very low temperatures the trains may need to reduce their speed, so that the rails will not crack due to the additional stresses caused by a passing train. At higher temperatures, the rails dilate, and when the temperature is high enough they will buckle. Due to that, the trains may need to reduce the speed, or even stop and wait for the rails to become colder. At least a part of the rails from Germany have also been updated with continuously-welded rails. In one of my trips, it was a hot summer day and because of the rail buckling all the trains had huge delays. Even if I should have arrived at the Frankfurt airport about 3 hours before my flight, due to the train delays caused by the hot weather, I have arrived so late that I have lost the flight.

dazc 4y ago

Considering this is Network Rail, I agree, the opportunity to answer a lot of obvious questions has been seriously overlooked.

scrlk 4y ago

I found this article and associated video, along with the Wikipedia article to be useful for filling in the gaps from the article: https://broadwayextensionblog.blogspot.com/2017/03/stressing-at-laverton.html https://broadwayextensionblog.blogspot.com/2017/03/stressing... https://www.youtube.com/watch?v=I8EZ6pEAyLc https://www.youtube.com/watch?v=I8EZ6pEAyLc https://en.wikipedia.org/wiki/Rail_stressing https://en.wikipedia.org/wiki/Rail_stressing

bombcar 4y ago

http://vinchad.blogspot.com/2014/06/ever-wondered-why-continuously-welded.html http://vinchad.blogspot.com/2014/06/ever-wondered-why-contin... > Its laid it's in tension by hydraulically stretching it before cutting to length and welding to the previous length. Sufficient tension is applied to achieve a 'Stress Free Temperature' (SFT) of 27 degrees C (i.e to relieve the tension by expansion the rail would need to be heated by the sun to 27C, whereupon it would neither be in tension or compression). Apparently they lay it "hot" and so normally when it is cooler than that it is actually "pulling" on itself trying to shrink, and when it gets hotter than that it begins to compress. If it can't compress it buckles, if it can't shrink then the tension grows, but steel has incredible tensile strength.

ssl232 4y ago
I wonder if you can combine rail sections with different zero-stress temperatures to cancel out across a wider range?
- Gare 4y ago
  The tension is between each pair of sleepers (60 cm distance), how would that work?
  - ssl232 4y ago
    Aha, I thought it was over longer segments of track.
robocat 4y ago
Here’s a link showing the tensioning process using a petrol powered hydraulic cylinder: https://broadwayextensionblog.blogspot.com/2017/03/stressing-at-laverton.html https://broadwayextensionblog.blogspot.com/2017/03/stressing...

gattilorenz 4y ago

It mentions the pre-stressing, but a better explanation is at https://worldwiderails.com/how-do-railroads-deal-with-thermal-expansion/ https://worldwiderails.com/how-do-railroads-deal-with-therma... It also explains some of the maintenance procedures.

robocat 4y ago
This article shows mechanical tensioning using a hydraulic cylinder: https://broadwayextensionblog.blogspot.com/2017/03/stressing-at-laverton.html https://broadwayextensionblog.blogspot.com/2017/03/stressing... although it is clearly a straight section. Do curved sections of rail just expand and contract? The parent link says “Railroads deal with thermal expansion by heating the rail prior to installation”. reddit/etmidust wrote “I was a manager of track maintenance for a US railroad for a while. When they lay new rail, part of the process is a ‘heater car’[1]. This machine rides the rail and is basically a multi headed blow torch to heat the new rail to the ‘rail neutral temperature’(SFT). At this point the rail is not yet spiked down to the ties so that it has a chance to grow and expand. After the heater car some other rail cars called spikers follow to spike the new rail down. That is how they ‘pre-stress’ the rail. I am skipping some steps, but that is the gist of it.” [1] https://imgur.io/tvCy9C2 https://imgur.io/tvCy9C2

aaaaaaaaaaab 4y ago

https://en.m.wikipedia.org/wiki/Rail_stressing https://en.m.wikipedia.org/wiki/Rail_stressing

smcl 4y ago

Pasting a couple of @GarethDennis tweets which answer this: It is worth pointing out that jointed rather than welded track WILL NOT solve the buckling problem. In fact, jointed track is at a MUCH HIGHER risk of buckling in heat than welded rails as gaps close and there are 160+ joints PER MILE to maintain... ...plus jointed track is generally lighter, weaker and thus at higher risk of buckling (most GB buckles are in jointed, not welded track). Bolted joints also have a nasty habit of disintegrating under traffic and derailing trains (hence use of welded track to start with)

adrian_b 4y ago
Your arguments make sense, so it appears that continuously-welded rails should be better than the traditional jointed rails. Nevertheless, when I was young I traveled frequently by train. During some decades, I have never seen problems caused to the train traffic by too high temperatures, on traditional jointed rails. On the other hand, in the last few years, whenever I happened to travel by train through Germany on continuously-welded rails and the weather was hot, there were train delays due to the rails. So it seems that there is some disconnection between theory and practice. Maybe the new continuously-welded rails have been designed based on ancient recorded temperature ranges that are no longer valid due to climate changes, as already suggested in the parent article, but in any case something is wrong with the design of modern rails. In the parent article it is mentioned that changing the stress-free temperature to a higher value is not good enough, because the strength of the rails could be exceeded during cold winters. So it is likely that the rails would have to also be thicker, increasing their cost.
- mook 4y ago
  I don't know anything about German weather, but according to a random article on Wikipedia: https://en.m.wikipedia.org/wiki/List_of_extreme_temperatures_in_Germany https://en.m.wikipedia.org/wiki/List_of_extreme_temperatures... says 9 of 16 extreme maximums are within the last year (with one about a month over).
vladvasiliu 4y ago
> In fact, jointed track is at a MUCH HIGHER risk of buckling in heat than welded rails as gaps close and there are 160+ joints PER MILE to maintain... Why? Don't the gaps give the track some amount of play which would lower the pressure and therefore the risk of buckling?

webmobdev 4y ago

How do engineers plan for thermal expansion when laying traintracks in deserts where the daytime and nighttime temperatures are vastly different? - https://old.reddit.com/r/askscience/comments/8yxd21/how_do_engineers_plan_for_thermal_expansion_when/ https://old.reddit.com/r/askscience/comments/8yxd21/how_do_e...

konschubert 4y ago

Steel is a bit like rubber if your holding it with enough force…

adrian_b 4y ago

It seems that the answer to your question is that the continuously-welded rails work only within a relatively narrow temperature range. As mentioned at this link, the continuously-welded rails are made to be stress free at a specified temperature, for example 27 degrees Celsius in UK. At lower temperatures the rails contract, which does not have bad consequences unless the temperature becomes so low that the rails will crack, because their strength has been exceeded by the contraction stress. At very low temperatures the trains may need to reduce their speed, so that the rails will not crack due to the additional stresses caused by a passing train. At higher temperatures, the rails dilate, and when the temperature is high enough they will buckle. Due to that, the trains may need to reduce the speed, or even stop and wait for the rails to become colder. At least a part of the rails from Germany have also been updated with continuously-welded rails. In one of my trips, it was a hot summer day and because of the rail buckling all the trains had huge delays. Even if I should have arrived at the Frankfurt airport about 3 hours before my flight, due to the train delays caused by the hot weather, I have arrived so late that I have lost the flight.