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Old March 3rd, 2008, 08:07 PM   #1
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MISC | Expansion and Contraction in Continuous Welded Rail

Does anybody know how contraction/expansion happens/is accommodated for between/along? long sections of welded rail nowadays?
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Old March 4th, 2008, 12:39 AM   #2
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Because the joint is staggered rather than end-on there's no perceptable motion or noise when passing over the joint.
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Old March 4th, 2008, 12:50 AM   #3
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This subject has always been of interest to Me. Having a few close calls nearly hitting the dirt on a few ocasions-- Especialy working on the Kalgoorlie Esperance line in very hot weather. Heat buckles were bad on that line and also the Leonora line.
Would hope we get some tech info from sombody who knows ect.
I did notice that when they re-railed the Kalgoorlie Main, they had gas burners on a rail trolley and heated the rails- pre -stressing them before the weld was done.
I always assumed that while it may stop heat buckles in hot weather-- surely the rails would be under extreme contraction stress in the very cold weather.
While this seems to work fine in Western Australia- I am curious also how they manage in places with very cold/hot summer and winter conditions.
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Old March 4th, 2008, 12:53 AM   #4
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Quote:
Originally Posted by Tubeman View Post
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Because the joint is staggered rather than end-on there's no perceptable motion or noise when passing over the joint.
I have never seen anything like that Rail Joint on our main lines!
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Old March 4th, 2008, 01:07 AM   #5
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Quote:
Originally Posted by tuckerbox View Post
This subject has always been of interest to Me. Having a few close calls nearly hitting the dirt on a few ocasions-- Especialy working on the Kalgoorlie Esperance line in very hot weather. Heat buckles were bad on that line and also the Leonora line.
Would hope we get some tech info from sombody who knows ect.
I did notice that when they re-railed the Kalgoorlie Main, they had gas burners on a rail trolley and heated the rails- pre -stressing them before the weld was done.
I always assumed that while it may stop heat buckles in hot weather-- surely the rails would be under extreme contraction stress in the very cold weather.
While this seems to work fine in Western Australia- I am curious also how they manage in places with very cold/hot summer and winter conditions.
Just more generous provision of expansion joint I guess, plus a good regime of regular greasing to ensure they slide ok.

Saying that I nearly derailed on the District Line one Summer's afternoon: they had been re-reailing between Barking and East Ham and hadn't finished the job and it was an intensely hot June day. I came hairing round the bend at about 90kmh and an oncoming train was flashing his headlights at me (a danger signal), so I whacked on the emergency brake. As I continued around the bend past the oncoming train a terrible kink in the rails came into view and I wasn't going to stop in time so I just winced and braced myself for what I though was the inevitable derailment. When the train came to a halt I opened my eyes to see I hadn't derailed and I'd gone about a car and a half past the kink. Not wanting to get marooned between two stations on a blistering hot day I guessed I might as well try to get the rest of my train over the kink so I gingerly inched forward whilst sticking my head out of the side of the cab to see if the back of my train was derailing!

What saved me was that the rails had buckled in perfect parallel, but they were distorted by about a metre and very sharply so if that oncoming driver hadn't slowed me down I'd have come off for sure, and at that point the District Line is right next to the fast lines out of Fenchurch Street complete with overhead wires, so it could have got very unpleasant indeed. I think he may well have saved my life.

It looked like this example of heat buckling, although not quite as severe:

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Old March 4th, 2008, 01:10 AM   #6
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Quote:
Originally Posted by tuckerbox View Post
I have never seen anything like that Rail Joint on our main lines!
Do your trains make the 'clackety clack' noise? If yes the rails comprise short sections of rail with end-on expansion joints rather than long continuous welds with the much longer, staggered joints.

You can spot them most easily on modern track as the sleepers switch from concrete to wood for about 4 sleepers, as these are what the stablising rails in the middle are bolted onto.
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Old March 4th, 2008, 01:40 AM   #7
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Quote:
Originally Posted by Tubeman View Post
Do your trains make the 'clackety clack' noise? If yes the rails comprise short sections of rail with end-on expansion joints rather than long continuous welds with the much longer, staggered joints.

You can spot them most easily on modern track as the sleepers switch from concrete to wood for about 4 sleepers, as these are what the stablising rails in the middle are bolted onto.
WELL- I am stunned. I never thought it got hot enough in England to have heat buckles. We operate Trains over here in extreemly hot conditions 45deg + and rail temps of 60deg+. If really hot weather is forecast we are ordered to run at reduced speed til 1800hrs.
As I stated previously-- No such joints like the one in the pic exist on our main lines- just continious welded rail for kilometers- some joints at track circuits- which are slightly offset.
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Old March 4th, 2008, 09:17 PM   #8
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Quote:
Originally Posted by tuckerbox View Post
WELL- I am stunned. I never thought it got hot enough in England to have heat buckles. We operate Trains over here in extreemly hot conditions 45deg + and rail temps of 60deg+. If really hot weather is forecast we are ordered to run at reduced speed til 1800hrs.
As I stated previously-- No such joints like the one in the pic exist on our main lines- just continious welded rail for kilometers- some joints at track circuits- which are slightly offset.
It's not so much how hot it gets as it is the difference between high and low maximums: Central areas of England have had a 50C+ extreme temperature range (e.g. up to 35C+ in Summer and down to -15C or less in Winter), of course the usual maximum / minimum is far more moderate which is why extreme highs can cause buckling in Summer.

Rest assured there is some provision for expansion in your rails, and more than most as I guess the range is wider due to freezing desert nights and incredible daytime sun temperatures. I must say such joints are easily missed unless you're looking out for them... As I said they're best spotted on modern track as you see 4 or so wooden sleepers instead of conrete.
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Old March 4th, 2008, 11:56 PM   #9
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Quote:
Originally Posted by Tubeman View Post
It's not so much how hot it gets as it is the difference between high and low maximums: Central areas of England have had a 50C+ extreme temperature range (e.g. up to 35C+ in Summer and down to -15C or less in Winter), of course the usual maximum / minimum is far more moderate which is why extreme highs can cause buckling in Summer.

Rest assured there is some provision for expansion in your rails, and more than most as I guess the range is wider due to freezing desert nights and incredible daytime sun temperatures. I must say such joints are easily missed unless you're looking out for them... As I said they're best spotted on modern track as you see 4 or so wooden sleepers instead of conrete.
NO- There are no timber sleepers on our East/West Main exept at some points and crossovers- Just continuos concrete sleepers.
Those timber sleepers in your pic look like Western Australian Hardwood Jarrah.
Give them back- We are running out of Trees!
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Old March 5th, 2008, 01:29 AM   #10
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Well, we've got them over here as well. Usually placed around junctions...

Greetings,
Glodenox
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Old March 5th, 2008, 05:39 AM   #11
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Quote:
Originally Posted by Glodenox View Post
Well, we've got them over here as well. Usually placed around junctions...

Greetings,
Glodenox
I think I am getting the picture now -Tubeman and Glodenox. In U.K. and Belgum its not so much extreem temps that call for your type of expansion joints but the large variation between minimum and maximum rail stress temps.
In Western Australia the lowest We can expect is minus 4 on rare ocasions and only for a few hours just before sunrise as a rule.
At Leonora which is semi desert country I have witnessed on many ocasions- as the sun comes up after a cold night- the sudden heating makes the track expand so quick that it goes off like a rifle shot.
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Old March 5th, 2008, 05:45 AM   #12
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Quote:
Originally Posted by tuckerbox View Post
NO- There are no timber sleepers on our East/West Main exept at some points and crossovers- Just continuos concrete sleepers.
Those timber sleepers in your pic look like Western Australian Hardwood Jarrah.
Give them back- We are running out of Trees!
Info obtained from Australasia Railway Corporation

Quote:
Originally Posted by Australasia Railway Corporation

Continuous Rail Welding

What are the welding processes used on this project?
There are two welding processes used;
  • Flash Butt Welding - this method is used to weld 13 shortwelded rail sections (27.5 metres) together into longwelded rail sections (LWR) of 357.5 metres, which are then used in the tracklaying process; and
  • Aluminothermic (Thermit) Welding - this method is used on site to weld LWR sections together.

What is flash butt welding?
Flash Butt Welding aligns the rail, charges rails electrically and hydraulically forges the ends together. The welderhead automatically shears upset metal to within 1/8" of the rail profile. A base grinder removes the 1/8" flashing material from the rail, which leaves a smooth base and greatly reduces the likelihood of stress risers, which shorten the life of the rail. The sides and head of the rail are also ground to the profile of the parent rail. As a final step in the welding process, a mag particle test is performed. These quality checks, plus two separate checks with a straight-edge and taper gauge, contribute to the complete job that makes a quality weld.

What is aluminothermic (Thermit) welding?
Thermit welding is a welding process, which produces coalescence of metals by heating them with superheated liquid metal from a chemical reaction between metal oxide and aluminium with or without the application of pressure.

Filler metal is obtained from an exothermic reaction between iron oxide and aluminium. The temperature resulting from this reaction is approximately 2500° C. The superheated steel is contained in a crucible located immediately above the weld joint. The superheated steel runs into a mould which is built around the parts to be welded. Since it is almost twice as hot as the melting temperature of the base metal, melting occurs at the edges of the joint and alloys with the molten steel from the crucible. Normal heat losses cause the mass of molten metal to solidify, coalescence occurs, and the weld is completed.

Why is the Alice Springs to Darwin railway constructed with continuous weld line?
To provide a low maintenance cost railway. The development of Continuously Welded rail was undertaken in Europe during the 1950's and 1960's and has been progressively introduced into Australia since that time until now it is the standard practice. Most of the rail tracks in Australia are constructed using this technique.

Why is continuous weld line low maintenance?
There are no joints to be maintained. In the early history of railways the rails were joined by mechanical joints which were designed to allow the rail to expand and contract as the temperature rose and fell. These joints were a significant source of maintenance as the bolts and plates that joined the rails often broke, the rails were damaged by the bolts and plates and could crack, the track was harder to keep level and the sleepers would be damaged.

How strong are the welds?
When the rail is trying to contract, the rails are trying to pull themselves apart. The point where this is most likely to occur is at the welds. The strength and the quality of the welds are sufficient to prevent this happening. An ongoing program of ultrasonic rail flaw inspections will be carried out to check the integrity of both the welds and the rails.

Older generation railway workers are adamant that you must have expansion joints otherwise the rail will buckle. How does the continuous rail overcome thermal expansion and contraction in the temperatures between Darwin and Alice Springs?
In order to balance the forces between those which want to buckle the track during high temperatures and those which want to pull the rails apart during cold temperatures the rail is layed at what is called the neutral temperature of 40 degrees Celsius. The range of rail temperature expected throughout the course of the year is approximately -10°C to +65°C.

On a railway the length of the Alice Springs to Darwin railway (1420km) this movement would be 16.3 metres for every degree of temperature change. It has been calculated that the rails are subjected to a temperature range of 45 degrees in Darwin and 74 degrees in Alice Springs. 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.

If the rail were free to move when heated or cooled it would expand or contract like all other steel. A small amount of the stress developed along the rail can be taken up with expansion across the rail. Its height and width expand due to their own dimension as well as some distributed stress from the longer length. The rail bulges slightly. As long as the column is prevented from moving sideways along its length it is very stable.

How is the rail constrained?
The rails are held to the sleepers by strong spring clips and prevent the rail moving along the track. The sleepers are very heavy concrete. Their weight and the friction of the ballast stop any movement. There are 2 clips for each rail at each sleeper. Each clip exerts a load of about 2 tonnes onto the foot of the rail.

When the rail is constrained from moving along the track the only potential expansion the rail experiences at any single point, is the expansion that could occur between two sleepers. Over 700mm, between the sleepers, the rail will try to expand 0.0077mm, about 8 thousandths of one mm.
There, that answers all questions regarding Australian tracks.

Also, British Rail began converting many lines to continuous welded rail following the Hither Green rail crash as continuous welded track is actually safer and requires far less maintenance than standard track. The only unfortunate thing is that it requires a higher initial cost.

Apparently all high speed rail is carried out on continuous welded track.

Last edited by Svartmetall; March 5th, 2008 at 05:50 AM.
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Old March 5th, 2008, 09:29 PM   #13
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Quote:
Originally Posted by Tubeman View Post
Do your trains make the 'clackety clack' noise?
Thank you. Does that mean the offset joint in the shot you shared earlier yields no noise, period?



Quote:
Originally Posted by tuckerbox View Post
the sudden heating makes the track expand so quick that it goes off like a rifle shot.
Yikes! Sounds like too much a snap for metal to withstand, no?
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Old March 6th, 2008, 10:20 PM   #14
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Thank you. Does that mean the offset joint in the shot you shared earlier yields no noise, period?
Yes pretty much so
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Old March 8th, 2008, 08:33 AM   #15
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In North America, thermal expansion/contraction is handled in the way described in that Aussie item above. During installation, the rail is heated to about 40C (or whatever the maximum local air temp is normally expected to be, if higher) and then rail anchors are clamped on. When it cools, the rail comes under tremendous tension and that thermal contraction is accounted for by a reduction in the cross-section profile area of the rail - the cooler the air temp, the greater the tension and reduction in profile.

It is normal for railroad section crews to have to more frequently inspect for and repair 'pull-parts' and broken rails when the air temp gets deep into the negative double digits C (steel also gets increasingly brittle as it gets colder) and -40 is not unusual for wintertime low temps in northwestern Wisconsin. Railroad operating rules include special cold-weather speed restrictions for that reason.

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Old March 8th, 2008, 10:11 AM   #16
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Surely these huge stored-up tensions could be hazardous? Doesn't it all suddenly go 'ping' sometimes?
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Old March 8th, 2008, 10:41 AM   #17
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@train rover....
you mean that you're looking for part's of railwais where the track is welded all togetter, so you won't get that clacky noise. well, in my place i've got a 20 year old track. it's all build in a huge curve and with some special 'in that time' new track technologie, i don't know much details of it. the whole piece is welded togetter so it's 50 kilometers of track without ignorant kbunk bkunk. i don't know if this is what you mean?
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Old March 8th, 2008, 06:11 PM   #18
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Quote:
Originally Posted by Tubeman View Post


Surely these huge stored-up tensions could be hazardous? Doesn't it all suddenly go 'ping' sometimes?
Rail anchors are pretty good at holding things in place. That said, as the weather gets colder, pull-aparts and broken rails do get more common (the contraction tied with steel getting more brittle as it gets colder) so section crews are busier and trains do have more rigorous speed limits in very cold weather.

Even with that, an occasional 'impassible sun kink' will still happen in hot weather, too.

Mike
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Old March 9th, 2008, 11:02 AM   #19
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Quote:
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Rail anchors are pretty good at holding things in place. That said, as the weather gets colder, pull-aparts and broken rails do get more common (the contraction tied with steel getting more brittle as it gets colder) so section crews are busier and trains do have more rigorous speed limits in very cold weather.

Even with that, an occasional 'impassible sun kink' will still happen in hot weather, too.

Mike
So if pull-apart breaks in extreme cold and expansion buckling in extreme heat are still a hazard, is this method really ideal?
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Old March 9th, 2008, 09:39 PM   #20
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Ten to fifteen years ago, I read a technical discusion of using very gently curving railway lines instead of straight lines to absorb the expansion and contraction of the actual rails on a continuously welded railway. The ballasted road bed on the curves was designed to absorb the changes in length of the rails by moving in and out. To balace the inside/outside rail effect, it required "S" curves!

I appologise, but unfortunately, I cannot find the original material to give you a citation.

The conclusion was that it would probably reduce the catastrophic "kinks' significantly but it required extremely costly maintenance which would limit its application. I have never heard of this actually being applied in practise.
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