If you weld all of the rails together how does it contract and expand due to temperature changes?
Thanks, Hans
Laying welded rail(CWR) is sort of an art form. Rail clamps that dig into the ballast are used, and the temperature when the rail is laid plays into this. There are charts to with information on how much rail expansion to allow for on joints.
Jim
When laying the rail and - if necessary - when doing maintenance there is a system of adjusting the rail called “stressing”. This involves anchoring the rail at one end and pulling it at the other with hydraulic rams temporarily set in the track. While this is being done the rail is free from its normal fixings and has rollers placed between it and the tie and guide rollers on both sides. Releasing the rail and putting all the bits in place and subsequrently reversing all this can involve a lot of parts and a pretty large team of guys… but an experienced team will whiz through the work.
That very broadly covers the initial solution…
CWR/ ribbon rail is not rigid. When it heats and cools it does move around. To allow for this each rail has what we unofficially call a “breather” which is a type of expansion joint. In one rail a breather looks like two switch points pointed toward each other. The inner one (in the 4’ way) which maintains the gauge face is fixed and the outer one is able to slide past it - outside the gauge. I’ve only ever seen them in matched pairs. They are normally 6 to 8 tie spaces long here (UK). They normally have two lengths of rail bolted or screwed to the ties in the 4’ way placed equally either side of the joint. At the start of the summer the joints are usually throughly greased with black gooey stuff (That’s a technical term for specialised grease).
Peco do a model of the standard UK type in 00 Gauge - there’s probably one in their catalogue…
I have loads of photos of variants in use and components waiting to go in or having been recently(ish) taken out… just need to get round to figuring out how to post them.
Breathers are normally installed as required in plain track subject to local conditions… PLUS they are usually put in on at least one side and often
The temperature of the rail is monitored when it is laid. The rail has either anchors or clips on it that restrain the linear movement of the rail and force the expansion of the rail vertically. The ballast section also restrains the movement.
I think you’ll find that the rail slides lengthways - hence the breathers I’ve described. It isn’t desireable for rail to move vertically as you can’t manage where (or when) this will happen. In exactly the same way you do not want the rail to move laterally. Either vertical or sideways movement is potentially a kink in the rail/track which can produce a derailment. Also vertical movement would be similar in effect to a dropped joint… it should be prevented by the ballast… but if it occurs it can produce voids under the ties (which are an elemenet of a dropped joint). Lifting of the rail - especially if repeated - would tend to rip the spikes (or whatever other fixings) from the tie looseneing the rail - this would affect both maintenance of the correct gauge and the ability of the rail to not roll outwards under load.
At an extreme suden rail movement due to expansion (more often than contraction) will cause either track buckling or a fractured rail… in jointed track the fishplates may fracture instead of the rails. Either can cause a derailment.
Hope this helps.
[:P]
PS… it occurs to me that there are also clips of various designs attached to the foot of the rail and set against the sides of the ties (on one or both sides) that will act to prevent rail creep. I’m trying to recall if/how much I’ve seen these in use on CWR… and I’m failing… They are pretty common in jointed track especially on heavy grades.
[:P]
PPS What is wanted is essential rail movement without track movement…
The other answer is that modern high-tech rail contracts and expands very little. This is due to advances in metallurgy and rail design. In some (problem) places they put coatings on the rails to reflect the sunlight… this is not supposed to be put on the north side! [banghead]
Who cares if the rail gets 1/16 in taller.
We don’t use “breathers” or all that hydraulic stuff you were talking about here in N America.
You are confusing the TRACK moving vertically with the rail itself EXPANDING vertically.
Not really because you may be describing UK practice but not N American practice.
CWR will have either clips (concrete ties) or rail anchors (wood ties) because they keep the rail from moving laterally.
N American railroads don’t want either. We don’t want the rail to run (screws up switches and other track appliances) and we don’t want it to move laterally. After the rail temperatures settle, US roads may actually cut pieces of the rail out to address expansion issues or cut in plugs if the rail is getting too tight.
As Dave H explained, North American practice is quite different from the UK practice. For any given region a “neutral” temperature is specified, which is the temperature at which the rail is completely unstressed. At temperatures colder than the neutral temperature the rail tries to shrink, and at higher temperatures tries to expand. It is restrained from doing either by the rail anchors pushing against the ties, which are embedded in the ballast. If the tension or pressure for a mile long length of CWR was allowed to build up there would be a major problem, but the rail anchors limit the forces to short 2’ to 6’ segments. Naturally it is important that the ballast section be good and the rail anchors firmly applied.
Note that rail temperature can be very much hotter than air temperature on a sunny day, so typically the “neutral” temperature is at the high end of what you might experience. Usually when CWR is laid it is at a lower than neutral temperature. Then the simple method is to calculate how much longer the 1/4 mile section would be if it were at the neutral temperature, cut out a piece an inch or two long, and heat the string until the gap closes. Quickly bolt it together, and then apply rail anchors. No need for any hydraulic pullers. If the rail being laid is above the neutral temperature, the gang will have to come back later and restress it. This will involve removing all the rail anchors, cutting out a section of rail, and inserting a new longer piece, usually heating the rail back up to the neutral temperature, and finally reapplying the rail anchors.
Rail anchors are necessary where the rail is held in place by traditional spikes. Some of the clip designs, especially common with concrete ties, also prevent longitudinal movement and the separate rail anchors are not needed.
Routine maintenance of jointed rail used to include oiling each joint to ensure the rail would move within it to take up the expans