ChatterBank77 mins ago
Expansion of Railway lines
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In the old days there where expansion gaps between rails so tat when they get hot they can expand rather than kinking. Now modern lines are welded so they are all in one peice. How is the expansion catered for, I mean is there room at the ends for longitudinal expansion? Any rail experts out there?
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Because welded track has very few expansion joints, if no special measures are taken, it could become distorted in hot weather and cause a derailment.
To avoid this, welded rails are very often laid on concrete or steel sleepers, which are so heavy they hold the rails firmly in place, and with plenty of ballast to stop the sleepers moving. After new segments of rail are laid, or defective rails replaced (welded in), the rails are artificially stressed.
The stressing process, involves either heating the rails causing them to expand,[1] or stretching the rails with hydraulic equipment. They are then fastened (clipped) to the sleepers in their expanded form. This process ensures that the rail will not expand much further in subsequent hot weather. In cold weather the rails try to contract, but because they are firmly fastened, cannot do so. In effect, stressed rails are a bit like a piece of stretched elastic firmly fastened down.
Engineers try to heat the rail to a temperature roughly midway between the average extremes of hot and cold (this is known as the 'rail neutral temperature'). If temperatures reach outside normal ranges however, welded rail can buckle in a hotter than usual summer or can actually break in a colder than anticipated winter.
Joints are used in continuously welded rail when necessary; instead of a joint that passes straight across the rail, producing a loud noise and shock when the wheels pass over it, two sections of rail are cut at a steep angle and put together with a gap between them (a breather switch). This gives a much smoother transition yet still provides some expansion room.
I didnt cut and paste this straight from Wikipedia.....honest!
To avoid this, welded rails are very often laid on concrete or steel sleepers, which are so heavy they hold the rails firmly in place, and with plenty of ballast to stop the sleepers moving. After new segments of rail are laid, or defective rails replaced (welded in), the rails are artificially stressed.
The stressing process, involves either heating the rails causing them to expand,[1] or stretching the rails with hydraulic equipment. They are then fastened (clipped) to the sleepers in their expanded form. This process ensures that the rail will not expand much further in subsequent hot weather. In cold weather the rails try to contract, but because they are firmly fastened, cannot do so. In effect, stressed rails are a bit like a piece of stretched elastic firmly fastened down.
Engineers try to heat the rail to a temperature roughly midway between the average extremes of hot and cold (this is known as the 'rail neutral temperature'). If temperatures reach outside normal ranges however, welded rail can buckle in a hotter than usual summer or can actually break in a colder than anticipated winter.
Joints are used in continuously welded rail when necessary; instead of a joint that passes straight across the rail, producing a loud noise and shock when the wheels pass over it, two sections of rail are cut at a steep angle and put together with a gap between them (a breather switch). This gives a much smoother transition yet still provides some expansion room.
I didnt cut and paste this straight from Wikipedia.....honest!
I wouldn't want to disagree with Ethel, however the technology and science for heat expansion in CWT (Continous Welded Track) has been in place for a number of years. Primarily, the tracks are held to the crossties and the crossties are more firmly embedded into the underlying ballast that the older individual tracks. A special type of tie spike is used. Either a large screw type or a hairpin type of spike is used to assure the non-slippage of the track to track plate to the rail tie... which is often made of concrete. The railway system in India has been responsible for testing new methods of preventing changes in the gauge of the tracks due to the extreme heat they experience... (Sorry, Ethel
i laid c.w.r. for a couples of summers in canada when i was younger and most of the posts are mostly correct as ianess says there are still periodic 'expansion rails' installed bracket/bolt assembly at the joint has built in room for movement, like a slip joint for expansion/contraction. work day starts as soon as it is light and the track is heated to a predetermined temperature and the steel is laid. when it comes to the hottest part of the day you find some shade and sleep. when the temperature is right again away you go, as it cools the heaters are on again and you work until just before dark. a long and gruelling day. but even with this, in extreme heat you will stll get a 'sun kink' as there is no where for the rail to go but sideways . sorry if i repeated anything as i just kept typing. gary baldy is talking about hydraulicly stretching the rail, this may be a technique used only with steel or concrete ties or sleepers as he's calling them. i am not familiar with this technique but i am sure he is correct. cheers!
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