Sorry for sharing my latest random trivial thought, but are sun kinks less likely to occur on lines with cement ties?
It is my understanding that if lines are installed and anchored correctly, the expansion of CWR will cause upward expansion rather than the outward expansion that would otherwise result in a rail kink on a hot day. As concrete ties are considerably more heavy than wood or plastic ties and the concrete rail fasteners appear to be more reliable than railroad spikes (I have often seen railroad spikes coming out of a tie on even well-maintained lines; I have never seen a concrete rail fastener come loose), I would think this system would provide a much better anchor for the rail and mitigate outward expansion.
Anyone care to edgumacate me?
Also, does heavier rail have any relation to rail kinks–i.e. assuming they make 95lb CWR, is it more or less likely to have a sun kink than 140lbs CWR? Part of me thinks that a heavier rail would be less likely to bend but another part of me thinks that there would be more rail to expand.
Finally, if due to the angle of the sun on a tree line, the inner rail is well shaded but the outer rail is exposed to the sun, will there be a bigger problem with anchoring/sun kinks because there is an unequal tension placed on the line-i.e. the outer rail is asserting considerably more tension than the inner rail?
Thanks in advance,
Gabe
P.S. Are there general rules regarding speed restrictions during times of high heat that causes rail kinks or is it line specific? I have seen 105 degree days with trains running like the dickens in southern Illinois, and I have seen 95 degree days with speed restrictions for fear of sun kinks on the same line.
Rail on concrete ties will kink just as it would on timber ties. The question will remain how close to the target temperature was the rail laid at.
Pandrol clips replace anchors in many applications, but they have similar issues to anchors in holding rail to the tie in the direction of travel. As with anchors, the more the wear - the less the holding power (and the bigger the problems). And rail can go up as well as right and left (big headache to get it back.) Big scratches near the clips are a warning!.
Insufficient shoulder ballast can eat your shorts in concrete tie and curve territory…
90/100 Lb CWR , though less common, will shift as well as the big 133/136/141/144 stuff. The big stuff, because there is more of it in x-section, has a slightly larger chance to heave - But it still is 0.0007 L delta T…the physics is constant. Any more getting anchors and new OTM for the 85/90/100# stuff is hard and worn anchors are almost useless. The least effective OTM will fail first along with I-Bonds/Insulated joints with timber ties under them in otherwise concrete tie territory.
Old roadmaster’s trick to cool off rail in the sun to stabilize it is to bury it to the top in ballast (but that does a number on your ballast budget)
This can be as much art as it is science, but the science behind it is sound. The art comes in the application.
The science:
The formula for the expansion of an unrestrained rail is L’=L x .0000067 x T
L’ = the change in length, in inches
L = the starting length, in inches
.0000067 is the coefficient of expansion for steel
T = the change in temperature in degrees F
So for 1000’ piece of rail subjected to a change in temperature of 50 degrees (morning temps of 50 and rising to 100 at mid afternoon is a typical occurence), the rail will grow about 4"
Anchoring the rail to the ties and embedding the ties is a good stable ballast structure is what is done to restrain this potential growth. If you can do that, using wood or concrete ties, you have dramatically reduced the potential for a sun kink. Note I did not say it was eliminated.
Becasue of the shape of the rail and that it is fastened to the ties, it is very unlikely that the rail will buckle in the vertical plane. It will go sideways.
Concrete tie fasteners combine the function of the typical track spike (to hold line) and the rail anchor (to restrain longitudinal movement) so they benefit from more restraining force per segment of track than wood ties track where only every other tie has anchors (which is typical and sufficient for most locations)
The sun/shade question often times doesn’t make a lot of difference as the shade is more often spotty and you are considering the rail temperatures over many miles of track and you focus on the higher (sunnier) locations. Again, sun or shine, hot or cold, if you have done a proper job of restaining the movement (both expansion and shrinkage) your risk of a sun kink or pull apart is reduced
There was a very interesting STB report on an Amtrak derailment in Florida in the early part of the decade. The report explained in detail the proper installation of welded rail, tamping, etc.
There was a discussion on the report here in which our experts added considerable information.
Sun kinks are really an amazing occurance, as long as it doesnt affect people and property.