The February issue of Trains Magazine has a good article about the 7 physical phenomena that cause derailments… They tried to make the explanation straightforward but some things seem to have been glossed over a bit.
Question- the part about sun kinks says that a mile of welded rail can grow 17" on the hottest days, causing potential problems. Were sun kinks not as big a problem with 39’ stick rail? The way I figure it each bolt would have had at least 1/16" of play in order to get the bolt to slide through the hole. That would mean 1/8" of play every 39 feet, which equals 16.92 inches of growth before running into problems?
A few years ago there was a picture in the magazine of a steam-era heat kink, which was offered as an exemplar of such behavior in jointed rail. According to the 1950 edition of Hay’s Railroad Engineering text, joint bars could “freeze” to the rail from corrosion and thus not allow thermal expansion/contraction to be properly compensated for, thus resulting in kinks or pull-aparts. (As an aside, in another post today, Jeff Hergert noted a number of pull-aparts in and around his territory.) According to Hay, strategies to combat joint-bar freezing involved some form of lubrication.
Interesting. You’d think the corrosion between the joint bar and the rail would be a pretty weak link that would let go pretty quickly when the rail grew or shrunk.
the track structure lomits expansion and there was a discussion of welded rail vs jointed rail in at least one previous thread.
I remember that the total epansion in a given length of connected jointed rails is more than than in the same length of welded rail because the welded rail is forced to expand in width and height instead of length. The track structure limits longitional expansion and there are only two ends to expand instead of many.
Do not forget that the joint bars are secured laterally with clamping tension by the bolts, which perhaps themselves are rusted so they don’t self-loosen. The effect is to key the joint with corrosion, making it far more resistant to longitudinal motion, until some of the clamping force is relieved. This was commonly done by section crews in the days of more hands-on line maintenance, with reference to the crack of rail ends coming together when enough bolt tension on the bars was relieved.
The ‘lubrication’ Hay mentions is partially to prevent intercorrosion in the joint, partially to assure movement when the bolts are loosened.
One must also consider the track bed. Back in the day, as I understand it, ties were only half-deep in the ballast - longitudinal support was less than we find today.
Nowadays, the ballast is kept right to the top of the ties, which helps keep the track in alignment, which is one reason that welded rail is forced to expand outward, as discussed.
Every now and then the expansion overwhelms holding ability of the ballast and you get one of those carnival ride kinks that show up occasionally on social media.
The slack in jointed rail may help deal with normal expansion, but provides than many more places where a pull-apart can occur. It just depends on which set of bolts fails first…
Welded rail is a technology that the railroads have yet to MASTER in all of the various weather conditions. When I was working, the first cold snap of the season ALWAYS produced a high number of broken rails and pull-a-parts when it hit. Trains moving over the territory were constantly leaving on track occupancy indicators on CTC model boards all over the system - when Signals & Roadway investigated the track circuits they found broken rails and pulled apart rail joints. In unsignalled territory the signal maintainers got called out for crossing protection operating without the presence of trains.
When the heat would hit during the summer you would end up with Sun Kinks - and the signal system did not help identify them, they would have to be seen.
I’m not sure how it translates to American practices. The physical pasics are the same but the fastener systems differ and thus the longitudinal resistance might differ.
Regards, Volker
Edit: Rails are usually fastened with elastic clips to the ties in Europe. These clips provide a vertical pressure between rail and tie and by resulting friction a resistance against longitudinal movement of the rail by changes of temperature or outer forces.
In spiked track the rail anchors are intended to do the same. How effective they are I can’t answer
I’m not aware of any modern-day practice - say, after 1940 - to loosen and lubricate bolts or joints generally so as to allow the rail freedom to move. That might have been done in a specific instance to relieve the accumulated thermal forces or slippage of the rail (sometimes called “running”) - either tension or compression - in the rails at a certain location at a particular time, but not elsewhere in the absence of an evident problem. Work on bolts and joints in my experience and knowledge was always to tighten them. Lubrication was generally applied only at the time of laying of the rail, rarely afterwards.
All that said, others may have had different experience and knowledge.
As to rail anchors, their purpose is to keep the rail from sliding past a tie by use of a mechanical compression (only) fixture - it clamps around the base of the rail and bears against the side of the tie. Without them, there’s very litt
That being said, this accident report concerning the Amtrak Auto Train hitting a sun kink in 2002 near Crescent City FL has a detailed discussion of track dynamics and structures. I think I’ve linked to it before but it is an interesting read on how track can “go bad” unexpectedly.
Ya know how hard it is to find a working mutiple bolt/ joint tightening machine anymore? - Those rascals are dinosaurs in a CWR world. (I had some 90 MPH territory with 132 CWR (laid 1954) in western KS that was a constant headache - no lubrication there unless you were backing off the bolts with penetrating oil to change out bars or a dutchman/bolt hole break.)
Anchors also solve the skew tie problem that used to be a big problem. rails tend not to run in anything resembling a uniform manner. However the anchors have to work and finding anchors for less than 112/115# rail is a problem. Those rails and turnouts have bigger headaches these days because they do not make the smaller anchors and used anchors are shot. (just slide along the B/R and fall off eventually).
Question - if rail anchors diminish or somewhat control the linear movement of rail caused by temporature change then rail must adjust by - getting taller and fatter within the confines of the area between the applied anchors? Further analysis please MC, Paul and any who choose to contribute.
From Armstrong’s book, The Railroad, what it is, what it does, the “secret” for CWR is laying it at near max temp so it is usually under tension. As temperatures drop, the height and width are reduced slightly (IIRC subject to Poisson’s ratio to exactly how much they are reduced). Conversely the rail should expand in cross section when the rail is above neutral temperature.
I suppose it would be possible that the neutral temperature could be set lower if there was a reasonable way to constrain the track structure in the same way that guy wires keep a guyed radio tower from buckling. (Had an 80’ foot tower in the back yard of my first house.)
And please keep in mind that I am not a structural engineer.
If a single stick of rail is heated, it will expand in all directions by a certain percent. So it will get longer, taller, and wider according to the percent of expansion.
If you constrain it lengthwise so it cannot get longer due to expansion; does it then get wider and taller than it would have, had it not been prevented from expanding lengthwise?
That has been my understanding, but I am not sure if it is correct.
If this is true, then the rail grows in height and width for two different reasons:
The direct thermal expansion of height and width if the length is not prevented from expanding.