Last weekend I went to Northlandz in Flemington N.J. In one of their display cases was a “rail thermometer” used to check the temperature of the rail before and after a train passed. Also said it was used by many eastern railroads PRR, B&O, ect. I’ve never heard of this or read about it, what would this info be used for or tell you?
The laying of welded rail…and before that, gauging the size of the gap in jointed rail to balance hot/cold pressures to avoid kinks and pull aparts.
Rail thermometers are still sold today. Any rail maintenance supervisor from foreman on up still has one. http://www.ptc1.com/thersur550.htm
The point being (for continuously welded rail) that there is such a thing as a ‘neutral’ temperature. Without getting too complicated, rail expands when it gets hot and contracts when it gets cold (or tries to). Jointed rail could, and the movement in 39 feet isn’t all that much – but there does have to be a gap as mc said. Continuously welded rail mustn’t move (the expansion or contraction, cold night to hot sunny day) is several inches (oh where is that formula when I need it?) per mile. The rail, however, is restrained against moving by rail anchors to the ties. The neutral temperature is that temperature at which the restrained rail has neither tension nor compression in it – if you took all the restraints off, it would just sit there. Anything colder, and there is tension. Anything hotter, and there is compression. Objective of the exercise is to get the neutral temperature so that the tension when it gets cold isn’t too great (which would give you a pull apart) and the compression when it is hot isn’t too great either (compression gives you kinks – ever push on a string?).
The rail doesn’t have to be laid at the neutral temperature – but if it is colder, it must be stretched to compensate, and there are tables for that.
[emphasis added - PDN]
The “before and after a train” part is new to me - I’ve never heard of a rail thermomenter being used to obtain the a temperature reading before and after the passage of a train. I can’t see that the train would affect the rail temp at all, other than maybe the shadowing effect of a long freight train from the sun might allow the rails to cool down a few degrees - but again, that information would be of no practical use that I’m aware of.
Alternatively, from a physics-work-energy standpoint, some of the energy expended by the locomotives to move the train over a given section of track might wind up being transferred to and absorbed by the rail as friction, wear, and elastic flexure (less the rebound). But that is pretty much a theoretical thing only, and outside of a lab with closely controlled conditions, could not be measured or quantified in a meaningful or useful way. And again, I’m not aware of any practical use for the information.
- Paul North.
.0007 x L x DeltaT
Wonder if they knew what a taper gauge was, or did they manage to throw that out?
The temperature before and after thing is most likely somebody’s local fiction.
The before and after thing strikes me as something that could be a factor, if there was enough heat generated, but it doesn’t appear that that’s the case.
MC - The link you provided is a direct-contact device. Have hand-held infrared thermometers found a home in this application?
DISCLAIMER: The supplied link is just one I found. No product endorsement given or implied.
Yes, you’re much more likely to see a gun style thermometer than the magnetic ones. You just point the thing at the rail and you immediately get the temp.
Came across a ‘rail temperature chart’ the other night.
A 1300 foot string of rail will expand/contract 4 5/8 inches with a 45 degree F temperature change according to the chart.
-00- in there somewhere. The only thing I remember thirty something years after taking the materials class, it would seem.
Thanks for the info guys. The info was hand written on an index card under the thermometer. The part about before and after a train passed got me wondering.
We can safely assume the shackles from the white boxcars are somewhere nearby?
I recall that pennies left on the rail head were pretty darn hot after being flattened by the train. With hat in mind, I could see the bearing surface of a rail getting warmer after a train passed, but would be surprised if there was a measurable temperature rise in the balance of the rail.
I wouldn’t. Between the ties, there is deflection of the rail as each wheel passes over it. That’s mechanically working the entire cross-section.
Chuck,
Good point, though the amount of deflection depends a lot on the rest of the track structure.
- Erik
Were the pennies placed there on a sunny day ? Are you sure that they weren’t warmed by the rail’s basic temperature, as opposed to the train’s wheels ? Once the pennies were flattened, they wouldn’t deform any more = not absorbing any more energy. Plus, being copper they would release the heat pretty quickly.
Instead, I surmise that the heat came from the rail. The rail can absorb a lot of sunlight and turn it into heat, and be quite a bit warmer than the ambient air temperature - 20-30 degrees, easy. One of the first hard lessons for a newbie to learn in the real-world of track maintenance is not to touch, lean on, or grab a rail in the sun on a warm day with bare skin - the rails can easily get hot enough to produce1st degree burns ! (whatever temperature that is) Anyone with experience from the Southwest US can attest to this, although it can and does happen just about anyplace.
- Paul North.
My recollection (this was pre-Amtrak) was that we did this at night and presumably the rail had a chance to cool down. If my less than perfect memory serves me, we were waiting for the southbound San Diegan at Anaheim and the pennies were overun by a northbound San Diegan.
FWIW, I’ve done a fair amount of track work at OERM in Perris, CA and am all too familiar with how hot steel can get in the hot sun.[:)]
Very true!
Your comment made me think of the BN in 1981 in Quincy, IL, just south of the Wisman Lane grade crossing, where they had a “soft spot” on the eastern rail just south of the crossing. I got stopped there a few times for freights and there was so much dip that it looked like some of the box cars were about to tip over. That rail got quite a workout.
I wonder how long that could have gone before the rail finally gave.
BTW, that is right where the Quincy Amtrak station is now. In 1981, the Amtrak station was in West Quincy, across the river.
I seem to recall a summertime rule-of-thumb of ambient plus 30 degrees in high sun times. That makes sense.
There was an article in Desert magazine about 40-50 years ago where the author was relating stories of his boyhood in Needles CA. One of the summertime tricks he and his buddies would play was to wait until a westbound passenger train would stop at the station in the middle of the day, then quickly jump onto the tracks and crack an egg on the tracks, where it would appear to fry. He said that one time they did that, the easterner on board who was standing on the rear platform got off and went to the ice house to keep cool and caught pneumonia. I didn’t really believe all of it then, but it makes for an amusing story.
Hmmm. OK, probably worth a quick check. Conceptually, it’s the area within the the plots of the stress-strain curve for steel as it is both loaded = stressed, and then unloaded = destressed. If I recall my "Nature and Properties of Engineering Materials class and text correctly, that’s called the “hysteresis loop”. Next time I see that book or a similar one for steel someplace - I seem to recall that we used to have a couple of those businesses around here in the Lehigh Valley and Eastern Pennsylvania once upon a time - I’ll look it up to see what the analysis looks like and what typical values are. But I believe that the far harder task will be to calculate the actual stress level in the rail - it is so variable, mainly dependent on subgrade conditions, that the only way to even begin to approach it here is to make a rough simplifying assumption. (Those who have read some of my previous posts know that I have no hesitiation in doing that to try to get a handle on some of these questions.) So we’ll see what comes of it when I have the time. Meanwhile, if anyone else wants to try, have at it.
- Paul North.
Have fun!
I had the materials class (required for everyone) and the solid mechanics class (one other EE weirdo in there, for whatever reason) as an elective, then it was all EE and math for the rest of my academic career. Those were fun things to think about, like, for instance, what are the differences when the rail is in, s