Welded Rail

[sooblue]

Some time ago right after the Amtrak autotrain derailed there was a discussion on welded rail and sun kinks.
One of the RR experts posting on that thread pointed out, if I'm remembering correctly, that rail anchors are used to force the rail to expand through the crossection and upwardly not lengthwise. I agreed, but because of what I know about steel and how it reacts to heat, even a small amount of heat, I went away still puzzled.
I have found the lost puzzle piece, that one piece of information that completes a story and solves the mystery.

Rail anchors alone will not stop a sun kink, They help to control the forces though. What than, really stops a sun kink from forming?

Before welded rail is laid down and anchored it is preheated, not much, just enough to cause it to expand an amount slightly over what it would be expected to expand with the heat from the sun.
Than when the rail is anchored down it cools and contracts but the rail anchors were put on when the rail was in an expanded state so the rail goes into a negatively tensioned condition between the ties, pulling on the ties. When the sun heats the rail it expands and the negative tension on the ties become neutral.
Too much heat and the negative tension becomes so great that they get what is appropriately called pullaparts. Not enough heat and you get sun kinks.

Side bar,
Steam boilers on locomotives are not immovably anchored in the back (firebox end)
they are sitting on slides. When a boiler gets to normal operating temperature it will grow up to an inch or more, longer, and the bottom of the boiler will be 1/4 of an inch to 3/8 of an inch shorter than the top!
Just call me "cliffy"

Sooblue

[Anonymous]

I've never heard of preheating the entire rail (that's not to say that they don't do it), but, I have seen/heard of them stretching or tensioning the rail before they weld it to the next section. I have used orgo thermite and butte welding processes where the ends of the rail to be joined must be preheated before the crucible can be ignited and the process started......for what its worth.
Ken

[cabforward]

is welded rail treated for cold weather? from montana to main and in alaska.. in places where all kinds of engines run 24/7, motor oil solidifies and metal tools snap like dried wood, what happens?

[dknelson]

Paul Mallory's bridge and trestle book makes a similar point about steel bridges: they are anchored on one end and sit on rollers on the other end because they expand in heat. There might be bridges that just rest on supports on both ends without being rigidly attached
Dave Nelson

[mudchicken]

Paragraphs 2 and 4 in the original post do not quite fly.

PP2 - Understand the condition that can be caused by skew ties and concept of balanced forces in the track structure?. Better yet, ever wondered why switches and the areas around them are more heavilly anchored than anyplace else? (if they were not anchored, the switch wouldn't always throw!)

You try to lay rail in the spring and fall. A 1440 ft. string of rail is hard to heat up with a set of propane burners on a rail trailer. As for cooling the rail down, about all you can do is bury it in wet ballast (and then you can't work on the rail or place anchors)

Bridges are not fixed on one end to allow for forces, including expansion and contract, to happen without damaging the bridge due to warp.
You cannot calculate the forces in a bridge either with both ends fixed. Engineers refefer to that condition as being "statically indeterminate". Bridges not fixed at either end risk damaging the headwalls or sliding off the top of the bents (piers)....

PP4 - Rail is NOT always preheated, the concept is a target temperature to balance tensile and compressive forces in an areas normal temperature range. Trackmen call rail laid at the proper temperature "happy rail".

-former railroad roadmaster, engineer, surveyor

[sooblue]

>PP4 - Rail is NOT always preheated, the concept is a target temperature to balance tensile and compressive forces in an areas normal temperature range. Trackmen call rail laid at the proper temperature "happy rail".
The heat added to a rail would never have to be greater than the heat added to the rail by the sun. Except that you would have to allow for added forces over a predetermined length of rail.
Heating rail doesn't mean hot enough to make bacon on. It would only need to be raised a few hundred degrees. If the ambient temperature was 100 at the time the rail is laid you may only need to raise it 200 more.
There are many places in this country where rail would never have to be heated. Any place that had consistently close temperature ranges will most likely never have rail heated. There has to be a temperature range where rail is nominally affected.
It may well be that a trackman or even an engineer (mechanical) would never see rail heated in his area.
But you referred to it though, "happy rail"

For the post that referred to Alaska - I know that steel can be "Styled" Metallurgicaly. Some steel reacts to cold by coiling up like a spring; steel can be made acid proof. I'm from Minnesota, with the temperature down in the teens I pass 300 deg. steam through a 1 1/2 inch strait pipe that is located outside, that pipe sags like it is melting down 1 foot/10 feet. Steel is quite interesting, two things you may not know.
Steel is a crystal and when steel gets to the temperature that is called red run it loses it's ability to be attracted to a magnet because it's molecules are moving too fast.

I will have to get out my Trains Magazine from last month (I think) that is where I first heard of this being done.
I meant to post this right after reading about it but with all that has happened in the last two months I forgot about it.

Sooblue

[Anonymous]

Sir, How do you fix a sun kink? Are sun kinks easy to spot? Why not install jointed rail at certain lenth's to take in expansion problems?
TIM A