Keith Lane - This one's for you......

That is cool.

So, Keith. Something I've been wondering. It seems that the rails in Europe are all welded rail where in the states we still have that bolted system to join rails. With the welded rail, how do they take care of thermal expansion? I thought that was the purpose to the bolted connections?

Thanks
 
I was wondering the same thing. NJ Transit put down new rails some years ago. The new rails were very long from a car...looked to be 1/2 mile long. How does thermal expansion work for those things?
 
NC Pilot said:
That is cool.

So, Keith. Something I've been wondering. It seems that the rails in Europe are all welded rail where in the states we still have that bolted system to join rails. With the welded rail, how do they take care of thermal expansion? I thought that was the purpose to the bolted connections?

Thanks
Click to expand...

Actually there are extremely few main line miles of jointed track left in the US. (No more clickety clack)
Continuously welded rail (called CWR in railroad lingo) is by far and away the most common now. CWR is actually made up of 39' joints welded into 1/4 mile sections by "flash butt welding". It's pretty inpressive. They put positive DC on one rail and mnNegative DC on the other and shove the two ends together with gobs of amps. The rail ends melt together consuming about an inch of the total length of rail. It's then put on a "steel train" which typically holds 40 pieces of rail about 1300 feet ling each. Heavy rail now weighs 141 pounds per yard.Thats a little under 2.5 million pounds of steel on a train. The old jointed rails were 39' long too. The rail rolling mills just never changed to run longer pieces.
As to thermal problems, it's called rail stress management, and it's a big part of what I do. Using climatology records for a given part of the country, the gang installing the rail installs the rail at a specific temperature. In most of the CONUS that temp (called the "Preferred Laying Temp" , or PT is 80°F. Higher in the desert Southwest and lower in places like North Dakota. The rail is heated to the PLT, and is spiked, or clipped as in that video before it can cool down. That means at 80°, the rail is neither trying to pull the curves straight (called stringlining) nor is it in compression trying to kink out (called Sun Kinks). This happy temperature is called the stress free or neutral temperature. For every degree F above the neutral temperature that the rail rises about a ton of compressive force is added to the rail. The only thing preventing rail armageddon is the ties, spikes and ballast (the rocks). If you lay the rail too hot in an extreme cold environment, it may pull itself apart (rail break) in winter as it goes into such extreme tension that a flaw in the steel gives. Sun kinks, however are much more dangerous as they are violent occurrences that usually happen while the train is passing over and they cause a massive pileup in the middle of the train. The compressive forces are waiting to go and the vibration of the train and the added heat of the wheels cause the track structure to give away. Pull aparts always happen in winter, and if the rails are being used for signalling purposes too, a loss of signal is usually an indication of the break. Several years ago, vandals in Arizona found a bolted joint in the rail and took the bolts out to derail a train. They also used a piece of wire to jumper over the break so the railroad signals would not fail. Amtrak came along and derailed in the desert. Killing one and injuring 78.
See: http://en.wikipedia.org/wiki/1995_Palo_Verde,_Arizona_derailment

I'll have to post a short video of a demonstration sun kink, done on purpose that I use for training rail crews. It's pretty impressive. It's at work on my Powerpoint Laptop, though. I train operators in the use of a device that will deterrmine the neutral temperature of rail after it's been laid. Sometimes as a quality check during construction, or after it's been laid for a few years to make sure the neutral temp is still in spec.
 
Nice treatise on rails.

It often amazes me how something that seems so basic -- a rail -- has so many complexities.
 
Keith,

Thanks for explanation. I appreciate it.

So, are the 1/4 mile sections welded together or somehow allowed to have a slip joint.

Thanks
 
Nope, welded. Some string go for a few miles. On signaled territories there has to be an insulated joint every now and then in order to create traffic "blocks". When a train is present, the axle shorts the two rails together, and gives the dispatchers, sometimes hundreds of miles away. an indication that there is a train in that bloc. Also is throws the local signals red. No other train is permitted in that block as long as the signals are red. A piece of conductive debris or wire can cause a false indication of a train as well.
The insulated joints don't really act as a stress relief, just as a break in the electrical trac signals.
 
Keith Lane said:
Nope, welded. Some string go for a few miles. On signaled territories there has to be an insulated joint every now and then in order to create traffic "blocks". When a train is present, the axle shorts the two rails together, and gives the dispatchers, sometimes hundreds of miles away. an indication that there is a train in that bloc. Also is throws the local signals red. No other train is permitted in that block as long as the signals are red. A piece of conductive debris or wire can cause a false indication of a train as well.
The insulated joints don't really act as a stress relief, just as a break in the electrical trac signals.
Click to expand...
That is interesting. As I read Mark's post before you responded I was thinking of how a red light is triggered. Then I thought of conductive debris like you mention.

But since you mention it, I have a few questions about that. You mention conductivity yet isn't there some ohm value to prevent false readings? And given the length of trains (on the mainline but not switching at a spur or near a yard) wouldn't several insulated joints in series need to be tripped, again to prevent false readings?
 
Richard said:
That is interesting. As I read Mark's post before you responded I was thinking of how a red light is triggered. Then I thought of conductive debris like you mention.

But since you mention it, I have a few questions about that. You mention conductivity yet isn't there some ohm value to prevent false readings? And given the length of trains (on the mainline but not switching at a spur or near a yard) wouldn't several insulated joints in series need to be tripped, again to prevent false readings?
Click to expand...

TO my knowledge, there is no ohm value, though I'd be the first to say I'm no signals expert. as far a switching, there are no signals in yards. There is a yard tower, like a airport tower with guys watching every move. There are many many radios in a yard as well. Everybody is talking to everybody.
 
"You know guys, laying all this track is hard frickin' work! What if I invented a monster robot train to do it all for us? All we'd have to do is sit back and watch....."

"Have you been drinking again?"
 
Thanks, Keith, for the inside info. I find rail operations to be very interesting.
 
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