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Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
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#1
Posted to rec.crafts.metalworking
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OT rail/thermite
"Oppie" wrote:
"Mike" wrote in message ... On Mon, 20 Aug 2007 14:05:35 GMT, "Oppie" wrote: Yes, the rail is thermite welded to a continuous rail except for insulated signaling joints. They ship it as 1000ft sections though. 1000ft? How? It rather amazed the crud out of me to see these long flatbed cars - about ten altogether, with the rails laid in grooves on the deck. I guess there is a limit on how many rails they can cary and still make it around a curve... How does this deal with the expansion and contraction of rails from daily and seasonal temperature changes? Somewhere there needs to be some sort of slip joint to deal with it. Wes |
#2
Posted to rec.crafts.metalworking
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OT rail/thermal expansion
"Wes" wrote in message ... "Oppie" wrote: "Mike" wrote in message ... On Mon, 20 Aug 2007 14:05:35 GMT, "Oppie" wrote: Yes, the rail is thermite welded to a continuous rail except for insulated signaling joints. They ship it as 1000ft sections though. 1000ft? How? It rather amazed the crud out of me to see these long flatbed cars - about ten altogether, with the rails laid in grooves on the deck. I guess there is a limit on how many rails they can cary and still make it around a curve... How does this deal with the expansion and contraction of rails from daily and seasonal temperature changes? Somewhere there needs to be some sort of slip joint to deal with it. Wes I wondered about that also since there don't seem to be any expansion joints that I could see. Found this explanation: http://en.wikipedia.org/wiki/Rail_tracks Page down to 'Continuous welded rail' more generally, http://www.google.com/search?sourcei...rail+expansion |
#3
Posted to rec.crafts.metalworking
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OT rail/thermite
How does this deal with the expansion and contraction of rails from daily and seasonal temperature changes? Somewhere there needs to be some sort of slip joint to deal with it. Wes Not there doesn't, as long as the saddle clips are tight enough. Friction does it for you! |
#4
Posted to rec.crafts.metalworking
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OT rail/thermite
On Tue, 21 Aug 2007 09:47:43 -0400, Wes wrote:
"Oppie" wrote: "Mike" wrote... On Mon, 20 Aug 2007 14:05:35 GMT, "Oppie" wrote: Yes, the rail is thermite welded to a continuous rail except for insulated signaling joints. They ship it as 1000ft sections though. No, that webpage clearly shows a welding machine at the end of the welded rail transport train - they preheat the ends to be welded with gas torches, then it looks like it's either stick,flux-core or MIG welded. The pictures didn't get close enough to tell. Thermite may be fun to use, but I'm betting it's not their preferred method if you have the right heavy equipment available. Especially here in So-Cal, where the Smog Police ;-) (SCAQMD) would object to any pollution source, no matter how small. 1000ft? How? It rather amazed the crud out of me to see these long flatbed cars - about ten altogether, with the rails laid in grooves on the deck. I guess there is a limit on how many rails they can cary and still make it around a curve... The bare rail is rather flexible when it isn't bolted or spiked down to the sleepers. It's not like thinwall tubing where it will buckle if that much bending force is applied, even at the very large bending radius of the average existing track. How does this deal with the expansion and contraction of rails from daily and seasonal temperature changes? Somewhere there needs to be some sort of slip joint to deal with it. Nope. A conventional slip joint on long sections of welded rail wouldn't work, there's too much weight involved - a train hitting the brakes or throttle would slam the ends around something fierce. I suppose they have something that will work for bridge approaches where you have to allow free movement... They would need to have an active (powered) hydraulic buffer at each joint to compensate for the trains braking or acceleration forces, and the power cylinder would shift it back into position after the train passes. The joint would require a long section of 'split rail' like a switch frog (with the wheel flange retaining lip) so the two halves can move a foot or more without the train falling off the track. Trains falling off the track is bad. ;-P A powered joint every mile or two with a computer interface to run it remotely from the railroad's Control Center (like a remote switch machine) would be really expensive to implement, and require continuous power and data line availability along the tracks - and unless they used backup batteries and 12V pumps to run the joints (like they use 12V equipment for crossing signals & gates) a power outage stops the trains cold. And that expansion joint would magnify the problems they had with the old bolted rails - the track sags at each joint, and that causes the roadbed to subside at that spot, and then the train rocks as it goes over the dip. Rock a high-speed passenger train or a light freight running flat out, and they tend to fall off the tracks. As was pointed out earlier, trains falling off the track is bad. ;-) One trick I've seen (but not everywhere) is not to run the track arrow-straight for 50 miles, put slight bends into the track so if they're going to kink they have a safe place to do it... Even a short-line built with sectional rails like Ventura County Railway does this on the long straight sections - every 1/4 mile or so the tracks shift over 20 feet on the ROW and straighten out again. Otherwise the tracks can grow a foot a mile in a severe temperature swing, and you end up with a "Sun Kink" (Google the term) where the tracks move sideways on their own to release the compressive stress. If the engineer is lucky they are visible and they can get the train stopped (or slowed) in time, and the tracks stay attached to the sleepers and stay in gauge so the train doesn't fall off the tracks when they hit the sudden S-curve... And trains falling... I won't say it a third time. ;-) -- Bruce -- |
#5
Posted to rec.crafts.metalworking
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OT rail/thermite
Bruce L. Bergman wrote:
And that expansion joint would magnify the problems they had with the old bolted rails - the track sags at each joint, and that causes the roadbed to subside at that spot, and then the train rocks as it goes over the dip. Rock a high-speed passenger train or a light freight running flat out, and they tend to fall off the tracks. As was pointed out earlier, trains falling off the track is bad. ;-) That part I understand. No load spreading. Wish my grandpa was still around to explain all this stuff. Googling sun kink was quite interesting. It seems the goal in joining track is to put it at the corrected for temperature stress or strain so the 12" is reduced to +/- 6" Wes |
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