Q) How do railroads weld the continuously welded rail when they change out a section of track like at a crossing?
A) I expect that there are various ways, but a few summers ago I watched a Conrail crew of two “welding” rail joints on a section of track that was to become a new crossing on a nearby street. I use the term “welding” loosely. They have a small furnace that they place over the joint. This will heat the metal and let it pour into the joint. Then they clean up the joint and move on to the next joint.
The track sections were brought in already fastened to the ties and were joined together on the spot by this crew. Several days later another crew came through and ripped out the old crossing, picked up the newly assembled “Snap Track” section with a crane, dropped it into place, welded it to the main and were ready to pave the crossing.
This took three or four days instead of the weeks that it used to take. It took less people with more mechanization.
Now, I have noticed more and more reports of US railroads using or beginning to make use of concrete ties as replacements for the old standby, the creosoted or pressurized wooden tie. BART (Bay Area Rapid Transit) in San Francisco rides on concrete pads an
They are welding a joint, but that’s not how railroads make continuous welded rail.
CWR is made in plants where 39 or 78 or a thousand foot sections of rail are eltrically butt welded together. A fixture clamps each section of the rail and then compresses the rail ends together while high voltage is fed through the joint. That heats the joint hot enough to melt the steel and fuse the rails together. A shear cuts off the overflowed metal from the weld and the joint is ground smooth.
The thermal weld being shown is for field repairs or for joining sections of CWR together. They are generally of lower quality than an electric weld. The railroads also lease portable electric butt welders that lower an electric butt welding rig onto the joint and make a near factory electric weld . They are normally housed in a hi-rail truck that is a 15-20 foot box truck.
Those on-site thermal welds usually leave some debris behand, including a reddish substance almost like lava rock. And chalked in data about the weld on the side of the rail. Details that could be modeled.
Those field welds use thermite in those pots. There’s a good video on YoouTube that shows the whole process, clamping the form on, and the pot, then lighting it off, then knocking the form off, chipping off the excess, and then bringing in a rail grinder to smooth it all out.
Basically the rail is placed when the temperature is midway between the extremes for the area.
It is constrained from longutudional expansion and contraction by the track structure forcing the rail to expand and contract in height and width not length.
The change in length will actually be less than for the same distance laid with jointed rail.
