Railroad tracks used to be joined with fish plates, metal gussets bolted across the sides of the joints between tracks. Now they are welded into continuous ribbons of steel. But the process is different than you might imagine; instead of using arc welders, oxy-acetylene welders, or gas shielded welding equipment, the people doing the work are likely to use a process called thermite welding (videos below).
After the ends of the rails have been ground clean and positioned approximately one inch apart they are encased in a hollow form and preheated with a powerful torch. A crucible is placed over the form and filled with thermite, a readily ignited aluminum-based powder that burns at about 4,500 degrees F. After being lit with what looks like a 4th of July sparkler the thermite turns its constituent parts into molten metal, which pours into the form below—filling the gap between the rails and welding them into a single piece of steel. The form is removed, the excess metal is beat or chiseled away, and the joint between the rails is ground smooth. Start to finish, the process takes maybe an hour to perform.
This is not the only way to weld railroad track (automated arc welding machines can do it too) but it’s certainly the most enjoyable to watch—because who doesn’t like sparks and molten metal? By the way, thermite welding is nothing new; it was invented in the 1890s and used for decades by the military for less "constructive" purposes.
This video was shot in Sweden—which makes sense given the Scandinavian style work pants being worn by the guys doing the work. At about the 3:30 mark you can see an awesome gas-powered grinding device.
This was shot in Folkston, Georgia, and shows the entire process. It begins with photos and switches to video at about the 40 second mark. Some cool hydraulic grinders (2) show up at about the 7:30 mark. I like the guy’s shin and foot protectors—they look like something from a knight’s suit of armor.
This one was shot somewhere in Siberia. I included it because I like the way you can hear the molten metal boiling inside the crucible (starts at about 1:58). The crucible contains enough thermite so that the slag from the reaction does not go into the joint. It floats to the top and comes out last—spilling into the trays on either side of the form after the joint is filled.