We mention Siberia only because it is a unique location, not because it is the only place where this practice is used. Now, we will say that further investigation yielded some more modern looking methods for doing this job, but clearly the well used looking crucible in this video has proven itself worthy of its occupation for some time now. The two guys involved in this operation have clearly done it about a million times because they move around like this is just another day on the job. So what is it exactly that they are doing? Basically they are doing what has been done (in one form or another) for more than 90 years to join train tracks together. The process is called Exothermic welding and in basic terms the guys are heating the ends of the rails up to very extreme temperatures and then pouring liquid steel into a mold that is housed in the unit clamped over the tracks. That steel is liquified by igniting a load of thermite (yes, the same stuff that is in thermite grenades) and using its intense heat to melt the steel.

Once the stuff gets to the point where it is completely molten and liquid, it pours from the bottom of the crucible into the mold below (which we think may be a sand style mold?) and that is what forms the bond that holds the lengths of track together. It is very fun to watch the whole thing happen, especially because the guys performing the operation look like they are just out digging holes or something when in fact they are running a tiny blast furnace/still mill! The best part of the whole thing? A train can run over this rail about an hour after the whole process is complete. How neat is that?! Before watching this video, we had never seen the process before and now we’re kind of obsessed with it.

Here’s a more detailed explanation from the video description:

Typically, the ends of the rails are cleaned, aligned flat and true, and spaced apart 25 millimetres (0.98 in).[2] This gap between rail ends for welding is to ensure consistent results in the pouring of the molten steel into the weld mold. In the event of a welding failure, the rail ends can be cropped to a 75 millimetres (3.0 in) gap, removing the melted and damaged rail ends, and a new weld attempted with a special mould and larger thermite charge. A two or three piece hardened sand mould is clamped around the rail ends, and a torch of suitable heat capacity is used to preheat the ends of the rail and the interior of the mould. The proper amount of thermite with alloying metal is placed in a refractory crucible, and when the rails have reached a sufficient temperature, the thermite is ignited and allowed to react to completion (allowing time for any alloying metal to fully melt and mix, yielding the desired molten steel or alloy). The reaction crucible is then tapped at the bottom. Modern crucibles have a self-tapping thimble in the pouring nozzle. The molten steel flows into the mould, fusing with the rail ends and forming the weld. The slag, being lighter than the steel flows last from the crucible and overflows the mould into a steel catch basin, to be disposed of after cooling. The entire setup is allowed to cool. The mould is removed and the weld is cleaned by hot chiselling and grinding to produce a smooth joint. Typical time from start of the work until a train can run over the rail is approximately 45 minutes to more than an hour, depending on the rail size and ambient temperature. In any case, the rail steel must be cooled to less than 370 °C (698 °F) before it can sustain the weight of rail locomotives.

PRESS PLAY BELOW TO SEE THE AWESOME PROCESS USED TO FUSE RAILROAD TRACKS TO EACH OTHER – EXOTHERMIC WELDING WITH THERMITE!