Nice perspective of rarely-seen activities. Keep these pictures coming!

Really nice!

nice pic!

@ Karthik..

Railway track is a flexible (floating) structure not like a building which is attached rigidly to the ground. So in a track the stresses developing due to expansion/contraction are absorbed by sleepers (rather a set of sleepers) themselves and transferred to subgrade below. Its because of this feature only that LWRs and CWRs has been made possible..

lot of thermite welding videos are available in you tube, pls check out one among that thru this link http://www.youtube.com/watch?v=nR6K90cR8Lg

by providing SEJ(switch expansion joint) from one stztion to next ,we minimizing the variations due to temp.

@ Karthik: By adding gaps but at large distances!

Informative image. Do you have an image from the other side of the rail? Or even top of the rail? Please email me the images of thermit welding at msm_saifullah@yahoo.com

If the gaps are welded, how does expansion and contraction due to variations in tempratures are taken care?

This is a good example of fusion of rails using the alumino-thermit process. Here a prefabricated mold is placed in between the rails and the whole assembly is pre-heated. A mixture of aluminium and iron oxide is ignited using magnesium, which results in an strongly exothermic reaction in which oxygen from iron is exchanged to aluminium.

Fe2O3 + 2Al -> 2Fe + Al2O3 + Heat

The molten iron is now poured in the mold which has a sprue (from where the hot metal is poured), mold cavity containing the rails to be fused and a runner (from where the molten metal rises up to indicate the filling level in the mold). The cylindrical structure that you see in the image is either a sprue or a runner, and most likely in my opinion a runner. An identical cylindrical portion should also exist on the other side with a basin which acts as sprue which receives the metal. Hot metal is NOT poured in the gap between the rails directly.

Lastly, this interesting technology is in fact very...

This is a good example of fusion of rails using the alumino-thermit process. Here a prefabricated mold is placed in between the rails and the whole assembly is pre-heated. A mixture of aluminium and iron oxide is ignited using magnesium, which results in an strongly exothermic reaction in which oxygen from iron is exchanged to aluminium.

Fe2O3 + 2Al -> 2Fe + Al2O3 + Heat

The molten iron is now poured in the mold which has a sprue (from where the hot metal is poured), mold cavity containing the rails to be fused and a runner (from where the molten metal rises up to indicate the filling level in the mold). The cylindrical structure that you see in the image is either a sprue or a runner, and most likely in my opinion a runner. An identical cylindrical portion should also exist on the other side with a basin which acts as sprue which receives the metal. Hot metal is NOT poured in the gap between the rails directly.

Lastly, this interesting technology is in fact very old and is called the "Goldschmidt reaction" or "Goldschmidt process" after the German chemist Hans Goldschmidt, who discovered in 1893.