Continuously Welded Rails
Rail sections are manufactured by steel plants in fixed lengths. In early days of railway development, two rails were fastened by means of a plate and bolts called a Fish Plate.
However, fish plates are required to be checked every once in awhile for looseness and are prone to sabotage. A solution to this problem was devised by means of welding tracks together to form what is called Continuously Welded Rails (CWR).
We will see how this is done.
first the rails are laid in normal manner using mechanized tools and the joints are brought together in close vicinity.
then a ladle along with fixtures is fixed on the joint.
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the ladle contains fine aluminum and iron oxide particles, which are ignited. this creates a highly exothermic reaction (heat generation) and temperatures upto 3500 deg F can be reached.
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The rails melt and fuse together to form a joint.
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The joint is the grinded off using tools and in this fashion the rails are welded in a very long length.
Welded rails are smooth and offer very little jerk even at high speed ensuring comfort to passengers.
Thermal Expansion in these lines is taken care by an overlap joint, which allows these long rails to contract and expand depending on ambient temperature.