Heat balance
Electric flash butt welding of railways rails

An average rail weighing 60 kg/m (like the UIC 60 used in continental Western Europe), with a hardness of 300-320 HB, requires 7 pulses of 4.2 s at 70,000 A and 5 V, or 10 MJ (million joules), on a fixed rectified-current machine, for preheating alone. Since the rail cross-section, deducted from its metric weight, is 7,643 mm ² , the energy ratio for UIC 60 is 1,300 J/mm ² . Note that this preheating energy represents 90% of the total energy supplied for welding.

Preheating ratios for other rails are given as examples in tables 2 , 3 and