Hammer Blow

Hammer blow, in rail terminology, refers to the vertical forces transferred to the track by the driving wheels of a steam locomotive and some diesel locomotives. The largest proportion of this is due to the unbalanced reciprocating motion, although the piston thrusts also contribute a portion to it. It is the result of a compromise made when a locomotive's wheels are balanced to off-set reciprocating masses, such as connecting rods and pistons, in order to keep the ride as smooth as possible. However, hammer blow occurs with the downward force of the wheel's balance weight onto the railway track, with the potential of causing damage. The rails are subjected to an intense and regular pounding, which can in some cases cause damage to the rails or other structures. The forces are also known as dynamic augment.