Drop hammer

The invention relates to a drop hammer rapping device comprising: a rotatable slightness shaft (6), which is held by at least two bearings; a unit (7) provided for rotating the shaft; a plurality of radial arms (9) which are rigidly connected with the shaft at a distance from each other, wherein each arm is rigidly fixed to the shaft with a orderly increasing circumference angle relative to its previous neighboring arm in the perpendicular direction of the shaft; a drop hammer (10) provided with a hammer head (11) and a hammer handle (12) and fixed at each radial arm at its outer end via a hammer joint (13); an anvil or a striking handle (4) mounted on or contacted with collecting pipes (3) of a tubular heat exchanger unit (1), wherein exposed ends (5) of the anvil or the striking handle are rapped by the drop hammer when the shaft rotates. In order to reduce or remove a repulsive force occurring inside the hammer joint when the drop hammer raps the exposed ends of the anvil or striking handle, the drop hamme