Top-Hammer Drilling

Top-hammer drilling machines are normally used in medium to hard rocks and for hole diameters up to 230 mm. Top hammer drills include:

hand held rock drills (jacklegs, sinkers, stopers)
light drills mounted on a feed device and boom for tunneling (jumbos)
medium to heavy crawler based or wheel based drill rigs with boom or mast, feed, and drifter.

Top hammer drilling combines: Percussion - Feed - Rotation - Flushing

Percussion

The energy produced in a percussive rock drill is transmitted to the rock by a piston in the drifter via a drill steel and a drill bit. When the stress wave reaches the drill bit, the energy is transmitted to the rock in the form of bit penetration.

The piston strikes a shank and the impact energy is transmitted to the drill steel in the form of a stress wave. The stress wave travels at a speed of 5200 m/s.

When integral steels are used, the piston strikes directly on the shank of the rod. For longer steels, the piston strikes a shank adaptor.

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Impact energy multiplied by impact frequency together create the percussive output of the drifter.

Pneumatic drilling 1600 to 3400 hits/min
Hydraulic drilling 2000 to 4500 hits/min

Hydraulic Drifter

Photo: Atlas Copco