By Greg Fenrick

A blasthole drill is a special type of track mounted rotary drill used in open pit mining and construction to drill holes in rock requiring blasting with explosives in order to be broken up for removal. These blastholes are set up in a defined grid and to certain depths in which explosives are placed to maximize blasting of the rock to be mined.

Typically, rotary drilling is done with roller-type bits, using compressed air for cuttings removal. Rotation is accomplished either by a conventional rotary table drive or a hydraulic motor, with hydraulic or wire-line mechanisms to add part of the weight of the drill to the weight of the tools to increase bit pressure.

Drag bits are less commonly used, and have hardened blades that act to penetrate soft rock and gouge it out. For harder rock, the blades can be tipped with tungsten carbide to increase the wear life. Drag bits are usually used in rock with compressive strength less than about 20,000 psi (140 MPa) and in small diameters (89-152 mm).

DM30 Blasthole Drill (Photo: Atlas Copco)

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