ABSTRACT
Rotary drilling by cutting action was at its peak in the forties, in American coal mines, for blastholes in overburden and in the ore itself. With growing use in surface operations using rotary rigs with rolling tricone rock bits, this method has been limited to soft rocks, usually with small to medium diameters, clearly competing with direct breakage systems. Eimco-Secoma has developed a test for measuring the drillability and abrasiveness of the rocks. It consists of drilling a hole in a rock sample with constant thrust and rotary speed. The rocks are clasified in four groups or zones, in function with the two parameters, which define the most adequate drilling methods. Apart from their use in exploration drilling, diamond bits are used in underground mining for coal, potash, salts and gypsums to drill small diameter blastholes, from 35 to 110 mm.
