ABSTRACT
In order to carry out a specific drilling job, various combinations of accessories can be chosen. The factors that have to be taken into consideration in the selection are: blasthole diameter and length, structure, strength and abrasiveness of the rocks, size and power of the rock drill, previous experiences, and supply facilities. The function of drill steel threads is to hold the shanks, coupling sleeves, rods and bits together during drilling. They should be efficiently adjusted so that the elements of the extension rod are tightly united in order to achieve direct transmission of energy. There are two types of drill bits for rotary percussive drilling: Insert bits, and Button bits. Button bits are better adapted to rotary drilling; obtaining advance velocities those of insert bits. They are also more wear resistant, due not only to the shape of the buttons but also to the more effective attachment of the buttons to the steel, by shrinking or cold-pressing.
