The invention relates to a method for drilling a hole in rock with a top-hammer rock drilling rig comprising a rock drill, to which is attached a drill rod, at one end of which there is attached a drill bit, and which includes a percussion device and a rotation motor, in which method the drill rod and the drill bit are rotated with the rotation motor, and stress pulses are directed with the percussion device via the drill rod and the drill bit to the rock for breaking the rock. The invention further relates to a rock drilling rig for drilling a hole in rock, the rock drilling rig comprising a top-hammer rock drill, a drill rod attached thereto and a drill bit attached to the end of the drill rod, and the rock drill includes a percussion device for providing stress pulses via the drill rod and the drill bit to the rock and a rotation motor for rotating the drill rod and the drill bit.
When hard rock types are concerned, rock drilling is carried out with so-called top-hammer rock drilling rigs, which comprise a rock drill, a drill rod consisting of one or more interconnected parts attached thereto and a tool at the end of the drill rod, i.e. a drill bit. In known solutions, the drill bit has a fixed body in whose surface facing the direction of drilling there are embedded hard metal buttons which perform the actual rock breaking by the effect of a stress pulse from the percussion device. The known solutions have a drawback that rock breaking requires great forces, and therefore the hard metal buttons must be designed more in view of the duration of loading than efficient rock breaking. As the diameter of the hole increases the number of buttons breaking the bottom of the hole should also be increased. The increase in the number of buttons, in turn, makes it more difficult to design the drill bits, because the buttons are to be loaded in an even manner. The fact that, in practice, the buttons are loaded in a relatively uneven manner, decreases the drilling rate.
Further, it is also difficult to drill large holes, the maximum hole size being 5.5 to 6 inches, with top-hammer drilling rigs, because considerable problems already arise in drilling holes having a diameter of 5 inches. In the known top-hammer rock drilling rigs also the amount of energy required for rock breaking is very high, typically about 600 to 800 J. In current rigs, the hard metal buttons of the drill bits are subjected to extremely high strain. As the drill bits are pushed against the rock with great force and the buttons move sliding on the rock surface, the result is intense wear, which must also be taken into account in button shape design.
Large holes having a diameter of 8 to 10 inches are typically drilled with rotary drills operating without percussion and using drill bits provided with rotary cone roller bits. These have a problem that rock breaking requires extremely great static force, and consequently these so-called rotary drilling rigs are heavy and require sturdy bases.