Percussion and rotary-percussion drilling are used in non-coring drilling operations for medium to hard rock; applications include exploration and blasting boreholes, and degassing shafts.
This type of drilling is used when a core is not needed for analysis. In percussion drilling, the main function is a pneumatic-force driven pounding tip, which produces a hammering action parallel to the drill hole angle (compressive force); whereas rotary-percussion drills include rotating drill bit for added shear force. Cuttings from the drill hole can be collected for analysis.
Figure: Percussion drills rely on a delivering rapid, powerful compressive forces to fracture and break rock in boreholes, while rotary-percussion drills also provide shearing force.
A rotary drill utilizes shear forces to fracture and penetrate solids. These drills may be used for collecting samples, creating blast holes, or holes for ventilation of underground mines; auger-type rotary drills can also be used for mining soft deposits like coal (auger mining). Rotary drills use a variety of very sharp drill bits to recover samples from the earth's crust.
Common rotary drill bits are shown in the figure below:
Figure: Different rotary drills can be used for specific mining operations.