A theoretical and experimental study of the percussive drilling of rock Part IV—application of the model to actual percussion drilling

Abstract

A series of full-time drilling tests was made using three different percussive machines. Blow energy, blow frequency, rotational speed (rpm), thrust, penetration rate, and the impact-produced strain waves were measured. Energy transfer to the rock, as determined from the analysis presented in Part I, was found to vary by as much as 15 per cent between individual force-penetration curves. The experimentally observed maximum energy transfer, of approximately 80 per cent of the impact energy, agreed closely with values predicted theoretically. The observed penetration rates were within 15 per cent of those predicted. The minimum thrust required for optimum energy transfer to the rock was shown to be a function of the blow frequency and the initial and rebound momentum of the piston, the latter depending on the incident waveform and the force-penetration curve. The predicted thrust values agreed closely with those actually required. Application of the theory to drilling system design is discussed.