Abstract
This paper discusses the recent development of rotary percussive drilling specially with reference to the relations between thrust, revolution per minute, torque and penetration rate. Sizing tests of cuttings and theoretical considerations were made to analyze the drilling mechanism of rotary-percussive drilling.The followings are brief statements of conclusions.1. Penetration rate is increased in accordance with the increasing thrust. The above relation is linear in the case of rotary percussive drilling but it shows parabolic curve in the case of rotary drilling. When thrust reaches a certain point (in this experiment, 170 to 190 kg. in thrust), both system of drilling has same penetration rate. If the thrust is increased over this point, rotary drilling will show higher penetration rate, on the contrary, rotary percussive drilling shows better results under lower thrust.2. Penetration rate is increased in accordance with the increasing rotation specially in rotary drilling. This increasing rate is, however, pretty small in the case of rotary percussive drilling when number of percussion is remained constant. Then, optimum rotation of rotary percussive drilling would be 200 r. p. m. in this-experiments. From above mentioned standpoint there would be optimum r. p. m. in relation with each number of percussion in the case of rotary percussive drilling.3. Large cuttings are seen when thrust is increased. Increasing rate is, however, big in rotary drilling. Also better petter penetration rate is obtained when revolution per minute is increased but size of cuttings is getting smaller and smaller.4. Essencial power for drilling is generally big in rotary percussive drilling needing the power for impact. Rotary percussive drill will need 1.5 to 2 times big power for rotation compared with conventional rotary drill.
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