Penetration Characteristics of a Rock Drill Bit into Rock

Abstract

Percussion rock drills have been widely used mainly for blast hole drilling in mineral extraction, tunnel excavation, and underground development. To advance the performance and efficiency of rock drills, it is essential to understand the complex mechanisms of percussive rock drilling: hydraulic mechanisms in a drill body, elastic wave propagation and attenuation in rods and rod joints, dynamic bit penetration into rock, and the effects of thrust, rotation, and flushing. This paper focused on and detailed the bit penetration into rock. Some theories concerning the penetration characteristics of rock drill bits were presented such as elastic contact theory, slip line field theory, and fracture theory. Recent authors’ studies on static and dynamic penetration tests with a single button were introduced as an elementary drilling process of a bit in which a number of buttons are embedded. Then, recent authors’ studies on dynamic penetration tests with a button bit were introduced with the calculation method of force and penetration depth at the bit tip and with the results of force-penetration curves. The loading and unloading phases of the curves were modeled by convex functions, and their variation was discussed with the relation between the force-penetration curves of a bit and buttons. Important future research issues on the bit penetration into rock were presented for the further progress of percussive rock drilling.

Keywords

• rock drill
• percussive drilling
• button bit
• penetration test
• force-penetration curve