Abstract
Rock drills are usually applied in petroleum engineering applications, tunnel excavation, and hard rock mining. The rock drills directly impacted the rock through the hydraulic impact power mechanism and are controlled by propulsion force and torque. However, there still exists the most serious problem in impact drilling which is low efficiency during the process of impact drilling, and thus the orthogonal experiment using Taguchi method L25 (56) is conducted to analyse the influence of the working parameters, including impact power, propulsion force, rotation speed and bit type, on the rock drilling efficiency. Unconfined compressive strength tests and Brazilian splitting tests are conducted first to present the bluestone characteristics. The drilling efficiency including drilling velocity and specific energy is the evaluating indicators for orthogonal experiments under different drilling conditions. The results demonstrate that the factor order affecting drilling efficiency is impact power, rotation speed, propulsion force and bit type. In addition, the impact power has a highly appreciable influence on the drilling efficiency, whereas the influence of rotation speed, propulsion force and bit type on that in their level range is slight. However, the influencing parameters of impact power, rotation speed, propulsion force and bit type in terms of percentage contribution on drilling velocity and specific energy is 38.54%, 20%, 20%, 20% and 35.307%, 20%, 20%, 20%, respectively. Moreover, the optimum combination in view of drilling velocity and specific energy are 6.4 kW, 240 r/min, 3800 N and 7-button for impact power, rotation speed, propulsion force, and bit type respectively. Based on the regression analysis of the main working parameters which affect drilling velocity, the relationship between drilling velocity and working parameters is obtained and verified, thus it easily provides a basis about equipment selection, optimal working parameters, equipment improvement and progress prediction.
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