Study On Percussive Drilling Efficiency Of Water Powered Percussive Rock Drill In Deep Mining

Development of mining, construction of railways, and the hydropower construction etc. involve large-scale excavations of underground engineering such as tunnels, culverts etc. Drilling and blasting is still the main construction method for underground engineering in a long time. Therefore, the rock drilling equipments is still vital for mines, tunnels and other underground constructions. Reviewing the history of the rock drilling equipments, the pneumatic rock drill was mostly used; however, its usage is limited by its energy and structural problems, low efficiency, high energy consumption, serious noise, dust pollution and other disadvantages. Over the past several decades, highly effective and energy-saving hydraulic rock drill has been developing vigorously. But problems such as waste oil emission and pollution, leakage and clean, inflammability and security, resource exhaustion and cost are still hard to be solved. Especially in recent years, cleaner production and low-carbon economy was proposed, which causing high demand for safety of deep rock mass engineering, environmental protection, energy-saving and efficiency. Thus, the development of the water powered percussive rock drill was promoted.In deep mining operations, the enormous power source born in high fall between surface and underground can be utilized by the water powered percussive rock drill directly. So the cost for power source and excavations was largely decreased, and lots of defects such as waste oil emission, pollution, leakage, inflammability etc. which the hydraulic rock drill can not avoid were eliminated. Water powered percussive rock drill have obvious advantages such as safety, environmental protection, energy-saving, high efficiency, up to now, its key limitation for industrial application is low energy efficiency. Based on the above considerations, the track-type water powered percussive rock drill SYYG65 is researched funded by national high technology research and development program (namely 863 Program)—water directly powered excavation techniques and equipments in deep metal mine. The main researches contain the followings. The water powered excavation test set-up was developed, and a complete experimental platform was constructed for the research on percussive drilling efficiency of water powered percussive rock drill. The whole system contains hydraulic power section, guideway, drilling bench and other mechanical parts, test and data acquisition system etc. The experimental set-up can be used to simulate deep high-pressure hydraulic environment. And the performances of the water powered excavation implements such as water powered percussive rock drill and water powered down-the-hole hammer (DTH) etc. can be directly measured and studied by this experimental system.From the drilling principle of the water powered percussive rock drill, according to the energy transformation and transmission, the main factors affecting the efficiency of rock drill were found, namely the energy transformation and transmission of the impact system and percussive penetration system.From the working principle of the impact system of the water powered percussive rock drill, its characteristics which are different from the general hydraulic machinery were described. It is hard to establish mathematical model for this special waterpower machinery, and the impact velocity, instantaneous flow and other parameters were still hard to measure. Thus, it was proposed that nonlinear numerical simulation is a simple, dynamic, integrated, and reality accordant method for researching the impact system. And a dynamic simulation model of water-powered percussive rock drilling system was built by SimHydraulics toolbox, and then the fluid/mechanical hybrid simulation was realized. The simple and effective coupling calculation of piston and valve core under the water pressure was carried out by avoiding transition of the running state of the system. Some post-processing functions were compiled to realize the identification of the piston stroke and motion cycle, data record and calculation, result output, loop computing and some other functions, and the efficiency of SimHydraulics dynamical simulation on water-powered percussive rock drilling system was validated.Three experiments for water powered percussive rock drill were done on the water powered excavation test set-up, which are impact performance test under the different working pressure, tests of the impact properties about different accumulator, synchronous tests about the pressure of front and back cavity and the displacement of the piston. Combining with the corresponding simulation results, some measures for improving the energy efficiency of the impact system were pointed out for SYYG65, which are larger diameter of the high-pressure water inlet; larger aqueduct diameter connected the front cavity with the port valve; different place of the signal orifice; appropriate inflation pressure and effective volume for the accumulator.The percussive penetration system of the water powered percussive rock drill was analyzed with the wave mechanics. The stress peak coefficient and the moment of energy distribution were introduced to evaluate the measured stress waveform. From the impact experiment, some conclusions were found. The stress peak coefficient and the moment of energy distribution were increased with the increasing of impact pressure; and the waveform is deviated from the rectangular wave, which is unfavourable for the energy to transfer from drill to rock. However, as the impact pressure reaches to a certain range, the stress peak coefficient and the moment of energy distribution present a local extremum. Results show that impact pressure also has the effect on stress waveform, and has an optimal impact pressure.The drilling experiment was done on the water powered excavation testing set-up. Testing data was analyzed by the Path Coefficient Analysis. Result shows that the high propulsion pressure and the high rotational speed of the drill steel are both needed for an ideal drilling speed. But the propulsion pressure has an indirectly reverse influence on the drilling speed through the rotational speed of the drill steel. In general, the impact effects for drilling speed in turn are the interaction of propulsion pressure and rotational speed of the drill steel, the rotational speed of the drill steel, the propulsion pressure.Based on the results mentioned above, some structural parameters of water powered impacter and accumulator were improved. Some key parts of the rock drill were over-manufactured. And the track-type water powered percussive rock drill SYYG65-B was developed successfully. The performance test and the rock drilling test showed that some parameters can reach a certain value under 9.124 MPa water pressure, such as single impact energy (?)85J, energy efficiency(?)20%, drilling speed(?)420mm/min, which are basically consistent with the design requirements. When the impact pressure was 9.61 MPa, keeping the propulsion pressure at 0.95MPa and rotational speed of the drill steel at 157.4r/min at the same time, the drilling speed could reach the maximum value of 449mm/min. Compared with the SYYG65, the energy efficiency of the SYYG65-B is improved nearly 10%, it can drill 200mm longer per minute than the SYYG65, and the percussive drilling efficiency was improved obviously.