Search Results (2)

With the increasing depth of mining operations and the emergence of complex geological conditions, pneumatic down-the-hole (DTH) hammers have become an efficient drilling technology. This method utilizes high-pressure air to drive hammering actions for rock fragmentation. However, the layout and durability of tungsten carbide buttons significantly affect the rate of penetration (ROP). This study focuses on optimizing the button arrangement for large-diameter reverse circulation pneumatic DTH hammers to improve drilling efficiency. A numerical model incorporating zero-thickness cohesive elements was developed to simulate rock fracturing. A comparative analysis of 16 mm and 22 mm buttons under varying drilling pressures (1–1.8 kN) and impact energies (20–40 J) was conducted. Key metrics, including penetration depth, fragmentation range, stress-affected zone, and specific energy consumption, were analyzed. The results indicate that 22 mm buttons under 35 J impact energy and 1.4 kN drilling pressure exhibit superior performance, with optimal circumferential (47.2 mm) and radial (51.2 mm) spacing determined through stress superposition analysis. This configuration enhances the weakened rock strength zone, providing critical guidance for DTH hammer design. Full article

Pneumatic down-the-hole (DTH) hammer drilling technology has been used extensively in the fields of heat reservoir exploitation and geological exploration owing to its advantages of high efficiency and low pollution. However, the vibration near the bit is up to 40 g while DTH hammer drilling, which significantly affects the performance and longevity of the near-bit measurement while drilling (MWD). To enhance the environmental adaptability of the near-bit MWD in pneumatic DTH operations, a design method for a vibration-damping system based on the parameter optimization of a non-dominated sorting genetic algorithm II (NSGA-II) is proposed in this study. First, the whole structure of the near-bit MWD is designed, including the MWD sub-shell, sensors, measurement circuits, batteries, and connecting structures (the circuit unit). Secondly, this study analyzes the vibration characteristics of the pneumatic DTH hammer near the bit. According to the damping structure, the vibration response model for the circuit unit and the damping model are established. Thirdly, NSGA-II is employed to optimize the parameters of the damping model in terms of the low-frequency, high-intensity vibration characteristics near the bit in pneumatic DTH operations, thereby devising a damping scheme tailored to the unique conditions of DTH hammer drilling. Finally, vibration experiments were conducted to verify the effectiveness of the vibration-damping device. The experimental results indicate that within the vibration frequency range of 5–20 Hz and vibration level of 10–40 g, the peak attenuation rate of the circuit unit is more than 86.446%, and the improvement rate of the vibration stability of the system is more than 75.214%; the anti-vibration performance of the near-bit MWD system in DTH hammer drilling is improved remarkably. This study provides strong technical support for the stability of MWD equipment under such special working conditions. It has broad engineering application prospects. Full article