The Selection of Optimum Nozzle Sizes for Air-Cooled Tricone Bits in Mining Operations

Air-cooled tricone bits are widely used on rotary drilling rigs to achieve high production rates in open-pit mines. Their performance and service life are influenced by rock properties, machine characteristics, and operational parameters. Hole flushing accounts for approximately 50% of the energy consumed during drilling and affects penetration rates, bit life, and drilling costs. Although studies have focused on selecting suitable tricone bits, nozzle diameter selection has received limited attention and is commonly based on manufacturer recommendations or theoretical calculations involving assumptions. In this study, a practical method was developed to determine an appropriate nozzle diameter for tricone bits used in an open-pit lignite mine in the Soma Basin of Türkiye. This method includes theoretical calculations, together with field measurements and observations, to verify whether the drill rig and compressor operate properly and whether the drilling-performance parameters remain within acceptable limits. The field results indicated that appropriately selected smaller nozzle diameters can direct more compressed air toward the bearings, improving cooling and reducing bearing-related wear, and contributing to longer bit life without adversely affecting drilling performance. The results show that nozzle selection should consider compressor capacity, airflow distribution, bearing protection, and field performance in addition to theoretical calculations.