Raise boring technology serves as a critical construction method for excavating ventilation shafts, backfill shafts and drainage shafts in mining, water conservancy and tunnel projects. The construction process consists of two stages: pilot hole drilling and reaming. The straightness and hole quality of the pilot hole directly determine the success of subsequent reaming operations. As a pilot bit developed by Sandvik specifically for raise boring machines, the RR890 Pilot Bit is the core drilling tool to guarantee efficient and stable pilot hole drilling. It is compatible with various raise boring machines, works for strata ranging from soft rock to extremely hard rock, and greatly improves construction efficiency and operational safety of raise projects.
During raise boring, the raise boring machine first drills downwards to form the pilot hole. Once the pilot bit penetrates the lower roadway, the reamer is installed for upward reaming to shape the shaft. Deviation of the pilot hole, premature bit wear or roller cutter failure will directly cause reaming sticking or shaft abandonment, resulting in heavy downtime losses. Optimized for heavy vibration and high-load working conditions of raise boring in structural design, material selection and bearing system, the RR890 Pilot Bit addresses common pain points of conventional pilot bits including short service life, prone failure and poor hole deviation control. It has become one of the main pilot bits supporting large and medium-sized raise boring machines.
The RR890 Pilot Bit is available in sizes from 229 mm to 406 mm, compatible with mainstream raise boring machines. Its self-weight ranges from 45 kg to 212 kg. The maximum load capacity of a single roller cutter reaches 27 tons, and the overall maximum load capacity of the bit is up to 52 tons. The allowable maximum rotating speed of roller cutters is 85 r/min. Adopting standard API thread connection, it can be quickly assembled with drill pipes for easy installation and disassembly. It adapts to various working conditions such as vertical raises and inclined shafts, and can be used for both conventional raise boring and blind raise construction.
In terms of core technology, the RR890 Pilot Bit is equipped with Power Carbide® SH75 carbide inserts and the patented Charger® double-sealed bearing system, alongside an optimized CSD cutting structure design. The carbide inserts deliver outstanding impact resistance and wear resistance. When encountering broken rock mass and hard granite strata, the wear rate of inserts is significantly reduced. The double-sealed bearing effectively blocks rock dust and slurry from entering the bearing assembly to prevent premature seizure and damage. Compared with traditional pilot bits, its overall service life is increased by more than 30%. Longer footage can be completed in one trip, which reduces downtime caused by frequent tripping operations for bit replacement and cuts safety risks for underground personnel handling drilling tools. The cutting structure rearranges roller cutter layout for more uniform rock breaking, mitigates shock and vibration during drilling, restrains hole deviation and ensures pilot hole straightness, laying a reliable guiding foundation for subsequent reaming.
For engineering applications, deep mining ventilation raises, hydraulic pressure pipeline shafts and tailings backfill shafts often feature complex strata with alternating soft and hard rock and heavily fractured rock mass. Ordinary pilot bits tend to suffer insert chipping and roller cutter seizure under such conditions, leading to sharp drops in drilling efficiency. The RR890 Pilot Bit can withstand alternating loads induced by high thrust and large torque from raise boring machines, maintaining stable rock breaking capacity in broken surrounding rock and reducing abnormal bit damage. Superior pilot hole quality prevents uneven loads on the reamer caused by hole deviation, protects the complete drilling system including the main unit of raise boring machine and drill pipes, and cuts equipment maintenance costs.
From the perspective of project economy, underground working space for raise projects is limited, and tripping operations are complicated and time-consuming. The extended service cycle of the RR890 Pilot Bit reduces tripping frequency and non-productive time. Although high-end pilot bits have higher procurement costs than ordinary bits, the overall comprehensive construction cost is lower when considering footage cost, downtime loss and equipment maintenance expense. For shaft projects with tight schedules, a stable and reliable pilot bit is essential to ensure on-time project delivery.
Meanwhile, proper operation of raise boring machines is required when using the RR890 Pilot Bit. Before construction, thrust and rotating speed parameters shall be set reasonably according to the uniaxial compressive strength of rock to avoid overload impact. Torque and weight on bit shall be monitored in real time during drilling, and cuttings removal shall be ensured to prevent accelerated roller cutter wear from accumulated rock dust. Protection shall be provided during bit storage and transportation to avoid collision damage to threads and roller cutters. Standardized operation and routine inspection can further exert bit performance and maximize service life.
In summary, with optimized rock breaking structure, high-performance carbide inserts and reliable double-sealed bearing system, the RR890 Pilot Bit adapts to harsh working conditions of pilot hole drilling for raise boring machines. It balances drilling accuracy, rock breaking efficiency and service life. In mining and hydraulic shaft projects, this pilot bit effectively controls hole deviation, reduces downtime failures and lowers underground operational risks. It provides a stable and reliable pilot solution for raise boring technology and serves as an indispensable core component in the complete drilling tool system of modern raise boring machines, promoting raise boring towards higher efficiency, improved safety and lower overall cost.