Raise Boring Machine is special core equipment for constructing vertical raises, ventilation shafts and filling shafts in mines and hydraulic projects. The Stabilizer Bar is an essential down hole component on drill string assembly, which directly affects trajectory accuracy of pilot hole, drill string stability and construction safety. During deep raise drilling in hard rock, the drill string is slender and heavy. The drill bit tends to deviate under uneven rock resistance. The core function of the Stabilizer Bar is to centralize drilling assembly, restrain lateral whirl of drill string and control borehole deviation.
The Stabilizer Bar is installed on the drill string behind the drill bit. Its base is forged from high-strength alloy steel. Straight or spiral stabilizer ribs are arranged on the outer surface, embedded with hard alloy buttons. The maximum outer diameter of the Stabilizer Bar is close to pilot hole size. When the Raise Boring Machine starts drilling, the drill string rotates with axial thrust. The ribs of the Stabilizer Bar contact borehole wall to form multi-point support, restrict radial displacement and keep the bit moving along borehole centerline. Without the Stabilizer Bar, the long drill string will whirl violently under rotation and thrust. Borehole deviation accumulates continuously. Excessive deviation may jam the reamer in later stage, and even cause drill pipe breakage or buried drilling accidents.
In process design of Raise Boring Machine, layout of the Stabilizer Bar is critical. In field practice, Stabilizer Bar units are arranged in sections: near-bit Stabilizer Bar, middle Stabilizer Bar and upper Stabilizer Bar. The near-bit Stabilizer Bar is mounted next to the bit to limit lateral sliding instantly. The middle Stabilizer Bar restrains flexural deformation of the mid drill string. The upper Stabilizer Bar further reduces whirl amplitude of the whole drill string. Fewer Stabilizer Bar can be adopted for shallow raises. For raises deeper than 50 meters, extra Stabilizer Bar must be arranged to calibrate borehole direction section by section. Industrial standards forbid starting drilling directly with Stabilizer Bar, to avoid premature rib wear and loss of stabilizing capacity.
Besides deviation control, the Stabilizer Bar can damp vibration and reduce wear. Rock breaking generates continuous impact vibration propagating upward and accelerating fatigue damage of drill pipes. Supported by borehole wall, the Stabilizer Bar absorbs partial radial impact, lowers resonance risk and reduces wear of bits and drill pipes. A qualified Stabilizer Bar extends service life of drilling tools, cuts down downhole failures and improves penetration rate of Raise Boring Machine. Cuttings passage should also be considered when selecting the Stabilizer Bar. Channels between ribs allow rock debris to circulate upward. Dense ribs of the Stabilizer Bar may block annulus, accumulate cuttings and result in sticking.
Selection and on-site maintenance determine service performance of the Stabilizer Bar. Before construction, outer diameter, rib shape and carbide material of the Stabilizer Bar are selected according to rock hardness, designed raise depth and pilot hole diameter. During drilling, tripping inspection on rib wear of the Stabilizer Bar is required. Replacement is necessary once carbide buttons fall off or outer diameter exceeds wear limit. A large number of Raise Boring Machine projects prove that proper deployment of Stabilizer Bar keeps pilot hole deviation within allowable range and guarantees smooth subsequent reaming.
In the Raise Boring Machine construction system, Stabilizer Bar is arranged in sections with different specifications matched according to drilling depth. Lightweight Stabilizer Bar is applicable for shallow raises, while high-strength thickenedStabilizer Bar must be equipped for raises deeper than 50 meters, realizing layered correction of drilling trajectories through multi-point layout near the bit, middle and upper drill string. In actual operation, the advantages of material and performance are directly converted into construction value. High-quality Stabilizer Bar reduces more than 80% of hole deviation failures, lowers tool wear rate and improves drilling efficiency. In contrast, low-quality Stabilizer Bar is prone to rib falling, rod deformation and rapid wear, resulting in hole deviation, reaming jamming and even major buried drilling accidents.
In daily maintenance, material loss and performance attenuation of the Stabilizer Bar are key inspection indicators. Construction personnel shall regularly check the alloy wear degree of ribs and fatigue cracks of the rod body, and replace it in time once the performance fails to meet standards. In conclusion, with high-grade alloy materials, excellent stability, vibration reduction, wear and impact resistance, the Stabilizer Bar has become an indispensable core component of Raise Boring Machine, playing a decisive role in ensuring drilling accuracy, construction safety and engineering efficiency.
To sum up, the Stabilizer Bar is an indispensable stabilizing part of drill string system for Raise Boring Machine. It achieves centralizing guidance by supporting borehole wall, suppresses borehole deviation, attenuates drilling vibration and protects drill components. In mine raise construction, rational layout and standardized operation of the Stabilizer Bar are vital to guarantee borehole precision, mitigate construction risks and manage project cost.
