Starter Rod
In a multi-section extended drill string assembly, the drill rod section closest to the drill bit—where the bit is directly attached—is known as the "bottom rod" (also referred to as the starter rod or lower rod).
- Product Introduction
In a multi-section extended drill string assembly, the drill rod section closest to the drill bit-where the bit is directly attached-is known as the "bottom rod" (also referred to as the starter rod or lower rod). This is complemented by intermediate extension rods ("middle rods") and the "top rod" that connects to the drill rig's power head. The bottom rod is the load-bearing component closest to the working face; it withstands the full impact, torque, and drilling pressure, operating under the harshest conditions and experiencing the highest rate of wear.
Drill String Hierarchy
Drill Rig Power Head → Top Rod → Intermediate Rods (connected/extended via couplings) → Bottom Rod → Drill Bit
Specialized Structural Design (Targeted Reinforcement)
Lower End (Drill Bit Connection End)
Customized adapter: Features a hexagonal socket or trapezoidal male thread for direct locking of flat-blade, button, or coal drill bits; thickened adapter wall with localized induction hardening for impact resistance and anti-slip threading.
Rod Body
Bottom rods in the series generally feature thicker walls than intermediate or top rods; hollow hexagonal models utilize the B19/B22 standard (hexagonal exterior with a central through-hole), while twisted models feature fully welded external spiral flights; a hollow channel runs through to the bit, delivering water or compressed air for wet dust removal and cooling.
Upper End (Coupling End)
Standardized for compatibility with coupling sleeves and adapters; specifications are identical to those of the intermediate rods in the same batch, facilitating on-site interchangeability and assembly.
Mainstream Materials and Common Specifications
Material and Processing
Premium alloy steels (55SiMnMo, 40Cr, 42CrMo) are selected; the rods undergo integral quenching and tempering, with high-frequency quenching applied to the ends. Hardness ranges from HRC 35 to 48. They offer superior bending, torsional, and fatigue resistance compared to standard intermediate rods, making them suitable for heavy-duty drilling in hard rock and fractured coal seams.
Popular Coal Mine Specifications
Hexagonal hollow starter rods: B19, B22; lengths of 1.0m, 1.2m, 1.5m, and 2.3m.
Wet-drilling twist starter rods: Φ28, Φ38, Φ42; lengths of 1.0–2.0m.
Starter rods for integrated bolting-mining machines: Mostly customized lengths of 1.5–2.5m.
Core Functions
Primary Force Transmission
Directly transfers torque and axial thrust from the entire drill string to the drill bit to break through rock or coal seams.
01
Front-End Cuttings Removal
Positioned immediately adjacent to the working face; spiral blades or internal water channels evacuate rock and coal dust instantly, minimizing bottom-hole sediment accumulation and preventing drill sticking.
02
Pressure Absorption & Cushioning
Absorbs high-frequency impact loads caused by the bit striking the rock, protecting intermediate and top rods from breakage.
03
Wet Drilling
A hollow water channel delivers fluid directly to the bit face, suppressing dust at the source and cooling the cutting edges to extend bit service life.
04
Unique Advantages Over Intermediate and Top Rods
Structural reinforcement
The end section is thickened and quenched to withstand impacts from borehole-bottom debris and instantaneous shock loads;
Flexible interchangeability
A bottom rod of a specific specification can replace the front-end drill rod of any unit within the same batch;
Cost reduction and efficiency
Only the bottom rod needs replacement, eliminating the need to discard the entire drill string;
Directional control
The rigid front section guides the drilling trajectory, reducing the risk of deep-hole deviation.
Typical Application Scenarios
Underground Coal Mining
Used with roadheaders, pneumatic rock drills, and roof bolters to drill gas drainage holes, water exploration/drainage holes, roof bolt/cable holes, and blasting holes.
Hard Rock Tunneling
Deep-hole drilling using YT28 drills with extended rod sections; the starter rod comes standard with a ballistic button bit.
Geological Exploration
Shallow and medium-to-deep hole drilling; thickened starter rods are preferred in fractured formations to prevent seizing.
Installation and Maintenance Guidelines
Before assembly, clean coal dust and rust from the bottom connector and apply thread lubricant to prevent high-temperature seizing.
Pair components of the same specification (drill rod and coupling sleeve); strictly prohibit forcing a connection between incompatible thread types.
Conduct routine inspections for bottom connector wear, rounded edges, and rod body bending or cracking; immediately discard any damaged parts to prevent drill string loss downhole.
Install a filter screen for water intake during wet drilling operations, as sediment accelerates clogging of the bottom water channels and wear on the cutting edges.
When storing, drain water from the internal cavity and elevate the rods to prevent moisture damage and rust.
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