Blast Hole Drill Rod for Quarry – 38mm Hexagonal Long Hole Drilling

Designed for large-diameter blast hole drilling in quarries and open-pit non-coal mines, this 38mm hex drill rod features extended length options up to 5.0 meters. The premium steel grade offers high tensile strength and resistance to bending under high feed pressure. An optimized thread profile reduces stress concentration at the joint, preventing whip cracking. The rod is fully compatible with hydraulic crawler drills and down-the-hole hammers from Ingersoll Rand, Furukawa, and Sandvik. Its larger cross-section transmits higher torque for efficient hole cleaning and chip removal. For quarry operators seeking to increase blast hole accuracy and reduce rod consumption, this heavy-duty Blast Hole Drill Rod delivers measurable ROI within weeks.

1 Scope of T/CSCS 046-2023 Standard

The Chinese industry standard T/CSCS 046-2023 applies to jumbo drill rods and drill rods sized from 25mm to 87mm in diameter. It covers terminology, ordering information, symbols, classification codes, dimensions and tolerances, technical requirements, testing methods, inspection rules, packaging, marking, transportation, and storage.

Key dimensions specified include:

Overall length: 800mm to 6,400mm depending on application

Body diameter: 32mm, 35mm, 38mm, 46mm, 52mm

Hexagonal sizes: H22, H25, H28, H32, H35 (across-flats dimensions)

Thread standards: R22, R25, R28, R32, R38, T38, T45, T51, T60

2 Thread Systems Explained

3 Cross-Section Selection: Hexagonal vs. Round

Hexagonal rods provide superior torque transmission and bending resistance, reducing hole deviation—particularly advantageous for drifting and tunneling. The corners of the hexagon engage with the chuck more positively, preventing slippage.

Round rods have less material, making them lighter to handle and less expensive. Round sections are more prevalent for extension drilling applications where hole depth exceeds 30 meters, as they offer better straightness when used with guide tubes.

4: Material Selection for Jumbo Drill Rods

4.1 Steel Grades and Composition

Manufacturers select specific alloy steels to balance the contradictory requirements of high strength, impact toughness, wear resistance, and fatigue life.

Common steel grades include:

22CrMoH: Chromium-molybdenum alloy steel offering excellent harden ability and toughness

55SiMnMo: Silicon-manganese-molybdenum steel with a bainite microstructure after heat treatment Cr-Ni-Mo-V proprietary alloys: Provide tensile strengths exceeding 1300 MPa for deep-hole applications. The steelmaking process incorporates multiple refining stages: EBT electric arc furnace melting → LF ladle refining → VOD vacuum degassing → continuous casting → billet rolling → mechanical drilling → center bar rolling.

Vacuum degassing removes hydrogen and oxygen inclusions that could initiate fatigue cracks. Electroslag remelting (ESR) further purifies the steel for premium-grade rods.

4.2 Mechanical Property Requirements

High-quality jumbo drill rods must meet stringent mechanical specifications:

Tensile strength: ≥ 758 MPa (premium grades ≥ 965 MPa)

Yield strength: ≥ 600 MPa

Elongation: ≥ 12%

Impact toughness (Charpy V-notch at -20°C): ≥ 54 J

Surface hardness: 48-52 HRC

Core hardness: 35-40 HRC

4.3 Microstructure Optimization

The ideal microstructure for drill rods is tempered martensite or bainite, providing a hard, wear-resistant case with a tough, ductile core. Metallographic examination verifies grain size, inclusion content, and the absence of detrimental phases like untempered martensite or retained austenite.

critical to final performance.

5.1 Steel Stock Preparation

Raw material selection: Vacuum-degassed alloy steel bars with mill certificates.

Sawing to length: Bars are cut to rough length plus machining allowances.

Center drilling: For hollow rods, a precision hole is gun-drilled through the entire length.

5.2 Hot Forging and Upsetting

Upsetting (end thickening): The rod ends are heated and forged to create larger-diameter sections for thread rolling. This upset end accommodates deeper threads without weakening the rod body. The process requires precise temperature control (950-1100°C) to avoid burning the steel.

5.3 Heat Treatment

Heat treatment releases the material's maximum potential performance.

Through-hardening (quench and temper): The entire rod is austenitized, quenched in oil or polymer, and tempered. This produces uniform mechanical properties throughout the cross-section—ideal for small-diameter rods under 32mm.

Carburizing (case hardening): Large-diameter rods (38mm+) benefit from carburization, which enriches the surface carbon content before quenching. This creates a deep case (1.5-2.0mm) with high wear resistance while maintaining a tough core. Carburized rods are preferred for underground applications and water-flushed systems.

Induction hardening: Only the thread ends are hardened via high-frequency induction heating. This reduces brittleness in the rod body while providing thread wear resistance. Used primarily for surface drilling with air flushing.

Shot peening: High-velocity steel shot impacts the rod surface, creating compressive residual stresses that close microscopic cracks and prevent fatigue crack initiation. Shot peening can increase fatigue life by 300% or more.

5.4 Thread Rolling

Threads are rolled, not cut, for all premium rods. Cold rolling displaces material rather than removing it, creating work-hardened surfaces with compressive residual stresses. Rolled threads exhibit 30% higher fatigue resistance than cut threads.

The process uses precision thread-rolling dies matched to the specific thread standard (R32, T38, etc.). Thread geometry is verified using optical comparators or thread gauges.

5.5 Straightening and Finishing

After heat treatment, rods may exhibit minor warpage. A roller straightening machine restores straightness to within 1.0mm per meter. For premium round rods used in deep-hole applications, straightness tolerance may be specified at 0.5mm/m.

Surface finishing includes:

Manganese phosphating: Creates a microporous coating that retains lubricating oil and resists corrosion 

Black oxide: Provides basic corrosion protection

Phosphating plus wax seal: Standard for most mining rods

5.6 Final Inspection and Packaging

Each rod undergoes dimensional checking, thread gauging, and non-destructive testing before packaging in wooden cases or plastic-wrapped bundles.