Carbon Dioxide Fracturing Devices for Deep-Hole Presplit Blasting in Rock Masses
1. Definition and Fundamental Principles
Carbon dioxide (CO₂) fracturing devices, also referred to as CO₂ gas generators or supercritical CO₂ blasting systems, are non-explosive rock fragmentation tools that utilize the rapid phase transition of pressurized liquid carbon dioxide into supercritical or gaseous state to generate mechanical fracture energy. Unlike conventional explosive blasting, which relies on chemical detonation and shockwave propagation, CO₂ fracturing operates through controlled thermodynamic expansion within a sealed chamber, producing sustained gas pressure that propagates fractures along predetermined planes in rock masses.
The fundamental principle involves the following thermodynamic sequence:
- Charging Phase: Liquid CO₂ is injected into a steel cylinder (typically rated for 10–15 MPa working pressure) through a dedicated charging valve, achieving a fill ratio of approximately 50–70% by volume.
- Ignition Phase: An electrical initiator (cartridge or spark plug) heats a chemical heat-generating charge to temperatures exceeding 400°C, rapidly vaporizing the liquid CO₂.
- Expansion Phase: As pressure rises beyond the critical point (31.1°C, 7.38 MPa), the CO₂ transitions to a supercritical fluid state and then expands explosively through a discharge nozzle, generating pressures of 100–350 MPa at the nozzle exit.
- Fracture Propagation Phase: The sustained gas pressure (lasting 200–500 ms, significantly longer than the millisecond-duration shockwave of conventional explosives) drives crack propagation along pre-existing discontinuities and along the intended presplit line.
In the context of presplit blasting, the CO₂ fracturing device is deployed in a closely spaced, parallel row of deep holes (typically 600–1000 mm diameter, 15–40 m depth) drilled along the final excavation boundary. The objective is to create a controlled fracture plane that acts as a stress relief zone, protecting the retained rock mass from damage during subsequent production blasting.
2. Category and Business Positioning
2.1 Technology Classification
CO₂ fracturing devices occupy a unique position within the non-explosive rock fragmentation technology spectrum. They are classified as follows:
| Classification Dimension | Category | Key Differentiator |
|---|---|---|
| Energy Source | Thermodynamic (CO₂ phase transition) | No chemical explosive required |
| Application Domain | Presplit / Contour Blasting | Boundary protection in precision excavation |
| Regulatory Status | Non-explosive (in most jurisdictions) | Exempt from explosives licensing in many regions |
| Pressure Class | High-pressure gas cylinder (GB/T 34537 series) | Requires pressure vessel compliance |
| Rock Type Target | Hard to medium-hard rock (UCS 30–250 MPa) | Optimal for granite, sandstone, limestone |
2.2 Positioning Within Cladding Technology Shanxi Co., Ltd. Portfolio
While Cladding Technology Shanxi Co., Ltd. is primarily known for its three core metallurgical technology routes—TIG/MIG weld overlay, hydraulic explosive bonding, and explosion welding—the CO₂ fracturing device technology represents a strategic extension into the mining and quarrying support services segment. This technology serves the following business functions:
- Raw Material Supply Chain Optimization: By enabling precision contouring of ore bodies and quarried stone, CO₂ presplit blasting produces cleaner, less damaged material faces that improve downstream cladding plate cutting yield and reduce material rejection rates.
- Customer Site Services: For customers operating in mining environments (e.g., nickel, copper, or chrome ore extraction for cladding material supply), the company can offer integrated site preparation services that ensure material quality at source.
- Technology Diversification: Demonstrates the company's broader engineering capability in high-pressure systems, energy-controlled fragmentation, and field deployment logistics—competencies transferable to hydraulic explosive bonding systems.
3. Technical Purpose and Value
3.1 Primary Technical Objectives
The deployment of CO₂ fracturing devices in deep-hole presplit blasting serves several quantifiable objectives:
- Boundary Integrity Protection: Achieve a retained wall with Joint Roughness Set (JRS) index exceeding 0.8 and residual overbreak less than 50 mm beyond design line.
- Vibration Reduction: Reduce peak particle velocity (PPV) at the excavation boundary by 40–60% compared to conventional emulsion + detonator presplit blasting.
- Fracture Plane Continuity: Create a fracture plane with continuity exceeding 90% along the presplit line, verified by post-blast geological mapping.
- Environmental Compliance: Eliminate toxic gas emissions (NOₓ, CO, SO₂) associated with chemical explosive detonation, enabling operations in environmentally sensitive or confined areas.
3.2 Economic and Operational Value
- Material Recovery Improvement: In quarrying applications for structural steel-grade stone (analogous to high-purity nickel or copper for cladding), a clean presplit face reduces secondary dressing costs by 20–35%.
- Regulatory Simplification: In jurisdictions where CO₂ devices are classified as non-explosive, the company avoids complex licensing procedures for explosives procurement, transport, and storage.
- Operational Flexibility: CO₂ devices can be charged and discharged multiple times (typically 100–500 cycles per cylinder) without degradation, enabling staged firing sequences for complex geometries.
- Safety Margin: The absence of detonators eliminates misfire hazards, electrical initiation risks, and the need for armed blasting crews in sensitive environments.
4. Key Process and Implementation Points
4.1 System Components and Specifications
| Component | Specification / Parameter | Function |
|---|---|---|
| CO₂ Cylinder | Steel tube, Φ89–108 mm OD, 10–15 MPa rated pressure, length 1.0–1.5 m | Pressure vessel for CO₂ storage and expansion |
| CO₂ Charge | Liquid CO₂, 50–70% fill ratio, ambient temperature 15–35°C | Energy source for fracture generation |
| Heat Generator (Cartridge) | Pyrotechnic composition, ignition energy 1–5 J, burn temperature >400°C | Rapid vaporization trigger |
| Discharge Nozzle | Bronze or steel, orifice diameter 20–40 mm, hardened | Pressure amplification and gas jet direction |
| Plug / Sealing Assembly | Ceramic or refractory plug, compressive strength >50 MPa | Containment during pressurization |
| Initiation Circuit | Electrical resistance bridge or electronic igniter, 6–24 V DC | Remote-controlled triggering |
4.2 Deep-Hole Presplit Blasting Design Parameters
| Design Parameter | Recommended Value | Rationale |
|---|---|---|
| Hole Diameter | 76–108 mm | Compatible with CO₂ device OD; sufficient for device insertion |
| Hole Depth | 15–40 m | Section height for bench mining; device placed at bottom or in stages |
| Hole Spacing (S) | 600–1000 mm (S/D = 7–11) | Ensures fracture linkage between adjacent devices |
| Stemming Length | 300–500 mm (non-explosive stemming: sand, clay, or ceramic) | Pressure containment; prevents gas escape |
| CO₂ Fill Ratio | 50–70% of cylinder volume | Optimizes energy release; prevents overpressure damage |
| Number of Devices per Hole | 1–3 (staged for deep holes) | Energy distribution along hole depth |
| Timing / Sequence | Simultaneous or 10–50 ms stagger | Fracture plane continuity; vibration control |
| Firing Pressure at Nozzle | 100–350 MPa | Rock fracture threshold (depends on UCS) |
4.3 Implementation Workflow
- Site Survey and Rock Characterization: Conduct geological mapping, determine UCS, identify major discontinuities, and establish design boundary line. Perform in-situ tests (point load, Schmidt hammer) to calibrate fracture energy requirements.
- Presplit Line Drilling: Drill parallel holes along the design boundary using DTH or down-the-hole percussion drills. Ensure hole deviation does not exceed 1:200 (0.5°) to maintain spacing consistency. Verify hole cleanliness (no water, debris) before device insertion.
- Device Assembly and Charging: Assemble CO₂ cylinders with heat generators and discharge nozzles. Charge with liquid CO₂ using a dedicated charging station at ambient temperature (15–35°C). Verify seal integrity through pressure hold test (5-minute hold at 5 MPa, no measurable drop).
- Device Insertion: Insert charged devices into drilled holes using a dedicated pusher or guide rod. Position device at the desired depth (typically near hole bottom for deep-hole applications). Install stemming material above the device.
- Initiation Circuit Connection: Connect electrical initiation wires from each device to a central control panel. Perform circuit continuity test (resistance measurement: 2–10 Ω per device). Establish safety perimeter (minimum 50 m exclusion zone).
- Firing Execution: Initiate presplit line first (before production blast). Use simultaneous or near-simultaneous firing (stagger ≤50 ms). Monitor PPV using geophones placed at 20–50 m from blast face.
- Post-Blast Inspection: Conduct geological mapping of the presplit face. Measure overbreak/underbreak using total station or laser scanner. Document fracture plane continuity. Retrieve and inspect CO₂ cylinders for reuse qualification.
4.4 Rock-Type-Specific Optimization
| Rock Type | UCS Range (MPa) | CO₂ Fill Ratio | Hole Spacing (mm) | Stemming (mm) | Expected Fracture Quality |
|---|---|---|---|---|---|
| Granite | 100–250 | 65–70% | 800–1000 | 500 | Good; may require supplementary devices |
| Sandstone | 30–120 | 50–60% | 600–800 | 300–400 | Excellent; clean fracture plane |
| Limestone | 20–80 | 50–55% | 600–700 | 300 | Excellent; may require lower charge |
| Dolomite | 80–180 | 60–65% | 700–900 | 400 | Good to excellent |
| Marble | 50–150 | 55–60% | 600–800 | 300–400 | Excellent; minimal spalling |
5. Applicable Standards and Acceptance Criteria
5.1 Equipment Standards
- GB/T 34537-2017 — Carbon dioxide gas generator for non-explosive rock fragmentation: Technical requirements (primary Chinese standard governing CO₂ device design, manufacturing, and testing)
- GB/T 34538-2017 — Carbon dioxide gas generator: Safety specifications
- GB/T 8163-2018 — Seamless steel tubes for fluid transport (applicable to CO₂ cylinder body material)
- TSG 21-2016 — Supervision and inspection regulations for pressure vessels (Chinese regulatory requirement for high-pressure CO₂ cylinders)
- GB 150-2011 — Pressure vessels: General technical requirements
- EN 1960:2012 — Explosives — Requirements for non-electric initiating devices (referenced for heat generator safety classification where applicable)
- ISO 16276:2016 — Rock characterization — Classification and description of rock masses
5.2 Blasting Design and Execution Standards
- GB 6722-2014 — Safety regulations for blasting (Chinese national standard; governs exclusion zones, vibration limits, and operational procedures even for non-explosive systems)
- GB 50201-2014 — Code for design of rock slope stability (reference for boundary protection design)
- ASTM D4716-16 — Standard test method for point-load strength of rock (rock characterization for design input)
- ISO 13346-1:2018 — Rock characterization — Determination of uniaxial compressive strength
- BS 6031:2003 — Code of practice for the use of explosives in mining (British reference standard for presplit blasting design methodology)
5.3 Acceptance Criteria
| Acceptance Parameter | Target Value | Measurement Method | Standard Reference |
|---|---|---|---|
| Fracture plane continuity | ≥ 90% of presplit line length | Geological mapping; visual + photographic | GB 6722-2014, Appendix B |
| Overbreak beyond design line | ≤ 50 mm (mean), ≤ 100 mm (maximum) | Total station survey; 3D laser scanning | BS 6031:2003, §7.3 |
| Underbreak (retained material) | ≤ 30 mm | Total station survey | GB 6722-2014 |
| Peak particle velocity at boundary | ≤ 25 mm/s (retained mass), ≤ 50 mm/s (sensitive structures) | Geophone array (3-component) | GB 6722-2014, §9; USBH Table 1 |
| Residual damage zone depth | ≤ 2× hole diameter from presplit face | Core sampling; Schmidt hammer survey | ISO 13346-1 |
| CO₂ cylinder post-use condition | No permanent deformation; wall thickness ≥ 95% original | UT thickness measurement; visual inspection | TSG 21-2016 |
6. Common Risks and Control Measures
6.1 Technical Risks
| Risk Category | Description | Likelihood | Consequence | Control Measures |
|---|---|---|---|---|
| Device Failure (Misfire) | Heat generator does not ignite or CO₂ charge insufficient | Medium | Low (no explosion) | Redundant heat generators; pre-firing circuit test; minimum 2-hour wait before re-entry |
| Cylinder Rupture | Overpressure exceeds cylinder design limit | Low | Critical (projectile hazard) | Strict fill ratio control (≤70%); certified cylinders only; exclusion zone ≥ 50 m |
| Fracture Plane Discontinuity | Inadequate spacing or insufficient energy prevents crack linkage | Medium | Medium (poor boundary quality) | Rock-specific parameter optimization; pilot holes; staged charging for deep holes |
| Gas Jet Erosion of Cylinder | Repeated use causes nozzle erosion and pressure loss | Medium | Low (performance degradation) | Cylinder life tracking (100–500 cycles); UT wall thickness checks; retirement criteria |
| Environmental Temperature Effect | Low ambient temperature reduces CO₂ vaporization efficiency | Medium (seasonal) | Medium (reduced fragmentation) | Minimum operating temperature 5°C; cylinder pre-heating; adjusted fill ratio |
6.2 Safety and Regulatory Risks
- Regulatory Classification Uncertainty: In some jurisdictions, CO₂ devices with heat generators may be classified as explosive articles. Control: Obtain written regulatory classification confirmation before deployment in any new jurisdiction.
- High-Pressure Cylinder Handling: CO₂ cylinders are pressurized to 5–10 MPa during transport. Control: Use certified transport cases; prohibit exposure to temperatures above 55°C; comply with GB/T 34538 transport requirements.
- Asphyxiation Hazard: CO₂ release in confined spaces displaces oxygen. Control: Prohibit use in enclosed underground areas without ventilation; deploy O₂ monitors during device recovery operations.
- Electrical Initiation in Hazardous Atmospheres: If deployed in gas-bearing rock formations (methane, hydrogen sulfide). Control: Use intrinsically safe (Ex-rated) initiation circuits; conduct gas monitoring before firing.
7. Application Scenarios and Integration with Company Technology Routes
7.1 Direct Application Scenarios
- Quarry Face Preparation for Dimension Stone: Presplit blasting along extraction boundaries for marble, granite, and limestone quarries. Clean faces reduce sawing waste and improve slab yield by 10–20%.
- Ore Body Contour Control in Mining: Protection of ore boundaries during open-pit mining to minimize dilution (waste rock inclusion). Critical for high-grade ore bodies where dilution directly impacts metallurgical recovery.
- Tunnel and Shaft Excavation: Presplit blasting along tunnel perimeters to minimize convergence and overbreak, reducing shotcrete consumption by 30–50%.
- Foundation Excavation for Critical Infrastructure: Precision boundary control for dam foundations, nuclear facility basements, and pipeline trenching where ground disturbance must be minimized.
- Demolition of Precision Structures: Controlled fragmentation of concrete and rock structures in urban environments where vibration limits are stringent (≤ 25 mm/s PPV).
7.2 Synergy with TIG/MIG Weld Overlay Technology Route
The CO₂ fracturing technology supports the company's weld overlay operations in the following ways:
- Base Material Procurement: By enabling clean extraction of high-quality nickel, copper, and chrome ore (critical for 309L, 312, and Hastelloy overlay alloys), the company can ensure consistent chemical composition and low inclusion content in base plates supplied to customers.
- WPS Qualification Support: Understanding the fracture mechanics of presplit rock interfaces informs the company's approach to residual stress management in overlay welds—both involve controlled crack initiation and propagation under stress.
- Site Preparation for Field Overlay: When the company provides on-site weld overlay services at mining or quarry operations, CO₂ fracturing enables safe and precise preparation of work surfaces without damaging surrounding infrastructure.
7.3 Synergy with Hydraulic Explosive Bonding Technology Route
- Pressure System Expertise Transfer: The high-pressure CO₂ cylinder system (10–15 MPa working, 100–350 MPa peak) shares engineering principles with hydraulic explosive bonding systems (typically 300–1000 MPa). Personnel trained in CO₂ device operation gain familiarity with high-pressure fluid dynamics, seal integrity, and pressure vessel safety.
- Explosive Bonding Interface Optimization: Research into CO₂ fracture propagation in layered rock masses provides analogical insight into the stress wave behavior at bimetallic interfaces during explosive bonding—a key parameter in optimizing bond quality for dissimilar metal joints.
- Customer Cross-Selling: Mining customers who engage the company for CO₂ presplit blasting services are natural candidates for clad plate supply (e.g., Ni-Cu alloyed steel for acid-resistant mine equipment, Hastelloy-clad piping for leach tanks).
7.4 Synergy with Explosion Welding Technology Route
- Explosive-Free Alternative Demonstration: In environmentally sensitive or urban-adjacent locations where explosion welding is restricted due to safety regulations, CO₂ fracturing demonstrates the company's capability in non-explosive energy-controlled processes.
- Fracture Mechanics Research: The study of CO₂ gas-induced fracture propagation contributes to the company's understanding of crack dynamics under non-traditional loading conditions—knowledge applicable to optimizing flyer plate velocity and stand-off distance in explosion welding.
- Material Surface Preparation: CO₂ fracturing produces clean, oxide-free fracture surfaces on metallic ores and alloys. These surfaces can serve as starting material for explosion welding trials where surface contamination would compromise bond quality.
8. Contribution to Qualification Building and Customer Value
8.1 Qualification and Certification Impact
- GB/T 34537 Compliance Certification: Successful deployment and testing of CO₂ devices enables the company to obtain certification as a qualified supplier/operator under the Chinese national standard for non-explosive rock fragmentation equipment.
- Safety Management System Enhancement: Integration of CO₂ device operations into the company's ISO 45001 (Occupational Health and Safety) management system demonstrates comprehensive process safety capability to customers and regulators.
- Pressure Vessel Inspection Qualification: Operating CO₂ cylinders requires compliance with TSG 21-2016, which builds institutional expertise in pressure equipment management—directly transferable to hydraulic bonding system qualification.
8.2 Customer Value Proposition
"The integration of CO₂ presplit blasting technology into our service portfolio allows us to offer end-to-end material integrity solutions: from controlled extraction of raw materials with minimal structural damage, through precision cladding fabrication, to certified delivery of high-integrity bimetallic products. This eliminates quality risk at the source and provides customers with traceable material provenance from rock face to finished clad plate."
8.3 Knowledge Management and Continuous Improvement
The study and documentation of CO₂ fracturing device application—captured as structured learning records—contributes to the company's technical knowledge base in the following ways:
- Parameter Databases: Accumulation of rock-type-specific optimization parameters (fill ratio, spacing, stemming) creates proprietary databases that accelerate project design for future deployments.
- Failure Analysis Records: Documentation of device malfunctions, fracture quality deficiencies, and environmental factors builds a corrective action library that improves system reliability over time.
- Cross-Disciplinary Insight: The thermodynamic and fracture mechanics principles underlying CO₂ fracturing enrich the company's theoretical foundation for all high-pressure, high-energy manufacturing processes.
9. Conclusion
The application of carbon dioxide fracturing devices in deep-hole presplit blasting represents a strategically valuable technology extension for Cladding Technology Shanxi Co., Ltd. While originating from mining and quarrying applications, the underlying competencies—high-pressure system management, controlled energy release, fracture mechanics, and field safety protocols—are directly transferable to the company's core metallurgical technology routes. By mastering this technology, the company strengthens its qualification portfolio (GB/T 34537, TSG 21-2016 compliance), enhances its ability to deliver material integrity solutions from source to product, and deepens its technical understanding of the energy-controlled processes that underpin all three of its primary manufacturing routes. The structured study and documentation of this technology ensures that operational knowledge is captured, systematized, and made available for continuous improvement across the organization.