In mineral extraction, filling drill hole construction is a crucial task. It not only effectively handles the filling of mine tailings and waste rock but also enhances the stability and safety of the mine. As the core tool in filling drilling operations, the setting of drilling parameters for the down-the-hole (DTH) hammer directly affects drilling efficiency, construction quality, and cost-effectiveness. Due to technological advancements, DTH drilling has become widely used in filling drilling operations because of its high efficiency, environmental benefits, and adaptability. However, to fully exploit the potential of this technology, it is key to scientifically and reasonably set the drilling parameters for the DTH hammer. These parameters affect drilling speed, tool wear, energy consumption, and safety during construction. Therefore, mastering the correct method of setting DTH hammer drilling parameters is essential for improving the overall effectiveness of filling drill hole construction. This article will discuss how to set these key parameters to ensure smooth operations.
Working Principle of a Down-the-Hole Hammer
High-pressure air enters the inside of the DTH hammer through the intake valve of the DTH drilling rig and the inner hole of the drill pipe. It is divided into two ways through the air distribution valve, one way enters the bottom of the hole through the center hole of the valve seat and piston and the exhaust hole of the DTH drill bit to discharge the rock slag at the bottom of the hole, and the other way is distributed to the cylinder to make it reciprocate to realize the impact work.
Key Factors for Setting Drilling Parameters
- Strata Characteristics: The hardness and permeability of the rock in different strata directly influence drilling efficiency and the choice of parameters.
- Hole Diameter and Depth: The diameter and depth of the drill hole determine the required drilling pressure, torque, and air volume.
- Equipment Performance: The performance limitations of the drill rig, air compressor, and other equipment also affect parameter settings.
Setting Drilling Parameters
The setting of drilling parameters is a key factor affecting the drilling efficiency of a DTH hammer, mainly including rotation speed, drilling pressure, torque, air pressure, and air volume.
Rotation Speed
Rotation speed refers to the number of rotations the DTH hammer makes per minute. When drilling through hard rock, it is ideal for the hammer to rotate the outer teeth (the outermost carbide teeth) of the bit by 1/3 to 1/2 with each impact. Both too fast and too slow a rotation speed will reduce drilling efficiency.
Calculation formula: n=f d/(πD)
- n: Rotation speed of DTH hammer (r/min)
- f: Impact frequency of DTH hammer (min⁻¹)
- d: Diameter of the carbide gauge button (mm)
- D: Hole diameter (mm)
A proper rotation speed enhances drilling efficiency and tool longevity. In practice, the rotation speed should be maintained between 15 and 25 r/min, depending on the encountered rock type and the type of DTH hammer used.
Drilling Pressure
Drilling pressure refers to the pressure applied to the bit, which primarily serves to overcome the reaction force during impact and ensure the bit’s carbide button makes close contact with the rock at the hole bottom. Drilling pressure should be determined based on the rock hardness and bit diameter.
- Theoretical Drilling Pressure: 60–146 N per mm of hole diameter.
- Actual Drilling Pressure: The drilling pressure is calculated theoretically, after subtracting the weight of the tool.
For softer rock, higher drilling pressure should be applied; for harder rock, lower pressure is preferable. Using the appropriate drilling pressure enhances efficiency, while thoughtlessly increasing pressure can cause excessive tool wear without improving impact effectiveness.
Torque
Torque refers to the resistance torque exerted on the drill rod during rotation. The torque required for DTH hammer drilling depends on the hole diameter, depth, and rock layer conditions.
Recommended Torque: 2.70 N·m per mm of hole diameter (considering other factors inside the hole).
As the hole depth and rock hardness increase, the torque must also increase accordingly. Properly controlling torque prevents drill rod breakage and bit damage.
Air Pressure
Air pressure is a key parameter in DTH hammer drilling operations as it directly affects the hammer’s impact frequency and energy.
Calculation formula: p=qL+pm+pc+ps
- p: Air pressure (MPa)
- q: Pressure drop per meter of dry hole (MPa/m), typically 0.0015 MPa/m
- L: Length of drill rod column (m)
- pm: Pressure loss in the pipeline (MPa), typically 0.1–0.3 MPa
- pc: Pressure drop across the DTH hammer (MPa)
- ps: Water column pressure inside the hole (MPa)
The air pressure must be sufficient to maintain the hammer’s impact frequency and energy. As drilling depth increases, so does the required air pressure. Thus, during construction, air compressors and booster pumps should be configured according to actual conditions to enhance drilling efficiency and cost-effectiveness.
Air Volume
Air volume is one of the most important parameters affecting the drilling efficiency of a DTH hammer. It determines the airflow speed and cutting removal ability in the hole.
Calculation formula: Q≥60K1K2π⁴(D²+d²)v
- Q: Air compressor air volume (m³/min)
- v: Annular air flow return velocity (m/s), typically 15–25 m/s
- D: Hole diameter (m)
- d: Outer diameter of the drill rod (m)
- K1: Hole depth correction factor
- K2: Air volume increase factor for water inflow in the hole
The greater the amount of groundwater inflow in the strata, the higher the required air volume. Therefore, when selecting air compressors, it is crucial to consider the effect of water inflow and hole depth to ensure adequate air volume.
Precautions for Using and Maintaining Down-the-Hole Hammers
- Pre-Use Inspection: Ensure that the joints at both ends of the DTH hammer are securely connected to the outer casing, the piston moves smoothly, the bit is correctly connected to the hammer, and the drill rig, compressor, and other equipment are ready, and the connections are secure.
- Lubrication During Use: Choose appropriate lubricants and lubricate regularly to reduce wear and fatigue damage to moving parts. High-quality lubricants with good wear resistance, rust resistance, oxidation resistance, and anti-foam properties are recommended. In dry drilling, timely supplementation of lubricants is needed.
- Maintenance and Servicing: Regular maintenance and servicing can extend the service life of the DTH hammer and improve drilling efficiency. It includes cleaning the cylinder and piston components, checking for wear, and replacing parts as needed.
Conclusion
Setting drilling parameters for a DTH hammer is a comprehensive process involving multiple factors. By thoroughly analyzing geological conditions, selecting appropriate tool configurations, adjusting impact frequency and pressure precisely, and integrating real-time monitoring and feedback mechanisms, we can enhance drilling parameters. It improves drilling efficiency, reduces energy consumption and tool wear, and ensures stability and safety throughout the construction process. With continuous technological advancements and improvements in automation, future DTH hammer parameter settings will become more precise and efficient, providing stronger support for mineral exploration and development. As professionals in the mining industry, we should keep an eye on the forefront of technology, continuously improve our skills and knowledge, and drive the filling drilling technology to new heights with a scientific and rigorous approach.
