In tunneling and underground space development projects, rock drilling jumbos are crucial as the “pioneers” that break new ground. However, just as a sharp blade gradually wears down with continuous use, the rock drilling tools of a rock drilling jumbo face the same issue. Tool wear directly impacts construction efficiency and affects project costs and safety. Effectively controlling and reducing the wear of rock drilling tools has become a key issue for contractors. This article will explore ways to reduce wear on the rock drilling tools, helping construction teams achieve more efficient and cost-effective operations.
Main Causes of Rock Drilling Tool Wear
Geological Conditions
Geological conditions are one of the key factors affecting tool wear. Different rock types, hardness, joint development, and groundwater conditions significantly impact the wear of rock drilling tools.
Rock Type and Hardness
- Hard Rocks: Granite, diabase, etc., have high hardness and cause significant wear on the tools. During drilling, the carbide buttons on the drill bit bear greater impact and friction, leading to wear and breakage.
- Soft Rocks: Mudstone, shale, etc., have lower hardness but tend to stick to and clog the tools, increasing drilling resistance and accelerating wear.
Degree of Joint Development
- Well-Developed Joints: Rocks with joints and fractures change the mechanical properties of the rock, causing the tools to experience uneven stress and impact, accelerating wear.
- Less Developed Joints: More intact rocks provide uniform stress during drilling, resulting in slower wear.
Groundwater Conditions
- Abundant Groundwater: Water softens the rock, reducing its strength, but increasing friction between the tool and rock, speeding up tool wear. Additionally, groundwater may carry impurities that clog the tools and affect drilling efficiency.
- Lack of Groundwater: Dryer rocks have lower friction, leading to slower wear, but dry conditions can cause the tools to overheat, accelerating wear.
Parameter Settings
- Impact Oil Pressure and Tool Wear: Excessively high or low impact oil pressure increases wear. If the pressure is too high, excessive rock breaking increases friction, while low pressure leads to insufficient rock fragmentation, causing greater resistance for the carbide buttons.
- Advancing Oil Pressure and Tool Wear: The setting of advancing oil pressure also affects wear. High pressure causes the drill rods to bend, increasing wear on the drill rod and carbide buttons, while low pressure leads to “idle” drilling, increasing wear on one side of the tool.
Measures to Reduce Rock Drilling Tool Wear
Understand Rock Drilling Jumbo Performance
Understanding the performance of the rock drilling jumbo is crucial to reducing tool wear. For example, the Atlas XE3C full computer-controlled rock drilling jumbo, equipped with a high-frequency COP2238HD+ rock drill, has a power of 22kW and an impact frequency of 73Hz. It is suitable for large tunnel excavations with a maximum excavation area of 206m². Understanding these parameters helps contractors choose the appropriate tools, such as T38 drill rods, T38/T38 couplings, and T38/R32 drill rods of 5530mm.
Choose the Right Tool Material
The material of rock drilling tools directly impacts their wear resistance and lifespan. High-quality alloy steel or tungsten carbide drill bits have greater hardness and wear resistance, allowing for longer tool life under high-intensity operations. Although these tools have higher initial costs, their durability, and stability can significantly reduce replacement frequency and maintenance costs in the long run.
Properly Adjust Rock Drill Parameters
During drilling, key factors such as impact oil pressure, advancing oil pressure, and rotation oil pressure affect tool wear. Research has shown that setting the impact oil pressure so that the depth of each impact is 1/3 to 1/2 of the carbide button length produces optimal breaking results. Similarly, adjusting the advancing oil pressure to minimize any bending of the drill rods during drilling can reduce wear.
Timely Tool Replacement
Although wear is inevitable, replacing the drill bit at the right time minimizes wear. If the carbide button is embedded too shallowly and the secondary re-sharpening value is not considered during design, replacing the drill bit when the drilling speed drops to a certain level (e.g., 1.6m/min) ensures faster drilling speeds and reduces wear on the drill rod.
In addition, the wear of the drill bit also affects the clearance of the spoil discharge channel. As the drill bit wears down, the gap becomes smaller, resulting in poor spoil removal, which reduces drilling speed and accelerates tool wear. Timely drill bit replacement is, therefore, an important measure to avoid potential wear.
Master Drill Rod Repair Techniques
Repairing and reusing drill rods is an effective way to reduce tool wear. During repair, ensure that the waviness of the connecting part of the drill rod matches the original curvature. Additionally, there is a new technology for repairing drill rods using high-speed friction welding to restore worn-out rods to standard sizes. This new process solves the problem of using repaired rods in the full-automatic mode for computer-controlled rock drilling jumbos and significantly extends their lifespan.
Enhance Personnel Training and Management
- Professional Training: Provide professional training to operators to improve their skills and safety awareness.
- Drilling Tool Management: Establish a comprehensive tool management system to record and track the use, maintenance, and replacement of tools.
Conclusion
Reducing wear on the rock drilling tools is a systematic process involving multiple factors. By understanding the performance of the jumbo, selecting the right material for the tools, adjusting parameters, timely replacing tools, mastering drill rod repair techniques, and enhancing personnel training, we can significantly extend the lifespan of the tools, reduce cost losses due to wear, and improve overall drilling efficiency. Implementing these strategies requires continuous monitoring and adjustment to adapt to changing geological conditions and operational demands. Industry professionals should keep exploring and practicing, combining theoretical knowledge with practical operations to contribute to the progress and development of drilling technology, ultimately achieving more efficient and cost-effective operations.
