How Rotary Drilling Rigs Break Rock During Drilling

When constructing in hard rock strata, rotary drilling rigs must overcome the high hardness and compressive strength of rocks. Unlike drilling in soft soil layers, rock penetration primarily relies on specialized drilling tools and impact methods to break the rock and achieve efficient construction. This article provides a detailed explanation of how rotary drilling rigs use impact methods to break rocks during drilling.

1. Principles of Rock Penetration

During rock penetration, rotary drilling rigs apply high-intensity impact and shear forces on the rock surface through drilling tools, breaking the rock into small pieces or powder. The drilling process typically combines rotation and impact actions, gradually penetrating the strata through repeated mechanical forces. The principles of rock penetration include:

• Impact Force: The drilling tools apply repeated impact on the rock surface under hydraulic pressure or the action of the power head, causing localized fragmentation.

• Shearing Force: Simultaneously, the rotational motion of the drilling tools generates shear forces that further destroy the rock's surface structure.

• Debris Removal: The broken rock fragments are transported to the surface via the drill rod’s internal spiral conveyor or mud flushing, keeping the borehole clean for smooth operations.

2. Selection of Drilling Tools for Rock Penetration

Rock penetration requires specialized drilling tools to handle the high hardness and specific requirements of rock drilling. Common types include:

• Bucket Drill Bits
  Bucket drill bits are made of high-strength alloy materials with carbide teeth or chisel teeth at the bottom, breaking rocks through rotation and impact. They are suitable for high-hardness strata with well-developed interlayer fissures.

• Core Drill Bits
  Core drill bits cut and extract rock cores while breaking rocks, allowing geological analysis. They are commonly used in exploratory drilling or situations requiring detailed rock properties.

• Roller Cone Drill Bits
  Roller cone drill bits are a core tool for rock penetration. The teeth on the bit apply impact and rolling pressure on the rock surface, causing spalling and fragmentation. These are suitable for dense, high-hardness strata.

• Percussion Drill Bits
  Percussion drill bits break rocks by repeatedly hammering the surface with high-frequency impacts, ideal for extremely hard strata.

3. Methods for Breaking Rocks with Rotary Drilling Rigs

The rock-breaking process involves the following steps:

1. Start the Power Head and Hydraulic System

• The power head provides rotational torque for the drill bit, ensuring stable and high-speed rotation, while the hydraulic system provides vertical pressure to transmit impact force to the rock surface.

2. Apply Downforce

• During penetration, operators adjust the downforce based on the rock’s hardness. Hard rocks require higher downforce to ensure impact efficiency, but excessive force can damage the tools or equipment.

3. High-Speed Rotational Impact

• The drill bit rotates at high speed on the rock surface while continuously applying impact forces. The combined action of rotation and impact efficiently breaks the rock’s surface structure.

4. Timely Debris Removal

• During impact, broken rock fragments must be promptly removed from the borehole. Mud pumps or the spiral conveyor within the drill rod can carry away the debris, preventing accumulation that could hinder efficiency.

5. Step-by-Step Drilling

• Rock penetration must proceed step-by-step. After drilling a certain depth, operations pause to clean the borehole, ensuring smooth progress and maintaining vertical accuracy.

4. Key Considerations During Rock Penetration

1. Equipment Tuning

• Before rock penetration, thoroughly inspect the rig, including the power head, hydraulic system, and drill rod, ensuring optimal equipment performance.

2. Proper Drill Tool Selection

• Select appropriate drill bits for different rock hardness and structure to avoid inefficiencies or equipment damage due to tool mismatch.

3. Control of Downforce and Rotational Speed

• Adjust downforce and rotational speed according to the rock hardness and drilling depth. Excessive downforce may deform the drill rod or damage the bit, while excessive rotational speed increases wear.

4. Borehole Cleaning

• Keep the borehole clean during operations to prevent broken rock fragments from accumulating and affecting impact efficiency.

5. Regular Tool Inspection

• Drill bits wear significantly during rock penetration. Regularly inspect and replace or repair worn-out teeth or chisels to maintain efficiency.

5. Conclusion

Rotary drilling rigs rely on impact methods to break rocks during penetration. This technically demanding process requires scientifically designed methods, proper equipment tuning, and the use of efficient tools. By optimizing the coordination of impact and rotation, construction efficiency can be significantly improved, and the difficulty of breaking hard rocks can be reduced. Simultaneously, regular maintenance and skilled operators are essential for successful operations.

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