Rock drilling operations are indispensable in various construction, mining, and geological exploration projects. Choosing the right drill bit is not only related to work efficiency but also directly affects the cost and quality of the project. This article will give you a detailed introduction to the different types of rock drill bits and how to choose and buy according to actual needs, helping you improve work efficiency and reduce costs.
Types of rock drill bits
Rock drill bits come in various types, categorized based on materials, structures, and applications.
Top hammer rock drill bit
Top hammer rock drill bits are a rock drilling tool used for drilling holes in rigid materials such as rocks.
Classification:
According to the thread form, there are R-type threads and T-type threads.
According to the shape and structure, they are chisel bit, cross bit, X-bit, and button bit. The button bit is the most commonly used structure in thread drill bits, so it includes ordinary flat face, retract flat face, reaming semi-dome, reaming guide, ordinary drop center, and retract drop center, etc.
Applicable geology
| Rock Type | Solid and homogeneous rock structure | Fissured and heterogeneous rock formations |
| Weakly abrasive rock | 1. Ballistic concave button bit 2. Spherical concave button bit 3. Flat drill bit | 1. Ballistic concave center guide bit 2. Concave center guide bit 3. Flat guide bit |
| Moderately abrasive rock | 1. Ballistic concave button bit 2. Spherical concave button bit 3. Flat button bit 4. Flat heavy button bit | 1. Ballistic concave center guide bit 2. Concave center guide bit 3. Flat guide bit |
| Highly abrasive rock | 1. Ballistic concave button bit 2. Spherical concave button bit 3. Flat button bit 4. Flat heavy button bit | 1. Flat guide bit 2. Concave center guide bit |
DTH drill bit
The DTH drill bit is a kind of drill tool connecting the hammer with the spline of the drill bit to guide and transmit the rotation energy for the impact, with the drill bit and the DTH hammer diving into the hole to break the rock.
Classification:
According to the air pressure, there are: high air pressure DTH drill bits, medium and low air pressure DTH drill bits.
According to the end surface design form, there are: center concave type, concave type, convex type, flat type and bilateral gauge button type.
Applicable geology:
- Center concave type: This shape is typically employed when drilling soft to medium-hard and fractured rock formations using medium and low air pressure. It aims to achieve rapid drilling speeds and minimize blast hole deflection rates.
- Concave type: It is suitable for all rock formations, especially the best results in rock formations with medium hardness and uniform lithology. The deviation of the blast hole is low, and the slag removal effect is good.
- Convex type: It’s tailored for soft to medium-hard rock formations under medium to low air pressure, boasting a durable steel body that resists abrasion. Side teeth endure minimal wear under low loads, enabling fast drilling, but controlling blast hole deviation can be challenging.
- Flat type: This type is ideal for very hard and highly abrasive rock formations under high air pressure, offering faster drilling speeds and reduced drill body wear.
- Bilateral gauge button type: This type is suitable for drilling very hard rock formations under high air pressure, providing fast drilling speeds with minimal wear on the drill bit body.
Working principle
When the DTH drill bit is working, the pressure regulating mechanism is advanced to push the drill tool continuously forward and keep the drill bit in contact with the rock at the bottom of the hole. The rotary mechanism makes the drilling tool rotate continuously. At the same time, under the action of air pressure, the impactor piston installed at the front end of the drill pipe continuously impacts the drill bit. The drill bit obtains energy after the impact, dives into the bottom of the hole, and generates an impact force that squeezes the rock. The rock drilling tools rotation avoids the drill bit hitting the same drilling trace repeatedly and generates a shear force scraping the rock at the bottom of the hole. Under the action of the impact force of the impactor piston and the shear force of the rotary mechanism, the rocks are constantly being crushed and sheared away. The air pressure enters through the gas joint, reaches the bottom of the hole through the hollow drill pipe, and blows the cut slag from the annular space between the drill pipe and the hole wall to the outside, thus forming a blast hole.
Roller Cone Bit
Roller cone bits are the most widely used medium and large diameter drilling bit. When the roller cone bit is working, the cutting teeth alternately contact the bottom of the well, while rock breaking torque is small, the contact area between the cutting teeth and the bottom of the well is small and the specific pressure is high, thus it is easy to penetrate into stratum. The total length of the working blade is large, so the wear is relatively reduced. Roller cone bits can adapt to various formations from soft to hard.
Classification:
According to the number of roller cones, it includes single-cone bits, tri-cone bits, and assembled multi-cone bits.
According to the cutting material, it includes milled tooth bits and insert roller cone bits.
According to the type of bearing, it includes two categories of rolling bearings and sliding bearings.
According to bearing seal type, it includes open roller, rubber sealed roller, and metal sealed bearing roller cone bits.
Working Principle
When the roller cone bit is working, by providing it with sufficient axial pressure and rotary torque by drill, the roller cone bit drills and rotates on the rock at the same time and generates static pressure and impact dynamic pressure on the rock to realize rolling at the bottom of the hole. The continuous extrusion and cutting impact break the rock.
Applicable geology:
It is suitable for soft and hard formations, and it is essential to select the appropriate roller cone bit based on the geological conditions, especially for drilling projects involving gravel, limestone, dolomite, and most other heterogeneous rock formations.
Applicable rock formation range: 2000~40000psi (27~275MPa)
PDC drill bit
The Polycrystalline Diamond Compact (PDC) drill bit is composed of polycrystalline diamond material, typically arranged in a thin disc shape. These diamond components are carefully mounted or sintered onto the drill bit’s body, forming small cutting blocks.
Classification:
According to the drill bit body material, there are steel body PDC drill bits and matrix PDC drill bits.
According to the number of blades, there are three-wing PDC drill bits, four-blade PDC drill bits, eight-blade PDC drill bits, etc.
Working principle:
The cutting teeth of the PDC drill bit are essentially small scrapers, which mainly have a shearing function and are supplemented by a plowing function. Because the polycrystalline diamond layer is thin (0.8~3 mm), ultra-hard, and more than 100 times more wear-resistant than the tungsten carbide substrate, the cutting edge can remain self-sharpening during rock cutting. After the sharp cutting edge cuts into the formation, it shears the rock along the torque and moves in the direction, taking advantage of the rock’s low shear strength.
Applicable geology:
Suitable for soft to medium-hard formations. Most drill bits are designed for drilling hard rock but are often limited to drilling very loose formations.
Applicable rock formation range: 2000~30000psi (13~206MPa)
How to choose the right rock drill bit?
- Rock properties: different types of rocks have different hardness and abrasiveness, and we should choose the drill bit according to the nature of the rock. For example, PDC drill bits perform well in soft to medium-hard rock formations but are not suitable for high-hardness formations.
- Drill bit diameter: the size of the drill bit diameter directly affects the size of the rock drilling hole. When selecting a drill bit, we should determine the diameter of the drill bit according to the actual needs to ensure that the rock drilling hole diameter meets the project requirements.
- Project requirements: select the appropriate drill bit type and specifications based on factors such as the scale of the project, schedule requirements, and cost budget.
- Equipment performance: ensuring proper compatibility between the drill bit and the rock drilling equipment is essential for optimal performance. It includes factors such as ensuring that the drill bit is compatible with the drilling rig’s power and capabilities. A mismatch between the drill bit and the drilling equipment can lead to inefficiencies, increased wear and tear, and potentially unsafe operating conditions.
Conclusion
Choosing the right rock drill bit is essential for improving work efficiency and reducing costs. When purchasing, comprehensive considerations should be made based on factors such as rock properties, drill bit diameter, engineering requirements, and equipment performance to select products with high-cost performance. At the same time, correct use and maintenance of drill bits and attention to the innovation and development trends of drill bit technology are the keys to ensuring the smooth progress of the project and improving project efficiency.
