Cross bits and
button bits are two core drilling components tailored for self-drilling anchor systems, engineered to address diverse geotechnical conditions in anchoring projects. While sharing the integrated functionality of drilling, anchoring, and synchronous grouting, they differ in cutting structure, wear resistance, and adaptability to strata—enabling optimized performance across soft soil, hard rock, fractured formations, and other complex ground scenarios. Below is a detailed technical overview:
Both cross bits and button bits are front-end drilling tools connected to self-drilling anchor rods, designed to work with hollow anchor systems for simultaneous drilling, rod advancement, and grouting. Their primary role is to break through subsurface materials (soil/rock) while facilitating grout injection to reinforce the bond between the anchor rod and the surrounding formation. The key distinction lies in their cutting mechanism: cross bits rely on sharp, intersecting carbide blades for shear cutting, while button bits use
Spherical tungsten carbide inserts for impact crushing—making them suited for different hardness and uniformity of strata.
- Cutting Structure Design: Features 2–4 intersecting tungsten carbide blades (cross-shaped layout) with sharp cutting edges. The blades are welded or brazed to a steel body, ensuring high structural rigidity and efficient shear cutting of strata.
- Strata Adaptability: Optimized for soft to medium-hard formations, including clay, sandy soil, weathered rock, and weakly consolidated sandstone. Excels in uniform, low-abrasion strata where rapid drilling speed is prioritized.
- Grouting Channel Configuration: Integrates internal hollow channels with side grout outlets (typically 2–4 holes) to ensure unobstructed grout flow during drilling. Prevents channel blockage by soil/rock debris, ensuring full contact between grout and borehole walls.
- Cost-Effective & Easy Maintenance: Simple blade structure reduces manufacturing costs; worn blades can be re-sharpened or replaced, extending the bit’s service life at a low maintenance cost.
- Tungsten Carbide Button Inserts: Embeds 4–8 spherical or hemispherical tungsten carbide buttons (HRC ≥ 90) on the drill face, arranged in triangular, hexagonal, or spiral patterns. The buttons provide exceptional impact resistance and wear resistance for crushing hard materials.
- Strata Adaptability: Ideal for hard, abrasive, or fractured formations, such as granite, basalt, dense limestone, and broken rock masses. The spherical design distributes impact force evenly, avoiding blade damage in uneven strata.
- Enhanced Drilling Stability: The button layout maximizes contact area with the formation, reducing vibration during high-speed drilling. Improves hole straightness and prevents bit deviation in deep anchoring projects.
- Grouting & Durability: Hollow body with precision-drilled grout channels ensures consistent grout distribution. Carbide buttons resist wear even in long-term drilling, maintaining performance in high-abrasion environments.
- Connection: Both bits are threaded to the front end of self-drilling anchor rods, forming a rigid assembly with the drill rig.
- Drilling & Advancement: The drill rig provides rotational torque and axial thrust, driving the bit to break strata. The anchor rod advances synchronously with drilling, eliminating borehole collapse risks.
- Synchronous Grouting: Grout (cement-based or polymer-modified) is pumped through the hollow anchor rod, flows through the bit’s internal channels, and is ejected from side outlets. Grout permeates surrounding strata and solidifies to form a high-strength bond with the anchor rod.
- Anchoring Formation: After reaching the designed depth, grouting continues until overflow. Once cured, the anchor rod and grout-rock/soil composite form a stable anchoring system, providing tensile and shear resistance.
- Cross Bit: Relies on the sharp edges of carbide blades to shear and scrape soil/rock, suitable for strata that can be easily sliced (e.g., soft soil, weathered rock). Drilling speed is fast in low-hardness materials but may dull quickly in abrasive strata.
- Button Bit: Uses the impact force of rotating carbide buttons to crush hard rock into fragments, which are then discharged through the bit’s flutes. Excels in high-hardness formations where shear cutting is ineffective, maintaining efficiency even in fractured rock.
- Choose cross bits for projects with soft-to-medium strata (compressive strength < 50 MPa), tight budgets, or short anchoring depths (≤ 10m).
- Select button bits for hard/abrasive/fractured strata (compressive strength > 50 MPa), deep anchoring (≥ 15m), or projects requiring high hole quality and long-term durability.
- For mixed strata (e.g., soft soil overlying hard rock), consider combining both bits: use a cross bit for upper soft layers and switch to a button bit for lower hard rock.
