Two crews, two identical rigs, the same button bit — and wildly different results, because they're drilling different rock. In mining and excavation, bit performance is a system: button geometry, carbide grade and how you run the rig all have to match the formation. Get the match right and you drill faster while replacing bits less often.
Button shape: speed vs survival
The shape of the carbide buttons is the first lever:
- Ballistic (pointed) buttons bite aggressively — higher penetration rate in soft-to-medium, less abrasive rock, but more exposed to breakage in hard ground.
- Spherical (rounded) buttons are the survivors — more resistant to impact and abrasion in hard, fractured or abrasive rock, at a slightly lower penetration rate.
- Semi-ballistic sits between the two for mixed formations.
Grade: hardness vs toughness, again
The same trade-off that governs every carbide part governs button bits. Hard, abrasive rock like granite and quartzite punishes buttons with abrasion — but impact and fracturing demand toughness. In practice, high-impact rock drilling favours tougher, higher-cobalt grades that resist cracking, accepting slightly faster abrasive wear. Softer, less abrasive ground can run a harder grade for maximum wear life.
| Formation | Button shape | Grade lean |
|---|---|---|
| Soft / medium, low abrasion | Ballistic | Harder (wear-resistant) |
| Hard, abrasive (granite, quartzite) | Spherical | Tougher (impact-resistant) |
| Fractured / mixed | Semi-ballistic | Balanced, tough |
The rig runs the bit
Even the perfect bit underperforms if the drilling parameters fight it:
- Feed pressure too low and buttons rub (accelerated abrasion); too high and you risk breakage.
- Rotation speed must be matched to feed so buttons index into fresh rock rather than re-crushing cuttings.
- Flushing (air or water) must clear cuttings — poor flushing means re-grinding debris, heat and premature wear.
Re-sharpen before you have to
Buttons wear flat, and a flat button drills slowly and heats up — which accelerates its own destruction. Re-grinding buttons back to shape on a schedule, before they're badly worn, restores penetration rate and extends total bit life significantly. It's the drilling equivalent of not running a tool to destruction.
Written by Alok Kanani — Chief Executive Officer, Carbide India. General guidance, not a substitute for application-specific engineering advice.