Granite's "Stubborn Streak" and the Challenge of Speed
Granite is akin to a "hard nut to crack"; its high hardness (Mohs hardness 6–7), high density (approx. 2.7 g/cm³), and compact structure make it prone to issues such as "slippage" and "drill jamming" during Down-the-Hole (DTH) hammer operations. When it comes to construction speed, faster isn't always better-an excessively high impact frequency can lead to drill bit overheating and premature wear, thereby actually reducing efficiency. The ideal scenario involves finding a delicate balance-a point that is "just right, with a little extra to spare." Depending on the degree of fracturing within the rock formation, the impact frequency is typically controlled at 800–1200 blows per minute; this approach maintains drilling momentum while preventing excessive equipment wear.
Equipment Selection: Pairing "Hard Nuts" with "Hard Tools"
The "combat effectiveness" of a DTH hammer system hinges on the synergy between its pneumatic system and the drill bit. For hard rocks like granite, priority should be given to DTH hammers driven by high air pressure (1.5–2.5 MPa), paired with tungsten carbide alloy drill bits. With a hardness second only to diamonds, this material allows the bit to penetrate rock strata as effortlessly as a "hot knife through butter." If the granite formation features well-developed joints or fractures, the impact energy can be adjusted accordingly: by lowering the air pressure to 1.8–2.0 MPa, the drill bit can simultaneously crush the rock matrix and utilize the existing joint planes to expand the fragmentation zone, potentially boosting drilling speed by 20%–30%.
Operational Techniques: Three Key Strategies to Make Hard Rock "Yield"
"Pulsed" Drilling: Pause drilling for 10 seconds after every 50–100 mm of penetration to allow rock cuttings to be evacuated. This prevents the drill bit from repeatedly crushing the same material, thereby boosting efficiency by 15%.
"Listening to the Rock": Experienced operators can discern the condition of the rock formation simply by listening to the sound of the drilling rig. If the sound becomes muffled or dull, it indicates that the drill bit is struggling to "chew through" particularly hard rock; at this juncture, the impact frequency can be reduced, and the operator can switch to a method utilizing rotation and thrust pressure to "grind" through the rock layer instead. "Cooling Magic": Spraying a small amount of water mist at the drill bit-note: this is not the same as dousing it with large quantities of water-serves a dual purpose: it lowers the bit's temperature while utilizing the lubricating properties of water to reduce friction, thereby stabilizing the drilling speed at 0.5 to 1 meter per hour (depending on the hardness of the rock).