Advances in DTH Drilling Technology Boost Mining Efficiency
What Actually Drives Cost per Metre
Down-the-hole (DTH) drilling technology has advanced on several fronts at once, and the payoff shows up in cost per metre drilled rather than in headline penetration rate alone. A rig that drills 10 percent faster but wears bits 30 percent sooner, or spends an extra hour per shift on rod handling, is not cheaper. The meaningful gains come from treating the hammer, bit, air package and control system as one design point.
Hammer and Bit Design
- Hammer design changes that raise energy per blow on the same air supply, typically by enlarging the piston striking face and tuning port timing, so more of the available air energy reaches the rock instead of being lost as heat and back-pressure.
- Bit metallurgy moving to tougher, more wear-resistant carbides and better braze and body steels, which extends button retention and reduces catastrophic button loss in abrasive ground.
- Button geometry selected to the rock: spherical buttons for hard, abrasive rock where wear life dominates; ballistic buttons for medium-hard rock where penetration rate matters more; parabolic buttons as a middle option for mixed ground.
- Higher working pressures, commonly 24 to 35 bar on larger hammers versus the older 7 to 17 bar range, which raises blow energy and flushing velocity without increasing hole size.
- Compressor technology that makes high pressure practical: two-stage screw air ends, improved coolers and better fuel efficiency per cubic metre of air delivered.
- Instrumentation and telemetry reporting penetration rate, air pressure and temperature, so crews can see a worn bit or a falling air supply before it costs a shift.
- Hole straightness and deviation control in deep holes, through bit face design, stabiliser geometry and feed force management.
- Automated rod handling that cuts non-drilling time and keeps crews away from the rotating string.
Matching the Whole String
A hammer optimised for maximum blow energy can starve its bit of flushing air; a bit with aggressive button geometry can out-drill the air package feeding it. The practical approach is to fix a design point, usually hole diameter, working pressure and available air volume, then select hammer and bit that perform best inside that window. This is why a matched hammer, bit and compressor package usually beats a mix of individually strong components.
Seeing Problems Before They Cost a Shift
Pressure and temperature trends are more useful than single readings. A gradual rise in return air temperature with stable pressure often points to a worn bit or restricted flushing. A falling standpipe pressure at constant air volume points to a supply problem. Catching either within minutes rather than at the end of a hole protects both the bit and the shift.
Straightness and Automation
In deep holes, deviation is a cost problem: a hole that wanders needs more correction, more steel and sometimes a re-drill. Bit face geometry, stabilisers and controlled feed force keep holes closer to line. Automated rod handling removes the heaviest manual task on the pattern and shortens the time between drilled metres.
Contact Kaishan engineers with your hole diameter, rock type and air package, and we will recommend a matched hammer, bit and compressor combination for your cost per metre target.
Frequently Asked Questions
What is DTH drilling technology?
DTH (down-the-hole) drilling uses a hammer mounted directly behind the bit at the bottom of the hole, so the piston strikes the bit without losing energy through a long drill string. Compressed air drives the piston and also flushes cuttings. It is widely used in mining, quarrying, water wells and construction because it holds hole diameter and straightness well in hard rock compared with top hammer drilling.
What working pressure do DTH hammers need?
It depends on hammer size. Smaller hammers commonly run at 7 to 17 bar, while larger production hammers often run at 24 to 35 bar. Higher pressure raises blow energy and flushing velocity, but the compressor must be able to deliver that pressure at the required air volume. Always match the compressor rating to the hammer's specified pressure and flow window.
Which button shape is best for hard rock?
For hard, abrasive rock, spherical buttons generally give the best wear life because the rounded profile resists chipping. Ballistic buttons penetrate faster in medium-hard rock but wear faster in abrasive conditions. Parabolic buttons sit between the two and suit mixed ground. The right choice depends on rock hardness, abrasiveness and how much bit life matters versus penetration rate.
How does telemetry improve DTH drilling?
Telemetry logs penetration rate, air pressure and temperature while drilling. Trends matter more than single readings: rising return temperature at steady pressure often signals a worn bit, while falling pressure at constant air volume points to an air supply problem. Catching either early lets crews change the bit or fix the supply before it costs a full shift.
Why does cost per metre matter more than penetration rate?
Penetration rate ignores bit wear, fuel, labour and non-drilling time. A faster bit that wears out quickly or a hammer that starves its flushing air can raise total cost even when instantaneous rate looks good. Cost per metre captures bit life, air consumption, rod handling time and hole quality, so it reflects the real economics of a DTH programme.