When you need to drill high quality holes with diameters between 100-254 mm, DTH (Down The Hole) drilling is by far the best and most effective method. DTH drilling can be performed in most types of rock, hard or soft. It's a commonly used method in the mining industry (blast hole drilling), waterwell drilling, construction, and in the oil and gas industry.

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In DTH drilling, the drill string rotates while the drilling hammer continuously strikes down into the rock. Inside the hammer, a piston powered by compressed air gives the drill bit its striking power. This combined with the rotational movement means the rock is crushed in a very efficient manner.

Because the power transfer takes place down in the hole when the piston strikes directly at the bit &#; hence the drilling method&#;s name &#; there is minimal energy losses along the drill string and holes can be drilled down to 6,000 meters in depth. DTH is a reliable method that drills stable holes with exceptional straightness.

The method is also excellent both environmentally and socially because it produces far less noise and vibration than many other drilling methods, making it a widely used drilling method in cities and other populated areas.

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The difference between 3 rock drilling methods &#; Rotary drilling, DTH drilling, and Top Hammer drill

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Original from Stella-Blog of BONMACH

Drilling and blasting is an important section during mining production. Let&#;s talk about the three methods of rock drilling &#; Rotary drilling, DTH (down the hole) drilling and Top hammer drilling. These three ways are suitable for different mining operations, and the wrong choice will cause huge loss.

First of all, we have to explain the working principles of them.

Rotary drilling

In rotary drilling, the rig provides enough shaft pressure and rotary torque. The bit drills and rotates on the rock at the same time, which exerts both static and dynamic impact pressure on the rock. The bits rotate and grind continuously in the bottom of the hole to make the rock to fracture. Compressed air under a certain pressure and flow rate are sprayed from the nozzle through the inner of the drill pipe, to make the slag continuously blown from the bottom of the hole along the annular space between the drill pipe and the whole wall to the outside.

Down the hole (DTH) drilling

Down-the-hole drilling is to drive the hammer which behind the drill bit by compressed air via the drill pipe. The piston strikes the bit directly, while the hammer external cylinder gives straight and stable guidance of the drill bit. This makes the impact of energy is not lost in joints and allowing for much deeper percussion drilling.

Furthermore, the impact force acts on the rock at the bottom of the hole, which is more efficient, and straighter than other methods of the drilling operation.

And DTH is more suitable for the big hole of hard rock drilling, special for rock hardness over 200Mpa. However, for the rock below 200 MPa, it will not only energy waste, but also in low drilling efficiency, and serious wear to the drill bit. It&#;s because while the piston of the hammer strike, the soft rock cannot absorb the impact completely, which seriously lower the efficiency of drilling and slagging.

Top Hammer Drilling

The percussive force of the top hammer drilling produced by the piston of the pump in the hydraulic drilling rig, it is transmitted to the drill bit via shank adaptor and drill pipe, This is the difference between DTH drilling. Meanwhile, the percussion system drives the drilling system rotation. When the stress wave reaches the drill bit, the energy is transmitted to the rock in the form of bit penetration. The combination of these functions enables drilling holes into the hard rock, and the air compressor only performs dust removal and slagging in top hammer drilling.

The combination of these functions enables drilling holes into the hard rock, and the air compressor only performs dust removal and slagging in top hammer drilling.

Impact energy multiplied by impact frequency together creates the percussive output of the drifter. However, usually, top hammer drilling used for hole diameter maximum 127mm, and hole depth less than 20M, which in high efficiency.

Conclusion

Characteristics of three rock drilling methods and comparison for adapted to hole size, depth, rock adaptation, slag flushing media, efficiency, and straightness.

Rotary Drilling

&#;Mainly suitable for large holes (coal, limestone) usually diameter larger than 200 mm.
&#;Drilling depths up to several thousand meters or even tens kilometers.
&#;Adapted to soft and medium hard rock.
&#;The slag flushing medium can be compressed air, air foam, mud, etc.
&#;Inefficient for hard rock drilling.
&#;Drilling straightness is lower than the down the hole (DTH) drilling type.

Down the hole (DTH) drilling

&#;The most suitable hole diameter is 100&#;254 mm, in special applications can be up to 2M And the minimum can be around 50 mm as well.
&#;Theoretically drilling depth is limited by back pressure only (can be up to several kilometers).
&#;Adapt to hard rock and rock formation conditions (compared to top hammer).
&#;Mainly use pressurized air for slag flushing, and sometimes air foam for special application.
&#;Highly efficient in hard rock drilling (compared to the rotary drilling).
&#;Drilling straightness is best in these three methods.

Top hammer

&#;The most suitable for hole diameter between 25&#;127 mm.
&#;Generally, the hole depth is less than 25 meters.
&#;Adapt to a stable and uniform hard rock.
&#;The slag flushing medium is compressed air or water.
&#;High efficiency in shallow holes drilling, the deeper the lower efficiency.
&#;Most easily to skew in these three drilling methods.

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