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Difference between DTH Drilling and Top Hammer Drilling
Aug 23, 2018

Difference between DTH Drilling and Top Hammer Drilling


DTH and top hammer work the same way, but the impact force is not the same.

DTH impact force acts on the hammerhead---bit;

The top hammer impact force acts on the tail of the shank;

As for the straightness and efficiency, it is only to look at the technical parameters of its work, to avoid overkill.


Top hammer hydraulic drill


The top hammer drill has a hole diameter of 127 mm or less, and the hole depth is usually not more than 20 m. When the hole depth is about 15 m, the top hammer type drilling efficiency is relatively high;

The borehole drilling rig has a hole diameter of 105 mm or more. Compared with the top hammer drill, the hole diameter is larger, the hole depth is 10m-45m, and the efficiency of using the down-the-hole hammer is high;

Generally speaking, the hole drilled by the downhole drilling rig will be straighter. Of course, if the rig is equipped with a computer instrument display, the rig operator does not need experience, and the hole verticality can be more accurately controlled by computer control. It is possible to make the punched holes very vertical. In this way, the blasted platform will be very flat, eliminating the need to use the excavator to level the flat for the platform.


Large-scale integrated hydraulic drilling rigs are usually used in large mines. Generally used in earth and stone works, the drilling machine and the air compressor are separated by a 115 mm aperture. The advantage of the split type is that the price is relatively cheap. Second, many earthwork projects do not completely cause the guns to go uphill. If there is no machine to repair the road, the large-scale integrated drilling rig can't get through. The split rig is relatively small and convenient.

In general, top hammer rigs use medium and low wind pressure compressors; they use rock drills on top of the rig. More suitable for rock operations with hardness below 200 MPa.

The down-the-hole drill is a high-pressure air compressor with a down-the-hole drill bit at the bit. Hard rock above 200 MPa is more suitable.

Both are suitable for different mine operations. However, if you choose the wrong one will bring you losses. If you choose to use a down-the-hole drilling rig in a mine below 200 MPa, it will not only waste fuel, but also have low operating efficiency, which will cause serious wear to the drill bit. Because, when the piston of the underground submersible moves, because the rock texture is too soft, the down-the-hole drill bit "jumps" during the operation. In this way, the efficiency of slagging and the efficiency of drilling are seriously affected. It also wastes the gas generated by the air compressor, causing the loss of energy.

Therefore, the correct choice of "tools used" is the key to improving production efficiency. Both rigs have their own advantages. Just look at how you choose. See what kind of working conditions you use. In order to achieve greater economic efficiency and minimum operating costs.



The impact mechanism of the top hammer drill is at the lowermost part of the hole, and the impact work is applied to the top of the drill pipe, so it is called the top hammer type.

    The impact mechanism of the down-the-hole drilling rig is at the lowermost part of the hole, and the impact work is directly applied to the tail of the drill bit, so it is called a down-hole type.

    Under normal circumstances, the top hammer is high in efficiency, the straight hole is straight, and the platform after the explosion is flat.

    The following three figures show the difference between the three different drilling methods: left to right are the downhole type, top hammer type and double pole type, and the red arrow indicates the impact.

Three Type.jpg

     The history of the top hammer type is the earliest. In general, it has the widest application range. Compared with the down-hole type, it can drill a small hole and can use a hydraulic impactor to achieve high efficiency and drilling speed. There are two reasons for the high efficiency of the hydraulic impactor. The first is that the hydraulic transmission efficiency is much larger than the pneumatic transmission, and the second is that the piston of the impactor is made into a slender shape due to the high system pressure (250 Pa). Long and burr-free shock waves increase the efficiency of the impact. Due to the limitation of the thread at the joint of the drill pipe, the top hammer type is difficult to drill a large hole for the simple reason that there is no large drill pipe. In addition, since the shock wave is lost through the threaded joint, the top hammer type does not drill well. In the application of small holes and down-holes, such as tunneling, anchoring, decorative stone, construction, etc., the top hammer type has an absolute market share. Since the drill pipe is subjected to the propulsive force and the rotational torque, it is also subjected to the shock wave, so it is also easier to deflect. In general, the design and manufacture of the top hammer drill is much more difficult than the downhole. Impactors and drilling tools are all difficult problems. We can see the submerged hole drills of domestic private enterprises, and it is rare to see the top hammer rigs of domestic enterprises.

DTH -2.jpg

    In addition, when the top hammer rig is used in the open pit mine, there is also a control system to automatically adjust the impact work, propulsion and propulsion speed according to the geological conditions of the drilled hole to avoid the deflection of the hole.

    Large diameter drill rods can greatly reduce the deflection of the drill hole, but this is very technical.

Due to the high efficiency of the top hammer drill, the general power is small, the engine is small, the fuel consumption is low, the outer shape is small, the ground shape adaptability is strong, and it is easy to transport. This is also related to the mining process of the mine owner. Some mine owners like large holes and can blast a large quantity at a time, but some mine owners, especially in some developed countries, do not need too much volume, like The small holes are closely packed and finely operated to greatly reduce the amount of crushing work in the back. There are also some coal mines that have chosen the top hammer type because the coal seam has burned and cannot use the downhole drilling rig.

     The top hammer type now has a tendency to develop toward larger holes, higher power and faster piercing speeds, and its development bottleneck is the drill pipe. I hope it is a large drill pipe that comes out earlier, more than 100mm.

    The history of the downhole type is much shorter. Since the down-the-hole hammer is at the bottom of the hole, the aperture cannot be too small. However, since the drill pipe only bears the propulsive force and the rotational torque and does not bear the shock wave, the true diameter of the drill pipe is generally large, and the impact directly acts on the drill bit, and there is no energy loss at the thread, so the hole is straight, and it can be very Deep holes, such as water well drills, can hit hundreds of meters.

DTH hammers are mostly pneumatic, there is no hydraulic pressure, so the pressure is low (maximum 30 bar), the piston diameter is large, the length is short, and the area changes greatly, so the efficiency is much lower than the top hammer. Some people are experimenting with a high-pressure water-driven down-the-hole hammer that can achieve a high efficiency similar to that of a top hammer, but is limited to a few deep underground mines.

Drilling rods such as drill pipes and drill tails have a longer life than the top hammer. But it consumes a lot more fuel because of the compressibility, viscosity, leakage of air and the inefficiency of the air compressor.

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