How to Select a Suitable Down the Hole (DTH) Drilling Equipment?
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Down the hole (DTH) drilling rig is the equipment that the impactor dives into the hole and directly impacts the drill bit, while the rotary machine drives the drilling hole to rotate and drill to the ore rock. In addition to drilling main blast holes in open-pit mines, down-the-hole (DTH) drilling rigs are also used to drill pre-split holes, anchor holes, slope treatment holes and groundwater drain holes, as well as vent holes, filling holes, pipe cable hole, etc. Down the hole (DTH) drilling rig is mainly composed of impactor, drill bit, lifting mechanism, pressure device, walking mechanism, slag discharging system, drilling rig and drill pipe. When choosing a down-the-hole (DTH) drilling rig，you need to consider various factors. This article will guide you on how to choose the right down-the-hole (DTH) drill from three important parts: drill bit, drill pipe, and impactor.
Down the Hole (DTH) Drilling Equipment Structure
01 Down the Hole (DTH) Drill BitBack
In order to achieve higher drilling speed and lower perforation cost, it is necessary to select a suitable down-the-hole drill bit to drill in a specific rock.
(1) When drilling in hard rock, due to its large rock drilling power, each column tooth and bit body bears a larger load, so the bit body and column tooth are required to have greater strength. When choosing the drill bit, the number of chipway should not be too many, generally choose the double-airfoil drill bit. The size of chipway should not be too large, so as not to reduce the strength of bit body. At the same time, the alloy tooth of the drill bit is recommended to choose the ball tooth, and the height of the ball tooth exposure should not be too large.
(2) When drilling in the soft rock with good drillability, the drilling speed is fast and the relative slag discharge quantity is large, which requires the drill bit to have a strong slag discharge capacity. It is recommended to choose the tri-airfoil or quad-airfoil drill bit. Slagging chute can be appropriately larger and deeper. Alloy teeth can choose spring teeth or chipped teeth, and tooth height can be relatively higher.
(3) When drilling in crushed zones with relatively developed joints, in order to reduce the deflection, it is recommended to use the middle concave or middle protruding drill bit with better steering.
(4) When drilling in the rock with better toughness, it is recommended to use the wedge-shaped tooth bit.
02 Down the Hole (DTH) Drill PipeBack
The shape of the drill pipe will affect the drilling efficiency. According to the hydrodynamic theory, only when the air velocity in the annular channel formed by the drill pipe and the hole wall is greater than the suspension velocity of the slag, the slag can be smoothly discharged out of the hole. The airflow velocity in the channel is mainly determined by the channel cross-sectional area, the channel length and the impactor discharge volume.
The smaller the channel cross-sectional area, the higher the flow velocity.
The longer the channel length, the lower the flow velocity.
It can be seen that the larger the drill pipe diameter, the higher the air velocity, and the better the slag discharge effect. Generally the diameter of the channel is between 10-25mm. Lower limit for deep holes and upper limit for high pressure.
The choice of drill pipe should not only consider the slag discharge effect, but also its bending resistance, torsion strength and weight, which are mainly determined by the wall thickness of the drill pipe. Under the premise of ensuring strength and rigidity, the selected drill pipe wall should be as thin as possible to reduce its weight, and the wall thickness is generally 4-7mm.
03 Down the Hole (DTH) Drill ImpactorBack
Geometric parameters of drilling hole, working pressure and rock consolidating coefficient are the original parameters for the design of drill impactor. Thus the appropriate size of the drill impactor can be determined and the ideal impact energy and impact frequency can be obtained. The drill impactor can only play a better rock drilling effect in the specific working pressure, specific process parameters and specific lithology.
(1) Working Pressure
The higher the working pressure of the down-the-hole drilling impactor, the faster the rock drilling speed. Since the drill impactor is designed according to a specific pressure, it performs best only within a given design pressure range. If the impactor is not used within the designed pressure range, not only will it not be able to exert its due efficiency, but it will cause the impactor to fail to work or prematurely damage. Therefore, the corresponding drill impactor must be selected according to the pressure grade.
(2) Impact Energy
The impact energy of the down-the-hole drilling impactor must ensure the specific energy of the drill bit, so as to effectively break the rock, and at the same time obtain a more economical specific energy and a higher drilling speed. If the impact energy is too large, it will not only cause energy waste, but also shorten the life of the drill bit. If the impact energy is too small, the rock cannot be broken effectively and the drilling speed will be reduced. Different rocks require different specific energies for chipping, so drill impactors with different impact energy need to be selected.
(3) Impact Frequency
Generally, when the impact energy is constant, the higher the impact frequency, the greater the impact power. However, the outer diameter of the impactor is constrained by the diameter of the borehole. The higher the impact frequency, the smaller its impact energy. Therefore, the increase of impact frequency is limited by the specific work of rock chipping.
04To Wrap UpBack
The above describes how to choose the right down-the-hole drill equipment from the perspective of the drill bit, drill pipe and impactor. In addition, the specific conditions of the mine, mining technology, blasting parameters, equipment prices and other factors must be considered comprehensively. Or you can directly consult a professional mining equipment manufacturer to choose a down-the-hole drilling rig that is really suitable for your mine.
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