This method is suitable for drilling hard rock strata, and the borehole is not easy to deflect, so it is more advantageous when using in water-deficient areas. It can be used to drill hard rock and pebble strata, and its drilling efficiency can be increased by several times to more than ten times than conventional rotary drilling and mechanical percussion drilling. It has been popularized as an advanced technology. Its application field is expanding continuously. In the past, it was mainly used to drill blasting holes in mines. At present, it has been applied in hydropower, railway, highway, water wells, building foundation piles, geological exploration and so on.
By its own valve distribution system, compressed air enters the front and rear chambers of the piston (hammer) alternately, so that the piston does the continuous reciprocating motion. When the piston moves downward to the end point, the tail of the hammer is impacted, and the rock is broken by the carbide spherical teeth at the bottom of the hammer head. According to the structural characteristics of the gas distribution system, DTH hammer can be divided into two types: valve hammer and valve-less hammer.
(1) Valved DTH hammer. The air flow is controlled by the valve disc. According to the gas distribution method, it can be divided into side gas distribution and central gas distribution. Side gas distribution valve DTH hammer is the earliest used, and its waste gas is discharged from the side of the hammer head. The waste gas of the central gas distribution valve DTH hammer is discharged from the central hole of the hammer head. Comparatively, it has good effect to remove cuttings by central gas distribution, and hammer head has long service life and drilling efficiency is high.
(2) Valveless DTH hammer. Without valve plates, the valve distribution system consists of a group of holes arranged on the cylinder wall, which automatically distributes gas in the piston movement. In the total stroke of piston motion, one section works by expanding compressed air. Under the same pressure, the compressed air consumption is only 2/3 of that of valve DTH hammer.
DTH hammers are divided into low pressure DTH hammers (0.5-0.7 MPa), medium pressure DTH hammers (0.56-1.05 MPa) and high pressure DTH hammers (0.56-2.46 MPa) according to working pressure, which are suitable for different working conditions.
Key Points for Use of DTH Hammer
(1) Guarantee the working air pressure. When the wind pressure is lower than the prescribed value, the impact energy and impact frequency decrease obviously, which can not effectively break the rock, but also affect the timely discharge of cuttings out of the hole.
(2) Provide enough wind. The size of wind supply should be considered in terms of the air consumption of the DTH hammer itself and the air up-and-down speed required for chip removal.
(3) Choose the best speed. If the speed is too high, the distance between the chisel marks caused by two adjacent shocks is too large, and the rock between them is not easy to collapse; if the speed is too low, and the impact energy can not be fully and effectively utilized, the optimum speed should be chosen under the condition of certain rock properties and impact frequency.
(4) Add appropriate drilling pressure. It is advisable not to rebound when DTH hammer works.
(5) Maintain reliable lubrication to reduce wear of piston and cylinder.
(6) Keep the air passage clean and unblocked.
(7) When stopping drilling, the air supply should not be stopped immediately, so as not to cause the "pinch drilling" accident when the debris from the outside of the hole falls back to the bottom of the hole.
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