DTH drilling tools are widely used in construction sites such as open-pit and underground mines, quarries, hydropower projects, water well drilling, mineral exploration, rock mass cable anchorage, geothermal excavation, and side pile support for subway engineering excavation. Compared with top hammer rock drilling tools, DTH drilling tools have the characteristics of long and deep drilling holes, large hole diameter, relatively high deep hole drilling efficiency, and wide application range. DTH drilling tools mainly include down-the-hole drilling rigs, drill pipes, DTH hammers, and DTH drill bits, among which the DTH hammer is the core component to realizing impact rotation.
What is a DTH hammer?
The DTH hammer is an integral part of the DTH drilling rig. The DTH hammer is an integral part of the DTH drilling rig to connect the DTH drill bit and the drilling rig. It includes low wind pressure DTH hammer, medium wind pressure DTH hammer, and high wind pressure DTH hammer. It is widely used in metallurgy, coal, chemical industry, mining, water conservancy, hydropower, highway, railway, national defense, construction, and other engineering hole forming operations.
Classification of DTH hammers
According to wind pressure:
- Low wind pressure DTH hammer: working wind pressure is lower than 0.7Mpa.
- Medium wind pressure DTH hammer: working wind pressure between 0.7Mpa-1.4Mpa.
- High wind pressure DTH hammer: working wind pressure greater than 1.4Mpa.
DTH hammer performance characteristics
- The single impact energy is high, and the energy consumption for breaking rocks is low.
- The weight ratio of the piston and the drill bit is close, and effective for a long time. It is beneficial to improve the rock crushing efficiency and prolong the life of the drilling tools.
- The central exhaust has a good slag discharge effect and reduces the repeated crushing of rock.
- It has a simple and reliable internal structure that is easy to assemble and disassemble, with few failures and easy maintenance.
- The hammer has a check valve device to drill holes in the water.
- It is always at the front end of the hole when working, and the transmission of the impact energy is not affected by the drilling depth.
Advantages and disadvantages of DTH hammer
Advantage:
- The hammer is located at the front end of the hole, and the impact energy acts directly on the drill bit. With no requirement for the drill pipe to transmit impact energy and consequently no energy transmission loss, theoretically, the drilling speed remains unaffected by hole depth, making it suitable for deep-hole drilling.
- The supporting drill pipe is thick and rigid, and the hole is straight.
- High-pressure air not only acts as the power source for the DTH hammer but also serves to eject broken rock and clear debris.
- Simple structure, reliable operation, simple and convenient maintenance, and low purchasing cost.
- Good adaptability. Except for very soft strata, the DTH hammer drilling rig is in the best working condition in all rock structures, and the hole diameter and depth drilled exceed those of the top-drive drilling rig.
- The hole diameter is large, and the maximum drilling diameter can reach more than one meter.
Disadvantages:
- The air pressure is low, the output power is small, and the drilling speed is low. The maximum air pressure can reach 2.5Mpa, which is only 1/7 of the 18Mpa working pressure of the top drive drilling rig.
- The energy utilization efficiency is low, far below the level of hydraulic rock drills. The energy consumption per meter of drilling is three times that of hydraulic rock drills.
- The environment is polluted greatly. Gas discharge produces a large amount of dust, which pollutes the environment and harms the health of operators.
- Noisy. The operation of compressed air generates substantial noise, as does the accompanying high-power air compressor.
- The service life of the drill bit is relatively short.
- Operating in high-altitude environments significantly reduces the efficiency of the air compressor and leads to a considerable increase in energy consumption.
- Due to structural limitations, it cannot be used for drilling small holes below φ50mm.
Components of DTH hammer
DTH hammer is mainly composed of the rear joint, iron gasket, plug, spring, valve cover, valve plate, valve seat, piston, guide sleeve, front joint, transition joint, rubber ring, and check valve.
Highlight one key component, which is the piston. The piston is the main moving part of the DTH hammer, even the only moving part. According to the structure, the DTH hammer piston includes three types: the same diameter piston, the different diameter piston, and the series piston. Judging from the role of the piston in the gas distribution device and the load it bears during work, the piston should have high dimensional accuracy and surface finish so that it has good air tightness and is suitable for reciprocating motion at high speeds. A reasonable geometry not only ensures that it has sufficient strength but also can effectively transmit impact energy.
How does the DTH hammer work?
At the beginning of the impact stroke, the piston and the valve piece are in the pole position, and the pressure air enters the upper chamber of the cylinder through the radial hole of the valve cover and seat and pushes the piston down at high speed to impact the drill bit. When the piston travels until the spline groove of the bushing is closed, the pressure in the lower chamber begins to rise, and the central hole at the upper end of the piston leaves the gas distribution rod, connecting the upper cavity with the air, then the pressure decreases, and the working stroke ends. When the piston impacts the tail of the drill bit, the valve plate changes direction due to the pressure difference between the upper and lower sides, and the piston repeats the return stroke movement.
Application scenarios of DTH hammer
DTH hammers are widely used in rock mining, tunnel engineering, underground engineering, and other fields.
In mining, DTH hammers are used for ore crushing, which facilitates subsequent collection and transportation.
In tunneling projects, DTH hammers cut rock efficiently, reducing construction time and costs.
In underground engineering, DTH hammers are helpful for the controlled blasting of rock formations to ensure construction safety and efficiency.
The importance of DTH hammers
DTH hammers have many advantages over traditional blasting techniques. First, liquid propellants replace explosives, making the blasting process safer and more environmentally friendly. Secondly, the energy conduction of the DTH hammer is more efficient, which can achieve precise rock fracture and reduce unnecessary energy loss. In addition, since the liquid accelerator can fill the drilling space, the blasting effect of the DTH hammer is more uniform, reducing the impact of blasting vibration on surrounding structures.
Future Prospects for DTH Hammers
With the continuous advancement of science and technology and the continuous pursuit of engineering safety and efficiency, the future development prospects of DTH hammers are broad. First, improve the performance of liquid accelerators to improve the conduction efficiency of blasting energy. Secondly, it is combined with sensing technology to realize real-time monitoring and control of the blasting process of the DTH hammer and improve construction safety. In addition, the scope of application of the DTH hammer can also be expanded, such as exploring its application in geotechnical engineering, underground gas storage, and other fields.
Because of its high efficiency, energy-saving, and environmentally friendly characteristics, the DTH hammer has a wide range of application prospects. Its birth made the large-diameter rock drilling industry into the era of mechanization, rock drilling efficiency significantly improved, and heralded the epoch-making development of rock drilling tools. In the future, with the continuous development of science and technology, the application range and performance of DTH hammers will continue to expand, bringing more innovation and growth to the engineering field.
