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Bonmach Q.D
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4 min read
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Feb 28,
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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.
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 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.
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.
Characteristics of three rock drilling methods and comparison for adapted to hole size, depth, rock adaptation, slag flushing media, efficiency, and straightness.
'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.
'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.
'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.
Are you interested in learning more about DTH drill pipes? Contact us today to secure an expert consultation!
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Pneumatic tools have been used to drill through rock since the 19th century. Back then, drillers would suspend themselves from a rope over a quarry face to put a drill from the right position and use small diameter holes. The process was inefficient and dangerous. It could send rocks flying and the accuracy was subject as much to luck as it was skill. After a while, drilling crews started carrying jackhammers on masts, beautiful boreholes were misaligned, the explosives that followed could be even more dangerous.
Thankfully, we live in the modern era, where down the hole (DTH) drilling has become one of the most efficient and safest methods since its invention in the mid s. Let's explore what DTH drilling is, why it's such a successful technique, and how it might be the perfect process for your drilling operation.
What is DTH Drilling and how does it work?
DTH drilling is a drilling method that's used to crush rock by using a drilling hammer to hit hard rock repeatedly. DTH drills are pneumatic tools that provide power by driving compressed air into a piston inside the hammer. This type of drilling has made it much easier to drill wells quickly and efficiently by allowing contractors to switch from dirt boring to rock boring simply by adding a compressor and hammer to a drill bit.
Before DTH became a widespread drilling technique, contractors would desert a dirt bore project after encountering hard rock, leaving it to a different set of drillers to continue. With DTH drilling, the same drilling team can work through multiple materials.
At its most basic level, DTH drilling involves attaching a drilling hammer to the bottom of a drill string. Small, percussive hammers are placed above the drill bit, allowing drill pipes to exert a feed force necessary to rotate the hammer and bit together with fluid (usually air, water, or mud). This actuates the hammer and flushes the cutting. Drill pipes are then added to the drill string as the hole gets deeper.
Because the air-powered piston strikes the bit directly, energy is transferred down the hole, minimizing any lost energy. This allows drilling to greater depths.
DTH Drilling is most often used in the mining industry, where blast hole drilling is necessary for projects like water well drilling, building construction, and oil and gas processes.
Types of DTH Drilling Hammers
DTH hammers are fully fluid actuated. There are two primary parts: a valve which controls the flow and a piston that strikes the impact surface. The hammer body allows for stable, straight guidance of the bit. There are three types of hammers that depend on the actuation fluid:
' These are typically limited to shallow holes of less than 200 meters.
' These require a lost water flow of between 55 and 744 L/min depending on hammer size to actuate the hammer. These allow for better borehole control and greater depth than air hammers.
' These are the newest types of drilling hammers, but they've shown a lot of promise so far. They're able to drill on every existing drilling rig by using classical mud composition. They are fantastic choices for drilling into hard rock in geothermal projects due to their ability to drill extremely deep.
What are the benefits of DTH drilling?
DTH drilling is extremely effective, which is why we've been using it for the past seven decades. Some of the major benefits include:
The use of air is extremely efficient. You don't have to buy, source, treat, or transport it for use.
DTH systems are simple to adapt to most directional drills, and it doesn't take long.
Very little rotational torque is required to cut rock that will allow the hammer to drill straight.
The same drill can be used to drill through both dirt and rock.
There isn't as much wear and tear on a drill bit since the hammer is doing most of the work.
There is a smaller carbon footprint than other techniques due to the use of less drilling mud and additives that need to be disposed of.
It can be used more often in cities because it produces less noise and vibrations than alternatives.
Fewer amounts of additives and drilling fluids are required than for alternatives.
The rate of penetrations is up to five times greater than rotary drilling techniques.
OK Bit has the DTH Drill Bits you need
If you've decided DTH is the right drilling method for your project, OK Bit can supply you with whatever bits you need to get the job done. If you aren't sure if DTH drilling is the best choice or if you need help choosing a specific hammer or bit, our expert staff will be happy to help. Contact us today.