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DTH drill tool operated with drilling mud (Drillstar MUDHammer)A down-the-hole drill, usually called DTH by most professionals, is basically a jackhammer screwed on the bottom of a drill string. The fast hammer action breaks hard rock into small cuttings and dust that are evacuated by a fluid (air, water or drilling mud). The DTH hammer is one of the fastest ways to drill hard rock. The system is thought to have been invented independently by Stenuick Frères in Belgium and Ingersoll Rand in the USA in the mid-1950s.
Origin of the name
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DTH is short for “down-the-hole”. Since the DTH method was originally developed to drill large-diameter holes downwards in surface-drilling applications, its name originated from the fact that the percussion mechanism followed the bit down into the hole. Applications were later found for the DTH method underground, where the direction of drilling is generally upwards instead of downwards.
Technical details
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In DTH drilling, the percussion mechanism – commonly called the hammer – is located directly above the drill bit. The drill pipes transmit the necessary feed force and rotation to the hammer and the bit, along with the fluid (air, water or drilling mud) used to actuate the hammer and flush the cuttings. The drill pipes are added to the drill string successively behind the hammer as the hole gets deeper.
The hammer is fully fluid actuated. It is composed of two mobile parts: a valve, controlling the flow and a piston that strikes on an impact surface directly linked to the bit. The hammer body gives straight and stable guidance of the drill bit.
There are three types of hammers, depending on the actuation fluid:
History
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A pneumatic tool is first thought to have been used for rock drilling in 1844. Many quarries used hand held tools that required the driller to suspend himself from a rope over the quarry face in order to place the drill hole in the required position. This system used small diameter holes and was not only terribly inefficient, but very dangerous due to flying rock as a result of the inaccuracy of the drilled borehole.
Some quarries used primitive top hammer machines that carried the jackhammer on a mast - the slenderness of the drill rods working with a relatively large diameter drill bit caused bore holes to deviate which sometimes meant that a bore hole might finish dangerously close to its neighbour or indeed be closer to the face of the quarry than had been intended. In any event boreholes that are not aligned correctly which are then loaded with high explosive can be extremely dangerous, resulting in rock being projected beyond the intended site.
Larger quarries used big rotary machines that required huge amounts of down thrust and high rotation speeds to drive the tri-cone bit hard enough to crush the rock. This system could not be successfully used for holes below 6 inches (150mm) and the machines were very expensive to buy and to run. Another system in use was the very primitive cable tool machine (or bash and splash as it was known by the drillers) which caused a heavy bar and chisel to be lifted and dropped on the rock to crush it whilst water was introduced to create a slurry, which in the process, enabled the hole to be drilled. This system could not guarantee a finished hole size and only pure vertical holes could be drilled as the system basically relied on gravity. Debris from the hole was baled out using a baling tube with a clack valve, which was periodically dropped on a winch to capture the slurry, which was then brought to the top of the hole to be discharged.
It was only when the DTH system came along that many of the problems associated with the other systems were overcome - with the DTH system the energy source is constantly behind the drill bit, the drill tubes (or drill string) are rigid being only slightly less in diameter than the drill bit, copious amounts of air can be passed through the drill string to operate the DTH Hammer which is then used to efficiently flush the bore hole clean. DTH did not require heavy down thrusts or high rotational speeds and as such a light, cheap machine could be employed to carry out the drilling process - the machine could also be worked by one man, whereas some other systems required two operatives. The benefits that DTH brought to the industry were enormous - for the first time a drill hole could be placed where it was required because DTH gave a truly aligned, straight, accurately placed, clean bore hole that could be easily charged with explosive to provide good control over the blasting process that was safer and which provided good fragmentation of the rock. Holes could be drilled to increasing depths without the loss of performance since the energy source was always directly behind the drill bit. The system was able to drill in almost all rock conditions that other systems were unable to do. Quarry faces became safer, well profiled and quarry floors were level and easier for loading equipment to operate and move across. Much higher penetration rates could be achieved by using DTH hammers which decreased the drilling Cost per Meter in smaller hole diameters.
The DTH system completely revolutionised the blast hole industry with many quarries embracing it with open arms. Eventually the larger DTH systems then found their way into other applications, such as water well drilling and construction work.
It still offers the same benefits to the operator that it initially brought to the quarry industry but it is now being used in many different applications such as gold exploration, ground consolidation, geo-thermal drilling, shallow oil and gas well, directional and piling. The advent of tungsten carbide for the drill bits (the first bits were all-steel) and the development of the button drill bit coupled with the introduction of high air pressures (25 bar plus) has meant that the DTH system can compete easily and efficiently with other drilling systems.[5]
DTH tools were used to locate the trapped miners in Chile and enabled food, water, and medicine to be passed to them and communication systems to be set up that eventually led to their safe rescue.
Uses
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DTH products can be used in the following applications:
See also
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References
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Drills have different mining functions, from providing geologists with different samples of soil for analysis to facilitating the extraction of precious minerals that would otherwise be difficult to reach.
How many methods of drilling are there?
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As the mining industry advances and more excavating opportunities present themselves, the number of drilling methods increases. Whether it is for exploration, production, land-clearing or geotechnical purposes, there are drilling methods that serve every mining purpose.
Auger Drilling
Auger drilling is the simplest form of drilling. It involves the manual rotation of a helical screw into the ground, usually by two people although auger drills can also be mounted to small vehicles. Once the auger drill is deep enough, the earth is lifted up by the blade of the screw. This kind of drill specializes as an initial geochemical reconnaissance technique, which means it is used in softer soil to find the optimal place to mount a larger drill.
Rotary Air Blasting
Rotary air blasting is the most common shallow drilling method, in which a piston-driven hammer-like object drives the drill bit into the rock, fragmenting the hard surface into chips that are then lifted to the surface via compressed air. This method is ideal for drilling multiple holes in a short period of time, and less ideal for producing geological samples because the airblasting process can compromise the quality of the rock.
Aircore
Aircore drilling involves a three-bladed drill bit with a hollow drill rod in order to penetrate loose soil and rock fragments. After the drilling is complete, compressed air is blasted through the drill rod in order to bring the cuttings to the surface. While this method is typically slower than rotary air blasting, it is more precise, meaning that the samples collected are less prone to contamination.
Reverse Circulation Drilling
Reverse circulation is a popular method for mining exploration that shares similarities with both rotary air blasting and aircore drilling. The same piston-driven hammer is used to drive the drill bit into the rock, however, the larger rigs and machinery associated with reverse circulation drilling allow for the drill bit to be driven even further into the earth. Compressed air is then used to drive the fragmented earth to the surface. This method is ideal for geological exploration, as it produces contaminant-free samples and requires less handling, resulting in cost reduction and faster turnaround times.
Diamond Core Drilling
Diamond core drilling is the most expensive drilling method, as it involves using a drill bit that has been fortified with industrial diamonds attached to hollow drill rods to extract a continuous cylinder of rock from several kilometers below the earth. However, this method also produces the most accurate rock samples as the entire core of a mineral can be brought to the surface as opposed to mere fragments, making it ideal for procuring records on their strength, composition, porosity, etc.
Blast Hole Drilling
Blast hole drilling is a method of drilling used to clear out large amounts of the earth and make the minerals below easier to access. It involves the drilling of holes into the earth. Explosive charges are then placed into each hole and detonated. After the explosion, the broken material is cleared and, if the drilling and blasting occurred underground, the tunnels created by the explosion are fortified to allow for safe human entry. Alternatively to explosives, gas pressure blasting pyrotechnics can also be used to displace the rock for excavation.
What types of drills are there?
As mining operations have become more sophisticated with the passage of time, new kinds of drill rigs have emerged to meet the demand of mining companies. Nowadays, various mining drills utilise different features to complete different kinds of mining tasks while being both manually operated and remotely automated. These rigs are available in various shapes and sizes, functioning in confined spaces as well as large quarries. As a result, there is a wide array of surface mining drill rigs available for many different kinds of operations.
Surface Top Hammer Drill Rigs
Top hammer drill rigs are equipped with powerful hydraulic drills as well as a hammer. The hammer strikes the drill rod, creating a percussive force that travels to the drill bit and displaces the rocks, leaving them susceptible to pressurized air or water. This kind of rig is renowned for its reliability in the toughest conditions, as well as its fuel economy and low operating costs. When partnered with the drill and blast method, this drill rig makes the excavation process efficient.
Surface Down-The-Hole Drill Rigs
The purpose of a down-the-hole drill rig is to drill large-diameter holes downwards, consisting of a jackhammer screwed to the bottom of a drill string. Like other drill rigs, the DTH breaks up the rock so it can be flushed out using air or water. This particular rig specializes in high-capacity rock drilling in quarries, opencast mines, and rock excavation projects.
Dimensional Stone Drill Rigs
The dimensional stone drill rig has a more esoteric function that its other drill rig counterparts, in that its purpose is to drill precise holes in the ground in order to excavate for natural rock such as granite, limestone, marble, or sandstone so that it can be extracted and fashioned into blocks for construction. This rig is designed to drill precise holes safely and efficiently.
Rotary Blasthole Drill Rigs
Rotary blasthole drill rigs drill into the earth in order to create holes that can then be filled with explosives that clear large sections of rock for subsequent mining operations. Rotary blasthole drill rigs are renowned for their precision and depth, boosting productivity by making the process of blast hole drilling easier and more cost-effective. In addition to the range of surface mining drill rigs, there is also a wide variety of underground drill rigs available that meet the stricter safety and logistical requirements that underground mining entails.
Development Drill Rigs
Development drill rigs are mining vehicles that drill holes into the surface of a coalbed that explosives can be inserted into and detonated. These vehicles are modular, meaning they can be disassembled, transported, and reassembled with ease. They can also be used for small-scale mine development and large-scale tunneling.
Tunneling Jumbos
Tunneling jumbos are versatile modular electro-hydraulic excavation machines that can be used for both fast face drilling and mechanized longhole drilling and bolting. Jumbos operate as stationary work stations that an operator safely conducts mining operations from, consisting of one, two or three drock drill carriages, ensuring high productivity and reliability. They are used specifically for underground drilling and blasting jobs, however, they can also be used in tunneling if the hardness of the surrounding rocks prevents the use of tunneling machines.
Top Hammer Longhole Drill Rigs
Top hammer longhole drill rigs are ideal for mining operations where the highest priority is ore recovery and minimizing the contamination of rock fragments. Like its surface mining counterpart, this drill contains a piston-powered hammer that impacts the drill in order to shatter the rock before using compressed air to disperse the debris.
Rock Support Drill Rigs
Rock support drill rigs are engineered to install rock bolts that stabilize the rock face by transferring the load from an unstable mine exterior to the confined (and therefore stronger) interior of the rock mass. These rigs ensure the safety of underground drilling and blasting by securing the rock mass and stopping it from caving in.
In-The-Hole Longhole Drill Rigs
In-The-Hole longhole drill rigs are mounted on tracked or articulated carriers in order to be transported into a mine where it uses extension rods to drill holes and extract ore with the aid of an ITH hammer similar to that of the top hammer drill rig. Additionally, the ITH longhole drill rig also flushes out debris with pressurized water. These rigs are designed with mobility and accuracy in mind.
Low Profile Drill Rigs
Low profile drill rigs are mining drills that are built at a low elevation so they can enter more confined spaces that regular drills cannot due to their size. They are ideal for development, rock support, and production drilling in tabular ore bodies such as platinum and chrome mines. These drills come in single and double boom variants, meaning that their specialization for spaces with low heights does not sacrifice their ability to reach higher spaces if the need be.
Narrow Vein Drill Rigs
Narrow vein drill rigs are similar to low profile drill rigs, in that they are designed to venture into and extract ore from confined spaces. However narrow vein drill rigs are designed less to accommodate height challenges and more for the general navigation of geologically complex mine spaces with widths less than 3-6m. Narrow vein deposits contain large amounts of gold, tin, copper, lead, and zinc that narrow vein drill rigs allow us to access and utilize.
Secondary Breaking Drill Rigs
Secondary breaking drill rigs are compact support drills that increase drawpoint availability in narrow vein mines and back caving operations by breaking oversized boulders that are causing blockages. These drills eliminate the need for explosives, which in turn eliminates the need for time-consuming ventilation and evacuation measures while promoting a safer mining environment. These small drill rigs are available in the form of jumbos, longhole rigs, and drill-charge and drill-split breaking units.
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