Rotary-percussion Drill
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A rotary-percussion drill is a type of rock drill that uses both rotary and percussive action in order to chip away rock and produce a hole. Useful in mining and construction applications, it can be used for constructing tunnels and wells, and for excavation and road construction. The rotary-percussion drill has been around for centuries. Modern-day rotary-percussion drills are also popular for the construction of oil wells.
The combination of rotation and percussion helps the drill achieve a cutting and grinding (rotary) action at the same time as a chipping (percussive) action. Usually these motions are hydraulically or pneumatically driven. Types of rotary-percussion drills include the blasthole drill and the down-the-hole (DTH) hammer drill.
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[edit] History
[edit] Early Bamboo Drills
Rotary-percussion drilling is derived from the oldest, as well as cheapest, methods of drilling: rotary drilling and cable drilling (also known as percussion). Dating back to China more than 4,000 years ago, the first primitive drill consisted of a bamboo stick. The device was made rotational with the use of manila rope that wound around the stick and was attached to an animal that would circle the drilling location. [1]
[edit] First Rock Drills
The modern-day use of drills grew with the appearance of oil well construction, some of the first of which were constructed in France in 1745. In exactly 100 years, a Briton named Robert Beart would patent the rotary drilling machine.
One of the first patented rock drills was invented in 1849 by J.J. Couch. C.H. Shaw, a Denver machinist, invented a drill in 1890. His rock drill operated with a hammering motion and was used for overhead drilling. Another rock drill was patented by Simon Ingersoll in 1871. Ingersoll’s invention would lead to the eventual formation of the Ingersoll Rand Co., still in existence today. Ingersoll-Sergeant drills, in fact, were crucial to the construction of the Panama Canal in 1904.
[edit] First Hammer Drills
George Leyner invented the hammer drill in 1896. This drill pushed manufacturers and pioneers further with their inventions and within the next 10 years, the imperial pneumatic tool was developed, as was the jackhammer drill. Ingersoll Rand similarly developed the Quarrymaster, the first modern air rock drill. The down-the-hole hammer drill was invented in the 1950s, around the same time that drill rigs became hydraulic.[2]
Tunnels such as the Mont Blanc Tunnel between France and Italy in the 1960s and the Mont Cenis Tunnel highlighted the effectiveness of drills and drill rigs in construction projects.
[edit] Features
Rotary-percussion drills use one of three types of drill bits:
- Drag bits, usually used for soft rock, can have two, three, or four wings and are sometimes tipped with tungsten carbide.
- Roller bits have wedge-shaped teeth and are used for harder rock.
- Diamond bits are used for grinding hard rock and producing an annular hole.
Rotary-percussion drills commonly use a tricone bit, but can also use a plug, fishtail, or drag bits, depending on the operation.
In addition to the drill bit, the drill also typically comprises a drill stem which houses the drill bit, as well as a drill rod that is responsible for pumping out the fluid or compressed air to produce a rotary-percussive motion and to clean cuttings. Drills can be mounted on a mast, a truck, or a rig. Depending on the type of drill, it may have other components. For more information, see rotary drill or cable drill.
[edit] Drilling Environment
Rotary-percussion drilling is best suited for rock formations that are medium to hard all the way through. It is usually used in applications that involve blasting holes, rock anchors, and grouting holes and wells. The machine's relatively light weight makes this type of drill rig very effective. [3]
Although it is unable to drill through formations that have been reinforced with steel, it can drill through concrete, masonry, and rock with a measured thickness of 0.4 to four inches (10 to 100 mm) and depths up to 16 feet (5 m). [4]
[edit] Advantages and Disadvantages
The rotary-percussion drill is capable of drilling through the hardest consolidated formations, including gravel, quite quickly. One of the biggest disadvantages, however, is that the operator must be experienced with using and maintaining this type of drill. [5]
Rotary-percussion drilling is only effective for medium-to-hard formations. It cannot, for example, drill through materials reinforced by steel.
[edit] How it Works
The rotary-percussion drill combines both the rotary (grinding) and percussive (chipping and hammering) action. A hole is formed when energy is transmitted pneumatically through the drill rod to the drill bit, prompting it to thrust into the formation using a repeated hammering motion. The impact of the percussion component is enough to break and dislodge rock, which subsequently removes debris and cuttings with compressed air or water flow. [6]
The rotational component of the drill occurs as the drill is producing percussion strikes against the formation. Rotary-percussion drilling is usually used for depths that do not exceed 492 feet (150 m). [7]
The rotary-percussion drill usually requires compressed air to drive the drill bit into the rock. The compressed air has a dual function—it also flushes out the cuttings produced from drilling. [8]
When the power is transmitted, the drill bit rotates at 10-30 revolutions per minute on a down-the-hole hammer drill for a straight, circular hole.
[edit] Types
Down-the-hole hammer drills (DTH) use a rotary percussive movement. Similar to that of a single jack drill, they use hydraulics or pneumatics to transmit force to the rotating drill bit. The force travels through a drill comprised of hollow steel before it is directed to the bit.
Water makes its way through the steel drill column to the drill bit, a feature that helps cool the bit, clean the surface and remove the cuttings. When enough volume or pressure is exerted, the cuttings are pushed to the outside of the column and away from the hole.
This method works best on rock walls that are solid and dry. Problems are caused with the vibration of the drill string or the abrasion from cuttings in that they may contaminate samples. Moisture, however, helps remedy this problem and stabilize the walls.
The DTH drill is the most common rotary-percussion machine. The DHT drill can come in sizes as small as 7/8 inch (2.2 cm) in diameter.
Blasthole drills are another type of rotary-percussion drill. Because they are able to handle environments of compressed air, blasthole drills are suitable for operations in underground mines. Also used for sampling, blasthole drills are most effective when it comes to drilling shorter holes. In the event that long holes are required, it could cause a raveling of the hole, usually made worse by downward directional drilling.[9]
[edit] Common Manufacturers
- Atlas Copco
- Creighton Rock Drill
- Furkura Rock Drill
- Ingersoll Rand
- Terex
[edit] References
- ↑ Drilling History. NTL World. 2008-10-17.
- ↑ Drilling Machinery. Britannica. 2008-10-17.
- ↑ Harris, Frank. Ground Engineering Equipment Methods. McGraw-Hill: New York: 1983.
- ↑ Drilling. Holemasters. 2008-10-17.
- ↑ Drilling Methods. LBORO. 2008-10-16.
- ↑ Drilling. Holemasters. 2008-10-17.
- ↑ Harris, Frank. Ground Engineering Equipment Methods. McGraw-Hill: New York: 1983.
- ↑ Drilling Methods. LBORO. 2008-10-16.
- ↑ Hartman, Howard L. Ed. SME Mining and Engineering Handbook. Society for Mining Metallurgy and Exploration: 1992. 314-315.
