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Down-the-hole Drill

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Construction Equipment
Mining Equipment

The down-the-hole drill is a machine used to produce large-diameter holes in rocks, usually in the initial stage prior to blasting, but it is also used in non-blasting applications. DTH drills, as they are commonly referred to, are used mostly in mining quarries but can be used in a variety of other construction applications. The DTH drill first appeared in the 1950s and is produced by major manufacturers such as Ingersoll Rand and Atlas Copco.

Contents

[edit] History

[edit] Chisels in Ancient China

The first drilling tools took the form of chisels, which were used throughout Asia in construction applications. Workers drilled chisels into rock, a task both slow and onerous. When bits of rock were chiseled away, they were loaded into carts and removed from the site. Ancient Chinese workers made this method of drilling more efficient with the inclusion of a spring pole from which the chisel was suspended and kicked down to produce a motion that would chip away at the rock and create a hole. This method allowed the Chinese to accomplish thousands of feet worth of holes to recover water and brine.[1]

[edit] Modern Drilling Implements

Modern drilling tools made their first appearance gradually after the advent of oil drilling in France, Germany, and the U.S. The first cable drill rig was invented in the early 19th century and an Englishman named Robert Beart took out the first patent on the rotary drilling method in 1845. From this point on, drilling tools experienced a gradual movement towards a modernization of different drilling methods and types. As the business of drilling for oil wells and other construction applications became more in demand in an ever-growing modern industry, drilling tools expanded to include a variety of different types to serve different purposes.[2]

[edit] Drake's Development

Drill equipment became more frequently used in the U.S. after Colonel Drake was hired by a businessman named James Townsend in Pennsylvania who thought oil could be drilled through rock. This task led to Drake to develop drills for modern usage in 1857. Drake’s steam-powered drill bit was designed to penetrate the rock with the chisel end used in drilling a hole.

[edit] Rotary Drilling Method

Drake’s cable rig tool proved successful for the oil drilling application, but soon other methods were being explored. In the 1860s, France devised a rotary drilling method whereby drill bits repeatedly rotated as they drilled into rock. This method was adopted by the U.S. 20 years later.[3]

[edit] Down-the-hole Drills

Major manufacturers began producing down-the-hole drills in the 1950s. Ingersoll Rand, a major manufacturer of drills, introduced its down-the-hole drill in 1955.[4]

Down-the-hole or DTH drills are primary tools used in both blasting and non-blasting applications. DTH drills are developed in a variety of configurations, powered by compressed air or hydraulics. Hydraulic DTH drills are said to be faster and more accurate in precision-drilling. The drills can be mounted on either crawler tracks or a rubber-tired vehicle, depending on the terrain.

Today, DTH drills are developed to drill faster and deeper. As these types of drills are often used in quarry mines, it is within this industry that they are becoming more advanced. It is in mining for gold where most DTH drills are make huge developments because gold requires more precision and tighter blast patterns. Some modern developments within DTH drills include a range manufactured by Furukawa. Their DCR-23 DTH drill is mounted on a crawler tractor and a 350-pound per square inch (2,413-kPa) capacity.

Similarly, the DTH produced by the Sandvik Group, the Titan 500, is another example of the direction that drills are changing. The Titan 500 is a self-powered, self-contained drill used in the mining industry. It is capable of drilling holes 115 feet (35 m) deep and four to six inches (10 to 15 cm) in diameter with a 365 horsepower engine and a six-cylinder Caterpillar engine.

The latest technology in drills, whether DTH or not, is emphasized in the drill bit and controls. Technology that manipulates the feed pressure of the bit and the rotation speed is an important factor that manufacturers are considering when producing a drill. Other improvements that are being made to current drills are to make them quieter and to implement functions that reduce the wear on the bit face. One change that is occurring in most equipment in this age is to make them more efficient while conserving energy.[5]

[edit] Features/How it Works

A DTH drill is powered by pneumatics or hydraulics. It consists of a drill bit that has three cones with teeth that are made out of tungsten carbide steel, but can also be made of industrial diamonds. The cones rotate and provide the drilling and cutting function.

The drill piston is powered by torque and typically rotates at a speed of zero to 50 revolutions per minute.

DTH drills contain a shell that houses the piston. Normally, the drills do not consist of a valve system and operate instead with the use of ports to control the oscillation of the pistons. The exhaust air also makes its way through the port and flushes out air to clean the bit of the drill and also to clear the hole of rock debris.

Bits can come in different types: flat-faced, convex, concave, kavex, double-domed, ballistic bits and dome bits. Bit sizes for the cones are typically between four and seven inches (10.2 and 16.5 cm).[6]

Flat-faced bits are used in heavy-duty drilling applications where the drilling is deep. As described, the face of the bit is flat as it drills.

The convex bit is used in applications where the rock is somewhat worn away and drills with two buttons as opposed to one.

The concave bit is one of the most common. It is practiced on medium to hard rock applications and drills a straight hole.

The kavex is a combination of both the concave and the convex with a bit that works best on abrasive materials and drilling straight holes.

Dome bits are spherical faces are the bits mostly utilized for DTH drills. Well-suited for a variety of applications, from medium to hard rock as well as broken formations, the dome shaped face is less likely to break than the other types.

The double-domed face is similar to the dome shape, but with an additional dome positioned on top of the other. The additional bit provides additional life to the bit while providing a sharper penetration.

Ballistic bits are capable of drilling in more rapid motions but are used less because it tends to break when used in certain formations it was not developed for.[7]

The DTH drill performs rotary drilling, a method whereby the pistons of the drill rotate on the device as it penetrates rocks or other hard materials. The weight of the drill on the piston pushes firmly into the rock to enable drilling precision. Drilling mud makes its way down the drill pipe to aid in the removal of the rocks as the drilling procedure is taking place. The pressure of the liquid from the drill bit pushes the rock debris to the surface.[8]

[edit] Common Manufacturers

[edit] References

  1. The Drill Rig. Goliath. 2008-09-09.
  2. Drilling History. Drillers Log. 2008-09-09.
  3. The Drill Rig. Goliath. 2008-09-09.
  4. History. Ingersoll Rand. 2008-09-09.
  5. Drilling Feat is More Feet. Rockproducts.com. 2008-09-09.
  6. Tatiya, Ratan Raj. Surface and Underground Excavations. A.A. Balkema, 2005.
  7. DTH Bits. Rockhog.com. 2008-09-09.
  8. The Drill Rig. Goliath. 2008-09-09.