What Is DTH Drilling?

Tungsten carbide is one of the most widely used tool materials globally. Numerous tungsten carbide products exist, including tungsten carbide buttons, which are integral to DTH drill bits. So, what exactly is DTH drilling? This article provides a brief introduction to DTH drilling.

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DTH, or Down-the-Hole drilling, was developed to create large-diameter holes downward in surface-drilling applications, which explains the origin of its name.

A complete down-the-hole drilling system typically comprises a drill rod, annulus with cuttings, drill fluid, threaded joint, valves, DTH hammer, hammer piston, drill bit, and tungsten carbide buttons (also known as tungsten carbide inserts). The system utilizes compressed air to drive the hammer. In DTH drilling, the hammer is positioned directly above the drill bit. Drill pipes provide feed to the hammer and bit while also transporting fluid to operate the hammer and clear the cuttings. As the hole deepens, drill pipes are successively added to the drill string behind the hammer.

The hammer consists of two mobile components: a valve that controls the flow and a piston that strikes an impact surface directly connected to the bit. The hammer body ensures straight and stable guidance for the drill bit.

DTH drilling is primarily employed in mining to create holes. Operators drill, fill these holes with explosives, and excavate rocks to access minerals. DTH drilling excels at creating large holes in hard rock but can also drill through softer rock formations. However, drilling in softer rock can lead to energy waste and reduced efficiency, and it may cause excessive wear on DTH drill bits.

Tungsten carbide buttons on DTH drill bits play a crucial role. They make direct contact with hard rock, and their high hardness, wear resistance, impact resistance, and durability enhance their performance.

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1. Excellent thermal stability and high-temperature resistance.

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3. Good resistance to thermal shock.

4. Outstanding oxidation control.

5. Corrosion resistance at high temperatures.

6. Exceptional chemical corrosion resistance.

7. High wear resistance.

8. Long service life.

9. Constructed from 100% raw tungsten carbide.

10. Sintered in a HIP furnace.

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Jackhammer-like tip for drilling deep into rock

A down-the-hole drill, often referred to simply as DTH by industry professionals, functions like a jackhammer attached to the bottom of a drill string. The rapid hammer action breaks hard rock into small cuttings and dust, which are removed by air, water, or drilling mud. The DTH hammer is one of the fastest means of drilling through hard rock, with origins attributed to independent inventions by Stenuick Frères in Belgium and Ingersoll Rand in the USA during the mid-20th century.

Origin of the Name

DTH is short for "down-the-hole." This method was initially developed for drilling large-diameter holes downward in surface-drilling applications, leading to the name's origin. As applications for the DTH method emerged underground, the drilling direction commonly shifted upward instead of downward.

Technical Details

In DTH drilling, the percussion mechanism—commonly termed the hammer—is situated directly above the drill bit. Drill pipes provide necessary feed force and rotation to the hammer and bit, along with the fluid (air, water, or drilling mud) used to operate the hammer and flush cuttings. The drill pipes are gradually added to the drill string behind the hammer as the hole deepens.

The hammer is entirely fluid-actuated and consists of two mobile components: a valve that controls the flow and a piston that impacts a surface directly connected to the bit. The hammer body offers consistent and stable guidance for the drill bit.

There are three types of hammers, classified based on the actuation fluid:

• Air hammers, initially developed for hard rock drilling, are limited to shallow holes (less than 200m).
• Water hammers, created by a Swedish company called Wassara, require a specific water flow (between 55 and 744 L/min, depending on hammer size) to actuate the hammer. This improves performance and allows for deeper drilling than air hammers.
• Hammers operated with drilling mud, developed by Drillstar Industries in France, can be used on existing rigs utilizing standard mud compositions. This technology is effective in drilling hard rock encountered in deep geothermal projects.

History

The use of pneumatic tools in rock drilling can be traced back to ancient times. Many quarries relied on manual tools requiring driller suspension from ropes over quarry faces for precise hole placement. This system was inefficient and hazardous, leading to flying rocks from inaccuracies in drilled boreholes.

Primitive top hammer machines were adopted, but issues arose due to the slenderness of drill rods paired with large-diameter bits, leading to borehole deviations that could be dangerously close to neighboring holes. Even larger quarries encountered difficulties with rotary machines that necessitated significant down thrust and high speeds for tri-cone bits to crush rock. Such systems could not effectively handle holes below 6 inches (150mm) and were costly to operate.

The introduction of DTH systems addressed many drawbacks of previous drilling methods. With the DTH system, the energy source is positioned directly behind the drill bit. Its design allows for rigorous air flow through the drill string, enabling efficient removal of cuttings, while also eliminating the need for heavy down thrusts or high rotational speeds. A single operator can effectively manage the DTH machinery, compared to several required for other systems.

DTH revolutionized the blast hole industry, improving hole placement accuracy, efficiency, and safety levels across various applications including water well drilling, construction, and mineral exploration. It continues to offer numerous benefits across diverse sectors such as geothermal drilling and oil exploration. The technology has evolved with the introduction of tungsten carbide drill bits and high-pressure air systems, further enhancing its effectiveness.

Uses

DTH products are applicable in the following areas:

• Mining: Used for drilling and blasting holes in open-pit mining, allowing operators to access ore bodies.
• RC: Mineral exploration and pit grade control utilizing specialized reverse circulation hammers.
• RAB: Rotary air blast for mineral exploration employing conventional DTH hammers.
• GW: Geothermal boreholes and water well drilling.
• Oil and Gas: Deep well boreholes; air hammers are effective when cutting uplift and borehole stability are accounted for. New DTH technologies, including water and mud hammers, are improving drilling rates in hard rocks.
• Construction: Piling, footings, and soil nailing applications.

See Also

• Deep hole drilling in manufacturing.

References

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