Down the Hole Hammers (DTH) | Complete Solution
Down the Hole Hammers (DTH) | Complete Solution
Optimal Hammer Selection
The ideal hole diameter for DTH drilling spans from 90 mm (3.5") to 254 mm (10"). For smaller boreholes, top-hammer drill rigs are typically employed, while larger holes are generally drilled using rotary rigs.
As a guideline, the smallest hole diameter a DTH hammer can drill corresponds to its nominal size. For instance, a 102 mm (4") hammer will drill a minimum hole diameter of 102 mm (4"). The outside diameter of the hammer restricts smaller hole sizes because wear on the bit decreases diameter and restricts airflow. The maximum hole size suitable for production drilling is approximately the hammer size plus 25 mm (1"), meaning a 102 mm (4") hammer is optimal for diameters up to 127-130 mm (5").
Selecting the appropriate hammer depends on the application type, hole size, and rock formation. Ideally, the hammer size should fit the required hole dimension closely, allowing sufficient space for efficient material evacuation.
Epiroc hammers are tailored for various rock types and high-performance applications, where low cost per drill meter is a critical factor. Their standard design is suitable for production drilling in quarries, shallow water well drilling, and underground blast hole drilling. For harsher, more abrasive conditions, the QM (quarry master) variant is optimal, featuring the same internal components as the standard model but with an enlarged OD chuck and wear sleeve, and a top sub with tungsten carbide buttons for enhanced wear resistance. This configuration also shields the top sub from excessive wear when drilling out from broken rocks.
Peak Performance
The COP M-series, Gold, and QLX hammers are engineered for extremely challenging drilling conditions, delivering premium performance. Equipped with cutting-edge technology, these hammers maximize productivity and profitability.
E-kit Utility
A general rule is to replace a DTH hammer used in production drilling once it loses about 10% of its penetration rate. Reduced productivity significantly increases total drilling costs per meter. Epiroc hammers offer a rebuild option via the E-kit, containing external and internal wear parts. This is especially beneficial in abrasive to medium-abrasive formations. Designed with the highest quality in mind, these hammers can be rebuilt to maintain performance.
The Evolution of DTH Hammers
THE HISTORY OF DTH HAMMERS
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The Down-the-Hole hammer, simply known as DTH hammer, is a versatile tool used for drilling through various rock types and materials. Originally designed for primary blast hole drilling, its usability has significantly expanded over time. The first commercialized DTH hammer was introduced by Andre Stenuick of Stenuick Freres, Belgium, in 1950.
In collaboration with Stenuick Freres, Halco spearheaded the distribution of the Down-the-Hole hammer, particularly in regions like the UK, Australia, New Zealand, Africa, and India during the 1950s. The term "Down the Hole" describes the hammer action location, which is different from Top Hammer (TH) systems that apply force from the drill string's top. The DTH hammer's piston directly contacts the drill bit, ensuring no energy loss, even when drilling deeper, unlike drifter rigs.
Before DTH hammers were introduced in the early 1950s, blast hole drilling mainly relied on drifter equipment, while hard formation water well drilling used cable tool rigs or rotary rigs with rock roller bits (tricones). Drifter drilling efficiency decreases with depth, which doesn't occur with DTH systems. Additionally, a DTH hammer can complete in a day what cable tool rigs require weeks for. Quarries, water wells, site investigations, civil engineering, and the mining sector quickly recognized DTH hammers' advantages over traditional methods, thanks to their advanced performance.
The DTH hammer concept was so successful that other manufacturers of drifter steels, bits, and accessories followed Halco's lead by developing their own DTH hammers and bits ranges.
HAMMER DEVELOPMENT
The earliest DTH hammers featured a "valved" design with an internal liner. Early compressor technology limited their air pressure capability to around 12 bar (170 psi). The valves often malfunctioned, especially when large water volumes or grit entered the hammer.
Modern hammers are predominantly valveless, with fewer internal parts requiring maintenance, making them more robust and capable of withstanding air pressures up to 28 bar (400 psi). DTH hammer penetration rates are almost directly proportional to air pressure; hence, doubling air pressure nearly doubles the penetration rate.
Future DTH hammer advancements aim to reduce drilling costs and extend hammer lifespans by increasing penetration rates. Achieving these goals involves delivering higher air pressures or exploring alternative power sources like water or oil. To enhance hammer component longevity, research into wear and impact-resistant materials will be crucial.
Water-powered hammers are under development for underground mining applications. Although performance results are promising, using these hammers is limited to sites with abundant water. Hydraulic oil-powered hammers tested in some quarries face issues such as spillage and environmental contamination risks, requiring an adapted drill rig and additional equipment. Consequently, air-driven hammers still dominate the market.
DTH hammers hold potential for applications usually drilled with other methods, such as shallow oil and gas field development, wide-hole piling, continuous drilling and casing systems, reverse circulation chip sampling, mole drilling, and large-diameter holes in mining and construction.
Beginning with quarries, DTH hammers have become a favored option across the drilling industry due to their notable advantages, including:
- Capability to drill in almost all rock types, from hard to medium to soft.
- Penetration rates surpassing other systems.
- Reduced costs.
- Straighter and cleaner holes.
- Availability of a wide range of hole sizes without high expenditure.
- Quieter operation compared to other percussive systems.
If you want to learn more, please visit our website High Pressure DTH Hammer.
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