Engineering & Mining Journal

SEP 2012

Engineering and Mining Journal - Whether the market is copper, gold, nickel, iron ore, lead/zinc, PGM, diamonds or other commodities, E&MJ takes the lead in projecting trends, following development and reporting on the most efficient operating pr

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DTH DRILLING Productivity and Cost-efficiency Drive DTH Drilling Down-the-hole (DTH) is one of the mainstream drilling technologies for mining and quarrying worldwide. Recent improvements have largely been aimed at making systems more fuel-efficient and at optimizing tool life. By Simon Walker, European Editor based, providing equipment that is com- patible with machines from the major manufacturers. Nonetheless, having a mature tech- nology does not mean that the industry stands still in terms of further develop- ment. Greater reliability, longer service lives, easier and more cost-effective maintenance and better energy-efficien- cy are all targets for improvement, espe- cially at a time when fuel costs seem to be rising inexorably. With some excep- tions, mainstream DTH drilling uses compressed air as its operating medi- um, so optimizing compressor-fuel usage can have a significant impact on operating costs. The business end of a DTH bit, with button and face profiles optimized for a specific application. (Photo courtesy of Sandvik) The development of down-the-hole (DTH) drilling stemmed from the realization that hole accuracy and the efficiency of transmitting power from drill to bit could be improved by placing the hammer as close as possible to the business-end of the drill string. As far as hole accuracy was concerned, by the late 1940s the need for deeper and deeper holes in both surface mines and quarries had led to problems with increasing deviation with depth, especially with small-diameter bits mounted on conventional sectional drill rods. Meanwhile, the nature of the rods themselves, and the way that they were joined using couplings, reduced the energy-transfer efficiency, a problem that only increased as the threads on rods and couplings alike became increasingly worn. The solution, which may appear obvious today but was radical at the time, was to 'hit the bit' directly. According to U.K.-based Halco Rock Tools, now an autonomous company with- 72 E&MJ; • SEPTEMBER 2012 in the Caterpillar group, it introduced DTH technology to the world in 1951. Working with the Belgian company, Stenuick—which is now operating in France and still supplies rigs and equip- ment to the quarrying, water-well and construction industries—it developed the first DTH hammer, which operated at an air pressure of 100 psi. Two years later, the first Halifax Tool Co. (today's Halco) DTH drill came on the market, with the world's first DTH-drilled blast taking place in a quarry in the U.K. To put this into context, other notable events that year included the first suc- cessful ascent of Mt. Everest, and the coronation of Queen Elizabeth II. It is not difficult to see, then, that DTH drilling is now a mature technology, with many companies worldwide supply- ing the equipment and consumables needed. Some, such as Atlas Copco, Boart Longyear, Halco and Sandvik, sup- ply world markets; others are regionally Surface Rigs in Yellow... Atlas Copco has recently been through a major rebranding exercise for its surface drill rigs, with three basic families in its range: FlexiROC, SmartROC and PowerROC. Each of these in turn con- sists of several models, with some machines in each family designed to carry DTH equipment. Machines thus equipped include the FlexiROC D45, D50, D55, D60 and D65, while the PowerROC family includes the D40 and D55 and SmartROC the D65. In general terms, the smaller rigs in each group are aimed at construction and quarrying markets, while the larger machines can also find surface-mining uses in applica- tions where a rotary blasthole rig would be too big. Introduced in 2010 as the Smartrig ROC D65, the now-renamed SmartROC D65 built on the mechanical concepts of the former L8 rig by combining these with Atlas Copco's Rig Control System (RCS) for automation and control. The company notes that RCS can be used to control all of the rig functions, including the complete drilling cycle, automated pipe handling, data transfer between the www.e-mj.com

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