Every day, the world’s quarries produce millions of tonnes of aggregate for a variety of industrial needs by drilling, blasting and crushing – but not always with the best results for their owners. However, there is a smart, easy and profitable way to get the job done.
Quarrying is a tough business at the best of times, but making it pay is even tougher. The reason is that there are a number of key parameters that must be made to work together in harmony – and that’s no easy task.
Mats Birkestål, Product Manager and quarrying specialist at Atlas Copco’s Surface and Exploration Drilling division, explains: “Quarrying should be seen in terms of one operation, not as a series of individual operations. The problem is that there are still too many quarries that may get good results in only one or maybe two areas and that puts pressure on the bottom line.”
What’s needed, says Birkestål, is to apply a total cost concept from the planning stage right through the operation to the final product. This means that the combination of drilling, blasting, loading, transportation and crushing have to be better synchronized in order to minimize errors and maximize results.
poorly positioned blast holes results in unpredictable fragmentation of blasted rock
fluctuating sizes of the rock fragments results in uneven truck loads, higher engine wear and excessive fuel consumption
oversize fragments affect throughput at the crusher station, slowing down the process of producing aggregate at the required size;
uneven flow at the station forces the crusher to work harder, which increases energy consumption
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The aim is to achieve an efficient, smooth-running process all from the beginning to the end, continues Birkestål, and maintains that the secret of success lies in the quality of the drilling. “This is the crucial point at which everything has to be done correctly,” he says. “If you get this part wrong, it will be so much more difficult to get the rest of it right.”
"If you get this part wrong, it will be so much more difficult to get the rest of it right."
Modern technology offered by today’s drill rigs such as Atlas Copco’s SmartROC T45 enables even the most inexperienced driller to “get it right”. This drill rig is packed with high-tech devices such as the Hole Navigation System (HNS), automatic inclination and collaring, and much more.
A typical benching scenario consists of 75 holes in five rows to be drilled to a depth of 15 m. To cover this area, and effectively remove the estimated round (about 31 000 tonnes of rock), Atlas Copco estimates that a conventional drill rig would need to drill eight more holes than with the SmartROC T45.
The reason is that with a conventional drill rig, the burden and spacing between the holes has to be reduced in order to compensate for possible errors in positioning and wrong angles, as any holes that end up too far apart jeopardizes the effectiveness of the blast. With the SmartROC T45, equipped with the Hole Navigation System (HNS), the rig automatically locates the position of each hole with pinpoint accuracy and drills it to the correct inclination and depth. As a result, the pattern needs no adjusting and gets drilled as planned.
There is money to save
In economic terms, the implication of this level of reliability is striking. The cost of having to drill eight more holes, or 120 drill meters, would amount to around USD 600, based on a typical average drilling cost of USD 5 per meter. With 40 blasts per year, this extra cost would amount to approximately USD 24 000 per annum, not including the added cost of explosives. Not only that, the effect of poorly positioned drill holes that affects all operations further downstream is considerable.
A typical case in point is the Akselberg limestone quarry in Norway. Here, the owner, Brønnøy Kalk AS, has achieved total efficiency throughout its operation thanks to its holistic approach to planning as well as meticulous attention to every detail in the production process.
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The drills conventionally used in quarries are designed to operate at a bench depth of about 12-15 meters. Trying to penetrate much deeper can cause Down-The-Hole and tophammer drills to deviate, creating accuracy and potential safety problems.