EXPLORATION
When planning rock excavation in hard-rock mining most operations depend on the drill pattern design. Maurice Jones reports.
Bei der Planung des Felsaushubs im Hartgesteinsbergbau hängen die meisten Vorgänge vom Bohrbild ab. Maurice Jones berichtet.
Cuando se planifica excavación en la roca en minería sobre roca dura, la mayoría de las operaciones dependen del patrón de diseño de la perforadora. Informe de Maurice Jones.
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Automatic choice for a big blast?
istorically rotary drilling has been developed for deep-hole drilling, such as in deep exploratory work, oil- and gas-field
exploitation, water-well drilling and, originally, brine solution mining. In mining blastholes the hole depth is probably only equal in importance to hole diameter, and which hole diameter, and thus grid spacing, makes for the optimum hole pattern. Great hole diameters can reduce hole spacing and therefore improve drilling productivity, commensurate with explosive capabilities. Te hole depth, and therefore the bench height, is usually restricted by safety considerations. Even in large open-pit mines small top-hammer rigs carry out some blasthole drilling, but this is mainly for pre-split drilling to create a smooth back-wall for the bench, preventing the blast damaging the neighbouring rock.
Mobility Rotary blasthole rigs are invariably mobile, which usually means based on a platform carried by a crawler chassis, rather than the highway trucks usually used for exploration or water- well drilling. For maximum efficiency in rig placement the platform and chassis has to carry all or nearly all the equipment required for drilling. In blasthole drilling, as the hole- flushing medium is compressed air, this will usually include a compressor of high pressure and delivery, although separate mobile compressors are sometimes used. Compressed air may also be required for a down-hole drill (ITH/DHD) if exceptionally hard strata may be encountered (see below).
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As well as any on-board compressor, on-board power must be sufficient to power the rotary drive for the whole drill string, hydraulic thrust to drive the bit against the hole bottom, and a hoist to handle lift and change pipes of the drill string. Generally the bigger the hole diameter and required depth, the more power is required on the rig, and the larger the whole unit will be. Tese power requirements require either an on-board diesel engine prime mover or a trailing cable from an external electrical power supply. Sandvik’s range of 12 basic
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