Страницы из Blasthole_Drilling_in_Open_Pit_Mining-8.pdf

Страницы из Blasthole_Drilling_in_Open_Pit_Mining-8.pdf

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BLASTHOLE DRILLING IN OPEN PIT MINING 35 TALKING TECHNICALLY Close attention When developing a rotary drilling system, most of the attention is usually given to the drill rig, the capital equip- ment that requires significant invest- ment and hence a planned payback. The second priority in the system tends to be choice of rotary tricone drill bit – the Tricone. However, to utilize the full power and capacity of the rig and the bit, and at the same time increase serv- ice life and productivity, consideration should also be given to the entire drill string. The optimal drill string includes a shock absorber at the top, a rotary deck bushing to centralize the drill string as it passes through the deck of the rig, strong and straight drill pipes and final- ly a hole stabilizing roller sta bili-zer or bit sub-adaptor to optimize the per- formance. Giving the necessary atten- tion to every part of the drill string will lead to the lowest total operating costs in rock excavation and fragmentation. The rotary drill string The primary purpose of the drill string is to transmit the rotational torque and weight from the power source – the rotary head of the rig – to the rock breaking drill bit. As for every rock drilling method, the power must be transmitted as efficiently as possible, and return as few vibrations as possi- ble, as these cause unnecessary wear on the rig and reduce penetration rates. When selecting components for the drill string, attention must be given to the different roles of the support tools in the string. The aim can be to: reduce wear and tear on the drill rig • absorb damaging vibrations travelling back up the drill string improve transmission of energy from the rotary head to drill bit centralize the drill bit within the hole • longer bit life • reduce friction as the drill string passes through the drill rig deck stabilize the hole wall to prevent hole caving increase penetration rates and lower drilling costs • achieve blast hole accuracy for im- proved blasting efficiency • improve the end result – the frag- mentation of the blasted rock. Shock absorber At the very top of the drill string – between the rotary head and drill pipe – a shock absorber is commonly used. As the name indicates, the intention of this tool is to reduce the negative effects of harmful vibrations that travel back up the string as a result of the drilling process. The benefits of using a shock absor- ber include: • improved torque control • increased drilling penetration rates better drill rig availability and exten- ded drill rig drive head and mast life longer service life of drill bits Giving the necessary attention to the drill string components will pave the way for quality drilling and lower total operating costs.
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