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MATCHING DRILLS TO JOBS
00:00 25 Aug 1994
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DRIFTER DRILLING
Uses either air or hydraulic powered drifters located on a drill guide outside the hole. The drifter piston discharges energy to the rock through the striking bar, couplings, drill rods and the bit. This energy crushers the rock into small chippings, or drill cuttings.
The drifter rotation motor turns the bit so it encounters fresh rock and breaks the rock chips into smaller pieces. Compressed air is used to flush drill cuttings from the hole.
A feed device keeps constant force on the bit and rock surface to use the maximum energy of the drifter. Adding drill rods and couplings dissipates drilling energy. Consequently, drilling speed decreases with depth.
ROTARY DRILLING
Is generally used for large diameter blastholes or for deep drilling and is most effective in soft to medium rock. Water and oil wells, geothermal research and drilling operations in large open-pit mines are typical rotary applications.
Rotary drills use high pull-down pressures on the bit and top drive rotation outside the hole. A hydraulic rotary head, or kellybar drive provides rotation. Feed pressure and rotary torque crush and grind the rock while compressed air, mud or foam is used to carry cuttings out of the hole.
The relationship between feed pressure and rotation rate determines drilling speed and efficiency. Soft rock requires lower feed pressure and faster rotation speed. Harder formations need the reverse. Optimum bit styles maximise penetration and bit life.
DOWNHOLE DRILLING (DHD)
The DHD hammer is located at the lower end of the drill string. The piston hammer contacts the bit itself so there is no loss of efficiency since energy is not dissipated through the string as the hole deepens.
The hydraulic or air powered rotary head, or kellybar drive outside the hole, provides rotation. Drill pipes carry compressed air to the DHD hammer and after cycling the hammer, the air passes through the bit and flushes cuttings out of the hole.
Although no energy is lost as drilling depth increases, friction between the drill pipe and hole wall reduces drill speed slightly. Increasing the air pressure increases piston energy and provides faster penetration.
DHD hammers drill straight holes because the drilling power comes from high frequency percussion, rather than from high rotation and pull-down - and because the piston impacts directly on the bit, rather than on drill strings which can deflect and bend over long hole lengths. This makes DHD suitable in broken ground conditions where hole deviation could be a problem.
Uses either air or hydraulic powered drifters located on a drill guide outside the hole. The drifter piston discharges energy to the rock through the striking bar, couplings, drill rods and the bit. This energy crushers the rock into small chippings, or drill cuttings.
The drifter rotation motor turns the bit so it encounters fresh rock and breaks the rock chips into smaller pieces. Compressed air is used to flush drill cuttings from the hole.
A feed device keeps constant force on the bit and rock surface to use the maximum energy of the drifter. Adding drill rods and couplings dissipates drilling energy. Consequently, drilling speed decreases with depth.
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ROTARY DRILLING
Is generally used for large diameter blastholes or for deep drilling and is most effective in soft to medium rock. Water and oil wells, geothermal research and drilling operations in large open-pit mines are typical rotary applications.
Rotary drills use high pull-down pressures on the bit and top drive rotation outside the hole. A hydraulic rotary head, or kellybar drive provides rotation. Feed pressure and rotary torque crush and grind the rock while compressed air, mud or foam is used to carry cuttings out of the hole.
The relationship between feed pressure and rotation rate determines drilling speed and efficiency. Soft rock requires lower feed pressure and faster rotation speed. Harder formations need the reverse. Optimum bit styles maximise penetration and bit life.
DOWNHOLE DRILLING (DHD)
The DHD hammer is located at the lower end of the drill string. The piston hammer contacts the bit itself so there is no loss of efficiency since energy is not dissipated through the string as the hole deepens.
The hydraulic or air powered rotary head, or kellybar drive outside the hole, provides rotation. Drill pipes carry compressed air to the DHD hammer and after cycling the hammer, the air passes through the bit and flushes cuttings out of the hole.
Although no energy is lost as drilling depth increases, friction between the drill pipe and hole wall reduces drill speed slightly. Increasing the air pressure increases piston energy and provides faster penetration.
DHD hammers drill straight holes because the drilling power comes from high frequency percussion, rather than from high rotation and pull-down - and because the piston impacts directly on the bit, rather than on drill strings which can deflect and bend over long hole lengths. This makes DHD suitable in broken ground conditions where hole deviation could be a problem.
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