Classifications

• • E—FIXED CONSTRUCTIONS
  • E21—EARTH OR ROCK DRILLING; MINING
  • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
  • E21B17/00—Drilling rods or pipes; Flexible drill strings; Kellies; Drill collars; Sucker rods; Cables; Casings; Tubings
  • E21B17/02—Couplings; joints
  • E21B17/04—Couplings; joints between rod or the like and bit or between rod and rod or the like
  • E21B17/07—Telescoping joints for varying drill string lengths; Shock absorbers
  • E21B17/076—Telescoping joints for varying drill string lengths; Shock absorbers between rod or pipe and drill bit
• • E—FIXED CONSTRUCTIONS
  • E21—EARTH OR ROCK DRILLING; MINING
  • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
  • E21B10/00—Drill bits
  • E21B10/36—Percussion drill bits

Definitions

• the present invention relates to a down-the-hole hammer drill.
• This invention has particular application to a reverse-circulation (RC) down-hole face sampling hammer drill, although it need not be so limited.
• RC reverse-circulation
• the bit is accelerated upwards, whereupon it impacts an adjacent face at or near the bottom of the drive sub. When high energy levels are present this can cause damage to either or both of the bit head and the drive sub.
• the invention may be said to reside in a bit for a percussive down-the-hole hammer comprising an elongate shank, a head, at least one channel extending lengthwise along the shank toward the head, wherein the width of the or each channel is reduced at a position toward the head, so as to create a narrower channel portion extending from this position to the head, and a wider channel portion extending to this position, and define at this position a contact area in an end of the wider channel portion for contact between the bit and a portion of a driver for the bit.
• the contact area is substantially planar.
• the contact area is normal to the direction of elongation of the channel.
• the contact area is a shoulder created by stepping down of the channel width.
• a plurality of spaced apart channels extend lengthwise along the shank toward the head.
• the position of the contact area is, for each channel, at the same point along the channel.
• both portions of each respective channel has a longitudinal centre line, and these centrelines are substantially longitudinally aligned.
• both portions of each respective channel has a longitudinal centre line, and these centrelines are longitudinally mis-aligned.
• the centreline of the narrow channel portion is offset to one side of the centreline of the wider channel portion.
• the contact area is divided into two portions separated by the narrower channel portion. In one form, the contact area is to one side of the narrower channel portion.
• each channel is defined between a pair of adjacent splines extending lengthwise along the bit shank.
• the driver for the bit is a drive sub.
• the or each contacting portion of the driver is a portion of an annular face thereof.
• the bit is for a reverse circulation (RC) percussive down-the-hole hammer.
• the invention may be said to reside in a percussive down-the-hole hammer comprising a splined drive sub comprising driving splines abutting driven splines on a drill bit, the drill bit comprising an elongate shank, a head, at least one channel extending lengthwise along the shank toward the head, wherein the width of the or each channel is reduced at a position toward the head, so as to create a narrower channel portion extending from this position to the head, and a wider channel portion extending to this position, and define at this position a contact area in an end of the wider channel portion for contact between the bit and a portion of the drive sub for the bit.
• each of the drive sub's driving splines locates in One wider channel portion defined between adjacent driven splines in such a way that the driving spline drives against one of these adjacent driven splines and defines an elongate space with the other.
• the elongate space is substantially longitudinally aligned with the narrower channel portion.
• the elongate space is of similar cross-sectional area to the narrower channel portion.
• Figure 1 is a perspective view of an assembly comprising a drill bit, drive sub and bit retaining ring;
• Figure 2 is a perspective view of the drill bit from the assembly of Figure 1 , where all but the splines of the drive sub have been removed to permit visibility of the drive sub splines and their relationship with the bit.
• like reference characters designate like or corresponding parts throughout the several views of the drawings.
• FIG. 1 where there is illustrated a down-the-hole hammer having a reverse circulation system comprising a cylindrical case (not illustrated), and a drive sub 10 threadably mounted in the case.
• a piston (not illustrated) will be vertically reciprocally mounted in the case to be reciprocated by pressurised air.
• a drill bit 20 is mounted in the drive sub 10 beneath the piston by bit retention means in the form of a bit retaining ring (or bit ring) 60.
• the drive sub 10 comprises an annular sleeve 12 and an array of spaced apart, inwardly directed driving splines 14.
• the drill bit 20 comprises a shank 22 and a drill bit head 23 with a bit face 23a.
• the shank 22 has a number of outwardly directed driven splines 24, which are so spaced and numbered as to form, with the driving splines 14, pairs of splines having abutting working faces when the shank 22 of the drill bit 20 is inserted into the drive sub 10 (see Figure 2).
• the driving splines 14 act against the driven splines 24 to drive rotation of the drill bit 20 while permitting the drill bit 20 to move longitudinally (under the effect of the hammer), with respect to the drive sub 10.
• the drill bit 20 further comprises a bore 30 which extends lengthwise through the shank 22 to sludge holes 32 extending from the bore 30 to the bit face 23a.
• the diameter of the bore 30 is sized so as to be ' sufficiently large enough to convey the largest of the cuttings produced and blown from the bit face 23a to the bore 30 via the sludge holes 32.
• a plurality of channels 40 extend lengthwise along the shank 22 of the bit 20 toward the head 23 so as to direct exhaust air from the hammer motor to the bit head 23. This air blows the bit face 23a clear of cuttings, and carries a mist of lubricant to the driving 14 and driven splines 24.
• the reverse circulation system involves the downward circulation of a flushing medium, such as air, via the channels 40 to the cutting face 23a of the bit, whereupon the air flows laterally across the cutting face 23a and eventually up through the bore 30 in the bit and the hammer to the ground level. Cuttings become entrained within the air as the air passes across the cutting face 23a of the bit 20 and are conducted to the surface along with the air for analysis.
• a flushing medium such as air
• each channel 40 is reduced at a position toward the head 23, so as to create a narrower channel portion 40a extending from this position to the head 23, and a wider channel portion 40b extending to this position, and define at this position a contact area 50 in an end of the wider channel portion 40b for contact between the bit 20 and an annular surface of the drive sub 10.
• the contact area 50 defined in each channel 40 then is a shoulder created by stepping the channel width down, resulting in a contact area 50 which is substantially planar, and which is divided into two portions separated by the narrower channel portion 40a.
• Each driving spline 14 locates in a wider channel portion 40b defined between adjacent driven splines 24 in such a way that the driving spline 14 drives against one of these adjacent splines 24 and defines an elongate space (in the wider channel portion 40b) with the other, which is substantially aligned with the narrower channel portion 40a.
• the clean lubricated air flows through these elongate spaces and on to the narrower channel portions 40a, which then directs this air to the face 23a of the bit 20 for flushing.
• Each exhaust air conduit thus formed by the elongate spaces (in the wider channel portion 40b) and narrower channel portions 40a will be of essentially constant cross-section along its entire length between the uppermost end (i.e. distal from the head) of the driven splines 24 and the back of the head 23 beneath the shroud.
• a significant advantage of the present invention is that it substantially ameliorates these difficulties associated with the air flow. Furthermore, computational flow dynamics studies have demonstrated that narrowing of the conduit at the back of the head (cf bits of the prior art) does not appreciably alter the flow conditions and therefore will not appreciably affect hammer performance.
• a significant advantage of the present invention is that it maximises the contact area between the back of the bit head 23 and the lower annular face of the drive sub 10 in order to reduce impact stresses during adverse operating conditions, thereby mitigating the issue of the bit 20 recessing itself into the drive sub 10 and changing the height of the contact plane between the bit 20 and piston.

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• Engineering & Computer Science (AREA)
• Life Sciences & Earth Sciences (AREA)
• Geology (AREA)
• Mining & Mineral Resources (AREA)
• Mechanical Engineering (AREA)
• Physics & Mathematics (AREA)
• Environmental & Geological Engineering (AREA)
• Fluid Mechanics (AREA)
• General Life Sciences & Earth Sciences (AREA)
• Geochemistry & Mineralogy (AREA)
• Percussive Tools And Related Accessories (AREA)
• Earth Drilling (AREA)

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Publications (2)

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• 2013
  • 2013-01-17 WO PCT/IB2013/000433 patent/WO2013108127A2/fr not_active Ceased

Non-Patent Citations (1)

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