Patent Description:
Percussion bits for fluid-operated percussion drill tools, such as down-the-hole hammers, typically comprise a bit head, populated with cutting inserts on the front face of the head. The bit head is formed with an axially extending shank having a smaller diameter than the bit head. As the hammer rotates, rotational drive is most commonly transmitted to the shank by way of splines provided on the external cylindrical wall of the shank which mate with splines provided internally of a drive chuck of the drill tool. During the drilling cycle, an impact piston collides with a rear end of the shank, forcing the cutting inserts on the bit head into the rock being drilled. Pressurised air, known as flushing air, is used to flush cuttings out of the hole while the hammer operates. Flushing air may be provided via a flushing bore through the centre of the piston and a corresponding bore through the bit shank. However, this arrangement typically requires a footvalve, which can be prone to breakage, to control the flushing air. Furthermore, the strike area of the piston is reduced due to the central bore, which also reduces the weight of the piston. The area of the lifting surface of the piston is also reduced. An alternative is to have the flushing air travel along the splines, with channels provided in the bit head to direct the air from the splines to the cutting face of the bit. As the splines require lubrication, lubricating oil may be added to the flushing air stream at the drill rig.

<CIT> proposes an alternative arrangement to the conventional splined engagement between the drive means of the drill tool and the bit, in which a drive ring is provided with a plurality of protrusions at a forward end therefore, each of which is received in one of a corresponding plurality of recesses on the bit head. Because the engagement means are provided at the head portion of the bit, the length of the bit may be reduced, thereby reducing the overall weight of the bit, enabling faster and more efficient drilling. It is desirable to provide a flushing arrangement for use with this drive mechanism, and others, that allows for increased piston weight and strike area and that optimises the piston to bit mass ratio.

<CIT> relates to a percussion tool. <CIT> relates to a drilling apparatus.

According to an aspect of the present invention, there is provided a fluid-operated percussion drill tool comprising:.

through hole and corresponding hole in the collar is configured to receive a fastener to connect the drive ring to a drive means of the percussion drill tool.

A bit retaining ring may be arranged to engage with the bit retaining portion of the percussion bit to retain the bit in the percussion drill tool. The bit retaining ring may be clamped in place between the drive ring and an aligner by engagement of the fasteners with the drive ring.

The bit retaining ring may be provided as a plurality of part-annular bit retaining portions and the depth of the holes in the collar of the drive ring may be greater than a height of the bit retaining portions such that the percussion bit is removable from the drill tool by withdrawing the fasteners from the holes by a distance greater than or equal to the height of the bit retaining portions but less than the depth of the holes such that when the outer wear sleeve is moved away from the percussion bit, an annular space is formed between the forward end of the wear sleeve and the internal shoulder of the drive ring, into which the bit retaining portions are moveable in a radially outward direction such that they no longer retain the percussion bit in the drill tool.

The fluid-operated percussion drill tool may further comprise an O-ring arranged around the bit retaining portions. Alternatively, the fluid-operated percussion drill tool may comprise a plurality of pins extending through the drive ring and arranged to engage the bit retaining portions.

According to an aspect of the invention, there is provided a method for removing a percussion drill bit from a fluid-operated percussion drill tool as set out above, the method comprising:.

The method may be further for replacing the percussion drill bit, and may further comprise:.

According to an aspect of the invention, the fluid-operated percussion drill tool is a down-the-hole hammer.

A down-the-hole hammer <NUM> according to a first embodiment of the present invention is illustrated in <FIG>. The hammer <NUM> comprises an outer wear sleeve <NUM> comprising a substantially cylindrical wall <NUM> and having inner <NUM> and outer <NUM> surfaces. The hammer also comprises a percussion bit <NUM> having a head portion <NUM> and a bit retaining shoulder <NUM>. The bit is located at a forward end <NUM> of the outer wear sleeve. The hammer further comprises a sliding piston <NUM> mounted for reciprocating movement within the outer wear sleeve to strike the percussion bit. A drive ring <NUM> having a substantially cylindrical wall <NUM> comprises connection means <NUM> adapted for connecting the drive ring to a drive means of the hammer. A bit retaining ring <NUM> is arranged to engage with the bit retaining shoulder <NUM> on the percussion bit to retain the bit in the hammer.

As best shown in <FIG>, a plurality of recesses <NUM> are provided at a rear end <NUM> of the head portion <NUM> of the percussion bit <NUM>. A corresponding plurality of protrusions <NUM> is provided at a forward end <NUM> of the drive ring <NUM>. Each protrusion <NUM> is received within a corresponding recess <NUM> to transmit rotational drive from the drive ring <NUM> to the percussion bit <NUM>.

The hammer further comprises an annular flange <NUM> arranged around the outer wear sleeve at the forward end <NUM> thereof. The flange is restrained from forward movement relative to the wear sleeve by engagement of an internal shoulder <NUM> provided on the flange with an external shoulder <NUM> provided at a forward end of the wear sleeve. The connection means <NUM> of the drive ring comprises an annular collar <NUM> provided at a rear end <NUM> of the drive ring, arranged to receive the forward end <NUM> of the wear sleeve such that the forward end of the wear sleeve abuts an internal shoulder <NUM> of the drive ring. A plurality of internally screw-threaded holes <NUM> are provided in a rear end <NUM> of the collar, and the rear end of the collar is arranged to abut a forward end <NUM> of the flange <NUM>. A plurality of through holes <NUM> are provided in the flange. Each through hole corresponds to one of the plurality of holes in the collar. A bolt <NUM> is inserted into each through hole <NUM> and screwed into the corresponding hole <NUM> in the collar to connect the drive ring to the wear sleeve and thus to the drive means of the percussion drill tool.

The clamping effect of this bolted arrangement also holds the bit retaining ring <NUM> in place between the drive ring <NUM> and an aligner <NUM>.

As best illustrated in <FIG>, the hammer <NUM> comprises a plurality of flushing channels <NUM> to provide a fluid path for a flushing medium. The flushing channels are provided in a radially spaced apart arrangement around the hammer. A first portion <NUM> of each flushing channel extends longitudinally within the wall <NUM> of the wear sleeve <NUM>. As shown in the figures, the first portion <NUM> of each flushing channel is internal to the wall <NUM> of the outer wear sleeve meaning that it is disposed within the wall of the wear sleeve rather than being disposed within an inner surface of the wear sleeve itself. The first portion <NUM> of each flushing channel has a first inlet <NUM> at an inner surface <NUM> of the outer wear sleeve. The first inlet <NUM> is positioned to exhaust air from a top chamber <NUM> of the hammer. The first portion of each flushing channel has a second inlet <NUM> at an inner surface <NUM> of the outer wear sleeve. As shown in <FIG> and <FIG>, the second inlet <NUM> is forward of the first inlet <NUM> for each flushing channel and is arranged to exhaust air from a bottom chamber <NUM> of the hammer. The first portion <NUM> of each flushing channel also comprises an outlet <NUM> at a forward end <NUM> of the wall of the outer wear sleeve.

A second portion <NUM> of each flushing channel <NUM> extends longitudinally within the wall <NUM> of the drive ring <NUM>. As shown in <FIG>, the second portion <NUM> of each flushing channel is internal to the wall of the drive ring, that is, the second portion of the flushing channel is disposed within and extends longitudinally through the wall of the wear sleeve rather than being disposed within the drive ring itself. The second portion <NUM> of each flushing channel has an inlet <NUM> at a rear end of the drive ring, wherein each inlet <NUM> is arranged to receive the flushing medium from the outlet <NUM> of the first portion of the corresponding flushing channel. The second portion <NUM> of each flushing channel has an outlet <NUM> at an inner surface <NUM> of the drive ring. As shown in <FIG>, each outlet <NUM> is provided in one of the protrusions <NUM> on the drive ring. In other embodiments, the outlet of the second portion of each flushing channel may be provided at a forward end of the drive ring, for example, in the forward end of one of the protrusions, or between two adjacent protrusions.

A third portion <NUM> of each flushing channel extends through the head portion <NUM> of the percussion bit <NUM> to a cutting face <NUM> of the bit. The third portion <NUM> of each flushing channel has an inlet <NUM> at a head portion of the percussion bit, wherein the inlet is arranged to receive the flushing medium from the outlet <NUM> of the second portion of the corresponding flushing channel. The third portion <NUM> of each flushing channel has an outlet <NUM> in a cutting face of the percussion bit.

In use, the top <NUM> and bottom <NUM> chambers are alternately supplied with pressurised air. When the piston is at top of stroke, as shown in <FIG>, the top chamber <NUM> is supplied with pressurised air. The inlets <NUM> of the flushing channels <NUM> are sealed by the piston <NUM>. The piston is forced down to strike the percussion bit <NUM>. Once the piston moves down (forward) to the position shown in <FIG>, the inlets <NUM> are open to exhaust air from the top chamber <NUM>. As shown in <FIG>, when the piston is in the strike position, the bottom chamber <NUM> is isolated from the flushing channels, thereby avoiding exposure of the bottom chamber to ambient pressure.

When the piston is in the strike position, pressurised air is supplied to the bottom chamber <NUM> via supply channels (not shown). As shown in <FIG>, the bottom chamber is isolated from the flushing channels and is sealed off by the piston <NUM>, the bit <NUM> and the aligner <NUM>. As a result, the piston <NUM> lifts and once the forward end of the piston clears the second inlets <NUM> of the flushing channels, air exhausts from the bottom chamber to the cutting face of the bit. The cycle then repeats with air being alternately supplied to the top and bottom chambers to cause reciprocating movement of the piston within the wear sleeve.

A down-the-hole hammer <NUM> according to a second embodiment of the present invention is illustrated in <FIG>. The hammer <NUM> of the second embodiment is similar to that of the first embodiment, and like reference numerals are used to refer to like elements. The second embodiment differs from the first embodiment in that the drive ring <NUM> comprises a plurality of part annular segments <NUM>, as shown in <FIG> and <FIG>. Each segment <NUM> is provided with three protrusions <NUM>. In other embodiments, each segment may be provided with a greater or lesser number of protrusions. Instead of a bit retaining ring, each segment <NUM> is formed with a shoulder <NUM>, so that when the drive ring <NUM> is assembled, a continuous bit retaining shoulder <NUM> engages with the bit retaining shoulder <NUM> on the percussion bit to retain the bit in the hammer.

As shown in <FIG>, the bit retaining ring <NUM> of the embodiment shown in <FIG> may be provided as two part-annular bit retaining portions or halves 21a, 21b. In alternate embodiments, the ring <NUM> may be split into a greater number of portions. As can be seen in <FIG> and as indicated in <FIG>, the depth D of the holes <NUM> in the collar <NUM> of the drive ring <NUM> is greater than a height H of the bit retaining ring. This allows the percussion bit <NUM> to be removed from the hammer without removing the drive ring <NUM>. This may be achieved by withdrawing the bolts <NUM> from the holes <NUM> by a distance greater than or equal to the height H of the bit retaining ring portions but less than the depth D of the holes. As shown in <FIG>, the outer wear sleeve <NUM> can then be moved away from the percussion bit <NUM>, for example by lifting the hammer, thereby creating an annular space <NUM> between the forward end <NUM> of the wear sleeve and the internal shoulder <NUM> of the drive ring. The bolts <NUM> are still engaged in the holes <NUM> and so the drive ring <NUM> is still retained in the hammer.

As shown in <FIG>, as the hammer is lifted further, the percussion bit <NUM> drops out of the hammer, so that the bit retaining portion of the bit engages the halves 21a, 21b of the bit retaining ring <NUM>. The mass of the bit causes the halves to move in a radially outward direction into the annular space <NUM> such that they no longer retain the percussion bit in the hammer, as shown in <FIG>. This allows the bit to be removed or replaced without removing the drive ring from the hammer. A new bit may be inserted and the bit retaining ring halves 21a, 21b returned to the bit retaining position by way of pins <NUM>, shown in <FIG>, extending through the drive ring <NUM> and arranged to engage the halves 21a, 21b. In an alternate embodiment, a resilient o-ring may be provided around the bit retaining ring halves 21a, 21b to bias the halves inwardly such that they return to their original bit retaining position when the bit is removed. Once the new bit has been inserted, the hammer is re-assembled by moving the wear sleeve towards the bit and inserting the bolts fully into the holes.

A down-the-hole hammer according to an embodiment of a second aspect of the invention is illustrated in <FIG>. The hammer <NUM> comprises an outer wear sleeve <NUM> and a percussion bit <NUM> having a head portion <NUM> and a bit retaining shoulder <NUM> located at a forward end <NUM> of the outer wear sleeve. The hammer <NUM> also comprises a sliding piston <NUM> mounted for reciprocating movement within the outer wear sleeve to strike the percussion bit.

The hammer further comprises a drive ring <NUM> which has an annular collar <NUM> provided at a rear end <NUM> thereof, arranged to receive the forward end <NUM> of the wear sleeve such that the forward end of the wear sleeve abuts an internal shoulder <NUM> of the drive ring. A plurality of internally screw-threaded holes <NUM> are provided in a rear end <NUM> of the collar, and the rear end of the collar is arranged to abut a forward end <NUM> of a flange <NUM>. A plurality of through holes <NUM> are provided in the flange. Each through hole corresponds to one of the plurality of holes in the collar. A bolt <NUM> is inserted into each through hole <NUM> and screwed into the corresponding hole <NUM> in the collar to connect the drive ring to the wear sleeve and thus to the drive means of the percussion drill tool. The clamping effect of this bolted arrangement also holds the bit retaining ring <NUM> in place between the drive ring <NUM> and an aligner <NUM>. Splines <NUM> on the drive ring engage with complementary splines <NUM> on the percussion bit to transfer rotational drive to the bit.

As shown in <FIG>, the bit retaining ring <NUM> is provided as two part-annular bit retaining ring halves 21a, 21b. In other embodiments, the ring may comprise a larger number of part-annular portions. The depth D of the holes <NUM> in the collar <NUM> of the drive ring is greater than a height H of the bit retaining portions such that the percussion bit is removable from the drill tool by withdrawing the bolts <NUM> from the holes <NUM> by a distance greater than or equal to the height of the bit retaining portions 21a, 21b but less than the depth of the holes such that when the outer wear sleeve <NUM> is moved away from the percussion bit <NUM>, an annular space is formed between the forward end of the wear sleeve and the internal shoulder of the drive ring, into which the bit retaining portions are moveable in a radially outward direction such that they no longer retain the percussion bit in the drill tool. The percussion bit <NUM> can thus be removed from the hammer <NUM> without removing the drive ring <NUM>, in a similar fashion to that described above with reference to <FIG>.

The words "comprises/comprising" and the words "having/including" when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

Claim 1:
A fluid-operated percussion drill tool (<NUM>) comprising:
an outer wear sleeve (<NUM>) comprising a substantially cylindrical wall (<NUM>) and having inner (<NUM>) and outer (<NUM>) surfaces;
a percussion bit (<NUM>) having a head portion (<NUM>) and a bit retaining portion (<NUM>) and located at a forward end (<NUM>) of the outer wear sleeve;
a sliding piston (<NUM>) mounted for reciprocating movement within the outer wear sleeve to strike the percussion bit;
a drive ring (<NUM>) having a substantially cylindrical wall (<NUM>) and comprising connection means (<NUM>) adapted for connecting the drive ring to a drive means of the fluid-operated percussion drill tool; and
characterised by an annular flange (<NUM>) arranged around the outer wear sleeve at the forward end thereof, wherein the flange comprises a plurality of through holes (<NUM>) provided therein and is restrained from forward movement relative to the wear sleeve by engagement of an internal shoulder (<NUM>) provided on the flange with an external shoulder (<NUM>) provided at the forward end of the wear sleeve; and
wherein the connection means of the drive ring comprises an annular collar (<NUM>) provided at a rear end of the drive ring, the collar comprising a plurality of holes (<NUM>) provided in a rear end (<NUM>) thereof, wherein each hole corresponds to one of the plurality of through holes in the flange, the collar arranged to receive the forward end of the wear sleeve such that the forward end of the wear sleeve abuts an internal shoulder (<NUM>) of the drive ring and the rear end of the collar is arranged to abut a forward end (<NUM>) of the flange and wherein each through hole and corresponding hole in the collar is configured to receive a fastener (<NUM>) to connect the drive ring to the drive means of the percussion drill tool.