FIELD OF THE INVENTION The present invention relates a down-the-hole hammer drill. This invention has particular application to a reverse-circulation (RC) down-hole face sampling hammer drill, and for illustrative purposes, reference will be made to this application.

PRIORITY

This patent application claims priority from:

Australian Provisional Patent Application 2011904443, titled " RC HAMMER SPLINE

ARRANGEMENT IMPROVEMENTS", and filed on 26 October 2011.

The entire content of this application is hereby incorporated by reference. BACKGROUND OF THE INVENTION

A drill bit of a percussive down hole hammer (be it normal or reverse circulation (RC)) is conventionally provided with a bit body and splined shank. This shank locates within a splined drive sub, which in turn is threadably engaged to an end of a hammer barrel. The use of the spline between the drill bit and drive sub enables rotation of the drill bit with the hammer while at the same time allowing longitudinal movement of the drill bit with respect to the hammer. Examination of used RC bits very often indicates an uneven wear pattern of bit inserts and bit body.

It is against this background that the problems and difficulties associated therewith that the present invention has been developed. Certain objects and advantages of the present invention will become apparent from the following description, taken in connection with the accompanying drawings, wherein, by way of illustration and example, an embodiment of the present invention is disclosed.

SUMMARY OF THE INVENTION

In one aspect, the invention may be said to reside in a percussive down hole hammer comprising a drill bit having a working face (or cutting face), the percussive down hole hammer further comprising means for preferentially directing a fluid to at least one portion of the cutting face in preference to other portions of the cutting face to flush the cutting face.

In a further aspect, the invention may be said to reside in a percussive down hole hammer comprising a drill bit having a cutting face and a means for delivering a fluid to the cutting face, the means and the cutting face being operatively complimentary for the purpose of flushing the cutting face using the fluid.

In one form, the fluid is a flushing fluid and the cutting face is cleaned by the flushing of cuttings.

That is to say, delivery of fluid to the cutting face is tailored to the design of the cutting face to improve flushing of the cutting face.

Air supply to a head of known down hole hammers is evenly distributed (i.e. via flow through spline channels in RC bits or flushing holes in conventional DTH bits), but because the working/cutting (or strike) face geometry is typically asymmetric, a considerable amount of air escapes via the sample tube and external annulus without affecting rock cuttings that are generated during the fracturing process. The immediate consequences are: > Reduction of drilling performance in the form of reduced penetration rate because of re- crushing of rock debris instead of cutting removal;

> Reduction of drilling efficiency due to an increase of required compressor power; > Increase of bit wear due to insufficient bit-rock face cleaning (re-crushing of rock debris).

In one form of the present invention then, the means for preferentially directing fluid to the cutting face preferentially directs fluid to portions of the cutting face having increased flushing needs. In one form, the means for preferentially directing fluid to the cutting face directs more fluid to portions of the cutting face having increased flushing needs than other portions of the cutting face.

The load on a cutting face insert is the result of insert spacing combined with the fliiid flow at the cutting face. If the fluid at the rock-cutting face interface is properly directed, then the load on the individual inserts reduces, which ultimately leads to an increase in drilling performance. In one form, the means for preferentially directing fluid to the cutting face comprises at least one fluid passage (or channel).

In one form, the means for preferentially directing fluid to the cutting face comprises at least two passages (or channels), where each channel directs fluid to a different portion of the cutting face, and at least one channel delivers a greater flow rate of fluid than the other.

In one form, the percussive down hole hammer comprises a splined drive sub comprising driving splines abutting driven splines on a shank of the drill bit.

In a further aspect, the invention may be said to reside in a drill bit for the above described percussive down hole hammer.

In yet a further aspect, the invention may be said to reside in a drive sub for the above described percussive down hole hammer.

In one form, the hammer is an RC hammer, and there is a channel defined between adjacent pairs of abutting splines, and fluid is supplied via the or each channel. The operating principle of RC hammers makes this invention particularly suitable for these. The main flow direction at the working (i.e. bit) face is from outside to inside, i.e. from the outer of the cutting face diameter inwards towards the hammer axis. The air distribution around the bit head is strongly affected by the flow field upstream of the cutting face and therefore offers potential to optimize the local supply of the flushing media to inserts with increased need for debris removal.

In one form, not all channels are of equal dimensions.

In one form, not all channels are equi-spaced around the circumference of the drill bit and drive sub. In one form, at least one channel is larger than others. In one form, at least one channel is wider than others. In one form, not all splines are of equal dimensions.

In one form, not all splines are equi-spaced around the circumference of the drill bit and drive sub. In one form, at least one spline is larger than others, In one form, at least one spline is wider than others.

In one form, the splines are not distributed symmetrically around their respective diameters.

In one form, the pitch angle between two neighbouring splines varies as a function of angle on the circumference.

In one form, a variation of the spline pitch angle and/or spline thickness of driving and/or driven splines may be limited to one or more sectors of the circumference or be continuous.

In one form, the spline variations are incorporated in a way that the parts cannot be misassembled (e.g. relative position of drive-sub to shank).

In one form, where the basic geometry does not prevent such mis-assembly, then features such as notches or shoulders are used and positioned so that these prevent mis-assembly.

In one form, to either side of the drill bit there are two driven splines (i.e. two pairs of these) spaced so that the width between these two splines is greater than the width between any other two splines around the drill bit.

In one form, to either side of the drive-sub there are two driving splines (i.e. two pairs of these) spaced so that the width between these two splines is greater than the width between any other two splines around the drive-sub.

In one form, one of each of the driving splines in these two pairs is considerably wider than the remainder of the driving splines.

In one form, the larger channels are primary channels, and smaller channels are secondary channels.

In one form, the primary channels direct fluid to sample holes in the cutting face.

In one form, in an alternative, the primary channels direct fluid substantially orthogonal to sample holes in the cutting face. For normal percussive down hole hammers the means for preferentially directing fluid to the cutting face comprises more than one channel having an outlet in the cutting face.

In one form, each outlet is a hole, and hole diameters are not constant but varying in size.

In a further aspect, the invention may be said to reside in a means for cleaning a cutting face of a percussive down hole hammer comprising a drill bit and a drive sub, wherein said means preferentially directs a fluid to at least one portion of the cutting face in preference to other portions of the cutting face. In a further aspect, the invention may be said to reside in a down-the-hole hammer comprising a drill bit and a drive sub, the drill bit comprising a shank, and a head having a cutting face, the drive sub surrounding at least a portion of the shank and cooperating with the drill bit to form fluid passages extending lengthwise along the shank to direct fluid to the cutting face to flush this, where each passage directs fluid to a different portion of the cutting face, and at least one passage is adapted to deliver a greater flow rate of fluid than the others, thereby directing fluid to at least one portion of the cutting face in preference to other portions thereof.

In a further aspect, the invention may be said to reside in a drill bit for a down-the-hole hammer comprising a shank, a head having a cutting face, and fluid passages extending lengthwise along the shank to direct fluid to the cutting face to flush this, where each passage directs fluid to a different portion of the cutting face, and at least one passage is adapted to deliver a greater flow rate of fluid than the others, thereby directing fluid to at least one portion of the cutting face in preference to other portions thereof.

In a further aspect, the invention may be said to reside in a drive sub for a down-the-hole hammer having a drill bit comprising a shank, and a head having a cutting face, the drive sub surrounding at least a portion of the shank and cooperating with the drill bit to form fluid passages extending lengthwise along the shank to direct fluid to the cutting face to flush this, where each passage directs fluid to a different portion of the cutting face, and at least one passage is adapted to deliver a greater flow rate of fluid than the others, thereby directing fluid to at least one portion of the cutting face in preference to other portions thereof.

A detailed description of one or more embodiments of the invention is provided below along with accompanying figures that illustrate by way of example the principles of the invention. While the invention is described in connection with such embodiments, it should be understood that the invention is not limited to any embodiment. On the contrary, the scope of the invention is limited only by the appended claims and the invention encompasses numerous alternatives, modifications and equivalents. For the purpose of example, numerous specific details are set forth in the following description in order to provide a thorough understanding of the present invention.

The present invention may be practiced according to the claims without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the invention has not been described in detail so that the present invention is not unnecessarily obscured.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of this disclosure it will now be described with respect to one or more exemplary embodiments, which shall be described herein with the assistance of drawings wherein: Figure 1 is a perspective view of a drive sub;

Figure 2 is an end view of the drive sub of Figure 1;

Figures 3 and 4 are perspective views of a drill bit;

Figure 5 is a perspective view of the assembled drive-sub and drill bit;

Figure 6 is a cross-sectional view, taken lengthwise, through the drive-sub and drill bit of Figure 5; and

Figure 7 is a cross-sectional view, taken crosswise, through the drive-sub and drill bit of Figure 5.

In the following description, like reference characters designate like or corresponding parts throughout the several views of the drawings.

DESCRIPTION OF A PREFERRED EMBODIMENT

Referring now to Figure 1, where there is illustrated drive-sub 10 for a pneumatically operated (i.e. in which air is the working and flushing fluid) percussive down hole RC hammer that combines the hammer (or hitting) action with the turning action of rotary drilling. This drive sub 10 comprises an annular sleeve 12 with an array of spaced apart, inwardly directed driving splines 14.

Referring now to Figures 3 and 4, where there is further illustrated a drill bit 20 for the RC hammer, the drill bit 20 comprising a shank 22 and a drill bit head 23, the drill bit head 23 having a cutting face 21 with carbide inserts 29. The shank 22 comprises 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 cutting faces when the bit 20 is inserted into the drive sub 10 (see Figure 6). A channel 25 is defined between adjacent pairs of abutting splines 14 and 24 (see Figure 7).

In use, 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.

With reference to Figure 7, it can be seen that to either side of the drill bit 20 there are two driven splines 24a and 24b (i.e. two pairs of these) spaced so that the width between these two driven splines 24a and 24b is greater than the width between any other two splines 24 around the shank 22 of the drill bit 20.

To either side of the drive-sub 10 there are two driving splines 14a and 14b (i.e. two pairs of these) spaced so that the width between these two splines 14a and 14b is greater than the width between any other two splines 14 around the drive-sub 10. One of each of the driving splines 14a in these two pairs is considerably wider than the remainder of the driving splines 14.

When the drive-sub 10 and drill bit 20 are assembled the two widest driving splines 14a locate between the most adjacently distant driven splines 24a and 24b so as to define between them a pair of passages (or channels) 25a which are larger (i.e. these are primary channels) than any of the other channels 25 (i.e. secondary channels) defined between adjacent pairs of abutting splines 14 and 24.

The mass flow rate of air directed down through the channels is not the same for each channel, but a function of the channel size, so a greater mass flow rate of air is passed through the primary channels 25a than is passed through the secondary channels 25.

By guiding the flushing air unequally around the shank 22 and to the perimeter of the head 23 of the bit 20, it is possible to direct air to areas of the cutting face 21 with increased flushing needs, such as around inserts 29 under high loads (i.e. critical inserts) and then to the inlets 40 for the "inner tube" 42, which returns the air (which now carries the entrained flushed cuttings) to the surface. If the fluid at the rock-cutting face 21 interface is properly directed by complimentary positioning of the primary channels 25 a relative to the critical inserts, then the load on inserts 29 reduces, which ultimately leads to an increase in drilling performance. Any machining method may be utilised for realizing these channels. Naturally, methods which are cost effective are given priority over machining procedures that require long machining times or pose otherwise special requirements on the manufacturing process Throughout the specification and the claims that follow, unless the context requires otherwise, the words "comprise" and "include" and variations such as "comprising" and "including" will be understood to imply the inclusion of a stated integer or group of integers, but not the exclusion of any other integer or group of integers.

The reference to any prior art in this specification is not, and should not be taken as, an

acknowledgement of any form of suggestion that such prior art forms part of the common general knowledge.

It will be appreciated by those skilled in the art that the invention is not restricted in its use to the particular application described. Neither is the present invention restricted in its preferred embodiment with regard to the particular elements and or features described or depicted herein. It will be appreciated that various modifications can be made without departing from the principles of the invention. Therefore, the invention should be understood to include all such modifications in its scope.