FIELD OF THE INVENTION

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.

PRIORITY

This patent application claims priority from:

Australian Provisional Patent Application No 2012900207, titled "HAMMER IMPROVEMENTS", and filed on 19 January 2012.

The entire content of this application is hereby incorporated by reference.

BACKGROUND

Recent developments in down-the-hole hammers has resulted in a hammer having a reverse circulation system (i.e. an RC hammer) which produces considerably greater power than existing hammers of equivalent size.

When drilling in particularly hard rock with a rotary percussion drill bit, the bit impacts the rock and crushes / fractures the rock face beneath the inserts located within the head of the bit. Work is expended in crushing and fracturing the rock, with this energy being transferred from the bit to the rock via hard inserts located in the face of the bit. However not all of this energy is transferred in this way, and a certain proportion elastically deforms the rock and is subsequently transferred back to the bit, the amount of energy returned in this way being dependent on, amongst other parameters, the resilience of the rock.

As a result of this reflection of energy, 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.

It is against this background, and the problems and difficulties associated therewith, that the present invention has been developed. Other 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 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.

In one form, the contact area is substantially planar.

In one form, the contact area is normal to the direction of elongation of the channel.

In one form, the contact area is a shoulder created by stepping down of the channel width.

In one form, a plurality of spaced apart channels extend lengthwise along the shank toward the head.

In one form, the position of the contact area is, for each channel, at the same point along the channel.

In one form, both portions of each respective channel has a longitudinal centre line, and these centrelines are substantially longitudinally aligned.

In one form, both portions of each respective channel has a longitudinal centre line, and these centrelines are longitudinally mis-aligned.

In one form, the centreline of the narrow channel portion is offset to one side of the centreline of the wider channel portion.

In one form, 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.

In one form, at least a portion of each channel is defined between a pair of adjacent splines extending lengthwise along the bit shank.

In one form, the driver for the bit is a drive sub.

In one form, the or each contacting portion of the driver is a portion of an annular face thereof. In one form, the bit is for a reverse circulation (RC) percussive down-the-hole hammer. In a further aspect 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.

In one form, 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.

In one form, the elongate space is substantially longitudinally aligned with the narrower channel portion.

In one form, the elongate space is of similar cross-sectional area to the narrower channel portion.

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 an assembly comprising a drill bit, drive sub and bit retaining ring; and

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. 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 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).

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.

Thus, rotation is transmitted to the case by means of the drill string (not illustrated), and the bit 20 is thus driven in rotation by the drive sub 10 while being impacted upon by the piston.

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. With reference to Figure 2, it can be seen that the width of 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.

In contrast to the above described arrangement, normal practise for the manufacture of bits of the prior art is to cut an axial groove of constant width along the bit, the width of which is selected to accommodate the driving spline of the drive sub. The result is that there exists a rapid increase in conduit flow area once the air travels past the end of the driving spline. This increase in area creates turbulence in the air flow, which in turn causes an unnecessary pressure loss.

A significant advantage of the present invention then, 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.

Moreover, in drill bits of the prior art, a result of the reflection of energy discussed in the background portion of this specification is that the bit is accelerated upwards, whereupon it impacts the adjacent face of the bottom of the drive sub. When high energy levels are present this can cause damage to either or both the bit head and the drive sub. Typically the damage will be manifest as either or both:

• Plastic material deformation of the impact land between adjacent air conduits at the back of the bit head, and • Plastic flow in the form of indentations produced in the adjacent area on the bottom face of the driver sub.

This deformation in turn has several consequences as follows:

• The sideways circumferential material flow at the back of the head causes a restriction /

obstruction to the exhaust air that is directed to the perimeter of the bit head

• As a result of the bit head indentation into the drive sub the bit can then move further into the base of the hammer and effectively raise the impact plane between the piston and bit during hammer operation. This changes the height of the switching points for the air flow into and out of the bottom chamber of the hammer and thereby can change its tuning, impacting both the power and the efficiency.

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.

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.