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; whilst it is not so limited, for illustrative purposes, reference will be made to this application.

PRIORITY

This patent application claims priority from:

Australian Provisional Patent Application No 2012900209, titled "HAMMER BIT RING 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 (RC hammer) which produces considerably greater power than existing hammers of equivalent size. This power of the down-the-hole hammer is transmitted from the hammer to the ground via the bit. Recent field tests by the applicant have demonstrated that the durability of the bits has been significantly reduced due to the higher stress levels created within the shank of the bit in particular. This has led to the need to increase the strength of the RC bits in order to produce a commercially viable product. However, the shank of the bit cannot be strengthened by merely making this larger as there are critical operational constraints that limit both the internal diameter of the bit and the external diameter of the drive sub.

In addition to the above, there is a requirement for an effective flow of exhaust air from the piston (or hammer) to the bit face. Analysis of the flow areas through the bit and drive sub interface indicate that one of the most restrictive areas for this flow is a bit retaining ring. It is against this background that 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 percussive down-the-hole hammer drill assembly comprising a drill bit having an elongate shank and a head, and a bit retention element disposed around the shank of the bit and comprising one or more channels for the passage of fluid along the bit.

In one form, the bit comprises at least one channel extending lengthwise along the shank toward the head thereof, and where for each bit channel the bit retention element comprises an aligned and opposing (or facing) channel.

In one form, the bit and bit retention element each comprise means operatively associated to maintain retention of the bit by the bit retention element.

In one form, the bit retention element comprises means for maintaining alignment of the respective channels of the bit and bit retention element.

In one form, bit comprises means for maintaining alignment of the respective channels of the bit and bit retention element. In one form, the bit and bit retention element each comprise means operatively associated to maintain alignment of the respective channels of the bit and bit retention element.

In one form, the hammer drill assembly further comprises a drive sub comprising means for maintaining alignment of the respective channels of the bit and bit retention element.

In one form, the bit and the drive sub each comprise means operatively associated to maintain alignment of the respective channels of the bit and bit retention element.

In one form, the bit shank has a circular cross-section shape and the bit retention element is shaped like a ring.

In one form, the hammer is a reverse-circulation (RC) down-hole face sampling one.

In a further aspect the invention may be said to reside in a percussive down-the-hole hammer drill assembly comprising a drill bit having an elongate shank and a head, and a bit retention ring disposed around the shank of the bit and comprising one or more channels defined in an inner diameter, annulus thereof for the passage of fluid along the bit.

In a further aspect the invention may be said to reside in a bit retention element for retaining a bit for a percussive down-the-hole hammer, the bit having an elongate shank and a head, wherein the bit retention element is adapted to be disposed around the shank of the bit and comprises one or more channels for the passage of fluid along the bit. In one form, the bit comprises at least one channel extending lengthwise along the shank toward the head thereof, and for each bit channel the bit retention element comprises an aligned and opposing channel.

In one form, the bit retention element further comprises means for maintaining alignment of the respective channels of the bit and bit retention element.

In one form, the bit retention element is shaped like a ring, and the or each of the channels thereof is defined in an inner diameter annulus thereof.

In yet a further aspect, the invention may be said to reside in a reverse-circulation (RC) down-hole face sampling hammer drill assembly comprising a bit having an elongate shank, a head, and at least one channel extending lengthwise along the shank toward the head thereof, the assembly further comprising a bit retention element disposed around the shank of the bit, and where for each bit channel the bit retention element comprises an aligned and opposing channel for the passage of fluid along the bit.

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:

Figures 1 through 3 are perspective views of an assembly comprising a drill bit, drive sub and bit retaining ring;

Figures 4 through 6 illustrate the drill bit and bit retaining ring without the drive sub, which has been removed to permit visibility of the remaining components;

Figure 7 is an end view of the assembly illustrated in Figures 1 through 3, taken from the end distal the head of the bit; Figure 8 is a cross-sectional view taken through the shank of the bit;

Figures 9 and 10 are perspective views of the bit retaining ring in isolation; and

Figure 1 1 is a side view of the drive sub.

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 the Figures, 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 with 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 splines 14 and driven splines 24.

The reverse circulation system involves the downward circulation of a flushing medium, such as 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.

At their upper ends external bit splines comprise outwardly extending annular radial shoulders 50 which form retention lugs configured to rest on the bit ring 60 so as to limit the travel of the bit 20 and retain this in the drive sub 10.

Adoption of a bit 20 design in which the root diameter of the splines 24 is maximised to increase the strength of the bit 20 would exacerbate the flow restriction beneath bit rings of hammer drills of the prior art, adversely affecting the performance of the hammer. Moreover, because the primary function of the bit retaining ring 60 is to retain the bit 20 within the drive sub 10 when the components are assembled, the features achieving this must be robust, because if the bit 20 becomes wedged in the bottom of a hole, high tensile loads (in excess of 40 tonne) may be applied during the extrication process.

In addition to the shear loads that may be applied to the bit ring 60 and shank retaining lugs 50, it is necessary that these features be able to withstand high cyclic impact loads, such as those produced when drilling soft ground using high air pressures, thereby causing significant reaching of the bit 20. This situation also arises when drilling through stopes and voids and the like, and also when lifting off bottom and engaging 'flushing' mode. These conditions are all frequently encountered during normal drilling operations. In order to address this requirement the bit rings 60 and retaining lugs 50 require relatively high surface hardness in order to prevent unacceptable deformation, as well as requiring a tough core to counter the associated brittleness of such a surface.

A means by which these structural requirements may be met whilst simultaneously minimising the restriction of the air flow in the space available is for the inner diameter edge of the annular bit ring 60 to define a plurality of channels 62, there being one for and aligned with each bit channel 40. In the embodiment illustrated, and as best illustrated in Figures 9 and 10, each bit ring channel 62 is a curved recess, circle segment (or scallop) formed into the inner edge of the annular bit ring 60. These bit ring channels 62 improve air flow past the bit ring 60, thereby improving the efficiency of the hammer. It will be apparent however that these bit ring channels 62 may be of other shapes.

This approach enables full contact to be made between the matching faces of the retention lugs 50 and the bit ring 60, thereby minimising the contact pressures generated when over reaching, whilst maximising the venting of the hammer exhaust air through the assembly.

A further requirement of such a design, particularly when the bit ring 50 is significantly scalloped relative to the fine profile used on the driven splines 24, is that should the bit 20 be rotated in the reverse direction the driving and driven splines 14 and 24 should remain adjacent and in close proximity to each other. By keying the bit retaining ring 60 relative to either of the bit 20 or drive sub 10, this ensures that the bit ring channels 62 remain misaligned with respect to the retaining lugs 50 (so as to prevent the bit 20 from dropping out of the drive sub 10), and ensure that each bit ring channel 62 remains aligned with its respective bit channel 40 (see Figures 7 and 8).

In the embodiment illustrated, the bit ring 60 is keyed to the drive sub 10 by diametrically opposed alignment lugs 64 extending from the bit ring 60 into slots 70 of matching shape in the drive sub 10. Alternatively, this arrangement may be reversed, or the bit ring 60 may be keyed to the drill bit 20 using a similar arrangement of keyed slot(s) and retaining lug(s). Moreover, it is desirable that the splines 14 and 24 are designed so that excessive backlash is prevented should reverse rotation be applied to the drill string and hammer, thereby ensuring that the bit ring channels (or scallops) 62 remain misaligned with respect to the bit retaining lugs 50.

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.