WO2013071360A1

WO2013071360A1 - Hammer bit shank enhancements

Info

Publication number: WO2013071360A1
Application number: PCT/AU2012/001417
Authority: WO
Inventors: Raymond Hill
Original assignee: Sandvik Intellectual Property Ab
Priority date: 2011-11-17
Filing date: 2012-11-16
Publication date: 2013-05-23

Abstract

This invention relates to a down-the-hole hammer drill, and has particular application (but need not be limited) to a reverse-circulation (RC) down-hole face sampling hammer drill. More particularly, a ratio of spline height to shank diameter is minimised without reducing an extent of torque transmissible via the splines. An associated drill bit and drive sub are also disclosed.

Description

HAMMER BIT SHANK ENHANCEMENTS

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 201 1904833, titled "HAMMER BIT

SHANK ENHANCEMENTS", and filed on 17 November 201 1. The entire content of this application is hereby incorporated by reference.

BACKGROUND

A drill bit of a percussive down-the-hole hammer drill (be it normal and reverse circulation (RC)) is conventionally provided with a splined shank, which locates within a splined drive sub, which in turn is threadably engaged to an end of a hammer barrel. The splines drive rotation of the drill bit while permitting this to move longitudinally (under the effect of the hammer) with respect to the drive sub.

The outside diameter of the drill bit shank must fit within the drive sub, which in turn screws into the base of the hammer barrel. The outside diameter of the outer cylinder is, in turn, determined by the size of the hammer, which is fixed for a particular model of drill.

Improvements in the design of RC hammer drills in particular have resulted in significantly increased power outputs. This power 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, due to the size constraints discussed above.

It is against this background and 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 of this invention, there is proposed a down-the-hole hammer drill comprising a drive sub comprising driving splines abutting driven splines on a drill bit, where the adjacent pairs of abutting driving and driven splines define between them an array of channels, each having a cross-sectional area which is substantially wider than it is high.

In one form, adjacent pairs of abutting driving and driven splines define between them an array of channels, each having a cross-sectional area which is in a range of one point one (1.1) to ten (10) times wider than it is high.

In one form, each channel has a cross-sectional area which is in a range of one point one (1.1) to five (5) times wider than it is high.

In a further aspect, the invention may be said to reside in a down-the-hole hammer drill comprising a drive sub comprising driving splines abutting driven splines on a drill bit, where, for each of the drive sub and drill bit, a spacing between adjacent splines is substantially greater than a spline height. In one form, spacing between adjacent splines is within a range of one point five ( 1.5) to ten ( 10) times greater than a spline height for each spline.

In one form, spacing between adjacent splines is within a range of one point five (1.5) to five (5) times greater than a spline height for each spline.

In one form, spacing between adjacent splines is within a range of one point one (1.1) to ten (10) times greater than a root thickness for each spline. In one form, spacing between adjacent splines is within a range of one point one (1.1) to five (5) times greater than a root thickness for each spline.

In a further aspect the invention may be said to reside in a drill bit for a down-the-hole hammer drill, the drill bit comprising a shank with an array of outwardly directed splines, wherein spacing between adjacent splines is substantially greater than a spline height and root thickness. In one form, spacing between adjacent splines is within a range of two (2) to ten (10) times greater than a spline height for each spline.

In one form, each spline has an asymmetric cross-sectional shape.

In one form, each spline has an abutting face and a non-abutting face which is longer than the abutting face. In one form, the abutting face of each spline is more steeply inclined than the non-abutting face. That is to say, the abutting face is more upright than the non-abutting face. In one form, each spline has a cross-sectional shape which is at least approximately triangular.

In one form, each spline comprises a top land connecting the abutting face and the non-abutting face, where the size of the top land between the faces is substantially less than that of a bottom land that extends between a pair of adjacent teeth on either of the drive sub or drill bit. In a further aspect, the invention may be said to reside in a down-the-hole hammer drill comprising a splined drive sub comprising driving splines abutting driven splines on a drill bit, where each spline has an abutting face and a non-abutting face which is longer than the abutting face.

In a further aspect the invention may be said to reside in a drill bit for a down-the-hole hammer drill, the drill bit comprising a spline having an abutting face and a non-abutting face which is longer than the abutting face.

In one form, for the or each spline the abutting face is more steeply inclined than the non-abutting face. That is to say, the abutting face is more upright than the non-abutting face. In a further aspect, the invention may be said to reside in a drill bit for a down-the-hole hammer drill, the drill bit comprising a shank with an array of outwardly directed splines, wherein a ratio of spline height to shank diameter is minimised without reducing an extent of torque transmissible via the splines, by way of comprising an increased number of smaller splines.

In one form, the diameter of the shank is within a range of six point seven (6.7) to ten (10) times greater than a spline height for each spline. In one form, the diameter of the shank is within a range of six point seven (6.7) to eight (8) times greater than a spline height for each spline. In a further aspect, the invention may be said to reside in a down-the-hole hammer drillcomprising a drive sub comprising driving splines abutting driven splines on a drill bit, where the adjacent pairs of abutting driving and driven splines define between them an array of channels, and wherein a ratio of spline height to shank diameter is minimised without reducing an extent of torque transmissible via the splines or effectiveness of lubricating air transmissible via the channels, by way of comprising an ^' increased number of smaller splines of increased radial spacing.

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 cross-sectional view taken lengthwise through a drive sub and drill bit of an RC hammer drill according to a first exemplary embodiment;

Figure 2 is a cross-sectional view, taken crosswise, through the drive sub and drill bit of Figure 1 ; Figure 3 is a cross-sectional view, taken crosswise, through the drive sub and drill bit of an RC hammer according to a second exemplary embodiment; and

Figure 4 is a cross-sectional view, taken crosswise, through a drive sub and drill bit of an RC hammer of the prior art.

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 Figures 1 and 2, where there is illustrated a pneumatically operated, reverse circulation, percussive down-the-hole hammer drill assembly (RC hammer) 1 comprising a drive sub 10 and a drill bit 20. The RC hammer 1 combines the hammer (or hitting) action with the turning action of rotary drilling.

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).

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 23 a. The diameter of the bore 30 is sized so as to be sufficiently large enough to convey the largest of the cuttings produced and passed from the bit face 23a to the bore by the sludge holes 32 (shown dashed). If the diameter Di of the bore 30 is too large it will reduce the material section of the shank 22 and thereby lead to higher stress levels within it. This can cause a significant reduction in the fatigue limit.

If the diameter Di of the bore 30 is too small it will restrict the flow of air and cuttings from the bit face 23a, increasing the back pressure and thereby reducing the flushing efficiency at the bit face 23a. This will potentially reduce the accuracy of the collected sample due to the extra material being forced past the transmission sleeve. It may also reduce the mechanical efficiency of the hammer 1 due to the increased restriction of the exhaust.

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.

Historically, RC bits and drive subs have both used square section splines (see Figure 4) with relatively large gaps between and around them being provided for exhaust air flow from the hammer. Significantly, when compared with conventional RC hammers of this type, the hammer 1 according to the present invention comprises a greater number of driving and driven splines 14 and 24. With a greater number of splines (or spline teeth), the torque transmitted per spline will be reduced (assuming all splines are evenly loaded), resulting in a lower shear stress at the root of each spline 14 and 24. This enables narrower splines 14 and 24 to be used.

Moreover, because there are more splines, the height of each spline may be reduced whilst maintaining the same total contact area between driving and driven splines 14 and 24 (assuming spline length remains the same). The shorter splines, combined with lower load per spline results in a reduced bending moment at the root of each spline, so the root thickness of the splines can be reduced.

Since the driven splines 24 are reduced in height, their root diameter (ie the diameter of the shank 22) can be increased.

Similarly, since the driving splines 14 are reduced in height, their root diameter (ie the inner diameter of the drive sub 10) can be increased.

So, in addition to there being a greater number of splines 14 and 24 than a conventional hammer, these splines are also smaller (in terms of both spline height and root thickness).

With the bore 30 and splines 14 and 24 sized so as to be no larger than is functionally necessary, the diameter Di of the annular cross section of the shank 24 of the drill bit 20 can be maximised so as to maximise the strength of the drill bit 20.

Should the width and cross-sectional area of the splines be undersized then during certain phases of operation (such as when the bit over reaches and the spline at the upper end of the bit impacts upon the bit retention rings) excessive damage and wear occurs that limit the life of the bit. This wear also places the bit at risk of being lost down the hole.

Another functional consideration to be taken into account is that RC down hole hammer drills of this type rely on a supply of clean lubricated air (ie oil entrained in air, or an oil mist) to operate reliably. To assist delivery of sufficient clean lubricated air, the adjacent pairs of smaller, more numerous abutting driving and driven splines 14 and 24 define between them an array of channels 40.

A pumping effect is created through the down hole hammer 1 by the pulsating pressures produced by the cyclic exhausting of the hammer's (not shown) top and bottom chambers, which drive its reciprocation. This effect will thereby assist delivery of the oil mist to the splines 14 and 24 via the array of channels 40 defined between the splines 14 and 24.

These channels 40 must be of sufficient cross-sectional area to enable the air to flow without excessive restriction. If smaller than optimum, the channels 40 will throttle the exhaust air flow from the hammer's top and bottom chambers and thereby reduce the impact power generated by the hammer.

Because the splines 14 and 24 (and channels in turn) are not as high, sufficient area and air flow in turn is assured by making the cross-sectional area of the channels 40 defined between the driving and driven splines 14 and 24 substantially wider than they are high.

So, in addition to there being a greater number of splines 14 and 24 than a conventional down hole hammer drill, these splines 14 and 24 are also smaller (in terms of both spline height and root thickness), and they are further spaced apart. Because the splines 14 and 24 are smaller, the design of these becomes critical, both in terms of maximising their mechanical strength, but also in terms of how they affect the air flow through the channels 40 defined between them.

Each driven (ie drill bit spline) 24 comprises an asymmetric, approximately triangular, cross-sectional shape (or profile) having an abutting (or working) face, and a non-abutting face which is longer than the abutting face. Since the shear stress increases linearly from the top of the spline to its root, it is a more efficient use of material and space if each spline profile is shaped in this way.

By 'approximately triangular', it is meant that the abutting and non-abutting faces of each spline are not parallel or even close to parallel, but inclined toward each other (ie converging) so as to either meet by intersecting or, preferably, separated by a top land of the spline. Where the approximately triangular splines of the present invention comprise a top land this is substantially shorter than the root dimension of the spline, and at most the same length as, but generally shorter than, the shorter of the abutting and non-abutting faces of each spline, so that the spline retains a generally triangular cross- sectional shape. The width of the 'top land' of each spline is important, as this should be sufficiently wide to accommodate the wear that occurs during use so as to not otherwise result in a reduction in the contact area between the abutting driving and driven splines that may result should a purely triangular spline profile (ie with no top land) be used. Although the wear on these faces for most bits is not significant compared with the wear of the bit components that interface the formation being drilled, the former normally only wearing a matter of microns during the life of the bit, it is known that bits which operate in relatively soft non-abrasive ground whereby the corresponding wear will be several millimetres during the. life of the bit.

In the embodiment illustrated, the abutting face of each spline 14 and 24 is more steeply inclined than the non-abutting face. That is to say, the abutting face is more upright than the non-abutting face, meaning, as a result, the non-abutting face is the longer of the two faces. This way there is additional material behind the abutting (or working) face, improving the strength of each spline.

Each spline 14 and 24 comprises a top land connecting the abutting face and the non-abutting face, where the size of the top land between the faces is substantially less than that of a bottom land that extends between a pair of adjacent splines on either of the drive sub 10 or drill bit 20. In this way, the spacing between adjacent splines is substantially greater than the spline height and root thickness of the driven splines 24.

Referring now to Figure 3, where in an alternative, the non-abutting face of each driving spline 14 on the drive sub 10 is radially blended (as opposed to straight cut) into the bottom land so as to maximise the flow area created between the splines 14 and 24.

While an RC hammer is discussed above, aspects of the disclosure made herein will be of use to conventional hammers and components (such as bits and drive subs) thereof.

It will be understood that the term "comprise" and any of its derivatives (eg comprises, comprising) as used in this specification is to be taken to be inclusive of features to which it refers, and is not meant to exclude the presence of any additional features unless otherwise stated or implied.

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.

Although an illustrative embodiment of the present invention has been described in the foregoing detailed description, it will be understood that the invention is not limited to the embodiment disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the scope of the invention as set forth and defined by the following claims.

Claims

1. A drill bit for a down-the-hole hammer drill, the drill bit comprising a shank with an array of outwardly directed splines, wherein spacing between adjacent splines is within a range of one point five (1.5) to ten (10) times greater than a spline height for each spline.

2. The drill bit of claim 1, wherein spacing between adjacent splines is within a range of one point one (1.1) to ten (10) times greater than a root thickness for each spline.

3. The drill bit as in either of the preceding claims, wherein each spline has an asymmetric cross- sectional shape. ,

4. The drill bit as in any one of the preceding claims, wherein each spline comprises an abutting and a non-abutting face, and these faces are not parallel but inclined toward each other so as to either meet by intersecting or being separated by a top land of the spline.

5. The drill bit of claim 4, wherein for each spline the non-abutting face is longer than the< abutting face.

6. The drill bit as in either of claims 4 or 5, wherein for each spline the abutting face is more steeply inclined than the non-abutting face.

7. The drill bit as in any one of claims 4 through 6, wherein for each spline the size of the any top land is substantially less than that of a bottom land that extends between a pair of adjacent splines.

8. The drill bit as in any one of the preceding claims, wherein each spline has a cross-sectional shape which is approximately triangular.

9. The drill bit as in any one of the preceding claims, wherein this is a drill bit for a reverse circulation down-the-hole hammer drill.

10. A drive sub for a down-the-hole hammer drill, the drive sub comprising an annular body with an array of inwardly directed splines, wherein spacing between adjacent splines is within a range of two (2) to ten (10) times greater than a spline height for each spline.

1 1. The drive sub of claim 10, wherein each spline has an asymmetric cross-sectional shape.

12. The drive sub as in either of claims 10 or 11,· wherein each spline comprises an abutting and a non-abutting face, and these faces are not parallel but inclined toward each other so as to. either meet by intersecting or being separated by a top land of the spline.

13. The drive sub as in any of claims 10 through 12, wherein for each spline the non-abutting face is longer than the abutting face.

14. The drive sub as in either of claims 12 or 13, wherein for each spline the abutting face is more steeply inclined than the non-abutting face.

15. The drive sub as in any one of claims 12 through 14, wherein for each spline the size of the any top land is substantially less than that of a^ottom land that extends between a pair of adjacent splines.

16. The drive sub as in any one of claims 10 through 15, wherein each spline has a cross-sectional shape which is approximately triangular.

17. A drill bit for a down-the-hole hammer drill, the drill bit comprising a shank with an array of outwardly directed splines, wherein a diameter of the shank is within a range of six point seven (6.7) to ten (10) times greater than a spline height for each spline.

18. A down-the-hole hammer drill comprising a drive sub comprising driving splines abutting driven splines on a drill bit, where the adjacent pairs of abutting driving and driven splines define between them an array of channels, each having a cross-sectional area which is in a range of one point one (1.1) to ten (10) times wider than it is high.

19. The down-the-hole hammer drill of claim 17, wherein this is a reverse circulation down-the-' hole hammer drill.