WO2010086576A1

WO2010086576A1 - A drill bit assembly

Info

Publication number: WO2010086576A1
Application number: PCT/GB2009/000262
Authority: WO
Inventors: Christopher David Bond
Original assignee: Halco Drilling International Limited
Priority date: 2009-01-30
Filing date: 2009-01-30
Publication date: 2010-08-05

Abstract

A drill bit assembly for a down-the-hole hammer drill, the assembly comprising: a drill bit (21) having a drill bit head (22) with a cutting face (39) and a drill bit shank (23); a chuck (24) for receiving the drill bit shank, the chuck having a radial groove (31) around the external circumference thereof and attachment means (32) for attachment to a hammer assembly of the drill; a locking collar (25) for receiving the drill bit and the chuck, the collar having at a first end thereof a radial projection (35) on the internal circumference of the collar for seating in the radial groove of the chuck and at a second end thereof a radial retaining lug (33) on the internal circumference of the collar; and a sleeve (26) for surrounding the locking collar and holding the locking collar in place, in use the sleeve being clamped between the chuck and a cylinder (28) of the hammer assembly, when the chuck is attached to the hammer assembly; wherein the drill bit head is provided with at least one channel (30) and the drill bit assembly further comprises at least one retaining arm (29) which is dimensioned and configured to be engaged at a first portion thereof in a channel of the drill bit head and at a second portion thereof is retained by the radial retaining lug of the locking collar.

Description

A DRILL BIT ASSEMBLY

The present invention relates to a drill bit assembly and more particularly to an improved drill bit assembly for a down-the-hole (DTH) hammer drill assembly.

Down-the-hole drilling or DTH drilling is a type of drilling often used in the drilling of hard rock. The term "down-the-hole" refers to the fact that the percussion mechanism follows the drill bit down into the hole which is being drilled. Typically, the percussion mechanism, known as the hammer, is located directly behind the drill bit. Drill pipes are connected to the hammer and these provide pneumatic force to the hammer. As the hole gets deeper, the drill pipes are fed down the hole.

The hammer incorporates a pneumatically operated piston by means of which successive blows are struck on the upper end of the drill bit shank to cause the lower, operative end or head of the drill bit to break away material from the lower end of the bore hole.

One problem associated with down-the-hole drilling is that there is a possibility that during the drilling the drill bit portion of the hammer assembly could suffer a breakage laterally either through the shank of the drill bit or through the head of the drill bit. This can cause the broken part of the drill bit to remain at the bottom of the bore hole so that the driller, having removed the drilling assembly, would have to carry out expensive and time consuming "fishing" i.e. retrieval procedures to remove the broken section of the drill bit from the hole before the drilled hole can be used. The drill bit assembly of the present invention overcomes the problems associated with a possible breakage of the drill bit head or shank by ensuring that the drill bit is securely retained to the hammer assembly along its entire length. Therefore, if a breakage were to occur at any point along the drill bit head or shank then the whole of the drill bit can nevertheless be retracted from the bore hole, leaving the drilled hole clear for use.

According to the present invention, there is provided a drill bit assembly for a down-the-hole hammer drill, the assembly comprising:

a drill bit having a drill bit head with a cutting face and a drill bit shank;

a chuck for receiving the drill bit shank, the chuck having a radial groove around the external circumference thereof and attachment means for attachment to a hammer assembly of the drill;

a locking collar for receiving the drill bit and the chuck, the collar having at a first end thereof a radial projection on the internal circumference of the collar for seating in the radial groove of the chuck and at a second end thereof a radial retaining lug on the internal circumference of the collar;

and a sleeve for surrounding the locking collar and holding the locking collar in place, in use the sleeve being clamped between the chuck and a cylinder of the hammer assembly, when the chuck is attached to the hammer assembly;

wherein the drill bit head is provided with at least one channel and the drill bit assembly further comprises at least one retaining arm which is dimensioned and configured to be engaged at a first portion thereof in a channel of the drill bit head and at a second portion thereof is retained by the radial retaining lug of the locking collar.

Preferably the drill bit head is provided with two or more channels and the assembly further comprises two or more corresponding retaining arms.

Advantageously the drill bit head is provided with three channels and the assembly further comprises three corresponding retaining arms.

Alternatively the drill bit head is provided with four channels and the assembly further comprises four corresponding retaining arms.

Conveniently the or each retaining arm or arms is engaged with a first part of the channel which is on or adjacent to the drill bit face and a with a second part of the channel that is set back from the drill bit face in the direction of the drill bit shank.

Preferably the or each retaining arm or arms is substantially L-shaped and wherein the first portion of the L is engaged with a first part of the channel which is on or adjacent to the drill bit face and wherein the second portion of the L is engaged with a second part of the channel that is set back from the drill bit face in the direction of the drill bit shank.

Advantageously the or each retaining arm or arms is provided with a groove at the second portion thereof, the groove being dimensioned and configured to receive the radial retaining lug of the locking collar, thereby retaining the or each retaining arm or arms. Conveniently the drill bit head is provided with a groove, and the groove of the drill bit head is dimensioned and configured to receive the radial retaining lug of the locking collar.

Preferably the groove on the drill bit head and the groove or grooves of the or each retaining arm or arms are mutually flush and wherein the combination of grooves from the drill bit head and the or each retaining arm or arms is dimensioned and configured to receive the radial retaining lug of the locking collar.

Advantageously the locking collar comprises two separable sections with respect to the longitudinal axis of the collar.

Preferably the sleeve comprises a radial abutment which, in use is clamped between the chuck and the cylinder thereby holding the sleeve in place.

Conveniently the attachment means comprises a screw thread.

Embodiments of the invention are described below with reference to the accompanying drawings in which:

Figures 1A, 1 B and 1 C show, in different positions, but in mutually perpendicular longitudinal sections a conventional down-the-hole hammer drill assembly as known in the prior art;

Figure 2 is an exploded perspective view of a drill bit catcher system according to the prior art;

Figure 3 is an exploded perspective view of a further drill bit catcher system according to the prior art; Figure 4 is an exploded perspective view of yet a further drill bit catcher system according to the prior art;

Figure 5 is an exploded perspective view of a drill bit assembly according to the present invention, with two retaining arms;

Figure 6 is an exploded perspective view of a drill bit assembly according to the present invention, with three retaining arms;

Figure 7 shows a longitudinal cross section of the drill bit assembly according to figure 6 in an operative drilling position;

Figure 8 shows a longitudinal cross section of the drill bit assembly according to figure 7 in the event of a failure in the shank of the drill bit;

Figure 9 shows a longitudinal cross section of the drill bit assembly according to figure 7 in the event of a failure in the head of the drill bit; and

Figures 10A-F illustrate, in exploded perspective view, the sequential assembly of a drill bit assembly according to figure 5.

Referring firstly to figures 1A, 1 B and 1C, there is illustrated a conventional down-the-hole arrangement in which a drill bit 1 having a drill bit head 2 and a drill bit shank 3 is retained within a splined chuck 4 by means of a retaining ring 5. In figures 1A, 1 B and 1C the bore hole being drilled is represented by reference numeral 6 and the bottom of the drilled hole is represented by reference numeral 7.

Figure 1A shows the in-use drilling position of the conventional down-the-hole hammer assembly. When drilling has completed and the hammer assembly is pulled back out of the hole, the drill bit retaining ring 5 ensures that the drill bit 1 is removed from the drilled hole 6 together with the entire hammer assembly (see figure 1B).

However, if the drill bit 1 was to suffer a lateral breakage below the level of retaining ring 5, in other words deeper down the hole than the position of the ring 5 then, as shown in figure 1C, when the hammer assembly is retracted from the drilled hole 6 the portion of the drill bit 1 below the breakage remains at the bottom of the hole 7. In this event, the driller would need to carry out an expensive and time consuming fishing procedure to remove the broken section of the drill bit 1 from the hole 6 before the drilled hole 6 can be used.

Several prior attempts have been made in the art to overcome this problem, using so called bit-catcher systems. However, all of the solutions proposed in the prior art have their own drawbacks and problems.

US Patent No. 5,065,827 in the name of Smith International describes one prior art attempt to solve the aforementioned problem. This is illustrated generally in figure 2.

The Smith International system uses a threaded shroud 10 that fits over the chuck 4 and is screwed past a corresponding thread 11 on the back of the drill bit head 2. The entire drill bit 1 , chuck 4 and shroud 10 is then screwed into the hammer of the drill assembly, thereby clamping the threaded shroud 10 in place between the chuck 4 and the cylinder of the hammer (not shown). If the drill bit 1 was to suffer a lateral breakage during operation then the head 2 of the bit 1 is not be able to pass through the threaded shroud 10 and would be removed from the hole being drilled when the hammer is pulled out. Furthermore, US Patent No. 6,827,162 in the name of CT Rock lnc also presents a prior proposed bit catcher system, which is here illustrated in figure 3. The CT Rock lnc system also uses a shroud 12 in which the shroud 12 has a retaining shoulder 13. The shroud 12 is split into two halves 12A and 12B and these two halves 12A and 12B are placed over the drill bit 1 and the chuck 4 and are held together by a square section ring (not shown). As with the Smith International system, in the CT Rock lnc system the drill bit 1 , chuck 4 and shroud 12 are screwed into the hammer (not shown) thereby clamping the shroud 12 in place between the chuck 4 and the cylinder of the hammer. A retaining shoulder 14 is machined into the back of the bit head 2 and if the bit 1 was to break during operation, the retaining shoulder 14 and the corresponding shoulder 13 on the shroud 12 would prevent the broken portion of the bit head 1 from remaining in the hole when the hammer is pulled out.

Although widely used, both of the systems described in US 5,065,827 and US 6,827,162 have a common design flaw and are not considered in the art to be an adequate solution to the problem of retaining the entire drill bit where a failure occurs. Both of the above mentioned prior art proposals are prone to experience failures of the drill bit below the catcher system, i.e. at the point of the drill bit deeper in the hole than the position of the respective catcher system. When such a failure occurs, the head portion of the bit is not retained within the catcher system and is left at the bottom of the hole when the hammer is removed. Therefore, although a catcher system has been fitted the catcher system has not completely removed the need to carry out fishing procedures to remove damaged portions of drill bit from the drill hole should such a lateral failure occur. The above mentioned systems only retain the drill bit when a failure occurs through the shank of the drill bit and not through the head of the drill bit. A further bit catcher system is described in US Patent 6,789,632 in the name of Halco Drilling International Ltd. This is illustrated generally in figure 4. In the Halco system, the back of the bit head 2 is provided with a series of machined slots 15A and 15B. These slots 15A and 15B are in corresponding positions on the bit head to externally machined channels 16A and 16B on the chuck 4. The Halco system also provides a shroud 17 having internal lugs 18A and 18B. The lugs 18A and 18B on the shroud 17 are dimensioned and configured to pass through channels 16A, 16B on chuck 4 and slots 15A and 15B on the drill bit head 2.

In use, the shroud 17 is passed over the chuck 4 and onto the drill bit head 2 such that the lugs 18A and 18B pass through channels 16A and 16B and into slots 15A and 15B. Shroud 17 is then rotated so that the lugs 18A and 18B are caught in pockets, for example pocket 19 in the bit head 2. A number of pegs 20 are subsequently inserted through the channels 16A, 16B and slots 15A, 15B to prevent lugs 18A and 18B from the rotating back out of pockets 19.

Therefore, in the event of a drill bit breakage, the drill bit head 2 is still retained by the bit catcher system, even if it is the head of the drill and not the shank of the drill bit which has broken. However, due to the arrangement of machined slots 15A, 15B and pockets 19 on the drill bit head 2, this system is time consuming and costly to manufacture. Also, due to the extra head length required to accommodate these features, a great deal of weight is added to the bit 1 that could itself contribute towards a potential failure in this area. Moreover, like both the Smith International and CT Rock systems, any failure of the bit head 2 below the bit catcher system (i.e. below the position of the channels 15A, 15B and pockets 19) would mean that broken parts of drill bit could still be lost to the hole such that a fishing operation would need to be carried out. Accordingly, there is a need in the art for a bit catcher system which can catch the entire bit, including the head, in the event of a breakage of the drill bit during the drilling operation. The system should be easy to manufacture and should not add excessive weight to the overall drilling assembly. The present invention meets these needs.

Figure 5 illustrates an embodiment of the drill bit assembly according to the present invention. It is to be appreciated that the embodiment depicted and discussed below is a preferred embodiment of the invention and that the invention is only limited by the language of the attached claims.

Figure 5 shows a drill bit assembly which corresponds in some respects to a conventional down-the-hole drilling assembly as previously described in Figure 1. The assembly has a drill bit 21 with drill bit head 22, drill bit shank 23 and a drill bit face or cutting face 39, which is at the extremity of the drill bit head 22 and will be at the bottom of a hole being drilled during a drilling operation. Once more, there is provided a chuck 24 and a tubular locking collar 25 which, as illustrated, is split longitudinally into two halves 25A and 25B of generally semi-circular cross section. There is also provided a tubular sleeve 26 and bit retaining rings 27. The whole assembly is to be screwed to cylinder 28 which represents the operative end of the drill hammer.

As shown in Figure 5 there may also be provided a bit retaining ring 27 which can be split into two halves 27A and 27B. Bit retaining rings 27 are dimensioned and configured to fit onto the bit shank 23.

The present invention provides at least one retaining arm 29. In the described embodiment, two retaining arms 29 are shown although it is to be appreciated that a different number of retaining arms could be provided, dependent upon the drill bit diameter and weight. In the depicted embodiment, the retaining arms have a substantially L shape.

As can be seen most clearly in figure 5, the drill bit head 22 is provided with at least one channel 30 that corresponds to the shape and dimension of the retaining arm 29. In figure 5, two channels 30 are depicted because there are two retaining arms 29. The L shaped retaining arms are to be inserted into the corresponding channels 30 and, the projecting foot of the L of each retaining arm fits into a part of the channel 30 in the region of the cutting face 39 of the drill bit head 22, whereas the sides of the L of retaining arms 29 fit into the part of channel 30 formed generally on the side of the drill bit head 22.

There is provided an equal number of channels 30 and retaining arms 29. Figure 5 shows an embodiment of the invention having two channels 30 and therefore two corresponding retaining arms 29, whereas figure 6 shows an embodiment with three channels 30 and three retaining arms 29. Other numbers of retaining arms and channels are possible, for example 4, 5, 6, 7 or 8 retaining arms 29 and corresponding channels 30. At least two retaining arms 29 and channels 30 are preferred, and three or four retaining arms 29 and channels 30 are appropriate.

The chuck 24 is provided with an external radial groove 31 and has an external screw head 32 for screw attachment to a hammer assembly 28 of the drill.

As the skilled person will appreciate, the retaining arms 29 are to be placed into the corresponding channels 30 and then the chuck 24 is fitted to drill bit 21. In order to keep the components in place, a cylindrical or tubular locking collar 25 is then provided. As depicted, the collar 25 is split into semi-circular halves 25A and 25B. Collar 25 is provided with a retaining lug 33 on its internal diameter, which is located toward the end of collar 25 that is to be closest to the drill bit head 22 in use, and furthest from the cylinder 28. The radial retaining lug 33 is dimensioned and configured to fit into a correspondingly dimensioned and configured retaining groove 34 in the retaining arms 29.

The retaining collar 25 is provided with a radial projection 35 at the opposed end to the retaining lug 33, i.e. at the end of the collar 25 furthest from the cutting face 39 of the drill bit 21. The radial projection 35 is dimensioned and configured for seating in the radial groove 31 of the chuck 24.

In short, it can be appreciated that the radial retaining lug 33 of locking collar 25 is seated in the corresponding notches 34 in retaining arms 29 whereas the radial projection 35 of the retaining collar 25 is to be seated in the radial groove 31 of chuck 24. It must further be noted that the radial retaining lug 33 of the collar 25 not only fits into the notches 34 in retaining arms 29, but also into a corresponding groove 36 that is machined around the circumference of the drill bit head 22. As shown in figure 5, the notches 34 of retaining arms 29 are of identical profile to the groove 36 of the drill bit head 22 such that when the retaining arms 29 are fitted to the drill bit head 22 as described, the notches 34 of retaining arms 29 and the groove 36 of drill bit head 22 are substantially flush.

It can be appreciated that the retaining lug 33 of the locking collar 25 secures the retaining arms 29 into position within the drill bit head 22. The radial projection 35 of the retaining collar 25 sits within the machined groove 31 of the chuck 24. This arrangement allows free vertical movement of the drill bit assembly relative to the hammer assembly, thereby not interfering with the normal operation of the down-the-hole hammer whilst also ensuring that the drill bit assembly is retained within the hammer assembly. The retaining collar 25 is held together (as it is split into two parts 25A and 25B as shown) and held in place by a sleeve 26 which fits over the locking collar 25 and is then clamped into position between the chuck 24 and the cylinder 28 of the hammer assembly when the chuck 24 is screwed into the cylinder 28 of the hammer. As can be seen for example in figure 7, the sleeve 26 has a radial projection at one end thereof, which is clamped between the cylinder 28 and chuck 24 and therefore held in place. The entire hammer and bit assembly is then attached to the drill bit as with conventional down-the-hole hammer and bit assemblies.

Should a breakage occur anywhere along the length of the drill bit 21 then the broken portion(s) of the bit 21 will still be retained by the retaining arms 29, because the retaining arms 29 embrace the front surface 39 of the drill bit head 22, i.e. the lower most point of the drill bit 21 when the drill bit is in use. If a breakage occurs and the drill string is retracted from the hole being cut then the entire broken drill bit 21 will be withdrawn from the hole, without leaving any fragments remaining in the hole, as explained in more detail below.

Figure 7 shows a cross-section through the drill bit assembly as shown in Figure 6. Figure 7 simply illustrates, in cross-section, the configuration of the drill bit assembly once assembled and in the drilling position.

Figure 8 is a corresponding view to that of figure 7 in which a breakage 37 has occurred in the shank 23 of the drill bit 21. As will be appreciated, when the drill bit assembly is withdrawn from the hole being drilled, in the direction of the arrow given in the figure 8 then, due to separation of the drill bit shank 23 into two pieces, whilst the sleeve 26 is maintained clamped between cylinder 28 and chuck 24, longitudinal movement is allowed for the radial projection 35 within the radial groove 31 of the chuck 24. However, radial projection 35 remains seated in the radial groove 31 of chuck 24 and is maintained in place by sleeve 26.

Radial retaining lug 33 at the other end of the split retaining collar 25 also remains seated in the groove 34 of retaining arm 29. Thus, as clearly shown in figure 7, the combination of retaining arm 29, locking collar 25 and groove 35 of chuck 24 ensures that the entire drill bit 21 both above and below lateral break 37 is retained to the cylinder 28 when cylinder 28 together with the rest of the drill string is retracted from the hole. Accordingly, the broken part of the drill bit 21 is also retracted from the hole together with the cylinder.

Figure 9 is a corresponding cross-section to that shown in figure 7 and figure

8, but where a lateral break 38 has occurred in the region of the drill bit head 22. Without wishing to repeat the course of action described in respect of figure 8, once more, the combined action of the retaining arm 29, retaining collar 25 and radial groove 31 of the chuck 24 ensures that when the drill string is retracted from the hole being drilled, as shown by the arrow in figure

9, the entire drill bit assembly is retracted from the hole being drilled, including the broken part of the drill bit head 22. As can clearly be seen in figure 9, the invention succeeds because the retaining arm 29 extends to the very cutting face 39 of the drill bit head 22 so that even a fracture in the drill bit head 22 is captured by the retaining arm 29.

Finally, figure 10 shows an exploded view of the drill bit assembly of the invention, having two retaining arms 29 and demonstrates how the drill bit assembly is assembled.

In figure 10A, retaining arms 29 are inserted into channels 30 in the drill bit head 22. The retaining arms 29 are seated flush with respect to drill bit head 22 so that grooves 34 are in line with corresponding groove 36 in bit head 22. Figure 1OB depicts the chuck 24 being fitted onto the drill bit 21. Then, in figure 1OC, the two halves 25A and 25B of the retaining collar 25 are fitted onto the bit 21 and chuck 24, ensuring that the radial retaining lug 33 of the collar 25 is seated securely in the retaining groove 34, 36 formed in combination between retaining arms 29 and bit head 22.

In figure 1OD, sleeve 26 is fitted over the chuck 24 and retaining collar 25. Then, in figure 1OE, bit retaining rings 27 are fitted to the shank 23 of the bit 21. Finally, in figure 1OF, the entire drill bit assembly is screwed onto cylinder 28 of the drill string, clamping the sleeve 26 in place.

Unlike the other prior art bit catcher systems, the present invention has the advantage of being able to retain almost the entire drill bit 21 within the hammer assembly, should a breakage occur at any point along the length of the drill bit 21 , including drill bit head 22 and the drill bit shank 23. Through the novel and inventive use of the retaining arms 29 which retain the drill bit 21 towards the face 39 of the drill bit 21 , whilst not interfering with the cutting action of the drill bit 21 , the present system ensures that any damaged portion of the drill bit 21 , which may cause significant problems for the future use of the drilled hole, are removed along with the entire hammer assembly.

Unlike the previous bit catcher systems, which retain the drill bit 21 toward the back of the drill bit head 22, thereby allowing the head portion of the drill bit 21 to remain at the bottom of the drilled hole should a breakage occur through the bit head 22 below the bit catcher, the present invention provides a method of bit retention which not only secures the drill bit 21 should a breakage occur to the bit shank 23 but also retains the drill bit 21 should a failure occur through the drill bit head 22. When used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

1. A drill bit assembly for a down-the-hole hammer drill, the assembly comprising:

a drill bit having a drill bit head with a cutting face and a drill bit shank;

2. A drill bit assembly according to claim 1 , wherein the drill bit head is provided with two or more channels and the assembly further comprises two or more corresponding retaining arms.

3. A drill bit assembly according to claim 2, wherein the drill bit head is provided with three channels and the assembly further comprises three corresponding retaining arms.

4. A drill bit assembly according to claim 2, wherein the drill bit head is provided with four channels and the assembly further comprises four corresponding retaining arms.

5. A drill bit assembly according to any preceding claim, wherein the or each retaining arm or arms is engaged with a first part of the channel which is on or adjacent to the drill bit face and a with a second part of the channel that is set back from the drill bit face in the direction of the drill bit shank.

6. A drill bit assembly according to any preceding claim, wherein the or each retaining arm or arms is substantially L-shaped and wherein the first portion of the L is engaged with a first part of the channel which is on or adjacent to the drill bit face and wherein the second portion of the L is engaged with a second part of the channel that is set back from the drill bit face in the direction of the drill bit shank.

7. A drill bit assembly according to claim 5 or claim 6, wherein the or each retaining arm or arms is provided with a groove at the second portion thereof, the groove being dimensioned and configured to receive the radial retaining lug of the locking collar, thereby retaining the or each retaining arm or arms.

8. A drill bit assembly according to claim 7, wherein the drill bit head is provided with a groove, and wherein the groove of the drill bit head is dimensioned and configured to receive the radial retaining lug of the locking collar.

9. A drill bit assembly according to claim 8 wherein the groove on the drill bit head and the groove or grooves of the or each retaining arm or arms are mutually flush and wherein the combination of grooves from the drill bit head and the or each retaining arm or arms is dimensioned and configured to receive the radial retaining lug of the locking collar.

10. A drill bit assembly according to any preceding claim, wherein the locking collar comprises two separable sections with respect to the longitudinal axis of the collar.

11. A drill bit assembly according to any preceding claim, wherein the sleeve comprises a radial abutment which, in use is clamped between the chuck and the cylinder thereby holding the sleeve in place.

12. A drill bit assembly according to any preceding claim, wherein the attachment means comprises a screw thread.

13. A drill bit assembly substantially as herein described with reference to figures 5 to 10.

14. Any novel feature or combination of features described herein.