AU2928802A - A plate drill bit with multiple prongs - Google Patents

Description

AUSTRALIA

Patents Act COMPLETE SPECIFICATION

(ORIGINAL)

Class Int. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority r Related Art: Name of Applicant: Sandvik AB Actual Inventor(s): Steven Lee Weaver Michael Andrew McLean David Alexander McCloskey Address for Service: PHILLIPS ORMONDE FITZPATRICK Patent and Trade Mark Attorneys 367 Collins Street Melbourne 3000 AUSTRALIA Invention Title: A PLATE DRILL BIT WITH MULTIPLE PRONGS Our Ref: POF Code: IRN 665937 The following statement is a full description of this invention, including the best method of performing it known to applicant(s): 1 N:\RN\665937\Complete fomns210302.doc -2- A PLATE DRILL BIT WITH MULTIPLE PRONGS Field of the Invention The present invention relates to a drill bit for use in rock bolting. The invention has been designed especially but not exclusively for use as part of a self drilling rock bolt and the invention is herein described in that context.

However, it is to be appreciated that the invention has broader application and may be used in other applications such as more conventional rock drilling operations including a drill rod.

'"Background of the Invention Rock bolts are commonly employed in the underground mining industry to support the walls of rock excavations against fragmentation or collapse. The normal procedure for installing such a bolt involves drilling a pilot hole into the S 15 rock wall using a drill rod incorporating a drill bit on its distal end, and inserting the bolt therein. The bolt is typically fixed within the hole using a settable glue, such as a resin or mortar cement. Alternatively, the bolt may include means to directly interlock with the surface of the pilot hole, such as a thread or an expanding sleeve.

20 A wide variety of rock bolts exist. One particular form is tubular and has a central bore formed lengthwise through the bolt. Advantageously, the central bore provides a conduit for the introduction of water during insertion of the bolt into the pilot hole. Water is employed to flush away rock segments, finings and dust, to reduce frictional resistance between the bolt and the rock, and to prevent excessive temperature generation. The central bore also provides a conduit for the injection of cement mortar or resin into the pilot opening to secure the bolt therein.

The above described methods of installing a rock bolt employ a two stage process, in which the pilot hole is first drilled, before the bolt is inserted and subsequently secured in the pilot hole by the appropriate means. This type of rock bolt therefore has no drilling capability.

N:YRNB665937CAP Case 3 A plate dill bit with multiple prongs.doc -3- Rock bolts having a drilling capability, and thereby referred to as "self drilling rock bolts", have previously been developed, but such bolts are not in common use in the mining industry. This is because to date the cost of such self drilling rock bolts has been prohibitive, despite their installation advantages.

This is due primarily because the drill bit is only used once in a self drilling rock bolt whereas in a conventional drilling technique using a drill rod, the drill bits can be re-used.

Prior art drill bits are expensive because the bit body is cast and as they are subjected to very high wear, it is normal for the drill bit to include a 10 hardened tip which is typically formed from tungsten carbide. Whilst it is economical to use such drill bits in drill rods where the bits can be re-used, they are too expensive to use in self drilling rock bolt applications.

It is an aim of the present invention to provide a drill bit which is less costly to manufacture than prior art arrangements, thereby making it ideally o 15 suited for use in self drilling rock bolts.

Summary of the Invention According to the present invention there is provided a drill bit having an axis of rotation, and including a drill bit body and a drill tip, said drill bit body 20 being formed of plate material and including a leading end and trailing end, said leading end including a central prong and two outer prongs, each of said prongs projecting outwardly in the direction of the axis with the central prong being generally located on said axis, and said outer prongs being radially spaced from said axis and being angularly spaced apart from each other about said axis, and wherein said drill tip is mounted on a distal end of one of said outer prongs.

An advantage of the present invention is that the drill bit body, which is formed from plate material is inexpensive to manufacture. Further, in view of the shape of the bit with the multiple prongs, only a small drill tip is required to be located on one of those prongs. The other outer prong is used to support the drill bit and to break up any material remaining in the aperture as it is being drilled. The centre prong aids in an initial location of the drill bit until the bit is N:JRNM85937\CAP Case 3 A plate drill bit with multiple pmrongs.doc -4collared in the hole and thereafter assists clearing the cut material during drilling.

In accordance with one embodiment of the invention, the central prong is longer than the outer prongs. The central prong is preferably arranged to wear away or breakaway after it has been used to locate the drill bit during the commencement of a drilling procedure.

In one form, the prongs taper inwardly to their respective distal ends. In another form, the outer prong which supports the drill tip includes at its distal end an outer side edge which is generally parallel to the axis of rotation. In this 10 way, the support prong includes a stub end which improves the wear characteristics of that prong so as to be better able to support the drill bit during a drilling procedure.

In one form, the leading edge of the outer prongs are generally aligned in the direction of the axis. In another form, the cutting prongs (which includes the 15 distal tip) extends beyond the other outer prong which supports the drill bit.

S* This arrangement facilitates in establishing a cleaner cut by the drill bit.

The drill tip is preferably located on a seat milled into a face of either of the outer prongs. The drill tip is preferably a tungsten carbide drill tip that is brazed or otherwise attached to the prong. A preferred material for the drill tip 20 is WC-Co sinter, 6 8% Co with 2 5 [tm WC grain size.

S iI The drill tip is preferably located on one of the outer prongs proud of the surface thereof.

The drill bit body preferably includes a pair of side faces which angle inwardly as they move away from a leading end of the drill bit. This configuration of the drill bit body provides relief for cut material during the drilling process and prevents the drill bit from rubbing against the hole as it is being drilled.

The drill bit is preferably pressed or stamped form a sheet of metal plate.

The metal plate is preferably Bisalloy 360. Another alternative material foe the metal plate is XK9258S. The plate preferably has a thickness of 6mm.

The drill bit body preferably includes a tongue at its trailing end which is arranged to be received in an aperture in a leading end of a drive element, such N:\IRN\685937CAP Case 3 A plate drill bit with multiple prOngs.dec as a drill rod or a rock bolt in a self drilling rock bolt arrangement. The tongue is preferably shaped so that it can be located within the aperture and transmit rotational and thrust forces from the drive element to the drill bit.

The tongue may include a wedge shaped portion which is arranged to be received in a correspondingly shaped portion of the aperture. In another form, the tongue may include a threaded portion which is arranged to engage in a threaded portion of the aperture in the drive element.

Brief description of the drawing An embodiment of the invention will now be described, by way of S- example only, with reference to the accompanying drawings in which: Figure 1 is a perspective view of a drill bit in accordance with an embodiment of the invention.

SFigure 1A illustrates a variation of the design of the support prong of the 15 distal bit of Figure 1.

Figure 2 illustrates the leading end of a rock bolt which is arranged to receive a drill bit of the type illustrated in Figurel.

Figure 3 is a perspective view of a drill bit in accordance with a second embodiment of the invention.

Figure 4 illustrates the leading end of a rock bolt which is arranged to receive the drill bit shown in Figure 3.

Detailed Description of the Preferred Embodiments Figure 1 illustrates a drill bit 10 which has a drill bit body 12, a pair of outer prongs 14, 16 and a central prong 18. The outer prong 14 has a drill tip mounted thereon. The drill tip 20 is mounted on a leading face of the outer prong 14 so that when the drill bit 10 is rotated about its axis CL the drill tip 20 is properly positioned for cutting.

The central prong 18 is longer than the outer prongs 14, 16 so that it can be used to locate the drill bit 10 in the required position as the drilling procedure commences. During use of the drill bit 10 the central prong 18 is arranged to wear away and may in fact break away during a normal drilling procedure.

N:YRNW65937CAP Case 3 A plate drill bit with multiple prongs.doc -6- The prongs 14, 16, 18 preferably adopt a substantially triangular configuration, although other shaped prongs are envisaged.

The drill tip 20 is located on a seat milled into the leading face of the outer prong 14. The drill tip 20 is a tungsten carbide drill tip that is brazed or otherwise attached to the outer prong 14. A preferred material for the drill tip is WC-Co sinter, 6 8% Co with 2 5 pm WC grain size. The drill tip 20 is located on the outer prong 14 proud of the leading surface thereof.

Located at an opposite end of the drill bit body 12 to the prongs 14, 16, 18 is a tongue 22. The tongue 22 is shaped so that it can be received within an aperture 50 located in a leading end 52 of a rock bolt 54. The leading end 52 of **such a rock bolt 54 is illustrated in Figure 2. As shown in this Figure, the aperture 50 is wedge shaped so as to receive the correspondingly shaped end C. Cl S. portion 22a of the tongue 22. The tongue 22 and aperture 50 are shaped so that they can be readily connected together in such a manner that any rotation or thrust of the rock bolt 54 will be transferred to the drill bit The drill bit body 12 includes a pair of side faces 24, 26 which angle inwardly in a direction towards the tongue 22. This configuration of the drill bit V. body 12 provides relief for cut material during the drilling process and also prevents the bit 10 from rubbing against the hole as it is drilled. The drill bit S 20 is preferably pressed, stamped or otherwise formed from a sheet of metal plate.

A suitable material for this purpose is Bisalloy 360 or XK9258S. It will, however, be appreciated that different materials could be used and the selection of the required material will depend on a number of factors, such as the nature of the material that the drill bit 10 is required to penetrate and the required life of the drill bit 10. The metal plate would ideally have a thickness of approximately 6 mm. It will, however, be appreciated that different thickness material plates could be used.

Figure 1A illustrates a variation on the design of the outer prong 16. In use, the outer prong 16 is designed to support the drill bit during a drilling procedure. To improve this function, the prong 16 includes a generally stub end which incorporates a face 27 which is generally parallel to the axis of rotation of the drill bit CL. This face 27 provides a wear surface which assists in N:JRNX665937\CAP Case 3 A plate drill bit with multiple pmrangs.doc supporting the drill tip. In addition, the outermost edge 28 of the prong 16 is designed to be slightly below the level of the outermost edge 29 of the cutting prong 14 so as to provide a cleaner cut by said drill tip.

Figure 3 illustrates an alternative form of the drill bit 100. The drill bit 100 is substantially identical to that illustrated in Figure 1 with the exception that the tongue 122 includes a threaded arrangement 125 on either side of the tongue 122. The threaded arrangement 125 is arranged to be received within the threaded aperture 150 formed in the leading end 152 of a rock bolt 154. The leading end 152 of such a rock bolt 154 is shown in Figure 4.

10 It will be appreciated that the drill tip 20 can be located on either of the "outer prongs 14, 16. The prong fitted with the drill tip 20 is used to cut the aperture in the rock into which the roof bolt is to be secured. The other outer prong is used to support the drill bit 10 in the aperture 50 and to break up any material remaining in the aperture as it is being drilled. In most circumstances ~15 at this stage the central prong 18 will either have worn away or have been Ssnapped.

A drill bit 10 in accordance with an embodiment of the invention is particularly advantageous because only a very small amount of drill tip 20 is required to be located on one of the prongs 14, 16. As the carbide drill tip 20 greatly increases the cost of any drill bit it is desirable to minimise the amount thereof. The cost of such a drill bit 10 is further reduced because the drill bit is readily formed from a sheet of plate material using a pressing, stamping or other forming process. It will also be appreciated that the outer prong 14, 16 without the drill tip 20 acts as a stabilizer during the drilling process.

The embodiments have been described by way of example only and modifications within the spirit and scope of the invention are envisaged.

N:JRN\865937CAP Case 3 A plate drill bit with multiple pmrngs.doc

Claims (15)

1. A drill bit having an axis of rotation, and including a drill bit body and a drill tip, said drill bit body being formed of plate material and including a leading end and trailing end, said leading end including a central prong and two outer prongs, each of said prongs projecting outwardly in the direction of the axis with the central prong being generally located on said axis, and said outer prongs being radially spaced from said axis and being angularly spaced apart from each other about said axis, and wherein said drill tip is mounted on a distal end of one of said outer prongs. 10

2. A drill bit according to claim 1, wherein the central prong projects beyond the outer edge of the outer prongs in the direction of the axis and is operative to break or wear away during a drilling procedure. 99°

3. A drill bit according to either claim 1 or 2, wherein the outer edges of the outer prongs are substantially aligned in the direction of the axis. 15

4. A drill bit according to either claim 1 or 2, wherein the outer edge of the said one outer prong extends beyond the outer edge of the other outer prong in the direction of the axis.

A drill bit according to any preceding claim, wherein each prong tapers inwardly to its distal end. .i 20

6. A drill tip according to any one claims 1 to 4, wherein said other outer prong includes at its distal end an outer side edge which is generally parallel to the axis.

7. A drill bit according to any preceding claim, wherein the drill bit is mounted on a seat milled into the face of said one outer prong.

8. A drill bit according to any preceding claim, wherein the central prong and the outer prongs are substantially aligned in a common plane.

9. A drill bit according to any preceding claim, wherein the drill bit body includes a tongue at a lower end which extends to said trailing end, said tongue being operative to be received in an aperture in a drive element and coupled thereto so that rotational and thrust forces are able to be transmitted from said drive element to said drill bit.

N:IRN\65937%CAP Case 3 A plate drill bit with multiple prongs.doc -9- A drill bit according to claim 9, wherein the tongue is wedged shaped and is operative to be received in a correspondingly shaped aperture in the drive element.

11. A drill bit according to claim 9, wherein the tongue includes a threaded portion which is arranged to engage a complementary threaded portion in the aperture of the drive element.

12. A drill bit according to any preceding claim, wherein the drill bit body is shaped from said metal plate by a pressing or stamping operation.

13. A self drilling rock bolt which includes a drill bit according to any 10 preceding claim, secured at a leading end thereof.

14. A drill bit substantially as herein described with reference to the accompanying drawings.

15. A self drilling rock bolt substantially as herein described with reference to the accompanying drawings. DATED: 28 March, 2002 PHILLIPS ORMONDE FITZPATRICK Attorneys for: SANDVIKAB N:MRN8665937CAP Case 3 A plate drill bi with multiple prongs doc