AU783955B2 - A plate drill bit with eccentric cutting profile - Google Patents

Description

AUSTRALIA

Patents Act COMPLETE SPECIFICATION

(ORIGINAL)

Class Int. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority Related Art:

*S

ofApplicant: I nventor(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 ECCENTRIC CUTTING PROFILE Our Ref: IRN 665955 POF Code: The following statement is a full description of this invention, including the best method of performing it known to applicant(s): -1- N URN 56 9551Comnplete ftom210302.doc A PLATE DRILL BIT WITH ECCENTRIC CUTTING PROFILE 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 A reference herein to a patent document or other matter which is given as prior art is not to be taken as an admission that that document or matter was, in Australia, known or that the information it contains was part of the common 15 general knowledge as at the priority date of any of the claims.

Rock bolts are commonly employed in the underground mining industry i 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 ol° 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.

A wide variety of rock bolts exist. One particular form is tubular and has 25 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 MIECPP*nsIent85955M885g5 sped amcd M911-05.do and subsequently secured in the pilot hole by the appropriate means. The type of rock bolt therefore has no drilling capability.

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 e M ECPPslen5M85g56M5955 spg. nendd 9 11-05 doc 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 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 suited for use in self drilling rock bolts.

15 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 having first and second cutting edges, said drill bit body being formed of plate material and including opposite leading and trailing ends, said first and second cutting edges being angularly spaced apart about said axis of rotation and being inclined to the direction of the axis so that each has a leading and trailing point, wherein the leading point of said first cutting edge is radially spaced from said axis by a lesser amount than the leading point of said second cutting edge.

An advantage of the present invention is that by using a drill bit body formed from plate material the cost of the bit is significantly reduced as compared to prior art arrangements using cast drill bit bodies. In addition, the drill bit is arranged to have an eccentric cutting profile. Such a cutting profile is advantageous as it is designed to generate pressure on the rock which induces cracking at the cutting surface to produce rock chips. By having the location of the cutting edges loading at different circumferences, more material can be chipped off leading to increased penetration rates.

Furthermore, the applicant has found that such a cutting profile is ideally N:\IRN\665955\CAP Case I A plate drill bit with eccentric cutting profile.doc suited for a drill bit body which is made from plate material as it enables stresses in the body to be more evenly distributed across the plate material.

Preferably, the trailing point of said first and second cutting edges are equally spaced from the drill axis in a radial direction.

Preferably, the first and second cutting edges are strip drill tips that are located on seats milled into the drill bit body. The drill tips are preferably tungsten carbide drill tips that are brazed or otherwise secured to the drill bit body. A preferred material for the drill tips is WC-Co sinter, 6-8 Co with 2p m WC grain size.

The drill tips are preferably located on the drill bit body so that they sit proud thereof. The drill bits are also positioned on the drill bit body so that oeoeo during rotation of the drill bit, the drill tips are located on a respective leading edge of the drill bit.

A channel is preferably located between said first and second drill tips.

15 The channel is preferably substantially v-shaped and has a lowermost point located on the drill axis.

In an alternative form, the cutting edges are integrally formed with the drill bit body. Preferably, the cutting edges undergo a heat treatment to form hardened zones.

The drill bit body is preferably pressed or stamped from a sheet of metal plate. The metal plate is preferably Bisalloy 360. Another alternative material for the metal plate is XK9258S. The plate preferably has a thickness of approximately 6mm.

The drill bit body preferably includes a tongue which is arranged to be received in an aperture in a leading end of a drive element. 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.

N:\IRN\665955\CAP Case I A plate drill bit with eccentric cutting profile.doc Brief Description of the Drawings Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a plan view of a drill bit in accordance with an embodiment of the invention.

Figure 2 is a top view of the drill bit shown in Figure 1.

Figure 3 is a perspective view of the drill bit shown in Figure 1.

Figure 4 illustrates the leading end of a rock bolt which is arranged to receive a drill bit of the type shown in Figures 1 to 3.

Figure 5 is a perspective view of a drill bit in accordance with a second embodiment of the invention.

Figure 6 illustrates the leading end of a rock bolt which is arranged to S• receive the drill bit shown in Figure Detailed Description of the Preferred Embodiments Figures 1 and 2 illustrate a drill bit 10 for a rock bolt. The drill bit includes a drill bit body 12, a first drill tip 14, a second drill tip 16 and a tongue 18. The first and second drill tips 14, 16 are angularly spaced apart ~about the axis of rotation of the drill bit 10. As depicted in Figures 1 and 2, the leading point 14a of the first drill tip 14 is off set from the axis of the drill bit 10 by a lesser amount than the leading point 16a of the second drill tip 16.

S"The first and second drill tips 14, 16 each have an trailing point 14b, 16b the trailing points 14b, 16b being equally spaced about the axis of the drill bit 10 in a radial direction.

The first and second drill tips 14, 16 are formed by strip drill tips which are located on seats milled into the upper or leading end of the drill bit body 12. The drill tips 14, 16 are tungsten carbide drill tips that are brazed or otherwise attached to the seats milled into the drill bit body 12.

As shown in Figure 2, the drill tips 14, 16 sit proud of the planar surface of the drill bit body 12 and are located on the drill bit body 12 so that during rotation of the drill bit 10, the drill tips 14, 16 are located on respective leading edges 20 of the drill bit 10. It is advantageous for the drill tips 14, 16 to sit proud as it allows a greater thickness of both the drill tip and the drill bit N:\IRN\665955\CAP Case I A plate drill bit with eccentric cutting prolile.doc body. This helps to prevent the drill tip from shattering and the plate body 12 failing under load. Although the drill tips 14, 16 sit proud as shown in the Figures, they may in fact sit flush with the planar surface of the drill bit body 12.

A channel 22 is located between the first and second drill tips 14, 16.

Thus, it will be appreciated, that the "cutting or leading end" of the drill bit adopts an inverted substantially W-shaped configuration.

The tongue 18 of the drill bit 10 is integral with the drill bit body 12 and is arranged to be received in 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 3. As shown in this Figure, the lower portion of the aperture 50 is wedge- .OOOOi shaped so as to receive the correspondingly shaped end portion 18a of the tongue 18. The tongue 18 and aperture 50 are shaped so that they can be readily connected together in such a manner that any rotation and thrust of "o 15 the rock bolt 54 will be transferred to the drill bit The drill bit body 12 and integral tongue 18 are designed so that they can be readily pressed, stamped or otherwise formed from a sheet of metal plate. It is preferable, for cost reasons, for the drill bit body and integral tongue to be formed in a single such forming operation. A suitable material for the metal plate is a Bisalloy 360 or XK9258S. It will, however, be appreciated that different materials could be used and that the selection of S-the required material will depend on a number of factors such as the nature of 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 6mm. It will, however, be appreciated that different thickness metal plates could be used.

The drill tips 14, 16 are preferably tungsten carbide drill tips that are brazed to the drill bit body. A preferred material for the drill tips is WC-Co sinter, 6-8 Co with 2-5 p.m WC grain size.

Figure 5 illustrates an alternative form of the drill bit 100. The drill bit 100 is substantially identical to that illustrated in Figures 1 and 2 with the exception that the tongue 118 includes a threaded arrangement 102 on either side thereof. The threaded arrangement 102 is arranged to be received N:\IRN\665955\CAP Case I A plate drill bit with eccentric cutting profile.doc within a 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 6.

The bits 10, 100 described herein have an eccentric cutting profile.

Such a cutting profile is advantageous because tip height variances are negated as the tips 14, 16 pass or rotate at different circumferences.

Furthermore, when rotary cutting, the edge of the tips generate a pressure on the rock and this pressure cracks off rock chips. By having the tips loading at different circumferences more material can be chipped off leading to increased penetration rates.

Drill bits made in accordance with embodiments of the invention are advantageous because the drill bit body 12 and integral tongue 18 are readily formed from a sheet of plate material and because the drill tips 14, 16 are simply brazed or otherwise attached to a seat milled in the drill bit body 12.

Accordingly, the manufacturing process for such a drill bit 10 is relatively 15 simple and thus the cost of producing such a drill bit 10 is much less than prior art drill bits. Drill bits according to an embodiment of the invention can S"also be readily mass produced.

Drill bits in accordance with an embodiment of the invention are also easy to use in that they can be readily attached to a rock bolt on site.

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

N:\IRN\665955\CAP Case I A plate drill bit with eccentric cutting profile.doc

Claims (15)

1. A drill bit having an axis of rotation and including a drill bit body having first and second cutting edges, said drill bit body being formed of plate material and including opposite leading and trailing ends, said first and second cutting edges being angularly spaced apart about said axis of rotation and being inclined to the direction of the axis so that each has a leading and trailing point, wherein the leading point of said first cutting edge is radially spaced from said axis by a lesser amount than the leading point of said second cutting edge.

2. A drill bit according to claim 1, wherein the radial distance from the axis to the trailing point of each of said first and second cutting edges is substantially the same.

3. A drill bit according to either claim 1 or 2, wherein the trailing point of each cutting edge is displaced further outwardly in an radial direction than said leading point of that cutting edge.

4. A drill bit according to any preceding claim, wherein the drill bit includes first and second drill tips which are mounted on said leading end, the drill tips incorporating respective ones of said first and second cutting edges.

5. A drill bit according to claim 4, wherein the first and second drill tips are located on seats which are milled into the drill bit body.

S6. A drill bit according to any one of claims 1 to 3, wherein the first and second cutting edges are integrally formed on said drill bit body.

7. A drill bit according to claim 6, wherein the cutting edges are formed on a hardened zone of said drill bit body.

8. A drill bit according to claim 7, wherein said hardened zone is formed from a heat treatment process.

9. 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.

10. 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 N:\IRN\665955\CAP Case I A plate drill bit with eccentric cutting profile.doc coupled thereto so that rotational and thrust forces are able to be transmitted from said drive element to said drill bit.

11. A drill bit according to claim 10, wherein the tongue is wedged shaped and is operative to be received in a correspondingly shaped aperture in the drive element.

12. A drill bit according to claim 10, wherein the tongue includes a threaded portion which is arranged to engage a complementary threaded portion in the aperture of the drive element.

13. A self drilling rock bolt which includes a drill bit according to any 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. 1A DATED: 28 March, 2002 r SEC 3 ouPHILLIPS ORMONDE FITZPATRICK /'tr cyAttorneys or: S B A. e N:\IRN\665955\CAP Case I A plate drill bit with eccentric cutting profile.doc