AU783956B2 - A drill bit with offset drill tip - Google Patents

Description

AUSTRALIA

Patents Act COMPLETE SPECIFICATION

(ORIGINAL)

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

SEC

S13 andvik*& Inventor(s): oo 1n i. $andvik-A& .'^2^Mlnventor(s): \r\ft~CC~NCc~ F~O~ity t4~ Steven Lee Weaver Michael Andrew McLean David Alexander McCloskey *O Address for Service: o o PHILLIPS ORMONDE FITZPATRICK Patent and Trade Mark Attorneys 367 Collins Street Melbourne 3000 AUSTRALIA Invention Title: A DRILL BIT WITH OFFSET DRILL TIP Our Ref: POF Code: IRN 665949 The following statement is a full description of this invention, including the best method of performing it known to applicant(s): 1 N :RNd 594CC lete ftorms210302 doc 2 A PLATE DRILL BIT WITH OFFSET DRILL TIP 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.

Backqround 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 general knowledge as at the priority date of any of the claims.

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 0 rock wall using a drill rod incorporating a drill bit on its distal end, and inserting 20 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 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 M ICPYstatl504940504 lmd arod 1145 c 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 *o o o *i *i M ECP M<Wp ci- m-f-a(M14l -(c 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 i 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, the drill bit body being formed from plate material and including opposite major faces which are bounded by a leading end, a trailing end and opposite side edges, 20 a centre plane of said drill bit body extending between said major faces and said axis of rotation extending generally in said centre plane, wherein a slot is formed in said leading end which is angularly displaced from said centre plane about said axis of rotation to form a pair of abutment elements having respective oppositely facing abutment surfaces, said drill tip being mounted in said slot in engagement with said oppositely facing abutment surfaces so that said abutment elements are operative to support said drill tip during a drilling procedure, and wherein the thickness of the respective abutment elements increases outwardly from the centre axis to be at least substantially the thickness of the body at their respective outer ends.

The advantage of the present invention is that the use of a drill bit body formed from plate material is significantly cheaper than a drill bit body formed by a casting process. In addition, by locating the slot angularly displaced from the centre plane in accordance with the invention maximises N:\IRN\665949\CAP Case 4 A Plate Drill Bit with Offset Drill Tip.doc the support the drill bit body can provide to the drill during a drilling procedure as the abutment elements utilise a major part of thickness of the drill bit body at their outer ends.

In a preferred form, the abutment elements extend to respective ones of the side edges of the drill bit body.

Preferably, the drill tip is a strip drill tip that is located on a seat milled into the drill bit body. The drill tip is preferably a tungsten carbide drill tip that is brazed or otherwise secured to the drill bit body. A preferred material for the drill tip is WC-Co sinter, 6-8 Co with 2-5 tm WC grain size.

The drill tip is preferably located on the drill bit body so that it sits proud thereof. This arrangement is advantageous because it provides a cutting clearance which encourages quicker drilling.

i 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 on the trailing end 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 firmly located within the 20 aperture and transmit rotational and thrust forces from the drive element to the drill bit. The drive element may be a drill rod, or an appropriately modified rock bolt.

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.

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 perspective view of a drill bit in accordance with an embodiment of the invention.

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

N:\IRN\665949\CAP Case 4 A Plate Drill Bit with Offset Drill Tip.doc Figure 3 illustrates the leading end of a rock bolt which is arranged to receive a drill bit of the type shown in Figure 1.

Figure 4 is a perspective view of a drill bit in accordance with a second embodiment of the invention.

Figure 5 illustrates the leading end of a rock bolt which is arranged to receive the drill bit shown in Figure 4.

Detailed Description of the Preferred Embodiments Figure 1 illustrates a drill bit 10 which includes a drill bit body 12 which has a leading end 14 and a trailing end 16. The leading end 14 of the drill bit body 12 has a slot formed therein. A drill tip 18 is located within the slot and is rigidly attached thereto in accordance with common practices.

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A tongue 20 extends from the trailing end 16 of the drill bit body 12 and is integrally formed therewith. The tongue 20 is arranged to be received S. 15 in an aperture 50 located in a leading end 52 of a rock bolt 54. This will be 9 described in more detail subsequently.

The drill bit body 12 and integral tongue 20 are designed so that they .o 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 12 and integral 20 tongue 20 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 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 metal plates could be used.

The drill tip 18 is located within the slot which is milled into the leading end 14 of the drill bit body 12. As clearly illustrated in Figure 2, the slot is milled into the leading end 14 so that the drill tip 18 is angularly displaced from the central plane CP of the drill bit body 12 about the drill bit axis CL. In this way abutment elements 27, 28 are formed which are operative to support the drill tip 18 during drilling. Further, the thickness of the abutment elements N:\IRN\665949\CAP Case 4 A Plate Drill Bit with Offset Drill Tip.doc increase outwardly from centre axis to be substantially the thickness of the body at their outer ends 29, 30. As a result the support the drill bit body 12 provides to the drill tip 18 is maximised.

The drill tip 18 is a strip drill tip that is brazed or otherwise secured to the slot formed in the leading end 14 of the drill bit body 12. A preferred material for the drill tip 18 is WC-Co sinter, 6 8 Co with 2 5 Im WC grain size. As is evident from the Figures, the drill tip 18 sits proud of the surface of the drill bit body 12.

The drill bit body 12 has a pair of side portions 22 which each include a first side surface 24 and a second side surface 26. The first side surface 24 extends substantially parallel to the centre line of the drill bit body 12, whilst the second side surface 26 angles inwardly towards the centre line of the drill bit body 12. The second side surface 26 is angled in this manner to reduce rubbing of the drill bit body 12 against the hole being drilled.

15 As stated previously, the tongue 20 is arranged to be received in an S°aperture 50 located in the leading end 52 of a rock bolt 54. The leading end 52 of such a rock bolt is illustrated in Figure 3. As shown in this Figure, the lower portion of the aperture 50 is wedge shaped so as to receive the correspondingly shaped end portion 20a of the tongue 20. The tongue 20 and the aperture 50 are shaped so that they can be readily connected together in such a manner that any rotation and thrust of the rock bolt 54 will be transferred to the drill bit Figure 4 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 120 includes a threaded arrangement 122 on either side thereof. The threaded arrangement 122 is arranged to be received 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 The embodiments described herein are considered to be particularly advantageous because the drill bit body 12 and integral tongue 20 are formed from a single forming operation and the drill bit 10 is arranged to readily support the drill tip 18.

N:\IRN\665949\CAP Case 4 A Plate Drill Bit with Offset Drill Tip.doc 7 It will be appreciated that this arrangement of the drill tip 18 can be successfully used with drill tips having alternative drill bit body configurations, such as a full spade or modified spade profile.

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

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Claims (14)

1. A drill bit having an axis of rotation and including a drill bit body, and a drill tip, the drill bit body being formed from plate material and including opposite major faces which are bounded by a leading end, a trailing end and opposite side edges, a centre plane of said drill bit body extending between said major faces and said axis of rotation extending generally in said centre plane, wherein a slot is formed in said leading end which is angularly displaced from said centre plane about said axis of rotation to form a pair of abutment elements having respective oppositely facing abutment surfaces, said drill tip being mounted in said slot in engagement with said oppositely facing abutment surfaces so that said abutment elements are operative to support said drill tip during a drilling procedure, and wherein the thickness of the respective abutment elements increases outwardly from the centre axis to be at least substantially the thickness of the body at their respective outer 15 ends.

2. A drill bit according to claim 1, wherein the abutment elements extend :X..to respective ones of the side edges of the drill bit body.

3. A drill bit according to either claim 1 or 2, wherein the drill tip is in the form of a strip drill tip and is located on a seat which is formed at the base of 20 said slot in said leading edge.

4. A drill bit according to any preceding claim, wherein the drill tip includes oppositely facing cutting faces, and wherein at least a substantial portion of each cutting face is exposed when said drill tip is mounted in said slot.

5. A drill bit according to any preceding claim, wherein said slot is formed from a milling operation.

6. 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.

7. A drill bit according to any preceding claim, wherein the drill tip is bonded to said abutment surfaces.

8. A drill bit according to claim 7, wherein the drill tip is brazed onto said abutment surfaces. N:\IRN\665949\CAP Case 4 A Plate Drill Bit with Offset Drill Tip.doc

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.

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

13. A drill bit substantially as herein described with reference to the 15 accompanying drawings.

14. A self drilling rock bolt substantially as herein described with reference to the accompanying drawings. DATED: 28 March, 2002 RA4, 20 HILLIPS ORMONDE FITZPATRICK SEC 113 orneys for: SAN V \w s Co N:\IRN\665949\CAP Case 4 A Plate Drill Bit with Offset Drill Tip.doc