AU2006204633A1 - Drill Bit - Google Patents

Description

I

1

AUSTRALIA

Patents Act 1990 Evelyn Frances Gray COMPLETE SPECIFICATION Invention Title: Drill Bit The invention is described in the following statement: Field of the Invention The present invention relates to a drill bit and relates particularly, though not exclusively, to a drill bit for use with hollow bars such as self drilling rock bolts.

S 5 Background of the Invention Drill bits are an integral part of drilling operations in the mining and tunnelling industries. Drill bits are particularly used to drill holes for exploration, blasting and for Nrock bolts. In the case of rock bolts, large mines may typically drill over 100,000 rock bolt holes per year. The drill bits used to drill these holes vary depending upon the rock type and the drilling machine used.

In the case of rotary drilling (ie a rotary drilling action only), the drill bits used may be a "two wing design" or a "spade design" or a "modified spade design" or some variation of these designs. In the case of rotary percussive drilling (ie both a rotary drilling action and a hammer drilling action), the drill bits used may be a "chisel bit design" or a "button bit design" or some variation of these designs. Different manufacturers have their own proprietary drill bit designs but they all fall within these general bit designs.

Most drill bits are manufactured from two major parts. These are the main "body" section of the drill bit, and the "cutting edge" or "crushing points" section of the drill bit.

The body section is either a cast, forged or machined section which includes an attachment means to fix the drill bit to the drill rod (usually a screw thread), and a "containment means" to hold and support the cutting edge or edges (this is typically a slot, but could also be a series of recessed holes).

The cutting edge section of the drill bit is typically an elongated tungsten carbide insert designed to fit into a slot in the body of the drill bit. The crushing points section could be a series spherical tungsten carbide "buttons" or "ballistic buttons" designed to be typically brazed, soldered or silver soldered into position into a series of recessed holes in the body of the drill bit.

Drill bits are often made from more than one material, which is time consuming and expensive.

In the case of rotary drill bits used in sedimentary rocks, the main body section of a drill bit is normally manufactured using an investment casting process. This enables fine definition on.the drill bit to be achieved and this is particularly important where a screw thread is required to be formed on the body. However, one disadvantage of this process is that the investment casting process is relatively expensive. Additional costs are then required for the tungsten carbide cutting edge itself, and for the costs of soldering or fixing the cutting tip to the body of the bit.

Another disadvantage of rotary drill bits in the size range 20 mm to 50 mm diameter, is that they normally use an M16 thread (a metric thread 16 mm in diameter) to attach the drill bit to the drill rod. This thread form can tend to jam on and it can become difficult to unscrew the drill bit from the drill rod when trying to change drill bits.

Drill bits, including those used with drill rods and self drilling rock bolts, typically have a circular or spiral shaped cross-section. See, for example, the integrated drilling and rock bolting apparatus disclosed in International Patent Application No PCT/AU1994/000177. These drill bits tend to minimise the volume of the swirl chamber for flushing out rock cuttings, making clogging of the water passageways likely.

There is a need for improved drill bits to overcome or ameliorate these disadvantages.

Summary of the Invention In a first aspect, the present invention provides a drill bit for insertion into a hollow bar comprising: at least one cutting surface or face at one end; and attachment means at an opposing end for securing the drill bit to a hollow bar, wherein the drill bit has a substantially planar profile along its length.

Preferred embodiments of the drill bit are adapted for appropriate engagement with a drilling means including, for example, drill rods, bars and bolts.

Preferably said drill bit is formed in a pressing or stamping operation where at least one attachment means includes at least one leg member pressed or stamped from said drill bit at opposite sides of said drill bit. Once formed, the leg member(s) may be bent away from opposing faces of said drill bit.

In one preferred embodiment a tongue extends from said drill bit between said leg members and, when the drill bit is secured to, or firmly located within the drilling means, the tongue is locatable within said drilling means. The leg members can be attached to either a support washer or to a drill rod itself typically by welding. The cutting surface or face design can be any suitable designed shape and can be made from any suitable cutting face material. Typically a drill bit designed for rotary applications will be a two winged or modified spade type design and be made from either hardened steel or have a hard insert or facing material attached such as tungsten carbide.

However, it is not essential for the cutting surface or face to be formed from a different material to that from which the remainder of the drill bit is formed. In one preferred embodiment, the entire drill bit, including the cutting surface or face is formed of one material.

Preferably said tongue is adapted to fit neatly into a hole, particularly preferably, a non-circular hole, in said drilling means. Preferably, said non-circular hole provides sufficient passageway for a cutting fluid to pass between the sides of said tongue on the drill bit and the sides of the non-circular hole. Preferably, the non-circular hole is designed such that the tongue will be a simple push fit in an axial direction, but will be locked into the hole with respect to rotational movement.

In an alternative embodiment of the present invention, the attachment means comprises a tapered tongue. The tapered tongue on the drill bit fits neatly into the tapered hole on the drilling means. The angle of the taper is sub-parallel to the central axial line of the tongue and is less than 45 degrees to the central axial line, and is preferably less than 10 degrees to the central axial line. As axial thrust is applied from the drilling means through to the drill bit via the tapered hole, the normal force generated on the contact surfaces between the tapered hole and the neatly fitting tapered tongue increases significantly such that the shear strength thus generated is sufficient to lock the drill bit into the tapered hole in the drilling means.

In this embodiment, the tapered hole in the drilling means is preferably conical in shape and can be machined or formed by any suitable process and the drilling means can be made from steel, fibreglass or any other suitable material. It is particularly suited to drill rods or self drilling rock bolts made from fibreglass.

In this embodiment, the tapered tongue is preferably made from a flat or planar steel and the sides of the tapered tongue are normally "as punched" or "as stamped" and are substantially flat with square edges. The generally square edges on the tapered tongue will bite into a tapered hole in a drill rod or self drilling rock bolt (which is made from softer material than the drill bit) when axial load is applied to the drill bit. In this way, the tapered tongue will lock itself into a tapered hole in a drill rod or self drilling rock bolt made from softer material. In a preferred embodiment the drill rod or self drilling rock bolt is made from fibreglass. In this embodiment, two passageways are formed between the tapered hole and the flat tapered tongue.

These passageways allow flushing fluid to flow past the tapered tongue and to the drilling contact face with the rock.

In this embodiment, the tapered tongue preferably extends beyond the end of the drilling means such that the drill bit only contacts the end of the drill rod or self drilling rock bolt in the tapered hole. Preferably, in such embodiments, substantially all the axial thrust from the drill rod is transferred onto the tapered tongue of the drill bit and not onto the legs as with other embodiments of the invention. Preferably the drill bit also has at least one surface at an angle to the axis of the drill rod, and more preferably the angle is approximately a right angle facing towards the drill rod and extending beyond the diameter of the drill rod or self drilling rock bolt, such that a hammer blow or similar force onto this surface can be used to remove the drill bit from the drill rod or self drilling rock bolt.

In a preferred embodiment of the drill bit, the central drive tongue of the drill bit can be any suitable shape but should have sufficient torsional and shear strength such that welding the drill bit onto the drill rod or self drilling rock bolt is not normally required. The central drive tongue of the drill bit can have surfaces which contact the drilling means which are parallel, or tapered, or have a combination of parallel and tapered surfaces. These surfaces can also be planar or irregular with small bumps or indentations to allow for small variations in the central hole size in the drilling means.

The central drive tongue of the drill bit may also have all or part of a hole or a recess located anywhere along a length of the tongue such that a locking pin, or like securing member, can be pushed through an aligned hole in the drill rod and through the hole or recess in the tongue to firmly locate the drill bit in the drill rod.

In a preferred embodiment of the drill bit, the drive tongue has a slot punched into it along a section of its length such that the width of the drive tongue can be subsequently increased by opening out the slot. The width of the drive tongue can therefore be increased to be slightly wider than the width of the hole in which it is to be fitted in the drill rod or self drilling rock bolt. In this embodiment, the leading end of the drive tongue is fitted into a hole in a drill rod or self drilling bolt when the sides of the drive tongue are compressed. In this manner, the sides of the drive tongue adjacent to the slot will act as a spring against the inside surfaces of the drill rod, or self drilling rock bolt, hole, preferably allowing the drive tongue width to adjust to a substantially adequate size for the hole in which it is to be inserted. In addition, the length and width of the slot are preferably designed to ensure that the drive tongue can be pushed into the hole and at the same time be firmly located in the hole such that it would not easily fall out of the hole.

The length of the central drive tongue can be any suitable length. In the case of drive tongues with parallel sides located in non-circular holes in steel drill rods or self drilling rock bolts, the length of the drive tongue is typically greater than 10 mm and less than 50 mm. Where the drive tongues are tapered and are located in tapered holes in fibreglass drill rods or self drilling rock bolts, the length of the drive tongue is typically greater than 20 mm and less than 200 mm. However, these are illustrative examples only as the invention envisages a wide range of lengths for the drive tongues.

The central drive tongue on the drill bit also preferably provides a simple means to centralize the cutting head of the drill bit with respect to the drill rod or self drilling rock bolt.

The drill bits are preferably formed from steel which is suitable for heat treating and hardening processes.

The invention can be used with existing drill rods by use of a short adaptor that will screw onto conventional drill rods and will also accommodate and drive the drill bit.

The present invention in its preferred form provides a drill bit which does not require a detailed investment cast, or forged or machined body. Instead the main body and structure of the drill bit is preferably made from a flat or planar sheet of steel which has been punched, or stamped or pressed to form the required shape. In addition, the shape of the drill bit, including the shape of the basic cutting head, the legs and the tongue can all be formed in one simple punching, stamping or pressing operation.

Moreover, in a preferred embodiment, the present invention provides a rotational drive means between the drill rod and the drill bit by having a flat tongue of steel on the drill bit which fits into a non-circular or a tapered hole in the drill rod. In this design, there is no requirement to have a thread form on the drill rod or the drill bit.

Furthermore, water or air used for flushing in the drilling operation can pass through the passageways on either side of the flat tongue of steel and the noncircular or tapered hole, thus removing the requirement to have a central hole within the drill bit.

The present invention preferably provides a drill bit which is economical to manufacture and is suited to high speed production using high speed pressing, stamping or punching operations.

The drill bit is suited to both a single use, for example, when using self drilling rock bolts, and to multiple uses, for example, when using conventional drill rods.

To make the drill bit suitable for cutting or drilling soft rock, such as coal and mudstone, it is possible to simply use heat treating processes on, for example, steel drill bits to form a hard cutting edge or edges. To make the drill bit suitable for cutting or drilling harder or more abrasive rocks, a tungsten carbide cutting face or hard facing can be fixed to the drill bit. The shape of the cutting head could be any suitable shape that can be preferably substantially formed in a pressing, punching or stamping operation and could be symmetric or asymmetric in design. The drill bit of preferred embodiments is suitable for a range of rotary drilling applications, but is not limited to rotary drilling only.

In a second aspect, the present invention provides a method of manufacturing a drill bit comprising punching, pressing or stamping a drill bit from a substantially planar sheet of material to form a substantially planar drill bit adapted for insertion into a hollow bar.

In a particularly preferred embodiment, the material is steel.

This method preferably provides a low cost and straight forward method of manufacturing drill bits, particularly drill bits used for rotary drilling applications.

In a third aspect, the present invention provides a drill bit manufactured according to the second aspect.

The present invention is particularly suited for use with self drilling rock bolts where a low cost disposable drill bit is required.

Throughout this specification, unless the context requires otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed in Australia before the priority date of each claim of this specification.

In order that the present invention may be more clearly understood, preferred embodiments will be described with reference to the following drawings and examples.

Brief Description of the Drawings The invention will now be further explained and illustrated by reference to the accompanying drawings in which: Figure 1 is a side view of a drill bit made in accordance with one preferred embodiment of the present invention located in a hole in a hollow drill rod, bar or bolt; Figure 2 is a front view of the drill bit shown in Figure 1; Figure 3 is a plan view of the drill bit shown in Figure 1; Figure 4 is a similar view to that of Figure 2 showing the cutting tip detail on the drill bit shown in Figure 1; Figure 5 is a plan view of the washer detail which, in some preferred embodiments, is welded to the main body of the drill bit of Figure 1; Figure 6 is a side view of a drill bit made in accordance with a second embodiment of the present invention located in a hole in a hollow drill rod, bar or bolt; Figure 7 is a front view of the drill bit shown in Figure 6; Figure 8 is a plan view of the drill bit shown in Figure 6; Figure 9 shows a plan view, a front view, and a side view of the cutting tip detail of the drill bit shown in Figure 6; Figure 10 is an end sectional view of the drive tongue or tang of the drill bit of a preferred embodiment of the invention where the tongue or tang is inserted into a non-circular hole in a drill rod or self drilling rock bolt and is shown as view C-C in Figure 11; Figure 11 is a front sectional view of the drill bit located in a non-circular hole as shown in view B-B in Figure Figure 12 is a side sectional view of the drill bit shown in Figure 11 as shown in view A-A in Figure Figure 13 is an end sectional view of the drive tongue or tang of the drill bit of a preferred embodiment of the invention where the tongue or tang is inserted into a non-circular hole in a drill rod or self drilling rock bolt and is shown as view F-F in Figure 14; Figure 14 is a front sectional view of the drill bit located in a non-circular hole as shown in view E-E in Figure 13; Figure 15 is a side sectional view of the drill bit shown in Figure 14 as shown in view D-D in Figure 13; Figure 16 is an end sectional view of the drive tongue or tang of the drill bit of a preferred embodiment of the invention where the tongue or tang is inserted into a non-circular hole in a non-circular drill rod or self drilling rock bolt and is shown as view I-I in Figure 17; Figure 17 is a front sectional view of the drill bit located in a non-circular hole as shown in view H-H in Figure 16 where part of the non-circular hole is tapered to accommodate a partly tapered drive tongue or tang; Figure 18 is a side sectional view of the drill bit shown in Figure 17 as shown in view G-G in Figure 16; Figure 19 is an end sectional view of the drive tongue or tang of the drill bit of a preferred embodiment of the invention where the tongue or tang is inserted into a non-circular hole in a drill rod or self drilling rock bolt and where the drill rod or self drilling rock bolt also has a cross hole which aligns with a recess in the drive tongue or tang to accommodate, for example, a locking pin and is shown as view L-L in Figure Figure 20 is a front sectional view of the drill bit located in a non-circular hole as shown in view K-K in Figure 19; Figure 21 is a side sectional view of the drill bit shown in Figure 20 as shown in view J-J in Figure 19; Figure 22 is an end sectional view of the drive tongue or tang of the drill bit of a preferred embodiment of the invention where the tongue or tang is inserted into a non-circular hole in a drill rod or self drilling rock bolt and where the drill rod or self drilling rock bolt also has a cross hole which aligns with a through hole in the drive tongue or tang to accommodate, for example, a locking pin and is shown as view O-O in Figure 23; Figure 23 is a front sectional view of the drill bit located in a non-circular hole as shown in view N-N in Figure 22; Figure 24 is a side sectional view of the drill bit shown in Figure 23 as shown in view M-M in Figure 22; Figure 25 is an end sectional view of the drive tongue or tang of the drill bit of a preferred embodiment of the invention where the tongue or tang is inserted into a non-circular hole in a drill rod or self drilling rock bolt and where the drive tongue or tang is spring loaded against the sides of the non-circular hole in a drill rod or self drilling rock bolt and is shown as view R-R in Figure 26; Figure 26 is a front sectional view of the drill bit located in a non-circular hole as shown in view Q-Q in Figure Figure 27 is a side sectional view of the drill bit shown in Figure 25 as shown in view P-P in Figure Figure 28 is an end plan view of the drill bit of a preferred embodiment of the invention where the drive tongue or tang is inserted into a tapered hole in a drill rod or self drilling rock bolt and is shown as view U-U in Figure 29; Figure 29 is a front sectional view of the drill bit located in a tapered hole as shown in view S-S in Figure 28; Figure 30 is a side sectional view of the drill bit shown in Figure 29 as shown in view T-T in Figure 28; t' Figure 31 is an end plan view of the drill bit of a preferred embodiment of the invention where the drive tongue or tang is inserted into a tapered hole in a drill rod or t' M 5 self drilling rock bolt and is shown as view X-X in Figure 32; Figure 32 is a front sectional view of the drill bit located in a tapered hole as Sshown in view V-V in Figure 31; NFigure 33 is a side sectional view of the drill bit shown in Figure 32 as shown in Sview W-W in Figure 31; Figure 34 is a close up sectional view through a tapered drive tongue or tang located in a tapered hole in a drill rod or self drilling rock bolt as shown in views Y-Y and Z-Z in Figures 29 and 32 respectively and where the corners of the tapered drive tongue are just touching the tapered hole; and Figure 35 is a close up sectional view through a tapered drive tongue or tang located in a tapered hole in a drill rod or self drilling rock bolt as shown in views Y-Y and Z-Z in Figures 29 and 32 respectively and where the corners of the tapered drive tongue have cut into the tapered hole.

Detailed Description of the Preferred Embodiments Any reference in the description to the terms listed below have the following meanings: A "drill bit", "drilling bit", "drill tip" or "drilling tip" is to be understood to include all such variations and modifications of the above, and any other member that could be used to drill a hole in rock.

References to "flat" are to be understood to include all such variations and modifications of the above, including "substantially flat" "planar" and "substantially planar"'.

References to "drilling", "rotary drilling", or "rotary percussive drilling" are to be understood to include all such variations and modifications of the above, and any other process that could be used to provide the energy to drill a hole in rock.

A "tongue" or "drive tongue" is to be understood to include all such variations and modifications of the above, and includes "tapered tongue", "tang", "drive tang",

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cK1 12 "lug", or "spigot" and any other substantially fiat member that could be used to lock a drill bit into a drill rod or self drilling rock bolt in a rotational direction or locate and t' centralise a drill bit into a drill rod or self drilling rock bolt.

A "cutting edge", "cutting face", "cutting surface", "cutting head" or "cutting M 5 insert" is to be understood to include all such variations and modifications of the above, and any other member that could be used to cut, crush or penetrate rock.

References to "hardened" or "hardening" are to be understood to include all IDsuch variations and modifications of the above, and any other process or metal or Smaterial that could be used to provide a hard surface suitable for drilling rock.

References to "pressing", "stamping" or "punching" are to be understood to include all such variations and modifications of pressing, stamping and punching but is not limited to these alone and includes any suitable manufacturing process.

A "leg" is to be understood to include all such variations and modifications of a "leg" but is not limited to these alone and includes one or many "legs", "braces", "elements", "shoulders" or any support member that is designed to provide additional torsional stiffness to a drill bit and/or to transfer some or all of the axial thrust from the drill rod to the drill bit.

The invention will be described with respect to the manufacture of rotary drill bits, but the invention is not limited to this application and could be applied to any drill bit. The invention is particularly applicable to rotary drill bits used to drill sedimentary rocks.

In the drawings, the same numerals have been used to designate similar integers in each figure to avoid duplication of description.

In the first embodiment shown in Figures 1 to 5 there is shown a drill bit 10 for use on a hollow drill rod, hollow bar, or hollow rock bolt 12. Drill bit 10 is typically made from a flat piece of steel that has been pressed and formed into its final shape to provide a pair of legs 14,16 and at least one cutting face or edge 18. Once the drill bit has been formed, legs 14,16 may be bent outwards on opposite sides to provide bracing support to the cutting faces 18 of drill bit 10. Legs 14,16 may be welded at 20, 22 to a support washer 24 as shown, or may be welded onto the end of drill rod 12, or may press against the end of drill rod 12. The hollow drill rod 12 has a noncircular central hole 26 into which fits a tongue 28 of drill bit 10. Tongue 28 is located between legs 14,16 and extends beyond the free ends on legs 14,16 to be inserted into hole 26 to be locked into its rotational position with respect to drill rod 12. Drill bit can also be locked into its axial position with respect to drill rod 12 by the subsequent insertion of a roll pin (not shown) through a hole in drill rod 12 at right angles to the axis of the drill rod such that it passes through a hole or a slot (not shown) in drill bit 10. Typically, tongue 28 would be a neat and tight push fit into hole 26.

As shown in Figures 2 and 3, the cutting faces or edges 18 have the largest diameter of the drill bit 10 and have a larger diameter than the drill rod 12. However the diameter of the drill bit 10 can be made to be only slightly greater than the diameter of the drill rod or self drilling rock bolt 12 as shown in Figures 3 and 8 because the drill bit 10 is not screwed onto the outside of the drill rod 12 as with conventional drill bits. In preferred embodiments, the drill bit 10 isfixed to the drill rod 12 and centralised on the drill rod 12 by the tongue 28 and may be further fixed to the drill rod 12 by welding. Therefore the diameter of the borehole created by the drill bit may be only slightly larger than the diameter of the drill rod 12 thus minimizing the annulus space between them as shown, for example, in Figures 3 and 8. The cutting faces 18 have a rake 30 as shown in Figures 3 and 4. The cutting faces 18 are typically manufactured by using heat treatment processes to form a hard edge or face on the parent metal. The cutting faces 18 can be any suitable shape or configuration such as the modified spade design as shown, or be a full spade design, or be a two wing design and can be symmetrical or asymmetrical. The cutting faces 18 can be offset with respect to a centre line axial plane as shown in Figures 3 and 8 since the cutting faces are on opposite sides of a flat piece of steel, or the flat piece of steel that comprises the body of the drill bit can be pressed and formed such that the cutting faces are substantially in line with a centre line axial plane.

Figure 5 shows a plan view of support washer 24 which can be any suitable shape and has a central hole 32. Drilling fluid (not shown) can pass along central hole 32 in drill rod 12 and through passageway 34 formed between drill bit 10 and drill rod 12 and then through hole 32 in support washer 24.

Figures 6 to 9 show a second embodiment of the drill bit 10 which has additional hardened cutting faces 40, 42 secured thereto. The additional hardened cutting faces 40, 42 could be an applied surface coating or surface treatment (not shown) or be a separately attached hard face or faces as shown. The hardened cutting face or faces 40, 42 would.normally be attached to the body of the drill bit by soldering, by silver soldering or by brazing.

Figures 10 to 27 show different embodiments of a substantially flat drive tongue 28. All of these different embodiments of a drive tongue 28 shown in Figures 10 to 27 are designed to be pushed or pressed into a non-circular hole 26 in a drill rod or a self drilling rock bolt 12 and are designed to be locked with respect to rotation movement to the drill rod or self drilling rock bolt 12.

Figure 10 shows a sectional view C-C shown in Figure 11 of a pressed drill bit inserted into a non-circular hole 26 in a drill rod or self drilling rock bolt 12.

Figure 11 shows a front sectional view B-B shown in Figure 10 of a pressed drill bit 10 showing the drive tongue 28 with substantially parallel sides 43 inserted into a non-circular hole 26 where the drive tongue 28 is essentially neatly fitting into the non-circular hole 26 in the drill rod or self drilling rock bolt 12.

Figure 12 shows a side sectional view A-A shown in Figure 10 of a pressed drill bit 10 with a substantially flat drive tongue 28 inserted into a drill rod or self drilling rock bolt 12.

Figure 13 shows a sectional view F-F shown in Figure 14 of a pressed drill bit 10 inserted into a non-circular hole 26 in a drill rod or self drilling rock bolt 12.

Figure 14 shows a front sectional view E-E shown in Figure 13 of a pressed drill bit 10 showing the drive tongue 28 with sides 44 with dimples, bumps, or any suitable irregular surface. The drive tongue 28 is shown inserted and tightly fitting into a non circular hole 26 in the drill rod or self drilling rock bolt 12.

Figure 15 shows a side sectional view D-D shown in Figure 13 of a pressed drilling rock bolt 12.

Figure 16 shows a sectional view I-I shown in Figure 17 of a pressed drill bit inserted into a non-circular hole 26 in a drill rod or self drilling rod bolt 12. In this embodiment, the end of the non-circular hole 26 in the drill rod 12 has been machined or otherwise formed into a tapered hole 47.

Figure 17 shows a front sectional view H-H shown in Figure 16 of a pressed drill bit 10 showing the drive tongue 28 with partially parallel sides 45 inserted into a non-

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c circular hole 26 and partially tapered sides 46 inserted into a section of tapered hole 47. The drive tongue 28 is essentially neatly fitting into both the section of tapered t' hole 47 and into the non-circular hole 26 in the drill rod or self drilling rock bolt 12.

Figure 18 shows a side sectional view G-G shown in Figure 16 of a pressed drill M 5 bit 10 with a substantially flat drive tongue 28 inserted into a drill rod or self drilling rock bolt 12.

SFigure 19 shows a sectional view L-L shown in Figure 20 of a pressed drill bit

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inserted into a non-circular hole 26 in a drill rod or self drilling rock bolt 12. A hole S49 is positioned close to the end of the drill rod 12 and is at right angles to the longitudinal axis of the drill rod 12, extending at least from the outside of the drill rod 12 to the position of the drive tongue 28. The drive tongue 28 has substantially parallel sides 48 inserted into a non circular hole 26 and the drive tongue 28 is essentially neatly fitting into the non circular hole 26 in the drill rod or self drilling rock bolt 12.

Figure 20 shows a front sectional view K-K shown in Figure 19 of a pressed drill bit 10. The drive tongue 28 has a recess, groove or other suitable indentation which, when the drive tongue 28 is inserted into the non-circular hole 26, lines up with the hole 49 in the drill rod 12.

Figure 21 shows a side sectional view J-J shown in Figure 19 of a pressed drill bit 10 with a substantially flat drive tongue 28. The drive tongue 28 has a recess adapted to receive a locking pin (not shown). The drill rod or self drilling rock bolt 12 has a hole 49 to receive a suitable locking pin (not shown) which can also pass through the recess 50 to lock the drive tongue 28 in the hole 26.

Figure 22 shows a sectional view 0-0 shown in Figure 23 of a pressed drill bit 10 inserted into a non-circular hole 26 in a drill rod or self drilling rock bolt 12, A hole 53 is positioned close to the end of the drill rod 12 and at right angles to the longitudinal axis of the drill rod 12, extending at least from the outside of the drill rod 12 to the position of the drive tongue 28 The drive tongue 28 has substantially parallel sides 51 essentially neatly fitting into a non-circular hole 26 in the drill rod or self drilling rock bolt 12.

Figure 23 shows a front sectional view N-N shown in Figure 22 of a pressed drill bit 10 showing the drive tongue 28 with a hole 52 which, when the drive tongue 28 is inserted into the non-circular hole 26, lines up with the hole 53 in the drill rod 12.

Figure 24 shows a side sectional view M-M shown in Figure 22 of a pressed drill bit 10 with a substantially flat drive tongue 28 with a hole 52. The drill rod or self drilling rock bolt 12 has a hole 53 to receive a suitable locking pin (not shown) which can also pass through the hole 52 to lock the drive tongue 28 in the hole 26.

Figure 25 shows a sectional view R-R shown in Figure 26 of a pressed drill bit inserted into a non-circular hole 26 in a drill rod or self drilling rock bolt 12 with external ribs 65 which may or may not be aligned to form a thread form.

Figure 26 shows a front sectional view Q-Q shown in Figure 25 of a pressed drill bit 10, showing the drive tongue 28 with a slot or recess 55 positioned close to the end of the drive tongue 28 such that the width of the drive tongue 28 can be made slightly wider where the slot is located. In this embodiment, the sides of the drive tongue 54 on the outside of the slot 55 can be compressed to allow the drive tongue 28 to be inserted into the non-circular hole 26. The drive tongue 28 is, preferably, essentially spring loaded into the non-circular hole 26 in the drill rod or self drilling rock bolt 12.

Figure 27 shows a side sectional view P-P shown in Figure 25 of a pressed drill bit 10 with a substantially flat drive tongue 28 with a slot 55. The drill bit 10 is inserted into a drill rod or self drilling rock bolt 12.

Figures 28 to 35 show different embodiments of a substantially flat drive tongue 28 which has tapered sides 57 over its entire length and is inserted into a tapered hole 56 in a drill rod or self drilling rock bolt 12. It is preferred that the drive tongue 28 shown in Figures 28 to 35 is formed of a harder material than the drill rod or self drilling rock bolt 12 into which it is inserted. However, as explained in other parts of the specification, the drive tongue 28 is not formed of a different material to the remainder of the drill bit 10 in some preferred embodiments.

In some preferred embodiments illustrated in Figures 28 to 35, the tapered sides 57 of the drive tongue 28 are inserted into a tapered hole 56 in a fibreglass drill rod or fibreglass self drilling rock bolt 12.

Figure 28 shows a plan view U-U shown in Figure 29 of a pressed drill bit inserted into a tapered hole 56 in a drill rod or self drilling rock bolt 12.

Figure 29 shows a front sectional view S-S shown in Figure 28 of a pressed drill bit 10 showing the drive tongue 28 with tapered sides 57 in a tapered hole 56. The tapered sides 57 on the drive tongue 28 extend beyond the end of the drill rod or self drilling rock bolt 12. As is also illustrated in more detail in Figures 34 and 35, the sides of the tapered drive tongue 57 have substantially flat edges and square corners.

The cutting faces 18 of this embodiment have a substantially modified spade type cutting head design.

Figure 30 shows a side sectional view T-T shown in Figure 28 of a pressed drill bit 10 with a substantially flat drive tongue 28 which is inserted into a tapered hole 56 at the end of a drill rod or self drilling rock bolt 12. The remaining non-tapered hole 58 in the drill rod or self drilling rock bolt 12 has substantially parallel sides but may be circular or non-circular.

Figure 31 shows a plan view X-X shown in Figure 32 of a pressed drill bit inserted into a tapered hole 56 in a drill rod or self drilling rock bolt 12.

Figure 32 shows a front sectional view V-V shown in Figure 31 of a pressed drill bit 10 showing the drive tongue 28 with tapered sides 57 in a tapered hole 56. The tapered sides 57 on the drive tongue 28 extend beyond the end of the drill rod or self drilling rock bolt 12. As is also illustrated in more detail in Figures 34 and 35, the sides of the tapered drive tongue 57 have substantially flat edges and square corners.

The cutting faces 18 of this embodiment have a substantially two-wing type cutting head design.

Figure 33 shows a side sectional view W-W shown in Figure 31 of a pressed drill bit 10 with a substantially flat drive tongue 28 which is inserted into a tapered hole 56 at the end of a drill rod or self drilling rock bolt 12. The remaining non-tapered hole 58 in the drill rod or self drilling rock bolt 12 has substantially parallel sides but may be circular or non-circular.

Figure 34 shows an expanded sectional view of the drive tongue 28 shown in Figure 29 as section Y-Y and in Figure 32 as section Z-Z, where the drive tongue 28 is tapered with tapered sides 57 and substantially square corners 59 that contact the inside surface 60 of the tapered hole 56. The inside surface of tapered hole 60 is preferably round at any cross sectional plane.

When the drill bit 10 is initially inserted into the tapered hole 56, the square corners 59 of the drive tongue 28 rest on the inside surface of the tapered hole

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c 18 ;As axial thrust is applied to the cutting surfaces 18 of the drill bit 10 during normal drilling operations, the corners 59 of the tapered sides 57 bite into the inside t' surface 60 of the tapered hole 56, thereby locking the drill bit 10 into the drill rod or self drilling rock bolt 12 with respect to rotational movement.

t' M 5 Figure 35 shows an expanded sectional view of the drive tongue 28 shown in Figure 29 as section Y-Y and in Figure 32 as section Z-Z, where the drive tongue 28 Sis tapered with tapered sides 57 and substantially square corners 59 that contact the Iinside surface 60 of the tapered hole 56. The inside surface of tapered hole 60 is Spreferably round at any cross sectional plane. As axial thrust is applied to the drill bit during drilling operations, the square corners 59 of the drive tongue 28 are forced into the inside surface 60 of the tapered hole 56 at position 61.

This particularly occurs where hardened steel drill bits are inserted into drill rods or self drilling rock bolts that are made from softer materials than the drill bit 10, such as non-heat treated steel and fibreglass. In this way, the tapered drill bit 10 is locked with respect to rotational movement to the drill rod or self drilling rock bolt 12. It should be noted that this is a different locking mechanism to conventional morse tapers which rely solely on friction to lock a taper. In contrast, the mechanism of some preferred embodiments of the invention relies on the hardened sharp corners of the taper 59 biting into the softer inside surface of the tapered hole Several of the figures additionally illustrate passageways 34 on either side of the drill bit for, for example, flushing fluid to be pumped through these passageways 34 to remove rock cuttings from the drill bit 10 down the outside of the drill rod or self drilling rock bolt 12.

The present invention enables a drill bit 10 to be inserted into a drill rod 12 very easily on site. The drill bit can be used with existing drill rods by using a short adaptor that will screw into the end of existing drill rods, or it can be used with hollow bars or bolts where the central hole has been custom designed to suit the drill bit.

Legs 14, 16 are designed to transmit some of the axial and rotational forces generated in the drilling process through to the hollow drill rod 12 or self drilling rock bolt. Where the tongue 28 has parallel sides, the legs 14, 16 also prevent tongue 28 from being pushed too far into central hole 26.

Many conventional rotary drill bits in the size range 20 mm to 50 mm diameter 19 use a metric 16 mm diameter thread (known as an M16 thread) such that they can be attached to a drill rod. This thread form often becomes jammed and is difficult to unscrew. It is also difficult to change drill bits when the thread form becomes worn.

This M16 thread form also limits the size of the central hole that can be used for flushing fluid in the centre of this thread form to a maximum diameter of about 7 mm.

If a larger central hole is used to increase the flow of a cutting fluid, then the screw thread section becomes too weak and can be sheared off at high torque.

In some preferred embodiments, the present invention overcomes these problems by having a tongue 28 (which is typically 15 mm wide by 6 mm thick and is any suitable length) which fits into a non-circular or tapered hole 26 such that the drill bit 10 is inhibited from rotating relative to the hole. There is at least one passageway 34 formed between the tongue 28 and the sides of the hole which is preferably not limited by the size of the tongue 28, thereby allowing the passageway 34 to have a greater total area than say a typically used 7 mm diameter hole in a conventional drill bit. The flat drill bit 10 extending beyond the drill rod 12 as shown in Figures 30 and 33 maximises the space available for flushing fluid and rock cuttings to mix together in a swirl chamber which enables more efficient removal of rock cuttings down the outside of the drill rod 12.

In practice, drill bit 10 is pushed into non-circular hole 26 in drill rod 12 or in a drill rod adaptor, and can be locked into its axial position by a roll pin which is hammered into a hole in the drill rod and into a locking slot in tongue 28. Drilling is then carried out in a conventional manner until the drill tip is worn and needs replacing. In this case, the roll pin is punched out of its hole, and the drill tip is prised out of non-circular hole 26 in drill rod 12 with a screwdriver. Alternatively, where the drill bit extends beyond the diameter of the drill rod, a hammer blow or similar force can be used to remove the drill bit from the drill rod. The drill tip can then be replaced as described above.

Where the drill bit is used with self drilling rock bolts, it is unlikely that the drill bit will need to be replaced whilst drilling one hole. However, the removal procedure of the drill bit if required would be similar to that described above. In the case of drill bits with drive tongues with parallel sides, the drive tongue is preferably designed to be a neat and tight fit in a non-circular hole such that some force would be required to remove it from the drill rod. In the case of drill bits with drive tongues with tapered sides, the drive tongue is preferably adapted for a neat and tight fit in the matching tapered hole such that some force would also be required to remove it from the drill rod.

In the case of conventional drilling sedimentary rocks, the drill tip would typically have tungsten carbide cutting edges 40, 42. In the case of conventional drilling very soft sedimentary rocks, the drill tip would typically have hardened steel cutting edges. In the case of self drilling rock bolts, the drill tip would typically have a cutting edge which would be capable of drilling one hole only into the rock type the bolt was being installed into.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims (19)

1. A drill bit for insertion into a hollow bar comprising: at least one cutting surface or face at one end; and attachment means at an opposing end for securing the drill bit to a hollow bar, wherein the drill bit has a substantially planar profile along its length.

2. The drill bit according to claim 1 formed from a substantially planar sheet of material.

3. The drill bit according to claim 2 wherein the material is steel.

4. The drill bit according to claim 2 or 3 formed in a punching, pressing or stamping operation.

The drill bit according to any one of claims 1 to 4 wherein the at least one attachment means is a tongue.

6. The drill bit according to claim 5, wherein at least one support leg is located on at least one side of the tongue.

7. The drill bit according to claim 6, wherein the at least one support leg is adapted to press against or be welded to an end of a hollow bar.

8. The drill bit according to claim 7, wherein a support washer is interposed between the at least one support leg and the end of the hollow bar.

9. The drill bit according to any one of claims 5 to 8, wherein the tongue is adapted to fit into a hole in the hollow bar.

The drill bit according to claim 9 wherein the hollow bar is a drill rod or self drilling rock bolt.

11. The drill bit according to claim 9 or 10, wherein the tongue further includes a hole or recess adapted to accommodate a fixing pin, lug or clip for retaining the drill bit in the hollow bar.

12. The drill bit according to any one of claims 5 to 11, wherein at least a portion of the sides of the tongue are parallel.

13. The drill bit according to any one of claims 5 to 12, wherein at least a portion of the sides of the tongue are tapered.

14. The drill bit according to claim 13, wherein the tapered portions of the sides of the tongue have substantially square corners.

The drill bit according to any one of claims 1 to 14 adapted so that when inserted into a hollow bar, at least one passageway on at least one side of the drill bit provides fluid communication between hollow portions of the hollow bar and a borehole created by the drill bit.

16. The drill bit according to any one of claims 1 to 15, wherein the attachment means is adapted so that when the drill bit is inserted into the hollow bar, relative rotational movement between the drill bit and the drill rod or self drilling rock bolt is substantially inhibited.

17. A drill bit substantially as hereinbefore described with reference to any one of the accompanying figures.

18. A method of manufacturing a drill bit comprising punching, pressing or stamping a drill bit from a substantially planar sheet of material to form a substantially planar drill bit adapted for insertion into a hollow bar.

19. The method of claim 18, wherein the material is steel. A drill bit manufactured according to the method of claim 18 or 19.