AU5428101A - Drill bit - Google Patents

Description

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EVELYN FRANCES GRAY

AUSTRALIA

Patents Act 1990 SPECIFICATION FOR THE INVENTION ENTITLED "DRILL BIT" This invention is described in the following statement: I -2- Drill Bit

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Field of the Invention I The present invention relates to a drill bit and relates particularly, though not I 5 exclusively, to a drill bit for use with rock bolts.

Background of the Invention Drill bits are an integral part of drilling operations in the mining and Stunnelling industries. Drill bits are particularly used to drill holes for exploration, blasting and for rock 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.

20 Most drill bits are manufactured from two major parts. These are the main S"body" section of the drill bit, and the "cutting edge" section of the drill bit. The body o section is either a cast, forged or machined section which includes an attachment ee. 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 25 could also be a series of recessed holes).

The cutting edge section of the drill bit is typically an elongated tungsten 3 carbide insert designed to fit into a slot in the body of the drill bit, or the cutting edge could be a series spherical tungsten carbide "buttons" or "ballistic buttons" 3 designed to be typically brazed, soldered or silver soldered into position into a series of recessed holes in the body of the drill bit.

I 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.

3 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 I of the bit.

Another disadvantage of rotary drill bits in the size range 20mm to diameter, is that they normally use an M16 thread (a metric thread 16mm in i 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.

I Objects of the Invention It is an object of the invention to provide a drill bit that is cheaper to produce Ithan current investment cast, or forged drill bits, and provides an attachment I means to a drill rod that overcomes some of the current problems with threaded drill bits.

1 15 A further object of invention is to provide a drill bit which overcomes many of the disadvantages with existing rotary drill bits as listed above, as well as providing some additional benefits for the installation and performance of drill bits.

20 Summary of the Invention o According to the present invention there may be provided a drill bit having a cutting surface or face at one end and at least one attachment means at the other opposing end for securing said drill bit to a drilling means.

Preferably said drill bit is formed in a pressing or stamping operation where 25 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. The leg member(s) 3may be bent away from opposing faces of said drill bit.

In a practical embodiment a tongue extends from said drill bit between said 3 leg members and is located 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 3cutting 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 1 -4made from either hardened steel or have a hard insert or facing material attached *such as tungsten carbide.

Preferably said tongue is adapted to fit neatly into a non-circular hole in said I 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 Isides 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 S 10 means comprises a tapered hole in the drive means and a tapered tongue on the Idrill bit. The tapered tongue on the drill bit fits neatly into the tapered hole on the drive means. The angle of the taper is sub-parallel to the central axial line of the I 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 S 15 means through to the drill bit via the tapered hole, the normal force generated on O 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 20 conical in shape and can be machined or formed by any suitable process and the I 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 flat steel and the sides of the tapered tongue are normally "as punched" or "as stamped" 25 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 3 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 3embodiment, two passageways are formed between the tapered hole and the flat tapered tongue. These passageways allow flushing fluid to flow pass the tapered m 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 such that 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 I one surface approximately at right angles to the axis of the drill rod and facing towards the drill rod that extends beyond the diameter of the drill rod or self drilling I 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 U strength such that welding the drill bit onto the drill rod or self drilling rock bolt is i not normally required. The central drive tongue of the drill bit can have surfaces I which contact the drilling means which are parallel, or tapered, or have a 15 combination of parallel and tapered surfaces. These surfaces can also be planar :or be irregular with small bumps or indentations to allow for small variations in the I **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 punched into it and be located anywhere along it such that a locking pin can be pushed through an aligned hole in the drill 20 rod and through the hole in the tongue such that the drill bit is firmly located in the Idrill 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 25 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, 3the leading end of the drive tongue can only be fitted into a hole in a drill rod or self drilling bolt if the sides of the drive tongue are compressed. In this manner, the 3 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 and therefore the drive tongue width will adjust itself to be exactly the right size for the hole in which it is to be inserted. In addition, the length and width of the slot are designed to ensure that the drive tongue can just be pushed into the hole but at the same time it is firmly located in the hole such that it would not easily fall out of the hole.

-6- The length of the central drive tongue can be any suitable length. In the I 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 U than 10mm and less than 50mm. 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 20mm and less than 200mm, but are not so limited in length.

The central drive tongue on the drill bit also provides a simple means to centralise 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.

I 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 15 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 made from steel which has been pressed into 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 the one simple pressing operation.

Moreover, 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 S. 25 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 n within the drill bit.

The present invention provides a drill bit which is economical to 3manufacture and is suited to high speed production using high speed pressing or stamping operations.

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

-7- Finally, for soft rocks such as coal and mudstone, it is possible to simply use heat treating processes to make the cutting edge of the drill bit suitable for cutting soft rock. For harder or more abrasive rocks, a tungsten carbide cutting I face or hard facing can be fixed to the drill bit to make it suitable for drilling these harder rocks. The shape of the cutting head could be any suitable shape that can i be substantially formed in a pressing or punching operation and could be symmetric or asymmetric in design. In this manner the drill bit design is suitable for I a range of rotary drilling applications but is not limited to rotary drilling only.

I 10 Description of the Drawings iIn order that the invention may be more readily understood and put into practical effect, reference will now be made to the accompanying drawings, in which:- I :Figure 1 is a side view of a drill bit made in accordance with a first 15 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; In..

Figure 3 is a plan view of the drill bit shown in Figure 1; I 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 is welded to the main body of the drill bit of Figure 1; FFigure 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 I detail of the drill bit shown in Figure 6; Figure 10 shows a sectional view C-C shown in Figure 11 of a pressed drill 3 bit 10 inserted into a non-circular hole 26 in a drill rod or self drilling rock bolt 12 showing passageways 34 on either side of the drill bit for flushing fluid; 3 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 -8into 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 I drill bit 10 with a substantially flat drive tongue 28 inserted into a drill rod or self drilling rock bolt 12 showing passageways 34 on either side of the drill bit for I flushing fluid; Figure 13 shows a sectional view F-F shown in Figure 14 of a pressed drill I bit 10 inserted into a non-circular hole 26 in a drill rod or self drilling rock bolt 12 showing passageways 34 on either side of the drill bit for flushing fluid; I 10 Figure 14 shows a front sectional view E-E shown in Figure 13 of a pressed idrill bit 10 showing the drive tongue 28 with sides 44 with dimples, bumps, or any suitable irregular surface inserted into a non-circular hole 26 where the drive tongue 28 is tightly fitting into the 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 drill bit 10 with a substantially flat drive tongue 28 inserted into a drill rod or self drilling rock bolt 12 showing passageways 34 on either side of the drill bit for flushing fluid; I Figure 16 shows a sectional view I-I shown in Figure 17 of a pressed drill bit 10 inserted into a non-circular hole 26 in a drill rod or self drilling rock bolt 12 I showing passageways 34 on either side of the drill bit for flushing fluid where 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 I 25 drill bit 10 showing the drive tongue 28 with partially parallel sides 45 inserted into a non-circular hole 26 and partially tapered sides 46 inserted into a section of 3 tapered hole 47 where the drive tongue 28 is essentially neatly fitting into both the section of tapered hole 47 and into the non-circular hole 26 in the drill rod or self 3 drilling rock bolt 12; Figure 18 shows a side sectional view G-G shown in Figure 16 of a pressed 3 drill bit 10 with a substantially flat drive tongue 28 inserted into a drill rod or self drilling rock bolt 12 showing passageways 34 on either side of the drill bit for n flushing fluid; Figure 19 shows a sectional view L-L shown in Figure 20 of a pressed drill m bit 10 inserted into a non-circular hole 26 in a drill rod or self drilling rock bolt 12 showing passageways 34 on either side of the drill bit for flushing fluid, and a hole I 49 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, and extends at least from the outside of the drill rod 12 to the position of the drive tongue 28, and the drive tongue 28 has substantially parallel sides 48 inserted into a non-circular hole 26 and the drive I tongue 28 is essentially neatly fitting into the non-circular hole 26 in the drill rod or I self drilling rock bolt 12; Figure 20 shows a front sectional view K-K shown in Figure 19 of a pressed drill bit 10 showing the drive tongue 28 with a recess, groove or other suitable indentation 50 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; SFigure 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 with a recess 50 which is inserted into a drill rod or self drilling rock bolt 12 which has a hole 49 to receive a *i. suitable locking pin (not shown) which can be inserted into the hole 49 and through the recess 50 to lock the drive tongue 28 in the hole 26, and passageways 34 are °I also shown on either side of the drill bit for flushing fluid; Figure 22 shows a sectional view 0-0 shown in Figure 23 of a pressed drill I bit 10 inserted into a non-circular hole 26 in a drill rod or self drilling rock bolt 12 showing passageways 34 on either side of the drill bit for flushing fluid and 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, and extends at least from the outside of the drill p 25 rod 12 to the position of the drive tongue 28, and the drive tongue 28 has substantially parallel sides 51 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; 3 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 3 28 is inserted into the non-circular hole 26 lines up with the hole 53 in the drill rod 12; I 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 which is inserted into a drill rod or self drilling rock bolt 12 which has a hole 53 to receive a suitable i locking pin (not shown) which can be inserted into the hole 53 and through the hole 52 to lock the drive tongue 28 in the hole 26, and passageways 34 are also I shown on either side of the drill bit for flushing fluid; Figure 25 shows a sectional view R-R shown in Figure 26 of a pressed drill I bit 10 inserted into a non-circular hole 26 in a drill rod or self drilling rock bolt 12 with external ribs 65 showing passageways 34 on either side of the drill bit for flushing fluid, and where the external ribs 65 may or may not be aligned to form a thread form; S 10 Figure 26 shows a front sectional view Q-Q shown in Figure 25 of a pressed i 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, and where the sides of the drive tongue 54 on the outside of the slot 55 can be compressed to allow the drive oooo 15 tongue 28 to be inserted into the non-circular hole 26, and thus the drive tongue 28 is 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 Sdrill bit 10 with a substantially flat drive tongue 28 with a slot 55 which is inserted into a drill rod or self drilling rock bolt 12, and passageways 34 are also shown on either side of the drill bit for flushing fluid; Figure 28 shows a plan view U-U shown in Figure 29 of a pressed drill bit 10 inserted into a tapered hole 56 in a drill rod or self drilling rock bolt 12 showing passageways 34 on either side of the drill bit for flushing fluid; iii f 25 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, and with cutting faces 18 which may be any suitable design and in this case is shown as a substantially modified spade type cutting head design, and with the 3 tapered sides 57 on the drive tongue 28 extending beyond the end of the drill rod or self drilling rock bolt 12, and with the sides of the tapered drive tongue 57 3 having substantially flat edges and square corners as shown in detail Figure 34 and Figure 3 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 -11hole 56 at the end of a drill rod or self drilling rock bolt 12, and where 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, and passageways i 34 are also shown on either side of the drill bit for flushing fluid; 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 showing passageways 34 on either side of the drill bit for flushing fluid; 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, and with cutting faces 18 which may be any suitable design and in this case is ishown as a substantially two-wing type cutting head design, and with the tapered sides 57 on the drive tongue 28 extending beyond the end of the drill rod or self I drilling rock bolt 12, and with the sides of the tapered drive tongue 57 having substantially flat edges and square corners as shown in detail Figure 34 and 15 Figure S. 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, and where the 3 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, and passageways 34 are also shown on either side of the drill bit for flushing fluid; Figure 34 shows an expanded sectional view of the drive tongue 28 shown tI in Figure 29 as section Y-Y and in Figure 32 as section Z-Z where the drive tongue 28 is tapered and has tapered sides 57 and has substantially square corners 59 i.i 25 that contact the inside surface 60 of the tapered hole 56, and where the inside surface of the tapered hole 60 is round at any cross sectional plane, and as the Sdrill 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 60; and 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 3 28 is tapered and has tapered sides 57 and has substantially square corners 59 that contact the inside surface 60 of the tapered hole 56, and where the inside 3 surface of the tapered hole 60 is round at any cross sectional plane, and as axial thrust is applied to the drill bit during drilling operations, the square corners 59 of -12the drive tongue 28 are forced into the inside surface 60 of the tapered hole 56 at I position 61.

This particularly occurs where hardened steel drill bits are inserted into drill I 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 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, whereas this mechanism relies on the hardened sharp corners of the taper 59 biting into the softer inside surface of the tapered hole Detailed Description of the Preferred Embodiments i 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 15 any drill bit. The invention is particularly applicable to rotary drill bits used to drill o sedimentary rocks.

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

I In the first embodiment shown in Figures 1 to 5 there is shown a drill bit 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.

Legs 14,16 are 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 I 25 washer 24 as shown, or may be welded onto the end of drill rod 12, or may press S0 against the end of drill rod 12. The hollow drill rod 12 has a non-circular central I 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 I hole 26 to be locked into its rotational position with respect to drill rod 12. Drill bit 10 can also be locked into its axial position with respect to drill rod 12 by the 3 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 3 shown) in drill bit 10. Typically, tongue 28 would be a neat and tight push fit into hole 26.

-13- As shown in Figures 2 and 3, the cutting faces or edges 18 have the largest I diameter of the drill bit 10 and have a larger diameter than the drill rod 12. 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 I 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 I pressed and formed such that the cutting faces are substantially in line with a centre line axial plane.

I 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.

i 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 I 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 i cutting face or faces 40,42 would normally be attached to the body of the drill bit 10 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 I!i 25 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.

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 3 tongue 28 shown in Figures 28 to 35 is a harder material than the drill rod or self drilling rock bolt 12 into which it is inserted but is not so limited. In a preferred 3 embodiment, the tapered sides 57 of the drive tongue 28 is inserted into a tapered hole 56 in a fibreglass drill rod or fibreglass self drilling rock bolt 12. Figure 34 -14shows that as the drive tongue 28 is first inserted into the tapered hole 56, the tapered sides 57 of the drive tongue 28 contact the inside surface 60 of the tapered hole 56 at the corners 59 of the tapered sides 57 only. As axial thrust is i 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 surface 60 of the tapered hole 56 and lock the drill bit 10 into the drill rod or self drilling rock bolt 12 with respect to rotational movement.

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 ihollow 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 15 tongue 28 from being pushed too far into central hole 26.

S: The present invention also provides a low cost method of manufacture for i" drill bits, particularly for drill bits used for rotary drilling applications. The present invention is particularly suited for use with self drilling rock bolts where a low cost disposable drill bit is required.

Many conventional rotary drill bits in the size range 20mm to i diameter use a metric 16mm 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, and change drill bits when they become worn. This M16 thread form also limits the size of the central hole that can be used for flushing fluid in the :i:i 25 centre of this thread form to a maximum diameter of about 7mm. If a larger central hole is used to increase the flow of a cutting fluid, then the screw thread section n becomes too weak and it can be sheared off at high torque.

The present invention avoids these problems by having a tongue 28 which l is typically 15mm wide by 6mm thick and is any suitable length and which fits into non-circular or tapered hole 26 such that the drill bit 10 cannot rotate relative to the Shole and there is a least one passageway 34 formed between the tongue 28 and the sides of the hole. Also the passageway 34 for drilling fluid is not limited by the Isize of the tongue and the passageway can have a greater total area than a 7mm diameter hole.

In practice, drill bit 10 is pushed into non-circular hole 26 in drill rod 12 or in I 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 i then carried out in a conventional manner until the drill tip is worn and the drill tip 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, i 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 i 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 would be designed to be a neat and tight fit in a non-circular hole such that some force S 15 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 would be 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.

t In the case of conventional drilling sedimentary rocks, the drill tip would S 20 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 have a cutting I edge which would just be capable of drilling one hole only into the rock type the bolt was being installed into.

i 25 Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described.

It is to be understood that the invention includes all such variations and modifications. The invention also includes all of the steps, features, compositions, and compounds referred to or indicated in this specification (unless specifically excluded) individually or collectively, and any and all combinations of any two or more of said steps or features. 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 integer or group of integers, but not to the exclusion of any other integer or group of integers.

-16- Where the specification refers to a "drill bit" or to a "drilling bit" or to a "drill i tip" or to a "drilling tip" it is to be understood that the invention includes all such variations and modifications of the above, and any other member that could be I used to drill a hole in rock.

Where the specification refers to a "drilling" or to "rotary drilling" or to "rotary I percussive drilling" it is to be understood that the invention includes 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.

I Where the specification refers to a "tongue" or to a "drive tongue" it is to be understood that the invention includes all such variations and modifications of the I above, and includes "tapered tongue", "tang", "drive tang", "lug", or "spigot" and any other substantially flat member that could be used to lock a drill bit into a drill i rod or self drilling rock bolt in a rotational direction.

Where the specification refers to a "cutting edge" or to a "cutting face" or to a "cutting surface" or to a "cutting head" or to a "cutting insert" it is to be understood that the invention includes all such variations and modifications of the *o above, and any other member that could be used to cut rock.

Where the specification refers to "hardened" or to "hardening" it is to be understood that the invention includes all such variations and modifications of the S 20 above, and any other process or metal or material that could be used to provide a I" hard surface suitable for drilling rock.

Where the specification refers to a "pressing" or to "stamping" it is to be I understood that the invention includes all such variations and modifications of pressing and stamping but is not limited to these alone and includes any suitable 25 manufacturing process.

Where the specification refers to a "legs" it is to be understood that the i invention includes 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 to transfer some of the axial thrust from the drill rod to the drill bit.

Claims (8)

1. A drill bit designed to drill rocks which consists of at least one I cutting surface or face at one end, and at least one attachment means at the other opposing end comprising a substantially flat drive and locating tongue which can be inserted into a non-circular hole in a drill rod or self drilling rock bolt to secure the said drill bit with respect to rotational I movement to the said drill rod or self drilling rock bolt.

2. A drill bit defined in Claim 1 which is made from steel. I 10 3. A drill bit defined in Claim 2 which is formed substantially from I flat steel in a pressing or stamping operation.

4. A drill bit defined in Claim 3 which has at least one support leg I on at least one side of a drive tongue.

5. A drill bit defined in Claim 4 which has at least one support leg on at least one side of a drive tongue which is designed to press against or :be welded to the end of a drill rod or the end of a self drilling rock bolt. S6. A drill bit defined in Claim 4 which has at least one support leg on at least one side of a drive tongue which is attached to a support t washer which designed to press against or be welded to the end of a drill rod or the end of a self drilling rock bolt.

7. A drill bit defined in any of the above Claims which has a central drive and locating tongue which fits neatly into a non-circular hole in a drill rod or in a self drilling rock bolt.

8. A drill bit defined in any of the above Claims which has a fo 25 central drive and locating tongue which fits neatly into a non-circular hole in a drill rod or in a self drilling rock bolt and which has a hole or recess in the central drive tongue which is designed to accommodate a fixing pin, lug or clip which prevents the drill bit from falling out of the non-circular hole. S9. A drill bit defined in any of the above Claims which has a central drive and locating tongue which will fit into a non-circular hole in a Sdrill rod or in a self drilling rock bolt where the central drive tongue is initially slightly wider than the non-circular hole in which it is to be inserted such that n some force is required to insert the drill bit in the hole.

18- A drill bit defined in any of the above Claims which has a i central drive and locating tongue which fits neatly into a non-circular hole in a drill rod or in a self drilling rock bolt and which has substantially parallel I sides. 11. A drill bit defined in any of the above Claims which has a central drive and locating tongue which has a central slot punched into it I such that in operation the width of the drive tongue can initially be slightly wider than the width of the non-circular hole such that the slot has to be closed slightly to enable the drill bit to be inserted into the non-circular hole in a drill rod or in a self drilling rock bolt. I 12. A drill bit defined in Claim 3 which has a central drive and locating tongue where the drive tongue has partially parallel sides and partially tapered sides which fits neatly into a partially tapered hole and partially non-circular hole in a drill rod or in a self drilling rock bolt. 13. A drill bit designed to drill rocks which consists of at least one cutting surface or face at one end, and at least one attachment means at the other opposing end comprising a substantially flat drive and locating tongue with tapered sides where the edges of the tapered sides are I substantially flat with square corners and which fits neatly into a tapered 20 hole in a drill rod or in a self drilling rock bolt. 14. A drill bit defined in Claim 13 which is made from steel. 15. A drill bit defined in Claim 14 which is formed substantially 3 from flat steel in a pressing or stamping operation. 16. A drill bit defined in Claimsl2, 13, 14 and 15 which does not I 25 have any support legs or support washers resting on the end of a drill rod or on the end of a self drilling rock bolt. i 17. A drill bit defined in any of the above Claims that does not have a support washer resting on the end of a drill rod or on the end of a i self drilling rock bolt. 18. A drill bit defined in any of the above Claims which has any suitable cutting head.

19. A drill bit defined in any of the above Claims which has any n suitable cutting head made from hardened steel. -19- A drill bit defined in any of the above Claims which has any I suitable cutting head which has any suitable hard facing or hard inserts attached to it. n 21. A drill bit defined in any of the above Claims which when inserted into a non-circular or tapered hole in a drill rod or a self drilling rock I bolt forms at least one passageway on at least one side of the drill bit to allow fluid to pass through the passageway or passageways. I I I 9 0