Field of the invention

[001] The present invention relates to a drill bit for drilling of a borehole. The invention is particularly suited for drilling of boreholes in rock or similar, for example as used in mining and civil engineering applications. The invention more particularly relates to drill bits being adapted for drill rods or self-drilling rock bolts and is described herein in that context, but is not so limited.

Background of the invention

[002] A wide variety of drill bits are used to drill rock in the mining and civil engineering industries. Drill bits for drilling rock fall into two major categories, namely, those used with rotary drilling, and those used with rotary percussive drilling.

[003] Drill bits used with rotary drilling are designed to cut the rock so they normally have one or more sharp edges made from a hard material, typically hardened steel or tungsten carbide, where the sharp edge or edges cut into the rock as the drill bit is rotated and is forced into the rock by the drilling machine. Typically the rotation speed of the drill bit is between 100 and 800 rpm depending on the borehole diameter, and either water or air is used to flush the drill cuttings away from the drill tip. Water or air is pumped up the hollow drill rod or hollow bolt, and the water or air and the drill cuttings are flushed away along the outside annulus space between the drill rod or bolt and the) borehole wall.

[004] There are many different designs of rotary drill bits including full spade, modified spade, and two wing drill bits which are designed to drill different rock types. Typically rotary drilling can be used to drill rocks with a compressive strength of up to about 70-100MPa.

[005] Drill bits for rotary drilling of 'soft' rock typically include a hardened cutting insert at the drill tip. The cutting insert for a rotary drill bit may be for example a triangular or 'house-shaped' insert of tungsten carbide, hardened steel or similar, inserted into a slot formed in the end surface of the drill bit body.

[006] U.S. Patent No. 5,464,068 includes in one embodiment a chevron-shaped drill insert. [007] Rotary drill bits may further include fluid passages for injection of a drilling fluid such as water for cooling the drill bit and lubricating the drilling. The fluid passages typically include fluid outlet apertures opening to the end of the drill bit, for example behind the tip of the drill insert, to assist with flushing away the drill cuttings.

[008] Drill bits used with rotary percussive drilling are designed to crush or smash the rock and are generally used with stronger or harder rocks, i.e. those with a compressive strength of greater than 100 MPa.

[009] Typically rotary percussive drill bits may have one or more chisel edges which are forced into the rock by the hammer action of the percussive drilling machine, and are also rotated at the same time such that the whole surface area of the end of the borehole is smashed by the chisel edges being hammered and rotated into the end of the borehole. Alternatively, rotary percussive drill bits may instead of chisel edges have button bits or ballistic button bits, which are tungsten carbide balls at the end of the drill bit to crush the rock as the drill bit is hammered into the rock by the percussive action of the drilling machine and rotated.

[010] Any reference herein to known prior art does not, unless the contrary indication appears, constitute an admission that such prior art is commonly known by those skilled in the art to which the invention relates, at the priority date of this application.

Summary of the invention

[011] An objective of one form of the present invention is to provide an alternative cutting insert and mounting arrangement for a rotary drill bit.

[012] Further forms of the invention aim to provide an alternative fluid passage arrangement for a rotary drill bit, to assist with flushing of drill cuttings.

[013] A first form of the invention provides a drill bit for rotary drilling of a borehole, including: a drill bit body having a rotary axis, a front end having a cutting surface adapted for drilling the borehole as the drill bit is rotated in a first direction and advanced forward axially, a rear end and at least one drill bit side surface; at least one fluid passage in the drill bit body, the or each fluid passage having an outlet aperture in a said drill bit side surface for expelling fluid as the borehole is being drilled; the or each outlet aperture of the fluid passage being located on a portion of the drill bit side surface which is disposed at an angle selected from a forwardly diminishing taper disposed at an angle of less than about 30 degrees from the rotary axis, a rearwardly diminishing taper, and a zero taper.

[014] To express this in a different way, the fluid passage outlets are located at portions of the drill bit side surface which are at an angled relative to the forward axial direction in a range between an obtuse angle of at least 150 degrees to a reflex angle.

[015] The drill bit can include a plurality of said fluid passages, all said fluid passages of the drill bit having outlet apertures located at side surface portions having a forwardly diminishing taper of about 20 degrees or less from the rotary axis, a zero taper, and a rearwardly diminishing taper.

[016] The drill bit can include at least one first fluid passage having a first outlet aperture in a first drill bit side surface portion having a forwardly diminishing taper, and at least one second fluid passage having a second outlet aperture in a second drill bit side surface portion having a zero taper or a rearwardly diminishing taper.

[017] The drill bit can include at least one set of outlet apertures comprising a first said outlet aperture and a second said outlet aperture.

[018] The first outlet aperture of the set can be located forward of the second outlet aperture.

[019] The second outlet aperture of the set can be angularly offset trailing the first outlet aperture relative to rotation of the drill bit in the first direction.

[020] The angular offset between the first outlet aperture and the second outlet aperture can be about 90 degrees.

[021] A second form of the invention provides a drill bit for rotary drilling of a borehole, including: a drill bit body having a rotary axis, a front end having a cutting surface adapted for drilling the borehole as the drill bit is rotated in a first direction and advanced forward axially, a rear end and at least one drill bit side surface; at least one set of fluid passages in the drill bit body for expelling fluid as the borehole is being drilled, each set of fluid passages including a first outlet aperture and a second outlet aperture, the first outlet aperture of the set being located forward of the second aperture of the set and also angularly leading the second aperture in the first direction of rotation. [022] The first outlet aperture can be formed in a first drill bit side surface inclined at a first angle relative to the rotary axis, and the second fluid passage is formed in a second drill bit side surface generally parallel to the rotary axis.

[023J The drill bit can include a cutting insert, the first outlet aperture angularly leading the cutting insert relative to the first direction of rotation, and the second outlet aperture angularly trailing the cutting insert relative to the first direction of rotation.

[024] The first outlet aperture can act to direct fluid to flush drilling debris from a region leading the cutting insert as the drill bit rotates, and the second outlet aperture acts to assist flushing of the drilling debris away from a region behind the cutting insert.

[025] The drill bit can include at least two said pairs of said fluid outlet apertures.

[026] The angular offset between the first outlet aperture and the second outlet aperture can be about 90 degrees.

[027] A third form of the invention provides a drill bit for rotary drilling of a borehole as the drill bit is rotated in a first direction, including: a drill bit body having front end, a rear end and a rotary axis; a cutting insert in the front end of the drill bit body; the cutting insert having a leading face and a trailing face relative to the first direction of rotation; the drill bit body having a face adjacent the trailing face of the cutting insert, said face of the drill bit body having an undercut portion relative to a plane which contains the rotary axis to form a re-entrant space, the trailing face of the cutting insert protruding into the re-entrant space thus formed to help retain the cutting insert in place during rotary drilling.

[028] The trailing face of the cutting insert and the at least the undercut portion of said face of the drill bit body can be inclined rearwardly relative to the plane containing the rotary axis.

[029] The trailing face and said face of the drill bit body can have substantially matching angles of inclination relative to the plane containing the rotary axis.

[030] The cutting insert can be substantially chevron-shaped.

[031] The front end of drill bit body can include a retention groove adapted to receive the chevron-shaped cutting insert, said groove including said face of the drill bit body. [032] Further aspects of the invention will be apparent from the following description and the drawings, and from the claims.

Brief description of the drawings

[033] A detailed description of example embodiments of a drill bit for rotary drilling according to the invention is given hereinafter with reference to the drawings, in which:

[034] Figs. 1 to 3 are a set of elevations of a drill bit with cutting insert, according to an example embodiment of the invention;

[035] Fig. 4 is front end view of the drill bit of Figs. 1 to 3;

[036] Figs. 5 and 6 are sections along lines A-A and B-B of Fig. 3 respectively;

[037] Fig. 7 is a perspective of the drill bit body, without the cutting insert;

[038] Figs. 8 to 11 are orthogonal views of the drill bit body of Fig. 7;

[039] Fig. 12 is an elevation of the cutting insert of the drill bit;

[040] Figs. 13 and 14 are sections along lines BB-BB and C-C of Fig. 12 respectively;

[041] Figs. 15 to 17 are side views of the drill bit including hidden detail of the fluid passages; and

[042] Figs. 18 and 19 are, respectively, section AZ-AZ and BZ-BZ of Fig. 16.

[043] Dimensions, where shown, are in millimetres and angles are in degrees, unless otherwise indicated.

Detailed description of the embodiment or embodiments

[044] The described drill bit is adapted for rotary drilling of a borehole in rock, and in particular to drilling of 'soft' rock of up to approximately 70-100 MPa compressive strength.

[045] The illustrated and described drill bit is particularly adapted for use in a self-drilling rock bolt of the general type described in International Patent Application PCT/AU2011/001146 and Australian Patent Application 2012900178, the contents of both being incorporated herein by reference. [046] Figs. 1 to 4 are orthogonal views of a drill bit including cutting insert according to a first example embodiment. Figs. 5 and 6 are enlarged sections taken along, respectively, lines A-A and lines B-B of Fig. 3.

[047] The illustrated drill bit is adapted for drilling a borehole of approximately

42mm diameter, though of course other diameters are contemplated. The illustrated drill bit is adapted for left hand rotation (i.e. anti-clockwise as viewed from the rear) for drilling.

[048] With reference to Figs. 1 to 6, drill bit 10 comprises a drill bit body 12 having a front end 1 , side surfaces 14, and a rear end 16.

[049] Figs. 7 to 11 illustrate the drill bit body without the cutting insert.

[050] The side surfaces of the drill bit body 12 include forwardly tapered side surfaces 18a, 18b proximal the front end of the drill bit. As labelled in Fig. 9, surfaces 18a taper back by an angle of about 23 degrees from the perpendicular, while surfaces 18b are more steeply inclined, and taper at an angle of approximately 20 degrees from the drill bit rotary axis.

[051] Rearwardly tapered side surfaces 19 taper at approximately 10 to 15 degrees towards the rear (shown in Fig. 8), and a generally cylindrical (i.e. zero taper) side surface 20 is proximal the rear of the drill bit body.

[052] The rear end of the drill bit includes a pivot shank 22 which is optionally offset from the rotary axis 24 of the drill bit, as illustrated, to allow the drill bit to pivot to act as a retention cam for the self-drilling rock bolt after drilling is completed, as described in PCT/AU2011/001146 and AU 2012900178. The pivot shank 22 may alternatively have no offset from the rotary axis 24 of the drill bit. The pivot shank 22 may be generally cylindrical along a shank axis 28 (Fig. 8), with a ring groove 23 for cooperating with a cylindrical retaining pin (not shown) for connecting the drill bit 10 to the body of a self-drilling rock bolt (also not shown).

[053] The rear end of the drill bit body includes a stepped drive surface 26 which with a co-operating drive surface on a connecting member (not shown) connected to the rock bolt or drill rod acts as a keyway for driving rotation of the drill bit about the rotary drilling axis 24 when the rock bolt or drill rod to which the drilling member is connected is rotated in a first, drilling direction, but allows the drive surfaces to separate and relative rotation of the drill bit and the rock bolt or drill rod in the opposite direction about the shank longitudinal axis 28 when the rock bolt or drill rod is rotated in a second, opposite direction.

[054] At the front end of the drill bit body is a groove 30 for locating the cutting insert 32.

[055] The groove 30 includes a trailing surface 36 - as considered in the direction of drilling rotation 34 shown in Figs. 4, 10 and 11 - the trailing surface 36 has an undercut portion relative to a plane which contains the rotary axis and which is angled rearwardly to form a re-entrant space together with the angled base 37 of the groove. See for example Fig. 2, in which it can be seen that the trailing surface 36 and the base 37 define an acute angle therebetween, as do the respective matching trailing surface 44 and bottom surface 39 of the insert.

[056] As shown in Figs 12, 13, and 14, the cutting insert 32 is generally arrow- or chevron-shaped, with a pair of wings 38a, 38b culminating in a tip 40. Each wing has a leading cutting surface 42 which is generally planar, and a trailing surface 44 which is raked back relative to the direction of drill rotation 34, to match the angle of the trailing surface 36 of the groove 30. When the cutting insert is inserted in the groove 30 of the drill bit body and rotated slightly into final position, the trailing surfaces of the cutting insert protrude into the respective re-entrant spaces of the groove 30. The cutting insert may then be attached permanently to the drill bit body 12, for example by brazing. The angles as marked in Figs 12, 13, and 14 help describe the general shape of the cutting insert 32 in this embodiment, but should not be taken to be limitations of the invention.

[057] In use, the vector force on the cutting insert 32 due to the combination of axial thrust and rotary drilling forces the angled trailing surfaces 44 of the cutting insert further into engagement in the re-entrant portion of the groove 30, to help secure the cutting insert in the groove. That is, the resultant vector force has an angular direction that is within the acute angular range between the base 37 and the trailing surface 36 of the re-entrant space, and the cutting insert 32 is fully supported by the drill bit body 12.

[058] ^! The drill bit body 2 may be formed of any suitably resilient material for its intended use, but is typically formed of metal by any suitable method, most typically by casting. The shank 22 may be formed integrally with the drill bit body, or may be separately formed and attached, for example by screw threads. [059] The cutting insert 32 is typically formed of hardened material, such as a tungsten carbide or hardened steel.

[060] The fluid passages for introduction of flushing fluid during drilling, and optionally of a cement grout or adhesive for securing the self-drilling rock bolt in the borehole following drilling, may be better understood with reference to the hidden detail shown in Fig. 1 and 15 to 17, and the sections of Figs. 8 and 19.

[061] Shank 22 of the drill bit has a central fluid passage 50 along its axis 28, adapted to co-operate with a corresponding fluid passage (not shown) of the drill rod or self-drilling rock bolt, for receiving a fluid pumped therethrough from the drilling head. This passage 50 extends into the drill bit body, and connects to a plurality of substantially perpendicular fluid passages 52a, 52b, 54a, 54b, extending perpendicular to the rotational axis of the drill bit out to the surface of the drill bit and ending with outlet apertures 56a, 56b, 58a, 58b in the side surfaces of the drill bit body.

[062] One or more outlets 56a, 56b, 58a and 58b may have an axis that is substantially perpendicular to the borehole axis, so that the likelihood of drill cuttings, particularly soft clay, being forced into the outlets by the rapid advance of the drill bit forwards into the rock, is reduced.

[063] As best shown in Fig. 4, the fluid outlets 56a and 56b are located on the tapered surfaces 18b of the drill bit body, which are steeply tapered relative to axial movement of the drill during operation. Therefore the apparent area of the outlets 56a and 56b visible from the front of the drill bit as depicted in Fig. 4 is very small, reducing the likelihood of blockage of the outlets 56a, 56b by clay or similar during drilling.

[064] Outlets 58a and 58b are located on the rearwardly tapered side surfaces

19 of the drill bit body, and are not visible at all from the front of the drill bit, and are thus well-protected from blockage.

[065] The outlets are arranged in pairs, each pair comprising one forward outlet

56a, 56b and one rearward outlet 58a, 58b. Each pair consists of one of the forward outlets 56a, 56b angularly leading the cutting insert of the drill bit in the rotary direction 34 of drilling - see Fig. 4 - and one rearward outlet 58a, 58b which is not only axially rearwards of the forward outlet, but also angularly trailing the cutting insert in the direction of drilling. See for example outlets pair 56a, 58a shown in Fig. 2. [066] In use, the forward outlet 56a directs flushing fluid - usually water - leading the cutting face of the insert 32 to mobilise and remove drill cuttings being formed at the leading face 42 of the insert. As the cutting face 42 of the drill bit rotates past the fluid introduced by outlet 56a, this fluid and the drill cuttings being carried encounter a second flow of fluid from outlet 58a, which, as this is introduced in a rearwardly angled face 19 behind widest point of the drill bit, helps expel the fluid and the drill cuttings back along the borehole to waste.

[067] Where ever it is used, the word "comprising" is to be understood in its

"open" sense, that is, in the sense of "including", and thus not limited to its "closed" sense, that is the sense of "consisting only of. A corresponding meaning is to be attributed to the corresponding words "comprise", "comprised" and "comprises" where they appear.

[068] It will be understood that the invention disclosed and . defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text. All of these different combinations constitute various alternative aspects of the invention.

[069] While particular embodiments of this invention have been described, it will be evident to those skilled in the art that the present invention may be embodied in other specific forms without departing from the essential characteristics thereof. The present embodiments and examples are therefore to be considered in all respects as illustrative and not restrictive, and all modifications which would be obvious to those skilled in the art are therefore intended to be embraced therein.