FIELD OF THE INVENTION

[0001] The invention relates to a self-drilling rock anchor with a drill bit which attaches to the rock anchor in friction fit. The means providing the friction fit may be integral with the drill bit or included in an adaptor.

BACKGROUND OF INVENTION

[0002] The drill bit of a hollow self-drilling rock anchor typically is threadedly engaged to one end of a hollow rod or bar. A part of the drill bit is formed with a female thread which engages with a male thread in a bore of the rod. [0003] To ensure that the drill bit does not break from the rod during energetic use, the body of the drill bit must be of a sufficient diameter to have the requisite material thickness for the support of a thread.

[0004] With an increase in diameter comes an increase in the cutting face of the bit and an increase in the size of hole drilled which, often, is beyond that which is necessary for the particular application.

[0005] With a larger hole comes the requirement for more resin to fill that hole once the rock anchor has been installed. This comes at additional cost, whilst decreasing the stiffness of the installation.

[0006] An alternative method of attachment is to machine a taper onto the proximal end of the hollow rod. This tapered end then inserts into a complementary recess in the drill bit. [0007] Again, if the rod is not sufficiently massive, the tapered end will not have enough inherent strength to withstand failure or plastic deformation during use involving high applied load.

[0008] The invention at least partially solves the aforementioned problems. SUMMARY OF INVENTION

[0009] The invention provides an adaptor for connecting a drill bit to a hollow shank of a self-drilling rock bolt, the adaptor including a body which extends in an axial direction between a distal end and a proximal end, a tubular conduit which extends between the ends, an abutment surface formed in an outer surface of the body that divides the body into a proximal portion and a distal portion, wherein at least a part of the proximal portion includes a first taper which tapers towards the proximal end, wherein at least a part of the distal portion includes a second taper which tapers towards the distal end, and wherein the first taper and the second taper are adapted for friction fit in a bore of the shank and a recess in the drill bit respectively. [0010] The invention also provides a friction fit drill bit kit which includes: a drill bit which has a drill bit body which extends in an axial direction between a drill face end and a trailing end, which body includes a tapered recess in the trailing end and at least one tubule which opens the recess to the drill face end; and an adaptor, for connecting the drill bit and a hollow shank, of a self-drilling rock bolt, which includes a body which extends in the axial direction between a distal end and a proximal end, a tubular conduit which extends between the ends, a surface formed in an outer surface of the body that divides the body into a proximal portion and a distal portion, wherein at least a part of the proximal includes a first taper which tapers towards the proximal end, wherein at least a part of the distal portion includes a second taper which tapers towards the distal end, and wherein the first taper and the second taper are adapted for friction fit in a bore of the shank and the tapered recess of the drill bit respectively.

[0011] The invention extends to a drill bit which is adapted for friction fit engagement with a hollow shank of a self-drilling rock bolt, the drill bit including a drill bit body which extends in an axial direction between a drill face end and a trailing end, a tubular conduit which extends between the ends, an abutment surface formed in an outer surface of the body that divides the body into a proximal portion, which ends at the drill face end, and a distal portion, wherein at least a part of the distal portion includes a taper which tapers towards the trailing end and which is adapted for friction fit in a bore of the shank.

BRIEF DESCRIPTION OF THE DRAWINGS [0012] The invention is described with reference to the following drawings in which:

Figure 1 is a view from the side of a disassembly of a self-drilling rock bolt, illustrating an adaptor, interposed between a hollow bolt and a drill bit, in accordance with the invention;

Figure 2 is a view in longitudinal section of the disassembled self-drilling rock bolt of Figure 1 ;

Figure 3 is a view from the side of an assembly of the self-drilling rock bolt illustrated in Figure 1 ; Figure 4 is a view in longitudinal section of the assembled self-drilling rock bolt of Figure 3;

Figure 5 is a view in longitudinal section of a drill bit in accordance with another aspect of the invention; Figure 6 is a view from the side of the drill bit of Figure 5;

Figure 7 is a view in perspective of the drill bit of Figures 5 and 6;

Figure 8 is a view in longitudinal section of the drill bit of the preceding Figures engaged with a hollow bar to provide a self-drilling rock bolt; and

Figure 9 is a view from the side of the self-drilling rock bolt of Figure 8. DESCRIPTION OF PREFERRED EMBODIMENTS

[0013] Figures 1 , 2 and 4 illustrate an adaptor 10 in accordance with the invention for connecting a drill bit 12 to a hollow resin bolt or shank 14 in assembly of a self drilling rock bolt.

[0014] The hollow resin bolt 14 is a typical steel bolt with a corrugated outer surface and a cylindrical bore 16 which extends longitudinally through the bolt, opening at a first end 18 and a second end (not shown) of the bolt. The bore is provided as a conduit for the passage of a resin and, following this, a flushing medium to flush away excess resin and debris after use.

[0015] The drill bit 12 has a largely cylindrical body 20 which extends, in the axial / longitudinal direction, between a drill face end 22 and a trailing end 24. Towards the drill face end, the body diverges outwardly, from a cylindrical shape, to a frusto- conical shape, ending at the drill face end which carries a plurality of abrasive protuberances 26.

[0016] A tapered recess 28 opens into the body 20 from the trailing end 24. A plurality of outlet tubules 30 open the recess to the drill face end 22. [0017] The adapter 10 has an elongate body 31 which extends between a distal end

32 and a proximal end 34. A tubular conduit 36 passes through the body, opening at both these ends (32, 34).

[0018] At a mid-point along the body, the outer surface is stepped to provide a laterally extending abutment surface 38. This abutment surface faces the proximal end 34 and divides the adaptor into a proximal portion 40 and a distal portion 42.

[0019] At least part of the outer surface of the proximal portion narrows, in a first taper 44, from a junction line of the abutment surface 38 to or towards the proximal end 34.

[0020] Likewise, at least part of the outer surface of the distal portion 42 narrows, in a second taper 46, from an outer edge of the abutment surface to or towards the distal end 32.

[0021] In this example, the taper angle of the first taper 44 is smaller than the taper angle of the second taper 46 to complement the dimensions and shape of the bore 16, the bolt 14, and the tapered recess 28, of the drill bit 12, respectively. [0022] As illustrated in Figure 4, the proximal portion 40 of the adaptor 10 is inserted into the bore 16 from the bolt’s first end 18, in assembly of a self-drilling rock bolt 50, in friction fit to the point at which the abutment surface 38 abuts or is positioned adjacent the first end.

[0023] The tight friction engagement of the proximal portion 40 within the bore, provided by the complementary shape of the first taper 44, creates a self-locking join that does not rotate and pull apart by the torque created in use.

[0024] Similarly, the distal portion 42 is inserted into the tapered recess 28 of the drill bit 12. With the tight taper tolerance between the second taper 46 and the tapered recess 28, a self-locking join is provided between the adaptor 10 and the drill bit 12. [0025] As a self-drilling rock bolt (illustrated in Figures 3 and 4), the bore 16 of the bolt, the tubular conduit 36 of the adaptor, the tapered recess 28 and the outlet tubules 30 are in fluid communication providing continuous passage to a resin or flushing medium, input into the second end of the bolt, to exit at the drill face 22.

[0026] As an alternative means of engaging the drill bit 12 to the bolt 14 without a thread or a weld, the invention provides a drill bit 12A which is integrally provided with the tapered engagement means of the adaptor 10.

[0027] In describing this aspect of the invention, like features bear like designations.

[0028] The drill bit 12A has an elongated body 20A which extends between the drill face end 22 and a trailing end 24. A tubular conduit 36A extends between these ends.

[0029] As with the adaptor 10, at a mid-point along the body 12A, the outer surface is stepped, providing an abutment surface 38 which faces the trailing end 24. [0030] This surface functionally divides the drill bit into a bolt engaging proximal portion 40 and a drill bit portion 52. The side wall of the drill bit portion diverges from the abutment surface in frusto-conical shape, terminating at the drill face end 22.

[0031] At least part of the outer surface of the proximal portion 40 narrows, in a taper, from the abutment surface to the proximal end.

[0032] As illustrated in Figure 8, the proximal portion 40 of the drill bit 12A is inserted into the bore 16, from the bolt’s first end 18, in friction fit, with the abutment surface 38 abutting or positioned adjacent the first end.

[0033]The tight friction engagement of the proximal portion 40 within the bore, provided by the complementary shape of the taper, creates a self-locking join that does not rotate and pull apart by the torque created in use.

[0034] As a self-drilling rock bolt (illustrated in Figures 8 and 9), the bore 16 of the bolt, the tubular conduit 36A of the drill bit 12A and the outlet tubules 30 are in fluid communication providing continuous passage to a resin or flushing medium, input into the second end of the bolt, to exit at the drill face 22.