BACKGROUND OF THE INVENTION

[0001] The invention relates to an adaptor or fug for use with a rock bolt to provide a tapered surface upon which an expansion shell of a mechanical anchor acts to mechanically anchor the rock bolt in a rock hole.

[0002] The applicant's specification to PCT/ZA2015/000055 describes an end anchored rock bolt, which includes a elongate cylindrical body which longitudinally extends between a proximal end and a distal end and a forged head at the distal end, which forged head is diametrically larger than the cylindrical body, is at least partially tapered, tapering towards the proximal end, and is integrally formed on the body.

[0003] The length and diameter of the forged head is important as it is these two dimensions that determine if the expansible shell radially will expand sufficiently into resistive contact with the walls of the rock hole in which the rock bolt is inserted, in larger diameter holes, the width and / or length of the forged head would have to increase to ensure that the shell expands sufficiently to fractionally contact the rock walls and anchor the rock bolt

[0004] To accommodate a range of hole diameters, a range of rock bolts, each varying in forged head dimension, would have to be made. This would complicate, and increase the cost of the manufacturing process. Tooling for each forged head variant would need to be made with consequent cost. [0005] The invention at least partially solves this problem. SUMMARY OF THE INVENTION

[0006] The invention provides an expansion iug which engages a rock bolt to provide a tapered surface upon which an expansion sleeve of a mechanical anchor acts to radially expand to mechanically anchor the rock bolt in a rock hole, the lug including a truncated conoidai body which is defined between a first end, a second end and the tapered surface and a passage through the body which opens at each end, wherein the passage includes a chamfered section between the first end and a partition edge and a tapered section between the partition edge and the second end, along at least part of which the passage tapers outwardly towards the second end.

[0007] The passage may be adapted to receive a shaft of the rock bolt in engagement of the lug with the rock bolt.

[0008] The body may be made of a suitable metal materiai.[James - what type of steel is used?]

[0009] The chamfered section may be a shallow section with a chamfered surface angled between 30' to 60*.

[0010] The invention extends to a rock bolt which includes: a) an elongate body which extends between a proximal end and a distal end and which has a distal end portion that ends adjacent the distal end; b) an expansion lug which is engaged with the rock bolt body over the distal end portion of the body which includes a truncated conotdal body which is defined between a first end, a second end and a tapered outer surface and a passage through the body which opens at each end, the passage including a chamfered section between the first end and a partition edge and a tapered section between the partition edge and the second end, along at least part which the passage tapers outwardly towards the second end; c) wherein the distal end portion is adapted to complement the tapered section of the passage and the chamfered section.

[0011] The rock bolt may include a radially expansible shell or sleeve which is engaged with the body, positioned thereon to move over the tapered outer surface into expansion.

[0012] In another aspect of the invention, the invention provides a method of manufacturing a rock bolt with an expansion wedge at one end which includes the steps of: a) providing a rock bolt with an elongate cylindrical body which extends between a proximal end and a distal end; b) providing an expansion lug as described above; c) passing the body through the passage of the lug with the first end of the lug facing the proximal end of the body; d) heating the body along a distal end portion which ends at the proximal end; e) placing the lug in a position over at least a part of the distai end portion; f) clamping the body to prevent the lug moving towards the proximal end from the position; and g) applying an axiaiiy directed force to the distai end to form the distal end portion, to complement the tapered section of the passage and the chamfered section, and to fix the iug onto the body.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The invention Is further described by way of example with reference to the accompanying drawings in which:

Figure 1 illustrates in perspective an expansion iug in accordance with the invention engaged with a rock bolt;

Figure 2 illustrates in perspective, and longitudinally sectioned, the expansion iug;

Figure 3 illustrates in perspective an end of the rock bolt with the expansion lug and a expansion shell engaged with the rock bolt; and

Figures 4A to 4D diagrammaticaiiy illustrate, in sequence, a method of manufacturing a rock bolt with an expansion wedge. DESCRIPTION OF PREFERRED EMBODIMENTS

[0014] Figure 2 illustrates an expansion lug 10 in accordance with a first aspect of the invention. The lug comprises of a truncated conoidal body 12, made of a suitable metal material in a cold forged process. [0015] The steel material is chosen to be similar in mechanical strength to the material of a rock bolt (to which It will be attached) and, also, sufficiently hard such that leaves of a mechanical anchor (described below) do not smear or fuse to the lug when subjected to large axial forces. The body is defined between opposed first and second ends (14, 16) and an outer tapered or conical surface 18. In this non-!imiting embodiment, the outer surface is not a regular cone, having a number of surfaces, respectively designated 18A, 186 and 18C, each slightly angled relatively to the adjacent surfaces. A passage 20 extends centrally through the body, opening to the first end at a mouth 22 and opening to the second end.

[0016] The passage has a shallow chamfered section 24 which is defined between the first end 14 and a partitioning ridge 26, and a tapered section 28 extending between the ridge and the second end 16. The chamfered section has a chamfered surface 30 angled, in this embodiment, at 45° to the axial direction. Along the tapered section, the passage tapers outwardly from the ridge 26 in two discrete sections, respectively designated 28A and 288, initiaily at a first taper angle, or parallel and then at a second taper angle which is larger than the first angle.

[0017] In use, as illustrated in Figure 1 , the expansion lug 10 is engaged with a rock bolt 30. The rock bolt has a cylindrical body 32 that extends between a proximal end 34 and a distal end 36. A proximal end portion 38 of the boit is formed with a thread to engage with a nut (not shown) and which will support a faceplate (not shown) in use. Alternatively, the proximal end portion can be shaped in the form of a pigtail or shepard's crookThe lug Is illustrated engaged with the body 32 over a distal end portion 40.

[0018] As Illustrated in Figure 3, the expansion lug 10, engaged with the rock bolt 30, forms part of a mechanical anchor 42 which is actuated when the rock bolt is inserted in a rock hole (not shown) to radially expand into frictional engagement with the walls of the rock hole to anchor the bolt in the hole. The mechanical anchor includes, at Its core, the lug 10. Configured about the lug, the anchor has an expansible shell 44, comprising a mounting collar 46 and a plurality of interlinked leaves 48 engaged with the collar in a radial array which encircles the body 32 and lug. Each of the leaves presents a plurality of ridged frictional surfaces 50. The anchor has a biasing spring 52 concentrically mounted on the body, behind the collar. In an unexpanded position, as illustrated in Figure 3, the spring is compressed between the collar and an annular rim (not shown) and the leaves engage a lower part of the tapered surface 18 of the lug 10, When the anchor is actuated, the spring relaxes from bias, forcing the collar and associated leaves forwardiy towards the distal end 14 and, In so doing, forcing the leaves to ride over the tapered surface into radial expansion.

[0019] In the prior art disclosed above, the conical or tapered outer surface of the forged head provides the expansion surface against which the leaves abut and move against to radially expand into contact with wails of a rock hole into which the rock bolt is inserted In use. However, the dimensions of the angie of taper and the length of the forged head are often insufficient to allow sufficient radial expansion of the leaves for frictionai contact with the walls. Furthermore, in the forging process, the outer surface oxidises leaving a skin that resists smooth un-resistive movement of the leaves over the surface.

[0020] The benefit with using the lug 10 of the invention is that it is a discrete component which is engaged with the rock boit 30 as will be described below. This allows the lug to be cold formed into a range of shapes and sizes, dependent upon requirement, without the need for changing tooling. And, being cold formed, the conoidai body 12 is dtmensionally precise with a cleaner surface finish on the tapered surface 18 which provides a low resistance surface over which the leaves 48 can move. Specifically, the dimensions of the lug, in terms of length and width, is chosen depending upon the circumference of the rock hole. Larger rock holes will, of course, require a lug of larger width and length. [0021] To engage the lug 10 to the rock bolt 30, as is illustrated in Figure 1, the lug is passed over an end of the bolt body, say, in this case the proximal end 34, with its first end 14 leading. The passage 20 Is, of course, of sufficient diameter to allow the rock bolt to pass through. This step is illustrated in Figure 4A.

[0022] The lug is slid along the length of the boit body 32, towards the distal end 36, into a position spaced from the end. The spacing is dependent upon the diameter of the bold body 32 and therefore the amount of material to be deformed in a process described below. This portion, being the distal end portion 40 referred to above, is heated from a source that engages the distal end. This step is illustrated in Figure 4B.

[0023] Figure 4C illustrates the next step. Here, the lug 10 is then moved over the heated distal end portion 40. The bolt body 32 is then clamped, with a clamp 54, behind the second end 16 of the lug body 12 to hold the bolt and prevent the lug form moving backwardly towards the proximal end 34.

[0024] In a last step, illustrated in Figure 4D, a forging force is axially applied to the distal end 36 of the bolt body 32. This force is illustrated with a directional arrow. The force is sufficient to cause the bolt body, along the distal end portion 40, to forge both into the chamfered section 24 and the tapered section 28. In doing so, the lug is now firmly and fixedly engaged with bolt body 32.

[0025] Due to the force, the distal end 36 deforms to overlap the mouth 22 of the lug to provide a rivet head 54.

[0026] With a back part 56 of the portion 40 comptementariiy shaped to that of the tapered section 28 of the passage, the lug is prevented from moving relatively to the bolt body 32 towards the proximal end 34. And, with a front part 58 of the portion 40 comptementariiy shaped to that of the chamfered section 24, the lug is prevented from moving off the bolt body from the distal end 36. The insert to Figure 4D best illustrates this. [0027] The expansible shell 44 can now be assembled on the bolt 30 about the lug 10 in a configuration described above. [0028] When the rock bolt 30 is put to use, anchored in a hole, load will be applied to the body as body of rock within which the hole is located begins to move. This load will be focussed on the point of anchor, being the mechanical anchor 42, and, more specifically, will hang on the lug. The load will be applied axially outwardly which would has the tendency of pulling the bolt body 32 through the lug. What stops this is the material of the portion front part 58 and the rivet head 54 which is held against the shallow angled chamfered surface 30 and the rim of the mouth 22 respectively.

[0029] A gradual taper of the tapered section 28, however, is sufficient to keep the lug from moving in the opposite axial direction which is not a load bearing direction in use.