WO2019056025A1

WO2019056025A1 - Expansion assembly

Info

Publication number: WO2019056025A1
Application number: PCT/ZA2018/050051
Authority: WO
Inventors: Adrian BERGHORST
Original assignee: Ncm Innovations (Pty) Ltd
Priority date: 2017-09-18
Filing date: 2018-09-03
Publication date: 2019-03-21
Also published as: CL2020000711A1; PE20210850A1; EP3685017A1

Abstract

An expansion assembly for a rock bolt (40) which includes: an expansion shell (12) which extends between a distal end and a proximal end, the shell comprising a joining formation (24) and a plurality of expansion leaves (22), each having a plurality of serrations (32); and a tapered plug (14) which is engageable to a rock bolt (40) and which is arranged to force apart the leaves (22); wherein each serration (32) is defined by a conical and an undercut surface; and wherein the plurality of serrations includes a first series of serrations (32A-32G) which starts adjacent the distal end, having an undercut surface with a width in a first range; and a second series of serrations (32I-32M), with each serration of this series having an undercut surface which is progressively wider than the preceding serration of the second series and with a width in a second range.

Description

EXPANSION ASSEMBLY

BACKGROUND OF THE INVENTION

[0001] This invention relates to an improved expansion assembly for a rock bolt.

[0002] A typical expansion assembly includes an expansion shell which has a plurality of leaves that are arcuate and arranged circumferentially, joined together by a connecting element, and a tapered plug, engaged with a rock bolt, that is drawn or pushed through the expansion shell to cause the shell to radially expand.

[0003] In use, with the expansion shell assembly engaged with a rock bolt, the expansion assembly is actuated, in a manner mentioned above, to expand into contact with the walls of a rock hole, in which the bolt is inserted, to anchor the bolt in the rock hole.

[0004] To assist with the anchoring, often the outer surfaces of each leaf is formed with a plurality of ridges, teeth or serrations which provide a frictional interface with the rock hole walls. These serrations, typically, are of standard and equal dimension.

[0005] Such expansion shells are prone to being pulled out of rock holes that are drilled in soft strata. The teeth fail to bite into the wall and, when load is applied to the bolt, the anchor offers little resistance, merely sloughing off a surface layer of the rock hole wall, as the anchor comes away.

[0006] The present invention at least partly solves the aforementioned problems. SUMMARY OF THE INVENTION

[0007] The invention provides an expansion assembly for a rock bolt which includes: an expansion shell which extends between a distal end and a proximal end, the shell comprising of; a joining formation; and a plurality of expansion leaves, each leaf having a body with a cylindrical outer surface formed with a plurality of serrations extending circumferentially around the outer surface, and a smooth tapered inner surface which, when the leaves are held together by the joining formation, provide a tapered passage which tapers inwardly from the distal end to the proximal end; and a tapered plug which is engageable to a rock bolt and which is arranged to pass into the tapered passage from the proximal end to force apart the leaves; wherein each serration is defined by a conical surface and an undercut surface which extends laterally relatively to the axis of the passage; and wherein the plurality of serrations includes a first series of serrations which starts adjacent the distal end, with each serration of this series having an undercut surface with a width in a first range; and a second series of serrations, with each serration of this series having an undercut surface which is progressively wider than the preceding serration of the second series, this series progresses towards the proximal end, with a width in a second range.

[0008] The shell may comprise of two, three or four leaves.

[0009] The joining formation may be at least one joining ring of a suitable resiliently deformable material, which encircles the leaves adjacent their proximal ends.

[0010] Each leaf may have a lip between the distal end and the start of the first series of serrations.

[0011] The lip may extend beyond the lateral extent of the serrations.

[0012] Preferably, the first range is between, and including, 0.5mm - 1 mm.

[0013] Preferably, each serration of the first series of serrations has an undercut surface with a uniform width.

[0014] Preferably, the second range is between, and including, 1 mm - 4mm.

[0015] The conical surface and the undercut surface may intersect along an edge, through which a plane of orientation is defined, and the conical surface may intersect the plane in a range 60° - 80°. Preferably the angle is 70°. [0016] The invention further provides an expansion assembly of a rock bolt expansion assembly which includes: a joining ring; and a body which extends between a distal end and a proximal end and which comprises; a plurality of expansion leaves, each leaf having a body with a cylindrical outer surface formed with a plurality of serrations extending circumferentially around the outer surface, and a smooth tapered inner surface which, when the leaves are held together by the joining ring, provide a tapered passage which tapers inwardly from the distal end to the proximal end; wherein each serration is defined by a conical surface and an undercut surface which extends laterally relatively to the axis of the passage; and wherein the plurality of serrations includes a first series of serrations which starts adjacent the distal end, with each serration of this series having an undercut surface with a width in a first range; and a second series of serrations, with each serration of this series having an undercut surface which is progressively wider than the preceding serration of the second series, as this series progresses towards the proximal end, with a width in a second range. [0017] Each leaf may have a lip between the distal end and the start of the first series of serrations.

[0018] The lip may extend beyond the lateral extent of the serrations.

[0019] Preferably, the first range is between, and including, 0.5mm - 1 mm. [0020] Preferably, each serration of the first series of serrations has an undercut surface with a uniform width.

[0021] Preferably, the second range is between, and including, 1 mm - 4mm.

[0022] The conical surface and the undercut surface may intersect along an edge, through which a plane of orientation is defined, and the conical surface may intersect the plane in a range 60° - 80°. Preferably the angle is 70°.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The invention is further described by way of example with relevance to the accompanying drawings in which:

Figure 1 A and 1 B respectively isometrically illustrate a tapered plug and an expansion shell as components of the expansion assembly of the invention;

Figure 2 is a view in elevation of the expansion assembly, with the tapered plug engaged with the expansion shell;

Figure 3 is a view in elevation of the expansion shell;

Figure 4 is an isometric sectioned illustration of a leaf of the expansion shell; and Figure 5 is a view in longitudinal section view of the tapered plug. DESCRIPTION OF PREFERRED EMBODIMENT

[0024] Figure 1 illustrates, side by side, the components making up the expansion assembly 10 of the invention, the components including an expansion shell 12 and a tapered plug 14.

[0025] The expansion shell has a generally cylindrical body 16 which extends between a distal end 18 and an opposed proximal end 20. In this particular non- limiting example, the body is comprised of a pair of leaves, respectively designated 22A and 22B. It is anticipated, within the scope of the invention, that the body can have, for example, three or four leaves.

[0026] The leaves (22) are connected, to provide the expansion shell, by joining rings 24 which fit within a complimentary arcuate groove 26 formed in an outer surface 28 of each leaf and running adjacent the proximal end. The joining rings are made of a suitable resiliently deformable material, such as for example rubber or spring steel, to allow a degree of expansionary flexibility when the expansion shell is caused to expand, in use, as will be more fully described below.

[0027] As best illustrated in Figures 1 B and 4, each leaf (22A, 22B) is defined by the outer surface 28, which generally delimits a semi-cylinder, and a tapered, or at least partially tapered, smooth inner surface 30. The outer surface is formed with a plurality of serrations, respectively designated 32A, 32B, 32C...32F and 32G...32N on Figure 2, each of which extends circumferentially around the outer surface, parallel to one another and perpendicular to the longitudinal axis of the expansion shell 12.

[0028] The leaves engage each other along respective parallel sides 33, as illustrated in Figure 1 , held together by the joining rings 24. By bringing the two leaves together in this manner, a tapered passage 34 is created by the tapered inner surface 30 of each leaf 22. The passage tapers from the distal end 18 towards the proximal end 20. In this example, as the passage closes in on the proximal end, the inner surfaces 30 straighten towards the perpendicular, taking on a more cylindrical shape. [0029] The tapered plug 14 has an outer surface 36 which is tapered over a significant portion of its length. The taper angle of this portion is substantially complementary to the angle of taper of the passage 34. This is illustrated in Figure 2. A threaded bore 38 is formed through the tapered plug, the threads of which are adapted to threadedly engage with a threaded end of a rock bolt 40. [0030] As illustrated in Figure 2, with the tapered plug 14 engaged with the rock bolt

40, and with the rock bolt passing through the passage 34, the tapered plug fits partially within the passage 34, abutting the distal end 18 of the expansion shell 12 at some point on its tapered outer surface. The illustrated configuration is prior to the expansion assembly 10 being actuated into expansion as described below. [0031] The plurality of circumferential serrations 32 is divided into a first series of serrations, starting with serration 32A and, in this non-limiting example, ending with serration 32H, and a second series of serrations beginning with serration 321 and ending with serration 32M which lies adjacent the proximal end 20. Each serration is defined by a conical surface 42 and an undercut surface 44. The undercut surface can be a planar surface. However, in this example, the surface is slightly outwardly sloped by 10^Q from a planar surface. [0032] An edge 46 is defined along the line of intersection of the conical surface 42 with the undercut surface 44. The undercut surface extends laterally from, or substantially perpendicularly to the axis of, the passage, with each circumferential edge 46 lying in a plane of orientation which is parallel to the planes of orientation of adjacent edges. [0033]The conical surface 42 of each serration 32 slopes onto this plane of orientation at an angle between 60° and 80°, preferably 70°. This angle is illustrated in Figure 3 and designated a.

[0034] What characterises the serrations of the first series (32A-32H) over those of the second series, is that each of the first series serrations is equidistant from edge- to-edge, a distance designated X on Figure 3, with the width of each undercut surface, designated β in an insert to Figure 3, being uniform. And, relatively to the second series of serrations, the edge-to-edge distance of each of these serrations (32I - 32M) and the width of the undercut surface are smaller.

[0035] With the second series of serrations, the edge-to-edge distance (X) progressively increases from the first serration of the series, i.e. serration 32I, to the last serration in the series, i.e. serration 32M. This also provides undercut surfaces with progressively increasing width (β) as the series advances towards the proximal end 20.

[0036] At the distal end 18, before a primary serration 32a and the first serration 32A of the first series, each leaf 22 is provided with a chamfered lip 48, the edge of which extends beyond the lateral extent of the serrations at their respective edges

46.

[0037] In use, with the expansion assembly 10 engaged with the rock bolt, the rock bolt is actuated in any manner to cause the tapered plug 14 to advance through the passage 34 towards the proximal end 20 to push the leaves (22) radially outwardly. The leaves pivot about the joining rings 24 when pushed outwardly, causing the leaves to part, and taking on the configuration of a segmented cone. This radial expansion causes the serrated outer surface 28 of each leaf 22 to contact with the walls of a rock hole, into which the rock bolt 40 is placed, to secure the rock bolt within the rock hole. [0038] As the tapered plug 14 is caused to move further into the passage 34 from its resting position, the distal end 18 portion of each leaf is kicked outwardly, by leveraged interaction of the tapered surface 36 of the plug 14 on the passage 34, allowing the lip 48 to hook into the rock hole wall, providing initial anchorage. This action prevents the shell shifting or sliding within the hole before a greater part of the serration 32 of outer surface 28 of the leaves 22 engage the rock hole wall.

[0039] Thereafter, as the tapered plug 14 is pulled through the passage 34, either by passive or active forces, progressively the first series of serrations (342A- 32H) engages with the rock hole wall to provide initial and progressive purchase. And, as the load applied to the rock bolt increases, pulling the tapered plug further through the passage 34, the serrations of the second series are progressively leveraged into engagement with the rock hole wall. Each serration of the second series provides an incremental increase in frictional engagement due to the increasing width (β) of the undercut surface 34.

Claims

1 . An expansion assembly for a rock bolt which includes an expansion shell which extends between a distal end and a proximal end, the shell comprising of a joining formation and a plurality of expansion leaves, each leaf having a body with a cylindrical outer surface formed with a plurality of circumferential serrations, and a smooth tapered inner surface which, when the leaves are held together by the joining formation, provide a tapered passage which tapers inwardly from the distal end to the proximal end; and a tapered plug which is engageable to a rock bolt and which is arranged to move into the tapered passage from the proximal end to force apart the leaves; wherein each serration is defined by a conical surface and an undercut surface which extends laterally relatively to the axis of the passage; and wherein the plurality of serrations includes a first series of serrations whilst starts adjacent the distal end, each serration of which has an undercut surface with a width in a first range, and a second series of serrations, each serration of which has an undercut surface which is progressively wider than the preceding serration of the second series, as this series progresses towards the proximal end, with a width in a second range.

2. An expansion assembly according to claim 1 wherein the joining formation is at least one joining ring which encircles the leaves adjacent their proximal ends. An expansion assembly according to claim 1 or 2 wherein each leaf has a lip between the distal end and the start of the first series of serrations.

An expansion assembly according to claim 3 wherein the lip extends beyond the extent of the serrations.

An expansion assembly according to any one of claims 1 to 4 wherein the first range is between, and including, 0.5mm - 1 mm.

An expansion assembly according to any one of claims 1 to 5 wherein each serration of the first series of serrations has an undercut surface with a uniform width.

An expansion assembly according to any one of claims 1 to 6 wherein the second range is between, and including, 1 mm - 4mm.

An expansion assembly according to any one of claims 1 to 7 wherein the conical surface and the undercut surface of each serration intersects along an edge through which a plane of orientation is defined, and wherein the conical surface intersects at an angle between 60° - 80°.

An expansion assembly according to claim 8 wherein the angle is 70°.

An expansion shell of a rock bolt expansion assembly which has a joining ring and a body which extends between a distal end and a proximal end and which comprises a plurality of leaves, each leaf having a cylindrical outer surface formed with a plurality of circumferential serrations, and a smooth tapered inner surface which, when the leaves are held together by the joining ring, provide a tapered passage which tapers inwardly from the distal end to the proximal end; wherein each serration is defined by a conical surface and an undercut surface which extends laterally relatively to the axis of the passage; and wherein the plurality of serrations includes a first series of serrations whilst starts adjacent the distal end, each serration of which has an undercut surface with a width in a first range, and a second series of serrations, each serration of which has an undercut surface which is progressively wider than the preceding serration of the second series, as this series progresses towards the proximal end, with a width in a second range.

1 . An expansion shell according to claim 10 wherein each leaf has a lip between the distal end and the start of the first series of serrations.

2. An expansion shell according to claim 1 1 wherein the lip extends beyond the extent of the serrations. 13. An expansion shell according to any one of claims 10 to 12 wherein the first range is between, and including, 0.5mm - 1 mm.

14. An expansion shell according to any one of claims 10 to 13 wherein each serration of the first series of serrations has an undercut surface with a uniform width. 15. An expansion shell according to any one of claims 10 to 14 wherein the second range is between, and including, 1 mm - 4mm.

16. An expansion shell according to any one of claims 7 to 10 wherein the conical surface and the undercut surface intersect along an edge through which a plane of orientation is defined, and wherein the conical surface intersects at plane at an angle between 60° - 80°. 17. An expansion shell according to claim 16 wherein the angle is 70°.