WO2016207868A1

WO2016207868A1 - An inflatable rock bolt

Info

Publication number: WO2016207868A1
Application number: PCT/IB2016/053817
Authority: WO
Inventors: Barry Graeme Holfeld
Original assignee: Barry Graeme Holfeld
Priority date: 2015-06-25
Filing date: 2016-06-27
Publication date: 2016-12-29
Also published as: ZA201708603B; WO2016207868A4

Abstract

The invention relates to a rock bolt (1A) comprising a pipe (12) with a cap (20) welded in sealing engagement over an open end of the pipe (12). The cap (20) has a substantially cylindrical skirt (22) welded to the end of the pipe (12) in a pre-formed tabular condition. The cap (20) also includes a substantially domed cover section with an end portion that is elongate along a line (y) that is transverse to a folding line (x) about which a channel (115) is formed along a length of the pipe (12) and through the cap (20). The invention extends to associated methods of forming a rock bolt (1A).

Description

AN INFLATABLE ROCK BOLT

FIELD OF THE INVENTION

The invention relates to an inflatable rock bolt of the kind that includes a sealed tubular body provided by a metal pipe with at least one longitudinal channel (provided by a folded or convoluted form of a body wall) that is, in use, located into a borehole and engaged frictionally with a wall of the borehole by introducing a pressurised fluid into an interior of the body.

BACKGROUND TO THE INVENTION

These inflatable rock bolts generally have a sealed tube with a longitudinal channel formed by a fold, which reduces the cross-sectional dimension of the tube (sufficiently for the required purpose). A check valve at one end which remains outside a borehole into which the rock bolt is inserted allows the tube to be inflated. The pressurised fluid is usually water. On expansion of the body through outward deformation of the fold, the surface of the tube engages in the borehole.

In the known manufacture of this type of rock bolt the folded or convoluted tubular body is formed using a suitable metal working system. Initially, opposed ends of the body are open. In order to seal these ends different techniques are employed. In one approach a solid insert, such as a length of round bar, is inserted into an open end and material of the body surrounding the insert is then swaged or crimped into intimate contact with the insert. This is followed by a welding process during which small gaps between an edge of the tubular body located around the insert are sealed. When the tubular body is crimped into tight engagement with the insert the cross- sectional dimension of the tubular body is reduced from a maximum value at a region at which the tubular body is not deformed to a minimum value which is usually at and/or adjacent an extremity of the body.

Typically the cross-sectional dimension tapers to its minimum size over a distance, in an axial direction of the body, which may be in the order of, at least, 10 or 15cm. When the body is placed into a borehole and is expanded into engagement with a wall of the borehole the tapered region (where it has been crimped and adjacent the welded end) is not meaningfully altered in dimension and thus is not brought into frictional engagement with the wall of the borehole.

If the rock bolt has a length of, say, 90cm then the non-expansion of the tapered end means that the length of the tubular body, which is engaged frictionally with the wall of the borehole, is of the order of 75 or 80cm. This reduces the loadbearing capability of the rock bolt and/or prevents optimal frictional engagement in the region of the rock bolt where expansion is limited. Additionally the tapered region represents waste material for, although the region makes up part of the cost of the rock bolt, it does not contribute to the loadbearing/engagement capability of the rock bolt.

In an alternative rock bolt, wall material adjacent an end of the pipe is crimped or folded and welded into a cylindrical sleeve of reduced diameter. This arrangement obviously suffers from the same disadvantage. In use, the sleeve does not expand and results in a tapering of the material leading to the sleeve.

The cross-sectional dimension of the post-formed rock bolt may also be referred to as a cross-sectional diameter for the forming process will usually take the folded tube back to having a substantially circular axial profile, as is suited for insertion into a borehole formed into a rock body, for example. OBJECT OF THE INVENTION

It is an object of the present invention is to address the aforementioned situation, at least to some extent, and/or to provide an effective means and method for sealing and reducing dimension at the end of a rock bolt.

SUMMARY OF THE INVENTION

In accordance with the invention there is provided a rock bolt comprising a pipe with a cap welded in sealing engagement over an end of the pipe and formed with a channel extending along a length of the pipe and through the cap.

The invention further provides for a rock bolt as defined, in which: the cap includes a skirt that is a close fit to a wall of the pipe; the skirt is substantially circular and welded to the pipe in a pre-formed tubular condition; the skirt is substantially cylindrical; and the skirt fits closely to an inner surface of the wall of the pipe.

Further features of the invention provide for a rock bolt as defined, in which: the cap includes a cover section that is extends away from a line along which the cap is welded to the pipe; the cover section is substantially domed; and the cover section has an end portion that is elongate along a line that is transverse to a folding line about which the channel of the rock bolt is formed.

Further features of the invention provide for a rock bolt as defined, in which: the cover section protrudes from the end of the pipe; alternatively, the cap includes a cover section that extends into the pipe.

A further feature of the invention provides for a rock bolt as defined, in which the pipe is formed with a channel and the cap provided with a complementary shape welded to the end of the pipe having a channel form. In accordance with another aspect of the invention there is provided a method of making a rock bolt which includes the steps of providing a length of pre-formed pipe with at least one open end, welding a cap to the open end thereby sealing the open end, and thereafter deforming the pipe and the cap into a folded form to provide a channel that extends along the pipe and through the cap.

The invention further provides for a method as defined, in which: the cap includes a skirt and a dome-shaped cover section and the cap is welded to the pre-formed pipe with the skirt located in overlapping engagement with the pipe.

Further features of the invention provide for a method as defined, in which: the skirt is located inside the pipe and the open end of the pipe welded to the cap; alternatively, the skirt is located around the pipe and an edge of the cap provided on the skirt is welded to a wall of the pipe adjacent to the open end of the pipe.

In accordance with another aspect of the invention there is provided a method of making a rock bolt which includes the steps of providing a length of pipe having an open end, forming the pipe with a longitudinal channel, providing a cap with a shape complementary to a channel form imparted to a wall of the pipe, and welding the cap over the open end thereby sealing the open end.

The invention further provides for a method as defined in which the cap includes a skirt provided as a close fit to the channel form imparted to the wall of the pipe. Further features of the invention provide for a method as defined, in which: the skirt is located inside the pipe and the open end of the pipe welded to the cap; alternatively, the skirt is located around the pipe and an edge of the cap provided on the skirt is welded to the wall of the pipe adjacent to the open end of the pipe. BRIEF DESCRIPTION OF THE DRAWINGS These and other features of the invention will become more apparent from the following description of embodiments, made by way of example, with reference to the accompanying drawings, in which: show two perspective views and a cross-sectional side view of a first embodiment of a pre-formed rock bolt;

shows a cross-sectional side view of an alternative embodiment;

show an embodiment similar to that of Figure 4 including views of a post-formed rock bolt;

show cross-sectional side views of further embodiments of pre-formed rock bolts;

show perspective views of two rock bolts constructed in accordance with a further aspect of the invention; and show end cross-sectional views of tools for use in a first and second step of a forming process for a rock bolt in accordance with the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Figures 1 and 2 of the accompanying drawings illustrate an end of a pre-formed rock bolt 1 A. The rock bolt 1 A is made from a suitable length of pipe 12 of circular cross-section having an end 10 which is open in Figure 1 . The pipe 12 is made from a suitable metal and a wall 13 of the pipe 12 has an outer surface 14 and an inner surface 16 which encloses a bore 18.

In accordance with the invention, a cap 20 is used to seal the open end 10 of the pipe 12. The cap 20 is prefabricated from a suitably ductile metal and has a skirt 22 and a cover section 24. The cover section 24 is generally domed providing the cap 20 with an outwardly curved contour. The cover section 24 is also provided with a generally domed configuration, with a curved profile extending from the skirt 22 that facilitates a folding operation to form a channel through the cap 20. In this embodiment the cover section 24 has a flat free end 26 provided by a substantially rectangular (with rounded edges) portion of material formed to be elongate along a line that is transverse to a bending or folding line as described in more detail below. The elongate portion at the end 25 of the cap 20 also facilitates the folding operation where it takes place through the profile of the cap 20. The skirt 22 has an inner diameter 28 that is a close fit to an outer diameter 30 of the pipe 12. Thus, as is shown in Figure 2, the cap 20 can be placed over the open end 10 and can then be welded at 36 to the outer surface 14 of the pipe 12 at a junction along an edge 34 of the skirt 22. Figure 3 illustrates in cross-section the configuration of the pipe 12 of the preformed rock bolt 1A (of Figure 2) with the cap 20 welded onto the open end 10. By securing the cap 20 to the pipe 12 in this manner the open end 10 is sealed.

Figure 4 shows that a cap 20A, which is similar to the cap 20, can be configured with a skirt 22A that fits inside the open end 10 of the pipe 12 abutting against or as a close fit to a portion of the inner surface 16. The skirt 22A of the cap 20A is welded at 36 to a rim 1 1 of the pipe 10, which extends around the open end 10.

In both Figures 3 and 4, it can be seen that the skirts 22 and 22A have a substantially cylindrical configuration to fit as a sleeve onto or into the pipe. These skirts 22 and 22A are also, accordingly substantially circular and the caps 20 and 20A both have an annular edge 34 on the respective skirts 22 and 22A. The configuration of these caps is suited for engagement over an open end of a preformed rock bolt 1 A. Figures 5, 7 and 8 show a pre-formed rock bolt 101 A having the construction of a cap 120 with a skirt 122 that fits into a pipe 1 12, as illustrated in Figure 4. A substantially cylindrical portion of the skirt 122 is located along an inside of the wall of the pipe 1 12 and therefore not visible in these drawings.

Figure 7 shows a side view with reference to the line "X" along which the pipe 1 12 will be folded in the forming process (described below). Figure 8 shows a plan view with respect to this folding line "X". The corresponding views of a post-formed rock bolt 101 B are shown in Figures 9 and 10 respectively. Whereas Figure 6 shows a perspective view of the post-formed rock bolt 101 B corresponding to the view of the pre-formed rock bolt 101 A in Figure 5.

The cap 120 is formed to the required configuration from suitably ductile metal (in this embodiment, through a deep-drawing process). The skirt 122, which is substantially cylindrical, is dimensioned as a close fit into the pipe 1 12. The cover section 124 is provided to be slightly elongate across a free end 126 of the cap 120 along a line "Y" that is transverse to the fold line "X" on the post-formed rock bolt 101 B. The cover section 124 is curved to either side of the line "Y". Once the cap 120 is welded at 136 to a rim 1 1 1 of the pipe 1 12, the pre-formed rock bolt 101 A is subjected to a subsequent metalworking process, in which the pipe 1 12 and the cap 120 are formed into a convoluted shape generally of the type shown in Figure 6, 9 and 10; that is, with a longitudinal fold forming a channel 1 15 of the kind commonly employed to reduce the cross-sectional dimension or diameter of a post-formed rock bolt 101 B.

After the welding has been completed the pipe 1 12 still has a circular outline in cross-section. The subsequent forming process is described below with reference to Figures 19 and 20. In a first step, the pipe 1 12 is placed in a trough-shaped cavity 103 of a first die 104. The cavity 103 is long enough to receive the pre- formed rock bolt over its full length, including the cap 12 (which is not shown in the cross-sections of Figures 19 and 20).

A tool 105 is then used to deform the pipe 1 12. The tool 105 is in the shape of an elongate blade with a straight working edge 106 (parallel to the pipe 1 12) that is curved between two planar sides. In use, the working edge 106 directly contacts the outer surface 1 14 of the pipe 1 12. The first die 104 is supported in a hydraulic press that is used to bias the tool 105 into engagement with the outer surface 1 16 of the pipe 1 12. The tool 105 deforms the pipe 1 12 radially inwardly (as shown) to form a relatively deep channel 1 15 that extends along the pipe 1 12 and through the cap 120.

The forces exerted by the tool 105 are such that when the channel 1 15 is formed the outer surface 1 16 of the pipe 1 12 is no longer generally of circular form - see Figure 19. As the finished product (post-formed rock bolt 101 B) is intended to be inserted into a borehole drilled in a body of rock and the borehole is substantially of a circular shape in cross-section, the cross-sectional shape of the rock bolt 101 B, in use, should as far as is practicable, also be of circular outline. For this reason, the rock bolt in intermediate form (having the cross-sectional profile shown in Figure 19) is subjected to a second step of the forming process. This involves placing the rock bolt into a second die set 107 of upper 107.1 and lower 107.2 dies which, together, define an elongate die cavity 108 that is circular in cross-section and which can accommodate the pipe 1 12 over the end with the cap 120. The second die set 107 is closed using hydraulic pressure with the convoluted pipe in the die cavity 108, which is thereby formed into a body that, except for the channel 1 15, has a substantially circular axial profile in accordance with the required production specifications. The cap 120, although deformed, remains integral and the leak-proof seal formed by the weld between the cap 120 and the pipe 1 12 is maintained. The pipe 1 12 then has an elongate longitudinally extending channel 1 15 which extends continuously into a region occupied by the skirt 122 and through the cover section 124 as illustrated in Figures 6, 9 and 10. The elongation of the cover section 124 at the free end 126 along the line "Y" facilitates the bending of the material of the cap 120 when the pipe 1 12 is folded to form the channel 15 along the pipe 1 12 and through the cap 120. This elongation in the material across the end 126 of the cap 120 and the curved or domed configuration (which extends across the skirt and cover section 124) of the cap 120 provide a reduced resistance to the forming of the fold and once an initial crease has been formed in the cap 120 material (along the line "X" and substantially the centre of the elongated portion at 126), the two halves of the cap 120 to either side tend to uniformly follow the required distortion providing a symmetrically folded and pointed end on the pipe 1 12, as illustrated.

As known in the art, inflatable rock bolts (with a tubular body of convoluted form) can be expanded into frictional engagement with a wall of a borehole (not shown). When this expansion occurs the pipe of a rock bolt made in accordance with the invention expands over practically its entire axial length into frictional engagement with the wall of the borehole. The material for the pipe is therefore used to a maximum extent (or it's full length) and the pipe, in the form of a rock bolt, is capable of providing substantially all of its designed frictional loading/engagement capability. The usage of the metal for the pipe is not defeated by an inability to fully expand at the end where it is sealed (as in the case of the prior art).

If a prior art rock bolt with a length of, say, 90cm is placed in a borehole then the borehole must be drilled to a depth of at least 90cm. If only 70cm of the rock bolt is engaged with the borehole then material wastage and expense are associated with the remaining 20cm of the borehole and of the rock bolt. The rock bolt of the invention can be made shorter so that it provides a gripping function over a length that is equivalent to that achieved with longer prior art rock bolts of the type referred to. It follows that the depth of the borehole that is drilled can also be shortened in that the depth is matched to the active length of the rock bolt.

Figure 1 1 illustrates an alternative construction of a cap 20B which has a cover section 24B shaped to extend into the bore 18 of a pipe 12. The skirt 22B is folded to define a fairly deep annular recess 48 and a rim 46 of the pipe 12 is inserted into the recess 48. The skirt 22B is welded to the outer surface 14 of the pipe along a 15 circumferential line 50. Figure 12 shows a configuration wherein a cap 20C also has a cover section 24C with a chisel shape. The cover section 24C extends from a circular, cylindrical skirt 22C generally conforming to what has been described, which surrounds an open end 10 of a pipe 12, and which is welded to an outer surface 14 along a circumferential line 54.

Figure 13 shows a construction wherein a cap 20D is similar to the cap 24C but with a skirt 22D of a smaller diameter that is positioned party inside a bore 18 of a pipe 12 and is welded to the pipe 12 along a circumferential line 56. Figure 14 shows the cap 20E configured to extend into the bore 18 of a pipe 12. The cover section 24E is located inside the bore 18 and the skirt 22E abuts against an inner surface 16 of the pipe adjacent a rim 46, which extends into an annular recess 48. The cap is welded to the pipe along a line 58. In the constructions described above, the cap is in each instance fixed in a leak- proof manner by means of appropriate welding to an open end of the pipe and only thereafter do the pipe and cap undergo a metal deformation process to produce a desired convoluted form. When the resulting, post-formed rock bolt is used, radial expansion of the tubular member (the convoluted pipe) can take place effectively over its entire length without any significant inhibiting effect arising from the cap, which has already been welded in place, working against such radial expansion. The rock bolt is accordingly expanded from a formed, folded condition towards a pre-formed condition, wherein the fully pre-formed condition represents a (substantially) maximal expansion which is in excess of that required for the rock bolt to engage in the borehole.

Figures 15 and 16 show a different construction or forming technique that is intended to fall within the scope of the current invention. A pipe 70 is formed in a metal rolling process to have a convoluted form. The pipe has an outer surface 72, an inner surface 74, which surrounds a U-shaped bore 76, and an elongate longitudinally extending channel 78. Opposed ends of the convoluted pipe 70 are open. In accordance with this aspect of the invention, a cap 80 of complementary or corresponding shape to the convoluted pipe 70 is pre-formed with a skirt 82 and a cover section 84. The skirt 82 conforms substantially, in this instance, to the shape of the bore 76 and thus can be inserted with a close fit to the inner surface 74 of the pipe 70. The cover section 84 also has a domed-shape, which follows a profile dependent on the cross-sectional shape of the convoluted pipe 70. The skirt 82 is welded along a line 90 to an edge 92 around the open end of the convoluted pipe 70.

The resulting rock bolt 60 can be expanded effectively over its full axial length without any significant restricting effect being produced by the shaped cap 80 of suitably ductile metal when such expansion is required. Figures 17 and 18 show a variation of the construction embodied in Figures 15 and 16. A cap 94 is shaped to conform to the shape or profile of the outer surface 72 of a convoluted or folder pipe 70 so that it can be placed with a close fit onto the outer surface 72. The cap 94 is accordingly provided with a channel 78.1 which corresponds to the channel 78 in the convoluted pipe 70. Through the use of, for example, a laser-welding machine it is possible to weld a rim 96 of the skirt 98 to the outer surface 72 of the pipe 70 along the curve edge of the rim 96 inside the channel 78 and so seal the convoluted pipe 70. In a development of this aspect of the invention, the channel 78 of the pipe 70 may also be provided in an "open" form as it exists after the first step of the metalworking process referred to above and illustrated in Figure 19. The actual profile will vary based on the pipe material and tools used. However, a correspondingly shaped cap can be provided to suit the profile resulting from a particular production set-up. The suitably profiled cap will be fitted to the intermediate form of the pipe and welded in place. The cap and pipe are then subjected to the second step of the metalworking process, which serves to impart the required (substantially) circular longitudinal profile. As is the case with the example shown in Figures 16 and 17, the resulting rock bolt product can, in use, be expanded effectively over its entire axial length.

The post-formed rock bolt 101 B shown in Figures 6, 9 and 10 is formed with the channel 1 15 having a substantially closed or abutting configuration where it extends along the pipe 1 12. The channel 1 15 is also formed deeper than the one shown in the cross-section of Figure 19; that is, the trough or bottom of channel 1 15 is formed against or close to the oppositely disposed region of the inner surface 1 16. It will be appreciated that performing the first and second steps to achieve these close and closed forms of the channel 1 15 will result in a greater reduction in the diameter of the post-formed rock bolt 101 B. The same design specifications may be applied to the other embodiments described herein.

The various embodiments that have been described provide substantially the same benefit in that in each case the resulting rock bolt can be expanded effectively over its full length. This means that when a rock bolt in accordance with the invention is inserted into a borehole it can be expanded into engagement with a wall of the borehole over substantially the full length of the borehole. The metal used in the rock bolt is thus fully employed. Additionally, the borehole is drilled to the length of the operative portion of the rock bolt and not longer, as is the case when prior art rock bolts as referred to are used.

A person skilled in the art will appreciate that a number of variations may be made to the features of the embodiments described without departing from the scope of the invention. The numerical values that have been given in this specification are exemplary only and not to be considered a limitation to the scope of the invention. The invention is to be applied to rock bolts for a range of holes and working conditions.

While the invention also described and illustrated with respect to the common configuration of having a single fold providing the longitudinal channel for the reduced dimension of the rock bolt, it may also be employed where more than one such channel is formed along the pipe.

The capped and folded configuration of a rock bolt end in accordance with the invention is particularly suited for the inner or leading end of a rock bolt that is, in use, inserted into the bottom of a borehole. This is not however a limitation and the invention may well be employed at either or both ends of a rock bolt. A pressurised fluid inlet may be provided through the wall of the pipe adjacent the outer end that protrudes from the borehole.

Claims

1 . A rock bolt comprising a pipe with a cap welded in sealing engagement over an end of the pipe and formed with a channel extending along a length of the pipe and through the cap.

2. A rock bolt as claimed in claim 1 in which the cap includes a skirt that is a close fit to a wall of the pipe.

3. A rock bolt as claimed in claim 2 in which the skirt is substantially circular and welded to the pipe in a pre-formed tubular condition.

4. A rock bolt as claimed in claim 3 in which the skirt is substantially cylindrical.

5. A rock bolt as claimed in claim 4 in which the skirt fits closely to an inner surface of the wall of the pipe.

6. A rock bolt as claimed in claim 1 or claim 2 in which the cap includes a cover section that is extends away from a line along which the cap is welded to the pipe.

7. A rock bolt as claimed in claim 6 in which the cover section is substantially domed.

8. A rock bolt as claimed in claim 6 in which the cover section has an end portion that is elongate along a line that is transverse to a folding line about which the channel of the rock bolt is formed.

9. A rock bolt as claimed in claim 6 in which the cover section protrudes from the end of the pipe.

10. A rock bolt as claimed in claim 6 in which the cap includes a cover section that extends into the pipe.

1 1 . A rock bolt as claimed in claim 1 in which the pipe is formed with a channel and the cap provided with a complementary shape welded to the end of the pipe having a channel form.

12. A method of making a rock bolt which includes the steps of providing a length of pre-formed pipe with at least one open end, welding a cap to the open end thereby sealing the open end, and thereafter deforming the pipe and the cap into a folded form to provide a channel that extends along the pipe and through the cap.

13. A method as claimed in claim 12 in which the cap includes a skirt and a dome-shaped cover section and the cap is welded to the pre-formed pipe with the skirt located in overlapping engagement with the pipe.

14. A method as claimed in claim 13 in which the skirt is located inside the pipe and the open end of the pipe welded to the cap.

15. A method as claimed in claim 13 in which the skirt is located around the pipe and an edge of the cap provided on the skirt is welded to a wall of the pipe adjacent to the open end of the pipe.

16. A method of making a rock bolt which includes the steps of providing a length of pipe having an open end, forming the pipe with a longitudinal channel, providing a cap with a shape complementary to a channel form imparted to a wall of the pipe, and welding the cap over the open end thereby sealing the open end.

17. A method as claimed in claim 16 in which the cap includes a skirt provided as a close fit to the channel form imparted to the wall of the pipe.

18. A method as claimed in claim 17 in which the skirt is located inside the pipe and the open end of the pipe welded to the cap.

19. A method as claimed in claim 17 in which the skirt is located around the pipe and an edge of the cap provided on the skirt is welded to the wall of the pipe adjacent to the open end of the pipe.