FRICTION BOLT

Abstract

A friction bolt for frictionally engaging the internal surface of a bore includes a circular tube, which is split longitudinally, and which has a leading end and trailing end. An expander mechanism is disposed within the tube towards the leading end. An elongate bar/cable is disposed within the tube and extends between the expander mechanism at one end and an anchor arrangement at the other end. The bar/cable extends through a ring attached to the trailing end into connection with the anchor arrangement. A restrainer member is disposed within the tube adjacent the ring and extends at least partially about and in engagement with the bar/cable. The tube has a weakened region adjacent the ring and the restrainer member extends longitudinally within the tube past the weakened region. The restrainer member includes a projection that projects through the longitudinal split of the tube for engagement with the bore.

Claims

1. A friction bolt, for frictionally engaging the internal surface of a bore drilled into a rock strata, the friction bolt comprising: an elongate, generally circular tube having a longitudinal split for radial expansion of the tube, the tube having a leading end and a trailing end; an expander mechanism disposed within the tube in a region of the leading end for applying a load tending to expand at least one section of the tube radially; an elongate bar or cable having opposed end disposed longitudinally within the tube a first end of the bar or cable being connected with the expander mechanism and a second end of the bar or cable being connected to an anchor arrangement positioned at the trailing end of the tube; a ring welded to the trailing end of the tube, the bar or cable extending through the ring beyond the trailing end of the tube into connection with the anchor arrangement; and a restrainer member disposed within the tube adjacent the ring, the restrainer member extending at least partly about the bar or cable and being in engagement with the bar or cable, the tube having a weakened region adjacent the ring and the restrainer member extending longitudinally within the tube past the weakened region in the direction of the leading end of the tube, the restrainer member including a projection that projects through the longitudinal split of the tube for engagement with a facing wall of a bore that the rock bolt is inserted into.

2. The friction bolt according to claim 1, wherein the projection extends longitudinally of the longitudinal split.

3. The friction bolt according to claim 1, wherein the projection has a profile that includes ribs or barbs extending laterally across the projection.

4. The friction bolt according to claim 1, wherein the restrainer member extends past the weakened region by an amount of between 40 and 300 mm.

5. The friction bolt according to claim 1, wherein a length of the restrainer member is from about 50 mm to about 300 mm.

6. The friction bolt according to claim 5, wherein a length of the restrainer member is about 150 mm.

7. The friction bolt according claim 1, wherein the restrainer member is tubular and has a central bore to receive the bar or cable.

8. The friction bolt according to claim 7, wherein the restrainer member is cylindrical.

9. The friction bolt according to claim 7, wherein the restrainer member has a diameter that is close to or equal to an inside diameter of the tube, prior to the tube being inserted into the bore.

10. The friction bolt according to claim 1, wherein the restrainer member is in engagement with an inside surface of the tube past the weakened region to create sufficient drag between the restrainer member and the inside surface of the tube past the weakened region, which upon failure of the tube in the weakened region and failure of the bar or cable form a leading bar or cable part and a trailing bar or cable part, the restrainer member restraining the trailing bar or cable part against ejection from the rock bolt.

11. The friction bolt according to claim 1, wherein the restrainer member is tubular and includes a central bore to receive the bar or cable and a slot or slit extending longitudinally through a length of the restrainer member between the outside surface of the part and the central bore.

12. The friction bolt according to claim 1, wherein the restrainer member is formed in two separate parts.

13. The friction bolt according to claim 12, wherein the two parts form an engagement when installed in the tube, the engagement occurring along inclined or angled faces of the two parts on either side of the bar or cable.

14. The friction bolt according to claim 13, wherein the engagement forms a wedge engagement.

15. The friction bolt according to claim 12, wherein one or both of the first and second parts include a lip or finger at a trailing end thereof that is positioned on a side of the ring of the rock bolt opposite the remainder of the restrainer member when the restrainer member is fully installed.

16. The friction bolt according to claim 12, wherein one or both of the first and second parts include an annular groove or channel at a trailing end thereof within which the ring of the rock bolt can seat.

17. The friction bolt according to claim 1, wherein the tube is deformed inwardly to form an indent that pushes into a side wall of the restrainer member.

18. The friction bolt according to claim 1, wherein the bar includes surface ribs or threads along a length of the bar which are removed in the section of the bar about which the restrainer member is installed.

19. The friction bolt according to claim 18, wherein the ribs or threads of the bar that are adjacent the leading end of the restrainer member form an abutment against which the leading end of the restrainer member abuts.

20. The friction bolt according to claim 1, wherein the restrainer member is formed in two parts, a first part being a body and a second part the projection.

21. The friction bolt according to claim 20, wherein the body and the projection include cooperating connectors that connect together.

22. The friction bolt according to claim 21, wherein the body includes an opening or openings to accept a pin or pins or the like formed to extend from an underside of the projection.

23. The friction bolt according to claim 22, wherein the pins are formed to provide a snap connection with the body.

24. A restrainer member for use with a friction bolt that is used for frictionally engaging an internal surface of a bore drilled into a rock strata, the friction bolt comprising; an elongate, generally circular tube including a longitudinal split for radial expansion, the tube having a leading end and a trailing end; an expander mechanism disposed within the tube in a region of the leading end for applying a load tending to expand at least a section of the tube radially; an elongate bar or cable having opposed ends disposed longitudinally within the tube, a first end of the bar or cable being connected with the expander mechanism and a second and opposite end of the bar or cable being connected with an anchor arrangement positioned at the trailing end of the tube; a ring welded to the trailing end of the tube, the bar or cable extending through the ring beyond the trailing end of the tube into connection with the anchor arrangement, the tube having a weakened region adjacent the ring, the restrainer member being arranged for insertion into the tube adjacent the ring, to extend longitudinally within the tube past the weakened region in the direction of the leading end of the tube and to extend about the bar or cable and to be in engagement with the bar or cable; and a projection projecting through the longitudinal split of the tube for engagement with a facing wall of the bore that the friction bolt is inserted into.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0049] In order that the invention may be more fully understood, some embodiments will now be described with reference to the figures in which:

[0050] FIG. 1 is a perspective view of a prior art rock bolt.

[0051] FIG. 2 is a cross-sectional view of the rock bolt of FIG. 1.

[0052] FIG. 3 is a perspective view of a restrainer member according to one embodiment of the invention.

[0053] FIG. 4 is a perspective view of the restrainer member of FIG. 3 installed in the trailing end of a rock bolt.

[0054] FIG. 5 is a cross-sectional view of the FIG. 4 arrangement.

[0055] FIG. 6 shows the trailing end of a rock bolt with one part of a restrainer member according to the invention installed.

[0056] FIG. 7 shows the arrangement of FIG. 6 with a second part of the restraining member positioned for installation.

[0057] FIG. 8 is a cross-sectional view of the arrangement of FIG. 7.

[0058] FIGS. 9 and 10 are perspective views of the separate parts of the restraining member of FIG. 3.

[0059] FIG. 11 is a perspective and exploded view of a restrainer member according to another embodiment of the invention.

[0060] FIG. 12 is a cross-sectional view of the restrainer member of FIG. 11 installed in a rock bolt.

[0061] FIG. 13 shows a section of bar with a ferrule attached by swaging.

DETAILED DESCRIPTION

[0062] FIG. 1 is a perspective view of an example rock bolt for use with a restrainer member according to the invention. The rock bolt 10 includes an elongate, generally circular tube 11, which includes a longitudinal split 12 which enables the tube 11 to be radially expanded. The tube 11 has a leading end 13 and a trailing end 14. An expander mechanism 15 is disposed within the tube 11 in the region of the leading end 13 and is operable to apply a load which tends to expand at least the leading end 13 of the tube 11 radially. The expander mechanism 15 can take any suitable form, and includes wedge arrangements that include at least a pair of wedge elements that expand as they move relative to one another.

[0063] The rock bolt 10 further includes a bar 16 that is disposed longitudinally within the tube 11 and which is connected at one end with the expander mechanism 15 and at the other end with an anchor arrangement generally designated by the reference numeral 17. In some forms of rock bolts, the end of the bar 16 that is connected to the anchor arrangement 17 is connected by a wedge arrangement.

[0064] The anchor arrangement includes a ring 18 that is welded to the trailing end 14 of the tube 11, a washer 19, a nut 20 that is threaded onto the trailing end of the bar 16 and a centering plug 21. The nut 20 is a blind nut that threads onto the end of the bar 16, but once the nut 20 is fully rotated onto the end of the bar, the nut will not rotate further relative to the bar 16. Accordingly, further rotation of the nut 20 causes the bar 16 to rotate. The nut 20 can glued to the end of the bar 16 for further attachment security.

[0065] In the rock bolt 10 which is illustrated, rotation of the nut 20 in one direction rotates the bar 16 in a direction that causes the expander mechanism 15 to expand. Alternative forms of rock bolt can include a cable rather than a rigid bar 16 and in those arrangements, expansion of the expander mechanism 15 is by applying a pull force to the cable.

[0066] Not shown in FIG. 1, is a rock plate, that would normally rest against the side of the ring 18 that faces the rock strata and which bears against the face of the rock strata into which the rock bolt 10 has been installed. The rock plate spreads load which is applied to the rock plate by the rock bolt across the rock face immediately adjacent the opening of the bore into which the rock bolt 10 is installed.

[0067] A cross-sectional view of the rock bolt 10 is illustrated in FIG. 2 and this also illustrates a problem which has been encountered in relation to the use of such rock bolts. In FIG. 2, an expansion mechanism is illustrated comprising a pair of wedge elements 25 and 26. The wedge element 25 is threadably connected to the bar 16 while the wedge element 26 is fixed to the inside surface of the tube 11, such as by welding. It will be appreciated that movement of the wedge element 25 relative to the wedge element 26 downwardly in the orientation of the rock bolt 10 of FIG. 2 will result in expansion of the expander mechanism 15 to cause radial expansion of the tube 11 at least in the region of the expander mechanism 15. Movement of the wedge element 25 relative to the wedge element 26 downwardly is by rotation of the bar 16 by rotating the nut 20. The interaction between the wedge elements 25 and 26 prevents the element 25 from rotating with the bar 16.

[0068] FIG. 2 also illustrates a rock plate 27, that rests against the inside surface of the ring 18. The weld shown in FIG. 2 is between the ring 18 and the tube 11. Other features which have already been described in relation to FIG. 1 and which appear in FIG. 2 retain the same reference numerals.

[0069] The cross-sectional view of the rock bolt 10 of FIG. 2 is modified from that shown in FIG. 1 to show failure of the rock bolt 10 at three positions. Firstly, the tube 11 has failed adjacent the ring 18. Secondly, the bar 16 has failed and now comprises separated leading and trailing parts 29 and 30. Thirdly, the tube 11 has failed adjacent the free end of the bar part 29. Failure of that kind often occurs when the bar 16 fails. Because of the first and second failures, the portion of the rock bolt 10 that comprises the trailing part 30 of the bar 16, the anchor mechanism 17, a small portion 31 of the tube 11 and the rock plate 27 can all be ejected under load from the bore 32 within which the rock bolt 10 is inserted.

[0070] It is to be noted that despite the failure of the tube 11 at two positions, the portion 33 of the tube 11 between the failures remains in place within the bore 32 and is not ejected, because the portion 33 of the tube 11 remains in frictional contact with the internal surface of bore 32.

[0071] The failure of the bar 16 can take place at any point along the length of the bar 16. However, failure of the tube 11 has been found to take place in a region of the tube which has been weakened through the action of welding the ring 18 to the tube. That action generally alters the strength of the tube 11 adjacent the ring 18 in a manner to weaken the strength of the tube in that region. That weakening occurs as a result of the heat generated during welding and the region is also known as a heat affected zone. The heat affected zone generally will occur within about 20 mm of the ring 18.

[0072] The invention resides in a rock bolt that employs a restrainer member and one form of that member is illustrated in FIG. 3. The restrainer member 35 is formed in two parts 36 and 37 and includes an integral projection 38 that projects from the part 36. Apart from the projection 38, the restrainer member 35 is part cylindrical as shown, but it could be non-cylindrical tubular in other forms of the invention. The restrainer member 35 is cylindrical (apart from the projection) to suit the inside diameter of the tube 11 into which the restrainer member 35 is to be inserted.

[0073] The restrainer member 35 further includes a central bore 39 which is of substantially the same diameter as the outside diameter of the bar of the rock bolt to which the invention applies. Again, the shape of the bore could be different to that shown in FIG. 3 to suit a non-circular bar, such as a square or hexagonal bar.

[0074] FIG. 4 illustrates the trailing end of a rock bolt 40 according to the invention in perspective view and shows the projection 38 extending through the longitudinal split 41 of the tube 42. The rock bolt 40 includes a ring 43, a washer 44 and a nut 45 which have the same operation as the same features of the rock bolt 10.

[0075] FIG. 5 shows the FIG. 4 arrangement in cross-section and that figure also shows the close fit of the restrainer member 35 about the bar 47. The fit about the bar 47 is close but does not prevent the bar 47 from being rotated as required for moving the wedge element 25 of the rock bolt 10 relative to the wedge element 26 to expand the expander mechanism 15. The restrainer member 35 could be a loose fit about the bar 47 or a tight fit as shown. A tight fit is preferred. FIG. 5 also shows the outer surface of the restrainer member 35 in engagement with the facing and inside surface of the tube 42. That engagement is optional, but if provided is preferably of significant frictional engagement.

[0076] When comparing the rock bolts of FIGS. 2 and 5, it can be seen that the restrainer member 35 extends well past the point at which the tube 11 has failed at reference numeral 31. In the illustrated embodiment, the restrainer member extends on either side of the weakened region, but in alternative embodiments, the restrainer member could extend only on the side of the weakened region that is towards the leading end 13 of the tube. The restrainer member could be spaced from the ring 18 or 43 such as up to about 650 mm from the ring.

[0077] Also, the restrainer member 35 extends in frictional engagement with the inside surface of the tube 42 for the full or at least the majority of its length. The restrainer member 35 thus frictionally engages the inside surface of the tube 42 inboard of and well past the weakened region or the heat affected zone (marked HAZ in FIG. 4) of the tube.

[0078] The illustrated form of the restrainer member 35 also includes the projection 38 for restraint against ejection of the trailing end of the rock bolt 40 from the bore. The projection 38 is formed to frictionally engage the inside surface of the bore into which the rock bolt 40 is inserted. The projection 38 has a profile that includes a plurality of barbs 46 that enhance frictional engagement with the bore wall (wall 32 in FIG. 2). The barbs 46 extend laterally across the projection 38 and are inclined so that movement of the restrainer member in an ejection direction causes the barbs 46 to tend to grip or bite into the bore wall upon that movement.

[0079] FIG. 5 also shows ribs 49 formed on the outer surface of the bar 47 over a section of the bar 47 inboard of the restrainer member 35. The ribs 49 have been removed from the section of the bar about which the restrainer member is installed and this allows the ribs 49 to form an abutment against which the leading end 48 of the restrainer member 35 can abut in the installed condition of the rock bolt. By that abutment, ejection of the bar 47 is restrained while the restrainer member 35 remains firmly secured in frictional engagement with the inside surface of the tube 42 and with the wall surface 32 of the bore in which the rock bolt 40 is installed. The tightness of the fit between the inside surface of the tube 42 and the facing surface of the restrainer member 35, and between the bore 39 of the restrainer member 35 and the bar 47, is preferably sufficient that the ribs 49 will not push into the bore 39 during operation of the rock bolt 40. As described earlier, other forms of abutment can be employed.

[0080] Thus, in the illustrated arrangement, failure at the HAZ zone combined with failure of the bar 16 does not free the trailing end of the tube 42 and the components and accessories at that end for ejection from the bore. Rather, the restrainer member 35 maintains frictional connection between the inside surface of the tube 42 inboard of the HAZ and the bar 16, as well as with the wall surface 32 so that ejection of the bar part 30 and the associated components and accessories is resisted and most preferably restrained.

[0081] The two part arrangement of the restrainer member 35 is preferred for ease of installation. With reference to FIGS. 6 and 7, the first part 36 is installed into the tube 42 about the bar 47 when the bar 47 is not inserted fully into the tube 42. The part 36 is more easily installed first into the tube 42 because it is otherwise difficult to insert the projection 38 past the ring 43 if the restrainer member 35 is formed in one piece. Clearly if the restrainer member 35 is formed completely as a cylinder, the difficulty with insertion of the member is not as difficult. However, when a projection is included, the two part construction is preferred.

[0082] With the first part 36 is installed into the tube 42 as shown in FIG. 6, the second part 37 can be installed and thereafter, the bar 47 can be pushed into the tube 42 to assume the position shown in FIG. 4. In FIG. 7, the part 37 is shown positioned for insertion with the leading end positioned at the opening 52 of the tube 42 and the trailing end in abutting engagement with the flange 53. The part 37 is pushed into the tube 42 as the bar 47 is pushed in.

[0083] The part 36 is prevented from movement from the installed position of FIG. 6 by the provision of a lip or finger 50 that is positioned on the trailing side of the ring 43. FIG. 8 shows the FIG. 6 arrangement in cross-section and shows that the ring 43 seats in a groove 51 adjacent the finger 50.

[0084] Also, the second part 37 does not engage the first part 36 until close to full insertion of the part 37 into the tube 42 because of the inclined engaging surface between them. FIGS. 9 and 10 illustrate the first and second parts 36 and 37 separately and show respective inclined engagement surfaces 54 and 55 that form an inclined engagement line 56 (see FIG. 3) in the engaged form of the first and second parts 36 and 37. Engagement surfaces 54 and 55 are shown to be smooth in the figures, but in other forms of the invention, those surfaces can be roughened to promote more secure engagement between the parts 36 and 37. Alternatively, one of the surfaces 54 or 55 could include dimples, and the other projections, so that the dimples and projections mate in the connected form of the part 36 and 37. Still further, the surfaces 54 and 55 could be stepped or otherwise shaped for engagement purposes.

[0085] An alternative arrangement of the invention in which the restrainer member is formed in two parts is illustrated in FIG. 11. In that figure, the restrainer member 60 comprises a first part which, in FIG. 11 is formed as a cylinder 61, which is a complete cylinder and which includes a central and circular bore 62. The cylinder 61 includes a pair of spaced apart openings 63 into which snap connectors 64, which extend from an underside 65 of a projection 66, can enter and be captured. The projection 66 includes a series of barbs 67 of the kind shown in the earlier figures as barbs 46. The barbs 67 operate in the same manner as the barbs 46 to engage the wall surface of a bore wall.

[0086] FIG. 12 shows a cross-sectional view of the trailing end of a rock bolt to which the restrainer member 60 has been fitted. The FIG. 12 illustration is shown outside of a bore for the purposes of clarity.

[0087] FIG. 12 shows a tube 70 that includes a longitudinal split like the earlier tubes 11 and 42 through which the projection extends. A bar 71 is disposed longitudinally within the tube 70 and extends to an anchor arrangement which includes a nut 72. The bar 71 extends through a washer 73 and a ring 74 which is welded to the outside surface of the tube 70. Each of the nut 72, the washer 73 and the ring 74 operate in accordance with the equivalent features of the earlier embodiments.

[0088] The cylinder 61 of the restrainer member 60 is disposed about the trailing portion of the bar 71. Different to the arrangement of FIG. 5, the ribs 75 of the bar 71 have not been removed in the region of the restrainer member 60, but rather, the ribs 75 continue along the bar 71 to the end of the bar and abutment between the restrainer member 60 and the bar 71 is provided by a swaged ferrule 76 which is swaged onto the bar 71. FIG. 13 illustrates the portion of the bar 71 to which the ferrule 76 is swaged. The ferrule 76 can be for example, a length of tube (30 mm for example) which is swaged as shown into position of the bar 71.

[0089] Interposed between the ferrule 76 and the facing end 77 of the cylinder 61 is a washer 78. The opposite end 79 of the cylinder 61 is shown in engagement with the washer 73.

[0090] FIG. 12 shows the projection 66 fitted in connection with the cylinder 61. It can be seen from FIGS. 11 and 12 that the snap connectors 64 have a neck portion 80 and a head portion 81 which is split centrally. The connectors 64 are also resilient so that opposite sides of the neck and head portions can shift inwardly towards each other as the connectors 64 enter the openings 63 through the sections of smaller diameter D.sub.1, and then can splay, flare or shift outwardly so that the head portions 81 shift into the larger diameter portion D.sub.2 of the openings 63. This captures the head portions 81 in the larger diameter portion D.sub.2 and secures the projection 66 to the cylinder 61.

[0091] The arrangements shown in FIGS. 11 to 13 provide an alternative arrangement for fitting the restrainer member 60 in place. The arrangement of those figures allows the cylinder 61 to be fitted to the bar 71, either before or after the ferrule 76 is swaged onto the bar 71 and once fitted, the bar 71 and associated components can be inserted fully into the tube 70. If the outside diameter of the cylinder 61 is slightly less than the inside diameter of the tube 70, then there will be no resistance to insertion of the bar and its associated components. The alternative is for the outside diameter of the cylinder 61 to be a light frictional fit, or even an interference fit with the inside diameter of the tube 70 and in those cases, the cylinder 61 will need to be forced into the tube 70.

[0092] Once the bar 71 has been positioned in the tube 70, the projection 66 can be fitted to the cylinder 61 by insertion of the snap connectors 64 into the openings 63. Once the connectors 64 splay or flare outwardly so that the head portions 81 move into the large diameter D.sub.2 of the openings 63, the projection 66 is firmly connected to the cylinder 61.

[0093] The assembly of FIG. 12 can then be inserted into a bore drilled into a rocket strata and when the outer barbed surface 67 of the projection 66 engages the facing bore wall, it will tend to push the cylinder 61 towards the opposite inner surface of the tube 70 and increase the frictional engagement between the cylinder 61 and the tube 70. There will therefore be frictional resistance between the barb surface 67 of the projection 66 and the facing surface of the bore wall, along with frictional engagement between the cylinder 61 and inside surface of the tube 70. All that resistance will tend to resist ejection of a portion of the bar 71 and the nut 72, washer 73 and ring 74 on failure of both the bar 71 and the tube 70.

[0094] Following on from discussion in relation to the two-part construction of the restrainer member 35, it will be readily understood that the cylinder 61 could also be formed into parts, which either form a complete cylinder 61 or a part cylinder.

[0095] Moreover, it will be readily appreciated that the snap connectors 64 are just one method by which the projection 66 could be connected to the cylinder 61, and that other arrangements such as discussed earlier herein could be adopted.

[0096] The invention described herein is susceptible to variations, modifications and/or additions other than those specifically described and it is to be understood that the invention includes all such variations, modifications and/or additions which fall within the spirit and scope of the present disclosure.