1. Field of the Invention
This invention relates to a rock bolt having an expandable tube and a shielded distal end, a method of making such a rock bolt, and a method of using such a rock bolt.
2. Description of Related Art
Rock bolts are used in underground mines, such as coal mines, to support the roof and ribs. Installation of conventional rock bolts involves drilling a borehole into the rock to a desired depth using an elongated drilling tool (termed the drill steel), removing the drill steel from the borehole, optionally inserting adhesive resin cartridges, and retaining the cartridges in the blind end of the borehole while a bolt, optionally bearing an expansion anchor, is installed into the borehole. The free end of the bolt extending out of the borehole is received by a chuck of a bolting machine. The bolting machine rotates the bolt within the borehole to mix the adhesive resin and/or expand the expansion anchor.
Other rock bolts comprise a longitudinally expandable tube that includes a longitudinally extending depression between two curved outer portions where the tube is partially collapsed on itself. The ends of the tube are folded over to create two enclosed cavities in the curved outer portions of the tube while a temporary passageway defined by the depression remains open on the ends. After placing the rock bolt in the pre-drilled borehole, pressurized fluid is delivered into the two cavities to force the depression outward, expand the tube, and compress it against the surrounding rock. Until the expansion has been completed, the ends of the passageway defined by the depression are open so that debris from the borehole can fall into the passageway defined by the depression.
The present invention includes a rock bolt having a longitudinally expandable tube. The tube includes a longitudinally extending depression that defines a temporary, enclosed longitudinal passageway. The rock bolt further includes a cover on the distal end of the rock bolt to prevent debris from entering the temporary, enclosed longitudinal passageway, ease insertion of the rock bolt into the borehole, and assist in alignment of the rock bolt in the borehole. The cover may be a plug or a cap and may provide a rounded tip for the rock bolt. The plug may be spherical. The cap may be attached such that its proximal end abuts the distal end of the rock bolt, is inserted into the distal end of the rock bolt, or extends beyond the distal end and along the sidewall of the rock bolt.
The present invention also includes a method of manufacturing a rock bolt, including providing an expandable member including an expandable tube and an end fitting where the expandable tube has a longitudinally extending depression disposed between a pair of outer portions of the tube, the exterior of the tube defines a temporary, enclosed longitudinal passageway having an open distal end, and the outer portions of the tube have closed distal ends; and enclosing the expandable member with a cover such that a distal open end of the temporary, enclosed longitudinal passageway of the expandable tube is covered. The cover may be a plug or a cap and may provide a rounded tip for the rock bolt. The method may also include placing a stiffening tube on a proximal end of the expandable tube such that the stiffening tube surrounds the proximal end of the expandable tube and has an opening that aligns with a corresponding opening in the expandable tube, thereby providing fluid communication to an interior of the expandable tube.
A method of using a rock bolt, including providing a rock bolt having an expandable member including an expandable tube having a temporary, enclosed longitudinal passageway with an open distal end; and a cover at a distal end of the rock bolt covering the temporary longitudinal passageway; drilling a borehole in rock; placing the rock bolt in the borehole; expanding the tube by providing pressurized fluid to the interior of the tube, thereby providing frictional engagement between an exterior of the tube and an interior of the borehole; and draining the fluid from the interior of the tube. The cover may be a plug or a cap and may provide a rounded tip for the rock bolt.
Referring now to the drawing figures in which like reference numbers refer to like elements,
A second stiffening tube 20, having a sidewall and two open ends, is attached to and surrounds a distal end 21 of tube 4 leaving the end of the tube 4 uncovered. A cover 22 covers the opening in a distal end 23 of second stiffening tube 20, the tube 4, or both and may be fixed thereto by welding or the like. The outer curved portions 8, 10 of tube 4 abut one another to define a temporary main passageway 26 as well as interior passageways 28, 30. Main passageway 26 is open at the distal end 21 of tube 4 while interior passageways 28, 30 are closed as shown in
In operation, a borehole is drilled into the rock to the desired depth and the bolt 2 is inserted through a bearing plate and into the borehole. A source of pressurized fluid, such as water, is delivered through the opening 34 of the first stiffening tube 14 and an opening in tube 4 into interior passageways 28, 30. When passageways 28, 30 are filled, the further addition of fluid creates sufficient hydraulic pressure to force open the tube 4, such that passageways 28, 30 are conjoined as an interior 35 of the tube 4 expanding the tube 4, and ultimately compressing the tube 4 against the surrounding rock of the borehole. See
The cover 22 may take the form of a plug or a cap. In one embodiment, the cover 22 is a plug 122 or a plug 222, as shown in
In one embodiment, such as for rock bolt 102, shown in
In another embodiment, rock bolt 202, shown in
Alternatively, the cover 22 may be a cap 322 or a cap 422, as shown in
In one embodiment, such as for rock bolt 302, shown in
In another embodiment, such as for rock bolt 402, shown in
In another embodiment (not shown), cap 422 could be sized such that its sidewall 436 fits inside the distal end 23 of tube 20 such that distal end 434 of cap 422 extends beyond distal end 23 of tube 20. A portion of sidewall 436 may extend beyond the distal end 23 of tube 20 or the length of the sidewall 436 may be adjusted so that only distal end 434 extends beyond distal end 23 of tube 20.
The rock bolt can be made by providing an expandable member which includes an expandable tube 4 and an end fitting (stiffening tube 20) on the distal end 21 of the expandable tube 4. The expandable tube 4 has a longitudinally extending depression 6 disposed between a pair of curved outer portions of the tube 8, 10. The exterior of the tube defines a temporary, enclosed longitudinal passageway 26 having an open distal end 23 and the outer portions of the tube 4 define internal passageways 28, 30 which have closed distal ends 23. The distal end of the tube 4 is then enclosed with a cover so as to cover the distal open end 23 of the temporary, enclosed longitudinal passageway 26. The cover may be in the form of a plug 122, 222 or a cap 322, 422 and may be rounded. The cover may be secured to the expandable member by welding or any other suitable method. The method may also include placing a stiffening tube 20 on a proximal end 15 of the expandable member such that the stiffening tube 20 surrounds the proximal end 15 of the expandable member and has an opening 34 that aligns with a corresponding opening in the expandable tube 4, thereby providing fluid communication to an interior of the expandable tube 4. The stiffening tube 20 may be attached to the expandable member by welding, crimping or any other suitable method.
The cover keeps debris from entering the main passageway of the rock bolt when the rock bolt is in the unexpanded condition. It also allows the rock bolt to be more easily inserted and centered in the borehole. The domed end of the rock bolt created by the cover eliminates the sharp angles at the distal end of the rock bolt which can tend to get caught on the sides of the borehole. The domed end also allows the rock bolt to be centered more easily in the borehole.
The cover also has the advantage of reduced manufacturing costs compared to other methods of rounding the end, for example, building up weld metal on top of a blank to round the end. The cover may be held in place with a minimal number of tack welds as described above simplifying fabrication and reducing costs. In addition, manufacturing becomes even easier when producing a rock bolt according to embodiment 102, shown in
The foregoing description sets forth the preferred embodiments of the invention at the present time. Various modifications, additions, and alternative designs will, of course, become apparent to those skilled in the art in light of the foregoing teachings without departing from the scope of the invention. The scope of the invention is indicated by the following claims rather than by the foregoing description. All changes and variations that fall within the meaning and range of equivalency of the claims are to be embraced within their scope. Specifically, while embodiments herein have been described as having a rounded cover, covers having any shape that covers the main passageway of the rock bolt are considered within the scope of the invention.
The present application claims priority to U.S. Provisional Patent Application No. 61/351,328, filed Jun. 4, 2010, entitled “Expandable Bolt with Shielded Tip”, the entire disclosure of which is herein incorporated by reference.
Number | Date | Country | |
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61351328 | Jun 2010 | US |