CA2353441A1 - Torque-tension anchor fitting - Google Patents
Torque-tension anchor fitting Download PDFInfo
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- CA2353441A1 CA2353441A1 CA 2353441 CA2353441A CA2353441A1 CA 2353441 A1 CA2353441 A1 CA 2353441A1 CA 2353441 CA2353441 CA 2353441 CA 2353441 A CA2353441 A CA 2353441A CA 2353441 A1 CA2353441 A1 CA 2353441A1
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- bolt
- cover
- roof
- threads
- bolt shaft
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Abstract
A roof bolt has a bolt shaft, external threads affixed to the bolt shaft, and a cover. The cover has internal threads threadably engaging the external threads.
The cover encloses the internal and external threads so as to protect the internal and external threads and to facilitate a consistent pre-established torque vs. tension relationship. The cover has a drive portion arranged to accept a drive tool so that torque may be applied to the roof bolt.
The cover encloses the internal and external threads so as to protect the internal and external threads and to facilitate a consistent pre-established torque vs. tension relationship. The cover has a drive portion arranged to accept a drive tool so that torque may be applied to the roof bolt.
Description
TORQUE-TENSION ANCHOR FITTING
Technical Field of the Invention The present invention relates to a roof bolt having a terminating end fitting, such as a barrel, to facilitate a consistent torque-tension relationship for the roof bolt.
Background of the Invention In cable based mine roof support systems, bore holes are usually drilled into the roof of a mine, one or more resin cartridges are inserted into each of the bore holes, and a roof bolt is then inserted into each bore hole.
As each of the roof bolts travels through its corresponding bore hole during insertion, it punctures the resin cartridges in its bore hole. Each of the roof bolts is then rotated in its bore hole in order to mix the resin. Once the resin is mixed, rotation (spinning) of the roof bolts is stopped and the resin is allowed to set, at which point the roof bolts are able to support at least a part of the weight of the mine's roof.
~0 A roof bolt is typically formed by suitably attaching an anchor head to a bolt shaft. The bolt shaft may be provided in the form of a rod having a substantially Attorney Docket 27855/36146 uniform cross-section, or in the form of twisted wires forming a strand. The anchor head is fashioned so as to accept a wrench or other spinning tool so that the roof bolt can be rotated in order to mix resin. An anchor plate is usually provided between the anchor head and the roof of the mine.
Roof bolts can be installed as passive roof bolts or as active roof bolts. A passive roof bolt does not carry any significant tension or load immediately following installation. The tension or load on the roof bolt develops over time as the roof of the mine settles against the roof bolt's anchor head and the roof bolt reacts to this settling. An active roof bolt, on the other hand, is pre-loaded during installation so that the roof bolt, immediately upon installation, transfers a portion of the weight of the mine roof as a reaction force back into the mine roof. This force is a portion of the capacity of the roof bolt.
There are different methods to pre-load an active ,0 roof bolt. For example, the exterior end of the roof bolt may be pulled, such as by a hydraulic jack, after the resin in the bore hole has set in order to pre-tension the roof Attorney Docket 27855/35146 bolt. The roof bolt is then arranged to hold this pre-tension force following release of the roof bolt by the pulling tool. For example, a threaded nut on a threaded portion of the bolt shaft may be tightened against the anchor plate to pick up any slack caused by the pulling.
Alternatively, shims may be inserted. under the anchor head to hold the pre-tension.
Another method of arranging the roof bolt to hold a pre-tension is to provide the roof bolt with a threaded anchor head. Following setting of the resin, torque is applied to the anchor head with respect to the bolt shaft until the anchor head/anchor plate interaction establishes the desired amount of pre-load on th.e roof bolt.
The amount of pre-load on the roof bolt is often determined in order to ensure that the roof bolt has the required amount of pre-load. In order to determine this pre-load, it is known to perform a lift-off test on, or to apply a load cell to, the roof bolt. However, these methods of determining pre-load are difficult, time consuming, and '0 expensive to effect.
It would be better to measure the torque applied to the roof bolt during pre-loading and to convert this Attorney Docket 27855/36146 torque into tension (load). In order to implement this approach of determining pre-load, a torque-tension relationship may be pre-established, such as in a laboratory. This approach assumes that the pre-established torque-tension relationship is valid during installation of the roof bolt in the roof of a mine. This assumption, however, is not always valid.
That is, the torque-tension relationship depends upon such considerations as thread geometry, thread efficiency, friction between threads, and friction on the load bearing surfaces. When threads become exposed to the elements, which frequently occurs before and during installation, corrosion, dirt, and/or mechanical damage can significantly change the conditions of the threads. If the conditions of the threads change, the torque-tension relationship can likewise change, so that torque measured during installation can no longer be relied upon to produce an accurate indication of tension based upon the pre-established torque-tension relationship.
0 The present invention is directed to a cover that protects the threads of a roof bolt against conditions, such Attorney Docket 27855/36146 as corrosion, dirt, and/or mechanical damage, that can alter the torque-tension relationship.
Summary of the Invention In accordance with one aspect of the present invention, a roof bolt comprises a bolt shaft, threads, and a cover. The threads are affixed to the bolt shaft, and the cover protectively encloses the threads.
In accordance with another aspect of the present invention, a roof bolt comprises a bolt shaft, threads; and a cover. The threads are affixed to the bolt shaft. The cover has threads that threadably engage the threads affixed to the bolt shaft. The cover encloses the threads affixed to the bolt shaft and the threads of the cover so as to protect both the threads affixed to the bolt shaft and the threads of the cover.
In accordance with yet another aspect of the present invention, a roof bolt comprises a bolt shaft, external threads affixed to the bolt shaft, and a cover.
The cover has internal threads threadably engaging the external threads. The cover encloses the internal and external threads so as to protect the internal and external Attorney Docket 27855/36146 threads, and the cover has a drive portion arranged to accept a drive tool.
Brief Description of the Drawing These and other features and advantages of the present invention will become more apparent from a detailed consideration of the invention when 'taken in conjunction with the drawing in which:
Figure 1 is a partially sectioned side view of a roof bolt according to a first embodiment of the present invention;
Figure 2 is a partially sectioned side view of a roof bolt according to a second embodiment of the present invention; and, Figure 3 is a partially sectioned side view of a roof bolt according to a third embodiment of the present invention.
Detailed Description As shown in Figure 1 of the drawing, a roof bolt 10 according to a first embodiment o:E the present invention includes a bolt shaft 12, which is shown in the form of a Attorney Docket 27855/36146 length of twisted steel wires having a plurality of steel wires twisted around a center steel wire, but which may be any other type of bolt shaft such as a solid rod, threadbar, rebar, etc. The roof bolt 10 also has a dead-end anchor head 14 which is suitably affixed to the bolt shaft 12 and which is provided with an external thread portion 16. The threads of the external thread portion 16 may be fine threads, for example. Also, although the dead-end anchor head 14 and the external thread portion 16 are shown as a unitary structure, they instead may be separate components.
A cover 18, which may be in the form of a sleeve or barrel or other housing, has internal threads that threadably engage the external thread portion 16. The cover 18 also has a drive portion 20, such as flats, that accepts a drive tool, such as a drill or wrench, so that torque can be applied to the cover 18. The cover 18 has a first open end 22 that is enclosed by a protective end cap 24 and a second open end 26 that is enclosed by a friction reducing washer 28.
0 The cover 18, the protective end cap 24, and the friction reducing washer 28 encase the internal threads of the cover 18 and the threads of the external thread portion -Attorney Docket 27855/36146 16 of the dead-end anchor head 14 so as to protect both sets of threads from corrosion, dirt, and/or mechanical damage.
The friction reducing washer 28 may be constructed of a low friction material such as Teflon or nylon and/or may be lubricated so as to minimize friction between the roof bolt and the bearing surface, such as a bearing washing 30, which contacts the roof bolt 10. A thread lubricant, such as dry moly, may be provided within the cover 18 to further protect the threads of the cover 18 and of the external 10 thread portion 16.
Also, the friction reducing washer 28 acts as a release mechanism. That is, the friction reducing washer 28 allows the cover 18 and the dead-end anchor head 14 to be turned in unison to mix the resin in the mine roof bore hole, as is customary. However, once the resin has set, the dead-end anchor head 14 can no longer be turned. Therefore, when the roof bolt 10 is to be pre-tensioned, the cover 18 is rotated against the friction reducing washer 28 which abuts the bearing washer 30 that in turn abuts a bearing or ~0 anchor plate. As the cover 18 rotates against the friction reducing washer 28 which abuts the bearing plate through the bearing washer 30, the dead-end anchor head 14 cannot rotate _ g _ Attorney Docket 27855/36146 and instead travels outwardly away from the bearing washer 30 thereby tensioning the roof bolt 10. This outward movement of the dead-end anchor head 14 is resisted by the friction reducing washer 28 until it is sheared into two or more pieces by a shear shoulder 31 attached to the external thread portion 16. Thus, the friction reducing washer 28 provides the release mechanism. The friction reducing washer 28 is preferably constructed to withstand a torque limit of about 50 ft-lb in order to allow the roof bolt 10 to turn during resin mixing.
Accordingly, as long as the torque applied to the roof bolt 10 is below the torque limit of the friction reducing washer 28, as will be the case prior to resin set-up, the cover 18 and the dead-end anchor head 14 rotate in unison. However, when the torque applied to the roof bolt 10 exceeds the torque limit of the friction reducing washer 28, as will be the case after the resin has set, the friction reducing washer 28 shears apart. Thus, the dead-end anchor head 14 is released so that the cover 18 turns 0 against the bearing washer 30 to pre-load the roof bolt 10.
A sheared off portion of the friction reducing washer 28 Attarney Docket 27855/36146 tends to remain thereby reducing friction between the cover 18 and the bearing washer 30.
As shown in Figure 2 of the drawing, a roof bolt 40 according to a second embodiment of the present invention includes a bolt shaft 42, which is shown in the exemplary form of a length of threadbar. The z-oof bolt 40 also has an insert 44. The insert 44 may be in t:he form of a cast insert, is suitably affixed to the bolt shaft 42, and is provided with external threads 46. 7.'he external threads 46 may be fine threads, for example.
A cover 48 has internal threads that threadably engage the external threads 46. The cover 48 also has a shape that accepts a drive tool, such as a drill or wrench, so that torque can be applied to the cover 48. Thus, the cover 48, for example, may be a hex nut which has a first open end 50 that is closed by the insert 44 and a second open end 52 that abuts against a flat washer 54 which in turn abuts against a friction reducing washer 56.
The cover 48, the insert 44, the flat washer 54, 7 and the friction reducing washer 56 encase the internal threads of the cover 48 and the external threads 46 of the insert 44 so as to protect both sets of threads from Attorney Docket 278SS/36146 corrosion, dirt, and/or mechanical damage. The friction reducing washer 56 may be constructed in a similar fashion to the friction reducing washer 28 so as to minimize friction between the roof bolt 40 anal the bearing surface, such as a dome washer 58, which contacts the roof bolt 40.
A thread lubricant may be provided within the cover 48 to further protect the threads of the cover 48 and of the external threads 46.
As in the case of the friction reducing washer 28, the friction reducing washer 56 acts as a release mechanism.
That is, the friction reducing washer 56 allows the cover 48 and the insert 44 to be turned in unison to mix the resin in the mine roof bore hole, as is customary. However, once the resin has set, the insert 44 can no longer be turned.
Therefore, when the roof bolt 40 is to be pre-tensioned, the cover 48 is rotated against the friction reducing washer 56 which abuts the dome washer 58 that in turn abuts a bearing or anchor plate. As the cover 48 rotates against the friction reducing washer 56 which abuts the bearing plate '0 through the dome washer 58, the insert 44 cannot rotate and instead travels outwardly away from the dome washer 58 thereby tensioning the roof bolt 40. This outward movement Attorney Docket 27855/36146 of the insert 44 is resisted by the friction reducing washer 56 until it is sheared. This outward movement of the insert 44 also tensions the bolt shaft 42.
As shown in Figure 3 of the drawing, a roof bolt 60 according to a third embodiment of the present invention includes a bolt shaft 62, which is shown in the exemplary form of a length of rebar. The bolt shaft 62 is externally threaded at an end 64. The threads of the externally threaded end 64 may be fine threads, for example. A cover 66 is provided around the externally threaded end 64 and includes a nut 68, a flat washer 70, a friction reducing washer 72, a dome washer 74, a plastic tube 76, and a seal 78. The seal 78 may be a rubber seal, for example.
The nut 68 may be in the form of a hex nut or have any other shape that is appropriate for accepting a drive tool, such as a drill or wrench, so that torque can be applied to the nut 68. The nut 68 has internal threads that threadably engage the externally threaded end 64. The nut 68 abuts against both the flat washer 70 and a first open 0 end 80 of the plastic tube 76. The flat washer 70 abuts against the friction reducing washer 72 which in turn abuts against the dome washer 74. The flat washer 70, the Attorney Docket 27855/36146 friction reducing washer 72, and the dome washer 74 internally receive the plastic tube 76. The plastic tube 76 has a second open end 82 which is sealed by the seal 78. If the nut 68 has an open end 84, the open end 84 may be enclosed by a cap 86.
The cover 66 encases the internal threads of the nut 68 and the externally threaded end 64 so as to protect both sets of threads from corrosion, dirt, and/or mechanical damage. The friction reducing washer 72 may be constructed in a similar fashion to the friction reducing washers 28 and 56 so as to minimize friction between the roof bolt 60 and the bearing surface, such as the dome washer 74. A thread lubricant may be provided within the cover 66 to further protect the threads of the nut 68 and of the externally threaded end 64.
The friction reducing washer 72 acts as a release mechanism. Thus, the friction reducing washer 72 allows the nut 68 and the externally threaded end 64 to be turned in unison to mix the resin in the mine roof bore hole, as is 0 customary. However, once the resin has set, the externally threaded end 64 can no longer be turned. Therefore, when the roof bolt 60 is to be pre-tensioned, the nut 68 is Attorney Docket 27855/36146 rotated against the friction reducing washer 72 which abuts the dome washer 74 that in turn abuts a bearing or anchor plate. As the nut 68 rotates against the friction reducing washer 72 which abuts the bearing plate through the dome washer 74, the externally threaded end 64 cannot rotate and instead travels outwardly away from the dome washer 74 thereby tensioning the bolt shaft 62 of the roof bolt 60.
This outward movement of the externally threaded end 64 is resisted by the friction reducing washer 72 until it shears.
The roof bolts 10, 40, and. 60, as described above, make it possible to reproduce, with a high degree of consistency, a pre-established torque-tension relationship and thus to provide a known and desired level of pre-load (pre-tension) based upon a measurement of the torque applied to the roof bolt 10 during its installation. Also, the thread and bearing friction can be minimized, resulting in maximum tension for a given input torque.
Certain modifications of the present invention have been discussed above. Other modifications will occur ,0 to those practicing in the art of the present invention.
For example, as described above, the release mechanism is provided by the friction reducing washer 28. However, the Attorney Docket 27855/36146 release mechanism may instead be provided by other mechanisms, such as by damaging or deforming a thread.
Accordingly, the description of the present inven-tion is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the best mode of carrying out the invention. The details may be varied substantially without departing from the spirit of the invention, and the exclusive use of all modifications which are within the scope of the appended claims is reserved.
Technical Field of the Invention The present invention relates to a roof bolt having a terminating end fitting, such as a barrel, to facilitate a consistent torque-tension relationship for the roof bolt.
Background of the Invention In cable based mine roof support systems, bore holes are usually drilled into the roof of a mine, one or more resin cartridges are inserted into each of the bore holes, and a roof bolt is then inserted into each bore hole.
As each of the roof bolts travels through its corresponding bore hole during insertion, it punctures the resin cartridges in its bore hole. Each of the roof bolts is then rotated in its bore hole in order to mix the resin. Once the resin is mixed, rotation (spinning) of the roof bolts is stopped and the resin is allowed to set, at which point the roof bolts are able to support at least a part of the weight of the mine's roof.
~0 A roof bolt is typically formed by suitably attaching an anchor head to a bolt shaft. The bolt shaft may be provided in the form of a rod having a substantially Attorney Docket 27855/36146 uniform cross-section, or in the form of twisted wires forming a strand. The anchor head is fashioned so as to accept a wrench or other spinning tool so that the roof bolt can be rotated in order to mix resin. An anchor plate is usually provided between the anchor head and the roof of the mine.
Roof bolts can be installed as passive roof bolts or as active roof bolts. A passive roof bolt does not carry any significant tension or load immediately following installation. The tension or load on the roof bolt develops over time as the roof of the mine settles against the roof bolt's anchor head and the roof bolt reacts to this settling. An active roof bolt, on the other hand, is pre-loaded during installation so that the roof bolt, immediately upon installation, transfers a portion of the weight of the mine roof as a reaction force back into the mine roof. This force is a portion of the capacity of the roof bolt.
There are different methods to pre-load an active ,0 roof bolt. For example, the exterior end of the roof bolt may be pulled, such as by a hydraulic jack, after the resin in the bore hole has set in order to pre-tension the roof Attorney Docket 27855/35146 bolt. The roof bolt is then arranged to hold this pre-tension force following release of the roof bolt by the pulling tool. For example, a threaded nut on a threaded portion of the bolt shaft may be tightened against the anchor plate to pick up any slack caused by the pulling.
Alternatively, shims may be inserted. under the anchor head to hold the pre-tension.
Another method of arranging the roof bolt to hold a pre-tension is to provide the roof bolt with a threaded anchor head. Following setting of the resin, torque is applied to the anchor head with respect to the bolt shaft until the anchor head/anchor plate interaction establishes the desired amount of pre-load on th.e roof bolt.
The amount of pre-load on the roof bolt is often determined in order to ensure that the roof bolt has the required amount of pre-load. In order to determine this pre-load, it is known to perform a lift-off test on, or to apply a load cell to, the roof bolt. However, these methods of determining pre-load are difficult, time consuming, and '0 expensive to effect.
It would be better to measure the torque applied to the roof bolt during pre-loading and to convert this Attorney Docket 27855/36146 torque into tension (load). In order to implement this approach of determining pre-load, a torque-tension relationship may be pre-established, such as in a laboratory. This approach assumes that the pre-established torque-tension relationship is valid during installation of the roof bolt in the roof of a mine. This assumption, however, is not always valid.
That is, the torque-tension relationship depends upon such considerations as thread geometry, thread efficiency, friction between threads, and friction on the load bearing surfaces. When threads become exposed to the elements, which frequently occurs before and during installation, corrosion, dirt, and/or mechanical damage can significantly change the conditions of the threads. If the conditions of the threads change, the torque-tension relationship can likewise change, so that torque measured during installation can no longer be relied upon to produce an accurate indication of tension based upon the pre-established torque-tension relationship.
0 The present invention is directed to a cover that protects the threads of a roof bolt against conditions, such Attorney Docket 27855/36146 as corrosion, dirt, and/or mechanical damage, that can alter the torque-tension relationship.
Summary of the Invention In accordance with one aspect of the present invention, a roof bolt comprises a bolt shaft, threads, and a cover. The threads are affixed to the bolt shaft, and the cover protectively encloses the threads.
In accordance with another aspect of the present invention, a roof bolt comprises a bolt shaft, threads; and a cover. The threads are affixed to the bolt shaft. The cover has threads that threadably engage the threads affixed to the bolt shaft. The cover encloses the threads affixed to the bolt shaft and the threads of the cover so as to protect both the threads affixed to the bolt shaft and the threads of the cover.
In accordance with yet another aspect of the present invention, a roof bolt comprises a bolt shaft, external threads affixed to the bolt shaft, and a cover.
The cover has internal threads threadably engaging the external threads. The cover encloses the internal and external threads so as to protect the internal and external Attorney Docket 27855/36146 threads, and the cover has a drive portion arranged to accept a drive tool.
Brief Description of the Drawing These and other features and advantages of the present invention will become more apparent from a detailed consideration of the invention when 'taken in conjunction with the drawing in which:
Figure 1 is a partially sectioned side view of a roof bolt according to a first embodiment of the present invention;
Figure 2 is a partially sectioned side view of a roof bolt according to a second embodiment of the present invention; and, Figure 3 is a partially sectioned side view of a roof bolt according to a third embodiment of the present invention.
Detailed Description As shown in Figure 1 of the drawing, a roof bolt 10 according to a first embodiment o:E the present invention includes a bolt shaft 12, which is shown in the form of a Attorney Docket 27855/36146 length of twisted steel wires having a plurality of steel wires twisted around a center steel wire, but which may be any other type of bolt shaft such as a solid rod, threadbar, rebar, etc. The roof bolt 10 also has a dead-end anchor head 14 which is suitably affixed to the bolt shaft 12 and which is provided with an external thread portion 16. The threads of the external thread portion 16 may be fine threads, for example. Also, although the dead-end anchor head 14 and the external thread portion 16 are shown as a unitary structure, they instead may be separate components.
A cover 18, which may be in the form of a sleeve or barrel or other housing, has internal threads that threadably engage the external thread portion 16. The cover 18 also has a drive portion 20, such as flats, that accepts a drive tool, such as a drill or wrench, so that torque can be applied to the cover 18. The cover 18 has a first open end 22 that is enclosed by a protective end cap 24 and a second open end 26 that is enclosed by a friction reducing washer 28.
0 The cover 18, the protective end cap 24, and the friction reducing washer 28 encase the internal threads of the cover 18 and the threads of the external thread portion -Attorney Docket 27855/36146 16 of the dead-end anchor head 14 so as to protect both sets of threads from corrosion, dirt, and/or mechanical damage.
The friction reducing washer 28 may be constructed of a low friction material such as Teflon or nylon and/or may be lubricated so as to minimize friction between the roof bolt and the bearing surface, such as a bearing washing 30, which contacts the roof bolt 10. A thread lubricant, such as dry moly, may be provided within the cover 18 to further protect the threads of the cover 18 and of the external 10 thread portion 16.
Also, the friction reducing washer 28 acts as a release mechanism. That is, the friction reducing washer 28 allows the cover 18 and the dead-end anchor head 14 to be turned in unison to mix the resin in the mine roof bore hole, as is customary. However, once the resin has set, the dead-end anchor head 14 can no longer be turned. Therefore, when the roof bolt 10 is to be pre-tensioned, the cover 18 is rotated against the friction reducing washer 28 which abuts the bearing washer 30 that in turn abuts a bearing or ~0 anchor plate. As the cover 18 rotates against the friction reducing washer 28 which abuts the bearing plate through the bearing washer 30, the dead-end anchor head 14 cannot rotate _ g _ Attorney Docket 27855/36146 and instead travels outwardly away from the bearing washer 30 thereby tensioning the roof bolt 10. This outward movement of the dead-end anchor head 14 is resisted by the friction reducing washer 28 until it is sheared into two or more pieces by a shear shoulder 31 attached to the external thread portion 16. Thus, the friction reducing washer 28 provides the release mechanism. The friction reducing washer 28 is preferably constructed to withstand a torque limit of about 50 ft-lb in order to allow the roof bolt 10 to turn during resin mixing.
Accordingly, as long as the torque applied to the roof bolt 10 is below the torque limit of the friction reducing washer 28, as will be the case prior to resin set-up, the cover 18 and the dead-end anchor head 14 rotate in unison. However, when the torque applied to the roof bolt 10 exceeds the torque limit of the friction reducing washer 28, as will be the case after the resin has set, the friction reducing washer 28 shears apart. Thus, the dead-end anchor head 14 is released so that the cover 18 turns 0 against the bearing washer 30 to pre-load the roof bolt 10.
A sheared off portion of the friction reducing washer 28 Attarney Docket 27855/36146 tends to remain thereby reducing friction between the cover 18 and the bearing washer 30.
As shown in Figure 2 of the drawing, a roof bolt 40 according to a second embodiment of the present invention includes a bolt shaft 42, which is shown in the exemplary form of a length of threadbar. The z-oof bolt 40 also has an insert 44. The insert 44 may be in t:he form of a cast insert, is suitably affixed to the bolt shaft 42, and is provided with external threads 46. 7.'he external threads 46 may be fine threads, for example.
A cover 48 has internal threads that threadably engage the external threads 46. The cover 48 also has a shape that accepts a drive tool, such as a drill or wrench, so that torque can be applied to the cover 48. Thus, the cover 48, for example, may be a hex nut which has a first open end 50 that is closed by the insert 44 and a second open end 52 that abuts against a flat washer 54 which in turn abuts against a friction reducing washer 56.
The cover 48, the insert 44, the flat washer 54, 7 and the friction reducing washer 56 encase the internal threads of the cover 48 and the external threads 46 of the insert 44 so as to protect both sets of threads from Attorney Docket 278SS/36146 corrosion, dirt, and/or mechanical damage. The friction reducing washer 56 may be constructed in a similar fashion to the friction reducing washer 28 so as to minimize friction between the roof bolt 40 anal the bearing surface, such as a dome washer 58, which contacts the roof bolt 40.
A thread lubricant may be provided within the cover 48 to further protect the threads of the cover 48 and of the external threads 46.
As in the case of the friction reducing washer 28, the friction reducing washer 56 acts as a release mechanism.
That is, the friction reducing washer 56 allows the cover 48 and the insert 44 to be turned in unison to mix the resin in the mine roof bore hole, as is customary. However, once the resin has set, the insert 44 can no longer be turned.
Therefore, when the roof bolt 40 is to be pre-tensioned, the cover 48 is rotated against the friction reducing washer 56 which abuts the dome washer 58 that in turn abuts a bearing or anchor plate. As the cover 48 rotates against the friction reducing washer 56 which abuts the bearing plate '0 through the dome washer 58, the insert 44 cannot rotate and instead travels outwardly away from the dome washer 58 thereby tensioning the roof bolt 40. This outward movement Attorney Docket 27855/36146 of the insert 44 is resisted by the friction reducing washer 56 until it is sheared. This outward movement of the insert 44 also tensions the bolt shaft 42.
As shown in Figure 3 of the drawing, a roof bolt 60 according to a third embodiment of the present invention includes a bolt shaft 62, which is shown in the exemplary form of a length of rebar. The bolt shaft 62 is externally threaded at an end 64. The threads of the externally threaded end 64 may be fine threads, for example. A cover 66 is provided around the externally threaded end 64 and includes a nut 68, a flat washer 70, a friction reducing washer 72, a dome washer 74, a plastic tube 76, and a seal 78. The seal 78 may be a rubber seal, for example.
The nut 68 may be in the form of a hex nut or have any other shape that is appropriate for accepting a drive tool, such as a drill or wrench, so that torque can be applied to the nut 68. The nut 68 has internal threads that threadably engage the externally threaded end 64. The nut 68 abuts against both the flat washer 70 and a first open 0 end 80 of the plastic tube 76. The flat washer 70 abuts against the friction reducing washer 72 which in turn abuts against the dome washer 74. The flat washer 70, the Attorney Docket 27855/36146 friction reducing washer 72, and the dome washer 74 internally receive the plastic tube 76. The plastic tube 76 has a second open end 82 which is sealed by the seal 78. If the nut 68 has an open end 84, the open end 84 may be enclosed by a cap 86.
The cover 66 encases the internal threads of the nut 68 and the externally threaded end 64 so as to protect both sets of threads from corrosion, dirt, and/or mechanical damage. The friction reducing washer 72 may be constructed in a similar fashion to the friction reducing washers 28 and 56 so as to minimize friction between the roof bolt 60 and the bearing surface, such as the dome washer 74. A thread lubricant may be provided within the cover 66 to further protect the threads of the nut 68 and of the externally threaded end 64.
The friction reducing washer 72 acts as a release mechanism. Thus, the friction reducing washer 72 allows the nut 68 and the externally threaded end 64 to be turned in unison to mix the resin in the mine roof bore hole, as is 0 customary. However, once the resin has set, the externally threaded end 64 can no longer be turned. Therefore, when the roof bolt 60 is to be pre-tensioned, the nut 68 is Attorney Docket 27855/36146 rotated against the friction reducing washer 72 which abuts the dome washer 74 that in turn abuts a bearing or anchor plate. As the nut 68 rotates against the friction reducing washer 72 which abuts the bearing plate through the dome washer 74, the externally threaded end 64 cannot rotate and instead travels outwardly away from the dome washer 74 thereby tensioning the bolt shaft 62 of the roof bolt 60.
This outward movement of the externally threaded end 64 is resisted by the friction reducing washer 72 until it shears.
The roof bolts 10, 40, and. 60, as described above, make it possible to reproduce, with a high degree of consistency, a pre-established torque-tension relationship and thus to provide a known and desired level of pre-load (pre-tension) based upon a measurement of the torque applied to the roof bolt 10 during its installation. Also, the thread and bearing friction can be minimized, resulting in maximum tension for a given input torque.
Certain modifications of the present invention have been discussed above. Other modifications will occur ,0 to those practicing in the art of the present invention.
For example, as described above, the release mechanism is provided by the friction reducing washer 28. However, the Attorney Docket 27855/36146 release mechanism may instead be provided by other mechanisms, such as by damaging or deforming a thread.
Accordingly, the description of the present inven-tion is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the best mode of carrying out the invention. The details may be varied substantially without departing from the spirit of the invention, and the exclusive use of all modifications which are within the scope of the appended claims is reserved.
Claims (45)
1. A roof bolt comprising:
a bolt shaft;
threads affixed to the bolt shaft; and, a cover protectively enclosing the threads.
a bolt shaft;
threads affixed to the bolt shaft; and, a cover protectively enclosing the threads.
2. The roof bolt of claim 1 further comprising a release mechanism permitting the cover and the bolt shaft to be turned in unison below a given torque and permitting the cover to be turned with respect to the bolt shaft above the given torque.
3. The roof bolt of claim 2 wherein the release mechanism is a friction reducing washer.
4. The roof bolt of claim 1 wherein the cover has an open end, and wherein the cover is enclosed at the open end so as to environmentally protect the threads.
5. The roof bolt of claim 4 further comprising a release mechanism, wherein the release mechanism permits the cover and the bolt shaft to be turned in unison below a given torque and permits the cover to be turned with respect to the bolt shaft above the given torque.
6. The roof bolt of claim 5 wherein the release mechanism is a friction reducing washer.
7. The roof bolt of claim 1 wherein the cover has first and second open ends, and wherein the cover is enclosed at both the first and second open ends so as to form a casing that environmentally protects the threads.
8. The roof bolt of claim 7 further comprising a release mechanism encloses at least one of the first and second ends, wherein the release mechanism permits the cover and the bolt shaft to be turned in unison below a given torque and permits the cover to be turned with respect to the bolt shaft above the given torque.
9. The roof bolt of claim 8 wherein the release mechanism is a friction reducing washer.
10. The roof bolt of claim 1 wherein the threads comprise an externally threaded member affixed to the bolt shaft.
11. The roof bolt of claim 10 wherein the externally threaded member comprises an anchor head, wherein the bolt shaft is a twisted strand bolt shaft, and wherein the anchor head is affixed to the twisted strand bolt shaft.
12. The roof bolt of claim 10 wherein the externally threaded member comprises an insert, wherein the bolt shaft is threadbar, and wherein the insert is affixed to the threadbar.
13. The roof bolt of claim 10 wherein the externally threaded member is a threaded end of the bolt shaft.
14. The roof bolt of claim 13 wherein the cover includes a plastic tube extending over at least a portion of the threaded end.
15. The roof bolt of claim 1 wherein the cover includes a plastic tube extending over at least some of the threads.
16. A roof bolt comprising:
a bolt shaft;
threads affixed to the bolt shaft; and, a cover having threads threadably engaging the threads affixed to the bolt shaft, wherein the cover encloses the threads affixed to the bolt shaft and the threads of the cover so as to protect both the threads affixed to the bolt shaft and the threads of the cover.
a bolt shaft;
threads affixed to the bolt shaft; and, a cover having threads threadably engaging the threads affixed to the bolt shaft, wherein the cover encloses the threads affixed to the bolt shaft and the threads of the cover so as to protect both the threads affixed to the bolt shaft and the threads of the cover.
17. The roof bolt of claim 16 further comprising a release mechanism permitting the cover and the bolt shaft to be turned in unison below a given torque and permitting the cover to be turned with respect to the bolt shaft above the given torque.
18. The roof bolt of claim 17 wherein the release mechanism is a friction reducing washer.
19. The roof bolt of claim 16 wherein the cover has an open end, and wherein the open end is enclosed so as to protect both the threads affixed to the bolt shaft and the threads of the cover.
20. The roof bolt of claim 19 further comprising a release mechanism, wherein the release mechanism permits the cover and the bolt shaft to be turned in unison below a given torque and permits the cover to be turned with respect to the bolt shaft above the given torque.
21. The roof bolt of claim 20 wherein the release mechanism is a friction reducing washer.
22. The roof bolt of claim 16 wherein the cover has first and second open ends, and wherein the first and second open ends are enclosed so as to form a casing that environmentally protects both the threads affixed to the bolt shaft and the threads of the cover.
23. The roof bolt of claim 22 further comprising a release mechanism, wherein the release mechanism permits the cover and the bolt shaft to be turned in unison below a given torque and permits the cover to be turned with respect to the bolt shaft above the given torque.
24. The roof bolt of claim 23 wherein the release mechanism is a friction reducing washer.
25. The roof bolt of claim 16 wherein the threads comprise an externally threaded member affixed to the bolt shaft.
26. The roof bolt of claim 25 wherein the externally threaded member comprises an anchor head, wherein the bolt shaft is a twisted strand bolt shaft, and wherein the anchor head is affixed to the twisted strand bolt shaft.
27. The roof bolt of claim 25 wherein the externally threaded member comprises an insert, wherein the bolt shaft is threadbar, and wherein the insert is affixed to the threadbar.
28. The roof bolt of claim 25 wherein the externally threaded member is a threaded end of the bolt shaft.
29. The roof bolt of claim 28 wherein the cover includes a plastic tube extending over at least a portion of the threaded end.
30. The roof bolt of claim 16 wherein the cover includes a plastic tube extending over at least some of the threads affixed to the bolt shaft.
31. A roof bolt comprising:
a bolt shaft;
external threads affixed to the bolt shaft; and, a cover having internal threads threadably engaging the external threads, wherein the cover encloses the external threads and the internal threads so as to protect the external and internal threads, and wherein the cover has a drive portion arranged to accept a drive tool.
a bolt shaft;
external threads affixed to the bolt shaft; and, a cover having internal threads threadably engaging the external threads, wherein the cover encloses the external threads and the internal threads so as to protect the external and internal threads, and wherein the cover has a drive portion arranged to accept a drive tool.
32. The roof bolt of claim 31 further comprising a release mechanism permitting the cover and the bolt shaft to be turned in unison below a given. torque and permitting the cover to be turned with respect to the bolt shaft above the given torque.
33. The roof bolt of claim 32 wherein the release mechanism is a friction reducing washer.
34. The roof bolt of claim 31 wherein the cover has an open end, and wherein the cover is enclosed at the open end so as to protect the external and internal threads.
35. The roof bolt of claim 34 further comprising a release mechanism, wherein the release mechanism permits the cover and the bolt shaft to be turned in unison below a given torque and permitting the cover to be turned with respect to the bolt shaft above the given torque.
36. The roof bolt of claim 35 wherein the release mechanism is a friction reducing washer.
37. The roof bolt of claim 31 wherein the cover has first and second open ends, and wherein the cover is enclosed at both of the first and second ends so as to form a casing that environmentally protects the external and internal threads.
38 The roof bolt of claim 37 further comprising a release mechanism, wherein the release mechanism permits the cover and the bolt shaft to be turned in unison below a given torque and permits the cover to be turned with respect to the bolt shaft above the given torque.
39. The roof bolt of claim 38 wherein the release mechanism is a friction reducing washer.
40. The roof bolt of claim 31 wherein the external threads comprise an externally threaded member affixed to the bolt shaft.
41. The roof bolt of claim 40 wherein the externally threaded member comprises an anchor head, wherein the bolt shaft is a twisted strand bolt shaft, and wherein the anchor head is affixed to the twisted strand bolt shaft.
42. The roof bolt of claim 40 wherein the externally threaded member comprises an insert, wherein the bolt shaft is threadbar, and wherein the insert is affixed to the threadbar.
43. The roof bolt of claim 40 wherein the externally threaded member is a threaded end of the bolt shaft.
44. The roof bolt of claim 43 wherein the cover includes a plastic tube extending over at least a portion of the threaded end.
45. The roof bolt of claim 31 wherein the cover includes a plastic tube extending over at least some of the external threads.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US62565800A | 2000-07-26 | 2000-07-26 | |
| US09/625,658 | 2000-07-26 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2353441A1 true CA2353441A1 (en) | 2002-01-26 |
Family
ID=24507029
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2353441 Abandoned CA2353441A1 (en) | 2000-07-26 | 2001-07-24 | Torque-tension anchor fitting |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2353441A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN108104857A (en) * | 2018-01-31 | 2018-06-01 | 南京品臻精密模具有限公司 | Anchor pole head protection cover |
-
2001
- 2001-07-24 CA CA 2353441 patent/CA2353441A1/en not_active Abandoned
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN108104857A (en) * | 2018-01-31 | 2018-06-01 | 南京品臻精密模具有限公司 | Anchor pole head protection cover |
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