Patent Application
20140308081
1. Field of the Disclosure
This disclosure relates to a tensionable elongated bolt disposed with a sleeve. This disclosure also relates to a method of reducing frictional resistance between a tensionable elongated bolt and a hardened resin nut, thus improving the ability to tension the elongated bolt in a rock formation or structural body.
2. Description of Related Art
Reinforcing or stabilizing bolts are employed in various fields of engineering, for example, as strengthening or reinforcing members in rock formations such as vertical walls, or slopes and as a means to support the “roof” or “top” in underground mining operations and civil tunneling operations. One type of reinforcing or stabilizing bolt can be used in engineered structural bodies such as concrete columns or decks. Another type of reinforcing or stabilizing bolt can be used to secure objects or equipment to the ceiling, wall or floor in an engineered structure or rock formation.
The reinforcing or stabilizing bolts can be inserted into drill holes in the rock formation or structural body, and often are fixed or anchored, at their inner end or over substantially their entire length, by means of a reactive grouting composition that hardens around the reinforcing or stabilizing bolt. When used in a mine roof, reinforcing or stabilizing bolts grouted in this manner help significantly to prevent mine roof collapse. When used in structural bodies, the reinforcing or stabilizing bolt can increase stabilization of the structural body.
A tensioned reinforcing or stabilizing bolt is desirable for applications such as mine support. Tensioning of the reinforcing or stabilizing bolt induces compression in the mine roof, rock formation or structural body, and this compression can increase the stability of the mine roof, rock formation or structural body.
There are many ways to induce tension in a reinforcing or stabilizing bolt. See
When torque is applied to the forged geometric shape 18 on the outer end of the reinforcing or stabilizing bolt 10, the mechanical anchoring device 12 expands and grips the wall of the drilled hole, providing an anchor point. As more torque is applied, the reinforcing or stabilizing bolt 10 is shortened between (i) the fixed end created by the bearing plate 16 and forged geometric shape 18, and (ii) the fixed end provided by the mechanical anchoring device 12. As more torque is applied, tension is induced in the reinforcing or stabilizing bolt 10 and subsequent compression is induced in the mine roof or structural body.
Another way to induce tension in a reinforcing or stabilizing bolt is to introduce a reactive grouting composition 22 into a drilled hole in a mine roof or structural body, and then fix the inner end of the reinforcing or stabilizing bolt 20 in the reactive grouting composition 22 while the reactive grouting composition 22 is in a pliable or liquid state. See
Yet another way to induce tension in a reinforcing or stabilizing bolt is described in U.S. Pat. No. 7,481,603. See
The reactive grouting composition is allowed to harden, and then torque is applied to the forged geometric shape 36 of the reinforcing or stabilizing bolt 30 causing the reinforcing or stabilizing bolt 30 to “wind” or “screw” itself into the reactive grouting composition 32. This action shortens the reinforcing or stabilizing bolt 30 between (i) the fixed end created by the forged head 36 and bearing plate 34, and (ii) the fixed end formed by the interface between the hardened reactive grouting composition 32 and the thread 38. As more torque is applied, tension is induced in the tensionable elongated bolt 30 and subsequent compression is induced in the mine roof or structural body.
The reactive grouting composition can contain a polyester resin and catalyst. Such a reactive grouting composition can be placed in a two compartment tubular shell, e.g., a resin cartridge. An example of such reactive grouting compositions is described, for example, in U.S. Pat. No. 4,280,943. Reactive grouting compositions can also be composed of, but not limited to, acrylic resins, silicate resins, methylacrylate resins and polyurethane resins. Reactive grouting compositions can also be composed of cement, water and inert fillers.
A current usage of the type of tensionable bolt shown in
The frictional drag between the surface of the thread on the tensionable bolt and the surface of the reactive grouting composition can be substantial. The frictional drag can limit the amount of tension that can be induced in a reinforcing or stabilizing bolt.
There is a need to reduce the frictional drag between the threads of a tensionable bolt and the surface of the reactive grouting composition. The bolt should be easily tensionable to compress and provide secure and reliable support for the adjacent strata once installed.
The present disclosure provides many advantages, which shall become apparent as described below.
This disclosure relates in part to an anchorable mine support for anchoring in a borehole with resin or grout. The anchorable mine support comprises a tensionable elongate metal member and a sleeve disposed on at least a portion of the tensionable elongate metal member. The sleeve has a thickness of less than about 1 mm. Frictional resistance between the tensionable elongate metal member, disposed with the sleeve, and the hardened resin or grout is reduced as compared to frictional resistance between a tensionable elongate metal member, not disposed with a sleeve, and a hardened resin or grout.
This disclosure also relates in part to an apparatus for installation in a borehole formed in a face of a mine passage. The apparatus comprises a tensionable elongated bolt including a proximal end having a fixed head, a distal end without an attachment, and an externally threaded portion for positioning in the borehole; and a stationary, hardened resin nut formed in a portion of the borehole. The resin nut includes an internal thread extending continuously along the entire length of the resin nut, and the continuous thread surrounds at least part of the threaded portion of the bolt. A sleeve is disposed on at least part of the threaded portion of the tensionable elongated bolt surrounded by the resin nut continuous thread, The sleeve has a thickness of less than about 1 mm. Frictional resistance between the tensionable elongated bolt, disposed with the sleeve, and the hardened resin nut is reduced as compared to frictional resistance between a tensionable elongated bolt, not disposed with a sleeve, and a hardened resin nut.
This disclosure further relates in part to a method of reducing frictional resistance between a tensionable elongated bolt and a hardened resin nut in a borehole formed in a face of a mine passage. The method comprises providing a tensionable elongated bolt including a proximal end having a fixed head, a distal end without an attachment, and an externally threaded portion for positioning in the borehole; wherein a sleeve is disposed on at least part of the threaded portion of the bolt surrounded by the resin nut continuous thread; wherein the sleeve has a thickness of less than about 1 mm; providing a stationary, hardened resin nut formed in a portion of the borehole, the resin nut including an internal thread extending continuously along the entire length of the resin nut, the continuous thread surrounding at least part of the threaded portion of the bolt; and rotating the threaded portion of the bolt disposed with the sleeve relative to the resin nut to thread the threaded portion of the bolt disposed with the sleeve along the continuous internal thread of the resin nut. Frictional resistance between the tensionable elongated bolt, disposed with the sleeve, and the hardened resin nut is reduced as compared to frictional resistance between a tensionable elongated bolt, not disposed with a sleeve, and a hardened resin nut.
This disclosure yet further relates in part to an apparatus for installation in a borehole having a proximal opening and a distal end formed in a face of a mine passage. The apparatus comprises a tensionable elongated bolt including an externally threaded portion for positioning in the borehole; wherein a sleeve is disposed on at least part of the threaded portion of the bolt, and wherein the sleeve has a thickness of less than about 1 mm; a stationary, hardened resin nut having an internal thread extending continuously along the entire length of the resin nut for receiving at least part of the threaded portion of the bolt disposed with the sleeve; and a drill head for rotating the bolt relative to the hardened resin nut. Frictional resistance between the tensionable elongated bolt, disposed with the sleeve, and the hardened resin nut is reduced as compared to frictional resistance between a tensionable elongated bolt, not disposed with a sleeve, and a hardened resin nut.
This disclosure also relates in part to a method of supporting a face of a mine passage including a borehole. The method comprises inserting resin and a tensionable bolt including an externally threaded portion in the borehole, the tensionable bolt having a distal end spaced from an upper, distal end of the borehole and a proximal end adjacent an open, proximal end of the borehole; wherein a sleeve is disposed on at least part of the threaded portion of the tensionable bolt, and wherein the sleeve has a thickness of less than about 1 mm; forming a stationary, hardened resin nut having an internal thread extending continuously along the length of the resin nut along the threaded portion of the bolt disposed with the sleeve; and rotating the threaded portion of the tensionable bolt disposed with the sleeve relative to the resin nut to thread the threaded portion of the bolt disposed with the sleeve along the continuous internal thread of the resin nut. Frictional resistance between the tensionable elongated bolt, disposed with the sleeve, and the hardened resin nut is reduced as compared to frictional resistance between a tensionable elongated bolt, not disposed with a sleeve, and a hardened resin nut.
This disclosure further relates in part to an apparatus for installation in a borehole formed in a face of a mine passage. The apparatus comprises a tensionable elongated bolt including an externally threaded portion for positioning in the borehole; wherein a sleeve is disposed on at least part of the externally threaded portion of the tensionable elongated bolt, and wherein the sleeve has a thickness of less than about 1 mm; and a stationary, hardened resin nut formed in a portion of the borehole. The resin nut includes an internal thread extending continuously along a length of the resin nut. The length of the resin nut surrounds at least a first part of the externally threaded portion of the tensionable elongated bolt disposed with the sleeve while exposing a second part of the externally threaded portion of the tensionable elongated bolt disposed with the sleeve. Frictional resistance between the tensionable elongated bolt, disposed with the sleeve, and the hardened resin nut is reduced as compared to frictional resistance between a tensionable elongated bolt, not disposed with a sleeve, and a hardened resin nut.
This disclosure relates in part to an apparatus for installation in a borehole formed in a face of a mine passage. The apparatus comprises an elongated bolt including an elongated shaft portion for positioning in the borehole. A sleeve is disposed on at least part of the elongated shaft portion of the bolt. The sleeve has a thickness of less than about 1 mm. A stationary, hardened resin nut is formed in a portion of the borehole for surrounding at least part of the elongated shaft portion of the bolt disposed with the sleeve. Rotation of the elongated shaft portion within the resin nut thus serves to move the bolt within the borehole, such as during tensioning.
This disclosure also relates in part to an apparatus for installation in a borehole formed in a face of a mine passage. The apparatus comprises an elongated bolt including a portion, such as for example a threaded portion, for positioning in the borehole. A sleeve is disposed on at least part of the portion of the bolt. The sleeve has a thickness of less than about 1 mm. A stationary, hardened resin nut is also provided for receiving a portion of the bolt disposed with the sleeve. The apparatus further includes a drill head for rotating the bolt relative to the hardened resin nut.
In accordance with the disclosure, an improvement is provided for use in a borehole formed in a face of a mine passage for receiving a bolt having an elongated shaft for extending into the borehole. The improvement comprises a resin nut formed in a portion of the borehole and having an internal thread surrounding only a portion of the shaft disposed with a sleeve. The shaft of the bolt is threaded and disposed with the sleeve, whereby rotating the threaded shaft relative to the internal thread serves to tension the bolt, and the sleeve facilitates tensioning of the bolt, i.e., frictional resistance between the tensionable elongated shaft, disposed with the sleeve, and the hardened resin nut is reduced as compared to frictional resistance between a tensionable elongated shaft, not disposed with a sleeve, and a hardened resin nut.
This disclosure further relates in part to a roof bolt for insertion in a borehole formed in a face of a mine passage. The bolt comprises a shaft having a threaded portion at least partially having a sleeve disposed thereon. Preferably, the sleeve is at a distal end of the shaft having a point for insertion in the borehole. The sleeve has a thickness of less than about 1 mm.
This disclosure yet further relates in part to a method of tensioning a bolt including a threaded shaft portion in a borehole formed in a face of a mine passage. The method comprises forming a stationary, hardened resin nut adjacent to at least the threaded shaft portion of the bolt disposed with a sleeve. The method further comprises rotating the threaded shaft portion disposed with the sleeve relative to the hardened resin nut. The sleeve has a thickness of less than about 1 mm.
This disclosure also relates in part to a method of installing an elongated bolt having a head end and a threaded portion disposed with a sleeve in a face of a mine passage having a borehole. The method comprises inserting the bolt at least partially within the borehole with the head end spaced from the opening. The bolt, at least a portion of the bolt disposed with the sleeve, is rotated in a first direction and at least partially within an uncured resin within the borehole, and the resin is allowed to substantially cure and form a nut surrounding the sleeve portion of the bolt. The bolt is rotated in a second direction opposite the first direction such that the bolt moves through the resin nut with the head end moving closer to the opening of the borehole. Preferably, the head end of the bolt is initially spaced from the open end of the borehole, and the step of rotating the bolt in the second direction advances the head end of the bolt toward the open end of the borehole.
The sleeved elongated bolt of this disclosure reduces the frictional drag of the bolting system. This reduced frictional drag improves the ability of the tensionable elongated bolt to achieve a highly tensioned state. The increased tension improves the ability of the bolt to provide compression and stabilization of a mine roof or structural body.
The present disclosure describes a way to reduce the frictional drag between the threads of a tensionable elongated bolt and the threads created in a hardened reactive grouting composition. The reduced frictional drag improves the ability of the threaded bolt to be tensioned. The increased tension improves the ability of the bolt to provide compression and stabilization of a mine roof or structural body.
The tensionable elongated bolts useful in this disclosure include, for example, conventional bolts used in mining operations that are made of steel, rebar, and the like. A variety of bolt lengths may be accommodated in accordance with the present disclosure, including bolts of about 36 inches, about 42 inches, and about 48 inches in length. Other bolt lengths as known in the art also may be accommodated.
The bolt may include a head end and a tail end as well. The tail end for advancing into the borehole may include a taper or point. Preferably, the construction of the bolt is such that it is formed of a single piece of material. A flange may also be provided adjacent the head end, with one side for engaging a plate or like structure adjacent the mine face and the opposite side providing a bearing surface for a device or means for rotating the bolt.
In an embodiment, the elongated shaft portion comprises a generally circular cross section, and may include approximately 4-5 threads for about every inch in the longitudinal direction. To facilitate rotation within the resin nut, at least part of the elongated portion includes a sleeve having a thickness of less than about 1 mm. Preferably, a colored agent is also applied along at least part of the elongated shaft portion to allow for identification of the bolt for use with the resin nut as described herein.
The elongated mine bolts disposed with a sleeve of the present disclosure may be provided with indicia. The indicia may be molded onto the mine bolts at the time of molding or alternatively may be stamped onto mine bolts such as with light heat subsequent to molding, or alternatively the indicia may be scored onto the mine bolts. Suitable indicia include product name or designation, logos or names designating the manufacturer or purchaser of the product, manufacturing information, governmental regulation compliance information, or patent marking data. Indicia that includes customer name may be desirable for marketing, and in general the indicia may improve workflow at the manufacturing location, shipping, and at the end-user site. Furthermore, indicia may be provided to permit users to easily determine the length of the bolt or the end use intended for the bolt (e.g., installation in a particular region of a mine). The sleeves on bolts additionally may be used to color code the bolts based on such factors as bolt length, bolt diameter, or bolt strength and thus the indicia may be in the form of color.
In order to reduce the frictional drag between the threads of a tensionable elongated bolt and the threads created in a hardened reactive grouting composition, this disclosure provides a tensionable elongated bolt 40 having a thin sleeve 42 that internally is molded to the threads 46 of the bolt 40. See
Preferably, a plastic sleeve can take the shape of flexible or rigid tubing that shrinks or is reduced in diameter when exposed to heat, thereby conforming and molding to the threads 46 of the bolt 40. There are several plastics that can achieve this goal including, but not limited to, polyolefin, polyvinyl chloride (PVC), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), fluoro elastomers, fluorinated ethylene propylene (FEP) and fluorinated elastomers.
Other illustrative sleeve 42 materials include, for example, poly(ethylene terephthalate), polymethylmethacrylate, polycarbonate, polyethylene, polypropylene, acrylonitrile butadiene styrene, nylon, polycarbonate, aramid, and mixtures thereof.
The sleeve 42 has a thickness of less than about 1 mm, a thickness of less than about 0.75 mm or a thickness of less than about 0.5 mm. In some embodiments, the sleeve 42 may have a thickness of less than about 0.9 mm, or instead the sleeve 42 may have a thickness of at least 0.2 mm and no more than 0.6 mm, or instead the sleeve 42 may have a thickness of at least 0.1 mm and no more than 0.4 mm. The sleeve 42 may cover only a portion of the surface of the bolt 40 or may cover the entire surface of the bolt 40. Preferably, the sleeve 42 covers the portion of the bolt 40 that is in contact with the reactive grouting composition 44.
The sleeve 42, e.g., plastic sleeve, can be created by an injection molding process (i) on the bolt 40 or (ii) off the bolt 40 and then threaded onto the bolt 40. Such a sleeve 42 is preferably thin and is designed solely to create a low friction interface between the threaded profile of the tensionable elongated bolt 40 and the reactive grouting composition 44. The outside surface of the sleeve 42 preferably maintains the contours of the threads 46 but can also assume any irregular surface contour suitable for anchoring in a reactive grouting composition 44.
A sleeve 42 can be composed of a plastic or paint that is sprayed onto the threads 46 of the bolt 40 and allowed to harden. This method would be designed so that a bond is not formed between the plastic or paint sleeve 42 and the threads 46 on the bolt 40. The outside surface of the sleeve 42 preferably maintains the contours of the thread 46 but can also assume any irregular surface contour suitable for anchoring in a reactive grouting composition 44.
A sleeve 42, e.g., metal sleeve, can take the shape of a metal foil that can be molded or cold worked to match the threads 46 of the elongated bolt 40. The outside surface of the sleeve 42 preferably maintains the contours of the threads 46 but can also assume any irregular surface contour suitable for anchoring in a reactive grouting composition 44.
Referring to
The reactive grouting composition can be inserted into the borehole, for example, as a two compartment tubular shell, generally described as a resin cartridge. An illustrative resin cartridge 50 is shown in
Rotation of the bolt 40 may cause frictional heating of the reactive grouting composition 44, and the frictional heating may be sufficient to substantially accelerate curing thereof. Also, when the bolt 40 is rotated, the grout 44 can be simultaneously mixed and distributed toward the closed end of the borehole.
The maximum width of the bolt may be at least the maximum width of the resin cartridge. The resin cartridge may have at least two compartments and the maximum width of the bolt may be at least the width of two of the compartments. The grout may contact a portion of the inner wall of the borehole.
The resin cartridge may be shredded. In one embodiment of the method, the resin cartridge is shredded so that the shredded portions of the vessel are disposed remote from the inner wall of the borehole. In another embodiment of the method, the resin cartridge is substantially shredded so that the shredded portions of the vessel are distributed throughout the resin. Additionally, the resin cartridge may be substantially shredded so that the shredded portions of the resin cartridge are substantially uniformly distributed throughout the resin. And, the resin cartridge may be substantially shredded so that the shredded resin cartridge does not substantially interfere with the anchorage strength of the bolt in the borehole.
The resin cartridge may have two compartments, with a first of the compartments containing unsaturated polyester resin and cross-linking agent and with a second of the compartments contains benzoyl peroxide catalyst. At least one of the two compartments may further contain limestone.
In one embodiment, the grout cures in between 10 seconds and 30 seconds. In another embodiment, the grout cures in between 15 seconds and 1 minute. In yet another embodiment, the grout cures in no more than 10 minutes.
In an embodiment, the forming of the hardened resin nut comprises: (i) providing uncured resin within the borehole adjacent to the threaded shaft portion of the bolt disposed with a sleeve; (ii) rotating the bolt in a first direction to substantially maintain the resin adjacent the threaded shaft portion disposed with the sleeve; and (iii) allowing the resin to substantially cure and form the hardened resin nut. Likewise, the step of rotating the bolt preferably comprises rotating the threaded shaft portion in a second direction opposite the first direction upon the substantial curing of the resin.
Illustrative methods for installing an elongated spiral bolt into a bore hole with resin nut are disclosed, for example, in U.S. Pat. Nos. 7,481,603 and 7,758,284, the disclosures of which are incorporated herein by reference in their entirety.
In some embodiments of the present disclosure, reflective elements can be interspersed in or otherwise added to the sleeve on the elongated bolt to enhance visibility of the finished bolt, particularly in the low-light areas within mines. For example, glass beads (also referred to as microspheres or microsphere lenses) that may be light transmissible may be added to the sleeve. The glass microspheres may be hollow. Also, a portion such as half of each microsphere may be provided with a mirror coating, so that when light hits a microsphere, it is refracted through the surface and transmitted back toward the light source.
The present disclosure further contemplates the use of pigments, extenders, diluents, plasticizers, leveling agents, and surfactants with the sleeves disposed on the mine bolts of the present disclosure. Optionally, the sleeves disposed on the mine bolts of the present disclosure may include a luminescent component.
The thin sleeve preferably forms to the contours of the bolt such that the outer surface of the sleeve maintains the threaded contours of the bolt. A preferred method to create this sleeve is to apply a length of thin flexible or rigid tubing over the threads.
When heat is applied, the tubing shrinks down and assumes the contours of the threads. Since the tubing is very thin, the outer surface of the heat shrinkable tubing also maintains the profile of the thread.
Conventional methods may be used to manufacture the tensionable elongated bolts disposed with a sleeve of this disclosure. For example, the sleeve can be coated onto the elongated bolt with a flowable polymer so that the coating has a maximum thickness of less than about 1 mm; allowing the polymer to solidify on the elongated bolt; and optionally texturing the polymer. The sleeve or coating step may include dip coating, injection molding and/or hot forging. Illustrative methods are described, for example, in U.S. Pat. No. 7,736,738, the disclosure of which is incorporated herein by reference in its entirety.
Referring to
The shaft 76 of the bolt 70 is generally round in cross-section and threaded along its length. The shaft 76 of the bolt 70 can also be square or round in cross-section and twisted along its length to form a spiral or helix.
As an example, the shaft 76 of the bolt 70 is shown as being generally round in cross-section, and includes a threaded portion formed by threads. Each inch of the shaft 76 preferably includes between about 4 to 5 complete (e.g., 360°) threads. Most preferably, each complete thread occupies about 0.22 inches of distance in the longitudinal direction, or length, which corresponds to about 4.5 complete twists per linear inch. Of course, a corresponding thread is formed in the resin nut once it is formed in the borehole and the threaded bolt 70 installed in the manner described in the foregoing passage.
While it is easier in terms of manufacturing to provide consistent threading continuously along the entire length of the shaft 76 (such as by cutting threads in round bar stock), it will be understood upon reviewing the description that follows that the threads may be provided along only a portion of the shaft 76. Preferably, in such case, the threads are along the tail end 78, or otherwise away from the head end 72.
Reference is now made to
Using a lift boom associated with a bolting machine or like structure, the bolt 70 is advanced into the borehole H such that the head end 72 remains spaced from the adjacent face of the roof a distance equal to or slightly less than the excess depth of the borehole H (e.g., about two inches). As shown in phantom in
Once the bolt 70 is partially inserted, uncured resin (also sometimes referred to as “grout”) is provided adjacent at least a portion of the elongated shaft 76 in the associated annulus (which is shown in
In accordance with another aspect of the disclosure, the bolt 70 with the threaded shaft 76 at least partially surrounded by uncured resin is rotated to effect the desired mixing and/or hardening, such as by using any conventional type of bolting machine. In the illustrated embodiment in which the thread is left-handed in nature, the rotation is in the opposite, or right-handed, direction (see action arrow R in
As should be appreciated, this rotation in combination with the elongated shaft 76 serves to create a “pumping” action that substantially holds the uncured resin in place, and may possibly advance or “push” this resin deeper within the borehole H. In other words, the elongated shaft 76 of the bolt 70 may essentially function as an auger or screw with flights that maintain the resin at a particular location within the upper end of the borehole H. In any case, the rotation of the threaded shaft 76 preferably is such that it prevents the uncured resin from advancing toward the opening O of the borehole H to any significant degree. As a result of this pumping action, once the resin sets or cures (normally, after a period of rest post-mixing), it surrounds only a portion of the threaded shaft 76 within the borehole H. The amount of resin supplied will of course depend on the relative sizes of the elongated shaft 76 and the borehole H, but is preferably sufficient to cover about 12-18 inches of the shaft 76 adjacent the tail end 78 or otherwise away from the head end 72 (which, of course, still remains spaced from the opening O of the borehole H).
When torque is applied to the forged head 72 of the tensionable elongated bolt 70, the sleeve 74 remains embedded in the reactive grouting composition 82 and the bolt 70 turns in the sleeve 74. The sleeved elongated bolt 70 of this disclosure reduces the frictional drag of the bolting system. This reduced frictional drag improves the ability of the tensionable elongated bolt 70 to achieve a highly tensioned state. The increased tension improves the ability of the bolt 70 to provide compression and stabilization of a mine roof or structural body.
Once the resin sets or cures (which normally takes only seconds after mixing), a stationary, hardened resin “nut” is thus formed around at least a portion of the elongated shaft 76 in the borehole H. As should be appreciated, this resin nut has an internal thread matching the thread of the adjacent shaft 76 and occupied by it. In the case of the left-handed thread (see
This rotation may be completed until any associated engagement hardware, such as a plate 80, is brought into secure engagement with the face F (which normally will take less than one complete turn). The appropriate amount of torque is then applied to ensure that the bolt 70 is fully tensioned and the strata compressed or anchored in the desired manner. As noted above, the depth of the borehole H is made at least slightly greater than the overall length of the bolt 70 such that the tail end 78 can freely advance and does not “bottom out” during the final advance caused by tensioning.
Numerous advantages may thus arise from the use of the above-described technique. First of all, the bolt 70 may be made of only one piece of material, and need not include any expansion shells or external nuts in order to be effective. Accordingly, no parts require assembly “on-site.” This not only substantially reduces the manufacturing cost, but also facilitates ease of installation and results in a stronger bolt.
Additionally, only partial grouting of the borehole H is required for effectively practicing the present disclosure. Thus, substantially less grout is required, as compared to arrangements in which the borehole H is fully grouted. A concomitant savings in material cost invariably results (possibly as much as 75%), as well as a reduction in the cost of transporting the grout into the mine and maintaining it in a “ready for use” state.
The completed installation of the bolt 70 also advantageously results in the head end 72 being positioned extremely close to face F of the mine roof (see
Finally, aside from being one piece, the bolt 70 can be manufactured in a relatively easy and inexpensive manner. Square or round bar stock of any suitable width dimension (e.g., ½″, ⅝″, or ¾″ for a 1″ borehole) can simply be worked to the desired pitch (whether considered twists per linear unit, or thread-to-thread spacing) to form the shaft 76. The head end 72a is typically forged. Conveniently, the thread can also be formed on a relatively long piece of stock, which can then be cut into lengths corresponding to the shaft 76 of the bolt 70.
During manufacturing, the working applied to the bar (which is typically made of steel or rebar) may result in the elimination of the exterior surface oxide layer, or “scale,” created during the hot roll process. The absence of the scale allows faster oxidation of the bar, especially when the bolt 70 is stored outdoors and exposed to the elements during the period between manufacturing and ultimate use in the mine. Any deterioration of the surface may inhibit the ability of the shaft 76 to turn freely within the resin nut during installation.
To ameliorate any such problem, it is possible to coat at least part of the elongated shaft 76 (such as the uppermost portion) after manufacture with either a lubricity agent or a rust-inhibiting agent, or both. The partial or full application of such agent(s), together with the sleeve 74, can ease the installation by allowing the elongated shaft 76 to rotate more freely relative to the resin nut during tensioning. Providing any coating agent with a coloring (e.g., a yellow pigment) is also contemplated. As a result, the installer may not only ensure that the coating remains present on an appropriate portion of the shaft 76, but also can readily differentiate the elongated bolts 70 for use in the present method from others.
During installation, it may also sometimes result that the resin cures not only along a portion of the elongated shaft 76, but also within the portion of the borehole H into which the bolt 70 must advance during tensioning. Although this does not preclude installation, it may be helpful to make the tail end of the bolt 70 with a point or taper, as shown. This will help it advance within the resin nut, if such is necessary.
Although the pitch of the threads may be varied, it is also desirable to ensure that the threaded bolts 70 for use in a common installation are consistent. This keeps the installation torque required consistent. Likewise, the threaded shaft 76 should also be consistent to facilitate its movement through the resin nut once formed. The pitch of the thread is also preferably such that there is noticeable movement of the head end 72 toward the opening O of the borehole H during installation, thus giving the installer a visual cue that the process is proceeding as expected.
The use of conventional types of washers, such as those made of, or coated, with TEFLON or other anti-friction types, is also possible between the head end 72 (or flange) and any associated structure (such as plate P). However, it is believed that the use of such anti-friction washers is less important with this type of arrangement than with conventionally threaded bolts, since conventionally threaded bolts require many revolutions for installation, resulting in greater friction and heat, and less effective tension/torque ratios.
The foregoing description of embodiments of the present disclosure has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise form disclosed. Obvious modifications or variations are possible in light of the above teachings. The present embodiments were chosen and described to provide the best illustration of the principles of the disclosure and its practical application to thereby enable one of ordinary skill in the art to utilize the disclosure in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the disclosure.
Several tensionable threaded bolts were formed from a known “mill grade” steel rod. The tensionable threaded bolt contained thread of conventional pitch and depth on one end.
On the other end, the steel rod was heated and a “head” was forged. The head is consistent with heads used on reinforcing or stabilizing bolts used in underground mining operations and takes the shape of a square, supported by a metal flange.
The threads of the tensionable elongated bolt were treated with various types of thin sleeves, no sleeve, or bonded paints of various composition. The threads were embedded in a reactive grouting composition composed of a polyester resin mastic and catalyst.
A reactive grouting composition was placed in a two compartment tubular shell, generally described as a resin cartridge. An illustrative resin cartridge is shown in
The tests were conducted in a test chamber that was sealed on the bottom and sides and was open on the top and assumed the shape of a drilled cylindrical hole. Installation and testing of each example proceeded as follows: (i) a resin cartridge was positioned in the bottom of the test chamber; (ii) a tensionable elongated bolt with a treatment on the threads was thrust into the test chamber and spun such that (iii) the resin cartridge was ruptured and the contents spilled into, and mixed in, the annular gap between the tensionable elongated bolt and the test chamber; and (iv) the resin was allowed to cure, and the cured resin molded to and assumed the shape of the threads.
After the resin cured, torque was applied to the forged head of the tensionable elongated bolt causing the bolt to rotate and “screw” into the reactive grouting composition (resin). The torque needed to induce rotation on the rod was noted and recorded.
While we have shown and described several embodiments in accordance with our disclosure, it is to be clearly understood that the same may be susceptible to numerous changes apparent to one skilled in the art. Therefore, we do not wish to be limited to the details shown and described but intend to show all changes and modifications that come within the scope of the appended claims.
This application claims the benefit of U.S. Provisional Application Ser. No. 61/811,561, filed on Apr. 12, 2013, which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61811561 | Apr 2013 | US |
