Abstract:
A mine roof bolt, preferably one inch or less in diameter, having an external coating configured with particles which mix resin as the mine roof bolt is rotated in a mine roof bore hole.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of earlier filed U.S. Provisional Patent Application Ser. No. 60/153,860, filed Sep. 14, 1999 entitled “Grit Surface Cable Products.” 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to mine roof cable bolts and, more particularly, to coated mine roof cable bolts that are configured to be resin grouted. 
     2. Brief Description of the Prior Art 
     A mine roof may be supported by a cable bolt positioned inside a bore hole in a mine roof and resin grouted into place. Examples of mine roof cable bolts are disclosed in U.S. Pat. No. 5,259,703 to Gillespie, U.S. Pat. Nos. 5,375,946 and 5,378,087 both to Locotos, and U.S. Pat. No. 6,074,134 to Stankus et al., herein incorporated by reference. 
     Cable bolts typically include a single or multi-strand cable segment, a drive head positioned on a first end of the cable segment. A plurality of mixing devices may be positioned along a longitudinal axis of the cable segment, and a stiffening sleeve may be positioned adjacent the first end of the cable segment. These prior art mine roof cable bolts may be tensionable and include one or more mixing devices thereon. 
     During installation of a cable bolt and mine roof plate system, the first end of a cable segment is generally positioned adjacent a mine roof plate, with the second end inserted into a bore hole created in the earth and rock adjacent a mine roof. Also inserted into the bore hole is a resin catalyst and an adhesive. The cable segment is rotated after insertion, causing the mixing devices to mix the resin catalyst and adhesive. The mixing devices also distribute the adhesive within the rock, in the cracks and crevices between individual strands of a multi-strand cable segment, and in voids between an outer surface of the cable segment and an inner wall of the bore hole. Once cured, the adhesive helps to anchor the cable segment to the earth and rock. Tensionable cable bolts are installed in a similar manner, except that an expansion assembly may also be included to further secure the cable bolt inside the bore hole and tension the bolt between the mine roof and the expansion assembly. 
     One universal drawback of the cable bolt and mine roof plate systems of the prior art is the trouble and expense associated with incorporating mixing devices, such as nut cages, buttons, or birdcages, into a cable segment. Another drawback is the stiffening sleeve positioned adjacent a first end of the cable segment. In theory, stiffening sleeves help protect the cable segment and prevent the cable bolt from kinking during insertion. However, stiffening sleeves do not prevent torsional deformation of the portion of the bolt not secured in the resin caused when torque is applied to the bolt drive head. When torque is applied during installation of the bolt to mix resin and/or engage a mechanical anchor, a second end of the cable segment decreases rotation as the mechanical anchor and resin restrain movement while the first end is unencumbered. This tends to cause twisting of the cable segment in the portion of the cable bolt between the mine roof and the resin. When installation is complete and torque from the bolt installation machine is removed, the twists in the non-resin grouted portion of the cable untwist which causes the tension applied to the bolt to be reduced. To counteract the twisting of the lower (ungrouted) portion of the cable, a plurality of sleeves or “buttons” are fixed to the cable lower portion. However, these additional components add to the cost of manufacturing a tensionable cable bolt. 
     Mixing devices and stiffening sleeves increase manufacturing costs, increase the risk of producing nonconforming goods, and do not prevent torsional deformation. Hence, a need remains for a mine roof cable bolt which resists torsional deformation during installation with subsequent loss of tension, while eliminating or minimizing the need for such extraneous mixing devices and/or stiffening sleeves. 
     SUMMARY OF THE INVENTION 
     To obviate the deficiencies of the prior art, one embodiment of the present invention generally includes a cable bolt having a coated cable segment. The cable segment generally includes a first end and a second end with a drive head positioned adjacent the first end of the cable segment. 
     In single cable segments, the coating is positioned adjacent an exterior surface of the cable segment coating all or only a portion of the exterior surface. In multi-strand cable segments, the coating may completely or partially coat an exterior surface of each strand. Positioned adjacent an exterior surface of the coating are particulates forming a textured surface on the exterior of the cable bolt. A tensioning device may also be positioned along a longitudinal axis of the cable segment. The coating serves three primary functions. First, the coating strengthens the cable segment eliminating the need for a stiffening sleeve in some applications. Second, the coating retards torsional deformation of the cable segment bearing the coating when torque is applied to the drive head. Third, the coating further provides an attachment medium for the particulates. The particulates increase the overall surface area of the cable segment providing more bonding area for the resin and providing agitation of the resin catalyst and adhesive during mixing. The particulates, therefore, reduce the need for mixing devices, such as bulbs and birdcages, in some applications. 
     It is therefore an object of the present invention to provide a cable bolt that resists torsional deformation, does not require a stiffening sleeve, and in some applications, traditional mixing devices. 
     These and other advantages of the present invention will be clarified in the Detailed Description of the Preferred Embodiments and the attached figures in which like reference numerals represent like elements throughout. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of a prior art cable bolt having a multi-strand cable, birdcages, and a stiffening sleeve inserted into a cross-sectional view of a bore hole; 
     FIG. 2 is a side view of one embodiment of the cable bolt of the present invention inserted into a cross-sectional view of a bore hole; 
     FIG. 3 is a side view of a second embodiment of the cable bolt of the present invention inserted into a cross-sectional view of a bore hole; 
     FIG. 4 is a side view of a third embodiment of the cable bolt of the present invention inserted into a cross-sectional view of a bore hole; 
     FIG. 5 is a side view of a fourth embodiment of the cable bolt of the present invention inserted into a cross-sectional view of a bore hole; and 
     FIG. 6 is a perspective view of a horizontally sectional multi-strand cable segment, as shown in FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiment of the cable bolt of the present invention is generally shown in FIG.  2 . For purposes of introduction, a prior art device shown in FIG. 1 will be discussed first. 
     FIG. 1 shows a typical prior art cable bolt C installed in a bore hole B. The cable bolt C generally includes a multi-strand M cable segment S, birdcages G formed in a second end E of cable segment S, a stiffening sleeve L positioned adjacent a first end F of the cable segment S, and a drive head H positioned adjacent the first end F of the cable segment S. The cable bolt C preferably is installed in a mine roof with a mine roof plate P positioned adjacent the drive head H and resin or adhesive A placed at the blind end of the bore hole B between an exterior surface ES of the cable bolt C and an interior surface IS of the bore hole B. Alternatively, the resin and adhesive A may fill all or nearly all of the bore hole B not occupied by the cable bolt C. 
     As shown in FIG. 2, the cable bolt  10  of the present invention includes a cable segment  14 , preferably, multi-strand cable  16  constructed from steel or other suitable material installed in a borehole  12  with a bearing plate  28 . The cable segment  14  has a drive head  26  with a conventional load bearing barrel and wedge assembly  52  positioned on a first end  24  of the cable segment  14  and is coated with a layer of a rigid or semi-rigid coating material  36 , such as plastic, epoxy, resin, or other suitable material. A suitable assembly of drive head  26  with barrel and wedge assembly  52  is disclosed in U.S. Pat. No. 5,829,922 to Calandra, Jr. et al., incorporated herein by reference. The entire length of cable segment  14  is preferably coated, as shown in FIG. 2, but partial coating is also envisioned. 
     As shown in detail in FIG. 6, coating material  36  preferably includes an epoxy material and a plurality of particulates  40 , such as grit, sand, rock, diamond dust, or other suitable material dispersed in the epoxy material either on the surface thereof or through the thickness of the coating material  36 . The individual particulates  40  should be large enough in diameter to give the exterior surface of the coating material  36  covering the cable segment  14  a textured appearance and feel, but not large enough to significantly alter the overall diameter of the cable segment  14 . The coating material  36  preferably is of the type disclosed in U.S. Pat. No. 5,208,777 to Proctor et al., incorporated herein by reference. 
     It should be apparent to those in the art that the coating material  36  and the particulates  40  need not be two distinct substances provided the coating material  36  forms a textured exterior surface and, preferably, makes the cable segment  14  more rigid. 
     The coating material  36  adds rigidity to the cable segment  14 , eliminating the need for a stiffening sleeve L, shown in FIG. 1, and reducing torsional rotation in tensionable cable bolts  10 ′ and  10 ″, shown in FIGS. 3 and 4. The coating material  36  also provides a surface of adhesion between resin in a bore hole  12  and the particulates  40 . The particulates  40  increase the total exterior surface area of the cable segment  14  which increases the resin catalyst and adhesive  30  bonding area. More importantly, the particulates  40  increase agitation of the resin catalyst and adhesive  30  when the cable segment  14  is rotated in the bore hole  12  during mixing of the resin catalyst and adhesive  30 . This agitation eliminates the need for adding birdcages or other traditional mixing devices to cable bolts  10  inserted into smaller bore holes  12 , such as those approximately one inch or smaller in diameter. 
     In a second embodiment, shown generally in FIGS. 3 and 4, the cable bolts  10 ′ and  10 ″ include the cable segment  14  with the coating material  36  and a mechanical anchor  44  threaded onto an externally threaded sleeve  46  surrounding the second end  20  of the cable segment  14  (FIG. 4) as disclosed in U.S. patent application Ser. No. 09/384,524, filed Aug. 27, 1999, entitled “Tensionable Cable Bolt,” which is a continuation-in-part of the application resulting in the &#39;134 patent, incorporated herein by reference. Alternatively, the mechanical anchor  44  and sleeve  46  may be located at a position intermediate the first end  24  and the second end  20  of the cable bolt  10 ″, also shown in FIG.  3 . 
     In a third embodiment, shown in FIG. 5, the cable bolt  10 ′″ includes at least one sleeve or “button”  18  surrounding the cable segment  14  at a position intermediate the first and second ends  24 ,  20  of the cable segment  14 . Preferably, a plurality of buttons  18  are included on cable bolt  10 ′″. The buttons  18  may include longitudinal flanges or wings  54  to increase the resin holding surface area thereof. The embodiment shown in FIG. 5 is used in larger bore holes  12 , such as those in the range of one and three-eighths inches diameter or larger. It is believed that in bore holes  12  of one inch in diameter, the cable bolts do not require any additional mixing device beyond the coating material  36 , as shown in FIG.  2 . 
     The installation process for the cable bolts  10 ,  10 ′,  10 ″, and  10 ′″ generally includes the steps of partially or completely coating a cable segment  14  with a textured surface, preferably, using a coating material  36  as described above; drilling a bore hole  12  in a mine roof; inserting resin in the form of two-part catalyst and hardenable component packages into the bore hole  12 ; inserting a second end  20  of the coated cable segment  14  into the bore hole  12  to rupture the catalyst and hardenable component packages; mixing the resin catalyst and adhesive  30  by rotating the coated cable segment  14  via mine roof bolt installation equipment attached to the drive head  26 ; and allowing the resin  30  to cure. For the cable bolts  10 ′ and  10 ″, rotation of the bolt also causes expansion of the mechanical anchor  44  which engages with and grips the interior surface  34  of the wall surrounding the bore hole  12 . Torsional deformation of the cable segment is significantly reduced and cable bolts  10 ′ and  10 ″ may be tensioned as described in the above-mentioned patents and patent applications. It has been found that the coating material  36  sufficiently stiffens the cable segment  14  which is below the resin  30  to prevent twisting of the cable segment  14  during installation and tension loss upon release of the bolts  10 ′ and  10 ″ from installation equipment. 
     It is believed that rotation of the cable segment  14  with the coating material  36  sufficiently mixes resin in a one-inch bore hole  12 . The particulates  40  embedded in the epoxy material of the coating material  36  provide enhanced mixing over uncoated cable. In addition, the increased surface area of the cable bolts  10 ,  10 ′,  10 ″, and  10 ′″ of the present invention over uncoated cable segments  14  creates higher holding strength with the resin. In pull tests, cable bolts according to the present invention resisted deflection when subjected to pull forces of between  20  and  29  tons. Hence, the present invention includes a cable bolt coated with a textured material without any alteration to the wrapped strands of the cable segment  14 , such as birdcages, nutcages, or bulbs and also includes a method of installing the inventive cable bolt in resin containing bore holes. For larger diameter bore holes (e.g., one and three-eighths inches), altered cable again is believed to be unnecessary to achieve sufficient resin and adhesive  30  mixing and bonding. However, in certain circumstances simple mixing devices, such as buttons, are required as shown in FIG.  5 . 
     The present invention eliminates the need for a stiffening sleeve L, traditional mixing devices, such as birdcages, or both from conventional mine roof cable bolts while still retarding torsional rotation (in tensionable cable bolts). The textured surface of the cable segment  14  serves to mix the resin  30 , provide increased bonding area on the cable segment  14 , and increase friction between the resin  30  and the cable bolts  10 ,  10 ′,  10 ″, and  10 ′″. Moreover, torsional rotation of cable segments  14  in tensionable cable bolts  10 ′ and  10 ″ is reduced within. 
     The invention has been described with reference to the preferred embodiments. Obvious modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations.