Abstract:
A rock bolt well adapted for use in mining is provided. The rock bolt includes an anchor tube that encloses an interior space, a fixing agent arranged inside the interior space for the substance-to-substance fixation of the anchor tube to stone, a mobile piston arranged inside the interior space for transporting the fixing agent out of the anchor tube when the anchor tube is arranged in a bore hole in the stone, a piston moving mechanism, an anchor nut, and an anchor plate supported by the anchor nut for support on the stone.

Description:
RELATED APPLICATIONS 
       [0001]    The present application claims priority to German Patent Application DE 10 2010 063 098.5, filed Dec. 15, 2010, and entitled “Gesteinsanker” (“Rock Bolt”), the entire content of which is incorporated herein by reference. 
       FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    [Not Applicable] 
       [MICROFICHE/COPYRIGHT REFERENCE] 
       [0003]    [Not Applicable] 
       BACKGROUND OF THE INVENTION 
       [0004]    The present invention relates to a rock bolt, for example, for mining applications, and a method for fixing a rock bolt in stone. 
         [0005]    In mining and tunnel construction rock bolts are used in order to prevent rock movements of adjacent stone, to slow such movements, or to secure larger split-offs of adjacent rock, and thus allow a safer operation. Here, two functional principles are known, which sometimes are combined. In mechanical systems the fastening of the anchor occurs by friction fitting, with mechanical stone and/or rock anchors generally also showing an expanding sleeve. In chemical rock bolts the anchor tubes are connected to a curing cement or resin as a fixation means in a substance-to-substance manner to the base and/or the adjacent stone. The rock bolts are installed here with or without any prestressing in the adjacent stone. Contrary to tunnel construction, rock bolts in mining, e.g., underground coal mining, serve only for a temporary securing of the stone, because generally the temporarily secured stone will be mined in a later processing step and thus the rock bolts are removed again from the stone. 
         [0006]    U.S. Pat. No. 4,601,614 shows a rock bolt for tunnel construction and mining. A two-component fixing agent in two cartridges is arranged inside an interior space enclosed by an anchor tube. The external end of the anchor tube comprises an opening to introduce water under high pressure into the interior space enclosed by the anchor tube. A piston is arranged articulate inside the interior space and by moving the piston the two-component fixing agent is transported and/or pressed through holes in the anchor tube into a space between the anchor tube and the stone. For this purpose, an opening is provided at the external end of the anchor tube, through which water can be introduced under high pressure into the interior space enclosed by the anchor tube and by this water the piston is pressurized, so that the piston is moved inwardly and thus the fixation means is expressed. It is therefore disadvantageously necessary to require a high pressure pump to create highly pressurized water to move the piston for a substance-to-substance fastening of the anchor tube with the fixing agent. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    An objective of aspects of the present invention therefore comprises providing a rock bolt and a method for fixing a rock bolt in stone, in which with little technical expense the fixing agent can be inserted into the space between the stone and the anchor tube and/or the rock bolt embodied as a gliding anchor requires only little space in the tunnel and/or work gallery produced underground. 
         [0008]    Such an objective may be attained in a chemical rock bolt, particularly for application in mining, comprising an anchor tube, which encloses an interior space, a fixing agent arranged inside the interior space for a substance-to-substance fixation of the anchor tube at the stone, a mobile piston arranged inside the interior space to transport the fixing agent out of the anchor tube when arranging the anchor tube in a bore hole in the stone, at least one means to move the piston, an anchor nut, and an anchor plate supported by the anchor nut to be placed upon the stone. The at least one means may be embodied as a spindle drive for moving the piston and/or the anchor nut and the anchor plate fastened at a rod arranged inside the anchor tube. The rod may be fastened at the anchor tube with a fastening device such that the fastening of the rod at the anchor tube is only released when a predetermined tensile force in the rod is exceeded, and thus the rod is partially mobile towards the outside such that the rock bolt represents a gliding anchor. The anchor nut and the anchor plate can be embodied as a single piece or as two separate components. 
         [0009]    In order to move the piston, i.e., to express the fixing agent out of the interior space into a space between the anchor tube and the stone, it is therefore no longer required to expensively provide a high-pressure pump in the tunnel or gallery in order to move the piston with high-pressurized water. The rock bolt comprises a spindle drive so that the piston can be moved by a mere application of a torque at the rock bolt, particularly at the outside. 
         [0010]    The rock bolt may also be further embodied as a gliding anchor. The gliding anchor shows a gliding function such that beginning at a predetermined tensile force compensated by the rock bolt, i.e., at the pressure acting upon the anchor plate which is caused by the stone, the rock bolt is extended in its length and thus a motion is permitted at the stone which reduces the tensile forces compensated at the rod (below the predetermined tensile force as a threshold, so that no more gliding occurs) and thus a better securing of the stone is ensured. Here, after the expression of the fixing agent from the interior space the rod is essentially arranged underneath the interior space, i.e., the rod projects only slightly beyond the exterior end of the anchor tube, so that the gliding anchor requires only little structural space outside the stone. In the gliding anchors known from prior art the gliding function at the anchor nut is implemented such that the anchor nut glides outwardly at a larger projection of the rod and/or the anchor tube. Thus, in the gliding anchors known from prior art a large amount of space is required prior to the gliding of the gliding anchor for the projection at the anchor tube and/or the rod for the nut. 
         [0011]    According to aspects of the present invention, if the tensile force to be compensated by the rod and/or the force at the rock bolt to be compensated by the rod at the fastening device falls below a predetermined tensile force the motion of the rod towards the outside is hindered again, relative to the anchor tube with the fastening device, so that greater forces can be compensated by the rock bolt. 
         [0012]    In an additional embodiment, the rod represents a threaded rod with an external thread and the fastening device is an annular part with an internal thread, e.g., a nut, and the annular part is fastened at the anchor tube and the internal thread of the annular part engages the external thread of the threaded rod. 
         [0013]    In an additional embodiment, the annular part is embodied in one piece at the anchor tube, particularly by an internal thread being embodied inside the anchor tube. The annular part can here represent a separate part fastened to the anchor tube or an annular part with an internal thread can be embodied in one piece with the anchor tube, for example, such that an internal thread is provided at the external end section inside the anchor tube. 
         [0014]    In another variant the internal thread of the annular part is embodied as a specialty thread, which destroys the external thread of the threaded rod only beginning at a predetermined tensile force or vice versa. 
         [0015]    Beneficially, the spindle drive to move the piston may be formed from the threaded rod and the annular part with the internal thread. 
         [0016]    In an additional embodiment, the piston is fastened directly or indirectly at the threaded rod. 
         [0017]    In an additional embodiment, the rear end of the anchor tube is closed by a cap, and the anchor tube and/or the cap comprise at least one opening to guide the fixing agent out of the interior space enclosed by the anchor tube. On the one hand, the cap can be a separate part, or also be embodied in one piece together with the anchor tube. 
         [0018]    In a supplementary embodiment, the fixing agent, particularly resin or cement, comprises two components, e.g., an adhesive component and a curing component. 
         [0019]    Preferably the two components are each arranged separated in a bag. Here, any device for storing the two separate components is considered a bag, for example a cartridge or any other container. 
         [0020]    In an amended embodiment a mixer is arranged between the fixing agent and at least one opening to mix the fixing agent, particularly the two components, before the fixing agent is ejected through at least one opening. 
         [0021]    Beneficially, the rod may be provided with a stop, preferably an annular stop, so that the mobility of the rod towards the outside is limited by said stop. Here, the stop may be a separate component or be embodied in one piece with the rod, particularly a threaded rod. Furthermore, the stop may also be formed by the piston. 
         [0022]    A method according to aspects of the present invention for fixing a rock bolt in stone, particularly a rock bolt as described in this application, includes the steps of implementing a bore hole in the stone, inserting the rock bolt into the bore hole, transporting a fixing agent from an interior space enclosed by an anchor tube of the rock bolt through at least one hole into a space, particularly an annular space between the anchor tube and the stone, by way of moving a piston in the interior space towards a fixing agent, a substance-to-substance fastening of the anchor tube by the fixing agent to the stone, and curing the fixing agent, with the piston being moved by a spindle drive at the rock bolt, particularly inside an interior chamber enclosed by the anchor tube. 
         [0023]    In an additional embodiment the spindle drive comprises a threaded rod. A torque is applied from the outside to the threaded rod such that the threaded rod is set into a rotary motion about the longitudinal axis of the threaded rod, and the threaded rod is screwed with an external thread to an internal thread at the anchor tube such that the threaded rod performs an axial motion towards the inside, i.e., the threaded rod is screwed into the interior space enclosed by the anchor tube. 
         [0024]    In an additional variant the piston fastened at the threaded rod performs the inwardly directed axial motion together with the threaded rod. 
         [0025]    In an additional variant, prior to the threaded rod being screwed into the interior space enclosed by the anchor tube, the threaded rod is only partially arranged in the interior space enclosed by the anchor tube, and during the expression of the fixing agent from the interior space enclosed by the anchor tube the threaded rod is essentially entirely screwed into the interior space enclosed by the anchor tube. Here, “essentially entirely screwed into the interior space enclosed by the anchor tube” means that the threaded rod is screwed into the interior space, for example, by at least about 70%, 80%, 90% or 95%. This way, only a small part of the threaded rod, i.e., for example, less than about 30%, 20%, 10%, or 5% is arranged outside the interior space so that after the screwing in and the compression of the space between the anchor tube and the stone with the fixing agent the rock bolt requires only little operating space in the tunnel or gallery. 
         [0026]    In an additional embodiment the components of the rock bolt, for example the anchor tube, the piston, the spindle drive, the anchor nut, the anchor plate, the rod, the fastening device, the annular part, the cap, and/or the stop are made at least partially, preferably entirely, from metal, for example steel or a steel alloy, or fiberglass-reinforced plastic. 
     
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
         [0027]    In the following an exemplary embodiment of the invention is described in greater detail with reference to the attached drawings. 
           [0028]      FIG. 1  shows a longitudinal cross section of a rock bolt formed in accordance with an embodiment of the present invention, which is inserted into a bore hole in stone with a fixing agent not yet inserted into the space between the stone and the anchor tube. 
           [0029]      FIG. 2  shows a longitudinal cross section of the rock bolt according to  FIG. 1 , in which the fixing agent is inserted into the space between the stone and the anchor tube. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0030]    In accordance with an embodiment of the present invention, a rock bolt  1  embodied as a gliding anchor  2  may be used in mining for the temporary securing of stone in galleries. The rock bolt  1  comprises an anchor tube  3 , which encloses an interior space  4 . The rock bolt  1  represents a chemical rock bolt  1 , i.e., using a fixing agent  5  arranged in the interior space  4  to the anchor tube  3  to be fastened in a substance-to-substance fashion to the stone  28 . For this purpose, a bore hole  29  must be implemented in the stone  28  and then the rock bolt  1  must be inserted into the bore hole  29 . This status is shown in  FIG. 1 , prior to the expression of the fixing agent  5  into a space between the anchor tube  3  and the stone  28 .  FIG. 2  shows the rock bolt  1  connected to the stone  28  in a substance-to-substance manner. In the illustrated embodiment, the fixing agent  5  represents a resin  6 , which includes an adhesive component  7  and a curing component  8 . The adhesive component  7  is stored in a first bag  9  and the curing component  8  is stored in a second bag  10 . The two bags  9 ,  10  are stored in the interior space  4 . 
         [0031]    Prior to the expression of the fixing agent from the interior space  4 , a rod  16 , embodied as a threaded rod  17  in the illustrated embodiment, is arranged approximately half in the interior space  4 , with the other half outside the interior space  4 , i.e., in an operating space  30  of a hollow space or gallery for mining. A fastening device  19  is fixed inside at the anchor tube  3  in the exterior end section as an annular part  20  at the anchor tube  3 . The annular part  20 , for example, a nut  21  with an internal thread  22 , is, in the illustrated embodiment, for example, welded to the anchor tube  3 . Here the external thread  18  of the threaded rod  17  engages the internal thread  22  of the annular part  20  so that this way the threaded rod  17  is indirectly fastened to the anchor tube  3 . A piston  11  is fastened at the interior end of the threaded rod  17 . The interior end of the anchor tube  3  is closed by a cap  23  with an opening  24 . Through the opening  24 , the fixing agent  5  can flow from the interior space  4  of the anchor tube  3  towards the outside into the space, particularly annular space, between the anchor tube  3  and the stone  28 . In the illustrated embodiment, a mixer  25  is arranged at the opening  24 , through which, due to the geometric arrangement of the mixer  25  in the interior space  4 , the fixing agent  5  must mandatorily flow from the two bags  9 ,  10  first through the mixer  25  and then through the opening  24  to the outside. Here, the mixer  25  comprises, for example an appropriate geometry, such that the fixing agent  5  flows meanderingly or tube-like through the mixer  25  and thus a mixing of the adhesive component  7  with the curing component  8  of the resin  6  occurs prior to flowing out of the opening  24 . 
         [0032]    At the exterior outer end of the threaded bolt  17  an anchor nut  14  is screwed onto the external thread  18  of the threaded rod  17  with an internal thread and an anchor plate  15  is placed on the anchor nut  14 . In the illustrated embodiment, the anchor plate  15  comprises a bore hole without an internal thread, with the threaded rod  17  being arranged therein. Thus, according to the illustration in  FIG. 2 , a pressure can be applied by the stone  28  upon the anchor plate  15 . This pressure is transferred from the anchor plate  15  to the anchor nut  14  and from the anchor nut  14  to the threaded rod  17  so that a tensile force is applied to the threaded rod  17 . This tensile force is transferred via the annular part  20  to the anchor tube  3  and from the anchor tube  3  at the outside in a substance-to-substance manner (by a substance-to-substance contact) by the fixing agent  5  to the stone  28 . 
         [0033]    The piston  11  is moved inwardly in order to insert the fixing agent  5  into the space between the anchor tube  3  and the stone  28 , i.e., according to the illustration of  FIG. 1 , upwardly. This way, the piston  11  destroys the first and second bag  9 ,  10  so that the adhesive component  7  and the curing component  8  move, and due to the reducing volume of the internal space  4  between the piston  11  and the cap  23 , the fixing agent  5  is pressed through the mixer  25  and the opening  24  into the space between the anchor tube  4  and the stone  28 , and subsequently cures. For this purpose, the rock bolt  1  comprises a spindle drive  13  as a mechanism  12  configured to move the piston  11 . Here, the threaded rod  17  and the annular part  20  with the internal thread  22  serve as the spindle drive  13 . The external end of the threaded rod  17  includes a respective geometry, for example the shape of a hexagon in the cross section, so that a torque can be applied upon the threaded rod  17 , for example via a pneumatic screw, and thus the threaded rod  17  is set into a rotary motion about its longitudinal axis. This way, the threaded rod  17  is moved inwardly, i.e., according to the illustration in  FIG. 1 , towards the top, due to the engagement of the external thread  18  of the threaded rod  17  with the internal thread  22  of the annular part  20 . 
         [0034]    With the motion of the threaded rod  17  the piston  11  also performs the motion according to the illustration of  FIG. 1  upwards, because the piston  11  is fastened to the threaded rod  17 . In  FIG. 2  the fixing agent  5  is already pressed into the space between the anchor tube  3  and the stone  28 , i.e., the anchor tube  3  is fastened to the stone  28  in a substance-to-substance fashion, particularly by way of gluing. Here, in the installed state shown in  FIG. 2 , the threaded rod  17  is essentially completely arranged inside the interior space  4 . Thus, only a small portion of the threaded rod  17 , for example less than about 10% or 5%, is located outside the interior space  4 . This way, in the installed state of the rock bolt  1  only very little operating space is required in the operating area  30  in the mining gallery. In the installed state according to  FIG. 2  the anchor plate  15  contacts the stone  28  and thus can compensate pressures. Further, shear forces perpendicular in reference to a longitudinal axis of the threaded rod  17  and/or the anchor tube  3  can also be compensated by the rock bolt  1  and thus the stone  28  can additionally be secured. 
         [0035]    In the illustrated embodiment, the rock bolt  1  is embodied as a gliding anchor  2 . For this purpose, the internal thread  22  of the annular part  20  is embodied as a specialty thread, which beginning at a predetermined tensile force in the threaded rod  17  destroys the external thread  18  of the threaded rod  17 , for example, by way of shearing, so that in this way the threaded rod  17  is moved outwardly, i.e., according to the illustration in  FIG. 2 , downwards in reference to the anchor tube  3 . Here, the anchor nut  14  as well as the anchor plate  15  move together with the threaded rod  17  outwardly. This way, movements of the stone  28  can be compensated by the rock bolt  1  being a gliding anchor  2  without this leading to the rock bolt  1  breaking. When the tensile force and/or the pressure to be compensated by the threaded rod  17  upon the anchor plate  15  falls back below the predetermined threshold for the tensile force, the external thread  18  of the threaded rod  17  is no longer destroyed by the specialty thread of the internal thread  22  of the annular part  20 , and the threaded rod  17  no longer moves towards the outside. 
         [0036]    A stop  26  embodied as an annular stop  27  in the upper end section of the threaded rod  17  provides that during gliding, i.e. during a motion of the threaded rod  17  towards the outside, the rod cannot completely move out. By the annular stop  27  contacting the annular part  20  a gliding of the gliding anchor  2  and/or a motion of the threaded rod  17  towards the outside is prevented. After the annular stop  27  has contacted the annular part  20 , the gliding anchor  2  is no longer able to glide and compensates the tensile forces at the threaded rod  17  until the tensile forces applied cause the rock bolt  18  to fail, for example the threaded bolt  17  breaking or the adhesive bonding failing between the fixing agent  5  and the stone  28 . 
         [0037]    Overall, the rock bolt described above provides valuable advantages. In order to move the piston  11 , i.e. the expression of the fixing agent  5  from the interior space  4 , provision of expensive high-pressure pumps is no longer required in mining operations. The piston  11  can be moved by only applying a torque upon the threaded rod  17  at the outside, for example via a pneumatic screw. In the installed state according to  FIG. 2 , the rock bolt  1  only requires little operating space  30 , because the threaded rod  17  is arranged only slightly outside the anchor tube  3  to accept the anchor nut  4  and the anchor plate  15 , and shows no increased length outside the interior space  4  in the installed state according to  FIG. 2  to compensate gliding motions of the anchor nut  14  on the threaded rod  17 .