Abstract:
A cable bolt comprising a plurality of flexible steel filaments formed around a central member, the cable bolt having spaced bulbous portions along the length of the bolt each bulbous portion defining a cavity containing a segmented ring that surrounds the central member to engage the filaments of the bulbous portion.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This Application is a divisional of U.S. patent application Ser. No. 13/852,503, filed on Mar. 28, 2013, which claims priority to AU 2012901303, filed on Apr. 2, 2012, the disclosures of which are incorporated herein by reference in their entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Technical Field 
         [0003]    This invention relates to cable for use in strata control, especially to reinforce the roof and/or walls of underground mines and tunnels, to methods of manufacturing cable bolts and to manufacturing components and systems used in such methods. 
         [0004]    2. Description of Related Art 
         [0005]    Cable bolts are usually made from cable comprising a plurality of steel filaments wound together around a central wire to form a tendon. Resin and/or cement grout is used to fix the cable bolt to a borehole. To increase the effective bond strength between the cable bolt and resin or grout the bolts are often provided with spaced protuberances along the length of the cable. These protuberances are often known as bulbs or cages. The protuberances assist in preventing cable bolts from being pulled through the resin or grout, thus providing improved anchorage and load transfer between the cable, resin/grout and the surrounding strata. 
         [0006]    It is known that tensioning of the cable prior to cement grouting can cause the protuberance to collapse thus reducing the cable&#39;s effectiveness. In Australian patent 2004260817 there is a proposal to insert ball bearings into the cavities defined by the protuberances to reduce the likelihood of the protuberances collapsing when the cable is tensioned. This proposal has proved expensive to manufacture and unreliable due to the ball bearings being pushed out of the protuberances. There is also a need to displace the central wire to locate each ball bearing. In some cable bolts the central wire is replaced by a hollow tube which extends along the centre of the cable. Other disadvantages relate to the difficulty in automating the placement of the ball bearings and the ball bearing creates a stress concentration on the strands of the cable creating loads that lead to failure loads up to 25% less than the original strands ultimate tensile strength. 
         [0007]    In our earlier Australian patent application 2008200918 we disclose a cable bolt having a hollow strand which facilitates the passage of grout along the cable. It is important that the hollow strand does not get crushed by radial loads in non collapsible protrusions. 
         [0008]    It is these issues that have brought about the present invention. 
       SUMMARY OF THE INVENTION 
       [0009]    According to one aspect of the present invention there is provided a cable bolt comprising a plurality of flexible steel filaments formed around a central member, the cable bolt having spaced bulbous portions along the length of the bolt each bulbous portion defining a cavity containing a segmented ring that surrounds the central member to engage the filaments of the bulbous portion. 
         [0010]    In accordance with a further aspect of the present invention there is provided a method of manufacturing a cable having twisted flexible steel filaments over a central member, the method comprising forcing the filaments apart without plastically deforming the filaments, inserting a spacer through the parted filaments to sit between the filaments and the central member, and releasing the parted filaments to return against the spacer to form a bulbous portion. 
         [0011]    In one form, the filaments are forced apart by applying torsion to the filaments. In one form, the torsion is applied over a length of the cable to form bulbous portions spaced along the cable. 
         [0012]    In one form, in addition to or instead of, the filaments are forced apart by inserting a spreading tool between the filaments. 
         [0013]    In one form, the spacer extends around the central member. In a particular form, the spacer is a segmented ring that is placed in pieces through the parted filaments and formed into a ring surrounding the central member. In another form, the spacer may be a unitary element, such as helical wound member that is rotated onto the inner member through the parted filaments. 
         [0014]    In one form the torsion and/or spreading is applied over a section of the pre-wound cable to open the outer filaments over a set length to allow insertion of the ring segments around the central member before releasing the filaments forming a permanent non-collapsible single protrusion. The process may be repeated further along the pre-wound cable. 
         [0015]    In a further aspect of the present invention, there is provided an apparatus for forming bulbs in a cable having twisted flexible steel filaments over a central member, the apparatus comprising: 
         [0016]    a bulbing assembly releasably engagable with said cable, said assembly being operative to force the filaments apart without plastically deforming the filaments; and 
         [0017]    an inserting device operative to insert a spacer through the parted filaments to sit between the filaments and the central member. 
         [0018]    In use on releasing the parted filaments they return against the spacer to form a bulbous portion in the cable. 
         [0019]    In one form, the apparatus further comprises a frame; and a securing device for holding at least a portion of a cable with respect to frame. 
         [0020]    In one form the cable is fed through the bulbing assembly so that a plurality of bulbing portions are able to be formed along the cable. 
         [0021]    In another form, the bulbing assembly is movable relative to the apparatus frame to form spaced apart bulbing portions in the cable. Typically in this latter arrangement the cable remains stationary during forming of the plurality of bulbs but in another form, the cable may be moved so that both the cable and the bulbing apparatus move during bulb forming. 
         [0022]    In one form, the apparatus includes a feed assembly to feed the cable from a coil into the apparatus. In one form the cable, with bulbs formed therein, is progressed to a table and the apparatus further includes a cutting device to cut the cable to length as required in formation of cable bolts. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0023]    An embodiment of the present invention will now be described by way of example only with reference to the accompanying drawings in which: 
           [0024]      FIG. 1  is a part sectioned side view of a typical cable bolt, 
           [0025]      FIG. 2  is a cross sectional view of the cable bolt, 
           [0026]      FIG. 3  is a schematic view of an apparatus for forming bulbs in a cable in accordance with an embodiment of this invention, 
           [0027]      FIG. 4  is a plan view of a bulbing apparatus of the apparatus of  FIG. 3 , 
           [0028]      FIG. 5  is a detailed view of the bulbing apparatus of  FIG. 4 , 
           [0029]      FIG. 6  is a perspective view of the bulb illustrating insertion of a segmented ring. For convenience components of the bulbing apparatus are not shown; and 
           [0030]      FIG. 7  is a perspective view illustrating the location of the segmented ring on a central strand of the cable bolt. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0031]      FIGS. 1 and 2  illustrate a cable bolt  10 . These drawings are taken from our earlier Australian patent application 2008200918, corresponding to U. S. Pat. No. 8,322,950, incorporated herein by reference. 
         [0032]    As illustrated in  FIG. 1 , an embodiment of a resin anchorable cable bolt  10  comprises a flexible cable  11  formed from a plurality of wound co-extending strands in the form of wound co-extending steel filaments that extends along an axis C between opposite ends (being, relative to the direction the bolt  10  is installed in a bore in a substrate, such as a mine shaft roof, a distal end  13  and a proximal end  14 ). The cable  11  has a first portion  15  adapted primarily for resin point anchoring, and a second portion  16  adapted predominantly for cement grouting. 
         [0033]    As illustrated in  FIG. 2 , the filaments comprise nine outer steel filaments  12   a  spiral wound about a central hollow filament, or strand  12   b , located axially within the cable  11 . In one form, the hollow strand  12   b  may comprise at least one region for resisting radial compression, in particular of a tensioning assembly which is discussed in more detail below. In alternative arrangements, the hollow strand  12   b  may be plain, and/or more or fewer outer steel filaments  12   a  may be used, in which case their relative diameter with respect to the hollow strand  12   b  would be adjusted accordingly such that they are close fitting about the hollow strand  12   b . The outer steel filaments, or strands,  12   a  are typically solid and of the type used for cable bolt or pre-stressed concrete applications. The hollow strand  12   b  extends in the second portion  16  and not in the first portion  15 , however in alternative embodiments, the hollow strand may extend into the first portion  15  also. 
         [0034]    In the embodiment of  FIG. 1 , the central hollow strand  12   b  comprises profiling allowing flexibility of the cable  11 , while providing strength to resist crushing of the strand (i.e. radial compression of the cable). The hollow strand  12   b  is flexible to allow coiling of the cable  11  such that the coil has a minimum diameter of 1.2 m without kinking the hollow strand  12   b . In alternative embodiments, the minimum coiling diameter without kinking the hollow strand may fall within the range of 0.8 m to 2.5 m, or 1 m to 2 m. In the embodiment illustrated in  FIG. 1 , the profiling is in the form of a helical or spiral ribs  17  (see  FIG. 7 ) along its entire length. The hollow strand  12   b  is formed from a metal material, in this embodiment steel, but may be formed from a polymeric material, such as polypropylene, a polyethylene, or other appropriate polymer. 
         [0035]    Referring again to  FIG. 1 , the cable bolt  10  further comprises a resin retainer  22  disposed between the first and second portions  15 ,  16  of the cable  11 . The resin retainer  22  is affixed to the cable  11  and extends radially outwardly from the cable so as to substantially reduce the migration of resin from the first portion to the second portion within the bore during point anchoring of the bolt  10 . The resin retainer is typically formed from metal, however may be formed from any suitable polymer such as polypropylene or a polyethylene. 
         [0036]    The hollow strand  12   b  is located in the second portion  16  of the cable bolt  10  and extends from the proximal end  14  of the cable  11  to a location  24  in the second portion  16  at or adjacent the retainer  22 . As illustrated in  FIG. 1 , a nut  26  is located on or near the hollow strand  12   b  at location  24  within the outer filaments  12   a , forming a bulb, or “nut cage”  28 . The nut cage is formed by spacing apart and forcing outwardly all of the steel filaments  12  along a discrete section of the cable  11  and placing the nut  26  about the hollow strand end  24 . 
         [0037]    The first portion  15  includes an end collar  31  for holding together the strands  12   a  at the distal end  13 , and a plurality (three in the illustrated case) of radially outwardly extending resin mixing protrusions in the form of “bird cages”  32 , where a ball bearing (or other rigid object) is inserted in a partially unwound portion of strands  12   a.    
         [0038]    It is desirable in some instances to form bulbs along the second portion  16  (in addition to the first portion  15 ) and/or to extend the hollow strand  12   b  into the first portion  16 . As such it is desirable to be able to form bulbs about the hollow strand  12   b . Further to facilitate manufacturing processes, it is desirable that the bulbs are formed without unwinding of the steel filaments. 
         [0039]      FIGS. 3 to 6  illustrate an apparatus for forming non collapsible spaced protrusions (or bulbs)  18  about the hollow strand  12   b  of the flexible cable  11 . These bulbs  18  incorporate a segmented ring  40  ( FIG. 7 ) that prevents collapse of the bulb  18  whilst ensuring against radial compression of the hollow strand  12   b.    
         [0040]    The method of forming the bulbs  18  and locating the segmenting ring  20  is discussed with particular reference to the bulbing apparatus  100  shown  FIGS. 3 to 5 . 
         [0041]    As best shown in  FIG. 3 , the apparatus  100  includes a bulbing assembly  102  mounted on a frame  104 . A cable  11  is arranged to be fed from a coil (not shown) mounted within a coil handler  106 . Once bulbs are formed in the cable  11  (as discussed in more detail below) by the bulbing assembly  102 , the cable is progressed to a payout table  108 . A cutting device  110  is disposed between the frame  104  and the payout table  108  and is arranged to cut the cable once a desired length (typically of 8 m but it may be more or less depending on requirements) is passed onto to the table. The cut lengths of cable can then be further processed to form the final cable bolts as required. The bulbing process is preferably fully automated and controlled by a control system  112  which may include, as illustrated, a control cabinet  114  and operator interface  116 . 
         [0042]    As best shown in  FIGS. 4 and 5 , bulbing assembly  102  includes three components; namely torsioning device  118 , spreader  120 , and inserter  122 . In general, the torsioning device  118  is designed to twist the cable bolt  10  to force the filaments  12   a  apart to define a gap. The spreader  120  (shown in the form as a pair of plates or knives  56 , 57 ) is designed to further spread adjacent filaments that allows the inserter  122  adequate space to enable the segmented ring  40  to pass through the parted filaments  12   a  to be located in an interfitting arrangement on the central strand  12   b.    
         [0043]    In the illustrated embodiment, the torsioning device  118  discloses the use of mandrels  51 ,  52  positioned around the cable  11  at spaced intervals to define a length of cable as shown in  FIGS. 4 and 5 . Each mandrel  51  or  52  includes a three jaw chuck  53 ,  54  which can be brought into clamped engagement with the periphery of the cable  11 . The chucks  53 ,  54  are clamped to the cable and are either rotated in opposite directions or one is rotated relative to the other to place the filaments  12   a  of the cable into torsion which has the effect of parting the filaments  12   a  and forming a protrusion  18  at the mid span of cable between the chucks  53 ,  54 . With the chucks  53 ,  54  held in position to maintain the torsion, spreader knives  56 ,  57  are pushed between selected parted filaments  12   a  and rotated to further move the filaments apart. This provides access to the inserter  122  (in the form of robotic arms  59 ,  60 ) which place segments  41 ,  42  of the ring  40  on opposite sides of the hollow strand  12   b  and then fitted together as shown in  FIGS. 6 and 7 . 
         [0044]    As shown in FIG. 7 , each ring segment  41 ,  42  has a projection  43  that is a snug fit within a similarly profiled recess  44  on the other segment  42  of the ring to allow the segments  41 ,  42  to form a circular one piece ring  40  as shown in the left hand side of  FIG. 6 . Once the ring  40  has been placed on the central strand  12   b  the knives  56 ,  57  can be removed and, the torsion applied by the mandrels  51 ,  52  can be released causing the parted filaments  12   a  to close onto the periphery of the ring  40  thereby locating the ring  40  in the cavity of each protrusion  18  on the central strand  12   b . By a steady release of the torsional load the parted gap between the filaments closes and the filaments  12   a  contact the ring  40  to form an expanded non-collapsible bulb  18 . 
         [0045]    The location of the ring  40  on the hollow central strand  12   b  ensures that when the cable bolt is tensioned the protrusion  18  does not collapse. The segmented ring  40 , by forming a single annular ring ensures that there is no danger of the segments  41 ,  42  crushing the central strand  12   b . The dovetailed inter fitting of the segments  41 ,  42  ensure that radial forces on the ring  40  are evenly distributed around the periphery of the strand  12   b . The segmented ring  40  whilst preventing radial collapse of the strand  12   b  can also allow a degree of movement between the strand  12   b  and ring  40  thus maintaining the flexibility of the final cable. 
         [0046]    In the form illustrated, the torsional and spreading forces that are placed on the cable bolt as it is twisted through use of the mandrels  51 ,  52  and spreader  120  is insufficient to cause plastic deformation of the wire filaments  12   a.    
         [0047]    Once the bulb  18  is formed, the cable  11  can then be fed through the bulbing assembly  102  (in a direction towards the payout table  108 ) such a subsequent portion of the cable  11  aligns with the bulbing assembly. The bulbing assembly is then able to form a further bulb  18  in the cable allowing separate spaced bulbs  18  to be formed in the cable  11 . 
         [0048]    In an alternative form, the bulbing assembly may be designed to move along the length of the cable  11  to form spaced apart bulbs in the cable  11 . In either process, in this manner the cable  11  can have non collapsible grouting protrusions (in the form of bulbs  18 ) at desired intervals along the length of the cable  11 . 
         [0049]    This process can be completed off a reel and wound back into smaller reels; or to cut to lengths. Alternatively, the process can use precut lengths. 
         [0050]    It is also envisaged that the mandrels  51 ,  52  and chucks  53 ,  54  may be split to facilitate attachment to the cable  10  without the need to pass the cable through the mandrels and chucks. 
         [0051]    It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country. 
         [0052]    In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word “comprise” or variations such as “comprises” or “comprising” is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.