Abstract:
A centralizer for use in a rock drill rig is disclosed. The centralizer includes a clamping member which moves generally tangentially to a bush, in order to clamp the bush in place within the centralizer.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is entitled to the benefit of and incorporates by reference essential subject matter disclosed in International Patent Application No. PCT/AU2011/001046 filed on Aug. 16, 2011 and Australian Patent Application No. 2010903662 filed Aug. 16, 2010. 
     FIELD OF THE INVENTION 
     The present invention relates to a centraliser clamp used within a rock drill rig, such as a face-drilling rock drill used in underground mining. 
     BACKGROUND TO THE INVENTION 
     An underground rock drill rig generally has at least one boom on which is mounted a feed rail. The feed rail supports a drill and its associated drill rod. 
     The drill is mounted to the rail, so as to be able to move along the length of the rail. When the drill is in an initial position at the rear of the rail, the drill rod is supported at the front of the rail by a bush, which is held in place by a centralising clamp. 
     Centralising clamps are generally formed from two pieces, each of which has a semi-circular recess which can locate about one side of the bush. The two pieces can be clamped together using a nut and bolt in order to hold the bush in place in between the two pieces. 
     There are some inherent weaknesses in this arrangement. The entire clamping force acts through the bolt, providing significant stress concentrations about the bolt. Away from the line of the bolt, the clamping forces are significantly dissipated, meaning that there can be a propensity for the bush to move or vibrate. Additionally, vibration during use can cause loosening of the nut, exacerbating the problem. Movement of the bush causes a significant increase in the wear rate of the centralising clamp, as well as a loss of accuracy in drilling. 
     As the two pieces must be able to move relative to each other, it is only possible to weld one of the pieces in position. This limits stability of the arrangement, and can lead to cracking and fatigue failure. 
     A further limitation of the known arrangement is that the bush is located at a designated height about the rail, being the same height as the drill. Should the rail bend, the location of the bush can not be adjusted. When this happens, it is necessary to cut away the centraliser clamp and reposition at a new location. This can cause significant down-time for the drill rig. 
     The present invention seeks to provide an alternative method of clamping a centralising bush in position. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention there is provided a centraliser clamp for a locating bush in a drilling rig, the clamp including an aperture for receiving a bush, and a clamping member having a bearing surface, the clamping member being movable relative to the bush-receiving aperture such that the bearing surface can be moved within the bush-receiving aperture in order to secure the bush within the aperture. 
     Preferably, the clamping member is movable in a direction substantially perpendicular to a central axis of the bush. 
     It is preferred that the clamping member be moveable by mechanical means. The clamping member may include an internally threaded cylindrical aperture arranged to engage with an externally threaded adjustment bolt, such that rotation of the adjustment bolt causes movement of the clamping member along the bolt. 
     In a preferred embodiment, the clamp has a body portion having a substantially cylindrical aperture in which the bush is received, the body portion having a first side opposite a second side, and a clamping member receiving aperture extending internally of the first side of the body portion and an adjustment bolt receiving aperture extending internally of the second side of the body portion. 
     Preferably, the clamping member is substantially prismatic. The bearing surface of the clamping member may be bevelled. The arrangement is such that in use the bearing surface is substantially tangential to the bush. 
     In a preferred embodiment, the bush has a substantially planar bearing flat arranged to engage with the bearing surface of the clamping member. 
     According to a second aspect of the present invention there is provided a centraliser for a locating bush in a drilling rig, the centraliser comprising a centraliser clamp and an associated supporting structure, the centraliser clamp including a body portion having an aperture for receiving a bush, and a base portion which is substantially perpendicular to the bush-receiving aperture, the base portion arranged to be fixed to the supporting structure, whereby the height of the base portion relative to the supporting structure can be adjusted. 
     Preferably, the supporting structure includes a top plate onto which the base portion of the clamp can be connected, and at least one spacer located between the top plate and the base portion in order to determine the height of the bush relative to the supporting structure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       It will be convenient to further describe the invention with reference to preferred embodiments of the centraliser clamp of the present invention. Other embodiments are possible, and consequently the particularity of the following discussion is not to be understood as superseding the generality of the preceding description of the invention. In the drawings: 
         FIG. 1  is a schematic view of a face-drilling rock drill rig within which a centraliser clamp in accordance with the present invention may be used; 
         FIG. 2  is a perspective of a centraliser in accordance with the present invention; 
         FIG. 3  is an enlarged perspective of a centraliser clamp within the centraliser of  FIG. 2 ; 
         FIG. 4  is a cross section through the centraliser clamp of  FIG. 3 ; 
         FIG. 5  is a side view of the centraliser clamp of  FIG. 3 , shown from the reverse side; 
         FIG. 6  is a perspective of the centraliser clamp of  FIG. 3 , shown from the reverse side with a bush and pin removed; 
         FIG. 7  is a perspective of a clamping member from within the centraliser of  FIG. 2 ; 
         FIG. 8  is a perspective of a bush for use in conjunction with the centraliser of  FIG. 2 ; 
         FIG. 9  is a perspective of a second embodiment of a centraliser clamp for use in the centraliser of  FIG. 2 ; and 
         FIG. 10  is a perspective of a third embodiment of a centraliser clamp for use in the centraliser of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to the Figures,  FIG. 1  shows a face-drilling rock drill rig  10  as used in underground mining operations. The drill rig  10  includes a boom  12 , on which is mounted a rail  14 . A drill  16  is mounted to the rail  14 , and is arranged to move along the rail  14  under the control of an operator. A drill rod  18  extends away from the drill  16 , parallel to the rail  14 . A centraliser  20  is located at an outer end of the rail  14 , in order to support the outer end of the drill rod  18 . 
       FIG. 2  shows a centraliser  20  having a supporting structure  22  and a centraliser clamp  24 . The supporting structure  22  includes a substantially rectangular top plate  26  having a bolt-receiving aperture near each of its corners. The top plate  26  has a substantially flat upper surface which is substantially horizontal when the centraliser  20  and drill rig  10  are in the position shown in  FIG. 1 . 
     The centraliser clamp  24  has a substantially rectangular base portion or base plate  30 , having a substantially flat lower surface of similar dimension to the upper surface of the top plate  26 . The base plate  30  has bolt-receiving apertures  28  which are aligned with the bolt-receiving apertures of the top plate  26  when the base plate  30  is placed over the top plate  26 . Bolts (not shown) can be located within the aligned bolt-receiving apertures in order to fix the centraliser clamp  24  to the supporting structure  22 . 
     The centraliser  20  includes a spacer  32  located between the top plate  26  of the supporting structure  22  and the base plate  30  of the centraliser clamp  24 . The spacer  32  is prismatic, with ends similar in size and shape to the flat surfaces of the top plate  26  and base plate  30 . It has apertures aligned with the bolt-receiving apertures  28  of the top plate  26  and base plate  30 . 
     The effect of the spacer  32  is to alter the height of the centraliser clamp  24  relative to the supporting structure  22 . It is envisaged that a number of spacers  32  of differing widths may be provided, with the choice of an appropriate spacer or spacers  32  providing a user with the ability to choose a desired height for the centraliser clamp  24 . 
     The centraliser clamp  24  can be seen more clearly in  FIGS. 3 to 6 . 
     The centraliser clamp  24  has a front end  34 , a rear end  36 , a first side  38  and a second side  40 . These can be seen as corresponding to the four sides of the rectangular base plate  30 . 
     The centraliser clamp  24  includes a body portion  42  which extends upwardly from the base plate  30  abutting the rear end  36 . The body portion  42  is prismatic, with its ends being arch-shaped, and has a thickness about one half that of the breadth of the base plate  30 . 
     The body portion  42  includes a cylindrical bush-receiving aperture  44 , arranged to receive a bush  46  such as that of  FIG. 8 . The bush-receiving aperture  44  passes from the rear end  36  of the body portion  42  to a front face  48  oriented towards the front end  34  of the centraliser clamp  24 . 
     Clamping of the bush  46  within the bush-receiving aperture  44  is achieved through use of a clamping member  50 . The clamping member  50 , which can be seen in  FIG. 7 , is formed from a substantially prismatic member having octagonal ends  52 . Each of the ends  52  has two vertical edges  54  representing about 60% of the height of the ends; two horizontal edges  56  having a length about one third of the vertical edges  54 ; and four diagonal edges  58  disposed at 45% to the vertical edges  54  and horizontal edges  56 , each having a length about one half of the vertical edges  54 . The clamping member  50  has a first end  62 , a second end  64 , a top wall  66  extending between the respective top horizontal edges  56  of the ends  52 ; a bottom wall extending between the respective bottom horizontal edges  56  of the ends  52 ; two side walls  68  extending between respective vertical edges  54  of the ends  52 ; two upper diagonal walls  70  extending between respective diagonal edges  58  adjacent the top horizontal edges  56  of the ends  52 ; and two lower diagonal walls extending between respective diagonal edges  58  adjacent the lower horizontal edges  56  of the ends  52 . An internally threaded longitudinal aperture  72  extends through the clamping member  50  from the first end  62  to the second end  64 , through the centre of the clamping member  50 . 
     The clamping member  50  has a bevelled bearing surface  74  located along its top wall  66 , extending from the second end  64 . The bearing surface  74  extends along about 40% of the top wall  66 , and is angled at about 15° relative to the top wall  66 . The bearing surface  74  causes a taper of the upper diagonal walls  70  towards the second end  64 . 
     The body portion  42  of the centraliser clamp  24  includes a clamping member receiving aperture  76 , which extends internally of the body portion  42  from the first side  38 . The clamping member receiving aperture  76  is sized and shaped so as to receive the clamping member  50  in a loose sliding fit, and positioned such that when the first end  62  of the clamping member  50  is generally flush with the first side  38  of the body portion  42 , the bearing surface  74  locates substantially tangentially to the bush-receiving aperture  44 . The clamping member receiving aperture  76  has an opening  78  within the bush-receiving aperture  44 , as can be seen in  FIG. 6 . 
     The body portion  42  of the centraliser clamp  24  also includes an adjustment bolt receiving aperture  80  extending from the second side  40  of the body portion  42  beneath the bush-receiving aperture  44  to the clamping member receiving aperture  76 . The adjustment bolt receiving aperture  80  is sized and aligned such that when the clamping member  50  is in position within the clamping member receiving aperture  76 , the adjustment bolt receiving aperture  80  is aligned with the internally threaded longitudinal aperture  72  of the clamping member  50 . 
     An externally threaded adjustment bolt  82  can thus be entered through the second side  40  of the body portion  42  and engage the internally threaded longitudinal aperture  72  of the clamping member  50 . 
     The bush  46  is generally cylindrical. It has an internal bore  84  arranged to receive and support a drill rod  18 . The internal bore  84  is tapered at either end of the bush  46 , forming introducing regions for ease of assembly. 
     The bush  46  has a stepped outer radius, with a smaller radius portion  86  sized to fit loosely within the bush-receiving aperture  44  and a larger radius portion  88  arranged to locate outside the bush-receiving aperture  44 , against the rear end  36  of the body portion  42 . 
     The bush  46  has a bearing flat  90  located on the smaller radius portion  86 . The bearing flat  90  comprises a portion of an outer surface of the bush  46  which is substantially planar, and parallel to a central axis of the bush  46 . 
     In use, the supporting structure  22  of the centraliser  20  is welded to the boom  12 . A drill  16  is located on the rail  14 . A centraliser clamp  24  is then bolted to the supporting structure  22 , with appropriate spacers  32  being used to ensure that the bush  46  is axially aligned with the drill  16 . 
     When the bush  46  is located within the bush-receiving aperture  44 , it can be rotated until the bearing flat  90  is positioned adjacent the opening  78 . The clamping member  50  can be inserted into the receiving aperture  76  from the first side  38  of the centraliser clamp  24 , and the adjustment bolt  82  inserted into the adjustment bolt receiving aperture  80  from the second side  40 . Once the adjustment bolt  82  engages the internally threaded longitudinal aperture  72  of the clamping member  50 , rotation of the adjustment bolt  82  translates to lateral movement of the clamping member  50 . 
     The adjustment bolt  82  is rotated to cause movement of the clamping member  50  into the body portion  42 , and of the bearing surface  74  into the bush-receiving aperture  44 . The bearing surface  74  acts against the bearing flat  90  of the bush  46 , clamping the bush  46  into position within the bush-receiving aperture  44 . The action is similar to a wedging action, allowing for tight clamping of the bush  46  into position despite variances in surface machining and the like. Should slight loosening occur, the clamping member  50  can be readily re-tightened. 
     An access hole  92  is provided in the body portion  42 , passing from the front end  34  to the rear end  36  through the base of the clamping member receiving aperture  76 . The access hole is provided so that if grit or fines particles become trapped within the receiving aperture  76 , they can be readily cleaned out. 
     It will be appreciated that the shape of the centraliser clamp  24  can be adjusted to suit particular drill rigs  10  without departing from the scope of the present invention.  FIGS. 9 and 10  show two such centraliser clamps  24 , with like numerals referring to like features. 
     Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.