PROGRESSIVE LOAD INDICATOR BACKGROUND OF THE INVENTION
[0001] The invention relates to a load indicator that, in a serial manner, indicates the application of a progressive load to, say, a rock bolt. [0002] It Is known, in the tensioning of rock bolts, to provide a load indicator which is configured or adapted to deform and indicate the achievement of a particular load applied to a rock anchor in pre-tension.
[0003] The load indicator, typically, is installed between a face plate and an associated spherical seat and a nut which is torqued to tension the rock anchor. Also, in another embodiment, the load indicator is included in a barrel which in use abuts the face plate and is driven against the face plate pulling on the rock bolt, wedged in place to maintain the rock anchor in pretension. However, the load indicators as described, which typicaiy have a material placed in a groove formed \n the indicator which extrudes from a groove in the indicator when pretension is achieved, is that subsequent to the initial pretension of the rock bolt, with deformation of the load indicator, further load applied along the rock anchor is not indicated.
(0004] The invention at least partially addresses the aforementioned problem. SUMMARY OF INVENTION [0005] The invention provides a progressive load indicator which includes a tubular body of a suitable metal material which extends between opposed first and second ends, a passage through the body between the ends for receiving the passage of a rock anchor in use and a plurality of grooves formed in an outer surface of the body, each groove circumscribing the body and each groove differing in volume to the others.
[0006] The grooves may be uniformly spaced. 10007] Each groove may have a deform able material placed within, preferably in the form of a ring of such material and, more preferably, the material in each groove may be of a different colour.
[0008] The invention also provides a burstable capsule which includes a ring-like tubular body, a wall of which is made of a frangible material, and a coloured liquid contained within the body.
[0009] The capsule may be sized to fit within one or more of the grooves of the progressive load indicator.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The invention is further described by way of example with reference to the accompanying drawing in which:
Figure 1 is an isometric view of a progressive load indicator according to the invention;
Figure 2 is a view in longitudinal section of the Indicator of Figure 1 ;
Figures 3A to 3C diagrarnrnatically illustrate the progressive collapse of the indicator under increased load; Figure 4 diagrammatically illustrates a progressive load indicator with a buretable ring indicator in accordance with another aspect of the invention housed within one of the annular grooves of the indicator; and
Figure 4A is a sectioned isometric view of the burstable ring indicator. DESCRIPTION OF PREFERRED EMBODIMENT
[0011] Figure 3 illustrates a typical rock anchor installation 10 with a rock anchor 12 installed into a rock hole 14 and which has an elongate body that extends between a distal end 16 and a proximal end 18.
[0012] Towards the distal end 16, the rock anchor 12 carries a mechanical anchor 20 of any known composition to anchor the rock anchor within the rock home. Although H is understood in the context of the invention that the rock anchor can be adhesively anchored within the rock hole.
[0013] A projecting section 22 of the rock anchor 12 is defined as the section of the rock anchor that projects from the hole 14. This section 22 terminates at the proximal end 18 and, typically, is threaded.
[0014] The projecting section 22 carries a load applicator assembly 23 which in this example comprises a domed face plate 24, a spherical seat 26, which accommodates angular misalignment between the face plate and the rock anchor, and a nut 28. In another example, the seat and the nut is replaced by a barrel and wedge device.
[0016] In use, with the mechanical anchor actuated to anchor the rock anchor within the rock hole, the nut 28 is run up the threads of (he projecting section to engage the underside of the seat 26 to move the faceplate into contact with the rock face 30. The nut is then torqued to force the faceplate, through the seat, against the face rock anchor is thus tensioned between the mechanical anchor 20 and the nut 28.
[0010] The extent to which the rock anchor Is tensioned is an important variable as it translates into the load support the anchor provides to the rock face 30 and it is important that an installer of the rock anchor knows if the anchor has been sufficiently tensioned. Thus, it is known to include a load indicator element or a stack of such elements within or interposed between the elements of the assembly 23 which is designed to deform when a predetermined optimal bad is achieved. [0017] However, the invention takes this further and provides a unitary progressive load indicator 40 which is interposed between the spherical seat 26 and the nut 28. Progressive load indication is advantageous as the rock anchor will experience in its installed fife not only the initial installed load but increasing loads as the supported rock face 30 moves outwardly due to geologic dynamics. Knowing a minimum load that the rock anchor is experiencing will assist mine workers in recognising areas of significant dynamic change and in determining if the rock anchor is close to failure.
[0018] Being unitary, the progressive load Indicator will not experience lateral movement as is the case with a stack of load indicating elements which tend to laterally slip past one another as perpendicularly applied load increases, alleviating load on a particular element which will then not indicate achievement of load by deforming.
[0019] With specific reference to Figures 1 and 2, the load indicator 40 includes a tubular body 42 of a suitable metal material which extends between opposed first and second ends 44 and 46 and through which runs a tubular passage 48 which is sized to receive the rock anchor 12.
[0020] The body 42 has a plurality of grooves, respectively designated 50A, 50B and 50C, machined in an exterior surface 52. The grooves are uniformly longitudinally spaced. Each of the grooves is differently geometrically sized to collapse at a different specified load.
[0021] In this example, the deepest groove 50A is towards the first end which, in use, is the end of the indicator body which abuts the spherical seat 26. The grooves progressively shallow towards the second end 46. The deeper the groove, the lower the toad necessary to collapse the groove. So, for example, groove 50A being the deepest groove, will collapse at a load that is sufficient to indicate optimal load support, say, 2 tonnes. Thereafter, the grooves may collapse at loads of, for example, 5 and 10 tonnes respectively. These loads wil be applied to the rock anchor when there is movement in the rock face 30 as described above. Rock face movement is illustrated in Figures 3B and 3C with prior rock face levels depicted as dotted lines.
[0022] Each of the annular grooves 50 has an indicator ring of a plastic or rubber material 54, preferably distinctly coloured, which will extrude from the respective annular groove when the groove collapses under the predefined load. This sequential indication of progressive load application to the rock anchor is illustrated in Figure 3A to 3C. In Figure 3A only the first groove 50A has collapsed to indicate the achievement of the application of an optimal preload. In Figure 3B and 3C, respectively the groove 52B and the grooves 52B and 52C are shown collapsed with the material extruding therefrom. This would indicate that the rock anchor subsequently had experienced increasing load due to rock dynamics.
[0023] In another aspect of the invention, which is illustrated in Figure 4, one or more of the grooves 50 houses a burstable ring 60.
[0024] The burstable ring 60 has a tubular ring housing 62 made of frangible material in which a coloured dye or pigment 64 is contained.
[0025] When the groove SO containing the ring 60 collapses or deforms, the frangible material making up the housing 62 bursts to release the dye 64 content which is fluid and which will then run down the exterior surface 52 of the load indicator body 42 to provide an obvious visual indication of a particular load being achieved or experienced by the load indicator 40 and the rock bolt installation 10 to which it is part
[0026] Preferably only one of the grooves houses a ring 60 to provide a distinguishable visual indication to that provided by the extrusion of the plastic or rubber material 54 which is included in the other grooves 50. This groove will be the groove that is adapted to collapse or deform at a load close to the failure load of the rock anchor 12, which in this particular example is the groove designated 50C.