AU2012101072A4 - Mine Roof Mesh - Google Patents

Abstract

A mine roof mesh comprising a grid of longitudinal and transverse wires welded at their intersections to form a sheet of said mesh; and wherein each of said transverse wires is provided with bends to form an array of troughs and apexes extending along at least a portion of said transverse wires; said longitudinal wires interconnecting corresponding ones of said troughs and apexes of said transverse wires. 1212A 22 2 22$12B Fig. 2 12C 12A 12B 14t Fig. 2A 247 \ 1 Fig. 2B Fig. 2C Fig. 2D

Description

P/00/009 Regulation 3.2 AUSTRALIA Patents Act 1990 INNOVATION SPECIFICATION Invention Title: MINE ROOF MESH The invention is described in the following statement including the best method of performing it known to us: Our Ref: 116007 -2 MINE ROOF MESH [0001] The present invention relates to welded steel meshes and, more particularly, to specialized mine roof 5 stabilizing meshes. BACKGROUND [0002] It is known to use welded steel mesh sheets in underground mining and tunnelling situations where loose material, which may detach from the overhead strata, 10 presents a danger. [0003] Sheets of mesh are secured to the strata by means of rock bolts, long steel shafts, secured in holes drilled into the strata at their distal ends, either by mechanical or chemical means. The bolts are threaded at their 15 proximate ends which project from the strata. Steel plates, of a size to overlap adjoining longitudinal and transverse wires of the mesh, are placed over the bolt ends and secured by a washer and nut. [0004] One problem with these sheets is that installers 20 have difficulty spacing sheets in the most economical yet effective fashion. [0005] Another problem the installers have is locating the bolts relative to the sheets in the most economical yet effective fashion. 25 [0006] Another problem with substantially planar meshes is that a heavy load impacting the mesh at some - 3 intermediate area of the mesh due to dislodgement of strata, can break the mesh at the rock bolts. [0007] An example of a mine roof mesh is disclosed in AU 200700078 in which the outer longer edges of the sheet are 5 bent out of the plane of the sheet in opposite directions for the purpose of providing some stiffening of the sheet. This is achieved by applying a single bend proximate the outer ends of each transverse steel rod or wire forming the mesh. However such a single bend provides only slight 10 stiffening. Moreover, the stiffening bends being applied in opposite directions dictates that at the overlap of adjacent sheets, the relatively sharp outer ends of the transverse steel rods project into the space below. [0008] Mine roof mesh sheets are typically supplied in 15 long lengths and even though one or two bends can provide some stiffening, the sheets remain difficult to handle because of excessive flexing. [0009] It is an object of the present invention to address or at least ameliorate some or one or more of the 20 above disadvantages in accordance with various embodiments as will be described below. 25 -4 Notes [0010] The term "comprising" (and grammatical variations thereof) is used in this specification in the inclusive sense of "having" or "including", and not in the exclusive 5 sense of "consisting only of". [0011} The above discussion of the prior art in the Background of the invention, is not an admission that any information discussed therein is citable prior art or part of the common general knowledge of persons skilled in the 10 art in any country. BRIEF DESCRIPTION OF INVENTION [0012] Accordingly, in a first broad form of the invention, there is provided a mine roof mesh comprising a 15 grid of longitudinal and transverse wires welded at their intersections to form a sheet of said mesh; and wherein each of said transverse wires is provided with bends to form an array of troughs and apexes extending along at least a portion of said transverse wires; said longitudinal 20 wires interconnecting corresponding ones of said troughs and apexes of said transverse wires. [0013] Preferably, selected ones of said longitudinal wires and/or transverse wires are distinguished by colour thereby to define a visual template or guide for insertion 25 of rockbolts or like fixing devices therebetween.

- 5 [0014] Preferably, opposing outer ends of each said transverse wire includes a straight section; corresponding said straight sections of said transverse wires interconnected by at least two longitudinal wires to form 5 coplanar side portions of said mine roof mesh. [0015] Preferably, said selected ones of said longitudinal wires include a pair of longitudinal side wires at each opposite outer edge of said sheet and a pair of central wires disposed symmetrically about a central 10 median plane of said sheet. [0016] Preferably, spacing of said pair of longitudinal wires at each opposite outer edge of said sheet is smaller than spacing of said longitudinal wires in the remaining areas of said sheet. 15 [0017] Preferably, said pair of longitudinal wires at each opposite outer edge of said sheet is distinguished from said longitudinal wires in said remaining areas of the mesh by being formed of galvanized wire. [0018] Preferably, each said outer edge of said sheet 20 comprises a straight edge portion of said sheet extending laterally from said portion formed with said troughs and apexes; each said edge portion parallel to a mid plane of said sheet passing through mid points between respective said troughs and apexes.

- 6 (0019] Preferably, said edge portions lie in a median plane passing through midpoints between said troughs and apexes. [0020] Preferably, said edge portions lie in a plane 5 proximate a plane passing through said troughs or apexes. [0021] Preferably, selected ones of pairs of longitudinal and transverse wires define preferred regions of said mesh for mesh securing rock bolts; said regions defined two-dimensionally by utilizing either colour, or a 10 combination of colour and variation in wire density. [0022] Preferably, spacing, as projected on said median plane of said sheet, between said pair of central wires is 80mm; spacing between respective ones of said pair of central wires and respective adjacent said longitudinal 15 wires, being 60mm; spacing between remaining longitudinal wires between said respective adjacent longitudinal wires and said edges of said sheet being 100mm, and wherein spacing between adjacent said transverse wires is 100mm. [0023] In another broad form of the invention, there is 20 provided a mine roof mesh comprising a grid of longitudinal and transverse wires welded at their intersections to form a sheet of said mesh; each of said transverse wires provided with bends to form an array of troughs and apexes extending along at least a central portion of said 25 transverse wires; said longitudinal wires interconnecting - 7 corresponding ones of said troughs and apexes of said transverse wires. [0024] Preferably, opposing outer ends of each said transverse wire includes a straight section; corresponding 5 said straight sections of said transverse wires interconnected by at least two longitudinal wires to form coplanar side portions of said mine roof mesh. [0025] Preferably, said coplanar side portions of said mine roof mesh define a median plane of said mesh; said 10 median plane lying approximately midway between said troughs and apexes of said transverse wires. [0026] Preferably, selected ones of said longitudinal wires are distinguished from remaining said longitudinal wires by colour. 15 [0027] Preferably, said colour of at least some of said selected ones of said longitudinal and/or transverse wires is provided by said selected ones being formed of galvanized wire. [0028] Preferably, said selected ones of said 20 longitudinal wires include a pair of longitudinal side wires at each opposite outer edge of said sheet. [0029] Preferably, said selected ones of said longitudinal wires include a pair of central wires; each wire of said pair symmetrically located at either side of a 25 median longitudinal plane of said sheet; said median - 8 longitudinal plane being normal to said median plane of said sheet. [0030] Preferably, spacing, as projected on said median plane of said sheet, between said pair of central wires is 5 80mm. [0031] Preferably, spacing, as projected onto said median plane of said sheet, between respective ones of said pair of central wires and respective adjacent said longitudinal wires, is less than spacing between remaining 10 said longitudinal wires between said respective adjacent longitudinal wires and said edges of said sheet. [0032] Preferably, said spacing between respective ones of said pair of central wires and respective adjacent said longitudinal wires is 60mm. 15 [0033] Preferably, said spacing between said remaining longitudinal wires between said respective adjacent longitudinal wires and said edges of said sheet, is equal. [0034] Preferably, said spacing is 100mm. [0035] Preferably, spacing between adjacent said 20 transverse wires is 100mm. [0036] Preferably, at least two selected pairs of transverse wires are differentiated in appearance from remaining said transverse wires. [0037] Preferably, said at least two pairs of transverse 25 wires are distinguished by colour applied as a layer of coloured galvanizing.

- 9 [0038] Preferably, said at least two pairs of transverse wires are distinguished by a variation in cross sectional area. [0039] Preferably, at least two selected pairs of 5 transverse wires are distinguished from remaining said transverse wires; each of said selected pairs comprising a first additional transverse wire and a second additional transverse wire; each of said additional transverse wires located near respective transverse wires of a said selected 10 pair. [0040] Preferably, intersections of said pair of central longitudinal wires and said pairs of longitudinal side wires with said at least two pairs of transverse wires define regions indicating preferred locations of rock 15 bolts. [0041] Preferably, all of said longitudinal wires lie on the same side of said transverse wires, so that said mesh is comprised of two layers of wires only. [0042] Preferably, said array of troughs and apexes of 20 said transverse wires comprises four troughs and five apexes. [0043] Preferably, said transverse and said longitudinal wires are of the same cross sectional dimension. [0044] Preferably, said dimension is 5mm diameter.

- 10 [0045] Preferably, cross sectional dimension of said longitudinal wires is different from cross sectional dimension of said transverse wires. [0046] Preferably, said dimension of said transverse 5 wires is 5.6mm diameter. [0047] Preferably, overall width of a sheet of said mine roof mesh between opposing outer edges is approximately 1.2m. [0048] In another broad form of the invention, there is 10 provided a method of manufacture of a mine roof mesh; said mine roof mesh formed of longitudinal and transverse wires welded at their intersections; said transverse wires formed with a number of bends into an array of troughs and apexes; said method including the steps of: 15 (a) placing an array of a predefined number of parallel longitudinal wires forming a first layer of said mesh, (b) placing an array of a predefined number of parallel transverse wires over said first layer to form a 20 second layer of said mesh, (c) welding wires of said second layer to wires of said first layer at their intersections to form a substantially planar sheet of said mesh, (d) drawing said sheet of said mesh through a series of 25 arrays rollers of a rollformer assembly.

- 11 [0049] Preferably, a first array of rollers of said rollformer assembly deflect to a first degree, intersections of selected longitudinal wires along each said transverse wire, alternately out of a median plane 5 of said planar sheet in a first direction and a second opposite direction to form respectively troughs and apexes; said first direction and said second direction being normal to said median plane. [0050] Preferably, subsequent said arrays of said series 10 of rollers of said rollformer assembly deflect in incrementally increasing degrees, said intersections of selected longitudinal wires along each said transverse wire alternately out of a median plane of said planar sheet in said first direction and in said second opposite 15 direction; said deflections increasing incrementally until longitudinal wires connecting respectively said troughs and apexes define an upper and a lower plane. [0046] Preferably, said upper and lower plane are separated by approximately 35mm. 20 [0051] In another broad form of the invention, there is provided a method of providing for deflection in a sheet of mine roof mesh when a load is applied to an area of said mesh intermediate rock bolts securing said mesh to mine roof strata; said method including the steps of: - 12 (a) forming said sheet of mine roof mesh of longitudinal and transverse wires welded at their intersections; (b) forming a number of bends into said transverse 5 wires to form an array of longitudinal troughs and apexes, and wherein said load is in at least a first instance absorbed by a deformation of said troughs and apexes towards a catenary form of said transverse wires; said deformation 10 relieving stress on longitudinal wires adjacent said rock bolts. [0042] In still a further broad form of the invention, there is provided a method of relieving stress in wires of a mine roof mesh adjacent rock bolts securing said mesh to 15 mine roof strata; said stress induced by loads applied to said mesh by dislodged strata at an area of said mesh intermediate said rock bolts; said method including the steps of: (a)forming said mine roof mesh of longitudinal and 20 transverse wires welded at their intersections; (b)providing an array of bends along at least a central portion of said transverse wires to form an array of longitudinal troughs and apexes in said mesh. 25 - 13 BRIEF DESCRIPTION OF DRAWINGS [0053] Embodiments of the present invention will now be 5 described with reference to the accompanying drawings wherein: Figure 1 is a plan view of a sheet of a mine roof mesh according to a preferred embodiment of the invention. Figure 2 is an end view of the sheet of mine roof mesh 10 of Figure 1. Figure 2A is an alternative end view of the mine roof mesh of Figure 1. Figure 2B to 2D are further alternative end views of the mine roof mesh of figure 1. 15 Figures 3 and 4 are plan views of a sheet of a mine roof mesh according to further preferred embodiments of the invention. Figure 5 is a plan view of one of the further preferred embodiments of the mine roof mesh of Figure 4 20 overlapping with a portion of a like sheet of mine mesh. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS First Preferred Embodiment [0055) With reference to Figures 1 and 2, a preferred 25 embodiment of a mine roof mesh 10 according to the invention comprises a grid of longitudinal wires 12 and - 14 transverse wires 14, welded together at their intersections 16. Each of the transverse wires 14 is provided with bends 18 to form an array of troughs 20 and apexes 22 extending along at least a central portion of the transverse wires 5 14. [0056] It can be seen that all of the longitudinal wires 12 lie on the same side of the transverse wires 14, so that the mesh 10 is comprised of two layers of wires only. The transverse and longitudinal wires in one preferred 10 arrangement, are of the same cross sectional dimension, preferably 5mm in diameter. In another preferred arrangement, the transverse wires may be of a larger cross sectional area, preferably 5.6mm in diameter. [0057] As can best be seen in the end view of a sheet 10 15 of the mesh in Figure 2, opposing outer ends of each of the transverse wires 14 comprise a straight section 24 and 26 respectively. These straight sections at either end of the transverse wires 14 are interconnected by at least two longitudinal wires 12 to form coplanar side portions of the 20 mine roof mesh, parallel to a median plane 25 of the sheet. [0058] In a first preferred arrangement as shown in figure 2, the first wire of each of the two wires lies adjacent to the first bend 11 and the second at the outer end of the transverse wires 14. 25 [0059] These coplanar side portions 24 and 26 of the sheet of mesh 10, may lie in the median plane 25 - 15 approximately midway between the troughs 20 and apexes 22 of the transverse wires 14. [0060] In some preferred forms at least as shown in figure 2B, the area of the sheet of mesh 10 in which the 5 transverse wires 14 are provided with troughs and apexes may extend from a first edge 13 of the sheet, substantially to the opposite second edge 15 of the sheet, leaving just one straight section 24A at the second edge. [0061] In yet other preferred arrangements, the side 10 portions 24 and 26 (or single side portion 24A) are not coplanar but lie at different levels both relative to each other and relative the median plane 25, as shown by way of example in figure 2C. Alternatively, the side portions may be coplanar but extend either at the level of the apexes or 15 the troughs. [0062] In a further alternative arrangement shown in figure 2D, the straight side portions 24 and 26 may include a pair of closely spaced wires 12D and 12E at the outer ends of the transverse wires of the sheet. 20 [0063] In one preferred form, the arrangement of the longitudinal wires 12 includes selected wires which are distinguished in appearance from the remainder of the longitudinal wires. In a preferred arrangement the selected longitudinal wires may firstly include one central pair of 25 wires 12A. Preferably, the spacing as projected on the median plane 25 of said sheet, between this pair of central - 16 wires is 80mm. Each longitudinal wire of the pair of longitudinal wires 12A is located symmetrically about a longitudinal median plane 27 normal to the median plane 25 of the sheet of mesh 10. Spacing, again as projected onto 5 said median plane of the sheet, between respective ones of the pair of central wires 12A and respective adjacent longitudinal wires, is less than the spacing between the remaining longitudinal wires located between these respective adjacent longitudinal wires and the edges of the 10 sheet. Preferably, this lesser spacing is 60mm. [0064] In addition to the pair of central wires 12A, the selected differentiating longitudinal wires may include the pair of longitudinal side wires, 12B and 12C respectively, at each opposite outer edge of the sheet 10. 15 [0065] These pairs of wires, the central pair 12A and the two outer side edge pairs 12B and 12C, are differentiated in appearance by the application of either plain or coloured galvanizing, thereby assisting at installation by defining preferred locations of rock bolts. 20 This process comprises drawing the wire to be colour differentiated through a hot zinc bath. [0066] The spacing between these pairs of edge wires is equal to the spacing between the remaining longitudinal wires and is preferably 100mm. 25 [0067] Preferably, the transverse wires 14 of the mine roof mesh of the invention include four troughs 20 and five - 17 apexes 22. Preferably, spacing along the transverse wires 14 between adjacent apexes 22 and between adjacent troughs 20 is approximately 170mm, with preferred spacing between adjacent transverse wires 14 being 100mm. 5 Second Preferred Embodiment [0068] In this second preferred embodiment, the transverse wires are not formed into troughs and apexes, but are straight so as to form a flat sheet of mesh as shown in the end section view of Figure 2A. The pattern of 10 longitudinal wires 12, transverse wires 14 as well as the distinguishing appearance of the central pair of wires 12A and the two side pairs 12B and 12C remain as described for the first preferred embodiment above. Third Preferred Embodiment 15 [0069] With reference to figure 3, there is illustrated a further embodiment wherein like components are numbered as for previous embodiments. In this instance, additional definition is provided for selected transverse wires, in this instance comprising at least two pairs of adjacent 20 transverse colour distinguished wires 14D located at some distance from the opposite outer ends of the sheet of mesh 10. [0070] In this embodiment these at least two pairs of wires 14D are also distinguished in colour by the 25 application of plain or coloured galvanizing. It can be seen that where the coloured pairs of wires 14D cross over - 18 the selected longitudinal pairs of coloured wires 12A, 12B and 12C, the coloured wires identify regions 30 as preferred bolting sections. Fourth Preferred Embodiment 5 [0071] In this further preferred embodiment of the invention, the sheet of mesh may be formed with the transverse wires 14 either provided with the troughs and apexes described above or straight to form a flat sheet of mesh. Again as described for the earlier embodiments, a 10 central pair of longitudinal wires 12A may be provided, as well as two side pairs of longitudinal wires 12B and 12C respectively, which are distinguished from the remaining wires by the application of plain or coloured galvanizing. [0072] In this embodiment also, at least two selected 15 pairs of transverse wires, located at some distance from the opposite ends of the sheet of mesh, are distinguished from the remaining transverse wires. Each pair comprises a first transverse wire 14A together with an additional transverse wire 14AA, each located near to respective 20 adjacent transverse wires 14. [0073] The intention of these additional wires is to define visually, in combination with the colour distinguished longitudinal wire pairs, regions 30 which act as visual templates or guides for location of rock bolts or 25 like fixing devices therebetween. The pairs of wires 14A and 14AA may or may not be plain or colour galvanized.

- 19 [0074] In alternative forms, the visual boundary is defined by use of wires 14A and 14AA of different cross sectional area to the adjacent wires. In a further alternative form, the visual boundary can be defined by 5 varying the density of wires in the regions 30 compared to other regions of the mesh. In yet further forms the regions 30 are defined by reference to components from overlapping ones of the mesh sheets as shown in Figure 5. [0075] In a further alternative form, the visual 10 boundary can be defined by varying the colour of one or more of wires 14,14A,14AA so as to define region 30 by reference to colour. [0076] That is, regions 30 can be defined by reference to one or more of colour of wires or cross section of wires 15 or density of wires. [0077] In preferred forms the number of regions 30 on a single mesh panel lies in the range 3 to 8. Manufacture 20 [0078] Sheets of the mine roof mesh of embodiments of the invention may be manufactured as a planar sheet of mesh in conventional manner. That is, the longitudinal and transverse wires may be cut from stock wire drawn from coils and passed through wire straighteners, as well known 25 in the industry. In the present preferred arrangement, the colour galvanized longitudinal wires are drawn from a - 20 separate coil source. The colour may be any suitable colour including the conventional silvery colour associated with plain galvanising or can be red, blue, black or any other colour which can serve to visually distinguish wires so 5 treated from wires not so treated in the mesh sheet. [0079] In a semi automatic process, these prepared lengths of wires are laid into the required grid pattern with an array of welding heads passing sequentially along the length of the sheet to weld the longitudinal and 10 transverse wires together at their intersections. Alternatively, the planar sheet may be formed by means of a fully automated, welded mesh forming machine. [0080] In those embodiments of the present invention in which the transverse wires are to take the form of troughs 15 and apexes, as in the first preferred embodiment above, a planar welded mesh sheet produced by either of these two methods is passed through a roll forming process. A rollformer assembly comprises a series of arrays of rollers; each array including an upper row of rollers and a 20 lower row. Each array includes one lower roller for forming each apex bend and one upper roller for each trough bend. [0081] A first array of rollers of the rollform assembly deflects to a first degree, intersections of the longitudinal wires along a transverse wire alternately out 25 of a median plane of the planar sheet in a first direction and a second opposite direction, both directions normal to - 21 the median plane of the sheet, to form respectively troughs and apexes. Each subsequent array of rollers of the series induces further deflections until the desired angle of the bends forming the troughs and apexes is achieved and the 5 longitudinal wires of the troughs and apexes define an upper and a lower plane separated by approximately 35mm. In Use [0082] In use, the mine roof mesh sheets of the 10 invention are secured to the roof of a mining area in the conventional manner. That is, sheets of mesh are positioned against the roof strata and holes a-e drilled in the roof strata as indicated by the rockbolt locations provided by the sheet for insertion of rock bolts. Rock bolts comprise 15 long steel shafts, threaded at their proximate ends and secured in the holes at their distal end by either mechanical of chemical means. The mesh sheet is then secured in position by placing steel plates over the proximate ends of the rock bolts. These plates are of a 20 size sufficient to overlap adjacent longitudinal and transverse wires of the mesh. A washer and nut secures the plate and the mesh in position against the strata. [0083] An advantage of certain embodiments of the invention is that the preferred location or region for 25 insertion of rock bolts or like fixing devices is defined visually for the installers. In further particular forms, - 22 the region 30 is defined two-dimensionally utilizing either colour, or a combination of colour and variation in wire density, so as to define a bounded region. [0084] A further advantage of particular forms of the 5 present mine roof mesh of the invention having troughs and apexes in the transverse wires, lies in their ability to at least reduce the likelihood of failure of the mesh at the rock bolt locations when force is applied to the mesh by dislodged strata at areas intermediate the rock bolts. In 10 conventional planar meshes such force is translated into tension forces transmitted through the mesh and concentrating at the rock bolt locations. This can cause breaking of the wires at the rock bolts with the possibility of the mesh failing to restrain the strata. 15 [0085] The arrangement of certain embodiments of the present mine roof mesh provide for deformation of the troughs and apexes towards a catenary form of the transverse wires when the mesh is placed under load by dislodged strata. This deformation, resisted by the tensile 20 strength of the transverse wires, relieves stress on the longitudinal and transverse wires adjacent the rock bolts. [0086] The above describes only some embodiments of the present invention and modifications, obvious to those 25 skilled in the art, can be made thereto without departing from the scope of the present invention.

Claims (5)

1. A mine roof mesh comprising a grid of longitudinal and transverse wires welded at their intersections to form a sheet of said mesh; and wherein each of said 5 transverse wires is provided with bends to form an array of troughs and apexes extending along at least a portion of said transverse wires; said longitudinal wires interconnecting corresponding ones of said troughs and apexes of said transverse wires. 10

2. The mine roof mesh of claim 1 wherein selected adjacent ones of said longitudinal wires and/or transverse wires are distinguished by colour thereby to define a visual template or guide for insertion of rockbolts or like fixing devices therebetween. 15

3. The mine roof mesh of claim 2 wherein said colour of at least some said selected ones of said longitudinal and/or transverse wires is provided by said selected ones being formed of galvanized wire.

4. The mine roof mesh of claim 1 or 2 wherein said 20 selected ones of said longitudinal wires include a pair of longitudinal side wires at each opposite outer edge of said sheet.

5. The mine roof mesh of claim 4 wherein each said outer edge of said sheet comprises a straight edge portion of 25 said sheet extending laterally from said portion formed with said troughs and apexes; each said edge portion - 24 parallel to a mid plane of said sheet passing through mid points between respective said troughs and apexes.