AU2012202308B2 - Mining rock bolt - Google Patents

Abstract

A MINING ROCK BOLT A mining rock bolt (100) comprises a longitudinally extending rigid bar (101) having a leading end portion (106) and a threaded trailing end portion (102). The mining rock bolt (100) further comprises a wire (105) fixed to and helically extending along the leading end portion (106) of the bar (101) and a ferrule (107) crimped onto the bar (101). The ferrule (107) fixes a trailing end (105b) of the wire (105) to the bar (101) without welding of the ferrule (107) or the trailing end (105b) of the wire (105) to the bar (101). 16-7 k05 z 103 o toc~l~4V 05 lob' Fig. 2 Fig. 1

Description

S&F Ref: P032450 AUSTRALIA PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name and Address DYWIDAG-Systems International Pty Limited, of Applicant: an Australian company, ACN 093 424 349, of 25 Pacific Highway, Bennett's Green, New South Wales, 2290, Australia Actual Inventor(s): David William Evans Andrew Simon Boychuk Address for Service: Spruson & Ferguson St Martins Tower Level 35 31 Market Street Sydney NSW 2000 (CCN 3710000177) Invention Title: Mining rock bolt Associated Provisional Application Details: [33] Country: [31] Appl'n No(s): [32] Application Date: AU 2011901499 20 Apr 2011 The following statement is a full description of this invention, including the best method of performing it known to me/us: 5845c(6214916_1) 1 MINING ROCK BOLT Field of the Invention 100011 The present invention relates to strata control in mining operations, and in particular relates to a rock bolt for securing the roof or wall of a mine. Background of the Invention [00021 One known method of stabilizing the roof or wall of an underground mine is to secure a rock bolt into a bore hole drilled into the face of the rock to be stabilized. Rock bolts are typically formed of a rigid steel bar with a trailing end portion of the bar being threaded over a length typically equal to about 150 mm. 10003] A known method of installing a rock bolt involves first drilling a bore hole into the rock face. A sausage-like two-component resin filled cartridge is then inserted into the bore hole, followed by the rock bolt which pushes the resin filled cartridge towards the top of the bore hole. The rock bolt is then rotated by the installation rig which also thrusts the rock bolt upwardly whilst it is rotating to mix the resin components and shred the frangible cartridge casing, pushing it towards the tip of the bore hole. Rotation of the rock bolt is then stopped for a few seconds to allow the resin to cure. The bolt is then tensioned by threading a nut along the threaded trailing end portion of the rock bolt, bearing the nut against a plate washer that engages the rock face adjacent to the bore hole opening. [00041 To assist in mixing of the resin, it has previously been proposed to secure a helically extending wire to the leading end portion of the bar forming the rock bolt. The wire forms a helical protrusion on the surface of the bar and assists in mixing of the resin. This is particularly advantageous in hard rock mining applications where oversized bore holes are typical, leaving a relatively large annulus between the rock bolt and the wall of the bore hole which results in the plain bar typically being unable to adequately mix the resin. In a previously proposed configuration, the helical wire has been fixed to the bar at its leading and trailing ends (and typically partway along its length) by welding the wire to the bar. The present inventors have found, however, that this may unacceptably weaken rock bolts formed of high tensile steel as a result of the heat generated by the welding process annealing the high tensile steel, thereby adversely affecting its desired high tensile properties that have been introduced into the bar during initial manufacture and heat treatment.

2 Object of the Invention [0005] It is the object of the present invention to substantially overcome or at least ameliorate one or more of the above disadvantages, or at least to provide a useful alternative to current mining rock bolts. Summary of the Invention [0006] The present invention provides a mining rock bolt comprising: a longitudinally extending rigid bar having a leading end portion and a threaded trailing end portion; a wire secured to and helically extending along said leading end portion of said bar; and a ferrule crimped onto said bar; wherein said ferrule fixes a trailing end portion of said wire to said bar without welding of said ferrule or said trailing end of said wire to said bar. [0007] In a preferred form, said trailing end of said wire is sandwiched between said ferrule and said bar. [0008] In an alternate form, said trailing end of said wire is secured to an exterior face of said ferrule. [0009] In one specific alternate form, said trailing end of said wire is welded to said exterior face of said ferrule. [0010] Preferably, said ferrule is crimped around substantially its entire periphery. [0011] In a second aspect, the present invention provides a method of securing a mine roof or wall, said method comprising: drilling a bore hole in a rock face of the roof or wall to be secured; providing a mining rock bolt as defined above; mounting a washer and drive nut onto said trailing end portion of said bar; inserting a two-component resin filled cartridge into said bore hole; inserting said rock bolt into said bore hole with said leading end portion of said bar leading; 3 thrusting said rock bolt towards the end of said bore hole, thereby rupturing said cartridge; rotatably driving said drive nut together with said bar, thereby mixing said resin with said wire; allowing said resin to cure; and rotatably driving said drive nut along said threaded trailing end portion of said bar, bearing said washer against said rock face to tension said bar. Brief Description of the Drawings 100121 A preferred embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings wherein: 100131 Figure 1 is a front elevation view of a rock bolt; [00141 Figure 2 is a cross-section of the rock bolt of Figure 1 taken at section 2-2 of Figure 1; and [00151 Figure 3 is a partially cross-sectioned front elevation view of a rock bolt installation incorporating the rock bolt of Figure 1. Detailed Description of the Drawings 100161 Referring to the accompanying drawings, a mining rock bolt 100 comprises a longitudinally extending rigid bar 101. The bar 101 is a standard bar as otherwise used in mining rock bolting applications, being formed of steel and having a threaded trailing end portion 102. The threaded trailing end portion 102 of the bar 101 typically has a length of the order of 150 mm, but in some applications may have a length of about 300 mm. The threaded trailing end portion 102 of the bar 101 typically has a thread major diameter of between 12 mm and 30 mm, with common diameters being 16 mm, 20 mm and 24 mm. In the specific arrangement depicted, the thread major diameter is 24 mm. A coarse left-handed helical thread 103, formed by a series of protrusions on the bar, extends from adjacent the trailing end portion 102 of the bar 101 to the leading end 104 of the bar 101 in a standard manner. 100171 A wire 105, typically formed of steel and here having a diameter of approximately 3.15 mm, is secured to and helically extends along a leading end portion 106 of the bar 101. The wire 105 preferably helically extends in a direction opposing the intended direction of rotation of 4 the bolt 100 during installation. Accordingly, for installation of the rock bolt 101 with a standard left-handed installation rig, the wire 105 will helically typically extend in a right-handed direction as depicted in the accompanying drawings. The wire 105 will typically extend over a length of leading end portion 106 of the bar which is intended to be resin anchored. Lengths of the order of 500 mm will be typical. 100181 A trailing end portion 105b of the wire 105 is fixed to the bar 101 by way of a ferrule 107. During production of the bolt 100, the wire 105 is positioned on the bar 101 with the leading end 105a of the wire 105 located adjacent the leading end 104 of the bar 101. The ferrule 107 is then positioned over the trailing end portion 105b of the wire 105, typically with the trailing end of the wire 105 located near the trailing end of the ferrule 107 so as to provide the maximum overlap of the wire 105 located within the ferrule 107. The ferrule 107 is then crimped onto the bar 101, thereby sandwiching the trailing end portion 105b of the wire 105 between the ferrule 107 and the bar 101. Two sets of opposing crimps 109 may be applied to the ferrule 107, typically with the two crimps 109 being mutually perpendicular. Alternatively, and preferably, the ferrule 107 is radially crimped around substantially its entire periphery, thereby minimizing the profile of the crimped ferrule. 100191 Securing the trailing end portion 105b of the wire 105 to the bar 101 in this manner, without the use of any welding, avoids any detrimental heating of the bar adjacent the trailing end portion 105b of the wire 105, which may otherwise weaken the bar and subject it to premature failure. It is also envisaged, though less preferred, that the trailing end portion 105b of the wire 105 may be secured to the bar by first crimping the ferrule 107 to the bar 101 and then subsequently securing the trailing 105b of the wire 105 to the exterior face of the ferrule 107 by welding or other means. Whilst welding the trailing end 105b of the wire 105 to the exterior face of the ferrule 107 will still result in heating of the underlying bar 101, given that the wire 105 is not welded directly to the bar 101 will result in a significantly lower heat load being applied to the bar 101 such that there might not be any significant weakening of the bar. [0020] As the loads carried by the leading end 104 of the bar 101 are significantly less than those carried partway along the bar (and in fact effectively zero at the extreme leading end of the bar), degradation of the load bearing characteristics of the bar 101 at the leading end 104 of the bar 101 is not of particular concern and, accordingly, the leading end 105a of the wire 105 may be simply welded directly to the bar 101 adjacent the leading end 104 of the bar 101.

5 100211 It is also envisaged, however, that the leading end 105a of the wire 105 may be fixed to the bar 101 by any other suitable means, including by way of a further crimped ferrule or by locating the leading end 105a of the wire 105 in a laterally extending slot which may be formed in the leading end 104 of the bar 101. [0022] The threaded trailing end portion 102 of the bar 101 may be fitted with standard end fittings in a known manner, including a drive nut 110, anti-friction washer 111 and ball washer 112. The drive nut 110 will typically be provided with a mechanism which fixes the drive nut 110 onto the threaded trailing end portion 102 of the bar 101 up to a predetermined torque at which the mechanism fails, enabling the drive nut 110 to be threadingly advanced along the threaded trailing end portion 102 of the bar 101. Such mechanism may take the form of a disc shaped insert 113 located in the trailing end of the aperture extending through the drive nut 110. The insert 113 engages the trailing end 114 of the bar 101 as the drive nut 110 attempts to advance, locking the drive nut 110 onto the bar 101 until a predetermined torque is exceeded, at which the insert 113 is ejected from the drive nut 110, allowing the drive nut 110 to advance along the trailing threaded portion 102 of the bar 101. Such a drive nut 110 housing an insert 113 is described in Australian Patent Publication No. AU 2007201848 Al, the entire contents of which are incorporated herein by cross-reference. Other known mechanisms for electively fixing the drive nut 110 to the bar 101 may, however, be utilized as desired. [0023] Figure 3 depicts a rock bolt installation utilising the rock bolt 100. The anti-friction washer 111, ball washer 112 and drive nut 110 are mounted on the threaded trailing end portion 102 of the bar, along with a standard plate washer 115. A bore hole 201 is drilled into the rock face 200 then a two-component resin filled cartridge is inserted into the bore hole 201. In hard rock applications, for a bar having a threaded end portion with a 24 mm major thread diameter, a bore hole having a diameter of approximately 35 mm would be typical. [00241 A two-component resin filled cartridge is then inserted into the bore hole 201. The rock bolt 100, with the assembled anti-friction washer 111, ball washer 112 and plate washer 115 is then inserted into the bore hole 201 with the leading end 104 of the bar 101 leading, pushing the resin filled cartridge up the bore hole 201 as the rock bolt is advanced. The rock bolt 100 is thrust towards the end of the bore hole 201, utilizing a standard rock bolt installation rig, rupturing the cartridge. At the same time, the installation rig rotates the drive head 110 of the rock bolt 100. The insert in the drive nut 110 retains the drive nut 110 in a fixed relationship to the bar 101, such that rotation of the drive head 110 results in rotation of the bar 101 in unison 6 with the drive nut 110. The leading end portion 106 of the bar 101, in particular the wire 105, mixes the resin 202. With the wire 105 helically extending in an opposing direction to the direction of rotation of the rock bolt 100, the resin is actively pumped towards the end of the bore hole 201. The resin 202 is then allowed to cure for a few seconds before rotatably driving the drive head 110 at an increased torque that results in failure of the mechanism of the drive nut 110, here the insert, that had locked the drive nut 110 onto the bar. Further torque applied to the drive head 110 thus threads the drive nut 110 along the threaded trailing portion 102 of the bar 101. Continued driving of the drive nut 110 bears the drive nut 110 against the anti-friction washer 111, which in turn bears against the ball washer 112 and plate washer 115 which bears against the rock face 200. Application of further torque to the drive nut 110 tensions the bar 101. Use of the ball washer 112 allows for some misalignment of the bore hole 201 in cases where the bore hole 201 is not drilled at right angles to the rock face 200 or where the rock face is uneven. The ball washer 112 allows the plate washer 115 to still properly engage the rock face 200 in such misaligned installations. 100251 A person skilled in the art will appreciate that various other modifications and alterations of the rock bolt may be made to suit specific applications.

Claims (7)

1. A mining rock bolt comprising: a longitudinally extending rigid bar having a leading end portion and a threaded trailing end portion; a wire fixed to and helically extending along said leading end portion of said bar; a ferrule crimped onto said bar; wherein said ferrule fixes a trailing end of said wire to said bar without welding of said ferrule or said trailing end of said wire to said bar.

2. The mining rock bolt of claim 1, wherein said trailing end of said wire is sandwiched between said ferrule and said bar.

3. The mining rock bolt of claim 1, wherein said trailing end of said wire is secured to an exterior face of said ferrule.

4. The mining rock bolt of claim 3, wherein said trailing end of said wire is welded to said exterior face of said ferrule.

5. The mining rock bolt of any one of claims 1 to 4, wherein said ferrule is crimped around substantially its entire periphery.

6. A method of securing a mine roof or wall, said method comprising: drilling a bore hole in a rock face of the roof or wall to be secured; providing a mining rock bolt as defined in any one of claims 1 to 5; mounting a washer and drive nut onto said trailing end portion of said bar; inserting a two-component resin filled cartridge into said bore hole; inserting said rock bolt into said bore hole with said leading end portion of said bar leading; thrusting said rock bolt towards the end of said bore hole, thereby rupturing said cartridge; rotatably driving said drive nut together with said bar, thereby mixing said resin with said wire; allowing said resin to cure; and 8 rotatably driving said drive nut along said threaded trailing end portion of said bar, bearing said washer against said rock face to tension said bar.

7. A mining rock bolt substantially as hereinbefore described with reference to the accompanying drawings. DYWIDAG-Systems International Pty Limited Patent Attorneys for the Applicant/Nominated Person SPRUSON & FERGUSON