AU2006252071A1 - Rock bolt tip, rock bolt & associated methods - Google Patents

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

Name of Applicant(s): Actual Inventor(s): Address for Service: Invention Title: Details of Associated Provisional Application: Industrial Roll Formers Pty Ltd David James FERGUSSON FRASER OLD SOHN Patent Attorneys PO Box 560 MILSONS POINT NSW 1565 Rock Bolt Tip, Rock Bolt Associated Methods Australian Provisional Application No. 2005 907 150 Filed 19 December 2005 The following statement is a full description of this invention, including the best method of performing it known to us: 2945DN-AU INO Field of the Invention The present invention relates to rock bolts and, in particular, to rock bolts 0 which are installed using a cartridge of resin or similar such chemical anchor.

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00 5 Background Art In general rock bolts can be divided into two main classes. One class uses a cartridge, generally having an appearance similar to that of a sausage, which is able to be ruptured and which contains two constituents which when mixed together harden to form a chemical anchor. Australian Patent No. 739,333 (the JUMBOLT) is O 10 representative of this art. The other class uses grout which is a flowable hardenable cementitious substance which is normally pumped into a tube associated with the rock bolt and which directs the grout to the rear of the hole. The grout under pressure then flows back around the rock bolt and finally exits from the hole, at which stage the pumping ceases.. Australian Patent No. 669,393 (the CT bolt) and Australian Patent Application No. 2003 232 521 (the CTT bolt) are representative of this art.

In addition to providing a mechanical interlock between the rock bolt and a hole, the resin or grout also provides a chemical coating which provides corrosion protection for the rock bolt. It is generally considered that grout is superior to resin in terms of corrosion protection since the grout is supplied under high pressure and is therefore more likely to permeate or infiltrate all the spaces around the rock bolt.

The genesis of the present invention is a desire to improve the installation of rock bolts which are installed using a resin cartridge.

Summary of the Invention According to a first aspect of the present invention there is disclosed a tip for the leading end of a rock bolt, said tip being plastically deformed by shearing in two opposite directions substantially transverse to the longitudinal axis of the bolt to form two part paddles which extend beyond the outer transverse dimension of the undeformed shank of the tip.

According to second aspect of the present invention there is disclosed a method of forming the tip of the leading end of a rock bolt, said method comprising the step of 2945DN-AU INO plastically deforming said tip to shear same in two opposed directions substantially transverse to the longitudinal axis of said tip.

d.) SAccording to another aspect of the present invention there is provided a method of oO 5 installing a rock bolt as defined above in a blind hole drilled in a rock or mineral surface, said method comprising the steps of: placing a two-part rupturable cartridge in said hole, (ii) placing the tip of said rock bolt into said hole, (iii) rotating said rock bolt whilst advancing same into said hole to thereby rupture O 10 said cartridge and mix the constituents thereof, and (iv) continuing step (iii) to drive said bolt fully into said hole to force said mixed constituents into the annular space between said bolt and hole.

Brief Description of the Drawings Some embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Fig. 1 is a truncated perspective view of a rock bolt of a first embodiment, Fig. 2 is perspective view of the tip of a rock bolt of a second embodiment, Fig. 3 is a longitudinal cross-sectional view through the rock bolt of the second embodiment installed in a blind hole drilled in a rock or mineral surface, and Fig. 4 is a perspective view similar to Fig. 2 but showing a tip of a third embodiment.

Detailed Description As seen Fig. 1, the rock bolt 10 of the first embodiment has a solid shaft of 11 which is threaded at the trailing end 12 and plastically deformed at the leading end 13.

At the trailing end 12 is provided in substantially conventional fashion a strata plate 14, a nut 15 and a shear pin 16. At the leading end 13, the tip 18 is plastically deformed by applying two forces in opposite directions transverse to the longitudinal axis of the bolt 10 in the manner disclosed in Australian Patent No. 751,611 (the SECURA-BOLT). These forces create a half paddle 19 having two blades 21, 22 which are similar to the blades of a fan or propeller.

2945DN-AU ICIn a second embodiment, a tip 118 is not integrally formed as in Fig. 1 but instead is detachably formed and is provided with a threaded stub 25 which, as Sillustrated in Fig. 3, is threadably engaged with the hollow stem of a rock bolt Again the tip 118 is plastically deformed so as to create the half paddle 19 and two 00o 5 blades 21, 22. The trailing end of the rock bolt 30 is substantially similar to the trailing end of the rock bolt In order to install the rock bolt 10 or 30, a blind hole 33 as illustrated in Fig. 3 is drilled in a rock or mineral surface 35. The length of the blind hole 33 should be only just longer than the length of the corresponding rock bolt 10, 30. One or more resin cartridges (not illustrated but conventional) are inserted into the blind hole 33 in advance of the tip 18, 118. The rock bolt is then spun (that is rotated about its longitudinal axis) utilising the nut 15 and the shear pin 16 which interconnects the nut with the bolt 10, 30. In this way the bolt is able to be rotated about its longitudinal axis so that the tip 18, 118 both shreds the cartridge and mixes the constituents thereof. In addition, the bolt 10, 30 is advanced longitudinally down the blind hole 33 so that the tip 18, 118 approaches the end of 34 of the blind hole 33.

During the spinning and advancing procedure, the blades 21, 22 of the half paddle 19 not only mix the resin 40 but also propel it forwardly towards the end 34.

As the bolt advances down the hole 33, the mixed resin 40 is placed under pressure and is forced past the blades 21, 22 and extends down the hole 33 towards the surface thereby completely coating the exterior surface of the bolt with the resin 40 as illustrated in Fig. 3. In addition, the resin 40 is also forced under pressure into the small cracks, fissures and like cavities in the rock or mineral thereby providing exceptional keying between the resin 40 and the rock or mineral.

After a short interval, typically 1-3 minutes, the resin 40 hardens. During this hardening interval, the bolt 10, 30 is not rotated. However, at the expiration of this hardening interval, the nut 15 is again rotated which has the consequence that the shear pin 16 fractures and the nut 15 is then advanced along the threaded trailing end 12 so as to clamp the strata plate 14 against the rock or mineral surface 35 and place the rock bolt 10, 30 in tension. This has the desired consequence of placing the rock or mineral in compression.

2945DN-AU IDIn experimental results to date, the applicants have experienced the need for considerable force in advancing the rock bolt 10, 30 down a hole 33 (modelled by a o cylindrical tube having one end closed). This is thought to be due to considerable resin pressure building up within the hole 33 as a consequence of the engagement 00 5 between the half paddle 19 with its blades 21, 22 and the resin It is known from the abovementioned Australian Patent No. 751,611 to form full paddles at spaced apart intervals along the shank of a rock bolt having a solid t shank. These full paddles are not formed at the leading end of the rock bolt. The O 10 purpose of these full paddles is to provide a mixing action for the resin. However, no substantial difficulty is encountered in advancing such prior art rock bolts with paddles into the hole in which they are to be installed. As a consequence, there can be no build up of pressure within the blind hole.

In a still further embodiment illustrated in Fig. 4, a hollow tip 218 is shown formed into the half paddle 19 by the same shearing deformation so as to produce two concave blades 121, 122. The tip 218 can be integrally formed with a rock bolt shank of tubular configuration, or can be detachably positioned at the leading end of a rock bolt shaft.

In coal mining, rock bolts having solid shafts are preferred since the drilling equipment used in coal mining is only able to drill relatively narrow blind holes 33.

However, in hard rock mining the drilling equipment drills relatively wide holes 33 and thus rock bolts having hollow shafts are to be preferred since this results in a saving of the volume of steel required to fabricate the rock bolt.

The foregoing describes only some embodiments of the present invention and modifications, obvious to those skilled in the rock bolt arts, can be made thereto without departing from the scope of the present invention.

The term "comprising" (and its grammatical variations) as used herein is used in the inclusive sense of "including" or "having" and not in the exclusive sense of "consisting only of".

2945DN-AU

Claims (13)

1. A tip for the leading end of a rock bolt, said tip being plastically deformed by o shearing in two opposite directions substantially transverse to the longitudinal axis of the bolt to form two part paddles which extend beyond the outer 00 transverse dimension of the undeformed shank of the tip.

2. The tip as claimed in claim 1 wherein said shank is substantially cylindrical _and said outer transverse dimension comprises the outer diameter of said shank.

3. The tip as claimed in claim 1 or 2 wherein said tip is attached to the leading INO end of said rock bolt.

4. The tip as claimed in claim 1 or 2 wherein said tip is integrally formed with said rock bolt. The tip as claimed in claim 3 or 4 wherein said rock bolt is solid.

6. The tip as claimed in claim 3 or 4 wherein said rock bolt is substantially tubular.

7. A tip for a rock bolt, said tip being substantially as herein described with reference to Fig. 1 or Figs. 2 and 3 or Fig. 4 of the drawings.

8. A rock bolt having a tip as claimed in any one of claims 1-7.

9. A rock bolt substantially as herein described with reference to Fig. 1 or Figs. 2 and 3 or Fig. 4 of the drawings A method of forming the tip of the leading end of a rock bolt, said method comprising the step of plastically deforming said tip to shear same in two opposed directions substantially transverse to the longitudinal axis of said tip.

11. The method as claimed in claim 10 including the step of applying two shear forces in opposite directions, said forces being substantially equally displaced one to either side of the longitudinal axis of said tip.

12. The method as claimed in claim 12 including the step of threading at least part of the tip.

13. The method as claimed in any one of claims 10-12 wherein said tip is hollow.

14. A method of forming the tip of the leading end of a rock bolt, said method being substantially as herein described. A method of installing a rock bolt as claimed in claim 8 in a blind hole drilled in a rock or mineral surface, said method comprising the steps of: placing a two-part rupturable cartridge in said hole, 2945DN-AU O (ii) placing the tip of said rock bolt into said hole, (iii) rotating said rock bolt whilst advancing same into said hole to thereby o rupture said cartridge and mix the constituents thereof, and (iv) continuing step (iii) to drive said bolt fully into said hole to force said 00 mixed constituents into the annular space between said bolt and hole.

16. The method as claimed in claim 15 including the further step of: waiting for said mixed cartridge constituents to harden and then tensioning said bolt. S17. A method of installing a rock bolt, said method being substantially as herein INO described with reference to the drawings. Dated this 15' h day of December 2006 INDUSTRIAL ROLL FORMERS PTY LIMITED By FRASER OLD SOHN Patent Attorneys for the Applicants 2945DN-AU