AU5933899A - Rock bolt drive system - Google Patents

Description

S F Ref: 485065

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

Name and Address of Applicant: The ANI Corporation Limited Level 5, Merlin Centre 235 Pyrmont Street Pyrmont NSW 2009

AUSTRALIA

Mieczyslaw Stanlslaw Rataj Actual Inventor(s): Address for Service: Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Wales, 2000, Australia Rock Bolt Drive System Invention Title: ASSOCIATED PROVISIONAL [311 Application No(s) APPLICATION DETAILS [33] Country

AU

[32] Application Date The following statement is a full description of this invention, including the best method of performing it known to me/us:- 5815 1 ROCK BOLT DRIVE SYSTEM FIELD OF THE INVENTION This invention relates to improvements in rock bolting, more particularly to a drive nut adapted for use with a rock bolt.

BACKGROUND OF THE INVENTION A roof of an underground mine is secured, using the rock bolting technique, by the insertion into the roof of a series of rock bolts spaced apart an appropriate distance to accommodate the particular roof material being secured. A hole is first drilled into the roof and a container of resin is then inserted into the hole to form a chemical anchor at the io top end of the hole. A rock bolt is then driven into the hole to puncture the walls of the :"resin container and mix the resin so as to secure the bolt in the hole once the resin has set.

The resin is mixed by spinning the bolt in the resin container, typically by applying torque to a nut threaded onto the bolt. In order to spin the bolt, the nut needs to be locked onto the bolt such that the torque applied to the nut will be transferred to the bolt rather than merely resulting in threading of the nut further along the bolt. However, S-the locking strength (torque) of the mechanism locking the nut on the bolt must be overcome by installation equipment to enable the nut to be threaded along the bolt and S: i tightened against the roof plate once the resin sets in the hole, fixing the bolt.

o:o•• Australian Patent No. 647259 describes a nut fitted with a removable metallic insert adapted for use with a rock bolt. The metallic insert engages the bolt to enable spinning of the bolt in the resin container. When the nut is tightened to a predetermined torque onto the rock bolt after setting of the resin, the removable insert is designed to dislodge from the nut, allowing the nut to be threaded along the bolt against the roof plate. There is a problem in some mines where such metallic or other displaceable inserts fall into the product being mined and are conveyed by production conveyors. The metal inserts can trip metal detectors resulting in automatic stopping of the production conveyors.

Another system being used for the installation of rock bolts consists of a machine washer welded to the bolt. The washer abuts the nut and thereby prevents the nut from unscrewing from the bolt during mixing operations when the nut is rotated in one direction only against the thread direction. The major disadvantage of this system is the [R:\LIBLL08804.doc:TCW:GJG need for bolting equipment which is bi-directional as the nut has to be tightened against the roof plate after resin setting in a direction which is opposite to the direction of resin mixing (spinning). Not all mines are equipped with bolting rigs having left and right hand rotation capabilities. Another disadvantage of this system is the fact that it will s allow for spinning the bolt in one direction only. Sometimes, however, it is necessary to spin the bolt in both directions during mixing of the resin in situations where the strata is cracked. In such areas, spinning of the bolt during resin mixing in one direction only may create an excessive resin pressure, causing much of the resin to be lost through injection into the cracks. Spinning of the bolt in both directions may alleviate the pressure built up in the resin and hence reduce resin loss. Providing for the possibility to spin the bolt in both directions during resin mixing is thus highly desirable.

OBJECT OF THE INVENTION ooooo It is an object of the invention to overcome or substantially ameliorate at least one of the above disadvantages.

.1 5 SUMMARY OF THE INVENTION There is disclosed herein a rock bolt drive system comprising: a rock bolt having an exterior surface threaded along at least a first end portion thereof and a protruberance protruding from, and fixed in relation to, said exterior surface at said threaded first end portion, and a nut having a threaded hole adapted to threadingly engage said rock bolt exterior surface threaded first end portion, an end portion of said threaded hole being countersunk so as to provide a frustoconical wall adapted to engage said protruberance upon threading of said nut along said rock bolt.

Preferably said protruberance is a weld nodule welded to said bolt exterior surface.

Alternatively said protruberance is a pin protruding from a hole provided in said bolt exterior surface.

Alternatively said protruberance is formed by deforming said bolt exterior surface.

[R:\L1BLL]08804.doc:TCW:GJG 3 There is further disclosed herein a method of forming a rock bolt drive system, comprising the steps of: providing a nut having a frustoconical wall defined by a countersunk end portion of the threaded hole of the nut, threading said nut onto a rock bolt from a first end thereof such that said frustoconical wall faces said rock bolt first end, providing a protruberance protruding from, and fixed in relation to, the exterior surface of the bolt between said nut and said rock bolt first end, unthreading said nut until said frustoconical wall engages said protruberance, and torqueing said nut, so as to wedge said frustoconical wall against said V* protruberance, to a predetermined torque, There is still further disclosed herein a method of installing a rock bolt, comprising the steps of: inserting a resin container into a rock bolt hole, providing a rock bolt drive system formed in accordance with the above method, fitting a roof plate to said rock bolt from a second end thereof, inserting said second end of said rock bolt into said bolt hole, piercing said resin container with said rock bolt second end, mixing said resin by rotation of said rock bolt via application of torque to said nut, allowing said resin to set, applying a torque to said nut in a direction opposite to said predetermined torque sufficient to dislodge said frustoconical wall from said protruberance, and engaging said nut with said roof plate.

[R:\LIBLL]08804.doc:TCW:GJG BRIEF DESCRIPTION OF THE DRAWINGS A preferred form of the present invention will now be described by way of example with reference to the accompanying drawings, wherein: Figure 1 is a fragmentary part cross sectional view of a rock bolt drive system according to a first embodiment of the present invention; Figure 2 is a fragmentary part cross sectional view of a rock bolt drive system according to a second embodiment of the present invention; and Figure 3 is a fragmentary part cross sectional view of the rock bolt drive system of Figure 1 installed in a rock bolt hole.

10 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to Figure 1 of the accompanying drawings, a rock bolt 2 has an exterior surface threaded along at least a first end portion 6 thereof and a protruberance protruding from, and fixed in relation to, said exterior surface at said threaded first end portion 6 and a protruberance or restrainer 4 protruding from, and fixed in relation to, the exterior surface at the threaded first end portion 6. The protruberance 4 is affixed to the bolt exterior surface 6 towards a first end 2a of the bolt. The protruberance may be located at the very end of the bolt 2 or may be displaced a short distance from the first 2a end as depicted in Figure 1 so as to provide a length 5 of bolt for placing another nut on the first end 2a of the bolt 2 if required for hanging of mining items from the roof of the mine.

A nut 1 has a threaded hole 8 which threadingly engages the rock bolt exterior surface threaded first end portion surface threaded along at least a first end portion thereof and a protruberance protruding from, and fixed in relation to, said exterior surface at said threaded first end portion 6. An end portion 9 of the threaded hole 8 is countersunk so as to provide a frustoconical wall 3 which, as can be seen in Figure 1, engages the protruberance 4 upon threading of the nut 1 along the rock bolt 2.

The protruberance 4 depicted in Figure 1 is in the form of a weld nodule welded to the bolt exterior surface, however may take any of various forms which will be apparent to the person skilled in the art. For example, as depicted in Figure 2, a protruberance 4' may be in the form of a pin 4' fixed in and protruding from a hole [R:\LIBLL08804.doc:TCW:GJG provided in the bolt exterior surface. Other forms of protruberance may be swaged to the bolt or threadingly engaged with the bolt. It is also envisaged that the protruberance may be formed by deforming of the bolt itself by, for example, crimping.

Whilst some rock bolts are threaded along their entire length, they are typically only provided with a thread at the first end portion 6, necessitating the threading of the nut 1 onto the rock bolt 2 from the first end 2a thereof. Accordingly, in such a case the nut 1 will be threaded onto the bolt 2, with the countersunk end portion 9 forming the frustoconical wall 3 facing the bolt first end 2a, prior to forming of the protruberance 4 between the nut 1 and the bolt first end 2a. The nut 1 is then unthreaded back along the rock bolt 2 until the frustoconical surface 3 engages the protruberance 4. Increasing torque is applied to the nut, resulting in the protruberance being wedged against the frustoconical surface 3 of the nut 1. A predetermined torque is applied in order to obtain a controlled predetermined frictional torque locking the nut 1 on to the bolt 2. This will typically be conducted at the manufacturing stage such that the rock bolt drive system is 0 15 supplied to the mine with the correct torque already applied.

If such a torque were to be applied to a standard nut, without the frustoconical engaging surface, to engage the protruberance, the end threads would be damaged by the protruberance. Such damage of the threads is avoided by the present configuration, along with enabling provision of a controlled frictional locking force as a result of the wedging 20 action of the frustoconical surface 3.

The method of installing the rock bolt utilising the described rock bolt drive system is best described with reference to Figure 3. A resin container 11 forming a chemical anchor is first inserted into a rock bolt hole 12 in the roof of the mine. A roof plate 13 is fitted to the rock bolt 2 from the second end 2b thereof in the usual manner and the bolt second end 2b is then inserted into the rock bolt hole 12, piercing the resin container 11 in the usual manner. The nut can then be rotated by standard bolting equipment, in both directions if the bolting equipment has such capability. As a result of the frictional lock between the nut 1 and bolt 2, such a rotation of the nut 1 will result in rotation of the bolt 2 to mix the resin. The resin is then allowed to set before applying a torque to the nut 1 in a direction opposite to the predetermined torque sufficient to dislodge the frustoconical wall 3 from the protruberance 4, thereby enabling the nut 1 to be threaded along the bolt to engage the roof plate and thereby lock the first end 2a of the rock bolt 2 against the roof of the mine.

[R:\LI BLL]08804.doc:TCW:GJG 6 The torque necessary to dislodge the frustoconical wall 3 from the protruberance 4, and thereby unlock the nut 1 from the bolt 2 will be dependent upon the predetermined torque applied to lock the nut 1 on to the bolt 2. This dislodging torque can thus be accurately selected so as to be sufficient to prevent unlocking of the nut 1 during the resin mixing process, but low enough so as to still to be within the capacity of the torque output of the installation.

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Claims (10)

1. A rock bolt drive system comprising: a rock bolt having an exterior surface threaded along at least a first end portion thereof and a protruberance protruding from, and fixed in relation to, said exterior surface at said threaded first end portion, and a nut having a threaded hole adapted to threadingly engage said rock bolt exterior surface threaded first end portion, an end portion of said threaded hole being countersunk so as to provide a frustoconical wall adapted to engage said protruberance upon threading of said nut along said rock bolt.

2. The system of claim 1 wherein said protruberance is a weld nodule welded to said bolt exterior surface.

3. The system of claim 1 wherein said protruberance is a pin protruding 9* 99 9 from a hole provided in said bolt exterior surface.

4. The system of claim 1 wherein said protruberance is formed by 15 deforming said bolt exterior surface.

5. A method of forming a rock bolt drive system, comprising the steps of: providing a nut having a frustoconical wall defined by a countersunk end portion of the threaded hole of the nut, threading said nut onto a rock bolt from a first end thereof such that said 20 frustoconical wall faces said rock bolt first end, providing a protruberance protruding from, and fixed in relation to, the exterior surface of the bolt between said nut and said rock bolt first end, unthreading said nut until said frustoconical wall engages said protruberance, and torqueing said nut, so as to wedge said frustoconical wall against said protruberance, to a predetermined torque,

6. A method of installing a rock bolt, comprising the steps of: inserting a resin container into a rock bolt hole, [R:\LIBLL]08804.doc:TCW:GJG 8 providing a rock bolt drive system formed in accordance with claim fitting a roof plate to said rock bolt from a second end thereof, inserting said second end of said rock bolt into said bolt hole, piercing said resin container with said rock bolt second end, mixing said resin by rotation of said rock bolt via application of torque to said nut, allowing said resin to set, applying a torque to said nut in a direction opposite to said predetermined torque sufficient to dislodge said frustoconical wall from said protruberance, and to engaging said nut with said roof plate. 0 S

7. A rock bolt drive system, substantially as hereinbefore described with reference to either of Figures 1 and 2 of the accompanying drawings.

8. A method of forming a rock bolt drive system, substantially as hereinbefore described with reference to either of Figures 1 and 2 of the accompanying drawings. Is5

9. A method of installing a rock bolt, said method being substantially as hereinbefore described with reference to Figure 3 of the accompanying drawings. Dated

10 November, 1999 The ANI Corporation Limited Patent Attorneys for the Applicant/Nominated Person SPRUSON FERGUSON [R:\LIBLL]08804.doc:TCW:GJG