GB2241998A

GB2241998A - Rock bolt

Info

Publication number: GB2241998A
Application number: GB9105385A
Authority: GB
Inventors: John Schott
Original assignee: NEWKEM AUSTRALIA
Current assignee: NEWKEM AUSTRALIA
Priority date: 1990-03-16
Filing date: 1991-03-14
Publication date: 1991-09-18
Also published as: DE4108500A1; ZA911968B; GB9105385D0

Abstract

The external screwthread (13) of a rock bolt (10) is coated with plastics to inhibit the rotation of a nut (11) along the thread (13) until an anchoring resin capsule (not shown) is ruptured, mixed and set. Initially the nut (11) is screwed onto the set coating (20), and can then be driven to rotate the bolt (10) to ensure mixing of the resin. As the resin sets, an increased torque is applied to the nut (11) sufficient to screw it along the bolt against a bearing plate (not shown), so as to tension the bolt (10). <IMAGE>

Description

1 IMPROVED ROCK BOLT BACKGROUND TO THE PRESENT INVENTION :2 -> Q X ca La

jE:3 THIS INVENTION relates to rock bolts, and in particular to rock bolts or anchor assemblies which are used, inter alia, in the mining and construction industries, such as to assist in the support and stressing of strata and the like.

Such rock bolts and anchor assemblies are well known and are provided in many forms which have been used over the years. in particular in the mining and construction industries. When using such rock bolts, it is desirable to have means whereby the rock bolt can be initially engaged with a nut (such as at the butt or driven end of the rock bolt), this nut allowing for the rock bolt to be inserted and essentially rotated into a bore formed in the strata or, for example, walls of a mine or construction site concerned. In the location of rock bolts, it is usual for some bonding agent or adhesive to be used to assist in locating the rock bolt within the bore formed in the strata. For example# it is well known to use chemical anchors which are first placed in the bore, and which are then broken and the contents thereof mixed, to form an adhesive or bonding agent, by the insertion and rotation of the rock bolt. Once the bonding agents or adhesives have cured or set, they hold the rock bolt in position within the bore. At that stage, it is desirable to be able to advance the nut axially and longitudinally of the rock bolt. so that the nut advances along the rock bolt to come into contact with the surface of the strata or alternatively a bearing plate previously located over the rock bolt. Thus, on the nut being tightened, the bolt will be tensioned and stressed relative to the strata concerned.

The present invention sets out to provide an improved rock bolt which allows for the efficient and straight-forward location of a rock bolt within a bore in strata or the like, 2 and thereafter the straight-forward and efficient tightening and tensioning of the rock bolt relative to the strata.

It is an object of this invention to provide a straightforward and efficient rock bolt.

Other objects of this invention will become apparent from the following description.

SUMMARY OF THE PRESENT INVENTION

According to one aspect of this invention there is provided a rock bolt including an elongate body portion formed or provided with an external thread extending at least part-way along the length thereof, from a butt or driven end of said body portion; a nut being engaged and axially advanced along said thread to be located at a position in which it is axially spaced apart from said butt or driven end; at least a Dortion of said thread between said butt or driven end and said nut having a coating material applied thereto.

According to a further aspect of this invention there is provided a rock bolt including an elongate body portion formed or provided with an external thread at or adjacent its butt or driven end; said thread extending at least part-way along the length of said elongate body portion; a nut being engaged with said thread and axially advanced along said thread so as to be spaced apart from said butt or driven end; at least part of said thread between said butt or driven end and said nut having a coating material applied thereto; the arrangement being such that on said nut being axially returned towards said butt or driven end, it will frictionally engage with said coating, until it reaches a predetermined or desired torque level; a forward rotational moment applied to said nut in such a position causing rotation of said nut and said elongate body portion together; 1 i 3 said nut being restrained from rotating and axially advancing along and relative to said elongate body portion, until the torque reaches a predetermined level.

According to a further aspect of this invention there is provided a method of stressing rock strata, using a rock bolt as hereinbefore defined, including forming at least one elongate bore in said strata and locating one or more chemical anchors. bonding or adhesive material within said bore; axially returning the nut rearwardly along the body portion of said rock bolt, towards the butt or driven end thereof. so that the nut frictionally engages with said coating; applying a forward rotational moment to said nut, such that said nut and body portion rotate together so that a forward end of said body portion advances into said bore to break said chemical anchor and mix components thereof. and/or mix bonding or adhesive material within said bore. such that a bonding agent or adhesive forms about said forward end of the rock bolt within said bore; allowing said bonding agent or adhesive to cure and set; applying a further forward rotational moment to said nut until the torque reaches a predetermined level, such that the nut is free to be axially advanced, forwardly along the body portion. to come into contact with said strata, or a bearing plate, so as to be tightened thereagainst.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

This invention will now be described by way of example only and with reference to the accompanying drawings, wherein:

4 Fig. 1 is a side view of a rock bolt according to one form of the present invention, Fig. 2 is a side view (together with a detailed view) of a rock bolt according to a further form of the present invention, and Fig. 3 is a side view of the rock bolt according to a further form of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to the accompanying drawings, the rock bolt is generally referenced 10 and an associated nut is referenced 11.

The rock bolt includes an elongate body portion 12 in the form of an elongate shaft or shank (which is shown by way of example, in broken form, in the accompanying drawings).

The elongate body portion 12 is provided with a threaded portion 13 on the outer surface thereof, the threaded portion 13 extending from the outer, butt or driven end 14 of the body portion to at least part-way along the length of the body portion 12. If desired, the threaded portion 13 can extend for the length of the body portion 12.

The thread 13 can be of any appropriate thread such as for example a nground" or "springlockn thread. It should be appreciated however, that any appropriate form of screw thread can be utilised, so long as it is capable of engaging with the thread of a nut 11.

The rock bolt 10 and nut 11 can be constructed of any suitable material such as metal, plastic. fibreglass or the like. The body portion 12 is preferably provided with a 1 1 is pointed or sharp end 15 at the forward, or distal end thereof such as shown in the accompanying drawings. If desired and in particular if constructed of plastic or fibreglass, the forward part of the body portion 12 can be formed or provided with a roughened surface or can have random projections 16 extending therefrom. for the purpose of permitting engagement of the rock bolt in a bore to be formed in strata and to allow for the mixing of adhesive and bonding agent components within such a bore (as will be described hereinafter).

In the preferred form of the invention and with reference to Fig. 1 of the drawings, a nut 11 is engaged with the screw thread 13 and is then axially advanced along the thread, relative to the longitudinal axis of the body portion 12 so that it is located at a position at least part-way along the screw thread 13 and spaced apart from the butt or driven end 14 of the rock bolt 10.

A coating composition is then applied to at least part of the thread 13, between the axially advanced nut 11 and the butt or driven end 14. The coating material or agent is preferably in the form of a resin or some other appropriate coating, and can, if desired, be in the form of a hot melt material. Resins or hot melts that can be used with the invention to advantage are, for example, polyester, vinyl ester, hot melt and polyurethane. The resin can be thermoplastic or thermoset.

It should be appreciated however that any appropriate coating can be utilised so long as it allows for the screw thread of the nut 11 to frictionally engage therewith in the manner described.

Referring to Fig. 2 of the accompanying drawings, the coating 20 is applied to the thread such that the coating material enters into the grooves 21 between the ribs or ridges of the 6 screw thread. The coating is preferably applied in such a manner that the ribs of the screw thread are left exposed but that the grooves or recesses 21 therebetween are essentially filled. If desired howeverr the coating can be applied over the whole surface of the screw thread, including the ribs. The coating can be applied by spraying. brush. dipping. or any other appropriate means.

Following appropriate application. the coating composition is allowed to set or cure. The coating can be applied during manufacture, or if desired, ' in situ, at a workplace, mine, construction site or the like.

In use, and as referred to hereinbefore, one or more bores are initially formed in a rock surface or strata. Thereafter, chemical anchors (containing the components of an adhesive or bonding agent), adhesives or bonding agents are placed into the bore. The rock bolt is then axially rotated into the bore so that the distal end 15 thereof and the protrusions 16 (if provided) break the chemical anchors and/or mix the components thereof or adhesive, so that the adhesive cures and bonds about the shaft 12 (within the bore), so as to locate and secure a substantial part of the body portion 12 of the rock bolt within the bore. This will however leave at least a portion of the screw threaded portion 13 extending outwardly from the rock surface or strata.

It is therefore to be appreciated that such location of the rock bolt within a bore is greatly assisted by there being a nut at the butt or driven end 14 of the rock bolt to enable the rock bolt to be axially advanced and rotated into the bore.

When the rock bolt of the present invention is to be used, and in order to provide a drive mechanism at the butt or driven end 14 of the rock bolt (and following the setting or 7 is curing of the coating 20), the nut 11 is axially returned and rotated rearwardly along the screw thread portion 13 of the rock bolt# towards the butt or driven end 14, (as indicated by the arrow in Figure 2 of the drawings), during which axial return it will frictionally engage with the coating 20 about the screw thread portion 13. Thus. following such engagement there will clearly be frictional engagement between the thread of the nut 11 and the coated thread 13 of the body portion. Thus, the nut 11 is actually returned towards the butt or driven end 14 until such time as a predetermined or desired torque is reached, at which time it will be firmly and frictionally engaged with the coated thread 13. By way of example only, the nut can be returned towards the butt or driven end 14 until torque reaches for example 40 foot pound. Following this, and when it is desired to rotate the rock bolt 10 forwardly, into a bore, a forward rotational moment is applied to the nut 11. This forward rotational moment will then cause the nut and rock bolt 10 to rotate and axially advance forwardly (such as in the direction of the arrow in Figure 3) into the bore together, having regard to the frictional engagement between the nut 11 and screw thread portion 13. This rotation, being a forward rotational moment applied to the nut, will cause the rock bolt 10 to rotate and axially advance into the bore. so that the forward end thereof is caused to mix adhesives or bonding agents, or to break the chemical anchor (this bringing about the mixing of the adhesive or bonding agent components within the bore). The rock bolt is then left so that the adhesives, bonding agents or components therefor can cure or set so that the forward end of the body portion 12 of the rock bolt as located within the bore in the stratai is firmly located within that bore and relative to the strata. That will however leave a screw.threaded portion of the rock bolt, together with the nut 11 engaged therewith, extending out of the bore and relative to the rock strata.

i 8 is Following the curing of the adhesive or bonding agent within the bore, such as to securely hold the rock bolt in position, a further forward rotational moment can be applied to the nut 11 (in the direction of the arrow shown in Figure 3 of the drawings), in excess of the predetermined torque, such that with the body portion 12 of the rock bolt 10 held firmly in the bore, the nut 11 will disengage from the coated thread 13 and axially advance along the screw thread. away from the butt or driven end 14, until it comes into contact with the strata surface surrounding the bore. Such a nut can then be tightened against the strata surface to stress and tension the rock bolt within the bore and thus to strengthen and tension the strata.

In one form of the invention (not shown) a bearing plate (such as a rectangular metal bearing plate with a bore therethrough) can have the body portion 12 fed therethrough prior to location, in a bore, so that it is located between the strata surface and the nut 11. Thus, on location of the body portion 12 within the bore and on the axial advancement of the nut 11 away from the butt or driven end 14 (following secure location of the body portion 12 within the bore), the nut 11 can butt up against and be tightened against th,e bearing plate (not shown).

It has been found that this invention provides a particularly efficient and straight-forward rock bolt which allows for the nut to engage with the screw thread of the rock bolt, in such a way as to allow for it to be used as a drive mechanism to advance the rock bolt into a bore and to allow for the mixing of adhesives or the breaking of chemical anchors, such as to allow for the main body portion of the rock bolt to be securely located within the bore. The present invention also allows for the nut to be thereafter axially advanced along the screw thread, to abut against a strata surface or rock z W 9 bolt bearing plate, to allow the rock bolt and thus the strata to be stressed and tensioned.

This invention has been described by way of example only and improvements and modifications may be made without departing from the scope thereof, as defined by the appended claims.

Claims

WE CLAIM:

1. A rock bolt (10) including an elongate body portion (12) formed or provided with an external thread (13) extending at least part-way along the length thereof, from a butt or driven end (14) of said body portion (12); a nut (11) being engaged and axially advanced along said thread (13) to be located at a position in which it is axially spaced apart from said butt (14) or driven end; at least a portion of said thread between said butt or driven end (14) and said nut (11) having a coating material (20) applied thereto.

2. A rock bolt (10) including an elongate body portion (12) formed or provided with an external thread (13) at or adjacent its butt or driven end (14); said thread (13) extending at least part-way along the length of said elongate body portion (12); a nut (11) being engaged with said thread (13) and axially advanced along said thread (13) so as to be spaced apart from said butt or driven end (14); at least part of said thread (13) between said butt or driven end (14) and said nut-(11) having a coating material (20) applied thereto, the arrangement being such that on said nut (11) being axially returned towards said butt or driven end (14), it will frictionally engage with said coating (20), until it reaches a predetermined or desired torque level; a forward rotational moment applied to said nut (11) in such a position causing rotation of said nut (11) and said elongate body portion (12) together; said nut (11) being restrained from rotating and axially advancing along and relative to said elongate body portion (12), until the torque reaches a predetermined level.

3. A rock bolt (10) as claimed in claim 2, wherein the coating (20) is a thermoplastic or thermoset resin.

1 11

4. A rock bolt (10) as claimed in claim 2, wherein the coating (20) is polyester, vinylester or polyurethane.

5. A rock bolt (10) as claimed in claim 1 or claim 2. wherein the coating (20) is applied by spraying, brush or dipping.

6. A rock bolt (10) as claimed in claim 1 or claim 2, wherein the coating material (20) is located in grooves between ribs or ridges of the screw thread (13).

7. A method of stressing rock strata using a rock bolt (10) as claimed in claim 1, including:

forming at least one elongate bore in said strata and locating one or more chemical anchorst bonding or adhesive material within said bore; axially returning the nut (11) rearwardly along the body portion (12) of said rock bolt (10), towards the butt or driven end thereof (14)r so that the nut (11) frictionally engages with said coating (20); applying a forward rotational moment to said nut (11), such that said nut (11) and body portion (12) rotate together so that a forward end (15) of said body portion (12) advances into said bore to break said chemical anchor and mix components thereof, and/or mix bonding or adhesive material within said bore, such that a bonding agent or adhesive forms about at least said forward end (15) of the rock bolt (10) within said bore; allowing said bonding agent or adhesive to cure and set; applying a further forward rotational moment to said nut (11) until the torque reaches a predetermined level, such p 0 12 that the nut (11) is free to be axially advanced, forwardly along the body portion (12), to come into contact with said strata, or a bearing plate, so as to be tightened thereagainst.

8. A rock bolt substantially as hereinbefore described with reference to the accompanying drawings.

9. A method substantially as hereinbefore described with reference to the accompanying drawings Published 1991 at The Patent Office. Concept House. Cardiff Road. Newport. Gwent NP9 IRH. Further copies may be obtained from Sales Branch. Unit 6. Nine Mile Point. Cwrnfelinfach. Cross Keys. Newport. NP l 7HZ. Printed by Multiplex techniques ltd. St Mary Cray. Kent.

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