AU784835B2 - Expansion shell - Google Patents

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

Name of Applicant: Actual Inventor: Address for Service: Invention Title: Details of Associated Provisional Applications: INDUSTRIAL ROLL FORMERS PTY LTD Jeffrey Robert FERGUSSON IIODGKiNSEW OLED ?vfcfNNES odd Patet&Trade Marfk Aftefney Llrvd CA L evl 3, 20 Alfred Street- a8~ (P~d MILtSONS POINT NSW 2061 rAPiYJ )MJT EXPANSION SHELL

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2 PR3575 filed 7 March, 2001 The following statement is a full description of this invention, including the best method of performing it known to us: EXPANSION SHELL FIELD OF THE INVENTION The present invention relates to expansion shells used to form mechanical anchors at the tips of rock bolts.

The invention has been developed primarily for use in the pretensioned, post-grouted solid rock-bolts used in tunnelling and other civil engineering works and will be described hereinafter with reference to this application. However, it will be appreciated that the invention is not limited to this particular field of use.

o BACKGROUND OF THE INVENTION Such rock bolts are typically many metres in length and the expansion shell is located at the tip of the rock bolt. The shell is expanded once the rock bolt is located in its final position wherein it is fully inserted into a previously drilled hole. Once located 15 in the hole the bolt is able to be rotated thereby drawing an internally threaded plug of the shell along the externally threaded tip of the rock bolt so as to expand a pair of leads forming part of the shell. The leads grip the interior surface of a blind end of the hole and thereby permanently locate the tip ofthe rock bolt.

20 The installation of such rock bolts is carried out by a bolting machine which firstly S drills a hole for the rock bolt, then withdraws the drill, and then inserts the rock bolt into the just drilled hole. This requires considerable skill by the operator since the rock bolt, although essentially formed from a rod of solid steel, is inclined to droop because of its length. Therefore the insertion of the tip of the rock bolt into the hole often involves some "trial and error".

As will be explained in more detail hereafter, hitherto the expansion shell has included a generally U-shaped bail the bight of which extends transversely over the tip of the shell and the arms of which extend longitudinally along the shell. The arms are connected to the pair of leads. Hitherto the bight of the bail has been proud of the tip of the expansion shell and is subject to damage if it comes into contact with the rock surface. Such contact occurs if the operator is not able to find the hole on the first forward motion of the rock bolt. If the expansion shell is damaged it is necessary for the rock bolt to be lowered, the damaged expansion shell to removed from the tip -2of the rock bolt, and a new expansion shell to be positioned in its place. Whilst the expansion shells are relatively inexpensive items, the loss of operator time in this procedure is extremely expensive.

OBJECT OF THE INVENTION The aim of the present invention is to provide an improved expansion shell which is less likely to be damaged during the rock bolt insertion manoeuvre and thereby ameliorate the expense of lost operator time.

10 SUMMARY OF THE INVENTION In accordance with a first aspect the present invention there is disclosed an expansion shell forming a mechanical anchor for the tip of a rock bolt, said shell comprising a generally tapered plug having an internally threaded aperture extending along the longitudinal axis of the plug, a tail at one end and a head at the other; a pair of 15 longitudinally extending curved leads facing towards each other adjacent the tail of said plug; and a generally U-shaped bail formed from a length of strip having opposite ends thereof each connected to a corresponding one of said leads; wherein the head of said plug is provided with a transverse bail receiving recess whereby said bail-is not proud of said plug head.

2 In accordance with another aspect of the invention there is provided a method of using the expansion shell according to the first aspect of the invention, said method comprising the steps of engaging the tip of the rock bolt with the shell and inserting the tip into a drilled hole, rotating the rock bolt to draw the plug along the rock bolt to secure the tip of the rock bolt in the hole such that the bail is not proud of the plug head.

DESCRIPTION OF THE FIGURES A preferred embodiment of the present invention will now be described, by way of example only, with reference to the drawings in which: Fig. 1 is a perspective view from above of an expansion shell of the prior art; Fig. 2 is a longitudinal cross sectional view through the plug of the prior art expansion shell of Fig. 1; -3- Fig.3 is a view similar to Fig. 1 but illustrating the expansion shell of the preferred embodiment according to the invention; Fig.4 is a view similar to Fig. 2 but of the plug of the expansion shell of Fig.3; Fig. 5 is a plan view of the plug of Figs. 3 and 4; Fig. 6 is a left side elevational view of the plug of Fig. 5, the right side elevational view been a mirror image thereof; Fig. 7 is a front elevational view of the plug of Fig. 5, the rear elevational view been a mirror image thereof; Fig. 8 is an inverted plan view of the plug of Fig. 5; and S: 10 Fig. 9 is a perspective view of the plug Fig. S"DETAILED

DESCRIPTION

S•As seen in Figs. 1 and 2, the prior art expansion shell 1 has a generally tapered plug 2 usually formed from cast iron and a generally U-shaped bail 3 having a pair of arms 4 S. 15 the free ends of which are connected by means of a spot weld to a corresponding one of a pair of curved leads 5. The bail 3 is preferably formed from strip steel.

The two leads 5 face each other and essentially form a split hollow cylinder the exterior surface of which is provided with protruding ridges 6. A rupturable rubber 20 keeper ring 7 is positioned around the leads 5 in order to keep them in place prior to insertion of the rock bolt (not illustrated).

The expansion shell 1 is fitted to the threaded tip of the rock bolt wherein the exterior threads of which mate with the threaded aperture 8 in the plug 2. Prior to the insertion of the rock bolt in the hole, the engagement of the plug 2 and rock bolt is such that the tip of the rock bolt does not extend beyond the plug 2. After the rock bolt has been inserted into the hole the rock bolt is rotated thereby drawing the plug 2 along the rock bolt and towards the leads 5. The plug 2 is generally frusto-conical and is provided with a series of flats 10 on its outer surface which engage the interior of the leads As the plug 2 moves along the rock bolt the leads 5 are pushed outwardly, the keeper ring 7 ruptures and the protruding ridges 6 are forced into engagement with the -4interior of the blind hole drilled to receive the rock bolt. This therefore securely anchors the tip of the rock bolt in the base of the hole.

In the particular form of prior art shell 1 illustrated in Figs. 1 and 2, four exterior grooves 9 are provided in the side surfaces of the plug 2 in order to locate the bail 3.

The grooves 9 form two sets and are provided so that the plug 2 can be positioned in any one of four positions. These are the position illustrated in Fig. 1, another position being rotated by ninety degrees relative to that illustrated in Fig. 1, a third position in which the plug is rotated by 180 degrees from the position illustrated in Fig. 1, and so on.

As best seen in Fig. 2, the bight of the bail 3 stands proud of the cast iron plug 2.

Since the bail 3 is fabricated from thin steel strip, it is very prone to damage by coming into contact with the drilled rock surface during slightly inaccurate attempts to S. 15 insert the rock bolt into the hole. Such damage to the bail 3 means that the entire shell 1 must be removed from the tip of the rock bolt and a new shell 1 positioned on the rock bolt before the insertion procedure can be tried again.

Turning now to Figs. 3-9, the expansion shell 21 of the preferred embodiment will 20 now be described with like parts being designated by like numbers but increased in magnitude by twenty. The general arrangement of the shell 21 with plug 22, bail 23, leads 25 and keeper ring 27 is as before. However, as best seen in Figs. 5 and 6, the top of the plug 22 is provided with a transversely extending recess 32 which is aligned with a single pair of grooves 29. The depth of the recess 32 exceeds the thickness of the steel strip from which the bail for 23 is fabricated so that, as seen in Fig. 4, the bight of the bail 3 is located below the upper surface of the plug 22 and is therefore protected from damage. As the plug 22 is fabricated from cast iron it is therefore much stronger than the steel strip of the bails 23. As best seen in Fig. 7, the exterior surface of the plug 22 is also provided with a series of six tapered flats 30 which, together with the two grooves 29, gives the plug 22 a generally octagonal appearance when viewed in plan or inverted plan.

The foregoing describes only one embodiment of the present invention and modifications, obvious to those school in the art, can be made thereto without departing from the scope to the present invention.

The term "comprising" is used here and is used in the inclusive sense of "including" or "having" and not in the exclusive sense of "consisting only of".

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Claims (9)

1. An expansion shell forming a mechanical anchor for the tip of a rock bolt, said shell comprising a generally tapered plug having an internally threaded aperture extending along the longitudinal axis of the plug, a tail at one end and a head at the other; a pair of longitudinally extending curved leads facing towards each other adjacent the tail of said plug; and a generally U-shaped bail formed from a length of strip having opposite ends thereof each connected to a corresponding one of said leads; wherein the head of said plug is provided with a transverse bail receiving recess whereby said bail is not proud of said plug head. 10

2. The shell according to claim 1 and having a rupturable keeper extending around said leads. S.

3. The shell according to claim 1 or 2 wherein said plug is generally frusto- conical.

4. The shell according to claim 3 wherein said plug is provided with at least one 15 exterior flat. S•

5. The shell according to claim 4 wherein the plug is provided at six spaced apart exterior flats disposed on the exterior surface of the plug.

The-shell according to claim 4 or 5 -wherein-the plug includes a pair of longitudinally extending grooves which are aligned with the bail receiving recess. 20

7. A method of using an expansion shell according to any one of the preceding claims, said method comprising the steps of engaging the tip of the rock bolt with the shell and inserting the tip into a drilled hole, rotating the rock bolt to draw the plug along the rock bolt to secure the tip of the rock bolt in the hole such that the bail is not proud of the plug head.

8. An expansion shell forming a mechanical anchor for the tip of a rock bolt, said expansion shell being substantially as herein described with reference to Figs 3 to 9 of the accompanying drawings.

9. A method of using an expansion shell for forming a mechanical anchor for the tip of a rock bolt, said method being substantially as herein described with reference to Figs 3 to 9 of the accompanying drawings. Dated this 6 h Day of March, 2002 INDUSTRIAL ROLL FORMERS PTY LIMITED BY: HODGKINSON OLD McINNES Patent Attorneys for the Applicant