WO2001046558A1

WO2001046558A1 - An anchor device for use in mining

Info

Publication number: WO2001046558A1
Application number: PCT/AU2000/001583
Authority: WO
Inventors: Jeffrey Robert Fergusson
Original assignee: Industrial Rollformers Pty Limited
Priority date: 1999-12-21
Filing date: 2000-12-21
Publication date: 2001-06-28
Also published as: AUPQ477699A0

Abstract

An anchor device (20) for engagement with a wall (29) of a bore (30), the device having a profile including two interconnected arms (22, 23) defining a gap (52) between free ends (34, 35) thereof to accommodate relative movement of the free ends resulting from deflection of the arms during insertion in the bore, wherein the arms are coupled via an intermediate section (24) which includes an inset portion (25), at which the profile is in use spaced from the bore wall, so as to define contact portions (27, 28) at either side thereof for contact with the wall and wherein the inset portion is located substantially diametrically opposite the gap.

Description

AN ANCHOR DEVICE FOR USE IN MINING

Field of the Invention

This invention relates to an anchor device for engaging in a bore and, more particularly, but not exclusively, to an anchor device for use in mining applications.

Background of the Invention

One form of anchor device used in the mining industry is know as a friction bolt. It comprises a tapered substantially tubular body, with a C-shaped transverse cross-section. The C-shaped cross-section enables the body to be radially compressed to fit within a bore such that when inserted into the bore, elastic compression of the body causes a radially outward force to be exerted upon the sides of the bore to thereby anchor the bolt in place. The bolt may be fitted with a load plate or the like which is fixed in place by a ring secured to a free end of the bolt.

It has been determined by the Applicant that the load bearing capacity of such a bolt is limited since force transfer between the bolt and the bore has been found to occur at three contact points on the C-shaped cross-section. Previous perception was that the bolt engaged the bore wall about the entire circumference of the bolt but closer analysis shows that the body of the bolt actually hinges about its geometric centre when the arms are deflected inwardly to provide only three contact points: one point at each free end of the cross-section and another contact point midway on the cross-section between the free ends.

Object of the Invention

The present invention seeks to provide an anchor device of alternative construction.

Summary of the Invention

In accordance with the present invention, there is provided an anchor device for engagement with a wall of a bore, the device having a profile including two interconnected arms defining a gap between free ends thereof to accommodate relative movement of the free ends resulting from deflection of the arms during insertion in the bore, wherein the arms are coupled via an intermediate section which includes an inset portion, at which the profile is in use spaced from the bore wall, so as to define contact portions at either side thereof for contact with the wall and wherein the inset portion is located substantially diametrically opposite the gap.

Preferably, the contact portions are respectively substantially diametrically opposite the free ends of the arms.

Preferably, the inset portion is defined by a concave section and a relative angle between an imaginary line drawn along any two parts of the section is less than 90°.

In another aspect, there is provided an anchor device for frictional engagement in a bore, including two arms extending from an intermediate section, the section being provided with lateral contact portions for engaging the bore wall and the arms being arranged to deflect about spaced apart loci.

Preferably, the device is provided with an inset portion intermediate the contact portions, about which the arms hinge.

Preferably, the contact portions substantially correspond to respective locations at which the arms couple to the intermediate section.

Preferably, the spaced apart loci are substantially congruent with a respective one of the contact portions.

In another aspect, there is provided an anchor device for frictional engagement in a bore, including an elongate body having a transverse cross-section defined by two arms coupled to an intermediate section, with free ends of the arms being separated by a gap which is sufficient to allow the device to be compressed during insertion of the device into the bore, wherein the section includes an inset portion opposite the gap with contact portions provided at either side thereof for engagement with a wall of the bore.

Preferably, the recessed region is defined by a concave section of the intermediate section.

Preferably, at least one end of the device is tapered.

In yet another aspect, there is provided an anchor device for frictional engagement in a bore, including two arms extending from an intermediate section, the intermediate section having a plurality of contact portions for engaging a wall of the bore.

Brief Description of the Drawings

The invention is described in more detail, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is an enlarged cross-sectional view of a prior art friction bolt in a compressed configuration within a bore;

Figure 2 is an enlarged cross-sectional view of an anchor device according to the present invention, the device being in a compressed configuration within a bore;

Figure 3 is a graph illustrating pressure profiles for the device of Figure 2 and the bolt of Figure 1; and

Figure 4 is a side view of the device shown in Figure 2.

Detailed Description of a Preferred Embodiment

Referring firstly to Figure 1 , a prior art of friction bolt 1 is shown as comprising a body 2 with a 'C'-shaped section terminating in free ends 3,4 which are arranged to deflect about a single locus 5, which corresponds to a geometric centre 6 of the body. The bolt is thereby arranged to frictionally engage a wall 7 of a bore 8 at only three points 9, 10, 11, which reduces the load bearing capacity of the bolt 1. Further, the distance between the free ends 3, 4 and the locus 5 is usually maximised which maximises bending moments applied to the free ends 3,4 of the body 2. That in turn can limit the contact force which may be applied between the bolt 1 and the bore, prior to failure of the bolt due to excessive bending moments being applied.

Referring now to Figure 2, an anchor device 20 of the present invention is shown as including a body 21 with a transverse cross-section defined by two arms 22,23 coupled to an intermediate section 24. The device 20 has an inset portion 25 defined by a concave section 26 of the intermediate section 24. Laterally spaced contact portions 27,28 are provided at either side of the portion 25, for engagement with a wall 29 of bore 30. The portion 25 is substantially diametrically opposite a gap 52 provided between the arms 22,23 and each contact portion 27,28 is arranged generally opposite a respective free end of the arms. The contact portions 27,28 substantially correspond to respective locations 31,32 where the arms 22,23 join with the section 24. The locations 31,32 also form or are substantially congruent with loci 33, about which the arms 22,23 deflect.

The device 20 thereby provides four contact points for engagement with the wall 29; two points adjacent free ends 34,35 of the arms 22,23 and two further points associated with the portions 27,28. The increased number of contact points, as compared to the bolt 1 of Figure 1, allows for greater load bearing capacity, as reflected in experimental results, shown in Figure 3. That Figure shows a plot of contact force versus radial angle, where 180° represents the locus 5 of the bolt 1 and the corresponding position of the device 20. The curves 40, 41 and 42 show sustainable contact forces about respective points 9, 10 and 11 of the bolt 1, while the curves 43, 44, 45 and 46 show sustainable contact forces about the free ends 34,35 and the contact portions 27,28, respectively.

Aside form providing an increased number of contact points, the device 20 also reduces the length of the arms 22,23, as a result of introduction of the intermediate section 24, as compared to the bolt 1 and that has the affect of reducing the bending moment for equivalent force application, which in turn increases the comparative load bearing limit of the device 20, prior to failure.

Further, it should be noted that the inset portion 25, although shown as being somewhat concave, is still reasonably flat, in order that the portion 25 does not itself function as a hinge point or section of weakness in the device. To ensure that is the case, the portion 25 is formed such that a relative angle "α", between an imaginary line 61,62, drawn along any two parts of the section 25 is less, and preferably substantially less, than 90°.

The above advantages may be utilised to reduce material required to produce a device having similar load bearing capabilities as the bolt 1 or alternatively a device may be provided using a similar amount of material with enhanced load bearing characteristics.

Referring lastly to Figure 4, the device 20 can be seen as being formed as an elongate friction bolt 50 with a tapered end 51 and an axially extending gap 52 defined between the free ends 34,35 of the arms 22,23. The device 20 may, however, instead comprise only a portion of the bolt, such as the tapered end 51 or, alternatively, be in the form of an attachment device which is simply fitted to an existing bolt or formed at an end thereof, in order to provide improved load bearing characteristics.

Expressed in a different manner to the above, the comparative load bearing advantage of the device of the invention may be seen as resulting from the shape of the bolt cross-section, and the resulting location and orientation of the four contact regions between the bolt and the bore wall, with the bolt cross-section functioning as an array of three relatively short, stiff beam- columns. During installation then, the free ends 34,35 of the cross-section close together pivoting at 33 with the arms 22,23 maintaining the original pre-installation radii. In effect then the arms 22,23 behave as short curved beams whereas in the prior art bolt configuration the curved sections are longer and less stiff. The curved section 25 is also quite rigid, which is the result of being of a relatively short length and having three small radii resulting from cold working of the metal during a roll forming process. The roll forming process takes the metal into the plastic or permanent deformation zone. Further, the curvature of each arm of the prior art configuration is around 175 degrees whereas the profile of the device 20 is around 155 degrees. This reduced curvature and resulting shorter arm length means that for the same deflection during installation (hole diameter does not change) a greater contact force or pressure is achieved at the ends 34,35. Bending moments at the contact portions 27,28 are greater than what is achieved at the single point 11 of the prior art configuration. This is supported by Figure 3 which shows higher local stress areas at portions 27,28. Resolving forces at the ends 34,35 into tangential and radial components and solving for forces at 27 and 28 results in higher contact forces or pressures at contact portions 27,28 than the equivalent at the prior art configuration at location 11. The sum of the four contact forces produced by the bolts of the invention is 30% to 60% higher than the sum of the three contact forces which are produced by prior art bolts of the same material, wall thickness and insertion depth which suit the same hole size. Accordingly, the pull-out force for a bolt formed in accordance with the invention will be correspondingly higher than that for the prior art "circular section" bolts.

The anchor device has been described, by way of non-limiting example only, and many modifications and variations may be made thereto without departing from the spirit and scope of the invention as described.

Claims

Claims:

1. An anchor device for engagement with a wall of a bore, the device having a profile including two interconnected arms defining a gap between free ends thereof to accommodate relative movement of the free ends resulting from deflection of the aims during insertion in the bore, wherein the arms are coupled via an intermediate section which includes an inset portion, at which the profile is in use spaced from the bore wall, so as to define contact portions at either side thereof for contact with the wall and wherein the inset portion is located substantially diametrically opposite the gap.

2. An anchor device as claimed in claim 1, wherein the contact portions are respectively substantially diametrically opposite the free ends of the arms.

3. An anchor device as claimed in claim 1 or 2, wherein the inset portion is defined by a concave section and a relative angle between an imaginary line drawn along any two parts of the section is less than 90°.

4. An anchor device for frictional engagement in a bore, including two arms extending from an intermediate section, the section being provided with lateral contact portions for engaging the bore wall and the arms being arranged to deflect about spaced apart loci.

5. An anchor device as claimed in claim 4, wherein the device is provided with an inset portion intermediate the contact portions, about which the arms hinge.

6. An anchor device as claimed in claim 4 or 5, wherein the contact portions substantially correspond to respective locations at which the arms couple to the intermediate section.

7. An anchor device as claimed in any one of claims 4 to 6, wherein the spaced apart loci are substantially congruent with a respective one of the contact portions.

8. An anchor device for frictional engagement in a bore, including an elongate body having a transverse cross-section defined by two arms coupled to an intermediate section, with free ends of the arms being separated by a gap which is sufficient to allow the device to be compressed during insertion of the device into the bore, wherein the section includes an inset portion opposite the gap with contact portions provided at either side thereof for engagement with a wall of the bore.

9. An anchor device as claimed in claim 8, wherein the recessed region is defined by a concave section of the intermediate section.

10. An anchor device for frictional engagement in a bore, including two arms extending from an intermediate section, the intermediate section having a plurality of contact portions for engaging a wall of the bore.

11. An anchor device as claimed in any one of the preceding claims, wherein at least one end of the device is tapered.