AU752771B2 - Cable tensioning device - Google Patents

Description

S&FRef: 439870D1

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

Name and Address of Applicant: Actual Inventor(s): Address for Service: Invention Title: DYWIDAG-Systems International Pty Limited 25 Pacific Highway Bennett's Green New South Wales 2290 Australia Mieczyslaw Stanislaw Rataj r Spruson Ferguson St Martins Tower,Level 31 Market Street Sydney NSW 2000 (CCN 3710000177) Cable Tensioning Device The following statement is a full description of this invention, including the best method of performing it known to me/us:- 5845c 1 CABLE TENSIONING

DEVICE

Field of the Invention The following invention relates to cable bolts and methods of installing same.

More particularly, though not exclusively, the invention relates to a cable bolt and a method and apparatus for pre-tensioning cable bolts as used in the underground mining industry. The invention also relates to the pre-tensioning of cables in pre-stressed concrete structures.

Tension induced in a roof bolt during installation is required for more effective ground reinforcement. When conventional solid bolts are used, the tension in the bolt is induced by tightening a nut against a load bearing mine plate.

Cable bolts, however, require a special wedging system including frustoconical wedges which are designed to mate with the inner frusto-conical surface of a collar.

In order to tension a cable bolt having a collar and wedge type fitting, special hydraulically powered equipment has to be used. The equipment currently available has several limitations. It is very cumbersome in use and is available only for a small size cable bolt, typically of 15.2 mm diameter. Also, the level of tension achieved by this equipment is relatively low due to the fact that when the cable is tensioned against the collar, on completion of the operation, the wedges do not move sufficiently deeply into the collar thus causing significant loss of the originally gained tension.

The main reason why the wedges do not move properly into the collar is lack of proper alignment of the mating components, i.e. cable, wedges and the collar. This lack of alignment is caused by tilting of the roof plate due to unevenness of the rock face when the system is loaded. Since the friction between the plate and the collar S 25 under the high load is significant, the collar is tilted together with the plate. When this happens, the cable is not in the centre of the collar and moreover, the edges on one side •do not have enough room to move into the required depth.

There is not known a simple pre-tensioning system which would allow larger diameter cable bolts (typically 23 mm to 24 mm diameter) to be tensioned to a load of 30 25 tonnes.

One system being used relies on pulling the bolt end away from the roof. The tension is then locked by using a spacer between the plate and the collar of the end fitting. The spacer consists of a threaded hollow bar (locker) and a supporting nut which is screwed against the roof plate. The main disadvantage of this system is that the length of the locker results in a 130 mm protrusion from the roof which in many mines is not acceptable.

IN:\LIBLLJO2024:PVH Object of the Invention It is the object of the present invention to overcome or substantially ameliorate at least one of the above disadvantages and/or more generally to provide an improved cable bolt tensioning system.

s Disclosure of the Invention There is disclosed herein a cable tensioning system for inducing tension in an in situ cable bolt, the system including: a bearing plate for bearing against a surface behind which said cable bolt is anchored and having an aperture therethrough and through which the cable bolt passes, engagement means including a collar surrounding the cable bolt, the collar having a central aperture therethrough, said aperture having a portion with an internal diameter substantially equal to the external diameter of the cable bolt and in contact therewith, the engagement means also being in contact with said bearing plate, the engagement means including wedge means located within the collar and engageable with the collar and the cable bolt, a top plate having an aperture therethrough and through which the cable bolt .passes, the top plate engageable with said engagement means, a main plate having gripping means for gripping said cable bolt and force inducing means engageable with said top plate for pushing said main plate away from said top plate, such that said gripping means induces tension in said cable bolt whereupon release of said gripping means from said cable bolt results in cable tension being at least substantially retained against said bearing plate by said engagement means.

S .Preferably, the collar is provided with an internally projecting annulus for engagement with the cable bolt.

000.

[R:\LIBLL] 189.doc:TCW Preferably, the cable tensioning system further includes a centralising insert between the collar and the cable bolt, the centralising insert having an internal diameter substantially equal to the external diameter of the cable bolt.

Preferably, said gripping means includes two or more jaws having a frustoconical outer surface engageable with a frusto-conical inner surface of an aperture passing through the main plate.

Preferably, the jaws are biased into engagement with the frusto-conical aperture of the main plate by means of a resilient member housed within a cap fixed to the main plate.

Preferably, said force inducing means is a single hollow ram.

Preferably, said force inducing means comprises two or more hydraulic rams, each being a single acting hydraulic ram adapted to apply a force in one direction only so as to move the top plate and main plate away from each other.

Preferably, a spring-loaded plate depends from the top plate and is adapted to bear against the wedge means of the collar.

i* t [R:\LIBLL] II 189.doc:TCW Brief Description of the Drawings Preferred forms of the present invention will now be described by way of example with reference to the accompanying drawings wherein: Figure 1 is a schematic cross-sectional elevation view of a cable tensioning system, Figure 2 is a schematic cross-sectional elevation view of a collar, Figure 3 is a schematic cross-sectional elevation view of a collar and a centralising insert, Figure 4 is a schematic cross-sectional elevation view of an alternative Io arrangement of components in a cable tensioning system, and Figure 5 is a schematic cross-sectional elevation view of an alternative collar fitted around a cable bolt.

Description of the Preferred Embodiments In Figure 1 of the accompanying drawings, there is schematically depicted a cable tensioning system associated with a cable bolt 5 extending into an underground mine roof 18. A bearing plate 4 is held against the roof 18 by means of a collar 2 which fits around the cable bolt 5. The collar 2 has located internally thereof a number of i wedges 3 having frusto-conically shaped outer surfaces which bear against an internal frusto-conical surface within the collar 2. The collar 2 sits upon a top plate 1 having a central aperture 25 having an internal annular ledge 26 above which there a [R:\LIBLL]I I 189.doc:TCW extends an upwardly diverging frusto-conical recess 10. The frusto-conical nature of recess 10 allows the collar 2 to be precisely positioned in relation to the jaws 6 to be described below. By doing this, the collar 2 is located centrally in relation to the cable bolt 5 which allows the wedges 3 which are typically provided in three separate segments to be precisely pushed by action of the spring-loaded plate 11. The frustoconical nature of the recess 10 ensures that the collar 2 is located centrally with respect to the cable bolt 5. Other means of centralising the collar can also be adopted. For example, spring-loaded locators can be used to eliminate the need for very close tolerance of the outside diameter of the collar. The lower edge of the collar 2 sits upon the ledge 26 as depicted.

Depending from the top plate 2 is a spring-loaded plate 11 having tension springs 27 extending upwardly therefrom into respective recesses 28 of the top plate 1.

The spring-loaded plate 11 has a central aperture through which the cable bolt passes.

The wedges 3 are supported by the spring-loaded plate 11 nearby its aperture.

A main plate 7 is located below the top plate 1 and includes a central frustoconical aperture 21 within which a number of jaws 6 are provided. Typically, three jaws 6 are provided, each having frusto-conical outer surfaces engageable with the frusto-conical surface 21 of the main plate 7. The jaws 6 have gripping teeth 29 which grip against the outer surface of the cable bolt 20 Threadingly engaged with the main plate 7 are a number of hydraulic rams 8, 9 which have their active components 30 extending upwardly therefrom to bear against :i the lower surface of the top plate 1. These active components 30 are adapted to push Supwardly onto the top plate 1 so as to cause the main plate 7 to force downwardly such that the jaws 6 tightly grip against the cable bolt 5 to induce tension therein. During 25 the induction of tension into cable bolt 5, the collar 2, wedges 3, bearing plate 4, top plate 1 and spring-loaded plate 11 are biased upwardly by the active components 30 of the hydraulic rams 8 and 9. When hydraulic pressure is released from the rams 8 and V 9, tension in cable 5 above the wedges 3 is retained by wedges 3 against the collar 2 *and the bearing plate 4. At this point, it is desirable to remove the main plate 7 and its associated components.

oeoIn the depicted embodiment, two or more hydraulic rams 8, 9 are used. As an *oe i *alternative, a single hollow ram might be used, which hollow ram would surround the cable bolt 5 and the gripping means.

Attached to the bottom surface of the main'plate 7 is a housing cap 24 within which a compression coil spring 23 resides. Coil spring 23 bears upwardly against the jaws 6 to maintain engagement of the jaws with the inner frusto-conical surface of the central aperture 21 of plate 7. The spring 23 maintains the jaws 6 in position for the purpose of inserting the apparatus over the tail of the cable bolt 5. Once tension in the [N:\LIBLLI02024:PVH 6 cable bolt 5 is induced by the wedges 3, the jaws 6 can remain firmly fixed between the main plate 7 and the tail of the cable bolt 5. For the purpose of disengagement, a cable, rope or other strap 20 is provided which extends from the jaws 6 downwardly through the coil 23 and out through an opening 31 in housing cap 24.

In use, the tensioning apparatus, i.e. the hydraulic rams and plate 7, is attached to the tail 14 of the cable bolt 5 which typically projects about 70 mm below the wedges 3. The tensioning apparatus is attached by sliding it over the bolt tail which is automatically gripped by the set of jaws 6. By extending the rams 8 and 9, the cable bolt 5 is pre-tensioned. Once the required load is achieved, the rams are allowed to retract and the apparatus is removed from the bolt by pushing it slightly up and pulling the jaws 6 down by pulling on cord 20 to disengage the jaws from the bolt tail.

The cable bolt fitting (Figure 5) consists of the collar 2 and a set of wedges 3.

The collar 2 can have a conical shaped hole to accommodate the wedges. The minimum internal diameter of the collar 2 at position 12 is almost equal to the outside diameter of the cable bolt 5 to keep the cable bolt always in the centre of the collar even when the cable bends due to roof plate tilting. The collar 2 can have other shapes adapted to ensure that the cable bolt 5 remains centralised. Two such examples are shown in Figures 2 and 3. In Figure 2, the collar 2 has an upper internally projecting annulus 32 for engagement with the cable bolt. In Figure 3, a centralising insert 16 is 20 provided in this region.

Known prior art collars do not contact the cable bolt 5 and therefore provide :i no centralising effect. As the angle of the internal taper of the collar should preferably .be retained within the range of 6 to 80, the height of the collar must be slightly greater than would otherwise be the case in the prior art collars. Therefore, a collar having an 25 internally projecting annulus such as indicated at 32 in Figure 2 can be shorter and S'therefore less expensive.

The angle of the engagement surfaces of the jaws 6 and the surface 21 as measured from the vertical is typically to be in the range of 12 to 150. If the angle is too small, the jaws 6 would jam with the aperture 21. On the other hand, if the angle is too large, the interaction between the jaws 6 and aperture 21 would be ineffective.

.An alternative arrangement for pulling down on the jaws 6 is depicted in Figure 4. In this arrangement, there is provided a spring attachment 22 having three holes 33 therein, one for in each jaw segment 6. The jaw segments 6, 6a and 6b (not shown) have a lower annular channel 35 across which a number of pins 34 extend.

These pins 34 pass through the holes 33 of the spring attachment 22. Once pressure has been released in the hydraulic rams, the plate 7 has to be pushed up and the jaw segments 6, 6a and 6b have to be pulled down by pulling on the attachment 22 which is loaded by spring 23. The spring attachment 22 allows the jaw segments 6, 6a and 6b to IN:\LIBLL1]02024:PVH move away from the cable while it is being pulled down. A cord 20 serves this purpose. The defined angle of the interface between the jaws 6 and the conical section of the main plate 7 allows for release of the jaws 6 from the main plate 7 by hand activation of the pull cord 20. The pull cord 20 obviates the need for double acting rams which are heavier, more complex and cumbersome than single acting rams of the type described above.

It should be appreciated that modifications and alterations obvious to those skilled in the art are not to be considered as beyond the scope of the present invention.

For example, the specific means for retaining tension in the cable bolt 5 against bearing plate 4 disclosed herein can be replaced by other known means of maintaining tension in a cable bolt.

*o* *ooo* *~o *~e *o*o* IN:\LIBLL]02024:PVH

Claims (9)

1. A cable tensioning system for inducing tension in an in situ cable bolt, the system including: a bearing plate for bearing against a surface behind which said cable bolt is anchored and having an aperture therethrough and through which the cable bolt passes, engagement means including a collar surrounding the cable bolt, the collar having a central aperture therethrough, said aperture having a portion with an internal diameter substantially equal to the external diameter of the cable bolt and in contact therewith, the engagement means also being in contact with said bearing plate, the I0 engagement means including wedge means located within the collar and engageable with the collar and the cable bolt, a top plate having an aperture therethrough and through which the cable bolt passes, the top plate engageable with said engagement means, a main plate having gripping means for gripping said cable bolt and force inducing means engageable with said top plate for pushing said main plate away from said top plate, such that said gripping means induces tension in said cable bolt whereupon release of said gripping means from said cable bolt results in cable tension being at least substantially retained against said bearing plate by said engagement means.

2. The cable tensioning system of claim 1 wherein the collar is provided 20 with an internally projecting annulus for engagement with the cable bolt.

3. The cable tensioning system of claim 1 further including a centralising insert between the collar and the cable bolt, the centralising insert having an internal diameter substantially equal to the external diameter of the cable bolt.

4. The cable tensioning system of any one of claims 1 to 3 wherein said gripping means includes two or more jaws having a frusto-conical outer surface engageable with a frusto-conical inner surface of an aperture passing through the main plate.

The cable tensioning system of claim 4 wherein the jaws are biased into engagement with the frusto-conical aperture of the main plate by means of a resilient member housed within a cap fixed to the main plate.

6. The cable tensioning system of claim 1 wherein said force inducing means is a single hollow ram.

7. The cable tensioning system of claim 1 wherein said force inducing means comprises two or more hydraulic rams, each being a single acting hydraulic ram [R:\LIBLL]I I 189.doc:TCW adapted to apply a force in one direction only so as to move the top plate and main plate away from each other.

8. The cable tensioning system of claim 1 wherein a spring-loaded plate depends from the top plate and is adapted to bear against the wedge means of the collar.

9. A cable tensioning system for inducing tension in an in situ cable bolt, substantially as hereinbefore described in relation to any one embodiment as that embodiment is depicted in the accompanying drawings. Dated 16 July, 2001 DYWIDAG-Systems International Pty Limited io Patent Attorneys for the Applicant/Nominated Person SPRUSON FERGUSON *e *o *o [R:\LIBLL]I I 189.doc:TCW