FIELD OF THE INVENTION

The present invention relates to a rock bolt hanger system for hanging mining services, such as pipes and cables, from the end of a rock bolt that has been installed through the rock face of a body of rock.

BACKGROUND OF THE INVENTION

Roof and wall support is vital in underground mining and tunneling operations. Mine and tunnel walls and roofs often consist of rock strata which requires reinforcement to prevent failure, such as fragmentation or collapse. Rock bolts are widely used for reinforcement purposes. Rock bolts are usually installed in a bore which is drilled into the rock body and the rock bolt is usually secured in the bore by a resin or a cement grout, or they can be frictionally fixed within the bore. Some rock bolts include a drilling tip applied to the leading end of the bolt for self drilling into the rock body.

Hangers are often fixed or applied to rock bolts that are installed in an underground mine or tunnel for supporting mining services such as pipes and cables. To support hangers, the rock bolts are installed in a manner to leave a short end portion protruding from the rock face and the hangers are attached to that protruding end portion. Rock bolts form a convenient anchor for hangers, given that they are securely anchored in the rock body and given that they can usually easily include at least a short section that protrudes from the rock wall that is not otherwise employed for another purpose.

One form of hanger arrangement that has been employed in the past includes a threaded connection between the hanger and the protruding end of the bar of the rock bolt. Thus, the hanger has included an internally threaded sleeve and a hanger loop or hook which is fixed to the sleeve, usually by welding. The sleeve is threaded onto the protruding end of the rock bolt which is also threaded. This form of hanger is a threaded nut hanger. A problem with this arrangement occurs when the room available in the underground mine in which the hanger is to be installed is very limited. In those circumstances, it is sometimes not possible or desirable to allow the end of the bar of the bolt to protrude to the extent necessary for the hanger to be attached to bar. This can for example, be because of the limited head room available within the mine or tunnel, or because the protruding end portions of the bolts protrude to the extent in the limited space available, that they could damage tyres of vehicles driving within the mine, i.e. the protruding end portions can come into contact with the side walls of vehicle tyres and damage the side walls, sometimes to the extent that the tyre fails.

Where there is insufficient room to allow an end of a rock bolt bar to protrude from the rock wall face enough for the connection of a hanger of the above described kind, "header bolts" can be employed in which the nut of the rock bolt is formed as an integral part of the rock bolt bar and at the extreme end of the bar. That is, the very end of the bar is formed by the nut and the bar does not protrude through the nut. With this type of rock bolt, plate hangers can be employed. Plate hangers are fitted about the bar adjacent the nut and are sandwiched between the rock face and the nut when the rock bolt is installed. Plate hangers include a loop or hook punched out of the plate through which a hanger can be inserted for supporting mining services as described above. A drawback with plate hangers is that they lack strength.

Even where there is room for a threaded nut hanger of the above described kind to be employed, sometimes the length of the bar that protrudes from the rock face after the rock bolt has been installed is insufficient for the threaded nut hanger to be properly attached. This occurs because most rock bolts are supplied with the nut locked to the end of the bar against rotation, for example with a shear pin extending through the nut and into the bar. The nut is locked relative to the bar in order facilitate rotation of the bar by rotating the nut as part of the rock bolt installation. Bar rotation is often required in order to mix resin components which are employed to fix the rock bolt into the rock body. Once the resin components have mixed and set, the lock applied to the nut is disabled (the shear pin is sheared for example) and the nut is rotated on the bar to sandwich a rock plate between the nut and the rock face. However, sometimes the nut cannot be rotated enough to leave a sufficient amount of the bar exposed for application of a threaded nut hanger. This occurrence is generally as a result of conditions at the particular site of rock bolt installation and is unpredictable. In these circumstances, a hanger is often applied to the protruding bar of a rock bolt in a less convenient or appropriate location. It is an object of the invention to overcome or at least alleviate one or more of the foregoing disadvantages associated with the prior art. SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided a rock bolt having an elongate shaft which has leading and trailing ends, a nut, and a hanger, the nut being attached to the trailing end of the elongate shaft and the hanger being releasably attached to the nut.

In a rock bolt according to the invention, the hanger is attached to the nut, which is attached to the trailing end of the rock bolt shaft. By attachment of the hanger to the nut, the need for a protruding section of the bar or shaft of the rock bolt beyond the nut is no longer necessary. This means that the extent to which the rock bolt protrudes from the rock face can be minimised, thereby maximising the amount of head room and minimising the prospect of damage to tyres of mine vehicles within the mine or tunnel. Moreover, there is nevertheless facility to include a hanger for the hanging of mining services, such as pipes and cables. Attachment of the hanger to the nut can be achieved in any suitable manner. In some forms, the attachment is to an external surface of the nut. Typically the external surface will be an axially extending surface of the nut, which extends co-axial to the axis of the rock bolt. In order to attach the hanger to the nut, the nut can include an externally threaded surface, while the hanger can include a complementary internally threaded bore. Threaded attachment of the hanger to the nut is a very convenient method of attachment, while the threads themselves can be made sufficiently coarse as not to be damaged or burred during transport, handling or installation of the rock bolt, or damaged by fly rock which occurs during tunnel blasting.

The nut of a rock bolt typically has at least a pair of flats on opposite sides of the nut to permit rotation of the nut by a suitable tool. Typically the nuts are hexagonal nuts, although square nuts or other shaped nuts can be employed. With these forms of nut, the externally threaded surface can be formed through the flats and corners of the nut, or through the corners only.

The invention can also apply to nuts which have a bore shaped for receipt of an Allen key for rotating the nut. Other nut constructions are also within the scope of the present invention.

Other arrangements to releasably attach the hanger to the nut include attachment by a bayonet fitting or a snap-fit arrangement. While these arrangements are given as examples of the type of releasable attachment that can be employed between the hanger and the nut, it is within the scope of the invention to employ any form of releasable attachment between the hanger and the nut.

The nut can include a threaded bore for threaded attachment to the trailing end of the elongate shaft of the rock bolt. The threaded bored can be a blind bore, which is closed at the inner end thereof, or the bore can extend through the nut so as to allow the trailing end of the elongate shaft to extend completely through the nut. In this latter arrangement, where the shaft extends completely through the nut, the hanger can be arranged so as not to impede that through movement. In some arrangements, this is achieved by the hanger having a construction including a connection portion for releasable attachment to the nut, and a hook or loop portion which extends from the connection portion for hanging items from the hanger and which is positioned not to impede the through passage of the shaft. For example, the hook or loop portion of the hanger can be offset from the axis of the elongate shaft.

Conversely, where the threaded bore of the nut is a blind bore, the hook or loop portion can be aligned with the axis of the elongate shaft.

The nut can be attachable to the elongate shaft of the rock bolt, or it can be formed integrally with that shaft. Typically where the nut is formed as an integral part of the rock bolt, the nut is a forged component and in the forging process a suitable attachment facility, such as a thread can be applied to the external surface of the nut. Alternatively, the nut can be applied to the trailing end of the elongate shaft threadably, but with a locking system applied to the nut to lock it against rotation relative to the shaft. The locking system can comprise a shear pin of the kind discussed above. Other methods for fixing the nut to the shaft include welding or crimping.

The rock bolt can be a self drilling rock bolt.

The present invention also extends to a rock bolt installation, including a rock bolt having an elongate shaft installed in a bore formed in a body of rock, a trailing end of the shaft protruding from the rock body, a nut applied to the trailing end and applying a load to a facing surface of the rock body, a hanger releasably attached to the nut.

The present invention further extends to a hanger for attaching to a rock bolt which has an elongate shaft and a nut attached to a trailing end of the shaft, the hanger having a connection portion for releasable connection to the nut and a hook or loop portion extending from the connection portion for hanging items from the hanger.

The hanger of the invention can be supplied separately to the rock bolt for use as required. Thus, the invention extends to a hanger which has a connection portion for releasable connection to the nut of a rock bolt and a hook or loop portion extending from the connection portion for hanging items from the hanger.

For example, it may be that existing hangers which are applied to a protruding portion of the rock bolt shaft are used where space availability does not dictate use of a hanger according to the invention. Accordingly, in some mines or tunnels, the invention might be used in some sections of the mine or tunnel and not in others. Rock bolts can be supplied with a nut formed to accept a hanger according to the invention, so that the option exists to adopt such a hanger if desirable. This leaves the option open to use existing hangers where the trailing end of the rock bolt shaft protrudes sufficiently, or to use the hanger of the invention where not enough of the shaft protrudes, or where space restraints apply. Alternatively, to reduce parts and to simplify the hanger installation process, the hanger of the invention could be employed regardless of whether a sufficient amount of shaft protrudes or not and thus mine operators would then have to deal with only one style of hanger.

It is possible that the hanger arrangement of the present invention will have a similar cost to the existing cost of a current hanger arrangement, although the cost of the rock bolt could be reduced because it could be shorter. Thus, use of the present invention could provide costs savings. An alternative and significant advantage could be that the full bolt length can be employed for rock reinforcement instead of requiring 50 -100mm at the trailing end of the bolt to project outside of the rock body for the hanger to be attached to. The hanger arrangement thus provides advantages over the prior art, potentially without a cost or operational penalty.

In order that the invention may be more fully understood, some embodiments will now be described with reference to the figures in which:

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a prior art rock bolt that can be employed with the present invention.

Figure 2 illustrates prior art hanger which has been fitted to the trailing end of a prior art rock bolt.

Figure 3 illustrates the invention as applied to the trailing end of a rock bolt. Figure 4 is a perspective view of a hanger according to the present invention.

Figures 5 and 6 are perspective views of hangers according to alternative

embodiments of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

With reference to Figure 1 , a rock bolt 10 is illustrated having an elongate shaft 1 1 , with a series of projections 12 formed in the length thereof, and threaded sections 13 and 14 formed at either end. The projections 12 are provided to assist anchoring the rock bolt 10 in a rock body. An expanding anchor 15 is attached to the threaded section 14 at a leading end of the shaft 1 1 , while a nut 16 is attached to the threaded section 13 at a trailing end of the shaft 1 1 .

The rock bolt 10 is a self-drilling bolt, as it includes a drill tip 17 at the leading end thereof. The rock bolt 10 is therefore rotated by a suitable drilling device to drill into a rock body and when the desired depth of drilling has been reached, the anchor 15 is activated, while a resin or grout mixture can also be inserted into the bore to set about the shaft 1 1 within the bore. The nut 16 remains outside the bore into which the rock bolt 10 is inserted. Typically the nut 16 is engaged by the drilling device to rotate the shaft 1 1 and thus to cause the rock bolt 10 to drill into the body of rock. For this, the nut is fixed on the shaft 1 1 against rotation initially, such as by a shear pin (not shown). Once drilling is complete, the arrangement fixing the nut 16 to the shaft 1 1 against rotation can be disabled and the nut 16 is then rotated on the threaded section 13 to impose a compression load against the facing surface of the rock body. A rock plate (not shown) is normally sandwiched between the nut 16 and the facing surface of the rock body. Once the rock bolt 10 has been installed in a rock body, a projecting end of the shaft 1 1 can be employed to support a hanger which can then be used to hang mining services, such as pipes and cables. Figure 2 illustrates the trailing end of the rock bolt 10 as inserted into a rock body 20 and showing a hanger 21 threadably

connected to the distal end of the threaded section 13.

The hanger 21 comprises a threaded sleeve 22 and a hanging portion 23 in the form of a loop. Figure 2 also illustrates a rock plate 24 which can be seen to be

sandwiched between the nut 16 and the facing surface 25 of the rock body 20. Referring now to Figures 3 and 4, an arrangement according to the invention is illustrated. The arrangement in Figure 3 shows an elongate shaft 30 of a rock bolt (the other components of which are not shown), which has a threaded end 31 . The elongate shaft 30 is inserted into a bore 32 drilled into a rock body 33 and the threaded end 31 of the shaft 30 can be seen to project from the bore 32. A nut 34 is threadably attached to the threaded end 31 . The nut can be a hexagonal nut of the same general shape as the nut 16 of Figure 1 . The nut 34 is threaded onto the threaded end 31 to apply a compressive load against the rock plate 35 which bears against the facing surface 36 of the rock body 33. In the illustrated

arrangement of Figure 3, the nut 34 has an internally threaded bore 37, which is blind, or closed at an inner end. By adopting a blind bore 37, the nut 34 can be securely locked onto the threaded end 31 . The nut 34 includes an externally threaded surface 40. Thus, the nut 30 is threaded both internally of the bore 37 and externally on the surface 40. Attached to the externally threaded surface 40 is a hanger 41 which is shown separated from the nut 34 and the shaft 30 in Figure 4. The nut 34, if shaped to be hexagonal or square or otherwise shaped, will usually have at least a pair of flats on opposite sides of the nut to permit rotation of the nut by a suitable tool, such as a drilling tool or a spanner. A square or hexagonal nut will include at least four flats, and corners between the flats where the flats intersect.

With these forms of nut, the externally threaded surface 40 can be threaded through both the flats and corners of the nut, or through the corners only. When threading through the corners only, it should be understood that the distinction between the corners and the flats is difficult to define, given that the flats usually extend to the actual ridge between the flats that forms the corners. Thus, formation of the thread through the corners is to be understood as including extending the threads into the flats in the immediate vicinity of the corners, so that the thread can be formed to extend through a portion of the flats in some embodiments of the invention and completely through the flats in other embodiments of the invention. The extent to which the thread is formed through the flats can therefore vary from a very small portion of thread formed in the flats up to a thread formed completely through the flats.

The hanger 41 includes a connection portion 42 and a loop portion 43. The loop portion 43 defines an opening 44 which can be employed for hanging mining services, such as pipes and cables. The connection portion 42 includes a threaded bore 45. The connection portion 42 threadably engages the externally threaded surface 40 of the nut 34. Like the bore 37 of the nut 34, the bore 45 of the hanger 41 is a blind bore to securely lock to the nut 34 (see Figure 3). An inspection opening can be provided in the base 46 of the hanger 41 , and through the base 47 of the nut 34 in order to allow inspection to ensure that the nut 34 is fully threaded onto the threaded end 31 of the shaft 30. Alternatively, the connection portion 42 can be open at either end so that an inspection opening need only be provided in the base 47 of the nut 34. While the loop portion 43 is shown in Figures 3 and 4 as extending substantially axially of the shaft 30, the loop 43 can alternatively offset from the axis of the shaft 30 and can, for example, be attached to one side of the connection portion 42 such as to extend from the side surface 48 of the connection portion 42. Examples of this are shown in Figures 5 and 6 in which connection portions 42 and 42 ₂ have loops 43i and 43 ₂ attached in an offset manner.

It will be evident from a comparison of Figures 2 and 3, that the extension of the respective shafts 1 1 and 30 beyond the rock body surfaces 25 and 36 is significantly different and much less in relation to Figure 3. This provides advantages in mines or tunnels where there is limited room available, such as for head room or for mining equipment, as the invention reduces the space needed to for the application of hangers.

It will be evident from a comparison of Figures 2 and 3, that the application of the invention is no more difficult than a prior art hanger of Figure 2, and includes no more additional parts.

The invention described herein is susceptible to variations, modifications and/or additions other than those specifically described and it is to be understood that the invention includes all such variations, modifications and/or additions which fall within the spirit and scope of the above description.

The disclosures in Australian provisional patent application No. 2010904643, from which this application claims priority, are incorporated herein by reference.