- 1 FITTING FOR A ROCK BOLT Technical Field The present invention relates generally to a rock bolt assembly including a fitting, and a method of forming a fitting on a rock bolt. 5 Background Art Rock bolt assemblies provide roof, wall and floor support. Roof and wall support is vital in mining and tunnelling operations. Mine and tunnel walls and roofs consist of rock strata, which must be reinforced to prevent the possibility of collapse. 1o Rock bolts include fittings which need to be able to accommodate significant loading to provide rock strata support. Fittings can be used as an end fitting to abut the rock face, to tension the bolt or to receive attachments. Fittings can also be used as an intermediate coupling to couple adjacent shafts or to tension the bolt. In some applications, such as cuttable bolts where the bolts are is destroyed during a mining operation on the strata support after their installation, it is suitable to make the fittings out of plastic. The above references to the background art do not constitute an admission that the art forms a part of the common general knowledge of a person of ordinary skill in the art. The above references are also not intended to limit the 20 application of the method and system as disclosed herein Summary According to a first aspect, disclosed is a rock bolt assembly comprising a rock bolt having an axis and a shaft extending between opposite first and second ends spaced apart along the axis, and a fitting mounted to the rock bolt and 25 operative to accommodate axial loading, the fitting comprising an inner member defining a passage through which the shaft locates, and a polymeric body being moulded over the inner member and at least a portion of the shaft, wherein the inner member is operative to engage with the shaft of the rock bolt to enable -2 the fitting to accommodate the axial loading. According to a second aspect, disclosed is a method of forming a fitting on a rock bolt comprising locating an inner member onto a shaft of the rock bolt, and over-moulding a polymeric body on the inner member. 5 Brief Description of the Drawings Embodiments of the present disclosure will now be described with reference to the following drawings by way of example only, where: Fig. 1 is a side view of an embodiment of a rock bolt assembly including a fitting; 10 Fig. 2 is a cross-sectional view of the embodiment shown in Fig. 1; and Fig. 3 is a perspective view of the inner member shown in Fig. 2 located on a rock bolt. Detailed Description The disclosed rock bolt assembly is suitable for use in hard rock applications as is well as in softer strata, such as that often found in coal mines, and it is to be appreciated that the term "rock" as used in the specification is to be given a broad meaning to cover both these applications. The following description relates to assemblies for reinforcement of rock strata through various bolting support mechanisms, including bolts bonding multiple layers or blocks together 20 and tension placed across joints and bedding mobilising frictional resistance to rock movement. According to a first aspect, disclosed is a rock bolt assembly comprising a rock bolt having an axis and a shaft extending between opposite first and second ends spaced apart along the axis, and a fitting mounted to the rock bolt and 25 operative to accommodate axial loading, the fitting comprising an inner member defining a passage through which the shaft locates, and a polymeric body being moulded over the inner member and at least a portion of the shaft, wherein the -3 inner member is operative to engage with the shaft of the rock bolt to enable the fitting to accommodate the axial loading. The fitting could be mounted anywhere along the shaft of the rock bolt. For example, the fitting could be an end fitting which is mounted to one of the first of second ends or an 5 intermediate fitting mounted between the first and second ends. To allow rock support to be achieved, the end of the rock bolt may be anchored mechanically to the rock formation by engagement of an expansion assembly on the end of bolt with the rock formation. Alternatively, the bolt may be adhesively bonded to the rock formation with a resin bonding material inserted 10 into the bore hole. Alternatively, a combination of mechanical anchoring and resin bonding can be employed by using both an expansion assembly and resin bonding material. According to the first aspect the fitting is over-moulded onto the shaft of the rock bolt, and thus a fixed connection is provided between the shaft and the is fitting. As a result, rock support is achieved through the rock bolt being thrust or driven into a bore in the rock strata. In some forms, the material of the inner member has a higher material strength than the polymeric body. The material of the inner member may be stronger and stiffer than material than the polymeric body. For example, the inner 20 member may be made from steel, copper, brass or carbon fibre which is able to accommodate load transfer from the rock bolt to allow for the inclusion of the polymeric body without premature failure of the rock bolt. The body may be formed from any type of polymer such as a thermoset glass reinforced polymer (e.g., nylon). This arrangement is advantageous as the 25 steel inner member accommodates the radial loading on the shaft of the rock bolt to prevent the polymer fitting from expanding under radial load which may otherwise cause fracture of the body. In some forms, the inner member is operative to engage with the shaft of the rock bolt to enable the fitting to accommodate the axial loading. The inner -4 member may engage the shaft by various means, for example, by threaded engagement, adhesive, welding, swaging or the like. When the inner member is in threaded engagement with the shaft of the rock bolt, the thread profile may be any shape and pitch (e.g., the thread profile may be sinusoidal). In some 5 forms, the inner member is operative to accommodate radial loading induced by axial loading of the fitting such that loading induced on the body is substantially axial. Axial loading of the fitting is caused by driving the rock bolt into the bore. Load transfer to the fitting also occurs through the fitting being in forced engagement with the rock face (either directly or indirectly). The inner member io may also be operative to accommodate radial loading induced by axial loading of the fitting such that loading induced on the body is substantially axial. In some forms, the body is moulded over the inner member and at least a portion of the shaft of the rock bolt. The inner member may be located anywhere in the body of the fitting. The body has a leading end and a trailing is end. The inner member may be located at or towards either the leading end or the trailing end or centred-between the ends of the body. In some embodiments, the inner member includes an abutment surface that extends radially in relation to the shaft, and in use the abutment surface is operative to engage an internal surface of the body so as to inhibit removal of 20 the fitting from the shaft. However, the inner member may also be any suitable shape, for example, a cylindrical member, a conical member, a hexagonal member a square or rectangular member, or a cylindrical member that is stepped or has a collar that extends radially in relation to the member anywhere along its length. 25 In addition, the shaft of the rock bolt may be formed from fibre-reinforced polymer. For example, the shaft may be manufactured from fibreglass, carbon fibre-reinforced polymer, or any type of fibre-reinforced-polymer including both natural and synthetic fibres. A fibre-reinforced polymer shaft is beneficial as it is cuttable without damaging mining equipment (as discussed above), and can 30 be manufactured by continuous extrusion and then cut to size. Although, the -5 fitting is discussed primarily in relation to a rock bolt assembly in the form of a cuttable bolt, embodiments of the fitting may be used with either a rigid bolt or a cable bolt, and are not limited to a cuttable bolt. According to a second aspect, disclosed is a method of forming a fitting on a 5 rock bolt comprising: locating an inner member onto a shaft of the rock bolt, and over-moulding a polymeric body on the inner member. In some forms, the method may also include one or more of the following steps: * moulding the body over the inner member and at least a portion of the shaft; 10 e the inner member is engaged with the shaft of the rock bolt; * the inner member is in threaded engagement with the shaft; and * positioning the inner member on the shaft such that, during moulding the fitting over the inner member, the inner member is positioned at or towards a trailing end of the body. is Referring to the Figures disclosed is an illustrative embodiment of a rock bolt assembly 10. Referring to Fig. 1, disclosed is an embodiment of the rock bolt assembly 10 including a rock bolt 12 and a fitting 14 mounted to the rock bolt 12. The rock bolt 12 has an axis A and a shaft 16 extending between opposite first 18 and second ends spaced apart along the axis A. The fitting may be used 20 as an end fitting which abuts the rock face, is able to tension the bolt, is able to receive a drive to tension the bolt or is able to receive an attachment. Fittings may also be used as an intermediate coupling to couple adjacent shafts or to tension the bolt. In the illustrated form, the fitting 14 is an end fitting that is arranged to be 25 connected to a drive (not shown) that is used to install the device. The fitting is also arranged to abut the rock surface (either directly or indirectly) on installation. As such the fitting is required to accommodate significant loading -6 (particularly axial loading) applied during both installation and tensioning of the bolt. In the illustrated embodiment, the body 20 has a leading end 24 and a trailing end 26. The leading end 24 is convex to facilitate alignment of the body 20 in 5 use in the rock bolt assembly. In some forms, the convex leading end 24 may be a dome-shaped end 28. In use, the rock bolt 12 is configured to be at least partially located in a bore formed in a rock substrate. The dome-shaped end 28 is partially located in the bore against the surface of the rock substrate, and increases in diameter extending from the leading end 24. The diameter of the 10 bore is smaller than at least the maximum diameter of the dome-shaped end 28 to allow the body 20 to locate partially in the bore of the rock substrate. In other words, the dome-shaped leading end 28 abuts against the surface of the rock substrate. The dome 28 is designed to form a spherical seating washer. In alternative non-illustrated embodiments, the rock bolt assembly may include is a plate, for example, a volcano plate. The plate is located between the surface of the rock substrate and the leading end of the body. In this embodiment, the plate and the dome-shaped leading end are designed to facilitate alignment by accommodating angled loading from the plate to the fitting for maximum load capacity. 20 The trailing end 26 of the body is in the form of a drive receiving portion 30 that is arranged to receive the drive to impart rotary and/or axial drive to the rock bolt assembly 10. In the illustrated embodiment, the drive receiving portion 26 is hexagonal, but may be any other non-circular profile. Alternatively, the driving receiving portion may be in the form of a recess formed in the end of the 25 body to receive a suitable male drive. In the illustrated form, the body 20 also includes an end surface 32 that extends in the same plane as the maximum diameter of the dome 28. The end surface 32 extends radially from the shaft 16. Extending from the end surface 32, the body 20 includes a coupling 34 in the form of a male thread 34 that extends 30 from the end surface 32 along an external surface of the body 20. The male -7 thread 34 may be used for receiving an attachment (not shown). The thread 34 extends to the trailing end 26 to be accessible and visible for facilitating receipt of the attachment. The thread 34 a minor thread diameter larger than maximum dimensions of the drive receiving portion 30 to allow attachments to 5 be attached. Attachments may be used with the bolts, and when installed, may be used to hang mesh to inhibit crumbling and breaking rock from falling on workers. During the development of a roadway or tunnel additional mining induced stress can break the rock surface about a tunnel, especially during the traction of the 10 ore. The mesh may be required for the protection of the workers. The mesh can be fixed close to the rock surface by a secondary plate that is coupled to the body of the fitting. The secondary plate may be coupled may any suitable means, for example, a threaded nut or fixed by any other means. Also, other embodiments of attachments may be used, such as an attachment to hang is mining services (e.g. water or power lines). To accommodate the loading applied to the fitting during installation and/or use, the fitting 14 as shown is formed in a two part construction that includes a body 20 and an inner member 22 (as shown in Fig. 2). The body 20 is polymeric and is moulded over the inner member 22 and the shaft (as will be described 20 below). As the body is moulded, it is able to be formed into a wide variety of shapes. Also by being polymeric it is able to be used in circumstances where the bolts are cut and passed through mining equipment without damage to the equipment, which protects the equipment. In the illustrated embodiment, the body 20 is formed from a thermoset glass 25 reinforced polymer (e.g. nylon) that is moulded over the steel inner member 22. It is understood that the body made be made from any mouldable plastic, such as any thermosetting plastic or thermosetting resin. Now turning to Fig. 2, the inner member 22 defines a passage 36 through which the shaft 16 locates. The inner member 22 is operative to engage with the 30 shaft 16 to enable the fitting 14 to accommodate the axial loading. In the -8 illustrated embodiment, the inner member 22 includes an internal thread and is in threaded engagement with an external thread of the shaft 16. The shaft 16 includes a sinusoidal thread, but the thread profile may be any shape and pitch. As a result of the shape and pitch of the thread both axial and radial load is 5 transferred to the fitting 14 through the shaft 16. The inner member 22 is operative to accommodate radial loading induced by axial loading to the fitting 14 such that loading induced on the body 20 is substantially axial. The inner member 22 is designed to provide radial confinement on the shaft 16 to inhibit the polymeric body 20 from expanding. For example, the inner member may be 10 formed from steel which, because of its material properties, is able to accommodate the loading transferred from the rock bolt. In some embodiments, the inner member 20 prevents the body 20 from expanding. This enables rock support to be achieved. The material of the inner member 22 has a higher material strength than the is polymeric body 20. The inner member 22 is made of a material that is able to withstand the load applied to the fitting while resisting failure. The shape and material of the inner member determines the maximum load the inner member is able to withstand without failing. The material strength of the inner member not only refers to its load carrying capacity, but also its stiffness (i.e., its ability 20 to resist deformation) and its stability (i.e., its ability to main maintain its original shape). The inner member has a high stiffness and stability and is able to restrict the radial stresses (or hoop stresses) induced by the thread of shaft without being permanently deformed. In the illustrated embodiment, the inner member is formed from steel. The steel inner member 22 provides radial 25 confinement on the thread of the shaft 16 to prevent the polymer body 20 expanding. For example, the combined steel inner member 22 with over moulded body 20 is able to withstand over 10 tonne and around 15 tonne load without failing while minimising the amount of steel in a cuttable bolt. To accommodate the transfer of the loading between the inner member 22 and 30 the body 20, in the illustrated embodiment, the inner member 22 has an abutment surface 38 that extends radially in relation to the shaft 16. The -9 abutment surface 38 engages an internal surface 40 of the body 20 so as to inhibit removal of the fitting 14 from the shaft 16. The abutment surface 38 acts to inhibit the body 20 from de-bonding from the shaft 16 and the inner member 22. In other words, the engagement between the abutment surface 38 and the 5 internal surface 40 provides resistance to the axial forces and, in some embodiments, prevents the body 20 from sliding off the shaft 16 and the inner member 22. In the illustrated embodiment, the inner member 22 is cylindrical, but the inner member may be any suitable shape. The abutment surface 38 is formed at a 10 leading end of the inner member 22. However, the inner member may also be stepped to so that one or more abutment surfaces are located towards a trailing end of the inner member, or the inner member may have a collar having an abutment surface. The inner member may be hexagonal or a non-circular shape to assist with locating of the inner member onto the shaft. is As mentioned above the fitting with the polymeric body is ideally for use in cuttable bolts. When used in such applications the shafts are typically also made from a polymer. In particular, the illustrated shaft is made from fibreglass but may be made from any fibre-reinforced polymer (natural or synthetic), such as carbon-fibre reinforced polymer. The combination of the polymeric shaft and 20 body with a small steel insert is advantageous. Where the bolt 12 is being cut to remove the mined material, the steel inner member 22 is minimal enough to pass through cutting and transport equipment without damage to the equipment. The rock bolt and the body of the fitting both are made from polymer which protects the equipment. 25 The fitting 14 is also low profile in relation to the surface of the rock substrate, which also protects the mining equipment. In this regard, the fitting does not protrude excessively from the surface of the rock substrate. Shaft tails protruding into a mine tunnel are susceptible to damaging equipment or equipment can hit and damage the ground support provided by the rock bolt 30 assembly.
-10 A method of forming the fitting on the rock bolt is illustrated in Fig. 3. First, the inner member 22 is located onto the shaft 16 of the rock bolt 12. The inner member 22 may be located anywhere along the shaft 16 and is not limited to be the first end 18 of the shaft 16. In the illustrated form, the inner member 22 is 5 engaged with the shaft 16 of the rock bolt 12 by threaded engagement. The inner member has an internal thread which corresponds to the external thread of the shaft. As a result, the inner member is screwed onto the shaft 16. Second, the polymeric body 20 is over-moulded on the inner member. In the illustrated embodiment, the body is moulded over the inner member and at io least a portion of the shaft. Again, the fitting may be an intermediate fitting and is not limited to being an end fitting as shown. The inner member 22 is positioned on the shaft 16 such that the inner member 22 is positioned at or towards the trailing end 26 of the body 20. Accordingly, embodiments of fittings and rock bolt assemblies are provided is which allow for the transfer of torque and tensioning of rock bolts. Furthermore, in at least one form, the fitting is multifunctional and is suitable in combination with cuttable bolts and for the attachment of related attachments. As will be understood, variations of the above described rock bolt assemblies can be made without departing from the scope of the claims. 20 While the fittings and rock bolt assemblies have been described in reference to its preferred embodiments, it is to be understood that the works which have been used are descriptive rather than limiting and that changes may be made without departing from its scope as defined by the claims. It is to be understood that a reference herein to a prior art document does not 25 constitute an admission that the document forms part of the common general knowledge in the art in Australia or in any other country. In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or -11 "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.