Field of the Invention

The present invention relates to a locking member and the use of that member in a nut break-out device. The invention also relates to the use of the break-out device in a nut break-out system.

Background to the Invention

Nut break-out systems are an integral part of rock bolting installation systems in the mining and tunnelling industries. Nut break-out systems are used particularly on rock bolts, which are installed using resin cartridges.

The resin is used to anchor the rock bolt in a borehole in the rock. This resin, usually comprising two components, namely a mastic compound and a catalyst compound, is normally supplied and contained within a rupturable cartridge. The two resin components are normally separated into separate compartments by a thin plastic film or membrane placed within the resin cartridge.

The rock bolting operation consists of drilling a borehole into the rockface to the required depth and then inserting the resin cartridge into the borehole. The rock bolt is then pushed into the same borehole forcing the resin cartridge towards the back of the borehole. Further pushing of the rock bolt into the borehole causes the cartridge containing the resin to rupture. The bolt is then rotated and is pushed further back into the borehole. This process causes the plastic membrane within the resin cartridge separating the two resin components to rupture and further rotation of the bolt facilitates the two resin components to be thoroughly mixed together to produce the required adhesive composition. This installation process also causes the mixed resin to flow within the borehole around the rock bolt in the annulus between the bolt and the wall of the hole, thus encapsulating the bolt. The mixed resin then cures and hardens, typically over a time period of 10 to 60 seconds, causing the rock bolt to be securely anchored in the borehole.

Once the bolt is securely anchored in the borehole by the hardened resin, the final step of the installation procedure takes place. A bearing plate previously positioned upon the bolt or bar, or subsequently located upon the bolt or bar, is placed over the borehole and against the rock surface. A nut essentially having an internal threaded form therein is then screwed upon or onto a matching male thread on the rock bolt and tightened up firmly against the bearing plate and/or the rock surface. Alternatively, the nut is usually locked onto the bolt at the outset or prior to the mixing of the resin components. In this way, the nut and bolt can be rotated together to mix the resin during the resin mixing stage of the installation process.

The existing mechanisms that are used to lock a nut onto a rock bolt are designed to "break-out" above a certain applied torque. In this instance, "break-out" means that when a nut is fixed to a bolt or bar, such that it will not rotate with respect to the bolt or bar until a certain torque value is applied to the nut and with the bolt or bar rotatably fixed, then the torque value required to rotate the nut with respect to the bolt, is known as the "break-out torque", because the mechanism fixing the nut to the bolt or bar is then "broken". Such systems are known as "break¬ out systems" or "break-out nuts". In this manner, once the bolt is securely anchored into the borehole by the cured resin, further rotation of the nut by a drilling machine by applying a high torque, causes the locking mechanism on the nut to "break-out" and the nut can then be tightened up against a bearing plate. These nut-locking systems are known as "nut break-out systems" or "break-out nuts".

Many different systems have been developed to enable rotation of rock bolts to mix resin and then allow subsequent nut tightening to occur. Some of the nut break-out systems that have been used in Australia are as outlined below:

1. Separate or Positive Bolt Drive System

This simple system uses an integral square drive on the end of a rock bolt or cable, such that a separate drive dolly can be used over the square drive to rotate the bolt and mix the resin. Once the bolt has been rotated, the drive dolly over the square drive is removed and then a hexagonal drive dolly is placed over the hexagonal nut to tighten it up. This system has the advantage that the drive is positive and the square drive can withstand very high applied torque loads without premature break-out of the drive. This system is only one of two nut break-out systems to provide an absolute guaranteed nut break-out system. The major disadvantage of this system is the requirement to change drive dollies and this can waste precious time in underground mining operations, when many thousands of bolts are being installed every day. This is called a "Separate or Positive Bolt Drive System". 2. Damaged or Different Nut Thread Drive System

This system uses a nut where the threads on the back of the nut have been damaged by "crimping". The crimped or damaged threads initially prevent the nut from advancing onto the bolt, but once a high torque is applied, the nut is forced onto the bolt. This has the advantage of being cheap and simple, but it has severe disadvantages, namely that the break-out torque achieved is highly variable; the threads in the nut are permanently damaged, which can permanently damage the threads on the bolt; and in some cases, the residual torque required to advance the nut onto the bolt can be very high. This, in turn, limits the extent to which the nut can be tightened up and the amount of pre-tensioning that can be generated in the bolt. This is called a "Damaged or Different Nut Thread Drive System".

3. Resin Plug System

This system uses a resin plug, containing the two resin components, placed in the end of the nut. Typically, a resin plug is cast into the nut over a few threads at the end of the nut, or alternatively, a pre-formed plug is pushed or screwed into the end of the nut. The advantage of this system is that it is simple and the nut can simply be screwed onto the bolt, until the end of the bolt contacts the resin plug. Further rotation of the nut will also cause the bolt to rotate with the nut, and the resin components can thus be mixed by rotation of the bolt. Once the resin has cured and hardened and the bolt is secured within the borehole, further rotation of the nut at a high torque, will cause the resin plug to be pushed out of the nut and the nut can then be tightened up. The main disadvantage of this system is that it is difficult to generate very high break-out torques using this system, because as the resin plug is only acting as an "end-stop" to the bolt, it is relatively easy for the bolt to break and push through the resin plug. Another disadvantage with this system is that resin debris often contaminates the threads after the resin plug is broken and pushed out of the nut. The nut therefore cannot be completely free running. A further disadvantage of this system is that it is labour-intensive to thoroughly clean the nuts, lay them out separately on a flat stainless steel table and then pour or inject a small amount of resin into the bottom of each nut to form the resin plug. Yet a further disadvantage of this system is that the resin plug itself can then fall into the drive dolly and create debris, which can ultimately clog the drive dolly after many bolts have been installed. This is called a "Resin Plug System".

4. Nut Shear Pin Drive System

This system uses a shear pin, which is inserted into a hole drilled through the nut and into the bolt. The advantage of this system is that the shear pin then locks the nut onto the bar and different pins can be used to generate different break-out torques. However, a disadvantage of this system is that a hole has to be drilled both in the nut and into the bolt itself and this is a costly exercise in itself. The nut has to be drilled when it is on the bolt itself creating a handling and cost issue. Further, it is difficult to know if the hole will pass through the crest of the thread or the base of the thread on the bolt and therefore the exact position at which the shear pin will shear through is unknown. This can cause the shear pin to break out at the wrong torque value. Also, if the shear pin does not shear through cleanly, it can damage the thread on the bar, and the nut will not then run freely onto the bolt. This again restricts the tensile load that can be generated in the bolt. Finally, the break-out torque is unreliable and can cover a wide range of break-out torques, hi addition, it is difficult to generate very high break-out torques with this system, because if the shear pin is very strong, it can severely damage the bolt threads when it finally does break-out. This is called a "Nut Shear Pin Drive System".

5. Nut End Stop Drive System

This is similar to system 4 above, except that the shear pin is only located in the nut. A hole is drilled all the way through a nut at one end of it and then a shear pin is placed in this hole, such that the shear pin goes across the central hole in the nut enabling the nut to be only partially screwed onto the bolt. In this manner, the shear pin in the nut is acting as an "end-stop" similar to the resin plug system. Once the bolt has been rotated mixing the resin components and once the resin has cured, further rotation of the nut causes the shear pin to bend and then break, thus allowing the nut to be screwed onto the bolt. The advantage of this system is that the nuts can be drilled separately from the bolts and then be screwed onto the bolts at a later stage. One disadvantage is that this system still requires expensive drilling operations to be undertaken and the nuts are not securely locked onto the bolts. Another disadvantage is that as the shear pin initially bends and deforms, it can damage the initial threads at the end of the bolt, thus making it difficult or impossible to screw anything else onto the end of the rock bolt. To overcome this problem, some manufacturers have put a recess approximately 10mm long into the end of the nut which is not threaded, and the shear pin has two small grooves machined into it at the position where the shear pin comes out of the nut, such that failure always occurs at this position. The disadvantage with this is that the nut has to be 10mm longer than would otherwise be required. Finally, the break-out torque is unreliable as with the system above and can cover a wide range of break-out torques. In addition, it is difficult to generate very high break-out torques with this system, because if the shear pin is very strong, it can severely damage the bolt threads when it finally does break-out. This is called a "Nut End Stop Drive System". 6. Damaged or Different Nut Thread Drive System

This system has a main nut and a smaller threaded nut which are screwed together tightly in the factory. The advantages of this system are that there is no expensive drilling required and no debris is left to impede the thread or clog the drive dolly. The disadvantages are that the break-out torque is unreliable and it requires two threaded nuts rather than one. In addition, there is the added cost of having two threaded nuts rather than just one. This is called a "Damaged or Different Nut Thread Drive System".

7. Nut End Stop Drive System

This system has a thin steel washer retained in the end of a recessed nut by a series of crimps situated over the end of the recess. At high torque, the steel washer pushes past the crimps and allows the nut to run freely along the bolt. The advantages are that the nut is free- running after the washer is pushed out of the nut and that the nut can be fabricated separately from the bolt and screwed onto the bolt later. The disadvantages are that this system can still damage the ends of the threads on the end of the bolt, thus preventing other support brackets and nuts being screwed onto the bolt; and the washer creates debris in the drive dollies and can eventually clog them up completely. A further disadvantage of this system is that custom made nuts, having a recess to accommodate the washer have to be used and this custom made, extra length nut, not only costs more than a standard nut, but does not add to the strength of the nut. This is called a "Nut End Stop Drive System".

8. Reverse Rotation Nut Break-out System

This system has a "stop device" or stop washer welded or otherwise fixed onto the rock bolt behind the nut. The "stop device" may be a crimped or larger diameter threaded section, a welded washer, a circlip or ring or any other device that will prevent the nut from unscrewing off the rock bolt. The simplest of these stop devices is a steel stop washer welded to the bar behind the nut. In operation, the nut is rotated in a direction such that it will contact the stop washer. The welded stop washer is immoveable and therefore the bolt is forced to rotate with the nut. When the resin is mixed and cured, the drilling machine is rotated in the opposite direction such that the nut screws away from the stop washer and tightens up against the bearing plate. The advantages of this system are that it is absolutely guaranteed to work correctly without premature break-out of the nut; and the nut is free to run up the thread on the bolt once the direction is reversed. It can withstand as much torque as the drilling machine can apply, including shock loading, without failure. The disadvantages of this system are that it does require welding of the bolt, once the nut has been screwed thereon. It can also necessitate that at least one nut length of thread be left on the end of the bolt below the stop washer to allow other services to be screwed onto the end of the bolt. Finally, the system requires the use of a steel stop washer and a slightly larger nut than normal, such that the nut is larger than the stop washer. This is known as a "Reverse Rotation Drive System" or a "Reverse Rotation Nut Break-out System".

All of the above systems have advantages and disadvantages and different rock bolt manufacturers prefer to use their own in-house developed systems. Nevertheless, all of the above systems, except for system (1) above, have some mechanism to prevent the nut from screwing onto or off a rock bolt. Most of these break-out systems have one or all of the following disadvantages:

• they can damage the thread on the nut or the bolt and the nut is therefore not free running on the bolt after nut break-out (eg. shear pins, retained washer systems etc.);

• the "end-stop" break-out systems (i.e. shear pins across nut, or resin plugs or steel washers) have to withstand both a torsional force as well as a pushing or bending force of both the nut trying to rotate and the end of the bolt trying to push through or past the pin, plug or washer. Therefore the pins, plugs or washers have to be strong enough to resist both forces, but may be too strong to provide a clean break or shear when the nut does finally break-out.

• they create debris that can clog drive dollies (eg. resin plugs, retained washer systems) or can create debris that can clog the thread on the bolt itself (eg. resin plugs);

• they have unreliable break-out torques and can have premature nut break-out, particularly if they are subjected to shock loading, such as a bolt catching on mesh as it is being installed into the borehole. Alternatively, when using hand-held bolting machines, the break-out system may not break-out at all;

• the "end-stop" nut break-out systems (i.e. shear pin through nut, washer in end of nut, resin plug) do not secure the nut onto the rock bolt and the nut can unscrew during transport and handling and fall off the bolt;

• they require the manufacture of custom made nuts, which add to the cost of the system (eg. they require drilling nuts or bolts for shear pins or manufacture of custom made nuts with a recess for retained stop washers and for shear pins). Where custom made nuts have a recess for a washer or a shear pin, the recess itself is approximately 10mm long and this is an extra length on the nut, which does not contribute to nut thread engagement length; • the reverse rotation drive systems or reverse rotation nut break-out systems require a lot of thread length. The "stop device" or "stop washer" must be located at least one nut length from the end of the rock bolt, such that services can be screwed onto the end of the rock bolt when it is installed. If we then allow for the length of the stop device or stop washer itself and for the length of the nut, then this system requires approximately 50 to 80mm of thread length on the bolt just to assemble the system. The cost of this extra length of rock bolt is approximately $A0.15 to $A0.25, which must be added to the cost of the break-out system. Allowance then also needs to be made for thread length to enable thread tightening. This has the disadvantage that it can cause long threaded ends or "tails" on the bolts to be sticking out of the roof. This can be a hazard, particularly in mines or tunnels with low roof heights; and

• they are relatively expensive, in particular, the nut break-out systems using shear pins necessitating drilling of the nut or bar or both and although the cost of a shear pin is small, the additional costs associated with drilling holes in nuts and/or rock bolts to accommodate shear pins is very expensive, since allowance has to be made for drill wear and re-sharpening, bar and nut handling and the labour to install the shear pin itself. These additional costs add considerably to the total cost of the rock bolt.

hi addition to the nut break-out systems, which are designed to be used with rock bolts, there are also a large number of locking nuts, which are primarily designed to screw onto bolts or threaded studs, but not to unscrew or come loose. Typically, such nuts are used where, for example, vibration may cause a nut to come loose. Most of these locking nuts have a tight or restricted thread form along at least one section of the thread in the nut, such that the nut can be screwed onto a bolt or threaded stud, but it is very difficult or impossible to unscrew it. One example of these are "castelated nuts", which have a series of grooves cut around one end of the nut, such that the nut can be deformed slightly to cause the central hole in the nut to be smaller in diameter adjacent to the grooves in the nut rather than through the remaining length of the nut. As the castlelated nut is screwed onto a bar, the castlelated segments are forced outwards enabling the nut to screw onto the bar, while at the same time forming a tight fit on the bar.

Another form of locking nut is where the locking nut has a nylon washer attached to one end of the nut. The nylon washer has a central round hole in it, which is slightly smaller than the diameter of the bar to be screwed through it. In operation, the nut is screwed onto a bar until the bar contacts the nylon washer. Further rotation of the nut causes the thread on the bar to cut through or to distort the nylon washer, such that the bar forms a female thread form in the nylon washer. However, the thread form created in the nylon washer by the bar, fits very tightly around the thread form on the bar and grips it to prevent the nut coming loose.

There are various forms of locking nut, each of which is designed to screw onto a threaded bolt or threaded stud, each having a substantially round hole located in the nut itself. It is important to note that all of these systems are designed to allow a nut to screw onto a bar, but not to allow it to unscrew from a bar.

Finally, two nuts have been used together to effectively form a locking nut on a threaded section. In operation, the two nuts are screwed together tightly such that they jam together and lock onto the threaded section, thereby allowing the threaded section to be rotated. This system uses two standard nuts, neither of which is a locking nut itself.

The problems associated with nut break-out systems that have been used in the past include damage caused to the thread in the nut or to the thread on the bar, the requirement for the nut or the bolt to be pre-drilled or machined, which can be expensive in terms of both materials and labour or they have required the use of specialist shear pins or custom made nuts or washers. Some previous systems have also required the use of special resin plugs to be cast into the end of nuts.

The advantages of the present invention are that it can be used with or uses conventional nuts where the full length of the nut is internally threaded, such that the nut can be threadably engaged with the bolt over the full length of the nut. However, it has been found that the use of the present invention will not cause damage to the thread of the nut as occurs with crimped nuts, thereby allowing the nut to rotate freely on the bar or bolt once "break-out" of the new system has occurred. In addition, at failure, there is minimal debris that is pushed out which can clog the thread on the bolt itself, as occurs with the use of nut stop systems and the like, as described above.

With the nut break-out system of the present invention, specialist machining, drilling, welding or alteration of the thread on the bolt or on the bar or in the nut is not required. A nut break-out device and the system has been found to be inexpensive to manufacture and it can be assembled very rapidly onto the bolt or bar either on-site or in the factory off-site, thus saving labour assembly costs. Summary of the Invention

According to the present invention, there is provided a locking member to facilitate securement of an internally threaded member or section to an externally threaded member or section, wherein the locking member is of a unitary construction and comprises a substantially open helical configuration, whereby the locking member is substantially cooperable with at least one groove of one of the threaded members and at least one rib of the other threaded member when the threaded members are brought into lockable engagement with each other with the locking member therebetween.

Preferably, the internally threaded member is the internal thread form of a nut and the externally threaded member is the external thread form of a bar or bolt member. More preferably, the helical configuration comprises a helical spiral. The spiral preferably comprises a passageway within the helix, which may be open or partially open at both ends or closed at one end and wherein the internal diameter of the spiral is adapted to at least partially receive the externally threaded member therethrough. Most preferably, the whole of the spiral is gradually tapered over part or all of its entire length where the leading edge of the spiral has the greater tapered or reduced area i.e. it is at its thinnest at the leading edge and as one moves along the spiral towards its other end, the taper becomes less or the area of the spiral is at its greatest thickness at this other end. The taper can be continuous along the length of the spiral or may contain discontinuous regions. Alternatively, the tapering may occur only along a portion of the length of the spiral with the remainder of the spiral having no tapering. Alternatively further, the tapering may occur at both free ends of the spiral relative to a substantially intermediate portion thereof where no tapering or reduction in thickness occurs.

When the locking member comprises an open helical spiral, it is essentially composed of ribs and gaps between the ribs. When the spiral cooperates with the threaded section, the ribs of the threaded section extend into the gaps of the spiral.

The internal diameter of the spiral is adapted to receive the threaded section, hi one form, the internal diameter provides a passageway through the spiral, hi another form, one end of the passageway may be partially or wholly closed and in this form, the closed region is at the opposite end of the passageway, which is open to receive the externally threaded section. When the externally threaded section is a bar having an external thread form thereon, the spiral is locatable over the bar itself and the ribs of the bar are able to cooperate with the gaps of the spiral. The partially or wholly closed end region is preferably adapted to be used as the means for fixing (eg. threading or screwing) the locking member onto the external thread form of the bar.

When the spiral is to be applied to a device having an internal thread form, such as a nut, the spiral is substantially locatable internally in the nut, such that the ribs of the nut cooperate with the gaps of the spiral and the ribs of the spiral cooperate with the grooves of the nut's thread form. When the locking member is to be applied to the internal thread form of a device, the partially or wholly closed end region can preferably be used as the means for fixing (eg. threading or screwing) the locking member onto the internal thread form of the device. Preferably, the closed region is in the form of an end cap which cap is adapted to be used to thread the locking member into engagement with the threaded member. More preferably, the end cap is adapted to advance the locking member along or into the threaded member.

According to a further aspect of the present invention, there may also be provided a nut break-out device comprising the locking member and a nut, wherein the locking member is substantially locatable within the at least one groove formed within the internal surface of the nut. The nut, when fitted with the locking member, is adapted to threadably engage with an elongate externally threaded section.

Preferably, the threaded section comprises discontinuous segments of thread located about its external surface being aligned to form a threaded helix. Alternatively, the threaded section comprises segments, which are continuous around the circumference of the bar. In this case, the locking member is preferably first assembled in the nut and the leading end of the threaded section will contact and "jam" against the locking member in the nut. Preferably further, the threaded section comprises a hot rolled, continuously threaded steel bar or rock bolt.

Typically, such a steel bar will have steel ribs formed on the top of the bar and on the bottom of the bar, but not on the sides of the bar. These steel ribs on the top and the bottom of the bar form the discontinuous segments of thread on the bar.

Preferably, the nut is formed with a helical groove inside the nut, which is aligned at the same thread helical angle as the steel ribs on the steel bar. Preferably, the size and shape of this groove in the nut will typically be slightly larger than the ribs on the bar such that there is a small clearance between the groove in the nut and the ribs on the bar. Preferably further, the nut is freely rotatable about and advanceable along the bar, depending upon the pitch or helical angle of the thread form. Preferably, the locking member itself is helically shaped, such that it is adapted to cooperate with the discontinuous segments of thread on the bar. More preferably, the locking member is a spiral or helically shaped ring, which fits neatly into the at least one groove in the nut, wherein the groove is either continuous or non-continuous.

The locking member preferably extends around and within the groove in the nut for a sufficient length, the end cap of the locking member acting as an adjustment means to adjust the degree of protrusion of the locking means into the nut, such that once substantially located within the nut, the locking member will substantially fill the depth of the nut's groove and will be retained in the groove without falling out of it. This length is preferably at least one full rotation of the thread helix. More preferably, the locking member has a cross-sectional shape, which approximates the shape of the groove in the nut, which is to be screwed onto the threaded bar.

In use, the locking member is preferably first fitted into the helical groove in the nut to form a nut-break-out device, hi another form, where the locking member has a partially or wholly closed end region, the locking member is first fitted into the helical groove of the nut, preferably by rotating the partially or wholly closed end region relative to the nut whereby the free end of the spiral is screwed into the inside of the nut. When the partially or wholly closed end region of the locking member is screwed up against the end face of the nut, the nut break-out device is formed. The nut, substantially holding the locking member therein, is then screwed onto the bar onto which it is to be located by rotating the nut relative to the bar. As the lead or engaging first end of the thread of the nut encounters the first discontinuous threaded segment of the bar, the groove in the nut will freely accommodate the discontinuous threaded segment and they will become threadably engaged with each other. As the nut break-out device is further rotated about the bar, a rib (the first discontinuous threaded segment) on the bar may encounter the lead tapered end of the locking member positioned within the groove in the nut.

There is typically a clearance gap between the rib on the bar and the groove in the nut. Preferably, the lead tapered end of the locking member is small or is the thinnest part of the spiral and similar in size to the clearance gap. As the rib encounters the tapered end of the locking member, the rib will tend to ride up over the tapered end of the locking member. Further rotation of the nut break-out device with respect to the bar, will cause the rib to advance along the bar and thus ride further up over the taper of the locking member. As the thickness of the locking member gradually increases along the length thereof, the locking member will rapidly become greater in thickness than the clearance gap between the rib and the groove in the nut. When this occurs, very high normal stresses are generated between the rib and the locking member, thereby preventing the locking member from freely rotating in the groove in the nut. Eventually, further rotation of the nut break-out device with respect to the bar can only be achieved by the locking member being crushed, fractured or deformed by the rib of the bar. However, since the locking member is substantially contained and supported by the groove in the nut, the crushing strength on the locking member is very high and considerable torque has to be applied to the nut to overcome this and cause the locking member to fail. In practice, the break¬ out torque can be varied by making the locking member from materials of different strength and/or thickness.

Typically, the nut break-out device is assembled off-site, where the locking member is substantially or completely fitted from one end and into the nut to form the nut break-out device and the opposite end of the nut of the device is then screw-fitted onto the bar. As the nut is screwed onto the bar, only the threaded ribs on the bar are threadably engaged with the nut, and the core diameter of the bar passes through the central hole in the nut. The threaded ribs on the bar are typically some distance back from the leading end of the bar and therefore the leading end of the bar forms the core diameter of the bar. Since the helical spiral of the locking member is preferably fully contained within the helical groove in the nut, the core diameter of the bar also passes through the passageway of the locking member. Once this occurs, the locking member is unable to move out of the groove in the nut except by being unscrewed.

Upon further rotation of the nut containing the locking member, the leading rib on the bar will eventually encounter the locking member positioned within the nut. Further rotation of the nut with respect to the bar causes the locking member to begin to "jam" itself between the rib on the bar and the groove in the nut.

In use, once the locking member is assembled inside the nut, the nut containing the locking member i.e. the nut break-out device, is screwed onto the bar and is rotated up to a pre¬ set torque value. This pre-set torque value is preferably below the ultimate break-out torque of the locking member, but it is of a sufficiently high value to cause the nut break-out device to be firmly secured to the bar such that it will not shake loose during transport and handling.

Another in use application is where the nut break-out device can be used to rotate the bar as an all-in-one assembly, such that the bar or bolt can first be installed into a borehole and by rotating it, preferably by means of the nut break-out device positioned thereon, one can break the plastic resin cartridge and mix the frangible resin contained therein. Once the resin has been mixed and has cured in the borehole, the nut is further rotated in the same direction until sufficient torque is applied by a drilling machine to cause the locking member to fail such that the nut can be tightened up against the bearing plate or rock face.

Preferably further, the locking member is formed in the same helical shape as the threaded helical spiral in the nut and is of sufficient length that it will retain itself in the groove in the nut when it located or fitted inside the nut. Preferably, the locking member is greater than one half a thread spiral in length (greater than 180 degrees of rotational length) and less than ten thread spirals in length and may be made up of discontinuous segments of the locking member.

The locking member is preferably tapered at at least one end and then gradually increases in thickness, such that it will substantially ultimately fill the groove in the nut.- The cross-sectional shape of the locking member is preferably similar to the cross-sectional shape of the groove in one end of the nut. It is preferable that the locking member contacts the angled sides of the groove in the nut, such that as the locking member is pushed into the groove in the nut it becomes wedged and jammed between the angled sides of the groove in the nut.

In an alternative preferred embodiment of the invention, the locking member is first assembled on the bar, and the nut is then screwed along the threaded section and over the locking member to form the nut break-out device upon the bar.

In a further alternative preferred embodiment, the locking member is first fitted to the nut to yield the nut break-out device and the bar is then fed through the central hole of the nut and the passageway of the locking member. Most preferably, the locking member is used with hot rolled threaded sections where the ribs formed on the section are discontinuous.

In yet a further preferred embodiment of the invention, the locking member is formed with a helical spiral having a taper at a first end and is fitted with a partially or wholly closed end member such as a washer at the second end. Preferably, the outer periphery of the washer is of any suitable shape eg. round, oval, square, rectangular, hexagonal, octagonal etc. The diameter or overall length of the end member or washer is preferably equal to or greater than the internal diameter of the nut and thus is preferably equal to or of greater overall diameter or length than the outside diameter of the spiral. Alternatively, the diameter or overall length of the end member or washer can be greater than the external diameter of the nut and can take the form of a cap, whereby the cap is adapted to partly or fully overlay the external surface of the nut. The end member preferably has a drive fitting or assembly rotating means formed onto it such as an opening or well to enable the member and helical spiral to be rotated and screwed into the nut. When screwed against the nut, further rotation of the end member or washer via the drive fitting can cause the nut to also rotate with it in unison. The end member can act to limit the helical spiral from being screwed too far into the nut and therefore the helical spiral is preferably located in the same position for every nut. Once the locking member is firmly screwed into the nut, the same drive fitting on the end member can be used to screw the nut break-out device onto the bar.

Preferably, the locking member is made from plastic, fibreglass, epoxy resin, aluminium, lead, copper or any other suitable material. More preferably, the locking member is made from plastic or most preferably, from fibre reinforced plastic.

The installation of the above described system comprises a break-out device which is only subjected to compression, shear and torsional forces and is not required to provide resistance to the end of the bolt trying to push past a conventional end stop nut break-out system. When the rock bolt is being installed into the rock face, the axial force required to push the rock bolt into the borehole and through the resin cartridge is all transferred through the main drive nut and the threads on the bolt only.

The system thereby maximises the effective bolt length by initially having the nut only partially threadably engaged with the bar, the remaining length of the nut being occupied by the nut break-out device. However, as the nut is tightened up and the locking member is effectively removed from the nut, the nut becomes fully threadably engaged with the bar over its full length. By using this new nut break-out device and system, the bolt length required to be protruding from the borehole is minimised and the bolt length in the borehole in the rock is maximised. This reduction in the length of the bolt protruding from the borehole is a further advantage of the invention in that in a low ceiling situation such as in an underground mine, there is less likelihood of injury to workers.

The scope of protection also extends to the use of the nut break-out device of the present invention in the installation process of rock bolts into rock faces or for use with threaded sections in general. Therefore, the scope extends to a process for installing threaded sections into rock faces using the nut break-out device of the present invention.

Description of the Drawings In order that the invention may be more readily understood and put into practical effect, reference will now be made to the accompanying drawings, in which:- Figure 1 is a plan view of one form of the locking member in an open helical spiral form;

Figure 2 is side view of the locking member of Figure 1; Figure 3 is a perspective view of the locking member of Figure 1;

Figure 4 is a plan view of an alternative embodiment of the locking member where it is in the open helical form being closed at one end;

Figure 5 is side view of the locking member of Figure 4;

Figure 6 is a perspective view of the locking member of Figure 4;

Figure 7 is another perspective view of the locking member of Figure 4;

Figure 8 is a an end view of a nut fitted with the locking member of Figure 4;

Figure 9 is a side view of the locking member of Figure 4;

Figure 10 is an exploded side view of the nut break-out device using a locking member of Figure 4;

Figure 11 is a further side view of the nut break-out device fitted with the locking member of Figure 4;

Figure 12 is a side view of the nut break-out device fitted with the locking member of Figure 4 screwed onto an externally threaded member or section;

Figure 13 is a sectional view of Figure 12.

Figure 14 is a perspective view of an alternate locking member.

Figure 15 is a further perspective view of the locking member of Figure 14.

Detailed Description of the Preferred Embodiments

The invention will be described with respect to the manufacture of rock bolts, but the invention is not to be taken as limited to this application and could be applied to any threaded member or section. The invention is particularly applicable to hot rolled threaded sections, but again is not to be taken to be so limited.

Many hot rolled threaded members or sections have external cross-sectional shapes, which are not perfectly circular. This is often the result of having a circular core and then having ribs, which extend from the core on both the top and the bottom of the bar. Other hot rolled bars have deliberate longitudinal ridges or "flash" on opposite sides of the bar. This flash makes it easier to hot roll a circumferential rib all the way around the circumference of a hot rolled bar. In the case of hot rolled threaded sections, the ribs rolled onto the top and the bottom of the bar are aligned such that they form a helical thread form. This is achieved by having synchronised rolls in the hot rolling mill such that the ribs are formed in their correct helical position with respect to each other. The ribs on the threaded section therefore form discontinuous segments of the thread helix.

Most rock bolts have a nut and a domed ball washer on one end of the bolt. The nut is used to tighten the bolt up against the bearing plate and hence the supported rock face. The domed ball washer is used to provide angular movement between the nut and the bearing plate such that irregular rock surfaces can be supported without causing excessive shear forces on the nut and the end of the bolt. A conventional nut is hexagonal and has a flat, load bearing end face that contacts the domed ball. A conventional domed ball has a flat, load bearing contact face with the nut and a curved, partially hemispherical face that contacts the bearing plate. The hemispherical contact face against the bearing plate can provide angular movement between the domed ball and the bearing plate and still maintain full and uniform contact with it. In some cases, a flat, low friction washer is installed between the nut and the domed ball.

In a preferred embodiment of the present invention, the basic configuration of a nut and domed ball is used with a hot rolled threaded bar.

In the drawings, the same numerals have been used to designate similar integers in each Figure to avoid duplication of description.

In the preferred embodiment shown in Figures 1 to 15, there is shown a locking member 10 for use on a substantially circular externally threaded bar 17 having a series of ribs 18 extending away from the core of the bar 20. The ribs 18 are formed from the same material as the core of the bar 20. The locking member 10 has a substantially circular passageway 13 such that it substantially surrounds the threaded bar 17 and the core diameter 19 of the threaded bar 17 can fit through the passageway 13 in the locking member 10. The locking member 10 consists of an open helical spiral as shown in Figures 1 to 3 or a partially closed spiral as shown in Figures 4 and 5, which is substantially contained within the helical groove 21 in the nut 16. The locking member 10 preferably has angled sides 27 which are similar to the angled sides 26 of the helical groove 21 in the nut 16.

The locking member 10 has a leading end 12 at which the tapering of the spiral commences. The tapering reduces i.e. the spiral becomes thicker in width at 24 than at the tapered end 11. In use, the locking member 10 is fitted inside the groove 21 in the nut 16 at one end 22 of the nut 16. Where the locking member 10 has a partially closed end region or member 30 or a wholly closed end region or member 14, the end region acts as an end cap or a stop washer. The stop washer 30 has a front face 31 and a back face 32 with a suitable thickness therebetween. The back face 32 is integral with the spiral and when the spiral extending therefrom is fully engaged within the nut 16, the back face 32 is preferably in direct contact with the first end of the nut 22. Preferably, when the nut 16 is of substantially square, hexagonal, octagonal etc. shape, the outer periphery of the stop washer 30 has a complementary outer configuration as the nut with which it is to be aligned.

In one form, the device fitting or assembly rotating means 15, preferably an opening in the form of a well or closed depression, as shown in Figure 7, extends from the front face 31, but does not pass through to the back face 32. In Figures 14 and 15, the device fitting is an opening 33, which extends through both the front face 31 and back face 32 of end member 30. The shape of the fitting 15 or 33 can be of any suitable form, such that it may be circular, rectangular, square, hexagonal, octagonal etc. The fitting 15 or 33 is preferably adapted to cooperate with a complementarily-shaped drive member, which drive member (not shown) may form part of a drilling machine (not shown) and/or drive dolly (not shown). When the back face 32 of the washer 30 is in substantially fixed engagement with the nut, as in Figures 11 and 12, any further rotation of the washer 30 independently of the nut is substantially prevented. Such rotation of the washer and therefore of the spiral attached thereto, causes simultaneous and equal rotation of the nut with which it is fully engaged.

The outer periphery of the washer 30 is preferably in substantial alignment with the outside shape of the nut i.e. where the nut 16 and end member (preferably a washer) 30 are both hexagonal in shape, the hexagonal surfaces on each are in substantial alignment, with the washer 30 abutting a first end of the nut 22. The second end of the nut 23 which is open is then rotatably assembled onto the bar 17 such that the ribs 18 on the bar 17 are threadably engaged with the helical groove 21 in the nut 16. Rotation of the nut 16 with respect to the bar 17 will initially cause the core diameter 19 of the bar 17 to pass through the central hole 25 of the nut and the passageway 13 of the locking member 10. Further rotation of the nut 16 with respect to the bar 17 will eventually cause the leading edge of the rib 18 to come into contact with the tapered face 11 of the locking member 10. Further rotation of the nut 16 with respect to the bar 17 will cause the leading edge of the rib 18 to ride up over the tapered face 11 of the locking member 10. Even furtSai'ttJtfttkSii^the nut 16 with respect to the bar 17 will cause the rib 18 to generate very high

normal stresses on the locking member 10 as it advances along the tapered surface 11 of the locking member 10. These normal stresses will increase as the locking member 10 increases in thickness to its full thickness 24. These very high normal stresses will effectively prevent the locking member 10 from rotating in the groove 21 in the nut 16. Once the locking member 10 is prevented from rotating in the groove 21 in the nut 16, further rotation of the nut 16 with respect to the bar 17 can only occur if the locking member 10 fails by crushing, fracturing or by deformation or by a combination of any two or more of these failure modes. However, since the locking member 10 is substantially contained within, and supported by, the groove 21 in the nut 16, the force required to fail the locking member 10 is high. In practice, the force required to fail the locking member 10 is the break-out torque applied to the nut.

hi this manner, the nut 16 can be assembled onto the externally threaded bar 17 and be secured to the bar 17 by engaging the locking member 10 and the ribs 18 of the bar 17 and the nut 16 will not come off the bar 17 during transport and handling. This can easily be achieved by applying a pre-set torque to the nut 16, which is below the torque that would cause failure of the locking member 10.

In practice, once a borehole (not shown) for a rock bolt has been drilled and a resin cartridge has been installed into it, the externally threaded bar 17 is inserted into the borehole and a drive dolly (not shown) is located over the nut 16.

The drilling machine (not shown) attached to the other end of the drive dolly (not shown), then rotates and pushes the nut 16 and the externally threaded bar 17 into the borehole and through the resin cartridge and thoroughly mixes the resin. The locking member 10 prevents the nut 16 from rotating on the threaded bar 17 during this resin mixing stage of the operation.

Once the resin has been thoroughly mixed by rotation of the bolt and the resin has been allowed to cure and harden, the drilling machine then further rotates the nut 16 by applying a high torque sufficient to cause the locking member 10 to fail and enable the nut 16 to be tensioned up against a bearing plate (not shown) or a rock face (not shown).

The drive member may in its simplest form be a spanner whereby the spanner may be an open C-mouthed spanner, where at least two diametrically opposed external edges of the end member, as shown in Figures 14 and 15, are held therebetween and are caused to rotate as the spanner is rotated. Likewise, the spanner could be of the ring-type, where the periphery of the end member and/or aligned nut are receivable therein and are caused to both rotate when the spanner is rotated. Alternatively, the spanner may be of the type that has a member protruding from a handle where the protrusion is adapted to fit into and cooperate with the fitting 15 or 33. The drive member may be of the type normally employed in the art. The present invention has the advantage that the torque required to fail the locking member 10 has to be sustained for at least one rotation of the nut, such that if a shock loading on the bolt or bar 17 causes an instantaneous peak torque to be generated in the nut 16 (for example if the bolt catches on mesh around the collar of the borehole), the locking member 10 will not fail completely and will still be able to rotate the bolt.

It should be noted that the invention operates by restricting the rotation of the nut 16 with respect to the bar 17. It does not operate by providing an end stop at the end of the nut like alternative break-out systems (e.g. resin plugs in the end of nuts, pins across the central hole at the end of the nut; steel washers at the end of the nut etc.). Rotation of the nut 16 with respect to the bar 17 is restricted by having a segment of a helical spiral 24 of the locking member 10 substantially occupying the helical groove 21 in the nut 16 through which the ribs 18 on the bar 17 must rotatably pass. The shape and design of the helical spiral 24 on the locking member 10 is such that it has a gradually thickening area that progressively jams itself between the rib 18 on the bar 17 and the groove 21 in the nut 16. It effectively "jams" or "locks" itself onto the bar 17 with progressive rotation of the nut 16 with respect to the bar 17 and is hence called a locking member.

It is to be understood that the present invention can be applied to both right handed threaded and left handed threaded bars and rock bolts and to single start and to multiple start thread forms.

Where the specification refers to a "nut" or to a "nut break-out device" it is to be understood that the invention includes all such variations and modifications of the above and any other member that could be used to screw onto a thread form on a bolt or a bar.

Where the specification refers to a "locking member" it is to be understood that the invention includes "rings", "clips", "wedges", "washers", "segments of a thread spiral" and "segments of a thread helix" and all such variations and modifications of the above and any other member that could be used to be jam or wedge or impede the free rotation of a nut on a threaded bar.

Where the specification refers to a "locking member" it is to be understood that the invention includes a locking member that is substantially contained within a nut or a locking member that can be assembled onto a threaded bar and all such variations and modifications of the above. Where the specification refers to a "threaded segment" or to a "discontinuous threaded segment" or to a "discontinuous segments of thread" or to a "threaded rib" or to a "rib", it is to be understood that this includes any rib on any threaded bar that forms part of a thread helix around the bar.

Where the specification refers to a "thread" or to a "spiral" or to a "helix" or to a "screw thread" it is to be understood that this includes any thread form either on a bar or in a nut.

Where the specification refers to a "groove" or "nut thread" it is to be understood that this includes any internal thread groove or grooves in a nut.

Where the specification refers to a "bolt" or to a "rock bolt" or to a "threaded bar" or to a "continuously threaded bar" or to a "hot rolled threaded bar" or to a "threaded member" or to a "threaded section" or to an "elongate threaded member", or to an "internally threaded section" or an "externally threaded section" or to an "internally threaded member" or an "externally threaded member", it is to be understood that the invention includes all such variations and modifications of the above and any other elongate member that has a full or partial thread form along all or part of its length.

Where the specification refers to a "drive fitting" or to a "drive" on the locking member it is to be understood that this includes any fitting, shape, hole or other shape or form that could be used to rotate the locking member.

Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the invention includes all such variations and modifications. The invention also includes all of the steps, features, compositions, and compounds referred to or indicated in this specification (unless specifically excluded) individually or collectively, and any and all combinations of any two or more of said steps or features.

Throughout this specification, unless the context requires otherwise, the word "comprise", or variations such as "comprises" or "comprising" will be understood to imply the inclusion of a stated integer or group of integers, but not to the exclusion of any other integer or group of integers.