BACKGROUND TO THE INVENTION

This invention relates to a shearing nut for a rock bolt such as a roof bolt. In particular, but not exclusively, the invention relates to a shearing nut for use with a mining roof bolt. The invention also relates to a rock bolt such as a roof bolt including a shearing nut and in particular a roof bolt including a shearing nut in accordance with the first aspect of the invention.

Roof bolts are commonly used for strengthening or supporting rock, typically the rock surrounding underground excavations or behind free standing rock surfaces, such as in road cuttings, rock faces or hanging walls in mines. When installing roof bolts, holes are drilled in the rock for receiving the roof bolts. The roof bolts are then fixed in the holes by grouting with resin or cementitious fillers, by friction between the roof bolts and the rock walls of the holes, or a combination of grouting and friction. Some roof bolts are fixed in the holes by way of what is known as a spin-to stall system. In this system, resin is introduced into the hole and then the roof bolt is inserted. A nut carried at the exposed end of the roof bolt is turned which in turn rotates the roof bolt in the hole. This rotation serves to mix the resin the hole. A shear pin, which determines a breakout torque of the nut, prevents the nut from running up the thread of the roof bolt and once the resin is set, the roof bolt stops rotating which allows the nut to break the shear pin. The nut is then allowed to fasten the roof bolt in order to tension the system.

A disadvantage of this system is the inconsistency in torque required to break the shear pin. The linear force exerted on the shear pin by the nut is different with each roof bolt and is highly dependent on the manufacturing of the roof bolt. In the case of a cable roof bolt, consistency in cutting is highly improbable due to the heat generated during the coiling of the cable. Furthermore, shear pins seldom perform their intended function due to the angular face of a cable bolt and its segmented configuration.

It is an object of this invention to alleviate at least some of the problems experienced with existing shearing mechanisms for use with roof bolts.

It is a further object of this invention to provide a shearing nut for a roof bolt that will be a useful alternative to existing shearing mechanisms for use with roof bolts.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the invention, there is provided a shearing nut for use with a bolt, the shearing nut comprising: a first portion having an internal thread configured to engage a threaded end of the bolt; a second portion configured, in use, to prevent rotation of the second portion beyond a predetermined position along the threaded end of the bolt; and a shearing portion connecting the first portion and the second portion; wherein the shearing portion is configured, in use, to shear when a predetermined torque is applied to the first portion, thereby allowing the first portion to rotate relative to the second portion and along the thread of the bolt.

There is provided for a wall thickness of the shearing portion to be substantially thinner than a wall thickness of the first portion and a wall thickness of the second portion. The predetermined torque may be a function of the wall thickness of the shearing portion. The wall thickness of the shearing portion may be selected specifically based on the predetermined torque.

During manufacture of the nut, a heat treatment process may be used to increase the hardness of the nut. The predetermined torque may also be a function of the hardness of the nut.

There is provided for the first portion, second portion and shearing portions to be integrally formed.

The second portion may comprise an arresting or stopping means to prevent rotation of the second portion beyond a predetermined position along the threaded end of the bolt. The arresting means may comprise a pressure plate or a ring carried by the second portion towards an operatively outer end thereof. Fixing means may be provided for fixing the arresting means relative to the second portion. The fixing means may comprise a circlip.

Alternatively, the second portion may include a blind hole. In such a case, the arresting means may be formed by an end surface of the blind hole.

Further alternatively, the second portion may comprise a hole extending there through, and the arresting means may comprise a shoulder or a lip formation, situated towards an operatively outer end of the second portion and extending inwardly from an inner surface of the hole.

The internal thread of the first portion may extend into the shearing portion. Furthermore, the internal thread of the first portion may extend at least partially into the second portion.

The first portion may be configured as a driving head. An outer surface of the first portion may be shaped for engaging with a tool used for transferring a torque to the shearing nut, in use. The first portion may typically be configured as a hexagonal driving head. Alternatively, the driving head may be a polygonal driving head, having 3, 4, 5, 6, 7, 8, 9 or 10 sides.

There is provided for the bolt to be a rock bolt, a roof bolt and/or a cable bolt. The nut may be adapted specifically for the type of bolt with which it is intended to be used.

In accordance with a second aspect of the invention, there is provided a method of installing a rock bolt in a rock body, the method comprising: drilling a hole in the rock body; providing a rock bolt having a first end portion and a second end portion, wherein at least a part of the second end portion comprises a threaded portion, inserting the rock bolt into the hole in the rock body, such that the second end portion extends at least partially out of the hole; threading a shearing nut in accordance with the first aspect of the invention onto the threaded portion of the rock bolt until the second portion of the nut prevents the nut from being threaded any further; applying a torque to the first portion of the shearing nut thereby to rotate the shearing nut and rock bolt together until a predetermined torque is reached, causing the shearing portion of the shearing nut to shear; and threading the first portion of the nut further along the rock bolt.

There is provided for the method to include the step of placing a bearing plate over the second end portion of the rock bolt, before threading the shearing nut onto the threaded portion of the rock bolt.

The method may include the step of placing a washer over the second end portion of the rock bolt, before threading the shearing nut onto the threaded portion of the rock bolt.

The first portion of the shearing nut may be threaded further along the rock bolt after the shearing portion has sheared, thereby to create tension in the rock bolt.

The method may include the step of injecting a bonding compound into the hole in the rock body, before inserting the rock bolt in the hole in the rock body.

Alternatively, the rock bolt may comprise an axially extending channel with an outlet towards the first end portion. The channel may be provided for conveying a bonding compound.

The method may include the step of injecting a bonding compound through the axially extending channel of the rock bolt, and through the outlet, into the hole in the rock body, after inserting the rock bolt in the hole in the rock body. The method may include the step of mixing the bonding compound in the hole in the rock body by rotating the shearing nut and rock bolt together in the hole, before the predetermined torque is reached and before the shearing portion of the shearing nut shears.

The mixing of the bonding compound may cause the bonding compound to solidify and become set, thereby resisting rotation of the rock bolt and causing the torque applied to the first portion to increase until the predetermined torque is reached, causing the shearing portion of the shearing nut to shear.

The bonding compound may comprise a resin.

The method may include the step of retaining the second portion of the nut on the threaded portion of the rock bolt, to provide a safety barrier for the second end portion of the roof bolt extending partially out of the hole.

In accordance with a third aspect of the invention, there is provided a bolt assembly comprising: a bolt having a first end portion and a second end portion, wherein at least a part of the second end portion comprises a threaded portion; and a shearing nut according to the first aspect of the invention.

There is provided for the bolt to comprise a rock bolt and/or a roof bolt and/or a cable bolt.

The bolt may comprise an axially extending channel with an outlet towards the first end portion, the channel for conveying a bonding compound such as a resin. BRIEF DESCRIPTION OF THE DRAWINGS

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

Figure 1 shows an enlarged perspective view of a shearing nut in accordance with the invention, engaged with a roof bolt;

Figure 2 shows a perspective view of the nut of Figure 1 engaged with the roof bolt, wherein the nut has not sheared;

Figure 3 shows a perspective view of the nut of Figure 1 engaged with the roof bolt, wherein the nut has sheared;

Figure 4 shows a perspective view of the nut of Figure 1 ;

Figure 5 shows a side view of the nut of Figure 1 ;

Figure 6 shows a cross-sectional side view of the nut of Figure 1 , sectioned along line 6-6 in Figure 5;

Figure 7 shows a bottom view of the nut of Figure 1 ;

Figure 8 shows a side view of the nut of Figure 1 engaged with the roof bolt, in use, inserted into a hole in a rock, wherein the nut has not sheared; and

Figure 9 shows a side view of the nut of Figure 1 engaged with the roof bolt, in use, inserted into a hole in a rock, wherein the nut has sheared. DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of "including," "comprising," or "having" and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms "mounted," "connected," "supported," and "coupled" and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings and are thus intended to include direct connections between two members without any other members interposed therebetween and indirect connections between members in which one or more other members are interposed therebetween. Further, "connected" and "coupled" are not restricted to physical or mechanical connections or couplings. The terminology includes the words specifically mentioned above, derivatives thereof, and words or similar import. It is noted that, as used in this specification and the appended claims, the singular forms "a," "an," and "the," and any singular use of any word, include plural referents unless expressly and unequivocally limited to one referent. As used herein, the term “include” and its grammatical variants are intended to be non-limiting, such that recitation of items in a list is not to the exclusion of other like items that can be substituted or added to the listed items.

Referring to the drawings, in which like numerals indicate like features, a non-limiting example of a shearing nut in accordance with the invention is generally indicated by reference numeral 10. Referring to Figures 1 to 3, the shearing nut 10 is configured to be used with a rock bolt, such as a roof bolt 100. In the illustrated embodiment the roof bolt 100 is a cable bolt. However, it is envisaged that the roof bolt may be in any suitable form. The roof bolt 100 includes a first, distal end or end region 100.1 and a second, proximal end or end region 100.2. The second end region 100.2 includes an at least partially threaded portion 100.3 for, in use, receiving the nut 10. In use, the roof bolt 100 is configured to be inserted into a hole 120 (shown in figures 8 and 9) in a rock face or body 122, such that at least a part of its second end portion 100.2, and typically a part of the threaded portion 100.3, protrudes from the hole 120. This is best shown in Figures 8 and 9. More about the installation of the roof bolt 100 with reference to the nut 10 is explained below.

Although the nut 10 in the illustrated embodiment is specifically for use with a roof bolt 100, it is envisaged that the nut 10 may be used in any application requiring a nut to shear at a predetermined torque.

Referring now to Figures 4 to 7, the nut 10 includes a first portion 12. The first portion 12 is internally threaded and configured to engage the threaded portion 100.3 of the second end 100.2 of the roof bolt 100. The first portion 12 is configured as a driving head for receiving a tool, such as a wrench or nut driver. In the illustrated embodiment, the first portion 12 is configured as a hexagonal driving head. However, any suitable driving head shape for receiving a complementary wrench or nut driver is envisaged.

The nut 10 further includes a second portion 14. The second portion 14 is configured to prevent or inhibit rotation of the nut 10, in particular the second portion 14 of the nut 10, beyond a predetermined position along the threaded portion 100.3 of the roof bolt 100, when, in use, the nut 10 is threaded on to the roof bolt 100, and before the first and second portions (12, 14) have sheared from each other (as is discussed in more detail below). In the illustrated embodiment, the second portion 14 includes stopping or arresting means for preventing the further rotation of the nut 10. The stopping or arresting means is preferably in the form of a pressure plate 16. The pressure plate 16 is located inside the second portion 14 such that the operatively outer end of the second portion 14 is blocked off by the pressure plate 16. The pressure plate 16 is held or retained in place, by a fixing means, typically in the form of a circlip 18.

The pressure plate 16 may alternatively be replaced by a ring (not shown), which may also be held in position by a fixing means, in the form of the circlip 18.

It is envisaged in an embodiment not illustrated, for the second portion to form a blind hole, where the stopping or arresting means is integrally formed with the second portion.

In a further alternative embodiment which is not shown, the stopping or arresting means comprises a shoulder or a lip extending inwardly from a side wall of the second portion 14, at the operatively outer end of the second portion.

It will be appreciated that in the embodiments where the arresting means comprises a ring, a shoulder or a lip, an end portion of the bolt 100 with a smaller diameter (not shown) can pass through or beyond the arresting means. Consequently, the shearing nut 10, and particularly the second portion 14, may, in some embodiments, be configured to be located at an axial position along the length of the bolt 100, which may be spaced from a very end of the bolt 100. In such cases, a “step” is formed along the length of the bolt (the step is formed at a location where the diameter of the bolt transitions from a smaller diameter to a larger diameter), on which the second portion 14 catches. The step therefore interacts with the arresting means of the nut shearing nut 10. In use, the nut 10 is threaded onto the threaded portion 100.3 the roof bolt 100 until the pressure plate 16 abuts the outer end of the roof bolt 100. This prevents the nut 10 from threading any further along the thread of the roof bolt 100. In the illustrated embodiment, the second portion 14 has a smooth outer surface. However, the shape and finish of the outer surface of the second portion 14 is irrelevant to the functioning of the nut 10, provided the outer surface of the second portion 14 does not interfere with a tool or mechanism used in the driving of the first portion 12.

The nut 10 further includes a shearing portion 20. The shearing portion 20 connects the first portion 12 and the second portion 14. The shearing portion 20 is characterised by a substantially thinner wall than that of the first and second portions (12, 14). The thinner wall of the shearing portion 20 allows the shearing portion 20 to shear when a predetermined torque, a break-out torque, between the first portion 12 and the second portion 14 is reached.

The wall thickness of the shearing portion 20 may be varied depending on the desired break-out torque. A thicker wall thickness will require a larger break out torque and a thinner wall thickness will require a smaller break out torque. It will furthermore be appreciated that the nut 10 may be heat- treated during manufacture, to increase the hardness of the nut, thereby increasing or better controlling the torque at which the shearing portion 20 shears.

In the illustrated embodiment, the first portion 12, shearing portion 20 and second portion 14 are integrally formed. The internal thread of the first portion 12 extends through the shearing portion 20 and at least partially through or into the second portion 14. This allows the second portion 14 to remain connected to the roof bolt 100 when, in use, the shearing portion 20 shears, and in doing so, covering an end of the bolt 100. However, it is envisaged that only the first portion 12 needs to be threaded and that the shearing portion 20 and the second portion 14 may have smooth internal sidewalls. In this embodiment, the second portion 14 falls away from the roof bolt 100 when, in use, the shearing portion 20 shears.

The functioning of the shearing nut 10 will now be described in more detail with specific reference to Figures 7 and 8. The hole 120 is first drilled in the rock face or body 122 for receiving the roof bolt 100. Before the roof bolt 100 is inserted into the hole 120, the hole 120 is filled with a resin 124. Alternatively, the roof bolt 100 may be a hollow roof bolt whereby the roof bolt 100 is first inserted into the hole and then the resin is injected into the hole via the roof bolt 100.

The roof bolt 100 is inserted into the hole such that its second end portion 100.2 extends at least partially out of the hole. A bearing plate 102 is placed over the second end portion 100.2 of the roof bolt 100. The bearing plate 102 provides support and load distribution to the rock surface in the vicinity of the roof bolt installation. The nut 10 is then threaded onto the second end 100.2 of the roof bolt 100 by engaging and rotating its first portion 12 with a wrench or nut driver relative to the bolt 100. The nut 10 is threaded until the second portion 14, in particular the pressure plate 16, prevents the nut 10 from threading any further along the thread of the roof bolt 100.

At this point the rotation of the shearing nut 10 relative to the bolt 100 is inhibited. Further rotation of the first portion 12 of the nut 10 by the nut or wrench driver causes the roof bolt 100 to be rotated relative to the hole 120. This rotation of the roof bolt 100 serves to mix the resin 124 in the hole 120. As the resin starts setting, the rotation of the roof bolt 100 becomes inhibited, until further rotation of the roof bolt 100 is prevented.

Flowever, a torque is still applied to the first portion 12 of the shearing nut 10. When the torque is increased and reaches the predetermined torque, the shearing portion 20 shears. This allows the first portion 12 to be rotated relative to the second portion 14 and the threaded portion 100.3 of the bolt 100, to continue threading along the threaded portion 100.3 of the roof bolt 100, without being inhibited by the second portion 14.

The first portion 12 is threaded along the threaded portion 100.3 of the roof bolt until contact is made with a washer 104 and/or the bearing plate 102. The roof bolt 100 can now be tensioned. The washer 104 is provided between the bearing plate and the first portion 12 of the nut 10. The second portion 14 remains connected to the roof bolt 100. This serves to protect the threaded portion 100.3 for future use (such as when further hardware needs to be threaded onto the bolt 100). It also provides a safety feature in that it provides a cover over the end of the roof bolt 100 which poses a safety risk to personnel working in the vicinity of the installed roof bolt 100.

It will be appreciated that the nut 10 according to the invention provides an effective alternative to shearing mechanisms commonly used in conjunction with mining roof bolts. The shearing portion 20 can be designed so as to shear at a particular torque which will remain consistent, regardless of the manufacturing conditions of the roof bolt 100.

It will be appreciated that the above is only one embodiment of the invention and that there may be many variations without departing from the spirit and/or the scope of the invention. It is easily understood from the present application that the particular features of the present invention, as generally described and illustrated in the figures, can be arranged and designed according to a wide variety of different configurations. In this way, the description of the present invention and the related figures are not provided to limit the scope of the invention but simply represent selected embodiments.

For example, any suitable bonding compound may be used to replace the resin. Also, the first portion 12 may be configured as a driving head any suitable shape, and need not specifically be hexagonal. For example, other polygonal driving heads, such as a polygonal head having 4, 5, 6, 7, 8, 9 10 or more sides. Alternative driving heads may also be possible. The skilled person will understand that the technical characteristics of a given embodiment can in fact be combined with characteristics of another embodiment, unless otherwise expressed or it is evident that these characteristics are incompatible. Also, the technical characteristics described in a given embodiment can be isolated from the other characteristics of this embodiment unless otherwise expressed.