EP0433342A4

EP0433342A4 - Rock bolt

Info

Publication number: EP0433342A4
Application number: EP19890910049
Authority: EP
Inventors: Peter Tooth
Original assignee: NEWKEM AUSTRALIA Pty Ltd
Current assignee: NEWKEM AUSTRALIA Pty Ltd
Priority date: 1988-09-06
Filing date: 1989-09-06
Publication date: 1992-08-12
Also published as: EP0433342A1; WO1990002866A1

Abstract

A rock bolt (1) has a body (2) formed of a synthetic material such as plastics to overcome problem associated with the use of metal materials, especially in the mining and construction industries. The rock bolt does, however, include a metal thread (15) at one end thereof, which is either integrally formed into the body of the bolt, or a helical spring housed in a recess formed in the body of the bolt. One or more reinforcing rods are moulded into the body (2) of the rock bolt (1) in a longitudinal direction.

Description

ROCK BOLT

THIS INVENTION relates to rock bolts and in particular to rock bolts for use in the construction and mining industries. In particular, the invention relates to a rock bolt which, in one form of the invention, allows for the tensioning of rock bolts in bore holes formed in strata, such as in mining and construction industry operations.

Rock bolts are well known in the mining and construction industries, such as for tensioning strata and for use in locating machinery and apparatus relative thereto. In particular, in mining operations it is known to form bores in a strata and for rock bolts to be inserted therein. The rock bolts are usually held within the bores, such as by chemical anchors, or other appropriate bonding or securing means, the located rock bolts thereafter being tensioned in order to reinforce and tension the strata.

Many rock bolts used up until this time have been formed of a metal material, the bolt having a thread extending along at least part the length thereof, such rock bolts being operated by being inserted into a bore formed into a strata and, as indicated, being held in the bore by a settable bonding agent or resin. For example, one or more suitable chemical anchors, as known and available, are inserted into a bore and on the distal end of a rock bolt coming into contact therewith, and/or being rotated, the chemical anchors are ruptured so that the components thereof react together to form a settable bonding agent which holds the rock bolt within the bore. The other end, being the butt end of the rock bolt, will extend outwardly from the bore and face of the strata, and such a butt end is preferably formed or provided with a thread. A nut is then passed over the thread and tightened along the thread so as, for example, to come into contact with a bearing plate between the nut and the strata surface, the nut then being tightened against the bearing plate to stress and tension the bolt and strata.

Rock bolts used up until this time have in many cases been constructed of a metal material. However, such metal rock bolts have a number of disadvantages, including, inter alia: the fact that they are prone to corrosion; they are expensive and are difficult to handle sometimes, especially when it is desired to change the length of the rock bolts. When it is desired to change the length of such rock bolts, it is necessary to cut the metal material, and this will often cause damage to mining or construction equipment. Further, in some mines or construction sites, where further excavation is to take place, machinery comes into contact with rock bolts already embedded in the strata. Where such rock bolts are constructed or made of a metal material, they can cause damage to excavation machinery and the like.

Suggestions have been made to utilize a rock bolt of a non- metal material, but these have not always been as successful as expected or desired.

An example of a rock bolt formed of a non-metal material, is found in Australian patent specification No 76314/87 which discloses a tensionable dowel for reinforcing walls in roofs in mining and excavation operations. Such a dowel is formed of a reinforced engineering synthetic material. It has, however, been found that such synthetic material, in use, is unable to be satisfacto ily tensioned, such as to the extent that a metal rock bolt is able to be tensioned. Thus, despite the statements within Australian patent specification No 76314/87 the rock bolt disclosed and defined therein fails to satisfactorily meet the stated objectives thereof and has not been successful in use. It is an object of this invention to go at least some way towards overcoming or minimizing the problems associated with rock bolts known and used up until this time.

Other objects of this invention will become apparent from the following description.

According to one aspect of this invention, there is provided a reinforcing bolt, having an elongate body formed of a synthetic material and including a metal thread at or adjacent one end thereof.

According to a further aspect of this invention there is provided a reinforcing bolt, having an elongate body formed of a synthetic material, and including an integrally formed metal thread at or adjacent one end thereof, said thread standing proud of said synthetic body portion.

According to a further aspect of this invention there is provided a reinforcing bolt, having an elongate body formed of a synthetic material and including an integrally formed metal thread, at or adjacent one end thereof, said metal thread being formed of an elongate helix formed of spring steel material and being integrally formed with said synthetic body portion.

According to a further aspect of this invention, there is provided a reinforcing bolt, having an elongate body formed of a synthetic material, and having a recessed thread formed or provided in or adjacent one end thereof; a metal thread being located and housed within said recessed thread such that at least a portion of said metal thread extends and stands proud of said body portion, along at least part the length thereof. 1*

According to a further aspect of this invention there is provided a reinforcing bolt having an elongate body portion formed of a synthetic material, and having a recessed thread formed or provided in or adjacent one end thereof; a metal thread member being provided and being adhered or bonded within said recessed thread such that said metal thread extends outwardly of and stands proud of said body portion, along at least part the length thereof.

According to yet a further aspect of the present invention, there is provided a reinforcing bolt formed of a synthetic material and having an elongate shaft; a recessed thread being formed or provided in or adjacent one end thereof; an elongate helical thread member formed of a spring steel material being provided and being bonded and/or adhered into and within said recessed thread such that a portion of said spring steel material extends and stands proud of said body portion along at least part the length thereof, such as to form a metal thread at or adjacent one end of the said synthetic shaft.

According to a further aspect of this invention there is provided a reinforcing bolt having an elongate body portion formed of a synthetic material, and having elongate and integrally formed reinforcing, extending longitudinally therethrough, for substantially the length thereof; and including a metal thread at or adjacent one end of said body portion.

This invention will now be described by way of example only and with reference to the accompanying drawings, wherein:

IN THE DRAWINGS

Fig. 1 is a partially exploded and partially sectional side view of a reinforcing rock bolt according to one form of the present invention, Fig. 2 is a partially exploded and partially sectional side view of a reinforcing rock bolt according to a second form of the present invention, Fig. 3 is a section side view of a die showing an arrangement and method for forming a rock bolt according to one form of the present invention, and Fig. 4 is a side view of a helical spring as used to form the thread of an elongate rock bolt, according to one form of the invention.

The present invention relates to a rock bolt or elongate dowel formed of a suitable synthetic material, such as for example a plastics material. The invention includes a rock bolt formed of or including normal plastics material, reinforced plastics material, or engineering plastics material. If desired, the synthetic material of the present invention can be suitably enforced, such as with fibreglass or the like.

The rock bolt 1 is preferably formed with an elongate plastics body portion 2 which is preferably formed at an inner or distal end thereof, with a sharpened end portion 3, and which end 3 is adapted to be inserted, in use, into a bore (not shown) formed in a rock strata or the like. Along the length of the elongate body portion 2 , there are preferably provided a plurality of longitudinally and circumferentially spaced apart ribs of teeth 5, so that as the rock bolt 1 is inserted and rotated into a bore, the ribs or teeth 5 will come into contact with, for example, chemical anchors that may be inserted into the bore hole (prior to insertion of the rock bolt), the action of the ribs or teeth 5 serving to brake or rupture the chemical anchors, and thus to cause the components thereof to react together, such as to form a bonding agent to hold the body portion 2 of the anchor within the bore hole. o

This is by way of example only, however other suitable bonding agents, resins, adhesives and the like can be used.

At or adjacent the butt end 7 of the rock bolt 1 (that is, the end that will protrude from the bore hole) a thread 10 is formed or provided in the elongate body portion of the rock bolt. The thread 10 may be formed into the butt end of the roc bolt such as by moulding, machining or the like. For example, the rock bolt can be formed with a recessed thread 10 formed at or adjacent one end thereof, and extending at least part the way along the length thereof. Alternatively, if desired, a recessed thread 10 can be machined or formed into an end of the body portion 2 following formation of the body portion. Yet a further alternative would be to have at or adjacent the butt end 7 of the rock bolt 1 a thread 10 formed in the rock bolt, the thread 10 being in the form of a metal thread which is integrally formed with the elongate body portion 2 of the bolt 1, and the thread 10 of which extends proud of the body portion 2.

The present invention also provides for a metal thread 11, such as for example an elongate helical thread, formed of a spring metal material which is adapted in use to be housed or located within the recessed thread 10. On location of the metal thread 11 within the recessed thread 10, the metal thread 11 will extend outwardly from and stand proud of the body portion 2 of the bolt.

In use the metal thread 11 may be adhered, bonded or glued into position within the recessed thread 10.

Preferably the metal thread is an elongate helical thread of a spring metal material.

Preferably the elongate metal thread extends part-way along the length of the plastics body portion 2, for example from a position at or adjacent a butt end 7 of the rock bolt 1, to a position part-way therealong, the length being determined by the length of thread 11 required.

The helical thread 11 preferably has outer rounded edges 15 so that when the metal thread 11 is housed within the recessed thread 10, the thread 11 with rounded corners will extend outwardly or proud of the outer surface of the body portion 2 of the bolt, so as to form a metal thread at the end of the synthetic plastics body portion.

It has been found that the use of a spring metal material in a substantially helical form allows for the compression of the thread 11 while tension is being built up during a nut 17 being moved over the thread 11 of the bolt, this allowing for a far more effective operation of the synthetic plastics body portion of the rock bolt than has been the case with plastics rock bolts used up until this time.

The metal thread 11 of the rock bolt 1 in the present invention stands proud of the plastics body portion 2, so as to extend outwardly and substantially radially from the plastics body portion of the bolt. The outer edges of the threads are, as indicated, substantially curved or rounded in formation, as at 15, and are separated by substantially flat or planar inner surfaces 16 of the plastics body portion 2. This then defines a thread, being a metal thread, over which a nut 17 is able to pass.

It has been found, in use, that the provision of such a metal thread 11 formed with or integrally formed into a plastics body portion 2 allows for appropriate compression and tension of the spring metal material, from which the metal thread 11 is formed, the movement of a nut over the thread 11 causing compression of the helical thread 11, and imparting stress to the elongate plastics body portion 2 of the rock bolt 1, as held in a hole or bore by a bonding agent, chemical anchor or the like.

In preferred forms of the present invention, the elongate body portion can be formed of any appropriate plastics material, although preferred plastics material can be, for example, engineering plastics material, polyurethane, acrylamates and the like. Plastics material can be reinforced if desired such as by using reinforcing material such as fibre, fibreglass and the like. In a preferred form of the invention, the thread is formed of a spring metal material of a generally helical or spiral form, but this is by way of example only. It should be appreciated that metal materials other than spring metal materials can be used to advantage.

Further, it should be appreciated that while the invention has been described by way of example only, with reference to the rock bolt having ribs or teeth 5, along the length thereof, these are not essential. If desired, the surface of the body portion can be provided with dimples or can be rotund so as to provide for effective use. If desired, the outer surface of the bolt can be substantially planar.

In use, the distal end of the bolt is inserted into a bore hole (not shown) and inserted axially or rotated so as to be held therewithin, by rupturing or mixing appropriate chemical anchors or bonding agents, the nut 17 then being engaged with the metal thread 10 and being passed along the length thereof. If desired, an appropriate bearing plate (not shown) can be provided between the nut and the strata surface (in which the bore is formed), and as the nut 17 passes along the thread 10, the sprung steel helical thread will be caused to compress and be tensioned, to impart the stress and compression into the body portion of the bolt. The present invention also provides for the reinforcement of the plastics body portion 2. If desired, the elongate body portion 2 can be formed of a normal plastics or engineering plastics material, which is not reinforced and which is able to be tensioned within the bore hole. It is further being suggested, for example in Australian patent specification No 76314/87 that the plastics material can be reinforced, prior to the body portion being formed and moulded, so that the resultant body portion of the rock bolt is formed of a reinforced plastics material. It has, for example, been suggested that the plastics material, prior to moulding, can be mixed with appropriate reinforcing materials such as, for example, fibreglass reinforcing or the like, so that the resultant moulded body portion is reinforced.

While this may be advantageous in certain applications, such an arrangement also presents problems. When reinforcing material is mixed with the plastics material, prior to moulding, the resultant moulded and reinforced plastics body portion certainly has reinforcing therewithin, but there is no way in which a user or operator can be sure as to where the reinforcing is located. In other words, the reinforcing material mixed with the plastics material, prior to moulding, is not always equally distributed over the length of the rock bolt so that one part of the rock bolt might be stronger (and reinforced) than another. Thus, the strength over the length of the rock bolt formed in the manner referred to above cannot be clearly defined or delineated.

In order to overcome or minimize this problem, the present invention provides for the elongate body portion 2 to be provided with one or more reinforcing rods or members, preferably extending the length thereof and being integrally moulded into the body portion 2 so as to be preferably substantially centrally located and extending the length thereof. Referring therefore to Figs 1 and 2 of the accompanying drawings, an elongate reinforcing member such as a reinforcing rod 40, formed of an appropriate reinforcing material, is provided and extends substantially the length of the body portion 2 of rock bolt 1, preferably along the longitudinal axis thereof, and preferably substantially centrally of the body portion 2. If desired, a plurality of spaced-apart reinforcing rods 40 could also be provided. Preferably, the reinforcing rod 40 is of a diameter substantially less than of the body portion 2 of the rock bolt 1 to be formed, so that the reinforcing rod in effect forms an elongate reinforcing core for the body portion 2 of the rock bolt 1.

The reinforcing rod 40 is preferably formed of a non-metal material, which is a material which is capable of being cut by normal machinery used in mining and construction industries, without damage to such machinery. Any appropriate reinforcing material can be used to advantage, although in a preferred form of the invention the reinforcing rod 40 may be constructed of a fibreglass material.

It will be appreciated that in use, the length, diameter and weight of the reinforcing material as to be inserted into the rock bolt during moulding can be predetermined and thus the exact strength and tensile strength of the rock bolt, along the length thereof, can be predetermined and calculated. This is because the strength of the reinforcing rod is known, as is the distance over which the rod extends, relative to the longitudinal length of the body portion of the rock bolt.

While in a preferred form of the invention the reinforcing rod will extend for substantially the length of the body portion of the rock bolt, it should be appreciated that this need not be the case. It will be appreciated from the above that the present invention therefore provides a substantial advantage over the use of reinforced plastics materials, in that the positioning and strength of the reinforcing can be readily calculated and defined, for use. It also allows for the reinforcing to be substantially regular over the length of the rock bolt and/or the length of the reinforcing rod within the rock bolt.

Referring now to Fig. 3 of the accompanying drawings, it will be seen that a mould 20 such as, for example, a single cavity mould can be provided for forming the rock bolt 1 of the present invention. The mould 20 is provided on its inner surface 22 of the cavity 26, with inner surfaces and recesses 28 and flats 28a corresponding to the outer formations of a helical thread 11. An appropriate elongate helix 12 of a metal material, such as, for example, a sprung metal material, is inserted into a first end of the die. The inner surfaces of the remaining length 27 of the cavity are formed or provided with indents or angled portions 29 to correspond substantially to the ribs or teeth 5 to be formed along the length thereof. Appropriate plastics material is forced into the die by appropriate known or suitable means, the material being a liquid plastics together with reinforcing materials such as fibreglass or other appropriate reinforcing materials. The plastics material can be of any desired formulation, although reinforced plastics material or engineering plastics material are preferable (although not essential). The die is then allowed to set the material so that the plastics material forms to and about and through the metal helix 12, so that after a predetermined period of time, and following the opening of the die and the removal of the rock bolt 1 of the die, a metal thread 10 is integrally formed into and/or with the plastics body portion 2, so that for at least part the length of the rock bolt (preferably extending from at' or adjacent the butt end 7 thereof) there is a metal thread 10 formed of a preferably sprung metal material and having a generally helical formation, standing proud of the plastics body portion 2, the thread 10 being rounded in formation as at 15 and having substantially flat or planar portions 16 formed therebetween as a result of the formation in the die.

It should be appreciated that this invention has been described by way of example only and that modifications and improvements may be made to this invention without departing from the scope or spirit thereof.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A reinforcing bolt formed of a synthetic material and including a metal thread at or adjacent one end thereof.

2. A reinforcing bolt, having an elongate body formed of a synthetic material, and including an integrally formed metal thread at or adjacent one end thereof, said thread standing proud of said synthetic body portion.

3. A reinforcing bolt, having an elongate body formed of a synthetic material and including an integrally formed metal thread, at or adjacent one end thereof, said metal thread being formed of an elongate helix formed of spring steel material and being integrally formed with said synthetic body portion.

4. A reinforcing bolt, having an elongate body formed of a synthetic material, and having a recessed thread formed or provided in or adjacent one end thereof; a metal thread being located and housed within said recessed thread such that at least a portion of said metal thread extends and stands proud of said body portion, along at least part the length thereof.

5. A reinforcing bolt, having an elongate body formed of a synthetic material, and having a recessed thread formed or provided in or adjacent one end thereof; an elongate helical thread member formed of a spring steel material being provided and being bonded and/or adhered into and within said recessed thread such that a portion of said spring steel material extends and stands proud of said body portion along at least part the length thereof, such as to form a metal thread at or adjacent one end of the said synthetic shaft. 7. A reinforcing bolt having an elongate body portion formed of a synthetic material, and having elongate and integrally formed reinforcing, extending longitudinally therethrough, for substantially the length thereof; an integrall ^"formed metal thread being formed or provided at or adjacent one end of said body portion.