Patent Application
20200088032
This invention relates to a rock bolt for use in a resin anchored application.
It is well known in the art to anchor a rock bolt into a rock hole with a grout or a two-part resin. The grout or resin is introduced into the rock hole, ahead of the bolt, by means of grout or resin capsules.
The rock bolt has to be adapted to puncture the capsule to release the contents. With the two-part resin, the contents have to be thoroughly mixed to achieve optimal setting.
Strictly, the resin is not an adhesive as it does not adhere the rock bolt to the rock hole. The resin mechanically locks the rock bolt in the rock hole. Thus, there is a reliance upon mechanical interlock with irregularities in the surface of the rock bolt and the rock hole walls to prevent the rock bolt from being pulled from the rock hole. The irregularities on the surface of the rock bolt are provided by a profiled surface.
Another factor influencing optimal mechanical lock is how efficient the rock bolt is at mixing the two parts of the resin. Typically mixing efficiency decreases in a radial direction from the surface of the rock bolt to the rock hole wall. This means that the larger the ratio between the diameter of rock hole and the rock bolt, i.e. the larger the annular space between the rock bolt and the rock hole wall, the greater the mixing inefficiency towards an outer circumference of the annular space. Potentially, this reduces the load bearing capacity of the rock bolt.
This factor places a limit on the diametric size of the rock bolt that can be used for a particular hole size. There is economic motive to using as small a rock bolt as possible.
A resin rock bolt therefore must have features which are a compromise between a mixing and an anchoring function. Unfortunately, the functions are not complementary. Optimising the mixing features tends to decrease the anchoring abilities of the bolt. A typical rock grouted resin anchored rock bolt is profiled with a series of ridges angled at 45°. These ridges provide a compromise between anchoring and mixing functionality.
Gloving is another problem in resin bolting. This phenomenon occurs when the plastic wall of the capsule is incompletely broken up or disrupted by the rock bolt when the bolt penetrates the capsule. The plastic then coats part of the rock bolt, covering the profiled surfaces of the rock bolt and decreasing its anchoring and mixing functionality.
Yet another issue in resin bolting is that the rock bolt is very rarely inserted in complete co-axial alignment with the rock hole causing eccentricity of the bolt to the rock hole, about the distal end of the bolt. At the distal end, the annular space is irregular, with a thin and a thick annular arc. In the thin annular arc there is insufficient resin to provide optimal mechanical interlock. Whilst in the thick annular arc, the resin is insufficiently mixed. And with insufficient resin in the small annular arc, the protective barrier provided by the resin is thinned, increasing the chance of acid mine water penetrating to the rock bolt.
Both eccentricity and gloving tends to occur in the critical top of the leading end section of the installed bolt.
The invention aims, at least partly, to address the aforementioned problems.
The invention provides a centralising positioner for a resin bolt which includes a central attachment part which is adapted to engage a leading end of the bolt and a positioning part integral with the attachment part that extends from the attachment part.
The attachment part may be a disc-shaped part.
The positioning part may be a circumscribing umbrella formation extending from a perimeter of the attachment part.
The umbrella formation may be biased in an open or flared position and is resiliently movable from the open position to a closed or folded position.
The unitary umbrella formation may be made of a sheet material which is perforated with a plurality of resin flow-through holes.
Alternatively, the positioning part may comprise a plurality of locating fingers integral with and projecting from a perimeter of the attachment part.
The fingers may extend backwardly in a first direction which is aslant to a plane of the attachment part.
The locating fingers may be evenly radially spaced about the perimeter and have equal lateral reach.
Preferably, the positioner has three or four locating fingers.
The positioner may be forged from a slug or blank metal or moulded using a rigid plastics material.
The positioner may have a penetrating formation upstanding from the plane of the attachment part in a second direction which is opposed to the first direction.
The penetrating formation may be comprised of a radial grouping of triangular, orthogonal or rectangular sections, or the like, bent away from the plane of the central attachment part.
Alternatively, the attachment part may have a central aperture for receiving a peaked formation on the leading end of the bolt.
The invention extends to a resin anchored rock bolt which has an elongate metal body which extends between a leading end and a trailing end and at least one centralising positioner which has a central attachment part which is adapted to engage the leading end of the bolt and a positioning part integral with the attachment part that extends from the attachment part in even lateral extent.
The attachment part may be a disc-shaped part.
The positioning part may be a circumscribing umbrella formation extending from a perimeter of the attachment part.
The unitary umbrella part may be perforated with a plurality of resin flow-through holes.
Alternatively, the positioning part may comprise a plurality of locating fingers integral with and projecting from a perimeter of the attachment part.
The positioning part may extend in a first direction which is aslant to a plane of the attachment part.
The locating fingers may be evenly radially spaced about the perimeter.
Preferably, the positioner has three or four locating fingers.
The positioner may be made punched from a blank of flat stock steel or moulded using a rigid plastics material.
The positioner may have a penetrating formation upstanding from the plane of the attachment part.
The penetrating formation may be comprised of a radial grouping of triangular, rectangular or orthogonal sections, or the like, bent away from the plane of the central part.
Alternatively, the leading end of the rock bolt is conically shaped and the attachment part may have a central aperture for receiving the conical leading end.
In an alternative to the single centralising positioner described above, the rock bolt may include at least two centralising positioners; a first pin and a second pin and a leading end of the rock bolt may be formed with a first formation and a second bore formed diametrically through a leading end portion of the body, wherein the first formation is orthogonal to the second bore and wherein the first pin and second pin are adapted to engage the first formation and second bores respectively with projecting parts of each pin evenly laterally extending from the bolt body.
The first formation may be a groove formed diametrically across the leading end. Alternatively the first formation may be a first bore formed diametrically through the leading end portion.
The pins may engage the first formation and the second bore in friction fit.
The invention is further described by way of example with reference to the accompanying drawings in which:
The shaft of the resin bolt 10 in this example is of typical manufacture with a series of profiled ridges 18 formed in an outer surface of the shaft. And, in this particular embodiment, the resin bolt has a paddle formation 20 which is integrally formed of the body. The paddle not only increases the diametric reach of the resin bolt in mixing the resin content of pre-installed resin capsules (not shown) but also increase the anchoring of the bolt within the rock hole.
To the leading end 14, a centralizing positioner 22 is attached by any suitable means, for example by tack welding. The centralizing positioner 22 is illustrated in greater detail in
The centralizing positioner 22 has a core ring 24 and a plurality of locating fingers, respectively designated 26A, 26B and 26C, integral with and projecting from a perimeter 28 of the core ring 24. In this example, there are three locating fingers which have lateral extension, so that an outer surface 30 of each finger can abut against a wall of a rock hole in use, as will be more fully described below, but which bend downwardly towards the trailing end of the bolt 10 so as to not to resist passage of the resin bolt 10 as it is inserted into the rock hole in use.
The locating fingers 26 are evenly radially spaced about the perimeter and are laterally co-extensive so as to keep a leading end of the bolt relatively concentric with the hole during insertion.
In the embodiment illustrated, the core ring 24 has a central aperture 32 which locates over a conical formation 34 on the leading end 14 of the rock bolt 10, before being welded in place. The conical formation 34 not only locates the centralising positioner 18, it also functions to puncture the frangible wall of pre-installed resin capsules.
In another embodiment, illustrated in
As illustrated, the penetrating formation 36 is comprised of a plurality of triangular sections 38 which are centrally grouped on the core ring 24. Each of the sections, which are provided by making a “+” shaped cut in the ring 24, is bent upwardly about a respective base to project from the plane of the ring 24. The bend angle of each section is uniform ensuring that the sections taper towards one another to a peak 40.
In a further embodiment, illustrated in
The umbrella formation 52 is comprised of a single sheet of suitable plastics or polymeric material. Radiating through the formation, from line 54, are a number of fold lines 62 dividing the umbrella formation into a number of segments 64.
A plurality of apertures (not shown) can be formed through the sheet of the umbrella formation to allow passage of grout from a grout capsule side 66 of the formation to an underside 68.
As illustrated in
The umbrella formation 52 extends, in a relaxed biased state, to define a circumferential maximum. However in use as will be more fully described below, the umbrella formation can move resiliently inwardly, relatively to the resin capsule locating formation 50, to a circumferential minimum by folding or buckling about the fold lines 62.
With the resin capsule engaged with the formation 50, the device can be inserted into a rock hole. As the umbrella formation 52, which is maximally flared prior to insertion, reaches the mouth of the rock hole, it will be forced inwardly by contact with the mouth of the hole into a folded or partially folded state and resiliently held in that folded state by contact with the rock hole walls. With the umbrella formation 54 accommodating ingress in this manner, the resin capsule 70 can be pushed up towards a blind end of the hole, with the resin capsule 66 leading.
The resin bolt 10 trails the resin capsule locating formation 50 in insertion into the rock hole. During insertion, a leading end 14 of the bolt will dock with the formation from an underside. A conical or penetrating formation (34 or 36) will penetrate through the hole 60 in the base 56 to contact and puncture the retained resin capsule 70.
Having a resin bolt that is centralised, during insertion, and a resin capsule that is held in the hole, in a concentric position, will ensure that the resin capsule is optimally positioned to be punctured and not to fall away from the bolt into the annular space. The umbrella formation 52 also ensures that the plastic packaging of the capsule is separated from the rock bolt so not as to glove about the bolt.
Once punctured, the grout contents are released to flow downwardly where it will optimally adhere the bolt to the rock walls because of annular regularity provided by the centralising positioner (22 or 22B).
In the embodiment of
In the embodiment of
The laterally extending end portions of each pin 80 are each of uniform length so as to position the resin bolt centrally within the rock hole when inserted.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2017/03954 | Jun 2017 | ZA | national |
| 2017/05037 | Jul 2017 | ZA | national |
| 2017/08056 | Nov 2017 | ZA | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/ZA2018/050032 | 6/8/2018 | WO | 00 |
