Note: Descriptions are shown in the official language in which they were submitted.
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RESIN ANCHORED ROCK BOLT WITH A LOCATING FORMATION AT A
LEADING END
BACKGROUND OF THE INVENTION
[0001] This invention relates to a rock bolt for use in a resin anchored
application.
[0002] 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.
[0003] 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.
[0004] 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.
[0005] 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.
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[0006] 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.
[0007] 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.
[0008] 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.
[0009] 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.
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[0010] Both eccentricity and gloving tends to occur in the critical top of the
leading
end section of the installed bolt.
[0011] The invention aims, at least partly, to address the aforementioned
problems.
SUMMARY OF THE INVENTION
[0012] 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.
[0013] The attachment part may be a disc-shaped part.
[0014] The positioning part may be a circumscribing umbrella formation
extending
from a perimeter of the attachment part.
[0015]The umbrela formation may be biased in an open or flared position and is
resiliently movable from the open position to a closed or folded position.
[0016] The unitary umbrella formation may be made of a sheet material which is
perforated with a plurality of resin flow-through holes.
[0017] Alternatively, the positioning part may comprise a plurality of
locating fingers
integral with and projecting from a perimeter of the attachment part.
[0018] The fingers may extend backwardly in a first direction which is aslant
to a
plane of the attachment part.
[0019] The locating fingers may be evenly radially spaced about the perimeter
and
have equal lateral reach.
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[0020] Preferably, the positioner has three or four locating fingers.
[0021] The positioner may be forged from a slug or blank metal or moulded
using a
rigid plastics material.
[0022] 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.
[0023] The penetrating formation may be comprised of a radial grouping of
triangular, othogonal or rectangular sections, or the like, bent away from the
plane of
the central attachment part.
[0024] Alternatively, the attachment part may have a central aperture for
receiving a
peaked formation on the leading end of the bolt.
[0025] 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
1 5 part that extends from the attachment part in even lateral extent.
[0026] The attachment part may be a disc-shaped part.
[0027] The positioning part may be a circumscribing umbrella formation
extending
from a perimeter of the attachment part.
[0028] The unitary umbrella part may be perforated with a plurality of resin
flow-
through holes.
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[0029] Alternatively, the positioning part may comprise a plurality of
locating fingers
integral with and projecting from a perimeter of the attachment part.
[0030] The positioning part may extend in a first direction which is aslant to
a plane
of the attachment part.
5 [0031] The locating fingers may be evenly radially spaced about the
perimeter.
[0032] Preferably, the positioner has three or four locating fingers.
[0033] The positioner may be made punched from a blank of flat stock steel or
moulded using a rigid plastics material.
[0034] The positioner may have a penetrating formation upstanding from the
plane
of the attachment part.
[0035] The penetrating formation may be comprised of a radial grouping of
triangular, rectangular or othogonal sections, or the like, bent away from the
plane of
the central part.
[0036] 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.
[0037] 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.
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[0038] 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.
[0039]The pins may engage the first formation and the second bore in friction
fit.
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] The invention is further described by way of example with reference to
the
accompanying drawings in which:
Figure 1 is a partial view in elevation of a resin anchored rock with a
centralising
positioner bolt in accordance with the one embodiment of the invention;
Figure 2 is an isometric view of a penetrating end of the resin bolt of Figure
1;
Figure 3 is a view in plan onto the penetrating end of the rock bolt;
Figure 4 is an isometric view of a centralising positioner in accordance with
a second
embodiment of the invention, with a penetrating formation as part of the
positioner;
and
Figure 5 diagrammatically illustrates a centralising positioner in accordance
with a
third embodiment engaged with a penetrating end of a resin anchored rock bolt
of
the invention;
Figures 6 diagrammatically illustrates a resin anchored rock bolt with a
centralising
positioner in accordance with a fourth embodiment of the invention; and
Figure 7 diagrammatically illustrates a resin anchored rock bolt with a
centralising
positioner in accordance with a fifth embodiment of the invention.
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DESCRIPTION OF THE PREFERRED EMBODIMENT
[0041] Figure 1 of the accompanying drawings illustrates a leading end portion
of a
resin bolt 10 which is in accordance with the invention. The resin bolt has an
elongate solid steel shaft 12 which extends between a leading end 14 and a
trailing
end (not shown).
[0042] 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.
[0043] 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 Figures 2 and 3. The centralizing positioner
22 can be
made, punched from a blank of flat stock steel or alternatively moulded using
a
suitable rigid plastics material. What is described hereafter is a positioner
made of
flat stock steel.
[0044] 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
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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.
[0045] 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.
[0046] 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.
[0047] In another embodiment, illustrated in Figure 4, where the resin bolt 10
does
not have the conical formation 34, the puncturing function can be provided by
a
penetrating formation 36 on the positioner 22A itself.
[0048] 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.
[0049] In a further embodiment, illustrated in Figure 5, a centralising
positioner 22B
is provided. The positioner includes a resin capsule locating formation 50 and
an
umbrella formation 52 which radiates from, and which is pivotally connected
about a
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circumferential connecting line 54 to, the formation 50. The locating
formation has a
base 56 and a circumferential wall 58 that is upstanding from the base. The
base
has a hole 60.
[0050] The umbrella formation 52 is comprosed 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.
[0051] 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.
[0052] As illustrated in Figure 5, the upstanding cupula provider within the
cylindrical wall 58 within which a resin capsule 70 can be inserted and
resiliently held
therein prior to insertion into a rock hole ahead of the rock bolt.
[0053] 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.
[0054] 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
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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.
[0055] 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
5 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.
[0056] 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
10 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.
[0057] 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).
[0058] Figures 6 and 7 illustrate another two embodiments of the invention. In
both
embodiments, the centralising positioner comprises a pair of pins
(respectively
designated 70A and 70B), either cylindrical or rectangular in shape, engaged
with a
leading end 14 of the resin bolt 10.
[0059] In the embodiment of Figure 6, the leading end of the bolt is formed
with a
groove 72 which diametrically extends across the end. The groove receives a
first
pin 70A, either in frictional fit or fixed by any suitable means. Below the
end, a
second bore 76 is formed through a leading end portion 78 of the bolt. The
bore
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extends diametrically through the body in a direction which is orthogonal to
the
groove 72. This orthogonal relationship is illustrated in Figure 6A and 7A.
The
second pin 70B engages with this bore, again either in friction fit or fixed
therein by
any suitable means.
[0060] In the embodiment of Figure 7, the groove 72 is replaced with a first
bore
72B. The first pin 70A is received through the first bore.
[0061] 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.
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