Note: Descriptions are shown in the official language in which they were submitted.
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AN INFLATABLE ROCK BOLT
FIELD OF THE INVENTION
The invention relates to an inflatable rock bolt of the kind that includes a
sealed
tubular (metal pipe) body formed with at least one longitudinal fold to
provide a
reduced and substantially circular cross-sectional profile for insertion into
a drill
hole and to, in use, be expanded into frictional engagement with a wall of the
drill
hole by introducing a pressurised fluid into an interior of the body.
BACKGROUND TO THE INVENTION
These inflatable rock bolts generally have a sealed tube with a longitudinal
channel
formed by a fold, which reduces the cross-sectional dimension of the tube
(sufficiently for the required purpose). A check valve at one end remains
outside a
drill hole into which the rock bolt is inserted and allows the tube to be
inflated or
expanded. The pressurised fluid is usually water. On expansion of the body
through outward deformation of the fold, the surface of the tube engages in
the
hole.
An improved version of such a rock bolt is disclosed in PCT/2016/053817 and
PCT/2016/054864. The first of these two International applications teaches a
beneficial construction of what is preferably an inner end of the rock bolt.
OBJECT OF THE INVENTION
It is an object of the present invention to provide an inflatable rock bolt
with a
sealed inner end having a configuration that provides improved durability to
the
stress placed on the folded regions of material during the expansion operation
in
use.
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SUMMARY OF THE INVENTION
In accordance with a first aspect of the invention, there is provided an
inflatable
rock bolt comprising:
a pipe with a cap welded in sealing engagement onto an end of the pipe in a
pre-formed condition;
the cap having a sidewall that extends from a rim of the cap to a closed end
provided by an end wall of the cap;
the rock bolt provided with a fold formed from a first side of the rock bolt
and
extending along a length of the pipe;
a bottom of the fold located adjacent an opposite, second side of the rock
bolt where it extends along the length of the pipe; and
the bottom of the fold extending from the pipe into the sidewall of the cap
and outwardly towards the first side of the rock bolt to a position separated
by a
ridge from a first portion of the end wall that remains outside the fold, with
a second
portion of the end wall drawn into the fold.
The invention provides for the second portion of the end wall to be arranged
at a
forward region of the fold with the first portion of the end wall in an
oppositely
disposed position at a front of the rock bolt.
The invention further provides for a rock bolt as defined, in which:
a greater portion of the end wall of the cap to be maintained substantially in
a pre-formed condition as the first portion with an adjacent lesser portion
curved
rearwardly and pressed toward the fold as the second portion.
The invention still further provides for a rock bolt as defined, in which:
the ridge extends from a front of the rock bolt as a substantially U-shaped
ridge formed around the fold at the cap of the rock bolt;
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the closed end of the cap is pressed outwardly in line with the fold where it
is formed into a forward most section of the U-shaped ridge;
an edge of the ridge is located on one side of an axis of the pipe as it
exists
in a pre-formed condition of the pipe;
the end wall of the cap transitions from the sidewall uniformly through a
curve to the closed end of the cap which is substantially flat [relative to
the
transition curve]; and
the sidewall of the cap includes a substantially cylindrical region at the rim
that locates with a press-fit into the pre-formed pipe.
lo
In accordance with a second aspect of the invention, there is provided a
method of
making an inflatable rock bolt which includes the steps of:
providing a length of pre-formed pipe with at least one open end,
welding a cap to the open end, and
thereafter deforming the pipe and the cap into a folded form to provide a fold
that extends along the pipe,
characterised in that the fold is formed by a tool that is sized with a
working
edge that stops sufficiently short of an end wall at a closed end of the cap
to:
- maintain a first portion of the end wall that is in line with the fold on
an
outside of the fold; and
- draw a second portion of the end wall in a curve rearwardly toward and
into the fold.
The invention further provides for a method as defined, in which the fold is
formed
to:
- provide a substantially U-shaped ridge that extends from a front of the
rock bolt around the fold at the cap with an edge of the ridge located to
one side of an axis of the pipe as it exists in a pre-formed condition of
the pipe.
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The invention still further provides for a method as defined, in which:
the fold is formed with the first portion as a greater portion of the end wall
and the second portion as a lesser potion of the end wall; and
the rock bolt is pressed closed around the fold in a second forming
operation.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other features of the invention will become more apparent from the
following description of a preferred embodiment, made by way of example only,
with reference to the accompanying illustrations, in which:
Figure 1
shows three inner ends of pre-formed, intermediate and final
formed rock bolts from a position facing the fold;
Figure 2 shows a perspective view of the intermediate and final formed
rock bolts;
Figure 3 shows a side view of the rock bolt ends in Figure 2 from a
position lateral to the fold; and
Figure 4
shows the pre-formed and final formed rock bolt ends marked
with an axis of the pre-formed rock bolt.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Referring to the accompanying drawings, a rock bolt (1) having a cap (2) at an
inner end manufactured in accordance with the invention is shown. The rock
bolt
(1) is illustrated in progressive forming conditions labelled as follows in
the Figures:
õA" pre-formed condition;
õB" intermediate condition; and
¶Cõ formed condition.
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The rock bolt (1) is made from a length of pipe (3) initially having a
circular cross-
section in the pre-formed condition. The pipe (3) is made from a suitable
metal.
The cap (2) is used to seal an open end of the pipe (3) that will be located
inside a
drilled rock bolt hole (not shown). It is only this inner end of the rock bolt
(1) that is
5 shown in the Figures.
The construction and components used at the opposite, outer end of the rock
bolt
(1) may be varied and will be within the understanding of a person skilled in
the art.
Examples are set out in the second of the two PCT applications referred to in
the
"Background" above.
The cap (2) is fabricated from a suitably ductile metal and has a sidewall or
skirt (5)
that extends from a rim (not shown) of the cap (2) to a closed end (6). The
sidewall
(5) extends forwardly from the pipe (3) with a slight inward taper. The closed
end of
the cap (2) in this embodiment is substantially flat and provides an end wall
(7) to
the front of the sidewall (5). The end wall (7) transitions substantially
uniformly
through a curve at an annular outer region from the sidewall (5) and into a
central
region of the closed end (6) which is, in this embodiment, substantially
flattened
(relative to the transition curve).
The sidewall (5) of the cap (2) has an outer diameter on a substantially
cylindrical
region at the rim (not shown). This short region (not shown) of the sidewall
(5)
adjacent the rim is be provided with a substantially parallel wall for press-
fitting with
a friction or interference fit into the pre-formed pipe (3). The pipe (3) with
the cap
(2) so fitted is shown as "A" in Figure 1. It will then be welded (8) at a
junction
along an edge at the end of the pipe (3). By securing the cap (2) to the pipe
(3) in
this manner the open and operatively inner end of the rock bolt (1) is sealed.
Once the cap (2) is welded in place, the pre-formed rock bolt is subjected to
a
subsequent metalworking process, in which the pipe (3) and the cap (2) are
formed
into an intermediate condition of the rock bolt (1) with convoluted or folded
shape
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as shown as "B" in Figures 1, 2, and 3. The configuration referred to involves
an
initial, first step of press-forming the longitudinal fold or channel (9) to
reduce the
cross-sectional dimension of a post-formed rock bolt (1) shown as "C" in
Figures 1,
2 and 3.
In accordance with the invention, the fold (9) is formed from a first side "x"
of the
rock bolt (1) and extending along a length of the pipe (3). A bottom (10) of
the fold
(9) located adjacent an opposite, second side "y" of the rock bolt (1) where
it
extends along the length of the pipe (3).
The fold (9) is formed so that the bottom (10) extends from the pipe (3) into
the
sidewall (5) and with a concave curve into a forward region (11) outwardly
towards
the first side "x" of the rock bolt (1) to a position separated by a front
region of a U-
shaped ridge (12) from a first portion (13) of the end wall (7) that remains
outside
the fold (9), with a second portion (14) of the end wall (7) drawn toward
and/or into
the forward region (11) of the fold (9).
In the current embodiment, a greater portion of the end wall (7) is maintained
substantially in a pre-formed condition [apart from being pressed slightly
forwardly
in the forming of a front of the U-shaped ridge (12)] as the first portion
(13) with an
adjacent lesser portion of the end wall (7) curved rearwardly and pressed
toward
and/or into the fold (9) as the second portion (14).
After the welding has been completed the pipe (3) and cap (2) still have a
circular
outline or profile in cross-section. In the first forming step, the pipe (3)
and cap (2)
assembly is placed in a trough-shaped cavity of a first die. A pressing tool
in a
hydraulic press is then used to deform the pipe (3) and cap (2) assembly into
the
intermediate condition, which is accompanied by some lateral bulging or
outward
distortion to either side of the fold as well as the forward displacement of
the end
wall (7) where the U-shaped ridge (12) takes form.
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The tool is in the shape of an elongate blade with a straight working edge
(parallel
to the pipe) that is curved between two planar sides. In use, the working edge
directly contacts the outer surface of the pipe (3) and cap (2) assembly. The
first
die is supported in a hydraulic press that is used to bias the tool into
engagement
with the outer surface of the pipe. The tool deforms the pipe (3) and cap (2)
assembly radially inwardly to form the relatively deep fold or channel (9) as
shown.
In accordance with previous versions of the rock bolt, a fold was formed to
extend
through the cap and past its closed end to reduce the profile of the cap in
line with
the forming process to which the length of pipe was subjected.
The modification which brings about the current invention involves, in the
first
forming operation, the use of a tool that is sized with a folding or working
edge that
stops sufficiently short of the closed end (6) of the cap (2). At the relevant
end
which locates over the cap (2), the tool will be radiused from the working
edge
(which is provided parallel to the pipe) to an end of the tool that is
perpendicular to
or inclined away from the working edge. It is this radiused portion of the
tool that is
pressed down in the required position to form the fold in the cap (2).
It follows that the pre-formed rock bolt needs to be placed in a predetermined
position in the hydraulic press so that the fold is formed by the pressing
tool with
the upwardly curved or radiused end of the working edge located to stop short
of
the closed end (6) of the cap (2). The arrangement avoids providing a lateral
compression force that would act in line with the material across the cap end
wall
(7) and particularly in the central flat region thereof. Instead, the tool
engages the
cap of pre-formed rock bolt where a lateral bending force can be applied to
the
sidewall (5).
The forming process of the invention provides for the following features:
- A substantially U-shaped ridge (12) is formed around the fold (9) at the cap
(2) of the rock bolt (1) ¨ see "B" and "C" in Figure 1;
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- A greater, first portion (13) of the end wall (7) that is in line with the
fold (9)
is maintained substantially in a pre-formed condition and outside of the fold
(9) with an adjacent lesser, second portion (14) formed rearwardly and
pressed toward and/or into the fold (9) ¨ see "B" and "C" Figure 3; and
- An edge "e"
of the ridge (12) is located to the first side "x" of an axis "a" of
the pipe (3) as it exists in a pre-formed condition of the pipe (3). This is
shown as "A" and "C" in the comparison of Figure 4.
In the result, the second portion (14) of the end wall is arranged at the
forward
region (11) of the fold (9) with the first portion (13) of the end wall in an
oppositely
disposed position at the front of the rock bolt (1) on an outside of the fold
(9). The
section at the bottom of the "U" of the U-shaped ridge (12) separates the
first
portion (13) from the second portion (14) of the end wall.
The forces exerted by the tool in the first forming step are such that when
the fold
(9) is formed, the outer surface of the pipe (3) and cap (2) assembly is no
longer
generally of circular form. The rock bolt (1) in intermediate form is then
subjected to
a second step of the forming process. This operation involves placing the rock
bolt
(1) into a second die set which includes upper and lower dies that together
define
an elongate die cavity of circular cross-section and which locates over the
pipe (3)
and the cap (2). The second die set is closed using hydraulic pressure with
the
intermediate condition rock bolt in the die cavity. In the result, a rock bolt
is formed
with a body that, except for the fold (9), has a substantially circular axial
profile.
This configuration of the finished product (post-formed rock bolt) is suited
for
insertion into a round drill hole and presents further capacity for expansion
over the
intermediate form.
The cap (2) remains connected with leak-proof seal provided by the weld to the
pipe (3). The pipe (3) then has an elongate longitudinally extending channel
(9)
which extends into a region occupied by the sidewall (5) of the cap (2).
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In the second forming operation, the rock bolt (1) is pressed closed around
the fold
(9). The post-formed rock bolt shown "C" in Figures 1, 2, 3 and 4 is thus
formed
with the fold (9) having a substantially closed or abutting configuration
where it
extends along the majority of the pipe length. This is not the case in the
region of
the cap (2) as illustrated in the drawings of the current embodiment. The
outer
diameter of the cap (2) is smaller than that of the pipe (3) into which it
fits and is
welded in place. In the first forming step, the material in the region of the
cap (2)
inside of the fold (9) is pressed close to an outside of portion of the cap
(2) around
the fold (9) at and around the second side "y" of the rock bolt (1). When the
two
dies of the set are closed onto the rock bolt (1) in the second forming step,
the cap
is not closed over the fold to the same extent as the larger diameter pipe
wall.
In use, the rock bolt is inserted into a drill hole and expanded from a
formed, folded
condition towards a pre-formed condition, wherein the fully pre-formed
condition
represents a (substantially) maximal expansion which is in excess of that
required
for the rock bolt to engage in the drill hole. In practice, the wall of the
drill hole is
usually engaged with the rock bolt resembling the intermediate condition shown
as
"B" in Figures 1, 2 and 3. In situ conditions and the particular embodiment of
the
rock bolt used will determine the form that the expanded rock bolt takes.
The configuration of the cap formed in the manner illustrated and described
serves
to provide a configuration that involves folded regions of material that
afford
improved durability to the stress placed on the material in those regions
during
expansion of the rock bolt.
The forming process involves a smaller component of lateral compression in the
region of the end wall of the cap. The majority of the deformation involves
bending
of the sidewall of the cap (similar to the sidewall of the pipe). The sidewall
of the
cap is more suitably arranged to accommodate bending than the end wall which
has a large component of material provided substantially at a right angle to
the
pressing tool. The bending at the end wall of the cap involves having the
material
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pressed or drawn by the pressing tool, rearwardly towards and/or into the fold
to
form the substantially U-shaped ridge around the front of the rock bolt.
This folded configuration has been found to mitigate weakening of the material
in
5 the cap
around the fold or folded regions and deter against any leaks forming when
the rock bolt is expanded.
The terms used to describe the forming of the components and the cap sidewall
and end wall are indicative and/or instructive of the process and components.
10 These
terms and description will be understood by a person suitably skilled in the
art and will allow the invention to be implemented as a modification or
improvement
over the teaching of PCT/162016/053817.
While the invention is described and illustrated with respect to a
configuration
having a single fold providing the longitudinal channel for the reduced
dimension of
the rock bolt, it may also be employed where more than one such channel is
formed along the pipe.
The capped and folded configuration of a rock bolt end in accordance with the
invention is particularly suited for the inner or leading end of a rock bolt
that is, in
use, located into and towards the bottom of a drilled hole. This is not
however a
limitation and the invention may well be employed at both ends of a rock bolt.
A
pressurised fluid inlet may be provided through the wall of the pipe adjacent
the
outer end that protrudes from the drill hole.
A person skilled in the art will appreciate that a number of variations may be
made
to the features of the embodiments described without departing from the scope
of
the invention.
