Note: Descriptions are shown in the official language in which they were submitted.
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EXPANDABLE BOLT WITH THRUST ELEMENT
BACKGROUND OF THE INVENTION
Field of the Invention
[0001] This invention relates to a rock bolt having an expandable tube and a
shielded distal
end bearing a thrust element, a method of making such a rock bolt, and a
method of using
such a rock bolt.
Description of Related Art
[0002] Rock bolts are used in underground mines, such as coal mines, to
support the roof
and ribs. Installation of conventional rock bolts involves drilling a borehole
into the rock to a
desired depth using an elongated drilling tool (termed the "drill steel"),
removing the drill
steel from the borehole, optionally inserting adhesive resin cartridges, and
retaining the
cartridges in the blind end of the borehole while a bolt, optionally bearing
an expansion
anchor, is installed into the borehole. The free end of the bolt extending out
of the borehole
is received by a chuck of a bolting machine. The bolting machine rotates the
bolt within the
borehole to mix the adhesive resin and.ior expand the expansion anchor.
[0003] Other rock bolts comprise a longitudinally expandable tube that
includes a
longitudinally extending depression between two curved outer portions where
the tube is
partially collapsed on itself. The ends of the tube are folded over to create
two enclosed
cavities in the curved outer portions of the tube while a temporary passageway
defined by the
depression remains open on the ends. After placing the rock bolt in the pre-
drilled borehole,
pressurized fluid is delivered into the two cavities to force the depression
outward, expand
the tube, and compress it against the surrounding rock. Until the expansion
has been
completed, the ends of the passageway defined by the depression are open so
that debris from
the borehole can fall into the passageway defined by the depression.
SUMMARY OF THE INVENTION
[0004] The present invention includes a rock bolt having a longitudinally
expandable tube.
The tube includes a longitudinally extending depression that defines a
temporary, enclosed
longitudinal passageway. A thrust element is positioned at a distal end of the
rock bolt and
may be arranged in use to deflect loose material disposed in the bore as the
rock bolt is
inserted, thus facilitating movement of the material past the rock bolt when
installed in a
borehole.
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[0005] The thrust element may assist insertion of the rock bolt in the bore
and/or may
inhibit compaction of that material in the blind end of the bore. Compaction
of loose material
in the bore is problematic as it reduces the effective length of the bore and
may prevent the
rock bolt from being fully inserted into bore unless that borehole is of
extended length.
[0006] The thrust element may form part of a cover of the rock bolt to prevent
debris from
entering the temporary, enclosed longitudinal passageway, ease insertion of
the rock bolt into
the borehole, and assist in alignment of the rock bolt in the borehole.
Alternatively the thrust
element may form an extension of that cover and be fixed to the cover. The
cover may be a
plug or a cap and may provide a rounded tip for the rock bolt. The plug may be
spherical.
The cap may be attached such that its proximal end abuts the distal end of the
rock bolt, is
inserted into the distal end of the rock bolt, or extends beyond the distal
end and along the
sidewall of the rock bolt. In another form, the thrust element may be fixed
directly to the rock
bolt.
[0007] In one form, the thrust element is fixed in place by welding, but may
be fixed by
other means such as crimping, or through a coupling (such as a threaded
coupling
arrangement) or by adhesive bonding. In a particular form, the connection is
only loaded in
compression as the rock bolt is driver into the bore without requiring
rotation. In one form,
this drive action is by a percussive force.
[0008] The thrust element may take various forms but in general includes a
profiling that
promotes radial deflection of the material as the rock bolt is inserted
axially into the bore. In
one form, the thrust element may be conical or frustoconical having a wall
surface that
extends from an apex of the element to an engagement end where the element is
mounted to
the rock bolt. The surface of the thrust element extending between the apex
and the
engagement end may be faceted.
[0009] In another form, the thrust element may be more akin to a drill bit and
may include
channels or flutes that allow for radial flow of material as the rock bolt is
inserted into the
bore.
[0010] The present invention also includes a method of manufacturing a rock
bolt,
including providing an expandable member including an expandable tube and an
end fitting
where the expandable tube has a longitudinally extending depression disposed
between a pair
of outer portions =of the tube, the exterior of the tube defines a temporary,
enclosed
longitudinal passageway having an open distal end, and the outer portions of
the tube have
closed distal ends, and enclosing the expandable member with a cover such that
a distal open
end of the temporary, enclosed longitudinal passageway of the expandable tube
is covered.
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The cover may be a plug or a cap and may provide a rounded tip for the rock
bolt. The cover
may also include a thrust element arranged in use to deflect loose material
disposed in the
bore as the rock bolt is inserted, thus facilitating movement of material past
the bolt when
installed in a borehole. The method may also include placing a stiffening tube
on a proximal
end of the expandable tube such that the stiffening tube surrounds the
proximal end of the
expandable tube and has an opening that aligns with a corresponding opening in
the
expandable tube, thereby providing fluid communication to an interior of the
expandable
tube.
[0011] The present invention further includes a method of using a rock bolt,
including
providing a rock bolt having an expandable member including an expandable tube
having a
temporary, enclosed longitudinal passageway with an open distal end, and a
cover at a distal
end of the rock bolt covering the temporary longitudinal passageway; drilling
a borehole in
rock; placing the rock bolt in the borehole; expanding the tube by providing
pressurized fluid
to the interior of the tube, thereby providing frictional engagement between
an exterior of the
tube and an interior of the borehole; and draining the fluid from the interior
of the tube. The
cover may be a plug or a cap and may provide a rounded tip for the rock bolt.
[0012] The present invention further includes a method of using a rock bolt
including
providing a rock bolt having an expEndable member including an expandable tube
having a
temporary enclosed longitudinal passageway with an open distal end, and a
thrust element at
the distal end; drilling a borehole in rock; inserting the rock bolt in the
borehole whereby
loose material in the bore is deflected by the thrust element; expanding the
tube by providing
pressurized fluid to the interior of the tube, thereby providing frictional
engagement between
an exterior of the tube and an interior of the tube thereby providing
frictional engagement
between an exterior of the tube and an interior of the borehole; and draining
fluid from the
interior of the tube. The thrust element may generally include a profiling
that promotes radial
deflection of the material as the rock bolt is inserted axially into the bore.
The thrust element
may comprise a cover for the distal end or may form an extension of that
cover.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] Fig. 1 is a side view of a rock bolt produced according to the present
invention;
[0014] Fig. 2 is a cross-section taken along lines 1-1 of Fig. 1;
[0015] Fig. 3 is a cross-section taken along lines 2-2 of Fig. 1, as installed
in rock strata;
[0016] Fig. 4 is a longitudinal cross-section of the distal end of a rock bolt
according to one
embodiment of the present invention;
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[0017] Fig. 5 is a longitudinal cross-section of the distal end of a rock bolt
according to a
second embodiment of the present invention;
[0018] Fig. 6 is a longitudinal cross-section of the distal end of a rock bolt
according to a
third embodiment of the present invention;
[0019] Fig. 7 is a longitudinal cross-section of the distal end of a rock bolt
according to a
fourth embodiment of the present invention;
[0020] Fig. 8 is a side view of a distal end of rock bolt according to a fifth
embodiment of
the present invention;
[0021] Fig. 9 is a longitudinal cross-section of the distal end of a rock bolt
according to
Fig. 8;
[0022] Fig. 10 is a side view of a thrust element for use in the rock bolt of
Fig. 8;
[0023] Fig. 11 is a perspective view of a thrust element for use in the rock
bolt of Fig. 8;
[0024] Fig. 12 is a longitudinal cross-section of the distal end of a rock
bolt according to a
sixth embodiment of the present invention;
[0025] Fig. 13 is a perspective view of a thrust element for use in the rock
bolt of Fig. 12;
[0026] Fig. 14 is a side view of a thrust element for use in the rock bolt of
Fig. 12;
[0027] Fig. 15 is a longitudinal cross-section of the distal end of a rock
bolt according to a
seventh embodiment of the present invention;
[0028] Fig. 16 is a perspective view of a thrust element for use in the rock
bolt of Fig. 15;
[0029] Fig. 17 is a side view of a thrust element for use in the rock bolt of
Fig. 15;
[0030] Fig. 18 is a longitudinal cross-section of the distal end of a rock
bolt according to an
eighth embodiment of the present invention;
[0031] Fig. 19 is a perspective view of a thrust element for use in the rock
bolt of Fig. 18;
and
[0032] Fig. 20 is a side view of a thrust element for use in the rock bolt of
Fig. 18.
DETAILED DESCRIPTION OF THE INVENTION
[0033] Referring now to the drawing figures in which like reference numbers
refer to like
elements, Fig. 1 shows a rock bolt 2 which includes an expandable tube 4
having an initial
cross-sectional profile as shown in Fig. 2. The tube 4 is partially collapsed
upon itself (such
as by rolling or drawing) so as to provide a depressed region 6 between two
curved outer
portions 8, 10 extending longitudinally along the tube 4. The tube 4 is
produced from a steel
alloy or the like having sufficient strength to function in rock support, even
after deformation
from internal hydraulic pressure as described below. A first stiffening tube
14, having a
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sidewall and two open ends, is attached to and surrounds a proximal end 15 of
the tube 4. A
lip 18 may extend from stiffening tube 14 for engaging with a rock surface
when the rock
bolt 2 is inserted in the borehole.
[0034] A second stiffening tube 20, having a sidewall and two open ends, is
attached to
and surrounds a distal end 21 of tube 4 leaving the end of the tube 4
uncovered. A cover 22
covers the opening in a distal end 23 of second stiffening tube 20, the tube
4, or both and may
be fixed thereto by welding or the like. The outer curved portions 8, 10 of
tube 4 abut one
another to define a temporary main passageway 26 as well as interior
passageways 28, 30.
Main passageway 26 is open at the distal end 21 of tube 4 while interior
passageways 28, 30
are closed as shown in Figs. 4-7. As shown in Fig. 1, the first stiffening
tube 14 defines an
opening 34 which is aligned with an opening (not shown) in tube 4, such that
the openings
are in fluid communication with interior passageways 28, 30.
[0035] In operation, a borehole is drilled into the rock to the desired depth
and the bolt 2 is
inserted through a bearing plate and into the borehole. A source of
pressurized fluid, such as
water, is delivered through the opening 34 of the first stiffening tube 14 and
an opening in
tube 4 into interior passageways 28, 30. When passageways 28, 30 are filled,
the further
addition of fluid creates sufficient hydraulic pressure to force open the tube
4, such that
passageways 28, 30 are conjoined as an interior 35 of the tube 4 expanding the
tube 4, and
ultimately compressing the tube 4 against the surrounding rock of the
borehole. See Fig. 3.
As a result, main passageway 26 no longer exists. When the tube 4 is fully
expanded and no
further fluid is received therein, the fluid supply is removed and the fluid
is drained. In this
manner, the expanded tube 4 frictionally anchors into and/or against the
surrounding rock R.
[0036] The cover 22 may take the form of a plug or a cap. In one embodiment,
the cover
22 is a plug 122 or a plug 222, as shown in Figs. 4 and 5, respectively. The
plug 122, 222 is
placed in the opening in the distal end 23 of tube 20 such that a first
portion 124, 224 thereof
is exposed and a second portion 125, 225 is in the interior of the tube 20.
The plug 122, 222
may take any suitable shape (such as rounded) as long as the main passageway
26 is covered.
The plug 122, 222 may be made of steel or any other suitable material. The
plug 122, 222
may be fixed to the rock bolt 102, 202 by welding or the like. For example,
tack welds 32,
spaced apart around the circumference of the plug 122, 222 may be used to
attach the plug
122, 222 to tube 20.
[0037] In one embodiment, such as for rock bolt 102, shown in Fig. 4, plug 122
is
spherical. Plug 122 may be placed such that the first exposed portion 124 is
one hemisphere
of spherical plug 122 and the second portion 125 inside the opening in the
distal end 23 of
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second stiffening tube 20 is the other hemisphere as shown. Alternatively, the
plug 122 may
be placed such that less of plug 122 exposed or more of plug 122 is exposed as
long as the
main passageway 26 is covered. Plug 122 may take the form of a polished or
unpolished ball
bearing.
[0038] In another embodiment, such as for rock bolt 202, shown in Fig. 5, the
first exposed
portion 224 of the plug 222 may be dome shaped and the second portion 225
extending into
tube 20 may be cylindrical. The second cylindrical portion 225 may further
have a beveled
edge 227 as shown.
[0039] Alternatively, the cover 22 may be a cap 322 or a cap 422, as shown in
Figs. 6 and
7, respectively. Cap 322, 422 may take any suitable shape (such as rounded) as
long as the
main passageway 26 is covered. The cap 322, 422 may be made of steel or any
other suitable
material. Cap 322, 422 may be fixed to the rock bolt 302, 402 by welding or
the like. For
example, tack welds 32 spaced apart around the circumference of the proximal
end 329, 429
of cap 322, 422 may be used to attach cap 322, 422 to respective tube 20.
[0040] In one embodiment, such as for rock bolt 302, shown in Fig. 6, cap 322
is
hemispherical, and the open proximal end 329 of cap 322 abuts distal end 23 of
tube 20.
Cap 322 is shown to be hollow but it could also be solid (not shown), for
example, a sphere,
such as plug 122 in Fig. 4, cut in half.
[0041] In another embodiment, such as for rock bolt 402, shown in Fig. 7, cap
422 has a
closed distal end 434, an open proximal end 429, and a sidewall 436 extending
from the
closed distal end 434 to the open proximal end 429 creating an inner cavity
438. Cap 422 is
placed over tube 20 such that tube 20 and the distal end 21 of tube 4 are
received in the inner
cavity 438. The sidewall 436 of cap 422 extends along the sidewall of tube 20.
Cap 422 can
be fabricated using any suitable means including, but not limited to,
stamping, molding, or
attaching a cover portion to a cylindrical tube. The distal end 434 of cap 422
may be hollow
(as shown) or may be solid (not shown) as described above for cap 322 of rock
bolt 302.
[0042] In another embodiment (not shown), cap 422 could be sized such that its
sidewall
436 fits inside the distal end 23 of tube 20 such that distal end 434 of cap
422 extends beyond
distal end 23 of tube 20. A portion of sidewall 436 may extend beyond the
distal end 23 of
tube 20 or the length of the sidewall 436 may be adjusted so that only distal
end 434 extends
beyond distal end 23 of tube 20.
[0043] In further embodiments such as for inserting the rock bolt into risible
ground or
ground into which it is difficult to insert an expandable bolt, a thrust
element (522, 622, 722,
or 822) may be provided at the distal end 23 of the rock bolt as shown in
Figs. 8- 20. The
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thrust element may comprise a cover for the distal end 23, or may be otherwise
associated
with the distal end 23, such as being directly connected to the distal end, or
form an extension
of the cover 22.
[0044] The thrust element may be arranged in use to deflect loose material
disposed in the
bore as the rock bolt is inserted. This may assist insertion of the rock bolt
in the bore and/or
may inhibit compaction of that material in the blind end of the bore.
Compaction of loose
material in the bore end is problematic as it reduces the effective length of
the bore and may
prevent the rock bolt from being fully inserted into a bore unless that
borehole is of extended
length. It is undesirable to extend the length of the borehole as this adds
both time and
expense to the strata support operation.
[0045] In the form illustrated in Figs. 8-11, thrust element 522 is in the
form of a cone and
extends from an apex 540 to an engagement end 542. The tapered surface of the
element 522
extending between the apex 540 and the engagement end 542 comprises a
plurality of angled
facets 544. These angled facets allow loose material within the bore to be
deflected in a
radial direction (relative to the axis of the bore). Such movement of the
loose material may
aid insertion of the rock bolt in the bore and may inhibit compaction of the
loose material in
the end of the bore.
[0046] In some forms the engagement end 542 comprises an engagement portion
525
adapted to be inserted into the distal end 23 of the stiffening tube 20. In
the form illustrated in
Figs. 8-11, the engagement portion 525 is in the form of a hemisphere adapted
to be inserted
into the distal end 23. The engagement portion further includes a collar
section 526 that
bears against the interior of the distal end 23 and a downwardly facing
engagement shoulder
527 that locates over the distal end 23, thereby providing a cover for the
distal end 23.
Further, as illustrated the thrust element 522 which is typically made from
metal, is fixed to
the distal end 23 by tack welds 32. It will be appreciated that the thrust
element 522 may be
fixed by other means such as by crimping, a coupling (such as a threaded
coupling) or by
adhesive bonding.
[0047] In the form illustrated in Figs. 12-15, thrust element 622 is
frustoconical and
extends from a truncated -apex 640 to an engagement end 642. The surface of
the element 622
extending between the apex 640 and the engagement end 642 comprises a
plurality of angled
facets 644. Similar to the previous embodiment, these angled facets 644
allow loose
material within the bore to be deflected in a radial direction (relative to
the axis of the bore).
Again, the thrust element 622 forms the cover for the distal end 23 and may be
welded by
tack welds 32 to the end 23 with the engagement end 642 comprising an
engagement portion
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625 and being adapted to be inserted into the distal end 23 of the stiffening
tube 20. In the
form illustrated in Figs. 12 through 14, the engagement portion 625 includes a
hemisphere
adapted to be inserted into the distal end 23, a collar section 626 which
bears against the
interior of the of the distal end 23 and ,a downwardly-facing engagement
shoulder that locates
over the distal end 23.
[0048] In the form illustrated in Figs. 15-17, thrust element 722 extends from
a thrust end
740 to an engagement end 742. The element 722 is made akin to a drill bit and
the thrust end
740 is in the form of a profiled head having opposing angled blade surfaces
746 spaced apart
about an upper surface of the thrust end 740. A central depression 747 is
positioned
intermediate the angled blade surfaces 746. The engagement end comprises an
engagement
portion 725 which comprises an engagement shoulder 748 that bears against the
distal end 23
and an engagement flange 749 that locates in facing relation with the interior
of the distal end
23. In this way, the thrust element 722 also forms a cover for the distal end
23. Channels
750 extend longitudinally along the element 722 between the blades 746. These
channels are
arranged to allow loose material to flow past the thrust element 722 as the
rock bolt is
advanced along the bore during insertion thereby inhibiting compaction of
material at the end
of the bore. Again, in the illustrated form, the thrust element 722 is welded
to the distal end
23 by tack welds 32.
[0049] In a further form illustrated in Figs. 18-20, thrust element 822
extends from a thrust
end 840 to an engagement end 842. The thrust end 840 is in the form of a
profiled head
having two protrusions 846 spaced apart about an upper surface of the thrust
end 840. A
domed surface 847 is positioned intermediate the protrusions 846. The
engagement end 842
comprises an engagement shoulder 848 which locates over the distal end 23 and
a threaded
shaft 849. The shaft 849 locates within the distal end and is arranged to
engage with a
complementary interior thread 36 formed on the interior of the tube 20 to
secure the element
822 to the end 23. The spacing between the protrusions 846 allows material
flow across the
element 822 on insertion of the rock bolt into a bore containing loose
material.
[0050] The rock bolt can be made by providing an expandable member which
includes an
expandable tube 4 and an end fitting (stiffening tube 20) on the distal end 21
of the
expandable tube 4. The expandable tube 4 has a longitudinally extending
depression 6
disposed between a pair of curved outer portions of the tube 8, 10. The
exterior of the tube
defines a temporary, enclosed longitudinal passageway 26 having an open distal
end 23 and
the outer portions of the tube 4 define internal passageways 28, 30 which have
closed distal
ends 23. The distal end of the tube 4 is then enclosed with a cover 22 so as
to cover the distal
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open end 23 of the temporary, enclosed longitudinal passageway 26. The cover
22 may be in
the form of a plug 122, 222 or a cap 322, 422 and may be rounded. The cover 22
may be
secured to the expandable tube 4 by welding or any other suitable method. The
method may
also include placing a stiffening tube 20 on a proximal end 15 of the
expandable tube 4 such
that the stiffening tube 20 surrounds 0e proximal end 15 of the expandable
tube 4 and has an
opening 34 that aligns with a corresponding opening in the expandable tube 4,
thereby
providing fluid communication to an interior of the expandable tube 4. The
stiffening tube 20
may be attached to the expandable tube 4 by welding, crimping or any other
suitable method.
[0051] The cover keeps debris from entering the main passageway of the rock
bolt when
the rock bolt is in the unexpandal condition. It also allows the rock bolt to
be more easily
inserted and centered in the borehole. The domed end of the rock bolt created
by the cover
eliminates the sharp angles at the distal end of the rock bolt which can tend
to get caught on
the sides of the borehole. The domed end also allows the rock bolt to be
centered more easily
in the borehole.
[0052] The cover also has the advantage of reduced manufacturing costs
compared to other
methods of rounding the end, for example, building up weld metal on top of a
blank to round
the end. The cover may be held in place with a minimal number of tack welds as
described
above simplifying fabrication and reducing costs. In addition, manufacturing
becomes even
easier when producing a rock bolt according to embodiment 102, shown in Fig.
4. The
spherical plug 122 may be placed in tube 20 in any orientation simplifying
assembly and,
thus reducing assembly time.
[0053] In general use, the expandable rock bolt with thrust element is
inserted into a pre-
drilled borehole, without rotation thereof necessary, although in certain
instances the
expandable rock bolt with thrust elerrient may be at least slightly rotated
about its longitudinal
axis. Such pre-drilled boreholes may at least partially refill with loose rock
or the like. The
thrust element deflects such loose material to ease the insertion of the bolt
into the borehole,
with the remainder of installation of the expandable rock bolt with thrust
element being the
same or similar to the expandable bolt with shielded tip as described above.
[0054] The thrust element positioned on the distal end of the expandable rock
bolt reduces
the difficulty of inserting the expandable rock bolt into a bore made in
risible or gravelly
earth. In these circumstances the material tends to move past or be deflected
by the element
into the wall of the bore. The thrust element allows the bolts to be more
easily inserted by
compacting the loose material against the wall of the bore or moving loose
earth material
away from the advancing front of the rock bolt as it is being inserted in the
bore. This allows
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the expandable bolt to be inserted into the bore without the risk that there
will be a build up
of material in the end of the bore that would prevent the rock bolt from being
fully inserted.
The use of a thrust element on the rock bolt is particularly useful when a
percussive force is
applied to drive the rock bolt in place and typically does not require any
rotation to be applied
to the bolt.
[0055] The foregoing description s=As forth the preferred embodiments of the
invention at
the present time. Various modifications, additions, and alternative designs
will, of course,
become apparent to those skilled in the art in light of the foregoing
teachings without
departing from the scope of the invention. The scope of the invention is
indicated by the
following claims rather than by the foregoing description. All changes and
variations that fall
within the meaning and range of equivalency of the claims are to be embraced
within their
scope. Specifically, while embodiments herein have been described as having a
rounded
cover, covers having any shape that covers the main passageway of the rock
bolt are
considered within the scope of the invention.
