Note: Descriptions are shown in the official language in which they were submitted.
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MINE ROOF BOLT ASSEMBLY
SCOPE OF THE INVENTION
The present invention relates to a mine roof bolt assembly, and more
particularly a bolt
assembly which includes a reinforcing anchor rod or rebar having a threaded
end which is
engaged by a nut, and wherein the nut is secured in an initial position
against movement relative
to the rod by a pair of shear pins, and which upon the application of a
predetermined minimum
torque force, fracture or shear to permit the nut to run freely onto the rod.
BACKGROUND OF THE INVENTION
In mine roof and wall support systems (hereinafter collectively referred to as
"mine roof
support systems"), a threaded rod-like reinforcing bolt or rebar is embedded
into a bolt hole
drilled in the rock face. A nut or threaded fastener is thereafter coupled to
the rod and tightened
against the rock face to consolidate forces therein and prevent or control
ground movement.
Typically, the rebar reinforcing rod comprises a four to eight foot length of
steel which is
threaded along its outermost proximal end. The rebar is inserted into a bore
hole drilled into the
rock so that the threaded end projects outwardly beyond the rock face,
permitting the threaded
coupling of the nut thereto.
United States Patent No. 5,873,689 to Mensour et al, which issued 23 February
1999,
discloses a prior method and system of securing an anchor rebar in a bolt hole
by the use of one
or more resin cartridges. The resin cartridges are inserted into the bolt hole
in advance of the
rebar. Following their insertion, the rebar is slid into the bolt hole and
driven through the resin
cartridges, causing their rupture and the mixing of the resin to fixedly
retain the rebar once the
resin has set.
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To enhance mixing of the resin, it is known to rotate the rebar about its
longitudinal axis.
United States Patent No. 5,873,689 discloses a dome-nut type fastener which is
characterized by
a covered nut end. The nut is positioned over the threaded end of the rebar
and rotated about its
axial length with a power winch or socket drive. The nuts are formed such that
the engagement
of the covered end of the nut under initial torque forces results in the rebar
rotating together with
the turning of the nut. As the resin sets, resistance to the rotation of the
rebar increases until the
rotational force applied to the nut exceeds a critical minimum torque force.
Upon reaching the
predetermined torque force, the cover portion or domed end distorts or splits
by contact forces
between the rebar and nut as the nut is moved along the rebar thread. The
deformation allows
the nut to thereafter be tightened along the rod and against the rock face.
Although the dome nut
of United States Patent No. 5,873,689 achieves satisfactory deformation with
low torque
applications where, for example, the covered end is adapted to deform or
detach at less than
about 50 Ft. Lbs. or less, conventional dome nuts have proven inconsistent in
providing a precise
torque deformation range where higher torque applications are desired. In
addition, where dome
nuts are made by casting, thickness cannot precisely be controlled, resulting
in imprecise control
in the breakage strength of the dome. In case the dome portion is not strong
enough, earlier
breakage occurs, which results in under-mixing of resin. On the other hand, if
the dome portion
is too strong to break, the nut cannot be rotated further and therefore the
bar cannot be tensioned.
Both cases are termed as failure of installation.
Various other manufacturers have proposed different torque nuts which
incorporate a nut
secured to the rod by means of a shear pin which fractures under higher
predetermined minimum
torques. United States Patent No. 4,173,918 to Piersall discloses an earlier
expansion bolt
construction in which a single shear pin is inserted through a bore hole
formed transversely
through a nut and mine roof anchor rod. The pin is used to permit rotation of
the rebar about its
axial length to permit the positioning of a threaded wedge anchor, and which
following its
placement, the predetermined minimum torque is applied to the nut, causing the
pin to shear, and
allowing the nut to be tightened along the rebar. The applicant has
appreciated, however, that
upon initial deformation of the pin of Piersall, the pin may initially be bent
into an S-shape,
rather than shearing cleanly. As a result, the S-shape bending of the shear
pin tends to result in
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the pin fragments partially wedging between the internal threads of the nut
and the external
threads of the bolt. This in turn may result in distortion or deformation of
the rebar threads, or
even the wedging of the nut on the rebar in an untightened position. The
wedging of the pin
fragments between the bolt and nut thread could disadvantageously result in
the over torqueing
of the rod in the set resin, resulting in the detachment of the rod from the
resin and its spinning in
the bolt hole, or the twist failure of the rod.
SUMMARY OF THE INVENTION
To at least partially overcome the disadvantages of prior art dome nuts used
in the mixing
of resins, the applicant has considered providing a mine roof bolt assembly
which includes a
threaded fastener or nut which is secured to the bolt or rebar by means of
pins which are adapted
to shear following the application of a predetermined minimum torque.
The applicant has further appreciated that where the pin fragments wedge
between the
nut and bolt, the fragments may adversely score, deform or otherwise distort
the bolt threads,
making it difficult to subsequently secure thereto mesh screens, push-on
plates, seal nuts or other
safety screens used in the mine roof bolt assembly.
Accordingly, one object of the invention is to provide a threaded fastener for
use in a
mine roof/wall reinforcing system which is inexpensive and is easy to
manufacture.
Another object of the invention is to provide a mine roof bolt assembly which
is suitable
for use with resin anchoring techniques, and which may be used in a variety of
torque
applications including, without restriction, high torque applications of more
than 100 Ft. Lbs.,
and more preferably more than about 125 Ft. Lbs. and in which a threaded
fastener is adapted for
reliable deformation with minimum tolerances upon the application of a
predetermined minimum
torque.
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Another object of the invention is to provide a pin nut construction for use
in a mine roof
or wall or other anchor support system which is constructed to minimize the
likelihood of the
wedging of pin fragments between the nut and anchor rod as the pins shear.
Another object of the invention is to provide a threaded fastener for use with
a
reinforcing rod in a mine roof support system which, in assembly, minimizes
any deformation,
scoring, scraping or otherwise adversely altering the threads of a reinforcing
rod.
A further object of the invention is to provide a mine roof support system for
use in hard
rock applications which incorporates a threaded fastener which is secured in
an initial position to
a roof bolt or rebar by one and more preferably a pair of shear pins, and
which upon exceeding a
precise predetermined minimum torque, shear to allow the nut to be threaded
onto the bolt
against the rock face.
Accordingly, to at least partially overcome the disadvantages of prior art
dome nuts, the
applicant has proposed a roof bolt assembly for use in a bolt hole which
includes an elongated
anchor rod or rebar which is characterized by an externally threaded end, and
a nut or other
suitable fastener which is configured to threadedly engage the threaded end of
the rebar. A bore
is formed through the sides of each of the anchor rod and the nut. The bores
formed through the
nut and rebar are configured for general alignment when the nut is positioned
on the rebar in a
first or initial position, as for example, so that the nut may be optimally
driven by a power socket
or wrench so as to rotate the rod in the bolt hole. The bore formed through
the nut most
preferably extends into the internally threaded nut aperture and is
characterized by a pair of bore
segments which extend inwardly from the side surfaces of the nut. The bore
segments, although
not essential, are most preferably aligned with each other. A pair of
retaining shear pins are
insertable in a retaining position so as to locate partially within one
respective bore segment, as
well as within the bore formed through the rebar. The pins have a sizing
selected so that when
inserted in the retaining position, a minimum spacing is maintained within the
rebar bore
between the innermost ends of the pins which are proximate to each other. Most
preferably, the
space in between the inner ends of the pins is selected at least as large as
twice the depth of the
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threads on the rebar and/or the nut, and more preferably at least greater than
twice the thread
Lager gap. Smaller gaps may be used, albeit with an increased risk of the
fractured pin causing
the nut and rebar to seize. The pins have a thickness and/or hardness selected
so that when the
fastener is rotated relative to the rebar under a predetermined minimum
torque, the pins fracture
and shear at the junction between the nut and the rebar. Most preferably, the
predetermined
minimum torque is selected at at least 100 Ft. Lbs., and more preferably about
125 to 150 Ft.
Lbs., however higher or lower torques may also be used. Upon fracture of the
pins, the pin
fragments located within the rebar bore thus may move radially inwardly
towards each other so
as not to interfere or otherwise wedge between the bolt and nut threads, as
the nut is threaded
onto the bolt.
Accordingly, in one aspect the present invention resides in a mine roof bolt
assembly for
use in a predrilled bolt hole comprising,
an anchor member being elongated along an axis and extending from a distal end
sized
for insertion into said bolt hole to an externally threaded proximal end, a
first bore extending
through said anchor member remote from said distal end, the first bore
extending in a direction
generally transverse to said axis,
a threaded fastener including,
a body having first and second end portions,
a generally cylindrical opening extending axially through said body from said
first
end portion to said second end portion,
internal threads being provided along at least part of said opening, the
internal
threads sized for threaded engagement with the externally threaded proximal
end of the
anchor member whereby the relative rotational movement of the threaded
fastener and
the anchor member moves the threaded fastener axially along the anchor member,
a second bore extending through said fastener from a first side of said body
to a
second generally opposing side, said second bore being oriented transverse to
said axis
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and being adapted for substantial alignment with said first bore when said
threaded
fastener is coupled in a first position to said anchor member, the second bore
including a
first bore segment extending inwardly from said first side to said cylindrical
opening, and
a second bore segment extending inwardly from the second side to the
cylindrical
opening,
a pair of retaining pins for limiting rotational movement of the threaded
fastener from a
first position relative to the anchor member up to a predetermined rotational
torque, whereby
when said threaded fastener in said first position, a first one of said pins
being located at least
partially within said first bore segment and said first bore, and the second
other pin being located
at least partially within said second bore segment and said first bore, and
wherein adjacent
innermost ends of the pins being spaced apart from each other within the first
bore by a
predetermined spacing.
In another aspect, the present invention resides in a roof or well bolt
assembly
comprising,
an anchor rod being elongated along an axis and extending from a distal end to
an
externally threaded proximal end, a first bore extending through an axial
centre of said threaded
proximal end,
a threaded fastener including,
a body extending axially from a first end portion to a second end portion and
further including at least one pair of generally planar opposing side
surfaces,
an internally threaded opening extending axially through said body,
the internal threads of said opening being sized for complementary threaded
engagement with the externally threaded proximal end of the anchor rod whereby
the
relative rotational movement of the threaded fastener and the anchor rod moves
the
threaded fastener axially along the proximal end,
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a second bore extending through said fastener from a first one of said planar
side
surfaces to the second other opposing side surface and said second bore being
movable
into substantial alignment with said first bore when said threaded fastener is
coupled in a
first position to said proximal end, including a first bore segment extending
inwardly
towards the axis from said first planar side to said opening, and a second
bore segment
extending inwardly towards the axis from the second other planar side to the
opening,
a pair of retaining pins for limiting relative rotational movement of the
threaded fastener
and the anchor rod from a first position up to a predetermined rotational
torque, whereby when
said threaded fastener is in said first position, a first one of said pins
locates at least partially
within said first bore segment and said first bore, and the second other of
the pins locates at least
partially within said second bore segment and said first bore, with adjacent
innermost ends of the
pins being spaced apart from each other in the first bore by a predetermined
spacing.
In a further aspect, the present invention resides in a mine roof bolt
assembly for use in a
mine roof support system, the assembly comprising,
a generally cylindrical anchor rod, the rod being elongated along an axis from
a distal end
to an externally threaded proximal end, a first bore extending through said
anchor rod remote
from said distal end,
a threaded fastener sized for threaded engagement with the proximal end of the
bolt and
including,
a body extending from a first end portion to a second end portion as further
including at
least two opposing pairs of generally planar axially extending side surfaces,
a generally cylindrical opening extending axially through said body from said
first end
portion to said second end portion,
an internal helical thread provided along at least part of said opening, the
internal thread
having a thread depth selected for complementary threaded engagement with the
externally
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threaded proximal end of the anchor rod whereby the relative rotational
movement of the
threaded fastener and the anchor rod moves the threaded fastener axially along
the rod,
a second bore extending through said fastener from a first one of a first of
said pair of
planar sides to the second other opposing one of said first pair of sides,
said second bore being
oriented for substantial alignment with said first bore when said threaded
fastener is coupled in a
first position to said anchor rod, the second bore including a first bore
segment extending
inwardly from said first side open to said cylindrical opening, and a second
bore segment
extending inwardly from the second side open to the cylindrical opening
a pair of shear pins for limiting rotational movement of the threaded fastener
from a first
position relative to the anchor member up to a predetermined rotational
torque, each of the
retaining pins including an inner end portion and an outer end portion with
said fastener in the
first position, a first one of said pins being located with its outer end
portion disposed within said
first bore segment and its inner end portion disposed within said first bore,
and said second pin
being located with its outer end portion within said second bore segment and
its inner end
portion disposed within said first bore, and whereby the adjacent inner end
portions of the pins
being spaced apart from each other within the first bore by a spacing selected
as large as at least
twice the thread depth of the internal fastener thread, and whereupon the
application of the
predetermined torque on one of the rod and the fastener results in the
shearing of each of the pins
between the respective inner and outer end portions to permit the fastener to
move axially along
the threaded end portions.
BRIEF DESCRIPTION OF THE DRAWINGS
Reference may now be had to the following detailed description taken together
with the
accompanying drawings in which:
Fig. 1 shows a conventional dome-nut type fastener fully installed as part of
a mine roof
support system;
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Fig. 2 shows a cross-sectional view of a mine roof bolt assembly in accordance
with a
preferred embodiment of the invention, with the anchor rod and fastening pin
nut provided in an
initial position and coupled against movement relative to each other for
mixing anchoring resin;
Figs. 3 to 5 show a series of schematic views of a rock structure,
illustrating the initial
placement of the mine roof bolt assembly to the position shown in Figure 2;
Fig. 6 shows a cross-sectional view of the mine roof bolt assembly shown in
Figure 2
with the pin nut tensioned against the rock face following the application of
a predetermined
minimum torque to the nut;
Fig. 7 illustrates a cross-sectional view of the mine roof bolt assembly shown
in Figure 6
illustrating the placement of a mesh screen and subsequent anchor nut on the
anchor rod,
following tightening of the fastening nut;
Fig. 8 shows an exploded end view of the anchor rod, pin nut and shear pins,
used in the
mine roof bolt assembly of Figure 2, illustrating the placement of the shear
pins in bores formed
through the nut and rod in the securing of the pin nut in the initial
position;
Fig. 9 illustrates a cross-sectional view of the pin nut and rod shown in
Figure 2 taken
along line 9-9;
Fig. 10 shows an exploded perspective view of the rod, pin nut and anchor pins
shown in
Figure 8;
Fig. 11 illustrates an exploded cross-sectional view of a anchor rod, pin nut
and retaining
shear pins for use in the mine roof bolt assembly in accordance with a further
embodiment of the
invention;
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Fig. 12 illustrates an exploded cross-sectional view of an anchor rod, pin nut
and shear
pins for use in the mine roof bolt assembly in accordance with a still further
embodiment of the
invention; and
Fig. 13 shows a perspective view of a threaded pin nut for use with the anchor
rod in
accordance with a further embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Figure 1 shows a conventional rock support assembly 10 used to reinforce a
rock
complex 8 and which, for example, would include a mine roof. The assembly 10
includes a cast
steel dome nut 12 and a steel rock bolt or reinforcing rod 14 or rebar. The
reinforcing rod 14 has
an externally threaded proximal end portion 16 and a distal portion 18 which
is sized for
placement within an elongated bolt hole 20. In the fully assembled
configuration, the distal end
portion 18 is inserted into the bolt hole 20 which is preferably preformed in
the rock complex 8
and is secured therein by a mixed resin 22. The dome nut 12 is tightened over
the threaded
portion of the proximal end portion 16 of the rod 14 which projects outwardly
from the bore hole
to secure a reinforcing plate under tension against the rock face 25.
In installation, the bore hole 20 is drilled to a desired diameter and depth
having regard to
the length and diameter of the rod 14, and typically extends between about 4
and 8 feet from the
rock face 25 into the rock complex 8. A number of two-part resin cartridges
24a,24b (shown in
Figure 3) are slid axially into the bolt hole 20 ahead of the distal end
portion 18 of the anchor rod
14. The distal end portion 18 of the rod 14 when inserted into the bolt hole
20, piercing and
shredding the cartridges 24a,24b and mixing the resin 22. The steel
reinforcing plate 26 is
thereafter positioned over the rod 14, and the dome nut 12 threaded onto the
proximal tip 28.
The dome nut 12 is rotated, turning the rod 14 while the resin 22 remains
unset. Once the resin
22 sets, it encases and fixedly retains the end portion 18 of the rod 14 in
the bolt hole 20. The
dome nut 12 is then driven in rotation on the threaded end portion 16 of the
rod 14 by a socket
driver power wrench (not shown) with a minimum required torque. The treaded
engagement of
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the proximal end portion 16 with the nut 12 causes the rock complex 8 to
compress, and the
threaded end portion 16 to deform the closed end of the nut 12.
Figures 2 to 10 show best a mine roof bolt assembly 30 for use in a predrilled
bolt hole
20 as part of a mine roof support system in accordance with a first embodiment
of the invention.
The assembly 30 incorporates a steel rock bolt or rod 14 which, as with prior
art systems, is
elongated along an axis A,-A1 (Figure 2) and which includes a distal end
portion 18 sized for
fitted insertion within the bolt hole 20, and an externally threaded proximal
end portion 16. As
will be described, the bolt 14 operates in conjunction with a pin nut 36 and a
pair of shear pins
60a,60b to achieve mixing of onset anchoring resin 22 (Figure 5) within the
bolt hole 20, and the
subsequent compression of a rock complex 8.
The threaded proximal end portion 16 of the rod 14 preferably extends
approximately
two to six inches from the proximal endmost rod tip 28 (Figure 4). As shown
best in Figures 2, 8
and 9, the rod 14 has a typical length of between about 4 and 8 feet,
depending on the depth of
the bolt hole 20. A through bore 34 is formed through the threaded proximal
end portion 16 of
the rod 14 adjacent to the proximal end tip The proximal end portion 16 is
characterized by a
helically extending thread 32 which has a thread depth d. The bore 34 is
formed through the
axial centre of the rod 14 extending in an orientation generally normal
thereto.
Figures 2, 6, 8, 9 and 10 further show the pin nut 36 as comprising a high
alloy steel body
3 8 having a generally flattened square configuration, and which extends from
an inner end face
surface 40 to an outer end face surface 42. 'The body 38 includes two opposing
pairs of parallel
side surfaces 44a,44b and 46a,46b. A through aperture 48 (Figure 10) extends
through the axial
centre of the body 38 from the inner end surface 40 to the outer end surface
42. As shown best
in Figure 10, the aperture 48 is characterized by an internal thread 50. The
internal threads 50
extend helically and have a thread depth d substantially equal to that of the
external rod thread
32, and which is oriented for complementary threaded engagement with the
external threads 32
provided on the proximal end portion 16 of the rod 14.
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Figures 8 to 10 further show the body 38 as including a through bore 52
extending
therethrough along the bore axis AB-AB (Figure 10) from side surface 44a to
side surface 44b.
The through bore 52 has essentially the same cross-sectional diameter as
through bore 34 and
extends as a cylindrical bore through the axis A~-A~ in an orientation
generally normal thereto.
The through bore 52 includes a first bore segment 54a which extends from the
central portion of
the sidewall 44a towards the axis A~-A~ to an opening into the through
aperture 48, and a second
coaxially aligned bore segment 54b which extends in an essential mirror
arrangement from the
side surface 44b towards the axis A1-A~ to and opening into an opposing side
of the through
aperture 48.
The through bores 34,52 are formed respectively through rod 14 and nut 36 so
as to
permit the coaxial alignment of the bores 34,52 in the position shown in
Figure 8 when the nut
36 is threaded on to the distal endmost portion 16 of the rod 14 in a first
initial position, as for
example is shown in Figure 2. It is to be appreciated that the initial
position at which the through
bores 34,52 align is preferably selected to enable the nut 36 to be engaged
and driven in rotation
about the bolt axis A1-A~ by a power socket or wrench.
Figures 2 and 8 to 10 show best the assembly 30 as further including a pair of
shear pins
60a,60b. In a simplified construction, the shear pins 60a,60b are formed as
steel roll pins. The
pins 60a,60b have a generally cylindrical shape and complementary cross-
sectional size to
permit their insertion in the through bores 52,34. The pins 66a,66b are
manufactured having a
hardness selected to fracture or shear cross-sectionally across their length
upon the application of
a predetermined minimum torque, and most preferably a torque of at least about
100 Ft. Lbs.,
and preferably about 125 to 50 Ft. Lbs.
The pins 60a,60b have a length selected to permit each pin 60a,60b to be
inserted from
each respective side 40a,40b of the nut 36 through a bore segment 54a,54b and
so as to locate in
a locking or retaining position partially within the through bore 34, as for
example is shown in
Figure 9. When so positioned, the pins 60a,60b each respectively locate
partially within the bore
segments 54a,54b and through bore 34, thereby preventing the movement of the
nut 36 relative
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to the rod 14 and along the threaded portion 16 under torque conditions which
do not exceed the
predetermined minimum threshold torque at which the pins 60a,60b shear. The
pins 60a,60b
have a length selected so that when positioned in the retaining position shown
in Figure 9, the
innermost ends 62a,62b of the pins 60a,60b, respectively, which are spaced
closest to each other
and the axis A1-Ai are separated from each other by a spacing distance D
(Figure 9). Most
preferably, the distance D separating the pins 60a,60b is selected at least as
large as twice the
thread depth d of the internal nut threads 50 provided along the through
aperture 48 and/or the
external threads 32 of the proximal end portion 16 of the rod 14. The
applicant has appreciated
that the provision of a spacing D between the innermost ends 62a,62b of the
shear pins 60a,60b
permits the fractured inner end fragments 64a,64b (Figure 3) of each pin
60a,60b to move
inwardly towards each other and the axis A,-A~ following the shearing of the
pins 60a,60b upon
the application of the predetermined minimum torque to the nut 30. The inner
movement of the
fractured ends 64a,64b of the pins 60a,60b ensures that the pin fragments
64a,64b do not lodge
between the threads 50 and exterior rod threads 72 where they may otherwise
score the threads
or deform the threads 50,32 or otherwise interfere with the threaded movement
of the nut 36
along the proximal end 16 of the rod 14.
Figures 3 to 7 illustrate the installation of the mine roof rock support
assembly 10 using
the nut 36 and shear pins 60a,60b in accordance with a first preferred
embodiment of the
invention. As shown best in Figure 3, a bolt hole 20 is initially drilled to a
depth of about 8 feet
in the rock complex 8 which is to be reinforced. The reinforcing rod 14 is
chosen from a suitable
iron or steel having an axially elongated length which most preferably is two
to six inches longer
than the bolt hole 20.
In a preferred construction, the nut 36 is pre-coupled to the rod 14 prior to
its insertion
into the bore hole 20. The nut 36 is initially threaded onto the externally
threaded portion 16 of
the rod and moved to the initial position with the through bores 52 and 34
aligned. As shown in
Figure 10, once so positioned, the pins 60a,60b are inserted laterally into
the respective bore
segments 54a,54b so that their outermost ends 66a,66b (Figure 9) lie flush
with the nut side
surfaces 44a,44b respectively, and the innermost ends 62a,62b locate within
the through bore 34
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with the spacing D as shown in Figure 9. Optionally, with the nut 36 so
prepositioned, the
reinforcing plate 26 may be slid over the distal end 18 of the rod 14 for
positioning against the
rock face 25. It is to be appreciated that when the nut 36 is moved to the
initial position shown
in Figure 2 and the pins 60a,60b are inserted into the respective bore
segments 54a,54b and
partially into the through bore 34 in the manner shown in Figure 9, the pins
60 act to couple the
nut 36 to the end of the rod 14. Rotational forces applied to the nut 36 which
do not exceed the
predetermined minimum torque thus act to rotate the rod 14 about its axis A~-
A1.
As with conventional systems, a number of two-part resin cartridges 24a,24b
(Figure 3)
are then slid into the bore hole 20, the number of which most preferably, are
selected to fully
grout the hole 20. Following the positioning of the resin cartridges 24a,24b,
the distal end
portion 18 of the rod 14 is inserted into the bore hole 20 and is forced
axially therein to crush and
rupture the cartridges 24a,24b, thereby releasing the resin 22. With the rod
14 fully inserted into
the bolt hole 20 as for example is shown in Figures 2 and 5, the threaded end
portion 16 projects
from the rock complex 8 a preferred distance of between about 1.5 to 6 inches.
The fully
inserted rod 14 is thereafter rotated about its axis A~-A1 by applying
rotational forces to the nut
36 by means of a socket drive. The initial rotational forces on the nut 36 and
the engagement of
the shear pins 60a,60b in each of the through bores 52 and 34 prevent relative
movement of the
nut 36 along the proximal end 16 of the rod 14, rotating the rod 14 together
with the nut 36 to
mix the liquefied resin 22 in the bore hole 20.
Following mixing of the resin 22, rotation of the pin nut 36 is stopped and
the resin 22 is
permitted to set, securing the rod 14 against further rotational movement in
the bolt hole 20.
Once the resin 22 has hardened, the socket drive is again activated to rotate
the pin nut 36 at the
predetermined minimum torque of preferably greater than about 100 Ft. Lbs. The
application of
the predetermined torque force on the nut 36 thus results in the pins 60a,60b
shearing at the
junction between each of the respective bore segments 54a,54b and the through
bore 34. As a
result, the portion of the pin 60a,60b which originally located in the through
bore 34 remain as
respective fragments 64a,64b, as for example is shown in Figures 6 and 7. The
portion of the
pins 60a,60b locating originally in the bore segments 54a,54b similarly
remains therein as pin
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fragments 68a and 68b, respectively. Because the pin fragments 64a,64b move
inwardly in the
through bore 34 towards the axis A1-A1, the pin fragments 64a,64b do not
otherwise interfere
with the threaded movement of the nut 36 along the proximal end portion 16.
The nut 36 thus
may thereafter be tightened against the reinforcing plate 26 and/or directly
against the rock face
as for example is shown in Figure 6.
Following securement of the nut 36 against the plate 26, a safety screen 72
may be
positioned over the remaining projecting portion of the proximal end portion
16, and a second
threaded fastener or nut 74 (or other suitable hardware) of a conventional
design thereafter used
to retain the safety screen 72 in place.
Although the preferred embodiment describes the prepositioning of the nut 36
prior to the
insertion of the rod 14 in the bore hole 20, it is to be appreciated that the
invention is not so
limited. If desired, the nut 36 and pins 60a,60b could be aligned through
bores 34,52 following
initial placement of the rod 14 for mixing the resin 22.
Figure 11 shows an alternate possible fastener arrangement wherein like
reference
numerals are used to identify like components. In Figure 1 l, the through bore
34 is provided as a
cylindrical bore having a reduced diameter relative to the through bore 52.
Each of the pins
60a,60b are provided with a reduced diameter end portion which is adapted to
shear as inner
fragments 64a,64b, and an enlarged diameter outer end portion which are
adapted to shear as
outer fragments 68a,68b, respectively. The inner and outer portions of the
pins 60a,60b are each
sized for complementary insertion within the respective through bores 34 and
52. The provision
of pins 60a,60b and through bores 34,52 with portions having differing cross-
sectional
diameters, advantageously act as locating elements which prevent the pins
60a,60b from being
inserted too far into the through bore 34, and maintain the optimum desired
spacing between the
inner ends 62a,62b of the pins when so inserted. In addition, the reduced
diameter fragment
64a,64b portions may be formed with a desired cross-sectional thickness which
is directly
proportional to the amount of predetermined minimum torque requirement for
shearing of the
pins. The construction of Figure 11 thus is suitable for lower torque
applications where, for
CA 02439397 2003-08-11
16
example, the pins 60a,60b are to shear upon the application of a comparatively
lower
predetermined minimum torque of between about 40 and 50 Ft. Lbs.
Figure 12 illustrates an alternate possible pin 60 construction, wherein like
reference
numerals are used to identify like components. Each of the pins 60a,60b are
provided at their
outer ends 66a,66b with an enlarged diameter flattened head flange 80. The
head flange 80
extends transverse to the direction of elongation of each of the pins 60 and
most preferably is
provided with a generally flat construction so as not to significantly project
outwardly beyond
the sides 44a,44b of the nut 36 where they may otherwise interfere with the
placement of a
socket during rotation of the nut 36 and rod 14. As with the differing
diameters of the pin
sections shown in Figure 11, the pin head flange 80 advantageously acts as a
locating element to
assist in positioning the pins 60a,60b in the through bores 52,34 with the
desired spacing D
(Figure 9) maintained between the inner ends 62a,62b.
In Figure 12, each of the pins 60a,60b is further provided with a reduced
diameter neck
86. The neck 86 provides a point of weakness, to facilitate shearing of the
pins 60 upon the
application of the predetermined minimum torque. Most preferably, the reduced
diameter neck
86 is provided along the longitudinal length of the pin so as to locate at the
internal thread
50/external thread 32 junction when the pins 60a,60b are fully inserted within
their respective
bore segments 54a,54b, with their head flange 80 engaging the nut sides
44a,44b. The reduced
diameter neck portion 86, although not essential, most preferably includes a
sloping edge surface
90. The sloping edge surface 90 advantageously acts as a Gaming surface upon
the shearing of
the pin 60, facilitating movement of the pin fragment 64a,64b (Figure 5)
radially inwardly into
the rod 14, and towards the axis A~-A~ upon shearing of the pins 60.
While Figures 9 to 12 illustrate the pin nut 36 as having four planar side
surfaces
44a,44b,46a,46b, the invention is not so limited. If desired, other fastener
shapes may also be
adopted and will now become apparent. By way of non-limiting example, Figure
13 illustrates a
further possible pin nut 36 construction in which the nut 36 is formed with a
generally hexagonal
CA 02439397 2003-08-11
17
profile having three pairs of parallel side surfaces 44a,44b,46a,46b and
124a,124b, each
symmetrically spaced around the centre axis A,-A1.
Although the preferred embodiment illustrates the mine roof bolt assembly as
including a
pair of shear pins 60a,60b, the invention is not so limited. In a less
preferred embodiment, the
applicant has appreciated that a single shear pin 60 could be used to couple
the nut to the rod
under torque forces less than the predetermined minimum torque. In testing,
however, the
applicant has found that the provision of two opposedly positioned and spaced
pins 60a,60b
provides more accurate and reliable pin shear rates. In particular, it has
been found that where a
single pin is used, there may exist up to a 10% deviation in required torque
forces needed to
produce pin shear. This deviation, however, is lowered to less than about 3%
where two shear
pins 60a,60b are provided, as for example, is shown in Figure 9.
Although the preferred embodiment describes the use of the roof bolt assembly
as being
used in mine roof support systems, it is to be appreciated that the assembly
is equally suited for
other reinforcing uses. These would include, without restriction, construction
and engineering
applications.
While the detailed description describes the anchor rod and pin nut as being
used in the
mixing of anchoring resins, it is to be understood that the present invention
is equally suited for
use with wedge-anchor and other such mechanically affixed rods.
Although Figure 5 illustrates the through bore 52 and through bore 34 as each
comprising
a cylindrical bore having the same cross-sectional diameter, the invention is
not so limited. If
desired, each of the through bores 34,52 could be provided with a square or
other geometric
cross-sectional profile, with a corresponding modification to the shear pins
60.
Although the detailed description of the invention describes and illustrates
various
preferred embodiments, the invention is not so limited. Many modifications and
variations will
CA 02439397 2003-08-11
18
now occur to persons skilled in the art. For a definition of the invention,
reference may be had to
the appended claims.
