Note: Descriptions are shown in the official language in which they were submitted.
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STEMMING PLUG
FIELD OF THE INVENTION
[0001] This invention relates to a stemming plug for confining explosive blast-
gasses in
a blast hole in mining, tunnelling or like operations.
BACKGROUND TO THE INVENTiON
[0002] A variety of stemming plugs are produced from natural rubber, synthetic
rubber
and other suitable polymers and have been used for the above application for
many
years. An unacceptably high degree of failure is, however, experienced by
miners and
the like as a result of the stemming plugs being expelled from blast holes
during a blast.
Difficulty in inserting existing plugs into holes. and, when occasion
requires, the removal
of a plug are problems frequently encountered in blasting operations.
SUMMARY OF THE INVENTION
[0003] A stemming plug which is made from a suitable resiliently deformable
plastics
material according to the invention comprises two cup-shaped members which
face
each other with their rims in abutment and means, which extends between the
centres
of the base portions of the cups in the plug, which is adapted to move the
bases of the
cups towards each other to compress the cups and cause a circumferential zone
of the
plug on either side of the abutting faces of the cups to increase in radial
dimension to be
brought into load bearing contact with the side of a predrilled hole in which
the plug is to
be located, in use, and to enable the bases of the cups to be moved away from
each
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other to allow the plug to be withdrawn from the hole in the event of a
misfire of the
explosive in the hole.
[0004] A portion of the wall of each cup-shaped member from its rim may be
substantially cylindrical around the axis of the plug which passes through the
centres of
the cup bases to define the circumferential load bearing zone of the plug.
[0005] Each cup-shaped member may include a substantially cylindrical skirt
which
extends from the substantially cylindrical portion of its wall away from the
abutting rims
of the cups to surround at least a portion of the cup wall.
[0006] The composite substantially cylindrical outer wall of the plug may be
divided into
segments by slots which are parallel to the plug axis.
[0007] The outer surface of each of the wall segments could include outwardly
projecting formations for gripping the surface of a hole when the segments are
brought
into load bearing contact with the surface, in use.
(0008] The gripping formations may be ribs which are parallel to the segment
defining
slots.
[0009] The non-cylindrical wall material of each cup-shaped member may include
a line
of weakness on the inside of and against the wall of the cup across each of
the wall
segment slots. The line of weakness may be defined by arcuate slots with the
ends of
each slot being spaced from the ends of adjacent slots.
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[0010] The non-cylindrical portion of each of the cup-shaped members may
include a
pleat which extends from the ends of each of the arcuate slots in a direction
towards the
plug axis to expedite expansion of the plug in a radial direction, in use. The
pleated wall
material of each cup-shaped member is preferably thinner than the adjacent cup
wall
material.
[0011] The pleats may be V or C-shaped in cross-section.
[0012] The non-cylindrical portion of each of the cup-shaped members may
include an
aperture through which a fuse or electrical detonator conductors may be
passed.
[0013] Each of the cup-shaped members preferably includes a formation which is
releasably engageable with a formation on the other cup to ensure that the
fuse
apertures are in register with each other and to prevent rotation of the cups
relatively to
each other about the plug axis.
[0014] The releasably engageable formations may be a plurality of
circumferentially
spaced sockets and spigots which are releasably engageable with the sockets
and
spigots of the other cup.
[0015] A first of the cup-shaped members may include a holed boss in its base
and the
second an aperture in its base and the cup base moving means could be a headed
elongated element which passes axially through the plug cavity between the
first and
second cups with its head, which is adapted for rotation by a removable tool,
bearing on
the outer surface of the second cup around the aperture with a portion of its
length from
its unheaded end including formations which are movably engageable with
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complementally shaped formations in the hole in the boss of the first cup
member. The
engageable formations on the end portion of the elongated element and in the
boss
hole may be helical thread formations.
[0016] In a variation of the above stemming plug a first of the cup-shaped
members
may include an aperture in its base around the plug axis, at least two
outwardly
projecting gripper formations which are attached to and project outwardly from
the base
of the cup to be biased towards the plug axis over the aperture and carry on
their faces
which face the plug axis ratchet teeth, the second cup-shaped member may carry
an
elongated element which passes through the aperture in the first cup and
between the
gripper formations and,carries ratchet teeth which are oppositely directed to
those on
the faces of the gripper formations with the directions of the ratchet teeth
being such
that the end of the elongated element may be pulled outwardly from between the
teeth
of the gripper formations to draw the cup bases towards each other to set the
plug, in
use, when the pulling tension on the elongated element is relaxed. The plug
could
include two gripper formations which face each other from opposite sides of
the
aperture in the base of the cup and the portion of the elongated element which
carries
its ratchet teeth may be square or rectangular in cross-section with the
ratchet teeth on
two opposite sides of the element while the remaining opposite sides are flat
so that the
ratchet teeth on the gripper formations will, when the elongated element and
the cup to
which it is attached is rotated through 90 , be disengaged from the ratchet
teeth on the
elongated element to enable the base portions of the cup-shaped elements of
the plug
to move away from each other to reduce the radial dimension of the plug to
enable it to
be removed from a predrilled hole in the event of a misfire of the explosive
in the hole.
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[0017] Each of the gripper formations could include at its free end a surface
which
tapers from the end of the formation inwardly towards the plug axis for
releasing its
ratchet teeth from those on the elongated element by means of a suitable tool.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] A number of embodiments of the invention are now described by way of
non-
limiting examples only with reference to the drawings in which:
Figure 1 is a half-sectioned side elevation of a first embodiment of the
stemming plug of
the invention,
Figure 2 is a plan view of the cup-shaped members of the Figure 1 stemming
plug,
Figure 3 is a sectioned side elevation of the Figure 1 stemming plug, in use,
Figure 4 is an isometric view of a tool for setting the Figure 1 stemming
plug,
Figure 5 is sectioned side elevation of a variation of the Figure 1 plug,
Figure 6 is a sectioned side elevation of a second embodiment of a cup-shaped
formation of the stemming plug of the invention,
Figure 7 is a plan view of the Figure 6 cup-shaped member,
Figure 8 shows two fragmentary sectional views which illustrate the function
of the
pleats in the cup-shaped member of Figures 6 and 7,
Figure 9 is a sectioned side elevation of a typicai cup-shaped member of the
stemming
plug,
Figure 10 is an under plan of the cup-shaped member of Figure 9,
Figure 11 is an under plan of the second cup-shaped member for use with that
of Figure
9, and
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Figure 12 is a sectioned side elevation of a third embodiment of the stemming
plug of
the invention.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
[0019] The first embodiment 10 of the stemming piug of the invention is shown
in
Figure 1 to include two cup-shaped members 12 and 14 with their rims abutting
each
other and a headed setting screw 16.
[0020] The cup-shaped members 12 and 14 are made from a suitable resilient
plastic.
material such as polypropylene, a polyamide or the like. The screw 16 is made
from a
suitably rigid polyamide.
[0021] The upper cup-shaped member 18 in Figures 1 and 2 is shown to include
an
outwardly domed wall portion 20 with the rim portion 22 of the cup being
inwardly.
directed to be almost cylindrical about the axis of the plug. The cylindrical
portion 22 of
each cup side wall is extended away from the portion 22 to provide cylindrical
extensions 28 which surround the domed wall portions 20 and bases of the cups.
[0022] The base portion of the cup 20 carries a boss 24 which has a threaded
bore
which is engaged by the male helical thread formation on the screw 16.
[0023] The cup-shaped formation 14 is substantially identical to the cup 12
save that it
carries in its base portion a holed recess formation 26 for accommodating and
locating
the head of the screw 16.
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[0024] As shown on the left in Figure 1 and in Figure 2 the cylindrical
portions 22 of the
cup-shaped members 12 and 14 together with their cylindrical extensions 28
provide a
substantially cylindrical composite wall which surround the remainder of the
cups.
[0025] The composite stemming plug wall is shown in Figures 1 and 2 to be
divided
into segments 30 by vertical slots 32 which penetrate the domed portion 20 of
the plug
to allow for movement of the segments away from the plug axis and one another,
in
use. The outer surfaces of each of the wall segments 30 carry an outwardly
projecting
rib 34 the purpose of which is to be deformed under radial pressure against a
wall of a
hole in which the plug 10 is located, in use, to key into irregularities in
the wall surface
and so to prevent rotation of the plug as it is being set in the hole. The
dome portion 20
of each of the plugs carries an aperture 36, shown only in Figure 2, for the
passage of a
fuse or the conductor leads to an electrically activated detonator.
[0026] Figure 3 illustrates the stemming plug 10 of Figures 1 and 2 set in a
predrilled
blast hole 38 with its cup-shaped members compressed towards each other by the
screw 16 with at least the radially so-moved wall portions 22 of the cup
segments 30
pressed hard up against the surface 40 of the hole 38.
[0027] The stemming plug 10 is set in the hole 40 by means of the tubular tool
42
shown in Figure 4. The tool includes, from one end, two opposed vertical slots
44 which
terminate in round ended circumferential slots 46. The diameter of the bore of
the tool
42 is slightly greater than the diameter of the outer portion of the screw 16
head and the
width of the slots 44 and 46 are similarly slightly larger than the diameter
of the trunnion
formations 48 which project from opposite sides of the screw head. The tool
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additionally carries a handle, at its opposite end to that at which the slots
44 and 46 are
located, by means of which the tool is rotated in setting the stemming plug.
[0028] The Figure 5 variation 50 of the stemming plug of the invention is
similar to that
of Figures 1 to 3 except that the domed wall portions 20 of the Figure 1 plug
is here
replaced by frusto conical wall portions 52 and the boss 24 is replaced by a
recessed
formation 26, which is identical to the screw head recess formation 26 of
Figure 1. The
upper formation 26 in Figure 5 carries a threaded plug 54 in which the screw
16 is
engaged. The plug carries a key, not shown, which is engageable with a key
groove in
the recess 26 to prevent rotation of the plug 54 during setting of the
stemming plug.
[0029] The composite cylindrical wall of the Figure 5 stemming plug includes
slots 32,
ribs 34 and the fuse aperture 36 in its wall portions 52 which are identical
to those
described with reference to Figures 1 and 2.
[0030] The second embodiment 56 of the stemming plug of the invention is shown
in
Figures 6 and 7 to include six pleats 58 which are located in the domed or
frusto conical
wall portions of the cup-shaped members and extend across the segment 30 wall
slots
32 as shown in Figure 7. The outer edges of the pleats 58 terminate in arcuate
slots 60
which are made through the cup material to separate the outer wider edges of
the
pleats 58 from the wall segments 30.
[0031] The pleats 58 in this embodiment of the invention are outwardly V-
shaped, as
most clearly shown in Figures 7 and 8. The upper sketch in Figure 8 shows the
shape
of the edge of the pleat at its slot 60 in the unstressed condition of the
stemming plug
and the lower sketch illustrates the degree of stretch provided, by the six
almost
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flattened pleats, to enable the cup segments to separate circumferentiaily
when the
stemming plug is stressed and set as illustrated in Figure 3. The pleats need
not
necessarily have the V-shape shown in Figures 7 and 8 and could be C-shaped or
have
any suitable stretchable shape such as a plurality of tapered corrugations or
the like.
Whatever the cross-sectional shape of the pleats is the material of the pleats
is made to
be thinner than the remaining domed or frusto conical cup material adjacent
them.
[0032] The pleats, and particularly those which are composed of a thinner
material,
facilitate outward radial and circumferential expansion of the segmented plug
wall and
markedly reduce the torque which is required to rotate the screw during
setting of the
stemming device. .
[0033] Figures 9, 10 and 11 illustrate the currently preferred arrangement for
preventing rotation of the stemming plug cup-shaped members relatively to each
other
during setting of the stemming plug. An arrangement of this sort is applicable
to all of
the stemming plug embodiments described in this specification.
[0034] The cup-shaped member of Figures 9 and 10 is shown to include two
spigot
formations 62 and four sockets 64 which are supported by and in protuberances
66
which project from the centres of the wall segments 30. The lower ends of the
protuberances 66 are flush with the outer surfaces of the rims of the cup
shaped
members. The plan view of the opposite cup-shaped member of the stemming plug
is
shown in Figure 11 to include two spigots 62 on either side of the fuse or
electrical cord
aperture 36 and four sockets 64.
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[0035] The sockets 62 and the spigot 64 of the two cup-shaped members are
engaged
with each other in the assembled stemming plug,
[0036] The arrangement of the sockets 64 and spigots 62 on the rim faces of
each of
the cup-shaped members is firstly to ensure that the two cups are connected in
a
specific circumferential relationship so that the fuse holes 36 will always be
in axial
register for the passage of a fuse or detonator conductors through the plug
and,
secondly, to hold the abutting cup faces together to avoid one segment face
portion
from being radially displaced from the other as the cups are activated by
compression
towards each other or by wall irregularities in the blast hole.
[0037] The third embodiment 68 of the stemming plug of this invention is shown
in
Figure 12 to include cup-shaped members 70 and 72, an actuator 74 and two
gripper
formations 76.
[0038] The substantially cylindrical wall of the stemming plug is the same
segmented
arrangement as that of Figure 1.
[0039] The actuator 74 is made integral with. and projects from the base of
the cup 72.
The portion of the length of the actuator which carries ratchet teeth 78 is
rectangular in
cross-section with its non-toothed sides being smooth. The two gripper
formations 76,
without the actuator between them, are strongly biased by the resilience of
the material
from which they are made, over the aperture in the plug towards the plug axis.
Each of
the gripper formations 76 carries, when the actuator is located between them,
ratchet
teeth which are biased into engagement with the teeth 78 on the actuator. The
tooth
direction of the engaged ratchet teeth, as shown in the drawing, enable the
actuator to
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be pulled upwardly in the drawing from between the actuator ratchet teeth to
compress
the cup-shaped members, as does the screw of Figure 1, to move the wall
segments
into pressure bearing contact with a hole wall, in use. When the plug is set
in a hole the
outward tension on the actuator is relaxed to allow the ratchet teeth to lock
the plug in
its activated state in the hole.
[0040] To release the hoiding tension on the actuator to enable the plug to be
removed
from the hole, after use, a tool having opposite triangular formations is
pressed into the
triangular gaps between the upper ends of the gripper formations 76. Pressure
on the
tool forces the gripper teeth out of engagement with the actuator teeth to
allow the
tension on the actuator to draw the actuator back into the plug cavity and so
release the
wall segments from the hole wall.
[0041] The invention is not limited to the precise details as herein described
and is
limited only by the scope of the invention as defined by the claims in this
specification.
