Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Improved Directional Gas Pressure Device
Field of the Invention
The present invention relates to directional gas pressure devices, typically
for use in the breaking
of rock or concrete, and in particular to a directional gas pressure device
that does not require backfilling
with sand or other sealants. The present invention also relates to a method of
breaking rock from a face
(a mine face or quarry face) using a directional gas pressure device of the
invention.
Background of the Invention
High explosives are widely used for breaking rock during quarrying and mining,
and in
demolition. Whilst explosives are effective, they are not particularly
efficient in terms of their energy use,
they are dangerous and hence are subject to specific regulation relating to
their use, storage and transport.
Where explosives are used for demolition, it is necessary to clear a large
area around the site because of
the distance both large and small particles are dispersed by explosive
material. Where explosives are used
in underground mines the whole mine must be cleared of personnel during
blasting. Further, it is
necessary to allow a certain period of time to elapse following blasting
because of the possibility of
rockfalls, and where blasting takes place underground, the existence of
dangerous gases.
High explosives have detonation speeds in the order of 6000 to 9000 metres per
second which
induces a shock wave in rock, thereby breaking it. In certain circumstances
high explosives may limit the
depth of rock which may be removed during one blasting episode. This is
because if the charge is placed
too deeply beyond the surface of the rock back fractures may occur, making the
mine or quarry unsafe.
In such applications it is generally considered that high explosive charges
should not be placed more than
1.2m beyond the rock face.
An alternative to splitting rock with explosive is the directional gas
pressure system. In this
system a hole is bored in a rock and a directional gas pressure device is
inserted therein. The bore is
backfilled with sand or another suitable sealant. When the device is fired,
rather than exploding, a
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chemical reaction is started which evolves a large volume of gas. The pressure
within the bore builds up
and is relieved by the rock splitting. The detonation speed of the pyrotechnic
charges used in directional
gas pressure devices is in the order of 40 to 60 metres per second. These
devices do not create a shock
wave. Therefore, it is possible to locate such devices further from the rock
surface, thereby allowing a
greater quantity of material to be removed from the face during one blasting
episode.
The directional gas pressure system is more efficient than explosive charges
in terms of the
amount of energy released to split a rock or demolish a building or structure.
For example, when using
the directional gas pressure system compared to an explosive charge,
significantly less dust is produced.
This has two benefits. First, it is possible to work in closer proximity to
rock being broken using the
directional gas pressure system than it is where explosive charges are used.
In the case of an underground
mine, generally the whole mine would be cleared whilst blasting is taking
place, whereas where the
directional gas pressure system is used work can continue much closer to the
area where rock is being
broken. Another benefit of the directional gas pressure system is that the
charges are intrinsically much
safer than explosives. Their classification and rules relating to their use
reflect this. A further benefit of
this system is that they create much less noise than high explosives and do
not cause problematic
emissions of toxic gases.
As mentioned above, the directional gas pressure device is inserted into a
bore and the bore
backfilled with sand or another suitable sealant material. Back filling with
sand is inexpensive in terms of
materials, but requires labour and a supply of sand where the rock is being
broken. Further, sand may
only be used where the direction of the bore is inclined above the horizontal,
otherwise the sand may run
out of the bore, in which case the rock would not be broken and the
directional gas pressure device
would not be safe. Also, the consistency of the sand used in stemming is
critical. For example, if the
sand is too dry or too wet a 'blow out' may occur. A blow out may also occur
if the sand grains are too
big or of inconsistent shape.
Other back filling materials may be used, but these may be expensive. For
example, resin based
fillers may be used, but even with such filler materials there remains the
problem that where the bore lies
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below the horizontal it is difficult to be certain that the bore is filled
adequately without pockets of air for
example. When using resins sometimes residual oil or water from the drilling
machine can have an
adverse effect on the resin and subsequently cause 'blow outs'.
Gas pressure devices that require stemming agents can only be used where a
bore of sufficient
depth can be formed. For example, where a gas pressure device of 30mm length
is to be used, this must
be packed with a 1 metre depth of stemming agent. Hence, such a gas pressure
device cannot be used to
break a relatively narrow concrete component of a building, such as a concrete
girder.
United Kingdom patent application published under number 2341917 describes a
directional gas
pressure device of the type described above.
International patent application number WO 2006/063369 describes a container
for a
pyrotechnic device. This invention relates to closing the container of a
pyrotechnic device so that the
device may be subject to less stringent rules when transported than is the
case for other closure
arrangements.
It would therefore be desirable to provide a directional gas pressure device
the operation of
which does not require backfilling.
A rock breaking cartridge is described in US 2008/0047455. In the device
described the charge is
housed in a tube which is closed at one end by a cap. The mid part of the tube
is filled with stemming
material (such as sand) and the other end is closed by a pair of wedges. When
the device is inserted into a
bore in rock to be broken one of the wedges is driven further into the tube
thereby securing the device in
the bore. The device may be used without the intermediary filler, in which
case the device is held in the
bore by the wedges which are forced further apart by the gas pressure within
the device.
Whilst the above-mentioned device does not require backfilling its use may be
limited to
relatively low gas pressures. This is because the device relies on the gas
pressure to be contained by the
wedges. If the wedges fail, it is likely that the increased gas pressure would
fire the device out of the bore.
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Mining typically involves breaking up material to be extracted at a face,
loading such material on
to a transport means and delivering the material to a processing plant. As
mentioned above, explosives
may be used to break material from the face, but the use of explosives
typically requires clearance of the
mine. Blasting would usually be done whilst miners are not present, for
example before the miners start
work each morning or between shifts. However, this means that a comparatively
large amount of
material must be broken from the face to provide sufficient work for the
miners to move during their
shift. Also, there is the danger that unauthorised personnel may be present
during blasting.
It would therefore be desirable to be able to mine material without using
explosives.
Some mining does take place without blasting, using machines for example.
Patent application
no CA 2060288 describes a machine which uses multiple cutting blades to cut
away material from a face.
However, such machines may not be used in all situations, require the
installation of rails and other
infrastructure, and are very expensive.
Where blasting is used it is nevertheless possible to automate the blasting
process to a certain
extent. For example, patent application no W097/21068 describes a vehicle
adapted to drill bores in a
material face and insert explosive charges.
The directional gas pressure device described in GB2468133 describes a
directional gas pressure
device that does not require backfilling with sand.
The directional gas pressure device described in GB2468133 represents a
significant step forward
insofar as no backfilling is required. Not only does this remove a step and
therefore reduce labour and
cost, but the directional gas pressure can also be used effectively when
oriented in the horizontal plane,
whereas devices requiring backfilling are known to not function well in such
an orientation.
However, it would be desirable to provide a direction gas pressure device
having the advantages
of the device described in GB2468133, yet which is simpler to assemble.
Summary of the Invention
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According to one aspect of the invention there is provided a directional gas
pressure device
comprising a body having openings at each end thereof, a closure member for
each end thereof, a tie
member extending through the body, the closure members being attached to the
tie member, wherein the
closure members are adapted to increase in size upon detonation of a
pyrotechnic charge material
contained within the body.
Brief Description of the Drawings
In the drawings, which illustrate preferred embodiments of a directional gas
pressure device
according to the invention:
Figure 1 is a schematic representation of a directional gas pressure device
according to the
invention;
Figure 2 is a schematic representation of the directional gas pressure device
illustrated in Figure 1
with a cover thereof opened;
Figure 3 is a schematic representation of a component of the directional gas
pressure device
illustrated in Figures 1 and 2;
Figure 4 is a schematic representation of another component of the directional
gas pressure
device illustrated in Figures 1 and 2;
Figure 5 is a schematic representation of end seals of the directional gas
pressure device
illustrated in Figures 1 and 2;
Figure 6 is a schematic representation of an encasing component in a closed
configuration;
Figure 7a is a schematic representation of lower collar elements of the
directional gas pressure
device illustrated in Figures 1 and 2;
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Figure 7b is a schematic representation of upper collar elements of the
directional gas pressure
device illustrated in Figures 1 and 2;
Figure 8 is a schematic representation of the encasing component illustrated
in Figure 6;
Figure 9 is a schematic representation of a device according to an alternative
embodiment of the
invention; and
Figure 10 is a schematic representation of a part of the device illustrated in
Figure 9.
Detailed Description of the Preferred Embodiments
Referring now to Figures 1 and 2, which illustrate a directional gas pressure
device 1 in assembled
form or substantially assembled form, the device 1 comprises a tube member 2,
end caps 3, 3', collars 4,
bosses 6, 6' and a cover 5.
The tube member 2 is illustrated in greater detail in Figure 4 and comprises a
chamber 2c formed
by wall members 2a, 2b. The wall member 2a is curved and is of constant
radius, the ends of the wall
member 2a intersecting the wall member 2b. The wall member 2b comprises two
substantially parallel
sides 2b' joined together by a substantially semi-circular end portion 2b".
The sides 2b' and the semi-
circular end portion 2h" together define a slot 2d extending axially along the
tube member 2. The inner
surface of the wall member 2a and the outer surface of the wall member 2b
together provide a chamber
2c, the ends of which are open.
Figures 5a and 5b illustrate end caps 3, which are adapted to engage with and
close the open ends
of the tube member 2. Each of the end caps 3 includes a lip portion 3a and
axially extending walls 3b, 3c
forming a tube engaging portion. Each of these portions has a cross-sectional
shape corresponding to
the cross-sectional shape of the chamber 2c of the tube 2. The walls 3b, 3c of
the tube engaging portion
have an external dimension corresponding to the internal dimension of the
chamber 2c of tube 2, such
that the end cap 3 is a push fit in the chamber 2c. The lip 3a limits the
extent to which the end cap 3 may
be pressed into the chamber 2c.
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The end cap 3 includes stiffening elements 3f extending between the walls 3b
and 3c of the tube
engaging portion and resist forces acting on the wall 3b to collapse the said
wall.
The end cap 3 illustrated in Figure 5b differs from the end cap 3 illustrated
in Figure 5a in that
the end cap 3 illustrated in Figure 5b includes a slot 3e, which is provided
to receive the wire(s) of an
electrical initiator. When an electric current is passed through the
initiator, the pyrotechnic material is
heated and a chemical reaction evolving gas initiated.
Referring now to Figures 7a and 7b, in each of these Figures there is
illustrated a collar element 4,
which in the illustrated example is substantially semi-circular in cross-
section. Whilst the collar elements
4 are semi-circular, they could be of different shape, and there may be more
collar elements 4. The collar
elements 4 illustrated in the respective figures being arranged to co-operate
with one another. The collar
element 4 of Figure 7a comprises an substantially flat end face 4a including a
first detent 4b of
substantially semi-circular cross section, and a second detent 4c of
substantially square cross-section, both
having an open edge. The outer surface of each collar element 4 is provided
with a slot 4d extending
circumferentially around the said outer surface.
The collar element 4 illustrated in Figure 7a includes bores 4f situated in a
wall 4e of the collar
element 4. The bores 4f are configured to receive protrusions in the form of
pegs 4f of the collar
element 4 illustrated in Figure 7b. The pegs 4f are a push fit into the bores
4f. Hence, when the bores 4f
of the collar element 4 of Figure 7a are aligned with the pegs 4f of the
collar element of Figure 7b and
the two elements are pressed together, the two collar elements will become
attached to one another.
Each collar element 4 includes a sloping surface 4g. The function of this
sloping surface is
described below.
Referring now to Figure 3, there is shown a rod member 6 supporting a boss 6,
6' at each end
thereof. The bosses 6, 6' are joined together by a stem 6e. The boss 6 and
boss 6' are both frusto-conical
in shape providing a sloping wall 6a, 6a' extending around the boss. The boss
6' mounts a T-shaped
member 6b extending from the end face of said boss 6'. The member 6b includes
a stem 6c. The
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function of the T-shaped member 6b is to provide a means by which a line may
be tied to the device,
allowing it to be retrieved in the event of a mis-fire.
The boss 6' also includes a detent 6d extending parallel with the longitudinal
axis of the rod
member 6.
A cover 5 which secures the component parts of the device together is best
appreciated from
Figures 2, 6 and 8. The cover 5 includes first and second elements 5a, 5b
attached together by a hinge 5f,
the first and second elements 5a, 5b and the hinge 5f being formed of a single
plastics moulding in the
present example. Protrusions 5e extend inwardly of the inner surface of first
and second elements 5a, 5b
at each end thereof. In the illustrated example, these protrusions extend
circumferentially around the first
and second elements 5a, 5b. The inner surface of the first element 5a is
provided with additional
protrusions 5e" extending in the axial direction of the cover 5. The
protrusions 5e are so shaped and
dimensioned as to engage with the slot 4d of the collar element 4 and prevent
any relative movement
between the collar elements 4 and the cover 5. The protrusions 5e' are so
shaped and dimensioned as to
engage with the slot 4c of the collar element 4.
The cover 5 includes a tamper proof fastening arrangement comprising
protrusions Sc extending
from the free edge of the first element 5a which are configured to engage with
recesses 5d located
proximate the free edge of the second element 5b. The protrusions Sc are of
the type that cannot be
released from the recesses 5d without fracturing at least one of the
protrusion Sc, the recess 5d or a part
of one of the first and second elements 5a, 5b.
Assembly of the directional gas pressure device of the invention is described
below.
First, an end cap 3 is fitted to one end of the tube member 2. The chamber 2c
of the tube
member 2 is then filled with pyrotechnic material, typically in powder form.
Once filled, the other end of
the tube member 2 is closed by a cap 3.
The stem 6e of rod member 6 is then aligned with the slot 2d of the tube
member 2.
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A pair of co-operating collar elements 4 is mounted on the rod member 6 at
each end thereof
such that the sloping surface 4g of the collar element 4 engages with the
correspondingly sloped surface
6a, 6a' of the boss 6, 6' of said rod member. The collar elements 4 are
pressed together so that pegs 4f
engage with the bores 4f.
The assembly is then placed within a part of the cover 5, which is then closed
to secured the
assembled components together.
The embodiment illustrated in Figures 9 and 10 does not include the cover 5.
The tube member
2 is held in place without aid of a cover 5. The stem 6e comprises four ribs
6e' extending at ninety
degrees to one another. The end cap 3 includes a detent 3g which one of the
ribs 6e' of the stem 6e
engages. The end cap 3 also includes protrusions 3h. Two of the ribs 6e'
engage with these protrusions.
To fit the tube member 2 to the stem 6e, the slot 2d is aligned with the stem
6e, which is pushed into the
slot 2d with one of the ribs 6e' aligned with the detent 3g of end caps 3, 3'.
The two ribs 6e' extending
perpendicular to the rib 6e' aligned with the detent 3g will first engage one
side of the protrusions 3h and
will then ride over those protrusions as the stem 6e is pushed further into
the slot 2d. The ribs 6e' then
engage the other side of the protrusions 3h, securing the stem 6e in position
in the tube member 2.
In the embodiment shown in Figure 9, the collar elements 4, 4' are joined
together by a hinge 4h,
which is preferably a live hinge formed during the moulding process which
forms the collar elements 4,
4', that is element of plastics material joining the two collar elements and
permitting pivoting
therebetween. In such an embodiment, the walls 4e distal from the hinge of the
collar elements 4, 4' are
provided with co-operating holes 4f and pegs 4f respectively.
To use the device 1, a hole is bored in a rock face for instance and the
device inserted into the
hole. An electric current is passed through the electrical initiator to
initiate the pyrotechnic material
contained within the tube member 2. Gas released from the pyrotechnic material
and a force is therefore
exerted on the end caps 3, the force pushing the end caps 3 axially out of the
tube member 2. However,
movement of the end caps 3 in the axial direction is constrained by the
collars 4, the sloping surfaces of
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which co-operate with the sloping surface of the bosses 6, 6'. The collars 4
are pushed outward against
the wall of the hole into which the device has been inserted. The movement of
the collars 4 and end caps
3 is not sufficient to allow the end caps to release from the tube member 2,
these components being held
in place by the stem 6e of the rod member 6.
The directional gas pressure device of the invention offers significant
advantages over those of
the prior art, including that described in GB2468133. Not only is the device
of the invention less costly
to manufacture, because there is no need to provide any threaded elements or
fasten together threaded
elements, but the device allows filling with pyrotechnic material to take
place separately of assembly of
the device. This is a major step forward, since it allows factories already
set up to fill pyrotechnic
materials to do so without having to engage in assembly of the more complex
aspects of the device.
Conversely, the device of the invention allows another party not necessarily
concerned with filling
pyrotechnic material to assemble filled tubes and the other components of the
device.
