Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Explosive Cartridge
The invention relates to an explosive cartridge.
The invention further relates to a method of filling an explosive
cartridge with an explosive material.
Explosive cartridges may be used in many technical fields for any
type of rock, rock mass, concrete or comparable material fragmentation.
When detonating in a borehole an explosive cartridge is creating cracks
and fragmentation in all directions around the hole. In typical rock
production blast this does not cause big problems as the bench face after
blasting can be scaled down with mechanical equipment and in that way
is made safe for the next blast.
However, in those situations where a blast is carried out along a
final rock wall or where in underground blasting the aim is to create
(leave behind) a drift side wall as competent as possible, the strong
radial fragmentation all around the borehole may be a challenge. The
amount and length of cracking an explosive charge is creating in a
borehole depends amongst other factors on the pressure generated
during detonation.
WO 2008/148544 discloses a device for receiving an explosive
material which comprises a receptacle unit for receiving the explosive
material, and an anchoring unit. The receptacle unit is adapted to be
filled with explosive material from outside of a borehole. The anchoring
unit is arranged on an outer surface of the receptacle unit. The anchoring
unit is adapted to anchor the flexible receptacle unit in a borehole. In
particular, the explosive material may be used in the form of a bulk
material or in the form of so-called explosive cartridges.
It is an object of the invention to provide an explosive cartridge
which is safe, reliable and accurate in operation and which is
manufacturable with reasonable effort.
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In order to achieve the object defined above, an explosive cartridge,
and a method of filling an explosive cartridge with an explosive material
according to the independent claims is provided.
According to an aspect of the present disclosure there is provided an
explosive cartridge for receiving an explosive material when being arranged
in a borehole, the explosive cartridge comprising: a supply body having a
supply channel through which the explosive material is supplyable from
outside of the borehole; a flexible tube being slid over an outer surface of
the supply body in a longitudinally compressed manner and being
configured so that, when the explosive material is supplied under pressure
from outside of the borehole through the supply channel and fills an inner
volume of the flexible tube, the flexible tube is longitudinally decompressed
and slides off from the supply body to proceed towards an interior of the
borehole, a plurality of ring-shaped spacer elements slid over an outer
surface of the flexible tube at a first distance (I) from one another when the
flexible tube is in the longitudinally compressed state and being spaced by a
second distance (L) from one another when the flexible tube is transferred
into the decompressed state, wherein the second distance (L) is larger than
the first distance (1), wherein the ring-shaped spacer elements have a
circular outer perimeter.
According to another aspect of the present disclosure there is
provided a method of filling an explosive cartridge with an explosive
material, the method comprising: arranging the explosive cartridge in a
borehole; supplying the explosive material from outside of the borehole to a
supply channel of a supply body of the explosive cartridge; transferring a
flexible tube of the explosive cartridge, being initially slid over an outer
surface of the supply body in a longitudinally compressed manner, into a
longitudinally decompressed state by supplying the explosive material under
pressure from outside of the borehole through the supply channel to fill an
inner volume of the flexible tube so that the flexible tube is longitudinally
decompressed while sliding off from the supply body to proceed towards an
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interior of the borehole, wherein a plurality of ring-shaped spacer elements
slid over an outer surface of the flexible tube at a first distance (I) from
one
another when the flexible tube is in the longitudinally compressed state and
being spaced by a second distance (L) from one another when the flexible
tube is transferred into the decompressed state, wherein the second
distance (L) is larger than the first distance (I), wherein the ring-shaped
spacer elements have a circular outer perimeter.
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The term "longitudinal" may particularly refer to a direction along
which explosive material is to be filled into the explosive cartridge, or to a
direction along which the flexible tube slides off from the supply body
upon supplying explosive material. The longitudinal direction may be
parallel or basically parallel to a central axis of the borehole or to the
supply channel of the supply body.
The term "transverse" may particularly refer to directions
perpendicular to the longitudinal direction. Transverse direction may
extend radially from an interior to an exterior of the supply body, or from
an interior to an exterior of the flexible tube.
The term "explosive material" may particularly denote material
capable of exploded upon receiving a corresponding trigger. Such an
explosive material may be a liquid, an emulsion, or even a solid (for
instance a granulate material).
The term "flexible" may particularly denote a material property of
the tube, namely that the tube can be reversibly deformed under the
influence of an external force having an order of magnitude of a pumping
force of a vehicle loaded with explosive material for supplying the
explosive material to boreholes. The term "flexible" may particularly
denote that the tube is made of a material and/or with dimensions so as
to alter its shape upon exerting a pressure in the order of magnitude of 1
bar or several bar.
According to an exemplary embodiment, an explosive cartridge is
provided which is particularly appropriate for use in a vertical or inclined
borehole and which allows to supply explosive material from outside of a
borehole within a compact device which has a structure being extendable
upon supply with explosive material. This compact device is easy to
handle in a save manner and is not prone to failure. First of all, the
explosive cartridge may be inserted in a surface portion of a borehole
without having explosive material therein. Then, a supply body of the
explosive cartridge may be coupled to a borehole external explosive
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material supply hose or the like so as to supply explosive material from
an exterior of the borehole into the supply body. From the supply body,
the explosive material is forwarded towards an interior volume of a
flexible tube which at the beginning is wrinkled in a longitudinally
compressed manner onto an outer surface of the supply body in a
compact form. By the pressure of the explosive material, the flexible tube
is unwound or removed from the supply body so that pumping explosive
material to the supply body will automatically forward the explosive
cartridge towards a deeper portion of the borehole and will draw the
flexible tube from the supply body. Since the flexible tube is made of a
flexible material, the explosive material will promote primarily
longitudinal elongation, but also to some extent transverse widening, of
the flexible tube so that the flexible tube will be centered in a borehole
automatically. This system is simple in manufacture, easy to use and safe
in operation, since the insertion of explosive material into the explosive
cartridge installed in the borehole will only be started after it has been
made sure that the explosive cartridge is not getting jammed, seized or
misaligned in the borehole.
In the following, further exemplary embodiments of the explosive
cartridge will be explained. However, these embodiments also apply to
the method of filling an explosive cartridge with an explosive material.
In an embodiment, the supply body has a widened end portion for
transversely widening up the flexible tube when sliding off from the
supply body. Thus, the flexible tube will slide over the widened end
portion of the supply body when being forwarded to a deeper portion of
the borehole and will simultaneously increase its transverse cross-
section. Such a geometry may advantageously prevent an undesired
backflow of explosive material from the supply channel to an
intermediate space between the supply body and the portion of the
flexible tube being still wrinkled on an exterior surface of the supply
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body. The prevention of such an undesired back flow is very important
from the safety point of view. Widening up the end portion of the supply
body has turned out to be a simple but very efficient means to achieve
this.
Particularly, the widened end portion may be conically tapering.
Thus, the widened portion may have the shape of a hollow truncated
cone or frustum. Alternatively, also a concave or a convex tapering
geometry of an outer surface of the widened portion is possible.
In an embodiment, the supply body may have a hollow cylindrical
portion connecting, particularly directly connecting, to the widened end
portion. Thus, the supply body may particularly have two parts. A
cylindrical portion along which the flexible tube is wrinkled up before
being filled with the explosive material, and a widened end portion
integrally formed with this hollow cylindrical portion as a circumferential
ramp for widening up the tube. This allows to store a very long flexible
tube in a longitudinally compressed manner on the hollow cylindrical
portion of the supply body before widened up so as to provide a proper
filling of the borehole with explosive material. At the same time, this may
prevent an undesired backflow of explosive material into a gap between
supply body and flexible tube.
Particularly, a ratio between a diameter (particularly an outer
diameter) of the widened end portion (at the end of the supply body at
which the flexible tube leaves contact with the supply body) and a
diameter (particularly an outer diameter) of the flexible tube in the
compressed state should be sufficiently large. Particularly, such a ratio
may be larger than approximately 1.2, particularly larger than
approximately 1.5, more particularly larger than approximately 2. It has
turned out that if this ratio is sufficiently large, an undesired only partial
filling of the tube can be prevented.
For safety reasons, it may be advantageous to prevent that the
explosive material flows back in an intermediate space between supply
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body and wrinkled flexible tube. Since a high local pressure may be
present in such small intermediate spaces, there is a risk that explosive
material is brought to explosion or ignition or reaction. By the disclosed
arrangement of supply body and flexible tube relative to one another in
combination with the widened end portion, such an undesired effect may
be safely prevented.
The supply body may have a hose adapter which may be
configured for engaging with a supply body adapter of a hose through
which the explosive material is supplied from an exterior of the borehole.
Such a connection may be achieved in a sealed way. For example, a
filling vehicle with an explosive material container and a pump may be
arranged externally of the borehole. The explosive material may be
pumped from the container of the filling vehicle through a hose, the
supply body adapter, the sealingly connected hose adapter and finally
into the supply body and from there to an interior of the flexible tube.
The adapter connection may be reversibly made by a user by simply
inserting the supply body adapter into the hose adapter, or vice versa.
This can be done by a snap-fit connection, a click connection, a bayonet
connection, a screwing connection or the like. By the sealing engagement
between supply body adapter and hose adapter, an undesired leakage of
explosive material at an interface between hose and explosive cartridge
may be safely prevented.
In an advantageous embodiment, the explosive cartridge may
comprise a plurality of ring-shaped spacer elements slid over (for
instance in a freely movable manner) an outer surface of the flexible tube
at a first distance from one another when the flexible tube is in the
longitudinally compressed state. The ring-shaped spacer elements may
be spaced by a second distance from one another when the flexible tube
is in the decompressed state. The second distance may be larger than the
first distance. In an embodiment, the elements are freely movable on the
flexible tube. In another embodiment, the elements may be secured (for
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instance adhered) to the flexible tube. By simply arranging a number of
annuluses around an exterior surface of the flexible tube without a
securing means, a very efficient way of anchoring the explosive cartridge
in lateral walls of a borehole may be achieved. Such an anchoring may be
on a purely frictional basis when the ring-shaped spacer elements consist
of rings or disks or hollow cylinders. The ring-shaped spacer elements
may have a smooth outer surface. The ring-shaped spacer elements may
have a circular outer perimeter. If such ring-shaped spacer elements are
made from a material with a high friction such as rubber, their outer
surface may abut to the borehole so as to provide some anchoring force
for anchoring the explosive cartridge sufficiently rigidly in the borehole.
Since the inner surface of the rings have some friction with the outer
surface of the flexible tube as well, they will follow a motion of the
flexible tube when being unwound or moved off from the supply body,
even when the ring-shaped spacer elements are not secured to the
flexible tube. Therefore, with the lateral decompression of the flexible
tube, also an increase of the distance of adjacent ring-shaped spacer
elements from one another will be automatically achieved.
Still referring to the previously described embodiment, the plurality
of ring-shaped spacer elements may be loosely slid over the outer
surface of the flexible tube when the flexible tube is in the longitudinally
compressed state and become tightly fit to the flexible tube when the
flexible tube is expanded by being filled with the explosive material. In
other words, it may be sufficient that the ring-shaped spacer elements
may simply be placed over the outer surface of the flexible tube without
being permanently connected thereto. However, in another embodiment,
such a permanent connection between ring-shaped spacer elements and
flexible tube may also be performed, for instance by using a suitable
adhesive. However, the mere friction between the ring-shaped spacer
elements and the flexible tube may be sufficient to provide a sufficient
mechanical coupling between them. When however the flexible tube is
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expanded in a transverse direction by being filled with explosive material,
the explosive material and the flexible tube will be pressed towards an
inner surface of the rings to provide a sufficient fastening in an interior of
the borehole. This is an extremely easy and efficient way of arranging the
flexible tube and the ring-shaped spacer element relative to one another.
In an expanded state of the flexible tube, the ring-shaped spacer
elements may serve as distance elements arranged, for instance, every
cm around the flexible tube. The tube may have, in a spatially
expanded state, a diameter between 3.5 cm and 5 cm. The stretching of
10 the flexible tube when being filled with explosive material may press
the
flexible tube against the ring-shaped spacer elements and will fix it there
by friction, thereby allowing a unique filling along a longitudinal extension
of the unwrinkled flexible tube. The fastening of the ring-shaped spacer
elements to the flexible tube may be obtained by merely pumping up the
tube.
However, the explosive cartridge may also comprise at least one
anchoring spacer element (particularly a plurality of anchoring spacer
elements) arranged between the plurality of ring-shaped spacer elements
and being adapted to anchor the explosive cartridge in the borehole by
means of exterior anchor means such as claws or spikes or springs. By
providing anchoring spacer elements, an even more reliable anchoring of
the explosive cartridge at the wall of the borehole may be ensured. Such
an anchoring spacer element may comprise a central annular part which
is adapted in such a way that the flexible tube can be accommodated
within the annular part, and may further comprise a flexible (for instance
spring-like) part, which may be adapted in such a way that the flexible
part fixes the flexible tube in a borehole by an expansion of the springs.
By providing the explosive cartridge with one or more anchoring
spacer elements it may be possible to anchor the explosive cartridge
(more particularly the flexible tube when filled with explosive material) at
a given predetermined distance to the wall of the borehole. For instance,
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a central positioning may be possible, so that the explosive material is
arranged centred with respect to the borehole. For example, the
anchoring spacer element may be formed by an element which can be
put over or pulled over the flexible tube and may be attached to the
same, for instance glued. Furthermore, the anchoring spacer element
may be adapted to decouple the explosive material with respect to a
borehole wall. That is, the anchoring spacer element may be used to
ensure that a gap is provided between the borehole wall and a filled
flexible tube for efficiently decoupling them from each other. In
particular, it may be ensured that a wall of the flexible tube may not
come in direct contact with the borehole wall. Investigations have shown
that leaving a gap, for instance an annulus gap, between the flexible tube
and the borehole wall may strongly reduce the damage or fragmentation
the explosive material is creating. This is advantageous for underground
applications, like mining, tunnel construction, or tunnel driving, even in
strongly inclined boreholes or even in vertical boreholes. In particular,
the use of an explosive cartridge according to an exemplary embodiment
may possibly be advantageous over a partly filling of the borehole with
bulk explosives, i.e. explosives not filled into receptacle units or
cartridges, which filling with bulk explosives may be done by pulling an
explosive charging hose during charging out of a borehole quicker than
the filling with explosives is done, since this can be done in general only
with horizontal or slightly inclined boreholes. The use of an explosive
cartridge according to an exemplary embodiment of the invention may
possibly be more efficient to ensure that the borehole is just partly filled
with explosives to reduce the detonating pressure inside the borehole and
thereby possibly reducing the fragmentation around the boreholes.
Additionally, it may be possible to ensure a more constant degree of a
borehole filling by using an explosive cartridge according to an exemplary
embodiment, even under difficult and varying conditions, so that a more
constant decoupling may be enabled. Furthermore, the cross section of
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the explosive may be more constant when using an explosive cartridge
according to an exemplary embodiment compared to the conventional
use of a bulk explosive. Thus, a detonating condition may be more
constant as well, so that the risk that the detonation stops in the
borehole due to a not constant cross section may be reduced when using
an explosive cartridge according to an exemplary embodiment.
However, for applications in a horizontal borehole, anchoring units
may be dispensable. For vertical or inclined applications, the provision of
centering rings or anchoring elements may be advantageous.
In still another embodiment, the plurality of ring-shaped spacer
elements may comprise at least two different groups of ring-shaped
spacer elements having different outer diameters. For example, a first
group of ring-shaped spacer elements may have a smaller outer diameter
than a second group of ring-shaped spacer elements. Elements relating
to the first group and to the second group, respectively, may be arranged
alternatingly along a longitudinal extension of the supply body. For
example, every third spacer element may have a larger outer diameter
than the remaining ones so as to promote the anchoring in the borehole
by friction.
In still another exemplary embodiment, the plurality of ring-shaped
spacer elements may be made of an elastomer. An elastomer may be
denoted as a polymer with a property of viscoelasticity generally having
notably low Young's modulus and high yield strain compared with other
materials. Rubber is an example for such an elastomer. Elastomer
material is sufficiently cheap and at the same time allows for a proper
rigidity and a high friction with a borehole wall. However, an elastomeric
material provides simultaneously some degree of flexibility which
prevents the explosive material from getting stuck or caught in the
borehole. Furthermore, an elastomer can be sufficiently smooth to
prevent any damage of the flexible tube arranged in an interior thereof.
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The flexible tube may be made of a thermoplastic polyurethane
(TPU). Thermoplastic polyurethanes may be denoted as a class of plastics
with many useful properties, including elasticity, resistance to abrasion
and mechanical stability. TPU has turned out to be a highly appropriate
material for the flexible tube because it is robust and flexible. Particularly
in combination with an elastomer as the ring, a mechanical stability, a
sufficient flexibility and also a longitudinal expansion of the spacer
elements may be ensured by using TPU for the flexible tube. Another
embodiment may use a flexible tube made of a polyethylene material.
The explosive cartridge may comprise an end piece (for instance
sealingly) connected to an end portion of the flexible tube. The end piece
may be adapted for closing the end portion of the flexible tube to seal a
lumen for receiving the explosive material. The end piece may either be
permanently closed or closable. The end piece itself may simply be a
dead end of the flexible tube. Alternatively, the end piece may be a
separate member attached to an end portion of the flexible tube and
being connected thereto.
The explosive cartridge may comprise a unidirectional restrictor
valve (for instance as part of the hose adapter) adapted for enabling
supply of explosive material from outside of the borehole into the
flexible tube under pressure (i.e. being open in this operation mode),
and which is adapted for disabling a backflow of explosive material out
of the flexible tube (i.e. being closed in this operation mode). Thus, as
long as explosive material is pumped from outside of the borehole in the
supply body and from there into the flexible tube, the valve remains
opened. When the flexible tube is properly filled with the explosive
material and is therefore under slight pressure, the hose can be
detached from the explosive cartridge. In this state, the explosive
material would have the tendency to flow, in opposite flowing direction
compared to the pumping, out of the explosive cartridge. However, the
provision of the unidirectional restrictor valve may prevent such an
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undesired backflow to ensure that the explosive remains within the
flexible tube with some overpressure. When the explosive material
tends to flow out of the explosive cartridge, it will actuate the
unidirectional restrictor valve so that it will be transformed in the closed
state.
Still referring to the previous embodiment, it has turned out to be
advantageous that the unidirectional restrictor valve comprises a
movable member, particularly a ball, for instance arranged in a recess
formed in the hose adapter. The movable member may be movable for
selectively opening or closing the recess depending on the actual
pressure conditions. For example, when a pumping pressure for filling
explosive material in an interior of the flexible tube is applied, this
pumping pressure may press the ball to one side of the recess where the
ball does not seal the recess. Therefore, as long as the pumping pressure
remains applied, no sealing effect will be provided. However, in the
absence of external pressure, the movable mounted member may move
back (under the influence of the explosive material within the explosive
cartridge) in the recess to another portion thereby sealing an interior of
the flexible tube with regard to an environment, if desired or required.
However, many alternatives to the described embodiment of the
unidirectional restrictor valve using a ball or any other member are
possible. For example, the unidirectional restrictor valve may be
configured as a plate having one or more blades which can be opened by
a pressure applied from one direction, but which remain(s) closed by a
pressure applied from the opposite direction. Alternatively, a spring
mechanism, a magnetic mechanism, etc. may be used for implementing
a unidirectional restrictor valve.
In an embodiment, the end piece may comprise a boost
accommodation space configured for accommodating an explosive
booster unit. In other words, a detonator hole may be formed in the end
piece (forming an explosive booster) to accommodate a detonator for
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ignition of the explosive booster. For safety reasons, such an explosive
booster unit may be inserted into the boost accommodation space
directly before inserting the explosive cartridge into the borehole.
The flexible tube may have a length in its compressed state in a
range of approximately 0,5 m to approximately 30 m, particularly in a
range of approximately 1,5 m to approximately 10 m. Therefore, a very
long flexible tube may be formed which has to be inserted into a surface
portion of a borehole and then extends automatically into the borehole by
the own pressure of the explosive material being pumped into the flexible
tube from an outer position of the borehole. However, in the compressed
state, the flexible tube may have a reduced length in a range of
approximately 0,1 m to approximately 1 m, particularly in a range of
approximately 0,2 m to approximately 0,5 m. This high degree of
longitudinal compression of the flexible tube shows that the explosive
cartridge may be formed as a very compact device which is extended into
its working configuration only upon pumping the explosive material under
a certain pressure into the borehole.
In an embodiment, the explosive cartridge may comprise an
ignition line extending along an outer surface of the flexible tube. Such
an ignition line may also be denoted as a fuse or match cord.
Alternatively, it may also be possible to guide the ignition line through an
interior of the flexible tube.
In still another embodiment, the explosive cartridge may comprise
a protection tube configured in a slidable manner so as to selectively
cover or expose the flexible tube and/or the supply tube at least partially.
The protection tube may allow for accommodating basically all remaining
components of the explosive cartridge in an interior thereof so as to form
one single piece which can be transported in a compact manner and can
be brought in an extended state directly prior to inserting it into the
borehole. Thus, the protection tube which may consist of a hollow
cylinder may also serve as a protection when inserting into a borehole. It
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is possible that the protection tube is configured so that it is
automatically retracted towards an opening of the borehole when the
supply of explosive material to the supply body starts. Alternatively, it is
possible that the protection tube is actuated from outside of the borehole
for being retracted.
In still another embodiment, the flexible tube may comprise
different sections having different degrees of mechanical stability. These
different sections may be provided so that, when the explosive material is
supplied under pressure, less stable sections are expanded to a larger
extent than more stable sections. For example, the Young's modulus may
have a larger value for the more stable sections as compared to the less
stable sections. By taking this measure, the provision of ring-shaped
spacer elements or anchor spacing elements may be completely
dispensable. In this embodiment, the flexible tube itself may be
configured to provide anchoring within the borehole. The portions or
sections having smaller degree of stability will, when being filled with the
explosive material, have a stronger tendency to expand in a lateral
direction as compared to the thicker, more stable sections of the flexible
tube. Therefore, the less stable sections will provide an anchoring force,
based on friction, in the borehole. Such a configuration allows for a very
compact manufacture of the explosive cartridge because spacer elements
are dispensable. According to still another embodiment, also a flexible
tube with different sections having different degrees of stability may be
combined advantageously with the provision of spacer elements of the
above-described type.
Tubes with sections having different material properties may be
formed by an extrusion process in which process and/or material
parameters are varied during the extrusion.
Still referring to the previously described embodiment, the
different sections having different degrees of stability may have different
thicknesses. Therefore, portions of the flexible tube which may be made
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from a single material in the described embodiment but have different
thicknesses will also show different flexibility or stability characteristics.
Thinner wall portions will have a smaller capability to withstand
expansion forces provided by the explosive material filled with the
interior of the flexible tube as compared to thicker wall portions.
Therefore, thinner portions have a stronger tendency to be laterally or
transversely expanded to abut against the borehole for anchoring
purposes as compared to thicker portions.
Additionally or alternatively, the different sections having different
degrees of stability may be made of different materials having different
values of Young's modulus. Thus, more flexible materials will form
portions that serve for anchoring, and more rigid materials may form
portions in between. For example, different kinds of thermoplastic
polyurethane or different kinds of plastic may form the different sections
of the flexible tube.
A longitudinal extension of the less stable sections may be less
than about 1/3, particularly may be less than about 1/5, of a longitudinal
extension of the more stable sections. Thus, a high stability may be
combined with a reliable anchoring of the flexible tube by the less stable
sections. In such an embodiment, ring-shaped spacer elements and/or
anchoring elements may also be omitted. For instance, the less stable
sections may have a longitudinal extension in a range between 1 cm and
2 cm, whereas the more stable sections may have a longitudinal
extension in a range between 10 cm and 15 cm.
In still another embodiment, the flexible tube may comprise
perforations. A perforation may be manufactured, for instance, using a
needle roller or spike roller. Such perforations may be small openings
which may provide some kind of filter function, i.e. allowing small
particles to pass through the perforations and prevent larger particles
from passing through the perforations. For example, the perforations
may allow water or other solvents having a small molecular dimension to
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pass through the perforations so as to enrich the concentration of
explosive material in an interior of the flexible tube. Hence, the
perforations may be dimensioned so that molecules of the explosive
material will not be able to pass through the perforations, due to their
larger size. Such an explosive material may be an emulsion explosive
material, particularly an emulsion comprising ammonium nitrate and oil.
Still referring to the previously described embodiment, the
perforations may, in a further embodiment, only be opened when the
explosive material is supplied under pressure. Thus, without external
pressure from the filling of explosive material, the perforations will be
closed or will have such a small diameter that basically no molecules of
the explosive material including solvents or matrix molecules such as
water can pass through the perforations. Therefore, the flexible tube is
basically tight or sealed in this configuration. If however the flexible tube
is laterally expanded due to the decompression in a longitudinal direction
and widening up in a lateral direction, the perforations may be opened,
allowing to pass specific materials (in accordance with a specific cut-off
value) through this wall.
The perforations may particularly be dimensioned so as to allow
water to pass through the perforations and prevent explosive material to
pass through the perforations. The skilled person will understand that
routine experiments may be useful to determine which dimensions of the
perforations are suitable.
The flexible tube may comprise sacrificial particles embedded in a
matrix material and being adapted for being removed from the matrix
material when the explosive material is supplied under pressure. For
example, chalk particles may be embedded in a plastics membrane for
instance made of thermoplastic polyurethane. Such chalk particles may
have the property that, under the pressure applied by the explosive
material filled to an interior of the tube, the chalk particles will be forced
to move radially outward of the flexible tube, thereby forming
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perforations. Alternatively, the particles may be formed from a soluble
material such as salt. When the explosive material is filled in the flexible
tube, an aqueous solvent of the explosive material will dissolve the salt
material from the plastic matrix, thereby opening the perforations.
In one embodiment, it is possible that the sacrificial particles (such
as salt particles) are removed from the matrix, for instance by being
dissolved, upon pumping the explosive material in the flexible tube. The
material selection of the sacrificial particles may be so that this material
reacts with the explosive material and/or with a fluid (provided in an
environment), for example to adjust the pH value and/or to trigger any
chemical reaction with the explosive material. This may allow to precisely
adjust the conditions of the explosion to be performed. For instance, it
may be possible to thereby promote the formation of gas bubbles within
the explosive material which may be desired under certain
circumstances. For example, such bubbles may be desired for selectively
weaken the explosion force. This may render an explosion very gentle.
Any other control of the explosion process based on an adaptation of the
sacrificial particles is of course possible.
Furthermore, the defined way of filling the flexible tube with
explosive material according to an exemplary embodiment allows to
precisely control the conditions under which the chemical reaction of the
explosion material takes place.
The filling procedure for filling explosive material into the flexible
tube may be performed from a borehole end. For this purpose, a compact
member which is only placed in a borehole end at a small distance may
be operated in a user-convenient manner. In case of a sticking of this
single piece when being inserted in a borehole by a user, such a sticking
can be recognized before starting to pump explosive material in the
flexible tube so that a retraction and correction procedure may be
performed without safety risks.
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Exemplary embodiments of the invention have the advantage that
a very good explosion effect can be achieved by a constant filling in a
constant cross-section. A high degree of safety against breakage between
different components of the explosive cartridge can be guaranteed. The
system is particularly appropriate for vertical applications. The unwinding
or unreeling of the wrinkled flexible tube can be controlled automatically
by controlling the filling or pumping procedure.
The aspects defined above and further aspects of the invention are
apparent from the examples of embodiment to be described hereinafter
and are explained with reference to these examples of embodiment.
The invention will be described in more detail hereinafter with
reference to examples of embodiment but to which the invention is not
limited.
Fig. 1 to Fig. 4 illustrate explosive cartridges according to
exemplary embodiments of the invention.
Fig. 5 and Fig. 6 illustrate flexible tubes of explosive cartridges
according to exemplary embodiments of the invention.
Fig. 7 and Fig. 8 illustrate a flexible tube of an explosive cartridge
according to exemplary embodiments of the invention in two different
states.
The illustration in the drawing is schematically. In different
drawings, similar or identical elements are provided with the same
reference signs.
In the following, referring to Fig. 1, an explosive cartridge 100
according to an exemplary embodiment of the invention will be
described.
The explosive cartridge 100 is adapted for receiving an emulsion
explosive material (see arrow 102) in a position in which the explosive
cartridge 100 is arranged in a borehole (not shown). The explosive
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material may be supplied from outside of the borehole. The explosive
cartridge 100 comprises a tubular supply body 104 shaped as a hollow
cylindrical body 106 with a conically tapering end portion 109. In an
interior of the supply body 104 a supply channel 108 is formed through
which the explosive material is supplyable from outside of the borehole.
At a position outside of the borehole, a filling vehicle (not shown) is
arranged having a filling container including explosive material in an
emulsive form. This will be supplied to a hose 110 having a first
connection adapter 112 at an end thereof. A second connection part 114
of the explosive cartridge 100 is adapted for engagingly receiving the
adapter 112 to provide for a sealing connection. Therefore, the explosive
material can be supplied from an exterior of the borehole via the hose
110 to the supply channel 108.
Furthermore, the explosive cartridge 100 comprises a flexible tube
116 which is made of a thermoplastic polyurethane (TPU) material. The
flexible tube 116 is tubular and has some flexibility and some stability.
Fig. 1 shows the flexible tube 116 in a state in which a part (see right
hand side) is slid over an outer surface of the supply body 104 in a
longitudinally compressed manner (a longitudinal direction can be defined
by the direction of the arrow 102 or by a central axis 155 of the supply
body 104). Another part of the flexible tube 116 (see left hand side) has
already left the outer surface of the supply body 104. When the explosive
material is supplied under pressure (see arrow 102) from outside of the
borehole through the supply channel 108 and filled in an inner volume
118 of the flexible tube 116, the flexible tube 116 is longitudinally
decompressed and slides off in direction of the arrow 102 from the supply
body 104 to proceed towards an interior of the borehole, i.e. according to
Fig. 1 to the left-hand side. Thus, the flexible tube 116 which is wrinkled
or folded and therefore laterally compressed at a portion on which it is on
the supply body 104 will be transferred into a flexible tube with a larger
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diameter and a basically smooth outer surface on the left-hand side of
the supply body 104, i.e. after having left the supply body 104.
The widened end portion 109 of the supply body 104 applies a
tension force on the flexible tube 116 particularly at the position where it
leaves the supply body 104, thereby preventing undesired backflow of
explosive material at a critical position 120 into an intermediate space
122 between the supply body 104 and the wrinkled flexible tube 116. As
can be taken from Fig. 1, a ratio between a diameter D of the widened
end portion 109 and a diameter d of the flexible tube 116 in the
compressed state is about 1,5. This makes it very difficult for explosive
material to be pressed into the intermediate space 122 at the gap at
portion 120.
Furthermore, the explosive cartridge 100 comprises an end piece
126 shaped as a basically hollow cylindrical body which is connected to
an end portion of the flexible tube 116 at an attachment section 128.
Therefore, there is a sealed connection between the flexible tube 116 and
the end piece 126 at the attachment section 128. The end piece 126
allows to close the end portion of the flexible tube 116. The end piece
126 has an inner recess 130allowing air or the like to be removed from
the interior of the flexible tube 116 to prevent bubbles within the
explosive material..
The end piece 126 further comprises a boost accommodation space
134 into which a user may insert an explosive booster unit 136. Also the
explosive booster unit 136 has a small internal channel allowing to
remove the air out of the flexible tube 116. Although not shown in Fig. 1,
an ignition line may extend along an outer surface of the flexible tube
116 between the end piece 126 and an outside of the borehole to initiate
an explosion. Such an ignition line may also be arranged at any other
suitable position.
The explosive cartridge 100 further comprises a unidirectional
restrictor valve 131 forming part of the hose adapter 114. The
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unidirectional restrictor valve 131 is adapted for enabling supply of
explosive material from outside of the borehole into the flexible tube
116 under pressure. The unidirectional restrictor valve 131 is further
adapted for disabling a backflow of explosive material out of the flexible
tube 116. In the shown embodiment, the unidirectional restrictor valve
131 comprises a movable ball 132 (movable to the left and the right) in
a tapering recess formed in the hose adapter 114. The movable ball 132
is movable for selectively opening or closing the recess depending on
the actual pressure conditions. When a pumping pressure for filling
explosive material 102 in an interior of the flexible tube 116 is applied,
this pumping pressure presses the ball 132 to the left hand side of the
recess (where the recess is widened as compared to the right hand side)
so that the ball 132 does not seal the recess and abuts to a mesh 139
(being permeable for the explosive material), thereby allowing the
explosive material to flow in the flexible tube 116. When the supply of
the explosive material 102 is finished, the explosive material 102 within
the flexible tube 102 presses the ball 132 to the right hand side in the
recess (where the recess is narrower as compared to the left hand side
so that the ball 132 cannot be pressed out of the recess) and hence
closes the recess, thereby sealing an interior of the flexible tube 116
with regard to an environment. Thus, any backflow of the explosive
material out of the flexible tube 116 is disabled. However, many
alternative configurations of unidirectional restrictor valves are possible.
A detailed view 150 shows the explosive cartridge 100 in a state
before being inserted into a borehole. The explosive cartridge 100 has
the appearance of a single component which can, although not shown in
Fig. 1, be circumferentially protected by a surrounding plastic tube or the
like (see Fig. 2). When being inserted by a user in a borehole, the
optional protection tube may be retracted so as to expose the portion of
the explosive cartridge 100 as shown in the detailed view 150.
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The explosive booster unit 136 may be inserted into the booster
accommodation space 134. The adapters 112, 114 may be connected to
one another. Now the explosive cartridge 100 may be inserted into a
borehole. Via the hose 110, explosive material may be pumped under
pressure along a direction 102 into the supply channel 108 and from
there into the inner volume 118 of the flexible tube 116. This will force
the explosive material to enter in the inner volume 118. At the same time
and automatically, the wrinkled flexible tube 116 will be removed
successively from the outer surface of the supply body 104 and will
assume the state as shown in the main view of Fig. 1. After a sufficient
amount of explosive material has been inserted into the inner volume
118 of the flexible tube 116, the explosion can be initiated.
Fig. 2 shows an explosive cartridge 200 according to another
exemplary embodiment of the invention.
The embodiment of Fig. 2 differs from the embodiment of Fig. 1
particularly in that the supply body 104 consists only of a hollow
cylindrical portion, and does not have a conically tapering portion. The
slight widening of the flexible tube 116 at the left side end of the supply
body 104 is performed solely by the own pressure of the explosive
material pumped along a direction 102 into the inner volume 118 of the
flexible tube 116.
In addition, the explosive cartridge 200 comprises a plurality of
ring-shaped spacer elements 202 made from an elastomer material. A
side view of the rings 202 is shown in Fig. 2 as well. The ring-shaped
spacer elements 202 are slid over an outer surface of the flexible tube
116 at a first distance I from one another in the part where the flexible
tube 116 which is in the longitudinally compressed or wrinkled state. In
the portion where the flexible tube is in the decompressed state, a
distance of adjacent ring-shaped spacer elements 202 is L>I. For
instance, L may be at least three time of I. This increase of the spacing
between adjacent ring-shaped spacer elements is performed
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automatically due to a friction force between the outer surface of the
flexible tube 116 and the inner surface of the ring-shaped spacer
elements 202. Thus, it is sufficient that the ring-shaped spacer elements
202 are only loosely slid over the outer surface of the flexible tube 116
when the flexible tube 116 is in the longitudinally compressed manner
(over the supply body 104), without the need of an adhesive or the like.
The ring-shaped spacer elements 202 become tightly fit to the flexible
tube 116 when the flexible tube 116 is laterally or transversely expanded
by being filled with the explosive material. Therefore, a tight connection
between the ring-shaped spacer elements 202 and the flexible tube 116
is only obtained on the left-hand side of the end section of the supply
body 104. The ring-shaped spacer elements 202 allow for a friction-based
centering of the explosive material in the borehole. They further prevent,
at the position where they are arranged over the supply body 104,
undesired backflow of explosive material at or close to the position 120 to
the intermediate space 122.
Due to the provision of the ring-shaped spacer elements 202, the
conically tapering end section 109 of the supply body 104 is omitted in
Fig. 2. However, if the ring-shaped spacer elements 202 are made of a
sufficiently flexible material and can be widened up by such a conically
tapering end section 109 as well or when a cross section of the ring-
shaped spacer elements 202 is sufficiently large, a tapering or widening
end section 109 can be provided in the embodiment of Fig. 2 as well.
Furthermore, the embodiment of Fig. 2 comprises a protection
tube 204 which may be made of acrylic glass or the like. It serves for
protecting the interior of the explosive cartridge 200 during transport and
insertion into a borehole. It can be retracted in antiparallel direction to
arrow 102 when the explosive cartridge 200 is or has been inserted in a
borehole. Alternatively, it can also remain in the borehole.
As can be taken from Fig. 2, the lateral extension of the spacer
elements 202 with respect to a central axis of the explosive cartridge 200
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is the largest in the section of the flexible tube 116 having left the outer
surface of the supply body 104. Therefore, it can promote frictional
holding.
Fig. 3 shows an explosive cartridge 300 according to still another
exemplary embodiment of the invention.
The explosive cartridge 300 is vertically arranged in a vertical
borehole being delimited by sidewalls 306. As compared to the explosive
cartridge 200 shown in Fig. 2, the explosive cartridge 300 shown in Fig. 3
has two different groups of ring-shaped spacer elements 302 and 304.
Each third spacer element 304 has a larger lateral extension A as
compared to a lateral extension a of the other group of ring-shaped
spacer elements 302. Side views of the ring-shaped spacer elements
302, 304 are also shown in Fig. 3. As can be taken from Fig. 3, when the
spacer elements 302, 304 have left the supply body 104, they have a
larger extension and may therefore provide some anchoring due to a
friction with the sidewalls 306.
Fig. 4 shows an explosive cartridge 400 according to still another
exemplary embodiment of the invention.
Particularly in contrast to Fig. 2, the explosive cartridge 400 shown
in Fig. 4 has, in addition to the ring-shaped spacer elements 202, spring-
shaped anchoring elements 402 which are interposed between the ring-
shaped spacer elements 202. As long as the spring-like anchoring
elements 402 are within a protection tube 204, they are in a
mechanically biased, compressed state. After leaving the protection tube
204, they will be forced, due to their biasing, to expand in a way that
they are anchored in the borehole, i.e. may contact a borehole sidewall
306 and may therefore center the explosive cartridge 400 with respect to
the borehole. Alternatively, it is also possible to omit the ring-shaped
spacer elements 202.
Fig. 5 shows a flexible tube 500 of an explosive cartridge
according to an exemplary embodiment of the invention inserted into a
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borehole which is vertically aligned in the shown embodiment and is
delimited laterally by a sidewall 306.
The flexible tube 500 may be implemented in any one of the
explosive cartridges disclosed herein, including the explosive cartridges
shown in Fig. 1 to Fig. 4. This may also render spacer elements 202, 302,
304 and/or anchoring elements 402 dispensable. The flexible tube 500 is
made as an integral piece of thermoplastic polyurethane material
however formed of an alternating sequence of two sections. First sections
502 have a wall thickness B which is larger than a wall thickness b of
second sections 504 and are arranged sandwiched between sections 502.
In one embodiment, it is possible that the wall thicknesses between the
sections 502, 504 are transient into one another in a continuous or
steady way. In another embodiment, the wall thickness can be stepped
at interfaces between a section 502 and a section 504. Upon filling an
inner volume 118 of the flexible tube 500 with explosive material as an
emulsion, sections 504 having a smaller wall thickness will be forced
outwardly, whereas sections 502 having the larger wall thickness
withstand the pressure and will maintain basically in their initial position.
Consequently, the laterally elongated sections 504 may allow to anchor
the flexible tube 500 at the borehole wall 306.
Fig. 6 shows a flexible tube 600 according to another exemplary
embodiment which is however similar to Fig. 5.
Also the flexible tube 600 has two different sections, i.e. first
sections 602 made of a first material and second sections 604 made of a
second material. In the shown embodiment, the material of the second
sections is mechanically less stable than those of the first section 602, so
that upon filling the inner volume 118 with explosive material under
pressure, the mechanically weaker section 604 will provide an anchoring
function at the borehole wall 306.
A longitudinal extension, d, of the less stable sections 604 can be
less than 1/3 of a longitudinal extension, D, of the more stable sections
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602. Thus, a high stability may be combined with a reliable anchoring of
the flexible tube 600 in the borehole. A corresponding geometric feature
can also be implemented in the embodiment of Fig. 5
Fig. 7 shows a flexible tube 700 of an explosive cartridge
according to an exemplary embodiment of the invention.
The flexible tube 700 may be implemented in any of the above-
described embodiments. As shown, the flexible tube 700 is made of a
thermoplastic polyurethane material 702 which has small perforations
704 provided therein. For instance, a needle roller may allow to form the
very small perforations 704. However, in the state shown in Fig. 7, the
flexible tube 700 has no inner overpressure so that the perforations 704
are so small that basically no material can pass through these
perforations 704.
Fig. 8 shows an embodiment, in which a large view of a portion
706 is shown in a state after an explosive material has been filled in the
inner volume 118. The explosive material is formed of an explosive agent
800 having molecules with a larger viscosity and a larger dimension as
compared to a water solvent 802. Due to the inner pressure in the inner
volume 118, the perforations 704 are now opened or enlarged to an
extent that only the small water molecules 802 can pass through the
perforations 704, but due to the higher viscosity and the larger molecular
size the explosive agent particles 800 remain within the volume 118.
Therefore, an enrichment of explosive agent 800 in an interior of the
flexible tube 700 takes place due to the configuration of the perforations
704.
It should be noted that the term "comprising" does not exclude
other elements or features and the "a" or "an" does not exclude a
plurality. Also elements described in association with different
embodiments may be combined.
It should also be noted that reference signs in the claims shall not
be construed as limiting the scope of the claims.
