Note: Descriptions are shown in the official language in which they were submitted.
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ELEMENT FOR If~JITIATtNG PROPELLANT
BACKGROUND OF THE INVENTION
This invention is concerned generally with a customized low energy method of
breaking rock in a controlled manner.
As used herein the word "rock" includes rock, ore, coal, concrete and any
similar
hard mass, whether above or underground, which is difficult to break or
fracture. It is
to be understood that "rock" is to be interpreted broadly.
A number of techniques have been developed for the breaking of rock using non-
explosive means. These include a carbon dioxide gas pressurisation method
(referred to as the Cardox method), the use of gas injectors (the Sunburst
technique), hydrofracturing and various methods by which cartridges containing
energetic substances pressurise the walls or base of a sealed drill hole to
produce
penetrating cone fractures (known as PCF)
These techniques may be an order of magnitude more efficient than conventional
blasting in that they require approximately 1/10 of the energy to break a
given
amount of rock compared to conventional blasting using explosives. The lower
energy reduces the resulting quantity of fly rock and air blast and to an
extent allows
the rockbreaking operation to proceed on a continuous basis as opposed to the
batch-type situation, which prevails with conventional blasting.
Most non-explosive rockbreaking techniques rely on the generation of high gas
pressures to initiate a tensile fracture at the bottom of a relatively short
drill hole.
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As used herein the term "propellant" is to be interpreted broadly to include a
blasting
agent, propellant, gas-evolving substance, explosive or similar means which,
once
initiated, generates high pressure jet material typically at least partly in
gaseous form.
Propellants of this nature are known in the art. "Blasting agent" and
"propellant" are
used interchangeably in this specification.
SUMMARY OF INVENTION
The invention provides apparatus for breaking rock which includes a cartridge
which
forms an enclosure, a propellant inside the enclosure, and at least one
element
which is electrically energisable and which is made from inert material
exposed to the
propellant.
As used herein "inert material" means a material which, unless energised,
cannot
give rise to a spark or other phenomenon which can initiate the blasting
agent.
The element may be in the nature of a filament or electrical resistor.
The element may be made from any appropriate material but a preferred material
is
carbon, eg. in the form of graphite.
The element may be treated in any appropriate way to enhance the efficiency
with
which the propellant is initiated. For example the element may be dipped in or
coated with aluminium powder or any similar agent which gives rise to a
sputtering
effect when the element is energised.
The element may be in the nature of a fusible link ie. a portion of the
element may be
disintegrate when an electric current in excess of a predetermined amount is
passed
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through the element. Disintegration of the element gives rise to the
generation of
high energy and relatively small particles which are propelled into the
propellant
thereby to initiate combustion of the blasting agent. This approach should be
contrasted with a technique wherein the element in the form of a filament wire
is
heated by the passage of electric current to a higher temperature at which the
propellant is initiated but wherein the filament remains integral and does not
disintegrate due to the direct effect of the electric current passing through
the
filament.
The filament may be coated to prevent the propellant, or moisture in the
propellant,
from reacting or fusing with the material contained in the filament.
The filament may for example be a wire or band made from aluminium, nickel-
chrome, carbon or a similar material, or a resistor such as a ceramic metal
device
which, when energized, does not fuse or disintegrate but instead, remains
integral
despite dissipating sufficient heat to initiate combustion of the propellant.
The cartridge may include a base and a side wall which extends from the base.
The
side wall may be generally cylindrical.
The cartridge may be made from a malleable material which, in this sense,
includes
a material which is capable of plastic deformation, without fracture, at least
to a
predetermined extent.
The cartridge is preferably made from a plastics material eg. polypropylene,
polyethylene or the like. The scope of the invention is not limited in this
regard.
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An upper end of the cartridge, ie. an end which opposes the base, may be domed
and the filament may be located at the upper end.
It falls however within the scope of the invention to locate the filament at
an
intermediate location ie. between opposing ends of the cartridge.
The filament may be relatively small and thus, when energized, cause the
production
of a localized relatively high energy hot spot. On the other hand the filament
may be
elongate so that, when energized, the propellant is initiated over a fairly
substantial
length or area or at a plurality of points.
It falls within the scope of the invention to include more than one element in
the
cartridge so that initiation of the propellant takes place at more than one
location.
Electrical leads to the element may be positioned inside the cartridge or on
an outer
surtace of the cartridge but preferably are embedded in the material from
which the
cartridge is made.
The electrical leads may be connected to terminals to facilitate connection of
the
leads to a control unit. The terminals are preferably on an outer side of the
cartridge.
The terminals may be covered with a removable closure. Alternatively the
terminals
may be covered with a frangible or breakable closure. The closure is designed
to
protect the terminals from damage or exposure prior to use of the cartridge.
The element, or elements, as the case may be, with suitable leads or
conductors to
the elements and, where applicable control devices such as timing circuits and
capacitors or other energy sources for operating the timing circuits, may be
mounted
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on a suitable substrate or motherboard, to facilitate handling of these
components
and assembly thereof together with the remainder of the cartridge.
The invention also extends to an element of the aforementioned kind, and to a
substrate which carries the element and, where required, one or more
components
for use with, or required to energize, the element.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is further described by way of examples with reference to the
accompanying drawings in which:
Figure 1 is a view in cross section and from the side~of blasting apparatus
according
to one form of the invention,
Figures 2 and 3 are views similar to Figure 1 of blasting apparatus according
to
second and third forms of the invention,
Figure 4 is an enlarged cross sectional view of a portion of a cartridge
illustrating
connecting terminals on the cartridge, and
Figure 5 shows a substrate which carries a filament, for use in the apparatus
of the
invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
Figure 1 of the accompanying drawings illustrates a hole 10 which is drilled
into a
rock mass 12 from a face 14 using conventional drilling equipment. A cartridge
16 is
loaded into the hole. In this example the cartridge has a base 18 and a
generally
cylindrical wall 20 which extends from the base and which terminates at an
upper
end, remote from the base, in a rounded shape 22.
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The cartridge is made from a plastics material using injection techniques
which are
known in the art. The cartridge is for example made from a high density
plastics
material such as high density polypropylene.
It is desirable to form the cartridge from a malleable material which enables
the
cartridge to be plastically deformed, without rupture, at least to a
predetermined
extent eg. of the order of 10%, or more.
The cartridge forms an enclosure for a propellant material 24 which is of
known
composition. The propellant is loaded into the cartridge under factory
conditions
using techniques which are known in the art.
An initiator 26 is located at an upper end of the cartridge. The initiator has
an
element when, in this case, is in the form of a filament made from inert
material such
as carbon wire which, preferably, is formed into a coil or with a zig zag
configuration.
The filament extends from two leads 30 and 32 which pass through the wall of
the
cartridge so that filament is exposed, in the interior of the cartridge, to
the propellant
24. The leads 30 and 32 extend to a blasting control unit, not shown, of a
type which
is known in the art.
Stemming 40 is placed into the hole from the rock face covering the cartridge
to a
desired extent and is consolidated by being tamped in position.
The filament is energized by sending a signal of a determined energy content
through the wires 30 and 32 to the filament. The filament is thereby heated
and
glows creating, in effect, a localized hot spot which transfers sufficient
energy to the
propellant, in the immediate vicinity of the filament, to cause ignition of
the propellant.
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The propellant, when ignited, causes the release of high pressure jet material
which
is substantially in gaseous form. This material produces a shock wave which is
used
to fracture the rock 12, typically with an initial fracture being established
at the bottom
40 of the hole 10.
The carbon filament 26 is, as noted, inert and consequently it is possible to
provide
the cartridge 16 in a form which is ready for use in the sense that the
propellant 24
can be loaded into the cartridge even though the initiator 26 is already fixed
to the
cartridge. In many other instances it is not possible to provide the
cartridge, loaded
with propellant, if the initiator is already fixed to the cartridge for it is
possible
inadvertently to energise the initiator and thus cause unwanted combustion of
the
propellant. Due to the fact that the filament is made from an inert material
it is
believed that this danger is effectively eliminated.
The filament may be coated with aluminium paint which, when heated, increases
the
quantity of energy which is released and, depending on circumstances, can give
rise
to a sputtering effect which enhances the efficiency with which the propellant
is
ignited.
The filament could alternatively be in the form of a wire or band and could be
made
from aluminium or nickel-chrome. These materials may be of a kind which, when
heated by electric current, fuse and disintegrate. In a variation use is made
of a
suitable resistor, made for example from a ceramic/metal composition which,
when
heated, glows but does not spatter or disintegrate, and which provides the
necessary
"hot spot" to initiate combustion.
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The arrangement shown in Figure 2 is similar in many respect to what is shown
in
Figure 1 and where applicable like reference numerals are used to designate
like
components. The filament initiator 26 is, however, in this case located at a
position
more or less midway between the base 18 and the rounded upper end of the
cartridge. The leads 30 and 32 extend from an upper entry point to the
filament and
are embedded in the wall 20 of the cartridge. The filament 26 is fired in the
same
way as what has been described in connection with Figure 1.
In the arrangement shown in Figure 3 the filament is not localized in the way
shown
in Figures 1 and 2 but, instead, is elongate. The filament extends from end
points of
wires 30 and 32 which, as is the case with the Figure 2 embodiment, are
embedded
in the side wall 20. The filament is shaped into the form of a ring which
extends
around an internal surtace of the wall 20. Consequently, when the filament is
initiated, combustion of the propellant 24 takes place over an extended length
or
area or, otherwise put, at a plurality of points.
The filament 26 may be designed and operated so that when energized it is
heated
to glow and cause a localized temperature increase of sufficient magnitude to
initiate
the blasting agent. Alternatively the filament may be in the form of a fusable
link
such that a region of the filament is heated to disintegration point by the
passage of
electrical current. Components of the filament which are released upon
disintegration are extremely hot and a sputtering-type action results as the
filament
disintegrates.
It is possible to enhance the combustion effect of the filament by coating the
filament
at one or more locations with an agent such as aluminium powder or any other
substance which is explosive or flammable by nature. Again small localized hot
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spots are generated when an appropriate electrical current is passed through
the
filament and combustion of the propellant is therefore initiated effectively
simultaneously at a plurality of locations. .
Also, to protect the filament against reacting with the propellant, or
moisture in the
propellant, the filament may be coated with an inert material such as a
suitable
lacquer, eg. of nitrocellulose.
Figure 4 is an enlarged view in cross section of an upper end 22 of a
cartridge which
may be of the type shown in any one of Figures 1 to 3. The leads 30 and 32
are, as
has been described, embedded in the wall 20 of the cartridge and terminate in
relatively rigid terminals 50 and 52 respectively, which project outwardly
from the
cartridge. The terminals are covered by means of a cap 54 which protects the
terminals during transport and storage of the cartridge. If the terminals are
to be
accessed to enable electrical connections to be made to the terminals then the
cap is
removed. The cap may for example be threadedly engaged with the cartridge.
Alternatively the cap may be formed substantially integrally with the
cartridge or be
secured thereto in a manner which inhibits removal of the cap. In this case
the cap
includes a lid 56 which is breakable, or which can be torn from the remainder
along a
line of weakness, not shown, to expose the terminals so that electrical
connections
can be made thereto.
Figure 5 illustrates another modification which can be made to the
aforementioned
principles. Figure 5 shows a cartridge 10 which is filled with propellant 24.
A
substrate 60 is located in the cartridge. The substrate is made from an
inexpensive
non-electrically conductive material, and may be in the nature of a printed
circuit
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board, be formed from a suitable plastic material, or the like. The substrate
may be
rigid or flexible.
Discrete components may be mounted directly to the substrate using techniques
which are known in the electronics art. Alternatively components may be formed
on
the substrate using deposition techniques similar to those employed in the
manufacture of printed circuit boards, integrated circuits and the like.
Thus, using an appropriate technique, a filament 26 is formed on, or is
mounted to,
the substrate and leads 62 are formed connecting the substrate to a timing
circuit 64.
The circuit is also formed on or bonded to the substrate and includes leads 66
which
extend to terminals 68. The conductors 30 and 32, which are inherently more
robust
than the leads 62 and 64 on the substrate, are directly connected to the
terminals.
The use of the substrate to carry the filament considerably facilitates the
manufacture
of the filament and its use and helps in reducing inadvertent damage to the
filament
which could arise during manufacture of the cartridge or when the cartridge is
installed in a hole in a rock face. The substrate may be of any appropriate
shape or
size so that when the substrate is positioned inside the cartridge the
filament 26 is
substantially automatically positioned at a desired location inside the
cartridge.
Clearly it is possible to form a plurality of filaments on the substrate so
that the
individual filaments are at precisely determined locations relatively to each
other
inside the cartridge.
