Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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1 BACKGROUND OF THE INVENTION
3 Field of the Invention
4 This invention relates to a flameproof instantaneous
fuse. ~-qore especially, this invention relates to an in-
stantaneous fuse useful in seismological measurements in
7 highly inflammable environments. This invention is particu-
8 larly concerned with an instantaneous fuse which can be
employed in operations where danger due to firedamp and
coal dust exists. In particular, this invention relates
11 to an instantaneous fuse containing at least one jacket
12 thereabout, which jacket contains a longitudinally running
13 air channel therein. The flameproof instantaneous fuse of
14 the present invention is one in which preferably the core
has wound or braided thereabout a fiber-wrapped material
16 composed of natural or synthetic threads, the fiber-wrapped
17 material being wrapped about the explosive core in a moisture-
,18 proof manner. Preferably, a thermoplas,tic material is
19 disposed between the explosive core and the fiber-wrapped
material.
'21
22 Discussion of the Prior Art
23 Instantaneous fuses are generally known. They comprise
24 a material which has a uniformly high detonation rate. The
fuses are relatively resistant to mechanical influences so
26 as to lessen the probability of accidental ignition by ex-
27 ternal influences. Such fuses can be readily stored and
28 readily handled, the explosive core being protected against
29 humidity and the action of water and other agressive liquids
by an appropriately positioned and selected plastic covering
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1 material.
The known instantaneous fuses, however, also have
4 certain disadvantages, especially with respect to lateral
propagation of flame. This lateral propagation of flame
6 has not been effectively reduced by the plastic covering
7 providing the protection against moisture. Attempts have
8 been made to overcome this disadvantage by covering the
9 explosive core with a plurality of successive layers, namely
first a textile fabric or braid. Such attempts have included
11 the use of an asphalt covering, a paper wrapping followed
12 by another textile fiber layer consisting usually of
13 cotton followed by a finishing layer of wax. Even these
14 fuses have, however, left some properties to be desired.
16 To provide instantaneous fuses safe in the presence of
17 firedamp, it has been known to embed into the thermoplastic
18 covering of the fuses a flame retardant or flame cooling
19 substance. It has also been known to impregnate fabric or
paper wi~h mineral substances or metal salts and to use
21 such impregnated material to wrap the fuses. Such measures
22 have not sufficed to improve the firedamp safety to the
23 degree desired.
24
In German Patent 1,916,685, there is disclosed instan-
26 taneous fuses made with the use of inert substances in
27 powder form, especially low energy instantaneous fuses.
28 According to this patent, the explosive core is covered with
29 a tube which is provided with a wrapping of natural or
synthetic (chemical) fibers produced by the spinning method
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: 1 (extruding a melt of polymer and cooling the extrudates).
~: 2 The instantaneous fuses of such patent are characterized
; 3 by the fact that around the core there is a layer of an
inert substance in powder form which is fixed in place with
a second layer of natural or synthetic fiber. The inert
6 substances in powder form can also be mixed with sodium
7 bicarbonate and sodium chloride or other inert substances
8 as well, such as ammonium carbonate, alkali metal fluorides
. 9 and alkaline earth metal fluorides, as. well as their double
salts with, for example, aluminum, especially cryolite.
11
12 An instantaneous fuse has also been proposed for use
13 in operations where the firedamp or coal dust hazard exists
14 and for the initiation of safety explosives, in which the
explosive inner core of the fuse, e.g., a phlegmatized ex-
16 plosive in dust form, has a hollow tube disposed within it,
17 and the core is pr.ovided with a ~acket made of inert sub-
18 stances which have a flame-cooling and flame-stopping action
19 (German OS 2,057,042). Cryolite, halides, sulfates,
bicarbonates and carbonates of the alkali and alkaline earth
~ 21 metals, the corresponding ammonium salts, and the oxides of
;~ 22 the alkaline earth metals, for example, are used both for
23 the phlegmatization of the explosive, which can be, for
24 example, pentaerythritol tetranitrate (nitropenta) or
cyclotrimethylenetrinitramine (hexogen), and for.the layer
. 26 of powdered, inert substances placed around the core and
.. held in place with a second layer of natural or synthetic
. . . (chemical) fibers.
29
30 ~ Thes pes of instantaneous fuses manufactured wlth
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1 the use of powdered inert substances do not have the dis-
2 advantages described above for the known instantaneous fuses
3 in the area of use for which they are normally supplied.
4 Thus, they bring advantages to this special field.
6 In the course of recent years, however, lnstanta-
7 neous fuses have found a new field of application in con-
8 nection with seismological blasting which has demanded
further improvements of the old and reliable instantaneous
fuses containing inert, flame-cooling and flame-stopping
11 substances. Whereas the instantaneous fuses were formerly a
12 mere ignition means serving for the ignition of explosives,
18 they are now used by themselves, without explosives, or with
14 only relatively small amounts of explosives in seismological
operations. In this new use for instantaneous fuses, there
16 is a fundamental departure from the conventional seismolog-
17 ical blasting method in which the drilling of rock is basic,
18 since then the fuse and the explosives are placed in bore
19 holes. Instead, in the new seismological blasting method,
the instantaneous fuses are laid out on the ground, some-
21 times in prepared troughs or furrows, but sometimes also in
22 simple contact with the surface of the ground. This use of
23 instantaneous fuses can be harmful to the environment,
24 especially when the fuses are not laid in furrows and cov-
ered over, since small or fairly large surface fires often
26 develop. For it has been found that instantaneous fuses are
27 quite capable, upon detonation, of setting fire to dry
28 grass, duff or even underbrush, it being mainly fuses made
29 with paper wrapping and/or hemp yarns which cause fire
damage by their flammability, particularly in hot countries
such as Africa or the Near East.
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1 SU~MARY OF THE INVENTION
3It is an object of this invention, therefore, not only
4 to improve instantaneous fuses with respect to their fire
safety, but to provide an instantaneous fuse which is use-
6 ful in seismological measurements. More especially, it is
7 an object of this invention to provide an instantaneous
8 fuse which does not readily laterally propagate flame.
9 More especially, it is desirable to provide an instanta-
neous fuse which can be disposed upon grass, dried grass,
11 duff, underbrush, or even a flammable composition and which
12 can be ignited without igniting the material disposed there-
13 beneath. It is a further object of this invention to pro-
14 vide such an instantaneous fuse which can be readily
manufactured at not excessive cost.
16
17The objects of this invention are provided by a flame-
18 proof instantaneous fuse which comprises a core of an ex-
1~ plosive material, said core having a fiber material wrapped
thereabout, said fiber-wrapped material in turn being en-
21 closed within a material, said material having at least one
22 longitudinally running air channel therein.
23
24In accordance with this invention, there is provided
a flameproof instantaneous fuse of the type described which
26 has in a material disposed about the fiber-wrapped material
28 at least one longitudinally running air channel. The longi-
tudinally running air channel is disposed in a material
29 which can comprise one or more or a series of jackets which
cooperate with one another so as to define air channels or
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1 spaces which run longitudinally. Preferably, the flame-
proof instantaneous fuse has a series of layers of fiber-
3 wrapped material.
In providing the air channel in the envelopin~ material
6 disposed about the fiber-wrapped material, pairs of en-
7 veloping jackets are employed wherein the jackets are at
8 least in part in non-contacting relationship with one
9 another. Preferably, an air channel is disposed by suit-
able selection of shape of the cooperating enveloping jackets,
11 which air channel encircles the explosive core.
12
13 Thus, the surprising solution to the problems inherent
14 in prior art-type instantaneous fuses are solved, according
to a preferred mode of the invention, by providing an ex-
16 plosive core composed of an inner explosive core and an
17 multi-layer fiber wrapped material enclosing or enveloping
18 the interior explosive core. This instantaneous fuse is
19 characterized by the fact that the core has two or more
jackets which enclose air spaces. It is desirable that the
21 first and/or all additional jackets be fluted and prefer-
22 ably dusted internally with an inert flame cooling and
23 flame stopping substance.
24
The core of explosive may itself be disposed about a
26 hollow tube or the like. Where present, the inner dia-
27 meter of said hollow tube is 0.8 to 1.5 mm, preferably
28 1.0 to 1.2 mm.
29
The material of the hollow tube can be thermoplastic
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material for example polypropylene, polyvinyle chloride
and polyethylene a.s.o. its dimensions depend on the
quantity of explosives filled in : this quantity can be
varied between 2 g and 100 g per current metre cord.
The core itself is of known construction.
Preferably, the core is made of an explosive of one of
the following groups: pentacrythritOl tetranitrate (petn)
cyclotrimethylenetrinitramine.
Over the core of the explosive there is preferably
- 10 disposed a plastic film. Generally, this plastic film
has a thickness of 0.03 to 0.05 mm, preferably 0,035 to
0,04 mm. Films which can be used for this purpose include
films of the following polymers: polyolefins, vinyl polymers,
polyamides, polyimides, polyester, polyacetals, polyepoxides,
polycarbonates, etc., as well as copolymers, terpolymers,
other condensation and/or addition polymers of other thermo-
plastic and thermosetting resins, to name a few.
Preferably disposed over the plastic film is a
layer or layers of a textile material. The textile material
can be woven or non-woven, knitted or non-knitted. It
generally has a thickness of 3.0 to 15.0 mm, and such
thickness can be obtained from
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1 a singly ply or by building up layers of textile material.
3 The textile material can be from natural or synthetic
fibers. Contemplated natural fibers are cotton, wool,
rayon, silk, hemp, jute, and the like. Contemplated syn-
6 thetic fibers include polyolefins, polyvinyls, nylon, poly-
7 esters, polyacrylates, polyacrylonitriles, etc.
9 The heart of the invention lies, of course, in pro-
viding at least one air channel in the covering over the
11 explosive core. This can be provided in any number of ways,
12 such as by suitable extrusion of a coating over the core
13 material so that at least one and preferably a plurality
14 of longitudinally running tubes is disposed in the core
covering. Thus, these longitudinal tubes can be present
16 in a single covering. Alternatively, longitudinally run-
17 ning tubes can be provided in the explosive core covering
18 by disposing a plurality of coatings thereon such that a
19 subsequently applied coating does not adhere entirely to
all points o a previously applied coating. This can be
21 ensured by regulation of t'ne shape of the coating (extrud-
22 ate) of the earlier applied material so that the subsequently
23 applied coating (extrudate) cannot engage all points of
24 the earlier applied coating (extrudate). For instance,
the initially applied extrudate can be in the form of a
26 jacket having a star-shaped cross section. The subse-
quently applied jacket can engage only the points so as to
28 leave at least one air channel running longitudinally.
29 The air channel itself can have any of a ~ide variety of
cross-sectional configurations. The air channel can
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circumscribe the explosive core or there can be segments
of air channels disposed about such core. For instance,
with reference to the star-shaped first jacket, if the
second jacket abuts the nadirs between the star points of
the first jacket, there will not be a single air channel
about the core of fluted configuration, but rather a plu-
rality of air channels lying at different places about
the core's circumference.
The air channels themselves can have a lateral
dimension regarded the facing surfaces of the 2 following
jeckets between 0.01 and 1.0 mm, preferably between OtO6
and 0.10 mm.
It will be appreciated that the air channels can
be made using jackets of the same or different compositions.
Compositions contemplated for use in defining the walls of
the air channels include: polypropylene, polyvinychloride
polyolefines and other thermoplastic material.
Preferably, the exterior walls of a first jacket
are coated at least partially with a dust coating of an inert
material. Such an inert material can be: halides, sulfate9,
bicarbonates and/or carbonates of alkali and/or alkaline
earth metals, corresponding ammonium salts, alkaline earth
oxides, oxides of metals of the Fourth to Sixth Group of
the Periodic Table, as well as perhalogenated hydrocarbons,
such as hexachloethane, for example, can be used to special
advantage for the dusting of the jackets and for the phleg-
matization, if desired, of the explosive in the core.
Especially preferred as the inert, flame-aooling and flame-
stopping substance is cryolite.
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It is especially advantageous for the air spaces to
2 form a star-shaped crown disposed at a distance from the
core. This can be brought about, for example, by providing
the core first with an outer fluted jacket, for example by
6 the extrusion of a plastic, and then to dust the jacket
with the inert, flame-cooling and flame-stopping substances,
whereupon the second jacket is built up around the first
dusted jacket, forming the air spaces by the extrusion
9 again of a plastic, for example, the instantaneous fuse of
the invention being obtained in final form in this manner.
11
12 Extrudable plastics, primarily, have proven to be
13 satisfactory substances for the jackets enclosing the air
14 spaces and covering the core, namely plastics suitable for
the application which can be easily selected at any time by
16 the technically skilled person, examples being polyvinyl
17 chloride and polyolefins; polyvinyl chloride, however, is
8 preferred.
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The inert, flame-cooling and flame-stopping substances
21 used in the jackets can be identical to the substances which
22 are used for the phlegmatization of the explosive in instan-
23 taneous safety fuses. A great number of suitable substances
24 are available for this purpose, and halides, sulfates,
bicarbonates and/or carbonates of alkali and/or alkaline
27 earth metals, corresponding ammonium salts, alkaline earth
oxides, oxides of metals of the Fourth to Sixth Group of
28 the Periodic Table, as well as perhalogenated hydrocarbons,
29 such as hexachloroethane, for example, can be used to special
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1 advantage for the dusting of the jackets and for the phleg-
2 matization, if desired, o the explosive in the core.
3 -Especially preferred as the inert, flame-cooling and flame-
4 stopping substance is cryolite.
6 It is also possible in accordance with the invention to
7 mix these just-mentioned inert substances directly into the
8 jacketing substances before the extruding operation, and
then incorporate them as additional inert, flame-cooling and
flame-stopping fillers into the jacketing of the fuse in the
11 extruding process.
12
13 Furthermore, in special cases it may be advantageous to
impregnate the fiber wrapping about the explosive core with
flame-retardant liqui~s to counteract any fl~ming.
16
17 The instantaneous safety fuses of the invention have
18 considerable advantages in practical application over the
19 known instantaneous fuses. They largely, or even com-
pletely, eliminate smoldering and burning of fragments
21 dispersed upon thq detonation of the fuse. Thus, they
22 also prevent the ignltion of materials in the blast area
23 which might easily burn or smolder.
24
BRIEF DESCRIPTION OF DRAWINGS
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26
27 Referring to the apended drawing, there is shown a
Z8 magnified cross-sectional diagram of an instantaneous
29 safety fuse according to a preferred mode of the invention.
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1 ¦ DESCRIPTION OF SPECIFIC EMBODI~ENT
2 I
3 ¦ Referring to the embodiment depicted in the accompa-
4 ¦ nying drawing, a hollow tube 1 is surrounded by an explosive
5 ¦ core 2 of nitropenta, which in turn is enclosed in a poly-
6 ¦ propylene film 3 over which are disposed threads 4 of natu-
7 ¦ ral or synthetic materials spun thereabout. The core
8 ¦ (1,2,3,4) formed from these components is, in turn, enclosed
¦ or enveloped in a first jacket 5 of polyvinyl chloride.
10 I This first jacket 5 has a star shape. Disposed thereabout
11 ¦ is a second or outer jacket 7 which abuts the star shaped
12 jacket only at the points of the star. Thus, between the
13 jackets there is enclosed an air,space 8 which itself has
14 a star-shaped crown. On the outside of the first jacket
is the dust coating 6 of inert material.
16
17 In order to more fully illustrate the nature of the
18 invention and the manner of practicing the same, the fol-
19 lowing examples are presented:
21 Example 1
22
23 An instantaneous fuse in açcordance with Figure 1 was
24 prepared, in which the explosive core consisted of 20 grams
per linear meter of pentaerythritol tetranitrate, and was
26 wrapped in a polypropylene ribbon 22 mm wide. One layer of
27 rayon threads and two additional layers of synthetic thread
28 were spun around this core. Around this composite core a
29 first jacket o star-shaped cross section of a thickness
correspon g to ~ to 20 gram- per linear meter was place2.
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1 After this first jacket had been dusted with talc, a second
2 jacket was extruded around it, which had no fluting. This
3 second jacket had a thickness corresponding to 30 to 32
4 grams per linear meter.
6 This instantaneous fuse was laid on dry grass and
7 detonated electrically. In none of the test shots performed
8 did any burning or smoldering of the grass ensue.
' 9
Additional shots were then performed under more dif-
11 ficult conditions. A test arrangement specially developed
12 for this purpose was used, in which a fine wood wool or
13 excelsior, which had been dried for 6 days at a constant
14 temperature of 38C was employed. To add to the severity of
the test conditions, the excelsior was dusted with an easily
16 flammable pyrotechnical priming composition. The instan-
17 taneous fuse to be tested was laid in the excelsior thus
18 prepared. After it had been detonated with an electrical
igniter, it was found that none of the test shots performed
resulted in any burning or smoldering of the excelsior.
22
23
24 Example 2
26 An instantaneous fuse was produced as in Example 1,
2 except that the explosive inner core consisted of a mixture
8 of pentaerythritol tetranitrate (PETN) and cryolite. The
29 ratio of admixture was 92 : 8 and the fill weight was 4
grams per linear meter. The explosive was wrapped in a fiLm
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1 ¦ tape in the customary manner with the aid of transport
2 threads. In the center of the explosive inner core thus
3 formed was a hollow tube of 2.5 mm diameter.
Three layers of filaments were spun around the continu-
, 6 ous core formed with the film tape. This "raw instantaneous
7 fuse" was provided with a first jacket by the extrusion of
8 a soft PVC, which had a star-shaped cross section and was -
9 powdered with talc. The jacket weight varied between 10 and
11 grams per linear meter. Then the second PVC jacket was
11 applied, also by the extrusion method. The weight of the
12 latter jacket was between 17 and 18.5 grams per linear
13 meter.
14
; This special instantaneous fuse was subjected to a
16 firing in a chamber containing firedamp atmosphere (air +
17 8.5 percent methane) on test grounds. Even in test arrange-
18 ments involving more stringent conditions, no ignition of
19 firedamp could be produced.
23
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27
28
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