Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02061409 2000-11-14
1 N 36209
p~~rotechnia Delay Composition Comprising Silicon and Ferric Oxide
This invention relates to a novel pyrotechnic delay composition
characterised by uniform burn rate, moisture resistance and low
toxicity and to ignition delay elements or devices containing
the said composition. The composition is useful in the range of
intermediate to slow-burning delay period. This is considered
to mean a burning time period of from about 400 to about 3200
milliseconds per centimetre length of the delay element. With
respect to electrically initiated systems, the delay time is
regarded as the time between application of the initiating
electric impulse to the pyrotechnic.composition of the delay
element and the subsequent detonation of the explosive charge of
an associated detonator.
Delayed action detonators, both non-electric and electric
are widely employed in mining, quarrying and other blasting
operations in order to permit sequential initiation of explosive
charges in a pattern of boreholes. Delay or sequential
initiation of shotholes is effective in controlling tie
fragmentation and throw of the rock being blasted and in
addition provides a reduction in ground vibration and in
airblast noise.
Modern commercial delay detonators, whether non-electric
or electric, comprise a metallic shell closed at one end which
shell contains in sequence from the closed end a base charge of
a detonating high explosive, such as for example, PETN and an
above adjacent, primer charge of a heat-sensitive detonable
material, such as for example, lead azide. Adjacent the
heat-sensitive material is an amount of deflagrating or burning
composition of sufficient quantity to provide a desired delay
time in the manner of a fuse. Above the delay composition is an
ignition charge adapted to be ignited by an electrically heated
bridge wire, or alternatively, by the heat and flame of a low
energy detonating cord or shock wave conductor retained in the
open end of the metallic shell. Such a delay detonator may
serve as an in-line delay as when coupled to a detonating cord
or shock wave conductor. However, a delay device need not also
CA 02061409 2000-11-14
2
be capable of serving as a detonator in order, for example, to
initiate a shock wave conductor. An ignition charge in close
proximity to the end of the shock wave conductor instead of a
base charge of detonating high explosive, will suffice.
A large number of burning delay compositions comprising
mixtures of fuels and oxidisers are known in the art. Many are
substantially gasless compositions; that is, they burn without
evolving large amounts of gaseous by-products which would
interfere with the functioning of a delay detonator. In addition
to an essential gasless requirement, delay compositions are also
required to be safe to handle, from both an explosive and health
viewpoint, they must be resistant to moisture and not deteriorate
over periods of storage and hence change in burning
characteristics, and they must be adaptable for use in a wide
range of delay units within the limitations of space available
inside a standard detonator shell. The numerous delay
compositions of the prior art have met with varying degrees of
success in use and application.
One such prior class of delay composition which has been
well-received is that described in GB-2 089 336,
which composition comprises silicon and
barium sulphate and optionally includes a proportion of red lead
oxide. The present invention also relates to silicon/oxidant
delay compositions and to delay devices and detonators containing
a column of such a composition. Although the delay composition
could be loaded directly into a detonator casing, it is
customary for the composition to be contained in an open-ended
tubular metal element e.g. a drawn lead element which is snugly
fitted into the detonator shell.
There is a desire in the explosive industry to phase out
all needless use.. of lead either as the metal (e. g. drawn-lead
elements) or as compounds in delay composition, e.g. red lead
oxide as described above. The alternatives to drawn-lead tubular
containment of delay compositions are drawn elements of another
metal, such as aluminium, and the so-called rigid element. A
rigid element is a pre-formed tube of the required dimensions
CA 02061409 2000-11-14
3
made of a metal such as zinc, which does not present an
environmental problem, into which the desired particulate
mixture of delay composition ingredients is pressed to provide
delay elements which afford the desired delay period.
An object of this invention is to provide further delay
compositions and delay devices containing same for use in
ignition delay trains. A further object is to provide a delay
composition which burns at a reproducible speed when compacted
in rigid metal elements.
Accordingly this invention provides a pyrotechnic delay
composition for use in delay devices or detonators comprising
from about 20 to 40~ particulate silicon (by mass), preferably
from about 25 to about 35~, with the balance being particulate
ferric oxide. The silicon ferric oxide (Si/Fe203) composition
preferably comprises silicon and ferric oxide in a ratio of
40:60 to 60:40 by volume a substantially 50:50 mixture by volume
being the most preferred. The advantage of such a composition
is that being essentially a binary system, it provides for more
reliable mixing especially if utilising a composition~based on
about 30~ (by mass) Si with about 70~ (by mass) Fe203 which
generally achieves the preferred 50:50 mixture by volume. This
is a~very desirable ratio from a mixing/particle packing point
of view, which is very important considering the method of
loading the delay devices and detonators used in the art. Other
advantages are that ferric oxide is, of course~insoluble in
water and should be storage stable against moisture in the locus
of storage or arising from environmental conditions. The
Si/Fe203 mixture is considered to be of the lowest possible
toxicity in comparison with commercially available compositions
such as those containing dichromates. It also appears to be
very safe when tested by typical impact, friction and static
tests (c.f. GB-A-2 089 336) and its ignition temperature appears
to be in the region of 1000°C.
The silicon preferably has a specific surface of 5 to
6m2/g and the ferric oxide preferably has a specific surface of
3 to 5m2/g .
2~~~~~9
The invention also includes an ignition delay element
comprising the above mentioned pyrotechnic delay composition and
a delay device or a detonator comprising the said ignition delay
element or the said composition. From a further aspect the
invention consists in the use of a composition comprising 20 to
40$ by mass of silicon, the balance being ferric oxide as the
delay burning composition providing a delay period in the
ignition train of a delayed action ignition device or detonator.
The invention is further illustrated by the following examples.
The compositions described in the Examples were formulated
from. particulate silicon having a specific surface of 5.4m2g-1
and ferric oxide having a specific surface of 4.3m2g-1. The
ingredients were mixed as an aqueous slurry, dried, and sieved
to obtain a relatively free-flowing powder which was
15 subsequently consolidated to a density of about 2.5g/cm3 in an
open-ended tubular zinc element of internal diameter 3.1mm and
outside diameter of 6.4mm.
Example 1
A delay composition containing silicon and ferric oxide in the
mass ratio 30:70 was prepared and consolidated in a 22mm long
zinc element as described above. The delay element was encased
in a delay detonator containing a high explosive base charge
which was capable of being initiated to detonation by the delay
composition. The delay composition was ignited at the end
remote from the high explosive base charge by means of an
electric fusehead. A sample of 20 such detonators were prepared
and fired successfully with a mean delay time of 3.583 ~ 0.031
seconds i.e. a~delay burning rate of 6.15mm/s.
2t~~~ZV9
Example 2
Delay detonators similar to those of Example 1 except that a
fast burning incendiary sealer composition consisting of 62~ by
weight of lead dioxide and 38~ silicon was consolidated in a 2mm
length at the end of the zinc element adjacent to the initiator
means and the initiation means was a length of shock wave
conductor tube (~EXEL, Registered Trade Mark). A sample of 20
detonators fired with a mean decay time of 3.329 ~ 0.071 seconds
i.e. a burning rate of 6.01 mm/s.
Example 3
Detonators were prepared as described in Example 2 except that
the zinc element was lOmm long and contained an 8mm length of
delay composition and 2mm length of the fast burning incendiary
composition sealing the end adjacent to the shock wave conductor
tube.
A sample of 20 detonators initiated with a length of EXEL tube
fired with a mean delay time of 806 ~ 23 milliseconds i.e. a
burning rate of 9.9 mm/s.
Example 4
Detonators were prepared as described in Example 3, except that
the delay composition contained silicon and ferric oxide in the
. mass ratio of 25 . 75. The detonators fired with a mean delay
time of 1.100 t 0.036 seconds i.e. a delay burning rate of
7.28mm/s.
Example 5
Detonators were prepared as described in Example 3, except that
the delay composition contained silicon and ferric oxide in the
mass ratio of 15:85: The detonators fired with a mean delay
time of 2.342 ~ 0.204 seconds i.e. a delay burning rate of
3 . 4 lnun/ s .
2C'~~.'~v9
Example 6
Detonators were prepared as described in Example 3, except that
the delay composition contained silicon and ferric oxide in the
mass ratio of 35:65. The detonators fired with an average delay
time of 1.067 ~ 0.245 seconds i.e. a delay burning rate of
7.5mm/s.
The Examples show that the delay compositions of this invention
burn at a reproducible speed with low variation between samples
for a given physical arrangement and initiation system.
