Note: Descriptions are shown in the official language in which they were submitted.
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FLARES HAVING tGNITERS FORMED FROM
FJCTRUDABLE IGNITER COMPOSITIONS
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to extrudable igniter
compositions, and extruded ignition sticks therefrom, in combination
with flares or other solid propellant devices, such as rockets or the
like.
2. Background Information
Igniter compositions ought to satisfy a number of design
criteria. The igniter composition, when formed, should be sufficiently
robust to remain in operable form prior to deployment of the device to
be ignited, such as a flare or other device.
One of the commonly proposed igniter systems uses solid
particles consisting of B/KNOs which, when ignited, initiate
combustion of the specified gas generant composition.
Other recent efforts in the civilian market have focused on
developing alternative cost-effective igniter compositions or igniter
compositions which are more easily manufactured. These efforts
have included proposals to use a hot-melt thermoplastic resin matrix
together with a particular igniter composition, such as KNOB. This
effort sought to marry a commercially available hot melt adhesive,
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1~V0 99111587 . PCT/US98/15064
such as one designed for so-called "glue-guns", with a common alkali
metal oxidizer. This effort to improve performance was less than
satisfactory. Extrudability and igniter performance proved difficult to
control, and the repeatable ballistic performance desired has not yet
been demonstrated.
Accordingly, despite these and still other efforts, relevant
objectives remain unattained. A simpler, more cost-effective igniter
composition for flares and decoys or other devices remains desired.
In particular, efforts are still on-going towards providing an igniter
composition which avoids the need for hot melting so-called
adhesives, and thus the consequent risks associated with processing
a pyrotechnic material at an elevated temperature, but which is facile
to manufacture and would be sufficiently robust.
It would, therefore, be a significant advance to provide igniter
compositions capable of being used as an igniter which satisfactorily
address these concerns in the industry.
SUMMARY AND OBJECTS OF THE PRESENT INVENTION
The present invention offers flares, solid propellant rockets,
decoy devices and the like incorporating one or more of the herein
disclosed igniter sticks.
The extrudable igniter is readily manufactured at low cost to
obtain a physically robust product. The igniter can be manufactured
without the use of a thermoplastic melt or hot-melt mixing equipment,
and thus avoids the potential hazards associated with processing at
such elevated temperatures. The extrudable igniter composition from
which the igniter stick can be formed is suitably processed at ambient
temperatures into robust products which have sufficiently relatively
selectable ignition characteristics. The igniter stick can have other
configurations, provided the configuration is consistent with the
objectives herein disclosed. The extrudable igniter composition can
be used to form a solid or hollow igniter "stick" capable of igniting a
flare or propellant composition in a flare or other pyrotechnic device.
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BRIEF DESCRIPTION OF THE DRAWING
Figure 1 illustrates an exemplary flare device (a XM212 type
flare) in longitudinal cross-section which includes an igniter stick
fom~ed from the extrudable igniter composition.
Figures 2, 3, 4 and 5 illustrate diameter cross-sectional views
of flares provided with igniter sticks fabricated from the disclosed
extrudable igniter composition.
DETAILED DESCRIPTION OF THE INVENTION
The extruded igniter sticks can be characterized as having a
configuration designed for rapid deflagration at a high temperature
upon ignition. Upon ignition an igniter stick is capable of igniting
another pyrotechnic composition. In flares, such as the XM212 flare,
the igniter sticks are sized to be capable of complete end to end
ignition, e.g., complete flame transition, in a short time, such as less
than 10 miiiseconds.
The igniter compositions which are capable of being extruded
are characterized as being obtainable from a combination of a binder,
water-soluble or dispersable oxidizing agent, water-soluble or
dispersable fuel, and a selected amount of water. By preference, the
extrudable compositions are essentially compositionally
homogeneous.
The binder is, by present preference, a water-soluble binder,
although water-swellable binder materials are not excluded provided
that the remaining solid constituents of the igniter are at least
substantially sufficiently homogeneously distributable therein. Typical
binders used in the present igniter composition include, by way of
example, water-soluble binders such as poly-N-vinyl pyrolidone,
polyvinyl alcohols and coplymers thereof, polyacryiamide, sodium
polyacryiates, copolymers based on acrylamide or sodium acrylate,
gums, and gelatin. These water soluble binders include naturally
occurring gums, such as guar gum, acacia gum, modified celluloses
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WO 99/11587 PCT/US98/15064
and starches. A detailed discussion of "gums" is provided by C.L.
Mantell; The Water-Soluble Gums, Reinhold Publishing Corp., 1947,
It is presently considered that the water-soluble
binders improve mechanical properties or
provide enhanced crush strength. Although water immiscible binders
can be used in the present invention, it is currently preferred to use
water soluble binders in combination with fuels and/or oxidizers
suitable for use in formulating an igniter. The suitable fuels and
oxidizers can be water soluble or water insoluble. Suitable fuels and
oxidizers can be inorganic or organic.
In the formulation from which the extrudate igniter stick is
formed, the binder concentration is such that a sufficiently
mechanically robust extrudate is obtained. The extnrdate, such as an
igniter stick, should be capable of retaining its shape, e.g. maintaining
its integrity, prior to ignition. By preference, the extruded igniter stick
is capable of being received (inserted) in a pyrotechnic composition,
e.g. a suitably configured bore (e.g. central bore) in a propellant
composition, and of shattering or fracturing when ignited. In general,
the binder can be in a range of, for example, of about 2 % by weight
to about 10 % by weight, and more particularly about 3% by weight to
about 7% by weight, relative to the dry ingredients in the formulation.
The binder can be comprised of more than one binder material.
The igniter composition includes at least one oxidizer, which is
preferably water soluble or at least water dispersable. The oxidizer
can therefore be organic or inorganic, although inorganic oxidizers are
presently preferred. Organic oxidizers which are dispersable in a
binder so that a sufficiently homogeneous igniter composition is
obtainable include amine nitrate salts, vitro compounds, nitramine,
nitrate esters, and amine perchlorates, of which methyl ammonium
nitrate, methyl ammonium perchlorate are are exemplary. Other
canditates include RDX and HMX, CL-20 and PETN. Inorganic
oxidizers include oxidizing ionic species such as nitrates, nitrites,
chlorates, perchlorates, peroxides, and superoxides. Typifying these
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inorganic oxidizers are metal nitrates such as potassium nitrate or
strontium nitrate, ammonium nitrate, metal perchlorates such as
potassium perchlorate, and metal peroxides such as strontium
peroxide. In general, the oxidizer is ordinarily present in an amount
effective to ensure oxidation of at least the fuel in the igniter and can
be in a range af, for example, of about 40% by weight to about 90%
by weight, and more particularly about 70% by weight to about 85%
by weight, relative to the dry ingredients in the formulation.
The igniter composition can be formulated with an additional
fuel, assuming that the binder may be capable of functioning as a
secondary, not primary, fuel for the igniter composition. These
additional fuels include powdered metals, such as powdered
aluminum, zirconium, magnesium and/or titanium, among others;
metal hydrides such as zirconium or titanium hydride; and so-called
metalloids, such as silicon and boron which are capable of being
sufficiently "dispensable" in the binder. Water-soluble or water-
dispersable fuels include, e.g., guanidine nitrate, cyano compounds,
nitramines (RDX andlor HMX), CL-20, tetranitrocarbazoles, organic
vitro compounds, and may, if desired, be "mufti-modal° in particle size
distribution. Water dispensable materials can be added in
substantially even particle size distribution or in mufti-modal
distributions depending on the ignition characteristics desired.
Water dispensable fuels are, by present preference, used in
fine particulate form, such as powder or ground to sufficient fine
particles, to ensure adequate distribution during the manufacturing
process. By preference, an at least substantially even distribution in
the resultant extrudable igniter composition is desired. In general, the
fuel is in pulverulent form, such as 100 p, or less, such as, for
example, from about 1 ~. to 30p,. Metals in powder form may have, if
desired, a smaller particle size range, such as from about 1 to 20p., or
even smaller such as 1 to about 5p,. The amount of fuel -- other than
the binder -- can be in a range of, for example, of about 5 to about
30% by weight, and more particularly about 10% by weight to about
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20% by weight, relative to the dry ingredients in the formulation.
The present igniter sticks can incorporate, if desired, a
reinforcement. Suitable reinforcement can be achieved with fibers,
such as combustible fibers, which serve to both strengthen the
extruded igniter stick, and, upon appropriate selection of the
reinforcement, can improve ingiter performance. The present igniter
sticks and related grains can incorporate, if desired, a reinforcement.
Suitable reinforcement can be achieved with fibers, such as
combustible fibers, which can serve to both strengthen the extruded
igniter stick, and, upon appropriate selection of the reinforcement,
improve igniter performance. The fibers are preferably generally
shorter in length (low aspect ratio). Fibers incorporated into
extrudable igniter formulations include, for instance, poiyolefin fibers,
polyamide fibers, polyester fibers and poly (2,2-(m-phenylene)-5,5-
bisbenzimidazole ("PBI") fibers. Polyolefin fibers include polyethylene
("PE") fibers, such as PE fibers having an outer diameter of about
0.005 mm and higher, such as to about 0.8 mm, and a length in a
range of 0.1 mm to about 3.2 mm, of which the Spectra 900 brand of
polyethylene fiber from Allied-Signal is illustrative. Suitable polyamide
fibers, such as Nylon 6 fibers, can have a suitably selected diameter,
such as 19 microns, and a length of 1.5 mm to about 6.4 mm.
Suitable polyester fibers include high tenacity polyester fibers having
lengths of about 1.5 mm to about 6.4 mm, and a suitable diameter of
about 25 microns. PBI fibers include those having lengths on the
order of 0.8 mm to 3.2 mm. Representative reinforced igniter sticks
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and the formulations therefor are reported in the Examples.
The present composition in extrudable form is readily
obtainable, for instance, by mixing binder, fuel, oxidizer and the
selected amount of water for such a period of time to achieve an at
least substantially even distribution of the fuel, if used, and oxidizer
throughout the binder. One method involves mixing a water-soluble
binder and a selected amount of water to form a pre-mix, and
admixing the pre-mix with (a) first the fuel and then the oxidizer, or (b)
the oxidizer and then the fuel, or (c) a combination of the oxidizer and
fuel. The amount of water is generally such that the resultant product
has a consistency which is extrudable, but, by preference, is not
runny. In principle greater amounts of water can be used but some
manufacturing concerns may arise, including an increase in waste
water laden with varying amounts of pyrotechnic species (fuel,
oxidizer etc.).
The igniter composition thus formed is capable of being
extruded to the desired physical geometry.
The igniter sticks can be used in combination with solid
propellant rockets or other apparatus which require ignition of solid
propellant. Other apparatus includes, without limitation, flares.
Among the suitable flares are those known to those skilled in the art
as thrusted flares of which the MJU-10 flare is exemplary. Other
flares such as M-206 flares (which may or may not be spectrally
matched) or a near IR flare, such as a M-278 type flare, are also
suitably combined with one or more igniter sticks. The suitable flares
are not restricted to the aforementioned MJU-10, M-206 or M-278
flares. For instance, a so-called standard 2.75 inch (cross-section
diameter) flare, including visible illuminating flares, are suitably
provided with at least one igniter stick. Non-commercial flare variants
of the standard flare, such as the M-257 type flare, are also suitably
provided with one or more igniter sticks. Advantagesously, the igniter
stick decreases the costs, decreases the fabrication time, and
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simplifies the design of flares, including the ignition system for a
thrusted flare such as the MJU-10 flare. Ign'tter sticks can be used in
a great number of decoy devices which include decoy flares which
are deployed to defend against an incoming threats, and particularly
against heat-seeking missiles. The igniter sticks) improve the
reliability of flare ignition by decreasing out-of-place first fire, and the
safety of manufacturing flares by eliminating the use of flammable
solvents commonly used when applying traditional first fires. Suitable
flares and/or flare compositions for combination with at least one
igniter stick are described in Encyiopedia of Chemical Technology,
20:680-697 (4th ed, 1996), including the references cited therein.
The igniter sticks can be used with larger sized solid propellant
launch vehicles, such as solid propellant rockets. In these larger
more complex systems, the igniter stick can be used as part of an
ignition system, e.g., as a starter in the pyrotechnic train to propagate
or initiate propagation of ignition. Solid propellant rockets which can
be equipped with at least one igniter stick as at least part of the
ignition system include those described in Solid Rocket Proalsion
Technolocay (Pergamon Press, 1 st Edition 1993) and Rocket
Propulsion Elements (lNiley Interscience, 4th Edition 1976) ,
The well-known Jane's Handbook describes flares and other solid
propellant devices suitably used in combination with the igniter sticks.
Extrusion and extruders are described generally in
Encyclopedia of Polymer Science and Engineering, 16:570-631 (2nd
Edition 1996), including references cited therein,
Fgure 1 illustrates, in cross-section, a type of flare known as a
XM212 flare. In the longitudinal cross section view, the casing is a
suitable pressure enclosure fabricated from steel or other material
capable of being used for a flare application. The cartridge case 18
can have a vented housing 17. One closed end is defined by the
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forward closure 19. The opposing end of the XM212 flare includes an
aft closure i 2, spacers 13, an ignition system with igniter i 5,
protective cap 10 and a piston 11. In a preferred embodiment, a
solidified (extruded) igniter stick 16, which may be solid or hollow,
extends lengthwise (completely or partially) through the propellant
grain as shown in Figure 1. The igniter stick can be formed by
extruding the hereinabove described exttudable igniter composition,
allowing the extrudate to solidify, and inserting it into the propellant
grain (preferably before its cured.) A selected propellant composition
14 surrounds the igniter stick. A so-called rapid deflagration cord, if
desired, can be disposed lengthwise, e.g., such as loosely sleeved,
within a hollow igniter stick. Although not illustrated, more than one
igniter stick can; if desired, be used.
Cross-sectional "diameter' views of flare casings with
propellant and igniter sticks are shown in Figures 2-5. In the diameter
cross-sectional view of Figure 2, the flare case 28 can, if desin~d,
have a foam layer 22 (e.g. a foamed nitrocellulose liner) sprayed on
its interior surface before propellant 24 is loaded. A center bore
having a pre-selected geometry 26 sleeves a hollow igniter stick 20
(in end view such as quargum binder/B/KNOa).
In the diameter cross-sectional view of Figure 3, the flare case
38 has been loaded with propellant 34 and provided with a centrally
positioned hollow igniter stick 36. Optionally, additional solid or hollow
igniter sticks 32 can be provided.
!n the diameter cross-sectional view of Figure 4, flare case 48
is loaded with propellant 44, and a centrally positioned shaped bore of
pre-selected geometry. The centrally positioned bore may have an
igniter stick 42 with igniter sticks 46 (in strip form) disposed radially in
the slots from the bore. The igniter sticks are fitted within the slots,
r and preferably are not loosly fitted.
In the diameter cross-sectional view of Figure 5, the flare case
58 is shown loaded with propellant 54 and a centrally positioned
igniter stick 56 having multiple axial bores therein.
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The igniter stick can, if desired, be fitted with a peelable
glove/sleeve prior to its insertion into the propellant grain. This can
protect an igniter stick during the manufacturing process or during
storage before use.
The ignitor sticks are preferably inserted into the propellant
grain before the latter is cured.
The invention is further described with reference to the
following non-limiting Examples.
Examales
Examale 1
To a one gallon Baker-Perkins planetary mixer, 1170 g (78%)
of 35 micron potassium nitrate and 105 g (7%) of Cytec Cyaname~N
300 brand ,polyacryiamide (15 million MW) were added. These
ingredients were then blended remotely in the dry state for one
minute. To this blend, 217.5 g (14.5 parts per 100 of igniter
formulation) of water were added and mixed for five minutes. The mix
blades and inner surface of the mix bowl were scraped with Velostat
(conductive plastic) spatulas followed by 15 additional minutes of
mixing. To the resulting thick white paste, 225 g (15%) of amorphous
boron powder (90-92% purity) were added and mixed remotely for
five minutes. While wearing approved protective clothing, the blades
and bowl were again "scraped down" manually and the formulation
was mixed for ten additional minutes. The resulting brown, dough-like
material was granulated to -4 mesh and fed into a Haake 25 mm
single-screw extruder. The igniter formulation was extruded through a
12 point star die with a maximum diameter of 0.33" and a minimum
r
diameter of 0.30". The die included a central 0.080° diameter pin,
thus producing a hollow rod-like configuration. The extruded igniter
formulation was cut into 7" lengths. Before drying, a 7.5° length of
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WQ 99/11587 PCT/US98/15064
0.07" diameter. Teledyne RDC (rapidly deflagrating cord) was
inserted into the 0.08" diameter perforation. The igniter sticks were
dried at 165°F overnight. The igniter sticks were tested to evaluate
their performance as an igniter in an inflator which was designed for
passenger side automotive safety bags. The igniter sticks pertormed
satisfactorily.
Example 2
A series of extruded igniter stick formulations containing boron,
potassium nitrate, a water-soluble binder, and optionally, fibers for
reinforcement were prepared. These formulations are reported in
Table I. The formulations were first mixed on a 10 g and then a 30 g
scale to determine their sensitivity towards stimuli including impact,
friction, electrostatic discharge, and heat (Table II). In general,
carbohydrate-based binders exhibited the greatest sensitivity with
respect to ABL friction. Formulations containing methyl cellulose,
guar gum, and locust bean gum as the binder were also used to
prepare igniter sticks.
The remaining formulations were mixed on a 325 g scale in a
one pint Baker-Perkins planetary mixer. Potassium nitrate and the
respective water-soluble binder were blended remotely in the dry
state for one minute. To this blend, the respective amount of water
(Table lll) was added and the slurry was mixed for five minutes. As in
Example 1, the bowl and blades were "scraped down". At this point,
fibers were added to fiber-containing formulations and the dough was
mixed for an additional 5 minutes. Alt formulations were mixed for 10
additional minutes before adding boron. One half of the boron was
added at this point followed by five minutes of mixing. The rest of the
boron was then added followed by an additional five minutes of
mixing. After a final "scrape down", the formulation was mixed for an
additional ten minutes. The resulting brown, dough-like material was
granulated to -4 mesh and fed into a Haake 25 mm single-screw
extruder. The igniter formulation was extruded through a 12 point star
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WO 99/11587 PCTIUS98/15064
die with a maximum diameter of 0.33" and a minimum diameter of
0.305". The die included a centrally located 0.80" diameter pin. The
extruded igniter formulation was cut into 7" lengths. Before drying, a
7.5" length of 0.07" diameter. Teledyne RDC (rapidly deflagrating
cord) was inserted. Ten additional 2" lengths were extruded. The
igniter sticks were dried at 165 F overnight.
Important factors in determining useful formulation include
quality of the grain after drying, actual performance as an igniter,
and drying rate. Leaching of a mixture of KNOa and binder to the
surface of the grain may occur for some formulations during drying.
Leaching in tha perforation is not desired. Leaching was found to
be least important in formulations containing tragacanth gum,
Cyanamer~ A-370 and Cyanamer~ P-21 (Table III). Igniter sticks
from the formulations containing Cyanamer~ A-370 and Cyanamer~l
P-21 were evaluated in content with an inflator device. Relative
drying rates of 10 : 1.7 : 1 were calculated for formulations
containing Cyanamer~ N-300, Cyanamer~ P-21 and Cyanamer~ A-
370, respectively. Thus, the formulation containing Cyanamer~ A-
370 was shown to dry quickly, with minimal KNOB leaching
producing a grain that ignites gas generant with minimal ignition
delays.
It is important to develop an extruded igniter stick for flares and
other solid propellant devices that will withstand decades of jolts and
vibrations while in senrice prior to deployment. Thus, a durability test
method was developed for the extruded igniter sticks. Durability tests
were performed in 3-point bending, with the load applied at mid-span.
Bending was selected since tensile, compressive, and shear stresses
are all present. Also, the sample configuration lends itself to this type
of loading, A span of 1.5 inches was used, with the loads applied
using 1/8- to '/a-inch diameter dowel pins. A nominal pre-load of 0.7
pounds was applied. The sample was then subjected to 1,000
loading cycles with the following conditions: cyclic amplitude 0.003
inch, frequency 10 Hertz. After the cyclic loading, the samples were
-12-
CA 02302359 2000-03-02
1~V0 99/11587 PCT/US98/1506a
tested to failure at a displacement rate of 0.2 inches per minute. The
durability of each sample is reported as the area under the load-
displacement curve. For simplicity, the units are maintained as
calibrated (load in pounds-force, displacement in miili-inches).
Therefore, the reported durability has units of milii-inch-pounds. All
testing was performed at lab ambient temperature (75° t 5°F~.
Durability test results indicated enhanced durability of extruded igniter
formulations containing fibers, e.g., formulation #13 and #15 in Table
-13-
CA 02302359 2000-03-02
WO 99111587 PCTIUS98/15064
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CA 02302359 2000-03-02
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CA 02302359 2000-03-02
'WO 99!11587 PCT/US98/15064
Example 3
A series of igniters containing fibers were formulated with the
goal of enhancing durability of the extruded igniter sticks as seen from
Table IV. All formulations exhibited favorable safety characteristics.
Samples (325 g) of each formulation were mixed in a Baker-Perkins
pint mixer with 13.5 parts/100 of water. After dry blending the KNOB
and Cyanamer~ A-370 for one minute, the water was added followed
by five minutes of mixing. The fiber was then added in two
increments and the boron in three increments with three minutes of
mixing after each addition. After a final "scrape down", the
formulation was mixed for an additional ten minutes. The resulting
brown, dough-like material was granulated to -4 mesh and fed into a
Haake 25 mm singla-screw extruder. The igniter formulation was
extruded through a 12 point star die with a maximum diameter of
0.33" and a minimum diameter of 0.305". The die included a centrally
located 0.15" diameter pin. The extruded igniter formulation was cut
into 7" lengths. Ten additional 2" lengths were extruded. The igniter
sticks were dried at 1 fi5 F overnight.
There were no signs of KN03/binder leaching outside of the
igniter grains after drying. Grains were ignited with the ignition plume
of an ES013 squib directed into the 0.15" ID perforation in the grain.
The igniter grain was held in a 0.4" ID, 0.49" wall, cylindrical fixture
with approximately 95 evenly distributed 0.109" ID holes drilled along
its length and diameter. The times required for the flame front to
reach the opposite end of the grain after ignition by the squib are
reported in Table V. The times were determined from 1000
frames/second video. Generally, only a few milliseconds were
required. Durability of 2" long grains was detemlined as described in
Example 2. The results are reported in Table V. By far, the
formulation containing 2% polyethylene fibers exhibited the greatest
durability. Firings were conducted using igniter grains from
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formulations #3 and #19 with RDC inserted into the 0.15" perforation.
Formulation #19 with polyethylene fibers produced the least amount
of delay before the pyrotechnic composition was ignited.
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Table IV
Igniter Formulations containing cyanamer~A-37o
and Selected Fibers.
Form%KN03 kBoron%Cyanamar Fibar ID ~6Fibar
A3T0
3 76.30 16.707.00 none 0.00
16 76.70 14.307.00 Pyrogra h III, 2.00
Mlcro
17 74.80 16.207.00 SaHil , Ty a 2.00
590, Micro
18 74.80 16.207.00 Nextei ,1!8" 2.00
Ceramic
19 77.20 13.807.00 Allied, Spectra 2.00
900, 1l8"
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Table V
Test Result Summary for Potential Extruded
Igniters Containing Fibers.
FormFiber 1~ IgnitionIgnitionDurabiliCoeftiden
3 none 2 2 96 39
3 none 0.125' ID 9 8 101 2S
16 ro ra h'" III 5 65 39
Mlcro
17 Satffl , Type 1 107 4
590, Micro
18 Nextel ,118" Ceramic3 76 69
19 Allied, Spectra 17 1 357 17
900,1/8
"
9I1 _ _~,~ l _1'~I _
I"_sisnana t/R~~ I
Dlal ~
'Formulation 3 with grains having a 0.125" ID instead of the nominal 0.15" ID.
2Time required for the flame front on a 7" grain ignited on one end to reach
the
opposite end. The time is in milliseconds. The data were acquired as described
in
F~cample 3.
~fhe same as in footnote 1 but cured epoxy blocking the .15" 1D perforation at
the
opposite end from where ignition was intiated.
°Units are in milli-inch-pounds.
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(n formulations 16, 17, 18, 19 and 20, respectively, the "fiber
ID" can be characterized as carbon fiber, alumina fiber,
aluminosilicate, polyethylene, and polybenzimidizoie.
Example 4
An extrudable igniter composition was obtained by forming a
pre-mix of guar gum (5.0 wt%, 0.25 gram) and water (deionized 15.0
wt%, 1.75 grams); combining the pre-mix with potassium nitrate
(average particle size of about 26 microns, 75 wt%, 3.75 grams}; and
adding thereto fuel, boron (amorphous; 20.0 wt%, 1.00 gram).
Example 5
An extrudable igniter composition was obtained as in Example
4, but 20.0 wt% of water was used.
Example 6
An extrudable igniter composition was prepared as in Example
4, except that the amount of fuel, boron, was increased to 22.0 wt%
(1.10 grams) and the amount of binder, guar gum, was reduced to 3.0
wt% (0.15 gram).
Example 7
An extrudable igniter composition was prepared according to
the procedure of Example 4, except that the binder was
polyacryfamide (cyanamer "N-300" from American Cyanamid, 5.0
wt%, 0.25 gram).
Examale 8
An extrudable igniter mixture is prepared by adding potassium
nitrate (210 grams) and a polyacrylamide (14 gram; cyanamer "N-
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300" from American Cyanamid) to a bowl; adding water (44.8 grams),
to the bowl and mixing for 1 minute; and adding boron (amorphous;
56.0 grams) thereto followed by mixing for about four minutes.
Example 9
An extrudable igniter composition was prepared as in Example
8, except that the amount of water is 50.4 grams, the potassium
nitrate and binder are first dry-blended together before adding the
water and mixing 1 minute. The powdered boron is then added and
the mixing is continued for four minutes.
Examale 10
The igniter composition prepared according to Example 8 was
granulated, dried and pressed into 1/2 inch diameter by 1 inch long
pellets. The pellets were then inhibited on all but one face and
combusted in a closed pressurized vessel at 1000, 2000 and 3000 psi
via ignition of the uninhibited face. Burning rates of 4.16 ips, 4.32 ips
and 4.42 ips respectively, were observed.
Example 11
A portion of the wet igniter composition prepared as described
in Example 9 was placed in a 2 in diameter ram extruder and forced
through an appropriate die so as to provide a center perforated
cylindrical extrudate of approx 0.3 in diameter with a perforation
diameter of approx 0.06 in. This extrudate was partially dried and cut
into 7 in lengths prior to fiinal drying. The resulting igniter sticks were
then tested in a gas generating device consisting of a tubular metal
cylinder approx 8 in long by approx 2 in diameter closed at both ends
and provided with radial ports. One of the end closures was further
provided with an initiating squib. The igniter stick was retained in the
center of the tube and a 7 in length of rapid deflagration cord (RDC)
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placed in the center perforation of the stick. The gas generating
device was then filled with a charge of gas generant pellets and
tested in a closed tank. Comparable results were obtained with the
igniter stick in contrast to those obtained with a conventional ignition
train in which a perforated metal tube filled with a like quantity of
ignition powder and the RDC replaces the igniter sticWRDC
combination. In all cases ignition of the gas generant pellets was
observed to occur within 8 msec.
Example 12
Two fifty gram mixes formulated from 20 percent boron, 75
percent potassium nitrate, 5 percent Cytec Cyanamer O N-300 brand
pofyacrylamide (15 million molecular weight, and 17.5 weight percent
of water were produced. The mixes were combined and then loaded
into a 2.0 inch diameter RAM extruder. The RAM was pressurized to
300 psi to extrude the ignitor sticks. The igniter composition was
originally extruded into 0.100 inch diameter solid sticks and also into
0.100 inch diameter with a 0.030 finch diameter center perforation.
The igniter sticks were cut into 6 inch lengths and dried at 135°F
overnight prior to use. The center perforated ignitor sticks were
successfully demonstrated in an XM-212 decoy flare. Two XM 212
grains were fabricated. One with the traditional slurry first fire and the
other with three center perforated igniter sticks. A flare configuration
with an igniter stick is shown in Figure 1.
Example 13
The igniter sticks were also incorporated in the main ignition
system of a MJU-10 decoy flare. The MJU-10 flare requires a larger
igniter than the XM-212 flare. Therefore, the igniter formulation was
extruded through a 12 point star die that has a 0.33 inch maximum
diameter a 0.30 inch minimum diameter. The extrusion die also
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included a 0.80 inch diameter pin used to produce a center perforated
grain. The extruded igniter sticks were cut to 5.0 inch lengths and
then dried at 135°F for 24 hours. The igniter sticks were then inserted
into the center perforation of the MJU-10 flare grain. The MJU-10
flare was successfully ignited with the igniter stick.
In view of the foregoing, the igniter stick will decrease the cost,
decrease the fabrication time, and simplify the design of an ignition
system for the thrusted MJU-10 flare.
In view of the Examples, igniter sticks can be used in a great
number of decoy flare devices. They will aid in improving the
reliability of Rare ignition by decreasing out-of-place first fire, and also
improve the safety of manufacturing flares by eliminating the use of
flammable solvents commonly used when applying traditional first
fires.
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