U.S. patent application number 11/285133 was filed with the patent office on 2006-10-05 for ignition material for an igniter.
This patent application is currently assigned to TRW Automotive U.S. LLC. Invention is credited to Harold R. Blomquist, Bryan W. Shirk, Timothy A. Swann.
Application Number | 20060219121 11/285133 |
Document ID | / |
Family ID | 38037916 |
Filed Date | 2006-10-05 |
United States Patent
Application |
20060219121 |
Kind Code |
A1 |
Blomquist; Harold R. ; et
al. |
October 5, 2006 |
Ignition material for an igniter
Abstract
An electrically actuatable igniter (24) comprises a pair of
electrodes (40) and (42). A heating element (44) is electrically
connected between said electrodes (40) and (42). An ignition
material (48) is in contact with the heating element (44). The
ignition material (48) comprises a metal powder and an oxidizer
that exothermically reacts with the metal powder. The metal powder
includes macro-agglomerates of metal particles. The metal particles
have an average diameter less than about 0.1 .mu.m and have an
oxide layer that prevents contact of the particles with the
oxidizer. The ignition material (48) deflagrates when the heating
element is heated to a temperature of at least about 250.degree.
C.
Inventors: |
Blomquist; Harold R.;
(Gilbert, AZ) ; Shirk; Bryan W.; (San Diego,
CA) ; Swann; Timothy A.; (San Diego, CA) |
Correspondence
Address: |
Tarolli, Sundheim, Covell, & Tummino L.L.P.
Suite 1111
526 Superior Avenue
Cleveland
OH
44114-1400
US
|
Assignee: |
TRW Automotive U.S. LLC
|
Family ID: |
38037916 |
Appl. No.: |
11/285133 |
Filed: |
November 22, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09634384 |
Aug 9, 2000 |
|
|
|
11285133 |
Nov 22, 2005 |
|
|
|
Current U.S.
Class: |
102/202.7 |
Current CPC
Class: |
F42B 3/103 20130101;
B60R 2021/26029 20130101 |
Class at
Publication: |
102/202.7 |
International
Class: |
F42C 19/12 20060101
F42C019/12 |
Claims
1. An electrically actuatable igniter comprising: a pair of
electrodes; a heating element electrically connected between said
electrodes; and an ignition material in contact with said heating
element, said ignition material comprising a metal powder and an
oxidizer that exothermically reacts with said metal powder, said
metal powder including macro-agglomerates of metal particles, said
metal particles having an average diameter less than about 0.1
.mu.m and having an oxide layer that prevents contact of said
particles with said oxidizer, wherein said ignition material
deflagrates when the heating element is heated to a temperature of
at least about 250.degree. C.
2. The electrically actuatable igniter of claim 1 wherein the
macro-agglomerates have an average diameter of about 1 .mu.m to
about 2 .mu.m.
3. The electrically actuatable igniter of claim 1 wherein said
oxidizer is selected from the group consisting of alkali metal
nitrates, alkaline earth metal nitrates, alkali metal perchlorates,
alkaline earth metal perchlorates, alkali metal chlorates, alkaline
earth metal chlorates, ammonium perchlorates, ammonium nitrate, and
mixtures thereof.
4. The electrically actuatable igniter of claim 3 wherein the
oxidizer has an average particle size of about 1 .mu.m to about 30
.mu.m.
5. The electrically actuatable igniter of claim 1 wherein the metal
powder is selected from the group consisting of electro-exploded
aluminum powder, electro-exploded titanium powder, electro-exploded
copper powder, electro-exploded zinc powder, and electro-exploded
yttrium powder.
6. The electrically actuatable igniter of claim 5 wherein the
electro-exploded metal powder is electro-exploded aluminum.
7. The electrically actuatable igniter of claim 1 wherein the
electro-exploded metal powder is about 15% to about 75% by weight
of the ignition material.
8. The electrically actuatable igniter of claim 1 wherein the
amount of oxidizer is about 25% to about 85% by weight of the
ignition material.
9. The electrically actuatable igniter of claim 1 wherein the
ignition material upon ignition deflagration produces an ignition
product with a temperature of about 3000.degree. C. to about
6000.degree. C.
10. The electrically actuatable igniter of claim 1 wherein the
ignition material does not thermally decompose at temperatures up
to about 120.degree. C.
11. An electrically actuatable igniter comprising: a pair of
electrodes; a heating element electrically connected between said
electrodes; and an ignition material in contact with said heating
element, said ignition material comprising an electro-exploded
metal powder and a particulate oxidizer, wherein said ignition
material deflagrates when the heating element is heated to a
temperature of at least about 250.degree. C.
12. The electrically actuatable igniter of claim 11 wherein said
oxidizer is selected from the group consisting of alkali metal
nitrates, alkaline earth metal nitrates, alkali metal perchlorates,
alkaline earth metal perchlorates, alkali metal chlorates, alkaline
earth metal chlorates, ammonium perchlorate, ammonium nitrate, and
mixtures thereof.
13. The electrically actuatable igniter of claim 12 wherein the
oxidizer has an average particle size of about 1 .mu.m to about 30
.mu.m.
14. An electrically actuatable igniter comprising: a pair of
electrodes; a heating element electrically connected between said
electrodes; and an ignition material in contact with said heating
element, said ignition material comprising a uniformly dispersed
mixture of a metal powder and a particulate inorganic salt oxidizer
that exothermically reacts with said metal powder, said oxidizer
having an average particle size of about 1 .mu.m to about 30 .mu.m,
said metal powder being selected from the group consisting of
electro-exploded aluminum powder, electro-exploded titanium powder,
electro-exploded copper powder, electro-exploded zinc powder, and
electro-exploded yttrium powder, wherein said ignition material
does not thermally decompose at temperatures up to about
120.degree. C. and deflagrates when the heating element is heated
to a temperature of at least about 250.degree. C., wherein said
ignition material is free of a binder and the mixture of metal
powder and particulate oxidizer being formed without the use of a
solvent.
15. The electrically actuatable igniter of claim 33 wherein the
oxidizer is selected from the group consisting of alkali metal
nitrates, alkaline earth metal nitrates, alkali metal perchlorates,
alkaline earth metal perchlorates, alkali metal chlorates, alkaline
earth metal chlorates, ammonium perchlorates, ammonium nitrate, and
mixtures thereof.
16. The electrically actuatable igniter of claim 33 wherein the
electro-exploded metal powder is electro-exploded aluminum.
17. The electrically actuatable igniter of claim 33 wherein the
electro-exploded metal powder is about 15% to about 75% by weight
of the ignition material.
18. The electrically actuatable igniter of claim 33 wherein the
amount of oxidizer is about 25% to about 85% by weight of the
ignition material.
19. The electrically actuatable igniter of claim 33 wherein the
ignition material upon ignition produces an ignition product with a
temperature of about 3000.degree. C. to about 6000.degree. C.
20. The electrically actuatable igniter of claim 33 wherein said
metal powder has a surface area of about 15 square meters per
gram.
21. An electrically actuatable igniter comprising: a pair of
electrodes; a heating element electrically connected between said
electrodes; and an ignition material in contact with said heating
element, said ignition material consisting essentially of a
uniformly dispersed mixture of a metal powder and a particulate
inorganic salt oxidizer, the metal power being present in the
ignition material in an amount of about 25% to about 50%, by weight
of the ignition material, said particulate oxidizer reacting
exothermically with said metal powder, said particulate oxidizer
having an average particle size of about 1 .mu.m to about 30 .mu.m,
wherein said metal powder consists of electro-exploded aluminum
powder and said ignition material deflagrates when the heating
element is heated to a temperature of at least about 250.degree.
C., the mixture of metal powder and particulate oxidizer being
formed without the use of a solvent.
22. The electrically actuatable igniter of claim 42 wherein said
oxidizer is selected from the group consisting of alkali metal
nitrates, alkaline earth metal nitrates, alkali metal perchlorates,
alkaline earth metal perchlorates, alkali metal chlorates, alkaline
earth metal chlorates, ammonium perchlorate, ammonium nitrate, and
mixtures thereof.
23. The electrically actuatable igniter of claim 42 wherein said
ignition material upon deflagration produces an ignition product
with a temperature of about 3000.degree. C. to about 6000.degree.
C.
Description
FIELD OF THE INVENTION
[0001] This application is a continuation-in-part of application
Ser. No. 09/634,384 filed Aug. 9, 2000.
[0002] The present invention relates to an igniter, and
particularly relates to an ignition material for an igniter for
inflating an inflatable vehicle occupant protection device.
BACKGROUND OF THE INVENTION
[0003] An inflatable vehicle occupant protection device, such as an
air bag, is inflated by inflation gas provided by an inflator. The
inflator typically contains ignitable gas generating material. The
inflator further includes an igniter to ignite the gas generating
material.
[0004] The igniter contains a charge of ignition material. The
igniter also contains a bridgewire that is supported in a heat
transferring relationship with the ignition material. When the
igniter is actuated, an actuating level of electric current is
directed through the bridgewire in the igniter. This causes the
bridgewire to become resistively heated sufficiently to ignite the
ignition material. The ignition material then produces ignition
products that, in turn, ignite the gas generating material.
SUMMARY OF THE INVENTION
[0005] The present invention is an electrically actuatable igniter.
The electrically actuatable igniter comprises a pair of electrodes.
A heating element is electrically connected between said
electrodes. An ignition material is in contact with the heating
element. The ignition material comprises a metal powder and an
oxidizer that exothermically reacts with the metal powder. The
metal powder includes macro-agglomerates of metal particles. The
metal particles have an average diameter less than about 0.1 .mu.m
and have an oxide layer that prevents contact of the particles with
the oxidizer. The ignition material deflagrates when the heating
element is heated to a temperature of at least about 250.degree.
C.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] The foregoing and other features of the invention will
become more apparent to one skilled in the art upon consideration
of the following description of the invention and the accompanying
drawings, in which:
[0007] FIG. 1 is a schematic view of a vehicle occupant protection
apparatus embodying the present invention; and
[0008] FIG. 2 is an enlarged sectional view of a part of the
apparatus of FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0009] Referring to FIG. 1, an apparatus 10 embodying the present
invention includes an inflator 14 and an inflatable vehicle
occupant protection device 26. The inflator 14 contains a gas
generating material 16. The gas generating material 16 is ignited
by an igniter 24 operatively associated with the gas generating
material 16. Electric leads 20 and 22 convey electric current to
and from the igniter 24. The electric current is conveyed to the
igniter 24 through a crash sensor 18 from a power source (not
shown). The crash sensor 18 is responsive to vehicle deceleration
indicative of a collision. A gas flow means 28, such as an opening
in the inflator 14, conveys gas, which is generated by combustion
of the gas generating material 16, to the vehicle occupant
protection device 26.
[0010] A preferred vehicle occupant protection device 26 is an air
bag that is inflatable to help protect a vehicle occupant in the
event of a collision. Other vehicle occupant protection devices
that can be used with the present invention are inflatable seat
belts, inflatable knee bolsters, inflatable air bags to operate
knee bolsters, inflatable head liners, and inflatable side
curtains.
[0011] Referring to FIG. 2, the igniter 24 has a central axis 39
and a pair of axially projecting electrodes 40 and 42. A heating
element in the form of a bridgewire 44 is electrically connected
between the electrodes 40 and 42 within the igniter 24. An ignition
material 48 is contained within the igniter 24. The ignition
material surrounds and is in contact with the bridgewire 44 so that
the ignition material is in a heat receiving relationship with the
bridgewire 44.
[0012] The igniter 24 further includes a header 50, a charge cup 52
and a casing 54. The header 50 is a metal part, preferably made of
304L steel, with a generally cylindrical body 60 and a circular
flange 62 projecting radially outward from one end of the body 60.
A cylindrical outer surface 64 of the body 60 has a recessed
portion 66 defining a circumferentially extending groove 68.
[0013] The charge cup 52 also is a metal part, and has a
cylindrical side wall 70 received in a tight fit over the body 60
of the header 50. The side wall 70 of the charge cup 52 is fixed
and sealed to the body 60 of the header 50 by a circumferentially
extending weld 72. The charge cup 52 is further secured to the
header 50 by a plurality of circumferentially spaced indented
portions 74 of the side wall 70 that are crimped radially inward
into the groove 68. In this arrangement, the side wall 70 and a
circular end wall 76 of the charge cup 52 together contain and hold
the ignition material 48 in a heat transferring relationship with
the bridgewire 44. A plurality of thinned portions (not shown) of
the end wall 76 function as stress risers that rupture under the
influence of the combustion products generated by the ignition
material 48.
[0014] The casing 54 is a sleeve-shaped plastic part that is
shrink-fitted onto the header 50 and the charge cup 52 so as to
insulate and partially encapsulate those parts. An opening 79 in
the casing 54 allows ignition products escaping through the
ruptured thinned portions of the charge cup 52 to exit the igniter
24.
[0015] The header 50 has a pair of cylindrical inner surfaces 80
and 82 that are axially aligned and together define a central
passage 84 extending fully through the header 50. The first
electrode 40 has an inner end portion 86 extending along the entire
length of the central passage 84. A pair of axially spaced apart
glass seals 88 and 90 surround the first electrode 40 in the
central passage 84, and electrically insulate the first electrode
40 from the header 50 and from the electrode 42. Preferably, the
glass seals 88 and 90 are formed from a barium alkali silicate
glass. The electrode 42, at one end 43, seats against the header 50
in direct contact with the header 50.
[0016] The bridgewire 44 extends from a radially extending surface
41 of the first electrode 40 to a radially extending surface 51 of
the header 50. The bridgewire 44 has flattened opposite end
portions 100 and 102, which are fixed to the electrode surface 41
and the header surface 51 by electrical resistance welds 104 and
106, respectively. The opposite end portions 100 and 102 of the
bridgewire 44 become flattened under the pressure applied by the
welding electrodes (not shown) that are used to form the resistance
welds 104 and 106. The bridgewire 44 thus has an unflattened major
portion 108 extending between the opposite end portions 100 and
102. The major portion 108 of the bridgewire 44 is bent so that the
major portion 108 lies in a plane spaced from the plane of the
opposite end portions 100 and 102 and from a radially extending
surface 89 of the first glass seal 88 and the header surface
51.
[0017] The bridgewire 44, in one embodiment, is formed from a high
resistance metal alloy. A preferred metal alloy is "NICHROME", a
nickel-chromium alloy. Other suitable alloys for forming a high
resistance bridgewire 44 include platinum-tungsten and 304L steel.
An electrical current flow in the bridgewire 44 resistively heats
the bridgewire to temperature of about 250.degree. C. to about
400.degree. C. The heat generated by the bridge wire 44 is
sufficient to ignite the ignition material 48.
[0018] A semi-conductor bridge (SCB) may be used in place of the
bridgewire 44. A semi-conductor bridge consists of dissimilar
conductive materials such as a thick resistive film on a ceramic
substrate, a thin resistive film deposited on a ceramic substrate,
or a semi-conductor junction diffusion doped onto a silicon
substrate. A current flow in the semi-conductor bridge heats the
semi-conductor bridge to a temperature of about 250.degree. C. to
about 400.degree. C., which is sufficient to ignite the ignition
material 48. Examples of semi-conductor bridges include: a
substrate that is formed of ceramic material such as dense alumina
(Al.sub.2O.sub.3), beryllia (BeO), or steatite and an alloy such as
nickel-chrome, phosphorous-chrome, or tantalum nitride on the
substrate.
[0019] In accordance with the present invention, the ignition
material 48 is a pyrotechnic composition that deflagrates when the
bridgewire 44 is heated to a temperature of at least about
250.degree. C. By deflagrate, it is meant that the ignition
material 48 undergoes an exothermic chemical reaction producing a
vigorous evolution of heat and sparks or flame that move through
the ignition material 48 at a speed less than the speed of
sound.
[0020] The ignition material 48 of the present invention comprises
a fuel and an oxidizer. The fuel is a metal powder that
exothermically reacts with the oxidizer upon actuation of the
igniter 24. The metal powder of the present invention is produced
by electro-explosion of a metal wire under controlled atmospheric
condition. The electro-explosion of metal wire to produce a
powdered metal is well known in the art. In the process, a metal
wire is placed in an inert atmosphere and connected in an
electrical circuit that includes a power source. The wire is pulsed
with an electrical current sufficient to increase the temperature
of the metal wire to a temperature of about 10,000.degree. C. to
about 20,000.degree. C. At a temperature of about 10,000.degree. C.
to about 20,000.degree. C., the metal wire vaporizes and forms
metal plasma. The pulse of electric current, which vaporizes the
metal wire, also produces an electromagnetic field that initially
contains the metal plasma. The vapor pressure of the metal plasma
overcomes the electromagnetic field, and the metal plasma explodes
into an aerosol of metal particles.
[0021] The metal particles so formed by explosion of the metal wire
have an essentially spherical configuration and have an average
particle size less than about 100 nm. Preferably, the metal
particles have an average particle size from about 20 nm to about
100 nm. Other methods for obtaining metal particles in this size
range are also known.
[0022] The metal particles agglomerate into macro-agglomerates
having the consistency of a metal powder. The macro-agglomerates
have an average diameter of about 1 .mu.m to about 2 .mu..
Preferably, the macro-agglomerates have an average diameter of
about 1 .mu.m.
[0023] Metal powders in the size range formed by the
electro-explosion of a metal wire react more readily with the
oxidizer of the present invention than metal powders formed by
conventional methods such as gas atomization. The rate of reaction
of the metal powder with the oxidizer is increased for metal
powders formed by electro-explosion of metal wires because the
activation barrier for particle reaction are reduced. One component
of this is facilitated heat transfer owing to greater surface area
than metal powders formed by conventional methods. Metal powders
formed by electro-explosion have a surface area of about 15 square
meters per gram, which is several orders of magnitude greater than
metal powders formed by conventional methods. Reactivity, reflected
in autoignition temperature or time to ignition involve melting the
aluminum, occurs at lower average temperature where the activation
barrier is reduced. Heat release from oxidation of the metal now
occurs in or near the reaction front affording the significantly
faster reaction rate. It is contemplated that mixtures of
electro-exploded metal particles, electro-exploded alloys of metals
and metals produced by conventional means can be used in varying
proportions to modify the properties or reactivity of the metal and
its oxide surface layer. For example, a composition employing a
mixture of 20% electro-exploded aluminum and 80% Valimet H-5
aluminum powder could be used to achieve reactivity and other
properties intermediate to compositions prepared with either metal
alone. Moreover, it is believed that metal powders formed by
electro-explosion have a strained crystal structure. This strained
crystal structure, during reaction of the metal powder with the
oxidizer, undergoes exothermic rearrangement. The exothermic
rearrangement of the crystal structure generates heat, which in
turn facilitate reaction of metal powder formed by
electro-explosion and the oxidizer.
[0024] Preferred metal powders formed by electro-explosion are
electro-exploded aluminum powder, electro-exploded titanium powder,
electro-exploded copper powder, electro-exploded zinc powder, and
electro-exploded yttrium powder.
[0025] These electro-exploded metal powders are commercially
available from Argonide Co. Other manufacturers have developed
processes capable of producing material of these and other metals
of similar dimensions which possess the same advantages as noted
for electro-exploded metal and are suitable for use in the present
invention.
[0026] These electro-exploded metal powders are preferred because,
upon reaction with the oxidizer of the present invention, they form
a non-toxic and environmentally benign ignition product. Moreover,
these electro-exploded metal powders, when combined with the
oxidizer of present invention, form ignition materials that do not
thermally decompose at temperatures up to about 120.degree. and do
not deflagrate when exposed to external stress such as impact.
[0027] The metal particles that form the electro-exploded aluminum
powder, electro-exploded titanium powder, electro-exploded copper
powder, electro-exploded zinc powder, and electro-exploded yttrium
powder are naturally coated, upon exposure to air, with a thin
metal oxide layer of, respectively, aluminum oxide, titanium oxide,
copper oxide, zinc oxide, and yttrium oxide. The coating of metal
oxide is about 1 nm to about 30 nm thick. The coating of metal
oxide passivates the metal surface since it does not readily react
with the oxidizer of the present invention. Alternate methods of
passivating the surface are known, such as organic or inorganic
coatings. As a result, the passivating coating acts as a buffer to
prevent the metal particles from contacting and reacting with
oxidizer during processing of the ignition material and storage of
the ignition material. Energy output is reduced to the extent that
a quantity of the metal is consumed during formation of the
non-reactive oxide. The preferred thickness is the minimum amount
to afford safe processing, thus maximizing the reactive metal
content at the core of the particle. Thus, ignition materials
comprising electro-exploded aluminum powder, electro-exploded
titanium powder, electro-exploded copper powder, electro-exploded
zinc powder, and electro-exploded yttrium powder may be processed
using conventional processing techniques.
[0028] A more preferred metal powder is electro-exploded aluminum
powder. Electro-exploded aluminum powder comprises
macro-agglomerates of aluminum particles. The aluminum particles
have an average particle size of about 20 nm to about 100 nm. The
macro-agglomerates have an average diameter of about 1 .mu.m.
[0029] The amount of metal powder in the ignition material is that
amount necessary to achieve sustained, rapid deflagration of the
ignition material upon ignition. Preferably, the amount of fuel is
from about 15% to about 75% by weight of the ignition material.
Metal from the particles in excess of that needed to react with the
solid oxidizer is available to transfer heat or burn when in
contact with other condensed or gaseous components of the system.
This affords an additional means of tuning the performance of the
system. More preferably, the amount of metal powder is from about
30% to about 60% by weight of the ignition material.
[0030] The oxidizer of the present invention may be any oxidizing
material that readily reacts with the metal powder of the present
invention and produces an ignition product that is non-toxic and
environmentally benign. A preferred oxidizer is an inorganic salt
oxidizer. Examples of inorganic salt oxidizers that can be used in
an ignition material of the present invention are alkali metal
nitrates such as sodium nitrate and potassium nitrate, alkaline
earth metal nitrates such as strontium nitrate and barium nitrate,
alkali metal perchlorates such as sodium perchlorate, potassium
perchlorate, and lithium perchlorate, alkaline earth metal
perchlorates, alkali metal permanganates such as potassium
permanganate, alkali metal chlorates such as sodium chlorate,
lithium chlorate and potassium chlorate, alkaline earth metal
chlorates such as magnesium chlorate and calcium chlorate, ammonium
perchlorate, ammonium nitrate, and mixtures thereof.
[0031] Other oxidizers that may be used in the present invention
are metal oxides, peroxides, and superoxides such as ferric oxide
(Fe.sub.2O.sub.3), cupric oxide (CuO), manganese dioxide
(MnO.sub.2), and molybdenum trioxide (MoO.sub.3).
[0032] The oxidizer is incorporated into the ignition material in
the form of particles. The sensitivity of the ignition material to
thermal decomposition and external stress such as impact, as well
as the burning rate of the ignition material, are dependent on the
average particle size of the oxidizer. If the particle size of the
oxidizer incorporated in the ignition material is less than about
0.1 .mu.m, the ignition material can auto-ignite at temperatures
below about 250.degree. C. or upon exposure to external stress such
as shock. If the average particle size of the oxidizer incorporated
in the ignition material is greater than about 100 .mu.m, the burn
rate of the ignition material will not be effective to ignite the
gas generating material and actuate the vehicle occupant protection
apparatus. Preferably, the oxidizer incorporated in the ignition
material has an average particle size of about 1 .mu.m to about 30
.mu.m.
[0033] The amount of oxidizer in the ignition material is that
amount necessary to achieve sustained, rapid deflagration of the
ignition material upon ignition. Preferably, the amount of oxidizer
in the ignition material is about 25% to about 85% by weight of the
ignition material. More preferably, the amount of oxidizer in the
ignition material is about 50% to about 75% by weight of the
ignition material.
[0034] In a preferred embodiment of the present invention, the
ignition material is prepared by adding the metal powder and the
particulate oxidizer to a conventional mixing device, without the
addition of any processing aids such as solvents or binders. The
metal powder and particulate oxidizer are then mixed until the
metal powder and particulate oxidizer are uniformly dispersed. The
ignition material so formed is pressed into the ignition cup 52 of
the igniter 24.
[0035] Alternatively, ignition material can be prepared by admixing
the metal powder and the particulate oxidizer with a binder.
Preferably, the binder is an oxidizable organic material. Examples
of oxidizable organic materials are organic polymers such as
cellulose esters, cellulose ethers, vinyl polymers, acrylates, and
methacryalates, phenolaldehydes, polyamides, natural and synthetic
rubber, natural resins and halogenated polymers.
[0036] The amount of binder mixed with the powdered metal and
particulate oxidizer is that amount sufficient to form a homogenous
mixture with the metal powder and particulate oxidizer without
impairing the sensitivity of the ignition material to ignition by
the heating element. Preferably, the amount of binder mixed the
powdered metal and the particulate oxidizer is from about 1% to
about 5% by weight of the ignition material.
[0037] The powdered metal, particulate oxidizer, and binder are
mixed by a conventional mixture until a homogeneous mixture is
formed. The homogeneous mixture of powdered metal, particulate
oxidizer, and binder is pressed into the ignition cup 52 and
allowed to dry.
[0038] When the igniter 24 is actuated, an actuating level of
electric current is directed through the bridgewire 44 between the
electrodes 40 and 42. As the actuating level of the electric
current is conducted through the bridgewire 44, the bridgewire 44
is heated to a temperature between about 250.degree. C. and about
400.degree. C. The heat is transferred directly to the ignition
material 48. The particles of ignition material adjacent to the
bridgewire 44 ignite, resulting in deflagration of the ignition
material. Deflagration of the ignition material produces ignition
products, including heat, hot gases and hot particles at a
temperature of about 3000.degree. C. to about 6000.degree. C. The
ignition products are spewed outward from the igniter 24 and ignite
the gas generating material.
EXAMPLE
[0039] This Example illustrates preparation of an ignition droplet
in accordance with the present invention.
[0040] 25 mg of electro-exploded aluminum powder and 75 mg of
particulate potassium perchlorate are added to a mixing device
("POWERGEN" No. 35 manufactured by Powergen Inc.). The
electro-exploded aluminum powder is commercially available from
Argonide Co. under the trade name ALEX. The electro-exploded
aluminum powder comprises macro-agglomerates of aluminum particles.
The aluminum particles have an average diameter of about 50 nm. The
macro-agglomerates have an average diameter of about 1 .mu.m. The
particles of the potassium perchlorate have an average diameter of
about 5 microns.
[0041] The electro-exploded aluminum powder and potassium
perchlorate are blended until the electro-exploded aluminum powder
is uniformly dispersed with the particles of potassium
perchlorate.
[0042] The ignition material so formed does not thermally decompose
at temperatures up to about 120.degree. C. and is resistant
ignition by impact. The ignition material produces an ignition
product upon deflagration that has a temperature greater than about
3000.degree. C.
[0043] From the above description of the invention, those skilled
in the art will perceive improvements, changes and modifications.
Such improvements, changes and modifications within the skill of
the art are intended to be covered by the appended claims.
* * * * *