U.S. patent number 3,858,392 [Application Number 05/409,756] was granted by the patent office on 1975-01-07 for controlled burning squib arrangement.
This patent grant is currently assigned to ICI United States Inc.. Invention is credited to John H. Evans, Frederick R. McEwen.
United States Patent |
3,858,392 |
Evans , et al. |
January 7, 1975 |
CONTROLLED BURNING SQUIB ARRANGEMENT
Abstract
A controlled burning squib arrangement is presented wherein a
first-stage ignition is used to heat an adjacent second-stage
deflagrator such that the explosive components are substantially
converted to gas in a first chamber prior to entering an expandable
second chamber. Such arrangements are particularly useful in
thrusters designed to drive pistons, bellows, or flexible membranes
in lateral displacement mechanisms.
Inventors: |
Evans; John H. (Lansdale,
PA), McEwen; Frederick R. (Lansdale, PA) |
Assignee: |
ICI United States Inc.
(Wilmington, DE)
|
Family
ID: |
23621821 |
Appl.
No.: |
05/409,756 |
Filed: |
October 25, 1973 |
Current U.S.
Class: |
60/637; 60/632;
102/531; 149/24; 89/1.14; 149/2 |
Current CPC
Class: |
F02N
13/02 (20130101); F02G 3/00 (20130101); F42B
3/04 (20130101) |
Current International
Class: |
F42B
3/00 (20060101); F42B 3/04 (20060101); F02N
13/00 (20060101); F02N 13/02 (20060101); F02G
3/00 (20060101); F01b 029/08 (); F02n 013/00 () |
Field of
Search: |
;60/632,637,635,638,633,634,636 ;102/39,28 ;149/2,24 ;89/1B |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Burns; Wendell E.
Claims
What is claimed is:
1. A controlled burning squib arrangement comprising:
a. a first-stage squib component having an electrically activated
pyrogenic explosive;
b. a second stage squib component having a pyrogenic,
non-detonatable explosive in a separate cavity adjacent to and
ignited by said first-stage squib;
c. a rigid chamber spacing and communicating with said first-stage
and said second-stage squib components; and
d. means for venting said rigid chamber between said squibs into an
expandable second chamber.
2. A controlled burning squib arrangement comprising:
a. a tubular rigid longitudinal casing;
b. an electrically activated first-stage squib sealed at one end of
said casing;
c. a second-stage, non-detonatable squib component at the other end
of said casing mounted in a foraminous end-closure in facing
alignment with said first-stage; and
d. an expandable shell encompassing said rigid casing in gas tight
relationship therewith and communicating with the longidutinal
casing between said first and second squibs such that gas formed by
the ignition of said second-stage can pass into said encompassing
expandable shell.
3. A controlled burning squib arangement of claim 2 wherein said
second-stage is a non-detonatable pyrogenic material contained in a
cavity having a cross-sectional opening area no greater than the
total opening area in said foraminous end-closure.
4. A squib arrangement of claim 2 wherein said expandable shell is
a metal bellows.
5. A squib arrangement of claim 2 wherein said expandable shell is
a flexible membrane.
6. A squib arrangement of claim 2 wherein said expandable shell
component comprises a movable piston.
7. A controlled burning squib arrangement of claim 1 wherein said
non-detonatable explosive is a deflagratable material having
burning rates of 0.5 - 20 inches per second.
8. A squib arrangement of claim 7 wherein said non-detonatable
explosive material is a deflagratable material under uniform
compression of 30,000 - 60,000 pounds per square inch.
9. A squib arrangement of claim 8 wherein said deflagratable
material is lead styphnate.
Description
The invention relates to an explosively activated thruster or squib
arrangement wherein an electrically activated first-stage squib
component is used to ignite an adjacent second-stage deflagrating
material held in a cavity near the first-stage component. The
second-stage burns completely in a chamber common to the
first-stage and which intercommunicates with a second expandable
chamber through openings having sufficient cross-sectional area to
permit the gases forming in the first chamber to exhaust or vent
into a second expandable chamber such that a very low pressure
differential is maintained between the first and second
chambers.
Gas pressure developed by the squib arrangement can be used to
force the lateral displacement of a piston, bellows, or flexible
component to act as a motor displacement mechanism. Such devices
are particularly useful in highly reliable, single-shot,
electrically activated control devices especially required in
aerospace controls and components. Furthermore, such devices can be
sufficiently shielded such that stray currents developed by
surrounding radiation will not preignite the squib.
It is an object of the present invention to provide a controlled
burning squib arrangement for use in lateral displacement
devices.
Another object of the present invention is to provide an
arrangement which permits relatively accurate control of gas
pressure generated by a burning squib within an expandable chamber
for use as a lateral displacement motor device.
Prior art devices are characterized in that the squib component
vents directly into the expandable chamber to be pressurized.
Typical examples of such arrangements are better described in U.S.
Pat. Nos. 3,133,408; 3,119,302; 3,111,808; 3,336,452; 3,354,634;
3,482,484; and 3,149,457. Such devices which generate very high
intital pressure are less easily controlled and the amount of gas
generated from one device to the next can vary over wider ranges
than that which occurs with the present invention. This variation
can be fatal to applications in which an expandable bellows is
driven a distance which is directly proportional to the developed
pressure. Under-pressurization results in insufficient driving
force while overpressurization results in rupture or destruction of
the device.
The present invention will become more apparent from the following
detailed description taken with regard to the accompanying drawings
in which like numerals represent the same elements throughout
several views.
FIG. 1 is a longitudinal midsectional view of one embodiment of the
present invention taken through section 1--1 of FIGS. 2 and 3.
FIG. 2 is a transverse sectional view taken through section 2--2 of
FIG. 1.
FIG. 3 is a transverse sectional view of FIG. 1 taken through
section 3--3.
FIG. 4 is an alternate configuration for the expandable chamber
wherein the expandable part is a bellows.
FIG. 5 is an alternate arrangement for an expandable chamber shown
in FIG. 1 and shown as a flexible diaphragm.
Referring now to the drawings of FIGS. 1 through 5, the rigid
tubular longitudinal casing 11 of metal or rigid plastic has
mounted therein in gas-tight relationship a first-stage squib
comprising an explosive material 16 held in place by spacer ring 15
at the closed end of the casing through a glass metal seal 13
through which pass electrical lead wires 17 and 18 which abut with
metal bridge wire 14. Held in alignment through a central axis with
the first-stage squib 12 is a second-stage squib cavity 22
containing a non-detonatable, pyrogenic, deflagratable material 20
such as lead styphnate under uniform compressions of 30,000 -
60,000 psi and having burning rates of 0.5 - 20 inches per second.
The cylindrical second-stage squib component 20 is held in place by
a foraminous retainer ring or end-closure 19 having a multiplicity
of intercommunicating conduits 21 which have a total
cross-sectional opening area at least equivalent to the
cross-sectional area of cavity 22. An exterior shell component 10
in gas-tight sealed arrangement with casing 11 forms a second
expandable chamber 9 which intercommunicates with burning chamber 8
through conduits 21. Expandable chamber 9 can expand through
increased gas pressure by forcing piston 24 having O-ring seal 26
and a push rod 25 such as shown in FIG. 1 or an expandable bellows
section 27 as shown in FIG. 4 or a flexible diaphragm 28 as shown
in FIG. 5.
In operation, electric current is passed through lead wires 17 and
18 to ignite explosive 16 or the first-stage squib 12. The heat
generated by the first-stage ignition ignites the pyrogenic
material 20 which fills chamber 8 with gas and which indirectly
passes through conduits 21 into chamber 9 forcing chamber 9 to
expand through the increased pressure generated therein.
By way of example it can be shown that the prior art squib
arrangements employing a single expandable chamber having an
initial volume of 0.01 cubic inches, a diameter of 0.25 inches, a
piston weight of 0.386 pounds, and a mass of 0.001 pound-sec.2/inch
require 93.11 milligrams of lead styphnate to accelerate the piston
to a velosity of 1,000 inches per second in a distance of one inch
to attain a kinetic energy value of 500 inch - pounds. The initial
pressure developed in the firing of such a device is 27,932 pounds
per square inch. Because of this high initial pressure the system
must be housed in a thick metal casing so that it will not be
destroyed or ruptured.
By comparison, a controlled burning squib arrangement such as that
for driving a piston as shown in FIG. 1 of like dimensions under
similar conditions of 500 inch - pounds of kinetic energy and
velocities of 1,000 inches/sec. can be made from a less substantial
light weight casing in that the controlled burning squib avoids the
very high initial peak pressure by supplying gas over a relatively
longer period of time at pressures of no greater than 10,186 psi
thus operating at relatively uniform pressures which are about one
third that of the peak pressure developed by a conventional one
chamber squib arrangement. Such savings in weight are important
when the arrangements are combined with aerospace and missile
components.
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