US3125025A

US3125025A - Pyrotechnic igniter

Info

Publication number: US3125025A
Authority: US
Publication date: 1964-03-17
Anticipated expiration: 1981-03-17

Description

March 17, 1964 B. F. BOGGS ETAL 3,125,025

PYROTECHNIC IGNITER Filed Jan. 4, 1960 2 Sheets-Sheefl FIG. I INVENTORS BRIAN F. 80663 STEVEN S. LAIFMAN ATTORNEY Ma h 1964 B. F. BOGGS ETAL PYROTECHNIC IGNITER 2 Sheets-Sheet 2 Filed Jan. 4, 1960 INVENTORS BRIAN F. BOGGS STEVEN S. LAIFMAN ATTORNEY United. States Patent Inc.

Filed Jan. 4, 1960, Ser. No. 198 3 Claims. (Cl. 102-48) This invention relates to an electrically actuatable pyrotechnic igniter or gas generator. More specifically, it refers to an hermetically sealed pyrotechnic igniter or solid propellant gas generator of simplified construction incorporating =a squib plate adaptable to a variety of applications.

Solid propellant ignite-r-s and gas generators of the prior art have generally been constructed with a single squib retained adjacent a pyrotechnic charge, the squib being a conventionally constructed unit having 'a pyrotechnic surrounded by a plastic shell and a pair of high resistance lead wires connected through the pyrotechnic for ignition purposes. Such igniters and gas generators have had a low reliability factor in that the failure of the single squib has caused the ultimate failure of the entire igniter with a consequent failure of ignition of the entire system to which it was adapted.

Further difiiculty has been experienced in the low resistance to humidity of such units. A low degree of humidity protection may be so detrimental to the pyrotechnic mixture that ignition cannot be initiated. Hence, reliability again suffers.

The present unit is usable either as a gas generator or igniter. However, its primary use is as an igniter and it will be generally discussed as such. It overcomes the above detrimental characteristics by providing a unit which utilizes a plurality of pyrotechnic squibs and which is easily hermetically sealed. This provides a simplified construction which assures a high degree of ignition reliability. A squib plate capable of containing the desired number of pyrotechnic squibs as an integral part thereof is insertable to a position adjacent the main pyrotechnic charge so that flame from the squib directly impinges upon the main charge surfiace.

It is a major object of this invention to provide a simple and reliable unit usable as a generator of hot combustion products.

-It is a further object to provide a pyrotechnic igniter having reusable components.

Another object of this invention is to provide simplified means whereby a plurality of pyrotechnic squibs may be etficiently utilized for the ignition of a main pyrotechnic charge.

Yet another object is to provide a pyrotechnic unit which is completely and hermetically sealed and capable of reliable service after storage over extended time periods.

A still further object of this invention is to provide an igniter easily adaptable to utilization in a variety of igniter structures.

Another object is to provide a highly adaptable squib plate for collecting and distributing electrical charges, directing generator ignition flames and controlling combustion products.

Other objects will become apparent from the following description taken in connection with the accompanying drawings, in which:

FIG. 1 is a cross sectional view of the basic pyrotechnic unit of this invention;

FIG. 2 is a sectional view taken along lines 22 of FIG. 1;

FIG. 3 is a sectional view taken along lines 3-3 of FIG. 2;

FIG. 4 is a perspective view of a sealed structure including the basic FIG. 1 unit adapted for gas generator applications; and

FIG. 5 is a perspective view of a Vernier engine igniter utilizing the basic unit of FIG. 1.

In detail, FIG. 1 illustrates the basic and central igniter or gas generator of the present invention. The overall unit is indicated as 1 and includes a cup-shaped body member 2 preferably of cylindrical shape. A pyrotechnic charge 3 is disposed within body member 2 against a closed end 4 of the body member. Charge 3 may be of any pyrotechnic composition such as a mixture of potassium perchlorate, ammonium perchlorate, boron aluminum powder and a binder composed of a polysuliide rubber polymer together with a polymer of a glycidyl polyether compound having terminal epoxy groups. An example of the polysulfide rubber polymer is LP-3, obtained by the reaction of dichloroethane and potassium sulfide. An example of a glycidyl polyether resin is one obtained by the reaction of 2,2-bis(4-hydroxyphenyl)propane and epichlorohydrin in an alkaline solution, as described in U.S. Patents 2,324,483 and 2,602,785. An ex ample of a specific composition is 54% potassium perchlorate, 11% ammonium perchlorate, 8% boron, 8% aluminum powder, 9.4% Thiokal LP-3, and an epoxy resin made by the reaction of 1,2,3-trihyd-roxy propane and epichlorohydrin.

Body member 2 may be provided with an internal shoulder 5. A squib plate, generally indicated as 6, and more clearly illustrated in FIGS. 2 and 3, is inserted within body member 2 until it abuts shoulder 5 or a similar stop means. In such position, the squib plate internal surface 7 is adjacently spaced from an exposed surface 8 of pyrotechnic charge 3. This space is indicated as A. Plate 6 includes electrically conductive means in the form of an inner metal current collector ring 9 and an outer metal current collector ring 10. An electrical insulating compound 11, e.g. molded plastic, rubber, etc., is disposed between

rings

9 and 10 and about ring 10, and a passage 12 is provided through the center of ring 9 communicating from space A to the external surrounding atmosphere as a means through which combustion products may exit from the unit. Pyrotechnic squibs 13, of a composition such as a mixture of lead peroxide, aluminum powder, boron powder and nitrocellulose lacquer, are inserted within cavities 14 extending into compound 11 from surface 7. As illustrated, four such squibs may easily be provided. However, a lesser or greater number might be utilized, dependent upon design criteria. 'It is generally desirable that the surfaces of squibs 13, compound 11, and metal rings 9 and 1t) be flush across surface 7 in order that a series of electrical resistance or bridge wires 15 may be connected to

rings

9 and 10 across and in contact with the surfaces of squibs 13. When desirable, bridge wires 15 may be positioned within the squibs proper.

Rings

9 and 10 include nibs or protrusions 16 and 17 respectively extending from their outer edges to which electrically conductive means may be attached.

In fabricating the unit, a pair of

pins

18 and 19 are inserted through closed end 4 of cup 2 and hermetically sealed by means of glass seals 20. A separate pair of

pins

21 and 22 are similarly inserted and sealed at positions removed from

pins

18 and 19.

Pins

18 and 19 extend through insulation 11 and make electrical contact with nibs 16 and 17.

Pins

21 and 22 extend through and protrude beyond the insulation of plate 6, and are adapted to having a flame detector means applied thereto. Here, the means is supplied by a break link or ignition detection Wire 23 electrically connected between the pin extremities across the exit of passage 12. Each of

pins

18, 19, 21, and 22 may be termed a feedd through pin for conducting electricity. Each includes a terminal 24 adapted for electrical connection.

Igniter 1 is easily adaptable to being hermetically sealed through the simple expedient of placing glass seals 20, as noted, between the feed-through pins and end 4 of body 2, and by soldering or otherwise adhering a metal foil closure member 25 over the open end of body member 2 to act as a burst diaphragm. Body member 2 is preferably made of metal in order that closure 25 may be easily soldered to its surface. This complete hermetic seal enables the basic igniter unit to be stored for extended periods under adverse conditions of humidity with no resultant danger of pyrotechnic deterioration.

operationally, the igniter is fired by connecting leads from conventional electrical source (not shown) to

pins

18 and 19. When a remotely located switch (not shown) is closed, current is transmitted through the circuit completed by pin 18, ring 9, bridge wires 15, ring It), and pin 19. Since bridge wires 15 are in actuality electrical heater means or resistance wires, the passage of electrical current causes them to be heated. The heat initiates ignition of squibs 13 against or within which they are positioned. Flames issuing from squibs 13 are directed toward surface 8 of pyrotechnic charge 3, causing that surface to be ignited. The plurality of squibs and their adjacently spaced relationship to surface 8, whereby they are caused to fire directly against specific portions of surface 8 and whereby hot combustion products may circulate over the balance of surface 8, assures a rapid and efi'icient ignition of the main pyrotechnic charge. Combustion products from the burning of squibs 13 and charge 3 issue with great force and high heat through restricted passage 12 in a confined flame pattern. As the flames and great quantities of hot gases leave passage 12 they impinge against break link 23 and closure member 25. The heat and pressure immediately bursts closure member 25, allowing the combustion products to escape from body 2 to accomplish their igniting function.

Break link 23 is burned through when the flames are sufficiently hot and/or have been burning a predetermined length of time. This is controlled by the heat resistance of the material from which link 23 is made and by the link thickness. An electric current normally flowing through pin 21, break link 23, and pin 22 from an electrical source (not shown) connected to terminals 24 of those pins is interrupted when break link 23 is burned through. This electrical circuit may be connected through a conventional electrical sensing device which detects the resistance increase when the wire burns through, indicating that combustion has been properly initiated and that an associated sequence of operations may begin.

It can be readily appreciated that a pyrotechnic unit having these characteristics is particularly adaptable to uses in rocket engines wherein a high degree of reliability is required to assure eventual functioning of the complete rocket engine system and wherein an indication of flawless ignition characteristics is required prior to actuation of further rocket engine functioning.

Squib plate 6 may be utilized as a unit in adaptation to variations of igniter 1 whenever the need for a squib retainer, including means for conducting electricity for squib ignition and a flame directing means (passage 12), are required.

The basic pyrotechnic unit of FIGS. 1 and 2 may be modified as illustrated in FIG. 4 for use in igniting a gas generator or for gas generating purposes per se. Here, the same essential components are utilized in a slightly changed configuration. A basic body or cup member includes a threaded shank 31 which is adapted to receive a conventional electrical connector. Upper portion 32 of body 30 is also threaded to accept a cap member 33. Cap member 33 may include, for example, a hexagon-shaped portion 34 adapted to receive a wrench for tightening cap member 33 upon body 30. A neck 35 is included in cap member 33 in order that combustion products issuing from the igniter might be confined to a circular pattern of desired diameter. Neck 35 is threaded for adaptation through the wall of a receptacle, e.g. a gas generator combustion chamber or a turbine housing. During operation the combustion products from the pyrotechnic unit are thereby directed internally of the ignition of propellants, driving of a turbine, or other similar functions.

A metal foil 36 may be sealed across neck 35 in essentially the same manner in which closure member 25 was adapted to body member 2 in the FIG. 1 configuration. This presents a double barrier to moisture since a similar seal or enclosure member 37 is also applied to body 30. The squib plate, pyrotechnic, and bridge wire of the FIG. 4 igniter are substantially the same as those of the FIG. 1 igniter. The feed-through pins, however, are shown to be somewhat different in their structural configuration in that they are jogged to match the shape of shank 31. Their extremities 38 are adapted for attachment to conventional electrical connectors of the socket variety. The current collector rings also vary in that they are narrower in their basic length, extension tips 39, only, extending from an embedded position into a position flush with the surfaces of squib plate 40. The sequence of operation of the FIG. 4 unit is essentially the same as that of the FIG. 1 unit.

The igniter of FIG. 5 is particularly adaptable to use with a small rocket engine of the Vernier type. It is desirable that the combustion products be discharged adjacent the rocket engine propellant injector in such applications. Therefore, the basic FIG. 1 unit is installed within a case 41 which is sufliciently long to extend through the length of the thrust chamber to which it is adapted and properly position the pyrotechnic charge. The pyrotechnic and squib plate may be disposed directly within case 41 over a retainer plate, or within a separate case or cup, as at 42 (shown in a representative shape). Either may be referred to as a pyrotechnic retainer. A spring clip 43 may be provided to clamp upon the end of the rocket engine nozzle as a retainer. Brackets or spacers 44 are spaced circumferentially about the case 41 and shaped to match the internal contour of the rocket engine nozzle in order that the igniter unit might be positioned essentially upon the longitudinal axis of the rocket engine combustion chamber. A series of electrical leads 45 are provided to conduct electricity from conventional electrical receptacle pins 46 to terminals 47 within case 41. Cap 48 is attached to the extremity of case 41 about the igniter unit. Cap 48 contains slots 49 through which combustion products issuing from the igniter unit might be redirected approximately circumferentially over the face of the rocket engine injector. The specific shape of cap 48 and slots 49 may be varied dependent upon particular design re quirements as dictated by the rocket engine injector and combustion configuration.

The material from which the metal foil closure members of this invention are constructed may be any metal which will prevent moisture passage, rupture easily and be easily susceptible of sealing to metal body. Thin aluminum foil has been found highly acceptable for this purpose.

The material of the feed-through pins and the rings of plate 6 may be any electrically conductive metal, e.g. copper or steel.

From the foregoing description it will be seen that the basic pyrotechnic unit of this invention provides a highly reliable ignition or hot gas source which is adaptable to a variety of applications when constructed and operated as set forth herein. It is simple and rugged in construction and can be manufactured economically.

Although the invention has been described and illus trated in detail, it is to be clearly understood that the same is by Way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of this invention being limited only by the terms of the appended claims.

We claim:

1. A pyrotechnic generator of hot combustion products comprising a cup member, a pyrotechnic charge disposed Within said .cup member, a pair of electrical conductive rings substantially concentrically positioned and adjacently spaced from said pyrotechnic, spaced from said cup member, and concentrically spaced from one another, said rings being mounted within and insulated from said cup and from one another, pyrotechnic squib means mounted between said rings, two pairs of electrical conductive leads through said cup member between and insulated from said rings, a first pair of said leads connected to said rings, one of said last-mentioned leads connected to each said ring, electrical heater means contacting said squib means and connected to said rings, and combustion sensing means connected across a second pair of said leads.

2. A pyrotechnic unit for generating hot combustion products comprising a hollow body member having a closed end and an open end, a pyrotechnic charge disposed within said body against said closed end, a squib plate spaced from said pyrotechnic charge and recessed within said body adjacent said open end, said squib plate including a pair of metal rings concentrically spaced from one another and from said body member, an electrical insulating material disposed between said rings and said body member, means in said plate defining a gas exit passage through said plate within an inner one of said rings, a plurality of pyrotechnic squibs embedded in said insulator, electrical resistance wires connected to said rings and contacting each of said squibs, a separate feedthrough pin electrically connected to each of said rings and extending through said pyrotechnic and said closed end of said body, a separate pair of feed-through pins substantially coextensive with said first mentioned pins and insulated from said rings, a glass seal disposed between each of said pins and said closed body end, a break link wire connected to said pair of pins and across said passage for detecting combustion of said pyrotechnic charge, and a metal foil sealed across said open end of said body so as to hermetically enclose the contents of said body.

3. A pyrotechnic generator of hot combustion products comprising a cup member having an open end, a pyrotechnic charge disposed within said cup member contacting a closed end thereof, a squib plate in said cup member adjacently spaced from said pyrotechnic charge, said plate being perforated and communicating between said charge and said open end, squib means attached to said plate facing and spaced from said charge, and means to ignite said squib means, said squib means including a pair of substantially concentric rings electrically insulated from one another and from said cup member and connected to separate electrical conductors, said perforation being within an inner one of said rings wherein said means to ignite said squib means includes an electric resistance wire connected to said rings in contact with said squib means, and wherein said squib means is a multiplicity of pyrotechnic squibs extending between said rings in said plate.

References Cited in the file of this patent UNITED STATES PATENTS 1,170,011 Smith Feb. 1, 1916 2,248,587 Seavey July 8, 1941 2,772,663 Barocca Dec. 4, 1956 2,988,876 Walden June 20, 1961

Claims

1. A PROTECHNIC GENERATOR OF HOT COMBUSTION PRODUCTS COMPRISING A CUP MEMBER, A PROTECHNIC CHARGE DISPOSED WITHIN SAID CUP MEMBER, A PAIR OF ELECTRICAL CONDUCTIVE RINGS SUBSTANTIALLY CONCENTRICALLY POSITIONED AND ADJACENTLY SPACED FROM SAID PYROTECHNIC, SPACED FROM SAID CUP MEMBER, AND CONCENTRICALLY SPACED FROM ONE ANOTHER, SAID RINGS BEING MOUNTED WITHIN AND INSULATED FROM SAID CUP AND FROM ONE NAOTHER, PYROTECHNIC SQUIB MEANS MOUNTED BETWEEN SAID RINGS, TWO PAIRS OF ELECTRICAL CONDUCTIVE LEADS THROUGH SAID CUP MEMBER BETWEEN AND INSULATED FROM SAID RINGS, A FIRST PAIR OF SAID LEADS CONNECTED TO SAID RINGS, ONE OF SAID LAST-MENTIONED LEADS CONNECTED TO EACH SAID RING, ELECTRICAL HEATER MEANS CONTACTING SAID SQUIB MEANS AND CONNECTED TO SAID RINGS, AND COMBUSTION SENSING MEANS CONNECTED ACROSS A SECOND PAIR OF SAID LEADS.