US3000311A

US3000311A - Igniter for rocket propellant

Info

Publication number: US3000311A
Application number: US620768A
Authority: US
Inventors: William G Stanley
Original assignee: Standard Oil Co
Current assignee: Standard Oil Co
Priority date: 1956-11-06
Filing date: 1956-11-06
Publication date: 1961-09-19
Anticipated expiration: 1978-09-19

Description

Sept. 19, 1961 w. G. STANLEY IGNITER FOR ROCKET PROPELLANT 2 Sheets-Sheet 1 Filed Nov. 6, 1956 INVENTOR. William 6. Stanley m QM ATTORNEY Sept. 19, 1961 w. e. STANLEY IGNITER FOR ROCKET PROPELLANT 2 Sheets-Sheet 2 Filed NOV. 6, 1956 OOOOOOO OOOOOOOOOOO OOOOOOOOQOO 76 INVENTOR.

William 6. Stanley BY I M 77 32 3/ /9 Fig. 3

ATTORNEY United States Patent 9 3,000,311 IGNITER FOR ROCKET PROPELLANT William G. Stanley, Seymour, Ind., assignor to Standard Oil Company, Chicago, 111., a corporation of Indiana Filed Nov. 6, 1956, Ser. No. 620,768 4 Claims. (Cl. 102-70) This invention relates to rocket propulsion and gas generation. More particularly it relates to an igniter for ammonium nitrate-type propellants,

In the military usage of solid propellants for rocketry and gas generation it is a requirement that the propellants be operative over the broad temperature range between about 70 F. and +130 F. Because of their relative cheapness ammonium nitrate based solid propellants are coming into prominence as solid propellants in the military field. Ammonium nitrate-type solid propellants are frequently sensitive to temperature and the combustion of the propellant can be initiated at the lowest atmospheric temperatures only with difliculty. Sometimes the problem can be overcome by modifying the composition of the propellant. However, such modifications frequently introduce problems at more elevated temperatures.

An object of the invention is an igniter which is suitable for igniting the combustion of ammonium nitrate based propellants at all atmospheric temperatures. A particular object is an igniter assembly suitable for initiating combustion of ammonium nitrate propellants which are difiicult to ignite the combustion thereof. Other objects become apparent in the course of the detailed description.

The igniter assembly of the instant invention comprises an igniter assembly comprising a vessel, having an open end, an igniter mixture, positioned in said vessel, consisting essentially of (a) a powder member selected from the class consisting of black powder, magnesium powderpotassium nitrate mixture, aluminum powder-potassium nitrate mixture, aluminum powder-alkali metal perchlorate mixture and magnesium powder-alkali metal perchlorate mixture and (b) lumps consisting essentially of ammonium nitrate, an oxidizable binder and a combination catalyst, the ammonium nitrate being the predominant component, said lumps having a minimum dimension of at least about inch and a maximum dimension of not more than about /8 inch, said igniter mixture containing an amount of said powder member at least sufiicient to initiate sustained combustion of said lumps, readily destructible means for maintaining said mixture within said vessel and means, positioned within said vessel, adapted for initiating burning of said powder member.

It has been found that ammonium nitrate propellants need to be brought up to a more or less definite temperature in order to initiate sustained combustion of the surface of the propellant. A difficulty with the more or less conventional black powder or powdered metal-nitrate or perchlorate mixtures is that the duration of the combus tion of the igniter is so short that the ammonium nitrate propellant is not brought at its surface to a temperature high enough to sustain combustion; or the volume of gases produced by the igniter is so small that a sufficient area of the propellant is not caused to burn and thereby sustained burning is not attained. This problem has been overcome by using as the igniter a mixture of the conventional black powder or powdered metal-nitrate or perchlorate mixtures with small lumps of an ammonium nitrate-type propellant. Suflicient amount of the black powder or powdered metal-nitrate or perchlorate material is present in the igniter to initiate sustained combustion of the surfaces of the lumps of ammonium nitrate-type propellant. The lumps of propellant are of such a size and amount that sufiicient volume of hot gases are proice duced for along enough time to initiate sustained combustion of the ammonium nitrate propellant which is to be ignited either in a rocket motor or a gas generator. The powder member of the igniter mixture is preferably black powder. The coarser grained black powder known as blasting powder is particularly suitable. A description of black powder, and particularly blasting powder, which are suitable for use in the igniter mixture of this invention is contained in the Blasters Handbook. When operating with ammonium nitrate-type propellants that are particularly dilficult to ignite it is preferred to use black powder which has an average screen size between about A and A; inch. These may be obtained by the use of the C grades of blasting powder available commercially.

Instead of black powder the igniter mixture may be any one of the mixtures of powdered aluminum or magnesium metal in conjunction with potassium nitrate or alkali metal perchlorates. For example, a mixture of about equal parts by weight of aluminum powder and potassium perchlorate is particularly suitable as the powder member of the igniter of this invention. This mixture is available commercially as Alclo. Mixtures of powdered aluminum metal or powdered magnesium metal with potassium nitrate powder are suitable for use as the powder member. Mixtures of powdered magnesium metal and potassium or sodium perchlorate are suitable for use as the powder member of the igniter.

In addition to the use of straight black powder as the powder member of the igniter of the invention there may be used mixtures of magnesium powder or aluminum powder and black powder. Such mixtures are well known in the fireworks industry and are used in pyrotechnic displays.

The ammonium nitrate propellant lumps present in the igniter mixture must be of a size such that the lumps will not be consumed completely until the propellant body has obtained a sustained combustion. It is to be understood that the propellant to be ignited could be made from the same material as the lumps are made and these lumps are properly designated as ammonium nitrate-type propellant material. In this description the term propellan is generally intended to mean the body of ammonium nitrate based material which drives the rocket or which burns to produce gases in a gas generator or acts as a booster charge or is the driving force in an assistedtake-otf unit. In this description the ammonium nitratetype propellant which forms the lump portion of the igniter mixture of this invention is spoken of as lumps of propellant or the lump member of the igniter mixture.

In general the lumps of propellant may be either uniform shapes such as small spheres, oval pills, irregular fragments from crushing of large masses of material or parallelepipeds of various shapes. The preferred configuration of the lumps is approximately cubical with a secondary preference for parallelepiped's having rectangular surfaces. Usually the lumps are solid but under some conditions the lumps may be perforated in order to increase the burning surface and reduce the burn out time of the igniter mixture.

The lumps of propellant present in the igniter mixture should have a minimum dimension of at least about inch and a maximum dimension of not more than about A; inch. For example, cubical lumps might be A; inch on a side or may be as much as inch on a side. Another lump having a slab shape may be 4 inch in one dimension by inch on another side and /2 inch in the third dimension. Spherical lumps may have a diameter varying from about /8 inch to as much as /3 inch. It is to be understood that the particular configuration of the lump will be determined by the composition of the propellant forming the lump and also by the composition of the rocket propellant to be ignited. Since military propellants must be readily ignited on the broad temperature range the igniter mixture will almost always be adapted to initiate sustained combustion of the main body of propellant at temperatures on the order of -70 F.

The igniter mixture must contain at least enough of the powder member to initiate sustained combustion of the lump member. The amount of powder member will be determined by the composition of the powder member as well as by the composition of the lump member. When utilizing as the powder member black powder having an average screen size between A and inch, it is preferred to have as the igniter mixture between about 3 parts by weight of powder member per part or lump present and about 1 part by weight of powder member per part of lump present,

The lumps are formed from ammonium nitrate propellant consisting essentially of ammonium nitrate oxidizable binder and a combustion catalyst. The lumps are formed by intimately mixing powdered ammonium nitrate, the binder and a combustion catalyst.

The combustion catalyst present in the lump propellant may be any one of those known to the art for use with ammonium nitrate explosives and ammonium nitrate propellants. The better known combustion catalysts are inorganic compounds of chromium, iron or copper for example, ammonium dichromate, chromic oxide, cupric oxide, yellow ferric oxide, Prussian blue, the various heavy metal cyanides and the various heavy metal cyanamides. Organic combustion catalysts are also known, a particularly suitable one is sodium barbiturate. Although finely divided carbon is not generally considered a combustion catalyst for ammonium nitrate it is present in moderate amounts and vastly increases the sensitivity of ammonium nitrate containing propellants; therefore herein finely divided carbon is considered as a combustion catalyst particularly in combination with one of the above designated inorganic or organic catalysts.

The binder portion of the lump member may be any oxidizable or combustible material which will permit the formation of a suitable configuration of ammonium nitrate powder, combustion catalyst powder and binder. The binder is oxidizible in order to take advantage of the free oxygen produced in the decomposition of ammonium nitrate. The binder is generally a thermoplastic material containing carbon, hydrogen and usually oxygen atoms. Also the binder may be a thermosetting organic material. Thus the lump member may be produced by intermingling ammonium nitrate powder catalyst and chemical reagents which under the action of heat react to form resinous or polymeric materials which set to form a suitable configuration having the appearance of a solid. These thermosetting materials may be of very high molecular weight polyesters, thiokol rubbers, vinyl pyn'llidone rubber, etc.

Thermoplastic binders are preferred because of the ease of preparation of the lump member. The thermoplastic binders may be a unitary material such as a petroleum asphalt or a multi component solution. In general the thermoplastic binders consist of a polymer or resin to provide strength and a single or dual plasticizer to impait sufiicient thermoplastic characteristics to the binder. Examples of strength affording materials are cellulose acetate of various acetic acid contents, cellulose acetate butyrates of various acid contents cellulose propion-ates (the cellulose derivatives are available over the entire spectrum of acid contents), polyvinyl acetate, polyvinyl chloride, mixtures of these two polystyrenes, and styrene acrylonitrile. This listing is not inclusive of all possible materials suitable.

The plasticizers may be any one of the multitudinous numbers known to the plastic art as suitable for plasticizing polymers and resins of the types set out above. Reference to any Plastics Handbook will produce sufi"1 cient representatives of these materials.

In general the lump ammonium nitrate propellant will contain at least about 65 weight percent of the ammonium nitrate and from about 2 to 5 weight percent of combustion catalyst, the remainder of the composition will consist of binder and possibly a few of other materials which are designed to improve the stability of the composition or act as ignition promoters for example, diphenyl amine is added to improve the stability at high temperature. Small amounts of surfactants are frequently used to improve the forming of the binder.

Examples of ammonium nitrate propellant compositions which have been found suitable for use as the lump member of the igniter mixture of this invention are set out below. Ammonium nitrate 72%, ammonium dichromate 2%, binder 24%; the binder consisted of 25% of lacquer grade commercial cellulose acetate, 37% of dinitrodiphenyl oxide and the remainder a polyester condensation product of ethyleneglycol and diglycolic acid. Ammonium nitrate 73%, Prussian blue 4% and the remainder binder having the approximate composition set out in the preceding propellant. Ammonium nitrate 74%, magnesium nitrate 2%, ammonium dichromate 2%, and the remainder binder; the binder consisted of 31% of cellulose acetate butyrate and 69% of 2,4-dinitrodiphenyl oxide. Ammonium nitrate 76%, ammonium dichromate 2%, Prussian blue 1%, and the remainder binder; the binder consisted of polyvinyl chloride, 25 dinitrodiphenyl oxide and dinitrophenyl allyl ether in equal parts. Ammonium nitrate 83%, Prussian blue 3%, carbon black 2%, and the remainder binder; the binder consisted of polyvinyl chloride 25 dinitrophenyl allyl ether 25 dinitrodiphenyl oxide 30%, and dinitrotoluene 20%. Ammonium nitrate 76%, Prussian blue 3%, carbon black 1%, and the remainder binder; the binder consisted of polyvinyl acetate 25 and bis- (dinitrodiphenyl) triglycol ether 75%. The polyvinyl acetate composition of the preceding sentence is modified by the presence of about 1% each of diphenyl amine and urea. Ammonium nitrate 70%, carbon black 3%, diamino toluene 1%, sodium barbiturate 3% and the remainder binder; the binder consisted of cellulose acetate lacquer grade 28%, asphalt 8%, acetyl triethyl citrate 34%, dinitrophenoxy ethanol 30%. Ammonium nitrate 79%, Prussian blue 3%, carbon black 2% and the remainder binder; the binder consisted of roofing asphalt 65%, polyisobutylenes 100,000 M.W. 11% and dinitrophenylethyl acetate 34%. Ammonium nitrate 79%, Prussian blue 3% and the remainder binder; the binder consisted of roofing asphalt 30%, styrene acrylo nitrile 29%, acrylonitrile units 20%, dinitrotoluene 20% and dinitrodiphenyl oxide 30%. Ammonium nitrate 77%, Prussian blue 1%, ammonium dichromate 2%, and the remainder binder; the binder consisted of styrene acrylonitrile 25%, dinitrodiphenyl oxide 31%, dinitrophenyl allyl ether 31%, dinitrostilbene 4% and rosin, 200F. softening point, 9%.

Example 1 In this example a gas generator suitable for use in the cartridge shown in the illustrations could not be ignited at temperatures of 40 F. and below by the use of a black powder igniter mixture consisting of 70 grams of CCC grade blasting powder having grains about /2 inch in sieve size.

A mixture consisting of 45 grams of this CCC blasting powder and 25 grams of lumps of propellant initiated sustained combustion of the propellant at temperatures below 70 F.

An igniter mixture consisting of 40 grams of CCC blasting powder and 15 grams of lumps of propellant was able to initiate sustained combustion of a gas generator propellant at 70 F. In both instances the lumps of propellant utilized in the igniter mixture were cubes approximately inch on a side.

The composition of the lump propellant was ammonium nitrate 80%, Prussian blue 3%, carbon black 1%,

diaminotoluene 1%, and the remainder binder; the binder consisted of 25% dinitrophenyl propyl ether, 25% dinitrodiphenyl oxide, 20% styrene acrylonitrile and 30% roofing asphalt. The ingredients were thoroughly intermingled at about 100 C. and cast into a slab; after the slab had cooled it was cut into cubes about inch on a side. The proper amount of cubes and blasting powder were then intermingled by simple shaking in a small cup and poured in a random mixture into the igniter. (The propellant had this same composition except that sodium barbiturate was substituted for Prussian blue.)

Example 2 In this example the igniter mixture consisted of irregular lumps of ammonium nitrate propellant ranging in size from about A; to inch. The igniter mixture consisted of FFF grade black powder and aluminum powder. This igniter mixture was successful in starting ammonium nitrate propellant at low temperature, which the powder member alone was unable to do.

In this instance the lump member had the same composition as the propellant being ignited. The composition of the propellant was ammonium nitrate 72.6%, Prussian blue 2%, yellow ferric oxide 1% and the remainder binder; the binder consisted of lacquer grade cellulose acetate 20%, dinitrodiphenyl oxide 40%, and polyester condensation product of ethyleneglycol and dirglycolic acid 41% Example 3 In this example the igniter mixture consisted of lumps of the ammonium nitrate propellant composition of Example 2. The powder member consisted of about equal parts by weight of powdered magnesium and potassium nitrate. This igniter mixture not only initiated combustion of the body of propellant having the same composition as the lump member but also markedly reduced the thrust surge caused by the brisance of the magnesium powder-potassium nitrate mixture.

The igniter assembly of the invention is described in detail and its use in a gas generator operation in connection with the annexed figures will form a part of this specification.

FIGURE 1 shows a partial section of one embodiment of an igniter assembly.

FIGURE 2 shows a plan view looking into the cup of the igniter assembly of FIGURE 1.

FIGURE 3 shows a section of a gas generator cartridge utilizing the embodiment of FIGURE 1.

FIGURE 4 is a partial section plan view of the cartridge of FIGURE 3.

The figures show in detail a gas generator cartridge suitable for use in turbojet starting. It is to be understood that this is only one of many places in which the igniter assembly of the instant invention may be used.

One of the simplest techniques now used for starting turbojet engines involves an auxiliary engine, called a turbojet starter, which auxiliary engine or starter turns over the main turbojet rotor and brings it up to the desired rotational speed before the injection of the fuel 'into the combustors. This turbojet starter comprises a gas-driven turbine which is connected, through gearing, to a clutch and the entire assembly is then mounted on the frame of and coupled to the shaft of the main turbojet rotor. The gas for driving the starter turbine is derived from the combustion of a solid propellant. The solid propellant is burned in a chamber which is mounted integrally as a part of the starter. This chamber is formed to receive a starter cartridge and is designed to be opened and closed manually. The chamber is divided at about its mid-portion into a lower section and an upper section; the two portions are locked together by an ordinary slip joint, which slip joint is not gas tight. This type of sealing means is used rather than a gas type screw thread in order to permi-tmanual operation without the use of tools. The solid propellant, whose combustion produces the gases that turn over the starter turbine, is contained in a cartridge case which is designed to fit into the starter chamber.

The igniter assembly is described in detail in connection with 'FIGURES 1 and 2. The igniter cup 11 is a shallow metal cup relatively wide in relationship to its depth. This relationship is in order to provide a burst of ignition gases covering a large portion of the end of starter grain and also in order to reduce the total length of the starter cartridge case. The shell of the cup is turned over at the ends in order to strengthen the cup. There is centrally located in cup 11 a hole wherein the electrical conducting elements are positioned. Tubular bushing 12 is fitted in this hole. The inner end of tubular bushing 12 is crimped over to form a tight fit between the metal of cup 11 and the bushing 12. An electrical conductor 14 is fastened to bushing 12 inside cup 11. In this instance, connection 14 is a copper washer and the connection is made by crimping the inner end of bushing 12 over washer 14. A female clamp electrical terminal 16 is fastened on to washer 14 in order to provide a connection for the wires of an electrical squib. An electrical conducting rod 17 passes through the interior of bushing 12 and extends from the inside of cup 11 to point somewhat beyond the outer end of said bushing to form an electrical contact point. In this embodiment, the end of rod 17 has been expanded to form a broad contact point 18. At the inside end of rod 17 there has been attached a female electrical clamp 19 to which the electrical leads of a squib are attached. The contact end 18 of conducting rod 17 is insulated from the interior of bushing 12 by means of an elastic moisture-impervious insulating means 21. Means 21 may be any elastic material which is not an electrical conductor and at the same time will prevent the ingress of moisture into the conduit formed by bushing 12. Silicone rubber is particularly suitable. A reinforcing and insulating washer is positioned below insulating means 21 in the conduit formed by bushing 12. This insulating means may be a simple paper washer. Below this Washer there is positioned about rod 17 in the conduit of bushing 12 a tubular insulating means preferably of silicone rubber. This tubular element insulates rods 17 from bushing 12. The contact end 18 of rod 17 is rigidly maintained in predetermined relation with the outer end of bushing 12 by a fastening means positioned about rod 17 inside the cup. In this embodiment, a washer 26 is forced against the crimped end of bushing 12 by means of fastener 27. Other means for maintaining the contact end at the predetermined position while insulating rod 17 from the lower end of the bushing 12 may be readily devised.

The ignition device comprising the cup and the electrical conduction means are rigidly attached to the hole provided in the end-closure of the shell of the cartridge in such a way that the contact point 18 is exposed beyond the outside wall of the end-closure. In FIGURE 1, there is shown one means of having this fastening. In this embodiment, the outside of the portion of bushing 12 extending outside of shell 11 is threaded and the igniter assembly is fastened to the end-closure by means of nut 31. Nut 31 is also shown in FIGURE 3. It is preferable that some means of vibration-proofing nut 31 be provided and in FIGURE 3 lock washer 32 is provided. The security of the igniter assembly may be further enhanced by having the radius of the curvature of cup 11 slightly greater than the radius of curvature of the end-closure. Thus when the ignition device is fastened by means of nut 31 the curved portion of cup 11 is forced into conformity with the curvature of end-closure, thereby providing an almost vibration-proof fit between the igniter assembly and the end-closure.

In FIGURE 2,

electrical squibs

33 and 34 are shown in position inside of cup 11. Cup '11, containing the squibs, is then filled with the particular igniter mixture utilized in the specific embodiment of the starter cartridge. It is necessary to close the end of cup 11 to keep the ignition mixture in place and also to have a moisture-impervious protection for the ignition mixture. A moisture-impervious film may be placed over the open end of cup 11 and then fastened by some fastening means passing around the rim 36 of cup 11. Another form of closure for cup 11 is made of moistureimpervious elastic material provided with a flange which snaps over rim 36 of cup 11. It is necessary that the moisture-impervious fi-lm closing beyond the cup 11 be held securely enough to avoid any slipping-off of the film during handling and also strong enough to avoid rupture of the film during handling. In the particular embodiment set out herein, the end of cup 11 is closed by means of a moisture-resistant paper 38 positioned over the open end of cup 11 and passing down the sides of the cup in an overlapping manner. Over the moistureresistant paper is positioned an aluminum foil sheet 39 also overlapping the sides of the cup 11. The two-layer film is securely fastened to the cup by means of wire 41. Instead of wire 41, a circular spring may be used to securely clamp the film to the sides of the cup. To complete a moisture-impervious covering for cup 11, a moisture-resistant tape 42 is wrapped over wire 41 extending beyond the end of

films

38 and 39.

The

squibs

33 and 34 are actuated by an electrical impulse from the cockpit of the airplane, for example. The electrical impulse is passed into the starter chamber, passes through contact point 16 into

squibs

33 and 34. When the cartridge case is unpainted and is made of electrical conducting material no special grounding means are needed. When the cartridge case is painted, as may be required for storage purposes, it is necessary to provide adequate grounding means for insuring proper firing of the squibs. In FIGURE 1, there is set out a particularly effective means for providing an electrical ground and also a safety device in the handling of the cartridge case prior to insertion in the chamber. This device is called a short-out clip and it comprises a curved portion 46 which extends over and is in spaced relation to contact point 18. The curved portion is then joined to the exterior of the bushing in a manner to form a good electrical contact. In this embodiment, a metal washer 47 provided with anti-vibration loosening teeth forms the contact between the curved portion 46 and the exterior bushing 12. In storage and handling, the tip 48 of the short-out clip prevents accidental electrical contact with the contact point 18. When the cartridge has been introduced into the starter chamber, curved portion 46 is straightened somewhat, and tip 48 is set out in such a position that when the chamber is closed, tip 48 is firmly touching the chamber and thereby provides a good electrical ground. Other means of grounding may readily be devised.

In the particular embodiment shown in FIGURE 1 the cup contains about 40 grams of CCC grade blasting powder. The blasting powder grains are depicted as ovals in the partial section, FIGURE 1. About 25 grams of ammonium nitrate propellant was cut into slabs and utilized as the lump portion of the igniter mixture. These lumps are shown as the rectangles in FIGURE 1.

In FIGURE 3, a thin-walled tubular body portion 61 is provided with a shallow groove 62. The tubular body portion may also be described as a cylinder. The wall of body portion 61 is made thick enough to withstand the handling requirements of turbojet starter cartridges. It is obvious that the thickness of the wall will be dependent upon the type of material used. It has been found that with ordinary mild steel material of construction sheet of 16 or 20 gauge is of sufficient strength. Groove 62 is positioned at about the midpoint of body portion 61 and runs around the entire periphery of the body portion. The depth of the groove 62 is such that the means for sealing the slide joint of the starter chamber will fit into the groove so as to provide a substantially flush surface with respect to the exterior side of the tubular body portion wall. It is to be understood that the sealing means need not be exactly flush with the outside wall as the cartridge case is not a sliding fit into the starter chamber.

Positioned in groove 62 are a plurality of

apertures

63, 64, etc. These apertures are substantially uniformly spaced about the periphery of body portion 61. The function of apertures 63, etc. is to permit gas produced from the combustion of the solid propellant grain 66 to pass through the wall of the case and exert pressure on the sealing means. Apertures 63, etc. may be small holes, for example one-eighth inch in diameter or they may be slots. The apertures 63, etc. are relatively small with respect to the width of groove 62. The apertures 63, etc. are substantially uniformly spaced around the periphery of the body portion 61 in order to insure sealing of the entire joint surrounding the case, the joint in the starter cartridge being located immediately adjacent the groove 62 provided in body portion 61. It has been found that a plurality of apertures are necessary in order to provide good sealing, the exact number of apertures being a function of the aperture size. Too large a number of apertures or too large a size relative to the width of groove 62 may cause destruction of the sealing means and permit leakage of gases out of the chamber by way of the joint. The exact number of apertures 63 and the size thereof may be readily determined by a small number of tests for each type of seallng means.

The cartridge must not be damaged by the entrance of moisture into the interior of the case. Moisture interferes with the proper burning of the solid propellant. The apertures 63, etc. are covered with a moisture-impervious film 67 which extends around the periphery of the body portion in groove 62. The moisture-impervious film 67 need not be impervious in the precise sense of that word. Hereinafter moisture-impervious is to be understood as a material which will prevent water entering the film of the particular thickness being used for a time substantially in excess of the specification requirement of no moisture peneration after 2 hours exposure to a driving rain.

The means for sealing the joint of the chamber in an elastic ribbon-like member 68 positioned in groove 62 and extending over apertures 63, etc. provided in the groove of body portion 11. Member 68, which may be described as a rubber-like elastic band, extends over apertures 63, etc. an appreciable distance. Gases from the combustion of solid propellant grain 66 break through the film 67 at apertures 63, etc. and exert pressure against band 68, expanding it against the joint in the starter chamber. It is preferred that band 68 be about the width and depth of groove 62. Band 68 may be any material which is sufiioiently elastic to be expanded the distance between the outside wall of groove 62 and the surface of the starter chamber to seal the joint in the chamber. The elastic member or band 68 may be made of various synthetic materials, such as polyethylene or polyvinyl acetate which has been plasticized to render it elastic. It is preferred that band 68 be rubber-like in characteristics and made from natural or synthetic rubbers. Because of its resistance to temperature, silicone rubber is preferred as a material of construction for rubber-like member 68.

There is attached to one end of body portion 61 a thinwalled end-closure means 71. End-closure means 71 may be fabricated integrally with body portion 61 or may be attached thereto by welding or by nuts and bolts or by rivets. It is desired that end-closure member 71 be substantially rigidly attached to body portion 61. It has been found that mild steel sheet of 16 gauge thickness is more than adequate for use in end-closure means 71.

End-closure 71 is adapted for the mounting of igniter assembly herein designated as numeral 73. Usually endclosure 71 will be provided with a hole which is centrally located with respect to the long axis of body portion 61 into which the igniter assembly is mounted by means hereinafter described.

End-closure means 71 is provided with a plurality of

apertures

76, 77, etc. These apertures 76, etc. are positioned on the end-closure so as to permit free flow of gases from the interior of the case through the apertures. The presence of combustion gas on the exterior of the end-closure end of the case has some beneficial effect on the operation of the starter, the number of apertures 76, etc. to be determined by the size of the aperture and also by the solid propellant itself. In general, 3 or 4 one-eigth inch apertures appears to be suflicient. These apertures 76, etc. should be placed uniformly on the end-closure about the central point thereof.

To exclude moisture from the interior of the case, apertures 76, etc. are covered by moisture-impervious film means. Apertures 77 in FIGURE 4 is shown covered by moisture-impervious film means 81. The film means used to cover apertures 76, etc. may be of the same material of construction as the films means 67 used to cover apertures 63, etc.

Solid propellant grain 66 is, in this embodiment, a tube. A gas flow passage must be provided along the interior wall of tubular portion 61. The outside diameter of grain 66 is set relative to the internal diameter of body portion 61 so that the necessary predetermined spacing for the flow of gases at the initial combustion is set. Grain 66 is cushioned against handling by means of resilient members positioned both on the cylindrical sides of the grain and also on the flat bottom and top sides. In this embodiment, four resilient side members and end members are utilized at each end of the grain to provide this support. In FIGURE 3, upper resilient side member 86 and lower resilient side member 87 are shown, the number of resilient members to be determined in part by the type of solid propellant used and also the material of construction of the resilient members themselves. The resilient members may be made from spring-like materials and may even be coil springs. However, it is preferred that the resilient members be made of materials such as felt, rubber, or cork. Felt is a particularly good material. The resilient side members are adapted to maintain a predetermined spacing between the interior side of the body portion wall and the exterior of the grain 66; or this may be described as a predetermined spacing between the interior of the body portion 61 and the inner surface of the side member since the inner surface of the side member must be in contact with the outer surface of the grain. The upper resilient side members are supported near the end-closure means.

Upper resilient end-members 87, etc., are supported near end-closure means 71 and are adapted to maintain a predetermined spacing between the inner side of the end-closure wall and the inner surface of the upper end member, i.e., the upper end of grain 66. In this embodiment, the upper side member and

upper end member

86 and 87 respectively are formed out of one L-shaped piece of resilient material and are mounted against the inner wall of tubular portion 61. The upper members are supported by means of an apertured doughnut plate 89 which is spaced from the end-closure by means of

legs

91, 92, 93 (and 94 not shown). These legs are spot-Welded to the inner surface of end-closure 71. Also, the flat portion of plate 89 is spot-Welded to the inner wall of body portion 61. Holes 96, etc. are provided in plate 89 to permit free flow of gases from igniter 73 along the inner wall of body portion 61 and thereby contacting of the exterior surface of grain 66. It is self-evident that other methods of supporting the resilient members may be devised, for example, individual metal portions just large enough to hold the resilient members. The side members may be readily attached to the interior of the body portion by adhesive when it is desired to use separate end members and side members.

At the end of the body portion 61 opposite that containing end-closure 71, there is a thin walled screen-like member 101. This screen-like member 101 is adapted to be attached to the end of the body portion 61 opposite that wherein end-closure 71 is attached. In this embodiment, the attachment is made by means of snap-on means positioned on the end of body portion 61 and on the flange 101 of member 101.

Screen-like member 101 is provided with a spacing element 111. Spacing element 111 provides a spring action which works against the bottom of the starter chamber to force the igniter assembly electrical contact point against the electrical connection positioned in the upper end of the chamber. Screen-like member 101 is provided with a multiplicity of holes which extend through the wall of the member. These holes occupy substantially all of the portion of the member except for that taken up by the spacing element 111. The holes permit the substantially unobstructed flow of combustion gases from propellant 66 out of the cartridge case and on into conduit leading to the starter turbine. In this regard, spacing element 111 also provides the necessary clearing between the bottom of the starter chamber and the case to form a passage permitting the flow of the combustion gases. The holes in screen member 101 are of a size such that any unburned lumps of propel-lant will be retained in the case until reduced to size which will not clog the conduit leading to the starter turbine. Screen member 101 is formed of material of sufl'icient thickness to impart the necessary strength to the member in view of the multiplicity of holes therein.

Resilient members are provided at the screen member end of the body portion to maintain the predetermined spacing between the inside Wall of the body portion 61 and the cylindrical side of the grain 66. Also, the resilient members maintain a predetermined spacing between the screen member and the end of the grain 66. In FIGURE 3, lower resilient side member 121 and lower resilient end member 122 are shown. Actually in this embodiment four lower resilient side members and four lower resilient end members, in the form of an L-shaped piece of felt, are utilized. The lower resilient members may be made of the same type of material and be of the same construction as the upper resilient members. In this embodiment, the L-shaped lower resilient end members are not fastened to the wall of tubular body portion 61. The clearance between the screen member 101 and the end of grain 66 is such that the resilient members are held in place by pressure from the screen member 101 when it is locked onto the end of body portion 61. However, suitable means for fixedly attaching the lower resilient members may be readily devised.

In order to exclude moisture from entering the case by way of screen member 101, a moisture-impervious film 124 is placed over the open end of body portion 61 after the lower resilient members have been put into place. The film 124 extends not only over the open end but overhangs the sides of portion 61 and is crimped between the flange 102 of screen member 101 and the end of the body port-ion 61. Moisture-impervious film 124 is preferably made of a plastic or rubberized material which, while excluding moisture, will disintegrate substantially instantaneously when pressure is imposed on it by the combustion gases from the burning of grain 66. Film 124 may be made of a very thin metal such as aluminum foil, although it is preferred that a combustible film be used. Polyethylene film is particularly suitable.

The igniter assembly used in a full size gas generator cartridge is described in detail. Igniter cup 11 used in this particular embodiment was 2% inches in outside diameter provided with a turned-over edge spaced somewhat from the cup so that the total overall diameter was 2% inches. The curved portion of the cup was a section of a sphere having a radius of inches. The bushing which extends through a centrally located hole in the cup was machined to provide a threaded portion on the exterior of the bushing and a necked-in straight portion. The total length of the bushing was $4 inch with the threaded portion being one-half the length. The interior of the bushing was machined to provide a shoulder on which to rest a washer. Electrical conductor rod 17 made of A inch drill rod and about inch overall length was passed through the interior of bushing 12. A brass washer was silver soldered to the end of rod 17 to provide a contact point. The contact point was Vs inch in diameter. A silicone rubber insulator in the form of a cup extends below the brass washer of the contact point and up the sides, insulating the rod and the washer from the bushing. Beneath the silicone rubber was positioned a hard fiber washer which rested on the shoulder inside bushing 12. A silicone rubber tube was placed around rod 17 and passed up into the bushing to insulate the rod from the bushing. A copper washer was placed around the inside end of the bushing inside the cup and the end of the bushing was then crimped against the washer to firmly seat the washer and the bushing against the curved end of cup 11. A female solderless terminal, capable of holding two No. 22 gauge copper wires, was attached to washer 14. A hard fiber washer was passed up rod 17 and was held rigidly against the cn'mped end of bushing 12 by means of a one-piece nut. A female terminal was then attached to the interior end of rod 17. Two regular electrical squibs were then attached to the terminals as shown in FIGURE 2.

The igniter cup was then filled with ignition mixture. The ignition mixture was held in place by means of a sisalkraft paper and aluminum foil sheet, the ends of which were securely wired to the cup below the flange 36. Drafting tape was then used to moisture-proof the edge of this paper-foil seal.

Thus having described the invention, what is claimed 1. An igniter assembly comprising a vessel, having an open end, an igniter mixture, positioned in said vessel, consisting essentially of (a) a number of grains of a powder member selected from the class consisting of black powder, magnesium powder-potassium nitrate mixture, aluminum powder-potassium nitrate mixture, aluminum powder-alkali metal perchlorate mixture and magnesium powder-alkali metal perchlorate mixture and (b) a number of lumps consisting essentially of ammonium nitrate, an oxidizible binder and a combustion catalyst, the ammonium nitrate being the predominant component, said lumps having a minimum dimension of at least about Vs inch and a maximum dimension of not more than about inch, said igniter mixture containing an amount of said powder member at least sufiicient to initiate sustained combustion of said lumps, readily destructible means for maintaining said mixture within said vessel and means, positioned within said vessel, adapted for initiating burning of said powder member.

2. The assembly of claim 1 wherein said lumps are approximately cubical in shape of about inch on a side.

3. The assembly of claim 1 wherein said powder member is black powder having an average screen size between about /1 and /1 inch.

4. An igniter assembly comprising a cup-like member, an igniter mixture positioned in said cup consisting essentially of (a) black powder grains having an average screen size between about 1 1 and inch and (b) a number of lumps consisting essentially of ammonium nitrate, an oxidizable binder and a combustion catalyst, said lumps containing at least about weight percent of ammonium nitrate, said lumps having a minimum dimension of at least about /a inch and a maximum dimension of not more than about inch, said igniter mixture containing between about 3 parts by weight of powder per part of lumps present and about 1 part by weight of powder per part of lumps present, readily destructible means for maintaining said mixture within said cup and means, positioned in said cup, adapted for initiating burning of said black powder.

References Cited in the file of this patent UNITED STATES PATENTS 802,347 Aspinwall Oct. 17, 1905 2,124,201 Lewis July 19, 1938 2,398,683 Whitworth Apr. 16, 1946 2,434,872 Taylor Jan. 20, 1948 2,530,493 Van Loenen Nov. 21, 1950 2,561,670 Miller July 24, 1951 2,637,274 Taylor May 5, 1953 2,696,191 Sheehan Dec. 7, 1954 FOREIGN PATENTS 10,883 Netherlands July 15, 1924 655,585 Great Britain July 25, 1951

Claims

1. AN IGNITER ASSEMBLY COMPRISING A VESSEL, HAVING AN OPEN END, AN IGNITER MIXTURE, POSITIONED IN SAID VESSEL, CONSISTING ESSENTIALLY OF (A) A NUMBER OF GRAINS OF A POWDER MEMBER SELECTED FROM THE CLASS CONSISTING OF BLACK POWDER, MAGNESIUM POWDER-POTASSIUM NITRATE MIXTURE, ALUMINUM POWDER-POTASSIUM NITRATE MIXTURE, ALUMINUM POWDER-ALKALI METAL PERCHLORATE MIXTURE AND MAGNESIUM POWDER-ALKALI METAL PERCHLORATE MIXTURE AND (B) A NUMBER OF LUMPS CONSISTING ESSENTIALLY OF AMMONIUM NITRATE, AN OXIDIZIBLE BINDER AND A COMBUSTION CATALYST, THE AMMONIUM NITRATE BEING THE PREDOMINANT COMPONENT, SAID LUMPS HAVING A MINIMUM DIMENSION OF AT LEAST ABOUT 1/8 INCH AND A MAXIMUM DIMENSION OF NOT MORE THAN ABOUT 5/8 INCH, SAID IGNITER MIXTURE CONTAINING AN AMOUNT OF SAID POWDER MEMBER AT LEAST SUFFICIENT TO INITIATE SUSTAINED COMBUSTION OF SAID LUMPS, READILY DESTRUCTIBLE MEANS FOR MAINTAINING SAID MIXTURE WITHIN SAID VESSEL AND MEANS, POSITIONED WITHIN SAID VESSEL, ADAPTED FOR INITIATING BURNING OF SAID POWDER MEMBER.