US3224373A - Igniter device for solid body of pyrotechnic material - Google Patents

Description

J. M. KRAMER Dec. 2l, 1965 IGNITER DEVICE FOR SOLID BODY PYROTECHNIC MATERIAL 2 Sheets-Shea?l 1 Filed May l, 1963 l, cri

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IGNITER DEVICE FOR SOLID BODY OF PYROTECHNIC MATERIAL INVENTOR JACK M. KRAMER mme@ ATTORNEY United States Patent O 3,224,373 IGNITER DEVICE FOR SLlD BODY OF PYROTECHNIC MATERAL Jack M. Kramer, Los Alamitos, Calif., assignor to Aerojet- General Corporation, Azusa, Calif., a corporation of Ohio Filed May 1, 1963, Ser. No. 277,392 1 Claim. (Cl. 102-70) 'and igniter basket, the ignition of the pellets by the heat from the flame tube serving to ignite the charge of solid propellant.

It is desirable that the propellant charge should be ignited evenly but without explosive force. It has been found that the currently used ignition arrangements are liable to perform imperfectly because of faulty performance.

It is an object of this invention to provide an igniter device, for solid bodies of pyrotechnic material, which will produce an evenly distributed and intense iiame over the whole area of the igniter body resulting in satisfactory initiation of ignition of the pyrotechnic material.

Another object of the invention is to provide an igniter device free from the danger of localized explosions due to accidental concentrations of pyrotechnic material in the igniter.

A further object of the invention is to provide an improved igniter construction which is simple in construction and may be applied to a conventional ame tube or may be formed so that it may be used without a separate flame tube.

Still further objects and features of the invention will `appear from the following description read with reference to the accompanying illustrated drawings, wherein:

FIGURE 1 is a View in elevation of an igniter device constructed according to the present invention, parts of the device being shown in sect-ion to clearly show the interior arrangement;

FIGURE 2 is a fragmentary plan view of a suitable forming means for a novel element of the device;

FIGURES 3 and 4 show steps in in forming said novel element;

FIGURE 5 is a fragmentary cross-section taken on the line 5 5 of FIGURE l;

FIGURE 6 is a View similar to FIGURE 5 but showing a modified form of the invention.

Referring now to FIGURE l of the drawings, the numeral 11 indicates a llame tube which may be a perforated plastic -tube held in a mounting plug 12 which is screwed into the head of a combustion chamber 13. The tube 11 is arranged to project into an axial hole in the solid propellant body 14.

An electrically ignited squib 15 is held in mounting plug 12 to project into the ame tube 11 by a threaded plug 16 screwed into plug 12. The wire lead 17 from `squib 15 is sealed by a bored stud 18. Pressure seals 19, 20 and 21 are provided as indicated to prevent blowback from the combustion chamber.

A novel double-walled sheath 22 is mounted on the rotor surface of the flame tube 11 and provides a multiplicity of pockets or concavities 23 formed between its inner and `outer walls. The formation of the sheath 22 will be described with reference to FIGURES 2 through 4, but it will be evident that it may be formed by other appropriate methods.

The sheath 22 may be formed in a box-like mold 24 comprising sides 25 secured together at their ends by welding or the like, and a bottom 2'6. The mold is provided with a detachable lid 27 which may be clamped thereon by bolts 28. A spacer frame 29 is fitted into the mold 24 resting upon the bottom 26 and a forming member 30, which may be a section of expanded metal, is supported by the spacer frame 29. A thin sheet of any suitable -thermosetting plastic 31 in not fully cured condition is laid upon the forming member 30 and the edges clamped thereagainst by a clamping frame 32. Frame 32 is secured by screw eyes 33 extending through plastic sheet 31 and forming member 30 into spacer frame 29. Lid 27 may be clamped shut and air under pressure admitted through fitting 34 into the mold above the plastic sheet resulting in the formation of a multiplicity of pockets or concavities 23 having a depth limi-ted by the spacing between forming member 30 and the bottom 26 of the mold. Air can then be shut off and the lid 27 27 and frame 32 may be removed. Thereafter, the cavities 23 in sheet 31 are filled level with the at side of the sheet with a powdered pyrotechnic material such as barium nitrate, powdered Alclo or other initiating powder. The formed sheet 31 constitutes the outer wall of the sheath 22. Care is taken to keep the flat portions of sheet 31 and the areas between the pockets 23 clear of the pyrotechnic material. t

A thin sheet 35 of material such as Mylar cut to accommodate the stems of screw eyes 33 and coated on both front and back with a pressure sensitive adhesive is then laid over the formed sheet 31 as seen in FIGURE 4. Then the lid 27 again is clamped in place and air under pressure again is supplied to thte box to cause the sheet 35 to bond evenly over the pocketed" sheet 31 and encapsulate the powdered pyrotechnic material in the pockets 23. Preferably, both layers 31 and 35 are made of plastic which is consumed by the hot gases from squib 15.

The formed sheet 31 with the encapsulated rapid burning powdered pyrotechnic material may then be removed from box 24 and wrapped around the flame tube 11 with the pockets 23 containing powdered pyrotechnic material overlying the -openings 11 in the walls of the ame tube 11 as indicated in FIGURE 5. The formed sheet 31 is wrapped around the flame tube under sufficient tension to effect bonding of the sheet to the flame tube, and bath are then positioned in the mounting plug 12. It will be understood that the mounting plug and igniter assembly form a separate fitting which need not be assembled into the combustion chamber until the rocket lis to be red.

An igniter basket 36, which is a rigid plastic tube having a perforated wall and of considerably greater diameter than sheath 22, is then positioned in the m-ounting plug 12. A U shaped locating ring 37 may be used to firmly maintain the accurate positioning of the ends of the tubular parts nested in the mounting plug 12. The ends of the parts are preferably secured to the mounting plug by a suitable adhesive applied to the contacting surfaces during assembly.

The space between the inner surface of the igniter basket 35 and the outer surface of sheath 22 is then filled with fast burning material in the form of pellets 38 of a size too large to pass through the perforations in the wall of the igniter basket 35. A suitable material is commercially available and sold under the registered trademark Alclo and is manufactured by the Aerojet-General Corporation.

The outer end of the whole assembly is closed, as for instance, as indicated in FIGURE 1 by a combustible cap 39. It will be observed that the igniter forms a selfcontained component with the double walled sheath 22 mounted on the flame tube 1l, and it need not be armed by the positioning of the squib 15 until the rocket is to be red.

The provision of the sheath carrying a layer of powdered fast burning pyrotechnic material extending over the whole surface of the lame tube ensures an evenly distributed and intense starting flame and is free from explosive effects.

If preferred, the member 22 may be formed to eliminate the requirement of the flame tube 11, as well as to transmit conagration to pellets of fast burning pyro` technic material, As shown in FIGURE 6, this may be accomplished by providing an inner skin 3S suihciently rigid to maintain the device in position for a suicient length of time to allow initiation of combustion of the charge of solid propellant i4, For instance, the inner skin may be comprised of a sheet of plastic impregnated asbestos punched with a pattern of holes aligned with the pockets Z3 of powdered fast burning pyrotechnic material. The sheet of asbestos impregnated with plastic is glued to the outer or powdered pyrotechnic covering skin 3l in a manner as previously described and the whole brought to cylindrical form and retained therein, for instance, by small staples.

In some cases it may be suliicient to provide only the pocketed powdered pyrotechnic material-containing sheath 22 Without using an igniter basket and pellets of fast burning pyrotechnic material.

Preferred embodiments of the invention have been described and shown in the accompanying drawings by way of illustrative example but not as limitative of the invention since various modifications and changes may be made i in the described embodiments by those skilled in the art without departing from the scope of the invention as dened by the appended claim.

What is claimed is:

An igniter device for initiating combustion of a surrounding solid body of pyrotechnic material, said igniter device comprising a double-walled tubular member having inner and outer walis, said walls being formed of a material consumable by heat, said outer wall being provided with a plurality of inwardly directed concavities, said inner wall being joined to the inner portions of said outer wall in areas other than those detining said concavities in said outer wall to provide separate pockets between said walls, and powdered fast-burning pyrotechnic material encapsulated in each of said pockets, said inner wall being further provided with a plurality of inwardly opening recesses extending partially through the thickness thereof, and said recesses being in underlying alinement with said pockets in which the powdered fast-burning pyrotechnic material is encapsulated.

References Cited by the Examiner UNTED STATES PATENTS 1,317,610 9/1919 Barlow 102-70 2,774,306 12/1956 MacLeod 102--70 2,998,777 9/1961 Ryan 102-865 3,014,425 12/1961 Turnbull et al. 102-86.5 X 3,017,836 l/l962 Guay 60-35.6 3,062,147 11/1962 Davis et al. 102-70 OTHER REFERENCES Rabern, I. W.: Systems for Ignition of Solid Propellants, presented at American Rocket Society 14th Annual Meeting, Nov. 16-20, 1956.

BENJAMlN A. BORCHELT, Primary Examiner.

SAMUEL FEINBERG, Examinez'.

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