US3120184A - Pyrotechnical devices and methods of making the same - Google Patents

Description

HIELLERN Feb. 4, 1964 PYROTECHNICAL DEVICES AND METHODS OF MAKING THE SAME 3 Sheets-Sheet 1 Filed April 22, 1960 FIG. 2

FIG. 3

IN V EN TOR.

HERBERT ELLERN ATTORNEY 4 8 J, o 2 JW 3% w T m I K W F 0 N m R v m ET um m S E C I V E D L A C I N H C E T m 4Y 6 9 1 4" h e F 3 Sheets-Sheet 2 Filed April 22, 1960 2 8 INVENTOR.

HERBERT ELLERN 6 FIG. 7

H. ELLERN Feb. 4, 1964 PYROTECHNICAL DEVICES AND METHODS OF MAKING THE SAME 3 Sheets-Sheet 3 Filed April 22, 1960 FIG.9

FIG.||

IN V EN TOR. HERBERT ELLERN ATTORNEY United States Patent Office 3,l2,l8l Fatented Felt. 4, 19%4 3,120,184 PYROTECEHJICAL DEVICE AND METHODS F MAKING THE SAME Herbert Ellern, Ferguson, Mo, assignor to Universal Match Corporation, Ferguson, Mo, a corporation of Delaware Filed Apr. 22, 196%, Ser. No. 24,063 11 Claims. ((Il. lll237.8)

This invention relates in general to certain new and useful improvements in pyrotechnical devices and methods of making the same and, more particularly, to pyrotechnical materials in which the incandescent exothermic reaction, once initiated, will proceed linearly in a prescribed direction at a constant rate and under preservation of constant area.

Many pyrotechnical devices and solid propellant grains, when ignited, will burn over all, or a substantial portion, of the surface area of the grain is a somewhat predictable pattern and, as the grain is consumed, the area of burning surface will change. This type of burning is frequently undesirable because of the shortness of time and sometimes erratic progression of the reaction. As a matter of fact, it is frequently desirable to arrange a pyrotechnical reaction in such a manner that the incandescent exothermic reaction or burning, as it is usually called, will take place across a known area of the material and that the burning will proceed linearly along the longest axis of the material while the area of burning remains constant. In this manner, it is possible to achieve very precise rates of burning and uniform production of pyrotechnically gen erated forces, such as gas-production, light-output, heat output, and the like.

In some cases, it is also desirable to provide a pyrotechnical device in which the reacting mass will burn from the central core outwardly while the external surfaces of the material are protected from burning, so that the pyrotechnical reaction will proceed at an accelerated rate from the internally exposed surface because of constant increase in burning area from the inside outwardly.

In all such cases, where the spread of the flame or glow front over a surface is to be avoided, efforts are usually made to inhibit the surface. For instance, a loose powder-mixture may be pressed into a tube made of some pyrotechnically inert material, such as cardboard, metal, or the like. Another method of surface inhibition which has been commonly employed is to wrap pre-manufactured grains in a sheet of suitable material. Unfortunately, the existing methods involve bonds between the pyrotechnical surface and the inhibiting material which do not stand up under mechanical stresses, vibration, or extreme changes in temperature. Since pyrotechnical materials of the type here under discussion are quite often subjected to extremes of mechanical stress and vibration as well as extremes of temperature change, conventional bonds frequently separate partially and cause increased burning rate of an erratic nature starting at the exposed surface or crevice Where the bond has broken away. It is a common experience in rocket motors as well as in flare candles and related devices that crevices of this type can become sufiiciently large to cause accelerated burning reaching explosive proportions.

Furthermore, the conventional methods of inhibition have numerous technical and economical drawbacks. In the case of pyrotechnical items, the pressing of the ingredients into a structural part requires often a complex and costly split mold-design. Pressing into the final structural components has other disadvantages, especially when pressing in several increments is necessary, such as difficult quality control because of inaccessibility of the compressed material.

It is, therefore, the primary object of the present invention to provide a surface-inhibited pyrotechnical material in which the surface-inhibition is entirely reliable and will not break away from the inhibited surface or otherwise expose such surface to erratic burning.

It is another object of the present invention to provide means and methods for reliably inhibiting the surface of pyrotechnical materials so as to establish precisely predetermined burning rates and reaction characteristics.

With the above and other objects in view, my invention resides in the novel features of form, construction, arrangement, and combination of parts presently described and pointed out in the claims.

In the accompanying drawings (three sheets)- FIG. 1 is a perspective view of a pyrotechnical device constructed in accordance with and embodying the present invention;

FIG. 2 is a vertical sectional view taken along line 2-2 of FIG. 1;

FIGS. 3 and 4 are transverse sectional views taken along lines 3-3 and 4-4, respectively, of FIG. 2;

FIGS. 5, 6, 7, and 8 are schematic views, some of which are in section, illustrating the method or process of manufacturing pyrotechnical devices according to the present invention;

FIG. 9 is a perspective view of a modified form of pyrotechnical device constructed in accordance with and embodying the present invention;

MG. 10 is a perspective view of the pyrotechnical charge forming a part of the device shown in FIG. 9; and

FIG. 11 is a longitudinal sectional view taken along line llll of FIG. 9.

Broadly speaking, the present invention relates to a method of inhibiting the external surfaces of pyrotechnical masses, such as, for example, cylindrical flare candles or cylindrical propellant powder grains, by coating the surfaces, on which burning is to be precluded, with a soft, homogeneous, semi-solid material of high consistency and of such physical character that within a wide range of temperatures neither liquefaction nor solidification of the semi-solid material takes plac Materials which have been used and found satisfactory in connec tion with the present invention are, for example, temperature resistant greases, and plastomeric materials, such as semi-solid silicone polymers which evidence very slight viscosity change over wide ranges of temperature variation. In this connection, it has been found that the most useful and satisfactory semi-solid materials, for purposes of the present invention, are the chemical compounds known as silicone oils, otherwise usually referred to as organo-poly-siloxanes, which are converted, by addition of very finely ground mechanical thickening agents, such as silica aerogel, or chemical agents such as lithium s'tearate, into stiff greases which do not change their semi-solid state at temperatures as low as l00 F. or as high as +300 F. The organo-siloxanes which are operative in the present invention are set forth in Table 9 on page 184 of Chemistry of the Silicones (Second Edition), Eugene G. Rochow, John Wiley & Sons, Inc, and discussed in Chapter 6 thereof. Silicone greases which have been found to be suitable in the present invention are also described in US. Patents Nos. 2,258,219, 2,258,- 222, 2,352,974, 2,371,068, 2,428,608, and 2,446,177.

Referring now in more detail and by reference characters to the drawings, which illustrate a practical embodiment of the present invention and the method of making same, A designates a pyrotechnical device consisting of an external canister 1, preferably, though not necessarily, of a cylindrical shape, and formed of metal, cardboard, or other suitable rigid material, which is noncombustible, or does not burn, melt or disintegrate at a faster rate than the burning flare candle recedes. The canister 1 is preferably provided with a flat integral bottom wall 2. Disposed entirely within the canister 1 and of smaller diametrical and axial size with respect thereto is a pyrotechnical material, such as a magnesium/oxidizer/binder flare candle 3, which is held in concentric spaced relation internally of the canister 1 by means of a plurality of short very small-diameter metallic pins 4, the latter being secured axially upon the outer surface of the candle 3 by means of short sections of pressure-sensitive tape 5. As will be noted by reference to FIGS. 2, 3 and 4, two axially spaced sets of pins 4 are preferably employed and are located at 120 intervals around the surface of the candle 3, thereby insuring a relatively uniform annular space between the interior face of the canister 1 and the exterior surface of the candle 3. Since the candle 3 is somewhat shorter in length than the canister l, the space will extend transversely between the bottom face of the candle 3 and the bottom wall 2 of the canister 1. This space is completely filled with a semi-solid material 6 of the type above stated.

Compressed into and forming the top layer of the candle f; is a conventional first-fire portion 7 which is annularly encircled with a rubber or neoprene O-ring 3, the latter being held in place by a gasket ring 9. Finally, the upper margin of the canister 1 is annularly crimped over in the usual manner to form a sealing bead 10 which holds the gasket ring 9 in place.

As schematically illustrated in FIGS. to 8, inclusive, the pyrotechnical device A is preferably manufactured in the following manner. The canister l is filled to a predetermined level with a quantity of semi-solid material 6. Meanwhile, the compressed candle 3 is provided around its outer surface with a series of pins 4 held in place by sections of pressure-sensitive tape 5, as above described. The candle 3 is then pushed firmly down into the canister It. In this condition, it should be noted that the quantity of semi-solid material is computed rather accurately to correspond to the displacement of the candle 3, so that when the latter is finally pushed down into place, the semisolid material will rise upwardly in the canister 1 to precisely fill the entire space between the inner surface of. the canister l and the outer surface of the candle 3, with just enough clearance at the top to permit insertion of the O-ring 8. Finally, the gasket ring 9 is inserted and pressed down on the O-ring 8 until it is flush with the top surface of the first-fire portion 7. As this is done, the O-ring 8 may tend to push the semi-solid material 6 back down into the cannister 1 to a slight degree but a slight amount of a hydraulic compensation automatically takes place. In other words, the candle 3 may ease back upwardly a few thousandths of an inch as the bead 10 is crimped over.

A pyrotechnical device thus designed will burn in a perfectly linear manner and with a precisely reproducible burning rate. Moreover, such a device will not alter its properties and will not burn erratically or explosively when exposed to numerous cycles of extreme temperasure variation on such as the frequently required cycle between -65 F. and +160 F. It will also retain its full inhibition bond on exposure to rough handling and prolonged vibration because of the cushioning effect of the semi-solid envelope around the candle. In addition, the danger of violent reaction because of accidental cracks in the pellet surface is much reduced because of the sealant character of the inhibitor.

On burning, the inhibiting compound evaporates or burns away at the rate flare candle burns down, depending on the reaction temperature and thickness of inhibitor which will usually be no less than 0.005 inch or no more than 0.125 inch thick. Because of its low heat conductivity, it remains in place in the unburned part of the flare.

Essentially, the same arrangement as outlined above can be achieved by embedding solid rocket-propellant grains in silicone-grease compounds in order to obtain linearly progressive end-burning or inside-to-outside burning in perforated mechanically top-end inhibited grains. This afifords a simple means of slowing down the burning rate of propellants for rocketry or when used as gasgenerators for pressurization, for work in gas-turbines and similar one-shot items where close control and gradual developement of gas is of importance.

While the inhibition of burning achieved with compounds based on silicone oils permits a particularly wide range of ambient temperature exposure, it should be noted that for many purposes other high consistency and more or less viscous, semi-solid, pasty chemical compounds or mixtures of chemical compounds can be employed as e.g. solid lubricants, petrolatum or highly plasticized lacquer bases with or without addition of chemical or mechanical thickeners.

Since pyrotechnical and some propellant mixtures are more or less porous, a need may arise to seal the surface pores of the compressed masses with a sealer which is impervious to any oily component of the inhibitor which may exude and gradually infiltrate by capillary action into the active material. Such protection will only be necessary if one or more of the following adverse conditions prevail: high porosity of the flare candle; tendency of the inhibitor to release low viscosity oil; and prolonged exposure to elevated temperature which may promote infiltration. I have found that an excellent sealant for pyrotechnical flare-candles is a very thin coat of shellac, but other lacquers or varnishes may be used and need be applied only sparingly in a manner to seal the pores within the surface area without leaving a substantial film.

Another application of the present invention is shown in F165. 9 and 10 which illustrate a modified form of pyrotechnical device B comprising an elongated canister or outer shell lll substantially similar to the previously described canister 1. The pyrotechnical charge 12, however, consists of a plurality of elongated compressed pyro; technical pellets 13 which are assembled and held in endto-end relation by narrow encircling strips of adhesive tape 14 or by some similar mechanical means. The assembled charge 12 is placed in the canister 1-1 and surrounded by a semi-solid inhibitor mass 15 in the same manner as previously described in connection with the pyrotechnical device A.

While my invention has been described as suitable for flares and propellant grains, it is applicable to any relatively slowly exothermically reacting, solid mixture of chemicals or any exothermically decomposing compound or compounds such as used for white and colored smokes, gas-cartridges as power sources, specific gas-producing mixtures, pyrochemical whistles, igniters and other heatsources. It should also be noted that pyrotechnical devices, such as the flarecandle above described, need not be cylindrical in shape, and it is also possible to use other very small mechanical spacing elements which will hold the pyrotechnical pellet in spaced relation within the canister without materially interfering with the upward flow of semi-solid inhibition material.

It should be understood that changes and modifications in the form, construction, arrangement, and combination of the several parts of the pyrotechnical device and in the steps of its production may be made and substituted for those herein shown and described without departing from the nature and principle of my invention.

Having thus described my invention, What I claim and desire to secure by Letters Patent is:

1. A pyrotechnical device comprising an external canister of generally tubular shape, said canister having a closed bottom wall and a continuous side wall, a solid pyrotechnical mass which is substantially similar in geometrical shape to the interior of the canister and being smaller in cross-sectional dimension than the corresponding inside cross-sectional dimension of the canister by an amount in the range of 0.005 to 0.125 inch in all lateral directions whereby to provide an annular space between the side wall of the canister and the pyrotechnical mass, said annular space having a width which is substantially uniform and is in the range of 0.005 to 0.125 inch, said pyrotechnical mass also having a bottom surface proximate to the bottom wall of the canister and disposed in spaced relation thereto, and a semi-solid non-pyrotechnical material disposed between the canister and the pyrotechnical mass, said semi-solid non-pyrotechnical material being only in contact with the bottom wall and cylindrical side wall of said mass.

52.. A pyrotechnical device comprising an external canister, of generally tubular shape, said canister having a closed bottom wall and a continuous side wall, a solid pyrotechnical mass which is substantially similar in geometrical shape to the interior of the canister and being smaller in cross-sectional dimension than the corresponding inside cross-sectional dimension of the canister by an amount in the range of 0.005 to 0.125 inch in all lateral directions whereby to provide an annular space between the side wall of the canister and the pyrotechnical mass, said annular space having a width which is substantially uniform and is in the range of 0.005 to 0.125 inch, said pyrotechnical mass also having a bottom surface proximate to the bottom wall of the canister and disposed in spaced relation thereto, a silicone grease disposed between the canister and the pyrotechnical mass, and sealing means within said canister for preventing the top wall of said mass from coming into contact with said silicone grease.

13. A pyrotechnical device comprising an external canister of generally cylindrical shape, said canister having a closed bottom wall and an annular side wall, a generally cylindrical solid pyrotechnical mass of a diameter which is smaller than the inside diameter of the canister by an amount which is in the range of 0.01 to .25 inch whereby to provide an annular space between the side wall of the canister and the pyrotechnical mass, said annular space having a width which is substantially uniform and is in the range of 0.005 to 0.125 inch, said pyrotechnical mass also having a bottom surface proximate to the bottom wall of the canister and disposed in spaced relation thereto, an organo-polysiloxane disposed between the canister and the pyrotechnical mass, and sealing means within said canister for preventing the top wall of said mass from coming into contact with said organo-poly-siloxane.

4. A pyrotechnical device comprising an external canister, a pyrotechnical mass disposed within the canister in spaced relation thereto, and a surface inhibiting agent consisting of a methyl silicone oil stiffened with a metal stearate disposed between the canister and the pyrotechnical mass forming a thin film between said mass and canister, said mass being completely enclosed within said film.

5. A pyrotechnical device comprising an external canister of generally cylindrical shape, said canister having a closed bottom wall and an annular side wall, a generally cylindrical solid pyrotechnical mass of a diameter which is smaller than the inside diameter of the can-ister by an amount which is in the range of 0.01 to 0.25 inch where by to provide an annular space between the side wall of the canister and the pyrotechnical mass, said annular space having a width which is substantially uniform and is in the range of 0.005 to 0.125 inch, said pyrotechnical mass also having a bottom surface proximate to the bottom wall of the canister and disposed in spaced relation thereto, and a surface inhibiting agent consisting of a methyl silicone oil stiffened with lithium stearate disposed between the canister and the pyrotechnical mass, said inhibiting agent having a relatively constant viscosity in the temperature range of 65 F. to +160 F. and being in a semi-liquid state in such temperature range.

6. A linearly burning pyrotechnical device comprising a pyrotechnical mass halving selected surfaces inhibited by a coating consisting of a methyl silicone oil stiffened with a metal stearate said metal stearate and methyl silicone oil combination being capable of maintaining a relatively constant viscosity between a temperature range of 65 F. and +160 F. and being in a semi-solid state in such temperature range.

7. A linearly burning pyrotechnical device comprising a pyrotechnical mass having selected surfaces inhibited by a coating consisting of a methyl silicone oil stiffened with lithium stearate, said metal stearate and methyl silicone 'oil combination being capable of maintaining a relatively constant viscosity between a temperature range of 65 F. and +160 F. and being in a semi-solid state in such temperature range.

8. A linearly burning pyrotechnical device comprising a pyrotechnical mass consisting of a plurality of elongated pyrotechnical pellets held in end-to-end alignment by sections of adhesive tape which extend annularly around and entirely cover each of the abutting margins, said pyrotechnical pellets having selected surfaces inhibited by a coating consisting of an organo-poly-siloxane.

9. A pyrotechnical device comprising an external canister, a pyrotechnical mass having a top wall and -a bottom wall which merge into a cylindrical side wall, said mass being disposed within the canister in spaced relation thereto, two sets of axially spaced pins mounted at degree intervals on the surface of said mass, thereby providing uniform spacing between said mass and canister, said pins having a comparatively small length relative to the length of said mass, and an organo-poly-siloxane disposed between the canister and the pyrotechnical mass, said organo-poly siloxane being only in contact with the bottom wall and cylindrical side wall of said mass.

10. A pyrotechnical device comprising an external canister, a pyrotechnical mass disposed within the canister in spaced relation thereto, and a methyl silicone oil stiffened with a metal stearate disposed between the canister and the pyrotechnical mass forming a thin film between said mass and canister, said metal stearate and methyl silicone oil combination being capable of maintaining a relatively constant viscosity between a temperature range of -65 F. and +l60 F. and being in a semi-solid state in such temperature range.

11. A pyrotechnical device comprising an external canister, a pyrotechnical mass disposed within the canister in spaced relation thereto, and a methyl silicone oil stiffened with a very finely ground mechanical thickening agent disposed between the canister and the pyrotechnical mass forming a thin film between said mass and canister, said mass being completely enclosed within said film, said film having a thickness of not less than 0.005 inch and not more than 0.125 inch.

References (Jilted in the file of this patent UNITED STATES PATENTS 958,990 Bourdelles May 24, 1910 1,187,779 Pattern June 20, 1916 1,785,529 Pratt Dec. 16, 1930 2,263,585 Moore et a1 Nov. 25, 1941 2,446,177 Hain June 21, 1945 2,455,242 =DWyer Nov. 30, 1948 2,479,828 Geckler Aug. 23, 1949 2,541,334 Carey et a1. Feb. 13, 1951 2,543,079 Veek Feb. 27, 1951 2,845,833 Davidson et a1. Aug. 5, 1958 2,877,504 Fox Mar. 17, 1959 2,877,709 Duckworth Mar. 17, 1959 2,986,001 Green May 30, 1961 3,054,253 Chung Sept. 18, 1962

Claims (1)

1. A PYROTECHICAL DEVICE COMPRISING AN EXTERNAL CANISTER OF GENERALLY TUBULAR SHAPE, SAID CANISTER HAVING A CLOSED BOTTOM WALL AND A CONTINUOUS SIDE WALL, A SOLID PYROTECHNICAL MASS WHICH IS SUBSTANTIALLY SIMILAR IN GEOMETRICAL SHAPE TO THE INTERIOR OF THE CANISTER AND BEING SMALLER IN CROSS-SECTIONAL DIMENSION THAN THE CORRESPONDING INSIDE CROSS-SECTIONAL DIMENSION OF THE CANISTER BY AN AMOUNT IN THE RANGE OF 0.005 TO 0.125 INCH IN ALL LATERAL DIRECTIONS WHEREBY TO PROVIDE AN ANNULAR SPACE BETWEEN THE SIDE WALL OF THE CANISTER AND THE PYROTECHNICAL MASS, SAID ANNULAR SPACE HAVING A WIDTH WHICH IS SUBSTANTIALLY UNIFORM AND IS IN THE RANGE OF 0.005 TO 0.125 INCH, SAID PYROTECHNICAL MASS ALSO HAVING A BOTTOM SURFACE PROXIMATE TO THE BOTTOM WALL OF THE CANISTER AND DISPOSED IN MATERIAL DISPOSED BETWEEN THE CANISTER AND THE PYROTECHNICAL MASS, SAID SEMI-SOLID NON-PYROTECHNICAL MATERIAL BEING ONLY IN CONTACT WITH THE BOTTOM WALL AND CYLINDRICAL SIDE WALL OF SAID MASS.

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