Patent Grant
5053088
The invention described herein may be manufactured, used, and licensed by or for the Government for governmental purposes without the payment to me of any royalties thereon. The mechanism of burning rate enhancement of solid propellant compositions are generally classified as chemical or mechanical or a combination of each type. Chemical enhancement of burning rate relates to either catalysis or chemical process interactions to yield increased burning rate, either or both of which may be influenced by or relate to surface phenomena, such as particle sizes, physical shapes, or mechanical interactions. Mechanical enhancement of burning rate is, as the name implies a material that because of its shape, its distribution within a propellant matrix, and how it reacts under burning conditions can interact to affect or influence burning rate by heat transfer, by alteration of surface area or conditions, or by other physical interactions which influences the chemical and burning processes. Various mechanical accelerators have been investigated. Some of these have been, (a) aluminum flakes, (b) aluminum staples, (c) aluminum whiskers, (d) graphite linters, (e) thermally-collapsible (shrinkable) tubings, sheets, rods, and hollow fibers, (f) microballoons, etc. Their use has been unsuccessful, when used in composite propellants, due to anisotropic burning characteristics of the propellant that these impart. The most recent material which has come to the fore as a mechanical accelerator is three-dimensional wire forms. The configuration of the wire forms is that of a paper staple in which one leg is at an angle of 90.degree. to the other leg. The situation, insofar as composite-modified, double-base propellant is concerned, is different from that of composite propellants because of the method of manufacture of the propellant. This process involves the use of casting powder in combination with casting solvent. When the casting powder is loaded into the motor, it is near-randomly oriented, and when solvated by the casting solvent, this produces a propellant which undergoes isotropic burning. An object of this invention is to provide a mechanical enhancement of the burning rate of solid propellants. A further object of this invention is to provide a mechanical enhancement of the burning rate of solid propellants by the incorporation of material in the form of heat-expandable beads for the mechanical enhancement of the burning rate of solid propellants. Still a further object of this invention is to provide heat-expandable beads which are comprised of an expanding or blowing agent which, after incorporating same into a solid propellant composition, results in bead expansion when the flame front of the burning propellant reaches the bead thereby causing rupturing of the bead to bring about disruption of the propellants' surface to thereby enable the flame to penetrate into the propellant which results in a major increase in the burning rate. Mechanical enhancement of the burning rate of solid propellants is achieved as a result of the incorporation into the solid propellant composition limited percentages of heat-expandable beads of discrete particles of thermoplastic styrene or its copolymers which contain about 5-8% of an expanding agent or blowing agent. The expanding or blowing agent is selected from pentane, Celogen OT, 4,4'-oxybis(benzenesulfonyl hydrazide), etc., in spherical form to facilitate uniform dispersion throughout the propellant matrix. When the flame front of the burning propellant reaches the heat-expandable bead, the blowing agent will cause the bead to expand several times its volume and rupture. Bead expansion or rupture will bring about disruption of the propellant's surface, and the flame penetrates into the propellant. This penetration results in a major increase in burning rate due to the many additional burning surface areas generated. The heat-expandable beads can be employed with a composite propellant composition, as well as with a composite-modified, double-base propellant composition.
| Number | Name | Date | Kind |
|---|---|---|---|
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| 3977922 | Inoue et al. | Aug 1976 | |
| 4008108 | Chrisp | Feb 1977 | |
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| 4133706 | Shoults | Jan 1979 | |
| 4141766 | Cameron et al. | Feb 1979 | |
| 4151022 | Donaghue et al. | Apr 1979 | |
| 4304185 | Sayles | Dec 1981 |
