Explosive and thermic compositions or charges – Structure or arrangement of component or product – Solid particles dispersed in solid solution or matrix
Reexamination Certificate
1998-10-26
2001-04-17
Jordan, Charles T. (Department: 3641)
Explosive and thermic compositions or charges
Structure or arrangement of component or product
Solid particles dispersed in solid solution or matrix
C149S019400, C149S044000, C149S113000, C060S219000, C060S039440
Reexamination Certificate
active
06217682
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to selected propellant formulations based on energetic oxetane binder systems exhibiting low, zero or negative pressure exponents across a pressure region, e.g., plateau ballistic behavior.
2. Background Information
Solid propellants are used extensively in the aerospace industry. Solid propellants have developed as the preferred method of powering most missiles and rockets for military, commercial, and space applications. Solid rocket motor propellants have become widely accepted because of the fact that the propellants are relatively simple to formulate and use and have excellent performance characteristics. Furthermore, solid propellant rocket motors are generally very simple when compared to liquid fuel rocket motors. For all of these reasons, it is found that solid rocket propellants are often preferred over other alternatives, such as liquid propellant rocket motors.
Typical solid rocket motor propellants are generally formulated having an oxidizing agent, a fuel, and a binder. At times, the binder and the fuel may be the same. In addition to the basic components set forth above, it is conventional to add various plasticizers, curing agents, cure catalysts, and other similar materials which aid in the processing and curing of the propellant. A significant body of technology has developed related solely to the processing and curing of solid propellants, and this technology is well known to those skilled in the art.
One type of propellant that is widely used incorporates ammonium perchlorate (“AP”) as the oxidizer. The AP oxidizer may then, for example, be incorporated into a propellant which is bound together by a hydroxy-terminated polybutadiene (HTPB) binder. These HTPB binders are widely used and commercially available. It has been found that such propellant compositions provide ease in manufacting and handling; exhibit good performance characteristics; and are at the same time economical and reliable. In essence, it can be said that AP composite propellants have been the backbone of the solid propulsion industry for approximately the past 40 years.
One of the problems encountered in the design of rocket motors is the control of the thrust output of the rocket motor. This is particularly true when it is desired to operate the motor in two or more different operational modes. For example, it is often necessary to provide a high level of launch-phase thrust in order to “boost” the motor and its attached payload from a starting position, such as during launch of a rocket or missile. Once the launch phase has been completed, it may be desirable to provide a constant output from the rocket motor over an extended “sustain” operation. This sustain may occur, for example, after the rocket has been placed in flight and while it is traveling to its intended destination.
The achievement of such multi-phased or biplateau operations has been extremely difficult. It has been necessary to resort to complex mechanical arrangements in the rocket motors. Alternatively, less efficient and less desirable liquid rocket motors have been used to obtain multi-phase operation.
In some cases, multiple-phase or biplateau operation has been attempted by constructing very complex propellant grains, such as grains having multiple propellants. In any case, achievement of multiple-phase operation has been complex, time consuming, and costly.
Single plateau propellant offers reduced temperature sensitivity, allows high pressure operation, and a higher expansion ratio for increased performance without affecting motor safety margins. Plateau propellant in general reduces margins required between the maximum expected operating pressure (MEOP) and the maximum nominal pressure. This in turn reduces motor case inert weight and makes high pressure motor operations advantageous.
Still further efforts have focused on non-energetic binder systems in an effort to develop plateau propellants. While offering some advantages, the art is still seeking IM propellants having a higher delivered impulse at lower solids loadings.
SUMMARY AND OBJECTS OF THE INVENTION
The formulation of the present invention provides the capability of achieving one or more regions of low pressure exponent with a propellant based on an energetic oxetane binder, such as, for instance, poly (nitratomethylmethyloxetane) (“NMMO”) poly(azidomethyl methyloxetane) (“AMMO”), and poly (bisazidomethyloxetane) copoly(azidomethyl methyloxetane) (“BAMO-AMMO”), which is plasticized with a plasticizing amount of, for instance, triethylethylene glycol dinitrate (“TEGDN”), glycidylazide plasticizer (“GAP”), or butyl (nitratomethyl) nitramine (“BuNENA”).
The ballistic plateau characteristics of the present propellant formulations are combined with the advantages of an energetic oxetane binder system. The present propellant formulations permit the propellant formulator to prepare propellant with energy partitioning between the binder and solids for IM improvement, reduced ESD sensitivity, and reduced solids loading. The use of energetic binders can be in the form of thermoplastic elastomers (“TPE”), verses conventionally chemically cured binders, which leads to still further advantages in processing and recycling.
The present formulations consequently offer a significant improvement over the existing art. The present formulations simplify and lower the cost of boost-sustain and sustain-boost motor manufacture by requiring only a single propellant. Using the formulations of the present invention, higher volumetric loading with a simple center perforate (CP) grain design for boost-sustain motors is provided. The selected formulations of the present invention are stable at operating pressures of approximately 4000 to 5000 psi. The present invention is applicable to reduced-smoke and also aluminized propellants.
An important ingredient in achieving the stable mono- or bi-plateau characteristics is the addition of an acceptable quantity of a refractory oxide. Such oxides are generally selected from the group consisting of TiO
2
, ZrO
2
, Al
2
O
3
,SnO
2
, and SiO
2
, and similar materials. These materials function essentially as burn rate modifiers in the propellant formulation and provide the ability to tailor the burn rate achieved by the propellant.
In certain preferred embodiments of the invention, TiO
2
is used and it is economical (low cost) and commercially available in large quantities.
For most applications, the preferred refractory oxide content in the propellant will be in the range of from approximately 0.2% to approximately 4.0% by weight. Excellent results have been achieved with refractory oxides added in the range of from approximately 1.0% to approximately 2.0% by weight. It has also been found that a wide range of particle sizes also provide good results. In particular, particles sizes of from approximately 0.4 microns to approximately 0.02 microns perform well, the former for lower burn-rate ranges and the latter for higher burn-rate ranges.
Other ingredients and composition characteristics may be varied in order to obtain specific desired characteristics. For example, variation of secondary factors and ingredients may influence the specific burn rates and pressure ranges of operation. Such factors may, for example, include AP particle size, distribution and content, plasticizer content, the type of cure agent used, and the presence of other trace components.
Accordingly, an object of the present invention is to provide improved propellant formulations which overcome the limitations of the art as set forth above and are capable of managed energy output, higher pressure operations, and increased performance.
It is an object to provide propellant formulations capable of achieving improved performance and mechanical properties while being suitable for insensitive munitions.
It is an object of the present invention to provide propellant formulations which exhibit the desired plateau ballistic characteristics.
It is an object to provide propellant formulations which
Baker Aileen J.
Cordant Technologies Inc.
Jordan Charles T.
Pillsbury Madison & Sutro Intellectual Property Group
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