Patent Application
20250001497
The present disclosure is related to methods and processes for forming pyrotechnic material extrudates.
Decoy flares for aircraft typically include pyrophoric material that produce heat and infrared radiation with a determined signature to simulate the aircraft's engine signature. One example of a pyrotechnic material well suited for use in decoy flares is a mixture of magnesium, Teflon® (polytetrafluoroethylene), and Viton® (a copolymer including vinylidene fluoride and hexafluoropropylene monomers) commonly referred to as “MTV.” Teflon® and Viton® are commercial products available from E.I. du Pont de Nemours and Company (Wilmington, Delaware). When MTV is deployed and exposed to air, the reaction is highly exothermic, producing a brief burst of high-intensity heat in a small area. The MTV reaction can be tuned to provide a heat/IR signature that substantially matches the heat/IR signature of, for example, an engine of a designated aircraft.
The most common conventional method for manufacturing MTV flare grains for the decoy flares is to extrude granular MTV material, which may be formed via a shock-gel method or other conventional method. The granular MTV material is forced through an extrusion die to form an elongated extrudate with a selected exterior shape and size. An example of techniques for extrusion of pyrotechnic material is disclosed in U.S. Pat. No. 11,167,346, titled Method for Making Pyrotechnic Material and Related Technology, which is incorporated herein in its entirety by reference thereto. Conventional extrusion processes of the pyrotechnic materials, however, can result in internal discontinuities or anomalies, such as cracks within the extrudate. For example,
Many aspects of the present technology can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale. Instead, emphasis is placed on clearly illustrating the principles of the present technology. For ease of reference, throughout this disclosure identical reference numbers may be used to identify identical, similar, or analogous components or features of more than one embodiment of the present technology.
Methods and systems for forming pyrophoric material extrudates, such as MTV flare grain materials and related processes and compositions in accordance with embodiments of the present technology overcome drawbacks experienced in the prior art. Embodiments of the present technology provide mixing a high-melting-temperature wax powder with a blend of a metal powder, fluoropolymer material, and a binder material to form an extrudable mixture. In the illustrated embodiment, the binder material can be a copolymer with vinylidene fluoride and hexafluoropropylene monomers that containing an adhesive, and the fluoropolymer can be a polytetrafluoroethylene material that acts as an oxidant. The extrudable mixture is configured to be forced through a die of an extruder to form a substantially uniform flare grain member free of substantive cracks or other discontinuities in the interior area caused during the extrusion. Accordingly, the extrudate is free of cracks that extend longitudinally within the flare grain in a direction parallel to the direction of flow of the extrusion.
In some embodiments, the extrudable mixture is subject to elevated extrusion temperatures upon being forced through the die of the extruder. The high-melting-temperature wax powder has a melting temperature that is greater than the extrusion temperatures, so the wax powder provides lubricity to the extrudable mixture but does not melt. In some embodiments, the high-melting-temperature wax powder comprises about one percent by weight of the extrudable mixture. This lubricious, unmelted wax material improves the extrusion process to result in the extrudate free of the longitudinal internal cracks.
In other embodiments, the present technology provides a method comprising mixing metal powder, fluoropolymer powder, adhesive polymer, and a high-melting-temperature wax powder to provide an extrudable material, wherein the wax powder constitutes about one percent by weight of the extrudable material. The method also comprises extruding extrudable material to form an extrudate, wherein the wax powder in the extrudate does not melt during extrusion.
Specific details of methods for improving the quality of pyrotechnic material extrudate and related methods, compositions, and systems in accordance with several embodiments of the present technology are described herein with reference to
In the illustrated embodiment, the metal powder 106 is magnesium powder, the fluoropolymer powder 108 is polytetrafluoroethylene powder, and the binder material 110 is a composite of polytetrafluoroethylene and a copolymer including vinylidene fluoride and hexafluoropropylene monomers. In other embodiments, one, some, or all of the metal powder 106, the fluoropolymer powder 108, and the binder material 110 can have other suitable compositions.
The high-melting-temperature wax powder 112 is an amide wax that has a melting temperature that is greater than the temperatures to which the powder materials are exposed during extrusion or other processing steps for formation of the extrudate 30, as discussed in greater detail below. In other embodiments, the high-melting-temperature wax powder 112 can be carnauba wax, paraffin wax, or another suitable high-melting-temperature powdered wax. The amide wax powder material forms only a small portion of the blend of powder materials that form the extrudate 30. For example, the wax powder material constitutes in the range of 0.8%-1.5% by weight of the blend of powder materials that form the extrudate 30. In the illustrated embodiment, the wax powder material constitutes approximately 1% by weight of the blend of powder materials that form the extrudate 30. While a greater amount of wax powder material may be used within the powder mixture, the greater amount does not further improve the quality and performance of the resulting extrudate. In other words, more wax powder does not make a better extrudate.
In the illustrated embodiment, the containers 102a-102d are hoppers that can be configured to meter and uniformly dispense the powder materials at selected proportions relative to the other powders. The containers 102a-102d dispense the respective powders to the transportation tubes 104a-104d, which carry and deliver the powder materials (106, 108, 110, 112) via gravity into a mixer 116. In other embodiments, the transportation tubes 104a-104d can be chutes, conduits, conveyor belts, carousels, or other delivery assemblies that may be configured to carry and deliver the powder materials (106, 108, 110, 112), such as pneumatically, by operation of mechanical feeders and/or in another suitable manner.
In the illustrated embodiment, the mixer 116 is an actively driven assembly that receives in a funnel 118 the metered portions of the powder materials (106, 108, 110, 112) and blends the powders to provide a substantially uniformly distributed mixture of the powder materials. The mixer 116 is configured to deliver the mixture of powder materials into an inlet 124 of an extruder 114.
In the illustrated embodiment, the extruder 114 includes an elongate housing 126 that receives the mixture of powder materials via the inlet 124. The housing contains an auger 130 or other mixture advancing system coupled to a driver 128 that rotates the auger 130 at a selected speed to steadily and firmly push the mixture of powder materials forwardly through the housing toward an extrusion die 132 at a distal end of the housing 126.
In addition, as the mixture of material is forced through the extrusion die 132, the mixture presses against the die surface forming the opening 134 of the die 132. This engagement with the die surface results in friction with the portion of the mixture on and adjacent to the die surface. The portion of the mixture passing through the center portion of the opening is not subjected to the same friction forces. As a result, the flow rate of material through the center portion of the opening is greater than the flow rate of the material at the die surfaces, thereby resulting in a velocity gradient across the material passing through the die opening 134. While the wax in the mixture does not melt, the wax material is warmed and is lubricious, so as to provide a lubricating layer at the die surface. This lubricating layer helps reduce any sticking of exterior portions of the mixtures to the die surface, thereby allowing the mixture to flow more evenly and decreasing the velocity gradient across the material. This reduction of the sticking on the die surface and the reduction of the velocity gradient results in reduced forces in the interior portions of the extruded material, so that cracks or other extrusion discontinuities do not form within the interior portion of the pyrotechnic extrudates 30. In addition, the resulting crack-free, uniform pyrotechnic extrudate 30 has a smooth, consistent exterior surface 32 (
The method 200 further includes extruding the powder mixture containing the wax powder with an extruder 114 to form an extrudate in which the adhesive material binds together the metal powder 106 and the fluoropolymer powder 108 (block 214). The process also acts to shear the binder 110 (block 214) to cause the adhesive material to bind together the metal powder 106 and the fluoropolymer powder 108. In some embodiments, the binder material can be heated to a selected temperature range to facilitate formation of the resulting extrudate. Such a temperature range, however, is still below the melting temperature of the wax material, and the temperature range also allows workers to effectively utilize the equipment during the extruding process.
As the powered mixture with the small amount of wax powder is forced through the die 132 under heat and pressure, the binder material 110 shears at the die 132 to help expose the adhesive material and to increase contact between the adhesive material and the metal powder 106. During this process, the wax powder 112 is warmed but not melted, so as to facilitate formation of the lubricating layer at the die surface to allow the powder mixture to be converted from a free-flowing powder form to a crack-free cohesive solid or semi-solid form. The lubricating characteristics of the wax powder 112 help avoid the accumulation of the shear forces acting on the mixture as it moves toward and through the die 132, resulting in the smooth formation of the pyrotechnic extrudate free of internal cracks or other substantive discontinuities.
This disclosure is not intended to be exhaustive or to limit the present technology to the precise forms disclosed herein. Although specific embodiments are disclosed herein for illustrative purposes, various equivalent modifications are possible without deviating from the present technology, as those of ordinary skill in the relevant art will recognize. In some cases, well-known structures and functions have not been shown and/or described in detail to avoid unnecessarily obscuring the description of the embodiments of the present technology. Although steps of methods may be presented herein in a particular order, in alternative embodiments the steps may have another suitable order. Similarly, certain aspects of the present technology disclosed in the context of particular embodiments can be combined or eliminated in other embodiments. Furthermore, while advantages associated with certain embodiments may have been disclosed in the context of those embodiments, other embodiments may also exhibit such advantages, and not all embodiments need necessarily exhibit such advantages or other advantages disclosed herein to fall within the scope of the present technology.
Throughout this disclosure, the singular terms “a,” “an,” and “the” include plural referents unless the context clearly indicates otherwise. Similarly, unless the word “or” is expressly limited to mean only a single item exclusive from the other items in reference to a list of two or more items, then the use of “or” in such a list is to be interpreted as including (a) any single item in the list, (b) all of the items in the list, or (c) any combination of the items in the list. Additionally, the terms “comprising” and the like are used throughout this disclosure to mean including at least the recited feature(s) such that any greater number of the same feature(s) and/or one or more additional types of features are not precluded. Reference herein to “one embodiment,” “an embodiment,” or similar formulations means that a particular feature, structure, operation, or characteristic described in connection with the embodiment can be included in at least one embodiment of the present technology. Thus, the appearances of such phrases or formulations herein are not necessarily all referring to the same embodiment. Furthermore, various particular features, structures, operations, or characteristics may be combined in any suitable manner in one or more embodiments of the present technology.
