Three part mixing process for energetic materials and epoxy binder

Abstract

The present invention relates to methods of preparing pre-mixed compositions that can be combined to form pyrotechnic compositions. In exemplary embodiments, a binder ingredient is premixed with the pyrotechnic fuels and can also include other pyrotechnic additives and processing aides. Other binder ingredients can be premixed with the pyrotechnic oxidizers and can also include other pyrotechnic additives and processing aides. The resulting mixtures are not explosive and are therefore easier to store and much safer to handle. These pre-mixed mixtures can be stored in bulk until needed and rapidly combined to achieve final composition.

Claims

1. A method of preparing pyrotechnic compositions comprising: selecting a first pre-mixed composition ingredients comprising at least one fuel and a binder curing agent; selecting a second pre-mixed composition ingredients comprising at least one oxidizer and a binder resin; preparing a first pre-mixed composition by mixing the first pre-mixed composition ingredients at a first predetermined mixing setting using resonant acoustic mixing with a resonant acoustic mixer (RAM); preparing a second pre-mixed composition by mixing the second pre-mixed composition ingredients at a second predetermined mixing setting using resonant acoustic mixing with the RAM; and preparing pyrotechnic compositions by mixing the first and the second pre-mixed compositions at a third predetermined mixing setting; wherein the first pre-mixed composition and the second pre-mixed composition each comprise a non-explosive, partially processed multi-part binder based pyrotechnic that is storable and has a longer storage shelf-life than a shelf-life of the prepared pyrotechnic compositions formed by mixing the first and the second pre-mixed compositions.

2. The method of claim 1, wherein the first predetermined mixing setting includes a first predetermined mixing speed and a first vacuum pressure over a first predetermined time period.

3. The method of claim 1, wherein the second predetermined mixing setting includes at least a second predetermined mixing speed and a second vacuum pressure over a second predetermined time period.

4. The method of claim 1, wherein selecting the first pre-mixed composition ingredients comprising the at least one fuel and the binder curing agent includes further selecting a processing aide for the first pre-mixed composition.

5. The method of claim 4, wherein the processing aide comprises acetone.

6. The method of claim 4, further comprising: preparing the first pre-mixed composition by: mixing the processing aide with the binder curing agent to create a first mixture; and combining the first mixture with the at least one fuel at the first predetermined mixing setting.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The detailed description of the drawings particularly refers to the accompanying figures in which:

(2) FIG. 1 shows an exemplary apparatus for creating an exemplary first pre-mixed composition.

(3) FIG. 2 shows an exemplary apparatus for creating an exemplary second pre-mixed composition.

(4) FIG. 3 shows an exemplary apparatus for creating a pyrotechnic composition by combining a first and second pre-mixed composition.

DETAILED DESCRIPTION OF THE DRAWINGS

(5) The embodiments of the invention described herein are not intended to be exhaustive or to limit the invention to precise forms disclosed. Rather, the embodiments selected for description have been chosen to enable one skilled in the art to practice the invention.

(6) FIG. 1 shows an exemplary apparatus 1 for creating an exemplary first pre-mixed composition 11. Fuel (e.g., magnesium, aluminum, sucrose) can added to a first container, then a binder curing agent (e.g., Versamid 140) and an optional process aide (e.g., acetone) can be added into a second container and mixed thoroughly until the binder curing agent is dissolved to create a first mixture, then the first mixture can be poured on top of the fuel and placed in a mixer 3 (e.g., a mix-muller mixer, a Resonant Acoustic Mixer (RAM), etc.). In at least some embodiments, processing aides can be preferred when the combination of fuel and curing agents do not mix well. A processing aide (e.g., acetone, polyethylene glycol) can prevent clumping and help mix the fuel and curing agents evenly, and can be beneficial for certain types of mixers (e.g., RAM). Highly viscous binder curing agents (e.g., Versamid 140) mix better with metallic, higher density, low hydroscosity materials, and high surface area, so highly viscous binder curing agents are well suited to be mixed with metallic fuels (e.g, magnesium, aluminum, copper, etc.). The first mixture and fuel can be mixed for various durations (e.g., 2 minutes) and mixing speeds (e.g., 65 G of acceleration), and, in at least some embodiments, under a vacuum setting (e.g., 22 inches of vacuum) dependent on mixing location (e.g., elevation). The resulting mixture is a first pre-mixed composition which can be safely stored for longer than the shelf life of a pyrotechnic composition.

(7) FIG. 2 shows an exemplary apparatus 1 for creating an exemplary second pre-mixed composition 21. An oxidizer (e.g., sodium nitrate, iron oxide, potassium chlorate, etc.) can be added to a third container, a binder resin (e.g., Araldite 507) can be added on top, and then a processing aide (e.g., acetone, polyethylene glycol) can added on top to create a second mixture. The second mixture can be placed in a mixer 3 and can be mixed for various durations (e.g., 1 minute) and mixing speeds (e.g., at 95 G's of acceleration, then reduced to 65 G of acceleration), and, in at least some embodiments, under a vacuum setting (e.g., 22 inches of vacuum). The resulting mixture is a second pre-mixed composition 21 which can be safely stored for longer than the shelf life of a pyrotechnic composition. Other additives (e.g, asphaltum, carbon black, etc.) can be added to the second mixture.

(8) In at least some embodiments, different combinations of fuel, oxidizer, binder curing agent, and binder resin can be used. The fuel and oxidizer should always be kept in separate pre-mixed compositions. Binder curing agents and binder resins should be kept in separate pre-mixed compositions to prevent premature hardening of the compositions. Additives generally have a tendency to act as either a fuel or an oxidizer, and it is preferred to add additives to the mixture matching their tendencies (e.g., oxidizer additives added to the oxidizer) to minimize potential for energetic reactions. For example, graphite tends to act as a fuel, and can be included as an additive in the first pre-mixed composition. By keeping fuel and oxidizer separate as well as curing agent and resin separate, there are two primary permutations of pre-mixed compositions: (1) fuel+curing agent and oxidizer+resin; and (2) fuel+resin and oxidizer+curing agent. Viscous curing agents (e.g., Versamid 140) can be effectively mixed with coarse oxidizers.

(9) The proportion of fuel to oxidizer will be set based on the desired pyrotechnic composition. The amount of binder ingredients required will be based on the selected fuel and oxidizer. Exemplary methods can use predetermined proportions of each ingredient typically used to prepare selected pyrotechnic combinations without varying the amount of binder required to evenly mix with other ingredients (e.g., fuel, oxidizer). By coating the fuel with binder ingredients, the fuel becomes far less likely to oxidize during storage, even when exposed to air. As such, a pre-mixed composition including fuel can be stored for long periods of time without needing to vacuum seal the pre-mixed composition. Mixing compatibility between binder ingredients and either fuel or oxidizer will depend on the type of mixer selected. For example, RAM mixers are more likely to cause clumping when adding a viscous curing agent to a fuel, whereas mix-muller mixers will be comparatively easier.

(10) FIG. 3 shows an exemplary apparatus 1 for creating a pyrotechnic composition 31 by combining a first and second pre-mixed composition. In most pyrotechnic compositions, the ratio of first to second pre-mixed composition can be very important. To ensure that the proper amounts of pre-mixed compositions are added, any processing aides used in either composition can be evaporated from the compositions prior to storing the compositions or before mixing the compositions together. In some embodiments, if the amount of processing aide (e.g., percent by weight) is known in both pre-mixed compositions, then the compositions can be mixed without removing (e.g., evaporating) the processing aide. The first and second pre-mixed compositions can then be combined and mixed with mixer 3 to create a pyrotechnic composition.

(11) This method can be utilized using a variety of mixers such as bowl, mix-muller, twin-screw extrusion or resonant acoustic mixing. The concept of separate mixing and holding can potentially be used for many different applications, the illumination flare just happened to be the flare of choice however, this method is adaptable to colored flares, IR flares, and any other pyrotechnic with a multi-part binder system.

(12) Although the invention has been described in detail with reference to certain preferred embodiments, variations and modifications exist within the spirit and scope of the invention as described and defined in the following claims.