The subject matter of the present application described herein may be manufactured, used and licensed by or for the United States Government for governmental purposes without the payment of any royalties.
The present disclosure generally relates to an acoustic mixing system for creating propellant mixture, and more specifically, to an acoustic mixing system for creating propellant mixture using an acoustic mixing process.
Acoustic mixing technology operates on the principle of resonance, in which low frequency acoustic energy creates a uniform shear field within a mixing vessel. An acoustic mixing system operates at a frequency substantially similar to a resonant frequency of the mixing system. This results in acoustic energy being directly transferred to a mixture located within the mixing vessel, resulting in significant forces (e.g., up to 200 g's) to be transferred to the mixture. Consequently, the acoustic mixing system results in a homogenous mixture made up of at least two different materials without the use of impellers or other additional mixing aids.
Acoustic mixing technology allows for the rapid, uniform dispersion of at least two different materials, decreasing processing time and waste associated with creating propellant mixtures. However, acoustic mixing technology works best with two or more materials having disparate densities. This creates an issue when mixing certain propellant mixtures that have two or more materials with closely matched densities. For example, mixtures including nitrocellulose have proven to be challenging to mix using acoustic mixing technology. Nitrocellulose is a compound that has an inherently fibrous nature. Consequently, when mixtures containing nitrocellulose are mixed using acoustic energy, the nitrocellulose absorbs the acoustic energy instead of working the nitrocellulose into other materials (e.g., plasticizer) to form a homogenous mixture.
Other mixing technologies (such as those described in U.S. Pat. No. 2,510,834—the disclosure of which is incorporated by reference herein in its entirety) have been used to mix propellant mixtures containing nitrocellulose. These other technologies include, for example, a water-slurry process that takes hours to process. Using this process, nitrocellulose is slurried with an anti-solvent while a plasticizer is slowly dripped into the slurry. Due to the chemical nature of the plasticizer and the anti-solvent, the slow dripping of the plasticizer into the slurry results in the plasticizer incorporating into the nitrocellulose. The propellant mixture is then subsequently filtered for further processing. In addition to long processing time, using the water-slurry process requires the propellant mixture to be done in a batch-process, which presents certain challenges as production levels increase. Also, the water-slurry process creates a lot of wastewater contaminated with nitrate esters. While wastewater can be minimized by re-using water for multiple batches, the wastewater does ultimately need to be treated and disposed of properly at the end of a manufacturing run.
Therefore, described herein is a system for creating propellant mixtures using an acoustic mixing process is needed. A new system would enable propellant mixtures having two or more materials with closely matched densities to be mixed, eliminating the need to use other mixing technologies with shortcomings such as wastewater and/or long processing times.
This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify indispensable features of the claimed subject matter, nor is it intended for use as an aid in limiting the scope of the claimed subject matter. In one embodiment, the present disclosure provides a method of creating a propellant mixture.
The present disclosure introduces a method of forming an explosive composition mixture, placing the explosive composition mixture into a mixing vessel assembly, and operating an acoustic mixing system at an operating frequency such that the acoustic mixing system causes a vertical displacement of the mixing vessel assembly. The explosive composition mixture includes an explosive material and one or more additives. The mixing vessel assembly includes an upper dish and a lower dish, with the upper and lower dishes collectively forming a closed mixing zone having a maximum vertical height. The acoustic mixing system has a resonant frequency. The resonant frequency is constant when the acoustic mixing system is at rest and varying when the acoustic mixing system is in operation. The acoustic mixing system is operated in a manner such that the operating frequency is substantially similar to the resonant frequency and a ratio of the maximum vertical height of the closed mixing zone to the vertical displacement of the mixing vessel assembly is 2.0 or less.
For a better understanding of the nature and objects of the disclosure, reference should be made to the following detailed description taken in conjunction with the accompanying drawings, in which:
Reference is made in the following detailed description of preferred embodiments to accompanying drawings, which form a part hereof, wherein like numerals may designate like parts throughout that are corresponding and/or analogous. It will be appreciated that the figures have not necessarily been drawn to scale, such as for simplicity and/or clarity of illustration. For example, dimensions of some aspects may be exaggerated relative to others. Further, it is to be understood that other embodiments may be utilized. Furthermore, structural and/or other changes may be made without departing from claimed subject matter. References throughout this specification to “claimed subject matter” refer to subject matter intended to be covered by one or more claims, or any portion thereof, and are not necessarily intended to refer to a complete claim set, to a particular combination of claim sets (e.g., method claims, apparatus claims, etc.), or to a particular claim.
In the following description, numerous details are set forth to provide an understanding of the present disclosure. However, it may be understood by those skilled in the art that the methods of the present disclosure may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible. At the outset, it should be noted that in the development of any such actual embodiment, numerous implementation—specific decisions may be made to achieve the developer's specific goals, such as compliance with system related and business related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time consuming but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. In the summary and this detailed description, each numerical value should be read once as modified by the term “about” (unless already expressly so modified), and then read again as not so modified unless otherwise indicated in context. Also, in the summary and this detailed description, it should be understood that a range listed or described as being useful, suitable, or the like, is intended to include support for any conceivable sub-range within the range at least because every point within the range, including the end points, is to be considered as having been stated. For example, “a range of from 1 to 10” is to be read as indicating each possible number along the continuum between about 1 and about 10. Furthermore, one or more of the data points in the present examples may be combined together, or may be combined with one of the data points in the specification to create a range, and thus include each possible value or number within this range. Thus, (1) even if numerous specific data points within the range are explicitly identified, (2) even if reference is made to a few specific data points within the range, or (3) even when no data points within the range are explicitly identified, it is to be understood (i) that the inventors appreciate and understand that any conceivable data point within the range is to be considered to have been specified, and (ii) that the inventors possessed knowledge of the entire range, each conceivable sub-range within the range, and each conceivable point within the range. Furthermore, the subject matter of this application illustratively disclosed herein suitably may be practiced in the absence of any element(s) that are not specifically disclosed herein.
The present disclosure provides an acoustic mixing system 10 for creating propellant mixture via an acoustic mixing process. The acoustic mixing system 10 includes an explosive composition mixture 12, a mixing vessel assembly 14, and an acoustic mixer 16.
In a first embodiment, the explosive composition mixture 12 includes an explosive material (EM), and one or more additives. In a specific embodiment, as shown in
Examples of suitable explosive materials (also referred to herein as “low-bulk density fibrous materials) include nitrocellulose, cellulose, Kevlar, and combinations thereof. The explosive material may be present in the explosive material composition mixture in an amount of from about 0.1% to about 95% by weight, from about 20% to about 80% by weight, and from about 30 to about 70% by weight.
As discussed above, the explosive composition mixture 12 may also include one or more additives. Examples of additives include plasticizers, stabilizers, burn-rate modifiers, lubricants, flow agents, curatives, binders, bonding agents, fuels, oxidizers, emulsifiers, colorants, dispersants, antioxidants, and preservatives. The one or more additives may be present, individually or in combination, in the explosive material composition mixture in an amount of from about 5% to about 99.9%, from about 20% to about 80%, and from about 30% to about 70%
Examples of stabilizers include phenylamines such as 2-nitrodiphenylamine (2-NDPA) or 4-nitrodiphenylamine (4-NDPA), anilines such as mononitroaniline, phenolics such as resorcinol, and phenylureas such as ethyl centralite. The stabilizers may be present in the explosive material composition mixture in an amount of from about 0% to about 30% from about 0.1% to about 15%, and from about 0.5% to about 5%.
Examples of plasticizers include isophorones such as 4-oxo-isophorone, terpenes such as laevo-carvone (1-carvone), nitrate esters such as nitroglycerin, adipates such as dioctyl adipate, and mellitates such as trioctyl mellitate. The one or more additives may be present in the explosive material composition mixture in an amount of from about 5% to about 99.9%, from about 20% to about 80%, and from about 30% to about 70%.
More specifically, in the first embodiment, the explosive composition mixture 12 consists of 32 g 25% water-wet 13.3%N nitrocellulose, 0.40 g 2-NDPA, and 15.6 g 4-oxo-isophorone (hereinafter, referred to as Mixture #1 throughout this disclosure). In second embodiment, the explosive material is nitrocellulose, the stabilizer is 2-Nitrodiphenylamine (2-NDPA), and the plasticizer is laevo-carvone (1-carvone). More specifically, in the second embodiment, the explosive composition mixture 12 consists of 15 g water-wet 12.6% N nitrocellulose, 0.25 g 2-NDPA, and 7.5 g 1-carvone (hereinafter, referred to as Mixture #2 throughout this disclosure). In an alternative embodiment, the explosive composition mixture 12 consists of 32 g water-wet 12.6% N nitrocellulose, 0.4 g 2-NDPA, and 15.6 g 1-carvone (hereinafter, referred to as Mixture #3 throughout this disclosure). A person of ordinary skill in the art will understand that an explosive material EM other than nitrocellulose could be used in the explosive composition mixture 12 in accordance with the present disclosure. Similarly, a person of ordinary skill in the art will further understand that the additive other than 4-oxo-isophorone and 1-carvone could be used in the explosive composition mixture 12 in accordance with the present disclosure, such as, for example, nitroglycerin. The explosive composition mixture 12 can be formed in the mixing vessel assembly 14, as shown in
The upper dish 18 is shown in
The lower dish 20 is shown in
Accordingly, the upper dish 18 and the lower dish 20 are designed such that when the mixing vessel assembly 14 is assembled, as shown in
After placing the explosive composition mixture 12 into one or both of the lower dish 20 and the upper dish 18, the mixing vessel assembly 14 is assembled to form a closed mixing zone 24. In an alternative embodiment, a plurality of filler beads can also be placed into the mixing vessel assembly. A person of ordinary skill in the art will understand that the filler beads can be either plastic or glass. The filler beads may assist in breaking up any conglomerates of the explosive composition mixture 12 formed in the mixing vessel assembly 14 formed during the mixing process.
As illustrated by
As with all physical objects, the acoustic mixing system 10 has a resonant frequency. The resonant frequency of the acoustic mixing system 10 is constant when at rest but is continually adjusting and changing when the acoustic mixer 16 is in operation. In one embodiment, the resonant frequency of the acoustic mixing system 10 is greater than about 20 Hz and less than about 100 Hz. More specifically, the resonant frequency of the acoustic mixing system 10 is greater than about 50 Hz and less than about 70 Hz. Even more specifically, the resonant frequency of the acoustic mixing system 10 is greater than about 58 Hz and less than about 62 Hz.
In accordance with a method of the present disclosure, the acoustic mixing system 10 is operated at an operating frequency that causes a vertical displacement of the mixing vessel assembly 14. In one embodiment, the vertical displacement of the mixing vessel assembly 14 is equal to or less than 14 mm (0.55 inches). Notably, the acoustic mixing system 10 is designed and operated such that a ratio of the maximum vertical height 26 of the closed mixing zone 24 to the vertical displacement of the mixing vessel assembly 14 is 2.0 or less, 1.5 or less or 1.0 or less. The ratio of the maximum vertical height 26 of the closed mixing zone 24 to the vertical displacement of the mixing vessel assembly 14 within the acoustic mixing system 10 ensures the explosive composition mixture 12 located within the mixing vessel assembly experiences a majority of the forces associated with the vertical displacement, thereby generating intense mixing of the explosive composition mixture 12 to create a homogenous mixture.
The following examples set forth methods in accordance with the present disclosure. It is to be understood, however, that these examples are provided by way of illustration and noting therein should be taken as a limitation upon the overall scope of any claims. For each of the below examples, the maximum vertical height of the closed mixing zone to the vertical displacement of the vessel was 1.4
This example describes a method for using an acoustic mixer 16, such as a LABRAM mixer similar to the image shown in
The mixing vessel assembly 14 was placed onto the acoustic mixer 16, and the acoustic mixer was operated at an operating frequency greater than 58 Hz and less than 62 Hz. This resulted in a vertical displacement of the mixing vessel assembly 14 equal to or less than 14 mm. The acoustic mixer 16 was operated for a total of approximately 8 minutes. The photo shown in
This example describes a method for using an acoustic mixer 16, such as a LABRAM mixer similar to the image shown in
The mixing vessel assembly 14 was placed onto the acoustic mixer 16, and the acoustic mixer was operated at an operating frequency greater than 58 Hz and less than 62 Hz. This resulted in a vertical displacement of the mixing vessel assembly 14 equal to or less than 14 mm. The acoustic mixer 16 was operated for a total of approximately 2 minutes. The photo shown in
This example describes a method for using an acoustic mixer 16, such as a LABRAM mixer similar to the image shown in
The mixing vessel assembly 14 was placed onto the acoustic mixer 16, and the acoustic mixer was operated at an operating frequency greater than 58 Hz and less than 62 Hz. This resulted in a vertical displacement of the mixing vessel assembly 14 equal to or less than 14 mm. The acoustic mixer 16 was operated for a total of approximately 13 minutes. The photo shown in
The foregoing description has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise form disclosed. Many modifications and variations are possible in light of this disclosure. Indeed, while certain features of this disclosure have been shown, described and/or claimed, it is not intended to be limited to the details above, since it will be understood that various omissions, modifications, substitutions and changes in the apparatuses, forms, method, steps and system illustrated and in its operation can be made by those skilled in the art without departing in any way from the spirit of the present disclosure.
A person of ordinary skill in the art would understand that the disclosed acoustic mixing system and corresponding method could be used with other low-bulk density fibrous materials other than nitrocellulose. For example, a person of ordinary skill in the art would understand that the acoustic mixing system and corresponding method disclosed herein could be used to mix cellulose and/or Kevlar. A person of ordinary skill in the art would further understand that additives other than plasticizers and/or stabilizers may be used in forming a mixture. In view of the foregoing, a person of ordinary skill in the art would understand that the disclosed acoustic mixing system and corresponding method could be used for forming mixtures other than propellant mixtures.
Further, the foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the disclosure. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the disclosure. Thus, the foregoing descriptions of specific embodiments of the present disclosure are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the disclosure to the precise forms disclosed, many modifications and variations are possible in view of the above teachings. The embodiments were chosen and described in order to best explain the principles of the disclosure and its practical applications, to thereby enable others skilled in the art to best utilize the disclosed system and method, and various embodiments with various modifications as are suited to the particular use contemplated.
This application claims priority as non-provisional patent application to U.S. Patent Provisional Application No. 62/899,247, filed Sep. 12, 2019, the disclosure of which is incorporated by reference herein in its entirety.
Number | Date | Country | |
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62899247 | Sep 2019 | US |