Title:
GRANULAR AMMONIUM PERCHLORATE PROPELLANT
United States Patent 3656432
Abstract:
Granular ammonium perchlorate having a particle size of -40 to -50 mesh is packed to a bulk density of from about 1.0 to 1.5 g/cc in a rocket motor casing restricted to maintain a chamber pressure in the range of from about 100 to about 2,000 psia and is used as the sole source of propellant gases for propelling a rocket. A flame similarly provided may be used for other pyrotechnic applications.
US Patent References:
Combustion system comprising metal foil and solid perchlorate
Fritzlen - October 1962 - 3056701
Self-contained welding torch
Billhardt - February 1965 - 3168090
Combustion system comprising metal foil and solid perchlorate
Fritzlen - October 1962 - 3056701
Self-contained welding torch
Billhardt - February 1965 - 3168090
Application Number:
04/827700
Publication Date:
04/18/1972
Filing Date:
05/26/1969
View Patent Images:
Export Citation:
Assignee:
Thiokol Chemical Corporation (Bristol, PA)
Primary Class:
Other Classes:
148/194, 60/253, 149/76, 266/48, 102/380
International Classes:
C06B29/22; F02K9/08; C06B29/00; F02K9/00; F42B15/00; C06D1/04
Field of Search:
102/99,34,49.3,49.4,49.5,49.6,49.7,99-104 149/76
Primary Examiner:
Stahl, Robert F.
Claims:
I claim
1. A pyrotechnic device having an open-ended combustion chamber having a restricted outlet and consisting essentially of, as substantially the sole gas or flame generating component contained in the device, ammonium perchlorate particles having a particle size in the range of from about -40 to about +50 U.S. Standard sieve size compacted in the combustion chamber to a density in the range from about 1.0 to about 1.5 g/cc, said outlet being restricted to maintain the pressure of the products of combustion in the combustion chamber in the range of from about 100 to about 2,000 psia during combustion of the ammonium perchlorate.
2. A pyrotechnic device according to claim 1 wherein the device is a rocket motor and the products of combustion are used to drive the motor.
3. A pyrotechnic device according to claim 1 wherein the device is a cutting torch and the flame of combustion is used as a cutting flame.
1. A pyrotechnic device having an open-ended combustion chamber having a restricted outlet and consisting essentially of, as substantially the sole gas or flame generating component contained in the device, ammonium perchlorate particles having a particle size in the range of from about -40 to about +50 U.S. Standard sieve size compacted in the combustion chamber to a density in the range from about 1.0 to about 1.5 g/cc, said outlet being restricted to maintain the pressure of the products of combustion in the combustion chamber in the range of from about 100 to about 2,000 psia during combustion of the ammonium perchlorate.
2. A pyrotechnic device according to claim 1 wherein the device is a rocket motor and the products of combustion are used to drive the motor.
3. A pyrotechnic device according to claim 1 wherein the device is a cutting torch and the flame of combustion is used as a cutting flame.
Description:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to rocket motors and particularly to a solid propellant system used to operate a rocket motor.
2. Description of the Prior Art
Solid propellants for operating rocket motors are usually "composite" types, such as rigid composites, elastomeric composites, or thermoplastic composites, such as those described, for example, in The Chemistry of Propellants, Penner and Ducarme, Pergamon Press, New York (1960), pages 285-302, chapter entitled "Methods of Burning Rate Control in Solid Propellants" by G.H.S. Young. Such composites generally are composed of an oxidizer, which usually is ammonium nitrate or a perchlorate, e.g. ammonium perchlorate, and a fuel, which may be an organic compound, e.g. pitch, styrene polymers, or a polysulfide rubber, and/or a metal fuel, for example, aluminum powder.
From the work of G.K. Adams, discussed at pages 297-298, supra, it is known also to burn ammonium perchlorate pellets under nitrogen pressure above 1,000 psi, or at a lower pressure, if a sufficiently large surface is exposed, or if a catalyst is used. However, as further discussed by G.H.S. Young at page 298, supra, the information so far available has not enabled one to make predictions about the burning rate of ammonium perchlorate, which is found to be the fastest of the group tested, consisting of ammonium nitrate, double base and ammonium perchlorate.
Also, in U.S. Pat. No. 3,056,701 is taught a composite solid fuel package useful in rocket gas generating systems, and employing a mixture of a granular solid perchlorate oxidant and aluminum or magnesium powder loosely disposed essentially between layers of flat aluminum or magnesium foil which serve both as a fuel and as a safeguard against penetration of hot gases throughout the mass thereby to reduce the risk of explosion.
Each of the above systems essentially comprises an organic or metal fuel in combination with the oxidizer, usually in at least a stoichiometric ratio. None teaches use of ammonium perchlorate alone as a self-sustaining sole, gas generating means, as does the present invention.
SUMMARY OF THE INVENTION
The present invention provides a means for operating a rocket motor or other pyrotechnic device, e.g. a metal cutting torch, with ammonium perchlorate as the sole source of propellant gases or flame. It has now been discovered that by packing granular ammonium perchlorate essentially having a particle size of from about -40 to about +50 mesh (all retained on U.S. Standard sieve size 40 mesh, all passes sieve size 50 mesh) to a density of from about 1.0 to about 1.5 g/cc, in a rocket motor casing fitted with an exhaust nozzle throttled or otherwise restricted, to maintain chamber pressure below about 2,000 psia, the ammonium perchlorate can be ignited and will burn without exploding while generating propellant gases in sufficient volume to propell the rocket in which it is contained. Contrary to former teachings, it has been found that compression of the ammonium perchlorate into a void-free mass is not necessary to achieve burning of the ammonium perchlorate without explosion. It has also been found that presence of a supplemental organic or inorganic fuel ingredient is not necessary to propagate the flame after ignition.
BRIEF DESCRIPTION OF THE DRAWING
The drawing illustrates schematically a cross-sectional, partially broken away, expanded view of the components of a rocket motor driven munition provided with propellant according to the invention.
More specifically, a rocket motor casing 1, made of high strength phenolic resin or other inert casing material and having a single open end 7, is packed first with a layer of lightweight, non-combustible wadding 2, which is used as a spacing material to vary the length of the propellant charge and, accordingly, its burning time. The casing 1 is then packed with propellant 3 which consists of -40 to +50 mesh granular ammonium perchlorate as the sole gas generating charge and which is densified by means of a vibrator to a density of about 1.0 to 1.5 g/cc. An igniter assembly 4, provided with electrical ignition means 5, is inserted into the propellant mass through an opening 6 provided near the open end 7. The open end 7 is then sealed with a sealing diaphragm 8 which is made of a rupturable plastic or elastomeric composition. A nozzle assembly 9 is attached to the open end 7 of the casing 1 by means of threads 10 which engage threads 11 of the casing. An ogive-shaped payload head 12, provided with a payload 13, is attached to the closed end 14 of the casing 1 by means of threads 15 which engage threads 16 on the head 12. The casing 1 is provided with stabilizer fins 17 in the usual way. The nozzle assembly 9 is coated internally with carbon throat lining 18 and has its restricted outlet 19 sized to maintain the pressure within the casing 1 below a desired design pressure in the range from about 100 to about 2,000 psia during combustion of the propellant 3.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention is practiced by using, as substantially the sole gas producing component in the propellant 3, ammonium perchlorate granules or crystals which are of the usual high grade chemical specifications used in rocket propellant compositions. However, the particle sizes of the granules or crystals is controlled by screening out particles finer than 40 mesh U.S. Standard sieve size and excluding particles over 50 mesh in size. The particles thus have a size of from about 300 to about 400 microns measured along their narrow axes. The granules may be in any form, e.g. crystals, spheres, or ground particles. Irregularly shaped particles are preferred for their better packability. The particles are poured, or otherwise charged, into the casing 1 and are compacted to a density of from about 1.0 to about 1.5 g/cc, for example, by placing the casing 1 in a vertical position with the closed end 14 resting on the surface of a vibrating table. The rocket casing 1 is then prepared for assembly and assembled substantially as described above and illustrated in the drawing.
A series of burning tests were carried out in a strandburner in order to determine the burning rates of high purity ammonium perchlorate at various pressures. The strandburner procedure used was patterned after that of B.L. Crawford et al. Anal. Chem., 19, 630 (1947), described and discussed at pages 288-289 of The Chemistry of Propellant, supra. In general, strandburner tubes having an inner diameter of 4 mm were used. Burning rates were determined at pressures of 1,520, 1,015, 615, 315 and 105 psia, using -40 to +50 mesh powder packed to a bulk density of 1.10 g/cc ±5 percent. The test data and results are shown in the table.
TABLE
Example No. of Test Burning Rate No. Samples Pressure psia inches/sec. 1 8 1520 12.31±23.6% 2 9 1015 9.49±11.3% 3 9 615 6.67±22.6% 4 9 315 4.52±25.4% 5 8 105 2.11±30.3%
From the data in the examples shown in the table, the formula for rate of burning of the ammonium perchlorate was calculated in accordance with the usual formula R b =kp n , where
R b is the rate of burning in inches per second,
k is a constant for the given propellant,
p is the combustion pressure in psia, and
n is the pressure exponent.
The burning rate may be modified by combining the ammonium perchlorate with small amounts of burning rate catalysts such as manganese compounds to increase the burning rate, or with finely divided refractory materials in a manner and in amounts known to be used in the burning of ammonium perchlorate compositions in the presence of a fuel, such as an elastomer.
In addition to the advantages and benefits described above, the use of ammonium perchlorate as the sole gas generating component in the rocket casing has the advantage that the rocket assembly has a greater resistance to shock of impact than does the usual composite type of ammonium perchlorate-containing propellant. Whereas the impact sensitivites of the latter composite types run about 20 inch pounds, that of the ammonium perchlorate sole propellant of the invention runs over 100 inch pounds.
Upon ignition, the compacted ammonium perchlorate burns to produce propellant gases substantially in accordance with the combustion equation of B. H. Newman, given at page 33 of ACS Monograph No. 146, Perchlorates, Reinhold Publishing Company, (1960):
10NH 4 ClO 3 ➝2.5CL 2 +2N 2 O+2.5NOCl+HClO 4 +1.5HCl+ 18.75H 2 O+1.75N+6.375O 2 .
While it is not known definitely why the ammonium perchlorate particles of -40 to +50 mesh size, when packed to a density of 1.0 to 1.5 g/cc, burn smoothly rather than explode, at a burning pressure in the pressure range of from about 100 to about 2,000 psia, it is theorized that the closely packed particles of ammonium perchlorate form a substantially solid barrier to gases which prevents the hot combustion gases from readily entering into the randomly occurring spaces between the particles without loss of sufficient heat to reduce the temperature of the particles below an explosive temperature at a given pressure. Whatever the reason, it has been found that the particulate ammonium perchlorate burns smoothly, forming a self-sustaining flame to provide the gases needed to propell a rocket motor designed and made in accordance with known rocket design and manufacturing principles.
The self-sustained burning of ammonium perchlorate particles according to the invention may also be used to provide a flame source for metal cutting. In such use, the oxygen and chlorine gases present in the products of combustion provide an added benefit in that they combine exothermically with the metal being worked, e.g. iron, to form an even hotter cutting flame. The invention thus provides a flame source which is particularly advantageous in performing rescue or demolition operations in remote locations where cylinder gases cannot be brought to the scene. A torch-type container for low pressure (e.g. about 100 - 200 psia) operation may readily be designed and built to carry out such an operation in combination with the present invention.
Although certain specific embodiments have been shown and described herein, it is to be understood that they are illustrative only and are not to be construed as limiting on the scope and spirit of the invention.
1. Field of the Invention
The invention relates to rocket motors and particularly to a solid propellant system used to operate a rocket motor.
2. Description of the Prior Art
Solid propellants for operating rocket motors are usually "composite" types, such as rigid composites, elastomeric composites, or thermoplastic composites, such as those described, for example, in The Chemistry of Propellants, Penner and Ducarme, Pergamon Press, New York (1960), pages 285-302, chapter entitled "Methods of Burning Rate Control in Solid Propellants" by G.H.S. Young. Such composites generally are composed of an oxidizer, which usually is ammonium nitrate or a perchlorate, e.g. ammonium perchlorate, and a fuel, which may be an organic compound, e.g. pitch, styrene polymers, or a polysulfide rubber, and/or a metal fuel, for example, aluminum powder.
From the work of G.K. Adams, discussed at pages 297-298, supra, it is known also to burn ammonium perchlorate pellets under nitrogen pressure above 1,000 psi, or at a lower pressure, if a sufficiently large surface is exposed, or if a catalyst is used. However, as further discussed by G.H.S. Young at page 298, supra, the information so far available has not enabled one to make predictions about the burning rate of ammonium perchlorate, which is found to be the fastest of the group tested, consisting of ammonium nitrate, double base and ammonium perchlorate.
Also, in U.S. Pat. No. 3,056,701 is taught a composite solid fuel package useful in rocket gas generating systems, and employing a mixture of a granular solid perchlorate oxidant and aluminum or magnesium powder loosely disposed essentially between layers of flat aluminum or magnesium foil which serve both as a fuel and as a safeguard against penetration of hot gases throughout the mass thereby to reduce the risk of explosion.
Each of the above systems essentially comprises an organic or metal fuel in combination with the oxidizer, usually in at least a stoichiometric ratio. None teaches use of ammonium perchlorate alone as a self-sustaining sole, gas generating means, as does the present invention.
SUMMARY OF THE INVENTION
The present invention provides a means for operating a rocket motor or other pyrotechnic device, e.g. a metal cutting torch, with ammonium perchlorate as the sole source of propellant gases or flame. It has now been discovered that by packing granular ammonium perchlorate essentially having a particle size of from about -40 to about +50 mesh (all retained on U.S. Standard sieve size 40 mesh, all passes sieve size 50 mesh) to a density of from about 1.0 to about 1.5 g/cc, in a rocket motor casing fitted with an exhaust nozzle throttled or otherwise restricted, to maintain chamber pressure below about 2,000 psia, the ammonium perchlorate can be ignited and will burn without exploding while generating propellant gases in sufficient volume to propell the rocket in which it is contained. Contrary to former teachings, it has been found that compression of the ammonium perchlorate into a void-free mass is not necessary to achieve burning of the ammonium perchlorate without explosion. It has also been found that presence of a supplemental organic or inorganic fuel ingredient is not necessary to propagate the flame after ignition.
BRIEF DESCRIPTION OF THE DRAWING
The drawing illustrates schematically a cross-sectional, partially broken away, expanded view of the components of a rocket motor driven munition provided with propellant according to the invention.
More specifically, a rocket motor casing 1, made of high strength phenolic resin or other inert casing material and having a single open end 7, is packed first with a layer of lightweight, non-combustible wadding 2, which is used as a spacing material to vary the length of the propellant charge and, accordingly, its burning time. The casing 1 is then packed with propellant 3 which consists of -40 to +50 mesh granular ammonium perchlorate as the sole gas generating charge and which is densified by means of a vibrator to a density of about 1.0 to 1.5 g/cc. An igniter assembly 4, provided with electrical ignition means 5, is inserted into the propellant mass through an opening 6 provided near the open end 7. The open end 7 is then sealed with a sealing diaphragm 8 which is made of a rupturable plastic or elastomeric composition. A nozzle assembly 9 is attached to the open end 7 of the casing 1 by means of threads 10 which engage threads 11 of the casing. An ogive-shaped payload head 12, provided with a payload 13, is attached to the closed end 14 of the casing 1 by means of threads 15 which engage threads 16 on the head 12. The casing 1 is provided with stabilizer fins 17 in the usual way. The nozzle assembly 9 is coated internally with carbon throat lining 18 and has its restricted outlet 19 sized to maintain the pressure within the casing 1 below a desired design pressure in the range from about 100 to about 2,000 psia during combustion of the propellant 3.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention is practiced by using, as substantially the sole gas producing component in the propellant 3, ammonium perchlorate granules or crystals which are of the usual high grade chemical specifications used in rocket propellant compositions. However, the particle sizes of the granules or crystals is controlled by screening out particles finer than 40 mesh U.S. Standard sieve size and excluding particles over 50 mesh in size. The particles thus have a size of from about 300 to about 400 microns measured along their narrow axes. The granules may be in any form, e.g. crystals, spheres, or ground particles. Irregularly shaped particles are preferred for their better packability. The particles are poured, or otherwise charged, into the casing 1 and are compacted to a density of from about 1.0 to about 1.5 g/cc, for example, by placing the casing 1 in a vertical position with the closed end 14 resting on the surface of a vibrating table. The rocket casing 1 is then prepared for assembly and assembled substantially as described above and illustrated in the drawing.
A series of burning tests were carried out in a strandburner in order to determine the burning rates of high purity ammonium perchlorate at various pressures. The strandburner procedure used was patterned after that of B.L. Crawford et al. Anal. Chem., 19, 630 (1947), described and discussed at pages 288-289 of The Chemistry of Propellant, supra. In general, strandburner tubes having an inner diameter of 4 mm were used. Burning rates were determined at pressures of 1,520, 1,015, 615, 315 and 105 psia, using -40 to +50 mesh powder packed to a bulk density of 1.10 g/cc ±5 percent. The test data and results are shown in the table.
TABLE
Example No. of Test Burning Rate No. Samples Pressure psia inches/sec. 1 8 1520 12.31±23.6% 2 9 1015 9.49±11.3% 3 9 615 6.67±22.6% 4 9 315 4.52±25.4% 5 8 105 2.11±30.3%
From the data in the examples shown in the table, the formula for rate of burning of the ammonium perchlorate was calculated in accordance with the usual formula R b =kp n , where
R b is the rate of burning in inches per second,
k is a constant for the given propellant,
p is the combustion pressure in psia, and
n is the pressure exponent.
The burning rate may be modified by combining the ammonium perchlorate with small amounts of burning rate catalysts such as manganese compounds to increase the burning rate, or with finely divided refractory materials in a manner and in amounts known to be used in the burning of ammonium perchlorate compositions in the presence of a fuel, such as an elastomer.
In addition to the advantages and benefits described above, the use of ammonium perchlorate as the sole gas generating component in the rocket casing has the advantage that the rocket assembly has a greater resistance to shock of impact than does the usual composite type of ammonium perchlorate-containing propellant. Whereas the impact sensitivites of the latter composite types run about 20 inch pounds, that of the ammonium perchlorate sole propellant of the invention runs over 100 inch pounds.
Upon ignition, the compacted ammonium perchlorate burns to produce propellant gases substantially in accordance with the combustion equation of B. H. Newman, given at page 33 of ACS Monograph No. 146, Perchlorates, Reinhold Publishing Company, (1960):
10NH 4 ClO 3 ➝2.5CL 2 +2N 2 O+2.5NOCl+HClO 4 +1.5HCl+ 18.75H 2 O+1.75N+6.375O 2 .
While it is not known definitely why the ammonium perchlorate particles of -40 to +50 mesh size, when packed to a density of 1.0 to 1.5 g/cc, burn smoothly rather than explode, at a burning pressure in the pressure range of from about 100 to about 2,000 psia, it is theorized that the closely packed particles of ammonium perchlorate form a substantially solid barrier to gases which prevents the hot combustion gases from readily entering into the randomly occurring spaces between the particles without loss of sufficient heat to reduce the temperature of the particles below an explosive temperature at a given pressure. Whatever the reason, it has been found that the particulate ammonium perchlorate burns smoothly, forming a self-sustaining flame to provide the gases needed to propell a rocket motor designed and made in accordance with known rocket design and manufacturing principles.
The self-sustained burning of ammonium perchlorate particles according to the invention may also be used to provide a flame source for metal cutting. In such use, the oxygen and chlorine gases present in the products of combustion provide an added benefit in that they combine exothermically with the metal being worked, e.g. iron, to form an even hotter cutting flame. The invention thus provides a flame source which is particularly advantageous in performing rescue or demolition operations in remote locations where cylinder gases cannot be brought to the scene. A torch-type container for low pressure (e.g. about 100 - 200 psia) operation may readily be designed and built to carry out such an operation in combination with the present invention.
Although certain specific embodiments have been shown and described herein, it is to be understood that they are illustrative only and are not to be construed as limiting on the scope and spirit of the invention.