Cartridge for Ammunition

Abstract

A single ply barrier foil is provided between the propellant in the cartridge casing and the pyrotechnic composition in the primer to prevent nitroglycerin migration from the propellant into the pyrotechnic composition. The single ply barrier foil is formed of ethyl cellulose and a plasticizer and has a thickness of 190 um.+-.10 um.

Description

[0001] This invention relates to a cartridge. More particularly, this invention relates to a cartridge for ammunition. Still more particularly, this invention relates to an arrangement for protecting the primer composition of ammunition from volatile materials in a propellant charge.

BACKGROUND OF THE INVENTION

[0002] Modern smokeless powder used as a propellant in ammunition contains various volatile substances and the particular effect they have on the priming composition will depend on the ingredients of the composition. If the primer is of the potassium chlorate type containing in addition lead sulfocyanide and trinitrotoluene and the propellant charge is double base powder containing nitroglycerine, the primer will gradually become desensitized by the nitroglycerine vapor. In fact, the certain volatiles from the propellant powders will act deleteriously on certain priming compositions.

[0003] As is known, ammunition cartridges are manufactured with a casing; a double-base propellant having nitroglycerin in the casing and a primer disposed at one end of the casing and including a pyrotechnic composition.

[0004] It is also known that the potential for nitroglycerin migration from the cartridge casing propellant into the pyrotechnic material in the primer may affect the sensitivity of the pyrotechnic primer material. The result of increased or decreased sensitivity of the pyrotechnic material creates an uncertain ignition of the cartridge propellant. This uncertainly must be avoided to maintain safety to all persons.

[0005] In the past, use has been made of a membrane between the primer and the cartridge propellant to block the migration of nitroglycerin into the primer. For example, U.S. Pat. Nos. 2,340,284, 2,974,592, 3,062,146, and 4,386,567 describe the use of a membrane material made from regenerated cellulose strip in a four ply laminated structure. See also, the National Military Establishment Specification JAN-C-677 dated 30 Sep. 1948 and amended 30 Mar. 1951 and 11 Dec. 1951 for a further example of the laminated membrane structure. A nitrocellulose lacquer is applied to both sides of the regenerated cellulose as the only protection against nitroglycerin migration from the cartridge double-base propellant into the pyrotechnic composition in the primer. Any void or lack of complete coverage of the nitrocellulose lacquer coating onto the regenerated cellulose laminated strip would allow nitroglycerin penetration and vapor migration, as regenerated cellulose, in and by itself, is not nitroglycerin resistant. The volatile constituents of the double-base propellant in the cartridge can easily transfer into the pyrotechnic primer composition compromising sensitivity of the ignition.

[0006] Multi-ply cellulose regenerated strips are also highly prone to delamination during the end use application and therefore create waste and loss of productivity.

[0007] Regenerated cellulose, also known as Cellophane, is manufactured using carbon disulfide, a known toxin and environmentally unfriendly chemical. Carbon disulfide must be recovered and properly disposed of to prevent environmental concerns. This environmental contamination concern requires complicated recovery processes or remediation concerns for the manufacturers of cellulose regenerated strip. Many have ceased the manufacturing of this product making availability of the prior art nitrocellulose lacquer coated regenerated cellulose strip difficult if not impossible to find.

[0008] Accordingly, it is an object of the invention to provide an improved barrier for preventing nitroglycerin migration from a cartridge double-base propellant into a pyrotechnic composition in a primer.

[0009] It is another object of the invention to provide an environmentally friendly barrier for preventing nitroglycerin migration from a cartridge double-base propellant.

[0010] Briefly, the invention is directed to a cartridge comprising a casing, a double-base propellant disposed in the casing and having nitroglycerin therein and a primer disposed at one end of the casing and including a pyrotechnic composition.

[0011] In accordance with the invention a single ply barrier foil is disposed between the propellant and the pyrotechnic composition to prevent nitroglycerin migration from the propellant into the pyrotechnic composition.

[0012] The foil is formed of ethyl cellulose.

[0013] Typically, the pyrotechnic composition is of a potassium chlorate type containing lead sulfocyanide and trinitrotoluene and the propellant is a powder.

[0014] These and other objects and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings wherein:

[0015] FIG. 1 illustrates a side view of a cartridge constructed in accordance with the invention; and

[0016] FIG. 2 illustrates an enlarged cross-sectional view of a primer employed in the cartridge of FIG. 1.

[0017] Referring to FIG. 1, the cartridge 1, for example, a 20 millimeter (mm) cartridge, is of conventional construction for ammunition having a casing 2, a double-base propellant 3 disposed in the casing and a primer 4 disposed at one end of the casing 2 and including a pyrotechnic composition 5.

[0018] The double-base propellant 3 typically includes nitroglycerin while the pyrotechnic composition 5 is of a potassium chlorate type containing lead sulfocyanide and trinitrotoluene.

[0019] In accordance with the invention, a single ply barrier foil 6 is disposed between the propellant 3 and the pyrotechnic composition 5 to prevent nitroglycerin migration from the propellant 3 into the pyrotechnic composition 5.

[0020] As illustrated in FIG. 2, the primer 4 is of conventional structure being formed of a cup-shaped casing 7 with an open base that houses an electrically conductive contact 8 between the pyrotechnic composition 5 and the open base of the casing 7. In addition, an insulating liner 9 separates the conductive contact 8 from the casing 7. The liner 9 is preferably formed from polymeric material such as, polypropylenes, polycarbonates, polysulfones, poly(ether imides), poly(amide imides), poly(ether sulfones), poly(benzimide azoles), and poly(ether ether ketones).

[0021] The pyrotechnic composition 5 is sandwiched between the conductive contact 8 and the single ply barrier foil 6. An anvil 10 of metal is press fit into the casing 7 over the top of the foil 6 to secure the foil 6 in place. As illustrated, the anvil 10 is of cup shape with an open base to expose the center of the top surface of the foil 6.

[0022] The single ply barrier foil 6 is uncoated and is made by cast extrusion or solvent cast process. The foil 6 is of a color, for example, red, in order to distinguish its presence for ammunition assemblers. In other uses, the foil 6 is of a light tan to dark tan color and a stack of such foils 6 may be sufficiently transparent so that print may be read through the stack.

[0023] In the solvent cast process, a mixture of ethyl cellulose, plasticizers, solvent(s) and dyes is distributed via a state of the art distributor onto a highly polished belt, such as a stainless steel belt. This process provides control of the foil thickness to a very tight tolerance. The foil then passes into drying sections to optimize the chemical structure and is finally wound onto cores as a finished product.

[0024] By way of example, the ethyl cellulose mixture is made of ethyl cellulose powder, medium viscosity Type 70 produced by Dow Chemical of Midland, Mich. and others; a plasticizer, such as, dibutyl phthylate, diphenyl phosphate, triphenyl phosphate, substituted diphenyl ether, substituted phenols, and alkylated diphenyl oxide; and a solvent, such as, 80:20 toluene:alcohol, butyl acetate, ethanol, methylene chloride, or ethylene glycol monobutyl ether, alone or in combination. Specifically, substituted diphenyl ether is the preferred plasticizer and methylene chloride is the preferred solvent. The foil 6 has a thickness of 190 um.+-.10 um.

[0025] The single ply barrier foil 6 does not require a nitrocellulose lacquer coating to prevent nitroglycerin migration. Testing was conducted per the National Military Establishment Specification JAN-C-677 section F-4C. According to the specification, samples approximately 3 inches in length were suspended horizontally by gripping the ends with a holder. Three drops of nitroglycerin were placed approximately 3/4 of the inch apart on each strip at a volume of .+-.0.06 ml via a class "A" volumetric pipette. The samples were then placed into an oven being held a 50 degree Celsius for 48 hours. At the end of that time, the samples were removed from the oven, allowed to cool, and the nitroglycerin was removed from the strips with blotting paper. The samples were then removed from the holder and individually examined for any swelling or signs that nitroglycerin had passed through the strips.

[0026] The clear single ply barrier foil showed that nitroglycerin did not pass through the barrier.

[0027] A single ply barrier foil formulated with a red dye was included in this test to determine potential influence of the required red color. Results of this testing indicate no influence to prevent nitroglycerin migration resulting from the red color addition.

[0028] During the pyrotechnic primer composition 5 loading process, proper placement of an uncoated single ply barrier foil 6 into the primer 4 will inhibit migration of the volatile constituent of the cartridge double-base propellant 3, nitroglycerin, into the pyrotechnic composition 5. This foil 6 need not rely on full nitrocellulose lacquer coverage onto both surfaces of a cellulose regenerated strip to prevent nitroglycerin intrusion into the pyrotechnic composition 5 in the primer 4. The uncoated foil 6 is sufficient, without any surface coatings, to withstand nitroglycerin absorption, migration or vapor permeability through its structure thus affecting the primer pyrotechnic composition 5 detonation timing.

[0029] The advantage of using an uncoated single ply barrier foil 6 as a membrane in the ammunition primer 4 is the simplicity of the foil to perform as a nitroglycerin barrier. A single-ply uncoated foil 6 will prevent nitroglycerin migration whereas a 4-ply regenerated cellulose strip requires a nitrocellulose lacquer coating applied to both sides. Any void in the application of the nitrocellulose lacquer coating will provide exposed regenerated cellulose strip insufficient, in and by itself, to prevent nitroglycerin migration into the primer pyrotechnic composition. As a single-ply foil, the foil 6 will not delaminate as the does the multi-ply prior art during the end use application process.

[0030] Advantageously, the single ply foil 6 is environmentally friendly as opposed to the process to produce lacquer coated regenerated cellulose strip as described in U.S. Pat. No. 3,983,201 requiring carbon disulfide (CS.sub.2) as part of the manufacturing process. Carbon disulfide (CS.sub.2) requires recovery or costly remediation to protect the environment from hazard. Acute (short-term) inhalation exposure of humans to carbon disulfide has caused changes in breathing and chest pains. Nausea, vomiting, dizziness, fatigue, headache, mood changes, lethargy, blurred vision, delirium, and convulsions have also been reported in humans acutely exposed by inhalation. Neurologic effects, including behavioral and neurophysiological changes, have been observed in chronic (long-term) human and animal inhalation studies. Reproductive effects, such as decreased sperm count and menstrual disturbances have been observed in humans exposed to carbon disulfide by inhalation. Animal studies support these findings. EPA has not classified carbon disulfide for human carcinogenicity.

[0031] The main sources of information are the Agency for Toxic Substances and Disease Registry's (ATSDR's) Toxicological Profile for Carbon disulfide and EPA's Integrated Risk Information System (IRIS), which contains information on oral chronic toxicity and the reference dose (RfD) and inhalation chronic toxicity and the reference concentration (RfC).

[0032] The single ply foil 6 is particularly useful as a protective barrier seal in 20 mm medium caliber ammunition preventing the diffusion of nitroglycerin, an energetic double-base propellant plasticizer, from contaminating the pyrotechnic composition 5 in the primer 4. Such contamination can lead to premature ignition, delayed ignition, referred to as a "hangfire", or zero ignition, also known as "misfire", each creating a hazardous situation.

[0033] Nitroglycerin Resistance analytical testing of the single ply barrier foil was conducted in January 2010 and repeated in January 2012 in accordance with the National Military Establishment Specification JAN-C-677, Amendment 2, dated Dec. 11, 1951, Section F-4c. The results concluded that the foil conforms to the requirements of Specification JAN-C-677 whereas clear cellulose acetate strips failed.

[0034] The single ply barrier foil is manufactured as an environmentally friendly product with no limitation of exposure or personal protective equipment required. The foil is biologically degradable under corresponding conditions of decomposition and can be stored on disposal sites without cause of danger.

Claims

1. A cartridge comprising a casing; a double-base propellant disposed in said casing, said propellant having nitroglycerin therein; a primer disposed at one end of said casing and including a pyrotechnic composition; and a single ply barrier foil disposed between said propellant and said pyrotechnic composition to prevent nitroglycerin migration from said propellant into said pyrotechnic composition.

2. A cartridge as set forth in claim 1 wherein said pyrotechnic composition is of a potassium chlorate type containing lead sulfocyanide and trinitrotoluene and said propellant is a powder.

3. A cartridge as set forth in claim 1 wherein said single ply barrier foil is formed of cellulose.

4. A cartridge as set forth in claim 1 wherein said single ply barrier foil is formed of ethyl cellulose and a plasticizer.

5. A cartridge as set forth in claim 1 wherein said single ply barrier has a thickness of 190 um.+-.10 um.

6. A cartridge as set forth in claim 1 wherein said casing is sized for a 20 millimeter ammunition cartridge.