US3723203A - Propellant charge for caseless ammunition - Google Patents

Abstract

A PROPELLANT CHARGE FOR CASELESS AMMUNITION IS PROVIDED. THE CHARGE IS PREPARED BY COMPRESSION MOLDING AN INTIMATE MIXTURE OF PROPELLANT GRANULES AND 0.1 TO 10% BY WEIGHT OF THE MIXTURE OF A POLYMERIC BINDER WHICH IS CERTAIN COLLOIDALLY DISPERSIBLE COPOLYMERS OF ETHYLENE AND AN A-OLEFIN AND/OR A NON-CONJUGATED HYDROCARBON DIENE, AND PREFERABLY AN ETHYLENE-PROPYLENE COPOLYMER OR TERPOLYMER.

Description

3,723,203 PROPELLANT CHARGE FOR CASELESS AMMUNITION Alan D. Craig and Carl A. Lukach, Wilmington, Del., assignors to Hercules Incorporated, Wilmington, Del. N Drawing. Filed Sept. 2, 1969, Ser. No. 854,755

1m. (:1. C061) 1/00 US. Cl. 149 19 13 Claims ABSTRACT OF THE DISCLOSURE This invention relates to propellant compositions and more particularly to a propellant charge for a caseless round of ammunition.

A caseless round of ammunition is a structurally integral, self-contained round having ballistic characteristics practically equivalent to those of a metal cased round of similar caliber. The components of a caseless round of ammunition are a propellant charge, a primer and a projectile, the propellant charge and primer being completely combustible.

Among the advantages of a caseless round of ammunition over the metal cased round are: (1) reduction of weight; (2) decrease in volume; (3) decrease in production cost; (4) elimination of the need for metals usually in short supply in time of war; (5) elimination of the need for extraction of the cartridge case; (6) elimination of the problems of disposal of used cartridge cases; and (7) higher cyclic rates of fire can be achieved. It is of major importance that the physical strength of the propellant charge be sufficient to withstand handling and transportation and to remain intact and unchanged when cycled through the weapon.

One technique which has been employed in the past to produce a high strength charge of good ballistic properties utilizes a combustible lacquer such as collodion to bond together the individual propellant granules. However, because good bonding requires about 5% or higher of collodion and the binder possesses a lower energy content than the propellant granules and a slower burning rate, a greater propellant charge is needed to produce practically equivalent ballistic properties than with a similar sized metal cased round.

Another method which has been proposed utilizes the self bonding achieved with a volatile solvent for the propellant grain. Although this method gives propellant charges of excellent strength and ballistic properties, the relatively long curing cycles which are required and the inherent safety problems associated with the solvents makes the operation time consuming and costly.

It is therefore the principal object of this invention to provide an improved molded propellant charge for a caseless round of ammunition yielding ballistic performance practically equal to a cased round of equal caliber, and having the necessary strength characteristics for use in caseless ammunition.

Another object of this invention is to provide a binder which does not affect the energy or burning rate of the propellant.

A further object of the invention is to produce a propellant charge for a caseless round of ammunition in an eflicient and economical manner.

nite States 31161 In accordance with the present invention it has been found that all of the above objects can be realized by using as the binder for the propellant granules certain finely divided copolymers of ethylene.

Accordingly the present invention relates to a propellant composition comprising propellant granules and 0.1 to 10% and preferably 0.2 to 5% by weight of the composition of a polymeric binder consisting essentially of a solid, colloidally dispersi-ble copolymer of ethylene and 2 to 25 mole percent of at least one other monomer which is an alpha-olefin having 3 to 20 carbon atoms and/or a non-conjugated hydrocarbon diene, said copolymer having an average primary particle size within the range of 0.02 to 0.5 micron, being more than 50% crystallizable and exhibiting a crystallinity equal to less than of the inherent crystallinity of polyethylene, to a method for producing a molded propellant charge for caseless ammunition therefrom, and the molded propellant charge so produced.

The ethylene copolymer which is used as binder in accordance with this invention is, as stated, a crystallizable copolymer of ethylene and 2 to 25 mole percent, preferably 8 to 22 mole percent of at least one other monomer which is an alpha-olefin or a diene, in the form of extremely finely divided particles within the colloidal size range. By the term crystallizable copolymer as employed in this specification is meant a copolymer of which at least about 50% is in the crystalline form or is structurally capable of assuming the crystalline form. This is in contrast to a totally amorphous material which cannot assume the crystalline form. It is not intended to include totally amorphous copolymers within the scope of the instant invention. The ethylene copolymer can be either the random (statistical) type wherein the other monomer (or monomers) is distributed randomly throughout the molecule, or the block type wherein the other monomer (or monomers) is present only in relatively clearly defined segments within the molecule.

These crystallizable copolymers comprise substantially continuous networks of polymer which is essentially nonspherulitic and is either in the monoclinic or smectic state Which exhibits a fine fibrous structure by electron microscopy. This continuous polymer network is believed to benefit the propellant composition by efiecting a stiffening action or increased modulus, a reduction in tackiness, modification of the flow properties and an increase in strength and elongation. All such benefits, of course, are not realized with every copolymer within the scope of the invention.

The monomers which are copolymerizable with ethylene to give the copolymers of this invention are, as stated, the u-olefins containing 3 to 20 carbon atoms and/or non-conjugated hydrocarbon dienes. Exemplary of the a-olefins which can be used are propylene, butene- 1, pentenel, 3-methyl-butene-l, hexene-l, 4-methylpentene-l, heptene-l, octene-l, decene-l, dodecene-l, tetradecene-d, hexadecene-l, octadecene-l, eicosene-l, styrene and the alkyl and halo-styrenes such as p-chlorostyrene, p-methylstyrene and the like. The non-conjugated hydrocarbon dienes can be acyclic or alicyclic compounds and are preferably the aliphatic dienes containing 6 to 22 carbon atoms or the endocyclic dienes, i.e., bridged ring hydrocarbons containing two double bonds, including endo and exo isomers of such hydrocarbons, Exemplary of the aliphatic dienes which can be used are 1,4-hexadiene;

4-methyl- 1 ,4-hexadiene; 1,9-octadecadiene; fi-methyl- 1 ,S-heptadiene; 7-1nethyl- 1,6-octadiene;

l 1-ethyl-1,l l-tridecadiene;

3 9-ethyll ,9undecadiene; 7-ethyl-1,7-nonadiene; 8-propyl-1,8-undecadiene; 8-ethyl1,8-decadiene; 10-ethyl-1,9-dodecadiene; 1Z-ethyl-1,12-tetradecadiene;

13 -n-butyl-1, IZ-heptadecadiene; and 15-ethyl-1,1S-heptadecadiene.

Exemplary of the endocyclic dienes are dicyclopentadiene;

tricyclopentadiene;

tetracyclopentadiene;

bicyclo (2,2,1 )hepta-2,5-diene; bicyclo(2,2,2) octa-2,5-diene; -methylene-Z-norbornene; S-ethylidene-Z-norbornene;

5- 2-butenyl -2-norbornene;

5( l-propenyl)-2-norbornene;

5 2'-ethyl-2-butenyl -2-norbornene; 5-(2-ethyl-1'-butenyl)-2-norbornene; 5-(2-methyl-1'-propenyl)-2-norbornene; 5- 2'-propyl-2'-pentenyl -2-norbornene; 5 2-hexyl-2'-undecenyl )-2-norbornene; 5- 2-nonyl-2-heptenyl -2-norbornene; 5 2-butyl- 1 -pentenyl -2-norbornene; 5-(2-pentyl-1'-octenyl)-2-norbornene;

5 2'-heptyll -undecenyl -2-norbornene; 5- 2-methyl-2-butenyl -2-norbornene; 5- 2-methyl-2-decenyl -2-norbornene; 5- 2-methyl- 1 '-butenyl -2-norbornene; 5- (2'-methyl-1-hexenyl )-2-norbornene;

5 2-methyl- 1 '-undecenyl -2-norbornene; 5- 2'-hexyl-2-butenyl -2-norb ornene;

5- (2'-octyl-2-butenyl -2-norbornene;

5 2'-ethyl-2-decenyl -2-norbornene;

5 2-ethyl- 1 -octenyl -2-norbornene; 2-methyl-2,S-norbornadiene; 2-ethyl-2,5-norbornadiene; 2-butyl-2,S-norbornadiene; and 2-octyl-2,S-norbornadiene.

The small particles of copolymer exist in the form of discrete, primary particles and reversible clusters of these discrete particles which can be up to about 5 microns in size. By reversible cluster is meant a very lightly held group of primary particles which can be readily disintegrated to reform the primary particles. Disintegration of such particles can be brought about very simply by, for example, vigorous agitation.

The small particles of copolymers which are used in the compositions according to the instant invention can be prepared by any technique which will result in sufficiently small particles of the desired crystallinity and which can be dispersed in inert media. A very eifective procedure for preparing colloidally dispersible copolymers of ethylene is described in Belgian Pat. No. 708,834.

The unique combination of properties of the ethylene copolymer particles of this invention permits them to be suspended or dispersed in liquid media to form very stable dispersions. Such dispersions can be prepared con veniently by employing the desired diluent as the medium for the polymerization. However, it is also practical to prepare the polymer in a relatively volatile diluent as, for example, heptane, hexane, butane, propane, etc., and then displace that diluent with a more inert diluent for storage or utilization. This diluent transfer is easily accomplished by adding the new diluent to the suspension and thereafter boiling off the original diluent under conditions whereby the new diluent does not also vaporize. Alternatively, the dispersion can be centrifuged to separate the particles, the original diluent decanted, the new diluent added and the particles redispersed by shaking. This diluent transfer can readily be etfected without changing the size of the copolymer particles. Surprisingly, the diluent transfer can even be accomplished from organic medium to water, although a suspending agent is usualy used in this case.

The colloidal dispersions can be used as such to form the propellant composition, can be dried, i.e., the diluent removed, to leave a substantially solvent-free mass which is then mixed with the propellant granules or, if desired, can be redispersed in a diluent to re-form a colloidal dispersion. The solid, crystallizable copolymer obtained on drying the colloidal dispersions is characterized by the primary particles having retained their colloidal size, i.e., an average particle size of from 0.02 to 0.5 micron. The dried copolymer will be in the form of clusters which are readily redispersed in a liquid, non-solvent diluent to form a stable dispersion of the original primary particles and which dispersion is essentially free of irreversible clusters of particles greater than about 5 microns. Removal of the diluent from the colloidal dispersions can be effected by any of the known methods such as spraydrying, vacuum stripping, drum drying, and the like, the diluent removal being carried out at a temperature below about C., and preferably below about 40 C.

As stated above, the copolymer particles are colloidal in nature, having in their maximum dimension an average primary particle size of from about 0.02 to about 0.5 micron, and the copolymer is more than 50% crystallizable and exhibits a crystallinity equal to or less than 90% of the inherent crystallinity of polyethylene. The cryslallizable copolymer can be of any desired molecular weight and generally will be one having a reduced specific viscosity of from about 1 to about 40 or higher. Reduced specific viscosity (RSV) is defined as the ratio of the specific viscosity (determined on a 0.1% solution of dried copolymer in decahydronaphthalene at C.) to concentration of this 0.1% solution.

The propellant which can be used to produce the propellant charge can be of the single base, double base, triple base or composite type. The propellant is preferably of the nitrocellulose type and is utilized in the form of small granules or grains. Illustrative single, double and triple base formulations which can be used are given below in Table I.

Potassium nitrate Ethyl centralite Cry0lite* The propellant charge is prepared by mixing the propellant granules or grains as they are sometimes called with the copolymer binder in a mixer of the type which will avoid crushing of the grains, as for example, in a Sigma blade type mixer, and then, molding the mixture to the desired configuration. The copolymer binder ingredient can be added dry or as a colloidal dispersion of the copolymer in a suitable diluent to the propellant granules and the diluent removed prior to molding. The use of a colloidal dispersion containing from about 2 to about 80% and preferably from about 5 to about 50% copolymer solids is preferred.

The molding of the composition into a propellant charge will usually be carried out at a temperature ranging from about 100 to about 175 C. and usually under pressures ranging from about 1000 to about 25,000 p.s.i.

In addition to the propellant granules and copolymer binder, the composition can also contain other additives such as plasticizers, foaming agents, stabilizers, crosslinking agents, burning rate catalysts and the like. In this connection, foaming agents such as azo-compounds, e.g. diazoaminobenzene, azodicarbonamide and azobisisobutyronitrile, N-nitroso compounds, e.g., N,N'-dimethyl-N, N dinitrosoterephthalamide and N,N' dinitrosopentamethylene tetramine, sulfonyl hydrazides, e.g., benzene sulfonyl hydrazide, 4,4'-oxybis(benzene sulfonyl hydrazide) and the like and plasticizers such as dioctylphthalate, dioctylazelate, di-2-ethylhexyl adipate, didecyl adipate, dioctyl sebacate, dibutyl phosphate, polybutadiene, polyisobutylene, naphthenic processing oils and particularly the oils containing aromatic, naphthenic and parafiinic type carbons and the like can be utilized. Certain well known stabilizers such as diphenylamine burning rate catalyst such as the ferrocene derivatives, cross-linking agents such as dicumyl peroxide, sulfur and the like can be present in minor amounts within the scope of the invention. The use of up to 20% and preferably from about 0.1 to about 10% plasticizer is particularly preferred.

The propellant charge can be of any desired configuration and can be secured to the projectile and primer of the caseless round of ammunition in known manner, as for example by cementing or by mechanical means such as using an interference fit with the propellant charge.

In order to point out more fully the nature of the present invention, the following examples are given to illustrate the preparation and testing of propellant charges, within the scope of the invention in a caseless round of ammunition. All parts and percentages are by weight unless otherwise specified. The ethylene copolymers used in the examples were prepared in the following manner.

A nitrogen filled reaction vessel, equipped with an agitator and cooled to C. by ice water, was charged with one mole of titanium tetrachloride added as a 25% solution in a purified petroleum fraction (boiling range 165-200 C.) over a period of 4 hours. There was then added 1.3 moles of ethylaluminum sesquichloride as a 25% solution in the purified petroleum fraction. The reaction mixture was agitated on additional 2 hours at 0 C. and then was allowed to warm to room temperature, after which it was heated to 80-85 C. for 3 hours to complete the reduction of tetravalent titanium to trivalent titanium. The titanium trichloride-containing precipitate was separated and washed with portions of kerosene, after which it was held at 100 C. for 24 hours to complete the activation of the catalyst.

A nitrogen filled reaction vessel was charged with 200 ml. of n-heptane, 12 millimoles of diethylaluminum chloride and 6 millimoles of the above prepared titanium trichloride catalyst. With the temperature adjusted to 50 C., there was then added 88 millimoles of n-octene-l in a single injection. The mixture was held for 1 hour at 50 C. during which time the titanium trichloride dispersed to a translucent red colloid.

To another reaction vessel equipped with a stainless steel head, cooling coils and an air driven stirrer were charged 2 liters of n-heptane. The reactor was evacuated and pressured to 30 p.s.i.g. with a gas mixture containing ethylene and the desired mole percent of the other monomer or monomers at 50 C. Then 20 millimoles of diethylaluminum chloride was added to the reactor. Addition of the colloidal titanium trichloride catalyst was begun and continued at a rate to maintain constant gas pressure in the reactor head space during the reaction pe' riod which was 54 minutes. Ethylene and the other monomer(s) were continuously monitored into the reactor for the entire reaction time through rotometers such that the mole ratio of the feed gas remained constant at the desired ethylene to monomer(s) raio. At the end of 54 minutes, the reaction mass was quenched by adding 20 ml. of n-butanol, then agitated for about 16 hours at 50 C. The mixture was washed with 5% hydrochloric acid and three times with distilled water to remove deactivated catalyst residues. The copolymer was recovered as a stable milky suspension.

Examples 1 to 5 Five propellant charges were prepared using an ethylene-propylene copolymer dispersion of 3.8% solids prepared according to the above procedure in n-heptane as diluent, the copolymer particles being less than 0.5 micron in size and containing no clusters of particles larger than 4 microns. The copolymer was about 75% crystalline, had a heat of fusion of 27.6 calories/ gram (heat of fusion of an ethylene homopolymer similarly prepared was 38.3 calories/gram), a propylene content of 10.4 moles percent and an RSV of 23. The charges of these examples were prepared by forming an intimate mixture of the copolymer dispersion, plasticizer and smokeless powder base granules according to the general procedure given above, removing the heptane diluent from the mixture under vacuum, and then compression molding 40 grains of the so produced copolymer coated granules into hollow right cylinders (1.2" long; outside diameter, 0.445"; inside diameter, 0.3.20") using a molding cycle of 4 minutes at C. under pressure. The smokeless powder base granules utilized were commercial type granules produced by extruding a double .base formulation containing by Weight 91.25% nitrocellulose (13.25% nitrogen), 7.00% nitroglycerin, 1.00% potassium nitrate and 0.75% diphenylamine, using a 0.041" diameter die and 0.015" diameter pin, drying and then cutting into granules (25 cuts/inch).

Each of the molded charges was strong and dimensionally stable and had a uniform granule distribution. Each charge was assembled into a caseless round of ammunition by inserting a booster charge and primer into the aft end of the axial cavity of the molded charge and securing a projectile to the forward end. The rounds were then fired in a 7.62 mm. caseless weapon. The propellant charges performed satisfactorily and left no residue in the weapon chamber. Details of the composition of those charges and test firing data are recorded in Table H.

Examples 6 to 14 Propellant charges were prepared according to the procedure of Examples 1 to 5 except that the following ethylene copolymer dispersions were used in place of the ethylene-propylene copolymer dispersions of Examples 1 to 5.

TABLE I Ethylene copolymer dispersion B Mole per- Pereent Mole Mole cent 4- Percent crystalpercent percent methyl-1,4-

solids RSV linity propylene butene-l hexadiene Particle size range was from less than 1 to 5 microns, with the average being 1 micron.

TABLE ll Firing data 3 Ingredients (wt. percent) Copper Molding crusher Ex. Propellant Plastipressure "elocity pressure No. Binder granules cizer 2 (p.s.i.) (it/sec.) (psi) 1 Dry weight.

3 A naphthenic processing oil containing 21% aromatic carbons, 39% naphthenic type carbons and 40% paraflinie type carbons and, having the following physical properties: average molecular weight 395; pour point, 10 F.; aniline point, 172 F.; the point, 495 F.; and flash point, 430 F.

3 A cased ammunition of equal caliber (42 grains of propellant) give; a velocity of 2, 750 ft./sec. at a pressure of 50,000 p.s.i.

4 Also contained 0.2% benzene sulionyl hydrazide.

b Molding cycle was mins. at 150 6 Also contained 0.02% dicnmyl peroxide.

7 Also contained 0.02% dicumyl peroxide and 0.002% sulfur.

Example 15 Example 5 was repeated except that 1.0 part of dry copolymer particles was substituted for the copolymer dispersion, 99.0 parts of smokeless powder granules were used and the diluent removal step was eliminated. The propellant charge, on firing in a caseless round of ammunition, gave a velocity of 2770 ft./sec. at a pressure of 50,000 p.s.i.

What we claim and desire to protect by Letters Patent is:

1. A propellant composition comprising nitrocellulose type propellant granules and 0.1 to 10% by weight of the composition of a polymeric binder consisting essentially of a solid, colloidally dispersible copolymer of ethylene and 2 to 25 mole percent of at least one other monomer selected from the group consisting of alphaolefins having 3 to carbon atoms, a non-conjugated hydrocarbon dienes and mixtures thereof, said copolymer having an average particle size within the range of 0.02 to 0.5 micron, being more than 50% crystallizable and exhibiting a crystallinity equal to less than 90% of the inherent crystallinity of polyethylene.

2. A molded propellant charge for caseless ammunition comprising an intimate mixture of nitrocellulose type propellant granules and 0.1 to 10% by weight of the mixture of a polymeric binder consisting essentially of a solid, colloidally dispersible copolymer of ethylene and 2 to mole percent of at least one other monomer selected from the group consisting of alpha-olefins having 3 to 20 carbon atoms, non-conjugated hydrocarbon 8 dienes and mixtures thereof, said copolymer having an average particle size within the range of 0.02 to 0.5 micron, being more than 50% crystallizable and exhibiting a crystallinity equal to less than of the inherent crystallinity of polyethylene.

3. The molded charge of claim 2 wherein the mixture also contains 0.1 to 10% plasticizer.

4. The molded charge of claim 2 wherein the alphaolefin is propylene.

5. The molded charge of claim 4 wherein the mixture also contains 0.1 to 10% plasticizer.

6. The molded charge of claim 2 wherein the diene is 4-methyl-1,4-hexadiene.

7. The molded charge of claim 6 wherein the mixture also contains 0.1 to 10% plasticizer.

8. The molded charge of claim 2 wherein the copolymer is a copolymer of ethylene and propylene.

9. The molded charge of claim 8 wherein the mixture also contains 0.1 to 10% plasticizer.

10. The molded charge of claim 2 wherein the copolymer is a tcrpolymer of ethylene, propylene and 4-methyl- 1,4-hexadiene.

11. The molded charge of claim 10 wherein the mixture also contains 0.1 to 10% plasticizer.

12. The method of preparing a molded propellant charge for caseless ammunition which comprises forming an intimate mixture of nitrocellulose type propellant granules and 0.1 to 10% by weight of the mixture of a polymeric binder consisting essentially of a solid, colloidally dispersible copolymer of ethylene and 2 to 25 mole percent of at least one other monomer selected from the group consisting of alpha-olefins having 3 to 20 carbon atoms, non-conjugated hydrocarbon dienes and mixtures thereof, said copolymer having an average particle size within the range of 0.02 to 0.5 micron, being more than 50% crystallizable and exhibiting a crystallinity equal to less than 90% of the inherent crystallinity of polyethylene, and then compression molding the mixture into a propellant charge.

13. The method of claim 12 wherein the step of forming an intimate mixture of propellant granules and binder comprises mixing the propellant granules with a dispersion of the copolymer in an inert diluent and then removing the diluent.

References Cited UNITED STATES PATENTS 3,449,l79 6/1969 Minekawa et a1. l49-l9 STEPHEN I. LECHERT, 111., Primary Examiner US. Cl. X.R.

PO-IO50 (5/69) UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. U.S.P. 3,723 203 Dated March 27, 1973 Inventofls) Alan D. Craig & Carl A. LukacIq (Case 1) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 4 of p.p. Page 8, Line 5 of spec. TABLE I under "Triple Base" opposite Nitrocellulose "90.0" should read' r"20.0"

Signedv and sealed this 27th day of November 1973.

(SEAL) Attest:

EDWARD M. FLETCHER,JR.

RENE D. TEGTMEYER Attesting Officer Acting Commissioner of Patents @2 33 v UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. U.S.P. 3,723.203 Dated March 27, 1973 Inventor(s) Alan D. Craig & Carl A. LukacI'I (Case 1) It is certified that error appears in the abate-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 4' cf p.p. Page 8, Line 5 of spec. TABLE I 1 under "Triple Base opposite Nitrocellul pse "90.0" should read 20.0"

Signed and sealed this 27th day Of November 1973.

(SI-EAL) Attest:

EDWARD M. FLETCHER,JR.

RENE D. TEGTMEYER Attesting Officer Acting Commissioner of Patents