FR2691963A1 - Extrudable gun propellant compsn. - Google Patents

Abstract

An extrudable gun propellant compsn. comprises 65-85 (70-82) wt.% particulate explosive filler, 1-12 (2-10) wt.% energetic plasticiser and 10-30 (12-25) wt.% curable mixt. of a functionally-terminated poly(nitratoalkyl-substd.) alkyl ether prepolymer and a crosslinking agent. The explosive filler comprises cyclic nitramine(s). Partic. upto 40 (10-25) wt.% of the filler comprises picrite, with the remainder having a specific energy content greater than picrite. The prepolymer comprises a hydroxy-terminated poly(nitratoalkyl-substd. cyclic ether) of average functionality (AF) 1.5-3.5. The crosslinking agent comprises an isocyanate which is difunctional when AF is above 2 and polyfunctional when AF is 1.5-2. The energetic plasticiser comprises a nitroplasticiser.

Description

 The invention relates to an extrudable barrel propellant composition and an extruded barrel propellant prepared therefrom.

 A wide range of extrudable propellant compositions are known based on mixtures of nitroglycerin (NG) and nitrocellulose (NC). The manufacture of an NC / NG-based propellant (also known as a colloidal propellant), such as a double-base propellant (based on NG and NC alone) or triple-base propellant (based mixtures of NG, NC and picrite), requires many steps of mixing the ingredients with a final step of incorporating a solvent so that an extrudable paste can be formed. After extrusion to the desired configuration in the form of tubes split or rods perforated longitudinally, the extruded material is put in 1 r oven so that the solvent is removed and a very fragile propellant is formed, its physical properties depending essentially on a cellulosic skeleton encapsulating an NG solution.

The main conditions to be met by an extrudable propellant for cannon are the fact that it must have a high specific energy content compatible with the needs of modern high performance ammunition for artillery guns and battle tanks in particular. , and that it must be capable of being treated in order to be made into the desired form of propellant. The first condition means that the force constant F of the hardened propellant must in an ideal case be at least 1100 kJ / kg, with
F = nRT
one being the number of moles of gaseous product of the propellant per kilogram of this agent, R being the gas constant and T being the adiabatic flame temperature.

o
The second condition is fulfilled by determining that, at a usual propellant treatment temperature (usually between 30 and 70 "C), the extrudable propellant has a viscosity in a range which allows relatively extrusion easy to the desired configuration for incorporation into the load and which also ensures, after the formation of the extruded element, the relative absence of adhesiveness of this agent and the preservation of its configuration without sagging.

 An additional condition which is of increasing importance is the fact that the propellant, in its final extruded and hardened form, must have a low vulnerability to accidental ignition or attack. This property is particularly important in the case of a propellant for cannon which must be used in an ammunition stored in a small space, for example in the hull of a combat tank, which risks being subjected to a attack by the enemy, in particular by high speed fragments from shrapnel and / or high speed penetration jets from hollow charge cones.

 Known colloidal propellants meet some, but not all, of these conditions. In particular, they tend to be highly vulnerable to attack by a shaped charge. It is known that the force constant of these compositions can be increased, for example by adding explosive particulate matter with a high energy charge, for example sensitive cyclic nitramines RDX and HMX, but this arrangement tends to further increase the vulnerability of the propellant.

 The object of the present invention is to eliminate or at least partially reduce this drawback.

 Thus, the present invention relates to an extrudable propellant composition for cannon, comprising 65 to 85% by weight of an explosive particulate charge, 10 to 30% by weight of a curable mixture of an alkyl ether prepolymer with substituent functional terminated nitratoalkyl and a crosslinking agent, and 1 to 12% by weight of a high energy plasticizing agent.

 It has been found that the gun propellant compositions according to the invention form extrudable pastes and, when extruded in usable and hardened form, have force constants greater than 1200 kJ / kg. However, although they may contain large amounts of sensitive particulate explosive such as RDX or HMX, they are notably less vulnerable to attack by shaped charges than colloidal propellants, unexpectedly.

 The composition according to the invention preferably contains 70 to 82% by weight of the explosive charge, 12 to 25% by weight of the mixture of the prepolymer and the crosslinking agent, and 2 to 10% by weight, preferably 4 to 8% by weight, of the high energy plasticizing agent. For loads of the mixture of prepolymer and crosslinking agent of less than 12% by weight, the composition tends to be rigid and difficult to extrude, whereas, for loads exceeding 25 g by weight, the extruded material tends to sag under its own weight.

 The explosive charge preferably contains at least one cyclic nitramine such as RDX or HMX, so that the composition has a high force constant.

 As the composition according to the invention contains both a high energy binder prepolymer and a high energy plasticizer, a relatively high force constant can be maintained by increasing to some extent the proportions of these ingredients in the composition with reduction of the amount of explosive charge. Although this has the advantage of reducing the vulnerability of the composition, a reduction in the amount of explosive charge has a significant effect on the processing properties of the composition. For example, when the filler is a cyclic nitramine in the form of fine particles, the composition must contain a high proportion of filler, for example greater than 78%, because, otherwise, the extruded material is too soft and tends to sag under its own weight.

 However, it has been found that when 40 s by weight maximum and preferably 10 to 25% by weight of the charge contained relatively low energy insensitive explosive picrite (nitroguanidine), the total proportion of the charge of the composition could advantageously be reduced to less than 78% and even less than 75%. The presence of needle-shaped crystalline particles of picrite in the composition facilitates the reinforcement of the extruded element without excessive reduction of the force constant. The effect of reducing both the total amount of charge and the high-energy explosive content of the charge (i.e. by incorporating picrite) is a further reduction in the vulnerability of the composition of the cured propellant.

 The prepolymer preferably contains a hydroxy terminated nitratoalkyl substituted cyclic ether, the cyclic ether preferably being an oxetane or an oxirane. The cyclic ether preferably has at most two nitratoalkyl substituent groups and very advantageously only one. Suitable examples of the cyclic ether are 3-nitromethyl-3-methyloxetane and glycidyl nitrate.

The molecular weight of the prepolymer, which is in an ideal case a viscous liquid at a temperature between 30 and 50 "C, is preferably between 2,000 and 15,000 and very advantageously between 3,000 and 10,000 so that the composition d extrudable propellant has suitable processing properties. Suitable hydroxy-terminated prepolymers based on nitratoalkyl-substituted cyclic ether are described in the pending applications PCT / GB 90/00838 and PCT / GB 90 / 00837 of the
Applicant.

 The average functionality of the prepolymer is preferably between 1.5 and 3.5 and very advantageously between 1.7 and 3.2. It is desirable that the combination of the prepolymer and the polymerization agent does not react giving a highly crosslinked structure in the composition, after extrusion and hardening. It is therefore preferable that, when the average functionality of the prepolymer is less than or equal to 2, the curing agent is polyfunctional whereas, when the functionality of the prepolymer exceeds 2, the curing agent is bifunctional.

 The amount of crosslinking agent is normally chosen so that it reacts roughly stoichiometrically with all of the terminal groups available on the prepolymer. It normally comprises more than 15% by weight of the mixture of the prepolymer and the crosslinking agent.

 The prepolymer is preferably of the hydroxy-terminated type and the crosslinking agent an isocyanate so that the mixture of the prepolymer and the crosslinking agent can undergo a urethane type polymerization reaction.

 It has been found that the presence of a high energy plasticizer is important for wetting the explosive charge, for softening the composition so that its extrusion properties are improved and so that the composition has a high force constant . The high-energy plasticizing agent preferably contains at least one plasticizing agent with a nitrato group, such as butanetriol trinitrate and very advantageously at least one nitrated plasticizing agent such as bis2,2-dinitropropylformal, bis-2,2 -dinitropropylacetal or mixtures of these two substances. Nitrated plasticizers, in particular in a weight ratio of the plasticizer to the prepolymer of between 1/2 and 1/5, are miscible with the prepolymer and considerably reduce the adhesiveness of the prepolymer, especially when it has hydroxy endings. In addition, nitrated plasticizers have the additional advantage that, when the prepolymer has hydroxy endings and the crosslinking agent is an isocyanate, the presence of these plasticizers has no detrimental effect on the polymerization reaction. of the type of a urethane between the prepolymer and the crosslinking agent and can even increase the pot life of the mixture which polymerizes at temperatures below 70 "C. This then increases the treatment time available before the reaction polymerization does not make the composition too rigid to be extruded.

 The extrudable gun propellant compositions according to the present invention and a hardened extruded member prepared therewith are now described by way of illustration only.

Ingredients
The following ingredients were used in the examples of extrudable propellants according to the invention.

Explosive charges
RDX: Micronized single-mode RDX [CH2NNO2] 3
HMX: Micronized single-mode HMX (CH2NN02] 4
Picrite: crushed crystalline nitroguanidine
Prepolymers
Poly (NIMMO) 1: bifunctional poly (3-nitratomethyl-3-methyloxetane) with hydroxy termination having the following properties
viscosity at 30 "C 1,610 poises
at 40 "C 560 poises
at 60 "C 100 poises
hydroxyl number 18 to 22 mg KOH / g
molecular mass 5,500
average functionality <2, for example 1.9
density 1.26 g / cm3
heat of formation - 73.9 kcal / mol
heat of explosion 28.8 kcal / mol
Poly (NIMMO) 2 :: poly (3-nitratomethyl-3-methyloxetane) tri functional with hydroxy termination having the following properties
viscosity at 30 "C 200 poises
molecular weight 2,000 to 3,000
average functionality about 3
Poly (NIMMO) 1 and 2 were both prepared by the general process described in PCT application under examination by Applicant No. PCT / GB90 / 00838.

Plasticizer:
BDNPA / F: 50/50 mixture by weight of bis-dinitropropylacetal and bis-dinitropropylformal, sold by Aerojet Corporation, United States of America.

Crosslinking agent
"Desmodur" N100: polyfunctional viscous isocyanate manufactured by Bayer AG, Germany
MDI: 4,4-diisocyanato-diphenylmethane
Catalyst
DBDTL: dibutyltin dilaurate
Example 1
Ingredients Parts by weight
RDX 80.4
Poly (NIMMO) 1 14.16
"Desmodur" N100 0.54
BDNPA / F 4.9
DBDTL 50 ppm poly (NIMMO) 1
The dough obtained by mixing these ingredients was found to be extrudable in a temperature range between 45 and 60 "C, it had a good pot life at these temperatures, and it formed a smooth, slightly sticky extruded element. The mechanical properties of the hardened extruded element were determined to be relatively soft due to the low crosslinking density of the hardened poly (NIMMO) 1, and its insoluble rubber content measured by solvent extraction was determined to be a variant. between 40 and 60%.

Example 2
Ingredients Parts by weight
RDX 78.7
Poly (NIMMO) 1 15.57
"Desmodur" N100 0.54
BDNPA / F 5.19
DBDTL 50 ppm poly (NIMMO) 1
The dough obtained by mixing these ingredients could be extruded at 45 "C and had a good pot life at this temperature.

Example 3
Ingredients Parts by weight
RDX 67.3
Picrite 7.8
BDNPA / F 6.4
Poly (NIMMO) 1 17.9
"Desmodur" N100 1.31
DBDTL 50 ppm poly (NIMMO) 1
Example 4
The ingredients and their parts by weight of the extrudable propellant of example were the same as those of example 3, but RDX was replaced by HMX.

Example 5
Ingredients Parts by weight
HMX 64.3
Picrite 9.1
BDNPA / F 6.8
Poly (NIMMO) 1 18.24
"Desmodur" N100 1.56
DBDTL 50 ppm poly (NIMMO) 1
Example 6
Ingredients Parts by weight
RDX 67
Picrite 8
Poly (NIMMO) 2 16.3
BDNPA / F 6.7
MDI 1.8
DBDTL
Each of the doughs produced by mixing the ingredients of Examples 3 to 6 was determined to be able to be extruded in the temperature range from 45 to 60 "C, it had a good pot life at these temperatures, it did not stick and it was found to flow under pressure so that, in the prepolymerized state, the extruded member retained its shape and did not collapse. The polymerized product of Example 6 was firmer than that produced with the ingredients of Examples 3 to 5, because its rubber component had a higher crosslinking density. The rubber component of the polymerized product of Example 6 had an insoluble rubber content of between 75 and 85 *.

Preparation process - general procedure
Extrudable barrel propellant compositions according to the compositions of the examples, and the extruded member formed therefrom, were prepared by the following procedure.

 1. A mixture of nitrated plasticizer, prepolymer and polymerization catalyst (if applicable) was added to a vertical planetary mixer. Mixing has started and a sufficient amount of cyclic nitramine in the form of dry particles has been added until a soft premix is formed. The temperature of the premix was kept at 50 "C permanently.

 2. The soft premix was transferred to a horizontal incorporator and the rest of the cyclic nitramine was added in portions and mixed with the premix. The operation was followed by a gradual addition and mixing of the picrite, if necessary. Finally, the crosslinking agent was added and mixed for 10 min. The temperature in the incorporating apparatus was maintained at 60 ° C during the addition and mixing.

 3. The resulting propellant paste was then removed from the incorporating apparatus and loaded into the body of a heating piston extruder, having a die for the formation of an extruded element in the form of 'a split tube. The extruder temperature was kept at 60 "C. The piston was pressurized so that the extrusion speed obtained was convenient. The extruded element was collected on trays and heated for 100 h at 60" C so that the polymerization of the prepolymer and of the crosslinking agent is ensured.

 When using a polymerization catalyst, the amount used was chosen so that the mixture of the prepolymer, the crosslinking agent and the plasticizing agent has a suitable shelf life, allowing mixing and extrusion before the propellant becomes too rigid due to polymerization. A suitable definition of the pot life has been determined to be the time required for the viscosity of the mixture of the prepolymer and the crosslinking agent to reach 20,000 poises. The observed storage times in pots for these mixtures are given in Table 1 below.

TABLE 1
Ingredients, parts by weight Duration of
Poly-tempera- ture (NIMMO) 1 BDNPA / F "Desmodur" DBDTL rature in pot
N100 (ppm) ("C) (min)
2.79 - 0.21 50 60 123
2.79 - 0.21 50 70 83
2.79 1 0.21 50 50 310
2.79 1 0.21 50 60 155
2.79 1 0.21 50 70 82
Studies have been carried out by determining the increase in viscosity during the polymerization of these mixtures and they have shown a well-defined termination of the shelf life with a very slight increase in viscosity until the mixtures gelatinize. . It can be noted in table 1 that the presence of the nitrated plasticizing agent has an advantageous effect of increasing the shelf life in pots at the polymerization temperature below 70 "C.

TABLE 2
Specific energy content of the polymerized propellant
Force constant example
(kJ / kg)
1 1200-1250
2 1200-1250
3 1213
4 1236
5 1228
6 1200-1250
Vulnerability assessment
A hollow charge attack test, described below, was used to assess the vulnerability of the propellant compositions according to the invention.

 A hollow charge is mounted six diameters of the charge above a 25.4 mm thick mild steel cover plate, and twelve diameters of the charge above a target comprising a mass of 2 kg of the composition of extruded polymerized propellant to be tested. The hollow charge consisted of a 63 mm diameter cylindrical explosive charge having a concave conical front end having a 45 "copper conical coating. The explosive charge was a molded mixture consisting of 86 * of particulate HMX dispersed in 14 * a rubbery binder.

 The target is formed from a 166 mm long section of a 120 mm diameter combustible cartridge case placed on the side, loaded with rods of the proven extruded polymerized propellant composition having a total mass of 2 kg . Each rod was formed from a tube of propellant open at both ends and having a longitudinal slot over its entire length.

The thickness or dimension of the stick sheet designates the difference between the external and internal diameters.

 A series of nested steel plates of cardboard intended to stop the jet of the shaped charge after it has passed through the target is placed below the target. A blast gauge was mounted 1.9 m from the target, just above the level of the cover plate.

 When firing the shaped charge, the overpressure created by the target's response is recorded. The net explosive signal is expressed in the form of a mass ratio which is the mass of a reference explosive mixture which detonates (60/40 mixture of RDX and TNT) giving the same overpressure divided by the mass of the propellant.

 For all the compositions tested, the shots were taken on a certain range of sheet dimensions and the results are presented in the form of the variation of the explosive signal (mass ratio) as a function of the sheet thickness.

 The composition of Example 5 was evaluated during the test and the results are shown in Figure 1.

For comparison, the results of the same vulnerability test carried out on a conventional colloidal propellant with triple base (nitroglycerin / nitrocellulose / picrite) with high energy content (force constant 1135 kJ / kg) are shown in Figure 2. These results show that the composition of Example 5 is much less vulnerable to attack by a hollow charge than a conventional triple base gun propellant.

Claims (10)

 1. Composition of extrudable propellant for cannon, characterized in that it contains the following ingredients  65 to 85% by weight of a particulate explosive charge,  10 to 30% by weight of a curable mixture of a prepolymer of a functional terminated nitratoalkyl-substituted alkyl ether and of a crosslinking agent, and  1 to 12% by weight of a high energy plasticizer.  2. Composition according to claim 1, characterized in that it contains the following ingredients  70 to 82% by weight of particulate explosive charge,  12 to 25% by weight of a curable mixture of a functional terminated nitratoalkyl-substituted alkyl ether prepolymer and of a crosslinking agent, and  2 to 10 tonnes by weight of a high energy plasticizer.  3. Composition according to claim 1, in which the explosive charge consists of at least one cyclic nitramine.  4. Composition according to claim 1, in which a maximum of 40% by weight of the explosive charge are formed from picrite and the rest of the explosive charge has a specific energy content greater than that of picrite.  5. Composition according to claim 4, in which 10 to 25% by weight of the explosive charge are formed from picrite.  6. Composition according to claim 4, in which the explosive charge forms less than 78% by weight of the composition.  7. The composition of claim 1, wherein the prepolymer is a hydroxy terminated nitratoalkyl substituted cyclic ether polymer and the crosslinking agent is an isocyanate.  8. Composition according to claim 1, characterized in that the average functionality of the prepolymer is between 1.5 and 3.5, and the crosslinking agent is bifunctional when the average functionality of the prepolymer is greater than 2 and is polyfunctional when the average functionality of the prepolymer is between 1.5 and 2.  9. Composition according to claim 1, characterized in that the high energy plasticizing agent is a nitrated plasticizing agent.  10. An extruded gun propellant having a composition containing the cured composition of claim 1.