FR2681065A2 - Moulding process for the manufacture of a block of dual-base rocket fuel with a high nitramine content and block of rocket fuel obtained by this process - Google Patents

Abstract

The invention which is the subject of this application for a certificate of addition to Patent Application No. 81.13838 of 16.7.1981 relates to a moulding process for the manufacture of a block of dual-base rocket fuel with a high nitramine content and the block of rocket fuel obtained. This process consists in casting a moulding solvent consisting of a nitric ester, a plasticiser and a stabiliser on a moulding powder placed in a mould and made up of nitrocellulose with a nitrogen content of between 11.5 and 13 %, a nitric ester, stabilisers, at least one nitramine, combustion catalysts and optionally plasticisers, in curing the whole, and is characterised in that the content of nitric ester and nitramine as a percentage by weight in the moulding powder is, respectively, between 0 and 30%, on the one hand, and 35 to 60%, on the other hand, the weight percentage ratio of plasticisation of the moulding powder being between 0 and 50%.

Description

Molding process for the production of a double base propellant block with a high nitramine content and propellant block obtained
The invention which is the subject of the present request for a certificate of addition to patent application No. 81.13838 of July 16, 1981 relates to a molding process for the manufacture of a double base propellant block with a high level of nitramine and the propellant block got.

In the context of improving the performance of double base propellants, research was directed towards the incorporation into energy binders (nitrocellulose + nitrated plasticizer such as nitroglycerine) of mineral or organic oxidizing charges such as ammonium perchlorate, l 'hexogen (RDX) or octogen (HMX).

These charges contribute, in fact, to the significant raising of the specific impulses (Isp) and volumic impulses (Isp), of these compositions.

In addition, compared to ammonium perchlorate, nitramine fillers offer certain advantages of discretion and safety.

However, the presence of nitramine also has certain drawbacks.

Incorporated in a non-catalyzed double base binder, these tend to decrease the level of combustion rate of the propellant.

On the other hand, incorporated in a catalyzed double base binder having a "plateau" or "mesa" effect, a disappearance of these "plateau" or "mesa" effects is observed as the level of nitramine increases. This therefore considerably limits the proportion of nitramine which it is possible to introduce into double base propellants if it is desired to maintain a satisfactory pressure exponent.

Recall that the combustion speed of a propellant at a given temperature is a direct function of the pressure at which combustion takes place. Mathematically this relation is expressed by the relation V = an in which v is the rate of combustion, P the pressure, has a constant related to the nature of the propellant, n is the exponent of pressure. When n is zero or negative, the rate of combustion has a "plateau" or "mesa" effect on the curve corresponding to the formula cited above. I1 is known that these "plateau" or "mesa" effects are very interesting because they entail the stabilization of combustion and, by this, a high operational safety of the loads which use these compositions.

These drawbacks due to the introduction of a high level of nitramines are well illustrated by the following publication: KUBOTA Proceedings
International Space Technol Symposium. Sci. llth, 1975 pp 157.176.

In this publication it is shown that for a percentage by weight of octogen equal to 26.8%, the combustion speed decreases considerably while the "plateau'1 disappears completely.

Certainly in French patent No. 2,165,093 of the applicant company, a block of double base propellant obtained by introducing a molding solvent into a base powder loaded with a nitramine and placed in a mold is well described, but the rate of nitramine in the base powder is however limited to 26% by weight precisely because of the disappearance of the "plateau".

The object of the invention is to remedy these drawbacks by proposing a method making it possible to obtain double base propellant blocks with a high rate of hexogen or octogen having a high combustion rate while retaining a suitable pressure exponent. .

This process consists in casting a molding solvent consisting of a nitric ester, a plasticizer, a stabilizer, on a molding powder placed in a mold and formed from nitrocellulose with a nitrogen content of between 11, 5 and 13%, of a nitric ester, of stabilizers, at least one nitramine, of combustion catalysts, optionally of plasticizers, to cook the whole and is characterized in that the rate of nitric ester and of nitramine in percentage by weight in the molding powder is respectively -between 0 and 30% on the one hand and 35 and 60% on the other hand, the percentage rate by weight of plasticization of the molding powder being between 0 and 50% , and in that the combustion catalysts consist of at least one lead oxide, at least one cuprous or cupric oxide, acetylene or benzene black and potassium cryolite.

By plasticization rate by weight is meant the ratio of nitrated oil rate, + optionally rate of plasticizers / rate of nitrocellulose + nitrated oil + optionally plasticizers.

The principle of the process for obtaining a block of double base propellant by molding is well known to those skilled in the art.

This process consists firstly in placing in a mold granules of so-called basic powder formed in particular of nitrocellulose, then in injecting a molding solvent formed mainly of nitric ester in order to gelatinize the basic powder.

The block thus obtained is then subjected, either to a ripening phase, at around 400 ° C., for a few hours and to baking between 60 and 650 ° C. for a few days, or to a continuous baking phase.

As the molding solvent, a solvent based on nitroglycerin, triacetin and centralite or 2-NDPA will preferably be used, but not necessarily, in the following limiting proportions by weight.
nitroglycerin 72 to 83
triacetin 27.5 to 16
2-NDPA or centrality 0.5 to 1
In general, the proportion by weight of the molding solvent relative to the total weight of molding solvent and molding powder varies between 25 and 38%. A proportion of between 27 and 35% will generally be used.

If the invention lies mainly in the fact that the base powder is loaded with a nitramine and nitroglycerin, the drawbacks due to the presence of a high level of nitramine being eliminated by the addition during the formation of the molding powder of a catalytic system, it should be emphasized that the other constituents are judiciously adapted to obtain the best performance of the assembly.

Thus, nitrocellulose must have a nitrogen content of between 11.5 and 13%. It is well known that the energy potential of propellant increases with the nitrogen content of nitrocellulose. In the present invention, the following two solutions will preferably be chosen
- either a mixture of nitrocellulose having different nitrogen levels
between 11.6% and 12.8%. Certainly it decreases slightly-
the energy potential but on the other hand improves
overall performance of the propellant (especially in terms of
pressure exponent).

 - or a nitrocellulose with a nitrogen content close to 12.7%.

The nitric ester which will preferably be used is nitroglycerin. The level of nitroglycerin which it is possible to introduce into the molding powder is limited to 30% for reasons of mechanical strength and not to exceed a plasticization rate greater than 50%.

It should be noted in this connection that for high nitramine levels the plasticization rate should preferably be less than 35%.

The nitramines which can be used are chosen from hexogen (RDX) or octogen (HMX) or a mixture of the two. It is however very advantageous to use hexogen. The latter makes it possible, in fact, to obtain compositions the speed level of which is also high, but the exponent of lower pressure.

Use will preferably be made of a rate by weight of nitric ester in the molding powder of between 9 and 21%.

Likewise, a nitramine content by weight of between 37 and 57% is preferably used.

As the first preferred solution, the combustion catalysts consist (by mass) of
. 0.5 to 4% of one or more lead oxides
. 0.5 to 4% cuprous or cupric oxide or a mixture of the two
. 0.1 to 2% acetylene or benzene black
. 0.5 to 4% potassium cryolite
The potassium cryolite makes it possible, under certain conditions, to improve the performance of the propellant block.

Any lead oxide or a mixture thereof may be suitable for the present invention, namely the compounds represented by the following chemical formulas
PbO, Pb304, 2 03r Pb2 0, PbO2
We prefer, however, to use lead monoxide or PbO.

In the case of copper oxides it has been found that cupric oxide (CuO) like cuprous oxide (cru2O) could be suitable for the invention.

 It is preferable that the mass catalyst ratio does not exceed 10%.

The association of lead and copper oxides and of benzene or acetylene black and potassium cryolite makes it possible to increase the speed level, compared to the non-catalyzed composition with the creation of a plateau or a low pressure exponent.

The acetylene or benzene black also makes it possible to regulate the combustion rate.

 It should be emphasized that the fact of incorporating a small amount of catalysts as is the case in the invention is very advantageous in terms of discretion and in terms of the pulse (less decrease in potential and therefore less energy loss) .

Another advantage of these systems with a low level of catalyst is that it makes it possible to increase the rate of energy plasticizer.

As even more advantageous solutions, the following solution will be used
PbO 1 to 3.5%
Cu0 or CU2O 1 to 3.5%
Acetylene black
or benzene black 0.5 to 1.8%
Potassium cryolite 1 to 3.5% I1 has been found surprisingly that with catalytic systems comprising potassium cryolite it was preferable to use cupric oxide. This clearly shows the difficulties in optimizing such propellant compositions and that those skilled in the art cannot anticipate the solutions to the various problems posed. In fact, compositions without potassium cryolite exhibit better performance with cuivruex oxide (cf. main patent).

As plasticizers, there may be mentioned aromatic diesters such as dioctylphthalate.

The injection of the molding solvent and the cooking of the assembly are carried out as indicated above.

The invention also relates to the propellant block obtained by the process of the invention.

The propellants obtained according to this process have an operating range of between 30 and 200 bars depending on the rate of acetylene or benzene black, a combustion speed of between 7 and 15 min / s and a calorimetric potential greater than 1000 cal / g.

Note that the same propellants obtained by the so-called "global method" or in American "slurry casting process" do not allow to obtain the same performance.

The invention also relates to a double base propellant block consisting in particular of nitrocellulose, of nitric ester, of at least one nitramine and of catalysts consisting of at least one lead oxide, of at least one cuprous or cupric oxide , acetylene or benzene black and potassium cryolite, the percentage by weight of plasticization being less than 75% by weight. Preferably the plasticization rate is less than 70%.

Preferably, the double base propellant block consists in mass, in particular, of 26 to 43% of nitroglycerin and of 24 to 42% of nitramine. The catalyst levels are easily deduced from the proportion of powder to be molded in the total composition of the propellant.

The examples below illustrate the invention
Example 1
A propellant was made using the following molding powder composition
- Nitrocellulose 33%
- Nitroglycerin 10%
- Hexogenic 47%
- 2-NDPA 2%
- PbO 2%
- Cu0 2%
- CK 3%
- 1% acetylene black
The energy potential is 1,050 cal / g.

The firing curves are shown in Figure 1.

Example 2
A propellant was produced using the following molding powder composition
- Nitrocellulose 31.5%
- Nitroglycerin 14.5%
- Hexogenic 43%
- 2-NDPA 2%
- PbO 3%
- CuO 3%
- CK 1.5%
- 1.5% acetylene black
The energy potential is 1,049 cal / g.

The firing curves are shown in Figure 2.

Claims (9)

Claims 1. Molding process for the manufacture of a double base propellant block with a high rate of nitramine, consisting in casting a molding solvent consisting of a nitric ester, a plasticizer, a stabilizer, on a molding powder placed in a mold and formed from nitrocellulose with a nitrogen content of between 11.5 and 13%, a nitric ester, stabilizers, at least one nitramine, catalysts for combustion, possibly plasticizers, to be cooked together and characterized in that the rate of nitric ester and nitramine in percentage by weight in the molding powder is respectively between 0 and 30% on the one hand and 35 and 60% on the other hand, the rate in percentage by weight of plasticization of the molding powder being between 0 and 50%, and in that the combustion catalysts consist of at least one lead oxide, at least one cuprous or cupric oxide, of black acetylene or benzene and potassium cryolite. 2. Molding process for the manufacture of a double base propellant block according to claim 1 characterized in that the nitramine is hexogen. 3. Molding process for the manufacture of a double base propellant block according to claim 2 characterized in that the rate by weight of hexogen in the molding powder is between 37 and 57%. 4. Molding process for the manufacture of a double base propellant block according to one of claims 2 or 3 characterized in that the level of nitric ester in the molding powder is between 9 and 21%. 5. Molding process for the manufacture of a double base propellant block according to one of the preceding claims, characterized in that the combustion catalysts consist (by mass) of  0.5 to 3% of one or more lead oxides  0.5 to 3% cuprous or cupric oxide or a mixture of the two  0.1 to 1.5% acetylene black or benzene black  0.5 to 4% potassium cryolite 6. Molding process for the manufacture of a double base propellant block according to one of the preceding claims characterized in that the catalytic system comprises as lead oxide lead monoxide. 7. Molding process for the manufacture of a double base propellant block according to claim 5 characterized in that the copper oxide is preferably cupric oxide. 8. Double base propellant block consisting in particular of nitrocellulose, nitric ester, at least one nitramine and catalysts consisting of at least one lead oxide, at least one cuprous or cupric oxide, of black acetylene or benzene and potassium cryolite, the percentage by weight of plasticization being less than 75%. 9. Double base propellant block according to claim 8 characterized in that it consists in particular of 26 to 43% of nitroglycerin and 24 to 42% of nitramine.