GB1585697A - Manufacture of double-base propergol propellant charges - Google Patents

Description

(54) MAUFACTURE OF DOUBLE-BASEi PROPERGOL PROPELLANT CHARGES (71) We, SOCIETE NATIONAL DES POUDRES ET EXPLOSIFS, a French body corporate, of 12 quai Henri IV, 75181 Paris Cedex 04, France, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement : The present invention is concerned with the production of propellant charges from two or more double-base propergol elements (the expression "double-base propergol" being used herein in its normal sense to refer to a propergol containing both nitrocellulose and nitroglycerine).

It has been proposed to manufacture propellant charges from a plurality of elements of propellant powder (such as the propellant powder available under the Trade Mark "Balistite") by hot rolling or by cold adhesion using a solvent, such as acetone or amyl acetate. However, such methods involve deformation of the interface between elements, and sometimes cracking, so that in use the flame front is likely to be irregular when it traverses the interface.

We have now developed a method of bonding elements of propellant powder which alleviates the above disadvantage.

According to the invention, there is provided a method of producing a propellant charge from a plurality of double-base propergol elements, which comprises compression moulding the elements in an evacuated mould cavity between complementary moulding surfaces at such an elevated temperature that the elements are welded together.

In a preferred method of carrying out the method according to the invention, the elements (which are preferably pre-heated to a temperature at which they can be welded, pre-heating being effected, for example, by placing the elements in a heated chamber) are disposed with the surfaces which are to be welded in juxta-position in a mould cavity between complementary mould members (one of which is a punch) which define the desired external profile of the charge. The cavity is then closed airtight, raised to the elevated temperature (preferably 50"C to 1200C, more preferably above 87 C) and evacuated to a high vacuum (preferably a pressure of less than 30 millibars, more preferably, not more than 10 millibars).The punch is then forced into the mould cavity (preferably at a pressure between 150 and 1200 bars, more preferably above 250 bars) so as to compression mould the elements and to weld them together. The mould is then cooled and the resulting propellant charge is withdrawn from the mould.

The method according to the invention is preferably carried out with an air-tight mould cavity which is evacuated throughout the entire duration of the compression moulding operation so that ignition due to residual air and the formation of air bubbles in the resulting charge are avoided. Hot decomposition gases which may be formed during compression moulding are also removed by this method.

The elements are preferably formed of different propergol compositions having different combustion rates and it is particularly preferred that the elements should have combustion rates which increase progressively from one element to the next so that the resultant propellant charge has a Drogressive action. Disturbance of a flame front traversing the interface(s) between adjacent elements is minimal.

Suitable propergol compositions from which the elements can be made are, for example, the following Compositions 1 to 3, in which all parts are by weight. Composition 2 has a relatively slow rate of combustion and Compositions 3 and 1 have relatively fast rates of combustion, the rate for Composition 1 being faster.

Composition No. I Nitrocellulose 58 parts Nitroglycerine 42 parts Centralite 1 part Composition No. 2 Nitrocellulose 59 parts Nitroglycerine 31 parts Triacetin 10 parts Centralite 3 parts Composition No. 3 Nitrocellulose 56 parts Nitroglycerine 37 parts Potassium cryolite 3 parts Centralite 2 parts.

Centralite is a generic designation of dialkyldiphenylureas which are conventionally used in double base propergols, such as dimethyldiphenylurea, methylethyldiphenylurea and diethyldiphenylurea.

Elements may be made from such compositions by, for example, solventless extrusion or machining or by the method disclosed in British Patent Application 54008/77 (Serial No. 15809489.

In the folowing description, reference will be made to the accompanying drawing, in which: Figure 1 is an elevation, the upper part of which is in axial section, of a preferred embodiment of a device suitable for carrying out the method according to the invention; Figure 2 is an axial section of a propellant charge obtained according to the invention; and Figure 3 is an axial section view of another propellant charge obtained according to the invention from several propergol elements.

Referring to Figure 1, the apparatus comprises a mould 1 having a horizontal axis and a cylindrical axial bore 2. The forward end of the bore is extended by a detachable base 3 in which a plug 4 can slide, which plug is pushed into axial bore 3a of the base through O-ring seal 5 by means of a hydraulic jack (not shown). The inner wall of the mould and the plug define a mould cavity corresponding to the external profile of the desired charge (the cavity having, for example, a diameter of 30 mm). The mould is surrounded by a heating jacket 6 with oil circulation whereby the mould can be heated to the desired temperature. A heat control circuit 7 with water circulation also passes through the body of the base 3 in order to facilitate cooling of the charge before withdrawal from the mould.

A vacuum point 8, connected to a vacuum pump (not shown), is provided at the rear end of the mould. This point communicates with the mould cavity via an annular groove 9 in the inner wall of the mould.

A cylindrical punch 10 which has a diameter which is less than that of the mould cavity is mounted along the axis of a cylindrical punch carrier 11 which has the same diameter as the mould cavity and which is capable of sliding, in an air-tight manner, into this cavity, an O-ring seal 12 being disposed between the inner wall of the mould and the punch carrier upstream of the vacuum point 8.

Movement of the punch 10 and of the punch carrier 11 is controlled by the piston 13 of the jack of a press 14, which piston moves between two limiting positions: a retracted position indicated by the letter A and a working position indicated by the letter B.

A typical cycle of operation of this apparatus will now be described. The mould 1 is fitted at the outlet of the body of the press 14 and the punch carrier 11 is in contact with the driving piston 13 in the retracted position A. With the plug 4 removed, the following are introduced into the mould cavity 2: a cylindrical element 16 of a double-base propergol (for example, of composition No. 3 as defined above and having a diameter of 30 mm and a length of 50 mm); and a cylindrical element 15 of a double-base propergol (for example, of composition No. 2 as defined above and having a diameter of 30 mm and a length of 10 mm).

With the plug 4 engaged in the axial bore 3a, the piston 13 is urged forwardly until the punch carrier 11 is engaged in the mould cavity at the level of the vacuum point 8.

The heating jacket 6 and the heat control circuit 7 are adjusted and the vacuum pumn is operated until a temperature of 95"C and a residual pressure of 10 millibars are reached in the mould cavity. After reheating the elements 15 and 16, the piston 13 is actuated so as to gradually move it forward into the position B and compress element 16 against element 15 by means of the punch 10 under a pressure of 250 bars.

The operation of the vacuum pump is maintained throughout the entire length duration of the forward movement of the punch.

The contacting faces of the elements are welded extremely rapidly under the combined effect of pressure and temperature.

A typical time for welding to take place is 2/100 second.

At the end of the operation, the vacuum is broken, the mould is cooled by circulating cooling water in the circuit 7, the plug 4 is slid out, and the propellant charge is ejected by the complementary forward movement of the driving piston 23.

By this method a propellant charge is produced which is as shown in Figure 2.

If the punch 10 has a cylindrical shape of diameter which is essentially equal to that of the mould cavity, it is posible to manufacture a propelant charge as shown in Figure 3 from cylindrical elements 15, l5a, 15b, etc. Elements 15, 15a, 15b may be of double-base soleventless propegol having different compositions (such as compositions No. 2, No. 3 and No. 1, respectively, which have different combustion rates).

WHAT WE CLAIM IS:- 1. A method of producing a propellant charge from a plurality of double-base propergol (as herein defined) elements, which comprises compression moulding the elements in an . evacuated mould cavity between complementary moulding surfaces at such an elevated temperature that the elements are welded together.

2. A method according to claim 1, in which the elevated temperature is between 50"C and 1200C.

3. A method according to claim 2, in which the elevated temperature is above 87"C.

4. A method according to any of claims ] to 3, in which the mould cavity is evacuated to a pressure of less than 30 millibars.

5. A method according to claim 4, in which the mould cavity is evacuated to a pressure of not more than 10 millibars.

6. A method according to any of claims 1 to 5, in which the mould cavity is evacuated throughout the entire duration of the compression moulding operation.

7. A method according to any of claims to 6, in which compression moulding is effected at a pressure between 150 and 1200 bars.

8. A method according to any of claims 1 to 7, in which the elements are pre-heated to the elevated temperature before being placed between the complemntary moulding surfaces.

9. A method of producing a propellant charge from a plurality of double-base propergol (as herein defined) elements, substantially as described herein with reference to Figure 1 of the accompanying drawing.

to 9.

10. A propellant charge manufactured by a method according to any of claims 1 to 9.

11. A propellant charge according to claim 10, substantially as described herein with reference to and as ilustrated in Figure 2 or Figure 3 of the accompanying drawing.

12. Apparatus when used for carrying out a method according to any of claims 1 to 9, which comprises a female moulding member, a male moulding member, means for forming an air-tight moulding cavity between the moulding members, means for heating at least one of the moulding members, means for cooling at least one of the moulding members, means for evacuating the moulding cavity and means for moving the male moulding member so that, when a plurality of double-base propergol elements is disposed in the cavity, the male moulding member can be moved so as to effect compression moulding thereof.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (12)

**WARNING** start of CLMS field may overlap end of DESC **. 15b, etc. Elements 15, 15a, 15b may be of double-base soleventless propegol having different compositions (such as compositions No. 2, No. 3 and No. 1, respectively, which have different combustion rates). WHAT WE CLAIM IS:-

1. A method of producing a propellant charge from a plurality of double-base propergol (as herein defined) elements, which comprises compression moulding the elements in an . evacuated mould cavity between complementary moulding surfaces at such an elevated temperature that the elements are welded together.

2. A method according to claim 1, in which the elevated temperature is between 50"C and 1200C.

3. A method according to claim 2, in which the elevated temperature is above 87"C.

4. A method according to any of claims ] to 3, in which the mould cavity is evacuated to a pressure of less than 30 millibars.

5. A method according to claim 4, in which the mould cavity is evacuated to a pressure of not more than 10 millibars.

6. A method according to any of claims 1 to 5, in which the mould cavity is evacuated throughout the entire duration of the compression moulding operation.

7. A method according to any of claims to 6, in which compression moulding is effected at a pressure between 150 and 1200 bars.

8. A method according to any of claims 1 to 7, in which the elements are pre-heated to the elevated temperature before being placed between the complemntary moulding surfaces.

9. A method of producing a propellant charge from a plurality of double-base propergol (as herein defined) elements, substantially as described herein with reference to Figure 1 of the accompanying drawing.

to 9.

10. A propellant charge manufactured by a method according to any of claims 1 to 9.

11. A propellant charge according to claim 10, substantially as described herein with reference to and as ilustrated in Figure 2 or Figure 3 of the accompanying drawing.

12. Apparatus when used for carrying out a method according to any of claims 1 to 9, which comprises a female moulding member, a male moulding member, means for forming an air-tight moulding cavity between the moulding members, means for heating at least one of the moulding members, means for cooling at least one of the moulding members, means for evacuating the moulding cavity and means for moving the male moulding member so that, when a plurality of double-base propergol elements is disposed in the cavity, the male moulding member can be moved so as to effect compression moulding thereof.