Device to minimize the explosive effects of a metal casing in the event of accidental internal overpressure

Abstract

To prevent the violent bursting of the casing of a thruster containing propergol during an accidental fire in its vicinity, a pyrotechnic composition (5, 6) is attached to this casing. This pyrotechnic composition locally heats the casing during this fire, and therefore embrittles this casing which opens at this place before the internal pressure becomes excessive. This prevents the fragmentation of the casing and the bursting out of the fragments.

Description

BACKGROUND OF THE INVENTION

[0001] The present invention pertains to a device for minimizing the explosive effects of a metal casing in the event of an accidental rise in internal pressure.

[0002] Certain missile thrusters have a metal structure and react violently when subjected to heating because of surrounding fire. In this case, a large number of significantly sized splinters of the metal structure are violently thrown out over long distances. This reaction results from the combination of two phenomena:

[0003] whatever the architecture of the thruster, the heating due to the fire prompts a pyrotechnic reaction on the part of the thrusters. The energy thus released prompts a rise in pressure in the casing of the thruster;

[0004] simultaneously, the properties of mechanical resistance of the casing are not sufficiently weakened by the fire. The casing breaks at high pressure, giving rise to big metal splinters.

SUMMARY OF THE INVENTION

[0005] An object of the present invention is a device to minimize the explosive effects of a metal casing subjected to internal overpressure, for example a missile thruster casing that gets excessively pressurized if it is subjected to a fire, this device being easily adaptable to different sorts of casings while being inexpensive and efficient in almost every instance.

[0006] The device according to the invention comprises a pyrotechnic system attached to the casing that is activated immediately upon detection of a phenomenon that causes a rise in overpressure in the casing. The ignition of this pyrotechnic system gives rise, by heating, to a limited local degradation of the mechanical characteristics of the casing.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The present invention will be understood more clearly from the following detailed description of an embodiment given by way of a non-restrictive example and illustrated by the appended drawing, wherein the single FIGURE is a partial sectional view of a missile thruster provided with the device according to the invention.

MORE DETAILED DESCRIPTION

[0008] The present invention is described here below with reference to a missile thruster that undergoes an accidental fire in its storage hangar, but it is clearly not limited to this single application and can be implemented in other applications comprising a metal casing, already pressurized internally, or else containing products that can place it under normal pressure or overpressure in the event of accidents, this overpressure prompting the explosion of the casing with violent outbursts of splinters from this casing.

[0009] The thruster 1 shown in the single FIGURE essentially has a circular cylindrical casing 2 enclosing a coaxial internal central channel 3, the space between this channel 3 and the casing 2 being filled with propergol 4. In order to provide for firm adhesion between the propergol and the casing, the internal face of the casing is lined with a binding agent 7 known as liner, generally made of polybutadiene or polyurethane.

[0010] According to the invention, a box 5 is attached to the external face of the casing 2. This box 5 contains a pyrotechnic composition 6. This pyrotechnic composition 6, when fired, releases a large quantity of calories, sufficient to locally degrade the mechanical properties of the casing to the point at which, when the propergol 4 undergoes spontaneous inflammation following its heating by a fire, the pressure thus generated in the casing does not have sufficient time to reach an excessively high value and cause the above-mentioned violent reaction. In fact, as soon as this internal pressure starts rising, while remaining relatively low (at a value that can be easily withstood by the casing under normal conditions), the part of the casing embrittled by the heavy heating due to the composition 6 opens, giving rise to practically no splinters at all, and lets out the pressurized gases produced by the inflammation of the propergol.

[0011] According to one embodiment of the invention, the composition 6 is a propergol composition or a pyrotechnic composition, and its volume is about 10 cm3 for a steel casing about 1.5 mm thick and 10 cm long. Naturally, the nature and quantity of the composition 6 are adapted to the characteristics of the casing 2 and of the propergol 4.

[0012] The ignition of the composition 6 can be either spontaneous following its heating due to the fire or activated by an appropriate ignition device connected to a heat sensor attached to the casing 2.

[0013] According to another characteristic of the invention, a layer of heat-insulating material is placed around the casing. This heat-insulating material is used to delay the heating of the propergol 4 to allow time for the composition 6 to sufficiently degrade the local mechanical characteristics of the casing 2.

[0014] According to one variant of the invention, the box 5 with the composition 6 is attached to the interior of the casing 2, in contact with this casing. An embodiment of this kind, although less simple to make than embodiment described here above, may have advantages in other applications, for example owing to the fact that the box 5 is not an “outgrowth” one the casing and hence does not risk getting accidentally wrenched off, for example during the handling of the casing, or does not in any way constitute a hindrance, for example when the casing is being shifted.

[0015] In general, the device of the invention prevents the violent explosion of a casing which either contains products capable of catching fire by spontaneous inflammation or exploding through an excessive heating of the casing or else is under internal pressure in normal conditions whereas, however, this internal pressure may rise exaggeratedly under normal conditions (over-heating, modification of the composition of the contents, internal short circuit etc.). In such cases, the ignition of the compound 6 is activated spontaneously or by an appropriate sensor of physical or chemical conditions (such as a pressure sensor, temperature sensor, gas sensor etc.).

Claims

1. A device for minimizing the explosive effects of a metal casing subjected to internal overpressure, comprising a pyrotechnic system attached to the casing that is activated immediately upon detection of a phenomenon that causes a rise in overpressure in the casing, the ignition of this pyrotechnic system causing a limited local degradation, through heating, of the mechanical characteristics of the casing.

2. A device according to claim 1, wherein the pyrotechnic system is attached to the exterior of the casing, in contact with it.

3. A device according to claim 1, wherein the pyrotechnic system is attached to the interior of the casing, in contact with it.

4. A device according to claim 1, 2 or 3, wherein the ignition of the pyrotechnic system is prompted by heating.

5. A device according to one of the claims 1 to 3, wherein the ignition of the pyrotechnic system is activated by a sensor of physical or chemical conditions.

6. A device according to one of the above claims, wherein the casing is lined with a layer of heat-insulating material.

7. A device according to one of the above claims, wherein the casing is that of a missile thruster.