FR2811053A1 - DEVICE FOR MINIMIZING THE EXPLOSION EFFECTS OF A METAL ENCLOSURE IN THE EVENT OF ACCIDENTAL INTERNAL OVERPRESSURE - Google Patents

Abstract

To prevent the violent bursting of the enclosure (2) of a propellant containing propellant (4) during an accidental fire in its environment, a pyrotechnic composition (5, 6) is attached to this enclosure which heats up locally the enclosure during this fire, and therefore weakens this enclosure, which opens at this location before the internal pressure is too great, which prevents the fragmentation of the enclosure and the violent projection of such fragments.

Description

DEVICE FOR MINIMIZING THE EXPLOSION EFFECTS OF A

  METAL ENCLOSURE IN THE EVENT OF INTERNAL OVERPRESSURE

ACCIDENTAL

  The present invention relates to a device for minimizing the explosion effects of a metal enclosure in the event of overpressure

accidental internal.

  Some missile boosters, which have a metallic structure, react violently when subjected to the test of fire due to a surrounding fire. In this case, a large number of shards of the metallic structure, of significant size, are violently projected at long distance. This reaction is the conjunction of two phenomena: whatever the architecture of the propellant, the heating due

  the fire causes the propellant's pyrotechnic reaction.

  the energy thus released causes a rise in pressure in the casing of the propellant; - simultaneously, the mechanical strength properties of

  the envelope is not sufficiently weakened by the fire.

  The rupture of the envelope therefore occurs at a pressure

  high, generating significant metallic shards.

  The subject of the present invention is a device making it possible to minimize the deflagrating effects of a metal enclosure subjected to an internal overpressure, for example a missile booster enclosure, put under overpressure in the event of a fire to which it would be subjected, this device simple to adapt to different kinds of speakers, while

  being inexpensive, and effective in almost all cases.

  The device according to the invention comprises a pyrotechnic system fixed to the enclosure which is triggered as soon as there is detection of a phenomenon causing the rise in overpressure in the enclosure, the ignition of this pyrotechnic system causing, by heating, the fall

  limited local mechanical characteristics of the enclosure.

  The present invention will be better understood on reading the

  detailed description of an embodiment, taken by way of example not

  limiting and illustrated by the appended drawing, the single figure of which is a partial sectional view of a missile propellant provided with a device according to the invention. The present invention is described below with reference to a missile propellant subjected, in its storage shed, to an accidental fire, but it is understood that it is not limited to this single application, and that it can be implemented in other applications comprising a metallic enclosure, already under internal pressure, or else containing products which can put it under normal pressure, and under overpressure in the event of an accident, this overpressure causing the explosion of

  the enclosure with violent projection of significant fragments of this enclosure.

  The propellant 1 shown in the single figure essentially comprises an enclosure 2 of circular cylindrical shape enclosing a central coaxial inner channel 3, the space between this channel 3 and the enclosure 2 being filled with propellant 4. In order to ensure good adhesion between the propellant and the enclosure, the internal face of the latter is coated with a binding agent 7 (known as "liner"), which is generally made of polybutadiene or

polyurethane.

  According to the invention, a box 5 containing a pyrotechnic composition 6 is fixed on the external face of the enclosure 2. This composition 6 releases, when it is ignited, a large amount of calories, sufficient to locally degrade the properties. mechanical of enclosure 2 to the point that during the self-ignition of propellant 4 due to its heating due to a fire, the pressure thus generated in the enclosure does not have time to reach a too high value and to provoke the aforementioned violent reaction. In fact, as soon as this internal pressure begins to increase, while remaining relatively low (at a value easily supported by the enclosure under normal conditions), the part of the enclosure weakened by the significant heating due to the composition 6 opens without practically producing splinters, and lets escape the gases under pressure produced by

propellant inflammation.

  According to one embodiment of the invention, composition 6 is propellant or a pyrotechnic composition, and its volume is approximately cm 3 for a steel enclosure, of a thickness of approximately 1.5 mm and of length 10 cm. Of course, the nature and the amount of composition 6 are

  adapted to the characteristics of enclosure 2, and of propellant 4.

  The ignition of composition 6 can either be spontaneous due to its heating due to the fire, or triggered by a device for

  appropriate firing connected to a thermal sensor fixed to the enclosure 2.

  According to another characteristic of the invention, there is a layer of thermal insulating material around the enclosure which makes it possible to delay the heating of the propellant 4 to allow time for the composition 6 to sufficiently weaken the local mechanical characteristics of

enclosure 2.

  According to a variant of the invention, the box 5 with the composition 6 are fixed inside the enclosure 2, in contact with the latter. Such an embodiment, although less simple to carry out than the embodiment described above, can have advantages in other applications, for example because the box 5 does not constitute a "wart" on the outside the enclosure and therefore does not risk being accidentally torn off, for example during handling of the enclosure, or does not constitute

  embarrassment, for example to move the enclosure.

  In general, the device of the invention makes it possible to avoid the violent explosion of an enclosure which either contains products which can ignite by self-ignition or explode as a result of overheating of the enclosure, or is under internal pressure under normal conditions, but this internal pressure can rise excessively under abnormal conditions (overheating, modification of the composition of the content, internal short-circuit ...). In such cases, the ignition of composition 6 is triggered spontaneously or by an appropriate physical or chemical condition sensor (

  pressure, temperature, gas sensor ...).

Claims (7)

  1. Device for minimizing the deflagrant effects of a metallic enclosure under accidental overpressure, characterized in that it comprises a pyrotechnic system (6) fixed to the enclosure (2), which is triggered as soon as there is detection of a phenomenon causing the rise in overpressure in the enclosure, the ignition of this pyrotechnic system causing, by heating, the limited local fall in the mechanical characteristics of the enclosure. 2. Device according to claim 1, characterized in that the pyrotechnic system is fixed outside the enclosure, in contact with l0 this one.   3. Device according to claim 1, characterized in that the   pyrotechnic system is fixed inside the enclosure, in contact with it   this. 4. Device according to claim 1, 2 or 3, characterized in that the ignition of the pyrotechnic system is caused by heating.   5. Device according to one of claims 1 to 3, characterized by   the fact that the ignition of the pyrotechnic system is triggered by a   sensor of physical or chemical conditions.   6. Device according to one of the preceding claims,   characterized by the fact that the enclosure is covered with a layer of material thermal insulator.   7. Device according to one of the preceding claims,   characterized by the fact that the enclosure is that of a missile booster.