EP1205727B1 - Pyrotechnic delay initiator - Google Patents

Abstract

A pyrotechnic initiation delay device intended in particular to cooperate with a device for firing a pyrotechnic charge of the fuze type, particularly for a hand grenade, having a delay composition located inside a delay column, the latter having a lower end and an upper end, a percussion primer being able to cooperate with the upper part of the delay column, and a striker piston held firmly under the lower end of the delay column and able to move axially in the direction of the element to be struck under the action of an explosive charge cooperating with the lower end of the delay column. The delay column communicates with the explosive charge through a cavity containing plugging means allowing or preventing movement of the striker piston under the effect of the explosive charge.

Description

The technical sector of the present invention is that of devices for igniting a pyrotechnic charge, in particular for hand grenade, and more particularly that of the pyrotechnic initiation means delaying a pyrotechnic chain.

The retarding pyrotechnic elements have been used for many years in various fields such as detonators for firing in mines and in quarries, rockets of all types (artillery, infantry mines, grenades, mortars, etc.). They are as numerous as they are essential and can be defined as being elements of a pyrotechnic chain in which they ensure a time interval between a priming action and a specific response.

The importance of this time is no longer to be demonstrated; whether in the use of civilian detonators or in the use of hand or rifle grenades, the malfunction of the retarding element can lead to catastrophic consequences.

It is therefore important to use perfectly controlled retarding devices, but it is also necessary to counter all of the unfortunate consequences that a construction or assembly error could have.

In this technical field, several achievements have been proposed.

The various means of initiating pyrotechnic retarders remain however quite similar in their general concept: it is a percussion primer intended to be struck by any striker to then allow the ignition of a retarding composition which it has for aim to be consumed and ignite in turn another element of the pyrotechnic chain.

This is particularly what teaches us the document DE 1.428.401 where the retardant pyrotechnic initiation means include a percussion primer being in direct contact with the retarding composition, which once the combustion is complete, ignites a charge explosive. This technique is also found in documents US 3,823,669 and FR 2,353,041.

Another similar technique consists in replacing the explosive or reinforcing charge with a detonator which will ensure that it continues to ignite the pyrotechnic chain. This is notably the technique used in documents FR 2,465,189 and FR 2,458,790.

In all of the aforementioned documents, the ignition of the explosive charge or the activation of the detonator by the retarding composition directly causes the propagation of fire in the pyrotechnic chain and the explosion of the pyrotechnic charge of the hand grenade type by the 'through the igniter plug in which the ignition device is located.

For security reasons, document FR 2,721,394 has proposed to insert a striker between the reinforcing charge ignited by the retarding composition and the rest of the pyrotechnic chain comprising in particular a detonator and another explosive charge. This striker is provided with an explosive charge allowing it, using the gases released by the reaction of the explosive charge, to pivot around its axis and thus to be able to strike another percussion primer to continue the ignition of the pyrotechnic chain. , see in this regard document FR-A-2 557 969 which covers the preamble of claim 1.

All of these documents, however, have a significant drawback insofar as when the retarding composition is consumed, the fire propagates instantly in the rest of the pyrotechnic chain. However, when they are ignited, these compositions normally burn regularly and, depending on their nature, determine a combustion time which is proportional to the height of the delay column in which this retarding composition is found or to the amount of powder itself. . Generally, the loading of this composition is done by metering and successive compressions of increments with high compression forces to ensure a high and constant density of the retarding composition. It is obvious that too low compression will not ensure sufficient compactness of the delay column for withstand external stresses from shocks, vibrations, transport, but above all will lead to erratic delay times which can seriously harm the user or cause uncontrolled destruction of the ignition devices. It should also be noted that these drawbacks remain in the event that the retarding composition is not loaded in the delay column.

We can nevertheless protect ourselves from these anomalies by techniques of the measurement type, X-ray examination or even by neutrinography; but even at the correct height, it is extremely difficult to assess the density of the column with this type of technique which is at the same time very expensive.

The object of the invention is therefore to remedy the drawbacks mentioned above by proposing retardant pyrotechnic initiation means improving safety during handling before launching the igniter plugs, in particular for hand grenade. Another object of the invention is to provide self-timer pyrotechnic initiation means for igniting pyrotechnic charge reducing the danger of explosion in the event of transport or port on potential combatants.

Another object consists in the possibility of storing grenades equipped with their igniter plug unlike conventional igniters which must be stored away from grenades.

Finally, the invention will aim to reduce the costs of pyrotechnic charge firing devices by using retarding pyrotechnic initiation means allowing a reduction in costs directly related to the analyzes of compactness of the retarding charge. To do this, the invention relates to retarding pyrotechnic initiation means intended in particular to cooperate with a device for igniting a pyrotechnic charge of the igniter plug type, in particular for hand grenade, comprising a retarding composition located at the inside a delay column, the latter having a lower end and an upper end, a percussion primer being able to cooperate with the upper part of the delay column, and a striker piston held firmly under the lower end of the delay column and able to move axially in the direction of the element to be struck under the action of an explosive charge cooperating with the lower end of the delay column. The delay column communicates with the explosive charge via a cavity comprising closure means authorizing or prohibiting the movement of the striker piston under the effect of the explosive charge.

According to a preferred embodiment of the invention, the means for closing the cavity consist of rigid slag resulting from the combustion reaction of the retarding composition.

The striker piston preferably comprises an internal cavity in which is capable of accommodating the explosive charge in order to substantially deform the walls of this internal cavity during the explosion of said explosive charge.

The percussion primer used is preferably of the boxer type and is set in a primer holder itself set in a delay holder comprising the delay column previously loaded with retarding composition.

The expansion chamber may be inside the delay holder and be between the retarder composition and the percussion primer.

According to a preferred embodiment of the invention, the delay holder is screwed onto a body comprising in particular a through bore capable of guiding the striker piston which is held under the lower end of the delay column by means of a collar.

The explosive charge used to move the striker piston can be found in an internal cavity of the piston and consists of lead azide, lead dinitro-resorcinate or lead styphnate.

Finally, these means can be associated with a detonator capable of being struck by the striker piston, the detonator being confined in a rotor or a lock which can pivot by means of an external stress.

These retarding pyrotechnic initiation means have the advantage of being perfectly mastered and are therefore capable of countering all the unfortunate consequences linked to a construction or assembly error. Another advantage lies in the prevention of a premature or instantaneous departure of a pyrotechnic charge located under the delay column, whether during handling before launch, during storage or during transport. These departures can come from an incomplete or not correctly loaded delay column of the type which is insufficiently compressed or which has a total absence of retarding composition.

Other characteristics and advantages of the invention will appear in the detailed, non-limiting description below.

• la figure 1 représente une vue en coupe longitudinale des moyens d'initiation pyrotechnique retardateurs avant la combustion de la composition retardatrice ;
• la figure 2 représenteune vue en coupe longitudinale des moyens d'initiation pyrotechnique retardateurs après la combustion de la composition retardatrice et avant l'explosion de la charge explosive ;
• la figure 3 représente une vue en coupe longitudinale des moyens d'initiation pyrotechnique retardateurs avant la combustion de la composition retardatrice et associés à un autre élément de la chaîne pyrotechnique comprenant un détonateur et un renforçateur.

This description will be made with reference to the attached drawings, in which:

• FIG. 1 represents a view in longitudinal section of the retarding pyrotechnic initiation means before the combustion of the retarding composition;
• FIG. 2 represents a view in longitudinal section of the retarding pyrotechnic initiation means after the combustion of the retarding composition and before the explosion of the explosive charge;
• FIG. 3 represents a view in longitudinal section of the retarder pyrotechnic initiation means before the combustion of the retarder composition and associated with another element of the pyrotechnic chain comprising a detonator and a booster.

Referring to Figures 1 and 2, we see self-timer pyrotechnic initiation means intended in particular to cooperate with a device for igniting a pyrotechnic charge (not shown). These means can be part of a device for igniting a pyrotechnic charge of the igniter plug type, in particular for hand grenades (as described in document FR 2,272,394), rifle grenades, mines, artillery or mortar rockets or any other pyrotechnic application requiring such delay.

These means include a percussion primer (1) of the boxer type inserted and set in a primer holder (2). The device can naturally operate with an electric primer instead of a percussion primer. The assembly constituted by the primer (1) and the primer holder (2) is itself positioned and crimped in a delay holder (3), the crimps being sealed by a bead of varnish, epoxy or cyanoacrylate. The delay holder (3) was previously loaded with a retarding composition (4) inside a delay column (4C) having two ends (4a, 4b). This retarding composition (4) will be of the "millisecond" or "second" type depending on the use made of the pyrotechnic train. For example, for a hand grenade, the nominal combustion time will be between 3.5 and 5 seconds, while for a mortar rocket with launch safety, the time will be between 100 and 500 milliseconds. These combustion times are governed by a multitude of parameters which it will be important to integrate during the preparation of the retarding composition (4); these parameters are very well known to those skilled in the art. These are in particular the nature of the ingredients, the nature of the binder, the particle size and the purity of the components, the hygroscopicity, the compression ratio of the retarding composition in the delay column, the gas pressure generated, the nature of the case or the diameter of the delay column.

The loading of this delay column (4c) is done by successive dosages of increments; it is also possible to add an ignition charge to the top of the delay column (4c); this ignition composition will then be compressed at the same pressure as the delay powder. The delay holder (3) comprises an expansion chamber (9) located between the percussion primer (1) and the upper end (4b) of the delay column (4c); this delay holder (3) is, in this preferred embodiment of the invention, screwed onto a body (7) provided with a through bore (17) allowing the displacement and the guiding of a striker piston (5). The latter is firmly fixed between the body (7) and the delay holder (3), and this under the lower end (4a) of the delay column.

The striker piston is held firmly in its position by a collar (5a), but could also be held by means such as a spring, a frangible cover or even an o-ring or a washer. The metallic nature of the striker piston (5) and the thickness of the flange (5a) will then define an explosive charge (10) to be administered to ensure the proper functioning of these means. In this embodiment, the explosive charge (10) is contained in an internal cavity (6) of the striker piston but could just as easily be outside the striker piston (5) as in particular in the delay holder (3 ). The advantage of this arrangement with the explosive charge (10) inside the striker piston (5) lies in the provision of additional security of the pyrotechnic initiation means which will be described in the operation of these means. This explosive charge (10) communicates with the lower end (4a) of the delay column (4c) via a cavity (8) comprising closure means (4d) and in which the gases generated by the explosion of the explosive charge (10). According to a preferred embodiment of the invention, the sealing means (4d) of the cavity (8) consist of solid slag resulting from the combustion reaction of the retarding composition (4) in the delay column (4c ).

With reference to FIG. 3, we see retarding pyrotechnic initiation means associated with another element of the pyrotechnic chain comprising a detonator (11), a relay (13) and a booster (14) ensuring the ignition of the continuation of the pyrotechnic chain. The detonator (11) is located inside a rotor or latch (12) which is able to align with the striker piston and the relay (13) after an external stress. It should be noted that the percussion primer (1) can be associated with a striker (15) and a spring (16) acting in compression.

The operation of these retarding pyrotechnic initiation means is as follows.

When the delay column (4c) is correctly loaded over the entire height and at the right density, it has a large mass of rigid solid slag formed by the combustion of the retarding composition (4) and occupying substantially the same volume as that of this retarding composition (4) before combustion. The fire propagates initially throughout the retarding composition (4) activated by the percussion primer previously struck. When the flame reaches the bottom of this delay column, it ignites the explosive charge (10) contained in the striker piston (5). This explosion generates a large quantity of gas which then remains confined in the cavity (8) thanks to the obturation of the delay column caused by solid slag (4d). The purpose of this reaction will be to shear the collar and project the striker piston downwards, the latter then being able to strike the detonator (11).

However, to reinforce the safety of these means during the accidental release of the striker piston (5) despite a correctly loaded retarding composition, these means according to a preferred embodiment of the invention are arranged so that the explosive charge (10 ) is located in an internal cavity (6) of the striker piston (5). These accidental departures can be due to multiple reasons influencing in particular the retarding composition (4) or even the explosive charge (10), both being reputed to be very sensitive. These are, among other things, extreme environmental conditions such as high temperatures or even accidental conditions occurring during storage, transport or handling before the use of such means. It should be noted that other factors can intervene in the accidental release of the piston such as the percussion of these means by a bullet or the detonation of the primary explosive by the influence of an external explosion. Despite the fact that the detonator (11) is misaligned with the striker piston (5), there is still a risk of propagation of hot gases or flames generated by the explosion of the explosive charge (10) which can then cause the combustion of the relay (13) as well as all the unfortunate consequences that the detonation could have. This is the reason why the explosive charge (10) is placed inside the striker piston (5) in this preferred embodiment. When the latter is released, the deformable walls of the internal cavity (6) of the piston (5) will deform following the explosion of the explosive charge (10) in order to be pressed against the bore (17) in which the piston (5) is able to translate. This effect of plating the deformable walls will have the consequence of preventing hot gases as well as flames from propagating between the bore (17) and the striker piston (5) as well as in the games of the moving parts of the means of pyrotechnic initiation. The flames and the gases generated will therefore remain confined in the upper part of the pyrotechnic initiation means following the seal created by the deformation of the walls of the internal cavity (6) which can then prevent the misalignment of the detonator (11). or more serious from the relay (13).

Still concerning the operation of the pyrotechnic initiation means, if for any reason such as the absence of retarding composition (4) or the incomplete, non-conforming or non-compact loading of the delay column (4c), the percussive primer ( 1) or the retarding composition (4) ignites the explosive charge (10) contained in the striker piston (5), the expansion of the gases will take place in a volume greater than that of the cavity (8); in fact, the quantity of rigid slag formed by the combustion of the retarding composition will not be large enough to withstand the pressure of the gases generated by this combustion. These gases will therefore pass through the slag plug to distribute themselves in a volume equal to that which contained the retarding composition (4) plus that of the expansion chamber (9). Therefore, the reaction will be insufficient to shear the flange and propel the striker piston down; there will therefore be no final effect on the pyrotechnic train, even if the detonator (11) is aligned.

We can therefore see in this principle all the security generated by this invention. Checks for the presence of delay compositions can be reduced and the simplicity of the device allows it to be adapted to all devices which include a pyrotechnic delay.

Of course, various modifications can be made by those skilled in the art to the retarder pyrotechnic initiation means which have just been described, only by way of nonlimiting example, without departing from the protective framework defined by the appended claims.

Claims (11)

1. Retarding means for pyrotechnic initiation, intended in particular to co-operate with a device for firing a pyrotechnic charge of the igniter-plug type, in particular for a hand grenade, comprising a retarding composition (4) situated inside a delay column (4c), this latter having a lower extremity (4a) and an upper extremity (4b), a percussion fuse (1) being capable of co-operating with the upper part (4b) of the delay column (4c), and a striker piston (5) maintained firmly under the lower extremity (4a) of the delay column (4c) and able to be displaced axially in the direction of the element to be struck under the action of an explosive charge (10) co-operating with the lower extremity (4a) of the delay column (4c), said means being characterised in that the lower extremity (4a) of the delay column (4c) communicates with the explosive charge (10) via a cavity (8) comprising sealing means (4d) permitting or prohibiting the displacement of the striker piston (5) under the action of the explosive charge (10).
2. Retarding means for pyrotechnic initiation according to Claim 1, characterised in that the sealing means (4d) are constituted by rigid scoria (4d) resulting from the reaction of combustion of the retarding composition (4).
3. Retarding means for pyrotechnic initiation according to Claim 1 or Claim 2, characterised in that the striker piston (5) comprises an internal cavity (6) in which the explosive charge (10) is capable of being accommodated so as to deform the walls of this internal cavity (6) appreciably in the course of the explosion of said explosive charge (10).
4. Retarding means for pyrotechnic initiation according to any one of the preceding claims, characterised in that the percussion fuse (1) is of the boxer type and is crimped in a fuse cap (2), these two elements both being crimped in a delay cap (3).
5. Retarding means for pyrotechnic initiation according to Claim 4, characterised in that the delay cap (3) comprises the delay column (4c) which has been charged beforehand with the retarding composition (4).
6. Retarding means for pyrotechnic initiation according to Claim 4 or Claim 5, characterised in that the delay cap (3) comprises the expansion chamber (9), this latter being situated between the percussion fuse (1) and the retarding composition (4).
7. Retarding means for pyrotechnic initiation according to any one of Claims 4, 5 or 6, characterised in that the delay cap (3) is screwed to a body (7) provided with an emerging bore (17) capable of guiding the striker piston (5).
8. Retarding means for pyrotechnic initiation according to Claim 7, characterised in that the striker piston (5) is placed firmly between the delay cap (3) and the body (7) through the agency of means of the flange type.
9. Retarding means for pyrotechnic initiation according to any one of the preceding claims, characterised in that the explosive charge (10) is of the lead-azide type, lead-dinitroresorcinate type or lead-styphnate type.
10. Retarding means for pyrotechnic initiation according to any one of the preceding claims, characterised in that the striker piston (5) is propelled onto a detonator (11) confined within a rotor or a lock (12) that is able to pivot by virtue of an external load so as to be aligned with the striker piston (5) and a relay (13) leading to a boosting charge (14).
11. Retarding means for pyrotechnic initiation according to any one of the preceding claims, characterised in that the percussive fuse (1) is capable of co-operating with a striker (15).