EP0183884B1 - Percussion-sensitive priming mixture and process for producing it - Google Patents

Description

The technical sector of the present invention is that of initiation compositions sensitive to percussion intended for example to equip the heads of percussion rockets.

The percussion rocket heads intended to ensure the initiation of deflagrant or detonating delay or instantaneous relays comprise an initiation or primer composition, sensitive to the penetration of a striker tip with a more or less sharp end. Under the effect of this percussion, this composition decomposes by detonating or exploding very strongly depending on the nature of the explosive used.

The initiation compositions exist in similar forms and belong to two distinct families; a first family which does not have a priming power and therefore serves either to initiate a delay or a composition with a special effect, or to initiate the detonation on condition of adding thereto a priming element generally consisting of azide lead ; the second family has sufficient ignition power to directly initiate the detonation of a relay without requiring an intermediate composition.

The first family belongs to the compositions based on basic lead styphnate called "NOL ₁₃₀ in the USA, lead dinitroresorcinate called" L mixture or RD 1651 in GREAT BRITAIN or lead thiocyanate in FRANCE.

The second family belongs to compositions based on primary explosives such as lead azide with the addition of tetrazene, especially used in France.

In all cases, these compositions, which are moreover very sensitive, have the drawback of not supporting storage at medium temperature, above 75 ° C., for periods of time greater than a few days and of not supporting temperature peaks either. , of the order of 100 to 120 ° C, for durations greater than a few hours, conditions which are frequently encountered in places of storage or use of ammunition equipped with these primers.

By way of indication, mention will be made of the US patents 3,634,155, French 2,386,505 which describe conventional priming compositions.

French patent 2,309,493 mainly describes a process for coating primary explosives and generally mentions the possibility of preparing primers from copper chlorotetrazolate, oxidants and reducing agents. However, it is above all a question of facilitating the handling of primary explosives by coating them with a binder; moreover, no priming composition is proposed.

Patent GB-A-384,608 relates above all to a process for the preparation of nitrotetrazole which makes it usable in priming compositions. A comparison table is given for the limit charges for detonation of tetryl and it is specified that these primary explosives are stable under usual storage conditions. It is also indicated that the limit load of mercury fulminate or lead trinitroresorcinate is very reduced by adding a percentage of nitrotetrazole of 10 or 20%. Mention is made of the use of nitrotetrazole in percussion primers and provision is made for the addition of oxygen donors, combustible substances and friction agents to increase the terminal effect and reduce the breaking effect. The addition of these oxidizing or other substances, in the eyes of a person skilled in the art, is made only with the aim of avoiding the use of sensitizing agents based on explosives, i.e. - to say, without naming it, the tetrazene in the case of priming with percussion by crushing. No initiation composition is described; in particular, it is not intended to combine the nitrotetrazoles with an oxidation-reducing composition.

Detonation initiation compositions are characterized by their sensitivity to percussion, by their heat stability and by their power to initiate a secondary explosive. Conventional compositions based on tetrazene have good sensitivity and good priming power but have the drawback of an alteration of these properties under the action of temperature. The conventional compositions based on lead thiocyanate have a good sensitivity which is not altered by temperature, but they do not have a priming power; they require the introduction into the pyrotechnic chain of an element generally consisting of lead azide.

The object of the present invention is to provide an initiation composition very sensitive to percussion, at least as sensitive as the conventional compositions mentioned above, but whose properties are preserved under severe environmental conditions.

The subject of the invention is therefore an initiation composition endowed with high thermal stability sensitive to percussion and comprising a primary explosive and a sensitizing additive, characterized in that it comprises 40 to 95% by mass of a explosive with tetrazolic cycle, 2.5 to 40% by mass of an oxidizing agent and 2.5 to 40% by mass of a reducing agent.

The primary explosive can be represented by 5-nitrotetrazole, the mercury or silver salt of 5-nitrotetrazole, neutral or basic azotetrazole of silver or lead, halogenated tetrazoles and their salts, or a mixture of these.

The oxidant can be represented by potassium chlorate or perchlorate, strontium or barium, lead or manganese dioxide, potassium permanganate, sodium or potassium dichromate or a mixture of xeux, and the reducing agent with antimony sulfide, lead thiocyanate, titanium, zirconium, boron or a mixture thereof.

• 40 à 80 % en masse de sel de mercure du 5-nitrotétrazole,
• 10 à 35 % en masse de chlorate de potassium,
• 5 à 18 % en masse de thiocyanate de plomb,
• 3 à 12 % en masse de sulfure d'antimoine.

Advantageously, the initiation composition according to the invention can comprise:

• 40 to 80% by mass of mercury salt of 5-nitrotetrazole,
• 10 to 35% by mass of potassium chlorate,
• 5 to 18% by mass of lead thiocyanate,
• 3 to 12% by mass of antimony sulfide.

A result obtained by the composition according to the invention lies in the fact that it has excellent thermostability properties while retaining its sensitivity to initiation even after a long stay in a harsh environment.

Another result resides in the fact that the primer according to the invention predominantly generates a shock wave capable of initiating the charge of a projectile, such as an explosive shell provided with its percussion rocket, a shell with a hollow charge, etc. .

The preparation of an initiation composition according to the invention does not present any particular difficulties. The compounds are used as commercially available. The primary explosive is in the form of a fine powder which is preferred to sieve to about 0.2 mm. As an indication, we can do it as follows:

are introduced into a rotary mixer intended for pyrotechnic compositions and comprising the necessary safety devices, successively the following ingredients previously dried and sieved without this order being imperative: primary explosive then the reducing agent and finally the oxidant.

After suitable homogenization, a determined charge of the mixture obtained is introduced by manual or mechanical, unitary or multiple process, into cells of miniature stainless steel detonators with an internal diameter of approximately 3.8 mm, then a sealing disc is placed. paper or plastic fiber and each load is compressed with a force of around 300 daN.

The detonators thus prepared can be initiated by percussion through the shutter disc using a steel tip with a frustoconical end.

The following examples illustrate the composition according to the invention.

Example 1

• 75 % en masse de sel de mercure du 5-nitrotétrazole,
• 14 % en masse de chlorate de potassium,
• 7 % en masse de thiocyanate de plomb,
• 4 % en masse de sulfure d'antimoine.

A first series of initiators in accordance with the invention is produced according to the method taught above, having the following composition:

• 75% by mass of mercury salt of 5-nitrotetrazole,
• 14% by mass of potassium chlorate,
• 7% by mass of lead thiocyanate,
• 4% by mass of antimony sulfide.

Another series of conventional initiators is produced in the same way, containing an initiation composition containing 95% by mass of lead azide and 5% of tetrazene.

• 1) stockage ordinaire à température ambiante à 20 °C environ pendant 15 jours ;
• 2) stockage isotherme à 75 °C pendant 15 jours ;
• 3) épreuves de 10 cycles climatiques de 36 heures comportant 12 heures à + 74°C, montée en 2 heures à + 100 °C et séjour de 4 heures à cette température, descente en 1 heure à -54 °C et séjour de 14 heures à cette température puis remontée en 3 heures à + 74 °C.

These two series of initiators are subjected to the following three tests:

• 1) ordinary storage at room temperature at around 20 ° C for 15 days;
• 2) isothermal storage at 75 ° C for 15 days;
• 3) tests of 10 climatic cycles of 36 hours comprising 12 hours at + 74 ° C, rise in 2 hours at + 100 ° C and stay of 4 hours at this temperature, descent in 1 hour at -54 ° C and stay of 14 hours at this temperature then rise in 3 hours to + 74 ° C.

The six groups of initiators for shooting are then tested on a fall sheep with initiation by a frustoconical striker propelled by a 3.2 g ball falling from a variable height according to the Bruceton sequential method making it possible to determine the sensitivity to the percussion. In addition, the apparatus includes a base allowing the estimation of the priming power by detonation, behind a variable aluminum barrier, of a charge of 50 mg of pentrite whose regime is verified by piercing or non-drilling of a 2 mm thick steel witness plate.

The results obtained are given in the table below in drop height with an explosion probability of 0.5 for the sensitivity, and in limit thickness of aluminum barrier for the priming power with respect to the pentrite.

It can be seen from reading this table that the primers according to the invention practically retain their characteristics of sensitivity and power after each of the tests, while the conventional primers are greatly degraded, especially in sensitivity.

Example 2

• 50 % en masse de sel de mercure de 5-nitrotétrazole,
• 29 % en masse de chlorate de potassium,
• 14 % en masse de thiocyanate de plomb,
• 7 % en masse de sulfure d'antimoine.

A third series of initiators in accordance with the invention is produced according to the method taught above, having the following composition:

• 50% by mass of 5-nitrotetrazole mercury salt,
• 29% by mass of potassium chlorate,
• 14% by mass of lead thiocyanate,
• 7% by mass of antimony sulfide.

• 25 % en masse de thiocyanate de plomb,
• 13 % en masse de sulfure d'antimoine,
• 52 % en masse de chlorate de potassium,
• 10 % en masse de pentrite (PETN).

A fourth series of conventional initiators is preferably produced in the same way as a reference, preferably containing:

• 25% by mass of lead thiocyanate,
• 13% by mass of antimony sulfide,
• 52% by mass of potassium chlorate,
• 10% by mass of pentrite (PETN).

These two series of initiators are subjected to the three tests described in Example 1 above, the sensitivity measurements being carried out in the same way. The results are collated in the following table (value in mm):

It is found that the initiators according to the invention produce in a very short time a deflagration similar to those which are necessary at the head of certain pyrotechnic chains such as those with short delay for example. They have a very good sensitivity which is little modified after each of the tests unlike the conventional primers which provide widely dispersed results.

Claims (6)

1. A priming composition with an elevated thermal stability at a temperature about 100°C, sensitive to percussion for generate a shock wave likely to prime directly the charge of a projectile, comprising a primary explosive and a sensitivity additive, wherein it comprises 40 to 95 weight percent of an explosive having a tetrazole part, the additive being represented by 2,5 to 40 weight percent of an oxidising agent and 2,5 to 40 weight percent of a reducing agent.

2. Composition of claim 1, wherein the primary explosive is represented by 5-nitrotetrazole, the mercuric or silver salt of 5-nitrotetrazole, neutral or basic silver - or lead-azotrazole, halogenated tetrazoles and their salts, and a mixture thereof.

3. Composition of claim 1 or 2, wherein the oxidizing agent is selected from the group consisting of potassium or sodium chlorate, potassium or sodium perchlorate, calcium or strontium or barium nitrate, lead or manganese dioxide, sodium or potassium permanganate, sodium or potassium dichromate, or a mixture thereof, and wherein the reducing agent is selected from the group consisting of antimony sulfide, lead thiocyanate, titanium zirconium, boron, and a mixture thereof.

4. The composition of claim 3, comprising :

40 to 80 weight percent of a mercuric salt of 5-nitrotetrazole,

10 to 35 weight percent of potassium chlorate,

5 to 18 weight percent of lead thiocyanate, and

3 to 12 weight percent of antimony sulfide.

5. The composition of claim 4 comprising :

75 weight percent of a mercuric salt of 5-nitrotetrazole,

14 weight percent of potassium chlorate,

7 weight percent of lead thiocyanate, and

4 weight percent of antimony sulfide.

6. The composition of claim 4 comprising :

50 weight percent of a mercuric salt of 5-nitrotetrazole,

29 weight percent of potassium chlorate,

14 weight percent of lead thiocyanate, and

7 weight percent of antimony sulfide.