DE69003627T2 - Primer composition for pyrotechnic delay element. - Google Patents

Description

The present invention belongs to the technical field of ignition charges with integrated technical delay for ammunition or a security defense device (DSA).

The delay fuse type pyrotechnic delays consist of an ignition charge, a pyrotechnic mixture with a delaying effect in a metal casing and possibly an explosive as an output relay. They are used within a pyrotechnic chain to create a delay.

Numerous pyrotechnic delays have already been proposed in order to achieve a burning rate of a few centimetres per second. In this context, patents US-A-4 144 814 and FRA-A-2 464 932 should be mentioned, which describe such ignition delays in detail. However, these ignition charges are always ignited electrically via a wire resistor, not by impact, so that they cannot be used for ammunition or a safety defence device. In addition, it is still impossible to ignite delay mixtures with a diameter of less than 3 mm.

When designing an ammunition or a safety defence device, it is often advantageous to resort to a delay by means of a pyrotechnic delay charge. The usual solution is to define a delay specifically for the system under study, usually a metal sleeve with a delay mixture pressed into it. Such a delay works accurately and reliably, but requires a relatively large amount of space, ie if adjustment of the delay time is required (as in the case of some rocket mortar projectiles), space requirements make it necessary to introduce the pressed delay mixture by mechanically moving one of the rocket parts (delay carrier or relay carrier) in closer or closer to the ignition relay. Such a solution is not very satisfactory because it results in a certain inaccuracy.

As a result, many delay problems have not yet found a pyrotechnic solution and we are forced to resort to more complex delay techniques (e.g. timers), which are often more space-consuming and expensive.

The purpose of the present invention is therefore to offer an ignition system for a pyrotechnic delay with percussion ignition that can be incorporated into a munition or security defense device, at low cost and of small diameter.

The purpose of the present invention is therefore to offer an ignition system for a pyrotechnic delay with impact ignition which is characterized in that it consists of a first impact ignition mixture and a second mixture of titanium and boron powder.

The first mixture may be a pill of potassium chlorate, lead thiocyanate, antimony sulfide and lead styphnate.

The second mixture can consist of 80% titanium powder and 20% boron powder.

The first mixture can be compressed at a pressure of 0.5.10⁸ to 2.10⁸ Pa, the second mixture at a pressure of 0.5.10⁸ to 2.5.10⁸ Pa.

The invention further relates to the use of this ignition system in the manufacture of a delay fuse surrounded by a metal sleeve, the outer diameter of which is less than or equal to 3 mm, with a pyrotechnic mixture, the burning rate of which is less than or equal to 4 mm/sec.

An advantage of the present invention is that it provides an ignition system that is simple to manufacture, easy to use and small in size.

A further advantage is the fact that the ignition mixture ignites delay fuses of small diameter, i.e. less than or equal to 3 mm. This means that the properties of known delay mixtures can be used in devices where this was previously impossible.

A further advantage lies in the fact that the delay mixture can be ignited without disorganization or destruction of the cell containing it, thus avoiding disruption of the ignition chain.

Further advantages of the invention emerge from the following additional description.

The retarder mixture itself is widely known in specialist circles. It consists of tungsten, barium chromate and potassium perchlorate, e.g. in the following weight percentages: 28, 62 and 10. The properties of this mixture are used, i.e.:

- combustion that releases few gases, thus reducing the risk of projecting residues and of disorganising any component of the ignition chain or even damaging the safety device,

- Safety during use and storage due to low sensitivity,

- excellent ageing behaviour (service life), 20 years at 20ºC, i.e. far longer than the storage time of most other ammunition, so that no inspection is required during this period.

However, it is known that this mixture has a disadvantage: it is difficult to ignite because it requires a lot of combustion heat.

Therefore, a special, guaranteed reliable and safe ignition mixture had to be defined, which has a high specific calorific value during the relatively long period of a few milliseconds.

This igniter consists of a percussion ignition mixture in combination with a titanium-boron mixture. Both mixtures are known as such, but have never been used together, and there is no known industrial use of the titanium/boron mixture in pyrotechnics.

The titanium-boron mixture has certain properties that make it particularly suitable for the intended use:

- a high specific calorific value,

- a completely gas-free combustion, i.e. without the risk of projection of residues or disorganization of the titanium-boron pill, which could affect the contact between this mixture and the delay mixture and thus prevent combustion transfer,

- raw materials (titanium and boron) without pyrotechnic character, easy and safe to use, which increases manufacturing safety,

- Ignition of the delay mixture by a combustion front.

The granulometry of the titanium and boron powder has no significant influence on the performance of the ignition mixture. The titanium powder has an average grain size of approx. 15 µm, the boron powder 1.2 µm.

Since it is impossible to ignite the titanium-boron mixture by impact, an ignition mixture must be provided. This consists of a pill of potassium chlorate, lead thiocyanate, antimony sulphide and lead styphnate. This mixture is well known and can be easily ignited by impact. Its energy is sufficient to ignite the hot titanium-boron mixture without disorganising it or destroying the cell. Its Impact energy is approximately 0.1 joules and it generates a high initial energy of approximately 100 joules. The deflagration of this mixture is not transferred to the titanium-boron mixture or to the pyrotechnic delay mixture.

With these two mixtures you can make a very small igniter, 4 mm in diameter and 5 mm high.

A delay is therefore created from a head fuse pressed onto one end of a metal sleeve. This metal sleeve can be made of lead or tin, for example, with an internal diameter of about 3 mm. At the other end of this fuse cord there is an output relay, which is made in the usual way and is not described further here.

The head ignition consists of a cell into which the first ignition mixture and the second mixture have been pressed. The cell has an opening for the firing pin at its end, which is tightly closed by a thin plate.

Industrially, the delay fuse is manufactured from a large-diameter sleeve that is cut to a specific length and filled with the delay mixture.

After sealing the ends, this tube is placed in a machine and rolled between rollers until the desired diameter is reached, the length of the fuse obviously depending on this diameter.

For example, fuses with a tin sleeve with an outer diameter of 3 mm can be made from a sleeve with an outer diameter of 17 mm. During this production, the delay mixture is exposed to a pressure that can be up to several hundred Pascals. However, as the tests carried out have shown, the compression of this mixture has no significant influence on the burning rate.

Various functional tests have proven the reliability of the pyrotechnic delay set, the pyrotechnic components are precisely determined and the quantities optimized. This results in the following mixtures (in weight percent):

- first mixture: 25 mg, pressure 10&sup8; Pa,

Potassium chlorate ... 52 %

Lead thiocyanate ... 25 %

Antimony sulphide ... 13 %

Lead styphnate ... 10 %

- second mixture: 80 mg, pressure 1.5.10&sup8; Pa,

Titanium ... 81.6%

Boron ... 18.4%

- a lead plate 0.05 mm thick,

- Fuse with tin or lead sleeve, outer diameter 3 mm

- Delay Mix:

Tungsten ... 28%

Barium chromate ... 62 %

Potassium perchlorate ... 10 %

The grain size of the tungsten is less than 20 um.

About fifty delays with the above proportions were ignited. No misfire was observed, although the impact energy is about 0.1 joules; with a 10 cm long fuse, the following results are obtained:

- maximum duration 15.9 sec.

- minimum duration 14.03 sec.

- average duration 14.8 sec.

- Standard deviation 0.45.

This design shows satisfactory performance.

The set is tested by setting minimum bending radii. There are no misfires and the operating times in this case vary between 14.54 and 15.98 seconds, values comparable to those obtained with a straight fuse. From these tests it can be seen that the use of gas-free mixtures that do not cause projections, destruction of the fuse casing or failure Furthermore, it is interesting to note that even under such unfavourable conditions the combustion is perfectly transmitted, despite the fractures resulting from the bends with very small radius.

Another series of tests dealt with the use at low temperatures, which are among the most difficult operating conditions of all, of four pyrotechnic delay sets that were placed in a climate chamber at -40ºC for 2H30. After that, their operating time fluctuated between 14.90 seconds and 15.83 seconds, i.e. it was quite comparable with the values that result at normal ambient temperature.

In addition, the retarder mixture was tested for its ageing ability, whereby a service life of over 20 years can be expected at 30ºC and around 10 years at 60ºC.

The delay according to the invention can be used whenever one wants to obtain the following properties:

- very slow burning rate (2 mm/sec), i.e. a long delay time with a fuse of small length and size, which is particularly important for built-in devices,

- The flexible fuse, which works well despite all the bends, makes it easier to install in a system,

- good repeatability of performance, which is not significantly influenced by the operating conditions,

- Maintaining performance at low temperatures,

- good ageing ability.

Other ignition mixtures, in which the respective proportions of titanium and boron vary between 68% and 32% on the one hand and 81.6% and 18.4% on the other, have also been tested successfully. If the titanium is partially replaced by zirconium, the same results are obtained.

Claims (5)

1 - Ignition composition for pyrotechnic delay element which can be ignited by percussion, characterized in that it consists of a first mixture for initial ignition by percussion and a second mixture of titanium and boron powder. 2 - Ignition composition according to claim 1, characterized in that the first mixture is a pressed part of potassium chlorate, lead thiocyanate, antimony sulfide and lead typhnate?. 3 - Ignition agent composition according to claim 2, characterized in that the second mixture consists quantitatively of 80% titanium powder and 20% boron powder. 4 - Ignition agent composition according to claim 3, characterized in that the first mixture is compressed at a pressure of 0.5.10⁸ to 2.10⁸ Pa, the second mixture at a pressure of 0.5.10⁸ to 2.5.10⁸ Pa. 5 - Use of the ignition composition according to one of the above claims in the manufacture of a detonation fuse integrated into a metal casing with an external diameter of less than or equal to 3 mm, which contains a pyrotechnic mixture which burns at a speed of less than or equal to 4 mm/sec.