EP2947063A1 - Method for increasing pressure of a composite charge - Google Patents

Abstract

The inventive method for maximizing blast performance proceeds as follows. For a given explosive charge formulation, add stoichiometrically the same amount of fuel powder that all metal ions can be oxidized with the entrained oxygen of the charge (without atmospheric oxygen). The C atoms, H atoms, etc. are later further oxidized by atmospheric oxygen. This maximizes blast performance.

Description

The invention relates to a method for increasing the pressure of a composite charge containing at least one explosive, an inert or energetic binder and a reactive metal powder.

Modern conventional and insensitive explosive charges contain mainly explosives such as RDX (hexogen) or HMX (octogen), mixed with plastic binders such as HTPB (hydroxyl-terminated polybutadiene). RDX is less sensitive than HMX and is often used for pressure-boosted explosive charges, for example, if high shock-wave immunity is required. HMX, on the other hand, is somewhat more powerful in terms of accelerating metal builds or sheaths, and is more likely to be used when the focus is on splitter performance rather than sensitivity.

Recently, other new explosives such as CL20, Fox 7, ... Fox 12 etc. gain in importance. In addition, instead of inert plastic binders (such as the mentioned HTPB), energetic binders (for example GAP) are used.

Increasing the pressure effect, more commonly known as "blast enhancement", can be achieved by admixing reactive metal powders (e.g., aluminum, boron, silicon, magnesium, etc.). The shape and size of the metal particles play an important role in the blast increase. Such charges are then referred to as "composite charge". Other ingredients such as plasticizers, adhesion promoters, etc. are added as needed. Such a combination is then referred to as formulation of the charge.

So far, the procedure for the above-mentioned optimization of the blast performance is such that formulations are produced (eg RDX / Al / HTPB) by varying the amount of ingredients in different proportions and then testing these cargoes for their performance in mostly large series of experiments. This procedure is time-consuming and cost-intensive.

The DE 40 02 157 A1 describes various examples of polymer-bound explosives, aiming at optimizing the mechanical properties.

In " Performance of High Explosives in Underwater Application. Part 2: Aluminized Explosives ", E. Strømsøe and SW Eriksen, Propellants, Explosives, Pyrotechnics 15, 52-53 (1990 ), various RDX / Al blends are described and compared for suitability to underwater loads.

From the DE 10 2005 011 535 A1 An explosive has become known which has an improved blast behavior above and below water due to the mixture with hydrogen-terminated silicon single crystal powder which has at least one particle size range.

That a composite explosive can be put together in a nearly stoichiometric ratio, is from the US 2004/0256038 A1 remains open, to which reaction equation refers to this statement.

To avoid the above drawback, this invention has for its object to provide a method for maximizing the blast performance of a charge, in particular for bunker control, which has the formulation of an explosive charge with optimized blast performance in a short time to result.

This object is achieved by first determining the proportion by weight of the explosive depending on the intended application, then the proportion by weight of the metal powder used as fuel according to the proviso is determined, and that each individual metal particle is completely oxidized with the entrained oxygen, wherein the minimum size of the metal particles is determined depending on the minimum time within which each metal particle is oxidized.

Further characteristic features of the method can be found in the subordinate claim.

To understand the process, a certain amount of detailed knowledge about the course of a detonation of an explosive charge is helpful. This knowledge, which also includes the core of the maximization process, is novel and has been developed in extensive test series.

• Phase I:
  • detonative Phase: Durchdetonation der Ladung (Zeitrahmen: 10 - 20 µsec);
• Phase II:
  • anaerobe Phase: Expansion der Detonationsschwaden ohne Zugabe / Vermischung mit Luftsauerstoff (Zeitrahmen: einige msec);
• Phase III:
  • aerobe Phase: Nachverbrennung unter Zusatz von Luftsauerstoff, durch Verwirbelung der Schwaden mit Luft (Zeitrahmen: 50-100 msec)

A detonation takes place in three phases:

• Phase I:
  • detonative phase: detonation of the charge (time frame: 10 - 20 μsec);
• Phase II:
  • anaerobic phase: expansion of the detonation swaths without addition / mixing with atmospheric oxygen (time frame: a few msec);
• Phase III:
  • aerobic phase: afterburning with the addition of atmospheric oxygen, by swirling the swaths with air (time frame: 50-100 msec)

In phase I and II so the oxidation and thus the energy can be accomplished only by the entrained oxygen. Only in the third phase III it comes to mixing with atmospheric oxygen and thus to afterburning. Almost all military explosive charges have an oxygen sub-balance, that is to complete conversion (post-combustion) they need oxygen from the air. This is especially the case if you add in addition Adds fuels such as reactive metal powder. This is exactly the method to increase the degree of reaction and thus the blast performance.

For example, in RDX- and HMX-containing explosive charges (so-called CHNO explosive charges), the C and H atoms are oxidized to CO ₂ and H ₂ O. The N atoms usually behave "neutrally" and combine to form N ₂ . Addition of additional metal powder (such as Al) leads to further oxidation, such as Al ₂ O ₃ .

Due to the above-mentioned oxygen sub-balance, during the detonation (in phases I and II) there is a "competition" between the individual fuels (eg C, H, Al) for the oxygen and not all atoms / molecules can be saturated with oxygen , However, the metal powder (eg Al) gives most of the combustion energy in oxidation, and it is usually very affine to oxygen, ie it oxidizes very easily and quickly (depending on grain size and shape). However, this requires a certain minimum temperature (for Al ₂ O ₃ in the order of 2000 K), which must not be undercut. In the anaerobic phase, the temperature within the gas ball is sufficiently high and there is enough time to oxidize all metal powder.

The method according to the invention for maximizing blast performance now proceeds as follows. For a given explosive charge formulation, add stoichiometrically the same amount of fuel powder that all metal ions can be oxidized with the entrained oxygen of the charge (without atmospheric oxygen). The C atoms, H atoms, etc. are later further oxidized by atmospheric oxygen. This maximizes blast performance.

The aim is to optimize the blast performance of any explosive charge formulation of the above-mentioned compositions by this procedure, ie to find the local maximum in a multi-dimensional parameter space on without to have to fall back on a purely statistical, time / cost consuming procedure and at the same time be able to do without extensive test series.

The first step of the method involves assembling the necessary explosive charge components. Emphasis will be placed on the suitability of the optimized charge for a particular application. For example, this relates to shockwave immunity in a planned bunker fight. Here, RDX is an explosive. For the other components is usually similar.

The second step is to optimize the blast performance. For this purpose, you add more fuel usually in the form of reactive metal powders, such as aluminum powder. Here, the key point of the maximization method according to the invention comes into play. The intrinsic oxygen balance must always be taken into account for any mixture of components. The oxygen content must be stoichiometrically sized so that each metal particle is saturated during the detonation with oxygen, so it can be completely oxidized.

In the third step, the selection of the type and condition of the metal particles takes place. In order for this point to be met, certain conditions must be observed by the specialist. In particular, the size and shape of the particles are crucial. Rapid oxidation of all powder particles during the anaerobic phase must be possible, otherwise the maximum will not be reached. If the particles are too large, the entire particles can not burn during the detonation phase. If they are too small, the relative proportion of the surface oxide layer which is usually present is too large and energy is lost again. The minimum size thus results from the available time (in the detonation phase) within which the metal particles must be completely oxidized. In addition, too small particles would be difficult to process because of increasing viscosity due to the rapidly increasing cumulative surfaces with decreasing radius, all of which must be wetted by the binder.

The possible inertia of the oxidation reaction is another parameter that has to be taken into account: boron, for example, is relatively inert and requires a reaction catalyst, which can be accomplished, for example, by admixing Al powder.

The size of the metal particles can not be chosen arbitrarily. Known charges contain aluminum particles with an average grain size of 35 μm. This has been reduced to an average value of 4 μm in the context of the preparatory work for this invention, which has proven to be particularly advantageous. A further reduction in the size of the particles brings no further increase, since the combustion of the micron particles is already fast enough to be completed in the above-mentioned phase II. On the contrary, a reduction to the nanometer range causes numerous disadvantages.

Another possibility for improving the combustion reaction would be the so-called "coating" (ie the coating) of small metal particles with, for example, RDX or HMX or the like, or by passivating measures. This is technically possible at the moment but has to be decided on a case by case basis. As a result, the disturbing oxidation of the particle surface could be avoided.

A charge optimized in the manner described for outdoor detonations, in which, in particular, the complete oxidation of the added fuel / metal powder has been taken into account and made feasible, achieves a maximum shock wave solely on the basis of the procedure and without having to carry out a long series of experiments.

The shock wave dissolves in the detonative phase (I and II) of the fireball, any aerobic post-reactions come too late for an increase in energy of the shock wave. If all metal powder is oxidized during this phase, maximum energy release is achieved, the maximum blast effect. If one had less metal powder in the formulation, one would "give away" oxygen to the C and H atoms and thus lose energy, since the oxidation of these atoms supplies less combustion energy. If too much metal powder had been added, these "superstoichiometric" metal ions would not be oxidized and one would not have reached the optimum point either. So there is a stoichiometric optimal mixture, in which all metal ions get their oxygen content, then the blast performance is maximum.

The optimization of the charge for indoor detonations differs from the charge for outdoor detonations. Typically, such explosive charges have metal sheaths (e.g., steel sheaths) for structural integrity, integration with a missile, and the like. In indoor detonations this is especially true because the explosive charge must be spent in the interior before detonation, i. The cargo must also perforate walls on board a penetrator.

In addition to the above-mentioned oxidation of all fuel / metal powder must now be ensured that all other combustion products (such as C, CO, OH ...), which are not yet saturated with oxygen, now fully oxidized (post-combustion reactions). The oxygen required for this purpose must be taken from the air, for which a thorough mixing of the combustion products with the air is necessary.

Existing metal shells of the charge can be more of a hindrance, since they must first expand radially and depending on the ductility and further nature of the metal shell more or less late tear and only then release the detonation products and bring into contact with the air. During this expansion phase However, the gases cool down. If the temperature falls below a critical temperature (for example, about 2000 K for aluminum), the chemical reactions are prevented and the afterburning stops or does not even begin.

To prevent this, precautions must be taken. This can be done in many ways. For example, material properties such as ductility or brittleness, design / geometry of the load such as wall thickness and finally predetermined breaking points are to be mentioned.

These measures or combinations of measures must ensure that all combustion products are completely oxidized and that the reactions are not stopped. In this way, in turn, the maximum of the blast power is given.

In a real interior detonation, the effect is implemented by means of quasi-stationary pressure (momentum). Although all molecules that are not saturated with oxygen can react afterwards. In practice, this does not always succeed, which is due to the necessary high reaction temperature.

In the following, the procedure according to the invention for maximizing the blast power is to be applied by way of example to a charge with aluminum powder. For this charge, the maximum obtained was validated by a conventional statistical approach, in which long and extensive series of tests were performed which confirmed the forecast maximum for both free-field and indoor detonations.

• RDX / Al / HTPB mit den Massenprozenten 67/18/15.

An existing explosive charge with Al powder is known as KS22, with the formulation:

• RDX / Al / HTPB with mass percentages 67/18/15.

• RDX / Al / HTPB mit den Massenprozenten 58/27/15

die in Analogie zu KS22 als KS23 bezeichnet werden soll.This explosive charge is not optimized with regard to the blast effect. Adding further aluminum powder until reaching the stoichiometric saturation point (according to the maximization procedure) gives the following formulation:

• RDX / Al / HTPB with the mass percentages 58/27/15

which should be referred to as KS23 in analogy to KS22.

Extensive trials in both open air and bunker systems (enclosed space and open spaces with windows and doors) confirmed the maximization of blast performance. The formulation is chemically different from KS22, but quite similar from the procedural point of view, so that similar manufacturing processes can be applied and thus the reproducibility etc. can be guaranteed.

Claims (2)

Process for increasing the pressure of a composite charge containing at least one explosive, an inert or energetic binder and a reactive metal powder,
characterized in that is used as an explosive RDX with a weight fraction of about 58%, the proportion by weight of the metal powder used as fuel is determined according to the proviso that each individual metal particle is completely oxidized with the entrained oxygen, - That that the grain size of the particles of the metal powder, depending on the particle shape and depending on the minimum time within which each metal particle is oxidized, is selected in the range of 1 .mu.m to 10 .mu.m. A method according to claim 1, characterized in that the grain size of the particles of the metal powder is selected in an average size of 4 microns.