GB1588621A - Method for the production of moulded high explosives - Google Patents

Description

(54) METHOD FOR THE PRODUCTION OF MOULDED HIGH EXPLOSIVES (71) We, MEssERscHMITT-BoLKow- BLOHM GESELLSCHAFT MIT BESCHRANKTER HAFTUNG, of 8000 Munchen, German Federal Republic, a company organised and existing under the laws of the German Federal Republic, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a method for the production of moulded high explosives, in which a high proportion of at least one nonmelted (solid) high explosive substance, particularly hexogen, in various grain sizes, is combined with a smaller proportion of at least one melted or fused explosive substance, particularly TNT, and if necessary a binding agent or wax.

Moulded explosives having these constituents are described in German Patent 1 207 842.

Highly explosive moulded bodies produced in this way are used in particular for hollow charges which are required to have high explosive power density, rotational symmetry and chemical and physical homogeneity and also, as a means of preventing cracks, insensitivity to temperature variations and mechanical strains.

It is only by provision of these properties that the formation of a faultless hollow charge spike of maximum penetrating capacity can be ensured. Compression of solid highgrade hexogen as described in the German Patent referred to above provides the condition for high specific explosive power. The homogeneity of the charge and its non-cracking properties ensure symmetrical formation of an armour piercing spike from a metal liner of a hollow change, and these conditions, combined with guiding of the detonation shock waves, the type of liner and the liner cone angle, ensure a sharp, elongated and thus penetrative spike of which the constituent parts follow one another in exact succession.

High explosive moulded bodies of this kind are produced by the casting of a suspension having the two explosive components in question, one of them being present in the liquid and the other in the solid phase. The casting of explosive masses of this kind is not only expensive from the point of view of the apparatus involved, and also time consuming, but is liable to lead, unless certain production parameters can be maintained, to an unacceptable worsening of the quality or to defects in the explosive charges.

Extreme temperature fluctuations, to which the warheads are subjected under desert and Arctic conditions, may lead to considerable internal stresses in the explosive moulded body causing cracks to form. This tendency is aggravated by the fact that the chemical explosive has considerably greater positive and negative expansion than the metal warhead casing. In addition, the chemistry of the explosives as such renders them liable to relatively rapid ageing forming cracks, particularly longitudinal cracks and cracks in the front part of the charge in the vicinity of the lining. These have a disastrous effect on the formation of a penetrative spike, inasmuch as in the zone of the longitudinal cracks the detonation front is in advance, resulting in a rotationally asymmetrical collapse state and in a scattered spike with only a fraction of the penetrating capacity.

Research and experiment have shown that various parameters, in the production of hollow charges by casting, govern their resistance to cracking and also their mechanical strength. It is known, for example, that when the molten TNT in the explosive suspension solidifies (the melting point being 80.60C), this results, according to the crystallization point, in various crystal forms of TNT, with different porperties.

If the crystallization point is above 70"C, e.g.

about 75 C, this results in large elongated crystals which connect satisfactorily with the adjacent hexogen grains and are highly resistant to cracks liable to occur as a result of internal stresses caused by high temperature fluctuations and external forces. On the other hand, crystallizations with a low setting point, e.g.

50-65"C, result in a finely crystalline structure, giving unsatisfactory results as regards strength and producing charges liable to develop cracks.

The decisive parameters for the control of the temperature level of the setting point for the TNT melt are the upper temperature limit of the melted TNT and the time for which the already molten TNT is kept at this temperature.

This is the casting temperature at which the heated suspension is poured into the moulds or immediately into the actual warhead casings.

Experiments have shown that if it is kept at the casting temperature for too long, for example over four hours, the setting point will be lowered (to below 70O) just as in the case of an excessive casting temperature, which for this reason should not be allowed to exceed 95 0C, or 1000C at the most.

Experiments have confirmed that the crystallization occurring when the melt cools is caused by so called crystallization nuclei, the crystallization starting from these latter and then proceeding very rapidly. The crystallization nuclei themselves consist, it is believed, of individual crystals or crystal residues which have remained in the liquid phase and which only exist for a certain limited period and only up to a certain temperature above melting point, after which they disappear completely.

The crystallization process is accompanied by interaction between the level of the temperature and the maintenance time for the heating temperaftire, i.e. the higher this heating temperature for the melting of the less highly explosive constituents of the explosive or the higher the casting temperature, the shorter must be the time for which the melt can remain at this temperature, to enable crystallization nuclei to survive in the melt. The converse also applies: the longer the maintenance time required, the lower must be the heating temperature (casting temperature), that is the less it may be allowed to exceed the melting point.

In this connection reference is made to our copending application No. 4436/76 (Serial No.

1588622).

On the other hand, it is desirable, particularly when warheads are mass-produced on an industrial scale, to adopt as high a casting temperature as possible, so that the suspension will remain easily castable, resulting in a cast body with a better cast structure and assisting sedimentation, or reducing the sedimentation time for a given sedimentation density. TNT melts at 80.6 C. The tolerance zone between the low temperatures required to obtain as high a crystallization point as possible, on the one hand, and the higher casting temperatures required from the point of view of the castability of the explosive suspension, on the other hand, is not very wide, in industrial mass production, if the casting quantities (size of batches) are to be economical.Furthermore, as already mentioned, the maintenance time for the casting temperature is a decisive factor, because the melt, throughout the entire casting time, that is even when the last of the moulds is being filled, has to be kept liquid and above its setting point.

In the mass production of highly explosive moulded bodies on an industrial scale, however, it has now been found that it is not always possible to adhere to the necessary comparatively narrow manufacturing tolerances as regards the aforementioned temperature limits and constant heating times, owing to the variations in the chemistry of the starting materials, the fluctuations in the apparatus and the inaccuracies in the dimensions and measurements of the apparatus employed. On the other hand full effectiveness of every warhead when used must be guaranteed.

This invention seeks to provide for moulded high explosives, a simplified production process which will be more economical, less expensive to operate, and more suitable and time-saving for industrial mass production as well as ensuring, at the actual production stage that they will be fully efficient when used for military purposes.

According to this invention there is provided a method for the production of moulded high explosives with a high proportion of at least one high explosive which is not melted at the production stage, and a low proportion of at least one other explosive which is melted at the production stage, in which method the high explosive used is a granular high explosive the grains of which are coated with the other explosive and then introduced, at room temperature, into a mould or a warhead casing and heated therein to above the melting point of the other explosive until all the other explosive has melted after which the melt is cooled slowly to prevent cracking.

A preferred starting material consists of a mixture of hexogen desensitized with TNT the hexagen having a grain size of 200-800,um, and accounting for about 70% of the weight of the entire quantity of hexogen, and hexogen desensitized with TNT the hexagen having a grain size of 1580um, and accounting for about 30% of the weight of the entire quantity of hexogen, the TNT accounting for 15-25% by weight of the entire quantity of explosive substance.

The mould or warhead casing or the cabinet in which the moulds or warhead casings are heated together with the explosive fillings can be subject to reduced pressure. This assists or intensifies the flow of the molten part of the explosive into the spaces between the individual grains of the solid part of the explosive, so that the charges are rendered more homogeneous and the porosity reduced.

Owing to the fact that in the method of the invention the melting of the explosive suspension takes place inside the mould or warhead casing and the actual filling is effected in a cold state, the production process is greatly simplified, as regards the apparatus involved, and the production times are considerably shortened.

The manufacturing process of the invention however, is not only more economical but also offers qualitative advantages, inasmuch as the critical temperatures and maintenance times can be adhered to without difficulty, and are controllable.

The heating of the mass filled into the mould can be effected in such a way that in the case of hexogen and TNT for example, the mass is first kept at a temperature below the melting point of TNT (80.6go) until the entire mass has reached this preliminary temperature (750C) throughout, and is only then heated to above the melting point of TNT, (about 92"C) so that this maximum temperature only.has to be maintained for a short time in order to cause the entire melt to reach the maximum temperature (92"C). This ensures that peripheral parts of the charge or the TNT do not have to be kept at 92"C longer than desired, which would lead to an undesirable reduction of the crystallization point in the subsequent cooling process.

The initial mass, particularly hexogen desensilized with TNT is readily available and can be stored in this form in a simple manner and with relatively little risk. In the production of this starting substance the hexogen moistened with liquid TNT (desensitized) forms in the heated mixing vessel, in various grain sizes, in clusters of considerable density, and it retains this form in the cold state; there is no subsequent demixing.

Octogen can be used in place of hexogen and trinitrobenzene in place of TNT.

The explosives may incorporate synthetic or natural waxes, and bonding agents, for example plastics in the form of thermoplastics with a low melting point, such as polyvinyl chloride, polyethylene and polypropylene.

WHAT WE CLAIM IS: 1. A method for the production of moulded high explosives with a high proportion of at least one high explosive which is not melted at the production stage, and a low proportion of at least one other explosive which is melted at the production stage, in which method the high explosive used is a granular high explosive the grains of which are coated with the other explosive and then introduced, at room temperature, into a mould or a warhead casing and heated therein to above the melting point of the other explosive until all the other explosive has melted, after which the melt is cooled slowly to prevent cracking.

2. A method in accordance with Claim 1, wherein the high explosive is used in various grain sizes.

3. A method in accordance with Claim 1 or 2, wherein the starting material used is a mixture of hexogen desensilized with TNT, the hexogen having a grain size of 200-800pm, accounting for about 70% of the weight of the entire quantity of hexogen, and of hexogen desensitized with TNT, the hexogen having a grain size of 15-80,um, accounting for about 30% of the weight of the entire quantity of hexogen, the TNT accounting for 15-25% by weight of the entire quantity of the explosive substance.

4. A method in accordance with any one of Claims 1 to 3, wherein the mould or the warhead casing, or a heating cabinet in which the moulds or warhead casings are heated together with the explosive filling, are subject to reduced pressure.

5. A method in accordance with Claim 1 carried out substantially as herein described.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. can be adhered to without difficulty, and are controllable. The heating of the mass filled into the mould can be effected in such a way that in the case of hexogen and TNT for example, the mass is first kept at a temperature below the melting point of TNT (80.6go) until the entire mass has reached this preliminary temperature (750C) throughout, and is only then heated to above the melting point of TNT, (about 92"C) so that this maximum temperature only.has to be maintained for a short time in order to cause the entire melt to reach the maximum temperature (92"C). This ensures that peripheral parts of the charge or the TNT do not have to be kept at 92"C longer than desired, which would lead to an undesirable reduction of the crystallization point in the subsequent cooling process. The initial mass, particularly hexogen desensilized with TNT is readily available and can be stored in this form in a simple manner and with relatively little risk. In the production of this starting substance the hexogen moistened with liquid TNT (desensitized) forms in the heated mixing vessel, in various grain sizes, in clusters of considerable density, and it retains this form in the cold state; there is no subsequent demixing. Octogen can be used in place of hexogen and trinitrobenzene in place of TNT. The explosives may incorporate synthetic or natural waxes, and bonding agents, for example plastics in the form of thermoplastics with a low melting point, such as polyvinyl chloride, polyethylene and polypropylene. WHAT WE CLAIM IS:

1. A method for the production of moulded high explosives with a high proportion of at least one high explosive which is not melted at the production stage, and a low proportion of at least one other explosive which is melted at the production stage, in which method the high explosive used is a granular high explosive the grains of which are coated with the other explosive and then introduced, at room temperature, into a mould or a warhead casing and heated therein to above the melting point of the other explosive until all the other explosive has melted, after which the melt is cooled slowly to prevent cracking.

2. A method in accordance with Claim 1, wherein the high explosive is used in various grain sizes.

3. A method in accordance with Claim 1 or 2, wherein the starting material used is a mixture of hexogen desensilized with TNT, the hexogen having a grain size of 200-800pm, accounting for about 70% of the weight of the entire quantity of hexogen, and of hexogen desensitized with TNT, the hexogen having a grain size of 15-80,um, accounting for about 30% of the weight of the entire quantity of hexogen, the TNT accounting for 15-25% by weight of the entire quantity of the explosive substance.

4. A method in accordance with any one of Claims 1 to 3, wherein the mould or the warhead casing, or a heating cabinet in which the moulds or warhead casings are heated together with the explosive filling, are subject to reduced pressure.

5. A method in accordance with Claim 1 carried out substantially as herein described.