GB2128177A

GB2128177A - Pressable explosive material

Info

Publication number: GB2128177A
Application number: GB08212652A
Authority: GB
Inventors: Dr Wolfgang Klohn; Dieter Heinz Muller; Dr Hilltmar Schubert
Original assignee: Fraunhofer Gesellschaft zur Foerderung der Angewandten Forschung eV
Current assignee: Fraunhofer Gesellschaft zur Foerderung der Angewandten Forschung eV
Priority date: 1980-07-18
Filing date: 1982-04-30
Publication date: 1984-04-26
Also published as: BE893143A; DE3027361C1; GB2128177B

Abstract

A high-performance explosive of suitable mechanical properties for preparing a shaped charge comprises one or more explosive substances and a polybutadiene styrene elastomer as binder. The binder may also contain polyvinyl nitrate and be present in the composition in amount of 3-10% by weight. The explosive substances suggested are RDX, HMX, PETN, di- or tri- amino trinitrobenzene, trinitrophenyl methyl nitramine, and hexanitrostilbene.

Description

SPECIFICATION Pressable explosive material The invention relates to an explosive, more particularly for shaped charges, comprising one or more explosive substances, such as hexogen, octogene, pentaerythritol tetranitrate, di- or triamino trinitrobenzene, trinitrophenyl methyl nitramine, hexanitrostilbene or the like, and at least one thermoplastic binder.

Various types of pressable or castable explosive mixtures for shaped charges are known. One example is the "Composition B" type, which comprises a mixture of hexogene and TNT, the TNT being melted and mixed with the hexogene for casting. This explosive mixture is very brittle and of relatively low strength, so that it does not satisfy current requirements for highperformance explosives. Such explosives, in addition to a detonation velocity > 8000 m/s, should have high compressive strength, good thermal stability, and low sensitivity to impact and friction and to detonation.

These requirements are better fulfilled by the PBX explosives (plastic bonded explosives).

These comprise an explosive substance such as hexogen, octogene or pentaerythritol tetranitrate and a polymeric binder. and processing aids. In addition metal additives such as aluminium powder or the like may be included to increase the effect. The binders used are reactive prepolymers with the addition of suitable hardeners which then produce corresponding crosslinking. Examples are unsaturated polyester or polyurethane casting resins. A disadvantage of these systems is the fact that the mixture must be processed within the pot time, since the hardeners used will harden even at room temperature. Also, highly crosslinked binders of this type such as unsaturated polyester resins exhibit poor mechanical properties, particularly brittleness at low temperatures.Compared with explosives of the "Composition B" type they have the disadvantage that they cannot be separated into their constituents by simple chemical or physical processes as is desirable in the inspection of munitions. To achieve satisfactory casting properties, moreover, the proportion of binder must be up to 15%, which reduces the performance (the binder being an inert substance), particularly the detonation velocity of the system.

Better results are obtained with thermoplastically deformable polymers such as Nylon (R), Teflon(R), Viton(R) or thermoplastic polyurethanes, not least because the proportion of binder is lower, at about 5%. These explosives are processed by pressing, which gives satisfactory density and compressive strength.

With these explosives, too, problems arise, however, particularly in the manufacture of large complicated moulded members. In these density variations persistently occur, causing uneven detonation. Because of the poor flowability complicated moulds (as required, for example, for shaped charges with built-in deflectors) are hard to fill and unlikely to produce satisfactory mouldings.

An object of the invention is to propose a high-performance explosive which has the desired mechanical properties, but does not suffer from the processing problems just mentioned.

In an explosive of the composition initially described, this object is achieved in that a thermoplasticaly deformable polybutadiene styrene elastomer is used as binder.

The butadiene styrene 3-block copolymer gives the processed explosive excellent elasticity, which prevents cracking within the structure of the explosive even under high stress. The explosive has excellent mechanical properties, better than those of known explosives at both low and high temperatures. Processing is particularly easy since the elastomer can be processed in solution. This means that the binder can be added to the granular explosive substance in liquid form and mixed thoroughly with it. When the solvent is evaporated (which may be performed with vacuum assistance), the binder collects on the granule of explosive substance, so producing, in a very simple process, a granulate which, once dried, out, flows well and will therefore fill the moulds thoroughly during processing.The mould containing the granulate is heated so that the binder softens and the explosive can be pressed into the shape desired. Even large or very complicated moulds which demand pressing in more than one stage present no problem, since pre-pressed parts of the mould can be joined satisfactorily to granulate poured on subsequently, as a result of heat treatment followed by pressing, The granulates can be stored as long as desired and also, in contrast to reactive polymers, processed after an extended period. There is no waste, moreover, since when particular grain sizes are desired the sieve residue can be used in a subsequent granulation process. This is not possible in the case of explosives with crosslinked binders, as the binders cannot be broken down or dissolved. This presents no problem in the case of an explosive embodying the invention.

In a preferred embodiment, polyvinyl nitrate is also used as binder. This polyvinyl nitrate may be partially substituted for the polybutadiene styrene elastomer.

The addition of polyvinyl nitrate increases the strength of the explosive, since polyvinyl nitrate acts as an adhesive, cementing the individual particles of solid material together. Polyvinyl nitrate, moreover, can be processed as indicated above. While the structure of the explosive is rendered somewhat more brittle by polyvinyl nitrate, the effect of the elastomer on the elasticity of the explosive is so great that this is still superior to known explosives overall. The inclusion of polyvinyl nitrate has the advantage that the performance of the explosive is substantially unaffected, since polyvinyl nitrate is itself an explosive with a high detonation velocity (approximately 7000 m/s).

By appropriate selection of the two binder constituents the properties of the explosive (performance, mechanical strength, density, thermal stability, etc). can be widely varied and adapted to the particular application. For example, whereas an explosive with only polyvinyl nitrate will have a particularly high detonation velocity and density, one with only polybutadiene styrene elastomer as binder will have particularly high thermal stability and high compression values.

A combination of 4% polybutadiene styrene elastomer and 2% polyvinyl nitrate has proved particularly advantageous.

Example 1 Hexogen 94% Thermoplastic polybutadiene styrene elastomer 4% Polyvinyl nitrate 2% The explosive granulate processed with the binders is placed in a mould heated to 1 1 0 C, and after adjustment of the temperature, is pressed at a pressure of 50-100 MPa to form an explosive member 21 mm in diameter and 20 mm in length. After the mould has been cooled with water, the moulded member can be ejected.The explosive members were found to have the following properties: Detonation velocity 8369 m/s j 0.21% Density 1.72 g/cm3 Gap test (for shock resistance) explosion at 16 mm water column Impact resistance 2.5 Nm Friction resistance 1 57 N (pin loading) T = 20'C Compressive strength 49.7 N/mm2 Compression 9% T= 50"C Compressive strength 32.2 N/mm2 Compression 7% T = 40"C Compressive strength 77.4 N/mm2 Compression 12% Vaporisation temperature 229"C Weight loss at 90"C, 0-48h No weight loss Extended storage at 90'C 0.4% weight loss after 40 days In another series of experiments the thermoplastic elastomer was substituted for the polyvinyl nitrate. This gave, for the next example, the following properties: Example 2 Hexogen 94% Thermoplastic polybutadiene styrene elastomer 6% This mixture was constituted and processed in a similar manner to that in Example 1.

Detonation velocity 8272 m/s + 0. 19% Density 1.72 g/cm3 Gap test (for shock resistance) explosion at 1 6 mm water column Impact resistance 3.9 Nm Friction resistance 21 2 N pin loading Test temperature T = 20"C Compressive strength 16.8 N/mm2 Compression 1 7.0 % T= 50"C Compressive strength 11.8 N/mm2 Compression 1 7.3 % T = 40'C Compressive strength 37.5 N/mm2 Compression 22.9% Vaporisation temperature 234"C Weight loss at 90"C, 0-48h No weight loss Extended storage at 90"C No weight loss after 40 days

Claims

1. An explosive, more particularly for shaped charges, comprising one or more explosive substances, such as hexagon, octogene, pentaerythritoltetranitrate, di- or triamino trinitrobenzene, trinitrophenyl methyl nitramine, hexanitrostilbene or the like, and at least one thermoplastic binder, characterised in that a thermoplastically deformable polybutadiene styrene elastomer is used as binder.

2. An explosive as claimed in claim 1, characterised in that polyvinyl nitrate is also used as binder.

3. An explosive as claimed in claim 1 or 2, characterised in that the polyvinyl nitrate is partially substituted for the polybutadiene styrene elastomer.

4. An explosive as claimed in any of claims 1 to 3, characterised in that the proportion of binder is 3 to 10%.

5. An explosive as claimed in any of claims 2 to 4, characterised in that the proportions of binder are 3 to 10% polybutadiene styrene elastomer and less than 3% polyvinyl nitrate.

6. A method of manufacturing an explosive as claimed in any of claims 1 to 5, characterised in that the or each explosive substance is mixed, the binder is added in solution, and the solvent is eliminated, forming granules.

7. A method of manufacturing moulded members such as shaped charges or the like from explosive granules manufactured as claimed in claim 6, characterised in that the granules are classified according to the desired grain size, and are then poured into the mould and pressed under the influence of heat.

8. A method as claimed in claim 7 for manufacturing, for example in multi-part moulds, moulded members which cannot be pressed in a single operation, characterised in that in a first operation part of the moulded member is finish-pressed and in a second operation the remainder of the mould is filled with granules, which are then pressed while heat is applied to the entire mould.