Improvements in or relating to explosive charges

Abstract

A concrete demolition charge is provided and comprises a shaped charge including a liner.

Description

[0001] HYDROBARIC CHARGE COMPRISING A SHAPED CHARGE INCLUDING A LINER

[0002] The present invention relates generally to explosive charges and particularly, but not exclusively, to charges, such as shaped charges, specifically for use in breaking, demolishing, or weakening concrete and concrete-based objects and structures.

[0003] Concrete is structural material consisting of a hard, chemically inert particulate substance, known as aggregate (usually sand and gravel), that is bonded together by cement (a powder made of a mixture of calcined limestone and clay) and water.

[0004] Concrete is the second-most-used substance in the world (after water) and is the most widely used building material. As a result there is often a requirement to break / demolish / weaken concrete.

[0005] The most efficient method of “blasting” concrete is to drill in hole into the concrete and place an explosive charge in the centre of the mass of concrete such that on initiation, the explosive exerts pressure from within upon which the concrete will fail, forming cracks and bursting outwards. In military applications, for example, this is normally not possible because tactics require that charges are positioned rapidly and sometimes silently so drilling is not possible. In this instance, the explosive must be placed outside the concrete and is therefore unable to produce the high internal pressures that facilitate breakup of the concrete.

[0006] The most common alternative is to position an explosive charge on the surface of the target and, if possible, to confine the explosion by placing a “tamping” medium behind the explosive to offer some resistance to the rapidly expanded gases that are liberated to enhance the efficiency.

[0007] An alternative is to shoot a projectile into the concrete so that it exerts lateral forces within the concrete as it forces its way into the concrete. This may be achieved using explosive shaped charges which typically form metallic jets travelling at velocities of 1500-8000m / s.

[0008] A typical shaped charge has a concave metal hemisphere or cone (known as a liner) backed by a high explosive, all in a casing. When the high explosive is detonated a detonation wave is generated; this causes the metal liner to be compressed and squeezed forward, forming a high velocity metallic jet. The present invention is based on observations that explosive shaped charges with a magnesium liner are significantly more effective at breaking concrete than existing charges, which are typically lined with copper.

[0009] Magnesium normally oxidises in air using the following reaction:

[0010] 2Mg + O2— >2MgO

[0011] In water, a second reaction occurs:

[0012] Mg + H2O — ►MgO + H2

[0013] This reaction is normally slow and it typically takes days or even years for this reaction to completely oxidize metallic magnesium.

[0014] When a magnesium shaped charge is fired the magnesium is travelling at hypersonic velocities and is combusting. When the shaped charge jet comes into contact with water, the high temperature and pressure accelerates the reaction which happens in fractions of a second, forming magnesium oxide and, critically, liberating gaseous hydrogen. This hydrogen then burns or explodes forming a secondary explosion.

[0015] If the magnesium jet is fired into water-containing medium, such as a mass of concrete or soil, there moisture content (e.g. in the concrete material) with which the magnesium reacts, rapidly evolving hydrogen gas which is ignited and which then explodes. This secondary explosion occurs within the concrete and, like a blasting explosive in a shothole, exerts a huge lateral force which causes it to break up.

[0016] An aspect of the present invention provides an enhanced blast explosive charge system based on a principle of a chain of reactions including the liberation of gas (creating a gas that is reactive) and using that gas to provide an explosion.

[0017] For example some embodiments use water from an environment, converting to hydrogen that gives an explosion; in some ways this could be thought of as liberating hydrogen from an environment and using it to provide a blast.

[0018] Water-reactive substances are those that spontaneously undergo a chemical reaction with water, as they are highly reducing in nature. Notable examples include alkali metals, lithium through caesium, and alkaline earth metals, magnesium through barium. Alloys may alternatively or additionally be used. Magnesium, for example, is capable of reducing water to highly-flammable hydrogen gas, which can, for example, be ignited by the excess heat given by the reduction reaction:

[0019] Mg(s)+2H2O^Mg(OH)2(S)+H2(S)

[0020] An aspect of the present invention provides a magnesium-based (or other waterreducing metal or metal alloy) hydrobaric charge.

[0021] An aspect of the present invention provides a magnesium-based hydrobaric shaped charge.

[0022] An aspect of the present invention provides a camouflet charge based on the principles described herein.

[0023] Some aspects and embodiments are based on a system or method of determining requirements for a magnesium shaped charge liner, comprising the steps of: setting a cone diameter; using a copper cone as a basis (e.g. for a required effect); calculating the mass of the copper cone; matching the mass to produce a magnesium cone, thereby dictating the thickness of the magnesium cone. For example, for a copper cone having a known diameter and known thickness a known mass will result; a magnesium cone with the same mass and same diameter is then determined, with the thickness adjusted to compensate for the difference in density between copper and magnesium. This principle could be used for other liner materials (the base material and / or the resulting material).

[0024] Some aspects and embodiments of the present invention seek to provide improvements in or relating to shaped charges.

[0025] An aspect of the present invention provides or relates to a shaped-charge based hydrobaric blast system. The shaped charge may be based on a water-reducing substance which liberates hydrogen. Rapid combustion of hydrogen can create an overpressure or explosion.

[0026] An aspect of the present invention provides a concrete demolition charge comprising a shaped charge including a liner, the liner is formed from magnesium or magnesium alloy such as magnalium. Other reactive materials such as sodium or even aluminium would also produce this phenomenon to a greater or lesser extent.

[0027] The liner may be a generally conical liner. Examples of embodiments include: a jet forming cone; an explosively formed projectile.

[0028] The liner may be formed as a section of a hemisphere.

[0029] The liner may be formed by die-casting or by hot stamping, for example.

[0030] Systems formed in accordance with the present invention may operate in such a way to produce a non-explosive reaction that does not cause a detonation, known as a low order event.

[0031] A further aspect provides a hydrobaric concrete demolition charge.

[0032] A further aspect provides a magnesium-lined concrete demolition charge.

[0033] A further aspect provides a magnesium-based concrete smashing charge.

[0034] The present invention also provides a method of demolishing concrete comprising the steps of: providing an explosive shaped charge, the shape charge including a liner and the liner is formed from magnesium or magnesium-based alloy, and explosively driving the liner to cause demolition of concrete.

[0035] Explosives can be categorised by their speed of detonation: low explosives which burn violently or high explosives which detonate. The speed of deflagration or detonation are a measure of the power and destructive force of an explosive.

[0036] High explosives detonate, producing a shockwave travelling through the explosive material at supersonic speed (typically from 4,000 to 8,000 m / s).

[0037] In some aspects and embodiments different cone angles are used to produce different effects. For example, in a camouflet charge a cone angle could be selected to provide rapid penetration into the ground and a subterranean explosion. A further aspect provides a hydrobaric concrete demolition charge comprising a shaped charge including a liner.

[0038] The liner may be formed from a water-reducing metal or metal alloy.

[0039] The liner may be formed from magnesium or magnesium alloy.

[0040] The liner may be generally frustoconical.

[0041] The liner may have a cone angle in the range 45 to 90 degrees.

[0042] The cone angle may be in the range 55 degrees to 75 degrees.

[0043] The cone angle may be approximately 60 degrees.

[0044] The material from which the liner is formed may comprises a binder, such as wax, lithium stearate, or polyisobutylene (PIB).

[0045] The material from which the liner is formed may comprise polytetrafluoroethylene (PTFE).

[0046] Embodiments of the present invention may comprise a liner formed from a “matrix” material e.g. metal power and binding material. Further additives may, for example, be included, such as polytetrafluoroethylene (PTFE). The material may then, for example, be pressed into a cone.

[0047] The liner may, for example, be formed by die-casting, hot stamping, casting, sintering, or pressing.

[0048] The present invention also provides a liner for a charge as claimed in any preceding claim.

[0049] The present invention also provides a method of demolishing concrete comprising the steps of: providing an explosive shaped charge as described herein; and explosively driving the liner to cause demolition of concrete. The present invention also provides a method of determining requirements for a magnesium shaped charge liner, comprising the steps of: setting a cone diameter; using a copper cone as a basis; calculating the mass of the copper cone; and matching the mass to produce a magnesium cone, thereby dictating the thickness of the magnesium cone.

[0050] The present invention also provides a magnesium-based concrete smashing charge.

[0051] The present invention also provides a magnesium-based camouflet charge.

[0052] Different aspects of the present invention may be used separately or together.

[0053] Further particular and preferred aspects of the present invention are set out in the accompanying independent and dependent claims. Features of the dependent claims may be combined with the features of the independent claims as appropriate, and in combination other than those explicitly set out in the claims.

[0054] Referring now to the drawings, wherein like reference numbers are used to designate like elements throughout the various views, several embodiments of the present invention are further described by way of example.

[0055] The example embodiments are described in sufficient detail to enable those of ordinary skill in the art to embody and implement the systems and processes herein described. It is important to understand that embodiments can be provided in many alternate forms and should not be construed as limited to the examples set forth herein.

[0056] Accordingly, while embodiment can be modified in various ways and take on various alternative forms, specific embodiments thereof are shown in the drawings and described in detail below as examples. There is no intent to limit to the particular forms disclosed. On the contrary, all modifications, equivalents, and alternatives falling within the scope of the appended claims should be included. Elements of the example embodiments are consistently denoted by the same reference numerals throughout the drawings and detailed description where appropriate.

[0057] Unless otherwise defined, all terms (including technical and scientific terms) used herein are to be interpreted as is customary in the art. It will be further understood that terms in common usage should also be interpreted as is customary in the relevant art and not in an idealised or overly formal sense unless expressly so defined herein.

[0058] In the following description, all orientational terms, such as upper, lower, radially and axially, are used in relation to the drawings and should not be interpreted as limiting on the invention.

[0059] Figures 1A to 1C and 2A to 2C show various different charges 10, 110, 210, 310, 410, 510 fitted with magnesium liners 15, 115, 215, 315, 415, 515.

[0060] Figure 3 shows an exploded view of a charge 610 fitted with a magnesium liner 615.

[0061] Figures 4A to 4D illustrate sectional views of four different charges 710, 810, 910, 1010 with concrete smashing Mg projectiles 715, 815, 915, 1015.

[0062] The charge 710 has a curved / hemispherical liner 715.

[0063] The charge 810 has a V-shape liner 815 with an apex angle of approximately 60 degrees.

[0064] The charge 901 has a curved V-shape liner 915.

[0065] The charge 1010 has a frustoconical liner 1015 with a cone angle of approximately 60 degrees.

[0066] Test Shot - Pluton with Cu 60° Cone (frustocone)

[0067] Figures 5A and 5B illustrate a test shot using a known, copper-based shaped charge.

[0068] Figure 5A shows the setup and Figure 5B shows the result.

[0069] Target: Reinforced Concrete Pad, 600mm thick.

[0070] Positioning: Pluton ( ) was positioned using the supplied alloy legs with a standoff of 150mm.

[0071] NEQ: 300g Peno

[0072] Result: The result showed the Pluton with the Cu 60° cone broke through the concrete down to about 15cm but the damage was very localised with not much sign of fracturing away from the impact area. Test Shot - Pluton with Mg 108° Cone (frustocone)

[0073] Figures 6A to 6C illustrate a test shot using a magnesium-based shaped charge. Figures 6A and 6B show the setup and Figure 6C shows the result.

[0074] Target: Reinforced Concrete Pad, 600mm thick.

[0075] Positioning: Pluton was positioned using the supplied alloy legs with a standoff of 150mm.

[0076] NEQ: 250g Peno

[0077] Result: The result showed the Pluton with the Mg 108° cone broke through the surface of the concrete down to about 15cm at its maximum. It did not strip much concrete from the rebar.

[0078] Test Shot - Pluton with Mg 60° Cone (frustocone)

[0079] Figures 7 A to 7C illustrate a test shot using a magnesium-based shaped charge. Figures 7A and 7B show the setup and Figure 7C shows the result.

[0080] Target: Reinforced Concrete Pad, 600mm thick.

[0081] Positioning: Pluton was positioned using the supplied alloy legs with a standoff of 150mm.

[0082] NEQ: 300g Peno

[0083] Result: The result showed the Pluton with the Mg 60° cone broke through the concrete down to about 30cm and stripped away significantly more of the concrete from the rebar than the 108° cone.

[0084] Figures 8A to 8C illustrate a test shot using a larger charge with 600g explosive material and a 108 degree magnesium cone completely smashing the top half of a 1.2m cube of concrete and breaking the bottom half as well. Several times as much explosive would be required to achieve a similar result with a copper cone.

[0085] Krakatoa with Mg 108 Cone (frustocone) against Reinforced Concrete Figures 9A to 9E illustrate a test shot using a Krakatoa charge. The concrete was 40cm thick.

[0086] Magma with Mg 108 Cone (frustocone) against a 40cm Reinforced Concrete Beam

[0087] Figures 10A to 10M illustrate a test shot using a Magma (https: / / www.explosives.net / products / maqma / ) charge.

[0088] Figures 10A to 10F show the setup; and Figures 10G to 10M show the result.

[0089] Pluton with Mg 60 Degree Cone (frustocone) against 60cm thick reinforced concrete

[0090] Figures 11A (setup) and 11 B (result) illustrate a test shot using a Pluton charge.

[0091] 3 x Pluton with 200g explosive load and Mg 108 Degree cones (frustocones) against 32cm x 28cm reinforced concrete

[0092] Figure 12A (setup) and 12B (result) illustrate a test shot using three Pluton charges.

[0093] 2 x Plutons with Mg 60 Degree cones (frustocones) against a concrete dragon’s tooth

[0094] Figures 13A to 13D show setup and Figure 13E shows the result.

[0095] 2 x Pluton firings with Mg Cones (frustocones) against reinforced concrete

[0096] Figure 14: Left one had a 108 degree cone. Right one had a 60 degree cone. Spaced 500mm apart.

[0097] Although illustrative embodiments of the invention have been disclosed in detail herein, with reference to the accompanying drawings, it is understood that the invention is not limited to the precise embodiments shown and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope of the invention.

Claims

CLAIMS1. A hydrobaric concrete demolition charge comprising a shaped charge including a liner.

2. A charge as claimed in claim 1 , in which the liner is formed from a water-reducing metal or metal alloy.

3. A charge as claimed in claim 2, in which the liner is formed from magnesium or magnesium alloy.

4. A charge as claimed in any preceding claim, in which the liner is generally frustoconical.

5. A charge as claimed in claim 4, in which the liner has a cone angle in the range 45 to 90 degrees.

6. A charge as claimed in claim 5, in which the cone angle is in the range 55 degrees to 75 degrees.

7. A charge as claimed in claim 5, in which the cone angle is approximately 60 degrees.

8. A charge as claimed in any preceding claim, in which the material from which the liner is formed comprises a binder.

9. A charge as claimed in any preceding claim, in which the material from which the liner is formed comprises polytetrafluoroethylene (PTFE).

10. A charge as claimed in any preceding claim, in which the liner is formed by diecasting, hot stamping, or pressing.

11. A liner for a charge as claimed in any preceding claim.

12. A method of demolishing concrete comprising the steps of: providing an explosive shaped charge as claimed in any of claims 1 to 10, and explosively driving the liner to cause demolition of concrete.

13. A method of determining requirements for a magnesium shaped charge liner, comprising the steps of: setting a cone diameter; using a copper cone as a basis; calculating the mass of the copper cone; and matching the mass to produce a magnesium cone, thereby dictating the thickness of the magnesium cone.

14. A magnesium-based concrete smashing charge.

15. A magnesium-based camouflet charge.

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