GB2533822A

GB2533822A - Explosive charge assembly and cartridge for use in same

Info

Publication number: GB2533822A
Application number: GB1500077.1A
Authority: GB
Inventors: Randall Stephen
Original assignee: ECS Special Projects Ltd
Current assignee: ECS Special Projects Ltd
Priority date: 2015-01-05
Filing date: 2015-01-05
Publication date: 2016-07-06
Also published as: WO2016110395A1

Abstract

An explosive charge assembly comprises a cartridge 1 and a housing 5. The cartridge 1comprises an end wall defining a forward face in a firing direction and at least one side wall. The end and side walls define a charge chamber for receiving explosive material. The housing 5 is configured to at least partially enclose the cartridge1 . The cartridge end and side walls may be integrally formed.

Description

EXPLOSIVE CHARGE ASSEMBLY AND CARTRIDGE FOR USE IN SAME The present invention relates generally to an explosive charge assembly, used for example to contain an explosive charge, and to a cartridge for use in an explosive charge assembly. Embodiments of the invention are suitable for use with shaped charges and systems and assemblies using shaped explosive charges, generally referred to in the art as "shaped charges". Embodiments of the invention have been developed for use in Explosive Ordnance Disposal (EOD), demolition and neutralisation principally but not exclusively in a marine environment. However embodiments of the invention have a wide range of other applications. Embodiments of the invention may be used in the rapid deployment and safe storage of explosive material. An assembly according to embodiments of the invention, loaded with a charge of explosive material, forms an explosive device.

Background

Explosive devices may be used to direct an explosive force towards a target. This direction is referred to herein as the firing direction and references to "forward" and "rearward" refer to the firing direction. The rear of an explosive device as described herein is the part remote from the target in use. In such devices a volume of explosive is contained, for example in a charge chamber.

The Monroe effect is well known and relates to enhancing the effectiveness of high explosives by the introduction of a cavity in the forward face of the explosive. In the case of plastic explosive this can be done by moulding the surface of the plastic material for example. A volume of explosive shaped to make use of the Monroe effect is commonly referred to as a "shaped charge". The shaping of a shaped charge has been found to assist in focussing energy in a desired, e.g. forward, direction. In an explosive device using a shaped charge, the charge may be retained in a charge chamber, which may comprise for example a cylinder open at both ends. It has been found that the effectiveness of a shaped charge may be further enhanced by the introduction of a "liner" to support and control the form of the cavity. The liner may in effect form the forward end wall of the charge chamber. Various geometric forms for the liner have been employed. Usually these are radially symmetric bodies with hemi-spherical, hyperbolic or other shapes of concavity or recess at acute or obtuse included angles, which may be pressed into the forward face of the explosive. Non radially-symmetric shapes have also been the subject of experimentation including wedge shapes. Liners may be formed in a variety of materials and used for various target effects.

An explosive device may be provided with some means defining a "standoff', the term commonly used to denote the distance between the forward face of the charge or liner and the target. Such means may abut the target prior to detonation.

In devices using shaped and other kinds of charges, the charge may comprise a so-called "insensitive" explosive material that is relatively stable such as a modern plastics explosive. If a flame is applied to a typical plastic explosive it will ignite but not explode. In order to make it explode, some means of initiation such as a detonator or "booster" charge of more sensitive explosive may be required. This means of initiation may be remotely operable, for example using a tube filled with explosive material, or a wired or wireless electrical connection. A booster charge which may be provided in a detonator is sometimes known as a "primary" explosive. It is standard practice for the two elements (e.g. the plastic explosive and the detonator) to be kept separate until the last conceivable minute and for the detonator to be removed if the operation is cancelled. Without the detonator fitted to a shaped charge device the two components may be transported provided that special precautions are taken. A device with the detonator fitted may be effectively a live bomb.

Depending on various parameters including the shape and material used for the liner, the use of the liner may have various effects. For example, the liner may be vaporised and form a hypersonic jet stream. If unobstructed, this stream may coalesce to form what is known as a "slug" of liner material, e.g. metal. In other applications a concave liner may be inverted and projected in a similar manner to a bullet.

Whilst the initial use for this effect has been for military purposes, for example in armour piercing warheads, more recently it has been found that shaped charges are particularly useful in the commercial Explosive Ordnance Disposal (EOD) field for seabed historic ordnance clearance for purposes such as wind farm construction and generally for subsea cutting and drilling of the seabed for oil well construction. Broadly, in the area of EOD such devices are used to either demolish e.g. high order (e.g. explode) a target, disrupt e.g. neutralise (e.g. deflagrate) a target without high ordering it or disarm a target e.g. render it inoperable. Thus assemblies according to embodiments of the invention may be used to provide devices for EOD, warheads and other explosive devices.

By experimentation and in use it has been discovered that a number of key factors affect the overall performance of a shaped charge including the three dimensional axial precision of the liner with respect to the charge chamber in which the explosive material is retained, the material used for the liner, the thickness of the liner, the shape of the cavity (usually as determined by the liner), the rigidity of the charge chamber, the amount of standoff and the volume of the explosive charge. It will be appreciated that some applications for explosive devices require more accuracy and/or higher performance than others.

When referring to shaped charge design suitable proportions for dimensions may be quoted in "Charge Chamber Diameters" (D). For certain applications of shaped explosive charges the liner diameter may be equal to D, the liner thickness may be 2% x D and the standoff distance should be 200% x D. When a shaped charge device, for example in the form of a demolition tool, disruption device or a disarmer is intended to be used subsea, the standoff must be maintained in the form of an hermetically sealed air filled enclosure.

Transporting explosive devices, particularly across national borders, it is naturally controlled by strict regulatory requirements; it has therefore been the trend, particularly but not exclusively in the field of commercial EOD, to move towards "self-fill" devices that are supplied devoid of explosive and either have the liner held at a particular position or with the liner provided loose as a disk with a concavity. As this concept affords a completely inert device it can be transported with little regulatory control and minimal safety precautions.

However, in use, it has been found that the packing of such "self-fill" devices with explosives is a skilful operation that must be undertaken with care as voids in the explosive may adversely affect the performance of the device. Also as it is usually difficult to undertake this operation in a small craft that is normally used for commercial marine EOD this operation is usually undertaken on the support vessel.

Should the operation be cancelled, due to inclement weather for instance, it is a painstaking task to remove the explosive from a shaped charge device so that it may be stored safely only to have to re-pack it if the mission is resumed.

Examples of shaped charge devices are disclosed in EP1476712B1 and US20120247358A1

Summary

Embodiments of the present invention provide a removable cartridge that combines the liner, e.g. a wall defining a forward face in the charging direction, with the charge chamber, e.g. a side wall such as a cylinder whose axis is parallel to the firing direction for containing the explosive material. The liner may be pre-formed with a cavity to form a shaped charge. An enclosure or housing may be provided to receive such a cartridge. The cartridge may be formed by in effect extending the liner reawardly to form the charge chamber. The cartridge may be factory formed. Significantly it has been found in tests that the factory, e.g. integral, forming of the cartridge comprising end wall and at least one side wall, improves the axial accuracy of the cavity to the charge chamber, e.g. the alignment of the centre of symmetry of the liner with the axis of the cylinder. This reduces the possibility of the liner being fitted out of square or off centre and causing an inefficient detonation. The extension of the liner or front wall which retains the explosive charge in the rearward direction assists in focusing the explosive force in the forward direction and may be useful with charges having flat or protuberant forward surfaces as well as with shaped charges of the kind described herein. Also, constraining the explosive material in a pre-formed chamber improves the performance notably.

Embodiments of the invention also provide an explosive charge assembly comprising a cartridge and a housing, the cartridge having an end wall defining a forward face in a firing direction and at least one side wall, the forward and side walls defining a charge chamber for receiving explosive material, and the housing being configured to at least partially enclose the cartridge.

The cartridge may be designed such that the whole is vaporised upon detonation of the charge, for example by the side and end walls being integrally formed or by the side and end walls being otherwise fixed together. The vaporisation may take place in a time interval of as little as a microsecond.

The housing may be manufactured from a polymer or other material to reduce fragmentation and the possibility of galvanic effect when dissimilar metals are deployed in a saline environment. Fragmentation may be problematic, especially in air environments, as it produces shrapnel that is potentially dangerous to people in the vicinity. Therefore depending on the intended use of a device or assembly according to embodiments of the invention it may be desirable to use a material that is not prone to fragmentation. Such materials are well known in the art.

The end wall of the cartridge may have a concave or other indented shape and thereby serve the function of a shaped liner in shaping the front face of the contained explosive.

An assembly according to embodiments of the invention enables the cartridges to be pre-filled on shore or on the support craft or even factory pre-filled. These could be easily fitted into the housings immediately prior to use even on a small support craft thereby improving safety. Should the operation need to be abandoned for whatever reason the cartridge containing the explosive material can be easily and quickly removed from the housing and made safe.

It should be noted that in an assembled explosive device according to embodiments of the invention, the cartridge contains only explosive material and does not contain a bullet or other projectile for example.

An assembly according to embodiments of the invention may include means defining a standoff, where some separation between the charge and the target is desired. According to some embodiments, for example for underwater use, such means may define a closed volume of air. According to other embodiments the standoff may simply comprise a spacer.

When it is a requirement to vary the amount of explosive for a particular application a variant of assembly according to embodiments of the present invention includes the ability to adjust the charge chamber volume. This may be achieved for example using a moveable end wall for the charge chamber which may be provided as part of a detonator carriage or charge former.

Previously variations in the charge chamber volume have been achieved by the introduction of spacers in front of the liner. This has the disadvantage of increasing the standoff length and thereby affecting the focus and thus the efficiency of the device. Embodiments of the present invention may enable the reduction of the enclosed volume of the charge chamber from the rear, for example by the employment of a moveable detonator carriage which may be moved in the firing direction using a screw thread, to allow for infinite or continuous rather than stepwise fine adjustment of the charge volume.

This adjustability of the size of the charge chamber may be provided in assemblies that do not use cartridge with integral liner. Thus embodiments of the invention provide an explosive charge assembly comprising a housing at least partially enclosing a charge chamber for receiving explosive material, and a forward end wall at least partially defining the charge chamber, in which the housing comprises a movable rear end wall for the charge chamber, the position of the end wall being variable along the firing direction to vary the volume of the charge chamber. Thus the forward end wall may comprise the liner, for example shaping the forward face of the charge.

Detailed Description

Embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings in which: Figure 1(a) is a perspective view of a cartridge according to embodiments of the invention, fitted with a cap; Figure 1(b) is longitudinal cross section of the cartridge of Figure 1 according to embodiments of the invention; Figure 2(a) is a perspective view of a housing for an explosive charge assembly according to embodiments of the invention; Figure 2(b) is a longitudinal cross section of an assembled explosive charge assembly according to embodiments of the invention including the housing shown in Figure 2(a) enclosing a cartridge of the kind shown in Figure 1(b); Figure 3 is an exploded cross sectional view of the assembly according to embodiments of the invention illustrated in Figure 2(b); Figure 4(a) is a perspective view of an alternative housing for an explosive charge assembly according to embodiments of the invention; Figure 4(b) is a longitudinal cross section of an assembled explosive charge assembly according to embodiments of the invention including the housing shown in Figure 4(a) enclosing a cartridge of the kind shown in Figure 1(b); Figure 4(c) is an exploded cross sectional view of the assembly according to embodiments of the invention illustrated in Figures 4(a) and 4(b).

Figure 5 is a perspective view of an alternative housing for an explosive charge assembly according to embodiments of the invention including articulated arms; Figure 6 is a perspective view of an explosive charge assembly according to embodiments of the invention including multiple housings each of which may enclose a cartridge.

Referring to Figure 1(a) and Figure 1(b), these illustrations show a shaped charge cartridge according to embodiments of the invention, Figure 1(a) being a perspective view and Figure 1(b) a longitudinal cross section. The illustrated cartridge, generally indicated by numeral 1, is a generally cylindrical receptacle having a cylindrical side wall 21 and a circular end wall 22 defining a charge chamber 3 which in this embodiment has one open or at least partially open end, shown closed by a removable cap 4. Other forms of closure may be provided according to embodiments of the invention. The closure may be removable and/or disposable but this is not essential. Cartridges according to embodiments of the invention may be provided with a sealed membrane that is ruptured but not necessarily removed prior to use.

The end wall 22 according to embodiments of the invention has a concave shape to form a concave depression in the forward surface of explosive material 15 contained in the cartridge 1. In the illustrated embodiment this depression is shown as a conical cavity or "concavity" 2. Other shapes are possible. The cavity or other depression 2 may be spun, machined or otherwise formed in the end of the shaped charge cartridge 1. Thus the end wall 22 may be integrally formed with the side wall 21. The side and end walls 21, 22 may be manufactured from metal such as but not limited to copper. This manufacturing may be undertaken to precise tolerances encapsulating the geometric shape required to maintain the optimum performance of the device. According to embodiments of the invention, the thickness of the walls 21 or 22 or both may be closely maintained to 2% of the diameter of the charge chamber 3 (illustrated as "D"). The removable cap 4 may be used to close the charge chamber 3, for example for transportation when the cartridge is filled with explosive material, indicated by reference numeral 15. The cap 4 may be made of plastic material and may be disposable.

Many other shapes are possible for the depression or concavity 2 for differing applications.

Such shapes include but are not limited to hemi-spherical, shallow cone, shallow parabola, wedge "V" shape, and bell shape. Whilst it has been found that copper is suitable due to its ductility and general range of desired effect, the shaped charge cartridge 1 may also be manufactured from other materials to achieve different applications. Such materials include but are not limited to aluminium, polymer, glass, molybdenum, and magnesium.

The circular end wall 22 of the cartridge 1 may take the place of the "liners" currently used in shaped charge devices. In other words, according to embodiments of the invention the cartridge may be considered to comprise a charge chamber with an integral liner. Alternatively, the whole side and end walls 21 and 22 may together be considered as forming a "liner. It will be seen from Figure 1(b) that the illustrated cartridge has an "M" shaped cross section. It will be appreciated by those skilled in the art that the wall 22 forms the front of the cartridge in the firing direction. In other words, the firing direction is generally parallel to the axis of the cylindrical wall 21 in the direction from the open end towards the wall 22.

Referring to Figures 2(a) this illustration shows in perspective view an embodiment of an enclosure or housing 5 suitable to house a charge cartridge such as the shaped charge cartridge shown in Figures 1(a) and (1 b). This housing may be manufactured from a range of materials such as a rigid polymer material. This and other similar materials would have the benefit of being able to encapsulate the shaped charge cartridge. Such materials could also reduce the possibility of fragmentation in use. However other materials may be employed to suit particular applications such as but not limited to metals including aluminium or steel. The housing 5 in the illustrated embodiments is formed of separable parts and may be provided with knurled or ribbed bands 25 to facilitate gripping of the housing outer surface, for example by hand.

Referring to Figure 2(b) this illustration is a longitudinal cross section of the housing 5 shown in Figure 2(a), enclosing a cartridge 1 filled with explosive material 15 and fitted with a detonator 9, which may be a proprietary detonator, thus forming an explosive device. The illustrated housing 5 has three sections which may interlock or connect to form a complete enclosure 5.

The three sections may be connected using screw threads or any other suitable means of interconnection.

From the right as illustrated, the housing comprises a rearward portion or closure which is removable to permit the insertion of a detonator 9. In this embodiment the rearward portion forms a retaining nut 6 for the detonator 9, which is designed to hold the detonator in position.

The removable rearward portion or detonator retaining nut 6 has an opening 26 at the rear for access to the detonator 9 to enable it to be remotely operated, which in this embodiment is illustrated as a cylindrical hole. In the illustrated embodiment it is assumed that the detonator is electrically operated and therefore wires 30 are shown protruding from the opening 26. Other types of detonator may be used which may be activated in different ways. Thus for example a tube containing explosive may be fed to the detonator 9 via the opening 26. It will be noted that in the illustrated embodiment only a small rearward portion of the detonator is located in the cylindrical through hole 26 of the nut 6. However in other embodiments a greater proportion of the detonator 9 may be encircled by the nut 6.

The central housing portion as illustrated is the housing body 7 designed to accept the shaped charge cartridge 1, and in this embodiment houses the major forward portion of the detonator 9. The forward housing portion 8 is removable to enable the insertion or removal of the cartridge 1 and is known as the standoff 8 since it defines the standoff distance. According to the illustrated embodiment the standoff 8 is designed to provide the necessary air environment for hypersonic jet formation as well as accurately controlling the standoff distance. The optimum standoff distance S shown in Figure 2(b) for certain applications is twice the cartridge internal diameter or 2 x D. The housing and the forward face of the cartridge 1 together define a standoff volume 35 in front of the forward face of the cartridge 1. The standoff 8 in this embodiment has generally cylindrical outer and inner surfaces with the forward end closed by a circular end wall 27. In the interior the standoff 8 defines a forward conical section formed in the end wall 27 whereby the thickness of end wall varies to a minimum and the apex of the cone, which defines one extreme of the standoff distance S. This conical formation is not absolutely necessary, but it renders the standoff easier to produce and it assists to a small degree when used at greater depths. In other embodiments of the invention, the internal end face of the standoff may be flat or planar.

The housing body 7 is a generally hollow cylinder with open ends closed by the retaining nut 6 and the standoff 8 respectively.

The detonator 9 may be a generally cylindrical device provided with an annular groove 32 around its outer surface towards the rear enabling it to be held in position by an 0-ring 10 received in the groove 32. The 0-ring 10 rests against an internal annular shoulder 33 formed at the rear open end of the housing body 7. As can be seen in Figure 3, the housing body 7 and the retaining nut 6 have mating screw threaded portions 6a and 7a which enable one to be screwed into the other, for example by turning retaining nut 6 with respect to body 7. The rearward portion in the form of retaining nut 6 comprises an internal forward facing annular shoulder 34. During the process of tightening the retaining nut 6, the 0-ring 10 is deformed between shoulders 33 and 34 and grips the detonator 9 in the annular groove 32. When used in a fluidic environment such as the sea, this 0-ring 10 also serves to exclude fluid from entering into the device. Thus, for example by means of the annular groove 34, the housing rearward portion is configured to prevent rearward travel of the detonator.

The standoff 8 is generally in the form of a front closure for the housing 5 which with the cartridge 1 enclosed in the housing defines a standoff space in front of the front face of the cartridge defined by the wall 22. In other words, according to embodiments of the invention, the wall 22 of the cartridge forms one wall of the standoff volume 35. As shown in Figure 3, the standoff 8 and body 7 have mating screw threaded portions 7b and 8b which enable one to be screwed into the other. The standoff includes an intemal annular shoulder 36 towards its rear on which an 0-ring 12 is seated.

As shown most clearly in Figure 3, the body 7 comprises two sections separated by an internal annular shoulder 37 whereby the forward section which houses the cartridge 1 has a larger diameter than the rear section which houses the detonator 9. This forward facing shoulder 37 is arranged to provide an abutment for a rearward facing surface on the cartridge, in the illustrated embodiment this is the cartridge annular surface 23 at the open end shown in Figure 1(b).

According to embodiments of the invention, the enclosure body 7 is manufactured to such dimensions that in the complete assembly as shown in Figure 2(b), with the standoff 8 and nut 6 screwed onto the body 7, the tip of the detonator 9 is able to enter the explosive 15 contained in the shaped charge cartridge 1 while simultaneously the front of the shaped charge cartridge 1 is able to protrude sufficiently from the front of the body 7 to seal on the cartridge 0-ring 12. The housing 5 is configured to retain the cartridge in a fixed axial position, e.g. in the firing direction, within the housing, for example by means of shoulders 36 and 37 provided within the housing. When the forward housing portion, standoff 8, is removed the cartridge 1 protrudes from the housing 5.

An additional 0-ring 11 is fitted on the enclosure body 7 in an annular groove 38 which is compressed against an internal annular shoulder 39 provided on the standoff 8 to prevent ingress of moisture, which is useful for example in underwater environments.

According to embodiments of the invention, 0-ring 12 serves to further prevent the ingress of moisture or any other external fluid into the assembly. It can also assist in providing an encapsulated air environment for the formation of a hypersonic jet. However it has been found that 0-ring 12 is not essential and where a seal is required 0-rings 10 and 11 have been found to be sufficient. Also a small amount of seepage of fluid, for example air or water, past these 0-rings would not be detrimental to the operation of an explosive device. The 0-ring 12 is an optional extra precaution.

Explosive charge assemblies according to embodiments of the invention may be deployed as follows: At a convenient approved location, either locally to or remotely from the location where the assemblies are to be used, explosive is carefully packed into one or more of the shaped charge cartridges 1 ensuring that no voids are present in the explosive itself or between the explosive and the cartridge walls. Temporary plastic caps 4 may then be fitted. The loaded shaped charge cartridges are then held securely, for example in an approved container such as a metal container, such as an ammunition box.

The detonators 9 may then be fitted to the empty housings 5, each being retained by a respective detonator 0-ring 10. Both the loaded shaped charge cartridges 1 and the enclosures with detonators 9 fitted can be safely transported to the operational area, be it on land or sea. Alternatively the detonators 9 may be transported completely separately from other components of the assembly. The standoffs 8 may be separately transported or screwed onto the bodies 7 for transport.

Immediately before use of an assembly, the enclosure standoff 8 (if already fitted) is removed from the enclosure assembly 5, an appropriate pre-loaded cartridge is selected, the plastic cap is removed and discarded and the shaped charge cartridge 1 is inserted into the receiving bore, open end first, in the enclosure body 7 or 14. The enclosure standoff 8 is then firmly attached to the enclosure body 7. An explosive device is now assembled and ready for use.

Certain types of detonator may need to be carefully handled to minimize distress (and possible risk of premature detonation). For such detonators, a tool called a "rectifier which is well known in the art is used to form an indentation in the explosive material prior to the detonator 7 contacting the explosive 15. This may achieved by introducing a pre-packed cartridge 1 into the housing 7, optionally without retaining nut 6, and screwing on the standoff 8 fully, then using a rectifier to pre-form the depression in the explosive 15 to accept the detonator 9. The detonator may then be fitted by guiding the detonator 9 through the rearward narrower diameter portion of housing body 7 until the 0-ring 10 on shoulder 34 enters the groove 32 around the detonator 9.

Once this "rectifying" operation had been completed once, if the cartridge was removed further "rectification" would not be required for next use. To ensure good contact between the detonator 9 and the explosive 15, the rectifier may have a conical or pointed front face and the detonator may have a flat front face, whereby the front face of the detonator to some extent itself forms an indentation in the surface of the explosive material 15.

Figures 4(a) and 4(b) show a modified version of the assembly shown in figures 1-3 configured to enable variation of the net explosive quantity "NEQ" contained in the cartridge 1. The cartridge and detonator used in the assembly of Figure 4 are the same as those used in the assembly of Figure 1 and other like components are designated with the same reference numerals.

Figure 4(a) is a perspective view of an explosive charge assembly housing 17 according to embodiments of the invention. The standoff 8 and retaining nut 6 may be the same as those used in the embodiment of Figures 1-3. The assembly comprises a modified housing body 14.

A retainer or locking ring 19 is provided for retaining the rearward portion in a position in the firing direction. As with the embodiment of Figures 1-3, portions of the surface of the housing 17 may be knurled or ribbed for easy gripping.

Referring to Figure 4(b) and 4(c) these illustrations are longitudinal and exploded sections of this embodiment showing a means of varying the volume in the charge chamber 3. In Figure 4(c) the detonator is omitted. The enclosure body 14 may be secured to the standoff 8 and retain the cartridge 1 in an axial position in the same manner as in the embodiment of Figures 1-3. However as illustrated, the standoff 8 in Figures 4(b) and 4(c) has rear section 8c with a thread on its outer surface designed to be screwed into a forward section 14c of body 14 which is threaded on its inner surface. 0-ring 11 is received in a groove in the outer surface of the standoff 8 and 0-ring 12 rests on a shoulder 36 at the rear of the standoff 8.The rear of the enclosure body 14, instead of receiving the detonator 9 itself, is adapted to include a charge former 13, into which the detonator 9 is inserted, and a locking ring 19.

The charge former 13 is generally cylindrical and comprises a forward portion 40 which together with the detonator 9 serves to close the charge chamber 3 from the rear and a rearwardly extending portion with a central bore in which the detonator is inserted. Thus the forward portion 40 can be considered to be a movable rear wall for the charge chamber 3. The rearwardly extending portion of charge former 13 comprises a first screw threaded section 13b of smaller external diameter than the forward portion 40 designed to cooperate with an internal screw threaded section 14b in the body portion 14, and a second screw threaded portion 13a of smaller external diameter than section 13b designed to cooperate with an internal screw threaded portion 6a in the retaining nut 6. The forward portion 40 is retained in the forward wider diameter portion of the enclosure body by means of the shoulder 37. The position of the charge former 13 along the firing direction may be variable according to embodiments of the invention. In the illustrated embodiment the charge former 13 is axially moveable with respect to the enclosure body 14, for example by means of respective screw threads on portions 13b and 14b on the charge former 13 and the housing body portion 14. The diameter of the forward portion 40 of the charge former 13 is less than the internal diameter of the cartridge 1 whereby the charge former may be received within or enter the cartridge 1.

In this embodiment the charge former forward portion 40 has a forward face 42 configured to compress or shape explosive material contained in the charge chamber 3 as the charge former 13 is screwed into the body 14. As illustrated this face is generally conical but other shapes may be used.

The charge former 13 is provided with a cylindrical bore through which the detonator 9 may be inserted in order to enable the tip of the detonator to penetrate a charge in the charge chamber 3. The detonator 9 may be inserted into the bore and held in place by means of nut 9 before the charge former 13 is screwed into the body 14. As such the charge former 13 may also be considered to be a carriage for the detonator 9.

The assembly of Figures 4(a) -4(c) additionally comprises an internally threaded locking ring 19 also designed to cooperated with externally threaded portion 13b of charge former 13.

The assembly illustrated in Figures 4(a) -4(c) may be assembled by the following operations, not necessarily in this order: * a desired amount of explosive material is packed into the cartridge 1 * the charge former 13 is inserted into the housing body portion 14 from the front until the screw threaded portions 13b and 14b meet, whereupon the charge former is screwed into the body 14 possibly as far as possible but at least sufficiently to allow locking ring 19 to be loosely screwed onto the rear of the charge former portion 13b with the rear of the charge former 13 protruding from the rear of the body 14 and locking ring 19, whereby the charge former 13, body portion 14 and locking ring 19 are securely attached to each other * the cartridge 1 is slid into the body portion 14 in such a way that the cylindrical wall 21 of the cartridge passes between the inner cylindrical surface of the foremost portion of body portion 14 and the outer cylindrical surface of charge former forward portion 40, or in other words with the charge former forward portion 40 entering the rear of the cartridge 1 * the standoff 8 is screwed onto the body portion 14 * the charge former 13, now protruding from the rear of body portion 14 and locking ring 14 is grasped and screwed in the other direction to cause the charge former to move forwardly in body portion 14 and bring face 42 into contact with the charge in the cartridge 1 whereby to compress or shape a rear face of explosive in cartridge 1 * the locking ring is tightened to hold the charge former 13 and body portion 14 in their respective positions * a rectifier may be used to form a guide depression in the rear face of the explosive to facilitate the insertion of the detonator 9 * the detonator 9 is inserted through the central bore in charge former 13 * the retaining nut is applied to the rear portion of the charge former 13 to compress 0-ring 10 and secure the detonator in position.

Thus this embodiment would allow for a shaped charge cartridge 1to be presented less than full allowing the charge former 13 to be wound down compressing the explosive 15 and thus ensuring lack of voids, and allowing entry of the tip of the detonator 9 into the explosive 15. The lock ring 19 would then be tightened to prevent the charge former from unscrewing. An assembly as shown in Figures 4(a) -4 (c) could be dismantled to remove the cartridge if an operation was postponed for example.

In all embodiments described above, the detonator could also be removed from the housing if desired, after initial assembly.

Many features of assemblies according to embodiments of the invention described herein are interchangeable and are not exclusive to one embodiment or another. Thus for example the assembly of Figure 3 may be modified to use a standoff 8 with an internal screw thread as shown in Figures 4(b) and 4(c).

Referring to Figure 5 this illustration is an embodiment of the present invention with the addition of one or more arms. These may be for example proprietary multi-sectional articulated arms 16.

Such arms are commonly available and the sections may be made from rigid polymer. These arms allow the device to be positioned or attached to target in a multitude of positions to achieve convenient or optimum position for a specific task. The arms 16 may be attached to the housing 5 or 17 in any suitable manner and may be provided in kit form, e.g. in the manner of a construction kit that enables a variety of shapes and configurations to be formed.

Figure 6 shows an embodiment of the invention in the form of a device comprising a plurality of explosive charge assemblies, and a carrier or holder 18 configured to retain the assemblies. In the embodiment shown in Figure 6, two housings 5 are retained in a carriage or holder 18. The two housings 5 are shown arranged in parallel and are retained in an axial position with respect to the carriage or holder 18 and each other. In other embodiments, the charge assemblies may be arranged with their axes divergent. In other embodiments the charge assemblies may be arranged with their axes convergent. In the illustrated embodiment they are positioned with their front faces aligned. In other embodiments the assemblies may be arranged with their front faces in different planes. The assemblies may be received as a sliding fit in the carriage, for example so that they can be positioned for a target with an irregular surface. It will be appreciated that the carriage 18 could be modified to accommodate any number of explosive charge assemblies.

Embodiments of the invention such as that shown in Figure 6 allow for two or more explosive charge assemblies to be held such that they could be deployed either simultaneously, singularly, sequentially or collectively and employing a common or variety of different concavity styles in the shaped charge cartridge. An arrangement with convergent charge assemblies may be useful for example to focus multiple directional explosive devices to a certain point.

In the case of the assembly shown in Figure 4, the cartridge may be presented less than full and inserted such that the cylindrical side wall passes between the inside of the housing portion 14 and the outside of the forward portion of the detonator carriage 13. The detonator carriage 13 is then screwed into the housing portion 14 to remove any air between the end of the detonator carriage 13 and the charge contained in the cartridge 1.

Should the operation need to be cancelled, due to inclement weather or other reason, the enclosure standoff 8 is removed and the shaped charge cartridge 1 is safely and easily unloaded, the plastic cap 4 is replaced and the loaded shaped charge cartridge 1 returned to its secure metal container, where it is ready to be re-used. In the case of the embodiment of Figure 4, removal of the cartridge might require the detonator carriage 13 to be unscrewed.

It should be noted that according to embodiments of the invention, the cartridge 1 protrudes slightly from the body 7 or 14 so that when the standoff has been removed the cartridge can be gripped with fingers to facilitate its removal. This may be useful but may be unnecessary, for example if there is no friction between the explosive 15 and the detonator 14. In some embodiments of the invention the full axial extent of the cartridge may be within the housing body 7 or 14 and may simply be tipped out if it is necessary to disarm the assembly.

Claims

Claims 1. An explosive charge assembly comprising a cartridge and a housing, the cartridge having an end wall defining a forward face in a firing direction and at least one side wall, the forward and side walls defining a charge chamber for receiving explosive material, and the housing being configured to at least partially enclose the cartridge.
2. An assembly as claimed in claim 1 in which the rear of the cartridge includes an opening and the assembly further comprises a removable closure for the opening.
3. An assembly as claimed in claim 1 or claim 2 in which the end wall of the cartridge has a concave shape.
4. An assembly as claimed in any preceding claim in which the cartridge end and side walls are integrally formed.
5. An assembly as claimed in any preceding claim in which the housing and the forward face of the cartridge together define a stand-off volume in front of the forward face of the cartridge.
6. An assembly as claimed in any preceding claim in which the housing is configured to retain the cartridge in a fixed position in the firing direction.
7. An assembly as claimed in claim 6 in which the housing comprises a forward facing shoulder arranged to provide an abutment for a rearward facing surface of the cartridge.
8. An assembly as claimed in any preceding claim in which a forward portion of the housing is removable to enable insertion or removal of the cartridge.
9. An assembly as claimed in claim 8 in which the housing is configured such that when the forward portion is removed, the cartridge protrudes from the housing.
10. An assembly as claimed in any preceding claim in which the housing is further configured to at least partially enclose a detonator for the explosive material.
11. An assembly as claimed in claim 10 in which a rearward portion of the housing is removable to permit insertion or removal of the detonator.
12. An assembly as claimed in claim 11 in which the rearward portion is configured to prevent rearward travel of the detonator.
13. An assembly as claimed in any preceding claim in which the housing comprises a movable rear end wall for the charge chamber, the position of the rear end wall being variable along the firing direction to vary the volume of the charge chamber.
14. An explosive charge assembly comprising a housing at least partially enclosing a charge chamber for receiving explosive material, and a forward end wall at least partially defining the charge chamber, in which the housing comprises a movable rear end wall for the charge chamber, the position of the end wall being variable along the firing direction to vary the volume of the charge chamber.
15. An assembly as claimed in claim 13 or 14 further comprising a retainer for retaining the charge chamber movable end wall in a position in the firing direction.
16. An assembly as claimed in any of claims 13 to 15 in which the charge chamber movable end wall comprises a forward surface configured to compress or shape explosive material contained in the charge chamber.
17. A directional explosive device comprising an assembly as claimed in any of claims 1 to 13 or claims 15 and 16 when dependent on any of claims 1 to 13, assembled with the housing at least partially enclosing the cartridge and in which the cartridge is at least partially filled with explosive material.
18. A cartridge for use in an assembly as claimed in any preceding claim comprising an end wall defining a forward face in a firing direction and at least one side wall, the forward and side walls defining a charge chamber for receiving explosive material, the side and end walls being integrally formed.
19. A device comprising a plurality of explosive charge assemblies each as claimed in any of claims 1 to 16, or a plurality of explosive devices as claimed in claim 17, and a carrier configured to retain the assemblies.
20. A device as claimed in claim 19 in which the carrier is configured to retain the assemblies such that their firing directions are parallel.
21. A device as claimed in claim 19 in which the carrier is configured to retain the assemblies such that their firing directions are divergent.
22. A device as claimed in claim 19 in which the carrier is configured to retain the assemblies such that their firing directions are convergent.
23. A device as claimed in any of claims 19 to 21 in which at least some of the cartridges have differently shaped forward faces.
24. An assembly as claimed in any of claims 1 to 16 or a device as claimed in claim 17 or 19 to 22, comprising one or more arms to facilitate positioning of the assembly or device relative to a target.
25. Any of the assemblies substantially as hereinbefore described with reference to the accompanying drawings.
26. Any of the devices substantially as hereinbefore described with reference to the accompanying drawings.
27. Any of the cartridges substantially as hereinbefore described with reference to the accompanying drawings.