FIELD OF THE INVENTION

The present invention relates to an explosive charge, particularly a charge suitable for use in a so-called "Bangalore Torpedo".

BACKGROUND OF THE INVENTION

A conventional explosive charge is described in WO2007/099362. The charge has one or more longitudinal concave grooves. Upon explosion, the contour of the groove results in a focussing effect on the wall material. The groove does not reduce the local thickness of the wall of the charge.

Another conventional explosive charge is described in GB-A-2214618. The inner face of the lining is formed with a set of V-shaped grooves interlinked around the axis of the charge. The grooves reduce the local thickness of the lining and result in material being ejected in a plurality of shaped charge jets one from each outward facing V-shaped region of the lining.

SUMMARY OF THE INVENTION

A first aspect of the invention provides an explosive charge comprising an elongate casing with elongate grooves running along the casing, each groove locally reducing the thickness of the casing, wherein the grooves are distributed in two or more groups around the circumference of the casing and the edge-to-edge spacing between each adjacent pair of grooves in a group is less than the edge-to-edge spacing between each pair of adjacent groups.

A second aspect of the invention provides a kit of parts comprising two or more charges according to the first aspect of the invention, each charge having a head end adapted to be coupled to the tail end of an adjacent charge, and a tail end adapted to be coupled to the head end of an adjacent charge.

A third aspect of the invention provides a method of cutting an obstacle using the explosive charge of the first aspect of the invention, the method comprising detonating explosive material in a compartment of the casing, the detonation causing the casing to break at a pair of grooves in one of the groups and form a fragment from material between the pair of grooves, the fragment cutting the obstacle.

In GB-A-2214618 the grooves are distributed uniformly around the circumference of the lining. In contrast, according to the present invention the grooves are distributed non-uniformly around the circumference of the casing so that they are bunched together in two or more groups. The relatively small edge-to-edge spacing between each adjacent pair of grooves in a group results in the generation of high energy fragments which can cut efficiently through an obstacle.

The edge-to-edge spacing between each groove in a group may be zero, but preferably it is greater than zero so that each groove has an edge which is separated from an adjacent edge of an adjacent groove by a non-grooved portion of the casing.

Various other preferred features of the invention are set out in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described with reference to the accompanying drawings, in which:

Figure 1 is a plan view of an explosive charge;

Figure 2 is a longitudinal sectional view taken along a line B-B in Figure 1;

Figure 3 is a transverse sectional view taken along a line A-A in Figure 1 ;

Figure 4 is a close up transverse sectional view showing a pair of grooves;

Figure 5 is a perspective view showing a set of charges in use as a Bangalore torpedo; and

Figure 6 is a schematic sectional view showing the torpedo exploding.

DETAILED DESCRIPTION OF EMBODIMENT(S) An explosive charge 1 shown in Figure 1 comprises an elongate casing 2 with grooves 3, 4 running along the external wall of the casing. Figure 3 is a transverse sectional view taken along a line A-A in Figure 1, which shows that there are four pairs of grooves distributed around the circumference of the casing. The grooves are all identical so only the pair 3, 4 will be described in detail with reference to Figure 4. Each groove is V-shaped with a depth d. Each groove locally reduces the thickness of the casing, so the thickness ti of the casing at the bottom of each groove is less than the thickness t ₂ in the un-grooved portion between adjacent pairs of grooves.

The grooves 3, 4 are separated from each other by a small non-grooved portion 10 of the casing in which the thickness of the casing is substantially constant. The grooves

3, 4 are relatively narrow, as is the width of the non-grooved portion 10 which separates the groove 3 from the groove 4. Specifically, each groove subtends an angle θ _g i of only about 4° and the edge-to-edge angular spacing θ _g2 between the edges of adjacent grooves within a pair is only about 2°. Therefore each pair subtends an angle θ _g3 between its two outer edges of about 10°, and the edge-to-edge angular spacing θ _pl

(shown in Figure 3) between the edges of adjacent pairs of grooves is about 80°.

The internal wall of the casing is circular in cross- section for ease of manufacture and to maximise the space available for explosive material.

Referring to Figure 2, which is a longitudinal sectional view taken along the line B-B shown in Figure 1, the casing has an internally threaded head end 11 adapted to be screwed to the tail end of an adjacent charge, and an externally threaded tail end 12 adapted to be screwed to the head end of an adjacent charge.

Figure 5 shows the device in use as a Bangalore torpedo being prepared to clear a path through a series of wires 20 (for instance barbed wire or razor wire). A number of casing units 21, 22 (in this case two, but optionally more than two) are screwed together head to tail. An explosive charge (not shown) is contained inside the torpedo along its full length. A nose cone 23 is screwed to the head end of the front casing unit, and a detonator housing 24 with an initiator is screwed to the tail end of the rear casing. The torpedo is fed under the barbed wire and placed on the ground with two pairs of grooves facing up and oriented at approximately +/- 45° to the vertical. The charge is then detonated, causing the casing to break initially at the bases of the eight grooves where the thickness t _\ is at a minimum. The casing material between the grooves forms four small pre-defined fragments which are ejected at approximately +/- 45° to the vertical. The fragments from the two downwardly pointed pairs of grooves impact the ground and are not shown in Figure 6. However the fragments 25, 26 from the two upwardly pointed pairs of grooves are ejected upwardly and cut the barbed wire at locations 27 and 28 respectively, clearing a path through the obstacle. The relatively large volume of casing between the pairs of grooves generates a set of relatively small and low energy particles 29, 30, 31 which have less cutting effect than the fragments 25, 26. Spacing the pairs of grooves apart, and making the spacing between adjacent grooves in a pair relatively small, ensures that the fragments 25, 26 have relatively high energy and cutting effectiveness. It is also believed that the tapering profile of the grooves (in this case a V-shaped profile) provides a focusing effect on the detonation wave.

Note that Figure 6 does not show the true shape of the fragments 25, 26 or lower energy particles 29-31 but merely intends to show the mode of operation schematically.

Although the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims.