Linear cutting charge

The application discloses improvements in hollow charges for linear cutting or demolition purposes wherein a bar formed from a composite of explosive material and a first pliant material has a V-shaped groove with a liner formed from a composite of particulate metal and a second pliant material. The metal may be copper and preferably the first and second pliant materials include the same constituents. The charge may include a casing having a spacing portion having an engagement surface for presentation to a work surface, which engagement surface is parallel to the outer edges of the liner and spaced therefrom to maintain an optimum stand-off distance. The casing may further include a groove filling portion of low density material which may be integrally constructed with the casing from a flexible material such as expanded polyethylene.

This invention relates to a hollow charge for linear cutting purposes. 
Hollow charges are known comprising a mass of explosive having a variously 
shaped cavity at one of its surfaces, the cavity being lined with a metal 
liner. Detonation of the charge violently compresses the metal liner 
converting it into an outwardly projected slug of metal, the shape of 
which is dependent upon the shape of the cavity. The slug has powerful 
penetrating properties which are utilized by detonating the charge with 
its cavity adjacent and facing a surface to be penetrated, i.e. the work 
surface. The penetration of the slug is dependent on the separation of the 
charge from the work surface, i.e. the stand-off distance, the optimum 
value of which is normally determined by experiment. 
One particular example of a hollow charge known for linear cutting purposes 
comprises an elongated mass of explosive material having a cavity in the 
form of a V-shaped groove along its length, which mass is encased by a 
thin walled metal casing. Detonation produces a planar slug along the 
length of the groove which can be utilized for linear cutting. In a known 
method of manufacture of such linear cutting charges, a lead tube is 
packed with explosive granules and then passed through a series of rollers 
arranged to form the packed tube into a bar of chevron cross-section 
thereby forming a lead-lined, V-shaped groove along the length of the bar. 
The thickness of the lead wall encasing the two outer apices of the 
V-shaped groove is relied upon to space the charge from the work surface 
and thus defines the stand-off distance. Linear cutting charges so 
produced often have a non-uniform wall thickness and when these 
non-uniformities occur at the stand-off region or in the lining of the 
groove, variations in cutting efficiency and a lack of uniformity in 
cutting power results. 
The present invention seeks to provide a linear cutting charge having a 
construction conducive to accurate and uniform formation of its effective 
dimensions. 
According to the present invention a linear cutting charge includes an 
explosive mass formed in the shape of a bar from a composite of explosive 
material and a first pliant material, the bar having a groove extending 
longitudinally along one of its faces, within which groove is located a 
liner formed from a composite of particulate metal and a second pliant 
material. 
Preferably, both the bar and the liner may be formed by extrusion, but 
formation may also be by other techniques, e.g. moulding or rolling. 
The particulate metal may advantageously be copper. 
The first and second pliant materials are chosen to be chemically 
compatible with the explosive material and are preferably identical. 
Preferably, the groove has an outwardly widening, triangular cross-section 
and both the bar and the liner may be of chevron cross-section, the liner 
being bonded to the bar so as to cover the surfaces of the groove. 
Preferably the linear cutting charge further includes a casing which may 
advantageously be substantially rigid to prevent distortion of the bar and 
the liner during handling, which casing may advantageously include a 
spacing portion having an engagement surface for presentation to a work 
surface, which engagement surface is parallel to the outer edges of the 
liner and spaced therefrom, thereby to maintain an optimum stand-off 
distance. Alternatively the casing may be flexible to facilitate cutting 
of curved surfaces and curved lines. 
When the flexible charge is intended for cutting curved lines in a planar 
surface, stiffening means may be advantageously included, which may 
comprise metallic strips embedded in the casing normal to the engagement 
surface and extending longitudinally on either side of the groove, whereby 
the bending of the linear cutting charge may be limited to lateral bending 
parallel with the engagement surface. 
The presence of dense material in the groove is detrimental to cutting 
efficiency and therefore the casing may advantageously include a groove 
filling portion of low density material to prevent the influx of dense 
material when, for example, the linear cutting change is used under water. 
Conveniently, the casing including the spacing portion and the groove 
filling portion may be integrally constructed from a low density flexible 
material such as expanded polyethylene.

The linear cutting charge of FIGS. 1 and 2 has an explosive bar 1 of 
chevron cross-section having a groove 2 defined by the intersecting 
surfaces 3 and 4 which are included one to the other at an angle of 120 
degrees. 
The bar 1 is formed by extrusion from a pliant mixture of 88% by weight of 
RDX (Cyclotrimethylenetrinitramine), 8.4% PIB (Polyisobutylene), 2.4% DEHS 
(2 (Diethylhexyl) sebacate), and 1.2% PTFE (polytetrafluroethylene). 
The thickness of the bar measured in a direction normal to either of the 
faces 3 or 4 is 6.35 mm. A V-section linear 5 of 0.635 mm thickness formed 
by extrusion from a pliant mixture of 85% by weight of 300 mesh copper 
powder and 5.6% PIB, 1.6% DEHS and 7.8% PTFE, is bonded to the surfaces 3 
and 4 by pressure. 
A flexible casing 6 of expanded polyethylene surrounds the bar 1 except for 
the groove 2 and includes spacing portions 7 and 8 which protrude beyond 
the edges 9 of the liner 5 by a distance of 3.8 mm which, for this 
configuration, is the optimum stand-off distance between the edges 9 and 
an engagement surface 12 presented to a work surface 10. The casing 6 and 
the bar 1 are bonded together by a compatible adhesive. 
The explosive bar 1 may conveniently be initiated by an electrically 
operated detonator (not shown) which may be affixed externally to the 
casing at one end of the linear cutting charge. 
A second embodiment of the invention is illustrated in FIG. 3 in which the 
bar 1 and liner 5 described with reference to FIGS. 1 and 2 are surrounded 
entirely by a casing 11 of a low density material such as expanded 
polyethylene having an engagement surface 12 which is placed in contact 
with a work surface 13. The casing 11 comprises a first portion 16 which 
is substantially the same as the casing 6 of FIG. 1 and a groove filling 
portion 17 which is bonded to the first portion 16 at surfaces 18 and 19 
by a suitable adhesive. 
Stiffening means comprising metallic strips 14 and 15 are embedded in the 
casing 11 on either side of the groove 2 and normal to the engagement 
surface 12, thereby limiting bending of the linear cutting charge to 
lateral bending parallel to the plane of the engagement surface 12. 
It will be apparent to those skilled in the art that various other 
arrangements of the present invention are possible. For example, the 
casing may be of a rigid material such as polystyrene, and any casing may 
or may not include a groove filling portion. A groove filling portion may 
alternatively comprise a thin walled, air filled compartment, thereby 
excluding material from the groove and providing minimal resistance to the 
cutting slug generated by detonation of the charge.