Shaped charge warhead with mechanical means for preventing rotation

Mechanical interference between a cast explosive material and a casing prnts rotation of the cast explosive material during machining thereof and improves symmetry and performance of the shaped-charge warhead. The cast explosive material may be keyed to the casing by flowing portions of the explosive material into a plurality of cavities in the casing before curing. Alternatively, pins may extend inward from the casing into the explosive material which surrounds them when cast and resists relative motion therebetween when cured. Alternatively, the explosive material may be pre-cast into an appropriate shape, cured and pressed into the casing. Protuberances to fit into holes in the casing or indentations to fit over pins extending into the casing may be formed on the pre-cast explosive. Engagement between the protuberances or indentations and the holes or pins respectively is attained when the explosive material is pressed into the casing.

BACKGROUND OF THE INVENTION 
The present invention relates generally to explosive charges, particularly 
as employed in projectiles and the like, and more specifically to 
explosive charges having a shaped body of explosive for enhancing 
penetration of remotely located material. Remotely located material is 
defined as material located a distance of about 20 times the diameter of 
the explosive charge along an axis of symmetry of the explosive charge. 
In a projectile explosive charge such as, for example, a rocket-launched or 
tube-launched projectile, armor piercing capability of a given quantity of 
explosive is substantially improved by shaping the forward portion of the 
charge to produce a cavity of appropriate size and shape. The cavity may 
conventionally be lined with a metal or metallic alloy which is collapsed 
and driven as a concentrated, fast moving jet of metal which is capable of 
penetrating remotely located monolithic steel to depths of as much as two 
to three times the diameter of the warhead. An especially advantageous 
cavity shape is a conical shape having an included angle of less than 90 
degrees and preferably from about 42 to 60 degrees. 
Shaped charges are conveniently formed by casting a mass of explosive in a 
casing, the end of which is closed off by a metallic, preferably copper, 
cone. The cone thus forms the conical forward cavity of the shaped charge. 
After the explosive has set, it is conventional to machine the rear end of 
the explosive material to adapt it to fit a rear body section and/or an 
explosive booster, primer or centering device. 
During machining of the rear portion of the cast explosive material, 
adhesion between the explosive material and the casing is relied on to 
prevent turning of the explosive material in the casing. The applicant has 
discovered that the bond between the cast explosive material and the 
casing is frequently unsatisfactory to prevent rotation of the explosive 
material in the casing. Such rotation disrupts the symmetry of the 
explosive, particularly near the junction of the cone and the casing where 
the section of explosive is quite thin. In addition, slight asymmetries in 
either the cone or the body produce corresponding asymmetries in the 
explosive material cast thereupon. Such asymmetries are exaggerated when 
the explosive material is rotated away from its original location. 
Even if the bond is sufficient to resist rotation of the explosive mass in 
the body, localized fracture of the explosive material may occur due to 
the stress applied therebetween during machining. 
The penetration performance of the shaped charge depends critically upon 
symmetry of each of the elements about the axial center line thereof. 
Anything which disrupts the symmetry of the charge also influences the 
symmetry of liner collapse. If the liner does not collapse in a 
symmetrical fashion, then the corresponding jet will not be straight and 
its penetration capability against remote targets is degraded. 
Prior attempts to improve the armor piercing performance of shaped charge 
warheads include changing the shape or density of the liner, improving the 
axial alignment of liner, explosive material and explosive initiator and 
increasing the diameter of the shaped charge. Changing the shape and/or 
increasing the density of the liner greatly increases the cost for the 
different material and requires new machinery for fabrication. Improved 
axial alignment implies a drastic improvement in machining and fabrication 
technology since current shaped charges already utilize tolerances near 
the limits of high production technology. Increasing the diameter of the 
shaped charge requires that the entire system for launch must be 
correspondingly increased and the weight of the larger warhead may make it 
unsuitable for lifting by military personnel. 
OBJECTS AND SUMMARY OF THE INVENTION 
It is an object of the present invention to produce a shaped charge warhead 
which overcomes the drawbacks of the prior art. 
It is a further object of the invention to produce a shaped charge warhead 
which resists asymmetry in a body of cast explosive material. 
It is a further object of the invention to provide means for preventing the 
rotation of a body of cast explosive material in a casing during machining 
of a portion of the cast explosive material. 
According to an aspect of the invention, there is provided a shaped charge 
warhead comprising a generally cylindrical casing, a cast mass of 
explosive material in the casing, means for forming a generally conical 
forward face of the mass of explosive material, and mechanical means for 
preventing rotation of the mass of explosive material in the casing. 
According to a feature of the invention, there is provided a method of 
producing a shaped charge warhead comprising a mass of explosive material 
in a casing having a conical forward surface, mechanically keying the mass 
of explosive material to the casing, curing the mass, machining a rear 
surface of the mass for installation of a primer and a detonator, and the 
keying being effective to prevent relative rotation of the mass with 
respect to the casing during the machining. 
The above, and other objects, features, and advantages of the present 
invention, will become apparent from the following description read in 
conjunction with the accompanying drawing, in which like reference 
numerals designate the same elements.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the figure, a shaped charge, shown generally at 10, suitable 
for use in an aerodynamic enclosure (not shown) such as, for example, a 
rocket-launched or tubelaunched projectile, includes a generally 
cylindrical casing 12 having one end closed by a conical liner 14 of any 
suitable material but preferably of copper, axially symmetrically disposed 
within casing 12. Liner 14 may optionally have a truncated apex 16. 
A retaining closure member 18 may optionally be employed for holding liner 
14 in place. 
A body of explosive material 20 is positioned within casing 12 in intimate 
contact therewith and with conical liner 14. 
A booster retaining cell 26 at the extremity of rear body section 24 
contains a booster charge 28 held accurately centered on rear surface 22 
by a centering device 30. A detonator 32 is also held centered against the 
rear surface of booster charge 28 by centering device 30. An opening 34 in 
centering device 30 permits entry of detonating wires 36. 
Two different methods may be used to fabricate shaped charge 10 in the 
structural relationship shown. In one method, explosive material 20 is 
poured as a flowable fluid into casing 12 through rear body section 24 
when the components are fully assembled except for booster charge 28, 
centering device 30, detonator 32, and detonating wires 36. When this is 
done, an excess of explosive material 20 is poured so as to form a "pipe" 
or "chimney" to assure that all bubbles escape from the main body of 
explosive material 20 and all voids within casing 12 are filled. This 
excess fills the volume within booster retaining cell 26, and is removed 
by machining after explosive material 20 cools and hardens. Alternatively, 
explosive material 20 may be pre-cast in a mold to produce the necessary 
shape and dimensions to fit within casing 12 in nesting contact with liner 
14 and rear body section 24. When pre-cast, explosive material 20 is 
formed with an excess of material to occupy cell 26 and must be machined 
in the same manner as for the cast-in-place method discussed above to make 
room for booster charge 28. 
Casing 12 may have a plurality of locking holes 38 therein into which the 
explosive material may flow when the first fabrication method described 
above is used, and which, when set, provide mechanical interference 
between the body of explosive material 20 and casing 12 to prevent 
rotation of explosive material 20 during machining of rear surface 22. 
When the second fabrication method is used, the protusions to fit into 
locking holes 38 are preformed on the explosive and then are pressed into 
locking holes 38 in base 24 during assembly. 
Locking holes 38 are preferably located as close as possible to the rear of 
casing 12 in order that the disturbance in pressure wave symmetry which 
they cause can be substantially damped out before the pressure wave 
reaches liner 14. For the same reason, a large number of small locking 
holes 38 is preferred to a few large locking holes. 
An alternative or complementary rotation prevention device includes a 
plurality of locking pins 40 which may be placed, for example, in casing 
12 or in rear body section 24 protruding into the volume occupied by 
explosive material 20. As explosive material 20 is cast in place, it 
surrounds locking pins 40 and, when set, engages locking pins 40 to 
prevent rotation of explosive material 20 in casing 12 and rear body 
section 24. When explosive material 20 is pre-cast, it may be provided 
with cast-in-place holes adapted to receive pins 40 which may be inserted 
later. 
The size and number of locking pins 40 is related to the torsional 
resistance required, and to the detonation wave used to collapse the 
liner. In order to permit perturbations introduced into the detonation 
wave by the presence of locking pins 40 to damp out, they should be placed 
as far from the forward end of the shaped charge as possible. In addition, 
the size of the perturbations increase with the size of locking pins 40. 
Consequently, a larger number of smaller pins is preferred to a small 
number of large pins. 
EXAMPLE 1 
A five-inch diameter shaped charge warhead having a 60 degree included cone 
angle was fabricated with eight locking holes, each 1/4 inch in diameter 
equally spaced about casing 12 approximately 1 inch forward of the forward 
surface of booster charge 28. 
The shaped charge warhead was detonated at a distance of 20 charge 
diameters (CD) from monolithic steel. A similar shaped charge formed 
without the use of locking holes 38 was also detonated for comparison 
purposes. The charge formed without locking holes 38 penetrated the steel 
to a distance of 2.88 CD. The charge according to the present invention 
with locking holes 38 penetrated the steel to a distance of 3.50 CD. This 
is an improvement of 21 percent. 
EXAMPLE 2 
A 5.5 inch diameter shaped charge warhead having a 42 degree included cone 
angle was fabricated with eight locking holes, each 1/4 inch in diameter 
equally spaced about the casing 12 approximately 1 inch forward of the 
forward surface of booster charge 28. 
The shaped charge warhead was detonated at a distance of 20 charge 
diameters (CD) from monolithic steel. A similar shaped charge formed 
without the use of locking holes 38 was also detonated for comparison 
purposes. Th charge formed without the locking holes 38 penetrated the 
steel to a distance of 2.67 CD. The charge according to the present 
invention with locking holes 38 penetrated the steel to a distance of 3.15 
CD. This is an improvement of 18 percent. 
The cost of forming locking holes 28 in casing 12 is minimal. 
Having described a specific preferred embodiment of the invention with 
reference to the accompanying drawing, it is to be understood that the 
invention is not limited to that precise embodiment, and that various 
changes and modifications may be effected therein by one skilled in the 
art without departing from the scope or spirit of the invention as defined 
in the appended claims.