[0001] The present invention relates to a method and a device to prevent the unintentional
initiation of a shaped charge caused by fire or other means spreading to other explosive
charges in the vicinity and causing a sympathetic detonation.
[0002] The invention is especially suitable for implementation in the storage and transportation
of anti-armour weapons with transverse shaped charges, that is such weapons which
have one or more shaped charges with a direction of effect which is transverse the
longitudinal direction of the weapon. Such anti-armour weapons are already in service
and they are expected to become increasingly common as modem armoured vehicles with
their improved armour protection consisting of both active and passive types at present
and for the foreseeable future are obviously easier to combat from above where for
both practical and weight reasons the armour is weakest
[0003] During storage and transportation it is always the case that several similar weapons
will be packed closely together in unit loads on pallets or simply lying next to each
other. In the case of fire or other external influence that results only in a limited
effect a small number of shaped charges can be unintentionally ignited. The shaped
charge jets from these weapons can then in their turn initiate one or more adjacent
charges with the result that an event which originally entailed limited damage results
in a mass sympathetic detonation. The risk of such an occurrence is regarded as especially
large in the case of transverse shaped charges where for practical reasons the direction
of effect of the shaped charges is towards an adjacent weapon when several such weapons
are lying next to each other.
[0004] The present invention now offers a solution to this problem based on the fact that
each shaped charge jet created by a detonating shaped charge is normally so well concentrated
that it affects only the area in the immediate vicinity of the jet's main axis while
the material around this area remains unaffected. In accordance with this invention,
during storage or transportation the shaped charges are provided with expendable bodies
which are made of a material which is resistant to shaped charges and which have their
longitudinal axes accurately directed so as to coincide with the effect direction
of the shaped charges and whose lengths are such that they exceed the maximum penetration
depth of the shaped charge jets in the material in question. The expendable bodies
can be made of steel or heavy metal for example but a body made of steel must have
a greater length than a body made of heavy metal. 'Heavy metal' here refers to metals
or metal alloys with a density higher than that of steel. As regards the cross-sectional
area of the expendable body, it must be adapted to the lateral propagation of the
shaped charge jet in question so that it is certain that the entire jet has effect
only within the expendable body and does not break through the sidewall formed. The
appropriate expendable body cross sections and lengths in accordance with the invention
for various shaped charges and in various materials can be calculated using computer
programs that are already available. In accordance with one development of the invention
the expendable body can be given different dimensions at different sections in one
longitudinal direction based on the calculated lateral and longitudinal propagation
of the shaped charge jet. It can thereby have a form of a truncated cone elongated
in one direction or the other or a combination of cylinder and truncated cone or other
form with varying cross-section. In accordance with one version of the invention the
expendable body itself can be surrounded by a tubular protecting part for example
a steel tube that is capable of gathering any radial spray which occurs at penetration.
The said tube can also gather the shaped charge jet in the event it should break through
the side of the expendable body.
[0005] Using expendable bodies in accordance with the invention which are correctly designed
and accurately directed, an unintentional initiation of one or more shaped charges
in a unit load will result only in the energy of the initiated shaped charge jet being
consumed by forming a hole in the expendable body and of course by causing a certain
amount of heat in the shell thus formed.
[0006] The method and design in accordance with the invention are especially suitable for
implementation in connection with unit loads where the expendable bodies can be included
as part of the packing material. As the attitude of the expendable bodies is so important
it can be advantageous for each charge or charge packaging to be fitted with a suitable
guide which ensures that the expendable body is correctly directed when the charges
are packed in each unit load. If such a guide is added it shall not have a design
that causes interference with the active function of the charge.
[0007] The invention is described in the subsequent patent claims and is now described in
more detail in combination with the following figures of which
Figure 1 shows the basic principle of the invention
Figure 2 shows a three-dimensional through-view of a unit load
Figure 3 shows section III-III in Figure 2
Figure 4 shows section IV-IV in Figure 2
Figure 5 shows another version of the expendable body shown in Figure 1 and
Figure 6 shows a partly sectioned version of the expendable body shown in Figure 1.
[0008] All the figures show one or several projectiles 1 intended for rechargeable anti-armour
weapons. Each such projectile includes a shaped charge 2 which is transverse the direction
of flight. How the projectiles are designed otherwise is of less interest in this
context but they can be expected to include propulsion rocket motors, target sensors
and possibly a guidance system. The projectiles are normally in individual containers
which are not shown in the figures. The reference to charges for rechargeable anti-armour
weapons in the figures is only one example. The invention can be used for all types
of shaped charges or weapons fitted with shaped charges, for example anti-armour weapons
of disposable type.
[0009] Figure 1 illustrates the basic idea behind the invention. An expendable body 4 made
of material which is resistant to shaped charge jets has been fitted as close as possible
outside the projectile with the said expendable body's longitudinal direction centred
around the direction of effect 3 of the shaped charge. The length of the expendable
body 4 is selected in relation to the material it is made of so as to ensure that
the shaped charge if initiated shall not pass through the entire length of the body.
As the capability of the shaped charged jet to penetrate another material depends
on how concentrated the jet is and that for this reason every effort is made to produce
charges which cause well-concentrated jets, the cross section of the expendable body
does not need to be greater than that required to cover the lateral propagation of
the jet which means that if the shaped charge is unintentionally ignited while the
expendable body is in place the jet from the shaped charge will function only in the
expendable body and there cause a longitudinal hole surrounded by thin but unbroken
sidewalls. From the above it is clear that the attitude of the expendable body is
of decisive importance for the function of the invention. The intention is that the
unintentionally ignited shaped charge shall use up all its energy to create a hole
in the expendable body instead of initiating the other charges in the vicinity. All
that is required in order to implement the invention therefore is a well-directed
expendable body in the form of a rod of steel, heavy metal or other material which
is resistant to the jet from a shaped charge. By making the expendable body of compacted
pulverised metal the possibility of the body being converted to a projectile when
affected by the shaped charge jet is avoided as an expendable body made of such material
will instead be reduced to powder.
[0010] While Figure 1 shows the basic principle of the invention, Figures 2-4 show proposals
as to how the invention can be used when four projectiles 5-8 are packed together
on a transport container 9. Of these projectiles, numbers 5 and 6 are positioned along
the container outer edges with their front sections containing the shaped charges
turned in the same direction but with a small longitudinal shift to provide space
for the projectiles and expendable bodies 10 and 11 which extend across a large portion
of the width of the container allowing expendable bodies 10 and 11 to be relatively
long and for this reason enabling them to be made of cheaper steel, while the other
two projectiles 7 and 8 facing the other direction have been fitted with expendable
bodies 12 and 13 which in the example shown have less space at their disposal and
it is therefore suggested that these should be made of more expensive heavy metal.
In the example shown it is assumed that the guides for the positions of the expendable
bodies are included in the container 9 fittings.
[0011] Figure 5 illustrates another version of the expendable body here designated 14 and
designed with consideration to the anticipated propagation of the shaped charge in
longitude and therefore has the form of a cylinder and a truncated cone directly combined.
Another shaped charge can require the reverse form or only a truncated cone facing
in one direction. The cylinder and the truncated cone can have a circular or non-circular
cross-section.
[0012] Figure 6 shows another version of the expendable body 15 surrounded by a concentric
metal tube 16 for gathering any lateral jet spray. Combinations of the features of
Figures 5 and 6 are of course possible.
1. A method to prevent the unintentional initiation of a shaped charge (2) caused by
fire or other means from resulting in the spread of the initiation to adjacent charges
wherein an expendable body (4, 10-13) made of material that is resistant to shaped charge
jets is fitted around the direction of effect (3) of each shaped charge (2) and is
accurately centred and lying in the direction of the said shaped charge and is of
a length that exceeds the maximum penetration length of the shaped charge jet in the
material in question and that this expendable body (4,10-13) is secured in the above
stated position and with unchanged attitude as long as the shaped charge is in store
or being transported.
2. Method as claimed in Claim 1 wherein the said expendable body (4, 10-13) is arranged with the end facing the charge (2)
as close to the charge as the design and individual packaging of the charge permit.
3. Method as claimed in Claim 1 and 2 wherein shaped charges (2) which are close to each other in unit loads (9) or in storage
are arranged so that their respective directions of effect (3) and expendable bodies
(4, 10-13) extend past each other.
4. Method as claimed in Claim 3 wherein the shaped charges (2) to be arranged in unit loads (9) or placed in storage are
adjusted longitudinally and/or transversely so that between, in front of or behind
them space is created for expendable bodies (4, 10-13) which shall prevent the unintentional
initiation of one charge spreading to other charges and causing a sympathetic detonation.
5. Device in accordance with the method in any of the Claims 1-4 to prevent an unintentional
initiation caused by fire or other means of a shaped charge (2) resulting in a spread
of the initiation to other adjacent explosive charges wherein the said device consists of a centred expendable body (4, 10-13) in the direction
(3) of the shaped charge (2) extending around the jet caused at the detonation of
the charge and made of material which is resistant to shaped charges and whose length
in the direction of the jet (3) exceeds that of the maximum penetration of the jet
in the material in question.
6. Method as claimed in Claim 5 wherein the said expendable body (4, 10-13) has the form of an extended rod with a cross
section which is adapted to the strength of each shaped charge.
7. Method as claimed in Claim 5 wherein the expendable body (4, 10-14) has a cross section that varies in its own longitudinal
direction.
8. Method as claimed in Claims 5-7 wherein the expendable body (15) is surrounded by a concentric body (16) of a material which
can absorb spray which is caused at penetration and/or fragments in the event the
shaped charge jet should break through the side of the expendable body.
9. Method as claimed in Claims 5-8 wherein the said expendable bodies (4, 10-15) are made of metal.
10. Method as claimed in Claims 5-9 wherein the said expendable bodies (4, 10-15) are made of heavy metal.
11. Method as claimed in Claims 9 or 10 wherein the said expendable bodies are made of compacted pulverised metal.