Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Security Barrier Structure and ~ethod of Making the Same
The present invention relates to barrier structures for
use eg in the walls and/or doors of safes, strongrooms
and the like security enclosures. Barrier structures
provided for this purpose must have a high degree of
resistance to the various forms of burglarious attack to
which the enclosure may be subjected and it is an aim of
the invention to provide an improved security barrier
structure in which materials resistive to different
classes of burglary tools can be combined in a
particularly effective manner.
There is no known single material which can be employed
on a practical basis in the construction of such
enclosures to resist all types of tool currently at the
disposal of the criminal. Various materials are known
which provide excellent resistance to specified classes
of tool when used in isolation, but for the same barrier
structure to be effective against a range of different
tool types a combination of different materials is
required. Moreover, these materials should be integrated
structurally in such a way as to resist the penetration
of the overall barrier by "multiple" attacks, w~ere
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concerted use is made of a range of different tools, but
without significant sacrifice to the resistance of the
structure to "single-tool" attac]cs. In particular, it
should not be possible readily to penetrate the barrier
by the successive penetration of each material
encountered with appropriately selected tools, as might
be the case with a barrier structure made up with simple
discrete layers of the different materials.
In seeking to provide a security barrier structure which
is capable of resisting both "single-tool" and "multiple"
attacks as aforesaid the invention is characterised by a
corrugated sheet of tough, heat conductive metal
resistant to penetration by percussive and thermal tools
and extending substantially continuously throughout the
structure; and
a layer consisting of or containing hard material
resistant to penetration by mechanical cutting and
drilling tools which layer is disposed in intimate
relationship with said corrugated sheet at least on the
remote side of said sheet as viewed from the external
face of the structure, with portions of said hard
material lying within the depressions of the corrugations
of said corrugated sheet on said remote side thereof;
the distribution of said hard material, and the spacing
and amplitude of the corrugations in said corrugated
sheet, being such as to provide that a burglarious
attempt to cut a generally cylindrical aperture through
said corrugated sheet with a diameter in the range of
about 40-125mm, from substantially any position on the
near side of the structure as viewed from the external
face of the structure and in a direction generally
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perpendicular to the structure, will result in the
simultaneous encountering by the tool of both the
material of said corrugated sheet and aportion of said
hard material disposed on the aforesaid remote side of
the sheet.
A particularly preferred material from which the
aforesaid corrugated sheet may be made is copper,
alternatives including stainless steel, aluminium and
10 cast iron.
The aforesaid cutting and drilling resistant layer which
is in intimate relationship with the corrugated sheet
preferably contains, (at least in that portion which is
15 disposed on said remote side of the corrugated sheet in
relation to an attack from outside the enclosure), at
least 10~ by volume of a material whose hardness is
in excess of 1000 kg/mm2. Suitable materials for this
purpose therefore include security-formulation concretes
20 containing hard aggregates such as quartzite, fused
alumina or the like (and which may also be reinforced
with steel or polypropylene fibres), and composites such
as cast aluminium or copper containing nuggets of fused
alumina or the like.
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By virtue of its rapid heat-dissipating ability the
copper or ot'ner said corrugated metal sheet can confer
upon a barrier structure according to the invention good
resistance to attack by oxy-acetylene, oxy-arc and the
like thermal tools, and can also provide good resistance
to power percussion tools by virtue of its ability to
deform without fragmentation under the action of such
tools (ie its toughness). On the other hand, being
relatively soft this type of element would be, in
isolation, vulnerable to attack by "sharp edge"
mechanical cutting tools such as drills, holesaws and
chisels, but these can be resisted in a structure
according to the invention by the hard material in the
surrounding matrix. It is in this respect that the
corrugated form of the sheet is of particular
advantage. As more fully discussed below, this sheet is
appropriately shaped such that any such tool adapted to
cut a hole of the above-specified diameter which is
applied to the corrugated element will inevitably
encounter some of the hard material in the layer behind
the corrugated sheet before that sheet is completely
penetrated. This action will of course rapidly blunt the
tool edge, and once blunted cutting tools become very
inefficient against ductile metals. In this way the
structure can offer high resistance even to multiple
attacks which attempt to penetrate the barrier structure
firstly by removing a portion of the hard layer in
front of the corrugated sheet by one class of tool to
which that layer is more vulnerable than the corrugated
sheet, and then attacking the exposed corrugated sheet
with another class of tool to which that element is
percieved to be more vulnerable than the hard layer. The
corrugated shape of the internal metal element may indeed
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also assist in resisting the first stage of such an
attack as considerably more difficulty may be experienced
in removing the hard layer material which is lodged in
the troughs or other depressions in the surface oE the
corrugated element than in the case of, say, an
equivalent material provided as a flat layer.
The copper or like metal sheet is also of advantage
in resisting another class of tool, namely diamond core
drills and the like abrasive tools which depend for their
operation on the continual wearing down of the tool tip
to expose new abrasive particles; when such a tool
encounters the corrugated element in a structure
according to the invention it will rapidly become clogged
by the ductile metal. A structure in accordance with the
invention may also offer high resistance to attacks using
explosives as the internal metal element can act
effectively to retain the integrity of the barrier when
subjected to shock loading, and such a structure can
furthermore provide the appropriate combination of hard
and tough materials for resisting ballistic projectiles
and the like.
If it is to be ensured that a cutting tool is blunted by
2~ the hard-layer material before penetration of the
internal metal sheet can be completed by that tool then
the corrugated form of the sheet must be related to the
tool size and direction of advance such as to provide
that parts of the tool tip will at one and the
same time encounter a portion of the metal element and a
portion of the hard material. A simple type of
corrugation comprising parallel rows of alternate peaks
and troughs can be provided by relatively inexpensive
sheet or plate forming techniques and can be effective
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by appropriate selection of the dimensions of the
corrugations, to ensure that the above-mentioned blunting
effect takes place for a wide range of the tool sizes and
directions of attack that would be likely to be met in
practice. In this respect tests indicate that the
amplitude of the corrugations (that is the peak-to-trough
height measured at the same aurface) is preferably 5-15mm
more than the thickness of the metal in the corrugated
sheet, so that for a sheet made from, say, a lOmm thick
material the amplitude may be about 20mm. Larger
amplitudes do not in general detract from security but
are likely to be impractical in safes for example where
the wall thickness is limited. It has also been found
that the pitch of the corrugations (that is the peak-to-
peak or trough-to-trough distance) preferably lies in the
range between one half and twice the diameter of the
typical penetration which the barrier is intended to
resist. For resisting a 125mm diameter "handhole"
penetration a corrugation pitch of between 60 and 250mm
may be best, therefore, or for resisting a 40mm diameter
penetration the preferred pitch may be between 20 and
80mm. A pitch of about 70mm might therefore be chosen
for optimum resistance to the whole range of penetration
diameters from 40-125mm. The pitch and amplitude will in
general be interrelated such that the angle subtended to
the plane of the barrier by an imaginary straight line
drawn between an adjacent peak and trough is in the range
of 5-60.
However, other more complex corrugated forms may be
provided instead of the parallel peak-and-trough form
indicated above, for example where there are ridges
running in two or more different directions or where
there are a plurality of discrete depressions or
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obtrusions distributed over the surface of the metal
sheet - such an element could be described as being
generally of "eggbox" shape - and the term "corrugated"
is accordingly to be interpreted broadly. Metal elements
of these shapes may be more appropriately produced by
casting from the molten metal than by sheet-forming.
Structures according to the invention may be produced eg
in the form of flat slabs for incorporation into the
walls and doors of safes or strongrooms. Alternatively,
in the construction of safe bodies it is of advantage if
the barrier structure is of "monolithic" form including a
suitably interconnected series of the metal sheets (eg
one each for the back, top, bottom and two side walls of
the safe) disposed within a single "bell" of cast hard
layer material. In addition to the main corrugated metal
sheet(s) in any such structure it is also possible to
incorporate specially formed strips or plates of the same
or similar metal into the same structure to give even
greater resistance to penetration in particularly
important areas of a security enclosure door or body.
In practice the barrier structure will generally be built
up on a backing plate which supports and locates the
structure in relation to the completed enclosure, (that
is the backing plate is located behind the aforesaid
hard-layer and corrugated sheet, and may define the inner
skin of a safe body for example). The overall structure
may then comprise anchors secured to the backing plate
and extending into the mass of the hard layer to secure
the latter to the plate. Preferably such anchors extend
through apertures in the corrugated sheet and are
interconnected in front of that element b~ a network of
rods or the like. The combination of these rods and
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anchors, (which will resist the corrugated element being
pulled away from the backing plate), and the disposition
of that element within the hard :Layer can offer excellent
resistance to "delamination" of the barrier structure as
a whole from the plate, w~ich might be attempted eg
through use of explosives or other gross force.
As a further feature of a barrier structure accordiny to
the invention it may be of advantage to have the internal
metal sheet coated with an electrically insulating and/or
fume-generating substance; one substance which couLd
provide both properties is bitumen, for example, but
others are possible. If the internal metal sheet can be
electrically insulated in this way from the usual steel
skins or other metal constituents of the security
enclosure then it will be very difficult to penetrate the
barrier using tools such as the oxy-arc torch - which
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depend for their operation on striking an arc. The
ability of such a coating to produce fumes when heated
will be of value in hindering thermal attacks in
general.
Illustrative embodiments of the present invention will
now be more particularly described, by way of example,
with reference to the accompanying drawings, in which:-
Figure 1 is a section through part of a slab or "bell"barrier structure according to one embodiment of the
invention;
Figure 2 shows a detail of the structure of Figure l;
Figure 3 is a horizontal section through the door/body
junction of a safe incorporating barrier structures
according to the invention; and
Figure 4 is a view similar to Figure 1 of a further
embodiment of the invention.
Referring to Figure 1 there is shown a high strength
steel backing plate 1 to which is secured an integral
barrier structure comprising a corrugated wrought copper
plate 2 disposed in intimate relation within a matrix of
cast alumihium alloy 3 containing also nuggets of fused
alumina 4 (eg ALOXITE - Registered Trade Mark) or the
like very hard, refractory material. In one specific
example of a structure as shown in Figure 1 the thickness
a of the copper plate was 13mm, the minimum thickness b
of matrix material between the copper plate 2 and backing
plate 1 was 25mm, the amplitude c of the corrugations in
plate 2 was 24mm, the pitch d of the corrugations was in
the region of 100-150mm, and the overall thickness e of
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the integral barrier was 65mm- As explained previously,
a structure of this type has a high resistance to attack
by a wide range of thermal and mechanical tools, and the
corrugated form of the copper plate 2 in this embodiment
is such as to ensure that the tip of any mechanical
cutting tool which is adapted to form a "handhole" size
aperture in the plate and which is advanced through the
barrier from the outside (that is the side remote from
the plate 1) will encounter hard elements 4 in the matrix
behind the plate 2 before that plate can be completely
penetrated.
To produce a structure of the type shown in Figure 1 the
ollowing procedure may be adopted. Rows of "L" anchors
5 (Figure 2) are welded to the backing plate 1 and the
preformed plate 2 is fitted over these anchors, the plate
2 first having been prepared with appropriately spaced
holes 6 in the troughs of selected corrugations (as
illustrated), or elsewhere, for this purpose. Cross rods
7 are introduced to run over the surface of the plate 2
and beneath the respective anchors 5 in each row, and the
assembly of rods 7 and anchors 5 is welded together. The
rods 7 and anchors 5 serve accurately to define the
position of the plate 2 in relation to the remainder of
the structure during the subsequent steps of manufacture
and, most importantly, offer high resistance to
separation of the completed security barrier from the
backing plate.
. .
After welding up the rods and anchors the plate 1 is
assembled with a re-usable mould structure to define an
appropriate mould cavity around the plate 2, and the
ALOXITE or like nuggets 4 are introduced into the
resulting volume. The whole is then preheated and molten
aluminium alloy is poured into the cavity to form the
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matrix 3, the aluminium completely filling the
interstices between the nuggets 4 and plates 1 and 2.
The aluminium flows around both sides of the copper plate
2 and through the holes 6 and further pepared holes 8 in
the plate so that the plate is intimately embedded in the
resultant matrix. Finally, when the casting has cooled
the plate l is removed from the mould structure to leave
a security barrier of the form shown in Figures 1 and 2.
10 Turning now to Figure 3 this shows one example of the
practical application to a security enclosure of barrier
structures according to the invention. In this, the door
9 and body 10 of a safe incorporate, respectively, slab
and "bell" type barrier structures comprising copper
15 plates 2 in aluminium/alumina matrices 3/4 as previously
described, the corrugations in the door plate 2 being
shown running vertically and the corrugations in the body
plate 2 being shown running horizontally. In addition,
wrought copper strips 11 and 12 are integrated into the
20 respective barrier structures at positions adjacent to
the junction between the door edge and safe body. These
strips 11 and 12 are especially useful in protecting
against a torch attack on the door bolts 13 and their
detentions 14 in the safe body - in particular they will
25 resist attempts to widen the gap 15 between the door and
body in an effort to direct a torch at the bolts
13/detentions 14 at a favourable angle through that gap.
In Figure 4 there is shown another embodiment of a
30 barrier structure in accordance with the invention-
There is a corrugated wrought copper plate 2' anchored to
a backing plate 1' generally as described before, but in
this case the plate 2' is disposed within a matrix 3' of
hard security concrete of a total thickness of, say,
35 150mm. The plate 2' is secured to the plate 1' by
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anchors S' and rods 7' functionally equivalent to the
anchors 5 and rods 7 previously described, additional
anchors 16 and rods 17 also being provided to increase
resistance to separation of the concrete 3' from the
plate 2'. An outer finishing skin is indicated at 18.
The concrete 3' is preferably a fibre-reinforced concrete
and contains a high proporation of quartzite or other
selected very hard aggregate.
