Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND of the INVENTION
The invention relates to a method of fabricating
three-piece type cartridge cases, and by extension,
to the cartridge case obtainable by implementation
of such a method.
05 Cartridge cases, in particular those for guns used
in hunting and competition shooting (skeet), are
fashioned conventionally by assembling a number of
discrete parts consisting but minimally in material
of any value, in order to gain economies both in
manufacture and ultimately in use, given that such
items are generally fired once and discarded.
In the method of fabrication most widely adopted
for three-piece cartridge cases, use is made of a
tube of plastic or paper material, a cylindrical
strengthening piece, also in plastic or paper, and
a metal base.
The base appears essentially as a cylinder of which
the bottom end is enclosed and enlarged around the
periphery by incorporation of a molded rim serving
to create an complementary internal seating, and is
holed at center to take a cap for detonation of the
propellant. The tube, likewise cylindrical, slots
into the base until fully abutted with the enclosed
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bottom, and the peripheral edge of the inserted end
may also be rolled inwards toward its axis, fox a
reason that will become apparent in due course. The
strengthening piece is also cylindrical externally,
05 affording a center hole designed to align coaxially
with the hole in the base which accommodates the
cap, and is fashioned in a deformable material for
a reason that will emerge from the brief outline of
the conventional method which follows.
For example, the strengthening piece is inserted
into one end of the tube, and this preassembled end
then pushed full into the base to the point where
contact is made with the enclosed bottom; in the
event that the edge of the tube is rolled inwards,
as aforementioned, the tube will be inserted into
the base, and the strengthening piece then inserted
into the tube and located against the rolled edge.
Thereafter, with the three pieces positioned one in
relation to the other and correctly held in place,
a compressive force is applied to the strengthening
piece, which under the resultant stress is required
to perform two basic functions: first, to compress
the tube against the internal cylindrical surface
of the base, and second, to deform the rolled edge
of the tube radially in such a way as forces it
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into the seating created within the molded rim of
the base. During such an operation, considerable
mechanical stresses are applied to the materials
both of the tube, and of the strengthening piece in
05 particular, which can cause irreparable damage if
not properly controlled. For example, if too great
a force is applied to the strengthening piece, the
stretch of the tube inserted into the base may be
pinched too tightly and its ability to withstand
tensile stress thus weakened, resulting in a loss
of strength when the cartridge is fired.
This complex and delicate assembly is nonetheless
indispensable in order to ensure that the tube does
not separate from the base on detonation of the
charge and enter the barrel of the gun, of which
the consequences would clearly be hazardous.
This same assembly procedure serves also to ensure
that the base of the cartridge, accommodating the
cap and bolstered by the strengthening piece, will
afford firm resistance to the firing pin of the gun
at the moment when the cap is struck; the requisite
properties of rigidity and strength, which can be.
ensured only where relative movement between the
three pieces is disallowed, roust be calculated with
absolute precision to avoid any risk of irregular
CA 02013981 1999-OS-14
initiation and detonation of the charge.
A further aim of the operation in question is to
eliminate or at least to minimize the leakages of
combustion gas that tend to occur from between the
05 tube and the strengthening piece, which distort the
base and thus affect the dimensional structure of
the cartridge case.
Numeronis intrinsic. problems are thus posed in the
assembly operation, first among which is the need
for technically complex and high powered machinery,
given the requirement for a considerable force to
b~~ generated internally of a restricted space such
as that afforded by a cartridge case. Moreover, the
part of the machine that engages the strengthening
piece and invests it with the compressive force
roust be of a precise shape, in order to permit of
applying the force correctly to ensure a tight
union of the three pieces and obtain the desired
rigidity of the base.
Neither is it possible to ignore the many external
factors adversely affecting the assembly operation
and tending to inhibit a firm association between
the three pieces. Among such adverse factors are
the restrictive dimensions of the seating afforded
by the molded rim of the base, the difficulty of
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bringing about a repeatable and uniform insertion
of the tube and strengthening piece materials into
the seating to provide an efficient anchorage, and
the possible tendency of the elastic strengthening
05 material to regain its original shape.
This entire range of factors is aggravated further
by the obvious difficulty of verifying with the aid
of non-destructive technical or visual means that
forcing of the strengthening piece has resulted in
the successful formation of a lip internally of the
base seating, this being in effect the one element
capable of ensuring a positive connection between
the three component pieces.
Accordingly, the object of the present invention is
to provide a method of fabricating three-piece type
cartridge cases whereby. the connection of the three
pieces can be maintained secure from assembly right
through detonation and c7ischarge without the aid of
powerful compressive forces during assembly tending
to deform and thus alter the geometry of one or
more of the component parts of the case.
A further object of the invention is to permit of
assembling cartridge cases by adoption of a simple,
rational and economic method capable of overcoming
' the drawbacks mentioned above.
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SUMMARY of the INVENTION
The stated objects are realized comprehensively by
adoption of a cartridge case design as disclosed,
05 of which the essential feature is that no reliance
is placed on deformation of the strengthening piece
to obtain a tight fit between the three component
parts; instead, by utilizing an open bottomed base
and a strengthening piece fashioned in essentially
rigid material with the necessary retaining flange
already incorporated, and inserting the tube and
the strengthening piece into the base from opposite
directions, the need for high compressive forces is
dispensed with, and it remains simply to crimp the
open bottom of the base in toward the center.
BRIEF DESCRIPTION of the DRAWINGS
The invention will now be described in detail, by
way of example, with the aid of the accompanying
drawings, in which;
-fig 1 illustrates the three pieces of a cartridge
case according to the invention, in axial section,
seen in readiness for assembly by implementation of
the method disclosed;
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figs 2...4 are further axial sections of the three
pieces of fig 1, seen during successive steps of
the method disclosed;
-fig 5 illustrates a different embodiment of the
05 cartidge case of fig 4, seen in axial section;
-figs 6...8 illustrate three different embodiments
of the strengthening piece shown in fig 1.
DESCRIPTION of the PREFERRED EMBODIMENTS
Referring now to the drawings, the method according
to the present invention permits of fabricating a
cartridge case, denoted l in its entirety, embodied
in three component parts: a cylindrical tube 2, a
15 strengthening piece 3 insertable into the tube, and
a base 4.
The method disclosed consists first and foremost in
fashioning a basically cylindrical strengthening
piece 3 from essentially non-deformable material,
20 of shape such at least as to exhibit a peripheral
lip, or flange, denoted 3l, which in the example
illustrated exhibits a maximum diameter 3d greater
than the maximum diameter 2d of the tube, and is
flared in relation to the cylindrical surface of
25 the component.
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Needless to say, the strengthening piece 3 will be
non-deformable not in any absolute sense, but only
insofar as no deforrnation occurs during the steps
of the method disclosed. Also, reference to the
05 strengthening piece 3 of a. cartridge case according
to the invention as being non-deformable permits
conveniently of drawing a clear distinction with
the corresponding component in a conventional
cartridge case, of which the drastic deformation
undergone during assembly is such as to alter both
its geometry and its mechanical properties; whereas
the application of a strong compressive force is
intended conventionally to enhance rigidity of the
flat bottom of the base, this very notion places a
marked limitation on the number of profiles that
can be adopted for the strengthening piece, which
in the finished cartridge is positioned in dixect
contact with the propellant.
mhe method according to the invention comprises the
further expedient of adopting a base 4 embodied
with two coaxial stretches 4l and 42 of dissimilar
internal diameter 41d and 42d, respectively, of ;
which the smaller diameter Old is substantially
equal to the external diameter 2d of the tube 2,
and the larger diameter 42d is substantially equal
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to the maximum diameter 3d of the flange 31 of the
strengthening piece 3. The two coaxial stretches 41
and 42 are interconnected by a stretch 43 serving
to create a peripheral rim, matched in profile with
05 the flared flange 31 of the strengthening piece 3,
internally of which a complementary seating 45 is
afforded of dimensions such as to accommodate the
flange 31 and one end 21 of the tube 2 together.
Utilizing a strengthening piece 3 and a base 4
10 embodied thus, the method disclosed comprises the
following steps:
-insertion of the tube 2 into the base 4 to the
point where the inserted end 21 projects beyond the
level, denoted 44, at which the smaller diameter
stretch 41 of the base 4 merges with the rim 43, by
a distance 1 not less than the axial dimension of
the peripheral flange 31 (fig 2);
-insertion of the strengthening piece 3 into the
base 4 and into the projecting end 21 of the tube 2
in such a way that the projecting end 21 is splayed
and driven into contact with the internal wall of
the seating 45 (fig 3);
-folding of the larger diameter stretch 42 of the
base 4 in toward center to the point where contact
is made with the strengthening piece 3 (fig 4).
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The length 1 of the inserted end 21 of the tube 2
may vary from the rninimum shown in fig 4, in which
case the flange 31 of the strengthening piece 3
registers in direct contact with the inside wall of
05 the larger diameter stretch 42 of the base 4, up to
a maximum that exceeds the.axial dimension of the
flange 31, measured parallel to its generators, in
such a way that the tube projects into the larger
diameter stretch 42 to the point of enveloping the
flange 31 entirely (see fig 5). In this instance,
the outer diameter 3d of the peripheral flange 31
will be substantially equivalent to the internal
diameter 42d of the relative stretch of the base 4,
minus twice the thickness s of the tube 2.
It will be apparent immediately that the method
disclosed hinges on the adoption of a strengthening
piece that is preformed, and can be assembled with
other components to create a rigid fabricated whole
by exploiting an established geometry that remains
unaltered throughout the assembl
y procedure.
Expressed in other terms, the stability of the fit
between tube 2, strengthening piece 3 and base 4 is
ensured by a geometrical shape that is discernible
and verifiable prior to assembly and remains stable
right through to completion of the assembly steps.
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Accordingly, the machine used to lock together the
three components, namely the tube 2, strengthening
piece 3 and base 4, will be a simple and economical
item of equipment when compared with the machines
05 currently in use; thus, the costs of manufacturing
cartridge cases can be cut drastically by virtue of
the substantially smaller capital outlay, and the
significant savings in expenditure on labor, raw
materials and maintenance of the equipment. In the
case of conventional equipment currently in use, in
effect, where one has considerable forces unleashed
in confined spaces such as that encompassed by a
cartridge tube, servicing of the higher precision
machines (presses in particular) is essentially an
on-going process. As to the consumption of raw
materials, this is undoubtedly reduced by adoption
of the method disclosed, inasmuch as the base 4 is
of open design rather than enclosed as in prior art
embodiments. What is more, the method disclosed
permits of eliminating the operation of roll-edging
one end of the tube 2 in order to improve tYie fit
between the three components.
As illustrated in fig 4, a typical cartridge case 1
obtained by implementation of the method disclosed
will be seen to consist in a tube 2, an open-ended
3
CA 02013981 1999-OS-14
13
base 4 ensheathing the tube, and a strengthening
piece 3 that is embodied with a radially projecting
peripheral flange 31 and inserted into the tube.
Given that the strengthening piece 3 is not subject
05 to appreciable deformation during assembly, it can
be embodied with the geometrical shape best able to
ensure that the cartridge case 1 is as functional
and ballistically effective as possible.
For example, 38 denotes the part of the piece 3 in
contact caith the propellant, which might be cupped
as illustrated in the drawings; this part could be
embodied faith projections 33 disposed peripherally
about an axial hole 32 in the strengthening piece 3
which serves to accommodate a detonation cap 5.
Such projections 33 have the function of ensuring
that the propellant powder, which is subsequently
packed into the cup 38, does not smother the fire
issuing from the cap 5 seated in the hole 32, and
might be embodied as a plurality of fins radiating
from the hole; in positive terms, the fins serve to
increase the propagation front of the flame thrown
by the cap 5.
The axial hole32 in the strengthening piece 3 might
be embodied in a variety of ways in order to enable
the accommodation of different types of cap 5; the
14
hole 32 could incorporate a rigid elernent 34, for ,
example, serving as the anvil for a conventional
"Berdan" type cap (fig 7).
In a further embodiment, the strengthening piece 3
05 could exhibit a peripheral groove 35, and created
between the groove 35 and the cup 38, a web 37 that
is able to flex in the face of thrust generated by
the detonating powder. In this type of embodiment,
the flexibility of the web 37 remains compatible
with the essentially non-deformable characteristic
of the strengthening piece 3 described earlier. In
effect, the web 37 undergoPS no defarmation during
assembly of the three components of the cartridge
case, even as a result of such forces as may be
generated in the course of the procedure, though
deformation is indeed envisaged thereafter, when
the cartridge is discharged and becomes subject to
forces infinitely greater in absalute terms than
those attributable to the steps of the method as
described above.
Fig 8 illustrates an embodiment of particular
' interest as regards the question of saving on raw
materials. More e:~actly, the strengthening piece 3
is relieved of matserial at points 36 on the side
25, accommodated by the larger diameter stretch 42 of
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the base, and in the case in question, simply by
sinking a number of blind holes. Such an expedient
is made possible by virtue of the fact that the
piece is not subject to any deforming stress worthy
05 of note during assembly of 'the cartridge case 1,
and being thus able to retain its shape unaffected,
can be embodied with any given geometry provided
that the peripheral flange 31 is included.
The method disclosed provides a facility not found
10 in'prior art cartridge case manufacture, namely, of
selecting the geometry of the strengthening piece 3
according to the features it may be sought to build
into the cartridge case; the strengthening piece 3
thus plays an active role in fabrication, given
15 that a variation in its shape has material bearing
on the performance of the finished cartridge.
