CARTRIDGE END CLOSURE USING A DISC OF RESILIENT, CLOSED-CELL FOAMED SYNTHETIC PLASTICS MATERIAL

OBTURATEUR DE CARTOUCHE FAIT D'UN DISQUE SOUPLE EN MATIERE PLASTIQUE SYNTHETIQUE MOUSSEE A ALVEOLES FERMEES

English Abstract

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Abstract:
Cartridge end-closure
A tubular explosives cartridge having at least
one end closed by a transverse closure disc of
resilient closed-cell foamed synthetics plastics
material, for example, foamed polyethylene, the
disc having an uncompressed diameter greater than
the internal diameter of the tubular cartridge case.
The closure provides a waterproof seal without
preventing communication of detonation between
cartridges and may be readily pierced for the in-
sertion of a detonator. When the closure consists
of nitrogen blown polyethylene, it does not increase
the risk of firedamp ignition in coal mines.

Claims

CLAIMS:
1. A tubular blasting cartridge case for use in
blasting operations wherein a plurality of such cart-
ridges are disposed in file, said case being closed
at least at one open end by a transverse closure
disc of resilient closed-cell foamed synthetics
plastics material, said disc having an uncompressed
diameter greater than the internal diameter of the
tubular case.
2. A cartridge case as claimed in Claim 1 wherein
the closure disc has dimensions such that the disc
resilience causes sufficient outward radial pressure
against the case that the case is sealed against the
ingress of ambient water.
3. A cartridge case as claimed in Claim 1 wherein
the end rim of the tubular case is folded over inter-
nally to form an end bead to retain the closure disc
in the cartridge case end.
4. A cartridge case as claimed in Claim 1 wherein
one or more cannelures are formed in the end portion
of the case to engage the closure disc and hold it
in position.
5. A cartridge case as claimed in Claim 1 wherein
the foamed material has a density of 30 to 70 kg/m3.
6. A cartridge case as claimed in Claim 1 wherein
the closure disc has a thickness to uncompressed
diameter of 1:2.5 to 1:5.
7. A cartridge case as claimed in Claim 1 wherein
the synthetics plastics material of the closure disc
is foamed by blowing with an inert gas.
8. A cartridge case as claimed in Claim 1 wherein
the closure disc has been shaped by stamping from
a sheet of foamed plastics material.
9. A cartridge case as claimed in Claim 8 wherein
the closure disc has been stamped from a sheet of

closed-cell foamed polyethylene.
10. A cartridge case as claimed in Claim 1 wherein
the uncompressed diameter of the closure disc is
10 to 25% greater than the internal diameter of the
cartridge case.
11. A cartridge case as claimed in Claim 1 wherein
the casing material is selected from the group consist-
ing of cardboard, helically wound multi-ply paper and
extruded plastics material.
12. An explosive cartridge comprising a casing as
claimed in Claim 1 containing an explosive composition
selected from the group consisting of gelatinous
nitroglycerine explosive compositions, aqueous slurry
explosive compositions and ammonium nitrate powder
explosive compositions.

Description

~1468~3
Cartridge end-closure
This invention relates to exnlosive cartridges
and to a method of closing an end of an explosive
cartridge. The invention is especially advantageous
ior cartridged nitroglycerine gelatinous explosives
and aqueous slurry explosive compositions.
Explosive compositions have for many years been
packaged in rigid tubular cardboard or tough plastics
containers, the ends o~ the containers being closed
by inwardly crimping a portion of the container wall
or by covering the end with a thin cardboard or
plastics disc. This form o~ closure is not water
resistant and the cartridges were not suitable ~or use
in wet surroundings unless the explosive composition
was itsel~ water resistant.
When employed in cartridged form in a wet drill-
hole for rock blasting, deformable, water sensitive
explosive com~osition such as aqueous slurry explosives
are usually pac~ed in closed waterproo~ bags of thin
flexible synthetic plastics such as polyethylene
and the bags are placed inside rigid or tough tubular
containers of cardboard or plastics material. Because
of the need to seal the plastics inner bags and plug
the ends of the rigid containers there is often
excessive space between the explosive contents of
adjacent cartridges so that with relatively insensitive
explosives in small diameters the detonation may fail

1146803
to propagate between adjacent cartridges in file.
There is therefore a requirement for a cartridge
case to protect the ex~losive composition from ambient
water without unduly interfering with the communication
of detonation between cartridges. Moreover for
cartridges to be used in coal mines it is desirable
that the materials used in the cartridge case should
not increase the risk of igniting firedamp in the
vicinity of the explosion.
Accordingly it is an object of this invention to
provide an improved waterproof end-closure for a rigid
cartridge case.
In accordance with this invention at least one
end of a tubular cartridge case is closed by a trans-
verse closure disc of resilient closed-cell foamed
synthetic ~lastics material, said disc having an
uncompressed diameter greater than the internal
diameter of the tubular case. The dimensions of the
closure disc may be readily chosen such that the
disc resilience causes sufficient outward radial
pressure against the case that the case is sealed
against the ingress of ambient water.
The cartridge case end may be plain but more
reliable retention of the closure disc is obtained if
~5 the end rim of the tubular case is ~olded over
internally to form an end bead, or if one or more
internal projections, ~or example, one or more
cannelures are formed in the end ~ortion of the case
to engage the closure disc and hold it in position.
The de~ree of foaming and the thickness of the
closure disc are not narrowly critical, the practical
re~uire~ent being that the foamed material should be
sufficiently resilient to provide the required seal.
Thus a foamed material having a density of 30 to 70
kg/m3 is generally satisfactory and discs having a
thickness to uncompressed diameter ratio of 1:2.5 to
1:5 are generally sufficiently robust to provide an

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adequate seal, to resist displacement and to be readily
pierced for the insertion of a detonator in the field.
~ or cartridges to be used in mines where incendive
gases are present, it is preferred that the
5 closure disc should be made from foamed polyethylene,
preferably blown with an inert gas, for example,
nitrogen. A convenient, easily made closure disc is
one shaped by stamping from a sheet of foa~,ed plastics
material, for example, closed-cell foamed polyethylene
commercially available under the name "Plastazote"
(Registered Trade Mark) from Bakelite Xylonite Limited.
The uncompressed diameter of the disc is pref-
erably 10 to 25~o greater than the internal diameter
o~ the cartridge case. Thus for a case having an
internal diameter of 30 mm a disc having a diameter
of 33 to 37.5 mm, pre~erabl~ 35 mm is convenient.
The thickness o~ the disc in this case is conveniently
7 to 12 mm.
The cartridge case may conveniently be made from
any of the materials commonly used for that purpose,
for example, cardboard, helically wound multi-ply
paper or extruded plastics material.
The invention is further illustrated by the
cartridge end-closures illustrated in the accompanying
drawings wherein
Figs. 1 to 4 inclusive are longitudinal medial
sections of cartridge ends closed in accordance with
the invention. In the drawings like parts are depicted
by the same numeral.
In the cartridge end of Fig. 1 a disc 11 of
resilient closed cell polyethylene is inserted into an
end portion of a cartridge case 12. In its normal
state the disc 11 has a greater diameter than the
internal diameter of the cartridge case 12 and is
compressed to permit its insertion into the cartridge
case. Because of its resilient nature the disc 11
presses tightly around its periphery against the

~1468~)3
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case 12 and seals the case against the ingress of
water, so that the explosive contents of the
cartridge, which may advantageously be aqueous slurry
explosive or a powdered explosive based on ammonium
nitrate, are protected from ambient water. The other
end of the cartridge case 12 may if desired be closed
with a similar closure although any other waterproof
closure may be used.
In Fig. 2 the end of the cartridge case 12 is
turned over to form a top bead 13 against which the
disc 11 abuts so that the disc is more difficult
to displace from the case 12 by distortion of the
case.
In the cartridge end of Fig. 3 the cartridge
case is shaped at the end by two cannelures 14 and 15
between which the disc 11 is positively located.
The cartridge end o~ Fig. 4 is a ~odification o~
the cartridge end of Fig. 3 in which the mouth end of
the cartridge case 12 is extended beyond the cann-
elure 14 to provide an internally threaded portion 16which is adapted to receive an externally threaded
portion of an end of an adjacent cartridge. By
screwing the cartridge ends together a ~ile o~
cartridges may be readily assembled ~or loading in a
borehole.