Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to tampable blasting cartridges
In the past it had been traditional for explosives intended
for use as blasting explosives in boreholes or shotholes to be
prepared as cartridges of conventional dynamite, which were
packed in paper of various qualities. These cartridges were
manufactured usually by spirally winding thick paper, often
impregnated with wax, into a hollow cylinder. The explosive
was retained in the cylinder by a closure at each of its op-
10 posite ends, the typical closure being known as a "crimp"The method of crimping essentially was a folding over and ra-
dially inwardly of the paper wall of the open end of the
cylinder and pressing the folded over paper against the explo-
sive Such cartridges were rigid tubes of predetermined
15 diameter.
The advent of synthetic resin plastics as a commodity
of commerce soon provided another material for packaging
explosives and rigid tubes of plastics with a type of plug
or cap at each end made their appearance. More commonly,
20 however, the modern types of explosive compositions such as
the ammonium nitrate/fuel oil blasting agents and the aqueous
slurry or water based gel explosives have been packed in
plastics bags or cylinders made of tubular plastics film with
closures at each end. The cylinder is available either as
25 a preformed, flattened tube, which is filled from one end, or
is made by continuously forming a tube from a flat length of
plastics film, which is folded over to a circular form and
welded or otherwise sealed by adhesive down the longitudinal
seam Such a continuously formed tube is filled, sealed
30 transversely at specified unit lengths of tubing and
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cut through adjacent the seal to provide the so-called
sausage of blasting explosive. Normally the
transverse sealing is effected by a loop or ring of
metal, which is bent and thus fastened around the
constricted plastics tube after completion of the
filling operation.
- In blasting operations it is of prime
importance that the blasting explosives totally fill
the cross-section of the drilled cavity at the place
where it will be initiated to ensure the maximum
effect of shock waves penetrating the surrounding
rock. The explosive charge may not perform its
designed task if cushioned by pockets of air or
allowed to expend itself uselessly in any direction.
In most blasting applications, for instance, the
slurry type of explosives needs to be well tamped in
holes of small diameter.
Present practice to achieve this objective
with known packaged explosives fails for several
reasons. If sausages of explosives are forcibly
compressed or tamped, the plastics film invariably
ruptures and the sausages burst open. It is known
that plastics films widely used for packaging
~ explosives have high tensile strength until a tear is
initiated and that the tear propagates eas1y. It
is also known that sausages made of a plastics film,
which does not propagate a tear easily, do not tamp
efficiently. It is known further that the
properties of the explosives will be affected
adversely when in contact with water in a wet
borehole. The practical disadvantage of having to
prevent water from mixing with the explosive ~-
composition when tamping it in the toe of a borehole
is a serious and difficult one.
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Attempts to overcome the problem by increasing
the diameter of the sausage to approximate as nearly as
is possible to that of a borehole are unsuccessful,
The sausages either become wedged some distance down
the hole due to the irregularities in the wall of the
hole and then burst when forcibly urged further on or.
the film of the sausages snags on projections in the wall
and the sausages expose or expel their contents,
In the sequential blasting of a large number
of boreholes, the failure of one or more blasting
agents to explode presents the underground miner or
the quarry operator with a hazardous and time wasting
task, The unblasted holes have to be cleaned out,
15 recharged and blasted, Routine work is interrupted
and mine production delayed,
The object of this invention is to provide
packaging for explosives compositions to eliminate or
minimise the disadvantages inherent in known packaging
20 for use in loading and blasting boreholes,
According to this invention a tamping cartridge
suitable for use in a borehole comprises a blasting
explosive composition sheathed in a tubular covering of
moisture impervious material sealed at its opposite ends
25 and including deforming means, which enable the cartridge
to expand across its width when tamped in the borehole
without rupturing the material and thereby exposing the
composition,
An embodiment of the invention is a tampable blasting
30 cartridge wherein the covering is an inner tube, the
material of which has an area of overlap in unsealed
contact along its lengitudinal edges, and an outer
tube such that the inner tube fits intimately within
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the outer tube of spirally wrapped material with areas
of overlap in unsealed contact at the edges of the material,
the deforming means comprising said areas of overlap of
material in unsealed contact
Another embodiment is a tampable blasting cartridge
wherein the covering is an inner tube of spirally wrapped
material with areas of overlap in unsealed contact at the
edges of the material and an outer tube such that the inner
10 tube fits intimately within the outer tube of spirally
counterwrapped material with areas of overlap in unsealed
contact at the edges of the material, the deforming means
comprising said areas of overlap of material in unsealed
contact
Tamping cartridges of this invention may be designed
to have preferential parts of expansion, depending on the
particular requirements of its application Thus any one
or more parts of a cartridge may have overlapping areas
of material in unsealed contact along the borders or edges
20 of the material in specific locations of the cartridge
where expansion is required. The material may be, for
example, waxed paper, thermoplastics coated paper, thermo-
plastics film and latex rubber A combination of any two
or more different materials may be desirable in a tamping
25 cartridge of the invention. The opposite ends of the
cartridge will be sealed in known manner by glueing, hot-
air or hot-melt welding or by metal clip, for example
While the tamping cartridge is adaptable to
blasting with any type of explosive composition
30 normally used for blasting purposes in boreholes, it
is especially suited to the packaging of water based
gel explosives and other similar explosive slurries
The invention provides a package for blasting agents
and a final product which combines economy of production
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and use with safety, convenience and explosive effective-
ness under unfavourable conditions,
The tampable cartridge of the invention may be
packed and supplied in case lots but it is a product
adapted to being provided also in a detachable train
form, Such a configuration permits the operator to
choose any number of cartridges as may suit the needs of
the blasting operation to be undertaken, The connected
10 cartridges for multiple use can be simply pleated together
in accordian fashion to provide longer blasting charges,
Single cartridges may be detached by tearing along a
perforated or otherwise weakened web between two sealed
ends of adjoining cartridges,
One embodiment of the invention will be described
by way of example with reference to the accompanying
drawings in which
Figure l shows a view of a tampable cartridge to
illustrate its construction, and
Figure 2 shows a view of the completed cartridge
of Figure l but after it has been tamped.
Referring to the drawings in which like numerals
designated like parts, the tampable cartridge shown in
Figure 1 has an inner tube 10 of low density polyethylene
25 which fits snugly within an outer tube ll of low density
polyethylene, The inner tube lO has an area of an over-
lap along its longitudinal edges as is indicated by numeral
12. The overlap is unsealed and the material is allowed
free movement as between the upper and lower layers in
30 contact but subject to the restrictions impased by the
mass of explosive composition filling the inner tube lO
and by the outer tube ll,
The outer tube ll has been wrapped spirally
around the inner tube lO so that the material along
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its edges overlap as is indicated by numeral 13.
These overlaps also are unsealed and the material is
allowed free movement as between the upper and lower
layers in contact but subject to the restrictions imposed
by the tightness of the wrapping upon the inner tube 10
and the pressure exerted radially outwards by the mass of
explosive in tube 10,
One end of the two tubes 10 and 11 has been sealed
10 by a metal clip 14 but the opposite end 15 has not been
completed and sealed so as to reveal its features,
After completion of filling tube 10 with explosives,
the opposite end 15 will be wrapped and sealed with a
metal clip 14 as is illustrated at the lower end of
15 Figure 1 to form a tamping cartridge,
In use in the field, a tampable cartridge as
exemplified above would be inserted into a borehole
and tamped home. The cartridge would expand during
tamping so as to become shorter in length and wider in
20 diameter as illustrated in Figure 2. In the form
shown in the drawing, the tamping operation has
compressed the explosive mass, which is in a plastic
state, so as to widen the cartridge transversely to
form a good seal with the periphery of the hole but
25 without any rupture in the covering material which
would expose the explosive composition to moisture,
It will be obvious to those skilled in the
art that various embodiments of the tampable cartridge
of this invention falling within the scope of the
30 accompanying claims may be suitably employed in the
exercise of this invention,
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