Note: Descriptions are shown in the official language in which they were submitted.
1055287
The prcsent invention relates to a method of
preparing an explosive charge from an explosive and a
detonator, such as an explosive charge intended for
insertion into a drill hole. The invention also relates
to an apparatus for use in performing the method of the
invention.
Explosive charges formed from a mouldable explosive
material and a detonator have previously been prepared by
- cutting off a portion of explosive material from an oblong block of
the explosive material and then applying this portion of explosive
material to a detonator, the explosive material being moulded
and shaped manually substantially to surround the detonator.
This prior art method and the subsequent use of
explosive charges made by this prior art method are associated
with serious drawbacks or disadvantages.
An explosive charge of a mouldable explosive
material applied to a detonator in the above described
conventional way can, of course, be lowered into a drill
hole to the desired position, by means of a detonating fuse
secured to the detonator. However, it has been found that
the slightest pull on the detonating fuse may result in the
explosive becoming separated from the detonator. If this
happens the explosive will not be detonated when the
detonator is activated. Also it has been found that
frequently not all the explosive material of a charge made by
the above described method is exploded when the detonator
is activated. Any explosive which is not detonated
and which remains in a drill
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hole and can cause extremely serious injuries when the
drill operator continues drilling without realizing that
there is any explosive left and unintentionally sets off
an explosion.
If the detonator is not completely covered by
explosive, a frequent occurrence with the above described methods,
there will be an angle between the drill hole and the explosive
charge when the charge is inserted into the hole and this may
easily result in the detonator becoming lodged i~ a crack in
the rock. In cases where this hashappened attempts to dislodge
the detonator with a so-called charge pin have often been
found to damage the detonator or cause insulation faults
in the detonating fuse of the detonator.
Another disadvantage of the above described method
is that the operator comes into direct skin contact with the
explosive while shaping it around the detonator. The
operator is therefore subjected to noxious gases emitted
from the explosive which may result in altered blood pressure.
When small explosive charges are being used in
shallow holes it is important for the diameter of the hole to
be as small as possible so that the pressure of gas acting
against the rock as a result of the explosion will give the
desired result. With a hole diameter of about 20 mm the
compression space will be reduced, and the area of rock
exposed to the high pressure gas during the explosion will
be low. With a hole diameter of about 30 mm for a drill hole
30 to 50 cm deep, when the explosion occurs plugging sand
will be thrown out, resulting in a "barrel shot". The charge
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quantity can be increased to avoid this phenomenon, but such a measure often
entails the risk of generating flying pieces of rock. Thus~ with the present
charging technique it has been impossible to achieve the ideal of using the
least possible quantity of explosive for a charge while at the same time ob-
taining the greatest possible effect.
According to one aspect of this invention there is provided a
method of preparing an explosive charge comprising a moldable explosive mate-
rial, a detonator, and a cartridge, comprising the steps of forming a cart-
ridge comprising a casing defining a cavity open at one end thereof and a
hollow tube of substantially the same length as the casing for accomodating
a detonator substantially centrally disposed within said casing and open at
an end thereof remote from the said one end of the cavity, a wall having at
least one hole therein connecting the periphery of the open end of said tube
to said casing, the end of said tube adjacent the open end of said casing
being tapered to facilitate entry of said moldable explosive material and
said casing being formed with a radially outwardly extending flange at said
open end to facilitate holding of said cartridge on introduction of said
moldable explosive material~ connecting the cartri.dge to a piston and cylinder
device which contains moldable explosive material; said cylinder having means
for securing the radial flange at the end of the cylinder, operating the
piston to urge said explosive material into said cavity to at least partially
fi~l said cavity with explosive, with said explosive surrounding said hollow
tube; and inserting a detonator into said hollow tube through the open end
thereof.
According to another aspect of this invention there is provided an
explosive cartridge comprising a cylindrical casing open at one end and a
coaxially hollow tube extending into said casing from the other end, a wall
integrally connecting the casing and the tube at the end opposite the open
end, said tube being of substantially the same length as said casing defining
A -4-
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a space for accomodating a blasting cap, said tube and casing defining there-
between a cavity for receipt of a moldable explosive material, the end of
said tube adjacent the open end of said casing being tapered to facilitate
entry of said moldable explosive material and the connecting wall having at
least one hole for the exhaust of air on introduction of the explosive materi-
al.
The cylinder of the apparatus preferably has an internal diameter
slightly larger than the diameter of the sticks of explosive material to be
used. Pieces of such sticks can be cut off and located in the cylinder, but
this may even be of such a length that a complete stick can be inserted there-
in. A suitable moldable gelatinized explosive is sold under the trade name
Dynamex. However, the invention is not limited to the use of this particular
explosive but may be used for any type of explosive which can be urged in the
cartridges by the piston and cylinder device.
It has been found that the present invention makes it possible to
use a very small quantity of explosive while achieving a relatively great
explosive effect for the gas pressure against the rock. The explosive charges
made by a method in accordance with the invention can with advantage be dimen-
sioned for use in drill holes about 20 mm in diameter. Since the explosive
need not be handled manually in order to surround the detonator *he invention
involves less risk of affecting the blood pressure of personnel performing
the invention. As a result of the central position of the det~nator in the
tube of the cartridge, surrounded by the outer casing~ the entire quantity
of explosive will always be detonated. The nose of the cartridge is prefer-
ably conical enabling the explosive charge to be lowered into a drill hole
safely without
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any risk of becoming lodged in a crack in the rock. Thus the
cartridge can be placed securely at the bottom of the drill
hole. Furthermore, by enclosing the explosive in a cartridge
in accordance with the present invention, the advantage is also
gained that such a cartridge can even be placed, if desired,
in a drill hole containing water, which ~s been substantially
impossible with charges prepared in conventional manner.
One of the more important advantages with the
explosive charges produced in accordance with the invention
is that their use increases safety in blasting work. The
invention also enables accurate measurement of the quantity of
explosive judged necessary for a certain purpose. When
making such decisions it is often necessary to take into~
consideration buildings or objects in the vicinity which
complicate satisfactory covering of the explosion spot or
make it impossible. The invention enables smaller charges to
be used as well as narrower drill holes (20 mm) than previously,
thus giving more reliable results and the depth of the hole
can be reduced without plugging sand being shot out. Less
dust is also caused when dry-drilling the smaller holes so
that half the weights applied on the drill can be removed
while still retaining the same drilling rate. This means a
reduction in the weight of the drill by about 7 kg which increases
the efficiency and reduces risks of accidents.
In order that the invention may be more readily
understood the following description is given by way of example
with reference to the accompanying drawings in which:
Figure 1 shows one embodiment of an apparatus
according to the invention comprising a cylinder fitted with
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a piston, a cartridge being connected to the apparatus,
Figure 2 shows a cartridge as illustrated in
Figure 1, with connecting sleeve, and
Figure 3 shows a finished explosive charge with an
inserted detonator.
Figure 1 of the drawings shows a cylindrical
cartridge 3 which is connected for filling with explosive
to a cylinder 1 provided with a piston 6. The lowermost end
of the cylinder l is provided with an externally threaded
section to receive an internally threaded connecting sleeve 2,
which may be in the form of a nut, to secure the cylindrical
cartridge 3 to the lowermost end of the cylinder 1. The
connecting sleeve 2 is provided with an inwardly directed,
annular flange 5 which encloses and presses against a corres-
ponding outwardly directed flange 4 provided on the cartridge
3, The flange 4 of the cartridge 3 is provided with two
opposing grooves 9 enabling the flange 4 to be easily
separated from the cartridge 3 after the cartridge has been
filled with explosive. The cartridge 3 is also provided
with a central tube 8 for receipt of a detonator 7
through an opening 10 in the end of the cartridge 3
facing away from the cylinder l.The end of the cartridge
3 provided with the opening 10 is preferably conical in
order to facilitate insertion of the cartridge into and ~~
passage of the cartridge down a drill hole. The cartridge
3 is also provided with one or more holes or openings 14 for
evacutation of air from the space 11 during the filling process.
One or more such holes can thus be arranged in the conical end wall
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12 or in the central tube close to the opening lO. The
space ll in the cartridge 3, which surrounds the central
tube 8, is in direct communication with the inside of the
cylinder 1 through an opening 15 in the cartridge. The
closed end 13 of the central tube, facing the cylinder 1,
is preferably pointed or rounded in order to facilitate insertion
of the explosive into the sp~ce and distribution of the explosive
around the central tube.
In order to prepare an explosive charge a cartridge 3
is first secured to the cylinder 1 by means of the connecting
sleeve 2. If not already done, the cylinder 1 is filled with a
mouldable explosive which is then pressed by the piston 6
into the space 11 in the cartridge. The quantity of explosive
pressed in in this way may vary from case to case and is dependent
upon the explosive action desired. The cartridge may preferably
be made of a translucent or transparent plastics material
enabling visual control of the filling level, in which case the
cartridge is preferably provided with visible markings or
graduations in charge quantities of, for instance, 10 and 20
gram. Corresponding graduations may also be marked on the
cylinder if desired, which may also be made of a suitable plastics
material. The piston 6 may also be graduated to indicate the
quantity of explosive pressed into the cartridge. When the
cartridge 3 has been filled with the desired quantity of
explosive 16, it is removed from t~ie cylinder 1 by unscrewing the
connecting sleeve 2, the cartridge then being released from the
connecting sleeve by axial displacement. The flange 4 on the
cartridge is removed by gentle pressure from the thumb, after
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which a detonator is inserted into the ccntral hole of the
cartridge as s]lown in Figure 3, in order to obtain a finished
explosive charge ready for immediate placing in a drill hole
- possibly with the help of a so-called charging pin, in which
case the collical end 14 is inserted first into the drill hole.
Alternatively the completed cartridge may be stored for later
use.
In one embodiment of the invention the cartridge and
its central tube 8 are ~ade in one piece from a suitable
plastics material. In alternative embodiments of the
invention the cartridge can be connected to the cylinder in
many ways other than that shown. For instance, the cylinder
may be provided with a groove, for example, a U-shaped
groove, into which the flange 4 can be inserted from the
side, in which case the connecting sleeve can be omitted.
The central tube normally extends the full length of the
cartridge. The mouldable explosive may be produced in the
form of cylindrical bodies with varying, predetermined w~ight
for instance, which bodies may be provided with cylindrical
holes or notches so that a body with the desired weight can be
inserted in a cartridge of the type described with the help of
the piston cylinder.
