[0001] The present invention relates to a device capable of positioning and securely retaining
a plurality of electrically actuable ignition assemblies, suitable for use in blasting
operations, in association with a cartridge of explosive.
[0002] The most common electrically actuable ignition assemblies currently used are those
disclosed in U.K. Patent Publications Nos 2,022,222B and 2,109,512A. Such ignition
assemblies are now sold under the tradename "MAGNADET", and are used in conjunction
with the "MAGNA" primer system. ("MAGNADET" and "MAGNA" are trade marks of Nitro-Nobel
AB, Sweden).
[0003] The "MAGNA" primer system has, however, the disadvantage of high cost over systems
using a cartridge of explosive. Further, until now, systems using a cartridge of explosive
have suffered from the problem of securely retaining the ignition assemblies within
the cartridge while the cartridge is being lowered down a bore-hole.
[0004] The cartridge would normally be lowered down the bore-hole by means of the supply
conductor to the ignition assemblies, the supply conductor being commonly known as
the "MAGNA" downline.
[0005] It is an object of the present invention to obviate or mitigate the aforesaid disadvantages.
[0006] Accordingly, the present invention provides a device for positioning and retaining
a plurality of electrically actuable ignition assemblies, in association with a cartridge
of explosive, comprising:
a housing having a lower portion adapted to receive at least a portion of said cartridge
therein, and an upper portion including a chamber adapted to receive and retain said
plurality of igniters adjacent said lower portion.
[0007] Preferably, said lower portion comprises a hollow body having a lower end which is
open to receive said portion of said cartridge, and an upper end adjoining said upper
portion, and is shaped and dimensioned so as to receive said portion of said cartridge
in an interference fit.
[0008] Preferably also, said upper portion comprises a hollow body having a lower, open
end adjoining the upper end of said lower portion, and an upper end closed by a topmost
surface, said topmost surface having an aperture formed therein and said chamber being
defined by walls extending downwardly from the periphery of said aperture into the
interior of the upper portion, the chamber being open at its top and bottom ends.
[0009] The device preferably further includes a cap member adapted to fit onto the upper
end of said upper portion.
[0010] Preferably also, first and second channels extend inwardly from the periphery of
the topmost surface of said upper portions and intersecting the walls of said chamber,
said channels being colinear and disposed opposite one another on opposite sides of
said aperture.
[0011] Preferably also, said upper portion further includes a plurality of webs interconnecting
the outer surface of the walls of said chamber and the inner surface of the upper
portion of the housing.
[0012] Preferably also, said chamber is provided with one or more lugs extending inwardly
from the walls thereof and against which said igniter assemblies may abut when located
in the chamber.
[0013] Preferably also, said upper portion further includes a shoulder extending around
the periphery of said topmost surface and adapted to receive said cap member in push-fit
engagement.
[0014] In the embodiment described herein, said lower portion is substantially cylindrical
in shape, said upper portion is substantially frustoconical in shape, and said chamber
is substantially rectangular in shape.
[0015] An embodiment of the invention will now be described by way of example only, with
reference to the accompanying drawings, in which:
Fig. 1 is an exploded schematic side view of a device embodying the invention, and
also shows two electrically actuable ignition assemblies and a cartridge of explosive;
Fig. 2 is a sectional side view of a preferred embodiment of the invention with the
nose piece removed;
Fig. 3 is a plan view from the top of the preferred embodiment of Fig. 2;
Fig. 4 is a plan view from the base of the preferred embodiment of Fig. 2;
Fig. 5 is a sectional side view of the preferred embodiment of Fig. 4, taken along
line A - A;
Fig. 6 is a sectional side view of a preferred embodiment of a nose piece of the invention;
Fig. 7 is a plan view from the base of the preferred embodiment of the nose piece
of Fig. 6;
Fig. 8 is a sectional side view of the preferred embodiment of the invention with
the nose piece in position.
[0016] Referring now to the drawings, the device comprises a hollow housing 1, consisting
of a lowermost, substantially cylindrical portion 2, the lower end 4 of which is open,
and an uppermost, substantially frustoconical portion 3, coaxial with the first portion
2, the upper end of which is closed by a top surface 14. The radius of the base of
the upper portion 3 is equal to the radius of the lower portion 2, the base of the
upper portion 3 adjoining the second end of the lower portion 2 to form the hollow
housing 1.
[0017] A rectangular aperture 15 is formed in the top surface 14 of the upper housing portion
3, and side walls 16, 17, 18 and 19 extend downwardly from each edge thereof into
the interior of the upper portion 3 to define a substantially rectangular chamber
10 therein, open at its top and bottom ends. The chamber 10 serves to receive and
retain a plurality (in this case, two) of electrically actuable igniter assemblies
5, each comprising a troidal transformer core (not shown) enclosed in a plastic casing
(not shown) and having an actuating conductor 20 extending therefrom for connection
to a suitable detonator (not shown).
[0018] The chamber 10 also provides access between the top of the upper housing portion
3 and the inside of the lower housing portion 2.
[0019] Two of the side walls 16 and 17 are provided with transverse lugs 13 extending laterally
into the chamber 10, such that the electrically actuable igniter assemblies 5, when
located in the chamber 10, rest on the lugs 13 such that they are substantially aligned
with the top of the upper housing portion 3.
[0020] The upper housing portion 3 is further provided with colinear, laterally extending
channels 6, which intersect the side walls 16 and 17 of the chamber 10, to allow a
supply conductor (not shown) access to the igniter assemblies 5. In practice, the
supply conductor passes through the toroidal cores of the igniter assemblies and its
free ends exit the chamber 10 via the channels 6.
[0021] The second housing section 3 also includes four webs 9 extending in a radial direction
from the four outer corners of the rectangular chamber 10 to the inner surface of
the upper frustoconical housing portion 3.
[0022] Finally, the device also includes a substantially hemispherical nose cap 7 which
is a push fit onto the top of the upper housing portion 3. The upper portion 3 is
provided with a circumferential shoulder 8 which receives the cap 7, and vertical
webs 21 are spaced around the shoulder to help retain the cap 7 in position. The cap
7 is itself provided with internal strengthening webs 22.
[0023] A cartridge of explosive 11 may be positioned and retained within the lower housing
portion 3 by an interference fit. Access to the end 12 of the cartridge 11 placed
within the housing 1 may therefore be gained via the chamber 10. A pricker, made from,
for example, aluminium or brass, may be used to puncture the outer skin of the cartridge
11 and form a hole suitable for the acceptance of a detonator (not shown) connected
to an electrically actuable igniter assembly 5. A number of such holes may be formed
to accept and retain a plurality of such detonators. The toroidal transformer cores
of the igniter assemblies 5 are positioned and retained within the chamber 10, the
central axis of the toroidal cores being substantially parallel to the direction of
the laterally extending channels 6. The cartridge of explosive 11 may consist of any
detonator-sensitive product e.g. slurry or emulsion explosives. Further, the outer
skin of the cartridge 11 can suitably be made from, for example, polythene, various
polyesters or nylon.
[0024] The housing 1 and nose piece 7 may be made from any suitable material, e.g. polypropylene.
It has been found that other plastics tend to be too brittle, and that nylon has the
disadvantage of being more expensive. It should, however, be appreciated that other
flexible plastics, e.g. polyethylene, and more specifically low density (LD) polyethylene,
may be used.
[0025] Having correctly inserted the detonators within the cartridge of explosive 11, and
the toroidal cores of the plurality of igniter assemblies 5 within the chamber 10,
the nose piece 7 may be attached to the upper housing portion 3, so protecting the
igniter assemblies 5 from the ingress or retention of any foreign matter, and further
ensuring retention of the igniter assemblies 5 within the chamber 10.
[0026] The electrical supply conductor, to the electrically actuable ignition assemblies
5 retained within the cavity 10, may be fed through the centre of the toroidal cores
of the ignition assemblies 5 via the laterally extending channels 6.
[0027] The assembly may then be lowered down a bore-hole by means of the electrical supply
conductor, with the nose piece 7 lowermost. The force of the assembly hitting the
bottom of the bore-hole will cause the radially extending webs 9 to pierce the outer
skin of the cartridge 11 and in so doing, allow explosive material to fill the upper
housing portion 3. The radially extending webs 9 may be serrated to aid in piercing
the skin of the cartridge, however in practice this has been found not to be necessary.
[0028] The nose piece 7 may be designed such that on the assembly hitting the bottom of
the bore-hole, the nose piece 7 will partially collapse and in so doing absorb part
of the force of impact.
[0029] Figs. 2 - 8 show the preferred embodiment of the device for use with a "POWERGEL"
cartridge of explosive and two "MAGNADET" ignition assemblies, the "POWERGEL" cartridge
having a typical outer diameter of 84 mm. ("POWERGEL" is a trade mark of Nitro-Nobel
AB, Sweden)
[0030] The preferred embodiment of the invention disclosed herein provides a particularly
simple device for positioning and retaining a plurality of igniter assemblies associated
with a cartridge of explosive. It will be appreciated, however, that other modifications
may be made within the scope of the invention, and that the dimensions of the device
will be suitably altered if igniter assemblies other than "MAGNADET" assemblies, and
cartridges of explosive other than "POWERGEL", are used.
1. A device for retaining and positioning a plurality of electrically actuable igniters
(5) in association with a cartridge of explosive (11) characterised in that said device
comprises a housing (1) having a lower portion (2) adapted to receive at least a portion
(12) of said cartridge (11) therein, and an upper portion (3) including a chamber
(10) adapted to receive and retain said plurality of igniters (5) adjacent said lower
portion (2).
2. The device of claim 1 characterised in that said lower portion (2) comprises a
hollow body having a lower end (4) which is open to receive said portion (12) of said
cartridge (11), and an upper end adjoining said upper portion (3), and is shaped and
dimensioned so as to receive said portion (12) of said cartridge (11) in an interference
fit.
3. The device of claim 1 characterised in that said upper portion (3) comprises a
hollow body having a lower, open end adjoining the upper end of said lower portion
(2), and an upper end closed by a topmost surface (14), said topmost surface (14)
having an aperture formed therein and said chamber (10) being defined by walls (16,
17, 18, 19) extending downwardly from the periphery of said aperture into the interior
of the upper portion (3), the chamber (10) being open at its top and bottom ends.
4. The device of claim 3 characterised in that there is provided a cap member (7)
adapted to fit onto the upper end of said upper portion (3).
5. The device of claim 3 or claim 4 characterised in that there are provided first
and second channels (6) extending inwardly from the periphery of the topmost surface
(14) of said upper portion (3) and intersecting the walls (16, 17) of said chamber
(10), said channels (6) being colinear and disposed opposite one another on opposite
sides of said aperture.
6. The device of any of claims 3 to 5 characterised in that said upper portion (3)
further includes a plurality of webs (9) interconnecting the outer surfaced of the
walls (16, 17, 18, 19) of said chamber (10) and the inner surface of the upper portion
(3) of the housing (1).
7. The device of any of claims 3 to 6 characterised in that said chamber (10) is provided
with one or more lugs (13) extending inwardly from the walls (16, 17) thereof and
against which said igniter assemblies (5) may abut when located in the chamber (10).
8. The device of any of claims 4 to 7 characterised in that said upper portion (3)
further includes a shoulder (8) extending around the periphery of said topmost surface
(14) and adapted to receive said cap member (7) in push-fit engagement.
9. The device of any preceding claim characterised in that said lower portion (2)
is substantially cylindrical in shape.
(10). The device of claim (9) characterised in that said upper portion (3) is substantially
frustoconical in shape.
11. The device of claim 9 or claim 10 characterised in that said chamber (10) is substantially
rectangular in shape.