EP0385612A2

EP0385612A2 - Device for retaining electric igniters in association with a cartridge of explosives

Info

Publication number: EP0385612A2
Application number: EP90301597A
Authority: EP
Inventors: Peter John Snodgrass
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1989-03-01
Filing date: 1990-02-14
Publication date: 1990-09-05
Also published as: ZM690A1; GB2228784A; NO900810L; GB9003350D0; GB8904636D0; ZW2190A1; NO900810D0; ZA901323B; EP0385612A3

Abstract

A device for positioning and retaining plurality of electrically actuable ignition assemblies (5), suitable for use in blasting operations in association with a cartridge of explosive (11) comprises a housing (1) consisting of first and second housing portions (2, 3). In use one end (12) of the cartridge of explosive (11) is retained by the first housing portion (2) by an interference fit, whilst the second portion (3) includes a chamber (10) for receiving and positioning the igniter assemblies (5) adjacent the end (12) of the cartridge (11). The housing (1) is fitted to the end of the cartridge (11) and a plurality of holes are formed therein for insertion of a plurality of detonators into the cartridge (11). The igniter assemblies (5) may then be located in the chamber (10). A supply conductor extends through the igniter assemblies (5) via channels (6) formed in the housing (1), and a nose cap (7) is fitted to the top of the device.

Description

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.
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).
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.
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.
It is an object of the present invention to obviate or mitigate the aforesaid disadvantages.
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.
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.
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.
The device preferably further includes a cap member adapted to fit onto the upper end of said upper portion.
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.
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.
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.
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.
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.
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.

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.
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).
The chamber 10 also provides access between the top of the upper housing portion 3 and the inside of the lower housing portion 2.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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)
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.

Claims

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.