EP0013473B1

EP0013473B1 - Cartridge end-closure

Info

Publication number: EP0013473B1
Application number: EP79302408A
Authority: EP
Inventors: Arthur Stephen Wright
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1979-01-15
Filing date: 1979-11-01
Publication date: 1986-12-17
Also published as: AU525543B2; JPS6350638B2; JPS5596899A; AU5283479A; GB2040412A; GB2040412B; EP0013473A1; CA1146803A

Description

This invention relates to a tubular blasting cartridge case closed at least at one end by a disc of synthetic plastics material.
Explosive compositions including gelatinous nitroglycerine explosives, aqueous slurry explosives and ammonium nitrate powder explosives have for many years been packaged in rigid tubular cardboard ortough plastics cartridge cases, the ends of the cases being closed by inwardly crimping a portion of the container wall or by covering the end with a thin cardboard or plastics disc. One form of closure disc described in US-A-2 345 887 is a solid synthetic plastics disc in sealing relationship with a cartridge case. However, we have found that, in a standard firedamp ignition test, cartridge end-closures consisting of solid plastics discs significantly increased the likelihood of firedamp ignition, and should therefore preferably not be employed in cartridges for use in coal mines.
Moreover, when employed in cartridged form in a wet drillhole for rock blasting, deformable, water sensitive explosive composition such as aqueous slurry explosives are usually packed in closed waterproof 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 exces- . sive space between the explosive contents of adjacent cartridges so that with relatively insensitive explosives in small diameters the detonation may fail to propagate between adjacent cartridges in file.
There is therefore a requirement for a cartridge case to protect explosive composition from ambient water without unduly interfering with the communication of detonation between cartridges and without increasing 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 blasting cartridge case is closed by a transverse closure disc of resilient closed-cell foamed synthetic plastics material foamed by blowing with inert gas, said disc having an uncompressed diameter greater than the internal diameter of the tubular case, the dimensions of the closure disc being 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 the end rim of the tubular case is folded over internally to form an end bead, or if one or more internal projections, for example, one or more cannelures are formed in the end portion of the case to engage the closure disc and hold it in position.
The degree of foaming and the thickness of the closure disc are not narrowly critical, the practical requirement 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 adequate seal, to resist displacement and to be readily pierced for the insertion of a detonator in the field.
For cartridges to be used in mines where incendive gases are present, it is preferred that the 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 foamed 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 preferably 10 to 25% greater than the internal diameter of 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, preferably 35 mm is convenient. The thickness of 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 pressed tightly around its periphery against the 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 of Fig. 4 is a modification of the cartridge end of Fig. 3 in which the mouth end of the cartridge case 12 is extended beyond the cannelure 14 to provide an internally threaded portion 16 which is adapted to receive an externally threaded portion of an end of an adjacent cartridge. By screwing the cartridge ends together a file of cartridges may be readily assembled for loading in a borehole.

Claims

1. A tubular blasting cartridge case (12) closed at least at one end by a transverse closure disc (11) made from synthetic plastics material and having an uncompressed diameter greater than the internal diameter of the tubular case characterised in that the closure disc (11) is made from resilient closed-cell foamed plastics material which is foamed by blowing with inert gas, the dimensions of said closure disc being such that the disc resilience causes sufficient outward radial pressure against the case (12) that the case is sealed against the ingress of ambient water.

2. A cartridge case as claimed in Claim 1 wherein the end rim of the tubular case (12) is folded over internally to form an end bead (13) to retain the closure disc (11) in the cartridge case end.

3. A cartridge case as claimed in Claim 1 wherein one or more cannelures (14, 15) are formed in the end portion of the case (12) to engage the closure disc (11) and hold it in position.

4. A cartridge case as claimed in any one of Claims 1 to 3 inclusive wherein the foamed plastics material has a density of 30 to 70 kg/m³.

5. A cartridge case as claimed in any one of Claims 1 to 4 inclusive wherein the closure disc (11) has a thickness to uncompressed diameter ratio of 1:2.5 to 1:5.

6. A cartridge case as claimed in any one of Claims 1 to 5 inclusive wherein the uncompressed . diameter of the closure disc (11) is 10 to 25% greater than the internal diameter of the cartridge case (12).

7. An explosive cartridge comprising gelatinous nitroglycerine explosive composition, aqueous slurry explosive composition or ammonium nitrate powder explosive composition encased in a tubular cartridge case (12) as claimed in any one of Claims 1 to 6 inclusive.