GB2326219A - Container for pyrotechnic material - Google Patents

Abstract

A pyrotechnic container comprising an elongate hollow plastics body (11) having an integral end wall (13) at one end thereof with an axially inwardly extending cavity (14) therein for receipt of an initiator. The open end (12) of the container is closable by a resilient stemming plug (20) having a first portion (21) which is an interference fit in the open end of the container, and a disc-like seal (90, fig.8) located internally of the stemming plug.

Description

A Pyrotechnic Device and Container therefore Field This invention relates to pyrotechnics device and a container therefore, and to a method of making the container.

Backqround of Invention Pyrotechnics comprise granular granular powder mix which when ignited produces large volumes of gas which has to be contained in a hole in rock, stone, masonry and the like, to produce any heaving action. Pyrotechnics are typically used in quarrying, tunnelling, demolition, mining or civil engineering. The granular powder mix is typically placed in tubular containers formed of rolled paper , cardboard or an extruded plastics tube and the ends of the tubes sealed by a plug or closure pushed into each end of the tube. The closure is punctured to permit the insertion of an initiator through the plug for contact with the explosive for the purposes of detonation.

The prior art containers are not particularly suitable for underwater work since the plugs may leak and the integrity of the container has been beached for insertion of the initiator.

Another problem with the prior art containers is that each tube is cut to a required length for a particular charge so that the manufacture of a selection of different charges is a time consumming business.

Statements of Invention Accordingly there is provided a container for a pyrotechnic device comprising an elongate hollow plastics body having an integral end wall at one end thereof with an axially inwardly extending cavity therein for receipt of an initiator.

The container is closed at its open end by a stemming plug having a first portion which is an interference fit in said open end and a second portion which is in the form of a funnel opening outwards in the direction away from the open end.

The open end may additionally or alternately be closed by a resilient disc-like seal Preferably the stemming plug and seal are made of an elastomeric material such as a melt processable rubber e.g a polyurethane elastomer, or a fluoroelastomer.

Preferably the end portion of the container adjacent the end wall has a smaller cross-section such that said end portion is a sliding or interference fit into the open end of a second container. Portions of the end wall surrounding the cavity may be thinned to allow flash over from one container to the other.

The invention also includes a pyrotechnic device having a container of the type described above.

Also according to the Invention there is provided a method of varying a pyrotechnic charge in which method containers, according to the above invention, are filled with a known charge, and one container having a known charge therein is connected to a second container having a second known charge therein by fitting the one end portion of the first container into the open end of the second container. The first and second known charges are not necssarily of the same weight.

There is also provided a method of manufacture of a pyrotechnic container as described above , wherein the container body is injection moulded around a parallel sided core held in a longitudinally split mould. The mould clamping pressure is partially relieved when the mould core is withdrawn so that the body is gripped by the mould as the core is withdrawn.

Description of Drawings The invention will be described by way of example and with reference to the accompanying drawings in which: Fig.l is a longitudinal cross-section through a container according to the present invention, Fig.2 is a view in the direction of arrow A of the container shown in Fig. 1, Fig.3 is a view in the direction of arrow B of the open end of the container shown in Fig.2, Fig.4 is a cross-section through a stemming plug, Fig.5 is a view of the end wall of the plug in the direction of arrow C, Fig.6 is a section through a second container according to the present invention, Fig.7 is a view of the end wall of the second container taken in the direction of arrow D, Fig.8 is a sectional view through a second container after assembly, Fig. 9 is a plan view of a seal used the containers, Fig. 10 is a section on the line X-X of Fig. 9, Fig.11 is a sectional view through two second containers assembled together, Fig.l2 is a view through a modified stemming plug, Fig.13 is a schematic drawing showing the moulding process, and Fig. 14 is also a schematic drawing of the moulding process.

Detailed Description of Invention With reference to Figs. 1 to 3, there is shown a pyrotechnic container body 11 with is in the form of an elongated cylindrical tube but could have other cross-sections if desired. The tubular body has an open upper end 12 and its lower end is closed by an end wall 13. The end wall 13 has an axially extending cavity 14 whose side walls 15 are integrally formed with the end wall 13 and extend inwardly of the container. The cavity wall 15 may be formed with internal raised ribs 16 for gripping an initiator located therein (see Fig 11) The body 11 is preferably injection moulded since this allows the body side walls to be formed with a substantially constant allover thickness which is important for the use of pyrotechnic devices underwater. The behaviour of the tubular body 11 must be predicable down to 100 ft of water pressure.

The body 11 is moulded from a low static or anti-static polypropylene.

The open end 12 of the container body 11 is closed by a stemming plug 20 as shown in Fig.4 and Fig. 8. The stemming plug 20 is hollow and has a first end portion 21 which is cylindrical and a second portion 22 which is a frustoconical funnel shape. The first portion is reinforced by three, or four, radial ribs 23. The stemming plug 20 is injection moulded from a resilient elastomeric material having a Shore A hardness of 65-80. Suitable materials may be a polyurethane rubber, a silicone rubber, a fluoroelastomer, a PVC plastisol.

The stemming plug is preferably moulded from a melt processable rubber e.g. Alcryn 2070 available from Dupont.

The first end portion 21 is of such a size that it is a push fit into the open end 12 of the body 11. The external surface 23 of the first portion may have a raised peripheral rib 24 or step formed thereon to improve its seal against the internal surface of the body 11.

The open end 12 of the container body 11 may optionally and/ additionally be closed by a disc-like seal 90 shown in Figs.

9 & 10. The seal 90 has thinned down membraneous areas 92 within a thickened peripheral and central portions 91 and 93.

Radial reinforcing ribs 94 connect the outer and central portions. The seal 90 is made from the same sort of material as the stemming plug and is an interference fit in the open mouth 12 of the tube.

With reference to Fig 6, there is shown a second type of container body 111 having an open end 112 as before. The other end of the container is closed by an end wall 113 which is on the end of a reduced diameter end portion 121 of the body 111.

The end portion 121 is an interference fit into the open end of another container as will be described. The shoulder 126 between the body 111 and the lower end portion 121 limits the insertion of one tube into another. The cavity 114 is formed in the end wall 113 which is formed with thinned down areas 122. The cavity wall 115 is connected to the body 111 by radial ribs 123, preferably four.

In Fig.8 there is shown a fully assembled container 81 . This container 81 is shown with a container body from Fig. 6 but could equally use a container body from Fig. 1. Pyrotechnic powder is put into the container body 111 upto the required weight. A seal 90 may be pushed into the container 111 to retain the powder and more thoroughly seal the container. A stemming plug 20 is then pushed into the open end of the container body 111. An initiator 130, see fig 11, is then inserted into the cavity.

In use a pyrotechnic device may be inserted in a drilled hole in say rock. The flexible funnel portion 22 helps seal the drilled hole when clay or other sealing medium is used to plug the drilled hole and is received in the funnel portion.

The above container and pyrotechnic device has a water proof body with an integral initiator holder . The initiator has not pierced the container body and is not in direct contact with the pyrotechnic material With reference to Fig 11, there is shown two containers 81A & 81B assembled together to form a second selected required charge. The stemming plug from the lower container 81B are removed leaving the seal 90 in place. The upper container 81A, without initiator present in the cavity 114 has its lower end 121 pushed into the open end 112 of the lower container. This may be repeated for a third container and possibly for upto five containers in assembly together.

An initiator 130 is pushed into the cavity 114 of the lower container. For underwater purposes the lower container should be of the type shown in Fig. 1.

In this way variable charges can be made up on site without breaching the integrity of the previously charged containers.

When the charge is detonated the initiator reaction flashes through the cavity wall into the lower container, and flashes through the thinned portions of seals 90 and end walls 113 to detonate all the assembled containers.

The container bodies may be made in a variety of different standard lengths for different charge weights, and could be different coloured for different applications.

With reference to Fig. 12 there is shown a modified stemming plug 120 which includes a more rigid plastics plug 130 inseted into the hollow cylindrical portion of the plug to squeeze the softer material of the cylindrical portion of the stemming plug against the wall of the body. For use underwater, a seal 90 may also be inserted.

With reference to Figs.13 & 14 , the container bodies 11 are formed by injection moulding techniques in which plastics material, preferably polypropylene, is injected into a longitudinally split mould 200 which is clamped under a clamp load of 20-25 tonnes. The bodies 11 are moulded around a cylindrical concentric parallel sided core 201 using hot runner systems. Since the length of cavity to be filled relative to its thickness is at least 60:1, the material is injected slowly, typically over about 2 seconds, and preferably the material is injected in two batches with a 0.25-0.5 second time delay between the two injection processes.

The material is cooled, the mould is relieved so that there is still a 1 -2 tonne load on the mould and the core is withdrawn whilst the body 11 is still under some load. The mould 200 is the opened by and the body can be removed.

The core 201 may be hollow and have a cooling medium passed therethrough.

The mould core may be clamped by core supports at its end adjacent the body end wall. the upper portion of the body is moulded first, the core supports withdrawn, and the lower portion is injected thereafter.

Claims (15)

Claims

1. A container for a pyrotechnic device comprising an elongate hollow plastics body having an integral end wall at one end thereof with an axially inwardly extending cavity therein for receipt of an initiator.

2. A container as claimed in claim 1 wherein the open end of the container is closeable by a stemming plug having a first portion which is an interference fit in the open end of the container, and a second funnel shaped portion which opens in the direction away from the open end.

3. A container as claimed in Claim 2 wherein the stemming plug is made from resilient material.

4. A container as claimed in any one of Claims 1 to 3 wherein the open end of the container further includes a resilient disc-like seal which seals within the internal walls of the container.

5. A container as claimed in Claim 4, wherein the disc-like seal has a thicker peripheral rim with a membraneous inner portion

6. A container as claimed in any one of claims 1 to 5 wherein the end portion of the container adjacent the end wall has a smaller cross-section such that said end portion is a sliding or interference fit into the open end of a second container.

7. A container as claimed in Claim 6 wherein the endwall surrounding the cavity has thinner portions.

8. A container as claimed in any one of Claims 1 to 7 wherein the container body is an injection moulding having thin sidewall such that the ratio of sidewall length to thickness is at least 60:1.

9. A pyrotechnic device having a container as claimed in any one of Claims 1 to 8.

10. A method of varying a pyrotechnic charge in which method containers according to Claim 6 or Claim 7 are filled with a known charge, and one container having a known charge therein is connected to a second container having a second known charge therein by fitting the one end portion of the first container into the open end of the second container.

11. A method as claimed in claim 10 wherein upto five containers may be assembled together.

12. A method of igniting a pyrotechnic device as claimed in Claim 9, wherein pyrotechnic material within the container is ignited by an initiator housed in said cavity, the initiator causing the pyrotechnic material in the container to ignite by flash through the cavity walls.

13. A method of manufacture of a pyrotechnic container as claimed in any one of Claims 1 to 9, wherein the container body is injection moulded around a parallel sided core held in a longitudinally split mould

14. A method as claimed in Claim 13 wherein the mould clamping load is partially relieved to allow the core to be withdrawn.

15. A method as claimed in any one of claims 12 to 14, wherein the body is injected in two stages with a small delay between the two injection processes.