GB2227816A - Pyrotechnic sealing - Google Patents

Abstract

A method of making a pyrotechnic in which a fuse end thereof is provided with a fuse passing through or around a seal. The seal may be a disc of foamed plastics material, either inserted or formed in situ, or it may comprise a solid wax, either solidified from a pourable wax composition, or produced by compaction of granular powdered wax.

Description

PYROTECHNIC SEALING The present invention relates to a method of making a pyrotechnic device including sealing at least one end thereof.

Pyrotechnics for display use generally comprise a tube of cardboard or other similar material, sealed at one end with clay or a cardboard disc, with the other end closed by a twisted touch-paper. When the touch-paper is lit, it burns down to ignite the pyrotechnic composition inside the tube. Pyrotechnic devices of this type suffer from two disadvantages. One is that the touch-paper may form only an imperfect seal at the one end of the tube, allowing the pyrotechnic composition to escape from the tube, especially during transit. The second is that the burning time of the touch-paper cannot be predetermined ignite. As a result of this second problem, fireworks may explode prematurely, late, or not at all. As a result of the former problem, boxes of fireworks may often include the spilt contents of one or more of the fireworks.

It is an object of the present invention to overcome these disadvantages.

According to a first aspect of the present invention there is provided a method of making a pyrotechnic device comprising the steps, after sealing one end of a tube and filling the tube with a pyrotechnic composition, these steps being carried out in any desired order, of inserting a fuse to be in contact with said composition at one end and having its other end free of said tube, and sealing said fused end of the tube by inserting thereinto a plug adapted to fit closely and sealingly within the tube with the fuse retained thereby.

Said plug may comprise a disc of foamed plastics material.

One form of plastics material which may be used is a disc of closed cell foamed polyethylene, the dimensions of the disc being slightly greater than the internal diameter of the tube.

In this case, the fuse may either pass between the disc and the internal wall of the tube, or the disc may be slit from one edge to the centre and the fuse may pass through the slit, being retained in place when the disc is compressed into the tube. In another embodiment, the plug may comprise foamed polyurethane, said foamed polyurethane having been produced in situ by reaction of one or more foamable liquid components.

In another alternative, the plug may comprise a solidifiable charge of liquid or particulate wax or other similar material.

The wax may be an animal, mineral or vegetable wax which is solid at ambient temperature but liquid at an elevated temperature. In this case, liquid wax is poured into the tube above the pyrotechnic composition and around the fuse, and allowed to solidify.

Alternatively, the wax may be a granular or microcrystalline powdered wax. In this case the wax particles are placed in the tube and compacted, the compaction causing sufficient frictional heat to fuse together the particles.

In a preferred embodiment, the tube may be placed on a pin and filled with pyrotechnic composition, optionally shaken to compact the composition, and have one end filled with microcrystalline wax. The wax may then be compacted to fuse it into a solid, which action will also serve to compact further the pyrotechnic composition. This may be particularly useful for sensitive compositions.

According to a second aspect of the present invention there is provided a pyrotechnic device made according to a method described above under the first aspect of the invention.

An example of a pyrotechnic device embodying the invention will now be described in more detail by way of Example.

A firework comprises a cardboard tube of internal diameter 13 mm or less. The firework tube is placed on a pin then filled with pyrotechnic composition. One end is then closed by filling with microcrystalline powdered wax, which is compacted to fuse into a solid seal. A fuse comprising an igniter cord is then placed in the upper end of the tube so that one end of the cord is in intimate contact with the composition, while the other end is clear of the tube. The inner end of the cord is bent through a right angle so that it will be more strongly retained against being pulled out.

A liquid composition comprising warmed mineral wax is then poured into the open end of the tube and allowed to solidify around the fuse and in contact with the internal walls of the tube.

The burning time of the igniter cord can be predetermined depending on its length and the upper end of the firework is securely sealed against spillage of the contents. The contents are also protected against ingress of moisture.

For larger diameter fireworks, it is preferred to use a disc of plastazote, a closed cell foamed polyethylene. If so desired, this may also be used in the smaller diameter fireworks. In these cases, the disc has a diameter slightly greater than the internal diameter of the tube and is compressed into place, expanding to fit tightly. The fuse may pass between an edge of the disc and the internal wall of the tube or, alternatively, the disc may have a slit from a point on its periphery towards the centre, and the fuse is passed into this slit. Again, when the disc is compressed within the tube, the fuse is tightly held within the slit.

Claims (12)

CLAIMS:

1. A method of making a pyrotechnic device comprising the steps, after sealing one end of a tube and filling the tube with a pyrotechnic composition, these steps being carried out in any desired order, of inserting a fuse to be in contact with said composition at one end and having its other end free of said tube, and sealing said fused end of the tube by inserting thereinto a plug adapted to fit closely and sealingly within the tube with the fuse retained thereby.

2. A method as claimed in claim 1, wherein said plug comprises a disc of foamed plastics material.

3. A method as claimed in claim 2, wherein the foamed plastics material comprises a disc of closed cell foamed polyethylene, the dimensions of the disc being slightly greater than the internal diameter of the tube.

4. A method as claimed in claim 3, wherein the fuse is adapted to pass between the disc and the internal wall of the tube.

5. A method as claimed in claim 3, wherein the disc is slit from one edge toward its centre and the fuse is passed through the slit, being retained in place when the disc is compressed into the tube.

6. A method as claimed in claim 2, wherein the plug comprises foamed polyurethane, said foamed polyurethane having been produced in situ by reaction of one or more foamable liquid components.

7. A method as claimed in claim 1, wherein the plug comprises a solidifiable charge of liquid or particulate wax or other similar material.

8. A method as claimed in claim 7, wherein the wax is an animal, mineral or vegetable wax which is solid at ambient temperature but liquid at an elevated temperature, and liquid wax is poured into the tube above the pyrotechnic composition and around the fuse, and allowed to solidify on cooling.

9. A method as claimed in claim 7, wherein the wax is a granular or microcrystalline powdered wax, and the wax particles are placed in the tube and compacted, the compaction causing sufficient frictional heat to fuse together the particles.

10. A method as claimed in claim 9, wherein the tube is placed on a pin, filled with the pyrotechnic composition, shaken to compact the composition, one end is then filled with microcrystalline wax, which is then compacted to fuse it into a solid, which action will also serve to compact further the pyrotechnic composition.

11. A method of making a pyrotechnic device substantially as described herein with reference to the Example.

12. A pyrotechnic device made according to a method as claimed in any one of the preceding claims.