GB2524043A - Pyrotechnic igniter and torch - Google Patents

Abstract

A kit of parts for assembling a pyrotechnic igniter includes a resistive heating element, fluoropolymer tape and aluminium powder. The aluminium powder comprising aluminium particles having an average particle size of at least 200 microns.

Description

Pyrotechnic Igniter and Torch

Field of the Invention

The present invention is concerned with improvements in or relating to the transport, creation, and utilisation of pyrotechnic articles, particularly (though not exclusively) pyrotechnic igniters, and pyrotechnic cutting torches used to destroy landmines and other unexploded ordnance.

Background of the Invention

1 0 Pyrotechnic and/or explosive articles (pyrotechnic articles) are often transported as ready to function units, such that they may be initiated and caused to function at their point of end use, simply by addition of the necessary activation energy to the pyrotechnic article. An example of such a pyrotechnic article is a fireworks rocket, which is shipped as a complete unit, and is activated by the addition of the necessary activation energy to the rocket's fuse using heat from a lighter, electric match, or other means. Completed pyrotechnic articles are often complex and costly to transport, and can generally not be transported on passenger aircraft.

Because of the risks of fire and explosion, and the transportation difficulties inherent in the transport of complete pyrotechnic articles, efforts have been made to limit these dangers by the invention and utilisation of pyrotechnic articles, which are shipped as a kit of parts for assembly by the end user, the parts of which are less hazardous than the finished, assembled article, An example of such a pyrotechnic article is Kinepactm'1, a two component explosives system that does not become explosive until the point of end use. Kinepac'TM is composed of a separate oxidiser (UN Number 1942, Packing group 3, Class 5.1), and a flammable liquid (UN Number 1261, Packing group 2, class 3).

An important consideration in the deployment of pyrotechnic articles is that generally their transport is controlled by hazardous goods regulations due to the fact that either the article itself, or one or more of the components of the article fall under the UN hazardous goods numbering system ("UN number"), UN numbers are four-digit numbers that identify hazardous substances and articles (such as explosives, flammable liquids, toxic substances, etc.) in the framework of international transport. Some hazardous substances have their own UN hazardous good numbers (e.g. acrylamide has 1JN2074), while sometimes groups of chemicals or products with similar properties receive a common UN hazardous goods number (e.g flammable liquids not otherwise specified have 1JN1993).

A significant limitation in the transportation of items bearing a tiN Number is that often they cannot legaHy be transported as checked baggage in the hold of a passenger aircraft, or sent through the postal service. As an example of this, flammable solids (UN Class 4) may not legally be sent through the UK postal system or carried in a passenger aircraft hold. Whilst it is clear that these limitations exist for good reasons and prevent danger to the public, it is also clear that these transport limitations can create difficulties for organizations which, as part of their work, must transport, use and/or travel with pyrotechnic articles. An example of such an organization would be a Non Governmental Organization involved in Explosives Ordnance Disposal (EOD), Such an organization may have a limited budget caused by the need to generate operational income via donor funding or chathable giving. Because the organization cannot legally transport hazardous goods necessary for EOD via low cost and convenient passenger aircraft, they must instead transport these hazardous goods via specialized hazardous goods transport services.

In one scenario, organization A based within the MC, must travel to country B to carry out specific EOD task C, Instead of simply taking their hazardous goods with them when they travel via passenger aircraft, they must arrange to ship their hazardous goods via a separate transport service. This situation creates two significant limiting factors: namely, increase in cost and reduction in operational speed and flexibility. As an example, instead of traveling with their hazardous goods during day one, canying out an explosives ordnance disposal task on day two, and returning to base on day three, the organization must arrange the logistics of expensive hazardous goods shipping and permissions during days 1 to 60, travel to their destination on day 61, carry out their task on day 62, and return to base on day 63, During this additional time an additional number oflocal people may have stepped on the landmines constituting the specific EOD task, leading to additional traumatic amputation, misery, and death.

Pyrotechnic igniters comprising PTFE tape having a vapour-coated metal layer are known in the art, For example, GB-A-23543 11, GB-A-2259753 and GB-A-2269379 all describe PTFE films having magnesium coated thereon by vapour deposition.

However, PTFE films having a vapour-coated magnesium layer cannot be safely transported safely due to their high flammability.

It is an object of the present invention to provide pyrotechnic igniters and torches, which may be transported safely as a kit-of-parts whilst not falling foul of regulations concerning the transport of hazardous goods.

Summary of the Invention

In a first aspect, there is provided a kit of parts suitable for assembling a pyrotechnic igniter at a point of end use, the kit comprising: 1 0 a resistive heating element; fluoropolymer tape; and aluminium powder comprising aluminium particles having an average particle size of at least 200 microns.

Advantageously, a pyrotechnic igniter assembled from the kit according to the 1 5 first aspect is sufficiently energetic to ignite, for example, thermite. Accordingly, the kit is useful in the field of explosive ordnance disposal, especially in countries where humanitarian aid is provided from overseas.

Moreover, aluminium particles having an average particle size of at least 200 microns fall outside the UN hazardous goods numbering system, and are not designated as flammable solids. Therefore, the aluminium particles (e.g. spherical aluminium particles) used in the present invention may be legally and safely transported via commercial airlines. By contrast, aluminium powders used in the field of pyrotechnics are typically flammable solids having the UN Number 1309, Group 4.1.

Preferably, the kit comprises instructions for assembling the pyrotechnic igniter, the instmctions describing a method comprising the steps of: coating the fluoropolymer film using the aluminium powder; and winding the aluminium-coated fluoropolymer film around the resistive heating element. Preferably, the coating step is a mechanical coating step, comprising, for example, dip coating and/or roller transfer coating.

Preferably, the resistive heating element comprises a carbon film resistor. The carbon film resistor may be connected to a pair of electrical cables (e.g. via a solder joint) to facilitate easy introduction of the resistors into a conventional electrical firing circuit, Advantageously, the carbon film resistor contains no hazardous component, and is therefore outside the UN hazardous goods numbering system. During use, an appropriate amount of electrical power is passed through the resistor, the amount being over and above the power the resistor is able to dissipate. Consequently, a runaway reaction is initiated where the coating of the carbon film resistor breaks down, and bursts into flame. An appropriate resistance for a particular voltage and current, so as to initiate pyrolysis and pyrogenesis, will be readily apparent to the person skilled in the art.

Alternatively, the carbon film resistor igniter may be substituted for one of many other existing types of pyrogen-free igniter, such as TalonTht igniters, Solar Flaretmt igniters, or any other type of igniter which uses heat generated by electrical resistance as its sole means of ignition.

Preferably, the fluoropolymer film is polytetrafluoroethylene (PTFE) tape. PTFE tape is, of course, non-hazardous, and falls outside the UN hazardous goods numbering system.

Preferably, the kit thrther comprises a mechanical device for coating the aluminium powder onto the fluoropolymer tape. The mechanical device may comprise a housing for containing the aluminium powder; a spindle mounted between sidewalls of the housing for rotatably mounting a spool of fluoropolymer tape; and a plurality of coating rods mounted between the sidewalls of the housing. Typically, the coating rods are positioned for immersion in the aluminium powder, in use, Further, the coating rods are preferably arranged for transferring the aluminium powder onto opposite surfaces of the fluropolymer tape supplied from the spool.

lii one embodiment, the kit is suitable for assembling a pyrotechnic torch and may further comprise a sealed container containing a dispersed mixture of plaster of Paris and sulphur, wherein a ratio of the plaster of Paris to sulphur is in the range of 90:10 to 50:50. Advantageously, mixtures containing plaster of Paris and sulphur within this range are considered to be non-flammable and may be safely transported.

Additionally, the kit may further comprises one or more of: tubes having pre-fitted nozzles; a non-sparking (e.g. wooden) ram rod suited to the bore of the tubes; a mixing container; a funnel; protective gloves and mask; a source of electrical power (e.g. battery, dynamo etc.); a syringe, a water container; a length of electrical cable; plugs for plugging the tubes; instructions for assembling a pyrotechnic igniter; and instructions for assembling a pyrotechnic torch.

In a second aspect, there is provided a coating apparatus comprising: a housing containing aluminium powder; a spindle mounted between sidewalls of the housing; a spool of fluoropolymer tape rotatably mounted about the spindle; and a plurality of coating rods mounted between sidewalls of the housing and immersed in the aluminium powder, the coating rods being arranged for transferring the aluminium powder onto opposite surfaces of fluropolymer tape supplied from the spool, wherein the aluminium powder comprises aluminium particles having an average particle size of at least 200 microns, In a third aspect, there is provided a method of assembling a pyrotechnic igniter, 1 0 the method comprising the steps of: (a) mechanically coating a fluoropolymer film with aluminium powder; and (b) winding a length of the aluminium-coated fluoropolymer film around a resistive heating element, wherein the aluminium powder comprises aluminium particles having an average particle size of at least 200 microns.

The fluoropolymer film may be coated by simply dipping the film in a container of aluminium powder. Alternatively, the fluoropolymer film may be passed over one or more rollers or coating rods immersed in the aluminium powder so as to provide a substmtially even coating of the aluminium powder on the fluoropolymer film. A mechanical device suitable for coating PTFE tape is described herein, In a fourth aspect, there is provided a pyrotechnic igniter obtainable by the method described above.

In a fifth aspect, there is provided a pyrotechnic torch comprising: a chamber having a nozzle; the pyrotechnic igniter, as described above, received in the nozzle; and a fuel mixture contained in the chamber, the fuel mixture being in contact with the pyrotechnic igniter.

The pyrotechnic torch according to the fourth aspect may be advantageously deployed for the disposal of Explosive Ordnance Devices (OEDs), such as landmines.

Typically, the chamber comprises a cardboard or paper tube fitted with a suitable nozzle, such as a clay or plaster nozzle.

Preferably, the fuel mixture comprises: sulphur, aluminium powder and plaster of Paris.

Preferably, a ratio of plaster of Paris to sulphur in the fuel mixture is in the range of 90:10 to 50:50. Accordingly, the sulpur component of the fuel mixture may be safely transported as mixture of sulphur and plaster of Paris, as described above.

Brief Description of the Drawings

Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings in which: Figure 1 is a schematic perspective view of a mechanical device for coating PTFE tape.

Detailed Description of Preferred Embodiments

Pyrotechnic Igniter Kit In one exemplary embodiment of the invention, a kit of parts for assembling a pyrotechnic igniter comprises the following items: Component A: One or more carbon film electrical resistors for use as igniters, which may be soldered to a pair of electrical cables to facilitate the easy introduction of the resistors into a conventional electrical firing circuit.

Component B: A sealed container of aluminum powder having an average particle size of at least 200 microns.

Component C: PTFE tape.

Component D: A mechanical device used for coating the PTFE tape with between 10 and 60 parts by weight of the aluminum powder (optional).

Component E: Electrical cables (optional).

Component F: Battery (optional) In order to assemble the pyrotechnic igniter, the following steps are performed: * A length of PTFE tape is pulled from a roll. The length of tape used is dictated by the task at hand, but to generalize, where a low activation energy is required a short length of PTFE tape can be used, 30cm as an example. For tasks where a higher activation energy is required, any length of tape up to and including a full roll of tape, or several complete rolls of tape combined can be used.

* The PTFE tape is inserted into a container of aluminum powder and the container shaken to ensure a complete and even coverage of the PTFE tape with the aluminum powder. Alternatively, the mechanical device may be used for coating the PTFE tape.

* The PTFE tape, now coated with aluminum powder, is removed from the container and excess aluminum powder is allowed to fall back into the container.

* The aluminum-coated PTFE tape is wound tightly around a carbon film resistor, ensuring that the aluminum powder coated PTFE tape is in intimate contact with the surface of the carbon film resistor.

* At this point, a pyrotechnic initiator has been created, which is simple to initiate via the conventional means of passing an appropriate amount of electrical power through the carbon film resistor via connection to the battery or other suitable power source.

Pyrotechnic Torch Kit In another exemplary embodiment of the invention, a kit of parts for assembling a high temperature pyrotechnic torch comprises the following items.

Component A: One or more carbon film electrical resistors for use as igniters, which may be soldered to a pair of electrical cables to facilitate the easy introduction of the resistors into a conventional electrical firing circuit.

Component B: A sealed container of aluminum powder having an average particle size of at least 200 microns.

Component C: PTFE tape.

Component D: A mechanical device for coating the PTFE tape with between 10 and 60 parts by weight of the aluminum powder.

Component E: A sealed container of Plaster of Paris powder mixed with between 10 and 50 wt. % sulphur powder, and measuring scoop. a

Component F: An empty non-metallic mixing pot, supplied with screw top lid.

Component G: A funnel.

Component H: One or more cardboard/paper tubes which may be pre-fitted with clay or plaster nozzles.

Component I: A length of wooden or otherwise non-sparking dowel, suitably sized to fit easily but without more than 2mm gap within the bore of the cardboard/paper tubes.

Component J: A medical syringe, capable of holding at least S cubic centimetres of water.

Component K: A bottle for containing water.

Component L: A quantity of paper or plastic plugs, suited to the internal diameter of the paper or cardboard tubes.

In order to assemble the pyrotechnic torch, the following steps are performed: * A resistor/aluminum/PTFE igniter is first prepared by coating a length of the PTFE tape with aluminium powder using the mechanical device and winding the aluminium-coated PTFE tape around a carbon film resistor, The igniter is inserted into the clay or plaster of Paris nozzle of an empty paper or cardboard tube, and held securely in place using a paper or plastic plug.

* A measured scoop of aluminum powder is poured into the empty mixing pot.

The precise amount required is found by first overfilling the scoop, and then drawing an elongate straight sided member such as a wooden tongue depressor over the top edge of the scoop to create a level surface.

* A measured scoop of plaster of Paris/Sulphur mixture is added to the mixing pot * The mixing pot is sealed, and shaken vigorously for 30 seconds.

* The syringe is used to draw up a measured quantity of water * The water is added to the mixing pot, by depressing the syringe plunger * The mixing pot is vigorously shaken for 30 seconds * A funnel is placed into the empty end of the paper or cardboard tube * V4 of the material in the mixing pot is poured into the tube and rammed into place over the resistor/PTFE/aluminium igniter using the ram rod.

* This stage is repeated a frirther 3 times until all the material from the mixing pot is compacted inside the tube * At this stage, the high temperature pyrotechnic torch is complete and ready to be used. A curing period of at least 1 hour will allow the torch to reach higher temperatures during combustion than if it is used immediately.

The completed pyrotechnic torch with igniter is capable of generating a jet of heated fluid at temperatures of 2000 degrees Celsius. The pyrotechnic torch may be used to destroy an unexploded ordnance such as a landmine. It will be readily apparent to those skilled in the art that simply by varying the internal diameter of the cardboard or paper tube, nozzle diameter, and amount of chemical constituent used, it is possible to increase or decrease the bum time in order to suit a particular EOD task.

Mechanical Dcvi? cc fbi (oatingPTFE Tape The pyrotechnic igniter and pyrotechnic torch kits, as described above, may comprise a mechanical device for coating the PTFE tape substantially evenly on both sides with aluminium powder.

Referring now to Figure 1, there is shown a mechanical device 1 suitable for coating PTFE tape with aluminium powder. The mechanical device I comprises a housing 10 having abase II and sidewalls 13 extending upwardly therefrom. A spindle 12 is removably mounted between opposite sidewalls 13 of the housing. The spindle 12 typically has an external diameter of less than 30mm to suit the internal diameter of a standard spool of PTFE tape. A spool 14 of PTFE tape is rotatably mounted about the spindle 12, such that a length of the PTFE tape 16 can be readily unfurled from the spool. It will be appreciated that the spindle 12 may be either rotatable or fixed relative to the housing 10 during use. However, the spindle 2 is removable from the housing 10 so as to allow fresh spoois 14 of PTFE tape to be loaded onto the spindle when required.

A plurality of coating rods 1 8A, I 8B and 1 8C are mounted parallel with the spindle 12 between opposite sidewalls 13 of the housing 10, The coating rods ISA, 18B and I SC are positioned for immersion in aluminium powder (not shown in Figure 1) contained in the housing. The coating rods I 8A, I 8B and I SC are arranged such that aluminium powder may be coated onto opposite sides of the length 16 of PTFE tape.

Typically, the coating rods I 8A, I 8B and I SC are rotatable to facilitate even transfer of aluminium powder onto the PTFE tape.

During use, the spool 14 of PTFE tape is loaded onto the spindle 12 and a free end 19 of the PTFE tape 16 is drawn under the first coating rod ISA, over the second coating rod SB and under the third coating rod I SC, The PTFE tape 16 exits the housing 10 via an open top section thereof Aluminum powder having an average particle size of less than 200 microns is then poured into the open housing 10, such that 1 5 a level of powder reaches a level higher than each of the coating rods 1 8A, I SB and isc.

The length 16 of PTFE tape is coated with the aluminum powder (not shown) by pulling the free end 19 of the PTFE tape so as to draw the tape through the aluminum powder, over and under the coating rods iSA, t8B and iSC. The coating rods ISA, t8B and ISC provide substantially even mechanical transfer of the aluminium powder onto both surfaces of the PTFE tape. Excess aluminum powder falls away from the coated PTFE tape and into the housing 10.

The resultant length of aluminum-coated PTFE tape is then ready for winding tightly around a carbon film resistor so as to furnish a pyrotechnic igniter.

It will, of course, be appreciated that the present invention has been described by way of example only and that modifications of detail may be made within the scope of the invention, which is defined in the accompanying claims.