AU2007202414B2 - Improved special effects and battle effect pyrotechnic items - Google Patents

Abstract

A pyrotechnic item for producing a special explosive effect; said item comprising a substantially spherical multi-layered casing; at least one layer of said multi layered casing formed of an elastomer material; said casing containing at least an electric igniter and an explosive composition; said composition formulated to produce a substantially smokeless pyrotechnic effect; said composition including at least nitrocellulose or nitrocellulose/nitroglycerine based smokeless powder.

Description

P/001009 Regulation 3 10 AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION Invention Title: IMPROVED SPECIAL EFFECTS AND BATTLE EFFECT PYROTECHNIC ITEMS The invention is described in the following statement, including the best method of performing it known to us: Our Ref: 072010 -2 IMPROVED SPECIAL EFFECTS AND BATTLE EFFECT PYROTECHNIC ITEMS 5 This invention relates to improvements in the propulsive capabilities and visual signature of pyrotechnic items designed to assist in the production of realistic but relatively non harmful explosions for the carrying out of special effects for the film and television industries or 10 battlefield effects for military and law enforcement training purposes. BACKGROUND Pyrotechnic items for producing explosions are well 15 known in prior pyrotechnic art. Stage Maroons, military "Thunderflashes", Special Effects bursting charges and maroons are frequently utilized in the Entertainment industries such as Film, Television, Live Events, Rock Concerts and the like. 20 These items usually consist of fibreboard cylindrical containers enclosing a pyrotechnic composition such as black gunpowder or "flash powder" which may be a mixture of potassium perchlorate and aluminium powder. There are many other compositions known and used by those skilled in the 25 art. The aforesaid closed fibreboard cylinders may be sealed by corks glued into the open ends of the cylinder, -3 or there may be fibreboard end caps. Electric igniters are usually sealed inside the closed cylinders, with their leadwires protruding from the device. Frequently these devices may be wrapped in friction 5 tape or cotton string to increase the strength of the fibreboard container, thus increasing the strength of the explosive burst when the pyrotechnic substance inside is initiated by the aforesaid electric igniter. Also the external tape or string wrapping may be dipped in lacquer 10 or latex for increased waterproofing. It is common prior art to use " Special Effects bursters" in the film and television special effects industries , These bursters typically have a black gunpowder filling and an electric igniter with above 15 described containment means. These above described devices are frequently used to provide the basis for the representation of shell and bomb bursts or other types of explosions during the filming of action movies where such explosions are required to add 20 realism to the production and advance the storyline of the film or television project. To provide the shell or bomb burst effects described above, it is common practice for special effects technicians skilled in the art to place a steel mortar 25 commonly called a "dishpan mortar" in the ground so the open end is flush with the ground surface. The mortar may -4 be a slope sided pan with a flat bottom or a rounded pan similar to a boiler end- there a many types of mortar along these general lines. A pyrotechnic device as above described is placed in 5 the bottom of the mortar, typically on a bed of sand or peat moss. More than one device may be placed in the mortar, depending on the size of the explosion required and the size of the mortar. Typically, the mortar will then be filled with a 10 variety of soft materials, exemplary of which may be lumps of low density cork, peat moss and dusts of various sorts. when the special effects bursters are initiated, the resultant explosion of the black gunpowder throws the contents of the mortar skywards in a characteristic fan 15 shaped plume resembling a real shell or bomb explosion but without the lethal effects. It is common practice in the film and television industries to place stunt action personnel very close to the afore described dishpan mortar explosions, 20 These devices are also used in many other aspects of special effects practice, for example as the propulsion and ignition agent for flammable fuels, to produce large fireballs, or as the propellant for wet sand contained in a cylindrical mortar, to disrupt , destroy and propel film 25 props such as breakaway building elements and the like.They may also be fired underwater, to simulate the bursting of - 5 bomb or shell, making a tall spray column of water burst from the surface of the body of water. A good description of these devices and their uses may be found in " The Technique of Special Effects in 5 Television" Focal Press, 1971 by the eminent British Special Effects Technician Mr. Bernard Wilkie , and subsequent editions. Military Battlefield Effects Simulators are well described in Australian Patent 2006201922. They consist 10 essentially of a closed, usually cylindrical, paper or plastic casing surrounding a pyrotechnic composition, that, when ignited by an in situ igniter, either electro pyrotechnic or pyrotechnic, will explode with a loud noise, flash and cloud of dense smoke , dust or flame. They are 15 used to train military and law enforcement personnel to function effectively amid the noise, flame, dust and smoke of a battlefield environment. They share many similarities with their Film and Television counterparts. There are some disadvantages evident in the practical 20 use of the above described special effects bursters, particularly when they are utilized in the above described mortars or in the water. One notable disadvantage is the production of copious quantities of white smoke on bursting of the item, This is a characteristic of both black 25 gunpowder and almost all common varieties of flash powder.

6 White smoke can frequently obscure action taking place on the "set", and also detracts from the realism of the explosive special effect, unless the scene storyline is supposed to be taking place before the use of high 5 explosives, like TNT or RDX/TNT. A characteristic of "modern" high explosives is that they generally detonate with the generation of black or deep grey smoke, or little smoke at all. The Boer War ( 1900-02 ) is generally accepted as 10 being the first war in which modern high explosives were used as shell filling, for example picric acid ( 2.4.6 trinitrophenol, lyddite ). The First World War( 1914-19 shell and bomb fillings were in the main TNT or Lyddite, which are notable for lack of oxygen balance and consequent 15 generation of dense black smoke clouds on detonation. All subsequent wars have utilized these " modern" high explosives, with the exception of some classes of "thermobaric" explosives used currently in the Afghanistan and Iraq conflicts- these materials have a very high 20 percentage of aluminium powder content, and thus produce copious quantities of whitish smoke. High Definition home entertainment television screens, the advent of DVD and computer hard drive stored movies and the ability to freeze frame at will or run 25 extreme slow motion means that special effects technicians strive to be as realistic as possible in the production of - 7 special effects explosions and the like. The ubiquity of real combat footage from the internet is also driving the effort towards maximum simulation of reality in filmmaking Another disadvantage of the use of black gunpowder in 5 the above described bursters is that this explosive substance is not very powerful, and consequently the special effects practicioner finds that he or she must use considerable quantities of "'bursters" to achieve the desired explosive effects. This need to use considerable 10 quantities of gunpowder dramatically increases the generation of the above described disadvantageous white smoke. Conversely, the above described flash powders are usually too brisant to be used in any but relatively small 15 quantities. These powders, contained in burster casings, may destroy a steel mortar, rupturing the welds and possibly flinging steel fragments long distances. The flash powder containing bursters also make large quantities of white smoke when exploded. 20 The above described cylindrical, wrapped, black powder filled bursters are also not very efficient at dispersing the gas and combustion products generated when the black powder is ignited. The cylindrical nature of the containment generally results in the container rupturing 25 along' a cylinder end, therefore venting the gasses and hot solids asymmetrically, which is inefficient, resulting in poor propulsion performance. 5 It is an object of the present invention to address or at least ameliorate some of the above disadvantages. Notes 1. The term "comprising" (and grammatical variations thereof) is used in this specification in the inclusive 10 sense of "having" or "including", and not in the exclusive sense of "consisting only of". 2. The above discussion of the prior art in the Background of the invention, is not an admission that any information discussed therein is citable prior art or 15 part of the common general knowledge of persons skilled in the art in any country. BRIEF DESCRIPTION OF INVENTION The invention consists of the following improvements to existing prior art. 20 The first improvement concerns the casing or containment; It has been found by extensive experimentation and trials that a spherical shape is better than a cylindrical shape because the explosion of the contents is more evenly 25 distributed within the above described mortar or mortars.

-9 It has also been found that a multi-layered spherical casing or containment advantageously includes a layer of rubber - it is thought that a rubber or other elastomer, spherical casing swells considerably before rupturing into 5 a few irregular pieces when the contents are exploded. This results in a more evenly distributed bursting effect, resulting in more efficient propulsion of the mortar contents, or a more efficient generation of a waterspout, should the device be placed underwater. 10 Also it has been found to be advantageous if the above described rubber or other elastomer, spherical casing is then wrapped with PVC or Cloth friction tape - this increases the confinement of the explosion products of the 15 contents until the containment bursts. It has also been found effective to dip the above described tape wrapped rubber or other elastomer spherical burster in latex two or three times. This ensures waterproofing and 20 also increases the burst strength of the whole containment assembly when the latex dries. Notwithstanding the above described rubber or other elastomer spherical containment, it has also been found 25 that a paper spherical shell, wrapped and latex dipped as described above,or coated with repeated layers of paper -10 sheet and glue and then latex or lacquer dipped, may also be used in lieu of a -rubber spherical container, with sufficiently good and efficient results on explosion. 5 It should be borne in mind that all of the above described spherical containers also have provision for the placement of electric or shock tube or other ignition means within the confines of the container, the purpose of which to ignite the explosive contents. 10 It should also be noted that the above described wrappings and dips may or may not be necessary in the construction of this device depending on the intended application; for example it may in certain circumstances desirable to have a 15 less confined casing so the exploding composition exerts less energy on its surrounding environment. The second improvement relates to the explosive composition within the above described burster containment. 20 It has been found that both or either nitrocellulose or nitrocellulose/nitroglycerine based smokeless powders (known respectively as single or double base powders in the art) with the addition of small quanities of pyrotechnic compositions of various formulations including but not 25 limited to or small quantities of Thermite compositions, for example copper Oxide/Aluminium, Iron Oxide / Zirconium, - 11 Molybdenum Trioxide/ Aluminium, Iron Oxide /Aluminium, Manganese Dioxide/Aluminium or other energetic, finely divided thermite mixtures, or any one of a great number of energetic pyrotechnic redox compositions, including but not 5 limited to Potassium Perchlorate/Aluminium, Potassium Nitrate/Aluminium, Barium Nitrate/Aluminium, Meal Powder/Aluminium, or many other suitable finely divided energetic composition, including but not limited to the addition of small quantities of finely divided molecular 10 explosives for example P.E.T.N ( penta erythrytol tetranitrate) or R.D.X ( cyclotrimethylene trinitramine) sufficient only to coat the grains of smokeless powder, may very effectively be used as the bursting composition. 15 It is thought that a coating of these finely divided and reactive energetic materials on each grain or flake of the above described smokless powders promotes very rapid burning of the smokeless powder formulations under conditions of relatively mild confinement. The smokeless 20 powder is also a very efficient gas producer, unlike either black gunpowder or flash powder, which are poor gas producers and generate mostly solid combustion products. The combination of the above described spherical 25 containment and the above described explosive compositions result, upon ignition of the explosive composition within - 12 the spherical containment, in a powerful, gassy, and substantially smokeless explosion. It has been found in extensive trials that this "smokeless" composition containing spherical burster is as powerful as 5 about two to three black powder filled spherical bursters, constructed as described above, and much more efficient than any cylindrical burster although it may be stated that the above described composition may be used to good effect in either spherical or cylindrical casings or casings of 10 other geometries. It may also be stated that this composition is preferable to flash powders above described, as the explosion of the nitrocellulose based composition is much more gassy but not as dangerously rapid as that of flash powder. The above 15 described bursters with the above described improvements may be used in special effects mortars with safety, unlike flash powder bursters. The virtual elimination of white smoke and the gassy power 20 of the novel burster result in a very much improved product for the special effects industry, and a substantial improvement in the ability of the film and television industries to present more realistic action scenes. It should also be noted that the above described burster 25 may also be filled, along with the above described smokeless powder compositions, with a great variety of - 13 other energetic materials, too numerous to list; for example, ammonium nitrate / fuel mixtures may be admixed with the aforesaid coated smokeless powder compositions to increase the gas production on explosion, or reactive metal grits, turnings and powders may be added to the above described compositions to produce, on explosion, bursts of sparks. There is an immense variety of possible and potentially desirable energetic mixtures and compounds known to those skilled in the art that could be used as the bursting composition, depending on requirement. Accordingly, in a one broad form of the invention, there is provided a pyrotechnic item for producing a special explosive effect; said device comprising a substantially spherical multi layered casing; at least one layer of said multi-layered casing formed of an elastomer material; said casing containing at least an electric igniter and an explosive composition; said smokeless composition formulated to produce a substantially smokeless pyrotechnic effect; said composition including at least nitrocellulose or nitrocellulose/nitroglycerine based smokeless powder. Preferably, a layer of said multi-layered casing includes a hollow substantially spherical shell of papier mach6. Preferably, said casing includes a paper and glue wrap.

- 14 Preferably, said casing includes an exterior coating of an elastomer material or lacquer. Preferably, said elastomer material is a natural rubber or latex coating. 5 Preferably, said electric igniter is ignited via leadwires; said leadwires passing through an aperture in said casing; said aperture sealed with a sealing compound. Preferably said electric igniter is ignited via a shocktube passing through an aperture in said casing.. 10 Preferably, said nitrocellulose or nitrocellulose/nitroglycerine based powder is dosed with small quantities of a thermite composition. Preferably, said thermite composition includes a copper oxide/aluminium composition. 15 Preferably, said thermite composition comprises a maximum of 20 percent by mass of said smokeless powder. Preferably, said item includes a potassium perchlorate/aluminiium composition. 20 - 15 BRIEF DESCRIPTION OF DRAWINGS Embodiments of the present invention will now be 5 described with reference to the accompanying drawings wherein: Figure 1 Black gunpowder 2 is ignited by electric igniter 3 via lead wires 4 and contained by fibreboard cylinder 5 and fibreboard endcaps 6 the whole assembly 10 wrapped with multilayered friction tape 7, Figure 2 Black gunpowder 9 is ignited by electric igniter 10 via lead wires 11 and contained by fibreboard cylinder 12 and fibreboard endcaps 13 the whole assembly wrapped with multilayered friction tape 14 and coated with 15 lacquer 15, Figure 3 Smokeless powder composition 17 is ignited by electric igniter 18 via wires 19 which exit through an aperture in the sphere and which is sealed by sealing compound 23. Composition 17 is contained by hollow rubber 20 sphere 20 which is wrapped in PVC or Friction tape wrap 21 and then coated in lacquer or latex exterior coating 22, Figure 4 Smokeless powder composition 25 is ignited by electric igniter 26 via lead wires 27 of which exit from sphere is sealed by sealing compound 31 and contained by 25 hollow papier mache sphere 28 which is wrapped in paper and - 16 glue wrap 29 and then coated in lacquer or latex exterior coating 30, Figure 5 Smokeless powder composition 33 is ignited by electric igniter 34 via lead wires 35 that exit from item 5 through cork end closure 37 and contained by fibreboard cylinder 38 and cork end closure 36 which end closures are glued in place by glue layer 37, the whole assembly being covered in lacquer or latex coating 39. 10 DETAILED DESCRIPTION OF PREFERR1D EMBODENEMTS With particular reference to the use of the above described burster items in film and television special effects practice, the described improvements enable special 15 effects practitioners to practically eliminate unwanted smoke from explosive special effects events and also to use less explosive items per event because of the enhanced power of the above described composition in the above described containment. 20 The elimination of excess smoke and the increase in controllable propulsive power engendered by the novel devices above described enhances the ability of skilled special effects technicians to simulate real explosive events and thus to materially contribute to the "suspension 25 of disbelief" so important in successful film making and film story telling.

17 The absence of copious white smoke produced by above described prior art bursters enables the skilled technician to more accurately represent the types of explosive effects required for modern film making, and adjust smoke and dust 5 levels to his or her requirements, without having to attempt to deal with the unwanted gusts of obscuring and irritant smoke from either black gunpowder or other redox type pyrotechnic compositions. The preferred embodiments are as described in Figs 3, 10 4 and 5 and 4, with Fig. 3 the preferred embodiment cf Fig 4 and 5, due to the unique properties of the rubber containment, It should be noted that other elastomers than natural or synthetic rubber may be used for the above described spherical containment, for example elastomeric 15 polyurethane. There are many other elastomers that may be suitable for use in the described application, but natural rubber is the preferred embodiment. It should be noted that those items described in Figs 24 & 32 are perfectly practical and usable, and may in some circumstances, be 20 preferable to preferred embodiment as described in Fig 16, and may offer more economical means of manufacture, depending on application.. The preferred burster item contains the above described smokeless powder composition, dosed with a small 25 quantity of the above described reactive substances, the preferred substances for the preferred embodiment being -18 copper oxide/aluminium thermite or potassium perchlorate / aluminium flash powder, with not more than 10 percent by mass of the mass of the smokeless powder being added. It should be noted, however, that it is perfectly practical 5 and may be desirable to add more of the reactive substances above described, with the effect that the resultant explosion, on ignition of the burster, may produce more smoke than is optimal for this class of composition. 10 The preferred embodiment also incorporates the above described tape wrap and latex or lacquer exterior covering - it has been found during extensive experimentation that this type of assembly offers the best confinement conditions and the best waterproofing. 15 It should be noted that the preferred embodiment may also have uses in Battlefield simulation for military training and is complementary to those devices described in Australian Patent 2006201922, which, conversely, may also have a role in film and television special effects. 20 Also, because of the exceptionally gassy nature of the described composition, it may be envisaged as a non detonating explosive charge for the purposes of excavation or mining operations, especially if the composition is placed in a robust waterproof plastic container suitable 25 for insertion into a borehole drilled into rock or concrete or the like- - 19 A suitable modification of the abovementioned composition for this purpose may be as follows: smokeless powder 40 percent by mass, ammonium nitrate prill 30 percent by mass, sodium nitrate prill 20 percent by mass, graphite 6 percent 5 by mass, very fine aluminium powder 4 percent by mass, or variations on these percentages to obtain optimum rock -or concrete breaking performance. With correct initiation, most probably by ignition rather 10 than detonation, a very useful rock and concrete breaking formulation in the appropriate containment may be envisaged. The above describes only some embodiments of the 15 present invention and modifications, obvious to those skilled in the art, can be made thereto without departing from the scope of the present invention.

Claims (11)

1. A pyrotechnic item for producing a special explosive effect; said item comprising a substantially spherical multi-layered casing; at least one layer of said multi-layered casing formed of an elastomer material; said casing containing at least an electric igniter and an explosive composition; said composition formulated to produce a substantially smokeless pyrotechnic effect; said composition including at least nitrocellulose or nitrocellulose/nitroglycerine based smokeless powder.

2. The pyrotechnic item of claim 1 wherein a layer of said multi-layered casing casing includes a hollow substantially spherical shell of papier mache.

3. The pyrotechnic item of claim 1 or 2 wherein said casing includes a paper and glue wrap.

4. The pyrotechnic item of any one of claims 1 to 3 wherein said casing includes an exterior coating of an elastomer material or lacquer.

5. The pyrotechnic item of claim 4 wherein said elastomer material is a natural rubber or latex coating.

6. The pyrotechnic item of any one of claims 1 to 5 wherein said electric igniter is ignited via -21 leadwires; said leadwires passing through an aperture in said casing; said aperture sealed with a sealing compound.

7. The pyrotechnic item of any one of claims 1 to 5 wherein said electric igniter is ignited via a shocktube passing through an aperture in said casing.

8. The pyrotechnic item of any one of claims 1 to 7 wherein said nitrocellulose or nitrocellulose/nitroglycerine based powder is dosed with small quantities of a thermite composition.

9. The pyrotechnic item of claim 8 wherein said thermite composition includes a copper oxide/aluminium composition.

10. The pyrotechnic item of any previous claim wherein said item includes a potassium perchlorate/aluminium composition.

11. The pyrotechnic item of claim 8 wherein said thermite composition comprises a maximum of 20 percent by mass of said smokeless powder.