Patent Application
20100275802
This invention relates to impact initiated pyrotechnic targets and impact initiated pyrotechnic compositions.
It is known to provide practice targets for various shooting purposes. For example, targets may be used in conjunction with firearms such as rifles and pistols, and air propelled arms such as air rifles and air pistols. The target may be of the type which is intended to be held in a fixed position, and which may have indicia located thereon such as a number of concentric rings defining a “bullseye”. Alternatively, the target may be intended to be used as a moving target such as a “clay pigeon”. It is known from U.S. Pat. No. 4,498,677 and WO02/35175 to provide an explosive target which registers a hit by providing an explosive event. However, it has proven difficult to produce a pyrotechnic which can be satisfactorily ignited by the impact of a relatively low energy projectile such as a pellet or slug discharged by a pneumatic weapon such as an air rifle. Additionally, whilst there is a need to provide a target which is sufficiently sensitive to provide a reaction to a hit by a relatively low energy projectile such as an air gun pellet, the active pyrotechnic used in the target should not be so sensitive as to present a hazard during manufacture, handling or storage. A related and important consideration is that the nature of the active pyrotechnic should not render its preparation illegal under national laws. The laws of the UK are particularly restrictive in terms of the nature of the pyrotechnic and its manufacture. For example, the explosive formulation described in U.S. Pat. No. 4,498,677 would not be legal under UK law.
The present invention, in at least some of its embodiments, addresses the above described problems and needs.
According to a first aspect of the invention there is provided an impact initiated pyrotechnic target including an impact initiated pyrotechnic composition which can be initiated by the impact of an inert projectile, said pyrotechnic composition including:
an oxidising agent;
optionally, a fuel or reducing agent;
a sensitiser in the form of a sulfur containing compound; and
optionally, a binder.
The sensitiser acts as a source of bound sulfur. This is advantageous, because the sulfur provides an initiation enhancing sensitisation. However, the pyrotechnic composition is safer than compositions which utilise elemental sulfur by virtue of being chemically bonded to other atomic constituents of the sensitiser. In this way, the stringent UK legislation governing pyrotechnics can be satisfied.
Very preferably, the sensitiser is thiourea. Surprisingly, it has been found that the presence of thiourea can act as a highly advantageous sensitiser, enabling the provision of a pyrotechnic composition which is sufficiently sensitive to provide enhanced impact initiation. A further advantage is that the thiourea can provide an accelerated burn rate. In at least some embodiments, the use of thiourea can permit impact initiation by a relatively low energy projectile such as an air rifle or air pistol pellet.
For the avoidance of doubt, the term “inert” as used herein refers to a projectile which ignites the target by virtue of its kinetic energy on impact, i.e., a projectile which is non-explosive and does not react chemically with the pyrotechnic composition.
Preferably, the oxidising agent is a chlorate, most preferably potassium chlorate.
Advantageously, a fuel or reducing agent is present. Preferably the fuel or reducing agent is charcoal. Other fuels or reducing agents, such as organic fuels, for example shellac, might be utilised. However, charcoal can provide excellent results and has the advantage that its use in the manufacture of pyrotechnics in the UK is legal.
Preferred embodiments utilise a chlorate in combination with charcoal and thiourea. A particular preferred combination is potassium chlorate, charcoal and thiourea. It should be noted that the present inventors have found that mixtures of potassium chlorate and charcoal without thiourea were not sensitive enough for use with relatively low energy projectiles such as air gun pellets at practical firing ranges. It is estimated that the presence of thiourea reduces the ignition temperature of the potassium chlorate/charcoal pyrotechnic composition by about 200° C., thereby providing greatly enhanced sensitivity to impact initiation.
Whilst it is preferred that a fuel or reducing agent is present in addition to the thiourea, it may be possible to provide an impact initiated pyrotechnic composition which does not include a fuel or reducing agent. Tests have revealed that combinations of potassium chlorate and thiourea (which acts as a fuel and a sensitiser) can be caused to react explosively at temperatures as low as 155° C.
Preferably, the impact initiated pyrotechnic composition includes, by weight, 30-70% of the oxidising agent, 0-60% of the fuel or reducing agent, 8-40% sensitiser and 0-15% of the binder, with the proviso that the total weight percentages of these components do not exceed 100%.
Preferably, the impact initiated pyrotechnic composition includes 40-60% by weight of the oxidising agent.
Preferably, the impact initiated pyrotechnic composition includes 20-40% by weight of the fuel or reducing agent.
Preferably, the impact initiated pyrotechnic composition includes 10-40% by weight of thiourea, more preferably 12-30% by weight of sensitiser.
Preferably, the impact initiated pyrotechnic composition includes 1-10% by weight of the binder.
The binder is preferably a resin, such as acaroid resin or shellac. Other suitable binders may be used. In general, the binder is a polymeric matrix of some sort.
The target may further comprise a secondary pyrotechnic composition which is formulated to be initiated by the impact initiated pyrotechnic composition to produce a desired signalling effect. The desired signalling effect may be one or more of an enhanced explosion, a desired flame colour, enhanced smoke production, a desired noise level on initiation, a desired burn rate and an incandescent display.
The secondary, pyrotechnic composition can be selected from a wide range of suitable candidates in order to provide the desired signalling effect. In preferred embodiments, the secondary pyrotechnic composition includes metal particles and an oxidizing agent. The metal particles may be aluminium, magnesium or a combination of both.
The secondary pyrotechnic composition may include a suitable binder.
In general, the secondary pyrotechnic composition will include an oxidising agent which is somewhat more stable than the oxidising agent used in the impact initiated pyrotechnic composition. Perchlorates may be used.
Typically, the impact initiated pyrotechnic composition and the secondary pyrotechnic composition are blended together. The blend ratio may be in the range 1.5:1 to 4:1 by weight of impact initiated pyrotechnic composition to secondary pyrotechnic composition. In general, the impact initiated pyrotechnic composition and the secondary pyrotechnic composition are granular, and the grains are blended together.
The impact initiated pyrotechnic composition may be disposed in front of a resilient surface, the resilient surface being sufficiently resilient to resist the impact of the projectile to an extent which allows initiation of the impact initiated pyrotechnic composition to take place.
Without wishing to be bound by any particular theory, it is believed that the resilience of the surface permits a compression of the pyrotechnic composition to occur upon impact which causes an increase in temperature which in turn causes the pyrotechnic composition to ignite. Depending on the impact initiating pyrotechnic composition and the envisaged implication, it may not be necessary to utilise a resilient surface in order to obtain impact initiation. The target may include a housing, in which the resilient surface acts as a backing plate of the housing, the backing plate having a wall upstanding therefrom forming an enclosure in which the impact initiating pyrotechnic composition is disposed. Typically the backing plate and wall are formed from a metal, such as aluminium. The housing may further include a lid which is disposed over the wall so that the housing fully encloses the impact initiating pyrotechnic composition. The lid may be formed from sheet material such as card or paper.
The compositions may be in granular form, in which instance a milling technique may be used to produce the granules. Alternatively, the compositions may be produced using a slurry of the constituents which is subsequently dried.
The targets of the invention may be used as targets for firearms, air-operated arms such as air rifles and air pistols, or even in archery. The targets may be intended for use as essentially a static target, in which instance the targets may consist essentially of the housing described above. Alternatively, the targets may be a moving target such as a clay pigeon.
According to a second aspect of the invention there is provided a solid impact initiated pyrotechnic composition including:
an oxidising agent;
optionally, a fuel or reducing agent;
a sensitiser in the form of a sulfur containing compound; and
optionally, a binder.
According to a third aspect of the invention there is provided the use of a solid impact initiated pyrotechnic composition of the second aspect of the invention as an impact initiated pyrotechnic.
According to a fourth aspect of the invention there is provided the use of a solid impact initiated pyrotechnic composition according to the second aspect of the invention in an impact initiated pyrotechnic target for signalling a strike by an impacting inert projectile.
Whilst the invention has been described above, it extends to any inventive combination or sub-combination of the features set out above or in the following description or drawings or claims.
Embodiments of targets and compositions in accordance with the invention will now be described with reference to the accompany drawing which shows
(a) an exploded view
(b) a perspective view
(c) a cross-sectional view of a target of the invention.
In one example, the explosive powder contains an impact initiated pyrotechnic composition which comprises 32% charcoal, 48% potassium chlorate, 4% acaroid resin, and 16% thiourea with all percentages being by weight. In a preferred embodiment, this composition acts as an “ignition composition”, and is used in conjunction with a secondary, “signal” composition which enhances the visual effect of a strike on the target by a projectile. The secondary “signal” composition may be as follows:
Potassium perchlorate 66%, Aluminium Powder, 28%, and acaroid resin 6%, all percentages being by weight.
The two compositions are wet milled to achieve full incorporation and granulated to form random cylindrical grains of varying lengths having an average diameter of 1.7 mm. These dimensions and the integrity of the grains are confirmed by separate screening, with over or under-sized or poorly compacted grains being removed. The subsequent compaction within the housing further ensures that physical integrity is maintained. A typical blend is 70% by weight of the ignition composition and 30% by weight of the signal composition.
When used in a target of the invention, the blended composition described above is capable of being impacted initiated by a projectile and provides a slow burning, bright but gentle white flame with a white smoke signature. The effect is not dissimilar to a theatrical stage effect with sparks produced and incandescent debris projected up to 1 m of the firing point. Greater or lesser effects can be produced as desired.
In representative examples, the target has a diameter range 40-90 mm and a depth in the range 10-15 mm, with the charge weight of the blended composition being 8 g or less. However, it will be understood that targets of the invention may be smaller or larger than these dimensions, and that different charges will be used in accordance with the precise nature of the composition and intended application.
The present invention also provides moving targets such as clay pigeon type targets. A clay pigeon target may incorporate one or more housings for the pyrotechnic composition which may be similar to the housing in
| Number | Date | Country | Kind |
|---|---|---|---|
| 0722384.5 | Nov 2007 | GB | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/GB2008/003831 | 11/14/2008 | WO | 00 | 5/14/2010 |
