TARGETS AND A METHOD OF MANOFACTURIWC SAMEThis invention relates to means for improving the degradable nature of spent targets for use in the sport of clay pigeon shooting, these targets commonly being referred to as "clay pigeons".
According to the prior art, targets (or clay pigeons) are manufactured from a mixture of limestone and petroleum based tar pitch, which is then moulded into the required form. The mouldings are then baked to vitrify and irreversibly change the mixture resulting in hard discs (or targets).
Among the disadvantages of the prior art are that the resulting product is non-degradable and carcinogenic. These disadvantages require the disposal of the spent target by means of landfill processes.
Accordingly, it is an object of the present invention to eliminate the aforesaid disposal disadvantages by means of a novel manufacturing process.
According to a broad aspect of this invention, a mixture of filler and binder or other such components are brought together under pressure to form the target, with no significant and irreversible chemical change occurring.
In a first embodiment of the invention, the mixture to form the said target comprises a filler, for example ash, and a binder, for example wax. The components are preferably in a ratio of between 95/5 W and 50/50 % by weight respectively. The mixture is moulded under pressure, preferably with a compressive force of between 10 and 50 tonnes, typically at a pressure of about 35210 MPa. The moulding is preferably carried out without the addition of heat, but it can be heated if necessary.
Preferably, the filler is easily dispersible and the binder is water-soluble. If materials of this nature are used, the target so formed will degrade and disperse under the action of the environment, such as wind and rain, and no special disposal means are required.
Thus in a particularly preferred embodiment, the filler is pulverised fuel ash and the binder salt. Such materials have been found, when consolidated under pressure, to provide a target sufficiently robust to withstand use but which will also degrade and disperse safely after use.
Thus according to a further broad aspect of the invention, there is provided a target comprising consolidated pulverised fuel ash and salt.
The invention also extends to a method for making a target for clay pigeon shooting, comprising the steps of mixing pulverized fuel ash and salt and consolidating the mixture under pressure.
The mechanism through which the salt and ash bind under pressure is not currently understood. However, it is believed that the high pressure may cause the salt to flow as a liquid, and then fuse to bind the ash together.
Not only do the above materials lead to an environmentally sound target, but they are readily available and inexpensive, which is an obvious advantage. Pulverized fuel ash is a by-product of electricity generation at coal-fired power stations.
The pulverized fuel ash is recovered from the smoke stacks of the power station using electrostatic precipitators, and is mixed with water to facilitate handling. Usually, around 10% or 20% water by weight is added.
A sample composition for pulverized fuel ash (without water) is as follows:
g Analyte W/W Pie203 10.2 My304 c O . 1
BaO < 0.1 TiO2 1.0 CaO 3.1 K20 2.4 A1203 23.8 Si02 48.7 P205 0.2 S03 0.8 Na2O 0.9 MgO 1.6 Loss on ignition 6.8 Moisture < 0.1 45jm sieve residue 28.5 The pulverized fuel ash is usually dumped in ash fields or used as roadfill. It does not have a particularly detrimental environmental effect, and is therefore suited to use in the invention.
Salt (ie common salt) is of course readily available in a number of forms. Preferably, however, the salt used is in a granular form, such as table salt.
The fuel ash and salt may be mixed in proportions between 90:10 and 50:50 by weight. It has been found that the mixture should be moist before pressing, or the resultant targets may disintegrate upon removal from the mould. Preferably, therefore, the mixture should have a moisture content of between about 5 and 20% water by weight. This water may already be present in the fuel ash; for example, if the fuel ash has a moisture content of 10% by weight, and the ash and salt are mixed 50:50 by weight, the resulting mixture will have a moisture content of 5% by weight. The completed targets are sufficiently strong to withstand being fired from a clay pigeon launcher.
Apart from the fuel ash and salt, other materials may be added to the mixture. For example, a colorant may be added if it is desired to have coloured targets.
Any other desired material can of course also be incorporated.
The consolidation occurs in a suitably shaped mould under high pressure. Preferably the pressure is above 35MPa, more preferably above 100 MPa and most preferably above 200MPa.
In a particular embodiment of the invention, a mixture of 50:50 the pulverized fuel ash and salt may be mixed in a ribbon mixer in the presence of moisture.
The mixture is fed from the mixer to a bilateral powder press, where it is pressed in a mould.
In tests, an annular mould having an inner diameter of 80mm and an outer diameter of 100mm has been used. A compressive force of 60 tonnes is applied to the mould, resulting in an applied pressure of 208 MPa. This has been found to produce a robust product. No heat is applied during the moulding.
Once made, the target, being strong enough for use, is placed on a spring loaded arm that is then released, resulting in the target being projected through the air to land some considerable distance, either whole or having been shattered by means of a fired shotgun cartridge. The said whole or fragmented target then degrades and disperses due to natural weathering. The salt dissolves in water when it rains, and the pulverized fuel ash is dispersed by winds. There is thus no need to provide special means for disposing of the targets.
Of course, various modifications and embellishments to the above disclosure can be envisaged by the skilled person without departing from the scope of the invention. For example, the targets once formed may be painted with a suitable paint (preferably water soluble) if desired.