Ammunition and explosives – Blasting – Terrain clearance
Reexamination Certificate
2000-04-24
2002-10-08
Nelson, Peter A. (Department: 3641)
Ammunition and explosives
Blasting
Terrain clearance
C102S312000, C102S313000
Reexamination Certificate
active
06460462
ABSTRACT:
FIELD OF THE INVENTION
This invention concerns field of the Invention rock or similar materials in surface or underground mining operations where bore holes are charged with explosives and detonators.
BACKGROUND OF THE INVENTION
Such blasting technologies are known from experience respectively from European patent application 0 147 688 A2 and the German disclosure document DE 197 21 839 A1.
It was discovered that for such blasting technologies the applied detonating agents have a decisive influence on the quality of the blast. Here discrimination is made between electric, nonelectric and electronic detonators.
Electric detonators feature a pyrotechnical compound together with a filament, which is heated by electric energy. A non-electric detonator mostly consists of a thin plastic hose containing explosives. This hose is ignited by an impact, respectively a fuse cap. The plastic hose then ignites the pyrotechnical delay composition in the detonator.
Electronic detonators do not need a pyrotechnical compound. They get the ignition energy from an energy-storing device like e.g. a capacitor. This capacitor heats a filament or any other device, which can be heated by electricity. Basically this is already described in the European document and the German disclosure document DE 197 21 839 A1. The blasting technologies known until now are not fully convincing. Because until now only a mutual support of neighboring bore holes can be achieved in the same row of bore holes in the sense of intensifying the disintegration of the rock masses to be blasted. In other words, the energy of a subsequent shot cannot or can only insufficiently be coupled to the energy of the preceding shot. Furthermore, such phenomena could until now only be observed by chance and they could not be predicted. This invention is supposed to improve this situation altogether.
This invention is based on the technical problem of further developing such a technology in a way that a focused mutual impact of the shock waves coming from the individual bore holes can be achieved.
To solve this task it is proposed by this invention utilizing a technology for blasting rock or similar material that electronic detonators and their respective time delays are programmed in consideration of the mineralogical and geological environment and the seismic velocities resulting thereof and the respective firing patterns. In most cases, an electronic detonator with a continuously, variable programmable moment of ignition is applied. With such electronic detonators, it is possible for the first time to freely program variable delay intervals from one detonator to the other, respectively from bore hole to bore hole. This is basically because electronic detonators, as mentioned before, do not have a pyrotechnical firing compound. Rather, they have an electronic switch which is connected after the battery (respectively the capacitor) that allows the electric energy to flow into the ignition device of the detonator when switched on. This electronic switch, specifically a switching transistor, can be correspondingly controlled by a data control part inclusive a control unit—i.e., actually a computer in form of a microchip. This design enables the electronic detonator to be accurately detonated with accuracy of one millisecond.
In order to increase the explosive effect, the invention proposes that shock wave fronts coming from the respective bore holes interfere with each other in order to open the structure of the rock to be blasted. So there is a wave interference of the shock waves and a wave interference of the seismic waves. This colliding and inter-reacting of various multiple wave fronts leads to the desired fracture of the structure, i.e. the connections in the respective solids are loosened from the excitation from the outside.
Shock waves are generally understood as being three-dimensionally spreading, abrupt and consistent changes of density, pressure and/or temperature of the material to be blasted. Such a shock wave develops when a huge amount of energy is suddenly released—such as by an explosion or the ignition of an explosive charge in a bore hole with the help of the (electronic) detonator. The leading edge of this spreading of energy represents a shock wave. The propagation velocity of this shock wave can be a multiple of the sonic velocity of the surrounding medium and mainly travels at supersonic speed.
Within the framework of this particular invention, seismic waves shall not only be regarded as shock waves, or tremor waves, but any kind of vibration waves which travel away from an epicenter (mostly a bore hole with an explosive charge) in the rock to be blasted.
As the propagation velocity of the respective seismic wave—apart from the so-called pressure waves or shock waves—depends on the material and its ability to be compressed, there is a certain and characteristic propagation speed at a given density and temperature, the sonic speed. This represents a parameter depending on the material and can, in case of rock mass, amount to more than 1,000 m/sec or even several 1,000 m/sec.
The field of elastic deformation and the given compressibility of the rock, which conducts the seismic wave or the sound wave are of concern if only waves with small amplitude are excited in the rock. If there is a bigger and sudden excitation, then the shock waves, or tremor waves are created. They have the favorable effect that at least in the area of the blast the atoms in the solid lattice are not elastically deformed against each other anymore, so their connections break up. The solid structure is destroyed (for the most part).
As the shock wave velocity is mostly supersonic, this speed amounts to Mach 1 and more. For the increase of the explosive effect, the firing sequence is arranged in such a way that the shock waves from the individual bore holes and the seismic waves, particularly sound waves, overlap and interfere [amplify]. The shock wave system in the area of the blast is being compressed. This means that wave amplitudes are created, which result from the (positive) overlapping of individual shock waves. This can be controlled with programmable delays in such a way that, altogether a shock wave system is created by the wave velocities of which propagate supersonically, i.e. their speed is above mach 1.
The procedure here is as follows. The sequence of ignition is arranged in such a way that the accumulated sum of the delay times is smaller than the traveling time of the sonic speed resulting from the rock to be blasted. In other words, the delays between the first bore hole to be fired and the last bore hole to be fired are chosen in such a way that the velocity of the ignition (horizontal ignition velocity) is equal to or faster than the sonic speed in the material to be blasted (rock velocity).
By this, it is possible to create calculated delay models of the individual ignition sequences, so called firing patterns. The choice of the individual delays determines the fragmentation of the blasted material (pile of debris). It even determines the distribution respectively of the accumulation of the material in the area of the blast. This is because individual seismic waves interfere in such a way that, at certain spatially exactly defined spots, wave interference peaks happen, leading to a particularly extensive fracture of the rock masses to be blasted in this particular area. But the wave interference minima, on the other hand, correspond in such a way that only a limited fracture of the rock is achieved.
But as the seismic waves spread from the respective bore hole with the sonic speed through the respective rock, the wave patterns move and hence the wave interference peaks and minima travel as well. This can either happen in the shape of counteracting or paralelly running waves and/or shock waves.
Thus, it can be observed as the overall result, that there are compression effects by the described wave collisions resulting from the multiple oscillations or flow of the respective wave fronts through the rock masses. Due t
Nelson Peter A.
Roboth Vertriebsgesellshaft mbH
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