Blast initiation device

Ammunition and explosives – Igniting devices and systems – Fuse cord

Reexamination Certificate

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Details

C102S275500, C102S275900

Reexamination Certificate

active

06513437

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to blast initiation devices. More specifically, the present invention relates to a detonator device having at least one signal transmission surface for communication of pressure impulse to neighbouring transmission lines or the like, in a detonator assembly or blasting system.
2. Description of Related Art
Concern about the versatility and precision of blasting systems has been the focus of the explosives industry for decades. Current blasting practices widely employ low brisance transmission lines as a non-electrical means of transmitting blasting signals to target detonators for initiating explosive columns in a precise and reliable manner.
Modern non-electric blasting systems typically comprise a series of shock tubes or signal transmission lines positioned in contact with a donor detonator within a connection block or the like. Transmission lines, or shock tubes as they are more commonly known, generally consist of a hollow tube housing a gas, and having an inner lining comprising a reactive material. The reactive material typically comprises aluminum powder and HMX explosive powder. These shock tubes are used to conduct an initiation impulse to the target detonators at remote locations within a blasting arrangement. Upon initiation, the pressure of an incoming impulse causes the wall of the shock tube to collapse, pressurizing and subsequently heating the gas within the tube and igniting the reactive lining.
A first detonator is generally initiated via an initiation shock tube to begin a chain of initiation steps within a blasting system. The pressure impulse generated by this first detonator is subsequently transmitted by neighbouring shock tubes to remote target detonators throughout the blasting system. Since the success of the ultimate blast or blasts is dependent on the reliability and timing of a pressure impulse arriving at the desired blast location(s), it is critical that all of the components of the blasting system are correctly and completely initiated. Upon initiation, the strength of the propagating pressure impulse is constant and independent of the mode of initiation and signal transmission line length. The propagation of such an impulse is therefore limited by the obstacles it encounters along a transmission pathway.
The prior art has largely focused on improving the precision and control of detonator initiation. In particular, the prior art teaches an extensive variety of detonator devices including timing control components for providing constant and stable ignition stimuli. The prior art also includes an abundance of connector components for use in blasting systems for precisely controlling the positioning of shock tubes with respect to detonators in blasting systems. These efforts have come a long way in improving the safety and reliability of detonator assemblies. However, given the nature of explosive compositions and devices, there is always room for improvement to the safety of the blasting systems employed worldwide.
European Patent No. 0 439 955 discloses a delay detonator having a transition element for providing a stable ignition signal to the delay train element of the detonator. According to this invention, a transition element separates the delay train element from the ignition source. This transition element comprises a material which, when ignited by an ignition signal, develops a substantially constant intensity for igniting the delay train element. As a result, this transition element stabilizes an ignition signal prior to igniting the delay train element of the detonator. More specifically, the delay time interval is dependent upon the intensity of the signal by which it is ignited. Accordingly, by providing a transition element of a suitable reactable material, the typical variable burn rate of an ignition signal can be transformed into a stable, quasi-steady state combustion rate for the controlled ignition of the delay train element. The time internal of the delay train element is therefore more precisely performed.
The detonator of this invention comprises of a typical tubular casing having a receiving end and a firing end. The exterior surface of the firing end of this detonator is shown to have a rounded shape As with most conventional detonator casings, the firing end of this detonator may be flat, rounded or otherwise shaped for convenience within a blasting system. An explosive composition is positioned within the tubular casing at a location most proximate to the firing end. The remaining components of the detonator are sequentially received through the receiving end according to their required role in the ultimate ignition of the explosive composition. The delay train element ignites the explosive composition contained at the firing end of the detonator. As a result, the delay train element must be positioned within the tubular casing of the detonator to contact the explosive composition. The explosive composition of this detonator includes both a primary charge and a base charge.
A detonation impulse initiated by a detonator of this type would naturally propagate from a point of initiation as a growing sphere. However, with the explosive composition confined to only one side of the initiation point, the propagating impulse will be concentrated in that direction. Further, heavy confining jackets may be provided within the tubular casing to position the delay train element, and subsequently confine the explosive composition. In this manner, the detonation impulse will be encouraged to propagate in a hemispherical fashion toward the firing end of the detonator.
As a result of the volume of explosive composition required by the detonator of EP 0 439 955, the delay train element is positioned a distance from the firing end which is substantially greater than the radius of the detonator. Accordingly, a propagating spherical or substantially hemispherical impulse will impact on the wall of the firing end at various rates.
U.S. Pat. No. 5,703,319 to J. E. Fritz et al. discloses a detonator assembly comprising a conventional flat end detonator and a connector block adaptable to receive six shock tubes. The connector block includes a rounded slot proximate a location for receiving the firing end of a detonator. According to this invention, a plurality of shock tubes can be receive into the rounded slot of the connector and extend in a direction perpendicular to the detonator. The rounded slot positions the plurality of shock tubes in fixed positions with respect to the firing end of the detonator.
When six shock tubes are received into the rounded slot of the connector, the two middle shock tubes are caused to shift away from the firing end of the detonator. This allows the next two shock tubes to be positioned closer to the centerline of the detonator. As a result, the positioning of the shock tubes of the detonator assembly of this invention is not spatially uniform and as a result, the shock tubes are not positioned to receive a uniform pressure impulse. As a result, the energy transfer efficiency to each shock tube will be variable.
U.S. Pat. No. 5,204,492 to Jacob et al. teaches of a detonator assembly comprising a low strength detonator containing low brisance primary explosives such as lead azide or lead styphate or compositions thereof, and a high confinement connection block. According to the invention of this patent, an assembly is provided which increases confinement of a plurality of signal transmission lines and facilitates the transfer of a pressure impulse upon detonation, while eliminating noise and shrapnel.
The connector block designs of this invention, increase the confinement of a plurality signal transmission tubes, thereby improving the energy transfer from the detonator to the lines, and subsequently reducing the amount of explosive composition required to obtain complete initiation. However, this reference does not provide for the uniform transmission of a pressure impulse from the firing end of a detonator to all signal transmissi

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