Ammunition and explosives – Igniting devices and systems – Electrical primer or ignitor
Reexamination Certificate
1997-06-27
2001-12-11
Tudor, Harold J. (Department: 3641)
Ammunition and explosives
Igniting devices and systems
Electrical primer or ignitor
C102S202500
Reexamination Certificate
active
06327978
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to the field of explosives and more particularly to means, known as detonators, used to detonate secondary explosives. More particularly, the present invention relates to an exploding thin film bridge fracturing flyer detonator for detonating secondary explosives.
It is well known that the passage of an electric current through a conductor generates a certain amount of heat, the amount of heat varying directly with the resistance of the conductor and with the square of the current. This phenomenon is relied upon in fusible links that are installed in electrical circuits to prevent the flow of more than a predetermined amount of current in such a circuit. When the predetermined flow is exceeded, the heat melts the fusible link so that the circuit is broken. If a sufficient current is passed through the link in a small period of time, the link is not only melted but may be vaporized. If the fusible link is enclosed in a small space the vaporizing of the link can increase the pressure in that space.
The blasting caps include a heat sensitive primary explosive set off by an electrical resistance heated by the passage of an electric current through the resistance. The exploding bridge wire devices detonate a primary explosive using a relatively low resistance bridge extending between conductors and through which a relatively high current is passed so that the bridge portion is not only heated to its melting point but is heated so much that it vaporizes and literally explodes to provide a shock wave to detonate the primary explosive. While such a system can use a primary explosive that is much less sensitive to heat and shock than a secondary explosive, there are still a distressing number of accidents that occur when the primary explosive is prematurely detonated, such a system does not provide the kinetic energy necessary to achieve reliable initiation of secondary explosives. Accordingly, a need exists for a more reliable and safe means for initiating secondary explosives.
Traditional exploding foil initiators, otherwise known as slappers, function by passing sufficient current through a metal foil or other conductor as to cause that material to vaporize. The pressure of this vaporization in concert with other vaporization phenomena cause a plate or disk to be driven to an acceptor explosive (i.e., a secondary explosive). The physical impact of this flying plate is such as to cause the explosive to be shock initiated. These devices have typically been constructed using materials for the flying plates which are organic or insulating layer which are organic. These organic materials have been limited to those that yield plastically before fracturing. This causes the effective surface area of the flying plate to be reduced by the amount of plastic deformation, otherwise known as the bubble effect.
Recently, it has been proposed to detonate these more stable explosives by an electrical means of some sort that creates a sudden pressure to shear a film and form a disk or flyer which is then impacted against the explosive material
One such example is disclosed in U.S. Pat. No. 4,602,565 (which is incorporated herein by reference) wherein an exploding foil detonator uses an explosive that is detonated by a flyer that is sheared form a sheet or film and propelled through a barrel to impact the explosive. The flyer is sheared from the sheet by the pressure generated when an electrical conductor adjacent the sheet is vaporized by the sudden passage of a high current (as by the discharge of a capacitor) through it. While this and other patents talk of the flyer being sheared this shearing does not occur until the material has experienced plastic deformation for the organic materials used to date, i.e. parylene and polymide. This plastic deformation, i.e., bubble effect, that occurs prior to shearing has the undesirable affect of reducing the effective surface are of the flyer. This reduction in flyer impact area reduces the kinetic energy transfer. This effectively reduces the likelihood that the impact will detonate a given explosive.
Organic compounds, e.g. parylene and polyamide, which have been used to date for the flyer and/or the insulating layer of prior art have susceptibility to the promotion of fungus growth and present considerable complexity to material compatibility, especially explosive compatibility analysis, due to both the complexity of their make up and the complexity of the chemical process and resulting chemical residue from their deposition.
As is typical in the prior art, the capacitor is in a circuit with the exploding thin film fracturing fragment detonator and a normally open switch. When it is desired to arm the system, the capacitor is charged, e.g., to 1000 volts; when it is desired to initiate the explosion, the switch is closed and the capacitor discharges through the thin film vaporizing the same.
SUMMARY OF THE INVENTION
The above-discussed and other problems and deficiencies of prior art are overcome or alleviated by the exploding thin film fracturing fragment detonator of the present invention. In accordance with the present invention, the exploding thin film bridge fracturing fragment detonator comprises a base with a bridge layer physically vapor deposited, e.g., sputtered, thereon. The bridge layer comprises a metal film or other thin film current conducting material having a defined bridge portion which interconnects significantly larger portions of this layer. The use of thin film sputtering allows the composition of the bridge layer to have superior homogeneity and superior uniformity of grain structure. These are significant in the determination of the statistical variance of the energy required to burst and in the thinness of a useful film deposition that can be achieved. This is an important feature of the present invention when low (e.g., less than 100 mili-joule) energy applications or energy input to output efficiencies are considered. A high variance in these parameters results in a high variance in the all fire to no fire ratios of the device itself (an undesirable effect from a safety viewpoint). The thinness of the bridge layer is a major determinate of the energy to burst level. An inorganic insulating layer of rigid material is physically vapor deposited, e.g. sputtered, on the metal layer. The rigidity of the insulator material is sufficiently high so as to promote fracture rather than plastic yielding and thus significantly reduce the adverse bubble effect common in prior art using more plastic materials. Further, this action promotes a smooth separation of a flyer (defined below) from the device under the pressure of the vaporization of the thin film bridge layer. A flyer comprised of a material having a density at least equal to that of the insulating material is vapor deposited on the insulating layer (e.g., of dielectric material). The insulating layer is comprised of a material which is materially compatible and stable with the material of the bridge layer, for electrically and/or thermally insulating between the bridge and flyer layers during the vaporization, at least until the flyer has separated and is in flight to the acceptor explosive. The flyer layer is positioned directly over the bridge portion and is of a tensile strength sufficient to remain intact while the insulating layer fractures freeing the flyer layer (or a portion thereof) for acceleration to the acceptor explosive as a single fragment of sufficient size (mass) that when sufficiently propelled causes on impact with the acceptor explosive the detonation of that explosive as a result of the shock impact.
During use a sufficient voltage is applied across the bridge whereby the resulting current passes through the bridge resulting in a vaporization of the bridge. The flow of this current is facilitated by the low resistance to the flow that the homogeneous uniform grained thin film metal provides. The expanding gas from the vaporization of the bridge portion causes the flyer layer together with a port
Spencer Dale L.
Turano Andrew
Cantor & Colburn LLP
Kaman Aerospace Corporation
Tudor Harold J.
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