The present invention relates to an explosive initiation device. In particular, embodiments of the invention include an imploding barrel initiator, other alternative apparatus embodiments, and related methods of making, use, etc.
Sensitivity of explosives can be referred to as a degree to which an explosive can be initiated by impact (or shock), heat, or friction. Sensitivity, stability and brisance are three significant properties of explosives that affect subsequent use and application. All explosive compounds have a certain level of of energy and power required to initiate. If an explosive is too sensitive, it may go off accidentally. A safer explosive is less sensitive and will not explode if exposed to certain inadvertent conditions, e.g. certain levels of energy in the form of heat, or shock. However, such explosives are more difficult to initiate intentionally—such a difficulty in initiation or detonation can increase as the size of an application gets smaller. High explosives can be conventionally subdivided into two explosives classes, differentiated by sensitivity: Primary explosives are extremely sensitive to mechanical shock, friction, and heat, to which they will respond by burning rapidly or detonating. Secondary explosives are relatively insensitive to shock, friction, and heat and are much less likely to be inadvertently initiated.
Some existing initiation systems can include hot wire (HW) detonators, Exploding Bridgewire (EBW) detonators, Exploding Foil Initiators (EFI), Low Energy Exploding Foil Initiators (LEEFI), and Ultra Low Energy Exploding Foil Initiators (ULEEFI). HW detonators can be manufactured using extremely sensitive primary explosive. EBWs often employ explosives e.g., Pentaerythritol, Tetranitrate (PETN), which are less sensitive than the explosives employed in the HW detonators. The EFI category (including EFI, LEEFI, and ULEEFI) use other explosives that are even less sensitive and more difficult to initiate. Examples of these explosives such as Hexanitro stilbene (e.g., HNS-IV) and RSI-007 explosives are so safe that they are approved for use in-line with the energetic firing train.
HW initiators employ very sensitive pyrotechnics or primary explosives, and require only a few amps of current to heat a resistive bridge of ˜1-10 Ohms. Such systems can have a very low input energy requirement (5-50 mJ), and can have a very low current rate of rise (Amps/millisecond) requirements. As a result, HW initiators can have unintentional firing sensitivities often due to factors such as electromagnetic radiation and electrostatic discharge; these can be initiated by many common intentional and unintentional sources such as common flashlight batteries. These sensitivities restrict HW initiators use to systems that keep the detonator out of line or separated until activation.
EBW detonators can be comprised of a thin gold wire that bridges the two input legwires. The bridge can burn out at several amps, but will not detonate the explosive that is packed next to it, unless hundreds of amps are sent to the bridge in a few microseconds. These types of detonators can be significantly safer than HW detonators, from both an electrostatic discharge (ESD) as well as hazard of electromagnetic radiation to ordnance (HERO) perspective, due to their significantly higher threshold current (hundreds of amps vs a few amps), and required current ramp rate (hundreds of amps per microsecond). For short distances between the firing circuit and the detonator, standard firing wire is used; for longer firing distances, a coaxial cable is employed. Such design approaches can make the EBW detonator cable assemblies easy to build and employ. One initial explosive that can be pressed against the bridgewire can be PETN. Experts disagree on whether PETN is a primary or secondary explosive. For this reason, PETN based detonators are frequently not approved for use in an explosive train unless there is an out of line safe and arming device included in the firing train.
EFI detonators are one class of existing explosive initiators (including LEEFI and ULEEFI), being both safer than some types of initiators and having similar energy requirements as EBW detonators. EFI detonators can include an insensitive explosive that is approved for in-line use, such as HNS-IV or RSI-007. EFI detonators can be resistant to HERO and ESD factors and can be designed to be safer than older options. Primary drawbacks of EFI detonators, relative to EBWs, include cost and a requirement of a current ramp rate that is approximately 10-100 times faster, thus requiring modifications such as, e.g., use of controlled impedance cables and significant restriction on component placement and supporting electronic hardware to reliably fire a EFI.
Some initiator designs use sensitive (e.g., primary) explosive within metallization structures. However, simply using a same or similar metallization of a barrel with respect to a detonator in a substrate holding a pyrotechnic mix and/or sensitive/primary explosives will not generate a sufficient shock effect to detonate a secondary explosive material. Any explosive column diameter smaller than a critical diameter will not sustain a detonation. A certain amount of explosive is needed in order for an explosive mass to create a self-sustaining explosive detonation (e.g., a detonation can be defined as a process where the explosive will react at a rate where the explosive is consuming itself faster than a speed of sound in the explosive material). A design for detonating secondary, as well as sensitive, explosives must have a barrel which is large enough in view of the secondary explosive's critical diameter (for detonation) but not too large that results in unnecessary energy requirements needed to achieve secondary explosive detonation pressure from vaporization of barrel metallization. In other words, significant effort and analysis has been necessary to determine, among other things, a barrel metallization thickness, along with other elements, required to generate a sufficient level of shock to detonate the secondary explosive but not be too thick so as to expend unnecessary energy (e.g., spending energy to vaporizing metal that was not necessary for detonation of the secondary explosives). Additional factors also impacting a design include a diameter of a barrel/hole and ensuring a means of conveying electricity to the barrel without losing a significant amount of energy that then results in a misfire, dud, or failure to detonate.
For example, a secondary explosive (e.g., Cyclotrimethylenetrinitramine (RDX)) might be used with a metallization barrel although its critical diameter of an explosive for RDX is ˜5.2 millimeters. If a design had a barrel diameter of 20 microns, that diameter would be on the order of two hundred and fifty times too small to detonate the RDX—certainly not reliably.
A variety of factors can render a design incapable of providing required conditions for detonating of a primary or insensitive explosive. For example, a detonator might use a semiconductor material to convey electrical energy into a metalized barrel containing an explosive such as, e.g. a secondary explosive. However, if the semiconductor's substrate is a doped silicon substrate, it may not conduct electricity as efficiently as metal and the overall device efficiency will be lower.
Other designs might try to use silicon to distribute current to a detonator barrel. In this scenario it is difficult to ensure uniform current density in the barrel. In that case, a primary consideration is delivery of uniform current density in the barrel structure, which can be difficult to achieve especially when the bottom of the barrel is also plated. Moreover, systems that merely rely on heating versus generating a shock from turning the metal into high speed plasma will not detonate secondary or insensitive explosives.
Yet other designs might try to use semiconductors in relation to detonation barrel design with respect to sensitive explosives using firing voltages of, e.g., 6-10 volts or, resistance of, e.g., 1-10 Ohms. As is such, these designs will not practically detonate a secondary explosive. Their predicted resistance is higher than an exemplary embodiment of the invention, which is capable of less than 1 Ohm resistance. Said embodiment offers additional resistance to inadvertent input stimulus such as radio frequency or electrostatic energy, as well as ensure that other inadvertent sources cannot provide the critical current ramp rate required to initiate insensitive or secondary explosives. Such a semiconductor design also does not address key mechanics of how to construct a detonator so that it will initiate insensitive or secondary explosives.
Thus, various improvements to existing designs are needed to produce desired results such as safety and reliability along with ease of use and cost all at an electrical input energy that is lower along with other needed utility and advantages provided by various embodiments of the invention. Exemplary apparatuses and methods are provided including electrically fired detonators employing secondary explosives, which increase safety and reliability relative to primary explosives. Primary explosives require a lower amount of energy or shock to detonate than secondary explosives and are thus easier to detonate; secondary explosives are less sensitive to shock or energy than primary explosives, increasing safety but still suffering from some design difficulties. Various embodiments are provided, one of which being a metalized barrel with a specific thickness; the barrel is filled with a secondary explosive, having a required diameter with structures that provide efficient transfer/conversion of electrical energy into detonation of the secondary explosive by, among other things, reducing electrical and mechanical/chemical losses. Embodiments of the invention also include various methods of design, use, and manufacturing.
Additional features and advantages of the present invention will become apparent to those skilled in the art upon consideration of the following detailed description of the illustrative embodiment exemplifying the best mode of carrying out the invention as presently perceived.
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