Detonators innovating for a wireless safer & more productive blasting and EMI/EMP immune laser detonators

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Energetic materials and munitions are used across DoD in mission critical applications such as rockets, missiles, ammunition, and pyrotechnic devices. In these applications, energetic materials and munitions must perform as designed to ensure success in both training and combat operations. Explosive substances are solid or liquid substances or mixtures, which can, by chemical reaction, generate gases of such a high temperature, pressure and speed that they can cause destruction in their vicinity. Explosives means blasting agents, propellants, initiating agents, igniting agents, pyrotechnic mixtures. High explosives means detonating agents or compositions.Explosives are used in munitions as the main charge in warheads and in the fuses, primers, and detonators used to initiate the main charge.

 

A detonator, frequently a blasting cap, is a device used to trigger an explosive device. A blasting cap is a small sensitive primary explosive device generally used to detonate a larger, more powerful and less sensitive secondary explosive such as TNT, dynamite, or plastic explosive. Blasting caps come in a variety of types, including non-electric caps, electric caps, and fuse caps. They are used in commercial mining, excavation, and demolition. Electric types are set off by a short burst of current sent by a blasting machine via a long wire to the cap to ensure safety. Traditional fuse caps have a fuse which is ignited by a flame source, such as a match or a lighter.

 

Blasting cap, also called Detonator, device that initiates the detonation of a charge of a high explosive by subjecting it to percussion by a shock wave. In strict usage, the term detonator refers to an easily ignited low explosive that produces the shock wave, and the term primer, or priming composition, denotes a substance that produces a sudden burst of flame to ignite the detonator. The primer may be set off by the brief application of heat (from a burning fuse or an electrically heated wire), by friction, or by mechanical shock (like the impact of the firing pin of a gun). Depending on the preferred method of initiating the explosion, the blasting cap may contain a primer alone or both a primer and a detonator.

 

Ordinary detonators

Detonators can be chemically, mechanically, or electrically initiated, the latter two being the most common.  The commercial use of explosives uses electrical detonators or the capped fuse which is a length of safety fuse to which an ordinary detonator has been joined. Many detonators’ primary explosive is a material called ASA compound. This compound is formed from lead azide, lead styphnate and aluminium and is pressed into place above the base charge, usually TNT or tetryl in military detonators and PETN in commercial detonators.

 

Ordinary detonators usually take the form of ignition-based explosives. While they are mainly used in commercial operations, ordinary detonators are still used in military operations. This form of detonator is most commonly initiated using a safety fuse, and used in non time-critical detonations e.g. conventional munitions disposal. Well known detonators are lead azide [Pb(N3)2], silver azide [AgN3] and mercury fulminate [Hg(ONC)2].

 

Other materials such as DDNP (diazo dinitro phenol) are also used as the primary charge to reduce the amount of lead emitted into the atmosphere by mining and quarrying operations. Old detonators used mercury fulminate as the primary, often mixed with potassium chlorate to yield better performance.

 

Electrical detonators

There are three categories of electrical detonators: instantaneous electrical detonators (IED), short period delay detonators (SPD) and long period delay detonators (LPD). SPDs are measured in milliseconds and LPDs are measured in seconds. In situations where nanosecond accuracy is required, specifically in the implosion charges in nuclear weapons, exploding-bridgewire detonators are employed. The initial shock wave is created by vaporizing a length of a thin wire by an electric discharge. A new development is a slapper detonator, which uses thin plates accelerated by an electrically exploded wire or foil to deliver the initial shock. It is in use in some modern weapons systems. A variant of this concept is used in mining operations, when the foil is exploded by a laser pulse delivered to the foil by optical fiber.

 

Non-electric detonators

A non-electric detonator is a shock tube detonator designed to initiate explosions, generally for the purpose of demolition of buildings and for use in the blasting of rock in mines and quarries. Instead of electric wires, a hollow plastic tube delivers the firing impulse to the detonator, making it immune to most of the hazards associated with stray electric current. It consists of a small diameter, three-layer plastic tube coated on the innermost wall with a reactive explosive compound, which, when ignited, propagates a low energy signal, similar to a dust explosion. The reaction travels at approximately 6,500 ft/s (2,000 m/s) along the length of the tubing with minimal disturbance outside of the tube. Non-electric detonators were invented by the Swedish company Nitro Nobel in the 1960s and 1970s, and launched to the demolitions market in 1973.

 

Wireless detonators

Wireless electronic detonators are beginning to be available in the civil mining market.  Encrypted radio signals are used to communicate the blast signal to each detonator at the correct time. While currently expensive, wireless detonators can enable new mining techniques as multiple blasts can be loaded at once and fired in sequence without putting humans in harm’s way.

 

Innovating for a safer & more productive blasting

On December 10th, 2019, in Doña Elba Mine, a mine of Group Las Cenizas, in Taltal, in the Antofagasta region in Chile, our team programmed and fired 185 DaveyTronic® detonators with 2-way wireless capabilities: a world premiere! One of the key value elements, besides the accuracy of the electronic delay, was the capacity to communicate back & forth with each detonator to ensure their readiness to blast: a major safety breakthrough in the blasting industry.

 

Each DaveyTronic® detonator is associated with its own surface module ensuring the 2-way radiocommunication and the supply of energy to the detonator. Each module will be enabled and programmed optically through 2 different ways:
– Manually, through a handheld device
– Autonomously, through a drone, whose flight path has been programmed based on GPS location of each blast hole

 

Each module will communicate back & forth to a communication manager located near the blast pad thus enabling radiocommunication checks in addition to downhole testing. This communication manager will then communicate with a firing device, located at safe distance from the blasting area, up to 1km away. This new system enables a new range of benefits without compromising safety: contactless and autonomous programming, no last-minute tie-in, seamless troubleshooting, faster firing procedure, and all those while handled by regular blast crews.

 

Explosives On A Chip: Unique Structure Enables New Generation Of Military Micro-detonators

Tiny copper structures with pores at both the nanometer and micron size scales could play a key role in the next generation of detonators used to improve the reliability, reduce the size and lower the cost of certain military munitions. Developed by a team of scientists from the Georgia Tech Research Institute (GTRI) and the Indian Head Division of the Naval Surface Warfare Center, the highly-uniform copper structures will be incorporated into integrated circuits — then chemically converted to millimeter-diameter explosives. Because they can be integrated into standard microelectronics fabrication processes, the copper materials will enable micro-electromechanical (MEMS) fuzes for military munitions to be mass-produced like computer chips.

 

“An ability to tailor the porosity and structural integrity of the explosive precursor material is a combination we’ve never had before,” said Jason Nadler, a GTRI research engineer. “We can start with the Navy’s requirements for the material and design structures that are able to meet those requirements. We can have an integrated design tool able to develop a whole range of explosive precursors on different size scales.” Nadler uses a variety of templates, including microspheres and woven fabrics, to create regular patterns in copper oxide paste whose viscosity is controlled by the addition of polymers. He then thermochemically removes the template and converts the resulting copper oxide structures to pure metal, retaining the patterns imparted by the template. The size of the pores can be controlled by using different templates and by varying the processing conditions.

 

So far, he’s made copper structures with channel sizes as small as a few microns — with structural components that have nanoscale pores. Based on feedback from the Navy scientists, Nadler can tweak the structures to help optimize the overall device — known as a fuze — which controls when and where a munition will explode. “We are now able to link structural characteristics to performance,” Nadler noted. “We can produce a technically advanced material that can be tailored to the thermodynamics and kinetics that are needed using modeling techniques.” Beyond the fabrication techniques, Nadler developed characterization and modeling techniques to help understand and control the fabrication process for the unique copper structures, which may also have commercial applications.

 

The copper precursor developed in GTRI is a significant improvement over the copper foam material that Indian Head had previously been evaluating. Produced with a sintered powder process, the foam was fragile and non-uniform, meaning Navy scientists couldn’t precisely predict reliability or how much explosive would be created in each micro-detonator. “GTRI has been able to provide us with material that has well-controlled and well-known characteristics,” said Michael Beggans, a scientist in the Energetics Technology Department of the Indian Head Division of the Naval Surface Warfare Center. “Having this material allows us to determine the amount of explosive that can be formed in the MEMS fuze. The size of that charge also determines the size and operation of the other components.”

 

The research will lead to a detonator with enhanced capabilities. “The long-term goal of the MEMS Fuze program is to produce a low-cost, highly-reliable detonator with built-in safe and arm capabilities in an extremely small package that would allow the smallest weapons in the Navy to be as safe and reliable as the largest,” Beggans explained. Reducing the size of the fuze is part of a long-term strategy toward smarter weapons intended to reduce the risk of collateral damage. That will be possible, in part, because hundreds of fuzes, each about a centimeter square, can be fabricated simultaneously using techniques developed by the microelectronics industry.

 

“Today, everything is becoming smaller, consuming less power and offering more functionality,” Beggans added. “When you hear that a weapon is ‘smart,’ it’s really all about the fuze. The fuze is ‘smart’ in that it knows the exact environment that the weapon needs to be in, and detonates it at the right time. The MEMS fuze would provide ‘smart’ functionality in medium-caliber and sub-munitions, improving results and reducing collateral damage.” Development and implementation of the new fuze will also have environmental and safety benefits.

 

“Practical implementation of this technology will enable the military to reduce the quantity of sensitive primary explosives in each weapon by at least two orders of magnitude,” said Gerald R. Laib, senior explosives applications scientist at Indian Head and inventor of the MEMS Fuze concept. “This development will also vastly reduce the use of toxic heavy metals and waste products, and increase the safety of weapon production by removing the need for handling bulk quantities of sensitive primary explosives.” The next step will be for Indian Head to integrate all the components of the fuze into the smallest possible package — and then begin producing the device in large quantities.

 

A specialist in metallic and ceramic cellular materials, Nadler said the challenge of the project was creating structures porous enough to be chemically converted in a consistent way — while retaining sufficient mechanical strength to withstand processing and remain stable in finished devices. “The ability to design things on multiple size scales at the same time is very important,” he added. “Designing materials on the nano-scale, micron-scale and even the millimeter-scale simultaneously as a system is very powerful and challenging. When these different length scales are available, a whole new world of capabilities opens up.”