Detonator
Detonators are objects that are suitable for detonating explosives .
history
Previously, blasting caps , ie capsules one initiating explosive (usually lead azide ) and a secondary charge (usually made of tetryl or PETN ) have, with a Anwürgezange a focal moment detonators , so an ignitable by an electric incandescence bridge pyrotechnic composition , is choking, so a detonator to receive.
Types
Detonators are differentiated in commercial blasting technology according to their triggering method:
- electric detonators
- electronic detonators
- non-electric detonators
- Ignition hose systems
- Ignition by means of a safety cord
Detonators for commercial blasting work are subject to a type test by BAM . These detonators essentially consist of energy pulse feed (electrical or thermal), energy pulse conversion and energy pulse transmission.
Electric detonators
Electric detonators have the following components:
- electric glow bridge with pyrotechnic set, so-called combustion moment igniter , also bridge igniter
- pyrotechnic delay set
- Initial charge or primary charge (usually 0.3 g lead azide )
- Secondary charge (usually 0.8 g Tetryl or PETN )
When an electric igniter is ignited, a current flows through its glow bridge, which is so large that the glow bridge finally begins to glow due to its electrical resistance. This generation of heat ignites a pyrotechnic charge that creates a flame. This initiates the pyrotechnic delay set, which in turn requires a precisely defined time to burn off. At the end of the delay set, the initial charge is ignited, which then ignites the secondary charge located behind it. Only this secondary charge has enough explosive energy to detonate so-called capsule-sensitive explosives. Some explosives, e.g. B. emulsion explosives or powdered explosives , require additional booster charges (also called boosters), z. B. from a detonating cord to detonate.
Depending on the pyrotechnic delay rate, a further distinction is made:
- Momentary detonator: without delay set (color code of one of the two cables: white)
- Short-term detonator: delay set with a delay interval of less than 100 ms, usually 25 ms (color code: green)
- Long-term detonator: delay set with delay interval of more than 100 ms, mostly 250 ms (color code: red)
The individual electric detonators also have different time levels to z. B. to be able to guarantee defined collapses when buildings are blown up. For example, a short-term detonator (25 ms) of time stage 10 triggers the detonation after just 10 · 25 ms = 250 ms after its ignition, i.e. just as quickly as a long-term detonator (250 ms) of time stage 1. The detonators are usually used as a set with the Time levels 1 to 20 sold.
In addition, the electrical properties of the glow bridge are crucial for a distinction with regard to sensitivity:
- A detonators (detonator class 1): are forbidden in blasting technology, require a response current pulse of at least 3.0 mJ / Ω and are only used in pyrotechnics .
- U detonators (insensitive, detonator class 2): are used for most work (color code: yellow).
- HU detonators (highly insensitive, detonator class 4): are used for work in which stray currents (e.g. from high-voltage lines or in the vicinity of electrified railway lines) are to be feared, which can cause the detonators to detonate prematurely and thus endanger the Worker (color code: blue).
HU detonators require a higher response current pulse of 2500 mJ / Ω in contrast to U detonators (16 mJ / Ω). The combination of HU and U detonators is not permitted, as the HU detonators would not trigger in such a mixed ignition circuit (" lack of power ").
The advantage of electric detonators lies in their universal applicability and the comparatively cheap procurement. The disadvantage is that the number of detonators is limited depending on the blasting machine used . This is due to the fact that every glow bridge requires a certain amount of electrical energy for ignition, but above a certain resistance of the ignition circuit the ignition machine can no longer supply it, or that this electrical energy is not in the glow bridges, but in the inlet and outlet Ignition leads is implemented (so-called power shortage failure).
For seismic investigations there are special seismic detonators that have a very precise trigger time. Here it is of particular importance to adhere to exact firing orders in order to correctly interpret the seismic waves and their results.
Electronic detonators
In electronic detonators, each detonator has a small microchip and a capacitor . The chip can be programmed using a programming device, whereby delay times can be individually adjusted. During ignition, the complete ignition circuit is supplied with power by a second device , which charges the capacitors of the individual detonators. After the pre-programmed time, the microchip transfers the charge from the capacitor to the glow bridge, which then detonates the igniter.
A disadvantage of the electronic ignition systems is the high purchase price and the high technical effort due to programming and ignition devices. The advantages, however, are the very finely adjustable ignition orders and the large number of detonators that can be ignited. By defining the ignition stages down to the millisecond, an improvement in the blasting results (smaller debris) is achieved in quarries. This also reduces follow-up costs for the removal of knuckles .
Ignition hose systems
A frequently used method of detonating explosive charges are the ignition hose systems. Ignition hoses are plastic hoses that are coated on the inside with a thin layer of explosive, which safely transmits the detonation. At the front end of an ignition hose, with lengths between 3 m and 60 m, clips are usually attached, into which detonators, detonating cords or other ignition hoses can usually be clipped for initiation . At the rear end there is either a delay set that can ignite additional ignition hoses itself, or a detonator that ignites the actual explosive charge. Ignition hose systems are used when buildings are blown up, especially when the number of impact cartridges to be ignited exceeds the capacity of the electric ignition machines.
Detonator and safety fuse cord
An ignition method that is only occasionally used is that with a detonator and a safety fuse cord . The detonator is strangled onto the fuse with a strangler. The detonator created in this way can then be attached to the explosive charge and detonated by igniting the fuse. The production of this fuse variant requires craftsmanship in order not to cause failure .
The main area of application is snowfield and ice blasting, other uses are prohibited by law.
Individual evidence
- ↑ Data sheet electric detonators. Austin, accessed May 3, 2017 .
- ↑ Manufacturer's website from Orica. Retrieved May 1, 2017 .
- ↑ Explosive TR310. Federal Ministry of Labor and Social Affairs, October 5, 2016, accessed on April 26, 2017 .