PIEZOELECTRICAL IGNITER

Abstract: The invention refers to an explosive substance detonator insensitive to any external influence that may only be triggered by a detonating charge intended for that purpose (6) or a pyrotechnic composition influencing a piezoelectric crystal (8).

Description: PIEZOELECTRICAL IGNITER . The present invention refers to a time-delay detonator of explosive substances, triggerd electronically, insensitive to outside influence by way of a detonating charge or a pyrotechnic composition that influences a piezoelectric crystal. Within the technical area of explosives, as within so many other technical areas, concepts can easily be confused, especially since within the military technical area of explosives terms are often used that are different from those used in the technical area of mining, ground, or other civilian explosives. However, here we have used the term explosive substance detonator for the entire detonator ready to be used with its built-in auxiliary system in the form of a piezoelectric crystal, capacitor, electronic time-delay, as well as fuse igniter, whereby the last term, fuse igniter, only refers to the detonator part itself in the form of, e.g., a fuse head or a thin-film detonator with an intensification charge. During interval blasting, a great number of explosive charges are triggerd within very short time intervals that are calculated in advance with reference to the desired blast result. Today, either a detonating fuse is thereby used that practically instantaneously triggers time-delayed detonators arranged in a pyrotechnical manner for each charge, or else an electrical ignition system is used where the detonators each one equipped with an electronic time delay are triggerd by the same current pulse. The simultaneous triggering of several charges with a detonating fuse is considered to be both an easy to handle and a safe method, since it is . difficult to actuate in a manner different from the one intended, however, the pyrotechnical time-delay compositions that it was previously necessary to use for interval blasting with this ignition system do not have the desired exact time delay. By contrast, with electric ignition systems it is possible to use electronic time-delay detonators that are very exact, although then problems of inducing current in the long connection cables may occur causing accidental triggering if care is not taken to eliminate all potential electromagnetic radiation sources in proximity such as radio and radar emitters, current-carrying cables, etc. Swedish Patent 8703157-1 (PCT/SE88/00409) describes a new interference- suppressing ignition system protected against outside influence in the form of a explosive substance detonator. It contains a.fuse igniter of a per se known type connected with an electronic time-delayed detonator, which in turn is connected with a transmitter that can convert energy generated during a detonation or, al ernatively, another pyrotechnical combustion in the absolute proximity of the transmitter to an electrical current pulse strong enough to trigger the electronic time-delay detonator. One type of transmitter with the ability to generate the necessary current pulse from a detonation or the like suggested in the patent is a piezoelectric crystal providing a current pulse when it is influenced by a detonating fuse in its absolute proximity which is sufficient to charge the capacitor that in turn triggers the electronic time detonator with its time-delay adjusted in advance, whereupon the l tter triggers the fuse igniter connected therewith and thus also the main charge. The safety requirements for explosive substance detonators are generally very high. Before introducing a new explosive substance detonator, one has to be certain that 1t cannot be accidentally triggerd through external influence. This applies not least for explosive substance detonators for interval blasting, where the charges are often very large. The present invention refers to a design of that part of the detonator, where the piezoelectric crystal generating the ignition pulse is located, providing maximum protection against accidental triggering, at the same time as it ensures the function of the piezoelectric crystal by forming a stable anvil between which and the detonating ignition fuse the piezoelectric crystal is compressed. The device according to the invention can thus be defined as an explosive substance detonator consisting of a piezoelectric crystal electrically connected to a fuse igniter that, during the triggering of the explosive substance detonator, is intended to be affected by the shock wave from a detonating charge or a pyrotechnical composition such as a low energy fuse or the like, so that it will emit a current pulse large enough to trigger the fuse igniter after potential intensification via a capacitor inserted between the piezoelectric crystal and the fuse igniter, which via a potential intensification charge or detonator in its turn triggers the main charge. It is thereby characteristic of the device according to the invention that the piezoelectric crystal is surrounded by a strong casing or shell through which a channel proceeds through which the shock wave from the detonating charge or the pyrotechnic composition can reach the piezoelectric crystal. If the detonating composition thereby consists of a detonating fuse of, e.g., the low-energy type, the channel may continue through whereby the detonating fuse may proceed through several explosive substance detonators and thereby form the connecting link between these. Since the detonation velocity in a detonating low-energy fuse can reach up to 7000 m/s, the triggering of several explosive substance detonators by one of the same or several similar connected detonating low-energy fuses is considered to be instantaneous. The above- mentioned casing or shell preferably consists of a piece of a tube consisting of metal or some other hard material a part of whose inside functions as an anvil or counter-support for one of the longer sides of the piezoelectric crystal, while between the other long side of the piezoelectric crystal and the corresponding inside of the tube, the actual channel proceeds. If the tube has a circular cross section, which should be considered desirable, an intermediate anvil of metal or some other hard material with a circular-segment-shaped cross section is placed between the inside of the tube and the piezoelectric crystal and whose bulging side is in direct contact with the inside of the tube, while the piezoelectric crystal with one of its long sides is in direct contact with the flush side of the intermediate anvil. The remaining space 1n the protective tube next to the other long side of the piezoelectric crystal may be filled by an intermediate part consisting of, e« ., polycarbonate plastic and through this intermediate part the channel for the detonating low-energy fuse proceeds. The channel, for Its part, may be lined with a thin metal tube. With this basic construction the piezoelectric crystal will be sOrrounded by a forceful cover protecting 1t from any. influence apart from the one intended, i.e., the compression of the crystal that can be effected during a detonation inside the protective tube. At the same time, other components contained in the explosive substance detonator, e.g., its capacitor, the time-delay circuit connected with the capacitor, as well as the fuse igniter are effectively protected against the influence of the detonation. Simultaneously, the tube functions as a counter support, and an anvil against the shock wave is thereby obtained through actual compression of the piezoelectric crystal and the current pulse thereby generated. Suitable material for the protective tube is steel or some other metal or other rigid material, whereas the explosive substance detonator is cast or welded integrally into a plastic shell. The invention is defined in the following claims and will be described here in more detail in connection with the attached drawings. Figures 1 and 2 show sectional front and side views of the explosive substance detonator according to the invention. It consists of an outer shell 1, a protective tube of steel or some other solid material 2, an anvil 3, a piezoelectric crystal 8, a fill-in part in this case consisting of polycarbonate plastic 4 provided with a through-channel 5 for a detonating low-energy fuse 6 (shown in Fig. 2). The channel 51s lined on the inside with a thin slightly deformable metal tube 7. The latter is normally included in order to make it easy to manufacture hermetically sealed explosive substance detonators. The fill-in part 4 may be manufactured of any suitable material allowing a sufficiently large part of the shock wave from the detonating low-energy fuse to reach the piezoelectric crystal 8 in order for it to sufficiently compress, so that it may produce the desired current pulse. The piezoelectric crystal 8 is connected via two electric conductors 9 and 10 to a capacitor 11 which in turn is connected to an electronic time-delay detonator 12 via the electric conductors 13 and 14. Moreover, a fuse head 17 placed in direct contact with an intensification charge 18 is connected to the electronic time-delay detonator 12 via two conductors 15 and 16. When the low-energy fuse 6 is detonated, the shock wave travels through the fill-in part 4 and compresses the piezoelectric crystal 8 against the anvil 3 whereby a current pulse proceeds through the cables 9 and 10 charging the capacitor 11 which discharges over the electronic time detonator 12 that after an adjusted interval triggers the fuse head 17 and the charge 18, whereby the main charge is detonated. 8y contrast, the steel pipe 2 protects the piezoelectric crystal 8 against any other influences even those that in reality result in the shell of the explosive substance detonator 1 will being destroyed.

Claims: CLAIMS 1. Explosive substance detonator consisting of a piezoelectric crystal (8) electrically connected with a fuse igniter (17) intended to be acted upon during the triggering of the detonator by a detonating charge (6) or a pyrotechnic composition, such as a detonating fuse, e.g., of the low-energy type in order to provide a current pulse large enough to trigger the fuse igniter (17) after a possible intensification via a capacitor (11) coupled between the piezoelectric crystal (8) and the fuse Igniter (17), w h e re i n the piezoelectric crystal (8) is surrounded by a so id casing (2) through which a channel (5) proceeds that may directly or indirectly influence the piezoelectric crystal (8) via a shock wave from the detonating charge or the pyrotechnic composition (6). 2. Explosive substance detonator as claimed in Claim 1, w h e e i n the casing (2) consists of a metal tube part of the -inside of which functions as an anvil or counter-support for one of the long sides of the piezoelectric crystal (8) whereas the mentioned channel (5) proceeds between the other long side of the piezoelectric crystal and the opposite inner side of the tube. 3. Explosive substance detonator as claimed in Claim 2, h e r e i n the metal tube (2) surrounding the piezoelectric crystal (8) and the channel (5) has a circular cross section and the long side of the piezoelectric crystal facing the inside of the metal tube lies snug and level with an intermediate anvil (3) of metal displaying a primary surface facing and flush with the mentioned crystal and a secondary bulging surface facing the inside of the tube and directly flush with it giving the intermediate anvil (3) a circular- segment-shaped cross section, while the opposite part of the inner volume of the metal tube (2) that is not in contact with the intermediate anvil (3) and that until the piezoelectric crystal (8) is in contact with an Intermediate part (4) of plastic, rubber or some other material through which the shock wave ^ from the detonating charge (6) may pass. 4. Explosive substance detonator as claimed in Claim 3, w h e r e i n the intermediate part (3) is manufactured of polycarbonate and the channel for the detonating charge (6) proceeds through and is lined with a soft thin-walled metal tube (7). 5. Explosive substance detonator as claimed in one of the Claims 1 through 4, w h e e i n an electronic time-delay detonator (12) is inserted between the piezoelectric crystal (8), possibly with the capacitor (11), and the fuse igniter (17).

Inventors: JONSSON BERT, JONSSON, BERT
Applicants: EXPLODET AB
Application year: 1991
Main classification: F42B3
IPC codes: F42C11, F42D1