GB2040025A - Sequential firing system, fuse initiating device and method of sequential firing for explosives - Google Patents

Abstract

A method of sequential firing for the detonation of explosives which includes the steps of, in succession, initiating a plurality of fuses 30 each leading to an explosive charge, initiating each fuse by means of a signal transmitted from the previous fuse and including the activation of a timer 14, the timer after a predetermined time lapse transmitting a similar signal to the succeeding fuse. The signal may, for example, be transmitted by means of a detonating cord or shock tube 28 and the timer may comprise pyrotechnic material such as antimony/potassium permanganate composition. The method provides more accurate delay times than the conventional method using igniter cord. <IMAGE>

Description

SPECIFICATION Sequential firing system, fuse initiating device and method of sequential firing for explosives This invention relates to a sequential firing system for the detonation of explosives. The invention relates also to a fuse initiating device and to a method of sequential firing for the detonation of explosives.

According to one aspect of the invention a method of sequential firing for the detonation of explosives includes the steps of, in succession, initiating a plurality of fuses each leading to an explosive charge, initiating each fuse being by means of a signal transmitted from the previous fuse and including the activation of a timer, the timer, after a predetermined time lapse transmitting a similar signal to the succeeding fuse.

Transmitting the signal, it will be appreciated, will involve a time lapse which is insignificant compared with the time lapse provided by the timer, the time lapse between ignition of successive fuses thus conforming essentially with the time lapses provided by the timers in question.

Transmitting the signal may be by electrical or shock tu be means, but is preferably by means of a detonating cord or tube e.g. NONEL. Similarly, the timer may comprise pyrotechnic material arranged to burn for a predetermined period before transmitting the signal to the succeeding fuse, and may be, for example, a delay element.

Preferably each timer is activated simultaneously with the initiation of the associated fuse by the signal from the preceding fuse, but it will be appreciated that said associated fuse may instead be initiated after operation of the timer simultaneously with the start of the transmission of the signal to the succeeding fuse.

According to another aspect of the invention a sequential firing system for the detonation of explosives comprises a plurality of explosive charges each provided with a fuse, the upstream end of each fuse being provided with a timer and the timers being interconnected in sequence by signal transmitting means, each timer being adapted, upon receiving a signal from the previous timer, to cause transmission after a predetermined time lapse of a signal to the succeeding timer, the signal transmitting means being adapted to initiate the fuses in succession with time lapses between successive initiations corresponding essentially with the time lapses provided between successive signals by the timers, Each timer may form part of a fuse initiating device as described hereunder.

According to yet another aspect of the invention a fuse initiating device comprises means for receiving a signal, a timer and means for initiating a like signal, the timer being operable in response to a received signal to transmit the like signal after a predetermined time lapse, and the device being adapted to initiate a fuse in response to a received signal.

The signal transmitting means may be electrical or may comprise a shock tu be means, but is preferably an elongated detonating element such as a NONEL detonating tube, or a detonating cord, e.g. low energy detonating cord (LEDC). Thus the means for receiving the signal may comprise a suitable pyrotechnic material capable of initiation by the signal transmitting means. Likewise the timer may comprise a suitable pyrotechnic material, capable of initiation by the means for receiving the signal. In turn, the means for initiating a signal may comprise a pyrotechnic or detonating material capable of initiation by the timer and capable of initiating the signal transmitting means to the succeeding fuse.

In this regard it will be appreciated that the means for receiving a signal, the timer and the means for initiating a signal are preferably, when pyrotechnic or detonic, arranged in series in contact or in close proximity with one another, conveniently located in a housing such as a moulding of synthetic plastics material. The upstream end of the associated fuse will enter or at least be exposed to the interior of the housing, and will be in close proximity to or in contact with pyrotechnic or detonic material capable of initiating it in the housing, at either end, for example the upstream end, of the timer.It will also be appreciated that, instead of using an intermediary pyrotechnic material as signal receiving or initiating means between the timer and the upstream and downstream detonating elements, said intermediary pyrotechnic material may be omitted, provided that the timer can be initiated by the upstream detonating element and is capable of initiating the fuse and initiating the downstream detonating element. The timer will thus act as both signal receiving and initiating means. A further possibility is to have the intermediary pyrotechnic material only either upstream or downstream of the timer, as dictated by the compatibility of the materials used for the timer and cord for initiation purposes, or if necessary for initiation of the fuse.

Waterproof sealing may be provided, if necessary, at access openings into the housing for the detonating element and the fuse.

The invention will now be described and illustrated, by way of example, with reference to the accompanying diagrammatic drawings, in which: Figure 1 shows a side elevation in section of a fuse starting device according to the invention; and Figure 2 shows a diagrammatic representation of a sequential firing system according to the invention.

In Figure 1 of the drawings, reference numeral 10 generally designates a fuse initiating device in accordance with the invention. The device 10 comprises means 12 for receiving a signal; a timer 14; and means 16 for initiating a signal of the same nature as that which the means 12 is intended to receive.

The means 12 is a body of pyrotechnic material capable of initiation by a NONEL detonating tube The timer 14 is an elongated delay element comprising a body of antimonylpotassium permanganate pyrotechnic material capable of initiation by the means 12. The means 16 in turn is a body of lead azide starting material capable of initiation by the timer 14, and is in turn capable of initiating a NONEL detonating tube. The means 12 is in contact with one end of the timer 14, the means 16 being in contact with the opposite end of the timer 14. The means 12, timer 14 and means 16 are held in contact with each other by means of a cylindrical tube 18, of suitable material such as waxed paper, synthetic plastics material, or the like, which grips the means 12 and 16.

The tube 18, containing the means 12, timer 14 and means 16, is located concentrically within a housing 20 in the form of a synthetic plastics moulding. The housing 20 is hollow cylindrical and has, at its ends, openings designated respectively 22 and 24. Adjacent the end having the opening 22, it is provided with a transversely opening socket 26.

Although they do not form part of the device 10, two NONEL detonating tubes 28 are shown in Figure 1, as is a capped safety fuse 30 having a cap 32. The tubes 28 are shown having their ends projecting respectively into the openings 22 and 24, and in contact respectively with the means 12 and 16. The fuse 30 is shown with its cap 32 projecting into the socket 26 and in contact with the means 12, via an opening at 34through the wall of the tube 18. The openings 22 and 24, and the mouth of the socket 26 are sealed by suitable waterproof sealing (not shown).

In Figure 2 of the drawings, reference numeral 36 generally designates a sequential firing system for the detonation of explosives, in accordance with the invention. Unless otherwise specified, the same reference numerals are used for the same parts as in Figure 1.

The system 36 comprises a plurality of devices 10 according to Figure 1, each connected at opposite ends to a tube 28 as shown in Figure 1, and to a fuse 30 as shown in Figure 1. As will become apparent from the description of the method of the invention given hereunder, the downstream end (not shown) of each fuse 30 is connected to an explosive charge, and the tubes 28 act as signal transmitting means to transmit a signal from each device 10 to the next in sequence, in the direction of arrow 38.

The method of sequential firing for the detonation of explosives according to the invention involves having a plurality of devices according to Figure 1 connected in sequence as shown in Figure 2, the upstream end of the sequence being connected via the first tube 28 to some suitable initiator. Upon initiation of the first tube 28, the detonation of the tube in the direction of arrow 38, i.e. the downstream direction, transmits a signal in the form of an initiating pulse to the first device 10 in the sequence.

When the signal provided by the pulse of the detonating tube 28 reaches the first device 10, it initiates the means 12. Initiation of the means 12 in turn activates the timer 14 by initiating its upstream end and initiates the associated fuse 30. The timer 14 thus activated burns for a predetermined time lapse, from its upstream end to its downstream end. When the burning of the timer 14 reaches its downstream end, it in turn initiates the signal initiating means 16 which in turn initiates the tube 28 downstream thereof, to transmit a like signal to the succeeding device 10.

The antimony/potassium permanganate timer 14 will in general provide a time lapse of the order of several seconds, with an accuracy of about five to fifteen percent. Thus the nominal time lapse of the timer may, for exaple, be 6 1 0,5 seconds. By comparison, the time lapse involved in transmitting the signal along the cords 18 from one device to the other; and the time lapse between initiation of the means 12 and initiation of the associated cap 32 and timer 14 by the means 12, and the time lapse between initiation of the means 16 by the associated timer 14 and initiation of the associated tube 28 by said means 16, are all negligible and amount to less than the variability in the nominal time lapse provided by the timer 14. The time lapse between ignition of successive fuses 30 thus conforms in essence with the nominal time lapse provided by the timers 14.

Atimer 14 with a nominal 61 0,5 second time lapse is suitably used with fuses 30 having a nominal 120 second burning time. With this arrangement the lag in detonation of each explosive charge in turn behind the pulse of the transmitted intiating signal will be 20 detonations + 10 percent. In other words, when a particular charge is detonated, the signal will be initiating the fuse of the charge 20 places downstream of the detonated charge along the sequence.

An advantage of the invention, compared with known sequential firing systems which do not have timers and which use igniter cord which is relatively slow-burning in place of the NONEL tubes 28, is that the igniter cords are erratic in burning behaviour. In the prior known systems the igniter cord itself is used to provide the time lapse between each detonation, and if the igniter cord burns too slowly there is a reduced burning front or lag of the type described above, leading to the possibility of a break in the sequential firing. On the other hand, if the igniter cord burns too rapidly, the time between initiation of fuses can be excessively reduced, thus increasing the probability of out of sequence detonation.

Because the timers 14 are far more accurate (to within about 10 percent) as regards the time lapses provided thereby when compared with the igniter cord previously used for this purpose, the present invention provides a more precise delay between initiation of fuses, and thus provides a consistent burning front of a desired magnitude, and a greater probability of correct sequential firing.

It will be appreciated that, in Figure 1, the direction of initiation is from leftto right in the direction of arrow 40, whereas in Figure2 it is from rightto left in the direction of arrow 38. However, although the fuse 30 is shown in Figure 1 in contact with the means 12 on the upstream side of the timer 14, it could equally easily be on the downstream side of the timer. Thus, if the means 12 and means 16 comprise the same pyrotechnic material, the attitude of the device 10 could be reversed, provided that all the devices in the system are aligned in the same direction.A possible simplification is that, if the timer 14 is of a pyrotechnic or detonic material capable of initiating the tube cord 28 and of being initiated thereby, and if it is capable of initiating the fuse 30, then the means 12 and 16 can be omitted, as the timer 14 will act both as the means 12 and as the means 16. A further possibility is that, depending on the compatability as regards initiation of the various pyrotechnic materials employed and the fuse 30 and tube 28, either one or the other of the means 12 or 16 can be omitted.

As far as setting up the system of Figure 2 is concerned, an operator can easily connect the tubes 28 and fuses 30 into the devices 10, and can seal the associated openings and sockets to waterproof them, if necessary. Little effort is required, and the use of an asymmetrically shaped device as shown in Figure 1 simplifies aligning all the devices 10 in the same direction. The method, device and system according to the invention thus provide for accurate in-sequence detonation in a sequential firing system, and are suitable for use when correct sequential firing is a prime consideration, providing a consistently long burning front or lag with relatively little or no out of sequence detonation.

Claims (18)

1. A method of sequential firing forthe detonation of explosives which includes the steps of, in succession, initiating a plurality of fuses each leading to an explosive charge, the initiating of each fuse being by means of a signal transmitted from the previous fuse and including the activation of a timer, the timer, after a predetermined time lapse transmitting a similar signal to the succeeding fuse.

2. A method as claimed in claim 1, in which the time lapse involved in transmitting the signal is insignificant compared with the time lapse provided by each timer, so that the time lapse between ignition of successive fuses conforms essentially with the time lapses provided by the timers.

3. A method as claimed in any one of the preceding claims, in which transmitting the signal is by electrical means.

4. A method as claimed in claim 1 or claim 2, in which transmitting the signal is by shock tube means.

5. A method as claimed in any one of the preceding claims, in which each timer is activated simultaneously with the initiation of the associated fuse by the signal from the preceding fuse.

6. A method of sequential firing for the detonation of explosives, substantially as described and as illustrated herein.

7. A sequential firing system for the detonation of explosives which comprises a plurality of explosive charges each provided with a fuse, the upstream end of each fuse being provided with a timer and the timers being interconnected in sequence by signal transmitting means, each timer being adapted, upon receiving a signal from the previous timer to cause transmission after a predetermined time lapse of a signal to the succeeding timer, the signal transmitting means being adapted to initiate the fuses in succession with time lapses between successive initiations corresponding essentially with the time lapses provided between successive signals by the timers.

8. A sequential firing system as claimed in claim 7, in which each timer forms part of a fuse initiating device as claimed in any one of claims 10 to 18 inclusive.

9. Asequential firing system for the detonation of explosives, substantially as described and as illustrated herein.

10. Afuse initiating device which comprises means for receiving a signal, a timer and means for initiating a like signal, the timer being operable in response to a received signal to transmit the like signal after a predetermined time lapse, and the device being adapted to initiate a fuse in response to a received signal.

11. A device as claimed in claim 10, in which the signal transmitting means is electrical.

12. A device as claimed in Claim 10, in which the signal transmitting means comprises shock tube means.

13. A device as claimed in any one of claims 10 to 12 inclusive, in which the means for receiving the signal comprises a pyrotechnic material capable of initiation by the signal transmitting means.

14. A device as claimed in claim 13, in which each timer comprises a pyrotechnic material capable of initiation by the means for receiving the signal.

15. A device as claimed in claim 14, in which the means for initiating a signal comprises a pyrotechnic or detonating material capable of initiation by the timer and capable of initiating the signal transmitting means to the succeeding fuse.

16. A device as claimed in any one of claims 10 to 15 inclusive, which is provided with a housing.

17. A device as claimed in claim 16, in which the housing is provided with waterproof sealing and access openings to its interior.

18. A fuse initiating device substantially as described and as illustrated herein.