GB2025005A

GB2025005A - Detonating Device

Info

Publication number: GB2025005A
Application number: GB7828823A
Authority: GB
Original assignee: Vickers Ltd
Current assignee: Vickers Ltd
Priority date: 1978-07-04
Filing date: 1978-07-04
Publication date: 1980-01-16

Abstract

A detonating device for detonating an explosive composition includes a base portion (1) including an ignition path (1a) communicating with the explosive composition (7) to be detonated, and a detonator (5) mounted on a member (3) moveable with respect to the base portion (1) between a first position in which the detonator (5) is out of alignment with said path (1a) and a second position in which the detonator (5) is in alignment with said path (1a). Only when the member (3) is in its second position will firing of the detonator (5) cause detonation of the explosive composition (7). The member (3) may be a rotatable shutter which is biased towards a third, fail-safe position by a torsion spring (8); two solenoids (9) in their deactivated state have cores (11) which hold the shutter at the first and second positions respectively and can be selectively energised as desired to retract the cores. <IMAGE>

Description

SPECIFICATION Improvements in or Relating to Detonating Devices This invention relates to detonating devices and more particularly, but not exclusively, is concerned with such devices for igniting explosives when carrying out underwater engineering operations such as, for example, explosive welding.

According to the present invention there is provided a detonating device for igniting an explosive composition which devices comprises: (i) a base portion including an ignition path communicating with the explosive composition, and (ii) a detonator mounted on a member moveable with respect to the base portion between a first position in which the detonator is out of alignment with said path and hence when fired is incapable of causing ignition of said composition and a second position in which the detonator is in alignment with said path and when fired is capable of causing ignition of the composition via said path.

In a particularly preferred embodiment, the member can move with respect to the base portion from its second position to a third position in which it is also out of alignment with said path.

In this case, the device preferably includes a biasing means which tends to move the member from the first position to the third position via the second position and also first and second releasable retaining means. The first of these retaining means is arranged to retain the member in its first position against the action of the biasing means and the second retaining means is arranged to retain the member in its second position against the action of the biasing means.

It is particularly preferred for these retaining means to be in the form of solenoids. In this case, the first solenoid is arranged to be operable to retain the member in its first position when the solenoid is in its deactivated state and the second solenoid is arranged to retain the member in its second position when it is in its deactivated state.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which: Figure 1 is a perspective view of a detonating device in accordance with the invention in its unarmed condition, Figure 2 is a cross-section through the device of Figure 1 in its armed condition, and Figures 3a, 3b and 3c are schematic top views of the device in its unarmed, armed and fail safe conditions, respectively.

Parts have been omitted from Figure 2 in the interests of clarity. Referring to the Figures, the device comprises a base portion 1 on which is mounted a body 2. A rotatable member in the form of a shutter 3 is mounted between the base portion 1 and the body 2. A detonator holder 4 carrying an electrical detonator 5 is screwed into a threaded bore provided in the shutter 3. The device includes a primer in the form of a tube 6 screwed into a threaded bore 1 a in the base portion 1 and carrying an explosive composition 7. The bore 1 a thus constitutes an ignition path communicating with the composition 7.The relative locations of the detonator 5 and composition 7 are such that they are not in alignment when the shutter 3 is rotated to a first position with respect to the base portion 1 (see Figure 3a); they are in alignment when the shutter 3 is rotated to a second position with respect to the base portion 1 (see Figure 3b); and they are not in alignment when the shutter 3 is rotated to a third position with respect to the base portion 1 (see Figure 3c). A torsion spring 8 is arranged so as to bias the shutter 3 towards its third position.

Mounted on the body 2 are first and second solenoids 9 and 10. The arrangement is such that the core 11 of the solenoid 9 engages in a hole in the shutter 3 when the shutter 3 is in its first position and when.the solenoid 9 is not activated.

Thus solenoid 9 retains the shutter in its first position when it is in its non-activated state.

When solenoid 10 is in its non-activated state, its core extends into a slot cut in the shutter 3.

Solenoid 9 is the arming solenoid. When it is activated its core 11 is withdrawn from the hole in the shutter and ailows the shutter to rotate under the influence of the spring 8 until the core of solenoid 10 engages with an abutment surface at the end of the slot in the shutter 3. At this stage, the shutter 3 is in its second position (Figure 3b) and the unit is armed since the detonator 5 is in line with the primer. When solenoid 10 is activated, its core is withdrawn from the slot and allows the shutter to rotate to its third position under the influence of the spring 8. Limit switches (not shown) are incorporated to indicate the position of the shutter at the extremities of its movement (i.e. the positions shown in Figures 3a and 3c.

In use in detonating a main explosive charge underwater e.g. when explosively welding an underwater pipeline to a surrounding annular flange, the detonating device is connected by means of a four core electrical umbilical to a console which is intended to remain on the surface. The detonating device is set so that the shutter 3 is in its first position and is held there by the non-activated solenoid 9. Then the detonator 5 in its holder 4 is secured to the shutter 3 and a blast shield 12 is fitted over the assembly. A safety pin (not shown) is then inserted so as to prevent the shutter from moving from its first position to its second position and the device is then fitted to the main explosive charge as appropriate. The electrical connections to the console are then made via the umbilical.The circuitry is such that an UNARMED signal (for example a green light) shows on the console whilst the shutter 3 is in its first position, The safety pin is then removed manually and the explosive charge and detonating device are taken to the pipe where the welding is to be effected by a submersible or the like. As a safety precaution, the submersible also carries the firing key which needs to be inserted and actuated in a control box on the console in order to fire the detonator. The explosive charge/detonating device assembly is placed in the pipe by means of the submersible and it then returns to the surface with the firing key. Thereafter, solenoid 9 is activated from the console via the umbilical.Thus, the core 11 of solenoid 9 is retracted out of engagement with the hole in the shutter 3 with the result that the shutter rotates, under the influence of the spring 8, to its second position where it is retained by the extended core of non-activated solenoid 10.

The device is now in its armed position and the circuitry is such that an ARMED signal (e.g. a red light) indicates on the surface console. The firing key is then inserted into the control box of the surface console so as to fire the detonator. The firing of the detonator causes the explosive composition 7 to ignite and this in turn detonates the main explosive charge. In the event that the detonator does not fire whilst the shutter 3 is in its second position, solenoid 10 may be activated so that the shutter 3 moves to its fail safe third position and the main charge will therefore be safe. In the event that the detonator fires but does not initiate the main charge, then again the solenoid 10 may be activated so that the shutter 3 moves to its third position. In the event that the umbilical becomes damaged and hence does not relay any electrical signals, the main explosive charge will be safe because solenoid 9 will not have been activated and hence the shutter 3 will still be retained in its safe first position. If solenoid 9 becomes activated prematurely, the shutter 3 would be free to move to its armed, second position. In such a situation, the fail safe solenoid 10 would be activated to allow the shutter to move to its fail safe third position.

Claims

1. A detonating device for igniting an explosive composition which device comprises:- (i) a base portion including an ignition path communicating with the explosive composition, and (ii) a detonator mounted on a member, the base portion and the member being moveable with respect to one another between a first position in which the detonator is out of alignment with said path and hence when fired is incapable of causing ignition of said composition and a second position in which the detonator is in alignment with said path and when fired is capable of causing ignition of the composition via said path.

2. A detonating device as claimed in Claim 1 wherein said member is moveable with respect to the base portion between said second position and a third position in which it is also out of alignment with said path.

3. A detonating device as claimed in Claim 2 and additionally including a biasing means which tends to move the member from the first position to the third position via the second position, a first releasable retaining means arranged to retain the member in its first position against the action of the biasing means, and a second releasable retaining means arranged to retain the member in its second position against the action of the biasing means.

4. A detonating device as claimed in Claim 3 wherein said retaining means include solenoids.

5. A detonating device as claimed in Claim 4 wherein the solenoid of the first retaining means is arranged to retain the member in its first position when it is in its deactivated state and the solenoid of the second retaining means is arranged to retain the member in its second position when it is in its deactivated state.

6. A detonating device as claimed in any one of the preceding claims wherein the detonator is mounted in a bore provided in the member and the explosive composition is in the form of a primer mounted in a bore provided in the base portion.

7. A detonating device as claimed in Claim 1 substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.