GB2490020A

GB2490020A - An explosive projectile

Info

Publication number: GB2490020A
Application number: GB1205858.2A
Authority: GB
Inventors: Andrew Laing; Robert William Torry
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 2011-04-11
Filing date: 2012-04-02
Publication date: 2012-10-17
Anticipated expiration: 2032-04-02
Also published as: GB201205858D0; GB201106126D0; WO2012140394A1; GB2490020B

Abstract

An explosive projectile 10 which is applicable to short and long range projectiles comprises a delay fuse where the delay fuse comprises a shock tube 8, a shock tube detonator and a means to initiate the shock tube which may comprise of a primary charge 6 which when detonated compresses the shock tube 8 against a flyer plate 3. This compressive force initiates the combustible material within the shock tube 8 and in turn the shock tube detonator initiates the main charge 9. Alternatively the shock tube maybe initiated using a mechanical impact fuse and an impact sensitive explosive. [Figure 2]

Description

I

An Explosive Proiectile

Field of Invention

This invention relates to an explosive projectile having a delay fuse, and is applicable to short and long range projectiles.

Explosive projectiles are used for a variety of applications, US 2004/0069133 Al provides for a mine excavation method and discloses a method of excavating mines using a projectile, the projectile having a non specified delay fuse. US 6032567 also provides for a method of clearing mines using a projectile with a delay fuse such as a timed programmable fuse. An example of a delay fuse used in a projectile is disclosed in GB 1416936 where an inertial spring fuse is used to delay detonation of the explosive within the projectile until after the projectile has penetrated a target. Similarly US 2009/0193995 Al also uses a mechanical fuse structure; in this case a delay gap built into the structure to delay explosive initiation after penetration of a target has occurred. Such fuse structures are expensive to construct and the delay is harder to adjust without changing the structural design. Timed fuses can be employed using electronic circuit initiation but the separation of the primary charge and main charge can be complex due to safety requirements as shown in US 2009/02600533.

In the field of demolition and mining industries shock tubing and shock tube detonators are used to safely ignite an explosive from a distance. Shock tubing is preferred in such industries because it removes the electrical cable based initiation systems for explosives and is insensitive to electrostatic charges from humans, therefore safe to handle when manual assembly is required. US 6272996 B1 also indicates the use of shock tubing within military fields for similar purpose as the mining and demolition industries namely to provide a means of initiating a remote explosive device from a safe distance. There are several types of shock tubing such as a plastic tube housing containing a fibre coated by aluminium or ammonium perchlorate, others comprise a gas filled plastic tubing but the most popular commercially used version is generally known to consist of small diameter hollow plastic tubing with a fine coating of combustible material layered onto the inside of the tubing.

Initiation of the shock tube can be carried out in a number of ways. There are several methods to initiate the shock tube, if the end of the shock tube it left open, the open end may be filled with primer and initiated by purpose built initiation devices such as disclosed in US 2007/0266881 Al. It is the shock wave from the primer explosive that ignites the combustible material within the plastic tubing. Other methods include ignition of the shock tube open end by an electrical discharge. Ignition is also possible through the shock tube wall by a strong shock wave originating from a detonator or similar explosive charge. Once ignition has occurred, a shock tube works by utilising the shock wave from the primary ignition and then a shock wave travels along the inside of the tube at speeds ranging from as low as lOOft to 5000 ft/s. Once the shock wave reaches the end of the shock tube it then initiates a shock tube detonator, before the shock tube detonator itself initiates the main explosive charge. The shock tube detonators normally contain a delay element themselves and are commercially available with varying delays from a few milliseconds up to several seconds. Therefore the combination of the shock tube and shock tube detonator can provide a reasonable delay before a main charge is initiated. This combination of shock tube and shock tube detonator also provides for a means of separating the primary charge and main explosive charge to ensure the initiation of each occurs separately and are commercially available at much less cost than bespoke projectile delay fuses. shock tube detonators can be commercially supplied already connected to one end of a length of shock tube, the shock tube can then be cut to the desired length dependent on its end purpose.

Summary of Invention

The invention addresses the problems of projectile delay fuses as defined above by providing a simple and cost effective delay mechanism which can be adjusted to the need of the user and which is safe to handle and assemble manually.

Accordingly the present invention provides an explosive projectile comprising a delay fuse wherein the delay fuse comprises: a shock tube, a shock tube detonator and means to initiate the shock tube.

The invention uses a shock tube and shock tube detonator as a simple cheap commercially available alternative to bespoke electronic or mechanical delay fuses for projectiles. The invention also allows the separation of the primary means of initiation such as a primer charge and the main charge in a projectile. Because shock tube and shock tube detonators are safe to handle by humans, projectile devices may be packed with explosives and assembled manually. With the shock tube detonator already connected to one end of a length of shock tube, the shock tube detonator can be inserted into a main charge of a projectile. The opposite end of the shock tube to the shock tube detonator should be positioned within proximity of the initiation means. The initiation means could be an electrical spark, a primary explosive charge or detonator, percussion cap or other means familiar to a person skilled in the art.

By initiating the shock tube using an explosive blast from a primary charge, it is possible to propel a projectile device in a required direction whilst simultaneously initiating the shock tube. This makes the design of such projectiles simple. Such projectiles can penetrate a surface and delay initiation of the main projectile charge being advantageous for mine clearance and other such short range disruption devices.

If the initiation of the shock tube is by using a mechanical impact fuse and impact sensitive explosive, the shock tube and shock tube detonator can be used as a delay fuse within a longer range projectile. This is because the delay fuse is only initiated on impact after the projectile has completed its flight path. The mechanical impact fuse and impact sensitive explosive can be situated in the front end of a projectile and once impact occurs, the projectile may continue to travel whilst the mechanical impact fuse initiates the impact sensitive explosive. The impact sensitive explosive will in turn initiate the shock tube and then the shock tube detonator will initiate the main charge. The skilled person will appreciate that several mechanical impact fuses can be used in conjunction with an impact sensitive explosive. Examples wouid be a piezoelectric fuse or a percussion cap for example as used in rocket propelled grenades.

Brief Description of Drawipg

Figure 1 shows an explosive projectile suitable forclearing mines buried in the ground.

Figure 2 shows an exploded view of the internal component parts of the explosive projectile shown in figure 1.

Specific Description

Figures 1 and 2 relate to a short range embodiment of an explosive projectile. Figure 1 is one embodiment of the invention and shows an explosive projectilel. The explosive projectilel comprises an elongated spike 2 a flyer plate 3, a casing 4 and an electric detonator 5. The casing 4 and elongated spike 2 contain explosive components (not shown) including a thin sheet of explosive material, a shock tube and a shock tube detonator, which are initiated once the electric detonator 5 is activated by means of an electric signal. The flyer plate 3 is attached to the elongated spike 2 to provide a robust platform to transfer explosive energy to the elongated spike 2 after initiation of the electric detonator 5.

Figure 2 illustrates the internal components 10 of the embodiment as shown in figure 1.

The internal components 10 have been separated in the diagram to aid understanding of the explosive projectile's construction. The electric detonator 5 is embedded into a thin sheet of explosive material 6. The explosive material 6 is positioned in contact with a foam spacer 7. The foam spacer 7 has a groove cut out to allow a shock tube 8 to be held in position against the flyer plate 3. The open end of the shock tube is aligned with the edges of the sheet of explosive 6, the foam spacer 7 and the flyer plate 3. The opposite end of the shock tube 8 is connected to a shock tube detonator (not shown) which is enclosed within a main charge 9. A hole is situated in the centre of the flyer plate 3 to enable the shock tube 8 to run from the flyer plate 3 to the main charge 9. Once an electrical signal is used to operate the electric detonator 5, the electric detonator S initiates the sheet of explosive 6.

The rapid combustion of the sheet of explosive 6 generates an explosive force that compresses the shock tube 8 against the flyer plate 3 and propels the flyer plate 3 and elongated spike 2 (shown in figure 1) towards a selected target. The compressive force of the explosive shock wave initiates the combustible material contained within the shock tube 8 and in turn the shock tube detonator initiates the main charge 9. The initiation of the main charge 9 will be delayed; the delay is dependent on the inherent delay associated with the selection of the type of shock tube, the length of shock tube, internal combustible material used within the shock tube and the shock tube detonator.

A person skilled in the art will understand that the inventive concept can also be applied to a longer range explosive projectile.

Claims

Claims 1. An explosive projectile comprising a delay fuse wherein the delay fuse comprises: a shock tube, a shock tube detonator and means to initiate the shock tube.
2. An explosive projectile according to claim 1 wherein the means to initiate the shock tube comprises a primary charge.
3. An explosive projectile according to claim 1 wherein the means to initiate the shock tube comprises a mechanical impact fuse and impact sensitive explosive.
4. A method of delaying initiation of an explosive projectile by initiating a length of shock tube connected to a shock tube detonator.
5. An explosive projectile substantially as herein described with reference to the accompanying drawings.