SHAPED CHARGE AND SHAPED CHARGE LINER FOR A SHAPED CHARGE

The invention relates to a shaped charge and a shaped charge liner for a shaped charge.

Explosive reactive armour (ERA) consists of a sheet of explosive sandwiched be- tween two metal plates and is designed to protect mainly vehicles against shaped charge weapons. Shaped charge weapons are used to focus the explosive effect in a minimal point in order to increase the penetration capability. Shaped charges use a hollow metal cone which is clad with explosive on the outside. Upon detonation a jet of metal is projected towards the surface to be penetrated. Explosively formed pene- trator (EFP) use a less angled liner shape, which causes the metal to be projected like a projectile. Shaped charges have a great armour penetration capability and require relatively simple launching devices. EFPs have a lower penetration capability, but are not dependent on the detonation occurring at the appropriate distance from the surface to be penetrated, which is the case for shaped charges.

The explosive of the ERA panel is initiated to detonation when a projectile with sufficiently high velocity hits the panel, which causes the metal plates to be accelerated in different directions. If the panel is angled to the shaped charge jet, the projected plates will interfere with the jet and significantly reduce its ability to penetrate the posteriorly situated regular armour. The explosive of the ERA panels is selected such that it will not be initiated by slow projectiles, such as small calibre projectiles and fragments.

Unconfined explosives are initiated by the shock wave generated when the shaped charge jet hits the surface of the explosive material. The contact pressure generated is in the order of 1 Mbar, which is sufficiently high to cause initiation of most of the explosives that would be suitable for an ERA panel. If the explosive is covered by a steel plate, which is the case of the ERA panel, a shock wave is generated in the plate when hit by the shaped charge jet, which shock wave is transmitted into the explo- sive, which is thus initiated. Depending on the thickness of the plate, the explosive will be initiated either by the shock wave (in the case of thin plates) or by the bow wave formed during the penetration of the explosive (in the case of thick plates).

By the introduction of ERA panels on tanks, the common, simple shaped charge warheads have become more or less ineffective and new solutions are therefore required to combat vehicles provided with ERA panels. The most common solution used to overcome the protection provided by the ERA panel is a tandem charge. This charge consists of a precursor which clears the reactive armour and a main charge which subsequently is able to penetrate the base armour relatively unhindered.

Another, less common type is a EFP which travels at such low velocity that the panel is penetrated without the explosive being initiated upon impact. Both types have a number of drawbacks. In the case of shaped charges, the main charge is to detonate after a time-delay, which is determined by the amount of time required for the ERA panel to move out of the way of the main charge. This requires knowledge about the duration of the effective action of the ERA panel. The precursor and the main charge must be sufficiently spaced apart in order for this time-delay to be obtained, which results in a warhead of considerable length. The non-initiating slow projectile also requires a considerable separation distance between the precursor and the main charge, since the penetrator of the main charge is much faster than that of the precursor. In both cases, parts of the precursor will be situated along the path of the main penetrator, thereby interfering with the same.

When drilling holes for the purpose of oil extraction shaped charges are used in an effort to penetrate the bedrock. The shaped charge enables loosening of the rock, so that the oil is able to reach the bore hole more easily for further transport to the surface. Shaped charges provided with an inner liner of solid metal produce a jet and a subsequent slug of metal, which results in the occurrence of metal fragments in the bore hole. To overcome the problem of metal fragments occurring in the bore hole, shaped charges which produce a powder jet are used. The powder jet is formed from the inner lining, the liner, which is made, for example, of a compacted metal powder. The advantage of a powder jet is that it disintegrates after impact without leaving any solid fragments in the bore hole. Moreover, it comprises basically no slug, which means that it does not cause clogging of the bore hole, either in the form of metal from the liner or rock material that has come loose.

US 6,371,219 relates to explosive shaped charges for perforating (drilling) an oil well, the explosive shaped charge having a liner and/or a moulded casing of metal or

metal powder in a polymer matrix. The metal is selected from the group consisting of copper, tungsten, lead, molybdenum, tantalum, zinc, aluminium, nickel and iron.

EP 1 241 433 relates to a perforating gun adapted for perforating (drilling) an oil well and carrying explosive shaped charges, in particular shaped charges comprising a liner made from a mixture of compacted powdered heavy metal and polymer material, most preferably powdered tungsten mixed with powdered teflon.

EP 1 757 896 Al relates to a method for manufacturing a liner for a shaped charge comprising mixing of a powdered metal with a binder and then injection moulding of said mixture to form a casing comprising said liner. The metal is selected among heavy metals, copper, cobalt, etc and combinations thereof. The binder is selected from the group consisting of polyolefin, styrene, polyvinyl chloride, paraffin, polyester, etc.

Powder jets do not create shock waves when impacting a cover material, but instead builds up an increasing pressure via the transfer of momentum. This is due to the fact that the powder jet can be compressed without building pressure, in contrast to a solid jet from a conventional shaped charge.

An object of the present invention is to suggest an alternative to the shaped charges known in the art, the shaped charge according to the invention first producing, upon detonation, a powder jet which penetrates an ERA panel without the explosive of the panel being initiated, and then producing a jet formed from a metal selected to pro- vide the appropriate penetration of the underlying armour.

A further object of the present invention is to provide a shaped charge liner which, upon detonation, first produces a powder jet which penetrates an ERA panel without the explosive of the panel being initiated, and then produces a jet formed from a metal selected to provide the appropriate penetration of the underlying armour.

This is achieved by means of a shaped charge and a shaped charge liner as defined in the appended claims.

According to the invention, a shaped charge is provided which is characterised in that it first produces, upon detonation, a powder jet and then a conventional shaped charge

jet, that is a jet formed from a metal selected to provide the appropriate penetration of the underlying armour.

Furthermore, a shaped charge liner is provided which is made up of two different materials, the first material being a compacted powdered material or a material which forms a powder jet in another way and the second material being a metal selected to provide the appropriate penetration capability. The material forming a powder jet constitutes a first part of the liner, in particular in the apex portion of the conical liner. The second material constitutes the second part of the liner.

It is preferred for the powder jet to be produced, upon detonation, from a shaped charge which totally or in part consists of compacted powdered material or material which forms a powder jet in another way, in particular material comprising compacted powder, brittle pulverizable materials, hard particles in a soft matrix or mate- rial of low sonic velocity which generates diverging jet tips.

It is further preferred that at least one jet should be produced, upon detonation of the shaped charge, from a metal selected to provide the appropriate penetration capability, said penetration capability relating to the penetration of the underlying armour.

It is still further preferred that the powdered jet should be produced, upon detonation, from a shaped charge liner which is spaced apart from a second shaped charge liner, which upon detonation produces at least one jet from a metal selected to provide the appropriate penetration capability.

Preferred materials for producing a powder jet are compacted aluminium powder, brittle glass and aluminium oxide in a polymer matrix.

It is preferred for the shaped charge liner according to the invention to comprise a first material and a second material, the first material consisting of a compacted pulverized material or a material which forms a powder jet in another way upon detonation and the second material consisting of a metal selected to provide the appropriate penetration capability. The material forming a powder jet upon detonation constitutes a first part and the metal constitutes a second part of the liner, in particular the mate- rial forming a powder jet constitutes the apex portion of the conical liner and the metal constitutes the remaining portion of the liner.

The invention will now be illustrated by means of examples of applications and with reference to the accompanying drawings.

Fig. 1 illustrates schematically two preferred embodiments of the shaped charge ac- cording to the invention, wherein

A. a shaped charge liner in the shaped charge produces jets from different materials;

B. a shaped charge liner is spaced apart from a second shaped charge liner in the shaped charge and wherein both produce jets from different materials.

Fig. 2 illustrates schematically two preferred embodiments of the shaped charge liner according to the invention, wherein

A. the apex portion of the cone consists of a material which produces a powder jet and the remaining portion consists of another material; B. the material producing a powder jet is placed on top of the other material in the apex portion of the cone.

Fig. 1 A shows a shaped charge liner (2) in the shaped charge (1) according to the invention, the apex portion of the conical liner consisting of a material which forms a powder jet (3) upon detonation and the remaining portion of the liner (4) consisting of a metal selected for its ability to penetrate the underlying armour. Furthermore, the shaped charge according to the invention comprises an explosive (5) arranged on the outside of the jet-forming material (3, 4) of the liner. The shaped charge liner (2) is placed in a casing (6) of steel, another metal or any other suitable material. When the explosive (5) is caused to detonate what happens first is that a powder jet is formed from the material (3) in the apex portion of the conical liner. The jet hits the ERA panel and penetrates the panel without the explosive of the panel being initiated to detonation. The metal (4) of the liner (2) then forms a conventional jet, which passes through the hole just formed in the ERA panel and is able to penetrate the underlying armour.

Fig. 1 B shows the shaped charge (11) according to the invention, the shaped charge liner (12), which consists of a material that forms a powder jet (13) upon detonation, being spaced apart from the second shaped charge liner (14) with metal liner (15), selected for its ability to penetrate the underlying armour. A high-explosive (16, 17) is applied on the outside of the shaped charge liners (12, 14) facing the liner casings (18, 19), which are made of steel, another metal or any other suitable material. The

high-explosive (16, 17) arranged on the outer walls (12, 14) of the two liners is caused to detonate, whereupon a powder jet is formed from the material (13) of the first liner (12). The jet hits the ERA panel and penetrates the panel without the explosive of the panel being initiated to detonation. A conventional metal jet is formed from the metal liner (15) of the second liner (14). This jet passes through the hole just formed in the ERA panel and penetrates the underlying armour.

Fig. 2 A shows a shaped charge liner (21) according to the invention, in which the apex portion of the conical liner is made of a material (22) that produces a powder jet upon detonation. The remaining portion of the shaped charge liner (23) is formed of a metal selected for its ability to penetrate the underlying armour.

Fig. 2 B shows a shaped charge liner (31) according to the invention, in which the material (32) that produces a powder jet upon detonation is attached to the surface of the second material in the apex portion of the conical liner. The whole shaped charge liner (33) is formed of a metal selected for its ability to penetrate the underlying armour.

The shaped charge with a shaped charge liner formed of materials which produce a powder jet was manufactured by placing different liners in a plexiglas casing into which plastic explosive was carefully pressed. The ERA panel was manufactured by arranging a 3 mm layer of Composition C-4 explosive between two 3 mm steel plates. Composition C-4 consists of 90% hexogen (RDX) and 10% plastic. For each type of liner the characteristics of the jet that was produced were recorded. In all the shots fired, the angle of the normal of the ERA panel to the direction of the jet was 60°. The results of the tests were established by ocular inspection, through which it could be determined whether the explosive of the ERA panel had been initiated to detonation or not.

Example 1. Copper liner reference

A cone of copper with a thickness of 1.2 mm was placed in a plexiglas casing. It was established through ocular inspection that the explosive of the ERA panel had been initiated to detonation by the copper jet and that the plates had been separated from each other. Liners of metallic copper do not produce a powder jet and the copper liner was thus used to verify that the manufactured ERA panel works.

Example 2. Glass liner

A cone of glass from Glafo, with a density between 2 900 and 3 100 kg/m ³ and a thickness of 3.5 mm, was placed in the plexiglas casing. The measured tip speed was 7 700 m/s. It was established through ocular inspection that the powdered glass jet penetrated the ERA panel without causing detonation thereof. The hole that was formed in the panel was relatively small, possibly too small, since it is desirable for the jet produced after the first jet to be able to pass freely through the hole thus formed without any interference.

Example 3. Ceramic liner A ceramic liner made of 55 g of highly fine-grained aluminium oxide and 13 g of araldite DBF (binder), with a thickness of 3.46 mm, was placed in the plexiglas casing. The powder jet diverged in such manner that the density of the jet tip was very low. It was not possible to determine the tip speed. It was established through ocular inspection that the diverging ceramic powder jet penetrated the ERA panel without causing detonation thereof. The hole that was formed in the panel was larger than with a glass liner. It should be possible for the jet produced after the first jet to pass freely through the holes formed.

Example 4. Aluminium powder liner An aluminium powder made of a loosely compacted (2.0-2.5 kbar) aluminium powder A20 with a particle size of approximately 250 μm, with a thickness of 4.0 mm, was placed in the plexiglas casing. The jet obtained was relatively dense and had one large first fragment. During the ERA panel test, said first fragment was removed by having it pass through an aluminium sheet with a thickness of 8 mm before it hit the ERA panel. It was established through ocular inspection that the aluminium powder jet did not initiate the ERA panel and that the hole formed was possibly too small for the jet formed after the first jet to be able to pass freely there through. A larger hole would have been obtained if the aluminium sheet had been removed, but this would have considerably increased the risk of the ERA panel being initiated to detonation.

Example 5. Shaped charge liner with ceramic liner in the whole apex portion of the cone

A shaped charge liner with a tip of ceramic material was manufactured by forming a mould of polymer material from the outside of a conventional copper liner. After the polymer had hardened the copper liner was removed, whereupon the apex portion of the cone of the copper liner was sawed off. The liner that was sawed off was returned to the mould. Powdered aluminium oxide mixed with araldite was placed in the apex

portion of the cone. The mixture was pressed into the mould to form a layer of uniform thickness. The mixture was pressed edge-to-edge with the copper liner. When the paste had been compacted, the liner was removed from the mould for use in the shaped charge.

Example 6. Shaped charge liner with ceramic line in the inner apex portion of the cone

A shaped charge liner with a ceramic layer on the metal liner was manufactured by forming a mould of polymer material from the inside of the liner. First, a plaster mould was formed from the inside of the liner, whereupon a polymer mould was made based on the plaster mould, such that the shape of the polymer mould would resemble the inside of the liner. Powdered aluminium oxide mixed with araldite was placed in the apex portion of the polymer mould. The mixture was pressed with a press tool to form a layer of uniform thickness, the diameter of the ceramic layer con- stituting a fourth of the diameter of the copper liner, as measured from the tip of the cone. The thickness of the ceramic layer was 2 mm. When the paste had been compacted, the ceramic liner was removed from the mould. When used in the shaped charge the outside of the ceramic liner was given a coat of araldite and was pressed in place in the apex portion of the shaped charge liner.