GB2105015A - Directed explosive cutting charge and method - Google Patents

Abstract

An explosive cutting charge comprising a plate member (32), Fig. 4, explosive material (34), means (35, 36) defining with the plate member an air space (37), and means (31) for initiating detonation of the explosive material. The plate member may be provided with a conical portion 33 that provides an additional hollow charge effect or, alternatively, Fig. 5, a separate hollow charge 47 is provided that is adapted to be detonated with delay by the cutting charge 45. In another embodiment Fig. 10 (not shown) the cutting charge is arranged to ignite a propellant (71) that drives a secondary charge (73) into the hole cut in the target by the cutting charge. <IMAGE>

Description

SPECIFICATION Directed explosive cutting charge and method This invention relates to directed explosive cutting charges, and particularly, although not exclusively, to explosive trepanning charges.

The invention also relates to a method of explosive cutting.

There are many industrial applications where the ability to cut holes, and particularly holes of relatively large diameter, with a reasonable degree of accuracy, in, for example, metal plates of 1 cm, or more in thickness by the use of explosive trepanning charges would be highly desirable. Unfortunately known explosive charges are either not suitable for trepanning or have severe limitations which render them unsuitable for many industrial trepanning uses.

It is known that directionality can be imparted to the energy released by a high explosive material by utilizing the energy release to propel a solid or liquid body towards a target.

Thus it is known, for example, that if a cylindrical body of explosive material having a flat metal disc in contact with one end thereof is detonated from the other end thereof then much of the energy released will be imparted to the disc causing it to fly in a direction away from the explosive material, see for example "The Science of High Explosives" by Melvin A. Cook, Reinhold Publishing Corp., New York, 1 958. If the metal disc of such a directional charge is relatively thick and is formed from a suitable material then when projected by detonation of the explosive material towards a target spaced therefrom it may remain intact and be capable of forming a hole in a relatively thin target.If the metal disc of the directional charge is thinner or is formed from a more brittle material then the energy released by detonation of the explosive material may cause the disc to disintegrate and to be projected at the target as a diverging cone of fragments which are capable of causing damage to or even forming a hole in the target. However, the damage to the target caused by such directional charges is irregular and difficult to control and this makes them unsuitable for use in industrial applications where a reasonable degree of accuracy is required.

Also known are conventional shaped cutting charges which comprise a hollow metal mem ber having opposed internal surfaces or surface portions and explosive material around the outside of the hollow metal member; the explosive material, when detonated, causing the hollow member to collapse so that said opposed internal surfaces or surface portions collide and produce a narrow extremely fast moving jet of metal having a high penetration capability. In shaped linear cutting charges the hollow metal member is usually in the form of an elongate member which is substantially V-shaped or U-shaped in cross-section whilst in shaped trepanning charges the hollow member is usually in the form of a cone or hemisphere.The fineness of the jet of metal produced by such shaped charges makes them unsuitable for cutting circular holes of relatively large diameter because such a large diameter hollow metal member and massive explosive charge would be required that the metal jet of the required diameter so produced would be so disproportionately penetrating as to render the shaped charge extremely dangerous in use. It is, of course, possible to bend a shaped linear cutting charge into a substantially circular configuration but unless the radius of curvature is several times the width of the shaped linear charge the penetrating power of the charge will be greatly diminished. This means that there is a lower limit on the size of hole which can be cut with a shaped linear charge of a given width.For example, a shaped linear cutting charge 25.4mm in width for cutting through steel plate having a thickness of 25.4mm will not be able to be bent through a radius smaller than about 1 02mm without serious attenuation of its penetrating power and cannot accordingly be used for cutting holes of less than about 204mm in diameter.

Increasing the size (width) of the charge to compensate for the loss of penetration only increases the minimum radius through which the charge can be bent.

Another known explosive cutting charge is disclosed in United States Patent No.

3,61 S,581 issued to J. Pearson et al. This charge, knawn as the "punch charge" or "tubular jet charge", is designed for the production of relatively large diameter holes in steel plate and the like and comprises a metal tube which of necessity is of strong and robust construction and which contains explosive material. One end of the said metal tube is adapted to be placed in contact with a steel plate or the like to be cut and the explosive material at the end of the tube is formed into a conical shape with the apex of the cone in the plane of said one end of the tube.Thus when said one end of the tube is placed in contact with a said plate to be cut the apex of the cone will also contact the plate and an air space will be defined between the conically formed end of the explosive material, a portion of the internal surface of the tube at said one end thereof and the plate to be cut.

Detonation of the explosive material is initiated from the other end of said tube, i.e., from the end thereof opposite said one end.

The aperture produced in a steel plate or the like by means of such a punch charge is always larger than the punch charge produc ing it. Cladding the conically formed surface of the explosive material with metal com pletely nullifies the effect of the punch charge.

The present invention provides an explosive cutting charge comprising a plate member, explosive material contained on one side of the plate member, means on the other side of the plate member defining with the plate member an air space and means for initiating detonation of the explosive material from that side thereof opposite the plate member.

The present invention also provides a method of explosive cutting which comprises the steps of providing a plate member having explosive material contained on one side thereof, providing an enclosed air space between the other side of the plate member and a target to be cut, and initiating detonation of the explosive material from that side thereof opposite the plate member.

Said air space may be a totally enclosed air space or may be an air space which is normally open and which is adapted to be closed by a surface of a target to be cut when the cutting charge of the present invention is properly positioned in contact with said surface.

According to a preferred embodiment of the present invention said air space is partially defined by walls which progressively converge away from the plate member, i.e., so that when the explosive cutting charge is properly positioned on a surface of a target to be cut said walls progressively converge towards the intended line of cut.

The explosive cutting charge of the present invention may be either a linear cutting charge or a trepanning charge, although it finds particular utility as a trepanning charge.

In order that the invenion may be more particularly understood reference will hereinafter be made to the accompanying drawings, in which: Figure 1 is a fragmentary diagrammatic perspective view of a linear explosive cutting charge according to the present invention shown positioned against a target plate to be cut.

Figures 2(A), (B), (C), and (D) are diagrammatic sectional views illustrating a very simple trepanning charge according to the present invention and what is believed to be the principle of operation thereof.

Figure 3 illustrates in cross-section an embodiment of a trepanning charge according to the present invention, Figure 4 is a diagrammatic sectional elevation of an embodiment of a trepanning charge according to the present invention which incorporates a shaped charge, Figure 5 is a diagrammatic sectional elevation of an embodiment of a trepanning charge according to the present invention which in corporate a secondary explosive charge, Figure 6 is a sectional elevation of another embodiment of a trepanning charge according to the present invention incorporating a second dary explosive charge, Figures 7 and 8 are diagrammatic fragmentary sectional elevations illustrating two further embodiments of trepanning charge according to the invention, Figure 9 is a sectional elevation of a conical member forming part of a trepanning charge according to another embodiment of the present invention, Figure 10 is a sectional elevation of a conical member forming part of a trepanning charge according to yet another embodiment of the present invention, and Figures ii to 14 illustrate a combined trepanning charge and linear cutting charge according to the present invention.

Referring to Fig. 1 of the drawings it will be seen that the linear explosive cutting charge illustrated therein comprises an elongate housing 1 which is triangular in section and has a base wall 2 and converging side walls 3.

Mounted within the housing 1 and extending parallel and in spaced relation to the base wall 2 is a strip-form plate member 4. The space between the base wall 2 and the plate member 4 is filled with explosive material 5 and a detonator 6 extending through the base wall 2 is provided for initiating detonation of the explosive material 5. The side walls 3 converge towards an intended line of cut 7 on a target plate 8 and define the plate member 4 and target plate 8 an enclosed air space 9.

The housing 1 may be of plastics material whilst the plate member 4 may be of copper or aluminium strip material, although it will be understood that other materials may be used if desired. When, in use, the explosive material 5 is detonated the plate member 4 is driven at high velocity and is directed by the converging walls 3 towards the intended line of cut.

The simple trepanning charge illustrated in Fig. 2 comprises a cylindrical housing 10 having a top wall 11 and peripheral wall 1 2.

Mounted in the housing 10 and extending parallel and in spaced relation to the top wall 11 is a plate member in the form of a disc 1 3. The space between the top wall 11 and the disc 1 3 is filled with explosive material 14 and a detonator 1 5 extending centrally through the top wall 11 is provided for initiating detonation of the explosive material 14.

The lower end of the housing 10 is left open and is adapted to be closed by a target plate 1 6 when placed in contact therewith as shown. It is believed that when the explosive material 1 4 is detonated the centre of the disc 1 3 is deformed axially and outwardly by the curvature of the detonation front as shown in Fig. 2(b) until it fragments as shown at 1 7 in Fig. 2(C). A majority of the extremely fastmoving fragments 1 7 of the disc 1 3 are directed by the wall 1 2 of the housing 10 onto the target plate 1 6 adjacent the wall 1 2 as shown in Fig. 2(D).

It will be understood that although in the simple trepanning charge of Fig. 2 the housing 10 is cylindrical it could be of any other suitable cross-sectional configuration depending upon the desired shape of the area one wishes to trepan. Thus the housing 10 could be square, triangular, ovular, polygonal or any other desired shape in cross-section. Likewise the housing 10 need not be of the same cross-sectional area over the whole of the axial length thereof and in particular it may progressively decrease in cross-sectional area from at least the level of the disc 1 3 to the lower end thereof, e.g., the housing 10 may be in the form of a hollow frusto-cone which will direct the fragments 1 7 of the disc 1 3 both downwardly and inwardly.

A surprising feature of the explosive cutting charge of the present invention is that the wall or walls serving to direct the fragments of the plate member onto the target need not be of strong and robust construction but can be relatively thin and fragile. For example, suitable materials for said wall or walls are light gauge sheet metal or ceramic materials, plastics materials and even synthetic resin-impregnated paper. Thus, referring to the embodiment of Fig. 2 a housing 10 of synthetic plastics material and having a wall 1 2 only 1 mm. thick gave good results in tests.

As has been mentioned hereinbefore, in a preferred cutting charge of the present invention the air space defined between the plate member and the target is partially defined by walls which converge from the plate member towards the intended line of cut when the cutting charge is correctly positioned on a target to be cut.This can be very simply achieved in the embodiment of Fig. 2 by mounting within the housing 10 a conical or frusto-conical member whose apex is in contact with the disc 1 3 and whose base rests on the target plate 1 6 and is of substantially the same diameter as the internal diameter of the peripheral wall 1 2. Said conical member can be either solid or hollow and can be either secured to the wall 1 2 and/or disc 1 3 or may be a separate member which can be placed on a target plate 1 6 and the housing 10 then positioned thereover.

Fig. 3 illustrates an explosive trepanning charge according to the present invention incorporating a frusto-conical member. The embodiment of Fig. 3 comprises a cylindrical housing 18 formed in two parts 1 8a and 1 8b which have a plate member in the form of a disc 1 9 sandwiched therebetween and which are secured together as by means of a weld 20. A plug 21, e.g., of synthetic plastics material, closes the outer end of the housing part 1 8a and defines with the housing part 1 8a and disc 1 9 a chamber for explosive material 22.The surface 23 of the plug 21 which partially defines the chamber is a 90 cone which serves to direct the explosive force of the explosive material 22 towards the disc 1 9. A detonator 24 is mounted centrally of the plug 21 for initiating detonation of the explosive material 22. Located within the housing part 1 8b by means of a disc 25 which is secured, e.g., welded, to and seals the outer end of the housing part 1 8b is a frusto-conical member 26 the apex of which is in contact with the disc 1 9 and the base of which is of the same diameter as the internal diameter of the housing part 1 8b and is in contact with the disc 25.The housing part 1 8b and cone member 26, together with the discs 1 9 and 25, define an enclosed air space 27 the peripheral walls of which progressively converge. The explosive trepanning charge of Fig. 3 is particularly useful for underwater applications because the chamber for explosive material 22 and the air space 27 can both be sealed against the ingress of water. If the charge is not required for underwater use the disc 25 can be omitted. The housing 18 in the illustrated embodiment was formed from steel tube having a wall thickness of 6.35mm and an internal diameter of 76.2mm, the housing part 1 8a having a length of 76.2mm and the housing part 18b having a length of 152.4mm. The discs 19 and 25 were each formed from 1 6 guage steel sheet.The plug 21 was formed from polyvinylchloride whilst the cone member 26 is a 25 frusto-cone of aluminium alloy. The explosive material 22 was RDX-based plastic explosive of the kind known as PE4.

In the embodiment shown in Fig. 4 a conventional shaped charge is incorporated in an explosive cutting charge according to the invention. The embodiment of Fig. 4 comprises a cylindrical housing 28 which terminates at one end in a conical portion 29 having a short cylindrical portion portion 30 at the apex thereof for mounting a detonator 31. A plate member in the form of a disc 32 h;nng a central portion formed into a cone 3-~J defines with that end of the housing 28 which terminates in the conical portion 29 a chamber which is filled with explosive material 34. Mounted within the housing 28 on the opposite side of the disc 32 to the explosive material 34 is an annular shaping element 35 which defines with the housing 28 and disc 32 an annular air space 36 and which also defines with the cone 33 a further air space 37. The margin of the disc 32 around the cone 33 acts in the same manner as the plate member of the previous embodiments and will be driven and guided along the space 36 towards a target to be cut when the cutting charge is positioned on the target and the explosive material 34 is detonated. At the same time the cone 33 surrounded on its outside by the explosive material 34 acts as a conventional shaped charge and the explosive effect thereof is directed through the space 37 and onto the target.The advantage of this charge is that, if the target is too thick to be trepanned, the more penetrating central jut may nevertheless perforate it. If on the other hand, a disc is trepanned from the target then the central jut adds to the damage produced beyond the target by the projected disc.

Fig. 5 illustrates another embodiment incorporating a shaped charge. This embodiment comprises a cylindrical housing 40 which terminates at one end in a conical portion 41 having a short cylindrical portion 42 at the apex thereof for mounting a detonator 43. A plate member in the form of a disc 44 defines with that end of the housing 40 which terminates in the conical portion 41 a chamber which contains explosive material 45.

Mounted within the housing 40 on the opposite side of the disc 44 to the explosive material 45 is a conical shaping element 46.

Thus far the explosive cutting charge of Fig. 5 is similar to that of Fig. 3. However, in the Fig. 5 embodiment the conical shaping element 46 is hollow and contains a secondary charge 47 of explosive material which surrounds the domed outer surface of a hollow metal charge lining 48, the secondary charge 47 and the charge lining 48 together forming a conventional shaped charge. A passage 49 extending from the apex of the conical shaping element 46 to the hollow interior thereof has mounted therein a percussion cap 50, a delay element 51 and a detonator 52 for initiating detonation of the secondary charge 47.When the explosive material 45 is detonated a fragment or fragments of the disc 44 will be driven along the passage 49 and will detonate the percussion cap 50 which will in turn, after a delay the extent of which is determined by the delay element 51, actuate the detonator 52. Thus the secondary charge 47 will be detonated at a predetermined later moment in time than the explosive material 45 so that the trepanning action of the projected disc material is not disrupted by the detonation of the secondary charge. The said secondary charge will then apply supplementary pressure to the rear of the trepanned disc which will be driven more violently through the target, shearing, if needs be, the edge of a partially cut disc. The liner material 48 of the secondary charge 47 will also penetrate the target material in front of it, whether or not the disc is completely excised.

Turning now to Fig. 6. it will be seen that the charge illustrated therein comprises a cylindrical housing 53, a disc 54 in the housing and defining therewith a chamber filled with explosive material 55, a detonator 56 for initiating detonation of the explosive material 55 and a conical shaping element 58 mounted within the housing 53 on the opposite side of the disc 54 to the explosive material. The conical shaping element 57 has a cavity therein which is closed by a threaded closure member 59 end which is filled with a relatively shock-insensitive secondary bursting charge 60 of explosive material. A passage 61 extends from the apex of the element 57 to the cavity 58 and contains at that end thereof adjacent the disc 54 a percussion cap 62 and at that end thereof adjacent the cavity 58 a pyrotechnic delay means 63 and a detonator 64.The secondary charge 60 is thus only detonated after a predetermined delay following detonation of the primary charge of explosive material 55, during which the disc material travels from its original position to the target, and either trepans a disc, or inscribes a circular groove, according to the thickness and composition of said target.

In the former case, the trepanned disc is driven more violently beyond the target than it would be if propelled by the explosive charge 55 alone and, in the latter case, the disc defined by the circular groove may be sheared by the secondary explosive charge 60. Thus the embodiment is able to trepan thicker target plates than the corresponding embodiment without a secondary charge.

Figs. 7 and 8 show two variations of the embodiment of Fig. 6 and accordingly like reference numerals have been used for like parts. In the embodiment of Fig. 7 the arrangement is the same as in the embodiment of Fig. 6 except that the passage 61, percussion cap 62, etc., are replaced by a detonator 65 which extends through the wall of the cavity 58 adjacent the base of the conical shaping element 57 and which has a percussion cap 65a at the outer end thereof. The embodiment of Fig. 8 is an improvement on that of Fig. 7 in that two detonators 66 mounted head to head in a passage 67 extending from the periphery of the base of the cavity 58 to the centre of the apex of the cavity are provided for initiating detonation of the secondary charge from the centre of the apex thereof.

The embodiment of Fig. 9 is again like that of Fig. 6 except that instead of the cavity 58 containing a secondary explosive charge it contains a fast-burning rocket propellant 68 which will be ignited after a suitable delay following ignition of the primary charge explosive material and will cause the element 57 to exert thrust on the area of the target circumscribed by the normal trepanning action of the primary charge. This thrust, provided that it exceeds the force with which the cone 57 tends to rebound from the surface of an elastic target, ensures that the cone 57 follows the trepanned disc through the hole produced by the trepanning action.

The embodiment of Fig. 10 is a combination of the embodiments of Figs. 6 and 9 in that the conical shaping element 57 has a first cavity 70 therein containing a fast-burning rocket propellant 71 and a second cavity 72 containing a relatively shock-insensitive secondary explosive bursting charge 73. The passage 61 and percussion cap 62 are provided as in the embodiment of Fig. 6. In addition a further passage 74 communicates the first cavity 70 with the second cavity 72 and contains a pyrotechnic delay means 75 leading to a detonator 76. This embodiment is intended to cause the secondary charge to burst only after passing through the target.

When using trepanning charges, that area of the target which is circumscribed by the line of cut can be projected at high velocity from the target. There are occasions when this projection at high velocity of the trepanned area is undesirable and must be avoided. This can be achieved by explosively cutting only part-way round the area to be removed so as to leave an integral hinge portion of the target material connecting the trepanned area to the remainder of the target.To give even better results and to ensure that the trepanned area is not simply torn off at said hinged portion as a result of the explosive effect it is advantageous to provide an integral hinge portion which extends for a distance outwardly of the trepanned area and to this end a trepanning charge according to the present invention can be used which incorporates a pair of spaced conventional linear cutting charges as shown in Figs. 11 to 14.Referring to Figs. 11 to 14 it will be seen that the cutting charge comprises a trepanning charge 77 of the general kind shown in Fig. 3 but wherein a wedge member 78 has been inserted between the housing part 1 8b and the conical shaping element 26 around a part of the periphery of the conical shaping element 26 as shown in Figs. 11 and 1 3. The wedge member 78 serves to shield a segment of the area to be trepanned from the effects of the explosive cutting charge. The trepanning charge 77 is mounted in an aperture adjacent one end of a rectangular plastics block 79 which has a pair of grooves 80 in a lower surface thereof which extend outwardly from opposite ends of said segment of the area to be trepanned.

Mounted within the grooves 80 are conventional linear cutting charges 81. Detonators 82 mounted in detonator holders 83 located adjacent the ends of grooves 80 remote from the trepanning charge 77 are provided for detonating the linear cutting charges 81. Thus when trepanning charge 77 and the linear cutting charges 81 are detonated substantially simultaneously the trepanned area will be left connected to the remainder of the target by an integral hinge portion which extends away from the trepanned area a distance substantially equal to the length of the linear cutting charges. Preferably the linear cutting charges 81 defining the hinge member progressively diverge as they extend away from the area to be trepanned to provide a hinge of differential stiffness. This gives controlled bending throughout the length of the hinge and obviates the tendency of parallel sided hinges to remain straight, but snap at the outer extremity.

Claims (22)

1. An explosive cutting charge comprising a plate member, explosive material contained on one side of the plate member, means on the other side of the plate member defining with the plate member an air space, and means for initiating detonation of the explosive material from that side thereof opposite the plate member.

2. An explosive cutting charge according to claim 1, wherein said air space is totally enclosed.

3. An explosive cutting charge according to claim 1, wherein said air space is normally open and is adapted to be closed by a surface of a target to be cut when the cutting charge is properly positioned in contact with said surface.

4. An explosive cutting charge according to any one of the preceding claims, wherein said air space is partially defined by walls which progressively converge away from the plate member.

5. An explosive cutting charge according to any one of the preceding claims, wherein the cutting charge is a linear cutting charge having an elongate housing which is triangular in cross section and has a first wall extending the length thereof and a pair of opposed walls which converge away from said first wall, a plate member spaced from said first wall and extending between said opposed walls, explosive material in the space between said first wall and said plate member, means for initiating detonation of the explosive material from adjacent said first wall, and an air space on the opposite side of said plate member to the explosive material, said air space being defined by the plate member and said opposed walls.

6. An explosive cutting charge according to any one of claims 1 to 4, wherein the cutting charge is a trepanning charge and comprises a hollow elongate housing having an end wall and at least one peripheral wall, a disc-like plate member in said housing in spaced relation to said end wall, explosive material in the space between said end wall and said plate member, means for initiating detonation of the explosive material from adjacent said end wall, and an air space on the opposite side of the plate member to said explosive material, said air space being defined by the plate member and said peripheral wall.

7. An explosive cutting charge according to claim 6, wherein said initiating means comprises a detonator which extends through said end wall.

8. An explosive cutting charge according to claim 6 or 7, wherein said housing has a second end wall closing said air space.

9. An explosive cutting charge according to claim 6, 7 or 8, wherein said housing is cylindrical.

1 0. An explosive cutting charge according to any one of claims 6 to 9, wherein said housing is of progressively decreasing crosssection away from said plate member.

11. An explosive cutting charge according to any one of claims 6 to 10, wherein said at least one peripheral wall is formed from sheet metal, ceramic material, plastics material or synthetic resin impregnated paper or board.

1 2. An explosive cutting charge according to claim 9, comprising a conical or frustoconical shaping member mounted in the housing with its apex in contact with that side of the plate member opposite the explosive material, said shaping member having a base of substantially the same diameter as the internal diameter of the housing.

1 3. An explosive cutting charge according to claim 12, comprising a cylindrical housing and a plug closing one end of said housing and forming said end wall, said plug defining with the plate member a chamber for the explosive material and the base of said shaping member closing the other end of said housing.

14. An explosive cutting charge according to claim 13, wherein the surface of the plug which partially defines the chamber for the explosive material is conical or frusto-conical to direct the explosive force towards the plate member.

1 5. An explosive cutting charge according to claim 1 3 or 14, wherein a detonator is mounted centrally of said plug for initiating detonation of the explosive material.

16. An explosive cutting charge according to any one of claims 1 2 to 15, wherein said shaping member contains a secondary bursting charge of explosive material and wherein means is provided for detonating said secondary bursting charge after the detonation of the main charge of explosive material.

1 7. An explosive cutting charge according to claim 16, wherein said shaping member further contains a rocket propellant and means is provided for firing said rocket propellant after the detonation of said main charge of explosive material.

1 8. An explosive cutting charge according to any one of claims 6 to 1 7, in combination with a pair of linear cutting charges, said air space being partially closed by a wedge member inserted therein whereby the trepanning charge will cut only part way round an area to be removed and wherein said linear cutting charges extend outwardly of the trepanning charge on either side of said wedge member and are adapted to cut an integral hinge which prevents projection of the trepanned area.

1 9. A method of explosive cutting comprising the steps of providing a plate member having explosive material contained on one side thereof, providing an enclosed air space between the other side of the plate member and a target to be cut, and initiating detonation of the explosive material from that side thereof opposite the plate member.

20. A method according to claim 19, wherein said air space converges from said plate member towards the intended line of cut.

21. An explosive cutting charge substantially as herein described with reference to any one of Figs. 1 to 10 or to Figs. 11 to 14 of the accompanying drawings.

22. A method of explosive cutting substantially as herein described with reference to any one of Figs. 1 to 10 or to Figs. 11 to 14 of the accompanying drawings.