FLEXIBLE LINEAR EXPLOSIVE CUTTING OR FRACTURING CHARGE

Abstract: The invention provides a linear explosive cutting or fracturing charge comprising a plurality of elements connected together for articulation. Each element comprises a body portion (1) defining a recess (9) for containing explosive material and connecting means (2) whereby a plurality of elements can be connected together for articulation.

Description: FLEXIBLE LINEAR EXPLOSIVE CUTTING OR FRACTURING CHARGE . The present invention relates to linear explosive cuttin or fracturing charges. A frequent requirement of demolition work, e.g., whe demolishing oil tankers or other large vessels for scrap, is th severing of steel targets by means of explosives. Among the advantages of explosives over other methods, suc as mechanical cutting methods or burning, are safety, since th operator does not need to be close to the target structure a the moment of demolition, speed, and the relative ease o transportation ' of the means of demolition, since explosiv charges are compact in comparison with the equipment require for mechanical cutting or burning. Explosives may be used for demolition by direct applicatio to the target surface, although attachment is often difficult the technique inefficient for a given quantity of explosive, an the result almost invariably disorderly and needlessl destructive for the task in hand. Also projected fragment constitute a particular hazard when this method is used. Much greater explosive efficiency results from the use o shaped charges, such as linear cutting charges wherein a hig explosive is caused to act on an angle-section strip of metal i such a way that the two limbs of the angle-section are drive towards each other, thereby generating an elongate jet o extremely fast-moving metal which has great penetrating power even on steel targets. However, such linear cutting charges ar rigid and cannot be conformed to targets which are not flat. An alternative method of imparting directionality to th energy released by an explosive depends upon the shaping o shock waves generated by the explosive within the target. Th shock waves may be caused to fracture targets according to t principle mechanisms. By initiating a mass of explosive i contact with, or close to, the target surface at its two oute extremities with respect to the plane of intending fracture, th two separate detonation wave fronts converge along the centr line, and collide. The first mechanism results from the extre violence of such a collision which generates a narrow zone o extremely high pressure on the target surface which fracture the target. If, on the other hand, the width of the charge i approximately twice the thickness of the target, and .th thickness of explosive sufficient only to - give a pressur pulse of sufficiently short duration, then the fracturin mechanism consists of the coincidence of reflected • tensio waves from the far side of the target surface. These reflecte tension waves cause a sudden application of tensile force across the plane of intended fracture, and the target split from the distal surface towards the surface on which th explosive was placed. In practice, both mechanisms usual occur at the same time, with one of the two mechanisms clear preponderant. One explosive cutting charge using such a mechanism disclosed in European Patent No. 0043215 wherein a series detonation wave collision charges are arranged in cavities in continuous rubber matrix. This charge has a small degree flexibility in the fracture plane but little or no later flexibility. Another linear cutting charge is disclosed in U. patent application No. 8513325 wherein a prism or lens-secti strip of inert material is interposed between a strip explosive and the target. This has the effect of focusing explosively generated shock wave along the intended fract plane within the target. Although this linear cutting cha can be made inherently but weakly magnetic by the use magnetic rubber for forming the wave-shaping element, it ag has the practical disadvantage of only very limited flexibili so that its stiffness coupled with a tendency to elastical recover its initial shape remain limiting factors when cutting charge is used in practice. The present invention has as its object to provide a lin explosive cutting or fracturing charge, and an element for in forming same, which overcomes or mitigates the problem inflexibility common to known linear cutting charges and enable a linear cutting or fracturing charge of a requir length to be produced quickly and easily. The present invention provides an element for use forming a linear explosive cutting or fracturing charge, t element comprising a body portion for receiving an explosi material and connecting means whereby two or more said elemen can be connected together for articulation relative to o another. The present invention also provides a linear explosi cutting or fracturing charge when formed from a plurality elements according to the present invention connected togeth to form a chain and charged with explosive material. The said connecting means may provide a hinge connecti or, more preferably, a universal joint. It will be appreciated that because the elements of linear cutting or fracturing charge according to the prese invention can be articulated relative to one another, the line cutting or fracturing charge can be conformed to surf ces whi are not flat. It will also be appreciated that any requir number of elements can be connected together to provide a line cutting charge of a required length. Preferably, said connecting means comprises a firs connector part on one side of the body portion and a secon connector part on the opposite side of the body portion, th first and second connector parts being adapted to connect wit the second and first connector parts respectively of furthe similar elements. Said first and second connector parts may b complementary parts of snap-fit connectors whereby a pluralit of said elements can be quickly and easily snap-fit together Said first connector part may be a ball member and said secon connector part may be a complementary socket member, whereby tw or more elements can be connected together by engaging the bal member of one element in the socket member of an adjacen element to provide a universal ball-and-socket joint between th two elements. Said body portion may comprise a recess for receiving sai explosive material. Thus, the body portion may comprise bottom wall and at least one peripheral wall extending outwardl of said bottom wall to define said recess. According to on embodiment, said at least one peripheral wall comprises oppose side walls and opposed end walls and said connecting means i located midway along said side walls. Said body portion may comprise initiation means on tha side thereof opposite said recess. The initiation means ma comprise a first channel portion extending centrally across sai body portion, e.g., between said connecting means, second a third channel portions extending outwardly on either side of t first channel portion and communicating with the first chann portion and apertures in the body portion communicating t outer extremities of said second and third channel portions wi said recess, said channels and said apertures being adapted receive explosive material. Said channels may be defined walls upstanding from said bottom wall on that surface of t bottom wall opposite said peripheral wall. The walls of sa second and third channels may diverge outwardly from said fir channel and said apertures may comprise a slot in said bott wall at the outer extremity of each of the second and thi channels and adjacent a said end wall. The body portion may further comprise at least one rece for receiving a magnet which will enable the element to magnetically secured to a ferrous target. The element may further comprise a cover member for closi said channel portions. Said cover member may be a sna friction or force fit with the upstanding walls defining sa channels and may comprise means for supporting a detonator one end of said first channel portion. Preferably, said connecting means are of hollow thin-wall construction and said first initiation channel exten between the first and second connector parts of each element that when a plurality of elements are connected together t first initiation channels thereof will be connected end to e to provide a continuous initiation train extending over t length of the linear cutting or fracturing charge. Thus, wi the channel portions and the hollow connecting means filled wi explosive material detonation can proceed in either directi from one element to adjacent elements through the thin end wal of the adjacent connector parts. As detonation of the explosi material in the first channel of each element takes place, detonation proceeds outwardly along the second and thi channels of the element and through said apertures at t extremities of the second and third channels to initia detonation of the main explosive charge contained in said rece from opposite outer extremities thereof. In this wa detonation of the main explosive charge contained in said rece proceeds from the opposite outer extremities thereof inwar towards the intended line of cut to provide -the most efficie detonation configuration and to maximise the proportion explosive energy imparted to the target. With such arrangement the proportion of explosive energy affecting t target greatly exceeds that of conventional linear explosi charges in which detonation proceeds in a direction parall with the intended line of cut. . The linear explosive or fracturing charge of the prese invention also has advantages over conventional linear cutti charges when used for cutting cylindrical targets such as lar diameter steel pipes. When a conventional linear cutting char of the kind wherein detonation proceeds along the line of cut applied to the outer circumference of a cylindrical target, t inner surface of the explosive cutting charge provides a short path around the target than does the outer surface so that the detonation wave front progresses around the target there a tendency for the detonation wave front to lean ba progressively. This causes an ever increasing proportion of t explosive energy to be directed tangentially away from t target and to be wasted in the surrounding medium. Since, wi the preferred - embodiment of the present invention, the ma charge of each element is initiated at the opposed out extremities and proceeds inwardly towards the intended line cut there is no tendency for the detonation wave front to le backwards and comparatively little of the explosive energy dissipated in the surrounding medium. In order to. ensure that detonation of the main charge each element proceeds from opposite outer extremities there inwardly towards the intended line of cut, it is necessary prevent the direct or sympathetic initiation of the main char of one element by the detonation of the main explosive charge a preceding element. This may be accomplished by spacing t adjacent elements sufficiently far apart by said connect means as to delay or prevent direct initiation or interposing ah inert barrier element between the main explos charges of adjacent elements. Such an inert barrier conveniently be provided by a magnetic element which will se the dual functions of providing an inert barrier and enabl the elements to be magnetically secured to a ferrous target. The tendency towards sympathetic initiation between main charges of adjacent elements may be further mitigated the use of an explosive material of relatively high detonat velocity for the initiation train. This ensures that desired initiation pattern of one element is further advan before the shock wave arrives from the initiation of the m explosive charge of the preceding element than would be the c if a single explosive material were used both for the m charge and the initiation train. As mentioned above, it is desirable that any particu element be in a sufficiently advanced state of initiation bef the destructive effects of the preceding element destroy it, damage it to an extent that would impair its corr functioning. The potentially destructive mechanism of the precedin element consists of the generation of a violent, forward travelling shock wave generated by the coincidence of the tw shock waves generated by the two converging detonation waves o that charge. The forward velocity of such a shock wave may, i some cases, exceed the detonation velocity of explosiv otherwise suitable for use in the present invention, and it effect would be to induce initiation of the subsequent charg prematurely at a point on its side; such premature initiatio would generate a third detonation front which interfere detrimentally with those fronts intentionally generated at th outer edges of the element. Greater separation of the elements mitigates this tendency but such separation is detrimental to the performance of th charge array. Use of an explosive of lower velocity than tha in the initiation train would tend to delay the generation o the destructive, forward-directed shock wave, but such explosiv would be less effective at fracturing or cutting the target. A preferred method of diminishing or eliminating thi undesirable effect utilises the so-called "channel" effect wherein the explosive of the initiation means is provided with hole or holes extending longitudinally along one or more of th first, second and third channels. The . hole or holes may b lined with thin-walled metal, plastic or ceramic, and is fille with air or other gas. The detonation products of that part the explosive first detonated are driven along the hole at velocity exceeding the normal velocity of detonation of t explosive, and initate detonation in that part of the explosi not yet reached by the normal detonation wave front. T detonation velocity is thus effectively raised in that part the explosive adjacent to the. hole. A rod or cylinder of explosive, provided with such channel, and initiated at one end, therefore attains detonation velocity substantially higher than that of otherwise similar body of explosive not thus provided. Although it is preferred that initiation of the main char of each element proceeds from opposite outer extremities there inwardly towards the intended line of cut, the present inventi can equally well be applied to simple concussion charges. this case, initiation of the main explosive charge of ea element may be along the centre line thereof, e.g. through sa connector parts, in which case said second and third channe and said apertures would be omitted. The present invention will be more particularly describ with reference to the accompanying drawings, in which:- Figure 1 is a top plan view of an element for use forming a linear explosive cutting or fracturing char according to the present invention, Figure 2 is an end elevation of the element shown Figure 1, Figure 3 is a sectional end elevation of the element sho in Figure 1, Figure 4 is a top plan view of a body portion of t element shown in Figure 1, Figure 5 is an underneath plan view of the body portion the element shown in Figure 1, Figure 6 is an end elevation of the body portion shown Figure 4, Figure 7 is a sectional end elevation of the body porti shown in Figure 4, Figure 8 is- a side elevation of the body portion shown Figure 4, Figure 9 is a side sectional elevation of the body porti shown in Figure 4, Figure 10 is an underneath plan view of a cover member the element shown in Figure 1, Figure 11 is a top plan view of the cover member shown Figure 10, and Figure 12 is a plan view showing a plurality of eleme according to Figure 1 connected together into a chain to for linear explosive cutting or fracturing charge according to present invention. Referring to Figures 1 to 3 of the drawings, it will seen that the element illustrated therein comprises a b portion 1, connecting means 2 and cover member 3. Referring now also to Figures 4 to 9 it will be seen t the body portion 1 comprises a bottom wall 4, opposed side wa 5, 6 and opposed end walls 7, 8 depending from the bottom wal to define a recess 9 for receiving a main charge of explos material. The connecting means 2 comprises a first connector part the form of a ball member 10 and a second connector part in form of a complementary socket member 11, the arrangement be such that the ball member 10 of one element is a snap fit w the socket member 11 of another similar element to provide articulated universal ball-and-socket joint between the adjac elements as illustrated in Figure 12. Upstanding from the bottom wall 4 are parallel walls defining a first, main, initiation channel 13 and walls 14 wh diverge outwardly from the walls 12 and define second and th initiation channels 15 and 16. Slots 17 in the bottom wall communicate the outer extremities of the second and thir initiation channels 15 and 16 with the recess 9 adjacent the en walls 7 and 8. The main initiation channel 13 extends centrall of the body portion 1 between the ball member 10 and socke member 11. Ball member 10 and socket member 11 are of hollo thin-walled construction so that detonation of an initiatio train of explosive material contained in the channels 13 an mmembers 10 and 11 of adjacent elements can proceed through sai thin walls to the main initiation channel 13 of an adjacen element. Cover member 3 illustrated also in Figures 10 and 1 comprises a top wall 18 and depending side walls 19 which are snap, force or friction fit with the walls 12 and 14 definin the channels 13, 15 and 16. A cylindrical holder 20 for detonator 21 (Figure 3) is upstanding from the cover member and has flexible tangential ribs 22 extending inwardly thereo for accommodating detonators of different diameters. Delay elements 23 may be provided in the second and thir initiation channels 15 and 16 to ensure that the detonatio fronts proceeding outwardly therealong towards the slots 1 proceed parallel to the slots 17. . In use, the recess 9 is filled with a main charge (Figure 4) of explosive material and the initiation channels 15 and 16 are- filled with an initiating charge 25 of explos material. Advantageously, the explosive material 25 is of higher detonation velocity than the explosive material 24. explosive material 25 communicates with the explosive mater 24 through the slots 17 which are also filled with one or ot of the explosive materials. With this arrangement initiation the main explosive charge 24 is from the outer extremit thereof with detonation proceeding inwardly towards the inten line of cut, which is along the centre line of the elem extending through the ball member 10 and socket member 11. many elements charged with explosive material as required can connected together as illustrated in Figure 12 in the form o chain to provide a linear explosive cutting or fracturing cha of any required length. ' Initiation of the explosive charges be from any one or more of the. elements and will then proc outwardly in both directions along the main initiation chann 13 of the adjacent elements. The initiation channels may, if desired, be provided w longitudinal holes which may be lined with thin-walled met plastic or ceramic and filled with air or other gas. The ho suitably extend substantially centrally of the explosive in e channel. As outlined above, the provision of such holes eliminates, or greatly mitigates, the problem of premature, mid-line initiation. By way of example, an 8 millimetre rod of the plastic explosive SX2, whose normal detonation velocity was found to be approximately 7,200 metres a second in that form, detonated at a velocity of approximately 9,100 metres second when provided with an air-filled axial channel 3.2 millimetres in diameter. As can be seen from Figure 12, due to the articulation of the connected elements by means of the ball-and-socket joints, the linear cutting charge of the present invention can adopt a required radius of curvature to provide arcuate cuts and/or to accommodate cylindrical or other non-planar targets. If desired the recess 9 may be divided by a partition wall 26 shown diagramatically in Figure 5 to provide a supplementary recess 9a. Supplementary recess 9a may contain explosive material 24 or, more preferably, an inert barrier element which may be in the form of a sintered ferrite or other magnet 27 which will serve both as a barrier to prevent sympathetic detonation of the main explosive charge 24 by the detonation of the main explosive charge of a preceding element and also to magnetically attach the element to a ferrous target. The element of the present invention may be moulded ' formed from plastics material or rubber. A particular suitable material is acrylonitrile butadiene styrene (AB plastics material. The. following examples are given by way of illustration. EXAMPLE 1 A linear cutting charge was assembled using the elemen illustrated in Figs 1 to 3 of the drawings. The plast explosive PE4 was used for both the main charge and initiati train and was inserted in the recess 9 and channels 13, 15 a 16 of each element. The main charge of each element measured x 28 x 19 mm and consisted of approximately 42g of explosiv With a spacing of 18.-5 elements per metre this corresponded an explosive load of 777g/m. The linear cutting charge was placed on the surface of target consisting of a flat plate of 43A grade mild steel havi a thickness of 50mm. When the charge was detonated the targ was cleanly fractured along the intended line of cut. EXAMPLE 2 A linear cutting charge was assembled as described i Example 1 and was placed on the surface of a target consistin of a flat plate of 43A mild steel having a thickness of 40mm The cutting charge was arranged with the centre-lines of th individual elements on an arc of a circle of approximately 150m radius. When the charge was detonated the target was cleanl fractured along the intended arcuate line of cut.

Claims: CLAIMS 1. . An element for use in forming a linear explosive cutting fracturing charge, the element ' comprising a body portion f receiving an explosive material and connecting means whereby t or more said elements can be connected together f articulation relative to one another. 2. An element according to Claim 1, wherein said connecti means provide a hinge connection. 3. An element according to Claim 1, wherein said connecti means provide a universal joint. 4. An element according to Claim 1, 2 or 3, wherein sa connecting means comprises a first connector part on one side the body portion and a second connector part on the opposi side of the body portion, the first and second connector par being adapted to connect with the second and first connect parts respectively of further similar elements. 5. An element according to Claim 4, wherein said first a second connector parts are complementary parts of snap-f connectors. 6. An element according to claim 5, wherein said fir connector part is a ball member and said second connector pa is a complementary socket member. 7. An element according to any one of the preceding claim wherein said body portion comprises a recess for receiving sa explosive material. 8. An element according to Claim 7, wherein said body porti comprises a bottom wall and at least one peripheral wa extending outwardly of said bottom wall to define said recess. 9. An element according to Claim 8, wherein said at least o peripheral wall comprises opposed side walls and opposed e walls and said connecting means is located midway along sa side walls. 10. An element according to claim 7, 8 or 9, wherein said -bo portion comprises initiation means on that side there opposite said recess. 11. An element according to claim 10, wherein said initiati means comprises a first channel portion extending central across said body portion, second and third channel portio extending outwardly on either side of the first channel porti and communicating with the first channel portion and apertur in the body portion communicating the outer extremities of sa second and third channel portions with said recess, sa channels and said apertures being adapted to receive explosi material. 12. An element according to Claim 11, when dependent upon Cla 9, wherein said channels are defined by walls upstanding fr said bottom wall on that surface thereof opposite sa peripheral walls. 13. An element according to Claim 12, wherein said fir channel portion extends between said connecting means. 14. An element according to Claim 12 or 13, wherein the wal of said second and third channels diverge outwardly from sa first channel and said apertures comprise a slot in said bott wall at the outer extremity of each of the second and thi channels and adjacent a said end wall. 15. An element according to any one of the preceding claim wherein said body portion comprises at least one recess f receiving a magnet or inert barrier member. 16. An element according to -any one of the preceding claim having its body portion filled with explosive. 17. An element according to claims 11, 12, 13 or 14 having i body portion filled with explosive, the explosive in one or mo of the channels being provided with a longitudinally extendi hole. 18. An element according to Claim 12, 13, or 14, comprising cover member for closing said channel portions. 19. An element according to Claim 16, wherein said cover memb comprises means for supporting a detonator at one end of sa " first channel portion. 20. An element according to any one of the preceding claim when moulded or formed from plastics material or rubber. 21. A linear explosive cutting or fracturing charge when form from a plurality of elements according to any one of t preceding claims connected together to form a chain and.charg with explosive material. 22. An element for use in forming a linear explosive cutting fracturing charge, substantially as herein described wi reference to the accompanying drawings. 23. A linear explosive cutting or fracturing char substantially as herein described with reference to t accompanying drawings.

Inventors: ALFORD SIDNEY CHRISTOPHER, ALFORD, SIDNEY, CHRISTOPHER
Applicants: ALFORD SIDNEY C, ALFORD, SIDNEY, CHRISTOPHER
Application year: 1990
Main classification: B21D28
IPC codes: B21D26, B21D28, F42B1, F42B3