Securement of liner for shaped charge

Abstract: The present invention relates to a method and an apparatus for securing the inlays, so-called liners (3) which, in the effect direction, define the explosive portion in charges for directed bursting (hollow charge) effect, so-called shaped charges, and which, on detonation of the explosive, are converted into a particle jet or more or less projectile-like so-called slug which accounts for the effect of the charge on the target. The object of the present invention is to solve those problems which occur when materials with excessively different coefficients of thermal expansion must be used in the inlay (3) and a case (1) surrounding the rest of the explosive portion. According to the present invention, this is solved by a specific securement of the inlay (3) in the form of a specially designed anchorage ring (4) which gives a securement which is rigid in the axial direction, i.e. parallel with the intended effect direction of the charge, but permits certain temperature movements across this direction.

Description: TECHNICAL FIELD The present invention relates to a method and an apparatus for securing (retaining) those inlays, so-called liners, which, forwardly in the effect direction, define the explosives in so-called shaped charges. BACKGROUND ART The expression shaped charges is understood to mean charges for directed bursting (hollow charge) effect. These consist of an explosive charge enclosed in a container or case and defined, forwardly in the intended effect direction, by inlays or liners which are of a concave bulging, conical or trumpet-shape. On detonation of the rearwardly located explosive charge, these liners or inlays are converted into particle jets or more or less projectile-like slugs which, at supersonic speeds, are flung forwards in the intended effect direction of the charge. It is primarily the shape and material of the liner or inlay that is decisive for whether the main effect of a shaped charge is of the nature of a jet or a projectile. The commonest material in the liner or inlay is pure copper, but other metals such as iron, spent uranium, aluminium and tantalum have also been employed. Ammunition must be capable of withstanding extreme temperature variations without its function being tangibly affected. As long as the shaped charge inlays were made of pure copper and the rest of the case surrounding the explosive charge was of steel, problems of temperature variation were not excessively difficult to solve, since steel and copper do not, after all, have all too different coefficients of thermal expansion. However, now that there is a steady move towards producing shaped charge inlays from tantalum in order to satisfy the demands placed on the efficiency of the charge, the problem becomes more acute, in particular as the shaped charge inlays are intended to be permanently mounted in the steel case which generally surrounds the explosive charge portion included in the shaped charge on all sides except in the intended effect direction where the inlay or liner forms the concave cavity in the explosive substance that gives rise to the directed explosive effect. The reason for this is that tantalum and steel display large differences in thermal expansion. Previously, the inlays have normally been secured in shaped charges by means of a screw ring threaded in the mouth of the steel case and fixedly clamping the inlay against a folded edge in the case. Provided that the clearance between the wall of the case and the inlay is not too large, this securement method gives the permanent securement of the inlay that has been deemed necessary for the satisfactory functioning of the shaped charge. However, it is known in the art that the reforming of the inlay into a projectile or particle jet on detonation of the explosive charge is affected by the anchorage ring and the securement fold along that edge zone which, as it were, is shielded from the explosive since this does not reach all the way out to the outer edge of the inlay. Now that the inlay is to be manufactured of tantalum, as this material gives an amplified effect as compared with the previously used copper, and the rest of the sleeve surrounding the explosive is made of steel, a clearance of 0.01 mm between inlay and case at ∼20 °C would cause the inlay to suffer from a subsequently permanent change in shape if the charge were to be exposed to a temperature of -40 °C, a circumstance which must be considered as fully conceivable at any rate in cold climates such as in Sweden. If greater clearance is to be permitted between the inlay and case, the folded edge and the screw ring fixedly clamping the inlay must be given a larger surface area which, in both cases, means parameters that negatively influence the effect of the charge on the target, as a larger portion of the inlay will then be shielded from the explosive. One suggestion to solve the problems caused by different thermal expansions in the liner and the casing of shaped charges is described in DE-A-3901474 on which disclosure the preambles of independent claims 1 and 4 are based. According to said suggestion the liner, defining the explosive of said shaped charge in its effect direction, should be fastened to the casing, surrounding the rest of the explosive, by an intermediate ring, which is connected to the circumferential area of the liner and which is also having a portion which is brought around another frontal circumferential attachment area of the casing. It is further stated that the liner should have a coefficient of thermal expansion which is at least as great as the coefficient of thermal expansion of the intermediate ring and that the casing preferably should have a thermal expansion which is greater that the thermal expansion of said intermediate ring. Even though this design may offer a solution to the problem in question it will also, at least some times, introduce certain material problems as materials with the correct thermal expansions always have to be choosen. Under certain circumstances high stresses may also be introduced into the different parts and especially in the intermediate ring. SOLUTION According to the present invention, this problem is now solved with the aid of a resiliently yieldable securement of the inlay that can compensate for the temperature movements of the different materials. However, this cannot be put into effect by any means whatever, as the effect of the charge must not be negatively influenced. Accordingly, the present invention may be defined as a method and an apparatus for securing in shaped charges the liner or inlay limiting the explosive portion of the charge forwardly in the effect direction, in the opening to the case surrounding the rest of the explosive portion, this opening also being directed forwardly in the effect direction. According to the present invention, this securement is rendered immobile in the axial direction, i.e. at right angles to the intended effect direction of the charge, but resiliently yieldable in the radial direction, i.e. parallel with the intended effect direction of the charge, and with a clearance between the inlay's own outer edge and the inner wall of the case. The radially resiliently yieldable securement permits necessary temperature movements between inlay and case, while the axially immobile securement must be so powerful as to be capable of absorbing the substantial acceleration and retardation stresses to which the charge can be subjected. The charge is, indeed, often included as a part in an artillery projectile or a missile. It further applies that shaped charges as a rule are of circular cross-section, and a further development of the present invention relates to shaped charges of this type, as will be disclosed in greater detail below. However, there are also shaped charges (primarily of the type employed as booby traps) which are of rectangular cross-section, in which event the present invention applies in its most generic form as defined in the foregoing, even though the expression "radial direction" may not perhaps then be fully adequate, but instead the definition "at right angles to the intended effect direction" should rather apply. In shaped charges of circular cross-section, it now applies that the inlay or liner according to the present invention is secured in the case by means of an anchorage ring which is connected with the inlay and produced from resiliently yieldable material such as high-grade steel, the ring displaying a first, inner, inwardly flaring frusto-conical shank collar extending in towards the case and the place for the explosive therein, this inner collar having a small top angle which, in a direction towards the case, is terminated by an annular inner support edge which faces away from the inlay and whose outside diameter is at least somewhat larger than the outside diameter of the inlay and is adapted to the inside diameter of the case, and an outer, similarly frusto-conical shank collar which faces in the opposite direction and flares outwardly, this outer collar having a small top angle which is outwardly terminated by an outwardly facing, annular outer support edge. This basic design thus gives inwardly and outwardly facing support edges which each terminate a frusto-conical, almost collar-shaped portion here designated shank collars. Since these collars have small top angles, the main direction of their walls will be quite close to but not parallel with the inside of the case, and since the inlay is connected to the anchorage ring where its shank collars have their smallest diameter, the anchorage ring will, as it were, have a rigid waist in which the inlay is secured, and inwardly and outwardly extending frusto-conical skirt portions or shank collars which, by being manufactured as a unit from a resiliently yieldable material, can be deformed and somewhat expanded respectively along the support edges. On the other hand, their main direction is, thanks to the small top angles, close on parallel with the longitudinal direction of the case, for which reason no movement in that direction can take place unless each respective shank collar collapses altogether, which can be avoided in that maximum acceleration and retardation forces are taken into account on mechanical strength calculations. The diameters of the outer and inner support edges of the shank collars are further both at least slightly larger than the diameter of the inlay and are further in turn adapted to the inside diameter of the case. By this means, a certain clearance will be guaranteed between the outer edge of the inlay, i.e. in practice the waist of the anchorage ring, and the inside of the case. On mounting the inlay in position, it is passed down into the case secured in the support ring until the inner support edge of this latter at the inner shank collar abuts against an annular stop edge formed in the inside of the case, and thereafter the outer shank collar is upset, or alternatively by yielding is snapped in so that its outer support edge abuts against an outer stop edge similarly formed on the inside of the case. The inlay is thus tensioned in between these two mutually counter-directed stop edges between the simultaneously pretensioned shank collars. The stop edges in the case wall may consist of, for instance, the two opposing edge sides of one and the same groove formed in the case wall. Once the inlay or liner has been mounted in place, the case behind the liner is filled with explosive. Thus, the explosive will support the inlay and assist in absorbing the acceleration forces in one direction. In order to compensate for the lack of support of the inlay in the intended effect direction of the charge, i.e. outwardly, it may be appropriate to manufacture the outer shank collar with a stiffer resilience than the inner. This may, for instance, be effected by giving this collar a somewhat shorter free length. To retain the inlay in the anchorage ring, this is ideally provided with an annular groove flush with its own waist. The anchorage ring may be made of profile-rolled and welded strip material or perhaps, even more suitable, directly from a tubular material which is cut and tapered, and provided with the groove for the inlay. The present invention has been defined in the appended claims and will now be described in greater detail hereinbelow with particular reference to the accompanying drawings which, in Fig. 1, show a longitudinal section through a shaped charge of circular cross-section, and, in Fig. 2, show a detail on a larger scale of the securement of the anchorage ring in the case. The figures show the charge before the case included therein has been filled with explosive. DESCRIPTION OF PREFERRED EMBODIMENT The shaped charge shown in the drawings consists of a steel case 1 in whose mouth 2 open in the intended effect direction a tantalum inlay or tantalum liner 3 is secured by means of an anchorage ring 4. The inlay or liner 3 is, along its periphery, secured in a groove 5 in an anchorage ring 4. The anchorage ring is, in its turn, secured in a groove 6 which has been milled from the inner wall of the case 1 proximal the opening of the mouth 2. The details intimately related to the anchorage ring and the securement thereof in the case are most readily apparent from Fig. 2. As is apparent from Fig. 2, the anchorage ring 4 includes, first, the groove 5 in which the inlay is secured and, secondly, an inner shank collar 7 which is in the form of a short truncated cone with a slight top angle which flares inwardly and whose inside is, thus, not parallel with the inside of the case but deviates at most about 10-15 degrees from the main angle thereof (the angle a). Thus, the shank collar is extremely rigid in a direction parallel to the main direction of the case which, in turn, coincides with the intended effect direction of the charge. The shank collar 7 is terminated inwardly by an annular support edge 8 facing away from the inlay 3. The support edge 8 has an outside diameter R 1. In the groove 5, there is a second support edge 9 along which the inlay is supported by the anchorage ring 4. In its turn, the support edge 8 abuts tight against an opposing stop edge 10 in the groove 6. Like the support edge 8, the stop edge 10 has the outside diameter R 1. In addition, the support and stop edges 8 and 10 are of the same width. The inlay 3 is, hence, extremely rigidly supported in a direction in towards the interior of the case 1 along its periphery via the support edge 9, the shank collar 7, the support edge 8 and the stop edge 10. Correspondingly, the ring is formed, in an outward direction in the intended effect direction, with a frusto-conical outwardly flaring, outer shank collar 11 which is terminated by an outer annular support edge 12 making an angle β with the inside of the case and having a support edge 13 against the inlay and abutting against the stop edge 14 in the groove 6. The inside diameter R 2 of the stop edge 14 is at least as large as R 1, this so as to enable the anchorage ring 4 to pass the stop edge 14 when the anchorage ring 4 is mounted in place. Hence, the groove 6 has an inner lesser diameter R 1 and an outside diameter equal to R 2 plus the width of the support surface 12. This latter is equal to the thickness of the outer shank collar 11. On mounting, the support ring 4 is passed in the groove 6 until the support and stop edges 8 and 10 abut against one another, whereafter the shank collar 11 is sprung or upset outwardly so that the support and stop edges 12 and 14 abut against one another. The shank collar 11 has the same frusto-conical main form as its inner counter form as its inner counterpart 7, but it is somewhat shorter and thereby more rigid than this. This is because the inlay 3 is supported inwardly by the explosive but is wholly without support in an outward direction. The anchorage ring 4 is thus tensioned in between the annular stop edges 10 and 14 via its own annular support edges 8 and 12. As is apparent from the figure, the anchorage ring 4 has a waist flush with the groove 5 and clearance is there formed between the inside of the anchorage ring and the inside of the case groove 6. Thus, there are possibilities here to absorb the main differences in temperature movements between the materials tantalum in the inlay 3 and steel in the case 1. As a consequence of its particular design, the securement of the inlay is, on the one hand, movable in the radial direction, and, on the other hand, rigid in the axial direction and also compensated for different stresses in different axial directions. Finally, the inlay is also tight. The specific sealing ring requires high-grade resilient material and is also far from easy to manufacture, but it does fulfil several different functions and is therefore well worth its cost. The present invention should not be considered as restricted to that described above and shown on the drawings, many modifications being conceivable without departing from the scope of the appended claims.

Claims: In shaped charges, a method of securing the liner or inlay (3) defining the explosive of the charge forwardly in the effect direction, in the opening (2) facing forwardly in the effect direction of the case (1) surrounding the rest of the explosive, characterized in that this is made immovable in the axial direction, i.e. parallel with the intended effect direction of the charge, but resiliently yieldable in the radial direction, i.e. at right angles to the intended effect direction of the charge, and with a clearance (a) between the inlay's own outer edge and the inner wall of the case. The method as claimed in Claim 1, characterized in that the inlay or liner (3), when this has a circular outer profile and the case has a cylindrical shape, is secured in the case by means of an anchorage ring (4) connected with the inlay and produced from resiliently yieldable material, the ring displaying a first, inner, inwardly flaring frusto-conical shank collar (7) extending in towards the case and the place for the explosive therein, said inner collar having a small top angle which, in a direction in towards the interior of the case, is terminated by an annular inner support edge (8) which faces away from the inlay (3) and whose outside diameter is at least somewhat larger than the outside diameter of the inlay, and an outer, similarly frusto-conical shank collar (11) which faces in the opposite direction and is expanded outwardly, said outer collar having a small top angle which is outwardly terminated by an outwardly facing, annular outer support edge (12), the anchorage ring (4) with the inlay (3) secured therein being, on mounting of the inlay, introduced down into the case (1) until said annular inner support edge (8) abuts against a counterdirected first stop edge (10) formed in the case, whereafter the outer shank collar (11) is upset or caused to flex in so that its outer support edge (12) is urged in beyond and into abutment against a second stop edge (14) formed in the case, this second stop edge being counterdirected to said first stop edge (10). The method as claimed in Claim 2, characterized in that the outer shank collar (11) is made with more rigid resilience properties than the inner (7). In shaped charges, an apparatus for securing, in accordance with the method as claimed in any one or more of Claims 1-3, the liner or inlay defining the explosive portion of the charge forwardly in the contemplated effect direction, in the opening (2) to the case (1) surrounding the explosive on other sides, characterized in that it includes means disposed about the outer edge of the inlay and fixedly secure thereto forwardly (7) and rearwardly (11), respectively, in the intended effect direction, rigid in the axial direction, i.e. parallel with the intended effect direction but resiliently yieldable in the radial direction, i.e. at right angles to the above-mentioned direction, the main direction of said means forming acute angles (α and β, respectively) with the inner wall of the case (1) and, at least at room temperature, holding the liner or inlay (3) a slight distance (a) from the inner wall of the sleeve (1). The apparatus as claimed in Claim 4, characterized in that said means (7, 11, respectively) extending forwardly and rearwardly in the intended effect direction respectively consist of different parts of one and the same anchorage ring (4) which is produced from resiliently yieldable material such as high-grade steel, and which is secured about the liner or outer periphery of the inlay (3) and which displays a first, inner, inwardly flaring frusto-conical shank collar (7) extending in towards the case and the place for the explosive therein, this inner collar having a small top angle which is inwardly terminated by an annular inner support edge (8) which faces away from the inlay and whose outside diameter is at least somewhat larger than the outside diameter of the inlay and adapted to the inside diameter of the case and is intended to be brought into abutment against a counter-directed first stop edge (10) formed in the case, and a second, outer frusto-conical shank collar (11) extending in the intended effect direction and expanded outwardly, this outer collar having a small top angle which is outwardly terminated by an annular outer support edge (12) facing away from the shank collar, the outside diameter of said support edge being also at least somewhat larger than the outside diameter of the inlay or the liner (3), and which is intended to be moved into abutment against a second stop edge (14) which is counterdirected and formed in the case (1). The apparatus as claimed in Claim 5, characterized in that the anchorage ring (4) also displays, in addition to the outer (11) and inner (7) shank collars, an inwardly facing annular groove (5) formed therebetween and in which the inlay (3), when it is united with the anchorage ring (4), is fixedly retained about its outer periphery. The apparatus as claimed in any one of Claims 4-6, characterized in that of said means for fixedly retaining the inlay, i.e. the inner (7) and the outer (11) shank collar, the outer is formed with more rigid resilience than the inner. The apparatus as claimed in Claim 7, characterized in that the outer shank collar (11) is shorter than the inner (7). The apparatus as claimed in any one of Claims 4-7, characterized in that the anchorage ring (4) is inwardly terminated by a support edge (8) whose outer periphery (R 1) is no larger than it can freely pass the mouth (2) of the case (1), the inner portion of the groove (6) being adapted to this outer periphery, while the shank collar (11) outwardly terminating the anchorage ring (4) has or may be given a larger outside diameter than the inner support edge (8), and the outer portion of the groove (6) being adapted to this larger outside diameter.

Inventors: EKHOLM OLOF, EKHOLM, OLOF
Applicants: BOFORS AB
Application year: 1993
Main classification: F42B1
IPC codes: F42B1