EP0519798A1 - Process for the making of high power explosive charge and device for implementing the process - Google Patents

Abstract

Process and device for the manufacture of a high-power explosive charge, of the type consisting in mixing a high-power explosive such as RDX or HMX in the form of solid particles with a liquid or molten binder such as molten TNT, in pouring the pasty mixture into a mould (2), in removing the excess liquid binder by natural or forced filtration through porous walls (3, 4) of the mould (2) and substantially over the whole height of the latter, and in obtaining the desired explosive charge after solidification of the mixture. <IMAGE>

Description

The present invention relates to a method for manufacturing a high-powered explosive charge, of the type consisting in mixing a high-power explosive in the form of solid particles with a liquid or molten binder, in pouring the pasty mixture obtained into a mold, evacuate the excess liquid binder and then allow the mixture to solidify to form said explosive charge.

In general, the field of application of the present invention is that of secondary explosives for charges, in particular explosives intended for hollow charges and for which charges are desired whose rate of high-powered explosive is very high, the very low degree of porosity and the lowest possible axial density gradient.

The industrial manufacture of hollow charges is preferably obtained by a casting method. One such method consists in mixing high-power explosive, for example hexogen and / or octogen, with an inert liquid component, for example a hardenable plastic resin, or an active one, for example molten TNT, the pasty mixture thus obtained being poured into the envelopes of hollow charges. Then the binder is allowed to harden. However, the binder, whether inert or active, inevitably constitutes a power reducer. The problem is therefore to reduce the rate of use of this binder as much as possible.

To carry out loads with a high rate of high-powered explosive, there is a technique known as die-casting which consists in filling a form with a mixture of high-power explosive and a liquid phase, then applying pressure to using a porous piston to compress the high-powered explosive and raise the binder as much as possible. Such a method is described in particular in the document DE-PS 12 07 842. Other documents describe variants of this process, in particular the document DE-OS 25 04 756 in which an airbag is used to compress the explosive, and the document DE 35 29 123 where the 'We use a non-sealed piston provided with a closable opening on its front face.

However, although all these methods lead to the production of explosive charges with a high rate of high-powered explosive, they have the disadvantage of necessarily passing through a compression step which requires an expensive installation and which is not without presenting security problems linked to the fact that this compression takes place on explosive maintained at temperature. In addition, they most often lead to the production of blocks of explosives in which the axial density gradient is high, especially when the length / diameter ratio is large. Indeed, the density of the solid explosive in the area near the piston can reach values 6% higher than those obtained in the most distant area. This is due to the fact that the removal of the liquid binder occurs at one end of the charge, which leads to an uneven distribution of the pressure throughout the charge.

The object of the invention is to design a method and a device which make it possible to overcome the abovementioned drawbacks while providing other advantages.

To this end, the invention provides a method of manufacturing a high-powered explosive charge, of the aforementioned type and which is characterized in that it consists in removing the excess of liquid binder by filtration through porous walls of the mold, this filtration taking place substantially over the entire height thereof

Thus, according to the invention, the conventional method casting-compression is replaced by a casting-filtration process.

According to another characteristic of the process according to the invention, the evacuation of the excess of the liquid binder is carried out either by natural filtration, or by forced filtration by vibrating the mixture for a predetermined time, of the order of a few minutes.

Thus, with such a method it is possible to improve the quality of the loadings by reducing the axial density gradient, since the elimination of the liquid binder takes place at all levels of the load and substantially over its entire height.

According to other characteristics of the process according to the invention, and in order to facilitate the filtration operation of the excess liquid binder, it is planned to create a depression around the mold and / or an overpressure above the mold at level of the surface of the mixture, and provision is also made for possibly applying a slight compressive force to the surface of the mixture by means of a porous or non-porous piston.

The invention also provides a device for implementing this method and which is characterized in that the mold has porous walls to allow filtration of the excess liquid binder.

In general, the mold consists of a rigid perforated grid against which a filtering envelope is applied, for example made of fabric, metallic or plastic fabric, or even filter paper, the envelope possibly comprising several filtering thicknesses.

The mold is advantageously of cylindrical shape and has a bottom wall bordered by a side wall open at its free end, and it is removably attached to a holding support.

In the various examples which will be described below, the holding support comprises a hollow body of cylindrical shape open at one end or upper end, and a receptacle into which opens the lower end of the body, the mold being housed in a removable manner inside this body by providing an annular space between the mold and the internal wall of the body for the free passage of the excess liquid binder which falls by gravity into the recovery receptacle.

Depending on the variants of the method as envisaged above, the implementation device is equipped with complementary means capable of creating in the body of the support for holding a depression around the mold and / or an overpressure at the level of the surface of the mixture. , as well as a porous or unmounted piston sliding in order to exert a compressive force on the surface of the mixture.

In general, this results in simple and inexpensive implementation devices, capable of industrially implementing charges whose rate of high-powered explosive is very high.

• la figure 1 est une vue en coupe transversale schématique d'un dispositif de mise en oeuvre du procédé conforme à l'invention selon un premier mode de réalisation,
• les figures 1a et 1b sont des vues en coupe partielle de la paroi d'un moule utilisé dans le dispositif de mise en oeuvre de la figure 1 suivant deux formes de réalisation,
• et les figures 2 à 7 sont des vues en coupe transversale schématiques qui illustrent chacune une variante du dispositif de mise en oeuvre représenté à la figure 1.

Other advantages, characteristics and details of the invention will emerge from the explanatory description which follows, made with reference to the appended drawings given solely by way of example and in which:

• FIG. 1 is a schematic cross-sectional view of a device for implementing the method according to the invention according to a first embodiment,
• FIGS. 1a and 1b are views in partial section of the wall of a mold used in the device for implementing FIG. 1 according to two embodiments,
• and FIGS. 2 to 7 are schematic cross-section views which each illustrate a variant of the implementation device shown in FIG. 1.

Before explaining in detail the different phases of the process for manufacturing a high-powered explosive charge, according to the invention, a device for its implementation will be described beforehand as illustrated in FIG. 1.

The device 1 for implementing the method mainly comprises a mold 2 advantageously of cylindrical shape which has a bottom wall 3 bordered by a side wall 4 open at its free end and determined by a radially external rim 4a, and a support for holding 5 to which the mold 2 is fixed removably.

The bottom wall 3 and the side wall 4 of the mold 2 are porous walls which are constituted, with reference to FIGS. 1a and 1b, by a rigid support 6 such as sheet metal having perforations 6a each having an opening of the order of 10 mm, and by a filter envelope 7 which covers the interior wall of the mold 2.

This envelope 7 is constituted by a filtering material, for example, metallic canvas, plastic canvas or filter paper for example. In the case of FIG. 1b, the casing 7 can be made up of two thicknesses 7a and 7b made up of different filtering materials.

Generally, the internal diameter of the mold 2 is slightly greater, of the order of 3 to 5 mm, than that of the filler that it is desired to obtain, and its height is sufficient to contain in addition to the filler , the extension which will then be removed by machining.

To facilitate the release operations of the load after application of the method according to the invention, the mold 2 can advantageously be made in two parts in the form of two semi-cylindrical shells and / or flaring slightly at its upper part by delimiting a frustoconical shoulder 8 extended by the aforementioned radially external rim 4a.

Such a mold 2 is removably attached to the holding support 5 as described below with reference to FIG. 1.

The support 5 includes a cylindrical hollow body 9 where the mold 2 is housed, means 10 for fixing the mold 2 to the body 9, and a receptacle 11 into which the lower end of the body 9 opens.

In the example considered here, the body 9 has, towards its end opposite to that opposite the receptacle 11, an internal wall which widens slightly outwards to form a frustoconical shoulder 9a of a shape complementary to that of the mold shoulder 8

The internal diameter of the body 9 is greater than the external diameter of the mold 2, so that the mold 2 can be freely mounted inside the body 9 by delimiting between them an annular space E. The mold 2 is retained in the body 9 by means of its shoulder 8 which bears on the complementary shoulder 9a of the body 9. In this position, the external rim 4a of the mold 2 is supported on the upper end surface of the body 9, the rim 4a forming the mold retaining element 2 in the absence of the shoulders 8 and 9a.

The fastening means 10 of the mold 2 inside the body 9 consist of a ring 10a with a diameter substantially equal to that of the body 9. This ring 10a is attached coaxially to the body 9, so as to come to bear on the rim 4a of the mold 2 to immobilize the latter, the ring 10a being itself fixed to the body 9 by any suitable means, known per se.

The receptacle 11 comprises a bottom wall 12 bordered by a lateral cylindrical wall 13 whose diameter is substantially equal to that of the body 9, and it forms a recovery chamber 14. This receptacle 11 once positioned under the body 9 is fixed to the latter by any suitable means known in oneself.

This device 1, as described above, makes it possible to manufacture a charge of explosive containing a high percentage of high-powered explosive according to the process according to the invention which takes place generally according to four main stages.

In a first step, a mixture of high power explosives is prepared, for example octogen and / or hexogen in the form of solid particles with a liquid binder such as molten TNT. The pasty mixture which must then be able to be poured inside the mold 2 comprises around 75% by weight of explosive and 25% by weight of TNT. Specific examples will be given later.

In a second step, the mixture M thus obtained is poured into the mold 2.

In a third step, or filtration step, the excess liquid binder in the mixture is evacuated naturally through the porous walls 3 and 4 of the mold 2 and is collected in the chamber 14 of the receptacle 11, after having passed through the filter envelope 7 and the perforations 6a of the perforated sheet 6 of the mold 2. On average, the duration of the filtration step is of the order of a few minutes, and in general, the mold 2 is kept at a temperature higher than that of the melting of the binder.

Finally, in a fourth step, the mixture is allowed to solidify inside the mold 2, and the explosive charge is then removed from the mold.

According to this first version of the process, the filtration operation takes place in a natural way. To facilitate this filtration operation, we vibrates the mixture simultaneously. For this, the device 1 is equipped with vibrating means shown diagrammatically at 20 and which act directly on the holding support (5) of the mold 2. These means can for example consist of a vibrating table on which the holding support 5 is fixed. .

The variants of the method and those corresponding to the implementation device will now be described with reference to FIGS. 2 to 7.

In the case of FIG. 2, a depression is created inside the space E provided between the mold 2 and the retaining body 5, so as to facilitate the filtration operation of the mixture contained in the mold 2. For this, at the body 9 of the holding support 5, there is provided a conduit 21 which is connected to a device 22 known per se which makes it possible to create this depression.

In the case of FIG. 3, an overpressure is created at the level of the upper surface of the mixture contained in the mold 2 to also favor the filtration operation. In this case, the implementation device is completed by a cover 25 which closes the upper end of the holding support 5 which then forms a closed enclosure. In this cover 25, a passage 26 is provided which communicates with a device 27, known per se, for sending pressurized air inside the holding body 5.

In the case of FIG. 4, the mixture is slightly compressed always to facilitate the filtration operation of the excess liquid binder in the mixture contained in the mold 2. This compression is ensured by means of a hollow piston 28 which is mounted sliding in the retaining body 5 and at the upper part thereof. In the example considered here, the piston 28 is hollow and its end surface adjacent to the mixture contained in the mold 2 is advantageously porous and constituted for example by a filtering wall 29 having the same constitution as the walls of the mold 2.

FIG. 5 shows an alternative embodiment of FIG. 4, in which the piston 28 is a full piston.

In the case of FIG. 6, the step of solidifying the mixture, after natural or forced evacuation of the excess liquid binder, is accompanied by an operation for cooling the mixture. This operation is advantageously carried out when the binder used is a fusible product, because it allows the shrinkage phenomenon to be limited to the upper part of the solidified block, part which is then eliminated. For the implementation of this cooling operation, there is provided in the holding support 5, a continuous channel 30 in the form of a serpentine which extends over the entire height of the mold 2. This inner channel 30 opens out to the outside. towards the lower and upper parts of the retaining body 5, and it communicates via outward and return conduits 32 with a cooling device 33, known per se, which circulates a coolant and comprises a circulation pump and an exchanger of heat for example.

In FIG. 7 is illustrated a variant of the embodiment of FIG. 6 to improve the cooling operation of the mixture during solidification. In the example considered here, the bottom wall 3 of the mold 2 is pierced with a central opening 35 on which rests by the base a conical block 36 supporting the hollow charge coating 37.

In a manner known per se, a hollow charge consists of a metallic coating of conical shape onto which the explosive is poured. Also, the device for implementing the method according to the invention in the example considered in FIG. 7 includes this coating of hollow charge 37 supported by the block conical 36, so as to directly obtain a hollow charge after solidification of the mixture which sticks to the coating. In the case of the other devices for implementing the process (FIGS. 1 to 6), when the solidified mixture once demolded is intended to constitute the explosive of a hollow charge, it must undergo a machining operation consisting in digging a conical recess in which the hollow charge coating is then bonded. Obviously, these other implementing devices can be equipped with these means 36 and 37 for manufacturing hollow charges.

In the implementation device, according to Figure 7, there is provided a cooling circuit of the mixture which comprises by two circuits respectively external and internal. The external circuit is similar to that shown in FIG. 6 with an internal channel 30 in the retaining body 5 which is connected by outward and return conduits 32 to a cooling device 33. The internal cooling circuit comprises a continuous channel 40 in the form of a coil which is housed inside the conical block 36, channel 40 which is connected by outward and return conduits 42 to a cooling device 43 similar to the device 33.

We will now give five examples generally illustrating the characteristics of the charges obtained according to the process according to the invention by using some of the devices described above.

1st EXAMPLE

The pasty mixture produced during the first step of the process initially contains 76% by weight of industrial quality octogen according to a particle size between 0 and 800 μm, and 24% of molten TNT. By implementing the method with the device according to the embodiment illustrated in FIG. 7, with forced vibration of the mixture for approximately five minutes and a filtering envelope 7 constituted by a metallic fabric with meshes delimiting passages of the order of 40 μm, an explosive charge containing 83.2% of high-powered explosives was obtained with a density gradient of the order of 2%.

2nd EXAMPLE

The pasty mixture produced during the first step of the process contains 80% by weight of octogen according to a particle size between 0 and 1600 μm, and 20% by weight of molten TNT. By implementing the method according to the embodiment illustrated in FIG. 6, with a forced vibration of the mixture for approximately five minutes and a filtering envelope 7 made of metallic fabric with meshes delimiting passages of the order of 40 μm and a double envelope thickness at the bottom wall 3 of the mold 2, a charge containing 90.5% octogen was obtained with a density gradient of 1%.

EXAMPLE 3

With an initial mixture containing 83% by weight of octogen according to a particle size of 0 to 1600 μm and 17% by weight of molten TNT, and by implementing the method according to the embodiment of FIG. 6 with the same conditions as those given for the second example, a charge was obtained containing on average 91.2% octogen with a density gradient of approximately 0.7%.

EXAMPLE 4

The pasty mixture produced during the first step of the process contains 83% by weight of octogen according to a particle size between 0 and 1000 μm and 17% by weight of molten TNT.

By implementing this method according to the embodiment illustrated in FIG. 6, with forced vibration of the mixture for approximately five minutes and a filtering envelope 7 constituted by a metallic fabric arranged in a thickness on the side wall 4 of the mold and in two thicknesses on the bottom wall 3 of the mold 2 with meshes delimiting passages of on the order of 40 μm, a charge was obtained containing on average 90.3% octogen with a density gradient of the order of 1.1%.

EXAMPLE 5

From an initial mixture of octogen of 75% by weight with two particle sizes 0/200 and 200/630 µm, and 25% by weight of a fusible nitrofluorine explosive (2-fluoro-2,2 ether -dinitroethyl 2,4,6-trinitrophenylic).

By implementing the method according to the embodiment illustrated in FIG. 6, with forced vibration of the mixture for approximately five minutes and a filtering envelope 7 constituted by a metallic fabric with meshes delimiting passages of the order of 40 μm, a charge was obtained containing on average 82.3% octogen with a density gradient of the order of 1.8%.

Of course, the invention is in no way limited to the above embodiments and examples given solely by way of example. In particular, the different variants described in the figures can be combined with one another.

Claims (22)

Process for manufacturing a high power explosive charge, of the type consisting in mixing a high power explosive, such as hexogen or octogen, in the form of solid particles with a liquid or molten binder such as TNT, pouring the pasty mixture obtained into a mold, removing the excess liquid binder, and then allowing the mixture to solidify to form said explosive charge, characterized in that it consists in removing the excess liquid binder by filtration through porous walls of the mold and substantially over the entire height thereof. Manufacturing process according to Claim 1, characterized in that it consists in removing the excess liquid binder by natural filtration. Manufacturing process according to Claim 1, characterized in that it consists in removing the excess of liquid binder by forced filtration. Manufacturing process according to Claim 3, characterized in that it consists in vibrating the mixture to obtain forced filtration. Manufacturing method according to any one of the preceding claims, characterized in that it also consists, during the filtration operation, of creating a depression around the mold. Manufacturing method according to any one of the preceding claims, characterized in that it also consists, during the filtration operation, of creating an overpressure above the mold. Manufacturing process according to any one of Claims 1 to 5, characterized in that it also consists, during the filtration operation, of applying a compressive force to the surface of the mixture. Manufacturing method according to any one of the preceding claims, characterized in that it consists, after the filtration operation, in cooling the mixture during its solidification. Device for carrying out the process as defined by any one of the preceding claims, of the type comprising a shape such as a mold for receiving a mixture of high power explosive and a liquid or molten binder, characterized in that the mold (2) has porous walls (3,4). Device according to Claim 9, characterized in that the mold (2) comprises a bottom wall (3) bordered by a side wall (4) open at its free end, each wall (3,4) being formed by a rigid grid perforated (6) and by at least one filter envelope (7). Device according to Claim 10, characterized in that the filtering envelope (7) is a metallic fabric, a plastic fabric, a fabric or a filter paper. Device according to any one of Claims 9 to 11, characterized in that the bottom wall (3) of the mold (2) comprises at least one double filter envelope (7). Device according to any one of Claims 9 to 12, characterized in that the mold (2) is supported by a retaining support (5) comprising a hollow cylindrical body (9) in which the mold (2) is housed, delimiting between them an annular space (E), means for fixing the mold (2) to the body (9) and a receptacle (11) placed below the body (9). Device according to Claim 13, characterized in that it comprises means (21,22) for creating a depression in the space (E) of the body (9). Device according to Claim 13 or 14, characterized in that the holding support (5) comprises a cover (25) which closes the body (9) and means (26, 27) for creating an overpressure in the body (9) above the mold (2). Device according to Claim 13, characterized in that it comprises, above the mold (2), a piston (28) slidably mounted inside the body (9). Device according to Claim 16, characterized in that the piston (28) is hollow with a porous end surface (29). Device according to any one of Claims 13 to 18, characterized in that the side wall (4) of the mold (2) ends at its free end by a radially external flange (4a) which bears on the end surface upper part of the body (9), and in that the fixing means (10) consist of a ring (10a) attached coaxially to the body (9) to come into tight contact with said flange (4a). Device according to any one of Claims 13 to 18, characterized in that it comprises means (20) for vibrating the holding support (5) of the mold (2). Device according to any one of Claims 13 to 19, characterized in that it comprises means (30 to 33) for cooling the mold (2), these means comprising a channel (30) in the form of a serpentine located at the inside the body (9) and connected by go (31) and return (32) conduits to a cooling device (33), known per se. Device according to any one of Claims 9 to 20, characterized in that the bottom wall (3) of the mold (2) supports a conical block (36) on which a coating of hollow charge (37) rests. Device according to Claim 21, characterized in that it comprises means for cooling (40 to 43) of the hollow charge coating (37), these means comprising a channel (40) in the form of a serpentine housed inside the block conical (36) and connected by supply (4) and return (42) conduits to a cooling device (43), known per se.

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