MXPA97003466A - Continuous procedure for the manufacture, without solvent, of composite pirotecnic products that are hardened with the ca - Google Patents

Abstract

The present invention relates to the domain of the manufacture, continuously, of pyrotechnic composite products. In a mixer (1) a liquid mortar (3), which hardens with heat, is mixed with a thickener charge (4), so that a premix (2) viscous and non-reactive at room temperature is obtained, which can then mix oxidizing loads (17) to obtain, after extrusion and cutting, intermediate products (24) that are not yet crosslinked but have stable geometric cuts. The structure of the products (24) is subsequently fixed by crosslinking the mortar in an oven (26). The invention allows the industrial manufacture, continuously in series, of small pyrotechnic, compound, crosslinked loads, without the problem of "reactor life", since the mortar is not evolutive at an ambient temperature.

Description

- - DESCRIPTION OF THE INVENTION The present invention relates to the domain of composite pyrotechnic products and especially composite powders for cannon weapons, composite propellants for reaction engines (rockets) and composite explosives for ammunition loads. More precisely, the invention concerns a continuous process for the preparation, without solvent, of these pyrotechnic products, comprising a mortar that hardens with heat. The pyrotechnic composite products constituted by an organic mortar and by a pulverulent energy charge, which can be a mineral charge, such as, for example, ammonium nitrate, ammonium perchlorate or potassium perchlorate; or even an organic load and especially a nitroamine, such as for example exogenous, octogen, nitroguanidine or 2, 4, 6, 8, 10, 12-hexanitro-2, 4, 6, 8, 10, 12-hexa-azatetracyclo (5.5.0.0 5.9.0 3.11) dodecane, still called hexanitrohexaaza-isowurzitano, are highly researched by those trained in the technique due to their great chemical stability and their low vulnerability to impacts and thermal aggressions. On the other hand, for reasons of safety and reproducibility of the fabrications, the one skilled in the art prefers the continuous procedures to the REF. 24582 discontinuous procedures. The mortars which can be used for the manufacture of the pyrotechnic composite products can be thermoplastic mortars or mortars which harden with heat. Thermoplastic mortars present the interest of being lent, in a relatively simple manner, to a continuous application thanks to the fact that it softens due to an increase in temperature. Thus, the French patent application FR-A-2 723 086 describes a method of manufacturing continuously, and without solvent, composite pyrotechnic products, based on mortars of thermoplastic type. However, thermoplastic type mortars have the drawback of leading to products that show a terrible behavior with temperature, because of the same softening of the mortar when there is an increase in temperature or certain applications, such as weapons With a large angle of shot, the trained in the art needs pyrotechnic products that show a good behavior with temperature. From this point of view, the pyrotechnic products with mortars that harden with heat offer the advantage of presenting a good behavior with temperature. But, for the same reason that their mortar hardens irreversibly with heat, by crosslinking, these products have the disadvantage that they do not lend themselves well to continuous processes. These products are often then applied in batch processes. Thus, US-A-4 128 441 discloses a discontinuous manufacturing process by "casting" of propellant blocks. This procedure is suitable for manufacturing large loads for jet engines, but it is not convenient to industrially manufacture small objects in series. Patent US-A-4,405,534 describes, as far as the same is concerned, a process for the manufacture of explosives composed by cold compression of explosive granules, covered by a polyurethane film that becomes plastic thanks to the presence of plasticizers . This procedure, except for the fact that it is discontinuous, has the additional drawback of requiring the presence of a large amount of plasticizer, which is not always favorable with respect to the energy plan. It has been proposed, by the application WO 94/05607, a semicontinuous process for the manufacture, with solvent, of these products? but the need to have to resort to a solvent that is necessary to eliminate immediately, limits the interest in this procedure. When the one trained in the art wants to apply the mortars that harden with heat in a continuous process, without solvent, is faced with the problem of the short "reactor life" of these compositions, which means that, after mixing the ingredients of the composition, only a short time is available to carry out the geometric molding of the product, before the crosslinking of the mortar makes any mechanical work of the paste containing the different ingredients impossible. It has already been proposed to extend the "reactor life" by retarding the final crosslinking, for example, by the fractional addition of the crosslinking agent, as described in US-A-4, 657, 607; or even using a double mortar system, where one of the systems can only be crosslinked by an energy input different from heat, as described in Patent Application EP-A-0 367 445. However, the possibilities of Application of these techniques are limited and those trained in the art do not have a general manufacturing procedure, in a continuous and solvent-free manner, of pyrotechnic products composed of mortars that harden with heat. The aim of the present invention is precisely to propose a method of this type, as well as the industrial installation that allows the application of this procedure. The invention then concerns a continuous process for the manufacture, without solvents, of finished composite pyrotechnic products, whose outlet constituents comprise in particular a liquid mortar which can be crosslinked at a temperature above 40 C and at least one energy charge of oxidant solid, where the process consists in particular of: i) mixing the initial constituents of the products in such a way that a homogeneous composite paste is obtained, with a sufficient viscosity to preserve the stable geometrical cuts, ii) to use the paste obtained in this way as the intermediate products that have the geometric cuts of the finished products, iii) to fix the shape and composition of the intermediate products thus obtained by means of the crosslinking of the mortar, and which is characterized because: iv) the liquid outgoing mortar is mixed from the beginning with a charge of a solid thickener and n powdery form, so that a premix of fatty consistency is obtained which is then mixed with the energy charges, v) the mixing and application operations are conducted at a temperature below 40 C. With respect to the methods known in the art prior, the most important originality of the method according to the invention resides in the fact that, except for the final phase, by means of which the structure and the composition of the intermediate products are fixed by crosslinking, the different operations are conducted to a temperature at which the mortar is almost not evolutionary in the chemical plane. Thus, the formulation of the composition of the products is perfectly reproducible insofar as it is carried out in an integral manner at the beginning of the procedure, without needing any subsequent adjustment. The one skilled in the art does not face any condition of the "reactor life" and the intermediate products, whose geometric cuts are imperfect, can be recycled in the manufacture. It is necessary to observe that, thanks to the use of solid thickeners, which cause the liquid mortar to not be evolutive in a sufficient mechanical behavior, no plasticizer is necessary in the frame of the present procedure, which allows to obtain pyrotechnic products with very good behavior characteristics. high It can also be said, contrary to the previous procedures that use an evolving mortar, which hardens with heat, during the process, where it is sought to decrease the viscosity through the use of a solvent and / or a plasticizer, the process according to the invention, it uses a mortar that is hardened with heat, liquid, non-evolving, during the process, where the apparent viscosity is increased by the use of thickening fillers. According to a first preferred variant of the invention, the solid thickener charge is constituted by a porous material, whose granulometry is comprised between 0. 1 and 10 microns and whose specific surface area is 2 between 60 and 500 m / g. Advantageously, the meterial will also possess properties that modify the combustion and will be chosen in the group consisting of carbon black, colloidal silica, aluminum, titanium oxide or polinorbornene. According to this first variant, the weight ratio between the thickener charge and the crosslinkable mortar is between 0.05 and 0.25. According to a second preferred variant of the invention, the solid thickener charge is constituted by a thermoplastic polymer with hydrocarbon domains which can comprise, in addition to the carbon and hydrogen atoms, oxygen and nitrogen atoms and where the average molecular mass , by weight, is between 3x10 and 3xl06. A first group of thermoplastic polymers which are used as a solid thickener, in the framework of the present invention, are thus constituted by the copolymers of styrene / butadiene / styrene, styrene / isoprene / styrene, styrene / ethylene / butylene / styrene and styrene / ethylene / propylene. A second group of thermoplastic polymers which are used as solid thickener fillers in the context of the present invention consists of polyurethanes with polyether and polycarbonate domains and polyether / polyamide block copolymers. According to this second variant, the weight ratio between the thickener charge and the crosslinkable mortar is between 10:90 and 50:50. In addition to the solid oxidant energy charges, at least one solid reducing energy charge, such as aluminum or boron powder, can also be incorporated into the pre-mix consisting of the liquid mortar and the thickener fillers. It is not until the mixing and molding operations of the intermediate products are carried out and that they are finished and judged as adequate, that the mortar is evolved causing its cross-linking by heating at a temperature above 40 ° C, so that the finished cross-linked products are obtained. The method, according to the invention, also makes it possible to obtain, continuously, without the problems of time linked to the questions of "reactor life" and without the use of solvents or undesirable plasticizers, in the energy plan, the products pyrotechnic compounds with reticulated mortar. These products find their preferential applications as powders of propulsion in the form of rods or of rods for the ammunition destined to the guns with cannon; as propellant blocks for rocket engines and jet engines; as explosive cargoes for explosive munitions; or even as pyrotechnic cargoes for gas generators, also intended for military applications as well as civil applications, such as automotive safety. The invention also concerns an installation which is particularly suitable for the application of the process according to the invention. This installation is characterized in that it comprises, in a progressive sense of the material: i) a shearing mill consisting of two rollers of equal length, which have helical grooves and whose axes are parallel and located in the same horizontal plane, separated so that there is a space between the two rollers that rotate in opposite directions one with respect to the other; ii) a volumetric pump that introduces, at the entrance end of material of the laminator, the premix constituted by the liquid mortar and the thickener charge; iii) at least one dosing hopper which, between the inlet end of the material and the exit end of the rolling mill material, pours the solid energy charges onto the rollers of the latter; iv) a device for granulating the homogeneous paste, constituted in this way, which is situated at the exit end of the rolling mill; v) an extruder in which the granules coming from the granulation device are collected; vi) a device for cutting (cutting) intermediate products, extruded sleeves leaving the extruder; vii) a conveyor belt, which ensures the transport and passage to a thermal oven of the intermediate products cut in this way. A detailed description is then made of the preferred application of the method, according to the invention, referring to Figure 1, which schematically represents the preferred installation presented above. Figure 2 represents, for reasons of clarity, a simplified top view of the shearing mill, used. The invention then consists of mixing, at room temperature, the output constituents of a crosslinkable composite pyrotechnic composition, until a homologous composite paste is obtained, which is sufficiently viscosity to be able, always at ambient temperature, to be molded in the form of intermediate products that already present in a stable manner the shape and final dimensions of the finished product that is to be obtained. The form and composition of these intermediate products are then fixed by hot crosslinking, so that the desired finished products are obtained. In order to achieve this, as shown in FIG. 1, a premix 2, consisting mainly of the mortar 3, which hardens by heat, in the liquid state and by the solid fillers, is manufactured in a mixer with multiple arms 1. In the case of thickeners, it is imperative, within the framework of the present invention, that the mortar that hardens with heat be liquid at room temperature and that its crosslinking can only begin at a temperature above 40 ° C, so that to ensure that, while remaining an ambient temperature below 40 C, this mortar will remain non-evolutionary in the chemical plane. It is understood, in the present description, by "liquid mortar", the set of reactive, liquid constituents that, after crosslinking, will cause the crosslinked mortar to solidify. The crosslinking reaction may be of the polycondensation reaction type, in which case the mortars will be especially of the polyurethane, polyester or polyamide type. The crosslinking reaction can be of the polyaddition reaction type with the opening of ethylenic unsaturations, in which case the mortars will be especially of the polyalkylene, polyacrylate or polymethacrylate type. In the latter case, the composition must contain crosslinking catalysts, such as, for example, peroxides. As already indicated above in the description, these thickening charges can be constituted by porous solid materials of small granulometry. In this case, certain additives commonly used as combustion modifiers, such as carbon black, will be advantageously used as thickener fillers; the method according to the invention offers in this case the advantage of allowing the obtaining, in a continuous manner, of pyrotechnic compositions already known, but which are accessible only by discontinuous processes. The thickening fillers can also be constituted by solid thermoplastic polymers of high molecular mass, so that a final product is obtained whose mortar is constituted by a mixture of thermoplastic polymers and crosslinked polymers. This type of mixtures allows obtaining composite products that have particularly high mechanical characteristics. The premix 2 constituted in this way may also contain other additives of the final composition.

It must have the consistency of a thick grease, so that it can be transported continuously by means of a volumetric pump, adhering, without flowing, on the surface of a cylinder that rotates with an angular velocity of a few tens of revolutions per minute. This premix is then transported by means of a circulation pump 34, for example a gear pump, in a reservoir 35, provided with a lid piston 36. The premix is then taken up again by means of a metering pump 5, with gears, to be driven to a team where the mixing operations with the solid energy charges and the molding of the composite paste that is obtained in this way in the form of intermediate products that already have the geometric cuts of the finished products will be carried out. These two operations can be carried out in a single equipment, such as a twin screw extruder whose extrusion head will be associated with a cutting device, but preferably these two operations will be carried out by two different equipment placed one next to the other. The premix 2 is transported by the pump 5 to a mixer, which may be a traditional mixer such as a "BUSS" co-kneader, but which preferably, and as shown in Figure 1, is a shearing laminator 6, consisting of two cylindrical rollers, 7 and 8, of identical length, which have helical grooves. The axes 9 and 10 of these two cylinders are parallel and are located in the same horizontal plane and are spaced apart so that they leave a distance 11 between the two rollers. The axes 9 and 10 are supported by support blocks 12 and 13; block 12 is a motor block that rotates the two cylinders 7 and 8, which rotate in the opposite direction of each other, at different speeds. A shearing mill of this type is known to those skilled in the art and is described in numerous applications, for example, in Patent Application FR-A-2 723 086, cited above. The pump 5 thus directs the premix 2 on the roller 7 that rotates faster, the premix forms on this roller a sheet that covers the latter. The premix is directed to the end 14 of the material input of the laminator 6. At least one dosing hopper 16 pours, between the inlet end of the material 14 and the exit end of the material, 15, of the laminator 6, the loads solid powders 17 on the premix sheet covering the roller 7. These solid energy charges are then intimately mixed with the premix 2 by the shearing action of the rolling mill 6, so that a sheet of steel is formed on the roller 7. compound paste, homogeneous, which already has a sufficient viscosity to be able to preserve the stable geometric cuts. The solid energy charges will consist mainly of the oxidizing charges of the composition, which can be mineral fillers such as, for example, ammonium perchlorate, potassium perchlorate or ammonium nitrate or organic fillers and especially nitroamines such as hexogen, the octogen, the nitroguanidine or the hexanitrohexa-azaisowurtzitano. Solid solids charges such as aluminum or boron, as well as solid additives that have not been incorporated into premix 2, can be added to the solid oxidant charges. In this case, the different charges could be contributed either in a mixture, by means of a single hopper, or separately by a succession of hoppers. The composite pulp sheet thus obtained is recovered in the form of granules 19 by a granulation device 18 located at the outlet end of the laminator 6. Preferably, as shown on FIG. 1, the output ends of the rollers 7 and 8 are not grooved, but are smooth. Then, the granules 19 are taken continuously in an extruder 20, for example, an extruder with two screws, equipped with an extrusion head 20, to be molded in the form of rods 23, which are carried by a conveyor belt 25. A cutting device 22 cuts the molded rods 23, which come out of the extrusion head 21, into intermediate products 24 that already have the final cuts of the finished products. The cutting device 22 has a displacement that commands the rapidity of progression of the tape 25 on which the rods rest. It should be noted that up to this cutting operation no heating of the pyrotechnic composition has been effected, the extruder 20 can be cooled. The mortar of the pyrotechnic composition has not evolved and the intermediates 24 can, if deemed unsatisfactory, be recycled in the manufacturing circuit. These intermediary products 24, when judged satisfactory, are then taken continuously by the conveyor belt 25, which ensures its transport and its passage to a thermal oven 26, where its geometric shape and its composition are definitively fixed by the cross-linking of its mortar at a temperature above 40 C. With the usual compositions known from the art, the crosslinking will often be carried out at a temperature close to 120 C for about 5 minutes. The finished products 27 leaving the furnace 26 can then be packaged in its container 28. The process according to the invention thus makes it possible to manufacture in series continuous pyrotechnic products composed of a cross-linked mortar and especially small-sized products, without the problem of " reactor life ", without solvent, and without undesirable plasticizers. The following examples illustrate certain possibilities of application of the invention. In these examples the following abbreviations have been used: PBHT = polybutadiene based mortar with hydroxylated endings, crosslinked by a polyisocyanate. PAG = mortar based on glycidyl polynitride with hydroxylated endings, crosslinked by an isocyanate. S.B.S = styrene / butadiene / styrene copolymer. S.I.S = styrene / isoprene / styrene copolymer. PE-PA = polyether / polyamide block copolymer 60/40. RDX = hexogen. PA = ammonium perchlorate. All the percentages indicated in the examples are percentages by weight; the percentages indicated for the mortar include the possible additives used.

Examples 1 to 3 Powder rods, cylindrical, multi-perforated, with 7 holes and 19 holes, were manufactured by the continuous process according to the invention, from the following three compositions: Composition 1 Composition 2 Composition 3 mortar PBHT: 9% PBHT: 10.5% PAGE: 13% load S.I.S: 6% PE-PA: 4.5% PE-PA: 7% thickener RDX load: 85% RDX: 85% RDX: 80% oxidant granulometry of the oxidant load 100 microns 150 microns 80 microns reductive load For a material temperature of 35 C during the extrusion, the following geometries were obtained: 7 holes 19 holes Composition 1 web (mm) 0.34 +/- 0.01 1.48 +/- 0.01 d (mm) 0.29 +/- 0.005 0.40 +/- 0.01 Composition 2 web (mm) 0.35 + / - JO., 01 * 1,51 +/- 0,01 d (mm) 3,30 '+/- 0,005 0,40 +/- 0,005 Composition 3 web (mm) 0,34 +/- 0,01 1.49 +/- 0.01 d (mm) 0.31 +/- 0.005 0.39 +/- 0.01 web = thickness to be burned, d = diameters of the holes.

Examples 4 to 6 Cylindrical propellant blocks, with a central channel, for small missile engines were manufactured by the continuous process according to the invention from the following three compositions: Composition 4 Composition 5 Composition 6 mortar PBHT: 10% PBHT: 12.2% PBHT: 10.5% polycarbonate load- black for car- Aluminum po-thickener no = 4% bonus (150m 2 / g: gray (80m2 / g: 1.8 %) 3.5%) PA load: 85% PA / 85% PA: 85% oxidant load Al: 1% Al: 1% Al: 1% reduction The mold was a cylindrical mold with an outer diameter of 30 mm and an internal diameter of 14 mm. On 20 meters of continuously extruded propellant, for each of the compositions, the dimensional variations obtained after cutting and hot crosslinking are the following: Example 4 Example 5 Example 6 outer diameter in mm 30.5 +/- 0.002 30.0 +/- 0.02 29.9 +/- 0.02 inner diameter in mm 13.8 +/- 0.003 13.9 + / - 0,02 14,05 +/- 0,02 length in mm 121 +/- 0,1 120,5 +/- 0,15 120,4 +/- 0,1 EXAMPLE 7 Compound explosive strips with a thickness comprised between 2 and 5 mm were manufactured from the following composition by means of the continuous process according to the invention: - mortar PBHT = 11% - thickener charge = SIS = 4% - Oxidizing charge: RDX (3 microns at 90 microns) = 85% meters of 90 mm wide tape, with thicknesses of 2, 3 and 5 mm, were continuously extruded. After the crosslinking of the mortar, the dimensional variation of the tapes was: thickness of thickness of extrusion extrusion extrusion 2 mm 3 mm 5 mm thickness in mm 1.98 +/- 0.01 2.95 +/- 0.015 4.99 +/- 0.02 width in mm 89.5 +/- 0.05 90.2 +/- 0.06 89.9 +/- 0.04 Example 8 They were manufactured, by the continuous process of according to the invention, propellant blocks for gas pyrotechnic generator from the following composition: - PBHT mortar 15.8% - thickener charge = SBS: 9.2% - oxidizing charge: PA (90 um, 15 um, 3 um): 73% - reductive load: Al = 2% The blocks had solid cylindrical shapes with the following dimensions: - diameter: 30 mm + 0.025 mm - width: 90 mm + 0.10 mm These blocks were taken to the test bench and the following results were obtained: - combustion rate at 13 MPa = 25.3 mm / s - pressure exponent = 0.35 It is noted that, in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects or substances to which it refers. Having described the invention as above, the content of the following is claimed as property.

Claims (11)

1. A continuous process for the manufacture, without solvent, of finished composite pyrotechnic products, where the outlet constituents comprise especially a liquid mortar which can be re-sealed at a temperature above 40 ° C and at least one solid oxidant energy charge, where the process is consists in particular of: i) mixing the initial constituents of the products so that a homogeneous composite paste is obtained, of sufficient viscosity to be able to preserve stable geometrical cuts; ii) bringing the paste obtained in this way to a form of intermediate products having geometric cuts of the finished products; iii) fixing the shape and composition of the intermediate products obtained in this way by crosslinking the mortar, where the process is characterized in that: iv) the initial liquid mortar is mixed from the beginning with a solid thickener load, in pulverulent form, so that a premix of a greasy consistency is obtained which is then mixed with the energy charges, v) the mixing and molding operations are conducted at a temperature lower than 40 C.

2. The process according to claim 1, characterized in that the solid thickener charge is constituted by a porous material, whose granulometry is comprised between 0.1 and 10 microns and whose specific surface 2 is comprised between 60 and 500 m / g.

3. The method according to claim 2, characterized in that the material is chosen from the group consisting of carbon black, colloidal silica, aluminum, titanium oxide, polynorbornene.

4. The process according to claim 1, characterized in that the solid thickener charge is constituted by a thermoplastic polymer with hydrocarbon domains which may comprise oxygen and nitrogen atoms, whose average molecular mass, by weight, is between 3 × 10 and 3x10

5. The method according to claim 4, characterized in that the thickening filler is selected from the group consisting of styrene / butadiene / styrene, styrene / isoprene / styrene, styrene / ethylene / butylene / styrene, styrene / ethylene / propylene copolymers. -log.

6. The method according to claim 4, characterized in that the thickener charge is chosen from the group consisting of the polyurethanes based on polyethers and polycarbonates, and the polyether / polyamide block copolymers.

7. The method according to claim 4, characterized in that the weight ratio between the thickener charge and the crosslinkable mortar is comprised between 10:90 and 50:50.

8. The method according to claim 2, characterized in that the weight ratio between the thickener charge and the crosslinkable mortar is between 0.05 and 0.25.

9. The method according to claim 1, characterized in that at least one solid reducing energy charge is used in addition to the solid oxidizing energy charges.

10. The method according to claim 9, characterized in that the reducing energy charge consists of aluminum or boron powder.

11. An installation for the application of the method according to any of claims 1 to 10, characterized in that it comprises, in the direction of progression of the material: i) a shearing mill consisting of two cylindrical rollers, grooved, of identical length, which carry grooves helical and whose axes are parallel and located in the same horizontal plane, and which are separated so as to leave a gap between the two rollers, which rotate in the opposite direction one with respect to the other; ii) a volumetric pump that drives the pre-mix consisting of the liquid mortar and the thickener load towards the entrance ends of the rolling mill material.; iii) at least one dosing hopper which, between the inlet end of the material and the exit end of the rolling mill material, pours the solid energy charges onto the rollers of the latter; iv) a granulation device for the homogeneous paste which is constituted in this way, which is located on the exit end of the laminator; v) an extruder in which the granules coming from the granulation device are collected; vi) a device for cutting intermediate products in the form of extruded rods emerging from the extruder; vii) a conveyor belt that ensures the transport and passage to a thermal oven of the intermediate products that are cut in this way.