IGNITION TUBE FOR A PROPELLER CHARGE

Description

Field of invention

[0001] The technical field of the invention is that of igniter tubes for propellant charges having a central (cylindrical) channel. State of the art

[0002] The propellant charges equipping shells and missiles are ignited by means of an igniter associated with an igniter tube. The igniter tube is formed of a fuel tube enclosing an ignition charge in the form of tablets and / or blocks arranged in the channel of the fuel tube; these tablets or blocks are removable and do not adhere to the fuel tube. The igniter tube thus formed is arranged in the channel of the propellant charge.

[0003] The composition of the ignition powder is most frequently black powder (NP) consisting of a mixture of potassium nitrate (saltpeter), charcoal and sulfur. There are also other compositions of ignition powder, in particular of the type: Boron / KNO 3 , in a ratio generally of 70 / 30 (% by mass), a metal (for example iron, aluminum, zinc), an oxidant of the perchlorate type (for example potassium perchlorate) or of the fluoropolymer type (for example PTFE (Teflon ®< ) or Viton ®< ). The ignition charges (tablets and / or block(s)) described in the prior art consist of an agglomerated ignition powder, possibly with a cellulose binder. In the latter case, the ignition charge is obtained by mixing the constituents of the ignition powder with a collodion (solvent + binder), followed by evaporation of the solvent from the collodion.The ignition charge usually called Bénite is black powder agglomerated with a nitrocellulose binder.

[0004] Patent application FR-A-2 593 905 describes an ignition charge arranged in a fuel tube consisting of a stack of agglomerated ignition powder tablets. These assemblies for igniter tubes require on the one hand the manufacture of agglomerated powder tablets, and on the other hand their placement in the fuel tube.

[0005] We therefore understand that the ignition charge, placed in the fuel tube, is made of a pyrotechnic material based on an agglomerated powder.

[0006] To ensure that the fuel tube (with a lower combustion speed than the ignition charge) does not shield the combustion gases from the ignition powder, combustible covers are distributed along the length of the tube. These combustible covers, about ten microns thick, rupture with the increase in pressure in the tube generated by the combustion of the ignition charge. Thus, the hot gases generated by the ignition powder can reach, from the start of ignition, the parts of the propellant charge located near the openings resulting from the rupture of the covers.

[0007] The prior art powder tablet-based ignition charges (familiar to those skilled in the art) have several drawbacks (which those skilled in the art are aware of).

[0008] First of all, the operation of filling the fuel tube with the ignition charge is a delicate operation, in reference to both the handling technique and the pyrotechnic risk (the ignition powder is classified in risk division 1.1 within the meaning of the UN GHS classification (UN Globally Harmonized System of Classification and Labeling of Chemicals). This operation requires special tools to be automated. In addition, when the ignition charge is introduced into the tube mixed with a collodion to obtain ( in situ ) of tablets, the evaporation time of the collodion solvent is long due to the confinement of the loaded collodion in the tube.

[0009] Then, the fuel tube has a length equivalent to that of the propellant charge channel, but the ignition charge occupies a volume related to its mass. The mass of the charge can vary according to the ignition specifications and / or the nature of the powder. The volume of the ignition charge specified for ignition can be less than that of the propellant charge channel. The ignition of the propellant charge is therefore not always homogeneous in the tube, and therefore synchronous over the length of the channel. This deviates from the ideal conditions of quasi-instantaneous ignition of the entire (internal) surface of the propellant charge.

[0010] Finally, it is sometimes necessary to dismantle the igniter tube of a propellant charge, for example when disposing of ammunition or its neutralization. This dismantling of the igniter tube involves extracting the ignition charge arranged in the fuel tube. This extraction by direct contact with the agglomerated powder generates a pyrotechnic hazard.

[0011] Patent application FR-A-2 725 781 proposes replacing the agglomerated powder tablets with an ignition material comprising an ignition composition in powder form (typically black powder) deposited on a flexible support sheet, which is then advantageously rolled up on itself in order to be inserted into a combustible tube to form an igniter tube. In order for the powder (which is just placed on the flexible support) not to fall to the bottom of the igniter tube, it is imperative to coat the powder composition with another flexible sheet (called a screen sheet), at least one of the screen and support sheets being coated with glue.

[0012] This method allows for a better distribution of the powder charge in the ammunition channel and facilitates the disassembly of the ignition material compared to agglomerated powder ignition material. The ignition material described in patent application FR-A-2 725 781 therefore offers a technical solution to the problems posed by ignition materials based on powder tablets.

[0013] However, its implementation is complex due to the handling of the explosive ignition powder classified in risk division 1.1, the control of the regularity of the quantities of powders deposited in piles on the flexible sheet and the geometries of the piles, the step of covering the piles of powders deposited on the flexible sheet by the sticky screen sheet. To the knowledge of the applicant, the method described has not been developed and industrialized since the publication of the application in 1994.

[0014] In terms of the materials used, the flexible sheet and the screen sheet are made of paper, nitrated paper, fabric, plastic or aluminum. These materials do not contribute significantly to the energy input of the ignition charge. The spatial distribution of the ignition energy of the charge is obtained solely by the distribution and volume of the powder piles. It is not envisaged to vary the composition of the ignition material to optimize the spatial distribution of the energy of the ignition charge. The configuration possibilities in terms of level and the spatial energy distribution of the pyrotechnic objects of patent application FR-A-2 725 781 are therefore limited and controlled solely by the mass and spatial distribution of the powder piles.

[0015] US4922823A discloses an igniter tube for a central channel propellant charge with an igniter charge in the form of a geometric pattern on the inner face.

[0016] It would therefore be useful to have an ignition charge that could be produced simply on an industrial scale and that would allow for great modularity in the level and spatial distribution of the ignition energy. The present invention aims to meet these specifications. Summary of the invention

[0017] The present invention relates to a central channel (cylindrical) propellant charge igniter tube according to claim 1, a method of preparing said igniter tube according to claim and a propellant charge comprising the igniter tube according to claim 12. The igniter tube comprises a fuel tube on the inner face of which an ignition charge is deposited. Brief description of the figures

[0018] There figure 1 represents a first variant of the process of depositing an ignition charge inside a fuel tube. The figure 2 represents a second variant of the process of depositing an ignition charge inside a fuel tube. The Figure 3A illustrates the circular deposition of a triangular section ignition charge in a fuel tube. The Figure 3B illustrates the linear deposition of a triangular section ignition charge in a fuel tube. Figure 3C illustrates the triangular section helical deposition of an ignition charge in a fuel tube. The figure 4 represents an ignition charge in the form of a helical pattern arranged in a fuel tube. The Figure 5 illustrates a fuel tube provided, on its internal face, with an ignition charge in the form of a helical ribbon. Description of the invention

[0019] The present invention relates, according to a first aspect, to a central channel (cylindrical) propellant charge igniter tube, said igniter tube comprising (consisting of) a combustible tube, made of a combustible material (having the appearance of a felt), comprising a cellulose ester, preferably nitrocellulose, on the internal face of which an ignition charge is deposited and adheres.

[0020] The ignition charge is deposited (adherently) on the internal face of the fuel tube, in the form of geometric patterns spaced along the length of said tube. The ignition charge contains as its main constituent at least one ignition powder agglomerated with a cellulose binder (not all the patterns necessarily contain the same powder), said ignition powder being a powdery granular material comprising an inorganic oxidizing compound. It is obtained by drying a collodion loaded with ignition powder deposited on the internal face of the tube.

[0021] To ensure easy insertion and extraction of the fuel tube from the propellant charge (during disassembly for example), the ignition charge does not conveniently cover the axial ends of the internal face of the tube, which thus leaves a free height to grip the tube without contact with the ignition charge.

[0022] Conventionally, the tube receives at each of its ends a cover (commonly called a straw) acting as a stopper. The covers (stoppers) are made of a combustible material generally identical to that of the tube.

[0023] The combustible materials constituting the fuel tube and the ignition charge must be chemically compatible and have the property of adhesion to each other. For this purpose, they have a common cellulose ester base, such as cellulose nitrate, cellulose acetate or nitrocellulose. Nitrocellulose is the preferred common base and is retained, in a non-limiting manner, in the remainder of the description.

[0024] In one embodiment, the fuel tube, such as those marketed by the company Eurenco, is made up of 60% to 80% by mass of cellulose ester, 17% to 37% by mass of cellulose, 3% to 7% by mass of resin and 0% to 2% by mass of stabilizing additive (the sum of these different constituents being equal to 100%). Its mass is approximately 15 g to 25 g. The fuel tube has a height of approximately 120 mm to 140 mm, for an internal diameter of 25 mm to 30 mm and a thickness of 1.5 to 2.5 mm.

[0025] Advantageously, the fuel tube has the composition given in Table 1 and the dimensions given below. Table 1 Composition % by mass Nitrocellulose powder cotton 69 Cellulose 25 Resin 5 Stabilizing additive 1

[0026] The mass of the fuel tube is 18 g + / - 3 g. The tube has a height of 126 mm, an internal diameter of 28 mm and a thickness of 1.8 mm.

[0027] In one embodiment, the ignition charge is obtained by drying a collodion (solvent + binder) loaded with an ignition powder. The ignition powder is a conventional ignition powder used for the ignition of propellant charge. The ignition powder is a powdered granular material classified in hazard division 1.1 within the meaning of the UN GHS classification (UN Globally Harmonized System of Classification and Labeling of Chemicals). The grains of the ignition powder comprise an inorganic oxidizing compound such as KNO 3 or KClO 4 , and are typically composed of such an inorganic oxidizing compound and a reducing compound forming an agglomerated mixture. These fast-burning, high-heat ignition powders are therefore not cellulosic materials such as a dried composite material based on nitrocellulose and nitroglycerin.Examples of ignition powder compositions are given in Table 2 below. Table 2 Ignition powder: constituents Chemical formulas Boron / potassium nitrate B / KNO 3 Aluminum / potassium perchlorate Al / KClO 4 Magnesium / Teflon ®< -Viton ®< Mg / PTFE- TV Zirconium / barium chromate Zr / BaCrO 4 Aluminum / Copper Oxide Al / CuO Black powder S / Charcoal / KNO 3 Magnesium / Sodium Nitrate / Potassium Nitrate Mg / NaNO 3 / KNO 3 Zirconium / lead chromate Zr / PbCrO 4 Zirconium-nickel / potassium perchlorate-barium nitrate ZrNi / KClO 4 -Ba(NO 3 ) 2 Cesium decahydroborate / potassium nitrate Cs 2 B 10 H 10 / KNO 3

[0028] The powder used is preferably black powder (NP) with mass composition: potassium nitrate (saltpeter): ~ 75% charcoal: ~ 15% sulfur: ~ 10%.

[0029] Black powder (NP) is conventionally classified according to an index relating to its particle size (see table 3 below). Table 3 Hint Refusal ≤ 3% Refusal ≥ 95% In the sieve In the colander In the sieve In the colander PN1 7.10 mm 10.00 mm 4.00 mm 5.00 mm PN2 4.50 mm 5.75 mm 2.50 mm 3.00 mm PN3 2.80 mm 3.20 mm 1.00 mm 1.40 mm PN4 1.25 mm 1.6 mm 0.71 mm 1.00 mm PN5 1.00 mm 1.25 mm 0.63 mm 0.80 mm PN6 0.80 mm 1.00 mm 0.45 mm 0.50 mm PN7 0.50 mm 0.60 mm 0.10 mm 0.10 mm

[0030] Fine-grained powders, such as PN5, PN6 or PN7, are best suited to the invention. A fine grain size ensures better dispersion of the powder in the collodion.

[0031] The collodion used in the context of the invention is of the cellulose ester base + solvent(s) type. In one embodiment, the cellulose ester base of the collodion consists of a cellulose ester (for approximately 70% to approximately 90% by mass) and generally additionally contains, conventionally, at least one plasticizer (approximately 1% to approximately 20% by mass, preferably approximately 10% by mass) and at least one stabilizer of the cellulose ester (approximately 0.5% to approximately 5% by mass). It also generally contains at least one additive (>0% to approximately 1% by mass), for example chosen from anti-adhesion agents, anti-glare agents, antioxidants. It is likely to contain a residual quantity of solvent(s), in particular phlegmatization solvent(s) or (and) solvent(s) for dissolving the cellulose ester used during its manufacture.

[0032] Advantageously, the cellulose ester used as the major component is selected from cellulose nitrate, cellulose acetate or nitrocellulose, the latter being preferred. The nitrogen content by mass of the nitrocellulose is suitably 10.5% to 13.5%, an example being grade E nitrocellulose with a nitrogen content by mass of 11.8% to 12.3%, advantageously equal to 12%.

[0033] The plasticizer used to prepare the collodion can be, in particular, a ketone (such as camphor), a vinyl ether (such as LUTONAL ®< A50 marketed by BASF), a polyurethane (such as NEP-PLAST 2001 marketed by Hagedorn-NC), an adipate (such as dioctyl adipate) or a citrate (such as triethyl 2-acetyl citrate).

[0034] The stabilizer used to prepare the collodion may be, in particular, a compound whose chemical formula includes aromatic nuclei (opportunely two aromatic nuclei), capable of fixing nitrogen oxides from the decomposition of nitric esters (presently nitrocellulose). Examples of stabilizers include 2-nitrodiphenylamine (2NDPA), 1,3-diethyl-1,3-diphenyl urea (centralite I), 1,3-dimethyl-1,3-diphenyl urea (centralite II), and 1-methyl-3-ethyl-1,3-diphenyl urea (centralite III).

[0035] The optional additive used to prepare the collodion may be selected from, among others, anti-adhesive agents, such as silicone-type anti-adhesive agents, anti-glare agents, antioxidants, colorants, surfactants, anti-caking agents and hydrophobic agents.

[0036] The solvent can be a double solvent of the acetone / butyl acetate (AB) type at 50% / 50% by mass.

[0037] Collodion is advantageously formulated to result in a dry extract (after evaporation of the solvent) of 10% to 40%, by mass.

[0038] Table 4 below shows a formulation of collodion at 14% dry extract by mass. Table 4 Collodion Composition (% by mass) Cellulose ester base Nitrocellulose 84 14 Plasticizer 10 Stabilizing 3,5 Others (additive(s), water, solvent, etc.) 2,5 Total 100 AB 43 Acetone 43 Total 100

[0039] In one embodiment, the collodion loaded with ignition powder(s) comprises about 50% to about 70% by mass of powder(s), and the balance to 100% (i.e., about 30% to about 50% by mass) of collodion. Conventionally, the ignition powder(s), previously constituted, is (are) added to the collodion.

[0040] The collodion loaded with ignition powder is advantageously obtained by adding the ignition powder, previously constituted, to the solvent. It is then called "Bénite B". It differs from those of the prior art, designated "Bénite", obtained by separate additions to the collodion of the constituents of the ignition powder and without plasticizer.

[0041] Table 5 below gives an example of collodion composition from Table 4, loaded with PN7 ignition powder. Table 5 Raw materials Mass (g) Composition (% by mass) PN 7 10,36 56 Collodion 8,14 44 Total 18,5 100

[0042] Collodion charged with ignition powder is classified in hazard division 1.4 according to the UN GHS classification (UN Globally Harmonized System of Classification and Labeling of Chemicals). The hazard zones to be taken into account when handling charged collodion are therefore reduced, which facilitates the operations of depositing the collodion on the tube.

[0043] After drying (evaporation of the solvent) of the charged collodion, the (dry) ignition charge adheres to the internal surface of the fuel tube and comprises approximately 88% to approximately 92% by mass of ignition powder(s), approximately 7% to approximately 10% by mass of cellulose ester, the remainder to 100% being provided by at least one compound chosen from a plasticizer, an additive and a residual solvent. For information purposes, the dry ignition charge obtained after drying (evaporation of the solvent) of the collodion of Table 5 contains the mass ratios indicated in Table 6 below. Table 6 Composition Benite B dry Mass (g) % by mass PN7 10,36 90,08 Nitrocellulose 0,96 8,35 Plasticizer 0,11 0,96 Stabilizing 0,04 0,35 Residues (water, solvent, etc.) 0,03 0,26 Total 11,50 100,00

[0044] According to a second aspect, the present invention relates to a method for preparing an igniter tube by (direct) deposition by extrusion of the collodion loaded with ignition powder on the internal face of a fuel tube.

[0045] In one embodiment, the surface of the tube intended to receive the deposit can be, if necessary, prepared by sanding prior to the deposition of the collodion. Such a step can promote the adhesion of the paste to the tube during deposition.

[0046] In one embodiment, the collodion deposition inside the tube is carried out by means of a telescopic rod 1 equipped at its end with at least one nozzle 3.In a tank, the collodion is conditioned by temperature. The collodion passes through a die of determined dimensions. The collodion is conveyed through the die by applying pressure. This pressure determines the flow rate. The die is extended by the rod equipped with one or more extrusion nozzles. Several extrusion nozzles may be used on the same manufacturing tool in order to be able to combine several formulations successively or simultaneously within the same load. The nozzle(s) can make several passes over the same deposition zone. 2 to superimpose layers and increase the local thickness and therefore the mass of the ignition charge. According to a first variant (see figure 1 ), the tube is stationary and the collodion deposits on the internal face of the tube are made by moving the nozzle. According to a second variant (see figure 2), the tube is mounted on a rotating and axially moving lathe, the nozzle then being stationary. The deposition process according to these two variants is easily industrializable. Once the collodion is deposited, it is left to dry (by evaporation of the solvent) to obtain an igniter tube in which the ignition charge adheres to the internal surface of the fuel tube.

[0047] The method according to the invention makes it possible to envisage any geometry and arrangement of the ignition charge on the internal face of the fuel tube, provided that this leads to the correct ignition of the ignition charge.

[0048] Advantageously, the ignition charge is deposited in the form of spaced point patterns, or spaced circular patterns along the length of the tube, or linear patterns along the length of the tube, or one or more helical patterns along the length of the tube. The deposits are not all necessarily identical in dimensions and / or composition and are not all necessarily arranged regularly. The number of deposits, their geometry, their arrangements constituting the ignition charge in the tube are parameters for adjusting the ignition charge.

[0049] In one embodiment, each pattern contains a substantially identical amount of ignition powder(s) (of the order of approximately 90% by mass). In another embodiment, the patterns deposited on the internal face of the fuel tube do not all contain the same amount of ignition powder(s), the amount of ignition powder(s) in each pattern being in the proportions indicated above (approximately 88% to approximately 92% by mass).

[0050] THE Figures 3A , 3B and 3C illustrate different geometries of the above-mentioned patterns (circular pattern, linear pattern, helical pattern), said patterns advantageously having a triangular section. An ignition charge in the form of one or more helical patterns is particularly advantageous in terms of ease of deposition and distribution of the charge in the tube.

[0051] The preferred geometry consisting of a helical pattern of an ignition charge deposited in a tube with an internal diameter of 2.8 cm and a length of 12.6 cm according to the invention is indicated below, by way of illustration (in no way limiting), for an equivalent of a total volume of ignition charge of approximately 10 g in a solid block (prior art) (see figure 4 ). Helical diameter of the pattern: d = 2.8 cm Axial length of the pattern: h = 10 cm Pitch of the helix: = 2 cm Number of turns n = 5 Length of the pattern = 45.1 cm Geometry of the section of the pattern: semi-circular Base length of the section = 0.6 cm Radius of section: 0.3 cm Sectional area of the pattern: 0.14 cm 2< Volume of the pattern: 0.14 x 45.1 = 6.3 cm 3< Density ~ 1.6 g / cm 3< Mass of the pattern + 10 g.

[0052] Tests on the deposition of collodion loaded with ignition powder were carried out on the internal face of a tube (see Figure 5 ) by means of a device as described in figure 2 The collodion was dried at room temperature for about 2.5 hours (this time can be greatly reduced by drying under hot air flow, for example at about 80°C). During this drying, the assembly (tube + ignition charge) was manipulable. The deposit after drying had a mass of about 10 g. It was regular in a helical pattern of 10 cylindrical turns of about 0.3 mm in diameter, and adhered perfectly to the internal surface of the tube.

[0053] According to a third aspect, the present invention relates to a propellant charge comprising an igniter tube as defined above.

[0054] The present invention has the advantage that, whatever its mass, the ignition charge can be distributed evenly over the internal face of the fuel tube (this ensures homogeneous ignition in the tube).

Claims

1. An igniter tube with a central channel consisting of a combustible tube, made of a combustible material comprising a cellulose ester, on the inner face of which an ignition charge is deposited in the form of geometric patterns spaced apart along the length of said combustible tube, and adheres to said combustible tube, said ignition charge comprising 88 wt% to 92 wt% of ignition powder(s) and 7 wt% to 10 wt% of cellulose ester, said ignition powder being a powdered granular material comprising an inorganic oxidant compound.

2. The igniter tube according to claim 1, wherein the ignition charge further comprises at least one compound chosen from a plasticiser, an additive and a residual solvent.

3. The igniter tube according to any one of claims 1 to 2, wherein the ignition powder is gunpowder.

4. The igniter tube according to any one of claims 1 to 3, wherein the cellulose ester of the ignition charge is nitrocellulose.

5. The igniter tube according to any one of claims 1 to 4, wherein the combustible tube comprises 60 wt% to 80 wt% of cellulose ester, 17 wt% to 37 wt% of cellulose, 3 wt% to 7 wt% of resin and 0 wt% to 2 wt% of stabilising additive.

6. The igniter tube according to any one of claims 1 to 5, wherein the ignition charge is deposited on the inner face of the combustible tube and along the length thereof, in the form of circular patterns.

7. The igniter tube according to any one of claims 1 to 5, wherein the ignition charge is deposited, on the inner face of the combustible tube and along the length thereof, in the form of linear patterns.

8. The igniter tube according to any one of claims 1 to 5, wherein the ignition charge is deposited, on the inner face of the combustible tube and along the length thereof, in the form of helical patterns.

9. A process for preparing an igniter tube according to any one of claims 1 to 8, which comprises depositing by extrusion a collodion loaded with an ignition powder on the inner face of the combustible tube, and drying the deposited collodion, said collodion loaded with ignition powder comprising 50 wt% to 70 wt% of ignition powder and 30 wt% to 50 wt% of collodion.

10. The process according to claim 9, wherein the collodion comprises 70 wt% to 90 wt% of cellulose ester, 1 wt% to 20 wt% of at least one plasticiser, 0.5 wt% to 5 wt% of at least one stabiliser of the cellulose ester and, optionally, up to 1 wt% of at least one additive.

11. The process according to claim 10, wherein the cellulose ester is nitrocellulose.

12. A propellant charge comprising an igniter tube according to any one of claims 1 to 8.