EP1072859B1 - Method of placing fibres in a container - Google Patents

Description

The technical field of the invention is that of processes for placing fibers of length less than 10 mm in a case, especially for make a munition dispersing such fibers, by example to ensure masking or decoy in the infrared and / or millimeter range.

We already know, in particular by patent US5659147, ammunition used to disperse carbon fibers or aluminized glass fibers. This ammunition is used for close defense aircraft or armored vehicles against the threat of missiles with radar seeker operating in the millimeter band (frequencies from 17 to 94 Ghz and more particularly from 35 to 94 GHz).

The main problem encountered with such ammunition is that of ensuring optimal filling of the ammunition with a maximum of fibers having a length scaled down. In fact, the length of the fibers to be dispersed must be less than 10mm to ensure the effectiveness of the masking in the desired wavelength band.

The length of the fibers to be dispersed must be the same order of magnitude that the wavelength of the radiation at mask, i.e. fibers from 3 to 6 mm for masking in the millimeter range (infrared masking is also provided by carbon fibers due to the absorption of radiation by these. last).

Generally the filling of ammunition is carried out by placing in bulk in the case. We do not provide thus an optimal filling of the case and the reproducibility of ammunition performance is not assured since the mass and / or distribution of the fibers may vary from ammunition to another.

We also know of ammunition in which the short fibers (aluminized glass fibers) are stored in small diameter pancakes (less than 40mm for fibers of length greater than or equal to 5mm). Such a solution improves the loading density.

The patent US5179778 thus describes a method of setting place fibers in an ammunition case. This process puts using a sleeve which is pulled with force important to ensure radial compaction of the fibers in a strand. A cutting of the strand into patties is then performed.

This process is complex and there is no guarantee that fibers will remain integral with the slabs thus cut, especially when the diameter of the pancakes is greater than 40mm, that their thickness is between 3 and 7 mm and that they have recesses to set up one or more pyrotechnic dispersion charges.

It is the object of the invention to propose a method allowing to overcome such drawbacks.

The method according to the invention thus allows in a way simple and inexpensive to ensure the establishment in a case of short fibers (less than 10mm) and in the form wafers whose diameter can be large (greater than 40mm) patties which may include recesses.

• on réalise au moins un regroupement de fibres longues en au moins un toron,
• on imprègne le ou les torons avec un matériau solidifiable à une première température,
• on dispose le ou les torons ainsi imprégnés dans un moule,
• on solidifie le ou les torons placés dans le moule en le portant à la première température,
• on découpe le ou les torons à l'état solidifié obtenus en au moins deux galettes ayant chacune pour épaisseur la longueur souhaitée pour les fibres,
• on élimine le matériau solidifiable en portant les galettes à une deuxième température avant ou après mise en place des galettes dans l'étui.

Thus, the subject of the invention is a method of placing fibers of length less than 10 mm in a case, in particular of ammunition, method comprising the following steps:

• at least one group of long fibers is produced in at least one strand,
• the strand (s) are impregnated with a solidifiable material at a first temperature,
• the strand or strands thus impregnated are placed in a mold,
• the strand (s) placed in the mold are solidified by bringing it to the first temperature,
• the strand (s) in the solidified state obtained are cut into at least two wafers each having a thickness the desired length for the fibers,
• the solidifiable material is removed by bringing the pancakes to a second temperature before or after placing the pancakes in the case.

The solidified strand can be cut when it is in the mold, the mold having notches allowing the passage of a means cutting.

Alternatively, the solidified strand can be removed of the mold then surround the strand thus solidified with a retaining sheath before cutting the strand into patties.

The mold may include an imprint semi-cylindrical to give the solidified strand a half cylinder shape and then we will do everything first at least two identical strands that we then assemble in a single retaining sheath cylindrical.

The mold may include a cover comprising a semi-cylindrical profile allowing to arrange a half channel cylindrical axial on the solidified strand.

An axial channel can be made by drilling the strand or solidified pancakes.

After completion of the axial channel in the strand solidified and before cutting, we can advantageously have inside the axial channel a tube filled with the same impregnation material and in the state solidified.

The retaining sheath may be constituted by a heat-shrink tubing or by an envelope metallic.

In this case, the metal envelope may be a sieve with a mesh width of less than 140 micrometers.

The metal envelope can be made from a sheet wrapped around the strand and welded edge to edge.

The grouping of long fibers in strand can be made by winding a long fiber between two studs secured to a support.

Alternatively, the grouping of long fibers into strand can be made by winding on itself unidirectional fabric.

The solidifiable material may be water or carry water.

The solidifiable material may have a point of solidification above 0 ° C and a melting point or boiling below 150 ° C. It could be constituted with a wax.

The fibers will be carbon fibers or else glass fibers covered with a conductive material by for example aluminum, or organic fibers conductive.

• la figure 1 représente en coupe longitudinale une munition obtenue avec le procédé selon l'invention,
• la figure 2 représente en perspective un outillage de réalisation d'un toron selon un mode particulier de réalisation de l'invention,
• la figure 3 représente en coupe transversale un premier exemple de moule utilisé dans une mode particulier de réalisation de l'invention,
• la figure 4a représente en coupe transversale un deuxième exemple de moule utilisé dans une mode particulier de réalisation de l'invention,
• la figure 4b est une variante de réalisation du moule selon la figure 4a,
• la figure 5 représente en perspective un mode particulier de réalisation d'un toron,
• la figure 6 schématise la succession des principales étapes du procédé selon l'invention,
• les figures 7 et 8 représentent un troisième exemple de moule utilisé dans une mode particulier de réalisation de l'invention, la figure 7 étant une coupe transversale de ce moule suivant le plan repéré BB sur la figure 8, la figure 8 étant elle même une coupe longitudinale de ce moule suivant le plan repéré AA sur la figure 7.

The invention will be better understood on reading the description which follows of particular embodiments, description made with reference to the appended drawings and in which:

• FIG. 1 represents in longitudinal section an ammunition obtained with the method according to the invention,
• FIG. 2 represents in perspective a tool for producing a strand according to a particular embodiment of the invention,
• FIG. 3 shows in cross section a first example of a mold used in a particular embodiment of the invention,
• FIG. 4a represents in cross section a second example of a mold used in a particular embodiment of the invention,
• FIG. 4b is an alternative embodiment of the mold according to FIG. 4a,
• FIG. 5 shows in perspective a particular embodiment of a strand,
• FIG. 6 diagrams the succession of the main steps of the method according to the invention,
• Figures 7 and 8 show a third example of a mold used in a particular embodiment of the invention, Figure 7 being a cross section of this mold along the plane marked BB in Figure 8, Figure 8 being itself a longitudinal section of this mold along the plane marked AA in FIG. 7.

Referring to Figure 1, a munition 1 obtained with the method according to the invention comprises a case 2, prefragmented or not, which is made for example in a plastic material such as plexyglas, polycarbonate or polyethylene and which is integral with a base 3, by metal example. The base is intended to allow the fixing the ammunition on a launch system known type and not shown.

This launch system can for example be worn by an aircraft or by a land vehicle. he will conventionally include a guide tube for the ammunition and an ejection piston which will be pushed by a gas generating charge.

The case 2 contains a stack of pancakes 4 of carbon fibers.

Each wafer 4 has a thickness of less than 10mm and the fibers are arranged all parallel to each other others in each cake. The fibers have a diameter of about 7 micrometers and they have a length equal to the thickness of the wafer. Preferably, wafers whose thickness will be between 3mm and 6mm.

Each wafer is surrounded by an outer sheath 5 which maintains the fibers. This sheath is made in plastic or metal. We could for example use heat shrinkable plastic. We will choose a heat shrink tubing defined to have a diameter after shrinking equal to that of the wafer and of which the shrinking temperature will be lower than the fiber decomposition temperature (below 150 ° C).

We can also use a sheet or fabric stainless steel 20 to 140 micrometers thick. The mode installation of the sheath and realization of pancakes will be described later.

As a variant, the sheath 5 could be omitted at condition to follow another mode of implementation described also thereafter.

Each wafer has an axial hole and the stack des- patettes 4 thus delimits an axial channel 6 to inside which is placed a cardboard tube 7 (or plastic) filled with a pyrotechnic charge of dispersion 8.

Alternatively each wafer could carry a portion of tube (washer) the juxtaposition of different washers forming the tube 7.

The dispersion load 8 is constituted for example by a pyrotechnic composition combining Aluminum and potassium perchlorate (Al / KClO4) in the proportions respective by mass of 20 to 30% of aluminum for 80 to 70% KClO4 (preferred proportions 24% aluminum for 76% perchlorate).

A fragmentable cover 9, for example in material plastic, close the case 2. The cover is returned secured to case 2 by gluing its rim device 10 on the outer cylindrical surface of the case. The cover could also be made of a single piece with case.

The base 3 carries a conventional ignition means 11 which is not described here in detail and which will include example a delay (pyrotechnic or electronic) which is intended to be triggered when the ammunition is fired and a inflammatory composition ensuring ignition of the charge dispersion pyrotechnics 8.

The gas pressure following the ignition of this charge causes the case 2 to burst and disperse fibers constituting the pancakes.

This generates a cloud of fibers ensuring masking in the millimeter and / or infrared range (or another function for example short circuits electric). A decoy ammunition may be made up using carbon fibers instead reflective flakes, for example filaments aluminum.

The external diameter of the pancakes is of the order of 70mm, the diameter of the axial channel 6 is around 15mm (it will vary depending on the nature of the case and the amount of charge 8 that is needed to break this case and scatter the fibers).

It is thus possible to group in each cake 4 nearly 88 million fibers 6mm long. With a stack of 100 mm high patties in a single munition almost 1.5 billion fibers.

Fiber storage is perfectly uniform and symmetrical the surface density of fibers is around of 24,000 fibers per square millimeter.

Such ammunition allows reliably and reproducible the generation of a cloud of dimensions important. We thus obtained by way of example a cloud 2 m in diameter with 40mm ammunition in diameter and 60mm long.

As a variant, it is also possible to replace the carbon fibers by covered glass fibers aluminum or aluminized or fiber tapes organic conductive or based on conductive polymer.

Such ammunition will be produced by implementing the method according to the invention.

The process will now be described with reference mainly in Figure 6 which schematizes the different stages leading to ammunition.

In a step A we first make a strand 12 fibers (carbon or aluminized glass or a aluminized organic material) parallel to each other. The strand must have an equal number of fibers in section the number of fibers desired in a section of ammunition.

This strand 12 can be produced for example by winding continuous of a single fiber between two pads. Figure 2 thus represents a tool 13 making it possible to produce a such winding.

The tool 13 includes a flat support 15 on which two cylindrical studs 14a, 14b are fixed. A fiber 16 is wound between the two studs with a machine winding (not shown). Alternatively we can fix the support 15 in one turn to allow winding fiber.

The spacing of the studs 14a / 14b makes it possible to define the length of the strand 12. The strand will be given a length compatible with the capabilities of the winding machine. We may if it is not too large, give the strand a length at least equal to the height of the stack of pancakes that we are trying to make.

We can also, if the length of the ammunition is too large, make several strands which will be then cut (with the process described below) to make the patties. We will then associate the number of wafers suitable for obtaining a length ammunition given.

It is thus possible to carry out in a precise manner a strand 12 having a given length and comprising the number of fibers desired.

For example, for an ammunition intended to receive 12 wafers 40 mm in diameter and 5 mm thick and containing 24,000 fibers of 7 micrometers in diameter per mm ² , it is possible to wind 322 m of fiber between two studs spaced 140mm. The number of wafers obtained with such a strand is greater than 15, only 12 wafers will be retained for the munition.

The strand 12 can also be produced by winding of a unidirectional fiber fabric. In one such a fabric well known to the skilled person the fibers are all parallel and they are interconnected in the fabric by nylon threads which are perpendicular to them and which provide low mechanical strength in the direction perpendicular to the fiber.

FIG. 5 thus shows a strand 12 in the process of realization by winding around an axis 17 of a sheet 18 of a fabric comprising carbon fibers (or aluminized glass) oriented parallel to axis 17.

We will roll up for example 150m to 200m of a fabric 7 micrometers carbon fiber unidirectional diameter to make a strand having the same density as that of the previous example.

Referring to Figure 6, the second step of the process (step B) is an impregnation of the strand 12 with a material 19 solidifiable at a first temperature.

The material may advantageously be water. he may alternatively be a wax or a material organic with low melting or evaporation point.

The impregnation is carried out by dipping the strand 12 in a tank 20 filled with the impregnation material 19.

In the third step (step C) we lay the strand 12 thus impregnated in a mold 21.

As a variant and to simplify the step of winding, we can make several strands which will then juxtaposed in the same mold.

Figure 3 shows a first embodiment of a such mold. This mold includes two shells 22a and 22b which position themselves precisely in relation to each other by means of grooves 23 and tabs 24.

The shells 22a and 22b define a cavity cylindrical 25 whose diameter is the desired diameter for the pancakes 4.

The mold will be made for example of aluminum.

When the initial strand is made by winding, preferably adopt a mold whose cavity 25 will have a length greater than the total length desired for stacking pancakes. So the ends of the strand where the fibers were wound on the pads 14 may be withdrawn. This ensures good homogeneity of the loading of fibers over the entire length of the ammunition.

We can also make several more strands shorter than the desired length for stacking. We will thus facilitate subsequent cooling of the strand and cutting the patties. The number of wafers desired will be obtained with several strands and will then be stacked in the ammunition.

In step D (FIG. 6), the mold 21 is placed in a enclosure 26 allowing it to be brought to a first temperature T1 which is less than or equal to the solidification temperature of the impregnation material 19.

For impregnation with water we will wear the mold at a temperature T1 of the order of -30 ° C.

The enclosure will be constituted by a type freezer conventional or any other cooling system. Alternatively, the mold 21 can be immersed in liquid nitrogen.

According to a first mode of implementation of the invention, the solidified strand is removed from the mold and surrounds it (step E1) with a retaining sheath 5.

This retaining sheath will preferably be constituted by a metal envelope made from a sheet 27 of a stainless steel sieve from 20 to 140 micrometers thick. The side of the nominal mesh of this sieve may vary between 30 and 210 micrometers. The sheet is wrapped around the strand and it is welded edge to edge (for example laser or tinning) so as to form a sheath 5. It is also possible use a heat-sealable aluminum film.

The function of the sheath 5 is to ensure the maintenance peripheral fibers during the operations of cutting patties 4 as will be described by after. It will however be chosen thin enough to do not disturb the dispersion of the fibers during ammunition operation.

As a variant, we can use to realize the sheath 5 a heat-shrinkable plastic material, by example a Kynar type heat shrink tubing (brand registered) offered by the company Raychem and whose shrinking temperature will be chosen below 150 ° C.

In step E1, a machining of a axial channel 6 (by means of a turn).

After machining the axial channel 6, we will have inside this tube 28 filled with material impregnation 19 in the solidified state.

This tube (cardboard or plastic) will function of ensuring the maintenance of fibers at the level of axial channel and during cutting operations wafers 4 as will be described later.

Of course we will avoid during operations (handling, welding, drilling) excessive heating of the strand 12 likely to lead to its decohesion.

It will suffice to regularly plunge the strand into liquid nitrogen to keep it in good condition solidified.

We proceed to step F to cut into patties 4 of the strand 12 fitted with its sheath 5 and tube 28.

The thickness of the wafers will be less than 10mm and preferably between 3 and 6 mm.

The cutting is carried out using for example a grinder 29 (or by laser cutting). We will maintain the temperature of the strand at a low level in order to avoid decohesion of the fibers.

For this we can make a cut under water and / or periodically cool the strand by immersed in liquid nitrogen.

Once the patties 4 cut, we place them (step G) in an oven 30 brought to a second temperature T2 chosen so as to eliminate the solidifiable material 19 (by evaporation or fusion).

The use of a sheath in the form of a screen ensures porosity which facilitates the removal of the material 19 without however free the fibers.

With water it will suffice to adopt an oven brought to T2 = 60 ° C.

Each wafer 4 will have at its surface outer sheath portion 5 and at the level of the axial channel a portion of the tube 28. The material filling the tube was eliminated with that which retained the fibers. Sheath 5 and tube 28 ensure a certain mechanical strength of each wafer 4, facilitating the subsequent mounting of the wafers in the case 2 of the ammunition (step H).

Then just introduce a load pyrotechnic dispersion in the axial channel. Load can be itself placed in a tube or be poured loose in the axial channel 6.

As a variant and when the diameter of the pancakes is very important (greater than 60mm) for a reduced thickness (less than 6mm), we can place the pancakes in the case when they are still in the state solidified. We will then have the case fitted with pancakes to the interior of the oven to ensure the evacuation of solidifiable material (step H then occurs before step G).

As a variant, it is also possible to carry out the drilling the axial channel after cutting the wafers and before baking.

According to a second mode of implementation of the invention, a mold 21 can be used according to that shown in Figure 4a.

This mold differs from the previous one in that the shell upper 22b takes the form of a flat cover. The mold therefore delimits an internal semicylindrical cavity 31.

With such a mold, a strand having a shape is produced. half cylinder. Two identical strands are thus produced solidified which is then assembled in a single sheath cylindrical holding 5.

The advantage of such an embodiment is allow a better loading density to be obtained, compression and insertion of fibers into the mold being facilitated.

The axial bore is drilled after sheath assembly.

Figure 4b shows a variant of this mode of embodiment, variant in which the cover 22b of the mold has a semi-cylindrical profile 32 which allows to arrange a half cylindrical axial channel on the strand.

Again, two strands 12a, 12b are produced having a form of half cylinder and they are assembled using a sheath 5 including the tube 28 containing the material solidified.

This variant of the process is shown diagrammatically in the figure 6 (step E3).

The advantage of such a variant is that the axial channel 6 is obtained directly without the need to drill.

Figures 7 and 8 show a mold used in a third embodiment of the invention.

This mold like that of FIG. 3 delimits a cylindrical axial cavity 25.

It differs from the previous one in that each shell 22a, 22b has notches 33 allowing passage cutting means, for example disc, saw, water jet or laser.

With this particular embodiment of the mold, it it is not necessary to surround the solidified strand with a sheath.

It is the mold itself which ensures the maintenance of peripheral fibers of the strand during the operation of cutting patties. The thermal inertia of the mold facilitates the maintenance of the strand in the solidified state.

The mold 21 will advantageously include bores axial 34 which allow the operation of drilling the strand directly inside the mold. After drilling the axial channel (before or after cutting the pancakes), we will have a tube 28 filled with a material solidified.

Drilling and cutting operations take place so directly after step D and we get pancakes that can be placed in a case of ammunition.

Steaming should preferably be carried out directly after placement in the case. It is also possible to place the stack of cut washers in a tube light paper or cardboard or a porous material that can allow the solidification material to escape.

The stack will be steamed with this tube porous then the assembly will be placed in the case of the ammunition.

Various variants are possible without leaving the frame of the invention.

Thus it is possible to associate either a strand produced according to the technique of FIG. 2 or a strand according to FIG. 5 with any of the molds described with reference to Figures 3, 4a, 4b, 7 and 8.

It is also possible to make a following mold Figure 3 equipped with a removable cylindrical core (represented by the dotted lines 35 in FIG. 3). This core will be kept supported on the bearing surfaces of the shell 22a and we will place in the cavity 25 of the mold several strands all around the nucleus. We will thus obtain, after solidification and removal of the core, a single strand solidified incorporating an axial channel.

We can make several strands in length reduced and having the desired diameter for the pancakes. After steps F or G we will stack the number of pancakes desired (which can therefore come from several strands) in a case to make ammunition (step H).

Ammunition produced with such a process will notably allow the dispersion of carbon fibers or conductive in order to achieve masking or decoy in the desired wavelength band.

We can also make ammunition allowing to disperse such carbon or conductive fibers in order to neutralize electrical systems, such power plants or transformer stations by creating short circuits.

Claims (17)

1. A method for stacking short fibers less than 10 mm long into a case (2), such as a munition, the method comprising:

   arranging at least one array of long fibers in at least one skein (12),

   impregnating the skein(s) with a material (19) which can solidify at a first temperature,

   placing the skein so impregnated into a mold (21),

   solidifying the skein(s) in the mold by changing the temperature of the mold to a first temperature,

   cutting the skein(s) (12) in solidified state into at least two slices (4), each slice being of a thickness which is the desired length of the short fibers,

   eliminating the solidifiable material (19) by changing the temperature of the slices to a second temperature, before or after the stacking of the slices in the case (2).
2. The fibre stacking method of claim 1, characterised in that the solidified skein (12) is sliced while inside the mold (21), the mold being fitted with recesses (33) permitting passage of a slicing means.
3. The fibre stacking method of claim 1, characterised in that the solidified skein (12) is removed from the mold (21), and then the solidified skein is enclosed by a support sheath (5) before the skein is cut into slices (4).
4. The fibre stacking method of claim 3, characterised in that the mold (21) comprises a semi-cylindrical cavity (31), for imparting a semi-cylindrical shape to a solidified skein and at least two substantially identical skeins are firstly manufactured, then assembled within a single supporting cylindrical sheath.
5. The fibre stacking method of claim 4, characterised in that the mold (21) comprises a cover (22b) having a semi-cylindrical contour (32) for forming a cylindrical, axial half duct in the solidified skein (12).
6. The fibre stacking method of one of the claims 1 to 4, characterised in that an axial duct (6) is made by drilling the skein (12) or the solidified slices.
7. The fibre stacking method of one of the claims 5 or 6, characterised in that, after forming of the axial duct (6) in the solidified skein and before slicing, a tube (28) filled with the same impregnation material (19) in the solidified state is installed inside the axial duct.
8. The fibre stacking method of one of the claims 3 to 7, characterised in that the support sheath (5) is a heat-shrinking sheath.
9. The fibre stacking method of one of the claims 3 to 7, characterised in that the support sheath (5) is a metal sheath.
10. The fibre stacking method of claim 9, characterised in that the metal sheath (5) is a mesh of width less than 140µ.
11. The fibre stacking method of one of the claims 9 or 10, characterised in that the metal sheath (5) is made of a foil (27) wound around the skein (12) and soldered edge on edge.
12. The fibre stacking method of one of the claims 1 to 11, characterised in that an array of long fibers of the skein (12) is produced by winding a long fibre (16) between two pins (14a, 14b) firmly affixed to a support (15).
13. The fibre stacking method of one of the claims 1 to 11, characterised in that long fibers are arrayed into a skein (12) by winding a unidirectional fabric (18) on itself.
14. The fibre stacking method of one of the claims 1 to 13, characterised in that the solidifiable material (19) is water or comprises water.
15. The fibre stacking method of one of the claims 1 to 13, characterised in that the solidification point of the solidifiable material (19) is higher than 0°C and its melting or boiling point is less than 150°C.
16. The fibre packing method of claim 15, characterised in that the solidifiable material is a wax.
17. The fibre stacking method of one of the claims 1 to 16, characterised in that the fibers are carbon fibers or glass fibers covered with a conductive material such as aluminium or conductive organic fibers.

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