Optimized covered yarn

Abstract

The invention relates to a covered yarn (400) intended for a textile operation for forming a fibrous preform, the covered yarn (400) comprising a central yarn (401) formed by one or more fibers made of refractory material and the covered yarn (400) comprising several covering yarns (402), the covered yarn (400) being characterized in that each covering yarn (402) is wound around the central yarn (401) at a winding rate of between 100 and 300 turns per meter of central yarn (401).

Description

Description Title of the invention: Optimized braided yarn Technical Field

[0001] The present invention relates to the covering of yarns intended to undergo a textile operation, for example weaving or braiding. Previous technique

[0002] The production of composite parts, for example with ceramic matrix composites (CMCs), is well established. The fibrous reinforcement of composite parts can be achieved by weaving or braiding yarns, for example, using three-dimensional weaving. Weaving can be carried out, for instance, using a Jacquard loom. The woven or braided yarns form a fibrous blank, which is then shaped to obtain a fibrous preform. This fibrous preform is subsequently densified by a matrix to produce the desired composite part.

[0003] During machine weaving or braiding, the yarns are subjected to significant stress, which can cause some yarns to break. Furthermore, the yarns can become contaminated by metallic particles from the machine, which can lead to defects during matrix densification, such as silicon carbide growths.

[0004] To remedy these drawbacks, it is common practice to cover the weaving or braiding threads, that is, to wrap them with so-called covering threads. These covering threads provide protection for the weaving or braiding threads.

[0005] However, it was found that the covering thread could slip along the yarn being woven or braided, thus reducing the protection of said yarn being woven or braided. Description of the invention

[0006] The present invention aims to provide a braided yarn with satisfactory protection.

[0007] To this end, the invention proposes a covered yarn intended for a textile operation for the formation of a fibrous preform, the covered yarn comprising a central yarn formed by one or more fibers of refractory material and the covered yarn comprising several covering yarns, the covered yarn being characterized in that each covering yarn is wound around the central yarn at a winding rate of between 100 and 300 turns per meter of central yarn.

[0008] The present invention thus proposes to increase the winding ratio of the covering yarn compared to the usual winding ratios for yarns made of refractory material, by exceeding 100 turns per meter of central refractory yarn. Such an increase in the winding ratio of the covering yarn ensures sufficient retention of the covering yarn around the central yarn, preventing any slippage. Increasing the winding ratio for central yarns made of refractory material is counterintuitive to those skilled in the art, since a higher winding ratio further increases the rigidity of the central yarn and makes it more difficult to weave or braid. The present invention therefore proposes a satisfactory compromise, in which the winding ratio is high enough to prevent slippage of the covering yarn, but not so high as to prevent the covering yarn from being used in a textile operation.

[0009] In particular, the winding rate can be between 150 and 250 turns per meter of center wire for an ideal compromise.

[0010] Preferably, the covering yarns have a count between 62 decitex and 110 decitex. Preferably, the central yarn has a count between 200 tex and 1500 tex.

[0011] Indeed, such thread counts are particularly suited to the winding ratio values ​​described above, and allow for further improvement of the compromise between protection of the central wire and flexibility of the wrapped wire.

[0012] According to a particular embodiment of the invention, the covered yarn comprises an even number of covering yarns, half of the covering yarns turning in a first direction around the central yarn and the other half of the covering yarns turning in a second direction opposite to the first direction around the central yarn.

[0013] This configuration, with the same number of wrapping threads, provides similar protection to a configuration where all the wrapping threads are wound in the same direction, but with a less rigid final wrapped thread. Two wrapping directions also prevent twisting of the wrapping thread during installation.

[0014] According to a particular embodiment of the invention, the number of covering threads is two. The number of covering threads can also be four.

[0015] Thus, the braided yarn contains enough braiding threads to provide protection without being too stiff. Furthermore, the numbers of two and four braiding threads are particularly well-suited to the winding ratio and yarn count values ​​indicated previously.

[0016] According to a particular embodiment of the invention, between 50% and 75% of the outer surface of the central wire is covered by the covering wires.

[0017] A winding rate of between 100 and 300 turns per meter of central yarn combined with covering yarns have a count of between 62 decitex and 110 decitex and a central yarn with a count of between 200 and 1500 tex allows to obtain such a cover rate of between 50% and 70% with optimal flexibility and strength of the covered yarn.

[0018] The invention also relates to a method of covering a central wire formed by one or more fibers of refractory material, the method comprising winding covering wires around the central wire so as to obtain a covered wire, the method being characterized in that each covering wire is wound around the central wire at a winding rate of between 100 and 300 turns per meter of central wire.

[0019] In particular, the winding rate can be between 150 and 250 turns per meter of center wire for an ideal compromise.

[0020] According to a particular embodiment of the invention, the number of covering threads is two or four, half of the covering threads turning in a first direction around the central thread and the other half of the covering threads in a second direction opposite to the first direction around the central thread.

[0021]

[0022] According to a particular embodiment of the invention, the wrapped yarn can comprise several central yarns, each formed by one or more fibers of refractory material.

[0023] The invention further proposes a method for manufacturing a fibrous preform for the production of a part in composite material, comprising weaving a plurality of wrapped yarns as described above.

[0024] The presence of wrapping threads inside the final composite part is often undesirable. Therefore, it is advantageous if the wrapping threads can be easily removed, preferably before the fiber preform is densified by a matrix.

[0025] According to a particular embodiment of the invention, the covering threads are made of fugitive material, said covering threads being eliminated after weaving.

[0026] The invention also relates to a method of manufacturing a part made of composite material comprising the manufacture of a fibrous preform by the method of manufacturing a fibrous preform as described above, and then the densification of said fibrous preform by a matrix. Brief description of the drawings

[0027] [Fig. 1] Figure 1 is a schematic perspective view of a first example of braided yarn according to the invention.

[0028] [Fig. 2] Figure 2 is a schematic cross-sectional view of the covered wire of Figure 1.

[0029] [Fig. 3] Figure 3 is a schematic perspective view of a second example of braided yarn according to the invention.

[0030] [Fig. 4] Figure 4 is a schematic cross-sectional view of the covered wire of Figure 3.

[0031] [Fig. 5] Figure 5 is a schematic perspective view of a Jacquard type loom in neutral position.

[0032] [Fig. 6] Figure 6 is a schematic perspective view of the loom in Figure 5 with a crowd creation. Description of the implementation methods

[0033] Figures 1 and 2 schematically illustrate a first example of 400-gabled yarn, and figures 3 and 4 schematically illustrate a second example of 200-gabled yarn. The 400-gabled yarn comprises a central yarn 401 and several covering yarns 402. The 200-gabled yarn comprises a central yarn 201 and several covering yarns 202.

[0034] The 201 or 401 core wire comprises one or more refractory fibers. The refractory material may be ceramic. In particular, the refractory material may be silicon carbide. The refractory material may also be an oxide. The refractory material may be one of the following materials: alumina, mullite, silica, an aluminosilicate, a borosilicate, carbon, or a mixture of several of these materials.

[0035] In the example illustrated in Figures 1 and 2, the braided yarn 400 comprises a central yarn 401 and two braided yarns 402a, 402c. The invention remains within the scope of the invention even if the braided yarn comprises several central yarns. Nor does the invention depart from the scope of the invention if the number of braided yarns is not two, in particular if it is four.

[0036] In the example illustrated in Figures 3 and 4, the braided yarn 200 comprises a central yarn 201 and four braided yarns 202a, 202b, 202c, 202d. The invention remains within the scope of the invention even if the braided yarn comprises several central yarns. Nor does the invention depart from the scope of the invention if the number of braided yarns is not four, in particular if it is two.

[0037] Preferably, the number of covering threads is even, in order to prevent the covered thread from twisting. In this configuration, half of the covering threads can rotate in one direction around the central thread, and the other half in a second direction opposite to the first around the central thread.

[0038] In the example illustrated in figures 1 and 2, the covered yarn 400 comprises a covering yarn 402a wound in a first direction of rotation and a covering yarn 402c wound in a second direction of rotation opposite to the first direction of rotation. Thus, the resulting 400 braided yarn is relatively balanced and straight, and does not twist excessively.

[0039] In the example illustrated in Figures 3 and 4, the braided yarn 200 comprises two braided yarns 202a and 202b wound in a first direction of rotation and two braided yarns 202c and 202d wound in a second direction of rotation opposite to the first. Preferably, the braided yarns 202a and 202b wound in the first direction of rotation are offset by 180° from each other along the central yarn 201. Similarly, the braided yarns 202c and 202d wound in the second direction of rotation are preferably offset by 180° from each other along the central yarn 201. Thus, the resulting braided yarn 200 is relatively balanced and straight, and does not twist excessively.

[0040] The 202 or 402 wrapping yarns can be made of a fugitive material. A "fugitive material" here refers to any material that can be removed without leaving residue on the central yarn 201 or 401 and without damaging the refractory fibers. In particular, the 202 or 402 wrapping yarns can be made of a water-soluble material. For example, the 202 or 402 wrapping yarns can be made of polyvinyl alcohol (PVA). The 202 or 402 wrapping yarns can also be made of a polymer that can be removed by heat treatment, such as polyvinyl acetate or polyethylene.

[0041] According to the present invention, the winding rate of each of the covering wires 202 or 402 is between 100 and 300 turns per meter of central wire 201 or 401. Preferably, the winding rate of each of the covering wires 202 or 402 is between 150 and 250 turns per meter of central wire 201 or 401.

[0042] To best benefit from the advantages offered by the previous winding ratios, it is preferable that the 202 or 402 covering yarns have a count between 31 decitex and 220 decitex. Specifically, the 202 or 402 covering yarns can have a count between 62 decitex and 110 decitex. These count values ​​are also particularly well-suited to configurations where the covered yarn comprises two or four covering yarns. It is also preferable that the central 201 or 401 wire(s) have a thread count between 200 tex and 1500 tex.

[0043] By adjusting the winding ratio, the number of center wires, the yarn count of the center wire(s), the yarn count of the covering wires, and the number of covering wires, the aim is to achieve a coverage rate of the center wire by the covering wires between 50% and 75%. Thus, between 50% and 75% of the center wire is covered by the covering wires.

[0044] The wrapping of the central thread is carried out using a well-known method, for example, with a wrapping machine called a wrapping machine. Setting up the wrapping machine requires general knowledge and the expertise of a skilled craftsman. The central thread should preferably be straight when wrapped with the wrapping threads.

[0045] The resulting 200 or 400 wrapped yarns are intended for use in textile operations. These operations may include weaving, braiding, or knitting. Other textile operations are also possible. For example, a fibrous roughing can be created by weaving the 200 or 400 wrapped yarns. The 200 or 400 wrapped yarns according to the present invention are particularly well-suited to three-dimensional weaving.

[0046] The term "three-dimensional weaving" refers to a weaving method in which at least some of the weft yarns interlock with warp yarns across multiple warp layers. A fiber blank or preform produced by three-dimensional weaving may include another type of weaving on its surface, such as two-dimensional weaving, to improve its surface finish.

[0047] The 200 or 400 wrapped yarns according to the present invention are particularly suitable for weaving on a Jacquard loom. Figures 5 and 6 illustrate a loom 100 for producing a fiber blank 300 intended to form a fiber preform. The loom 100 produces the fiber blank 300 by weaving a plurality of warp yarns 210 with a plurality of weft yarns 220. The fiber blank 300 extends lengthwise along a horizontal direction DH and in thickness along a vertical direction Dv on the loom 100.

[0048] Preferably, the warp yarns 210 and the weft yarns 220 are covered yarns 200 or 400 as described above. However, it does not depart from the scope of the invention if only the warp yarns 210 are covered yarns 200 or 400 as described above, or if only the weft yarns 220 are covered yarns 200 or 400 as described above.

[0049] The loom is equipped with a Jacquard mechanism 110 supported by a superstructure not shown in Figures 5 and 6. The loom 100 also includes a harness 120 comprising control or heddle wires 121, each control wire 121 being connected at one end to a control element 111 of the Jacquard mechanism 110. In the example illustrated in Figures 5 and 6, each control wire 121 is connected at one end to a control hook 111 of the Jacquard mechanism 110 and at the other end to a return spring 112 fixed to the frame 113 of the loom 100. The control wires 121 extend in the vertical direction Dv. The harness 120 may also include a heddle board 122.

[0050] Each control wire 121 includes an eyelet 121a through which a warp wire 210 passes. Each warp wire 210 of the loom 100 passes through an eyelet 121a of the harness 120. The warp wires 210 are arranged at the harness 120 of the loom 100 in a plurality of horizontal layers and vertical columns which are manipulated by the loom 100 to allow the insertion of weft wires 220 according to the weaving pattern(s) programmed in the loom 100. The weft wires 220 are inserted between the warp wires 210 by column extending along the vertical direction Dv. In order to allow the introduction of each column of weft yarns 220 during the weaving of the rough 300, a warp yarn calling system 210 (not shown in figures 5 and 6) is associated with the loom 100.This system, placed downstream of the loom 100, has the role of holding all the warp threads 210 together in a bridling device and of allowing the advancement of the warp threads 210 a determined distance along the horizontal direction DH after the insertion of each weft column 220.

[0051] The terms "upstream" and "downstream" are defined here according to the direction of advance of the warp threads 210 in the loom 100, that is, according to the direction of weaving, along the horizontal direction DH.

[0052] The control wires 121 and their associated eyelets 121a are able to move along the vertical direction Dv. In Figure 5, all the control wires 121 are in a neutral position in which no tension is exerted by the Jacquard mechanism 110. In this configuration, no swarm is created and all the warp wires 210 extend parallel to the horizontal direction DH.

[0053] During the creation of a swarm, as illustrated in Figure 6, a portion of the control wires 121 are subjected to tensile forces exerted by the control hooks 111. In this configuration, the control wires allow warp wires to be raised or lowered, so as to separate an upper layer of warp wires from a lower layer of warp wires by an opening, called a swarm.

[0054] The loom 100 also includes a spear 130, located downstream of the control wires 121. The spear 130 consists of a rod 131, the first end of which is connected to an actuation system (not shown in figures 5 and 6) allowing the rod 131 to be animated with a back-and-forth movement. The other end of the rod 131 is equipped with a gripper 132 which, after passing through the swarm during the rod 131's forward journey, can grasp a weft yarn 220 stored on a reel 140 and unwind it into the swarm during the rod 131's return journey. The weft yarn 220 thus placed inside the swarm is then cut in the vicinity of the reel 140 by a cutting tool 150 and released at its other end by the gripper 132. A comb 160 located upstream of the spear 130 and downstream of the harness 120 in its resting position is then folded down to compact the weft yarn(s) 220 introduced into the swarm.The lance 130 is then ready to pick up a new weft yarn 220 from the bobbin 140 and place it either in the same sheaf or in a different one, depending on the defined weave. In this way, the fibrous blank 300 is progressively formed, exhibiting a three-dimensional weave between the warp yarns 210 and the weft yarns 220.

[0055] Preferably, the loom 100 further includes a guiding device 170 for the fiber blank 300 located downstream of the drive wires 121 and the spear 130. Such a guiding device 170 is described in particular in document FR 3 074 195 A1. In the example described here, the guiding device 170 comprises a lower jaw 171 and an upper jaw 172, each connected to an actuation means (not shown in Figures 5 and 6) which is capable, on the one hand, of holding the fiber blank 300 and, on the other hand, of moving the jaws 171 and 172 along the vertical direction Dv. It is thus easier to create shovels in the lower or upper layers of warp wires 210, even with a large number of superimposed layers of warp wires 210 along the vertical direction Dv.

[0056] The 200 or 400 wrapped yarns according to the invention limit the risk of breakage of the warp yarns 210 and the weft yarns 220 during weaving, and limit the risk of control yarns 121 being caught in the spool 130. Weaving defects are thus reduced and the loom is less likely to be damaged.

[0057] A fiber blank 300 is thus produced by weaving. This fiber blank 300 can then be shaped to obtain a fiber preform. The fiber preform is intended to form the fibrous reinforcement of the composite part to be produced. The fiber preform can then be densified by a matrix to obtain the desired composite part.

[0058] As previously stated, the wrapping yarns 202 or 402 are preferably fugitive. In a preferred embodiment, the wrapping yarns 202 or 402 can be removed after the formation of the fibrous blank 300 and before shaping into a fibrous preform. The wrapping yarns 202 or 402 can, for example, be water-soluble. The fibrous blank 300 is then wetted to disintegrate the wrapping yarns 202 or 402. In this first embodiment, the wrapping yarns 202 or 402 can also be made of a polymer that can be removed by heat treatment, such as polyvinyl acetate or polyethylene. Other types of fugitive material are, of course, possible. However, the wrapping yarns 202 or 402 can also be The 202 or 402 wrapping yarns may be removed during the shaping of the fiber blank 300 into a fiber preform, or may be removed after the formation of the fiber preform but before any deposition of a matrix or matrix precursor in the pores of said fiber preform. Finally, the 202 or 402 wrapping yarns may also be removed during the deposition of a matrix or matrix precursor in the pores of said fiber preform. In particular, the 202 or 402 wrapping yarns may be fugitive during a specific operation involving the deposition of a matrix or matrix precursor in the pores of said fiber preform, for example, during chemical vapor infiltration (CVI).

[0059] The wrapped yarns according to the invention can thus be used to produce composite material parts, for example, composite turbomachine parts. For example, the wrapped yarns according to the invention can be used to produce turbine blades, rings, distributors, gas flow sections, or exhaust nozzles.

Claims

Demands

1. Wrapped yarn (200, 400) intended for a textile operation for the formation of a fibrous preform, the wrapped yarn (200, 400) comprising a central yarn (201, 401) formed from one or more refractory material fibers and the wrapped yarn (200, 400) comprising several wrapping yarns (202, 402), the wrapped yarn (200, 400) being characterized in that each wrapping yarn (202, 402) is wound around the central yarn (201, 401) at a winding rate of between 100 and 300 turns per meter of central yarn (201, 401), the wrapping yarns (202, 402) having a density of between 62 and 110 decitex and the central yarn (201, 401) having a titration between 200 and 1500 tex.

2. Covered yarn (200, 400) according to claim 1, wherein the covered yarn (200, 400) comprises an even number of covering yarns (202, 402), half of the covering yarns (202a, 202b, 402a) turning in a first direction around the central yarn (201, 401) and the other half of the covering yarns (202c, 202d, 402c) turning in a second direction opposite to the first direction around the central yarn (201, 401).

3. Covered yarn (200, 400) according to claim 1 or 2, wherein the number of covering yarns (202, 402) is two or four.

4. Covered yarn (200, 400) according to any one of claims 1 to 3, wherein between 50% and 75% of the outer surface of the central yarn (201, 401) is covered by the covering yarns (202, 402).

5. A method for wrapping a central yarn (201, 401) formed by one or more fibers of refractory material, the method comprising winding wrapping yarns (202, 402) around the central yarn (201, 401) so as to obtain a wrapped yarn (200, 400), the method being characterized in that each wrapping yarn (202, 402) is wound around the central yarn (201, 401) at a winding rate of between 100 and 300 turns per meter of central yarn (201, 401), the wrapping yarns (202, 402) having a count of between 62 and 110 decitex and the central yarn (201, 401) having a count of between 200 and 1500 tex.

6. A covering method according to claim 5, wherein the number of covering threads (202, 402) is two or four, half of the covering threads (202a, 202b, 402a) turning in a first direction around the central thread and the other half of the covering threads (202c, 202d, 402c) turning in a second direction opposite to the first direction around the central thread (201, 401).

7. Method of manufacturing a fibrous preform for the production of a part in composite material, comprising weaving a plurality of wrapped yarns (200, 400) according to any one of claims 1 to 4.

8. A method for manufacturing a fibrous preform according to claim 7, wherein the covering yarns (202, 402) are made of fugitive material, said covering yarns (202, 402) being removed after weaving.

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