Optimized braided yarn

Abstract

Optimized Wrapped Yarn The invention relates to a wrapped yarn (400) intended for a textile operation for the formation of a fibrous preform, the wrapped yarn (400) comprising a central yarn (401) formed by one or more fibers of refractory material and the wrapped yarn (400) comprising several wrapping yarns (402), the wrapped yarn (400) being characterized in that each wrapping 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). Figure for the abstract: Fig. 1

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 a ceramic matrix (CMC), is well known. The fibrous reinforcement of composite parts can be achieved by weaving or braiding yarns, for example by three-dimensional weaving. Weaving can, for example, be carried out using a Jacquard loom. The woven or braided yarns form a fibrous blank, which is then shaped to obtain a fibrous preform. The resulting fibrous preform is then densified by a matrix to obtain the desired composite part.

[0003] During machine weaving or braiding, the yarns are subjected to significant stresses, which can cause some yarns to break. In addition, the yarns can be contaminated by metallic particles from the machine, which can lead to defects during matrix densification, for example, silicon carbide outgrowths.

[0004] To remedy these drawbacks, it is known to cover the yarns to be woven or braided, that is to say, to wrap so-called covering yarns around the yarns to be woven or braided. These covering yarns provide protection for the yarns to be woven or braided.

[0005] However, it was found that the covering thread could slip along the yarn to be woven or braided, thus reducing the protection of said yarn to be 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 rate of the covering wire compared to the usual winding rates for wires made of refractory material, by exceeding 100 turns per meter of central wire made of refractory material. 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, as a higher winding ratio further increases the rigidity of the central yarn, making it more difficult to weave or braid. The present invention thus 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] According to a particular embodiment of the invention, the covering yarns have a count between 31 decitex and 220 decitex.

[0011] Indeed, such titles are particularly suited to the winding ratio values ​​described above, and make it possible to further improve the compromise between protection of the central wire and flexibility of the wrapped wire.

[0012] In particular, the count of the covering yarns can be between 62 decitex and 110 decitex for an ideal compromise.

[0013] According to a particular embodiment of the invention, the covered yarn comprises an even number of covering yarns, half of the covering yarns rotating in a first direction around the central yarn and the other half of the covering yarns rotating in a second direction opposite to the first direction around the central yarn.

[0014] Such a configuration, with the same number of covering threads, provides protection similar to a configuration in which all the covering threads rotate in the same direction, but with a final covered thread that is less rigid. Two directions of wrapping also prevent twisting of the covering thread during its installation.

[0015] According to a particular embodiment of the invention, the number of covering threads is two. The number of covering threads can also be four.

[0016] Thus, the braided yarn comprises enough braiding yarns to be protected without being too rigid. Furthermore, the numbers of two and four braiding yarns are particularly well-suited to the winding ratio and thread count values ​​indicated above.

[0017] 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.

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

[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 covering yarns have a count between 31 decitex and 220 decitex.

[0021] In particular, the count of the covering yarns can be between 62 decitex and 110 decitex for an ideal compromise.

[0022] 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.

[0023] According to a particular embodiment of the invention, the central wire has a count between 200 tex and 1500 tex.

[0024] 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.

[0025] 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.

[0026] The presence of wrapping threads inside the final composite part is often undesirable. It is therefore advantageous that the wrapping threads can be easily removed, preferably before the densification of the fibrous preform by a matrix.

[0027] According to a particular embodiment of the invention, the covering threads are made of fugitive material, said covering threads being eliminated after weaving.

[0028] The invention also relates to a method of manufacturing a part made of composite material comprising manufacturing a fibrous preform by the method of manufacturing a fibrous preform as described above, and then densifying said fibrous preform by a matrix. Brief description of the drawings

[0029] [Fig. 1] The [Fig. 1] is a schematic perspective view of a first example of braided yarn according to the invention.

[0030] [Fig.2] The [Fig.2] is a schematic cross-sectional view of the covered wire of the [Fig.1].

[0031] [Fig.3] Fig.3 is a schematic perspective view of a second example of braided thread according to the invention.

[0032] [Fig.4] The [Fig.4] is a schematic cross-sectional view of the covered wire of the [Fig.3].

[0033] [Fig.5] The [Fig.5] is a schematic perspective view of a Jacquard type loom in neutral position.

[0034] [Fig.6] The [Fig.6] is a schematic perspective view of the loom of the [Fig.5] with a crowd creation. Description of the implementation methods

[0035] Figures 1 and 2 schematically illustrate a first example of a covered yarn 400 and Figures 3 and 4 schematically illustrate a second example of a covered yarn 200. The covered yarn 400 comprises a central yarn 401 and several covering yarns 402. The covered yarn 200 comprises a central yarn 201 and several covering yarns 202.

[0036] The central wire 201 or 401 comprises one or more fibers of refractory material. 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.

[0037] In the example illustrated in Figures 1 and 2, the braided yarn 400 comprises a central yarn 401 and two braided yarns 402a, 402c. It is of course not outside the scope of the invention if the braided yarn comprises several central yarns. Nor is it outside the scope of the invention if the number of braided yarns is not two, in particular if it is four.

[0038] 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. It is of course not outside the scope of the invention if the braided yarn comprises several central yarns. Nor is it outside the scope of the invention if the number of braided yarns is not four, in particular if it is two.

[0039] Preferably, the number of covering threads is even, in order to keep the covered thread from twisting. In this configuration, half of the covering threads can rotate in a first direction around the central thread and the other half of the covering threads in a second direction opposite to the first around the central thread.

[0040] 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 covered yarn 400 is relatively balanced and straight, and does not twist excessively.

[0041] In the example illustrated in Figures 3 and 4, the covered yarn 200 comprises two covering yarns 202a and 202b wound in a first direction of rotation and two covering yarns 202c and 202d wound in a second direction of rotation opposite to the first direction of rotation. Preferably, the covering threads 202a and 202b wound in the first direction of rotation are offset by 180° from each other along the central thread 201. Similarly, the covering threads 202c and 202d wound in the second direction of rotation are preferably offset by 180° from each other along the central thread 201. Thus, the resulting covered thread 200 is relatively balanced and straight, and does not twist excessively.

[0042] The wrapping yarns 202 or 402 may be made of a fugitive material. "Fugitive material" here means any material that can be removed without leaving any residue on the central yarn 201 or 401 and without altering the fibers to a refractory material. In particular, the wrapping yarns 202 or 402 may be made of a water-soluble material. For example, the wrapping yarns 202 or 402 may be made of polyvinyl alcohol (PVA). The wrapping yarns 202 or 402 may also be made of a polymer that can be removed by heat treatment, such as polyvinyl acetate or polyethylene.

[0043] 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.

[0044] In order to best benefit from the advantages offered by the preceding winding ratio values, it is preferable that the 202 or 402 covering yarns have a count between 31 decitex and 220 decitex. In particular, the 202 or 402 covering yarns may have a count between 62 decitex and 110 decitex. These count values ​​are also particularly well-suited to the configuration in which the covered yarn comprises two or four covering yarns. It is also preferable that the 201 or 401 center yarn(s) have a count between 200 tex and 1500 tex.

[0045] 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 ratio of the center wire by the covering wires of between 50% and 75%. Thus, between 50% and 75% of the center wire is covered by the covering wires.

[0046] The wrapping of the central thread is carried out in a well-known manner, for example using a wrapping machine called a wrapping machine. Setting up the wrapping machine requires general knowledge and the expertise of a person skilled in the art. The central thread is preferably straight during wrapping with the wrapping threads.

[0047] The 200 or 400 wrapped yarns obtained are intended for use in a textile operation. The textile operation may include weaving, braiding, or knitting. Other textile operations are also possible. It is thus possible to produce a fibrous roughing by weaving the 200 or 400 wrapped yarns. The wrapped yarns 200 or 400 according to the present invention are particularly suitable for three-dimensional weaving.

[0048] By "three-dimensional weaving" is meant a weaving method in which at least some of the weft yarns bind warp yarns over several warp layers. A fibrous blank or fibrous preform produced by three-dimensional weaving is considered to include another type of weaving on its surface, for example two-dimensional weaving, in order to improve its surface finish.

[0049] The wrapped yarns 200 or 400 according to the present invention are particularly suitable for weaving on a Jacquard-type 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.

[0050] 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.

[0051] 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 along the vertical direction Dv. The harness 120 may also include a heddle board 122.

[0052] 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 in 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 into the loom 100. The weft wires 220 are inserted between the warp wires 210 by columns extending along the vertical direction Dv. In order to allow the introduction of each column of weft wires 220 during the In the weaving of the rough 300, a warp thread call 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.

[0053] 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 to say according to the direction of weaving, along the horizontal direction DH.

[0054] The control wires 121 and their associated eyelets 121a are able to move along the vertical direction Dv. In [Fig. 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.

[0055] During the creation of a swarm, as illustrated in [Fig.6], part 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.

[0056] The loom 100 also includes a spear 130, located downstream of the control wires 121. The spear 130 is composed 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 sheaf depending on the defined weave. The fibrous blank 300 is thus progressively formed, exhibiting a three-dimensional weave between the warp yarns 210 and the weft yarns 220.

[0057] Preferably, the loom 100 further comprises a guiding device 170 for the fiber blank 300 located downstream of the control wires 121 and the spear 130. Such a guiding device 170 is described in particular in the 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 actuating means (not shown in Figures 5 and 6) which is capable, on the one hand, of holding the fibrous 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 swarms in the lower or upper layers of warp yarns 210, even with a large number of superimposed layers of warp yarns 210 along the vertical direction Dv.

[0058] The wrapped yarns 200 or 400 according to the invention make it possible to limit the risk of breakage of the warp yarns 210 and the weft yarns 220 during weaving, and make it possible to limit the risk of control yarns 121 being drawn into the spool 130. Weaving defects are thus reduced and the loom is less likely to be damaged.

[0059] A fibrous blank 300 is thus produced by weaving. The fibrous blank 300 can then be shaped to obtain a fibrous preform. The fibrous preform is intended to form the fibrous reinforcement of the composite part to be produced. The fibrous preform can then be densified by a matrix to obtain the desired composite part.

[0060] 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 soluble in water. 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 202 or 402 covering yarns can also be removed during the shaping of the fiber blank 300 into a fiber preform, or they can 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 covering yarns can 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 covering yarns can be fugitive during a specific operation of deposition of a matrix or matrix precursor in the pores of said fiber preform, for example, during chemical vapor infiltration (CVI).

[0061] The wrapped yarns according to the invention can thus be used to obtain parts made of composite material, for example turbomachine parts made of composite material. For example, the braided wires according to the invention can be used to obtain blades, turbine rings, distributors, portions of gas flow duct or exhaust nozzles.

Claims

Demands

1. Covered yarn (200, 400) intended for a textile operation for the formation of a fibrous preform, the covered yarn (200, 400) comprising a central yarn (201, 401) formed by one or more fibers of refractory material and the covered yarn (200, 400) comprising several covering yarns (202, 402), the covered yarn (200, 400) being characterized in that each covering 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).

2. Covered yarn (200, 400) according to claim 1, wherein the covering yarns (202, 402) have a count between 31 decitex and 220 decitex.

3. Covered yarn (200, 400) according to claim 1 or 2, 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).

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

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

6. Method for wrapping a central wire (201, 401) formed by one or more fibers of refractory material, the method comprising winding wrapping wires (202, 402) around the central wire (201, 401) so as to obtain a wrapped wire (200, 400), the method being characterized in that each wrapping wire (202, 402) is wound around the central wire (201, 401) at a winding rate of between 100 and 300 turns per meter of central wire (201, 401).

7. A wrapping method according to claim 6, wherein the wrapping yarns (202, 402) have a count between 31 decitex and 220 decitex.

8. A covering method according to claim 6 or 7, 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).

9. 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 5.

10. A method for manufacturing a fibrous preform according to claim 9, wherein the covering yarns (202, 402) are made of fugitive material, said covering yarns (202, 402) being removed after weaving.

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