EP0670921A1

EP0670921A1 - Warp and weft fabric based on predominantly untwisted multifilament yarn and method for producing same

Info

Publication number: EP0670921A1
Application number: EP94900890A
Authority: EP
Inventors: Jean Pierre-Blanche Aucagne; Bruno Bompard; Alain Bruyere; Christian Debaille; Bertrand Germain; Jean-Paul Lamarie; Laurent Martinet; Franck Perret; Jean-François VEAUVILLE
Original assignee: Brochier SA
Current assignee: Hexcel Fabrics SA
Priority date: 1992-11-30
Filing date: 1993-11-30
Publication date: 1995-09-13
Anticipated expiration: 2013-11-30
Also published as: ES2155469T3; JP3954090B2; FR2698640A1; CA2150468C; US5939338A; CA2150468A1; JPH08503747A; FR2698640B1; DE69330100T2; ATE200312T1; JP2007169873A; WO1994012708A1; DE69330100D1; US5732748A; AU5567494A; AU673872B2; EP0670921B1

Abstract

A woven fabric to be used in formation of a composite material includes multifilament warp and weft threads. Each of the warp threads and the weft threads have a total weight less than 80% of the weight of the fabric. The woven warp and weft threads have O twist/m and a torsion no greater than an original torsion of the threads before weaving. Each woven warp and weft thread has a width over the entire length thereof that is greater than or equal to an original width before weaving. The fabric is woven to have a given weight per unit area and a fiber volume ratio that is approximately constant throughout the fabric and that is satisfactory for use of the fabric in a composite material. The warp and weft threads of a yarn count that is greater than a yarn count traditionally used to achieve the fiber volume ratio for the given weight per unit area.

Description

Warp and weft fabric based on predominantly twist-free multifilament technical yarns and process for obtaining it

The invention relates to the field of textile structures intended for the production of composite materials. It relates more particularly to a warp and weft fabric produced, for the most part, based on multifilament technical yarns of relatively high titer for a relatively low grammage, and to the corresponding production process.

It is known that composite materials are experiencing great development, due to their excellent mechanical properties combined with low weight. Such materials essentially comprise a textile reinforcement and a resin matrix. Those skilled in the art know that the production of these materials causes a number of difficulties. Indeed, for certain uses, in particular in the aeronautical field, the mechanical properties of the composite materials are strictly defined.

It is often required that the textile structures used in the composite materials be tight enough to maintain a regular geometry and a suitability for handling, while allowing satisfactory penetration of the resin during the manufacture of the composite. This makes it possible to obtain satisfactory mechanical properties in the final composite. We are then led to use fibers that are sufficiently fine to constitute such tight structures. Depending on the grammage desired for the structure, a wire is chosen which makes it possible to obtain perfect coverage, that is to say a regular spreading which does not reveal porosities or even correlatively, making it possible to obtain a high volume rate. . It is noted that the lower the grammage of the textile structure, the lower the titer of the fibers, that is to say the linear mass of each fiber. However, fine yarns have a relatively high cost and this is particularly true for the carbon yarns currently available on the market. Thus, the price of 1K carbon threads (1000 filaments) reaches approximately four times that of 3K threads and six to eight times that of 6K threads. It is understood that the greater the number of filaments constituting the son, the higher the titer of the son.

It is therefore advantageous to use coarser yarns, the price of which decreases as their size increases. For example, 6K carbon threads (6000 filaments), which are twice as large as 3K threads, are significantly 30% cheaper. The same is true for 12 K wires which are currently available on the market and whose price is 30% lower than that of 6K wires.

To maintain and increase their market share, composite materials must be offered at prices lower than those currently practiced. In particular in the field of aeronautics, it is desired that the price of a composite part corresponds to that of the aluminum part, which requires significant cost reductions. The price fibers and in particular carbon fibers, having a direct influence on the costs of composite parts, the choice of the type of fibers is decisive.

It is in particular the 6K and 12K wires which make it possible to reduce costs. Thus, a fabric based on 6K yarns is approximately 30% cheaper than a fabric based on 3K yarns, for the same grammage. A fabric made from 12K yarn is about 50% cheaper than a fabric of the same weight, made from 3K yarn.

However, if fine yarns are replaced by yarns of higher titer, while retaining the same grammage, for example four 3K yarns by a 12K yarn, voids are created within the fabrics produced that are all the more important as the -grams are low.

Thus, coarser yarns are unsuitable for use in textile structures whose grammage or even the surface mass is relatively low, when using conventional weaving methods. In fact, the structures obtained are too loose and, moreover, they cannot be easily manipulated on leaving the loom. This is why the use of coarser yarns is today limited to fabrics of relatively high grammage. Analysis of the balanced carbon fabrics available on the market, that is to say the mass of the warp threads being identical to the mass of the weft threads, and having a uniform surface without porosity, makes it possible to establish a relationship between the thread used and the grammage of the fabric. Thus, 1K threads are used for fabrics whose grammage is generally between 90 and 210 g / m ² .

Fabrics weighing less than 90 g / m ² can be produced from 1K yarns, but they have a porosity incompatible with a perfect coverage objective.

With regard to 3K yarns, the grammage of the fabrics is generally between 180 and 400 g / m ² ; for 6K wires, it usually ranges from 260 to

600 g / m ² and finally for 12K wires, it is generally between 465 and 800 g / m ² .

The remark made for carbon fabrics based on 1K threads relating to the minimum mass of fabrics is also applicable to carbon fabrics obtained from 3K, 6K and 12K threads.

In the textile industry, various methods are known for reducing the porosity originally existing in a textile structure.

Thus, document FR-2 418 693 describes a process making it possible to reduce the porosity of a prepreg fabric, and more particularly an impregnated fabric consisting of carbon fibers, without requiring finer fibers.

This process successively consists of forming a fiber of filaments having a relatively circular cross section, weaving the fiber to form a fabric having relatively large interstices, impregnating the fabric with an uncured resin, loading a cylinder against one side of the fabric impregnated while supporting the other side of the fabric at least in front of the cylinder and moving the cylinder on the fabric a sufficient number of times to obtain the desired flattening of the fiber.

The calendering thus carried out makes it possible to flatten the fiber and thus to reduce the dimensions of the interstices, which makes it easier to fill the interstices when the resin hardens and therefore to reduce the porosity in the finished cured laminated product.

However, producing a dry fabric presents greater difficulties due to the absence of an additional material which can fill the interstices between the threads.

However, in the context of the manufacture of composite materials, it is desired to have non-impregnated or dry fabrics. This is in particular due to the fact that they can be used very generally, with any type of resin.

Mention may also be made of document EP-0 302 449, which describes a method for reducing the intestines in a tissue. This process was designed for conventional fabrics, made from fine threads, in particular 3K fibers. It has in fact been found that such fabrics have porosities which it is necessary to reduce in order to obtain a uniform distribution of the fibers and of the resin, in the final composite.

This document does not provide for the use of relatively high titer threads. The process is also not designed for high titer yarns, since the document notes that conventional fabrics based on fine yarns already have porosities compromising the properties of the final composite. It therefore appeared necessary to propose a fabric produced from technical yarns, the titer of which is relatively high compared to the grammage of the fabric, the fabric having a porosity or even a volume content of fibers compatible with use in the manufacture of a composite material having satisfactory mechanical properties.

Throughout the description, the quantity by fiber ratio (TVF) will denote the quantity defined as follows: mass of the fabric / density of the material of the yarn

TVF = unit width x unit length x thickness

It is understood that the volume ratio of the fibers can be calculated at any point of the fabric.

Likewise, throughout the description, the expression “a substantially constant FST in the tissue” will be understood to mean a FST whose mean value is constant, a local dispersion of ± 3% being tolerated.

The invention therefore relates to a warp and weft fabric based on technical yarns of microns, of which at least 80% by weight of the yarns have the following characteristics in combination:

(a) - the title of the threads, for a given grammage of the fabric, is greater than that traditionally used,

(b) - the threads do not have a twist greater than the original twist of the threads before weaving, which are, in the same proportion, threads with 0 twist turn / m. (c) - the width of the threads is over the entire length of the threads, greater than or equal to the original width of the threads before weaving;

These threads constituting all the threads in the direction comprising the largest proportion of threads by weight when the weight ratio of the weft threads and warp threads is greater than or equal to 80/20 and all the threads of the fabric when this ratio is less than

80/20, the volume content of fibers being substantially constant in the fabric and greater than or equal to that of a traditional fabric based on threads of equal or lower titer.

The invention also relates to a warp and weft fabric, based on multifilament technical yarns, having the following characteristics in combination:

(a) - the title, for a given grammage of the fabric, is greater than that traditionally used; (b) - the warp and weft threads do not have a twist greater than the original twist of the threads before weaving, which are threads with 0 twist turn / m;

(c) - the width of the warp and weft threads is over the entire length of the threads, greater than or equal to the original width of the threads before weaving;

(d) - the volume content of fibers is substantially constant in the fabric and greater than or equal to that of a traditional fabric based on yarns of equal or lower titer. The invention also relates to a fabric such that the weight share of the warp (or weft) threads is less than or equal to 20%, these threads constituting the binding weave of the unidirectional weft (or warp) fabric.

Preferably also, the warp and weft fabric according to the invention is produced on the basis of carbon, glass, high density polyethylene, aramid, silicon carbide, ceramic yarns or else based on mixtures and combinations of such sons.

More particularly, the invention relates to a warp and weft fabric made from 6K carbon yarns, the grammage of the fabric being approximately 200 g / m ² , in particular 193 g / m ² and the volume content of fibers d '' about 38%, under a pressure of 10 ⁴ Pa.

The invention also relates to a warp and weft fabric made from 12K carbon threads, the grammage of the fabric being approximately 200 g / m ² , in particular

193 g / m ² and the volume content of fibers greater than or equal to 38%, under a pressure of 10 ⁴ Pa.

It also relates to a warp and weft fabric made from aramid yarns, the titer of which is approximately 240 tex, the grammage of the fabric being approximately 180 g / m ² , in particular 175 g / m ² and the volume rate. of fibers greater than or equal to 42%, under a pressure of 10 ⁴ Pa.

The invention further relates to a fabric made from glass yarns, 80% by weight of the weft (or warp) yarns being yarns whose title is approximately 320 tex, the grammage of the fabric being approximately 120 g / m ² and the volume rate of fibers being greater than or equal to 26%, under a pressure of 10 ⁴ Pa.

The invention also relates to a process for obtaining a warp and weft fabric based on multifilament technical yarns of which at least 80% by weight are yarns with 0 twist turn / m whose title, for a given grammage of the fabric , is higher than that traditionally used, consisting of:

- unwind the wires at 0 twist turns without bringing them twist,

- weaving the threads so that their width is, over their entire length, greater than or equal to the original width of the threads before weaving, said untwisted threads being placed in the direction (warp or weft) having the largest share of yarns by weight when the weight ratio of warp and weft yarns is greater than 80/20, these yarns constituting all the yarns of the fabric when said ratio is less than 80/20, the volume content of fibers in the fabric being substantially constant and greater than or equal to that of a traditional fabric based on threads of equal or lower titer. Preferably, when the weight share of the warp (or weft) threads is less than 20%, these threads are unwound and woven in the conventional manner.

Preferably, the method also consists in spreading the threads in the fabric obtained. In a first embodiment of the method, the spreading step is carried out after weaving. In a second embodiment, the spreading step is carried out before a subsequent transformation of the fabric, such as dusting, prepreg or laminating. In another mode, the method also consists in spreading the threads before weaving. This means contributes to obtaining an appropriate volume content of fibers in the final fabric.

The invention also relates to a device for spreading the threads in the fabric, in accordance with the production process according to the invention. According to the invention, the device comprises a vibrator on which is mounted a rotating roller, intended to come into contact with the fabric. Preferably, the vibrator is a pneumatic vibrator whose frequency is 100 Hertz under a pressure of 6 10 ⁵ Pa.

The invention will be better understood and other objects, advantages and characteristics thereof will appear more clearly on reading the description which follows, given with reference to the appended drawings in which:

- Figure 1 schematically illustrates an overview of an installation for obtaining a fabric according to the invention;

- Figure 2, which schematically shows a frame unwinding device, is a partial section of Figure 1 along II-II;

FIG. 3 schematically represents a device for spreading the fibers in the fabric,

- Figure 4 includes Figures 4a to 4d which are histograms illustrating the volume rate fibers for a given fabric, obtained by three different embodiments,

- Figure 5 includes Figures 5a to 5c which illustrate Example 1, Figure 5a showing a warp and weft fabric made according to a standard weaving, Figure 5b a fabric made according to a weaving with unwound weft and Figure 5c a fabric obtained by weaving with an unwound weft and vibration and - Figure 6 includes Figures 6a and 6b and illustrates the Fabric n ° 4 of Example n ° 1, Figure 6a representing the Fabric n ° 4 after weaving with unwound weft and Figure 6b, Fabric # 4 after weaving with unwound weft and vibration. The elements common to the different figures will be designated by the same references.

Reference is made to FIG. 1 which is a diagram illustrating the continuous production of warp and weft fabrics according to the invention. As shown in Figure 1, a device

1 allows the weaving loom 4 to be supplied with warp threads 2. It is designed to unwind warp threads without providing them with torsion, and by giving them appropriate tension. Thus, the warp threads 2 do not have a twist greater than the original twist of the threads.

Preferably, in warp and weft, threads are used which do not initially have a twist. These threads are commonly called twist / twist yarns or "twist" threads. The advantage of not making the wires twist will be explained in more detail with regard to the weft wires. The warp threads 2 are brought (arrow FI) to the weaving loom 4. This is shown diagrammatically and comprises frames 5, a comb 6 and a lance 7. The lance 7 introduces, in the warp threads, a weft thread 8 which comes (arrow F2) from a weft reel 9 unwound by a device 10, here called weft unwinder.

This device 10 is designed not to twist or twist the weft threads. Thus, the weft threads 8, inserted by the lance 7, do not have a twist greater than the original twist of the threads.

In the context of the invention, it has been observed that, if we insert twisted weft threads or else having a twist greater than the original twist of the threads, it is not possible to obtain a fabric having a high volume rate of fibers. Indeed, whatever the type of thread, the width of the thread would be less than the original width of the threads before weaving, in particular at the place of the twists and no treatment carried out after weaving would allow the threads to be spread out so to make the tissue closed and thus obtain an appropriate volume content of fibers. This observation must be qualified with regard to the unidirectional fabrics which will be mentioned later.

Today, we use so-called "parade" frame donors. This type of device brings a twist to the wire since the wire receives a twist per length of wire equivalent to the perimeter of the reel from which it is unwound. This is why it is proposed to use, in the context of the invention, a frame unwinder of the "unrolled" type. In this type of unwinder which is also illustrated in FIG. 2, the weft thread 8 is unwound perpendicular to the axis 11 of the reel 9, a brake 12 being provided at the reel 9.

The coil of wire 9 is unwound using two pressure rollers 13 which drive the wire by means of a direct current motor 14. At the exit of the rollers, the wire 8 forms a loop whose position is transmitted to the using a puppet 15 connected to a potentiometer 16 acting on an amplifier 17. This amplifier controls the motor 14 so that the length differences absorbed by the loom are compensated for by accelerating or slowing down the motor 14.

Identical problems arise for the warp threads, and it is therefore also necessary that these are unwound by the device 1, without twisting.

Referring again to FIG. 1, the fabric 18 obtained after passing through the loom 4 is routed (arrow F3) in the rest of the manufacturing operations, after having passed over a trio 19. The fabric 18 is then optionally led into a spreading device 20. As will be seen later on reading ^" the examples, this spreading device is not always necessary.

This can be provided in certain cases, after the weaving operation, when the volume content of fibers is not appropriate. This additional step makes it possible to obtain a volume rate of fibers which is substantially constant in the fabric and suitable for the use of fabric to obtain composite materials having satisfactory mechanical properties.

FIG. 3 illustrates a non-limiting example of embodiment of such a spreading device 20. It essentially comprises a vibrator 21 on which is mounted a rotating roller 22, intended to come into contact with the fabric 18.

One can envisage other means than the roller 22. This can be replaced by another device coming into contact with the fabric 18.

Preferably, the vibrator 21 is a pneumatic vibrator whose frequency is 100 Hertz, under a pressure of 6 x 10 ^& Pa. It is understood that by passing over the fabric 18, the device 20 makes it possible to spread the wires in the fabric, by means of the vibrations communicated by the roller 22.

Throughout the description, the term “spreading the threads in the fabric” is understood to mean increasing a dimension of the cross section of the threads in the plane of the fabric and correspondingly decreasing a dimension of the cross section threads in a direction perpendicular to the plane of the fabric.

It can be noted here that the device 20 is only effective if the warp and weft threads do not have a twist greater than the original twist of the threads before weaving. Indeed, if the weft threads, or even only some of them, were twisted, gaps would still be present at the twists, even after passing under the device 20. This remark must be qualified for the unidirectional fabrics which will be described later.

The advantage of this spreading device 20 will be detailed in the following description, in particular with reference to FIG. 4.

Other spreading devices can also be provided, in particular by ultrasound, by fluid jet or by sound waves. Still with reference to FIG. 1, after having been led by means of the deflection rollers 25 and 26, possibly under the device 20, the fabric 18 is conveyed (arrow F4) via the deflection roller 27, towards a roller 28 on which it is wound.

In this regard, it can be emphasized that the spreading step is not necessarily carried out as soon as the fabric is obtained, that is to say as soon as it leaves the loom, after any intermediate storage.

Indeed, the fabric is generally not used immediately after its weaving. It can be stored for some time before n • a transformation takes place such as dusting, prepreg or laminating. It appeared advantageous to spread the fibers in the fabric just before the transformation to be carried out.

In order to contribute to a better volume ratio of fibers in the fabric, it is also possible to provide a device making it possible to spread the threads before weaving. Thus, a spreading device can be provided before weaving, after weaving or before and after weaving.

In the above description, the method according to the invention has been applied to all the threads of the fabric, both in warp and in weft. It is also possible to envisage applying this process to only part of the threads, in particular for obtaining unidirectional fabrics. Throughout the description, the term "unidirectional fabric" means a fabric comprising at least 80% by weight of warp or weft threads.

The term “weight ratio of warp threads and weft threads” will also be used to denote the warp / weft or weft / warp ratio, the most important ratio being retained.

Thus, a unidirectional warp fabric will be a fabric of which 80% by weight of the threads are warp threads while a unidirectional weft fabric will be a fabric of which 80% by weight of the threads are weft threads, these two fabrics having a ratio by weight of warp threads and weft threads greater than or equal to 80/20. Thereafter, reference will be made to a unidirectional weft fabric. The warp threads of such a fabric constitute in practice binding threads.

In this case, all the weft threads are threads with 0 twist / m, the warp threads can be any.

The device 1 for supplying the weaving loom with warp threads can be a classic device, possibly bringing a twist to the wires.

On the other hand, as before, a device such as that referenced 10 is used for the weft yarns which does not bring any twist to the yarns.

The rest of the operations are carried out as above, the fabric 18 obtained also being led into a spreading device if necessary. It should be emphasized that all of the threads placed in the direction comprising the largest share of the threads by weight, that is to say the weft threads, are woven in accordance with the method according to the invention. This is necessary so that the fabrics obtained have a volume ratio greater than or equal to that of a traditional fabric based on threads of equal or lower title, for a given grammage of the fabric.

Thus, the method according to _the invention may be used only for part of the son when it is desired to carry out a unidirectional weave. However, in this case, no weft thread has a twist greater than the original twist of the threads. Indeed, in the opposite case, the width of the thread would be less than the original width of the threads before weaving and it would not be possible to obtain a fabric having a high volume content of fibers. Likewise, the spreading device 20 would not be effective. It has been observed that, insofar as the fabric has at least 80% of the threads by weight in the weft direction, which are woven according to the method according to the invention, the fabric has a volume ratio of satisfactory fibers even if the warp threads are woven in a conventional manner.

The proportion of warp threads cannot however be greater than 20%. When it is desired to produce a fabric whose weight ratio of weft threads and warp threads is less than 80/20, the method according to the invention must be applied to all of the threads of the fabric, in accordance with the initial description. These remarks can easily be transposed to a unidirectional warp fabric in which all the warp threads are twist yarns, the weft threads can be any.

In this case, the device making it possible to feed the loom with weft threads can be a conventional device and a device such as that referenced 1 is used for the warp threads which does not bring any twist to the threads.

The advantage of the method which has just been described with reference to FIGS. 1 to 3 will be highlighted with regard to the following examples.

EXAMPLE 1;

Five balanced fabrics based on carbon threads having a surface mass of 193 g / m ² were produced for comparison. Conventionally, the term "balanced fabric" denotes a fabric comprising substantially as many warp threads as weft.

The weave of the fabrics is a taffeta. The title of the sons

12 K is greater than that of 6K wires which is itself greater than that of 3K wires. Fabric # l: . High resistance carbon wires TORAYCA FT 300B 3K 40B (commercial reference from the supplier Toray).

. 3000 filaments (3K) (Title: 198 tex). Yarns at 0 turns of twist / m

. Carbon density: 1.76 g / cm ³

. Initial width of the wire on spool:

1.74 mm. Fabric 2:. Carbon wires TORAYCA FT 300B 6K 40B

(Toray commercial reference), having the same characteristics as that used for the manufacture of fabric n ° l but comprising. 6000 filaments (6K) (Title: 396 tex). Yarns at 0 turns of twist / m

. Carbon density: 1.76 g / cm ³ . Initial width of the wire on spool: 2.1 mm. Fabric # 3:

. High resistance carbon wires TORAYCA T700SC 12K 50C (commercial reference from the supplier Toray). . 12,000 filaments (12 K) (Title: 800 tex). Yarns at O twist / m. . Carbon density: 1.8 g / cm ³ . . Initial width of the wire on spool: 6 mm.

Fabric # 4:

. High resistance carbon wires TORAYCA T300JC 12K 50C (commercial reference from the supplier Toray). . 12,000 filaments (12 K) (Title: 800 tex)

. Yarns at 0 twist turns / m. Carbon density: 1.78 g / c. Initial width of the wire on spool: 5 mm. Fabric 5:

. AKZO Tenax HTA 5131 800 tex F 12 000 high resistance carbon threads (commercial reference from the supplier Akzo). . 12,000 filaments (12 K) (Title: 800 tex).

. Yarns at O twist turn / m. Carbon density: 1.78 g / cm ³ . Initial width of the wire on spool = 3.2 mm. Three weaving methods are used, it being understood that in the three methods, the warp threads are unwound without bringing them any twist, in particular by using "unwound" type chain unwinders. - Standard weaving (S): the weft threads are unwound by weft feeders "on the run", which bring a twist to the thread.

- Weaving with unwound weft (SD): weft yarns are unwound by "unwound" weft unwinders, which do not twist the yarn.

Weaving with unwound weft and vibration fSDVl: This is the previous weaving process in which a vibration system such as that described above with regard to FIG. 3 is used.

Fabric n ° 1 is intended to serve as a reference for other fabrics, for ^" the three weaving processes envisaged. It is woven only according to standard weaving (S). It is recognized that such a fabric has a volume content of fibers which is entirely compatible with use in the manufacture of a composite material having 21

satisfactory mechanical properties. The volume content of fibers in Fabric No. 1 is 38%.

The results obtained are summarized in the following tables 1 to 3 (the thickness measurements are carried out under a pressure of 10 ⁴ Pa):

TABLE N ^β l

22

TABLE N ° 3

FIG. 4 also illustrates the preceding results in the form of histograms, FIGS. 4a to 4d for each of the tissues 2 to ₄ .

In each of Figures 4a to 4d is indicated on the ordinate, the value of 38% of the TVF that _of the corre Fabric No. l which serves as a reference.

Fabric n ° 2: A volume rate of fibers greater than or equal to 38% is obtained with a weaving with an unwound weft and vibration (SDV). (TVF = ₃₈ %).

Fabric N 3: A volume rate of fibers greater than or equal to 38% is already obtained with a weaving with an unwound weft (SD) (TVF = ₄ 7% ₎ . The volume content of fibers is even higher with a weaving with an unwound weft and vibration (SDV) (TVF = 54%).

Fabric # 4: A fi volume rate _b er greater than or equal to 38% was also obtained with weaving with a weft using the unwound (FST = 39%). The volume ratio is even more important with a weaving with weft in the place and vibration (TVF = 5 ₁ % ₎ .

Fabric n ° 5: A volume rate of fibers greater than or equal to 38% is obtained with a weaving with an unwound weft and vibration (TVF = 48% ₎ . Thus, thanks to the invention, a fabric based on 6K yarns (Fabric n ° 2) has a constant volume density of fibers in the fabric and which is greater than or equal to that of a fabric based on 3K yarns (Fabric n ° 1) obtained by standard weaving.

It can be noted that when Fabric No. 2 is obtained by standard weaving, the volume content of fibers is much lower than that of Fabric No. 1 (TVF = 29%). It would therefore not be suitable for obtaining a composite material having acceptable mechanical properties.

We also note that the width of the warp and weft threads (3 mm) is over the entire length of the threads, greater than or equal to the original width of the threads before weaving (1.74 mm).

In the example of Fabric No. 2, an adequate volume rate is only obtained with a weaving with an unwound weft and vibration (SDV). However, such a volume ratio can also be obtained with a weaving with an unwound weft only, as will appear from the analysis of the results obtained with Fabrics Nos. 3, 4 and 5.

Fabrics 3, 4 and 5 are fabrics made from 12K yarns. When obtained by traditional weaving, the volume content of fibers in the fabric is much lower than that of a fabric made from yarns. 3K (Fabric n ^β l) obtained by this same weaving. Such fabrics would therefore not be suitable for producing composite materials having acceptable mechanical properties.

On the other hand, it can be seen that by using the method according to the invention, it is possible to obtain fabrics based on 12 K yarns which have a volume ratio of fibers greater than or equal to that of Fabric No. 1.

Such a volume ratio of fibers can be obtained by a weaving with an unwound weft only (Fabric n ° 3: TVF = 47% and Fabric n ° 4: TVF = 39%) or by a weaving with an unwound weft and vibration (Fabric 5: TVF = 48%). These fabrics based on 12 K wires can therefore be used to obtain composite materials having satisfactory mechanical properties.

We also note that the width of the warp and weft threads is, over the entire length of the threads, greater than or equal to the original width of the threads before weaving (Fabric n ° 3: 6; 7 or 8 mm and 6 mm; Fabric n ° 4: 5.2; 7 or 8 mm and 5 mm; Fabric n ° 5: 7 mm and 3.2 mm).

In order to better understand the process according to the invention, reference can be made to FIGS. 5 and 6. FIG. 5 illustrates the three types of weaving that are used (S, SD, SDV).

The reference 29 designates for example warp threads and the reference 30 weft threads.

After standard weaving (Figure 5a) _; the fabric has a relatively large thickness, which leads to a relatively low volume ratio of fibers. This is illustrated by the results obtained for Fabrics n ° 2 to n ° 5 (Cf Figure

4).

A weaving with an unwound weft (FIG. 5b) leads to fabrics having a smaller thickness and therefore to a higher volume content of fibers. Figure 4 also shows this increase in the fiber volume rate. Finally, weaving with an unwound weft and vibration (Figure 5c) makes it possible to obtain a fabric whose thickness is even thinner and the volume rate of fibers is greater. This is shown by the results appearing in Figure 4.

We can also refer to Figure 6 which shows diagrams of Fabric n ° 4 after weaving with an unwound weft (Figure 6a) and after weaving with an unwound weft and vibration (Figure 6b). In both cases, the volume content of fibers is higher than that obtained for Fabric No. 1 which serves as a reference. However, it can be seen that the interstices between the threads are less significant in FIG. 6b than in FIG. 6a, the vibration step having led to spreading of the fibers in the fabric. EXAMPLE N ^e 2:

The two fabrics compared are balanced fabrics, made from aramid yarns: KEVLAR 49 1270 dtex T968 for Fabric n ° l and KEVLAR 49 2400 dtex T968 for Fabric n ° 2, (Dupont de Nemours commercial reference) and have a surface mass of 175 g / m ² . The density of the wires is 1.45 g / cm ³ and the wires have a twist / m turn. Fabric # 1:. Thread count = 127 tex

. Initial width of the wire on spool = 1.1 mm. Armor = Satin 4 Fabric n ° 2:

. Thread count: 240 tex. Initial wire width on spool = 1.8 mm

. Armor = taffeta.

As in Example 1, three weaving methods are used: standard weaving (S), weaving with unrolled weft (SD) and weaving with unrolled weft and vibration (SDV).

Fabric no. 1 serves as a reference for Fabric no. 2, for the three weaving processes used. Fabric n ° 1 is woven only according to standard weaving (S). This fabric has a volume content of fibers that is entirely compatible with use in the manufacture of a composite material having satisfactory mechanical properties. The volume rate of fibers in Fabric 1 is 42%.

The results obtained are collated in Tables 4 to 6 (the thickness measurements are carried out under a pressure of 10 ⁴ bar):

TABLE N ° 6

It can be seen that for Fabric No. 2, a volume content of fibers greater than or equal to 42% is obtained with a weaving with an unwound weft and vibration (SDV) (TVF = 45%). This fabric is therefore perfectly suitable for obtaining a composite material having satisfactory mechanical properties. On the other hand, when Fabric n ° 2 is woven according to a standard weaving (S), the volume content of fibers is 38%, lower than that of Fabric n ° 1. This fabric would therefore not be suitable for obtaining a composite material having good mechanical properties.

Thus, it can be seen that the method according to the invention makes it possible to obtain a fabric produced from yarns with a higher titer than Fabric n ° 1, while having a constant volume density of fibers in the fabric and greater than that Fabric # 1.

It is also noted that the width of the warp and weft threads is, over the entire length of the threads, greater than or equal to the original width of the threads before weaving. FIG. 5 also illustrates this exemplary embodiment of the invention. EXAMPLE 3: The two fabrics of this example are unidirectional fabrics produced on the basis of glass strands and have a surface mass of 120 g / m ² . The chosen armor is taffeta. The weight distribution of the threads is as follows: 80% in weft and 20% in warp, for the two fabrics. These therefore practically have the form of a unidirectional ply, the warp threads playing the role of binding threads. In this example, it is more particularly a unidirectional weft fabric.

Fabric # l:

. Chain material: EC9 34 x 2 glass yarn S150 1383 wire density = 2.54

. Weft material: glass yarn: ROVING 160 tex

(Cosmostrand 160 tex) Yarn title: 160 tex Initial width of the yarns on the spool = 0.9 mm Yarn at 0 twist / m Fabric n ° 2:

Warp material: Yarns with the same characteristics as the warp yarns of Fabric No. l

. Weft material: ROVING 320 tex glass yarn (R099 320 TEX L 177)

Title of the threads: 320 tex initial width of the thread on the spool: 2.4 mm threads with 0 twist turn / m As in Examples 1 and 2, three weaving methods are used: standard weaving (S), weaving with unwound weft (SD) and weaving with unwound weft and vibration (SDV).

In accordance with the preceding description, the method according to the invention is applied here only to the weft threads, the warp threads being woven in a conventional manner.

Fabric no. 1 serves as a reference for Fabric no. 2, for the three weaving processes used. Fabric n ° l is woven only according to standard weaving (S). It has a volume content of fibers compatible with use in the manufacture of a composite material having satisfactory mechanical properties. The volume content of fibers in fabric No. 1 is 26%.

The results obtained are collated in Tables 7 to 9 (the thickness measurements are made under a pressure of 10 ⁴ Pa):

TABLE N ° 7

TABLE N ° 8

TABLE N ° 9

Thus, for Fabric n ° 2, a volume content of fibers greater than 26% is obtained with a weaving with an unwound weft and vibration (SDV) (TVF = 28%). Such a fabric is perfectly suitable for producing a composite material having satisfactory mechanical properties. Fabric n ° 2 is not suitable for such an application when it is obtained by a standard weaving, the volume rate being much lower than that of Fabric n ° 1 (20.5%).

The process according to the invention therefore makes it possible to obtain a fabric produced from yarns which are, in a proportion of 80% by weight corresponding to the weft yarns, of higher titer than the weft yarns of Fabric No. 1, this fabric having a volume content of fibers constant in the fabric and greater than that of Fabric No. 1.

It is noted that over the entire length of the threads, the width of the weft threads is greater than or equal to the original width of the threads before weaving.

These examples show all the interest of the process according to the invention. This allows, thanks to original weaving methods, to use threads of relatively high titer for a relatively low grammage, while having an appropriate volume content of fibers.

Such properties are obtained in particular by the fact that the warp and / or weft threads are used so that the twist which they present in the fabric is not greater than their original twist. When the device for spreading the threads in the fabric is necessary, the absence of additional twisting allows it to be fully effective and to lead to maximum spreading of the fibers in order to obtain a closed fabric.

Claims

CLAIMS 1. Warp and weft fabric based on multifilament technical yarns, of which at least 80% by weight of the yarns have the following characteristics in combination:

(b) - the threads do not have a twist greater than the original twist of the threads before weaving, which are, in the same proportion, threads with 0 twist turn / m,

(c) - the width of the threads is over the entire length of the threads, greater than or equal to the original width of the threads before weaving;

These threads constituting all the threads in the direction comprising the largest proportion of threads by weight when the weight ratio of the weft threads and warp threads is greater than or equal to 80/20 and all the threads of the fabric when this ratio is less than 80/20, the volume content of fibers being substantially constant in the fabric and greater than or equal to that of a traditional fabric based on yarns of equal or lower titer.

2. Warp and weft fabric based on multifilament technical yarns according to claim 1, characterized in that it has the following characteristics in combination:

(b) - the warp threads and the weft threads do not have a torsion greater than the original twist of the threads before weaving, which are threads with 0 twist turn / m, (c) - the width of the warp and weft threads is over the entire length of the threads, greater than or equal to the width of origin of the threads before weaving,

(d) - the volume content of fibers is substantially constant in the fabric and greater than or equal to that of a traditional fabric based on yarns of equal or lower titer.

3. Fabric according to claim 1 characterized in that when the weight share of the warp (or weft) threads is less than or equal to 20%, these threads constitute the binding weave of the unidirectional weft (or warp) fabric.

4. Fabric according to one of claims 1 to 3, characterized in that it is made on the basis of carbon threads, glass, high density polyethylene, aramid, silicon carbide, ceramic or even based on mixtures or combinations of such threads.

5. warp and weft fabric according to claims 2 and 4, characterized in that it is produced on the basis of 6K carbon threads, the grammage of the fabric being approximately 200 g / m ² , in particular 193 g / m ² and the volume content of fibers greater than or equal to 38%, under a pressure of 10 ⁴ Pa.

6. warp and weft fabric according to claims 2 and 4, characterized in that it is produced on the basis of 12 K carbon threads, the grammage of the fabric being approximately 200 g / m ² , in particular 193 g / m ² and the volume content of fibers greater than or equal to 38%, under a pressure of 10 ⁴ Pa.

7. warp and weft fabric according to claims 2 and 4, characterized in that it is made from aramid yarns whose titer is approximately 240 tex, the grammage of the fabric being approximately 180 g / m ² , in particular 175 g / m ² , and the volume content of fibers being greater than or equal to 42%, under a pressure of 10 ⁴ Pa.

8. Fabric according to claims 3 and 4, characterized in that it is made from glass son, 80% by weight of the weft (or warp) son being son whose title is about 320 tex , the grammage of the fabric being approximately 120 g / m ² and the volume content of fibers being greater than or equal to 26%, under a pressure of 10 ⁴ Pa.

9. Method for obtaining a warp and weft fabric based on multifilament technical yarns of which at least 80% by weight are yarns with 0 twist turn / m whose title, for one. given grammage of the fabric, is higher than that traditionally used, the process consisting in:

- unroll the threads at 0 twist turn / m without adding any twist to them, - weave these threads so that their width is, over their entire length, greater than or equal to the original width of the threads before weaving, said twist-free yarns being placed in the direction (warp or weft) comprising the largest share of yarns by weight when the weight ratio of warp and weft yarns is greater than 80/20, these yarns constituting all the yarns of the fabric when said ratio is less than 80/20, the volume ratio of fibers in the fabric being substantially constant and greater than or equal to that of a traditional fabric based on threads of equal or lower titer.

10. Method according to claim 9, characterized in that when the weight share of the warp (or weft) threads is less than 20%, these threads are unwound and woven in a conventional manner.

11. Method according to claims 9 or 10, characterized in that it further consists in spreading the son in the fabric obtained (18).

12. Method according to claim 11, characterized in that the spreading step is carried out after weaving.

13. Method according to one of claims 11 or 12 characterized in that the spreading step is carried out before a subsequent transformation of the fabric, such as dusting, prepreg or laminating.

14. Method according to claims 9 to 13, characterized in that it also consists in spreading the threads before weaving.

15. Device for spreading the threads in a fabric according to the method according to claims 11 to 14, characterized in that it comprises a vibrator (21) on which is mounted a rotating roller (22), intended to come into contact with the fabric (18).

16. Device according to claim 15, characterized in that the vibrator (21) is a pneumatic vibrator whose frequency is 100

Hertz under a pressure of 6 x 105 Pa.