EP0553000B1 - Process for securing a fibrous structure - Google Patents

Description

The present invention relates to the production of reinforcements for the production of fiber-matrix composite parts with high mechanical and / or thermal performance.

It is known that, for the production of such composite parts, fibrous reinforcements are produced which are trapped in a hardenable matrix. The fibers which can be used for the production of such fibrous reinforcements are for example made of carbon, boron, glass, aramid, etc. In the following, such fibers will be called "technical fibers".

• assembler des pièces fibreuses individuelles pour former l'armature désirée :
• lier entre elles des couches de matière fibreuse superposées pour former une pièce fibreuse, à partir de laquelle on réalisera une armature ou un élément d'armature ;
• introduire des fibres de direction désirée dans une pièce fibreuse.

It is moreover known that, in the production of said fibrous reinforcements, stitching processes are often carried out by means of such technical fibers. Indeed, by stitching one can, for example:

• assemble individual fibrous pieces to form the desired reinforcement:
• bonding superimposed layers of fibrous material together to form a fibrous part, from which a reinforcement or a reinforcement element will be produced;
• introduce desired direction fibers into a fibrous piece.

The tests of stitching such fibrous parts with continuous threads made up of technical fibers, by the use of conventional sewing machines, have proved disappointing, if not impossible. Indeed, because of their nature, the technical fiber threads introduced by the stitching needle into said fibrous parts are deteriorated by this needle, at point of breaking frequently, stopping an ongoing stitching process. Furthermore, the frequency of breakage of the stitching threads is then all the greater the thicker the fibrous piece, so that the stitching of thick fibrous pieces is impossible.

Anyway, even when the technical fiber thread does not break during the stitching, it can break after it, because, at each stitch, a weakened area is created at the intersection of the needle thread and the shuttle bus.

This known prior art is for example described in document DE-A-2 704 378. It can be seen there that the stitching of the fibrous piece is carried out with interlacing of a needle thread formed by the technical fiber thread and of '' a shuttle thread in such a way that, at each stitching point, the technical thread is introduced into said fibrous part by a needle, which is driven in an alternating movement and which, in its forward stroke, crosses said part fibrous by penetrating by a first face of the latter and by coming out of it by a second face opposite to the first, said shuttle wire then being entangled with said technical wire on the side of said second face, while, during the course of said needle, the shuttle wire is pulled by said technical wire inside said fibrous part. It will be noted that, in an attempt to avoid breaking the technical thread in contact with the needle, document DE-A-2 704 378 provides an auxiliary needle.

Anyway, in industrial reality, to be able to stitch a fibrous piece with a technical fiber thread, we have to make complex stitching devices and / or comprising a special support for the fibrous piece to stitch, as those for example described in documents US-A-2,283,802 and US-A-3,322,868.

The object of the present invention is to remedy these drawbacks and to allow the stitching of parts made of technical fibers by means of threads, also of technical fiber, by using conventional sewing machines, even in the case where said parts are thick.

• ledit fil d'aiguille est constitué par un fil auxiliaire résistant à la traction ;
• ledit fil de navette est constitué par ledit fil en fibre technique ; et
• la tension du fil de navette et la tension du fil d'aiguille sont réglées à des niveaux suffisamment faible et suffisamment élevé, respectivement, pour que, à la fin dudit point de piqûre, ledit fil de navette fasse saillie à l'extérieur de ladite pièce fibreuse, du côté de ladite première face de celle-ci, et ledit fil d'aiguille se trouve complètement à l'extérieur de ladite pièce fibreuse, également du côté de ladite première face de celle-ci.

To this end, according to the invention, the process for the stitching, by means of a technical fiber thread, of a fibrous piece intended for the production of a composite fiber-matrix piece, process according to which the stitching is carried out with interlacing of a needle thread and a shuttle thread in such a way that, at each stitching point, the needle thread is introduced into said fibrous part by a needle, which is animated by a reciprocating movement and which, in its forward stroke, passes through said fibrous part by penetrating by a first face of the latter and by coming out of it by a second face opposite to the first, said shuttle thread then being intermingled with said needle thread side of said second face, while, during the return stroke of said needle, the shuttle thread is pulled by said needle thread inside said fibrous part, is remarkable in that:

• said needle thread is constituted by an auxiliary tensile thread;
• said shuttle wire consists of said technical fiber wire; and
• the shuttle thread tension and the needle thread tension are adjusted to sufficiently low and sufficiently high levels, respectively, so that, at the end of said stitching, said shuttle thread protrudes outside said fibrous part, on the side of said first face thereof, and said needle thread is completely outside of said fibrous part, also on the side of said first face thereof.

Thus, thanks to the invention, the technical fiber thread can not be broken or weakened by the stitching needle. The technical fiber thread is only in contact with the auxiliary needle thread, which pulls it into the fibrous part. It will be noted that the present invention goes against the knowledge of those skilled in the art, since the latter has always used as a needle thread, the technical thread with which he wished to piguage (see DE-A-2 704 378).

Because of the particular adjustment of the thread tensions used in the present invention, only the technical fiber thread is trapped inside said fibrous part. The auxiliary wire is external to it and cannot therefore constitute heterogeneity for said fibrous part. Such an auxiliary wire, acting only as a means of pulling the wire shuttle in technical fiber, can be formed by any known wire having the tensile strength appropriate to its office. It can, for example, be constituted by a known textile yarn, made of natural or synthetic fiber.

In addition, being external to said fibrous part, it can be easily eliminated from the latter.

It will also be noted that, given the fibrous texture of said piece, the portions of the technical fiber yarn located inside the fibrous piece are held in place by the lateral pressure exerted by the other fibers of said piece . As a result, it is possible, if necessary, to eliminate the parts of the technical fiber yarn which appear on said first and second faces of the fibrous part, without thereby affecting the solidity of the stitches.

It is known that, on conventional sewing machines, there are means for adjusting the tension of the needle thread and means for braking the shuttle thread.

In order to obtain the puncture "point" in accordance with the present invention, it may be necessary to provide additional means, such as baffles, flanged wire brakes, etc., to increase the tension to the appropriate level. needle textile thread. On the other hand, it may be necessary to reduce the tension imposed on the shuttle wire by said braking means, for example by reducing as much as possible the friction involved in their operation.

Furthermore, it will be noted that it is advantageous that the sewing machine used to implement the method according to the present invention usually comprises a presser foot for engaging and guiding said fibrous piece in a relative displacement relative to the needle, allowing the production of stitches. Indeed, the presser foot exerts pressure on said fibrous part and therefore a compaction thereof. Such packing favors the production of the stitch according to the invention and the thickening of said fibrous part.

Such a fibrous piece can be intended for producing a composite fiber-matrix piece subjected to a stitching operation using a needle thread and a shuttle thread and remarkable in that it comprises technical fibers passing through it parallel to its thickness and formed by said shuttle wire.

A composite fiber-matrix part can be produced from such a fibrous part by forming said matrix in the latter. Preferably, in this composite part, said technical fibers are not connected to each other by portions of shuttle wire transverse to the thickness of said fibrous part.

The figures of the appended drawing will make it clear how the invention can be implemented. In these figures, identical references designate similar elements.

FIG. 1 is a diagrammatic view, in section, of a fibrous piece, making it possible to illustrate the formation, in known manner, of stitches in said piece using a needle thread and a shuttle wire.

Figure 2 is a schematic sectional view, similar to Figure 1, illustrating the stitching in accordance with the present invention.

FIG. 3 shows, in a similar view, the fibrous part of FIG. 2, after elimination of the parts of the needle and shuttle threads external to said fibrous part.

The part 1, shown in FIGS. 1 to 3, is made up of technical fibers (carbon, glass, aramid, boron, etc.) and it has opposite faces 2 and 3. It can be in the form of a fabric, possibly impregnated with hardenable resin, or else in the form of a mattress in which the fibers, dry or pre-impregnated with hardenable resin, are arranged in an organized fashion, in two or more determined directions or else distributed randomly. The fibrous part 1 can even be made up of several individual superposed layers.

In FIG. 1, the process of stitching said fibrous piece 1 is illustrated schematically by means of a needle thread 4 coming from a reel, by means of tension adjustment means, and a thread shuttle 5 from a bobbin, by means of wire braking means. In this figure, for clarity, the needle, the shuttle, the needle thread spool, the bobbin, said tension adjustment means and said braking means have not been shown; in addition, it was assumed that a relative movement of displacement existed between the needle and the fibrous part 1, this relative displacement being symbolized by the arrow D.

Thus, as illustrated diagrammatically at the right end of FIG. 1, the needle through which the needle thread 4 enters the fibrous part 1 through the face 2 thereof, crosses said fibrous part parallel to its thickness e and projects outside the face 3 by forming a loop 6 with the needle thread 4. The shuttle, arranged on the side of the face 3 and containing the shuttle thread bobbin 5, crosses then the loop 6. As soon as the loop 6 has thus been crossed by the shuttle thread 5, the needle rises, draws with it its own needle thread 4 and tightens the loop 6 which traps the thread 5 coming from the shuttle and pulls it through the needle thread 4. This process is repeated throughout a stitch line thanks to the relative movement of movement D. A series of stitch stitches 7 is thus obtained.

At each completed stitching point 7, the needle thread 4 and the shuttle thread 5 each form a loop, respectively 8 and 9, said loops 8 and 9 passing one inside the other and forming a contact point 10 between needle thread 4 and shuttle thread 5.

Usually, the means for adjusting the tension of the needle thread 4 and the braking means for the shuttle thread 5 are adjusted so that the contact points 10 are within the thickness of the fibrous part 1, like this is shown in figure 1.

The various stitching points 7 are connected to each other by bridges 11 of the needle thread and by bridges 12 of the shuttle thread, said bridges 11 resting on the face 2 of the fibrous part 1, while the bridges 12 rest on the face 3 of the latter.

If it is desired to introduce technical fibers into the fibrous part 1 by stitching and that, for this purpose, continuous threads made of such technical fibers are used for the needle thread 4 and for the shuttle thread 5, as the needle thread 4 frequently breaks, all the more frequently the thicker the fibrous part 1, making stitching practically impossible. In addition, in the points 7 made between two breakages of thread, at the contact points 10, the needle thread 4 is greatly weakened, so that breaks in said needle thread 4 can occur at the contact points. 10 after stitching.

• on choisit, pour le fil d'aiguille 4, un fil textile classique résistant à la traction ;
• on choisit, pour le fil de navette 5, le fil en fibre technique que l'on veut introduire dans la pièce fibreuse 1 ;
• on règle la tension du fil d'aiguille 4 à un niveau élevé, par réglage adéquat desdits moyens de réglage de tension et, éventuellement, en prévoyant de tels moyens additionnels ; et
• on règle la tension du fil de navette 5 à un niveau faible, par réduction du freinage procuré par lesdits moyens de freinage.

To overcome this drawback and allow technical fibers to be introduced into the fibrous part 1 by stitching using an ordinary sewing machine, according to the invention:

• one chooses, for the needle thread 4, a conventional textile thread resistant to traction;
• we choose, for the shuttle wire 5, the technical fiber wire that we want to introduce into the fibrous part 1;
• the tension of the needle thread 4 is adjusted to a high level, by adequate adjustment of said tension adjustment means and, optionally, by providing such additional means; and
• the tension of the shuttle wire 5 is adjusted to a low level, by reduction of the braking provided by said braking means.

• la boucle 8 du fil d'aiguille 4 disparaît, ledit fil 4 reposant de façon rectiligne sur la face 2 de la pièce fibreuse 1 ; et
• la boucle 9 du fil de navette 5, traversée par ledit fil 4, est tirée par celui-ci, jusqu'à ce que son extrémité 9A (qui coopère avec le fil d'aiguille 4 pour la traction à travers la pièce fibreuse 1) fasse saillie par rapport à ladite face 2 de la pièce fibreuse 1.

Thus, by adequate adjustment of the tensions of the needle thread 4 and the shuttle thread 5 at these levels, high and low, respectively, it is ensured that, according to the invention, at the end of a stitching point ( carried out as explained above with regard to the right part of FIG. 1):

• the loop 8 of the needle thread 4 disappears, said thread 4 resting rectilinearly on the face 2 of the fibrous part 1; and
• the loop 9 of the shuttle thread 5, crossed by said thread 4, is pulled by the latter, until its end 9A (which cooperates with the needle thread 4 for pulling through the fibrous part 1) protrudes from said face 2 of the fibrous part 1.

Thus, inside the fibrous part 1, only the two branches 9B of each of the loops 9 remain, the wire 4 resting, stretched, on the face 2 of the fibrous part 1, while, on the side of the face 3 there remain bridges 12. This is illustrated diagrammatically in FIG. 2.

The branches 9B of the loops 9 of the shuttle wire 5 (technical fiber wire) are pressed and held in place inside the fibrous part 1 by the fibers constituting the latter. As a result, as illustrated in FIG. 3, after stitching, it is possible to eliminate, on the side of the face 2, the textile yarn 4 and the ends 9A of the loops 9 of the shuttle yarn 5, and / or, on the side of face 3, the bridges 12 of said shuttle wire 5, without harming the quality of the connection established through the fibrous part 1 by the branches 9B, thus constituting technical fibers transverse to the fibrous part 1.

Such transverse fibers 9B can be used to join individual fibrous layers of the fibrous part 1 (to form a thick fibrous element or else to join the overlapping edges of two individual fibrous elements), or even to form technical reinforcing fibers parallel to the thickness of said fibrous part 1.

If, in the usual way, the sewing machine used to implement the invention comprises a presser foot intended to guide the fibrous part 1 in its movement D relative to the needle, it is understood that this foot -biche can be used for compaction, parallel to the thickness of the fibrous piece 1, of the fibers constituting the latter, so that this thickness is regulated and that the formation of the stitching point, in accordance with the invention and illustrated by the Figure 2, is facilitated.

Of course, after completion of the stitching according to the invention, the fibrous part 1 can undergo all the known operations of impregnation and hardening of the matrix. It will also be noted that the elimination of the wire 4, of the ends 9A and / or of the bridges 12 can possibly be carried out after obtaining the composite-matrix part produced from the fibrous part 1.

Claims (4)

1. Process for the stitching, by means of an engineering-fibre thread (5), of a fibrous component (1) intended for the production of a fibre/matrix composite component, according to which process the stitching is produced by interlacement of a needle thread (4) with a shuttle thread (5) in such a way that, at each lock stitch (7), the needle thread is inserted into the said fibrous component by a needle which is given an alternating movement and, in its forward stroke, passes through the said fibrous component by penetrating via a first face (2) thereof and by emerging therefrom via a second face (3) opposite the first, the said shuttle thread then being interlocked with the said needle thread on the said second face side, while, during the return stroke of the said needle, the shuttle thread is drawn by the said needle thread into the said fibrous component, the tensions in the said shuttle threads and needle threads being different, characterized in that:

   - the said needle thread (4) consists of an auxiliary thread strong in tension;

   - the said shuttle thread (5) consists of the said engineering-fibre thread; and

   - the tension in the shuttle thread (5) and the tension in the needle thread (4) are adjusted, respectively, to sufficiently low and sufficiently high levels so that, at the end of the said stitch (7), the said shuttle thread (5) projects (at 9A) outside the said fibrous component (1), on the side of the said first face (2) thereof, and the said needle thread (4) lies completely outside the said fibrous component (1) also on the side of the said first face (2) thereof.
2. Process according to Claim 1, characterized in that the said auxiliary thread forming the needle thread is a textile thread made of natural or man-made fibre.
3. Process according to Claim 2, characterized in that the said auxiliary thread forming the needle thread is removed after stitching the said fibrous component.
4. Process according to either of Claims 1 and 2, characterized in that those parts (9A, 12) of the shuttle thread which appear on the said first and second faces (2, 3) of the said fibrous component (1) are removed after stitching the latter.

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