Abstract:
A device for spreading a cable of carbon fibers or carbon yarns, includes a disk mounted on a rotary shaft and provided with at least one comb adapted to comb a cable of carbon fibers or carbon yarns in a direction substantially parallel to the longitudinal direction of the fibers or yarns of the cable. The comb includes a plurality of teeth protruding radially toward the outside of the disk, and a device for rotating the disk around its rotary axis. Furthermore, a method for spreading a cable of carbon fibers or carbon yarns, includes at least making the teeth of the comb of the device flush with the cable in a direction substantially parallel to the longitudinal direction of the fibers or yarns of the cable.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based upon and claims the benefit of priority from French Patent Application No. 1258429, filed Sep. 10, 2012, the entire content of which is incorporated herein by reference. 
       BACKGROUND  
       [0002]    The present invention relates to the general field of producing fibrous sheets obtained by spreading several cables of fibers or yarns. 
         [0003]    One favored, but nonexclusive field of application of the invention is that of the production of three-dimensional fibrous preforms intended for the manufacture of annular parts made from a carbon-carbon (C-C) composite material, in particular the manufacture of brake disks. 
         [0004]    Brake disks made from composite material, in particular a composite material reinforced with carbon fibers and a carbon matrix, are well known. Their manufacture comprises the production of an annular fibrous preform and the densification thereof by a matrix. 
         [0005]    One known method for producing an annular fibrous preform consists of producing annular fibrous sheets (i.e., a so-called transverse sheet and a so-called circumferential sheet) by spreading and juxtaposition of several cables of carbon fibers or carbon yarns. The transverse and circumferential sheets are then bonded to each other by needling and are rotated. A thick annular fibrous structure is obtained by bonding several layers to each other by circular needling. 
         [0006]    This method, one example embodiment of which is described in document WO 2007/048946, thus makes it possible to obtain an annular fibrous preform directly from cables of carbon fibers or carbon yarns with practically no wastage. 
         [0007]    With such a method, the cables forming the transverse sheet are more precisely laid alternating in one direction and the other between the outer and inner coaxial rings of an installation. Inevitably, such a laying causes tightening of the carbon fibers or yarns toward the inner ring (relative to the outer ring). 
         [0008]    Consequently, to obtain an annular fibrous sheet that is completely homogenous over its entire width, it is necessary to compensate the increase in the surface density of the transverse sheet at the inner ring due to this tightening through a corresponding decrease in the surface density of the circumferential sheet in that location. 
         [0009]    To give the circumferential sheet a decreasing surface density between the outer ring and the inner ring of the installation, it is possible to form said sheet with cables having a same width, but having decreasing weights between the rings. However, this solution is relatively impractical to implement and requires the use of cables with different weights. 
         [0010]    Another solution consists of further spreading the cable(s) in question before they are laid. However, the known spreading solutions have a certain number of drawbacks. In particular, a spreading device by blowing air does not make it possible to freeze the width of the cable and thus prevent it from returning to its initial appearance before it was placed between the rings of the installation. It is also important for the spreading of the cable to be done while preserving the homogeneity of fibers within the cable. Lastly, it must be possible to spread the cable without creating tension in the cable. 
       SUMMARY  
       [0011]    There is therefore a need to be able to have a device for spreading a cable of carbon fibers or carbon yarns that meets all of these constraints. 
         [0012]    According to an aspect of the invention, this goal is achieved by a device for spreading a cable of carbon fibers or carbon yarns, comprising 
         [0013]    a disk mounted on a rotary shaft and provided with at least one comb adapted to comb a cable of carbon fibers or carbon yarns in a direction substantially parallel to the longitudinal direction of the fibers or yarns of the cable, said comb including a plurality of teeth protruding radially toward the outside of the disk, and means for rotating the disk around its rotary axis. 
         [0014]    With such a device, by causing the cable of carbon fibers or carbon yarns to pass through the teeth of the comb (or by making it flush with the teeth of the comb), it is possible to spread the fibers or yarns so as to widen the cable upon leaving the device. In fact, it has been observed that the teeth of the comb that penetrate the cable (or that are flush with it) to comb it in a direction substantially parallel to the longitudinal direction of the fibers or yarns forming the cable make it possible to spread the cable in the direction of its width. Furthermore, it has been observed that after combing, the cable remains at its width. It is in particular not necessary to use thermo-bonding fibers to ensure that the width of the cable is maintained. Furthermore, by causing the cable to pass in the same direction of movement as the direction of rotation of the disk of the device, it is possible to achieve widening of the cable without creating tension therein at the outlet of the device. Lastly, this device is easy to implement, does not create noise disturbance, and can easily be integrated into an installation for manufacturing an annular fibrous sheet. 
         [0015]    In an embodiment, the device further comprises means for adjusting the radial position of the comb on the disk. For example, a radial position adjusting device may be used. Thus, the comb may be mounted on the disk in a radial groove and capable of sliding inside the latter so as to allow adjustment of the radial position of said comb on the disk. 
         [0016]    Also in an embodiment, the device further comprises means for adjusting the orientation of the teeth of the comb. For example, an orientation adjusting device may be used. Thus, the comb may be mounted on the disk by means of a pivoting link so as to make it possible to adjust the orientation of the teeth of said comb. 
         [0017]    An aspect of the invention also relates to a method for spreading a cable of carbon fibers or carbon yarns, consisting of at least making the teeth of the comb of the device as previously defined flush with the cable in a direction substantially parallel to the longitudinal direction of the fibers or yarns of said cable. 
         [0018]    The cable of carbon fibers or carbon yarns may move relative to the device in a direction substantially tangential to the disk. 
         [0019]    Furthermore, the cable of carbon fibers or carbon yarns may move relative to the device in the same direction as the direction of rotation of said disk. It is thus possible not to generate tension in the cable. 
         [0020]    The teeth of the combs of the device may penetrate the cable without passing through it. In this way, it is easy to preserve homogeneity of fibers in the cable after it has passed through the teeth of the combs of the device. 
         [0021]    Another aspect of the invention also relates to the use of such a method to produce a fibrous sheet by spreading and juxtaposing several cables of carbon fibers or carbon yarns. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    Other features and benefits of the present invention will emerge from the description provided below, in reference to the appended drawings, which illustrate one non-limiting example embodiment thereof. In the figures: 
           [0023]      FIG. 1  is a perspective view of a device for spreading a cable of carbon fibers or carbon yarns according to the invention; 
           [0024]      FIGS. 2 and 3  diagrammatically show the operation of the device of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    An embodiment of the invention is particularly applicable to installations for manufacturing an annular fibrous preform intended to produce annular parts made from a carbon-carbon (C-C) composite material, in particular for the manufacture of brake disks. 
         [0026]    An installation for manufacturing an annular fibrous preform is described in patent application WO 2007/048946, the content of which is integrated by reference and will therefore not be outlined here. 
         [0027]    In substance, such an installation comprises a device for bringing in a first fibrous sheet and laying the latter on an annular support alternating in one direction and then the other between the outer and inner coaxial circular rings situated on either side of the annular support to form a first annular sheet, or transverse sheet. 
         [0028]    Such an installation also comprises a device for bringing in a second fibrous sheet on the annular support and laying the latter in the circumferential direction between the outer and inner rings to form a second annular sheet, or circumferential sheet. A device is provided to rotate the transverse and circumferential sheets around the axis of the rings. 
         [0029]    With this type of installation, it is necessary to give the circumferential sheet a decreasing surface density between the outer ring and the inner ring to balance the increasing surface density of the transverse sheet and thus to obtain an assembly having a substantially uniform surface density over its entire width. 
         [0030]    The device according to an embodiment of the present invention allows performing such a function by performing spreading (or widening) of one or more fibers or yarns cables (or tows)—here carbon cables—used to produce the circumferential sheet. 
         [0031]    It will be appreciated that the spreading device according to an embodiment of the present invention more generally applies to any installation in which one wishes to obtain widening of a fibers or yarns cable, this widening having to remain frozen after the cable has passed through the device. 
         [0032]    The spreading device  10  shown in  FIGS. 1 to 3  may thus adapt to an installation for manufacturing an annular fibrous preform like that described in patent application WO 2007/048946. In particular, this spreading device may be mounted just upstream from the device for bringing in the second fibrous sheet on the annular support of the installation. 
         [0033]    In this type of installation, the cable of carbon fibers or carbon yarns intended to form the circumferential sheet of the annular fibrous preform generally pass through eyelet plates  12 . At the outlet of these eyelets, each cable  100  passes over a guide bar  14  before being conveyed toward the spreading device  10  according to the invention. 
         [0034]    The cables of carbon fibers or carbon yarns  100  used may be formed from 50,000 filaments (50 K) or 24,000 filaments (24 K), having respective masses of 3.85 kTex and 1.6 kTex. 
         [0035]    The spreading device  10  according to an embodiment of the invention comprises a disk  16  that is mounted on a support (not shown) rotatably relative to it is axis of revolution  18 . The rotation of the disk around its axis of revolution is ensured by an electric motor  20  also mounted on the support of the spreading device (or by any other means or devices). 
         [0036]    The disk  16  is provided with at least one comb  22  (there are 8 in the example illustrated in  FIGS. 1 to 3 ) that is adapted to comb one or more cables of carbon fibers or carbon yarns in a direction substantially parallel to the longitudinal direction of the fibers or yarns of the cable. To that end, the bars  14  are positioned relative to the disk  16  so as to ensure guiding of one or more cables to be spread toward the disk in a direction substantially tangential thereto. 
         [0037]    To ensure such combing, each comb  22  comprises multiple teeth  24  ( FIG. 3 ) protruding radially outward from the disk. Owing to the guiding of the cable(s) to be spread by the bars  14  of the spreading device, at least some of the teeth  24  of the combs at least partially penetrate the corresponding cable(s) to spread them, as will be described later relative to  FIGS. 2 and 3 . 
         [0038]    It should be noted that the combs  22  mounted on the disk of the device do not necessarily have the same characteristics. For example, it is possible to have combs whereof the geometry and nature of the teeth (length, diameter, profile, geometry of the tip, material, etc.) differ. These characteristics are parameters that influence the degree of widening of the cable. 
         [0039]    According to one beneficial arrangement shown more specifically in  FIG. 1 , each comb  22  is mounted in a radial groove  26  formed in the disk  16  and can slide inside the latter so as to make it possible to adjust the radial position of said comb on the disk. Notches  28  formed in the radial grooves  26  ensure that the combs are kept in position. It is thus possible to adjust the position of the columns as a function of the cables used. 
         [0040]    According to another beneficial arrangement, each comb  22  is mounted on the disk  16  by means of a pivot link (not shown in the figures) so as to make it possible to adjust the orientation of the teeth of said comb (arrows F in  FIG. 1 ). In particular, it is thus possible to adjust the angle between the cable to be combed and the teeth of the comb. 
         [0041]      FIGS. 2 and 3  diagrammatically show one example of embodiment of such a spreading device. 
         [0042]    A cable  100  of carbon fibers or carbon yarns supplies the spreading device by traveling through the eyelet plates  12  thereof. The cable  100  reaches the bars  14 , which guide it toward the disk  16  of the spreading device. More specifically, as shown in  FIG. 2 , the cable  100  is guided to progress tangentially relative to the disk  16 . 
         [0043]    The disk  16  of the spreading device is rotated around its axis of revolution  18  such that at least one of its combs  22  combs the cable in a direction substantially parallel to the longitudinal direction of the fibers or yarns forming said cable. During this movement, the teeth  24  of the combs that comb the cable during the rotation of the disk penetrate at least partially the fibers or yarns of the cable. 
         [0044]    It has been observed that simple combing (that does or does not go through the cable) of the fibers or yarns of the cable makes it possible to obtain spreading thereof (the width L 1  of the cable  100  at the outlet of the spreading device is greater than its width L 2  at the inlet— FIG. 3 ). Furthermore, the spreading is obtained while preserving the homogeneity of the fibers in the direction of the width of the cable after the passage thereof in the teeth of the comb. 
         [0045]    In particular, the final width of the cable may be controlled as follows. Once an optimal configuration has been defined (in particular in terms of number of combs, number and geometry of teeth of the combs, radial position of the combs, angle between the teeth of the comb and the cable etc.), the final length of the cable may be regulated simply by adjusting the speed of rotation of the disk. Furthermore, regarding overlap of the combing, at a certain speed of rotation of the disk, the cable may be combed several times in the same location, which will make it possible to obtain a more significant final widening. 
         [0046]    A widening test was done on a cable taking a cable of carbon fibers or yarns made up of 50,000 filaments and having an initial width of approximately 20 to 25 mm. The device used during this test comprised 6 combs each having a width of 60 mm and being provided with teeth with sharp ends (with a gap between two adjacent teeth of approximately 2 mm). The columns were mounted on a disk having a diameter of 200 mm and driven at a speed of rotation of 140 revolutions per minute in the direction of movement of the cable. 
         [0047]    This test made it possible to obtain, at the outlet of the device, a cable width of approximately 50 mm, compared to the initial width of 20 to 25 mm. It is thus easy to double the width of the cable. 
         [0048]    It was also observed that the spreading of the cable remained frozen after it passed through the teeth of the comb, i.e., it did not return it to its initial width after being combed. 
         [0049]    Various parameters influence the spreading of the cable that passes through the teeth of the comb. Thus, if one wishes for the combing not to create tension in the cable, it is desirable for the movement direction S 1  of the cable to be identical to the direction of rotation S 2  of the disk  16  of the spreading device. Conversely, if one wishes to generate tension in the cable, it is desirable for these directions of movement to be contrary. 
         [0050]    Likewise, the number of combs that penetrate the cable, the length of their travel in the cable, the number of combing cycles, etc. are all parameters that have a direct impact on the spreading of the cable.