Machine for producing multiaxial fibrous webs

Abstract

A plurality of unidirectional sheets ( 30 a, 30 b, 30 c ) are superposed in different directions and they are bonded together. At least one of the unidirectional sheets is made by spreading a tow so as to obtain uniform thickness, width not less than 5 cm, and a weight of no more than 300 g/m 2 , cohesion being imparted to the sheet so as to enable it to be handled prior to being superposed with other sheets. Advantageously, the unidirectional sheets are made of carbon fibers and are obtained by spreading out large tows.

1 . A laying machine for making a multiaxial fiber sheet by superimposing unidirectional fiber sheets in different directions, the machine comprising: 
 apparatus for advancing the multiaxial sheet, the apparatus comprising support means for supporting the multiaxial sheet that is being made and drive means for driving the support means in a direction of advance;    feed means for feeding longitudinal unidirectional sheet in a direction parallel to the direction of advance;    a plurality of cross-laying devices each including feed means for feeding the cross-laying device with continuous unidirectional sheet, a moving grasping head for taking hold of the free end of a sheet, and means for laying successive segments of sheet parallel to a transverse direction at a selected angle relative to the direction of advance, said laying means comprising means for driving the grasping head; and    bonding means for bonding the superposed unidirectional sheets together, the bonding means being located downstream from the support means in the direction of advance;    the machine being characterized in that each cross-laying device includes cutter means; and in that means are provided for performing successive cycles comprising, for each cross-laying device, grasping the free end of a unidirectional sheet by means of the grasping head, moving the grasping head to fetch a segment of unidirectional sheet, cutting off the fetched segment of unidirectional sheet, and laying the cutoff segment of unidirectional sheet on the support means.    
   
   
       2 . A machine according to  claim 1 , characterized in that each cross-laying device comprises a grasping head that is movable in translation back and forth in one direction and in the opposite direction along a rectilinear path.  
   
   
       3 . A machine according to  claim 1 , characterized in that each cross-laying device comprises a plurality of grasping heads movable along a closed-loop path.  
   
   
       4 . A machine according to  claim 1 , characterized in that each cross-laying device further comprises reinforcement fixing means for reinforcing a unidirectional sheet in each zone where it is to be cut.  
   
   
       5 . A machine according to  claim 4 , characterized in that the reinforcement fixing means comprises means for fetching a film onto at least one face of the sheet, transversely relative thereto, and means for fixing the film to the sheet.  
   
   
       6 . A machine according to  claim 5 , characterized in that the fixing means include heating presser means.  
   
   
       7 . A machine according to  claim 1 , characterized in that the advance device includes means for continuously driving the support means.  
   
   
       8 . A machine according to  claim 7 , characterized in that each cross-laying device further includes means for transferring a cutoff unidirectional sheet segment so as to lay it on the continuously-driven support means.  
   
   
       9 . A machine according to  claim 1 , characterized in that holding means are provided to hold sheet segments in place on the sheet support means.  
   
   
       10 . A machine according to  claim 9 , characterized in that the holding means comprise bonding means for bonding contiguous sheet segments at their ends.  
   
   
       11 . A machine according to  claim 10 , characterized in that the holding means comprise means for fixing at least one film at the longitudinal edges of a multiaxial sheet that is being made.  
   
   
       12 . A machine according to  claim 9 , characterized in that the holding means comprise spikes carried by support means for the multiaxial sheet.  
   
   
       13 . A machine according to  claim 1 , characterized in that the angle between the path of a grasping head and the direction of advance is adjustable.  
   
   
       14 . A machine according to  claim 1 , characterized in that the longitudinal sheet feed means are disposed in such a manner as to fetch a longitudinal sheet onto the support means between two cross-laying devices.  
   
   
       15 . A machine according to  claim 1 , characterized in that the means for bonding together the superposed unidirectional sheets include a needling device.  
   
   
       16 . A machine according to  claim 1 , characterized in that the means for bonding together the superposed unidirectional sheets include a stitching or knitting device.  
   
   
       17 . A machine according to  claim 1 , characterized in that the means for bonding together the superposed unidirectional sheets include a device for fetching an adhesive bonding agent between the sheets.  
   
   
       18 . A machine according to  claim 17 , characterized in that the means for bonding together the superposed unidirectional sheets include a device for inserting heat-fusible thread between the sheets.  
   
   
       19 . A machine according to  claim 2 , characterized in that each cross-laying device further comprises reinforcement fixing means for reinforcing a unidirectional sheet in each zone where it is to be cut.  
   
   
       20 . A machine according to  claim 3 , characterized in that each cross-laying device further comprises reinforcement fixing means for reinforcing a unidirectional sheet in each zone where it is to be cut.