Machine for producing multiaxial fibrous webs
View Patent ↗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 method of making a multiaxial fibre sheet having a longitudinal direction, the method comprising: superposing at least two unidirectional sheets fed in different directions onto a support that moves in a direction of advance parallel to the longitudinal direction of the multiaxial sheet to make, and bonding the superposed sheets together,
wherein at least one of the unidirectional sheets is formed by spreading at least one tow of filaments so as to obtain a sheet of substantially uniform thickness, having a width of not less than 5 cm and a weight of not more than 300 g/m 2 , and the at least one unidirectional sheet is fed in a direction transverse to the direction of advance, and successive segments of unidirectional sheet are fed at a selected angle relative to the direction of advance by repeating a sequence comprising: moving the at least one unidirectional sheet above said support parallely to the transverse direction, cutting out a segment from the at least one unidirectional sheet, and depositing the cut off segment on said support or on the multiaxial sheet that is being made to be superposed with at least one other unidirectional sheet, and
transverse cohesion is provided to the at least one unidirectional sheet and maintained while the at least one unidirectional sheet is handled prior to being deposited as successive segments.
2. A method according to claim 1 , wherein at least one of the unidirectional sheets is made by providing a plurality of tows, spreading the tows so as to form unidirectional strips, and placing the strips side by side to obtain a unidirectional sheet having a width of not less than 5 cm and having a weight of not more than 300 g/m 2 .
3. A method according to claim 1 , wherein the fibres of the unidirectional sheets are of a material selected from carbon, ceramics, carbon or ceramic precursors, glasses, and aramids.
4. A method according to claim 3 , wherein at least one of the unidirectional sheets is obtained by spreading at least one carbon tow in which the number of filaments is not less than 12 K.
5. A method according to claim 1 , wherein unidirectional sheets made of fibres of different materials are superposed.
6. A method according to claim 1 , wherein at least one unidirectional sheet is made of fibres constituted by a plurality of different materials.
7. A method according to claim 1 , wherein at least one of the unidirectional sheets is made of continuous filaments.
8. A method according to claim 1 , wherein at least one of the unidirectional sheets is made of discontinuous filaments.
9. A method according to claim 8 , wherein at least one of the unidirectional sheets is made by spreading at least one hybrid tow constituted by intimately mixed discontinuous filaments of a plurality of different materials.
10. A method according to claim 1 , wherein transverse cohesion is imparted to said at least one unidirectional sheet made of discontinuous filaments by lightly intermingling discontinuous filaments.
11. A method according to claim 10 , wherein the intermingling is performed by subjecting the sheet as it passes over a plate to a jet of water under pressure.
12. A method according to claim 10 , wherein the intermingling is performed by needling.
13. A method according to claim 10 , wherein, after transverse cohesion has been imparted, the sheet is widened.
14. A method according to claim 1 , wherein transverse cohesion is imparted to at least one of the unidirectional sheets by applying a chemical bonding agent.
15. A method according to claim 14 , wherein a bonding agent is used that can be eliminated.
16. A method according to claim 15 , wherein a water-soluble bonding agent is used.
17. A method according to claim 14 , wherein the bonding agent is applied by depositing on the unidirectional sheet a liquid compound containing the bonding agent or a precursor therefor.
18. A method according to claim 17 , wherein the bonding agent is applied by depositing, on the unidirectional sheet, a liquid compound containing a polymer in solution.
19. A method according to claim 17 , wherein the bonding agent is applied by depositing, on the unidirectional sheet, a liquid compound containing a resin, and by polymerizing the resin.
20. A method according to claim 17 , wherein the bonding agent is deposited by spraying the liquid compound onto the unidirectional sheet.
21. A method according to claim 17 , wherein the bonding agent is deposited by soaking the unidirectional sheet in a bath containing the liquid compound.
22. A method according to claim 1 , wherein transverse cohesion is imparted to at least one of the unidirectional sheets by fixing at least one heat-fusible thread.
23. A method according to claim 1 , wherein a multiaxial sheet is made by superposing two transverse unidirectional sheets at opposite angles relative to the direction of advance.
24. A method according to claim 1 , wherein a multiaxial sheet is made by superposing at least two unidirectional sheets, one of the unidirectional sheets being a longitudinal sheet of direction parallel to the direction of advance.
25. A method according to claim 24 , wherein a multiaxial sheet is made by superposing at least three unidirectional sheets, one of the unidirectional sheets being a longitudinal sheet of direction parallel to the direction of advance, and at least two other unidirectional sheets being transverse sheets of directions at different angles to the direction of the longitudinal sheet.
26. A method according to claim 25 , wherein the longitudinal sheet is disposed between two transverse sheets of directions that form angles of opposite signs relative to the direction of the longitudinal sheet.
27. A method according to claim 24 , wherein the longitudinal sheet is made by placing side by side a plurality of unidirectional strips each obtained by spreading a tow, thereby obtaining a longitudinal sheet having a width of not less than 10 cm.
28. A method according to claim 27 , wherein the longitudinal sheet is made by placing side by side a plurality of unidirectional strips each obtained by spreading a carbon tow having a number of filaments that is not less than 12 K.
29. A method according to claim 1 , wherein said at least one unidirectional sheet is fed transversely to the direction of advance as successive segments disposed so as to be adjacent.
30. A method according to claim 1 , wherein said at least one unidirectional sheet is fed transversely to the direction of advance as successive segments disposed with partial overlap.
31. A method according to claim 1 , wherein the moving support is moved continuously in the direction of advance while successive segments of said at least one unidirectional sheet are being deposited and the multiaxial sheet is being made.
32. A method according to claim 1 , wherein said at least one unidirectional sheet is locally reinforced in the zones where it is cut out.
33. A method according to claim 32 , wherein said at least one unidirectional sheet is reinforced by fixing a film on at least one of its faces.
34. A method according to claim 33 , wherein said at least one unidirectional sheet is reinforced by fixing a thermo-adhesive film and by heating under pressure.
35. A method according to claim 1 , wherein the at least two superposed unidirectional sheets are held relative to one another at least until they have been bonded together.
36. A method according to claim 35 , wherein the at least two superposed unidirectional sheets are held by being fixed on spikes.
37. A method according to claim 35 , wherein the at least two superposed unidirectional sheets are held by fixing at least one film along each longitudinal edge of the multiaxial sheet that is being made.
38. A method according to claim 33 , wherein the reinforcing film is used to hold the segments of said at least one unidirectional sheet in the positions into which they are deposited.
39. A method according to claim 1 , wherein the superposed unidirectional sheets are bonded together by needling.
40. A method according to claim 1 , wherein the superposed unidirectional sheets are bonded together by sewing or knitting.
41. A method according to claim 1 , wherein the superposed unidirectional sheets are bonded together by adhesive.
42. A method according to claim 41 , wherein the superposed unidirectional sheets are bonded together by inserting a heat-fusible thread between the sheets.
43. A method of making a multiaxial fiber sheet having a longitudinal direction, the method comprising: superposing at least two unidirectional sheets fed in different directions onto a support that moves in a direction of advance parallel to the longitudinal direction of the multiaxial sheet being made, and bonding the superposed sheets together;
wherein at least one of the unidirectional sheets is formed from at least one spread tow and has a substantially uniform thickness, a width of not less than 5 cm and a weight of not more than 300 g/m 2 ;
the at least one unidirectional sheet is fed in a direction transverse to the direction of advance as successive segments which form a same selected angle relative to the direction of advance and which are superposed with at least one other unidirectional sheet;
each of the successive segments is obtained by advancing the at least one unidirectional sheet above said support, cutting out a segment from the at least one unidirectional sheet and depositing the cut off segment on said support or on the multiaxial sheet that is being made;
transverse cohesion of the at least one unidirectional sheet is maintained while being handled prior to being deposited as successive segments; and
the deposited successive segments of the at least one unidirectional sheet are held on said support relative to the at least one other unidirectional sheet at least until the unidirectional sheets have been bonded together.
44. A method according to claim 43 , wherein said at least one unidirectional sheet is made of continuous filaments.
45. A method according to claim 44 , wherein transverse cohesion of the at least one unidirectional sheet is given by a chemical bonding agent.
46. A method according to claim 43 , wherein said at least one unidirectional sheet is made of discontinuous filaments of at least one stretch-broken carbon tow.
47. A method according to claim 46 , wherein transverse cohesion of the at least one unidirectional sheet is given by light intermingling of the discontinuous filaments.
48. A method according to claim 43 , wherein the deposited successive segments are held relative to the at least one unidirectional sheet by engagement of the segment ends on spikes.
49. A method of making a composite material part having a fiber reinforcement densified with a matrix, wherein the fiber reinforcement is made by using at least one multiaxial fiber sheet obtained by the method of claim 1 .
50. A method of making a composite material part having a fiber reinforcement densified with a matrix, wherein the fiber reinforcement is made by using at least one multiaxial fiber sheet obtained by the method of claim 43 .