Fibrous preform and related manufacturing method

Abstract

The present invention relates to a preform (1) having a circular or annular shape and comprising a plurality of layers (2, 3, 4, 5) of carbon fibers, or fibers of a carbon precursor, stacked along an overlap axis (Z), wherein each of said layers (2, 3, 4, 5) consists of transverse segments (6) and wherein, with respect to the overlap axis (Z), the transverse segments (6) of a layer are angularly offset with respect to the transverse segments of an adjacent layer.

Description

[0001] FIBROUS PREFORM AND RELATED MANUFACTURING METHOD

[0002] Description

[0003] Field of the invention

[0004] The present invention relates to a fibrous preform made of carbon fibers and / or fibers of a carbon precursor and a method for the manufacturing thereof . More speci fically, the fibrous preform of the invention is used to produce shaped materials , for example components of C / C ( carbon / carbon) braking systems such as discs for disc brakes .

[0005] Background art

[0006] The use of discs for disc brakes made of carbon-based materials , so-called "Carbon-Carbon" or "C / C" , is known . These are composite materials consisting of a carbon matrix in which carbon reinforcing fibers are arranged .

[0007] Conventionally, carbon fibers , or fibers of a carbon precursor, are aggregated ( alone or with the use of binding agents , for example resins ) to form a three-dimensional structure called "preform" . The most used carbon precursors are PAN, pitch and rayon . The preform thus obtained is subj ected to carbon densi f ication processes , which can be performed in various manners , for example by means of CVD ( Chemical Vapor Deposition) , CVI ( Chemical Vapor Infiltration) , LPI ( Liquid Polymer Infiltration) , PIP ( Polymer Infiltration and Pyrolysis ) , or impregnation with resin and / or pitch . These processes lead to an increase in density such as to give the material adequate mechanical , thermal and tribological properties , for example a 2 to 6- fold increase in density .

[0008] The "C / C" material discs are therefore obtained by a process that involves the stacking of layers or sheets of carbon fibers in the form of woven and / or non-woven fabric or the use of short fibers to form a carbonaceous preform, the optional addition of resins , optional subsequent thermal treatments , and carbon densi f ication processes .

[0009] As is known, discs for disc brakes comprise an annular portion, called braking band, intended to cooperate with brake pads . In case of discs of the ventilated type , the braking band comprises two plates whose outer surfaces define opposite braking surfaces , while the inner surfaces delimit the portion of the disc comprising the ventilation holes for cooling the disc . The braking band is intended to cooperate with calipers of disc brakes , which are adapted to apply a braking action on the vehicle by applying, by means of the aforesaid pads , friction on the opposite braking surfaces .

[0010] Like the pads , the discs of disc brakes are also subj ect to wear over time . In particular, due to the rubbing of the braking surfaces against the pads of a disc brake , the plates of the disc wear out over time . The wear limit of a disc is identi fiable as the thickness below which the correct ef fectiveness of the braking action is no longer guaranteed . In fact , a reduction in the thickness of the disc reduces its heat dissipation capacity and its mechanical strength, triggering a series of critical issues and mal functions , such as the formation of thermal cracks on the braking band, disc deformation leading to vibrations and noise , and an increase in pedal travel .

[0011] Therefore , it is desirable to limit disc wear as much as possible and, in particular for higher performance usage ranges as well as for more extreme braking applications , there is a strong need to reduce the minimum admissible thickness for the plates of the disc, i . e . , the minimum admissible thickness of the worn plates .

[0012] EP 3 308 053 describes a disc comprising a plurality of layers of carbon fibers , in which within each layer five radial segments are alternated with at least six or seven transverse segments . The architecture of such a disc imposes a minimum thickness of the plates equal to four layers , which is desirable to reduce in higher performance usage ranges .

[0013] This thickness was reduced by the disc obj ect of EP 4 326 996 , which provides for an alternation of radial and transverse segments in each layer . The minimum admissible thickness for the plates of such a disc consists of three layers .

[0014] Although in the disc of EP 4 326 996 the flexural strength of the plates is ensured with a relatively low number of layers in the plate , the need to further reduce the minimum admissible thickness for the worn plates is increasingly felt in order to increase the service li fe of the disc and its performances , especially in higher performance usage ranges .

[0015] Therefore , the problem underlying the present invention is to provide a disc for disc brakes , as well as a preform for the manufacture thereof , with a minimum admissible thickness for the plates that is further reduced compared to known solutions , while ensuring at the same time flexural strength and dragging resistance .

[0016] Summary of the invention

[0017] The above-mentioned problem is solved by a preform and a method for manufacturing said preform, as wel l as by a shaped material and a method for manufacturing said shaped material , as defined in the appended claims , the definitions of which form an integral part of the present description .

[0018] A first obj ect of the invention is a preform having a circular or annular shape and comprising a plural ity of layers of carbon fibers , or fibers of a carbon precursor, stacked along an overlap axis Z and comprising a plurality of transverse segments , said transverse segments being segments in which the carbon fibers , or the fibers of said carbon precursor, are mainly oriented in a direction I incident to a radial direction R with respect to the overlap axis Z , said preform being characteri zed in that each of said layers consists of transverse segments , and in that , with respect to the overlap axis Z , the transverse segments of one layer are angularly of fset with respect to the transverse segments of an adj acent layer .

[0019] A second obj ect of the present invention is a shaped material , for example a disc for disc brakes of the ventilated type , obtainable by means of a carbon densi f ication treatment of the aforementioned preform, preferably said densi f ication treatment being selected from CVD ("Chemical Vapour Deposition" ) , CVI ("Chemical Vapour Infiltration" ) , LPI ("Liquid Polymer Infiltration" ) and PIP ("Polymer Infiltration and Pyrolysis" ) .

[0020] A further obj ect of the present invention is a method for manufacturing the preform as defined above, comprising a step a ) of stacking a plurality of layers of carbon fibers , or fibers of a carbon precursor, along an overlap axis Z , each of said layers consisting of transverse segments , so that , with respect to the overlap axis Z , the transverse segments of a layer are angularly of fset with respect to the transverse segments of an adj acent layer, preferably said method further comprising a step b ) of needling the stacked layers resulting from step a ) .

[0021] Another obj ect of the present invention is a method for manufacturing the shaped material as defined above , comprising the following steps : c ) subj ecting the preform as defined above to a carbon densi f ication treatment , preferably selected from CVD ("Chemical Vapour Deposition" ) , CVI ("Chemical Vapour Infiltration" ) , LPI ("Liquid Polymer Infiltration" ) and PIP ("Polymer Infiltration and Pyrolysis" ) ; d) optionally, infiltrating the shaped material resulting from said step c ) with an infiltrating agent , for example silicon ( Si ) or silicon carbide ( SiC ) .

[0022] It has surprisingly been found that , thanks to the architecture of the preform obj ect of the present invention, where the shaped material is a disc for disc brakes of the ventilated type , the flexural strength of the disc plates is ensured with a number of layers in the plate which is lower than the known ventilated discs . This advantageously translates into a minimum thickness admissible for the worn-out plates which is less than that of the known ventilated discs . In particular, it has been surprisingly found that the flexural strength of the ventilated disc is ensured with only two layers in the plate .

[0023] Further features and advantages of the invention will be more apparent from the description of some illustrative embodiments , given here by way of non-limiting example .

[0024] Brief description of the figures

[0025] Figure 1 illustrates a perspective view of a manufacturing step of the preform according to an embodiment of the invention .

[0026] Figure 2 illustrates , schematically, a top view of the architecture of a preform according to an embodiment of the present invention, wherein the layers consist of transverse segments and the transverse segments of adj acent layers are angularly of fset .

[0027] Figures 3 and 4 schematically illustrate , respectively, a transverse segment and a radial segment .

[0028] Figure 5A illustrates a layer ( coil ) of a preform according to an embodiment of the invention in which the segments develop in a spiral around the overlap axis .

[0029] Figure 5B illustrates the layer ( coil ) of Figure 5A and the first segment of a layer ( coil ) adj acent thereto .

[0030] Figures 6A, 6B, 6C illustrate the arrangement of two successive transverse segments in a layer of the preform, according to three di f ferent embodiments of the present invention . Figure 7 illustrates a side view of a disc for disc brakes of the ventilated type according to an embodiment of the invention .

[0031] Figure 8 schematically illustrates the 360 ° development of the architecture of a shaped material according to an embodiment of the invention .

[0032] Figure 9 schematically illustrates the 360 ° development of the so-called " 1- 1" architecture of a known shaped material , in which, in each layer, a radial segment is alternated with a transverse segment .

[0033] Detailed description of the invention

[0034] The subj ect of the present invention is a preform of circular or annular shape comprising a plurality of layers of carbon fibers , or fibers of a carbon precursor, stacked along an overlap axis Z , also referred to as construction axis Z , wherein each layer is formed by a plural ity of transverse segments , and wherein, with respect to the overlap axis Z , the transverse segments of a layer are angularly of fset with respect to the transverse segments of an adj acent layer .

[0035] Advantageously, the preform according to the present invention constitutes the starting material for producing a shaped material which, preferably, is a disc for disc brakes , preferably of the ventilated type . It has surpris ingly been found that such an architecture , in which the layers of the preform, as well as of the shaped material , are formed exclusively by transverse segments and in which the segments of a layer are angularly of fset with respect to the segments of the adj acent layer, ensures that , in discs for discs brakes of the ventilated type , the flexural strength is ensured by two layers in the disc plate , maximi zing the flexural resistance of the braking bands of the disc and, at the same time , ensuring suf ficient resistance of the attachment to the bell and the corresponding hub carrier .

[0036] A first advantage linked to the reduction in the number of layers in the plate concerns the possibility of increasing the thickness that can be worn out of the disc and consequently increasing the useful li fe of the disc itsel f , keeping unchanged the thickness of the plate at the beginning of the li fe cycle .

[0037] A further advantage linked to such feature concerns the possibility of reducing the thickness of the plate at the beginning of the li fe cycle of the disc, keeping unchanged the thickness that can be worn out , and therefore of increasing the number of ventilation holes and the thermal exchange of the disc by virtue of the greater space available for ventilation . Also by virtue of a better heat dissipation, the disc according to the present invention is suited for use in braking systems of sports and high- performance cars.

[0038] With reference to the figures, the preform object of the present invention is denoted, in its entirety, by the reference number 1.

[0039] The preform 1 comprises a plurality of layers 2, 3, 4, 5 of carbon fibers, such layers being stacked along an overlap axis Z, also called construction axis Z, for example shown vertically in Figure 1. For simplicity of representation, Figure 1 shows four layers 2, 3, 4, 5, but such number of layers is merely given by way of example and is not to be understood as limiting for the purposes of the present invention.

[0040] In the present description, unless otherwise specified, the terms "radial", "axial", "angularly", "circumferential" will always be understood with respect to the overlap axis Z.

[0041] In the present description, when referring to "successive segments" in a layer, it is understood that the segments are successive in a circumferential direction .

[0042] According to one embodiment, said overlap axis Z is oriented parallel to a rotation axis of a shaped material, for example a disc for disc brakes, manufactured from the preform 1, during its use. Each layer 2 , 3 , 4 , 5 consists of a plurality of transverse segments 6 . In the embodiment illustrated in Figure 1 , the transverse segments 6 are placed side by side and j oined together to form each layer 2 , 3 , 4 , 5 .

[0043] The transverse segments 6 are segments in which the carbon fibers are predominantly directed in a direction I incident to a radial direction R with respect to the overlap axis Z .

[0044] The radial direction R ( also referred to as "vertical" or "axial" or "pseudo-radial" ) is the direction of the fibers arranged along the axis indicated in Figure 4 and of the fibers arranged parallel to said axis . The direction I is also referred to as "hori zontal" or "transverse" or "pseudo-chordal" .

[0045] In a preferred embodiment , the incident direction I is substantially orthogonal with respect to the radial direction R .

[0046] In this regard, the schematics of Figure 3 and Figure 4 show, respectively, the orientations of the carbon fibers in a transverse direction and in a radial direction on respective transverse segments 6 (which constitute the layers of the preform 1 ) and radial segments 60 (which are not included in the layers of the preform obj ect of the present invention) . Advantageously, the segments 6 are in the form of a circular sector or a circular crown arc ( the latter also referred to as a ring sector ) .

[0047] As seen from Figure 3 , each segment 6 has an inner radius Ri and an outer radius Ro, and defines an angle a around the overlap axis Z . Consequently, each segment 6 is delimited by an arc Ai of a circumference with radius Ri and an arc Ao of a circumference with radius Ro . The angle a of each segment 6 defines the circumferential width of said circular sectors or circular crown arcs , determining the number of segments 6 per each layer 2 , 3 , 4 , 5 .

[0048] Preferably, the fibers of each transverse segment 6 are parallel or substantially parallel to the tangent line at a point P of the circumferential arc Ai , wherein said point P is located at the midpoint or substantially at the midpoint of the circumferential arc Ai .

[0049] Preferably, the circumferential width of said circular sectors or circular crown arcs is between 45 and 90 ° , more preferably between 50 and 80 ° , or between 60 and 75 ° , for example about 68 ° .

[0050] According to one embodiment , each layer 2 , 3 , 4 , 5 consists of transverse segments 6 having the same circumferential width . According to this embodiment , preferably, the circumferential width of the transverse segments 6 of a layer is the same as that of the transverse segments 6 of the other layers . According to this latter embodiment , preferably, the layers of the preform all have the same number of transverse segments 6 .

[0051] According to an embodiment of the invention, the transverse segments 6 of each layer are placed side by side to form the layer itsel f . According to this embodiment , successive segments are adj acent to each other, defining j oining zones 7 between segments 6 . The arrangement of two transverse segments 6 according to this embodiment is illustrated in Figure 6A.

[0052] According to another embodiment of the invention, in each layer there is an overlap between successive transverse segments 6 . The arrangement of two transverse segments 6 according to this embodiment is illustrated in Figure 6B, where the overlap area is indicated by reference number 6 ' . According to this embodiment , preferably, a segment overlaps with the following segment over a portion of up to 50% of its circumferential width, for example from 5% to 50% , or from 10% to 40% , or from 15% to 35% .

[0053] According to another embodiment of the invention, in each layer there is a spacing between successive transverse segments 6 . The arrangement of two transverse segments 6 according to this embodiment is illustrated in Figure 6C . According to this embodiment , preferably, the distance between two successive segments is up to 50% of the circumferential width of a segment, for example from 5% to 50%, or from 10% to 40%, or from 15% to 35%.

[0054] With respect to the overlap axis Z, the segments 6 of a layer are angularly offset with respect to the segments

[0055] 6 of an adjacent layer, in such a way that the ends (edges or radii) of the segments 6 do not overlap across the thickness S of the preform 1.

[0056] In accordance with the embodiment of Figure 6A, in which the segments of a layer are adjacent to each other, with respect to the overlap axis Z, the segments 6 of a layer are angularly offset with respect to the segments 6 of an adjacent layer, in such a way that the joining zones

[0057] 7 between the segments 6 do not overlap across the thickness S of the preform 1. Consequently, with respect to the overlap axis Z, each segment 6 of layer 2 overlaps with two adjacent segments 6 of the adjacent layer 3; each segment 6 of layer 3 overlaps, on one side, with two adjacent segments 6 of the adjacent layer 2 and, on the other side, with two adjacent segments 6 of the adjacent layer 4; and so on. According to this embodiment, preferably, with respect to the overlap axis Z, each segment 6 of a layer overlaps with a first segment 6 of an adjacent layer over a portion equal to 5%-50%, preferably equal to 10%-40% or 15%-35%, of its circumferential width, and with a second segment 6 (adjacent to the first) of the same adjacent layer over a portion equal to 50%-95%, preferably equal to 60%-90% or 65%-85%.

[0058] According to an embodiment, each segment 6 predominantly or exclusively comprises unidirectional carbon fibers, arranged in the incident direction I.

[0059] According to an embodiment, the segments 6 develop in a spiral around the overlap axis Z in a substantially continuous manner through the plurality of layers 2, 3, 4, 5 of carbon fibers, or fibers of a carbon precursor. In this case, the layers 2, 3, 4, 5 are represented by coils.

[0060] In the present description, reference is made indiscriminately to layers and coils. Therefore, when the segments 6 develop to form a spiral, it is to be understood that the layers 2, 3, 4, 5 are coils.

[0061] According to this embodiment, preferably, each coil has an inclination comprised in the range from 1° to 10°, preferably from 1° to 5°, for example about 1°, with respect to an axis orthogonal to the construction axis Z.

[0062] According to this embodiment, as visible in Figures 5A and 5B, with respect to the overlap axis Z, the last segment 6B of a layer 2 is partially overlapped with the first segment 6A of the same layer 2 (Figure 5A) and is adjacent to the first segment 6C of an adjacent layer 3 (shaded in Figure 5B) . The first segment 6C of the layer 3 will, in turn, be overlapped in part with the first segment 6A of the layer 2 and in part with the segment 6D adjacent to said segment 6A.

[0063] Preferably, the last segment 6B of the layer 2 overlaps with the first segment 6A of the layer 2 over a portion equal to 5%-50%, preferably equal to 10%-40% or 15%-35%, of its circumferential width.

[0064] Preferably, the first segment 6C of the layer 3 overlaps with the first segment 6A of the adjacent layer

[0065] 2 over a portion equal to 50%-95%, preferably equal to 60%-90% or 65%-85%, of its circumferential width.

[0066] In the embodiment illustrated in Figures 5A and 5B, the segments of the same layer 2, except the first segment 6A and the last segment 6B, are placed side by side as in Figure 6A. However, this embodiment is only an example and is not to be considered limiting in any way.

[0067] According to another embodiment, each layer 2, 3, 4, 5 develops in a plane orthogonal, or substantially orthogonal, to the overlap axis Z.

[0068] According to this embodiment, for example, each segment 6 of a layer 2 overlaps, with respect to the overlap axis Z, with a first segment 6 of an adjacent layer

[0069] 3 over a portion equal to half of its circumferential width and with a second segment 6 (adjacent to the first) of the layer 3 over the other half of its circumferential width. According to an embodiment, the number of layers 2,

[0070] 3, 4, 5 of carbon fibers or coils is comprised in the range between 10 and 50, preferably between 18 and 40, for example between 20 and 35 or between 24 and 30. According to a specific embodiment, the number of layers or coils is comprised between 21 and 26.

[0071] Merely by way of example, each of said layers 2, 3,

[0072] 4, 5 of carbon fibers may have a thickness comprised between 0.5 mm and 3 mm, for example of about 1.25 mm or about 1.5 mm.

[0073] Merely by way of example, along the overlap axis Z, the preform 1 may have a thickness S equal to or greater than about 5 millimeters, for example equal to or greater than about 25 millimeters, for example comprised between about 25 millimeters and about 300 millimeters, for example 28 millimeters, 32 millimeters, 38 millimeters or 40 millimeters .

[0074] According to an embodiment, at least a part of the fibers of said carbon precursor are oxidized polyacrylonitrile fibers. Preferably, all the fibers of said carbon precursor are oxidized polyacrylonitrile fibers. For example, said fibers are produced by the company SGL Carbon SE under the trade name Panox®. Said precursor may also be pitch or rayon. A further obj ect of the present invention is a shaped material obtainable by means of a carbon densi f ication treatment of the aforesaid preform 1 comprising a plurality of layers 2 , 3 , 4 , 5 of carbon fibers . Preferably, said densi f ication treatment is selected from the group consisting of : CVD ("Chemical Vapour Deposition" ) , CVI ("Chemical Vapour Infiltration" ) , LPI ("Liquid Polymer Infiltration" ) and PIP ("Polymer Infiltration and Pyrolysis" ) .

[0075] Advantageously, said shaped material has the layered configuration of the preform 1 from which it is made . Advantageously, said shaped material has a circular or annular shape and comprises a plurality of layers o f carbon fibers stacked along an overlap axis Z , wherein each of said layers cons ists of transverse segments and wherein, with respect to the overlap axis Z , the transverse segments of a layer are angularly of fset with respect to the transverse segments of an adj acent layer .

[0076] Preferably, said shaped material comprises a carbonaceous matrix within which at least one part of said carbon fibers is incorporated . The expression " carbonaceous matrix" denotes a matrix composed of at least 50% carbon .

[0077] According to an embodiment of the invention, said shaped material comprises silicon carbide ( SiC ) obtained by reaction of part of the carbon ( C ) of the carbon fibers and / or of the carbonaceous matrix of the shaped material with at least part of silicon ( Si ) infiltrated in the shaped material . Preferably, the silicon carbide ( SiC ) is arranged as a bridge between adj acent layers of carbon fibers .

[0078] Preferably, said shaped material has a residual porosity of less than 5% , for example equal to or less than 3% . Preferably, the value of such residual porosity is considered for a shaped material comprising zones of silicon carbide ( SiC ) , speci fically at the end of at least one step of infiltration with silicon ( Si ) .

[0079] According to a preferred embodiment of the invention, said shaped material is a disc for disc brakes of the ventilated type , illustrated merely by way of example in Figure 7 .

[0080] The ventilated disc in Figure 7 is indicated, in its entirety, by reference number 8 . Said ventilated disc comprises a first plate 9 and a second plate 10 , which together form the so-called braking band . Said first plate 9 is delimited by an outer surface 11 and an inner surface 12 and has a thickness y that extends between said two surfaces 11 , 12 . Similarly, said second plate 10 is delimited by an outer surface 13 and an inner surface 14 and has a thickness y that extends between said two surfaces 13, 14.

[0081] Said outer surfaces 11, 13 define opposite braking surfaces intended to cooperate with pads of a disc brake. Said braking surfaces 11, 13 are subject to wear.

[0082] The thickness y of each plate 9, 10 is given by the sum of two dimensions represented by the "minimum thickness K" admissible for a plate and by the "thickness that can be worn out (y-K)". The expression "minimum thickness K" refers to the minimum admissible thickness for a worn-out plate, i.e., consumed due to the rubbing of the braking surface against the pad of a disc brake, without the disc showing structural failures. In other words, the "minimum thickness K" is the thickness of the worn-out plate at the end of the life cycle of the disc. The "thickness that can be worn out (y-K)" is the thickness that is worn out, i.e., consumed, over time. The latter takes on a variable value. It is desirable that the "minimum thickness K" be as small as possible, so as to ensure a longer useful life of the ventilated disc.

[0083] Advantageously, the "minimum thickness K" of the plates 9, 10 of a disc 8 according to the present invention is formed by two of the aforesaid layers stacked along the overlap axis Z. In fact, it has surprisingly been found that the flexural strength of the plates 9, 10 is ensured by the overlap o f only two layers . Reference is made in this regard to Figure 8 , from which the absence of alignments of the j oining zones 7 between segments 6 across the thickness S of the shaped material is evident , which would cause minima in flexural resistance .

[0084] Conversely, in known discs , the f lexural strength of the plates is ensured with a greater number of layers . For example , in discs that have a " 1- 1" architecture , given by the alternation of a transverse segment 6 and a radial segment 60 in each layer and illustrated in Figure 9 , the flexural strength of the plates is ensured by the overlapping of three layers . Therefore , the "minimum thickness K" admissible for a plate of a disc with " 1- 1" architecture is necessarily greater .

[0085] It has also surprisingly been found that the architecture of the preform obj ect of the present invention results in the direction of the fibers not being perfectly transverse at the traction teeth of a disc brake disc, thus allowing for the minimum necessary resistance in these zones . The traction teeth are those portions of the disc that include the holes through which the bell is attached . These areas do not rub against the brake pads to generate friction, but rather transmit the braking torques to the vehicle wheel ; for this reason, it is necessary that these zones are able to withstand, without failure , the maximum torques that can be generated . In this regard, it has surprisingly been found that the shear breaking load of a disc originating from the preform obj ect of the present invention is 25 MPa .

[0086] Moreover, the architecture of the preform obj ect of the present invention advantageously allows maximi zing the circumferential flexural sti f fness of a disc for disc brakes (which can be up to twice as high as that of a disc obtained from a preform whose architecture also includes radial segments ) and, consequently, facilitating the final machining thus obtaining better dimensional tolerances on the finished disc . For example , discs made from a preform according to the invention have shown lower flatness values compared to discs made from preforms also including radial segments , resulting in a reduction o f scrap and reworking times . By definition, the flatness requirement speci fies the uni formity of a surface , or how precisely flat a target plane should be . The highest protrusion and the deepest concavity must lie within a specific distance between two vertically separated planes ; this distance is the flatness value . For example , discs made from a preform according to the invention have shown average flatness values of 43pm, while discs made from a preform whose architecture also includes radial segments have shown average flatness values of 67pm . The preform and the shaped material according to the present invention are obtained using respective methods as defined in the claims.

[0087] Even where not expressly indicated, preferred or accessory variants of such methods may comprise any feature which can be deduced even only implicitly, from a structural point of view, from the above description.

[0088] The method for manufacturing the preform 1 according to the present invention comprises a step a) that involves stacking a plurality of layers 2, 3, 4, 5 of carbon fibers, or fibers of a carbon precursor, along an overlap axis Z, wherein each of said layers 2, 3, 4, 5 consists of transverse segments 6, in such a way that, with respect to the overlap axis Z, the transverse segments 6 of one layer are angularly offset with respect to the transverse segments of an adjacent layer.

[0089] According to an embodiment, said step a) comprises a step of arranging the segments 6 in a spiral around the construction axis Z in a substantially continuous manner through the plurality of layers 2, 3, 4, 5 of carbon fibers or fibers of a carbon precursor.

[0090] Preferably, said method further comprises a step b) of needling the stacked layers 2, 3, 4, 5 resulting from said step a) . According to an embodiment, said step b) of needling comprises one or more steps of transposing, for example by means of shaped needles, the carbon fibers or the fibers of a carbon precursor through the thickness S of the various layers 2, 3, 4, 5 of the preform, forming an entangled three-dimensional structure.

[0091] The method for manufacturing the shaped material according to the present invention comprises the following steps : c) subjecting the preform 1 obtained by the above- mentioned method to a carbon densif ication treatment, preferably until a material density greater than 1.5 g / cm3or greater than 1.7 g / cm3is obtained; d) optionally, infiltrating the shaped material resulting from said step c) with an infiltrating agent, for example silicon (Si) or silicon carbide (SiC) .

[0092] In the case where the preform 1 obtained by the respective method comprises a plurality of layers of fibers of a carbon precursor (preferably oxidized polyacrylonitrile fibers, for example Panox® fibers, or pitch or rayon) , the method for manufacturing the shaped material comprises, prior to said step c) , a step cl) of carbonizing said fibers of a carbon precursor into carbon fibers. Preferably, said carbonization step cl) involves heating the fibers to a temperature between 1500°C and 2000°C, which varies depending on the type of precursor.

[0093] The preform 1, before being subjected to the carbon densif ication step c) , is optionally impregnated with resins, for example selected from the group consisting of phenolic resins, acrylic resins, polystyrene, furanic resins or cyanate esters, and / or is optionally subjected to a thermal pretreatment. The latter is such as to provide high thermal conductivity to the material and preferably comprises treatment in a furnace in an inert atmosphere or under vacuum up to temperatures between 1800°C and 2550°C.

[0094] If the shaped material is a disc for disc brakes, after step c) , a step c2) is carried out which provides for the creation of ventilation channels and / or draggings which are characteristic of a disc for disc brakes. According to various embodiments, step c2) is conducted either before or after the optional step d) of infiltration with an infiltrating agent. For example, the ventilation channels may be created before step d) , and the draggings after step d) .

[0095] The carbon densif ication treatment carried out during step c) is preferably selected from the group consisting of: CVD ("Chemical Vapour Deposition") , CVI ("Chemical Vapour Infiltration") , LPI ("Liquid Polymer Infiltration") and PIP ("Polymer Infiltration and Pyrolysis") . With CVD (Chemical Vapour Deposition) or CVI

[0096] (Chemical Vapour Infiltration) , a coating or an infiltration of carbon in vapor form are obtained, respectively. Typically, if the material is fibrous and therefore has high porosity, it is referred to as Chemical Vapor Infiltration (CVI) . These methods involve the use of hydrocarbon mixtures (for example, methane and propane) and the exposure of the material to be treated to such mixtures at high temperatures and low pressures. Typically, operating temperatures are in the range of 900- 1200°C, preferably 1000-1100°C, and pressures are below 300 mbar, preferably of a few tens of mbar. The hydrocarbon mixtures decompose to form elemental carbon, which is then deposited or infiltrated into the matrix of the material to be treated. This method, which requires the use of dedicated furnaces, involves the deposition of a thin layer (typically a few microns) on the fibers; therefore, in order to obtain the desired densif ication, several cycles of infiltration and overall coatings on the fibers higher than ten microns (typically 10-20 microns) are required.

[0097] In contrast, LPI (Liquid Polymer Infiltration) or PIP (Polymer Infiltration and Pyrolysis) involves infiltration of the matrix of the material to be treated with a liquid polymer and the subsequent high-temperature thermal treatment (pyrolysis) which causes the carbonization of the polymer deposited on the carbon fibers. Such method is performed by immersing one or more preforms in a bath of liquid polymer inside an autoclave. Preferably, the infiltration step is carried out at a pressure comprised between 50 and 500 mbar and at a temperature comprised between 20 and 50°C, preferably at room temperature. The preform is left immersed for a time preferably comprised between 10 and 120 minutes, for example between 15 and 45 minutes. Following the infiltration, the polymer is cured at a temperature that depends on the material used. Lastly, the material is pyrolyzed in an inert environment at a temperature preferably comprised between 700 and 1000°C, for example comprised between 850°C and 950°C, to convert the polymeric matrix into carbon. Also in this case, several steps of infiltration and pyrolysis are required before achieving appropriate densif ication of the preform. The entire process is typically repeated at least three times until the desired density is achieved.

[0098] According to an embodiment, the infiltrating agent used in the aforementioned phase d) comprises silicon (Si) . During this step, part of the infiltrated silicon (Si) reacts with part of the carbon (C) of the carbon fibres and / or of the carbonaceous matrix of the shaped material to form silicon carbide (SiC) . According to a preferred embodiment , during step d) , silicon is infiltrated into the shaped material by means of an LS I ( liquid silicon infiltration) process , during which the silicon is brought to a temperature higher than its melting temperature so as to melt and infiltrate into said shaped material by capillarity . According to this embodiment , preferably, the shaped material is placed on a layer or bed of silicon, preferably in powder form, for example by means of porous septa, such as felts , elements of pyrolyzed wood or pegs .

[0099] Preferably, the LS I process is carried out in a suitable treatment chamber . Said treatment chamber is typically introduced into a suitable furnace of the conventional type , which is heated to a temperature preferably above 1410 ° C, more preferably comprised between 1420 ° C and 1700 ° C, for example at about 1500 ° C . At these temperatures the silicon melts , rises by capillarity into the pores of the shaped material and reacts at least partially with part of the carbon of the carbon fibers and / or of the carbonaceous matrix to form silicon carbide ( SiC ) .

[0100] Both the heating to the treatment temperature and the subsequent cooling are conducted gradually . For example, it can take up to 8 or more hours to reach a treatment temperature of about 1500 ° C and a similar amount of time to cool the infiltrated material .

[0101] Preferably, said silicon infiltration process is conducted at a reduced pressure comprised between 20 mbar and 150 mbar, more preferably between 80 mbar and 120 mbar .

[0102] Preferably, the shaped material obtained from the aforementioned step c ) or, i f present , from the aforementioned step d) , is subj ected to a thermal treatment . The latter is such as to confer high thermal conductivity to the material and preferably comprises treatment in a furnace in an inert atmosphere or under vacuum at temperatures between 1800 ° C and 2550 ° C .

[0103] Preferably, after undergoing the aforementioned thermal treatment , the shaped material is subj ected to a second processing, or finishing, during which it is brought to its final shapes and / or dimensions , for example of a disc for disc brakes . This final processing is often necessary because thermal treatments can deform the shape of the shaped material . During this processing, any surface deformation is therefore removed . This finishing treatment is preferably carried out dry, for example using diamond wheels .

[0104] Advantageously, the methods of the present invention can be implemented with great simplicity in any existing production line . Advantageously, the methods of the present invention make it possible achieve signi ficant manufacturing savings , by virtue of the fact that speci fic processes do not require supplementary or additional machinery beyond those usually provided .

[0105] To the embodiments described herein, in order to satis fy speci fic needs , a person skilled in the art could make variations or replacements of elements with other functionally equivalent ones . Such variants are also included within the scope of protection as defined by the appended claims . Furthermore , each variant described as belonging to a possible embodiment may be implemented independently of the other variants described .

Claims

CLAIMS1. A preform (1) having a circular or annular shape and comprising a plurality of layers (2, 3, 4, 5) of carbon fibers, or fibers of a carbon precursor, stacked along an overlap axis (Z) and comprising a plurality of transverse segments ( 6 ) , said transverse segments (6) being segments in which the carbon fibers, or the fibers of said carbon precursor, are mainly oriented in a direction (I) incident to a radial direction (R) with respect to the overlap axis (Z) , said preform being characterized in that each of said layers (2, 3, 4, 5) consists of transverse segments (6) , and in that, with respect to the overlap axis (Z) , the transverse segments (6) of a layer are angularly offset with respect to the transverse segments of an adjacent layer .

2. The preform (1) according to claim 1, wherein the incident direction (I) of the carbon fibers, or the fibers of a carbon precursor, is substantially orthogonal to the radial direction (R) .

3. The preform (1) according to claim 1 or 2, wherein the transverse segments (6) are in the shape of a circularsector or a circular crown arc with a circumferential width preferably between 45 and 90°, more preferably between 50 and 80° or between 60 and 75°, for example of about 68°.

4. The preform (1) according to claim 3, wherein each layer (2, 3, 4, 5) consists of transverse segments (6) having the same circumferential width.

5. The preform (1) according to any one of the preceding claims, wherein the circumferential width of the transverse segments (6) of a layer is the same as that of the transverse segments (6) of the other layers.

6. The preform (1) according to any of the preceding claims, wherein the transverse segments (6) of each layer (2, 3, 4, 5) are placed side by side to form the layer itself .

7. The preform (1) according to claim 6, wherein, with respect to the overlap axis (Z) , each segment (6) of a layer overlaps with a first segment (6) of an adjacent layer over a portion equal to 5%-50%, preferably equal to 10%-40% or equal to 15%-35%, of the circumferential width thereof, and with a second segment (6) adjacent to thefirst one over a portion equal to 50%-95%, preferably equal to 60%-90% or equal to 65%-85%.

8. The preform (1) according to any one of claims 1 to 5, wherein in each layer (2, 3, 4, 5) there is either an overlap or spacing between successive transverse segments ( 6 ) .

9. The preform (1) according to any one of the preceding claims, wherein each transverse segment (6) mainly or exclusively comprises unidirectional carbon fibers arranged in the incident direction (I) .

10. The preform (1) according to any one of the preceding claims, wherein the transverse segments (6) develop as a spiral around the overlap axis (Z) in a substantially continuous manner through the plurality of layers (2, 3, 4, 5) of carbon fibers, or fibers of said carbon precursor.

11. The preform (1) according to claim 10, wherein each layer (2, 3, 4, 5) has an inclination comprised in the range from 1° to 10°, preferably from 1° to 5°, for example of about 1°, with respect to an axis orthogonal to the overlap axis (Z) .

12. The preform (1) according to claim 8 or 9, wherein the last segment (6B) of a layer partially overlaps with the first segment ( 6A) of the same layer, preferably over a portion equal to 5%-50%, or equal to 10%-40%, or equal to 15%-35%, of the circumferential width thereof.

13. The preform (1) according to any one of claims 1 to 9, wherein each layer (2, 3, 4, 5) develops in a plane orthogonal, or substantially orthogonal, to the overlap axis ( Z ) .

14. The preform (1) according to claim 13, wherein each segment (6) of a layer overlaps with a first segment (6) of an adjacent layer over a portion equal to half of the circumferential width thereof and with a second segment (6) adjacent to the first one over the other half of the circumferential width thereof.

15. The preform (1) according to any one of the preceding claims, wherein at least part of the fibers of said carbon precursor, preferably all the fibers, are oxidized polyacrylonitrile fibers, for example Panox® fibers .

16. A shaped material (8) obtainable by means of a carbon densif ication treatment of the preform (1) according to any one of the preceding claims, preferably said densif ication treatment being selected from CVD ("Chemical Vapor Deposition") , CVI ("Chemical Vapor Infiltration") , LPI ("Liquid Polymer Infiltration") and PIP ("Polymer Infiltration and Pyrolysis") .

17. The shaped material (8) according to claim 16, comprising silicon carbide (SiC) obtained by reaction of part of the carbon (C) of said carbon fibers and / or of a carbonaceous matrix of said shaped material (8) with at least part of silicon (Si) infiltrated into said shaped material (8) , preferably the silicon carbide (SiC) being arranged as a bridge between adjacent layers of carbon fibers .

18. The shaped material (8) according to claim 16 or17, being a disc for disc brakes, for example of the ventilated type.

19. The shaped material (8) according to claim 18, wherein said disc for disc brakes is of the ventilated type and comprises a braking band comprising two plates (9, 10) , the outer surfaces (11, 13) of which defineopposite braking surfaces intended to cooperate with pads of a disc brake, wherein each of said plates (9, 10) has a thickness (y) defined as the sum of "minimum thickness" (K) and "thickness that can be worn out" (y-K) , said "minimum thickness" (K) being equal to the thickness of two layers and said "thickness that can be worn out" (y- K) being variable.

20. A method for manufacturing the preform (1) according to any one of claims 1 to 15, comprising a step a) of stacking a plurality of layers (2, 3, 4, 5) of carbon fibers, or fibers of a carbon precursor, along an overlap axis (Z) , each of said layers (2, 3, 4, 5) consisting of transverse segments (6) , so that, with respect to the overlap axis (Z) , the transverse segments (6) of a layer are angularly offset with respect to the transverse segments of an adjacent layer, preferably said method further comprises a step b) of needling the stacked layers (2, 3, 4, 5) resulting from step a) .

21. The method according to claim 20, wherein said step a) comprises a step of arranging the segments (6) in a spiral around the overlap axis (Z) in a substantiallycontinuous manner through the plurality of layers (2, 3, 4, 5) of carbon fibers or fibers of a carbon precursor.

22. A method for manufacturing the shaped material (8) according to any one of claims 16 to 19, comprising the following steps: c) subjecting the preform (1) obtained by the method according to claim 20 or 21 to a carbon densi f ication treatment, preferably selected from CVD ("Chemical Vapor Deposition") , CVI ("Chemical Vapor Infiltration") , LPI ("Liquid Polymer Infiltration") and PIP ("Polymer Infiltration and Pyrolysis") ; d) optionally, infiltrating the shaped material (8) resulting from said step c) with an infiltrating agent, for example silicon (Si) or silicon carbide (SiC) .

23. The method according to claim 22, wherein the preform (1) comprises a plurality of layers (2, 3, 4, 5) of fibers of a carbon precursor, preferably oxidized polyacrylonitrile fibers, for example Panox® fibers, and said method comprises, before said step c) , a step cl) of carbonizing said fibers of a carbon precursor into carbon fibers .

24. The method according to claim 22 or 23, wherein said infiltrating agent comprises silicon (Si) , and during said step d) , part of the infiltrated silicon (Si) reacts with part of the carbon (C) of the carbon fibers and / or of a carbonaceous matrix of said shaped material (8) to form silicon carbide (SiC) .

25. The method according to any one of claims 22 to 24, wherein the shaped material (8) is a disc for disc brakes and said method further comprises, after said step c) , a step c2) of making ventilation channels and / or drags characteristic of a disc for disc brakes.

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