Method for manufacturing a brake band for a brake disc, method for manufacturing a brake disc, brake disc and brake band for a brake disc

Abstract

A method for manufacturing a brake band (2) of a brake disc (1) of a disc brake, comprising the following steps: a) preparing a mould (10) having an internal cavity (11) comprising a first portion (11a) having a shape corresponding to the shape of the brake band (2) to be manufactured; b) providing a band preform (20) comprising a central preform (200), an upper outer preform (201) and a lower outer preform (202), said central preform (200) being made of a porous ceramic material comprising silicon carbide (SiC), said upper outer preform (201) and said lower outer preform (202) being made of a porous ceramic material comprising silicon carbide (SiC) and infiltrated with silicon (SiC+Si), wherein a carbon barrier layer (201a, 200a, 200b, 202a) made of carbon is interposed between the upper outer preform (201) and the central preform (200) and between the lower outer preform (202) and the central preform (200), said preforms (200, 201, 202) having the shape of the brake band (2) to be manufactured; c) placing said band preform (20) inside the mould at the first portion (11a) of the internal cavity (11); and d) injecting a liquid or semi-solid aluminium alloy into the entire internal cavity (11) of the mould (11) to infiltrate the central preform (200) of said band preform (20) made of porous ceramic material with said aluminium alloy, so as to obtain, at the first portion (11a), an aluminium metal matrix composite reinforced by said central preform (200) defining the brake band (2) to be manufactured. At least the brake band and the brake disc are manufactured using the above method.

Description

TECHNICAL FIELD

[0001] The present invention relates to a method for manufacturing a brake band of a brake disc, to a method for manufacturing a brake disc, to a brake disc manufactured by the above-mentioned method and to a brake band for a brake disc. BACKGROUND

[0002] The brake disc of a disc brake system of a vehicle comprises an annular structure or brake band and comprises a central fixing element, called bell, through which the disc is attached to the rotating part of the vehicle suspension, for example to the wheel hub. The brake band is provided with two opposite braking surfaces adapted to cooperate with friction elements, brake pads, housed in at least one gripping body arranged astride of said brake band and integral with the non-rotating part of the vehicle suspension. The controlled interaction between the two opposite brake pads and the two opposite braking surfaces of the brake band causes, through friction, a braking action allowing the vehicle to decelerate or stop.

[0003] Generally, the brake discs are made of grey cast iron or steel. In fact, these materials allow to obtain good braking performances, particularly in terms of wear limitation, at a relatively low cost. Discs made of carbon or carbon ceramic materials provide higher performances, but at a higher cost.

[0004] As an alternative to grey cast iron discs or steel discs, discs made of aluminium have been proposed, in order to reduce the weight of the disc. The aluminium discs are equipped with a protective coating. The protective coating serves, on the one hand, to reduce the wear of the disc and thus to ensure similar performances to the cast iron discs, and on the other hand to protect the aluminium base from the temperatures generated during braking, which are much higher than the softening temperature of aluminium (200-400°C).

[0005] However, the protective coatings available today and applied to aluminium discs, while providing resistance to wear, are often prone to flaking, which causes the coating to separate from the disc. This complicates the production process of the disc. In fact, the disc must be subjected to a surface finishing treatment and must also be prepared for connection to the bell.

[0006] From the above it is evident that aluminium or aluminium alloy discs with protective coating are not yet able to completely replace steel or grey cast iron discs.

[0007] However, aluminium has a lower density with respect to steel and grey cast iron, so that the braking system industry is very interested in aluminium as a potential excellent alternative to steel and grey cast iron.

[0008] Therefore, in the relevant sector, there is a need for an aluminum-based brake disc which, on the one hand, can exploit the special operating characteristics of aluminum (first and foremost due to the low density of aluminum) and, on the other hand, can obtain mechanical strength and wear characteristics at least comparable to those of a steel disc or a gray cast iron disc. There is also a need to manufacture these discs through a production process as simple and economical as possible.

[0009] In WO 2019 / 123222 A1, a method is described for manufacturing an aluminum disc with a porous ceramic preform which is infiltrated with molten aluminum (in liquid or semi-solid state). Unfortunately, the disc obtained in this way provides for a direct contact between the brake pad and the aluminum metal matrix, which generates possible local degradation phenomena on the disc at the points where the aluminum is overheated by friction to the melting point of aluminum. SUMMARY

[0010] Therefore, there is an urgent need in the sector for an aluminum-based brake disc which is not locally degraded and which, on the one hand, can exploit the special operating characteristics of aluminum (mainly the low density) and, on the other hand, can obtain mechanical strength and wear resistance characteristics comparable to those of a steel disc or a gray cast iron disc, while being manufactured through a production process as simple and economical as possible.

[0011] In addition to the above requirements, there is also a need to make the brake disc more resistant to corrosion with respect to a cast iron disc or a steel disc and to make the brake disc less polluting in terms of metal particles emissions.

[0012] The above requirements are met by the method for manufacturing a brake band for a brake disc, the method for manufacturing a brake disc, the brake disc for a disc brake and the brake band according to the appended independent claims.

[0013] The method for manufacturing a brake band according to the present application comprises the following steps:

[0014] a) preparing a mold having an internal cavity comprising a first portion having a shape corresponding to the shape of the brake band to be manufactured;

[0015] b) preparing a band preform comprising a central preform, an upper outer preform and a lower outer preform; the central preform is made of a porous ceramic material containing silicon carbide (SiC); the upper outer preform and the lower outer preform are made of a porous ceramic material containing silicon carbide infiltrated with silicon (SiC + Si); a carbon barrier layer is interposed between the upper outer preform and the central preform and between the lower outer preform and the central preform; furthermore, the preform has the shape of the brake band to be manufactured;

[0016] c) placing the strip preform inside the mould and at the first portion of the internal cavity;

[0017] d) injecting a liquid or semi-solid aluminium alloy into the entire internal cavity of the mould so as to: infiltrate the central preform of the strip preform made of porous ceramic material with the aluminium alloy, thereby obtaining at the first portion an aluminium metal matrix composite reinforced by the central preform defining the braking band to be manufactured; and fill the second portion with the aluminium alloy, thereby obtaining an aluminium alloy fusion body connected in a unitary manner with the braking band made of metal matrix composite and defining the bell of the braking disc to be manufactured.

[0018] Advantageously, in order to manufacture the strip preform, the method comprises the following steps:

[0019] a1) preparing a central preform, an upper outer preform and a lower outer preform, each made of porous ceramic material containing silicon carbide (SiC) and having the shape of the braking band (2) of the braking disc (1) to be manufactured;

[0020] a2) infiltrating the upper outer preform and the lower outer preform with silicon (Si);

[0021] a3) depositing on the central preform a material containing carbon in particulate form to obtain at least one carbon barrier layer made of carbon.

[0022] As an alternative to step a3), the method advantageously provides a step a4) of depositing on the upper outer preform and on the lower outer preform a material containing carbon in particulate form to obtain at least one carbon barrier layer made of carbon.

[0023] In addition, as an alternative to step a3) and step a4), the method advantageously comprises a step a5) of depositing on the central preform and on the upper outer preform and / or on the lower outer preform a material containing carbon in particulate form to form on the central preform and on the upper outer preform and / or on the lower outer preform at least one carbon barrier layer made of carbon (C).

[0024] In addition, preferably, the method provides a step a6) of joining together the central preform, the upper outer preform and the lower outer preform by placing silicon at each carbon barrier layer and heating the preforms until a bond is formed between the preforms and at the carbon barrier layers, thereby obtaining the strip preform.

[0025] Advantageously, the junctions of the central preform with the upper outer preform and with the lower outer preform are formed due to the fusion of the silicon placed at each carbon barrier layer, which reacts with the carbon deposited in the barrier portion to form silicon carbide (SiC). The silicon carbide (SiC) thus formed acts as a junction between the preforms.

[0026] According to an embodiment, in step a2), the upper outer preform and the lower outer preform are placed in a crucible coated with a release layer, for example a release layer based on boron nitride (BN), a predetermined quantity of silicon (Si) powder is added to the crucible according to the dimensions of the preforms, and the upper outer preform and the lower outer preform are heated to obtain the fusion of the added silicon.

[0027] Preferably, the upper outer preform and the lower outer preform are heated to a temperature above the melting temperature of Si (1414°C) at atmospheric pressure and in an inert atmosphere, preferably the upper outer preform and the lower outer preform are heated to a temperature above the melting temperature of Si (1414°C) at atmospheric pressure and in an argon atmosphere.

[0028] Advantageously, in step a3) or step a4) or step a5), the step of depositing a material containing carbon in particulate form to obtain at least one carbon barrier layer made of carbon (C) is obtained by chemical vapor deposition.

[0029] Preferably, gaseous methane as a carbon precursor is used for chemical vapor deposition; the temperature is between 1100°C and 1300°C and the pressure is between 10 mbar and 50 mbar.

[0030] Advantageously, during the step of chemical vapor deposition, the contributions in the gas mixture are:

[0031] - methane between 0.4 standard liters per minute and 3 standard liters per minute (slm);

[0032] - hydrogen between 0.2 standard liters per minute and 5 standard liters per minute (slm);

[0033] - argon between 0 standard liters per minute and 4 standard liters per minute (slm);

[0034] and the ratio of methane to hydrogen is between 0.3 and 5.

[0035] According to a variant embodiment, in step a3) or step a4) or step a5), the step of depositing a material containing carbon in particulate form to obtain at least one carbon barrier layer made of carbon (C) is obtained by sputtering or physical vapor deposition (PVD) techniques or by laser cladding techniques.

[0036] According to a variant embodiment, the step of depositing a material comprising carbon in the form of particles to obtain at least one carbon barrier layer made of carbon (C) in step a3) or step a4) or step a5) is achieved by using a bonding technique based on graphite-based glue.

[0037] Preferably, in step a6), the method provides for placing stoichiometric carbon according to the dimensions of the carbon surface of the preform, heating the preform to a temperature of about 1450°C for a time of about 2 hours. Preferably, step d) of placing the aluminum alloy inside the mold is carried out according to semi-solid or liquid infiltration techniques or extrusion casting techniques.

[0038] Advantageously, the central preform, the lower outer preform and the upper outer preform are obtained by subjecting a mass of ceramic material particles coated with a polymeric bonding composition to molding, possible dewaxing and sintering in sequence.

[0039] Preferably, sintering is carried out in two separate sintering cycles, wherein the first sintering cycle is carried out at a temperature not lower than 1600°C and the second sintering cycle is carried out at a temperature not lower than 2000°C, both the first sintering cycle and the second sintering cycle being carried out in an inert atmosphere, preferably the first sintering cycle is carried out at a temperature of about 1800°C, preferably the second sintering cycle is carried out at a temperature ranging from 2100°C to 2200°C.

[0040] In addition, preferably, in step d) the mold is closed on the upper outer preform and on the lower outer preform so that, during the injection of aluminum into the mold, the aluminum is prevented from infiltrating above the upper outer preform and the lower outer preform, so that the outer braking surface of the brake band is free of aluminum.

[0041] The method for manufacturing a brake disc comprising a brake band and a bell according to an embodiment of the present application comprises the following steps:

[0042] a) preparing a mold having an internal cavity comprising a first portion having a shape corresponding to the shape of the brake band to be manufactured and a second portion having a shape corresponding to the shape of the bell of the brake disc to be manufactured, wherein the first portion and the second portion of the internal cavity communicate with each other;

[0043] b) preparing a band preform comprising a central preform, an upper outer preform and a lower outer preform; the central preform being made of a porous ceramic material comprising silicon carbide (SiC); the upper outer preform and the lower outer preform being made of a porous ceramic material comprising silicon carbide and infiltrated with silicon (SiC + Si); a carbon barrier layer being placed between the upper outer preform and the central preform and between the lower outer preform and the central preform and serving to react with silicon (Si) to act as a joint of the upper outer preform and of the lower outer preform with the central preform; furthermore, said preform having a shape identical to that of the braking band of the brake disc to be manufactured;

[0044] c) placing said band preform inside a mould and at a first portion of said internal cavity;

[0045] d) injecting a liquid or semi-solid aluminium alloy into the entire internal cavity of the mould so that: the central preform of said band preform made of a porous ceramic material is infiltrated with said aluminium alloy, obtaining in the first portion an aluminium metal matrix composite reinforced by said central preform, which defines the braking band of the brake disc to be manufactured; and the second portion is filled with said aluminium alloy, obtaining an aluminium alloy fusion body connected in a unitary manner with the braking band made of a metal matrix composite and defining the bell of the brake disc to be manufactured.

[0046] The disc brake according to the present application comprises a braking band and a bell connected with said braking band.

[0047] Preferably, in an advantageous manner, the bell is connected in a unitary manner with the braking band and comprises an aluminium alloy co-cast with the metal matrix of the composite material forming the braking band.

[0048] According to the present application, the brake band comprises a central band made of an aluminum metal matrix composite reinforced with a ceramic material containing silicon carbide (SiC). The composite material is obtained by infiltrating an aluminum alloy into a central preform made of a porous ceramic material, the central preform having a shape corresponding to the shape of the brake band. The brake band further comprises an upper band and a lower band. The upper band is joined to the central band along an upper bonding layer. The upper band is made of a porous ceramic material containing silicon carbide (SiC) and infiltrated with silicon (SiC+Si) and covers the central band on one of the side portions of the central band. The lower band is joined to the central band along a lower bonding layer, the lower bonding layer being arranged opposite, i.e. facing, the upper bonding layer. The lower band is made of a porous ceramic material containing silicon carbide (SiC) and infiltrated with silicon (SiC+Si) and covers the central band from the other side portion, i.e. opposite the upper band.

[0049] Preferably, the matrix of aluminum alloy has a structure with a uniform distribution in the composite material. BRIEF DESCRIPTION OF DRAWINGS

[0050] Further features and advantages of the present application will become more apparent from the following detailed description of preferred, non-limiting embodiments thereof, taken in conjunction with the accompanying drawings, in which:

[0051] - Figure 1 is a perspective view of a brake disc according to an embodiment of the present application;

[0052] - Figure 2 schematically depicts some of the steps, in particular the initial steps, of a method for manufacturing a brake band for a brake disc according to an embodiment of the present application;

[0053] - Figure 2a schematically depicts the steps of a method for manufacturing a brake band for a brake disc according to a first embodiment of the method of the present application;

[0054] - Figure 2b schematically depicts the steps of a method for manufacturing a brake band for a brake disc according to a second embodiment of the method of the present application;

[0055] - Figure 2c schematically depicts the steps of a method for manufacturing a brake band for a brake disc according to a third embodiment of the method of the present application;

[0056] - Figure 2dThe steps of the method for manufacturing a brake band of a brake disc according to a fourth embodiment of the method according to the present application are schematically depicted, wherein the step of infiltrating silicon into the upper outer preform and into the lower outer preform is performed after the step of mechanically joining the upper preform and the lower preform with the central preform;

[0057] - Figure 2e The steps of the method for manufacturing a brake band of a brake disc according to a fifth embodiment of the method according to the present application are schematically depicted, wherein the step of infiltrating silicon into the upper outer preform and into the lower outer preform is performed after the step of mechanically joining the upper preform and the lower preform with the central preform;

[0058] - Figure 2f The steps of the method for manufacturing a brake band of a brake disc according to a sixth embodiment of the method according to the present application are schematically depicted, wherein the step of infiltrating silicon into the upper outer preform and into the lower outer preform is completed after the step of mechanically joining the upper preform and the lower preform with the central preform;

[0059] - Figure 3 is a perspective view of a preform according to an embodiment of the present application;

[0060] - Figure 4 , Figure 5 , Figure 6 and Figure 7 each show steps in a method for manufacturing a brake disc according to an embodiment of the present application, wherein the steps are performed in the order from Figures 4 to 7 ; in particular, Figure 7 shows a cross section of a rough brake disc taken in a diameter plane of the rough brake disc; the rough brake disc is an intermediate product immediately preceding the final brake disc shown in Figure 1 , which is obtained by removing unnecessary parts of the rough brake disc by means of subsequent machining.

[0061] Elements or parts of elements common to the embodiments described hereinafter will be denoted by the same reference signs. DETAILED DESCRIPTION

[0062] With reference to the above figures, reference 1 generally indicates a brake disc according to the present application.

[0063] According to a general embodiment of the present application shown in the figures, the brake disc 1 comprises a brake band 2 provided with two opposite outer braking surfaces 2a and 2b, each of which at least partially defines one of the two main faces of the disc.

[0064] The brake disc 1 further comprises a bell 3 connected to the brake band 2.

[0065] According to a first aspect of the present application, the brake band 2 comprises a central band 200’ made of an aluminum-based metal matrix composite reinforced with a ceramic material containing silicon carbide (SiC).

[0066] The above-mentioned composite material belongs to the class of composites known in the sector as MMCs (Metal Matrix Composites).

[0067] The use of said MMC composite containing aluminum in the brake band 2 allows to obtain even more mechanical and chemico-physical properties with respect to those of aluminum (see in particular the density and therefore the lightness) and at the same time (with respect to a simple fusion of aluminum or aluminum alloys) to increase the functional properties in heavy applications, such as those required in brake systems, without the need for protective coatings on the braking surfaces.

[0068] In addition, the brake band 2 further comprises an upper band 201’ joined to the central band 200’ along an upper bonding layer 22a. The upper band 201’ is made of a porous ceramic material containing silicon carbide (SiC) and infiltrated with silicon (SiC+Si). In addition, the upper band 201’ covers the central band 200’ on one side of the latter so that the central band 200’ does not come into contact with the brake pad on said side when the brake disc is mounted on a disc brake.

[0069] Furthermore, the brake band 2 comprises a lower band 202’ joined to the central band 200’ along a lower bonding layer 22b, arranged opposite, i.e. facing, the upper central layer 201’. The lower band 202’ is also made of a porous ceramic material containing silicon carbide (SiC) and infiltrated with silicon (SiC+Si). In addition, the lower band 202’ covers the central band 200’ on the other side, i.e. opposite the upper band 201’. In this way, as a result, the central band 200’ is interposed between the upper band 201’ and the lower band 202’. In particular, the external braking surfaces 2a, 2b of the brake band 2 are respectively the outermost surfaces of the upper band 201’ and of the lower band 202’ not joined to the central band 200’.

[0070] The presence of the reinforcement made of ceramic material in the central band 200' and of the upper band 201'and of the lower band 202, with respect to a braking band made only of aluminum or of one of the aluminum alloys, allows to obtain greater hardness, greater stiffness, higher coefficient of friction and greater wear resistance. All these characteristics make the braking band suitable for use with braking discs.

[0071] In this way, it is possible to form a braking band having the advantageous properties of aluminum, in particular see lower density with respect to steel and cast iron, while at the same time avoiding the need to provide the braking surface with a protective coating and the limitations and inconveniences of the braking band in terms of production and handling.

[0072] The above-mentioned ceramic material with which the reinforcement is made is silicon carbide.

[0073] As will be discussed later in the description, the MMC composite material forming the central band 200' is obtained by infiltrating a preform of porous ceramic material with an aluminum alloy. Advantageously, the above-mentioned ceramic materials, including silicon carbide, are able to withstand the step of infiltration by molten metal without altering the chemical and physical structure of the ceramic material and without subjecting the ceramic material to any degree of macroscopic and microscopic damage. The ceramic material is therefore particularly suitable also for the preparation of the above-mentioned composite material.

[0074] Preferably, the aluminum alloy is selected from alloys suitable for the fusion process, preferably comprising at least silicon, at least manganese, at least magnesium.

[0075] An advantageous embodiment provides that the aluminum alloy has a high magnesium (Mg) content, more preferably a high magnesium and silicon (Si) content.

[0076] Preferably, the magnesium (Mg) content is less than 15%, even more preferably less than 10%, but at least 0.2%. This provides increased mechanical properties and machinability on machine tools and ensures increased corrosion resistance and improved ability of the alloy to fill complex mold shapes by reducing the surface tension of the alloy in the liquid state. Preferably, the aluminum alloy is the AlSi13Mg9Ti alloy.

[0077] Advantageously, the aluminum alloy matrix has a uniform distribution within the composite material. As will be discussed below, this can be achieved by infiltrating a preform made of porous ceramic material having a uniform porosity throughout the volume with an aluminum alloy. As a result of the infiltration process, the aluminum alloy permeates the pores of the ceramic material, thus forming a uniform structure.

[0078] According to another aspect of the application, the brake disc 1 is provided with the above-mentioned bell 3 connected integrally with the brake band 2, and comprises an aluminium alloy co-cast with the metal matrix of the composite material forming the brake band 2.

[0079] As will be discussed in the following description, in this variant the bell 3 is obtained in the same mould, in which an aluminium alloy infiltration is performed on a preform made of ceramic material using the same aluminium alloy. In this way, in the same operating step, the formation of the composite material and the fusion of the bell are obtained, thus achieving a complete joining of the two materials.

[0080] The co-casting of the bell with the brake band allows a significant simplification of the production process. In fact, this avoids the need to set up both a dedicated production line for producing the bells and an assembly line for assembling the bells on the band.

[0081] The combination of the two fundamental aspects of the application described above makes it possible to obtain an aluminium-based brake disc which, on the one hand, can take advantage of the particular operating characteristics deriving from aluminium (first and foremost, lower density), and on the other hand, can have mechanical and wear characteristics comparable to those of a steel or grey cast iron disc, and at the same time can be manufactured through a production process as simple and economical as possible.

[0082] It is clear that, according to embodiments, the brake band 2 according to the application can also be connected with a bell 3 which is not co-fused (or made in one piece), but connected through bell-band connection means according to the prior art (assembly, interference fit, riveting, etc.).

[0083] In other words, when only the brake band 2 is manufactured, it is adapted to be assembled with the bell 3 in a known manner for manufacturing a brake disc, thus obtaining the brake disc, for example, through a floating compound or an interference fit.

[0084] It can therefore be understood that, in the present discussion, the aim is also to protect a method for manufacturing a brake disc, which also comprises a last step of the method, in which the connection between the brake band 2 according to the application and the bell 3 is provided, not in a co-fused one-piece manner, but through bell-band connection means, for example through assembly, interference fit, riveting, etc.

[0085] For the sake of simplicity of discussion, the brake band 2 and the brake disc 1 will now be described in connection with the respective methods for manufacturing the brake band 2 and the brake disc 1 according to the application. The brake disc 1 is preferably, but not necessarily, manufactured with the method according to the application that will now be described.

[0086] According to a general embodiment of the method of the present invention, the method for manufacturing a brake disc 1 includes the following first operation step a): preparing a mold 10 having an inner cavity 11, the inner cavity 11 including a first part 11a and a second part 11b, the first part 11a having a shape corresponding to the shape of the brake band 2 of the brake disc 1 to be manufactured, and the second part 11b having a shape corresponding to the shape of the bell-shaped member 3 of the brake disc 1 to be manufactured.

[0087] The first part 11a and the second part 11b of the inner cavity 11 are connected to each other, as shown below. Figure 5 and Figure 6 As shown, Figure 5 and Figure 6 An example of a mold that can be used in accordance with the method according to the invention is shown schematically.

[0088] Advantageously, such as Figure 4 and Figure 5 As shown, the mold includes one or more inlet openings 13 for directly injecting aluminum alloy into a second portion of the cavity 11 of the mold 10. The inlet openings 13 extend coaxially with a circumferential extension of the second portion 11b, which has a shape corresponding to the shape of the bell-shaped element 3 of the brake disc 1 to be manufactured. Therefore, in terms of operability, aluminum alloy can be injected through the inlet openings 13, and the aluminum alloy subsequently propagates from the inlet openings 13 into the first portion 11a.

[0089] The method includes the following second operational step b): preparing a preform 20, which includes a central preform 200, an upper outer preform 201, and a lower outer preform 202. The central preform 200 is made of a porous ceramic material containing silicon carbide (SiC). Additionally, the upper outer preform 201 and the lower outer preform 202 are made of a porous ceramic material containing silicon carbide (SiC) and permeated with silicon (SiC+Si). Carbon barrier layers 201a, 200a, 200b, and 202a made of carbon are placed between the upper outer preform 201 and the central preform 200, and between the lower outer preform 202 and the central preform 200.

[0090] Advantageously, the carbon barrier layers 201a, 200a, 200b, and 202a, made of carbon, allow for a more stable and reliable connection between the preforms 200, 201, and 202, and serve as an auxiliary barrier layer in the step of permeating aluminum into the central preform 200, further limiting the possibility of aluminum permeating into the upper outer preform 201 and the lower outer preform 202. The aforementioned preforms 200, 201, and 202 have a shape substantially the same as the brake band 2 of the brake disc 1 to be manufactured.

[0091] The method also comprises the following additional operating steps:

[0092] c) placing the strip preform 20 inside the mould and at the first portion 11a of the internal cavity 11; and

[0093] d) injecting the aluminium alloy in liquid or semi-solid state into the entire internal cavity 11 of the mould 10.

[0094] The injection of the aluminium alloy is performed so as to infiltrate the central preform 200 of the strip preform 20 with the aforementioned aluminium alloy, so as to obtain, at the first portion 11a, an aluminium metal matrix composite reinforced by the central preform 200, which partially defines the braking band 2 of the brake disc to be manufactured; and to fill the second portion 11b with the aforementioned aluminium alloy, so as to obtain an aluminium alloy fusion body which is connected in an integral manner to the braking band 2 made of metal matrix composite and which defines the bell 3 of the brake disc 1 to be manufactured.

[0095] According to the general embodiment, the method for manufacturing the braking band 2 of the brake disc 1 comprises a series of steps similar to those of the method for manufacturing the brake disc, except for the fact that the mould 10 is shaped so as to be used only for manufacturing the braking band 2 and not for manufacturing the bell 3. Therefore, with respect to the steps of the method for manufacturing the brake disc, in step a) the mould does not comprise a second portion 11b having a shape corresponding to that of the bell 3 of the brake disc 1 to be manufactured. Moreover, with respect to the method for manufacturing the brake disc 1, in step d) only the infiltration of the aluminium alloy is performed, so as to infiltrate the central preform 200 of the strip preform 20 with the aforementioned aluminium alloy, so as to obtain, in the first portion 11a, an aluminium metal matrix composite reinforced by the central preform 200, which partially defines the braking band 2 of the brake disc to be manufactured. Obviously, in order to manufacture only the braking band, it is not necessary to provide the aluminium alloy to fill the second portion 11b, since it is not necessary to manufacture the bell 2 of the brake disc at the same time by co-casting. Although the mould for the method for manufacturing the braking band is not depicted in the attached drawings, the person skilled in the art can clearly and univocally deduce how to modify the aforementioned mould 10 so that it does not have the second portion 11b for manufacturing the bell.

[0096] Therefore, in the general embodiment, the method for manufacturing the braking band according to the present application comprises a first operating step a) of preparing a mould 10 having an internal cavity 11 comprising a first portion 11a having a shape corresponding to that of the braking band 2 of the brake disc 1 to be manufactured.

[0097] Moreover, in this case, the mould comprises one or more inlet openings 13 for the direct injection of the aluminium alloy into the second portion of the inner cavity 11 of the mould 10.

[0098] The method comprises a second operating step b) of preparing a strip preform 20 comprising a central preform 200, an upper outer preform 201 and a lower outer preform 202. Said central preform 200 is made of a porous ceramic material comprising silicon carbide (SiC). In addition, the upper outer preform 201 and the lower outer preform 202 are made of a porous ceramic material comprising silicon carbide (SiC) and infiltrated with silicon (SiC+Si). Carbon barrier layers 201a, 200a, 200b, 202a made of carbon are interposed between the upper outer preform 201 and the central preform 200 and between the lower outer preform 202 and the central preform 200. Said preforms 200, 201, 202 have a shape substantially identical to the shape of the braking band 2 of the brake disc to be manufactured.

[0099] The method further comprises the following additional operating steps:

[0100] c) placing the above-mentioned strip preform 20 inside the mould and at the first portion 11a of said inner cavity 11; and

[0101] d) injecting an aluminium alloy in liquid or semi-solid state inside the entire inner cavity 11 of the mould 10.

[0102] The injection of the aluminium alloy is performed so as to infiltrate the central preform 200 of the strip preform 20 with the above-mentioned aluminium alloy, so as to obtain, at the first portion 11a, an aluminium metal matrix composite reinforced by the central preform 200, which partially defines the braking band 2 of the brake disc to be manufactured.

[0103] Advantageously, the step b) of injecting the aluminium alloy inside the mould, in order to manufacture the brake disc 1 and in order to manufacture the braking band 2, can be performed according to any technique suitable for this purpose.

[0104] In particular, the step b) can be performed according to a liquid infiltration technique, according to an extrusion casting technique, according to a gravity infiltration technique, or according to a semi-solid infiltration technique, or by means of a die casting with liquid aluminium.

[0105] In the case of gravity infiltration, the infiltration is preferably performed in an inert atmosphere, such as a nitrogen atmosphere.

[0106] The above-mentioned infiltration techniques are well known to the person skilled in the art and will therefore not be described here again.

[0107] Preferably, the step b) of injecting the aluminium alloy into the mould is carried out according to the semi-solid infiltration technique. In fact, it has been found that this technique is more suitable for infiltrating the ceramic preforms, so that at the end of the process the resulting disc made of MMC material has uniform characteristics throughout the structure of the disc. At the same time, this technique is suitable for forming the bell in the same process.

[0108] More specifically, the infiltration at the semi-solid stage takes place at a temperature between the liquidus and the solidus of the aluminium alloy used, i.e. with the alloy in semi-solid state. Since the viscosity of semi-solid substances is low, the process of injection into the mould and the infiltration process take place smoothly and with low turbulence.

[0109] It is particularly advantageous that the presence of the upper and lower outer bands infiltrated with silicon prevents the aluminium from infiltrating said upper and lower outer bands. The result is a pair of opposite braking surfaces 2a, 2b particularly suitable for use in a brake disc, since said pair of opposite braking surfaces 2a, 2b is free of aluminium and has an improved coefficient of friction with respect to the aluminium discs of the prior art. In addition, the further presence of the carbon barrier layer even more advantageously ensures that, during the aluminium infiltration step, no migration of aluminium from the central preform to the upper and lower outer preforms occurs.

[0110] According to a preferred embodiment of the method for manufacturing the brake band 2 or of the method for manufacturing the brake disc 1, the above-mentioned band preform 20 made of porous ceramic material is obtained by subjecting a mass of ceramic material particles coated with a polymeric binding composition on the surface to the following sequence of operating steps: moulding, debinding (or defatting) and sintering.

[0111] Advantageously, the above-mentioned ceramic material particles are powder particles known as "ready-to-press". This powder, commercially available on the market, allows to obtain a "net shape moulding" product, without the need for other ingredients or additives in addition to the powder itself.

[0112] Preferably, the above-mentioned ceramic material for forming the particles is silicon carbide.

[0113] Preferably, the polymeric binding composition with which the ceramic material particles are coated is selected from thermoplastic polymers and thermosetting polymers.

[0114] Preferably, the moulding of the mass of ceramic material particles is done uniaxially or isostatically or using any other technique that allows to obtain a preform of such dimensions and shape.

[0115] At the end of the moulding process, an aggregate of the above-mentioned particles of ceramic material is obtained, which is connected by the ceramic microstructure promoted by the respective coating of the polymeric binding composition. Said aggregate contains organic residues from the coating of the particles. These organic residues are removed in a debinding (or defatting) step.

[0116] Advantageously, the debinding is carried out at a temperature lower than 700°C under air flow conditions until the organic phase present in the mass of particles of ceramic material after moulding is completely eliminated.

[0117] According to a variant, the debinding is carried out under inert atmosphere conditions.

[0118] At the end of the debinding step, a green body is obtained which essentially comprises ceramic material only. This green body is then subjected to a sintering phase which transforms the green body into a continuous structure obtained by the formation of bridges connecting the individual ceramic particles. This produces a body which presents uniform properties throughout the structure.

[0119] Preferably, the sintering is carried out in two separate sintering cycles. The first sintering cycle is carried out at a temperature not lower than 1600°C, preferably about 1800°C, and the second sintering cycle is carried out at a temperature not lower than 2000°C, preferably in the range from 2100°C to 2200°C, and both the first sintering cycle and the second sintering cycle are carried out under inert atmosphere.

[0120] Advantageously, the resulting preform 20 made of porous ceramic material has a uniform density and porosity distribution throughout the volume of the preform 20. Said characteristics make the preform suitable for manufacturing a uniformly distributed matrix of aluminium alloy after infiltration of the preform with said aluminium alloy.

[0121] According to an advantageous embodiment, both the method for manufacturing a brake band and the method for manufacturing a brake disc comprise a series of operating steps to be carried out before step b), such as the steps schematically shown in Figure 2 、 Figure 2a 、 Figure 2b 、 Figure 2c . In particular, the above-mentioned series of operating steps envisages an initial operating step al) of preparation of a central preform 200, an upper outer preform 201 and a lower outer preform 202. Each of said central preform 200, upper outer preform 201 and lower outer preform 202 is made of porous ceramic material containing silicon carbide (SiC). The respective shape of said preforms is such that, when joined together, they present a shape substantially identical to that of the brake band 2 of the brake disc 1 to be manufactured.

[0122] Furthermore, the above series of operating steps provides a subsequent operating step a2) of infiltrating the upper outer preform 201 and the lower outer preform 202 with silicon (Si). The infiltration with silicon prevents the presence of spaces in which the aluminum infiltrates the preforms during the infiltration step of the aluminum alloy.

[0123] Preferably, in this step a2) the upper outer preform 201 and the lower outer preform 202 are placed in a crucible coated with a release layer, for example based on boron nitride (BN), and a predetermined quantity of silicon (Si) powder is added to the crucible. Subsequently, the upper outer preform 201 and the lower outer preform 202 are heated to achieve the fusion of the added silicon and thus the infiltration.

[0124] Advantageously, the upper outer preform 201 and the lower outer preform 202 are heated to a temperature above the melting temperature of Si (1414°C) at atmospheric pressure and in an inert atmosphere, preferably in an argon environment. This process can be completed using an industrial furnace appropriately sized.

[0125] According to a variant, the upper outer preform 201 and / or the lower outer preform 202 are heated to a temperature above the melting temperature of Si (1414°C) at a pressure other than atmospheric pressure, for example even in controlled vacuum.

[0126] Furthermore, preferably, after the infiltration process, the upper and lower outer preforms are optionally flattened (ground) before the subsequent steps described below are carried out.

[0127] The above series of operating steps provides a further operating step a3) of depositing a material containing carbon in the form of particles on the central preform 200 to obtain at least one carbon barrier layer 200a, 200b made of carbon, as shown, for example, in Figure 2a .

[0128] As an alternative to step a3), a step a4) can be provided of depositing a material containing carbon in the form of particles on the upper outer preform 201 and on the lower outer preform 202 to provide at least one carbon barrier layer 201a, 202a made of carbon (C) on each of the upper outer preform 201 and the lower outer preform 202, as shown, for example, in Figure 2b .

[0129] Moreover, as an alternative to steps a3) and a4), step a5) can be provided to deposit a material comprising carbon in the form of particles on the central preform 200 and on the upper outer preform 201 and / or on the lower outer preform 202, to achieve at least one carbon barrier layer 200a and / or 200b, 201a and / or 202a made of carbon (C) on the central preform 200 and on the upper outer preform 201 and / or on the lower outer preform 202, as shown for example in Figure 2c

[0130] In other words, in any variant of the method described herein, preferably, the carbon barrier layer is formed between the upper outer preform 201 and the central preform 200 and between the lower outer preform 202 and the central preform 200, by providing for the deposition only on the upper outer preform and on the lower outer preform, or by providing for the deposition only on the two opposite faces 2000, 2001 of the central preform, or by providing for the deposition on both the central preform 200 and the upper outer preform 201 and on the lower outer preform 202.

[0131] It is evident that, preferably, the carbon barrier layer is formed (and therefore the deposition of the carbon barrier layer is performed) only on one face of the two opposite faces 2010, 2011; 2020, 2021 of each of the upper outer preform and of the lower outer preform.

[0132] It is also evident that, preferably, the central preform 200, the upper outer preform 201 and the lower outer preform 202 have a ring-shaped disc shape, preferably, the central preform 200, the upper outer preform 201 and the lower outer preform 202 have a central through hole 5. Preferably, the two opposite faces 2000, 2001; 2010, 2011; 2020, 2021 are the two opposite faces having the greatest extension of the disc-shaped piece.

[0133] Therefore, the two opposite faces 2000, 2001; 2010, 2011; 2020, 2021 of each preform comprise an upper face 2000, 2010, 2020 and an opposite lower face 2001, 2011, 2021 joined together by a lateral wall 2002, 2012, 2022 extending in association with the upper face 2000, 2010, 2020 and the lower face 2001, 2011, 2021, preferably perpendicularly to the upper face 2000, 2010, 2020 and to the lower face 2001, 2011, 2021, i.e. so as to form a shell of a disc.

[0134] ​Preferably, in the case where each preform has already been provided with a central through hole 5, it is clear that said preform will therefore also have an inner lateral wall 2003, 2013, 2023 opposite the lateral wall 2002, 2012, 2022.

[0135] The above series of operating steps provides for the following further operating step a6) of joining together the central preform 200, the upper outer preform 201 and the lower outer preform 202 by placing silicon (Si) at each carbon barrier layer 200a and / or 200b, 201a and / or 202a and heating said preforms 200, 201, 202 until a joint is formed between said preforms 200, 201, 202 and at the carbon barrier layers 200a and / or 200b, 201a and / or 202a, thus obtaining a band preform 20. Preferably, therefore, silicon (Si), for example solid silicon, is placed between each carbon barrier layer 200a and / or 200b and the upper outer preform 201 and the lower outer preform 202, or between each carbon barrier layer 201a and / or 202a and the central preform 200, or between each carbon barrier layer 200a and / or 200b and the facing corresponding carbon barrier layer 201a and / or 202a.

[0136] Advantageously, said step a6) of forming a joint between the central preform 200 and the upper outer preform 201 and the lower outer preform 202 is provided for by placing a stoichiometric amount of silicon according to the dimensions of the preforms between said preforms, heating the preforms 200, 201, 202 to a temperature of about 1450°C for about 2 hours.

[0137] For example, the stoichiometric amount of silicon (MSi) can be calculated as follows. When the total volume of carbon is defined as follows:

[0138] VC = Π (R2- r2) h, where the radii R and r are the outer radius R and the inner radius r of the annular crown described by the preform 200, 201 or 202, respectively, and h is the thickness of the carbon barrier layer (assuming that the layer is compact and has no porosity);

[0139] The mass of the deposited carbon C can be calculated as follows:

[0140] MC = VC x DC, where Dc is the density of carbon.

[0141] Given the formula Si + C = SiC, so that 1 mole of silicon (Si) reacts with 1 mole of carbon (C) to produce 1 mole of silicon carbide (SiC), and the atomic weight of the components is known, the stoichiometric amount of silicon can be calculated as follows:

[0142] MSi = atomic weight of MSi / atomic weight of C.

[0143] For example, in the case where the preform has a diameter of about 40 millimetres and the amount of Si required is about 3 grams, said parameters allow to obtain sufficiently reliable joints between the preforms.

[0144] It is clear that, depending on the process adopted, when the minimum stoichiometry of Si required to react with carbon C according to the above formula (MSi) is known, it can optionally be increased to introduce more or less super-stoichiometric conditions, thus ensuring the completion of the chemical reaction.

[0145] Obviously, when the band preform 20 is obtained as described above, the central preform 200 corresponds to the central band 200' of the brake band 20, and the upper outer band 201 and the lower outer band 202 correspond to the upper outer band 201' and the lower outer band 202' of the brake band 20, respectively.

[0146] According to a preferred embodiment, the step of depositing the material in particulate form comprising carbon to obtain at least one carbon barrier layer 200a, 200b, 201a, 202a made of carbon (C) in step a3) or step a4 or step a5) is carried out by chemical vapour deposition.

[0147] Preferably, gaseous methane as carbon precursor is used for the chemical vapour deposition, the temperature is 1100°C to 1300°C and the pressure is 10 mbar to 50 mbar.

[0148] Even more preferably, during the step of chemical vapour deposition, the contributions in the gas mixture are:

[0149] - methane between 0.4 standard litres per minute and 3 standard litres per minute (slm);

[0150] - hydrogen between 0.2 standard litres per minute and 5 standard litres per minute (slm);

[0151] - argon between 0 standard litres per minute and 4 standard litres per minute (slm);

[0152] and the ratio between methane and hydrogen is between 0.3 and 5.

[0153] The above parameters allow to obtain a carbon barrier layer, i.e. a carbon coating, on the preform, thus minimising as much as possible the risk of penetration into said preform.

[0154] Advantageously, in step d) of the method according to the application, for example Figures 5 to 6As can be seen, the mould is closed on the upper outer preform 201 and on the lower outer preform 202, so that during the injection of aluminium into the mould, the penetration of aluminium onto the upper outer preform 201 and onto the lower outer preform 202 is prevented, thus making the outer braking surfaces 2a, 2b of the disc free of aluminium. In other words, the flow and spread of the aluminium alloy on the upper outer preform 201 and on the lower outer preform 202, i.e. on the side portions of each outer preform 201, 202 not joined to the central preform 200, is prevented.

[0155] According to a variant of the method, in Figure 2d , Figure 2e and Figure 2f it can be appreciated more clearly that the operation step a2) of permeation of the upper outer preform 201 and of the lower outer preform 202 with silicon (Si) is not envisaged before the execution of the step a6) as described above. However, in this variant of the method, after the aforementioned step al) and after the aforementioned step a3) or step a4) or step a5), the method initially comprises an operation step al l) of protection of one or more areas of the upper outer preform 201, of the lower outer preform 202 and of the central preform 200 by means of release layers 200", 201" and 202" and subsequently the execution of the step a6) as described above. The release layers 200", 201" and 202" prevent the penetration of silicon (Si) into the protected areas through the release layers. This is obtained, for example, by means of boron nitride-based release layers.

[0156] Preferably, in this step al l), the protection of one or more areas of the upper outer preform 201, of the lower outer preform 202 and of the central preform 200 is achieved by placing the aforementioned preforms 200, 201, 202, when necessary, in a crucible coated with a release layer, for example a release layer based on boron nitride (BN).

[0157] Preferably, the release layers 200", 201" and 202" are positioned in the vicinity of the side wall 2002 of the central preform 200 and / or of the side wall 2012 of the upper outer preform 201 and / or of the side wall 2022 of the lower outer preform, so as to prevent the penetration of silicon through the disc in the radial direction R.

[0158] In this variant, after the step a6), i.e. after the formation of the joint between the preforms 200, 201, 202 at the carbon barrier layers 200a and / or 200b, 201a and / or 202a to obtain the preform 20 with preforms, the method comprises the execution of the following steps:

[0159] a61) protecting one or more areas of the central preform 200 by means of a release layer 200" previously used, for example a release layer based on boron nitride (BN), or by means of a different or additional release layer, for example a release layer based on boron nitride (BN);

[0160] a62) infiltrating the upper outer preform 201 and the lower outer preform 202 with silicon (Si) in the same way as described in step a2). Infiltration with silicon prevents the presence of spaces in which the aluminum infiltrates the preform during the infiltration step of the aluminum alloy.

[0161] It is clear that the main difference in this variant of the method is that the silicon infiltration step is performed in the upper outer preform 201 and in the lower outer preform 202 after the mechanical joining between the lower outer preform and the central preform and between the upper outer preform and the central preform along the carbon barrier layer.

[0162] Therefore, the additional steps of the method described above, for example step a3), step a4) or step a5 and all the other steps and the details of the individual steps are understood as equally valid and applicable to this variant of the method, as more clearly shown in Figures 2d to 2f .

[0163] According to an embodiment of the above variant of the method, in particular as shown in Figure 2e and Figure 2f , the method comprises the operating step of protecting at least one portion of the upper outer preform 201 and / or of the lower outer preform 202, for example by placing a sheet of graphite paper on each portion of the upper outer preform or of the lower outer preform, when performing step a3), step a4) or step a5). This allows to mask the individual portions of the upper preform and / or of the lower preform so that subsequently the upper preform and / or the lower preform can be infiltrated with silicon Si.

[0164] In particular, for example, the method provides to mask at least partially or completely the upper face 2010, 2020 and / or the opposite lower face 2011, 2021 of the upper outer preform 201 and / or of the lower outer preform 202.

[0165] As can be understood from what has been described, the brake band, the brake disc and the method for manufacturing said brake disc and said brake band according to the present application make it possible to overcome the drawbacks present in the prior art.

[0166] In fact, in a particularly innovative way, by placing two external braking bands made of ceramic composite material between the braking pad and the central band made of composite material with an aluminum alloy metal matrix, the braking band and the braking disc of the present application allow the problems found in the prior art related to the localized deterioration due to overheating of aluminum to be reduced, if not eliminated. Moreover, the braking band and the braking disc of the present application allow a greater braking force to be generated at the same time, since the pad is coupled on a material with a higher coefficient of friction. At the same time, problems of high efficiency, simplicity, low implementation costs and reduction of corrosion are ensured. The reduction of corrosion is particularly advantageous for electric vehicles, in which the introduction of regenerative braking involves discontinuous use of the disc brake, which can cause corrosion phenomena.

[0167] In order to satisfy the possible and specific needs, the person skilled in the art can make numerous modifications and variants to the above-described disc and disc brake, which, however, all fall within the scope of the present application as defined in the attached claims.

Claims

1. A method for manufacturing a brake band (2) of a brake disc (1) of a disc brake, said method comprising the following steps: a) preparing a mould (10) having an internal cavity (11) comprising a first portion (11a) having a shape corresponding to that of the brake band (2) to be manufactured; b) providing a band preform (20) comprising a central preform (200) made of a porous ceramic material comprising silicon carbide, an upper outer preform (201) and a lower outer preform (202) made of a porous ceramic material comprising silicon carbide and infiltrated with silicon, wherein a carbon barrier layer (201a, 200a, 200b, 202a) made of carbon is interposed between the upper outer preform (201) and the central preform (200) and between the lower outer preform (202) and the central preform (200), the central preform (200), the upper outer preform (201) and the lower outer preform (202) having the shape of the brake band (2) to be manufactured; c) placing the band preform (20) inside the mould and at the first portion (11a) of the internal cavity (11); and d) injecting a liquid or semi-solid aluminium alloy into the entire internal cavity (11) of the mould (10) to infiltrate the central preform (200) of the band preform (20) made of a porous ceramic material with the aluminium alloy, so as to obtain, at the first portion (11a), an aluminium metal matrix composite reinforced with the central preform (200), which defines the brake band (2) to be manufactured.

2. The method of claim 1, wherein, Before the step b) of manufacturing the band preform (20), the method comprises the following steps: a1) providing a central preform (200), an upper outer preform (201) and a lower outer preform (202), each made of a porous ceramic material comprising silicon carbide; a2) infiltrating the upper outer preform (201) and the lower outer preform (202) with silicon; a3) depositing a material comprising carbon in the form of particles on the central preform (200) to obtain at least one carbon barrier layer (200a, 200b) made of carbon; a4) instead of step a3), depositing a material comprising carbon in particulate form on said upper outer preform (201) and on said lower outer preform (202) to provide at least one carbon barrier layer (201a, 202a) made of carbon (C) on each of said upper outer preform (201) and said lower outer preform (202); a5) instead of step a3) and step a4), depositing a material comprising carbon in particulate form on said central preform (200) and on said upper outer preform (201) and / or on said lower outer preform (202) to provide at least one carbon barrier layer (200a and / or 200b, 201a and / or 202a) made of carbon (C) on said central preform (200) and on said upper outer preform (201) and / or on said lower outer preform (202); a6) joining together said central preform (200), said upper outer preform (201) and said lower outer preform (202) by interposing silicon at each carbon barrier layer (200a and / or 200b, 201a and / or 202a) and heating said central preform (200), said upper outer preform (201) and said lower outer preform (202) until a bond is formed between said central preform (200), said upper outer preform (201) and said lower outer preform (202) and at said carbon barrier layer (200a and / or 200b, 201a and / or 202a), thereby producing said belt preform (20).

3. The method of claim 1, wherein, Before step b) of manufacturing said belt preform (20), the method comprises the following steps: a3) depositing a material comprising carbon in particulate form on said central preform (200) to obtain at least one carbon barrier layer (200a, 200b) made of carbon; a4) instead of step a3), depositing a material comprising carbon in particulate form on said upper outer preform (201) and on said lower outer preform (202) to provide at least one carbon barrier layer (201a, 202a) made of carbon (C) on each of said upper outer preform (201) and said lower outer preform (202); a5) instead of step a3) and step a4), depositing a material comprising carbon in particulate form on said central preform (200) and on said upper outer preform (201) and / or on said lower outer preform (202) to provide at least one carbon barrier layer (200a and / or 200b, 201a and / or 202a) made of carbon (C) on said central preform (200) and on said upper outer preform (201) and / or on said lower outer preform (202); a6) joining together said central preform (200), said upper outer preform (201) and said lower outer preform (202) by interposing silicon at each carbon barrier layer (200a and / or 200b, 201a and / or 202a) and heating said central preform (200), said upper outer preform (201) and said lower outer preform (202) until a bond is formed between said central preform (200), said upper outer preform (201) and said lower outer preform (202) and at said carbon barrier layer (200a and / or 200b, 201a and / or 202a), thereby producing said belt preform (20). a11) protecting one or more areas of the upper outer preform (201), the lower outer preform (202) and the central preform (200) by a release layer (200", 201", 202"); a6) joining together the central preform (200), the upper outer preform (201) and the lower outer preform (202) by interposing silicon at each carbon barrier layer (200a and / or 200b, 201a and / or 202a) and heating the central preform (200), the upper outer preform (201) and the lower outer preform (202) until a bond is formed between the central preform (200), the upper outer preform (201) and the lower outer preform (202) and at the carbon barrier layer (200a and / or 200b, 201a and / or 202a); a61) protecting one or more areas of the central preform (200) by the release layer (200") used in step a11) or by a different or additional release layer; a62) infiltrating the upper outer preform (201) and the lower outer preform (202) with silicon.

4. The method of claim 2 or 3, wherein, In step a2) or step a62), the upper outer preform (201) and the lower outer preform (202) are positioned in a crucible coated with a release layer, a predetermined amount of powdered silicon is added to the crucible, and the upper outer preform (201) and the lower outer preform (202) are heated to obtain fusion of the added silicon.

5. The method of claim 4, wherein, The upper outer preform (201) and the lower outer preform (202) are heated above the melting temperature of silicon at atmospheric pressure and in an inert atmosphere.

6. The method of claim 2, wherein, In step a3) or step a4) or step a5), the step of depositing a material comprising carbon in particulate form to obtain at least one carbon barrier layer (201a, 202a) made of carbon (C) is achieved by a method selected from: chemical vapor deposition; sputtering; physical vapor deposition (PVD); bonding with graphite-based glue.

7. The method of claim 6, wherein, Gaseous methane is used as carbon precursor for chemical vapor deposition, and wherein the temperature is between 1100°C and 1300°C, the pressure is between 10 mbar and 50 mbar.

8. The method of claim 7, wherein, During the step of chemical vapor deposition, the contribution in the gas mixture is: - between 0.4 standard liters per minute and 3 standard liters per minute (slm) of methane; - between 0.2 standard liters per minute and 5 standard liters per minute (slm) of hydrogen; - between 0 standard liters per minute and 4 standard liters per minute (slm) of argon; and wherein the ratio of methane to hydrogen is between 0.3 and 5.

9. The method of claim 2, wherein, In step a6), the method involves: - heating the central preform (200), the upper outer preform (201) and the lower outer preform (202) to a temperature of 1450°C for a time of 2 hours by placing between the central preform (200), the upper outer preform (201) and the lower outer preform (202) a stoichiometric quantity of silicon defined according to the dimensions of the central preform (200), the upper outer preform (201) and the lower outer preform (202).

10. The method of claim 1, wherein, The step d) of introducing the aluminium alloy into the mould is performed according to semi-solid or liquid infiltration techniques or by squeeze casting.

11. The method of claim 1, wherein, The central preform (200), the lower outer preform (202) and the upper outer preform (201) are obtained by subjecting a mass of ceramic material particles coated with a polymeric bonding composition to sequential moulding, de-waxing and sintering.

12. The method of claim 11, wherein, The sintering is performed in two separate sintering cycles, wherein a first sintering cycle is performed at a temperature not lower than 1600°C and a second sintering cycle is performed at a temperature not lower than 2000°C, both in an inert atmosphere.

13. The method of claim 1, wherein, In step d) the mould is closed on the upper outer preform (201) and on the lower outer preform (202) so that during the introduction of aluminium into the mould, the penetration of aluminium above the upper outer preform (201) and below the lower outer preform (202) is prevented so that the outer braking surfaces (2a, 2b) of the disc are free from aluminium.

14. A method for manufacturing a brake disc comprising a braking band (2) and a bell (3), the method comprising the following steps: a) preparing a mould (10) having an internal cavity (11) comprising a first portion (11a) having a shape corresponding to the shape of the braking band (2) of the brake disc (1) to be manufactured and a second portion (11b) having a shape corresponding to the shape of the bell (3) of the brake disc (1) to be manufactured, wherein the first portion (11a) and the second portion (11b) of the internal cavity (11) communicate with each other; b) providing a band preform (20) comprising a central preform (200) made of a porous ceramic material comprising silicon carbide, an upper outer preform (201) and a lower outer preform (202) made of a porous ceramic material comprising silicon carbide and infiltrated with silicon, wherein carbon barrier layers (201a, 200a, 200b, 202a) made of carbon are interposed between the upper outer preform (201) and the central preform (200) and between the lower outer preform (202) and the central preform (200), the central preform (200), the upper outer preform (201) and the lower outer preform (202) having the shape of the braking band (2) of the brake disc (1) to be manufactured; c) placing the band preform (20) inside the mould and at the first portion (11a) of the inner cavity (11); and d) injecting a liquid or semi-solid aluminium alloy into the entire inner cavity (11) of the mould (10) so that: only the central preform (200) of the band preform (20) made of porous ceramic material is infiltrated with the aluminium alloy, obtaining at the first portion (11a) an aluminium metal matrix composite reinforced by the central preform (200), which defines the braking band (2) of the brake disc to be manufactured; and the second portion (11b) is filled with the aluminium alloy, obtaining an aluminium alloy fusion body connected in a unitary manner with the braking band (2) made of composite metal matrix and defining the bell (3) of the brake disc (1) to be manufactured.

15. A braking band (2) of a brake disc for disc brakes, the braking band (2) comprising: a central band (200') made of an aluminium metal matrix composite reinforced with a ceramic material comprising silicon carbide, the composite material being obtained by infiltrating a central preform (200) made of a porous ceramic material with an aluminium alloy, the central preform (200) having a shape corresponding to that of the braking band, an upper band (201') joined to the central band (200') along an upper bonding layer (22a), the upper band (201') being made of a porous ceramic material comprising silicon carbide and infiltrated with silicon, and the upper band (201') covering the central band (200') on one side thereof, and an outer braking surface (2a) of the upper band (201') being free of aluminium, a lower band (202') joined to the central band (200') along a lower bonding layer (22b) arranged on the opposite side, i.e. on the opposite side with respect to the upper bonding layer (22a), the lower band (202') being made of silicon carbide- containing and silicon-infiltrated porous ceramic material, and the lower band (202') covering the central band (200') on the other side, i.e. on the opposite side with respect to the upper band (201'), and the outer braking surface (2b) of the lower band (202') being free of aluminum; wherein the upper bonding layer (22a) and the lower bonding layer (22b) comprise silicon carbide formed by reacting silicon with the carbon barrier layer during the infiltration and heating step.

16. A brake disc for a disc brake, comprising a brake band (2) according to claim 15 and a bell (3) connected with the brake band (2).

17. The brake disc for a disc brake according to claim 16, wherein The bell (3) is connected in an integral manner with the brake band (2), and the bell (3) comprises an aluminum alloy co-cast with the metal matrix of the composite material constituting the brake band (2).

18. The brake disc of claim 16 or 17, wherein, The matrix of the aluminum alloy has a homogeneous distribution within the composite material.

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