Method for manufacturing brake bands for brake discs, method for manufacturing brake discs, brake discs and brake bands for brake discs

Abstract

A method for manufacturing a brake band (2) for a brake disc (1) for a disc brake includes the steps of: a) providing a mould (10) having an inner cavity (11), said mould consisting of a first part (11a) of a shape corresponding to the brake band (2) to be produced; b) preparing a band preform (20) consisting of a central layer (200) made of a porous ceramic material made of silicon carbide (SiC), an upper outer layer (201) and a lower outer layer (202), said upper outer layer (201) and said lower outer layer (202) being made of a porous ceramic material made of silicon carbide (SiC) and infiltrated with silicon (SiC+Si), said upper outer layer (201) and said lower outer layer (202) being arranged opposite and facing said central layer (200); c) placing the band preform (20) in a mold in the first portion (11a) of the internal cavity (11); and d) injecting a liquid or semi-solid aluminum alloy inside the entire inner cavity (11) of the mould (11) so as to infiltrate only the central layer (200) of said band preform (20) made of porous ceramic material with said aluminum alloy, obtaining in the first part (11a) an aluminum metal matrix composite reinforced by said central preform (200) defining the brake band (2) to be manufactured. The brake band and brake disc are manufactured at least by the method described above.

Description

Technical Field

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[0003]

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

Background Art

[0002] The brake disc of a vehicle's disc brake system consists of an annular structure, i.e., a brake band, and a central fixing element known as a bell. The disc is attached to a rotating part of the vehicle suspension, such as a hub, by this fixing element. The brake band has opposing brake surfaces suitable for cooperating with friction elements (brake pads), and is housed in at least one gripper body that is arranged across the brake band and integrated with a non-rotating part of the vehicle suspension. The controlled interaction between the opposing brake pads and the opposing brake surfaces of the brake band causes a braking action by friction, decelerating or stopping the vehicle.

[0003] Generally, brake discs are made of gray cast iron or steel. In fact, these materials can obtain relatively good braking performance (especially wear resistance) at a relatively low cost. Discs made of carbon or carbon ceramic materials provide much higher performance but are much more costly.

[0004] As an alternative to gray cast iron or steel discs, aluminum discs have been proposed to reduce the weight of the disc. The aluminum discs are provided with a protective coating. The protective coating, on the one hand, reduces the wear of the disc and ensures performance similar to that of cast iron discs, and on the other hand, protects the aluminum base from the temperature generated during braking, which far exceeds the softening temperature of aluminum (200 - 400°C). [[ID=​Currently available protective coatings applied to aluminum discs, while providing wear resistance, often cause peeling, resulting in the coating detaching from the disc. This complicates the disc manufacturing process. In effect, the disc must undergo surface finishing and be prepared for connection to the bell.

[0006] As is clear from the above, aluminum or aluminum alloy discs with protective coatings cannot currently completely replace steel or gray cast iron discs.

[0007] However, because aluminum has a lower density than both steel and gray cast iron, there is considerable interest in aluminum among those in the brake system industry as an excellent potential substitute for both steel and gray cast iron.

[0008] Therefore, this field requires aluminum-based brake discs that, on the one hand, allow us to utilize aluminum's unique operational characteristics (primarily due to its low density), while on the other hand, provide mechanical strength and wear characteristics at least comparable to those of steel or gray cast iron discs. Furthermore, these discs must be manufactured using the simplest and most economical manufacturing process possible.

[0009] WO2019 / 123222A1 describes a method for manufacturing aluminum discs using porous ceramic preforms impregnated with molten aluminum (in a liquid or semi-solid state). Unfortunately, discs obtained by this method result in direct contact between the brake pad and the aluminum-based metal matrix, which can lead to localized degradation of the disc where the aluminum is overheated to its melting point due to friction. [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] Therefore, there is a strong need in the industry for aluminum-based brake discs that do not undergo localized degradation, that allow the use of aluminum's special operational characteristics (primarily its low density), and that achieve mechanical strength and wear characteristics comparable to steel or gray cast iron discs, while simultaneously being manufactured using the simplest and most economical manufacturing process possible.

[0011] Along with the above requirements, there is also a need for brake discs that have higher corrosion resistance than cast iron or steel discs and emit fewer contaminating metal particles.

[0012] The aforementioned requirements are satisfied by the method for manufacturing a brake band for a brake disc, a method for manufacturing a brake disc, a brake disc for a disc brake, and a brake band according to the attached independent claims. [Means for solving the problem]

[0013] The method for manufacturing a brake band according to this invention consists of the following steps. a) A step of preparing a mold having an inner cavity that constitutes a first part of the shape corresponding to the brake band to be manufactured; b) A step of preparing a band preform comprising a central layer, an upper outer layer, and a lower outer layer made of a porous ceramic material made of silicon carbide (SiC), wherein the upper outer layer and the lower outer layer are made of silicon carbide (SiC) and are made of a porous ceramic material impregnated with silicon (SiC+Si), and the upper outer layer and the lower outer layer are further arranged opposite each other on the opposite side of the central layer; c) The step of placing the band preform in the mold in the first portion of the internal cavity; d) A step of injecting a liquid or semi-solid aluminum alloy into the entire interior cavity of a mold such that the aluminum alloy permeates only the central layer of the band preform made of porous ceramic material, thereby obtaining in the first part an aluminum metal matrix composite reinforced by the central layer that partially defines the brake band to be manufactured.

[0014] Advantageously, to manufacture a band preform, this method includes the following steps: a1) A step of preparing a rough preform made of a porous ceramic material made of silicon carbide (SiC), wherein the rough preform has an upper surface and an opposing lower surface, and is joined to each other by side walls incident on the upper and lower surfaces, for example, the rough preform has a cylindrical or other centrally hollow cylindrical shape (as shown in the figure), the lower and upper surfaces are the base of the cylindrical shape, and the side walls are the sides of the cylindrical shape; a2) A step of depositing a masking layer on the sidewall that is at least partially suitable for preventing the infiltration of silicon (Si) in step a3); a3) A step of impregnating a rough preform with silicon (Si) to a predetermined depth through the upper and lower surfaces in order to obtain a band preform consisting of a central layer in which silicon (Si) has not penetrated, an upper outer layer in which silicon (SiC+Si) has penetrated, and a lower outer layer in which silicon (SiC+Si) has penetrated, wherein the upper outer layer and the lower outer layer are arranged opposite to each other and on the opposite side of the central layer.

[0015] Preferably, in step a2), the step of depositing a masking layer consists of depositing a boron nitride (BN) layer.

[0016] Advantageously, in step a2), the masking layer is applied to the entire sidewall but not to the top and bottom surfaces of the rough preform.

[0017] Preferably, in step a3), the crude preform is placed in a crucible, a predetermined amount of silicon (Si) powder is added to the crucible, and the crude preform is heated at atmospheric pressure in an inert atmosphere, preferably an argon atmosphere, to a temperature above 1414°C for at least 5 minutes.

[0018] Preferably, the crude preform is heated to a temperature between 1500°C and 1650°C at time intervals between 15 and 90 minutes.

[0019] More preferably, the green preform is heated at a temperature between 1550 °C and 1600 °C for a time interval between 30 minutes and 60 minutes.

[0020] Preferably, the green preform has a thickness between 4 millimeters and 40 millimeters, that is, the distance between the upper surface and the lower surface, including both ends, more preferably between 10 millimeters and 20 millimeters, and the predetermined amount of silicon is up to between 0.5 millimeter and 3 millimeters, preferably about 2 millimeters, of the thickness of the upper outer layer and / or the lower outer layer, and is determined according to the size of the preform. Preferably, the step d) of placing the aluminum alloy in the mold is carried out according to the semi-solid or liquid infiltration technique or the squeeze casting technique, or by die casting with liquid aluminum.

[0021] In the case of gravity infiltration, the infiltration is preferably carried out in an inert atmosphere, such as a nitrogen atmosphere.

[0022] Advantageously, the green preform is obtained by successively subjecting a mass of granules composed of a ceramic material surface-coated with a polymer binder composition to shaping, debinding, and sintering.

[0023] Preferably, the sintering is carried out in two separate sintering cycles. The first sintering cycle is carried out at a temperature of 1600 °C or higher, preferably about 1800 °C, and the second sintering cycle is carried out at a temperature in the range of 2000 °C or higher, preferably 2100 °C to 2200 °C, and both are carried out in an inert atmosphere.

[0024] More preferably, in step d), the mold closes over the upper outer layer and the lower outer layer of the band preform so as to prevent the intrusion of aluminum onto the upper outer layer and the lower outer layer during the injection of aluminum into the mold, and there is no aluminum on the outer braking surface of the brake band.

[0025] The method for manufacturing a brake disk composed of a brake band and a bell according to the present invention comprises the following steps. a) Preparing a mold having an internal cavity composed of a first part corresponding to the brake band of the brake disk to be manufactured and a second part corresponding to the bell of the brake disk to be manufactured, wherein the first and second parts of the internal cavity communicate with each other; b) Preparing a band preform composed of a central layer, an upper outer layer, and a lower outer layer (202) made of a porous ceramic material made of silicon carbide (SiC), wherein the upper outer layer and the lower outer layer are made of silicon carbide (SiC) and are made of a porous ceramic material infiltrated with silicon (SiC+Si), and the upper outer layer and the lower outer layer are arranged on opposite sides of the central layer in an opposing manner; c) Placing the band preform into the mold of the first part of the internal cavity; d) Injecting a liquid or semi-solid aluminum alloy into the entire inner cavity of the mold to infiltrate the aluminum alloy only into the central layer of the band preform made of a porous ceramic material, obtaining an aluminum metal matrix composite reinforced by the central layer that partially defines the brake band of the brake disk to be manufactured in the first part, filling the aluminum alloy in the second part, and obtaining an aluminum alloy fusion that is connected to the brake band made of a metal matrix composite and defines the bell of the brake disk to be manufactured.

[0026] The disc brake according to this invention consists of a brake band and a bell connected to the brake band.

[0027] Preferably, in an advantageous aspect, the bell is integrally connected to the brake band and is composed of a co-cast made of the metal matrix of the composite material forming the brake band and an aluminum alloy.

[0028] According to the present invention, the brake band is composed of a central portion made of an aluminum metal matrix composite reinforced with a ceramic material made of silicon carbide (SiC). The composite is obtained by impregnating an aluminum alloy with a central layer made of a porous ceramic material made of silicon carbide (SiC) in a rough preform. The brake band is also composed of an upper portion which is joined to the central portion. The upper portion is made of a porous ceramic material made of silicon carbide (SiC) in which silicon has been impregnated (forming SiC+Si), and covers the central portion on one side. The brake band is also composed of a lower portion which is joined to the central portion on the opposite side, i.e., the side opposite to the upper portion. The lower portion is also made of a porous ceramic material made of silicon carbide (SiC) in which silicon has been impregnated (forming SiC+Si). Furthermore, the lower portion covers the central portion on the opposite side, i.e., the side opposite to the upper portion.

[0029] Preferably, the upper and lower portions have a thickness between 2 and 4 millimeters.

[0030] Preferably, the aluminum alloy matrix has a structure in which it is homogeneously distributed within the composite material. [Brief explanation of the drawing]

[0031] Further features and advantages of the present invention will become more apparent from the following detailed description of its preferred non-limiting embodiments: [Figure 1] Figure 1 is a perspective view of a brake disc according to an embodiment of the present invention; [Figure 2] Figure 2 is a schematic diagram showing the steps of a method for manufacturing a brake band for a brake disc according to an embodiment of the present invention; [Figure 3] Figure 3 is a perspective view of a band preform according to an embodiment of the present invention; [Figure 4]Figures 4, 5, 6, and 7 each illustrate the steps in a method for manufacturing a brake disc according to an embodiment of the present invention, with the steps progressing sequentially from Figure 4 to Figure 7. In particular, Figure 7 shows a cross-section of a rough brake disc made on the 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, and is obtained by removing the unnecessary portion of the rough brake disc through subsequent machining. [Figure 5] Figure 5 shows the steps in the method for manufacturing a brake disc according to an embodiment of the present invention. [Figure 6] Figure 6 shows the steps in a method for manufacturing a brake disc according to an embodiment of the present invention. [Figure 7] Figure 7 shows the steps in a method for manufacturing a brake disc according to an embodiment of the present invention. In particular, Figure 7 shows a cross-section of a rough brake disc made on the 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, and is obtained by removing unnecessary parts of the rough brake disc through subsequent machining.

[0032] Elements or parts of elements common to the embodiments described below are denoted by the same reference numeral. [Modes for carrying out the invention]

[0033] Referring to the aforementioned figure, reference numeral 1 shows the brake disc according to this invention in its entirety.

[0034] According to a general embodiment of the present invention shown in the attached figures, the brake disc 1 comprises a brake band 2 having two opposing outer brake surfaces 2a and 2b, each brake surface 2a and 2b defining at least partially one of the two main surfaces of the disc.

[0035] The brake disc 1 further includes a bell 3 connected to the brake band 2.

[0036] According to a first aspect of the present invention, the brake band 2 is composed of a central portion 200' made of an aluminum-based metal matrix composite material reinforced with a ceramic material made of silicon carbide (SiC). The composite material is obtained by impregnating the central layer of a porous ceramic material made of silicon carbide (SiC) of a rough preform 20' with an aluminum alloy.

[0037] The aforementioned composite material falls under the category of composite materials known in this industry as MMC (Metal Matrix Composite).

[0038] By using the MMC composite material made of aluminum for the brake band 2, even greater mechanical and chemical-physical properties can be obtained compared to those of aluminum, and at the same time, functional properties suitable for heavy applications such as those required of a brake system can be added without requiring a protective coating on the brake surface (with respect to simple fusion in aluminum or its alloys).

[0039] Furthermore, the brake band 2 also consists of an upper portion 201' which is integrally joined to the central portion 200', and is obtained by silicon infiltration of a single initial rough preform 20' to a predetermined depth D1, thereby determining the thickness of the upper portion 201'. Thus, the upper portion 201' is made of silicon carbide (SiC) and consists of a porous ceramic material infused with silicon (SiC+Si). Furthermore, the upper portion 201' covers the central portion 200' on one side, so that the central portion 200' does not come into contact with the brake pad on that side when the brake disc is mounted on the disc brake.

[0040] In other words, the upper portion 201' is the region of the initial rough preform 20' in which silicon has permeated to a predetermined depth.

[0041] Furthermore, the brake band 2 consists of a lower portion 202' which is integrally joined to the central portion 200' and is obtained by silicon impregnation of a single rough preform 20' to a predetermined depth D2, preferably D1, thus determining the thickness of the lower portion 202'. Thus, the lower portion 202' is also made of silicon carbide (SiC) and consists of a porous ceramic material impregnated with silicon (SiC+Si). Furthermore, the lower portion 202' covers the central portion 200' on the opposite side, i.e., the side opposite to the upper portion 201'. In this way, as a result, the central portion 200' is interposed between the upper portion 201' and the lower portion 202'. In particular, the outer brake surfaces 2a and 2b of the brake band 2 are the outermost surfaces of the upper portion 201', the lower portion 202', and the lower portion, respectively, and are not joined to the central portion 200' in the sense that they are not integrated.

[0042] It is clear that the central portion 200' is interposed between the upper portion 201' and the lower portion 202' in the axial direction of the brake band, that is, in the rotational axis direction of the brake band when it forms part of the brake disc 1. In other words, the central portion 200' is interposed between the upper portion 201' and the lower portion 202' in the direction of the braking force (i.e., pressure) acting on the outer brake surfaces 2a and 2b by the friction element (brake caliper pad).

[0043] Preferably, the central portion 200', the upper portion 201', and the lower portion 202' are the central band, upper band, and lower band, respectively, in the sense that each portion extends radially over the brake band 2. In other words, each central portion 200', upper portion 201', and lower portion 202' has a footprint in a plane perpendicular to the axial direction, such as a disc-shaped or circular crown footprint, which is substantially equal to the footprint of the entire brake band 2.

[0044] In other words, the brake band 2 is obtained by upper (upper 201') and lower (lower 202') infiltration of silicon into a given depth of a single coarse preform 20'. It is clear that the infiltration depth is much smaller than the total thickness of the preform 20', i.e., much smaller than the height of the sidewalls.

[0045] According to an advantageous embodiment, the upper portion 201' and the lower portion 202' have a thickness of 2 to 4 millimeters, preferably 3 millimeters. This allows for a good compromise between rigidity, wear resistance, and weight.

[0046] Regarding brake bands made solely of aluminum or one of its alloys, the presence of a ceramic reinforcement in the central 200' section, along with the upper 201' and lower 202 sections, results in greater hardness, greater rigidity, a higher coefficient of friction, and higher wear resistance. These characteristics make this brake band suitable for use with brake discs.

[0047] In this way, it is possible to create brake bands that possess the advantageous properties of aluminum (in particular, refer to its lower density compared to steel and cast iron), while simultaneously avoiding the need for protective coatings on the brake surface, as well as production and operational constraints and inconveniences.

[0048] The ceramic material from which the reinforcing material is preferably made is silicon carbide.

[0049] As will be discussed later, the MMC composite material forming the central portion 200' is obtained by impregnating a porous ceramic material preform with an aluminum alloy. Advantageously, the aforementioned ceramic material containing silicon carbide can withstand the impregnation process with molten metal without altering its chemical and physical structure, and without any damage to the macroscopic or microscopic extent. For this reason, they are particularly suitable for the manufacture of the aforementioned composite.

[0050] Preferably, the aluminum alloy is selected from the group of aluminum alloys known to be used for casting, or from the group of aluminum alloys containing at least magnesium, manganese, or silicon.

[0051] Advantageously, the aluminum alloy matrix has a homogeneously distributed structure within the composite material. As will be discussed later, this can be achieved by impregnating an aluminum alloy into a preform made of a porous ceramic material having a homogeneous porosity throughout its entire volume. Through the impregnation process, the aluminum alloy penetrates the porosity of the ceramic material, forming a homogeneous structure.

[0052] According to another aspect of this invention, the brake disc 1 is provided such that the bell 3 is integrally connected to the brake band 2, and is made of an aluminum alloy co-cast with a metal matrix of a composite material forming the brake band 2.

[0053] As described below, Bell 3 is preferably obtained using the same aluminum alloy, within the same mold in which the aluminum alloy infiltration of the ceramic material preform is carried out. In this way, the molding of the composite material and the fusion of the Bell are achieved in the same operating process, and a complete bond between the two materials is achieved.

[0054] By co-casting the bell with the brake band, the manufacturing process can be significantly simplified. In fact, it eliminates the need for both a dedicated production line for manufacturing the bell and an assembly line for attaching the bell to the band.

[0055] The combination of the two essential aspects of the present invention makes it possible to have an aluminum-based brake disc that, on the one hand, can utilize special operational characteristics derived from aluminum (first and foremost its low density), and on the other hand, can have mechanical and wear-resistant characteristics comparable to steel or gray cast iron discs, while simultaneously being manufactured using the simplest and most economical manufacturing process possible.

[0056] To simplify the discussion, the brake band 2 and the brake disc 1 will be described in relation to their respective manufacturing methods according to the present invention. The brake disc 1 is preferably manufactured by the method according to the present invention described below, but is not necessarily required. Embodiments of the Invention

[0057] According to a general embodiment of the method of this invention, the method for manufacturing a brake disc 1 comprises a first operating step a) of preparing a mold 10 having an inner cavity 11 consisting of a first portion 11a shaped to correspond to the brake band 2 of the brake disc 1 to be manufactured and a second portion 11b shaped to correspond to the bell 3 of the brake disc 1 to be manufactured.

[0058] The first portion 11a and the second portion 11b of the internal cavity 11 communicate with each other, as shown in Figures 5 and 6 which schematically illustrate an example of a mold usable in the context of the method according to the present invention.

[0059] Advantageously, as shown in Figures 4 and 5, the mold includes one or more inlets 13 for directly injecting aluminum alloy into a second portion of the inner cavity 11 of the mold 10. The inlets 13 are coaxial with the circumferential development of the second portion 11b, which has a shape corresponding to the bell 3 of the brake disc 1 to be manufactured. Thus, operationally, the injection of aluminum alloy can be performed from the inlet opening 13 and then propagate from the inlet opening 13 to the first portion 11a.

[0060] This method consists of a second operating step b) which prepares a band preform 20 comprising a central layer 200 made of a porous ceramic material made of silicon carbide (SiC), an upper outer layer 201, and a lower outer layer 202. The upper outer layer 201 and the lower outer layer 202 are made by impregnating a porous ceramic material made of silicon carbide (SiC) with silicon (SiC + Si). Furthermore, the upper outer layer 201 and the lower outer layer 202 are arranged opposite each other and on the opposite side of the central layer 200. In other words, the band preform 20 is a multilayer preform in which the lower outer layer 201, the central layer 200, and the upper outer layer 201 are arranged in order.

[0061] As will be clarified below, the lower outer layer 201, the middle layer 200, and the upper outer layer 201 are preferably obtained from a single coarse preform 20' that is permeated vertically.

[0062] Advantageously, the silicon infiltration into the upper outer layer 201 and the lower outer layer 202 occupies space within the porous ceramic material, thus preventing aluminum from migrating and infiltrating the upper layer 201 and the lower layer 202 during the subsequent aluminum alloy infiltration process. In this way, the aluminum remains trapped in the central layer 200.

[0063] Preferably, the band preform 20 has substantially the same shape as the brake band 2 of the brake disc 1 to be manufactured. For example, it is preferably a disc, and preferably a disc having a circular through-opening in the center.

[0064] This method further includes the following additional steps: - c) the step of placing the band preform 20 in the mold of the first portion 11a of the internal cavity 11; and - d) A step of injecting a liquid or semi-solid aluminum alloy into the entire inner cavity 11 of the mold 10.

[0065] The injection of the aluminum alloy is carried out so as to permeate only the central layer 200 of the band preform 20, obtaining an aluminum metal matrix composite reinforced by the central layer 200 in the first portion 11a, which partially defines the brake band 2 of the brake disc to be manufactured. This is done by filling the second portion 11b with the aforementioned aluminum alloy, obtaining a fusion of aluminum alloy that is integrally connected with the brake band 2 made of the metal matrix composite and defines the bell 3 of the brake disc 1 to be manufactured.

[0066] According to a general embodiment, a method for manufacturing a brake band 2 for a brake disc 1 consists of a series of steps similar to the steps of a method for manufacturing a brake disc, except that the mold 10 is shaped for manufacturing only the brake band 2 and not for manufacturing the bell 3. As a result, with respect to the steps of the brake disc manufacturing method, in step a), the mold does not constitute a second portion 11b that corresponds to the shape of the bell 3 of the brake disc 1 to be manufactured. Furthermore, with respect to the brake disc manufacturing method, in step d), the infiltration of the aluminum alloy is carried out so as to infiltrate the central layer 200 of the band preform 20 with the aluminum alloy, resulting in an aluminum-based metal matrix composite reinforced by the central preform 200 that partially defines the brake band 2 to be manufactured in the first portion 11a. When manufacturing only a brake band, it is clear that there is no need to provide an aluminum alloy to fill the second portion 11b, as simultaneous manufacturing of the brake disc bell 2 by mixing is not required. Although a mold for manufacturing a brake band is not shown in the attached figure, how to modify the aforementioned mold 10 so as to be absent from the second part 11b intended for manufacturing a bell can be clearly and obviously derived by those skilled in the art.

[0067] Therefore, in a general embodiment, the method for manufacturing a brake band according to this invention comprises a first operating step a) of preparing a mold 10 having an internal cavity 11 consisting of a first portion 11a corresponding to the shape of the brake band 2 of the brake disc 1 to be manufactured.

[0068] In this case, the mold also includes one or more injection ports 13 for directly injecting the aluminum alloy into the second portion of the inner cavity 11 of the mold 10.

[0069] This method comprises a second operation step b) for preparing a band preform 20 consisting of a central layer 200 made of a porous ceramic material made of silicon carbide (SiC), an upper outer layer 201, and a lower outer layer 202. The upper outer layer 201 and the lower outer layer 202 are made by impregnating a porous ceramic material made of silicon carbide (SiC) with silicon (SiC + Si). The upper outer layer 201 and the lower outer layer 202 are arranged opposite each other on the opposite side of the central layer 200.

[0070] This method further includes the following additional steps: c) The step of placing the band preform 20 in the mold of the first portion 11a of the internal cavity 11; and d) A step of injecting a liquid or semi-solid aluminum alloy into the entire inner cavity 11 of the mold 10.

[0071] The injection of the aluminum alloy is carried out so as to permeate the central layer 200 of the band preform 20, and in the first portion 11a, an aluminum metal matrix composite is obtained which is reinforced by the central preform 200 that partially defines the brake band 2 to be manufactured.

[0072] Advantageously, for both the manufacture of the brake disc 1 and the manufacture of the brake band 2, the step b) of injecting an aluminum alloy into a mold can be carried out according to any technique suitable for the purpose.

[0073] In particular, step b) can be carried out according to liquid state infiltration techniques, squeeze casting techniques, gravity infiltration techniques, semi-solid state infiltration techniques, or die casting using liquid aluminum.

[0074] In the case of gravity infiltration, infiltration is preferably carried out in an inert atmosphere, such as a nitrogen atmosphere.

[0075] Since the aforementioned infiltration technique is well known to those skilled in the art, its explanation will be omitted here.

[0076] Preferably, step b) in which the aluminum alloy is injected into the mold is carried out according to a semi-solid infiltration technique. In fact, this technique is suitable for infiltrating ceramic preforms and has been found to achieve complete infiltration of the preform, such that at the end of the process, the disc made of MMC material has homogeneous characteristics throughout its entire structure. At the same time, this technique is particularly suitable for forming bells in the same process.

[0077] More specifically, infiltration at the semi-solid stage occurs at a temperature between the liquidus and solidus of the aluminum alloy being used, i.e., when the alloy is in a semi-solid state. Due to the low viscosity of the semi-solid mass, the injection and infiltration processes into the mold proceed smoothly with minimal turbulence.

[0078] A particular advantage is that the presence of silicon-impregnated upper and lower outer bands prevents aluminum from impregnating the upper and lower outer bands. As a result, the pair of opposing brake surfaces 2a and 2b are aluminum-free and have an improved coefficient of friction compared to prior art aluminum discs, making them particularly suitable for use in brake discs.

[0079] According to an advantageous embodiment, both the method for manufacturing a brake band and the method for manufacturing a brake disc include a series of operational steps performed prior to step b), as schematically shown in Figure 2, for example. In particular, the aforementioned series of operational steps assume a first operational step a1) of preparing a rough preform 20' made of a porous ceramic material made of silicon carbide (SiC). The rough preform 20' consists of an upper surface 20a and a lower surface 20b opposite to it, and is joined to the upper surface 20a and the lower surface 20b by side walls 20c which preferably unfold vertically. Preferably, the rough preform 20' already has a central through hole 5 and therefore has an inner side wall 20d opposite to the side wall 20c.

[0080] Preferably, the rough preform 20' has a shape substantially equal to the brake band 2 of the brake disc 1 to be manufactured.

[0081] Furthermore, the aforementioned series of operations provides a subsequent operation a2) which at least partially deposits a masking layer 21 on the sidewall 20c, which is suitable for preventing silicon (Si) from infiltrating through it in the subsequent infiltration operation a3).

[0082] The silicon infiltration of the wall 20c prevents the aluminum alloy from entering the preform during the aluminum alloy infiltration process.

[0083] Preferably, in step a2), the step of depositing the masking layer 21 consists of depositing a boron nitride (BN) layer.

[0084] According to an advantageous modified embodiment, the deposition of the masking layer 21 is applied to the entire side wall 20c, but not to the upper surface 20a and lower surface 20b of the rough preform 20'.

[0085] In a further modification, the masking layer 21 is deposited over the entire inner sidewall 20d, but not over the upper surface 20a and lower surface 20b of the rough preform 20'.

[0086] In another variation, the masking layer 21 is deposited on the entire inner side wall 20d and the side wall 20c.

[0087] The masking layer 21 advantageously ensures that silicon does not penetrate through the sidewalls 20c and / or sidewalls 20d. Thus, when the masking layer 21 is removed, aluminum penetrates through the sidewalls 20c and / or sidewalls 20d into the core layer 200, depending on the manufacturing method of the mold 10.

[0088] The aforementioned series of operations includes an additional operation a3) to impregnate the rough preform 20' with silicon (Si) to a predetermined depth through the upper surface 20a and the lower surface 20b, in order to obtain a band preform 20 consisting of a central layer 200 in which silicon has not penetrated, an upper outer layer 201 in which silicon (SiC+Si) has penetrated, and a lower outer layer 202 in which silicon (SiC+Si) has penetrated. The upper outer layer 201 and the lower outer layer 202 are arranged opposite each other and are located on the opposite side of the central layer 200.

[0089] Preferably, in step a3), the crude preform 20' is placed in a crucible, a predetermined amount of silicon (Si) powder is added to the crucible, and the crude preform 20' is heated at atmospheric pressure in an inert atmosphere, preferably an argon atmosphere, to a temperature above 1420°C for at least 5 minutes.

[0090] This process can be achieved using an industrial furnace of appropriate size. Furthermore, preferably, following the immersion process, the upper and lower outer preforms are grounded before being subjected to the subsequent processes described below.

[0091] According to one embodiment of this method, the crude preform 20' is heated to a temperature in the range of 1500°C to 1650°C at time intervals of 15 to 90 minutes.

[0092] More advantageously, the crude preform 20' is heated to a temperature in the range of 1550°C to 1600°C at time intervals of 30 to 60 minutes, and with a thickness suitable for manufacturing brake discs, a surprisingly more homogeneous propagation front can be obtained, resulting in proper and homogeneous silicon infiltration.

[0093] Preferably, the rough preform 20' has a thickness between 10 mm and 20 mm, with extreme values ​​ranging from 4 mm to 40 mm, i.e., the distance between the top surface 20a and the bottom surface 20b, and the predetermined amount of silicon depends on the diameter of the preform.

[0094] For example, the volume of the layer to which silicon is to be infiltrated can be calculated as follows: Vtot = π(R² - r²)h, where radii R and r are the outer radius R and inner radius r of the circular crown described by the rough preform 20', respectively, and h is the desired silicon infiltration depth. The apparent density is defined as follows: Da = Mass of porous material / Total volume of porous material (including voids) And porosity is defined as follows: P = 1 - Dsolid / Da Here, the solid density Dsolid is the density of a non-porous artifact. The predefined amount of silicon (Msi) can be calculated as follows: Msi = Silicon volume × Silicon density Here, the volume of silicon is equal to Vtot·P.

[0095] In this way, given a preform with a certain porosity and a certain volume of the layer into which silicon is impregnated, it is possible to define the mass of silicon used a priori.

[0096] According to a preferred embodiment of the method for manufacturing a brake band 2 or a brake disc 1, a rough preform 20' made of porous ceramic material is obtained by subjecting a mass of ceramic material granules surfacely coated with a polymer binding composition to the following sequential operations: molding, peeling (or degreasing), and sintering.

[0097] Advantageously, the aforementioned ceramic material granules are powder granules known as "Ready-to-Press." This type of commercially available powder, along with pressing technology, allows for the production of "net-shape molded" products without requiring any other components or additives beyond the powder itself.

[0098] Preferably, the ceramic material on which the granules are formed is silicon carbide.

[0099] Preferably, the polymer binding composition coating the ceramic material granules is selected from the group consisting of thermoplastic polymers and thermosetting polymers.

[0100] Preferably, the formation of the mass of ceramic material granules is carried out uniaxially or isostatically, or by any other technique that enables obtaining a preform of such size and shape.

[0101] At the end of the molding process, an aggregate of the aforementioned ceramic material granules is obtained, linked by a ceramic microstructure facilitated by each coating of the polymer bonding composition. The aggregate contains organic residues from the granule coating. These organic residues are removed in a debonding (or dewaxing) step.

[0102] Advantageously, delamination is performed under airflow conditions at a temperature below 700°C until the organic phase present in the mass of ceramic material granules after molding is completely removed.

[0103] According to the modified example, the delamination is performed under inert atmospheric conditions.

[0104] At the end of the peeling process, a green body consisting essentially of only ceramic material is obtained. This green body is then subjected to a sintering stage, which transforms it into a continuous structure by forming bridges that connect the individual ceramic particles. As a result, a body exhibiting homogeneous properties throughout the entire structure is obtained.

[0105] Preferably, sintering is carried out in two separate sintering cycles. The first sintering cycle is carried out at a temperature of 1600°C or higher, preferably about 1800°C, and the second sintering cycle is carried out at a temperature of 2000°C or higher, preferably in the range of 2100°C to 2200°C, both under an inert atmosphere.

[0106] Advantageously, the resulting crude preform 20' made of porous ceramic material has a homogeneous density and porosity distribution throughout its entire volume. Due to these characteristics, the preform is suitable for producing a homogeneously distributed aluminum alloy matrix after the alloy has been impregnated.

[0107] According to a particular embodiment, the method for manufacturing a brake band provides that the crude preform 20' has a density of 40%. In this embodiment, a crude preform with a height of 13 mm is placed in a graphite crucible having silicon powder on its upper and lower outer surfaces and weighing 10 to 20 grams, with a masking layer 21 of boron nitride on the side walls 2c. The preform is subjected to a thermal cycle in a furnace for silicon fusion and infiltration for a time between 1 and 3 hours in fluid argon at a temperature between 1430°C and 1550°C at atmospheric pressure. Advantageously, at a temperature of 1550°C, a time of 60 minutes, and a silicon content of 14 grams, an average thickness of the upper and lower outer layers between 2 to 3 mm is obtained (minimum 2 mm, preferably maximum 2.6 mm).

[0108] Clearly, once the band preform 20 is obtained as described above, the central layer 200 corresponds to the central portion 200' of the brake band 20, and the upper 201 and lower 202 outer layers correspond to the upper outer band 201' and lower outer band 202' of the brake band 20, respectively.

[0109] Advantageously, in step d) of the method according to this invention, as can be seen, for example in Figures 5-6, the mold closes over the upper outer layer 201 and the lower outer layer 202 so as to prevent aluminum from penetrating onto the upper outer layer 201 and the lower outer layer 202 during the injection of aluminum into the mold, so that there is no aluminum on the outer brake surfaces 2a and 2b of the disc. In other words, the aluminum alloy is prevented from flowing and creeping on the upper 201 and lower 202 outer layers, i.e., on the side of each outer layer 201, 202 that is not bonded to the central layer 200.

[0110] As can be understood from the above explanation, the brake band, brake disc, and method for manufacturing the brake disc and brake band according to the present invention make it possible to overcome the shortcomings of the prior art.

[0111] In a particularly innovative aspect, the brake band and brake disc of the present invention, by interposing two outer brake bands made of ceramic material between the brake pad and a central portion made of a composite material having a metal matrix made of MMC (metal matrix composite) aluminum alloy, makes it possible to reduce, if not eliminate, the problems associated with localized degradation due to overheating of aluminum, which have been found in the prior art. Furthermore, the outer brake bands enable the simultaneous generation of greater braking force by bonding the pad on a material with a high coefficient of friction. At the same time, efficiency, simplicity, low implementation cost, and reduced corrosion problems are ensured. The reduction in corrosion is particularly advantageous in electric vehicles, where the introduction of regenerative braking involves discontinuous use of disc brakes, which can lead to corrosion.

[0112] Those skilled in the art can make numerous modifications and variations to the present invention as described above to satisfy incidental and specific needs, and all such modifications and variations fall within the scope of the present invention as defined in the following claims.

Claims

1. A method for manufacturing a brake band (2) for a brake disc (1) for a disc brake, wherein the method is: a) A step of preparing a mold (10) having an internal cavity (11), wherein the mold (10) consists of a first portion (11a) having a shape corresponding to the brake band (2) to be manufactured; b) A step of preparing a band preform (20) comprising a central layer (200) made of a porous ceramic material made of silicon carbide (SiC), an upper outer layer (201), and a lower outer layer (202), wherein the upper outer layer (201) and the lower outer layer (202) are made of the porous ceramic material made of silicon carbide (SiC), with silicon (SiC + Si) permeating through them, and the upper outer layer (201) and the lower outer layer (202) are arranged opposite each other on the opposite side of the central layer (200); c) the step of placing the band preform (20) in the mold of the first portion (11a) of the internal cavity (11); and d) A method comprising the step of injecting a liquid or semi-solid aluminum alloy into the entire internal cavity (11) of the mold (11) to permeate only the central layer (200) of the band preform (20) made of porous ceramic material, thereby obtaining an aluminum metal matrix composite in the first portion (11a) reinforced by the central layer (200) that partially defines the brake band (2) to be manufactured.

2. Prior to step b), in order to manufacture the band preform (20), a1) A step of arranging a rough preform (20') made of a porous ceramic material made of silicon carbide (SiC), wherein the rough preform (20') has an upper surface (20a) and an opposite lower surface (20b) joined together by side walls (20c) that are incident on and unfold on the upper surface (20a) and lower surface (20b); a2) A step of depositing at least partially a masking layer (21) on the side wall (20c), wherein the masking layer (21) is suitable for preventing the intrusion of silicon (Si) in the subsequent step (a3); a3) The method according to claim 1, comprising the step of impregnating the coarse preform (20') with silicon (Si) to a predetermined depth through the upper surface (20a) and the lower surface (20b) to obtain the band preform (20) comprising the central layer (200) in which Si has not been impregnated, wherein the upper outer layer (201) and the lower outer layer (202) are impregnated with silicon (SiC + Si), the upper outer layer (201) and the lower outer layer (202) are arranged opposite to each other and are located on the opposite side of the central layer (200), the upper outer layer (201) and the lower outer layer (202

3. The method according to claim 2, wherein the step of depositing the masking layer (21) in step a2) includes depositing a layer of boron nitride (BN).

4. The method according to claim 2 or 3, wherein in step a2), the deposition of the masking layer (21) is applied to the entire side wall (20c) but not to the upper surface (20a) and lower surface (20b) of the rough preform (20').

5. The method according to any one of claims 2 to 4, wherein in step a3), the crude preform (20') is placed in a crucible, a predetermined amount of silicon (Si) powder is added to the crucible, and the crude preform (20') is heated at atmospheric pressure in an inert atmosphere, preferably in an argon atmosphere, to a temperature above 1414°C for at least 5 minutes.

6. The method according to claim 5, wherein the crude preform (20') is heated to a temperature between 1500°C and 1650°C for time intervals between 15 minutes and 90 minutes.

7. The method according to claim 6, wherein the crude preform (20') is heated to a temperature between 1550°C and 1600°C for a time between 30 minutes and 60 minutes.

8. The method according to any one of claims 5 to 7, wherein the coarse preform (20') is configured such that the distance between the upper surface (20a) and the lower surface (20b) is between 4 millimeters and 40 millimeters (including the values ​​at both ends), and the predefined amount of silicon is a function of the diameter of the coarse preform.

9. The method according to any one of claims 1 to 8, wherein step d) of introducing the aluminum alloy into the mold is carried out according to a semi-solid or liquid penetration technique, or according to a gravity penetration technique, or by die casting with liquid aluminum, or according to a squeeze casting technique.

10. The method according to claim 2, wherein the crude preform (20') is obtained by sequentially subjecting a mass of ceramic material granules surface-coated with a polymer-binding composition to molding, degreasing, and sintering.

11. The method according to claim 10, wherein the sintering is carried out in two separate sintering cycles, the first sintering cycle being carried out at a temperature of 1600°C or higher, preferably about 1800°C, and the second sintering cycle being carried out at a temperature of 2000°C or higher, preferably in the range of 2100°C to 2200°C, both carried out in an inert atmosphere.

12. The method according to any one of claims 1 to 11, wherein in step d), the mold (10) closes over the upper outer layer (201) and the lower outer layer (202) of the band preform (20) so that during the introduction of aluminum into the mold, aluminum does not penetrate above the upper outer layer (201) and below the lower outer layer (202), and aluminum is not present on the outer brake surfaces (2a, 2b) of the brake band (2).

13. A method for manufacturing a brake disc, wherein the brake disc includes a brake band (2) and a bell (3), and the method for manufacturing the brake disc is: a) A step of preparing a mold (10) having an internal cavity (11) comprising a first portion (11a) shaped to correspond to the brake band (2) of the brake disc (1) to be manufactured, and a second portion (11b) shaped to correspond to 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) are in communication with each other; b) A step of preparing a band preform (20) comprising a central layer (200) made of a porous ceramic material made of silicon carbide (SiC), an upper outer layer (201), and a lower outer layer (202), wherein the upper outer layer (201) and the lower outer layer (202) are made of a porous ceramic material made of silicon carbide (SiC) and impregnated with silicon (SiC + Si), and the upper outer layer (201) and the lower outer layer (202) are arranged opposite to the central layer (200); c) the step of placing the band preform (20) in the mold of the first portion (11a) of the internal cavity (11); and d) A method for manufacturing a brake disc, comprising the steps of: injecting a liquid or semi-solid aluminum alloy into the entire internal cavity (11) of the mold (10) to permeate only the central layer (200) of the band preform (20) made of porous ceramic material with the aluminum alloy to obtain an aluminum metal matrix composite in the first portion (11a) reinforced by the central layer (200) that partially defines the brake band (2) of the brake disc to be manufactured; and filling the second portion (11b) with the aluminum alloy to obtain a fusion of aluminum alloy that is integrally connected with the brake band (2) made of the aluminum metal matrix composite and defines the bell (3) of the brake disc (1) to be manufactured.

14. A brake band (2) for a brake disc for a disc brake, wherein the brake band (2) is A central portion (200') made of a composite material of an aluminum metal matrix reinforced with a ceramic material made of silicon carbide (SiC), wherein the composite material is obtained by impregnating an aluminum alloy into a central layer (200) made of a porous ceramic material made of silicon carbide (SiC) of a rough preform (20'), and The upper portion (201') is joined to the central portion (200'), and the upper portion (201') is made of silicon carbide (SiC), and is made of a porous ceramic material impregnated with silicon (SiC + Si), and covers the central portion (200') on one side, and A brake band (2) comprising: a lower portion (202') joined to the central portion (200') on the opposite side to the upper portion (201'), the lower portion (202') being made of a porous ceramic material made of silicon carbide (SiC) and impregnated with silicon (SiC + Si), and covering the central portion (200') on the opposite side to the upper portion (201').

15. The brake band (2) according to claim 14, wherein the upper portion and the lower portion (202') preferably have a thickness between 0.5 and 4 millimeters.

16. A brake disc for the disc brake, comprising a brake band (2) according to any one of claims 14 or 15, and a bell (3) connected to the brake band (2).

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

18. The brake disc according to claim 16 or 17, wherein the aluminum metal matrix is ​​uniformly distributed within the composite material.

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