Brake pad preform and method for manufacturing brake pad, and related brake pad

Abstract

The method for producing a brake pad preform (6) for a disc brake includes the steps of (a) preparing a thermosetting mixture (2) by mixing a polymer resin in a liquid state (21) or in a particulate powder state (22) with powdered ceramic particles (25), (b) combining the thermosetting mixture (2) obtained in (a) with a carbonaceous material (3) made of carbon fibers to obtain a molding compound (4), (c) molding the molding compound (4) obtained in (b) by compression and heat treatment to obtain a rough preform (5), and (d) subjecting the rough preform (5) obtained in (c) to a pyrolysis treatment to obtain a brake pad preform (6). The brake pad preform (6) or brake pad (1) obtained by this method is made of a carbon-carbon composite material made of a matrix of a carbonaceous material and carbon fibers, and the ceramic particles are uniformly dispersed in the matrix of the carbonaceous material.

Description

[Technical field]

[0001] The present invention relates to a brake pad preform, in particular a brake pad for disc brakes, to a method for producing a brake pad and to said brake pad. [Background technology]

[0002] It is known to use disc brake pads made of carbon-based materials, so-called carbon-carbon or "C / C" composites, which are pads made of composite materials consisting of reinforced carbon fibres in a carbonaceous matrix. These pads are generally adapted to cooperate with discs for disc brakes, which are also made of "C / C" materials.

[0003] Carbon-carbon composites are lightweight materials and are used in the manufacture of brake pads where large amounts of energy dissipation is required (e.g. in racing cars and aerospace vehicles). The friction behavior of such materials can be significantly improved by introducing small amounts of abrasive particles, which act as tribological modifiers by increasing the coefficient of friction at low temperatures. For this reason, controlling the amount, distribution and size of the abrasives is of utmost importance in the manufacture of carbon-carbon friction parts.

[0004] Current methods for producing carbon-carbon composites doped with abrasive particles involve infiltration of the carbonaceous part with silica colloids, which are then converted to silicon carbide (SiC) by a hydrocarbon reaction. An example of such a production method is described in document EP1763644A1.

[0005] Disadvantageously, brake pads obtained by the aforementioned methods of the prior art suffer from an uneven distribution of particles in the carbonaceous portion, as the concentration of silicon carbide (SiC) gradually decreases from the surface towards the core of the brake pad, resulting in undesirable changes in the performance of the brake pad over time as wear of the brake pad exposes areas of the brake pad with less and less silicon carbide (i.e. the abrasive portion).

[0006] Moreover, the prior art manufacturing methods disadvantageously do not allow sufficient control of the size of the (silicon carbide) abrasive particles.) Furthermore, the particle morphology depends on the size of the starting silica particles, on the agglomeration after the infiltration step, and on the interface between the silica and the carbon. This is contrary to the need to keep the abrasive performance of the brake pads constant (the friction coefficient of the material requires particles with a uniform shape and a narrow range of diameters).

[0007] Furthermore, in the prior art manufacturing methods, the high operating temperatures (above 1400° C.) in the step of thermally converting silica to silicon carbide result in the production of silicon monoxide (SiO), which condenses and accumulates in the low temperature areas of the furnace (e.g., gaskets, pumps, filters and piping), necessitating careful and expensive cleaning operations after the heat treatment and significantly shortening the lifespan of some furnace components.

[0008] The problem underlying the present invention is therefore to provide a disc brake pad that overcomes the drawbacks of the prior art and maintains high performance characteristics even in extreme applications, and a process for obtaining it in a simple and feasible way. More specifically, the present invention proposes to modify the braking action of the pad itself by distributing the amount and size of the abrasive particles more uniformly, in order to obtain the abrasive performance of the brake pad as constant as possible. Summary of the Invention

[0009] There is therefore a need felt in the art to have a method for manufacturing a brake pad preform and a brake pad that can overcome the aforementioned drawbacks of the prior art, in particular to implement a brake pad that has a performance as uniform as possible as a function of wear over time and that at the same time can be manufactured in a more efficient and convenient manner.

[0010] These needs are met by a method for producing a brake pad preform, a method for producing a brake pad and a brake pad for disc brakes according to the claims, the definitions of which form an integral part of this specification.

[0011] According to the invention, a method for manufacturing a brake pad preform for a disc brake comprises the following operational steps:

[0012] (a) preparing a thermosetting mixture by mixing a polymer resin in liquid or particulate powder form with ceramic particles in powder form;

[0013] (b) combining the thermosetting mixture obtained in step (a) with a carbonaceous material constituted by carbon fibers to obtain a molding compound.

[0014] (c) molding the molding compound obtained in step (b) by compression and heat treatment, for example in a mold for brake pad preforms, to obtain a rough preform.

[0015] (d) subjecting the crude preform obtained in step (c) to a pyrolysis treatment to obtain a brake pad preform.

[0016] An alternative variation of the method provides a step (a1) instead of step (a), in which the thermosetting mixture is prepared by mixing a liquid or solid particulate polymer resin with a liquid preceramic resin as a precursor of the ceramic particles. In this alternative variation of the method, the ceramic particles are formed during the heat treatment of step (c) or during step (d) starting from the preceramic liquid resin.

[0017] Furthermore, the brake pad for a disc brake according to the present invention is made of a carbon-carbon composite material consisting of a matrix of a carbonaceous material (or a carbonaceous matrix) and carbon fibers. Furthermore, ceramic particles are uniformly dispersed in the carbonaceous matrix.

[0018] Further characteristics and advantages of the invention will appear more clearly from the description of some preferred embodiments thereof given below, by way of non-limiting example only. [Brief description of the drawings]

[0019] [Figure 1A] FIG. 1A is an axial view of a portion of a disc brake pad according to an embodiment of the present invention, viewed from above.

[0020] [Figure 1B] FIG. 1B shows a scanning electron microscope (SEM) image of a cross section of the brake pad of FIG. 1A.

[0021] [Figure 1C] FIG. 1C is an optical microscopy image of a portion of the cross section of FIG. 1B showing carbon fibers, carbon formed by the CVI process (shown as CVI matrix), carbon formed by pyrolysis of the polymer (shown as pyrolyzed resin), and residual porosity.

[0022] [Figure 2A] FIG. 2A shows an image obtained with a scanning electron microscope (SEM) of a portion near the outermost surface of a brake pad preform obtained according to a manufacturing method of the prior art.

[0023] [Figure 2B] FIG. 2B shows a scanning electron microscope (SEM) image of a portion of the brake pad preform of FIG. 2A adjacent the innermost core of the preform.

[0024] [Figure 3A] FIG. 3A is a scanning electron microscope (SEM) image of a portion of a brake pad preform obtained according to a method for making a brake pad preform according to an embodiment of the present invention, proximate the outermost surface of the preform.

[0025] [Figure 3B] FIG. 3B is a scanning electron microscope (SEM) image of a portion of the brake pad preform of FIG. 3A, proximate the innermost core of the preform.

[0026] [Figure 4] FIG. 4 is a schematic block diagram of a method for manufacturing a brake pad preform according to a first embodiment of the invention (blocks A1, B1, C1, D and E) and of a method according to a second embodiment of the method according to the invention, which is an alternative to the first embodiment (blocks A2, B2, C2, D and E).

[0027] [Figure 5A-5C] 5A-5C each exemplarily show a sequence of steps of a method for manufacturing a brake pad preform according to a first embodiment of the invention. [Fig. 5D-5E] 5A-5C each exemplarily show a sequence of steps of a method for manufacturing a brake pad preform according to a first embodiment of the invention.

[0028] [Figure 6A-6C] 6A-6C each show, in an exemplary manner, a sequence of steps of a method for manufacturing a brake pad preform according to a second embodiment of the present invention. [Fig. 6D-6E] 6D-6E each show, in an exemplary manner, a sequence of steps of a method for manufacturing a brake pad preform according to a second embodiment of the present invention. Detailed Description of the Invention

[0029] With reference to the above figures, reference numeral 6 indicates as a whole a brake pad preform for a disc brake according to the invention.

[0030] The invention also relates to a brake pad 1 for a disc brake, which is obtained directly from a brake pad preform 6, which has been subjected to dry and / or wet finishing processes, for example turning and milling, to achieve the desired geometrical design.

[0031] The brake pad 1 for disc brakes according to the present invention is made of a carbon-carbon composite material consisting of a matrix of carbonaceous material and carbon fibers. In particular, ceramic particles are uniformly dispersed in the matrix of the carbonaceous material.

[0032] According to one embodiment of the carbon-carbon composite, 5 mm 3 The volume concentration of ceramic particles in the volume varies within limits of ±20% between two different randomly identified areas of the pad.

[0033] In order to obtain the aforementioned brake pad preform 6, the main subject of the invention is a method for manufacturing a brake pad preform 6 for a disc brake, which method comprises a series of operating steps that are explained in detail below. A typical embodiment of the method for manufacturing a brake pad preform 6 for a disc brake comprises the following steps:

[0034] (a) A thermosetting mixture 2 is prepared by mixing a liquid polymer resin 21 or a particulate powder-like polymer resin 22 with powder-like ceramic particles 25.

[0035] (b) The thermosetting mixture 2 obtained in step (a) is combined with a carbonaceous material 3 consisting of carbon fibers to obtain a molding compound 4.

[0036] (c) The molding compound 4 obtained in step (b) is molded, for example in a mold for brake pad preforms, by compression and heat treatment to obtain a rough preform 5 (or polymerized composite).

[0037] (d) The crude preform 5 obtained in step (c) is subjected to a pyrolysis treatment to obtain a brake pad preform 6.

[0038] According to one embodiment of the method, the polymeric resin in liquid form 21 or particulate solid form 22 is composed of one or more resins selected from the group consisting of phenolic resins, acrylic resins, furan resins, isocyanate resins, polystyrene.

[0039] Preferably, the ceramic particles 25 of step (a) are comprised of silicon carbide (SiC) and / or silicon nitride (Si3N4).

[0040] According to an advantageous embodiment of the method, the ceramic particles 25 of step (a) have an average particle size of 0.5-100 micrometers, preferably 1-50 micrometers, and even more preferably 2-30 micrometers.

[0041] Preferably, step (a) also includes mixing a dispersing agent, such as a polyacrylic acid compound or a polyethyleneimine compound, to improve dispersion of the ceramic particles.

[0042] According to an embodiment, step (a) further provides for the use of a mechanical mixing process or an ultrasonic treatment to improve the deagglomeration and dispersion of the ceramic particles 25.

[0043] According to an embodiment, the thermosetting mixture 2 contains 3%-20% by weight of ceramic particles 25 in powder form relative to the total weight of the thermosetting mixture 2, preferably 9%-15% by weight of ceramic particles 25 in powder form relative to the total weight of the thermosetting mixture 2. Based on the content of ceramic particles 25, it is possible to adjust the friction behavior of the material and optimize it for the respective application.

[0044] In particular, in embodiments in which the thermosetting mixture 2 is composed of at least 10% by weight of powdered ceramic particles 25 relative to the total weight of the thermosetting mixture 2, friction can be advantageous at temperatures below 300° C. at the expense of higher temperatures.

[0045] According to a further embodiment in which the thermosetting mixture 2 is composed of at least 3% by weight and at most 10% by weight (except in extreme cases) of ceramic particles 25 in powder form relative to the total weight of the thermosetting mixture 2, the friction effect has a more balanced behavior even at temperatures higher than 300°C.

[0046] It is clear that step (b) of combining the thermosetting mixture 2 obtained in step (a) with the carbonaceous material 3 consisting of carbon fibres can be carried out in different ways, for example by immersion, or by compression, or by mixing, etc.

[0047] According to an embodiment, the carbonaceous material 3 is composed of a two-dimensional or substantially two-dimensional woven layer 31, preferably a layer of woven carbon fibre fabric. In this embodiment, step (b) consists of an operation step of impregnating the two-dimensional fabric layer 31 with the thermosetting mixture 2 and bonding the layers together to form a moulding compound 4 which is moulded in step (c). In this case, the moulding compound is also called a prepreg.

[0048] According to a variant of embodiment, the carbonaceous material 3 is composed of chopped carbon fibres 32. Preferably, in step (b), after the chopped carbon fibres 32 have been bonded to the thermosetting mixture 2 of step (a), the moulding compound 4 thus obtained is then moulded in step (c) by hot moulding to form a rough preform 5, which is preferably a polymer (polymer composite).

[0049] According to an advantageous embodiment, the carbonaceous compound 4 is composed of between 50% and 80% by weight of this carbonaceous material 3 and between 20% and 50% by weight of said thermosetting mixture 2, and preferably between 65% and 75% by weight of said carbonaceous material 3 and between 25% and 35% by weight of said thermosetting mixture 2. This allows to obtain a sufficient amount of resin 2 to bond the carbonaceous material 3, while at the same time preserving as many carbonaceous fibers as possible in order to increase the mechanical resistance.

[0050] According to one embodiment, the step (c) of shaping the moulding compound 4 consists in a subsequent operational step (c1) of compressing the moulding compound 4, for example by means of a vacuum moulding technique, for example by means of a vacuum bag.

[0051] More preferably, the operating step (c1) also comprises subjecting the moulding compound 4 to an autoclave curing treatment. This embodiment is preferred when the carbonaceous compound 4 is composed of a two-dimensional or substantially two-dimensional fabric layer 31.

[0052] In this embodiment, in step (c1), the autoclaving is carried out at a pressure between 5-15 bar, inclusive.

[0053] According to an embodiment variant, the step (c) of shaping the moulding compound 4 provides an operation step (c2) of hot shaping the moulding compound 4 by moulding in a uniaxial press. This embodiment is preferred when the carbonaceous compound is constituted by chopped carbon fibres 32.

[0054] According to an embodiment, in step (c2), the hot forming is carried out at a pressure between 5-50 bar.

[0055] Preferably, step (c1) or step (c2) is carried out at a temperature comprised between 100° C. and 160° C. (inclusive) for at least 30 minutes, which allows to obtain complete crosslinking of the polymer resin.

[0056] According to one embodiment, after step (d), the method further comprises an operational step (e) of subjecting the brake pad preform 6 to a carbon densification process to obtain a densified pad preform 7. The carbon densification process comprises for example the CVD (Chemical Vapor Deposition) technique, or CVI (Chemical Vapor Infiltration), or PIP (Polymer Infiltration and Pyrolysis), or PIP with pitch.

[0057] The first densification technique is CVD (Chemical Vapor Deposition) or CVI (Chemical Vapor Infiltration), depending on whether the carbon is only coated in the form of a vapor or penetrates. Generally, if the material is fibrous and highly porous, it is called CVI (Chemical Vapor Infiltration). These methods involve the use of hydrocarbon mixtures (such as methane or propane) and exposing the material to be treated to these mixtures at high temperature and low pressure. The operating temperatures are on the order of 900-1200 °C, preferably 1000-1100 °C, and pressures below 300 mbar, preferably 10-100 mbar, are used. The hydrocarbon mixture decomposes to form elemental carbon, which is deposited or penetrated into the matrix of the material to be treated. This method requires the use of special dedicated furnaces and deposits a thin layer (usually a few microns) on the fibers, thus requiring tens to hundreds of hours of processing time to obtain the desired densification. With this method it is possible to achieve an overall coverage on the fibers of 10 microns or more (typically 10-20 microns).

[0058] Another method, known as LPI (Liquid Polymer Infiltration) or PIP (Polymer Infiltration and Pyrolysis), involves infiltrating the matrix of the material being processed with a liquid polymer, followed by a high-temperature heat treatment (pyrolysis) to carbonize the polymer deposited on the carbon fibers. In this case, several infiltration and pyrolysis steps are required before adequate densification of the preform is obtained.

[0059] According to an embodiment, it is possible to use a combination of densification techniques, for example a combination of PIP and CVI techniques.

[0060] According to an embodiment, step (e) comprises providing a concentration of at least 1.5 grams per cubic centimeter (g / cm 3 ), preferably 1.65 grams per cubic centimeter (g / cm 3 densifying the brake pad preform 6 obtained in step (d) until a final material density of at least 1000 MPa is obtained.

[0061] These density values ​​provide the densified brake pad preform 7 material with suitable properties of mechanical strength, thermal conductivity and wear resistance.

[0062] For the manufacture of the brake pad preform 6, the manufacturing method optionally also includes the following steps.

[0063] (i) Optionally, the superimposed two-dimensional or substantially two-dimensional woven layers are needled to form an interwoven three-dimensional structure.

[0064] (ii) Optionally, the chopped fibers are needled to form a three-dimensional woven structure.

[0065] The needling can be carried out by a method that provides for the use of special needles that allow some of the fibers to be engaged by being axially oriented in the pad, thus obtaining a three-dimensional structure.

[0066] An example embodiment of a brake pad preform 6 obtained according to one embodiment of the method according to the invention is described below and in this regard some details obtained by SEM are shown in FIGS. 3A and 3B.

[0067] The brake pad preform 6 according to this example embodiment was obtained by the following operating steps:

[0068] The thermosetting mixture 2 was prepared by mixing a solid isocyanate polymer resin 22 with powdered silicon carbide (SiC) ceramic particles 25. Each ceramic particle had an average particle size of about 2 micrometers.

[0069] The thermosetting mixture 2 obtained in step (a) was combined with a carbonaceous material 3 consisting of chopped carbon fibers 32 to obtain a molding compound 4.

[0070] The molding compound 4 obtained in this embodiment is composed of 30% by weight of isocyanate polymer resin, 3% by weight of silicon carbide (SiC) ceramic particles, and 67% by weight of chopped carbon fibers.

[0071] Thereafter, the above molding compound 4 was molded by pressing and heat treating in a brake pad preform mold to obtain a rough preform 5.

[0072] Next, this crude preform 5 was subjected to a pyrolysis treatment and a heat treatment to obtain a brake pad preform 6 having a carbon-carbon compound formed therein.

[0073] Thereafter, the brake pad preform 6 was also subjected to a densification treatment by CVI (Chemical Vapor Infiltration) densification technology to obtain a densified brake pad preform 7.

[0074] Figures 3A and 3B show SEM images of this example embodiment and can be easily compared with Figures 2A and 2B, respectively, which show SEM images of corresponding portions of a brake pad preform 6 obtained with a method according to the prior art. In the images, silicon carbide (SiC) particles correspond to the bright spots (white / light grey) compared to the background.

[0075] A comparison between the images clearly shows that in FIGS. 3A and 3B (i.e., in the present invention), there is no significant decrease in the density of silicon carbide (SiC) particles in the transition from the surface region of the preform (FIG. 3(A)) to the deeper region of the preform (FIG. 3(B)).

[0076] In contrast, in the preform produced by known techniques, FIG. 2B shows a clear decrease in the density of silicon carbide particles with respect to FIG. 2A for the most superficial portion of the preform.

[0077] As can be seen from the above, the brake pad preform 6, the brake pad 1 and the associated manufacturing method of said preform 6 and said brake pad 1 according to the present invention make it possible to overcome the drawbacks presented in the prior art.

[0078] In particular, the present invention provides a method for producing a carbon-carbon composite doped with ceramic particles uniformly dispersed in a matrix of carbonaceous material, which composite can ensure consistent braking performance regardless of pad wear.

[0079] Moreover, advantageously, the method according to the invention is more efficient than the prior art methods, since it does not require high temperatures for the conversion of silicon oxide to silicon carbide during the infiltration process, and therefore does not require the use of high temperatures and reduces the risk of the formation of silicon oxide deposits on the cold parts of the machinery used in the process. Furthermore, the size of the introduced powder can be controlled by using SiC particles instead of silica, which must be converted.

[0080] It is obvious that a person skilled in the art can make some modifications and adjustments to the pad preform, pad, and the above-mentioned method to meet specific contingency needs, and all such modifications fall within the scope of protection defined in the appended claims.

Claims

1. A method for manufacturing a brake pad preform (6) for a disc brake, comprising: (a) preparing a thermosetting mixture (2) by mixing a polymer resin in liquid form (21) or in particulate powder form (22) with powdered ceramic particles (25); Step (b) of combining the thermosetting mixture (2) obtained in step (a) with a carbonaceous material (3) consisting of carbon fibers to obtain a molding compound (4); Step (c) of molding the molding compound (4) obtained in step (b) by compression and heat treatment to obtain a rough preform (5); The method includes a step (d) of subjecting the crude preform (5) obtained in the step (c) to a pyrolysis treatment to obtain the brake pad preform (6).

2. 2. The method according to claim 1, wherein the polymer resin in the liquid state (21) or particle powder state (22) is composed of one or more resins selected from the group consisting of phenolic resin, acrylic resin, furan resin, isocyanate resin, and polystyrene.

3. 3. The method of claim 1 or 2, wherein the ceramic particles (25) of step (a) comprise silicon carbide (SiC) and / or silicon nitride (Si3N4).

4. 2. The method of claim 1, wherein the ceramic particles (25) of step (a) have an average particle size comprised between 0.5 and 100 micrometers, preferably between 1 and 50 micrometers, and more preferably between 2 and 30 micrometers.

5. 2. The method according to claim 1, wherein the thermosetting mixture (2) comprises 3 to 20% by weight of powdered ceramic particles (25) relative to the total weight of the thermosetting mixture, preferably 9 to 15% by weight of powdered ceramic particles relative to the total weight of the thermosetting mixture.

6. 2. The method of claim 1, wherein step (a) further comprises mixing a dispersing agent, preferably a polyacrylic acid compound or a polyethyleneimine compound.

7. The carbonaceous material (3) is composed of a two-dimensional woven fabric layer (31), 2. The method of claim 1, wherein step (b) comprises impregnating the two-dimensional fabric layer (31) with the thermosetting mixture (2) and bonding the layers together to form the molding compound that is molded in step (c).

8. 8. The method of claim 7, wherein the carbonaceous material (3) is composed of 50% to 80% by weight of the carbonaceous material and 20% to 50% by weight of the thermosetting mixture (2), preferably 65% ​​to 75% by weight of the carbonaceous material and 25% to 35% by weight of the thermosetting mixture.

9. The method of claim 1, wherein the carbonaceous material (3) comprises chopped carbon fibers (32).

10. The step (c) of molding the molding compound (4) comprises: (c1) compressing said molding compound (4) by vacuum molding techniques, e.g., vacuum bagging, and subjecting said molding compound (4) to an autoclave curing treatment; 2. The method of claim 1, comprising the step of (c2) hot compacting said molding compound (4) by compacting in a uniaxial press.

11. 11. The method of claim 10, wherein step (c1) or step (c2) is carried out at a temperature of 100°C, 160°C, or between 100°C and 160°C for at least 30 minutes.

12. In step (c1), the hot forming is carried out at a pressure of 5 bar, 50 bar or between 5 bar and 50 bar; 12. The method according to claim 10 or 11, wherein in step (c2), the autoclaving is carried out at a pressure of 5 bar, 15 bar or between 5 bar and 15 bar.

13. 2. The method of claim 1, further comprising an operating step (e) after step (d) of subjecting the brake pad preform (6) to a carbon densification process, such as a CVD (Chemical Vapor Deposition) technique, CVI (Chemical Vapor Infiltration), PIP (Polymer Infiltration and Pyrolysis) or pitch impregnation densification process, to obtain a densified brake pad preform (7).

14. A method for producing a brake pad preform (6) according to claim 1, comprising: and an operating step of subjecting said brake pad preform (6) to dry finishing and / or wet finishing.

15. A brake pad preform (6) obtained by the method of claim 1.

16. A brake pad (1) obtainable by the method according to claim 14.

17. The brake pad (1) is for a disc brake and is made of a carbon-carbon composite material consisting of a matrix of a carbonaceous material and carbon fibers, with ceramic particles uniformly dispersed in the carbonaceous material matrix.

18. A brake pad (1) for a disc brake according to claim 17, characterized in that it has a thickness of 5 mm ３ A brake pad (1) for a disc brake, characterized in that the volume concentration of ceramic particles in the volume varies within a limit of ±20% between two different randomly identified areas of the pad.

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