Method for the manufacture of carbon -ceramic brake discs with optimized performance and reduced wear and product so developed

Abstract

A method for the manufacture of a carbon-ceramic material including subjecting a carbonaceous preform to densification including the steps of: d1) of first densification obtaining a partially densified carbonaceous preform, and d2) of second densification obtaining a densified carbon-ceramic composite. The carbon-ceramic material obtained according to this method, which is used for a disc brake.

Description

[0001] "Method for the manufacture of carbon -ceramic brake discs with optimized performance and reduced wear and product so developed"

[0002] ★ ★ ★

[0003] DESCRIPTION

[0004] The present invention concerns a method for the manufacture of a carbon-ceramic material for applications in the automotive sector, as well as the material itsel f and its possible applications .

[0005] Today the adoption of carbon-ceramic materials in the development of brake discs for automotive applications is widespread . Carbon- ceramics provide a compromise between good tribological properties and lightweight components .

[0006] For some applications , for example in the racing sector, excellent wear resistance is also required considering that , to ensure good braking, the discs are often coupled with highly abrasive ceramic pads .

[0007] It is therefore necessary to optimize the mechanical properties of the materials ( e . g . impact resistance , flexural strength) , heat dissipation ( i . e . thermal conductivity) , as well as the composition of the carbon-ceramics themselves ( adequate content of abrasive components ) .

[0008] There are already various technological solutions used at the production level , especially for application in the production of brake discs in the automotive sector .

[0009] Carbon preforms can be obtained by mixing resins and short fibers ( chopped) or from pre-impregnated, hot-formed fabrics in compression molding or autoclave . The green-bodies thus obtained are then pyrolyzed at high temperature (e.g. 700°-1000°C) and the resulting product is a very porous preform consisting of carbon fiber and a carbon matrix derived from the pyrolysis of the resin (EP 2.989.343, EP 2.849.942) .

[0010] The carbon preform is very porous and is generally subjected to a densif ication / ceramization phase that can be obtained through different techniques.

[0011] Commonly, for reasons of cost, speed of process and quality of the result, Liquid Silicon Infiltration (LSI) is often preferred.

[0012] Through this process, the preform is vacuum impregnated and at temperatures higher than 1410°C with molten silicon. A large part of the molten silicon that enters the preform reacts with the carbon present to form silicon carbide (SiC) , while a part of the silicon solidifies in the pores without reacting with the carbon (unreacted silicon) and becomes part of the carboceramic matrix.

[0013] The main limitations of the process above described concern the fact that the organic resin used in the pre-impregnated fabric (or prepreg) or in the printing mix (commonly phenolic resins, preferably resols, but also novalacches) significantly reduces its mass during the thermal decomposition that occurs during pyrolysis, leaving a carbon residue often less than 50% of the original mass.

[0014] As a result, micropores and macropores in the preform are difficult to fill simultaneously with LSI, which often result in microstructural defects in the carbon ceramic, as well as cracking trigger points during use.

[0015] The presence of macropores filled with silicon (and not carbon) also leads to relatively high values of average density of the carboceramic and, therefore, high weight of the disc .

[0016] In addition, the pyrolysis residue of the resin does not continuously cover the fiber, limiting the degree of protection guaranteed during ceramization (LSI ) ; as a result , part of the carbon fibers reacts with molten silicon to become SiC fibers , which are more fragile than carbon fibers . This impacts the flexural , compressive and tensile strength of the carbon-ceramic .

[0017] Alternatively, carbonaceous preforms can be obtained directly from carbon fabrics or felts without an organic matrix, that are overlapped and subj ected to needling . Through needlingrit is possible to improve the adhesion between the various overlapping layers and improve the thermal conductivity of the finished product . A preform thus obtained is completely free of carbon matrix, which can be introduced, for example, through the Chemical Vapor Infil tration (CVI ) of carbon . Among the limitations related to the discs currently used, it can be noted that they must be carbonized if they derive from Panox fiber (CN 103553695B, KR 101304303 ) and that the CVI densif ication of carbon, though rapid, still implies quite long times ( from 20 to 40 hours ) (CN 112707735, CN 112707735 ) , while needling (WO 2019 / 180550 ) leads to a reduction in mechanical characteristics and / or the presence of macroporosities , which during LS I treatment are destined to fill with silicon .

[0018] Other methods of densif ication of carbonaceous preforms thus obtained involve additional costs and / or strong technical limitations .

[0019] For example , SiC CVI is an extremely time-consuming and expensive process and does not allow for the complete filling of larger pores, which generally remain empty.

[0020] The Polymer Impregnation and Pyrolysis (PIP, IN-418737) process with pre-ceramic resins (e.g. polysilazanes and / or polysiloxanes) involves the use of very expensive raw materials, a long process (due to the repetition of 5-10 PIP cycles, necessary to achieve the desired densities) and generally does not allow to obtain carbon-ceramic materials, and therefore products made with them, characterized by good heat dissipation (i.e. poor thermal conductivity) , with important consequences on the behavior of the disc under braking.

[0021] High-performance carbon-ceramic production processes, which include a multi-stage densif ication of a carbonaceous preform, are also known art (e.g. US 7,736,554; US 2011 / 0311753) . In these cases, the carbonaceous preform is densified in three steps by carbon CVI, SiC CVI and subsequent LSI (US 7,736,554) or by carbon CVI, LSI and subsequent carbon PIP (US 2011 / 0311753) .

[0022] Obviously, although it is understandable that such an articulated process can facilitate the achievement of optimal characteristics of the carbon-ceramic, it must be considered that the densif ication techniques involved require the use of complex and expensive technologies and extremely long processing times. This complexity makes costs and process times difficult to reconcile with mass production of automotive components.

[0023] Overall, therefore, the industrially available solutions have technological limitations that may concern process times, costs, the thermo-mechanical properties of the product (which reflect its microstructures ) and their tribological properties .

[0024] Summary of the invention

[0025] The inventors of the present patent application have surprisingly developed a method for the manufacture of a carbon-ceramic material with improved performance in terms of flexural strength and thermal conductivity, which can be carried out more quickly and at lower cost .

[0026] This material can be advantageously used for the production of disc brake discs .

[0027] Obj ect of the invention

[0028] In a first obj ect, the present invention describes a method for the manufacture of a carbon-ceramic material .

[0029] The carbon-ceramic material thus obtained represents a second obj ect of the invention .

[0030] In a third obj ect, the present invention describes a product made of carbon-ceramic material .

[0031] In a preferred aspect, said product is represented by a disc for a disc brake .

[0032] Brief description of the figures

[0033] Figure 1 shows images in which the microstructure of the carbonceramic disc is evident and a detail of the microstructure in which its constituents can be seen : carbon fibers , carbon matrix, silicon carbide matrix and silicon .

[0034] Detailed description of the invention

[0035] According to a first obj ect of the invention, it is described a method for the manufacture of a carbon-ceramic material .

[0036] In particular, said method comprises subj ecting a carbonaceous preform to a two-stage densification.

[0037] In this respect, this densification includes the following steps: dl ) of first densification obtaining a partially densified carbonaceous preform, and d2 ) of second densification obtaining a densified carbon-ceramic composite .

[0038] For the purposes of the present invention, the first phase dl) of densification introduces a carbon matrix into the preform.

[0039] Phase dl) produces the deposition of a layer of pyrolytic carbon on the fibers, a layer having a thickness of less than 10 pm and preferably less than 5 pm.

[0040] According to a preferred aspect of the invention, this phase is carried out by means of the rapid Chemical Vapor Infiltration (rapid CVI) technique, for example described in the prior-art art document EP 946.459.

[0041] According to one aspect of the present invention, this phase is carried out for a period of time of about 1 to 25 hours.

[0042] Preferably, this phase dl ) of first densification is carried out at a temperature of 1, 000-1, 700°C and optionally of 1, 000-1, 200°C.

[0043] Preferably, this phase dl ) of first densification is carried out at a pressure of 300-600 mbar.

[0044] According to one aspect of the present invention, the first densification dl) can be carried out under the conditions shown in Table 1 below:

[0045] Table 1

[0046] As for phase d2 ) of second densi f ication, this introduces silicon into the partially densified carbonaceous preform.

[0047] This phase is carried out using the Liquid Silicon Infil tra tion (LSI ) technique .

[0048] According to one aspect of the present invention, said phase d2 ) is carried out for a period of time of about 2 to 8 hours .

[0049] Preferably, said phase d2 ) of second densif ication is carried out at a temperature above l , 410 °C and optionally about 1 , 500-1 , 700 °C .

[0050] Preferably, said phase d2 ) of second densif ication is carried out at a pressure of less than 15 mbar and optionally less than 1 mbar .

[0051] For the purposes of the present invention, phase d2 ) is carried out in an inert atmosphere and preferably is carried out under nitrogen or argon .

[0052] According to an aspect of the present invention, phase d2 ) of second densi f ication can be carried out under the conditions shown in Table 2 below :

[0053] Table 2

[0054] Advantageously, the material subj ected to densif ication ( stages dl ) and d2 ) is characteri zed by a higher flexural strength of up to about 40% compared to an equivalent material that has not undergone densif ication . According to an aspect of the present invention, after phase dl) of first densif ication and before phase d2) of second densif ication, a phase gl) of first graphitization is carried out.

[0055] Said phase gl) of first graphitization can be carried out at a temperature above l, 800°C, optionally about 1 , 800-2 , 600 °C .

[0056] In an optional aspect, said first graphitization phase gl) is carried out at a temperature of 2 , 100-2 , 600 °C .

[0057] According to an aspect of the present invention, the phase gl) of first graphitization can be carried out under the conditions shown in Table 3 below:

[0058] Table 3

[0059] In an aspect of the present invention, the phase gl) of first graphitization is carried out for a period of time of 5-60 minutes and optionally of 30-60 minutes.

[0060] In accordance with an alternative embodiment of the present invention, phase dl) of first densif ication can be replaced by a phase dl ' ) of alternative first densif ication carried out by impregnation technology.

[0061] A resin with a high carbon yield (greater than 40%) can be used for this purpose.

[0062] This resin can be chosen, for example, from: furan resin, phenolic resin, biophenolic resin, phthalonitrile resin.

[0063] Pitch can be used as an alternative to a resin with a high carbon yield. For the purposes of the present invention, the alternative first densif ication phase dl ' ) is carried out at a temperature of 0-400 ° C and optionally at a temperature of 25-400 °C .

[0064] This phase of first alternative densif ication dl ' ) by impregnation is always followed by a pyrolysis phase .

[0065] This pyrolysis phase is carried out at a temperature of 700- 1 , 000 °C .

[0066] This pyrolysis phase is carried out in an inert atmosphere and preferably is carried out under nitrogen or argon .

[0067] According to an aspect of the invention, this pyrolysis phase can be followed by a gl ' ) phase of alternative first graphiti zation carried out at a temperature above l , 800 °C and optionally about 1 , 800- 2 , 600 °C .

[0068] In an optional aspect, said the alternative graphitization phase gl ' ) is carried out at a temperature of 2 , 100-2 , 600 °C .

[0069] In one aspect of the invention, the phase gl ' ) of alternative first graphitization is carried out under the conditions shown in Table 3 above .

[0070] When carried out, also said phase gl ' ) of alternative first graphitization, it is carried out in an inert atmosphere or preferably carried out under nitrogen or argon .

[0071] In one aspect of the present invention, the phase gl ' ) of alternative first graphiti zation is carried out for a period of time of 5- 60 minutes and optionally of 30- 60 minutes .

[0072] Advantageously, the material that has undergone the graphitization phases is characterized by a higher thermal conductivity of up to about 20- 60% .

[0073] Advantageously, the impregnation technique has a lower cost and allows to adapt to di fferent preforms with the use of suitably diluted products .

[0074] In accordance with another alternative embodiment of the invention, phase gl ) of first graphitization and / or phase gl ' ) of first alternative graphitization are carried out , independently of each other, at a temperature below l , 800 ° C and optionally at a temperature of 1 , 600-1 , 800 °C .

[0075] Such embodiment has an advantage in terms of economic savings due to the lower temperature .

[0076] Advantageously, this reduces process costs ; In addition, the carbon / silicon carbide ratio increases in favor of carbon, resulting in a decrease in the density of the material and a change in its tribological properties .

[0077] In particular, a reduction in density of about 5- 10% and an increase in tribological properties of 5-15% were observed, at the expense of a smaller improvement in thermal conductivity (<20% ) .

[0078] In accordance with a further embodiment of the invention, the phase gl ) of first graphiti zation and / or phase gl ' ) of first alternative graphiti zation are not carried out .

[0079] According to a yet another embodiment of the invention, a phase gO ) of preliminary graphitization can be carried out before phase dl ) of first densif ication .

[0080] For the purposes of the present invention, the phase gO ) of preliminary graphiti zation is carried out at a temperature above l,800°C and optionally at a temperature of 1, 800-2, 600°C.

[0081] In an optional aspect, called the gO) phase of preliminary graphitization is carried out at a temperature of 2, 100-2, 600°C .

[0082] Depending on one aspect of the present invention, the phase gO) of preliminary graphitization can be carried out under the same conditions as shown in Table 3 above.

[0083] In accordance with another embodiment of the invention, the phase gO) of preliminary graphitization is carried out at a temperature below l,800°C and optionally at a temperature of 1, 600-1, 800°C.

[0084] In an aspect of the present invention, the phase gO) of preliminary graphitization is carried out for a period of time of 5- 60 minutes and optionally of 30-60 minutes.

[0085] According to an aspect of the present invention, the carbonaceous preform subjected to the method described above is itself obtained by means of a method comprising the following steps: pl) obtain a green body, p2 ) pyrolyze said green body to obtain a carbonaceous preform.

[0086] In the context of the present invention, with the term "green body" it is intended a composite product with a polymer matrix before it is subjected to heat treatments.

[0087] For the purposes of the present invention, in step pl) a carbon fiber material is used to obtain the green body, represented by a fabric or a non-woven fabric of long carbon fibers.

[0088] A non-woven fabric, for example, is represented by a felt.

[0089] In an aspect of the invention, these long carbon fibers are represented by PAN fibers and / or pitch fibers. In an aspect of the invention, the fabrics and / or nonwovens used have a grammage between about 200 and 800 g / m2 and optionally about 500 to 700 g / m2 .

[0090] In one aspect of the invention, the long carbon fibers that make up the fabrics and / or nonwovens are pre-impregnated with resin .

[0091] In an aspect of the invention, the long carbon fibers preimpregnated with resin are processed in compression molding / autoclave to obtain the green body.

[0092] In another aspect of the invention, the pl ) phase can be carried out using chopped fibers mixed with a resin .

[0093] Chopped fibers can be about 1-100 mm in size and preferably 6- 25 mm.

[0094] The green body can be obtained by mixing the chopped fibers with the resin ( solid or powder) and processing the product in compression molding / autoclav .

[0095] Or chopped or long fibers ( in the form of fabrics or non-woven fabrics ) can be placed in a mold and the resin can be placed through the techniques of Resin Infusion, Vacuum assisted Resin Infusi on, Resin Transfer Molding or Vacuum Assi sted Resin Transfer Molding .

[0096] With these four techniques it is also possible to process three- dimensional preforms , i . e . obtained from three-dimensional fabrics of long carbon fibers (pan / pi tch) .

[0097] In one aspect of the invention, phase pl ) is carried out for a period of time of at least 30 minutes and optionally of at least 60 minutes .

[0098] In one aspect of the invention, phase pl ) is carried out at a temperature of 130-180°C and optionally about 150°C.

[0099] For the purposes of the present invention, the green bodies obtained from the pl) phase have a density of about 1.40-1.65 g / cm3and preferably about 1.56-1.62 g / cm3.

[0100] For the purposes of the present invention, the resin is represented by a resin with a high carbon yield.

[0101] A resin with a high carbon yield can be chosen, for example, from: furan resin, phenolic resin, biophenolic resin, phthalonitrile resin .

[0102] In an aspect of the invention, said resin is represented by a phenolic resin.

[0103] Pitch can be used as an alternative to a resin with a high carbon yield.

[0104] According to an alternative embodiment of the invention, in pl) phase of preparation of the green body, a prepreg can be used that is laminated and printed in the press by compression molding or autoclave, or even a fabric or a carbon non-woven fabric that is first laminated and then impregnated with a polymer matrix through Resin Infusion, Vacuum assisted Resin Infusion, Resin Transfer Molding or Vacuum Assisted Resin Transfer Molding .

[0105] In both cases, the pl) phase still involves a treatment at 130- 180°C to polymerize the resin.

[0106] As regards phase p2) in an aspect of the present invention, pyrolysation is carried out at a temperature of at least 700-1000°C, and may be followed by a phase gO) of preliminary graphitisation carried out in one of the ways described above. For the purposes of the present invention, phase p2) is carried out in an inert atmosphere and preferably is carried out under nitrogen or argon.

[0107] For the purposes of the present invention, this carbonaceous preform is very porous and preferably has a density of about 1.25- 1.50 g / cm3and even more preferably about 1.40-1.48 g / cm3.

[0108] The carbon-ceramic material obtained according to the method and its variants as described above represents a second object of the invention .

[0109] In accordance with a third object, it is described a product made with the carbon-ceramic material of the invention.

[0110] In a preferred aspect, said product is represented by a disc for a disc brake.

[0111] In an aspect of the invention, said disc brake is intended for a disc brake in the racing sector.

Claims

CLAIMS1. A method for the manufacture of a carbon-ceramic material including subjecting a carbonaceous preform to densif ication including the steps of: dl ) of first densif ication obtaining a partially densified carbonaceous preform, and d2 ) of second densif ication obtaining a densified carbon-ceramic composite .

2. The method according to the preceding claim, wherein said phase dl ) of first densif ication is carried out at a temperature of 1, 000-1, 700°C, and preferably 1, 000-1, 200°C.

3. The method according to any one of the preceding claims, wherein said d2) phase of second densif ication is carried out at a temperature above l,410°C, and optionally 1 , 500-1 , 700 °C .

4. The method according to any one of the preceding claims wherein after said phase dl) of first densif ication and before said phase d2) of second densif ication a phase gl) of first graphitization is carried out at a temperature of 1, 800-2, 600°C.

5. The method according to the preceding claim, wherein said phase gl) of first graphitization is carried out at a temperature of 2, 100-26.00°C.

6. The method, according to any one of the preceding claims, whereby said phase dl) of first densif ication is replaced by a phase dl ' ) of alternative first densif ication carried out by impregnation with a resin with a high carbon yield or pitch followed by a pyrolysis step .

7. The method according to the preceding claim, wherein said phase dl ' ) of alternative first densif ication is carried out at a temperature of 0-400°C.

8. The method according to the preceding claim, wherein said phase dl ' ) of alternative first densif ication is carried out at a temperature of 25-400°C.

9. The method according to any one of the preceding claims 6 to 8, wherein said pyrolysis step is carried out at a temperature of 700- 1, 000°C.

10. The method according to any one of the preceding claims 6 to 9 including, after said pyrolysis step, a phase gl ' ) of alternative first graphitization carried out at a temperature of about 1,800 to 2, 600°C.

11. The method according to the preceding claim, wherein said phase gl ' ) of alternative first graphitization is carried out at a temperature of 2 , 100-2 , 600 °C .

12. The method according to any one of the preceding claims, wherein a preliminary graphitization phase gO) is carried out at a temperature of 1, 800-2, 600°C before phase dl) of first densif ication .

13. The method according to the preceding claim, wherein said phase gO) of preliminary graphitization is carried out at a temperature of 2 , 100-2 , 600 °C .

14. The method according to any one of the preceding claims 4 to 13, wherein that phase gl) of first graphitization is alternately carried out at a temperature below l,800°C and optionally at 1,600 to 1, 800°C.

15. The method according to any one of the preceding claims 10 to 14, wherein said phase gl ' ) of alternative first graphitization is carried out alternately at a temperature below l,800°C and optionally at a temperature of 1, 600 to l,800°C.

16. The method according to any one of the preceding claims 12 to 15, wherein said phase gO) of preliminary graphitization is alternately carried out at a temperature below l,800°C and optionally at 1,600 to l,800°C.

17. The carbon-ceramic material obtained according to the method f any one of the preceding claims.

18. A product made of the carbon-ceramic material of the receding claim, which is represented by a disc for a disc brake.

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