Method for producing a carbon ceramic brake disc and carbon ceramic brake disc

Abstract

This disclosure relates to a method for producing a carbon ceramic brake disc with a thermal bridge, and the carbon ceramic brake disc produced by the method.

Description

[0001] This disclosure relates to a method for producing a carbon ceramic brake disc with a thermal bridge, and the carbon ceramic brake disc produced by the method.

[0002] Methods for producing carbon ceramic brake discs have been described in the prior art.

[0003] For example, U.S. Patent Application Publication No. US 2018 / 0209498 A1 discloses a hybrid lightweight brake disc and a method for producing the hybrid lightweight brake disc. The method provides a brake cavity comprising a material containing an aluminum forged alloy, and a friction ring with a rapidly solidifying aluminum alloy constructed on the edge region of the brake cavity using a laser deposition welding process or a 3D printing process.

[0004] In addition, German patent application publication number DE 10 2017 217 292 A1 discloses a ceramic component containing silicon carbide (SiC) and the use of the component.

[0005] A major problem with existing brake discs is that they typically cannot provide high thermal conductivity, while the desired outcome is that heat generated during braking dissipates more quickly from the friction surfaces to prevent overheating and optimize braking and material wear. For existing carbon-ceramic brake discs, even with the use of a friction layer (which typically has higher thermal conductivity than the base material), the material's thermal conductivity is primarily dependent on the base material, as the base material dominates the thickness of the rotor cheek plates.

[0006] Furthermore, it is well known that carbon fiber ceramic composites exhibit relatively low thermal conductivity due to the discontinuous micro-connections of the conductive parts (SiC and Si). The silicon channels are quite small, and SiC is a polycrystalline material with multiple interruptions and grain boundaries, which further reduces the thermal conductivity (from over 100 W / mK to below 30 W / mK).

[0007] In addition, graphite-modified carbon materials have anisotropic thermal conductivity, which often hinders efficient heat dissipation in brake discs.

[0008] Therefore, one object of this disclosure is to provide a method for producing carbon ceramic brake discs and a carbon ceramic brake disc with improved thermal conductivity, which can be produced on a large scale and with high production quality. The carbon ceramic brake disc should maintain improved braking performance even after multiple braking actions within a short period. Furthermore, it is desirable that the method be both cost-effective and energy efficient.

[0009] The inventors of this disclosure unexpectedly discovered that all the above-mentioned objectives can be achieved by the method of producing carbon ceramic brake discs of this disclosure and the carbon ceramic brake discs of this disclosure produced by the method.

[0010] In a first aspect, this disclosure relates to a method comprising the following steps. In step a), a carbon- or silicon carbide-based preform is provided. The preform can be produced by a 3D printing method. The preform has the form of a disc having a top surface from which a plurality of vertical pins extend. In step b), carbon fiber blocks are added to the preform. In step c), the preform with the added carbon fiber blocks is pressed. In step d), the pressed preform can be carbonized. In this step, a porous, foam-like carbon skeleton can be generated from the pressing system. In step e), a plurality of thermal bridges can be generated by siliconizing the carbon ceramic brake disc. A carbon ceramic brake disc is thus obtained.

[0011] In a preferred embodiment, the vertical pin evaporates or is destroyed in step c) or d), thereby creating voids in the blank. Furthermore, in this embodiment, in step e), the voids are filled with a filler material, thereby creating multiple thermal bridges within the carbon ceramic brake disc. Most preferably, the vertical pin evaporates or is destroyed in step d), thereby creating voids in the blank.

[0012] In another preferred embodiment, in step e), the vertical pin is replaced or impregnated with filler material, thereby creating multiple thermal bridges within the carbon ceramic brake disc.

[0013] Preferably, the vertical pins are replaced or impregnated by a silicon impregnation step of impregnating the carbide preform with liquid silicon.

[0014] Preferably, the filler material is selected from metals, alloys, carbon, silicon, or combinations thereof. Most preferably, the filler material is silicon. The inventors of this disclosure have surprisingly discovered that if the filler material is selected from the above-mentioned materials, or preferably silicon, the carbon ceramic disc has better corrosion resistance and improved heat transfer characteristics compared to prior art carbon ceramic brake discs.

[0015] To avoid being bound by specific theories, the introduction of thermal bridges (such as silicon thermal bridges) can improve thermal conductivity, thereby bringing significant benefits to brake pads and friction behavior.

[0016] Without being bound by a specific theory, thermal bridges (channels) can be formed in the substrate through voids or by material substitution. Voids can be filled, and the substitute material can react accordingly during liquid silica infiltration to form a composite material.

[0017] Preferably, the cross-section of the pin can be selected from elliptical, circular, square, or rectangular.

[0018] Typically, the plurality of vertical pins extending from the top surface of the disk can be cylindrical. In a preferred embodiment, the plurality of vertical pins extending from the top surface of the disk have a pyramidal shape.

[0019] According to this disclosure, the inventors have surprisingly come to realize that if a system comprising a carbon- or silicon carbide-based preform is produced from a pressing system, the preform being manufactured by a 3D printing method, wherein the preform is in the form of a disk with a top surface, wherein multiple vertical pins extend from the top surface of the disk, and added carbon fiber blocks are pressed and carbonized. If the term "sponge-like carbon skeleton" is used subsequently, it also refers to a foam-like carbon skeleton. When such a preform is subjected to siliconizing, the pores of the preform can be filled with a filler material (e.g., silicon), so that the pore volume of the sponge-like carbon skeleton is almost entirely filled with silicon carbide. As a result of this pore filling, the number of relatively large pool-like or localized regions of free filler material is significantly reduced compared to the prior art. Therefore, the filler material no longer exists in the form of large pool-like or localized regions, but rather in silicon carbide structures within these pores. The presence of these pore-filling silicon carbide structures leads to higher chemical stability, higher hardness, and higher heat resistance in the ceramic components. During the silicon infiltration process, this causes the carbonized resin carbon to be converted into SiC only on the surface. Since silicon cannot access the internal carbon, most of the internal carbon is retained, so the SiC content increases only slightly in comparison.

[0020] The carbon-based preform in step a) is produced by 3D printing. Such a preform can be produced according to the method described in WO 2017 / 089494.

[0021] In this method, a powdered composition and a liquid binder are provided. The powdered composition has a particle size (d50) of 3 μm to 500 μm, preferably 50 μm to 350 μm, more preferably 100 μm to 250 μm, and contains at least 50% by weight, preferably at least 80% by weight, more preferably at least 90% by weight, and particularly preferably at least 95% by weight of coke. A layer of the powdered composition is then deposited on its surface, followed by the local deposition of liquid binder droplets. These steps are repeated until a component of the desired shape is produced, wherein each step is adjusted according to the desired shape of the component. The binder is then at least partially cured or dried to obtain a preform having the desired component shape. The powdered composition can be a powder or granules of primary particles. The term "d50" indicates that 50% of the particles are smaller than a specified value. d50 is determined by laser particle size analysis (ISO 13320) using measuring equipment and related evaluation software from Sympatec GmbH.

[0022] Obtaining a preform with the desired component shape is understood to mean that, after the binder has cured or dried, the preform is still surrounded by bulk powder composed of loose particles of a powdered composition. Therefore, the preform must be removed from the bulk powder or separated from the loose, uncured particles. In the literature on 3D printing, this is also referred to as "unpacking" the printed component. After unpacking, the preform can be (finely) cleaned to remove any attached particle residue. Unpacking can be done, for example, by removing the loose particles using a powerful vacuum cleaner. However, there are no particular limitations on the method of unpacking; all known techniques can be used.

[0023] While there are no particular limitations on the type of coke used, according to a preferred embodiment of this disclosure, the green body in step a) is produced using coke, preferably selected from acetylene coke, flexible coke, fluidized coke, petroleum coke, shot coke, coal tar pitch coke, carbide ion exchange bead coke, and any mixture thereof, more preferably selected from acetylene coke, flexible coke, fluidized coke, shot coke, carbide ion exchange bead coke, and any mixture thereof. The advantage of using these cokes is that they have a coke shape that is as round as possible, where the round shape results in good flowability, thus ensuring a smooth 3D printing process. Furthermore, the round coke shape helps improve the fracture resistance of the ceramic component. This is likely due to the round and partially onion-skin-like structure of these coke varieties. These cokes can be used as so-called green coke or as calcined coke, carbide coke, or graphitized coke. Green coke is coke that still contains volatile components. These volatile components are almost absent in calcined coke or carbide coke, where the coke has undergone temperature treatment typically from 700°C to 1400°C. The terms "calcination" or "carbonization" are considered synonyms. Graphitized coke is obtained by processing coke at temperatures typically above 2000°C to 3000°C.

[0024] In the production of the preform, adding a liquid activator (e.g., a liquid sulfuric acid activator) to the coke may be advantageous. By using such an activator, curing time can be shortened and the temperature required to cure the binder can be lowered, while dust generation from the powdered composition can be reduced. Advantageously, the amount of activator used is 0.05% to 3.0% by weight, more preferably 0.1% to 1.0% by weight, based on the total weight of the coke and activator. If more than 3.0% by weight (based on the total weight of the activator and coke) is used, the powdered composition will clump together, and its flowability will decrease; if less than 0.05% by weight based on the total weight of the coke and activator, the amount of activator that can react with the binder (more precisely, the resin component of the binder) is too small to achieve the desired benefits.

[0025] There are no particular limitations on the choice of binder for producing 3D printed preforms. Suitable binders include, for example, phenolic resins, furan resins, polyimides, cellulose, starch, sugars, silicates, silicon-containing polymers, bitumen, polyacrylonitrile (PAN), or any mixture thereof. Solutions of the above binders are also included. Generally, the binder should be designed in such a way that a stable preform can be obtained after carbonization, which can withstand the handling during transfer to the siliconizing equipment and the temperatures applied during siliconizing. In this case, when using silicone binders after pyrolysis, the binder should have a sufficiently high final carbon yield, or a silicon-containing inorganic yield. When thermoplastic binders (such as bitumen) are selected, it may be necessary to carbonize the entire powder bed to decompose and eventually crosslink it. The same applies to PAN. The powder bed without additive binders serves as the support for the component, while the thermoplastic binder (such as bitumen or PAN) is carbonized. Furthermore, the powder bed advantageously provides oxidative protection for the printed preform during the subsequent carbonization process.

[0026] As adhesives, phenolic resins, furan resins, or polyimides represent resins and polymers with relatively high carbon yields. They belong to the category of adhesives that are converted into infusible adhesive systems through curing and are largely converted to SiC during silicon infiltration. Due to their high carbon yield, not all carbon is typically converted to SiC during silicon infiltration, and carbon inclusions are formed, resulting in lighter overall components. Furthermore, the high carbon yield means a correspondingly lower content of free silicon in the component, thereby improving chemical stability and heat resistance.

[0027] However, cellulose, starch, or sugar (preferably in solution form) can also be used as binders. These binders only require drying, are inexpensive, and the carbon residues produced during carbonization are ideally (i.e., substantially completely) converted to SiC during the siliconizing process.

[0028] Using silicates or silicon-containing polymers as binders (preferably in solution form) also has advantages, as these binders only require pressing. They spontaneously form SiC during the carbonization process. Furthermore, wetting with liquid silicon is better than wetting with carbon, which is beneficial for the silicon diffusion step.

[0029] Preferably, based on the total weight of the preform, the amount of binder in the preform is 1.0% to 35.0% by weight, preferably 1.0% to 10.0% by weight, and most preferably 1.5% to 5.0% by weight.

[0030] In another preferred embodiment of this disclosure, the green body according to step a) comprises silicon carbide in addition to carbon, preferably containing up to 50% by weight of SiC relative to the total weight of the green body. The SiC used is in powder form, and its particle size (d50) is preferably from 50 μm to 500 μm, more preferably from 75 μm to 200 μm. To determine the d50 value, laser particle size analysis (ISO 13320) is also used here, employing measuring equipment and related evaluation software from Sympatec GmbH.

[0031] By using SiC powder in the green body production, the oxidation stability of the resulting ceramic component is improved from the outset because the amount of free carbon in the component is reduced. Furthermore, the component exhibits high inertness to acids and alkalis, while maintaining heat resistance. The higher final SiC content also increases the component's hardness.

[0032] To produce a blank containing silicon carbide in addition to carbon, the aforementioned 3D printing method for coke can be applied, wherein a mixture of coke and silicon carbide is used instead of coke in the surface deposition step.

[0033] The sponge-like carbon skeleton preferably has an average pore size of less than 50 μm, more preferably less than 20 μm, particularly preferably less than 10 μm, and most preferably less than 5 μm. The average pore size can be determined by quantitative framework analysis, for example, using an optical microscope or a scanning electron microscope. This porosity formation significantly increases the accessible surface area of ​​the carbon skeleton produced from the pressing system, ensuring that the liquid silicon according to step e) can largely completely fill these voids and pores. The smaller the average pore size, the larger the accessible surface area of ​​the carbon skeleton. Due to the rapid reaction of the carbon in the aforementioned carbon skeleton with the liquid silicon, most of the carbon can be converted into silicon carbide. At the same time, the sponge structure fills the original pores of the preform as much as possible, which significantly reduces the pool-like or localized areas of free silicon during subsequent silicon infiltration.

[0034] According to another preferred embodiment of this disclosure, the pressing of the preform in step c) can be carried out at room temperature or at a temperature below the boiling point of the solvent or solvent mixture used. Preferably, the pressing is carried out at room temperature.

[0035] The term "carbonization" (according to step d) refers to the process of thermally converting the system contained in the green body into carbon. Carbonization can be achieved by heating to a temperature of 500°C to 1100°C, preferably 800°C to 1000°C, under a protective gas atmosphere (e.g., argon or nitrogen) and then holding that temperature for a period of time. Regarding the solvent trapped in the pores, it is advantageous to heat carefully to the carbonization temperature, as these trapped solvents (usually water) must be drained first. If this draining is not slow or careful, the green body may explode.

[0036] According to step e), the formation of thermal bridges typically occurs under a protective gas atmosphere (e.g., Ar or He), overpressure, atmospheric pressure, or vacuum, preferably under vacuum. To form intricate and complex structures (e.g., undercuts, cavities, or cooling channels), liquid silicon must be able to self-infiltrate the carbide preform solely by capillary force. The carbide preform of this disclosure possesses precisely this desired characteristic: its porous system can be designed using 3D printing methods to allow the preform to be completely and almost non-porously infiltrated with silicon solely by capillary force, without additional pressure. Furthermore, apart from conventional silicon leakage based on variations in silicon density, the cooling process after infiltration does not lead to further silicon leakage. Infiltrating the carbide preform with liquid silicon in a vacuum is particularly effective because the carbon is better wetted by silicon, and the preform's absorption behavior is improved. Moreover, silicon infiltration can be carried out in a vacuum at a lower temperature, which must, of course, be above the melting temperature of silicon. Therefore, step e) above (e.g., forming thermal bridges by silicon infiltration) is preferably performed under vacuum. Within the scope of this disclosure, liquid silicon as referred to in this context also includes silicon alloys with a silicon content of at least 50% by weight. However, pure silicon is preferred.

[0037] During step e), when the thermal bridge is generated, the preform is preferably placed on a wicking structure protruding from the molten silicon bath. Similar to the preform itself, in this case, the wicking structure is able to conduct liquid silicon via capillary force through its porous structure. The preform itself is not immersed in the silicon bath, but rather sits above it. After siliconizing and cooling to room temperature, the wicking structure is connected to the component via solidified silicon and therefore must be mechanically removed. To further simplify the method according to this disclosure, the wicking structure is preferably already provided as part of the preform, i.e., "printed" onto the preform during the production of the preform by 3D printing. Thus, the preform with the downward-pointing wicking structure can be simply placed in the container provided for the silicon bath. After siliconizing and cooling are complete, the wicking structure is mechanically removed as described above.

[0038] Within the scope of this disclosure, steps d) and e), namely the carbonization of the pressed preform and the subsequent siliconizing, can actually be carried out in a single process step, since the preform has already been carbonized during the siliconizing process when heated to the siliconizing temperature—it can be said to be in-situ carbonization.

[0039] According to another preferred embodiment of this disclosure, prior to silicon infiltration according to step e), the steps of adding carbon fiber blocks according to step b), pressing according to step c), and carbonizing according to step d) can be repeated at least once in the above-described order. Through these additional steps, the pores of the preform skeleton are more completely filled by the fine-pored, sponge-like carbon skeleton produced by the carbonization and pressing resin system. Due to the higher amount of this sponge-like carbon skeleton, the amount of carbon converted to SiC during the subsequent silicon infiltration process is further increased; as a result, the amount of SiC in the ceramic component is further increased, while the amount of free silicon in the component is advantageously reduced.

[0040] The reduction in free silicon content improves the chemical resistance and heat resistance of ceramic components, while the increase in silicon carbide content improves the hardness, stiffness and strength of ceramic components.

[0041] This porosity formation significantly increases the accessible surface area of ​​the carbon skeleton produced from the pressed resin system, ensuring that the liquid silicon according to step e) can largely completely fill these pores. Due to the rapid reaction between the carbon in the aforementioned carbon skeleton and the liquid silicon, most of this carbon can be converted into silicon carbide.

[0042] In this disclosure, multiple thermal bridges within the carbonized disk are understood as regions within the carbonized disk that have a higher thermal conductivity than the surrounding material, thereby creating paths with minimal heat transfer resistance. Thermal bridges can lead to a reduction in the overall thermal resistance of the object. Preferably, the thermal bridges are regions within the carbonized disk with a thermal conductivity exceeding 100 W / mK, more preferably exceeding 130 W / mK.

[0043] In a second aspect, this disclosure relates to a carbon ceramic brake disc manufactured using the first aspect of this disclosure.

[0044] Various aspects of this disclosure will now be described by way of example and with reference to the accompanying drawings, in which:

[0045] Figure 1 The process steps according to the method of this disclosure are shown.

[0046] Figure 2 shows the heat transfer analysis results of the carbon ceramic brake disc according to this disclosure compared with the prior art carbon ceramic brake disc.

[0047] Figure 3 The results of a thermal matrix test on a bench are shown for a carbon ceramic brake disc according to this disclosure, compared to prior art carbon ceramic brake discs.

[0048] exist Figure 1 The diagram illustrates the process steps of a method according to this disclosure. The method comprises the following sequential steps: In step a), a carbon-based preform is provided using a 3D printing method. The preform has the form of a disc with a top surface from which a plurality of vertical pins extend. The design of the vertical pins can be selected according to the needs of the ceramic brake disc and will affect the adjustable crack pattern. In step b), carbon fiber blocks are added to the preform. In step c), the preform and the added carbon fiber blocks are pressed in a mold. Subsequently, in step d), the pressed preform is carbonized. This step produces a porous, foam-like carbon skeleton from the pressed resin system. In step e), multiple thermal bridges are generated within the carbon ceramic brake disc by infiltrating with liquid silicon to fill the voids created by pin breakage with a mixture of silicon and silicon carbide.

[0049] Figure 2 shows the heat transfer analysis results of the carbon ceramic brake disc according to this disclosure compared to prior art carbon ceramic brake discs. Figure 2a The paper presents the heat transfer analysis results of a carbon ceramic brake disc with a friction layer. Compared with existing carbon ceramic brake discs, the thermal diffusivity α (in mm²) of the carbon ceramic brake disc disclosed in this paper is significantly higher. 2 The average increase (measured in units of / s) increased by 47.84%. Figure 2b The paper presents the heat transfer analysis results of a carbon ceramic brake disc without a friction layer. Compared with existing carbon ceramic brake discs, the thermal diffusivity α (in mm²) of the carbon ceramic brake disc disclosed in this paper is significantly higher. 2 The average increase (measured in units of / s) increased by 53.02%. The test results clearly show that the thermal diffusivity α of the carbon ceramic brake disc obtained according to the method of this disclosure is greatly improved.

[0050] exist Figure 3 The results of a bench thermal matrix test of the carbon ceramic brake disc according to this disclosure versus a prior art carbon ceramic brake disc are shown. Braking characteristics were measured during 30 braking cycles at a limited speed from 200 km / h to 100 km / h. The results show that, compared to a prior art carbon ceramic brake disc, the braking pressure (measured in bars) increases significantly after 22 braking cycles. In contrast, for the carbon ceramic brake disc according to this disclosure, the braking pressure (measured in bars) does not increase even after 30 or more braking cycles. The test results clearly demonstrate that the braking performance of the carbon ceramic brake disc produced using the method of this disclosure is significantly improved.

Claims

1. A method for producing carbon ceramic brake discs, comprising the following steps: a) Provide a carbon- or silicon carbide-based preform, the preform being produced by a 3D printing method, wherein the preform is in the form of a disk with a top surface, wherein a plurality of vertical pins extend from the top surface of the disk. b) Add carbon fiber blocks. c) Pressing the preform with added carbon fiber blocks. d) Carbonizing the pressed preform, wherein a fine-porous, foam-like carbon skeleton is generated from the pressing system. e) A carbon ceramic brake disc is obtained by siliconizing the carbonized disc to generate multiple thermal bridges.

2. The method according to claim 1, wherein in step c) or d), the vertical pin evaporates or is destroyed, thereby creating voids in the blank, and in step e), the voids are filled with a filler material, thereby creating a plurality of thermal bridges within the carbon ceramic brake disc.

3. The method according to claim 1, wherein in step e), the vertical pin is replaced or impregnated with a filler material, thereby creating a plurality of thermal bridges within the carbon ceramic brake disc.

4. The method of claim 3, wherein the vertical pin is replaced or impregnated by a silicon impregnation step of impregnating the carbide preform with liquid silicon.

5. The method according to any one of the preceding claims, wherein the filler material is selected from metals, alloys, carbon, silicon, or any combination thereof.

6. The method according to any one of the preceding claims, wherein the filler material is silicon.

7. The method according to any one of the preceding claims, wherein the plurality of vertical pins extending from the top surface of the disk have a cross-section selected from elliptical, circular, square or rectangular.

8. The method according to any one of the preceding claims, wherein the plurality of vertical pins extending from the top surface of the disk have a pyramidal shape.

9. A carbon ceramic brake disc produced by the method according to any one of claims 1.

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