Preparation method of acrylic pulp and aramid hybrid reinforced friction material

Abstract

The present application relates to the technical field of friction material preparation, and particularly relates to a preparation method of acrylic pulp and aramid hybrid reinforced friction material, which comprises the following preparation steps: mixing weighed reinforcing fibers, friction performance regulators, binders and powder fillers to obtain a friction material mixture; the binders comprise nitrile rubber powder and phenolic resin powder, and the reinforcing fibers comprise acrylic pulp, aramid pulp, carbon ceramic fibers and mineral fibers; the friction material mixture is loaded into a mold and hot-pressed to form a friction material blank; the friction material blank is placed in an oven and gradient heat-treated to obtain the friction material. The organic fiber hybrid network formed by the acrylic pulp and the aramid pulp, in combination with the rigid support of the carbon ceramic fibers and the mineral fibers and the close packing of the gradient graded powder fillers, significantly reduces the wear rate and prolongs the service life.

Description

Technical Field

[0001] This invention relates to the field of friction material preparation technology, and in particular to a method for preparing a friction material reinforced by a mixture of acrylic pulp and aramid. Background Technology

[0002] Friction materials are a core component of braking systems, and their performance directly determines braking safety, stability, and service life. An ideal friction material needs to have a stable coefficient of friction, a low wear rate, and excellent mechanical strength, while also maintaining high-temperature stability and noise reduction performance.

[0003] Currently, some of the mainstream automotive disc brake pads and other braking components on the market still use copper-containing friction materials. These materials improve friction performance and thermal conductivity by adding copper fibers or copper powder, which can meet the requirements of friction coefficient stability and high-temperature heat dissipation during braking to a certain extent, and are widely used in various motor vehicle braking systems.

[0004] However, these friction materials generate a large amount of wear dust during braking. The copper heavy metal ions contained in this dust can enter the soil, rivers, and groundwater systems through rainwater runoff and surface runoff, causing cumulative damage to aquatic ecosystems and disrupting the water balance. In addition, traditional copper-containing friction materials are prone to oxidation and corrosion, leading to a decrease in the structural stability of the friction material. This not only causes excessive fluctuations in the coefficient of friction but also triggers severe thermal fade, affecting braking safety. Summary of the Invention

[0005] In view of the defects mentioned in the background art, the present invention provides a method for preparing a friction material reinforced by acrylonitrile pulp and aramid fiber. By combining the synergistic reinforcement of the hybrid fibers with the compounding of multi-component friction performance modifiers, an environmentally friendly, high-performance copper-free friction material is obtained.

[0006] To solve the above-mentioned technical problems, the preparation method of the present invention includes the following steps: S1. Prepare the following components by weight percentage: 18%–35% friction modifier, 10%–23% reinforcing fiber, 10%–18% binder, with the balance being powder filler; The binder comprises 4% to 8% nitrile rubber powder and 6% to 10% phenolic resin powder, and the reinforcing fiber comprises 1.5% to 2.5% acrylic pulp, 1% to 2.5% aramid pulp, 4.5% to 10% carbon ceramic fiber and 3% to 8% mineral fiber. S2. Mix the weighed friction performance modifier, reinforcing fiber, binder and powder filler to obtain friction material mixture; S3. Load the friction material mixture into the mold and hot press it to form a friction material blank; S4. Place the friction material blank in an oven and perform gradient heat treatment to obtain the friction material.

[0007] Preferably, the friction modifier comprises, by weight percentage, 3% to 6% flake graphite, 6% to 10% granular graphite, 4% to 8% coke powder, 2% to 6% friction powder, and 3% to 5% molybdenum disulfide.

[0008] Preferably, the powder filler is composed of barium sulfate, nano-calcium carbonate, glass microspheres, and alumina in a mass ratio of 3-6:6-10:4-8:2-6.

[0009] Preferably, the barium sulfate is graded according to particle size, with 0.8–2 μm accounting for 20%–40% by weight percentage, 2–5 μm accounting for 40%–60%, and 5–10 μm accounting for 10%–30%.

[0010] Preferably, the nano-calcium carbonate is graded by particle size, with 20-40 nm accounting for 15%-30% by weight percentage, 40-60 nm accounting for 45%-65%, and 60-100 nm accounting for 10%-25%.

[0011] Preferably, the glass microspheres are graded by particle size, with 40-60 μm accounting for 20%-40% by weight percentage, 60-80 μm accounting for 40%-55%, and 80-100 μm accounting for 10%-40%.

[0012] Preferably, the alumina is graded by particle size, with 1-3 μm accounting for 20%-35% by weight percentage, 3-6 μm accounting for 45%-55%, and 6-10 μm accounting for 20%-25%.

[0013] Preferably, in step S4, the gradient heat treatment process is as follows: (1) Raise the temperature from room temperature to 140℃~150℃, with a heating time of 30~60min and a holding time of 30~60min; (2) Continue to raise the temperature to 160℃~170℃, raise the temperature for 45~60min, and keep warm for 30~60min; (3) Raise the temperature again to 180℃~190℃, raise the temperature for 30~45min, and hold for 60~120min; (4) After the heat preservation is completed, open the door and let it cool naturally to room temperature.

[0014] After adopting the above technical solution, the beneficial effects of the present invention are: This invention's formulation contains no copper or copper-containing components, avoiding heavy metal pollution of the aquatic ecosystem by braking dust and complying with increasingly stringent environmental regulations. Through the synergistic blending of flake graphite, granular graphite, coke powder, friction powder, and molybdenum disulfide, the friction coefficient fluctuates minimally, effectively suppressing thermal fade and ensuring braking safety. The organic fiber hybrid network formed by acrylic and aramid pulp, combined with the rigid support of carbon ceramic and mineral fibers, and the dense packing of gradient-graded powder fillers, significantly reduces wear rate and extends service life. Detailed Implementation

[0015] The features and exemplary embodiments of various aspects of the present invention will now be described in detail. To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are only configured to explain the present invention and are not configured to limit the present invention. For those skilled in the art, the present invention can be practiced without some of these specific details. The following description of the embodiments is merely intended to provide a better understanding of the present invention by illustrating examples of the invention.

[0016] Step 1: Raw Material Preparation The formulation of the friction-enhancing material made by blending acrylic pulp and aramid fiber consists of the following components by weight percentage: 18%–35% friction modifier, 10%–23% reinforcing fiber, 10%–18% binder, 3%–12% negative thermal expansion material (NTE), and the balance being powder filler.

[0017] The friction performance modifier comprises the following components (by weight percentage): 3%–6% flake graphite (from Qingdao Guangxing Electronic Technology Co., Ltd., -195 mesh), 6%–10% granular graphite (from Shanghai Xili Carbon Co., Ltd., model XLJ-01), 4%–8% coke powder (from Laiwu Bangtai Industry and Trade Co., Ltd., 30–80 mesh), 2%–6% friction powder (from Qingdao Zhongfuxing Trading Co., Ltd., model NX-1820A), and 3%–5% molybdenum disulfide (from Shanghai Yixi Industrial Co., Ltd., model TG, D50 12–16μm).

[0018] Friction modifiers are core components that determine the stability of a material's coefficient of friction, wear resistance, and braking comfort. Through the synergistic effect of particles with different hardness, particle size, and lubricity, the coefficient of friction can be stabilized over a wide temperature range, braking noise can be suppressed, and the thermal degradation properties of the material can be adjusted.

[0019] The reinforcing fiber comprises the following components: 1.5%–2.5% acrylic pulp (from Changzhou Wujin Huadong Special Fiber Co., Ltd., white, fiber length 1.5–3.5 mm), 1%–2.5% aramid pulp (from Changzhou Gaoyuan Chemical Co., Ltd., model 1F1710), 4.5%–10% carbon ceramic fiber (from Tianxuan Composite Materials (Shanghai) Co., Ltd., model CCCF-B2), and 3%–8% mineral fiber (from Qingdao Zhongfuxing Trading Co., Ltd., model FM1250).

[0020] Reinforcing fibers form the mechanical skeleton of friction materials, determining their strength, toughness, thermal shock resistance, and crack resistance. Mixing multiple fibers can achieve complementary properties, forming a multi-scale, multi-modulus reinforcing network and improving the overall structural integrity of the material.

[0021] The binder comprises the following components: 4% to 8% nitrile rubber powder (from Hengshui Jiansheng Rubber & Plastics Technology Co., Ltd., model P830) and 6% to 10% phenolic resin powder (from Shandong Chenghui New Materials Co., Ltd., model PF214).

[0022] The binder binds the powder particles and fibers together into a whole, providing the bonding force and elasticity required for molding. The composite binder system can take into account both low-temperature elasticity and high-temperature strength.

[0023] The negative thermal expansion material is selected from one or more of zirconium tungstate (sourced from Hubei Hanqing Biomedical Technology Co., Ltd., with a D90 particle size of 1-5μm), β-nepheline (D90 particle size of 2-8μm), and tungsten scandium trioxide (D90 particle size of 3-6μm).

[0024] Heat fade is a major safety hazard for brakes. At high temperatures, the coefficient of friction drops sharply, weakening braking performance. This is closely related to the thermophysical properties of the friction material. Negative thermal expansion materials, which are anomalous functional materials whose volume shrinks with increasing temperature within a specific temperature range, can counteract the thermal expansion effect of positive thermal expansion components such as nitrile rubber powder and reinforcing fibers in the friction material. This reduces the accumulation of thermal stress caused by thermal expansion mismatch within the material, preventing the generation and propagation of microcracks, and minimizing thermal damage such as thermal warping and interface delamination.

[0025] Introducing negative thermal expansion materials such as zirconium tungstate into friction materials can significantly improve the dimensional stability, thermal shock resistance, and structural integrity of brake pads under wide temperature range cycling, extend the service life of the product, and ensure the safety and reliability of the braking process.

[0026] The powder filler is composed of barium sulfate, nano calcium carbonate, glass microspheres and alumina in a mass ratio of (3-6):(6-10):(4-8):(2-6). Each filler adopts a multi-level particle size gradient distribution to achieve close packing of particles, optimize the interface structure of friction materials, improve the mechanical properties and friction stability of materials, and help achieve uniform distribution among the components.

[0027] The particle size classification of each packing material (based on the weight percentage of the total mass of the packing material) is as follows: Barium sulfate: 0.8–2 μm, 20%–40%; 2–5 μm, 40%–60%; 5–10 μm, 10%–30%; Nano-calcium carbonate: 20–40 nm, 15%–30%; 40–60 nm, 45%–65%; 60–100 nm, 10%–25%; Glass microspheres: 40–60 μm, 20%–40%; 60–80 μm, 40%–55%; 80–100 μm, 10%–40%; Alumina: 1–3 μm, 20%–35%; 3–6 μm, 45%–55%; 6–10 μm, 20%–25%.

[0028] Step 2: Mixing The weighed friction modifier, reinforcing fiber, binder and powder filler are placed in a high-speed mixer and mixed evenly to obtain a friction material mixture.

[0029] Step 3: Hot pressing The friction material mixture is loaded into a mold preheated to 140±5℃, and the hot pressing temperature is set to 140℃ and the pressure to 400Kg / cm. 2 .

[0030] During the hot pressing process, in order to expel the gas in the mixture and the adhesive layer and avoid molding defects, a multi-stage degassing cycle is performed: the first stage pressurizes for 12 seconds and then depressurizes for 4 seconds; the second stage pressurizes for 8 seconds and then depressurizes for 4 seconds; the third stage pressurizes for 5 seconds and then depressurizes for 4 seconds; and the fourth stage pressurizes for 5 seconds and then depressurizes for 4 seconds.

[0031] After completing the above degassing cycle, the mold is closed and pressure is maintained for 300 seconds, then the mold is demolded to obtain the friction material blank.

[0032] Step 4: Gradient heat treatment The hot-pressed friction material blank is placed in an oven for gradient heat treatment, as follows: (1) Starting from room temperature, gradually increase the temperature to 140℃~150℃, control the heating time to be 30~60min, and keep warm for 30~60min after the heating is completed; (2) After the above heat preservation is completed, continue to raise the temperature, gradually increasing it from 140℃~150℃ to 160℃~170℃. The heating time is controlled at 45~60min. After the heating is completed, keep the temperature for 30~60min. (3) Then gradually increase the temperature from 160℃~170℃ to 180℃~190℃, control the heating time to be 30~45min, and keep warm for 60~120min; (4) After all the above heat preservation processes are completed, open the equipment door and allow it to cool naturally to room temperature.

[0033] Gradient heat treatment can fully release the internal stress generated inside the friction material blank, resulting in a friction material with stable dimensions and dense internal structure.

[0034] Example 1 The composition of the acrylonitrile-aramid hybrid friction material is as follows by weight percentage: flake graphite 3%, granular graphite 6%, coke powder 4%, friction powder 2%, molybdenum disulfide 3%, acrylonitrile pulp 1.5%, aramid pulp 1%, carbon ceramic fiber 4.5%, mineral fiber 3%, nitrile rubber powder 4%, phenolic resin powder 6%, β-lithium nepheline 3%, and powder filler 59%.

[0035] The powder filler is composed of barium sulfate, nano-calcium carbonate, glass microspheres, and alumina in a mass ratio of 3:6:4:2. Each filler adopts a three-stage particle size gradient compounding system, as detailed below: In barium sulfate, particles with a diameter of 0.8–2 μm account for 30%, particles with a diameter of 2–5 μm account for 40%, and particles with a diameter of 5–10 μm account for 30%. In nano-calcium carbonate, particles with a diameter of 20–40 nm account for 15%, particles with a diameter of 40–60 nm account for 65%, and particles with a diameter of 60–100 nm account for 20%. In the glass microspheres, particles with a diameter of 40–60 μm account for 20%, particles with a diameter of 60–80 μm account for 40%, and particles with a diameter of 80–100 μm account for 40%. In alumina, particles with a diameter of 1–3 μm account for 28%, particles with a diameter of 3–6 μm account for 50%, and particles with a diameter of 6–10 μm account for 22%.

[0036] Weigh out the acrylic pulp (opened), aramid pulp (opened), carbon ceramic fiber, mineral fiber, and powder filler, and put them into a high-speed mixer. Premix at 1500 r / min for 5 min. Then add the remaining components and continue mixing at 2000 r / min for 13 min to obtain a uniform friction material mixture.

[0037] The friction material mixture is loaded into a mold preheated to 135°C, and the hot pressing temperature is set to 140°C and the pressure to 400 kg / cm².2 During the hot pressing process, multiple degassing cycles are performed: The first stage involves pressurizing for 12 seconds followed by depressurization for 4 seconds; the second stage involves pressurizing for 8 seconds followed by depressurization for 4 seconds; the third stage involves pressurizing for 5 seconds followed by depressurization for 4 seconds; and the fourth stage involves pressurizing for 5 seconds followed by depressurization for 4 seconds.

[0038] After completing the above degassing cycle, the mold is closed and pressure is maintained for 300 seconds, then the mold is demolded to obtain the friction material blank.

[0039] The hot-pressed blank is placed in an oven and subjected to gradient heat treatment according to the following process: (1) Gradually increase the temperature from room temperature to 140℃ for 30 minutes, and keep warm for 30 minutes after the temperature increase is completed; (2) Continue heating to 160℃ for 60 minutes, and then keep warm for 60 minutes after heating is completed; (3) Continue to raise the temperature to 180℃ for 30 minutes and hold for 120 minutes; (4) After the heat preservation is completed, open the equipment door and let it cool naturally to room temperature.

[0040] After heat treatment, the friction material blank is removed and subjected to thickness grinding, grooving, and chamfering processes to obtain a friction material reinforced by a mixture of acrylic pulp and aramid.

[0041] Example 2 The composition of the acrylonitrile-aramid hybrid friction material is as follows by weight percentage: flake graphite 4%, granular graphite 8%, coke powder 5%, friction powder 4.5%, molybdenum disulfide 3.5%, acrylonitrile pulp 2%, aramid pulp 1.5%, carbon ceramic fiber 5%, mineral fiber 7%, nitrile rubber powder 5%, phenolic resin powder 8%, zirconium tungstate 6.5%, and powder filler 40%.

[0042] The powder filler is composed of barium sulfate, nano-calcium carbonate, glass microspheres, and alumina in a mass ratio of 5:8:6:4. Each filler adopts a three-stage particle size gradient compounding system, as detailed below: In barium sulfate, particles with a diameter of 0.8–2 μm account for 20%, particles with a diameter of 2–5 μm account for 60%, and particles with a diameter of 5–10 μm account for 20%. In nano-calcium carbonate, particles with a diameter of 20–40 nm account for 30%, particles with a diameter of 40–60 nm account for 45%, and particles with a diameter of 60–100 nm account for 25%. In the glass microspheres, particles with a diameter of 40–60 μm account for 40%, particles with a diameter of 60–80 μm account for 50%, and particles with a diameter of 80–100 μm account for 10%. In alumina, particles with a diameter of 1–3 μm account for 20%, particles with a diameter of 3–6 μm account for 55%, and particles with a diameter of 6–10 μm account for 25%.

[0043] Weighed acrylic pulp (opened), powdered filler, aramid pulp (opened), and friction modifier were added in batches to a high-speed mixer and premixed for 5 minutes at 1500 rpm. The two batches of mixed materials were then added back to the high-speed mixer, along with the remaining components, and mixed for another 13 minutes at 2000 rpm to obtain a uniform friction material mixture.

[0044] The friction material mixture is loaded into a mold preheated to 135°C, and the hot pressing temperature is set to 140°C and the pressure to 400 kg / cm². 2 During the hot pressing process, multiple degassing cycles are performed: The first stage involves pressurizing for 12 seconds followed by depressurization for 4 seconds; the second stage involves pressurizing for 8 seconds followed by depressurization for 4 seconds; the third stage involves pressurizing for 5 seconds followed by depressurization for 4 seconds; and the fourth stage involves pressurizing for 5 seconds followed by depressurization for 4 seconds.

[0045] After completing the above degassing cycle, the mold is closed and pressure is maintained for 300 seconds, then the mold is demolded to obtain the friction material blank.

[0046] The hot-pressed blank is placed in an oven and subjected to gradient heat treatment according to the following process: (1) Gradually increase the temperature from room temperature to 150℃ for 60 minutes, and then keep warm for 60 minutes after the temperature increase is completed; (2) Continue heating to 170℃ for 45 minutes, and then keep warm for 30 minutes after heating is completed; (3) Continue heating to 190℃ for 45 minutes and hold for 60 minutes; (4) After the heat preservation is completed, open the equipment door after 2 hours and let it cool naturally to room temperature.

[0047] After heat treatment, the friction material blank is removed and subjected to thickness grinding, grooving, and chamfering processes to obtain a friction material reinforced by a mixture of acrylic pulp and aramid.

[0048] Example 3 The composition of the acrylonitrile-aramid hybrid friction material is as follows by weight percentage: flake graphite 6%, granular graphite 10%, coke powder 8%, friction powder 6%, molybdenum disulfide 5%, acrylonitrile pulp 2.5%, aramid pulp 2.5%, carbon ceramic fiber 10%, mineral fiber 8%, nitrile rubber powder 8%, phenolic resin powder 10%, tungsten trioxide scandium 12%, and powder filler 12%.

[0049] The powder filler is composed of barium sulfate, nano-calcium carbonate, glass microspheres, and alumina in a mass ratio of 6:10:8:6. Each filler adopts a three-stage particle size gradient compounding system, as detailed below: In barium sulfate, particles with a diameter of 0.8–2 μm account for 40%, particles with a diameter of 2–5 μm account for 50%, and particles with a diameter of 5–10 μm account for 10%. In nano-calcium carbonate, particles with a diameter of 20–40 nm account for 28.5%, particles with a diameter of 40–60 nm account for 61.5%, and particles with a diameter of 60–100 nm account for 10%. In the glass microspheres, particles with a diameter of 40–60 μm account for 30%, particles with a diameter of 60–80 μm account for 55%, and particles with a diameter of 80–100 μm account for 15%. In alumina, particles with a diameter of 1–3 μm account for 35%, particles with a diameter of 3–6 μm account for 45%, and particles with a diameter of 6–10 μm account for 20%.

[0050] Weighed acrylic fiber pulp (opened), granular graphite, coke powder, and powder filler were added to a high-speed mixer and premixed at 1500 r / min for 5 min. The remaining components were added, and the mixture was continued to mix at 2000 r / min for 13 min to obtain a uniform friction material mixture.

[0051] The friction material mixture is loaded into a mold preheated to 135°C, and the hot pressing temperature is set to 140°C and the pressure to 400 kg / cm². 2 During the hot pressing process, multiple degassing cycles are performed: The first stage involves pressurizing for 12 seconds followed by depressurization for 4 seconds; the second stage involves pressurizing for 8 seconds followed by depressurization for 4 seconds; the third stage involves pressurizing for 5 seconds followed by depressurization for 4 seconds; and the fourth stage involves pressurizing for 5 seconds followed by depressurization for 4 seconds.

[0052] After completing the above degassing cycle, the mold is closed and pressure is maintained for 300 seconds, then the mold is demolded to obtain the friction material blank.

[0053] The hot-pressed blank is placed in an oven and subjected to gradient heat treatment according to the following process: (1) Gradually increase the temperature from room temperature to 145℃ for 40 minutes, and then keep warm for 40 minutes after the temperature increase is completed; (2) Continue heating to 165℃ for 50 minutes, and then keep warm for 40 minutes after heating is completed; (3) Continue heating to 185℃ for 40 minutes and hold for 80 minutes; (4) After the heat preservation is completed, open the equipment door after 3 hours and let it cool naturally to room temperature.

[0054] After heat treatment, the friction material blank is removed and subjected to thickness grinding, grooving, and chamfering processes to obtain a friction material reinforced by a mixture of acrylic pulp and aramid.

[0055] Comparative Example 1 Zirconium tungstate was not added, the amount of powder filler added remained unchanged, and everything else was the same as in Example 2.

[0056] Comparative Example 2 Instead of using a three-stage particle size gradient compounding, the powder filler employs a single particle size range for coarse filling, as detailed below: The particle size D90 of barium sulfate is 0.8–10 μm; that of calcium carbonate is 20–100 nm; that of glass microspheres is 40–100 μm; and that of alumina is 1–10 μm.

[0057] Everything else is the same as the process in Example 2.

[0058] Five pieces were randomly selected from the acrylonitrile pulp and aramid hybrid reinforced friction materials obtained in Examples 1-3 and Comparative Examples 1-2, processed to standard size, and tested for physical and chemical properties and tribological properties (US SAE J661 standard). The test parameters (average values) were compared.

[0059] Table 1 Comparison of Physicochemical Properties

[0060] Table 2. Comparison of Friction Properties (Chase Test)

[0061] Comparative Example 1, without the addition of NTE material, could not effectively counteract the thermal expansion effect, resulting in thermal expansion during gradient heat treatment and a slight increase in thickness. Comparative Example 2, using coarse, single-particle-size powder filler, exhibited loose particle packing, numerous internal voids, and weak interfacial bonding, thus exhibiting the highest wear across the entire group.

[0062] Example 1: When acrylic pulp is mixed with aramid pulp, mineral fibers, etc., it easily entangles and agglomerates, forming large fiber clusters. Example 2: When powdered filler is first mixed and dispersed with acrylic pulp, static electricity is less likely to be generated. During stirring, the powder fills the pores of the acrylic fibers, facilitating easier dispersion when mixed with other materials later, and minimizing agglomeration. Example 3: When granular materials collide with acrylic fibers first, entanglement easily occurs using this as a base point, leading to a small amount of fiber agglomeration. The experimental results show that well-dispersed reinforcing fiber materials improve material strength, stabilize the coefficient of friction, and reduce wear.

[0063] The embodiments described above are not exhaustive, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the above description. These embodiments are selected and specifically described in this specification to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to effectively utilize the invention and its modifications. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. A method for preparing a friction material reinforced by a mixture of acrylic pulp and aramid fiber, characterized in that, The preparation steps include the following: S1. Prepare the following components by weight percentage: 18%–35% friction modifier, 10%–23% reinforcing fiber, 10%–18% binder, with the balance being powder filler; The binder comprises 4% to 8% nitrile rubber powder and 6% to 10% phenolic resin powder, and the reinforcing fiber comprises 1.5% to 2.5% acrylic pulp, 1% to 2.5% aramid pulp, 4.5% to 10% carbon ceramic fiber and 3% to 8% mineral fiber. S2. Mix the weighed friction performance modifier, reinforcing fiber, binder and powder filler to obtain friction material mixture; S3. Load the friction material mixture into the mold and hot press it to form a friction material blank; S4. Place the friction material blank in an oven and perform gradient heat treatment to obtain the friction material.

2. The method for preparing the acrylonitrile-aramid hybrid friction material according to claim 1, characterized in that: The friction modifier comprises, by weight percentage, 3% to 6% flake graphite, 6% to 10% granular graphite, 4% to 8% coke powder, 2% to 6% friction powder, and 3% to 5% molybdenum disulfide.

3. The method for preparing the acrylonitrile-aramid hybrid friction material according to claim 1, characterized in that: The powder filler is composed of barium sulfate, nano-calcium carbonate, glass microspheres, and alumina in a mass ratio of 3-6:6-10:4-8:2-6.

4. The method for preparing the acrylonitrile-aramid hybrid friction material according to claim 3, characterized in that: The barium sulfate is graded according to particle size, with 0.8–2 μm accounting for 20%–40% by weight percentage, 2–5 μm accounting for 40%–60%, and 5–10 μm accounting for 10%–30%.

5. The method for preparing the acrylonitrile-aramid hybrid friction material according to claim 3, characterized in that: The nano-calcium carbonate is graded by particle size, with 20–40 nm accounting for 15%–30% by weight, 40–60 nm accounting for 45%–65%, and 60–100 nm accounting for 10%–25%.

6. The method for preparing the acrylonitrile-aramid hybrid friction material according to claim 3, characterized in that: The glass microspheres are graded by particle size, with 40-60 μm accounting for 20%-40% by weight, 60-80 μm accounting for 40%-55%, and 80-100 μm accounting for 10%-40%.

7. The method for preparing the acrylonitrile-aramid hybrid friction material according to claim 3, characterized in that: The alumina is graded by particle size, with 1–3 μm accounting for 20%–35% by weight percentage, 3–6 μm accounting for 45%–55%, and 6–10 μm accounting for 20%–25%.

8. The method for preparing the acrylonitrile-aramid hybrid friction material according to claim 1, characterized in that, In step S4, the gradient heat treatment process is as follows: (1) Raise the temperature from room temperature to 140℃~150℃, with a heating time of 30~60min and a holding time of 30~60min; (2) Continue to raise the temperature to 160℃~170℃, raise the temperature for 45~60min, and keep warm for 30~60min; (3) Raise the temperature again to 180℃~190℃, raise the temperature for 30~45min, and hold for 60~120min; (4) After the heat preservation is completed, open the door and let it cool naturally to room temperature.

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