Electromagnetic brake friction material prepared from granular material and preparation process of electromagnetic brake friction material

Abstract

The invention relates to the technical field of friction materials, and particularly discloses an electromagnetic brake friction material prepared from granules and a preparation process of the electromagnetic brake friction material in order to solve the problem that an existing electromagnetic brake friction plate is difficult to prepare or insufficient in performance. The reinforcing material comprises plasma modified aramid pulp, coupling modified composite mineral fibers, SiO2 coated tetrapod-like zinc oxide whiskers and carbon fiber-aluminum silicon whiskers; the filler comprises modified needle-like wollastonite and organic modified precipitated barium sulfate; the adhesive comprises boron-silicon synergistic modified phenolic resin and modified carboxy nitrile rubber. The raw materials are improved, and granules are prepared by adopting a mixing and crushing process, so that the content of an adhesive can be greatly reduced, meanwhile, the die filling efficiency can be improved, the die thickness and the high-temperature heat fading of the friction material can be reduced, a cold press molding process can be omitted, and the qualification rate of finished friction materials can be improved.

Description

Technical Field

[0001] This invention relates to the field of friction material technology, and more specifically, to an electromagnetic brake friction material made of granular material and its preparation process. Background Technology

[0002] Friction materials are typically made by mixing, molding, and pressing binders, reinforcing materials, and various fillers. The fillers are often fine-particle materials such as mineral powder, metal oxide powder, and organic friction powder. The large specific surface area of ​​fine-particle fillers leads to a large wetting area, thus increasing the amount of binder required. Excessive binder can cause high-temperature degradation in the friction system, significantly reducing the stability of the friction performance. Furthermore, electromagnetic brake friction pads contain a central hole, requiring extremely high flowability of the molding compound for smooth pressing. However, traditional powdered materials require cold pressing followed by hot pressing, a complex and inefficient process that also makes it difficult to guarantee the quality of the finished friction material.

[0003] For example, patent CN112852034 provides a friction material, a synthetic brake shoe, and a preparation method, including the following raw material components and volume parts: 6-26 parts of binder, 10-40 parts of rubber powder, 5-30 parts of reinforcing fiber, 5-21 parts of friction-increasing filler, 10-25 parts of friction-reducing filler, and 5-36 parts of other fillers. The preparation method of the friction material includes the following steps: placing the prepared friction material in the cavity of a cold-pressing mold, adding a pad material and a steel backing, demolding after molding, and then placing it in a hot-pressing mold for hot pressing.

[0004] However, although existing technologies have optimized and improved the raw material formulations of some friction materials, the following problems still exist: First, the adhesive has insufficient heat resistance and is prone to decomposition at high temperatures, leading to a decline in friction performance; second, the reinforcing material has poor dispersibility, making it difficult to form a stable support structure, affecting the material's strength and wear resistance; third, the filler has weak bonding force with the matrix, easily causing agglomeration and reducing the overall performance of the material; and fourth, in the preparation process, the mixing efficiency is low, the fiber dispersibility is poor, and the hot pressing parameters are unreasonable, further affecting the stability of product quality.

[0005] In summary, the current production and manufacturing of materials such as friction pads for electromagnetic brakes faces challenges such as difficulties in filling molding materials, complex processes, low efficiency, and high adhesive content. Summary of the Invention

[0006] The purpose of this invention is to solve the problems of difficulty in preparing or insufficient performance of existing electromagnetic brake friction pads. By improving the raw materials and using a intensive mixing and pulverizing process to produce granules, the binder content can be greatly reduced. At the same time, the molding efficiency can be improved, the mold thickness can be reduced and the high-temperature thermal decay of the friction material can be reduced. It can also eliminate the cold pressing process and improve the yield of finished friction materials.

[0007] This invention is achieved through the following technical solution: This invention provides an electromagnetic brake friction material made of granular material, comprising reinforcing material, filler, binder and compounding agent; Reinforcing materials include plasma-modified aramid pulp, coupling-modified composite mineral fibers, SiO2-coated tetraneedle zinc oxide whiskers, and carbon fiber-aluminum silicon whiskers. The fillers include modified needle-shaped wollastonite and organically modified precipitated barium sulfate; The adhesives include boron-silicon synergistic modified phenolic resin and modified carboxylated nitrile rubber.

[0008] Preferably, in the reinforcing material, the plasma-modified aramid pulp is an aramid pulp with active groups introduced on its surface, the coupling-modified composite mineral fiber is a composite mineral fiber with an organic coating layer formed on its surface by a titanate coupling agent, the SiO2-coated tetraneedle zinc oxide whiskers are tetraneedle zinc oxide whiskers with a SiO2 film coated on their surface, and the carbon fiber-aluminum-silicon whiskers are a composite of short-cut carbon fibers and aluminum-silicon whiskers forming an interwoven structure.

[0009] Preferably, in the filler, the modified acicular wollastonite is made from acicular wollastonite as raw material, first modified by sodium secondary alkyl sulfonate, and then modified by γ-aminopropyltriethoxysilane to form modified acicular wollastonite with both oleophilic and hydrophilic groups on the surface. Organically modified precipitated barium sulfate is an inorganic core-organic shell structured composite material with phenolic resin prepolymer coated on the surface of precipitated barium sulfate.

[0010] Preferably, in the adhesive, the boron-silicon synergistic modified phenolic resin is a compound containing a BO-Si network structure formed by first modifying phenolic resin with boron and then introducing silicon for secondary modification.

[0011] Preferably, in the adhesive, the modified carboxyl-based nitrile rubber is a modified rubber whose molecular chain contains polar groups, formed by grafting carboxyl groups onto nitrile rubber and then chemically modifying it with maleic anhydride.

[0012] Preferably, by mass parts, the reinforcing material includes 1-3 parts plasma-modified aramid pulp, 1-3 parts acrylic pulp, 10-15 parts coupling-modified composite mineral fiber, 1-2 parts SiO2-coated tetraneedle zinc oxide whiskers, and 1-3 parts carbon fiber-aluminum silicon whiskers. The filler includes 10-15 parts modified acicular wollastonite, 8-15 parts organically modified precipitated barium sulfate, 5-10 parts alumina, 8-12 parts light calcium carbonate, 4-8 parts flake graphite, 1-3 parts carbon black, and 5-8 parts modified silica. The adhesive comprises 3-5 parts boron-silicon synergistic modified phenolic resin and 10-15 parts modified carboxylated butadiene-acrylonitrile rubber; The compounding agents include 0.1-0.5 parts vulcanizing agent, 0.3-1 parts accelerator, and 0.1-0.5 parts stearic acid.

[0013] The present invention also provides a preparation process for the above-mentioned electromagnetic brake friction material made of granular material, comprising the following steps: S1 Internal mixing: The raw materials of each component are put into the internal mixer in the order of binder, reinforcing material, filler and compounding agent, and mixed at 50~80℃ for 10~30 minutes to obtain the internally mixed material; S2 Crushing and Screening: The intensively mixed material is crushed and screened to obtain the initial material of the required particle size; S3 Hot pressing: Place the granular material at 175±5℃ and hot press at 10~30MPa for 60~80s / mm; S4 Heat treatment: The hot-pressed material is placed in a heat treatment furnace, heated, cooled, and then removed. S5 Grinding: Surface grinding of heat-treated granules to obtain electromagnetic brake friction material made of granules.

[0014] Preferably, in step S2, the particle size is controlled to be 1~2mm after sieving.

[0015] Preferably, in step S3, before holding the pressure, 3 to 5 venting processes are performed, each venting process including 10 seconds of pressing and 2 seconds of venting.

[0016] Preferably, in step S4, the temperature conditions of the heat treatment process include the following stages: The temperature is raised from room temperature to 120±5℃ over 0.8-1.2 hours and held for 1-2 hours. Then, after 0.8-1.2 hours, the temperature is increased from 120±5℃ to 180±5℃ and held for 1 hour. Then, the temperature is increased from 180±5℃ to 220±5℃ over 0.8-1.2 hours and held for 6-10 hours. Finally, cool it in the furnace to 50°C or below, then remove it.

[0017] The technical solution of the present invention has the following beneficial effects: (1) A boron-silicon synergistic modified phenolic resin and modified carboxylated nitrile rubber synergistic system is used as an adhesive. Through the synergistic modification of boron and silicon, a BO-Si network structure is introduced into the molecular chain of phenolic resin, which increases the decomposition temperature and high-temperature carbon residue of the resin. Combined with maleic anhydride graft-modified carboxylated nitrile rubber, an interpenetrating network of rigid skeleton and flexible chain segments is constructed to improve the tensile strength and stability of the material, effectively suppress high-temperature degradation, and ensure the stability of friction performance. In addition, maleic anhydride graft modification makes the carboxylated nitrile rubber and boron-silicon modified phenolic resin highly compatible, avoiding the generation of wear debris due to interface peeling during friction.

[0018] (2) Traditional reinforcing materials tend to agglomerate in the matrix due to their surface inertness, resulting in stress concentration points and insufficient strength. This invention enhances the interfacial bonding strength of aramid pulp by treating it with air plasma, improves the dispersion uniformity of composite mineral fibers with titanate coupling agent, and then uses SiO2 to coat tetrane needle-shaped zinc oxide whiskers and carbon fiber-aluminum silicon whiskers to form a three-dimensional reinforcing structure and a dot-line interwoven structure, effectively solving the agglomeration problem and improving impact strength.

[0019] (3) A composite system of modified needle-shaped wollastonite and core-shell structured barium sulfate is used as a filler. The needle-shaped wollastonite is modified by sodium secondary alkyl sulfonate and γ-aminopropyltriethoxysilane. The surface has both oleophilic and hydrophilic groups, which can achieve good bonding with rubber and inorganic fillers at the same time, thereby improving the bonding strength of the interface. The inorganic core and organic shell modification of precipitated barium sulfate can not only improve its compatibility with the matrix, but also enhance the fluidity of the granules, achieve better filling effect, and reduce the agglomeration problem of the granules during the reheat pressing process.

[0020] (4) In this invention, each component raw material is added in a specific order of binder, reinforcing material, filler and compounding agent. First, the binder and reinforcing material form a preliminary matrix, then the filler is added and evenly dispersed, and finally the compounding agent is added to ensure the uniformity of the vulcanization system. This can effectively improve the uniformity of the mixture, and the process improvement method is simple and operable, and has strong scalability. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, they are performed according to conventional conditions or conditions recommended by the manufacturer; where the manufacturers of the instruments, equipment, reagents, or raw materials used are not specified, they are all conventional products that can be purchased commercially.

[0022] This invention provides an electromagnetic brake friction material made of granular material, comprising the following raw material system (by mass parts): (1) Reinforcing materials: including 1-3 parts of plasma-modified aramid pulp, 1-3 parts of acrylonitrile pulp, 10-15 parts of coupling-modified composite mineral fiber, 1-2 parts of SiO2-coated tetra-needle zinc oxide whiskers, and 1-3 parts of carbon fiber-aluminum silicon whiskers.

[0023] Plasma-modified aramid pulp: Aramid pulp is treated with air plasma to introduce active groups such as hydroxyl and carboxyl groups on the fiber surface, increasing the surface energy from 40mN / m to 65mN / m and improving the interfacial bonding force with adhesives by 30%.

[0024] Coupling-modified composite mineral fibers: After heating and drying the composite mineral fibers, add 1-2 wt% of titanate coupling agent (NDZ-101), place them in a high-speed mixer, and stir at high speed to form an organic coating layer on the fiber surface, which significantly improves dispersibility and forms a uniform support network in the matrix.

[0025] SiO2-coated tetrapter zinc oxide whiskers: A sol-gel method is used to coat the surface of tetrapter zinc oxide whiskers with a SiO2 film with a thickness of 5-10 nm. This method retains the three-dimensional reinforced structure, improves the compatibility with the organic matrix, and solves the agglomeration problem.

[0026] Carbon fiber-aluminum-silicon whiskers: 0.5-1wt% of short-cut carbon fibers with a length of 0.5-1mm are introduced and compounded with aluminum-silicon whiskers in a ratio of 1:2~5. The point-line interwoven structure is built by utilizing the aspect ratio advantage of carbon fibers. Through mechanical stirring and ultrasonic waves with a power of 500W, the materials are dispersed in a coordinated manner, which improves the dispersion uniformity of the reinforcing material in the matrix by 40%.

[0027] (2) Filler: including 10-15 parts modified needle wollastonite, 8-15 parts organic modified precipitated barium sulfate, 5-10 parts alumina, 8-12 parts light calcium carbonate, 4-8 parts flake graphite, 1-3 parts carbon black, and 5-8 parts modified silica.

[0028] Modified needle-shaped wollastonite: First, it is modified by sodium secondary alkyl sulfonate, and then modified by adding γ-aminopropyltriethoxysilane. The specific process is as follows: Wollastonite modified by surfactant is added to 1wt% KH550 and ethanol solution and stirred at 60℃ to react, so that the surface of the filler has both oleophilic and hydrophilic groups, and the bonding force with organic matrix and inorganic filler is improved.

[0029] Organically modified precipitated barium sulfate: A layer of phenolic resin prepolymer is coated on the surface of barium sulfate using an in-situ polymerization method to form an inorganic core-organic shell structure. The particle size is controlled at 5-10μm, which increases the interfacial bonding strength between barium sulfate and the matrix by 25% and improves the flowability of the granules.

[0030] This invention designs a filler gradient distribution system that combines rigidity and flexibility. The outer layer is a 1000-mesh modified silica transition layer to improve interfacial compatibility; the middle layer is a 400-mesh precipitated barium sulfate layer to provide rigid support; and the inner layer is a flake graphite layer to form a lubricating layer and reduce friction coefficient fluctuations. This gradient distribution design allows the bonding force between the filler and the matrix to exhibit a gradient change, ensuring overall strength while retaining the toughness and lubricity of the friction material, resulting in a 20-30% reduction in wear rate compared to traditional formulations.

[0031] (3) Adhesive: including 3-5 parts boron-silicon synergistic modified phenolic resin and 10-15 parts modified carboxylated nitrile rubber.

[0032] Boron-silicon synergistic modification of phenolic resin: Boron modification is performed first, followed by secondary modification with the introduction of silicon. Phenolic resin is mixed with boric acid (3-5 wt%) and tetraethyl orthosilicate (2-4 wt%) in xylene solvent and refluxed at 80°C to form a network structure containing BO-Si bonds. After modification, the resin decomposition temperature increases to over 550°C, and the carbon residue at 1000°C increases to over 65%, representing a 10% improvement compared to boron-only modification.

[0033] Modified carboxylated nitrile butadiene rubber: Maleic anhydride is used to chemically modify the grafted carboxylated nitrile butadiene rubber. During the initial mixing stage, 0.5-1 wt% MAH and 0.1-0.3 wt% dicumyl peroxide (DCP) are added, and the mixture is reacted at 120℃, introducing more polar groups into the rubber molecular chain. The modified rubber exhibits a 20% improvement in compatibility with phenolic resin and a 15% increase in interfacial bonding strength.

[0034] A three-dimensional interpenetrating network structure was constructed using resin, rubber, and nanofillers. Boron-silicon modified phenolic resin forms a rigid framework, providing high-temperature stability; maleic anhydride-grafted carboxylated butadiene-acrylonitrile rubber forms flexible segments, improving toughness; and 1-2 wt% of nano-montmorillonite modified with octadecyltrimethylammonium chloride is added to further enhance heat resistance and mechanical properties through intercalation. After synergistic modification, the tensile strength retention rate of the adhesive system increased from 70% to over 85% after aging at 250℃ for 100 hours.

[0035] (4) Compounding agents: including 0.1-0.5 parts vulcanizing agent, 0.3-1 parts accelerator, and 0.1-0.5 parts stearic acid.

[0036] The electromagnetic brake friction material made of granular material provided by the present invention is prepared by the following steps: S1 Secret Refinement: Weigh each component raw material according to the proportion, and put them into the internal mixer in the order of binder, reinforcing material, filler and compounding agent for internal mixing. Control the mixing temperature to 50~80℃, the top bolt pressure to 0.5~0.7MPa, the rotor speed to 30~50r / min, and the mixing time to 10~30min to obtain the internally mixed material.

[0037] Following the above feeding sequence ensures that all components are fully mixed, avoiding uneven dispersion caused by adding filler too early.

[0038] S2 Crushing and Screening: The well-mixed material is placed in a crusher for crushing, and then sieved to strictly control the particle size to 1~2mm to obtain granular material.

[0039] This particle size range ensures good flowability of the granules during subsequent hot pressing, while avoiding dust problems caused by excessively small particle sizes and uneven molding problems caused by excessively large particle sizes.

[0040] S3 Hot Press: A 100T four-column hydraulic press is used for hot pressing. The granules are evenly put into the hot pressing mold and spread out. The pressing temperature is controlled at 175±5℃, the pressing pressure is 10~30MPa, and the holding time is 60~80s / mm. Before holding the pressure, the air is vented 3~5 times according to the rhythm and process of pressing for 10s and venting for 2s. The venting operation can effectively remove air from the granules and prevent defects such as bubbles and pores from appearing in the finished product. After holding the pressure, the friction material semi-finished product is obtained.

[0041] S4 heat treatment: The semi-finished friction material is placed in a heat treatment furnace and heated from room temperature to 120±5℃ over 0.8-1.2 hours, and held for 1-2 hours; then heated from 120±5℃ to 180±5℃ over 0.8-1.2 hours, and held for 1 hour; then heated from 180±5℃ to 220±5℃ over 0.8-1.2 hours, and held for 6-10 hours; finally, it is cooled to 50℃ in the furnace and removed.

[0042] The stepped heating and heat preservation process can slowly release the internal stress of the material, further promote the cross-linking reaction, and improve the stability of the material performance.

[0043] S5 Grinding: The heat-treated friction material is surface-ground using a double-end belt abrasive mill to remove surface oxide scale, burrs, and flash, ensuring the surface flatness and dimensional accuracy of the friction material to meet the assembly requirements of the electromagnetic brake.

[0044] Example 1 This embodiment mainly focuses on the modified raw materials required for preparing the electromagnetic brake friction material made of granular material according to the present invention.

[0045] (1) Preparation of plasma-modified aramid pulp: Aramid pulp was taken and treated with air plasma at a power of 300W for 30s to obtain plasma-modified aramid pulp.

[0046] (2) Preparation of coupling-modified composite mineral fibers: Rock wool fiber, glass fiber and carbon fiber were mixed to form a composite mineral fiber. The composite mineral fiber was dried at 80°C for 2 hours, and 1.5% of its mass of titanate coupling agent was added. The mixture was then placed in a high-speed mixer and treated at 800 rpm for 15 minutes to obtain the coupling-modified composite mineral fiber.

[0047] (3) Preparation of SiO2-coated tetrane needle-like zinc oxide whiskers: Four needle-shaped zinc oxide whiskers were taken, and a SiO2 film with a thickness of about 7 nm was coated on the surface of the four needle-shaped zinc oxide whiskers using the sol-gel method to obtain SiO2 coated four needle-shaped zinc oxide whiskers.

[0048] (4) Preparation of carbon fiber-aluminum silicon whiskers: Take aluminum-silicon whiskers and add short-cut carbon fibers with a length of about 0.8 mm at a mass ratio of 1:3. Use ultrasonic co-dispersion with a power of 500 W and a time of 10 min to obtain carbon fiber-aluminum-silicon whiskers.

[0049] (5) Preparation of modified acicular wollastonite: First, the acicular wollastonite was treated with sodium secondary alkyl sulfonate. Specifically, the acicular wollastonite was soaked in a 2% (w / w) dilute hydrochloric acid solution for 1.5 hours, filtered, rinsed three times with deionized water, and dried at 95°C for 1.5 hours. Then, the acicular wollastonite was placed in deionized water with a solid-liquid ratio of 20:100 and ultrasonically vibrated for 45 minutes to form a suspension. Next, a saturated sodium secondary alkyl sulfonate aqueous solution was added in a 60°C constant temperature water bath, with the amount of sodium secondary alkyl sulfonate added being 2% of the mass of the acicular wollastonite. Sodium hydroxide solution was added dropwise until the pH of the reaction system reached 7.2. The reaction was ultrasonically vibrated for 2 hours, then allowed to stand for 7 minutes, filtered, rinsed five times with deionized water, and dried at 80°C for 2 hours.

[0050] The modified acicular wollastonite was further modified by γ-aminopropyltriethoxysilane. Specifically, the acicular wollastonite treated with sodium secondary alkyl sulfonate was added to a 1 wt% solution of KH550 and ethanol, and stirred at 60°C for 2 h to obtain the modified acicular wollastonite.

[0051] (6) Preparation of organically modified precipitated barium sulfate: Take precipitated barium sulfate and use an in-situ polymerization method to form a phenolic resin prepolymer coating layer on the precipitated barium sulfate, thus obtaining organically modified precipitated barium sulfate.

[0052] (7) Preparation of boron-silicon synergistic modified phenolic resin: Phenolic resin was mixed with 4 wt% boric acid and 3 wt% tetraethyl orthosilicate in xylene solvent and refluxed at 80°C for 3 h to form a boron-silicon synergistic modified phenolic resin with a network structure containing BO-Si bonds.

[0053] (8) Preparation of modified carboxylated butadiene-acrylonitrile rubber: Take carboxyl-grafted nitrile rubber, add 0.8wt% MAH and 0.2wt% dicumyl peroxide in the initial stage of internal mixing, and react at 120℃ for 15min to obtain modified carboxyl-grafted nitrile rubber.

[0054] (9) Preparation of modified silica: The silica was placed in a drying oven and dried at 100℃ for 1.5 hours. Then the silica was put into a high-speed mixer and stirred at 95℃ for 55 minutes with the speed controlled at 800 rpm. Si69 was then added, and the amount of Si69 added was controlled to be 4% of the mass of silica. The mixture was stirred for another 40 minutes, heated to 130℃, held for 2 hours, and cooled to room temperature to obtain modified silica.

[0055] Example 2 Step 1: Take 1 part by weight of plasma-modified aramid pulp, 2 parts of acrylic pulp, 15 parts of coupling-modified composite mineral fiber, 1 part of SiO2-coated tetrane needle-shaped zinc oxide whiskers, 1.5 parts of carbon fiber-aluminum-silicon whiskers, 14 parts of modified needle-shaped wollastonite, 10 parts of organically modified precipitated barium sulfate, 5 parts of alumina, 8 parts of light calcium carbonate, 5 parts of flake graphite, 1.2 parts of carbon black, 5 parts and 3 parts of boron-silicon synergistic modified phenolic resin, 14 parts of modified carboxylated nitrile rubber, 0.3 parts of vulcanizing agent, 0.3 parts of accelerator, and 0.1 parts of stearic acid. All the above raw materials are from the raw materials prepared in Example 1 or existing raw materials that can be directly purchased.

[0056] Step 2: Add the above raw materials and components into the internal mixer in the order of binder, reinforcing material, filler and compounding agent. Set the mixing temperature to 60℃, the top jack pressure to 0.6MPa, the rotor speed to 45r / min, and mix for 20min to obtain the internally mixed material.

[0057] Step 3: Crush the intensively mixed material and then sieve it to select granules with a particle size in the range of 1~2mm.

[0058] Step 4: Use a 100T four-column hydraulic press for hot pressing. Put the granular material into the hot pressing mold, spread it flat, and press it. The pressing temperature is controlled at 175±5℃, the pressing pressure is 20MPa, and the holding time is 70s / mm. Before holding the pressure, vent the air 4 times alternately by pressing for 10s and venting for 2s. After the holding pressure is completed, the friction material semi-finished product is obtained.

[0059] Step 5: Place the friction material semi-finished product in a heat treatment furnace, raise the temperature from room temperature to 120±5℃ over 1 hour, and hold for 1.5 hours; then raise the temperature from 120±5℃ to 180±5℃ over 1 hour, and hold for 1 hour; then raise the temperature from 180±5℃ to 220±5℃ over 1 hour, and hold for 8 hours; finally, cool it in the furnace to below 50℃ and remove it.

[0060] Step 6: Grind the heat-treated friction material using a double-end belt mill to remove surface oxide scale, burrs, flash, etc., to obtain the electromagnetic brake friction material.

[0061] Example 3 The difference between this embodiment and Embodiment 2 is that the raw materials include, by mass, 2 parts of plasma-modified aramid pulp, 2.5 parts of acrylic pulp, 10 parts of coupling-modified composite mineral fiber, 1.2 parts of SiO2-coated tetrane needle-shaped zinc oxide whiskers, 3 parts of carbon fiber-aluminum-silicon whiskers, 12 parts of modified needle-shaped wollastonite, 15 parts of organically modified precipitated barium sulfate, 8 parts of alumina, 12 parts of light calcium carbonate, 6 parts of flake graphite, 1.8 parts of carbon black, 6 parts of modified silica, 4 parts of boron-silicon synergistic modified phenolic resin, 13 parts of modified carboxylated nitrile rubber, 0.4 parts of vulcanizing agent, 0.4 parts of accelerator, and 0.2 parts of stearic acid.

[0062] Example 4 The difference between this embodiment and Embodiment 2 is that the raw materials include, by mass, 2.5 parts of plasma-modified aramid pulp, 1 part of acrylic pulp, 13 parts of coupling-modified composite mineral fiber, 1.5 parts of SiO2-coated tetrane needle-shaped zinc oxide whiskers, 2 parts of carbon fiber-aluminum-silicon whiskers, 10 parts of modified needle-shaped wollastonite, 8 parts of organically modified precipitated barium sulfate, 10 parts of alumina, 10 parts of light calcium carbonate, 8 parts of flake graphite, 2.5 parts of carbon black, 8 parts of modified silica, 5 parts of boron-silicon synergistic modified phenolic resin, 12 parts of modified carboxyl-based nitrile rubber, 0.5 parts of vulcanizing agent, 0.5 parts of accelerator, and 0.3 parts of stearic acid.

[0063] Comparative Example 1 The difference between this comparative example and Example 2 is that the raw materials include, by mass, 0.5 parts of plasma-modified aramid pulp, 1 part of acrylic pulp, 3 parts of coupling-modified composite mineral fiber, 0.5 parts of SiO2-coated tetrane needle-shaped zinc oxide whiskers, 0.5 parts of carbon fiber-aluminum-silicon whiskers, 5 parts of modified needle-shaped wollastonite, 3.5 parts of organically modified precipitated barium sulfate, 10 parts of alumina, 10 parts of light calcium carbonate, 8 parts of flake graphite, 2.5 parts of carbon black, 8 parts of modified silica, 1 part of boron-silicon synergistic modified phenolic resin, 5 parts of modified carboxylated nitrile rubber, 0.5 parts of vulcanizing agent, 0.5 parts of accelerator, and 0.3 parts of stearic acid.

[0064] Comparative Example 2 The difference between this comparative example and Example 2 is that the raw materials include, by mass, 5 parts of plasma-modified aramid pulp, 1 part of acrylic pulp, 18 parts of coupling-modified composite mineral fiber, 3 parts of SiO2-coated tetrane needle-shaped zinc oxide whiskers, 5 parts of carbon fiber-aluminum-silicon whiskers, 18 parts of modified needle-shaped wollastonite, 18 parts of organically modified precipitated barium sulfate, 10 parts of alumina, 10 parts of light calcium carbonate, 8 parts of flake graphite, 2.5 parts of carbon black, 8 parts of modified silica, 8 parts of boron-silicon synergistic modified phenolic resin, 18 parts of modified carboxylated nitrile rubber, 0.5 parts of vulcanizing agent, 0.5 parts of accelerator, and 0.3 parts of stearic acid.

[0065] Comparative Example 3 The difference between this comparative example and Example 2 is that: untreated aramid pulp is used instead of plasma-modified aramid pulp, untreated composite mineral fibers are used instead of coupling-modified composite mineral fibers, untreated zinc oxide whiskers are used instead of SiO2-coated tetra-needle zinc oxide whiskers, and aluminum-silicon whiskers are used instead of carbon fiber-aluminum-silicon whiskers.

[0066] Comparative Example 4 The difference between this comparative example and Example 2 is that the modified acicular wollastonite was replaced with untreated acicular wollastonite, and the organically modified precipitated barium sulfate was replaced with untreated precipitated barium sulfate.

[0067] Comparative Example 5 The difference between this comparative example and Example 2 is that the boron-silicon synergistic modified phenolic resin was replaced with untreated phenolic resin, and the modified carboxylated nitrile rubber was replaced with untreated nitrile rubber.

[0068] Test case Samples: Examples 2-4, Comparative Examples 1-5 (1) The friction properties and wear of the above friction material samples were determined according to the method of GB-T 5764-2023 "Automotive Clutch Face Plates". The results are summarized in Table 1 below: Table 1 Test results of friction properties of different friction material samples

[0069] (2) Using the above-mentioned friction material samples, they were assembled into electromagnetic brakes. The rated torque of the brakes was set to 1.5 N·m. Static torque tests were performed on the assembled electromagnetic brakes according to the method in GB / T 34114-2017 "General Technical Conditions for Electromagnetic Brakes for Electric Motors". Each sample was tested twice. The results are summarized in Table 2 below: Table 2 Static torque test results of samples of different friction materials

[0070] The above experiments show that, based on the sample material properties and performance results measured in Tables 1 and 2, the electromagnetic brake friction material proposed in this invention, through improvements to the raw materials and the synergistic effect between the components, and by using granules prepared by a compaction and pulverization process, can achieve significantly lower wear rate and good friction performance under conditions of lower binder usage, even after high temperature or repeated use. Furthermore, the electromagnetic brake friction material of this invention has a simple preparation process and strong scalability.

[0071] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An electromagnetic brake friction material made of granular material, characterized in that, Includes reinforcing materials, fillers, adhesives, and compounding agents; Reinforcing materials include plasma-modified aramid pulp, coupling agent-modified composite mineral fibers, SiO2-coated tetraneedle zinc oxide whiskers, and carbon fiber-aluminum silicon whiskers. The fillers include modified needle-shaped wollastonite and organically modified precipitated barium sulfate; The adhesives include boron-silicon synergistic modified phenolic resin and modified carboxylated nitrile rubber.

2. The electromagnetic brake friction material made of granular material according to claim 1, characterized in that, In the reinforcing materials, plasma-modified aramid pulp is aramid pulp with active groups introduced on its surface, coupling-modified composite mineral fiber is composite mineral fiber with an organic coating layer formed on its surface by titanate coupling agent, SiO2-coated tetraneedle zinc oxide whiskers are tetraneedle zinc oxide whiskers with a SiO2 film coated on their surface, and carbon fiber-aluminum silicon whiskers are composites of short-cut carbon fibers and aluminum silicon whiskers that form an interwoven structure.

3. The electromagnetic brake friction material made of granular material according to claim 1, characterized in that, In the filler, modified acicular wollastonite is made from acicular wollastonite as raw material. It is first modified by sodium secondary alkyl sulfonate and then modified by γ-aminopropyltriethoxysilane to form modified acicular wollastonite with both oleophilic and hydrophilic groups on the surface. Organically modified precipitated barium sulfate is an inorganic core-organic shell structured composite material with phenolic resin prepolymer coated on the surface of precipitated barium sulfate.

4. The electromagnetic brake friction material made of granular material according to claim 1, characterized in that, In adhesives, boron-silicon synergistic modified phenolic resin is a compound containing a BO-Si network structure formed by first modifying phenolic resin with boron and then introducing silicon for secondary modification.

5. The electromagnetic brake friction material made of granular material according to claim 4, characterized in that, Among adhesives, modified carboxylated nitrile rubber is a modified rubber whose molecular chain contains polar groups, formed by grafting carboxyl groups onto nitrile rubber and then chemically modifying it with maleic anhydride.

6. The electromagnetic brake friction material made of granular material according to claim 1, characterized in that, By mass fraction, the reinforcing materials include 1-3 parts plasma-modified aramid pulp, 1-3 parts acrylic pulp, 10-15 parts coupling-modified composite mineral fiber, 1-2 parts SiO2-coated tetra-needle zinc oxide whiskers, and 1-3 parts carbon fiber-aluminum-silicon whiskers. The filler includes 10-15 parts modified acicular wollastonite, 8-15 parts organically modified precipitated barium sulfate, 5-10 parts alumina, 8-12 parts light calcium carbonate, 4-8 parts flake graphite, 1-3 parts carbon black, and 5-8 parts modified silica. The adhesive comprises 3-5 parts boron-silicon synergistic modified phenolic resin and 10-15 parts modified carboxylated butadiene-acrylonitrile rubber; The compounding agents include 0.1-0.5 parts vulcanizing agent, 0.3-1 parts accelerator, and 0.1-0.5 parts stearic acid.

7. A process for preparing the electromagnetic brake friction material made of granular material as described in any one of claims 1 to 6, characterized in that, Includes the following steps: S1 Internal mixing: The raw materials of each component are put into the internal mixer in the order of binder, reinforcing material, filler and compounding agent, and mixed at 50~80℃ for 10~30 minutes to obtain the internally mixed material; S2 Crushing and Screening: The intensively mixed material is crushed and screened to obtain the initial material of the required particle size; S3 Hot pressing: Place the granular material at 175±5℃ and hot press at 10~30MPa for 60~80s / mm; S4 Heat treatment: The hot-pressed material is placed in a heat treatment furnace, heated, cooled, and then removed. S5 Grinding: Surface grinding of heat-treated granules to obtain electromagnetic brake friction material made of granules.

8. The preparation process of the electromagnetic brake friction material made of granular material according to claim 7, characterized in that, In step S2, the particle size is controlled to be 1~2mm after sieving.

9. The preparation process of the electromagnetic brake friction material made of granular material according to claim 7, characterized in that, In step S3, before holding the pressure, 3 to 5 venting operations are performed. Each venting process includes 10 seconds of pressing and 2 seconds of venting.

10. The preparation process of the electromagnetic brake friction material made of granular material according to claim 7, characterized in that, In step S4, the temperature conditions of the heat treatment process include the following stages: The temperature is raised from room temperature to 120±5℃ over 0.8-1.2 hours and held for 1-2 hours. Then, after 0.8-1.2 hours, the temperature is increased from 120±5℃ to 180±5℃ and held for 1 hour. Then, the temperature is increased from 180±5℃ to 220±5℃ over 0.8-1.2 hours and held for 6-10 hours. Finally, cool it in the furnace to 50°C or below, then remove it.

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