Friction material for electromagnetic brake with stable friction coefficient and preparation method thereof

Abstract

The present invention relates to the field of friction materials, and discloses a friction material for an electromagnetic brake with a stable friction coefficient and a preparation method thereof, wherein the adhesive comprises polysiloxane-modified phenolic resin, benzoxazine, and nitrile rubber powder; the reinforcing material comprises 1414 para-aramid pulp, calcium sulfate whiskers, composite mineral fibers, copper fibers, and modified needle-shaped wollastonite; the friction-increasing material comprises macroporous nutshell activated carbon, friction particles, garnet powder, barite, and nano hafnium nitride; the friction-reducing material comprises fluorinated graphite, nylon, and composite modified hydroxy silicate; the composite modified hydroxy silicate refers to a hydroxy silicate modified by diisocyanate and stearic acid, and then compounded with silane-modified micro-nano calcium carbonate. The friction material provided by the present invention is used to improve the braking stability of an electromagnetic brake and reduce equipment vibration.

Description

Technical Field

[0001] The invention relates to the technical field of friction materials, in particular to a friction material for an electromagnetic brake with a stable friction coefficient and a preparation method thereof. Background Art

[0002] Electromagnetic brakes are widely used in various industries, such as servo motors, aerial work vehicles, forklifts, elevators, wind power, robots and other industries. Friction materials are the key materials of electromagnetic brakes, and different industries have different requirements for friction materials. For example, some industries require stable braking torque to reduce equipment vibration. At present, most friction materials are within 200°C, and the friction coefficient will increase with the increase of temperature. The main reason is that the adhesives of most friction materials are phenolic resin and rubber, and the lubricating materials are mainly flake graphite. The phenolic resin and rubber matrix soften with the increase of temperature, the actual contact surface increases, and the friction coefficient increases. At the same time, as the pressure increases, when it reaches a certain critical value, the friction coefficient will also decrease, resulting in fluctuations in the friction coefficient. At present, the friction coefficient of most friction materials fluctuates greatly with temperature and pressure changes.

[0003] Based on this, the present invention provides a friction material with a stable friction coefficient to improve the braking stability of the electromagnetic brake and reduce equipment vibration. Summary of the invention

[0004] Technical problems solved by the present invention:

[0005] It is used to solve the problem that the friction coefficient of the current friction material fluctuates greatly with temperature and pressure changes.

[0006] The technical solution adopted by the present invention is:

[0007] In view of the above technical problems, an object of the present invention is to provide a friction material for an electromagnetic brake with a stable friction coefficient and a preparation method thereof.

[0008] The specific contents are as follows:

[0009] First, the present invention provides a friction material for an electromagnetic brake with a stable friction coefficient, wherein the raw material components include an adhesive, a reinforcing material, a friction-increasing filler, and a friction-reducing filler;

[0010] The adhesive includes polysiloxane-modified phenolic resin, benzoxazine, and nitrile rubber powder;

[0011] The reinforcing materials include 1414 para-aramid pulp, calcium sulfate whiskers, composite mineral fibers, copper fibers, and modified needle-shaped wollastonite;

[0012] Friction-increasing materials include macroporous nutshell activated carbon, friction particles, garnet powder, barite, and nano-hafnium nitride;

[0013] Friction-reducing materials include graphite fluoride, nylon, and composite modified hydroxy silicate;

[0014] The composite modified hydroxy silicate refers to a hydroxy silicate modified by diisocyanate and stearic acid and then compounded with silane-modified micro-nano calcium carbonate.

[0015] According to some preferred embodiments, the raw material components, measured by weight, include 10 to 20 parts of adhesive, 50 to 60 parts of reinforcing material, 30 to 50 parts of friction-increasing filler, and 10 to 20 parts of friction-reducing filler.

[0016] According to some preferred embodiments, the raw material components, by weight, include 2 to 4 parts of polysiloxane-modified phenolic resin, 6 to 8 parts of nitrile rubber powder, 8 to 10 parts of benzoxazine, 1 to 5 parts of 1414 para-aramid pulp, 10 to 20 parts of calcium sulfate whiskers, 20 to 30 parts of composite mineral fibers, 2 to 8 parts of copper fibers, 8 to 14 parts of modified needle-shaped wollastonite, 5 to 10 parts of macroporous nutshell activated carbon, 10 to 20 parts of friction particles, 6 to 10 parts of barite, 3 to 5 parts of garnet powder, 2-8 parts of nano-hafnium nitride, 3 to 6 parts of graphite fluoride, 2 to 5 parts of nylon, and 2 to 5 parts of composite modified hydroxy silicate.

[0017] According to some more preferred embodiments, the components of the raw materials are, by weight, combination one, combination two or combination three;

[0018] Combination 1: 3 parts of polysiloxane modified phenolic resin, 6 parts of nitrile rubber powder, 10 parts of benzoxazine, 2 parts of 1414 para-aramid pulp, 12 parts of calcium sulfate whiskers, 30 parts of composite mineral fiber, 5 parts of copper fiber, 10 parts of modified needle-shaped wollastonite, 6 parts of macroporous nutshell activated carbon, 15 parts of friction particles, 6 parts of barite, 5 parts of garnet powder, 3 parts of nano-hafnium nitride, 4 parts of graphite fluoride, 4 parts of nylon, and 3 parts of composite modified hydroxy silicate.

[0019] Combination 2: 2 parts of polysiloxane modified phenolic resin, 8 parts of nitrile rubber powder, 8 parts of benzoxazine, 3 parts of 1414 para-aramid pulp, 15 parts of calcium sulfate whiskers, 25 parts of composite mineral fibers, 3 parts of copper fibers, 8 parts of modified needle-shaped wollastonite, 8 parts of macroporous fruit shell activated carbon, 20 parts of friction particles, 8 parts of barite, 3 parts of garnet powder, 6 parts of nano-hafnium nitride, 6 parts of graphite fluoride, 2 parts of nylon, and 4 parts of composite modified hydroxy silicate.

[0020] Combination three: 4 parts of polysiloxane modified phenolic resin, 6 parts of nitrile rubber powder, 9 parts of benzoxazine, 1 part of 1414 para-aramid pulp, 20 parts of calcium sulfate whiskers, 20 parts of composite mineral fibers, 6 parts of copper fibers, 12 parts of modified needle-shaped wollastonite, 10 parts of macroporous nutshell activated carbon, 14 parts of friction particles, 10 parts of barite, 5 parts of garnet powder, 5 parts of nano-hafnium nitride, 5 parts of graphite fluoride, 4 parts of nylon, and 2 parts of composite modified hydroxy silicate.

[0021] According to some preferred embodiments, in the adhesive, the model of the polysiloxane-modified phenolic resin is PF6536, and the manufacturer is Jinan Shengquan Group Co., Ltd.

[0022] According to some preferred embodiments, in the reinforcing material, the preparation method of the modified needle-shaped wollastonite is as follows: the needle-shaped wollastonite is baked, then activated and ultrasonically treated, and then dried. Baking: 500-600°C for 1-2 hours; the activation process maintains a treatment temperature of 60-100°C, and the ultrasound is ultrasonically oscillated. The concentration of the activation solution is 3-5wt%, and the activation solution is prepared by mixing at least one of potassium phthalate, potassium citrate, potassium succinate, and triethanolamine oleate with deionized water.

[0023] According to some preferred embodiments, in the reinforcing material, the model of the composite mineral fiber is REK-3CS, and the manufacturer is Jiangsu Ruike High-tech Materials Co., Ltd.

[0024] According to some preferred embodiments, in the friction-increasing filler, the friction particles are of model TKL-01-P / GJ, and the manufacturer is Shijiazhuang Shuoruo Technology Co., Ltd. The friction particles are made of synthetic rubber, high temperature resistant resin, inorganic adhesive, friction-increasing material, wear-reducing material and other materials through special processing.

[0025] According to some preferred embodiments, in the friction-increasing filler, the macroporous fruit shell activated carbon includes at least one of apricot shell activated carbon, coconut shell activated carbon, walnut shell activated carbon, jujube shell activated carbon, and peach shell activated carbon. The macroporous fruit shell activated carbon referred to in the present invention refers to a macroporous material with a pore size of more than 50nm. Due to the large pore size and irregular pore structure, the macroporous material has a high surface area and porosity, can adsorb small molecular substances, has the effects of reducing noise, reducing thermal decay, and maintaining a stable high-temperature friction coefficient.

[0026] According to some preferred embodiments, in the friction-reducing filler, the preparation method of the composite modified hydroxy silicate is to soak the hydroxy silicate in NH4OH, ultrasonically disperse it, and then modify it with diisocyanate and stearic acid, and then blend it with silane-modified micro-nano calcium carbonate. The concentration of NH4OH is 5-8wt%, soaking at room temperature for 10-12 hours, and then ultrasonically treated for 2-3 hours. The treated hydroxy silicate is ultrasonically blended with N,N-dimethylformamide, that is, treated at 40-70°C for 30-60 minutes, and then diisocyanate (such as isophorone diisocyanate-IPDI) is added to continue ultrasonic blending for 30-60 minutes, and then dibutyltin dilaurate is dripped, and the temperature is maintained for 24-48 hours. After the end, it is washed, centrifuged, and dried. The ratio of hydroxy silicate, N,N-dimethylformamide, diisocyanate, and dibutyltin dilaurate is 1:50~200: 50~150:0.1~0.5. Then, stearic acid is dissolved in toluene, stirring is maintained, and diisocyanate-modified hydroxy silicate and dibutyltin dilaurate are added. The modified hydroxy silicate is obtained by reaction (90~120℃, 1~5h), washing, filtering, and drying. The mass ratio of diisocyanate-modified hydroxy silicate, stearic acid, dibutyltin dilaurate, and toluene is 1:0.2~0.5:0.02~0.15:100~300. The silane coupling agent in the silane-modified micro-nano calcium carbonate can be KH550, and the modification method can be conventional operation. In micro-nano calcium carbonate, if micron calcium carbonate is used, its particle size can be selected from 5 to 15 μm, and if nano calcium carbonate is used, its particle size can be selected from 60 to 100 nm. The mass ratio of silane-modified micro-nano calcium carbonate to modified hydroxy silicate is 1:3 to 8. Finally, the modified hydroxy silicate and silane-modified micro-nano calcium carbonate are ball-milled, and the ball mill speed is 1000 to 1400 r / min, 30 to 60 min.

[0027] According to some preferred embodiments, polysiloxane-modified phenolic resin 200 mesh, nitrile rubber powder 40 mesh, benzoxazine 200 mesh, 1414 para-aramid pulp length 1.5~2mm, calcium sulfate whisker 10~300μm, composite mineral fiber 100-250μm, copper fiber 1~3mm, modified needle-shaped wollastonite aspect ratio of 15:1~20:1, macroporous nutshell activated carbon 16~40 mesh, friction particles 16~40 mesh, barite 325 mesh, garnet powder 325 mesh, nano hafnium nitride particle size 20~40nm, graphite fluoride 100 mesh, nylon 400 mesh, composite modified hydroxy silicate powder 600 mesh.

[0028] Second, the present invention provides a method for preparing the friction material for electromagnetic brake with stable friction coefficient, comprising the following steps:

[0029] S1 Weigh the raw materials in proportion and blend them to obtain a mixed material;

[0030] S2 Drying of the molded material after mixing;

[0031] S3 is dried and then cold pressed to obtain a semi-finished product 1;

[0032] S4 is then subjected to hot pressing to obtain semi-finished product 2;

[0033] S5 is then heat treated to obtain the friction material;

[0034] S6 friction material has a ground surface.

[0035] Specifically, it means:

[0036] S1 Mixing: Weigh the raw materials of each component according to the proportion, and put them into the plowshare mixer for blending. The main shaft speed of the mixer is 250~300r / min, and the reamer speed is 2500~3000r / min.

[0037] S2 Drying: Dry the mixed molding material in an oven at 80°C for 1 to 2 hours.

[0038] S3 Pre-pressing: Add the molding material into the cold pressing mold and flatten it, and press the mixture into a blank. The cold pressing pressure is 50~60MPa, and the pressing is repeated twice. The pressing machine stops when the pressure is in place.

[0039] S4 Hot pressing: Use 150T four-column hydraulic press for hot pressing. Put the cold blanks into the hot pressing mold for pressing. The pressing temperature is 170±5℃, the pressing pressure is 20~40MPa, and the pressure is maintained for 60~80s / mm. Exhaust gas is carried out before pressure maintenance. Press for 15s and exhaust gas for 5s. After 3 exhaust gas treatments, the pressure maintenance stage is entered. After the pressure maintenance, the semi-finished friction material is obtained.

[0040] S5 Heat treatment: heat from room temperature to 100℃ over 1h, keep warm for 1~2h, heat from 100℃ to 140℃ over 30min, keep warm for 2~3h, heat from 140℃ to 180℃ over 30min, keep warm for 1~2h, heat from 180 to 220℃ over 30min, keep warm for 3~4h, then cool to 50℃ and take out.

[0041] S6 Grinding: Grind the heat-treated friction material through a double-end belt grinder to remove surface oxide scale, burrs and flash.

[0042] The beneficial effects achieved by the present invention are:

[0043] (1) Adhesives include polysiloxane-modified phenolic resin, benzoxazine, and nitrile rubber powder;

[0044] When heated and cured, the oxazine ring opens to produce a large number of methylene groups, which undergo ortho-substitution reactions with the oxazine rings on other benzoxazine rings to generate phenolic hydroxyl groups. The presence of these phenolic hydroxyl groups can effectively catalyze the ring-opening reaction of the oxazine rings, and finally obtain a cured product with a dense cross-linked network structure. This network structure gives the matrix excellent mechanical properties and wear resistance. The blending of phenolic resin, nitrile rubber and benzoxazine further improves the toughness of the matrix and reduces the curing temperature of the system.

[0045] (2) The reinforcing material provided by the present invention comprises 1414 para-aramid pulp, calcium sulfate whiskers, composite mineral fibers, copper fibers, and modified needle-shaped wollastonite;

[0046] 1414 para-aramid pulp is used as the main reinforcing material, which plays the role of the skeleton of the friction material.

[0047] Copper fiber plays a role in heat transfer and heat conduction, which can quickly transfer the heat from the friction surface and reduce the heat accumulation on the friction surface. At the same time, copper fiber also has a certain friction reduction and lubrication effect, and accelerates the formation of the transfer film on the friction surface.

[0048] Modified needle-shaped wollastonite can significantly enhance the strength of the friction material matrix, improve the cold friction coefficient, and keep the cold and hot friction coefficients stable. The carboxylate ions in the activation solution react chemically with the calcium silicate ions in the wollastonite, enhancing the chemical activity of the needle-shaped wollastonite and improving the bonding strength between the needle-shaped wollastonite and adhesives such as resins and rubbers, thereby greatly improving the local reinforcement effect of the needle-shaped wollastonite.

[0049] At the same time, composite mineral fibers, calcium sulfate whiskers, and modified needle-shaped wollastonite are used to play a local reinforcement role. Compared with other mineral fibers, composite mineral fibers have the advantages of high strength, low slag ball content, easy dispersion, and good bonding performance with resin. The use of multi-fiber hybrid can improve the strength and heat resistance of friction materials and reduce the fluctuation of friction coefficient.

[0050] (3) The friction-increasing material provided by the present invention comprises macroporous fruit shell activated carbon, friction particles, garnet powder, barite, and nano hafnium nitride;

[0051] Macroporous fruit shell activated carbon is used as filler. Fruit shell activated carbon has good wear resistance, high strength, developed pores and strong adsorption capacity. It can adsorb gases and small molecules produced by high-temperature decomposition on the surface of friction materials, reduce thermal decay of friction materials, and maintain a stable friction coefficient.

[0052] Nano hafnium nitride has uniform particle size distribution, large specific surface area, and high surface activity. It can be closely combined with materials such as adhesive fibers to improve the strength of the matrix. Compared with ordinary hafnium nitride powder, it can accommodate more friction heat, reduce the temperature of the friction surface, and reduce the high-temperature wear of the friction material. In particular, hafnium nitride exhibits excellent wear resistance and stability under high temperature and high-speed conditions. In particular, the heat capacity of hafnium nitride changes with temperature. In the temperature range of 0~2200K, the heat capacity of hafnium nitride increases with increasing temperature. Therefore, hafnium nitride can significantly improve the stability of the friction coefficient of the friction material in the high temperature stage.

[0053] (4) The friction-reducing material provided by the present invention comprises graphite fluoride, nylon, and composite modified hydroxy silicate;

[0054] Fluorinated graphite is an important inorganic non-metallic material with excellent lubricity. The lubrication performance of fluorinated graphite is better than that of commonly used flake graphite. It has a smaller friction coefficient at high temperatures and a better friction reduction effect. Fluorinated graphite can also maintain a good lubrication effect under harsh conditions such as high temperature, high speed and high pressure, and can reduce the fluctuation of the friction coefficient of friction materials at high temperatures. The friction coefficient of nylon decreases with the increase of load. Under high load conditions, the friction coefficient can be reduced to about 0.1~0.15. The friction coefficient of nylon also decreases with the increase of speed or the increase of surface temperature. Nylon and fluorinated graphite work together to reduce the friction coefficient at high temperatures and keep the friction coefficient stable at different temperatures.

[0055] The hydroxy silicate is soaked in ammonium hydroxide solvent and ultrasonically treated, so that its layered structure is destroyed, thereby increasing the interlayer pores and specific surface area of ​​the hydroxy silicate. It is then modified with diisocyanate. By introducing diisocyanate, on the one hand, it is used to avoid the agglomeration of hydroxy silicate after stripping, and on the other hand, it is convenient to graft stearic acid, and on the other hand, it is introduced. The hydrophobic long-chain molecules are introduced to improve the interfacial compatibility with the adhesive. In addition, it is ball-milled with micro-nano calcium carbonate modified with silane (silane coupling agent), so that the micro-nano calcium carbonate can fill the tiny pores and slip marks generated during the friction process, thereby further reducing wear; nano-scale calcium carbonate can form a layered structure that is easy to slide at the friction interface, thereby reducing the friction coefficient. Furthermore, calcium carbonate has excellent thermal stability and can accelerate the formation of a protective film layer by hydroxy silicate. By treating nano calcium carbonate with silane, it can not only avoid the agglomeration problem, but also be evenly dispersed in silicate. Based on this, the modified composite hydroxy silicate with high chemical activity provided by the present invention is very easy to adsorb on the surface of the dual parts, and diffuse and deposit on the friction surface to produce a series of friction chemical reactions, forming a self-lubricating protective film with self-repairing function. As the braking process proceeds, the protective film expands to the entire friction surface, thereby reducing the friction coefficient and wear rate of the material. DETAILED DESCRIPTION

[0056] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0057] Examples 1-3

[0058] The preparation method of the friction material for electromagnetic brake with stable friction coefficient comprises the following steps:

[0059] (1) Mixing: Weigh the raw materials of each component according to the proportion, and put them into the plowshare mixer for blending. The main shaft speed of the mixer is 250~300r / min, and the reamer speed is 2500~3000r / min.

[0060] (2) Drying: Dry the mixed molding material in an oven at 80°C for 1 to 2 hours.

[0061] (3) Pre-pressing: Add the molding material into the cold pressing mold and flatten it, then press the mixture into a blank. The cold pressing pressure is 50~60MPa. The press stops when the pressure is in place.

[0062] (4) Hot pressing: Use a 150T four-column hydraulic press to hot press. Put the cold blanks into the hot pressing mold for pressing. The pressing temperature is 170±5℃, the pressing pressure is 20~40MPa, and the pressure is maintained for 60~80s / mm. Exhaust gas is performed before pressure maintenance. Press for 15s and exhaust gas for 5s. After exhaust gas is performed three times, the pressure maintenance stage begins. After the pressure maintenance, the semi-finished friction material is obtained.

[0063] (5) Heat treatment: heat from room temperature to 100°C over 1 hour, keep warm for 1-2 hours, heat from 100°C to 140°C over 30 minutes, keep warm for 2-3 hours, heat from 140°C to 180°C over 30 minutes, keep warm for 1-2 hours, heat from 180 to 200°C over 30 minutes, keep warm for 3-4 hours, then cool to 50°C and take out.

[0064] (5) Grinding: Grind the heat-treated friction material using a double-end belt grinder to remove surface oxide scale, burrs, and flash.

[0065] In Examples 1-3, the proportions of the various components of the raw materials are shown in Table 1.

[0066] Table 1 Distribution ratio of each group of raw materials (A1-A3 in the examples)

[0067]

[0068] In Table 1:

[0069] Modified needle-shaped wollastonite: bake the needle-shaped wollastonite at 550℃ for 2h to remove surface impurities, then put the baked needle-shaped wollastonite into a 5wt% activation solution (prepared by dissolving potassium phthalate in deionized water), and oscillate it by ultrasonic for 1~2h, heating it during the process at a heating temperature of 90℃. Then filter out the needle-shaped wollastonite, dry it in an oven at a drying temperature of 60~80℃ for 2~3h for standby use.

[0070] Composite modified hydroxy silicate: put the hydroxy silicate into 5wt% NH4OH solution, soak for 10~12h, and then ultrasonically strip for 2~3h for standby use. Then, treat the hydroxy silicate and N,N-dimethylformamide at 60℃ for 45min, add IPDI and continue to treat for 45min, then drop dibutyltin dilaurate and keep for 36h. After the end, wash, centrifuge and dry, the mass ratio of the hydroxy silicate, N,N-dimethylformamide, diisocyanate and dibutyltin dilaurate in the above-mentioned medium is 1:200:120:0.5. Then put it into stearic acid toluene solution, add dibutyltin dilaurate, treat at 120℃ for 4h, wash, filter and dry, the mass ratio of the hydroxy silicate, stearic acid, dibutyltin dilaurate and toluene in the above-mentioned medium modified by diisocyanate is 1:0.3:0.15:200. The mass ratio of silane-modified nano-calcium carbonate to modified hydroxy silicate is 1:5, and the milling process is performed at 1400 r / min and 45 min.

[0071] Comparative Examples 1-10

[0072] The raw materials of each component in the comparative example are shown in Table 2-3, and the preparation method is the same as that in the example.

[0073] Table 2 Distribution ratio of each group of raw materials (comparative examples are represented by B1-B5)

[0074]

[0075] Table 3 Distribution ratio of each group of raw materials (comparative examples are represented by B6-B10)

[0076]

[0077] Test example

[0078] The friction materials prepared in Examples 1-3 and Comparative Examples 1-10 were used as samples and tested according to the test method of GB / T 5764. The test results are shown in Tables 4-5.

[0079] Table 4 Friction material constant speed test results

[0080]

[0081] Table 5 Installation test results (A1-A3 in the examples)

[0082]

[0083]

[0084]

[0085] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A friction material for an electromagnetic brake having a stable friction coefficient, characterized in that: Including adhesives, reinforcing materials, friction-increasing materials, and friction-reducing materials; The adhesive includes polysiloxane-modified phenolic resin, benzoxazine, and nitrile rubber powder; The reinforcing material includes 1414 para-aramid pulp, calcium sulfate whisker, composite mineral fiber, copper fiber, and modified needle-shaped wollastonite; the model of the composite mineral fiber is REK-3CS; the preparation method of the modified needle-shaped wollastonite is as follows: the needle-shaped wollastonite is baked, activated and ultrasonically treated, and then dried; Baking: 500-600℃ treatment for 1-2h; the activation process maintains the treatment temperature at 60-100℃, and the ultrasound adopts the ultrasonic oscillation method; the concentration of the activation solution is 3-5wt%, and the activation solution is prepared by mixing at least one of potassium phthalate, potassium citrate, potassium succinate, and triethanolamine oleate with deionized water; The friction-increasing materials include macroporous nutshell activated carbon, friction particles, garnet powder, barite, and nano hafnium nitride; the model of the friction particles is TKL-01-P / GJ; Friction-reducing materials include graphite fluoride, nylon, and composite modified hydroxy silicate; Composite modified hydroxy silicate refers to hydroxy silicate modified by diisocyanate and stearic acid, and then compounded with silane-modified micro-nano calcium carbonate; The raw material components are calculated by weight, including 10-20 parts of adhesive, 50-60 parts of reinforcing material, 30-50 parts of friction-increasing filler, and 10-20 parts of friction-reducing filler; Polysiloxane modified phenolic resin 200 mesh, nitrile rubber powder 40 mesh, benzoxazine 200 mesh, 1414 para-aramid pulp length 1.5~2mm, calcium sulfate whisker 10~300μm, composite mineral fiber 100~250μm, copper fiber 1~3mm, modified needle-shaped wollastonite aspect ratio of 15:1~20:1, macroporous fruit shell activated carbon 16~40 mesh, friction particles 16~40 mesh, barite 325 mesh, garnet powder 325 mesh, nano hafnium nitride particle size 20~40nm, graphite fluoride 100 mesh, nylon 400 mesh, composite modified hydroxy silicate 600 mesh.

2. The friction material for electromagnetic brakes having a stable friction coefficient according to claim 1, characterized in that: The raw material components are calculated by weight: 2-4 parts of polysiloxane modified phenolic resin, 6-8 parts of nitrile rubber powder, 8-10 parts of benzoxazine, 1-5 parts of 1414 para-aramid pulp, 10-20 parts of calcium sulfate whiskers, 20-30 parts of composite mineral fibers, 2-8 parts of copper fibers, 8-14 parts of modified needle-shaped wollastonite, 5-10 parts of macroporous fruit shell activated carbon, 10-20 parts of friction particles, 6-10 parts of barite, 3-5 parts of garnet powder, 2-8 parts of nano-hafnium nitride, 3-6 parts of graphite fluoride, 2-5 parts of nylon, and 2-5 parts of composite modified hydroxy silicate.

3. The friction material for electromagnetic brakes having a stable friction coefficient according to claim 2, characterized in that: The components of the raw materials are calculated by weight and are combination one, combination two or combination three; Combination 1: 3 parts of polysiloxane modified phenolic resin, 6 parts of nitrile rubber powder, 10 parts of benzoxazine, 2 parts of 1414 para-aramid pulp, 12 parts of calcium sulfate whiskers, 30 parts of composite mineral fiber, 5 parts of copper fiber, 10 parts of modified needle-shaped wollastonite, 6 parts of macroporous nutshell activated carbon, 15 parts of friction particles, 6 parts of barite, 5 parts of garnet powder, 3 parts of nano-hafnium nitride, 4 parts of graphite fluoride, 4 parts of nylon, 3 parts of composite modified hydroxy silicate; Combination 2: 2 parts of polysiloxane modified phenolic resin, 8 parts of nitrile rubber powder, 8 parts of benzoxazine, 3 parts of 1414 para-aramid pulp, 15 parts of calcium sulfate whiskers, 25 parts of composite mineral fibers, 3 parts of copper fibers, 8 parts of modified needle-shaped wollastonite, 8 parts of macroporous nutshell activated carbon, 20 parts of friction particles, 8 parts of barite, 3 parts of garnet powder, 6 parts of nano-hafnium nitride, 6 parts of graphite fluoride, 2 parts of nylon, 4 parts of composite modified hydroxy silicate; Combination three: 4 parts of polysiloxane modified phenolic resin, 6 parts of nitrile rubber powder, 9 parts of benzoxazine, 1 part of 1414 para-aramid pulp, 20 parts of calcium sulfate whiskers, 20 parts of composite mineral fibers, 6 parts of copper fibers, 12 parts of modified needle-shaped wollastonite, 10 parts of macroporous nutshell activated carbon, 14 parts of friction particles, 10 parts of barite, 5 parts of garnet powder, 5 parts of nano-hafnium nitride, 5 parts of graphite fluoride, 4 parts of nylon, and 2 parts of composite modified hydroxy silicate.

4. The friction material for electromagnetic brakes having a stable friction coefficient according to claim 1, characterized in that: In the adhesive, the model of the polysiloxane-modified phenolic resin is PF6536.

5. The friction material for electromagnetic brakes having a stable friction coefficient according to claim 1, characterized in that: Friction-increasing materials include the following features (2-1): (2-1) The macroporous fruit shell activated carbon includes at least one of apricot shell activated carbon, coconut shell activated carbon, walnut shell activated carbon, jujube shell activated carbon, and peach shell activated carbon.

6. The friction material for electromagnetic brakes having a stable friction coefficient according to any one of claims 1 to 5, characterized in that: Anti-friction fillers include the following features (3-1): (3-1) The preparation method of the composite modified hydroxy silicate is as follows: soaking the hydroxy silicate in NH4OH and ultrasonically dispersing it to obtain a first treated body; ultrasonically blending the first treated body with N,N-dimethylformamide, then adding diisocyanate for ultrasonic blending, and dripping dibutyltin dilaurate to obtain a second treated body; the second treated body is reacted with stearic acid and dibutyltin dilaurate to obtain a third treated body; the third treated body is ball-milled with silane-modified micro-nano calcium carbonate to obtain a composite modified hydroxy silicate.

7. The friction material for electromagnetic brakes having a stable friction coefficient according to claim 6, characterized in that: Feature (3-1) includes at least one of features (3-1-1) to (3-1-5) or feature (3-1) includes at least one of features (3-1-1) to (3-1-4) and (3-1-6): (3-1-1) The concentration of NH4OH is 5~8wt%, soaking at room temperature for 10~12h, and then ultrasonic treatment for 2~3h; (3-1-2) The ratio of hydroxy silicate, N,N-dimethylformamide, diisocyanate and dibutyltin dilaurate is 1:50~200: 50~150:0.1~0.5; (3-1-3) The mass ratio of the second treated body, stearic acid, dibutyltin dilaurate, and toluene is 1:0.2~0.5:0.02~0.15:100~300; (3-1-4) The mass ratio of the silane-modified micro-nano calcium carbonate to the third treated body is 1:3-8; (3-1-5) Among micro-nano calcium carbonate, micron calcium carbonate is selected, and its particle size is selected to be 5~15μm; (3-1-6) Among micro-nano calcium carbonate, nano calcium carbonate is selected, and its particle size is selected to be 60~100nm.

8. A method for preparing a friction material for an electromagnetic brake having a stable friction coefficient as claimed in any one of claims 1 to 7, characterized in that: The steps include: S1 Weigh the raw materials in proportion and blend them to obtain a mixed material; S2 Drying of the molded material after mixing; S3 is dried and then cold pressed to form; and pressed by a mold to obtain a semi-finished product 1; S4 is then subjected to hot pressing to obtain semi-finished product 2; S5 is then heat treated to obtain the friction material; S6 friction material has a ground surface.

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