A dimensionally stable and anti-adhesion friction material for electromagnetic brakes and a preparation method thereof

Abstract

The present invention relates to the technical field of friction materials, and discloses a dimensionally stable and anti-adhesive friction material for electromagnetic brakes and a preparation method thereof. The raw materials of the friction material include benzoxazine, bismaleimide, cyanate resin, nitrile rubber powder, zinc fiber, modified bamboo fiber, ceramic fiber, silicon carbide whiskers, calcium sulfate whiskers, modified poly(p-phenylene benzobisoxazole) pulp, calcined kaolin, precipitated barium sulfate, magnesium oxide, cashew nut shell liquid-modified phenolic resin-coated amorphous silica, polytetrafluoroethylene powder, flake graphite, and modified layered magnesium phosphate. The friction material of the present invention has excellent dimensional stability under hot and humid conditions and can prevent rusting of mating parts, thereby preventing adhesion and corrosion.

Description

Technical Field

[0001] The present invention relates to the technical field of friction materials, in particular to a dimensionally stable and anti-adhesion friction material for electromagnetic brakes and a preparation method thereof. Background Art

[0002] Electromagnetic brakes are widely used in various industries, such as servo motors, robots, forklifts, aerial work platforms, fans, stage lifts, elevators, and robotic arms, playing a vital role in the control and safety of mechanical equipment. However, China's vast territory and diverse environmental conditions, such as the high humidity in the southwest and the high-salt, high-temperature, and high-humidity environments of the southeast coastal areas, place higher demands on the stability of electromagnetic brake performance in these environments. Electromagnetic brake friction materials are generally polymer composites—resin-based or rubber-based. Polymer composites have a long-chain matrix structure, with molecules primarily bound by van der Waals forces and hydrogen bonds. These materials are more susceptible to molecular chain motion under heat and high humidity. Therefore, environmental conditions have a more pronounced impact on polymer composites. The working principle of an electromagnetic brake is that electromagnetic force attracts the moving plate, causing the friction plate to contact the mating member, generating friction for braking. During operation, there is a working gap between the friction plate and the moving plate flange. This gap is typically 0.1-0.3 mm. The thickness of the electromagnetic brake friction plate after processing is generally 0.4-3 mm. If friction plates operate in harsh environments for extended periods, they may expand, reducing the clearance or even completely blocking it, or contract, increasing the clearance and causing it to malfunction. Furthermore, in high-humidity environments, expansion of the friction plates and rusting of the mating parts can cause adhesion between the friction material and the mating parts. Excessive adhesion torque can also cause the brake to malfunction. Therefore, ensuring the dimensional stability and adhesion resistance of the friction material is crucial for ensuring the proper functioning of electromagnetic brakes. Summary of the Invention

[0003] Technical problems solved by the present invention:

[0004] The invention solves the problem that the friction material adheres to the mating part and the gap cannot meet the design requirements due to the expansion or contraction of the friction material in a high temperature and high humidity environment due to the long-term closure of the electromagnetic brake.

[0005] The technical solution adopted in the present invention is:

[0006] In view of the above technical problems, an object of the present invention is to provide a dimensionally stable and anti-adhesion friction material for electromagnetic brakes and a preparation method thereof.

[0007] The specific contents are as follows:

[0008] First, the present invention provides a dimensionally stable and anti-adhesion friction material for electromagnetic brakes, wherein the raw material components include an adhesive, a reinforcing material, a friction-increasing filler, and a friction-reducing filler;

[0009] Adhesives include benzoxazine, bismaleimide, cyanate resin, and nitrile rubber powder;

[0010] The reinforcing materials include zinc fiber, modified bamboo fiber, ceramic fiber, silicon carbide whisker, calcium sulfate whisker, and modified poly(p-phenylene benzobisoxazole) pulp; the modified bamboo fiber is made from bamboo fiber with silicon dioxide loaded on its surface; the modified poly(p-phenylene benzobisoxazole) pulp is made from poly(p-phenylene benzobisoxazole) pulp treated with a maleic anhydride and hydrogen peroxide solution;

[0011] The friction-increasing material includes calcined kaolin, precipitated barium sulfate, magnesium oxide, and cashew nut shell liquid-modified phenolic resin-coated amorphous silica; the cashew nut shell liquid-modified phenolic resin-coated amorphous silica is obtained by modifying silica with silane, and the modified silica is dispersed in a prepolymer solution and polymerized; the raw materials of the prepolymer solution include phenol, cashew nut shell liquid, formaldehyde, a catalyst, a solvent, and a dispersant;

[0012] The friction-reducing material comprises polytetrafluoroethylene micropowder, flake graphite and modified layered magnesium phosphate; the modified layered magnesium phosphate is obtained by taking layered magnesium phosphate as raw material and sequentially treating with sodium dodecylbenzene sulfonate and tartaric acid.

[0013] According to some preferred embodiments, the raw material components, by weight, include 20-25 parts of adhesive, 35-45 parts of reinforcing material, 25-35 parts of friction-increasing filler, and 10-20 parts of friction-reducing filler.

[0014] According to some preferred embodiments, the raw material components, by weight, include 8-12 parts of benzoxazine, 5-8 parts of bismaleimide, 2-5 parts of cyanate resin, 4-6 parts of nitrile rubber powder, 5-10 parts of zinc fiber, 3-8 parts of modified bamboo fiber, 8-12 parts of ceramic fiber, 4-8 parts of silicon carbide whiskers, 8-15 parts of calcium sulfate whiskers, 1-3 parts of modified poly(p-phenylene benzobisoxazole) pulp, 10-15 parts of calcined kaolin, 5-8 parts of precipitated barium sulfate, 3-8 parts of cashew nut shell oil-modified phenolic resin-coated amorphous silica, 5-10 parts of magnesium oxide, 4-6 parts of polytetrafluoroethylene powder, 2-6 parts of flake graphite, and 3-6 parts of modified layered magnesium phosphate.

[0015] Preferably, benzoxazine 200 mesh, bismaleimide 200 mesh, cyanate resin 200 mesh, nitrile rubber powder 40-60 mesh, zinc fiber 1-2 mm, modified bamboo fiber 1-3 mm, ceramic fiber length 0.3-0.5 mm, silicon carbide whisker length 50-200 μm, calcium sulfate whisker 50-300 μm, modified poly(p-phenylene benzobisoxazole) pulp length 1-1.4 mm, calcined kaolin 325 mesh, precipitated barium sulfate 325 mesh, cashew nut shell liquid modified phenolic resin coated amorphous silica 1000 mesh, magnesium oxide 325 mesh, polytetrafluoroethylene powder 600 mesh, flake graphite 100 mesh, and modified layered magnesium phosphate 1250 mesh.

[0016] According to some more preferred embodiments, the raw material components are calculated by weight, including any one of combination A, combination B, and combination C:

[0017] Combination A: 10 parts of benzoxazine, 6 parts of bismaleimide, 4 parts of cyanate resin, 5 parts of nitrile rubber powder, 7 parts of zinc fiber, 3 parts of modified bamboo fiber, 11 parts of ceramic fiber, 5 parts of silicon carbide whiskers, 12 parts of calcium sulfate whiskers, 1 part of modified poly(p-phenylene benzobisoxazole) pulp, 13 parts of calcined kaolin, 6 parts of precipitated barium sulfate, 4 parts of cashew nut shell oil-modified phenolic resin-coated amorphous silica, 6 parts of magnesium oxide, 4 parts of polytetrafluoroethylene powder, 3 parts of flake graphite, and 5 parts of modified layered magnesium phosphate.

[0018] Combination B: 8 parts of benzoxazine, 7 parts of bismaleimide, 3 parts of cyanate resin, 6 parts of nitrile rubber powder, 5 parts of zinc fiber, 7 parts of modified bamboo fiber, 12 parts of ceramic fiber, 4 parts of silicon carbide whiskers, 10 parts of calcium sulfate whiskers, 2 parts of modified poly(p-phenylene benzobisoxazole) pulp, 10 parts of calcined kaolin, 8 parts of precipitated barium sulfate, 6 parts of cashew nut shell oil-modified phenolic resin-coated amorphous silica, 5 parts of magnesium oxide, 5 parts of polytetrafluoroethylene powder, 5 parts of flake graphite, and 4 parts of modified layered magnesium phosphate.

[0019] Combination C: 12 parts of benzoxazine, 5 parts of bismaleimide, 2 parts of cyanate resin, 4 parts of nitrile rubber powder, 9 parts of zinc fiber, 5 parts of modified bamboo fiber, 9 parts of ceramic fiber, 7 parts of silicon carbide whiskers, 8 parts of calcium sulfate whiskers, 3 parts of modified poly(p-phenylene benzobisoxazole) pulp, 12 parts of calcined kaolin, 5 parts of precipitated barium sulfate, 8 parts of cashew nut shell oil-modified phenolic resin-coated amorphous silica, 7 parts of magnesium oxide, 6 parts of polytetrafluoroethylene powder, 6 parts of flake graphite, and 3 parts of modified layered magnesium phosphate.

[0020] According to some preferred embodiments, in the reinforcing material, the preparation method of the modified bamboo fiber is:

[0021] (1) The bamboo fibers are washed, impregnated, and dried with anhydrous ethanol to obtain pretreated bamboo fibers;

[0022] (2) The pretreated bamboo fiber was immersed in the precursor solution, reacted at room temperature, and then taken out and allowed to stand, and then dried, washed, and oven-dried to obtain the modified bamboo fiber. The molar ratio of tetrabutyl orthosilicate, ethanol, water, and formic acid in the precursor solution was 1:4~8:2~8:0.01. The reaction was stirred at room temperature for 3~8 hours, dried in a 90℃ oven, washed with deionized water, and then dried at 100℃. The mass ratio of pretreated bamboo fiber to tetrabutyl orthosilicate was 1:8~12.

[0023] According to some preferred embodiments, in the reinforcing material, the ceramic fiber includes at least one of aluminum silicate fiber, mullite fiber, and alumina fiber.

[0024] According to some preferred embodiments, in the reinforcement material, the modified poly(p-phenylene benzobisoxazole) pulp is prepared by treating it with a maleic anhydride hydrogen peroxide solution.

[0025] Specifically:

[0026] (1) Prepare a maleic anhydride hydrogen peroxide solution, wherein the maleic anhydride concentration is 0.5-2% and the hydrogen peroxide concentration is 0.5-1%;

[0027] (2) Immerse the poly(p-phenylene benzobisoxazole) pulp in a maleic anhydride hydrogen peroxide solution and heat it to 60±5°C for 12 to 15 hours;

[0028] (3) The poly(p-phenylene benzobisoxazole) pulp is filtered out, washed with distilled water for 3 to 5 times, and then dried at a drying temperature of 80 to 100°C for 2 to 3 hours to obtain modified poly(p-phenylene benzobisoxazole) pulp.

[0029] According to some preferred embodiments, in the friction-increasing material, the preparation method of the cashew nut shell liquid modified phenolic resin coated amorphous silica is:

[0030] SiO2 was treated with an ethanol solution of the silane coupling agent KH550 to obtain modified SiO2. Specifically, SiO2 was dispersed in anhydrous ethanol to obtain a 3% ethanol solution, which was then subjected to ultrasonic oscillation. KH550, which accounted for 2% by mass of SiO2, was then added to prepare a 3% aqueous solution of KH550, and the pH was adjusted to 10. The SiO2 ethanol solution and the KH550 aqueous solution were then blended and treated at 80°C for 4 hours. The modified SiO2 was then washed with ethanol, washed with water, filtered, and dried.

[0031] Modified SiO2 is dispersed in a prepolymer solution for coating polymerization. The raw materials in the prepolymer solution are phenol, cashew nut shell liquid, formaldehyde, oxalic acid as a catalyst, ethanol as a solvent, and polyethylene glycol 400 as a dispersant. The ratio of these raw materials in the prepolymer solution is 100:30-50:120-150:0.5-1:200-260:1-2. The specific polymerization process is: controlling the temperature at 70-85°C for 0.5-1.5 hours; then controlling the temperature at 85-95°C for 1-3 hours; and then maintaining the temperature at 95°C until the viscosity exceeds 2000 cP, thereby obtaining amorphous silica coated with cashew nut shell liquid-modified phenolic resin.

[0032] According to some preferred embodiments, the modified layered magnesium phosphate in the friction-reducing filler is activated by sodium dodecylbenzenesulfonate and then modified with tartaric acid.

[0033] Specifically:

[0034] (1) Prepare a sodium dodecylbenzenesulfonate solution with a concentration of 1-5%, and add 1-2% ethanol to form a sodium dodecylbenzenesulfonate ethanol solution;

[0035] (2) Add layered magnesium phosphate to sodium dodecylbenzenesulfonate ethanol solution and ultrasonically vibrate for 1 to 2 hours at a temperature of 40 to 80°C to allow for sufficient contact reaction;

[0036] (3) After the oscillation is completed, the mixture is allowed to stand for 1 to 2 hours so that the adsorption of sodium dodecylbenzenesulfonate on the surface of magnesium phosphate becomes more stable, further improving the activation effect;

[0037] (4) Filtering the layered magnesium phosphate and washing it with distilled water for 3 to 5 times, and drying it at 60 to 100 ° C for 1 to 2 hours to obtain activated layered magnesium phosphate;

[0038] (5) Tartaric acid is prepared into a 0.1-1 mol / L aqueous solution. The activated layered magnesium sulfate is added to the tartaric acid solution and subjected to ultrasonic oscillation at a temperature of 30-50°C for 6-12 hours. After the reaction is completed, the modified layered magnesium phosphate is obtained by filtration, washing with distilled water 3-5 times, and drying at 80-120°C for 10-12 hours.

[0039] Second, the present invention provides a method for preparing the aforementioned dimensionally stable and anti-adhesion friction material for electromagnetic brakes, comprising the following steps:

[0040] S1 Weigh the raw materials in proportion and blend them to obtain a mixed material;

[0041] S2 Drying of the molded material after mixing;

[0042] S3 is dried and then cold pressed; and then pressed into a mold to obtain a semi-finished product I;

[0043] S4 is then subjected to hot pressing to obtain semi-finished product II;

[0044] S5 is then heat treated to obtain friction material;

[0045] S6 friction material has a ground surface.

[0046] Specifically, it means:

[0047] S1 Mixing: Weigh the raw materials of each component according to the proportion and put them into a plowshare mixer for blending. The mixer's main shaft speed is 250-300 rpm, and the reamer speed is 2500-3000 rpm.

[0048] S2 Drying: Dry the mixed molding material in an oven at 80°C for 1 to 2 hours.

[0049] S3 Pre-pressing: Add the molding material to the cold press mold and flatten it. Press the mixture into a blank. The cold press pressure is 50-60MPa. Repeat the pressing twice and stop when the pressure is reached.

[0050] S4 Hot Pressing: Using a 100T four-column hydraulic press, the cold billets are placed in the hot press mold and pressed at a temperature of 200±5°C, a pressure of 30-40 MPa, and a holding time of 60-80 seconds / mm. Before holding, venting is performed: press for 10 seconds, vent for 5 seconds, and repeat this 3-5 times before entering the holding stage. After the holding stage, the semi-finished friction material is obtained.

[0051] S5 Heat treatment: Heat from room temperature to 140°C over 1 hour, keep warm for 1-2 hours, heat from 140°C to 180°C over 1 hour, keep warm for 1 hour, heat from 180°C to 240°C over 1 hour, keep warm for 8-12 hours, then cool to 50°C and take out.

[0052] S6 Grinding: Grind the heat-treated friction material through a double-end belt grinder to remove surface oxide scale, burrs and flash.

[0053] The beneficial effects achieved by the present invention are:

[0054] (1) The adhesive provided by the present invention includes benzoxazine, bismaleimide, cyanate resin, and nitrile rubber powder.

[0055] Benzoxazine has a high glass transition temperature (Tg), typically between 150 and 250°C, and a low coefficient of thermal expansion at high temperatures, maintaining excellent mechanical properties and dimensional stability over a wide temperature range. The benzene and heterocyclic rings in the benzoxazine resin's molecular structure impart excellent water and chemical resistance, making it resistant to attack by media such as water, acids, and alkalis, ensuring a long service life in harsh environments. Blending benzoxazine with bismaleimide improves the heat resistance and hydrophobicity of the matrix, reducing dimensional changes in the friction material caused by water absorption in humid environments. Bismaleimide exhibits excellent thermal stability, fatigue resistance in high-humidity environments, and a low coefficient of thermal expansion, but bismaleimide is also brittle. During curing, benzoxazine forms intramolecular and intermolecular hydrogen bonds. These bonds have high bond energies, resulting in a decrease in the crosslink density of the benzoxazine. The introduction of bismaleimide disrupts the hydrogen bonds formed by the benzoxazine, further increasing the crosslink density of the matrix, thereby improving its strength and reducing the swelling effect of water on the resin matrix. Cyanate ester resins offer excellent heat resistance, good mechanical properties, and resistance to moisture and heat. They also have low water absorption and minimal molding shrinkage, which can reduce deformation and dimensional deviation caused by shrinkage. Blending cyanate ester resins with benzoxazine further improves the heat resistance and dimensional stability of the resin matrix. Blending cyanate ester resins with benzoxazine produces low-polarity diphenyl ether structures, which alter the resin's molecular structure and disrupt the order of the benzoxazine resin's covalent bond structure, thereby improving its flexibility.

[0056] The addition of nitrile rubber powder improves the toughness of the matrix, thereby reducing braking noise.

[0057] (2) The reinforcing material provided by the present invention includes zinc fiber, modified bamboo fiber, ceramic fiber, silicon carbide whisker, and modified poly(p-phenylene benzobisoxazole) pulp; the standard electrode potential of zinc is -0.763V, and the standard electrode potential of iron is -0.44V. The electrode potential of zinc is more negative than that of iron. When zinc fiber acts as an anode, zinc will preferentially lose electrons to protect the metal of the mating part when it contacts the electrolyte, and the metal part will gain electrons and be protected. Therefore, zinc fiber can prevent the mating part from rusting and prevent the friction material from sticking. At the same time, zinc is relatively soft and has good ductility. It can form a metal film and has a certain friction reduction effect. When it is oxidized to zinc oxide at about 200°C, zinc oxide can fill the microscopic unevenness of the friction surface during the friction process, forming a relatively smooth protective film, isolating the direct contact between the friction pairs, thereby reducing friction and wear. Zinc has good thermal conductivity and can quickly conduct the friction heat of the contact surface, reducing the thermal wear of the friction material. Modified poly(p-phenylene benzobisoxazole) pulp improves fiber dispersion and bonding, enhancing the overall strength and dimensional stability of the friction material. Zinc fiber, modified bamboo fiber, and calcium sulfate whiskers work together to enhance the zinc fiber's protective effectiveness against mating parts. Modified bamboo fiber is made from bamboo fiber with silica loaded on its surface. Bamboo fiber is an environmentally friendly material with excellent heat and wear resistance. However, bamboo fiber's surface contains numerous polar hydroxyl groups, making it highly hygroscopic. Directly adding this to the friction material can cause internal cracks and interfacial delamination. To address this, we modified the bamboo fiber and introduced silica on its surface, facilitating stress transfer and preventing interfacial cracking. The uniform silica loading further enhances the wear resistance of the friction material. Calcium sulfate whiskers combine the advantages of reinforcing fibers and ultrafine inorganic fillers, acting as a fiber-like reinforcement to enhance the dimensional stability and wear resistance of the resin matrix. Calcium sulfate forms a thin protective film on the anode surface, isolating the anode from direct contact with the electrolyte solution and reducing electrolyte corrosion. It prevents corrosive ions such as chloride and sulfate from reacting with the anode metal, thereby extending the life of the zinc fiber as an anode. Furthermore, the calcium sulfate protective film reduces the polarization of the zinc fiber, allowing the anodic reaction to proceed more smoothly and improving the electrochemical performance of the anodic reaction. This in turn increases the zinc fiber's protective effectiveness against the mating component and reduces the risk of friction material adhesion.

[0058] Silicon carbide has a high Mohs hardness, which can improve the friction coefficient and high-temperature stability of friction materials. Because silicon carbide whiskers are small, they can play a local reinforcement and dispersion strengthening role in the matrix, greatly improving the strength and dimensional stability of the friction material matrix.

[0059] (3) The friction-increasing material provided by the present invention comprises calcined kaolin, precipitated barium sulfate, and magnesium oxide;

[0060] Calcined kaolin has good insulation and chemical stability, can improve the processing performance and physical properties of the material, reduce the thermal expansion coefficient of the material, and improve its resistance to thermal deformation.

[0061] Magnesium oxide, an alkaline filler, can significantly increase the pH value of friction materials, thereby improving the corrosion resistance of mating parts. In an alkaline environment, steel forms a dense protective film of iron hydroxide on its surface, which prevents further contact with water and oxygen, thereby slowing corrosion. Furthermore, the alkaline environment neutralizes acids, inhibiting their corrosion on the metal and reducing adhesion of the friction material. Magnesium oxide, with its high hardness and excellent thermal and chemical stability, can improve the wear resistance and thermal stability of friction materials and adjust friction properties.

[0062] Amorphous silica has a low coefficient of thermal expansion. When frictional heat generates a temperature rise, amorphous silica can suppress the overall thermal expansion of the material, thereby reducing the dimensional changes of the friction material caused by temperature changes. Although directly adding amorphous silica can avoid material deformation caused by local overheating and improve dimensional stability, amorphous silica has the problem of poor compatibility with the matrix material. Based on this, we coat amorphous silica by using cashew nut shell liquid modified phenolic resin to coat amorphous silica. The long carbon chain structure contained in cashew nut shell liquid and its hydrophobicity can improve its compatibility with the matrix material. The cashew nut shell liquid modified phenolic resin decomposes into a lubricating carbon layer when working at high temperature. The lubricating carbon layer covers the surface of the silica, thereby improving the dispersibility of silica. The low friction characteristics weaken the interaction between silica and the matrix resin. At the same time, we coat the silica with a carbon layer, which can effectively isolate water molecules from contacting the silica surface, thereby reducing hygroscopicity. This can prevent problems such as friction coefficient fluctuations and adhesive hydrolysis and aging caused by moisture absorption in high-temperature and high-humidity working environments.

[0063] (4) The friction-reducing material provided by the present invention includes polytetrafluoroethylene powder, flake graphite, and modified layered magnesium phosphate;

[0064] Polytetrafluoroethylene (PTFE) micropowder can be used for extended periods at temperatures between -200°C and 260°C, exhibiting excellent lubricity and significantly improving the wear resistance of friction materials. The high electronegativity of fluorine atoms in PTFE's molecular structure, coupled with high carbon-fluorine bond energy, results in a tightly packed molecular chain, resulting in extremely low surface energy and excellent hydrophobicity and lubricity. During braking, PTFE forms a thin film on the friction material's surface, effectively isolating moisture and reducing the material's water absorption rate and swelling. This also enhances lubrication, improving the friction material's dimensional stability and anti-adhesion properties.

[0065] Layered magnesium phosphate is a type of inorganic compound with a layered crystal structure. Its main layer is composed of MgO6 octahedrons and PO4 tetrahedrons. On a microscopic scale, it has a layered structure similar to traditional solid lubricant additives such as molybdenum disulfide and graphite. The bonding force between the layers is relatively weak, which makes it easy for the layers to slide relative to each other, thus showing good lubrication performance. Compared with other layered phosphates, layered magnesium phosphate has the following advantages: (1) good thermal stability and can withstand higher temperatures; (2) good balance between hardness and toughness, which can better withstand the pressure during friction and is not easily worn. At the same time, it has a certain toughness. Compared with some layered phosphates with greater brittleness, it is less likely to crack or peel off when subjected to impact or friction stress changes, thereby maintaining the integrity and effectiveness of the lubricating film for a longer period of time; (3) the lubricating film formed on the friction surface is more uniform and dense, which can more effectively reduce the friction coefficient. At the same time, layered magnesium phosphate has good adhesion and bonding with the metal surface, which can produce an anti-corrosion effect similar to phosphating treatment, reducing the possibility of rust adhesion. The layered structure of layered magnesium phosphate enables it to form a dense lubricating film on the surface of objects. This film can effectively block external corrosive media such as oxygen, moisture, acid, alkali, and salt, thereby slowing down the occurrence of corrosion and the swelling effect of water on the friction material, and also reducing wear and adhesion of the friction material.

[0066] The modified layered magnesium phosphate is activated with sodium dodecylbenzenesulfonate. The sodium dodecylbenzenesulfonate molecule consists of a hydrophilic sulfonic acid group (-SO3Na) and a hydrophobic dodecylphenyl group. One end of the sulfonic acid group adsorbs on the surface of the layered magnesium phosphate, while the dodecylphenyl group faces outward. This hydrophobic organic group covers the surface of the layered magnesium phosphate, altering its wettability and enhancing its bonding with other groups. Further modification with tartaric acid increases the interlayer spacing of the layered magnesium phosphate, reducing interlayer slip resistance and enhancing its lubricating properties. Layered magnesium phosphate forms a uniform protective film on surfaces. This film separates contacting surfaces, reducing direct contact and friction. Furthermore, due to the structural characteristics of the layered magnesium phosphate, this film possesses a certain degree of flexibility and self-healing capabilities, allowing it to adapt to surface changes and movement to a certain extent, maintaining the stability of the lubricating effect. When slight wear occurs on the surface of an object, tiny particles of layered magnesium phosphate can fill the worn area, play a role in repairing and protecting, and further reduce the occurrence of wear.

[0067] (5) The friction material and its preparation process provided by the present invention have a hot pressing pressure that is 10-20 MPa higher than that of conventional friction materials, further improving the density of the friction material, reducing the porosity, and reducing the probability of water vapor and rust products diffusing into the friction material, thereby improving the dimensional stability and anti-adhesion properties of the friction material. At the same time, the high-temperature treatment time is extended to 8-12 hours, which increases the crosslinking density of the resin matrix, improving the dimensional stability and hydrophobicity of the resin matrix. DETAILED DESCRIPTION

[0068] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0069] Examples 1-3

[0070] This embodiment provides a dimensionally stable and anti-adhesion friction material for an electromagnetic brake, comprising the following steps:

[0071] (1) Mixing: Weigh the raw materials of each component in proportion and put them into a plowshare mixer for blending. The main shaft speed of the mixer is 250~300rpm, and the reamer speed is 2500~3000rpm.

[0072] (2) Drying: Dry the mixed molding material in an oven at 80°C for 1 to 2 hours.

[0073] (3) Pre-pressing: Add the molding material into the cold pressing mold and flatten it. Press the mixture into a blank. The cold pressing pressure is 50~60MPa. Repeat the pressing twice and stop when the pressing pressure is in place.

[0074] (4) Hot pressing: A 100T four-column hydraulic press is used for hot pressing. The cold blanks are placed in the hot pressing mold and pressed at a temperature of 200±5°C, a pressure of 30-40 MPa, and a holding time of 60-80 s / mm. Before holding, exhaust is performed. Press for 10 seconds and exhaust for 5 seconds. After 3-5 exhaust cycles, the pressure holding stage is entered. After the holding stage, the friction material semi-finished product is obtained.

[0075] (5) Heat treatment: Heat from room temperature to 140°C over 1 hour, keep warm for 1-2 hours, heat from 140°C to 180°C over 1 hour, keep warm for 1 hour, heat from 180°C to 240°C over 1 hour, keep warm for 8-12 hours, then cool to 50°C and take out.

[0076] (6) Grinding: Grind the heat-treated friction material through a double-end belt grinder to remove surface oxide scale, burrs, and flash.

[0077] In Examples 1-3, the proportions of the raw material components are shown in Table 1.

[0078] Comparative Examples 1-13

[0079] The proportions of the raw material components in Comparative Examples 1-9 are shown in Table 1, and the preparation methods are the same as those in the Examples.

[0080] Comparative Example 10

[0081] The difference between this comparative example and Example 3 is that bamboo fiber is used instead of modified bamboo fiber.

[0082] Comparative Example 11

[0083] The difference between this comparative example and Example 3 is that poly(p-phenylene benzobisoxazole) pulp is used instead of the modified poly(p-phenylene benzobisoxazole) pulp.

[0084] Comparative Example 12

[0085] The difference between this comparative example and Example 3 is that layered magnesium phosphate is used instead of modified layered magnesium phosphate.

[0086] Comparative Example 13

[0087] The difference between this comparative example and Example 3 is that amorphous silica is used instead of cashew nut shell liquid-modified phenolic resin to coat the amorphous silica.

[0088]

[0089] In the aforementioned:

[0090] (1) Ceramic fiber is aluminum silicate fiber.

[0091] (2) The preparation method of modified bamboo fiber is as follows: after washing the bamboo fiber with anhydrous ethanol, the bamboo fiber is immersed in anhydrous ethanol solution for 4 hours, taken out, and then dried at 100°C to obtain pretreated bamboo fiber. The pretreated bamboo fiber is immersed in a precursor solution. In the precursor solution, the molar ratio of tetrabutyl orthosilicate, ethanol, water, and formic acid is 1:5:5:0.01, and the mass ratio of pretreated bamboo fiber to tetrabutyl orthosilicate is 1:10. Stirring is maintained during the impregnation process, and the reaction is carried out at room temperature for 4 hours. Then, the bamboo fiber is dried in a 90°C oven, washed with deionized water, and then dried at 100°C to obtain modified bamboo fiber.

[0092] (3) The preparation method of modified poly(p-phenylene benzobisoxazole) pulp is as follows: prepare a maleic anhydride hydrogen peroxide solution, wherein the maleic anhydride concentration is 1% and the hydrogen peroxide concentration is 0.8%; immerse the poly(p-phenylene benzobisoxazole) pulp in the maleic anhydride hydrogen peroxide solution and heat it to 60±5°C for 14 hours; filter out the poly(p-phenylene benzobisoxazole) pulp, wash it with distilled water for 3 to 5 times, and then dry it at a drying temperature of 90°C for 2 hours to obtain modified poly(p-phenylene benzobisoxazole) pulp.

[0093] (4) The preparation method of cashew nut shell oil modified phenolic resin coated amorphous silica is as follows: SiO2 is dispersed in anhydrous ethanol to obtain an ethanol solution with a concentration of 3%, and then subjected to ultrasonic oscillation treatment. KH550 accounting for 2% by mass of SiO2 is added to prepare a 3% aqueous solution of KH550, and the pH value is adjusted to 10. The SiO2 ethanol solution and the KH550 aqueous solution are then blended and treated at 80°C for 4 hours. The modified SiO2 is then washed with ethanol, washed with water, filtered, and dried to obtain the modified SiO2. The modified SiO2 is dispersed in a prepolymer solution and subjected to coating polymerization; wherein the raw materials in the prepolymer solution are phenol, cashew nut shell oil, formaldehyde, catalyst oxalic acid, solvent ethanol, and dispersant polyethylene glycol 400, and the ratio of the raw material components in the prepolymer solution is 100:40:140:0.8:240:1.5. The specific polymerization process is as follows: controlling the temperature at 80°C for 1 hour; then controlling the temperature at 90°C for 2 hours; and then maintaining the temperature at 95°C until the viscosity is greater than 2000 cP to obtain cashew nut shell liquid-modified phenolic resin coated amorphous silica.

[0094] (5) The preparation method of modified layered magnesium phosphate is as follows: prepare a sodium dodecylbenzenesulfonate solution with a concentration of 3%, and add 1% ethanol to form a sodium dodecylbenzenesulfonate ethanol solution; add the layered magnesium phosphate to the sodium dodecylbenzenesulfonate ethanol solution and ultrasonically oscillate for 1 hour at 60°C to allow for sufficient contact reaction; after the oscillation is completed, let it stand for 1 hour; filter the layered magnesium phosphate and wash it with distilled water 3 to 5 times, and dry it at 80°C for 1 hour to obtain activated layered magnesium phosphate; prepare tartaric acid into a 0.5 mol / L aqueous solution, add the activated layered magnesium sulfate to the tartaric acid solution and ultrasonically oscillate at 40°C for 10 hours. After the reaction is completed, filter, wash with distilled water 3 to 5 times, and dry it at 100°C for 10 hours to finally obtain modified layered magnesium phosphate.

[0095] Test example

[0096] The friction materials prepared in Examples 1-3 and Comparative Examples 1-13 were used as samples and tested according to the test method of GB / T 5764. The test results are shown in Table 2.

[0097] Table 2 Friction material constant speed test results (Example is represented by A, Comparative Example is represented by B)

[0098]

[0099] The friction materials prepared in Examples 1-3 and Comparative Examples 1-13 were used as samples. The thickness change rate of the friction materials was calculated according to GB / T 7345-2008 “Basic Technical Requirements for Controlled Motors”. The test results are shown in Table 3.

[0100] Table 3 Friction material thickness change rate measurement results (Example is represented by A, Comparative Example is represented by B)

[0101]

[0102] The friction materials prepared in Examples 1-3 and Comparative Examples 1-13 were used as samples. The friction materials were assembled on a brake for adhesion testing. The brake model was Z269-C08 (24V11) 8G, with a rated torque of 8 N·m. The test method was as follows:

[0103] (1) At room temperature (23±5℃), place the brake in a water tank with the brake 10mm~15mm above the water surface.

[0104] (2) Place the brake in a sealed water tank for 15 days, remove the brake, and disengage the brake friction plate from the dynamic plate flange.

[0105] (3) If the friction plate is stuck, test the maximum torque required to separate the rotor from the armature cover. After the friction plate sticking test, the separation torque must not exceed 20% of the rated torque. The test results are shown in Table 4.

[0106] Table 4 Friction material anti-adhesion test (Example is represented by A, Comparative Example is represented by B)

[0107]

[0108] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A dimensionally stable and anti-adhesion friction material for an electromagnetic brake, characterized in that: The raw material components include adhesives, reinforcing materials, friction-increasing fillers, and friction-reducing fillers; Adhesives include benzoxazine, bismaleimide, cyanate resin, and nitrile rubber powder; The reinforcing materials include zinc fiber, modified bamboo fiber, ceramic fiber, silicon carbide whisker, calcium sulfate whisker, and modified poly(p-phenylene benzobisoxazole) pulp; the modified bamboo fiber is made from bamboo fiber with silicon dioxide loaded on its surface; the modified poly(p-phenylene benzobisoxazole) pulp is made from poly(p-phenylene benzobisoxazole) pulp treated with a maleic anhydride and hydrogen peroxide solution; The friction-increasing material includes calcined kaolin, precipitated barium sulfate, magnesium oxide, and cashew nut shell liquid-modified phenolic resin-coated amorphous silica; the cashew nut shell liquid-modified phenolic resin-coated amorphous silica is obtained by modifying silica with silane, and the modified silica is dispersed in a prepolymer solution and polymerized; the raw materials of the prepolymer solution include phenol, cashew nut shell liquid, formaldehyde, a catalyst, a solvent, and a dispersant; The friction-reducing material comprises polytetrafluoroethylene micropowder, flake graphite and modified layered magnesium phosphate; the modified layered magnesium phosphate is obtained by taking layered magnesium phosphate as raw material and sequentially treating with sodium dodecylbenzene sulfonate and tartaric acid.

2. The dimensionally stable and anti-adhesion friction material for electromagnetic brake according to claim 1, characterized in that: Among the raw material components, benzoxazine 200 mesh, bismaleimide 200 mesh, cyanate resin 200 mesh, nitrile rubber powder 40~60 mesh, zinc fiber 1~2 mm, modified bamboo fiber 1~3 mm, ceramic fiber length 0.3~0.5 mm, silicon carbide whisker length 50~200 μm, calcium sulfate whisker 50~300 μm, modified poly(p-phenylene benzobisoxazole) pulp length 1~1.4 mm, calcined kaolin 325 mesh, precipitated barium sulfate 325 mesh, cashew nut shell liquid modified phenolic resin coated amorphous silica 1000 mesh, magnesium oxide 325 mesh, polytetrafluoroethylene micropowder 600 mesh, flake graphite 100 mesh, and modified layered magnesium phosphate 1250 mesh.

3. The dimensionally stable and anti-adhesion friction material for electromagnetic brake according to claim 1, characterized in that: The raw material components are calculated by weight and include 20-25 parts of adhesive, 35-45 parts of reinforcing material, 25-35 parts of friction-increasing filler, and 10-20 parts of friction-reducing filler.

4. The dimensionally stable and anti-adhesion friction material for electromagnetic brake according to claim 1, characterized in that: The raw material components, calculated by weight, include 8-12 parts of benzoxazine, 5-8 parts of bismaleimide, 2-5 parts of cyanate resin, 4-6 parts of nitrile rubber powder, 5-10 parts of zinc fiber, 3-8 parts of modified bamboo fiber, 8-12 parts of ceramic fiber, 4-8 parts of silicon carbide whiskers, 8-15 parts of calcium sulfate whiskers, 1-3 parts of modified poly(p-phenylene benzobisoxazole) pulp, 10-15 parts of calcined kaolin, 5-8 parts of precipitated barium sulfate, 3-8 parts of cashew nut shell oil-modified phenolic resin-coated amorphous silica, 5-10 parts of magnesium oxide, 4-6 parts of polytetrafluoroethylene micropowder, 2-6 parts of flake graphite, and 3-6 parts of modified layered magnesium phosphate.

5. The dimensionally stable and anti-adhesion friction material for electromagnetic brake according to claim 4, characterized in that: The raw material components are calculated by weight, including any one of combination A, combination B, and combination C: Combination A: 10 parts benzoxazine, 6 parts bismaleimide, 4 parts cyanate resin, 5 parts nitrile rubber powder, 7 parts zinc fiber, 3 parts modified bamboo fiber, 11 parts ceramic fiber, 5 parts silicon carbide whiskers, 12 parts calcium sulfate whiskers, 1 part modified poly(p-phenylene benzobisoxazole) pulp, 13 parts calcined kaolin, 6 parts precipitated barium sulfate, 4 parts cashew nut shell liquid-modified phenolic resin-coated amorphous silica, 6 parts magnesium oxide, 4 parts polytetrafluoroethylene powder, 3 parts flake graphite, 5 parts modified layered magnesium phosphate; Combination B: 8 parts of benzoxazine, 7 parts of bismaleimide, 3 parts of cyanate resin, 6 parts of nitrile rubber powder, 5 parts of zinc fiber, 7 parts of modified bamboo fiber, 12 parts of ceramic fiber, 4 parts of silicon carbide whiskers, 10 parts of calcium sulfate whiskers, 2 parts of modified poly(p-phenylene benzobisoxazole) pulp, 10 parts of calcined kaolin, 8 parts of precipitated barium sulfate, 6 parts of cashew nut shell liquid-modified phenolic resin-coated amorphous silica, 5 parts of magnesium oxide, 5 parts of polytetrafluoroethylene powder, 5 parts of flake graphite, and 4 parts of modified layered magnesium phosphate; Combination C: 12 parts of benzoxazine, 5 parts of bismaleimide, 2 parts of cyanate resin, 4 parts of nitrile rubber powder, 9 parts of zinc fiber, 5 parts of modified bamboo fiber, 9 parts of ceramic fiber, 7 parts of silicon carbide whiskers, 8 parts of calcium sulfate whiskers, 3 parts of modified poly(p-phenylene benzobisoxazole) pulp, 12 parts of calcined kaolin, 5 parts of precipitated barium sulfate, 8 parts of cashew nut shell oil-modified phenolic resin-coated amorphous silica, 7 parts of magnesium oxide, 6 parts of polytetrafluoroethylene powder, 6 parts of flake graphite, and 3 parts of modified layered magnesium phosphate.

6. The dimensionally stable and anti-adhesion friction material for electromagnetic brakes according to any one of claims 1 to 5, characterized in that: The preparation method of modified bamboo fiber is as follows: (1) The bamboo fibers are washed, impregnated, and dried with anhydrous ethanol to obtain pretreated bamboo fibers; (2) Immersing the pretreated bamboo fiber in the precursor solution, reacting at room temperature, taking it out and letting it stand, and then drying, washing, and baking to obtain the modified bamboo fiber; The molar ratio of tetrabutyl orthosilicate, ethanol, water and formic acid in the precursor solution is 1:4-8:2-8:0.01; the mass ratio of pretreated bamboo fiber to tetrabutyl orthosilicate is 1:8-12.

7. The dimensionally stable and anti-adhesion friction material for electromagnetic brakes according to any one of claims 1 to 5, characterized in that: The preparation method of the modified poly(p-phenylene benzobisoxazole) pulp comprises the following steps: immersing the poly(p-phenylene benzobisoxazole) pulp in a maleic anhydride hydrogen peroxide solution, and performing heating, soaking, filtering and drying to obtain the modified poly(p-phenylene benzobisoxazole) pulp.

8. The dimensionally stable and anti-adhesion friction material for electromagnetic brakes according to any one of claims 1 to 5, characterized in that: The preparation method of cashew nut shell liquid modified phenolic resin coated amorphous silica comprises: pre-treating silica with a silane coupling agent ethanol solution to obtain modified silica; dispersing the modified silica in a prepolymer solution and performing coating polymerization; the raw materials in the prepolymer solution are phenol, cashew nut shell liquid, formaldehyde, a catalyst, a solvent, and a dispersant, and the ratio of the raw material components in the prepolymer solution is 100:30-50:120-150:0.5-1:200-260:1-2; and the polymerization process comprises: controlling the temperature at 70-85°C for 0.5-1.5 hours; Then, the temperature is controlled to be 85-95°C for 1-3 hours; and then the temperature is maintained at 95°C until the viscosity reaches >2000 cP to obtain the finished product.

9. The dimensionally stable and anti-adhesion friction material for electromagnetic brakes according to any one of claims 1 to 5, characterized in that: The preparation method of the modified layered magnesium phosphate comprises the following steps: placing the layered magnesium phosphate in a sodium dodecylbenzenesulfonate ethanol solution for ultrasonic oscillation, washing and drying the layered magnesium phosphate, placing the layered magnesium phosphate in a tartaric acid solution for ultrasonic oscillation, filtering, washing and drying the layered magnesium phosphate.

10. A method for preparing a dimensionally stable and anti-adhesion friction material for an electromagnetic brake according to any one of claims 1 to 9, 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; and then pressed into a mold to obtain a semi-finished product I; S4 is then subjected to hot pressing to obtain semi-finished product II; S5 is then heat treated to obtain friction material; S6 friction material has a ground surface.

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