Low-friction composition brake shoe and preparation method thereof

Abstract

The invention discloses a low-friction composite brake shoe and a preparation method thereof in the field of brake shoes. The composite material is prepared from the following raw materials: 25 to 30 parts of cashew nut shell oil modified phenolic resin, 8 to 12 parts of nitrile rubber, 18 to 25 parts of metal fiber complex, 15 to 20 parts of crystalline flake graphite, 14 to 18 parts of sepiolite fiber, 6 to 8 parts of molybdenum disulfide, 4 to 6 parts of silicon carbide, 3 to 5 parts of talcum powder and 1 to 3 parts of epoxidized soybean oil. Wherein the metal fiber complex is obtained by firstly attaching two metal fibers with different linear thermal expansion coefficients side by side, fusing end points and then coating the surfaces with a boron nitride silicone rubber buffer layer. The cashew nut shell oil modified phenolic resin is adopted, and the metal fiber complex is used for replacing conventional metal reinforced fibers, so that crack initiation and expansion of the brake shoe can be delayed, uniaxial tension or shear stress caused by external loads can be weakened, the overall toughness of the brake shoe can be improved, and the high-temperature friction resistance of the brake shoe can be improved.

Description

Technical Field

[0001] The invention relates to the technical field of brake shoes, and in particular to a low-friction synthetic brake shoe and a preparation method thereof. Background Art

[0002] Brake shoes are mainly used as brake parts for directly rubbing the wheels to stop the train when the train is running. Of course, they can also be used in aviation, aerospace and other fields. According to the friction coefficient, they can be divided into high-friction brake shoes and low-friction brake shoes. In terms of materials, the brake shoes in trains have been made of cast iron brake shoes for more than a hundred years since 1853. With the increase in speed, the friction of cast iron brake shoes at high speeds easily causes fires, and the noise is loud and the wear is too fast. The shortcomings have become prominent contradictions, so people began to use synthetic brake shoes.

[0003] Among them, low-friction synthetic brake shoes are made of synthetic materials such as resin, rubber, metal fiber and friction modifier. Through optimized formula, they achieve brake shoes with a lower friction coefficient (usually in the range of 0.25-0.35). Compared with high-friction synthetic brake shoes, they have the advantages of small friction temperature rise, low wear rate, good environmental protection and low noise. They are mainly used in places with frequent starting and stopping, noise sensitivity and high environmental protection requirements, such as urban subway / light rail.

[0004] However, the existing low-friction synthetic brake shoes do not add asbestos and glass fibers due to environmental factors, which leads to poor bonding of the materials within the brake shoes, and in turn leads to poor mechanical and friction properties. Summary of the invention

[0005] The object of the present invention is to provide a low-friction synthetic brake shoe and a preparation method thereof, which solves the problem that the existing low-friction synthetic brake shoe has poor mechanical properties and friction properties.

[0006] The present invention achieves the above-mentioned purpose through the following technical solutions: A low-friction synthetic brake shoe, wherein the raw materials for its preparation include, by weight: 25-30 parts of cashew nut shell oil-modified phenolic resin, 8-12 parts of nitrile rubber, 18-25 parts of metal fiber composite, 15-20 parts of flake graphite, 14-18 parts of sepiolite fiber, 6-8 parts of molybdenum disulfide, 4-6 parts of silicon carbide, 3-5 parts of talc and 1-3 parts of epoxidized soybean oil; The metal fiber composite is obtained by firstly placing two metal fibers with different linear thermal expansion coefficients side by side and fusing their ends, and then coating the surface with a boron nitride silicone rubber buffer layer.

[0007] A further improvement is that the metal fiber is a combination of 4130 alloy steel fiber and C26000 brass fiber, or a combination of SAE1008 low carbon steel fiber and C11000 copper fiber.

[0008] A further improvement is that the length of the metal fiber is 3-6 mm.

[0009] A further improvement is that the buffer layer has a thickness of 20-40 μm.

[0010] The present invention also provides a method for preparing the low-friction synthetic brake shoe, the steps comprising: S1, preparing cashew nut shell oil modified phenolic resin, then mixing the cashew nut shell oil modified phenolic resin and nitrile rubber and heating to 60-65° C. to soften, and then stirring at a speed of 400-600 rpm for 3-6 minutes to obtain a mixture A; S2, preparing a metal fiber composite, adding the metal fiber composite and sepiolite fiber to the mixture A, and stirring at a speed of 800-1200 rpm for 8-12 minutes to obtain a mixture B; S3, adding flake graphite, molybdenum disulfide, silicon carbide, talc and epoxidized soybean oil to the mixture B, and stirring at a speed of 1200-1500 rpm for 8-12 min to obtain a mixture C; S4, preheat the molding mold to 75-85°C and pre-coat the mold release agent, then put the mixture C into the mold, control the temperature to 160-180°C, the pressure to 25-30MPa, and maintain the pressure for 12-15min; S5. Demolding to obtain a primary product, immediately placing the primary product into an annealing furnace, heat treating it at 180-200° C. for 2-3 hours, and finally sandblasting to remove burrs, thereby obtaining the low-friction synthetic brake shoe.

[0011] A further improvement is that in step S1, the specific operation of preparing the cashew nut shell oil modified phenolic resin is: prepare a container, first add cashew nut shell oil and phosphoric acid into the container, then add paraformaldehyde while stirring, after the paraformaldehyde is completely dissolved, heat the solution to 85-95°C and keep the temperature for reaction for 2-5h to obtain a reaction solution, take the reaction solution and vacuum dehydrate it at a temperature of 80-90°C for 2-4h to obtain the cashew nut shell oil modified phenolic resin.

[0012] A further improvement is that the mass ratio of cashew nut shell liquid, phosphoric acid and paraformaldehyde is cashew nut shell liquid: phosphoric acid: paraformaldehyde = 100: 0.4-0.6: 6-8.

[0013] A further improvement is that in step S2, the specific operation of preparing the metal fiber composite is: S2.1. Take two metal fiber filaments with a length of 20-50 cm, a diameter of 200-250 μm and different linear thermal expansion coefficients, ultrasonically clean and dry them with acetone, and then use a ceramic V-groove fixture to place and fix the two metal fiber filaments side by side, and then use a pulsed fiber laser to perform laser welding in an argon atmosphere. The welding adopts a dot-marking method with an interval of 3-6 mm to obtain a bundled fiber filament, and then cut the bundled fiber filament at each welding point to obtain a bundled short fiber that is side by side and fused at the end points for use; S2.2, dispersing the boron nitride nanosheets in ethanol with a mass concentration of 5-10% by weight at 10-15 times the mass of the boron nitride nanosheets, adding a silane coupling agent accounting for 1-3% of the mass of the boron nitride nanosheets, and then using an ultrasonic treatment with a power of 300-350W for 30-60min, and then centrifugally drying to obtain modified boron nitride nanosheets; S2.3, take silicone rubber and white carbon black and mix them, add modified boron nitride nanosheets, heat to 50-60 ° C, add flame retardant and platinum catalyst, mix for 20-30 minutes, filter through a sieve, and vacuum degas to obtain a rubber mixture, dissolve the rubber mixture in 5-8 times the mass of xylene, add 0.5-1.5% of the mass of silicone rubber, and obtain a coating liquid; S2.4, completely immersing the bundled short fibers in the coating liquid and leaving for 15-20 seconds, then taking them out, pre-curing the bundled short fibers at 70-80° C. for 20-30 minutes, and then vulcanizing the bundled short fibers at 160-170° C. for 4-6 minutes; S2.5. Repeat the operation of step S2.4 until a buffer layer of desired thickness is obtained.

[0014] A further improvement is that in step S2.1, the parameters of the laser welding are: power 10-30 W, pulse frequency 5-20 Hz, pulse width 1-5 ms, and spot diameter 80-100 μm.

[0015] A further improvement is that in step S2.3, the mass ratio of the silicone rubber raw rubber, white carbon black, modified boron nitride nanosheets, flame retardant and platinum catalyst is 100:10-30:5-20:5-10:0.5-1.

[0016] The beneficial effects of the present invention are: (1) The present invention adopts cashew nut shell oil modified phenolic resin, which introduces a flexible segment through copolymerization reaction, thereby improving the overall toughness of the brake shoe and improving the high temperature friction performance of the brake shoe.

[0017] (2) The present invention replaces conventional metal reinforcing fibers with metal fiber composites, which improves their own toughness and compatibility with the matrix, and has a good bonding effect. When the brake shoe is heated up during braking, the fibers with a larger linear thermal expansion coefficient in the metal fiber composite will elongate to a greater extent, thereby causing the metal fiber composite to generate lateral bending stress, which is transmitted outward through the extrusion buffer layer, so that internal stresses uniformly distributed in all directions and positions are generated inside the brake shoe. These internal stresses restrain each other to form a self-balancing network, which can inhibit local stress concentration, delay the initiation and expansion of brake shoe cracks, and improve high-temperature friction performance. At the same time, it helps to reduce the unidirectional tensile or shear stress caused by external loads and improve the fracture toughness of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Surface micromorphology of the samples in each experimental group after friction and wear. DETAILED DESCRIPTION

[0019] The present application is further described in detail below in conjunction with the accompanying drawings. It is necessary to point out here that the following specific implementation methods are only used to further illustrate the present application and cannot be understood as limiting the scope of protection of the present application. Technical personnel in this field can make some non-essential improvements and adjustments to the present application based on the above application content.

[0020] 1. Main Materials Cashew nut shell liquid: JT-002 type, purchased from Boxing County Deyi Trading Co., Ltd.; Phenolic resin: Sumitomo PR-12603, purchased from Waidian International Chemical Store; Nitrile rubber: P830E type, purchased from Hengshui Ruien Rubber & Plastic Technology Co., Ltd.; 4130 alloy steel fiber and SAE1008 low carbon steel fiber were purchased from Yu Antai Technology Co., Ltd., C26000 brass fiber and C11000 copper fiber were purchased from Dongguan Jinlei Copper and Aluminum Materials Co., Ltd.; Flake graphite: purchased from Qingdao Haida Graphite Co., Ltd. Sepiolite fiber: purchased from Zhejiang Fenghong New Materials Co., Ltd.; Molybdenum disulfide: purchased from Henan Yingtou Chemical Products Co., Ltd.; Silicon carbide: purchased from Zhengzhou Haixu Abrasive Co., Ltd. Talc: purchased from Anhui Xuanlang New Material Technology Co., Ltd.; Epoxidized soybean oil: purchased from Nanjing Rongji Chemical Co., Ltd.

[0021] 2. Implementation of the experiment

[0022] Example 1

[0023] A low-friction synthetic brake shoe, whose preparation raw materials include, by weight: 25 parts of cashew nut shell oil modified phenolic resin, 12 parts of nitrile rubber, 18 parts of metal fiber composite, 15 parts of flake graphite, 14 parts of sepiolite fiber, 6 parts of molybdenum disulfide, 4 parts of silicon carbide, 3 parts of talc and 1 part of epoxidized soybean oil.

[0024] The preparation method of the low-friction synthetic brake shoe comprises the following steps: S1. Prepare a container, first add cashew nut shell liquid and phosphoric acid into the container, then add paraformaldehyde while stirring, the mass ratio of cashew nut shell liquid: phosphoric acid: paraformaldehyde = 100: 0.4: 6, after the paraformaldehyde is completely dissolved, heat the solution to 85 ° C and keep the temperature for 5 hours to obtain a reaction solution, take the reaction solution and vacuum dehydrate it at 80 ° C for 4 hours to obtain cashew nut shell liquid modified phenolic resin, then mix the cashew nut shell liquid modified phenolic resin and nitrile rubber and heat to 60 ° C to soften, and then stir at a speed of 400 rpm for 6 minutes to obtain a mixture A; S2, preparing a metal fiber composite, adding the metal fiber composite and sepiolite fiber to the mixture A, and stirring at a speed of 800 rpm for 12 minutes to obtain a mixture B; The specific operation of preparing the metal fiber composite is as follows: S2.1. Take two metal fiber filaments (4130 alloy steel fiber and C26000 brass fiber) with a length of 20 cm and a diameter of 200 μm and different linear thermal expansion coefficients, clean them ultrasonically with acetone and dry them, and then use a ceramic V-groove fixture to place and fix the two metal fiber filaments side by side, and then use a pulsed fiber laser to perform laser welding in an argon atmosphere (power 10 W, pulse frequency 5 Hz, pulse width 1 ms, spot diameter 80 μm), with a dot-marking method at an interval of 3 mm to obtain bundled fiber filaments, and then cut the bundled fiber filaments at each welding point to obtain bundled short fibers with a length of 3 mm, side by side and fused at the end points for use; S2.2, dispersing the boron nitride nanosheets in ethanol with a mass concentration of 5% and 10 times the mass of the boron nitride nanosheets, adding a silane coupling agent with a mass concentration of 1% of the boron nitride nanosheets, and then subjecting the mixture to ultrasonic treatment at a power of 300 W for 60 min, and then centrifugally drying to obtain modified boron nitride nanosheets; S2.3, mix the raw silicone rubber with white carbon black, add modified boron nitride nanosheets, heat to 50°C, add flame retardant (halogen-free flame retardant ADK STAB FP-2200, the same below) and platinum catalyst (chloroplatinic acid tetramethyl divinyl disiloxane complex, the same below), mix for 20 minutes, filter through a sieve, and vacuum degas to obtain a rubber mixture, dissolve the rubber mixture in 5 times the mass of xylene, add 0.5% of the mass of the raw silicone rubber with a dipentadienyl vulcanizing agent to obtain a coating liquid; wherein the mass ratio of the raw silicone rubber, white carbon black, modified boron nitride nanosheets, flame retardant, and platinum catalyst is 100:10:5:5:0.5; S2.4, completely immersing the bundled short fibers in the coating liquid and taking them out after staying for 15 seconds, pre-curing the bundled short fibers at 70° C. for 30 minutes, and then vulcanizing the bundled short fibers at 160° C. for 6 minutes; S2.5, repeat the operation of step S2.4 twice to obtain a buffer layer with a thickness of 20 μm; S3, adding flake graphite, molybdenum disulfide, silicon carbide, talc and epoxidized soybean oil to the mixture B, and stirring at a speed of 1200 rpm for 12 minutes to obtain a mixture C; S4, preheat the molding mold to 75°C and pre-coat the mold release agent, then put the mixture C into the mold, control the temperature to 160°C, the pressure to 25MPa, and maintain the pressure for 15 minutes; S5. Demolding to obtain a primary product, immediately placing the primary product into an annealing furnace, heat treating it at 180° C. for 3 hours, and finally sandblasting to remove burrs, thereby obtaining the low-friction synthetic brake shoe.

[0025] Example 2

[0026] A low-friction synthetic brake shoe, whose preparation raw materials include, by weight: 28 parts of cashew nut shell oil modified phenolic resin, 10 parts of nitrile rubber, 22 parts of metal fiber composite, 18 parts of flake graphite, 16 parts of sepiolite fiber, 7 parts of molybdenum disulfide, 5 parts of silicon carbide, 4 parts of talc and 2 parts of epoxidized soybean oil.

[0027] The preparation method of the low-friction synthetic brake shoe comprises the following steps: S1. Prepare a container, first add cashew nut shell liquid and phosphoric acid into the container, then add paraformaldehyde while stirring, the mass ratio of cashew nut shell liquid: phosphoric acid: paraformaldehyde = 100: 0.5: 7, after the paraformaldehyde is completely dissolved, heat the solution to 90 ° C and keep it for 3 hours to obtain a reaction solution, take the reaction solution and vacuum dehydrate it at 85 ° C for 3 hours to obtain cashew nut shell liquid modified phenolic resin, then mix the cashew nut shell liquid modified phenolic resin and nitrile rubber and heat to 62 ° C to soften, and then stir at a speed of 500 rpm for 5 minutes to obtain a mixture A; S2, preparing a metal fiber composite, adding the metal fiber composite and sepiolite fiber to the mixture A, and stirring at a speed of 1000 rpm for 10 minutes to obtain a mixture B; The specific operation of preparing the metal fiber composite is as follows: S2.1. Take two metal fiber filaments (SAE1008 low-carbon steel fiber and C11000 copper fiber) with a length of 35 cm and a diameter of 220 μm and different linear thermal expansion coefficients, clean them ultrasonically with acetone and dry them, then use a ceramic V-groove fixture to place and fix the two metal fiber filaments side by side, and then use a pulsed fiber laser to perform laser welding in an argon atmosphere (power 20 W, pulse frequency 15 Hz, pulse width 3 ms, spot diameter 90 μm), with a dot-marking method with an interval of 5 mm to obtain a bundled fiber filament, and then cut the bundled fiber filament at each welding point to obtain a bundled short fiber with a length of 5 mm, side by side and fused at the end points for use; S2.2, dispersing the boron nitride nanosheets in ethanol with a mass concentration of 8% and 12 times the mass of the boron nitride nanosheets, adding a silane coupling agent accounting for 2% of the mass of the boron nitride nanosheets, and then subjecting the mixture to ultrasonic treatment at a power of 320 W for 45 min, and then centrifugally drying to obtain modified boron nitride nanosheets; S2.3, take silicone rubber raw rubber and white carbon black, mix them, add modified boron nitride nanosheets, heat to 50°C, add flame retardant and platinum catalyst, mix for 25 minutes, filter through a sieve, and vacuum degas to obtain a rubber mixture, dissolve the rubber mixture in 6 times the mass of xylene, add a di-pentane vulcanizing agent accounting for 1% of the mass of the silicone rubber raw rubber, and obtain a coating liquid; wherein the mass ratio of silicone rubber raw rubber, white carbon black, modified boron nitride nanosheets, flame retardant, and platinum catalyst is 100:20:15:8:0.8; S2.4, completely immersing the bundled short fibers in the coating liquid and leaving them there for 18 seconds, then taking them out, pre-curing the bundled short fibers at 75° C. for 25 minutes, and then vulcanizing the bundled short fibers at 165° C. for 5 minutes; S2.5, repeat the operation of step S2.4 three times until a buffer layer with a thickness of 30 μm is obtained; S3, adding flake graphite, molybdenum disulfide, silicon carbide, talc and epoxidized soybean oil to the mixture B, and stirring at a speed of 1300 rpm for 10 min to obtain a mixture C; S4, preheat the molding mold to 80°C and pre-coat the mold release agent, then put the mixture C into the mold, control the temperature to 170°C, the pressure to 28MPa, and maintain the pressure for 14 minutes; S5. Demolding to obtain a primary product, immediately placing the primary product into an annealing furnace, heat treating it at 190° C. for 2.5 hours, and finally sandblasting to remove burrs, thereby obtaining the low-friction synthetic brake shoe.

[0028] Example 3

[0029] A low-friction synthetic brake shoe, whose preparation raw materials include, by weight: 30 parts of cashew nut shell oil-modified phenolic resin, 8 parts of nitrile rubber, 25 parts of metal fiber composite, 20 parts of flake graphite, 18 parts of sepiolite fiber, 8 parts of molybdenum disulfide, 6 parts of silicon carbide, 5 parts of talc and 3 parts of epoxidized soybean oil.

[0030] The preparation method of the low-friction synthetic brake shoe comprises the following steps: S1. Prepare a container, first add cashew nut shell liquid and phosphoric acid into the container, then add paraformaldehyde while stirring, the mass ratio of cashew nut shell liquid: phosphoric acid: paraformaldehyde = 100: 0.6: 8, after the paraformaldehyde is completely dissolved, heat the solution to 95 ° C and keep it for 2 hours to obtain a reaction solution, take the reaction solution and vacuum dehydrate it at 90 ° C for 2 hours to obtain cashew nut shell liquid modified phenolic resin, then mix the cashew nut shell liquid modified phenolic resin and nitrile rubber and heat to 65 ° C to soften, and then stir at a speed of 600 rpm for 3 minutes to obtain a mixture A; S2, preparing a metal fiber composite, adding the metal fiber composite and sepiolite fiber to the mixture A, and stirring at a speed of 1200 rpm for 8 minutes to obtain a mixture B; The specific operation of preparing the metal fiber composite is as follows: S2.1. Take two metal fiber filaments (SAE1008 low-carbon steel fiber and C11000 copper fiber) with a length of 50 cm and a diameter of 250 μm and different linear thermal expansion coefficients, ultrasonically clean and dry them with acetone, and then use a ceramic V-groove fixture to place and fix the two metal fiber filaments side by side, and then use a pulsed fiber laser to perform laser welding in an argon atmosphere (power 30 W, pulse frequency 20 Hz, pulse width 5 ms, spot diameter 100 μm). The welding adopts a dot-marking method with an interval of 6 mm to obtain a bundled fiber filament, and then cut the bundled fiber filament at each welding point to obtain a bundled short fiber with a length of 6 mm, side by side and fused at the end points for use; S2.2, dispersing the boron nitride nanosheets in 15 times the mass of ethanol with a mass concentration of 10%, adding a silane coupling agent accounting for 3% of the mass of the boron nitride nanosheets, and then using an ultrasonic treatment with a power of 350W for 30min, and then centrifugally drying to obtain modified boron nitride nanosheets; S2.3, take silicone rubber raw rubber and white carbon black, mix them, add modified boron nitride nanosheets, heat to 60°C, add flame retardant and platinum catalyst, mix for 30 minutes, filter through a sieve, and vacuum degas to obtain a rubber mixture, dissolve the rubber mixture in 8 times the mass of xylene, add 1.5% of the mass of silicone rubber raw rubber dipentane vulcanizer, and obtain a coating liquid; wherein the mass ratio of silicone rubber raw rubber, white carbon black, modified boron nitride nanosheets, flame retardant, and platinum catalyst is 100:30:20:10:1; S2.4, completely immersing the bundled short fibers in the coating liquid and taking them out after staying for 20 seconds, pre-curing the bundled short fibers at 80° C. for 20 minutes, and then vulcanizing the bundled short fibers at 170° C. for 4 minutes; S2.5, repeat the operation of step S2.4 four times until a buffer layer with a thickness of 40 μm is obtained; S3, adding flake graphite, molybdenum disulfide, silicon carbide, talc and epoxidized soybean oil to the mixture B, and stirring at a speed of 1500 rpm for 8 minutes to obtain a mixture C; S4, preheat the molding mold to 85°C and pre-coat the mold release agent, then put the mixture C into the mold, control the temperature to 180°C, the pressure to 30MPa, and maintain the pressure for 12 minutes; S5. Demolding to obtain a primary product, immediately placing the primary product into an annealing furnace, heat treating it at 200° C. for 2 hours, and finally sandblasting to remove burrs, thereby obtaining the low-friction synthetic brake shoe.

[0031] Comparative Example 1 A low-friction synthetic brake shoe, whose preparation raw materials include, by weight: 28 parts of cashew nut shell oil modified phenolic resin, 10 parts of nitrile rubber, 11 parts of SAE1008 low-carbon steel fiber, 11 parts of C11000 copper fiber, 18 parts of flake graphite, 16 parts of sepiolite fiber, 7 parts of molybdenum disulfide, 5 parts of silicon carbide, 4 parts of talc and 2 parts of epoxidized soybean oil.

[0032] The preparation method of the low-friction synthetic brake shoe comprises the following steps: S1. Prepare a container, first add cashew nut shell liquid and phosphoric acid into the container, then add paraformaldehyde while stirring, the mass ratio of cashew nut shell liquid: phosphoric acid: paraformaldehyde = 100: 0.5: 7, after the paraformaldehyde is completely dissolved, heat the solution to 90 ° C and keep it for 3 hours to obtain a reaction solution, take the reaction solution and vacuum dehydrate it at 85 ° C for 3 hours to obtain cashew nut shell liquid modified phenolic resin, then mix the cashew nut shell liquid modified phenolic resin and nitrile rubber and heat to 62 ° C to soften, and then stir at a speed of 500 rpm for 5 minutes to obtain a mixture A; S2, adding SAE1008 low carbon steel fiber, C11000 copper fiber and sepiolite fiber to the mixture A, and stirring at a speed of 1000 rpm for 10 min to obtain a mixture B; S3, adding flake graphite, molybdenum disulfide, silicon carbide, talc and epoxidized soybean oil to the mixture B, and stirring at a speed of 1300 rpm for 10 min to obtain a mixture C; S4, preheat the molding mold to 80°C and pre-coat the mold release agent, then put the mixture C into the mold, control the temperature to 170°C, the pressure to 28MPa, and maintain the pressure for 14 minutes; S5. Demolding to obtain a primary product, immediately placing the primary product into an annealing furnace, heat treating it at 190° C. for 2.5 hours, and finally sandblasting to remove burrs, thereby obtaining the low-friction synthetic brake shoe.

[0033] Comparative Example 2 A low-friction synthetic brake shoe, whose preparation raw materials include, by weight: 28 parts of cashew nut shell oil modified phenolic resin, 10 parts of nitrile rubber, 22 parts of metal fiber composite, 18 parts of flake graphite, 16 parts of sepiolite fiber, 7 parts of molybdenum disulfide, 5 parts of silicon carbide, 4 parts of talc and 2 parts of epoxidized soybean oil.

[0034] The preparation method of the low-friction synthetic brake shoe comprises the following steps: S1. Prepare a container, first add cashew nut shell liquid and phosphoric acid into the container, then add paraformaldehyde while stirring, the mass ratio of cashew nut shell liquid: phosphoric acid: paraformaldehyde = 100: 0.5: 7, after the paraformaldehyde is completely dissolved, heat the solution to 90 ° C and keep it for 3 hours to obtain a reaction solution, take the reaction solution and vacuum dehydrate it at 85 ° C for 3 hours to obtain cashew nut shell liquid modified phenolic resin, then mix the cashew nut shell liquid modified phenolic resin and nitrile rubber and heat to 62 ° C to soften, and then stir at a speed of 500 rpm for 5 minutes to obtain a mixture A; S2, preparing a metal fiber composite, adding the metal fiber composite and sepiolite fiber to the mixture A, and stirring at a speed of 1000 rpm for 10 minutes to obtain a mixture B; The specific operation of preparing the metal fiber composite is as follows: take two metal fiber filaments (SAE1008 low-carbon steel fiber and C11000 copper fiber) with a length of 35 cm and a diameter of 220 μm and different linear thermal expansion coefficients, ultrasonically clean and dry them with acetone, and then use a ceramic V-groove clamp to place and fix the two metal fiber filaments side by side, and then use a pulsed fiber laser to perform laser welding in an argon atmosphere (power 20 W, pulse frequency 15 Hz, pulse width 3 ms, spot diameter 90 μm), and the welding adopts a dot method with an interval of 5 mm to obtain a bundled fiber filament, and then cut the bundled fiber filament at each welding point to obtain a bundled short fiber with a length of 5 mm, side by side and fused at the end points, and use it as a metal fiber composite; S3, adding flake graphite, molybdenum disulfide, silicon carbide, talc and epoxidized soybean oil to the mixture B, and stirring at a speed of 1300 rpm for 10 min to obtain a mixture C; S4, preheat the molding mold to 80°C and pre-coat the mold release agent, then put the mixture C into the mold, control the temperature to 170°C, the pressure to 28MPa, and maintain the pressure for 14 minutes; S5. Demolding to obtain a primary product, immediately placing the primary product into an annealing furnace, heat treating it at 190° C. for 2.5 hours, and finally sandblasting to remove burrs, thereby obtaining the low-friction synthetic brake shoe.

[0035] Blank group A low-friction synthetic brake shoe, whose preparation raw materials include, by weight: 28 parts of cashew nut shell oil-modified phenolic resin, 10 parts of nitrile rubber, 18 parts of flake graphite, 16 parts of sepiolite fiber, 7 parts of molybdenum disulfide, 5 parts of silicon carbide, 4 parts of talc and 2 parts of epoxidized soybean oil.

[0036] The preparation method of the low-friction synthetic brake shoe comprises the following steps: S1. Prepare a container, first add cashew nut shell liquid and phosphoric acid into the container, then add paraformaldehyde while stirring, the mass ratio of cashew nut shell liquid: phosphoric acid: paraformaldehyde = 100: 0.5: 7, after the paraformaldehyde is completely dissolved, heat the solution to 90 ° C and keep it for 3 hours to obtain a reaction solution, take the reaction solution and vacuum dehydrate it at 85 ° C for 3 hours to obtain cashew nut shell liquid modified phenolic resin, then mix the cashew nut shell liquid modified phenolic resin and nitrile rubber and heat to 62 ° C to soften, and then stir at a speed of 500 rpm for 5 minutes to obtain a mixture A; S2, adding sepiolite fiber to the mixture A, and stirring at a speed of 1000 rpm for 10 min to obtain a mixture B; S3, adding flake graphite, molybdenum disulfide, silicon carbide, talc and epoxidized soybean oil to the mixture B, and stirring at a speed of 1300 rpm for 10 min to obtain a mixture C; S4, preheat the molding mold to 80°C and pre-coat the mold release agent, then put the mixture C into the mold, control the temperature to 170°C, the pressure to 28MPa, and maintain the pressure for 14 minutes; S5. Demolding to obtain a primary product, immediately placing the primary product into an annealing furnace, heat treating it at 190° C. for 2.5 hours, and finally sandblasting to remove burrs, thereby obtaining the low-friction synthetic brake shoe.

[0037] 3. Performance Test Sample requirements: According to the sample size requirements of "TB / T3196-2015 Synthetic Brake Shoes for Locomotives", the following samples were prepared from the brake shoes prepared in Example 2, Comparative Examples 1-2 and the blank group: 120mm×15mm×10mm unnotched samples were used for impact strength testing; 25.4mm×25.4mm×8mm samples were prepared for abrasion testing. The length, width and thickness of the sample were required to be consistent with those of the brake shoe.

[0038] in: (1) Impact strength: Tested using an XJJ-5 impact testing machine in accordance with GB / T1043.1-2008 Determination of impact properties of simply supported beams of plastics Part 1: Non-instrumented impact test. The impact strength calculation formula is as follows:

[0039] Where: a is the impact strength, unit kJ / m 2 ; A is the impact energy absorbed by the sample, unit is J; b is the width of the sample, unit is m; d is the thickness of the sample, unit is m.

[0040] (2) Wear and friction coefficient: The test was conducted using a QDM150 adjustable speed and pressure friction material performance testing machine in accordance with GB / T17469-2012 Test Method for Evaluation of Friction Performance of Automobile Brake Linings. The parameter settings were as follows: friction disc (HT180-250HB) diameter 30 cm, applied pressure 0.98 MPa, speed 1500 r / min, and number of revolutions 5000 rpm.

[0041] In addition, the worn samples of each experimental group were taken and the surface microstructures of the samples after friction and wear were scanned using a FEI Quanta 200 scanning electron microscope.

[0042] IV. Results Analysis The test results of impact strength, abrasion and friction coefficient of Example 2, Comparative Examples 1-2 and the blank group were statistically analyzed to obtain the following Table 1: Table 1: Impact strength, abrasion and friction coefficient test results

[0044] It can be seen from Table 1 that the synthetic brake shoe prepared in Example 2 of the present invention has excellent mechanical properties and high temperature friction properties, and the impact strength reaches 5.95 kJ / m 2 , wear as low as 0.213cm 3 / MJ, the friction coefficient is also low, only 0.29, which belongs to low-friction brake shoes. In comparative example 1, the metal fiber composite is replaced with separate SAE1008 low-carbon steel fiber and C11000 copper fiber. The total amount of fiber added remains unchanged, but the impact strength decreases by 18.3% and the wear increases by 20.7%. The difference is very significant, indicating that the unique composite structure plays a key role, not just the effect of the two metal fibers themselves. In comparative example 2, the boron nitride silicone rubber buffer layer coated on the surface of the metal fiber composite is removed, resulting in a 21.5% decrease in impact strength and a 26.3% increase in wear. The difference is also very significant, indicating that the buffer layer also plays a key role in improving material compatibility and providing space for stress deformation of the metal fiber composite. Otherwise, the effect of adding the metal fiber composite cannot be fully exerted.

[0045] like Figure 1 As shown in the figure, it is the surface microscopic morphology of the samples in each experimental group after friction and wear, where A is the sample of Example 2, B is the sample of Comparative Example 1, C is the sample of Comparative Example 2, and D is the sample of the blank group. It can be seen that the friction surface of the sample surface material of Example 2 is still smooth, without obvious scratches, cracks, etc., and the wear amount is small; Comparative Examples 1 and Comparative Examples 2 both present different degrees of rough surfaces, and wrinkles, certain scratches and more wear debris appear; while the blank group presents an obvious rough surface, with deeper scratches, and a larger wear amount under the cutting action.

[0046] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A low-friction synthetic brake shoe, characterized in that: The raw materials for its preparation include, by weight: 25-30 parts of cashew nut shell oil-modified phenolic resin, 8-12 parts of nitrile rubber, 18-25 parts of metal fiber composite, 15-20 parts of flake graphite, 14-18 parts of sepiolite fiber, 6-8 parts of molybdenum disulfide, 4-6 parts of silicon carbide, 3-5 parts of talc and 1-3 parts of epoxidized soybean oil; The metal fiber composite is obtained by firstly placing two metal fibers with different linear thermal expansion coefficients side by side and fusing their ends, and then coating the surface with a boron nitride silicone rubber buffer layer.

2. A low-friction synthetic brake shoe according to claim 1, characterized in that: The metal fiber is selected from a combination of 4130 alloy steel fiber and C26000 brass fiber, or a combination of SAE1008 low carbon steel fiber and C11000 copper fiber.

3. A low-friction synthetic brake shoe according to claim 1, characterized in that: The length of the metal fiber is 3-6 mm.

4. A low-friction synthetic brake shoe according to claim 1, characterized in that: The thickness of the buffer layer is 20-40 μm.

5. A method for preparing a low-friction synthetic brake shoe as claimed in any one of claims 1 to 4, characterized in that the steps include: S1, preparing cashew nut shell oil modified phenolic resin, then mixing the cashew nut shell oil modified phenolic resin and nitrile rubber and heating to 60-65° C. to soften, and then stirring at a speed of 400-600 rpm for 3-6 minutes to obtain a mixture A; S2, preparing a metal fiber composite, adding the metal fiber composite and sepiolite fiber to the mixture A, and stirring at a speed of 800-1200 rpm for 8-12 minutes to obtain a mixture B; S3, adding flake graphite, molybdenum disulfide, silicon carbide, talc and epoxidized soybean oil to the mixture B, and stirring at a speed of 1200-1500 rpm for 8-12 min to obtain a mixture C; S4, preheat the molding mold to 75-85°C and pre-coat the mold release agent, then put the mixture C into the mold, control the temperature to 160-180°C, the pressure to 25-30MPa, and maintain the pressure for 12-15min; S5. Demolding to obtain a primary product, immediately placing the primary product into an annealing furnace, heat treating it at 180-200° C. for 2-3 hours, and finally sandblasting to remove burrs, thereby obtaining the low-friction synthetic brake shoe.

6. The method for preparing a low-friction synthetic brake shoe according to claim 5, characterized in that: In step S1, the specific operation of preparing the cashew nut shell oil modified phenolic resin is as follows: prepare a container, first add cashew nut shell oil and phosphoric acid into the container, then add paraformaldehyde while stirring, after the paraformaldehyde is completely dissolved, heat the solution to 85-95° C. and keep the temperature for reaction for 2-5 hours to obtain a reaction solution, take the reaction solution and vacuum dehydrate it at 80-90° C. for 2-4 hours to obtain the cashew nut shell oil modified phenolic resin.

7. The method for preparing a low-friction synthetic brake shoe according to claim 6, characterized in that: The mass ratio of cashew nut shell liquid, phosphoric acid and paraformaldehyde is cashew nut shell liquid: phosphoric acid: paraformaldehyde = 100: 0.4-0.6: 6-8.

8. The method for preparing a low-friction synthetic brake shoe according to claim 5, characterized in that: In step S2, the specific operation of preparing the metal fiber composite is: S2.

1. Take two metal fiber filaments with a length of 20-50 cm, a diameter of 200-250 μm and different linear thermal expansion coefficients, ultrasonically clean and dry them with acetone, and then use a ceramic V-groove fixture to place and fix the two metal fiber filaments side by side, and then use a pulsed fiber laser to perform laser welding in an argon atmosphere. The welding adopts a dot-marking method with an interval of 3-6 mm to obtain a bundled fiber filament, and then cut the bundled fiber filament at each welding point to obtain a bundled short fiber that is side by side and fused at the end points for use; S2.2, dispersing the boron nitride nanosheets in ethanol with a mass concentration of 5-10% by weight at 10-15 times the mass of the boron nitride nanosheets, adding a silane coupling agent accounting for 1-3% of the mass of the boron nitride nanosheets, and then using an ultrasonic treatment with a power of 300-350W for 30-60min, and then centrifugally drying to obtain modified boron nitride nanosheets; S2.3, take silicone rubber and white carbon black and mix them, add modified boron nitride nanosheets, heat to 50-60 ° C, add flame retardant and platinum catalyst, mix for 20-30 minutes, filter through a sieve, and vacuum degas to obtain a rubber mixture, dissolve the rubber mixture in 5-8 times the mass of xylene, add 0.5-1.5% of the mass of silicone rubber, and obtain a coating liquid; S2.4, completely immersing the bundled short fibers in the coating liquid and leaving for 15-20 seconds, then taking them out, pre-curing the bundled short fibers at 70-80° C. for 20-30 minutes, and then vulcanizing the bundled short fibers at 160-170° C. for 4-6 minutes; S2.

5. Repeat the operation of step S2.4 until a buffer layer of desired thickness is obtained.

9. The method for preparing a low-friction synthetic brake shoe according to claim 8, characterized in that: In step S2.1, the laser welding parameters are: power 10-30 W, pulse frequency 5-20 Hz, pulse width 1-5 ms, and spot diameter 80-100 μm.

10. The method for preparing a low-friction synthetic brake shoe according to claim 8, characterized in that: In step S2.3, the mass ratio of the silicone rubber, white carbon black, modified boron nitride nanosheets, flame retardant and platinum catalyst is 100:10-30:5-20:5-10:0.5-1.

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