A low-friction synthetic brake shoe and its preparation method

Abstract

The present invention discloses a low-friction synthetic brake shoe in the field of brake shoes and a preparation method thereof. By weight, the preparation raw materials include: 25-30 parts of cashew 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 talcum powder, and 1-3 parts of epoxy soybean oil; wherein, the metal fiber composite is obtained by first arranging two metal fibers with different linear thermal expansion coefficients side by side and fusing the endpoints, and then coating a boron nitride silicone rubber buffer layer on the surface. The present invention uses cashew shell oil modified phenolic resin and replaces conventional metal reinforcing fibers with metal fiber composites, which can delay the initiation and propagation of brake shoe cracks, weaken the unidirectional tensile or shear stress caused by external loads, improve the overall toughness of the brake shoe, and improve the high-temperature friction performance of the brake shoe.

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:

[0007] 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;

[0008] 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.

[0009] 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.

[0010] A further improvement lies in that the length of the metal fiber is 3 - 6 mm.

[0011] A further improvement lies in that the thickness of the buffer layer is 20 - 40 μm.

[0012] The present invention also provides a preparation method of the low - friction synthetic brake shoe, and the steps include:

[0013] S1. Prepare cashew shell oil modified phenolic resin, then mix the cashew shell oil modified phenolic resin and nitrile rubber and heat to 60 - 65 °C for softening, and then stir - process at a speed of 400 - 600 rpm for 3 - 6 min to obtain mixture A;

[0014] S2. Prepare a metal fiber composite, then add the metal fiber composite and sepiolite fiber to the mixture A, and then stir - process at a speed of 800 - 1200 rpm for 8 - 12 min to obtain mixture B;

[0015] S3. Add flake graphite, molybdenum disulfide, silicon carbide, talcum powder and epoxy soybean oil to the mixture B, and then stir - process at a speed of 1200 - 1500 rpm for 8 - 12 min to obtain mixture C;

[0016] S4. Preheat a molding die to 75 - 85 °C and pre - coat a release agent, then load the mixture C into the die, control the temperature at 160 - 180 °C and the pressure at 25 - 30 MPa, and perform pressure - maintaining treatment for 12 - 15 min;

[0017] S5. Demold to obtain a preliminary product, immediately put the preliminary product into an annealing furnace, perform heat treatment at 180 - 200 °C for 2 - 3 h, and finally perform sandblasting treatment to remove burrs, thus obtaining the low - friction synthetic brake shoe.

[0018] A further improvement lies in that in step S1, the specific operation for preparing the cashew shell oil modified phenolic resin is as follows: Prepare a container, first add cashew shell oil and phosphoric acid to the container, then add paraformaldehyde while stirring. After the paraformaldehyde is completely dissolved, heat the solution to 85 - 95 °C and keep it warm for reaction for 2 - 5 h to obtain a reaction solution. Take the reaction solution and perform vacuum dehydration at 80 - 90 °C for 2 - 4 h, thus obtaining the cashew shell oil modified phenolic resin.

[0019] A further improvement lies in that the mass ratio of the cashew shell oil, phosphoric acid, and paraformaldehyde is cashew shell oil: phosphoric acid: paraformaldehyde = 100:0.4 - 0.6:6 - 8.

[0020] A further improvement lies in that in step S2, the specific operation for preparing the metal fiber composite is as follows:

[0021] 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. After ultrasonic cleaning with acetone and drying, place and fix the two metal fiber filaments side by side and in contact using a ceramic V-groove fixture. Then, use a pulsed fiber laser to perform laser welding in an argon atmosphere. The welding is carried out in a dotting manner with a spacing of 3 - 6 mm to obtain a combined fiber filament. Then, cut the combined fiber filament at each welding point position to obtain combined short fibers that are side by side and in contact with their ends fused for standby;

[0022] S2.2. Disperse boron nitride nanosheets in ethanol with a mass 10 - 15 times that of the boron nitride nanosheets and a mass concentration of 5 - 10%. Add a silane coupling agent accounting for 1 - 3% of the mass of the boron nitride nanosheets. Then, perform ultrasonic treatment at a power of 300 - 350 W for 30 - 60 min, and then centrifuge and dry to obtain modified boron nitride nanosheets;

[0023] S2.3. Mix raw silicone rubber with silica white, add the modified boron nitride nanosheets, heat to 50 - 60 °C, then add a flame retardant and a platinum catalyst, and knead for 20 - 30 min. Then, filter through a sieve and degas under vacuum to obtain a kneaded rubber. Dissolve the kneaded rubber in xylene with a mass 5 - 8 times that of the raw silicone rubber, and add a bis(2,5-dimethyl-2,5-di(t-butylperoxy)hexane) vulcanizing agent accounting for 0.5 - 1.5% of the mass of the raw silicone rubber to obtain a coating liquid;

[0024] S2.4. Completely immerse the combined short fibers in the coating liquid, take them out after staying for 15 - 20 s, place the combined short fibers at a temperature of 70 - 80 °C for pre-curing for 20 - 30 min, and then place the combined short fibers at a temperature of 160 - 170 °C for vulcanization for 4 - 6 min;

[0025] S2.5. Repeat the operation in step S2.4 until a buffer layer with the required thickness is obtained, and that's it.

[0026] Further improvement lies in 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.

[0027] Further improvement lies in that in step S2.3, the mass ratio between the raw silicone rubber, silica white, modified boron nitride nanosheets, flame retardant, and platinum catalyst is 100:10 - 30:5 - 20:5 - 10:0.5 - 1.

[0028] The beneficial effects of the present invention are as follows:

[0029] (1) The present invention uses cardanol-modified phenolic resin, which introduces flexible chain segments through copolymerization reaction, improves the overall toughness of the brake shoe, and improves the high-temperature friction performance of the brake shoe.

[0030] (2) In the present invention, the conventional metal reinforcing fibers are replaced with metal fiber composites, which improves the toughness of the composites themselves and their compatibility with the matrix, resulting in good bonding effects. When the brake shoe brakes and the temperature rises, the fibers with a relatively large linear thermal expansion coefficient in the metal fiber composites will elongate to a greater extent, causing the metal fiber composites to generate lateral bending stress, which is then transmitted outward through the extrusion of the buffer layer, resulting in the generation of internal stresses uniformly distributed in all directions and at all positions within the brake shoe. These internal stresses restrict each other to form a self-balancing network, which can inhibit local stress concentration, delay the initiation and propagation of cracks in the brake shoe, improve the high-temperature friction performance, and at the same time help to weaken the unidirectional tensile or shear stress caused by external loads and improve the fracture toughness of the material. Description of the Drawings

[0031] Figure 1 It is the surface microtopography diagram of the specimens after friction and wear for each experimental group. Detailed Embodiments

[0032] The present application will be further described in detail below with reference to the drawings. It is necessary to point out here that the following detailed embodiments are only used to further illustrate the present application and should not be construed as limiting the protection scope of the present application. Those skilled in the art can make some non-essential improvements and adjustments to the present application based on the above application content.

[0033] I. Main Materials

[0034] Cardanol: Model JT-002, purchased from Deyi Trading Co., Ltd. in Boxing County;

[0035] Phenolic resin: Sumitomo PR-12603, purchased from the Foreign Electric International Chemicals Franchise Store;

[0036] Nitrile rubber: Model P830E, purchased from Hengshui Ruien Rubber and Plastic Technology Co., Ltd.;

[0037] 4130 alloy steel fibers and SAE1008 low-carbon steel fibers were purchased from Advanced Technology & Materials Co., Ltd., and C26000 brass fibers and C11000 copper fibers were purchased from Dongguan Jinlei Copper and Aluminum Materials Co., Ltd.;

[0038] Flake graphite: purchased from Qingdao Haida Graphite Co., Ltd.;

[0039] Sepiolite fibers: purchased from Zhejiang Fenghong New Materials Co., Ltd.;

[0040] Molybdenum disulfide: purchased from Henan Yingtou Chemical Products Co., Ltd.;

[0041] Silicon carbide: purchased from Zhengzhou Haixu Abrasives Co., Ltd.;

[0042] Talc powder: purchased from Anhui Xuanlang New Materials Technology Co., Ltd.;

[0043] Epoxidized soybean oil: purchased from Nanjing Rongji Chemical Co., Ltd.

[0044] II. Conduct experiments

[0045] Example 1

[0046] A low-friction synthetic brake shoe, calculated by weight parts, its preparation raw materials include: 25 parts of cashew 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 talcum powder and 1 part of epoxidized soybean oil.

[0047] The preparation method of the low-friction synthetic brake shoe includes the following steps:

[0048] S1. Prepare a container, first add cashew shell oil and phosphoric acid into the container, and then add paraformaldehyde while stirring. The mass ratio of cashew shell oil: phosphoric acid: paraformaldehyde = 100:0.4:6. After the paraformaldehyde is completely dissolved, heat the solution to 85 °C and keep it reacting for 5 h to obtain a reaction solution. Take the reaction solution and carry out vacuum dehydration at 80 °C for 4 h to obtain cashew shell oil modified phenolic resin. Then mix the cashew shell oil modified phenolic resin and nitrile rubber and heat them to 60 °C to soften, and then stir and process at a speed of 400 rpm for 6 min to obtain mixture A;

[0049] S2. Prepare the metal fiber composite, and then add the metal fiber composite and sepiolite fiber into the mixture A, and then stir and process at a speed of 800 rpm for 12 min to obtain mixture B;

[0050] Among them, the specific operation for preparing the metal fiber composite is as follows:

[0051] S2.1. Take two metal fiber filaments (4130 alloy steel fiber and C26000 brass fiber) with a length of 20 cm, a diameter of 200 μm and different linear thermal expansion coefficients. After ultrasonic cleaning and drying with acetone, use a ceramic V-groove fixture to place and fix the two metal fiber filaments side by side and in contact. Then use a pulsed fiber laser to carry out laser welding in an argon atmosphere (power 10 W, pulse frequency 5 Hz, pulse width 1 ms, spot diameter 80 μm). The welding adopts a dotting method with an interval of 3 mm to obtain a combined fiber filament. Then cut the combined fiber filament at each welding point position to obtain combined short fibers with a length of 3 mm, side by side and in contact and the endpoints fused for standby;

[0052] S2.2. Take boron nitride nanosheets and disperse them in ethanol with a mass 10 times and a mass concentration of 5%. Add a silane coupling agent accounting for 1% of the mass of the boron nitride nanosheets, and then carry out ultrasonic treatment at a power of 300 W for 60 min, and then centrifuge and dry to obtain modified boron nitride nanosheets;

[0053] 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;

[0054] 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;

[0055] S2.5, repeat the operation of step S2.4 twice to obtain a buffer layer with a thickness of 20 μm;

[0056] 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;

[0057] 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;

[0058] 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.

[0059] Example 2

[0060] 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.

[0061] The preparation method of the low-friction synthetic brake shoe comprises the following steps:

[0062] S1. Prepare a container. First, add cashew shell oil and phosphoric acid to the container, and then add paraformaldehyde while stirring. The mass ratio of cashew shell oil: phosphoric acid: paraformaldehyde is 100:0.5:7. After the paraformaldehyde is completely dissolved, heat the solution to 90 °C and keep it reacting for 3 h to obtain a reaction solution. Take the reaction solution and dehydrate it under vacuum at 85 °C for 3 h to obtain cashew shell oil modified phenolic resin. Then mix the cashew shell oil modified phenolic resin and nitrile rubber and heat them to 62 °C to soften, and then stir and process at a speed of 500 rpm for 5 min to obtain mixture A;

[0063] S2. Prepare a metal fiber composite, and then add the metal fiber composite and sepiolite fiber to the mixture A, and then stir and process at a speed of 1000 rpm for 10 min to obtain mixture B;

[0064] Among them, the specific operation for preparing the metal fiber composite is as follows:

[0065] S2.1. Take two metal fiber filaments (SAE1008 low-carbon steel fiber and C11000 copper fiber) with a length of 35 cm, a diameter of 220 μm and different linear thermal expansion coefficients. After ultrasonic cleaning and drying with acetone, use a ceramic V-groove fixture to place and fix the two metal fiber filaments side by side and in contact. Then use a pulsed fiber laser to perform laser welding (power 20 W, pulse frequency 15 Hz, pulse width 3 ms, spot diameter 90 μm) in an argon atmosphere. The welding is carried out in a dotting manner with a spacing of 5 mm to obtain a combined fiber filament. Then cut the combined fiber filament at each welding point position to obtain combined short fibers with a length of 5 mm, side by side and in contact and with the ends fused for standby;

[0066] S2.2. Take boron nitride nanosheets and disperse them in ethanol with a mass 12 times that of the boron nitride nanosheets and a mass concentration of 8%. Add a silane coupling agent accounting for 2% of the mass of the boron nitride nanosheets, and then perform ultrasonic treatment at a power of 320 W for 45 min, and then centrifuge and dry to obtain modified boron nitride nanosheets;

[0067] S2.3. Take raw silicone rubber and mix it with white carbon black, add the modified boron nitride nanosheets, heat to 50 °C and then add a flame retardant and a platinum catalyst, knead for 25 min, and then filter through a sieve and degas under vacuum to obtain a kneaded rubber. Dissolve the kneaded rubber in xylene with a mass 6 times that of the raw silicone rubber, and add a bis(2,5-dimethyl-2,5-di(tert-butylperoxy)hexane) vulcanizing agent accounting for 1% of the mass of the raw silicone rubber to obtain a coating solution; among them, the mass ratio of raw silicone rubber, white carbon black, modified boron nitride nanosheets, flame retardant, and platinum catalyst is 100:20:15:8:0.8;

[0068] S2.4. Immerse the combined short fibers completely in the coating solution and take them out after staying for 18 s. Place the combined short fibers at 75 °C for pre-curing for 25 min, and then place the combined short fibers at 165 °C for vulcanization for 5 min;

[0069] S2.5, repeat the operation of step S2.4 three times until a buffer layer with a thickness of 30 μm is obtained;

[0070] 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;

[0071] 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;

[0072] 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.

[0073] Example 3

[0074] 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.

[0075] The preparation method of the low-friction synthetic brake shoe comprises the following steps:

[0076] 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;

[0077] 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;

[0078] The specific operation of preparing the metal fiber composite is as follows:

[0079] S2.1. Take two metal fiber filaments with a length of 50 cm, a diameter of 250 μm and different linear thermal expansion coefficients (SAE1008 low-carbon steel fiber and C11000 copper fiber). After ultrasonic cleaning and drying with acetone, place and fix the two metal fiber filaments side by side using a ceramic V-groove fixture. Then, perform laser welding in an argon atmosphere using a pulsed fiber laser (power 30 W, pulse frequency 20 Hz, pulse width 5 ms, spot diameter 100 μm). The welding is carried out in a dotting manner with a spacing of 6 mm to obtain a bundled fiber filament. Then, cut the bundled fiber filament at each welding point position to obtain bundled short fibers with a length of 6 mm, side by side and end-fused for standby;

[0080] S2.2. Disperse boron nitride nanosheets in ethanol with a mass 15 times and a mass concentration of 10%. Add a silane coupling agent accounting for 3% of the mass of the boron nitride nanosheets, then perform ultrasonic treatment at a power of 350 W for 30 min, and then centrifuge and dry to obtain modified boron nitride nanosheets;

[0081] S2.3. Mix raw silicone rubber with fumed silica, add the modified boron nitride nanosheets, heat to 60 °C and then add a flame retardant and a platinum catalyst, knead for 30 min, then filter through a sieve and degas under vacuum to obtain a kneaded rubber. Dissolve the kneaded rubber in xylene with a mass 8 times, and add a bis(2,5-dimethyl-2,5-di(tert-butylperoxy)hexane) vulcanizing agent accounting for 1.5% of the mass of the raw silicone rubber to obtain a coating liquid; wherein, the mass ratio among the raw silicone rubber, fumed silica, modified boron nitride nanosheets, flame retardant, and platinum catalyst is 100:30:20:10:1;

[0082] S2.4. Immerse the bundled short fibers completely in the coating liquid and take them out after staying for 20 s. Place the bundled short fibers at 80 °C for pre-curing for 20 min, and then place the bundled short fibers at 170 °C for vulcanization for 4 min;

[0083] S2.5. Repeat the operation in step S2.4 four times until a buffer layer with a thickness of 40 μm is obtained, and that's it;

[0084] S3. Add flake graphite, molybdenum disulfide, silicon carbide, talcum powder and epoxidized soybean oil to the mixture B, and then stir and process at a speed of 1500 rpm for 8 min to obtain a mixture C;

[0085] S4. Preheat a molding die to 85 °C and pre-coat a mold release agent, then load the mixture C into the mold, control the temperature at 180 °C, the pressure at 30 MPa, and perform pressure holding treatment for 12 min;

[0086] S5. Demold to obtain a preliminary product, immediately put the preliminary product into an annealing furnace, perform heat treatment at 200 °C for 2 h, and finally perform sandblasting treatment to remove burrs, thus obtaining the low-friction synthetic brake shoe.

[0087] Comparative Example 1

[0088] A low-friction synthetic brake shoe, calculated by weight parts, its preparation raw materials include: 28 parts of cashew 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 talcum powder and 2 parts of epoxidized soybean oil.

[0089] The preparation method of this low-friction synthetic brake shoe, the steps include:

[0090] S1. Prepare a container, first add cashew shell oil and phosphoric acid into the container, then add paraformaldehyde while stirring, the mass ratio of cashew shell oil: phosphoric acid: paraformaldehyde = 100:0.5:7. After the paraformaldehyde is completely dissolved, heat the solution to 90 °C and keep it for reaction for 3 h to obtain a reaction solution. Take the reaction solution and carry out vacuum dehydration at 85 °C for 3 h to obtain cashew shell oil modified phenolic resin. Then mix the cashew shell oil modified phenolic resin and nitrile rubber and heat to 62 °C to soften, and then stir and process at a speed of 500 rpm for 5 min to obtain mixture A;

[0091] S2. Then add SAE1008 low-carbon steel fiber, C11000 copper fiber and sepiolite fiber into the mixture A, and then stir and process at a speed of 1000 rpm for 10 min to obtain mixture B;

[0092] S3. Add flake graphite, molybdenum disulfide, silicon carbide, talcum powder and epoxidized soybean oil into the mixture B, and then stir and process at a speed of 1300 rpm for 10 min to obtain mixture C;

[0093] S4. Preheat a molding die to 80 °C and pre-coat a release agent, then load mixture C into the die, control the temperature at 170 °C, the pressure at 28 MPa, and carry out pressure holding treatment for 14 min;

[0094] S5. Demold to obtain a primary product, immediately put the primary product into an annealing furnace, carry out heat treatment at 190 °C for 2.5 h, and finally carry out sandblasting treatment to remove burrs to obtain the said low-friction synthetic brake shoe.

[0095] Comparative Example 2

[0096] A low-friction synthetic brake shoe, calculated by weight parts, its preparation raw materials include: 28 parts of cashew shell oil modified phenolic resin, 10 parts of nitrile rubber, 22 parts of metal fiber complex, 18 parts of flake graphite, 16 parts of sepiolite fiber, 7 parts of molybdenum disulfide, 5 parts of silicon carbide, 4 parts of talcum powder and 2 parts of epoxidized soybean oil.

[0097] The preparation method of this low-friction synthetic brake shoe, the steps include:

[0098] 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;

[0099] 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;

[0100] 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;

[0101] 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;

[0102] 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;

[0103] 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.

[0104] Blank group

[0105] 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.

[0106] The preparation method of the low-friction synthetic brake shoe comprises the following steps:

[0107] S1. Prepare a container. First, add cashew shell oil and phosphoric acid into the container, and then add paraformaldehyde while stirring. The mass ratio of cashew shell oil: phosphoric acid: paraformaldehyde is 100:0.5:7. After the paraformaldehyde is completely dissolved, heat the solution to 90 °C and keep it for reaction for 3 h to obtain a reaction solution. Take the reaction solution and dehydrate it under vacuum at 85 °C for 3 h to obtain cashew shell oil-modified phenolic resin. Then mix the cashew shell oil-modified phenolic resin and nitrile rubber and heat them to 62 °C for softening, and then stir and process them at a speed of 500 rpm for 5 min to obtain mixture A;

[0108] S2. Add sepiolite fiber into the mixture A, and then stir and process it at a speed of 1000 rpm for 10 min to obtain mixture B;

[0109] S3. Add flake graphite, molybdenum disulfide, silicon carbide, talcum powder and epoxy soybean oil into the mixture B, and then stir and process them at a speed of 1300 rpm for 10 min to obtain mixture C;

[0110] S4. Preheat a molding die to 80 °C and pre-coat a release agent, then load mixture C into the die, control the temperature at 170 °C, the pressure at 28 MPa, and carry out pressure holding treatment for 14 min;

[0111] S5. Demold to obtain a preliminary product, immediately put the preliminary product into an annealing furnace, heat-treat it at 190 °C for 2.5 h, and finally carry out sandblasting treatment to remove burrs to obtain the low-friction synthetic brake shoe.

[0112] III. Performance test

[0113] Specimen requirements: According to the specimen size requirements of "TB / T 3196-2015 Synthetic Brake Shoes for Locomotives", the following specimens are prepared from the brake shoes prepared in Example 2, Comparative Examples 1-2 and the blank group: A 120 mm × 15 mm × 10 mm specimen without notch is used for the test of impact strength; A 25.4 mm × 25.4 mm × 8 mm specimen is prepared for the test of wear amount. It is required that the length, width and thickness directions of the specimen are consistent with the length, width and thickness directions of the brake shoe.

[0114] Among them:

[0115] (1) Impact strength: Test according to "GB / T 1043.1-2008 Plastics - Determination of Charpy impact properties - Part 1: Non-instrumented impact test" with an XJJ-5 impact testing machine. The impact strength calculation formula is as follows:

[0116]

[0117] In the formula: a is the impact strength, and the unit is kJ / m2 ; A is the impact energy absorbed by the specimen, in J; b is the width of the specimen, in m; d is the thickness of the specimen, in m.

[0118] (2) Abrasion loss and friction coefficient: Test according to "GB / T 17469-2012 Small Sample Bench Test Method for Evaluating Friction Performance of Automotive Brake Linings" using a QDM150 adjustable speed and pressure friction material performance testing machine. Parameter settings: The diameter of the friction disc (HT180 - 250HB) is 30 cm, the applied pressure is 0.98 Mpa, the rotational speed is 1500 r / min, and the number of rotations is 5000 rotations.

[0119] In addition, take the specimens after wear of each experimental group and scan the surface microtopography of the specimens after friction and wear with a FEI Quanta 200 type scanning electron microscope.

[0120] IV. Result Analysis

[0121] Statistically analyze the test results of the impact strength, abrasion loss, and friction coefficient of Example 2, Comparative Examples 1 - 2, and the blank group to obtain Table 1 below:

[0122] Table 1: Test Results of Impact Strength, Abrasion Loss, and Friction Coefficient

[0123]

[0124] 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. The impact strength reaches 5.95 kJ / m 2 , the abrasion loss is as low as 0.213 cm 3 / MJ, and the friction coefficient is also relatively low, only 0.29, belonging to a low-friction brake shoe. In Comparative Example 1, the metal fiber composite is replaced with separate SAE1008 low-carbon steel fibers and C11000 copper fibers, and the total fiber addition amount remains unchanged, but the impact strength decreases by 18.3% and the abrasion loss increases by 20.7%. The difference is very significant, indicating that the unique composite structure plays a key role, rather than just the effects 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 abrasion loss. 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 addition effect of the metal fiber composite cannot be fully exerted.

[0125] Such as Figure 1As 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.

[0126] 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 preparation method of a low-friction synthetic brake shoe, characterized in that, By weight, the preparation raw materials include: 25-30 parts of cashew 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 powder, and 1-3 parts of epoxy soybean oil; wherein, the metal fiber composite is obtained by first arranging two metal fibers with different linear thermal expansion coefficients side by side and fusing their endpoints, and then coating a buffer layer of boron nitride silicon rubber on the surface; The steps of the preparation method include: S1. Prepare cashew shell oil modified phenolic resin, then mix the cashew shell oil modified phenolic resin and nitrile rubber and heat them to soften at 60-65°C, and then stir and process at a speed of 400-600 rpm for 3-6 minutes to obtain mixture A; S2. Prepare the metal fiber composite, then add the metal fiber composite and sepiolite fiber to the mixture A, and then stir and process at a speed of 800-1200 rpm for 8-12 minutes to obtain mixture B; The specific operation for 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. After ultrasonic cleaning and drying with acetone, 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 for laser welding in an argon atmosphere. The welding adopts a dotting method with an interval of 3-6 mm to obtain a combined fiber filament, and then cut the combined fiber filament at each welding point position to obtain combined short fibers with side-by-side and fused endpoints for standby; S2.

2. Take boron nitride nanosheets and disperse them in ethanol with a mass 10-15 times and a mass concentration of 5-10%, add a silane coupling agent accounting for 1-3% of the mass of the boron nitride nanosheets, then perform ultrasonic treatment at a power of 300-350 W for 30-60 minutes, and then centrifuge and dry to obtain modified boron nitride nanosheets; S2.

3. Take raw rubber of silicone rubber and mix it with white carbon black, add the modified boron nitride nanosheets, heat to 50-60°C, then add a flame retardant and a platinum catalyst, mix and knead for 20-30 minutes, then filter through a sieve and degas under vacuum to obtain a kneaded rubber. Dissolve the kneaded rubber in xylene with a mass 5-8 times, and add a bis(2,5-dimethyl-2,5-di(t-butylperoxy)hexane) vulcanizing agent accounting for 0.5-1.5% of the mass of the raw rubber of silicone rubber to obtain a coating liquid; S2.

4. Immerse the combined short fibers completely in the coating liquid and stay for 15-20 s, then take them out, place the combined short fibers at 70-80°C for pre-curing for 20-30 minutes, and then place the combined short fibers at 160-170°C for vulcanization for 4-6 minutes; S2.

5. Repeat the operation of step S2.4 until a buffer layer with the required thickness is obtained; S3. Add flake graphite, molybdenum disulfide, silicon carbide, talc powder and epoxy soybean oil to the mixture B, and then stir and process at a speed of 1200-1500 rpm for 8-12 minutes to obtain mixture C; S4. Preheat the forming mold to 75 - 85 °C and pre - coat with a release agent, then load mixture C into the mold, control the temperature at 160 - 180 °C, the pressure at 25 - 30 MPa, and perform a pressure - holding treatment for 12 - 15 min; S5. Demold to obtain the preliminary product, immediately put the preliminary product into an annealing furnace, perform heat treatment at 180 - 200 °C for 2 - 3 h, and finally perform sandblasting treatment to remove burrs, thus obtaining the low - friction synthetic brake shoe.

2. The preparation method of the low-friction synthetic brake shoe according to claim 1, characterized in that, The metal fibers are selected from the combination of 4130 alloy steel fibers and C26000 brass fibers, or the combination of SAE1008 low - carbon steel fibers and C11000 pure copper fibers.

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

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

5. The preparation method of the low-friction synthetic brake shoe according to claim 1, characterized in that, In step S1, the specific operation for preparing the cashew - shell - oil - modified phenolic resin is as follows: Prepare a container, first add cashew - 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 it reacting for 2 - 5 h to obtain a reaction solution. Take the reaction solution and perform vacuum dehydration at 80 - 90 °C for 2 - 4 h, thus obtaining the cashew - shell - oil - modified phenolic resin.

6. The preparation method of the low-friction synthetic brake shoe according to claim 5, characterized in that, The mass ratio among the cashew - shell oil, phosphoric acid, and paraformaldehyde is cashew - shell oil: phosphoric acid: paraformaldehyde = 100:0.4 - 0.6:6 - 8.

7. The preparation method of the low-friction synthetic brake shoe according to claim 1, characterized in 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.

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

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