Aging-resistant and heat-fading-resistant environment-friendly friction material for plateau railway and a preparation method thereof

Abstract

This invention discloses an environmentally friendly friction material for high-altitude railways that is resistant to aging and heat fading, and its preparation method. It relates to the field of railway vehicle braking materials and is composed of the following components by weight percentage: modified phenolic resin 7.7%~11.7%, hydrogenated nitrile butadiene rubber 14.4%~16.6%, aluminum dihydrogen phosphate 7.7%~11.0%, basalt fiber 12.1%~14.4%, tungsten disulfide 2.7%~3.3%, zirconium silicate 3.8%~5.1%, flake graphite 9.3%~10.8%, barium sulfate 27.6%~33.1%, potassium feldspar powder 3.8%~5.1%; and accelerators CZ, zinc oxide, stearic acid, and sulfur, each accounting for 8% of the weight of the hydrogenated nitrile butadiene rubber; the sum of the weight percentages of the modified phenolic resin to the potassium feldspar powder is 100%. This invention uses hydrogenated nitrile butadiene rubber (HNBR) as a toughening component, which has an extremely low double bond content in its molecular chain.

Description

Technical Field

[0001] This invention relates to rail vehicle braking material technology, specifically to an environmentally friendly friction material for high-altitude railways that is resistant to aging and heat fade, and its preparation method. Background Technology

[0002] Plateau railways are characterized by high altitude (maximum altitude 4476m), long tunnels (tunnels account for 82.6% of the total, the longest tunnel is 42.4km), and long gradients (the longest gradient is about 74km, the maximum gradient is 30‰). Under the combined external conditions of high altitude, long tunnels, and long gradients, the braking system of the Sichuan-Tibet Railway faces numerous challenges, including poor heat dissipation conditions for the brake friction pairs, insufficient braking capacity of existing trains, insufficient air supply to existing trains, and difficult rescue conditions. Furthermore, in the event of a malfunction, mobile equipment rescue is difficult and challenging, necessitating ensuring that the synthetic brake shoes do not fail during braking on long gradients to guarantee train operation safety. This is especially true on plateau railways. In plateau regions, air pressure is typically only 50%-70% of that at sea level (e.g., air pressure at 4000 meters is about 60kPa). The thin air significantly reduces convective heat dissipation efficiency, and since synthetic friction materials rely on friction to generate heat during braking, heat easily accumulates inside the material, causing a series of problems. Thermal fade is exacerbated, as the friction coefficient of synthetic friction materials is temperature-sensitive; excessively high temperatures lead to "thermal fade" (a significant decrease in μ). Poor heat dissipation under low air pressure causes materials to quickly exceed critical operating temperatures (e.g., resin in resin-based materials begins to decompose above 250℃), leading to a sharp drop in the coefficient of friction, decreased braking efficiency, and a risk of brake failure. Material structural damage: At high temperatures, organic binders in the material (such as phenolic resin) may decompose more rapidly, releasing gases (such as CO and small organic molecules), resulting in pores and cracks within the material. Simultaneously, the interfacial bonding force between metal fibers (such as steel fibers) and the matrix weakens due to differences in thermal expansion, potentially causing surface peeling. Increased wear on mating parts: Overheating of the friction material can lead to a thickening of the oxide layer on the wheel surface or the appearance of thermal cracks, which in turn accelerates the wear of the friction material (forming a "vicious cycle of mutual wear"), resulting in increased wear and increased braking dust in long tunnels, thus affecting the health of subsequent passengers.

[0003] Existing freight cars on plateau railways use tread braking, employing synthetic brake shoes that rub against the wheels for braking. These synthetic brake shoes are made by mixing metal fibers, metal powder, and inorganic abrasive fillers with resin as a binder, molding them through hot pressing, and then curing them to form a resin-based composite material. The brake shoes stop the train by wearing down against the wheels during braking. However, on plateau railways with gradients exceeding 30‰, emergency braking can occur, leading to prolonged braking. Existing products are prone to friction performance degradation during long-distance, prolonged friction braking, resulting in a decreased coefficient of friction and thus an increased braking distance, posing a safety hazard. Summary of the Invention

[0004] The purpose of this invention is to provide an environmentally friendly friction material for high-altitude railways that is resistant to aging and thermal degradation, and its preparation method, in order to overcome the above-mentioned shortcomings in the prior art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: an environmentally friendly friction material for high-altitude railways that is resistant to aging and heat degradation, comprising the following components by weight percentage:

[0006] Modified phenolic resin 7.7%~11.7%, hydrogenated nitrile rubber 14.4%~16.6%, aluminum dihydrogen phosphate 7.7%~11.0%, basalt fiber 12.1%~14.4%, tungsten disulfide 2.7%~3.3%, zirconium silicate 3.8%~5.1%, flake graphite 9.3%~10.8%, barium sulfate 27.6%~33.1%, potassium feldspar powder 3.8%~5.1%;

[0007] And accelerators CZ, zinc oxide, stearic acid and sulfur, each accounting for 8% of the weight of the hydrogenated nitrile rubber;

[0008] The total weight percentage of the modified phenolic resin to potassium feldspar powder is 100%.

[0009] Furthermore, the modified phenolic resin is a boron-modified phenolic resin with a particle size of 325 mesh.

[0010] Furthermore, the aluminum dihydrogen phosphate has a particle size of 200 mesh and a P2O5 content of ≥60%.

[0011] Furthermore, the basalt fibers are pretreated with a silane coupling agent and have a length of 9-12 mm.

[0012] Furthermore, the tungsten disulfide has a particle size of 325 mesh and a WS2 content of ≥96%; the zirconium silicate has a particle size of 325 mesh and a ZrO2 content of ≥60%; the barium sulfate has a particle size of 325 mesh and a barium sulfate content of ≥99%; and the potassium feldspar powder has a particle size of 325 mesh.

[0013] Furthermore, it consists of the following components by weight percentage:

[0014] Modified phenolic resin 9.5%, hydrogenated nitrile rubber 15.5%, aluminum dihydrogen phosphate 9.1%, basalt fiber 13.5%, tungsten disulfide 3.1%, zirconium silicate 4.6%, flake graphite 10.2%, barium sulfate 30.2%, potassium feldspar powder 4.6%;

[0015] And accelerators CZ, zinc oxide, stearic acid and sulfur, each accounting for 8% of the weight of the hydrogenated nitrile rubber.

[0016] A method for preparing an environmentally friendly friction material for high-altitude railways that is resistant to aging and heat degradation includes the following steps:

[0017] Sa, weigh each component according to the ratio, add toluene (1% of the total weight of the mixture) as a wetting agent, and mix in an internal mixer;

[0018] Sb, Crush the mixed material to a particle size of no more than 10mm;

[0019] Sc. Place the crushed material into a mold that has been heated to 160±5℃, and then place the mold on the hydraulic station of the hydraulic press for hot pressing to obtain the blank.

[0020] Sd. The blank is placed in an oven for secondary curing to obtain the friction material.

[0021] Furthermore, in step Sa, the internal mixer rotates at a speed of 20-60 r / min, the mixing time is 10-15 min, and the mixing temperature does not exceed 90℃.

[0022] Furthermore, in step Sc, the hot pressing temperature is 155~165℃, the hot pressing pressure is 25~30MPa, and the hot pressing time is 40~50min.

[0023] Furthermore, in step Sd, the secondary curing process employs a stepped temperature increase method:

[0024] Hold at 80℃ for 1 hour, raise the temperature to 100℃ and hold for 0.5 hours, raise the temperature to 120℃ and hold for 1 hour, raise the temperature to 140℃ and hold for 1 hour, raise the temperature to 160℃ and hold for 1 hour, and finally raise the temperature to 170℃ and hold for 4 hours.

[0025] Compared with existing technologies, this invention provides an environmentally friendly friction material for high-altitude railways that is resistant to aging and heat fading, and its preparation method. It uses hydrogenated nitrile butadiene rubber (HNBR) as a toughening component. Its molecular chain has an extremely low double bond content, making it less susceptible to free radical chain breakage caused by oxygen, ozone, ultraviolet radiation, and heat. Therefore, it exhibits outstanding resistance to oxidation, ozone, heat aging, and long-term fatigue. Simultaneously, the use of boron-modified phenolic resin, where the phenolic hydroxyl groups are partially replaced by borate ester bonds, significantly improves the thermal stability and UV aging resistance of the resin matrix. The synergistic effect of these two components allows the friction material to maintain the integrity of its matrix structure and the stability of its mechanical properties during long-term service in harsh environments with high altitude and strong ultraviolet radiation, effectively avoiding problems such as breakage and spalling caused by aging.

[0026] This invention employs a composite adhesive system, in which boron-modified phenolic resin has a significantly higher thermal decomposition temperature than ordinary phenolic resin, while aluminum dihydrogen phosphate, as an inorganic adhesive, can form a ceramic-like network structure at high temperatures, exhibiting extremely high thermal stability and thermal shock resistance. The blending and fusing of these two adhesives leverages both the strength and toughness of the organic adhesive in the room and medium temperature ranges, and the structural retention capability of the inorganic adhesive in the high-temperature range, thus preventing significant softening or decomposition of the matrix under the heat load generated by continuous braking. Furthermore, basalt fiber, as a reinforcement, possesses excellent high-temperature strength retention, while flake graphite and zirconium silicate, as high-temperature friction modifiers, stabilize the friction interface, jointly suppressing the thermal decay of the friction coefficient and ensuring the stability and safety of the braking distance during long slopes and prolonged braking.

[0027] This invention completely eliminates the use of metal fibers (such as steel fibers and copper fibers) and metal powders (such as iron powder and copper powder) in its entire formulation system. It utilizes only inorganic mineral materials (barium sulfate, potassium feldspar, zirconium silicate, flake graphite, etc.) and basalt fibers as reinforcements and fillers. All raw materials are derived from natural minerals or inorganic materials. The frictional dust generated during braking does not contain harmful heavy metals and will not cause secondary pollution to water bodies or soil along the route, making it particularly suitable for ecologically sensitive areas in high-altitude regions.

[0028] This invention achieves low wear through a multi-scale dense filling and interfacial lubrication synergistic mechanism: micron-sized fillers such as barium sulfate and potassium feldspar powder densely fill the pores of the matrix, reducing the initial wear rate of the friction material; flake graphite forms a continuous and stable transfer lubrication film at the friction interface, reducing abrasive wear; basalt fiber acts as a skeleton to bear the main load and prevent large-scale material spalling. Simultaneously, tungsten disulfide, as an extreme pressure additive, decomposes at the high friction temperature and reacts with the wheel's metal surface to generate a low-shear-stress sulfide protective layer, preventing metal embedding and interfacial micro-cutting. The combined effect significantly reduces the wear of the friction material during braking, thereby reducing the generation of braking dust in tunnels, improving air quality in confined spaces within tunnels during rescue or emergency situations, and reducing potential health risks to personnel.

[0029] This invention achieves a stable friction coefficient across a wide temperature range by selecting flake graphite and potassium feldspar powder of specific particle size and purity as friction coefficient modifiers, combined with the high-temperature friction-enhancing effect of zirconium silicate and the extreme-pressure lubrication effect of tungsten disulfide. Especially under conditions of continuous braking leading to temperature increases, the intervention of inorganic binders and basalt fibers prevents a sharp drop in the friction coefficient, while the stable lubricity of flake graphite prevents excessive increases in the friction coefficient, thus ensuring a smooth and controllable braking process and good consistency in braking distance. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0031] Figure 1 This is a schematic flowchart illustrating the method for preparing an environmentally friendly friction material resistant to aging and thermal degradation for high-altitude railways, as provided in an embodiment of the present invention. Detailed Implementation

[0032] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0033] In the following embodiments, the national standards upon which the methods for measuring each performance parameter are based are as follows:

[0034] I. Mechanical property testing:

[0035] Compressive strength: Tested according to GB / T 1041 "Determination of compressive properties of plastics";

[0036] Impact strength: Tested according to GB / T 1043.1 "Determination of impact properties of simply supported plastic beams - Part 1: Non-instrumental impact test";

[0037] II. Friction cleaning performance test:

[0038] The average friction coefficient at 120 km / h, the friction coefficient during continuous braking at 120 km / h (simulating continuous braking on a long gradient), and the wear were tested using a scaled-down friction braking test bench for rail vehicles. The test method is as follows:

[0039] A. Average friction coefficient test at 120 km / h: Braking speed is calculated at 120 km / h, axle load is calculated at 25 tons, and braking pressure is calculated at 20 kN. The test is repeated 10 times to calculate the average friction coefficient, with a braking time interval of 120 seconds.

[0040] B. Calculate the friction coefficient during continuous braking at 120 km / h, with braking speed at 120 km / h, axle load at 25 tons, braking pressure at 20 kN, and continuous braking for 10 minutes.

[0041] C. Wear test, calculate the wear reduction of friction materials for both common braking and continuous braking (unit: g).

[0042] D. Friction coefficient decay rate: Based on the average friction coefficient of 10 braking cycles at 120 km / h, compare the decay of the average friction coefficient during continuous braking at 120 km / h; the calculation formula is: (average friction coefficient at 120 km / h - average friction coefficient during continuous braking at 120 km / h) / average friction coefficient at 120 km / h × 100%.

[0043] E. Existing product friction performance test: Select existing brake shoes that meet the standards for synthetic brake shoes for railway freight cars for testing. Samples are randomly selected from the site, and the method is as above.

[0044] III. The description provided by this invention:

[0045] The phenolic resin is boron-modified phenolic resin with a particle size of 325 mesh;

[0046] Nitrile rubber is hydrogenated nitrile rubber, with the grade Therban A3406;

[0047] Aluminum dihydrogen phosphate, 200 mesh, P2O5 content ≥60%;

[0048] Basalt fibers, pretreated with a silane coupling agent (a conventional technique in this field), are 9-12 mm in length; silane coupling agent pretreatment:

[0049] (1) Preparation of silane coupling agent solution: Weigh silane coupling agent KH550: anhydrous ethanol: deionized water in a mass ratio of 5:90:5. Slowly add KH550 to the mixed solvent of anhydrous ethanol and deionized water. Adjust the pH value to 4.0-5.0 with glacial acetic acid. Stir magnetically for 30 minutes at room temperature to fully hydrolyze the silane coupling agent and obtain a transparent hydrolysate.

[0050] (2) Fiber soaking treatment: Basalt fibers with a length of 9-12 mm are evenly laid in a high-temperature resistant tray, and the hydrolysate prepared in step (1) is added. The amount of hydrolysate is 2-3 times the mass of the basalt fibers to ensure that the fibers are completely submerged. Soak at room temperature for 60 minutes, turning the fibers every 15 minutes during this period to ensure that the surface of the fibers is evenly adsorbed with silane coupling agent.

[0051] (3) Drying and curing: After soaking, the basalt fiber is taken out of the hydrolysate and placed in a fume hood to drain naturally for 30 minutes. Then it is transferred to a forced-air drying oven and dried at 80°C for 1 hour. Then it is heated to 120°C and cured for 2 hours to form a strong chemical bond between the silane coupling agent and the fiber surface.

[0052] (4) Post-treatment: Take out the solidified basalt fiber, cool it to room temperature, and use a 100-mesh sieve to remove the small amount of debris generated during the treatment process. The basalt fiber pretreated with silane coupling agent KH550 is then obtained and sealed for storage.

[0053] Tungsten disulfide has a particle size of 325 mesh and a WS2 content of ≥96%.

[0054] The zirconium silicate has a particle size of 325 mesh and a ZrO2 content of ≥60%.

[0055] Flake graphite is L185;

[0056] The barium sulfate has a particle size of 325 mesh and a barium sulfate content of ≥99%.

[0057] The potassium feldspar powder has a particle size of 325 mesh, and the rest are commercially available industrial products;

[0058] The wetting agent is toluene with a purity of ≥99%.

[0059] Raw materials - basic materials: phenolic resin is from Sumitomo Bakelite Co., Ltd., Japan; nitrile rubber is from Lanxess, Germany; accelerator, zinc oxide, stearic acid and sulfur are commercially available industrial products; aluminum dihydrogen phosphate is from Xinmi Dongfang Chemical Co., Ltd.; basalt fiber is from Jiangsu Lvcaigu New Material Technology Development Co., Ltd.; tungsten disulfide is from Huangshi Jinchaoyang Technology Co., Ltd.; zirconium silicate is from Xingyang Shenzhou Abrasives Co., Ltd.; potassium feldspar is from Shijiazhuang Chenxing Industrial Co., Ltd.; barium sulfate is from Shijiazhuang Xinji Chemical Co., Ltd.

[0060] IV. Key Manufacturing and Testing Equipment:

[0061] The scaled friction braking test bench for rail vehicles, model TM-Ⅱ, is manufactured by Xi'an Shuntong Electromechanical Technology Research Institute.

[0062] Internal mixer, model 10L, Baihong Machinery (Shanghai) Co., Ltd.;

[0063] Hydraulic press, model 315 tons, Nantong Juneng Forging and Pressing Machinery Co., Ltd.;

[0064] Drying oven (curing oven), maximum temperature 250℃, Ningbo Hongling Electric Heating Oven Co., Ltd.

[0065] Hot pressing molds, Zhengzhou Sanhuan Mold Co., Ltd.

[0066] V. The curing program described in this invention is a stepped temperature increase program:

[0067] That is, keep the temperature at 80℃ for 1 hour, raise the temperature to 100℃ and keep it for 0.5 hours; raise the temperature to 120℃ and keep it for 1 hour, raise the temperature to 140℃ and keep it for 1 hour; raise the temperature to 160℃ and keep it for 1 hour, and finally raise the temperature to 170℃ and keep it for 4 hours.

[0068] Comparative Example 1

[0069] Sample Preparation: 800g of nitrile rubber powder, 550g of phenolic resin powder, 300g of aluminum dihydrogen phosphate, 690g of basalt fiber, 100g of tungsten disulfide, 240g of zirconium silicate, 500g of flake graphite, 1200g of barium sulfate, 150g of potassium feldspar powder, 64g of zinc oxide, 64g of accelerator CZ, 64g of stearic acid, and 64g of sulfur were weighed and poured into a production internal mixer. The machine speed was set to 20 rpm, and the mixture was mixed for 13 minutes. After uniform mixing, the mixture was crushed and hot-pressed using a 315-ton hydraulic press at a molding pressure of 30MPa, a hot-pressing temperature of 160℃, and a hot-pressing time of 45 minutes. After hot pressing, the material was cured a second time in an oven according to the set curing program to obtain a high-performance friction material product.

[0070] The performance test results are shown in Table 1.

[0071] Table 1 Performance of Comparative Example 1

[0072]

[0073] Comparative Example 2

[0074] Sample Preparation: 600g of nitrile rubber powder, 390g of phenolic resin powder, 550g of aluminum dihydrogen phosphate, 550g of basalt fiber, 160g of tungsten disulfide, 160g of zirconium silicate, 400g of flake graphite, 1550g of barium sulfate, 250g of potassium feldspar powder, 48g of zinc oxide, 48g of accelerator CZ, 48g of stearic acid, and 48g of sulfur were weighed and poured into a production internal mixer. The machine speed was set to 20 rpm, and the mixture was mixed for 13 minutes. After uniform mixing, the mixture was crushed and hot-pressed using a 315-ton hydraulic press at a molding pressure of 30MPa, a hot-pressing temperature of 160℃, and a hot-pressing time of 45 minutes. After hot pressing, the material was cured a second time in an oven according to the set curing program to obtain a high-performance friction material product.

[0075] The performance test results are shown in Table 2.

[0076] Table 2 Performance of Comparative Example 2

[0077]

[0078] Existing synthetic brake shoes (current samples) primarily use nitrile rubber and thermoplastic phenolic resin as binders, copper and steel fibers as reinforcing fibers, iron and copper powder as main metal fillers, and barium sulfate and feldspar powder as inorganic fillers. The mixture is then hot-pressed and cured twice to form the final product. However, existing high-altitude railway freight train routes do not have long gradients or tunnels, and the environmental conditions along these routes differ from those of the future high-altitude railways opening in Southwest China. There is insufficient consideration given to braking emissions from long gradients and tunnels. Therefore, existing technologies have limitations when applied to freight train braking in long gradients and tunnels, potentially leading to insufficient braking capacity, excessive emissions that could harm passenger health, and environmental pollution.

[0079] The performance test results are shown in Table 3.

[0080] Table 3 Performance of Existing Samples

[0081]

[0082] Example 1

[0083] Existing products experience accelerated aging under high-altitude ultraviolet conditions and alternating hot and humid conditions in deep tunnels, leading to aging, cracking, and spalling of the adhesive matrix, as well as a decline in physical, mechanical, and frictional properties, thus posing a threat to driving safety. Brake shoes made from this material, even under prolonged ultraviolet radiation, exhibit aging resistance in the friction material matrix, ensuring stable mechanical properties of the brake shoes during vehicle braking and preventing problems such as cracking and spalling.

[0084] During braking on steep gradients exceeding 30‰ on plateau railways, continuous braking may occur in emergencies. The duration of continuous braking is relatively long. Existing products are prone to friction performance degradation during long-distance and long-term friction braking, resulting in a decrease in the coefficient of friction and thus an increase in braking distance, which poses a potential threat to train safety.

[0085] This embodiment involves sample preparation using the following ingredients: 750g hydrogenated nitrile rubber powder, 350g phenolic resin powder, 500g aluminum dihydrogen phosphate, 550g basalt fiber, 120g tungsten disulfide, 170g zirconium silicate, 420g flake graphite, 1500g barium sulfate, 170g potassium feldspar powder, 60g zinc oxide, 60g accelerator CZ, 60g stearic acid, and 60g sulfur. Figure 1As shown, the weighed mixture is mixed with 1% toluene (by weight) as a wetting agent and poured into a mixing mill. The machine speed is set to 60 rpm, and the mixture is mixed for 13 minutes at a temperature not exceeding 90°C. The mixed material is then crushed to a particle size no larger than 10mm. The crushed material is then placed into a mold heated to 160±5°C. The mold containing the crushed mixture is then hot-pressed using a 315-ton hydraulic press at a pressure of 30MPa, a temperature of 160°C, and a time of 45 minutes. After hot pressing, the material is cured a second time in an oven according to a set curing procedure to obtain a high-performance friction material product. Brake shoes made from this material exhibit excellent aging resistance of the friction material matrix under prolonged ultraviolet radiation, ensuring stable mechanical properties during vehicle braking and preventing breakage or chipping.

[0086] The hydrogenated nitrile butadiene rubber and the inorganic binder aluminum dihydrogen phosphate used have several advantages. Firstly, the hydrogenated nitrile butadiene rubber exhibits high aging resistance. In high-altitude railway applications, due to a significant reduction in double bond content, the molecular chain is more stable and less susceptible to free radical breakage caused by oxygen, ozone, heat, and light. This results in excellent resistance to oxidation, ozone, heat aging, and long-term fatigue, ensuring performance stability under high-altitude ultraviolet radiation. The use of the inorganic binder further ensures high-temperature structural strength, wear resistance, resistance to thermal fading, and prevents flaking at high temperatures.

[0087] Because it uses inorganic basalt fiber and tungsten disulfide, the two have good compatibility. When used together, they significantly improve the stability of the friction coefficient of the synthetic friction material, reduce wear, and enhance interface stability, thereby reducing wear emissions and preventing metal embedding.

[0088] The performance test results are shown in Table 4.

[0089] Table 4 Performance of Example 1

[0090]

[0091] Example 2

[0092] The plateau railway is located in the upper reaches of the Yangtze and Yellow Rivers. The existing products contain metal fibers, iron powder, copper powder and other metal materials. During braking, friction dust will be discharged into the rivers with rainwater, which will affect the fragile ecological environment along the line.

[0093] Existing products have limited application in tunnels, resulting in high wear and tear. Furthermore, braking emissions in long, high-altitude tunnels can negatively impact personnel health. This invention addresses this issue by minimizing wear and tear during braking in long, high-altitude railway tunnels, ensuring minimal dust emissions and minimizing impact on personnel.

[0094] This embodiment involves sample preparation using the following ingredients: 700g hydrogenated nitrile rubber powder, 430g phenolic resin powder, 410g aluminum dihydrogen phosphate, 610g basalt fiber, 140g tungsten disulfide, 210g zirconium silicate, 460g flake graphite, 1360g barium sulfate, 210g potassium feldspar powder, 56g zinc oxide, 56g accelerator CZ, 56g stearic acid, and 56g sulfur. Figure 1 As shown, the weighed mixture is mixed with 1% toluene (by weight) as a wetting agent and poured into a mixing mill. The machine speed is set to 60 rpm, and the mixture is mixed for 13 minutes at a temperature not exceeding 90°C. The mixed material is then crushed to a particle size no larger than 10 mm. The crushed material is then placed into a mold preheated to 160±5°C. The crushed mixture is then hot-pressed into shape using a 315-ton hydraulic press at a pressure of 30 MPa, a temperature of 160°C, and a pressing time of 45 minutes. After hot pressing, the material is cured a second time in an oven according to a set curing program to obtain a high-performance friction material product.

[0095] By employing a composite adhesive, based on modified phenolic resin with a higher thermal decomposition temperature and inorganic binder aluminum dihydrogen phosphate, and adding hydrogenated nitrile butadiene rubber (HNBR) to improve the overall matrix's resistance to UV aging, this composite material, after hot pressing, exhibits high temperature resistance, non-flammability, radiation resistance, good aging resistance, and a low coefficient of thermal expansion, making it suitable for extreme braking conditions on long slopes. To ensure environmental performance and prevent heavy metal emissions in high-altitude protected areas, inorganic fibers replace steel and copper fibers, and basalt fibers are used for reinforcement, guaranteeing matrix strength and high-temperature resistance. The fibers undergo silane coupling treatment. To prevent metal embedding at the wheel, tungsten disulfide, an extreme pressure additive containing active groups, is added to the friction interface. This extreme pressure additive decomposes under high frictional temperatures, and the decomposition products react with the wheel metal to generate sulfides, phosphides, and halides with lower shear stress and melting points than the wheel metal, thus preventing contact closure and forming a protective layer on the wheel surface to avoid metal embedding. To avoid significant frictional dust emissions in the tunnel, high-temperature stable oxides and inorganic fillers such as zirconium silicate (a high-temperature friction modifier) ​​and barium sulfate (a friction modifier) ​​are used to form a composite of dense filler, stable lubricating film, and high-strength skeleton, thereby reducing emissions. Furthermore, all materials are derived from natural minerals, resulting in no environmental pollution. Potassium feldspar powder and flake graphite are used to adjust the coefficient of friction, ensuring that the braking distance meets requirements.

[0096] The performance test results are shown in Table 5.

[0097] Table 5 Performance of Example 2

[0098]

[0099] Example 3

[0100] Sample preparation: 650g of hydrogenated nitrile rubber powder, 530g of phenolic resin powder, 350g of aluminum dihydrogen phosphate, 650g of basalt fiber, 150g of tungsten disulfide, 230g of zirconium silicate, 490g of flake graphite, 1250g of barium sulfate, 230g of potassium feldspar powder, 52g of zinc oxide, 52g of accelerator CZ, 52g of stearic acid, and 52g of sulfur. Figure 1 As shown, the weighed mixture is mixed with 1% toluene (by weight) as a wetting agent and poured into a mixing mill. The machine speed is set to 60 rpm, and the mixture is mixed for 13 minutes at a temperature not exceeding 90°C. The mixed material is then crushed to a particle size no larger than 10 mm. The crushed material is then placed into a mold preheated to 160±5°C. The crushed mixture is then hot-pressed into shape using a 315-ton hydraulic press at a pressure of 30 MPa, a temperature of 160°C, and a pressing time of 45 minutes. After hot pressing, the material is cured a second time in an oven according to a set curing program to obtain a high-performance friction material product.

[0101] The performance test results are shown in Table 6.

[0102] Table 6 Performance of Example 3

[0103]

[0104] In one embodiment, the material formulation composition and performance test results are summarized and analyzed as follows:

[0105] Table 7 Comparison of Performance Test Results between Examples and Comparative Examples

[0106]

[0107] Results analysis:

[0108] Thermal degradation resistance: As shown in Table 7, the friction coefficient degradation rates of Examples 1-3 of the present invention were 8.80%, 8.53%, and 9.04%, respectively, significantly lower than those of Comparative Example 1 (19.58%), Comparative Example 2 (22.71%), and prior art samples (28.27%). Meanwhile, the highest friction temperatures of Examples 1-3 during continuous braking were 279℃, 281℃, and 284℃, respectively, far lower than the 310℃~339℃ of Comparative Examples 1-3. This indicates that the present invention, through the organic-inorganic composite adhesive system formed by boron-modified phenolic resin and aluminum dihydrogen phosphate, combined with the high-temperature reinforcement effect of basalt fiber, effectively suppresses friction coefficient degradation at high temperatures, improves heat dissipation conditions, and meets the stringent requirements of continuous braking on long, steep slopes in high-altitude regions.

[0109] Wear resistance: The wear amounts of Examples 1-3 of this invention are 4.92g, 5.43g, and 4.17g, respectively, while the wear amounts of Comparative Examples 1 and 2 and prior art samples are 10.1g, 11.2g, and 21.3g, respectively. It is evident that the wear amount of the friction material of this invention is significantly reduced, especially superior to prior art samples (existing samples) containing metal fibers / powder. This low wear characteristic directly reduces the total amount of dust generated during braking, which is beneficial for reducing the concentration of particulate matter in enclosed spaces such as high-altitude tunnels, reducing the impact on personnel health, and demonstrating environmental advantages.

[0110] Mechanical properties: The compressive strength (37~38MPa) and impact strength (3.9~4.3KJ / m) of Examples 1-3 of this invention 2 The compressive strength of the material is at a high level, meeting the mechanical performance requirements for composite brake shoes of railway freight cars. Compared with the comparative example, the present invention has higher compressive strength while ensuring good toughness, indicating that the internal structure of the material is dense and the interface bonding is good.

[0111] Overall Results: Based on the above data, the friction material provided by this invention achieves the "three lows" characteristics of low friction fade rate, low continuous braking temperature, and low wear while maintaining good mechanical properties. In particular, compared with Comparative Example 3 (existing technology sample), this invention reduces the friction fade rate by approximately 68%, the wear by approximately 76%, and the maximum continuous braking temperature by approximately 60°C without adding any metal components, achieving better technical results.

[0112] No metal components are used in the entire formula system, and all raw materials are environmentally friendly and pollution-free, ensuring that no secondary heavy metal pollution is caused during use. This effectively expands the application range of friction materials in environmentally sensitive areas of high altitudes. At the same time, its own low wear can effectively avoid emissions during braking in long tunnels, improving passenger health.

[0113] In the overall design of the formulation and material performance, considering the friction interface surface, extreme pressure additives containing active groups are added. The extreme pressure additives decompose under the high temperature of friction, and the decomposition products can interact with the wheel metal to generate sulfides, phosphides and halides with lower shear stress and melting point than the wheel metal, thereby preventing the contact from closing and forming a protective layer on the wheel surface to avoid metal embedding.

[0114] This environmentally friendly friction material does not use toxic or heavy metal substances, thus improving the overall environmental friendliness of the product; moreover, the raw materials for this environmentally friendly friction material composition are widely available and environmentally friendly without pollution.

[0115] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. An environmentally friendly friction material for high-altitude railways that is resistant to aging and heat degradation, characterized in that: It consists of the following components by weight percentage: Modified phenolic resin 7.7%~11.7%, hydrogenated nitrile rubber 14.4%~16.6%, aluminum dihydrogen phosphate 7.7%~11.0%, basalt fiber 12.1%~14.4%, tungsten disulfide 2.7%~3.3%, zirconium silicate 3.8%~5.1%, flake graphite 9.3%~10.8%, barium sulfate 27.6%~33.1%, potassium feldspar powder 3.8%~5.1%; And accelerators CZ, zinc oxide, stearic acid and sulfur, each accounting for 8% of the weight of the hydrogenated nitrile rubber; The total weight percentage of the modified phenolic resin to potassium feldspar powder is 100%.

2. The environmentally friendly friction material for high-altitude railways that is resistant to aging and heat degradation according to claim 1, characterized in that, The modified phenolic resin is a boron-modified phenolic resin with a particle size of 325 mesh.

3. The environmentally friendly friction material for high-altitude railways that is resistant to aging and heat degradation according to claim 1, characterized in that, The aluminum dihydrogen phosphate has a particle size of 200 mesh and a P2O5 content of ≥60%.

4. The environmentally friendly friction material for high-altitude railways that is resistant to aging and heat degradation according to claim 1, characterized in that, The basalt fibers are pretreated with a silane coupling agent and have a length of 9-12 mm.

5. The environmentally friendly friction material for high-altitude railways that is resistant to aging and heat degradation according to claim 1, characterized in that, The tungsten disulfide has a particle size of 325 mesh and a WS2 content of ≥96%; the zirconium silicate has a particle size of 325 mesh and a ZrO2 content of ≥60%; the barium sulfate has a particle size of 325 mesh and a barium sulfate content of ≥99%; and the potassium feldspar powder has a particle size of 325 mesh.

6. The environmentally friendly friction material for high-altitude railways that is resistant to aging and heat degradation according to claim 1, characterized in that, It consists of the following components by weight percentage: Modified phenolic resin 9.5%, hydrogenated nitrile rubber 15.5%, aluminum dihydrogen phosphate 9.1%, basalt fiber 13.5%, tungsten disulfide 3.1%, zirconium silicate 4.6%, flake graphite 10.2%, barium sulfate 30.2%, potassium feldspar powder 4.6%; And accelerators CZ, zinc oxide, stearic acid and sulfur, each accounting for 8% of the weight of the hydrogenated nitrile rubber.

7. A method for preparing an environmentally friendly friction material for high-altitude railways that is resistant to aging and thermal degradation according to any one of claims 1 to 6, characterized in that, Includes the following steps: Sa, weigh each component according to the ratio, add toluene (1% of the total weight of the mixture) as a wetting agent, and mix in an internal mixer; Sb, Crush the mixed material to a particle size of no more than 10mm; Sc. Place the crushed material into a mold that has been heated to 160±5℃, and then place the mold on the hydraulic station of the hydraulic press for hot pressing to obtain the blank. Sd. The blank is placed in an oven for secondary curing to obtain the friction material.

8. The preparation method according to claim 7, characterized in that, In step Sa, the internal mixer rotates at a speed of 20-60 r / min, the mixing time is 10-15 min, and the mixing temperature does not exceed 90℃.

9. The preparation method according to claim 7, characterized in that, In step Sc, the hot pressing temperature is 155~165℃, the hot pressing pressure is 25~30MPa, and the hot pressing time is 40~50min.

10. The preparation method according to claim 7, characterized in that, In step Sd, the secondary curing process employs a stepped heating method: Hold at 80℃ for 1 hour, raise the temperature to 100℃ and hold for 0.5 hours, raise the temperature to 120℃ and hold for 1 hour, raise the temperature to 140℃ and hold for 1 hour, raise the temperature to 160℃ and hold for 1 hour, and finally raise the temperature to 170℃ and hold for 4 hours.

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