High-stability low-wear disc brake friction plate and preparation method thereof

Abstract

The invention relates to a preparation method of a high-stability low-wear disc brake friction plate, which comprises the following steps of: mixing a resin-assistant-hydroxypropyl chitosan compound which is obtained by special modification of phenolic resin and is used as an effective component with other raw materials and auxiliary materials, pressing into a green body, and carrying out graded curing. Through particle size matching of the components, a complete particle size chain from coarse to fine is formed, hardness change uniformity is improved, wear resistance is guaranteed, the contradiction between wear resistance and protection of mating plates can be balanced, through graded curing treatment, it is guaranteed that the mechanical property and wear resistance of a blank are stable, a stable'resin-hard phase 'bonding interface is constructed, and the service life of the blank is prolonged. The heat conductivity is larger than or equal to 18 W / (m.K), the friction coefficient fluctuation ratio is smaller than or equal to 0.04, and the normal-temperature abrasion rate is smaller than or equal to 0.5 * 10 <-7 > cm / (N.m).

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology for automotive braking, specifically to a high-stability, low-wear disc brake friction pad and its preparation method. Background Technology

[0002] Based on the functional components and braking scenarios of the automotive braking system, brake pads are mainly divided into three categories: new car brake pads, parking brake pads, and auxiliary brake pads. Among them, the service brake pads (main brake pads) are the most important braking components of a car, corresponding to the "foot brake," responsible for actively decelerating or stopping the vehicle while it is in motion, and are the core actuator of the braking system. According to the form of service braking, they are further divided into disc brake pads and drum brake pads. Brake pads need to withstand frequent light braking and emergency braking, so they need to meet the requirements of high-frequency use, as well as high temperature resistance and excellent thermal stability to reduce the decay of the friction coefficient. In addition, the friction uniformity of the pads ensures stable braking without jamming or sudden changes in braking strength.

[0003] Disc brake pads are mounted on both sides of the brake disc and clamped by calipers for friction braking. They are characterized by a small friction area and rapid heat dissipation, but are used frequently (e.g., in urban traffic jams), are sensitive to heat fade, and need to balance quiet operation with brake disc protection. Therefore, while disc brakes dissipate heat quickly, the brake disc temperature can still rise sharply to 300-500℃ (500-600℃ or even higher for heavy commercial vehicles) during frequent emergency braking or long downhill runs. This necessitates excellent resistance to heat fade (severe heat fade will result in a softer brake surface with each stop, significantly increasing braking distance during high-speed emergency braking). Secondly, disc brakes need to adapt to different operating conditions, such as low-speed light braking (e.g., following other vehicles) and high-speed emergency braking (e.g., hazard avoidance), and the friction coefficient cannot fluctuate excessively. Therefore, the friction coefficient must fluctuate minimally under all operating conditions. Furthermore, since the disc brake pads are in direct contact with the brake disc, they must avoid excessive wear and scratching of the brake disc, requiring low wear rate and suitable hardness.

[0004] While existing commercial vehicle disc brake friction pads use a composite ratio of mineral fiber, organic fiber, and steel fiber to meet basic strength and temperature resistance requirements, they suffer from the following technical challenges: 1. Under long-term, high-frequency braking, insufficient bonding between fibers can easily lead to delamination, causing the coefficient of friction to fluctuate by more than ±0.06; 2. The thermal expansion rate is close to the upper limit of 1%, making it prone to uneven adhesion to the brake disc at high temperatures, with the wear rate increasing to over 0.15 over time; 3. Although they comply with the environmental limits of GB5763-2018, there is still room for improvement in the amount of harmful substances (such as cadmium and lead), and traditional mixing processes can easily lead to uneven component distribution, affecting braking consistency. Summary of the Invention

[0005] The purpose of this invention is to provide a disc brake friction pad suitable for use in commercial vehicles. This friction pad has excellent resistance to heat fade, a moderate and stable coefficient of friction, and a low wear rate.

[0006] Another objective of this invention is to provide a method for preparing a highly stable, low-wear disc brake friction pad. This method solves the problems of insufficient inter-fiber bonding strength leading to delamination under long-term braking, resulting in large fluctuations in the coefficient of friction, as well as excessively high thermal expansion coefficients causing uneven adhesion to the brake disc at high temperatures and excessively rapid wear.

[0007] The objective of this invention is achieved through the following technical solution: A disc brake friction pad suitable for use in commercial vehicles is characterized by being prepared from raw materials including phosphate-modified steel fibers, silane-modified wollastonite fibers, aramid organic fibers, resin-auxiliary-hydroxypropyl chitosan complex prepared by melt modification of phenolic resin, silicon dioxide, boron carbide, aluminum oxide, silicon carbide, copper powder, and iron powder.

[0008] Further, by weight, the phosphate-modified steel fiber comprises 8-12 parts, the silane-modified wollastonite fiber comprises 12-18 parts, the aramid organic fiber comprises 1-3 parts, the silicon dioxide comprises 2-5 parts (particle size 0.8-1.5 μm), the boron carbide particles comprises 0.7-1.6 parts, the resin-auxiliary-hydroxypropyl chitosan complex comprises 12-18 parts, the iron powder comprises 21-27 parts, the copper powder comprises 14-18 parts, the aluminum oxide comprises 10.5-14 parts (particle size 3-5 μm), and the silicon carbide comprises 4.5-6.0 parts.

[0009] Furthermore, the boron carbide is composed of 60% boron carbide with a particle size of 13-15 μm and 40% boron carbide with a particle size of 7-9 μm by mass ratio.

[0010] Furthermore, the silicon carbide is composed of 70% silicon carbide with a particle size of 2-4 μm and 30% silicon carbide with a particle size of 0.5-1 μm by mass ratio.

[0011] Furthermore, the silica particles have a diameter of 0.8~1.5μm, and the alumina particles have a diameter of 3~5μm.

[0012] Furthermore, the modified steel fiber is prepared by placing hooked steel fibers with a diameter of 0.2-0.3 mm and a length of 3-5 mm into a phosphating tank, adding phosphating solution to submerge the hooked steel fibers by 1-2 cm, controlling the temperature at 48-52℃, soaking for 25-30 minutes, then removing them, rinsing them with deionized water 3-5 times, and then placing them in an oven at 70-80℃ for drying for 1-2 hours.

[0013] Furthermore, the phosphating solution is composed of 15% zinc phosphate, 8% manganese nitrate, 2% nickel nitrate, and the remainder being water by mass fraction.

[0014] Furthermore, the silane-modified wollastonite fiber is prepared by adding wollastonite fiber (particle size 5-10μm) and coupling agent KH-550 into a high-speed mixer, setting the speed to 600-800rpm, and stirring at 55-60℃ for 15-20min. The KH-550 is 0.4-0.6% of the mass of the wollastonite fiber.

[0015] Furthermore, the resin-auxiliary-hydroxypropyl chitosan complex is formed by heating environmentally friendly phenolic resin to 55~65℃, stirring at 200~300rpm, melting it, adding environmentally friendly auxiliary agent ST-602 and hydroxypropyl chitosan ethanol-propylene glycol solution, and continuing to stir for 20~30min.

[0016] Furthermore, the mass ratio of the phenolic resin, environmentally friendly additive ST-602, and hydroxypropyl chitosan ethanol propylene glycol solution is 72~78:1.5~2.5:20~26.

[0017] Furthermore, the hydroxypropyl chitosan ethanol-propylene glycol solution is obtained by slowly adding hydroxypropyl chitosan to ethanol, stirring until completely dispersed, adding deionized and propylene glycol solutions, stirring continuously until the solution is clear, and filtering through a 200-mesh sieve.

[0018] Furthermore, the mass ratio of hydroxypropyl chitosan, ethanol, deionized water, and propylene glycol is 1:50~55:36~42:3~5.

[0019] A method for preparing a high-stability, low-wear disc brake friction pad is characterized by: using phosphate-modified steel fibers, silane-modified wollastonite fibers, aramid organic fibers, resin-auxiliary-hydroxypropyl chitosan composite prepared by melt modification of phenolic resin, silicon dioxide, boron carbide, aluminum oxide, silicon carbide, copper powder, iron powder, and tin powder as raw materials, mixing them, pressing them into a blank, and then subjecting them to graded curing.

[0020] Further, by weight, the phosphate-modified steel fiber comprises 8-12 parts, the silane-modified wollastonite fiber comprises 12-18 parts, the aramid organic fiber comprises 1-3 parts, the silicon dioxide comprises 2-5 parts (particle size 0.8-1.5 μm), the boron carbide particles comprises 0.7-1.6 parts, the resin-auxiliary-hydroxypropyl chitosan complex comprises 12-18 parts, the iron powder comprises 21-27 parts, the copper powder comprises 14-18 parts, the tin powder comprises 2-3 parts, the aluminum oxide comprises 10.5-14 parts (particle size 3-5 μm), and the silicon carbide comprises 4.5-6.0 parts.

[0021] Furthermore, the boron carbide is composed of 60% boron carbide with a particle size of 13-15 μm and 40% boron carbide with a particle size of 7-9 μm by mass ratio.

[0022] Furthermore, the silicon carbide is composed of 70% silicon carbide with a particle size of 2-4 μm and 30% silicon carbide with a particle size of 0.5-1 μm by mass ratio.

[0023] Furthermore, the silica particles have a diameter of 0.8~1.5μm, and the alumina particles have a diameter of 3~5μm.

[0024] Boron carbide, with a Mohs hardness of 9.3, is the primary wear-resistant phase, while silicon carbide (Mohs hardness 9.0) provides auxiliary wear resistance. This creates a hardness gradient with the low-hardness resin fiber matrix. By employing 13-15μm boron carbide as the main skeleton, 7-9μm boron carbide filling the gaps in the main skeleton, and using two particle sizes of silicon carbide (2-4μm and 0.5-1μm), micron-sized silicon carbide fills the remaining gaps between the boron carbide main skeleton, thus strengthening the "B4C-SiC" structure. The composite wear-resistant gradient structure prevents wear debris from cutting the matrix after entering the gaps. 0.5~1μm fine-grained silicon carbide fills the small gaps between small-grained boron carbide while also assisting in filling the large-diameter micropores of the resin. 3~5μm alumina (Mohs hardness 9.0) has a dual function of assisting wear resistance and filling gaps. Its particle size is between boron carbide (7~15μm) and silicon carbide (0.5~4μm), which can accurately fill the "particle size gap" between the two and enhance the continuity of the wear-resistant gradient. Silica (Mohs hardness 7.0) serves as a low-hardness buffer phase. On the one hand, it uniformly coats the surface of hard phases such as boron carbide and silicon carbide to form a flexible transition layer, avoiding direct scratches from the hard phases on the mating parts. On the other hand, its micro-nano scale characteristics can fill the small-diameter micropores of the resin matrix, reducing the risk of wear debris embedding, while also helping to balance the stability of the friction coefficient. By matching the particle size of the above components, a continuous gradient connection is formed, creating a complete particle size chain from coarse to fine. The resulting stepped distribution of hardness structure improves the uniformity of hardness variation, ensuring wear resistance while balancing the contradiction between wear resistance and protection of mating parts.

[0025] Furthermore, the modified steel fiber is prepared by placing hooked steel fibers with a diameter of 0.2-0.3 mm and a length of 3-5 mm into a phosphating tank, adding phosphating solution to submerge the hooked steel fibers by 1-2 cm, controlling the temperature at 48-52℃, soaking for 25-30 minutes, then removing them, rinsing them with deionized water 3-5 times, and then placing them in an oven at 70-80℃ for drying for 1-2 hours.

[0026] Steel fibers have a smooth surface and weak physical adsorption to phenolic resin. During braking, steel fibers are easily detached from the resin, forming internal voids, causing delamination of the friction pads and shortening their service life. Wollastonite fibers are inorganic mineral fibers with a polar surface, while phenolic resin is an organic polymer with weak polarity. Direct mixing of the two will result in uneven dispersion due to the polarity mismatch, ultimately leading to uneven hardness distribution on the friction surface of the friction pads and large fluctuations in the coefficient of friction.

[0027] In this invention, a rough phosphate film (containing phosphate groups) is formed on the surface of steel fibers through phosphate treatment. On the one hand, this increases the mechanical bonding area with the resin. On the other hand, the hydroxypropyl chitosan added during the resin melt modification stage can introduce hydroxyl and hydroxypropyl groups to the surface of the phenolic resin, transforming ordinary phenolic resin into a special phenolic resin. In the special phenolic resin, these active groups interact with the phosphate groups of the phosphate film through hydrogen bonding and coordination, forming a stable chemical bond. This significantly improves the bonding strength between the steel fibers and the resin, preventing the steel fibers from detaching and forming voids during braking. Furthermore, wollastonite fibers are modified with the silane coupling agent KH-550 (aminopropyltriethoxysilane). During the mixing process, the siloxy groups at one end of the molecular chain hydrolyze to generate silanol groups, which undergo a condensation reaction with the hydroxyl groups on the surface of the wollastonite fibers to form Si-O-Si covalent bonds. The amino groups at the other end can undergo nucleophilic addition reactions with the modified phenolic resin (containing hydroxypropyl and hydroxyl groups), constructing a "molecular bridge" between the inorganic wollastonite fibers and the organic phenolic resin, achieving molecular-level compatibility between the two, effectively preventing the agglomeration of wollastonite fibers, and ensuring uniform hardness distribution on the friction surface.

[0028] Furthermore, the phosphating solution is composed of 15% zinc phosphate, 8% manganese nitrate, 2% nickel nitrate, and the remainder being water by mass fraction.

[0029] Furthermore, the silane-modified wollastonite fiber is prepared by adding wollastonite fiber (particle size 5-10μm) and coupling agent KH-550 into a high-speed mixer, setting the speed to 600-800rpm, and stirring at 55-60℃ for 15-20min. The KH-550 is 0.4-0.6% of the mass of the wollastonite fiber.

[0030] Furthermore, the resin-auxiliary-hydroxypropyl chitosan complex is formed by heating environmentally friendly phenolic resin to 55~65℃, stirring at 200~300rpm, melting it, adding environmentally friendly auxiliary agent ST-602 and hydroxypropyl chitosan ethanol-propylene glycol solution, and continuing to stir for 20~30min.

[0031] Furthermore, the mass ratio of the phenolic resin, environmentally friendly additive ST-602, and hydroxypropyl chitosan ethanol propylene glycol solution is 72~78:1.5~2.5:20~26.

[0032] Furthermore, the hydroxypropyl chitosan ethanol-propylene glycol solution is obtained by slowly adding hydroxypropyl chitosan to ethanol, stirring until completely dispersed, adding deionized and propylene glycol solutions, stirring continuously until the solution is clear, and filtering through a 200-mesh sieve.

[0033] Furthermore, the mass ratio of hydroxypropyl chitosan, ethanol, deionized water, and propylene glycol is 1:50~55:36~42:3~5.

[0034] Furthermore, the graded curing process involves placing the pressed preform into a curing oven and heating it to 105-115°C at a heating rate of 15-20°C / min, holding it at that temperature for 2-3 hours; then heating it to 135-140°C at a heating rate of 8-10°C / min, holding it at that temperature for 3-4 hours; then heating it to 155-160°C at a heating rate of 3-5°C / min, holding it at that temperature for 1-1.5 hours; finally, under a nitrogen atmosphere, heating it to 180-190°C at a heating rate of 3-5°C / min, holding it at that temperature for 1-1.5 hours, and then cooling it to room temperature at the same rate.

[0035] First-stage low-temperature curing (105~115℃): Targets the trace air remaining in the pre-compressed green body, achieving initial cross-linking in a low-viscosity resin state, fixing the green body structure, and preventing air bubbles from being generated during subsequent heating; Second-stage medium-temperature curing (135~140℃): Gently raises the temperature to extend the cross-linking time, allowing the resin molecular chains to diffuse fully, ensuring that both the fiber and hard phase surfaces are wetted by the resin, and improving the uniformity of cross-linking; Third-stage medium-high temperature curing (155~160℃): Promotes further cross-linking of the low-activity hydroxymethyl groups in the phenolic resin, generating methylene bridges with higher bond energy, and improving the strength of the green body; Fourth-stage high-temperature nitrogen curing (180~190℃): The nitrogen atmosphere inhibits the oxidative degradation of the resin, while simultaneously achieving resin densification and hardening combined reinforcement, ultimately ensuring the stability of the green body's mechanical properties and wear resistance. The final stage of high-temperature curing in a nitrogen atmosphere (180~190℃) promotes deep cross-linking of phenolic resin, forming a dense three-dimensional network structure. On the other hand, the modified groups in the resin matrix (such as hydroxypropyl and hydroxyl groups) can form strong hydrogen bonds with the hydroxyl groups (or residual active groups of coupling agents) on the surface of hard phase particles such as alumina and silicon carbide. At the same time, the densified resin can form a "mechanical encapsulation" of hard phase particles, constructing a stable "resin-hard phase" bonding interface and reducing the high-temperature shedding rate of hard phase particles.

[0036] Most specifically, a method for preparing a high-stability, low-wear disc brake friction pad is characterized by comprising the following steps: S1. Modification treatment (1) Modified steel fiber Take hook-shaped steel fibers (purchased from Hebei Shangze Rubber & Plastic Products Co., Ltd.) with a diameter of 0.2-0.3 mm and a length of 3-5 mm and place them in a phosphating tank. Add phosphating solution (the phosphating solution consists of 15% zinc phosphate, 8% manganese nitrate, 2% nickel nitrate, and the remainder water by mass) to submerge the hook-shaped steel fibers by 1-2 cm. Control the temperature at 48-52℃ and soak for 25-30 minutes. After soaking, remove the fibers, rinse them 3-5 times with deionized water, and then place them in an oven at 70-80℃ to dry for 1-2 hours. (2) Modified mineral fibers Add wollastonite fibers (particle size 5-10μm, purchased from Shijiazhuang Tuoju Mineral Products Co., Ltd.) and coupling agent KH-550 (added at 0.5% of the mass of wollastonite fibers) to a high-speed mixer, set the speed to 600-800 rpm, and stir at 55-60℃ for 15-20 minutes to ensure that the coupling agent uniformly coats the surface of the wollastonite fibers, and set aside for later use; (3) Resin melt modification Environmentally friendly phenolic resin is placed in a reaction vessel, the temperature is set to 55~65℃, and stirring is started at a speed of 200~300 rpm. After melting, environmentally friendly additive ST-602 and hydroxypropyl chitosan ethanol-propylene glycol solution are added, and stirring is continued for 20~30 minutes to form a resin-additive-hydroxypropyl chitosan complex. The mass ratio of the phenolic resin, environmentally friendly additive ST-602, and hydroxypropyl chitosan ethanol-propylene glycol solution is 72~78:1.5~2.5:20~26. The hydroxypropyl chitosan ethanol-propylene glycol solution is obtained by slowly adding hydroxypropyl chitosan to ethanol, stirring until completely dispersed, adding deionized water and propylene glycol solution, and continuing to stir until the solution is clear. The solution is then filtered through a 200-mesh sieve. The mass ratio of hydroxypropyl chitosan, ethanol, deionized water, and propylene glycol is 1:50~55:36~42:3~5. S2. Mixing Add the modified steel fiber, modified mineral fiber, and aramid organic fiber from step S1 to a twin-screw mixer, heat to 50-60℃, start stirring at 400-500 rpm, and stir for 30-35 minutes under the heat-maintaining condition. While keeping the temperature and speed constant, add silicon dioxide, boron carbide particles, and aluminum oxide to the twin-screw mixer, and continue stirring for 20-25 minutes. Then add iron powder, copper powder, and tin powder, and continue stirring for 20-25 minutes. Slowly add silicon carbide and resin-auxiliary-hydroxypropyl chitosan complex to the mixer, and stir for 15-18 minutes. Afterwards, a uniform friction material mixture is formed and discharged for later use. The components, by weight, are: 8-12 parts modified steel fiber, 12-18 parts modified mineral fiber, 1-3 parts aramid organic fiber, 2-5 parts silica (particle size 0.8-1.5 μm), 0.7-1.6 parts boron carbide particles (specifically composed of 60% 13-15 μm and 40% 7-9 μm boron carbide particles), 12-18 parts resin-auxiliary-hydroxypropyl chitosan complex, 21-27 parts iron powder (passed through a 100-mesh sieve), 14-18 parts copper powder (passed through a 100-mesh sieve), 2-3 parts tin powder (passed through a 100-mesh sieve), 10.5-14 parts alumina (particle size 3-5 μm), and 4.5-6.0 parts silica (based on a weight ratio of 70% 2-4 μm and 30% 0.5-1.5 μm and 4.5-6.0 parts silica). (composition of silicon carbide in μm). S3. Compression molding (1) Pre-pressing: Pour the friction material mixture into the mold and pre-press it using a hydraulic press. The pressure is set to 10~12MPa and the temperature is set to 80~85℃. The pressure is maintained for 5~7 minutes to remove the air in the mixture and form a pre-pressed blank. (2) Final pressing: Transfer the pre-pressed blank to a hot press mold, heat it to 150~160℃, set the pressure to 30~36MPa, maintain the pressure for 10~15min, ensure the density of the blank is ≥2.6g / cm³, take it out and let it cool naturally to room temperature to obtain the pressed blank for later use; S4. Curing The pressed preform is placed in a curing oven and heated to 105-115℃ at a heating rate of 15-20℃ / min, and held for 2-3 hours; then heated to 135-140℃ at a heating rate of 8-10℃ / min, and held for 3-4 hours; then heated to 155-160℃ at a heating rate of 3-5℃ / min, and held for 1-1.5 hours; finally, under a nitrogen atmosphere, heated to 180-190℃ at a heating rate of 3-5℃ / min and held for 1-1.5 hours. The edges and corners of the cured blank are ground to ensure dimensional accuracy (error ≤ 0.1mm) and meet the vehicle installation requirements.

[0037] The present invention has the following technical effects: This invention achieves a continuous gradient by matching the particle size of the components, forming a complete particle size chain from coarse to fine. This improves the uniformity of hardness variation, ensuring wear resistance while balancing the conflict between wear resistance and protection of mating parts. Through graded curing treatment, resin densification and hardening are combined and strengthened, ultimately ensuring stable mechanical and wear-resistant properties of the preform. A stable "resin-hard phase" interface is constructed, reducing the high-temperature shedding rate of hard phase particles. With a thermal conductivity ≥18W / (m·K), frictional heat can be quickly transferred to the brake disc, avoiding localized overheating. At high temperatures, resin softening and hard phase particle shedding accelerate wear. The final friction pad has a friction coefficient fluctuation rate ≤0.04 and a room-temperature wear rate ≤0.5×10⁻⁴. -7 cm³ / (N·m). Detailed Implementation

[0038] The present invention will be specifically described below through embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above description.

[0039] Example 1 A method for preparing a high-stability, low-wear disc brake friction pad includes the following steps: S1. Modification treatment (1) Modified steel fiber Take hook-shaped steel fibers with a diameter of 0.2-0.3 mm and a length of 3-5 mm and place them in a phosphating tank. Add phosphating solution (the phosphating solution consists of 15% zinc phosphate, 8% manganese nitrate, 2% nickel nitrate, and the remainder water by mass) to submerge the hook-shaped steel fibers by 1-2 cm. Control the temperature at 50℃ and soak for 28 minutes. After soaking, remove the fibers, rinse them four times with deionized water, and then place them in a 75℃ oven to dry for 1.5 hours. (2) Modified mineral fibers Add wollastonite fibers (particle size 5-10μm) and coupling agent KH-550 (added at 0.5% of the mass of wollastonite fibers) to a high-speed mixer, set the speed to 700rpm, and stir at 58℃ for 18min to make the coupling agent uniformly coat the surface of the wollastonite fibers, and set aside. (3) Resin melting Environmentally friendly phenolic resin was placed in a reactor, the temperature was set to 60℃, and stirring was started at 250 rpm. After melting, environmentally friendly additive ST-602 and hydroxypropyl chitosan ethanol-propylene glycol solution were added. Stirring was continued for 25 minutes to form a resin-additive-hydroxypropyl chitosan complex. The mass ratio of the phenolic resin, environmentally friendly additive ST-602, and hydroxypropyl chitosan ethanol-propylene glycol solution was 75:2:25. The hydroxypropyl chitosan ethanol-propylene glycol solution was obtained by slowly adding hydroxypropyl chitosan to ethanol, stirring until completely dispersed, adding deionized water and propylene glycol solution, and continuing to stir until the solution was clear. The solution was then filtered through a 200-mesh sieve. The mass ratio of hydroxypropyl chitosan, ethanol, deionized water, and propylene glycol was 1:52:40:4. S2. Mixing Add the modified steel fiber, modified mineral fiber, and aramid organic fiber from step S1 to a twin-screw mixer, heat to 55°C, start stirring at 450 rpm, and stir for 32 minutes under the heat preservation condition. While maintaining the temperature and speed, add silicon dioxide, boron carbide particles, and aluminum oxide to the twin-screw mixer, and continue stirring for 22 minutes. Then add iron powder, copper powder, and tin powder, and continue stirring for 22 minutes. Slowly add silicon carbide and resin-auxiliary-hydroxypropyl chitosan complex to the mixer, and stir for 16 minutes. Afterwards, a uniform friction material mixture is formed and discharged for later use. The components, by weight, are as follows: 8-12 parts modified steel fiber, 15 parts modified mineral fiber, 2 parts aramid organic fiber, 4 parts silicon dioxide (particle size 0.8-1.5μm), 1.2 parts boron carbide particles (specifically composed of 60% boron carbide with a particle size of 13-15μm and 40% boron carbide with a particle size of 7-9μm), 15 parts resin-auxiliary-hydroxypropyl chitosan complex, 25 parts iron powder (passed through a 100-mesh sieve), 14-18 parts copper powder (passed through a 100-mesh sieve), 2.5 parts tin powder (passed through a 100-mesh sieve), 12 parts aluminum oxide (particle size 3-5μm), and 5 parts silicon carbide (composed of 70% silicon carbide with a particle size of 2-4μm and 30% silicon carbide with a particle size of 0.5-1μm by weight). S3. Compression molding (1) Pre-pressing: Pour the friction material mixture into the mold, pre-press it using a hydraulic press, set the pressure to 11MPa, set the temperature to 80℃, maintain the pressure for 6min, remove the air from the mixture, and form a pre-pressed blank; (2) Final pressing: Transfer the pre-pressed blank to a hot press mold, heat it to 155℃, set the pressure to 32MPa, maintain the pressure for 12min, and ensure that the density of the blank is ≥2.6g / cm³. After taking it out, let it cool naturally to room temperature to obtain the pressed blank for later use. S4. Curing The pressed preform is placed in a curing oven and heated to 110°C at a rate of 18°C / min, and held for 2.5 hours. Then, it is heated to 138°C at a rate of 9°C / min and held for 3.5 hours. Next, it is heated to 158°C at a rate of 4°C / min and held for 1 hour. Finally, under a nitrogen atmosphere, it is heated to 185°C at a rate of 4°C / min and held for 1.5 hours. Then, it is cooled to room temperature at the same rate. The edges and corners of the cured blank are ground to ensure dimensional accuracy (error ≤ 0.1mm) and meet the vehicle installation requirements.

[0040] Comparative Example 1: Compared with Example 1, the boron carbide used has a single particle size of 13~15μm and the silicon carbide has a single particle size of 2~4μm, and the remaining steps are the same as in Example 1.

[0041] During this process, the connection of the "B4C-SiC" composite wear-resistant gradient structure is discontinuous, resulting in unsatisfactory overall performance of the friction plate. The loose structure makes it easy for the wear-resistant phase to separate and migrate, reducing the stability of the friction surface and causing a sharp increase in the wear rate. Furthermore, the lack of a continuous transition structure hinders heat transfer, affecting the overall heat dissipation.

[0042] Comparative Example 2: Compared with Example 1, the phenolic resin was not melt-treated. The phenolic resin, additives and hydroxypropyl chitosan ethanol propylene glycol solution were directly added and mixed in the mixing step. The remaining steps were the same as in Example 1.

[0043] The phenolic resin was melt-premixed to guide the subsequent anchoring reaction with the fiber. The phenolic resin, additives and hydroxypropyl chitosan ethanol propylene glycol solution were not melt-treated, but added in the subsequent mixing process. This resulted in uneven dispersion, component agglomeration and incomplete reaction. Ultimately, the friction surface of the final friction pad still had uneven hardness distribution, leading to large fluctuations in the coefficient of friction and fiber delamination during long-term braking.

[0044] Comparative Example 3: Compared with Example 1, only a three-stage heating curing process was used in the curing process. That is, the fourth step in Example 1, "finally heating to 190°C at 4°C / min and holding for 1 hour in a nitrogen atmosphere", was not used. The remaining steps were the same as in Example 1.

[0045] The product prepared in Comparative Example 3 has a relatively low degree of crosslinking, residual internal stress, and a significantly increased expansion rate, making it prone to cracking when braked at high temperatures.

[0046] The friction performance, mechanical properties, and thermal properties of the friction pads were tested according to QC / T 239-2015 "Technical Requirements and Bench Test Methods for Commercial Vehicle Service Brakes" and GB / T5763-2022 "Automotive Brake Liners".

[0047] (a) Mechanical properties (1) Shear strength: Tested in accordance with GB / T 5763-2022.

[0048] (2) Shore hardness variation: Tested according to GB / T 5763-2022 to evaluate the surface uniformity of the friction pad and reflect the elastic hardness of the matrix.

[0049] (3) Rockwell hardness variation: The test was conducted according to QC / T 239-2015 to evaluate the scratching effect of particle hardness control on the brake disc and to reflect the overall resistance to plastic deformation. The test results are shown in Table 1.

[0050] Table 1:

[0051] Shear strength reflects the bonding reliability between the friction material and the metal backing plate. As shown in the table above, the shear strength of the friction pad prepared in Example 1 reached 16.8 MPa. The hardness of the friction pad determines its wear resistance; however, excessive hardness will scratch the brake disc, while excessive softness will lead to wear. Therefore, the hardness of the friction pad needs to balance "self-wear resistance" and "brake disc protection." The hardness of the friction pad prepared in Example 1 of this invention is 94 HRR.

[0052] (ii) Friction properties (1) Coefficient of friction: The static coefficient of friction, dynamic coefficient of friction, and coefficient of friction variation in the range of temperature (25℃) to high temperature (600℃) of the friction pads were tested according to QC / T 239-2015, and the coefficient of friction retention rate was calculated by the following formula: .

[0053] (2) Wear rate: GB / T 5763-2022 tests the volume wear rate of friction pads in the range of room temperature (25℃) to high temperature (600℃).

[0054] (3) Friction fade and recovery: Following QC / T 239-2015, dynamic high-temperature cycling was used to simulate the long downhill driving conditions of commercial vehicles. Continuous braking caused the brake temperature to rise to 300-600℃ several times. The brake torque decay was recorded. After cooling to 100℃, the brake torque retention rate after recovery was tested. The difference between the thermal fade rate and the recovery rate was calculated using the following formula:

[0055] Where M F1 As the reference braking force, M Fmin This is the minimum braking torque during thermal decay.

[0056]

[0057] Where M R Braking torque after no response.

[0058] Table 2:

[0059] Excessive or insufficient friction coefficients can directly compromise the stability of the braking system, leading to safety hazards. A low high-temperature retention rate results in thermal fade during downhill driving, causing a sudden drop in braking force. Excessive fluctuations in the friction coefficient can cause localized pressure concentration during braking, either exacerbating wear due to excessive pressure or damaging the brake disc due to concentrated hard points. Calculations show that the friction coefficient fluctuation rate in Example 1 is ≤0.04. Wear rate testing is a core indicator for evaluating the durability of friction materials. As shown in the table above, the friction pads prepared in Example 1 have low wear rates, and the wear rate does not significantly increase at 600℃. The wear rate at room temperature is ≤0.5×10⁻⁶. - 7 cm³ / (N·m), high-temperature wear rate at 600℃ ≤0.8×10 -7 cm³ / (N·m) (A low wear rate means that the friction pads have less volume loss under the same number of braking cycles / loads, directly extending their service life).

[0060] (III) Thermal properties (1) Thermal expansion coefficient: The linear expansion coefficient α in the range of room temperature (25℃) to high temperature (600℃) was tested according to GB / T 5763-2022 Thermomechanical Analysis (TMA). The expansion coefficient at 600℃ was calculated according to the formula:

[0061] (2) Thermal conductivity: The change in thermal conductivity from room temperature (25℃) to high temperature (600℃) was tested according to the hot wire method in GB / T 10294-2008.

[0062] (3) Thermal stability: Keep at a high temperature of 600℃ for 2 hours and observe the structural changes of the friction plate.

[0063] Table 3:

[0064] In Example 1, the friction pad has a thermal expansion rate of ≤0.6% at 600℃ (to prevent the friction pad from seizing the brake disc due to thermal expansion, leading to dragging and wear), and a thermal conductivity of ≥18W / (m·K) (to quickly transfer frictional heat to the brake disc, avoiding local overheating, resin softening at high temperatures, and hard phase particle shedding, which accelerates wear). It exhibits excellent thermal stability. In contrast, the friction pad prepared in the comparative example has a significantly increased expansion rate at 600℃, which can easily lead to brake disc seizing due to thermal expansion. It also has a lower thermal conductivity, resulting in reduced heat transfer efficiency at high temperatures. During friction, it accelerates the shedding of hard phase particles, thereby accelerating wear.

[0065] Example 2 A method for preparing a high-stability, low-wear disc brake friction pad includes the following steps: S1. Modification treatment (1) Modified steel fiber Take hook-shaped steel fibers with a diameter of 0.2-0.3 mm and a length of 3-5 mm and place them in a phosphating tank. Add phosphating solution (the phosphating solution consists of 15% zinc phosphate, 8% manganese nitrate, 2% nickel nitrate, and the remainder water by mass) to submerge the hook-shaped steel fibers by 1-2 cm. Control the temperature at 48℃ and soak for 30 minutes. After soaking, remove the fibers, rinse them three times with deionized water, and then place them in a 70℃ oven to dry for 2 hours. (2) Modified mineral fibers Add wollastonite fibers (particle size 5-10μm) and coupling agent KH-550 (added at 0.5% of the mass of wollastonite fibers) to a high-speed mixer, set the speed to 600 pm, and stir at 60℃ for 15 min to make the coupling agent uniformly coat the surface of the wollastonite fibers, and set aside. (3) Resin melting Environmentally friendly phenolic resin was placed in a reactor, the temperature was set to 55℃, and stirring was started at 300 rpm. After melting, environmentally friendly additive ST-602 and hydroxypropyl chitosan ethanol-propylene glycol solution were added, and stirring was continued for 20 minutes to form a resin-additive-hydroxypropyl chitosan complex. The mass ratio of the phenolic resin, environmentally friendly additive ST-602, and hydroxypropyl chitosan ethanol-propylene glycol solution was 72:1.5:20. The hydroxypropyl chitosan ethanol-propylene glycol solution was obtained by slowly adding hydroxypropyl chitosan to ethanol, stirring until completely dispersed, adding deionized water and propylene glycol solution, and continuing to stir until the solution was clear. The solution was then filtered through a 200-mesh sieve. The mass ratio of hydroxypropyl chitosan, ethanol, deionized water, and propylene glycol was 1:50:36:3. S2. Mixing Add the modified steel fiber, modified mineral fiber, and aramid organic fiber from step S1 to a twin-screw mixer, heat to 50°C, start stirring at 500 rpm, and stir for 30 minutes under the heat preservation condition. While maintaining the temperature and speed, add silicon dioxide, boron carbide particles, and aluminum oxide to the twin-screw mixer, and continue stirring for 20 minutes. Then add iron powder, copper powder, and tin powder, and continue stirring for 20 minutes. Slowly add silicon carbide and resin-auxiliary-hydroxypropyl chitosan complex to the mixer, and stir for 15 minutes. Afterwards, a uniform friction material mixture is formed and discharged for later use. The components, by weight, are as follows: 8 parts modified steel fiber, 12 parts modified mineral fiber, 1 part aramid organic fiber, 2 parts silicon dioxide (particle size 0.8~1.5μm), 0.7 parts boron carbide particles (specifically composed of 60% 13~15μm and 40% 7~9μm boron carbide particles), 12 parts resin-auxiliary-hydroxypropyl chitosan complex, 21 parts iron powder (passed through a 100-mesh sieve), 14 parts copper powder (passed through a 100-mesh sieve), 2 parts tin powder (passed through a 100-mesh sieve), 10.5 parts aluminum oxide (particle size 3~5 μm), and 4.5 parts silicon carbide (composed of 70% 2~4μm and 30% 0.5~1 μm silicon carbide particles by weight). S3. Compression molding (1) Pre-pressing: Pour the friction material mixture into the mold, pre-press it using a hydraulic press, set the pressure to 10MPa, set the temperature to 85℃, maintain the pressure for 7min, and remove the air from the mixture to form a pre-pressed blank; (2) Final pressing: Transfer the pre-pressed blank to a hot press mold, heat it to 150℃, set the pressure to 36MPa, maintain the pressure for 10min, and ensure that the density of the blank is ≥2.6g / cm³. After taking it out, let it cool naturally to room temperature to obtain the pressed blank for later use. S4. Curing The pressed preform is placed in a curing oven and heated to 105°C at a rate of 15°C / min, and held for 3 hours. Then, it is heated to 140°C at a rate of 8°C / min, held for 3 hours, then heated to 160°C at a rate of 3°C / min, and held for 1 hour. Finally, under a nitrogen atmosphere, it is heated to 190°C at a rate of 3°C / min and held for 1 hour, and then cooled to room temperature at the same rate. The edges and corners of the cured blank are ground to ensure dimensional accuracy (error ≤ 0.1mm) and meet the vehicle installation requirements.

[0066] The friction pad material prepared in Example 2 has a shear strength of 16.1 MPa and a hardness of 96 HRR.

[0067] Calculations show that the dynamic friction coefficient of Example 2 is 0.35~0.40, the friction coefficient fluctuation rate is ≤0.05, and the wear rate at room temperature is 0.45×10⁻⁶.-7 The wear rate was 0.60 × 10⁻⁶ cm³ / (N·m), and did not increase significantly at 600℃. -7 cm³ / (N·m). In Example 2, the friction plate has a thermal expansion rate of 0.52% at 600℃, a thermal conductivity ≥24.7W / (m·K), and excellent thermal stability.

[0068] Example 3 A method for preparing a high-stability, low-wear disc brake friction pad includes the following steps: S1. Modification treatment (1) Modified steel fiber Take hook-shaped steel fibers with a diameter of 0.2-0.3 mm and a length of 3-5 mm and place them in a phosphating tank. Add phosphating solution (the phosphating solution consists of 15% zinc phosphate, 8% manganese nitrate, 2% nickel nitrate, and the remainder water by mass) to submerge the hook-shaped steel fibers by 1-2 cm. Control the temperature at 52℃ and soak for 25 minutes. After soaking, remove the fibers, rinse them 5 times with deionized water, and then place them in an 80℃ oven to dry for 1 hour. (2) Modified mineral fibers Add wollastonite fibers (particle size 5-10μm) and coupling agent KH-550 (added at 0.5% of the mass of wollastonite fibers) to a high-speed mixer, set the speed to 800rpm, and stir at 55℃ for 20min to make the coupling agent uniformly coat the surface of the wollastonite fibers, and set aside. (3) Resin melting Environmentally friendly phenolic resin was placed in a reactor, the temperature was set to 65℃, and stirring was started at 200 rpm. After melting, environmentally friendly additive ST-602 and hydroxypropyl chitosan ethanol-propylene glycol solution were added, and stirring was continued for 30 minutes to form a resin-additive-hydroxypropyl chitosan complex. The mass ratio of the phenolic resin, environmentally friendly additive ST-602, and hydroxypropyl chitosan ethanol-propylene glycol solution was 78:2.5:26. The hydroxypropyl chitosan ethanol-propylene glycol solution was obtained by slowly adding hydroxypropyl chitosan to ethanol, stirring until completely dispersed, adding deionized water and propylene glycol solution, and continuing to stir until the solution was clear. The solution was then filtered through a 200-mesh sieve. The mass ratio of hydroxypropyl chitosan, ethanol, deionized water, and propylene glycol was 1:55:42:5. S2. Mixing Add the modified steel fiber, modified mineral fiber, and aramid organic fiber from step S1 to a twin-screw mixer, heat to 60°C, start stirring at 400 rpm, and stir for 35 minutes under the heat preservation condition. While maintaining the temperature and speed, add silicon dioxide, boron carbide particles, and aluminum oxide to the twin-screw mixer, and continue stirring for 25 minutes. Then add iron powder, copper powder, and tin powder, and continue stirring for 25 minutes. Slowly add silicon carbide and resin-auxiliary-hydroxypropyl chitosan complex to the mixer, and stir for 18 minutes. Afterwards, a uniform friction material mixture is formed and discharged for later use. The components, by weight, are: 12 parts modified steel fiber, 18 parts modified mineral fiber, 3 parts aramid organic fiber, 5 parts silicon dioxide (particle size 0.8~1.5μm), 1.6 parts boron carbide particles (specifically composed of 60% boron carbide with a particle size of 13~15μm and 40% boron carbide with a particle size of 7~9μm), 18 parts resin-auxiliary-hydroxypropyl chitosan complex, 27 parts iron powder (passed through a 100-mesh sieve), 18 parts copper powder (passed through a 100-mesh sieve), 3 parts tin powder (passed through a 100-mesh sieve), 14 parts aluminum oxide (particle size 3~5 μm), and 6.0 parts silicon carbide (composed of 70% silicon carbide with a particle size of 2~4 μm and 30% silicon carbide with a particle size of 0.5~1 μm by weight). S3. Compression molding (1) Pre-pressing: Pour the friction material mixture into the mold, pre-press it using a hydraulic press, set the pressure to 12MPa, set the temperature to 80℃, maintain the pressure for 7min, and remove the air from the mixture to form a pre-pressed blank; (2) Final pressing: Transfer the pre-pressed blank to a hot press mold, heat it to 160℃, set the pressure to 30MPa, maintain the pressure for 15min, and ensure that the density of the blank is ≥2.6g / cm³. After taking it out, let it cool naturally to room temperature to obtain the pressed blank for later use. S4. Curing The pressed preform is placed in a curing oven and heated to 115°C at a rate of 20°C / min, and held for 2 hours; then heated to 135°C at a rate of 10°C / min, and held for 4 hours; then heated to 155°C at a rate of 5°C / min, and held for 1.5 hours; finally, under a nitrogen atmosphere, heated to 180°C at a rate of 5°C / min, and held for 1.5 hours, and then cooled to room temperature at the same rate. The edges and corners of the cured blank are ground to ensure dimensional accuracy (error ≤ 0.1mm) and meet the vehicle installation requirements.

[0069] The friction pad material prepared in Example 3 had a shear strength of 16.4 MPa and a hardness of 96 HRR.

[0070] Calculations show that the dynamic friction coefficient of Example 3 is 0.36~0.42, the friction coefficient fluctuation rate is ≤0.06, and the wear rate at room temperature is 0.47×10⁻⁶.-7 The wear rate was 0.65 × 10⁻⁶ cm³ / (N·m), and did not increase significantly at 600℃. -7 cm³ / (N·m). In Example 3, the friction plate has a thermal expansion rate of 0.51% at 600℃, a thermal conductivity ≥24.0W / (m·K), and excellent thermal stability.

Claims

1. A method for preparing a high-stability, low-wear disc brake friction pad, characterized in that: The mixture consists of a resin-auxiliary-hydroxypropyl chitosan complex obtained by melt modification of phenolic resin, phosphate-modified steel fiber, silane-modified wollastonite fiber, aramid organic fiber and other raw and auxiliary materials, which are then pressed into a blank and then cured in stages.

2. A method for preparing a high-stability, low-wear disc brake friction pad, characterized in that: The raw materials are phosphate-modified steel fiber, silane-modified wollastonite fiber, aramid organic fiber, resin-auxiliary-hydroxypropyl chitosan complex obtained by melt modification of phenolic resin, silicon dioxide, boron carbide, aluminum oxide, silicon carbide, copper powder, iron powder and tin powder, mixed, pressed into a blank, and then cured in stages.

3. The method for preparing a high-stability, low-wear disc brake friction pad as described in claim 2, characterized in that: Based on weight, the composition includes 8-12 parts of phosphate-modified steel fiber, 12-18 parts of silane-modified wollastonite fiber, 1-3 parts of aramid organic fiber, 2-5 parts of silicon dioxide (particle size 0.8-1.5μm), 0.7-1.6 parts of boron carbide particles, 12-18 parts of resin-auxiliary-hydroxypropyl chitosan complex, 21-27 parts of iron powder, 14-18 parts of copper powder, 2-3 parts of tin powder, 10.5-14 parts of aluminum oxide (particle size 3-5μm), and 4.5-6.0 parts of silicon carbide.

4. A method for preparing a high-stability, low-wear disc brake friction pad as described in claim 2 or 3, characterized in that: The boron carbide is composed of 60% boron carbide with a particle size of 13-15 μm and 40% boron carbide with a particle size of 7-9 μm by mass ratio; the silicon carbide is composed of 70% silicon carbide with a particle size of 2-4 μm and 30% silicon carbide with a particle size of 0.5-1 μm by mass ratio; the silicon dioxide has a particle size of 0.8-1.5 μm; and the aluminum oxide has a particle size of 3-5 μm.

5. A method for preparing a high-stability, low-wear disc brake friction pad as described in any one of claims 2-4, characterized in that: The modified steel fiber is prepared by placing hooked steel fibers with a diameter of 0.2-0.3 mm and a length of 3-5 mm into a phosphating tank, adding phosphating solution to submerge the hooked steel fibers by 1-2 cm, controlling the temperature at 48-52℃, soaking for 25-30 minutes, then removing them, rinsing them 3-5 times with deionized water, and then placing them in an oven at 70-80℃ for drying for 1-2 hours.

6. A method for preparing a high-stability, low-wear disc brake friction pad as described in any one of claims 2-5, characterized in that: The silane-modified wollastonite fiber is prepared by adding wollastonite fiber (particle size 5-10μm) and coupling agent KH-550 into a high-speed mixer, setting the speed to 600-800rpm, and stirring at 55-60℃ for 15-20min. The KH-550 is 0.4-0.6% of the mass of the wollastonite fiber.

7. A method for preparing a high-stability, low-wear disc brake friction pad as described in any one of claims 8, characterized in that: The resin-auxiliary-hydroxypropyl chitosan complex is formed by heating environmentally friendly phenolic resin to 55~65℃, stirring at 200~300rpm, melting it, adding environmentally friendly auxiliary agent ST-602 and hydroxypropyl chitosan ethanol-propylene glycol solution, and continuing to stir for 20~30min.

8. The method for preparing a high-stability, low-wear disc brake friction pad as described in claim 7, characterized in that: The mass ratio of the phenolic resin, environmentally friendly additive ST-602, and hydroxypropyl chitosan ethanol propylene glycol solution is 72~78:1.5~2.5:20~26.

9. The method for preparing a high-stability, low-wear disc brake friction pad as described in claim 8, characterized in that: The hydroxypropyl chitosan ethanol-propylene glycol solution is obtained by slowly adding hydroxypropyl chitosan to ethanol, stirring until completely dispersed, adding deionized and propylene glycol solutions, stirring continuously until the solution is clear, and filtering through a 200-mesh sieve.

10. The method for preparing a high-stability, low-wear disc brake friction pad as described in claim 9, characterized in that: The graded curing process involves placing the pressed preform in a curing oven and heating it to 105-115°C at a rate of 15-20°C / min, holding it at that temperature for 2-3 hours; then heating it to 135-140°C at a rate of 8-10°C / min, holding it at that temperature for 3-4 hours; then heating it to 155-160°C at a rate of 3-5°C / min, holding it at that temperature for 1-1.5 hours; finally, under a nitrogen atmosphere, heating it to 180-190°C at a rate of 3-5°C / min, holding it at that temperature for 1-1.5 hours, and then cooling it to room temperature at the same rate.

Images