Powder metallurgy friction material, and powder metallurgy brake pad and preparation method therefor

Abstract

The present invention provides a powder metallurgy friction material, and a powder metallurgy brake pad and a preparation method therefor. The powder metallurgy friction material comprises, in percentages by mass, 50-65 wt% of copper powder, 20-30 wt% of iron powder and 10-20 wt% of graphite-ceramic composite particles. On the basis of 100 wt% of the mass of the graphite-ceramic composite particles, the graphite-ceramic composite particles comprise: 50-70 wt% of expandable graphite, 5-10 wt% of ceramic powder and 20-45 wt% of micro-powder graphite. In the present invention, all non-metallic phases are added to a metal matrix as a whole in the form of graphite-ceramic composite particles, thereby reducing the degree of fragmentation of the non-metallic phases relative to the matrix skeleton and solving the problem of poor bonding of the non-metallic phases to the metal. In addition, the powder metallurgy brake pad prepared by means of low-temperature sintering has low hardness, and thus can reduce damage and performance fluctuation due to disc scratching.

Description

A powder metallurgy friction material, a powder metallurgy brake pad and its preparation method

[0001] Cross-reference information

[0002] This application claims priority to Chinese Patent Application No. 202510357870.2, filed on March 25, 2025, entitled "A Powder Metallurgy Friction Material, a Powder Metallurgy Brake Piece and a Method for Preparing the Same", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention belongs to the field of friction materials, specifically relating to a powder metallurgy friction material, a powder metallurgy brake pad, and its preparation method. Background Technology

[0004] With the large-scale addition of urban rail transit lines and vehicles, while promoting social and economic development, the consumption of electricity has also increased significantly. Vehicle lightweighting technology has always been a hot topic in the field of energy conservation and consumption reduction. The lightweighting solution of replacing cast iron brake discs with lighter aluminum alloy brake discs has been successfully applied on urban rail lines.

[0005] Aluminum alloy brake discs have lower hardness and strength, and are typically used with synthetic brake pads. As aluminum alloy brake disc technology matures, its application is expanding from low- and medium-speed metro and urban rail lines to higher-speed suburban lines. However, the polymer materials in synthetic brake pads can carbonize or vaporize under the heat load of suburban braking conditions, leading to problems such as decreased friction coefficient and increased emissions.

[0006] Based on this, the research direction for matching brake pads with medium and high-speed aluminum alloy brake discs has shifted from synthetic materials to powder metallurgy materials with higher temperature resistance. However, powder metallurgy brake pads are usually used with cast steel brake discs, and their friction materials have high hardness and strength. When rubbing against aluminum alloy brake discs, they are prone to scratching the disc surface and forming metal inlays, resulting in abnormal wear of the friction pair and large fluctuations in the coefficient of friction.

[0007] Currently, there are few research reports on the compatibility of aluminum alloy brake discs and powder metallurgy brake pads in the industry, and related work is still in its early stages. Therefore, there is a current need to provide a powder metallurgy brake pad with a high coefficient of friction and low wear for use with aluminum alloy brake discs. Summary of the Invention

[0008] To address the aforementioned technical problems, the present invention aims to provide a powder metallurgy friction material, a powder metallurgy brake pad, and a method for preparing the same.

[0009] To achieve the above objectives, the present invention provides a powder metallurgy friction material, wherein, by weight percentage, the powder metallurgy friction material comprises:

[0010] Copper powder 50wt%-65wt%, iron powder 20wt%-30wt%, graphite ceramic composite particles 10wt%-20wt%;

[0011] Based on a mass of 100wt% of the graphite ceramic composite particles, the graphite ceramic composite particles comprise: 50wt%-70wt% expandable graphite, 5wt%-10wt% ceramic powder, and 20wt%-45wt% micronized graphite.

[0012] In some specific embodiments, preferably, the amount of micronized graphite added is 20wt%-30wt%, based on 100wt% of the mass of the graphite ceramic composite particles.

[0013] According to a specific embodiment of the present invention, preferably, the particle size of the expandable graphite is 150-250 μm, and the expansion ratio of the expandable graphite at 750-850℃ is 20-40 times.

[0014] According to a specific embodiment of the present invention, preferably, the particle size of the micronized graphite is 10-20 μm, the particle size of the ceramic powder is 10-20 μm, and the particle size of the graphite-ceramic composite particles is 150-300 μm.

[0015] In this invention, the micro-powdered graphite has an extremely fine particle size, making it easier to form a lubricating protective film layer on the friction surface. Furthermore, the use of large-particle-size expandable graphite as a carrier to support the small-particle-size micro-powdered graphite and ceramic powder to form composite particles has both lubrication and friction-enhancing functions. This allows the composite particles to detach as a whole under the shearing and peeling of friction force during braking, reducing the embedding and jamming of ceramic powder on the friction surface, thereby effectively avoiding scratches on the friction surface.

[0016] According to a specific embodiment of the present invention, preferably, the ceramic powder includes one or more of silicon oxide, zirconium oxide, aluminum oxide, silicon carbide, and chromium carbide; more preferably, the ceramic powder is silicon oxide and / or zirconium oxide.

[0017] The present invention also provides a powder metallurgy brake pad, which is prepared from the above-mentioned powder metallurgy friction material.

[0018] According to a specific embodiment of the present invention, preferably, the hardness of the powder metallurgy guillotine is below 15 HBW, and the wear amount of the powder metallurgy guillotine is 0.3 cm. 3 / MJ or less; more preferably, the hardness of the powder metallurgy guillotine is 12-13 HBW, and the wear of the powder metallurgy guillotine is 0.15-0.29 cm. 3 / MJ; More preferably, the wear amount of the powder metallurgy guillotine is 0.15-0.25cm. 3 / MJ.

[0019] According to a specific embodiment of the present invention, preferably, the powder metallurgy brake pad is a powder metallurgy brake pad for an aluminum alloy brake disc.

[0020] In some specific embodiments, preferably, the powder metallurgy gate has a shear strength of 14 MPa or higher, a bonding strength of 15 MPa or higher, and a compressive strength of 95 MPa or higher; more preferably, the powder metallurgy gate has a shear strength of 14-20 MPa, a bonding strength of 15-18 MPa, and a compressive strength of 95-119 MPa.

[0021] In some specific embodiments, preferably, the aluminum alloy brake disc has a hardness of 120-170 HBW, a tensile strength ≥250 MPa, and a braking speed of 120-200 km / h (more preferably 160-200 km / h).

[0022] The present invention also provides a method for preparing the above-mentioned powder metallurgy gate, wherein the preparation method includes:

[0023] Step 1: Mix expandable graphite, micronized graphite, and ceramic powder and shape them to obtain graphite-ceramic composite particles;

[0024] Step 2: Mix copper powder, iron powder and graphite ceramic composite particles, and after stirring, cold pressing and sintering, obtain powder metallurgy gate pads.

[0025] In some specific implementations, preferably, the stirring speed in step two is 200-400 r / min and the stirring time is 15-30 min.

[0026] In some specific implementations, preferably, the pressing pressure in step two is 10-15 MPa, and the holding time is 8-15 s.

[0027] According to a specific embodiment of the present invention, preferably, in step one, the preparation of the graphite ceramic composite particles includes the following steps:

[0028] Step a: Mix expandable graphite, micronized graphite, and ceramic powder to obtain a premixed dry powder;

[0029] Step b: Based on the mass of the premixed dry powder as 100%, add 10wt%-20wt% of molding agent to the premixed dry powder and stir, then dry to remove the solvent from the molding agent;

[0030] Step c: The product from step b is compressed into blocks, then crushed and sieved to obtain graphite ceramic composite particles.

[0031] In some specific embodiments, preferably, the molding agent includes one or a combination of two or more of resin-based molding agents, rubber-based molding agents, and ester-based molding agents. The molding agent can be conventionally selected as needed.

[0032] In some specific embodiments, preferably, the mixing speed in step a is 80-120 r / min and the mixing time is 10-15 min.

[0033] In some specific implementations, preferably, the temperature for drying and removing the solvent in step b is 40-70°C, and the time is 1.5-3 hours.

[0034] In some specific implementations, preferably, the pressing pressure for forming the briquette in step c is 3-5 MPa.

[0035] According to a specific embodiment of the present invention, preferably, the sintering temperature is 750-850℃, the holding time of the sintering is 1.5-3h, and the pressure of the sintering is 1-2MPa.

[0036] In some specific embodiments, preferably, the sintering process is carried out under a nitrogen-hydrogen protective atmosphere.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0038] (1) The powder metallurgy friction material provided by the present invention contains expandable graphite, which can generate pores in the metal matrix through volume expansion during sintering. These pores, as a natural friction-enhancing phase, can replace traditional hard alloys or ceramics as the main friction-enhancing agent, effectively reducing wear and damage to the brake disc while maintaining the friction coefficient of the brake pad.

[0039] (2) The powder metallurgy brake pad preparation method provided by the present invention adds all non-metallic phases in the friction material as a whole to the metal matrix in the form of graphite ceramic composite particles, reducing the degree of separation between the non-metallic phase and the matrix skeleton, solving the problem of poor bonding between the non-metallic phase and the metal, and enabling the friction material to obtain sufficient mechanical strength at a lower sintering temperature. In addition, the powder metallurgy brake pad prepared by the present invention using low-temperature sintering has low hardness, which can further reduce damage and performance fluctuations caused by scouring.

[0040] (3) The performance requirements of matching brake pads also vary depending on the hardness and strength of aluminum alloy brake discs produced according to different line requirements and design and manufacturing processes. This invention can obtain powder metallurgy brake pads that are suitable for aluminum alloy brake discs by adjusting the composition ratio of graphite ceramic composite particles and the type of ceramic powder. It has high adaptability and wide application, and is especially suitable for aluminum alloy brake discs with high hardness and tensile strength for high-speed braking. Attached Figure Description

[0041] Figure 1 shows the surface condition of the aluminum alloy brake disc after the powder metallurgy brake pads prepared in Example 1 are applied during braking.

[0042] Figure 2 shows the surface condition of the aluminum alloy brake disc after the powder metallurgy brake pads prepared in Comparative Example 1 are applied to brakes. Detailed Implementation

[0043] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0044] Example 1:

[0045] This embodiment provides a powder metallurgy gate, and the specific steps are as follows:

[0046] (1) Weigh 100g of expandable graphite, 35g of micronized graphite and 15g of ceramic powder zirconium oxide according to the proportion, put them into a mixer for premixing, stir at a speed of 100r / min for 15min, and obtain premixed dry powder; wherein, the particle size of the expandable graphite is 150-200μm, the particle size of the micronized graphite is 10-15μm, and the particle size of the ceramic powder is 10-15μm;

[0047] (2) Based on the mass of the premixed dry powder as 100%, add 15wt% of resin-based molding agent to the premixed dry powder and continue stirring for 15min; then put it in an oven at 60℃ for 2h to remove the solvent in the molding agent.

[0048] (3) The product from step (2) is placed in a cold press to form a block. The pressing pressure is 5 MPa and the pressure is held for 10 seconds. Then the block is placed in a pulverizer to crush it and the powder is sieved. Particles with a particle size range of 150-300 μm are retained to obtain graphite ceramic composite particles.

[0049] (4) Weigh 550g of copper powder and 170g of iron powder according to the proportion, and put them into a mixer together with the sieved graphite ceramic composite particles in step (3). The mixer speed is 400r / min and the mixing time is 20min to obtain mixed powder.

[0050] (5) The mixed powder is cold-pressed into shape with a pressing pressure of 15MPa and a holding pressure of 10s. Then the pressed blank is placed on a steel back for sintering with a nitrogen-hydrogen mixture in a protective atmosphere. The sintering pressure is 2MPa, the sintering temperature is 800℃, and the holding temperature is 2h. After that, it is cooled to 60℃ in the furnace and taken out of the furnace to obtain powder metallurgy gate piece.

[0051] Example 2:

[0052] This embodiment provides a powder metallurgy gate, and the specific steps are as follows:

[0053] (1) Weigh 114g of expandable graphite, 39g of micronized graphite and 17g of ceramic powder zirconium oxide according to the proportion, put them into a mixer for premixing, stir at a speed of 100r / min for 15min, and obtain premixed dry powder; wherein, the particle size of the expandable graphite is 150-250μm, the particle size of the micronized graphite is 15-20μm, and the particle size of the ceramic powder is 15-20μm;

[0054] (2) Based on the mass of the premixed dry powder as 100%, add 15wt% of resin-based molding agent to the premixed dry powder and continue stirring for 15min; then put it in an oven at 60℃ for 2h to remove the solvent in the molding agent.

[0055] (3) The product from step (2) is placed in a cold press to form a block. The pressing pressure is 5 MPa and the pressure is held for 10 seconds. Then the block is placed in a pulverizer to crush it and the powder is sieved. Particles with a particle size range of 150-300 μm are retained to obtain graphite ceramic composite particles.

[0056] (4) Weigh 430g of copper powder and 250g of iron powder according to the proportion, and put them into a mixer together with the sieved graphite ceramic composite particles in step (3). The mixer speed is 400r / min and the mixing time is 20min to obtain mixed powder.

[0057] (5) The mixed powder is cold-pressed into shape, with a pressing pressure of 15MPa and a holding pressure of 10s; then the pressed blank is placed on a steel back for sintering, with a nitrogen-hydrogen mixture as the protective atmosphere, a sintering pressure of 2MPa, a sintering temperature of 800℃, and a holding temperature of 2h. After that, it is cooled to 60℃ with the furnace and taken out of the furnace to obtain powder metallurgy gate piece.

[0058] Example 3:

[0059] This embodiment provides a powder metallurgy gate, and the specific steps are as follows:

[0060] (1) Weigh 60g of expandable graphite, 21g of micronized graphite and 9g of ceramic powder zirconium oxide according to the proportion, put them into a mixer for premixing, stir at a speed of 100r / min for 15min, and obtain premixed dry powder; wherein, the particle size of the expandable graphite is 200-250μm, the particle size of the micronized graphite is 10-15μm, and the particle size of the ceramic powder is 15-20μm;

[0061] (2) Based on the mass of the premixed dry powder as 100%, add 15wt% of resin-based molding agent to the premixed dry powder and continue stirring for 15min; then put it in an oven at 60℃ for 2h to remove the solvent in the molding agent.

[0062] (3) The product from step (2) is placed in a cold press to form a block. The pressing pressure is 5 MPa and the pressure is held for 10 seconds. Then the block is placed in a pulverizer to crush it and the powder is sieved. Particles with a particle size range of 150-300 μm are retained to obtain graphite ceramic composite particles.

[0063] (4) Weigh 510g of copper powder and 250g of iron powder according to the proportion, and put them into a mixer together with the sieved graphite ceramic composite particles in step (3). The mixer speed is 400r / min and the mixing time is 20min to obtain mixed powder.

[0064] (5) The mixed powder is cold-pressed into shape, with a pressing pressure of 15MPa and a holding pressure of 10s; then the pressed blank is placed on a steel back for sintering, with a nitrogen-hydrogen mixture as the protective atmosphere, a sintering pressure of 2MPa, a sintering temperature of 800℃, and a holding temperature of 2h. After that, it is cooled to 60℃ with the furnace and taken out of the furnace to obtain powder metallurgy gate piece.

[0065] Example 4:

[0066] This embodiment provides a powder metallurgy gate, and the specific steps are as follows:

[0067] (1) Weigh 83g of expandable graphite, 39g of micronized graphite and 8g of ceramic powder zirconium oxide according to the proportion, put them into a mixer for premixing, stir at 100r / min for 15min to obtain premixed dry powder; wherein, the particle size of the expandable graphite is 150-200μm, the particle size of the micronized graphite is 10-15μm, and the particle size of the ceramic powder is 15-20μm;

[0068] (2) Based on the mass of the premixed dry powder as 100%, add 15wt% of resin-based molding agent to the premixed dry powder and continue stirring for 15min; then put it in an oven at 60℃ for 2h to remove the solvent in the molding agent.

[0069] (3) The product from step (2) is placed in a cold press to form a block. The pressing pressure is 3MPa and the pressure is held for 10s. Then the block is placed in a pulverizer to crush it and the powder is sieved. Particles with a particle size range of 150-300μm are retained to obtain graphite ceramic composite particles.

[0070] (4) Weigh 550g of copper powder and 170g of iron powder according to the proportion, and put them into a mixer together with the sieved graphite ceramic composite particles in step (3). The mixer speed is 400r / min and the mixing time is 20min to obtain mixed powder.

[0071] (5) The mixed powder is cold-pressed into shape, with a pressing pressure of 10MPa and a holding pressure of 10s; then the pressed blank is placed on a steel back for sintering, with a nitrogen-hydrogen mixture as the protective atmosphere, a sintering pressure of 2MPa, a sintering temperature of 850℃, and a holding temperature of 2h. After that, it is cooled to 60℃ with the furnace and taken out of the furnace to obtain powder metallurgy gate piece.

[0072] Example 5:

[0073] This embodiment provides a powder metallurgy gate, and the specific steps are as follows:

[0074] (1) Weigh 83g of expandable graphite, 39g of micronized graphite and 8g of ceramic powder zirconium oxide according to the proportion, put them into a mixer for dry powder premixing, stir at 100r / min for 15min to obtain premixed dry powder; wherein, the particle size of the expandable graphite is 150-250μm, the particle size of the micronized graphite is 10-20μm, and the particle size of the ceramic powder is 10-20μm;

[0075] (2) Based on the mass of the premixed dry powder as 100%, add 15wt% of resin-based molding agent to the premixed dry powder and continue stirring for 15min; then put it in an oven at 60℃ for 2h to remove the solvent in the molding agent.

[0076] (3) The product from step (2) is placed in a cold press to form a block. The pressing pressure is 5 MPa and the pressure is held for 10 seconds. Then the block is placed in a pulverizer to crush it and the powder is sieved. Particles with a particle size range of 150-300 μm are retained to obtain graphite ceramic composite particles.

[0077] (4) Weigh 550g of copper powder and 170g of iron powder according to the proportion, and put them into a mixer together with the sieved graphite ceramic composite particles in step (3). The mixer speed is 400r / min and the mixing time is 20min to obtain mixed powder.

[0078] (5) The mixed powder is cold-pressed into shape, with a pressing pressure of 15MPa and a holding pressure of 10s; the pressed blank is placed on a steel back for sintering, with a nitrogen-hydrogen mixture as the protective atmosphere, a sintering pressure of 2MPa, a sintering temperature of 750℃, and a holding temperature of 2h. Then it is cooled to 60℃ with the furnace and taken out of the furnace to obtain powder metallurgy gate piece.

[0079] Example 6:

[0080] This embodiment provides a powder metallurgy gate, and the specific steps are as follows:

[0081] (1) Weigh 100g of expandable graphite, 35g of micronized graphite and 15g of ceramic silicon dioxide according to the proportion, put them into a mixer for dry powder premixing, stir at 100r / min for 15min to obtain premixed dry powder; wherein, the particle size of the expandable graphite is 150-200μm, the particle size of the micronized graphite is 10-15μm, and the particle size of the ceramic powder is 10-15μm;

[0082] (2) Based on the mass of the premixed dry powder as 100%, add 15wt% of resin-based molding agent to the premixed dry powder and continue stirring for 15min; then put it in an oven at 60℃ for 2h to remove the solvent in the molding agent.

[0083] (3) The product from step (2) is placed in a cold press to form a block. The pressing pressure is 5 MPa and the pressure is held for 10 seconds. Then the block is placed in a pulverizer to crush it and the powder is sieved. Particles with a particle size range of 150-300 μm are retained to obtain graphite ceramic composite particles.

[0084] (4) Weigh 550g of copper powder and 170g of iron powder according to the proportion, and put them into a mixer together with the sieved graphite ceramic composite particles in step (3). The mixer speed is 400r / min and the mixing time is 20min to obtain mixed powder.

[0085] (5) The mixed powder is cold-pressed into shape, with a pressing pressure of 15MPa and a holding pressure of 10s; the pressed blank is placed on a steel back for sintering, with a nitrogen-hydrogen mixture as the protective atmosphere, a sintering pressure of 2MPa, a sintering temperature of 750℃, and a holding temperature of 2h. Then it is cooled to 60℃ with the furnace and taken out of the furnace to obtain powder metallurgy gate piece.

[0086] Example 7:

[0087] This embodiment provides a powder metallurgy gate, and the specific steps are as follows:

[0088] (1) Weigh 100g of expandable graphite, 35g of micronized graphite and 15g of ceramic chromium carbide according to the proportion, put them into a mixer for dry powder premixing, stir at 100r / min for 15min to obtain premixed dry powder; wherein, the particle size of the expandable graphite is 150-200μm, the particle size of the micronized graphite is 10-15μm, and the particle size of the ceramic powder is 10-15μm;

[0089] (2) Based on the mass of the premixed dry powder as 100%, add 15wt% of resin-based molding agent to the premixed dry powder and continue stirring for 15min; then put it in an oven at 60℃ for 2h to remove the solvent in the molding agent.

[0090] (3) The product from step (2) is placed in a cold press to form a block. The pressing pressure is 5 MPa and the pressure is held for 10 seconds. Then the block is placed in a pulverizer to crush it and the powder is sieved. Particles with a particle size range of 150-300 μm are retained to obtain graphite ceramic composite particles.

[0091] (4) Weigh 550g of copper powder and 170g of iron powder according to the proportion, and put them into a mixer together with the sieved graphite ceramic composite particles in step (3). The mixer speed is 400r / min and the mixing time is 20min to obtain mixed powder.

[0092] (5) The mixed powder is cold-pressed into shape, with a pressing pressure of 15MPa and a holding pressure of 10s; the pressed blank is placed on a steel back for sintering, with a nitrogen-hydrogen mixture as the protective atmosphere, a sintering pressure of 2MPa, a sintering temperature of 750℃, and a holding temperature of 2h. Then it is cooled to 60℃ with the furnace and taken out of the furnace to obtain powder metallurgy gate piece.

[0093] Comparative Example 1:

[0094] This comparative example provides a powder metallurgy gate, and the specific steps are as follows:

[0095] (1) Place 550g of copper powder, 170g of iron powder, 100g of expandable graphite, 35g of micronized graphite, and 15g of zirconium oxide ceramic powder into a mixer. Based on the mass of the premixed dry powder as 100%, add 10wt% of resin-based molding agent to mix. The particle size of the expandable graphite is 150-200μm, the particle size of the micronized graphite is 10-15μm, and the particle size of the ceramic powder is 10-15μm. The mixer speed is 300r / min, and the mixing time is 20min. Then place it in an oven at 60℃ for 2h to dry and remove the solvent in the molding agent to obtain the mixed powder.

[0096] (2) The mixed powder is cold-pressed into shape, with a pressing pressure of 15MPa and a holding pressure of 10s; the pressed blank is placed on a steel back for sintering, with a nitrogen-hydrogen mixture as the protective atmosphere, a sintering pressure of 2MPa, a sintering temperature of 800℃, and a holding temperature of 2h. Then it is cooled to 60℃ with the furnace and taken out of the furnace to obtain powder metallurgy gate piece.

[0097] Comparative Example 2:

[0098] This comparative example provides a powder metallurgy gate, and the specific steps are as follows:

[0099] (1) Place 550g of copper powder, 170g of iron powder, 100g of expandable graphite, 35g of micronized graphite, and 15g of zirconium oxide ceramic powder into a mixer. Based on the mass of the premixed dry powder as 100%, add 10wt% of resin-based molding agent to mix. The particle size of the expandable graphite is 150-200μm, the particle size of the micronized graphite is 10-15μm, and the particle size of the ceramic powder is 10-15μm. The mixer speed is 300r / min, and the mixing time is 20min. Then place it in an oven at 60℃ for 2h to dry and remove the solvent in the molding agent to obtain the mixed powder.

[0100] (2) The mixed powder is cold-pressed into shape, with a pressing pressure of 15MPa and a holding pressure of 10s; the pressed blank is placed on a steel back for sintering, with a nitrogen-hydrogen mixture as the protective atmosphere, a sintering pressure of 2MPa, a sintering temperature of 950℃, and a holding temperature of 2h. Then it is cooled to 60℃ with the furnace and taken out of the furnace to obtain powder metallurgy gate piece.

[0101] Comparative Example 3:

[0102] This comparative example provides a powder metallurgy gate, and the specific steps are as follows:

[0103] (1) Weigh 83g of expandable graphite, 39g of micronized graphite and 8g of ceramic powder zirconium oxide according to the proportion, put them into a mixer for dry powder premixing, stir at 100r / min for 15min to obtain premixed dry powder; wherein, the particle size of the expandable graphite is 75-150μm, the particle size of the micronized graphite is 4-10μm, and the particle size of the ceramic powder is 10-20μm;

[0104] (2) Based on the mass of the premixed dry powder as 100%, add 15wt% of resin-based molding agent to the premixed dry powder and continue stirring for 15min; then put it in an oven at 60℃ for 2h to remove the solvent in the molding agent.

[0105] (3) The product from step (2) is placed in a cold press to form a block. The pressing pressure is 5 MPa and the pressure is held for 10 seconds. Then the block is placed in a pulverizer to crush it and the powder is sieved. Particles with a particle size range of 150-300 μm are retained to obtain graphite ceramic composite particles.

[0106] (4) Weigh 550g of copper powder and 170g of iron powder according to the proportion, and put them into a mixer together with the sieved graphite ceramic composite particles in step (3). The mixer speed is 400r / min and the mixing time is 20min to obtain mixed powder.

[0107] (5) The mixed powder is cold-pressed into shape, with a pressing pressure of 15MPa and a holding pressure of 10s; the pressed blank is placed on a steel back for sintering, with a nitrogen-hydrogen mixture as the protective atmosphere, a sintering pressure of 2MPa, a sintering temperature of 750℃, and a holding temperature of 2h. Then it is cooled to 60℃ with the furnace and taken out of the furnace to obtain powder metallurgy gate piece.

[0108] Comparative Example 4:

[0109] This comparative example provides a powder metallurgy gate, and the specific steps are as follows:

[0110] (1) Weigh 83g of expandable graphite, 39g of micronized graphite and 8g of ceramic powder zirconium oxide according to the proportion, put them into a mixer for dry powder premixing, stir at 100r / min for 15min to obtain premixed dry powder; wherein, the particle size of the expandable graphite is 150-250μm, the particle size of the micronized graphite is 20-40μm, and the particle size of the ceramic powder is 10-20μm;

[0111] (2) Based on the mass of the premixed dry powder as 100%, add 15wt% of resin-based molding agent to the premixed dry powder and continue stirring for 15min; then put it in an oven at 60℃ for 2h to remove the solvent in the molding agent.

[0112] (3) The product from step (2) is placed in a cold press to form a block. The pressing pressure is 5 MPa and the pressure is held for 10 seconds. Then the block is placed in a pulverizer to crush it and the powder is sieved. Particles with a particle size range of 150-300 μm are retained to obtain graphite ceramic composite particles.

[0113] (4) Weigh 550g of copper powder and 170g of iron powder according to the proportion, and put them into a mixer together with the sieved graphite ceramic composite particles in step (3). The mixer speed is 400r / min and the mixing time is 20min to obtain mixed powder.

[0114] (5) The mixed powder is cold-pressed into shape, with a pressing pressure of 15MPa and a holding pressure of 10s; the pressed blank is placed on a steel back for sintering, with a nitrogen-hydrogen mixture as the protective atmosphere, a sintering pressure of 2MPa, a sintering temperature of 750℃, and a holding temperature of 2h. Then it is cooled to 60℃ with the furnace and taken out of the furnace to obtain powder metallurgy gate piece.

[0115] The properties of the powder metallurgy gate electrode prepared above are investigated in detail below:

[0116] Table 1 compares the performance parameters of the powder metallurgy brake pads prepared in Examples 1-7 and Comparative Examples 1-4. The friction and wear test was conducted on aluminum alloy brake discs prepared by casting. The hardness of the aluminum alloy brake discs used in the test was 140-150 HBW, and the tensile strength was 260-280 MPa. Among them, compared with Example 1, Comparative Example 1 did not pre-form graphite ceramic composite particles, but directly mixed all the powders; Comparative Example 2 increased the sintering temperature based on Comparative Example 1.

[0117] The wear of the powder metallurgy brake pads was tested using a friction and wear test bench, as detailed below:

[0118] First, the brake pads are broken in. Once the brake pads are fully in contact with the brake disc, they are removed and weighed, and the weight is recorded as m0. Then, the formal test begins. The formal test includes braking 5 times at an initial speed of 120 km / h, braking 5 times at an initial speed of 160 km / h, and braking 5 times at an initial speed of 200 km / h. After that, the brake pads are removed and weighed, and the weight is recorded as m.

[0119] The average friction coefficient at each speed in Table 1 is the average of 5 data points, and the wear of the powder metallurgy brake pad is the total wear of 15 braking cycles. The wear is calculated by the weight reduction m-m0 of the brake pad, the density of the powder metallurgy friction material, and the braking energy.

[0120] Table 1. Comparison of performance parameters of powder metallurgy throttle plates

[0121] As can be seen from the data in Table 1, the average friction coefficients of Comparative Example 1 and Comparative Example 2 show a significant decrease with increasing braking speed, failing to meet the lower limit of 0.310 at 200 km / h braking speed, and exhibiting high wear. In terms of mechanical properties, Comparative Example 1 exhibits lower shear strength, bond strength, and compressive strength, while Comparative Example 2, although increasing the sintering temperature to improve strength, also increases the hardness of the friction material, resulting in even greater wear.

[0122] In comparison, the shear strength and bond strength of Examples 1-7 are higher than those of Comparative Examples 1-2, and the compressive strength is also at a high level. Furthermore, the average coefficient of friction does not decrease significantly with the increase of braking speed, and still meets the lower limit value of 0.310 when braking at 200km / h, indicating good temperature resistance. At the same time, the powder metallurgy brake pads of Examples 1-7 have lower hardness, and the wear is significantly reduced compared with Comparative Examples 1-2.

[0123] Comparative Examples 3 and 4 used micronized graphite and expandable graphite exceeding the particle size range specified in this application, serving as a control experiment with Example 5. In Comparative Example 3, both types of graphite had relatively small particle sizes, resulting in more weak bonding interfaces within the friction material matrix, leading to reduced material strength and a weakened friction-enhancing effect during high-speed braking. In Comparative Example 4, the micronized graphite had relatively large particle sizes, resulting in poor lubrication and causing jamming between the discs, manifested as a decreased friction coefficient and increased wear during high-speed braking.

[0124] Furthermore, Examples 6-7 used different types of ceramic powder than those used in Examples 1-5, serving as a control experiment with Example 1. Specifically, the silicon dioxide used in Example 6 has a relatively low hardness, which can reduce scratches on the brake disc and weaken the plowing behavior between the disc and pads, thereby stabilizing the high-speed friction coefficient and reducing brake pad wear. In contrast, the chromium carbide used in Example 7 has a higher hardness and easily forms compounds with the metal matrix during sintering, significantly improving the mechanical strength of the friction material. However, this results in some scratches on the disc surface during braking, causing a decrease in the high-speed braking friction coefficient and an increase in brake pad wear.

[0125] Referring to the test results in Table 1, Figures 1 and 2 show the surface condition of the aluminum alloy brake disc after the powder metallurgy brake pads prepared in Example 1 and Comparative Example 1 were subjected to the same braking conditions. The braking conditions were: initial braking speed of 200 km / h, double-sided brake pad thrust of 40 kN, and the disc surface condition was observed after 5 braking cycles.

[0126] As can be seen from Figures 1 and 2, the brake disc surface of Example 1 has uniform and fine friction marks, while the brake disc surface of Comparative Example 1 has obvious peeling scratches, which is consistent with the results in Table 1. Therefore, the powder metallurgy brake pads provided by this invention can match the friction coefficient and wear requirements of aluminum alloy brake discs, and the brake disc surface condition is good, comparable to that of cast steel brake discs, which can meet the usage requirements of urban and intercity vehicles equipped with aluminum alloy brake discs.

Claims

1. A powder metallurgy friction material, wherein, By weight percentage, this powder metallurgy friction material comprises: Copper powder 50wt%-65wt%, iron powder 20wt%-30wt%, graphite ceramic composite particles 10wt%-20wt%; Based on a mass of 100wt% of the graphite ceramic composite particles, the graphite ceramic composite particles comprise: 50wt%-70wt% expandable graphite, 5wt%-10wt% ceramic powder, and 20wt%-45wt% micronized graphite.

2. The powder metallurgy friction material according to claim 1, wherein, The expandable graphite has a particle size of 150-250 μm and an expansion ratio of 20-40 times at 750-850℃.

3. The powder metallurgy friction material according to claim 1 or 2, wherein, The micronized graphite has a particle size of 10-20 μm, the ceramic powder has a particle size of 10-20 μm, and the graphite-ceramic composite particles have a particle size of 150-300 μm.

4. The powder metallurgy friction material according to claim 1, wherein, The ceramic powder includes one or more of silicon oxide, zirconium oxide, aluminum oxide, silicon carbide, and chromium carbide.

5. A powder metallurgy brake pad, which is prepared from the powder metallurgy friction material according to any one of claims 1-4.

6. The powder metallurgy gate according to claim 5, wherein, The hardness of this powder metallurgy guillotine is below 15 HBW, and the wear rate is 0.3 cm. 3 / MJ and below.

7. The powder metallurgy gate according to claim 5 or 6, wherein, This powder metallurgy brake pad is a powder metallurgy brake pad for aluminum alloy brake discs.

8. The method for preparing the powder metallurgy gate electrode according to any one of claims 5-7, wherein, The preparation method includes: Step 1: Mix expandable graphite, micronized graphite, and ceramic powder and shape them to obtain graphite-ceramic composite particles; Step 2: Mix copper powder, iron powder and graphite ceramic composite particles, and after stirring, cold pressing and sintering, obtain powder metallurgy gate pads.

9. The preparation method according to claim 8, wherein, In step one, the preparation of the graphite ceramic composite particles includes the following steps: Step a: Mix expandable graphite, micronized graphite, and ceramic powder to obtain a premixed dry powder; Step b: Based on the mass of the premixed dry powder as 100%, add 10wt%-20wt% of molding agent to the premixed dry powder and stir, then dry to remove the solvent from the molding agent; Step c: The product from step b is compressed into blocks, then crushed and sieved to obtain graphite ceramic composite particles.

10. The preparation method according to claim 8, wherein, The sintering temperature is 750-850℃, the holding time is 1.5-3h, and the pressure is 1-2MPa.

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