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

Abstract

The invention provides a powder metallurgy friction material, a powder metallurgy brake pad and a preparation method of the powder metallurgy friction material. The powder metallurgy friction material comprises, by mass, 50 wt%-65 wt% of copper powder, 20 wt%-30 wt% of iron powder and 10 wt%-20 wt% of graphite ceramic composite particles. Based on 100 wt% of the mass of the graphite ceramic composite particle, the graphite ceramic composite particle comprises 50 wt%-70 wt% of expandable graphite, 5 wt%-10 wt% of ceramic powder and 20 wt%-45 wt% of micro-powder graphite. All non-metal phases are added into a metal matrix as a whole in the form of graphite ceramic composite particles, so that the splitting degree of non-metal relative to a matrix framework is reduced, and the problem of poor combination of the non-metal phases and metal is solved. In addition, the powder metallurgy brake pad prepared through low-temperature sintering is low in hardness, and damage and performance fluctuation caused by disc scratching can be further reduced.

Description

Technical Field

[0001] The present invention belongs to the field of friction materials, and particularly relates to a powder metallurgy friction material, a powder metallurgy brake pad and a preparation method thereof. Background Art

[0002] With the large increase in urban rail transit lines and vehicles, while promoting social and economic development, it has also significantly increased power consumption. Vehicle lightweight technology has always been a hot topic in the field of energy conservation and consumption reduction. The lightweight solution of replacing cast iron brake discs with lighter aluminum alloy brake discs has been maturely applied on urban rail lines.

[0003] The hardness and strength of aluminum alloy brake discs are relatively low, and they are usually used in combination with synthetic brake pads. With the gradual maturity of aluminum alloy brake disc technology, its application scenarios have also advanced from medium- and low-speed subway and urban rail lines to higher-speed suburban lines. However, the polymer materials contained in synthetic brake pads will carbonize or gasify under the thermal load of suburban braking conditions, resulting in problems such as friction coefficient decline and flue gas emissions.

[0004] Based on this, the research direction of brake pads matching medium- and high-speed aluminum alloy brake discs has shifted from synthetic materials to more temperature-resistant powder metallurgy materials. However, powder metallurgy brake pads are usually used in combination with cast steel brake discs. The hardness and strength of their friction materials are relatively high, and they are prone to scratching the brake disc surface and forming metal inlays when rubbing against aluminum alloy brake discs, resulting in abnormal wear of the friction pair and large fluctuations in the friction coefficient.

[0005] Currently, there are few research reports on the compatibility between aluminum alloy brake discs and powder metallurgy brake pads in the industry, and related work is still in its infancy. Therefore, there is a current need to provide a powder metallurgy brake pad with a high friction coefficient and a small wear amount for aluminum alloy brake discs. Summary of the Invention

[0006] To solve the above technical problems, the purpose of the present invention is to provide a powder metallurgy friction material, a powder metallurgy brake pad and a preparation method thereof.

[0007] To achieve the above object, the present invention provides a powder metallurgy friction material, wherein, by mass percentage, the powder metallurgy friction material comprises:

[0008] 50wt%-65wt% of copper powder, 20wt%-30wt% of iron powder, 10wt%-20wt% of graphite ceramic composite particles;

[0009] Based on the mass of the graphite ceramic composite particles being 100wt%, the graphite ceramic composite particles comprise: 50wt%-70wt% of expandable graphite, 5wt%-10wt% of ceramic powder, 20wt%-45wt% of micro powder graphite.

[0010] In some specific embodiments, preferably, based on the mass of the graphite ceramic composite particles being 100 wt%, the addition amount of the micro-powder graphite is 20 wt% - 30 wt%.

[0011] According to the specific embodiments of the present invention, preferably, the particle size of the expandable graphite is 150 - 250 μm, and the expansion multiple of the expandable graphite at 750 - 850 °C is 20 - 40 times.

[0012] According to the specific embodiments of the present invention, preferably, the particle size of the micro-powder 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.

[0013] In the present invention, the particle size of the micro-powder graphite is extremely fine, and it is easier to form a lubricating film protection layer on the friction surface; further, using large-particle-size expandable graphite as a carrier to support the composite particles composed of small-particle-size micro-powder graphite and ceramic powder has both lubricating and friction-increasing functions, so that the composite particles can fall off as a whole under the shear peeling of the frictional force during braking, reducing the situation of the ceramic powder being embedded and stuck on the friction surface, and thus effectively avoiding scratching of the friction surface.

[0014] According to the specific embodiments of the present invention, preferably, the ceramic powder includes one or a combination of two 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.

[0015] The present invention also provides a powder metallurgy brake pad, which is prepared from the above-mentioned powder metallurgy friction material.

[0016] According to the specific embodiments of the present invention, preferably, the hardness of the powder metallurgy brake pad is below 15 HBW, and the wear amount of the powder metallurgy brake pad is below 0.3 cm 3 / MJ; more preferably, the hardness of the powder metallurgy brake pad is 12 - 13 HBW, and the wear amount of the powder metallurgy brake pad is 0.15 - 0.29 cm 3 / MJ; further preferably, the wear amount of the powder metallurgy brake pad is 0.15 - 0.25 cm 3 / MJ.

[0017] According to the specific embodiments of the present invention, preferably, the powder metallurgy brake pad is a powder metallurgy brake pad for an aluminum alloy brake disc.

[0018] In some specific embodiments, preferably, the shear strength of the powder metallurgy brake pad is above 14 MPa, the bonding strength is above 15 MPa, and the compressive strength is above 95 MPa; more preferably, the shear strength of the powder metallurgy brake pad is 14 - 20 MPa, the bonding strength is 15 - 18 MPa, and the compressive strength is 95 - 119 MPa.

[0019] In some specific embodiments, preferably, the hardness of the aluminum alloy brake disc is 120-170 HBW, the tensile strength is ≥250 MPa, and the braking speed is 120-200 km / h (more preferably 160-200 km / h).

[0020] The present invention also provides a method for preparing the above-mentioned powder metallurgy brake pads, wherein the preparation method includes:

[0021] Step 1: Mix and mold expandable graphite, micro-powder graphite, and ceramic powder to obtain graphite-ceramic composite particles;

[0022] Step 2: Mix copper powder, iron powder, and graphite-ceramic composite particles, and after stirring, cold pressing, and sintering, obtain powder metallurgy brake pads.

[0023] In some specific embodiments, preferably, the stirring speed in Step 2 is 200-400 r / min, and the stirring time is 15-30 min.

[0024] In some specific embodiments, preferably, the pressing pressure for cold pressing in Step 2 is 10-15 MPa, and the pressure holding time is 8-15 s.

[0025] According to the specific embodiments of the present invention, preferably, in Step 1, the preparation of the graphite-ceramic composite particles includes the following steps:

[0026] Step a: Mix expandable graphite, micro-powder graphite, and ceramic powder to obtain a premixed dry powder;

[0027] Step b: Based on the mass of the premixed dry powder being 100%, add 10 wt%-20 wt% of a molding agent to the premixed dry powder and stir, and then dry to remove the solvent in the molding agent;

[0028] Step c: Compress and mold the product of Step b, and then break it up, screen it, and obtain graphite-ceramic composite particles.

[0029] In some specific embodiments, preferably, the molding agent includes one or a combination of two or more of a resin-based molding agent, a rubber-based molding agent, and an ester-based molding agent. The molding agent can be conventionally selected as needed.

[0030] In some specific embodiments, preferably, the stirring speed for mixing in Step a is 80-120 r / min, and the stirring time is 10-15 min.

[0031] In some specific embodiments, preferably, the temperature for drying and removing the solvent in Step b is 40-70 °C, and the time is 1.5-3 h.

[0032] In some specific embodiments, preferably, the pressing pressure for briquetting in step c is 3 - 5 MPa.

[0033] According to the specific embodiments of the present invention, preferably, the temperature of the sintering treatment is 750 - 850 °C, the heat preservation time of the sintering treatment is 1.5 - 3 h, and the pressure of the sintering treatment is 1 - 2 MPa.

[0034] In some specific embodiments, preferably, the sintering treatment is carried out under a nitrogen-hydrogen protective atmosphere.

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0036] (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 can serve as natural friction increasing phases to replace traditional hard alloys or ceramics as the main friction increasing agents, effectively reducing the wear amount and damage to the brake disc while maintaining the friction coefficient of the brake pad.

[0037] (2) The preparation method of the powder metallurgy brake pad provided by the present invention adds all non-metallic phases in the friction material as a whole in the form of graphite-ceramic composite particles to the metal matrix, reducing the degree of splitting of the non-metallic phase relative to the matrix skeleton, solving the problem of poor bonding between the non-metallic phase and the metal, and enabling the friction material to still obtain sufficient mechanical strength at a relatively low sintering temperature. In addition, the powder metallurgy brake pad prepared by low-temperature sintering in the present invention has a low hardness, which can further reduce the damage and performance fluctuations caused by disc scratching.

[0038] (3) Due to the differences in hardness and strength of aluminum alloy brake discs produced according to different line requirements and design and manufacturing processes, the performance requirements for matching brake pads also vary. The present invention can obtain powder metallurgy brake pads adapted to the requirements of aluminum alloy brake discs by adjusting the component ratio of graphite-ceramic composite particles and the type of ceramic powder, with high adaptability and wide application, especially suitable for aluminum alloy brake discs with high hardness and tensile strength for high-speed braking. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 The surface state of the aluminum alloy brake disc after braking with the powder metallurgy brake pad prepared in Example 1.

[0040] Figure 2 The surface state of the aluminum alloy brake disc after braking with the powder metallurgy brake pad prepared in Comparative Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0041] For a clearer understanding of the technical features, objectives, and beneficial effects of the present invention, the following detailed description of the technical solution of the present invention is provided, but it should not be construed as a limitation on the scope of implementation of the present invention.

[0042] Example 1:

[0043] This example provides a powder metallurgy brake pad, and the specific steps are as follows:

[0044] (1) Weigh 100 g of expandable graphite, 35 g of micro-powder graphite, and 15 g of ceramic powder zirconia in proportion, put them into a mixer for premixing, with a stirring speed of 100 r / min and a stirring time of 15 min to obtain a premixed dry powder; among them, the particle size of the expandable graphite is 150 - 200 μm, the particle size of the micro-powder graphite is 10 - 15 μm, and the particle size of the ceramic powder is 10 - 15 μm;

[0045] (2) Based on the mass of the premixed dry powder being 100%, add 15 wt% of a resin-based molding agent to the premixed dry powder and continue stirring for 15 min; then put it into an oven and dry at 60 °C for 2 h to remove the solvent in the molding agent;

[0046] (3) Put the product of step (2) into a cold press for briquetting, with a pressing pressure of 5 Mpa and a pressure holding time of 10 s; then put the green compact into a crusher to break it, and screen the powder, and retain the particles in the particle size range of 150 - 300 μm to obtain graphite-ceramic composite particles.

[0047] (4) Weigh 550 g of copper powder and 170 g of iron powder in proportion, and put them into a mixer together with the sieved graphite-ceramic composite particles from step (3) for mixing, with a mixer rotation speed of 400 r / min and a mixing time of 20 min to obtain a mixed powder;

[0048] (5) Cold-press the mixed powder into shape, with a pressing pressure of 15 MPa and a pressure holding time of 10 s; then place the green compact on a steel back for sintering, with a protective atmosphere of nitrogen-hydrogen mixed gas, a sintering pressure of 2 MPa, a sintering temperature of 800 °C, and a heat preservation time of 2 h, and then cool it in the furnace to 60 °C and take it out of the furnace to obtain a powder metallurgy brake pad.

[0049] Example 2:

[0050] This example provides a powder metallurgy brake pad, and the specific steps are as follows:

[0051] (1) Weigh 114 g of expandable graphite, 39 g of micro-powder graphite, and 17 g of ceramic powder zirconia in proportion, put them into a mixer for premixing, with a stirring speed of 100 r / min and a stirring time of 15 min to obtain a premixed dry powder; among them, the particle size of the expandable graphite is 150 - 250 μm, the particle size of the micro-powder graphite is 15 - 20 μm, and the particle size of the ceramic powder is 15 - 20 μm;

[0052] (2) Based on the mass of the premixed dry powder being 100%, add 15 wt% of the resin-based molding agent to the premixed dry powder and continue stirring for 15 min; then place it in an oven and dry at 60°C for 2 h to remove the solvent in the molding agent.

[0053] (3) Put the product of step (2) into a cold press for briquetting, with a pressing pressure of 5 Mpa and a pressure holding time of 10 s; then put the green compact into a crusher to break it, and screen the powder, retaining the particles in the particle size range of 150 - 300 μm to obtain graphite-ceramic composite particles.

[0054] (4) Weigh 430 g of copper powder and 250 g of iron powder proportionally, and put them together with the sieved graphite-ceramic composite particles in step (3) into a mixer for mixing. The rotation speed of the mixer is 400 r / min, and the mixing time is 20 min to obtain a mixed powder.

[0055] (5) Cold-press the mixed powder into a shape, with a pressing pressure of 15 MPa and a pressure holding time of 10 s; then place the green compact on a steel back for sintering. The protective atmosphere is a nitrogen-hydrogen mixture, the sintering pressure is 2 MPa, the sintering temperature is 800°C, and the heat preservation time is 2 h. Then cool it in the furnace to 60°C and take it out of the furnace to obtain a powder metallurgy brake pad.

[0056] Example 3:

[0057] This example provides a powder metallurgy brake pad, and the specific steps are as follows:

[0058] (1) Weigh 60 g of expandable graphite, 21 g of micro-powder graphite, and 9 g of ceramic powder zirconia proportionally, put them into a mixer for premixing, with a stirring speed of 100 r / min and a stirring time of 15 min to obtain a premixed dry powder; among them, the particle size of the expandable graphite is 200 - 250 μm, the particle size of the micro-powder graphite is 10 - 15 μm, and the particle size of the ceramic powder is 15 - 20 μm.

[0059] (2) Based on the mass of the premixed dry powder being 100%, add 15 wt% of the resin-based molding agent to the premixed dry powder and continue stirring for 15 min; then place it in an oven and dry at 60°C for 2 h to remove the solvent in the molding agent.

[0060] (3) Put the product of step (2) into a cold press for briquetting, with a pressing pressure of 5 Mpa and a pressure holding time of 10 s; then put the green compact into a crusher to break it, and screen the powder, retaining the particles in the particle size range of 150 - 300 μm to obtain graphite-ceramic composite particles.

[0061] (4) Weigh 510 g of copper powder and 250 g of iron powder proportionally, and put them into a blender together with the sieved graphite-ceramic composite particles in step (3) for mixing. The rotation speed of the blender is 400 r / min, and the mixing time is 20 min to obtain a mixed powder.

[0062] (5) Cold-press the mixed powder into a shape with a pressing pressure of 15 MPa and keep the pressure for 10 s. Then place the green compact on the steel back for sintering. The protective atmosphere is a nitrogen-hydrogen mixture. The sintering pressure is 2 MPa, the sintering temperature is 800 °C, and the holding time is 2 h. Then cool it in the furnace to 60 °C and take it out of the furnace to obtain a powder metallurgy brake pad.

[0063] Example 4:

[0064] This example provides a powder metallurgy brake pad, and the specific steps are as follows:

[0065] (1) Weigh 83 g of expandable graphite, 39 g of micro-powder graphite, and 8 g of ceramic powder zirconia proportionally, and put them into a blender for premixing. The stirring speed is 100 r / min, and the stirring time is 15 min to obtain a premixed dry powder. Among them, the particle size of the expandable graphite is 150 - 200 μm, the particle size of the micro-powder graphite is 10 - 15 μm, and the particle size of the ceramic powder is 15 - 20 μm.

[0066] (2) Based on the mass of the premixed dry powder being 100%, add 15 wt% of a resin-based molding agent to the premixed dry powder and continue stirring for 15 min. Then put it into an oven and dry it at 60 °C for 2 h to remove the solvent in the molding agent.

[0067] (3) Put the product of step (2) into a cold press to form a block with a pressing pressure of 3 Mpa and keep the pressure for 10 s. Then put the green compact into a crusher to break it up, and screen the powder to retain the particles in the particle size range of 150 - 300 μm to obtain graphite-ceramic composite particles.

[0068] (4) Weigh 550 g of copper powder and 170 g of iron powder proportionally, and put them into a blender together with the sieved graphite-ceramic composite particles in step (3) for mixing. The rotation speed of the blender is 400 r / min, and the mixing time is 20 min to obtain a mixed powder.

[0069] (5) Cold-press the mixed powder into a shape with a pressing pressure of 10 MPa and keep the pressure for 10 s. Then place the green compact on the steel back for sintering. The protective atmosphere is a nitrogen-hydrogen mixture. The sintering pressure is 2 MPa, the sintering temperature is 850 °C, and the holding time is 2 h. Then cool it in the furnace to 60 °C and take it out of the furnace to obtain a powder metallurgy brake pad.

[0070] Example 5:

[0071] This example provides a powder metallurgy brake pad, and the specific steps are as follows:

[0072] (1) Weigh 83 g of expandable graphite, 39 g of micronized graphite, and 8 g of zirconia ceramic powder proportionally, put them into a blender for dry premixing, with a stirring speed of 100 r / min and a stirring time of 15 min to obtain premixed dry powder; among them, the particle size of the expandable graphite is 150 - 250 μm, the particle size of the micronized graphite is 10 - 20 μm, and the particle size of the ceramic powder is 10 - 20 μm;

[0073] (2) Based on the mass of the premixed dry powder being 100%, add 15 wt% of a resin-based molding agent to the premixed dry powder and continue stirring for 15 min; then put it into an oven and dry at 60 °C for 2 h to remove the solvent in the molding agent;

[0074] (3) Put the product of step (2) into a cold press for briquetting, with a pressing pressure of 5 Mpa and a pressure holding time of 10 s; then put the green compact into a crusher to break it, and screen the powder, retaining particles in the particle size range of 150 - 300 μm to obtain graphite ceramic composite particles.

[0075] (4) Weigh 550 g of copper powder and 170 g of iron powder proportionally, and put them into a blender together with the sieved graphite ceramic composite particles from step (3) for mixing, with a blender rotation speed of 400 r / min and a mixing time of 20 min to obtain mixed powder;

[0076] (5) Cold press the mixed powder into a shape, with a pressing pressure of 15 MPa and a pressure holding time of 10 s; place the green compact on a steel back for sintering, with a protective atmosphere of nitrogen-hydrogen mixture, a sintering pressure of 2 MPa, a sintering temperature of 750 °C, and a heat preservation time of 2 h, and then cool it in the furnace to 60 °C and take it out of the furnace to obtain a powder metallurgy brake pad.

[0077] Example 6:

[0078] This example provides a powder metallurgy brake pad, and the specific steps are as follows:

[0079] (1) Weigh 100 g of expandable graphite, 35 g of micronized graphite, and 15 g of silicon oxide ceramic powder proportionally, put them into a blender for dry premixing, with a stirring speed of 100 r / min and a stirring time of 15 min to obtain premixed dry powder; among them, the particle size of the expandable graphite is 150 - 200 μm, the particle size of the micronized graphite is 10 - 15 μm, and the particle size of the ceramic powder is 10 - 15 μm;

[0080] (2) Based on the mass of the premixed dry powder being 100%, add 15 wt% of a resin-based molding agent to the premixed dry powder and continue stirring for 15 min; then put it into an oven and dry at 60 °C for 2 h to remove the solvent in the molding agent;

[0081] (3) Put the product of step (2) into a cold press for briquetting. The pressing pressure is 5 Mpa and the pressure is maintained for 10 s. Then put the green compact into a crusher to break it up, and screen the powder to retain particles in the particle size range of 150 - 300 μm, obtaining graphite ceramic composite particles.

[0082] (4) Weigh 550 g of copper powder and 170 g of iron powder proportionally, and put them together with the sieved graphite ceramic composite particles in step (3) into a blender for mixing. The rotation speed of the blender is 400 r / min and the mixing time is 20 min, obtaining mixed powder.

[0083] (5) Cold-press the mixed powder into a compact. The pressing pressure is 15 MPa and the pressure is maintained for 10 s. Place the green compact on a steel back for sintering. The protective atmosphere is a nitrogen-hydrogen mixture. The sintering pressure is 2 MPa, the sintering temperature is 750 °C, and the holding time is 2 h. Then cool it in the furnace to 60 °C and take it out of the furnace to obtain a powder metallurgy brake pad.

[0084] Example 7:

[0085] This example provides a powder metallurgy brake pad, and the specific steps are as follows:

[0086] (1) Weigh 100 g of expandable graphite, 35 g of micro-powder graphite, and 15 g of ceramic powder chromium carbide proportionally, and put them into a blender for dry premixing. The stirring speed is 100 r / min and the stirring time is 15 min, obtaining premixed dry powder. Among them, the particle size of the expandable graphite is 150 - 200 μm, the particle size of the micro-powder graphite is 10 - 15 μm, and the particle size of the ceramic powder is 10 - 15 μm.

[0087] (2) Based on the mass of the premixed dry powder being 100%, add 15 wt% of a resin-based molding agent to the premixed dry powder and continue stirring for 15 min. Then put it into an oven and dry it at 60 °C for 2 h to remove the solvent in the molding agent.

[0088] (3) Put the product of step (2) into a cold press for briquetting. The pressing pressure is 5 Mpa and the pressure is maintained for 10 s. Then put the green compact into a crusher to break it up, and screen the powder to retain particles in the particle size range of 150 - 300 μm, obtaining graphite ceramic composite particles.

[0089] (4) Weigh 550 g of copper powder and 170 g of iron powder proportionally, and put them together with the sieved graphite ceramic composite particles in step (3) into a blender for mixing. The rotation speed of the blender is 400 r / min and the mixing time is 20 min, obtaining mixed powder.

[0090] (5) Cold-press the mixed powder materials with a pressing pressure of 15 MPa and hold the pressure for 10 s; place the green compact on the steel back for sintering. The protective atmosphere is a nitrogen-hydrogen mixture. The sintering pressure is 2 MPa, the sintering temperature is 750 °C, and the heat preservation time is 2 h. Then cool it in the furnace to 60 °C and take it out of the furnace to obtain the powder metallurgy brake pad.

[0091] Comparative Example 1:

[0092] This comparative example provides a powder metallurgy brake pad, and the specific steps are as follows:

[0093] (1) Put 550 g of copper powder, 170 g of iron powder, 100 g of expandable graphite, 35 g of micro-powder graphite, and 15 g of ceramic powder zirconia into a mixer. Based on the mass of the premixed dry powder being 100%, add 10 wt% of a resin-based molding agent for mixing; among them, the particle size of the expandable graphite is 150 - 200 μm, the particle size of the micro-powder graphite is 10 - 15 μm, the particle size of the ceramic powder is 10 - 15 μm, the mixer rotation speed is 300 r / min, and the mixing time is 20 min; then put it into an oven and dry it at 60 °C for 2 h to remove the solvent in the molding agent to obtain the mixed powder materials;

[0094] (2) Cold-press the mixed powder materials with a pressing pressure of 15 MPa and hold the pressure for 10 s; place the green compact on the steel back for sintering. The protective atmosphere is a nitrogen-hydrogen mixture. The sintering pressure is 2 MPa, the sintering temperature is 800 °C, and the heat preservation time is 2 h. Then cool it in the furnace to 60 °C and take it out of the furnace to obtain the powder metallurgy brake pad.

[0095] Comparative Example 2:

[0096] This comparative example provides a powder metallurgy brake pad, and the specific steps are as follows:

[0097] (1) Put 550 g of copper powder, 170 g of iron powder, 100 g of expandable graphite, 35 g of micro-powder graphite, and 15 g of ceramic powder zirconia into a mixer. Based on the mass of the premixed dry powder being 100%, add 10 wt% of a resin-based molding agent for mixing; among them, the particle size of the expandable graphite is 150 - 200 μm, the particle size of the micro-powder graphite is 10 - 15 μm, the particle size of the ceramic powder is 10 - 15 μm, the mixer rotation speed is 300 r / min, and the mixing time is 20 min; then put it into an oven and dry it at 60 °C for 2 h to remove the solvent in the molding agent to obtain the mixed powder materials;

[0098] (2) Cold-press the mixed powder materials with a pressing pressure of 15 MPa and hold the pressure for 10 s; place the green compact on the steel back for sintering. The protective atmosphere is a nitrogen-hydrogen mixture. The sintering pressure is 2 MPa, the sintering temperature is 950 °C, and the heat preservation time is 2 h. Then cool it in the furnace to 60 °C and take it out of the furnace to obtain the powder metallurgy brake pad.

[0099] Comparative Example 3:

[0100] This comparative example provides a powder metallurgy brake pad, and the specific steps are as follows:

[0101] (1) Weigh 83 g of expandable graphite, 39 g of micro-powder graphite, and 8 g of ceramic powder zirconia in proportion, put them into a blender for dry premixing, with a stirring speed of 100 r / min and a stirring time of 15 min to obtain premixed dry powder; among them, the particle size of the expandable graphite is 75 - 150 μm, the particle size of the micro-powder graphite is 4 - 10 μm, and the particle size of the ceramic powder is 10 - 20 μm;

[0102] (2) Based on the mass of the premixed dry powder being 100%, add 15 wt% of a resin-based molding agent to the premixed dry powder and continue stirring for 15 min; then put it into an oven and dry at 60 °C for 2 h to remove the solvent in the molding agent;

[0103] (3) Put the product of step (2) into a cold press for briquetting, with a pressing pressure of 5 Mpa and a pressure holding time of 10 s; then put the green compact into a crusher to break it, and screen the powder, retaining the particles in the particle size range of 150 - 300 μm to obtain graphite-ceramic composite particles.

[0104] (4) Weigh 550 g of copper powder and 170 g of iron powder in proportion, and put them into a blender together with the sieved graphite-ceramic composite particles from step (3) for mixing, with a blender rotation speed of 400 r / min and a mixing time of 20 min to obtain mixed powder;

[0105] (5) Cold-press the mixed powder into a shape, with a pressing pressure of 15 MPa and a pressure holding time of 10 s; place the green compact on a steel back for sintering, with a protective atmosphere of nitrogen-hydrogen mixture, a sintering pressure of 2 MPa, a sintering temperature of 750 °C, and a heat preservation time of 2 h, and then cool it in the furnace to 60 °C and take it out of the furnace to obtain a powder metallurgy brake pad.

[0106] Comparative Example 4:

[0107] This comparative example provides a powder metallurgy brake pad, and the specific steps are as follows:

[0108] (1) Weigh 83 g of expandable graphite, 39 g of micro-powder graphite, and 8 g of ceramic powder zirconia in proportion, put them into a blender for dry premixing, with a stirring speed of 100 r / min and a stirring time of 15 min to obtain premixed dry powder; among them, the particle size of the expandable graphite is 150 - 250 μm, the particle size of the micro-powder graphite is 20 - 40 μm, and the particle size of the ceramic powder is 10 - 20 μm;

[0109] (2) Based on the mass of the premixed dry powder being 100%, add 15 wt% of a resin-based molding agent to the premixed dry powder and continue stirring for 15 min; then put it into an oven and dry at 60 °C for 2 h to remove the solvent in the molding agent;

[0110] (3) Put the product of step (2) into a cold press for briquetting. The pressing pressure is 5 Mpa and the pressure is maintained for 10 s. Then put the green compact into a crusher to break it, and screen the powder. Retain the particles in the particle size range of 150 - 300 μm to obtain graphite ceramic composite particles.

[0111] (4) Weigh 550 g of copper powder and 170 g of iron powder proportionally, and put them into a mixer together with the sieved graphite ceramic composite particles in step (3). The rotation speed of the mixer is 400 r / min and the mixing time is 20 min to obtain a mixed powder.

[0112] (5) Cold press the mixed powder into a compact. The pressing pressure is 15 MPa and the pressure is maintained for 10 s. Place the green compact on a steel back for sintering. The protective atmosphere is a nitrogen-hydrogen mixture. The sintering pressure is 2 MPa, the sintering temperature is 750 °C, and the heat preservation time is 2 h. Then cool it in the furnace to 60 °C and take it out of the furnace to obtain a powder metallurgy brake pad.

[0113] Next, explore the various properties of the powder metallurgy brake pad prepared above, specifically as follows:

[0114] Table 1 shows the comparison of the performance parameters of the powder metallurgy brake pads prepared in Examples 1 - 7 and Comparative Examples 1 - 4. The object of the friction and wear test is an aluminum alloy brake disc prepared by the casting method. The hardness of the aluminum alloy brake disc used for the test is 140 - 150 HBW, and the tensile strength is 260 - 280 MPa. Among them, compared with Example 1, in Comparative Example 1, no graphite ceramic composite particles were prefabricated, but all the powder materials were directly mixed; in Comparative Example 2, the sintering temperature was increased based on Comparative Example 1.

[0115] Among them, the wear amount of the powder metallurgy brake pad is tested through a friction and wear bench test, specifically as follows:

[0116] First, run in the brake pad. After the brake pad is completely fitted with the brake disc, disassemble the brake pad and weigh it, denoted as m0, and start the formal test. 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. Then disassemble the brake pad and weigh it, denoted as m.

[0117] The average friction coefficient at each speed in Table 1 is the average value of 5 data, and the wear amount of the powder metallurgy brake pad is the total wear amount of 15 brakings. Among them, the wear amount is calculated from the weight reduction m - m0 of the brake pad, the density of the powder metallurgy friction material, and the braking energy.

[0118] Table 1. Comparison of Performance Parameters of Powder Metallurgy Brake Pads

[0119]

[0120]

[0121] As can be seen from the data in Table 1, the average friction coefficients of Comparative Example 1 and Comparative Example 2 showed a significant decline as the braking speed increased, and could not meet the lower limit value of 0.310 during braking at 200 km / h, and the wear amount was relatively high. In terms of mechanical properties, the shear strength, bonding strength and compressive strength of Comparative Example 1 were relatively low, while although the strength of Comparative Example 2 was increased by increasing the sintering temperature, the hardness of the friction material was also increased at the same time, resulting in a greater wear amount.

[0122] In contrast, the shear strength and bonding strength of Examples 1-7 were higher than those of Comparative Examples 1-2, the compressive strength was also at a relatively high level, and the average friction coefficient did not decline significantly as the braking speed increased. It still met the lower limit value of 0.310 during braking at 200 km / h, showing good temperature resistance; at the same time, the powder metallurgy brake pads of Examples 1-7 had relatively low hardness, and the wear amount was significantly reduced compared with Comparative Examples 1-2.

[0123] Comparative Examples 3-4 used micro-powder graphite and expandable graphite outside the particle size range defined in this application, and were used as control experiments with Example 5. Among them, the particle sizes of the two kinds of graphite in Comparative Example 3 were relatively small, forming more weak bonding interfaces dispersed in the friction material matrix, resulting in a decrease in material strength and a weakening of the friction increasing effect during high-speed braking. In Comparative Example 4, the particle size of the micro-powder graphite was relatively large, and the poor lubrication ability caused jamming between the disc and the pad, manifested as a decrease in the friction coefficient during high-speed braking and an increase in the wear amount.

[0124] In addition, Examples 6-7 used different types of ceramic powders from those in Examples 1-5, and were used as control experiments with Example 1. Among them, the silicon oxide used in Example 6 had relatively low hardness, and could weaken the plowing behavior between the disc and the pad by reducing the scratching of the brake disc, thereby stabilizing the high-speed friction coefficient and reducing the wear amount of the brake pad. The chromium carbide used in Example 7 had relatively high hardness, and was easy to form a compound bond with the metal matrix during sintering, thus significantly improving the mechanical strength of the friction material. However, this would cause a certain scratching of the disc surface during braking, resulting in a decline in the high-speed braking friction coefficient and an increase in the wear amount of the brake pad.

[0125] Comparing the test results in Table 1, Figure 1 and Figure 2 respectively show the surface states of the aluminum alloy brake discs after the same braking conditions for the powder metallurgy brake pads prepared in Example 1 and Comparative Example 1. The braking conditions were: initial braking speed 200 km / h, bilateral brake pad thrust 40 kN, and the disc surface state was observed after 5 times of braking.

[0126] From Figure 1 、 Figure 2It can be seen that the braking disc surface of Example 1 has uniformly fine friction marks, while the braking 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 the present invention can meet the requirements of the friction coefficient and wear amount of the aluminum alloy brake disc, the state of the braking disc surface is good, comparable to that when matching the cast steel brake disc, and can meet the use requirements of urban and intercity vehicles equipped with aluminum alloy brake discs.

Claims

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

2. The powder metallurgy friction material according to claim 1, wherein, The particle size of the expandable graphite is 150-250μm, and the expansion multiple of the expandable graphite at 750-850°C is 20-40 times.

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

4. The powder metallurgy friction material according to claim 1, wherein The ceramic powder includes one or a combination of two 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 brake pad according to claim 5, wherein, The hardness of the powder metallurgy brake pad is below 15 HBW, and the wear of the powder metallurgy brake pad is below 0.3 cm 3 / MJ.

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

8. The preparation method of the powder metallurgy brake pad according to any one of claims 5-7, wherein, The preparation method includes: Step 1: Mix and mold expandable graphite, micro-powder graphite, and ceramic powder to obtain graphite ceramic composite particles; Step 2: Mix copper powder, iron powder with the graphite ceramic composite particles, and after stirring, cold pressing and sintering, obtain the powder metallurgy brake pad.

9. The preparation method according to claim 8, wherein, In Step 1, the preparation of the graphite ceramic composite particles includes the following steps: Step a: Mix expandable graphite, micro-powder graphite, and ceramic powder to obtain a premixed dry powder; Step b: Based on the mass of the premixed dry powder being 100%, add 10wt%-20wt% of a molding agent to the premixed dry powder and stir, and then dry to remove the solvent in the molding agent; Step c: Compress and mold the product of Step b, and then break and screen it to obtain graphite ceramic composite particles.

10. The preparation method according to claim 8, wherein The temperature of the sintering treatment is 750-850°C, the heat preservation time of the sintering treatment is 1.5-3h, and the pressure of the sintering treatment is 1-2MPa.

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