CN109139755B - Preparation method of iron-copper-based composite friction material - Google Patents

Abstract

A preparation method of an iron-copper-based composite friction material comprises the steps of mixing raw materials, cold-pressing, and then high-temperature hot-pressing and sintering to obtain the iron-copper-based composite friction material, wherein compression molding is carried out under the pressure of 450-550 MPa; placing the pressed compact in a heating furnace and carrying out pressure sintering in a nitrogen protective atmosphere, wherein the sintering process comprises the following steps: preserving heat for 2-3 h at 1000 ℃ and under the pressure of 2.5-2.8 MPa, and cooling along with the furnace; the friction material is obtained by cold pressing and then high-temperature hot-pressing sintering, the respective advantages of iron and copper are exerted, and meanwhile, the carbon fiber with high specific modulus and specific strength is applied to the iron-copper-based friction material, so that the matrix strength is enhanced, the impact toughness is improved, the braking noise is reduced, the friction coefficient is proper, and the high-temperature wear resistance is excellent.

Description

Preparation method of iron-copper-based composite friction material

Technical Field

The invention relates to a preparation method of a composite friction material, in particular to a preparation method of an iron-copper-based composite friction material for braking and driving of various engineering machinery.

Background

The friction material is a material for transmitting or absorbing power by utilizing friction action, mainly comprises a brake lining and a clutch plate, and is widely applied to various engineering mechanical equipment such as automobiles, trains, airplanes, petroleum drilling machines and the like. Commonly used friction materials are NAO type, semi-metal type, and metal type friction materials. The NAO type friction material mainly uses glass fiber, aromatic fiber, or other fiber (carbon, ceramic, etc.) as a reinforcing material, and the performance thereof mainly depends on the type of the fiber and other additive mixture. The brake pad has excellent characteristics in the aspects of abrasion resistance, noise reduction and the like, but is sensitive to temperature, and after repeated braking, organic matters are easily decomposed, so that the braking performance is obviously reduced. The semimetal type friction material usually contains about 30-50% of ferrous metal (such as steel fiber, reduced iron powder and foam iron powder) in the composition, and has the advantages of good heat resistance, high absorption power per unit area, high heat conductivity coefficient and the like, but the semimetal type friction material has large braking noise and is easy to crack. The metal type friction material is usually prepared by a powder metallurgy method, comprises two main types of iron base and copper base, has long service life, and is suitable for braking and transmission conditions at higher temperature. The iron-based friction material is high-temperature resistant, can bear larger load, has high mechanical strength and is low in price; however, iron-based friction materials have a large friction coefficient and high strength, but tend to adhere to the surfaces of mating parts, and have poor friction coefficient stability and inferior wear resistance to copper-based friction materials. The copper-based friction material has the advantages of good process performance, stable friction coefficient, good anti-bonding and anti-seizing performances, good thermal conductivity, small friction coefficient and higher economic cost, and after being abandoned, the heavy metal Cu element can be activated and migrated in a large scale due to long-term stockpiling, so that heavy metal pollution and harm are caused to the surrounding environment.

The iron-copper based friction material takes copper powder and iron powder as main components, the mass of the copper-iron based friction material accounts for more than fifty percent of the total weight of the powder metallurgy friction material, the organization structure, the bearing capacity and the property of the copper-iron based friction material determine the mechanical property and the heat resistance of the material, and the matrix must have enough bearing capacity and heat conduction capacity to protect the material from being damaged and influenced by heat. In order to enhance the strength of the matrix, metal elements such as titanium, nickel, molybdenum, etc. may be added to the matrix, because the metal elements such as titanium, nickel, molybdenum, etc. may be added to the matrix to refine the structure and cause lattice distortion, resulting in an increase in the strength and hardness of the matrix. Common friction components include TiC, SiC, TiN, and high melting point metal (Ni, Fe, Mo) powder, metal oxide (Al)₂O₃、SiO₂、Fe₂O₃) And mullite, boride and the like, which are used for improving the friction coefficient of the material, namely increasing the sliding resistance, and the commonly used friction elements are added into the material in a combined manner, so that the comprehensive performance is better than that of adding the single friction elements. The materials required by the friction component require high melting point and dissociation heat, and have no polycrystalline transformation in the range from room temperature to sintering temperature or use temperature; does not react with other components or sintering atmosphere; the alloy has high enough strength and hardness to ensure that the alloy is not easy to damage in the friction process, but the strength and hardness are not too high, otherwise, the alloy can excessively wear the dual matrix alloy; the wetting property to the base component is good. The addition of proper lubricating components in the friction material can improve the lubricating performance of the friction material, thereby reducing the wear rate of the material in the braking process. Graphite, molybdenum disulfide, lead, and the like are generally used as the main components, and a solid lubricant such as molybdenum sulfide, copper sulfide, barium sulfide, boron nitride, or the like is sometimes used. Lead, tin, etc. having a low melting point are locally melted at a high temperature, and can absorb frictional heat and form a thin film on the frictional surface to prevent sticking, biting and scratching.

With the increasing living standard and the rapid development of urbanization of people, various vehicles emerge endlessly, the power, the load and the speed of the machine are further improved, and people have higher requirements on safety, environmental protection and comfort while going out conveniently. The iron-copper based friction material prepared by combining the advantages of iron base and copper base in the metal type friction material has the advantages of high temperature resistance and high matrix strength of the iron-base friction material, also has the advantages of good copper-base heat-conducting property and stable friction coefficient, reduces the consumption of copper, reduces the cost and reduces the environmental pollution, but the iron-copper based friction material has higher braking noise and high brittleness. How to improve the impact toughness of the iron-copper based friction material and reduce the vibration noise is an important direction for improving the performance of the iron-copper based friction material. If the carbon fiber with high specific modulus and specific strength is applied to the iron-copper-based friction material, the matrix strength can be enhanced, the impact toughness can be improved, and the braking noise can be reduced.

Disclosure of Invention

In order to overcome the defects of the prior art and solve the problems of easy adhesion of the surface of the existing single iron-based friction material, poor stability of the friction coefficient, insufficient wear resistance, small friction coefficient of the single copper-based friction material, higher economic cost, pollution of heavy metal Cu and the like, the invention aims to provide a preparation method of an iron-copper-based composite friction material, which exerts the respective advantages of iron and copper, and simultaneously applies carbon fibers with high specific modulus and specific strength to the iron-copper-based friction material to enhance the matrix strength, improve the impact toughness, reduce the braking noise, have proper friction coefficient and excellent high-temperature wear resistance.

In order to achieve the purpose, the technical scheme of the invention is as follows:

a preparation method of an iron-copper-based composite friction material comprises the following steps:

step 1, preparing materials, wherein the following percentages are mass percent

30-40% of dendritic electrolytic copper powder of 40-60 microns, 25-35% of spherical or nearly spherical atomized iron powder of 40-60 microns in particle size, less than 72% of total amount of iron powder and copper powder, and 2-3% of titanium powder, nickel powder and molybdenum powder of 40-60 micronsThe sum of titanium powder, nickel powder and molybdenum powder is controlled to be 6-9%, 8-10% of 60-80 micron flaky graphite powder, 2-4% of short carbon fiber with the diameter of 5-7 micron and the length of 1-3 mm, 2-4% of 60-80 micron near-spherical molybdenum disulfide, the sum of graphite powder, carbon fiber and molybdenum disulfide is not more than 15%, and then 70-100 micron kaolin, feldspar powder and mullite which are 2-3% respectively and 1-2% of 70-100 micron vermiculite powder are mixed; and calculating the theoretical density according to formula 1, unit: rho g/cm³；

The formula 1 is as follows, wherein the symbols before the percentage numbers indicate the names of the respective components, and the total is 100%

Step 2, mixing the materials

Weighing the raw materials in the step 1 in proportion, then loading the raw materials into a Y-shaped mixer, adding solvent 120# gasoline according to the proportion of 10-15 ml/kg, and then mixing the raw materials for 2-3 hours at the speed of 30-50 r/min; then adding 5-10 ml/kg of glycerol solution with the mass concentration of 80%, kneading and stirring uniformly by hands, granulating through a sieve with 30-40 meshes, and standing for 2-4 hours at room temperature in the shade;

step 3, forming

Firstly, the volume V cm of the friction block is calculated according to a drawing of the friction block³Then, calculating the weight M g of the mixed powder required by the pressed compact by using a formula 2; weighing the powder with the weight by using a balance, loading the powder into a cavity formed by a female die and a lower die in a steel pressing die (designed and processed in advance according to a drawing), finally placing an upper die, and applying the pressure of 600-700 MPa on a hydraulic machine for cold press molding:

formula 2M ═ 95% ρ · V (gram)

Step 4, loading the boat

Placing the green body formed in the step (3) in a boat, placing a graphite punch with the same section size on the green body, and taking heat-resistant steel plates of 5-10 mm as trays above and below the whole graphite boat;

step 5, sintering

Stacking the boats loaded in the step 4 into a heating furnace cavity from bottom to top in sequence, covering a furnace cover, connecting a pressurizing device, and introducing nitrogen in a protective atmosphere for pressure sintering; controlling the heating rate at 200-250 ℃/h, heating to 950-1000 ℃, preserving heat for 2-3 h, simultaneously applying pressure of 1.0-2.5 MPa, then cooling along with the furnace, opening a furnace cover when the temperature is reduced to below 300 ℃, and closing protective atmosphere; taking out the friction block from the graphite boat after staying for 2 hours;

step 6, sand blasting

Removing the surface pollution of the friction block fired in the step 5 by using solid sand blasting; the sand grains are white corundum sand with the diameter of about 0.5-1 mm, and impact the surface of the friction block at a high speed of 5-8 m/s for 1-3 minutes.

The friction material is obtained by cold pressing and then high-temperature hot-pressing sintering, and has the beneficial effects that:

1. the formula composition of the iron-copper-based friction material is adjusted, and metal elements such as titanium, nickel, molybdenum and the like are added into the matrix, so that the structure can be refined, lattice distortion is caused, and the strength and hardness of the matrix are increased. The lubricating component, or graphite and MoS2, which is called friction reducer, is comprised of a number of layers or sheets that are strong in themselves but weak in bonding between the layers, resulting in materials that are strong in compression and weak in shear, and therefore have a suitable range of amounts.

2. The prepared iron-copper based friction material has moderate and stable friction coefficient, good wear resistance, no pollution, simple process flow, low cost, no brake noise and small heat fading.

Drawings

FIG. 1 is a schematic structural diagram of a three-high graphite boat.

FIG. 2 is a microstructure view of the friction material, and FIG. 2A is a low magnification micrograph; fig. 2B is a high magnification micrograph.

FIG. 3 is a graph comparing the noise of a conventional friction block with that of the friction block of the present invention.

Detailed Description

The invention is described in detail below with reference to the drawings and the detailed description.

Example one

Preparing a cylindrical friction block with a diameter of about 25 mm and a height of 10 mm, comprising the following steps:

step 1, batching. 30 percent of dendritic electrolytic copper powder of 40 microns, 35 percent of spherical or nearly spherical atomized iron powder of 40 microns in particle size, 3 percent of titanium powder, nickel powder and molybdenum powder of 40 microns respectively, 9 percent of scaly graphite powder of 60 microns, 4 percent of short carbon fiber of 5 microns in diameter and 1 millimeter in length, 2 percent of nearly spherical molybdenum disulfide of 60 microns, 3 percent of kaolin, feldspar powder and mullite of 70 microns respectively and 2 percent of vermiculite powder of 70 microns are mixed. And the theoretical density rho is calculated to be 4.88 g/cm according to the formula 1³。

And 2, mixing materials. Weighing the raw materials in the step 1 in proportion, then loading the raw materials into a Y-shaped mixer, adding 120# solvent gasoline according to 10 ml/kg, and then mixing the raw materials for 2 hours at the speed of 30 r/min; then, the mixed materials are added with 5 ml/kg of glycerol solution with the mass concentration of 80%, and the mixture is kneaded and stirred uniformly by hands, granulated through a 30-mesh sieve and dried in the shade at room temperature (kept for 2 hours).

And 3, forming. Firstly, the volume V of the friction block is calculated to be 4.9 cm according to a drawing of the friction block³Then, the weight M of the mixed powder required by the pressed compact is calculated to be 22.7 g by using a formula 2; then weighing the powder by a balance, loading the powder into a cavity formed by a female die and a lower die in a steel pressing die (designed and processed in advance according to a drawing), finally placing an upper die, and applying a pressure of 600MPa (namely 30 tons of pressure) on a hydraulic press for cold press molding.

And 4, loading the boat. And (3) placing the green body formed in the step (3) in a boat or a die made of high-strength, high-density and high-conductivity three-high graphite (the size of a cavity in the graphite boat is the same as that of a friction block) according to the diagram shown in fig. 1, placing a graphite punch with the same section size (the same as that of a pressed blank) on the graphite boat, and taking heat-resistant steel plates of 5mm as trays above and below the whole graphite boat.

And 5, sintering. Stacking the boats loaded in the step 4 into a heating furnace cavity from bottom to top in sequence, covering a furnace cover, connecting a pressurizing device, introducing nitrogen in protective atmosphere for pressurizing and sintering, controlling the heating rate at 200 ℃/h, heating to 950 ℃, preserving heat for 3h, applying pressure of 1.0MPa, cooling along with the furnace, opening the furnace cover when the temperature is reduced to below 300 ℃, and closing the protective atmosphere; after 2 hours of dwell, the rub blocks were removed from the graphite boat.

And 6, sandblasting. Removing the surface pollution of the friction block fired in the step 5 by using solid sand blasting; the sand used was white corundum sand having a diameter of about 0.5mm, and was impacted on the surface of the pad at a high speed of 5 m/sec for 1 minute.

The microstructure of the iron-copper based composite friction material manufactured in this example is shown in fig. 2. The density of the iron-copper based friction material is 4.5-5.1 g/cm³(ii) a The average hardness is HV200 to HV 227. The friction coefficient is 0.40-0.45. Noise contrast ratio as shown in FIG. 3, FIG. 3A is for a conventional friction material with a relatively large amplitude, and FIG. 3B is for a friction material made according to the present invention without substantial visibility of the amplitude.

Example two

Preparing a cuboid friction block with the length of 40 mm, the width of 20 mm and the height of 10 mm, comprising the following steps:

step 1, batching. 40 percent of dendritic electrolytic copper powder of 60 microns, 30 percent of spherical or nearly spherical atomized iron powder of 60 microns in particle size, 2.5 percent of each of titanium powder, nickel powder and molybdenum powder of 60 microns, 8 percent of flaky graphite powder of 80 microns, 3 percent of short carbon fiber with the diameter of 7 microns and the length of 3 millimeters, 4 percent of nearly spherical molybdenum disulfide of 80 microns, 2 percent of kaolin, feldspar powder and mullite of 100 microns and 1.5 percent of vermiculite powder of 100 microns are mixed. And the theoretical density rho is calculated to be 5.31 g/cm according to the formula 1³。

And 2, mixing materials. Weighing the raw materials in the step 1 in proportion, then loading the raw materials into a Y-shaped mixer, adding 120# solvent gasoline according to 12 ml/kg, and then mixing the raw materials for 3 hours at the speed of 50 r/min; then, the mixed materials are added with 10 ml/kg of glycerol solution with the mass concentration of 80%, and the mixture is kneaded and stirred uniformly by hands, granulated through a 40-mesh sieve and dried in the shade at room temperature (kept for 4 hours).

And 3, forming. Firstly, the volume of the friction block is calculated according to a drawing of the friction blockV is 8 cm³Then, the weight M of the mixed powder required by the pressed compact is calculated to be 40.4 g by using a formula 2; then weighing the powder by a balance, loading the powder into a cavity formed by a female die and a lower die in a steel pressing die (designed and processed in advance according to a drawing), finally placing an upper die, and applying a pressure of 700MPa (namely 56 tons of pressure) on a hydraulic press for cold press molding.

And 4, loading the boat. And (3) placing the green body formed in the step (3) in a boat or a die made of high-strength, high-density and high-conductivity three-high graphite (the size of a cavity in the graphite boat is the same as that of a friction block) according to the diagram shown in fig. 1, placing a graphite punch with the same section size (the same as that of a pressed blank) on the graphite boat, and taking 7 mm heat-resistant steel plates as trays above and below the whole graphite boat.

And 5, sintering. Stacking the boats loaded in the step 4 into a heating furnace cavity from bottom to top in sequence, covering a furnace cover, connecting a pressurizing device, and introducing nitrogen in a protective atmosphere for pressure sintering; controlling the heating rate at 250 ℃/h, heating to 1000 ℃, preserving heat for 2 h, simultaneously applying pressure of 2.5MPa, then cooling along with the furnace, opening a furnace cover when the temperature is reduced to below 300 ℃, and closing the protective atmosphere; after 2 hours of dwell, the rub blocks were removed from the graphite boat.

And 6, sandblasting. And (5) removing the surface pollution of the friction block fired in the step (5) by using solid sand blasting, wherein the sand grains are white corundum sand with the diameter of about 1mm, and impacting the surface of the friction block at a high speed of 8 m/s for 3 minutes.

The density of the iron-copper-based composite friction material prepared in the embodiment is 4.8-5.1 g/cm³(ii) a The average hardness is HV200 to HV 210. The friction coefficient is 0.40-0.42. In a noise comparison experiment, the amplitude can not be basically seen.

EXAMPLE III

The method for preparing the fan-shaped friction block with the outer arc radius of 80 mm, the inner arc radius of 60 mm, the central angle of 80 degrees and the thickness of 10 mm comprises the following steps:

step 1, batching. 37 percent of dendritic electrolytic copper powder with the diameter of 50 microns, 33 percent of spherical or near-spherical atomized iron powder with the particle diameter of 50 microns, 2 percent of titanium powder, nickel powder and molybdenum powder with the diameter of 50 microns, 10 percent of scaly graphite powder with the diameter of 6 microns2 percent of rice, 3 mm short carbon fiber, 2.7 percent of 70 micron near-spherical molybdenum disulfide, 2.7 percent of 80 micron kaolin, feldspar powder and mullite, and 1.2 percent of 80 micron vermiculite powder are mixed, and the theoretical density rho is calculated according to the formula 1 and is 5.05 g/cm³。

And 2, mixing materials. Weighing the raw materials in the step 1 in proportion, then loading the raw materials into a Y-shaped mixer, adding 120# solvent gasoline according to 15 ml/kg, and then mixing the raw materials for 2.5 hours at the speed of 40 r/min; then, the mixed materials are added with 8 ml/kg of glycerol solution with the mass concentration of 80%, and the mixture is kneaded and stirred uniformly by hands, granulated through a 30-mesh sieve and dried in the shade at room temperature (kept for 3 hours).

And 3, forming. Firstly, the volume V of the friction block is calculated to be 19.5 cm according to a drawing of the friction block³Then, the weight M of the mixed powder required for green compact was calculated to be 93.6 g using equation 2. Then weighing the powder by a balance, loading the powder into a cavity formed by a female die and a lower die in a steel pressing die (designed and processed in advance according to a drawing), finally placing an upper die, and applying 650MPa pressure (namely 130 tons of pressure) on a hydraulic press for cold press molding.

And 4, loading the boat. And (3) placing the green body formed in the step (3) in a boat or a die made of high-strength, high-density and high-conductivity three-high graphite (the size of a cavity in the graphite boat is the same as that of a friction block) according to the diagram shown in fig. 1, placing a graphite punch with the same section size (the same as that of a pressed blank) on the graphite boat, and taking 10-millimeter heat-resistant steel plates as trays above and below the whole graphite boat.

And 5, sintering. Stacking the boats loaded in the step 4 into a heating furnace cavity from bottom to top in sequence, covering a furnace cover, connecting a pressurizing device, and introducing nitrogen in a protective atmosphere (which is favorable for reacting with the added components of iron and titanium to form nitride and improve the wear resistance) for pressurizing and sintering; controlling the heating rate at 220 ℃/h, heating to 970 ℃, preserving the temperature for 2.5 hours, simultaneously applying the pressure of 2.0MPa, then cooling along with the furnace, opening a furnace cover when the temperature is reduced to below 300 ℃, and closing the protective atmosphere. After 2 hours of dwell, the rub blocks were removed from the graphite boat.

And 6, sandblasting. And (5) removing the surface pollution of the friction block fired in the step (5) by using solid sand blasting, wherein the sand grains are white corundum sand with the diameter of about 0.8mm, and impacting the surface of the friction block at a high speed of 7 m/s for 2 minutes.

The density of the iron-copper-based composite friction material prepared in the embodiment is 4.8-5.1 g/cm³(ii) a The average hardness is HV210 to HV 220. The friction coefficient is 0.42-0.45. In a noise comparison experiment, the amplitude can not be basically seen.

Claims (1)

1. The preparation method of the iron-copper-based composite friction material is characterized by comprising the following steps of:

step 1, preparing materials, wherein the following percentages are mass percent

Mixing 30-40% of dendritic electrolytic copper powder of 40-60 microns, 25-35% of spherical or nearly spherical atomized iron powder of 40-60 microns in particle size, 6-9% of the sum of the iron powder and the copper powder, 8-10% of scaly graphite powder of 60-80 microns, 2-4% of short carbon fiber of 5-7 microns in diameter and 1-3 mm in length, 2-4% of nearly spherical molybdenum disulfide of 60-80 microns, and not more than 15% of the sum of graphite powder, carbon fiber and molybdenum disulfide, adding kaolin of 70-100 microns, feldspar powder and mullite of 2-3% and 1-2% of vermiculite powder of 70-100 microns, wherein the total amount of the iron powder and the copper powder is not more than 72%, the titanium powder, the nickel powder and the molybdenum powder of 40-60 microns are respectively 2-3%, and the sum of the titanium powder, the nickel powder and; and calculating the theoretical density according to formula 1, unit: rho g/cm³；

Formula 1 is as follows, wherein the symbols preceding the percentage numbers indicate the names of the individual components, and the sum is 100%;

step 2, mixing the materials

Weighing the raw materials in the step 1 in proportion, then loading the raw materials into a Y-shaped mixer, adding solvent 120# gasoline according to the proportion of 10-15 ml/kg, and then mixing the raw materials for 2-3 hours at the speed of 30-50 r/min; then adding 5-10 ml/kg of glycerol solution with the mass concentration of 80%, kneading and stirring uniformly by hands, granulating through a sieve with 30-40 meshes, and standing for 2-4 hours at room temperature in the shade;

step 3, forming

Firstly, the volume V cm of the friction block is calculated according to a drawing of the friction block³Then, calculating the weight M g of the mixed powder required by the pressed compact by using a formula 2; and weighing the powder with the weight by using a balance, loading the powder into a cavity formed by a female die and a lower die in a steel pressing die, finally placing an upper die, and applying the pressure of 600-700 MPa on a hydraulic press for cold press molding:

formula 2M ═ 95% ρ · V (gram)

Step 4, loading the boat

Placing the green body formed in the step (3) in a boat, placing a graphite punch with the same section size on the green body, and taking heat-resistant steel plates of 5-10 mm as trays above and below the whole graphite boat;

step 5, sintering

Stacking the boats loaded in the step 4 into a heating furnace cavity from bottom to top in sequence, covering a furnace cover, connecting a pressurizing device, and introducing nitrogen in a protective atmosphere for pressure sintering; controlling the heating rate at 200-250 ℃/h, heating to 950-1000 ℃, preserving heat for 2-3 h, simultaneously applying pressure of 1.0-2.5 MPa, then cooling along with the furnace, opening a furnace cover when the temperature is reduced to below 300 ℃, and closing protective atmosphere; taking out the friction block from the graphite boat after staying for 2 hours;

step 6, sand blasting

Removing the surface pollution of the friction block fired in the step 5 by using solid sand blasting; the sand grains are white corundum sand with the diameter of about 0.5-1 mm, and impact the surface of the friction block at a high speed of 5-8 m/s for 1-3 minutes.

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