CN112059189B - Powder metallurgy brake pad with stable friction coefficient in wide temperature range and preparation method - Google Patents
Powder metallurgy brake pad with stable friction coefficient in wide temperature range and preparation method Download PDFInfo
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- CN112059189B CN112059189B CN202010855694.2A CN202010855694A CN112059189B CN 112059189 B CN112059189 B CN 112059189B CN 202010855694 A CN202010855694 A CN 202010855694A CN 112059189 B CN112059189 B CN 112059189B
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F5/00—Manufacture of workpieces or articles from metallic powder characterised by the special shape of the product
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/10—Metallic powder containing lubricating or binding agents; Metallic powder containing organic material
- B22F1/105—Metallic powder containing lubricating or binding agents; Metallic powder containing organic material containing inorganic lubricating or binding agents, e.g. metal salts
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/20—Ferrous alloys, e.g. steel alloys containing chromium with copper
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
Abstract
The invention provides a powder metallurgy brake pad with stable friction coefficient in a wide temperature range and a preparation method thereof. The prepared iron-based brake pad is prepared by mixing powder, pressing and sintering under oscillating pressure. The invention can give full play to the lubricating advantages of different lubricating components at different temperatures, and promote the uniformity and density of brake pad tissues by spraying mixed materials and oscillating, pressurizing and sintering. The prepared brake pad is low in price, can be matched with a carbon ceramic disc to provide a stable and high friction coefficient at a high speed, is low in abrasion loss and prolongs the service life of the brake disc, and is suitable for a high-speed railway train braking system with the speed grade of 350km/h or more.
Description
Technical Field
The invention belongs to the technical field of producing high-speed train brake pads by a powder metallurgy process, and particularly provides a powder metallurgy brake pad with stable wide-temperature-range friction coefficient.
Background
At present, brake discs used in large scale in commerce on high speed railway trains with various speed grades are all alloy steel discs. Although alloy steel discs are relatively low cost and easy to replace, they are heavy. And along with the improvement of train operating speed, the brake disc also more and more easy fracture, unusual wearing and tearing to cause alloy steel brake disc life to shorten and even cause the safety problem. In order to meet the requirements of light weight and high speed of trains, carbon ceramic brake discs which are applied to high-end sports cars, airplanes and the like are expected to become brake disc materials for future use of high-speed trains. The carbon ceramic disc has the characteristics of high strength, high temperature resistance, low density and the like. However, the temperature rise at the friction interface is higher when it is rubbed against a counterpart brake pad compared to an alloy steel disc, which makes the conventional copper-based brake pad face more severe tests. This is mainly because the coefficient of friction of the brake lining material deteriorates and becomes unstable and the amount of wear increases abnormally when the copper matrix softens at high temperatures.
Based on the method, the content of copper powder in the brake pad is changed, and the content of iron powder is increased, so that the iron powder is used as a matrix to prepare a brand-new iron-based powder metallurgy brake pad capable of being matched with a carbon ceramic disc. Iron powder has a number of advantages as a matrix, such as the higher melting point and higher high temperature strength of iron relative to copper powder. In addition, the iron powder has wider sources and lower cost. In the past, iron-based powder metallurgy friction materials have been widely used, for example, patent CN104399970A "an iron-based powder metallurgy friction material and a preparation method thereof", patent CN104399970A "an iron-based powder metallurgy friction material and a preparation method thereof", and patent CN106086718A "a clutch iron-based composite friction material and a preparation method thereof" invented an iron-based friction material, but the used field is not the braking field of high-speed trains. One of the reasons is that iron powder is similar to a brake disc made of alloy steel, and welding and adhesion are easily generated between iron and iron, so that the friction coefficient is unstable and the abrasion loss is abnormally increased. For a brake disc made of carbon ceramic, the defect does not exist any more, and the iron-based friction material can better exert excellent mechanical and frictional wear properties. However, the temperature of a friction interface is increased when the carbon ceramic disc and the brake pad are abraded, which means that the brake pad needs to undergo more frequent and severe cold and hot temperature cycles in the process of multiple continuous braking of a high-speed train, which is a great test for the lubrication performance of the brake pad, because graphite and molybdenum disulfide are usually added into the brake pad as lubrication components, the working temperature of the graphite and the molybdenum disulfide in an oxidizing atmosphere cannot exceed 450 ℃ and 500 ℃, otherwise, the layered easy-to-slip structure is damaged. When the lubrication performance of the damper blade material is reduced due to oxidation, the friction coefficient stability and wear resistance of the damper blade material are severely reduced.
Disclosure of Invention
The invention aims to prepare a brake pad which can be well matched with a carbon-ceramic brake disc, has stable friction coefficient in a wide temperature range and is suitable for emergency braking of a high-speed railway train under the high-speed and heavy-load conditions by taking iron powder as a brake pad material substrate and accurately designing and regulating the type and content of a lubricating component.
Based on the above concept, we invented an iron-based powder metallurgy brake pad which has friction coefficient stability in a wide temperature range and is matched with a carbon ceramic disc. In the preparation process of the brake pad, a multi-component solid lubricant is designed, and two components capable of playing a lubricating role at different temperatures are added simultaneously, wherein the low-temperature lubricating component and the high-temperature lubricating component are included, the temperature of the low-temperature lubricating component which mainly plays a role is not more than 500 ℃, and the temperature of the high-temperature lubricating component which mainly plays a role can reach 800 ℃ or even higher. The method specifically comprises the following steps: the low temperature lubricating component comprises graphite, and WS2，WSe2One of FeS; the high-temperature lubricating component is fluoride (CaF)2，BaF2，LaF3，CeF3) And oxide (MoO)3，WO3，ZnO，B2O3，V2O3，Re2O3) To (3) is provided. The crystals of the low-temperature lubricating component are of a layered structure, and a crystal plane which is easy to slip under the action of shearing force exists. The graphite has good lubricating effect between room temperature and the oxidation temperature of 425 ℃, has good interface combination with an iron matrix, but has lower mechanical strength and is easy to break and peel off when being used alone under the condition of high stress braking; WS2，WSe2FeS can have a lubricating effect at a temperature lower than 500 ℃, has high mechanical strength and good interface bonding with an iron matrix, and can generate a good lubricating effect at a low temperature when used in combination with graphite; fluoride exhibits brittleness at low temperatures and limited lubricity. But at high temperatures the brittle to plastic transition and the plastic particles can coat the friction surfaces to produce a lubricating effect, such as CaF2Can still be used at high temperature of 1000 DEG CEffective lubrication effect is generated on metal and ceramic; the lubricating effect of oxides is mainly caused by the tendency of oxide particles to deform or shear at high temperatures, and there are two fundamental reasons for this phenomenon, one of which is that the ability of the oxides to form low melting or shear-prone complex compounds increases with increasing differences in ionic potential. Because anions can better shield or mask cations and make them less reactive with surrounding cations, they tend to have low hardness and shear strength at high temperatures. The second reason is that as the difference in ion potential increases, the ability or affinity of ions to form highly stable compounds increases with little exertion of chemical or electrostatic attraction. Lower attraction forces between the sliding surfaces are indicative of lower adhesion at the sliding contact interface, thus achieving low friction. In addition, when fluoride and oxide are added as high temperature lubricating components, the particle size is matched to a nano-particle size. This is mainly because both of them have high brittleness at low temperature, and when the particle size is large, the carbon ceramic brake disc is abnormally scratched, so that the service life of the carbon ceramic brake disc is shortened. In addition, fluoride and oxide particles with nanometer particle diameters can participate in the formation of a friction film during friction, and play a role in strengthening the friction film, so that the stability of the friction film on the friction surface is promoted at low temperature, and the lubrication effect is further played on the friction surface at high temperature. The addition of more lubricating components can block the sintering process of the iron-based brake pad material, so that the porosity of the prepared brake pad material is increased, the iron-based brake pad is further sintered by using an oscillating pressure sintering mode, and the densification of the iron-based brake pad is greatly promoted. The iron-based brake pad with the wide temperature range friction coefficient stability is designed and prepared after the factors are comprehensively considered, and when the iron-based brake pad is matched with a carbon ceramic disc to form a brake pair, the iron-based brake pad has a stable friction coefficient during emergency braking under the high-speed and heavy-load conditions.
In order to realize the purpose of the invention, the following preparation technical scheme is adopted:
the powder metallurgy brake pad with stable friction coefficient in a wide temperature range is characterized by comprising the following components:
iron powder: 50-70 parts by weight, 45-75 μm; copper powder: 10-20 parts by weight, 13-25 μm; graphene: 0.1-1 weight parts, 0.01-0.1 μm; ferrochrome powder: 1-5 parts by weight, 50-200 μm; ferro-molybdenum alloy powder: 1-5 parts by weight, 50-200 μm; chromium powder: 1-5 parts by weight, 50-200 μm; molybdenum powder: 1-5 parts by weight, 50-200 μm; a low-temperature lubricating component: 5-15 parts by weight; high temperature lubrication component: 1-8 parts by weight.
Further, the low-temperature lubricating component contains flaky graphite with the granularity of 300-500 mu m, and the optimal content is 5-10 parts by weight.
Further, the low-temperature lubricating component also contains WS2，WSe2One of FeS, with a particle size of 48-75 μm, the optimum content being between 1 and 5 parts by weight.
Further, the high temperature lubricating component contains CaF2，BaF2，LaF3，CeF3The particle size of one of the above-mentioned materials is 0.05-0.5 micrometer, and its optimum content is 1-4 portions by weight.
Further, the high-temperature lubricating component also contains MoO3，WO3，ZnO，B2O3，V2O3，Re2O3The particle size of one of the above-mentioned materials is 0.05-0.5 micrometer, and its optimum content is 1-4 portions by weight.
The preparation method of the brake pad is characterized by comprising the following steps:
(1) weighing the raw material powder according to the weight parts;
(2) pouring the weighed raw material powder, except for graphene and nano-sized high-temperature lubricating component particles, into a double-cone mixer, continuously rotating a mixing cylinder to stir and mix the materials, spraying the graphene-nano-sized high-temperature lubricating component particle-ethanol dispersion liquid into a mist shape under the drive of high-pressure gas, and uniformly wrapping the dispersion liquid on the dispersed large-particle powder particles to finally obtain uniformly-mixed powder;
(3) cold-pressing and molding the uniformly mixed powder;
(4) sintering the cold blank in a bidirectional oscillation pressure sintering furnace;
(5) cooling to below 100 deg.C, taking out, and maintaining pressure oscillation during cooling process.
Further, in the step (2), the rotation speed of the mixing barrel is 120-.
Further, in the step (2), the graphene and the nano-sized high-temperature lubricating component particles are added into the ethanol together, and the adding amount is 0.5g/100ml-2g/100 ml. Mechanically stirring the solution for 1.5 hours in advance to fully disperse the graphene and the nano-sized high-temperature lubricating component particles in ethanol; and then spraying the graphene-ethanol dispersion liquid into a mist under the drive of high-pressure gas, and allowing the graphene-ethanol dispersion liquid to enter a mixing cylinder which rotates for 40-70 min.
Further, in the step (3), the pressure is 500-800MPa, and the pressure maintaining time is 50-130 s.
Further, in the step (4), the sintering temperature is 950-1050 ℃, the atmosphere is hydrogen-nitrogen mixed gas, and the temperature is kept for 40-100 min. During sintering, the bidirectional pressure is in 2-4MPa and the frequency of 2Hz generates sinusoidal oscillation.
The technical scheme of the invention has the following advantages:
1. the powder metallurgy brake pad with stable friction coefficient in wide temperature range simultaneously comprises a low-temperature lubricating component and a high-temperature lubricating component in a raw material formula. Wherein the low temperature lubricating component comprises graphite, and WS2、WSe2One of FeS and high-temperature lubricating component comprises CaF2、BaF2、LaF3、CeF3And MoO3、WO3、ZnO、B2O3、V2O3、Re2O3One kind of (1). The iron-based brake pad with stable friction coefficient in a wide temperature range can be prepared by regulating and controlling the types and components of the lubricating components, and the iron-based brake pad has high friction coefficient and low abrasion when being subjected to opposite-grinding braking with a carbon ceramic disc, and effectively solves the problems of friction coefficient reduction and brake pad abrasion caused by the rise of the temperature of a friction interface during emergency braking under the condition of high speed and heavy load under the damage to the carbon ceramic disc.
2. The preparation method of the brake pad comprises the steps of accurately weighing raw material powder, fully mixing and cold-pressing to form, sintering a cold-pressed blank under oscillating pressure, and cooling to obtain the iron-based brake pad with wide temperature range friction coefficient stability. In the material mixing process, for graphene with small particle size and a high-temperature lubricating component, a solution spraying mode is adopted for mixing, so that nano powder is prevented from agglomerating, the nano powder is more uniformly distributed in a matrix of the iron-based brake pad, and the material mixing time can be shortened. Considering that the sintering of the brake pad material is difficult due to excessive components in the iron matrix, the pressure oscillates at a certain frequency in the sintering process, and the powder can move to fill the pores, so that the uniformity and the density of the prepared brake pad material are greatly improved. The structure, the structure and the mechanical property of the brake pad material are better and stable, and similar substances can be provided in the matrix for lubrication after the lubricating substances on the friction surface are consumed in the friction process. Therefore, in the continuous emergency braking process of the high-speed train, the friction pair consisting of the iron-based brake pad and the carbon ceramic disc always has the characteristics of stable friction coefficient and low abrasion.
Drawings
Fig. 1 is a schematic diagram of graphene spray mixing:
wherein 1, a double-cone mixer bracket; 2. a mixing barrel; 3. a vacuum pump; 4. controlling a first valve; 5. a pressure gauge; 6. a liquid container (for holding solvent before spraying); 7. a mechanical mixer; 8. a liquid mixing vessel (for raw liquid mixing); 9. a mechanical mixer holder; 10. a mechanical mixing blade; 11. a high pressure gas cylinder; 12. a second control valve; 13. controlling a valve III; 14. and controlling a valve IV.
FIG. 2. variation with time of instantaneous coefficient of friction at 600 ℃ and 800 ℃ for 600s of sliding friction at a speed of 1m/s for example 1 and comparative example 1, respectively.
Detailed Description
The graphene spraying and mixing steps shown in fig. 1 are as follows: when the test is started, ethanol, nano graphene and a high-temperature lubricating component are placed in the container 8, and the container 10 is continuously stirred; closing the first valve 4 and the second valve 12, opening the third valve 13 and the fourth valve 14, evacuating by the vacuum pump 3, and allowing the liquid in the container 8 to flow into the container 6 under the action of atmospheric pressure; immediately thereafter, valve two 13 and valve four 14 are closed, valve one 4 and valve two 12 are opened, and the liquid in 6 is sprayed into mixing drum 2 under the action of the high-pressure gas.
Example 1:
1. a powder metallurgy brake pad with stable friction coefficient in wide temperature range comprises the following components:
iron powder: 50 parts by weight; copper powder: 18 parts by weight; graphene: 0.3 part by weight; chromium powder: 4 parts by weight; molybdenum powder: 4 parts by weight; ferrochrome powder: 3 parts by weight; ferro-molybdenum alloy powder: 3 parts by weight; flake graphite, 6 parts by weight, particle size 350 μm; FeS powder: 5 parts by weight, particle size 58 μm; CaF2Powder: 3.2 parts by weight, particle size 0.1 μm; MoO3Powder, 3.5 parts by weight, particle size 0.1 μm.
2. Pouring the weighed raw material powder, except the graphene and the nano-sized high-temperature lubricating component particles, into a double-cone mixer, continuously rotating a mixing cylinder to turn over and mix the materials, wherein the rotating speed is 150 revolutions per minute, and mixing the powder particles in the mixing cylinder; adding graphene and nano-sized high-temperature lubricating component particles into ethanol, wherein the adding amount is 1g/100 ml. Mechanically stirring the solution for 1.5 hours to fully disperse the graphene and the nano-sized high-temperature lubricating component particles in ethanol to form a dispersion liquid; then spraying the dispersion liquid into a mist under the drive of high-pressure gas, feeding the mist into a mixing cylinder which rotates for 50min, uniformly wrapping the graphene and the small-particle-size high-temperature lubricating component on the large-particle-size raw material powder particles mixed in the mixing cylinder, and mixing for 3 hours to obtain uniformly mixed composite powder;
3. cold-pressing the uniformly mixed powder for forming, wherein the pressure is 600MPa, and the pressure maintaining time is 120 s;
4. and sintering the cold blank in a bidirectional oscillation pressure sintering furnace, heating to 1050 ℃, sintering in a hydrogen-nitrogen mixed gas, and keeping the temperature for 70 min. In the sintering process, the bidirectional pressure is between 2 and 4MPa and the sine oscillation is generated at the frequency of 2 Hz;
5. cooling to below 100 deg.C, taking out, and maintaining pressure oscillation during cooling process.
Example 2:
1. a powder metallurgy brake pad with stable friction coefficient in wide temperature range comprises the following components:
iron powder: 55 parts by weight; copper powder: 15 parts by weight; graphene: 0.5 part by weight; chromium powder: 3 parts by weight; molybdenum powder: 3 parts by weight; ferrochrome powder: 3 parts by weight; ferro-molybdenum alloy powder: 3 parts by weight; 7 parts by weight of flaky graphite, and the particle size is 380 μm; WS powder: 6 parts by weight, particle size 62 μm; BaF2Powder: 2 parts by weight, particle size 0.15 μm; ZnO (zinc oxide)32.5 parts by weight of powder, and the particle size is 0.15 mu m.
2. Pouring the weighed raw material powder, except the graphene and the nano-sized high-temperature lubricating component particles, into a double-cone mixer, continuously rotating a mixing cylinder to turn over and mix the materials at a rotating speed of 140 revolutions per minute, and mixing the powder particles in the mixing cylinder; adding graphene and nano-sized high-temperature lubricating component particles into ethanol, wherein the adding amount is 0.8g/100 ml. Mechanically stirring the solution for 1.5h to fully disperse the graphene and the nano-sized high-temperature lubricating component particles in ethanol to form a dispersion liquid; then spraying the dispersion liquid into a mist form under the drive of high-pressure gas, allowing the dispersion liquid to enter a mixing cylinder which rotates for 60min, uniformly wrapping the graphene and the small-particle-size high-temperature lubricating component on the large-particle-size raw material powder particles mixed in the mixing cylinder, and mixing for 3.5 hours to obtain uniformly mixed composite powder;
3. cold-pressing the uniformly mixed powder for forming, wherein the pressure is 650MPa, and the pressure maintaining time is 100 s;
4. and sintering the cold blank in a bidirectional oscillation pressure sintering furnace, heating to 1030 ℃, sintering in a hydrogen-nitrogen mixed gas, and keeping the temperature for 90 min. In the sintering process, the bidirectional pressure is between 2 and 4MPa and the sine oscillation is generated at the frequency of 2 Hz;
5. cooling to below 100 deg.C, taking out, and maintaining pressure oscillation during cooling process.
Example 3:
1. a powder metallurgy brake pad with stable friction coefficient in wide temperature range comprises the following components:
iron powder: 60 parts by weight; copper powder: 12 parts by weight; graphene: 0.7 part by weight; chromium powder: 3 parts by weight; molybdenum powder: 3 parts by weight; ferrochrome powder: 2 parts by weight; ferro-molybdenum alloy powder: 2 parts by weight; 8 parts by weight of flaky graphite, the particle diameter of which is 425 μm; WS powder: 5 parts by weight, particle size 62 μm; LaF3Powder: 2.3 parts by weight, particle size 0.2 μm; b is2O32 parts by weight of powder, the particle size is 0.2 mu m.
2. Pouring the weighed raw material powder, except the graphene and the nano-sized high-temperature lubricating component particles, into a double-cone mixer, continuously rotating a mixing cylinder to turn over and mix the materials, wherein the rotating speed is 160 revolutions per minute, and mixing the powder particles in the mixing cylinder; adding graphene and nano-sized high-temperature lubricating component particles into ethanol, wherein the adding amount is 1.2g/100 ml. Mechanically stirring the solution for 1.5h to fully disperse the graphene and the nano-sized high-temperature lubricating component particles in ethanol to form a dispersion liquid; then spraying the dispersion liquid into a mist under the drive of high-pressure gas, feeding the mist into a mixing cylinder which rotates for 65min, uniformly wrapping the graphene and the small-particle-size high-temperature lubricating component on the large-particle-size raw material powder particles mixed in the mixing cylinder, and mixing for 4 hours to obtain uniformly mixed composite powder;
3. cold-pressing the uniformly mixed powder for forming, wherein the pressure is 700MPa, and the pressure maintaining time is 90 s;
4. and sintering the cold blank in a bidirectional oscillation pressure sintering furnace, heating to 1010 ℃, sintering in a hydrogen-nitrogen mixed gas, and keeping the temperature for 60 min. In the sintering process, the bidirectional pressure is between 2 and 4MPa and the sine oscillation is generated at the frequency of 2 Hz;
5. cooling to below 100 deg.C, taking out, and maintaining pressure oscillation during cooling process.
Example 4:
1. a powder metallurgy brake pad with stable friction coefficient in wide temperature range comprises the following components:
iron powder: 65 parts by weight; copper powder: 8 parts by weight; graphene: 0.8 part by weight; chromium powder: 3 parts by weight; molybdenum powder: 3 parts by weight; ferrochrome powder: 2 parts by weight; ferro-molybdenum alloy powder: 2 parts by weight; 7 parts by weight of flaky graphite, the particle diameter of which is 500 μm; WSe2Powder: 4 parts by weight, particle size 53 μm; CeF3Powder: 1.5 parts by weight, particle size0.3μm；WO32.7 parts by weight of powder, and the particle size is 0.3 mu m.
2. Pouring the weighed raw material powder, except the graphene and the nano-sized high-temperature lubricating component particles, into a double-cone mixer, continuously rotating a mixing cylinder to turn over and mix the materials, wherein the rotating speed is 170 revolutions per minute, and mixing the powder particles in the mixing cylinder; adding graphene and nano-sized high-temperature lubricating component particles into ethanol, wherein the adding amount is 1.5g/100 ml. Mechanically stirring the solution for 1.5h to fully disperse the graphene and the nano-sized high-temperature lubricating component particles in ethanol to form a dispersion liquid; then spraying the dispersion liquid into a mist under the drive of high-pressure gas, feeding the mist into a mixing cylinder which rotates for 70min, uniformly wrapping the graphene and the small-particle-size high-temperature lubricating component on the large-particle-size raw material powder particles mixed in the mixing cylinder, and mixing for 4.5 hours to obtain uniformly mixed composite powder;
3. cold-pressing the uniformly mixed powder for forming, wherein the pressure is 750MPa, and the pressure maintaining time is 80 s;
4. and sintering the cold blank in a bidirectional oscillation pressure sintering furnace, heating to 1000 ℃, sintering in a hydrogen-nitrogen mixed gas, and keeping the temperature for 80 min. In the sintering process, the bidirectional pressure is between 2 and 4MPa and the sine oscillation is generated at the frequency of 2 Hz;
5. cooling to below 100 deg.C, taking out, and maintaining pressure oscillation during cooling process.
Comparative example 1:
1. an iron-based powder metallurgy brake pad without high-temperature lubricating components comprises the following components:
iron powder: 59.5 parts by weight; copper powder: 15 parts by weight; graphene: 0.5 part by weight; chromium powder: 3 parts by weight; molybdenum powder: 3 parts by weight; ferrochrome powder: 3 parts by weight; ferro-molybdenum alloy powder: 3 parts by weight; 7 parts by weight of flaky graphite, and the particle size is 380 μm; WS powder: 6 parts by weight, particle size 62 μm.
2. Pouring the weighed raw material powder, except the graphene and the nano-sized high-temperature lubricating component particles, into a double-cone mixer, continuously rotating a mixing cylinder to turn over and mix the materials, wherein the rotating speed is 150 revolutions per minute, and mixing the powder particles in the mixing cylinder; adding graphene and nano-sized high-temperature lubricating component particles into ethanol, wherein the adding amount is 1g/100 ml. Mechanically stirring the solution for 1.5 hours to fully disperse the graphene and the nano-sized high-temperature lubricating component particles in ethanol to form a dispersion liquid; then spraying the dispersion liquid into a mist under the drive of high-pressure gas, feeding the mist into a mixing cylinder which rotates for 50min, uniformly wrapping the graphene and the small-particle-size high-temperature lubricating component on the large-particle-size raw material powder particles mixed in the mixing cylinder, and mixing for 3 hours to obtain uniformly mixed composite powder;
3. cold-pressing the uniformly mixed powder for forming, wherein the pressure is 600MPa, and the pressure maintaining time is 120 s;
4. and sintering the cold blank in a bidirectional oscillation pressure sintering furnace, heating to 1050 ℃, sintering in a hydrogen-nitrogen mixed gas, and keeping the temperature for 70 min. In the sintering process, the bidirectional pressure is between 2 and 4MPa and the sine oscillation is generated at the frequency of 2 Hz;
5. cooling to below 100 deg.C, taking out, and maintaining pressure oscillation during cooling process.
The physical properties prepared in examples 1 to 4 and comparative example 1 are shown in Table 1:
TABLE 1 physical Property parameters of the above examples 1 to 4 and comparative example 1
As can be seen from Table 1, the physical properties of comparative examples 1-4 are similar, and the compactness of comparative example 1 is slightly higher, due to the sintering inhibition caused by the addition of nano-sized particles of the high-temperature lubricating component in examples 1-4.
The friction coefficient and the amount of wear measured in five consecutive brakes at 350km/h on a brake tester are shown in Table 2 below (model number of machine: MM-1000, initial rotational speed: 7400r/min, moment of inertia: 0.4 kg-2And applying pressure: 0.48 MPa):
TABLE 2 average coefficient of friction and total wear (cm) after braking for the brake lining of each of examples 1-4 and comparative example 1 described above3/MJ)
As can be seen from Table 2 above, the coefficient of friction of the materials of examples 1-4 can be maintained between 0.4 and 0.45 during continuous high speed emergency braking, and is stable without significant high speed high temperature induced coefficient of friction decay. The wear loss of the iron-based brake pad prepared in examples 1-4 of the present invention is significantly lower than that of comparative example 1 in terms of the total wear loss, which indicates that the pad materials prepared in examples 1-4 have excellent wear resistance.
As can be seen from fig. 2, at 600 ℃, the fluctuation of the instantaneous friction coefficient was small for both example 1 and comparative example 1, and the instantaneous friction coefficient value for example 1 was slightly higher, which is caused by the increased friction coefficient of the hard phase at this time for the high-temperature lubricating unit. The instantaneous friction coefficient fluctuation of comparative example 1 increased drastically at 800 c, fluctuating between about 0 and 0.5, while the instantaneous friction coefficient fluctuation of example 2, although increasing at 600 c, was still small in magnitude and still large in coefficient of friction value. This shows that the addition of the high-temperature lubricating component and the low-temperature lubricating component enables the iron-based brake pad material to realize the stability of the friction coefficient in a wide temperature range.
While the present invention has been described by way of example, and not by way of limitation, reference is made to the description of the invention, other variations of the disclosed embodiments and their equivalents should fall within the scope of the invention as defined by the claims.
Claims (6)
1. The powder metallurgy brake pad with stable friction coefficient in a wide temperature range is characterized by comprising the following components:
iron powder: 50-70 parts by weight, 45-75 μm; copper powder: 10-20 parts by weight, 13-25 μm; graphene: 0.1-1 weight parts, 0.01-0.1 μm; ferrochrome powder: 1-5 parts by weight, 50-200 μm; ferro-molybdenum alloy powder: 1-5 parts by weight, 50-200 μm; chromium powder: 1-5 parts by weight, 50-200 μm; molybdenum powder: 1-5 parts by weight, 50-200 μm; a low-temperature lubricating component: 5-15 parts by weight; high-temperature lubricating component: 1-8 parts by weight;
the low-temperature lubricating component contains flaky graphite with the granularity of 300-500 mu m;
the low-temperature lubricating component also contains WS2，WSe2One of FeS with the granularity of 48-75 μm;
the high-temperature lubricating component contains CaF2，BaF2，LaF3，CeF3One of (1), the particle size is 0.05-0.5 μm;
the high-temperature lubricating component also contains MoO3，WO3，ZnO，B2O3，V2O3，Re2O3One of (1), the particle size is 0.05-0.5 μm;
the preparation method of the brake pad comprises the following steps:
(1) weighing the raw material powder according to the weight parts;
(2) pouring the weighed raw material powder, except for graphene and nano-sized high-temperature lubricating component particles, into a double-cone mixer, continuously rotating a mixing cylinder to stir and mix the materials, spraying the graphene-nano-sized high-temperature lubricating component particle-ethanol dispersion liquid into a mist shape under the drive of high-pressure gas, and uniformly wrapping the dispersion liquid on the dispersed large-particle powder particles to finally obtain uniformly-mixed powder;
(3) cold-pressing and molding the uniformly mixed powder;
(4) sintering the cold blank in a bidirectional oscillation pressure sintering furnace;
(5) cooling to below 100 deg.C, taking out, and maintaining pressure oscillation during cooling process.
2. A method for preparing a brake pad according to claim 1, comprising the steps of:
(1) weighing the raw material powder according to the weight parts;
(2) pouring the weighed raw material powder, except for graphene and nano-sized high-temperature lubricating component particles, into a double-cone mixer, continuously rotating a mixing cylinder to stir and mix the materials, spraying the graphene-nano-sized high-temperature lubricating component particle-ethanol dispersion liquid into a mist shape under the drive of high-pressure gas, and uniformly wrapping the dispersion liquid on the dispersed large-particle powder particles to finally obtain uniformly-mixed powder;
(3) cold-pressing and molding the uniformly mixed powder;
(4) sintering the cold blank in a bidirectional oscillation pressure sintering furnace;
(5) cooling to below 100 deg.C, taking out, and maintaining pressure oscillation during cooling process.
3. The method for preparing a brake pad according to claim 2, wherein in the step (2), the rotation speed of the mixing barrel is 120-.
4. The method for preparing the brake pad according to claim 2, wherein in the step (2), the graphene and the nano-sized high-temperature lubricating component particles are added into the ethanol together in an amount of 0.5g/100ml to 2g/100 ml; mechanically stirring the solution for 1.5 hours in advance to fully disperse the graphene and the nano-sized high-temperature lubricating component particles in ethanol; and then spraying the graphene-ethanol dispersion liquid into a mist under the drive of high-pressure gas, and allowing the graphene-ethanol dispersion liquid to enter a mixing cylinder which rotates for 40-70 min.
5. The method for preparing a brake pad according to claim 2, wherein in the step (3), the pressure is 500-800MPa, and the dwell time is 50-130 s.
6. The method for preparing the brake pad according to claim 2, wherein in the step (4), the sintering temperature is 950-1050 ℃, the atmosphere is hydrogen-nitrogen mixed gas, and the temperature is kept for 40-100 min; during sintering, the bidirectional pressure is in 2-4MPa and the sinusoidal oscillation is generated at the frequency of 2 Hz.
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