CN109385586B

CN109385586B - Powder metallurgy friction material and preparation method of friction block

Info

Publication number: CN109385586B
Application number: CN201811357250.5A
Authority: CN
Inventors: 燕青芝; 彭韬; 张肖璐
Original assignee: University of Science and Technology Beijing USTB
Current assignee: University of Science and Technology Beijing USTB
Priority date: 2018-11-15
Filing date: 2018-11-15
Publication date: 2020-07-10
Anticipated expiration: 2038-11-15
Also published as: CN109385586A

Abstract

The invention provides a low-abrasion and high-stability powder metallurgy friction material for a high-speed train brake pad and a preparation method of a friction block, and belongs to the technical field of powder metallurgy friction materials. The formula of the powder metallurgy friction material comprises, by weight, 40-65% of copper powder, 16-35% of iron powder, 5-15% of ferrochrome powder, 0.6-6% of ceramic fiber, 0.5-3% of chromium powder, 7-15% of graphite, 1-6% of molybdenum disulfide and 0.5-4% of polyvinyl alcohol. The preparation method comprises the following steps: step 1, mixing materials according to weight percentage and uniformly mixing to obtain mixed powder; step 2, pressing the mixed powder obtained in the step 1 with a friction block back plate to obtain a biscuit; and 3, preparing the biscuit obtained in the step 2 into the required friction material through a high-temperature sintering process. The brake pad prepared from the friction material has the advantages of high and stable friction coefficient, small abrasion loss, long service life and the like under the condition of high-speed braking.

Description

Powder metallurgy friction material and preparation method of friction block

Technical Field

The invention relates to the field of powder metallurgy friction materials, in particular to a low-abrasion high-stability powder metallurgy friction material for a high-speed train brake pad and a preparation method of a friction block.

Background

The friction material is a structure-function composite material which converts the kinetic energy of a moving object into heat energy by utilizing the friction force generated by the contact of the friction material and a dual material, and is one of indispensable materials in brakes, clutches and friction transmission devices of various mechanical equipment. The friction stability, wear resistance, heat resistance, fatigue resistance and the like of the equipment determine whether the equipment can stably and safely operate.

With the increasing frequency of the movement of population, economy and production elements, the speed of railway transportation is also required to be higher and higher. The prior polymer synthetic material used for the speed per hour lower than 250km/h can not meet the requirement of vehicles with higher speed due to low strength, poor heat resistance and serious heat fadingThe requirement for vehicle braking. At present at the speed per hour>The brake pad adopted on the high-speed motor train unit of 250km/h is mainly a copper-based powder metallurgy friction material with high heat conductivity, good heat resistance and high friction coefficient. The base body of the material is mainly copper and is supplemented with a small amount of iron, so that the requirements on heat conductivity and strength can be better considered; to ensure that sufficient engagement resistance is provided, the material often also includes a certain amount of hard particulate component, such as Al₂O₃、SiO₂、Si₃N₄TiC, etc.; in addition, in order to ensure the stable friction process and reduce the material abrasion, a proper amount of graphite, molybdenum disulfide and other lubricating components can be added into the material.

However, in practice, the wear of the currently commercial copper-based powder metallurgy friction material during braking under the condition of the speed per hour being more than 250km/h can be changed from a slight oxidation wear to a severe delamination wear mechanism. The reason for this transformation is that, due to the poor wettability of the ceramic/graphite particles and the copper matrix, there are many defects such as pores or cracks at the phase interface, which develop into delamination fatigue cracks under the cyclic action of severe frictional thermal stress and frictional shear stress during high-speed braking, and these cracks propagate and propagate continuously, resulting in severe wear of the material. Since the occurrence of such wear causes a significant destruction of the near-surface structure of the material, the friction stability is often also reduced with a decline in the friction coefficient of the material. And with the extension of service time, the strength and the friction performance of the material are continuously attenuated, and compared with a brand new state, the friction coefficient is greatly reduced, the abrasion loss is increased, and the braking efficiency is low.

Therefore, how to improve the formula and the preparation process of the existing copper-based powder metallurgy material to overcome the above disadvantages is an important issue to be solved in the field.

Disclosure of Invention

The invention aims to solve the problems of reduced braking stability and deteriorated abrasion of the conventional copper-based powder metallurgy brake pad under high-speed and high-temperature conditions, and further provides a brake pad material with stable friction performance and low abrasion under the high-speed condition and a preparation technology thereof.

According to the invention, 0.6-6% by mass of ceramic fiber is introduced into the existing powder metallurgy brake pad raw material system to replace Al originally used in the material₂O₃、SiO₂、Si₃N₄And TiC and other granular ceramic phases. Because the ceramic fiber is fibrous and has larger length-diameter ratio, fatigue delaminating cracks under the high-speed braking condition can deflect, thereby improving the toughness of the material, inhibiting the initiation and the expansion of delaminating cracks and thermal fatigue cracks and overcoming the problems of serious delaminating abrasion and braking force recession of the existing copper-based powder metallurgy brake pad under the high-speed braking condition.

The technical scheme adopted by the invention comprises the following steps:

a powder metallurgy friction material is prepared from the following components in percentage by weight: 40-65% of copper powder, 16-35% of iron powder, 5-15% of ferrochrome powder, 0.6-6% of ceramic fiber, 0.5-3% of chromium powder, 7-15% of graphite, 1-6% of molybdenum disulfide and 0.5-4% of polyvinyl alcohol.

Further, the ceramic fibers include, but are not limited to, high alumina aluminosilicate fibers, ordinary alumina silicate fibers, polycrystalline alumina fibers, ZrO-containing fibers₂、B₂O₃Or Cr₂O₂Alumina silicate fiber, SiO 2-CaO-MgO-based ceramic fiber, forsterite fiber, or special oxide fiber.

Further, the ceramic fiber is a sodium titanate whisker or a potassium titanate whisker. The titanium contained in the sodium titanate whisker or the potassium titanate whisker has strong affinity with carbon atoms in graphite, has good wettability with a copper matrix, and is combined with the fiber characteristics of the sodium titanate whisker or the potassium titanate whisker, so that the interface combination can be improved, the interface defect can be reduced, the number of heterogeneous interfaces contained in the material can be reduced, the toughness of the material can be improved, and the delamination crack can be inhibited.

Further, the length of the sodium titanate whisker or the potassium titanate whisker is 20-100 μm, and the length-diameter ratio is 5-10: 1.

if the length of the sodium titanate whisker or the potassium titanate whisker is too short, the improvement effect on the toughness, the wear resistance, the anti-peeling crack and the like of the powder metallurgy friction body is not obvious enough, and if the length of the sodium titanate whisker or the potassium titanate whisker is too long, the sodium titanate whisker or the potassium titanate whisker is easy to twine and disperse during material mixing and pressing to form a blank, so that the distribution of each component in the powder metallurgy friction body is very uneven, and the performance of the powder metallurgy friction body is influenced.

Further, the sodium titanate whisker or the potassium titanate whisker accounts for 0.6-1.5%, 1.5-3% or 3-6% of the powder metallurgy friction material by mass percent.

When the mass percentage of the sodium titanate whisker or the potassium titanate whisker is 0.6-1.5%, the prepared metallurgical powder friction body has obviously excellent performance in the aspect of decay resistance.

When the mass percentage of the sodium titanate whisker or the potassium titanate whisker is 1.5 to 3 percent, the prepared metallurgical powder friction body has obviously better performance in the aspect of wear resistance.

When the mass percentage of the sodium titanate whisker or the potassium titanate whisker is 3 to 6 percent, the performance of the prepared metallurgical powder friction body in the aspects of strength and toughness is obviously superior.

Further, the copper source of the copper powder is one or a mixture of water atomized copper powder and electrolytic copper powder, the particle size of the water atomized copper powder and the particle size of the electrolytic copper powder are 1-32 mu m, and the particle size of the ferrochrome powder is 10-300 mu m.

Further, the graphite is one or a mixture of two of artificial graphite and flake graphite, and the particle size of the artificial graphite and the flake graphite is 60-600 mu m.

The particle sizes of the copper powder, the ferrochrome powder and the graphite are all larger, compared with granular materials, the fiber-shaped material can improve the toughness of the material, inhibit the initiation and the propagation of stripping cracks and thermal fatigue cracks, and overcome the problems of serious stripping abrasion and braking force recession of the existing copper-based powder metallurgy brake pad under the high-speed braking condition.

The invention also provides a preparation method of the powder metallurgy friction block, which comprises the following steps:

step 1: weighing and proportioning the materials according to the formula of the powder metallurgy friction material of any one embodiment, and uniformly mixing to obtain mixed powder;

step 2, pressing the mixed powder obtained in the step 1 with a friction block back plate to obtain a biscuit;

and 3, preparing the biscuit obtained in the step 2 into the required friction material through a high-temperature sintering process.

However, some ceramic fibers, particularly sodium titanate whiskers or potassium titanate whiskers, tend to be agglomerated and unevenly dispersed because of their relatively low specific gravity. Therefore, the invention also overcomes the problem of agglomeration and distribution of the sodium titanate whiskers or the potassium titanate whiskers in the matrix through a proper mixing process.

Thus, further, the step 1 specifically includes: the components except the ceramic fiber and the graphite in the formula are primarily mixed by a high-speed stirrer, and then the ceramic fiber and the graphite are added and uniformly mixed in a ball-milling mixer to obtain mixed powder.

Further, when mixing in the ball-milling blendor, in order to ensure that the sodium titanate whisker or the potassium titanate whisker is distributed in the matrix as much as possible more evenly on the premise of not damaging the fiber structure, the concrete mixing parameters are as follows: the ball material ratio is as follows: 1: 3-10; the grinding ball is made of the following materials: a steel ball; the ball milling medium is as follows: ethanol; the atmosphere is: ar; the ball milling time is 2-4h, and the rotating speed is 50-200 rpm. Under the condition of the material mixing, the sodium titanate whisker or the potassium titanate whisker can be distributed in the matrix as uniformly as possible on the premise of not damaging the fiber structure.

Further, the pressure in the step 2 is 100-700 MPa; the high-temperature sintering process in the step 3 specifically comprises the following steps: controlling the temperature of the sintering furnace at 850-.

The technical scheme of the invention has the following beneficial effects:

1. compared with the brake pad prepared by the copper-based powder metallurgy, the brake pad has higher toughness, better high-temperature stability and better friction stability. The powder metallurgy friction material has the advantages of high and stable friction coefficient, small abrasion loss, long service life and the like under the condition of high-speed braking.

2. The ceramic fiber is adopted to replace various ceramic particles adopted in the conventional powder metallurgy brake pad, so that fatigue cracks are promoted to continuously deflect during expansion, the expansion path is prolonged, and the toughness of the material is improved; in addition, the number of heterogeneous interfaces contained in the material is obviously reduced, so that the material composition is simpler and purer.

3. The invention uses the sodium titanate whisker or the potassium titanate whisker, on one hand, the sodium titanate whisker or the potassium titanate whisker has the characteristics of high elastic modulus, high specific strength, good high-temperature stability, high hardness and the like, and is very suitable for the working environment with ultrahigh friction strength such as high-speed rails, on the other hand, titanium contained in the sodium titanate whisker or the potassium titanate whisker has stronger affinity with carbon atoms in graphite, and the fiber characteristics of the sodium titanate whisker or the potassium titanate whisker are combined, so that the interface combination can be improved, the interface defect can be reduced, the number of heterogeneous interfaces contained in the material can be reduced, the toughness of the material can be improved, and the delamination crack can be inhibited.

4. The invention adopts sodium titanate whisker or potassium titanate whisker with proper length and length-diameter ratio, so that the prepared metallurgical powder friction body has the most excellent wear resistance and anti-stripping crack characteristic. The invention also adopts a ball milling premixing process, and solves the problems of agglomeration and uneven distribution in the matrix caused by light specific gravity of the sodium titanate whisker or the potassium titanate whisker on the premise of ensuring that the fiber structure is not damaged.

Drawings

FIG. 1 is a fracture micro-topography of the powder metallurgy friction material of example 1.

FIG. 2 is a typical friction curve diagram of the friction material A in the embodiment 1 at the braking time of 300-380 km/h.

FIG. 3 is a typical friction curve diagram of the friction material B in the embodiment 3 at the braking time of 300-380 km/h.

FIG. 4 is a typical friction curve diagram of the friction material C in the embodiment 5 at the braking time of 300-380 km/h.

FIG. 5 is a typical friction curve diagram of the friction material in the embodiment 2 at the braking time of 300-380 km/h.

FIG. 6 is a typical friction curve diagram of the friction material in the embodiment 4 at the braking time of 300-380 km/h.

FIG. 7 is a typical friction curve diagram of the friction material in the embodiment 6 at the braking time of 300-380 km/h.

FIG. 8 is a schematic diagram of a typical friction curve of the friction material D in comparative example 1 at 300-380km/h braking.

FIG. 9 is a schematic diagram of a typical friction curve of the friction material D in comparative example 2 at 300-380km/h braking.

FIG. 10 is a schematic diagram of a typical friction curve of the friction material D in comparative example 3 at 300-380km/h braking.

FIG. 11 is a schematic diagram of a typical friction curve of the friction material D in the comparative example 4 at 300-380km/h braking.

FIG. 12 is a schematic diagram showing a typical friction curve of the friction material D in the comparative example 5 at 300-380km/h braking.

FIG. 13 is a graph showing the results of measuring the average friction coefficient at different initial braking speeds of the friction materials A to D in examples 1, 3, 5 and comparative example 1.

FIG. 14 is a graph showing the results of measuring the wear rates of the friction materials A to D in examples 1, 3, and 5 and comparative example 1 at different initial braking speeds.

Detailed Description

In order to make the technical problems, technical solutions and advantages of the present invention more apparent, the following detailed description is given with reference to the accompanying drawings and specific embodiments.

Example 1

In this embodiment, the low-wear and high-stability powder metallurgy friction material comprises the following components in parts by weight: 54% of copper powder, 22% of iron powder, 10% of ferrochrome powder, 1% of sodium titanate whisker, 0.5% of chromium powder, 9% of graphite, 2.5% of molybdenum disulfide and 1% of polyvinyl alcohol. Wherein the length of the sodium titanate whisker is 50-80 μm, and the length-diameter ratio is 6-8: 1.

And carrying out ball milling and mixing on the metal powder (copper, iron and chromium) and the crystal whisker in the powder according to weight percentage to obtain mixed powder 1. The ball material ratio is as follows: 1: 3; the grinding ball is made of the following materials: a steel ball; the ball milling medium is as follows: ethanol; the atmosphere is: ar; the ball milling time is 2h, and the rotating speed is 200 rpm. And then, mixing the mixed powder 1 and the rest of the powder according to the weight percentage, and placing the mixture into a ball milling mixer to be uniformly mixed to obtain mixed powder 2. Sodium titanate/potassium, pressing the obtained mixed powder 2 with a friction block back plate under the pressure of 600MPa to obtain a biscuit; and sintering the biscuit for 1h by a sintering process at 980 ℃ under the protection of a nitrogen-hydrogen mixed atmosphere (gas flow ratio: nitrogen: hydrogen: 3:1), and cooling to room temperature along with the furnace to obtain the friction material A.

The fracture morphology of the friction material obtained in the embodiment is shown in fig. 1, and fig. 1 includes sodium titanate whisker or potassium titanate whisker 1, so that as can be seen from fig. 1, the interface bonding is improved, and the interface defects are reduced.

Example 2

In this example, the percentage of potassium titanate whiskers was adjusted to 1.5% based on example 1. The paint specifically comprises the following components in parts by weight: 53% of copper powder, 22% of iron powder, 10% of ferrochrome powder, 1.5% of sodium titanate whisker, 1% of chromium powder, 9% of graphite, 2.5% of molybdenum disulfide and 1% of polyvinyl alcohol. The other operations were the same as in example 1.

Example 3

In this embodiment, the low-wear and high-stability powder metallurgy friction material comprises the following components in parts by weight: 59% of copper powder, 18% of iron powder, 6% of ferrochrome powder, 2% of potassium titanate whisker, 1% of chromium powder, 11% of graphite, 1% of molybdenum disulfide and 2% of polyvinyl alcohol. Wherein the length of the potassium titanate whisker is 80-100 mu m, and the length-diameter ratio is 8-10: 1.

And carrying out ball milling and mixing on the metal powder (copper, iron and chromium) and the crystal whisker in the powder according to weight percentage to obtain mixed powder 1. The ball material ratio is as follows: 1: 7; the grinding ball is made of the following materials: a steel ball; the ball milling medium is as follows: ethanol; the atmosphere is: ar; the ball milling time is 3h, and the rotating speed is 120 rpm. And then, mixing the mixed powder 1 and the rest of the powder according to the weight percentage, and placing the mixture into a ball milling mixer to be uniformly mixed to obtain mixed powder 2. Sodium titanate/potassium, pressing the obtained mixed powder 2 with a friction block back plate under the pressure of 400MPa to obtain a biscuit; and sintering the biscuit for 1.5h by a sintering process at 900 ℃ and a heating rate of 3 ℃/min under the protection of a nitrogen-hydrogen mixed atmosphere (gas flow ratio: nitrogen: hydrogen is 4:1), and cooling to room temperature along with a furnace to obtain the friction material B.

Example 4

In this example, the percentage of potassium titanate whiskers was adjusted to 3% based on example 3. The paint specifically comprises the following components in parts by weight: 58% of copper powder, 18% of iron powder, 6% of ferrochrome powder, 3% of potassium titanate whisker, 1% of chromium powder, 11% of graphite, 1% of molybdenum disulfide and 2% of polyvinyl alcohol. The other operations were the same as in example 3.

Example 5

In this embodiment, the low-wear and high-stability powder metallurgy friction material comprises the following components in parts by weight: 45% of copper powder, 28% of iron powder, 12% of ferrochrome powder, 4.5% of potassium titanate whisker, 1.5% of chromium powder, 7% of graphite, 1.5% of molybdenum disulfide and 0.5% of polyvinyl alcohol. Wherein the length of the potassium titanate whisker is 20-50 mu m, and the length-diameter ratio is 5-8: 1.

And carrying out ball milling and mixing on the metal powder (copper, iron and chromium) and the crystal whisker in the powder according to weight percentage to obtain mixed powder 1. The ball material ratio is as follows: 1: 10; the grinding ball is made of the following materials: a steel ball; the ball milling medium is as follows: ethanol; the atmosphere is: ar; the ball milling time is 4h, and the rotating speed is 60 rpm. And then, mixing the mixed powder 1 and the rest of the powder according to the weight percentage, and placing the mixture into a ball milling mixer to be uniformly mixed to obtain mixed powder 2. Sodium titanate/potassium titanate, pressing the obtained mixed powder 2 with a friction block back plate under the pressure of 200MPa to obtain a biscuit; and sintering the biscuit for 0.5h by a sintering process under the protection of 1025 ℃, the heating rate of 15 ℃/min and a nitrogen-hydrogen mixed atmosphere (gas flow ratio: nitrogen: hydrogen is 2:1), and cooling to room temperature along with a furnace to obtain the friction material C.

Example 6

In this example, the percentage of potassium titanate whiskers was adjusted to 6% based on example 5. The paint specifically comprises the following components in parts by weight: 45% of copper powder, 26.5% of iron powder, 12% of ferrochrome powder, 6% of potassium titanate whisker, 1.5% of chromium powder, 7% of graphite, 1.5% of molybdenum disulfide and 0.5% of polyvinyl alcohol. The other operations were the same as in example 5.

Comparative example 1

The composition of the copper-based powder metallurgy friction material D provided by the present comparative example was different from that of example 3 in that alumina particles and silica particles were used in the raw material without using sodium titanate whiskers or potassium titanate whiskers. The weight ratio of the components is as follows: 45% of copper powder, 28% of iron powder, 12% of ferrochrome powder, 1.5% of alumina, 3% of silicon dioxide, 1.5% of chromium powder, 7% of graphite, 1.5% of molybdenum disulfide and 0.5% of polyvinyl alcohol.

Firstly, preliminarily mixing the powder (except graphite) by a high-speed stirrer, adding the graphite into a ball-milling mixer, uniformly mixing, and pressing the obtained mixed powder with a friction block back plate under the pressure of 200MPa to obtain a biscuit; and sintering the biscuit for 0.5h by a sintering process under the protection of 1025 ℃, the heating rate of 15 ℃/min and a nitrogen-hydrogen mixed atmosphere (gas flow ratio: nitrogen: hydrogen is 2:1), and cooling to room temperature along with a furnace to obtain the friction material D.

Comparative example 2

In the comparative example, sodium titanate whiskers with the length of less than 20 microns and the length-diameter ratio of 1-3: 1 are used instead of example 1. The other operations were the same as in example 1.

Comparative example 3

In the comparative example, sodium titanate whiskers with the length of more than 120 mu m and the length-diameter ratio of 12-15: 1 are used instead of the sodium titanate whiskers in example 1. The other operations were the same as in example 1.

Comparative example 4

In the comparative example, on the basis of example 1, the percentage content of the sodium titanate whisker is adjusted to 10%, and the sodium titanate whisker specifically comprises the following components in percentage by weight: 50% of copper powder, 20% of iron powder, 8% of ferrochrome powder, 10% of sodium titanate whisker, 0.5% of chromium powder, 8% of graphite, 2.5% of molybdenum disulfide and 1% of polyvinyl alcohol. The other operations were the same as in example 1.

Comparative example 5

In the comparative example, on the basis of example 1, the percentage content of the sodium titanate whisker is adjusted to 0.3%, and the sodium titanate whisker specifically comprises the following components in percentage by weight: 54% of copper powder, 23% of iron powder, 10% of ferrochrome powder, 0.2% of sodium titanate whisker, 0.5% of chromium powder, 8.8% of graphite, 2.5% of molybdenum disulfide and 1% of polyvinyl alcohol. The other operations were the same as in example 1.

Test comparison

The TM-I type railway train friction material inertia scaling test bed is used as friction material performance test equipment, and emergency braking simulation tests are carried out on the friction materials obtained in the embodiments 1, 2, 3, 4, 5 and 6 and the comparative examples 1-5. The simulated speeds are respectively 50, 80, 120, 160, 200, 250, 300, 350 and 380km/h, the braking load is 1.27MPa, and the braking inertia is 47kg m²The initial temperature of the surface of the material was 55 ℃ and 6 parking brake tests were carried out at each speed. Typical instantaneous coefficient of friction versus speed curves for the friction materials of examples 1-6 and comparative examples 1-5 are shown in FIGS. 2-12 (FIGS. 2, 3, 4 correspond to examples 1, 3, 5, respectively, FIGS. 5, 6, 7 correspond to examples 2, 4, 6, and FIGS. 8, 9, 10, 11, 12 correspond to comparative examples 1-5), respectively. In addition, the average friction coefficient and the wear rate of each friction material measured according to the above-described method were summarized, and the results are shown in fig. 13 and 14, respectively.

According to the experimental result, the friction materials A-C can keep higher and stable friction coefficients within the braking speed range of 50-380km/h, and the friction coefficient stability coefficients are respectively 96.3%, 93.8% and 95.1%. In addition, the abrasion rate is always lower than 0.20cm at all braking speeds³and/MJ. Under the same test condition, the friction coefficient stability coefficient of the friction material D is 86.4 percent, and when the brake speed is high>At 250km/h, a clear decay is shown, with a significant increase in abrasion. The friction material prepared by the invention has the advantages that the friction coefficient is not declined during high-speed braking, high friction coefficient stability is shown, the abrasion loss within the braking speed range of 50-380km/h is low, the comprehensive friction performance is good, and the braking requirement of a high-speed train can be met.

According to the experimental result, when the addition amount of the sodium titanate whisker is 0.6-1.5% (examples 1-2), the performance of the prepared metallurgical powder friction body in the aspect of decay resistance is excellent. When the addition amount of the sodium titanate whisker is 1.5-3% (examples 3-4), the prepared metallurgical powder friction body has excellent performance in the aspect of wear resistance. When the addition amount of the sodium titanate whisker is 3-6% (examples 5-6), the prepared metallurgical powder friction body has excellent performance in the aspects of strength and toughness. When the amount of the sodium titanate whisker or the potassium titanate whisker is less than 0.6% (see comparative example 5), the prepared metallurgical powder friction body has poor performance in resisting recession and fatigue, stripping and abrasion, and the wear resistance and stripping crack resistance of the friction body are not obviously improved. When the amount of sodium titanate whiskers or potassium titanate whiskers is used in an amount too high, more than 10% (see comparative example 4), the contents of other components (particularly the contents of iron chromium powder and iron powder) are severely compressed, resulting in insufficient performance of the resultant metallurgical powder friction body in terms of heat conduction.

In addition, when the length of the sodium titanate whisker or the potassium titanate whisker used is too short or too long (as in comparative examples 2 to 3), the performance of the prepared metallurgical powder friction body in terms of recession resistance and strength is insufficient. Presumably, when the length of the sodium titanate whisker is too short, the improvement effect on the toughness, wear resistance, spalling crack resistance and the like of the powder metallurgy friction body is not obvious enough; if the used sodium titanate whisker or potassium titanate whisker is too long, the sodium titanate whisker or potassium titanate whisker is easy to stir together when the materials are mixed and pressed into a blank, so that the particle powder is separated from the fiber material, the distribution of each component in the powder metallurgy friction body is very uneven, and the performance of the powder metallurgy friction body is influenced.

The foregoing is a preferred embodiment of the present invention, and it should be noted that it is obvious to those skilled in the art that various modifications and improvements can be made without departing from the principle of the present invention, and these modifications and improvements should be considered as the protection scope of the present invention.

Claims

1. The powder metallurgy friction material is characterized in that the formula of the powder metallurgy friction material comprises the following components in percentage by weight: 40-65% of copper powder, 16-35% of iron powder, 5-15% of ferrochrome powder, 0.6-6% of ceramic fiber, 0.5-3% of chromium powder, 7-15% of graphite, 1-6% of molybdenum disulfide and 0.5-4% of polyvinyl alcohol; the particle size of the ferrochrome powder is 10-300 mu m;

the ceramic fiber is sodium titanate whisker or potassium titanate whisker, the mass percentage of the ceramic fiber in the powder metallurgy friction material is 2%, the length of the whisker is 80-100 mu m, and the length-diameter ratio is 5-10: 1.

2. the powder metallurgy friction material of claim 1, wherein the copper source of the copper powder is one or a mixture of water atomized copper powder and electrolytic copper powder, and the particle size of the water atomized copper powder and the electrolytic copper powder is 1-32 μm.

3. The powder metallurgy friction material of claim 1, wherein the graphite is one or a mixture of two of artificial graphite and flake graphite, and the particle size of the artificial graphite and the flake graphite is 60-600 μm.

4. The preparation method of the powder metallurgy friction block is characterized by comprising the following steps:

step 1: weighing and proportioning the materials according to the formula of the powder metallurgy friction material according to any one of claims 1 to 3, and uniformly mixing to obtain mixed powder;

step 2: pressing the mixed powder obtained in the step 1 with a friction block back plate to obtain a biscuit;

and step 3: and (3) preparing the biscuit obtained in the step (2) into the required friction material through a high-temperature sintering process.

5. The method for preparing the powder metallurgy friction block according to claim 4, wherein the step 1 is specifically as follows: the preparation method comprises the steps of preliminarily mixing the components except the ceramic fiber and the graphite in the formula through a high-speed stirrer, adding the ceramic fiber and the graphite, and uniformly mixing in a ball-milling mixer to obtain mixed powder.

6. The method for preparing the powder metallurgy friction block according to claim 5, wherein the specific mixing parameters during mixing in the ball mill mixer are as follows: the ball material ratio is as follows: 1: 3-10; the grinding ball is made of the following materials: a steel ball; the ball milling medium is as follows: ethanol; the atmosphere is: ar; the ball milling time is 2-4h, and the rotating speed is 50-200 rpm.