CN113770347B - Method for regulating and controlling friction coefficient of copper-graphite composite material through orientation of graphite flakes - Google Patents
Method for regulating and controlling friction coefficient of copper-graphite composite material through orientation of graphite flakes Download PDFInfo
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- CN113770347B CN113770347B CN202110977297.7A CN202110977297A CN113770347B CN 113770347 B CN113770347 B CN 113770347B CN 202110977297 A CN202110977297 A CN 202110977297A CN 113770347 B CN113770347 B CN 113770347B
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Abstract
A method for regulating and controlling the friction coefficient of Cu-graphite composite material by the orientation of graphite flakes uses natural graphite flakes and trace alloy element CrTin and superfine copper powder, the graphite flakes are directionally arranged through a hot pressing process to obtain a sintered body with a laminated structure, and the sintered body is finely cut at a specific angle to obtain a specific angle between the graphite flakes and a contact surface
By varying the angle between the graphite sheet and the sliding surface
The mechanical and physical properties of the composite material on the friction contact surface are changed, including friction coefficient, wear rate and conductivity, the composite material has low friction coefficient, small wear rate and good conductivity, and can effectively relieve the antagonism between lubrication and conductivity of the laminar graphite.
Description
Technical Field
The invention relates to the field of friction composite materials, in particular to a method for regulating and controlling a friction coefficient of a copper-graphite composite material through graphite flake orientation.
Background
The pantograph slide plate is a key part of an electric locomotive and is required to be in sliding contact with a lead to deliver stable current for the locomotive. Therefore, the pantograph pan material is required to have good conductivity, wear resistance, high mechanical strength, a low friction coefficient, and the like. The conventional pantograph pan material mainly comprises: copper-based powder metallurgy sliding plates, pure carbon sliding plates and metal-impregnated carbon sliding plates all have some defects. The copper-based powder metallurgy sliding plate is high in hardness, good in strength, conductivity and wear resistance, but hard components contained in the copper-based powder metallurgy sliding plate often cause severe abrasion on a contact net lead, and the tendency of adhesive abrasion and fusion welding is increased when the copper content is high; the pure carbon sliding plate has good lubrication contact with a contact net lead, but has low strength and is easy to break; the impregnated metal carbon sliding plate can improve the density of the sliding plate, reduce the contact resistance and improve the strength of the sliding plate, but is affected by the distribution of holes in the early-stage sintered carbon material, so that the process of impregnating metal is complex, and the difficulty and the cost are increased. In addition, the metal impregnated carbon sliding plate material is made of artificial graphite particles in order to promote stacking formation and later metal impregnation of the sintered carbon material. On one hand, the graphitization degree of the artificial graphite particles is low, which is not beneficial to the full exertion of the conductivity of the composite material; on the other hand, artificial graphite particles are highly brittle, highly porous, strongly abrasive, and poorly lubricious, often resulting in high wear rates and friction fluctuations.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention aims to provide a method for regulating and controlling the friction coefficient of a copper-graphite composite material by the orientation of graphite flakes, which adopts natural graphite flakes, trace alloy elements of chromium, tin and superfine copper powder, leads the graphite flakes to be directionally arranged by a hot pressing process to obtain a sintered body with a laminated structure, and the sintered body can obtain a sintered body with a specific angle between the graphite flakes and a contact surface by fine cutting processing at a specific angle
The copper-graphite composite material has low friction coefficient, small wear rate and good conductivity, and can effectively relieve the antagonism between lubrication and conductivity of the laminar graphite.
In order to achieve the purpose, the technical scheme of the invention is as follows:
a method for regulating and controlling the friction coefficient of a copper-graphite composite material through graphite sheet orientation comprises the following steps:
step 1: putting the graphite flake into 0.2-0.6mol/L dilute hydrochloric acid, stirring in a constant-temperature water bath at 60-80 ℃ for 2-40min, centrifugally cleaning to neutrality, and drying in a vacuum oven for 20-40h;
step 2: weighing 50-70% of graphite flake, 30-50% of copper powder, 1-5% of chromium powder and 2-10% of tin powder which are treated in the step 1 according to the volume percentage, placing the mixed powder in a drum type mixer, and mixing for 4-6h;
and step 3: putting the mixed powder in the step 2 into a graphite die, performing prepressing molding, keeping the pressure at 15-30MPa for 30-60s, then putting a green body into a sintering furnace, heating to 900-1000 ℃ at the speed of 8-10 ℃/min, performing hot-pressing sintering under the pressure of 10-15MPa, keeping the temperature for 1-3h, and then cooling along with the furnace to obtain a layered sintered body with oriented graphite;
and 4, step 4: cutting the layered sintered body having oriented graphite in step 3 at a specific angle to obtain a specific angle between the graphite sheet and the cut sliding contact surface
The copper-graphite composite material of (1),
the diameter of the graphite sheet is 300-500 μm, and the thickness of the graphite sheet is 10-20 μm; the granularity of the chromium powder is less than 10 mu m, the granularity of the tin powder is less than or equal to 1 mu m, and the granularity of the copper powder is less than 5 mu m.
The invention has the advantages that:
(1) The copper in the composite material is used as a matrix and is also used as a binder, so that the composite material has good electric and thermal conductivity; the flake graphite is a light conductive lubricating phase and has anisotropy; the alloy elements of chromium and tin play roles in enhancing the abrasion resistance and corrosion resistance of the matrix, improving the wetting of a Cu/graphite interface and promoting the densification and sintering. Through hot-pressing sintering, the flake graphite is directionally arranged in a direction perpendicular to the hot-pressing direction to form a layered structure with orientation, and fine cutting under a specific angle can change an included angle between the graphite flake and the sliding surface (namely, the orientation of the graphite on the sliding surface). The experimental results show that: included angle of
The composite material has low friction coefficient, small wear rate and good conductivity.
The prepared composite material with the lamellar structure inherits the anisotropy of the graphite flake and changes the included angle between the graphite flake and the sliding surface
The mechanical and physical properties of the composite material at the wiping contact surface will change, including coefficient of friction, wear rate and electrical conductivity. The best comprehensive characteristic verified in the experiment is that the included angle is
To (3).
Drawings
FIG. 1 (a) shows an orientation graphite sheet having a specific angle with respect to a sliding contact surface
The copper-graphite composite material of (1) is prepared schematically; in FIG. 1, (b) is an angle of
The friction process of the contact surface is shown schematically.
FIG. 2 shows the preparation of different angles according to the present invention
Corresponding morphology of friction surface tissue; FIG. 2 (a) is
FIG. 2 (b) is
FIG. 2 (c) is
FIG. 2 (d) is a schematic view of
FIG. 3 shows the included angle of the mechanical properties of lamellar graphite in a polar coordinate system in theoretical calculation
In fig. 3, (a) is the elastic modulus E, and (b) in fig. 3 is the poisson's ratio ν.
Detailed Description
The present invention will be described in detail with reference to the accompanying drawings.
A method for regulating and controlling the friction coefficient of a copper-graphite composite material through graphite sheet orientation comprises the following steps:
step 1: putting the graphite flake into 0.2-0.6mol/L dilute hydrochloric acid, stirring in a constant-temperature water bath at 60-80 ℃ for 2-40min, centrifugally cleaning to neutrality, and drying in a vacuum oven for 20-40h;
and 2, step: weighing 50-70% of graphite flake, 30-50% of copper powder, 1-5% of chromium powder and 2-10% of tin powder which are treated in the step 1 according to the volume percentage, placing the mixed powder in a drum type mixer, and mixing for 4-6h;
and step 3: putting a proper amount of the mixed powder in the step 2 into a graphite die, performing prepressing molding, keeping the pressure at 15-30MPa for 30-60s, then putting a green body into a sintering furnace, heating to 900-1000 ℃ at the speed of 8-10 ℃/min, performing hot-pressing sintering under the pressure of 10-15MPa, keeping the temperature for 1-3h, and then cooling along with the furnace to obtain a layered sintered body with oriented graphite;
and 4, step 4: finely cutting the layered sintered body having oriented graphite in step 3 at a specific angle to obtain a sheet having a specific angle with respect to the sliding contact surface
The copper-graphite composite material.
The diameter of the graphite sheet is 300-500 μm, and the thickness of the graphite sheet is 10-20 μm; the granularity of the chromium powder is less than 10 mu m, the granularity of the tin powder is less than or equal to 1 mu m, and the granularity of the copper powder is less than 5 mu m.
The friction material prepared by the steps is carried out on a CFT-I type multifunctional material surface property comprehensive tester, a ball-disc type reciprocating dry friction system is adopted, the grinding ball material is H62 brass, and the graphite flakes prepared by the grinding disc have different orientations
The sliding friction speed of the copper-graphite composite material is 0.08m/s, and the positive pressure is 10N. The hardness of the contact surface of the test piece was measured by an ASTM-E10-070 Brinell hardness tester, and the test load was 7.8Kg, the diameter of the steel ball was 2.5mm, and the average value obtained by testing each sample 5 times was taken as the final result. The electrical conductivity in the contact surface of the composite was measured using an eddy current conductivity tester, and the average of 3 measurements per sample was taken as the final result.
Specific examples are shown in Table 1, and the corresponding mechanical, tribological and electrical properties are shown in Table 2. The prepared Cu30Gr70 composite material has the contact surface structure with different graphite sheet orientations shown in figure 2.
Description of the mechanism: natural graphite flakes exhibit mechanical and physical anisotropy in macroscopic view due to the difference in interplate (van der waals) and intraplate (covalent bond) forces, i.e. the properties in the direction perpendicular and parallel to the graphite layers vary greatly, as shown in table 3. It is generally known that parallel layers have low directional shear resistance and are advantageous for lubrication and are therefore commonly used as lubricants. In theoretical and practical studies, the graphite layer is at an angle to the direction of the graphite layer (i.e. to the basal plane)
There are few examples of applications. Based on theoretical mechanics calculation, the invention discovers that the graphite-copper composite material with orientation has an included angle
The modulus of elasticity (E) and shear modulus (G, which can be calculated from the modulus of elasticity and poisson's ratio) of the contact surface exhibit regular changes when varying from 0 ° to 90 ° (i.e., one cycle), as shown in fig. 3. While the coefficient of friction is mainlyDepending on the variation of the G/E ratio. Based on the results, a series of experimental researches are carried out, and the experimental results show that: at an included angle
When the method is used, the corresponding friction coefficient of the contact surface is small and stable, the wear rate is low, and the conductivity is good.
The natural graphite flake has high graphitization degree and is easy to compact during pressure sintering. Because the natural graphite flake has anisotropy, the direction vertical to the graphite flake has small compression modulus, high shear modulus and poor conductivity; the compression modulus in the direction parallel to the graphite sheet is high, the shear modulus is small, and the conductivity is excellent. The included angle between the oriented graphite sheet and the friction contact surface is influenced by the distribution direction of the graphite sheets in the contact surface
The friction coefficient, wear rate and conductivity of the system vary over a wide range when varying between 0 and 90 deg.. Under a certain component proportion, the friction coefficient, the wear rate and the electric conduction characteristic of the system can be regulated and controlled by changing the included angle between the oriented graphite sheet and the friction contact surface in the composite material.
Compared with artificial particle graphite, the natural lamellar graphite has low porosity and high graphitization degree, is easy to be directionally arranged in hot-pressing sintering, and is beneficial to densification and sintering of composite materials. The copper-graphite composite material prepared by the method can adjust and control the friction coefficient, the wear rate and the conductivity through the orientation of the graphite flakes. The angle between the orientation graphite sheet and the sliding contact surface is
The composite material has low friction coefficient, small wear rate and good conductivity. The invention can realize the change and adjustment of the friction coefficient of the copper-based composite material containing 50-70% volume fraction of graphite flakes through simple preparation process and processing method, reduces the antagonistic phenomenon between lubrication and conduction of natural graphite flakes in sliding electrical contact application, and is beneficial to reducing energy consumption and saving cost.
Table 1: material ratios and Process parameters of the examples
Table 2: performance of the examples.
Table 3: the direction parallel to the graphite sheet layer (9553;) and the direction perpendicular to the graphite sheet layer (vert).
Claims (2)
1. A method for regulating and controlling the friction coefficient of a copper-graphite composite material through graphite sheet orientation is characterized by comprising the following steps:
step 1: putting the graphite flake into 0.2-0.6mol/L dilute hydrochloric acid, stirring in a constant-temperature water bath at 60-80 ℃ for 2-40min, centrifugally cleaning to neutrality, and drying in a vacuum oven for 20-40h;
and 2, step: weighing the copper powder, the graphite flake, the chromium powder and the tin powder processed in the step 1 according to the volume percentage, and placing the mixed powder into a drum type mixer for mixing for 4-6h;
the volume ratio of the copper powder, the graphite flake, the chromium powder and the tin powder is as follows: 30:67:1:2 or 35:58:2:5 or 40:50:3:7;
and step 3: putting the mixed powder in the step 2 into a graphite die, performing prepressing molding, keeping the pressure at 15-30MPa for 30-60s, then putting the green body into a sintering furnace, heating to 900-1000 ℃ at the speed of 8-10 ℃/min, performing hot-pressing sintering under the pressure of 10-15MPa, and cooling along with the furnace after heat preservation for 1-3h to obtain a layered sintered body with oriented graphite;
and 4, step 4: cutting the layered sintered body having oriented graphite in step 3 at a specific angle to obtain a specific angle between the graphite sheet and the cut sliding contact surface
The copper-graphite composite material of (a),
2. the method for regulating the friction coefficient of a copper-graphite composite material through the orientation of graphite flakes according to claim 1, wherein the graphite flakes have a diameter of 300 to 500 μm and a thickness of 10 to 20 μm; the granularity of the chromium powder is less than 10 mu m, the granularity of the tin powder is less than or equal to 1 mu m, and the granularity of the copper powder is less than 5 mu m.
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| RU2224920C2 (en) * | 2001-09-18 | 2004-02-27 | Сергей Михайлович Романов | Anti-friction material romanit-n, method of production of such material and friction unit member |
| UA83677C2 (en) * | 2006-03-29 | 2008-08-11 | Сергей Михайлович Романов | Antifriction romanit-uvlbn material based on copper, method for obtaining thereof and element of friction unit with sintered layer of this material |
| CN107502767B (en) * | 2016-06-14 | 2019-03-19 | 宁波晨鑫维克工业科技有限公司 | A kind of orientation super-high heat-conductive, high strength graphite-carbon/carbon-copper composite material and its preparation method and application |
| CN106191497B (en) * | 2016-08-16 | 2018-06-05 | 泉州市鸿运生态农业发展有限公司 | A kind of preparation method of copper-base pantograph slide plate composite material |
| CN106086585B (en) * | 2016-08-17 | 2017-11-28 | 西安交通大学 | A kind of copper and iron base braking composite material and preparation method thereof |
| CN107116210B (en) * | 2016-10-27 | 2018-11-27 | 北京科技大学 | The Cu-base composites cooling fin and preparation method thereof of the oriented laminated arrangement of graphite flake |
| CN110715005B (en) * | 2019-09-25 | 2020-11-03 | 南阳理工学院 | Preparation method of high-thermal-conductivity copper-based brake pad with orientation structure |
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