Shaft end grounding friction disc and preparation method thereof

Abstract

The invention relates to the technical field of powder metallurgy materials, in particular to a shaft end grounding friction disc and a preparation method thereof. The shaft end grounding friction disc is manufactured according to the method. The method comprises the following steps: uniformly mixing all raw material components with required amounts to obtain mixed powder, filling a mold with the mixed powder, carrying out cold press molding, and demolding to obtain a pressed blank; the pressed blank is sintered, cooled to the room temperature and discharged out of a furnace, and a sintered blank is obtained; and the sintered blank is machined into the shaft end grounding friction disc. The shaft end grounding friction disc can be ensured to have good conductivity and self-lubricating effect, friction heat production can be reduced, and heat accumulation is prevented from influencing functions of products and peripheral parts.

Description

Technical Field

[0001] This invention relates to the field of powder metallurgy materials technology, and in particular to a shaft-end grounding friction disk and its preparation method. Background Technology

[0002] Axle-end grounding friction discs are mainly used in rail transit vehicles (such as high-speed trains and subways). They can safely divert the strong operating current and system fault current (including lightning strike current) from the vehicle body to the rails, preventing current from passing through the axle and causing bearing damage, premature failure, or seizure. The installation and operation of the axle-end grounding friction disc are as follows: The axle-end grounding friction disc is installed in an axle-end grounding device, which mainly includes a housing, friction disc, brushes, springs, and other components. Within the enclosed space formed by the housing, the axle-end grounding friction disc, which acts as the rotor, and the brushes, which act as the stator, maintain sliding contact under the constant pressure applied by the springs. The axle-end grounding friction disc is connected to the wheel via wires, and the brushes are connected to the vehicle body via wires, thus grounding the vehicle body.

[0003] However, the existing shaft-end grounding friction discs are mainly made of copper alloy, which makes them not only expensive, but also not wear-resistant and have a short service life. In addition, they are also prone to heat accumulation due to friction during use, which affects the function of the product and its peripheral components.

[0004] Therefore, it is necessary to provide a shaft-end grounding friction disc and its preparation method to solve the technical problems of existing copper alloy shaft-end grounding friction discs, such as high cost, poor wear resistance, short service life, and easy heat accumulation due to friction affecting the function of the product and peripheral components. Summary of the Invention

[0005] The purpose of this invention is to provide a shaft-end grounding friction disk and its manufacturing method, the specific technical solution of which is as follows: In a first aspect, the present invention provides a method for preparing a shaft-end grounding friction disk, comprising: Step S1: Mix the raw material components, including the following mass percentages, to obtain a mixed powder: 40%~89% aluminum-based powder, 10%~40% silicon carbide powder and 1%~20% copper-plated graphite powder; Step S2: Fill the mold with the mixed powder, and after cold pressing, demold to obtain the pressed blank; Step S3: After the pressed billet is sintered, it is cooled to room temperature and then removed from the furnace to obtain a sintered billet; Step S4: The sintered billet is machined into a shaft-end grounding friction disc.

[0006] Optionally, the steps for obtaining the copper-plated graphite powder include: First, the pretreated graphite powder is immersed in a plating solution containing copper salt and auxiliary salt for chemical plating to obtain a copper-plated graphite powder precursor; wherein, the mass concentration of copper salt in the plating solution is 5~10 g / L; the mass concentration of graphite powder in the plating solution is 10~15 g / L; and the total mass concentration of auxiliary salt in the plating solution is 25~55 g / L. Next, the copper-plated graphite powder precursor is removed from the plating solution and kept at 600~750℃ for 1~2 hours; subsequently, it is subjected to ultrasonic dispersion treatment to obtain uniformly dispersed copper-plated graphite powder.

[0007] Optionally, the electroless plating treatment uses a plating temperature of 20~30℃, a plating time of 15~20min, and a plating pH value of 12.0~12.5; The pretreatment includes washing the graphite powder with alcohol to remove grease.

[0008] Optionally, the auxiliary salt includes disodium EDTA and sodium potassium tartrate; the mass concentration of disodium EDTA in the plating solution is 10-30 g / L; and the mass concentration of sodium potassium tartrate in the plating solution is 15-25 g / L.

[0009] Optionally, the D50 particle size of the copper-plated graphite powder is 75~150μm; the thickness of the copper layer coated on the surface of the graphite powder is 1~3μm.

[0010] Optionally, the D50 particle size of the aluminum-based powder is 1~50μm; the D50 particle size of the silicon carbide powder is 1~30μm.

[0011] Optionally, the aluminum-based powder comprises raw material components in the following mass ratio: aluminum powder, copper powder, and magnesium powder in a mass ratio of 47:2:1.

[0012] Optionally, the cold pressing process uses a pressure of 100~200MPa and a holding time of 5~15s.

[0013] Optionally, the sintering treatment uses a sintering temperature of 580~650℃ and a sintering time of 0.5~2h; the heating rate of the pressed blank in the sintering treatment is 2~10℃ / min.

[0014] In a second aspect, the present invention provides a shaft-end grounding friction disk, which is prepared by the aforementioned method for preparing a shaft-end grounding friction disk.

[0015] The application of the technical solution of the present invention has at least the following beneficial effects: (1) The present invention provides a method for preparing a shaft-end grounding friction disk, which uses a required amount of silicon carbide powder as a reinforcing phase to prepare a wear-resistant shaft-end grounding friction disk and extend its service life; by combining a required amount of aluminum-based powder with a required amount of copper-plated graphite powder, it is possible not only to ensure that the shaft-end grounding friction disk has good conductivity and self-lubricating effect, but also to reduce frictional heat generation and prevent heat accumulation from affecting the function of the product and peripheral components. Wherein: In terms of conductivity: both graphite and aluminum matrix (i.e. aluminum-based powder) are good conductors. The copper layer on the graphite surface improves its wettability with aluminum, inhibits the formation of poor interfaces and pores, and forms a continuous conductive path. Although silicon carbide is an insulator, it plays a particle-reinforcing role on the shaft-end grounding friction disk, which helps to stabilize the conductive network structure.

[0016] In terms of self-lubrication and wear resistance: During the friction process, after the copper layer peels off, the graphite, being a layered structure, allows for relative sliding between its layers, gradually forming a continuous solid lubricating film on the friction surface, thus significantly reducing the coefficient of friction. Simultaneously, the added hard silicon carbide particles, acting as a reinforcing phase, primarily bear the load and reduce the plowing effect on the aluminum matrix. During silicon carbide wear, they can form a mechanically mixed layer with the aluminum matrix, contributing to a smoother friction surface and further optimizing the friction state. Therefore, through the synergistic effect of copper-plated graphite powder, the aluminum matrix, and silicon carbide, the shaft-end grounding friction disc exhibits excellent self-lubricating and wear-resistant properties under dry friction conditions.

[0017] Regarding the reduction of frictional heat generation: During the friction process, the continuous and well-adhesive solid lubricating film formed by graphite on the friction surface directly transforms the sliding friction between the friction pairs into shear sliding between graphite layers, thereby significantly reducing the coefficient of friction and reducing the generation of frictional heat at its source. Simultaneously, the hard silicon carbide particles, as a reinforcing phase, play a crucial role in bearing most of the load, reducing the plowing effect of the friction pairs on the softer aluminum matrix, which also suppresses the generation of frictional heat.

[0018] Furthermore, compared to copper alloy shaft-end grounding friction discs, this invention combines the required amount of aluminum powder or aluminum alloy powder with the required amount of copper-plated graphite powder, significantly reducing the amount of copper used and lowering the manufacturing cost. Moreover, the density of the shaft-end grounding friction disc is 2.6~2.9 g / cm³. 3 Compared to copper alloy materials with a density of 7~9g / cm³, 3 The density and weight reduction effect are obvious.

[0019] (2) In the step of obtaining copper-plated graphite powder, the present invention adopts pretreatment to remove grease from the surface of graphite powder, which facilitates subsequent plating; adopts chemical plating treatment with required control parameters, which can suppress the formation of strong mechanical interlocking and chemical bonding between the copper layer and the aluminum substrate, and the copper layer with weak bonding force with graphite particles, so as to promote the peeling of the copper layer during friction, and then the graphite forms a continuous solid lubricating film on the friction surface, improving the self-lubricating effect; wherein, the combination of auxiliary salt and copper salt in the plating solution creates conditions that are not conducive to the regular and dense deposition of copper atoms, which facilitates the reduction of the density and strength of the copper layer itself, thereby weakening the bonding force between the copper layer and graphite particles, so as to promote the peeling of the copper layer during friction; the copper-plated graphite powder precursor is taken out from the plating solution and kept at 600~750℃ for 1~2h, which can provide kinetic conditions, and use the thermodynamic driving force brought by the high interface energy between copper and graphite to promote the weak spheroidization of the copper layer, inducing the initial and weak spheroidization phenomenon of the copper layer, which facilitates the weakening of the bonding force between the copper layer and graphite particles. Subsequently, ultrasonic dispersion treatment is performed to obtain uniformly dispersed copper-plated graphite powder and avoid clumping.

[0020] (3) The copper layer on the surface of the copper-plated graphite powder in the present invention has a thickness of 1~3μm, which can isolate the graphite from the aluminum matrix, inhibit the formation of Al4C3 brittle phase and avoid the formation of poor interface, improve the poor wettability of graphite and aluminum matrix liquid phase, reduce the porosity of sintered blank, and also cause the copper layer to break rapidly during the friction process and release graphite particles to produce a self-lubricating effect.

[0021] (4) In step S1 of this invention, the copper-plated graphite powder has a D50 particle size of 75~150μm, the aluminum powder or aluminum alloy powder has a D50 particle size of 1~50μm, and the silicon carbide powder has a D50 particle size of 1~30μm. This facilitates the formation of a mixed powder with a reasonable particle size gradient distribution. The finer silicon carbide powder can effectively fill the gaps between the aluminum powder or aluminum alloy powder, while the larger copper-plated graphite powder can be completely coated by the aluminum powder or aluminum alloy powder, thereby increasing the packing density of the mixed powder, reducing the segregation tendency of each component, and promoting the formation of a dense and uniform composite structure during subsequent sintering. Furthermore, in step S2, the cold pressing is performed at a pressure of 100~200MPa and a holding time of 5~15s. This facilitates the densification of the powder into a blank with a certain shape, strength, and density. At the same time, the lower pressure molding does not increase the bonding force between the graphite powder and the copper plating layer. Furthermore, in step S3, the sintering temperature is 580~650℃, and the sintering time is 0.5~2h, which facilitates the formation of a dense silicon carbide-coated graphite-aluminum matrix composite structure in the billet. A copper layer with low adhesion, low density, and low strength is present on the graphite powder surface. This copper layer tends to form a coarse and discontinuous CuAl2 phase with the aluminum matrix. Compared to a dense and fine CuAl2 phase, this CuAl2 phase has lower strength and is less wear-resistant, making it easier to peel off during friction, thus exposing the graphite powder on the friction surface and achieving a self-lubricating effect. Additionally, the heating rate used in the sintering process for the pressed billet is 2~10℃ / min, which helps to reduce the temperature difference between the inside and outside of the sintered billet and promotes a uniform densification process. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1: A method for preparing a shaft-end grounding friction disk includes: Step S1: Mix the raw material components, including the following mass percentages, to obtain a mixed powder: 40%~89% (specifically 80%) aluminum-based powder, 10%~40% (specifically 15%) silicon carbide powder and 1%~20% (specifically 5%) copper-plated graphite powder; Step S2: Fill the mold with the mixed powder, and after cold pressing, demold to obtain the pressed blank; Step S3: After the pressed billet is sintered, it is cooled to room temperature and then removed from the furnace to obtain a sintered billet; Step S4: The sintered billet is machined into a shaft-end grounding friction disc.

[0024] The steps for obtaining the copper-plated graphite powder include: First, the pretreated graphite powder is immersed in a plating solution containing copper salt and auxiliary salt for chemical plating to obtain a copper-plated graphite powder precursor. The copper salt concentration in the plating solution is 5-10 g / L (specifically 8 g / L); the graphite powder concentration in the plating solution is 10-15 g / L (specifically 14 g / L); and the total concentration of the auxiliary salt in the plating solution is 25-55 g / L (specifically 40 g / L). The solvent used in the plating solution is water. Next, the copper-plated graphite powder precursor is removed from the plating solution and kept at 600~750℃ (specifically 650℃) for 1~2 hours (specifically 1 hour); then, it is subjected to ultrasonic dispersion treatment to obtain uniformly dispersed copper-plated graphite powder.

[0025] The electroless plating process uses a plating temperature of 20~30℃ (specifically 24℃), a plating time of 15~20min (specifically 18min), and a plating pH value of 12.0~12.5 (specifically 12.2). The pretreatment includes washing the graphite powder with alcohol (specifically, ethanol) to remove grease.

[0026] The auxiliary salts include disodium EDTA and sodium potassium tartrate; the mass concentration of disodium EDTA in the plating solution is 10-30 g / L (specifically 20 g / L); the mass concentration of sodium potassium tartrate in the plating solution is 15-25 g / L (specifically 20 g / L).

[0027] The D50 particle size of the copper-plated graphite powder is 75~150μm (specifically 100μm); the thickness of the copper layer coated on the surface of the graphite powder is 1~3μm (specifically 2μm).

[0028] The aluminum-based powder has a D50 particle size of 1~50μm (specifically 30μm); the silicon carbide powder has a D50 particle size of 1~30μm (specifically 20μm).

[0029] The aluminum-based powder comprises raw material components in the following mass ratio: aluminum powder, copper powder, and magnesium powder in a mass ratio of 47:2:1.

[0030] The cold pressing process uses a pressure of 100~200MPa (specifically 150MPa) and a holding time of 5~15s (specifically 8s).

[0031] The sintering process uses a sintering temperature of 580~650℃ (specifically 590℃) and a sintering time of 0.5~2h (specifically 0.5h); the heating rate of the pressed blank during the sintering process is 2~10℃ / min (specifically 5℃ / min).

[0032] Example 2: Unlike Example 1, the amount of copper-plated graphite powder was increased to 20%, and the amount of aluminum-based powder was decreased to 65%.

[0033] Example 3: Unlike Example 1, the amount of copper-plated graphite powder was reduced to 1%, and the amount of aluminum-based powder was increased to 84%.

[0034] Example 4: Unlike Example 1, the amount of copper-plated graphite powder was increased to 10%, and the amount of silicon carbide powder was decreased to 10%.

[0035] Comparative Example 1: Unlike Example 1, the copper layer thickness on the graphite powder surface is 5 μm. Specifically, the parameters used in the electroless plating process are as follows: the mass concentration of copper salt in the plating solution is 15 g / L, and the electroless plating time is 30 min.

[0036] Comparative Example 2: Unlike Example 1, the copper layer thickness on the graphite powder surface is 0.5 μm. Specifically, the parameters used in the electroless plating process are as follows: the mass concentration of copper salt in the plating solution is 3 g / L, and the electroless plating time is 10 min.

[0037] Comparative Example 3: Unlike Example 1, the copper-plated graphite powder was replaced with unplated graphite powder.

[0038] Comparative Example 4: Unlike Example 1, the amount of copper-plated graphite powder was increased to 25%, and the amount of aluminum-based powder was decreased to 60%.

[0039] Comparative Example 5: Unlike Example 1, the amount of copper-plated graphite powder was reduced to 0.2%, and the amount of aluminum-based powder was increased to 84.8%.

[0040] Comparative Example 6: Unlike Example 1, the pH value of the electroless plating was adjusted to 10.0.

[0041] The sintered blanks prepared in Examples 1-4 and Comparative Examples 1-6 were subjected to electrical conductivity and tribological wear tests, and the test results are shown in Table 1.

[0042] The conductivity test method is as follows: Ensure the surface of the sintered billet being tested is flat and clean. Turn on the conductivity meter and allow it to preheat for 5 minutes. Place the probe stably and firmly on the calibration block and start the calibration program. Place the calibrated probe vertically and firmly into contact with the surface of the sintered billet. Press the measurement button; the conductivity meter will complete the measurement and display the result on the screen. The conductivity test equipment used is a Sigma 2008A digital eddy current metal conductivity meter.

[0043] The friction and wear performance testing method is as follows: Using a testing machine, the friction coefficient and volumetric wear rate of the sintered billet were tested under the following conditions: 60N test force, 200r / min rotation speed, 10min test time, room temperature test temperature (specifically 25±5℃), and C45 steel grinding pin testing conditions. The friction and wear performance testing equipment was the MMW-1A model friction and wear testing machine.

[0044] Table 1 Results of electrical conductivity and tribological wear performance tests

[0045] From the data in Table 1, we know that: Compared to Comparative Examples 1-6, the sintered blanks prepared using Examples 1-4 of this invention all exhibited better electrical conductivity, as well as lower coefficients of friction and volumetric wear rates. Specific analysis is as follows: By comparing Example 1 and Comparative Example 1, it is known that if the copper layer on the graphite powder surface is too thick, the shear force required for the copper layer to crack and peel off will increase, resulting in a decrease in the exposed area of ​​graphite, a deterioration of the lubrication mechanism, and consequently an increase in the friction coefficient of the sintered blank. At the same time, the excessive thickness of the copper layer will cause copper element segregation, further deteriorating the wear resistance and increasing the volumetric wear rate of the sintered blank. If the copper layer on the graphite powder surface is too thick and is a non-dense copper layer, micropores will appear on the copper layer and between the copper layer and the graphite, reducing the conductive area and thus reducing the conductivity.

[0046] By comparing Example 1 and Comparative Example 2, it is known that if the copper layer on the graphite powder surface is too thin, the copper layer's ability to inhibit the reaction between Al and C is weakened, leading to the formation of the Al4C3 brittle phase through the sintering reaction between Al and C. The Al4C3 brittle phase is easily detached during friction, causing graphite particles to detach from the friction surface prematurely, reducing the lubrication effect, and consequently increasing the friction coefficient of the sintered blank and raising the volumetric wear rate. Due to the formation of the Al4C3 brittle phase, its conductivity is poor, resulting in a decrease in conductivity.

[0047] Comparing Example 1 and Comparative Example 3, it is evident that replacing the copper-plated graphite powder with unplated graphite powder worsens the wettability between the graphite powder and the aluminum-based powder, leading to increased porosity in the sintered blank and reduced conductive area, thus decreasing conductivity. Furthermore, increased porosity results in a less dense structure, making the blank more susceptible to frictional spalling, increasing the coefficient of friction and volumetric wear rate. Additionally, direct contact sintering of unplated graphite powder with aluminum-based powder causes Al and C to react and form a brittle Al4C3 phase. This brittle Al4C3 phase is prone to detachment during friction, causing graphite particles to prematurely detach from the friction surface, reducing lubrication and further increasing the coefficient of friction and volumetric wear rate. The formation of the brittle Al4C3 phase also leads to decreased conductivity.

[0048] By comparing Example 1 and Comparative Example 4, it is known that if the amount of copper-plated graphite powder is too high, the number of interfaces between the copper-plated graphite powder and the aluminum-based powder will increase, the conductivity will decrease, and the conductivity will decrease. Due to the increase in interfaces, the sintered blank will be non-dense and prone to frictional spalling, resulting in an increase in the coefficient of friction of the sintered blank and an increase in the volumetric wear rate.

[0049] By comparing Example 1 and Comparative Example 5, it is known that if the amount of copper-plated graphite powder is too low, the interface between the copper-plated graphite powder and the aluminum-based powder will be reduced, the conductivity will increase, and the conductivity will increase. Due to the reduction of the interface, although the sintered blank will be relatively dense, there will not be enough graphite to form a continuous solid lubricating film on the friction surface during the friction process, which will lead to an increase in the friction coefficient of the sintered blank and an increase in the volume wear rate.

[0050] By comparing Example 1 and Comparative Example 6, it is known that if the pH value of chemical plating is too low, although it has little effect on the conductivity of the sintered blank, it is easy to form a dense copper layer on the surface of graphite powder. This leads to an increase in the shear force required for the copper layer to crack and peel off, which reduces the exposed area of ​​graphite, worsens the lubrication mechanism, and consequently increases the friction coefficient of the sintered blank and the volumetric wear rate.

[0051] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. All equivalent structural transformations made using the present invention's specification under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for preparing a shaft-end grounding friction disk, characterized in that, include: Step S1: Mix the raw material components, including the following mass percentages, to obtain a mixed powder: 40%~89% aluminum-based powder, 10%~40% silicon carbide powder and 1%~20% copper-plated graphite powder; Step S2: Fill the mold with the mixed powder, and after cold pressing, demold to obtain the pressed blank; Step S3: After the pressed billet is sintered, it is cooled to room temperature and then removed from the furnace to obtain a sintered billet; Step S4: The sintered billet is machined into a shaft-end grounding friction disc.

2. The method for preparing the shaft-end grounding friction disk as described in claim 1, characterized in that, The steps for obtaining the copper-plated graphite powder include: First, the pretreated graphite powder is immersed in a plating solution containing copper salt and auxiliary salt for chemical plating to obtain a copper-plated graphite powder precursor; wherein, the mass concentration of copper salt in the plating solution is 5~10 g / L; the mass concentration of graphite powder in the plating solution is 10~15 g / L; and the total mass concentration of auxiliary salt in the plating solution is 25~55 g / L. Next, the copper-plated graphite powder precursor is removed from the plating solution and kept at 600~750℃ for 1~2 hours; subsequently, it is subjected to ultrasonic dispersion treatment to obtain uniformly dispersed copper-plated graphite powder.

3. The method for preparing the shaft-end grounding friction disk as described in claim 2, characterized in that, The electroless plating process uses a plating temperature of 20-30℃, a plating time of 15-20 min, and a plating pH value of 12.0-12.

5. The pretreatment includes washing the graphite powder with alcohol to remove grease.

4. The method for preparing the shaft-end grounding friction disk as described in claim 1, characterized in that, The auxiliary salts include disodium EDTA and sodium potassium tartrate; the mass concentration of disodium EDTA in the plating solution is 10-30 g / L; and the mass concentration of sodium potassium tartrate in the plating solution is 15-25 g / L.

5. The method for preparing the shaft-end grounding friction disk as described in claim 1, characterized in that, The D50 particle size of the copper-plated graphite powder is 75~150μm; the thickness of the copper layer coated on the surface of the graphite powder is 1~3μm.

6. The method for preparing the shaft-end grounding friction disk as described in claim 1, characterized in that, The aluminum-based powder has a D50 particle size of 1~50μm; the silicon carbide powder has a D50 particle size of 1~30μm.

7. The method for preparing the shaft-end grounding friction disk as described in claim 1, characterized in that, The aluminum-based powder comprises raw material components in the following mass ratio: aluminum powder, copper powder, and magnesium powder in a mass ratio of 47:2:

1.

8. The method for preparing the shaft-end grounding friction disk as described in claim 1, characterized in that, The cold pressing process uses a pressure of 100~200MPa and a holding time of 5~15s.

9. The method for preparing the shaft-end grounding friction disk as described in claim 1, characterized in that, The sintering process uses a sintering temperature of 580~650℃ and a sintering time of 0.5~2h; the heating rate of the pressed blank during the sintering process is 2~10℃ / min.

10. A shaft-end grounding friction disc, characterized in that, The shaft end grounding friction disk is prepared by the method described in any one of claims 1 to 9.

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