A process for soft anti-friction coating by electric spark alloying on the surface of tin-bronze bearing

Abstract

The invention discloses a tin bronze bearing surface electric spark alloying soft anti-friction coating process, comprising the following steps: step 1, grinding the tin bronze bearing and electrode with sandpaper until the surface roughness of the tin bronze bearing and electrode is 1-2 μm; step 2, cleaning the tin bronze bearing and electrode with ultrasonic wave in anhydrous ethanol at room temperature to remove grease and impurities on the surface, and drying the tin bronze bearing and electrode after cleaning; step 3, coating silver on the surface of the tin bronze bearing by electric spark alloying process to form a silver coating; step 4, coating copper on the surface of the tin bronze bearing by electric spark alloying process to form a copper coating on the basis of the silver coating; step 5, coating babbitt alloy on the surface of the tin bronze bearing by electric spark alloying process to form a babbitt alloy coating on the basis of the copper coating. The coated tin bronze bearing surface obtained by the technology has low friction coefficient, excellent anti-friction performance and strong fatigue resistance.

Description

Technical Field

[0001] The invention relates to the technical field of electric spark alloying, in particular to a process for electric spark alloying soft anti-friction coating on the surface of a tin-bronze bearing bush. Background Art

[0002] The bearing shell is an important component of the sliding bearing and is present in the rotating parts of industrial machinery and equipment. It can support the shaft and parts on the shaft, ensure the rotation accuracy of the shaft, and reduce the friction between the shaft and the supporting parts.

[0003] Electric spark alloying is a process method that utilizes the spark discharge effect between electrode materials and the surface of metal parts to melt and infiltrate the conductive material as the spark discharge electrode into the metal surface to form a surface alloy coating layer. It is a technology that directly uses high-density electric energy to coat the metal surface. Electric spark coating can effectively improve the wear resistance, corrosion resistance and heat resistance of the surface of parts without affecting the structure and performance of the substrate. It is particularly suitable for local processing of tools and large mechanical parts, and is widely used in electrical transmission, aerospace, military industry, automobile, turbine and other industries.

[0004] The rotating parts of industrial machinery and equipment often work under heavy load, high speed and high temperature environment. At the same time, they are also exposed to corrosive liquids during work, which will accelerate the corrosion and wear process of the rotating parts. Usually, the surface layer of industrial machinery and equipment bears the greatest load and is most affected by the external environment. Therefore, the performance of the surface layer of industrial machinery and equipment directly determines the service life and stability of the parts.

[0005] At present, copper-based alloy bearings are widely used in industrial machinery and equipment due to their excellent mechanical properties and thermal conductivity. However, analysis of the operation of copper-based alloy bearings shows that the existing bronze bearings have a large friction coefficient and are easy to wear the shaft diameter, and their tribological properties have become an obstacle to their further application. Summary of the invention

[0006] In view of the shortcomings of the prior art, the present invention provides a process for preparing a soft anti-friction coating on the surface of a tin-bronze bearing by electric spark alloying. The soft anti-friction coating on the surface of a tin-bronze bearing prepared by this method has the characteristics of good comprehensive surface performance, excellent anti-friction performance, strong fatigue resistance, high reliability and good durability, thereby solving the problem that the existing copper-based alloy bearings have a large friction coefficient and are easy to wear the shaft diameter.

[0007] To achieve the above object, the present invention provides the following technical solution: a process for preparing a soft anti-friction coating on the surface of a tin-bronze bearing bush by electric spark alloying, comprising the following steps:

[0008] Step 1, grinding the tin bronze bearing bush and the electrode with sandpaper, grinding the tin bronze bearing bush and the electrode with sandpaper in sequence until the surface roughness of the tin bronze bearing bush and the electrode is 1 to 2 μm;

[0009] Step 2, cleaning the surfaces of the tin bronze bearing bush and the electrode, using ultrasonic cleaning in anhydrous ethanol at room temperature to remove grease and impurities on the surface, and blowing the tin bronze bearing bush and the electrode dry after cleaning;

[0010] Step 3, alloying and coating silver, coating silver on the surface of the tin bronze bearing bush by an electric spark alloying process to form a silver coating;

[0011] Step 4, alloying and coating copper, coating copper by an electrospark alloying process to form a copper coating on the basis of the silver coating;

[0012] Step 5, alloying and coating the babbitt alloy, coating the babbitt alloy by an electric spark alloying process, forming a babbitt alloy coating on the basis of the copper coating, and the metallic copper and the metallic tin in the tin-based babbitt alloy form ε phase Cu6Sn5.

[0013] Preferably, the electrode in step 1 includes a silver electrode, a copper electrode, or a babbitt alloy electrode.

[0014] Preferably, the silver coating is a transition coating, and the voltage of the silver electrode during spark alloying is 60-100V, the capacitance is 90-240μF, and the working efficiency is 2-4min / cm 2 , speed is 2600r / min, and discharge frequency is 2500~3500Hz.

[0015] Preferably, the copper coating is a transition coating, and the voltage of the copper electrode during the electric spark alloying is 60-100V, the capacitance is 90-240μF, and the working efficiency is 2-4min / cm 2 , speed is 2600r / min, and discharge frequency is 3500~4500Hz.

[0016] Preferably, the voltage of the babbitt alloy electrode during spark alloying is 20-30V, the capacitance is 90-150μF, and the efficiency is 3-6min / cm 2 , speed is 2600r / min, frequency is 4500~5500Hz.

[0017] Preferably, the copper content of the tin bronze bearing is 89.10%, the tin content is 9.38%, the phosphorus content is 0.72%, and the impurity content is 0.80%; the silver content of the silver electrode is 99.99%, the impurity content is 0.01%, and the diameter of the silver electrode is 3mm and the length is 100mm; the copper content of the copper electrode is 99.99%, the impurity content is 0.01%, and the diameter of the copper electrode is 3mm and the length is 100mm; the babbitt alloy electrode is a tin-based babbitt alloy, and the tin content of the tin-based babbitt alloy is 83.10%, the antimony content is 11.02%, the copper content is 5.83%, the impurity content is 0.05%, and the diameter of the babbitt alloy electrode is 3mm and the length is 100mm.

[0018] Preferably, in the electric spark alloying process, the silver electrode, copper electrode, babbitt alloy electrode maintain an angle of 40 to 50 degrees with the surface of the tin bronze bearing, the left and right swing amplitude is 15 to 25 mm, and the movement speed of the electrode is 1 to 4 mm / s.

[0019] Preferably, in the electric spark alloying process, the alloying process is carried out at room temperature, using argon as the protective gas with a flow rate of 0.2 L / s.

[0020] Preferably, the thickness of the silver coating is between 30 and 80 μm, the thickness of the copper coating is between 40 and 80 μm, the thickness of the babbitt alloy coating is between 50 and 100 μm, and the thickness of the composite coating is between 120 and 260 μm.

[0021] The present invention has the following beneficial effects: the tin-bronze bearing surface electric spark alloying soft anti-friction coating process, which uses electric spark alloying technology to apply a composite coating including a silver coating, a copper coating, and a babbitt alloy coating on the surface of the tin-bronze bearing, can effectively reduce the friction coefficient of the tin-bronze bearing surface, and obtain a tin-bronze bearing with good comprehensive surface performance, excellent anti-friction performance, strong fatigue resistance, high reliability, and good durability. DETAILED DESCRIPTION

[0022] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without making any creative work shall fall within the scope of protection of the present invention.

[0023] Example 1

[0024] A process for preparing a soft anti-friction coating on the surface of a tin-bronze bearing bush by electric spark alloying, comprising the steps of grinding, cleaning, and electric spark alloying coating, specifically comprising the following steps:

[0025] Step 1, polishing the tin bronze bearing and the electrode with sandpaper, wherein the electrode includes a silver electrode, a copper electrode, and a babbitt alloy electrode, and polishing the tin bronze bearing and the electrode with sandpaper of types 400#, 600#, 800#, 1000#, 1200#, and 1500# in sequence until the surface roughness of the tin bronze bearing and the electrode is 1 to 2 μm;

[0026] Step 2, cleaning the surface of the tin bronze bearing and the electrode. Before the electrospark alloying coating, the tin bronze bearing and the electrode are cleaned with ultrasound in anhydrous ethanol at room temperature for 20 minutes to remove grease and impurities on the surface. After cleaning, the tin bronze bearing and the electrode are blown dry; Step 3, alloying and coating silver. Silver is coated on the surface of the tin bronze bearing by an electrospark alloying process to form a silver coating. The silver coating is a transition coating. When the silver electrode is electrospark alloyed, the voltage is 60V, the capacitance is 150μF, and the working efficiency is 3min / cm 2 , speed is 2600r / min, discharge frequency is 3000Hz;

[0027] Step 4, alloying and coating copper, coating copper on the surface of the tin bronze bearing by an electrospark alloying process, forming a copper coating on the basis of the silver coating, the copper coating is a transition coating, and the voltage of the copper electrode during electrospark alloying is 60V, the capacitance is 150μF, and the working efficiency is 3min / cm 2 , speed is 2600r / min, discharge frequency is 4000Hz;

[0028] Step 5, alloying and coating babbitt alloy, coating babbitt alloy on the surface of tin bronze bearing bush by electric spark alloying process, forming babbitt alloy coating on the basis of copper coating, metal copper forms ε phase Cu6Sn5 with tin in tin-based babbitt alloy, and the Cu6Sn5 can improve the bonding force between coatings, and the voltage of babbitt alloy electrode is 30V, the capacitance is 90μF, and the efficiency is 4min / cm 2 , speed is 2600r / min, frequency is 5000Hz.

[0029] After the above steps, the tin bronze bearing bushing has a coating on the surface. The coating is divided into three layers, the first layer is a silver coating, the second layer is a copper coating, and the third layer is a babbitt alloy coating. The coating hardness gradient is reduced and there are fewer cracks on the coating surface. The thickness of the silver coating is 50μm, the thickness of the copper coating is 60μm, the thickness of the babbitt alloy coating is 80μm, and the thickness of the composite coating is 190μm.

[0030] Furthermore, the copper content of the tin bronze bearing is 89.10%, the tin content is 9.38%, the phosphorus content is 0.72%, and the impurity content is 0.80%; the silver content of the silver electrode is 99.99%, the impurity content is 0.01%, and the diameter of the silver electrode is 3mm and the length is 100mm; the copper content of the copper electrode is 99.99%, the impurity content is 0.01%, and the diameter of the copper electrode is 3mm and the length is 100mm; the babbitt alloy electrode is a tin-based babbitt alloy, and the tin content of the tin-based babbitt alloy is 83.10%, the antimony content is 11.02%, the copper content is 5.83%, the impurity content is 0.05%, and the diameter of the babbitt alloy electrode is 3mm and the length is 100mm.

[0031] Furthermore, the silver electrode, copper electrode, and babbitt alloy electrode maintain an angle of 40 degrees with the surface of the tin-bronze bearing, the left-right swing amplitude is 15 mm, and the moving speed of the electrode is 2 mm / s.

[0032] Furthermore, the alloying process is carried out at room temperature, using argon with a purity of more than 99% as a protective gas at a flow rate of 0.2 L / s to prevent the coating area from being affected by the air.

[0033] Working principle: The wetting angle between silver and copper is small, which is beneficial to strengthen the metallurgical bonding between coatings and is suitable for use as a transition coating. Copper forms ε phase Cu6Sn5 with tin in tin-based babbitt alloy. The intermetallic compound Cu6Sn5 can prevent gravity segregation during solidification and improve the bonding between coatings. It is also suitable for transition layers. Therefore, the surface of the tin-bronze bearing is first electrospark alloyed with a silver coating, then with a copper coating, and finally with a babbitt coating. The coating consists of three layers, namely a silver coating, a copper coating, and a babbitt coating. The coating hardness gradient is reduced, which can reduce cracks on the material surface and reduce the friction coefficient.

[0034] Example 2

[0035] A process for producing a soft anti-friction coating on the surface of a tin-bronze bearing bush by electric spark alloying, comprising the steps of grinding, cleaning, and electric spark alloying coating, and comprising the following steps:

[0036] Step 1, polishing the tin bronze bearing and the electrode with sandpaper, wherein the electrode includes a silver electrode, a copper electrode, and a babbitt alloy electrode, and polishing the tin bronze bearing and the electrode with sandpaper of types 400#, 600#, 800#, 1000#, 1200#, and 1500# in sequence until the surface roughness of the tin bronze bearing and the electrode is 1 to 2 μm;

[0037] Step 2, cleaning the surface of the tin bronze bearing and the electrode. Before the electrospark alloying coating, the tin bronze bearing and the electrode are cleaned with ultrasonic waves in anhydrous ethanol at room temperature for 20 minutes to remove grease and impurities on the surface. After cleaning, the tin bronze bearing and the electrode are blown dry;

[0038] Step 3, alloying and coating silver, coating silver on the surface of the tin bronze bearing bush by an electrospark alloying process to form a silver coating, wherein the silver coating is a transition coating, and the voltage of the silver electrode during electrospark alloying is 100V, the capacitance is 90μF, and the working efficiency is 2min / cm 2 , speed is 2600r / min, discharge frequency is 3000Hz;

[0039] Step 4, alloying and coating copper, coating copper on the surface of the tin bronze bearing by an electrospark alloying process, forming a copper coating on the basis of the silver coating, the copper coating is a transition coating, and the voltage of the copper electrode during electrospark alloying is 80V, the capacitance is 150μF, and the working efficiency is 2min / cm 2 , speed is 2600r / min, discharge frequency is 4500Hz;

[0040] Step 5, alloying and coating babbitt alloy, coating babbitt alloy on the surface of tin bronze bearing bush by electric spark alloying process, forming babbitt alloy coating on the basis of copper coating, metal copper forms ε phase Cu6Sn5 with tin in tin-based babbitt alloy, and the Cu6Sn5 can improve the bonding force between coatings, and the voltage of babbitt alloy electrode is 25V, the capacitance is 90μF, and the efficiency is 5min / cm 2 , speed is 2600r / min, frequency is 4500Hz.

[0041] After the above steps, the tin bronze bearing bushing has a coated surface. The coating is divided into three layers, the first layer is a silver coating, the second layer is a copper coating, and the third layer is a babbitt alloy coating. The coating hardness gradient is reduced and there are fewer cracks on the coating surface. The thickness of the silver coating is 60μm, the thickness of the copper coating is 60μm, the thickness of the babbitt alloy coating is 90μm, and the thickness of the composite coating is 210μm.

[0042] Furthermore, the copper content of the tin bronze bearing is 89.10%, the tin content is 9.38%, the phosphorus content is 0.72%, and the impurity content is 0.80%; the silver content of the silver electrode is 99.99%, the impurity content is 0.01%, and the diameter of the silver electrode is 3mm and the length is 100mm; the copper content of the copper electrode is 99.99%, the impurity content is 0.01%, and the diameter of the copper electrode is 3mm and the length is 100mm; the babbitt alloy electrode is a tin-based babbitt alloy, and the tin content of the tin-based babbitt alloy is 83.10%, the antimony content is 11.02%, the copper content is 5.83%, the impurity content is 0.05%, and the diameter of the babbitt alloy electrode is 3mm and the length is 100mm.

[0043] Furthermore, the silver electrode, copper electrode, and babbitt alloy electrode maintain an angle of 50 degrees with the surface of the tin-bronze bearing, the left-right swing amplitude is 15 mm, and the moving speed of the electrode is 4 mm / s.

[0044] Furthermore, the alloying process is carried out at room temperature, using argon with a purity of more than 99% as a protective gas at a flow rate of 0.2 L / s to prevent the coating area from being affected by the air.

[0045] Example 3

[0046] A process for producing a soft anti-friction coating on the surface of a tin-bronze bearing bush by electric spark alloying, comprising the steps of grinding, cleaning, and electric spark alloying coating, and comprising the following steps:

[0047] Step 1, polishing the tin bronze bearing and the electrode with sandpaper, wherein the electrode includes a silver electrode, a copper electrode, and a babbitt alloy electrode, and polishing the tin bronze bearing and the electrode with sandpaper of types 400#, 600#, 800#, 1000#, 1200#, and 1500# in sequence until the surface roughness of the tin bronze bearing and the electrode is 1 to 2 μm;

[0048] Step 2, cleaning the surface of the tin bronze bearing and the electrode. Before the electrospark alloying coating, the tin bronze bearing and the electrode are cleaned with ultrasonic waves in anhydrous ethanol at room temperature for 20 minutes to remove grease and impurities on the surface. After cleaning, the tin bronze bearing and the electrode are blown dry;

[0049] Step 3, alloying and coating silver, coating silver on the surface of the tin bronze bearing bush by an electrospark alloying process to form a silver coating, wherein the silver coating is a transition coating, and the voltage of the silver electrode during electrospark alloying is 80V, the capacitance is 150μF, and the working efficiency is 4min / cm 2 , speed is 2600r / min, discharge frequency is 3000Hz;

[0050] Step 4, alloying and coating copper, coating copper on the surface of the tin bronze bearing by an electrospark alloying process, forming a copper coating on the basis of the silver coating, the copper coating is a transition coating, and the voltage of the copper electrode during electrospark alloying is 60V, the capacitance is 150μF, and the working efficiency is 4min / cm 2 , speed is 2600r / min, discharge frequency is 4500Hz;

[0051] Step 5, alloying and coating babbitt alloy, coating babbitt alloy on the surface of tin bronze bearing bush by electric spark alloying process, forming babbitt alloy coating on the basis of copper coating, metal copper forms ε phase Cu6Sn5 with tin in tin-based babbitt alloy, and the Cu6Sn5 can improve the bonding force between coatings, and the voltage of babbitt alloy electrode is 20V, the capacitance is 150μF, and the efficiency is 6min / cm 2 , speed is 2600r / min, frequency is 4500Hz.

[0052] After the above steps, the tin bronze bearing bushing has a coated surface. The coating is divided into three layers, the first layer is a silver coating, the second layer is a copper coating, and the third layer is a babbitt alloy coating. The coating hardness gradient is reduced and there are fewer cracks on the coating surface. The thickness of the silver coating is 70μm, the thickness of the copper coating is 70μm, the thickness of the babbitt alloy coating is 90μm, and the thickness of the composite coating is 230μm.

[0053] Furthermore, the copper content of the tin bronze bearing is 89.10%, the tin content is 9.38%, the phosphorus content is 0.72%, and the impurity content is 0.80%; the silver content of the silver electrode is 99.99%, the impurity content is 0.01%, and the diameter of the silver electrode is 3mm and the length is 100mm; the copper content of the copper electrode is 99.99%, the impurity content is 0.01%, and the diameter of the copper electrode is 3mm and the length is 100mm; the babbitt alloy electrode is a tin-based babbitt alloy, and the tin content of the tin-based babbitt alloy is 83.10%, the antimony content is 11.02%, the copper content is 5.83%, the impurity content is 0.05%, and the diameter of the babbitt alloy electrode is 3mm and the length is 100mm.

[0054] Furthermore, the silver electrode, copper electrode, and babbitt alloy electrode maintain an angle of 45 degrees with the surface of the tin-bronze bearing, the left-right swing amplitude is 20 mm, and the moving speed of the electrode is 3 mm / s.

[0055] Furthermore, the alloying process is carried out at room temperature, using argon with a purity of more than 99% as a protective gas at a flow rate of 0.2 L / s to prevent the coating area from being affected by the air.

[0056] Comparative Example

[0057] The comparative example uses an uncoated tin bronze bearing as a control group to compare and verify the performance of the coated tin bronze bearing in Example 1. The surface hardness, friction coefficient, operating stability and durability of the tin bronze bearing are tested by measuring Vickers hardness, friction and wear tests, and trial run tests.

[0058] The microhardness distribution of the coating cross section was measured using a Vickers hardness tester. The microhardness of the soft anti-friction coating was measured at different positions using an indenter at a pressure of 0.098N and a holding time of 12s. The microhardness change from the surface of the soft anti-friction coating to the substrate shows an obvious gradient distribution, which can be divided into four parts: tin-based babbitt alloy coating area, copper transition area, silver transition area and substrate. The material deposited on the surface of the soft anti-friction coating is tin-based babbitt alloy, and the coating is relatively soft with a microhardness of 29HV 0.01 The microhardness of the copper transition zone coating is 157HV 0.01 The microhardness of Ag transition zone coating is about 95HV 0.01 Subsequently, the hardness of the composite coating gradually increased and transitioned to the substrate, and the microhardness of the substrate was 161HV 0.01 The microhardness of the soft anti-friction coating gradually changes from the surface to the substrate, which is beneficial to improve the bonding strength between metals and reduce cracks. From the surface of the soft anti-friction coating to the substrate, its hardness first increases, then decreases, and finally increases. The hardness of the composite coating is 82% lower than that of the tin bronze substrate.

[0059] The friction properties of the bearing surface were studied using a friction and wear tester. The friction data of the bearing reciprocating under dry friction conditions at 25°C were detected. The corresponding friction pair was made of a bearing steel (GCr15) ball with a diameter of 8 mm. The sliding speed was 20 mm / s, the pressure loading speed was 10 mm / min, and the friction contact distance was 6 mm. The applied pressure was 5N, 10N and 15N in sequence, and each test time was 600 seconds. Under a load of 5N, the average friction coefficient for the initial 600 seconds was about 0.4. In the next 600 seconds, under a load of 10N, the friction coefficient was about 0.24. Then under a load of 15N, in the last 600 seconds, the friction coefficient was about 0.18. The friction coefficient of the uncoated tin bronze bearing under the same conditions was about 0.32. The study of the tribological properties of the coating under dry friction shows that the coating deposited with a soft anti-friction material has a lower friction resistance. The surface friction coefficient of the anti-friction coating is about 56% of that of the tin bronze bearing. For the EDM alloying coating, the friction coefficient is large at the beginning of friction, which is mainly affected by the surface roughness. Therefore, within the initial 600 seconds under a load of 5N, the friction coefficient is about 0.4 due to the influence of the surface roughness. The soft anti-friction coating with lower hardness is plastically deformed due to the higher hardness of GCr15. With the formation of the friction film, the friction track of the soft anti-friction coating-GCr15 friction pair appears on the surface. Similar to other common friction pairs, the steady-state friction coefficient is no longer affected by the surface roughness of the friction pair. After the first running-in stage, under a load of 10N, the friction coefficient of the soft anti-friction coating showed a relatively stable state in the next 600 seconds, with an average value of about 0.24. After that, under a load of 15N, the friction coefficient dropped to 0.18. After the running-in stage, the friction coefficient of the soft anti-friction coating gradually stabilized.

[0060] After the machined bearings are filled with lubricating oil, the running test is carried out for a total of 3 hours with a light load of 10N and a speed of 700r / min, and the external temperature of the bearings is checked at any time. After the light load running test, a trial run test is carried out for 8 hours with a load of 30N and a speed of 700r / min, and the external temperature of the bearings is checked at any time. According to the analysis of the trial run test data, the tin bronze bearings without anti-friction coating run stably, and the external temperature of the bearings increases by 12°C; the tin bronze bearings with anti-friction coating run stably, and the external temperature of the bearings only increases by 8°C. After the trial run, it was found that the surface of the bearings without anti-friction coating was burned and blackened, and the surface wear was serious; the surface of the bearings with anti-friction coating did not show any burning phenomenon, the scratches were not obvious, and the wear was slight. Overall, the temperature rise of the coated sliding bearing bearings is small, the operation is stable and reliable, and the durability is good.

[0061] The test results show that the coated tin bronze bearing in the embodiment of the present invention has a lower friction coefficient, stronger fatigue resistance and better durability than the uncoated tin bronze bearing.

[0062] In summary, the tin-bronze bearing surface electrospark alloying soft anti-friction coating process solves the problem of large friction coefficient and easy wear of the shaft diameter of the existing bronze bearing by coating the surface of the tin-bronze bearing.

[0063] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A process for producing a soft anti-friction coating on the surface of a tin-bronze bearing bush by electric spark alloying, characterized in that The following steps are involved: Step 1, grinding the tin bronze bearing bush and the electrode with sandpaper, grinding the tin bronze bearing bush and the electrode with sandpaper in sequence until the surface roughness of the tin bronze bearing bush and the electrode is 1 to 2 μm; Step 2, cleaning the surfaces of the tin bronze bearing bush and the electrode, using ultrasonic cleaning in anhydrous ethanol at room temperature to remove grease and impurities on the surface, and blowing the tin bronze bearing bush and the electrode dry after cleaning; Step 3, alloying and coating silver, coating silver on the surface of the tin bronze bearing bush by an electric spark alloying process to form a silver coating; Step 4, alloying and coating copper, coating copper by an electrospark alloying process to form a copper coating on the basis of the silver coating; Step 5, alloying and coating the babbitt alloy, coating the babbitt alloy by an electric spark alloying process, forming a babbitt alloy coating on the basis of the copper coating, and the metallic copper and the metallic tin in the tin-based babbitt alloy form ε phase Cu6Sn5.

2. The process for preparing a soft anti-friction coating on the surface of a tin-bronze bearing bush by electric spark alloying as claimed in claim 1, characterized in that: The electrodes described in step 1 include silver electrodes, copper electrodes, and babbitt alloy electrodes.

3. The process for preparing a soft anti-friction coating on the surface of a tin-bronze bearing bush by electric spark alloying as claimed in claim 2, characterized in that: The silver coating is a transition coating. When the silver electrode is subjected to electric spark alloying, the voltage is 60 to 100 V, the capacitance is 90 to 240 μF, and the working efficiency is 2 to 4 min / cm 2 , speed is 2600r / min, and discharge frequency is 2500~3500Hz.

4. The process for preparing a soft anti-friction coating on the surface of a tin-bronze bearing bush by electric spark alloying as claimed in claim 2, characterized in that: The copper coating is a transition coating. When the copper electrode is subjected to electric spark alloying, the voltage is 60 to 100 V, the capacitance is 90 to 240 μF, and the working efficiency is 2 to 4 min / cm 2 , speed is 2600r / min, and discharge frequency is 3500~4500Hz.

5. The process for preparing a soft anti-friction coating on the surface of a tin-bronze bearing bush by electric spark alloying as claimed in claim 2, characterized in that: The voltage of the babbitt alloy electrode during the electric spark alloying is 20-30V, the capacitance is 90-150μF, and the efficiency is 3-6min / cm 2 , speed is 2600r / min, frequency is 4500~5500Hz.

6. The process for preparing a soft anti-friction coating on the surface of a tin-bronze bearing bush by electric spark alloying as claimed in claim 2, characterized in that: The tin bronze bearing has a copper content of 89.10%, a tin content of 9.38%, a phosphorus content of 0.72%, and the remainder is impurities; the silver electrode has a silver content of 99.99%, the remainder is impurities, and the diameter of the silver electrode is 3 mm and the length is 100 mm; the copper electrode has a copper content of 99.99%, the remainder is impurities, and the diameter of the copper electrode is 3 mm and the length is 100 mm; the babbitt alloy electrode is a tin-based babbitt alloy, and the tin content of the tin-based babbitt alloy is 83.10%, the antimony content is 11.02%, the copper content is 5.83%, and the remainder is impurities, and the diameter of the babbitt alloy electrode is 3 mm and the length is 100 mm.

7. The process for preparing a soft anti-friction coating on the surface of a tin-bronze bearing bush by electric spark alloying as claimed in claim 2, characterized in that: In the electric spark alloying process, the silver electrode, copper electrode, babbitt alloy electrode and the surface of the tin bronze bearing bush maintain an angle of 40 to 50 degrees, the left and right swing amplitude is 15 to 25 mm, and the moving speed of the electrode is 1 to 4 mm / s.

8. The process for preparing a soft anti-friction coating on the surface of a tin-bronze bearing bush by electric spark alloying as claimed in claim 2, characterized in that: In the EDM alloying process, the alloying process is carried out at room temperature, using argon as the protective gas with a flow rate of 0.2 L / s.

9. The process for preparing a soft anti-friction coating on the surface of a tin-bronze bearing bush by electric spark alloying as claimed in claim 2, characterized in that: The thickness of the silver coating is between 30 and 80 μm, the thickness of the copper coating is between 40 and 80 μm, the thickness of the babbitt alloy coating is between 50 and 100 μm, and the thickness of the composite coating is between 120 and 260 μm.