Preparation method of water-lubricated graphite bearing material for nuclear power main pump

Abstract

The invention provides a preparation method of a water-lubricated graphite bearing material for a nuclear power main pump, which adopts ultrafine powder as a main aggregate and high-wear-resistance carbon black as an additive, and adopts a two-time mixing and high-pressure impregnation production process to improve the uniformity of an internal structure of a graphite product and improve various properties of the product. Further, the high-temperature and high-pressure wear resistance and the radioactive medium irradiation resistance of the material are improved; an isostatic pressing forming mode is adopted to improve the microstructure of the material, and the anisotropy ratio of traditional pressing forming is reduced; the two-time mixing and high-pressure impregnation process is adopted, the material strength is improved, meanwhile, air holes in a graphite material base body are distributed more uniformly, and the obtained graphite material base body has the excellent performance of being uniform in distribution, high in density, low in air hole and high in strength.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of non-metallic graphite bearing material preparation, in particular to a nuclear power main pump water-lubricated graphite bearing material preparation method. BACKGROUND

[0002] Bearing is an important part in modern mechanical equipment, mainly used for supporting mechanical rotating body, reducing its friction coefficient in the process of movement, and ensuring its rotation accuracy. Common bearings include sliding bearings, rolling bearings and joint bearings. Among them, sliding bearing refers to the bearing working under sliding friction, and the lubrication mode of sliding bearing mainly includes water lubrication and oil lubrication. Oil leakage often occurs in oil lubrication, which pollutes the environment. Compared with oil lubrication bearing, water lubrication bearing uses water as lubricant, which has the performance advantages of green environmental protection and low energy consumption, and is widely used in fields such as ships, water pumps and water turbines.

[0003] In nuclear power plant, the main pump is the only rotating equipment, which mainly adopts water lubrication mode, and the quality of water lubrication bearing material is closely related to the safety and reliability of nuclear pump. In view of the harsh environment of high temperature and radiation in nuclear power plant, the water lubrication bearing material is generally prepared by inorganic materials such as graphite or siliconized graphite at present, and the graphite bearing material obtained by the existing preparation method has the problems of poor flexibility, poor strength and poor wear resistance. When impacted by load in the use process, brittle fracture is easy to occur, thereby affecting the safe operation of nuclear pump.

[0004] Based on this, the present application provides a nuclear power main pump water-lubricated graphite bearing material preparation method to solve the above technical problems. SUMMARY

[0005] The technical problem solved by the present application is to overcome the defects of poor flexibility, poor strength and poor wear resistance of the bearing material of the existing main pump, and to provide a nuclear power main pump water-lubricated graphite bearing material preparation method.

[0006] The present application solves the above technical problems by the following technical scheme:

[0007] The present application provides a nuclear power main pump water-lubricated graphite bearing material preparation method, comprising:

[0008] Step 1, put graphite powder and high wear-resistant carbon black into a mixing tank and mix uniformly to obtain mixed powder;

[0009] Step 2, put the mixed powder and ultra-fine coke powder into a mixing and kneading pot and stir to mix uniformly, and add pitch during heating and kneading and continue to knead to obtain a first kneaded paste;

[0010] Step 3, roll the first kneaded paste to obtain a first sheet with a thickness not higher than 2mm.

[0011] Step 4: Place the first material sheet into a kneading pot with an initial temperature of 150±10℃ and knead it. After heating and kneading, a second kneaded paste is obtained.

[0012] Step 5: Roll the second mixed paste into sheets to obtain a second sheet with a thickness not exceeding 2 mm;

[0013] Step 6: After cooling the second sheet, crush and grind it to obtain pressed powder with a particle size of no more than 45 μm, and then perform isostatic pressing to obtain a blank.

[0014] Step 7: After subjecting the billet to a first firing, a first high-pressure asphalt impregnation, a second firing, a second high-pressure asphalt impregnation, a third firing, and graphitization treatment, the product is obtained.

[0015] According to an embodiment of the present invention, in step 1,

[0016] The graphite powder and the high abrasion-resistant carbon black are mixed in the mixing tank at a ratio of 50 wt% to 50 wt%; wherein the particle size of both the graphite powder and the high abrasion-resistant carbon black is not higher than 45 μm, the rotation speed of the mixing tank is 150 rpm, and the mixing time is 24 h.

[0017] According to an embodiment of the present invention, in step 2,

[0018] After the mixed powder and the ultrafine coke powder are mixed evenly, they are heated and kneaded to 100-120°C within 1 hour. Then the asphalt is added and kneaded for 2 hours to obtain the first kneaded paste.

[0019] According to an embodiment of the present invention, in step 2,

[0020] The content of the ultrafine coke powder is 80 wt%, and the particle size of the ultrafine coke powder is not higher than 10 μm; the content of the mixed powder is 20 wt%.

[0021] According to an embodiment of the present invention, in step 2,

[0022] The asphalt is added at a temperature of 160-180℃, the softening point of the asphalt is 80-105℃, and the residual carbon content is 35-45%; the mass of the asphalt added is 50-60% of the total mass of the mixed powder.

[0023] According to one embodiment of the present invention, in step 4,

[0024] The first material has a content of 100wt%, the mixing pot temperature is 150±10℃, and the outlet temperature of the second mixed paste is 165±5℃.

[0025] According to one embodiment of the present invention, in step 5,

[0026] The second mixed paste is rolled at a temperature of 130-150℃ to obtain the second sheet.

[0027] According to one embodiment of the present invention, in step 6,

[0028] The isostatic pressing process pressure is 150 MPa.

[0029] According to one embodiment of the present invention, in step 7,

[0030] The conditions for the first calcination treatment are: heating to 1100℃ at a heating rate of 5℃ / h and holding at that temperature for 30h;

[0031] The conditions for the second and third roastings are as follows: heating to 900°C at a heating rate of 10°C / h and holding for 1 hour.

[0032] According to one embodiment of the present invention, in step 7,

[0033] The conditions for the first and second high-pressure asphalt impregnation treatments are as follows:

[0034] Under conditions of temperature of 180-200℃ and pressure of 2.2-3.0MPa, medium-temperature asphalt with a softening point of 70-90℃ was used as an impregnating agent for 15 hours.

[0035] According to one embodiment of the present invention, in step 7,

[0036] The graphitization treatment conditions are as follows: starting from room temperature, the temperature is increased to 2300±10℃ at a heating rate of 50℃ / h, and held for 5h.

[0037] The positive and progressive effects of this invention are as follows:

[0038] This invention relates to a method for preparing water-lubricated graphite bearing materials for nuclear power plant main pumps. The method uses ultrafine powder as the main aggregate and high-wear-resistant carbon black as an additive. It employs a two-stage mixing and high-pressure impregnation process to improve the internal structural uniformity of the graphite product, enhance various product properties, and thereby improve the material's resistance to high-temperature and high-pressure wear and its resistance to radiation from radioactive media.

[0039] Isostatic pressing is used to improve the microstructure of materials and reduce the anisotropy ratio of traditional compression molding.

[0040] By employing a two-stage mixing and high-pressure impregnation process, the strength of the material is improved while the internal distribution of the graphite matrix and the pores are more uniform. The resulting graphite matrix has excellent properties such as uniform distribution, high density, low porosity, and high strength. Attached Figure Description

[0041] The above and other features, properties and advantages of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings and embodiments, wherein:

[0042] Figure 1 This is a process flow diagram of the method for preparing water-lubricated graphite bearing material for nuclear power main pumps according to the present invention. Detailed Implementation

[0043] The present invention will be further described below with reference to specific embodiments and accompanying drawings. More details are set forth in the following description in order to provide a full understanding of the present invention. However, the present invention can obviously be implemented in many other ways different from those described herein. Those skilled in the art can make similar extensions and derivations based on actual application situations without departing from the spirit of the present invention. Therefore, the scope of protection of the present invention should not be limited by the content of this specific embodiment.

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0045] Reference Figure 1 This invention proposes a method for preparing a water-lubricated graphite bearing material for a nuclear power plant main pump, comprising:

[0046] Step 1: Put graphite powder and high abrasion-resistant carbon black into a mixing tank and mix them evenly to obtain a uniform powder.

[0047] Specifically, the graphite powder and high abrasion-resistant carbon black were mixed in a mixing tank at a ratio of 50 wt% and 50 wt% respectively. The particle size of both the graphite powder and the high abrasion-resistant carbon black was no higher than 45 μm. The rotation speed of the mixing tank was 150 rpm and the mixing time was 24 h.

[0048] Step 2: Put the mixed powder and ultrafine coke powder into a kneading pot and stir to mix evenly. Add asphalt while heating and kneading and continue kneading to obtain the first kneaded paste.

[0049] Specifically, after mixing the powdered material and the ultrafine coke powder, they are heated and kneaded simultaneously to 100-120°C within 1 hour. Then, asphalt is added and kneaded for 2 hours to obtain the first kneaded paste.

[0050] The content of ultrafine coke powder is 80 wt%, and the particle size of ultrafine coke powder is not higher than 10 μm; the content of the mixed powder is 20 wt%. The asphalt addition temperature is 160-180℃, the softening point of the asphalt is 80-105℃, and the residual carbon rate is 35-45%; the asphalt addition mass is 50-60% of the total mass of the mixed powder.

[0051] Step 3: Roll the first mixed paste into sheets to obtain a first sheet with a thickness not exceeding 2mm.

[0052] Step 4: Place the first material into a kneading pot with an initial temperature of 150±10℃ and knead it. After heating and kneading, the second kneaded paste is obtained.

[0053] Specifically, the first batch of material has a content of 100 wt%, the mixing pot temperature is 150 ± 10 ℃, and the discharge temperature of the second batch of mixed paste is 165 ± 5 ℃.

[0054] Step 5: Roll the second mixed paste into sheets to obtain a second sheet with a thickness not exceeding 2mm.

[0055] Specifically, the second mixed paste is rolled at a temperature of 130-150℃ to obtain the second sheet.

[0056] Step 6: After cooling the second sheet, crush and grind it to obtain pressed powder with a particle size of no more than 45 μm, and then perform isostatic pressing to obtain a blank.

[0057] Specifically, the isostatic pressing process pressure is 150 MPa.

[0058] Step 7: After the billet undergoes a first firing, a first high-pressure asphalt impregnation, a second firing, a second high-pressure asphalt impregnation, a third firing, and graphitization treatment, the product is obtained.

[0059] The first calcination treatment conditions were: heating to 1100℃ at a heating rate of 5℃ / h and holding for 30h. The second and third calcination treatment conditions were: heating to 900℃ at a heating rate of 10℃ / h and holding for 1h. The first and second high-pressure asphalt impregnation treatment conditions were: impregnation with medium-temperature asphalt with a softening point of 70-90℃ as the impregnating agent at a temperature of 180-200℃ and a pressure of 2.2-3.0MPa for 15h. The graphitization treatment conditions were: starting from room temperature, heating to 2300±10℃ at a heating rate of 50℃ / h and holding for 5h.

[0060] Example 1

[0061] Example 1 is a preparation method that meets the requirements of the present invention, wherein the steps include:

[0062] First, graphite powder with a content of 50wt% and a particle size of 45μm and high abrasion-resistant carbon black with a content of 50wt% and a particle size of 45μm are placed in a mixing tank and mixed. The mixing tank rotates at 150 rpm and the mixing time is 24 hours to obtain a uniform powder.

[0063] Then, ultrafine coke powder with a particle size of less than 10μm (D50≤5μm) and a content of 80wt% and a mixed powder content of 20wt% are placed in a kneading pot and heated and mixed for 1 hour. After the temperature of the powder in the pot gradually rises to 110℃, medium-temperature asphalt with a temperature of 178℃, a softening point of 85℃, and a residual carbon content of 35% is added. 60wt% of the total dry powder in the pot is added to the kneading pot, and after heating and kneading for 2 hours, the temperature of the paste in the pot reaches 170℃ and is removed from the pot. The first kneaded paste is rolled into sheets with a sheet thickness of 2mm in a rolling mill at a temperature of 150℃ to obtain the first sheet.

[0064] The first material with a content of 100wt is further placed into a kneading pot with an initial temperature of 150℃, heated and kneaded for 1 hour, and the temperature is gradually raised to 170℃ before being removed from the pot to obtain a second kneaded paste. The second kneaded paste is then rolled into a sheet in a rolling mill with a temperature of 150℃ to obtain a second material sheet with a thickness of 2mm.

[0065] After the second sheet cools naturally, it is crushed and ground into powder with a particle size of less than 45μm to form pressed powder. The pressed powder is then subjected to cold isostatic pressing at a pressure of 150MPa to obtain a billet.

[0066] The obtained billet was subjected to a first firing, a first high-pressure pitch impregnation, a second firing, a second high-pressure pitch impregnation, a third firing, and graphitization treatment in sequence to obtain a product with a bulk density of 1.91–1.94 g / cm³, a porosity of 3.2–3.7%, a flexural strength of 63.3–65.1 MPa, and a compressive strength of 176.8–177.1 MPa. The product serves as the graphite material matrix.

[0067] The conditions for the first roasting were: heating to 1100℃ at a heating rate of 5℃ / h and holding for 30h; the conditions for the second and third roasting were: heating to 900℃ at a heating rate of 10℃ / h and holding for 15h.

[0068] The treatment conditions for the first and second high-pressure asphalt impregnation were as follows: impregnation with a medium-temperature asphalt impregnating agent with a softening point of 78℃ for 10 hours at a temperature of 200℃ and a pressure of 2.3MPa.

[0069] The graphitization process conditions were as follows: starting from room temperature, the temperature was increased to 2300℃ at a rate of 50℃ / h, and held at that temperature for 5h.

[0070] Example 1 is an example prepared in accordance with the requirements of the preparation method of the present invention.

[0071] Example 2

[0072] The preparation steps of Example 2 include:

[0073] First, graphite powder with a content of 50 wt% and a particle size of 45 μm and high wear-resistant carbon black with a content of 50 wt% and a particle size of 45 μm are placed in a mixing tank and mixed. The mixing tank rotates at 150 rpm and the mixing time is 24 h to obtain mixed material A (mixed material powder).

[0074] Then, ultrafine coke powder with a particle size of less than 10 μm (D50≤5 μm) and a content of 80 wt% and mixed powder with a content of 20 wt% were placed in a kneading pot and heated and mixed for 1 hour. After the temperature of the powder in the pot gradually rose to 110°C, medium-temperature asphalt with a temperature of 178°C, a softening point of 85°C, and a residual carbon content of 35% was added. 60 wt% of the total dry powder in the pot was added to the kneading pot, and after heating and kneading for 2 hours, the paste temperature in the pot reached 170°C and was removed from the pot. The removed paste was then rolled into a sheet with a thickness of 2 mm in a rolling mill at a temperature of 150°C to obtain sheet B (corresponding to the first sheet in Example 1).

[0075] Material B is crushed and ground to a particle size of less than 45μm to make pressed powder C. Pressed powder C is then subjected to cold isostatic pressing at a pressure of 150MPa to obtain billet D.

[0076] The obtained blank D was subjected to a first calcination, a first high-pressure asphalt impregnation, a second calcination, a second high-pressure asphalt impregnation, a third calcination, and graphitization treatment to obtain product E with a bulk density of 1.81–1.92 g / cm3, a porosity of 5.9–8.3%, a flexural strength of 48.7–62.5 MPa, and a compressive strength of 142.6–159.8 MPa.

[0077] The first calcination treatment conditions were: heating to 1100℃ at a heating rate of 5℃ / h and holding for 30h; the second and third calcination treatment conditions were: heating to 900℃ at a heating rate of 10℃ / h and holding for 15h. The first and second high-pressure asphalt impregnation treatment conditions were: impregnation with a medium-temperature asphalt impregnating agent with a softening point of 78℃ for 10h at a temperature of 200℃ and a pressure of 2.3MPa. The graphitization treatment conditions were: starting from room temperature, heating to 2300℃ at a heating rate of 50℃ / h and holding for 5h.

[0078] As can be seen, the second embodiment, as a comparative example of the present invention, does not involve further kneading and rolling after obtaining the first sheet, but instead directly crushes and grinds it.

[0079] Example 3

[0080] The preparation steps in Example 3 include:

[0081] First, graphite powder with a content of 50 wt% and a particle size of 45 μm and high abrasion-resistant carbon black with a content of 50 wt% and a particle size of 45 μm are placed in a V-shaped mixing tank for mixing. The mixing tank rotates at 150 rpm and the mixing time is 24 h to obtain mixed material A (mixed material powder).

[0082] Then, ultrafine coke powder with a particle size of less than 10 μm (D50≤5 μm) and a content of 80 wt% and mixed material A with a content of 20 wt% were placed in a kneading pot and heated and mixed for 1 hour. After the temperature of the powder in the pot gradually rose to 110°C, medium-temperature asphalt with a temperature of 178°C, a softening point of 85°C, and a residual carbon content of 35% was added. 60 wt% of the total dry powder in the pot was added to the kneading pot, and after heating and kneading for 2 hours, the temperature of the paste in the pot reached 170°C and the paste was removed from the pot. The paste was then rolled into sheets with a thickness of 2 mm in a rolling mill at a temperature of 150°C to obtain sheet B (corresponding to the first sheet in Example 1).

[0083] Material B is crushed and ground to a particle size of less than 45μm to make pressed powder C. Pressed powder C is then subjected to cold isostatic pressing at a pressure of 150MPa to obtain billet D.

[0084] The obtained blank D was subjected to a first firing, a first pitch impregnation, a second firing, a second pitch impregnation, a third firing, and graphitization treatment in sequence to obtain product E with a bulk density of 1.73-1.82 g / cm3, a porosity of 7.30-10.21%, a flexural strength of 44.3-51.2 MPa, and a compressive strength of 131.6-146.8 MPa.

[0085] The first calcination treatment conditions were: heating to 1100℃ at a heating rate of 5℃ / h and holding for 30h; the second and third calcination treatment conditions were: heating to 900℃ at a heating rate of 10℃ / h and holding for 15h. The first and second high-pressure asphalt impregnation treatment conditions were: impregnation with a medium-temperature asphalt impregnating agent with a softening point of 78℃ for 10h at a temperature of 200℃ and a pressure of 1.0MPa. The graphitization treatment conditions were: starting from room temperature, heating to 2300℃ at a heating rate of 50℃ / h and holding for 5h.

[0086] Compared to the first embodiment, the third embodiment does not perform a second kneading after obtaining material B, but directly performs crushing and grinding. At the same time, the treatment conditions for the first and second high-pressure asphalt impregnation are also different, with the pressure value reduced to 1.0 MPa.

[0087] Compared to the second embodiment, the treatment conditions for the first and second high-pressure asphalt impregnations are also different, with the pressure value reduced to 1.0 MPa.

[0088] The properties of the graphite materials obtained in Examples 1-3 were tested, and the results are shown in the table below:

[0089]

[0090]

[0091] It can be seen that the role of graphite powder as a raw material is lubrication and heat conduction, improving the lubricity and thermal conductivity of the product; the role of high wear-resistant carbon black is to ensure the structural strength of the product; ultrafine coke powder is ultrafine pitch coke powder, and the role of ultrafine pitch coke powder is a binder, used to better and more uniformly mix graphite powder and high wear-resistant carbon black.

[0092] For the above embodiments 1-3, the variables of embodiments 1 and 2 are: Embodiment 2 omits the further processing steps of the first sheet in embodiment 1. A single rolling process cannot ensure the uniformity of the product, which results in: a decrease in the bulk density of the graphite material product, an increase in porosity, a decrease in Shore hardness, a decrease in flexural strength and a decrease in compressive strength.

[0093] Furthermore, based on Example 2, if the treatment conditions of the first and second high-pressure asphalt impregnation are adjusted, i.e., the pressure is reduced, the following will occur: reduced bulk density, increased porosity, reduced Shore hardness, reduced flexural strength, and reduced compressive strength.

[0094] That is, in the preparation method provided by the present invention, by adopting a production process of two mixing and high pressure impregnation, the internal structure uniformity of graphite products is improved, the bulk density, Shore hardness, flexural strength and compressive strength of the products are increased, and the porosity is reduced.

[0095] In summary, the method for preparing water-lubricated graphite bearing material for nuclear power main pumps provided by this invention uses ultrafine pitch coke powder (D50 = 5μm) as the main raw material and employs a two-stage mixing and high-pressure pitch impregnation process, which improves the material's sealing performance and resistance to high-temperature wear, while also exhibiting high density and uniformity.

[0096] Furthermore, isostatic pressing improves the microstructure of the material and reduces the anisotropy ratio of traditional pressing (to 1.05:1), thereby improving wear resistance. Thus, the preparation method provided by this invention helps to improve the yield and makes the product matrix have low porosity and uniform distribution. The obtained graphite matrix has the advantages of high bulk density, high strength and uniform performance distribution.

[0097] In the description of the embodiments of this application, unless otherwise expressly specified and limited, the technical terms such as "installation", "connection", "joining", and "fixing" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can also refer to mechanical connections. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0098] This application uses specific terms to describe embodiments of the application. Terms such as "an embodiment," "one embodiment," and / or "some embodiments" refer to a particular feature, structure, or characteristic associated with at least one embodiment of the application. Therefore, it should be emphasized and noted that references to "an embodiment," "one embodiment," or "an alternative embodiment" in different locations throughout this specification do not necessarily refer to the same embodiment. Furthermore, certain features, structures, or characteristics in one or more embodiments of the application can be appropriately combined.

[0099] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Any variations and modifications can be made by those skilled in the art without departing from the spirit and scope of the invention. Therefore, any modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention, without departing from the scope of the invention, fall within the protection scope defined by the claims of the present invention.

Claims

1. A method of producing a nuclear power primary pump water-lubricated graphite bearing material, characterized by, The application relates to a preparation method of a high-performance graphite product. The method comprises the following steps: 1, putting graphite powder and high-wear-resistant carbon black into a mixing tank to mix and obtain mixed powder; 2, putting the mixed powder and superfine coke powder into a kneading pot to stir and mix, adding pitch during heating and kneading, and continuously kneading to obtain first kneading paste; 3, sheeting the first kneading paste to obtain first sheet with a thickness not higher than 2 mm; 4, putting the first sheet into the kneading pot with an initial temperature of 150+ / -10 DEG C to knead, and obtaining second kneading paste after heating and kneading; 5, sheeting the second kneading paste to obtain second sheet with a thickness not higher than 2 mm; 6, after cooling the second sheet, crushing and grinding to obtain compressed powder with a particle size not greater than 45 um, and performing isostatic pressing forming treatment on the compressed powder to obtain a blank; and 7, after first roasting, first pitch high-pressure impregnation, second roasting, second high-pressure pitch, third roasting and graphitization treatment of the blank, the product is obtained. In the step 1, the mixed tank is used to mix the graphite powder and the high-wear-resistant carbon black in a proportion of 50wt% of the graphite powder and 50wt% of the high-wear-resistant carbon black; wherein the particle size of the graphite powder and the high-wear-resistant carbon black is not higher than 45 um, the rotating speed of the mixed tank is 150 rpm, and the mixing time is 24 h. In the step 2, after mixing the mixed powder and the superfine coke powder, the mixed powder and the superfine coke powder are heated and kneaded to be heated to 100-120 DEG C within 1 h, then the pitch is added, and the first kneading paste is obtained after kneading for 2 h. In the step 2, the content of the superfine coke powder is 80wt%, and the particle size of the superfine coke powder is not higher than 10 um; the content of the mixed powder is 20wt%. In the step 2, the adding temperature of the pitch is 160-180 DEG C, the softening point of the pitch is 80-105 DEG C, the residual carbon rate is 35-45%, and the added mass of the pitch is 50-60% of the total mass of the mixed powder. In the step 4, the content of the first sheet is 100wt%, the temperature of the kneading pot is 150+ / -10 DEG C, and the out-pot temperature of the second kneading paste is 165+ / -5 DEG C. In the step 5, the second kneading paste is sheeted at a temperature of 130-150 DEG C to obtain the second sheet.

2. The method of claim 1, wherein the method further comprises the step of: In the step 6, the isostatic pressing forming treatment pressure is 150 MPa. In the step 7, the first roasting treatment condition is that the temperature is increased to 1100 DEG C at a temperature increasing rate of 5 DEG C / h, and the temperature is kept for 30 h; the second roasting and the third roasting treatment condition is that the temperature is increased to 900 DEG C at a temperature increasing rate of 10 DEG C / h, and the temperature is kept for 1 h.

3. The method of claim 1, wherein the method further comprises the step of: In the step 7, the first pitch high-pressure impregnation and the second pitch high-pressure impregnation treatment condition is that the medium-temperature pitch with a softening point of 70-90 DEG C is used as the impregnation agent to impregnate for 15 h under the conditions of a temperature of 180-200 DEG C and a pressure of 2.2-3.0 MPa. In the step 7, the graphitization treatment condition is that the temperature is increased to 2300+ / -10 DEG C at a temperature increasing rate of 50 DEG C / h from room temperature, and the temperature is kept for 5 h.

4. The method of claim 3, wherein the water lubricated graphite bearing material is prepared by the steps of: ​ ​ 5. The method of claim 3, wherein the water lubricated graphite bearing material for nuclear primary pumps is prepared by the steps of: ​ ​ 6. The method of claim 1, wherein the water lubricated graphite bearing material for nuclear primary pump is prepared by the steps of: ​ ​ 7. The method of claim 1, wherein the method further comprises the step of: ​ ​ 8. The method of claim 1, wherein the method further comprises the step of: ​ ​ 9. The method of claim 1, wherein the method further comprises the step of: ​ ​ ​ 10. The method of claim 1, wherein the method further comprises the step of: ​ ​ ​ 11. The method of claim 1, wherein the method further comprises: ​ ​

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