Oil reservoir with gradient pore structure and preparation method thereof

Abstract

The application provides an oil reservoir with a gradient pore structure and a preparation method thereof. The preparation method is as follows: first, according to the designed gradient components, gradient layers and component content in each layer, the required raw materials of each layer are fully mixed to obtain the required raw materials of each layer; all the raw materials contain 70-100% polyimide by weight percentage, and the particle size of polyimide in the raw materials used from the middle part to the upper and lower end parts decreases in a gradient manner; then, the required raw materials of each layer are respectively cold isostatic pressed to obtain blanks; the blanks are stacked and then cold isostatic pressed to obtain a preform blank; the preform blank is placed in a mold and subjected to discharge plasma sintering to obtain a sintered blank; finally, the sintered blank is processed to obtain the oil reservoir. The oil reservoir has a large porosity in the middle part and a small porosity at both ends. Under the premise of ensuring the amount of lubricating oil, the problem that a large amount of oil is discharged from the bearing assembly at a high temperature section or under high-low temperature alternation to cause unstable current can be effectively solved, so that the oil reservoir slowly discharges oil under the condition, and the oil supply system realizes long-time accurate oil supply.

Description

Technical Field

[0001] This invention relates to the field of oil reservoir manufacturing, specifically to an oil reservoir with a gradient pore structure and its preparation method. Background Technology

[0002] With the increasing development of China's space program, space motion components are being used more and more in space payloads, and their operational reliability is one of the main factors affecting satellite lifespan. The oil supply system for rolling bearings in space motion components consists of a porous oil-filled cage and an auxiliary oil reservoir. This is because the oil content in the cage is insufficient to meet design requirements. To ensure the long lifespan of the rolling bearings, an oil reservoir is typically designed at the bearing mounting location. As the bearing rotates, the lubricating oil inside the reservoir slowly moves from both ends towards the bearing, replenishing the lubricating oil consumed by the bearing.

[0003] Most oil reservoirs are made of the same porous polyimide material as oil-containing cages. To ensure lubrication life requirements, the oil content of the oil reservoir is generally designed to be around 22-25%. Therefore, the material has a relatively large pore size and porosity. However, due to the harsher service environment, higher temperatures, and more frequent high and low temperature alternation cycles, existing porous oil reservoirs are prone to excessively fast oil output and excessive oil volume during simulated ground running-in tests. This leads to unstable frictional torque in the oil supply system and large fluctuations in the current during bearing assembly running-in tests, making it impossible to guarantee accurate oil supply over a long period of time.

[0004] Therefore, it is necessary to design a new oil reservoir that can effectively reduce the oil output rate at high temperatures. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides an oil reservoir with a gradient pore structure and its preparation method. The oil reservoir has a large porosity in the middle and a small porosity at both ends. Under the premise of ensuring the amount of lubricating oil, it can effectively solve the problem of unstable current caused by a large amount of oil leakage from the bearing assembly during high temperature range or high and low temperature alternation. This allows the oil reservoir to slowly release oil under such conditions, enabling the oil supply system to achieve long-term and precise oil supply.

[0006] To achieve the above objectives, the specific solution adopted by the present invention is as follows:

[0007] On one hand, the present invention provides a method for preparing an oil reservoir with a gradient pore structure, wherein the porosity of the oil reservoir gradually decreases from the middle to the upper and lower ends in the axial direction, and the preparation method mainly includes the following steps:

[0008] S1. According to the designed gradient components, number of gradient layers and component content in each layer, the raw materials required for each layer are fully mixed to obtain the raw materials required for each layer; all raw materials contain 70-100% polyimide by weight percentage, and the particle size gradient of polyimide in the raw materials used from the middle to the top and bottom ends decreases.

[0009] S2. The raw materials required for each layer are cold isostatically pressed separately to obtain billets; then the billets are stacked according to the designed gradient components, gradient layers and component content in each layer and cold isostatically pressed to obtain preforms.

[0010] S3. Place the preform in a mold and perform spark plasma sintering to obtain a sintered preform;

[0011] S4. Demold the sintered blank and process it into an oil reservoir of the target size.

[0012] Furthermore, the porosity of the middle part of the oil reservoir is 30-40%, and the porosity of the upper and lower ends is 15-20%.

[0013] Furthermore, in step S1, the raw materials required for each layer, by weight percentage, include 70-100% polyimide, 0-10% polyetheretherketone, and 0-20% polytetrafluoroethylene.

[0014] Further, in step S1, the polyimide is a monoether anhydride polyimide with a particle size of 10–30 μm.

[0015] Furthermore, in step S1, the preparation method of the raw materials required for each layer is as follows:

[0016] Step (1): Weigh the raw materials according to the weight percentage; if the raw materials contain only polyimide, the preparation of the raw materials is complete; if the raw materials contain other raw materials, proceed to the next step.

[0017] Step (2): Pre-treat polyimide at 200°C for 2 hours under vacuum conditions, and pre-treat polyether ketone at 160°C for 2 hours under vacuum conditions. Then, place them in an acoustic resonance mixer and mix thoroughly. If the raw materials only contain polyimide and polyether ketone, the preparation of the raw materials is complete. If the raw materials also contain polytetrafluoroethylene, proceed to the next step.

[0018] Step (3): Place the polytetrafluoroethylene in a low-temperature environment below 5°C for 12 hours, then put it into an acoustic resonance mixer, control the temperature inside the acoustic resonance mixer to be below 10°C, and mix it evenly again.

[0019] Furthermore, in step S2, when the mixed powder is pressed into a blank, the pressure of cold isostatic pressing is 80-110 KN, and the height of the blank is 3-15 mm;

[0020] When pressing the billet into a preform, the pressure of cold isostatic pressing is 50-100 kN, and the pressure is held for 3-5 minutes.

[0021] Further, in step S3, the mold is prepared using carbon microsphere-based fine-particle isostatically pressed graphite, with a thermal conductivity of 90–140 W / m·K, a porosity of 7–10%, and a density of 1.80–1.95 g / cm³. 3 .

[0022] Furthermore, in step S3, the mold is cylindrical in shape, the mold height = 3 × oil reservoir height, the mold inner diameter = oil reservoir outer diameter + (6~10) mm, and the mold outer diameter = (1.5~2) × mold inner diameter.

[0023] Further, in step S3, the mold and the preform are placed together in a spark plasma sintering apparatus. Under a vacuum of less than 10 Pa and a constant pressure of 3–10 MPa, the temperature is rapidly increased to 230–270 °C at a heating rate of 60–150 °C / min and held for 2–5 min. Then, the temperature is increased to 340–370 °C at the same heating rate and held for 10–20 min. Subsequently, the temperature is water-cooled for 3–5 min to reduce the temperature to below 100 °C.

[0024] On the other hand, the present invention provides an oil reservoir with a gradient pore structure, which is prepared by the above-described method.

[0025] Beneficial effects:

[0026] (1) The oil reservoir with a gradient pore structure designed in this invention has a large porosity in the middle, resulting in a high oil content, and a small porosity at both ends, resulting in a low oil content. This effectively solves the problem of excessive oil leakage from bearings during operation at high temperatures or during alternating high and low temperatures, allowing the oil reservoir to slowly release oil under these conditions, and enabling the oil supply system to achieve long-term precise oil supply. In addition, by using pre-formed blanks, compared with directly laying powder layer by layer, the overall porosity of the material can be effectively controlled, ensuring the initial oil content and expected design lubrication life of the material, and the batch consistency of the material is high.

[0027] (2) The present invention uses spark plasma sintering, which, compared with traditional vacuum sintering, nitrogen sintering and hot pressing sintering of porous polyimide materials, effectively shortens the sintering time from the traditional 2 to 4 hours to less than 25 minutes, and improves the production efficiency by at least 3.8 times.

[0028] (3) The raw materials of the present invention contain polyether ether ketone. Polyether ether ketone flows and diffuses at high temperature, which can effectively bond each gradient layer and block pores at the same time, so as to achieve the purpose of controlling the pores of the oil reservoir material. In addition, after all the blanks are pressed, they are stacked and cold isostatic pressing is performed, which can further reduce the gap between layers. This combination technology effectively solves the problem of gradient stacking delamination and non-bonding.

[0029] (4) This invention uses carbon microsphere-based fine-particle isostatically pressed graphite as the mold for the spark plasma sintering equipment. For this type of non-conductive organic polymer material, the graphite mold has good thermal conductivity. In addition, the design of the sintering process can effectively solve the problems of excessive temperature gradient during sintering, which leads to uneven material structure and even cracking. At the same time, the graphite has low porosity and high density, and the material is uniform and has high density, avoiding the blockage of micropores in the composite material by fine graphite particles.

[0030] (5) The present invention uses an acoustic resonance instrument for mixing and adopts a step-by-step mixing method, which not only achieves uniform mixing, but also avoids polytetrafluoroethylene fiberization caused by long-term mixing and equipment heating. Compared with traditional high-speed mixers, high-speed tissue homogenizers and other equipment, this method does not have mixing dead corners and avoids uneven mixing of multi-component materials. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the stacked billets and the finished product oil reservoir in Example 1. Detailed Implementation

[0032] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0033] It should be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0034] This invention provides an oil reservoir with a gradient pore structure and its preparation method. The porosity of the oil reservoir gradually decreases from the middle to the upper and lower ends in the axial direction. The preparation method mainly includes the following steps:

[0035] S1, Mixing

[0036] The raw materials required for each layer are thoroughly mixed according to the designed gradient components, number of gradient layers and component content in each layer to obtain the raw materials required for each layer; all raw materials contain 70-100% polyimide, 0-10% polyether ether ketone and 0-20% polytetrafluoroethylene by weight percentage, and the particle size gradient of polyimide in the raw materials used from the middle to the top and bottom ends decreases.

[0037] Step (1): Weigh the raw materials according to the weight percentage; if the raw materials contain only polyimide, the preparation of the raw materials is complete; if the raw materials contain other raw materials, proceed to the next step.

[0038] Step (2): Pre-treat polyimide at 200°C for 2 hours under vacuum, and pre-treat polyetheretherketone at 160°C for 2 hours under vacuum. Then, place them in an acoustic resonance mixer and mix thoroughly. The mixing process is as follows: mixing acceleration 30-100, vibration frequency 20-60Hz, and mixing time 5-10 minutes. If the raw materials only contain polyimide and polyetheretherketone, the preparation of the raw materials is complete. If the raw materials also contain polytetrafluoroethylene, proceed to the next step.

[0039] Step (3): Place polytetrafluoroethylene in a low temperature environment below 5°C for 12 hours, then put it into an acoustic resonance mixer, control the water cooling flow rate of the acoustic resonance mixer so that the temperature of the acoustic resonance mixer is below 10°C, mix it evenly again, with a mixing acceleration of 20-50, a vibration frequency of 10-30Hz, and a mixing time of 1-3 minutes.

[0040] S2, Cold Isostatic Pressing

[0041] Raw materials with different formulation systems are pre-pressed sequentially in a steel mold using the same height limiting fixture. The pressure is 80-110KN, and the height of the pressed billet is 3-15mm. The pre-pressed billets are stacked in a certain order without wiping the surface: the billets with high porosity are placed in the middle, and the billets with low porosity are placed on top and bottom. Depending on the height, there can be 3-7 layers or even more. Then, they are placed in a polyurethane mold and cold isostatically pre-formed at a pressure of 50-100KN for 3-5 minutes to obtain the preform.

[0042] S3, Spark Plasma Sintering

[0043] The preform is placed in a mold and then placed in a spark plasma sintering equipment. Under low vacuum (vacuum degree less than 10 Pa) and constant pressure of 3-10 MPa, the temperature is rapidly increased to 230-270℃ at a rate of 60-150℃ / min and held for 2-5 min. The temperature is then increased to 340-370℃ at the same rate and held for 10-20 min. The preform is then water-cooled to below 100℃ in 3-5 min.

[0044] S4, Processing

[0045] The sintered blank is demolded and machined into an oil reservoir of the target size.

[0046] It should be noted that in step S1, the polyimide powder is monoether anhydride polyimide with a particle size of 10-30 μm, the polyether ether ketone grade is 770PF, and the polytetrafluoroethylene grade is M18F.

[0047] In step S3, the mold used for spark plasma sintering is prepared from carbon microsphere-based fine-particle isostatically pressed graphite with a thermal conductivity of 90–140 W / m·K, a porosity of 7–10%, and a density of 1.80–1.95 g / cm³. 3 Mold height = 3 × oil reservoir height, mold inner diameter = oil reservoir outer diameter + (6~10) mm, mold outer diameter = (1.5~2) × mold inner diameter.

[0048] Example 1

[0049] This embodiment provides a method for preparing an oil reservoir with a gradient pore structure, mainly including the following steps:

[0050] S1. Material Preparation

[0051] Pure polyimide with a particle size of 28μm was used as the first raw material;

[0052] Polyimide and polyetheretherketone (PEEK) were pretreated under vacuum at 200°C and 160°C for 2 hours, respectively. 80% polyimide, 5% PEEK, and 15% polytetrafluoroethylene (PTFE) with a particle size of 18 μm were taken by weight percentage. First, the polyimide and PEEK were thoroughly mixed in an acoustic resonance mixer with a mixing acceleration of 100, a vibration frequency of 30 Hz, and a mixing time of 5 min. Then, PTFE was added and mixed again with a mixing acceleration of 30, a vibration frequency of 30 Hz, and a mixing time of 1 min, yielding the second raw material.

[0053] S2, Cold Isostatic Pressing Preforming

[0054] The first and second raw materials are pre-pressed sequentially in a steel mold using the same height-limiting fixture, with pressures of 60 and 30 kN respectively, producing billets with a height of 15 mm. The pre-pressed billets are then stacked without wiping their surfaces, in the following order: the billets made from the first raw material are placed in the middle, and the billets made from the second raw material are placed on the top and bottom sides, for a total of three layers. Please refer to [reference needed]. Figure 1 (a) Then it is placed in a polyurethane mold and cold isostatically preformed at a pressure of 80KN for 5 minutes to obtain a preform.

[0055] S3, Mold Composition

[0056] The mold used for spark plasma sintering is prepared from carbon microsphere-based fine-particle isostatically pressed graphite with a thermal conductivity of 100 W / m·K, a porosity of 9%, and a density of 1.90 g / cm³. 3 The outer diameter of the oil reservoir is 40mm and the height is 39mm. The mold height = 3 × oil reservoir height = 117mm. The inner diameter of the mold = outer diameter of the oil reservoir + 10 = 50mm. The outer diameter of the mold = 2 × inner diameter of the mold = 100mm.

[0057] S4, Spark Plasma Sintering

[0058] The preform is placed in the mold of step S3 and put into the spark plasma sintering equipment. Then, under low vacuum (vacuum degree less than 10 Pa) and constant pressure of 10 MPa, the temperature is rapidly increased to 270°C at 100°C / min and held for 3 min. The temperature is then increased to 370°C at the same rate and held for 10 min. Finally, the temperature is cooled by water to below 100°C in 5 min.

[0059] S5. Demold the sintered blank and process it into an oil reservoir of the target size. Please refer to [reference needed]. Figure 1 (b)

[0060] Example 2

[0061] This embodiment provides a method for preparing an oil reservoir with a gradient pore structure, mainly including the following steps:

[0062] S1. Material Preparation

[0063] By weight percentage, 80% polyimide, 10% polyetheretherketone (PEEK), and 10% polytetrafluoroethylene (PTFE) with a particle size of 30 μm were taken. The polyimide and PEEK were placed in an acoustic resonance mixer and thoroughly mixed. The mixing process was: mixing acceleration 80, vibration frequency 50 Hz, and mixing time 7 min. Then, PTFE was added and mixed again. The mixing process was: mixing acceleration 50, vibration frequency 30 Hz, and mixing time 1 min, to obtain the first raw material.

[0064] By weight percentage, 70% polyimide, 10% polyetheretherketone (PEEK), and 20% polytetrafluoroethylene (PTFE) with a particle size of 23 μm were taken. The polyimide and PEEK were placed in an acoustic resonance mixer and thoroughly mixed. The mixing process was: mixing acceleration 60, vibration frequency 60 Hz, and mixing time 5 min. Then, PTFE was added and mixed again. The mixing process was: mixing acceleration 40, vibration frequency 20 Hz, and mixing time 2 min, to obtain the second raw material.

[0065] By weight percentage, 85% polyimide, 5% polyetheretherketone (PEEK), and 10% polytetrafluoroethylene (PTFE) with a particle size of 16 μm were taken. The polyimide and PEEK were placed in an acoustic resonance mixer and thoroughly mixed. The mixing process was: mixing acceleration 40, vibration frequency 60 Hz, and mixing time 6 min. Then, PTFE was added and mixed again. The mixing process was: mixing acceleration 30, vibration frequency 20 Hz, and mixing time 2 min, yielding the third raw material.

[0066] Take 97% polyimide and 3% polyether ether ketone with a particle size of 10μm by weight percentage, and put the polyimide and polyether ether ketone into an acoustic resonance mixer to mix them thoroughly and evenly. The mixing process is: mixing acceleration 30, vibration frequency 20Hz, mixing time 10min, to obtain the fourth raw material.

[0067] S2, Cold Isostatic Pressing Preforming

[0068] The first to fourth raw materials are pre-pressed sequentially in a steel mold using the same height limiting fixture, with pressures of 100, 60, 50, and 30 KN respectively, resulting in a billet height of 3 mm. The pre-pressed billets are then stacked in a specific order: the billet made from the first raw material is placed in the middle, and the second, third, and fourth raw materials are stacked sequentially from near to far at the top and bottom ends, for a total of 7 layers. The billets are then placed in a polyurethane mold and cold isostatically pre-formed at a pressure of 100 KN for 3 minutes to obtain a preform.

[0069] S3, Mold Composition

[0070] The mold used for spark plasma sintering is prepared from carbon microsphere-based fine-particle isostatically pressed graphite with a thermal conductivity of 90 W / m·K, a porosity of 10%, and a density of 1.80 g / cm³. 3 The outer diameter of the oil reservoir is 29mm, and the height is 15mm. The mold height = 3 × oil reservoir height = 45mm. The inner diameter of the mold = outer diameter of the oil reservoir + 6 = 35mm. The outer diameter of the mold = 1.8 × inner diameter of the mold = 63mm.

[0071] S4, Spark Plasma Sintering

[0072] The preform is placed in the mold of step S3 and put into the spark plasma sintering equipment. Then, under low vacuum (vacuum degree less than 10 Pa) and constant pressure of 5 MPa, the temperature is rapidly increased to 230°C at 150°C / min and held for 2 min. The temperature is then increased to 350°C at the same heating rate and held for 13 min. Finally, the temperature is water cooled for 4 min to reduce the temperature to below 100°C.

[0073] S5. Demold the sintered blank and process it into an oil reservoir of the target size.

[0074] Example 3

[0075] This embodiment provides a method for preparing an oil reservoir with a gradient pore structure, mainly including the following steps:

[0076] S1. Material Preparation

[0077] By weight percentage, 90% polyimide, 8% polyetheretherketone (PEEK), and 2% polytetrafluoroethylene (PTFE) with a particle size of 25 μm were taken. The polyimide and PEEK were placed in an acoustic resonance mixer and thoroughly mixed. The mixing process was: mixing acceleration 60, vibration frequency 40 Hz, and mixing time 6 min. Then, PTFE was added and mixed again. The mixing process was: mixing acceleration 30, vibration frequency 20 Hz, and mixing time 2 min, to obtain the first raw material.

[0078] Take 80% polyimide and 20% polytetrafluoroethylene with a particle size of 14μm by weight percentage. The mixing process is as follows: mixing acceleration of 40, vibration frequency of 20Hz, and mixing time of 1min to obtain the second raw material.

[0079] By weight percentage, 90% polyimide, 5% polyetheretherketone (PEEK), and 5% polytetrafluoroethylene (PTFE) with a particle size of 10 μm were taken. The polyimide and PEEK were placed in an acoustic resonance mixer and thoroughly mixed. The mixing process was: mixing acceleration 50, vibration frequency 50 Hz, and mixing time 7 min. Then, PTFE was added and mixed again. The mixing process was: mixing acceleration 20, vibration frequency 20 Hz, and mixing time 2 min, yielding the third raw material.

[0080] S2, Cold Isostatic Pressing Preforming

[0081] The first to third raw materials are pre-pressed sequentially in a steel mold using the same height limiting fixture, with pressures of 40 and 30 KN respectively, resulting in a billet height of 10 mm. The pre-pressed billets are then stacked in a specific order: the billet made from the first raw material is placed in the middle, and the second and third raw materials are stacked sequentially from near to far at the top and bottom ends, for a total of 5 layers. The billets are then placed in a polyurethane mold and cold isostatically pre-formed at a pressure of 110 KN for 3 minutes to obtain a preform.

[0082] S3, Mold Composition

[0083] The mold for spark plasma sintering is made of carbon microsphere-based fine-particle isostatically pressed graphite with a thermal conductivity of 140 W / m·K, a porosity of 7%, and a density of 1.95 g / cm³. The oil reservoir has an outer diameter of 29 mm and a height of 36 mm. The mold height = 3 × oil reservoir height = 108 mm. The mold inner diameter = oil reservoir outer diameter + 8 = 37 mm. The mold outer diameter = 1.5 × mold inner diameter = 55.5 mm.

[0084] S4, Spark Plasma Sintering

[0085] The preform is placed in the mold of step S3 and put into the spark plasma sintering equipment. Then, under low vacuum (vacuum degree less than 10 Pa) and constant pressure of 3 MPa, the temperature is rapidly increased to 250°C at 60°C / min and held for 5 min. The temperature is then increased to 340°C at the same rate and held for 20 min. Finally, the temperature is cooled by water to below 100°C in 3 min.

[0086] S5. Demold the sintered blank and process it into an oil reservoir of the target size.

[0087] Comparative Example 1

[0088] Comparative Example 1 is a traditional porous polyimide material, ZYS-MPPI01.

[0089] The porosity, oil content, and oil retention rate of the products obtained in Examples 1-3 and the comparative examples were tested below, and the results are shown in Table 1. The porosity test method is described in GB / T 21650.1-2008, and the oil content and oil retention rate test methods are described in GJB 9288-2017.

[0090] Table 1. Test results of porosity, oil content, and oil retention rate of the products obtained in Examples 1-3 and comparative examples.

[0091] The table above shows that the oil reservoir prepared by this invention has an oil content that meets the bearing lubrication life requirements, and the oil retention rate is significantly improved. Compared with the comparative example, it can effectively reduce the high-temperature oil output rate.

[0092] Upon inspection, the oil reservoir was found to have a good appearance, a dense structure, no defects such as delamination, and good bonding at the gradient layer interface.

[0093] The bearing assembly of the oil reservoir with this gradient pore structure showed excellent running performance after 200 hours of running at 60℃, with no abnormalities such as current fluctuations. After disassembling the bearing, there was no excess lubricating oil in the raceway.

[0094] This gradient pore structure oil reservoir can be widely used in long-life, high-precision bearings and bearing assemblies for deep space exploration such as lunar and Mars exploration, meeting the future development needs of my country's aerospace industry and yielding significant economic and social benefits.

[0095] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the invention in any way. All equivalent transformations or modifications made in accordance with the essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for preparing an oil reservoir with a gradient pore structure, characterized in that, The porosity of the oil reservoir gradually decreases axially from the middle to the upper and lower ends, with a porosity of 30-40% in the middle and 15-20% at the upper and lower ends. Its preparation method mainly includes the following steps: S1. According to the designed gradient components, number of gradient layers and component content in each layer, the raw materials required for each layer are fully mixed to obtain the raw materials required for each layer; all raw materials contain 70~100% polyimide by weight percentage, and the particle size gradient of polyimide in the raw materials used from the middle to the top and bottom ends decreases. S2. The raw materials required for each layer are cold isostatically pressed separately to obtain billets; then the billets are stacked according to the designed gradient components, gradient layers and component content in each layer and cold isostatically pressed to obtain preforms. S3. Place the preform in a mold and perform spark plasma sintering to obtain a sintered preform; S4. Demold the sintered blank and process it into an oil reservoir of the target size.

2. The method for preparing an oil reservoir with a gradient pore structure according to claim 1, characterized in that, In step S1, by weight percentage, the raw materials required for each layer include 70-100% polyimide, 0-10% polyether ether ketone, and 0-20% polytetrafluoroethylene.

3. The method for preparing an oil reservoir with a gradient pore structure according to claim 2, characterized in that, In step S1, the polyimide is a monoether anhydride polyimide with a particle size of 10~30μm.

4. The method for preparing an oil reservoir with a gradient pore structure according to claim 2, characterized in that, In step S1, the preparation method of the raw materials required for each layer is as follows: Step (1): Weigh the raw materials by weight percentage; if the raw materials contain only polyimide, the preparation of the raw materials is complete; if the raw materials contain other raw materials, proceed to the next step. Step (2): Pre-treat polyimide at 200°C for 2 hours under vacuum conditions, and pre-treat polyether ketone at 160°C for 2 hours under vacuum conditions. Then, place them in an acoustic resonance mixer and mix thoroughly. If the raw materials only contain polyimide and polyether ketone, the preparation of the raw materials is complete. If the raw materials also contain polytetrafluoroethylene, proceed to the next step. Step (3): Place the polytetrafluoroethylene in a low-temperature environment below 5°C for 12 hours, then put it into an acoustic resonance mixer, control the temperature inside the acoustic resonance mixer to be below 10°C, and mix it evenly again.

5. The method for preparing an oil reservoir with a gradient pore structure according to claim 1, characterized in that, In step S2, when the mixed powder is pressed into a blank, the pressure of cold isostatic pressing is 80~110KN and the height of the blank is 3~15mm. When pressing the billet into a preform, the pressure of cold isostatic pressing is 50~100KN, and the pressure is held for 3~5 minutes.

6. The method for preparing an oil reservoir with a gradient pore structure according to claim 1, characterized in that, In step S3, the mold is prepared using carbon microsphere-based fine-particle isostatically pressed graphite with a thermal conductivity of 90~140 W / m·K, a porosity of 7~10%, and a density of 1.80~1.95 g / cm³. 3 .

7. The method for preparing an oil reservoir with a gradient pore structure according to claim 1, characterized in that, In step S3, the mold is cylindrical in shape, the mold height = 3 × oil reservoir height, the mold inner diameter = oil reservoir outer diameter + (6~10) mm, and the mold outer diameter = (1.5~2) × mold inner diameter.

8. The method for preparing an oil reservoir with a gradient pore structure according to claim 1, characterized in that, In step S3, the mold and the preform are placed together in a spark plasma sintering equipment. Under a vacuum of less than 10 Pa and a constant pressure of 3-10 MPa, the temperature is rapidly increased to 230-270 °C at a heating rate of 60-150 °C / min and held for 2-5 min. Then, the temperature is increased to 340-370 °C at the same heating rate and held for 10-20 min. Subsequently, the temperature is water-cooled for 3-5 min to reduce the temperature to below 100 °C.

9. An oil reservoir with a gradient pore structure, characterized in that, It is prepared by the method described in any one of claims 1-8.

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