Oil reservoir with gradient pore structure and preparation method thereof

Abstract

The invention provides an oil reservoir with a gradient pore structure and a preparation method thereof, and the preparation method comprises the following steps: firstly, fully mixing raw materials required by each layer according to designed gradient components, gradient layer number and component content in each layer to obtain the raw materials required by each layer; all the raw materials comprise 70-100% by weight of polyimide, and the particle size gradient of the polyimide in the raw materials used from the middle part to the upper and lower end parts is reduced; performing cold isostatic pressing on the raw materials required by each layer to obtain a blank; the blanks are stacked and then subjected to cold isostatic pressing, and prefabricated blanks are obtained; the prefabricated blank is placed in a mold to be subjected to spark plasma sintering, and a sintered blank is obtained; and finally, processing the sintered blank to obtain the oil reservoir. The porosity of the middle of the oil storage device is large, the porosity of the two ends of the oil storage device is small, on the premise that the lubricating oil amount is guaranteed, the problem that a large amount of oil flows out in the high-temperature section or during high-low temperature alternating, and consequently current is unstable can be effectively solved, oil flows out of the oil storage device slowly in the state, and an oil supply system achieves long-time accurate oil supply.

Description

Technical Field

[0001] The invention relates to the field of oil storage device manufacturing, in particular to an oil storage device with a gradient pore structure and a preparation method thereof. Background Art

[0002] With the increasing development of the country's aerospace industry, space motion components are increasingly used in space payloads, and their operational reliability is one of the main factors affecting the life of satellites. The rolling bearing oil supply system in space motion components is composed of a porous oil-containing cage and an auxiliary oil reservoir. This is because the oil content in the cage is not enough to meet the design requirements. In order to ensure the long life of the rolling bearing, an oil reservoir is usually designed at the installation location of the bearing. As the bearing runs, the lubricating oil inside the oil reservoir slowly moves from the upper and lower ends to the bearing to replenish the lubricating oil consumed by the bearing.

[0003] Most oil reservoirs are made of the same material as the oil-containing retainer, which is a porous polyimide material. To ensure the lubrication life requirements, the oil content of the oil reservoir is generally designed to be around 22-25%, so the pore size and porosity of the material are relatively large. However, due to the more severe service environment, higher temperatures, and more high and low temperature alternation cycles, the existing pore structure of the oil reservoir is prone to excessive oil discharge during the simulated ground running-in test, resulting in unstable friction torque of the oil supply system and large fluctuations in the current of the bearing assembly running-in test, making it impossible to guarantee long-term accurate oil supply.

[0004] Based on this, it is necessary to design a new oil reservoir that can effectively reduce the high-temperature oil output rate. Summary of the invention

[0005] In order to address the deficiencies in the prior art, the present invention provides an oil reservoir with a gradient pore structure and a preparation method thereof. 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, the oil reservoir can effectively solve the problem of unstable current caused by a large amount of oil discharge from the bearing assembly in a high temperature section or when high and low temperatures alternate. The oil reservoir can slowly discharge oil in this state, and the oil supply system can achieve long-term and accurate oil supply.

[0006] In order to achieve the above object, the specific scheme adopted by the present invention is:

[0007] On the one hand, the present invention provides a method for preparing an oil reservoir having 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 comprises 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 the raw materials contain 70-100% polyimide by weight percentage, and the particle size gradient of the polyimide in the raw materials used from the middle to the upper and lower ends decreases; S2, cold isostatically pressing the raw materials required for each layer to obtain blanks; then stacking the blanks according to the designed gradient components, number of gradient layers and component content in each layer and cold isostatically pressing them to obtain preforms; S3, placing the preform in a mold and performing spark plasma sintering to obtain a sintered blank; S4, demoulding the sintered blank into an oil reservoir of target size.

[0008] Furthermore, the porosity of the middle portion of the oil reservoir is 30-40%, and the porosity of the upper and lower ends is 15-20%.

[0009] Furthermore, in step S1, the raw materials required for each layer include, in addition to 70-100% of polyimide, 0-10% of polyetheretherketone, and 0-20% of polytetrafluoroethylene, by weight percentage.

[0010] Furthermore, in step S1, the polyimide is monoether anhydride polyimide, and the particle size is 10 to 30 μm.

[0011] Furthermore, in step S1, the preparation method of the raw materials required for each layer is: Step (1), weighing the raw materials according to weight percentage; if the raw materials only contain polyimide, the preparation of the raw materials is completed; if the raw materials also contain other raw materials, proceed to the next step; Step (2), pretreating polyimide at 200° C. for 2 h under vacuum conditions, pretreating polyetheretherketone at 160° C. for 2 h under vacuum conditions, and then placing in an acoustic resonance mixer to fully mix; if the raw materials only contain polyimide and polyetheretherketone, the preparation of the raw materials is completed; if the raw materials also contain polytetrafluoroethylene, proceed to the next step; Step (3), placing the polytetrafluoroethylene in a low temperature environment below 5° C. for 12 hours, then placing it in an acoustic resonance mixer, controlling the temperature in the acoustic resonance mixer to be below 10° C., and mixing again to be uniform.

[0012] Furthermore, in step S2, when the mixed powder is pressed into a blank, the cold isostatic pressing pressure is 80 to 110 KN, and the blank height is 3 to 15 mm; When the blank is pressed into a preform, the cold isostatic pressing pressure is 50 to 100 KN, and the pressure is maintained for 3 to 5 minutes.

[0013] Furthermore, in step S3, the mold is prepared by isostatically pressed graphite based on carbon microspheres, the thermal conductivity of graphite is 90-140 W / m·K, the porosity is 7-10%, and the density is 1.80-1.95 g / cm 3 .

[0014] Furthermore, in step S3, the mold is in a cylindrical shape as a whole, the mold height = 3×the height of the oil reservoir, the mold inner diameter = the outer diameter of the oil reservoir + (6-10) mm, and the mold outer diameter = (1.5-2)×the inner diameter of the mold.

[0015] Further, in step S3, the mold is placed together with the preform in a spark plasma sintering device, and under a vacuum degree of less than 10Pa, at a constant pressure of 3 to 10MPa, the temperature is rapidly increased to 230-270°C at a heating rate of 60 to 150°C / min, and kept warm for 2 to 5min; then the temperature is increased to 340 to 370°C at the same heating rate, and kept warm for 10 to 20min; then the temperature is cooled by water for 3 to 5min to reduce to below 100°C.

[0016] On the other hand, the present invention provides an oil reservoir having a gradient pore structure, which is prepared by the above method.

[0017] Beneficial effects:

[0018] (1) The oil reservoir with a gradient pore structure designed by the present invention has a large porosity in the middle, which means a high oil content, and a small porosity at both ends, which means a low oil content. This can effectively solve the problem of large amounts of oil being discharged from the bearing during operation at high temperatures or when high and low temperatures alternate, so that the oil reservoir can slowly discharge oil in this state, and the oil supply system can achieve long-term and accurate oil supply. In addition, by prefabricating the blank, compared with directly laying the powder layer by layer, the overall pores of the material can be effectively controlled, the initial oil content of the material and the expected design lubrication life can be ensured, and the batch consistency of the material is high.

[0019] (2) The present invention adopts spark plasma sintering. Compared with the traditional porous polyimide material vacuum sintering, nitrogen sintering and hot pressing sintering, the sintering time is effectively shortened from the traditional 2 to 4 hours to within 25 minutes, and the production efficiency is increased by at least 3.8 times.

[0020] (3) Polyetheretherketone is added to the raw materials of the present invention. Polyetheretherketone flows and diffuses at high temperature, which can effectively bond the gradient layers and seal the pores, thereby achieving the purpose of regulating the pores of the oil reservoir material. In addition, after all the blanks are pressed, they are stacked and cold isostatically pressed, which can further reduce the gap between layers. This combined technology effectively solves the problems of gradient stacking stratification and non-bonding.

[0021] (4) The present invention uses carbon microsphere-based fine-grained isostatically pressed graphite as a mold for spark plasma sintering equipment. For such organic polymer non-conductive materials, 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 the sintering process, resulting in uneven material structure and even cracking. At the same time, the graphite has a small porosity, a large density, a uniform material and a high density, which prevents fine graphite particles from clogging the micropores of the composite material.

[0022] (5) The present invention adopts an acoustic resonance instrument for mixing and a step-by-step mixing method, which not only achieves uniform mixing but also avoids the fibrosis of polytetrafluoroethylene caused by long-term mixing and heating of the equipment. Compared with traditional high-speed mixers, high-speed tissue pounders and other equipment, this method does not have a mixing dead corner and avoids the unevenness of multi-component mixtures. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the stacked blanks and the finished product oil reservoir in Example 1. DETAILED DESCRIPTION

[0024] The technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0025] It should be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the presence of other identical elements in the process, method, article or device including the element.

[0026] The present invention provides an oil reservoir with a gradient pore structure and a preparation method thereof, 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 comprises the following steps: S1. Mixing The raw materials required for each layer are fully mixed according to the designed gradient components, the number of gradient layers and the content of the components in each layer to obtain the raw materials required for each layer; all the raw materials contain 70-100% of polyimide, 0-10% of polyetheretherketone, and 0-20% of polytetrafluoroethylene by weight percentage, and the particle size gradient of the polyimide in the raw materials used from the middle to the upper and lower ends decreases; Step (1), weighing the raw materials according to weight percentage; if the raw materials only contain polyimide, the preparation of the raw materials is completed; if the raw materials also contain other raw materials, proceed to the next step; Step (2), pretreating polyimide at 200° C. for 2 h under vacuum conditions, pretreating polyetheretherketone at 160° C. for 2 h under vacuum conditions, and then placing them in an acoustic resonance mixer to fully mix them, wherein the mixing process is: mixing acceleration 30 to 100, vibration frequency 20 to 60 Hz, and mixing time 5 to 10 min; if the raw materials only contain polyimide and polyetheretherketone, the preparation of the raw materials is completed; if the raw materials also contain polytetrafluoroethylene, proceed to the next step; Step (3), placing the polytetrafluoroethylene in a low temperature environment below 5° C. for 12 hours, then placing it in an acoustic resonance mixer, controlling the water cooling flow rate of the acoustic resonance mixer so that the temperature of the acoustic resonance mixer is below 10° C., and mixing again, with a mixing acceleration of 20 to 50, a vibration frequency of 10 to 30 Hz, and a mixing time of 1 to 3 minutes; S2, cold isostatic pressing The raw materials of different formula systems are pre-pressed in a steel mold in sequence using the same height limiting tooling, with a pressure of 80-110KN, and the height of the pressed blanks is 3-15mm; the pre-pressed blanks are stacked together in a certain order without wiping the surface, the order is: put the blanks with large porosity in the middle, and put the blanks with small porosity on the top and bottom, and there can be 3-7 layers or even more according to the height, and then placed in a polyurethane mold, cold isostatically pressed for preforming, with a pressure of 50-100KN, and the pressure is maintained for 3-5 minutes to obtain a prefabricated blank; S3, Spark Plasma Sintering The preform is placed in a mold and put into a spark plasma sintering device, and then the temperature is rapidly increased to 230-270°C at 60-150°C / min under low vacuum (vacuum degree less than 10Pa) and constant pressure of 3-10MPa, and the temperature is kept for 2-5min. The temperature is increased to 340-370°C at the same heating rate, and the temperature is kept for 10-20min, and then water-cooled to below 100°C in 3-5min; S4. Processing The sintered green body is demolded and processed into an oil reservoir of target size.

[0027] It should be noted that in step S1, the polyimide powder is monoether anhydride polyimide with a particle size of 10 to 30 μm, the polyetheretherketone brand is 770PF, and the polytetrafluoroethylene brand is M18F.

[0028] In step S3, the mold for spark plasma sintering is made of carbon microsphere-based fine-grained isostatically pressed graphite, with a thermal conductivity of 90 to 140 W / m·K, a porosity of 7 to 10%, and a density of 1.80 to 1.95 g / cm 3 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.

[0029] Example 1

[0030] This embodiment provides a method for preparing an oil reservoir having a gradient pore structure, which mainly comprises the following steps: S1. Material preparation Pure polyimide with a particle size of 28 μm is taken as the first raw material; Pre-treat polyimide and polyetheretherketone at 200℃ and 160℃ for 2 hours under vacuum conditions, respectively, and take 80% polyimide, 5% polyetheretherketone, and 15% polytetrafluoroethylene with a particle size of 18μm by weight, first put polyimide and polyetheretherketone into an acoustic resonance mixer and mix them evenly, and the mixing process is: mixing acceleration 100, vibration frequency 30Hz, mixing time 5min. Then put polytetrafluoroethylene in and mix again, and the mixing process is: mixing acceleration 30, vibration frequency 30Hz, mixing time 1min, to obtain the second raw material; S2, cold isostatic pressing preforming The first raw material and the second raw material are pre-pressed in the steel mold in sequence using the same height limiting fixture, with the pressures of 60 and 30 KN respectively, and the height of the pressed blanks is 15 mm; the pre-pressed blanks are stacked together in a certain order without wiping the surface, the order is: put the blank made of the first raw material in the middle, and the blank made of the second raw material on the upper and lower sides, a total of 3 layers, please refer to Figure 1 (a), then placed in a polyurethane mold, cold isostatically pressed for preforming at a pressure of 80 kN and maintained for 5 min to obtain a preform; S3. Mould composition The spark plasma sintering mold is made of carbon microsphere-based fine-grained isostatically pressed graphite, with a graphite thermal conductivity of 100 W / m·K, a porosity of 9%, and a density of 1.90 g / cm 3 , the outer diameter of the oil reservoir is 40mm, the height is 39mm, the mold height = 3×the height of the oil reservoir = 117mm, the mold inner diameter = the outer diameter of the oil reservoir + 10 = 50mm, the mold outer diameter = 2×the inner diameter of the mold = 100mm; S4, spark plasma sintering The preform is placed in the mold of step S3, put into the spark plasma sintering equipment, and then rapidly heated to 270°C at 100°C / min under low vacuum (vacuum degree less than 10Pa) and constant pressure of 10MPa, and kept warm for 3min, and then heated to 370°C at the same heating rate, and kept warm for 10min, and then water-cooled to below 100°C in 5min; S5. De-mold the sintered blank into an oil reservoir of target size. Please refer to Figure 1 (b).

[0031] Example 2

[0032] This embodiment provides a method for preparing an oil reservoir having a gradient pore structure, which mainly comprises the following steps: S1. Material preparation Take 80% polyimide, 10% polyetheretherketone, and 10% polytetrafluoroethylene with a particle size of 30 μm by weight, put the polyimide and polyetheretherketone into an acoustic resonance mixer and mix them evenly. The mixing process is: mixing acceleration 80, vibration frequency 50 Hz, and mixing time 7 minutes. Then put polytetrafluoroethylene in and mix again. The mixing process is: mixing acceleration 50, vibration frequency 30 Hz, and mixing time 1 minute to obtain the first raw material; Take 70% polyimide with a particle size of 23 μm, 10% polyetheretherketone, and 20% polytetrafluoroethylene by weight, put the polyimide and polyetheretherketone into an acoustic resonance mixer and mix them evenly. The mixing process is: mixing acceleration 60, vibration frequency 60Hz, and mixing time 5min. Then put polytetrafluoroethylene in and mix again. The mixing process is: mixing acceleration 40, vibration frequency 20Hz, and mixing time 2min to obtain the second raw material; Take 85% of polyimide with a particle size of 16μm, 5% of polyetheretherketone, and 10% of polytetrafluoroethylene by weight, put the polyimide and polyetheretherketone into an acoustic resonance mixer and mix them evenly. The mixing process is: mixing acceleration 40, vibration frequency 60Hz, mixing time 6min. Then put polytetrafluoroethylene in and mix again. The mixing process is: mixing acceleration 30, vibration frequency 20Hz, mixing time 2min, to obtain the third raw material; 97% of polyimide with a particle size of 10 μm and 3% of polyetheretherketone are taken by weight respectively, and the polyimide and polyetheretherketone are put into an acoustic resonance mixer and fully mixed. The mixing process is: mixing acceleration 30, vibration frequency 20 Hz, mixing time 10 min, to obtain a fourth raw material; S2, cold isostatic pressing preforming The first to fourth raw materials are pre-pressed in a steel mold in sequence using the same height limiting tooling, with pressures of 100, 60, 50, and 30 KN, respectively, and the height of the pressed blanks is 3 mm; the pre-pressed blanks are stacked together in a certain order, the order is: the blank made of the first raw material is placed in the middle, and the second raw material, the third raw material, and the fourth raw material are stacked in sequence from near to far at the upper and lower ends, a total of 7 layers, and then placed in a polyurethane mold, cold isostatically preformed, with a pressure of 100 KN, and the pressure is maintained for 3 minutes to obtain a preform; S3. Mould composition The spark plasma sintering mold is made of carbon microsphere-based fine-grained isostatically pressed graphite, with a thermal conductivity of 90 W / m·K, a porosity of 10%, and a density of 1.80 g / cm3 ; The outer diameter of the oil reservoir is 29mm, the height is 15mm, the mold height = 3×the height of the oil reservoir = 45mm, the mold inner diameter = the outer diameter of the oil reservoir + 6 = 35mm, the mold outer diameter = 1.8×the inner diameter of the mold = 63mm; S4, spark plasma sintering The preform is placed in the mold of step S3 and placed in a spark plasma sintering device. Then, under low vacuum (vacuum degree less than 10Pa), the temperature is rapidly increased to 230°C at 150°C / min at a constant pressure of 5MPa, and the temperature is kept for 2min. At the same heating rate, the temperature is increased to 350°C, and the temperature is kept for 13min. Then, the temperature is cooled by water for 4min to reduce to below 100°C. S5. Demolding the sintered blank into an oil reservoir of target size.

[0033] Example 3

[0034] This embodiment provides a method for preparing an oil reservoir having a gradient pore structure, which mainly comprises the following steps: S1. Material preparation Take 90% polyimide with a particle size of 25 μm, 8% polyetheretherketone, and 2% polytetrafluoroethylene by weight, put the polyimide and polyetheretherketone into an acoustic resonance mixer and mix them evenly. The mixing process is: mixing acceleration 60, vibration frequency 40Hz, and mixing time 6min. Then put polytetrafluoroethylene in and mix again. The mixing process is: mixing acceleration 30, vibration frequency 20Hz, and mixing time 2min to obtain the first raw material; 80% of polyimide with a particle size of 14 μm and 20% of polytetrafluoroethylene are taken by weight percentage, and the mixing process is: mixing acceleration 40, vibration frequency 20 Hz, mixing time 1 min, to obtain a second raw material; Take 90% polyimide, 5% polyetheretherketone, and 5% polytetrafluoroethylene with a particle size of 10μm respectively by weight percentage, put the polyimide and polyetheretherketone into an acoustic resonance mixer and mix them evenly. The mixing process is: mixing acceleration 50, vibration frequency 50Hz, and mixing time 7min. Then put polytetrafluoroethylene in and mix again. The mixing process is: mixing acceleration 20, vibration frequency 20Hz, and mixing time 2min to obtain the third raw material; S2, cold isostatic pressing preforming The first to third raw materials are pre-pressed in a steel mold in sequence using the same height limiting tooling, with pressures of 40 and 30 KN respectively, and the height of the pressed blanks is 10 mm; the pre-pressed blanks are stacked together in a certain order, the order is: the blank made of the first raw material is placed in the middle, and the second raw material and the third raw material are stacked in sequence from near to far at the upper and lower ends, a total of 5 layers, and then placed in a polyurethane mold, cold isostatically preformed, with a pressure of 110 KN, and the pressure is maintained for 3 minutes to obtain a preform; S3. Mould composition The mold for spark plasma sintering is made of carbon microsphere-based fine-grained isostatic graphite, with a thermal conductivity of 140 W / m·K, a porosity of 7%, and a density of 1.95 g / cm3. The outer diameter of the oil reservoir is 29 mm, the height is 36 mm, the mold height = 3 × the oil reservoir height = 108 mm, the mold inner diameter = the outer diameter of the oil reservoir + 8 = 37 mm, and the mold outer diameter = 1.5 × the mold inner diameter = 55.5 mm. S4, spark plasma sintering The preform is placed in the mold of step S3, put into the spark plasma sintering equipment, and then rapidly heated to 250°C at 60°C / min under low vacuum (vacuum degree less than 10Pa) and constant pressure of 3MPa, and kept warm for 5min, and then heated to 340°C at the same heating rate, kept warm for 20min, and then water-cooled to below 100°C in 3min; S5. Demolding the sintered blank into an oil reservoir of target size.

[0035] Comparative Example 1

[0036] Comparative Example 1 is a traditional porous polyimide material, ZYS-MPPI01.

[0037] The porosity, oil content and oil retention rate of the products obtained in Examples 1-3 and Comparative Examples were tested, and the results are shown in Table 1. The porosity test method refers to GB / T 21650.1-2008, and the oil content and oil retention test method refers to GJB 9288-2017.

[0038] Table 1 Test results of porosity, oil content and oil retention of products obtained from Examples 1-3 and Comparative Examples

[0039] It can be analyzed from the above table that the oil content of the oil reservoir prepared by the present invention meets the lubrication life of the bearing, and the oil retention rate is significantly improved, and the high-temperature oil output rate can be effectively reduced compared with the control example.

[0040] After testing, the oil reservoir has a good appearance, a dense structure, no defects such as stratification, and good interface bonding strength of the gradient layer.

[0041] The bearing assembly using the oil reservoir with the gradient pore structure had excellent running-in performance after running-in for 200 hours at 60°C, without any abnormal performance such as current fluctuation. After the bearing was disassembled, no excess lubricating oil was found in the ring groove.

[0042] The oil reservoir with gradient pore structure can be widely used in long-life high-precision bearings and bearing components for deep space exploration such as lunar exploration and Mars exploration, meeting the future development needs of my country's aerospace industry, with significant economic and social benefits.

[0043] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any equivalent changes or modifications made according to the essence of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing an oil reservoir having a gradient pore structure, characterized in that: 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 thereof mainly comprises 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 the raw materials contain 70-100% polyimide by weight percentage, and the particle size gradient of the polyimide in the raw materials used from the middle to the upper and lower ends decreases; S2, cold isostatically pressing the raw materials required for each layer to obtain blanks; then stacking the blanks according to the designed gradient components, number of gradient layers and component content in each layer and cold isostatically pressing them to obtain preforms; S3, placing the preform in a mold and performing spark plasma sintering to obtain a sintered blank; S4, demoulding the sintered blank into an oil reservoir of target size.

2. The method for preparing an oil storage container having a gradient pore structure according to claim 1, characterized in that: The porosity in the middle of the oil reservoir is 30-40%, and the porosity in the upper and lower ends is 15-20%.

3. The method for preparing an oil storage container having a gradient pore structure according to claim 1, characterized in that: In step S1 , the raw materials required for each layer include 70-100% of polyimide, 0-10% of polyetheretherketone, and 0-20% of polytetrafluoroethylene in terms of weight percentage.

4. The method for preparing an oil storage container having a gradient pore structure according to claim 3, characterized in that: In step S1, the polyimide is monoether anhydride polyimide with a particle size of 10-30 μm.

5. The method for preparing an oil storage container having a gradient pore structure according to claim 3, characterized in that: In step S1, the preparation method of the raw materials required for each layer is: Step (1), weighing the raw materials according to weight percentage; if the raw materials only contain polyimide, the preparation of the raw materials is completed; if the raw materials also contain other raw materials, proceed to the next step; Step (2), pretreating polyimide at 200°C for 2h under vacuum conditions, pretreating polyetheretherketone at 160°C for 2h under vacuum conditions, and then placing them in an acoustic resonance mixer to fully mix them; if the raw materials only contain polyimide and polyetheretherketone, the preparation of the raw materials is completed; if the raw materials also contain polytetrafluoroethylene, proceed to the next step; Step (3), placing the polytetrafluoroethylene in a low temperature environment below 5°C for 12 hours, then placing it in an acoustic resonance mixer, controlling the temperature in the acoustic resonance mixer to be below 10°C, and mixing again to be uniform.

6. The method for preparing an oil storage container having a gradient pore structure according to claim 1, characterized in that: In step S2, when the mixed powder is pressed into a blank, the cold isostatic pressing pressure is 80-110 KN, and the blank height is 3-15 mm; When the blank is pressed into a preform, the cold isostatic pressing pressure is 50~100KN, and the pressure is maintained for 3~5min.

7. The method for preparing an oil storage container having a gradient pore structure according to claim 1, characterized in that: In step S3, the mold is made of carbon microsphere-based fine-grained isostatically pressed graphite, the graphite has a thermal conductivity of 90-140 W / m·K, a porosity of 7-10%, and a density of 1.80-1.95 g / cm 3 .

8. The method for preparing an oil storage container having a gradient pore structure according to claim 1, characterized in that: In step S3, the mold is in a cylindrical shape as a whole, 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.

9. The method for preparing an oil storage container having a gradient pore structure according to claim 1, characterized in that: In step S3, the mold and the preform are placed in a spark plasma sintering device, and under a vacuum degree of less than 10Pa and a constant pressure of 3-10MPa, the temperature is rapidly increased to 230-270°C at a heating rate of 60-150°C / min, and kept warm for 2-5min; then the temperature is increased to 340-370°C at the same heating rate, and kept warm for 10-20min; then the temperature is cooled by water for 3-5min to reduce to below 100°C.

10. An oil storage tank having a gradient pore structure, characterized in that: The method is prepared by the method described in any one of claims 1 to 9.

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