Method for coating a porous material for a cylindrical structure and coated structure

Abstract

The application discloses a method for preparing a coating layer of a porous material for a cylindrical structure. The method fully utilizes the structural characteristics of the porous material for the cylindrical structure, and organically combines a product to be coated with upper and lower cover plates. A special tool is used for the base material, and a coating cavity is formed on the surface, inner wall and inner cavity of the base material to be coated, so that the surface to be coated is completely exposed to the cavity, and the non-coated surface is isolated. The coating is forced to penetrate into all open pores on the surface layer of the porous material through pressure difference, so that the coating fully covers the inner wall of the pores, and a continuous, dense and high-strength integrated coating layer is formed.

Description

Technical Field

[0001] This invention relates to the fields of surface engineering and porous material modification technology, specifically to a method for preparing a coating of porous material for a cylindrical structure and the coating structure thereof; a pressure impregnation coating method that utilizes pressure to drive the coating material to penetrate into the pores on the surface of the porous material to form a continuous and dense coating. Background Technology

[0002] Porous materials (such as carbon / carbon composites, powder metallurgy parts, foam ceramics, and wood) are widely used due to their lightweight, breathability, and energy absorption properties. However, their surfaces contain numerous open pores, and the size, shape, and distribution of these pores are often extremely uneven (ranging from micrometers to hundreds of micrometers). In practical applications, functional coatings are often prepared on the surface of porous materials to achieve functions such as corrosion resistance, oxidation resistance, insulation, or wear resistance.

[0003] Traditional coating methods have the following prominent problems: 1) Atmospheric pressure impregnation: The coating relies solely on capillary action to penetrate into the pores, with a limited penetration depth (usually less than 100 micrometers), and it is easy to form a "sealing" at the pore entrance, resulting in the internal pores not being filled and causing the coating to be discontinuous; 2) Brush or spray coating: The coating cannot penetrate deep holes and narrow gaps, leaving the inner walls of the pores exposed, which become channels for the rapid diffusion of corrosive or oxidizing media; 3) Vacuum impregnation: Although it can remove some gas, it lacks sufficient driving force to allow high-viscosity coatings to enter the micropores, and it is ineffective for closed pores with poor connectivity. 4) Poor coating adhesion: Because the inner walls of the pores are not covered, the actual contact area between the coating and the substrate is small, making it prone to peeling.

[0004] Therefore, it is essential to invent a coating method that can force the coating to penetrate the complex pore network on the surface of porous materials and achieve full coverage of the inner walls of the pores. Summary of the Invention

[0005] This invention addresses the problem that existing traditional coating methods cannot fully penetrate the pores on the surface of porous materials, which easily leads to discontinuous coatings and poor adhesion. It provides a method for preparing a coating for porous materials with a cylindrical structure and a coating structure thereof. This method can drive the coating to penetrate into all the pores on the surface of the porous material through pressure difference, so that the coating can fully cover the inner wall of the pores and form a continuous, dense, and highly bonded integrated coating.

[0006] This invention fully utilizes the structural characteristics of porous materials in cylindrical structures to organically combine the product to be coated with the upper and lower cover plates. The substrate is formed into a sealed coating cavity by using special tooling and the surface / inner wall / inner cavity of the substrate to be coated, so that the surface to be coated is completely exposed in the cavity, while the non-coated surface is isolated.

[0007] By continuously increasing or decreasing the pressure inside the cavity through the pressure regulating device, the coating is driven to repeatedly penetrate the surface pore network, expel the gas trapped in the pores, and allow the coating to fully wet the inner walls of all pores. Finally, a continuous coating filling layer is formed within a certain depth range on the surface. After curing and sintering, an integrated coating that is firmly bonded to the substrate can be obtained.

[0008] To achieve the above objectives, the present invention is implemented through the following technical solution: A method for preparing a coating for a cylindrical structure using a porous material is disclosed, comprising the following steps: S1. Pretreatment: Prepare the coating and clean the porous material substrate to be coated to remove residual oil, dust and impurities on the substrate surface to ensure the bonding effect between the coating and the substrate; S2. The porous material substrate is clamped between the upper and lower cover plates as part of the entire clamping, forming a closed cavity with the upper and lower cover plates for inputting the coating from the cover plates to the area to be coated; S3. By introducing coating into the sealed cavity, alternating the increase and decrease of the pressure in the sealed cavity and maintaining the pressure, the pressure change is used to drive out the gas trapped inside the pores, driving the coating to fully penetrate into the interior of the surface pores and fully wet the inner wall of the pores. S4. After the coating has completely wetted the pores, the excess coating in the sealed cavity is discharged. Finally, the coated substrate is cured and sintered to obtain the target coating.

[0009] Furthermore, the porous material is any one of carbon / carbon composite material, powder metallurgy metal parts, porous ceramics, foam metal or wood, and its open porosity is 5%-40%.

[0010] Furthermore, a sealing ring is provided between the upper and lower cover plates and the end face of the porous material substrate to ensure that the sealed cavity does not leak during the pressurization process; the pressure adjustment range is 0.01MPa-0.4MPa, and the pressure holding time is 30min-120min to ensure that the coating fully penetrates into the pores.

[0011] Furthermore, when the porous material is a carbon / carbon composite material, the coating material is: boron-modified phenolic resin is selected as the antioxidant coating matrix, and 10%-20% by mass of ethanol, 5%-10% by mass of nano-silicon carbide, and 0.5%-1% by mass of dispersant are added to the boron phenolic resin.

[0012] Furthermore, after preparing the coating, it is mixed evenly using magnetic stirring at a temperature of 20℃-30℃, a stirring speed of 500r / min-950r / min, and a stirring time of 30min-60min. After stirring, it is placed in a vacuum drying oven for vacuum defoaming at 0.85Mpa-0.1Mpa for 15min-30min.

[0013] Furthermore, the coating curing and sintering adopts a segmented heating method: heating from room temperature to 80°C at a heating rate of 0.8°C / min-1.5°C / min, and holding for 1 hour; heating from 80°C to 120°C at a heating rate of 0.8°C / min-1.5°C / min, and holding for 1 hour; heating from 120°C to 180°C at a heating rate of 0.3°C / min-0.5°C / min, and holding for 2 hours; and then naturally cooling to room temperature.

[0014] The present invention also discloses a coating structure used in the above method, including an upper cover plate and a lower cover plate. A sealing cover is provided on the inner side of the upper cover plate. The outer edge of the sealing cover abuts against the inner wall of the open end of the cylindrical structure. When the upper cover plate is pressed, the sealing cover forms a sealed coating cavity with the inner wall of the cylindrical structure and the bottom corner area.

[0015] Furthermore, the upper cover plate is provided with a paint injection hole connected to the delivery pump pipeline, and an exhaust overflow port is provided on one side of the paint injection hole near the edge of the upper cover plate. The exhaust overflow port is connected to a ball valve and a discharge pipe and is used to adjust the pressure of the paint chamber and discharge excess paint.

[0016] Furthermore, the bottom of the lower cover plate supports the cylindrical structure and is provided with a second sealing cover that is opposite to the first sealing cover. The second sealing cover abuts against the inner wall of the lower end of the cylindrical structure. The lower cover plate and the second sealing cover are coaxially provided with a weight-reducing groove. The outer edges of the first sealing cover and the second sealing cover are both fitted with rubber sealing rings, which are press-fitted against the inner walls of the upper and lower ends of the cylindrical structure to achieve sealing.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention utilizes pressure difference to drive forced penetration. Compared to traditional capillary penetration and vacuum impregnation, the coating can penetrate to a depth of over 100 micrometers into the surface of porous materials, achieving complete coverage of the inner walls of all open pores and avoiding premature sealing of the coating and exposure of pores. The contact area between the coating and the substrate is significantly increased, resulting in significantly improved coating adhesion and reduced peeling.

[0018] The cylindrical substrate can be quickly and tightly sealed using specialized tooling, exposing only the area to be coated. The uncoated surface does not require additional masking. The operation is simple, the process is highly controllable, and it is suitable for industrial mass production.

[0019] By clamping a cylindrical porous substrate to form a closed cavity, the coating is forced to penetrate into the open pores on the surface of the porous material by pressure regulation. This avoids the problems of limited penetration depth and easy sealing caused by traditional methods that rely solely on capillary action. It can fully cover the inner wall of the pores, and the resulting coating is continuous and dense with high bonding strength to the substrate. It is not easy to peel off and can meet the application requirements of various functional coatings for porous materials. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the clamping cross-sectional structure of the coating structure described in this invention; In the diagram: 1. Upper cover plate; 2. Lower cover plate; 3. Sealing gland one; 4. Sealing gland two; 5. Paint injection hole; 6. Exhaust overflow port; 7. Rubber sealing ring; 8. Cylindrical structure; 9. Fastening screw. Detailed Implementation

[0021] The above are merely embodiments of the present invention. The present invention is not limited to the field covered by this embodiment, and common knowledge such as specific structures and characteristics in the solution are not described in detail here. It should be noted that those skilled in the art can make several modifications and improvements without departing from the content of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application shall be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

[0022] The method for preparing a coating using a porous material for a cylindrical structure according to the present invention includes the following steps: S1. Pretreatment: Prepare the coating and clean the porous material substrate to be coated; S2. The porous material substrate is clamped between the upper and lower cover plates to form a closed cavity, which is used to input the coating from the cover plates to the area to be coated; S3. Adjust the pressure of the sealed cavity to increase or decrease the pressure of the sealed cavity and maintain the pressure; S4. Drain excess coating from the sealed cavity and cure and sinter the coating.

[0023] Among them, the porous material is any one of carbon / carbon composite material, powder metallurgy metal parts, porous ceramics, foam metal or wood, and its open porosity is 5%-40%.

[0024] Taking carbon / carbon composite materials as an example, the specific implementation method is as follows. Example 1

[0025] The coating structure of this embodiment includes an upper cover plate 1 and a lower cover plate 2. A sealing cap 3 is provided on the inner side of the upper cover plate 1. The outer edge of the sealing cap 3 abuts against the inner wall of the opening end of the cylindrical structure 8. When the upper cover plate 1 is pressed, the sealing cap 3 forms a sealed coating cavity with the inner wall of the cylindrical structure 8 and the bottom corner area.

[0026] The upper cover plate 1 is provided with a paint injection hole 5 that connects to the delivery pump pipeline. An exhaust overflow port 6 is provided on one side of the paint injection hole 5 near the edge of the upper cover plate 1. The exhaust overflow port 6 is connected to the ball valve and the discharge pipe and is used to adjust the pressure of the paint chamber and discharge the paint.

[0027] The bottom of the lower cover plate 2 supports the bottom of the cylindrical structure 8 and is provided with a second sealing cover 4 opposite to the first sealing cover 3. The second sealing cover 4 abuts against the inner wall of the lower end of the cylindrical structure 8. The lower cover plate 2 and the second sealing cover 4 are coaxially provided with a weight reduction groove (inner groove structure). The outer edges of the first sealing cover 3 and the second sealing cover 4 are both fitted with rubber sealing rings 7, which are press-fitted against the inner walls of the upper and lower ends of the cylindrical structure 8 to achieve sealing. The upper cover plate 1, the cylindrical structure 8 and the lower cover plate 2 are locked and clamped by the fastening screws 9.

[0028] This coating structure, through the use of sealing cap 3 and sealing cap 4 in conjunction with rubber sealing ring 7, can reliably seal the coating cavity, maintain stable pressure during the pressurization process, expose only the coating area on the inner wall of the crucible, and reliably isolate the non-coated areas such as the outer wall. No additional masking treatment is required for the non-coated surface. It is convenient and quick to clamp, has good sealing stability, and can adapt to the clamping and sealing requirements of porous materials for cylindrical structures with different wall thicknesses. It can provide a stable sealed space for pressure-driven coating penetration, ensuring stable coating process and uniform coating quality. Example 2

[0029] A square crucible made of needled carbon / carbon composite material, deposited and densified, was used as the substrate. The crucible dimensions were: external length 320mm × width 320mm × height 280mm, wall thickness 12mm, and internal clear dimensions 296mm × width 296mm × height 268mm. The density, measured by the water displacement method, was 1.38 g / cm³, and the porosity was 17.5%.

[0030] This embodiment describes a method for preparing an antioxidant coating on the inner wall of a carbon / carbon square crucible. The specific steps are as follows.

[0031] S1. Substrate Pretreatment: Wipe the inner wall and bottom of the crucible with a lint-free cloth soaked in acetone to remove residual oil and debris from the surface processing. Rinse with deionized water and dry in an oven at 120°C for 4 hours. After drying, allow to cool naturally to room temperature for later use.

[0032] The coating preparation procedure is as follows.

[0033] The solvent used is anhydrous ethanol (industrial grade), and the dispersant used is BYK-163 (0.5% of the mass of SiC).

[0034] Preparation method: Add 20% (w / w) ethanol to boron phenolic resin and stir thoroughly until homogeneous. Add nano-SiC and dispersant, and stir magnetically at 950 r / min for 30 min. Then place in a vacuum drying oven and defoam under vacuum at 0.85 MPa for 30 min to eliminate air bubbles introduced by stirring.

[0035] S2. Pressure Impregnation Coating Step S21. Clamping and sealing: Place the carbon / carbon square crucible horizontally with the opening facing upward in a special square crucible pressure impregnation fixture.

[0036] The tooling is specifically as follows: Lower cover plate (base): A square platform with positioning features that mates with the outer bottom surface of the crucible to restrict horizontal displacement. Upper cover plate (with sealing cap): A square plate structure, slightly larger than the outer diameter of the crucible (350mm long × 350mm wide). A square sealing ring is attached to the lower surface, with an outer diameter of 325mm, an inner diameter of 298mm, and a thickness of 10mm. When the upper cover plate is tightened, the sealing ring, along with the crucible port and bottom corner area, forms a sealed coating cavity (only the inner wall and bottom of the crucible are exposed to the coating; the outer wall of the crucible is isolated).

[0037] S22. Fixing method: The upper cover plate and the lower cover plate are locked together by external hexagonal screws and nuts arranged at the four corners.

[0038] Inlet and outlet: A paint injection hole 6 is opened in the center of the upper cover plate to connect the conveying pump pipeline; an exhaust overflow port (inner diameter 6mm) is opened at the highest point of the edge of the upper cover plate (near one corner) to connect the ball valve and the discharge pipe.

[0039] S3. Pressure Impregnation S31. Injection and Venting: Open the venting ball valve, start the delivery pump, and pump the prepared boron-modified phenolic resin coating into the coating chamber through the central injection hole. Observe the venting port; after the coating flows out continuously (indicating that the air in the chamber has been expelled), close the venting ball valve.

[0040] S32. Pressure Buildup and Holding: Continue operating the delivery pump and build up pressure in the cavity by adjusting the opening of the outlet ball valve (i.e., reducing the outlet flow rate). The pressure gauge reading will gradually rise. After adjusting to 1.0 MPa (gauge pressure), maintain the pump's delivery state and fine-tune the ball valve to stabilize the pressure at 1.0 ± 0.05 MPa, and hold the pressure for 30 minutes.

[0041] S33. Pressure relief and material discharge Turn off the delivery pump. Slowly open the discharge valve (and vent) to release the pressure inside the chamber, discharge excess paint and recycle it to the storage tank (for reuse). Once the paint stops flowing out, loosen the four corner screws and remove the top cover sealing cap.

[0042] S4: Consolidation and Sintering The segmented heating and curing process was carried out in an air-circulating oven: heating from room temperature to 80℃ at a rate of 1℃ / min and holding for 1 hour; heating from 80℃ to 120℃ at a rate of 1℃ / min and holding for 1 hour; heating from 120℃ to 180℃ at a rate of 0.5℃ / min and holding for 2 hours; and then naturally cooling to room temperature. Example 3

[0043] The method for preparing the coating of the cylindrical structure using porous materials in this embodiment is similar to that in Embodiment 2, except for the following aspects.

[0044] A square crucible of needled carbon / carbon composite material with a porosity of 35% was used as the substrate.

[0045] Antioxidant coating preparation: Boron-modified phenolic resin was selected as the matrix for the antioxidant coating. 15% ethanol by mass was added to the boron phenolic resin, followed by 8% nano-silicon carbide by mass, and 0.8% dispersant by mass of the nano-silicon carbide. After preparation, the mixture was magnetically stirred at 25°C at a stirring speed of 800 r / min for 45 min. After stirring, the mixture was placed in a vacuum drying oven for vacuum defoaming, with the vacuum pressure maintained at 0.09 MPa for 20 min.

[0046] Connect the assembled cavity to the paint delivery pipeline, close the ball valve of the exhaust overflow port, inject the prepared paint into the sealed paint cavity, and after filling, open the ball valve of the exhaust overflow port to release excess gas. After the paint flows out of the overflow port steadily, close the ball valve. Then start the pressurization and pressure holding process, pressurize to 0.2MPa, and hold the pressure for 90 minutes to allow the paint to fully penetrate into the pores of the inner wall of the crucible under pressure and wet the inner wall of the pores.

[0047] After the pressure holding is completed, open the overflow ball valve to drain the excess coating from the cavity, loosen the locking device and take out the coated substrate. Then, perform curing and sintering according to the preset segmented heating program: heat from room temperature to 80℃ at a heating rate of 0.8℃ / min and hold for 1 hour; heat from 80℃ to 120℃ at a heating rate of 1.5℃ / min and hold for 1 hour; heat from 120℃ to 180℃ at a heating rate of 0.4℃ / min and hold for 2 hours; then cool naturally to room temperature to complete the preparation of the anti-oxidation coating.

[0048] Testing revealed that the coating obtained in this embodiment is continuous and dense, with a penetration depth exceeding 180μm. The inner walls of the pores are completely covered by the coating, and the coating exhibits high bonding strength. After 10 thermal shock cycles from 500℃ to room temperature, there was no peeling or cracking, and the antioxidant performance meets the requirements for use. Example 4

[0049] The method for preparing the coating of the cylindrical structure using porous materials in this embodiment is similar to that in Embodiment 2, except for the following aspects.

[0050] A square crucible of needled carbon / carbon composite material after deposition and densification was used as the substrate, with an open porosity of 10%.

[0051] Antioxidant coating preparation: Boron-modified phenolic resin was selected as the matrix for the antioxidant coating. 10% ethanol by mass was added to the boron phenolic resin, followed by 5% nano-silicon carbide by mass, and 1% dispersant by mass of the nano-silicon carbide. After preparation, the mixture was magnetically stirred at 25°C for 500 r / min for 60 min. After stirring, the mixture was placed in a vacuum drying oven for vacuum defoaming, with the vacuum pressure maintained at 0.1 MPa for 15 min.

[0052] Connect the assembled cavity to the paint delivery pipeline, close the ball valve of the exhaust overflow port, inject the prepared paint into the sealed paint cavity, and after filling, open the ball valve of the exhaust overflow port to release excess gas. After the paint flows out of the overflow port steadily, close the ball valve. Then start the pressurization and pressure holding process, pressurize to 0.2 MPa, and hold the pressure for 120 minutes to allow the paint to fully penetrate into the pores of the inner wall of the crucible under pressure and wet the inner wall of the pores.

[0053] After the pressure holding is completed, open the overflow ball valve to drain the excess coating from the cavity, loosen the locking device and take out the coated substrate. Then, perform curing and sintering according to the preset segmented heating program: heat from room temperature to 80℃ at a heating rate of 1.5℃ / min and hold for 1 hour; heat from 80℃ to 120℃ at a heating rate of 0.8℃ / min and hold for 1 hour; heat from 120℃ to 180℃ at a heating rate of 0.3℃ / min and hold for 2 hours; then cool naturally to room temperature to complete the preparation of the anti-oxidation coating.

[0054] Testing revealed that the coating obtained in this embodiment is continuous and dense, with a penetration depth exceeding 180μm. The inner walls of the pores are completely covered by the coating, and the coating exhibits high bonding strength. After 10 thermal shock cycles from 500℃ to room temperature, there was no peeling or cracking, and the antioxidant performance meets the requirements for use. Comparative Example 1

[0055] Impregnation was performed in an impregnation furnace under normal pressure. The coating and product were placed together in a container, with the coating completely submerging the product. Solvent was added to the impregnation furnace, the furnace lid was closed and locked, and nitrogen gas was introduced to pressurize the furnace to 0.2 MPa. This pressure was maintained for 30 minutes throughout the process. After impregnation, the vent valve was opened, the furnace lid was opened, and the product was removed. The product was still completely submerged in coating. After removing the product and allowing excess coating to self-level, the remaining coating was scraped off. The product was then weighed and subjected to the same subsequent treatment as in Example 2. The coating and substrate density were 1.35 g / cm³. 3 The open area ratio is 19.4%. Comparative Example 2

[0056] Vacuum impregnation in an impregnation furnace was used. The coating and product were placed together in a container, with the coating completely submerging the product. The container was placed in the furnace, the furnace lid was closed and locked, and then the vacuum pump was turned on to evacuate to 0.1 MPa and maintained at 0.1 MPa for 30 minutes. After impregnation, the air inlet valve was opened, the furnace lid was opened, and the product was removed. The product was still completely submerged in coating. After removing the product and allowing excess coating to self-level, the remaining coating was scraped off, and the product was weighed and processed in the same manner as in Example 2. The density of the coating substrate was 1.33 g / cm³. 3 The open area ratio is 20%.

[0057] Example 2 15.57% Good 2.5 mm Example 3 16.14% Good 1.8 mm Example 4 20.05% Good 1.87 mm Comparative Example 1 10.13% Fair 0.5 mm Comparative Example 2 10.25% Fair 0.75 mm The weight gain percentage in the examples (15.57%-20.05%) was significantly higher than that in the comparative examples (10.13%-10.25%), indicating that more coating penetrated into the carbon / carbon substrate under pressure. The weight gain mainly came from the coating filling the open pores of the substrate.

[0058] The weight gain of Examples 2-4 was 1.5-2.0 times that of the control examples, demonstrating that pressure effectively overcomes capillary resistance and drives the coating into a deeper and finer pore network. Example 3 showed the highest weight gain (20.05%), which was related to the holding time. The coating density was comprehensively evaluated by combining the porosity from high-temperature sintering tests and CT scan results. Density was obtained through airtightness testing. Using an airtightness testing fixture, nitrogen gas was introduced into a sealed cavity consisting of a square crucible / plate and the fixture to increase the pressure. When the pressure reached 40 kPa, the gas supply was stopped, and the pressure drop time was measured.

[0059] The results of the airtightness test in Examples 2-4 are as follows: the time it took for the air pressure to drop from 40 kPa to 5 kPa was longer than that of the control group, at 80 s, 75 s, and 81 s respectively, while the control group took 35 s and 40 s respectively.

[0060] The results show that the pressure impregnation method proposed in this invention can effectively drive the coating into the non-uniform pore network of carbon / carbon composite materials, achieve deep filling, and form a dense and continuous coating-matrix composite structure. It is significantly superior to the traditional atmospheric pressure impregnation method in terms of weight gain, penetration depth and density.

Claims

1. A method for preparing a coating of a porous material for a cylindrical structure, characterized in that, Includes the following steps: S1. Pretreatment: Prepare the coating and clean the porous material substrate to be coated; S2. The porous material substrate is clamped between the upper and lower cover plates to form a closed cavity, which is used to input the coating from the cover plates to the area to be coated; S3. Adjust the pressure of the sealed cavity to increase or decrease the pressure of the sealed cavity and maintain the pressure; S4. Drain excess coating from the sealed cavity and cure and sinter the coating.

2. The method for preparing a coating using a porous material for a cylindrical structure according to claim 1, characterized in that, The open porosity of the porous material is 5%-40%.

3. The method for preparing a coating using a porous material for a cylindrical structure according to claim 1, characterized in that, A sealing ring is provided between the upper and lower cover plates and the end face of the porous material substrate to ensure that there is no leakage in the sealed cavity during the pressurization process; the pressure adjustment range is 0.01MPa-0.4MPa, and the pressure holding time is 30min-120min to ensure that the coating fully penetrates into the pores.

4. The method for preparing a coating using a porous material for a cylindrical structure according to claim 2, characterized in that, The porous material is any one of carbon / carbon composite material, powder metallurgy metal parts, porous ceramics, foam metal or wood. When the porous material is carbon / carbon composite material, the coating is: boron-modified phenolic resin is selected as the antioxidant coating matrix, and 10%-20% by mass of ethanol, 5%-10% by mass of nano-silicon carbide and 0.5%-1% by mass of dispersant are added to the boron phenolic resin.

5. The method for preparing a coating from a porous material with a cylindrical structure according to claim 4, characterized in that, Magnetic stirring is used at a speed of 500 r / min-950 r / min for 30 min-60 min; then it is placed in a vacuum drying oven for vacuum defoaming at a pressure of 0.85 MPa-0.1 MPa for 15 min-30 min.

6. The method for preparing a coating using a porous material for a cylindrical structure according to claim 1, characterized in that, The coating curing and sintering process employs a segmented heating method: heating from room temperature to 80°C at a rate of 0.8°C / min-1.5°C / min, holding for 1 hour; heating from 80°C to 120°C at a rate of 0.8°C / min-1.5°C / min, holding for 1 hour; heating from 120°C to 180°C at a rate of 0.3°C / min-0.5°C / min, holding for 2 hours; and then naturally cooling to room temperature.

7. The coating structure used in the method for preparing a coating of a cylindrical structure using a porous material according to any one of claims 1-6, characterized in that, It includes an upper cover plate and a lower cover plate. A sealing cover is provided on the inner side of the upper cover plate. The outer edge of the sealing cover abuts against the inner wall of the open end of the cylindrical structure. When the upper cover plate is pressed, the sealing cover forms a sealed coating cavity with the inner wall of the cylindrical structure and the bottom corner area.

8. The coating structure according to claim 7, characterized in that, The upper cover plate is provided with a paint injection hole that connects to the delivery pump pipeline. An exhaust overflow port is provided on one side of the paint injection hole near the edge of the upper cover plate. The exhaust overflow port is connected to a ball valve and a discharge pipe and is used to adjust the pressure of the paint chamber and discharge the paint.

9. The coating structure according to claim 8, characterized in that, The bottom of the lower cover plate supports the bottom of the cylindrical structure and is provided with a second sealing cover that is opposite to the first sealing cover. The second sealing cover abuts against the inner wall of the lower end of the cylindrical structure. The lower cover plate and the second sealing cover are coaxially provided with a weight reduction groove. The outer edges of the first sealing cover and the second sealing cover are both fitted with rubber sealing rings, which are press-fitted against the inner walls of the upper and lower ends of the cylindrical structure to achieve sealing.

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