Flexible graphite gasket for ultra-high temperature sealing and method of making same

Abstract

The application relates to a flexible graphite gasket for ultra-high temperature sealing and a preparation method thereof, and belongs to the technical field of flexible graphite gasket processing. The flexible graphite gasket is prepared by pressing and forming graphite worms obtained by intercalation treatment and high-temperature expansion of natural flake graphite with a carbon content of 95-99.9%. The flexible graphite gasket is obtained by wrapping an intermediate skeleton between two outer graphite foils, so that the intermediate skeleton is provided with through holes. The intermediate skeleton with through holes is prepared by using low-expansion-ratio graphite worms, and the outer graphite foils are prepared by using high-expansion-ratio graphite worms. In the process of hot pressing and compounding, the outer graphite foils can penetrate the through holes of the intermediate skeleton to form a mechanical anchoring interlocking structure, effectively strengthen the interlayer bonding performance of the gasket, significantly improve the overall tensile strength, and prevent the gasket from being prone to problems such as delamination, tearing and damage under the working conditions of precise punching, assembly and stress, and the structure has excellent stability.

Description

Technical Field

[0001] This invention belongs to the field of flexible graphite pad processing technology, specifically relating to a flexible graphite pad for ultra-high temperature sealing and its preparation method. Background Technology

[0002] Flexible graphite is a new type of sealing engineering material developed in recent years. It is made from natural flake graphite or pyrolytic graphite through special chemical treatment and heat treatment, and then pressed or rolled without the need for any binder.

[0003] Most existing flexible graphite gaskets are made by integrally pressing graphite worms with a single expansion ratio. Some multi-layer composite gaskets rely on simple stacking for molding, lacking effective anchoring structures between layers, resulting in low interlayer bonding strength. Under precision punching, assembly, and alternating loads, they are prone to delamination, tearing, and damage. At the same time, a single homogeneous structure cannot balance load-bearing capacity and interface adhesion performance, easily leading to insufficient rebound and large creep. During long-term service, the sealing preload decreases significantly. Summary of the Invention

[0004] The purpose of this invention is to provide a flexible graphite gasket for ultra-high temperature sealing and its preparation method in order to solve the above-mentioned problems.

[0005] The present invention achieves the above objectives through the following technical solutions: This invention provides a flexible graphite gasket for ultra-high temperature sealing. The flexible graphite gasket is made of natural flake graphite with a carbon content of 95-99.9%, which is intercalated and expanded at high temperature to obtain graphite worms, and then the graphite worms are pressed into shape. The flexible graphite pad is formed by wrapping an intermediate skeleton between two outer graphite foils, so the intermediate skeleton has through holes.

[0006] As a further optimization of the present invention, the hole is circular or triangular.

[0007] As a further optimization of the present invention, triangles are divided into straight-sided triangles and curved-sided triangles.

[0008] This invention also provides a method for preparing a flexible graphite gasket for ultra-high temperature sealing, comprising the following steps: S1, Intercalation and High-Temperature Expansion: Natural flake graphite is chemically intercalated using an intercalating agent; after intercalation, the pretreated graphite powder is washed with water, neutrally filtered, and dried before being sent to a high-temperature expansion furnace for instantaneous high-temperature expansion. The expansion temperature is controlled at 850-950℃, and the instantaneous expansion holding time is 5-15s, resulting in low-expansion-ratio graphite worms with an expansion ratio of 80-150 times; the expansion temperature is controlled at 980-1050℃, and the instantaneous expansion holding time is 15-25s, resulting in high-expansion-ratio graphite worms with an expansion ratio of 200-300 times. The two types of graphite worms are collected separately for later use. S2, Forming of intermediate skeleton and outer graphite foil: The intermediate skeleton and outer graphite foil are formed by multi-level gradient calendering process. First, the intermediate skeleton is pressed with low expansion ratio graphite worms, and then the outer graphite foil is pressed with high expansion ratio graphite worms. The outer graphite foil is made to penetrate the through hole of the intermediate skeleton through the hot pressing composite process to form a mechanical anchoring structure, and a composite graphite blank is obtained. S3, Precision punching and forming: The composite graphite blank is punched and processed to obtain the formed composite graphite gasket substrate; S4, Inorganic Antioxidant Modification of Surface Layer: The composite graphite pad substrate after molding is impregnated with an impregnation solution in a thin layer, and then cured at low temperature to form a dense antioxidant protective thin layer on the surface of the graphite pad, thus obtaining a flexible graphite pad.

[0009] As a further optimization of the present invention, in step S1, the intercalating agent is selected from a sulfuric acid and nitric acid compound system, and the mass ratio of sulfuric acid to nitric acid is 4-6:1.

[0010] As a further optimization of the present invention, in step S2, the thickness of the intermediate skeleton accounts for 60-70% of the total thickness; the thickness of the outer foil on one side is 15-20% of the overall thickness.

[0011] As a further optimization of the present invention, in step S2, the multi-stage gradient calendering process is divided into three stages: pre-calendering, intermediate calendering, and fine calendering. The pre-calendering pressure is 0.5-1.5 MPa, the intermediate calendering pressure is 2.0-4.0 MPa, and the fine calendering pressure is 5.0-8.0 MPa.

[0012] As a further optimization of the present invention, in step S4, the inorganic antioxidant is a borate and phosphate composite inorganic system, and the mass ratio of borate to phosphate is 1:1-3.

[0013] As a further optimization of the present invention, an impregnation solution is prepared by mixing an inorganic antioxidant with deionized water. The solid content of the impregnation solution is 5-10%, and a thin-layer impregnation method is adopted, with an impregnation time of 3-10 seconds.

[0014] As a further optimization of the present invention, in step S4, the low-temperature curing temperature is 120-150℃, the curing time is 15-30min, and a micron-level antioxidant protective film is formed on the surface of the gasket after curing.

[0015] The beneficial effects of this invention are as follows: A middle framework with through holes is prepared using low-expansion-ratio graphite worms, and an outer graphite foil is prepared using high-expansion-ratio graphite worms. During the hot-pressing composite process, the outer graphite foil can penetrate the through holes of the middle framework to form a mechanical anchoring and interlocking structure, effectively strengthening the interlayer bonding performance of the gasket and significantly improving the overall tensile strength. This makes the gasket less prone to delamination, tearing, and damage under precision punching, assembly, and stress conditions, exhibiting excellent structural stability. Simultaneously, this invention uses a borate and phosphate composite inorganic antioxidant system to impregnate and modify the gasket surface. After low-temperature curing, a continuous and dense micron-level inorganic antioxidant protective layer can be formed on the gasket surface, effectively blocking oxygen diffusion into the graphite matrix, significantly inhibiting the high-temperature oxidation and burning behavior of graphite materials, reducing high-temperature thermal weight loss, and greatly improving the sealing stability and service durability of the flexible graphite gasket under aerobic ultra-high temperature conditions. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the intermediate skeleton in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the intermediate skeleton in Embodiment 2 of the present invention; Figure 3 This is a schematic diagram of the intermediate skeleton in Embodiment 3 of the present invention. Detailed Implementation

[0017] The present application will now be described in further detail. It should be noted that the following specific embodiments are only used to further illustrate the present application and should not be construed as limiting the scope of protection of the present application. Those skilled in the art can make some non-essential improvements and adjustments to the present application based on the above application content.

[0018] Unless otherwise specified, all methods used in this invention are conventional methods known to those skilled in the art, and all reagents and materials used are commercially available products.

[0019] In this invention, the borate used is sodium tetraborate; the phosphate used is aluminum dihydrogen phosphate.

[0020] Example 1

[0021] A method for preparing a flexible graphite gasket for ultra-high temperature sealing includes the following steps: S1, Intercalation and High-Temperature Expansion: Natural flake graphite with a carbon content of 98.9% was chemically intercalated (the intercalating agent used in the chemical intercalation was a mixture of sulfuric acid and nitric acid, with a mass ratio of sulfuric acid to nitric acid of 5:1). After intercalation, the pretreated graphite powder was washed with water, neutrally filtered, and dried. Then, it was sent to a high-temperature expansion furnace for instantaneous high-temperature expansion. The expansion temperature was controlled at 900℃, and the instantaneous expansion holding time was 10s, resulting in low-expansion-ratio graphite worms with an expansion ratio of 120 times. The expansion temperature was controlled at 1000℃, and the instantaneous expansion holding time was 20s, resulting in high-expansion-ratio graphite worms with an expansion ratio of 250 times. The two types of graphite worms were collected separately for later use. S2, Forming of the intermediate skeleton and outer graphite foil: The intermediate skeleton and outer graphite foil are formed by multi-stage gradient calendering process. First, the intermediate skeleton is pressed with low expansion ratio graphite worms. The intermediate skeleton has a through hole, which is circular (the thickness of the intermediate skeleton accounts for 60% of the total thickness). Then, the outer graphite foil is pressed with high expansion ratio graphite worms (the thickness of the outer foil on one side is 20% of the overall thickness). The two outer graphite foils are then connected through the through hole of the intermediate skeleton by hot pressing composite process to form a mechanical anchoring structure, resulting in a composite graphite slab (the multi-stage gradient calendering process is divided into three stages: pre-pressing, intermediate pressing, and fine pressing. The pre-pressing pressure is 1.2 MPa, the intermediate pressing pressure is 3 MPa, and the fine pressing pressure is 6 MPa). S3, Precision punching and forming: The composite graphite blank is punched and processed to obtain the formed composite graphite gasket substrate; S4, Inorganic Antioxidant Modification of the Surface: The composite graphite pad substrate after molding is impregnated with an impregnation solution (the impregnation solution is prepared by mixing inorganic antioxidants and deionized water, the solid content of the impregnation solution is 8%, and the thin layer is impregnated by immersion for 8 seconds; the inorganic antioxidant is a borate and phosphate composite inorganic system, and the mass ratio of borate to phosphate is 1:2). Then, it is cured at low temperature (the low temperature curing temperature is 135℃, the curing time is 25min, and a micron-level antioxidant protective film is formed on the surface of the pad after curing), forming a dense antioxidant protective thin layer on the surface of the graphite pad, thus obtaining a flexible graphite pad.

[0022] Example 2

[0023] A method for preparing a flexible graphite gasket for ultra-high temperature sealing includes the following steps: S1, Intercalation and High-Temperature Expansion: Natural flake graphite with a carbon content of 98.9% was chemically intercalated (the intercalating agent used in the chemical intercalation was a mixture of sulfuric acid and nitric acid, with a mass ratio of sulfuric acid to nitric acid of 5:1). After intercalation, the pretreated graphite powder was washed with water, neutrally filtered, and dried. Then, it was sent to a high-temperature expansion furnace for instantaneous high-temperature expansion. The expansion temperature was controlled at 900℃, and the instantaneous expansion holding time was 10s, resulting in low-expansion-ratio graphite worms with an expansion ratio of 120 times. The expansion temperature was controlled at 1000℃, and the instantaneous expansion holding time was 20s, resulting in high-expansion-ratio graphite worms with an expansion ratio of 250 times. The two types of graphite worms were collected separately for later use. S2, Forming of the intermediate skeleton and outer graphite foil: The intermediate skeleton and outer graphite foil are formed by multi-stage gradient calendering process. First, the intermediate skeleton is pressed with low expansion ratio graphite worms. The intermediate skeleton has through holes with straight-edged triangles (the thickness of the intermediate skeleton accounts for 60% of the total thickness). Then, the outer graphite foil is pressed with high expansion ratio graphite worms (the thickness of the outer foil on one side is 20% of the overall thickness). The two outer graphite foils are then connected through the through holes of the intermediate skeleton by hot pressing composite process to form a mechanical anchoring structure, resulting in a composite graphite slab (the multi-stage gradient calendering process is divided into three stages: pre-pressing, intermediate pressing, and fine pressing. The pre-pressing pressure is 1.2 MPa, the intermediate pressing pressure is 3 MPa, and the fine pressing pressure is 6 MPa). S3, Precision punching and forming: The composite graphite blank is punched and processed to obtain the formed composite graphite gasket substrate; S4, Inorganic Antioxidant Modification of the Surface: The composite graphite pad substrate after molding is impregnated with an impregnation solution (the impregnation solution is prepared by mixing inorganic antioxidants and deionized water, the solid content of the impregnation solution is 8%, and the thin layer is impregnated by immersion for 8 seconds; the inorganic antioxidant is a borate and phosphate composite inorganic system, and the mass ratio of borate to phosphate is 1:2). Then, it is cured at low temperature (the low temperature curing temperature is 135℃, the curing time is 25min, and a micron-level antioxidant protective film is formed on the surface of the pad after curing), forming a dense antioxidant protective thin layer on the surface of the graphite pad, thus obtaining a flexible graphite pad.

[0024] Example 3

[0025] A method for preparing a flexible graphite gasket for ultra-high temperature sealing includes the following steps: S1, Intercalation and High-Temperature Expansion: Natural flake graphite with a carbon content of 98.9% was chemically intercalated (the intercalating agent used in the chemical intercalation was a mixture of sulfuric acid and nitric acid, with a mass ratio of sulfuric acid to nitric acid of 5:1). After intercalation, the pretreated graphite powder was washed with water, neutrally filtered, and dried. Then, it was sent to a high-temperature expansion furnace for instantaneous high-temperature expansion. The expansion temperature was controlled at 900℃, and the instantaneous expansion holding time was 10s, resulting in low-expansion-ratio graphite worms with an expansion ratio of 120 times. The expansion temperature was controlled at 1000℃, and the instantaneous expansion holding time was 20s, resulting in high-expansion-ratio graphite worms with an expansion ratio of 250 times. The two types of graphite worms were collected separately for later use. S2, Forming of the intermediate skeleton and outer graphite foil: The intermediate skeleton and outer graphite foil are formed by multi-stage gradient calendering process. First, the intermediate skeleton is pressed with low expansion ratio graphite worms. The intermediate skeleton has through holes with arc-edged triangular holes (the thickness of the intermediate skeleton accounts for 60% of the total thickness). Then, the outer graphite foil is pressed with high expansion ratio graphite worms (the thickness of the outer foil on one side is 20% of the overall thickness). The two outer graphite foils are then connected through the through holes of the intermediate skeleton by hot pressing composite process to form a mechanical anchoring structure, resulting in a composite graphite slab (the multi-stage gradient calendering process is divided into three stages: pre-pressing, intermediate pressing, and fine pressing. The pre-pressing pressure is 1.2 MPa, the intermediate pressing pressure is 3 MPa, and the fine pressing pressure is 6 MPa). S3, Precision punching and forming: The composite graphite blank is punched and processed to obtain the formed composite graphite gasket substrate; S4, Inorganic Antioxidant Modification of the Surface: The composite graphite pad substrate after molding is impregnated with an impregnation solution (the impregnation solution is prepared by mixing inorganic antioxidants and deionized water, the solid content of the impregnation solution is 8%, and the thin layer is impregnated by immersion for 8 seconds; the inorganic antioxidant is a borate and phosphate composite inorganic system, and the mass ratio of borate to phosphate is 1:2). Then, it is cured at low temperature (the low temperature curing temperature is 135℃, the curing time is 25min, and a micron-level antioxidant protective film is formed on the surface of the pad after curing), forming a dense antioxidant protective thin layer on the surface of the graphite pad, thus obtaining a flexible graphite pad.

[0026] Comparative Example 1 A method for preparing a flexible graphite gasket for ultra-high temperature sealing includes the following steps: S1, Intercalation and High-Temperature Expansion: Natural flake graphite with a carbon content of 98.9% is chemically intercalated (the intercalating agent used in the chemical intercalation treatment is a mixture of sulfuric acid and nitric acid, with a mass ratio of sulfuric acid to nitric acid of 5:1); after intercalation, the pretreated graphite powder is washed with water, neutrally filtered, and dried, and then sent to a high-temperature expansion furnace for high-temperature instantaneous expansion. The expansion temperature is controlled at 900℃, and the instantaneous expansion holding time is 10s, resulting in graphite worms with an expansion ratio of 120 times, which are collected for later use. S2, Calendering process forming: The graphite worms are pressed into composite graphite slabs using a multi-stage gradient calendering process (the multi-stage gradient calendering process is divided into three stages: pre-pressing, intermediate pressing, and fine pressing. The pre-pressing pressure is 1.2 MPa, the intermediate pressing pressure is 3 MPa, and the fine pressing pressure is 6 MPa). S3, Precision punching and forming: The composite graphite blank is punched and processed to obtain the formed composite graphite gasket substrate; S4, Inorganic Antioxidant Modification of the Surface: The composite graphite pad substrate after molding is impregnated with an impregnation solution (the impregnation solution is prepared by mixing inorganic antioxidants and deionized water, the solid content of the impregnation solution is 8%, and the thin layer is impregnated by immersion for 8 seconds; the inorganic antioxidant is a borate and phosphate composite inorganic system, and the mass ratio of borate to phosphate is 1:2). Then, it is cured at low temperature (the low temperature curing temperature is 135℃, the curing time is 25min, and a micron-level antioxidant protective film is formed on the surface of the pad after curing), forming a dense antioxidant protective thin layer on the surface of the graphite pad, thus obtaining a flexible graphite pad.

[0027] Comparative Example 2 A method for preparing a flexible graphite gasket for ultra-high temperature sealing includes the following steps: S1, Intercalation and High-Temperature Expansion: Natural flake graphite with a carbon content of 98.9% is chemically intercalated (the intercalating agent used in the chemical intercalation treatment is a mixture of sulfuric acid and nitric acid, with a mass ratio of sulfuric acid to nitric acid of 5:1); after intercalation, the pretreated graphite powder is washed with water, neutrally filtered, and dried, and then sent to a high-temperature expansion furnace for high-temperature instantaneous expansion. The expansion temperature is controlled at 1000℃, and the instantaneous expansion holding time is 20s, resulting in graphite worms with an expansion ratio of 250 times, which are collected for later use. S2, Calendering process forming: The graphite worms are pressed into composite graphite slabs using a multi-stage gradient calendering process (the multi-stage gradient calendering process is divided into three stages: pre-pressing, intermediate pressing, and fine pressing. The pre-pressing pressure is 1.2 MPa, the intermediate pressing pressure is 3 MPa, and the fine pressing pressure is 6 MPa). S3, Precision punching and forming: The composite graphite blank is punched and processed to obtain the formed composite graphite gasket substrate; S4, Inorganic Antioxidant Modification of the Surface: The composite graphite pad substrate after molding is impregnated with an impregnation solution (the impregnation solution is prepared by mixing inorganic antioxidants and deionized water, the solid content of the impregnation solution is 8%, and the thin layer is impregnated by immersion for 8 seconds; the inorganic antioxidant is a borate and phosphate composite inorganic system, and the mass ratio of borate to phosphate is 1:2). Then, it is cured at low temperature (the low temperature curing temperature is 135℃, the curing time is 25min, and a micron-level antioxidant protective film is formed on the surface of the pad after curing), forming a dense antioxidant protective thin layer on the surface of the graphite pad, thus obtaining a flexible graphite pad.

[0028] Comparative Example 3 A method for preparing a flexible graphite gasket for ultra-high temperature sealing includes the following steps: S1, Intercalation and High-Temperature Expansion: Natural flake graphite with a carbon content of 98.9% was chemically intercalated (the intercalating agent used in the chemical intercalation was a mixture of sulfuric acid and nitric acid, with a mass ratio of sulfuric acid to nitric acid of 5:1). After intercalation, the pretreated graphite powder was washed with water, neutrally filtered, and dried. Then, it was sent to a high-temperature expansion furnace for instantaneous high-temperature expansion. The expansion temperature was controlled at 900℃, and the instantaneous expansion holding time was 10s, resulting in low-expansion-ratio graphite worms with an expansion ratio of 120 times. The expansion temperature was controlled at 1000℃, and the instantaneous expansion holding time was 20s, resulting in high-expansion-ratio graphite worms with an expansion ratio of 250 times. The two types of graphite worms were mixed at a mass ratio of 1:1 and collected for later use. S2, Calendering process forming: The composite graphite slab is formed by multi-stage gradient calendering process (the multi-stage gradient calendering process is divided into three stages: pre-calendering, intermediate calendering and fine calendering. The pre-calendering pressure is 1.2MPa, the intermediate calendering pressure is 3MPa, and the fine calendering pressure is 6MPa). S3, Precision punching and forming: The composite graphite blank is punched and processed to obtain the formed composite graphite gasket substrate; S4, Inorganic Antioxidant Modification of the Surface: The composite graphite pad substrate after molding is impregnated with an impregnation solution (the impregnation solution is prepared by mixing inorganic antioxidants and deionized water, the solid content of the impregnation solution is 8%, and the thin layer is impregnated by immersion for 8 seconds; the inorganic antioxidant is a borate and phosphate composite inorganic system, and the mass ratio of borate to phosphate is 1:2). Then, it is cured at low temperature (the low temperature curing temperature is 135℃, the curing time is 25min, and a micron-level antioxidant protective film is formed on the surface of the pad after curing), forming a dense antioxidant protective thin layer on the surface of the graphite pad, thus obtaining a flexible graphite pad.

[0029] Comparative Example 4 A method for preparing a flexible graphite gasket for ultra-high temperature sealing includes the following steps: S1, Intercalation and High-Temperature Expansion: Natural flake graphite with a carbon content of 98.9% was chemically intercalated (the intercalating agent used in the chemical intercalation was a mixture of sulfuric acid and nitric acid, with a mass ratio of sulfuric acid to nitric acid of 5:1). After intercalation, the pretreated graphite powder was washed with water, neutrally filtered, and dried. Then, it was sent to a high-temperature expansion furnace for instantaneous high-temperature expansion. The expansion temperature was controlled at 900℃, and the instantaneous expansion holding time was 10s, resulting in low-expansion-ratio graphite worms with an expansion ratio of 120 times. The expansion temperature was controlled at 1000℃, and the instantaneous expansion holding time was 20s, resulting in high-expansion-ratio graphite worms with an expansion ratio of 250 times. The two types of graphite worms were mixed at a mass ratio of 1:1 and collected for later use. S2, Calendering process forming: The intermediate skeleton and outer graphite foil are formed by multi-stage gradient calendering process. First, the intermediate skeleton is pressed, and a hole is passed through the intermediate skeleton. The hole is a triangular arc edge (the thickness of the intermediate skeleton accounts for 60% of the total thickness). Then, the outer graphite foil is pressed (the thickness of the outer foil on one side is 20% of the overall thickness). The two outer graphite foils are connected by a hot-pressing composite process to penetrate the through hole of the intermediate skeleton and form a mechanical anchoring structure, resulting in a composite graphite slab (the multi-stage gradient calendering process is divided into three stages: pre-pressing, intermediate pressing, and fine pressing. The pre-pressing pressure is 1.2 MPa, the intermediate pressing pressure is 3 MPa, and the fine pressing pressure is 6 MPa). S3, Precision punching and forming: The composite graphite blank is punched and processed to obtain the formed composite graphite gasket substrate; S4, Inorganic Antioxidant Modification of the Surface: The composite graphite pad substrate after molding is impregnated with an impregnation solution (the impregnation solution is prepared by mixing inorganic antioxidants and deionized water, the solid content of the impregnation solution is 8%, and the thin layer is impregnated by immersion for 8 seconds; the inorganic antioxidant is a borate and phosphate composite inorganic system, and the mass ratio of borate to phosphate is 1:2). Then, it is cured at low temperature (the low temperature curing temperature is 135℃, the curing time is 25min, and a micron-level antioxidant protective film is formed on the surface of the pad after curing), forming a dense antioxidant protective thin layer on the surface of the graphite pad, thus obtaining a flexible graphite pad.

[0030] Comparative Example 5 A method for preparing a flexible graphite gasket for ultra-high temperature sealing includes the following steps: S1, Intercalation and High-Temperature Expansion: Natural flake graphite with a carbon content of 98.9% was chemically intercalated (the intercalating agent used in the chemical intercalation was a mixture of sulfuric acid and nitric acid, with a mass ratio of sulfuric acid to nitric acid of 5:1). After intercalation, the pretreated graphite powder was washed with water, neutrally filtered, and dried. Then, it was sent to a high-temperature expansion furnace for instantaneous high-temperature expansion. The expansion temperature was controlled at 900℃, and the instantaneous expansion holding time was 10s, resulting in low-expansion-ratio graphite worms with an expansion ratio of 120 times. The expansion temperature was controlled at 1000℃, and the instantaneous expansion holding time was 20s, resulting in high-expansion-ratio graphite worms with an expansion ratio of 250 times. The two types of graphite worms were collected separately for later use. S2, Forming of the intermediate skeleton and outer graphite foil: The intermediate skeleton and outer graphite foil are formed by multi-stage gradient calendering process. First, the intermediate skeleton is pressed with low expansion ratio graphite worms. The intermediate skeleton has through holes with arc-edged triangular holes (the thickness of the intermediate skeleton accounts for 60% of the total thickness). Then, the outer graphite foil is pressed with high expansion ratio graphite worms (the thickness of the outer foil on one side is 20% of the overall thickness). The two outer graphite foils are then connected through the through holes of the intermediate skeleton by hot pressing composite process to form a mechanical anchoring structure, resulting in a composite graphite slab (the multi-stage gradient calendering process is divided into three stages: pre-pressing, intermediate pressing, and fine pressing. The pre-pressing pressure is 1.2 MPa, the intermediate pressing pressure is 3 MPa, and the fine pressing pressure is 6 MPa). S3, Precision punching and forming: The composite graphite blank is punched and processed to obtain a flexible graphite pad.

[0031] Performance testing (I) The performance of the flexible graphite gaskets obtained by the methods of Examples 1-3 and Comparative Examples 1-4 was tested according to GB / T20671.2-2006 "Classification System and Test Methods for Non-metallic Gasket Materials Part 2: Test Methods for Compression Ratio and Resilience of Gasket Materials". The test results are shown in Table 1. Table 1

[0032] As can be seen from Table 1, the compression rate of the flexible graphite gaskets prepared in Examples 1-3 is 35.1%-35.3%, which is within the applicable compression rate range for flexible graphite gaskets for sealing. After being compressed, they can fully conform to the sealing surface of the flange. The rebound rate reaches 18.4%-18.6%, which is significantly higher than all comparative sample samples. It has excellent deformation compensation ability and can maintain the required clamping force for sealing for a long time.

[0033] The compression ratios of Comparative Examples 1-4 were all higher than 36%, and the material structure was loose. Among them, Comparative Examples 1 and 2 had excessively high compression ratios and the worst resilience performance. They were prone to plastic creep under long-term continuous pressure, and the sealing pre-tightening force was severely reduced. Although the resilience performance of Comparative Examples 3 and 4 was better than that of Comparative Examples 1 and 2, it was still significantly lower than that of the sample in the example.

[0034] In summary, the flexible graphite pads prepared in Examples 1-3 achieved a good match between compression performance and resilience performance, and their overall sealing performance was superior to that of the comparative examples.

[0035] (II) The performance of the flexible graphite pads obtained by the methods of Example 3 and Comparative Example 5 was tested according to GB / T33920-2025 "Test Methods for Flexible Graphite Plates". The test results are shown in Table 2: Table 2

[0036] As shown in Table 2, the thermal weight loss of the sample in Example 3 after being kept at 600℃ for 2 hours was only 11%, while the thermal weight loss of the sample in Comparative Example 5 was as high as 31%. The results indicate that the present invention, through surface inorganic antioxidant modification treatment, forms a continuous and dense inorganic antioxidant protective layer on the gasket surface, effectively blocking oxygen diffusion into the graphite matrix, significantly inhibiting high-temperature oxidation and burning of graphite, and greatly improving the antioxidant performance of the flexible graphite gasket under high-temperature and oxygen-containing conditions, which is beneficial for extending the high-temperature sealing service life of the gasket.

[0037] (III) The performance of the flexible graphite gaskets obtained by the methods of Examples 1-3 and Comparative Examples 1-4 was tested according to GB / T12385-2025 "Test Method for Sealing Performance of Gaskets for Pipe Flanges". The test results are shown in Table 3. Table 3

[0038] As can be seen from Table 3, the leakage rates of Examples 1-3 are all lower than those of all comparative samples, with Example 3 having the lowest leakage rate and the best sealing performance. The flexible graphite gaskets prepared in Examples 1-3 use low-expansion-ratio graphite worms as the middle skeleton and high-expansion-ratio graphite worms as the outer graphite foil. Through the hot-pressing anchoring composite structure, the outer graphite foil can fully fit the sealing interface, reduce the leakage channels between the gasket and the flange contact surface, and effectively improve the sealing barrier capability.

[0039] (iv) The performance of the flexible graphite pads obtained by the methods of Examples 1-3 and Comparative Examples 1-4 was tested according to GB / T33920-2025 "Test Methods for Flexible Graphite Plates". The test results are shown in Table 4. Table 4

[0040] As shown in Table 4, the tensile strength of Examples 1-3 is higher than that of all comparative examples. Among them, the tensile strength of Example 3 reaches 6.4 MPa, which is the highest among all samples; the tensile strength of Example 1 is 5.8 MPa, and the tensile strength of Example 2 is 5.6 MPa.

[0041] The tensile strength of Comparative Examples 1-4 ranged from 4.7 to 5.5 MPa, which was lower than that of the Example Group. This is because the present invention uses low expansion ratio graphite worms to construct the intermediate skeleton, and combines them with high expansion graphite foil to form a mechanical anchoring and interlocking structure through hot pressing. The interlayer bonding is firm, which effectively improves the overall mechanical strength of the gasket and reduces the risk of tearing and breakage during precision punching and assembly under stress.

[0042] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A flexible graphite gasket for ultra-high temperature sealing, characterized in that, The flexible graphite pad is made from natural flake graphite with a carbon content of 95-99.9%, which is intercalated and expanded at high temperature to obtain graphite worms, and then the graphite worms are pressed into shape. The flexible graphite pad is formed by wrapping an intermediate skeleton between two outer graphite foils, so the intermediate skeleton has through holes.

2. A flexible graphite gasket for ultra-high temperature sealing as described in claim 1, characterized in that, The hole is circular or triangular.

3. A flexible graphite gasket for ultra-high temperature sealing as described in claim 2, characterized in that, The triangle is divided into straight-sided triangles and curved-sided triangles.

4. A method for preparing a flexible graphite gasket for ultra-high temperature sealing as described in claim 3, characterized in that, Includes the following steps: S1, Intercalation High-Temperature Expansion: Natural flake graphite is chemically intercalated using an intercalating agent; After intercalation, the pretreated graphite powder is washed with water, neutrally filtered, and dried. Then, it is sent to a high-temperature expansion furnace for high-temperature instantaneous expansion. The expansion temperature is controlled at 850-950℃, and the instantaneous expansion holding time is 5-15s, resulting in low expansion ratio graphite worms with an expansion ratio of 80-150 times. The expansion temperature is controlled at 980-1050℃, and the instantaneous expansion holding time is 15-25s, resulting in high expansion ratio graphite worms with an expansion ratio of 200-300 times. The two types of graphite worms are collected separately for later use. S2, Forming of intermediate skeleton and outer graphite foil: The intermediate skeleton and outer graphite foil are formed by multi-level gradient calendering process. First, the intermediate skeleton is pressed with low expansion ratio graphite worms, and then the outer graphite foil is pressed with high expansion ratio graphite worms. The outer graphite foil is made to penetrate the through hole of the intermediate skeleton through the hot pressing composite process to form a mechanical anchoring structure, and a composite graphite blank is obtained. S3, Precision punching and forming: The composite graphite blank is punched and processed to obtain the formed composite graphite gasket substrate; S4, Inorganic Antioxidant Modification of Surface Layer: The composite graphite pad substrate after molding is impregnated with an impregnation solution in a thin layer, and then cured at low temperature to form a dense antioxidant protective thin layer on the surface of the graphite pad, thus obtaining a flexible graphite pad.

5. The method for preparing a flexible graphite gasket for ultra-high temperature sealing according to claim 4, characterized in that, In step S1, the intercalating agent is a mixture of sulfuric acid and nitric acid, with a mass ratio of sulfuric acid to nitric acid of 4-6:

1.

6. The method for preparing a flexible graphite gasket for ultra-high temperature sealing according to claim 4, characterized in that, In step S2, the thickness of the intermediate skeleton accounts for 60-70% of the total thickness; the thickness of the outer foil on one side is 15-20% of the overall thickness.

7. The method for preparing a flexible graphite gasket for ultra-high temperature sealing according to claim 4, characterized in that, In step S2, the multi-stage gradient calendering process is divided into three stages: pre-calendering, intermediate calendering, and fine calendering. The pre-calendering pressure is 0.5-1.5 MPa, the intermediate calendering pressure is 2.0-4.0 MPa, and the fine calendering pressure is 5.0-8.0 MPa.

8. The method for preparing a flexible graphite gasket for ultra-high temperature sealing according to claim 4, characterized in that, An impregnation solution is prepared by mixing an inorganic antioxidant with deionized water. The solid content of the impregnation solution is 5-10%. Thin-layer impregnation is carried out by immersion for 3-10 seconds.

9. The method for preparing a flexible graphite gasket for ultra-high temperature sealing according to claim 8, characterized in that, In step S4, the inorganic antioxidant is a borate and phosphate composite inorganic system, with a mass ratio of borate to phosphate of 1:1-3.

10. The method for preparing a flexible graphite gasket for ultra-high temperature sealing according to claim 4, characterized in that, In step S4, the low-temperature curing temperature is 120-150℃, the curing time is 15-30min, and a micron-level antioxidant protective film is formed on the surface of the gasket after curing.

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