Preparation method of modified polytetrafluoroethylene sealing ring and double-eccentric gasket

Abstract

The invention relates to the technical field of double eccentric gaskets, and discloses a preparation method of a modified polytetrafluoroethylene sealing ring and the double eccentric gaskets, the preparation method comprises the following steps: (1) adding graphite powder, diatomite and silicon dioxide hollow microspheres into an aqueous solution of polyacrylamide, and carrying out ball milling to obtain a mixture I; (2) drying the mixture I, and performing primary sintering to obtain a mixture II; (3) mixing the mixture II with polytetrafluoroethylene, polyphenylene sulfide and polyethylene wax, and then loading the mixture into a mold for primary pressurization to obtain a preformed blank; and (4) carrying out secondary sintering on the preformed blank, and then carrying out secondary pressurization to obtain the modified polytetrafluoroethylene sealing ring. The modified polytetrafluoroethylene sealing ring has excellent sealing performance, tensile strength, wear resistance and creep relaxation resistance, and the obtained double-eccentric gasket can meet the strict sealing requirements of various high-frequency double-eccentric butterfly valves.

Description

Technical Field

[0001] The invention relates to the technical field of double eccentric gaskets, in particular to a preparation method of a modified polytetrafluoroethylene sealing ring and a double eccentric gasket. Background Art

[0002] The butterfly valve is a kind of valve that uses a disc-type opening and closing member to reciprocate about 90 degrees to open, close or adjust the flow of the medium. It has a simple structure, small size, light weight, small installation size, small driving torque, easy and quick operation, and also has good flow regulation function and closing sealing characteristics. Therefore, it is widely used in industries such as petroleum, chemical industry, shipbuilding and power. The double eccentric butterfly valve is a type of butterfly valve. Its structural feature is that the axis of the valve stem deviates from the center of the butterfly plate and the center of the body. The effect of the double eccentricity is that the butterfly plate can quickly separate from the valve seat after the valve is opened, which greatly eliminates the unnecessary excessive extrusion and scraping between the butterfly plate and the valve seat, reduces the opening resistance, reduces wear, and increases the life of the valve seat.

[0003] The gasket of the double eccentric butterfly valve in the prior art has problems such as low strength, poor sealing performance, poor wear resistance, low creep relaxation rate, etc., which in turn affects the service life of the gasket. In actual application, as the number of times the valve is adjusted increases, the sealing ring is prone to wear and loosening, and the sealing ring in the butterfly valve is prone to failure, resulting in medium leakage, which poses a major safety hazard and greatly affects the reliability of the double eccentric butterfly valve. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a preparation method of a modified polytetrafluoroethylene sealing ring and a double eccentric gasket. The composite filler is first prepared by mixing graphite powder, diatomaceous earth and hollow silica microspheres, and then mixed with polytetrafluoroethylene, polyphenylene sulfide and polyethylene wax. The modified polytetrafluoroethylene sealing ring is obtained by segmented pressurization and sintering. The modified polytetrafluoroethylene sealing ring has excellent wax lightness, sealing resilience and creep resistance. The obtained double eccentric gasket can meet the stringent sealing requirements of various high-frequency double eccentric butterfly valves.

[0005] The purpose of the present invention is achieved through the following technical solutions: In a first aspect, the present invention provides a method for preparing a modified polytetrafluoroethylene sealing ring, comprising the following steps: (1) adding graphite powder, diatomaceous earth and hollow silicon dioxide microspheres into an aqueous solution of polyacrylamide and ball milling to obtain a mixture I; (2) After drying the mixed material I, sintering is performed once to obtain the mixed material II; (3) Mixing the mixed material II with polytetrafluoroethylene, polyphenylene sulfide, and polyethylene wax, and then placing the mixed material II into a mold for pressurization to obtain a preformed embryo; (4) The preformed body is subjected to secondary sintering and then secondary pressurization to obtain a modified polytetrafluoroethylene sealing ring.

[0006] The present invention uses polytetrafluoroethylene as the main raw material to prepare the sealing ring, and adds polyphenylene sulfide as a reinforcing material. Polyphenylene sulfide has the advantages of high mechanical strength, high temperature resistance, good thermal stability, etc., and can improve the tensile strength and wear resistance of pure polytetrafluoroethylene. At the same time, inorganic reinforcing fillers including graphite, hollow silicon dioxide microspheres and diatomaceous earth are added to further fill and modify the polytetrafluoroethylene, which can improve the anti-creep relaxation performance of the sealing ring, and the added polyethylene wax can play a good lubricating role between the filler and the polytetrafluoroethylene base material, thereby improving the dispersibility and compatibility.

[0007] In addition, by pre-ball-milling and mixing graphite, hollow silica microspheres and diatomaceous earth, graphite powder can be filled into the pore structure of hollow silica microspheres and diatomaceous earth. Combined with the compounding of hollow silica microspheres and diatomaceous earth, the composite filler formed can have higher strength and toughness. The addition of polyimide can promote adsorption and bonding, and gas will be generated during the first sintering to reform the pores and obtain a large specific surface area, which is conducive to compatibility with subsequent polymer high molecular mixing, thereby improving the material's creep resistance and compression rebound performance and extending its service life.

[0008] Preferably, in step (1), the mass ratio of the graphite powder, diatomaceous earth, hollow silicon dioxide microspheres and the aqueous solution of polyacrylamide is 2-4:7-9:22-25:50; and the mass concentration of the aqueous solution of polyacrylamide is 1-3%.

[0009] Preferably, in step (1), the graphite powder comprises nano-scale graphite powder and micron-scale graphite powder in a mass ratio of 3 to 4:1; the particle size of the nano-scale graphite powder is 10 to 200 nm; the particle size of the micron-scale graphite powder is 1 to 10 μm; the particle size of the diatomaceous earth is 5 to 30 μm, and the specific surface area is 20 to 70 m 2 / g; the particle size of the hollow silica microspheres is 5 to 30 μm and the density is 0.35 to 0.70 g / cm 3 .

[0010] By compounding the particle size, pore size and mass ratio of graphite powder, diatomaceous earth and hollow silica microspheres, the combined stability of the mixed filler can be improved while having a larger specific surface area, which helps to make it compatible with the polytetrafluoroethylene substrate.

[0011] Preferably, in step (1), the ball milling conditions are: ball milling at a rotation speed of 100 to 200 rpm for 30 to 50 min.

[0012] Preferably, in step (2), the drying condition is: drying at 100-120°C for 3-5h; the primary sintering condition is: heating from room temperature to 200-300°C at a heating rate of 1-3°C / min, and keeping warm for 1-2h.

[0013] Preferably, in step (3), the mass ratio of the mixture II, polytetrafluoroethylene, polyphenylene sulfide and polyethylene wax is 18-25:100:10-15:2-7.

[0014] Preferably, in step (3), the pressure of the primary pressurization is 25 to 30 MPa.

[0015] Preferably, in step (4), the conditions for the secondary sintering are: from room temperature to 200-300°C at a heating rate of 1-3°C / min, keeping warm for 3-5h, then heating to 285-320°C at a heating rate of 1-3°C / min, keeping warm for 10-15h, then heating to 370-420°C at a heating rate of 1-3°C / min, keeping warm for 1-3h, and finally naturally cooling to room temperature.

[0016] The segmented pressure sintering method is adopted to make the components in the material evenly blended, and the polymer macromolecular chain and the filler can be tightly bonded. The temperature-differentiated sintering method can also make the bonding stability of the sintering process higher and the overall performance of the material better.

[0017] Preferably, in step (4), the pressure of the secondary pressurization is 10 to 20 MPa.

[0018] In a second aspect, the present invention further provides a double eccentric gasket, comprising a modified polytetrafluoroethylene sealing ring and a rubber compensation O-ring, wherein the rubber compensation O-ring is arranged in an inner ring groove of the modified polytetrafluoroethylene sealing ring.

[0019] The rubber compensation O-ring is an auxiliary seal and is arranged in the inner ring groove of the modified polytetrafluoroethylene sealing ring. It not only plays an axial sealing role, but also provides sealing force for the modified polytetrafluoroethylene sealing ring, reduces vibration, and realizes the automatic compensation function of the deformation of the sealing ring after wear, and can still ensure reliable sealing.

[0020] Compared with the prior art, the present invention has the following beneficial effects: (1) The sealing ring is prepared with polytetrafluoroethylene as the main raw material, polyphenylene sulfide is added as a reinforcing material, and inorganic reinforcing fillers including graphite, hollow silica microspheres and diatomaceous earth are added to further fill and modify the polytetrafluoroethylene, which can improve the tensile strength, wear resistance and creep relaxation resistance of pure polytetrafluoroethylene.

[0021] (2) The modified polytetrafluoroethylene sealing ring has excellent sealing performance. The rubber compensation O-ring is used to compensate for the dynamic and static switch sealing of the stacking plate in the butterfly valve. The double eccentric gasket is a combination of modified polytetrafluoroethylene and rubber O-ring, which is suitable for the sealing performance of the stacking plate when it is frequently opened.

[0022] (3) Double eccentric gaskets can be widely used in petroleum, chemical, shipbuilding, metallurgy, electric power and other industries, and are suitable for the stringent sealing requirements of various high-frequency double eccentric butterfly valves. DETAILED DESCRIPTION

[0023] The technical solution of the present invention is described below with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0024] 1. Modified polytetrafluoroethylene sealing ring The preparation method thereof comprises the following steps: (1) adding graphite powder, diatomaceous earth and hollow silica microspheres to an aqueous solution of polyacrylamide having a mass concentration of 1 to 3%, wherein the mass ratio of the graphite powder, diatomaceous earth, hollow silica microspheres and the aqueous solution of polyacrylamide is 2 to 4:7 to 9:22 to 25:50, and then ball milling at a speed of 100 to 200 rpm for 30 to 50 minutes to obtain a mixture I; (2) drying the mixed material I at 100-120° C. for 3-5 hours, and then sintering the mixed material I once, heating the mixed material I from room temperature to 200-300° C. at a heating rate of 1-3° C. / min, and keeping the temperature for 1-2 hours to obtain the mixed material II; (3) Mixing the mixed material II with polytetrafluoroethylene, polyphenylene sulfide, and polyethylene wax in a mass ratio of 18-25:100:10-15:2-7, and then loading the mixed material into a mold and pressurizing the mold once at 25-30 MPa to obtain a preformed embryo; (4) The preformed body is subjected to secondary sintering, from room temperature to 200-300°C at a heating rate of 1-3°C / min, kept at this temperature for 3-5h, then to 285-320°C at a heating rate of 1-3°C / min, kept at this temperature for 10-15h, then to 370-420°C at a heating rate of 1-3°C / min, kept at this temperature for 1-3h, and finally cooled naturally to room temperature; then, secondary pressurization is performed under the condition of 10-20MPa to obtain a modified polytetrafluoroethylene sealing ring.

[0025] In a specific embodiment of the present invention, the graphite powder includes nano-scale graphite powder and micro-scale graphite powder in a mass ratio of 3 to 4:1, the particle size of the nano-scale graphite powder is 10 to 200 nm, and the particle size of the micro-scale graphite powder is 1 to 10 μm. The particle size of diatomaceous earth is 5 to 30 μm, and the specific surface area is 20 to 70 m 2 / g. The particle size of hollow silica microspheres is 5-30 μm, and the density is 0.35-0.70 g / cm 3.

[0026] 2. Double eccentric gasket The double eccentric gasket comprises the modified polytetrafluoroethylene sealing ring and the rubber compensation O-ring prepared above, and the rubber compensation O-ring is arranged in the inner ring groove of the modified polytetrafluoroethylene sealing ring.

[0027] Example 1 The preparation of modified polytetrafluoroethylene sealing ring includes the following steps: (1) Graphite powder (including nano-graphite powder with an average particle size of 60 nm and micro-graphite powder with an average particle size of 3 μm in a mass ratio of 4:1) and diatomaceous earth (with an average particle size of 14 μm and a specific surface area of ​​45 m 2 / g) and hollow silica microspheres (average particle size 20 μm, density 0.44 g / cm 3 ) was added into an aqueous solution of polyacrylamide with a mass concentration of 2%, wherein the mass ratio of graphite powder, diatomaceous earth, hollow silica microspheres and the aqueous solution of polyacrylamide was 3:7:23:50, and then ball-milled at a speed of 100 rpm for 40 minutes to obtain a mixture I.

[0028] (2) After drying the mixture I at 100°C for 5 h, sintering is performed once, heating the temperature from room temperature to 250°C at a rate of 2°C / min and maintaining the temperature for 2 h to obtain the mixture II.

[0029] (3) Mixing material II with polytetrafluoroethylene, polyphenylene sulfide, and polyethylene wax in a mass ratio of 18:100:14:3, then loading into a mold and pressurizing once at 25 MPa to obtain a preformed embryo.

[0030] (4) The preformed body is subjected to secondary sintering, from room temperature to 250°C at a heating rate of 2°C / min, kept at this temperature for 4 hours, then to 295°C at a heating rate of 1°C / min, kept at this temperature for 10 hours, then to 390°C at a heating rate of 1°C / min, kept at this temperature for 2 hours, and finally cooled naturally to room temperature; then, secondary pressurization is performed under the condition of 13 MPa to obtain a modified polytetrafluoroethylene sealing ring.

[0031] Example 2 The preparation of modified polytetrafluoroethylene sealing ring includes the following steps: (1) Graphite powder (including nano-graphite powder with an average particle size of 60 nm and micro-graphite powder with an average particle size of 3 μm in a mass ratio of 4:1) and diatomaceous earth (with an average particle size of 14 μm and a specific surface area of ​​45 m 2 / g) and hollow silica microspheres (average particle size 20 μm, density 0.44 g / cm 3) was added into an aqueous solution of polyacrylamide with a mass concentration of 2%, wherein the mass ratio of graphite powder, diatomaceous earth, hollow silica microspheres and the aqueous solution of polyacrylamide was 3:7:23:50, and then ball-milled at a speed of 100 rpm for 40 minutes to obtain a mixture I.

[0032] (2) After drying the mixture I at 100°C for 5 h, sintering is performed once, heating the temperature from room temperature to 250°C at a rate of 2°C / min and maintaining the temperature for 2 h to obtain the mixture II.

[0033] (3) Mixing material II with polytetrafluoroethylene, polyphenylene sulfide, and polyethylene wax in a mass ratio of 22:100:13:5, then loading into a mold and pressurizing once at 25 MPa to obtain a preformed embryo.

[0034] (4) The preformed body is subjected to secondary sintering, from room temperature to 250°C at a heating rate of 2°C / min, kept at this temperature for 4 hours, then to 295°C at a heating rate of 1°C / min, kept at this temperature for 10 hours, then to 390°C at a heating rate of 1°C / min, kept at this temperature for 2 hours, and finally cooled naturally to room temperature; then, secondary pressurization is performed under the condition of 13 MPa to obtain a modified polytetrafluoroethylene sealing ring.

[0035] Example 3 The preparation of modified polytetrafluoroethylene sealing ring includes the following steps: (1) Graphite powder (including nano-graphite powder with an average particle size of 60 nm and micro-graphite powder with an average particle size of 3 μm in a mass ratio of 4:1) and diatomaceous earth (with an average particle size of 14 μm and a specific surface area of ​​45 m 2 / g) and hollow silica microspheres (average particle size 20 μm, density 0.44 g / cm 3 ) was added into an aqueous solution of polyacrylamide with a mass concentration of 2%, wherein the mass ratio of graphite powder, diatomaceous earth, hollow silica microspheres and the aqueous solution of polyacrylamide was 3:7:23:50, and then ball-milled at a speed of 100 rpm for 40 minutes to obtain a mixture I.

[0036] (2) After drying the mixture I at 100°C for 5 h, sintering is performed once, heating the temperature from room temperature to 250°C at a heating rate of 2°C / min and maintaining the temperature for 2 h to obtain the mixture II.

[0037] (3) Mixing material II with polytetrafluoroethylene, polyphenylene sulfide, and polyethylene wax in a mass ratio of 25:100:11:7, then loading into a mold and pressurizing once at 25 MPa to obtain a preformed embryo.

[0038] (4) The preformed body is subjected to secondary sintering, from room temperature to 250°C at a heating rate of 2°C / min, kept at this temperature for 4 hours, then to 295°C at a heating rate of 1°C / min, kept at this temperature for 10 hours, then to 390°C at a heating rate of 1°C / min, kept at this temperature for 2 hours, and finally cooled naturally to room temperature; then, secondary pressurization is performed under the condition of 13 MPa to obtain a modified polytetrafluoroethylene sealing ring.

[0039] Example 4 The preparation of modified polytetrafluoroethylene sealing ring includes the following steps: (1) Graphite powder (including nano-graphite powder with an average particle size of 45 nm and micro-graphite powder with an average particle size of 5 μm in a mass ratio of 3:1) and diatomaceous earth (with an average particle size of 14 μm and a specific surface area of ​​45 m 2 / g) and hollow silica microspheres (average particle size 20 μm, density 0.44 g / cm 3 ) was added into an aqueous solution of polyacrylamide with a mass concentration of 2%, wherein the mass ratio of graphite powder, diatomaceous earth, hollow silica microspheres and the aqueous solution of polyacrylamide was 2:7:25:50, and then ball-milled at a rotation speed of 150 rpm for 30 minutes to obtain a mixture I.

[0040] (2) After drying the mixture I at 100°C for 5 h, sintering is performed once, heating the temperature from room temperature to 250°C at a rate of 2°C / min and maintaining the temperature for 2 h to obtain the mixture II.

[0041] (3) Mixing material II with polytetrafluoroethylene, polyphenylene sulfide, and polyethylene wax in a mass ratio of 18:100:14:3, then loading into a mold and pressurizing once at 25 MPa to obtain a preformed embryo.

[0042] (4) The preformed body is subjected to secondary sintering, from room temperature to 250°C at a heating rate of 2°C / min, kept at this temperature for 4 hours, then to 295°C at a heating rate of 1°C / min, kept at this temperature for 10 hours, then to 390°C at a heating rate of 1°C / min, kept at this temperature for 2 hours, and finally cooled naturally to room temperature; then, secondary pressurization is performed under the condition of 13 MPa to obtain a modified polytetrafluoroethylene sealing ring.

[0043] Example 5 The preparation of modified polytetrafluoroethylene sealing ring includes the following steps: (1) Graphite powder (including nano-graphite powder with an average particle size of 60 nm and micro-graphite powder with an average particle size of 3 μm in a mass ratio of 4:1) and diatomaceous earth (with an average particle size of 20 μm and a specific surface area of ​​58 m 2 / g) and hollow silica microspheres (average particle size of 12 μm, density of 0.60 g / cm 3) was added into an aqueous solution of polyacrylamide with a mass concentration of 2%, wherein the mass ratio of graphite powder, diatomaceous earth, hollow silica microspheres and the aqueous solution of polyacrylamide was 4:8:24:50, and then ball-milled at a speed of 100 rpm for 40 minutes to obtain a mixture I.

[0044] (2) After drying the mixture I at 100°C for 5 h, sintering is performed once, heating the temperature from room temperature to 250°C at a rate of 2°C / min and maintaining the temperature for 2 h to obtain the mixture II.

[0045] (3) Mixing material II with polytetrafluoroethylene, polyphenylene sulfide, and polyethylene wax in a mass ratio of 18:100:14:3, then loading into a mold and pressurizing once at 25 MPa to obtain a preformed embryo.

[0046] (4) The preformed body is subjected to secondary sintering, from room temperature to 250°C at a heating rate of 2°C / min, kept at this temperature for 4 hours, then to 295°C at a heating rate of 1°C / min, kept at this temperature for 10 hours, then to 390°C at a heating rate of 1°C / min, kept at this temperature for 2 hours, and finally cooled naturally to room temperature; then, secondary pressurization is performed under the condition of 13 MPa to obtain a modified polytetrafluoroethylene sealing ring.

[0047] Comparative Example 1 The difference from Example 1 is that no ball milling was performed.

[0048] The preparation of modified polytetrafluoroethylene sealing ring includes the following steps: (1) Graphite powder (including nano-graphite powder with an average particle size of 60 nm and micro-graphite powder with an average particle size of 3 μm in a mass ratio of 4:1) and diatomaceous earth (with an average particle size of 14 μm and a specific surface area of ​​45 m 2 / g) and hollow silica microspheres (average particle size 20 μm, density 0.44 g / cm 3 ) are mixed in a mass ratio of 3:7:23 to obtain mixture I.

[0049] (2) Mixture I is mixed with polytetrafluoroethylene, polyphenylene sulfide, and polyethylene wax in a mass ratio of 18:100:14:3, and then loaded into a mold and pressurized once at 25 MPa to obtain a preformed embryo.

[0050] (3) The preformed body is subjected to secondary sintering, with the temperature being increased from room temperature to 250°C at a heating rate of 2°C / min, kept at that temperature for 4 hours, then increased to 295°C at a heating rate of 1°C / min, kept at that temperature for 10 hours, then increased to 390°C at a heating rate of 1°C / min, kept at that temperature for 2 hours, and finally cooled naturally to room temperature; thereafter, secondary pressurization is performed under the condition of 13 MPa to obtain a modified polytetrafluoroethylene sealing ring.

[0051] Comparative Example 2 The difference from Example 1 is that only micron-sized graphite powder is used and the size of the hollow silicon dioxide microspheres is too large.

[0052] The preparation of modified polytetrafluoroethylene sealing ring includes the following steps: (1) Graphite powder (with an average particle size of 3 μm) and diatomaceous earth (with an average particle size of 14 μm and a specific surface area of ​​45 m 2 / g) and hollow silica microspheres (average particle size 40 μm, density 0.36 g / cm 3 ) was added into an aqueous solution of polyacrylamide with a mass concentration of 2%, wherein the mass ratio of graphite powder, diatomaceous earth, hollow silica microspheres and the aqueous solution of polyacrylamide was 3:7:23:50, and then ball-milled at a speed of 100 rpm for 40 minutes to obtain a mixture I.

[0053] (2) After drying the mixture I at 100°C for 5 h, sintering is performed once, heating the temperature from room temperature to 250°C at a heating rate of 2°C / min and maintaining the temperature for 2 h to obtain the mixture II.

[0054] (3) Mixing material II with polytetrafluoroethylene, polyphenylene sulfide, and polyethylene wax in a mass ratio of 18:100:14:3, then loading into a mold and pressurizing once at 25 MPa to obtain a preformed embryo.

[0055] (4) The preformed body is subjected to secondary sintering, from room temperature to 250°C at a heating rate of 2°C / min, kept at this temperature for 4 hours, then to 295°C at a heating rate of 1°C / min, kept at this temperature for 10 hours, then to 390°C at a heating rate of 1°C / min, kept at this temperature for 2 hours, and finally cooled naturally to room temperature; then, secondary pressurization is performed under the condition of 13 MPa to obtain a modified polytetrafluoroethylene sealing ring.

[0056] Comparative Example 3 The difference from Example 1 is that diatomaceous earth is not added.

[0057] The preparation of modified polytetrafluoroethylene sealing ring includes the following steps: (1) Graphite powder (including nano-graphite powder with an average particle size of 60 nm and micro-graphite powder with an average particle size of 3 μm in a mass ratio of 4:1) and hollow silica microspheres (with an average particle size of 20 μm and a density of 0.44 g / cm 3 ) was added into an aqueous solution of polyacrylamide with a mass concentration of 2%, wherein the mass ratio of graphite powder, hollow silica microspheres and the aqueous solution of polyacrylamide was 3:23:50, and then ball milled at a speed of 100 rpm for 40 minutes to obtain a mixture I.

[0058] (2) After drying the mixture I at 100°C for 5 h, sintering is performed once, heating the temperature from room temperature to 250°C at a heating rate of 2°C / min and maintaining the temperature for 2 h to obtain the mixture II.

[0059] (3) Mixing material II with polytetrafluoroethylene, polyphenylene sulfide, and polyethylene wax in a mass ratio of 18:100:14:3, then loading into a mold and pressurizing once at 25 MPa to obtain a preformed embryo.

[0060] (4) The preformed body is subjected to secondary sintering, from room temperature to 250°C at a heating rate of 2°C / min, kept at this temperature for 4 hours, then to 295°C at a heating rate of 1°C / min, kept at this temperature for 10 hours, then to 390°C at a heating rate of 1°C / min, kept at this temperature for 2 hours, and finally cooled naturally to room temperature; then, secondary pressurization is performed under the condition of 13 MPa to obtain a modified polytetrafluoroethylene sealing ring.

[0061] Comparative Example 4 The difference from Example 1 is that no polyethylene wax is added.

[0062] The preparation of modified polytetrafluoroethylene sealing ring includes the following steps: (1) Graphite powder (including nano-graphite powder with an average particle size of 60 nm and micro-graphite powder with an average particle size of 3 μm in a mass ratio of 4:1) and diatomaceous earth (with an average particle size of 14 μm and a specific surface area of ​​45 m 2 / g) and hollow silica microspheres (average particle size 20 μm, density 0.44 g / cm 3 ) was added into an aqueous solution of polyacrylamide with a mass concentration of 2%, wherein the mass ratio of graphite powder, diatomaceous earth, hollow silica microspheres and the aqueous solution of polyacrylamide was 3:7:23:50, and then ball-milled at a speed of 100 rpm for 40 minutes to obtain a mixture I.

[0063] (2) After drying the mixture I at 100°C for 5 h, sintering is performed once, heating the temperature from room temperature to 250°C at a heating rate of 2°C / min and maintaining the temperature for 2 h to obtain the mixture II.

[0064] (3) Mixing material II with polytetrafluoroethylene and polyphenylene sulfide in a mass ratio of 18:100:14, then loading into a mold and pressurizing once at 25 MPa to obtain a preformed embryo.

[0065] (4) The preformed body is subjected to secondary sintering, from room temperature to 250°C at a heating rate of 2°C / min, kept at this temperature for 4 hours, then to 295°C at a heating rate of 1°C / min, kept at this temperature for 10 hours, then to 390°C at a heating rate of 1°C / min, kept at this temperature for 2 hours, and finally cooled naturally to room temperature; then, secondary pressurization is performed under the condition of 13 MPa to obtain a modified polytetrafluoroethylene sealing ring.

[0066] Performance Testing: The polytetrafluoroethylene sealing rings prepared in Examples 1-5 and Comparative Examples 1-4 were subjected to performance tests. The test standard for tensile strength was GB / T20671.7-2006; the test standard for compression rate and rebound rate was GB / T12622-2008 Test method for compression rate and rebound rate of gaskets for pipe flanges, and the test load was 35 MPa; the test standard for creep relaxation rate was GB / T20671.5-2020 Classification system and test method for non-metallic gasket materials, and the test temperature was 200°C; the test standard for leakage rate was GB / T12385-2008 Test method for sealing performance of gaskets for pipe flanges.

[0067] Table 1 As shown in Table 1, the modified polytetrafluoroethylene sealing rings prepared in Examples 1-5 have excellent tensile strength, sealing resilience and creep resistance, and can adapt to the stringent sealing requirements of various high-frequency double-eccentric butterfly valves. In Comparative Example 1, graphite powder, diatomaceous earth and hollow silica microspheres were not mixed and milled, and directly added to the polytetrafluoroethylene material, which will result in poor dispersion uniformity, especially the graphite powder is easy to agglomerate, and the way of adding the polytetrafluoroethylene material with a composite filler will make the tightness between the materials better, and the composite filler will also have better strength and sealing resilience than a single filler. The graphite powder used in Comparative Example 2 is a single micron-grade graphite powder, and the size of the hollow silica microspheres is large, which will cause the synergistic effect between the graphite powder, diatomaceous earth and hollow silica microspheres to deteriorate, and the bonding stability of the composite filler is affected, which in turn causes the overall performance of the sealing ring to be affected. In Comparative Example 3, the synergistic effect of the composite filler is deteriorated, and the tensile strength, sealing resilience and creep resistance of the modified polytetrafluoroethylene sealing ring are affected. In Comparative Example 4, the compatibility and dispersibility of the composite filler in the polytetrafluoroethylene material are affected, and the overall performance of the modified polytetrafluoroethylene sealing ring is deteriorated.

[0068] The above are only preferred embodiments of the present invention, and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the specification of the present invention, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for preparing a modified polytetrafluoroethylene sealing ring, characterized in that: The steps include: (1) adding graphite powder, diatomaceous earth and hollow silicon dioxide microspheres into an aqueous solution of polyacrylamide and ball milling to obtain a mixture I; (2) After drying the mixed material I, sintering is performed once to obtain the mixed material II; (3) Mixing the mixed material II with polytetrafluoroethylene, polyphenylene sulfide and polyethylene wax, and then placing the mixed material II into a mold for pressurization to obtain a preformed embryo; (4) The preformed body is subjected to secondary sintering and then secondary pressurization to obtain a modified polytetrafluoroethylene sealing ring.

2. The method for preparing the modified polytetrafluoroethylene sealing ring according to claim 1, characterized in that: In step (1), the mass ratio of the graphite powder, diatomaceous earth, hollow silicon dioxide microspheres and the aqueous solution of polyacrylamide is 2-4:7-9:22-25:50; and the mass concentration of the aqueous solution of polyacrylamide is 1-3%.

3. The method for preparing the modified polytetrafluoroethylene sealing ring according to claim 1, characterized in that: In step (1), the graphite powder comprises nano-scale graphite powder and micro-scale graphite powder in a mass ratio of 3 to 4:1; the particle size of the nano-scale graphite powder is 10 to 200 nm; the particle size of the micro-scale graphite powder is 1 to 10 μm; the particle size of the diatomaceous earth is 5 to 30 μm, and the specific surface area is 20 to 70 m 2 / g; the particle size of the hollow silica microspheres is 5~30μm and the density is 0.35~0.70 g / cm 3 .

4. The method for preparing the modified polytetrafluoroethylene sealing ring according to any one of claims 1 to 3, characterized in that: In step (1), the ball milling conditions are: ball milling at a rotation speed of 100-200 rpm for 30-50 min.

5. The method for preparing the modified polytetrafluoroethylene sealing ring according to any one of claims 1 to 3, characterized in that: In step (2), the drying condition is: drying at 100-120°C for 3-5 hours; the primary sintering condition is: heating from room temperature to 200-300°C at a heating rate of 1-3°C / min, and keeping warm for 1-2 hours.

6. The method for preparing the modified polytetrafluoroethylene sealing ring according to claim 1, characterized in that: In step (3), the mass ratio of the mixture II, polytetrafluoroethylene, polyphenylene sulfide and polyethylene wax is 18-25:100:10-15:2-7.

7. The method for preparing a modified polytetrafluoroethylene sealing ring according to claim 1 or 6, characterized in that: In step (3), the pressure of the first pressurization is 25-30 MPa.

8. The method for preparing the modified polytetrafluoroethylene sealing ring according to claim 1, characterized in that: In step (4), the conditions for the secondary sintering are: heating from room temperature to 200-300°C at a heating rate of 1-3°C / min, keeping warm for 3-5 hours, then heating to 285-320°C at a heating rate of 1-3°C / min, keeping warm for 10-15 hours, then heating to 370-420°C at a heating rate of 1-3°C / min, keeping warm for 1-3 hours, and finally cooling naturally to room temperature.

9. The method for preparing a modified polytetrafluoroethylene sealing ring according to claim 1 or 8, characterized in that: In step (4), the pressure of the secondary pressurization is 10-20 MPa.

10. A double eccentric gasket, characterized in that: It comprises a modified polytetrafluoroethylene sealing ring and a rubber compensation O-ring obtained by the preparation method according to any one of claims 1 to 9, wherein the rubber compensation O-ring is arranged in the inner ring groove of the modified polytetrafluoroethylene sealing ring.

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