High-temperature anti-oxidation graphite packing and preparation method thereof

Abstract

The invention relates to the technical field of graphite packing, and provides high-temperature anti-oxidation graphite packing and a preparation method thereof. A preparation method of a high-temperature anti-oxidation graphite packing comprises the following steps: step A1, immersing a flexible graphite wire into a polytetrafluoroethylene impregnant for 20-22 minutes, taking out the flexible graphite wire, drying the flexible graphite wire, and rolling the flexible graphite wire to obtain the immersed flexible graphite wire; and A2, carrying out primary heat treatment, secondary heat treatment, third heat treatment and packing shaping on the impregnated flexible graphite wire to obtain the high-temperature anti-oxidation graphite packing. In conclusion, the problem that the traditional packing is insufficient in temperature resistance is solved, and the graphite packing has important application value in the technical field of graphite packing.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of graphite packing, in particular, to a high-temperature oxidation-resistant graphite packing and a preparation method thereof. BACKGROUND

[0002] The packing is also called sealing packing, which is a strip-shaped object with a square cross-sectional area woven by soft linear objects. The sealing effect is achieved by filling the packing in the sealing cavity. The packing was originally used to prevent liquid leakage by inserting cotton and hemp fibers into the leakage channel. It is mainly used as the shaft seal of water lifting machinery. Because of its wide source, easy processing, low price, reliable sealing and simple operation, it has been used to this day.

[0003] With new carbon materials as the focus of research and development in the field of carbon materials, it covers various types such as diamond, flexible graphite, porous carbon, nuclear graphite, and graphite intercalation compounds. Flexible graphite packing prepared from flexible graphite is widely used in high-temperature and high-pressure sealing scenarios in petrochemical, electric power, metallurgy and other industries due to its excellent compression resilience and self-lubricating properties. However, the performance of traditional flexible graphite packing under extreme working conditions still has obvious defects, which mainly comes from its special material composition and structural characteristics. In order to maintain sufficient flexibility and weavability, traditional graphite packing usually needs to incorporate a certain proportion of organic or natural fibers as reinforcing framework in the expanded graphite matrix, such as cotton fibers, polyester fibers or aramid fibers. Although the introduction of such fiber materials effectively improves the bending performance and installation convenience of the packing, their temperature resistance often becomes the short board that restricts the high-temperature stability of the overall material. For example, cotton fibers begin to thermally decompose above 200℃, the long-term use temperature of polyester fibers does not exceed 150℃, and even the performance of aramid fibers is better, but they will also experience significant strength decay above 300℃. The inherent defects of this material system lead to problems such as fiber carbonization and loose structure in traditional flexible graphite packing under high-temperature working conditions, ultimately resulting in sealing failure.

[0004] Furthermore, the industry generally uses a polytetrafluoroethylene (PTFE) impregnation process to modify the packing. PTFE, as an excellent high polymer material, has excellent chemical inertness and a low friction coefficient, which can fill the interlayer gaps of graphite and wrap the fiber reinforcement to some extent. Through vacuum impregnation or pressure impregnation process, PTFE emulsion can fully penetrate into the microstructure of the graphite packing, improving the density and medium barrier ability of the packing. In existing research, heat-resistant fillers are added to PTFE, and then the impregnation process is used to treat the graphite wire, which can effectively enhance the high-temperature resistance of the material. However, due to the poor compatibility of heat-resistant fillers with PTFE, a compatibilizer is usually needed. However, the commonly used compatibilizers lack sufficient heat resistance, which cannot meet the demand.

[0005] In summary, in view of the poor stability of the graphite packing in the high-temperature oxidation environment at present, it is urgent to invent a high-temperature oxidation-resistant graphite packing to meet the higher demand in the technical field of graphite packing. SUMMARY

[0006] The application provides a high-temperature oxidation-resistant graphite packing and a preparation method thereof, and solves the problem of poor stability of the graphite packing in the high-temperature oxidation environment in the related art.

[0007] The technical scheme of the application is as follows: The application provides a high-temperature oxidation-resistant graphite packing, which comprises a flexible graphite wire and a polytetrafluoroethylene impregnating agent.

[0008] As a further technical scheme, the flexible graphite wire is prepared by the following steps: Step B1, mixing natural flake graphite and concentrated sulfuric acid solution (mass fraction 98%, intercalation agent), stirring for 12-24 h, washing to neutral, drying in an oven at 80-100 DEG C, rapid expansion at high temperature, and obtaining worm-like expanded graphite; Step B2, coating the polyester fiber with a binder, uniformly covering the expanded graphite on the polyester fiber, and using a double-roller calender to calender the graphite felt into a composite tape; Step B3, slitting and twisting the composite tape to obtain the flexible graphite wire.

[0009] As a further technical scheme, the mass ratio of the natural flake graphite, the concentrated sulfuric acid solution and the polyester fiber is 1:2.5-3:0.6-0.7.

[0010] As a further technical scheme, the temperature of the high temperature is 900-1000 DEG C.

[0011] As a further technical scheme, the binder is a polytetrafluoroethylene binder.

[0012] As a further technical scheme, the polytetrafluoroethylene impregnating agent is prepared by the following steps: Mixing polytetrafluoroethylene emulsion, heat-resistant filler, deionized water and dispersant, using high-speed shearing stirring for 20-30 min to obtain a mixed solution, and then ultrasonic treating the mixed solution for 20-30 min to obtain the polytetrafluoroethylene impregnating agent.

[0013] As a further technical scheme, the raw materials are as follows in terms of weight fraction: 72-86 parts of polytetrafluoroethylene emulsion, 8-16 parts of heat-resistant filler, 40-50 parts of deionized water and 1-3 parts of dispersant.

[0014] As a further technical scheme, the solid content of the polytetrafluoroethylene emulsion is 60%.

[0015] As a further technical solution, the dispersing agent is one of polyethylene glycol and sodium dodecyl sulfate.

[0016] As a further technical solution, the heat-resistant filler is prepared by the following steps: Step C1, phenyltrichlorosilane, solvent and 2-hydroxybenzimidazole are added to a three-necked flask equipped with a constant pressure dropping funnel, after uniform magnetic stirring, triethylamine is added through the constant pressure dropping funnel, the temperature is controlled not to exceed 25 DEG C during the dropping process, after the dropping is completed, the device is heated until the temperature is maintained at 60-70 DEG C, the reaction is carried out at this temperature for 4-6 h, after the reaction is completed, the product is obtained after treatment. Step C2, the initial product, solvent and piperidinol are added to a three-necked flask equipped with a constant pressure dropping funnel, after uniform magnetic stirring, triethylamine is added through the constant pressure dropping funnel, the temperature is controlled not to exceed 25 DEG C during the dropping process, after the dropping is completed, the device is heated until the temperature is maintained at 70-80 DEG C, the reaction is carried out at this temperature for 6-8 h, after the reaction is completed, the heat-resistant filler modifier is obtained after treatment. C1, C2, the reaction formula for preparing the heat-resistant filler modifier is as follows:

[0017] Step C3, firstly, the alumina is ultrasonically cleaned with methanol for 3 times to remove organic residues, then vacuum dehydration is carried out at 120-130 DEG C for 2-4 h to ensure that the surface hydroxyl groups are fully exposed, then the alumina is mixed with the solvent, ultrasonic treatment is carried out for 10-20 min, then the heat-resistant filler modifier and triethylamine are added, the temperature is raised to 80-90 DEG C, the reaction is carried out at this temperature for 10-12 h, after the reaction is completed, the product is centrifuged and washed with toluene for multiple times, vacuum drying is carried out to obtain the heat-resistant filler.

[0018] As a further technical solution, the amount ratio of phenyltrichlorosilane, solvent, 2-hydroxybenzimidazole and triethylamine in step C1 is 21.3-22.6 g:100 mL:13.4 g:10.1 g, preferably 21.3 g:100 mL:13.4 g:10.1 g.

[0019] As a further technical solution, the amount ratio of the initial product, solvent, piperidinol and triethylamine in step C2 is 31.2-33.7 g:100 mL:17.1 g:10.1 g, preferably 31.2 g:100 mL:17.1 g:10.1 g.

[0020] As a further technical solution, the amount ratio of alumina, solvent, heat-resistant filler modifier and triethylamine in step C3 is 10 g:100 mL:3.7-4.1 g:0.93 g, preferably 10 g:100 mL:3.7 g:0.93 g.

[0021] As a further technical solution, the solvents in steps C1, C2 and C3 are all toluene.

[0022] The preparation principle of the heat-resistant filler is as follows: the heat-resistant filler modifier is first prepared through steps C1 and C2, in the process of step C1, the nucleophilic substitution reaction of phenyltrichlorosilane and 2-hydroxybenzimidazole occurs, it should be noted that the molar ratio of phenyltrichlorosilane to 2-hydroxybenzimidazole is controlled to be 1:1, and phenyltrichlorosilane needs to be excessive, in the process of step C2, the same as step C1, it should be noted that the molar ratio of the initial product to piperidinol is controlled to be 1:1, and the initial product needs to be excessive; finally, in step C3, the chlorine group in the heat-resistant filler modifier can react with the hydroxyl group on the surface of the aluminum oxide, and the heat-resistant filler is finally obtained.

[0023] The performance of the heat-resistant filler is as follows: the aluminum oxide is modified in the present application, firstly, the aluminum oxide is an inorganic material with extremely strong heat resistance, secondly, the heat-resistant filler modifier contains multiple hydrophobic groups, which can improve the hydrophobicity of the heat-resistant filler, and further improve the compatibility of the heat-resistant filler with the polytetrafluoroethylene emulsion, so that it is easier to disperse in the polytetrafluoroethylene emulsion and is not easy to agglomerate; in addition, the heat-resistant filler modifier also contains multiple Si-O bonds, benzimidazole and hindered amine groups, among which the Si-O bond and the benzimidazole belong to heat-resistant groups, which improves the high-temperature resistance of the material to a certain extent, and the hindered amine group as an antioxidant group can delay the thermal aging of the material, further improving the high-temperature resistance of the material.

[0024] The present application also provides a preparation method of the high-temperature antioxidant graphite packing, which comprises the following steps: Step A1, immerse the flexible graphite wire into the polytetrafluoroethylene impregnant for 20-22 min, take out, dry at 80-100 DEG C for 2-3 h, and wind through the winding device to obtain the impregnated flexible graphite wire; Step A2, first heat the impregnated flexible graphite wire to 150-170 DEG C for primary heat treatment for 6-10 min, then heat to 230-250 DEG C for secondary heat treatment for 6-10 min, then heat to 330-350 DEG C for tertiary heat treatment for 10-20 min, and finally perform packing shaping to obtain the high-temperature antioxidant graphite packing.

[0025] The working principle and beneficial effects of the present application are as follows: 1. The present application uses polyester fiber composite expanded graphite to make graphite wire, and the polyester fiber endows the graphite wire with excellent flexibility. 2. The present application uses the polytetrafluoroethylene impregnation process to make the polytetrafluoroethylene uniformly wrap the flexible graphite wire, fill the interlayer space of the graphite layer, and improve the density of the packing. 3、The heat-resistant filler prepared by the application takes alumina as a base material, introduces heat-resistant and antioxidant groups such as Si-O bonds, benzimidazole and hindered amine groups through modification, and compared with existing compatilizers (such as silane coupling agents), the heat-resistant filler improves the compatibility of the heat-resistant filler with polytetrafluoroethylene emulsion, and also improves the high-temperature resistance of the packing to a certain extent; 4、The heat-resistant filler modifier contains multiple hydrophobic groups, improves the compatibility of the heat-resistant filler with polytetrafluoroethylene emulsion, makes the heat-resistant filler more easily dispersed in the polytetrafluoroethylene impregnant, and not easily agglomerated, and ensures that the impregnant can uniformly penetrate into the structure of the flexible graphite wire, thereby greatly improving the heat-resistant performance of the packing. In summary, the application solves the problem of insufficient temperature resistance of the traditional packing caused by the incorporation of organic fibers, significantly improves the sealing reliability of the packing under extreme working conditions such as high temperature and high pressure, and has important application value in the field of graphite packing technology. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the application will be clearly and completely described below in combination with the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the application.

[0027] In the following examples and comparative examples, the polytetrafluoroethylene emulsion is DuPont 30B emulsion.

[0028] Example 1 The heat-resistant filler is prepared by the following steps: Step C1, 21.3g of phenyltrichlorosilane, 100mL of toluene and 13.4g of 2-hydroxybenzimidazole are added to a three-necked flask equipped with a constant pressure dropping funnel, after uniform magnetic stirring, 10.1g of triethylamine is added through the constant pressure dropping funnel, the temperature is controlled not to exceed 25℃ during the addition process, after the addition is completed, the device is heated until the temperature is maintained at 60℃, and the reaction is carried out at this temperature for 4h, after the reaction is completed, the post-treatment is carried out, and the initial product is obtained; Step C2, 31.2g of the initial product, 100mL of toluene and 17.1g of pentamethylpiperidinol are added to a three-necked flask equipped with a constant pressure dropping funnel, after uniform magnetic stirring, 10.1g of triethylamine is added through the constant pressure dropping funnel, the temperature is controlled not to exceed 25℃ during the addition process, after the addition is completed, the device is heated until the temperature is maintained at 70℃, and the reaction is carried out at this temperature for 6h, after the reaction is completed, the post-treatment is carried out, and the heat-resistant filler modifier is obtained; Step C3, first 10g of alumina is washed with methanol for 3 times by ultrasonic, remove organic residues, then dehydrated at 120℃ for 2h in vacuum, ensure the surface hydroxyl group is fully exposed, then mix it with 100mL of toluene, ultrasonic treatment for 10min, then add 3.7g of heat-resistant filler modifier and 0.93g of triethylamine, heat to 80℃, react for 10h at this temperature, the reaction is completed, centrifugal separation of the product, washed with toluene for several times, vacuum drying, get heat-resistant filler; The flexible graphite wire is prepared by the following steps: Step B1, 10g of natural flake graphite is mixed with concentrated sulfuric acid solution (mass fraction 98%), stirred for 12h, then washed to neutral, dried in an oven at 80℃, rapidly expanded at 900℃ high temperature, get worm-like expanded graphite; Step B2, 6g of polyester fiber is coated with polytetrafluoroethylene binder, then the expanded graphite is evenly covered on the polyester fiber, then use double-roller calender to calender the graphite felt into a composite tape; Step B3, the composite tape is cut and twisted to get flexible graphite wire; The polytetrafluoroethylene impregnant is prepared by the following steps: 72g of polytetrafluoroethylene emulsion (solid content 60%), 8g of heat-resistant filler, 40g of deionized water and 1g of polyethylene glycol are mixed, high-speed shearing stirring for 20min, get the mixed solution, then ultrasonic treatment for 20min, get the polytetrafluoroethylene impregnant; A preparation method of high-temperature antioxidant graphite packing, comprising the following steps: Step A1, the flexible graphite wire is immersed in the polytetrafluoroethylene impregnant for 20min, then taken out and dried at 80℃ for 2h, then collected by winding device, get the impregnated flexible graphite wire; Step A2, first heat the impregnated flexible graphite wire to 150℃ for primary heat treatment for 6min, then heat to 230℃ for secondary heat treatment for 6min, then heat to 330℃ for tertiary heat treatment for 10min, finally, the packing is shaped, get the high-temperature antioxidant graphite packing.

[0029] Example 2 The heat-resistant filler is prepared by the following steps: Step C1, 22.6g of phenyltrichlorosilane, 100mL of toluene and 13.4g of 2-hydroxybenzimidazole are added to a three-necked flask equipped with a constant pressure dropping funnel, after magnetic stirring, 10.1g of triethylamine is added through the constant pressure dropping funnel, the temperature is controlled not to exceed 25℃ during the addition, after the addition is completed, the device is heated until the temperature is maintained at 70℃, react for 6h at this temperature, after the reaction is completed, the initial product is obtained after treatment; Step C2, 33.7 g of the initial product, 100 mL of toluene and 17.1 g of pentamethylpiperidinol were added to a three-necked flask equipped with a constant pressure dropping funnel, after uniform magnetic stirring, 10.1 g of triethylamine was added dropwise through the constant pressure dropping funnel, the temperature was controlled not to exceed 25 DEG C during the dropping process, after the dropping was completed, the device was heated until the temperature was maintained at 80 DEG C, the reaction was carried out at this temperature for 8 h, after the reaction was completed, the product was obtained after treatment, and the heat-resistant filler modifier was obtained; Step C3, first, 10 g of alumina was cleaned with methanol for 3 times by ultrasonic, then dehydrated at 130 DEG C for 4 h under vacuum, to ensure that the surface hydroxyl group was fully exposed, then it was mixed with 100 mL of toluene, ultrasonic treatment for 20 min, then 4.1 g of heat-resistant filler modifier and 0.93 g of triethylamine were added, heated to 90 DEG C, and reacted at this temperature for 12 h, after the reaction was completed, the product was separated by centrifugation, washed with toluene for several times, and dried under vacuum to obtain the heat-resistant filler; The flexible graphite wire was prepared by the following steps: Step B1, 10 g of natural flake graphite was mixed with concentrated sulfuric acid solution (mass fraction 98%, intercalation agent), stirred for 24 h, washed to neutral, dried in an oven at 100 DEG C, and expanded at a high temperature of 1000 DEG C to obtain worm-like expanded graphite; Step B2, 7 g of polyester fiber coated with polytetrafluoroethylene binder was evenly covered with expanded graphite, and then the graphite felt was calendered into a composite tape by using a double-roller calender; Step B3, the composite tape was cut and twisted to obtain the flexible graphite wire; The polytetrafluoroethylene impregnant was prepared by the following steps: 79 g of polytetrafluoroethylene emulsion (solid content 60%), 12 g of heat-resistant filler, 45 g of deionized water and 2 g of sodium dodecyl sulfate were mixed, and high-speed shearing stirring was carried out for 30 min to obtain a mixed solution, and then the mixed solution was ultrasonically treated for 30 min to obtain the polytetrafluoroethylene impregnant; A preparation method of a high-temperature antioxidant graphite packing, comprising the following steps: Step A1, the flexible graphite wire was immersed in the polytetrafluoroethylene impregnant for 22 min, taken out and dried at 100 DEG C for 3 h, and then wound by a winding device to obtain the impregnated flexible graphite wire; Step A2, first, the impregnated flexible graphite wire was heated to 170 DEG C for primary heat treatment for 10 min, then heated to 250 DEG C for secondary heat treatment for 10 min, then heated to 350 DEG C for tertiary heat treatment for 20 min, and finally the packing was shaped to obtain the high-temperature antioxidant graphite packing.

[0030] Example 3 The difference between this embodiment and embodiment 2 is that the polytetrafluoroethylene impregnant is prepared by the following steps: 86 g of a polytetrafluoroethylene emulsion (solid content of 60%), 16 g of heat-resistant filler, 50 g of deionized water and 3 g of sodium dodecyl sulfate are mixed, high-speed shearing stirring is used for 30 min, the mixed solution is ultrasonically treated for 30 min, and a polytetrafluoroethylene impregnant is obtained; A preparation method of a high-temperature oxidation-resistant graphite packing, comprising the following steps: Step A1, after the flexible graphite wire is immersed in the polytetrafluoroethylene impregnant for 22 min, it is taken out and dried at 100 DEG C for 3 h, and is wound by a winding device to obtain the impregnated flexible graphite wire; Step A2, the impregnated flexible graphite wire is first heated to 170 DEG C for primary heat treatment for 10 min, then is heated to 250 DEG C for secondary heat treatment for 10 min, then is heated to 350 DEG C for tertiary heat treatment for 20 min, and finally is subjected to packing shaping to obtain the high-temperature oxidation-resistant graphite packing.

[0031] Comparative example 1 The difference from embodiment 2 is that a commercially available silane coupling agent KH-550 is used to modify the heat-resistant filler, and the remaining steps are the same as those of embodiment 2 to prepare the graphite packing.

[0032] Comparative example 2 The difference from embodiment 2 is that 12 g of unmodified alumina is used, and the remaining steps are the same as those of embodiment 2 to prepare the graphite packing.

[0033] 5 g of the graphite packing of embodiments 1, 2, 3 and comparative examples 1 and 2 is taken as a sample, heated to 500 DEG C at a rate of 10 DEG C / min in a nitrogen atmosphere, the final mass is recorded, and the mass retention rate is calculated; mass retention rate = (final mass / 5 g) x 100%.

[0034] The determination results are shown in the following table:

[0035] From the above table, it can be seen that the mass retention rate of the embodiment of the application is higher than that of the comparative examples, and therefore the sealing reliability of the packing under extreme working conditions such as high temperature and high pressure is significantly improved, and the application has important application value in the technical field of graphite packing.

[0036] The above is only a preferred embodiment of the application, and is not intended to limit the application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the application shall be included in the protection scope of the application.

Claims

1. A method for preparing a high-temperature oxidation-resistant graphite packing, characterized in that, It comprises the following steps: Step A1, dip the flexible graphite wire into the polytetrafluoroethylene impregnant for 20-22 min, take it out, dry it, and roll it up to obtain the impregnated flexible graphite wire; Step A2, perform primary heat treatment on the impregnated flexible graphite wire, then perform secondary heat treatment, then perform tertiary heat treatment, and finally perform packing shaping to obtain the high-temperature oxidation-resistant graphite packing.

2. The method for preparing a high-temperature antioxidant graphite packing according to claim 1, characterized in that, The flexible graphite wire is prepared by the following steps: Step B1, mix the natural flake graphite with the concentrated sulfuric acid solution, stir, wash with water until neutral, dry, and rapidly expand at high temperature to obtain expanded graphite; Step B2, coat the polyester fiber with adhesive, uniformly cover the expanded graphite on the polyester fiber, and use a double-roller calender to calender the graphite felt into a composite tape; Step B3, cut and twist the composite tape to obtain the flexible graphite wire.

3. The method for preparing a high-temperature antioxidant graphite packing according to claim 1, characterized in that, The polytetrafluoroethylene impregnant comprises the following raw materials by weight: 72-86 parts of polytetrafluoroethylene emulsion, 8-16 parts of heat-resistant filler, 40-50 parts of deionized water, and 1-3 parts of dispersant.

4. The method for preparing a high-temperature antioxidant graphite packing according to claim 3, characterized in that, The heat-resistant filler is prepared by the following steps: Step C1, add phenyltrichlorosilane, solvent, and 2-hydroxybenzimidazole into a flask, stir, add triethylamine dropwise, react at 60-70℃ for 4-6h, and obtain the primary product after the reaction is completed; Step C2, add the primary product, solvent, and pentamethylpiperidinol into a flask, stir, add triethylamine dropwise, react at 70-80℃ for 6-8h, and obtain the heat-resistant filler modifier after the reaction is completed; Step C3, first clean the alumina, then dehydrate it at 120-130℃ under vacuum for 2-4h, then mix it with the solvent, ultrasonic treatment, then add the heat-resistant filler modifier and triethylamine, and react at 80-90℃ for 10-12h to obtain the heat-resistant filler after the reaction is completed.

5. The method for preparing a high-temperature antioxidant graphite packing according to claim 4, characterized in that, In step C1, the amount ratio of phenyltrichlorosilane, solvent, 2-hydroxybenzimidazole, and triethylamine is 21.3-22.6g:100mL:13.4g:10.1g.

6. The method for preparing a high-temperature antioxidant graphite packing according to claim 4, characterized in that, In step C2, the amount ratio of the primary product, solvent, pentamethylpiperidinol, and triethylamine is 31.2-33.7g:100mL:17.1g:10.1g.

7. The method for preparing a high-temperature antioxidant graphite packing according to claim 4, characterized in that, In step C3, the amount ratio of alumina, solvent, heat-resistant filler modifier, and triethylamine is 10g:100mL:3.7-4.1g:0.93g.

8. The method for preparing a high-temperature antioxidant graphite packing according to claim 2, characterized in that, The mass ratio of the natural flake graphite, concentrated sulfuric acid solution, and polyester fiber is 1:2.5-3:0.6-0.

7.

9. The method for preparing a high-temperature antioxidant graphite packing according to claim 2, characterized in that, The temperature of the high temperature is 900-1000℃.

10. A high temperature oxidation resistant graphite disc, characterized in that, Prepared according to the method of any one of claims 1-9.

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