Dry repair mud for ceramic disc forming die repair, and preparation method and application thereof

Abstract

The application provides dry repair mud for repairing a ceramic disc forming die, a preparation method and application thereof, wherein the preparation method comprises the following steps: S100, raw material pretreatment, including: S101, plasma hydroxyl activation treatment of boron nitride powder, S102, graft modification treatment of the activated boron nitride powder, and S103, dispersion pretreatment of boron nitride nanofibers; S200, batching and preparation treatment, including: S201, preparation of a composite sintering aid and S202, preparation of a mixed solvent; S300, ball milling treatment, including: S301, primary ball milling and S302, secondary ball milling; S400, forming treatment, including: S401, vacuum defoaming treatment and S402, drying and forming to obtain a dry repair mud embryo; the prepared dry repair mud can directly repair the defect position of the inner wall of the graphite die and realize further densification when following the hot pressing of a normal product, thereby completely matching the forming requirement and greatly reducing the production cost.

Description

Technical Field

[0001] This invention relates to the field of ceramic repair materials technology, and in particular to a dry patch for repairing ceramic disc forming molds, its preparation method, and its application. Background Technology

[0002] The ceramic heating plate consists of an interconnected plate body and a cylindrical body, which are separately processed and then joined together by welding or bonding. The plate body is manufactured using a graphite mold. Specifically, a layer of graphite paper is attached to the inner wall of the graphite mold, and then ceramic powder and heating wire are placed inside the mold and hot-pressed and sintered together. However, the ceramic powder and heating wire exert uneven pressure on the inner wall of the graphite mold during the forming process, resulting in localized uneven stress on the inner wall of the mold. During hot pressing and sintering, the inner wall of the graphite mold reacts with the graphite paper, generating tiny pore defects. During subsequent use and storage, these pore defects gradually pulverize, forming pits of varying sizes. (See Appendix) Figure 1 , attached Figure 1 The example demonstrates three circular defects formed on the inner wall of a graphite mold. In reality, these defects are irregular pits of varying sizes and depths. The presence of these pits causes powder irregularities during powder pressing, hindering the proper pressing and sintering of ceramic powder, rendering it unusable for disc processing. However, graphite molds are expensive, and frequent replacements keep production costs high.

[0003] Accordingly, the present invention aims to provide a method for preparing dry patching putty for repairing defects in ceramic disc forming molds and its repair application, which can replace the direct replacement of graphite molds to reduce overall costs. Summary of the Invention

[0004] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a dry patch for repairing ceramic disc forming molds, its preparation method and application, which can directly repair defects on the inner wall of graphite molds and achieve further densification during hot pressing with the product. It can not only fully meet the high temperature, wear resistance and precision forming requirements of graphite molds, but also significantly reduce production costs.

[0005] To achieve the above and other related objectives, in a first aspect, the present invention provides a method for preparing dry patching putty for repairing ceramic disc forming molds, the preparation steps including:

[0006] S100, Raw material pretreatment includes:

[0007] S101, hexagonal boron nitride (h-BN) powder plasma hydroxyl activation treatment: Weigh 93-94 parts of the original hexagonal boron nitride (h-BN) powder by weight and spread it evenly on the tray of the plasma treatment instrument. Close the chamber door and introduce oxygen into it, controlling the flow rate to be stable at 5-8L / min to exhaust the air in the chamber. Start the plasma treatment instrument and set the start-up power to 300W. Set the treatment time to 8-10min to enter the activation treatment.

[0008] S102. Graft modification treatment of activated hexagonal boron nitride (h-BN) powder: The activated hexagonal boron nitride (h-BN) powder obtained in step S100 after cooling to room temperature is transferred into a reactor. 1.5-1.8 parts of castor oil with a castor oil content of 80-85% and 0.5 parts of phosphoric acid are added and stirred for 5 minutes. The temperature is raised to 120℃ and kept constant at a stirring speed of 200r / min for 2 hours. The material obtained after the reaction is completed is placed in a vacuum drying oven at 60℃ and dried for 2 hours to obtain modified hexagonal boron nitride (h-BN) powder.

[0009] S103. Weigh 0.8-1 parts of boron nitride nanofibers (BNNF) and add 5 times the weight of anhydrous ethanol. Place the mixture in an ultrasonic cleaner and set the power to 300W and the ultrasonic frequency to 40kHz for ultrasonic dispersion for 10 minutes to obtain boron nitride nanofiber ethanol slurry.

[0010] S200, ingredient preparation and processing includes:

[0011] S201. Take 1-1.2 parts of sodium silicate (Na2O·nSiO2) and 1-1.3 parts of yttrium oxide (Y2O3) and mix them evenly to obtain a composite sintering aid;

[0012] S202. Mix anhydrous ethanol and ethylene glycol evenly in a 9:1 ratio to obtain a mixed solvent;

[0013] S300, ball milling process includes:

[0014] S301. Initial ball milling: Pour the modified hexagonal boron nitride (h-BN) powder obtained in step S102 into a boron nitride ball mill jar and add 2-2.5 parts of composite sintering aid, 50% of mixed solvent and zirconia balls with a ball-to-material ratio of 4:1. Seal the ball mill jar and load it into a ball mill and ball mill at 350 r / min for 1.5 hours.

[0015] S302, Secondary ball milling: Add 1-1.2 parts of polyethylene glycol, the boron nitride nanofiber ethanol slurry obtained in step S103, and the remaining 50% of the mixed solvent to the ball milling jar after the first ball milling. Seal the ball milling jar and load it into the ball mill to continue ball milling at 250 r / min for 1 hour.

[0016] S400, molding process includes:

[0017] S401. Vacuum degassing treatment: The slurry after ball milling is transferred into a vacuum mixing tank and stirred at a vacuum level of -0.09MPa for at least 30 minutes.

[0018] S402. Drying and shaping: Pour the degassed slurry from step S401 into a shallow pan and place it in a vacuum drying oven to dry at a vacuum degree of -0.08MPa for at least 2 hours to obtain a dry patching mud body.

[0019] To achieve the above technical solution, the hexagonal boron nitride (h-BN) powder and yttrium oxide (Y2O3) used in the dry patch are both inert materials that do not chemically react with the graphite matrix, will not corrode the inner wall of the mold, and will not contaminate the ceramic disc product. The boron nitride nanofibers have wear resistance similar to that of the graphite matrix, and their uniform dispersion in the dry patch forms a "fiber bridge" structure, which not only improves the wear resistance of the repair layer but also inhibits crack propagation. The surface hydroxyl groups of the modified hexagonal boron nitride (h-BN) powder, after plasma activation and ricinoleic acid grafting modification, form a weak chemical bond with the graphite mold matrix. This, combined with the mechanical interlocking formed by the compacted and cured dry patch and the micropores and rough surfaces of the graphite inner wall, creates a "chemical + mechanical dual fixation," resulting in an interfacial peel strength ≥14MPa, far exceeding that of ordinary repair materials (≤6MPa).

[0020] As a preferred embodiment of step S402, the drying process is stopped when the solidification amount reaches 85% to obtain a dry patching mud blank.

[0021] To achieve the above technical solution, when the dry putty is dried to 85% of its solidified state, the dry putty blank is in a state of "flexible and malleable, non-sticky, and non-flammable". The remaining approximately 15% solvent acts as a "wetting medium". During filling, the solvent can slightly penetrate into the tiny pores of the graphite mold wall, making the contact between the dry putty and the graphite matrix closer. After subsequent curing, a strong mechanical bond and a weak chemical bond are formed.

[0022] As a preferred embodiment of step S101, the thickness of the original hexagonal boron nitride (h-BN) powder spread on the plasma processing instrument tray in step S101 is controlled to be within 5 mm.

[0023] As a preferred embodiment of step S101, the original hexagonal boron nitride (h-BN) powder in step S101 is spread on the plasma processing instrument tray to a thickness of 3 mm.

[0024] To achieve the above technical solution, the effective depth of plasma is limited. The industry standard effective penetration depth is ≤6mm. If the powder layer thickness exceeds 5mm, the upper powder layer can fully contact the plasma, while the middle and lower powder layers are blocked by the upper layer, making it difficult for the plasma to penetrate. This results in a layering phenomenon of "complete activation of the surface layer and weak activation of the inner layer". Controlling the thickness to ≤5mm allows the plasma to act evenly on each powder layer.

[0025] As a preferred embodiment of step S102, step S102 involves heating to 120°C at a heating rate of 5°C / min.

[0026] To achieve the above technical solution, a rate of 5℃ / min allows the system temperature to rise uniformly. As the temperature increases, the fluidity of ricinoleic acid gradually improves, reaching the optimal dispersion state at 100℃, which is synchronously matched with the reactivity of the hydroxyl groups on the surface of hexagonal boron nitride (h-BN).

[0027] As a preferred embodiment of step S201, step S201 includes:

[0028] S2011. Take 1-1.2 parts of sodium silicate (Na2O·nSiO2) and 1-1.3 parts of yttrium oxide (Y2O3), mix them evenly, and put them into a zirconia ball mill jar;

[0029] S2012. Add anhydrous ethanol to the ball mill jar to form a solid-liquid ratio of 1:0.8, and add zirconia balls at a ball-to-material ratio of 3:1 and ball mill at 300 r / min for 2 minutes.

[0030] S2013. Filter the composite sintering aid obtained from S2012 using a standard 250-mesh stainless steel sieve, and then dry the sieved composite sintering aid in a 60°C forced-air dryer for 30 minutes before sealing and storing it for later use.

[0031] To achieve the above technical solution, the modulus and purity of the composite sintering aid are refined, and its compatibility with the graphite mold matrix is ​​improved.

[0032] Secondly, the present invention provides a dry patching compound for repairing ceramic disc forming molds, which is prepared according to the preparation method of the dry patching compound for repairing ceramic disc forming molds described in any of the above claims.

[0033] Thirdly, the present invention provides an application of dry putty for repairing ceramic disc forming molds, used for repairing defects on the inner wall of graphite molds, the steps of which include:

[0034] S1. Clean the defects in the graphite mold, increasing the cleaning depth by 1-1.5mm from the original depth;

[0035] S2. Blow and clean the defective area, and then apply a small amount of anhydrous ethanol to wipe the inner wall and edges of the defective area evenly.

[0036] S3. Fill the defect with the dry patching mortar in layers and compact it until the compacted dry patching mortar is higher than the surface of the inner wall around the defect.

[0037] S4. Gradient drying and curing: In the first stage, the graphite mold repaired in S3 is placed in a drying chamber with a set temperature of 45℃ and a wind speed of 2m / s and dried for 1.5 hours. In the second stage, the wind speed is kept constant and the temperature is raised to 60℃ and dried for another 2 hours. Then, the drying chamber is closed and allowed to cool naturally to room temperature.

[0038] S5. Scrape off the dry putty that protrudes above the inner surface of the graphite and polish the repaired area.

[0039] S6. Apply graphite-specific adhesive to the back of the graphite paper using a "dot application" method and quickly attach it to the surface of the graphite mold. Gently roll it with a rubber roller to remove air bubbles. Place the mold with the graphite paper attached into a 60°C forced-air drying oven and dry for 30 minutes to allow the adhesive to initially cure. Then, heat-press it together with the hot-pressing conditions of the main product to make the graphite paper, repair layer, and mold base form a whole.

[0040] To achieve the above technical solution, the cleaning depth is increased by 1-1.5mm to thoroughly remove loose graphite, crack layers, and deep slag from defects, avoiding later detachment caused by "surface repair" and allowing the dry putty to form a "deep fit" with the mold substrate. Fine dust is removed through blowing and cleaning, and anhydrous ethanol is used to further dissolve oil stains and activate the graphite surface, while rapid evaporation removes residual moisture, preventing impurities or moisture from affecting the adhesion between the dry putty and the substrate. Layered filling gradually removes air from the dry putty, avoiding air bubble residue caused by one-time filling. Combined with layered compaction, the dry putty fully conforms to the defect contour, especially suitable for micro-cracks and curved surface defects, forming a strong mechanical bond. The dry putty protrudes above the inner wall surface, leaving room for subsequent grinding and ensuring a smooth repair surface after grinding. Gradient drying and curing effectively controls shrinkage, and compared to natural drying, gradient drying is unaffected by ambient temperature and humidity, resulting in strong consistency in repair effects across different batches.

[0041] As a preferred embodiment of step S3, the dry patching mud is filled into the defect in three layers and compacted in step S3.

[0042] As a preferred embodiment of step S3, in step S3, the first layer is filled with 1 / 3 volume of dry putty at the defect and compacted; the second layer is filled with another 1 / 3 volume of dry putty and compacted; the third layer is filled with and compacted dry putty so that the repaired area is 0.8-1.0 mm higher than the inner surface of the graphite wall.

[0043] As described above, the dry patching putty for repairing ceramic disc forming molds, its preparation method, and its application provided by the present invention have at least the following beneficial effects:

[0044] 1. The hexagonal boron nitride (h-BN) powder and yttrium oxide (Y2O3) used in the dry patch are both inert materials that do not chemically react with the graphite matrix, will not corrode the inner wall of the mold, and will not contaminate the ceramic disc products. The hexagonal boron nitride (h-BN) powder undergoes dual modification through plasma activation and ricinoleic acid grafting, which allows the surface hydroxyl groups of the modified hexagonal boron nitride (h-BN) powder to form a weak chemical bond with the graphite matrix. This, combined with the compacted and cured dry patch in the repair application and the mechanical interlocking formed by the tiny pores and rough surfaces of the graphite inner wall, creates a "chemical + mechanical dual fixation". The interfacial peel strength is ≥14MPa, far exceeding that of ordinary repair materials (≤6MPa).

[0045] 2. Boron nitride nanofibers have wear resistance similar to that of graphite matrix. They are uniformly dispersed in dry patching material to form a "fiber bridge" structure, which not only improves the wear resistance of the repair layer, but also inhibits crack propagation, prevents the repaired area from becoming a "weak link" of the mold, and reduces the overall maintenance frequency of the mold.

[0046] 3. By adopting segmented ball milling and vacuum degassing processes, the particle size of the dry patching slurry agglomerates is ≤5μm. After filling, the repair layer has no visible pores, the flatness error after curing is ≤0.1mm, and after grinding, it can achieve the same surface roughness as the graphite mold body (Ra≤0.8μm).

[0047] 4. The gradient drying process, which is precisely controlled by a vacuum drying oven, keeps the curing shrinkage rate of dry patching at a low level. Compared with natural drying, gradient drying is not affected by ambient temperature and humidity, and the repair effect is highly consistent across different batches.

[0048] 5. Filling the dry putty in three layers can gradually expel the air inside the dry putty. Combined with the step-by-step compaction process, the dry putty can fully conform to the contour of the defect. It is especially suitable for small cracks and curved surface defects, forming a strong mechanical bond. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of the defects on the inner wall surface of a graphite mold as described in the background art.

[0050] Figure 2 This is a step-by-step diagram illustrating the application of dry putty for repairing graphite molds using ceramic disc forming molds;

[0051] Figure 3 It is a tensile stress-strain curve of the interfacial peel strength;

[0052] Figure 4 It is a comprehensive curve of thermal cycling and high-temperature aging stability. Detailed Implementation

[0053] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0054] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0055] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0056] Unless otherwise specified, the instruments, reagents, and materials used in the following embodiments are all conventional instruments, reagents, and materials already available in the prior art and can be obtained through legitimate commercial channels. Unless otherwise specified, the experimental methods and detection methods used in the following embodiments are all conventional experimental methods and detection methods already available in the prior art.

[0057] Experimental example:

[0058] This invention provides a method for preparing dry putty for repairing ceramic disc molding molds, the preparation steps of which include:

[0059] S100, Raw material pretreatment includes:

[0060] S101, hexagonal boron nitride (h-BN) powder plasma hydroxyl activation treatment: Weigh 93-94 parts of the original hexagonal boron nitride (h-BN) powder by weight and spread it evenly on the tray of the plasma treatment instrument. Close the chamber door and introduce oxygen into it, controlling the flow rate to be stable at 10-11 L / min to exhaust the air in the chamber. Start the plasma treatment instrument and set the start-up power to 300W and the treatment time to 14min to enter the activation treatment.

[0061] Because the effective penetration depth of plasma is limited (the industry standard is ≤6mm), to avoid the upper layer from fully contacting the plasma while the middle and lower layers are blocked by the upper layer, resulting in a layering phenomenon of "complete surface activation and weak inner layer activation," the thickness of the original hexagonal boron nitride (h-BN) powder spread on the plasma processor tray is controlled to be within 5mm. Preferably, in this embodiment, 93 portions of original hexagonal boron nitride (h-BN) powder are weighed and spread on the plasma processor tray with a thickness of 3mm to ensure that the plasma can act uniformly on each layer of powder.

[0062] To ensure complete purging of the air from the plasma treatment chamber, oxygen is introduced into the chamber after the door is closed, and the flow rate is kept stable at 5-8 L / min. After confirming that the air in the chamber has been completely purged, the plasma instrument is started, with the starting power set to 300W and the treatment time set to 8-10 min. During the plasma activation process, firstly, high-energy particle bombardment causes the BN bonds on the boron nitride surface to break, forming dangling bonds and defect sites. Secondly, water molecules decompose in the plasma to generate hydroxyl radicals (-OH). Finally, the hydroxyl radicals combine with surface-active B atoms to form stable B-OH bonds.

[0063] S102. Graft modification treatment of activated hexagonal boron nitride (h-BN) powder: The activated hexagonal boron nitride (h-BN) powder obtained in step S100 after cooling to room temperature is transferred into a reactor. 1.5-1.8 parts of castor oil with a castor oil content of 80-85% and 0.5 parts of phosphoric acid are added and stirred for 5 minutes. The temperature is raised to 120℃ and kept constant at a stirring speed of 200r / min for 2 hours. The material obtained after the reaction is completed is placed in a vacuum drying oven at 60℃ and dried for 2 hours to obtain modified hexagonal boron nitride (h-BN) powder.

[0064] Preferably, the reactor is a polytetrafluoroethylene-lined reactor. 1.6 parts of ricinoleic acid and 0.5 parts of phosphoric acid are added to the reactor. The stirred paddle is turned on to mix the activated hexagonal boron nitride (h-BN) powder, ricinoleic acid, and phosphoric acid in the reactor for 5 minutes to ensure complete contact between the powder and the additives. Then, the temperature is increased to 120°C at a rate of 5°C / min, and maintained at a constant temperature with stirring at 200 r / min for 2 hours. During the reaction, the -OH group of the carboxyl group combines with the -H group of the hydroxyl group to generate water, forming a stable ester bond (BOC=O). The reaction equation can be expressed as: B-OH + HOOC-R → BO-OC-R + H2O. At a reaction temperature of 120°C, phosphoric acid acts as a catalyst to effectively promote the esterification reaction. After the reaction, the material in the reactor is evenly spread on a stainless steel tray and placed in a vacuum drying oven at 60°C. It is then dried at a vacuum of -0.08 MPa for 2 hours to obtain modified hexagonal boron nitride (h-BN) powder. Preferably, the material is turned over periodically during the drying process to improve the uniformity of drying. Heating at a rate of 5°C / min allows the system temperature to rise uniformly. The fluidity of ricinoleic acid gradually increases with temperature, reaching its optimal dispersion state at 100°C, which synchronously matches the reactivity of the hydroxyl groups on the surface of hexagonal boron nitride (h-BN).

[0065] S103. Weigh 0.8-1 parts of boron nitride nanofibers (BNNF) and add 5 times the weight of anhydrous ethanol. Place them in an ultrasonic cleaner and ultrasonically disperse them for 10 minutes at 300W power and 40kHz frequency to obtain boron nitride nanofiber ethanol slurry.

[0066] S200, ingredient preparation and processing includes:

[0067] S201. Take 1-1.2 parts of sodium silicate (Na2O·nSiO2) and 1-1.3 parts of yttrium oxide (Y2O3) and mix them evenly to obtain a composite sintering aid. The specific steps include: S2011. Take 1-1.2 parts of sodium silicate (Na2O·nSiO2) and 1-1.3 parts of yttrium oxide (Y2O3) and mix them evenly and put them into a zirconia ball mill jar;

[0068] S2012. Add anhydrous ethanol to the ball mill jar to form a solid-liquid ratio of 1:0.8, and add zirconia balls at a ball-to-material ratio of 3:1 and ball mill at 300 r / min for 2 minutes.

[0069] S2013. Filter the composite sintering aid obtained from S2012 using a standard 250-mesh stainless steel sieve, and then dry the sieved composite sintering aid in a 60°C forced-air dryer for 30 minutes before sealing and storing it for later use.

[0070] S202. Mix anhydrous ethanol and ethylene glycol evenly in a ratio of 9:1 to obtain a mixed solvent. After mixing anhydrous ethanol and ethylene glycol in the ratio, stir with a stirrer at a speed of 150 r / min for 10 minutes to ensure uniform mixing.

[0071] S300, ball milling process includes:

[0072] S301. Initial ball milling: Pour the modified hexagonal boron nitride (h-BN) powder obtained in step S102 into a boron nitride ball mill jar and add 2-2.5 parts of composite sintering aid, 50% of mixed solvent, and zirconia balls with a ball-to-material ratio of 4:1. Seal the ball mill jar and load it into a ball mill. Mill at 350 r / min for 1.5 hours. The zirconia balls used are zirconia balls with a diameter of 1 mm / 10 mm in a 3:1 ratio.

[0073] S302, Secondary ball milling: Add 1-1.2 parts of polyethylene glycol, the boron nitride nanofiber ethanol slurry obtained in step S103, and the remaining 50% of the mixed solvent to the ball milling jar after the first ball milling. Seal the ball milling jar and load it into the ball mill to continue ball milling at 250 r / min for 1 hour.

[0074] S400, molding process includes:

[0075] S401. Vacuum degassing treatment: Transfer the ball-milled slurry into a vacuum mixing tank and stir at a vacuum level of -0.09 MPa for at least 30 minutes. Specifically, transfer the ball-milled slurry into a vacuum mixing tank. Preferably, the vacuum mixing tank is made of polytetrafluoroethylene (PTFE), and the amount of slurry added does not exceed 60% of the volume of the vacuum mixing tank. Start the vacuum pump to draw a vacuum level of -0.09 MPa, turn on the agitator and set the speed to 80 r / min to stir for at least 30 minutes. In this embodiment, the stirring is carried out for 35 minutes. During the stirring process, the overflow of bubbles in the tank can be observed at the same time. If there are too many bubbles, the stirring can be paused for 1 minute before continuing.

[0076] S402. Drying and Shaping: Pour the degassed slurry from step S401 into a shallow dish and place it in a vacuum drying oven to dry at a vacuum degree of -0.08MPa for at least 2 hours to obtain a dry patching mortar blank. Specifically, when pouring the degassed slurry from step S401 into the shallow dish, a thin layer of graphite powder can be pre-coated on the inner wall of the shallow dish to prevent sticking. Place it in a vacuum drying oven, set the vacuum degree to -0.08MPa and the temperature to 60℃, and dry for at least 2 hours. Stop drying when the curing amount reaches 85%. In this embodiment, the dry patching mortar blank is obtained after drying for 2.5 hours. The dry patching mortar blank with 85% curing amount is in a state of "flexible and malleable, non-sticky, and non-flaking".

[0077] The hexagonal boron nitride (h-BN) powder and yttrium oxide (Y2O3) used in this invention are both inert materials that do not chemically react with the graphite matrix, will not corrode the inner wall of the mold, and will not contaminate the ceramic disc product. The boron nitride nanofibers have wear resistance similar to that of the graphite matrix. They are uniformly dispersed in the dry patch material to form a "fiber bridge" structure, which not only improves the wear resistance of the repair layer but also inhibits crack propagation. The surface hydroxyl groups of the modified hexagonal boron nitride (h-BN) powder, after plasma activation and ricinoleic acid grafting modification, form a weak chemical bond with the graphite mold matrix. This, combined with the mechanical interlocking formed by the compacted and cured dry patch material and the micropores and rough surfaces of the graphite inner wall, creates a "chemical + mechanical dual fixation," with an interfacial peel strength ≥14MPa, far exceeding that of ordinary repair materials (≤6MPa).

[0078] A dry patching compound for repairing ceramic disc forming molds was prepared using the above method. It is applied to the repair of ceramic disc forming molds, specifically for repairing defects on the inner wall of graphite molds. The steps include:

[0079] S1. Clean the defects in the graphite mold, increasing the cleaning depth by 1-1.5mm. Specifically, first use a small file to clean the cracked but not completely detached graphite blocks in the defect area, and then use a brush to remove the ash and dust in the defect area. Increase the cleaning depth by 1-1.5mm to thoroughly remove loose graphite, cracked layers, and deep ash in the defect area, avoiding later detachment caused by "surface repair", and allowing the dry putty to form a "deep fit" with the mold substrate.

[0080] S2. Clean the defect by blowing and sweeping, and then apply a small amount of anhydrous ethanol to wipe the inner wall and edges of the defect evenly. Specifically, first use an air gun to blow from the inside of the pit outward at a 45° angle for 30 seconds, then use an industrial vacuum cleaner (suction power ≥12kPa) to remove dust within a 5cm radius around the pit, and finally use a rubber bulb to repeatedly squeeze and blow the bottom and corners of the pit 10 times. After that, use a cotton swab to apply a small amount of anhydrous ethanol to wipe the inner wall and edges of the pit evenly, and let it stand for 5 minutes to allow the anhydrous ethanol to evaporate, while removing the tiny moisture from the inner wall of the pit, thus improving the compatibility between the dry putty and the graphite.

[0081] S3. Fill the defect with dry putty in layers and compact it until the compacted dry putty is higher than the surface of the inner wall around the defect. Specifically, fill the defect with dry putty in three layers and compact it. The first layer fills the defect with 1 / 3 of the volume of dry putty and compacts it. The second layer fills the defect with another 1 / 3 of the volume of dry putty and compacts it. The third layer fills the defect with dry putty and compacts it so that the repaired area is 0.8-1.0mm higher than the inner wall surface of the graphite. Layered filling can gradually remove the internal air of the dry putty and avoid the air bubbles left by filling it all at once. Combined with layered compaction, the dry putty can fully conform to the contour of the defect, especially suitable for small cracks and curved surface defects, forming a strong mechanical interlock. The dry putty is higher than the inner wall surface to leave room for subsequent grinding and ensure that the repaired surface is flat after grinding.

[0082] S4. Gradient drying and curing: In the first stage, the graphite mold repaired in step S3 is placed in a drying chamber with a set temperature of 45℃ and a wind speed of 2m / s for 1.5 hours. In the second stage, the wind speed remains constant, and the temperature is increased to 60℃ for another 2 hours. The drying chamber is then closed and allowed to cool naturally to room temperature. The stress generated during the drying process is the main cause of cracking in the green body. The stress mainly originates from: rapid evaporation of moisture on the surface of the green body, while the internal moisture migration rate is slower, resulting in surface shrinkage but no internal shrinkage, generating shrinkage stress; inconsistent drying speeds in different parts of the green body, resulting in uneven shrinkage; and thermal stress caused by temperature gradients. Studies have shown that the constant-rate drying stage is the most prone to cracking because the green body undergoes volume shrinkage at this time. If drying is too fast, deformation and cracking are very likely to occur. This invention employs a gradient drying process (45℃→60℃). In the low-temperature stage (45℃), surface moisture is slowly removed, preventing rapid surface crusting and allowing sufficient time for internal moisture to migrate to the surface. Secondly, the heating stage (45℃→60℃) gradually increases the internal temperature of the green body, reducing the temperature gradient and lowering thermal stress. Thirdly, the high-temperature stage (60℃) accelerates the migration rate of internal moisture, improving drying efficiency. The gradient drying process can effectively control stress during the drying process, keeping the curing shrinkage rate at a low level. Compared with natural drying, gradient drying is not affected by ambient temperature and humidity, resulting in strong consistency in repair effects across different batches.

[0083] S5. Scrape off the dry putty that protrudes above the inner surface of the graphite and polish the repair area. Specifically, use a small scraper to scrape off the dry putty that protrudes above the inner surface of the graphite, and then use diamond sandpaper to polish the repair area. The polishing can be done in steps. First, use 400-grit diamond sandpaper to polish until the repair layer is flush with the surrounding graphite substrate, then switch to 800-grit diamond sandpaper for fine polishing, and finally use graphite polishing paste for manual polishing.

[0084] S6. Apply graphite-specific adhesive to the back of the graphite paper using a "dot application" method and quickly attach it to the surface of the graphite mold. Gently roll it with a rubber roller to remove air bubbles. Place the mold with the graphite paper attached into a 60℃ forced-air drying oven and dry for 30 minutes to allow the adhesive to initially cure. Then, heat-press it together with the hot-pressing conditions of the main product to form a whole with the graphite paper, repair layer, and mold base. Among them, phenolic resin-based graphite adhesive can be used. After quickly attaching the back of the graphite paper to the surface of the graphite mold, gently roll it with a rubber roller to remove air bubbles so that the graphite paper is free from curling and wrinkles.

[0085] Experimental example:

[0086] Prepare all necessary raw materials, ingredients, instruments, equipment, auxiliary tools, and consumables, including:

[0087] Raw materials: raw hexagonal boron nitride (h-BN) powder, boron nitride nanofibers (BNNF), castor oil, phosphoric acid (H3PO4), sodium silicate (Na2O·nSiO2), yttrium oxide (Y2O3), polyethylene glycol (PEG);

[0088] Ingredients: Anhydrous ethanol, ethylene glycol;

[0089] Instruments and equipment: electronic balance, plasma processor, reaction vessel, ultrasonic cleaner, ball mill, boron nitride ball mill jar, zirconia balls, vacuum mixing tank, vacuum drying oven, forced-air drying oven;

[0090] Auxiliary tools: standard 250 mesh stainless steel sieve, preparation bucket, shallow tray, sealed storage tank;

[0091] Consumables: graphite powder, label paper, sampling spoon.

[0092] Step 1, Raw material pretreatment:

[0093] Step 11: Weigh 93 parts of raw hexagonal boron nitride (h-BN) powder using an electronic balance according to the weight percentage. Spread the powder evenly on the tray of the plasma processor with a thickness of 3 mm. Close the chamber door and control the flow rate to stabilize at 5-8 L / min to introduce oxygen into the chamber to purge the air. Set the start-up power to 300W and the processing time to 8 minutes to start the plasma processor and enter the activation process.

[0094] Step 12: Transfer the activated hexagonal boron nitride (h-BN) powder cooled to room temperature into a reactor, add 1.5 parts of castor oil with a castor oil content of 80-85% and 0.5 parts of phosphoric acid, stir and mix for 5 minutes, then raise the temperature to 120°C at a heating rate of 5°C / min and maintain the constant temperature, and react for 2 hours at a stirring speed of 200 r / min. After the reaction is completed, put the material obtained into a vacuum drying oven at 60°C and dry for 2 hours to obtain modified hexagonal boron nitride (h-BN) powder.

[0095] Step 13: Weigh 0.8 parts of boron nitride nanofibers (BNNF) using an electronic balance and add 5 times the weight of anhydrous ethanol. Place the mixture in an ultrasonic cleaner and ultrasonically disperse it for 10 minutes at 300W power and 40kHz frequency to obtain boron nitride nanofiber ethanol slurry, and then load it into the container.

[0096] Step 2: Prepare the ingredients:

[0097] Step 21: Prepare the composite sintering aid:

[0098] Step 211: Weigh 1 part of sodium silicate (Na2O·nSiO2) and 1 part of yttrium oxide (Y2O3) using an electronic balance, mix them evenly, and place them into a zirconia ball mill jar;

[0099] Step 212: Add anhydrous ethanol to the ball mill jar to form a solid-liquid ratio of 1:0.8, and add zirconia balls at a ball-to-material ratio of 3:1 and ball mill at 300 r / min for 2 minutes.

[0100] Step 213: Filter the composite sintering aid obtained in step 212 using a standard 250-mesh stainless steel sieve, and then dry the sieved composite sintering aid in a 60°C forced-air dryer for 30 minutes before sealing and storing it for later use.

[0101] Step 22: Prepare the mixed solvent by adding anhydrous ethanol and ethylene glycol to the preparation tank in a ratio of 9:1 and stirring at 150 r / min for 10 minutes with a stirrer to obtain the mixed solvent.

[0102] Step 3: Perform segmented ball milling.

[0103] Step 31: Pour the modified hexagonal boron nitride (h-BN) powder into a boron nitride ball mill jar. Weigh 2 parts of the composite sintering aid using an electronic balance and add them to the boron nitride ball mill jar. At the same time, add 50% of the mixed solvent and zirconia balls with a ball-to-material ratio of 4:1. Seal the ball mill jar, load it into the ball mill, and set the speed to 350 r / min for 1.5 hours. The zirconia balls used are zirconia balls with a diameter of 1 mm / 10 mm in a 3:1 ratio.

[0104] Step 32: After the initial ball milling, open the ball mill jar and use an electronic balance to weigh 1 part of polyethylene glycol, as well as the boron nitride nanofiber ethanol slurry stored in a sealed storage container and the remaining 50% of the mixed solvent, and add them to the ball mill jar. Seal the ball mill jar, load it into the ball mill, and set the speed to 250 r / min to continue ball milling for 1 hour.

[0105] Step 4: Molding process

[0106] Step 41: Transfer the ball-milled slurry into a vacuum mixing tank with a vacuum degree of -0.09MPa, turn on the agitator and set the speed to 80r / min to mix for 35 minutes. During the mixing process, observe the overflow of air bubbles in the tank.

[0107] Step 42: Apply a thin layer of graphite powder to the inner wall of the shallow dish, pour the degassed slurry into the shallow dish and place it in a vacuum drying oven. Set the vacuum degree to -0.08MPa and the temperature to 60℃ for drying. Stop drying when the curing amount reaches 85% to obtain the dry patching mud body.

[0108] The prepared dry putty was used to repair defects on the inner wall of the graphite mold. The repair steps included:

[0109] a. First, use a small file to clean the graphite blocks that have cracks but have not completely fallen off at the defect. Use a brush to remove the ash and dust at the defect. The cleaning depth should be increased by 1-1.5mm from the original pit depth of the defect.

[0110] b. First, use an air gun to blow from the inside of the pit at a 45° angle outwards for 30 seconds. Then, use an industrial vacuum cleaner to remove dust within a 5cm radius around the pit. Finally, use a rubber bulb to repeatedly squeeze and blow the bottom and corners of the pit 10 times. After that, use a cotton swab dipped in a small amount of anhydrous ethanol to wipe the inner wall and edges of the pit evenly and let it stand for 5 minutes.

[0111] c. Fill the defect with dry putty in three layers and compact it. The first layer is filled with 1 / 3 of the volume of dry putty and compacted. The second layer is filled with another 1 / 3 of the volume of dry putty and compacted. The third layer is filled with and compacted dry putty so that the repaired area is 0.8-1.0 mm higher than the inner surface of the graphite.

[0112] d. First, place the repaired graphite mold in a drying oven with a set temperature of 45℃ and a wind speed of 2m / s for 1.5 hours. Keep the wind speed constant and raise the temperature to 60℃ to continue drying for 2 hours. Then, close the drying oven and let it cool naturally to room temperature.

[0113] e. Use a small scraper to scrape off the dry patch that protrudes above the inner surface of the graphite, then use 400-grit diamond sandpaper to sand until the repair layer is flush with the surrounding graphite substrate, then use 800-grit diamond sandpaper for fine sanding, and finally use graphite polishing paste for manual polishing.

[0114] f. Apply phenolic resin-based graphite adhesive to the back of graphite paper using a "dot coating" method and quickly attach it to the surface of the graphite mold. Gently roll it with a rubber roller to remove air bubbles. Place the mold with the attached graphite paper into a 60°C forced-air drying oven and dry for 30 minutes to allow the adhesive to initially cure. Then, heat press it together with the hot pressing conditions of the main product.

[0115] Systematic experimental tests were conducted on the repaired graphite mold. Currently, the best-performing high-temperature graphite repair agent on the market, HR-8768, has the following main performance indicators: long-term temperature resistance 1650℃, instantaneous temperature resistance 1800℃, shear strength 83MPa, tensile strength 39MPa, and interfacial peel strength ≤6MPa. Detailed test data after repair in this application are shown in Table 1 below:

[0116] Table 1:

[0117]

[0118] Among them, the performance index corresponding to the thermal cycling stability test is the interface peel strength, and the calculation formula is:

[0119] Performance retention rate (%) = (Performance value after thermal cycling / Initial performance value) × 100%;

[0120] That is, the interfacial peel strength of the dry patch was 14.5 MPa before the thermal cycling was performed, and then after 50 cycles of "room temperature -> 1600℃ -> room temperature", the interfacial peel strength was tested again and it was 12.5 MPa.

[0121] The performance retention rate (%) is calculated as 12.5 / 14.5 × 100% = 86.2%.

[0122] The performance index corresponding to the high-temperature aging stability test is compressive strength, and the calculation formula is:

[0123] Performance degradation rate (%) = [(Initial performance value - Performance value after high temperature aging) / Initial performance value] × 100%;

[0124] That is, the compressive strength of the dry patch was 85.8 MPa before the high temperature aging test, and then 82.5 MPa was obtained after heating at 1200℃ for 90 hours.

[0125] The performance degradation rate (%) is calculated as follows: [(85.8-82.5) / 85.8]×100%=3.8%.

[0126] It should be noted that the actual use of the mold is not continuous, but rather multiple times at intervals. During the process of pressing and molding the ceramic disc, a sintering time of 20-30 hours is required. A new mold can be used about 5-6 times, while a repaired mold can be used 3-4 times, effectively extending its service life by more than 50%.

[0127] While foreign BN Cera Patch products offer superior performance, their main component is pure boron nitride (BN), resulting in high costs and requiring specialized application techniques, making implementation difficult.

[0128] This invention provides a method for preparing dry patching putty for repairing ceramic disc molds. The method involves plasma activation and ricinoleic acid grafting of inert hexagonal boron nitride (h-BN) powder, resulting in a weak chemical bond between the surface hydroxyl groups of the modified h-BN powder and the graphite matrix. This bond, combined with the compacted and cured dry patching putty and the mechanical interlocking with the micropores and rough surfaces of the graphite inner wall, forms a "chemical + mechanical dual fixation." Compared to simple physical adsorption, this significantly improves the interfacial peel strength, thereby extending the service life of the graphite mold. Furthermore, the method incorporates boron nitride nanofibers with wear resistance similar to the graphite matrix, forming a "fiber bridge" structure. This prevents the repaired area from becoming a "weak link" in the mold, reducing the overall frequency of mold maintenance.

[0129] In addition, the segmented ball milling and vacuum degassing process ensures that the agglomerates of the dry patching slurry have a particle size of ≤5μm. After filling, the repair layer has no visible pores, and the flatness error after curing is ≤0.1mm. After polishing, it can achieve the same surface roughness as the graphite mold body (Ra≤0.8μm). At the same time, the gradient drying process with precise control in the vacuum drying oven keeps the curing shrinkage rate of the dry patching at a low level. The dry patching is filled and compacted in three layers to fully conform to the defect contour and form a strong mechanical interlock.

[0130] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing a dry patching clay for repairing a ceramic disc forming mold, characterized by, The preparation steps comprise: S100, raw material pretreatment comprises: S101, hexagonal boron nitride (h-BN) powder plasma hydroxyl activation treatment, 93-94 parts of raw hexagonal boron nitride (h-BN) powder is weighed and laid on the tray of the plasma treatment instrument, the cabin door is closed, oxygen is introduced into the cabin and the flow is controlled to be stable at 5-8 L / min to exhaust the air in the cabin, the plasma treatment instrument is started and the starting power is set to 300 W, the treatment time is set to 8-10 min, and the activation treatment is started; S102, after the activation of the hexagonal boron nitride (h-BN) powder, the activated hexagonal boron nitride (h-BN) powder obtained in step S100 is transferred into a reaction kettle, 1.5-1.8 parts of castor oil containing 80-85% of ricinoleic acid and 0.5 parts of phosphoric acid are added and stirred for 5 minutes, the temperature is raised to 120°C and kept constant, and the stirring speed is 200 r / min for 2 hours. The material obtained after the reaction is dried in a vacuum drying oven at 60°C for 2 hours to obtain modified hexagonal boron nitride (h-BN) powder; S103, 0.8-1 parts of boron nitride nanofiber (BNNF) is weighed and added with 5 times the weight of anhydrous ethanol, put into an ultrasonic cleaning machine and set the power to 300 W, the ultrasonic frequency to 40 kHz and ultrasonic dispersion for 10 minutes to obtain boron nitride nanofiber ethanol slurry; S200, batching and preparation treatment comprises: S201, 1-1.2 parts of sodium water glass (Na2O·nSiO2) and 1-1.3 parts of yttrium oxide (Y2O3) are uniformly mixed to obtain a composite sintering aid; S202, uniformly mix anhydrous ethanol and ethylene glycol in a ratio of 9:1 to obtain a mixed solvent; S300, ball milling treatment comprises: S301, primary ball milling, the modified hexagonal boron nitride (h-BN) powder obtained in step S102 is poured into a boron nitride ball mill tank, 2-2.5 parts of a composite sintering aid, 50% of a mixed solvent and zirconia balls with a ball-to-material ratio of 4:1 are added, the ball mill tank is sealed, loaded into a ball mill and ball milled at 350 r / min for 1.5 hours; S302, secondary ball milling, 1-1.2 parts of polyethylene glycol, boron nitride nanofiber ethanol slurry obtained in step S103 and the remaining 50% of the mixed solvent are added to the ball mill tank after the primary ball milling is completed, the ball mill tank is sealed, loaded into a ball mill and continuously ball milled at 250 r / min for 1 hour; S400, forming treatment comprises: S401, vacuum degassing treatment, the slurry after ball milling is transferred into a vacuum stirring tank and stirred in a vacuum degree environment of-0.09 MPa for at least 30 minutes; S402, drying and forming, the slurry after degassing in step S401 is poured into a shallow tray and placed in a vacuum drying oven to dry at a vacuum degree of-0.08 MPa for at least 2 hours to obtain a dry patch mud embryo.

2. The method for preparing the dry patching clay for repairing ceramic disc forming molds according to claim 1, characterized in that, The drying is stopped when the drying and curing amount reaches 85% in step S402 to obtain a dry patch mud embryo.

3. The method for preparing the dry patching clay for repairing ceramic disc forming molds according to claim 1, characterized in that, The thickness of the raw hexagonal boron nitride (h-BN) powder laid on the tray of the plasma treatment instrument in step S101 is controlled to be within 5 mm.

4. The method for preparing the dry patching clay for repairing ceramic disc forming molds according to claim 3, characterized in that, The thickness of the raw hexagonal boron nitride (h-BN) powder laid on the tray of the plasma processing instrument in the S101 step is 3 mm.

5. The method for preparing the dry patching clay for repairing ceramic disc forming molds according to claim 1, characterized in that, The temperature in the S102 step is raised to 120℃ at a rate of 5℃ / min.

6. The method for preparing the dry patching clay for repairing ceramic disc forming molds according to claim 1, characterized in that, The S201 step comprises: S2011, 1-1.2 parts of sodium water glass (Na2O·nSiO2) and 1-1.3 parts of yttrium oxide (Y2O3) are uniformly mixed and put into a zirconium oxide ball mill jar; S2012, anhydrous ethanol is added to the ball mill jar to form a solid-liquid ratio of 1:0.8, and zirconium oxide balls are put in at a ball-material ratio of 3:1 and ball-milled at 300 r / min for 2 minutes; S2013, the composite sintering aid obtained in S2012 is filtered using a standard 250-mesh stainless steel sieve, and the sieved composite sintering aid is put into a 60℃ air-drying oven for 30 minutes and then sealed for standby use.

7. A dry patching clay for repairing a ceramic disc forming mold, characterized by, The dry repair mud for repairing a ceramic disc forming mold is prepared according to the preparation method of any one of claims 1-6.

8. Use of the dry patching clay for repairing ceramic disc forming molds according to claim 7, characterized in that, The steps for repairing defects on the inner wall of a graphite mold include: S1, cleaning the defect part of the graphite mold, the cleaning depth being increased by 1-1.5 mm over the original depth; S2, blowing and cleaning the defect part and wiping the inner wall and edge of the defect part with a small amount of anhydrous ethanol; S3, filling the dry repair mud into the defect part in layers and compacting until the compacted dry repair mud is higher than the surface of the inner wall around the defect part; S4, gradient drying and curing, the graphite mold repaired in S3 is put into an air-drying oven with a set temperature of 45℃ and an air speed of 2 m / s for 1.5 hours in the first section, the air speed remains unchanged and the temperature is raised to 60℃ for 2 hours in the second section; the drying oven is closed and naturally cooled to room temperature; S5, scraping off the dry repair mud higher than the surface of the graphite inner wall and polishing the repaired part; S6, applying a graphite special adhesive to the back of the graphite paper in a "dot coating" manner and quickly attaching it to the surface of the graphite mold, rolling it gently with a rubber roller to expel air bubbles, and putting the mold with the attached graphite paper into a 60℃ air-drying oven for 30 minutes to preliminarily cure the adhesive, and then hot-pressing it together with the hot-pressing conditions of the normal product to form an integral whole of the graphite paper, the repair layer and the mold substrate.

9. Use of a dry patching clay for repairing ceramic disc forming molds according to claim 8, characterized in that, In S3, the dry repair mud is filled into the defect part in three layers and compacted.

10. Use of a dry patching clay for repairing ceramic disc forming molds according to claim 9, characterized in that, In S3, 1 / 3 of the volume of dry repair mud is filled into the defect part in the first layer and compacted, 1 / 3 of the volume of dry repair mud is filled into the defect part in the second layer and compacted, and the dry repair mud is filled into the defect part in the third layer and compacted to make the repaired part higher than the surface of the graphite inner wall by 0.8-1.0 mm.

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